Me2Si(C5Me4)2Cr: Synthesis and crystal structure of a ligand-free ansa-chromocene

Article abstract of DOI:10.1021/om049901x

Me₂Si(C₅Me₄)₂Cr, the first example of an ansa-chromocene containing no additional Uganda at chromium, was synthesized from Me₂Si(C₅Me₄₂Li ₂ and CrCl₂(THF)_x in the presence of 2,6-xylyl isocyanide. The crystal structure of the complex was determined. The complex is paramagnetic and does not coordinate phosphines, phosphites, nitriles, amines, or acetylenes, but it reacts readily with 2,6-xylyl isocyanide to give mono-and diisocyanide complexes.

Full text of DOI:10.1021/om049901x

3552
Organometallics 2004, 23, 3552-3555
Me2Si(C5Me4)2Cr : Syn th esis a n d Cr ysta l Str u ctu r e of a
Liga n d -F r ee a n sa -Ch r om ocen e
Frank Schaper,*,† Olaf Wrobel,‡ Ralf Schwo¨rer,‡ and Hans-Herbert Brintzinger‡
Department of Chemistry, University of Basel, Spitalstrasse 51, CH-4056 Basel, Switzerland,
and Fachbereich Chemie, Universita¨t Konstanz, D-78457 Konstanz, Germany
Received February 6, 2004
Ch a r t 1
Summary: Me2Si(C5Me4)2Cr, the first example of an
ansa-chromocene containing no additional ligands at
chromium, was synthesized from Me2Si(C5Me4)2Li2 and
CrCl2(THF)x in the presence of 2,6-xylyl isocyanide. The
crystal structure of the complex was determined. The
complex is paramagnetic and does not coordinate phos-
phines, phosphites, nitriles, amines, or acetylenes, but
it reacts readily with 2,6-xylyl isocyanide to give mono-
and diisocyanide complexes.
In tr od u ction
Although chromocene has been known for just over
50 years,1 only a few examples of bridged ansa-chro-
mocenes have been reported in the literature, mostly
originating from the groups of Shapiro and Brintzinger
(Chart 1).2 A consistent characteristic of these complexes
is their increased tendency, in comparison to unbridged
chromocenes, to complete their 18-electron shell by
coordinating an additional ligand, such as CO or iso-
cyanide, to the metal center. While Cp2CrCO is only
stable under an atmosphere of CO, the bridged com-
plexes 1, 4, 6, and 8 are stable in the absence of CO;
complex 4 is stable even under sublimation conditions.3
The preformed bending of the cyclopentadienyl rings by
the ansa bridge seems to be mainly responsible for this
behavior.4 Coordination of an additional ligand to the
metal center appears to be, in fact, an essential require-
ment for the synthesis of ansa-chromocene complexes:
Reactions of lithium or magnesium salts of cyclopenta-
dienyl ligands with CrCl2(THF)x in the absence of CO
or isocyanide gave insoluble, uncharacterized, and prob-
ably polymeric products.2a,d Consequently, simple, bridged
ansa-chromocenes of the general formula X(C5R4)2Cr (X
) bridging group) are absent from the chemical litera-
ture.5 In one case, oxidation of an ansa-chromocene
carbonyl complex to Cr(III) led to dissociation of the
carbonyl ligand and formation of the CO-free complex
9.2f In this complex, however, coordination of the anion
obviously replaces the interaction with CO, as docu-
mented by the short Cr-F distances (Chart 1).2f Here,
we report the surprising synthesis of Me2Si(C5Me4)2Cr
(10), the first ansa-chromocene without additional
ligands at the chromium center, under conditions where
the formation of the corresponding isocyanide adduct
Me2Si(C5Me4)2Cr(CNC6H3Me2) would have been ex-
pected.
Resu lts
Syn th esis of th e Com p lexes. When THF is added
to a mixture of Me2Si(C5Me4)2Li2 and 2,6-xylyl isocya-
nide at 0 °C, the resulting solution turns deep blue
immediately. Addition of a CrCl2(THF)x suspension in
THF at 0 °C and stirring at ambient temperatures for
several hours yielded, after removal of THF and extrac-
tion with pentane, Me2Si(C5Me4)2Cr (10) in 46% yield
as deep red crystals (Scheme 1). Complex 10 is para-
* To whom correspondence should be addressed. E-mail: Frank.
Schaper@unibas.ch.
† University of Basel.
‡ Universita¨t Konstanz.
(1) Fischer, E. O.; Hafner, W. Z. Naturforsch., B 1953, 8B, 444.
