The isolation and chemistry of tantalum dimethylamides containing resolved 3,3′-disubstituted-1,1′-bi-2,2′-naphthoxide ligands

Article abstract of DOI:10.1039/b212910h

Reaction of the tantalum dimethylamide substrates [Ta(NMe₂) ₅] or mer,cis-[Ta(NMe₂)₂Cl ₃(HNMe₂)] with one equivalent of the 3,3′- disubstituted-2,2′-dihydroxy-1,1′-binaphthyl [H₂O ₂C₂₀H₁₀(R)₂-3,3′] (R = SiMe₃, 1; SiMe₂Ph, 2; SiMePh₂, 3; SiPh ₃,4) leads to the series of amine adducts [Ta(O₂C ₂₀H₁₀R₂-3,3′)(NHMe₂)(NMe ₂)₃] (R = SiMe₃, 5; SiMe₂Ph, 6; SiMePh₂) 7; SiPh₃, 8) and [Ta(O₂C ₂₀H₁₀R₂-3,3′)(NHMe₂)(NMe ₂)Cl₂] (R = SiMe₃, 9; SiMe₂Ph, 10; SiMePh₂, 11; SiPh₃,12). Structural analyses by X-ray diffraction of (S)-5, (R)-7 and (R,S)-8 show a pseudooctahedral geometry about tantalum with the coordinated dimethylamine ligand located cis to the two naphthoxide oxygen atoms. In the case of (S)-9, (R)-10 and (S)12, the solid-state structure consists of both chloride ligands being located trans to the two naphthoxide oxygen atoms. Solution NMR spectroscopic properties of 5-12 are consistent with an identical structure being adopted in solution with the amine ligands being strongly bound in all cases. When (S)-5 is heated under vacuum the dimethylamine ligand is lost leading to [Ta(O₂C ₂₀H₁₀{SiMe₃}₂-3,3′)(NMe ₂)₃] (S)-13. Reaction of (S)-5 with SiCl₄ leads to a mixture of [Ta(O₂C₂₀H₁₀{SiMe ₃}₂-3,3′)(NHMc₂)Cl₃] (S)-14 and [Ta(O₂C₂₀H₁₀-{SiMe₃} ₂-3,3′)Cl₄][Me₂NH₂] (S)-15. The solid-state structure of (S)-15 was determined. The amine/ amide ligands in (S)-12 undergo insertion of CS₂ leading to the dimethyldithiocarbamate, (S)-[Ta(O₂C₂₀H ₁₀-3,3′{SiPh₃}₂)(CS₂NMe ₂)₂Cl] (S)-16. The solid state structure of (S)-16 consists of a pentagonal bipyramidal geometry about Ta with an axial oxygen and chloride ligand. The Royal Society of Chemistry 2003.

Full text of DOI:10.1039/b212910h

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The isolation and chemistry of tantalum dimethylamides
containing resolved 3,3Ј-disubstituted-1,1Ј-bi-2,2Ј-naphthoxide
ligands†
Au Ji Ru Son, Scott W. Schweiger, Matthew G. Thorn, John E. Moses, Phillip E. Fanwick and
Ian P. Rothwell*
Purdue University, Department of Chemistry, 560 Oval Drive, West Lafayette, IN 47907-2038,
USA. E-mail: rothwell@purdue.edu
Received 3rd January 2003, Accepted 31st January 2003
First published as an Advance Article on the web 10th March 2003
Reaction of the tantalum dimethylamide substrates [Ta(NMe2)5] or mer,cis-[Ta(NMe2)2Cl3(HNMe2)] with one
equivalent of the 3,3Ј-disubstituted-2,2Ј-dihydroxy-1,1Ј-binaphthyl [H2O2C20H10(R)2-3,3Ј] (R = SiMe3, 1; SiMe2Ph,
2; SiMePh2, 3; SiPh3, 4) leads to the series of amine adducts [Ta(O2C20H10R2-3,3Ј)(NHMe2)(NMe2)3] (R = SiMe3,
5; SiMe2Ph, 6; SiMePh2, 7; SiPh3, 8) and [Ta(O2C20H10R2-3,3Ј)(NHMe2)(NMe2)Cl2] (R = SiMe3, 9; SiMe2Ph,
10; SiMePh2, 11; SiPh3, 12). Structural analyses by X-ray diffraction of (S)-5, (R)-7 and (R,S)-8 show a pseudo-
octahedral geometry about tantalum with the coordinated dimethylamine ligand located cis to the two naphthoxide
oxygen atoms. In the case of (S)-9, (R)-10 and (S)-12, the solid-state structure consists of both chloride ligands being
located trans to the two naphthoxide oxygen atoms. Solution NMR spectroscopic properties of 5–12 are consistent
with an identical structure being adopted in solution with the amine ligands being strongly bound in all cases.
When (S)-5 is heated under vacuum the dimethylamine ligand is lost leading to [Ta(O2C20H10{SiMe3}2-3,3Ј)(NMe2)3]
(S)-13. Reaction of (S)-5 with SiCl4 leads to a mixture of [Ta(O2C20H10{SiMe3}2-3,3Ј)(NHMe2)Cl3] (S)-14 and
[Ta(O2C20H10-{SiMe3}2-3,3Ј)Cl4][Me2NH2] (S)-15. The solid-state structure of (S)-15 was determined. The amine/
amide ligands in (S)-12 undergo insertion of CS2 leading to the dimethyldithiocarbamate, (S)-[Ta(O2C20H10-3,3Ј-
{SiPh3}2)(CS2NMe2)2Cl] (S)-16. The solid state structure of (S)-16 consists of a pentagonal bipyramidal geometry
about Ta with an axial oxygen and chloride ligand.
Ta–NMe2 groups. The equivalence of the three dimethylamido
Introduction
ligands in the 1H NMR spectra of 5–8 implies that dissociation/
The inorganic and organometallic chemistry of niobium and
re-coordination of the HNMe2 group occurs on the NMR
tantalum supported by simple aryloxide ligands continues to
timescale.
be an area of research interest.1–5 A number of interesting
Reaction of the mixed amido–chloride mer,cis-[Ta(NMe2)2-
Cl3(HNMe2)] with 1–4 does not lead to protonation of two
dimethylamido ligands. Instead the products obtained (9–12,
Scheme 2) arise via the elimination of one chloride ligand (via
the amine salt) and one amide ligand. A similar reactivity has
been reported for both mono(aryloxide) and non-chiral,
stoichiometric and catalytic reactions have been developed
using these substrates. We have recently begun an exploration
of the chemistry of these metals associated with the chiral
3,3Ј-disubstituted-2,2Ј-dihydroxy-1,1Ј-binaphthyl ligands [H2-
O2C20H10(R)2-3,3Ј] (R = SiMe3, 1; SiMe2Ph, 2; SiMePh2, 3;
SiPh3, 4) with the expectation of uncovering asymmetric
bis(aryloxide) ligands. The lack of protonation of the second
examples of the reactivity previously established. In this
Ta–NMe2 group has been discussed in detail in a previous
paper we report an investigation of the reaction chemistry of
study.13 In the 1H NMR spectra of 9–12 the Ta–HNMe2 group
the compounds [Ta(NMe2)5]6 and mer,cis-[Ta(NMe2)2Cl3-
appears as a pair of diastereotopic methyl resonances (well
separated doublets) and a broad septet for the amine proton.
