Synthesis and reactivity of neutral, Zwitterionic and cationic pentamethylcyclopentadienyl-tantalum-phosphinimide complexes

Article abstract of DOI:10.1021/om0009785

This paper focuses on the synthesis and reactivity of Cp*Ta(V)-phosphinimide complexes. Reaction of stoichiometric mixtures of Cp*TaCl₄ and phosphinimine R₃PNSiMe₃ affords the complexes Cp*Ta(NPR₃)Cl₃

Full text of DOI:10.1021/om0009785

1442
Organometallics 2001, 20, 1442-1450
Syn th esis a n d Rea ctivity of Neu tr a l, Zw itter ion ic a n d
Ca tion ic
P en ta m eth ylcyclop en ta d ien yl-Ta n ta lu m -P h osp h in im id e
Com p lexes
Silke Courtenay and Douglas W. Stephan*
School of Physical Sciences, Chemistry and Biochemistry, University of Windsor,
Windsor, Ontario, Canada N9B 3P4
Received November 17, 2000
This paper focuses on the synthesis and reactivity of Cp*Ta(V)-phosphinimide complexes.
Reaction of stoichiometric mixtures of Cp*TaCl4 and phosphinimine R3PNSiMe3 affords the
complexes Cp*Ta(NPR3)Cl3, R ) t-Bu 1, i-Pr 2. These species are readily derivatized to the
alkylated complexes Cp*Ta(NPR3)Me3, R ) t-Bu 3, i-Pr 4; Cp*Ta(NPt-Bu3)(CH2Ph)Cl2, 5;
and Cp*Ta(NPt-Bu3)(CH2Ph)Me2, 6. Reaction with 3 equiv of BnMgCl afforded the robust
alkylidene species Cp*Ta(NPR3)(CHPh)(CH2Ph), R ) t-Bu 7, i-Pr 8. Reaction of 7 with MeI
gives the metallacycle Cp*Ta(NPt-Bu3)(η2-CHPhCH2)(CH2Ph), 9. Alkylation of 1 and 2 with
2 equiv of EtMgCl results in formation of the complexes Cp*Ta(NPR3)(η2-C2H4)Cl, R ) t-Bu
10, i-Pr 11, while further reaction of 10 with EtMgCl affords Cp*Ta(NPt-Bu3)(η2-C2H4)(CH2-
CH3), 12. Reaction of 1 with 1 equiv of B(C6F5)3 results in generation of the salt [Cp*Ta-
(NPt-Bu3)Cl2][ClB(C6F5)3], 13, while the analogous reaction with Ph3C[B(C6F5)4] affords the
related salt [Cp*Ta(NPt-Bu3)Cl2][B(C6F5)4], 14. The zwitterionic species Cp*Ta(NPR3)Me2-
(MeB(C6F5)3) (R ) t-Bu 15, i-Pr 16) are derived via reaction of 3 or 4 with B(C6F5)3. The
analogous reaction of 3 and 4 with [Ph3C][B(C6F5)4] affords the related salts [Cp*Ta(NPR3)-
Me2][B(C6F5)4] (R ) t-Bu 17, i-Pr 18). Treatment of 10 with Ph3CB(C6F5)4, Ph3CBF4, or
B(C6F5)3 gives the complexes [Cp*Ta(NPt-Bu3)(Cl)CH2CH2CPh3][B(C6F5)4], 20, [Cp*Ta(NPt-
Bu3)(Cl)(CH2CH2CPh3)][BF4], 21 and the zwitterionic species [Cp*Ta(NPt-Bu3)(Cl)(CH2CH2B-
(C6F5)3)], 22, respectively. The relevance of this chemistry to the related group IV metal
olefin polymerization catalysts is discussed and considered. X-ray structural studies of 1, 3,
5, 7, 9, 10, and 22 are reported.
In tr od u ction
imide complexes in catalysis,4-7 we are investigating the
chemistry of related group V complexes. While others
have recently demonstrated that selected nonmetal-
locene derivatives of Ta do show moderate activity in
olefin polymerization catalysis,8 our perspective is that
the chemistry of Ta-phosphinimide systems may provide
insight relating to our active group IV systems. Thus,
in this article we report the synthesis and structure of
a family of neutral, zwitterionic and cationic Ta-phos-
phinimide complexes. The chemistry exhibited is con-
sidered in relation to the analogous group IV systems.
The advent of industrial interest in early metal
metallocene-based single-site olefin polymerization ca-
talysis some twenty years ago has spurred more recent
studies of related systems that incorporate non-cyclo-
pentadienyl ancillary ligands. A growing variety of such
systems have and continue to be examined.1 In our own
efforts, we have recently implemented the steric analogy
between phosphinimide ligands and cyclopentadienyl
groups to prepare several families of titanium-based
ethylene polymerization precatalysts.2,3 In some cases,
unprecedented activity was seen for the resulting
catalysts.2 This was attributed to the unique synergy
of steric features of phosphinimide ligands which pro-
vide significant steric encumbrance that is somewhat
remote from the metal, thus making the immediate
coordination sphere of the metal center accessible.
Continuing to probe the utility of group IV phosphin-
Exp er im en ta l Section
Gen er a l Da ta . All preparations were done under an
atmosphere of dry, O2-free N2 employing both Schlenk line
techniques and Innovative Technologies, Braun, or Vacuum
Atmospheres inert atmosphere gloveboxes. Solvents were
(4) Guerin, F.; Stephan, D. W. Angew. Chem. 2000, 112, 1354-1356.
(5) Gue´rin, F.; Stewart, J . C.; Beddie, C.; Stephan, D. W. Organo-
metallics 2000, in press.
(1) Britovsek, G. J . P.; Gibson, V. C.; Wass, D. F. Angew. Chem.,
Int. Ed. Engl. 1999, 38, 428-447.
(6) Kickham, J . E.; Guerin, F.; Stewart, J . C.; Stephan, D. W. Angew.
Chem. 2000, 112, 3406-3409.
(2) Stephan, D. W.; Guerin, F.; Spence, R. E. v.; Koch, L.; Gao, X.;
Brown, S. J .; Swabey, J . W.; Wang, Q.; Xu, W.; Zoricak, P.; Harrison,
D. G. Organometallics 1999, 17, 2046-2048.
(7) Sung, R. C. W.; Courtenay, S.; McGarvey, B. R.; Stephan, D. W.
Inorg. Chem. 2000, 39, 2542-2546.
(3) Stephan, D. W.; Stewart, J . C.; Guerin, F.; Spence, R. E. v.; Xu,
W.; Harrison, D. G. Organometallics 1999, 17, 1116-1118.
(8) Decker, J . M.; Geib, S. J .; Meyer, T. Y. Organometallics 1999,
18, 4417-4420.
10.1021/om0009785 CCC: $20.00 © 2001 American Chemical Society
Publication on Web 03/01/2001

Tantalum-Phosphinimide Complexes
Organometallics, Vol. 20, No. 7, 2001 1443
purified employing a Grubb’s type column system manufac-
tured by Innovative Technology. All organic reagents were
purified by conventional methods. 1H, 13C{1H}, and 31P{1H}
NMR spectra were recorded on a Bruker Avance-300 and 500
operating at 300 and 500 MHz, respectively. Trace amounts
of protonated solvents were used as references, and chemical
shifts are reported relative to SiMe4. 31P NMR, 11B NMR, and
19F NMR spectra were recorded on a Bruker Avance-300 and
are referenced to 85% H3PO4, NaBH4/H2O, and F3CCOOH,
respectively. Guelph Chemical Laboratories in Guelph Ontario
performed combustion analyses. TaCl5 and Cp* were pur-
to dryness, giving the product in 72% yield: 1H NMR (C6D6) δ
7.91 (d, |J H-H| ) 7.3 Hz, 2H, CH2C6H5), 7.35 (t, |J H-H| ) 7.5
Hz, 2H, CH2C6H5) 6.87 (t, |J H-H| ) 7.2 Hz, 1H, CH2C6H5), 2.40
(s, 2H, CH2C6H5), 2.10 (s, 15H, C5(CH3)5), 1.07 (d, |J P-H| ) 13.5
Hz, 27H, PC(CH3)3); 13C{1H} NMR (C6D6) δ 151.36, 130.55,
126.93, 122.44 (s, CH2C6H5), 121.31 (s, C5(CH3)5), 77.11(s,
CH2C6H5), 42.36 (d, |J P-C| ) 44.2 Hz, PC(CH3)3), 29.68 (s, PC-
(CH3)3), 12.83 (s, C5(CH3)5); 31P{1H} NMR (C6D6) δ 55.87 (s).
Anal. Calcd for C29H49Cl2NPTa: C, 50.15; H, 7.11; N, 2.02.
Found: C, 50.36; H, 6.93; N, 1.96.