(2) (a) 1: Schwemlein, H.; Zsolnai, L.; Huttner, G.; Brintzinger, H.-
H. J . Organomet. Chem. 1983, 256, 285. (b) 2: Foo, D. M. J .; Shapiro,
P. Organometallics 1995, 14, 4957. (c) 3: Paolucci, G.; Ossolo, F.;
Bettinelle, M.; Sessoli, R.; Benetollo, F.; Bambieri, G. Organometallics
1994, 13, 1746. (d) 4: Schaper, F.; Rentzsch, M.; Prosenc, M.-H.; Rief,
U.; Schmidt, K.; Brintzinger, H.-H. J . Organomet. Chem. 1997, 534,
67. (e) 5-8: Matare, G. J .; Foo, D. M.; Kane, K. M.; Zehnder, R.;
Wagener, M.; Shapiro, P. J . Organometallics 2000, 19, 1534. (f) 9:
Sinnema, P.-J .; Shapiro, P. J .; Foo, D. M. J .; Twamley, B. J . Am. Chem.
Soc. 2002, 124, 10996. (g) For Cr(III) and Cr(IV) ansa-chromocenes
see: Foo, D. M. J .; Sinnema, P.-J .; Twamley, B.; Shapiro, P. J .
Organometallics 2002, 21, 1005. Sinnema, P.-J .; Nairn, J .; Zehnder,
R.; Shapiro, P. J .; Twamley, B.; Blumenfeld, A. Chem. Commun. 2004,
1, 110.
1
magnetic, and in its H NMR spectrum only one, very
broad signal is observed. If a THF solution of Me2Si-
(C5Me4)2Li2 is added at 0 °C slowly to a suspension of
CrCl2(THF)x and 2,6-xylyl isocyanide in THF, however,
a mixture of Cr(CNC6H3Me2)6 (11)7 and the isocyanide
adduct Me2Si(C5Me4)2Cr(CNC6H3Me2) (12) was ob-
(3) Rentzsch, M. Dissertation, Universita¨t Konstanz, 1995.
(4) (a) Simpson, K. M.; Rettig, M. F.; Wing, R. M. Organometallics
1992, 11, 4363. (b) Green, J . C.; J ardine, C. N. J . Chem. Soc., Dalton
Trans. 1999, 3767.
(5) A special case is 3, where the additional ligand is incorporated
in the bridge.2c
(6) Van Raaij, E. U.; Mo¨nkeberg, S.; Kiesele, H.; Brintzinger, H.-H.
J . Organomet. Chem. 1988, 356, 307.
10.1021/om049901x CCC: $27.50 © 2004 American Chemical Society
Publication on Web 06/10/2004

Notes
Organometallics, Vol. 23, No. 14, 2004 3553
Ta ble 1. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (°) for 10, 12, a n d 4
10
12
1.818
1.817
2.155(3)- 2.145(5)-
2.223(3) 2.220(5)
1.876(4) 1.844(6)
4a
1.808
1.809
Cr(1)-Z(1)b
Cr(1)-Z(2)b
Cr(1)-C(Cp)b
1.785; 1.781
1.785; 1.787
2.077(5)-2.243(5);
2.073(5)-2.246(5)
Cr(1)-C(21)
Z(1)-Cr(1)-Z(2)b 158.3; 158.3
Si(1)-C(1)-Z(1)b 148.4; 148.4
Si(1)-C(6)-Z(2)b 147.6; 148.2
C(1)-Si(1)-C(6)
Cr(1)-C(21)-N(1)
C(21)-N(1)-C(22)
146.1
153.0
153.7
91.15(14) 91.7(2)
172.0(3)
153.2(3)
147.4
152.9
151.9
96.3(2); 96.0(2)
178.5(6)c
a
Taken from ref 2d. b Z(1) ) centroid C(1)-C(5), Z(2) ) centroid
C(6)-C(10), C(Cp) ) C(1)-C(10). c Cr(1)-C(21)-O(1).
to chromium (1, 4, 8, 9, 12).2 The bending of the C(Cp)-
Si bond out of the mean plane of the cyclopentadienyl
ring, i.e., the complementary angle to Z(Cp)-C(Cp)-
Si, which can be considered as a measure of the steric
strain introduced by the bridging group, has a rather
large value of 32° for 10, compared to values of 26-28°
for Me2Si-bridged complexes (4,2d 12) and 2-8° for R4C2-
bridged (1, 8, 9)2 complexes with CO or isocyanide
coordinated to chromium.
