Tantalum-mediated substitution at germanium: A germolyl-to-germole transformation leading to η4-C4Me4GeMeCl complexes

Article abstract of DOI:10.1021/om000518b

The germole reagent C₄Me₄GeMeSiMe₃ (1), synthesized via reaction of K[C₄Me₄GeSiMe₃] with MeI, reacted with TaCl₅ to give [(η⁴-C₄Me₄GeMeCl)TaCl₃(Et₂O)_x]₂ (2; x = 0.5-1.0) with loss of Me₃SiCl. Complex 2 reacted with various two-electron donors to give stable adducts (η⁴-C₄Me₄GeMeCl)TaCl₃L (3, L = PPh₃; 4, L = CNXyl; Xyl = 2,6-dimethylphenyl) and (η⁴-C₄Me₄GeMeCl)TaCl₃L₂ (5, L = CNXyl; 6, L = pyridine). The X-ray structure of (η⁴-C₄Me₄-GeMeCl)TaCl₃(CNXyl)₂ (5) confirmed η⁴-coordination of the germole unit and the exo orientation of the Ge-Cl bond. Complex 2 also reacted with CpTl to give air-stable Cp(η⁴-C₄Me₄GeMeCl)TaCl₂ (7), which was also characterized by X-ray crystallography. Attempts to generate η⁵-germolyl tantalum complexes are described.

Full text of DOI:10.1021/om000518b

4720
Organometallics 2000, 19, 4720-4725
Ta n ta lu m -Med ia ted Su bstitu tion a t Ger m a n iu m : A
Ger m olyl-to-Ger m ole Tr a n sfor m a tion Lea d in g to
η4-C4Me4GeMeCl Com p lexes
J effrey M. Dysard and T. Don Tilley*
Department of Chemistry, University of California at Berkeley,
Berkeley, California 94720-1460
Received J une 19, 2000
The germole reagent C4Me4GeMeSiMe3 (1), synthesized via reaction of K[C4Me4GeSiMe3]
with MeI, reacted with TaCl5 to give [(η4-C4Me4GeMeCl)TaCl3(Et2O)x]2 (2; x ) 0.5-1.0) with
loss of Me3SiCl. Complex 2 reacted with various two-electron donors to give stable adducts
(η4-C4Me4GeMeCl)TaCl3L (3, L ) PPh3; 4, L ) CNXyl; Xyl ) 2,6-dimethylphenyl) and (η4-
C4Me4GeMeCl)TaCl3L2 (5, L ) CNXyl; 6, L ) pyridine). The X-ray structure of (η4-C4Me4-
GeMeCl)TaCl3(CNXyl)2 (5) confirmed η4-coordination of the germole unit and the exo
orientation of the Ge-Cl bond. Complex 2 also reacted with CpTl to give air-stable Cp(η4-
C4Me4GeMeCl)TaCl2 (7), which was also characterized by X-ray crystallography. Attempts
to generate η5-germolyl tantalum complexes are described.
In tr od u ction
with a metal halide,5 we anticipated that a similar
method might be useful in preparing germolyl com-
plexes of the group 4 and 5 metals. Here we report an
attempt to employ this strategy in the synthesis of η5-
germolyl complexes of tantalum, which leads to re-
arrangements that instead give η4-germole complexes.
Recently, considerable progress has been made in
developing the chemistry of silolyl and germolyl anions.1
Free silolyl and germolyl anions of the type [C4Me4ER]-
(E ) Si or Ge) have been shown to possess pyramidal
Si or Ge centers and bond-localized structures.2 How-
ever, we have shown that coordination of these species
to an electron-rich or electron-poor transition metal
fragment promotes delocalization of electron density in
the heterole ring.3 Furthermore, it appears that zirco-
nium and hafnium complexes of [C4Me4ER]- exhibit a
rich reaction chemistry.4 Unfortunately, the develop-
ment of this chemistry has been somewhat limited by
the lack of general routes to d0 complexes with germolyl
and silolyl ligands.
The synthesis of early transition metal complexes
containing the Cp* (Cp* ) C5Me5) ligand typically
involves reaction of a transition metal halide with an
alkali metal derivative of Cp* in a salt metathesis
reaction. Initially, we sought to employ an analogous
method (starting from M[C4Me4ER] reagents, where M
) Li or K)2 in the synthesis of η5-germolyl and η5-silolyl
complexes of the early transition metals. However, this
technique is not general, as only metal complexes of
zirconium and hafnium have been synthesized by this
route.3,4 Given the fact that early transition metal Cp*
complexes may also be prepared via reaction of Cp*SiMe3
Resu lts a n d Discu ssion
The synthesis of η5-germolyl complexes via Me3SiCl
elimination requires a reagent analogous to Cp*SiMe3.
