Reduction of titanium(IV)-phosphinimide complexes: Routes to Ti(III) dimers, Ti(IV)-metallacycles, and Ti(II) species

Article abstract of DOI:10.1021/om049826q

The redox chemistry of phosphinimide-containing group IV metal complexes has been investigated. Reaction of the simple phosphinimide species CpTi(NPR₃)Cl₂ (R = Me 1, i-Pr 2) with Mg affords complexes formulated as [CpTiCl(μ-NPR₃)]₂ (R = Me 3, i-Pr 4). In contrast, CpTi(NPt-Bu₃)Cl₂ (5) is reduced by Mg to a putative Ti(II) species that can be intercepted by a variety of reagents including 2,3-dimethyl-1,3-butadiene, diphenylacetylene, phenylacetylene, bis(trimethylsilyl)acetylene, ethylene, and propylene to give monometallic metallacyclic complexes. In this fashion, the Ti(IV) metallacycles CpTi(NPt-Bu₃)(CH₂C(Me)C(Me)CH₂), 6, CpTi(NPt-Bu₃)(CPh)₄, 7, CpTi(NPf-Bu₃)(C(Ph) CHC(Ph)CH), 8, CpTi(NPt-Bu₃)(η²-C ₂(SiMe₃)₂), 9, CpTi(NPt-Bu₃)(CH ₂)₄, 10, CpTi(NPt-Bu₃)(CH₂CHMe) ₂, 15, and CpTi(NPt-Bu₃)(CH₂) ₂(CPh)₂, 16, were prepared. Related intramolecular formation of metallacycle complexes was achieved upon reduction of Cp′Ti(t-Bu₂(2-C₆H₄Ph)PN)Cl₂ (Cp′ = Cp 18, Cp* 19). The products [Cp′Ti(NPtBu ₂(2-C₆H₄Ph)] (Cp′ = Cp 20, Cp* 21) contained η⁶-interactions between Ti and the 2-phenyl substituent of the biphenyl unit. While Ti(II)-phosphinimide complexes have proven difficult to handle due to their reactivity, an unequivocal example of a Ti(II) species was obtained via reduction of Cp*Ti(NPt-Bu₃)Cl ₂ (11) with Mg in the presence of CO, affording the species Cp*Ti(NPt-Bu₃)(CO)₂ (22). X-ray data for 4, 6, 7, 9, 10, 15, and 17-22 are reported.

Full text of DOI:10.1021/om049826q

Organometallics 2004, 23, 3309-3318
3309
Red u ction of Tita n iu m (IV)-P h osp h in im id e Com p lexes:
Rou tes to Ti(III) Dim er s, Ti(IV)-Meta lla cycles, a n d Ti(II)
Sp ecies
Todd W. Graham, J ames Kickham, Silke Courtenay, Pingrong Wei, and
Douglas W. Stephan*
Chemistry and Biochemistry, University of Windsor, Windsor, Ontario, Canada, N9B 3P4
Received March 10, 2004
The redox chemistry of phosphinimide-containing group IV metal complexes has been
investigated. Reaction of the simple phosphinimide species CpTi(NPR3)Cl2 (R ) Me 1, i-Pr
2) with Mg affords complexes formulated as [CpTiCl(µ-NPR3)]2 (R ) Me 3, i-Pr 4). In contrast,
CpTi(NPt-Bu3)Cl2 (5) is reduced by Mg to a putative Ti(II) species that can be intercepted
by a variety of reagents including 2,3-dimethyl-1,3-butadiene, diphenylacetylene, phenyl-
acetylene, bis(trimethylsilyl)acetylene, ethylene, and propylene to give monometallic met-
allacyclic complexes. In this fashion, the Ti(IV) metallacycles CpTi(NPt-Bu3)(CH2C(Me)-
C(Me)CH2), 6, CpTi(NPt-Bu3)(CPh)4, 7, CpTi(NPt-Bu3)(C(Ph)CHC(Ph)CH), 8, CpTi(NPt-Bu3)-
(η2-C2(SiMe3)2), 9, CpTi(NPt-Bu3)(CH2)4, 10, CpTi(NPt-Bu3)(CH2CHMe)2, 15, and CpTi(NPt-
Bu3)(CH2)2(CPh)2, 16, were prepared. Related intramolecular formation of metallacycle
complexes was achieved upon reduction of Cp′Ti(t-Bu2(2-C6H4Ph)PN)Cl2 (Cp′ ) Cp 18, Cp*
19). The products [Cp′Ti(NPtBu2(2-C6H4Ph)] (Cp′ ) Cp 20, Cp* 21) contained η6-interactions
between Ti and the 2-phenyl substituent of the biphenyl unit. While Ti(II)-phosphinimide
complexes have proven difficult to handle due to their reactivity, an unequivocal example of
a Ti(II) species was obtained via reduction of Cp*Ti(NPt-Bu3)Cl2 (11) with Mg in the presence
of CO, affording the species Cp*Ti(NPt-Bu3)(CO)2 (22). X-ray data for 4, 6, 7, 9, 10, 15, and
17-22 are reported.
In tr od u ction
activations of Ti-Me units, affording unprecedented
carbide derivatives.6-8 In an effort to further study the
fundamental chemistry of Ti-phosphinimide complexes,
we are exploring their reduction chemistry. We have
previously reported that the reduction of CpTi(NPt-Bu3)-
Cl2 by Mg in benzene affords the dimer [CpTi(NPt-Bu3)-
(µ-Cl)]2. This chloro-bridged species was characterized
in the solid state by both X-ray crystallography and
single-crystal EPR spectroscopy.9 In this paper, we
probe phosphinimide ligand effects on the redox chem-
istry of these species. In these cases, the products de-
rived include Ti(III) dimers, Ti(IV) metallacycles, and
the first formal Ti(II)-phosphinimide derivative. The
implications of these results are discussed and the po-
tential for the utility of such redox chemistry considered.
Phosphinimide ligand complexes of transition metal
and main group elements have been the subject of
numerous studies and reviews.1,2 Recently our attention
has focused on transition metal complexes containing
sterically demanding phosphinimide ligands, as these
systems mimic cyclopentadienyl groups, affording highly
efficient olefin polymerization catalysts.3,4 Our studies
have indicated that such ligands provide effective steric
protection of the active site and at the same time offer
increased accessibility of the metal center to substrate
molecules.5 In less sterically demanding systems, the
accessibility of the phosphinimide N donor atom prompts
the formation of bridging phosphinimide units in di-,
tri-, and tetrametallic aggregates.1 We have previously
shown that the interaction of the phosphinimide N atom
in the less sterically demanding systems results in
reaction with AlMe3, prompting multiple C-H bond
Exp er im en ta l Section
Gen er a l Da ta . The syntheses were performed employing
an atmosphere of dry, oxygen-free nitrogen in a Vacuum
Atmospheres inert atmosphere glovebox or standard Schlenk
techniques. Solvents were purified employing Grubbs type
column systems manufactured by Innovative Technology. 1H,
13C{1H}, and 31P{1H} NMR data were acquired on a Bruker
* Corresponding author. Fax: 519-973-7098. E-mail: Stephan@
uwindsor.ca.
(1) Dehnicke, K.; Krieger, M.; Massa, W. Coord. Chem. Rev. 1999,
182, 19-65.
(2) Dehnicke, K.; Weller, F. Coord. Chem. Rev. 1997, 158, 103-169.
(3) Stephan, D. W.; Guerin, F.; Spence, R. E. v. H.; Koch, L.; Gao,
X.; Brown, S. J .; Swabey, J . W.; Wang, Q.; Xu, W.; Zoricak, P.; Harrison,
D. G. Organometallics 1999, 18, 2046-2048.
(4) Stephan, D. W.; Stewart, J . C.; Guerin, F.; Spence, R. E. v. H.;
Xu, W.; Harrison, D. G. Organometallics 1999, 18, 1116-1118.
(5) Stephan, D. W.; Stewart, J . C.; Guerin, F.; Courtenay, S.;
Kickham, J . E.; Hollink, E.; Beddie, C.; Hoskin, A. J .; Graham, T.; Wei,
P.; Spence, R. E. v. H.; Xu, W.; Koch, L.; Gao, X.; Harrison, D. G.
Organometallics 2003, 22, 1937-1947.
(6) Kickham, J . E.; Guerin, F.; Stewart, J . C.; Urbanska, E.; Ong,
C. M.; Stephan, D. W. Organometallics 2001, 20, 3209.
(7) Kickham, J . E.; Guerin, F.; Stephan, D. W. J . Am. Chem. Soc.
2002, 124, 11486-11494.
