Boron and aluminum complexes of sterically demanding phosphinimines and phosphinimides

Article abstract of DOI:10.1021/ic0700351

Reactions of sterically demanding phosphinimines R₃PNH [R = i-Pr (1), t-Bu (2)] were examined. Reactions with B(C₆F₅) ₃ formed the adducts (R₃PNH)B(C₆F ₅)₃ [R = i-Pr (

Full text of DOI:10.1021/ic0700351

Inorg. Chem. 2007, 46, 3623−3631
Boron and Aluminum Complexes of Sterically Demanding
Phosphinimines and Phosphinimides
Silke Courtenay, Denise Walsh, Sarah Hawkeswood, Pingrong Wei, Anjan Kumar Das, and
Douglas W. Stephan*
Department of Chemistry & Biochemistry, UniVersity of Windsor, Windsor,
Ontario, Canada N9B 3P4
Received January 9, 2007
Reactions of sterically demanding phosphinimines R3PNH [R
B(C6F5)3 formed the adducts (R3PNH)B(C6F5)3 [R i-Pr (3), t-Bu (4)] in high yield. On the other hand, 2 reacts
with HB(OBu)2, evolving H2 to give t-Bu3PNB(OBu)2 (5). The reaction of 2 equiv of 2 with BH3 SMe2 affords the
species (t-Bu3PN)2BH (6). In contrast, the reaction of n-Bu(t-Bu)2PNH with BH3 SMe2 results in the formation of the
robust adduct n-Bu(t-Bu)2PNH BH3 (8). An alternative route to borane phosphinimide complexes involves Me3SiCl
elimination, as exemplified by the reaction of BCl2Ph with n-Bu3PNSiMe3, which gives the product n-Bu3PNBCl(Ph)
(9). The corresponding reactions of the parent phosphinimines 1 and 2 with AlH3 NMe2Et give the dimers [( -i-
Pr3PN)AlH2]2 (10) and [( -t-Bu3PN)AlH2]2 (11). Species 11 reacts further with Me3SiO3SCF3 to provide [( -t-Bu3-
) i-Pr (1), t-Bu (2)] were examined. Reactions with
)
‚
‚
‚
−
‚
µ
µ
µ
PN)AlH(OSO2CF3)]2 (12). The reaction of the lithium salt [t-Bu3PNLi]4 (13) with BCl3 proceeds smoothly to give
t-Bu3PNBCl2 (14), which is readily alkylated to give t-Bu3PNBMe2 (15). Subsequent reaction of 15 with B(C6F5)3
results in methyl abstraction and the formation of [(
ratio with BCl3 gives the salt [(t-Bu3PN)2B]Cl (17). This species can be methylated to give (t-Bu3PN)2BMe (18),
which undergoes subsequent reaction with [Ph3C][X] (X [B(C6F5)4], [PF6]) to form the related salts [(t-Bu3PN)2B]-
µ-t-Bu3PN)BMe]2[MeB(C6F5)3]2 (16). The reaction of 13 in a 2:1
)
[B(C6F5)4] (19) and [(t-Bu3PN)2B][PF6] (20), respectively. Analogous reactions with [Ph3C][BF4] afforded [t-Bu3-
PNBF2]2 (21). Compounds 3, 4, 6, 8, 11, 12, 17, 19, and 21 were characterized by X-ray crystallography.
Introduction
viewed.5 In contrast, the related chemistry of main-group
phosphinimines and phosphinimides has recently drawn
much less attention. Dehnicke and Weller described much
of the older literature in a review nearly 10 years ago.6 More
recently, we and others have begun to examine main-group
phosphinimine and phosphinimide derivatives. For example,
in some elegant work, Meyer and co-workers7,8 have
demonstrated that phosphinimines themselves undergo me-
tathesis with imines and catalyze imine/imine and imine/
carbodiimine cross-metathesis. We have probed the synthesis,
structure, and reactivity of lithium,9 magnesium,10,11 silicon,
tin, and germanium12 as well as aluminum alkyl13 phosphin-
Transition-metal complexes incorporating phosphinimide
ligand complexes have proven to be an active area of research
in recent years. While Cavell and co-workers have made a
number of reports on the extremely interesting carbenoid
complexes for a variety of metals derived from the phos-
phinimines of 1,1-diphosphinomethanes,1-4 we have probed
the chemistry of a variety of metal phosphinimide complexes,
ultimately developing commercially viable early-transition-
metal catalysts for olefin polymerization based on titanium
phosphinimides. This latter work has been recently re-
(5) Stephan, D. W. Organometallics 2005, 24, 2548.
(6) Dehnicke, K.; Weller, F. Coord. Chem. ReV. 1997, 158, 103.
(7) Bell, S. A.; Meyer, T. Y.; Geib, S. J. J. Am. Chem. Soc. 2002, 124,
10698.
(8) Burland, M. C.; Meyer, T. Y. Inorg. Chem. 2003, 42, 3438.
(9) Courtenay, S.; Wei, P.; Stephan, D. W. Can. J. Chem. 2003, 81, 1471.
(10) Wei, P.; Stephan, D. W. Organometallics 2003, 22, 601.
(11) Hollink, E.; Wei, P.; Stephan, D. W. Can. J. Chem. 2005, 83, 430.
(12) Courtenay, S.; Ong, C. M.; Stephan, D. W. Organometallics 2003,
22, 818.
* To whom correspondence should be addressed. E-mail:
stephan@uwindsor.ca. Fax: 519-973-7098.
(1) Aparna, K.; Babu, R. P. K.; McDonald, R.; Cavell, R. G. Angew.
Chem., Int. Ed. 2001, 40, 4400.
