review metal chalcogenide nanoclusters with...

Phil. Trans. R. Soc. A (2010) 368, 1455–1472doi:10.1098/rsta.2009.0276

REVIEW

Metal chalcogenide nanoclusters with ‘tailored’surfaces via ‘designer’ silylated chalcogen

reagentsBY DANIEL G. MACDONALD AND JOHN F. CORRIGAN*

Department of Chemistry, The University of Western Ontario, London,Ontario, Canada N6A 5B7

Silylated chalcogen reagents are proven entry points for the preparation of ligand-stabilized, nanometre-sized metal–chalcogen clusters. More recently, these reagents havebeen developed to incorporate specific functionalities onto the surfaces of nanoclusters.The group 11 metals Cu and Ag in particular yield a wealth of structural types, thefeatures for which are dependent on the nature of the surface chalcogenolate ligands. Thecontent of this review focuses on complexes that have been structurally characterized bysingle-crystal X-ray diffraction studies and illustrates the ease by which these frameworkscan be assembled.

Keywords: chalcogens; ferrocene; ferrocenyl; functionalized; nanocluster

1. Chalcogen-containing ligands

(a) Chalcogenide (E 2−) ligands

The preparation, structural characterization and properties of nanometre-sizedmetal–chalcogen cluster complexes (‘nanoclusters’) continue to be at the forefrontof chemical research efforts. The controlled synthesis of numerous high-nuclearityassemblies with different global structural characteristics results from theflexibility of chalcogenide (E2−) and chalcogenolate (RE−) moieties to adoptseveral bridging coordination modes (Müller & Diemann 1987). This tendencycan be attributed to the highly polarizable chalcogen centres and the anionicnature of these ligands. Chalcogenide ligands typically adopt m3-, m4- and highercoordination interactions in high-nuclearity clusters. Although m2-coordination(figure 1) is possible, it is less likely as the additional lone pairs of electrons willtypically bridge additional metal centres. Terminal coordination can be observedfor chalcogenides but generally only in clusters of main group metals (Krebs et al.1982; Krebs & Henkel 1991). The ability to bridge multiple metal centres increasesgoing down the chalcogens from sulphur to selenium and tellurium, a consequence

*Author for correspondence ([email protected]).

One contribution of 13 to a Theme Issue ‘Metal clusters and nanoparticles’.

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1456 D. G. MacDonald and J. F. Corrigan

EE

EE

E

MM M M M

M

M

MM

MM

M M

M

Figure 1. Common coordination modes of chalcogenide (E2−) ligands.

of the larger ionic radii and larger polarizability of these heavier elements. For thisreason, neutral metal–chalcogen clusters must typically be kinetically protectedfrom further condensation reactions to yield the thermodynamically favouredbinary solids (Dehnen et al. 2004). To prevent the formation of bulk solids,ancillary ligands, such as tertiary phosphines, amines or the above-mentionedorganochalcogenolate anions, are incorporated onto the surfaces in order torestrict the number of vacant coordination sites about the metals and stabilizethe cluster core.

(b) Organochalcogenolate (RE−) ligands

Organochalcogenolate ligands are often used in conjunction with E2− ligandsin the synthesis of metal–chalcogen clusters (Dehnen et al. 2002) and, much likethe more electron-rich chalcogenides, they have a high tendency to bridge metalcentres. In contrast to chalcogenides, however, terminal coordination is muchmore common for these ligands. Although the most common bonding mode ofRE− ligands is doubly bridging, m3- and m4-coordination is also possible and morecommon for the heavier elements. The coordination can also be manipulatedby modifying the steric requirements on the organosubstituent (R) and/or byaltering the ancillary ligand sphere around the metal centre.

2. Chalcogen delivery methods

(a) Alkali-metal-stabilized chalcogenide and chalcogenolate anions

There are now numerous solution-based methodologies for the controlled mixingof chalcogen and metal centres, which lead to well-defined cluster architectures.One common approach to the synthesis has been the addition of alkali-metal-stabilized chalcogen anions to a ligand-stabilized metal salt. These reactions aredriven by the thermodynamically favourable formation of an alkali metal halide(Roof & Kolis 1993). Chalcogenide anions (E2−) can be generated in situ fromH2E through deprotonation in basic solutions or are introduced via reaction asalkali metal chalcogenide salts. H2Se and H2Te, however, do not find widespread

Phil. Trans. R. Soc. A (2010)



Review. Metal chalcogenide nanoclusters 1457

use in cluster synthesis, as these reagents are very toxic, more difficult to handleand can often lead to a mixture of products (Roof & Kolis 1993). Chalcogenolateanions (RE−) can be introduced using related chalcogenol reagents (RE–H) ormetal-stabilized anion (RE–M), the latter often formed in situ by the reductionof diorganodichalcogenides (REER; R = alkyl, aryl, ferrocenyl; E = S, Se, Te) withan alkali metal, organolithium reagents or metal hydrides (Herberhold & Leitner1987; Burgess & Morley 2001). These reagents are often used together withchalcogenides to generate metal chalcogenide/chalcogenolate clusters. In thesesystems, the chalcogenolate ligands occupy surface sites while chalcogenides formthe components of the cluster core, but may also be present on the surface. Thechalcogenolates serve to stabilize the cluster from further condensation reactionsand, most importantly, can serve to introduce a specific functionality onto thenanocluster surface.

(b) Silylated chalcogen reagents

The use of silylated chalcogen reagents has developed into a powerful approachin the synthesis of nanometre-sized metal–chalcogen clusters (Fenske 1994;Dehnen et al. 2002; DeGroot & Corrigan 2004). These reagents provide a solublesource of chalcogen under very mild reaction conditions, making them an idealchalcogen delivery agent. Compounds of the type E(SiMe3)2 and E(R)SiMe3react readily with a wide range of metal salts or metal alkyls (Wehnschulte &Power 1997; DeGroot & Corrigan 2000), forming metal–chalcogenide and–chalcogenolate bonds, respectively:

M−Xn + nRESiMe3 −→ (1/m)[M(ER)n]m + nXSiMe3, (2.1)

