Syntheses and structure of heterometallic complexes containing tripodal group 13 ligands [RE(2-py)3]- (E = Al, In)

Article abstract of DOI:10.1021/om0600691

Reactions of the Al(III) complex [{MeAl(2-py)₃}Li·HF] (1), containing the tripodal [MeAl(2-py)₃]ligand, with [(C ₇H₈)Mo(CO)₃], Cal₂, and ZnCl ₂ give the trimetallic and bimetalli

Full text of DOI:10.1021/om0600691

Organometallics 2006, 25, 2561-2568
2561
Syntheses and Structure of Heterometallic Complexes Containing
Tripodal Group 13 Ligands [RE(2-py)3]- (E ) Al, In)†
Felipe Garc´ıa, Alexander D. Hopkins,* Richard A. Kowenicki, Mary McPartlin,
Michael C. Rogers, Jared S. Silvia, and Dominic S. Wright*
Chemistry Department, UniVersity of Cambridge, Lensfield Road, Cambridge CB2 1EW, U.K.
ReceiVed January 23, 2006
Reactions of the Al(III) complex [{MeAl(2-py)3}Li‚THF] (1), containing the tripodal [MeAl(2-py)3]-
ligand, with [(C7H8)Mo(CO)3], CaI2, and ZnCl2 give the trimetallic and bimetallic complexes [{MeAl-
(2-py)3}Mo(CO)3Li(THF)3] (2), [{MeAl(2-py)3}2Ca] (3), and [{MeAl(2-py)3}ZnCl] (4), respectively. [{n-
BuIn(2-py)3}Li‚THF] (5), an InIII analogue of 1 containing the [nBuIn(2-py)3]- anion, is obtained by the
one-pot reaction of nBuLi with InCl3 followed by reaction with 2-Li-py. Complex 5 reacts with [(C7H8)-
Mo(CO)3] to give [{nBuIn(2-py)3}Mo(CO)3Li(THF)2]∞ (6) (analogous to the AlIII complex 2). The X-ray
structures of the new complexes 2, 3, 4, 5, and 6 are reported.
Introduction
Major interest in tris-pyrazolyl-borate and -methane ligands1
and related tris-pyridyl ligands2 (Figure 1) has focused on their
broad applications in coordination, bioinorganic, and organo-
metallic chemistry as well as in heterogeneous catalysis.
Modification of the bridgeheads in these systems provides an
Figure 1. Structure of tris-pyridyl ligands.
obvious way by which the coordination characteristics can be
changed, in terms of both their ligand bites and potentially their
Y-C bond lengths. In addition, replacment of nonmetallic
bridgehead groups by metallic ones introduces the potential for
variable oxidation states at the bridgehead atoms as well as
electrochemical activity. The ability for the metal bridgehead
to possess various oxidation states was illustrated by the
syntheses of the anionic group 14 ligands [nBuSn(2-py)3]7a and
[Pb(2-py)3],7b containing metallic bridgehead atoms in the IV
and II oxidation states, respectively. An indication of the
electrochemical activity of metallic bridgeheads was provided
by the reaction of [{nBuSn(2-py)3}LiBr] with CuIICl2,7b the
product being the CuI complex [{nBuSn(2-py)3}CuBr], presum-
ably formed by the coupling of 2-py groups into 2,2′-bipyridine.
In more recent studies we have shown that the AlIII complex
[{MeAl(2-py)3}Li‚THF] (1) is readily prepared in good yield
via the reaction of 2-Li-py with MeAlCl2.8a Complex 1 provides
a good source of the tripodal [MeAl(2-py)3]- ligand. We
showed, for example, that the reactions of 1 with FeBr2 or Cp2-
Mn give the bis-coordinate complexes [{MeAl(2-py)}2M] (M
electronic character as ligands. However, the vast majority of
studies of tris-pyridyl ligands reported to date contain nonmetal-
lic main group element bridgeheads, commonly with Y ) CX
(X ) H, OH, OR, NH2), N, P, and PdO.3-6
Our interests in this area have involved the development of
synthetic routes to tris-pyridyl ligands containing main group
metal bridgeheads.7,8 These species usually have greater ligand
bites than their nonmetallic counterparts, as a result of the greater
† Dedicated to Prof. Victor Riera (Oviedo University, Spain) on the
occasion of his 70th birthday.
* To whom correspondence should be addressed. E-mail: dsw1000@
cus.cam.ac.uk. Tel: 0044 1223 763122.
(1) Reger, D. L. Comments Inorg. Chem. 1999, 21, 1. Trofimenko, S.
Chem. ReV. 1993, 93, 943. Trofimenko, S. Scorpionates: The Coordination
Chemistry of Polypyrazolylborate Ligands; Imperial College Press: London,
1999.
(2) Szezepura, L. F.; Witham, L. M.; Takeuchi, K. J. Coord. Chem. ReV.
1998, 174, 5.
(3) For examples involving CH bridgeheads, see: Keene, F. R.; Snow,
M. R.; Stephenson, P. J.; Tiekink, E. R. T. Inorg. Chem. 1988, 27, 2040.
Canty, A. J.; Minchin, N. J.; Skelton, B. W.; White, A. H. Aust. J. Chem.
Soc. 1992, 45, 423. Lee, F. W.; Chan, M. C.-W.; Cheung, K.-K.; Che, C.-
M. J. Organomet. Chem. 1998, 563, 191. Kodera, M.; Katayama, K.; Tachi,
Y.; Kano, K.; Hirota, S.; Fujinami, S.; Suzuki, M. J. Am. Chem. Soc. 1999,
121, 11006. Anderson, R. A.; Astley, T.; Hitchman, M. A.; Keene, F. R.;
Monbarak, B.; Murray, K. S.; Skelton, B. N.; Tiekink, E. R. T.; Toftland,
H.; White, A. H. J. Chem. Soc., Dalton, Trans. 2000, 3505.
(4) For examples involving C(OR), C(NH2) bridgeheads, see: Kanty,
A. J.; Chaichit, N.; Gatehouse, B. M.; Goerge, E. E. Inorg. Chem. 1981,
20, 4293. Keene, F. R.; Szalda, D. J.; Wilson, T. A. Inorg. Chem. 1987,
26, 2211. Jonas, R. T.; Stack, T. D. P. Inorg. Chem. 1998, 37, 6615. Brunner,
H.; Maier, R. J.; Zabel, M. Synthesis 2001, 2484. Arnold, P. J.; Davies, S.
C.; Dilworth, J. R.; Durrant, M. C.; Griffiths, D. V.; Hughs, D. L.; Richards,
R. L.; Sharpe, P. C. J. Chem. Soc., Dalton Trans. 2001, 736.
(5) For examples involving N bridgeheads, see: Kucharski, E. S.;
McWhinnie, A. H.; White, W. R. Aust. J. Chem. Soc. 1978, 31, 2647.