(2) Babu, R. P. K.; McDonald, R.; Cavell, R. G. Chem. Commun. 2000,
6, 481.
(3) Kasani, A.; Babu, R. P. K.; McDonald, R.; Cavell, R. G. Angew.
Chem., Int. Ed. 1999, 38, 1483.
(4) Kasani, A.; McDonald, R.; Cavell, R. G. Chem. Commun. 1999, 1993.
10.1021/ic0700351 CCC: $37.00
Published on Web 03/23/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 9, 2007 3623

Courtenay et al.
Chart 1
Solvents were purified by employing Grubbs-type column systems
manufactured by Innovative Technologies or were distilled from
1
the appropriate drying agents under N2. H and 13C{1H} NMR
spectra were recorded on Bruker Avance 300 and 500 spectrometers
operating at 300 and 500 MHz, respectively. Deuterated benzene,
toluene, and methylene chloride were purchased from Cambridge
Isotopes Laboratories, freeze-pump-thaw-degassed (three times),
and vacuum distilled from the appropriate drying agents. Trace
1
amounts of protonated solvents were used as references, and H
and 13C{1H} NMR chemical shifts are reported relative to SiMe4.
31P{1H}, 11B{1H}, 27Al{1H}, and 19F NMR spectra were referenced
to external 85% H3PO4, BF3‚Et2O, AlCl3 in H2O, and CFCl3,
respectively. Combustion analyses were performed at the University
of Windsor Chemical Laboratories employing a Perkin-Elmer CHN
analyzer. R3PNH [R ) i-Pr (1), t-Bu (2)]21 and [t-Bu3PNLi]49 (13)
were prepared by published methods. n-Bu(t-Bu)2PNH (7) was
prepared via the method previously described, with the appropriate
replacement of the precursor phosphine.21
Synthesis of (R3PNH)B(C6F5)3 [R ) i-Pr (3), t-Bu (4)]. These
complexes were prepared in a similar manner, and thus only a single
representative preparation is described. To a solution of 2 (250 mg,
1.150 mmol) in 5 mL of CH2Cl2 was added B(C6F5)3 (589 mg,
1.150 mmol). The solution was stirred for 1 h and concentrated,
resulting in the formation of colorless crystals of 4 in 95% yield.
3. Yield: 93%. 1H NMR (CD2Cl2): 2.97 (s, br, 1H), 2.17 (m, 3H),
1.20 (dd, 3JP-H ) 16 Hz, 3JH-H ) 7 Hz, 18H). 13C{1H} NMR (CD2-
imide derivatives. Our interest in the group 3 phosphinimine
and phosphinimide chemistry has prompted continuing
investigations. Boron phosphinimide derivatives of sterically
less demanding phosphinimides including such compounds
as [(Et3PN)2B)2]2+,14 [(Et3PNBH)3]3+,15 [(Et3PNBH)4NPEt3]3+,16
or [(Ph3PN)3B]17 have been described by Dehnicke and
Weller. Known aluminum phosphinimides exhibit dimeric
structures exclusively.6,13 Recently, we probed steric effects
that control the reactions of catechol and pinachol boranes
with phosphinimines.18,19 In these cases, both monomeric and
dimeric complexes, such as R3PNB(O2C2Me4) and [R3PNB-
(O2C6H4)]2, were prepared as a result of the incorporation
of sterically demanding phosphinimide ligands (Chart 1). We
have also previously communicated a case where such large
steric demands prompt the spontaneous formation of the salt
[(t-Bu3PN)2B]Cl.20 In this present full report, we include this
latter chemistry and related work, exploring several synthetic
pathways to both boron and aluminum complexes with
sterically demanding phosphinimine and phosphinimide
ligands. The range of products is described, and in selected
cases, the chemistry of the resulting species is also probed.
1
Cl2): 147.0-135.8 (br m), 25.7 (d, JP-C ) 55 Hz), 17.5 (s). 31P-
{1H} NMR (CD2Cl2): 64.0. 11B{1H} NMR (CD2Cl2): -7.5 (s).
19F NMR (CD2Cl2): -55.4 (d, 3JF-F ) 20 Hz, 6F), -83.0 (t, 3JF-F
) 20 Hz, 3F), -87.8 (m, 6F). Anal. Calcd for C27H22BF15NP: C,
45.34; H, 3.10; N, 1.96. Found: C, 44.98; H, 3.18; N, 1.88. 4. 1H
3
NMR (CD2Cl2): 3.30 (s, br, 1H), 1.41 (d, JP-H ) 14 Hz, 27 H).
1
13C{1H} NMR (CD2Cl2): 149.9-135.6 (br m), 41.0 (d, JP-C
)
42 Hz), 29.4 (s). 31P{1H} NMR (CD2Cl2): 78.8. 11B{1H} NMR
(CD2Cl2): -9.5 (s). 19F NMR (CD2Cl2): -51.4 (d, JF-F ) 11
3
Hz, 6F), -82.8 (t, 3JF-F ) 21 Hz, 3F), -87.9 (m, 6F). Anal. Calcd
for C30H28BF15NP: C, 49.41; H, 3.87; N, 1.92. Found: C, 49.16;
H, 4.08; N, 2.07.
