Concerning the question of f- and d-electron interactions inheterodinuclear compounds: synthesis, structure and 103Rh NMR

investigations of La�/Rh-bimetallics

Henrik Noss a, Wolfgang Baumann a, Rhett Kempe b,d,*, Torsten Irrgang d,Axel Schulz c

a Institut fur Organische Katalyseforschung Rostock (IfOK), Buchbinderstrasse 5-6, 18055 Rostock, Germanyb Fachbereich Chemie, Carl von Ossietzky Universitat Oldenburg, P.O. Box 2503, 26111 Oldenburg, Germany

c Department Chemie, Ludwig-Maximilians Universitat Munchen, Butenandtstrasse 5-13 (Haus D), 81377 Munchen, Germanyd Chair of Inorganic Chemistry II, University of Bayreuth, 95440 Bayreuth, Germany

Received 27 May 2002; accepted 2 September 2002

Dedicated to Professor Richard R. Schrock

Abstract

The reaction of the lanthanum ate-complex [{O(SiMe2�/Ap)2}2LaLi(thf)4] (1) (Ap�/H�/2-amino-4-methylpyridine, thf�/

tetrahydrofuran) with [(cod)RhCl]2 (cod�/cycloocta-1,5-diene) and [(C2H4)2RhCl]2 gave rise to three lanthanum�/rhodium

bimetallic compounds: [{O(SiMe2�/Ap)2}2LaRh(cod)] (2), [{O(SiMe2�/Ap)2}2LaRh(C2H4)] (3), and [{O(SiMe2�/Ap)2}2(th-

f)LaRh(C2H4)] (4). The metal�/metal distances observed for 2, 3 and 4 are 3.3052(9), 3.0585(8), and 3.1598(7) A, respectively.

The structure and 103Rh NMR chemical shifts of the La�/Rh-bimetallics are discussed with regard to metal�/metal interactions.

# 2002 Elsevier Science B.V. All rights reserved.

Keywords: Crystal structures; Lanthanum complexes; Rhodium complexes; Heterobimetallic complexes

1. Introduction

One challenge facing coordination chemistry today is

the preparation of heterobimetallic complexes that

contain an early (electron-deficient) and a late (elec-

tron-rich) transition metal. Interesting characteristics

such as multi-functionality and cooperative effects of the

different transition metals can be expected [1,2]. It has

been shown that the cooperation of two different metals

can result in unique properties for material science [3�/5]

and homogeneous catalysis [6]. Furthermore, a well

defined single metal centre can benefit from a second

metal in terms of reactivity. The synthesis of early�/late

heterobimetallics (ELHB) is complicated due to the

different coordination demands of the two metals,

especially if close proximity is desired. Considering

possible combinations of early and late transition

metals, Group 3 (G3) metals or lanthanides and Group

8�/10 metals seem to have the most varied coordination

chemistry behaviour and thus, are considered as the

most challenging metals to establish metal�/metal com-

munication. Only a few of such complexes have been

described [7]. The immense interest in combining f- and

late d- metals, especially carbonyl containing com-

pounds, might have been motivated by the development

of homogenous analogues of the heterogeneous

Fischer�/Tropsch catalysts [8]. However, no break-

through has been observed so far. Too many compro-

mises have to be made to synthesise the bimetallics, and

the introduction of known patterns of intrinsically active

catalysts had little attention. In addition to catalysis,

other applications of heterobimetallics are in discussion.

[Ln(hfa)3Ni(salen)] (Ln�/Y, Gd) [9] for example, sub-

limes under vacuum and thus, might be of interest with

regard to metal�/organic chemical vapour deposition [3].

* Corresponding author. Tel.: �/49-921-55 2540; fax: �/49-921-55

2157

E-mail address: kempe@uni-bayreuth (R. Kempe).

Inorganica Chimica Acta 345 (2003) 130�/136

www.elsevier.com/locate/ica

0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.

PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 1 2 9 8 - 7

Furthermore, the combination of unpaired f- and d-

electrons is a promising candidate in terms of the

development of materials that may act as molecular

magnets [4,5]. Lanthanide copper complexes have beeninvestigated with regard to their magneto-chemical

behaviour [4,10�/12]. Strong interactions of f- and d-

metals lead to unique magnetic behaviour and could be

expected in compounds with very short distances

between the two centres due to the possibility of better

overlapping magnetic orbitals. Amido metal complexes

[13,14] have been rarely investigated with regard to any

f, d metal combinations [15]. The fact that very shortmetal�/metal distances are observed makes amido and,

especially aminopyridinato (aminopyridinato�/Ap) li-

gands, interesting. In this study the synthesis, structure

and 103Rh NMR investigations of Ap�/La�/Rh-bimetal-

lics are reported.

2. Results and discussion

2.1. Synthesis and structure

Salt metathesis reactions are a common protocol to

synthesise ELHB [2]. The reaction of a Ln-ate-complex

with late metal chlorides is one version of this procedure

[16] and often gives rise to heterodinuclear compounds

in which a lanthanide ion is in close proximity to atransition metal centre [15]. The reaction of [{O(SiMe2�/

Ap)2}2LaLi(thf)4] (1) (Ap�/H�/2-amino-4-methylpyri-

dine, thf�/tetrahydrofuran) [22] with [(cod)RhCl]2(cod�/cycloocta-1,5-diene) in hexane at room tempera-

ture afforded [{O(SiMe2�/Ap)2}2LaRh(cod)] (2) as a

yellow crystalline material in good yield (Scheme 1). The1H NMR spectra of 2 indicated either a high symmetric

complex or rapidly exchange species was present sincetwo signals for the four Ap moieties and two signals for

the methylsilyl groups were observed. Details of the X-

ray crystal structure analysis of 2 are listed in Table 1.

The molecular structure of 2 including selected bond

lengths and angles are shown in Fig. 1. One of the

bis(Ap) ligands is chelated solely to the La atom whereas

the other bridges between the two metal centres via the

amido-N atoms. An amido metal bond is formed to thelanthanum centre and a dative bond to the rhodium.

Since the lone pairs are not involved in the formation of

the amido metal bonds the two bridging La�/N bond

lengths [La(1)�/N(1), La(1)�/N(3)] are about 0.1 A

longer than the other amido lanthanum bonds [La(1)�/Scheme 1. Synthesis of 2.

Table 1

Details of the X-ray crystal structure analyses of 2, 3 and 4

Compound 2 3 4

T (K) 293(2) 200(2) 200(2)

Crystal system monoclinic triclinic monoclinic

Space group P21/c /P1/ P21/n

a (A) 13.331(3) 11.840(2) 12.464(2)

b (A) 11.877(2) 13.344(2) 16.441(2)

c (A) 33.102(7) 17.885(2) 25.346(3)

a (8) 80.32(1)

b (8) 91.04(3) 87.26(1) 101.980(10)

g (8) 56.30(1)

V (A3) 5240(2) 2529.8(6) 5080.8(12)

Z 4 2 4

rcalc (g cm�3) 1.336 1.344 1.390

Crystal size (mm) 0.3�/0.3�/0.3 0.3�/0.2�/0.2 0.3�/0.2�/0.2

u Range (8) 1.53�/21.10 1.89�/24.21 1.49�/21.03

m (cm�1) (Mo Ka) 1.249 1.291 1.290

Reflections collected 10 241 7327 9964

Reflections ob-

served [I �/2s (I )]

3977 5063 4364

Reflecions unique 5551 7327 5365

Parameters 511 457 507

Final R indices

[I �/2s (I )]

0.038 0.041 0.030

vR2 (all data) 0.102 0.107 0.089

Fig. 1. ORTEP view of 2. Selected bond lengths (A) and angles (8):N(1)�/Rh(1) 2.165(6), N(1)�/La(1) 2.736(6), N(2)�/La(1) 2.655(6),

