Inorganic Chemistry Communications 14 (2011) 1932–1936

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Inorganic Chemistry Communications

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Illusive tungsten-imido-dithiocarbamate complexes: Facile carbon–nitrogenbond formation

Alexander Edwards, Graeme Hogarth ⁎, Nathan Hollingsworth, Joseph J. OllerDepartment of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK

⁎ Corresponding author.E-mail address: g.hogarth@ucl.ac.uk (G. Hogarth).

1387-7003/$ – see front matter © 2011 Elsevier B.V. Alldoi:10.1016/j.inoche.2011.09.014

a b s t r a c t

a r t i c l e i n f o

Article history:Received 29 July 2011Accepted 11 September 2011Available online 17 September 2011

Keywords:TungstenImidoDithiocarbamateOxoUreato

Heating [WO2(S2CNBui2)2] with a slight excess of ArNCO (Ar=Ph, p-tolyl) results in the rapid formation of

imido-ureato complexes [W(NAr){κ2-ArNC(O)NAr}(S2CNBui2)2], a transformation believed to occur via the bis

(imido) intermediates [W(NAr)2(S2CNBui2)2]. The ureato ligand is easily removed (as the urea) upon addition

of gaseous HCl to afford the dichloride [W(NAr)Cl2(S2CNBui2)2]. While bis(imido) complexes are unavailable

from the direct reaction of isocyanates (or amines) with [WO2(S2CNBui2)2], they can be prepared upon addition

of dithiocarbamate salts to [W(NBut)2(NHBut)2] addition of two equivalents of [NH2Bui2][Bui

2NCS2] affording[W(NBut)2(S2CNBu

i2)2] in which both imido groups are linear.

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© 2011 Elsevier B.V. All rights reserved.

While both tungsten-dithiocarbamate [1] and tungsten-imido [2]chemistry are well developed, somewhat surprising tungsten-imido-dithiocarbamate complexes have to date proved elusive [3].The precise reason(s) for this are unclear, especially since molybdenum-imido-dithiocarbamate chemistry has been so extensively described[3,4], but a contributing factor is likely the lack of suitable tungsten-oxo-dithiocarbamate precursors since a common route to transitionmetal imido complexes involves the reactions of metal oxides withprimary amines, isocyanates and other imido sources [5]. Young com-mented on the paucity of tungsten-oxo-dithiocarbamate complexes sug-gesting that this may be due to their propensity to decompose withformation of the very stable polytungstates [6]. At the time only a fewsuch species were known, including; [WO2(S2CNR2)2] (R=Cy, Bz)[7], [WO(S2CNBz2)2] [8] and [WO2Cl2(S2CNMe2)2] [9]. In the in-tervening 15 years little progress has been made in tungsten-oxo-dithiocarbamate chemistry, with one notable exception. In 2004,Unoura and co-workers reported a relatively simple preparation of theair and moisture stable complex [WO2(S2CNBui

2)2] [10], being formedupon addition of sodium tungstate to an aqueous solution of the di-thiocarbamate while carefully regulating the pH. Both the formationand stability of the latter are surprising. Unoura reported that all at-tempts to make other dithiocarbamate derivates via this simplemethod failed, while in previously both [WO2(S2CNCy2)2] [7] and[WO2(S2CNBz2)2] [8] were reported to be unstable. We wereattracted to the potential use of [WO2(S2CNBui

2)2] (1) as a gatewayinto tungsten-imido-dithiocarbamate chemistry. In particular, we

hoped that reaction with arylisocyanates might lead to CO2 elimina-tion and formation of the desired imido complexes.We have extensivelydeveloped this approach towards the synthesis of molybdenum-imido-dithiocarbamate complexes [11–13], andwhile the reaction out-comes are not always simple [12,13], in all cases imido-dithiocarbamatecomplexes result.Wewere, however, concerned by the report of an earlyunsuccessful attempt to prepare a tungsten-imido-dithiocarbamate com-plex upon heating [WOCl2(S2CNMe2)2] with excess PhNCO [9]. Thespectator effect in multiply bonded ligands is well-documented [14]and we anticipated that the presence of two oxo ligands in [WO2

(S2CNBui2)2] may significantly enhance their reactivity. Indeed this

is the case and herein we describe two facile routes into tungsten-imido-dithiocarbamate complexes namely the reaction of ArNCO with[WO2(S2CNBui

2)2] which affords ureato complexes and the additionof the dithiocarbamate salt [NH2Bui