F igu r e 1. Crystal structure of 10. Hydrogen atoms and
the second independent molecule are omitted for clarity.
Thermal ellipsoids are drawn at the 50% probability level.
Sch em e 1
Complex 12 crystallizes from pentane solution in the
orthorhombic space group P212121. Within error mar-
gins, the coordination geometry around the chromium
center is identical with that observed in the CO-
coordinated complex 4 (Table 1, Figure 2). Cr-Z(Cp)
distances are slightly longer, by 0.02 Å, in 12 than in
10. This might be due either to steric interactions
between the isocyanide ligand and the methyl groups
at the cyclopentadienyl rings or to the antibonding
nature of the HOMO in bent chromocene complexes,4b
which is only singly occupied in paramagnetic 10. The
C(21)-N(1)-C(22) angle of 153° is significantly smaller
than 180°, in accord with substantial back-bonding to
the isocyanide ligand. There are several indications that
coordination of isocyanide reduces the steric strain
introduced by the silyl bridge: (i) the deviation of the
C(Cp)-Si bond from the mean plane of the cyclopenta-
dienyl rings is reduced from 32 to 27°, (ii) the η5
coordination of chromium is more symmetric and devia-
tions in Cr-C(Cp) distances are reduced from (0.09 to
(0.03 Å, and (iii) the Z(Cp)-Cr-Z(Cp) angle is smaller
by 12° in 12 than in 10.
tained, from which 12 was isolated by repeated crystal-
lization (Scheme 1). Complex 12 is diamagnetic and its
1H NMR spectrum is in accord with C2v-symmetry in
solution (see the Experimental Section).
Cr ysta l Str u ctu r es of 10 a n d 12. Complex 10
crystallizes from pentane solutions in the triclinic space
group P1h with two independent molecules per asym-
metric unit. The crystal structure clearly displays that
the steric strain resulting from the introduction of the
Me2Si bridge overrides the preference of chromocene for
coplanar coordination of the cyclopentadienyl rings
(Figure 1 and Table 1; details of the crystal structure
determinations of 10 and 12 are given in Table 2).4b,8
The Cr-Z(Cp) distance (Z(Cp) ) centroid of the cyclo-
pentadienyl rings) is the same as that found in
(C5Me5)2Cr.8 While coplanar coordination of the cyclo-
pentadienyl rings is prohibited by the silyl bridge, the
Z(Cp)-Cr-Z(Cp) angle of 158° in 10 is considerably
larger than corresponding values of 143-149°, observed
in ansa-chromocenes with CO or isocyanide coordinated
Rea ctivity of 10. NMR-scale reactions of 10 with
P(OPh)3, P(OMe)3, PMe3, CH3CN, NMe3, NEt3, 1-hex-
ene, PhCCPh and Me3SiCCSiMe3 did not lead to any
coordination products detectable by NMR.9 Reaction of
10 with 2,6-xylyl isocyanide, however, immediately
yielded the isocyanide complex 12.10 Under otherwise
identical conditions, no coordination of 2,6-xylyl isocya-
nide to Cp2Cr or Cp*2Cr was observed in NMR control
experiments.
(7) (a) Single crystals of 11 were obtained in small amounts during
the recrystallization of the crude reaction mixture containing 11 and
12 (Table 2). The values dCr-C ) 1.92 Å, Cr-C-N ) 177-178°, and
C-N-C ) 165-170° are in the range expected for hexakis(isocya-
nide)chromium(0) complexes (dCr-C ) 1.87-1.96 Å, Cr-C-N ) 174-
178°, and C-N-C ) 150-173°). (b) Ljungstrom, E. Acta Chem.
Scand. A 1978, 32, 47. (c) Lentz, D. J . Organomet. Chem. 1990, 381,
205. (d) Anderson, K. A.; Scott, B.; Wherland, S.; Willett, R. D. Acta
Crystallogr., Sect. C: Cryst. Struct. Commun. 1991, 47, 2337. (e) Acho,
J . A.; Lippard, S. J . Organometallics 1994, 12, 1294. (f) Barybin, M.;
Holovics, T. C.; Deplazes, S. F.; Lushington, G. H.; Powell, D. R.;
Toriyama, M. J . Am. Chem. Soc. 2002, 124, 13668.
