Di-terf-butylbiphenylphosphinimide titanium and zirconium complexes: Pendant arene-metal interactions

Article abstract of DOI:10.1021/om060569u

Reaction of t-Bu₂(2-C₆H₄Ph)PNSiMe ₃ (1), with TiCl₄, affords the product t-Bu ₂(2-C₆H₄Ph)PNTiCl₃ (4). This species is readily alkylated with MeMgBr to give t-Bu₂(2-C₆H ₄Ph)PNTiMe₃ (5). X-ray crystallographic studies reveal that both 4 and 5 adopt conformations in which the biphenyl substituent is oriented toward the metal center. In contrast, the species derived from alkylation or animation and subsequent chemistry including t-Bu ₂(2-C₆H₄Ph)PNTi(CH₂Ph)₃ (6), t-Bu₂(2-C₆H₄Ph)PNTi(NMe₂) ₃ (7), t-Bu₂(2-C₆H₄Ph)PNTi(NMe ₂)₂Cl (8), and t-Bu₂(2-C₆H ₄Ph)PNTi(CH₂Ph)(NMe₂)₂ (9) exist in solution as two isomers in which the biphenyl fragment is oriented toward and away from the metal center. The barriers to interconversion of these isomers were determined by variable-temperature NMR studies to be ca. 92 kJ/mol. The analogous Zr complexes t-Bu₂(2-C₆H₄Ph) PNZr(NEt₂)₃ (10), t-Bu₂(2-C₆H ₄Ph)PNZrCl₃ (11), and r-Bu₂(2-CoH ₄Ph)PNZrMe₃ (12) showed behavior similar to 6-9. Reduction of 4 with Mg powder prompted disproportionation, affording [t-Bu ₂(2-C₆H₄Ph)PN]₂TiCl₂ (13). This species also exists as two isomers: in the minor isomer one of the biphenyl substituents is oriented toward and the other away from the Ti center, while in the major isomer both biphenyl units are oriented away from the metal center. A similar observation was made for [t-Bu₂(2-C ₆H₄Ph)PN]₂TiMe₂ (14) and [t-Bu ₂(2-C₆H₄Ph)-PN]₂ZrMe₂ (15). The latter species was formed in a second-order ligand redistribution reaction from 12 with a rate constant of 4 × 10^-4 s ^-1 at 333 K and ΔH? = 69(2) kJ/mol and ΔS? = -108(6) J/(mol K). Reaction of 5 with B(C₆F₅) ₃ generates [t-Bu₂(2-C₆H₄Ph) PNTiMe₂][MeB(C₆F₅)₃] (16). 16 is a remarkably stable salt in which the Ti-cation is arene-stablized, although the arene is readily displaced by THF to give [t-Bu₂(2-C ₆H₄Ph)PNTiMe₂(THF)][MeB(C₆F ₅)₃] (18). In a similar fashion two isomers of [(t-Bu ₂(2-C₆H₄Ph)PN)₂TiMe][MeB(C ₆F₅)₃] (19) are formed. The biphenyl substituents of the major isomer of 19 are oriented in opposing directions, while in the minor isomer both biphenyl substituents are oriented toward the Ti center. In the latter isomer the arene rings are involved in an intramolecular exchange process (ΔH? = 69(2) kJ/mol, ΔS= 60(2) J/(mol K)).

Full text of DOI:10.1021/om060569u

Organometallics 2006, 25, 4985-4995
4985
Di-tert-butylbiphenylphosphinimide Titanium and Zirconium
Complexes: Pendant Arene-Metal Interactions
Ioan Ghesner, Andrew Fenwick, and Douglas W. Stephan*
Department of Chemistry and Biochemistry, UniVersity of Windsor, Windsor, Ontario, N9P 3B4 Canada
ReceiVed June 28, 2006
Reaction of t-Bu2(2-C6H4Ph)PNSiMe3 (1), with TiCl4 affords the product t-Bu2(2-C6H4Ph)PNTiCl3
(4). This species is readily alkylated with MeMgBr to give t-Bu2(2-C6H4Ph)PNTiMe3 (5). X-ray
crystallographic studies reveal that both 4 and 5 adopt conformations in which the biphenyl substituent
is oriented toward the metal center. In contrast, the species derived from alkylation or amination and
subsequent chemistry including t-Bu2(2-C6H4Ph)PNTi(CH2Ph)3 (6), t-Bu2(2-C6H4Ph)PNTi(NMe2)3 (7),
t-Bu2(2-C6H4Ph)PNTi(NMe2)2Cl (8), and t-Bu2(2-C6H4Ph)PNTi(CH2Ph)(NMe2)2 (9) exist in solution as
two isomers in which the biphenyl fragment is oriented toward and away from the metal center. The
barriers to interconversion of these isomers were determined by variable-temperature NMR studies to be
ca. 92 kJ/mol. The analogous Zr complexes t-Bu2(2-C6H4Ph)PNZr(NEt2)3 (10), t-Bu2(2-C6H4Ph)PNZrCl3
(11), and t-Bu2(2-C6H4Ph)PNZrMe3 (12) showed behavior similar to 6-9. Reduction of 4 with Mg powder
prompted disproportionation, affording [t-Bu2(2-C6H4Ph)PN]2TiCl2 (13). This species also exists as two
isomers: in the minor isomer one of the biphenyl substituents is oriented toward and the other away
from the Ti center, while in the major isomer both biphenyl units are oriented away from the metal
center. A similar observation was made for [t-Bu2(2-C6H4Ph)PN]2TiMe2 (14) and [t-Bu2(2-C6H4Ph)-
PN]2ZrMe2 (15). The latter species was formed in a second-order ligand redistribution reaction from 12
with a rate constant of 4 × 10-4 s-1 at 333 K and ∆Hq ) 69(2) kJ/mol and ∆Sq ) -108(6) J/(mol K).
Reaction of 5 with B(C6F5)3 generates [t-Bu2(2-C6H4Ph)PNTiMe2][MeB(C6F5)3] (16). 16 is a remarkably
stable salt in which the Ti-cation is arene-stablized, although the arene is readily displaced by THF to
give [t-Bu2(2-C6H4Ph)PNTiMe2(THF)][MeB(C6F5)3] (18). In a similar fashion two isomers of [(t-Bu2(2-
C6H4Ph)PN)2TiMe][MeB(C6F5)3] (19) are formed. The biphenyl substituents of the major isomer of 19
are oriented in opposing directions, while in the minor isomer both biphenyl substituents are oriented
toward the Ti center. In the latter isomer the arene rings are involved in an intramolecular exchange
process (∆Hq ) 69(2) kJ/mol, ∆Sq ) 60(2) J/(mol K)).
Scheme 1. Hemilabile Complexes
Introduction
An area of organometallic chemistry that has drawn recent
attention involves the use of hemilabile ligands.1 Such ligands
combine a strong donor group with a fragment that weakly
interacts with a metal center. Such systems have been developed
to exploit the chelate effect to stabilize a reactive metal center
in the absence of other reagents, but at the same time the weak
donor group is readily displaced by substrate, allowing reactions
to go forward. Examples of such hemilabile ligand systems that
have been studied include phosphine-ether, phosphine-thio-
ether, phosphine-arene, cyclopentadienyl-alkene, and cyclo-
pentadienyl-arene ligands (Scheme 1).1 Of particular interest
to our group have been the latter two systems, in which pendant
groups on cyclopentadienyl ligands have been used to stabilize
cationic early metal complexes. In particular, Hessen and co-
workers2 recently exploited CpTi complexes with a pendant
arene fragment to stabilize cationic Ti species that effect the
specific catalytic trimerization of ethylene. In our own work,
we have previously established that the steric analogy between
cyclopentadienyl and phosphinimide ligands is a concept that
can be used to develop highly effective olefin polymerization
catalysts.3-6 In extending our chemistry to systems incorporating
hemilabile ligands, we have previously reported complexes
(3) Stephan, D. W. Organometallics 2005, 24, 2548-2560.
(4) 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.
(5) Stephan, D. W.; Stewart, J. C.; Guerin, F.; Courtenay, S.; Kickham,
J.; Hollink, E.; Beddie, C.; Hoskin, A.; Graham, T.; Wei, P.; Spence, R. E.
v. H.; Xu, W.; Koch, L.; Gao, X.; Harrison, D. G. Organometallics 2003,
22, 1937-1947.
(6) Stephan, D. W.; Stewart, J. C.; Guerin, F.; Spence, R. E. v. H.; Xu,
W.; Harrison, D. G. Organometallics 1999, 18, 1116-1118.
* Corresponding author. E-mail: stephan@uwindsor.ca.
(1) Stone, C. S.; Weinberger, D. A.; Mirkin, C. A. Prog. Inorg. Chem.
1999, 48, 233.
(2) Deckers, P. J. W.; Hessen, B.; Teuben, J. H. Angew. Chem., Int. Ed.
2001, 40, 2516.
10.1021/om060569u CCC: $33.50 © 2006 American Chemical Society
Publication on Web 09/02/2006

4986 Organometallics, Vol. 25, No. 21, 2006
Ghesner et al.
2
Scheme 2. Reduction of Cp′(t-Bu2(2-C6H4Ph)PN)TiCl2 to
Give Cp′(t-Bu2(2-C6H4Ph)PN)Ti
125.31 (d, JCP ) 8 Hz), 127.08 (s), 127.15 (s), 128.08 (s, br),
129.93 (s, br), 133.55 (s, br), 134.07 (br, Cipso), 147.33 (s, br, Cipso).
31P{1H} NMR (THF-d8, 55 °C): 11.4 (s, br). Li NMR (THF-d8,
7
55 °C): -1.4 (s). Anal. Calcd for C20H27NPLi: C, 75.22; H, 8.52;
N, 4.39. Found: C, 74.45; H, 8.13; N, 4.79.
Synthesis of t-Bu2(2-C6H4Ph)PNTiCl3, 4. To a solution of TiCl4
(0.72 g, 3.78 mmol) in 20 mL of toluene at 0 °C was added 1
(1.46 g, 3.78 mmol) in 10 mL of toluene. The solution was refluxed
for 16 h, the volatiles were removed under vacuum, and the residue
was dissolved in CH2Cl2 and passed through a plug of Celite.