Synthesis of t-Bu3PNB(OBu)2 (5). To a solution of 2 (30 mg,
0.138 mmol) in 5 mL toluene was added a solution of HB(OBu)2
(46 µL, 3 M in THF, 0.138 mmol). The solution was stirred
overnight, and the solvent was evaporated, leaving the product as
a fine white powder in 95% yield. 1H NMR (C6D6): 4.17 (t, 3JH-H
) 6 Hz, 4H), 1.90 (m, 4H), 1.57 (m, 4H) 1.30 (d, 3JP-H ) 13 Hz,
27H), 0.97 (t, 3JH-H ) 7 Hz, 6H). 13C{1H} NMR (C6D6): 63.6 (s),
1
40.6 (d, JP-C ) 52 Hz), 35.4 (s), 30.0 (s), 20.3 (s), 14.7 (s). 31P-
Experimental Section
{1H} NMR (C6D6): 38.4. 11B{1H} NMR (C6D6): 17.1. Anal. Calcd
for C20H45BNO2P: C, 64.34; H, 12.15; N, 3.75. Found: C, 64.20;
H, 12.02; N, 3.71.
General Data. All preparations were performed under an
atmosphere of dry O2-free N2 employing either Schlenk-line
techniques or a Vacuum Atmospheres inert-atmosphere glovebox.
Synthesis of (t-Bu3PN)2BH (6). To a solution of 2 (150 mg,
0.690 mmol) in toluene (10 mL) was added BH3‚SMe2 (173 µL, 2
M in diethyl ether). The resulting suspension was refluxed for 1 h
and cooled to 25 °C, and the solvent was removed in vacuo. The
product was isolated as a white powder in 75% yield. Uptake of
the powder in a minimum amount of toluene and addition of a
couple of drops of hexane resulted in isolation of X-ray-quality
(13) Ong, C. M.; McKarns, P.; Stephan, D. W. Organometallics 1999, 18,
4197.
(14) Moehlen, M.; Neumuller, B.; Faza, N.; Muller, C.; Massa, W.;
Dehnicke, K. Z. Anorg. Allg. Chem. 1997, 623, 1567.
(15) Mo¨hlen, M.; Neumu¨ller, B.; Harms, K.; Krautscheid, H.; Fenske, D.;
Diedenhofen, M.; Frenking, G.; Dehnicke, K. Z. Anorg. Allg. Chem.
1998, 624, 1105.
(16) Mo¨hlen, M.; Neumu¨ller, B.; Dehnicke, K. Z. Anorg. Allg. Chem. 1999,
625, 197.
(17) Moehlen, M.; Neumueller, B.; Dehnicke, K. Z. Anorg. Allg. Chem.
1998, 624, 177.
1
3
crystals. H NMR (C6D6) partial: 1.37 (d, JP-H )12 Hz, 54H).
13C{1H} NMR (C6D6): 40.8 (d, 1JP-C ) 50 Hz), 30.5 (s). 31P{1H}
NMR (C6D6): 31.2. 31P{1H} NMR (CD2Cl2): 35.4. 11B{1H} NMR
(18) Hawkeswood, S.; Stephan, D. W. Dalton Trans. 2005, 2182.
(19) Hawkeswood, S.; Wei, P.; Gauld, J. W.; Stephan, D. W. Inorg. Chem.
2005, 44, 4301.
(20) Courtenay, S.; Mutus, J. Y.; Schurko, R. W.; Stephan, D. W. Angew.
Chem., Int. Ed. 2002, 41, 498-501.
(21) 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. Organome-
tallics 2003, 22, 1937.
3624 Inorganic Chemistry, Vol. 46, No. 9, 2007

Sterically Demanding Phosphinimines and Phosphinimides
(C6D6): 24.6 (br). Anal. Calcd for C24H55BN2P2: C, 64.86; H,
12.47; N, 6.30. Found: C, 64.20; H, 12.82; N, 5.96.
suspension was stirred overnight, and then the solvent was
evaporated. The product was dissolved in toluene, filtered, and dried
in vacuo, resulting in isolation of 14 in 78% yield. 1H NMR
(C6D6): 1.14 (d, 3JP-H ) 14 Hz, 27H). 13C{1H} NMR (C6D6): 39.8
(d, 1JP-C ) 52 Hz), 28.8 (s). 31P{1H} NMR (C6D6): 41.7. 11B{1H}
NMR (C6D6): 20.3 (br, s). Anal. Calcd for C12H27BCl2NP: C,
48.36; H, 9.13; N, 4.70. Found: C, 48.19; H, 9.01; N, 4.31.
Synthesis of t-Bu3PNBMe2 (15). To a solution of 14 (75 mg,
0.252 mmol) in 5 mL of toluene was added MeMgBr (168 µL, 3
M solution in ether, 0.504 mmol). The resulting white suspension
was stirred for 1 h and filtered, and the solvent was evaporated,
Synthesis of n-Bu(t-Bu)2PNH‚BH3 (8). To a solution of
phosphinimine 7 (0.150 g, 0.690 mmol) in 10 mL of hexane was
added BH3‚SMe2 (2 M, 0.173 mL, 0.345 mmol) in diethyl ether.
The solution was stirred for 4 h and filtered. X-ray-quality crystals
were collected from the hexane supernatant kept at -30 °C.
Yield: 87%. 1H NMR (C6D6): 1.76 (m, 2H), 1.60 (m, 2H), 0.1.26
(sextet, 2H, 3JH-H ) 7 Hz), 0.89 (d, 18H, 3JP-H ) 14 Hz), 0.84 (t,
3
3H, JH-H ) 8 Hz). 31P{1H} NMR (C6D6): 61.6. 13C{1H} NMR
3
2
(C6D6): 27.7, 25.8 (d, JP-C ) 19 Hz), 25.5 (d, JP-C ) 26 Hz),
19.0 (d, 1JP-C ) 30 Hz), 14.1. 11B{1H} NMR (C6D6): -21.0. Anal.
Calcd: C, 62.35; H, 13.52; N, 6.06. Found: C, 62.02; H, 13.22;
N, 5.90.