Hence, dissociation of this ligand does not occur on the NMR
timescale, presumably reflecting the more Lewis acidic metal
center in 9–12 compared to 5–8. The strong binding of the
dimethylamine ligands in 9–12 leads to a lack of any symmetry
(HNMe2)]7,8 with predominantly resolved examples of these
ligands.9,10 We have recently reported on the related reactivity
of the dimeric [(Et2N)2Cl2Ta(µ-Cl)2TaCl2(NEt2)2]11 with these
ligands, which leads to a series of chiral compounds containing
two of these resolved ligands.12
elements in the molecules on the NMR time-scale. The spectro-
scopic details of the dimethylphenylsilyl compound (S)-10 are
particularly informative. In the 1H NMR spectrum (Fig. 1) the
non-equivalent, diastereotopic SiMe2Ph methyl groups appear
as three singlets (two singlets overlapping), while four distinct
Si-methyl resonances are clearly resolved in the 13C NMR
spectrum.
The fluxionality difference between the tris-amido com-
pounds 5–8 compared to 9–12 is consistent with the observ-
ation that the dimethylamine ligand can be thermally lost from
the coordination sphere of 5. Hence, heating the crude product
obtained by adding 1 to [Ta(NMe2)5], leads to the tris(amide) 13
as shown in Scheme 3. An attempt to thermally remove the
dimethylamine ligands from adducts 9–12 failed. It is not
unusual for dimethylamine adducts of early transition metals to
even sublime in vacuum intact.14
Results and discussion
Synthesis and characterization of dimethylamido compounds
The treatment of hydrocarbon solutions of the compound
[Ta(NMe2)5] with 3,3Ј-disubstituted-2,2Ј-dihydroxy-1,1Ј-bi-
naphthyl ligands 1–4 leads to the rapid (NMR) formation of a
series of new tantalum compounds 5–8 which contain only one
binaphthoxide ligand in the metal coordination sphere (Scheme
1). The solution NMR spectroscopic properties of 5–8 indicate
the presence of a coordinated Me2NH, formed during the
protonolysis reaction, as well as a single resonance for the three
† Electronic supplementary information (ESI) available: ORTEP views
of (R)-7, (R,S)-8, (S)-9 and (S)-12. See http://www.rsc.org/suppdata/
dt/b2/b212910h/
D a l t o n T r a n s . , 2 0 0 3 , 1 6 2 0 – 1 6 2 7
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
1620

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Scheme 1
Scheme 2
Fig.
1
1H NMR spectrum (C6D6) of [Ta(O2C20H10{SiMe2Ph}2-
3,3Ј)(NHMe2)(NMe2)Cl2] (S)-10.
Structural studies
Fig. 2 Molecular structure of [Ta(O2C20H10{SiMe3}2-3,3Ј)(NHMe2)-
(NMe2)3] (S)-5.
The compounds (S)-5, (R)-7, (R,S)-8, (S)-9, (S)-10, and (S)-12
have been subjected to single crystal X-ray diffraction analysis.
Two representative ORTEPs are shown in Figs. 2 and 3 while
selected bond distances and angles are collected in Tables 1–6.
All six compounds can be seen to adopt a slightly distorted
octahedral geometry about the tantalum metal center. In
all cases the dimethylamine ligand is located cis to the two,
chelated aryloxide oxygen atoms and also is located trans to a
dimethylamido ligand. In compound 7 there is a disorder
involving the position of the tantalum atom along the amido,
amine axis. In compounds 5–8 there are two dimethylamido
ligands positioned trans to the binaphthoxide oxygens whereas
in 9–12 two chloride ligands occupy these positions. The
replacement of two amide ligands by chlorides would be pre-
dicted to lead to an increase in the electron deficiency (Lewis
acidity) of the metal center. Dialkylamido ligands are
well known to be able to π-donate to metal centers to which
they are bound, with demonstrable structural effects and
chemical consequences.15 The structural parameters for those
compounds studied do show the effect of the chloride for amide
D a l t o n T r a n s . , 2 0 0 3 , 1 6 2 0 – 1 6 2 7
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Scheme 3
Table 2 Selected bond distances (Å) and angles (Њ) for [Ta(O2C20H10-
{SiMePh2}2-3,3Ј)(NHMe2)(NMe2)3] (R)-7
Ta–O(1)
Ta–O(1Ј)
Ta–N(3)
2.043(3)
2.061(3)
1.995(3)
Ta–N(4)
Ta–N(3Ј)
Ta–N(4Ј)
2.005(3)
2.038(3)
2.428(4)
Ta–O(1)–C(1)
Ta–O(1Ј)–C(1Ј)
O(1)–Ta–O(1Ј)
O(1)–Ta–N(3)
O(1)–Ta–N(4)
O(1)–Ta–N(3Ј)
O(1)–Ta–N(4Ј)
O(1Ј)–Ta–N(3)
O(1Ј)–Ta–N(4)
133.6(2)
125.0(2)
86.4(1)
91.8(1)
90.7(1)
164.6(2)
80.6(1)
171.3(2)
91.2(1)
O(1Ј)–Ta–N(3Ј)
O(1Ј)–Ta–N(4Ј)
N(3)–Ta–N(4)
N(3)–Ta–N(3Ј)
N(3)–Ta–N(4Ј)
N(4)–Ta–N(3Ј)
N(4)–Ta–N(4Ј)
N(3Ј)–Ta–N(4Ј)
90.1(1)
79.3(1)
97.4(2)
89.5(2)
104.4(2)
92.0(2)
167.4(2)
84.0(2)
Table 3 Selected bond distances (Å) and angles (Њ) for [Ta(O2C20H10-
{SiPh3}2-3,3Ј)(NHMe2)(NMe2)3] (R,S)-8
Fig.
3
Molecular structure of [Ta(O2C20H10{SiMe2Ph}2-3,3Ј)-
(NHMe2)(NMe2)Cl2] (S)-10.