(9) Some evidence for an interaction between diphenylacetylene and
10 might be derived from a series of m/z ) m(10) + n × m(PhCCPh)
(n ) 1-4) in EI or FAB mass spectra of mixtures of 10 and
diphenylacetylene after evaporation of the volatiles. This series was
not observed when the residue was exposed to air. No analogous series
of m/z ) x + n × m(PhCCPh) were observed in mass spectra of 10,
diphenylacetylene, Cp2Cr/diphenylacetylene mixtures, or Cp*2Cr/
diphenylacetylene mixtures.
(8) Blu¨mel, J .; Herker, M.; Hiller, W.; Ko¨hler, F. H. Organometallics
1996, 15, 3474.

3554 Organometallics, Vol. 23, No. 14, 2004
Notes
Ta ble 2. Deta ils of th e Cr ysta l Str u ctu r e Deter m in a tion sa
10
12
11
formula
C
20H30CrSi
C29H39CrNSi
230673
C54H54CrN6
230674
CCSD no.b
230672
diffractometer used
Mw; F(000)
cryst color and form
cryst size (mm)
T (K); dcalcd (g/cm3)
cryst syst
Enraf-Nonius CAD4
350.53; 752
deep red plates
0.3 × 0.2 × 0.1
153; 1.277
triclinic
Enraf-Nonius CAD4
481.70; 1032
deep blue cubes
0.4 × 0.4 × 0.4
173; 1.250
Bruker P4
839.03; 444
red plates
0.2 × 0.2 × 0.1
233; 1.180
triclinic
orthorhombic
P212121
space group
unit cell
P1h
P1h
a (Å)
b (Å)
c (Å)
10.068(2)
12.804(3)
15.302(3)
100.87(4)
105.80(6)
98.45(2)
1822.6(6); 4
2.2-25.0; 99.9
6788/6382; 4.09
0.689; none
5.63; 12.62
13.08; 15.06
0.996
10.002(2)
12.855(3)
19.902(4)
90
90
90
2558.9(9); 4
2.1-23.0; 99.5
4046/3522; 2.05
0.511; none
3.19; 7.16
4.45; 7.67
0.981; 0.00(2)
0.172
10.761(6)
11.709(6)
11.885(5)
108.78(4)
102.63(5)
114.25(4)
1181.1(10); 1
2.2-24.0; 83.7
3313/3108; 6.23
0.284; none
7.28; 12.18
17.33; 15.83
1.020
R (deg)
â (deg)
γ (deg)
V (Å3); Z
θ range (deg); completeness (%)
no. of collected/indep rflns; Rint (%)
µ (mm-1); abs cor
R1(F); wR2(F2) (I > 2σ(I)) (%)
R1(F); wR2(F2) (all data) (%)
GOF(F2); Flack X
resid electron dens (e Å-3
)
0.814
0.215
a
Conditions: Mo KR radiation (71.073 pm); graphite monochromator. Crystal decay was monitored by measuring 3 standard reflections
every 100 reflections or every 1 h. Structures were solved using direct methods.16 All non-hydrogen atoms were refined anisotropically by
least-squares procedures based on F2. Hydrogens were refined on calculated positions with fixed isotropic U values, using riding model
techniques.16 Crystallographic data (excluding structure factors) for the structures in this paper have been deposited with the Cambridge
b
Crystallographic Data Centre. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, by emailing
data_request@ccdc.cam.ac.uk, or by contacting the CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K.; fax +44 1223 336033.
Sch em e 2
F igu r e 2. Crystal structure of 12. Hydrogen atoms are
omitted for clarity. Thermal ellipsoids are drawn at the
50% probability level.