2][Bui2NCS2] to tungsten bis(tert-

butylimido) precursors which affords the bis(imido) complex[W(NBut)2(S2CNBui

2)2].Heating a toluene solution of 1 and ca. 3 equivalents of ArNCO

(Ar=Ph, p-tolyl) in toluene for 1 h results in a marked colour changefrom pale yellow to bright orange and lead to the isolation of [W(NAr){κ2-ArNC(O)NAr}(S2CNBui

2)2] (2–3) in yields of 30–35% after chro-matographic work-up and crystallization from ether (Scheme 1) [15].The molecular structures of 2–3 were determined [16] and while inboth gross structural features were the same, due to a substantial disor-der problem in 3 (Ar=p-tolyl) only that of [W(NPh){κ2-PhNC(O)NPh}(S2CNBui

2)2] (2) will be discussed (Fig. 1). The coordination geometryabout tungsten is an approximate pentagonal bipyramid with theimido ligand and one nitrogen of the ureato ligand, N(5), taking up theaxial sites. Such a gross coordination is similar to that found in the cationof the related seven-coordinate complex, [WS(S2CNEt2)3][BF4] [17];

OSS

S

SW

ON

RR

NRR

3 ArNCO

S

SN

N

SW

NArN

RR

C

S

R = iBu

110 oC

Ar = Ph, p-tolyl

Ar

Ar

O

NR

R1

2-3

2 HCl

- (ArNH)2COS

SCl

Cl

SW

NArN

RR

S

NR

R

4 (Ar = p-tolyl)

S

SS

W

NArN

RR

S

NR

RS

S

NRR

HBF4.Et2O [S2CNR2]-

NButSS

S

SW

NBut

NR

R

NRR

6

ButH2N

ButH2NW

NBut

NBut

2 [S2CNR2]-

5

Scheme 1. Synthesis of tungsten-imido-dithiocarbamate complexes.

1933A. Edwards et al. / Inorganic Chemistry Communications 14 (2011) 1932–1936

here the sulfide and one sulfur of a dithiocarbamate ligand occupying theaxial sites. The imido group displays the classic linear coordination envi-ronment [W(1)-N(3)-C(20) 178.7(6)°] and short tungsten–nitrogen in-teraction [W(1)-N(3) 1.737(7) ] [5]. The ureato ligand is approximatelyplanar and the phenyl rings lie in this plane. Angles at N(4) and N(5)are close to 360° suggesting that these atoms are sp2 hybridized. Thetungsten–nitrogen bond lengths [W(1)-N(4) 2.077(6) & W(1)-N(5)2.144(7) ] vary by only 0.07 suggesting that the imido ligand effectsonly a weak trans-influence. The bite-angle at tungsten is small [N(4)-W(1)-N(5) 62.1(3)°] and this leads to a deformation of both nitrogen

Fig. 1.Molecular structure of [W(NPh){κ2-PhNC(O)NPh}(S2CNBui2)2] (2) with selected bond leW(1)-S(1) 2.521(2), W(1)-S(2) 2.524(2), W(1)-S(3) 2.484(2), W(1)-S(4) 2.535(2), C(19)-O(1N(3)-C(20) 178.7(6), S(1)-W(1)-S(2) 67.66(7), S(3)-W(1)-S(4) 68.02(7), N(4)-W(1)-N(5) 62

atoms from their idealized positions. Thus the angle between the twoaxial nitrogen atoms is 165.7(3)°, while N(4) is distorted out of the pen-tagonal plane by 0.595 Å. A hand full of tungsten ureato complexeshave previously been reported [18].

In previous work we have noted that addition of arylisocyanate toa bridging imido ligand of the dimeric molybdenum(V) complexes,[Mo(NAr)(S2CNEt2)(μ-NAr)]2, affords a bridging ureato complex viaa process which is both reversible and regioselective [13]. The latteris a result of the quite asymmetric binding of the ureato ligand tothe dimolybdenum centre leading to the suggestion that it is a weakly

ngths (Å) and angle (°): W(1)-N(3) 1.737(7), W(1)-N(4) 2.077(6), W(1)-N(5) 2.144(7),) 1.225(10), N(3)-C(20) 1.377(10), N(4)-C(19) 1.349(11), N(5)-C(19) 1.424(10), W(1)-.1(3), N(3)-W(1)-N(5) 165.7(3).