Syn th esis of Cp *Ta (NP t-Bu 3)(CH2P h )Me2, 6. To a solu-
tion of 5 (150 mg, 0.216 mmol) in 3 mL of THF was added
MeLi (10 mg, 0.455 mmol) in 2 mL of THF. The orange solution
was stirred for 2 h, evaporated to dryness, dissolved in
benzene, and filtered. Evaporation of the solvent resulted in
isolation of the product as a red powder in 58% yield: 1H NMR
9
chased from the Strem Chemical Co. Cp*TaCl4 and the
phosphinimines R3PNSiMe3 (R ) t-Bu, i-Pr) were prepared by
literature methods.10,11
Syn th esis of Cp *Ta (NP R3)Cl3 (R ) t-Bu 1, i-P r 2). These
compounds were prepared in a similar fashion, and thus only
one preparation is detailed. To a suspension of Cp*TaCl4 (1.00
g, 2.183 mmol) in 70 mL of toluene was added t-Bu3PNSiMe3
(630 mg, 2.176 mmol). The reaction mixture was heated under
reflux for 6 h and then allowed to cool to room temperature.
The solvent was evaporated, and the resulting deep yellow
powder 1 was washed twice with toluene, yielding the product
in 77% yield: 1H NMR (C6D6) δ 2.26 (s, 15H, C5(CH3)5), 1.23
(d, |J P-H| ) 13.8 Hz, 27H, PC(CH3)3), (CD2Cl2) δ 2.29 (s, 15H,
C5(CH3)5), 1.56 (d, |J P-H| ) 13.8 Hz, 27H, PC(CH3)3); 13C{1H}
NMR (C6D6) δ 127.61 (s, C5(CH3)5), 46.28 (d, |J P-C| ) 43 Hz,
(C6D6) δ 7.67 (d, |J H-H| ) 7.6 Hz, 2H, CH2C6H5), 7.31 (t, |J H-H
|
) 7.4 Hz, 2H, CH2C6H5), 6.93 (t, |J H-H| ) 7.3 Hz, 2H,
CH2C6H5), 2.11 (s, 2H, CH2C6H5) 1.88 (s, 15H, C5(CH3)5), 0.98
(d, |J P-H| ) 13.0 Hz, 27H, PC(CH3)3), 0.78 (s, 6H, Ta-CH3);
13C{1H} NMR (C6D6) δ 155.32, 126.93, 121.03, 113.71 (s,
CH2C6H5), 110.00 (s, C5(CH3)5), 62.37 (s, CH2C6H5), 45.12 (s,
Ta-CH3), 41.60 (d, |J P-H| ) 45.6 Hz, PC(CH3)3), 29.79 (s, PC-
(CH3)3), 11.79 (s, C5(CH3)5); 31P{1H} NMR (C6D6) δ 50.41 (s).
Anal. Calcd for C31H55NPTa: C, 56.96; H, 8.48; N, 2.14.
Found: C, 56.55; H, 8.34; N, 2.01.
1
PC(CH3)3), 33.36 (s, PC(CH3)3), 16.83 (s, C5(CH3)5); H NMR
Syn th esis of Cp *Ta (NP R3)(CHP h )(CH2P h ), R ) t-Bu 7,
i-P r 8. These compounds were prepared in a similar fashion,
and thus only one preparation is detailed. To a suspension of
1 (300 mg, 0.469 mmol) in 5 mL of benzene was added BnMgCl
(1.41 mL, 1 M solution in ether). The resulting red solution
was stirred for 2 h, filtered, and evaporated to dryness.
Addition of 1 mL of hexane resulted in the formation of red
crystals in 51% yield: 1H NMR (C6D6) δ 9.13 (s, 1H, CHC6H5),
7.62 (d, |J H-H| ) 7.5 Hz, 2H, C6H5) 7.37 (t, |J H-H| ) 7.7 Hz,
2H, C6H5) 7.14-6.78 (m, C6H5) 3.22 (d, |J H-H| ) 11.4 Hz, 1H,
CH2C6H5), 2.23 (d, |J H-H| ) 11.4 Hz, 1H, CH2C6H5), 1.95 (s,
15H, C5(CH3)5), 1.14 (d, |J P-H| ) 12.9 Hz, 27H, PC(CH3)3); 13C-
{1H} NMR (C6D6) δ 213.11 (s, CHC6H5), 153.31, 152.46, 130.89,
130.39,129.03, 128.51, 122.24, 121.87 (s, C6H5) 112.98 (s, C5-
(CH3)5), 50.49 (s, CH2C6H5) 41.03 (d, |J P-C| ) 46.5 Hz,
PC(CH3)3), 29.97 (s, PC(CH3)3), 12.07 (s, C5(CH3)5); 31P{1H}
NMR (C6D6) δ 49.03 (s). Anal. Calcd for C36H55NPTa: C, 60.58;
(CD2Cl2) δ 124.30 (s, C5(CH3)5), 43.10 (d, |J P-C| ) 43 Hz,
PC(CH3)3), 29.87 (s, PC(CH3)3), 13.03 (s, C5(CH3)5); 31P{1H}
NMR (C6D6) δ 60.89, (CD2Cl2) δ 63.69 (s). Anal. Calcd for
C
22H42Cl3NPTa: C, 41.36; H, 6.63; N, 2.19. Found: C, 41.67;
1
H, 6.24; N, 2.13. 2: 80% yield, H NMR (C6D6) δ 2.28 (s, 15H,
C5(CH3)5), 2.03 (m, 3H, PCH(CH3)2), 0.93 (dd,|J P-H| ) 15.7 Hz,
|J H-H| ) 7.2 Hz, 18H, PCH(CH3)2); 13C{1H} NMR (C6D6) δ
123.96 (s, C5(CH3)5), 24.88 (d, |J P-C| ) 56 Hz, PCH(CH3)2),
16.85 (s, PCH(CH3)2), 13.31 (s, C5(CH3)5); 31P{1H} NMR (C6D6)
δ 51.81 (s). Anal. Calcd for C19H36Cl3NPTa: C, 38.24; H, 6.08;
N, 2.35. Found: C, 38.21; H, 6.09; N, 2.30.
Syn t h esis of Cp *Ta (NP R 3)Me3 (R ) t-Bu 3, i-P r 4).
These compounds were prepared in a similar fashion, and thus
only one preparation is detailed. To a suspension of 1 (200 mg,
0.318 mmol) in 10 mL of THF was added a suspension of MeLi
(21 mg, 0.955 mmol) in 2 mL of THF. After 2 h of stirring the
solvent was evaporated, and the resulting yellow solid was
taken up in 3 mL of toluene, filtered, and evacuated to dryness.
The yellow-white powder 3 was isolated in 72% yield: 1H NMR
(C6D6) δ 1.93 (s, 15H, C5(CH3)5), 1.15 (d, |J P-H| ) 13.0 Hz, 27H,
PC(CH3)3), 0.56 (s, 6H, Ta-CH3), 0.46 (s, 3H, Ta-CH3); 13C-
{1H} NMR (C6D6) δ 116.32 (s, C5(CH3)5), 48.47 (s, Ta-CH3),
45.43 (s, Ta-CH3), 45.14 (d |J P-C| ) 46.5 Hz, PC(CH3)3), 33.31
(s, PC(CH3)3), 15.18 (s, C5(CH3)5); 31P{1H} NMR (C6D6) δ 50.30.
Anal. Calcd for C25H51NPTa: C, 51.99; H, 8.90; N, 2.42.
Found: C, 51.91; H, 8.54; N, 2.38. 4: 83% yield; 1H NMR
(C6D6) δ 1.96 (s, 15H, C5(CH3)5), 1.72 (m, 3H, PCH(CH3)2), 0.88
(dd, |J P-H| ) 14.7 Hz, |J H-H| ) 7.2 Hz, 18H, PCH(CH3)2), 0.54
(s, 6H, Ta-CH3), 0.49 (s, 3H, Ta-CH3); 13C{1H} NMR (C6D6)
δ 113.23 (s, C5(CH3)5), 45.82 (s, Ta-CH3), 41.06 (s, Ta-CH3),
25.40 (d, |J P-C| ) 57.3 Hz, PCH(CH3)2), 17.01 (s, PCH(CH3)2),
11.71(s, C5(CH3)5); 31P{1H} NMR (C6D6) δ 39.94. Anal. Calcd
for C22H45NPTa: C, 49.34; H, 8.47; N, 2.62. Found: C, 48.52;
H, 8.43; N, 2.27.