M−Xn + (n/2)E(SiMe3)2 −→ (1/m)[MEn/2]m + nXSiMe3 (2.2)

and

M−Xn + (n/2)RESiMe3 + (n/4)E(SiMe3)2

−→ (1/m)[M(ER)n/2En/4]m + nXSiMe3, (2.3)

where X = halide, acetate; E = S, Se, Te.The driving force behind these reactions is the formation of an X–Si bond

and elimination of X–SiMe3 (X = halide, OAc, alkyl, etc.). The reagents arehighly soluble in common organic solvents, even at low temperatures in non-polar solvents. The slow, controlled condensation reactions thus made possiblehave led to the formation and crystallization of nanoscopic metal chalcogenidenanocluster frameworks, most notably for the group 11 metals. Just as importantfor the crystallizations, the silane by-product is also soluble and does nottypically interfere with the crystallization process (DeGroot & Corrigan 2006).The successes of this approach are exemplified with selective and high-yieldpreparation of the structurally characterized nanoclusters [Cu146Se73(PPh3)30]and [Ag188S94(PPr3)20] (Krautscheid et al. 1993; Wang et al. 2002). The propertiesof these and related binary 11–16 nanocluster complexes have been thoroughlyreviewed (Dehnen et al. 2002, 2004). The clusters prepared using this generalstrategy range from small molecular clusters [Ag4(SeiPr)4(dppm)2] (Fenske &Langetepe 2002) (dppm = bis(diphenylphosphino)methane) to extremely largeclusters such as the recently reported [Ag490S188(StC5H11)114] (Anson et al. 2008).





Ultimately, the nature of the products obtained from reactions of metal saltswith silylated chalcogens can be highly dependent on the conditions, although anunderstanding of the parameters for cluster growth is at present largely unknown.The chalcogen sources are typically added to the solubilized metal coordinationcomplexes at low temperatures (Dehnen & Fenske 1996; Aharoni et al. 2003).The solvent system, reaction and crystallization temperatures, reactant ratio andthe nature of the coordinating ligand can all strongly influence the nuclearityand structure of the products formed (Dehnen et al. 2002). Similarly, thenature of surface RE− can also have a strong structure-directing role, especiallywhen the size of the organosubstituent is very large, or the chalcogenolateligand has more than one donor atom to the cluster framework (i.e. −E–R–E−)(Wallbank & Corrigan 2001).

3. Preparation of silylated reagents

Silylated chalcogen reagents are readily prepared, easily handled and can bestored for long periods. RESiMe3 (R = alkyl or aryl; E = S, Se, Te) can beprepared via numerous synthetic methods although Grignard or alkyllithiumreagents are the most common entry point. Elemental chalcogens insert into themetal–carbon bonds of these reagents to yield REMgX (X = Cl, Br) and RELi,respectively, and the silylated product is subsequently generated through theaddition of chlorotrimethylsilane, yielding RESiMe3 and the corresponding metalhalide (Haller & Irgolic 1972; Schmidt et al. 1986). An alternative route for thesynthesis of RESiMe3 involves the reductive cleavage of diorganodichalcogenides(REER) with alkali metals

REER + 2Na −→ 2RE−Na+, (3.1)

alkyllithium reagents or metal hydrides, and silylation (Liesk et al. 1977;Krief et al. 1992)

2RE−Na+ + 2ClSiMe3 −→ 2RESiMe3 + 2NaCl. (3.2)

Recently, the reagents Li[ESiMe3] have been used to prepare ferrocenyl(Fc) and ferrocenoyl chalcogenides via nucleophilic displacement reactions(MacDonald & Corrigan 2008)

FcC(O)Cl + LiESiMe3 −→ FcC(O)ESiMe3 + LiCl. (3.3)

Bis(trimethylsilyl)chalcogenides, E(SiMe3)2, are prepared via the addition ofchlorotrimethylsilane, ClSiMe3, to an alkali metal chalcogenide, M2E (M = Na, Li)(So & Boudjouk 1989), generated from either the reduction of elemental chalcogenwith sodium metal in aqueous ammonia or ethereal solvents (So & Boudjouk1989; DeGroot et al. 2003), or with lithium triethylborohydride (Thompson &Boudjouk 1988; So & Boudjouk 1989).

Although these reagents are comparatively easy to handle and store, theytoo are sensitive to air and moisture, and undergo rapid hydrolysis/oxidation tothe elemental chalcogen in the case of E(SiMe3)2 or to diorganodichalcogenidesin the case of RESiMe3. In addition to the silylated chalcogen reagents beinga convenient and efficient method for the delivery of E2− and RE−, the ‘tun-ability’ of the substituent ‘R’ in the latter presents the opportunity to





control the characteristics of these capping ligands, which have been referredto as ‘chalcogenides with a handle’ (Dance 1986). They can be tailored tointroduce specific chemical functionalities into the cluster. For example, thesilylated ferrocenyl selenide reagents 1,1′-Fe(h5-C5H4SeSiMe3)2 and CpFe(h5-C5H4SeSiMe3) have been prepared in order to functionalize the surface of metal–chalcogen cluster cores with redox active units (see below) (Wallbank & Corrigan2001; Lebold et al. 2003). The preparation of Et2N–C6H4–N=N–C6H4–SSiMe3 also holds promise for the ultimate assembly of metal chalcogenidenanoclusters whose cores are stabilized with strongly absorbing (dye) ligands(Fuhr & Fenske 2004). In a complementary study, silylated metal chalcogenolatecomplexes with the chelating ligand tetramethylethylenediamine [(N ,N ′-tmeda)Zn(ESiMe3)2] (E = Se, Te) are used as soluble delivery agents of surface[(N ,N ′-tmeda)Zn(E−)2] capping units onto the high-nuclearity CdE nanoclusters[(N ,N ′-tmeda)5Zn5Cd11E13(EPh)6] (DeGroot et al. 2003; DeGroot & Corrigan2005). In contrast, similar coordination complexes stabilized with monodentateligands (e.g. [(lut)2Zn(ESiMe3)2]; lut = 3,5-C5H3N) serve as a soluble source ofinterstitial ZnE22− for the preparation of the ternary adamantoid nanoclusters[ZnxCd10−xE4(EPh)12(PPr3)4] (DeGroot & Corrigan 2005).

4. Surface functionalization of metal chalcogenide nanoclusters

(a) Mixed chalcogen clusters

Metal chalcogenide nanoclusters have been of interest for some time owing inpart to the unique size-dependent properties that they exhibit (Alivisatos 1996;Nirmal & Brus 1999; Murray et al. 2000; Soloviev et al. 2000, 2001). More recently,the manipulation of their surfaces via ligand selection/design has become animportant focus in this arena of chemistry. The incorporation of specific ligandsonto nanoclusters has been found to have marked effects on the optical andelectronic properties of these materials (DeGroot et al. 2003).