Ta–O(1)
Ta–O(2)
Ta–N(3)
2.021(2)
2.075(2)
1.991(3)
Ta–N(4)
Ta–N(5)
Ta–N(6)
2.010(3)
1.983(3)
2.441(3)
Table 1 Selected bond distances (Å) and angles (Њ) for [Ta(O2C20H10-
{SiMe3}2-3,3Ј)(NHMe2)(NMe2)3] (S)-5
Ta–O(1)–C(11)
Ta–O(2)–C(21)
O(1)–Ta–O(2)
O(1)–Ta–N(3)
O(1)–Ta–N(4)
O(1)–Ta–N(5)
O(1)–Ta–N(6)
O(2)–Ta–N(3)
O(2)–Ta–N(4)
139.2(2)
123.7(2)
86.75(9)
166.0(1)
94.3(1)
89.0(1)
77.9(1)
87.3(1)
170.9(1)
O(2)–Ta–N(5)
O(2)–Ta–N(6)
N(3)–Ta–N(4)
N(3)–Ta–N(5)
N(3)–Ta–N(6)
N(4)–Ta–N(5)
N(4)–Ta–N(6)
N(5)–Ta–N(6)
97.3(1)
81.1(1)
89.6(1)
104.3(1)
88.7(1)
91.8(1)
90.2(1)
166.9(1)
Ta–O(1)
Ta–O(2)
Ta–N(3)
2.036(4)
2.039(3)
2.006(5)
Ta–N(4)
Ta–N(5)
Ta–N(6)
2.009(5)
2.000(5)
2.456(5)
Ta–O(1)–C(11)
Ta–O(2)–C(21)
O(1)–Ta–O(2)
O(1)–Ta–N(3)
O(1)–Ta–N(4)
O(1)–Ta–N(5)
O(1)–Ta–N(6)
O(2)–Ta–N(3)
O(2)–Ta–N(4)
130.3(4)
132.5(3)
84.9(2)
175.1(2)
89.2(2)
94.9(2)
81.9(2)
94.1(2)
164.7(2)
O(2)–Ta–N(5)
O(2)–Ta–N(6)
N(3)–Ta–N(4)
N(3)–Ta–N(5)
N(3)–Ta–N(6)
N(4)–Ta–N(5)
N(4)–Ta–N(6)
N(5)–Ta–N(6)
91.5(2)
79.2(2)
90.5(3)
89.9(3)
93.2(2)
103.1(2)
86.0(2)
170.3(2)
Table 4 Selected bond distances (Å) and angles (Њ) for [Ta(O2C20H10-
{SiMe3}2-3,3Ј)(NHMe2)(NMe2)Cl2] (S)-9
Ta–O(2)
Ta–N(3)
Ta–Cl(2)
1.938(5)
2.027(6)
2.364(2)
Ta–O(1)
Ta–N(4)
Ta–Cl(1)
1.916(5)
2.318(7)
2.390(2)
replacement. This is particularly evident in the Ta–HNMe2 dis-
tances (Tables 1–6). In tris-amides (S)-5, (R)-7 and (R,S)-8, the
Ta–N(amine) distances are 2.456(5), 2.428(4) and 2.441(3) Å
respectively. These are among the longest distances so far
reported for amine adducts of this metal. Comparable or longer
Ta–N(dative) bonds are typically found in TMEDA and related
adducts such as in [(Et2NCH2CH2NEt2)(Cl)2Ta(µ-Cl)2Ta(Cl)2-
(Et2NCH2CH2NEt2)], 2.464(8) Å.16 Distances of 2.48–2.53 Å
are reported in a series of cyclometallated adducts.17 A distance
of 2.487(5) Å is reported for the central Ta–N(donor) bond in
[{N(CH2CH2NSiMe3)3}TaTe].18 Banaszak Holl and Wolczan-
ski reported a Ta–NH3 distance of 2.508(28) Å for an interest-
ing ammonia cluster of tantalum.19 Perhaps the most dramatic
examples are the TMEDA adducts [(C6H3Pri2-2,6-N)Ta(X)3-
O(2)–Ta–O(1)
O(1)–Ta–N(3)
O(1)–Ta–N(4)
O(2)–Ta–Cl(2)
N(3)–Ta–Cl(2)
O(2)–Ta–Cl(1)
N(3)–Ta–Cl(1)
Cl(2)–Ta–Cl(1)
C(21)–O(2)–Ta
86.4(2)
98.9(3)
87.0(3)
172.3(2)
94.5(2)
91.7(2)
88.4(2)
90.41(7)
131.0(4)
O(2)–Ta–N(3)
O(2)–Ta–N(4)
N(3)–Ta–N(4)
O(1)–Ta–Cl(2)
N(4)–Ta–Cl(2)
O(1)–Ta–Cl(1)
N(4)–Ta–Cl(1)
C(11)–O(1)–Ta
93.0(2)
88.1(2)
174.1(3)
90.5(2)
84.7(2)
172.5(2)
85.7(3)
136.2(4)
(TMEDA)] (X = Cl, Br) where the NMe2 group trans to the Ta–
imido bond is elongated to 2.561(7) and 2.544(11) Å respect-
ively.20 In the chloro compounds (S)-9, (S)-10, and (S)-12 the
D a l t o n T r a n s . , 2 0 0 3 , 1 6 2 0 – 1 6 2 7
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Table 5 Selected bond distances (Å) and angles (Њ) for [Ta(O2C20H10-
{SiMe2Ph}2-3,3Ј)(NHMe2)(NMe2)Cl2] (S)-10
Ta–O(2)
Ta–N(3)
Ta–Cl(2)
1.914(4)
2.069(6)
2.379(2)
Ta–O(1)
Ta–N(4)
Ta–Cl(1)
1.928(4)
2.246(5)
2.390(2)
O(2)–Ta–O(1)
O(1)–Ta–N(3)
O(1)–Ta–N(4)
O(2)–Ta–Cl(2)
N(3)–Ta–Cl(2)
O(2)–Ta–Cl(1)
N(3)–Ta–Cl(1)
Cl(2)–Ta–Cl(1)
C(21)–O(2)–Ta
87.5(2)
96.3(2)
87.5(2)
174.1(1)
92.1(2)
91.5(1)
90.5(2)
89.77(6)
135.6(4)
O(2)–Ta–N(3)
O(2)–Ta–N(4)
N(3)–Ta–N(4)
O(1)–Ta–Cl(2)
N(4)–Ta–Cl(2)
O(1)–Ta–Cl(1)
N(4)–Ta–Cl(1)
C(11)–O(1)–Ta
93.7(2)
89.4(2)
175.2(2)
90.6(1)
84.9(2)
173.2(1)
85.8(2)
127.7(4)
Table 6 Selected bond distances (Å) and angles (Њ) for [Ta(O2C20H10-
{SiPh3}2-3,3Ј)(NHMe2)(NMe2)Cl2] (S)-12
Ta–O(2)
Ta–N(31)
Ta–Cl(1)
1.956(5)
1.998(6)
2.3584(2)
Ta–O(1)
Ta–N(41)
Ta–Cl(2)
1.911(4)
2.326(7)
2.385(2)
Fig. 4 Molecular structure of [Me2NH2][Ta(O2C20H10{SiMe3}2-3,3Ј)-
Cl4] (S)-15.
bis(aryloxide) has been reported.22 The Ta–O distances in the
anion of (S)-15, 1.889(6) and 1.893(7) Å, are slightly shorter
than those observed in the neutral amido derivatives above,
again reflecting an increase in the l-electron deficiency of the
metal center upon replacement of dialkylamido ligands by
chloride groups.