H, 7.77; N, 1.96. Found: C, 59.98; H, 7.64; N, 1.85. 8: 63%
1
yield; H NMR (C6D6) δ 8.40 (s, 1H, CHC6H5), 7.49 (d, |J H-H
|
) 7.3 Hz, 2H, C6H5), 7.33 (t, |J H-H| ) 7.5 Hz, 2H, C6H5), 7.12-
6.67 (m, C6H5), 2.50 (d, |J H-H| ) 11.7 Hz, 1H, CH2C6H5), 2.36
(d, |J H-H| ) 11.7 Hz, 1H, CH2C6H5), 1.99 (s, 15H, C5(CH3)5),
1.67 (m, 3H, PCH(CH3)2), 0.85 (dd, |J P-H| ) 14.7 Hz, |J H-H| )
7.1 Hz, 9H, PCH(CH3)2) 0.80 (dd, |J P-H| ) 14.6 Hz, |J H-H| )
7.2 Hz, 9H, PCH(CH3)2); 13C{1H} NMR (tol-d8) δ 222.88 (s,
CHC6H5), 154.07, 152.68, 130.14, 127.33, 127.06, 125.31,
125.12, 121.30 (s, C6H5), 112.67 (s, C5(CH3)5), 52.41 (s, CH2C6H5),
26.09 (d, |J P-C| ) 57.2 Hz, PCH(CH3)2), 16.88 (s, PCH(CH3)2),
11.79 (s, C5(CH3)5); 31P{1H} NMR (C6D6) δ 40.44 (s).
F or m a tion of Cp *Ta (NP t-Bu 3)(η2-CHP h CH2)(CH2P h ),
9. To a solution of 7 (100 mg, 0.140 mmol) in 0.5 mL of C6D6
was added MeI (20 mg, 0.141 mmol) in a resealable NMR tube.
The tube was heated for 2 h at 87 °C, resulting in a product
mixture by 1H NMR. After 1 week, deep brownish red crystals
of 9 were isolated from the product mixture in 19% yield: 1H
Syn th esis of Cp *Ta (NP t-Bu 3)(CH2P h )Cl2, 5. To a sus-
pension of 1 (100 mg, 0.156 mmol) in 5 mL of toluene was
added BnMgCl (0.08 mL, 2 M solution in ether). The yellow-
orange solution was stirred for 2 h, filtered, and evaporated
NMR (C6D6) δ 7.63 (d, |J H-H| ) 7.8 Hz, 2H, C6H5), 7.25 (t, |J H-H
|
) 7.6 Hz, 2H, C6H5), 7.13-6.98 (m, C6H5), 2.82 (d, |J H-H| )
14.4 Hz, 1H, CH2C6H5), 2.45 (d, |J H-H| ) 14.3 Hz, 1H,
CH2C6H5), 1.86 (m, 1H, CHPh), 1.68 (s, 15H, C5(CH3)5), 1.52
(m, 1H CHPh) 1.03 (d, |J P-H| ) 13.1 Hz) 0.64 (m, 1H, CHPh);
13C{1H} NMR (C6D6) δ 145-124 (s, C6H5), 114.26 (s, C5(CH3)5),
70.18 (s, CH2C6H5) 62.74 (s, CHR), 53.52 (s, CHPh) 44.75 (d,
|J P-C| ) 45.2 Hz, PC(CH3)3), 33.46 (s, PC(CH3)3), 17.85 (s, C5-
(CH3)5); 31P{1H} NMR (C6D6) δ 52.01 (s). The low yield and
sensitivity of this species precluded elemental analysis.
(9) Cardoso, A. M., Clark, R. J . H., Moorehouse, S. J . Chem. Soc.,
Dalton Trans. 1980, 1156.
(10) Latham, I. A.; Leigh, G. J .; Huttner, G.; J ibril, I. J . Chem. Soc.
(D) 1986, 377-384.
(11) Rubenstahl, T.; Weller, F.; Harms, K.; Dehnicke, K. Z. Anorg.
Allg. Chem. 1994, 620, 1741-1749.

1444 Organometallics, Vol. 20, No. 7, 2001
Courtenay and Stephan
Syn th esis of Cp *Ta (NP R3)(η2-C2H4)Cl, R ) t-Bu 10, i-P r
11. These compounds were prepared in a similar fashion, and
thus only one preparation is detailed. To a suspension of 1
(200 mg, 0.313 mmol) in 5 mL of toluene was added EtMgCl
(0.314 mL, 2 M solution in ether) and stirred overnight. The
suspension was filtered, and the solvent evaporated, isolating
the reddish product in 63% yield: 1H NMR (C6D6) δ 2.35 (m,
|J 2H-H| ) 9.0 Hz, |J 3H-H| ) 12.5 Hz, |J 3H-H| ) 9.2 Hz, Ta(η2-
C2H4)), 1.94 (s, 15H, C5(CH3)5), 1.82 (m, |J 3H-H| ) 10.7 Hz,
NMR (CD2Cl2) δ -54.57 (s, 6F), -82.37 (s, 3F), -88.84 (s, 6F).
14: 1H NMR (CD2Cl2) δ 7.25 (m, br, (C6H5)3CCl), 2.44 (s, 15H,
C5(CH3)5), 1.58 (d, |J P-H| ) 14.7 Hz, 27H, PC(CH3)3); 13C{1H}
NMR (CD2Cl2) δ 145.58, 138.29, 131.47, 129.99 (s, (C6H5)3CCl),
128.13 (s, C5(CH3)5), 43.18 (d, |J P-C| ) 37.8 Hz, PC(CH3)3),
29.66 (s, PC(CH3)3), 12.62 (s, C5(CH3)5); 31P{1H} NMR (CD2-
Cl2) δ 74.68 (s); 11B NMR (CD2Cl2) δ -18.84 (s); 19F NMR (CD2-
Cl2) δ -55.78 (s, 8F), -86.45 (t, |J F-F| ) 20.3 Hz, 4F), -90.27
(s, 8F). 15: 1H NMR (CD2Cl2) δ 2.10 (s, 15H, C5(CH3)5), 1.51
(d, |J P-H| ) 14.0 Hz, 27H, PC(CH3)3), 0.44 (s, 9H, Ta-CH3);
13C{1H} NMR (CD2Cl2) δ 150-130 (br, B(C6F5)3), 121.85 (s, C5-
(CH3)5), 58.73 (s, Ta-CH3), 42.43 (d, |J P-C| ) 41.4 Hz, PC(CH3)3),
29.84 (s, PC(CH3)3), 11.86 (s, C5(CH3)5); 31P{1H} NMR (CD2-
Cl2) δ 66.62 (s); 11B NMR (CD2Cl2) δ -17.08 (s); 19F NMR (CD2-
Cl2) δ -55.44 (d, |J F-F| ) 20.0 Hz, 6F), -87.70 (t, |J F-F| ) 20.0
Hz, 3F), -90.23 (t, |J F-F| ) 19.1 Hz, 6F). 16: 1H NMR (CD2-
Cl2) δ 2.45 (m, 3H, PCH(CH3)2) 2.15 (s, 15H, C5(CH3)5), 1.38
(dd, |J P-H| ) 15.9 Hz, |J H-H| ) 7.2 Hz, 18H, PCH(CH3)2), 0.49
(s, 9H, Ta-CH3); 13C{1H} NMR (CD2Cl2) δ 150-130 (br,
B(C6F5)3), 121.68 (s, C5(CH3)5), 57.94 (s, Ta-CH3), 26.48 (d,
|J P-C| ) 54.4 Hz, PCH(CH3)2), 16.84 (s, PCH(CH3)2), 11.69 (s,
C5(CH3)5); 31P{1H} NMR (CD2Cl2) δ 58.30 (s); 11B NMR (CD2-
Cl2) δ -17.12 (s); 19F NMR (CD2Cl2) δ -55.91 (d, |J F-F| ) 20.6