Anderson, P. A.; Keene, F. R.; Gulbis, J. M.; Tiekink, E. R. T. Z. Kristallogr.
1993, 206, 275. Mosney, K. K.; de Gala, S. R.; Crabtree, R. H. Transition
Met. Chem. 1995, 29, 595. Wang, W.; Schmider, H.; Wu, Q.; Zhang, Y.-
S.; Wang, S. Inorg. Chem. 2000, 39, 2397.
(6) For examples involving P and PdO bridgeheads, see: Schutte, P.
R.; Rettig, S. J.; Joshi, A.; Janes, B. R. Inorg. Chem. 1997, 36, 5809.
Gregorzik, R.; Wirbser, J.; Vahrenkamp, H. Chem. Ber. 1992, 125, 1575.
Espinet, P.; Hernando, R.; Iturbe, G.; Villafane, F.; Orpen, A. G.; Pascual,
I. Eur. J. Inorg. Chem. 2000, 1031. Casares, J. A.; Espinet, P.; Martin-
Alvarez, J. M.; Espino, G.; Perez-Maurique, M.; Vattier, F. Eur. J. Inorg.
Chem. 2001, 289.
(7) (a) Beswick, M. A.; Davies, M. K.; Raithby, P. R.; Steiner, A.;
Wright, D. S. Organometallics 1997, 16, 1109. (b) Beswick, M. A.; Belle,
C. J.; Davies, M. K.; Halcrow, M. A.; Raithby, P. R.; Steiner, A.; Wright,
D. S. J. Chem. Soc., Chem. Commun. 1996, 2619. (c) Morales, D.; Pe´rez,
J.; Riera, L.; Riera, V.; Miguel, D. Organometallics 2001, 20, 4517. (d)
Garc´ıa, F.; Hopkins, A. D.; Humphrey, S. M.; McPartlin, M.; Rogers, M.
C.; Wright, D. S. Dalton Trans. 2004, 361.
(8) (a) Garc´ıa, F.; Hopkins, A. D.; Kowenicki, R. A.; McPartlin, M.;
Rogers, M. C.; Wright, D. S. Organometallics 2004, 23, 3884. (b) Alvarez,
C. S.; Garc´ıa, F.; Humphrey, S. M.; Hopkins, A. D.; Kowenicki, R. A.;
McPartlin, M.; Layfield, R. A.; Raja, R.; Rogers, M. C.; Woods, A. D.;
Wright, D. S. J. Chem. Soc., Chem. Commun. 2005, 198.
10.1021/om0600691 CCC: $33.50 © 2006 American Chemical Society
Publication on Web 04/08/2006

2562 Organometallics, Vol. 25, No. 10, 2006
Garc´ıa et al.
Scheme 1
Scheme 2
framework itself [Zn2+ 0.88 Å; cf. the ionic radii for bis-
coordinated complexes, Ca2+ 1.14, Mn2+ 0.97, Fe2+ 0.92 Å].9
Several attempts were made to prepare InIII analogues of 1
of the type [RIn(2-py)3Li‚THF] via various routes. In particular,
the in situ preparation of MeInCl2 from Me3In and InCl3,
followed by reaction with 2-Li-py in THF (Scheme 2a), proved
to be problematic owing to the apparent instability of the
product(s) and the resulting formation of In metal. However,
the sequential reaction of InCl3 with nBuLi followed by reaction
with 2-Li-py (Scheme 2b) under nitrogen was successful, giving
[{nBuIn(2-py)3}Li‚THF] (5) as the only isolatable product. The
low yield of 5 (only 13%) appears to be mainly the result of
decomposition into In metal during its formation. Nonetheless,
5 is stable enough in solution to act as a source of the [nBuIn-
(2-py)3]- ligand. Although the reactions of 5 with Cp2Mn or
FeBr2 result in extensive decomposition into In metal [cf. the
reactions of 1, which give [{MeAl(2-py)3}2M] (M ) Fe, Mn)8a],
no such decomposition occurs in the reaction of 5 with [(C7H8)-
Mo(CO)3]. The product [{nBuIn(2-py)3}Mo(CO)3Li(THF)2]∞ (6)
is similar to the analogous AlIII complex 2 (Scheme 3), apart
from the fact that there is only bis-solvation of the Li+ cation.
The lower solvation of the Li+ cations of 6 results in a polymeric
structure in the solid state, as shown by an X-ray structural study
of the complex. Attempts to obtain a GaIII derivative by a route
similar to that employed for 5 have so far been unsuccessful.
Complexes 2, 3, 4, 5, and 6 were characterized using a
combination of elemental analysis, IR and NMR spectroscopy,
and X-ray crystallography. All of the complexes are air- and
moisture-sensitive, decomposing in a few minutes in air and
reacting exothermically with protic solvents. This sensitivity and
the tendency to lose THF solvation when placed under vacuum
during isolation led to problems in obtaining satisfactory
elemental analysis on all the complexes. These problems were
compounded in the case of 6, which is thermally unstable and
decomposes slowly under nitrogen atmosphere at room tem-
perature in the solid state or under reflux in THF solution, with
the disappearance of the CtO stretching band in its IR spectrum
suggesting attack of the metal-bonded 2-py groups onto the CO
ligands. Since the Zn complex 4 could be isolated only in low
yield, it was characterized only by X-ray crystallography. The
room-temperature 1H NMR spectra of the related AlIII/Mo0 and
InIII/Mo0 complexes 2 and 6 (respectively) in benzene reveal
the presence of broad pyridyl C-H resonances in the region
) Fe, Mn).8b Such ligand transfer reactions provide a simple
approach to well-defined heterometallic group 13 complexes,
which have potential applications in catalysis in a number of
important areas. For example, it was shown that the FeII complex
[{MeAl(2-py)}2Fe] is the most selective catalyst for the
industrially important oxidation of styrene into styrene oxide
in air.8b
In view of the potentially broad applications of 1 and related
group 13 anionic ligands in a range of catalytic systems, it was
decided to investigate the coordination chemistry of the [MeAl-
(2-py)3]- ligand with a broader range of metals. We present
here the syntheses and structures of the new complexes [{MeAl-
(2-py)3}Mo(CO)3Li(THF)3] (2), [{MeAl(2-py)3}2Ca] (3), and
[{MeAl(2-py)3}ZnCl] (4), prepared from metal-exchange reac-
tions of 1 with the appropriate metal sources. We also report
the syntheses and structures of [{nBuIn(2-py)3}Li‚THF] (5) and
[{nBuIn(2-py)3}Mo(CO)3Li(THF)2]∞ (6), containing the first InIII
tris-pyridyl ligand. These studies, together with those of [{MeAl-
(2-py)}2M] (M ) Fe, Mn) communicated previously,8b illustrate
the broad applications of group 13 tris-pyridyl ligands of this
type across the periodic table.