The flexibility of incorporating different chalcogens in mixed chalcogenide/chalcogenolate complexes via the equation

10(R3P)2 · CdX2 + 12E′(Ph)SiMe3 + 4E(SiMe3)2

−→ [Cd10(E′Ph)12E4(PR3)4] + 20XSiMe3 (4.1)

has led to the preparation of the mixed chalcogen [Cd10E4(E′Ph)12(PPr3)4],E = Te, E′ = Te, and [Cd10E4(E′Ph)12(PPr2Ph)4], E = Te, E′ = Se; E = Te, E′ =S; E = Se, E′ = S, from the corresponding silylated reagents (figure 2). Thephotophysical properties of these mixed chalcogen nanoclusters are sensitiveto changes to both the interstitial and surface chalcogen ligands (Eichhöferet al. 2002; Aharoni et al. 2003). In the UV–Vis spectra for these ternary12–16 complexes, the onset of the absorption displays a shift to higher energywhen varying E and E′ from Te to Se to S, consistent with the change inbandgap energy in the corresponding bulk 12–16 materials. Emission from the[Cd10E4(E′Ph)12(PR3)4] clusters is only observed at low temperatures and theenergies and lifetime of these emissions in the photoluminescence spectra dependon the nature of the E′ chalcogen centres on the cluster surfaces, with the lightercongeners displaying higher-energy emissions (Aharoni et al. 2003).





Figure 2. Molecular structure of [Cd10Te4(SePh)12(PPr2Ph)4]: black, Cd; light grey, Te; mediumgrey, Se; small grey spheres, C, P.

The preparation of the mixed selenide/thiolate nanocluster [Cu72Se14(SPh)36(OAc)8(PPh3)6] (figure 3) and related CuxSey(SPh)z polynuclear complexes wasalso developed using this mixed chalcogen methodology (Fuhr et al. 2005).The nature of the structures of Cu(I) and Ag(I) chalcogenide nanoclusters inparticular is wide and varied, with the coordination flexibility of these metalcentres introducing an additional structural degree of freedom. The structure of[Cu72Se14(SPh)36(OAc)8(PPh3)6] displays a central Cu16Se14 that is envelopedbelow the surface of the cluster, which is primarily composed of Cu–SPh inaddition to the ligands PPh3 and OAc. The authors have further developed theapproach to incorporate substituted phenyl rings onto the S–Ar surfaces (Fuhret al. 2007; Langer et al. 2009). The mixed selenide/thiolate clusters [Cu28Se6(S-p-C6H4-Br)16(PPh3)8], [Cu50Se24(S-thiaz)2(dppm)10] (thiaz = 2-thiolatothiazoline)and [Cu22Se6(S-p-C6H4NO2)10(PPh3)8] have been reported recently (Fuhr et al.2007; Fernandez-Recio et al. 2008; Langer et al. 2009). Although the nitro groupsin the latter are not directly bonded to the cluster core (figure 4), they areobserved to have a pronounced effect on the UV–Vis absorption profiles of[Cu22Se6(S-p-C6H4NO2)10(PPh3)8] when compared with the comparatively sizedcluster [Cu28Se6(SPh)16(PPh3)6]. Whereas the former displays a strong absorptionmaximum in the visible region at approximately 400 nm from the –S-p-C6H4NO2moieties, this profile is not observed in spectra of the latter complex.

Much larger architectures have now been prepared from Ag(I) salts,and the silver selenide dimethylaminophenylthiolate clusters [Ag76Se13(S-p-C6H4NMe2)50(PPh3)6.5] (figure 5) and [Ag88Se12(S-p-C6H4NMe2)63(PPh3)6] alsodisplay similar ‘core’ (Ag2Se)/‘shell’ (AgS-S-p-C6H4NMe2) arrangements of thetwo chalcogen types found in the copper(I) systems (Chitsaz et al. 2006).





Figure 3. Molecular structure of [Cu72Se14(SPh)36(OAc)8(PPh3)6]: black, Cu; light grey, Se;medium grey, S; small grey spheres, C, O and P.

Figure 4. Molecular structure of [Cu22Se6(S-p-C6H4NO2)10(PPh3)8]: black, Cu; light grey, Se;medium grey, S; small grey spheres, C, O, P. NO2 on phenyl rings emphasized for clarity.





Figure 5. Molecular structure of [Ag76Se13(S-p-C6H4NMe2)50(PPh3)6.5]: black, Cu; light grey, Se;medium grey, S; small grey spheres, C, O, P. NMe2 on phenyl rings emphasized for clarity.

(b) Ferrocenyl chalcogen reagents

As has been demonstrated recently for 12–16 semiconductor nanoparticles(Mulrooney et al. 2009), the inclusion of redox active ferrocenyl units canalter the optical properties of the material (on/off quenching of luminescence)and introduce a functionality that may be used for chemical sensing. Silylatedferrocenyl chalcogen reagents offer a controlled route to the formation ofstructurally characterized metal chalcogenolate and chalcogenide clusters andnanoclusters with multiple ferrocenyl moieties incorporated onto the surface. Theassembly of ferrocenyl units onto the surface of both small and high-nuclearityclusters opens the door for a wide range of applications, including sensing andmolecular electronic devices (Lebande et al. 2002; Mulrooney et al. 2009).

The incorporation of one or two chalcogen sites via substitution on oneor both of the cyclopentadienyl rings allows for multiple bonding modes,owing to the flexible nature of the S/Se/Te sites, in addition to the freerotation about the C5 rings. The latter has been well developed for the relatedcarboxylate ligands CpFe(h5-C5H4C(O)O−) and 1,1′-Fc(C(O)O−)2 on metaloxide clusters (Chandrasekhar et al. 2000; Zheng et al. 2004). Stannoxaneframeworks, for instance, are relatively robust and themselves not redoxactive, thus the core does not interfere with the redox processes of thesurface ferrocenyl units (Chandrasekhar et al. 2000). The first of these





Figure 6. Molecular structure of [nBuSn(O)OC(O)(C5H4)Fe(C5H5)]6: black, Sn; light grey, O;medium grey, Fe; small grey spheres, C.