Cooling the CH2Cl2 solution at -35 °C afforded 0.74 g (74%) of
a light yellow crystalline solid. X-ray-quality crystals were obtained
by the slow diffusion of pentane into a CH2Cl2 solution of the title
compound. 1H NMR (CDCl3): 1.61 (d, 18H, t-BuP, 3JHP ) 16 Hz),
7.28-7.61 (m, 9H, 2-C6H4Ph). 13C{1H} NMR (CDCl3): 28.48 (s,
incorporating the di-tert-butylbiphenylphosphinimide ligand.7
The pendant arene fragment of the biphenyl has been shown to
oxidatively add to Ti upon reduction of the precursor Ti-
dichloride complex, affording the species Cp′(t-Bu2(2-C6H4Ph)-
PN)Ti (Cp′ ) Cp, Cp*) (Scheme 2).7 While these complexes
are best formulated as Ti(IV) species in which a formally Ti-
(II) center has oxidatively added to the arene ring, this result
suggests the potential of the di-tert-butylbiphenylphosphinimide
ligand to act as a hemilabile ligand. In this paper we probe the
chemistry of such phosphinimide complexes further. Herein,
we report the synthesis and characterization of a series of Ti
and Zr complexes bearing the di-tert-butylbiphenylphosphin-
imide ligand and explore the nature of the resulting hemilabile
ligand complexes.
1
1
t-Bu), 41.43 (d, t-Bu, JCP ) 48 Hz), 121.41 (d, Cipso, JCP ) 76
2
Hz), 126.15 (d, JCP ) 12 Hz), 128.28 (s), 129.10 (s), 129.16 (s),
2
3
131.67 (d, JCP ) 14 Hz), 131.94 (s), 135.59 (d, JCP ) 9 Hz),
140.96 (s, Cipso), 149.69 (s, Cipso). 31P{1H} NMR (C6D6): 42.7 (s).
Anal. Calcd for C20H27Cl3NPTi: C, 51.48; H, 5.83; N, 3.00.
Found: C, 51.66; H, 5.62; N, 3.30.
Synthesis of t-Bu2(2-C6H4Ph)PNTiMe3, 5. To a suspension of
4 (0.635 g, 1.36 mmol) in Et2O (10 mL) was added MeMgBr (1.49
mL, 3.0 M, 4.48 mmol) at 25 °C. The mixture was stirred overnight,
the solvent removed under vacuum, and the residue dissolved in
toluene and filtered through Celite. The clear solution was cooled
Experimental Section
1
at -35 °C to give 452 mg (82%) of colorless crystals. H NMR
(C6D5Br): 0.72 (s, 9H, MeTi), 1.27 (d, 18H, t-BuP, 3JHP ) 14 Hz),
6.91-6.94 (m, 1H, 2-C6H4Ph), 7.10-7.19 (m, 5H, 2-C6H4Ph),
7.24-7.26 (m, 2H, 2-C6H4Ph), 7.49-7.53 (m, 1H, 2-C6H4Ph). 13C-
{1H} NMR (C6D5Br, partial): 28.41 (s, t-Bu), 39.28 (d, t-Bu, 1JCP
General Procedures. All operations were performed under
nitrogen atmosphere using glovebox or Schlenk line techniques.
Solvents were purified employing Grubbs-type column systems
manufactured by Innovative Technologies or were distilled from
the appropriate drying agents under N2. Deuterated solvents d8-
toluene (C7D8) and d6-benzene (C6D6) were dried and distilled from
sodium/benzophenone ketyl, while d5-bromobenzene (C6D5Br), d3-
chloroform, and d2-dichloromethane were dried and distilled from
2
) 54 Hz), 53.25 (s, MeTi), 125.17 (d, JCP ) 11 Hz), 126.76 (s),
127.33 (s), 129.13 (s), 129.97 (s), 131.84 (d, 2JCP ) 12 Hz), 134.69
3
3
(d, JCP ) 9 Hz), 142.70 (s, Cipso), 149.55 (d, Cipso, JCP ) 5 Hz).
31P{1H} NMR (C6D6): 21.3 (s). Anal. Calcd for C23H36NPTi: C,
68.15; H, 8.95; N, 3.46. Found: C, 67.91; H, 8.30; N, 3.49.
1
7
CaH2. H, 11B{1H}, 13C{1H}, 19F, Li, and 31P{1H} NMR experi-
ments were performed on Bruker Avance 300 and 500 MHz
spectrometers. Data are given in ppm relative to residual solvent
signals for 1H and 13C spectra. Spectra were recorded at 25 °C unless
Synthesis of t-Bu2(2-C6H4Ph)PNTi(CH2Ph)3, 6. To a suspen-
sion of 4 (0.235 g, 0.50 mmol) in Et2O (10 mL) was added PhCH2-
MgCl (1.67 mL, 1.0 M, 1.66 mmol) at room temperature. The
mixture was stirred overnight, the solvent removed under vacuum,
and the residue dissolved in toluene and filtered through Celite.
The clear yellow solution was cooled to -35 °C to give 254 mg
(76%) of the title compound as a 1:1.4 mixture of two isomers. 1H
otherwise noted. 11B, 19F, Li, and 31P spectra were referenced to
7
external BF3‚OEt2, CCl3F, LiCl(aq), and 85% H3PO4, respectively.
Elemental analyses were performed in the microanalytical laboratory
of the Department of Chemistry (University of Windsor). t-Bu2(2-
C6H4Ph)PNSiMe3 (1) was prepared as previously reported.7
Synthesis of t-Bu2(2-C6H4Ph)PNH, 2. Compound 1 (2.00 g,
5.19 mmol) was stirred in a mixture of toluene/methanol (20 mL/5
mL) for 20 h at 25 °C. The volatiles were removed, and the title
compound was isolated as a white powder in quantitative yield.
1H NMR (CDCl3): -0.88 (s, br, 1H, NH), 1.25 (d, 18H, t-BuP,
3JHP ) 13.7 Hz), 7.02-7.20, 7.31-7.38, 7.59-7.64 (m, 9H, 2-C6H4-
3
NMR (toluene-d8): 0.86 (d, 18H, t-BuP, JHP ) 15 Hz, minor
3
isomer), 0.99 (d, 18H, t-BuP, JHP ) 14 Hz, major isomer), 2.41
(s, 6H, CH2Ph, major isomer), 2.66 (s, 6H, CH2Ph, major isomer),
6.73-7.24 (m, 2-C6H4Ph, major isomer and minor isomer), 9.00
3
3
(dd, 1H, 2-C6H4Ph, JHH ) 13 Hz, JHH ) 8 Hz, minor isomer).
13C{1H} NMR (toluene-d8) partial: 27.98 (s, t-Bu, minor isomer),
28.57 (s, t-Bu, major isomer), 38.31 (d, t-Bu, 1JCP ) 52 Hz, minor
1
Ph). 13C{1H} NMR (CDCl3): 28.16 (s, t-Bu), 37.15 (d, t-Bu, JCP
1
isomer), 39.51 (d, t-Bu, JCP ) 53 Hz, major isomer), 78.87 (s,
) 61 Hz), 125.26 (d, 2JCP ) 8 Hz), 126.92 (s), 127.07 (s), 129.23
CH2Ph, minor isomer), 84.63 (s, CH2Ph, major isomer), 121.70
(s), 121.99 (s), 127.26 (s), 127.45 (s), 127.78 (s), 129.81 (s), 130.31
(d, 2JCP ) 11 Hz), 130.95 (s), 132.08 (d, 2JCP ) 13 Hz), 133.16 (d,
1
3
(s), 129.28 (s), 131.11 (d, Cipso, JCP ) 48 Hz), 132.17 (d, JCP
)
,
2
7 Hz), 133.23 (d, JCP ) 8 Hz), 142.79 (s, Cipso), 149.63 (d, Cipso
3JCP ) 6 Hz). 31P{1H} NMR (C6D6): 42.3 (s). Anal. Calcd for
C20H28NP: C, 76.64; H, 9.00; N, 4.47. Found: C, 76.60; H, 9.28;
N, 4.41.
3
3
2JCP ) 9 Hz), 135.46 (d, JCP ) 9 Hz), 139.37 (d, JCP ) 9 Hz),
143.41 (s, Cipso), 144.62 (s, Cipso), 147.04 (s), 148.38 (s), 149.59
(s, Cipso). 31P{1H} NMR (toluene-d8): 25.5 (s, major isomer), 37.6
(s, minor isomer). Anal. Calcd for C41H48NPTi: C, 77.71; H, 7.64;
N, 2.21. Found: C, 73.83; H, 8.13; N, 2.29.
Synthesis of t-Bu2(2-C6H4Ph)PNLi, 3. To a solution of 2 (272
mg, 0.87 mmol) in 5 mL of hexane was added t-BuLi (56 mg, 0.5
mL, 1.7 M in n-hexane) at 25 °C. The mixture was stirred for 16
h, and the resulting white precipitate filtered to yield 255 mg (92%)
of the title compound. 1H NMR (THF-d8, 55 °C): 1.15 (d, br, 18H,
Synthesis of t-Bu2(2-C6H4Ph)PNTi(NMe2)3, 7. To a solution
of Ti(NMe2)4 (0.385 g, 1.72 mmol) in toluene (10 mL) was added
2 (0.538 g, 1.72 mmol) at 25 °C. The mixture was stirred overnight
at 70 °C, the volatiles were removed under vacuum, and the residue
was dissolved in a minimum amount of toluene and cooled at -35
°C to give 0.82 g (97%) of orange crystals. Compound 7 exists as
a 2.2:1 mixture of two isomers at 25 °C. Only the major isomer
3
t-BuP, JHP ) 11.1 Hz), 6.89 (s, br, 2H, 2-C6H4Ph), 7.21-7.28
(m, 6H, 2-C6H4Ph), 7.81 (s, br, 1H, 2-C6H4Ph). 13C{1H} NMR
1
(THF-d8, 55 °C): 30.25 (s, t-Bu), 39.13 (d, t-Bu, JCP ) 50 Hz),
(7) Graham, T. W.; Kickham, J.; Courtenay, S.; Wei, P.; Stephan, D.
W. Organometallics 2004, 23, 3309-3318.
1
crystallizes and was characterized by X-ray diffraction. H NMR

Di-tert-butylbiphenylphosphinimide Ti and Zr Complexes
Organometallics, Vol. 25, No. 21, 2006 4987
(C6D6): 1.20 (d, 18H, t-BuP, 3JHP ) 15.1 Hz, minor isomer), 1.37
(d, 18H, t-BuP, 3JHP ) 14 Hz, major isomer), 3.27 (s, 18H, NMe,
major isomer), 3.53 (s, 18H, NMe, minor isomer), 7.05 (m, br,
3H, 2-C6H4Ph, minor isomer), 7.14 (m, br, 4H, 2-C6H4Ph, major
isomer), 7.28 (m, 2H, 2-C6H4Ph, minor isomer), 7.31 (m, br, 3H,
2-C6H4Ph, major isomer), 7.50 (m, br, 1H, 2-C6H4Ph, minor
isomer), 7.57 (m, 2H, 2-C6H4Ph, major isomer), 7.64 (m, 2H,
2-C6H4Ph, minor isomer), 9.72 (m, 1H, 2-C6H4Ph, minor isomer).