Results and Discussion
The room-temperature reaction of [(C7H8)Mo(CO)3] with
[{MeAl(2-py)3Li‚THF] (1) in THF under dinitrogen occurs
rapidly to give a deep red solution, from which the red,
trimetallic complex [{MeAl(2-py)3}Mo(CO)3Li(THF)3] (2) is
isolated in good yield (66%) (Scheme 1). The 1:2 reaction of
CaI2 with 1 under nitrogen gives [{MeAl(2-py)3}2Ca] (3)
(Scheme 1). The disubstitution of the metal center observed here
is similar to that observed in the reactions of 1 with FeBr2 and
Cp2Mn reported previously.8b In contrast, the 1:1 or 1:2 reactions
of ZnCl2 with 1 under nitrogen both give the bimetallic AlIII/
Zn complex [{MeAl(2-py)3}ZnCl] (4) after reflux in THF
(Scheme 1) (as shown by unit cell analysis of the crystals
produced in both reactions). Although the formation of 4 is
reproducible, owing to the high solubility of the complex in a
range of solvents, only a few crystals of the complex could be
isolated. Presumably the smaller size of the Zn2+ ion makes
coordination by two [MeAl(2-py)3]- ligands unfavorable both
on steric grounds and for reasons of strain within the ligand
n
ca. δ 8.7-6.4, as well as the Me-Al (δ 0.38) or Bu-In (δ
(9) Huheey, J. E.; Keiter, E. A.; Keiter, R. L. Inorganic Chemistry-
Principles of Structure and ReactiVity, 4th ed.; pp 114-117.

Heterometallic Complexes Containing Group 13 Ligands
Organometallics, Vol. 25, No. 10, 2006 2563
Scheme 3
2.44-1.00) resonances for the metal-attached alkyl groups. The
IR spectra of solid 2 and 6 both show two major resonances in
the CO region, at 1886 (m) and 1873 (s) cm-1 in 2 and 1900
(s) and 1890 (sh) cm-1 in 6, which can be assigned tentatively
to symmetric and asymmetric stretching bands. It can be noted,
however, that there is another minor band present in 2 at 1670
cm-1 (absent in 6). The fact that the IR spectra of both
complexes are not altered significantly in THF solution indicates
that this minor band is not simply due to ion-pairing with the
Li+ cations in the solid state (see their later structural charac-
terization). The appearance of the IR spectrum of 2 is similar
to that of the neutral SnIV complex [{nBuSn(2-py)3}Mo(CO)3]
(with CO stretching bands at 1900, 1788, 1739 cm-1 7c), and
the major bands found in the spectra of 2 and 6 are also similar
to those observed in the IR spectrum of the tris-pyrazolylborate
complex [TpMo(CO)3]- [1890 (s), 1750 (vs) cm-1] (Tp )
hydridotripyrazolylborato).10 The similarity of the vibrational
frequencies in 2 and 6 suggests that the π-donor/acceptor
character of the [MeAl(2-py)3]- and [nBuIn(2-py)3]- ligands
are similar and affected only to a minor extent by the group 13
metal bridgehead and R group. Bearing this in mind, the large
difference in color between them [deep-red for 2, yellow-brown
for 6] is surprising.
solution of 5 results in simplification of the spectrum, with one
dominant species (presumably intact 5) now being apparent in
the H NMR spectrum [2-py, δ 8.44 [d, C(6)-H], 7.90 (d),
1
7.12 (mult), 6.72 (mult); nBu, 2.50 (mult), 2.00 (mult), 1.65 (t,
CH3), 1.30 (t, R-CH2)]. Somewhat anomalously, however, the
7Li NMR spectrum still shows at least two dominant solution
species at δ 2.94 and 2.25 (298-250 K). In the case of the
AlIII complex 2, we were able to isolate and structurally
characterize the desolvated species (the dimer [MeAl(2-
py)3Li]2), by placing 2 under vacuum at elevated temperature
and crystallizing the powder produced from toluene. Unfortu-
nately, similar treatment of 5 resulted in an impure powder that
was completely insoluble in nondonor solvents, so could not
be characterized by X-ray crystallography or NMR spectroscopy.
The low-temperature X-ray structures of 2, 3, 4, 5, and 6
were obtained. Details of the data collections and structure
refinements of these complexes are given in Table 1. Selected
bond lengths and angles for 2, 3, 4, 5, and 6 are presented in
Tables 2, 3, 4, 5, and 6, respectively.
The low-temperature X-ray structure of 2 reveals that the
complex is a monomeric, trimetallic species, [{MeAl(2-py)3}-
Mo(CO)3Li(THF)3] (2), consisting of a [{MeAl(2-py)3}2Mo-
(CO)3]- anion that coordinates a [Li(THF)3]+ cation using one
of the O centers of a CO ligand (Figure 2). The structure
confirms that the C7H8 ligand present in the precursor has been
substituted by a [MeAl(2-py)3]- ligand. The chelation of the
Mo center by the three N atoms of this ligand is similar to that
observed previously in transition metal complexes [{MeAl(2-
py)3}2M] (M ) Fe, Mn).8b However, 2 is the first transition
metal complex in which a low oxidation state, carbonyl fragment
is coordinated by this ligand. As such, 2 is related to the
previously reported, neutral complex [{nBuSn(2-py)3}Mo(CO)3],
which was obtained by substitution of [(THF)Mo(CO)5] by the
neutral ligand [nBuSn(2-py)3].7c
The Ca complex 3 was crystallized as the tris-toluene solvate
1
[3‚3toluene] from toluene solvent. Elemental analysis and H
NMR spectroscopy show that this lattice solvation is removed
by placing the complex under vacuum (0.1 atm). Repeated
analysis, however, gave a C content ca. 2% too low, although
the H and N content was as expected for unsolvated 3. The 1H
NMR spectrum of 3 in toluene shows four aromatic C-H
resonances for the 2-py group [8.03 (ddd), 7.92 (ddd), 7.09 (dt),
6.33 (ddd)] and the Me resonance for the [MeAl(2-py)3]- anion
as a singlet at δ 0.48. This shows that there is only one solution
species present, presumably the intact, bis-coordinated structure
found later in the solid state. In contrast, the InIII complex 5 is
clearly highly dynamic in solution, its behavior in toluene
solution being very similar to that reported previously for the
AlIII relative 2.8a At low concentration [0.02 mol L-1] in toluene
at room temperature two singlet resonances are observed in the
7Li NMR spectrum, at δ 2.86 and 2.83. However, at higher
concentration [0.08 mol L-1] only the resonance at the lower
The bond lengths and angles within the [MeAl(2-py)3]- ligand
of 2 are very similar to those observed previously in the solid-
1
chemical shift is observed. Although the H NMR spectra in
toluene at both of these concentrations are highly complicated
in the aromatic (δ 8.51-6.70) and nBu (δ 2.20-0.85) regions,
at least two distinct solution species are again apparent, as
indicated in particular by the presence of two distinct C(6)-H
resonances for the 2-py groups (at δ 8.51 and 8.39) (whose
relative integrals are also concentration dependent). These
observations suggest that (like 28a) 5 is involved in a dynamic
equilibrium involving loss of THF ligands. Consistent with this
hypothesis, the addition of a small amount of THF to a toluene
Figure 2. Structure of the trimetallic [{MeAl(2-py)3}Mo(CO)3Li-
(THF)3] (2). H atoms gave been omitted for clarity.