multiferrocenyl stannoxane assemblies reported was that of a drum-like corewith six ferrocene units about the surface, [(n-BuSn(O)OC(O)(C5H4)Fe(C5H5)]6(figure 6) (Chandrasekhar et al. 2000). The core comprised two hexameric Sn3O3rings in a puckered chair-like conformation. The two rings are then further joinedto one another, giving rise to six Sn2O2 units, which comprise the side facesof the cluster. This particular arrangement is a common feature of stannoxaneclusters (Chandrasekhar et al. 1987; Holmes et al. 1987). The ferrocenylunits of the ferrocenyl carboxolate ligands are spatially arranged around thedrum in a wheel-like fashion. This arrangement of both core and ferrocenylunits is also observed in [n-BuSn(O)OC(O)(CH2C5H4)Fe(C5H5)]6, the onlydifference being the incorporation of a CH2 spacer between ferrocenyl unitsand carboxylate moieties. This spacer, however, is important, as it allowsadditional flexibility in the ferrocene units and, ultimately, hydrogen bondinginteractions. These hydrogen bonding interactions provide the ability for theassembly of supramolecular grids of these clusters (Chandrasekhar et al. 2002).Cyclic voltammetry of each of these compounds shows a single reversibleoxidation, with all six ferrocenyl units oxidized at the same potential, even afterseveral cycles.

Unlike the synthesis of the drum-like ferrocenyl assemblies from the 1 : 1addition of ferrocenyl carboxylic acid to n-BuSn(O)OH in refluxing benzene,the mixed valence [Sn8O4OC(O)(C5H4)Fe(C5H5)6] (figure 7) was prepared viasolvothermal methods (Zheng et al. 2004). The central core comprised four endoSn3+ atoms, four exo Sn2+ atoms and four m4-O atoms occupying the four cornersof a distorted cube. The iron atoms sit at the vertices of a regular octahedron,with a ferrocenyl moiety spanning each face of the cube. The extensive effect thatthe ligands used can have on the structure of the core is highly evident in thesestannoxane clusters. As the use of the ferrocenyl carboxylate yields a drum-like





Figure 7. Molecular structure of [Sn8O4(Fe(C5H5(O)CO)2)6]: black, Sn; light grey, O; medium grey,Fe; small grey spheres, C.

core structure, the use of the disubstituted 1,1′-ferrocene dicarboxylate gives riseto a completely different cube-like arrangement of the core. Cyclic voltammetryof this compound shows an irreversible oxidation at 0.95 V, indicating that thecluster is not stable and decomposes upon oxidation.

Recently, the related heavier chalcogenolate ligands FcC(O)E− have beenincorporated onto metal cluster frameworks using the silylated reagentsFcC(O)ESiMe3 (E = S, Se, Te), themselves prepared via the addition ofLi[ESiMe3] to FcC(O)Cl (MacDonald & Corrigan 2008). These complementtrimethylsilylselenoferrocene (Lebold et al. 2003), which is prepared from Na[(h5-C5H5)Fe(h5-C5H4Se)] and ClSiMe3, and 1,1′-[Fe(h5-C5H4SeSiMe3)2], preparedfrom Li2[Fe(h5-C5H4Se)2] and ClSiMe3, as new reagents for the incorporationof multiple ferrocenyl moieties onto metal–chalcogen cores.

The coordination mode of the Se centres in the ferrocenyl selenolates inthese clusters is typically doubly bridging; however, triply bridging modesare also observed. The frameworks of the copper selenolate clusters [Cu4(m2-Se2Fc)2(PnPr3)4] (Nitschke et al. 2006), [Cu8(m2-Se2Fc)4(PPh2Et)4] (Wallbank &Corrigan 2001) and [Cu4(m2-SeOCFc)4(PPh3)4] (MacDonald & Corrigan 2008)exemplify the flexible coordination of the ligands (figure 8). The Cu atomsall adopt trigonal planar geometry, bridged by either: two selenolates andterminated by a phosphine, three Cu–Se interactions, or one selenolate and twophosphine ligands. In each cluster, the ferrocenyl moieties occupy surface sites.Unlike surface-modified stannoxane clusters, cyclic voltammetry of these copperselenolate clusters indicates an initial irreversible oxidation followed by either oneor two reversible waves (depending on the ligand used), indicating decompositionof the cluster upon oxidation of the ferrocenyl units and concomitant Se–Se bondformation (Wallbank & Corrigan 2001).





(a) (b) (c)

Figure 8. Molecular structures of (a) [Cu4(m2-FcSe2)2(PnPr3)4], (b) [Cu8(m2-FcSe2)4(PPh2Et)4]and (c) [Cu4(m2-SeOCFc)4(PPh3)4]: black, Cu; light grey, Se; medium grey, Fe; small greyspheres C, P.

Figure 9. Molecular structure of [Ag4(FcSe2)3]2−: black, Ag; light grey, Se; medium grey, Fe; smallgrey spheres C.

Silver(I) selenolate clusters can also be prepared in high yields using theseligands. The addition of FcC(O)SeSiMe3 to (Ph3P)3·AgOAc at low temperatureyields the cluster [Ag4(m2-SeOCFc)4(PPh3)4] (MacDonald & Corrigan 2008),which is composed of four equivalent [Ag(SeOCFc)(PPh3)] units and isstructurally isomorphous to [Cu4(m2-SeOCFc)4(PPh3)4]. The silver atoms alladopt a trigonal planar geometry, with one Ag–Se bond shorter than the other,and is terminated with a triphenylphosphine ligand. The twist conformationof the Ag4Se4 core contrasts with the chair conformation observed for theAg4S4 thiolate [Ag4(m2-SOCFc)4(PPh3)4]. Of all the ferrocenyl functionalizedclusters, [NBu4]2[Ag4(FcSe2)3] (Wallbank & Corrigan 2004) is the only homolepticcomplex, with an overall 2− charge on the cluster frame. The structure compriseda non-bonded Ag4 tetrahedron with all ferrocenyl selenolates m2-bridging tothe metals (figure 9). Each silver atom has a distorted trigonal planar geometry.The overall structure has also been observed in other silver chalcogenolate clusters(Henkel et al. 1988; Canales et al. 2003).





(a) (b)

Figure 10. Molecular structure of (a) [Ag8(Se2Fc)4(PnPr3)4] and (b) [Ag16(Se2Fc)8(PPh2Et)6]:black, Ag; light grey, Se; medium grey, Fe; small grey spheres C, P.