Reaction of the previously reported dimer (C4Me4-
GeSiMe3)2 with 2 equiv of potassium metal in THF
resulted in formation of a deep red solution of the alkali
metal salt K[C4Me4GeSiMe3].2 Treatment of this solu-
tion with a slight excess of MeI cleanly gave the new
germole C4Me4GeMeSiMe3 (1, eq 1). Compound 1 was
isolated as a colorless oil in 80% yield after removal of
the volatile materials and extraction into pentane.
(1) For a review on the recent chemistry of group 14 metalloles see:
Dubac, J .; Gue´rin, C.; Meunier, P. In The Chemistry of Organic Silicon
Compounds, Part II; Rappoport, Z., Apeloig, Y., Eds.; Wiley: New York,
1998; Vol. 3, Chapter 34.
Reaction of 1 with TiCl4, ZrCl4, or HfCl4 (CH2Cl2,
benzene, or THF; room temperature) did not result in
(2) Freeman, W. P.; Tilley, T. D.; Liable-Sands, L. M.; Rheingold,
A. L. J . Am. Chem. Soc. 1996, 118, 10457.
(5) (a) Llina´s, G. H.; Mena, M.; Palacios, F.; Royo, P.; Serrano, R. J .
Organomet. Chem. 1988, 340, 37. (b) Okamoto, T.; Yasuda, H.;
Nakamura, A.; Kai, Y.; Kanehisha, N.; Kasai, N. Organometallics 1988,
7, 2266. (c) Yamamoto, H.; Yasuda, H.; Tatsumi, K.; Lee, K.; Naka-
mura, A.; Chen, J .; Kai, Y.; Kasai, N. Organometallics 1989, 8, 105.
(d) Okamoto, T.; Yasuda, H.; Nakamura, A.; Kai, Y.; Kanehisa, N.;
Kasai, N. J . Am. Chem. Soc. 1988, 110, 5008.
(3) (a) Freeman, W. P.; Tilley, T. D.; Rheingold, A. L.; Ostrander,
R. L. Angew. Chem., Int. Ed. Engl. 1993, 32, 1744. (b) Freeman, W.
P.; Tilley, T. D.; Rheingold, A. L. J . Am. Chem. Soc. 1994, 116, 8428.
(c) Dysard, J . M.; Tilley, T. D. J . Am. Chem. Soc. 1998, 120, 8245.
(4) (a) Dysard, J . M.; Tilley, T. D. J . Am. Chem. Soc. 2000, 122, 3097.
(b) Dysard, J . M.; Tilley, T. D. Organometallics 2000, 19, 2671.
10.1021/om000518b CCC: $19.00 © 2000 American Chemical Society
Publication on Web 09/28/2000

Tantalum-Mediated Substitution at Ge
Organometallics, Vol. 19, No. 23, 2000 4721
the clean formation of germolyl-containing species (by
1H NMR spectroscopy). In addition, 1 did not react
with other Hf-containing starting materials (CpHfCl3,
Cp*HfCl3, or Cp*HfMe2Cl) even after refluxing in
CH2Cl2 or THF. In contrast, treatment of a suspension
of TaCl5 in CH2Cl2 with a colorless pentane solution of
1 at room temperature resulted in the immediate
formation of a deep purple solution. Addition of Et2O
to this solution, followed by concentration and cooling
to -80 °C, gave a green microcrystalline precipitate
(71% yield), which was characterized by NMR spectros-
copy as a germole complex of tantalum. Additional
characterization data (vide infra) allowed us to formu-
late the product as [(η4-C4Me4GeMeCl)TaCl3(Et2O)x]2 (2,
x ) 0.5-1, eq 2). Whereas the reaction in eq 2 proceeds
in CH2Cl2 solvent, no reaction occurs in benzene,
toluene, tetrahydrofuran, diethyl ether, or pentane.
We sought to obtain structural information on 2 to
define the coordination mode of the germole ring.
Unfortunately, X-ray quality crystals of 2 could not be
obtained despite repeated attempts. Fortunately, com-
pound 2 reacts with two-electron donors to give stable
adducts (eq 5, Xyl ) 2,6-dimethylphenyl). The formula-
tion of compounds 3 and 4 as monomers is based on a
solution molecular weight determination of the xylyl-
isocyanide adduct 4.6
The characterization of 2 as a dimer is based on a
solution molecular weight measurement (Signer meth-
od).6 Dimer 2 crystallizes with variable amounts of
coordinated Et2O (between 1 and 2 equiv per dimer, by
1
1H NMR spectroscopy). It is worth noting that the H
NMR spectrum of 2 exhibits only one set of resonances
for the germole ligands, independent of the amount of
ether present. Interestingly, 2 could not be isolated in
the absence of ether, and exposure of isolated 2 to
dynamic vacuum resulted in loss of the ether and
decomposition of the dimer to a brown oily material,
which exhibited an array of peaks in its 1H NMR
spectrum. Given these facts, we assume that the ether
is coordinated to the Ta center in 2, although this has
not been proven definitively. Finally, we believe that
the chloride atom bound to Ge adopts an exo position
relative to Ta. This formulation is based on the structure
of an adduct of 2 (vide infra).