Hz, 6F), -88.12 (t, |J F-F| ) 20.3 Hz, 3F), -90.68 (t, |J F-F| )
18.9 Hz, 6F). 17: 1H NMR (CD2Cl2) δ 2.13 (s, 15H, C5(CH3)5),
1.55 (d |J P-H| ) 14.0 Hz, 27H, PC(CH3)3), 0.48 (s, 6H, Ta-CH3);
13C{1H} NMR (CD2Cl2) δ 121.28 (s, C5(CH3)5), 58.12 (s, Ta-
CH3), 41.86 (d, |J P-C| ) 41.5 Hz, PC(CH3)3), 29.25 (s, PC(CH3)3),
11.25 (s, C5(CH3)5); 31P{1H} NMR (CD2Cl2) δ 66.68 (s); 11B NMR
(CD2Cl2) δ -19.06 (s); 19F NMR (CD2Cl2) δ -55.80 (s, 8F),
-86.46 (t, 18.0 Hz, 4F), -90.29 (s, 8F). 18: 1H NMR (CD2Cl2)
δ 7.30-7.11 (m, 15H, (C6H5)3CCH3) 2.44 (m, 3H, PCH(CH3)2)
2.19 (s, 3H, (C6H5)3CCH3) 2.14 (s, 15H, C5(CH3)5), 1.37 (dd
|J P-H| ) 15.9 Hz, |J H-H| ) 7.2 Hz, 18H, PCH(CH3)2), 0.49 (s,
6H, Ta-CH3); 13C{1H} NMR (CD2Cl2) (partial) δ 149.53, 129.07,
128.20, 126.31 (s(C6H5)3CCH3), 121.52 (s, C5(CH3)5), 57.81 (s,
Ta-CH3), 30.64 (s, (C6H5)3CCH3) 26.32 (d, |J P-C| ) 54.9 Hz,
PCH(CH3)2), 16.73 (s, PCH(CH3)2), 11.61 (s, C5(CH3)5); 31P{1H}
NMR (CD2Cl2) δ 58.28 (s); 11B NMR (CD2Cl2) δ - 18.79 (s);
19F NMR (CD2Cl2) δ - 55.75 (s, 8F), - 86.42 (t, 20.3 Hz, 4F),
|J 2H-H| ) 5.9 Hz, |J 3H-H| ) 9.2 Hz, Ta(η2-C2H4)), 1.68 (m, |J 3
|
H-H
) 10.0 Hz, |J 2H-H| ) 5.9 Hz, |J 3H-H| ) 12.5 Hz, Ta(η2-C2H4)),
1.11 (d, |J P-H| ) 13.1 Hz, 27H, PC(CH3)3), 0.79 (m, |J 3H-H| )
10.0 Hz, |J 3H-H| ) 10.7 Hz, |J 2H-H| ) 9.0 Hz, Ta(η2-C2H4)); 13C-
{1H} NMR (C6D6) δ 111.93 (s, C5(CH3)5), 57.31 (s, Ta(η2-C2H4)),
46.45 (s, Ta(η2-C2H4)), 41.00 (d, |J P-H| ) 46.3 Hz, PC(CH3)3),
29.67 (s, PC(CH3)3), 11.71 (s, C5(CH3)5); 31P{1H} NMR (C6D6)
δ 54.16 (s); 1H NMR (CD2Cl2)(partial) δ 1.88 (s, 15H, C5(CH3)5),
1.36 (d, |J P-H| ) 13.1 Hz, 27H, PC(CH3)3), 0.12 (m, Ta(η2-
C2H4)); 13C{1H} NMR (CD2Cl2) δ 111.98 (s, C5(CH3)5), 55.25(s,
Ta(η2-C2H4)), 45.45 (s, Ta(η2-C2H4)), 41.31 (d, |J P-H| ) 46.3 Hz,
PC(CH3)3), 29.57 (s, PC(CH3)3), 11.37 (s, C5(CH3)5); 31P{1H}
NMR (CD2Cl2) δ 54.85 (s). Anal. Calcd for C24H46ClNPTa: C,
48.36; H, 7.78; N, 2.35. Found: C, 48.57; H, 7.34; N, 2.35. 11:
58% yield. H NMR (C6D6) δ 2.29 (m, Ta(η2-C2H4)), 1.97 (s, 15H,
C5(CH3)5), 1.83 (m, Ta(η2-C2H4)), 1.71 (m, Ta(η2-C2H4)), 1.60
(m, 3H, PCH(CH3)2), 0.84 (dd, |J P-H| ) 14.8 Hz, |J H-H| ) 7.3
Hz, 9H, PCH(CH3)2), 0.83 (obscured, Ta(η2-C2H4)), 0.82 (dd,
|J P-H| ) 14.8 Hz, |J H-H| ) 7.3 Hz, 9H, PCH(CH3)2; 13C{1H}
NMR (C6D6) δ 115.75 (s, C5(CH3)5), 60.37 (s, Ta(η2-C2H4)), 49.90
(s, Ta(η2-C2H4)), 28.92 (d, |J P-H| ) 57.2 Hz, PCH(CH3)2), 20.31
(s, PCH(CH3)2), 15.35 (s, C5(CH3)5); 31P{1H} NMR (C6D6) δ
43.44 (s). Anal. Calcd for C21H40ClNPTa: C, 45.53; H, 7.28;
N, 2.53. Found: C, 45.40; H, 6.91; N, 2.34.
Syn th esis of Cp *Ta (NP t-Bu 3)(η2-C2H4)(CH2CH3), 12. To
a suspension of 10 (200 mg, 0.313 mmol) in 5 mL of toluene
was added EtMgCl (0.470 mL, 2 M solution in ether). The
suspension was stirred overnight, filtered, and evaporated to
dryness, giving the product as an orange, crystalline solid in
60% yield: 1H NMR (tol-d8) δ 2.02 (t, |J H-H| ) 7.6 Hz, Ta-
CH2CH3), 1.90 (s, 15H, C5(CH3)5), 1.71 (m, Ta(η2-C2H4)), 1.49
(m, |J H-H| ) 7.6 Hz, Ta-CH2CH3), 1.08 (m, Ta(η2-C2H4)), 1.08
(d, |J P-H| ) 12.9 Hz, 27H, PC(CH3)3), 0.73 (m, Ta(η2-C2H4)),
0.16 (m, Ta(η2-C2H4)); 13C{1H} NMR (tol-d8) δ 108.28 (s, C5-
(CH3)5), 48.40 (s, Ta(η2-C2H4)), 40.56 (d, |J P-C| ) 47.1 Hz,
PC(CH3)3), 33.17 (s, Ta(η2-C2H4)), 29.39 (s, PC(CH3)3), 27.40
(s, Ta-CH2CH3), 18.08 (s, Ta-CH2CH3), 11.38 (s, C5(CH3)5); 31P-
{1H} NMR (C6D6) δ 48.14 (s). Anal. Calcd for C26H51NPTa: C,
52.96; H, 8.72; N, 2.38. Found: C, 52.58; H, 8.22; N, 2.23.
Preliminary X-ray data: P21/c a ) 8.7750(2) Å, b ) 14.6401-
(3) Å, c ) 21.6376(5) Å, â ) 90.564(1)°, Z ) 4.
- 90.26 (t, 19.4 Hz, 8F). 19: 1H NMR (CD2Cl2) δ 7.25 (t, |J H-H
|
) 7.5 Hz, 2H, Ta-CH2(C6H5)), 7.01 (t, |J H-H| ) 7.5 Hz, 1H, Ta-
CH2(C6H5)), 6.90 (d, |J H-H| ) 7.5 Hz, 2H, Ta-CH2(C6H5)), 3.40
(d, |J H-H| ) 14.4 Hz, 1H, Ta-CH2(C6H5)) 2.59 (d, |J H-H| ) 14.4
Hz, 1H, Ta-CH2(C6H5)) 2.20 (s, 15H, C5(CH3)5), 1.50 (d, |J P-H
|
) 14.7 Hz, 27H, PC(CH3)3); 13C{1H} NMR (CD2Cl2) δ 150-
135 (br, B(C6F5)4), 141.97, 130.69, 128.62, 126.25 (s, Ta-CH2-
(C6H5)), 125.45(s, C5(CH3)5), 78.61 (s, Ta-CH2(C6H5)) 42.60 (d,
|J P-C| ) 39.3 Hz, PC(CH3)3), 29.70 (s, PC(CH3)3), 12.22 (s, C5-
(CH3)5); 31P{1H} NMR (CD2Cl2) δ 72.13 (s); 11B NMR (CD2Cl2)
δ -2.64 (br); 19F NMR (CD2Cl2) δ -54.00 (s, 6F), -82.38 (s,
br, 3F), -88.58 (s, 6F).