(8) Kickham, J . E.; Guerin, F.; Stewart, J . C.; Stephan, D. W. Angew.
Chem., Int. Ed. 2000, 39, 3263-3266.
(9) Sung, R. C. W.; Courtenay, S.; McGarvey, B. R.; Stephan, D. W.
Inorg. Chem. 2000, 39, 2542-2546.
10.1021/om049826q CCC: $27.50 © 2004 American Chemical Society
Publication on Web 05/27/2004

3310 Organometallics, Vol. 23, No. 13, 2004
Graham et al.
3
Avance 300 or 500 MHz spectrometer. 1H and 13C NMR
chemical shifts are listed downfield from SiMe4 in parts per
million (ppm) and were referenced to the residual proton or
carbon peak of the solvent. 31P NMR data were referenced
using an external standard relative to 85% H3PO4. All NMR
spectra were recorded in C6D6 unless otherwise stated. Gal-
braith Laboratories Inc. or in-house EA services performed the
combustion analyses. In the case of compounds 9, 14, and 15
repeated attempts to obtain satisfactory carbon analyses, even
with use of added oxidant, were unsuccessful. We have
previously attributed such problems to partial formation of
Ti-C during combustion of the Ti-organometallic derivatives.10
C6D6 and CD2Cl2 were purchased from Canadian Isotopes
Laboratories; C6D6 and CD2Cl2 were vacuum distilled be-
fore use from Na/benzophenone and CaH2, respectively.
CpTi(NPMe3)Cl2, 1, CpTi(NPi-Pr3)Cl2, 2, CpTi(NPt-Bu3)Cl2, 5,
Cp*Ti(NPt-Bu3)Cl2, 11 and (indenyl)Ti(NPt-Bu3)Cl2, 13 were
prepared as previously published.10,11 Pt-Bu2(2-C6H4Ph) was
purchased from the Strem Chemical Co.
Syn th esis of [Cp TiCl(µ-NP R3)]2 (M ) Me 3, i-P r 4).
These compounds were prepared in a similar manner, and thus
one such preparation is detailed. A solution of 2 (430 mg, 1.117
mmol) in 5 mL of THF was added at -80 °C to a suspension
of Mg powder (100 mg, 4.114 mmol) in THF (5 mL). The
mixture was warmed to 25 °C and stirred for 1 h, over which
time a brown solution was obtained. The solvent was removed
in vacuo, and the residue was extracted with 5 × 5 mL of
methylene chloride. The extracts were filtered through Celite,
and then the solvent was removed. The brown solid was
triturated with pentane and was then dried in vacuo. 3:
6.39 (s, 5H, Cp); 1.18 (d, J P-H ) 13 Hz, 27H, t-Bu). 13C{1H}
NMR: 203.1, 148.7, 142, 131.4, 127.4, 127.1, 124.8, 123.0, 41.1
(d, 1J PC ) 40.4 Hz), 29.4. Anal. Calcd for C45H52NPTi: C, 78.8;
H, 7.6; N, 2.0. Found: C, 78.6; H, 7.7; N, 1.7. 8: Yield: 70%.
31P{1H} NMR: 35.9. 1H NMR: 8.05 (d, J HH ) 4 Hz, CHC-
(Ph)CH); 7.64 (m, 2H, Ph); 7.58 (d, J HH ) 4 Hz, 2H, TiCH);
4
4
7.30 (m, 6H, Ph); 7.12 (m, 2H, Ph); 6.30 (s, 5H, Cp), 1.18 (d,
3J Ph ) 15 Hz, 27H, t-Bu). 13C{1H} NMR: 203.2, 149.3, 145.4,
142.1, 129.3, 128.8, 127.1, 126.4, 126.3, 125.4, 111.3, 41.7 (d,
45.7 Hz), 29.9. Anal. Calcd for C33H44NPTi: C, 74.3; H, 8.3;
N, 2.6. Found: C, 73.1; H, 7.9; N 2.3. 9: red-brown crystals.
Yield: 80%. 31P{1H} NMR: 31.8. H NMR: 6.70 (s, 5H, Cp);
1
3
1.56 (d, J PH ) 13 Hz, 27H, t-Bu); 0.08 (s, 18H, SiMe3).
13C{1H} NMR (partial): 113.6, 41.7 (d, J PC ) 47 Hz); 30.4,
1
1.5. IR: νCO (KBr, cm-1) 1597. Anal. Calcd for C25H50NPSi2Ti:
C, 60.1; H, 10.1; N, 2.8. Found: C, 59.1; H, 10.1; N, 2.8.
Syn th esis of Cp Ti(NP t-Bu 3)(CH2)4, 10, Cp *Ti(NP t-Bu 3)-
(CH2)4, 12, (In d en yl)Ti(NP t-Bu 3)(CH2)4, 14, a n d Cp Ti(NP t-
Bu 3)(CH2CHMe)2, 15. These compounds were prepared in a
similar manner, and thus one such preparation is detailed. A
10 mL portion of THF was added to 5 (227 mg, 0.567 mmol)
and Mg powder (100 mg, 4.114 mmol) in a 400 mL heavy-
walled glass vessel. The mixture was degassed by with two
freeze-pump-thaw cycles and was then cooled to -80 °C
unless otherwise noted. Ethylene was admitted to the flask
to a pressure of ca. 1 atm, after which the flask was sealed
and the mixture warmed to room temperature. After stirring
for 90 min, the solvent was removed in vacuo and the residue
was extracted with 5 × 5 mL of pentane. The extracts were
filtered through Celite, and the solvent was then removed in
vacuo, yielding 153 mg (70%) of 10. Yield: 80%. Crystalline
material may be obtained by crystallization from ether at -35
1
3
Yield: 65%. H NMR: 5.88 (s, 5H, Cp); 0.87 (d, J HH ) 13 Hz,
Me). 31P{1H} NMR: 36.7. Anal. Calcd for C16H28P2N2Ti2Cl2:
C, 40.3; H, 5.2; N, 5.9. Found: C, 40.2; H, 5.1; N, 5.7. 4:
1
°C. 31P{1H} NMR: 32.8. H NMR: 6.30 (s, 5H, Cp); 2.58 (m,
1
3
3
Yield: 54%. H NMR: 6.17 (s, 5H, Cp); 2.15 (sept., J HH ) 7
2H, TiCH2CH2); 2.18 (m, 2H, CH2CH2); 1.75 (t, J HH ) 6 Hz,
3
3
4H, CH2CH2); 1.26 (d, J PH ) 13 Hz, 27H, t-Bu). 13C{1H}
3
Hz, 3H, CH); 1.03 (dd, J HH ) 7 Hz, J Ph ) 14 Hz, 18H, Me).
31P{1H} NMR: 57.6. Anal. Calcd for C28H52P2N2Ti2Cl2: C, 52.1;
H, 8.1; N, 4.3. Found: C, 51.9; H, 7.9; N, 4.2.
1
NMR: 112.0, 55.8, 41.7 (d, J PC ) 84 Hz); 32.2, 30.2. Anal.
Calcd for C21H40NPTi: C, 65.5; H, 10.5; N, 3.6. Found: C, 65.3;
H, 10.5; N, 3.6. 12: This reaction was done at -80 °C. Yield:
85%. 31P{1H} NMR: 32.1. 1H NMR: 2.49 (m, 2H, TiCH2); 2.05
Syn th esis of Cp Ti(NP t-Bu 3)(CH2C(Me)C(Me)CH2), 6. To
a solution of 5 (200 mg, 0.50 mmol) in 10 mL of THF was added
Mg powder (15 mg, 0.616 mmol). The solution was stirred for
5 min, then 2,3-dimethyl-1,3-butadiene (41 mg, 0.50 mmol) in
1 mL of THF was added. After stirring for 24 h, the solvent
was removed in vacuo, and the resulting brown oily residue
was taken up in 5 mL of toluene. After filtration through Celite
the solvent was removed and the residue was washed several
times with hexanes, affording a dark brown solid in 85% yield.
31P{1H} NMR (tol-d8): 33.3. 1H NMR (tol-d8): 5.63 (s, 5H, Cp),
3.28 (d, 2J H-H ) 7 Hz, 2H, CH2), 1.73 (s, 6H, Me), 1.50 (d, 2J H-H
3
(s, 15H, Cp*); 1.92 (m, 2H, TiCH2); 1.38 (d, J PH ) 8 Hz, 27H,
t-Bu); 1.25 (m, 2H, CH2CH2); 0.99 (m, 2H, CH2CH2). 13C{1H}
NMR: 119.0, 59.8, 41.9 (d, 1J PC ) 47 Hz), 31.7, 30.6, 12.7. Anal.