The 1H NMR spectrum of 2 is quite simple, as it
exhibits three resonances at δ 2.31, 3.10 (ring Me
protons), and 0.82 (Ge-Me protons) for equivalent η4-
germole ligands (eq 2). The 13C NMR spectrum of 2
contains resonances at δ 109.0 and 145.5 corresponding
to the germole ring carbons. The large separation
between these shifts, as well as the upfield shift for the
resonance of the carbon R to Ge, indicates a σ2-π type
bonding of the diene portion of the germole ring to
tantalum.4 For comparison, the analogous resonances
in the η5-germolyl complex Cp*(η5-C4Me4GeSiMe3)HfCl2
appear at δ 135.8 and 146.0, while the germole complex
Cp*(η4-C4Me4GetBuMe)HfMe exhibits comparable shifts
at δ 96.0 and 131.1.3c,4 It is interesting to note that
related processes of this type, involving migration to
germanium, seem to pervade the early-metal chemistry
of germolyl ligands, as previously observed for a related
Hf system (eqs 3 and 4).4
Compounds 4, 5, and 6 are formed in excellent yields
(86-94%), while 3 could only be isolated as a somewhat
1
impure, green solid in 67% yield (ca. 90% pure by H
NMR spectroscopy). All of these compounds, like 2,
display very large differences in the 13C NMR chemical
shifts for their germole ring carbons, suggesting η4-
coordination. It is worth noting that the 1H NMR
spectra for the monoadducts 3 and 4 exhibit rather
broad resonances at room temperature which sharpen
upon warming to 70 °C. This may indicate a ligand
dissociation/association process.
X-ray quality crystals of bright green 5 were obtained
by slow cooling of a concentrated toluene solution to -35
(6) (a) Signer, R. Liebigs Ann. Chem. 1930, 478, 246. (b) Zoellner,
R. W. J . Chem. Educ. 1990, 67, 714.

4722 Organometallics, Vol. 19, No. 23, 2000
Dysard and Tilley
Sch em e 1
atoms of the diene unit. The C(2)-C(3) distance, 1.415(9)
Å, is shorter than both the C(1)-C(2) (1.456(8) Å) and
C(3)-C(4) (1.425(9) Å) distances, although the differ-
ences are relatively small. These C-C distances are very
similar to the corresponding ones in TaCl(η4-C10H8)-
(dmpe)28 (1.416(7), 1.457(7), and 1.435(7) Å, respectively)
and follow a pattern previously observed for Fe-diene
complexes.9 Interestingly, the Ge-Cl bond in 5 is long
(2.250(2) Å) and comparable in length with the exo-Ge-
Cl bond in Cp*RuCl(η4-C4Me4GeCl2) (2.246(2) Å).3a For
the latter case, the discrepancy between this Ge-Cl
bond length and the other (2.151(3) Å) was interpreted
in terms of donation of electron density from the Ru
atom into the exo-Ge-Cl σ* orbital.3a This back-bonding
may also be occurring in 5, and this could explain a
thermodynamic preference for the observed germole
bonding mode. Finally, the three chlorine atoms bound
to Ta and one XylNC ligand are bent away from the
germole and define a Cl3C plane from which the Ta
center is displaced by 0.66 Å.
F igu r e 1. ORTEP diagram of (η4-C4Me4GeMeCl)TaCl3-
(CNXyl)2 (5).
°C, and the molecular structure is shown in Figure 1.
X-ray crystallography clearly confirmed η4-coordination
of the germole ring to the Ta center of 5. Interestingly,
the chlorine atom bonded to Ge is exo to the metal atom.
This suggests that the process by which the chlorine
atom shifts to Ge may not involve simple migration to
an η5-germolyl ligand and that the reaction may occur
via bimolecular chlorine transfer or ionization of a
chloride ligand. Alternatively, the germole Me4C4-
GeMeCl may form by reductive elimination from an η1-
germole complex (eq 6). The germole ligand may then
simply bind preferentially to the face of the ring which
allows for back-donation into the Ge-Cl σ* orbital. The
lengthening of the Ge-Cl bond in 2 (vide infra) suggests
that such donation may significantly influence the
energy of the germole-tantalum bonding.
We envisioned converting the η4-germole in 2 to an
η5-coordinated ligand via exchange of the chloride atom
bound to Ge for a less coordinating anion (Scheme 1).