Gen er a t ion /Syn t h esis of [Cp *Ta (NP t-Bu 3)Cl2]A (A )
[ClB(C6F 5)3]- 13, [B(C6F 5)4]- 14), Cp *Ta (NP R3)Me2(MeB-
(C6F5)3) (R ) t-Bu 15, i-P r 16), [Cp*Ta(NP R3)Me2][B(C6F5)4]
(R ) t-Bu 17, i-P r 18), [Cp *Ta (NP t-Bu 3)Bn Cl][ClB(C6F 5)3],
19. These compounds were generated in similar NMR experi-
ments using the appropriate neutral precursor and either
B(C6F5)3 or [Ph3C][B(C6F5)4]; thus only one preparation is
detailed. To a solution of 3 (33 mg, 0.057 mmol) in CH2Cl2 was
added [Ph3C][B(C6F5)4] (53 mg, 0.057 mmol). The solution was
stirred for 1 h, the solvent removed, and the residue washed
several times with hexanes. The solid was recrystallized to
give 17 in 68% yield. In cases where the products were only
generated in solution, the reactions were monitored by NMR
spectroscopy. The extreme sensitivity of these species pre-
cluded satisfactory elemental analysis; 1H NMR spectra of
these species have been deposited as supplementary data. 13:
1H NMR (CD2Cl2) δ 2.44 (s, 15H, C5(CH3)5), 1.57 (d, |J P-H| )
14.7 Hz, 27H, PC(CH3)3); 13C{1H} NMR (CD2Cl2) δ 150-130
(br, B(C6F5)3), 128.13 (s, C5(CH3)5), 43.17 (d, |J P-C| ) 37.8 Hz,
PC(CH3)3), 29.66 (s, PC(CH3)3), 12.64 (s, C5(CH3)5); 31P{1H}
Syn th esis of [Cp *Ta (NP t-Bu 3)(Cl)(CH2CH2CP h 3)]A (A
) [B(C6F 5)4] 20, BF 4 21). These compounds were generated
in similar NMR experiments using the appropriate neutral
precursor and either Ph3C[B(C6F5)4] or Ph3C[BF4]; thus only
one preparation is detailed. To a solution of 10 (30 mg, 0.050
mmol) in CD2Cl2 was added Ph3C[B(C6F5)4] (46 mg, 0.050
mmol). Evaporation of the solvent yielded the product in
quantitative yield. The extreme sensitivity of this species
precluded satisfactory elemental analysis; 1H NMR spectra of
these species have been deposited as supplementary data. 20:
1H NMR (CD2Cl2) δ 7.30-7.18 (m, 15H, CH2C(C6H5)3) 3.11 (m,
TaCH2CH2CPh), 2.90 (m, TaCH2CH2CPh) 2.22 (m, TaCH2CH2-
CPh), 2.12 (s, 15H, C5(CH3)5), 1.46 (d |J P-H| ) 14.4 Hz, 27H,
PC(CH3)3) 1. 02 (m, TaCH2CH2CPh); 13C{1H} NMR (CD2Cl2)
δ 146.72, 129.57, 128.38, 126.59 (s, CH2C(C6H5)3)) 124.88 (s,
C5(CH3)5), 70.65 (s, TaCH2CH2CPh), 62.48 (s, TaCH2CH2CPh),
42.72 (d, |J P-C| ) 14.1 Hz, PC(CH3)3), 42.29 (s, TaCH2CH2-
CPh), 29.74 (s PC(CH3)3), 12.13 (s, C5(CH3)5); 31P{1H} NMR
(CD2Cl2) 71.06 (s); 11B NMR (CD2Cl2) δ -22.88 (s); 19F NMR
NMR (CD2Cl2) δ 74.69 (s); 11B NMR (CD2Cl2) δ -0.16 (br); 19
F

Tantalum-Phosphinimide Complexes
Organometallics, Vol. 20, No. 7, 2001 1445
Ta ble 1. Cr ysta llogr a p h ic P a r a m eter s
1
3
5
7
9
10
22
formula
fw
a (Å)
b (Å)
c (Å)
C22H42Cl3NPTa C25H51NPTa C29H49 Cl2NPTa C36H55NPTa C37H56NPTa C24H46ClNPTa C42H46BClF15NTa
638.84
577.59
694.51
713.73
726.75
595.99
16.9128(2)
14.853
21.16780(10)
90.00
90.00
90.00
Orthorhombic
Pbca
5317.51(7)
1.489
1107.98
9.667(3)
19.373(7)
11.920(2)
90.00
92.20(3)
90.00
monoclinic
P21
8.6056(9)
14.8186(16)
20.613(4)
90.00
90.00
90.00
orthorhombic
P212121
2628.6(6)
1.614
8.5530(12)
17.7655(15)
17.775(3)
90.00
96.635(13)
90.00
monoclinic
P21/c
2682.7(6)
1.430
10.9948(5)
19.1989(8)
15.0970(6)
90.00
91.8000(10)
90.00
monoclinic
P21/n
3185.2(2)
1.448
12.1887(17)
17.329(5)
16.950(2)
90.00
103.290(10)
90.00
monoclinic
P21/c
3484.2(12)
1.361
11.668(16)
12.359(18)
13.053(13)
87.37(10)
71.97(9)
74.65(12)
Triclinic
P1h
R (deg)
â (deg)
γ (deg)
cryst syst
space group
vol (Å3)
Dcalcd
1725(4)
1.399
2230.6(12)
1.650
(g cm-1
)
Z
4
4
4
4
2
8
2
abs coeff, µ
4.556
4.167
3.686
3.223
3.257
4.305
2.654
(mm-1
)
no. of data
collected
no. of data
Fo2>3σ(F
no. of
3564
1561
138
13 620
4689
253
16 302
5576
307
17 008
6093
352
9115
5946
361
25 136
4676
253
4440
4100
359
2
)
o
variables
R (%)
Rw (%)
goodness
of fit
0.0499
0.1519
1.432
0.0288
0.0950
0.834
0.0381
0.0955
1.011
0.0351
0.0857
0.625
0.0281
0.0883
0.746
0.0351
0.0883
1.028
0.0735
0.1392
1.224
All data collected at 24 °C with Mo KR radiation (λ ) 0.71069 Å), R ) ∑||Fo| - |Fc||/∑|Fo|, Rw ) [∑[ω(Fo - Fc2)2]/∑[wFo2)2]]0.5
.
a
2
(CD2Cl2) δ -40.41 (s, 8F), -71.11 (t, 17.7 Hz, 4F), -74.89 (d,
16.0 Hz, 8F). 21: 1H NMR (CD2Cl2) δ 7.30-7.18 (m, 15H,
CH2C(C6H5)3), 3.09 (m, TaCH2CH2CPh), 2.90 (m, TaCH2CH2-
CPh), 2.21 (m, TaCH2CH2CPh), 2.14 (s, 15H, C5(CH3)5), 1.47
(d |J P-H| ) 14.4 Hz, 27H, PC(CH3)3), 1. 01 (m, TaCH2CH2CPh);
13C{1H} NMR (CD2Cl2) δ 146.73, 129.39, 128.39, 126.62 (s,
CH2C(C6H5)3)), 124.91 (s, C5(CH3)5), 70.51 (s, TaCH2CH2CPh),
62.48 (s, TaCH2CH2CPh), 42.59 (d, |J P-C| ) 14.1 Hz, PC(CH3)3),
42.63 (s, TaCH2CH2CPh), 29.81 (s PC(CH3)3), 12.27 (s, C5-
(CH3)5); 31P{1H} NMR (CD2Cl2) 71.23 (s); 11B NMR (CD2Cl2) δ
-7.35 (s); 19F NMR (CD2Cl2) δ -60.54 (s, 4F).
Syn t h esis of [Cp *Ta (NP t-Bu 3)(Cl)(CH 2CH2B(C6F 5)3)],
22. To a solution of 10 (50 mg, 0.084 mmol) in CD2Cl2 was
added B(C6F5)3 (43 mg, 0.084 mmol). Evaporation of solvent
gave the crystalline product in quantitative yield: 1H NMR
(CD2Cl2) δ 2.54 (br m, TaCH2CH2B), 2.28 (m, TaCH2CH2CB),
using the SHELXTL solution package operating on a Pentium
computer.
St r u ct u r e Solu t ion a n d R efin em en t . Non-hydrogen
atomic scattering factors were taken from the literature
tabulations.12 The heavy atom positions were determined using
direct methods employing either the SHELXTL or direct
methods routines. The remaining non-hydrogen atoms were
located from successive difference Fourier map calculations.
The refinements were carried out by using full-matrix least-
squares techniques on F, minimizing the function w(|F o| -
|Fc|)2 where the weight w is defined as 4Fo2/2σ(Fo2) and Fo and
Fc are the observed and calculated structure factor amplitudes.
In the final cycles of each refinement, all non-hydrogen atoms
were assigned anisotropic temperature factors. Carbon bound
hydrogen atom positions were calculated and allowed to ride
on the carbon to which they are bonded assuming a C-H bond
length of 0.95 Å. Hydrogen atom temperature factors were
fixed at 1.10 times the isotropic temperature factor of the
carbon atom to which they are bonded. The hydrogen atom
contributions were calculated, but not refined. For chiral space
groups, the correct enantiomorph was confirmed by data
inversion and refinement. The final values of refinement
parameters are given in Table 1. The locations of the largest
peaks in the final difference Fourier map calculation as well
as the magnitude of the residual electron densities in each case
were of no chemical significance. Positional parameters,
hydrogen atom parameters, thermal parameters, and bond
distances and angles have been deposited as Supporting
Information.