N(3)�/Rh(1) 2.155(6), N(3)�/La(1) 2.769(5), N(4)�/La(1) 2.645(6),

N(5)�/La(1) 2.585(6), N(6)�/La(1) 2.581(7), N(7)�/La(1) 2.519(6),

N(8)�/La(1) 2.599(6), Rh(1)�/La(1) 3.3052(9), N(1)�/Rh(1)�/N(3)

85.1(2), N(7)�/La(1)�/N(6) 131.0(2), N(6)�/La(1)�/N(5) 52.5(2), N(7)�/

La(1)�/N(8) 53.2(4), N(2)�/La(1)�/N(1) 50.3(2), N(4)�/La(1)�/N(3)

50.6(2).

H. Noss et al. / Inorganica Chimica Acta 345 (2003) 130�/136 131

N(5), La(1)�/N(7)]. The coordination number of the

lanthanum is eight. The late metal centre is additionally

coordinated by a cod ligand with the coordination best

described as square planar considering the centroids of

the two double bonds of cod. The two N atoms bound

to the rhodium form a N(1)�/Rh�/N(3) angle of 85.18.The differences between the La�/Namido and La�/

Npyridine bond lengths are small which indicates the

anionic charge is delocalised across the Namido�/C�/

Npyridine backbone. The metal�/metal distance of 2

[3.3052(9) A] is relatively short but a direct metal�/metal

bond is unlikely. Rhodium orbitals, which could con-

tribute to such an interaction, are oriented perpendicu-

lar to the square planar coordination plane of this metal

[17], and are not directed towards the La ion. The angle

between the vector parallel to the metal�/metal distance

and the vector perpendicular to the coordination plane

of the rhodium is 51.28 (‘alignment angle’). The ideal

‘alignment angle’ for an interaction would be 08. In case

of [{O(SiMe2�/Ap)2}2LaRh(C2H4)] (3) an angle of 26.08is observed.

A salt metathesis reaction between 1 and [(C2H4)2-

RhCl]2 in hexane (Scheme 2) affords the bimetallic

complex 3 as a yellow micro-crystalline material as well

as the by-product [{O(SiMe2�/Ap)2}2(thf)LaRh(C2H4)]

(4). The molecular structure of 3 was determined by X-

ray crystallography and is depicted in Fig. 2. Crystal-

lographic details of the investigation are listed in Table

1. Both bis(Ap) ligands are involved in the coordination

of the two metals. One Ap moiety of each of the two

bis(Ap) ligands binds the lanthanum ion whilst the

second Ap unit of one of the bis(Ap) ligands, as well as

the pyridine moiety of the other bis(Ap) ligand coordi-

nate the rhodium. Remarkably, a small N(8)�/Rh(1)�/

N(7) angle of 64.9(2)8 results. The rhodium metal is also

surrounded by an ethylene ligand and a four-coordinate

(distorted square planar) environment is observed. The

coordination number of the lanthanum is 6 which is

lower than for 2. The short lanthanum rhodium distance

[3.0585(8) A], the alignment of the rhodium orbitals

perpendicular to the coordination plane (‘alignment

angle’�/268) and the low coordination number of the

lanthanide ion of 3 are indicative of a metal�/metal

interaction. Coordination compounds with an unsup-

ported metal�/metal bond between a Group 9 metal and

any of the lanthanides have not yet been observed to the

best of our knowledge [7]. The only throughly char-

acterised compound with an unsupported lanthanide�/

transition-metal bond is [Cp2(thf)Lu�/RuCo(CO)2]

(Cp�/cyclopentadienyl anion)*/metal�/metal dis-

tance�/2.995(2) A [18]. Considering the fact that

lanthanum has an ion radius of about 0.2 A longer

than lutetium [19] the metal�/metal distance of 3 is in

good agreement with the expected value of a

lanthanum�/rhodium single bond.

Compound 4 was isolated as a red crystalline

material. The large red crystals of 4 were easily

separated from the yellow powder of 3 and 4 and was

characterized by NMR, X-ray analysis and elemental

analysis. The molecular structure of 4 is shown in Fig. 3.