13C{1H} NMR (C6D6, partial): 28.23 (s, t-Bu, minor isomer), 28.77
(0.834 g, 2.66 mmol) at 25 °C. The mixture was stirred overnight,
and the volatiles were removed under vacuum to give the title
compound as a white solid in quantitative yield. The compound
exists at room temperature as a 1.4:1 mixture of two isomers. The
major isomer crystallizes from benzene and was characterized by
1
3
X-ray diffraction. H NMR (C6D6): 1.08 (d, 18H, t-BuP, JHP
)
15 Hz, minor isomer), 1.18 (t, 18H, NCH2Me, 3JHH ) 7 Hz, major
3
isomer), 1.25 (d, 18H, t-BuP, JHP ) 14 Hz, major isomer), 1.31
(t, 18H, NCH2Me, 3JHH ) 7 Hz, minor isomer), 3.43 (q, 12H, NCH2-
Me, 3JHH ) 7 Hz, major isomer), 3.62 (q, NCH2Me, 3JHH ) 7 Hz,
minor isomer), 6.94-7.58 (m, 2-C6H4Ph, minor isomer and major
isomer), 9.50 (dd, 1H, 2-C6H4Ph,3JHP ) 13 Hz, 3JHH ) 8 Hz, minor
isomer). 13C{1H} NMR (C6D6): 15.61 (s, NCH2Me, major isomer),
16.50 (s, NCH2Me, minor isomer), 28.30 (s, t-Bu, minor isomer),
28.99 (s, t-Bu, major isomer), 36.85 (d, t-Bu, 1JCP ) 57 Hz, minor
1
(s, t-Bu, major isomer), 36.96 (d, t-Bu, JCP ) 55.4 Hz, minor
1
isomer), 38.46 (d, t-Bu, JCP ) 52.7 Hz, major isomer), 46.08 (s,
MeNTi, minor isomer), 46.37 (s, MeNTi, major isomer), 124.68
2
(d, JCP ) 11 Hz), 126.62 (s), 126.99 (s), 127.38 (s), 128.29 (s),
128.50 (s), 129.28 (s, Cipso), 129.52 (s), 129.88 (s), 130.36 (s),
2
2
131.13 (s), 132.53 (d, JCP ) 11 Hz), 132.90 (d, JCP ) 9 Hz),
135.20 (d, 2JCP ) 9 Hz), 139.21 (d, 2JCP ) 7 Hz), 142.55 (s, Cipso),
isomer), 38.42 (d, t-Bu, JCP ) 54 Hz, major isomer), 43.56 (s,
1
3
144.07 (d, Cipso, JCP ) 6 Hz), 145.47 (s, Cipso), 150.17 (d, Cipso
,
NCH2Me, major isomer), 44.36 (s, NCH2Me, minor isomer), 124.66
3JCP ) 5 Hz). 31P{1H} NMR (C6D6): 20.6 (s, major isomer), 33.1
(s, minor isomer). Anal. Calcd for C26H45N4PTi: C, 63.41; H, 9.21;
N, 11.38. Found: C, 63.19; H, 9.60; N, 11.01.
(d, JCP ) 11 Hz), 126.73 (d, JCP ) 10 Hz), 126.92 (s), 127.26
(s), 127.36 (s), 129.37 (s), 129.94 (s), 130.61 (s), 131.17 (s), 132.60
(d, 2JCP ) 11 Hz), 132.83 (d, 2JCP ) 8 Hz), 133.16 (s, Cipso), 133.62
(s, Cipso), 135.08 (d, 3JCP ) 8 Hz), 139.04 (d, 3JCP ) 8 Hz), 142.79
(s, Cipso), 143.97 (s, Cipso), 145.67 (s, Cipso), 149.97 (s, Cipso). 31P-
{1H} NMR (C6D6): 21.4 (s, major isomer), 35.1 (s, minor isomer).
Anal. Calcd for C32H57N4PZr: C, 61.99; H, 9.27; N, 9.04. Found:
C, 62.87; H, 9.18; N, 9.00.
2
2
Synthesis of t-Bu2(2-C6H4Ph)PNTi(NMe2)2Cl, 8. To a solution
of 7 (0.486 g, 0.98 mmol) in toluene (15 mL) was added Me3SiCl
(0.107 g, 0.98 mmol) in 5 mL of toluene at 25 °C. The mixture
was stirred overnight, and the volatiles were removed under vacuum
to give the title compound in quantitative yield as a 3.6:1 mixture
of two isomers. 1H NMR (C6D6): 1.18 (d, 18H, t-BuP, 3JHP ) 15
Synthesis of t-Bu2(2-C6H4Ph)PNZrCl3, 11. To a solution of
10 (562 mg, 0.90 mmol) in toluene (20 mL) was added Me3SiCl
(590 mg, 5.4 mmol) at 25 °C. The mixture was stirred for 3 days
at 80 °C, the volatiles were removed under vacuum, and the residue
was washed with CHCl3. The compound is isolated as a white solid
3
Hz, minor isomer), 1.40 (d, 18H, t-BuP, JHP ) 14 Hz, major
isomer), 3.30 (s, 12H, NMe, major isomer), 3.50 (s, 12H, NMe,
minor isomer), 7.00-7.29, 7.44-7.52 (m, 2-C6H4Ph, minor isomer
and major isomer), 7.14 (dd, br, 1H, 2-C6H4Ph, 3JHP ) 12 Hz, 3JHH
) 8 Hz, minor isomer). 13C{1H} NMR (C6D6): 27.79 (s, t-Bu,
1
in 87% (402 mg) yield. H NMR (THF-d8): 1.22 (d, 18H, t-BuP,
1
minor isomer), 28.79 (s, t-Bu, major isomer), 37.61 (d, t-Bu, JCP
3JHP ) 16 Hz), 7.08-7.10, 7.35, 7.46-7.50, 7.52-7.54 (m, 2-C6H4-
1
) 55 Hz, minor isomer), 39.30 (d, t-Bu, JCP ) 53 Hz, major
Ph), 9.37 (dd, 1H, 2-C6H4Ph,3JHP ) 13 Hz, 3JHH ) 8 Hz). 13C{1H}
1
isomer), 45.87 (s, MeNTi, minor isomer), 46.33 (s, MeNTi, major
NMR (THF-d8): 25.60 (s, t-Bu), 37.09 (d, t-Bu, JCP ) 53 Hz),
2
isomer), 124.93 (d, JCP ) 11 Hz), 126.65 (s), 127.28 (s), 129.69
124.37 (d, 2JCP ) 10 Hz), 125.53 (s), 125.94 (s), 126.82 (s, Cipso),
(s), 129.93 (s), 130.86 (s, Cipso), 132.19 (d, 2JCP ) 12 Hz), 134.90
(d, 3JCP ) 9 Hz), 142.19 (s, Cipso), 149.92 (s, Cipso). 31P{1H} NMR
(C6D6): 21.9 (s, major isomer), 35.7 (s, minor isomer). Anal. Calcd
for C24H39N3PClTi: C, 59.57; H, 8.12; N, 8.68. Found: C, 59.39;
H, 8.62; N, 8.60.
127.97 (s), 128.72 (s), 130.76 (d, 2JCP ) 10 Hz), 137.79 (d, 3JCP
)
1
8 Hz), 142.33 (d, JCP ) 8 Hz, Cipso), 142.63 (s, Cipso). 31P{1H}
NMR (THF-d8): 33.6 (s). Anal. Calcd for C20H27NCl3PZr: C,
47.10; H, 5.34; N, 2.75. Found: C, 47.48; H, 5.86; N, 2.85.
Synthesis of t-Bu2(2-C6H4Ph)PNZrMe3, 12. To a suspension
of 11 (1.6 g, 3.14 mmol) in Et2O (20 mL) was added MeMgBr
(3.36 mL, 3.0 M, 10.08 mmol) at 25 °C. The mixture was stirred
for 4 h at 25 °C, the solvent removed under vacuum, and the residue
dissolved in toluene and filtered through Celite. The clear solution
was cooled at -35 °C to give 1.1 g (78%) of colorless crystals. 1H
NMR (C6D6): 0.49 (s, 9H, MeTi), 1.30 (d, 18H, t-BuP, 3JHP ) 14
Hz), 7.05-7.43 (m, 2-C6H4Ph). 13C{1H} NMR (C6D6): 28.40 (s,
Synthesis of t-Bu2(2-C6H4Ph)PNTi(CH2Ph)(NMe2)2, 9. To a
suspension of 7 (0.200 g, 0.41 mmol) in Et2O (10 mL) was added
PhCH2MgCl (0.4 mL, 1.0 M, 0.41 mmol) at room temperature.
The mixture was stirred overnight, the solvent removed under
vacuum, and the residue dissolved in toluene and filtered through
Celite. The clear yellow solution was cooled at -35 °C to give
212 mg (95%) of the title compound as a 4:1 mixture of two
1
3
1
isomers. H NMR (C6D5Br): 1.01 (d, 18H, t-BuP, JHP ) 15 Hz,
minor isomer), 1.27 (d, 18H, t-BuP, 3JHP ) 14 Hz, major isomer),
2.15 (s, 2H, CH2Ph, major isomer), 2.51 (s, 2H, CH2Ph, minor
isomer), 2.92 (s, 12H, NMe, major isomer), 3.13 (s, 12H, NMe,
minor isomer), 6.74-7.56 (m, 2-C6H4Ph, minor isomer and major
isomer), 7.14 (dd, 1H, 2-C6H4Ph, 3JHP ) 13 Hz, 3JHH ) 8 Hz, minor
isomer). 13C{1H} NMR (C6D5Br): 26.75 (s, t-Bu, minor isomer),
27.78 (s, t-Bu, major isomer), 36.24 (d, t-Bu, 1JCP ) 54 Hz, minor
t-Bu), 38.61 (d, t-Bu, JCP ) 55 Hz), 41.60 (s, MeTi), 125.20 (d,
3JCP ) 11 Hz), 127.04 (s, Cipso), 127.30 (s), 127.33 (s), 129.21 (s),
3
2
129.83 (d, JCP ) 3 Hz, Cipso), 132.06 (d, JCP ) 11 Hz), 134.69
(d, 3JCP ) 9 Hz), 143.06 (s, Cipso), 149.97 (s, Cipso). 31P{1H} NMR
(C6D6): 20.5 (s). Anal. Calcd for C23H36NPZr: C, 61.56; H, 8.09;
N, 3.12. Found: C, 60.65; H, 8.72; N, 3.02.