Fig. 2.Molecular structure of [W(NBut)2(S2CNBui2)2] (6) with selected bond lengths (Å) and angle (°): W(1)-N(3) 1.752(3), W(1)-N(4) 1.752(3), W(1)-S(1) 2.7167(9), W(1)-S(2)

2.4592(9), W(1)-S(3) 2.6973(10), W(1)-S(4) 2.4645(9), N(3)-W(1)-N(4) 107.4(1), S(1)-W(1)-S(2) 67.66(3), S(3)-W(1)-S(4) 68.14(3), W(1)-N(3)-C(19) 166.8(2), W(1)-N(4)-C(23) 167.7(2).

1934 A. Edwards et al. / Inorganic Chemistry Communications 14 (2011) 1932–1936

bound isocyanate complex. In a similar manner here, the formation of2–3 can be envisaged to occur via an intermediate bis(imido) com-plex, [W(NAr)2(S2CNBui

2)2]. Since such a species must necessarilyhave a cis-arrangement of imido ligands, and thus 2–3 are nominal-ly formed upon addition of an isocyanate [O(1)-C(19)-N(5)-C(32)to C(37)] with concomitant movement of a dithiocarbamate ligandinto the pentagonal plane. In order to try and generate [W(N-p-tolyl)2(S2CNBui

2)2], we heated 3 in toluene for 4 h; however, there was no ev-idence of isocyanate loss under these conditions. Considering that lossmay be reversible but the equilibrium strongly favoured theureato complex, we added one equivalent of benzylamine inorder to trap the released isocyanate (as the urea) and generatethe desired bis(imido) complex, however, no such transformationwas observed.

The ureato complexes 2–3 provide a useful entry into tungsten-imido-dithiocarbamate as the ureato ligand is easily removed. Thus,addition of two equivalents of HCl (in ether) to a dichloromethanesolution of 3 results in an immediate colour change from orange to yel-low resulting from the clean formation of [W(N-p-tolyl)Cl2(S2CNBui

2)2](4) and di-p-tolylurea [19]. Formation of 4 is interesting since, as previ-ously mentioned, the direct reaction of [WOCl2(S2CNMe2)2] withPhNCO fails [9]. Dichloride 4 in turn reacts with a further equivalent ofdithiocarbamate to give [W(N-p-tolyl)(S2CNBui

2)3][Cl] (5-Cl). This cat-ion is also themajor product of the addition of HBF4 in ether to 3, whichleads to isolation of [W(N-p-tolyl)(S2CNBui

2)3][BF4] (5-BF4) [19]. It ispresumed to proceed via initial formation of the five-coordinate dica-tion, [W(N-p-tolyl)(S2CNBui

2)2]2+, although this has yet to be isolatedor trapped.

While the ureato complexes provided a convenient entry intotungsten-imido-dithiocarbamate chemistry we have yet to iso-late target bis(imido) complexes [W(NAr)2(S2CNBui

2)2] from thisroute.We have therefore explored a second avenue, namely the additionof dithiocarbamate ligands to pre-formed tungsten bis(imido) com-plexes. Thus addition of two equivalents of [NH2Bui

2][S2CNBui2] to either

[W(NBut)2(NHBut)2] [20] (Scheme 1) or [W(μ-NBut)Cl2(NH2But)(NBut)]2[21] resulted in the formation of [W(NBut)2(S2CNBui

2)2] (6)as a yellow crystalline solid in good yield [22]. The molecular

structure [23] is shown in Fig. 2, key features being the linear geometryof both imido ligands [W(1)-N(3)-C(19) 166.8(2), W(1)-N(4)-C(23)167.7(2)°] and the elongation of the tungsten–sulfur bond lying transto the latter [W(1)-S(1) 2.7167(9), W(1)-S(3) 2.6973(10) Å] versusthose that are cis [W(1)-S(2) 2.4592(9),W(1)-S(4) 2.4645(9) Å]. A relat-ed trans-influence has previously been noted in [Mo(NBut)2(S2CNEt2)2][24] and 1[10]. It is possibly the reasonwhy the 1HNMR spectrum of 6 isbroad at room temperature, while at lower temperatures a series ofmul-tiplets as expected for the structure seen in the solid-state are observed.Likewise, upon raising the temperature a very simple spectrum is ob-served attributed to the rapid interconversion of the two dithiocarba-mate ligands on the NMR timescale. Initial attempts at reacting 6with arylisocyanates were somewhat disappointing. Thus, 6 doesreact with PhNCO but only at elevated temperatures and over a numberof hours. We have not yet fully identified the product(s) of thisbut the timeframe suggests that putative aryl bis(dimido) complexes[W(NAr)2(S2CNBui