salt with CrCl2(THF)x. The fast reaction of 10 with 2,6-
xylyl isocyanide clearly indicates that major amounts
of isocyanide cannot be present in reaction mixtures
from which 10 was isolated. A probable fate of the
isocyanide might be the trimerization to 13-Li, which
was reported for the reaction of 2,6-xylyl isocyanide with
MeLi or nBuLi (Scheme 2).11 The anionic ligand 13 is
structurally analogous to diphenyl-“nacnac” ligands,
which have been shown to react with CrCl2 salts with
substitution of chloride.12 Diphenyl-“nacnac” or -diimine
ligands with substituents in the ortho position of the
phenyl groups are employed as ligands for olefin po-
lymerization catalysts and are to be considered as
sterically bulky ligands, due to the perpendicular ori-
entation of the phenyl rings.13 We thus propose the
reaction mechanism outlined in Scheme 2 for the
formation of 10: reaction of 2,6-xylyl isocyanide with
Discu ssion
The crystal structure of 10 confirms not only that
coordination of an additional ligand to the chromium
center is stabilized by the bridging of the cyclopenta-
dienyl rings but also that the absence of such a ligand
enhances the steric strain in the complex introduced by
the bridge. The question thus arises as to why 10 is
obtained from 2,6-xylyl isocyanide/ligand lithium salt
mixtures but not by direct reaction of the ligand lithium
(10) In the presence of excess isocyanide 12 is converted slowly over
hours to a C1-symmetric diisocyanide complex. Due to the strong
similarity of its NMR spectrum with that of Me2Si(η5-C5Me4)[η2-C5-
Me3(H)(η1-CH2)]Cr(CO)2, which was obtained by reaction of Me2Si(C5-
Me4)2Cr(CO) with excess CO,2d the diisocyanide adduct is most
probably Me2Si(η5-C5Me4)[η2-C5Me3(H)(η1-CH2)]Cr(CNC6Me2H3)2. If 10
is obtained as a powder instead of crystalline material from the pentane
solutions, reaction with 2,6-xylyl isocyanide yields a mixture of mono-
and diisocyanide adducts immediately. The presence of CrIII impurities
might catalyze the isocyanide addition to 12 by way of an electron-
transfer mechanism, as observed for the CO addition to Me4C2(C5H4)2-
CrCO (Van Raaij, E. U.; Brintzinger, H.-H. J . Organomet. Chem. 1988,
356, 315).
(11) (a) The color of a THF solution of the reaction product was
reported to be deep blue. (b) Murakami, M.; Ito, H.; Ito, Y. Chem. Lett.
1996, 7.
(12) (a) Gibson, V. C.; Newton, C.; Redshaw, C.; Solan, G. A.; White,
A. J . P.; Williams, D. J . Eur. J . Inorg. Chem. 2001, 1895. (b)
MacAdams, L. A.; Kim, W.-K.; Liable-Sands, L. M.; Guzei, I. A.;
Rheingold, A. L.; Theopold, K. H. Organometallics 2002, 21, 952.
(13) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2003, 103, 283.

Notes
Organometallics, Vol. 23, No. 14, 2004 3555
Me2Si(C5Me4)2Li2 (or possibly also with nBuLi if present
as an impurity) yields the trimerization product 13-Li,
which reacts with CrCl2(THF)x by substitution of a
chloride ligand to form 13-CrCl(THF)x (or its dimer {13-
Cr(µ-Cl)}2).12b Reaction of 13-CrCl(THF)x with the re-
maining Me2Si(C5Me4)2Li2 yields the monocyclopenta-
dienyl complex 14. Coordination of the second cyclopenta-
dienyl ring then proceeds with elimination of 13-Li and
formation of 10, since the 20-electron complex [Me2Si-
(C5Me4)2Cr(13)]Li is disfavored by steric as well as by
electronic effects.
Three reasons seem thus to be responsible for the
unexpected formation of 10:14 (i) trimerization of 2,6-
xylyl isocyanide to the bulky, chelating anion 13, (ii)
reaction of 13-Li with CrCl2(THF)x, which prevents the
formation of polymeric products in the same way that
CO or isocyanides do, and (iii) the steric demand and
the anionic, chelating nature of 13, which leads to its
elimination from the complex upon coordination of the
second cyclopentadienyl ring. Since 13-Li is regenerated
in the reaction sequence depicted in Scheme 3 and since
13-CrCl(THF)x is probably more soluble and thus more
reactive than CrCl2(THF)x, it might not be necessary
that 13-Li is present in stoichiometric amounts. In
agreement with this proposal, the isolated yield of 10
is higher, even after crystallization, than the theoretical
yield of 13-Li.
was cooled to 0 °C and added to this mixture via syringe
to yield a deep blue-violet solution. CrCl2(THF)x (180
mg) was suspended in THF (15 mL) and added over a
period of 45 min, while the temperature was kept at 0
°C. The ice bath was removed and the reaction mixture
was stirred overnight to yield a brown solution. The
solvent was removed under vacuum and the residue
extracted with pentane (6 × 10 mL) until the filtrate
was nearly colorless. The brown filtrate was concen-
trated to ca. 20 mL and cooled to -80 °C. After 3 days,
deep red crystals of 10 were isolated by filtration (104
mg, 46%). Anal. Calcd for C20H30CrSi: C, 68.53; H, 8.63.