(10) Curtis, M. D.; Shiu, K.-B. Inorg. Chem. 1985, 24, 1213.

2564 Organometallics, Vol. 25, No. 10, 2006
Garc´ıa et al.
Table 1. Details of Data Collections and Structural Refinements for [{MeAl(2-py)3}Mo(CO)3Li(THF)3] (2),
[{MeAl(2-py)3}2Ca]‚3toluene (3‚3toluene), [{MeAl(2-py)3}ZnCl] (4), [{nBuIn(2-py)3}Li‚THF] (5), and
[{nBuInAl(2-py)3}Mo(CO)3Li(THF)2]∞ (6)
2
3‚3toluene
4
5
6
empirical formula
fw
C31H39AlLiMoN3O6
679.51
C53H54Al2CaN6
869.06
C16H15AlClN3Zn
377.11
C23H29InLiN3O
485.25
C30H37InLiMoN3O5
737.33
cryst syst
space group
a (Å)
b (Å)
c (Å)
monoclinic
P2(1)/c
14.170(3)
13.738(3)
18.244(4)
monoclinic
C2/c
9.493(2)
22.857(5)
22.727(5)
triclinic
P1h
triclinic
P1h
monoclinic
P2(1)/c
17.895(4)
17.909(4)
10.100(2)
8.558(2)
9.239(2)
12.713(3)
84.73(3)
70.83(3)
65.04(3)
859.5(4)
2
8.756(2)
15.522(3)
17.899(4)
74.98(3)
89.87(3)
84.23(3)
2336.8(9)
4
R (deg)
â (deg)
110.26(3)
94.80(3)
99.91(3)
γ (deg)
V (Å3)
3332(1)
4
4914 (2)
4
3189(1)
4
Z
F(000)
1408
1840
384
992
1488
cryst size (mm)
θ range (deg)
0.30 × 0.23 × 0.10
3.57-23.00
1.355
0.464
21 560
0.16 × 0.12 × 0.12
3.57-27.47
1.175
0.204
20 493
0.25 × 0.21 × 0.07
3.63-25.00
1.457
1.633
7522
0.12 × 0.16 × 0.21
3.541-27.51
1.379
1.028
25 224
0.10 × 0.16 × 0.18
3.53-25.00
1.536
1.157
22 656
F
calc (Mg m-3
)
µ (mm-1
)
no. of reflns collected
no. of ind reflns
Rint
4611
0.046
5569
0.041
2998
0.045
10624
0.042
5574
0.041
absorp corr
multiscan
0.930/0.843
4611/0/389
multiscan
0.980/0.949
5569/0/299
multiscan
0.892/0.671
2998/0/200
multiscan
0.884/0.821
10 624/10/498
multiscan
0.891/0.812
5574/0/368
max., min. transmn
no. of data/restraints/
params
goodness-of-fit on F2
R indices (I >2σI)
1.040
1.024
1.147
1.049
1.009
R1 ) 0.032,
wR2 ) 0.088
R1 ) 0.040
wR2 ) 0.092
0.368/-0.493
R1 ) 0.049,
wR2 ) 0.121
R1 ) 0.067
wR2 ) 0.131
0.893/-0.500
R1 ) 0.056,
wR2 ) 0.126
R1 ) 0.0731
wR2 ) 0.1301
0.546/-0.550
R1 ) 0.047,
wR2 ) 0.120
R1 ) 0.073
wR2 ) 0.135
1.456/-1.397
R1 ) 0.032,
wR2 ) 0.069
R1 ) 0.046
wR2 ) 0.073
0.604/-0.388
R indices (all data)
largest peak and hole
(e Å-3
)
a Data in common; λ ) 0.71073 nm, T ) 180(2) K.
Table 2. Selected Bond Lengths and Angles for [{MeAl(2-py)3}Mo(CO)3Li(THF)3] (2)
Bond Lengths (Å)
C(1)-Al(1)
1.976(4)
1.977(3)
1.968(3)
1.971(3)
2.335(2)
2.305(2)
2.313(3)
1.910(3)
Mo(1)-C(3)
Mo(1)-C(2)
C(2)-O(2)
1.948(4)
1.952(3)
1.165(4)
1.170(4)
1.195(3)
1.926(6)
Al(1)-C(11)
Al(1)-C(21)
Al(1)-C(31)
N(16)-Mo(1)
N(26)-Mo(1)
N(36)-Mo(1)
Mo(1)-C(4)
C(3)-O(3)
C(4)-O(4)
O(4)-Li(1)
Li-O(1T,1U,1V)
Mo(1)‚‚‚Al(1)
1.911(6)-1.925(6)
3.532(1)
Bond Angles (deg)
CR-Al(1)-C(1)a
CR-Al(1)-CR
112.5(2)-115.0(2)
104.3(1)-105.2(1)
av 123.6
C(4)-Mo(1)-C(2)
90.5(1)
85.6(1)
90.0(1)-95.5(1)
146.3(3)
C(4)-Mo(1)-C(3)
N-Mo(1)-C(2,3,4)
C(4)-O(4)-Li(1)
CR-N-Mo(1)
N(26)-Mo(1)-N(16)
N(36)-Mo(1)-N(16)
N(26)-Mo(1)-N(36)
C(3)-Mo(1)-C(2)
87.81(9)
89.09(9)
88.53(9)
84.1(1)
a CR are the R-C atoms of the 2-pyridyl groups [C(11), C(21), C(31)].