Treatment of the bis(triphenylsilyl) compound (S)-12 with
carbon disulfide was found to generate a reaction mixture from
which red crystals of the bis(dithiocarbamate) (S)-16 were iso-
lated and structurally characterized (Scheme 4, Fig. 5 and Table
O(1)–Ta–O(2)
O(1)–Ta–N(31)
O(1)–Ta–N(41)
O(1)–Ta–Cl(1)
O(1)–Ta–Cl(2)
O(2)–Ta–Cl(2)
N(41)–Ta–Cl(2)
C(321)–N(31)–Ta
C(21)–O(2)–Ta
86.22(2)
92.9(2)
O(2)–Ta–N(31)
O(2)–Ta–N(41)
O(2)–Ta–Cl(1)
O(2)–Ta–Cl(2)
N(31)–Ta–N(41)
N(31)–Ta–Cl(1)
N(31)–Ta–Cl(2)
C(11)–O(1)–Ta
C(322)–N(31)–Ta
102.8(4)
83.61(2)
88.40(1)
165.8(2)
173.4(4)
93.08(2)
91.4(3)
88.83(2)
172.71(1)
92.82(1)
170.88(6)
82.20(2)
123.1(7)
122.0(4)
141.0(4)
124.5(5)
Table 7 Selected bond distances (Å) and angles (Њ) for [Ta(O2C20H10-
{SiMe3}2-3,3Ј)Cl4][(NH2Me2)] (S)-15
Ta–O(1)
Ta–O(2)
Ta–Cl(3)
1.889(6)
1.893(7)
2.420(3)
Ta–Cl(4)
Ta–Cl(5)
Ta–Cl(6)
2.431(3)
2.362(2)
2.379(2)
Ta–O(1)–C(21)
Ta–O(2)–C(11)
O(1)–Ta–O(2)
O(1)–Ta–Cl(3)
O(1)–Ta–Cl(4)
O(1)–Ta–Cl(5)
O(1)–Ta–Cl(6)
O(2)–Ta–Cl(3)
O(2)–Ta–Cl(4)
135.7(6)
134.7(6)
89.8(3)
89.8(2)
173.4(2)
96.0(2)
90.0(2)
176.3(2)
93.2(2)
O(2)–Ta–Cl(5)
O(2)–Ta–Cl(6)
Cl(3)–Ta–Cl(4)
Cl(3)–Ta–Cl(5)
Cl(3)–Ta–Cl(6)
Cl(4)–Ta–Cl(5)
Cl(4)–Ta–Cl(6)
Cl(5)–Ta–Cl(6)
89.5(2)
93.0(2)
87.6(1)
86.9(1)
90.7(1)
89.9(1)
84.0(1)
173.5(1)
Scheme 4
Ta–HNMe2 distances are shorter, 2.318(7), 2.246(5) and
2.326(7) Å respectively, presumably due to the increased elec-
tron deficiency of the metal center.
The Ta–O(binaphthoxide) distances in the six-coordinate
adducts span the narrow ranges of 2.021(2)–2.075(2) Å in the
tris-amides (Tables 1–3) and slightly shorter 1.911(4)–1.956(5)
Å in the chlorides (Tables 4–6). The binaphthoxide ligands
chelate to the metal with O–Ta–O angles of 84–88Њ and Ta–O–
C angles of 122–141Њ. The Ta–O–C angles are constrained by
the eight-membered ring, and are much lower than typically
found for terminal, non-chelated aryloxide ligands.21
Reactivity of the Ta–NMe2 bonds
The Ta–NMe2 bonds in tris-amido (S)-5 react with SiCl4 in
hydrocarbon solvents to produce the corresponding tris-chlor-
ide (Scheme 3). This is a significant result, as it has proved
difficult to isolate mixed binaphthoxide, chlorides of tantalum
directly from the halide substrate. However, the reaction was
found to lead to a mixture of two products, (S)-14 and (S)-15
(Scheme 3). These can be seen to be the adducts of the tri-chlor-
ide with Me2NH and [Me2NH2][Cl] respectively. A few quality
crystals of (S)-15 were isolated and characterized (Table 7, Fig.
4). A related phosphonium salt containing a 2,2Ј-methylene-
Fig. 5 Molecular structure of [Ta(O2C20H10{SiPh3}2-3,3Ј)(CS2NMe2)2-
Cl] (S)-16.
D a l t o n T r a n s . , 2 0 0 3 , 1 6 2 0 – 1 6 2 7
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Table 8 Selected bond distances (Å) and angles (Њ) for [Ta(O2C20H10-
{SiPh3}2-3,3Ј)(CS2NMe2)2Cl] (S)-16
NMR spectra were recorded on a Bruker DRX-500 NMR
spectrometer at 125.7 MHz and were internally referenced to
the solvent signal.
Ta–O(2)
Ta–S(1)
Ta–S(3)
Ta–Cl
1.907(3)
2.5495(9)
2.589(1)
2.3809(9)
Ta–O(1)
Ta–S(2)
Ta–S(4)
2.014(2)
2.552(1)
2.5385(8)
Synthesis
[Ta(O2C20H10{SiMe3}2-3,3Ј)(NHMe2)(NMe2)3] (S )-5. A 50
mL round bottom flask was charged with [Ta(NMe2)5] (500 mg,
1.25 mmol), a stir bar and benzene (3 mL). This solution
was stirred as (S)-3,3Ј-bis(trimethylsilyl)-2,2Ј-dihydroxy-1,1Ј-
dinaphthyl 1 (536 mg, 1,25 mmol) dissolved in benzene was
slowly added. This mixture was stirred for 1 hour and evapor-
ated to dryness. The crude solid that resulted was dissolved in a
minimal amount of benzene and layered with pentane affording
yellow crystals (200 mg, 22%), which were washed with pentane
and dried in vacuo. Anal. calc. for C34H53N4O2Si2Ta: C, 51.89;
H, 6.79; N, 7.12. Found: C, 51.14; H, 6.54; N, 6.30%. 1H NMR
(C6D6, 30 ЊC): δ 8.12 (s), 7.77 (d), 6.82–7.20 (m, aromatics); 3.19
(s, NMe2); 1.87 (br, NHMe2); 0.47 (s, SiMe3). 13C NMR (C6D6,
30 ЊC): δ 164.9 (Ta–O–C); 46.7 (NMe2); 40.5 (NHMe2); Ϫ0.1
(SiMe3).