2)2] are more reactive than 6. This may be due tothe linear nature of the two imido ligands in 6 and we have previouslyshown in related molybdenum chemistry that while both imido ligandsare linear in [Mo(NBut)2(S2CNEt2)2], in contrast in the related arylimidocomplex [Mo(NPh)2(S2CNEt2)2] they rapidly interconvert between line-ar and bent coordination modes even at low temperatures in solution[24]. Thus, we are currently attempting to use methodology developedbyMountford [25] to exchange the tert-buyl imido ligands for arylimidogroups.

In conclusion we have found and developed a simple route intotungsten-imido-dithiocarbamate chemistry which has previouslybeen neglected and preliminary studies suggest that they are quitereactive. We are currently focussing our efforts on the synthesis of[W(NAr)2(S2CNBui

2)2] complexes and also trying to determine ifthe di-iso-butyldithiocarbamate ligand is a pre-requisite for the iso-lation of stable tungsten-imido-dithiocarbamate complexes.

Acknowledgements

We thank Professor James C. Anderson and Dr Rafa Moreno fortheir help with the aspects of this work, Dr Stephan E. Potts for the

1935A. Edwards et al. / Inorganic Chemistry Communications 14 (2011) 1932–1936

preparation of [W(NBut)2(NHBut)2] and [W(μ-NBut)Cl2(NH2But)(NBut)]2 and the EPSRC for funding (NH).

Appendix A. Supplementary material

Crystallographic data for 2 and 6 have been deposited at the Cam-bridge Crystallographic Centre with CCDC Reference Numbers 837342and 837343. Copies of the data can be obtained free of charge viawww.ccdc.cam.ac.uk/conts/retrieving.html (or from Cambridge Crystal-lographic Data Centre, 12Union Road, Cambridge CB2 1EZ, UK (Tel:+441223 336408; fax: +44 1223 336033; Email: deposit@ccdc.cam.ac.uk).Supplementary data associated with this article can be found, in the on-line version, at doi:10.1016/j.inoche.2011.09.014.

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[15] To a stirredmixture of [WO2(S2CNBui2)2] (0.353 g, 0.56mmol) in dry toluene (10mL)in a flame dried Schlenk tube under an argon atmosphere was added a solutionof p-tolylisocyanate (0.231 g, 1.73 mmol) in toluene (10 mL). The mixture washeated to reflux for 1 h resulting in formation of a deep orange solution. Thiswas cooled to room temperature before removal of volatiles in vacuo followed by pu-rification by flash chromotography (90% Et2O/hexane) yielding a dark orange oilwhich was triturated with hexane (5 mL) to afford 3 (0.174 g, 33%) as a fluffy brightorange solid. Complex 2was prepared in a similar fashion and for both large orange-red blocks suitable for X-ray diffraction were grown upon slow evaporation of Et2Osolutions. 21H NMR (400MHz, CDCl3) δ 0.89 (24H, d, J = 7.0 Hz, CHMe2), 2.11 (2H,septet, J = 7.0 Hz, CHMe2), 2.23 (2H, septet, J = 7.0 Hz, CHMe2), 3.32-3.39 (4H, m,NCH2), 3.53-3.61 (4H, m, NCH2), 6.77 (1H, t, J = 8.0 Hz, ArH), 6.84 (1H, t, J = 8.0Hz, ArH), 7.07-7.15 (10H, m, ArH), 7.45 (2H, d, J = 8.0 Hz, ArH), 5.58 (2H, d, J =8.0 Hz, ArH); 31H NMR (500 MHz, CDCl3) δ 0.89 (24H, d, J = 6.6 Hz, CHMe2), 2.04-2.30 (4H, m, CHMe2), 2.23 (3H, s, ArCH3), 2.25 (3H, s, ArCH3), 2.45 (3H, s,W=NArCH3), 3.29-3.37 (4H, m, NCH2), 3.52-3.60 (4H, m, NCH2), 6.88-6.93 (4H, m,ArH), 7.04-7.12 (4H, m, ArH), 7.32 (2H, d, J = 8.3, ArH), 7.52 (2H, J = 8.4, ArH);13C NMR (500 MHz MHz, CDCl3) δ 19.8 (CH(CH3)2), 19.9 (CH(CH3)2), 20.0-20.2(CH(CH3)2), 20.8 (CH(CH3)2), 21.4 (CH(CH3)2), 26.8 (ArCH3), 27.0 (ArCH3), 55.6(NCH2), 57.5 (NCH2), 119.5 (CAr), 122.6 (CAr), 124.0 (CAr), 127.5 (CAr), 127.9(CAr), 128.0 (CAr), 128.5 (CAr), 128.7 (CAr), 128.8 (CAr), 137.7 (ipso-CAr), 163.9(ipso-CAr), 200.95 (CS2); m/z (FAB+) 936 (20%, M+), 802 (45%, M+ − p-tolyl-NCO), 697 (13%, 697, M+ − (p-tolyl-NH)2CO); HRMS C40H58N5OS2W calcd.936.3034, found 936.2984; elemental analysis calc. for W1S4N5O1C40H57 (found) %C 51.34 (50.82), %H 6.10 (6.18), %N 7.49 (7.69), %S 13.69 (13.13).