Table 3. Selected Bond Lengths and Angles for [{MeAl(2-py)3}2Ca] (3)
Bond Lengths (Å)
C(1)-Al(1)
Al(1)-C(11)
Al(1)-C(21)
Al(1)-C(31)
1.978(2)
2.024(2)
2.015(2)
2.023(2)
N(16)-Ca(1)
N(26)-Ca(1)
N(36)-Ca(1)
Al(1)‚‚‚Ca(1)
2.481(2)
2.476(2)
2.489(2)
3.630(1)
Bond Angles (deg)
CR-Al(1)-C(1)a
CR-Al(1)-CR
112.44(9)-113.75(9)
105.36(8)-106.66(8)
Al(1)-CR-N
N-Ca(1)-N range
av 118.4
87.41(5)-92.59(5)
a CR are the R-C atoms of the 2-pyridyl groups [C(11), C(21), C(31)].
state structures of other complexes containing this ligand. In
particular, the range of angles at the Al(III) bridgehead in 2
[CR-Al(1)-CR 104.3(1)-105.2(1)°] closely matches the ranges
found in both transition metal and lithium complexes of this
type [101.8(1)-104.7(2)°],8 suggesting little strain results from
the coordination even of a large Mo0 center. The coordination
of this Mo0 in 2 by the three N atoms of the 2-py groups is not
entirely regular [Mo(1)-N(16,26,36) range 2.305(2)-2.335-
(2) Å], and it is noticeable that the longest Mo-N bond [N(16)-
Mo(1) 2.335(2) Å] appears to give rise to a short, trans-Mo-C

Heterometallic Complexes Containing Group 13 Ligands
Organometallics, Vol. 25, No. 10, 2006 2565
Table 4. Selected Bond Lengths and Angles for the Disordered Molecule [MeAl(2-py)3}ZnCl] (4)
Bond Lengths (Å)
Bond Angles (deg)
Al(1)-C(1)
Al(1)-C(11)
Al(1)-C(21)
Al(1)-C(31)
2.075(5)
2.019(5)
2.009(5)
1.999(5)
Zn(1)-Cl(1)
N(16)-Zn(1)
N(26)-Zn(1)
N(36)-Zn(1)
Zn(1)‚‚‚Al(1)
2.210(2)
2.034(4)
2.043(4)
2.021(5)
a
C(1)-Al(1)-CR
CR-Al(1)-CR
111.2(2)-118.2(2)
100.1(2)-104.1(2)
103.3(2)
N(3)-Zn(1)-N(2)
N(1)-Zn(1)-N(2)
N-Zn(1)-Cl(1)
104.2(2)
97.9(2)
112.4(1)-115.1(1)
N(3)-Zn(1)-N(1)
a CR are the R-C atoms of the 2-pyridyl groups [C(11), C(21), C(31)].
Table 5. Selected Bond Lengths and Angles for [nBuIn(2-py)3Li‚THF] (5)
Bond Lengths (Å)
In(1)-C(1)
In(1)-CRb
N(py)-Li
2.186(5)
In(1)‚‚‚Li(1)
Li(1)-O(THF)
3.157(6)
[3.126(6)]
1.996(6)
[2.169(5)]a
2.211(4)-2.222(4)
[2.215(4)-2.224(4)]
2.057(6)-2.082(6)
[2.050(6)-2.081(6)]
[2.001(7)]
Bond Angles (deg)
N(py)-Li(1)-N(py)
C(1)-In(1)-CR
CR-In(1)-CR
114.6(2)-119.7(2)
[115.9(2)-118.5(2)]
100.3(2)-101.8(2)
[97.6(1)-102.6(1)]
105.4(3)-107.5(3)
[104.1(3)-108.5(4)]
107.3(9)-114.2(3)
[109.0(3)-116.0(4)]
N(py)-Li(1)-O(THF)
a Values in parentheses are for molecule B. b CR are the R-C atoms of the 2-pyridyl groups [C(11), C(21), C(31)].
Table 6. Selected Bond Lengths and Angles for [{nBuIn(2-py)3}Mo(CO)3Li(THF)2]∞ (6)
Bond Lengths (Å)
In(1)-C(1)
2.196(3)
2.187(3)
2.197(4)
2.197(3)
2.343(3)
2.338(3)
2.337(3)
1.905(4)
Mo(1)-C(3)
Mo(1)-C(2)
C(2)-O(2)
1.908(4)
1.949(4)
1.164(4)
1.181(4)
1.189(4)
1.926(6)
1.900(6)
1.926(6)
3.724(1)
In(1)-C(11)
In(1)-C(21)
In(1)-C(31)
N(16)-Mo(1)
N(26)-Mo(1)
N(36)-Mo(1)
Mo(1)-C(4)
C(3)-O(3)
C(4)-O(1B)
O(3)-Li
O(1)-Li
Li-O(THF) (mean)
Mo(1)‚‚‚In(1)
Bond Angles (deg)
CR-In(1)-C(1)a
113.8(2)-120.9(1)
98.5(1)-101.5(1)
av 125.6
C(4)-Mo(1)-C(3)
N-Mo(1)-C(2,3,4)
C(4)-O(1B)-LiB
O(1B)-LiB-O(3B)
C(3)-O(3)-Li
80.9(2)
91.4(1)-94.9(1)
167.5(3)
117.3(3)
159.4(3)
117.5(3)
CR-In(1)-CR
CR-N-Mo(1)
N(26)-Mo(1)-N(16)
N(36)-Mo(1)-N(16)
N(26)-Mo(1)-N(36)
C(3)-Mo(1)-C(2)
C(4)-Mo(1)-C(2)
92.1(1)
90.2(1)
89.5(1)
84.0(1)
O(3)-Li-O(1)
84.1(1)
a CR are the R-C atoms of the 2-pyridyl groups [C(11), C(21), C(31)].
bond [Mo(1)-C(4) 1.910(3) Å]. At first sight this pattern of
bond lengths might be taken to suggest a trans-influence of the
pyridyl-N metal bonding on the metal carbonyl bonding, i.e.,
that as the extent of bonding of the p orbital of the pyridyl-N
atom with the Mo (dxy, dxz, or dyz) orbitals decreases, a greater
extent of back-bonding to the trans-CO ligand would be
expected. However, this does not seem to be the case, as no
such correlation between the Mo-N and Mo-C bond lengths
is discernible in the structure of the closely related complex
[{nBuIn(2-py)3}Mo(CO)3Li(THF)2]∞ (6) (see later discussion,
Figure 6). Rather, the common effect in both 2 and 6 is the
influence of the Li+ cations on the pattern of carbonyl bonding.