More recently, two higher-nuclearity ‘open’ silver ferrocenyl selenolate clusters,[Ag8(Se2Fc)4(PnPr3)4] and [Ag16(Se2Fc)8(PPh2Et)6] (Nitschke et al. 2007), havebeen synthesized (figure 10). The Ag8 complex consists of linear, trigonal planarand tetrahedral coordinated silver centres. The ferrocenyl selenolates adopt eithera m2- or m4-bridging interaction. The choice of phosphine ligands used can have amarked effect on the size of the cluster that is obtained, as is seen when using thelarger ligand PPh2Et, which results in the formation of [Ag16(Se2Fc)8(PPh2Et)6].Here, the core consists of tetrahedral and trigonal planar silver atoms allbridged by the eight ferrocenyl selenolates, which adopt m2- or m4-coordinationmodes. The core can be loosely described as two linked Ag8Se8 moieties, thedimerization occurring to compensate for the reduced P : Ag ratio in the largerframework.

Reactions using a combination of both Fc(SeSiMe3)2 and Se(SiMe3)2 offera controlled route to the formation of larger, more condensed frameworks,with Se(SiMe3)2 providing a source of interstitial Se2−. The copper(I) clusters[Cu20Se6(Se2Fc)4(PPh2Et)10], [Cu20Se6(Se2Fc)4(PnBu3)10] (Wallbank & Corrigan2001), [Cu20Se6(Se2Fc)4(PnPr3)10], [Cu36Se12(FcSe2)6(PnPr3)10(Ph2P(CH2)3SH)2],[Cu36Se12(FcSe2)6(PnPr2Ph)12] (Nitschke et al. 2006) and [Cu40Se12(FcSe2)8(PPh3)9] (Wallbank & Corrigan 2001) have all been prepared in good yieldsusing this methodology. The Cu–Se framework of the three [Cu20Se6(Se2Fc)4(PPh2Et)10], [Cu20Se6(Se2Fc)4(PnBu3)10] and [Cu20Se6(Se2Fc)4(PnPr3)10] are verysimilar, with only minor differences due to the different tertiary phosphinesused, illustrating the structure-directing control of the FcSe2 ligands (figure 11).The selenium framework consists of six m5-selenide ligands with m3-selenolateligands all bonded to copper centres, which adopt both trigonal planar andtetrahedral geometries. The ferrocenyl units exposed on the surface of thecluster are sandwiched between 10 surface phosphine ligands. The use ofFcSe2 ligands imparts greater stability to these clusters in solution (Nitschkeet al. 2006). In contrast, Cu2Se clusters whose surfaces are passivated uniquelywith phosphines typically undergo condensation reactions when redissolved inorganic solvents (Fuhr et al. 2002). At present, there remains, however, much





Figure 11. Molecular structure of [Cu20Se6(Se2Fc)4(PPr3)10]: black, Cu; light grey, Se; mediumgrey, Fe; small grey spheres C, P.

to develop in terms of the applications of these modified materials, includingimproving the kinetic stability of these species when they are re-dispersed inorganic solvents.

The incorporation of an even larger number of interstitial selenide ligandsallows for the corresponding growth into larger copper selenide clusters andthe incorporation of a greater number of redox active ferrocenyl units ontothe surface. [Cu36Se12(FcSe2)6(PnPr2Ph)12] (figure 12) (Nitschke et al. 2006) isobtained using a combination of CuOAc, PnPr2Ph, Se(SiMe3)2 and Fc(SeSiMe3)2.The cluster can be described as consisting of three Cu10(Se2Fc)2Se3 units abouta central Cu6Se3 core, with a single m9-selenide and two m6-selenides bridgingnine interstitial copper atoms. There is thus a clear structural relationshipobserved between the surfaces of Cu20 and Cu36 frameworks, the latterhaving an expanded central copper selenide core. The Cu36 cluster frameworkcan also be grown via the partial substitution of the tertiary phosphines,as reported for the synthesis of [Cu36Se12(FcSe2)6(PnPr3)10(Ph2P(CH2)3SH)2](Nitschke et al. 2006).

Currently, the highest-nuclearity ferrocenylated copper selenide cluster thathas been structurally characterized is [Cu40Se12(FcSe2)8(PPh3)9] (figure 13)(Wallbank & Corrigan 2005). In this layered framework, there are 12 selenideligands distributed in what is best described as an ABC-type Se20 packing.The selenide ligands are m4- and m8-ligating, while the selenium centres on theselenolate ligands are m2-, m3- or m4-bonded to the copper centres.





Figure 12. Molecular structure of [Cu36Se12(Se2Fc)6(PnPr3)10(Ph2P(CH2)3SH)2]: black, Cu; lightgrey, Se; medium grey, Fe; small grey spheres C, P. S atoms emphasized for clarity.

Figure 13. Molecular structure of [Cu40Se12(Se2Fc)8(PPh3)9]: black, Cu; light grey, Se; mediumgrey, Fe; small grey spheres C, P.





5. Conclusions and outlook

Chalcogen reagents that are freely soluble in common solvents (even at lowtemperatures) and by-products that do not interfere with the crystallizationprocesses are extremely effective for the synthesis of the largest, monodispersemetal–chalcogen nanoclusters. The reactions of ligand-solubilized metal saltswith a combination of E(SiMe3)2 and RESiMe3 are now a proven strategy toaccess high-nuclearity metal chalcogenolate/chalcogenide nanoclusters. Single-crystal X-ray diffraction studies on these clusters clearly identify the arrangementof the metal–chalcogen core, the structure of which can be highly dependent onthe bonding nature of the surface chalcogenolate ligands. In order to achieve along-term goal of producing functional nanomaterials using this methodology,the design and preparation of new RESiMe3 reagents is required. This area ofdevelopment is, relatively speaking, still in its infancy; however, new RESiMe3reagents incorporating absorbing dye and redox active moieties have resulted inmore tailored surfaces being incorporated onto metal chalcogenide frameworks.These clearly indicate the viability of further developing this general reactionstrategy where the nanocluster cores can serve as tethers for the anchoring ofmultiple, functional surface chalcogenolate units.