Calcd for C26H40NPTi: C, 70.1; H, 9.1; N, 3.1. Found: C, 67.6;
H, 11.18; N, 3.0. 14: Yield 60%. 31P{1H} NMR: 33.1. 1H
NMR: 7.75 (m, 2H, indenyl); 7.24 (m, 2H, indenyl); 6.29 (d,
3J HH ) 3 Hz, 2H, indenyl), 5.82 (t, J HH ) 3 Hz, 1H, indenyl);
2.34 (m, 4H, CH2CH2), 1.64 (m, 4H, CH2CH2); 1.26 (d, J PH
3
3
)
13 Hz, 27H, t-Bu). 13C{1H} NMR: 127.9, 125.8, 124.3, 114,6,
101.2, 61.7, 41.8, 32.3, 30.4. Anal. Calcd for C27H42NPTi: C,
69.0; H, 9.7; N, 3.2. Found: C, 66.8; H, 10.0; N, 3.2. 15: Propene
was added at -40 °C, and the mixture was warmed to 25 °C
and stirred for 90 min. Yield: 96%. 31P{1H} NMR: 32.1. 1H
NMR: 6.27 (s, 5H, Cp); 2.58 (m, 1H, CH); 2.12, (dd, 3J HH ) 11
Hz, 2J HH ) 11 Hz, 1H, CH2); 1.85 (dd, 3J HH ) 12 Hz, 3J HH ) 12
3
) 7 Hz, 2H, CH2), 1.17 (d, J P-H ) 12 Hz, 27H, t-Bu). 13C{1H}
1
NMR (tol-d8): 104.8, 62.1, 40.9 (d, J P-C ) 46 Hz), 30.0, 23.9.
Anal. Calcd for C23H42NPTi: C, 67.1; H, 10.3; N, 3.4. Found:
C, 66.8; H, 10.0; N, 3.2.
Syn th esis of Cp Ti(NP t-Bu 3)(CP h )4, 7, Cp Ti(NP t-Bu 3)-
(C(P h )CHC(P h )CH), 8, a n d Cp Ti(NP t-Bu 3)(η2-C2(SiMe3)2),
9. These species were prepared in a similar manner, and only
one representative procedure is provided. A 5 mL portion of
THF was added to 100 mg (0.250 mmol) of CpTi(NPt-Bu3)Cl2
and 50 mg (2.057 mmol) of Mg powder, and the mixture was
cooled to -35 °C. Diphenylacetylene (90 mg, 0.501 mmol) was
then added, and the mixture was stirred for 90 min. The
solvent was removed in vacuo, and then the residue was
extracted with 3 × 5 mL of ether (for 7) or pentane (for 8 and
9); the extracts were filtered through Celite and then the
2
3
Hz, 1H, CH2); 1.70 (m, 1H, CH); 1.33 (dd, J HH ) 11 Hz, J HH
3
) 5 Hz, 1H, CH2); 1.26 (d, J PH ) 13 Hz, 27H, t-Bu); 1.10 (d,
3J HH ) 6 Hz, 3H, Me); 1.08 (d, 3J HH ) 6 Hz, 3H, Me); 1.04 (dd,
2J HH ) 11 Hz, J HH ) 5 Hz, 1H, CH2). 13C NMR: 112.0, 66.3,
3
1
66.1, 45.7, 44.5, 41.7 (d, J PC ) 47 Hz) 30.2, 26.4, 26.2. Anal.
Calcd for C23H44NPTi: C, 66.8; H, 10.7; N, 3.4. Found: C, 62.9;
H, 10.7; N, 3.7.
Syn th esis of Cp Ti(NP t-Bu 3)(CH2)2(CP h )2, 16. A 34 mg
(0.191 mmol) sample of diphenylacetylene in 1.5 mL of ben-
zene was added to 73 mg (0.189 mmol) of 10 in 1.5 mL of
benzene. The mixture was stirred for 40 min, and then the
solvent was removed in vacuo. Yield: 90%. 31P{1H} NMR:
1
solvent was removed. 7: Yield: 75%. 31P{1H} NMR: 37.0. H
NMR: 7.03 (m, 8H, Ph); 6.95 (m, 4H, Ph); 6.87 (m, 2H, Ph);
1
(10) Stephan, D. W.; Stewart, J . C.; Gue´rin, F.; Courtenay, S.;
Kickham, J .; Hollink, E.; Beddie, C.; Hoskin, A.; Graham, T.; Wei, P.;
Urbanska, E.; Spence, R. E. v. H.; Xu, W.; Koch, L.; X.Gao; Harrison,
D. G. Organometallics 2003, 22, 1937-1947.
(11) Gue´rin, F.; Beddie, C. L.; Stephan, D. W.; Spence, R. E. v. H.;
Wurz, R. Organometallics 2001, 20, 3466-3475.
34.7. H NMR: 7.50 (m, 2H, Ph); 7.28-6.91 (m, 8H, Ph); 6.30
(s, 5H, Cp); 3.24 (m, 2H, TiCH2CH2); 2.20 (m, 1H, TiCH2); 1.80
(m, 1H, TiCH2); 1.24 (d, 3J PH ) 12.9 Hz, 27H, t-Bu). Anal. Calcd
for C33H46NPTi: C, 74.0; H, 8.6; N, 2.6. Found: C, 73.8; H,
8.4; N, 2.5.

Reduction of Ti(IV)-Phosphinimide Complexes
Organometallics, Vol. 23, No. 13, 2004 3311
Syn th esis of t-Bu 2(2-C6H4P h )P NSiMe3, 17. t-Bu2(2-C6H4-
Ph)P (2.055 g, 6.89 mmol) and azidotrimethylsilane (5.0 mL,
38 mmol) were combined in a 100 mL Schlenk flask. The slurry
was refluxed vigorously for two weeks, during which time the
phosphine dissolved and the solution developed a lemon-yellow
color. Excess azidotrimethylsilane was removed in vacuo, and
the solid was recrystallized from pentane. Yield: 1.319 g; 50%.
2H, Ph); 4.27 (m, 2H, m, 2H, Ph); 3.65 (m, 1H, m, 2H, Ph);
3
1.99 (s, 15H, Cp*); 1.02 (d, J PH ) 7 Hz, 27H, t-Bu). 13C{1H}
NMR: 149.6 (d, J PC ) 7 Hz), 133.6 (d, J PC ) 55 Hz), 133.1 (d,
J PC ) 8 Hz), 129.4, 129.4, 125.3, 124.9 (d, J PC ) 4 Hz), 124.6
1
(d, J PC ) 8 Hz), 117.4, 114.5, 104.4, 101.4, 37.3 (d, J PC ) 61
Hz), 29.2, 13.7. Anal. Calcd for C30H52NPTi: C, 71.3; H, 10.4;
N, 2.8. Found: C, 70.9; H, 10.3; N, 2.5.
1
31P{1H} NMR: 22.3. H NMR: 7.54 (m, 1H, Ph); 7.20 (m, 5H,
Syn th esis of Cp *Ti(NP t-Bu 3)(CO)2, 22. A solution of 230
mg (0.489 mmol) of 11 in 5 mL of THF was added dropwise at
-80 °C to 100 mg (4.114 mmol) of Mg powder in 5 mL of THF
in a 200 mL glass vessel. The mixture was frozen and degassed
by two freeze-pump-thaw cycles, and then CO was admitted
at -80 °C to atmospheric pressure. The vessel was sealed, and
the solution was warmed slowly to room temperature with
vigorous stirring. After stirring overnight, the solvent was then
removed in vacuo and the residue was extracted repeatedly
with pentane (ca. 5 × 10 mL). The extracts were filtered
through Celite, and the solvent was removed in vacuo to give
157 mg (70%) of a green crystalline product. X-ray quality
crystals may be obtained by recrystallization of the material
3
H
e,f); 6.90 (m, 3H, Ph); 1.15 (d, J PH ) 14 Hz, 18H, t-Bu); 0.07
(s, 9H, SiMe3). 13C{1H} NMR: 149.7, 144.2, 135.3 (d, J PC ) 8
1
Hz), 131.0 (d, 2J PC ) 14 Hz), 129.7 (s, Ph), 129.2, 128.3, 127.7,
4
1
126.3, 124.6 (d, J PC ) 12 Hz), 38.4 (d, J PC ) 57 Hz), 28.7,
4.6. Anal. Calcd for C23H36NPSi: C, 71.6; H, 9.4; N, 3.6.
Found: C, 71.5; H, 9.2; N, 3.7.