2.11 (s, 15H, C5(CH3)5), 1.78 (br m, TaCH2CH2B), 1.50 (d |J P-H
|
) 14.4 Hz, 27H, PC(CH3)3), 1.27 (m, TaCH2CH2B); 13C NMR
(CD2Cl2) (partial) δ 150-130 (br, B(C6F5)3) 122.77 (s, C5(CH3)5),
82.62 (s, TaCH2CH2), 42.35 (d, |J P-C| ) 42.0 Hz, PC(CH3)3),
29.71 (s, PC(CH3)3), 11.99 (s, C5(CH3)5); 31P NMR (CD2Cl2) δ
68.03 (s); 11B NMR (CD2Cl2) δ -17.66 (s). 19F NMR (CD2Cl2) δ
-38.65 (s, 8F), -71.40 (t, 17.4 Hz, 4F), -74.59 (s, 8F). Anal.
Calcd for C42H46BClF15NPTa‚2CH2Cl2: C, 41.36; H, 3.94; N,
1.09. Found: C, 40.22; H, 3.67; N, 1.10.
X-r a y Da ta Collection a n d Red u ction . X-ray quality
crystals were obtained as described above. The crystals were
manipulated and mounted in capillaries in a glovebox, thus
maintaining a dry, O2-free environment for each crystal.
Diffraction experiments were performed either on a Rigaku
AFC6 four-circle or a Siemens SMART System CCD diffrac-
Resu lts a n d Discu ssion
tometer. In the later case the data were collected in
a
hemisphere of data in 1329 frames with 10 s exposure times.
Crystal data are summarized in Table 1. The observed
extinctions were consistent with the space groups in each case.
The data sets were collected (4.5° < 2θ < 45-50.0°). A measure
of decay was obtained by re-collecting the first 50 frames of
each data set. The intensities of reflections within these frames
showed no statistically significant change over the duration
of the data collections. The data were processed using the
SAINT and XPREP processing package. An empirical absorp-
tion correction based on redundant data was applied to each
data set. Subsequent solution and refinement was performed
Refluxing stoichiometric mixtures of Cp*TaCl4 and
the phosphinimines R3PNSiMe3 in toluene for 6 h
affords the complexes Cp*Ta(NPR3)Cl3 (R ) t-Bu 1, i-Pr
1
2) in 77-80% isolated yields (Scheme 1). H, 13C{1H},
and 31P{1H} NMR data were consistent with these
formulations. In addition the nature of 1 was confirmed
by X-ray crystallographic methods (Figure 1). The Ta-
Cl distances range from 2.437(5) to 2.449(5) Å, while
(12) Cromer, D. T.; Mann, J . B. Acta Crystallogr. A 1968, A24, 390.

1446 Organometallics, Vol. 20, No. 7, 2001
Courtenay and Stephan
F igu r e 2. The tert-butyl group resonances region of the
1H NMR spectrum of 1 as a function of temperature.
F igu r e 1. ORTEP drawings of 1, 30% thermal ellipsoids
are shown. Hydrogen atoms have been omitted for clarity.
Selected bond distances (Å) and angles (deg): Ta(1)-N(1)
1.870(13), Ta(1)-Cl(1) 2.437(5), Ta(1)-Cl(2) 2.440(5),
Ta(1)-Cl(3) 2.449(5), P(1)-N(1) 1.585(14), N(1)-Ta(1)-Cl-
(1) 127.8(4), N(1)-Ta(1)-Cl(2) 89.4(4), N(1)-Ta(1)-Cl(3)
87.0(4), Cl(1)-Ta(1)-Cl(2) 78.7(2), Cl(1)-Ta(1)-Cl(3)
78.8(2) Cl(2)-Ta(1)-Cl(3) 148.22(19), P(1)-N(1)-Ta(1)
165.7(8).
1
Variable-temperature H NMR studies of 1 reveal a
temperature dependence of the resonances associated
with the t-Bu groups. Upon cooling, the resonances
attributable to the methyl groups broaden and split into
two peaks in a ratio of 2:1. The coalescence occurs at
approximately -40 °C. These observations are consis-
tent with restricted rotation about the Ta-N bond. The
temperature dependence infers a cogwheel effect of the
phosphinimide substituents and the pentamethylcyclo-
pentadienyl group. The 2:1 intensities of the resonances
are consistent with mirror molecular symmetry. Upon
further cooling of 1, the more intense of these reso-
nances broadens and splits into three signals at -85
°C (Figure 2). These data suggest that the lower energy
process involves inhibited rotation of the tert-butyl
groups, presumably a secondary result of the cogwheel
effect. Analysis of these complex processes for kinetic
and thermodynamic data was not performed, as these
processes are neither independent nor simple two-site
exchange. In contrast, while cooling of a solution of 2
results in a broadening of the methyl resonance, the
signal does not split into separate resonances upon
cooling to -90 °C.
Sch em e 1
Alkylation of 1 and 2 have been studied (Scheme 1).
Reaction with MeLi afforded the yellow-white complexes
Cp*Ta(NPR3)Me3 (R ) t-Bu 3, i-Pr 4) in 72 and 84%
isolated yield, respectively. X-ray structural data con-
firms the similarity of the molecular geometries of 3 and
1 (Figure 3). Stoichiometric alkylation of 1 with BnMgCl
gives the yellow-orange species Cp*Ta(NPt-Bu3)(CH2-
Ph)Cl2, 5. The NMR data are consistent with the
formation of only one isomer of this species, and X-ray
data affirm that the benzyl group replaces the central
chloride of 1, thus yielding the isomer of 5 with mirror-
symmetry (Figure 4). The Ta-N distance in 5 (1.882(4)
Å) is similar to that seen in 1 and 3. The Ta-C and
Ta-Cl distances of 2.309(5) and 2.4576(13) Å in 5 are
slightly longer than those seen in 3. These observations
are consistent with the presence of a benzyl substituent,
which is electron poor compared to a methyl group but
more electron donating than a chloride.
Further alkylation of 5 is readily achieved by reaction
with MeLi. This affords the species Cp*Ta(NPt-Bu3)(CH2-
Ph)Me2, 6. In contrast, reaction of 1 and 2 with greater
than 1 equiv of BnMgCl affords the alkylidene species
Cp*Ta(NPR3)(CHPh)(CH2Ph) (R ) t-Bu 7, i-Pr 8). These
species exhibit the characteristic 1H NMR shift for the
alkylidene proton at 9.13 and 8.40 ppm and the 13C
resonances for the alkylidene carbons at 213.1 and 222.9
ppm, respectively. The formulations of these compounds
the Ta-N distance is 1.870(13) Å. This compares with
Ta-N distances of 1.801(3) Å seen in [TaCl4(NPt-
13
Bu3)3]2 and is slightly shorter than those seen in
[TaCl2(NP(NMe2)3)3].14 The geometry about Ta mimics
that seen in Cp*2TaCl3 in that the three chlorine atoms
are approximately coplanar with the larger Cl-Ta-Cl
angle of 148.22(19)° and the smaller Cl-Ta-Cl angles
of 78.7(2)°. The geometry within the phosphinimide
ligand is similar to that seen in other early metal
phosphinimide complexes with P-N and Ta-N dis-
tances of 1.585(14) and 1.870(13) Å, respectively, and a
P-N-Ta angle of 165.7(8)°. This geometry of the
phosphinimide ligand is not unlike those seen in Ti-
phosphinimide complexes,2-5,7 although the metal-N
distance is longer, as expected.
(13) Bezler, H.; Strahle, J . Z. Naturforsch. B 1983, 38, 317-320.
(14) Weber, K.; Korn, K.; Schulz, M.; Korth, K.; Sundermeyer, J . Z.
Anorg. Allg. Chem. 1999, 625, 1315-1320.

Tantalum-Phosphinimide Complexes
Organometallics, Vol. 20, No. 7, 2001 1447
F igu r e 5. ORTEP drawings of 7, 30% thermal ellipsoids
are shown. Hydrogen atoms have been omitted for clarity.
Selected bond distances (Å) and angles (deg): Ta(1)-N(1)
1.877(5), Ta(1)-C(30) 1.957(7), Ta(1)-C(23) 2.235(7), P(1)-
N(1) 1.593(5), N(1)-Ta(1)-C(30) 105.0(3), N(1)-Ta(1)-
C(23) 94.6(2), C(30)-Ta(1)-C(23) 101.2(3), P(1)-N(1)-
Ta(1) 169.7(4).
F igu r e 3. ORTEP drawings of 3, 30% thermal ellipsoids
are shown. Hydrogen atoms have been omitted for clarity.
Selected bond distances (Å) and angles (deg): Ta(1)-N(1)
1.902(3), Ta(1)-C(23) 2.257(4), Ta(1)-C(25) 2.259(5),
Ta(1)-C(24) 2.280(5), P(1)-N(1) 1.579(3), N(1)-Ta(1)-
C(23) 89.04(15), N(1)-Ta(1)-C(25) 89.13(16), C(23)-
Ta(1)-C(25) 139.5(2), N(1)-Ta(1)-C(24) 124.31(18), C(23)-
Ta(1)-C(24) 73.5(2), C(25)-Ta(1)-C(24) 74.3(3), P(1)-
N(1)-Ta(1) 169.8(2).