Details of this investigation are listed in Table 1. For 4 a

different coordination pattern, in comparison to 2 and

3, is observed. One of the bis(Ap) ligands chelates solely

to the lanthanum while the other bridges the rhodium

metal via the two amido-N atoms. Furthermore, one of

the pyridine moieties of the bridging ligand coordinates

the rhodium centre. Thus, in comparison to compound

2, a coordination site of the lanthanum is ‘open’ and an

additional thf ligand binds this metal. The La�/Rh

distance of 4 is 3.1598(7) A and the ‘alignment angle’

is 48.98. This angle indicates that no direct metal�/metal

interaction can be proposed for 4.Scheme 2. Synthesis of 3 and 4.

Fig. 2. ORTEP view of 3. Selected bond lengths (A) and angles (8):N(1)�/La(1) 2.539(5), N(2)�/La(1) 2.587(6), N(3)�/La(1) 2.448(5),

N(4)�/La(1) 2.683(5), N(5)�/La(1) 2.523(5), N(6)�/Rh(1) 2.056(5),

N(7)�/Rh(1) 2.137(5), N(7)�/La(1) 2.718(5), N(8)�/Rh(1) 2.026(5),

C(15)�/C(16) 1.374(11), Rh(1)�/La(1) 3.0585(8), N(8)�/Rh(1)�/N(7)

64.9(2), N(6)�/Rh(1)�/N(7) 105.1(2), N(3)�/La(1)�/N(5) 99.4(2), N(1)�/

La(1)�/N(2) 54.0(2), N(3)�/La(1)�/N(4) 52.2(2).

H. Noss et al. / Inorganica Chimica Acta 345 (2003) 130�/136132

2.2. 103Rh NMR investigations and calculations

The three lanthanum rhodium bimetallic compounds

2, 3 and 4 have different molecular structures and thus

different metal�/metal distances and ‘alignment angles’.

Considering these two structural parameters a metal�/

metal interaction can be proposed in 3 but not for 2 and

4. 103Rh NMR spectroscopy is a sensitive tool to

investigate the binding environment in a rhodium centre

[20,23]. The 103Rh�/1H correlation spectra of 2, 3 and 4

in benzene at room temperature are shown in Figs. 4

and 5. Due to the different coordination environment of

the rhodium centre in 2 and the rhodium centre of 3 a

drastic change of the chemical shifts is expected [21].

This is in good agreement with the chemical shift of 1087

ppm for 2 and the signal for 3 at 2151 ppm. Comparing

the chemical environments of 3 and 4 one finds a

threefold N coordinated as well as ethylene coordinated

rhodium ion in both cases and thus a small change in the

chemical shift should be observed. The chemical shift

difference of the 103Rh NMR signal of 3 and 4 was less

than 100 ppm. In the case of a direct lanthanum�/

rhodium interaction one would observe a five-coordi-

nate rhodium centre in 3 (threefold N coordinated,

ethylene coordinated as well as ‘lanthanum’ coordi-

nated) and a four coordinate rhodium for compound 4.

This metal environment should give rise to a large

difference in the chemical shift, much greater than 100

ppm [21]. Thus the 103Rh NMR data in 3 indicates no

direct lanthanum�/rhodium interaction. The close proxi-

mity of the two metals in 3 is most probably due to the

steric constraints of the aminopyridinato ligands. Cal-

culations on the Hartree�/Fock level were performed to

Fig. 3. ORTEP view of 4. Selected bond lengths (A) and angles (8):N(5)�/Rh(1) 2.102(5), N(5)�/La(1) 2.732(4), N(6)�/Rh(1) 2.038(5),

N(7)�/Rh(1) 2.111(4), N(7)�/La(1) 2.745(4), N(1)�/La(1) 2.556(4),

N(2)�/La(1) 2.585(5), N(3)�/La(1) 2.552(5), N(4)�/La(1) 2.622(4),

N(8)�/La(1) 2.670(5), C(38)�/C(39) 1.385(9), Rh(1)�/La(1) 3.1598(7),

N(5)�/Rh(1)�/N(6) 65.9(2), N(5)�/Rh(1)�/N(7) 94.9(2), N(1)�/La(1)�/

N(2) 52.55(15), N(3)�/La(1)�/N(4) 52.47(14), N(7)�/La(1)�/N(8)

50.38(14).