1
isolating the product as a white powder in 64% yield. H NMR
(C6D6): 1.17 (d, 3JP-H ) 13 Hz, 27H), 0.87 (s, 6H). 13C{1H} NMR
(C6D6): 40.3 (d, 1JP-C ) 53 Hz), 29.9 (s), 26.5 (s). 31P{1H} NMR
(C6D6): 31.1. 11B{1H} NMR (C6D6): 45.0 (br s). Anal. Calcd for
C14H33BNP: C, 65.38; H, 12.93; N, 5.45. Found: C, 64.81; H,
12.02; N, 5.21.
Synthesis of n-Bu3PNBCl(Ph) (9). A solution of BCl2Ph (0.2
mL, 1.542 mmol) in 5 mL of toluene was slowly added via syringe
to a solution of n-Bu3PNSiMe3 (0.446 g, 1.541 mmol) in 35 mL of
toluene. The Schlenk flask was put under a static vacuum and stirred
for 72 h. The solvent was removed in vacuo, and the remaining
white solid was washed with n-pentane. 1H NMR (C6D6): 8.72 (d,
Synthesis of [t-Bu3PNBMe]2[(MeB(C6F5)3)]2 (16). To a solution
of 15 (20 mg, 0.08 mmol) in 2 mL of CD2Cl2 was added B(C6F5)3
(40 mg, 0.08 mmol). A white suspension formed instantly. Removal
of the solvent resulted in isolation of the product in >95% yield.
1H NMR (C6D6): 1.52 (d, 3JP-H ) 15 Hz, 27H), 1.18 (s, 3H), 0.46
(br, 3H). 13C{1H} NMR (C6D6): 150.0, 148.0, 139.2, 137.3 (br s),
40.9 (d, 1JP-C ) 54 Hz), 31.7 (s), 30.3 (s), 27.9 (s). 31P{1H} NMR
(C6D6): 63.0. 11B{1H} NMR (C6D6): 23.0 (br s), -19.1 (s). 19F
3
3
3
2H, JH-H ) 7 Hz), 7.47 (t, 2H, JH-H ) 7 Hz), 7.28 (t, JH-H
)
3
7 Hz), 1.60 (m, 6H), 1.22 (m, 6H), 1.02 (tq, 6H, JH-H ) 7 Hz,
3JH-H ) 7 Hz), 0.73 (t, 9H, 3JH-H ) 7 Hz). 31P{1H} NMR (C6D6):
39.8. 13C{1H} NMR (C6D6): 135.0, 127.6, 127.1, 24.7, 24.1, 23.8,
14.0. 11B{1H} NMR (C6D6): 11.0. Anal. Calcd: C, 63.64; H, 9.50;
N, 4.12. Found: C, 63.39; H, 9.73; N, 4.08.
3
NMR (CD2Cl2): -55.9 (d, JF-F ) 21 Hz, 6F), -88.1 (m, 3F),
3
-90.7 (t, JF-F ) 23 Hz). Anal. Calcd for C32H33B2F15NP: C,
Synthesis of [(µ-R3PN)AlH2]2 [R ) i-Pr (10), t-Bu (11)]. These
compounds were prepared in a similar fashion, and thus only one
preparation is detailed. To a solution of 1 (2.036 g, 11.620 mmol)
in 40 mL of toluene was added 23.22 mL of a 0.5 M solution of
AlH3‚NMe2Et in toluene. Gas evolution was observed upon the
addition of the alane complex. The solution was stirred for 16 h,
after which the solution was reduced to a white slurry in vacuo,
followed by the addition of 20 mL of pentane. The resulting mixture
was filtered, and a fine white powder was collected, washed with
49.97; H, 4.32; N, 1.82. Found: C, 49.72; H, 3.90; N, 1.61.
Synthesis of [(t-Bu3PN)2B]Cl (17). To a suspension of 5 (100
mg, 0.448 mmol) in toluene (10 mL) was added BCl3 (0.224 mmol,
224 µL, 1 M in heptane). The resulting white suspension was
refluxed overnight, the solvent evaporated, the product dissolved
in toluene, and the solution filtered. Compound 17 crystallized in
72% yield. 1H NMR (CD2Cl2): 1.46 (d, 3JP-H ) 14 Hz, 54H). 13C-
1
{1H} NMR (CD2Cl2): 40.7 (d, JP-C ) 48 Hz), 29.3 (s). 31P{1H}
1
5 mL of pentane, and dried in vacuo in 79% yield. 10. H NMR
NMR (CD2Cl2): 55.7. 11B{1H} NMR (CD2Cl2): 11.9 (br). 1H NMR
(C6D6): 1.35 (d, 3JP-H )13 Hz, 54H). 13C{1H} NMR (C6D6): 41.0
(d, 1JP-C ) 53 Hz), 30.2 (s). 31P{1H} NMR (C6D6): 28.5. 11B{1H}
NMR (C6D6): -6.1 (br). Anal. Calcd for C24H54BClN2P2: C, 60.19;
H, 11.37; N, 5.85. Found: C, 59.66; H, 11.80; N, 5.47.