In 2, the result of bonding of the Li+ cation to O(4) is to lengthen
the C-O bond of the carbonyl ligand [C(4)-O(4) 1.195(3) Å]
and shorten the associated C-Mo bond [Mo(1)-C(4) 1.910(3)
Å] [cf. 1.165(4)-1.170(4) Å and 1.948(3)-1.952(4) Å for the
other C-O and Mo-C bonds, respectively, in 2]. The same
effect is also seen in 6, in which two of the longest C-O bonds
are associated with the CO ligands bonded to the Li+ cations
[C-O(1B,3) 1.181(4)-1.189(4) Å; cf. C(2)-O(2) 1.164(4) Å],
with the corresponding Mo-C bond lengths being the shortest
[Mo(1)-C(3,4) 1.903(4)-1.908(4) Å; cf. 1.949(4) Å]. This
pattern of C-O and Mo-C bond lengths can be explained by
a classical resonance model in which transfer of electron density
from Mo to the CO ligand results in transfer of negative charge
to the O atom, optimizing O-Li bonding. The observation of
CO-Li bonding in 2 and 6 is not unusual.11 A large number of
alkali and alkaline earth complexes of this type have been
reported previously.12
(11) Wong, W.-T.; Wong, W.-K. Acta Crystallogr. 1994, 50C, 1404.
Leiner, E.; Hampe, O.; Scheer, M. Eur. J. Inorg. Chem. 2002, 584. Fretzen,
A.; Ripa, A.; Liu, R.; Bernardinelli, G.; Kundig, E. P. Chem. Eur. J. 1998,
4, 251. Heyn, R. H.; Huffman, J. C.; Caulton, K. G. New J. Chem. 1993,
17, 797. Neumu¨ller, B.; Petz, W. Organometallics 2001, 20, 163. Balema,
V.; Goesmann, H.; Materu, W.; Fritz, G. Z. Anorg. Allg. Chem. 1996, 35,
622. Hou, H.; Rheingold, A. L.; Kubiak, C. P. Organometallics 2005, 24,
231.
(12) Conquest software for searching the Cambridge Structural Data Base
and Visualizing Crystal Structures (January 2006). Bruno, I. J.; Cole, J. C.;
Edgington, P. R.; Kessler, M.; Macrae, C. F.; McCabe, P.; Pearson, J.;
Taylor, R. Acta Crystallogr. 2001, B58, 389.

2566 Organometallics, Vol. 25, No. 10, 2006
Garc´ıa et al.
Figure 3. Structure of [{MeAl(2-py)3}2Ca] (3). H atoms and
toluene molecules in the lattice have been omitted for clarity.
Symmetry A: 1.5 - x, 0.5 - y, -z.
Figure 6. Part of the polymeric structure [{nBuIn(2-py)3}Mo-
(CO)3Li(THF)2]∞ (6): symmetry A x, 1.5 - y, -0.5 + z; B x, 1.5
- y, 0.5 + z.
rangement of 3 is the same as that observed previously for
[{MeAl(2-py)}2M] (M ) FeII, MnII).8b The bond lengths and
angles found in the [MeAl(2-py)3]- anions in 3 are very similar
to those found in these complexes [Al-C range 1.978(2)-2.023-
(2) Å, CR-Al(1)-CR 105.36(8)-106.66(8)° in 3; cf. 1.969-
(3)-2.014(3) Å, CR-Al(1)-CR 104.3(1)-105.2(1)° for the
corresponding values in [{MeAl(2-py)}2M] (M ) FeII, MnII)8b].
The Ca-N bonds in 3 [range 2.476(2)-2.489(2) Å] are in the
range found previously in Ca-N bonded complexes [mean 2.52
Å].12
The structure of 4 is that of a simple monomer [{MeAl(2-
py)3}ZnCl], in which the pseudotetrahedral Zn2+ ion is coor-
dinated by one [MeAl(2-py)3]- ligand (Figure 4). Molecules
of 4 exhibit unusual crystallographic disorder about a virtual
inversion center between the Zn and Al atoms so the metal atom
positions shown in Figure 5 are Zn(1) 80:20% Zn:Al and Al(1)
20:80% Zn:Al (with the 2-py and Me groups and Cl atom also
being similarly disordered). As a result of this disorder,
meaningful discussion of the bond lengths and angles in 4 is
not possible.
Figure 4. Structure of the monomeric molecule of [MeAl(2-py)3}-
ZnCl] (4) illustrated by the 80% component of the disorder. H atoms
have been omitted for clarity.
Monomeric molecules of 5 are directly related to the structure
of the AlIII precursor [{MeAl(2-py)3}Li‚THF] (1), being an ion-
paired complex composed of the [nBuIn(2-py)3]- anion coor-
dinated to a THF-solvated Li+ cation (Figure 5). There are two
chemically identical but crystallographically independent mol-
ecules present in the unit cell (Figure 5). Table 5 includes
selected bond lengths and angles for both independent mol-
ecules. However, the following discussion will concern averages
or ranges of bond lengths and angles for both forms. The most
obvious effect of changing the bridgehead atom from Al to In
is an increase in the ligand bite. Although there is a small
reduction in the bridgehead CR-In-CR angle [range 100.2(1)-
102.6(2)° in 5; cf 103.83(9)-104.4(1)° in 18a], which would
tend to reduce the ligand bite compared to the related AlIII
complex, the major factor dictating the ligand bite is the increase
in the CR-metal bond length. Thus, in 5 the CR-In bond lengths
[2.207(4)-2.226(4) Å] are ca. 0.2 Å longer than the CR-Al
bonds in 1, resulting in a net increase in the bite from 3.23 Å
in 18a to 3.34 Å in 5 (in both cases expressed as the mean N‚
‚‚N separation). The dominant influence of the CR-metal bond
length on the ligand bite is the same as that found for the neutral
counterparts [MeE(2-py)3] (E ) C,3 Si,7c Sn7a,b) as group 14 is
descended.
Figure 5. The two independent molecules of [{nBuIn(2-py)3}Li‚
THF] (5) present in the unit cell. H atoms have been omitted for
clarity.