Synthesis of [t-Bu2(2-C6H4Ph)PN]2TiCl2, 13. (a) To a solution
of TiCl3 (320 mg, 2.07 mmol) in 15 mL of THF was added 3 (660
mg, 2.07 mmol) in 10 mL of THF at -78 °C and the solution
allowed to warm to 25 °C. Afterward the volatiles were removed,
and the residue was dissolved in Et2O and passed through a plug
of Celite. Removal of Et2O gave 353 mg (46%) of the title
compound as a 2.2:1 mixture of two isomers. Crystals were grown
by slow diffusion of hexanes into a solution of the title compound
in Et2O/C6H6. (b) To Mg powder (35 mg, 1.45 mmol) in 5 mL of
Et2O was added at room temperature 135 mg (0.29 mmol) of 4 in
10 mL of Et2O. Afterward 1 mL of THF was added and the mixture
stirred for 24 h at room temperature. The volatiles were removed
under vacuum, and the residue was extracted in toluene and filtered
through Celite. Removal of toluene gave 45 mg (42%) of the title
1
isomer), 38.07 (d, t-Bu, JCP ) 54 Hz, major isomer), 44.06 (s,
NMe, minor isomer), 44.44 (s, NMe, major isomer), 56.81 (s, CH2-
Ph, minor isomer), 58.99 (s, CH2Ph, major isomer), 118.27 (s),
123.87 (d, 2JCP ) 10 Hz), 124.33 (s), 124.58 (s), 124.78 (s), 125.11
(s), 125.64 (s), 126.43 (s), 126.71 (s), 127.21 (s), 128.01 (s), 128.12
(s), 128.51 (s), 130.91 (d, 2JCP ) 11 Hz), 133.50 (d, 3JCP ) 9 Hz),
136.42 (s), 141.10 (s), 148.39 (s), 150.58 (s). 31P{1H} NMR (C6D5-
Br): 17.5 (s, major isomer), 33.1 (s, minor isomer). Anal. Calcd
for C31H46N3PTi: C, 69.01; H, 8.59; N, 7.79. Found: C, 70.67; H,
8.86; N, 6.99.
Synthesis of t-Bu2(2-C6H4Ph)PNZr(NEt2)3, 10. To a solution
of Zr(NEt2)4 (1.01 g, 2.66 mmol) in toluene (20 mL) was added 2

4988 Organometallics, Vol. 25, No. 21, 2006
Ghesner et al.
1
compound as a 2.2:1 mixture of two isomers. H NMR (CDCl3):
1.16 (d, br, 18H t-BuP, 3JHP ) 18 Hz, minor isomer), 1.19 (d, 36H,
t-BuP, 3JHP ) 15 Hz, major isomer), 1.51 (d, br, 18H, t-BuP, 3JHP
) 14 Hz, minor isomer), 7.11-7.70 (m, 2-C6H4Ph, major isomer
minor isomer). Anal. Calcd for C42H60N2P2Zr: C, 67.61; H, 8.11;
N, 3.75. Found: C, 67.26; H, 9.01; N, 3.51.
Synthesis of [t-Bu2(2-C6H4Ph)PNTiMe2][MeB(C6F5)3], 16. A
solution of B(C6F5)3 (25 mg, 0.049 mmol) in C6D5Br (0.3 mL)
was added via syringe to a frozen (liquid N2) solution of 5 (20 mg,
0.049 mmol) in C6D5Br (0.3 mL). The mixture was warmed to 25
°C with vigorous shaking. 1H NMR (C6D5Br): 0.80 (s, 6H, MeTi),
and minor isomer), 9.37 (dd, 1H, 2-C6H4Ph, 3JHP ) 12 Hz, 3JHH
)
8 Hz, major isomer). 13C{1H} NMR (CDCl3): 27.93 (s, Me3CP,
major isomer and minor isomer), 28.90 (s, t-Bu, minor isomer),
1
1
3
38.79 (d, t-Bu, JCP ) 52 Hz, major isomer), 38.91 (d, t-Bu, JCP
1.22 (d, 18H, t-BuP, JHP ) 16 Hz), 1.25 (s, br, 3H, Me-B), 6.64
1
) 54 Hz, minor isomer), 40.03 (d, t-Bu, JCP ) 52 Hz, minor
(m, 2H, 2-C6H4Ph), 7.09-7.13 (m, 2H, 2-C6H4Ph), 7.49-7.60 (m,
3H, 2-C6H4Ph), 7.70-7.82 (m, 2H, 2-C6H4Ph). 13C{1H} NMR
(C6D5Br): 11.21 (s, br, Me-B), 27.16 (s, t-Bu), 38.49 (d, t-Bu, 1JCP
) 52 Hz), 54.46 (s, MeTi). 31P{1H} NMR (C6D5Br): 34.1 (s). 11B-
{1H} NMR (C6D5Br): -15.0 (s). 19F NMR (C6D5Br): -166.8 (m,
m-C6F5), -164.2 (t, p-C6F5), -132.2 (d, o-C6F5). Anal. Calcd for
C41H36BF15NPTi: C, 53.68; H, 3.96; N, 1.53. Found: C, 51.48;
H, 4.11; N, 1.19.
2
isomer), 126.84 (d, JCP ) 11 Hz), 127.47 (s), 127.72 (d, Cipso
,
1JCP ) 24 Hz), 128.01 (s), 129.92 (s), 130.69 (s), 132.73 (d, JCP
3
3
2
) 10 Hz), 139.26 (d, JCP ) 7 Hz), 143.81 (d, Cipso, JCP ) 10
Hz), 144.23 (s, Cipso). Only the aromatic carbons of the major isomer
were detected. 31P{1H} NMR (CDCl3): 23.7 (s, minor isomer), 36.
9 (s, minor isomer), 37.0 (s, major isomer). Anal. Calcd for C40H54-
Cl2N2P2Ti: C, 64.61; H, 7.32; N, 3.77. Found: C, 64.64; H, 7.30;
N, 3.46.
Synthesis of [t-Bu2(2-C6H4Ph)PNTi(NMe2)2][PhCH2B(C6F5)3],
17. A solution of B(C6F5)3 (98 mg, 0.19 mmol) in C6D5Br (0.4
mL) was added via syringe to a frozen (liquid N2) solution of 9
(103 mg, 0.19 mmol) in C6D5Br (0.3 mL). The mixture was warmed
to 25 °C with vigorous shaking. 1H NMR (C6D5Br): 1.01 (d, 18H,
t-BuP, 3JHP ) 15 Hz), 2.91 (s, 12H, NMe), 3.28 (s, br, 2H, PhCH2-
B), 6.66-7.37 (m, 14H, 2-C6H4Ph, C6H5CH2). 13C{1H} NMR
(C6D5Br): 27.62 (s, t-Bu), 32.26 (s, br, CH2-B), 37.91 (d, t-Bu,
1JCP ) 50.5 Hz), 48.75 (s, MeNTi). 31P{1H} NMR (C6D5Br): 28.9
(s). 11B{1H} NMR (C6D5Br): -15.0 (s). 19F NMR (C6D5Br): -163.8
Synthesis of [t-Bu2(2-C6H4Ph)PN]2TiMe2, 14. (a) To a solution
of 5 (189 mg, 0.46 mmol) in 10 mL of toluene was added 2 (146
mg, 0.46 mmol) in 10 mL of toluene at 25 °C, and the mixture
was heated to 80 °C for 4 h. Thereafter the volatiles were removed
to give the title compound as a 2.4:1 mixture of two isomers in
quantitative yield (by NMR). (b) To a solution of 13 (360 mg, 0.48
mmol) in Et2O (10 mL) was added MeMgBr (0.33 mL, 3.0 M,
0.96 mmol) at 25 °C. The mixture was stirred overnight, the solvent
removed under vacuum, and the residue dissolved in toluene and
filtered through Celite. The clear yellow solution was cooled at
-35 °C to give 292 mg (86%) of the title compound as a white
solid. 1H NMR (C6D5Br): 0.27 (s, 6H, Ti-Me, major isomer), 0.67
(s, 6H, Ti-Me, minor isomer), 1.02 (d, 36H, t-BuP, 3JHP ) 15 Hz,
major isomer), 1.05 (d, br, 18H, t-BuP, JHP ) 15 Hz, minor
isomer), 1.27 (d, br, 18H, t-BuP, JHP ) 14 Hz, major isomer),
6.80-7.55 (m, 2-C6H4Ph, minor isomer and major isomer), 9.39-
9.55 (m, 2-C6H4Ph, minor isomer and major isomer). 13C{1H} NMR
(C6D5Br): 28.11 (s, t-Bu, major isomer and minor isomer), 28.95
(s, t-Bu, minor isomer), 37.87 (d, t-Bu, 1JCP ) 55 Hz, minor isomer),
3
3
(dd, m-C6F5, JFF ) 23 Hz), -161.06 (t, p-C6F5, JFF ) 23 Hz),
-127.55 (d, o-C6F5, 3JFF ) 23 Hz). Anal. Calcd for C49H46BF15N3-
PTi: C, 55.97; H, 4.41; N, 4.00. Found: C, 54.67; H, 4.75; N,
3.46.
3
Generation of [t-Bu2(2-C6H4Ph)PNTiMe2(THF)][MeB(C6F5)3],
18. This species was generated by the addition of THF (0.1 mL) to
a C6D5Br solution of 16. 1H NMR (C6D5Br): 0.99 (s, 6H, MeTi),
1.26 (s, br, 3H, MeB), 1.34 (d, 18H, t-BuP, 3JHP ) 15 Hz), 6.71-
7.27 (m, 9H, 2-C6H4Ph). 31P{1H} NMR (C6D5Br): 36.4 (s). 11B-
{1H} NMR (C6D5Br): -15.00 (s).
3
1
38.06 (d, t-Bu, JCP ) 56 Hz, minor isomer), 38.19 (s, Ti-Me),
39.26 (d, Me3CP, JCP ) 54 Hz, major isomer), 41.87 (s, TiMe),
Synthesis of [(t-Bu2(2-C6H4Ph)PN)2TiMe][MeB(C6F5)3], 19.