2
3
(C6D6): 1.98 (d of sept, 6H, JP-H ) 11 Hz, JH-H ) 3 Hz), 1.11
(d of d, 36H, JH-H ) 14 Hz, JH-H ) 7 Hz). 31P{1H} NMR
(C6D6): 46.6 (s). 13C{1H} NMR (C6D6): 26.9 (d, 1JP-C ) 62 Hz),
17.6 (s). 27Al{1H} NMR (C6D6): 122.5 (br). Anal. Calcd for C18H46-
Al2N2P2: C, 53.19; H, 11.41; N, 6.89. Found: C, 53.05; H, 11.39;
N, 6.49. 11. Yield: 80%. Some of the white powder was dissolved
in minimal amounts of toluene and stored at -33 °C in which
X-ray-quality crystals were grown. 1H NMR (C6D6): 1.43 (d, 54H,
3JP-H ) 13 Hz). 31P{1H} NMR (C6D6): 58.0 (s). 13C{1H} NMR
(C6D6): 42.2 (d, 1JP-C ) 62 Hz), 30.9 (s). 27Al{1H} NMR (C6D6):
120.4 (br). Anal. Calcd for C24H58Al2N2P2: C, 58.75; H, 11.92; N,
5.71. Found: C, 58.21; H, 12.06; N, 5.10.
3
3
Synthesis of (t-Bu3PN)2BMe (18). To a suspension of 16 (25
mg, 0. 052 mmol) in 2 mL of toluene was added MeLi (40 µL, 1.4
M solution in ether, 0.056 mmol). The resulting white suspension
was stirred over night, filtered and the solvent was evaporated. The
1
product was isolated as a white powder in 69% yield. H NMR
(C6D6): 1.34 (d, 3JP-H ) 13 Hz, 54H), 0.9 (s, 3 H). 13C{1H} NMR
(C6D6) (partial): 41.0 (d, 1JP-C ) 53 Hz), 30.5 (s). 31P{1H} NMR
(C6D6): 20.1 (s). 11B{1H} NMR (C6D6): 29.8 (br). Anal. Calcd
for C25H57BN2P2: C, 52.02; H, 9.95; N, 4.85. Found: C, 51.81;
H, 9.75; N, 4.96.
Synthesis of [(µ-t-Bu3PN)AlH(O3SCF3)]2 (12). To a solution
of 11 (2.00 g, 4.07 mmol) in 20 mL of toluene was added 2.17 g
of Me3SiO3SCF3. The solution was stirred for 16 h, during which
time a white precipitate formed. The precipitate was allowed to
settle, and the solvent was decanted off. The white solid was washed
with 2 mL of pentane and dried in vacuo. A white fine powder
was isolated in 82% yield. 1H NMR (CD3CN): 1.49 (d, 54H, 3JP-H
) 14 Hz). 31P NMR (CD3CN): 72.2 (s). 13C{1H} NMR (CD3CN):
Synthesis of [(t-Bu3PN)2B][B(C6F5)4] (19) and [(t-Bu3PN)2B]-
[PF6] (20). These complexes were prepared in a similar manner,
and thus only a single representative preparation is described. To
a solution of 17 (320 mg, 0.720 mmol) in CH2Cl2 (5 mL) was added
[Ph3C][B(C6F5)4] (664 mg, 0.720 mmol). The solution was stirred
overnight, the solvent removed in vacuo, and the resulting white
powder washed with hexane (2 × 1 mL) and toluene (1 mL). This
afforded 19 as a white powder in 65% yield. Uptake of the powder
in a minimum amount of toluene and addition of a couple of drops
29.3 (s), 1.8 (q, JF-C ) 21 Hz), 1.7 (q, JF-C ) 21 Hz), (d, 1JP-C
)
Hz), (s). 19F{1H} NMR: -78.9. 27Al{1H} NMR (CD3CN): 69.9
(br). Anal. Calcd for C26H56Al2F6N2P2O6S2: C, 39.69; H, 7.17; N,
3.56. Found: C, 40.01; H, 7.39; N, 3.72.
1
of hexane resulted in isolation of X-ray-quality crystals. 19. H
3
Synthesis of t-Bu3PNBCl2 (14). To a suspension of 13 (150 mg,
0.672 mmol) in 10 mL of ether was added a solution of BCl3 (225
µL, 1 M solution in heptane, 0.225 mmol). The resulting white
NMR (C6D6): 1.46 (d, JP-H ) 14 Hz, 54H). 13C{1H} NMR
(C6D6): 150.4-135.2 (br), 40.8 (d, 1JP-C ) 48 Hz), 29.3 (s). 31P-
{1H} NMR (C6D6): 55.0 (s). 31P{1H} NMR (CD2Cl2): 55.8 (s).
Inorganic Chemistry, Vol. 46, No. 9, 2007 3625

Courtenay et al.
Table 1. Crystallographic Data
3
4
8
11
12
21
formula
fw
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
C27H22BF15NP
687.24
monoclinic
P2(1)/n
12.331(14)
18.87(2)
12.398(14)
C30H28BF15NP
729.31
monoclinic
P2(1)/c
11.384(18)
12.84(2)
21.46(4)
C12H31BNP
231.16
triclinic
P1h
8.212(5)
8.397(5)
11.678(6)
84.132(12)
85.683(10)
85.338(10)
796.7(8)
2
C24H58Al2N2P2
490.62
tetragonal
Pa3h
14.486(4)
C26H56Al2F6N2O6P2S2
786.75
triclinic
P1h
13.640(8)
17.599(10)
19.094(11)
112.843(11)
108.234(12)
90.847(12)
3963(4)
4
1.319
0.325
17 049
11283
845
0.0695
0.1662
0.855
C24H54B2F4N2P2
530.25
tetragonal
Pa3h
14.298(4)
98.320(16)
91.77(4)
γ (deg)
V (Å3)
2855(6)
4
1.599
0.215
11 220
4055
3135(9)
4
1.545
0.200
13 287
4451
3039.5(14)
4
1.072
0.214
12 178
732
2922.9(16)
4
1.205
0.190
3111
644
Z
d(calc), g cm-1
abs coeff µ, cm-1
data collected
0.964
0.149
3401
2262
data Fo2 > 3σ(Fo )
2
variables
R
Rw
406
433
152
56
61
0.0635
0.1378
1.082
0.0499
0.1234
0.979
0.0551
0.1516
1.013
0.0482
0.1423
1.058
0.0588
0.1571
1.047
GOF
11B{1H} NMR (C6D6): 11.1 (br), -20.8 (s). 19F{1H} NMR (CD2-
Cl2): -133.4 (s), -164.1 (pst, JF-F ) 18 Hz), -167.9 (s). Anal.
were initiated based on the crystallographic results presented
herein (Table 1).