This strategy has been employed previously in attempts
to generate η5-germolyl complexes of the later transition
metals, albeit without success.10
Reactions of 2 with Cp*Li and Cp*MgCl (tetrahydro-
furan or toluene, -80 °C) yielded only complex mixtures
1
of products (by H NMR spectroscopy). Also, treatment
of 2 with several Cp-transfer reagents (CpNa, CpMgCl,
Cp2Mg, in THF, Et2O, or benzene) did not produce the
desired product cleanly. However, reaction of 2 with
CpTl in toluene at -78 °C resulted in formation of a
deep green solution, from which Cp(η4-C4Me4GeMeCl)-
TaCl2 (7) was isolated as bright green crystals in 78%
yield. Surprisingly, compound 7 is air-stable in both the
solid state and in benzene-d6 solution for a period of
days and is only slowly hydrolyzed (several hours,
benzene-d6, room temperature, large excess of water),
giving an array of unidentified products as determined
The molecular structure of 5 may be described as
involving a pseudo-octahedral tantalum center ligated
by η4-germole, Cl, and XylNC ligands. The Ge atom in
the ring is pseudo-tetrahedral, and the Ge-C bonds in
the ring (1.932(6) and 1.924(6) Å) are similar in length
to those for the neutral germole C4Me4GeHSi(SiMe3)3
(1.944(3) and 1.948(3) Å).7 In addition, the Ge atom is
displaced 0.75 Å from the plane defined by the four C
1
by H NMR spectroscopy. In addition, as in the case of
η4-germole complexes described earlier, the difference
(8) Albright, J . O.; Datta, S.; Dezube, B.; Kouba, J . K.; Marynick,
D. S.; Wreford, S. S.; Foxman, B. M. J . Am. Chem. Soc. 1979, 101,
611.
(9) Cotton, F. A.; Day, V. W.; Frenz, B. A.; Hardcastle, K. I.; Troup,
J . M. J . Am. Chem. Soc. 1973, 95, 4522.
(7) Freeman, W. P.; Tilley, T. D.; Arnold, F. P.; Rheingold, A. L.;
Gantzel, P. K. Angew. Chem., Int. Ed. Engl. 1995, 34, 1887.
(10) Colomer, E.; Corriu, R. J . P.; Lheureux, M. Chem. Rev. 1990,
90, 265-282.

Tantalum-Mediated Substitution at Ge
Organometallics, Vol. 19, No. 23, 2000 4723
ceeded via chloride transfer to Ge with formation of an
η4-germole ligand. It would seem that early metal
germolyl complexes are prone to this type of process,
as it has now been observed in several different
systems.4a Thus far, the compounds in hand have not
proven to be viable precursors to tantalum η5-germolyl
complexes.
Exp er im en ta l Section
All manipulations were performed under an argon atmo-
sphere using standard Schlenk techniques or a nitrogen-filled
glovebox. Dry, oxygen-free solvents were employed throughout.
Pentane, THF, toluene, and diethyl ether were distilled from
sodium/benzophenone, CH2Cl2 was distilled from CaH2, and
benzene-d6 and toluene-d8 were distilled from Na/K alloy. The
compounds [C4Me4GeSiMe3]2 and CpTl12 were prepared ac-
2
F igu r e 2. ORTEP diagram of Cp(η4-C4Me4GeMeCl)TaCl2
(7).
cording to literature procedures. MeI and pyridine were
purchased from Aldrich and distilled prior to use. PPh3 and
XylNC were purchased from Aldrich and recrystallized prior
to use, while TaCl5 was purchased from Strem and sublimed.