O(1)–Ta–O(2)
O(1)–Ta–S(1)
O(1)–Ta–S(2)
O(1)–Ta–S(3)
O(1)–Ta–S(4)
O(2)–Ta–Cl
S(1)–Ta–Cl
S(4)–Ta–S(3)
S(2)–Ta–S(3)
86.32(10)
73.73(7)
140.96(8)
82.48(7)
149.83(8)
175.73(8)
88.15(3)
67.51(3)
136.49(3)
O(2)–Ta–S(1)
O(2)–Ta–S(2)
O(2)–Ta–S(3)
O(2)–Ta–S(4)
S(4)–Ta–S(1)
S(2)–Ta–Cl
S(3)–Ta–Cl
S(1)–Ta–S(3)
C(34)–S(4)–Ta
95.83(8)
91.70(8)
88.49(8)
89.73(8)
136.45(3)
91.26(3)
87.24(3)
155.45(3)
90.61(12)
8). Compound (S)-16 presumably arises via initial reaction of
free dimethylamine with CS2, the resulting dithiocarbamic acid
then carries out protonolysis reactions with a Ta–NMe2 bond
to form another equivalent of HNMe2. The second equivalent
of HS2CNMe2 generated then leads to displacement of HCl
and formation of the final product.
[Ta(O2C20H10{SiMe2Ph}2-3,3Ј)(NHMe2)(NMe2)3] (R)-6. To a
5 mm NMR tube was added solid [Ta(NMe2)5] and benzene-d6
(∼1 mL). This solution was slowly titrated with (R)-3,3Ј-bis(di-
methylphenylsilyl)-2,2Ј-dihydroxy-1,1Ј-dinaphthyl 2 until reac-
tion was complete as monitored by NMR. The compound was
The molecular structure of (S)-16 (Fig. 5) is best described as
a pentagonal bipyramidal geometry about the seven-coordinate
tantalum metal atom. The four sulfur atoms of the two dithio-
carbamate ligands occupy equatorial sites. A chloride and one
binaphthoxide oxygen occupy the axial sites. An O–Ta–O angle
of 86Њ exists between the axial and equatorial binaphthoxide
oxygen atoms. Although there are no related tantalum com-
pounds, there are a few structurally characterized, pentagonal
bipyramidal dithiocarbamates of niobium, which are structur-
ally similar to (S)-16. The seven-coordinate species [Nb-
(S2CNEt2)Cl3]23 and [Nb(S2CNEt2)2(X)(OMe)2] (X = Cl, Br)24
contain axial chloro or methoxy groups. Also related are the
tris(dithiocarbamato) compounds [Nb(S2CNEt2)3(X)] (X = O,
S, NAr, ½N2) in which the axial X group is trans to a sulfur
atom of a dtc ligand.25
1
only characterized spectroscopically. H NMR (C6D6, 30 ЊC):
δ 8.09 (s), 7.63–7.76 (m), 6.86–7.25 (m, aromatics); 3.14 (s,
NMe2); 1.98 (s, NHMe2); 0.70 (s), 0.69 (s, SiMe2Ph). 13C NMR
(C6D6, 30 ЊC): δ 165.0 (Ta–O–C); 47.1 (NMe2); 39.6 (NHMe2);
Ϫ0.8, Ϫ1.4 (SiMe2Ph).
[Ta(O2C20H10{SiMePh2}2-3,3Ј)(NHMe2)(NMe2)3] (R)-7. To a
5 mm NMR tube was added solid [Ta(NMe2)5] and benzene-d6
(∼1 mL). This solution was slowly titrated with (R)-3,3Ј-bis-
(methyldiphenylsilyl)-2,2Ј-dihydroxy-1,1Ј-dinaphthyl
3
until
reaction was complete as monitored by NMR. Upon standing
yellow crystals of 7 (benzene solvate) formed which were
washed with pentane and dried in vacuo. Anal. calc. for C54H61-
N4O2Si2Ta: C, 62.65; H, 5.94; N, 5.41. Anal. calc. for C72H79-
N4O2Si2Ta (ϩ 3C6H6): C, 68.12; H, 6.27; N, 4.41. Found: C,
We have also carried out a preliminary study of the reactivity
of the mono-amido compound [Ta(O2C20H10{SiPh3}2-3,3Ј)-
(NHMe2)(NMe2)Cl2] (S)-12 with racemic and chiral forms of
the alcohol HOCH(Me)Ph. Unfortunately the reactions did
not lead to isolable, pure materials. However, it was possible to
spectroscopically identify two α-methylbenzyl alkoxide com-
1
67.81; H, 6.21; N, 4.99%. H NMR (C6D6, 30 ЊC): δ 7.88 (s),
7.72 (m), 7.40 (d), 6.81–7.30 (m, aromatics); 2.89 (s, NMe2);
1
pounds using H NMR spectroscopy. Hence with the racemic
1.81 (s, NHMe2); 1.00 (s, SiMePh2). 13C NMR (C6D6, 30 ЊC):
alcohol, two well resolved Ta–OCH(Me)Ph quartets were
observed at δ 5.51 and 5.77 ppm due to the presence of two
diastereoisomers in solution. This was confirmed by use of (R)-
HOCH(Me)Ph which led to only one signal in this region of the
spectrum at δ 5.51 ppm. Further studies of the reaction of
theses new resolved tantalum compounds with other chiral
reagents is underway.
δ
165.8 (Ta–O–C); 46.9 (NMe2); 40.9 (NHMe2); Ϫ2.1
(SiMePh2).