Syn th esis of Cp ′Ti(NP t-Bu 2(2-C6H4P h ))Cl2 (Cp ′ ) Cp
18, Cp * 19). These compounds were prepared in a similar
fashion, and thus one preparation is detailed. Compound 17
(1.006 g, 2.61 mmol) and CpTiCl3 (0.514 g, 2.34 mmol) were
added to a 400 mL glass bomb with 70 mL of toluene. The
flask was evacuated, sealed, and heated at 75 °C for 48 h. The
yellow solution was filtered through Celite, and the solvent
was removed in vacuo. The yellow solid was washed with
hexanes (3 × 10 mL) and dried under vacuum. Yield: 1.036
g; 89%. 18: 31P{1H} NMR: 45.5 (75%, major); 31.7 (25%,
1
from ether at -35 °C. 31P{1H} NMR: 34.2. H NMR: 1.60 (s,
3
15H, Cp*); 1.08 (d, J PH ) 13 Hz, 27H, t-Bu). 13C NMR (par-
1
tial): 109.2, 40.1 (d, J PC ) 45.8 Hz), 29.8, 12.0. IR: νCO (pen-
tane solution, cm-1) 1948, 1840. Anal. Calcd for C24H42NO2-
PTi: C, 63.3; H, 9.3; N, 3.1. Found: C, 63.1; H, 9.6; N, 3.5.
X-r a y Da ta Collection a n d Red u ction . Crystals were
manipulated and mounted in capillaries in a glovebox, thus
maintaining a dry, O2-free environment for each crystal.
Diffraction experiments were performed on a Siemens SMART
System CCD diffractometer. The data were collected in a
hemisphere of data in 1329 frames with 10 s exposure times.
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 packages.
An empirical absorption correction based on redundant data
was applied to each data set. Subsequent solution and refine-
ment were performed using the SHELXTL solution package.
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 the SHELXTL direct methods
routine. The remaining non-hydrogen atoms were located from
successive difference Fourier map calculations. The refine-
ments were carried out by using full-matrix least-squares
techniques on F, minimizing the function w(|Fo| - |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 in the absence of
disorder or insufficient data. In the latter cases atoms were
treated isotropically. C-H 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. H atom temperature
factors were fixed at 1.10 times the isotropic temperature
factor of the C atom to which they are bonded. The H atom
contributions were calculated, but not refined. 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.
Additional details are provided in the Supporting Information.
1
3
3
minor). H NMR: 9.19 (dd, J HH ) 9 Hz, J PH ) 13 Hz, 1 H,
Ph); 7.39 (br, 1 H, Ph); 7.30 (t, 3J HH ) 8 Hz, 1 H, Ph); 6.94 (m,
5 H, Ph); 6.80 (dd, 3J HH ) 5 Hz, 4J PH ) 5 Hz, 1 H, Ph); 6.48 (s,
3
Cp, major); 6.11 (s, Cp, minor); 1.28 (d, J PH ) 15 Hz, t-Bu,
minor); 1.00 (s, J PH ) 15 Hz, t-Bu, major). 13C{1H} NMR:
3
2
4
144.2, 143.9, 139.3 (d, J CP ) 8 Hz), 133.4 (d, J CP ) 11 Hz),
3
131.0, 130.7, 128.3, 127.7, 127.2 (d, J CP ) 10 Hz), 116.2 (s,
1
Cp, minor), 115.3 (s, Cp, major), 42.6 (d, J CP ) 50 Hz, t-Bu,
minor); 39.7 (d, 1J CP ) 50 Hz, t-Bu, major), 28.8 (s, t-Bu, minor),
27.7 (s, t-Bu, major). Anal. Calcd for C25H32Cl2NPTi: C, 65.5;
H, 5.7; N, 12.5. Found: C, XXX; H, XXX; N, XXX. 19: Yield:
96%. 31P{1H} NMR: 43.0. H NMR: 8.99 (ddd, J HH ) 8 Hz,
1
3
3J PH ) 13 Hz, J HH ) 1 Hz, 1H, Ph); 7.29 (tdd, J HH ) 8 Hz,
4
3
4J PH ) 1 Hz, J HH ) 1 Hz, 1H, Ph); 7.1-6.9 (m, 6H, Ph, Ph);
4
3
4
4
6.83 (ddd, J HH ) 8 Hz, J PH ) 5 Hz, J HH ) 1 Hz, 1H, Ph);
2.20 (s, 15 H, Cp*); 1.13 (d, 3J PH ) 16 Hz, 18 H, t-Bu). 13C{1H}
2
4
NMR: 144.1, 139.3 (d, J CP ) 7 Hz), 133.2 (d, J CP ) 10 Hz),
3
130.8, 130.7, 128.2, 127.6, 126.9 (d, J CP ) 10 Hz), 125.6 (s,
Cp*), 40.4 (d, 1J CP ) 51 Hz), 28.3 (s, t-Bu); 13.2 (s, Cp*). Anal.
Calcd for C30H42Cl2NPTi: C, 72.7; H, 8.5; N, 2.8. Found:
C,72.5; H, 8.3; N, 2.6.
Syn th esis of Cp Ti(NP t-Bu 2(2-C6H4P h )), 20. A 5 mL
sample of ether was added to a mixture of 225 mg (0.479 mmol)
of compound 18 and 70 mg (2.879 mmol) of Mg powder. Then
150 µL of THF was added dropwise, and the mixture was
stirred vigorously for 5 days. The solvent was then removed
in vacuo and the residue extracted repeatedly with pentane;
the extracts were filtered through Celite, after which the
solvent was removed. Yield: 60%. 31P{1H} NMR: 18.6. 1H
NMR: 7.54 (m, 1H, C6H4); 7.07 (m, 1H, C6H4); 7.02 (m, 1H,
C6H4); 6.78 (m, 1H, C6H4); 6.22 (m, 5H, Cp); 4.53 (m, 2H, o-Ph);
3
4.40 (m, 2H, m-Ph); 3.48 (m, 1H, p-Ph); 0.96 (d, J PH ) 13.7
Hz, 27H, t-Bu). 13C{1H} NMR: 148.8 (d, J PC ) 6 Hz), 131.9
(m, J PC ) 58), 131.3 (d, J PC ) 8 Hz), 130.2 (d, J PC ) 7 Hz),
130.1, 125.6 (d, J PC ) 9 Hz), 125.1, 118.8, 104.0, 103.8, 100.2,
37.0 (d, J PC ) 61.0 Hz), 28.6. Anal. Calcd for C25H32NPTi: C,
70.6; H, 7.6; N, 3.3. Found: C, 70.4; H, 7.3; N, 3.0.
Syn th esis of Cp *Ti(NP t-Bu 2(2-C6H4P h )), 21. A solution
of 19 (805 mg, 1.622 mmol) in 10 mL of THF was added
dropwise to 200 mg (8.227 mmol) of Mg powder in 10 mL of
THF at -80 °C. The solution was warmed to 25 °C and stirred
for 90 min, over which time it turned red-brown. The solvent
was removed in vacuo, and the residue was extracted with 5
× 5 mL of pentane. The extracts were filtered, and the solvent
was removed in vacuo. Yield: 31% of a red-brown solid.. 21:
31P{1H} NMR: 18.6. 1H NMR: 7.57 (m, 1H, C6H4); 7.17 (m,
1H, C6H4); 7.01 (m, 1H, C6H4); 6.78 (m, 1H, C6H4); 4.42 (m,
Resu lts a n d Discu ssion
Dim er ic Ti(III) Com p lexes. The reduction of tita-
nium phosphinimide complexes by Mg has been inves-
(12) Cromer, D. T.; Mann, J . B. Acta Crystallogr. A 1968, A24, 321-
324.

3312 Organometallics, Vol. 23, No. 13, 2004
Ta ble 1. Cr ysta llogr a p h ic Da ta
Graham et al.