NMR spectra were recorded at 300 or 500 MHz (1H) with
Bruker AMX-300 and DRX-500 spectrometers or at 125 MHz
(13C{1H}) with a DRX-500 spectrometer at ambient tempera-
ture unless otherwise noted. Elemental analyses were per-
formed by the microanalytical laboratory at the University of
California, Berkeley. IR samples of solid materials were
prepared as KBr pellets, while IR spectra of oils were obtained
with neat samples between CsI plates. All IR absorptions are
reported in cm-1 and were recorded with a Mattson Infinity
60 MI FTIR spectrometer.
in the 13C NMR shifts for the germole ring carbons of 7
is quite large (53.7 ppm) compared with analogous shifts
for an η5-coordinated germolyl ligand.3c,4
The molecular structure of 7 was established by
single-crystal X-ray diffraction (Figure 2). As for 5, the
structure of 7 is best described as involving a 1,4-diyl
bonding mode for the germole ligand. The Ge atom is
displaced 1.07 Å from the least-squares plane defined
by C(1), C(2), C(3), and C(4). Also, in contrast to 5, the
C(2)-C(3) bond distance (1.401(5) Å) is somewhat
shorter than both the C(1)-C(2) (1.470(5) Å) and C(3)-
C(4) (1.465(5) Å) bond lengths, as seen in the related
complex CpTaCl2(C4H6).11 In addition, the Ta-C bond
lengths to the diene portion of the η4-germole ligand
(2.411(4), 2.408(4), 2.298(4), 2.282(4) Å) are more similar
to the related distances in CpTaCl2(C4H6) (2.424(11),
2.410(12) Å; 2.257(11), 2.258(12) Å) than to those in 5.11
Finally, the angle between the C(1)-C(2)-C(3)-C(4)
and C(1)-Ta-C(4) planes (91.04°) is similar to the same
angles in both 5 (95.24°) and CpTaCl2(C4H6) (94.9°).11
We initially focused on the conversion of 7 to a dialkyl
species according to Scheme 1. Reactions with various
alkylating reagents (Me2Zn, MeMgCl, BnMgCl, Bn2Mg,
BnLi(Et2O), BnK, ClMgCH2SiMe3, LiCH2SiMe3, Me3Al,
NpLi, NpMgBr; Bn ) CH2Ph, Np ) CH2CMe3) gave only
complex mixtures of products (by 1H NMR spectros-
copy). In addition, reactions of 7 with lithium amides
(LiN(SiMe3)2, LiNEt2) and LiPhCdCPh-CPhdCPhLi
did not result in isolated products. However, analysis
of the NMR spectra of these product mixtures suggests
that alkylation occurs most rapidly at germanium, as
species containing only one alkyl substituent appear to
possess mirror-plane symmetry. Finally, reactions of 7
with Me3SiOTf or AgOTf in benzene-d6 resulted in an
array of unidentified products (by 1H NMR spectros-
copy).
C4Me4Ge(Me)SiMe3 (1). A 200 mL Schlenk tube was
charged with [C4Me4GeSiMe3]2 (2.000 g, 3.94 mmol) and K
metal (0.320 g, 8.18 mmol), and 100 mL of THF was added to
generate a light orange solution. This solution was stirred for
1 week, after which time all of the potassium had been
consumed and the solution had turned to a deep red color. The
flask was placed in an ice bath, and the solution was cooled to
0 °C. MeI (0.520 mL, 8.27 mmol) was then added to the flask,
resulting in formation of a white cloudy suspension. This
suspension was allowed to warm to room temperature and was
then stirred for 1 h. The volatile materials were removed under
dynamic vacuum, and the resulting residue was extracted with
pentane (3 × 30 mL). Pentane was removed from the extracts
to give the product as a colorless oil in 80% yield (1.690 g, 6.30
mmol). This oil was purified by a short-path distillation (bp
1
48 °C, 1 × 10-3 Torr). H NMR (benzene-d6): δ 0.16 (s, 9 H,
GeSiMe3), 0.43 (s, 3 H, GeMe), 1.82 (s, 6 H, C4Me4Ge), 2.03 (s,
6 H, C4Me4Ge). 13C{1H} NMR (benzene-d6): δ -7.31 (s, GeMe),
-0.29 (s, GeSiMe3), 16.72, 14.88 (s, C4Me4Ge), 146.02, 135.04
(s, C4Me4Ge). Anal. Calcd for C12H24GeSi: C, 53.58; H, 8.99.
Found: C, 52.66; H, 9.26. IR: 2951 s br, 2905 s br, 2851 s br,
1551 w, 1441 m, 1399 sh, 1245 s, 1058 m, 839 s, 785 s, 741 m,
693 m, 622 m, 578 m, 484 m.
[(η4-C4Me4GeMeCl)Ta Cl3(OEt2)0.8]2 (2). A 150 mL Schlenk
tube was charged with TaCl5 (1.92 g, 5.36 mmol). A separate
100 mL Schlenk tube was charged with 1 (1.44 g, 5.36 mmol).
Then 50 mL of CH2Cl2 was added to the flask containing TaCl5,
generating a cloudy white suspension, and 1 was dissolved in
50 mL of pentane. The pentane solution of 1 was added to the
flask containing TaCl5 at room temperature via cannula, to
give a deep purple solution. This solution was stirred for 1 h,
after which time it was filtered via cannula into a 200 mL
Schlenk tube. To the resulting purple solution was added 50
mL of Et2O, and the solution was concentrated until a green
precipitate began to form (to ca. 100 mL). The resulting
mixture was cooled to -80 °C to give 2 as a green powder in
In conclusion, we have shown that loss of Me3SiCl
upon reaction of a germole reagent possessing a Me3Si
substituent with an early metal halide is a viable route
to metal germole complexes. The reaction of C4Me4-
GeMeSiMe3 (1) with TaCl5 did not produce the desired
η5-germacyclopentadienyl complex, but instead pro-
(11) Yasuda, H.; Tatsumi, K.; Okamoto, T.; Mashima, K.; Lee, K.;
Nakamura, A.; Kai, Y.; Kanehisa, N.; Kasai, N. J . Am. Chem. Soc.