Found: C, 68.24; H, 8.78. EI-MS (70 eV, 185 °C): 350
(100%, M+), 335 (5%, M+ - Me), 320 (4%, M+ - 2 Me),
175 (7%, M2+), 52 (40%, Cr+). UV/vis (methylcyclohex-
ane, 296 K): 278 nm, ꢀ > 6000 L/(mol cm); 348 nm, ꢀ )
3800 L/(mol cm); 506 nm, ꢀ ) 430 L/(mol cm).
Me2Si(η5-C5Me4)2Cr (CNC6Me2H3) (12). A mixture
of CrCl2(THF)x (357 mg) and 2,6-xylyl isocyanide (205
mg, 1.6 mmol) in THF (30 mL) was cooled to 0 °C. A
solution of Me2Si(C5Me4)2Li2 (400 mg, 1.3 mmol) in THF
(30 mL) was added over a period of 1 h. The ice bath
was removed and the reaction mixture stirred for 3 h.
The solvent was evaporated and the residue extracted
with pentane (3 × 30 mL). The solution was concen-
trated to 20 mL and cooled to -80 °C. Filtration yielded
a mixture of “black” crystals of 12 and red powder of
Cr(CNC6Me2H3)6 (11). Repeated crystallization from
pentane yielded pure 12 (62 mg, 0.13 mmol, 9.9%). Anal.
Calcd for C29H39CrNSi: C, 72.30; H, 8.16; N, 2.91.
Found: C, 71.45; H, 8.29; N, 3.23. 1H NMR (296 K,
C6D6): δ 6.6-7.0 (m, 3H), 2.48 (s, 6H, C6Me), 1.79 (s,
12H, â-C5Me), 1.64 (s, 12H, R-C5Me), 0.57 (s, 6H, SiMe).
IR (pentane): 1950 cm-1 (νCN).
To establish whether the presence of an anionic,
chelating ligand of the type N∧N- represents a general
synthetic route to ansa-chromocene complexes, subse-
quent investigations will be aimed at the synthesis of
defined (N∧N)CrCl complexes and their use as precur-
sors for ansa-chromocene syntheses.
Exp er im en ta l Section
Cr (CNC6Me2H3)6 (11). Small quantities of crystalline
11 were obtained by slow evaporation of a solution
containing a mixture of 11 and 12, followed by hand-
All reactions were carried out under an argon or
nitrogen atmosphere using Schlenk-line or glovebox
techniques. THF and pentane were distilled from Na
under an argon atmosphere and degassed at -78 °C
under a dynamic vacuum. C6D6 was dried over molec-
1
picking red crystals of 11. H NMR (296 K, C6D6): δ
n.r., 6.78 (m, 2H), 2.48 (s, 6H, C6Me).
NMR-Sca le Rea ction s. Two to four equivalents of
the desired ligand were added, by use of Eppendorf
pipets in the case of liquids, in the glovebox to an NMR
tube containing a red solution of 10 (10 mg, 0.03 mmol)
in C6D6 (0.6 mL). The tube was sealed with a rubber
stopper. NMR spectra were recorded immediately after
mixing and after storing the NMR tube for 24 h at
ambient temperatures under an inert atmosphere. With
the exception of 2,6-xylyl isocyanide, neither a color
change nor NMR signals indicating the formation of an
18-electron complex were observed.
15
ular sieves (4 Å). Me2Si(C5Me4)2Li22d and CrCl2(THF)x
were synthesized as described in the literature. All other
chemicals were obtained from commercial suppliers and
used as received.
Me2Si(η5-C5Me4)2Cr (10). A mixture of Me2Si(C5-
Me4)2Li2 (200 mg, 0.64 mmol) and 2,6-xylyl isocyanide
(105 mg, 0.80 mmol) was cooled to 0 °C. THF (15 mL)
(14) While it might be debatable whether complex 10 is a Cr(III)
hydride, the absence of any extra electron density attributable to a
hydride ligand in the vicinity of the Cr center in the crystal structure
data and the clean and complete conversion of 10 to 12 without
detectable side products provide evidence for the correct structural
assignment of 10.
(15) Ko¨hler, F. H.; Pro¨ssdorf, W. Z. Naturforsch., B 1977, 32B, 1026.
(16) (a) Sheldrick, G. M. SHELXS93: Program for the Solution of
Crystal Structures; University of Go¨ttingen, Go¨ttingen, Germany,
1997. (b) Sheldrick, G. M. SHELXL97: Program for Crystal Structure
Refinement; University of Go¨ttingen, Go¨ttingen, Germany, 1997.
Su p p or tin g In for m a tion Ava ila ble: Details of the crys-
tal structure determinations for 10-12; these data are also
available as CIF files. This material is available free of charge
via the Internet at http://pubs.acs.org.
OM049901X