4‚0.5C6H6
6
7.0.5(PhC)2
9
10
15
formula
fw
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C
31H55Cl2N2P2Ti2
C
23H42NPTi
C52H57NPTi
774.86
monoclinic
P21/c
13.673(8)
10.905(7)
30.72(2)
90
90.861(12)
90
4580(5)
4
1.124
0.255
19 199
6547
449
C25H47NPSi2Ti
496.69
orthorhombic
Pnma
17.654(10)
15.355(9)
11.611(6)
90
90
90
3147(3)
4
1.048
C21H40NPTi
335.41
monoclinic
P21/c
14.704(8)
19.551(11)
16.030(8)
90
92.247(11)
90
4605(4)
8
1.112
0.444
19 475
6546
433
C23H44NPTi
413.46
triclinic
P1h
8.398(2)
10.683(3)
14.425(4)
92.977(6)
97.380(6)
106.036(6)
1228.3(6)
2
684.41
monoclinic
P21/c
17.100(8)
11.452(5)
19.780(10)
90
114.213(8)
90
3533(3)
4
1.287
0.716
14 517
5054
352
411.45
monoclinic
P21/n
11.5454(12)
15.1684(16)
13.9632(14)
90
107.109(3)
90
2337.1(4)
4
Z
d(calc) (g cm-1
)
1.169
0.442
7296
2468
1.118
0.420
5058
3461
abs coeff, µ (cm-1
)
0.410
12 811
2324
no. of data collected
data Fo2 >3σ(Fo
)
2
no. of variables
235
145
253
R
Rw
GOF
0.0320
0.0869
1.030
0.0930
0.1495
0.964
0.0645
0.1465
0.817
0.0439
0.1275
1.001
0.0569
0.1524
0.965
0.0530
0.1515
1.136
17
18.0.5C6H6
19.0.5C6H6
20
21
22
formula
fw
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C
23H36NPSi
C28H35Cl2NPTi
535.34
triclinic
P1h
10.394(6)
11.240(7)
12.855(8)
81.526(10)
77.385(10)
88.547(11)
1449.4(14)
2
C33H45Cl2NP Ti
605.47
monoclinic
P21/n
12.409(7)
19.664(11)
14.132(7)
90
100.792(11)
90
3388(3)
4
1.187
0.479
14 263
4803
336
C25H32NPTi
425.39
monoclinic
P21/n
9.370(5)
20.591(12)
12.046(7)
90
100.181(11)
90
2288(2)
4
C30H42NPTi
495.56
monoclinic
P21/c
20.261(19)
9.274(9)
29.54(3)
90
91.409(17)
90
5548(9)
8
1.186
0.384
19 011
7715
595
C14H42NO2PTi
455.46
orthorhombic
Pna21
20.510(10)
8.536(4)
15.276(8)
90
90
90
2675(2)
4
1.131
385.59
monoclinic
Cc
15.861(13)
12.409(10)
12.468(10)
90
102.927(14)
90
2392(3)
4
Z
d(calc) (g cm-1)
1.071
0.172
4950
3253
1.227
0.550
6229
4144
1.235
0.454
9752
3289
abs coeff, µ (cm-1
)
0.397
10 795
3737
no. of data collected
no. of data Fo2 >3σ(Fo
)
2
no. of variables
235
283
253
262
R
Rw
GOF
0.0330
0.0829
1.008
0.0561
0.1665
1.057
0.0412
0.1076
0.867
0.0378
0.0851
0.853
0.0591
0.1406
0.871
0.0271
0.0636
0.923
tigated. Reaction of the simple phosphinimide complexes
CpTi(NPR3)Cl2 (R ) Me 1, i-Pr 2) with Mg in THF
afforded complexes formulated as [CpTiCl(µ-NPR3)]2 (R
) Me 3, i-Pr 4). In the case of 4 crystals were obtained
and the resulting crystallographic data confirmed the
dimeric formulation in which the phosphinimide ligands
bridge the two metal centers (Figure 1). The cyclopen-
tadienyl ligands adopt a cisoid conformation, while a
chloride ligand completes the coordination sphere of
each of the Ti centers. The Ti-N and Ti-Cl distances
average 2.014(2) and 2.3819(12) Å, respectively. The
Ti-N-Ti and N-Ti-N angles within the Ti2N2 core
average 82.60(8)° and 93.37(8)°, respectively, affording
a Ti-Ti separation of 2.6612(10) Å. The Ti-N distances
of 2.013(2) and 2.024(2) Å and the average P-N-Ti
angles of 137.48(12)°, 139.14(13)°, 139.53(12)°, and
137.27(13)° reflect the slight dissymmetry of the bridg-
ing phosphinimide core. It is particularly noteworthy
that the structure of 4 stands in contrast to that
previously reported for the chloro-bridged Ti(III) dimer
[CpTi(NPt-Bu3)(µ-Cl)]2 (Scheme 1), derived from reduc-
tion of CpTi(NPt-Bu3)Cl2 (5) with Mg in benzene.9 This
dramatic structural difference for these Ti(III) spe-
cies is attributed to the greater steric demands of the
t-Bu3PN ligand. A related Ti(III)-phosphinimide-bridged
species, [TiBr2(µ-NPPh3)]2, has been previously de-
scribed by Dehnicke et al. In this species the Ti-N and
Ti‚‚‚Ti separations are somewhat shorter than in 3.13
Ti(IV) Meta lla cycles. In contrast to the above
chemistry, CpTi(NPt-Bu3)Cl2 (5) is reduced by Mg to a
putative Ti(II) species when the reduction is performed
in THF. This intermediate can be intercepted by reac-
tion with a variety of reagents to give monometallic,
metallacyclic complexes. In the case of reduction in the
presence of 2,3-dimethyl-1,3-butadiene, the very sensi-
tive species CpTi(NPt-Bu3)(CH2C(Me)C(Me)CH2) (6) is
obtained in 85% yield. This species exhibited a single
1
resonance in the 31P{1H} NMR spectrum, and the H
and 13C{1H} NMR data were consistent with the above
formulation. Both cis and trans conformations of the
butadiene as well as prone and supine isomers (Scheme
2), in which only the orientation of the butadiene ligand
with respect to the cyclopentadienyl ligands differs, are
conceivable. At ambient temperature, two doublets of
equal intensity attributable to the terminal CH2 of the
1
diene are observed in the H NMR spectrum of 6. The
lower and higher field resonances of these were assigned
to the syn and anti protons, respectively. A NOESY
NMR experiment shows a correlation between the
methyl protons and the Cp protons, which suggests that
(13) Li, J .-s.; Weller, F.; Schmock, F.; Dehnicke, K. Z. Anorg. Allg.
Chem. 1995, 621, 2097-2103.

Reduction of Ti(IV)-Phosphinimide Complexes
Organometallics, Vol. 23, No. 13, 2004 3313
F igu r e 2. ORTEP drawings of 6, 30% thermal ellipsoids
are shown. Hydrogen atoms are omitted for clarity. Dis-
tances (Å) angles (deg): Ti(1)-N(1) 1.852(9), Ti(1)-C(21)
2.141(11), Ti(1)-C(18) 2.157(11), Ti(1)-C(20) 2.409(12), Ti-
(1)-C(19) 2.417(11), P(1)-N(1) 1.558(9), C(18)-C(19) 1.450-
(16), C(19)-C(20) 1.398(16), C(19)-C(22) 1.523(15), C(20)-
C(21) 1.441(15), C(20)-C(23) 1.540(16), C(21)-Ti(1)-C(20)
36.3(4), C(18)-Ti(1)-C(20) 66.2(5), N(1)-Ti(1)-C(19)
127.7(4), C(21)-Ti(1)-C(19) 65.3(5), C(18)-Ti(1)-C(19)
36.4(4), C(20)-Ti(1)-C(19) 33.7(4), P(1)-N(1)-Ti(1) 178.0-
(6), C(19)-C(18)-Ti(1) 81.6(7), C(20)-C(19)-C(18) 122.8-
(12), C(20)-C(19)-Ti(1) 72.9(7), C(18)-C(19)-Ti(1) 62.0(6),
C(19)-C(20)-C(21) 121.0(12), C(19)-C(20)-Ti(1) 73.5(7),
C(20)-C(21)-Ti(1) 82.0(7).