1985, 107, 2410.
(12) Nielson, A. J .; Rickard, C. E. F.; Smith, J . M. Inorg. Synth. 1990,
28, 315.

4724 Organometallics, Vol. 19, No. 23, 2000
Dysard and Tilley
1
Ta ble 1. Cr ysta llogr a p h ic Da ta for Com p ou n d s 5
a n d 7
71% yield (2.20 g, 3.81 mmol). H NMR (benzene-d6): δ 0.82
(s, 3 H, GeMe), 1.11 (t, 4.8 H, (CH3CH2)2O), 2.31 (s, 6 H,
C4Me4Ge), 3.10 (s, 6 H, C4Me4Ge), 3.26 (q, 3.2 H, (CH3CH2)2O).
13C{1H} NMR (benzene-d6): δ 5.94 (s, GeMe), 15.58, 16.93 (s,
C4Me4Ge), 16.03 (s, (CH3CH2)O), 66.37 (s, (CH3CH2)O), 109.02,
145.51 (C4Me4Ge). Anal. Calcd for C12.2H23Cl4GeO0.8Ta: C,
25.36; H, 4.01. Found: C, 25.67; H, 4.10. IR: 2945 br s, 2909
s, 2856 s, 1442 s, 1379 s, 1319 w, 1108 m, 1014 m, 801 s, 757
br m. Mp: 120-123 °C dec. Molecular weight in CH2Cl2: 1110
g mol-1. Calcd for the dimer (including 0.8 mol of OEt2 per
5
7
(a) Crystal Parameters
TaGeCl4C27H25N2
772.86
formula
fw
TaGeCl3C14H20
548.21
size mm
cryst syst
space group
a (Å)
0.12 × 0.10 × 0.08
0.19 × 0.11 × 0.09
monoclinic
P21/n (#14)
8.4579(7)
triclinic
P1h (#2)
10.0714(2)
Ta): 1155 g mol-1
.
b (Å)
11.3404(3)
15.917(1)
(η4-C4Me4GeMeCl)Ta Cl3(P P h 3) (3). A 50 mL Schlenk tube
was charged with 2 (0.257 g, 0.44 mmol), and a separate 50
mL Schlenk tube was charged with PPh3 (0.117 g, 0.44 mmol).
Then 20 mL of toluene was added to each flask via cannula.
The colorless solution of PPh3 was added to the flask contain-
ing the purple solution of 2. An immediate reaction took place,
as evidenced by the precipitation of a green solid. The purple
solution was cooled to -35 °C to give 3 as a green microcrys-
talline solid in 67% yield (0.233 g, 0.30 mmol). This material
could not be separated from impurities (ca. 90% pure by 1H
NMR), and thus satisfactory combustion analysis data could
c (Å)
16.1556(3)
12.535(1)
R, â, γ (deg)
88.569(1), 77.068(1), 90, 93.308(1), 90
67.275(1)
V (Å3)
1654.92(6)
4
1684.8(2)
4
Z
D
calc (g cm-3
)
3.102
2.161
F000
1496.00
1040.00
(b) Data Collection
-158.0
5628/9206
temp (°C)
no. of unique/total
reflens
-151.0
3049/7941
Rint
0.022
0.020
1
empirical absorption
correction: Tmax/Tmin
0.977/0.711
0.745/0.521
not be obtained. H NMR (toluene-d8, 70 °C): δ 0.86 (s, 3 H,
GeMe), 2.45 (s, 6 H, C4Me4Ge), 3.13 (s, 6 H, C4Me4Ge), 7.06,
7.34 (br m, 15 H, PPh3). 13C{1H} NMR (toluene-d8, 70 °C): δ
5.4 (s, GeMe), 15.1, 16.4 (s, C4Me4Ge), 109.0 (s, C4Me4Ge), 134.2
(br d, PPh3), 137.4, 137.6, 137.8 (s, PPh3), 144.7 (s, C4Me4Ge).
IR: 2961 br m, 2907 br m, 2854 br m, 1651 m, 1438 s, 1262 w,
1101 m, 1016 w, 1019 m, 746 m.