Fig. 4. 103Rh�/1H correlation spectra of 2.

Fig. 5. 103Rh�/1H correlation spectra of 3 and 4.

Scheme 3. Structures of 2 and 3 as well as structures of the model

compounds 2a and 3a used for QC calculations.

H. Noss et al. / Inorganica Chimica Acta 345 (2003) 130�/136 133

support the experimental findings. The ligand was

simplified by removing unnecessary substituents. The

model compounds 2a and 3a (Scheme 3, right) were

built up by using X-ray analysis data of the compounds2 and 3 (Scheme 3, left) except for hydrogen atoms.

Hydrogen atoms were added in accordance with the

hybridisation of the corresponding carbon or silicon

atom and their geometry optimised. Single point calcu-

lation of the geometry optimised structure of 3a

followed by population analysis gave rise to several

occupied molecular orbitals (Fig. 6) which ‘contribute’

to the metal�/metal interaction of 3a. These molecularorbitals are delocalised over the entire structure. This

finding supports the idea that the close proximity of

rhodium and lanthanum in 3 is forced by the ligands and

that most of the electron interactions between the two

metals proceed through the ligand. Nevertheless parts of

the molecular orbitals localised at the metals indicate p�/

p interaction where electron density of the electron rich

rhodium centre is transferred to the electron poorlanthanum ion. Moreover, inspection of the charge

distribution for the complexes 2a and 3a showed a

smaller ‘polarization’ of the two metal centres in the case

of 3a (3a: Rh �/0.27e, La �/0.06e; 2a: Rh �/0.52e, �/

0.44e) indicating a larger charge transfer.

3. Experimental

3.1. General methods

The lanthanum ate-complex 1 was prepared accord-

ing to a previously published procedure [22]. All other

reagents were obtained commercially (Strem) and usedas supplied. All manipulations were performed with

rigorous exclusion of oxygen and moisture in dried

Schlenk-type glassware on a Schlenk line, or in an Ar-

filled glovebox (mBraun lab-master 130) with a high-

capacity re-circulator (B/1.5 ppm O2). Solvents (Al-

drich, Fluka) and NMR solvents (Cambridge IsotopLaboratories, all 99 atom % D) were freshly distilled

from sodium tetraethylaluminate. NMR spectra were

recorded on a Bruker ARX 400 instrument at 297 K. 1H

and 13C chemical shifts are referenced to the solvent

resonance and reported relative to TMS. 29Si chemical

shifts are reported relative to TMS. 103Rh chemical

shifts are given relative to J�/3.16 MHz [23]. IR spectra

were recorded on a Nicolet Magna 550 (Nujol mullsusing KBr plates). Not all IR signals could be assigned.

M.p.s were analysed in sealed capillaries on a Buchi 535

apparatus. Elemental analyses were performed with a

Leco CHNS-932 elemental analyser.

3.2. X-ray crystallography

X-ray diffraction data were collected on a Stoe-IPDS-

diffractometer using graphite-monochromated Mo Karadiation. The crystals were mounted in a cold nitrogen

stream or sealed inside a capillary under Ar. The

structure was solved by direct methods (SHELXS-86)

[24] and refined by full-matrix least-squares techniques

against F2 (SHELXL-93) [25]. ORTEP-3 was used for

structural representation [26].

3.3. Computational details

All calculations (geometry optimisation and Mulliken

population analysis) were performed with the program

package GAUSSIAN-98 [27] (Hartree�/Fock level). A 6-

31G(d) basis set was used for C, N, O and H atoms and

the LANL2DZ basis set including pseudo potentials for

Si, Rh and La.