F igu r e 1. ORTEP drawings of 4, 30% thermal ellipsoids
are shown. Hydrogen atoms are omitted for clarity. Dis-
tances (Å) angles (deg): Ti(1)-N(2) 2.011(2), Ti(1)-N(1)
2.017(2), Ti(1)-Cl(1) 2.3806(12), Ti(1)-Ti(2) 2.6612(10), Ti-
(2)-N(1) 2.013(2), Ti(2)-N(2) 2.024(2), Ti(2)-Cl(2) 2.3832-
(14), P(1)-N(1) 1.617(2), P(2)-N(2) 1.612(2), N(2)-Ti(1)-
N(1) 93.51(9), N(2)-Ti(1)-Cl(1) 105.39(7), N(1)-Ti(1)-
Cl(1) 95.12(7), N(1)-Ti(2)-N(2) 93.24(8), N(1)-Ti(2)-Cl(2)
104.55(7), N(2)-Ti(2)-Cl(2) 96.38(7), P(1)-N(1)-Ti(1)
137.48(12), P(1)-N(1)-Ti(2) 139.14(13), Ti(1)-N(1)-Ti(2)
82.67(8), P(2)-N(2)-Ti(1) 139.53(12), P(2)-N(2)-Ti(2)
137.27(13), Ti(1)-N(2)-Ti(2) 82.53(8).
at N, although the Ti-N distance of 1.852(9) Å is
significantly longer than that seen in the related dichlo-
ride or dialkyl complexes. The Ti-C distances for the
R- and â-butadiene carbon atoms average 2.149(11) and
2.413(11) Å, while the C-C distances of the central bond
of the butadiene ligand are 1.398(16) Å. These data
suggest that 6 may be described as a Ti(IV) species in
which the butadiene is best bound via a σ2, π-bonded
η4-interaction. The structural parameters of the buta-
diene moieties are typical of those seen for a number of
other early metal butadiene complexes.14-16 and as
well as the constrained geometry derivative (C5Me4-
SiMe2Nt-Bu)Ti(CH2C(Me)C(Me)CH2).17
Sch em e 1
In a similar manner, the reduction of 5 in the
presence of diphenylacetylene gave the species CpTi-
(NPt-Bu3)(C2Ph2)2 (7) in 70% yield. While NMR data are
consistent with the diphenylacetylene-to-Ti ratio, X-ray
data were required to determine the structure (Figure
3). These data confirm the metallocyclopentadiene
structure, in which reductive coupling of two acetylene
units has occurred to form the five-membered ring. The
structural parameters of the CpTi(NPt-Bu3) fragment
are similar to that observed in 6. However, the central
Câ-Câ bond length of the metallocyclopentadiene por-
tion of the molecule (1.502(7) Å) is significantly longer
than the other two C-C bonds in the metallacycle
(1.396(7), 1.355(7) Å). These data support the formula-
tion of 7 as a Ti(IV) species. The related reaction of
phenylacetylene affords a similar metallacyclic product,
CpTi(NPt-Bu3)(CPhCHCPhCH) (8), in good yield. NMR
data indicate a head-to-tail coupling, with the non-
equivalent vinylic C-H resonances appearing at 8.05
and 7.58 ppm in the 1H NMR spectrum. This orientation
presumably results in lower steric congestion. The
Sch em e 2
the butadiene fragment is in the prone configuration.
The 13C{1H} NMR spectrum displays resonances at
116.3 and 62.4 ppm for the internal and terminal diene
carbon atoms, respectively. This significant chemical
shift difference between the two carbon atoms is in
accord with a substantial σ-complex character in the
conjugated diene, which supports a Ti(IV) formulation.
The precise nature of 6 was unambiguously confirmed
via X-ray crystallography (Figure 2). These data reveal
coordination of cis-butadiene ligands, such that the
butadiene substituents are oriented toward the cyclo-
pentadienyl ligand. This orientation presumably avoids
unfavorable steric interactions between the butadiene-
methyl substituents and the phosphinimide ligand. The
phosphinimide ligand geometry is approximately linear
(14) Dorf, U.; Engel, K.; Erker, G. Organometallics 1983, 2, 462-
463.
(15) Beckhaus, R.; Thiele, K. H. J . Organomet. Chem. 1986, 317,
23-31.
(16) Yamamoto, H.; Yasuda, H.; Tatsumi, K.; Lee, K.; Nakamura,
A.; Chen, J .; Kai, Y.; Kasai, N. Organometallics 1989, 8, 105-119.
(17) Devore, D. D.; Timmers, F. J .; Hasha, D. L.; Rosen, R. K.;
Marks, T. J .; Deck, P. A.; Stern, C. L. Organometallics 1995, 14, 3132-
3134.

3314 Organometallics, Vol. 23, No. 13, 2004
Graham et al.
F igu r e 4. ORTEP drawings of 9, 30% thermal ellipsoids
are shown. Hydrogen atoms are omitted for clarity. Dis-
tances (Å) angles (deg): Ti(1)-N(1) 1.842(3), Ti(1)-C(1)
2.062(3), Ti(1)-C(1)′ 2.062(3), C(1)-C(1)′ 1.314(6), P(1)-
N(1) 1.575(3), N(1)-Ti(1)-C(1) 109.06(12), N(1)-Ti(1)-
C(1) 109.06(12), C(1)-Ti(1)-C(1) 37.14(16), P(1)-N(1)-
Ti(1) 173.5(2).
F igu r e 3. ORTEP drawings of 7, 30% thermal ellipsoids
are shown. Hydrogen atoms are omitted for clarity. Dis-
tances (Å) angles (deg): Ti(1)-N(1) 1.796(5), Ti(1)-C(18)
2.138(6), Ti(1)-C(21) 2.153(6), P(1)-N(1) 1.609(5), C(18)-
C(19) 1.396(7), C(19)-C(20) 1.502(7), C(20)-C(21) 1.355-
(7), N(1)-Ti(1)-C(18) 104.8(2), N(1)-Ti(1)-C(21) 104.3(2),
C(18)-Ti(1)-C(21) 82.9(2), P(1)-N(1)-Ti(1) 175.3(3), C(19)-
C(18)-Ti(1) 108.8(4), C(22)-C(18)-Ti(1) 128.5(4), C(18)-
C(19)-C(20) 117.8(5), C(21)-C(20)-C(19) 120.2(5), C(20)-
C(21)-Ti(1) 109.0(4).
Sch em e 3
F igu r e 5. ORTEP drawings of one of the two molecules
of 10 in the asymmetric unit, 30% thermal ellipsoids are
shown. Hydrogen atoms are omitted for clarity. Distances
(Å) angles (deg): Ti(1)-N(1) 1.813(3), Ti(1)-C(4) 2.131(5),
Ti(1)-C(1) 2.155(6), P(1)-N(1) 1.583(3), N(1)-Ti(1)-C(4)
104.71(19), N(1)-Ti(1)-C(1) 105.7(2), C(4) Ti(1)-C(1) 86.2-
(3), C(2)-C(1)-Ti(1) 101.9(5), C(3)-C(2)-C(1) 114.7(7),
C(2)-C(3)-C(4) 116.8(8), C(3)-C(4) Ti(1) 103.0(5).
analogous regiochemistry has been described for the
thermodynamically favored isomer of CpTi(OC6HPh4)-
((t-Bu)CCHC(t-Bu)CH) and Cp2Ti((t-Bu)CCHC(t-Bu)-
CH).18 An analogous reaction with bis(trimethylsilyl)-
acetylene resulted in the formation of the species
CpTi(NPt-Bu3)(η2-C2(SiMe3)2) (9) (Scheme 3). Structural
data confirmed the 2-fold symmetry of this titanocyclo-
propene molecule (Figure 4). The Ti-C bond length for
the η2-acetylene fragment is 2.062(3) Å. The correspond-
ing bond lengths of 2.125(3) and 2.144(3) Å reported for
(C5Me4SiMe3)2Ti(η2-C2(SiMe3)2)19 are longer than those
in 9, consistent with the presence of the electron-
donating Cp ligand. The C-C bond length of 1.314(6)
Å is indicative of back-donation to the acetylene ligand
and suggests a Ti(IV)-metallacyclic structure. Nonethe-
less, a Ti(II) formulation is suggested by literature
precedent of the related species Cp′2Ti(η2-C2(SiMe3)2).
These metallocene analogues have been shown to be
effective synthons for a variety of titanocene derivatives
as a result of the lability of the acetylene.20,21
a five-membered ring. The 1H NMR spectrum shows
diastereotopic R-H resonances appearing at 2.58 and
2.18 ppm, and the â-H signals, which are coincidently
degenerate, appear at 1.75 ppm. The X-ray structure
for 10 reveals the Ti-C bond lengths in the two
molecules in the asymmetric unit range from 2.130(6)
to 2.155(6) Å (Figure 5). The CR-CR bond distances
within the TiC4 rings are typical of C-C single bonds.
The Câ-Câ bond lengths were found to be 1.373(12) and
1.388(13) Å. These unexpectedly short C-C bonds are
thought to reflect some disorder of these carbon posi-
tions, although efforts to model such a disorder were
unsuccessful. Nonetheless, the structural data indicate
a Ti(IV) formulation. In a manner similar to that used
for the synthesis of 10, the species Cp*Ti(NPt-Bu3)-
(CH2)4 (12) and (indenyl)Ti(NPt-Bu3)(CH2)4 (14) were
prepared from 11 and 13, respectively.
The analogous reaction of 5 with propylene afforded
the complex formulated as CpTi(NPt-Bu3)(CH2CHMe)2
The reduction of 5 in the presence of ethylene affords
the compound CpTi(NPt-Bu3)(CH2)4 (10), in which two
ethylene ligands have been reductively coupled to form
1
(15). H and 13C{1H} NMR data were consistent with
the formation of only the meso diasteromers (Figure 6)
in which both methyl groups reside on the carbon atoms
â to the metal center. X-ray data for 15 confirmed this
formulation (Figure 7), although the data also revealed
the disorder of the â-carbon positions. The metric
parameters were similar to those observed for 10 as
expected. The formation of the isomer of the 3,4-
dimethyltitanocyclopentane 15 stands in contrast to the
(18) Lee, J .; Fanwick, P. E.; Rothwell, I. P. Organometallics 2003,
22, 1546.