(c) Refinement
4870
no. of observations
[I > 3σ(I)]
2640
no. of variables
333
172
reflection/param ratio
R ) ∑||Fo| - |Fc||/∑|Fo|
Rw ) [∑w(|Fo| -
14.62
0.034
0.044
15.35
0.019
0.028
(η4-C4Me4GeMeCl)Ta Cl3(CNXyl) (4). To a toluene (10 mL)
solution of 2 (0.205 g, 0.35 mmol) was added XylNC (0.047 g,
0.35 mmol) in 10 mL of toluene. The resulting solution was
stirred for 1 h and then concentrated to 10 mL and cooled to
-35 °C to give 4 as a red crystalline solid in 93% yield (0.214
g, 0.33 mmol). 1H NMR (benzene-d6): δ 1.14 (br s, 3 H, GeMe),
1.92 (br s, 6 H, C4Me4Ge), 2.61 (br s, 6 H, C4Me4Ge), 3.03 (s, 6
H, (C6H3Me2)NC), 6.43 (br d, 3J HH ) 8 Hz, 2 H, (C6H3Me2)NC),
|Fc|)2/∑wFo2)]1/2
goodness of fit
1.57
1.43
max. and min. peaks in
final diff map (e-/Å3)
2.23/-2.13
1.15/-1.05
solution. This solution was concentrated to 15 mL and cooled
to -35 °C to give 6 as a green crystalline solid in 86% yield
(0.214 g, 0.32 mmol). 1H NMR (benzene-d6): δ 1.28 (s, 3 H,
GeMe), 2.78 (s, 6 H, C4Me4Ge), 2.94 (s, 6 H, C4Me4Ge), 6.28
6.66 (br t, J HH ) 8 Hz, 1 H, (C6H3Me2)NC). 13C{1H} NMR
3
(benzene-d6): δ 5.55 (br s, GeMe), 15.83 (s, (C6H3Me2)NC),
18.51, 18.85 (s, C4Me4Ge), 106.81 (br s, C4Me4Ge), 129.81,
130.51, 131.21, 136.75 (s, XylNC), 136.55 (br s, C4Me4Ge),
185.90 (s, XylNC). Anal. Calcd for C17H24Cl4GeNTa: C, 32.02;
H, 3.79; N, 2.20. Found: C, 32.41; H, 3.78; N, 1.94. IR: 2960
br s, 2191 s (CN), 1647 m, 1489 m, 1378 w, 1115 w, 1086 w,
1019 m, 782 m. Mp: 137-141 °C dec. Molecular weight in
3
3
(dd, J HH ) 7 Hz, 4 H, C5H5N), 6.65 (t, J HH ) 7 Hz, 2 H,
C5H5N), 8.99 (d, J HH ) 7 Hz, 4 H, C5H5N). 13C{1H} NMR
3
(benzene-d6): δ 10.22 (s, GeMe), 16.25, 16.38 (s, C4Me4Ge),
106.03 (s, C4Me4Ge), 124.15, 137.92, 152.69 (s, C5H5N), 135.32
(s, C4Me4Ge). Anal. Calcd for C19H25Cl4GeN2Ta: C, 33.72; H,
3.72; N, 4.14. Found: C, 34.08; H, 4.09; N, 4.37. IR: 2948 br
s, 2898 s, 1605 s, 1488 m, 1442 s, 1226 m, 1071 m, 1008 m,
862 br w, 757 m. Mp: 78-80 °C dec.
CH2Cl2: 615 g mol-1. Calcd: 650 g mol-1
.
(η4-C4Me4GeMeCl)Ta Cl3(CNXyl)2‚0.8P h Me (5). A 50 mL
Schlenk tube was charged with 2 (0.206 g, 0.35 mmol) and
XylNC (0.093 g, 0.71 mmol). To this flask was added 25 mL of
toluene to give a deep green solution. The volume of the
solution was concentrated to 15 mL, and the solution was
cooled to -35 °C to give 5 as a green crystalline solid in 94%
yield (0.262 g, 0.34 mmol). 5 crystallized with 0.8 equiv of
toluene, which was not removed under vacuum over 12 h at
room temperature. 1H NMR (benzene-d6): δ 1.08 (s, 3 H,
GeMe), 2.08 (s, 6 H, C4Me4Ge), 2.17 (s, 6 H, C4Me4Ge), 2.91 (s,
Cp (η4-C4Me4GeMeCl)Ta Cl2 (7). A 100 mL Schlenk tube
was charged with 2 (2.50 g, 4.33 mmol) and 50 mL of toluene.
A separate 500 mL round-bottom Schlenk flask was charged
with CpTl (1.17 g, 4.33 mmol) and 200 mL of toluene to give
a cloudy white suspension. This flask was then cooled in a dry
ice/acetone bath to -78 °C. The solution containing 2 was then
added to this flask at -78 °C to give a deep green solution.
The resulting mixture was allowed to warm to room temper-
ature and was stirred for an additional 10 h. After this time,
the volatile substances were removed under dynamic vacuum.