A solution of B(C6F5)3 (17.5 mg, 0.034 mmol) in C6D5Br (0.3 mL)
was added via syringe to a frozen (liquid N2) solution of 14 (24
mg, 0.034 mmol) in C6D5Br (0.3 mL). The mixture was warmed
to 25 °C with vigorous shaking. The NMR spectra show the
formation of two isomers in 2:1 ratio at 25 °C and 1:1 ratio at -20
1
2
2
124.66 (d, JCP ) 10 Hz), 126.08 (d, JCP ) 9 Hz), 126.56 (m),
127.66 (s), 127.70 (s), 129.25 (s, br), 129.62 (s), 129.79 (s), 130.84
(s), 131.37 (s), 132.33 (d, 3JCP ) 8 Hz), 132.44 (d, 2JCP ) 11 Hz),
134.73 (d, 3JCP ) 9 Hz), 139.44 (d, 3JCP ) 8 Hz), 139.72 (s), 139.83
2
1
(s), 142.83 (s, Cipso), 143.58 (d, Cipso, JCP ) 8.8 Hz), 145.07 (d,
°C. H NMR (C6D5Br): 0.29 (s, 3H, TiMe, minor isomer), 0.45
ipso, JCP ) 6.0 Hz), 149.94 (s, Cipso). 31P{1H} NMR (C6D5Br):
2
3
C
(s, 3H, TiMe, major isomer), 0.91 (d, 9H, t-BuP, JHP ) 15 Hz),
3
3
13.8 (s, major isomer), 26.5 (s, major isomer), 27.1 (s, minor
isomer). Anal. Calcd for C42H60N2P2Ti: C, 71.78; H, 8.61; N, 3.99.
Found: C, 70.97; H, 9.09; N, 3.93.
0.95 (d, 9H, t-BuP, JHP ) 16 Hz), 1.00 (d, 9H, t-BuP, JHP ) 15
3
Hz), 1.10 (d, 9H, t-BuP, JHP ) 14 Hz), 1.11 (s, br, 6H, Me-B),
6.81-7.58 (m, 35H, 2-C6H4Ph major isomer and minor isomer),
8.95 (dd, 1H, 2-C6H4Ph,3JHP ) 13 Hz, 3JHH ) 8 Hz, major isomer).
31P{1H} NMR (C6D5Br): 27.6 (s, major isomer), 29.0 (s, br, minor
isomer), 39.7 (s, major isomer). 11B{1H} NMR (C6D5Br): -14.0
(s). 19F NMR (C6D5Br): -167.63 (m, m-C6F5), -165.21 (t, p-C6F5,
3JFF ) 23 Hz), -132.84 (d, o-C6F5, 3JFF ) 23 Hz). 1H NMR (C6D5-
Br, -20 °C): 0.31 (s, 3H, TiMe), 0.43 (s, 3H, TiMe), 0.86-1.29
(m, t-BuP, Me-B), 6.10 (s, br, 1H, 2-C6H4Ph), 6.66 (d, 2H, 2-C6H4-
Ph, 3JHH ) 7.3 Hz), 6.88-7.47 (m, 32H, 2-C6H4Ph), 9.00 (dd, 1H,
Synthesis of [t-Bu2(2-C6H4Ph)PN]2ZrMe2, 15. To a solution
of 12 (120 mg, 0.26 mmol) in 2 mL of toluene was added 2 (84
mg, 0.26 mmol) in 2 mL of toluene at 25 °C, and the mixture was
stirred for 1 h. Thereafter the volatiles were removed under vacuum
to give the title compound as a 24:1 mixture of two isomers in
quantitative yield (by NMR). H NMR (C6D6): 0.38 (s, 6H, Zr-
Me, major isomer), 0.76 (s, 6H, ZrMe, minor isomer), 1.27 (d, 18H,
t-BuP, JHP ) 15 Hz, major isomer), 1.48 (d, 18H, t-BuP, JHP
15 Hz, major isomer), 7.07-7.73 (m, 2-C6H4Ph, minor isomer and
major isomer), 9.07 (m, 1H, 2-C6H4Ph, major isomer), 9.86 (m,
2H, 2-C6H4Ph, minor isomer). 13C{1H} NMR (C6D6): 28.07 (s,
t-Bu, major isomer), 28.78 (s, t-Bu, major isomer), 31.56 (s, ZrMe),
1
3
3
)
3
2-C6H4Ph,3JHP ) 12 Hz, JHH ) 9 Hz). 31P{1H} NMR (C6D5Br,
-20 °C): 27.0 (s), 27.6 (s, br), 28.6 (s, br), 38.5 (s). 11B{1H} NMR
(C6D5Br): -14.1 (s). 19F NMR (C6D5Br, -20 °C): -166.38 (m,
3
m-C6F5), -163.86 (t, p-C6F5, JFF ) 23 Hz), -132.27 (d, o-C6F5,
3JFF ) 23 Hz). Anal. Calcd for C60H60BF15N2P2Ti: C, 59.33; H,
1
1
37.39 (d, t-Bu, JCP ) 56 Hz, major isomer), 38.54 (d, t-Bu, JCP
) 55 Hz, major isomer), 124.53 (d, 2JCP ) 10 Hz), 126.16 (d, 2JCP
) 10 Hz), 127.00 (s), 127.22 (s), 127.44 (s), 128.08 (s), 129.13
(s), 129.49 (s), 129.94 (s), 130.94 (s), 132.28 (d, 2JCP ) 11.0 Hz),
4.98; N, 2.31. Found: C, 56.65; H, 4.82; N, 2.17.
X-ray Data Collection. Crystals were manipulated and mounted
in capillaries in a glovebox, thus maintaining a dry, O2-free
environment for each crystal. Diffraction experiments were per-
formed 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
3
3
3
132.41 (d, JCP ) 8 Hz), 134.54 (d, JCP ) 7 Hz), 139.46 (d, JCP
2
) 7 Hz), 143.09 (s), 143.81 (d, JCP ) 6 Hz), 145.53 (s), 150.24
(s). Signals for the minor isomer were not detected. 31P{1H} NMR
(C6D6): 20.3 (s, major isomer), 34.7 (s, major isomer), 35.2 (s,

Di-tert-butylbiphenylphosphinimide Ti and Zr Complexes
Table 1. Crystallographic Data
Organometallics, Vol. 25, No. 21, 2006 4989
2
3
4
7
10
12
13
formula
fw
C20H28NP
313.40
C20H27Cl3NPTi
466.65
C23H36NPTi
405.40
C26H45N4PTi
492.53
C32H54N4PZr
616.98
C23H36NPZr
448.72
C46H60Cl2N2P2Ti
821.70
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
monoclinic
P21/n
7.5461(8)
18.4617(19)
13.6904(14)
monoclinic
P21/n
9.8980(16)
18.636(3)
12.627(2)
monoclinic
P21/c
10.1625(18)
23.486(4)
11.204(2)
monoclinic
C2/c
36.987(7)
8.9097(17)
20.268(4)
triclinic
P1h
monoclinic
P21/c
15.766(4)
10.345(3)
15.789(4)
monoclinic
P21/c
10.176(2)
32.413(8)
14.192(3)
11.705(11)
16.532(15)
18.632(17)
89.866(10)
89.743(9)
84.667(10)
3590(6)
4
100.0490(10)
92.086(2)
115.851(2)
120.594(2)
105.277(2)
102.166(3)
1878.0(3)
4
1.108
0.144
17 699
2327.5(6)
4
1.332
0.785
22 021
2406.5(7)
4
1.119
0.428
22 876
5749.4(19)
8
1.138
0.372
26 865
2484.1(10)
4
1.200
0.513
13 665
4575.7(19)
4
1.193
0.406
43 725
Z
d(calc) (g cm-1
)
1.142
0.374
34 371
abs coeff, µ (cm-1
no. of data
)
collected
no. of data
3287
4090
4221
5068
12 543
2825
8061
2
Fo2 > 3σ(Fo )
no. of variables
203
235
235
289
685
235
478
R
Rw
GOF
0.0446
0.1191
1.014
0.0371
0.1002
1.034
0.0471
0.1467
0.743
0.0589
0.1573
1.007
0.0477
0.1285
1.014
0.0379
0.0863
0.728
0.0518
0.1195
0.995
Scheme 3. Synthesis of Compounds 2-9
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 refinement was performed
using the SHELXTL solution package.
Structure Solution and Refinement. Non-hydrogen atomic
scattering factors were taken from the literature tabulations.8 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 refinements were carried out by using
full-matrix least-squares techniques on F, minimizing the function
2
2
w(|Fo| - |Fc|)2, where the weight w is defined as 4Fo /2σ(Fo ) 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 Table 1 and are deposited as
supplementary data.
1
at -0.88 ppm in the H NMR spectrum is attributable to the
single NH proton. Moreover the 1H NMR data were consistent
with only a single conformation in solution. An X-ray crystal-
lographic study of 2 confirmed the formulation and revealed a
geometry in which the biphenyl unit is oriented toward the PNH
fragment (Figure 1). A similar orientation was previously
observed for 1, and this was presumed to be a result of the
minimization of steric conflicts between the biphenyl and tert-
butyl groups. The P-N bond distance in 2 was found to be
1.5557(18) Å, typical of phosphinimines.5,7 Compound 2 serves
as the precursor to the phosphinimide salt t-Bu2(2-C6H4Ph)-
PNLi (3), as treatment with t-BuLi readily effects deprotonation.
The air- and moisture-sensitive species 3 was isolated as a white
solid in 92% yield (Scheme 3). The relatively poor solubility
of 3 dictated that the NMR spectra were recorded in THF-d8,
at 55 °C. The 31P{1H} and7Li NMR spectra showed resonances
at 11.4 and -1.4 ppm, respectively, reflecting the anionic nature
of the phosphinimide unit.
Results and Discussion
Mono-phosphinimide Complexes. We have previously
reported the synthesis of t-Bu2(2-C6H4Ph)PNSiMe3 (1).7 Fol-
lowing typical phosphinimine chemistry, compound 1 is readily
converted to the white solid t-Bu2(2-C6H4Ph)PNH (2) in
quantitative yield via treatment with methanol in toluene
followed by subsequent isolation (Scheme 3). The 31P{1H} NMR
for 2 shows a significant downfield chemical shift at 42.3 ppm
in comparison to 1, which is observed at 22.3 ppm. A resonance
(8) Cromer, D. T.; Waber, J. T. International Tables for X-ray Crystal-
lography; 1974; Vol. 4, pp 71-147.

4990 Organometallics, Vol. 25, No. 21, 2006
Ghesner et al.
Figure 1. POV-ray representation of 2. C: black, N: blue, P:
orange, H: gray. Hydrogen atoms, except for the NH atom, are
omitted for clarity. P(1)-N(1) ) 1.5557(18) Å.