(19) Horacek, M.; Kupfer, V.; Thewalt, U.; Stepnicka, P.; Polasek,
M.; Mach, K. Organometallics 1999, 18, 3572-3578.
(20) Rosenthal, U.; Burlakov, V. V.; Arndt, P.; Baumann, W.;
Spannenberg, A. Organometallics 2003, 22, 884-900.
(21) Rosenthal, U.; Pellny, P.-M.; Kirchbauer, F. G.; Burlakov, V.
V. Acct Chem. Res. 2000, 33, 119-129.

Reduction of Ti(IV)-Phosphinimide Complexes
Organometallics, Vol. 23, No. 13, 2004 3315
F igu r e 8. ORTEP drawings of 17, 30% thermal ellipsoids
are shown. Hydrogen atoms are omitted for clarity. Dis-
tances (Å) angles (deg): P(1)-N(1) 1.531(2), Si(1)-N(1)
1.674(2), P(1)-N(1)-Si(1) 160.76(15).
vealed that the Ti(IV) formulation is a simplistic view
and that like the Cp*-analogue, the C-C bond formation
is readily reversible. For example, 10 reacts with
PhCCPh to generate the species CpTi(NPt-Bu3)(CH2)2-
(CPh)2 (16), via the putative Ti(II) species CpTi(NPt-
Bu3)(C2H4)2 (Scheme 4). This suggests that 10 could be
useful as a Ti(II) synthon.
F igu r e 6. 1H NMR spectrum of the methylene (a, b) and
methine (c) protons of 15.
In tr a m olecu la r Ti(IV) Meta lla cycles. In an at-
tempt to effect intramolecular metalation, an analogous
complex incorporating a pendant biphenyl group was
prepared. This effort began with the conventional oxida-
tion of Pt-Bu2(2-C6H4Ph) with N3SiMe3, which afforded
the phosphinimine t-Bu2(2-C6H4Ph)PNSiMe3 (17)5 after
a two week period at reflux. In contrast, t-Bu3P is
completely oxidized with N3SiMe3 after several hours
at 90 °C. The resistance to oxidation of the biphen-
ylphosphine is evidence of the crowding provided by the
biphenyl substituent, and X-ray data for 17 (Figure 8)
show the orientation of the biphenyl substituent is
toward the NSiMe3 fragment. Employing literature
methods, the Ti complexes Cp′Ti(t-Bu2(2-C6H4Ph)PN)-
Cl2 (Cp′ ) Cp 18, Cp* 19) were prepared from reaction
of the 17 with Cp′TiCl3 in yields of 89 and 96%,
respectively.5 Subsequently, crystallographic data for 18
and 19 (Figure 9) revealed similar Ti-N distances of
1.759(3) and 1.791(3) Å, respectively, and P-N distances
of 1.619(3) and 1.609(3) Å. For 19, the slightly longer
Ti-N distance and shorter P-N bond length are
consistent with greater electron donation from Cp*. The
P-N-Ti angles in 18 and 19 are approximately linear
at 177.0(2)° and 172.71(16)°, respectively, typical of
terminal phosphinimide ligand complexes.1 31P{1H}, 1H,
and 13C{1H} NMR data revealed the presence of two
isomers in a ratio of 3:1 for 18 and a single isomer for
19. These data imply inhibited rotation of the biphenyl
substituents (Scheme 5). This view is consistent with
the observation of only a single isomer of 19, where the
increased steric demands of the Cp* ligand preclude
rotation about the P-C(biphenyl) bond. The relatively
poor solubility of 18 precluded a determination of the
rotational barrier.
F igu r e 7. ORTEP drawings of 15, 30% thermal ellipsoids
are shown. One of the two disordered positions of C(2) and
C(3) is shown. Hydrogen atoms are omitted for clarity.
Distances (Å) angles (deg): Ti(1)-N(1) 1.804(2), Ti(1)-C(1)
2.146(3), Ti(1)-C(4) 2.150(3), N(1)-Ti(1)-C(1) 105.45(12),
N(1)-Ti(1)-C(4) 104.71(13), P(1)-N(1)-Ti(1) 171.39(16).
Sch em e 4
2,4-substitution pattern seen in 8. This is attributable
to additional steric crowding that results in the planar
titanocyclopentadiene ring of 8.
The isolation and characterization of 10, 12, 14, and
15 stand in contrast to the isolation of Cp*2Ti(C2H4) and
the instability of Cp*2Ti(CH2)4, described by Bercaw et
al.22,23 The presence of the phosphinimide ligand ap-
pears to provide room at the metal, thus stabilizing the
bis-ethylene species. Nonetheless, reactions of 10 re-
Reduction of 18 and 19 with Mg in THF/Et2O pro-
ceeds cleanly to give red-brown products, formulated as
(22) Cohen, S. A.; Auburn, P. R.; Bercaw, J . E. J . Am. Chem. Soc.
1983, 4, 1136.
(23) Cohen, S. A.; Bercaw, J. E. Organometallics 1985, 4, 1006-1014.

3316 Organometallics, Vol. 23, No. 13, 2004
Graham et al.
F igu r e 9. ORTEP drawings of (a) 18 and (b) 19, 30%
thermal ellipsoids are shown. Hydrogen atoms are omitted
for clarity. Distances (Å) angles (deg): 18: Ti(1)-N(1)
1.759(3), Ti(1)-Cl(1) 2.3087(17), Ti(1)-Cl(2) 2.3139(16),
P(1)-N(1) 1.619(3), N(1)-Ti(1)-Cl(1) 102.62(11), N(1)-
Ti(1)-Cl(2) 102.19(10), Cl(1)-Ti(1)-Cl(2) 101.73(7), P(1)-
N(1)-Ti(1) 177.0(2). 19: Ti(1)-N(1) 1.791(3), Ti(1)-Cl(2)
2.3091(13), Ti(1)-Cl(1) 2.3219(14), N(1)-P(1) 1.609(3),
N(1)-Ti(1)-Cl(2) 102.70(9), N(1)-Ti(1)-Cl(1) 102.84(9),
Cl(2)-Ti(1)-Cl(1) 101.23(5), P(1)-N(1)-Ti(1) 172.71(16).
F igu r e 10. 1H NMR spectrum of arene protons of the
Ti-arene interaction in 20.
Sch em e 5
Sch em e 6
F igu r e 11. ORTEP drawing of (a) 20 and (b) 21 (one
molecule from the asymmetric unit), 30% thermal ellipsoids
are shown. Hydrogen atoms are omitted for clarity. Dis-
tances (Å) angles (deg): 20: Ti(1)-N(1) 1.887(2), Ti(1)-
C(12) 2.388(3), Ti(1)-C(13) 2.236(3),Ti(1)-C(14) 2.472(4),
Ti(1)-C(15) 2.465(4), Ti(1)-C(16) 2.254(4), Ti(1)-C5 2.388-
(4), Ti(1)-C(17) 2.398(3), P(1)-N(1) 1.564(2), P(1)-N(1)-
Ti(1) 145.3(2). 21: Ti(1)-N(1) 1.918(4), Ti(1)-C(18) 2.236-
(5), Ti(1)-C(21) 2.242(6), Ti(1)-C(17) 2.397(5), Ti(1)-C(22)
2.416(5), Ti(1)-C(20) 2.447(7), Ti(1)-C(19) 2.456(6), P(1)-
N(1) 1.557(4), P(1)-N(1)-Ti(1) 145.9(2).
[Cp′Ti(NPt-Bu2(2-C6H4Ph)] (Cp′ ) Cp 20, Cp* 21)
(Scheme 6). These products were isolated in 60 and 50%
yields, respectively. NMR data were consistent with the
presence of the Cp and phosphinimide ligand resonances
in a 1:1 ratio in both cases. In the case of 20 resonances
observed at 7.54, 7.07, 7.02, 6.78, 4.53, 4.40, and 3.48
ppm were attributed to biphenyl protons. Similar reso-
nances were observed for the biphenyl protons of 21
(Figure 10). The dramatic upfield shift of phenyl protons
to 4.42, 4.27, and 3.65 ppm (Figure 10a,b) and the well-
separated phenyl protons at 7.57, 7.17, 7.01, and 6.78
ppm (Figure 10c) are consistent with a significant
perturbation of one of the arene rings via interaction
with the Ti center. X-ray crystals of 20 and 21 were
obtained via recrystallization, and the solutions con-
firmed metal-arene interactions (Figure 11). The ge-
ometries about each of the Ti atoms are similar with
coordination to the phosphinimide nitrogen atom, the
η5-cyclopentadienyl ring, and η6-interaction with the
pendant arene ring of the biphenyl substituent. The
Ti-N distances in 20 and 21 average 1.887(2) and

Reduction of Ti(IV)-Phosphinimide Complexes
Organometallics, Vol. 23, No. 13, 2004 3317
F igu r e 12. Ti-Arene interactions in (a) 20 and (b) 21.