[Ta(O2C20H10{SiPh3}2-3,3Ј)(NHMe2)(NMe2)3] (R,S )-8. To a 5
mm NMR tube was added solid [Ta(NMe2)5] and benzene-d6
(∼1 mL). This solution was slowly titrated with racemic-3,3Ј-
bis(triphenylsilyl)-2,2Ј-dihydroxy-1,1Ј-dinaphthyl 4 until reac-
tion was complete as monitored by NMR. Upon standing
yellow crystals of 8 (benzene solvate) formed which were
washed with pentane and dried in vacuo. Anal. calc. for
C64H65N4O2Si2Ta: C, 66.30; H, 5.65; N, 4.83. Anal. calc. for
C70H71N4O2Si2Ta (ϩ C6H6): C, 67.94; H, 5.78; N, 4.52. Found:
C, 66.81; H, 5.49; N, 4.74%. 1H NMR (C6D6, 30 ЊC): δ 8.12 (s),
7.85–8.12 (m), 7.44 (d), 7.29 (d), 7.10–7.16 (m), 6.86–6.97 (m,
aromatics); 2.70 (s, NMe2); 1.79 (s, NHMe2). 13C NMR (C6D6,
30 ЊC): δ 165.7 (Ta–O–C); 46.1 (NMe2); 40.0 (NHMe2).
Experimental
General remarks
All manipulations were carried out using standard syringe,
Schlenk line, and glovebox techniques.26 Benzene, toluene,
ether, THF, and n-hexane were dried over sodium benzophen-
one ketyl and were freshly distilled before use. Pentane was
dried over sodium ribbon. The substrates [Ta(NMe2)5] and
mer,cis-[Ta(NMe2)2Cl3(HNMe2)]13 were obtained by literature
procedures. CAUTION! Explosions have been associated with
the synthesis of [Ta(NMe2)5].6,27 The 3,3Ј-disubstituted-2,2Ј-di-
hydroxy-1,1Ј-binaphthyl ligands [H2O2C20H10(R)2-3,3Ј] (R =
SiMe3, 1; SiMe2Ph, 2; SiMePh2, 3; SiPh3, 4) were prepared
according to literature procedures or slight variations
thereof.28,29 1H NMR spectra were recorded on a Varian
INOVA-300 NMR spectrometer or a Bruker DRX-500 NMR
[Ta(O2C20H10{SiMe3}2-3,3Ј)(NHMe2)(NMe2)Cl2] (S )-9. To a
50 mL solvent seal round bottom flask was added [TaCl3-
(NMe2)2(NHMe2)] (230 mg, 0.55 mmol) and benzene (15 mL).
One equivalent of 1 (240 mg, 0.55 mmol) dissolved in 10 mL of
benzene was slowly added with stirring. This mixture was
stirred for 1 hour and then evaporated to dryness. The crude
solid was dissolved in a small amount of benzene and filtered
through Celite to remove salts. The yellow–orange supernatant
spectrometer and were referenced to residual protio solvent. 13
C
D a l t o n T r a n s . , 2 0 0 3 , 1 6 2 0 – 1 6 2 7
1624

View Article Online
was reduced in volume to 5 mL and carefully layered with pen-
tane–hexane to afford yellow–orange crystals. Yield: 0.39 g
(79%). Anal. calc. for C30H41O2Cl2Si2N2Ta: C, 46.81; H,5.40; N,
3.64; Cl, 9.22. Found: C, 46.60; H, 5.09; N, 3.62; Cl, 9.25%. 1H
NMR (C6D6, 25 ЊC): δ 8.17 (s, 1H, meta H); 8.13 (s, 1H, meta
H); 6.76–7.72 (aromatics); 3.70 (s, 6H, NMe2); 2.36(d, 3H,
HNMe); 1.95 (septet, 1H, HNMe2); 1.75 (d, 3H, HNMe); 0.61
(s, 9H, SiMe3); 0.59 (s, 9H, SiMe3). 13C NMR (C6D6, 25 ЊC):
δ 163.7, 160.43 (Ta–O–C); 48.40 (NMe2); 42.14 (HNMe); 40.90
(HNMe); 0.21 (SiMe3); Ϫ0.12 (SiMe3).
[Ta(O2C20H10{SiMe2Ph}2-3,3Ј)(NHMe2)(NMe2)Cl2] (S )-10.
An identical procedure was used as for 9 above. Yield: 1.93 g
(81%) based on 1.11 g of [TaCl3(NMe2)2(NHMe2)]. Anal. calc.
for C40H45O2Cl2Si2N2Ta: C, 53.75; H, 5.07; N, 3.13; Cl, 7.93.
Found: C, 53.71; H, 5.24; N, 3.10; Cl, 7.96%. 1H NMR (C6D6,
25 ЊC): δ 8.24 (s, 1H, meta H); 8.09 (s, 1H, meta H); 6.79–7.77
(aromatics); 3.57 (s, 6H, NMe2); 2.41 (br, 1H, HNMe2); 1.97 (d,
3H, HNMe); 1.57 (d, 3H, HNMe); 1.02 (s, 3H, SiMePh); 0.92
(s, 6H, SiMe2Ph); 0.67 (s, 3H, SiMePh). 13C NMR (C6D6, 25
ЊC): δ 164.26, 160.27 (Ta–O–C); 48.89 (NMe2); 42.74 (HNMe);
40.44 (HNMe); 0.69 (SiMePh); Ϫ0.83 (SiMePh); Ϫ1.60
(SiMePh); Ϫ3.21 (SiMePh).
[Ta(O2C20H10{SiMePh2}2-3,3Ј)(NHMe2)(NMe2)Cl2] (S )-11.
An identical procedure was used as for 9 above. Yield: 1.54 g
(89%) based on 0.71 g [TaCl3(NMe2)2(NHMe2)]. Anal. calc. for
C50H49O2Cl2Si2N2Ta: C, 58.99; H, 4.85; N, 2.75; Cl 6.97. Found:
1
C, 58.75; H, 4.85; N, 2.70; Cl, 7.03%. H NMR (C6D6, 25 ЊC):
δ 8.22 (s, 1H, meta H); 8.15 (s, 1H, meta H); 6.81–7.88 (aromat-
ics); 3.44 (s, 6H, NMe2); 2.03 (br, 1H, HNMe2); 1.84 (d, 3H,
HNMe); 1.50 (d, 3H, HNMe); 1.35 (s, 6H, SiMePh2); 1.33 (s,
6H, SiMePh2). 13C NMR (C6D6, 25 ЊC): δ 164.17, 160.14
(Ta–O–C); (115.37–140.87 (aromatics); 48.49 (NMe2); 42.62
(HNMe); 39.91 (HNMe); Ϫ3.42 (SiMePh2); Ϫ3.99 (SiMePh2).
[Ta(O2C20H10{SiPh3}2-3,3Ј)(NHMe2)(NMe2)Cl2] (S )-12. An
identical procedure was used as for 9 above. Yield: 0.35 g (57%)
based on 0.22 g of [TaCl3(NMe2)2(NHMe2)]. Anal. calc. for
C60H53O2Cl2Si2N2Ta: C, 63.10; H, 4.68; N, 2.45; Cl, 6.21.