3
Calcd for C48H54B2F20N2P2: C, 51.36; H, 4.84; N, 2.50. Found:
X-ray Data Collection and Reduction. Crystals were manipu-
lated 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 (4.5° < 2θ < 45-50.0°) 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. A
measure of decay was obtained by re-collecting the first 50 frames
of each data set. The intensities of the reflections within these frames
showed no statistically significant change over the duration of the
data collections. The data were processed using the SAINT and
SHELXTL 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.
1
C, 51.62; H, 4.94; N, 2.33. 20. Yield: 66%. H NMR (CD2Cl2):
3
1.47 (d, JP-H ) 14 Hz, 54H). 13C{1H} NMR (CD2Cl2): 40.8 (d,
1JP-C ) 48 Hz), 29.2 (s). 31P{1H} NMR (CD2Cl2): 55.9 (s), -144.0
(sept, 1JP-F ) 707 Hz). 11B{1H} NMR (CD2Cl2): -3.9(s). 19F NMR
1
(CD2Cl2): 3.8 (d, JF-P ) 710 Hz). Anal. Calcd for C24H54-
BF6N2P3: C, 48.99; H, 9.24; N, 4.76. Found: C, 48.59; H, 9.34;
N, 4.27.
Synthesis of [(µ-t-Bu3PN)2BF2]2 (21). To a solution of 17 (50
mg, 0.104 mmol) in 2 mL of CH2Cl2 was added Ph3CBF4 (34 mg,
0.103 mmol). The resulting red solution was stirred for 2 h, during
which time the color disappeared. The solvent was evaporated, and
the resulting white powder was washed with hexane. The product
is isolated in 86% yield. X-ray-quality crystals were obtained from
a saturated CD2Cl2 solution of the compound. 1H NMR (CD2Cl2):
3
1.49 (d, JP-H ) 14 Hz, 54H). 13C{1H} NMR (CD2Cl2): 40.7 (d,
1JP-C ) 48 Hz), 29.3 (s). 31P{1H} NMR (CD2Cl2): 55.3 (s). 11B-
{1H} NMR (CD2Cl2): 11.8 (br). 19F NMR (CD2Cl2): -75.5 (s).
Anal. Calcd for C12H27BF2NP: C, 54.36; H, 10.26; N, 5.28.
Found: C, 54.50; H, 10.08; N, 4.96.
Structure Solution and Refinement. Non-H atomic scattering
factors were taken from the literature tabulations.27 The heavy-
atom positions were determined using direct methods, employing
the SHELXTL direct methods routine. The remaining non-H atoms
were located from successive difference Fourier map calculations.
The refinements were carried out by using full-matrix least-squares
techniques on F 2, minimizing the function ω (Fo - Fc)2, where
Molecular Orbital Computations. All density functional theory
(DFT) calculations were performed using the Gaussian 03 suite of
programs.22 The basis set consisted of the B3LYP/6-31g(d) basis
set23-26 on all atoms. The geometries for the computational models
2
2
the weight ω is defined as 4Fo /2σ(Fo ) and Fo and Fc are the
observed and calculated structure factor amplitudes, respectively.
In the final cycles of each refinement, all non-H 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 C 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.
(22) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A. J.;
Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels,
A. D. K. K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.;
Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford,
S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma,
K.; Salvador, P.; Dannenberg, J. J.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Baboul,
A. G.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi,
I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M.
A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Andres, J. L.; Gonzalez, C.;
Head-Gordon, M.; Replogle, E. S.; Pople, J. A. Gaussian 03; Gaussian,
Inc.: Pittsburgh, PA, 2001.
(23) Ditchfield, R.; Hehre, W. J.; Pople, J. A. J. Chem. Phys. 1971, 54,
724.
(24) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta 1973, 28, 213.
(25) Hariharan, P. C.; Pople, J. A. Mol. Phys. 1974, 27, 209.
(26) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972, 56,
2257.
(27) Cromer, D. T.; Waber, J. T. Int. Tables X-Ray Crystallogr. 1974, 4,
71.
3626 Inorganic Chemistry, Vol. 46, No. 9, 2007

Sterically Demanding Phosphinimines and Phosphinimides
Scheme 1
Figure 1. POV-ray drawing of 3. Color code: C, black; N, light blue; B,
blue; P, orange; F, pink; H, gray. H atoms except for the NH are omitted
for clarity. Selected distances (Å) and angles (deg): P-N 1.620(5), N-B
1.584(8), B-N-P 144.1(4).
Discussion
We have previously described the formation of the
phosphinimine adduct (Me3PNSiMe3)B(C6F5)3 in which the
N-B bond is typical of a Lewis acid-base interaction.12 In
contrast, sterically demanding (trimethylsilyl)phosphinimines
react with B(C6F5)3, resulting in the abstraction of a methyl
group from Si to give species such as [R3PNSiMe2(N(PR3)-
SiMe3][MeB(C6F5)3] (R ) i-Pr, Ph) and [(µ-t-Bu3PN)SiMe2]-
[MeB(C6F5)3].12 In probing of the reactivity of the parent
phosphinimines, the corresponding reactions of R3PNH [R
) i-Pr (1), t-Bu (2)] with B(C6F5)3 were investigated. These
reactions proceed under mild conditions and in a facile
fashion to form the white crystalline adducts (R3PNH)B-
(C6F5)3 [R ) i-Pr (3), t-Bu (4)] in yields of 93 and 95%,
1
respectively (Scheme 1). The H, 13C{1H}, and 19F NMR
Figure 2. POV-ray drawing of 4. Color code: C, black; N, light blue; B,
blue; P, orange; F, pink; H, gray. H atoms except for the NH are omitted
for clarity. Selected distances (Å) and angles (deg): P-N 1.649(3), N-B
1.614(4), B-N-P 148.70(17).