References

Aharoni, A., Eichhöfer, A., Fenske, D. & Banin, U. 2003 Optical spectroscopy of cadmium-chalcogenide clusters of the type [Cd10E4(E′Ph)12(PR3)4], (E = Te, Se; E′ = Se, S). Opt. Mater.24, 43–49. (doi:10.1016/S0925-3467(03)00103-4)

Alivisatos, A. P. 1996 Perspectives on the physical chemistry of semiconductor nanocrystals.J. Phys. Chem. 100, 13 226–13 239. (doi:10.1021/jp9535506)

Anson, C. E., Eichhöfer, A., Issac, I., Fenske, D., Fuhr, O., Sevillano, P., Persau, C., Stalke, D. &Zhang, J. 2008 Synthesis and crystal structures of the ligand-stabilized silver chalcogenideclusters [Ag154Se77(dppxy)18], [Ag320(StBu)60S130(dppp)12], [Ag352S128(StC5H11)96], and[Ag490S188(StC5H11)114]. Angew. Chem. Int. Edn. 47, 1326–1331. (doi:10.1002/anie.200704249)

Burgess, M. R. & Morley, C. P. 2001 Electrochemical and NMR spectroscopic studies of seleniumand tellurium substituted ferrocenes I: Ferrocenyl alkyl chalcogenides [Fe(h-C5H5)(h-C5H4ER)].J. Organomet. Chem. 623, 101–108. (doi:10.1016/S0022-328X(00)00738-5)

Canales, S., Crespo, O., Gimeno, M. C., Jones, P. G., Laguna, A., Silvestru, A. & Silvestru, C.2003 Gold and silver complexes with the diselenium ligand [Ph2P(Se)NP(Se)Ph2]−. Inorg. Chim.Acta 347, 16–22. (doi:10.1016/S0020-1693(02)01440-8)

Chandrasekhar, V., Schmid, C. G., Burton, S. D., Holmes, J. M., Day, R. O. & Holmes,R. R. 1987 New drum and ladder organooxotin carboxylates. Inorg. Chem. 26, 1050–1056.(doi:10.1021/ic00254a017)

Chandrasekhar, V., Nagendran, S., Bansal, S., Kozee, M. A. & Powell, D. R. 2000 An iron wheelon a tin drum: a novel assembly of a hexaferrocene unit on a tin–oxygen cluster. Angew. Chem.Int. Edn. 39, 1833–1835. (doi:0570-0833/00/3910-1833)

Chandrasekhar, V., Nagendran, S., Bansal, S., Cordes, A. W. & Vij, A. 2002 Rangoli withtin drums: C–H–O bond-assisted supramolecular grids involving organostannoxane clusters.Organometallics 21, 3297–3300. (doi:10.1021/om0203025)

Chitsaz, S., Fenske, D. & Fuhr, O. 2006 Silver chalcogenide clusters with dimethylanilino-mercapto ligands: syntheses and crystal structures of [Ag65S13(SC6H4NMe2)39(dppm)5],[Ag76Se13(SC6H4NMe2)50(PPh3)6.5], and [Ag88Se12(SC6H4NMe2)63(PPh3)6]. Angew. Chem.Int. Edn. 45, 8055–8059. (doi:10.1002/anie.200602709)

Dance, I. G. 1986 The structural chemistry of metal thiolate complexes. Polyhedron 5, 1037–1104.(doi:10.1016/S0277-5387(00)84307-7)



http://dx.doi.org/doi:10.1016/S0925-3467(03)00103-4

http://dx.doi.org/doi:10.1021/jp9535506

http://dx.doi.org/doi:10.1002/anie.200704249

http://dx.doi.org/doi:10.1016/S0022-328X(00)00738-5


http://dx.doi.org/doi:10.1021/ic00254a017

http://dx.doi.org/doi:0570-0833/00/3910-1833

http://dx.doi.org/doi:10.1021/om0203025





DeGroot, M. W. & Corrigan, J. F. 2000 Polynuclear bismuth selenolates: rings en route to clusters.J. Chem. Soc., Dalton Trans. 1235–1236. (doi:10.1039/b001417f)

DeGroot, M. W. & Corrigan, J. F. 2004 Comprehensive coordination chemistry II, vol. 7 (eds M.Fujita, A. Powell & C. Creutz), pp 57–123. Oxford, UK: Pergamon.

DeGroot, M. W. & Corrigan, J. F. 2005 Coordination complexes of zinc with reactive ESiMe3(E = S, Se, Te) ligands. Organometallics 24, 3378–3385. (doi:10.1021/om050088v)

DeGroot, M. W. & Corrigan, J. F. 2006 Metal-chalcogenolate complexes with silyl functionalities:synthesis and reaction chemistry. Z. Anorg. Allg. Chem. 632, 19–29. (doi:10.1002/zaac.200500314)

DeGroot, M. W., Taylor, N. J. & Corrigan, J. F. 2003 Zinc chalcogenolate complexes ascapping agents in the synthesis of ternary II–II′–VI nanoclusters. Structure and photophysicalproperties of [(N ,N ′-tmeda)5Zn5Cd11Se13(SePh)6(thf)2. J. Am. Chem. Soc. 125, 864–865.(doi:10.1021/ja028800s)

Dehnen, S. & Fenske, D. 1996 Cu24S12(PMeiPr2)12], [Cu28S14(PtBu2Me)12], [Cu50S25(PtBu2Me)16], [Cu70Se35(PtBu2Me)21], [Cu31Se15(SeSiMe3)(PtBu2Me)12] and [Cu48Se24(PMe2Ph)20]:new sulfur- and selenium-bridged copper clusters. Chem. Eur. J. 2, 1407–1416.(doi:10.1002/chem.19960021113)

Dehnen, S., Eichhöfer, A. & Fenske, D. 2002 Chalcogen-bridged copper clusters. Eur. J. Inorg.Chem. 2002, 279–317. (doi:10.1002/1099-0682(20022)2002:2<279::AID-EJIC279>3.0.CO;2-H)

Dehnen, S., Eichhöfer, A., Corrigan, J. F. & Fenske, D. 2004 Synthesis and characterizationof Ib–VI nanoclusters. In Nanoparticles (ed. G. Schmid), pp. 107–185. Weinheim, Germany:Wiley-VCH.

Eichhöfer, A., Ajaroni, A. & Banin, U. 2002 Synthesis, structure, and optical properties ofnew cadmium chalcogenide clusters of the type [Cd10E4(E′Ph)12(PR3)4], (E, E′ = Te, Se, S).Z. Anorg. Allg. Chem. 628, 2415–2421. (doi:0044_2313/02/628/2415_2421)

Fenske, D. 1994 Clusters and colloids, from theory to applications (ed. G. Schmid), pp. 212–297.Weinheim, Germany: VCH.