Found: C, 63.50; H, 4.99; N, 2.07; Cl, 6.45%. 1H NMR (C6D6):
δ 8.34 (s, 1H, meta H); 8.24 (s, 1H, meta H); 6.80–7.91 (aromat-
ics); 3.57 (s, 6H, NMe2); 1.15 (br, 1H, NHMe2); 1.28 (d, 3H,
NHMe); 1.76 (d, 3H, NHMe). 13C NMR (C6D6, 25 ЊC): 164.79,
160.11 (Ta–O–C); 49.61 (NMe2); 43.40 (NHMe2); 40.08
(NHMe2).
[Ta(O2C20H10{SiMe3}2-3,3Ј)(NMe2)3] (S )-13. A flask was
charged with [Ta(NMe2)5] (1.0 g, 2.5 mmol) and benzene (20
mL). This solution was stirred as (S)-3,3Ј-bis(trimethylsilyl)-
2,2Ј-dihydroxy-1,1Ј-dinaphthyl 1 (1.1 g, 2.6 mmol) dissolved in
benzene was slowly added. The mixture was stirred for 20 min-
utes and evacuated to dryness. The resulting solid was heated at
100 ЊC under vacuum for several minutes affording 1.7 g of 8
(92%). 1H NMR (C6D6, 30 ЊC): δ 8.14 (s), 7.78 (d), 7.28 (d), 7.08
(t), 6.89 (t, aromatics); 3.07 (s, NMe2); 0.48 (s, SiMe3). 13C
NMR (C6D6, 30 ЊC): δ 164.9 (Ta–O–C); 45.6 (NMe2); Ϫ0.1
(SiMe3).
[Ta(O2C20H10{SiMe3}2-3,3Ј)(NHMe2)Cl3]
(S )-14
and
[Me2NH2][Ta(O2C20H10{SiMe3}2-3,3Ј)Cl4] (S )-15. A flask was
charged with [Ta(NMe2)5] (1.0 g, 2.5 mmol) and benzene (50
mL). This mixture was stirred as (S)-3,3Ј-bis(trimethylsilyl)-
2,2Ј-dihydroxy-1,1Ј-dinaphthyl 1 (1.1 g, 2.6 mmol) dissolved in
benzene was slowly added. The reaction was stirred for 30 min-
utes and [SiCl4] (1.4 mL, 12.2 mmol) added under a nitrogen
flush. The resulting red solution was stirred for 30 minutes and
evacuated to dryness affording a red solid which was washed
with CHCl3 and pentane successively and dried in vacuo (1.8 g,
95%). Microanalysis data leads to the conclusion that a mixture
D a l t o n T r a n s . , 2 0 0 3 , 1 6 2 0 – 1 6 2 7
1625

View Article Online
3 (a) V. M. Visciglio, J. R. Clark, M. T. Nguyen, D. R. Mulford,
of 14 and 15 were formed. A few crystals of 15 (½ benzene
solvate per Ta) were isolated from benzene solution. Anal. calc.
for 14, C28H35Cl3NO2Si2Ta: C, 44.19; H, 4.64; N, 1.84; Cl, 13.97.
Calc. for 15, C28H36Cl4NO2Si2Ta: C, 42.17; H, 4.55; N, 1.76; Cl,
17.78. Found: C, 42.87; H, 4.60; N, 1.58; Cl, 15.66%. 1H NMR
(C6D6, 30 ЊC): δ 8.23 (s), 7.65 (d), 6.65–7.16 (m, aromatics); 6.77
(br, NH ); 2.07 (br, NMe2); 0.77 (s, SiMe3). 13C NMR (C6D6,
30 ЊC): δ 163.0 (Ta–O–C); 35.8 (NMe2); 0.4 (SiMe3). Attempts
at separation/purification have thus far failed.
P. E. Fanwick and I. P. Rothwell, J. Am. Chem. Soc., 1997, 119, 3490;
(b) T. W. Coffindaffer, B. D. Steffy, I. P. Rothwell, K. Folting,
J. C. Huffman and W. E. Streib, J. Am. Chem. Soc., 1989, 111,
4742.
4 (a) I. P. Rothwell, Acc. Chem. Res., 1988, 21, 153; (b) L. R.
Chamberlain, J. L. Keddington and I. P. Rothwell, Organometallics,
1992, 1, 1098; (c) L. R. Chamberlain, I. P. Rothwell and J. C.
Huffman, Inorg. Chem., 1984, 23, 2575; (d ) L. R. Chamberlain, I. P.
Rothwell and J. C. Huffman, J. Am. Chem. Soc., 1986, 108, 1502;
(e) L. R. Chamberlain, I. P. Rothwell, K. Folting and J. C. Huffman,
J. Chem. Soc., Dalton Trans., 1987, 155; ( f ) L. R. Chamberlain and
I. P. Rothwell, J. Chem. Soc., Dalton Trans., 1987, 163; (g) R. W.
Chesnut, L. D. Durfee, P. E. Fanwick and I. P. Rothwell, Polyhedron,
1987, 6, 2019; (h) L. R. Chamberlain, J. L. Kerscher, A. P. Rothwell,
I. P. Rothwell and J. C. Huffman, J. Am. Chem. Soc., 1987, 109,
6471; (i) L. R. Chamberlain, B. D. Steffey and I. P. Rothwell,
Polyhedron, 1989, 8, 341; (j) B. D. Steffey, R. W. Chesnut, J. L.
Kerschner, P. J. Pellechia, P. E. Fanwick and I. P. Rothwell, J. Am.
Chem. Soc., 1989, 111, 378; (k) B. D. Steffey, L. R. Chamberlain,
R. W. Chesnut, D. E. Chebi, P. E. Fanwick and I. P. Rothwell,
Organometallics, 1989, 8, 1419; (l ) R. W. Chesnut, J. S. Yu, P. E.
Fanwick and I. P. Rothwell, Polyhedron, 1990, 8, 1051; (m) B. D.
Steffey, P. E. Fanwick and I. P. Rothwell, Polyhedron, 1990, 9, 963;
(n) J. S. Yu, P. E. Fanwick and I. P. Rothwell, J. Am. Chem. Soc.,
1990, 112, 8171; (o) R. W. Chesnut, G. G. Jacob, J. S. Yu,
P. E. Fanwick and I. P. Rothwell, Organometallics, 1991, 10, 321;
(p) J. S. Vilardo, M. A. Lockwood, L. G. Hanson, J. R. Clark,
B. C. Parkin, P. E. Fanwick and I. P. Rothwell, J. Chem. Soc.,
Dalton Trans., 1997, 3353; (q) P. N. Riley, M. G. Thorn, J. S. Vilardo,
M. A. Lockwood, P. E. Fanwick and I. P. Rothwell, Organometallics,
1999, 18, 3016; (r) M. G. Thorn, P. E. Fanwick and I. P. Rothwell,
Organometallics, 1999, 18, 4442; (s) M. G. Thorn, P. E. Fanwick,
R. W. Chesnut and I. P. Rothwell, J. Chem. Soc., Chem. Comm.,
1999, 2543.