The resulting dark green residue was extracted into pentane
(3 × 50 mL). The pentane extracts were concentrated to 20
mL, and the bright green solution was cooled to -35 °C to give
7 as bright green crystals in 78% yield (1.86 g, 3.39 mmol). 1H
NMR (benzene-d6): δ 0.73 (s, 3 H, GeMe), 1.78 (s, 6 H,
C4Me4Ge), 2.53 (s, 6 H, C4Me4Ge), 5.84 (s, 5 H, C5H5). 13C{1H}
NMR (benzene-d6): δ 9.00 (s, GeMe), 14.69, 17.57 (s, C4Me4Ge),
82.94, 136.64 (s, C4Me4Ge), 113.67 (s, C5H5). Anal. Calcd for
3
6 H, (C6H3Me2)NC), 3.03 (s, 6 H, (C6H3Me2)NC), 6.33 (d, J HH
) 8 Hz, 2 H, (C6H3Me2)NC), 6.51 (d, J HH ) 8 Hz, 2 H, (C6H3-
Me2)NC), 6.56 (t, J HH ) 8 Hz, 1 H, (C6H3Me2)NC), 6.70 (t,
3
3
3J HH ) 8 Hz, 1 H, (C6H3Me2)NC). 13C{1H} NMR (benzene-d6):
δ 6.65 (s, GeMe), 15.79, 16.54 (s, (C6H3Me2)NC), 18.53, 19.04
(s, C4Me4Ge), 103.04 (s, C4Me4Ge), 130.88 (s, C4Me4Ge), 126.14,
129.01, 129.78, 130.43, 133.00, 135.65, 136.73 (s, XylNC),
161.60, 169.12 (s, XylNC). Anal. Calcd for C29.8H39.4Cl4GeN2-
Ta: C, 44.59; H, 4.78; N, 3.40. Found: C, 44.18; H, 4.44; N,
3.46. IR: 2917 br s, 2204 s (CN), 2190 s (CN), 1637 m, 1474
m, 1380 w, 1170 w, 1028 w, 782 m. Mp: 128-130 °C dec.
(η4-C4Me4GeMeCl)Ta Cl3(p yr )2 (6). A 50 mL Schlenk tube
was charged with 2 (0.216 g, 0.37 mmol) and 25 mL of toluene.
A solution of pyridine (0.062 g, 0.74 mmol) in 10 mL of toluene
was then added, resulting in generation of a deep green
C
14H20Cl3GeTa: C, 30.67; H, 3.68. Found: C, 30.98; H, 3.74.
IR: 3114 s, 2860 br s, 1438 s, 1369 m, 1373 w, 1284 w, 1261
m, 1207 w, 1102 br s, 1017 br s, 850 s, 833 s, 803 s, 750 m,
602 m, 527 m, 425 m. Mp: 198-204 °C dec.
X-r a y Str u ctu r e Deter m in a tion s. X-ray diffraction meas-
urements were made on a Siemens SMART diffractometer

Tantalum-Mediated Substitution at Ge
Organometallics, Vol. 19, No. 23, 2000 4725
with a CCD area detector, using graphite-monochromated Mo
KR radiation. The crystal was mounted on a glass fiber using
Paratone N hydrocarbon oil. A hemisphere of data was
collected using ω scans of 0.3°. Cell constants and an orienta-
tion matrix for data collection were obtained from a least-
squares refinement using the measured positions of reflections
in the range 4° < 2θ < 45°. The frame data were integrated
using the program SAINT (SAX Area-Detector Integration
Program; V4.024; Siemens Industrial Automation, Inc.: Madi-
son, WI, 1995). An empirical absorption correction based on
measurements of multiply redundant data was performed
using the program SADABS. Equivalent reflections were
merged. The data were corrected for Lorentz and polarization
effects. A secondary extinction correction was applied if
appropriate. The structures were solved using the teXsan
crystallographic software package of the Molecular Structure
Corporation, using direct methods, and expanded with Fourier
techniques. All non-hydrogen atoms were refined anisotropi-
cally unless otherwise noted, and the hydrogen atoms were
included in calculated positions but not refined. The function
minimized in the full-matrix least-squares refinement was
∑w(|Fo| - |Fc|)2. The weighting scheme was based on counting
statistics and included a p-factor to downweight the intense
reflections. Crystallographic data are summarized in Table 1.
F or 5. Crystals were grown from a concentrated toluene
solution at -35 °C. The non-hydrogen atoms that displayed
no disorder were refined anisotropically. Hydrogen atoms were
included but not refined. A molecule of toluene in the structure
was displaced about an inversion center. This molecule was
modeled as four full occupancy carbon atoms (C(28), C(29),
C(30), and C(31)) which were refined isotropically. The other
atoms of the toluene were generated using a full symmetry
expansion.
F or 7. Crystals were grown from a concentrated pentane
solution at -15 °C.
Ack n ow led gm en t is made to the National Science
Foundation of their generous support of this work. We
thank Dr. Fred Hollander for assistance with the X-ray
structure determinations.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal,
data collection, and refinement parameters, bond distances
and angles, and anisotropic displacement parameters for 5 and
7. This material is available free of charge via the Internet at
http://pubs.acs.org.
OM000518B