[16] Crystallographic data for 2.Et2O - Single crystals were mounted on a glass fibreand all geometric and intensity data were taken from these samples using a Bru-ker SMART APEX CCD diffractometer with graphite-monochromated Mo-Ka radi-ation (λ = 0.71073 Å) at 150 ± 2 K. Data reduction was carried out with SAINTPLUS and absorption correction applied using the programme SADABS. Structureswere solved by direct methods and developed using alternating alternating cy-cles of least-squares refinement and difference-Fourier synthesis. All non-hydrogen atoms were refined anisotropically and hydrogen atoms were generallyplaced in calculated positions (riding model). Carbon atoms C(20)-C(25) on thephenyl ring of the imido ligand were fixed in a plane. Structure solution usedSHELXTL PLUS V6.10 program package. Orange block, dimensions 0.28 × 0.09 ×0.03 mm, orthorhombic, space group Pca21, a = 30.598(3), b = 13.398(1), c =10.9634(9) Å, V = 4494.4(6) Å3, Z = 4, F(000) 1984, dcalc = 1.431 g cm-3, μ =2.795 mm-1. 38018 reflections were collected, 10540 unique [R(int) = 0.0550] ofwhich 8848 were observed [I N 2.0σ(I)]. At convergence, R1 = 0.0612, wR2 =0.1157 [I N 2.0σ(I)] and R1 = 0. 0753, wR2 = 0.1207 (all data), for 430 parameters.

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Society, Chemical Communications (2002) 2618;L.M. Atagi, J.M. Mayer, Organometallics 13 (1994) 4794;D.L. Morrison, P.M. Rodgers, Y.-W. Chao, M.A. Bruck, C. Grittini, T.L. Tajima, S.J.Alexander, A.L. Rheingold, D.E. Wigley, Organometallics 14 (1995) 2435;P. Legzdins, E.C. Phillips, S.J. Rettig, J. Trotter, J.E. Veltheer, V.C. Yee, Organometallics11 (1992) 3104.

[19] To a stirred solution of 3 (0.014 g, 0.015 mmol) in dry CH2Cl2 (2 mL) at room temper-ature in airwas addedHCl in dry Et2O (0.04M, 0.75mL). This resulted in a rapid colourchange from orange to yellow. Solvent was removed in vacuo, affording a yellow solidconsisting of a mixture of 4 and the urea, p-tolylNHC(O)NHp-tolyl, as identified byproton NMR spectroscopy (ca. 100% conversion). A pure sample of 4 was isolatedafter addition of further acid and extraction with CHCl3. 41H NMR (500 MHz,CDCl3) δ 0.94-0.98 (24H, m, CHMe2), 2.25-2.31 (4H, m, CHMe2), 2.47 (3H, s,W=NArCH3), 3.45-3.64 (8H, m, NCH2), 7.08-7.14 (2H, m, ArH), 7.24-7.28 (2H, m,ArH); m/z (FAB+) 734 (75%, M+ − Cl); HRMS (for M+ − Cl) C25H43ClN3S4Wcalcd. 732.1538, found 732.1575. ArNHC(O)NHAr1H NMR (500 MHz, CDCl3) δ 2.30(6H, s, ArCH3), 6.59 (2H, br s, NH), 7.10 (2H, d, J = 8.1 Hz, ArH), 7.23 (2H, d, J =8.3 Hz, ArH). To a stirred solution of 3 (0.014 g, 0.015 mmol) in dry CH2Cl2 (2 mL)at room temperature in a flame dried Schlenk tube under an argon atmospherewas added HBF4.Et2O (0.005g, 0.030 mmol) in dry CH2Cl2 (0.5 mL) resulting in arapid colour change from orange to yellow. Solvent was removed in vacuo and theresulting solid extracted with Et2O to afford 5-BF4. 5-BF41H NMR (500 MHz, CDCl3)δ 0.88-0.99 (36H, m, CHMe2), 2.14-2.36 (6H, m, CHMe2), 2.48 (3H, s, W=NArCH3),3.43-3.62 (12H, m, NCH2), 7.05 (2H, d, J = 8.2 Hz, ArH), 7.17 (2H, d, J = 8.1 Hz,ArH); 13C NMR (600 MHz, CDCl3) δ 20.1-20.2 (CH(CH3)2), 21.7 (ArCH3), 27.0(CH(CH3)2), 27.1 (CH(CH3)2), 27.3 (CH(CH3)2), 27.4 (CH(CH3)2), 55.6 (NCH2), 57.0(NCH2), 57.9 (NCH2), 58.9 (NCH2), 128.0 (CAr), 129.2 (CAr), 141.0 (ipso-CAr),150.4 (ipso-CAr), 198.8 (CS2), 203.0 (CS2); m/z (FAB+) 901 (100%, M+), 697(15%, M+ − S2CNiBu2).