The structure of 3 (Figure 3) is that of a monomer of formula
[{MeAl(2-py)3}2Ca], in which the Ca2+ ion is coordinated by
two [MeAl(2-py)3]- anions. The Ca2+ ion is coordinated by
six N atoms of the two tris-pyridyl ligands [N-Ca range 2.476-
(2)-2.489(2) Å] in an almost regular octahedral geometry
[N-Ca(1)-N range 87.41(5)-92.59(5)°]. The structural ar-

Heterometallic Complexes Containing Group 13 Ligands
Organometallics, Vol. 25, No. 10, 2006 2567
The structure of the trimetallic complex [{nBuIn(2-py)3}Mo-
(CO)3Li(THF)2]∞ (6) is very similar to that of the AlIII complex
2 (Figure 6), the major difference being that the Li+ cation in
6 is only bis-coordinated by THF ligands (as a opposed to being
tris-coordinated as in 2). This difference results in a polymeric
structure for 6 in which molecules are linked together, via Ct
O‚‚‚Li‚‚‚OtC bridges, into a zigzag arrangement generated by
the c-glide. The reason for this difference is probably steric in
origin, in particular stemming from the presence of an nBu group
on the InIII center in 6 as opposed to a Me group in 2. The
bond lengths and angles within the [nBuIn(2-py)3]- anion of 6
are very similar to those found in the structure of the precursor
5 [e.g., In-C range 2.186(4)-2.197(4) Å, CR-In(1)-CR 98.5-
(1)-101.4(1)° in 6; cf 2.159(5)-2.226(4) Å, 97.5(1)-102.6-
(2)° in 5]. The Mo-N and Mo-C bond lengths in 6 [Mo(1)-
N range 2.337(3)-2.343(3) Å, Mo(1)-C range 1.903(4)-
1.952(4) Å] are similar to those found in the related AlIII
complex 2.
solution of [(C7H8)Mo(CO)3] intensifying. The solvent was removed
under vacuum, together with any volatile products. The residue was
dissolved in THF (15 mL) and the solution stored at -5 °C (1
week) to give red, hexagonal plates (0.45 g, 0.66 mmol, 66%).
Decomposition ca. 125 °C to black solid. IR (solid, Nujol, NaCl):
1
ν/cm-1 1886 (m), 1873 (s) (CO str). H NMR (500.2 MHz, d6-
benzene, +25 °C): δ/ppm 8.65 [br d, 3H, C(5)-H], 6.75 [br s,
C(3,4)-H, 6H], 6.42 [br s, 3H, C(2)-H], 3.70 [m, 4H, -CH2-O,
THF], 1.52 [m, 4H, -CH2-, THF], 0.38 [s, 3H, Me-Al]. 7Li NMR
(194.40 MHz, d6-benzene, +25 °C, rel to saturated LiCl/D2O):
δ/ppm -0.58. Anal. Found: 54.6, H 5.6, N 6.3. Calcd for 2: C
54.8, H 5.7, N 6.2.
Synthesis of 3. A mixture of CaI2 (0.5 mmol) and 1 (0.355 g,
1.0 mmol) was dissolved in toluene (30 mL). The mixture was
stirred at room temperature for 3 days to give a yellow solution
with a fine white precipitate. The mixture was filtered through
Celite, and the volume of solvent was reduced under vacuum to
ca. 10 mL. The filtrate was stored at -20 °C for 2 days to give
colorless, rectangular crystals. X-ray crystallography showed that
these are the tris-solvate 3‚3toluene. Placing the crystals under
vacuum during isolation (10-1 atm, 15 min) removed almost all of
the lattice-bound toluene and resulted in the formation of an
amorphous powder of 3. The following data refer to this material.
Yield: 0.15 g, 51%). Decomposition ca. 300 °C to black solid. 1H
NMR (500.2 MHz, d6-toluene, +25 °C): δ/ppm 8.03 (ddd, 6H,
C(5)-H, J ) 7.4 Hz, J ) 1.2 Hz, J ) 1.2 Hz), 7.92 (ddd, 6H,
C(3)-H, J ) 5.2, J ) 1.6, J ) 1.2 Hz), 7.09 (dt, 6H, C(4)-H, J
) 7.6, J ) 1.7 Hz), 6.33 (ddd, 6H, C(2)-H, J ) 7.6, J ) 5.2, J )
1.5 Hz), 0.48 (s, 6H, CH3-Al). Anal. Found: C 62.8, H 5.4, N
14.1. Calcd for 3: C 64.8, H 5.1, N 14.2.
Conclusions
The results reported here and by us previously8 show that
group 13 tris-pyridyl ligands of the type [RE(2-py)3]- have
broad applications in coordination chemistry, in the coordination
of harder main group metal ions (Li+, Ca2+, Zn2+), and for
higher (MnII, FeII) and lower oxidation state [Mo0] transition
metals. Future studies will be aimed at exploring the electro-
chemical activity of the group 13 bridgehead atoms in various
complexes (especially transition metal complexes) and the
potential catalytic activity of these species. A further direction
of interest to us in future studies is the formation of related 3-
and 4-pyridyl derivatives and the exploration of the potential
supramolecular chemistry of these ligands.
Synthesis of 4. A mixture of solid ZnCl2 (0.134 g, 1.0 mmol)
and 1 (0.355 g, 1.0 mmol) was dissolved in THF (10 mL) and
brought to reflux (2 h). The volume of the resulting orange solution
was then reduced under vacuum to ca. 4 mL and the solution stored
at 5 °C for 48 h to give a few colorless needles of 4. Owing to the
very low yield of the complex, it could be characterized only by
X-ray crystallography.
Experimental Section
General Procedures. Compounds 2, 3, 4, 5, and 6 are air- and
moisture-sensitive. They were handled on a vacuum line (in an
efficient cupboard) using standard inert-atmosphere techniques and
under dry/oxygen-free argon. 2-Bromopyridine, ZnCl2 (99.99%),
InCl3 (99%), and CaI2 (99.9%) were acquired from Aldrich
Chemical Co. 2-Bromopyridine was freshly distilled over CaH2
prior to lithiation reactions. [(C7H8)Mo(CO)3] was prepared by the
literature route.13 THF was dried by distillation over sodium/
benzophenone prior to the reactions. The products were isolated
and characterized with the aid of an argon-filled glovebox fitted
with a Belle Technology O2 and H2O internal recirculation system.
Melting points were determined by using a conventional apparatus
and sealing samples in capillaries under argon. IR spectra were
recorded as Nujol mulls using NaCl plates and were run on a Perkin-
Elmer Paragon 1000 FTIR spectrophotometer. Elemental analyses
were performed by first sealing the samples under argon in airtight
aluminum boats (1-2 mg), and C, H, and N content was analyzed
Synthesis of 5. To a solution of InCl3 (2.21 g, 10 mmol) in THF
(40 mL) was added nBuLi (6.25 mL, 1.6 mol dm-3 in hexanes, 10
mmol) dropwise at -78 °C. The reaction mixture was stirred at
room temperature (2 h) to give a clear, colorless solution. This
solution was added dropwise to a solution of 2-Li-py [obtained by
n
the addition of BuLi (18.75 mL, 1.6 mol dm-3 in hexanes, 30
mmol) to 2-Br-py (2.85 mL, 30 mmol) in THF (100 mL) at -78
°C (stirred for 3 h)]. The reaction mixture was allowed to warm to
room temperature, then stirred (16 h), producing a gray suspension.