1
spectra of compound 3 are as expected, with a H NMR
resonance attributable to the NH proton at 2.97 ppm. The
31P{1H} NMR resonance is shifted downfield to 64.0 ppm,
consistent with coordination of B to N. The 11B{1H} NMR
signal is seen at -7.5 ppm, typical of four-coordinate B
1
centers. In a similar sense, compound 4 gives rise to a H
NMR resonance at 3.30 ppm from the NH group and 31P-
{1H} and 11B{1H} NMR signals at +78.8 and -9.5 ppm,
respectively. The formulations of these phosphinimine-
borane adducts were unambiguously confirmed via X-ray
crystallography (Figures 1 and 2). The B-N distances in 3
and 4 were found to 1.584(8) and 1.614(4) Å, respectively.
The longer B-N distance in 4 is attributed to the steric
demands of the tert-butyl substituents. Notably, the P-N
distances of 1.620(5) and 1.649(3) Å and the B-N-P angles
of 144.1(4)° and 148.70(17)° in 3 and 4, respectively, also
reflect the influence of the greater steric demands in 4.
Figure 3. POV-ray drawing of 6. Color code: C, black; N, light blue; B,
blue; P, orange. H atoms are omitted for clarity. Selected distances (Å)
and angles (deg): P-N 1.535(7), B-N 1.41(5), N-B-N 117(2), B-N-P
148.2(16).
species is thought to be structurally analogous to the
previously reported t-Bu3PNB(O2C2Me4).19
In a similar protonolysis reaction, 2 equiv of 2 with BH3‚
SMe2 under reflux afforded the white powder 6 in 75% yield
(Scheme 1). Similar to 5, the 31P{1H} NMR resonance of 6
was at 31.2 ppm and the 11B{1H} NMR signal at 24.6 ppm;
nonetheless, the data did not provide an unambiguous
formulation. A single-crystal X-ray diffraction study of 6
confirmed this formulation as (t-Bu3PN)2BH (Figure 3).20
The structural refinement shows a 6-fold disorder of a B
atom about the center of the -3 symmetry. The N-B-N
bend is approximately 117(2)°, while the angle at P-N-B
The parent phosphinimine 2 reacts with HB(OBu)2, with
evolution of H2 ultimately affording the fine white powder
5 in 95% yield. This product 5 exhibits a 31P{1H} NMR
signal at 38.4 ppm as well as a 11B{1H} NMR resonance at
17.1 ppm. These data are consistent with the formulation of
5 as t-Bu3PNB(OBu)2, in which the B center is three-
coordinate (Chart 1). Despite repeated efforts, this could not
be confirmed by X-ray crystallography because efforts to
obtain suitable crystals were unsuccessful. Nonetheless, this
Inorganic Chemistry, Vol. 46, No. 9, 2007 3627

Courtenay et al.
Figure 5. POV-ray drawing of 11. Color code: C, black; N, light blue;
Al, rich blue; F, pink; H, gray; P, orange. H atoms are omitted for clarity.
Selected distances (Å) and angles (deg): Al-N 1.887(3), Al′-N 1.905(3),
P-N 1.598(4), N-Al-N 89.86(19), P-N-Al 134.65(11).
Figure 4. POV-ray drawing of 8. Color code: C, black; N, light blue; B,
blue; P, orange. H atoms except for the BH and NH hydrogens are omitted
for clarity. Selected distances (Å) and angles (deg): P-N 1.592(3), N-B
1.580(5), B-N-P 130.6(3).
Scheme 2
is 148.2(2)°. The P-N and B-N distances are 1.535(7) and
1.41(5) Å, respectively.
A similar reaction of 1 equiv of the phosphinimine 7 with
BH3‚SMe2 resulted in the formation of X-ray-quality crystals
of 8 in 87% yield. The 1H NMR spectrum shows a signal at
0.84 ppm attributable to three BH protons. The dramatic
downfield shift of the 31P{1H} NMR resonance to 61.6 ppm
and the 11B{1H} NMR chemical shift of -21.0 ppm suggest
the formulation of 8 as n-Bu(t-Bu)2PNH‚BH3 (Scheme 1).
This formulation was unambiguously confirmed via a
crystallographic study of 8 (Figure 4). Interestingly, the P-N
and N-B distances in 8 of 1.592(3) and 1.580(5) Å,
respectively, are significantly shorter than those seen in the
B(C6F5)3 adducts, 3 and 4. The B-N-P angle in 8 was found
to be 130.6(3)°, which is also significantly smaller than those
seen in 3 and 4. These findings are consistent with the weaker
Lewis acidity and steric demands of BH3 versus B(C6F5)3.