3.4. Synthesis of [{O(SiMe2�/Ap)2}2LaRh(C8H12)]

(2)

To a vigorously stirred suspension of 1 (946 mg, 0.90

mmol) in C6H14 (60 ml) was added [(cod)RhCl]2 (222

mg, 0.45 mmol). An orange colour was observed within

a few minutes. The suspension was stirred for 16 h at

room temperature (r.t.). The mixture was filtered, theresidue (LiCl) was washed two times with 20 ml of

C6H14 and the combined filtrates were concentrated to

about 30 ml. Yellow crystals were obtained at �/30 8C.

Yield: 789 mg (0.76 mmol, 84%), m.p. 147 8C; 1H NMR

(400.13 MHz, C6D6): d�/8.07 (m, 3H, H6), 6.53 (s, 1H,

H6), 6.40 (m, 3H, H5), 6.30 (m, 1H, H5), 6.16 (m, 3H,

H3), 5.79 (m, 1H, H3), 3.90 (m, 2H), 3.14 (m, 2H), 2.25

(m, 2H), 2.12 (m, 2H) (cod), 2.08 (s, 3H), 1.78 (s, 3H),1.76 (s, 6H) (Me�/pyridine), 1.45 (m, 2H), 1.01 (m, 2H)

(cod), 0.84 (s, 6H), 0.57 (s, 6H), 0.29 (s, 6H), 0.23 (s, 6H)

(Me�/Si); 13C NMR (100.62 MHz, C6D6): d�/171.1,Fig. 6. Occupied molecular orbital diagram of 3a which contributes to

metal�/metal binding.

H. Noss et al. / Inorganica Chimica Acta 345 (2003) 130�/136134

170.7 (C2), 150.0, 149.0, 148.9 (C4); 147.4, 145.1, 144.2

(C6); 119.3, 117.0, 116.0 (C5); 115.1, 110.0, 108.5 (C3);

84.8, 84.7, 80.9, 80.8, 31.2, 30.4, 30.1 (cod); 21.6, 21.3,

21.1 (Me�/pyridine); 6.3, 3.0, 2.1, 0.7 (Me�/Si); 29SiNMR (79.49 MHz, C6D6): d�/�/10.2; �/16.2; �/18.6;103Rh NMR (C6D6): d�/1087; IR (Nujol, cm�1): n�/

1608 vs, 1544 m, 1531 m (arom.), 1415 s, 1394 s, 1331 m,

1315 m, 1295 s, 1286 s, 1249 s (Me�/Si), 1171 s, 1058 s,

1016 m, 1001 s, br. (Si�/O�/Si), 970 m, 887 m, 875 s, 848

m, 841 s, 810 s (Me2Si), 783 s, 779 s, 724 m, 675 w, 631

w, 622 w, 578 m, 560 w, 530 w. Anal . Calc. for

C40H60LaN8O2RhSi4 (1039.12): C, 46.24; H, 5.82; N,10.78. Found: C, 45.97; H, 5.75; N, 10.52%.

3.5. Synthesis of [{O(SiMe2�/Ap)2}2LaRh(C2H4)] (3)

Compound 1 (988 mg, 0.94 mmol) and freshly

prepared [(C2H4)2RhCl]2 [28] (194 mg, 0.50 mmol)

were suspended in C6H14 (80 ml) and stirred at r.t. for

72 h. The mixture was filtered and the residue was

washed two times with 10 ml of C6H14/ether 1:1 (v/v).The combined filtrates were concentrated under vacuum

to about 30 ml. Cooling to �/30 8C afforded yellow

crystals. Yield: 660 mg (0.69 mmol, 73%), m.p. 179 8C;1H NMR (400.13 MHz, C6D6): d�/7.52 (d, 2H, J�/5.5

Hz, H6); 7.14 (d, 2H, J�/5.8 Hz, H6); 6.39 (m, 2H, H5);