Carbon atoms marked with b are σ-bound to Ti.
1.913(4) Å, respectively, consistent with the greater
electron donation to Ti in 21. In contrast to 18 and 19,
the P-N-Ti angles in 20 and 21 are bent dramatically
from linearity, being 145.3(2)° and 145.9(2)°, respec-
tively. This angle is similar to the P-N-Ti angles seen
for average doubly and triply bridging phosphinimide
fragments in [Ti3Cl6(NPMe3)5][BPh4].24 Presumably, the
bend at N does not lead to dimerization or a bridging
arrangement, as this atom resides in a rigid pocket
which is sterically protected by the two tert-butyl groups
on one side and the chelation of the biphenyl unit to Ti
on the other.
The metric parameters associated with the η6-arene
interactions suggest a reduction of the ring and thus a
formal Ti(IV) formulation. The variations of the C-C
bond lengths about the arene unit are consistent with
a cyclohexadiene dianion resonance form (Figure 12).
In 20, the Ti-C(13) and Ti-C(16) distances of 2.236(3)
and 2.254(4) Å are significantly shorter than the other
Ti-C distance of the η6-arene, which range from 2.388-
(3) to 2.472(4) Å. Similarly in 21, C(18) and C(21) are
only 2.236(5) and 2.242(6) Å from Ti, while the remain-
ing arene carbon atoms are between 2.398(5) and 2.454-
(6) Å from Ti. The result is a significant departure from
planarity, as the dihedral angles through the close
approach carbon atoms are 25.3° and 25.9° in 20 and
21, respectively. This is consistent with the sp3 char-
acter at C(13) and C(16) in 20 and C(18) and C(21) in
21 (Figure 12). Thus these species are best viewed as
Ti(IV) metallacyclic species in which the arene ring is
formally reduced. This geometry of the Ti-arene inter-
action is reminiscent of that seen in the Ti-bis-amidi-
nate-toluene species described by Hagadorn and Ar-
nold,25 where similar bending of the arene ring gave rise
to a dihedral angle of 20.0°.
F igu r e 13. ORTEP drawings of one of the two molecules
of 22 in the asymmetric unit, 30% thermal ellipsoids are
shown. Hydrogen atoms are omitted for clarity. Distances
(Å) angles (deg): Ti(1)-N(1) 1.841(2), Ti(1)-C12 2.021(3),
Ti(1)-C11 2.028(4), Ti(1)-C5 2.341(3), Ti(1)-C(4) 2.352-
(3), Ti(1)-C(1) 2.366(3), Ti(1)-C(3) 2.403(3), Ti(1)-C(2)
2.413(3), P(1)-N(1) 1.586(2), C(11)-O(1) 1.150(4), C(12)-
O(2) 1.146(3), N(1)-Ti(1)-C(12) 97.82(11), N(1)-Ti(1)-
C(11) 100.42(11), C(12)-Ti(1)-C(11) 88.07(14), P(1)-N(1)-
Ti(1) 172.30(14), O(1)-C(11)-Ti(1) 179.2(3), O(2)-C(12)-
Ti(1) 178.1(3). N(1)-Ti(1)-C(12) 97.82(11), N(1)-Ti(1)-
C(11) 100.42(11).
reduction of 5 in the presence of PMe3, Me2PCH2CH2-
PMe2, or nitriles afforded extremely sensitive products.
Although preliminary spectral data suggested a flux-
ional Ti(II)-phosphine adduct, these compounds have
not yet been fully characterized. The reduction of 5 in
the presence of CO gave a mixture of products that could
not be characterized. However, reduction of Cp*Ti(NPt-
Bu3)Cl2 (11) in the presence of CO resulted in the clean
production of the green crystalline species Cp*Ti(NPt-
Bu3)(CO)2 (22). IR stretching frequencies at 1948 and
1840 cm-1 were attributed to the coordinated CO. In
comparison, the corresponding bands observed for
Cp2Ti(CO)2 (1977, 1899 cm-1 26
)
and Cp*2Ti(CO)2 (1930,
1850 cm-1 27
)
suggest that the phosphinimide ligand is
a better electron donor than Cp, comparable to Cp*.
X-ray data confirmed the formulation of 22 as the
unequivocal Ti(II)-phosphinimide derivative (Figure 13).
The phosphinimide and carbonyl ligands are approxi-
mately linear. The Ti(1)-N(1) distance in 22 is 1.841-
(2) Å, which is significantly longer than the Ti-N bond
distance seen in 5 (1.775(11) Å), presumably a result of
the decreased electron donation from the phosphinimide
ligand upon reduction from Ti(IV) to Ti(II). The Ti-C
distances for the carbonyl groups were found to be
2.021(3) and 2.028(4) Å, while the C-O distances
were 1.150(4) and 1.146(3) Å. These data are similar to
those reported for Cp2Ti(CO)2.28 The N-Ti-CCO angles
of 97.82(11)° and 100.42(11)° and CCO-Ti-CCO angle
of 88.07(14)° are significantly different from the
Mechanistically, it is suggested that reduction of the
Ti(IV)-dichlorides 18 and 19 generates transient Ti(II)
species, which effects reduction of the arene unit and
formal reoxidation of the metal to Ti(IV). Efforts to
support this view via the interception of a Ti(II)
intermediate with CO using the precursors 18 and 19
led instead to a inseparable mixture of products.
Ti(II) Sp ecies. In an effort to trap an unequivocal
example of a Ti(II)-phosphinimide species, reductions
were done in the presence of simple donor ligands. The
(26) Edwards, B. H.; Rogers, R. D.; Sikora, D. J .; Atwood, J . L.;
Rausch, M. D. J . Am. Chem. Soc. 1983, 105, 416-426.
(27) Brintzinger, H.; Marvich, R. H. J . Am. Chem. Soc. 1971, 93,
2046-2048.
(28) Atwood, J . L.; Stone, K. E.; Alt, H. G.; Hrncir, D. C.; Rausch,
M. D. J . Organomet. Chem. 1975, 96, C4-C6.
(24) Ruebenstahl, T.; Weller, F.; Harms, K.; Dehnicke, K. Z. Anorg.
Allg. Chem. 1994, 620, 1741-1749.
(25) Hagadorn, J . R.; Arnold, J . Angew. Chem., Int. Ed. 1998, 37,
1813-1815.

3318 Organometallics, Vol. 23, No. 13, 2004
Graham et al.
N-Ti-Cl and Cl-Ti-Cl angles of 102.6(2)°, 102.7(2)°,
and 102.69(12)° of 5, consistent with reduction of the
Ti center.
also support the view that the ligand scaffold of CpTi-
(NPt-Bu3) is a steric equivalent to Cp2Ti, a concept that
was previously employed in the design of phosphinim-
ide-based olefin polymerization catalysts.4,10 The utility
of the transient-phosphinimide Ti(II) species in a variety
of applications is currently under investigation. The
results of these efforts will be reported in due course.
Su m m a r y
The reduction chemistry described above illuminates
several keys points. The reduction of Cp-Ti-phosphin-
imide species with small phosphinimide substituents
affords phosphinimide-bridged Ti(III) dimers. Surpris-
ingly, further reduction of these dimeric species does
not appear to occur readily. This stands in marked
contrast to the reduction of 5, where either chloro-
bridged Ti(III) species9 or putative Ti(II) species are
generated. The larger steric demands of the t-Bu3PN
ligand cause the redox chemistry of 5 and 11 to mimic
that of titanocene, affording Ti(IV) cycloaddition prod-
ucts with olefins and acetylenes20,29 and the interception
of a Ti(II) species with carbon monoxide. These results
Ack n ow led gm en t. Financial support from NSERC
of Canada and NOVA Chemicals Corporation is grate-
fully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
data. This material is available free of charge via the Internet
at http://pubs.acs.org.
OM049826Q
(29) Rosenthal, U.; Burlakov, V. V. Titanium Zirconium Org. Synth.
2002, 355-389.