The phosphinimine 1 reacts with TiCl4 in refluxing toluene.
Subsequent workup affords the product 4 in 74% yield. Ti
coordination by phosphinimide is inferred by the downfield shift
of the 31P{1H} NMR resonance to 42.7 ppm, suggesting the
formulation of 4 as t-Bu2(2-C6H4Ph)PNTiCl3 (Scheme 3).
Recrystallization from CH2Cl2/pentane gave yellow crystals,
which were confirmed by X-ray crystallographic study to be 4
(Figure 2a). This molecule is pseudo-tetrahedral at Ti with a
Ti-N distance of 1.7311(19) Å, which is significantly shorter
than the Ti-N distances reported for Cp′(t-Bu2(2-C6H4Ph)PN)-
TiCl2 (Cp′ ) Cp, Cp*) of 1.759(3) and 1.791(3) Å, respectively.7
In contrast, the P-N distance in 4 of 1.6132(19) Å is similar
to those seen in the Cp′ derivatives, where the P-N distances
are 1.619(3) and 1.609(3) Å, respectively. 7 Similarly, the Ti-
Cl distances in 4 ranging from 2.2262(8) to 2.2385(9) Å are
significantly shorter than the Ti-Cl distances of 2.3087(17) and
2.3139(16) Å found in Cp(t-Bu2(2-C6H4Ph)PN)TiCl2. The
P-N-Ti angle in 4 of 167.53(13)° approaches linearity, as is
the case with the majority of Ti-phosphinimide complexes. The
biphenyl substituent is oriented proximal to the metal center.
The closest approach of a biphenyl C atom to Ti is 3.695 Å,
while the distance of Ti to the mean plane of C6H5 ring is 3.6973
Å. This approach gives rise to a distortion in the biphenyl
fragment as the C(1)-C(2)-C(7) angle of 127.5(1)° deviates
from that expected for an sp2 carbon. The angle between the
planes of the phenyl rings in the biphenyl substituent is 58.1°.
It is noteworthy that this approach of Ti to the pendant arene is
significantly longer than that seen in the species [Ti(η6-
biphenyl)2]- (Ti-ring plane: 1.78 Å).9
Alkylation of the Ti center proceeds via treatment of 4 with
MeMgBr (Scheme 3). The product 5 exhibits a 1H NMR
resonances at 0.72 ppm attributable to the Ti-bound methyl
groups, while the 31P{1H} NMR resonance was observed at 21.3
ppm, consistent with the formulation of 5 as t-Bu2(2-C6H4Ph)-
PNTiMe3. A single-crystal X-ray study of 5 (Figure 2b) revealed
that the average Ti-C distance is 2.097(5) Å, which is typical
of LTiMe3 complexes. The Ti-N distance of 1.791(2) Å is
longer and the P-N distance of 1.576(2) Å is shorter than the
corresponding distances in 4. These observations are consistent
with the increased electron density at Ti in 5 as a result of the
electron-donating methyl substituents. The P-N-Ti angle of
166.33(16)° in 5 is similar to that seen in 4. In addition the
biphenyl substituent in 5 is oriented in a fashion similar to that
seen in 4, with the closest approach of a biphenyl C atom to Ti
Figure 2. POV-ray representation of (a) 4 and (b) 5. C: black, N:
blue, P: orange, Ti: gray, Cl: green. Hydrogen atoms are omitted
for clarity. Selected distances (Å) and angles (deg): 4: Ti(1)-
N(1) 1.7311(19), Ti(1)-Cl(2) 2.2262(8), Ti(1)-Cl(1) 2.2382(8),
Ti(1)-Cl(3) 2.2385(9), P(1)-N(1) 1.6132(19), N(1)-Ti(1)-Cl-
(1) 112.55(7), Cl(2)-Ti(1)-Cl(1) 112.72(4), N(1)-Ti(1)-Cl(3)
110.60(7), Cl(2)-Ti(1)-Cl(3) 105.09(4), Cl(1)-Ti(1)-Cl(3) 105.57-
(4), P(1)-N(1)-Ti(1) 167.53(13). 5: Ti(1)-N(1) 1.791(2), Ti(1)-
C(23) 2.088(4), Ti(1)-C(21) 2.098(4), Ti(1)-C(22) 2.104(4),
P(1)-N(1) 1.576(2), N(1)-Ti(1)-C(23) 111.48(14), N(1)-Ti(1)-
C(21) 113.11(16), C(23)-Ti(1)-C(21) 104.7(2), N(1)-Ti(1)-
C(22) 112.13(14), C(23)-Ti(1)-C(22) 111.77(16), C(21)-Ti(1)-
C(22) 103.1(2), P(1)-N(1)-Ti(1) 166.33(16), C(1)-C(2)-C(7)
127.5(1).
being 3.976 Å and the distance between Ti and the mean plane
of the C6H5 ring of 3.757 Å. This slightly longer approach is
consistent with the greater angle of 74.3° between the plane of
the phenyl rings of the biphenyl substituent.
The corresponding alkylation of 4 with 3 equiv of PhCH2-
MgBr proceeds in a fashion similar to give a yellow solution
of the product t-Bu2(2-C6H4Ph)PNTi(CH2Ph)3 (6), which was
subsequently isolated in 76% yield (Scheme 3). In contrast to
4 and 5, NMR data revealed that two isomers of 6 exist in
solution at 25 °C in a 1.4:1 ratio. The major isomer exhibits a
31P{1H} NMR resonance at 25.5 ppm, while the minor isomer
1
shows a signal at 37.6 ppm. Similarly, the H NMR spectrum
showed resonances at 0.99 and 0.86 ppm attributable to tert-
butyl groups of the major and minor isomers, respectively. The
corresponding resonances arising from the benzylic protons were
seen at 2.66 and 2.41 ppm, respectively. A variable-temperature
31P{1H} NMR experiment over the temperature range 303-
353 K revealed coalescence of the two signals at 343 K. These
data were consistent with a rotational barrier to interconversion
(9) Blackburn, D. W.; Britton, D.; Ellis, J. E. Angew. Chem., Int. Ed.
Engl. 1992, 31, 1495.

Di-tert-butylbiphenylphosphinimide Ti and Zr Complexes
Organometallics, Vol. 25, No. 21, 2006 4991
Scheme 4. Interconversion of Rotational Isomers
Figure 4. Portion of the variable-temperature 1H NMR spectra of
7 showing methylene and methyl resonances.
Figure 3. 1H-1H NOESY spectrum of 7.
of the two isomers of 6.10 The activation barrier was calculated
to be 92 kJ/mol (Scheme 4). On the basis of the similarity of
the 31P chemical shift to 5, the more abundant isomer is thought
to be the conformer in which the biphenyl group is oriented
toward the metal center. A similar observation of two rotational
isomers was reported for Cp′(t-Bu2(2-C6H4Ph)PN)TiCl2 (Cp′
) Cp, Cp*), although in those cases poor solubility precluded
the determination of the barrier.7 Subsequent data on related
compounds in this paper support the present interpretation (vide
infra). The upfield 31P chemical shift of the more abundant
isomer is attributed to shielding effects resulting from the
proximity of the arene ring of the biphenyl fragment.
The direct synthesis of a related tris-amido derivative is
achieved via the reaction of Ti(NMe2)4 with 2 (Scheme 3). The
NMR data for the resulting product 7 are consistent with the
formation of a 2.2:1 mixture of two isomers of t-Bu2(2-C6H4-
Ph)PNTi(NMe2)3 at 25 °C. This product was isolated as orange
crystals in 97% yield. As for 6, the 31P{1H} NMR spectrum of
7 showed two resonances at 20.6 and 33.1 ppm for the major
and minor isomers, respectively, and the corresponding 1H NMR
resonances for the tert-butyl groups gave rise to signals at 1.37
and 1.20 ppm. Similarly, the NMe groups gave distinct signals
for the two isomers at 3.27 ppm (major isomer) and 3.53 ppm
(minor isomer). Assignment of the aromatic regions to the two
isomers was assisted by a 2D-NOESY spectrum (Figure 3),
which revealed correlations of the resonances arising from the
NMe groups in the major isomer to aromatic proton signals at
7.14, 7.31, and 7.57 ppm. These data support the proposition
that the biphenyl group in the major isomer is oriented toward
the amido substituents. This orientation of the biphenyl unit
presumably shields the P-N fragment and accounts for the
upfield 31P{1H} resonance for the major isomer. Nonetheless,
it is surprising that the orientation of the biphenyl appears to
have a larger impact on the 31P{1H} chemical shift than
substitution on Ti. Variable-temperature 1H (Figure 4) and 31P-
{1H} NMR spectra over the temperature range 303-353 K
revealed a barrier to interconversion of the two isomers of 94-
Figure 5. POV-ray representation of 7. C: black, N: blue, P:
orange, Ti: gray. Hydrogen atoms are omitted for clarity. Selected
distances (Å) and angles (deg): Ti(1)-N(1) 1.843(3), Ti(1)-N(4)
1.907(3), Ti(1)-N(3) 1.917(3), Ti(1)-N(2) 1.934(3), P(1)-N(1)
1.567(3), N(1)-Ti(1)-N(4) 114.12(14), N(1)-Ti(1)-N(3) 110.77-
(14), N(4)-Ti(1)-N(3) 110.83(15), N(1)-Ti(1)-N(2) 115.48(13),
N(4)-Ti(1)-N(2) 102.20(15), N(3)-Ti(1)-N(2) 102.61(16), P(1)-
N(1)-Ti(1) 159.24(19).
(1) kJ/mol, as coalescence was observed at 333 K (Scheme 4).10
The proposed structure of the preferred isomer was subsequently
confirmed, as this isomer afforded suitable crystals for X-ray
diffraction studies (Figure 5). The overall complex geometry
of 7 is similar to that seen in 4 and 5, with a pseudo-tetrahedral
Ti center and the biphenyl substituent oriented toward the metal
center. The strong σ- and π-donation from the amido ligands
results in Ti-Namide distances that range from 1.907(3) to 1.934-
(3) Å and a Ti-Nphosphinimide of 1.843(3) Å. This latter bond
length is significantly longer than those seen in 4 or 5. The
P-N distance of 1.567(3) Å in 7 is slightly shorter and the
P-N-Ti angle of 159.24(19)° is more distorted from linearity
than the corresponding values in 5. This is attributed to the
greater steric demands and donor ability of the amide ligands
over methyl. The approach of the biphenyl rings to Ti in 7 is
slightly longer than in 4 or 5, as the mean distance between the
C6H5 plane and Ti is 3.8857 Å. This is consistent with the
greater steric conflict between the biphenyl substituents and the
amido ligands in 7. This also accounts for the increase in the
angle between the phenyl ring planes of the biphenyl substituent
to 76.4°.