6.04 (m, 2H, H5); 5.85 (m, 2H, H3); 5.80 (m, 2H, H3);

3.73 (m, 2H, ethylene); 3.39 (m, 2H, ethylene); 1.79 (s,

6H), 1.74 (s, 6H) (Me�/pyridine); 0.59 (s, 6H), 0.57 (s,6H), 0.54 (s, 6H), 0.21 (s, 6H) (Me�/Si); 13C NMR

(100.62 MHz, C6D6): d�/171.7, 168.1 (C2); 149.6, 148.1

(C4); 146.6, 145.2 (C6); 115.8, 114.5 (C5); 114.2, 110.0

(C3), 54.7, 54.5 (ethylene); 21.2, 20.9 (Me�/pyridine);

2.6, 1.9, 1.8, 0.4 (Me�/Si); 29Si NMR (79.49 MHz, C6D6)

d�/�/10.1; �/14.6; 103Rh NMR (C6D6): d�/2152. Anal .

Calc. for C34H52LaN8O2RhSi4 (958.99): C, 42.58; H,

5.47; N, 11.69. Found: C, 42.45; H, 5.52; N, 11.24%.

3.6. Synthesis of [{O(SiMe2�/

Ap)2}2(thf)LaRh(C2H4)] (4)

Compound 1 (946 mg, 0.90 mmol) and freshly

prepared [(C2H4)2RhCl]2 [28] (175 mg, 0.45 mmol)

were suspended in C6H14 (80 ml) and stirred at r.t. for

16 h. The mixture was filtered and the residue (LiCl) waswashed two times with 10 ml of C6H14/ether 1:1 (v/v).

The combined filtrates were concentrated under vacuum

to about 30 ml. Cooling to �/30 8C afforded a yellow

powder (3) and red crystals (4). The large red crystals of

4 can easily be separated from 3. Yield of 4: 93 mg (0.69

mmol, 10%), m.p. 167 8C; 1H NMR (400.13 MHz,

C6D6): d�/7.98 (d, 1H, J�/5.9 Hz, H6), 7.31 (m, 2H,

H6); 6.28 (m, 2H, H5), 6.24 (s, 1H, H5); 6.05 (s, 1H,H3), 6.03 (s, 2H, H3); 5.86 (m, 2H, H3), 5.69 (m, 1H,

H3); 3.64 (m, thf); 3.31 (m, 2H, ethylene), 3.11 (m, 2H,

ethylene); 1.82 (s, 6H), 1.78 (s, 6H) (Me�/pyridine); 1.28

(m, thf); 0.81 (s, 3H), 0.63 (s, 6H), 0.48 (s, 3H), 0.47 (s,

6H), 0.21 (s, 3H) (Me�/Si); 13C NMR (100.62 MHz,

C6D6): d�/175.2, 171.9, 169.9 (C2); 148.6, 148.1 (C4);

146.1, 145.3, 143.6 (C6) 115.6, 114.9, 114.4 (C5); 110.0,108.8 (C3); 69.3 (thf), 56.7, 56.6 (ethylene); 25.6, 21.3

(Me�/pyridine); 21.3 (thf); 6.0, 4.9, 2.4, 2.3, 0.8, �/0.3

(Me�/Si); 29Si NMR (79.49 MHz, C6D6): d�/�/7.9;

�/14.2, �/17.6; 103Rh NMR (C6D6): d�/2242. Anal .

Calc. for C34H60LaN8O3RhSi4 (1031.10): C, 44.27; H,

5.87; N, 10.87. Found: C, 43.91; H, 5.79; N, 10.73%.

4. Supplementary material

Crystallographic data (excluding structure factors)

for the structures reported in this paper have been de-

posited with the Cambridge Crystallographic Data

Centre, CCDC Nos. 185595�/185597 for compounds 2,

3 and 4. Copies of the data may be obtained free of

charge from The Director, CCDC, 12 Union Road,

Cambridge, CB2 1EZ, UK (fax: �/44-1223-336-033;

e-mail: deposit@ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).

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