5 (a) I. P. Rothwell, Chem. Commun., 1997, 1331 (Feature Article);
(b) J. R. Clark, P. E. Fanwick and I. P. Rothwell, J. Chem. Soc.,
Chem. Commun., 1995, 553; (c) B. C. Parkin, J. C. Clark, V. M.
Visciglio, P. E. Fanwick and I. P. Rothwell, Organometallics, 1995,
14, 3002.
6 P. N. Riley, J. R. Parker, P. E. Fanwick and I. P. Rothwell,
Organometallics, 1999, 18, 3579.
7 P. J. H. Carnell and G. W. Fowles, J. Chem. Soc., 1959, 4113.
8 M. H. Chisholm, J. C. Huffman and L. S. Tan, Inorg. Chem., 1981,
20, 1859.
9 M. G. Thorn, J. E. Moses, P. E. Fanwick and I. P. Rothwell, J. Chem.
Soc., Dalton Trans., 2000, 2659.
[Ta(O2C20H10{SiPh3}2-3,3Ј)(CS2NMe2)2Cl] (S )-16. A 50 mL
solvent seal round bottom flask was charged with (S)-12 (430
mg, 0.42 mmol) and dissolved in 20 mL of benzene. An excess
of CS2 (0.2 mL, 3.3 mmol) was slowly added to the stirring
reaction mixture. This mixture was stirred for 24 h and evapor-
ated to dryness. A pure red solid was obtained from layering a
benzene solution with hexane. (Yield = 0.34 g, 67%). Anal. calc.
for C62H52O2ClS4Si2N2Ta: C, 56.66; H, 4.16; N, 2.23; Cl, 2.81.
Found: C, 56.46; H, 4.61; N, 2.00; Cl, 2.25%. 1H NMR(C6D6);
δ 8.51 (s, 1H, meta H); 8.25 (s, 1H, meta H); 6.66–8.23
(aromatics); 0.84–2.31 (m, CS2NMe2).
X-Ray data collection and reduction
Crystal data and data collection parameters are contained in
Table 9. A suitable crystal was mounted on a glass fiber in a
random orientation under a cold stream of dry nitrogen. Pre-
liminary examination and final data collection were performed
with Mo-Kα radiation (λ = 0.71073 Å) on a Nonius Kappa
CCD. Lorentz and polarization corrections were applied to the
data.30 An empirical absorption correction using SCALEPACK
was applied.31 Intensities of equivalent reflections were aver-
aged. The structure was solved using the structure solution pro-
gram PATTY in DIRDIF92.32 The remaining atoms were
located in succeeding difference Fourier syntheses. Hydrogen
atoms were included in the refinement but restrained to ride on
the atom to which they are bonded. The structure was refined in
full-matrix least-squares where the function minimized was
2
Σw(|Fo|2 Ϫ |Fc|2)2 and the weight w is defined as w = 1/[σ2(Fo ) ϩ
2
(0.0585P)2 ϩ 1.4064P] where P = (Fo ϩ 2Fc2)/3. Scattering
factors were taken from the International Tables for Crystallo-
graphy.33 Refinement was performed on a AlphaServer 2100
using SHELXS97.34 Crystallographic drawings were done using
ORTEP.35
CCDC reference numbers 200553–200559 and 203123.
See http://www.rsc.org/suppdata/dt/b2/b212910h/ for crystal-
lographic data in CIF or other electronic format.
10 For some related halo(dialkylamido)compounds of Nb and Ta see
(a) P. A. Fox, S. D. Gray, M. A. Bruck and D. E. Wigley,
Inorg. Chem., 1996, 35, 6027; (b) Zhongzhi Wu, J. B. Diminnie and
Ziling Xue, J. Am. Chem. Soc., 1999, 121, 4300; (c) D. M. Hoffman
and S. P. Rangarajan, Acta Crystallogr., Sect. C, 1996, 52, 1616;
(d ) P. Berno and S. Gambarotta, Organometallics, 1995, 14, 2159;
(e) L. Scoles, K. B. P. Ruppa and S. Gambarotta, J. Am. Chem. Soc.,
1996, 118, 2529; J. C. Fuggle, D. W. A. Sharp and J. M. Winfield,
J. Chem. Soc., Dalton Trans., 1972, 1766.
11 Y. W. Chao, P. A. Wexler and D. E. Wigley, Inorg. Chem., 1989, 28,
Acknowledgements
3860.
12 C. S. Weinert, P. E. Fanwick and I. P. Rothwell, J. Chem. Soc.,
Dalton Trans., 2002, 2948.
13 S. W. Schweiger, D. L. Tillison, M. G. Thorn, P. E. Fanwick and
I. P. Rothwell, J. Chem. Soc., Dalton Trans., 2001, 2401.
14 Including mer,cis-[Ta(NMe2)2Cl3(HNMe2)] itself.
15 P. N. Riley, P. E. Fanwick and I. P. Rothwell, J. Chem. Soc., Dalton
Trans., 2001, 181 and references therein.
16 J. A. M. Canich and F. A. Cotton, Inorg. Chem., 1987, 26, 4236.
17 (a) M. H. P. Rietveld, W. Teunissen, H. Hagen, L. van de Water,
D. M. Grove, P. A. van der Schaaf, A. Muhlebach, H. Kooijman,
W. J. J. Smeets, N. Veldman, A. L. Spek and G. van Koten,
Organometallics, 1997, 16, 1674; (b) M. H. P. Rietveld, H. Hagen,
L. van de Water, D. M. Grove, H. Kooijman, N. Veldman, A. L.
Spek and G. van Koten, Organometallics, 1997, 16, 168; (c) H. C. L.
Abbenhuis, R. van Belzen, D. M. Grove, A. J. A. Klomp, G. P. M.
van Mier, A. L. Spek and G. van Koten, Organometallics, 1993, 12,
210.
18 (a) V. Christou and J. Arnold, Angew. Chem., Int. Ed. Engl., 1993,
32, 1450; (b) J. A. R. Schmidt, S. A. Chmura and J. Arnold,
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We thank the National Science Foundation (Grant CHE-
0078405) for financial support of this research.
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