The isolation of 7 afforded further derivatization in a clean
fashion. Treatment of 7 with Me3SiCl afforded the quantitative
isolation of t-Bu2(2-C6H4Ph)PNTi(NMe2)2Cl (8) (Scheme 3).
(10) Reich, H. J. WinDNMR: Dynamic NMR Spectra for Windows, 3D2;
J. Chem. Educ. Software: 1996.

4992 Organometallics, Vol. 25, No. 21, 2006
Ghesner et al.
Figure 7. POV-ray representation of 12. C: black,-N: blue, P:
orange, Zr: yellow. Hydrogen atoms are omitted for clarity.
Selected distances (Å) and angles (deg): Zr(1)-N(1) 1.922(3), Zr-
(1)-C(23) 2.233(6), Zr(1)-C(21) 2.239(5), Zr(1)-C(22) 2.247-
(6), P(1)-N(1) 1.573(3), N(1)-Zr(1)-C(23) 110.34(19), N(1)-
Zr(1)-C(21) 111.85(18), C(23)-Zr(1)-C(21) 105.3(3), N(1)-
Zr(1)-C(22) 113.20(19), C(23)-Zr(1)-C(22) 105.7(3), C(21)-
Zr(1)-C(22) 110.0(2), P(1)-N(1)-Zr(1) 164.2(2).
Figure 6. POV-ray representation of one of the two molecules of
10 in the asymmetric unit. C: black, N: blue, P: orange, Zr:
yellow. Hydrogen atoms are omitted for clarity. Selected distances
(Å) and angles (deg): Zr(1)-N(1) 1.981(3), Zr(1)-N(2) 2.051(4),
Zr(1)-N(4) 2.082(4), Zr(1)-N(3) 2.170(4), P(1)-N(1) 1.522(3),
N(1)-Zr(1)-N(2) 117.19(14), N(1)-Zr(1)-N(4) 112.74(14), N(2)-
Zr(1)-N(4) 93.03(15), N(1)-Zr(1)-N(3) 106.34(14), N(2)-Zr-
(1)-N(3) 105.54(16), N(4)-Zr(1)-N(3) 121.93(14), P(1)-N(1)-
Zr(1) 165.24(18).
seen in 7, as the distance between Zr and the plane of the C6H5
ring is 3.8441 Å and the angle between the phenyl rings of the
biphenyl substituent is 71.9°.
Two isomers of this product were also observed, as evidenced
by the 31P{1H} NMR resonances at 21.9 and 35.7 ppm. The
former resonance resulted from the more dominant isomer in
the 3.6:1 mixture at 25 °C. On the basis of the chemical
similarities, the dominant isomer was again ascribed to the
isomer in which the C6H5 ring is oriented toward the metal
center. The increase in the proportion of this isomer in solution
is consistent with the reduced steric crowding at Ti. Compound
8 was readily alkylated with PhCH2MgCl to give the species
t-Bu2(2-C6H4Ph)PNTi(CH2Ph)(NMe2)2 (9) in 95% yield (Scheme
3). This species exists as a mixture of two isomers in a 3:1
mixture in solution at 25 °C, giving rise to 31P{1H} NMR
resonances at 17.5 and 33.1 ppm, respectively. In a similar sense
Treatment of 10 with excess Me3SiCl provides a convenient
route for the synthesis and subsequent isolation of t-Bu2(2-C6H4-
Ph)PNZrCl3 (11) in 87% yield. Subsequent methylation of 11
afforded t-Bu2(2-C6H4Ph)PNZrMe3 (12) in 78% isolated yield.
The observation of a single 31P{1H} NMR signal at 20.5 ppm
suggests a geometry similar to that seen for 5, where the
biphenyl unit is oriented toward the metal center. Indeed this
proposition was confirmed via a crystallographic study of 12
(Figure 7). The Zr-N and average Zr-C distances were found
to be 1.922(3) and 2.240(7) Å, respectively. The Zr-N distance
in 12 is significantly shorter than that seen in 10. A similar
result was described above for the related Ti species 7 and 4
and is attributed to the σ- and π-donor ability of amido ligands.
The P-N-Zr angle remains approximately linear at 164.2(2)°.
The methyl substitution on Zr in 11 appears to reduce the impact
on the biphenyl substituent relative to that seen in the complexes
above: the closest approach of Zr to the C6H5 ring is 4.033 Å,
with the distance of Zr to the mean plane of this ring being
3.9097 Å, and the inter-phenyl ring angle is 88.4°. It is also
noteworthy that the C(1)-C(2)-C(7) angle is 114.3°, which is
significantly smaller than those reported above. Thus the
biphenyl fragment appears unperturbed by the proximity to the
ZrMe3 unit. Nonetheless, the observation of a consistent
preference for an orientation in which the biphenyl is disposed
toward the metal suggests an electrostatic attraction between
the electron-rich arene and the Lewis acidic metal centers.
However, the role of steric conflict between biphenyl and tert-
butyl substituents in the minor conformer cannot be dismissed.
Bis-phosphinimide Complexes. Efforts to stabilize a Ti(III)
center with such pendant arene ligands prompted examination
of the reduction of 3 with Mg powder in Et2O. This resulted in
isolation of the diamagnetic compound 13 in 42% yield. The
31P{1H} NMR spectrum of 13 shows three resonances attribut-
able to the presence of two isomers in a 2.2:1 ratio. The minor
isomer gives rise to two signals at 23.7 and 36.9 ppm, inferring
the presence of two inequivalent P centers, while the major
isomer shows one signal at 37.0 ppm. Similarly in the 1H NMR
spectrum, doublets at 1.16 and 1.51 ppm were attributed to the
1
to 6 and 7, H NMR resonances attributed to the tert-butyl
groups, the benzylic protons, and the NMe groups of the major
and minor isomers were seen at 1.27 and 1.01 ppm, 2.15 and
2.51 ppm, and 2.92 and 3.13 ppm, respectively.
In an analogous fashion, Zr complexes were synthesized.
Reaction of Zr(NEt2)4 with 2 afforded the quantitative synthesis
of t-Bu2(2-C6H4Ph)PNZr(NEt2)3 (10). The 31P{1H} NMR reso-
nances at 21.4 and 35.1 ppm revealed a 1.4:1 ratio of the two
conformational isomers. 1H and 13C{1H} NMR spectra showed
similar evidence of isomerism. For example, the methylene
1
groups of the amido ligands showed H NMR resonances at
3.43 and 3.62 ppm and 13C resonances at 43.56 and 44.36 ppm
for the major and minor isomers, respectively. The major isomer
of 10 crystallized, allowing an X-ray diffraction study (Figure
6). The overall geometry is similar to that seen in 7. The Zr-
Namide bond lengths ranged from 2.051(4) to 2.170(4) Å, while
the Zr-Nphosphinimide averaged 1.984(4) Å. This latter distance
is slightly longer than those seen in the species Cp*Zr(NPt-
Bu3)Cl2 (1.923(2) Å) and Cp2Zr(NPt-Bu3)Cl (1.978(5) Å).11
Similarly, the average P-N-Zr angle seen in 10, 165.25(18)°,
falls in the range of 163.49(12)° and 171.9(3)° seen for Cp*Zr-
(NPt-Bu3)Cl2 and Cp2Zr(NPt-Bu3)Cl, respectively.11 The prox-
imity of the biphenyl substituent to the metal is similar to that
(11) Hollink, E.; Wei, P.; Stephan, D. W. Organometallics 2004, 23,
1562-1569.

Di-tert-butylbiphenylphosphinimide Ti and Zr Complexes
Organometallics, Vol. 25, No. 21, 2006 4993
Scheme 5. Rotational Isomers of 13
Scheme 6. Formation of 15
determined to be 1.591(3) and 1.583(3) Å, while the P-N-Ti
angles range from 172.19(18)° to 176.5(2)°. The Cl-Ti-Cl
angle was found to be 109.43(5)°, slightly larger than that in
(t-Bu3PN)2TiCl2 (106.93(7)°).
The mechanism of formation of 13 is unknown. However,
an alternative and more direct synthesis of this mixture of
isomers of 13 was found to involve the direct reaction of TiCl3
with the Li salt 3. In either synthesis it is thought that the Ti-
(III) species t-Bu2(2-C6H4Ph)PNTiCl2 is generated. This species
undergoes disproportionation to the Ti(IV) product 13 and TiCl2.
Although the latter product has not been unambiguously
identified, the black, insoluble precipitate that is filtered from
the solution may be this material or its degradation products.
In related chemistry we have previously reported the analogous
reduction of Cp′(t-Bu2(2-C6H4Ph)PN)TiCl2 (Cp′ ) Cp, Cp*)
with Mg.7 In these cases, the reactions gave Ti(IV) species Cp′-
(t-Bu2(2-C6H4Ph)PN)Ti in which the pendant phenyl ring was
reduced by the transient Ti(II) center (Scheme 2).7
Compound 13 is alkylated with MeMgBr to give [t-Bu2(2-
C6H4Ph)PN]2TiMe2 14 in 46% yield. In a similar fashion 14 is
formed by the reaction of 5 with 2 in quantitative yield by NMR
spectroscopy and could be isolated in 86% yield. NMR data
showed that like 13, 14 exists as two isomers in a 2.4:1 ratio.
However in contrast to 13, the major isomer of 14 gave rise to
two 31P{1H} NMR resonances at 13.8 and 26.5 ppm, while the
minor isomer gave a signal at 27.1 ppm. These data are
consistent with the major isomer of 14 adopting a conformation
in which one of the biphenyl substituents is oriented toward
the metal while the other is oriented away from the metal center.
Variable-temperature NMR experiments10 revealed coalescence
at 348 K and an activation barrier for the interconversion of
these rotation isomers of 92 kJ/mol.
The analogous Zr complex [t-Bu2(2-C6H4Ph)PN]2ZrMe2 (15)-
is accessible by a protolysis of a methyl group on 12 with 2
(Scheme 6). The product 15 exists in solution as two isomers
in a 24:1 ratio. The major isomer exhibits two 31P{1H} NMR
resonances at 20.3 and 34.7 ppm, while the minor isomer shows
a resonance at 35.2 ppm. Like 14, these data are consistent with
the major isomer of 15, in which the two biphenyl substituents
are oriented toward and away from Zr.