Fenske, D. & Langetepe, T. 2002 Synthesis and structures of silver-selenide clustercomplexes [Ag4(SeiPr)4(dppm)2], [Ag8(SeEt)8(dppp)]∞ [Ag28Se6(SenBu)16(dppp)4], and[Ag124Se57(SePtBu2)4Cl6(tBu2P(CH2)3PtBu2)12]. Angew. Chem. Int. Edn. 41, 300–304.(doi:10.1002/1521-3773(20020118)41:2<300::AID-ANIE300>3.0.CO;2-T)

Fernandez-Recio, L., Fenske, D. & Fuhr, O. 2008 Copper chalcogenide cluster compoundswith nitro-functionalized ligand shell. Z. Anorg. Allg. Chem. 634, 2853–2857. (doi:10.1002/zaac.200800208)

Fuhr, O. & Fenske, D. 2004 Sulfur bridged copper complexes with dye ligands. Z. Anorg. Allg.Chem. 630, 1607–1612. (doi:10.1002/zaac.200400219)

Fuhr, O., Meredith, A. & Fenske, D. 2002 New copper selenium clusters with a sulfur functionalisedligand shell. J. Chem. Soc., Dalton Trans. 4091–4094. (doi:10.1039/b205057a)

Fuhr, O., Fernandez-Recio, L. & Fenske, D. 2005 New copper chalcogenide clusters with a selenidecore and a sulfide shell. Eur. J. Inorg. Chem. 2005, 2306–2314. (doi:10.1002/ejic.200400758)

Fuhr, O., Fernandez-Recio, L., Castineiras, A. & Fenske, D. 2007 Synthesis and structure ofthe clusters [Cu50Se24(S-thiaz)2(dppm)10] and [Cu48Se24(S-thiazH)2(dppm)10. Z. Anorg. Allg.Chem. 633, 700–704. (doi:10.1002/zaac.200600359)

Haller, W. S. & Irgolic, K. J. 1972 Diaryl ditellurides from Grignard reagents and elementaltellurium. J. Organomet. Chem. 38, 97–103. (doi:10.1016/S0022-328X(00)81365-0)

Henkel, G., Krebs, B., Betz, P., Fietz, H. & Saatkamp, K. 1988 [Au2Ag4L4]−2 , [Au2Cu4L4]−2 ,[Au3Cu3L4]−2 , [Cu4L3]−2 , and [Ag9L6]−3 (L = ethane-1,2-dithiolate)—novel homoleptic complexesof the coinage metals, including the first heteronuclear metal thiolates. Angew. Chem. Int. Edn.27, 1326–1329. (doi:10.1002/anie.198813261)

Herberhold, M. & Leitner, P. 1987 Ferrocenylchalkogenide. J. Organomet. Chem. 336, 153–161.(doi:10.1016/0022-328X(87)87165-6)

Holmes, R. R., Schmid, C. G., Chandrasekhar, V., Day, R. O. & Holmes, J. M. 1987 Oxocarboxylate tin ladder clusters. A new structural class of organotin compounds. J. Am. Chem.Soc. 109, 1408–1414. (doi:10.1021/ja00239a022)



http://dx.doi.org/doi:10.1039/b001417f

http://dx.doi.org/doi:10.1021/om050088v

http://dx.doi.org/doi:10.1002/zaac.200500314


http://dx.doi.org/doi:10.1021/ja028800s

http://dx.doi.org/doi:10.1002/chem.19960021113

http://dx.doi.org/doi:10.1002/1099-0682(20022)2002:2<279::AID-EJIC279>3.0.CO;2-H

http://dx.doi.org/doi:0044protect LY1extunderscore 2313/02/628/2415protect LY1extunderscore 2421

http://dx.doi.org/doi:10.1002/1521-3773(20020118)41:2<300::AID-ANIE300>3.0.CO;2-T




http://dx.doi.org/doi:10.1039/b205057a

http://dx.doi.org/doi:10.1002/ejic.200400758


http://dx.doi.org/doi:10.1016/S0022-328X(00)81365-0


http://dx.doi.org/doi:10.1016/0022-328X(87)87165-6

http://dx.doi.org/doi:10.1021/ja00239a022



Krautscheid, H., Fenske, D., Baum, G. & Semmelmann, M. 1993 A new copper selenidecluster with PPh3 ligands: [Cu146Se73(PPh3)30]. Angew. Chem. Int. Edn. 32, 1303–1305.(doi:0570-0X33/93/0909-I303)

Krebs, B. & Henkel, G. 1991 Transition-metal thiolates: from molecular fragments of sulfidicsolids to models for active centers in biomolecules. Angew. Chem. Int. Edn. 30, 769–788.(doi:10.1002/anie.199107691)

Krebs, B., Voelker, D. & Stiller, K. O. 1982 Novel adamantane-like thio- and seleno anionsfrom aqueous solution: Ga4S8−

10 , In4S8−10 , In4Se8−

10 . Inorg. Chim. Acta 65, L101–L102.(doi:10.1016/S0020-1693(00)93508-4)

Krief, A., Trabelsi, M. & Dumont, W. 1992 Syntheses of alkali selenolates from diorganicdiselenides and alkali metal hydrides: scope and limitations. Synthesis 10, 933–935.(doi:10.1055/s-1992-26266)

Langer, R., Wünsche, L., Fenske, D. & Fuhr, O. 2009 Copper chalcogenide clustercompounds with bromo-functionalized ligand shell. Z. Anorg. Allg. Chem. 635, 2488–2494.(doi:10.1002/zaac/200900233)

Lebande, A., Ruiz, J. & Astruc, D. 2002 Supramolecular gold nanoparticles for the redoxrecognition of oxoanions: syntheses, titrations, stereoelectronic effects, and selectivity. J. Am.Chem. Soc. 24, 1782–1789. (doi:10.1021/ja017015x)

Lebold, T. P., Stringle, D. L. B., Workentin, M. S. & Corrigan, J. F. 2003 Functionalizingthe surface of II–VI clusters: redox active centers on the adamantoid complex [Cd4Cl4m-(SeC5H4)Fe(C5H5)6]2−. Chem. Commun. 1398–1399. (doi:10.1039/b302829a)

Liesk, J., Schulz, P. & Klar, G. 1977 Chalkogenolat-Ionen und ihre Derivate. I. Darstellungund Eigenschaften salzartiger Chalkogenophenolate. Z. Anorg. Allg. Chem. 435, 98–102.(doi:10.1002/zaac.19774350113)

MacDonald, D. G. & Corrigan, J. F. 2008 New reagents for the synthesis of a series offerrocenoyl functionalized copper and silver chalcogenolate complexes. Dalton Trans. 5048–5053.(doi:10.1039/b804597f)

Müller, A. & Diemann, E. 1987 Polysulfide complexes of metals (eds H. J. Emeléus & A. G. Sharpe).Advances in Inorganic Chemistry, vol. 31, pp. 89–122. New York, NY: Academic Press.