F igu r e 6. ORTEP drawings of 9, 30% thermal ellipsoids
are shown. Hydrogen atoms have been omitted for clarity.
Selected bond distances (Å) and angles (deg): Ta(1)-N(1)
1.898(5), Ta(1)-C(24) 2.186(5), Ta(1)-C(31) 2.272(5),
Ta(1)-C(23) 2.299(5), P(1)-N(1) 1.597(4), C(23)-C(24)
1.458(-6), N(1)-Ta(1)-C(24) 99.4(2), N(1)-Ta(1)-C(31)
99.1(2), C(24)-Ta(1)-C(31) 114.38(18), N(1)-Ta(1)-C(23)
119.75(18), C(24)-Ta(1)-C(23) 37.83(17), C(31)-Ta(1)-
C(23) 79.11(19), P(1)-N(1)-Ta(1) 168.7(2).
F igu r e 4. ORTEP drawings of 5, 30% thermal ellipsoids
are shown. Hydrogen atoms have been omitted for clarity.
Selected bond distances (Å) and angles (deg): Ta-N(1)
1.882(4), Ta-C(23) 2.309(5), Ta-Cl(2) 2.4572(13), Ta-Cl-
(1) 2.4580(12), P(1)-N(1) 1.614(4), N(1)-Ta-C(23)
128.85(18), N(1)-Ta-Cl(2) 87.99(12), C(23)-Ta-Cl(2)
77.69(14), N(1)-Ta-Cl(1) 88.76(12), C(23)-Ta-Cl(1)
78.22(14), P(1)-N(1)-Ta 169.6(3).
tively. The Ta-benzyl carbon distance is 2.235(7) Å,
which is slightly shorter than that seen in 3 or 5,
consistent with both steric accessibility and electronic
deficiency of the Ta center.
The alkylidene species 7 and 8 were remarkably
robust. In refluxing d8-toluene, there is no evidence of
benzyl exchange. Moreover, these species fail to react
with a variety of other reagents including AlMe3, MeLi,
PhCN, acetylenes, and olefins. In addition, in contrast
to the reactivity of the metallocene alkylidene species
Cp2TaMe(CH2), 7 or 8 show no reactivity with B(C6F5)3.21
These observations seem to imply that the electron
deficiency of the Ta center diminishes the nucleophilic
nature of the alkylidene.
However, 7 did undergo reaction with methyl iodide
in benzene upon heating for 2 h. NMR data revealed a
complex mixture of products; however, one of these
products was isolated as red-brown crystals upon stand-
ing of the solution for 1 week. The product 9 was isolated
in 19% yield and characterized by X-ray crystallography.
These data confirmed that 9 was the species Cp*Ta-
(NPt-Bu3)(η2-CHPhCH2)(CH2Ph) (Figure 6). The struc-
tural data show that newly formed styrene-Ta metal-
lacycle and the remaining benzyl carbon are approxi-
are also supported by the X-ray structural determina-
tion of 7 (Figure 5). The akylidene ligand gives rise to
a relatively short Ta-C distance of 1.957(7) Å, compared
to the Ta-C bond lengths of 2.09(2), 2.030(6), 2.026-
(10), 1.860(11), and 1.883(14) Å seen in [PhP(CH2SiMe2-
NSiMe2CH2)2PPhTaMe(CH2)],15 [Cp2TaCl(CHt-Bu)],16
[Cp2TaMe(CH2)],17,18 [TaCl2(CHt-Bu)(Me2NCH2CH2N-
(Me)CH2C6H4)],19 and Cp*Ta(CH2Ph)2(CHPh),20 respec-
(15) Fryzuk, M. D.; J ohnson, S. A.; Rettig, S. J . Organometallics
1999, 18, 4059-4067.
(16) Churchill, M. R.; Hollander, F. J .; Schrock, R. R. J . Am. Chem.
Soc. 1978, 100, 647-648.
(17) Schrock, R. R.; Sharp, P. R. J . Am. Chem. Soc. 1978, 100, 2389-
2399.
(18) Schrock, R. R.; Messerle, L. W.; Wood, C. D.; Guggenberger, L.
J . J . Am. Chem. Soc. 1978, 100, 3793-3800.
(19) Rietveld, M. H. P.; Teunissen, W.; Hagen, H.; Water, L. V. D.;
Grove, D. M.; Schaaf, P. A. V. D.; Muhlebach, A.; Kooijman, H.; Smeets,
W. J . J .; Veldman, N.; Spek, A. L.; Koten, G. V. Organometallics 1997,
16, 1674-1684.
(20) Messerle, L. W.; J ennische, P.; Schrock, R. R.; Stucky, G. J .
Am. Chem. Soc. 1980, 102, 6744-6752.
(21) Cook, K. S.; Piers, W. E.; Rettig, S. J .; McDonald, R. Organo-
metallics 2000, 19, 2243-2245.

1448 Organometallics, Vol. 20, No. 7, 2001
Courtenay and Stephan
F igu r e 8. ORTEP drawings of 10, 30% thermal ellipsoids
are shown. Hydrogen atoms have been omitted for clarity.
Selected bond distances (Å) and angles (deg): Ta(1)-N(1)
1.873(4); Ta(1)-C(23) 2.220(7); Ta(1)-C(24) 2.313(5);
Ta(1)-Cl(1)2.455(2); P(1)-N(1) 1.603(4); C(23)-C(24)
1.464(13); N(1)-Ta(1)-C(23) 109.5(3); N(1)-Ta(1)-C(24)
94.3(2); C(23)-Ta(1)-C(24) 37.6(3); C(23)-Ta(1)-Cl(1)
86.1(4); C(24)-Ta(1)-Cl(1) 122.4(2); P(1)-N(1)-Ta(1)
170.9(3); C(24)-C(23)-Ta(1) 74.6(4); C(23)-C(24)-Ta(1)
67.7(4).
1
F igu r e 7. Methylene proton resonances region of the H
NMR spectrum of 10.
fragment are comparable to those seen in Ta(Ot-Bu)2-
(CHt-Bu)(Me2NCH2CH2N(Me)CH2C6H4).19
mately coplanar. The central carbon is the substituted
carbon of the styrene fragment with the phenyl ring
oriented down away from the Cp* ligand. The Ta-C
distances within the metallacycle are 2.186(5) and
2.299(5) Å, while the Ta-C distance for the benzyl group
is 2.272(5) Å.
The formation of 9 presumably results from the
nucleophilic attack of methyliodide by the alkylidene
with the presumed loss of HI. Loss of toluene with the
formation of Cp*Ta(NPt-Bu3)(η2-CHPhCH2)(I) was an-
ticipated based on the analogy to the work of Schrock
et al.18 While the formation of some toluene is indeed
evidenced by the appearance of toluene resonances in
the 1H NMR spectra of the reaction mixture, the Ta-
iodide complex was separable. Geometric isomers of 9
and the Ta-iodide species may account for additional
products evidenced by the 31P NMR spectra of the
reaction mixture.
Alkylation of 1 and 2 with 2 equiv of EtMgCl results
in â-hydrogen elimination and formation of the com-
plexes Cp*Ta(NPR3)(η2-C2H4)Cl (R ) t-Bu 10 and i-Pr
11) in 63 and 58% yield, respectively. The 1H NMR
spectra for these compounds revealed four complex
signals for the ethylene protons, as each of the protons
are chemically inequivalent, exhibiting resonances cen-
tered at 2.4, 1.9, 1.8, and 0.9 ppm. In the case of 10, a
series of NMR experiments, including 1H-13C HET-
COR, NOESY, and COSY, were employed to assign the
resonances to the respective protons. In addition, the
ethylene resonances were simulated using the reported
coupling constants (Figure 7). It is important to note
that these resonances are temperature invariant, af-
firming a rigid metallocyclic structure and consistent
with a Ta(V) formulation. The structure of 10 was
confirmed crystallographically as well (Figure 8). The
Ta-C distances within the metallacycle are 2.220(7) and
2.313(5) Å, which is slightly longer than the correspond-
ing distances in 9. This is consistent with the presence
of the relatively electron-rich ancillary chloride ligand.
The metric parameters of this metallocyclopropane
Further reaction of 10 with EtMgCl affords Cp*Ta-
(NPt-Bu3)(η2-C2H4)(CH2CH3), 12, in 60% yield. While
the NMR data are consistent with the formulation, the
1H NMR spectrum of 12 is complex. Each of the
methylene protons are chemically inequivalent, as they
are in 10. Furthermore, HETCOR and COSY experi-
ments revealed that the resonances for the tert-butyl
groups overlap with one of the protons of the ethylene
fragment. Variable-temperature NMR studies of 12
showed no evidence of proton migration and ethylene-
ethyl group interchange. While crystallographic data
confirmed the formulation of 12, the quality of the
solution was poor. Repeated attempts to obtain better
crystals were unsuccessful.