Compound 15 is also formed spontaneously from 12 on
standing in toluene solution for several hours. Stoichiometry
suggests that the formation of 15 is concurrent with liberation
of ZrMe4, although the instability of this byproduct precluded
unambiguous confirmation of this proposition (Scheme 6). The
kinetics of this transformation was monitored by NMR spec-
troscopy. The concentration dependence of the rate was
consistent with second-order kinetics (Figure 9), suggesting an
associative mechanism for ligand exchange affording 15 and
ZrMe4. The rate constant was determined to be 4 × 10-4 s-1 at
333 K. Eyring plots over a 40 K range (311-351 K) provide
the activation parameters: ∆Gq(329 K) ) 104(2) kJ/mol, ∆Hq
) 69(2) kJ/mol, and ∆Sq ) -108(6) J/(mol K) (Figure 10).
Figure 8. POV-ray representation of 13. C: black,-N: blue, P:
orange, Ti: gray, Cl: green. Hydrogen atoms are omitted for clarity.
Selected distances (Å) and angles (deg): Ti(1)-N(2) 1.784(3), Ti-
(1)-N(1) 1.784(3), Ti(1)-Cl(1) 2.2920(12), Ti(1)-Cl(2) 2.2991-
(13), P(1)-N(1) 1.591(3), P(2)-N(2) 1.583(3), N(2)-Ti(1)-N(1)
112.04(13), N(2)-Ti(1)-Cl(1) 108.46(9), N(1)-Ti(1)-Cl(1) 110.45-
(10), N(2)-Ti(1)-Cl(2) 107.93(9), N(1)-Ti(1)-Cl(2) 108.47(10),
Cl(1)-Ti(1)-Cl(2) 109.43(5), P(1)-N(1)-Ti(1) 176.5(2), P(2)-
N(2)-Ti(1) 172.19(18).
tert-butyl resonances of the minor isomer, while the corre-
sponding signal for the major isomer was seen at 1.19 ppm.
These data suggest the formulation of 13 as two conformations
of [t-Bu2(2-C6H4Ph)PN]2TiCl2. In the minor isomer, the two
phosphorus centers are inequivalent: one of the biphenyl
substituents oriented toward and the other away from the Ti
center. On the other hand, the single downfield 31P NMR
resonance seen for the major isomer indicates that the two
biphenyl units are equivalent and oriented away from the metal
(Scheme 5). The reason for the preponderance of this isomer
of 13 is not clear, although clearly steric congestion between
the substituents on adjacent ligands is an issue.
The nature of the major isomer of 13 was confirmed
unequivocally by X-ray diffraction (Figure 8).This crystal-
lographic study of 13 revealed the pseudo-tetrahedral geometry
about the Ti center with Ti-N bond lengths of 1.784(3) Å and
Ti-Cl bond lengths of 2.2920(12) and 2.2991(13) Å. These
compare with the corresponding distances of 1.791(4) and 2.290-
(2) Å found in (t-Bu3PN)2TiCl2.4 Similarly, the N-Ti-N angle
in 13 and (t-Bu3PN)2TiCl2 is in the same range, being 112.04-
(13)° and 112.9(2)°, respectively. The P-N distances in 13 were

4994 Organometallics, Vol. 25, No. 21, 2006
Ghesner et al.
Figure 9. Typical kinetic data for the transformation of 12 to 15
([12]o ) 0.0982 M), T ) 329 K.
Figure 11. Variable-temperature 31P{1H} NMR spectra of 14.
Scheme 8. Isomers of 19: (a) Major Isomer at 25 °C, (b)
Arene Exchange in Minor Isomer at 25 °C
Figure 10. Eyring plot for the transformation of 12 to 15 over the
temperature range 311-351 K.
Scheme 7. Formation of Cationic Ti Species 16-18
formulation of 16 as a salt in which the Ti cation is arene-
stablized (Scheme 7). Solutions of 16 in C6H5Br are stable for
several days. This stands in marked contrast to stabilities of
12
the products derived from t-Bu3PNTiMe3/B(C6F5)3 or Cp-
TiMe3/B(C6F5)3,13 where the absence of a donor ligand results
in prompt degradation of the transient products of methyl
abstraction. The stability of the present cation 16 may be
attributed to the chelate effect. As the molecular structure of
the 16 was not determined, the hapticity of the arene-metal
interaction is not unambiguously known; however it is note-
worthy that an η6-arene interaction was observed for the Hf
cation [Cp*HfMe2(η6-toluene)][MeB(C6F5)3].14 While the barrier
to arene dissociation could not be determined, the work of Casey
et al. has shown that the barrier to alkene dissociation from the
Zr cation in Cp2Zr[η1,η2-CH2SiMe2CH2CHdCH2][B(C6F5)4] is
∆Gq(245 K) ) 53.3 kJ/mol15 and ∆Gq ) 44.9 and 44.6 kJ/mol
for the diastereomers of Cp*2Zr[η1,η2-CH2CHMeCH2CHdCH2]-
[B(C6F5)4].16 Thus it is suggested from the stability of 16 that
the barrier to arene dissociation is significantly higher than these
values.
The negative entropy term is consistent with the proposition of
a bimolecular ligand exchange process, while the enthalpic
barrier to ligand exchange is accessible albeit endothermic.
Zwitterionic and Cationic Species. Given the propensity of
the biphenyl substituent, in the absence of steric restrictions, to
be oriented toward the metal center in the above compounds,
the potential for a direct interaction with metal was probed.
Compound 5 reacts with B(C6F5)3 to generate a species
formulated as [t-Bu2(2-C6H4Ph)PNTiMe2][MeB(C6F5)3] (16). A
similar situation was observed for the reaction of 9 with
B(C6F5)3. In this case abstraction of the benzyl group generates
[t-Bu2(2-C6H4Ph)PNTi(NMe2)2][PhCH2B(C6F5)3] (17) (Scheme
7). In both cases, the observation of a 11B NMR chemical shift
at -15.00 ppm and the 19F NMR data are consistent with
uncoordinated borate anions, while the downfield shifts of the
31P{1H} NMR resonances are consistent with the generation of
Addition of THF to solutions of 16 results in a new species,
18. This species shows no change to the 11B and 19F NMR
1
resonances; however the H NMR spectrum exhibits signals
consistent with THF coordination and the arene signals are
grouped between 6.8 and 7.2 ppm. These data infer the
formulation of 18 as [t-Bu2(2-C6H4Ph)PNTiMe2(THF)][MeB-
(C6F5)3]. A similar change was observed for the arene region
(12) Guerin, F.; Stewart, J. C.; Beddie, C.; Stephan, D. W. Organome-
tallics 2000, 19, 2994-3000.
(13) Gillis, D. J.; Tudoret, M. J.; Baird, M. C. J. Am. Chem. Soc. 1993,
115, 2543-2545.
(14) Gillis, D. J.; Quyoum, R.; Tudoret, M.-J.; Wang, Q.; Jeremic, D.;
Roszak, A. W.; Baird, M. C. Organometallics 1996, 15, 3600-3605.
(15) Casey, C. P.; Carpenetti, D. W., II; Sakurai, H. Organometallics
2001, 20, 4262-4265.
(16) Casey, C. P.; Carpenetti, D. W., II. Organometallics 2000, 19,
3970-3977.
1
cationic Ti centers. In the case of 16, the H NMR spectrum
shows a disperse aryl region with resonances at 6.64, 7.09-
7.13, 7.49-7.60, and 7.70-7.82 ppm. These data support the

Di-tert-butylbiphenylphosphinimide Ti and Zr Complexes
Organometallics, Vol. 25, No. 21, 2006 4995
1
of the H NMR spectra when THF was added to 17, although
for the site epimerization of the Zr center in Cp*2Zr[η1,η2-CH2-
CHMeCH2CHdCH2][B(C6F5)4] (∆Gq ) 60.5 kJ/mol) reported
by Casey and co-workers.16
these products could not be isolated in an analytically pure form.
In the similar reaction of 14 with B(C6F5)3, the product [(t-
Bu2(2-C6H4Ph)PN)2TiMe][MeB(C6F5)3] (19) is formed. 11B{1H}
and 19F NMR data reflect the formation of free borate anion.
1H and 31P{1H} NMR spectra show the formation of two
isomers in 2:1 ratio at 25 °C. The 31P{1H} NMR spectrum of
the major isomer shows resonances at 27.6 and 39.7 ppm, while
the minor isomer shows a signal at 29.0 ppm (Figure 11). These
data suggest that, like the precursor 14, the biphenyl substituents
of the major isomer of 19 are oriented in opposing directions,
one being toward the metal and the other away from Ti (Scheme
8a). The 31P chemical shift of the minor isomer suggests a
conformation in which both biphenyl substituents are oriented
toward the Ti center. As the temperature is decreased from 303
to 243 K, the relative proportion of the major and minor isomers
of 14 becomes 1:1 at 243 K. In addition, the minor isomer is
shown to give rise to an intramolecular process by variable-
temperature 31P{1H} NMR data. As the temperature is reduced,
the signal attributable to the minor isomer broadens, ultimately
splitting into two well-resolved signals at 27.6 and 28.6 ppm.
Line-shape analyses10 of these spectra reveal the activation
parameters as follows: ∆Gq(268 K) ) 52(2) kJ/mol, ∆Hq )
69(2) kJ/mol, ∆Sq 60(2) J/(mol K). The positive entropy term
is consistent with an intramolecular process proposed to involve
exchange of the arene rings in the coordination sphere of Ti
(Scheme 8b). This process amounts to the inversion of chirality
at the cationic Ti center. This barrier is comparable to that found
Summary
The synthesis and characterization of a series of Ti and Zr
bis-tert-butylbiphenylphosphinimide complexes has been achieved.
In the absence of steric conflicts with metal substituents, the
preferred orientation of the biphenyl fragment appears to be
one in which it is oriented toward the metal center. On the other
hand, steric congestion as a result of other bulky ligands on Ti
or Zr prompts rotational conformers which interconvert under
thermal duress. Interactions of the pendant arene with the metal
center act to stabilize cationic species. In bis-phosphinimide
complex cations, such stabilization may be enhanced due to the
possibility of intramolecular arene exchange. It is clear that the
present work illustrates the potential of tert-butylbiphenylphos-
phinimide ligands to provide a stabilizing influence on otherwise
highly reactive species. Current efforts are targeting exploitation
of these findings for applications in catalysis.
Acknowledgment. Financial support from NSERC of Canada
and NOVA Chemical Corporation is gratefully acknowledged.
Supporting Information Available: Crystallographic data are
deposited as CIF files. This material is available free of charge via
the Internet at http://pubs.acs.org.
OM060569U