The solvent was removed under vacuum and the residue extracted
with n-pentane (60 mL) and filtered. The volume of the residue
was reduced under vacuum until precipitation occurred. The
precipitate was dissolved by heating gently. Storage at room
temperature (16 h) gave colorless crystalline blocks of 5 (0.67 g,
13%; the reaction can be scaled up to 20 mmol with only a small
reduction in the yield). IR (solid, Nujol, NaCl): ν/cm-1 3028 (w)
1
(aryl C-H). H NMR (500.2 MHz, d6-benzene, +25 °C): δ/ppm
1
using an Exeter Analytical CE-440 elemental analyzer. H, 13C,
8.51 (dd, C(6)-H 2-py), 8.39 (d, C(6)-H, 2-py), 7.59 (mult, 2-py),
7.15 (mult 2-py), 6.70 (mult, 2-py) (total integral 12H), 3.60 (mult,
4H, THF), 1.49 (mult, 4H, THF), 2.20-0.85 (overlapping mult,
7
and Li NMR spectra were recorded on a Bruker DPX 400 MHz
spectrometer in dry benzene or toluene (using the solvent resonances
1
as the internal reference standard for H and 13C studies and a
n
7
9H, Bu). Li (194.40 MHz, d6-benzene, +25 °C, rel to saturated
LiCl/D2O): δ/ppm 2.86 (s), 2.83 (s) [0.02 mol L-1], 2.83 (s) [0.08
mol L-1]. Anal. Found: C 56.0, H 5.9, N 8.6. Calcd for 5, C 56.9,
H 6.0, N 8.7.
saturated solution of LiCl/D2O as the external standard for 7Li NMR
studies). The synthesis of 1 has been described elsewhere. Details
of the syntheses only of the new compounds (2-6) are reported
here.
Synthesis of 6. To a solution of 5 (0.295 g, 0.61 mmol) in THF
(10 mL) at room temperature was added solid [(C7H8)Mo(CO)3]
(0.166 g, 0.61 mmol). The reaction changed color from deep red
to brown-yellow over the course of 1 h. Stirring was continued for
a further 1 h before the solvent was removed under vacuum and
the oily solid pumped on for ca. 1 h to remove volatile components.
Synthesis of 2. Solid cycloheptatrienylmolybdenum tricarbonyl,
[(C7H8)Mo(CO)3] (0.272 g, 1.0 mmol), was added to a solution of
1 in THF (20 mL) at room temperature. The mixture was stirred at
room temperature (2 h), resulting in the dark red color of the starting
(13) Hooker, R. H.; Rest, A. J. J. Chem. Soc., Dalton Trans. 1982, 2029.

2568 Organometallics, Vol. 25, No. 10, 2006
Garc´ıa et al.
This was then washed with hexane (2 × 10 mL) and the yellow-
brown powder of 6 dried under vacuum (10-1 atm, 15 min). This
treatment resulted in the loss of ca. 0.5-1.0 of the coordinated
THF ligands. The following data refer to this material. Yield: 0.31g
(69%). IR (solid, Nujol, NaCl): ν/cm-1 1890 (s), 1890 (m) (CO
str). 1H NMR (500.2 MHz, d6-benzene, +25 °C): δ/ppm 8.52 [br
s, 3H, C(5)-H], 7.20 [t, 3H, C(3,4)-H], 6.65 [t, 3H, C(2)-H],
3.63 [m, ca. 5.8H, -CH2-O, THF], 1.43 [m, ca. 5.8H, -CH2-,
THF], 2.46-1.00 [overlapping mults, 9H, nBu-In]. 7Li (194.40
MHz, d6-benzene, +25 °C, rel to saturated LiCl/D2O): δ/ppm
-0.50 (s). Anal. Found: C 46.3, H 4.8, N 5.4. Calcd for 6-THF:
C 46.9, H 4.4, N 6.3. Crystals of 6 were grown by storage of a
THF solution of 6 for several weeks (-15 °C).
Crystal Structures of 2-6. Crystals of 2-6 were mounted
directly from solution under argon using an inert oil, which protects
them from atmospheric oxygen and moisture. X-ray intensity data
were collected using a Nonius Kappa CCD diffractometer. Details
of the data collections and structural refinements are given in Table
1. For all the crystals the positions of the non-hydrogen atoms were
located by direct methods and refinement was based on F2.14 In
the crystals of compounds 3 the Ca(1) atom is on an inversion
center, so the overall molecular structure has crystallographic Ci
symmetry. There are also three half toluene solvates per asymmetric
unit, two across C2 axes and the third disordered across an inversion
center. Throughout the crystal of 4 there is a random distribution
of two orientations of the molecule, which superimpose almost
exactly so that there is 80:20 disorder at each site, with Al
superimposed on Zn and vice versa, with a corresponding disorder
of the donor atoms. The bond lengths therefore cannot be discussed
meaningfully, but the overall structure is well established. In the
crystals of 5 there are two independent molecules per equivalent
position that are chemically identical and approximately related by
a noncrystallographic inversion center broken only by the atoms
of the butyl ligands, which are in different orientations. To minimize
the effects of correlation, the pairs of approximately centrosym-
metrically related bond lengths of the coordination spheres of the
two independent molecules were constrained to be equal within an
esd of 0.01 Å. Relatively high atomic displacement parameters
indicate some conformational disorder of the THF ligands in 2, 5,
n
and 6 and of the Bu ligands in 5 and 6. This disorder was only
resolved for one nBu C atom (70:30%) in 5 and two THF C atoms
(50:50) in 6. The hydrogen atoms for all five structures were placed
in calculated positions with displacement parameters set equal to
1.2Ueq (or 1.5Ueq) for methyl groups of the parent carbon atoms.
In the final cycles of full-matrix least-squares refinement, the non-
hydrogen full-occupancy atoms were assigned anisotropic displace-
ment parameters. Atomic coordinates, bond lengths and angles, and
thermal parameters for 2, 3, 4, 5, and 6 have been deposited with
the Cambridge Crystallographic Data Centre.
Acknowledgment. We thank the EPSRC (F.G., R.A.K.,
M.C.R., M.McP., D.S.W.), Churchill and Fitzwilliam Colleges
(Fellowship for A.D.H.), Wolfson College (Fellowship for F.G.),
and Churchill College (Winston Churchill Fellowship for J.S.S.)
for financial support.
Supporting Information Available: Full listings of X-ray
crystallographic data, atomic coordinates, thermal parameters, bond
distances, bond angles, and hydrogen parameters for 2, 3, 4, 5, and
6. This material is available free of charge via the Internet at
http://pubs.acs.org.
(14) Sheldrick, G. M. SHELX-97; Go¨ttingen, 1997.
OM0600691