Ca tion ic Com p lexes. The generation of a variety of
zwitterionic and cationic complexes has been studied
(Scheme 2). Reaction of 1 with 1 equiv of B(C6F5)3
results in chloride abstraction and initial generation of
the salt [Cp*Ta(NPtBu3)Cl2][ClB(C6F5)3], 13, as evi-
denced by a downfield shift in the 31P NMR by 11 ppm.
1H, 13C, 11B, and 19F NMR spectroscopy are also
consistent with formation of 13. The resulting anion
[ClB(C6F5)3]- is not stable in CD2Cl2 over prolonged
periods of time. 19F NMR spectra showed resonances
attributable to at least three different species including
[B(C6F5)4]- in solution after 24 h. This is consistent with
substituent redistribution affording several borate an-
ions. The analogous reaction with Ph3C[B(C6F5)4] af-
fords the related salt [Cp*Ta(NPtBu3)Cl2][B(C6F5)4], 14.
Decker and co-workers8 have recently structurally
characterized the related salt [Cp*Ta((i-PrN)2CMe)Cl2]-
SbF6, while Bercaw et al.22 have examined the chem-
istry of cationic Ta-imido complex [Cp*2Ta(NCMe3)-
(THF)][B(C6F5)4].
Generation of the zwitterionic species Cp*Ta(NPR3)-
Me2(MeB(C6F5)3) (R ) t-Bu 15, i-Pr 16) via reaction of
(22) Blake, R. E.; Antonelli, D. M.; Henling, L. M.; Schaefer, W. P.;
Hardcastle, K. I.; Bercaw, J . E. Organometallics 1998, 17, 718-725.

Tantalum-Phosphinimide Complexes
Organometallics, Vol. 20, No. 7, 2001 1449
Sch em e 2
F igu r e 9. ORTEP drawings of 22, 30% thermal ellipsoids
are shown. Hydrogen atoms have been omitted for clarity.
Selected bond distances (Å) and angles (deg): Ta(1)-N(1)
1.818(16); Ta(1)-C(23) 2.10(3); Ta(1)-C(2) 2.32(4); Ta(1)-
Cl(1) 2.342(4); Ta(1) C(1) 2.37(3); Ta(1)-C(3) 2.47(3);
Ta(1)-C(5) 2.46(3); Ta(1)-C(4) 2.54(3); P(1)-N(1)
1.639(18); N(1)-Ta(1)-C(23) 100.5(10); N(1)-Ta(1)-Cl(1)
102.5(5); C(23)- Ta(1)-Cl(1) 112.4(9); P(1)-N(1)-Ta(1)
171.2(11); C(24)-C(23)-Ta(1) 103(2); C(23)-C(24)-B(1)
115(2).
is consistent with the formulation of 20 as the cationic
complex [Cp*Ta(NPt-Bu3)(Cl)(CH2CH2CPh3)][B(C6F5)4].
In a similar manner [Cp*Ta(NPt-Bu3)(Cl)(CH2CH2-
CPh3)][BF4], 21, is formed via reaction of 10 with Ph3-
CBF4.
3 or 4 with B(C6F5)3 is consistent with the downfield
1
31P NMR chemical shifts for 15 and 16. H NMR data
show single resonances attributable to the nine methyl
protons. Despite cooling to -80 °C, no appreciable
broadening or splitting of these resonances was ob-
served. This suggests a dynamic exchange process that
is rapid on the NMR time scale and results in the
interchange of Ta and B bound methyl groups. The
analogous reaction of 3 and 4 with Ph3C[B(C6F5)4]
affords the related salts [Cp*Ta(NPR3)Me2][B(C6F5)4] (R
) t-Bu 17, i-Pr 18). The formation of these products is
unequivocally established by NMR spectroscopy. In a
similar manner, 17 can be generated by treatment of 6
with Ph3C[B(C6F5)4]. A related Ta-methyl cation, [Cp*-
TaMe(MeN(C6H3Me)2NSiMe3)]I, has been recently struc-
turally characterized by Gountchev and Tilley.23
The analogous reactions of 5 with B(C6F5)3 and Ph3C-
[B(C6F5)4] were also performed. In the case of the borane
reaction, chloride abstraction results in the formation
of the salt [Cp*Ta(NPt-Bu3)BnCl][ClB(C6F5)3], 19. This
is evidenced by NMR spectral data. For example, the
benzylic protons of 19 give rise to an AB quartet for the
diastereotopic protons. In contrast, the trityl borate
attacks the Ta-benzyl bond, affording 14 and Ph3CCH2-
Ph. The differing reaction pathways for these two
reagents are presumably a result of the relative bond
strengths of B-Cl versus B-C and C-C versus C-Cl
bonds.
Treatment of 10 with [Ph3C][B(C6F5)4] results in a
downfield shift of about 16 ppm in the 31P NMR
resonance. The new species 20 also exhibits downfield
shifts for the Cp*, t-Bu, and ethylene resonances in the
1H NMR spectrum. The ethylene carbons are also
shifted, one being 15 ppm downfield and the other 3
ppm upfield from the corresponding resonances in 10.
11B, 19F, 1H-NOESY, COSY, HETCOR, and gradient
HMBC provided data that confirmed the long-range
carbon-hydrogen connectivities, establishing that the
ethylene protons are adjacent to the trityl group. This
In an analogous manner, treatment of 10 with 1 equiv
of B(C6F5)3 in CD2Cl2 results in the formation of a new
1
species 22. 31P, H, 13C, 11B, and 19F NMR spectra are
consistent with the formation of a zwitterionic complex.
Small yellow crystals were obtained upon standing of
the solution. X-ray crystallographic study confirmed the
formulation of 22 as the zwitterionic species [Cp*Ta-
(NPt-Bu3)(Cl)(CH2CH2B(C6F5)3)] (Figure 9). Attack of
the metallocyclopropane ring of 10 by the borane results
in an ethylene tether between the anionic borate and
cationic tantalum centers, which are 4.427 Å apart.
While the remaining metric parameters are unexcep-
tional, it is noteworthy that one of the hydrogen atoms
on the â-methylene carbon is 2.728 Å from Ta in the
plane of the chloride and C(23). Although this approach
in the solid state suggests a weak agostic interaction,
NMR data show that this interaction does not persist
in solution. This is in contrast to the strong R-agostic
interactions observed in the related complexes Cp2-
TaMe(CH2B(C6F5)3) and [Cp2Zr(PPh2Me)CH2CH2B-
(C6F5)3] recently described by Piers et al.21,24 Analogous
â-interactions are thought to precipitate â-hydrogen
elimination in related group IV metal species.
Consideration of the above chemistry of pentameth-
ylcyclopentadienyl-tantalum-phosphinimide complexes
affords some general observations regarding the effect
of the use of phosphinimide ligands. In the present Ta
chemistry, Ta-alkyl and -alkylidene species appear less
reactive than the corresponding tantalocene analogues.
This is attributed to greater Lewis acidity at the metal
center as a result of replacement of a cyclopentadienyl
ligands with a bulky phosphinimide ligand. However,
it is interesting to contrast the absence of â-agostic-H
interactions with the metal center in zwitterionic and
cationic alkyl Ta phosphinimide complexes with the
(23) Gountchev, T. I.; Tilley, T. D. J . Am. Chem. Soc. 1997, 119,
12831-12841.
(24) Sun, Y. M.; Piers, W. E.; Rettig, S. J . Chem. Commun. 1998,
127-128.

1450 Organometallics, Vol. 20, No. 7, 2001
Courtenay and Stephan
presence of such interactions in analogous tantalocene
and zirconocene species. This apparently conflicting
observation suggests the LUMO responsible for the
Lewis acidity is not appropriately directed for inter-
action with groups in the plane orthogonal to the CpM-
(NPR3) fragment. This view is consistent with recent
solid state EPR studies of [CpTi(NPR3)µ-Cl]2, which
suggest the LUMO of the CpTi(NPR3) fragments is
compounds have been employed to synthesize a number
of zwitterionic and cationic complexes. Reactivity of
these species as well as the effect of phosphinimide
ligands on the chemistry of other metals continue to be
subjects of study.
Ack n ow led gm en t . Financial support from the
NSERC of Canada and NOVA Chemicals Corporation
is gratefully acknowledged.
2
2
primarily dz -x in character in contrast with the corre-
sponding LUMO of the Cp2M fragments, which is
principally dz in nature.7
2
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
and 1H NMR data. This material is available free of charge
via the Internet at http://pubs.acs.org.
Su m m a r y
A series of neutral tantalum phosphinimide com-
plexes have been prepared and characterized. These
OM0009785