Mulrooney, R. C., Singh, N., Kaur, N. & Callan, J. F. 2009 An ‘off–on’ sensor forfluoride using luminescent CdSe/ZnS quantum dots. Chem. Commun. 686–688. (doi:10.1039/b817569a)

Murray, C. B., Kagan, C. R. & Bawendi, M. G. 2000 Synthesis and characterization of monodispersenanocrystals and close-packed nanocrystal assemblies. Annu. Rev. Mater. Sci. 30, 545–610.(doi:10.1146/annurev.matsci.30.1.545)

Nirmal, M. & Brus, L. 1999 Luminescence photophysics in semiconductor nanocrystals. Acc. Chem.Res. 32, 407–414. (doi:10.1021/ar9700320)

Nitschke, C., Fenske, D. & Corrigan, J. F. 2006 Ferrocenyldiselenolate-stabilized copper–silverclusters. Inorg. Chem. 45, 9394–9401. (doi:10.1021/ic061111n)

Nitschke, C., Wallbank, A. I., Fenske, D. & Corrigan, J. F. 2007 Facile synthesis of highnuclearity silver-ferrocenyldiselenolate clusters. J. Clust. Sci. 18, 131–140. (doi:1040.7278/07/0300-0131/0)

Roof, L. C. & Kolis, J. W. 1993 New developments in the coordination chemistry of inorganicselenide and telluride ligands. Chem. Rev. 93, 1037–1080. (doi:10.1021/cr00019a010)

Schmidt, M., Kiewert, E., Lux, H. & Sametschek, C. 1986 Beitrag zur Synthese von Organyl-trimetylsilyl-seleniden, R–Se–Si(CH3)3. Phosphorus Sulfur Silicon Relat. Elem. 26, 163–167.(doi:10.1080/03086648608083090)

So, J. & Boudjouk, P. 1989 Convenient syntheses of hexamethyldisilathiane and tetramethyl-disilathiane. Synthesis 1989, 306–307. (doi:10.1055/s-1989-27235)

Soloviev, V. N., Eichhöfer, A., Fenske, D. & Banin, U. 2000 Molecular limit of a bulksemiconductor: size dependence of the ‘band gap’ in CdSe cluster molecules. J. Am. Chem.Soc. 122, 2673–2674. (doi:10.1021/ja9940367)

Soloviev, V. N., Eichhöfer, A., Fenske, D. & Banin, U. 2001 Size-dependent optical spectroscopyof a homologous series of CdSe cluster molecules. J. Am. Chem. Soc. 123, 2354–2364.(doi:10.1021/ja003598j)



http://dx.doi.org/doi:0570-0X33/93/0909-I303



http://dx.doi.org/doi:10.1055/s-1992-26266

http://dx.doi.org/doi:10.1002/zaac/200900233

http://dx.doi.org/doi:10.1021/ja017015x



http://dx.doi.org/doi:10.1039/b804597f



http://dx.doi.org/doi:10.1146/annurev.matsci.30.1.545

http://dx.doi.org/doi:10.1021/ar9700320

http://dx.doi.org/doi:10.1021/ic061111n

http://dx.doi.org/doi:1040.7278/07/0300-0131/0

http://dx.doi.org/doi:1040.7278/07/0300-0131/0

http://dx.doi.org/doi:10.1021/cr00019a010

http://dx.doi.org/doi:10.1080/03086648608083090

http://dx.doi.org/doi:10.1055/s-1989-27235

http://dx.doi.org/doi:10.1021/ja9940367

http://dx.doi.org/doi:10.1021/ja003598j



Thompson, D. P. & Boudjouk, P. 1988 A convenient synthesis of alkali metal selenides anddiselenides in tetrahydrofuran and the reactivity differences exhibited by these salts towardorganic bromides. Effect of ultrasound. J. Org. Chem. 53, 2109–2112. (doi:10.1021/jo00244a051)

Wallbank, A. I. & Corrigan, J. F. 2001 1,1′-Bis(trimethylsilylseleno)ferrocene in clustersynthesis: a redox active surface on a copper–selenide core. Chem. Commun. 377–378.(doi:10.1039/b010023o)

Wallbank, A. I. & Corrigan, J. F. 2004 A homoleptic silver-ferrocenylselenolate: synthesis andcharacterization of [Ag4(fcSe2)3]2−. J. Clust. Sci. 15, 225–232. (doi:1040-7278/04/0600-0225)

Wallbank, A. I. & Corrigan, J. F. 2005 Ferrocenyl-passivated nanoclusters: synthesis of[Cu20Se6(Se2fc)4(PR2R′)10] and [Cu40Se12(Se2fc)8(PPh3)10. Organometallics 24, 788–790.(doi:10.1021/om049238c)

Wang, X. J., Langetepe, T., Persau, C., Kang, B. S., Sheldrick, G. M. & Fenske, D. 2002Synthesis and crystal structures of the new Ag–S clusters [Ag70S16(SPh)34(PhCO2)4(triphos)4]and [Ag188Se94(PR3)30]. Angew. Chem. Int. Edn. 41, 3818–3822. (doi:0044-8249/02/4120-3818)

Wehnschulte, R. J. & Power, P. P. 1997 Low-temperature synthesis of aluminum sulfide asthe solvate Al4S6(NMe3)4 in hydrocarbon solution. J. Am. Chem. Soc. 119, 9566–9567.(doi:10.1021/ja972111c)

Zheng, G. L., Ma, J. F., Su, Z. M., Yan, L. K., Yang, J., Li, Y. Y. & Liu, J. F. 2004 A mixed-valence tin–oxygen cluster containing six peripheral ferrocene units. Angew. Chem. Int. Edn.43, 2409–2411. (doi:10.1002/anie.200353359)



http://dx.doi.org/doi:10.1021/jo00244a051

http://dx.doi.org/doi:10.1039/b010023o


http://dx.doi.org/doi:10.1021/om049238c


http://dx.doi.org/doi:10.1021/ja972111c



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