[20] W.A. Nugent, R.L. Harlow, Inorganic Chemistry 19 (1980) 777.[21] R.G. Gordon, J.S. Becker, S. Suh, S. Wang, Chemistry of Materials 15 (2003) 2969.[22] A mixture of [W(NBut)2(NH2But)2] (0.19 g, 0.40 mmol) and [NH2Bui

2][S2CNBui2]

(0.28 g, 0.80 mmol) in a flame dried Schlenk tube under an argon atmospherewas dissolved in Et2O (15 mL). The yellow solution was stirred for 15 h resultingin a slight darkening of the solution. The solution was concentrated in vacuo andstored at−18 °C for 24 h to afford large yellow crystals of 6 (0.13 g, 44%) suitable

1936 A. Edwards et al. / Inorganic Chemistry Communications 14 (2011) 1932–1936

for X-ray diffraction. A similar procedure starting from [W(μ-NBut)Cl2 (NH2But)(NBut)]2 (0.11 g, 0.20 mmol) and [NH2Bui

2][S2CNBui2] (0.14 g, 0.40 mmol) gave

6 (0.096 g, 65%). 1H NMR (400 MHz, d8-toluene) δ 0.81 (24H, d, J = 6.7 Hz,CHMe2), 1.53 (18H, s, NBut), 2.19 (4H, m, CHMe2), 3.50 (8H, m, NCH2); 13CNMR (600 MHz, d8-toluene) δ 19.4 (CH(CH3)2), 21.6 (CH(CH3)2), 56.6 (NCH2),66.8 (NCMe3), 205.0 (CS2); elemental analysis calc. for W1S4N4C26H54 (found) %C 42.67 (42.62), %H 7.02 (7.48), %N 7.66 (7.49).

[23] Collection and solution of crystallographic data for 6 were as described above for2 but in this case all non-hydrogen atoms were refined anisotropically and freely.Yellow block, dimensions 0.20 × 0.08 × 0.05 mm, monoclinic, space group P21/n,a=9.341(2), b=20.146(5), c= 18.851(4) Å, β= 98.813(4)°, V=3505.8(1) Å3,

Z = 4, F(000) 1504, dcalc = 1.392 g cm-3, μ= 3.553 mm-1. 29254 reflections werecollected, 8144 unique [R(int) = 0.0471] of which 5922 were observed [I N2.0σ(I)]. At convergence, R1 = 0.0294, wR2 = 0.0549 [I N 2.0σ(I)] and R1 = 0.0472, wR2 = 0.0571 (all data), for 316 parameters.

[24] P. Barrie, T.A. Coffey, G.D. Forster, G. Hogarth, Journal of the Chemical Society, DaltonTransactions (1999) 4519.

[25] P.E. Collier, S.C. Dunn, P. Mountford, O.V. Shishkin, D. Swallow, Journal of theChemical Society, Dalton Transactions (1995) 3743;A.J. Blake, P.E. Collier, S.C. Dunn, W.-S. Li, P. Mountford, O.V. Shishkin, Journal ofthe Chemical Society, Dalton Transactions (1997) 1549.