Compound 8 was formed even in the presence of 2 equiv of
the phosphinimine 7 and under reflux conditions. This is
perhaps surprising because this stands in contrast to the
reaction of the phosphinimine 2. This finding suggests that
steric demands encourage H2 elimination. It is noteworthy
that steric demands also have been shown to impact the
reactions of phosphinimines R3PNH with HBpin (pin )
O2C2Me4). In these cases, sterically demanding phosphin-
imines prompted H2 elimination to give R3PNBpin, whereas
smaller phosphinimines were reduced to give free phosphine
and HN(Bpin)2.18,19
the presence of the R3P fragment, the observation of 31P-
{1H} NMR chemical shifts at 46.6 and 57.8 ppm and 27Al
NMR resonances at 122.5 and 120.4 ppm for 10 and 11,
respectively, support coordination of phosphinimide to four-
coordinate Al centers. Given that the elemental analysis of
these products suggested the empirical formula R3PNAlH2,
these products were formulated as 10 and 11 (Scheme 2).
In the latter case, this formulation was unambiguously
confirmed by an X-ray diffraction study (Figure 5). Similar
to 6, the crystal packing of 11 is dominated by the t-Bu3PN
ligands, resulting in a disorder of the AlH2 units. However,
in this case, the site occupancy revealed that two Al centers
are bridged by the phosphinimide ligands. The Al-N
distances were found to range from 1.887(3) to 1.905(3) Å,
significantly longer than the B-N distances and yet consis-
tent with typical Al-NPR3 bridges. The N-Al-N and Al-
N-Al′ angles in these four-membered rings were determined
to be 89.9(2)° and 90.1(2)°, respectively. These values are
similar to those previously reported for the species [(µ-t-
Bu3PN)AlMe2]2.13 The corresponding P-N distance in 11
was found to be 1.598(4) Å, while the P-N-Al angle was
found to be 134.7(1)°. The parameters are also similar to
those reported for [(µ-t-Bu3PN)AlMe2]2 although slightly
smaller than those seen in [(µ-t-Bu3PN)AlCl2]2, consistent
with the more electron-deficient Al center in 11 and [(µ-t-
Bu3PN)AlMe2]2.13 It is noteworthy that, despite the fact that
6 and 11 are formed in similar fashions, the former species
contains only a single B center while the Al analogue is
dimeric. This presumably is attributable to the longer Al-N
bond distances that accommodate the bridging phosphinimide
motif.
An alternative strategy to borane-phosphinimide com-
plexes is exemplified by the reaction of BCl2Ph with n-Bu3-
PNSiMe3. Under a static vacuum for 72 h, this reaction
proceeds to evolve SiMe3Cl and, subsequently, to afford the
formation of the white solid 9 in near-quantitative yields
1
(Scheme 1). This formulation was consistent with the H
and 13C{1H} NMR data as well as the downfield shifts of
the 31P{1H} and 11B{1H} NMR resonances to 39.8 and 11.0
ppm, respectively. Efforts to confirm this crystallographically
were unsuccessful because of the inability to obtain X-ray-
quality crystals despite repeated attempts.
The corresponding reactions of the phosphinimines 1 and
2 with AlH3‚NMe2Et proceed in a facile fashion with gas
evolution, ultimately affording the white solids 10 and 11
1
in 79 and 80% yield, respectively. While the H and 13C-
Compound 10 reacts with 2 equiv of Me3SiO3SCF3 to yield
a new species 12, which gives rise to a new 31P NMR signal
{1H} NMR data for these compounds were consistent with
3628 Inorganic Chemistry, Vol. 46, No. 9, 2007

Sterically Demanding Phosphinimines and Phosphinimides
Scheme 3
Figure 6. POV-ray drawing of 12 (one molecule from the asymmetric
unit is shown). Color code: C, black; N, light blue; Al, rich blue; O, red;
S, yellow; F, pink; H, gray; P, orange. H atoms are omitted for clarity.
Selected distances (Å) and angles (deg): Al-O 1.828(4), 1.811(4), Al-N
1.875(5), 1.878(5), 1.866(5), 1.889(5), Al-Al′ 2.626(3), P-N 1.612(5),
1.625(5), O-Al-N 107.7(2), 110.3(2), 108.3(2), 110.1(2), N-Al-N
90.9(2), 90.8(2), P-N-Al 135.1(3), 132.9(3).
via the subsequent reaction with MeMgBr, affording the
species 15 in 64% isolated yield. The 1H and 13C{1H} NMR
data were consistent with the formulation of 15 as t-Bu3-
PNBMe2 (Scheme 2). The 31P{1H} NMR resonance of 15
shifts upfield to 31.1 ppm. The presence of a three-coordinate
B center in 15 is supported by the downfield 11B NMR signal
at 45.0 ppm. Subsequent reaction of 15 with B(C6F5)3 results
in the formation of 16 in >95% yield. The 31P{1H} NMR
resonance of 16 shifts dramatically upfield to 63.0 ppm. The
1H NMR spectrum of 16 shows two resonances attributable
to B-bound methyl groups at 1.18 and 0.46 ppm, with the
corresponding 13C NMR resonances at 30.3 and 27.9 ppm.
The 11B NMR spectrum of 16 shows two resonances at 23.0
and -19.1 ppm consistent with the presence of both three-
and four-coordinate B centers. These data are consistent with
the presence of the anion [MeB(C6F5)3] and thus support the
formulation of 16 as [(µ-t-Bu3PN)BMe]2[MeB(C6F5)3]2
(Scheme 3). It has been previously shown that, in the related
aluminum chemistry, only one methyl group is abstracted
from [Me2Al(µ-NPR3)]2 upon reaction with B(C6F5)3, af-
fording the dimeric monocation [(Me2Al(µ-NPR3)2AlMe-
(MeB(C6F5)3)].13
at 72.2 ppm. This product was isolated in 82% yield (Scheme
2). 19F NMR confirms the presence of the triflate fragments
with a resonance at -78.9 ppm. The nature of 12 was
confirmed unambiguously via X-ray crystallography as [(µ-
t-Bu3PN)AlH(OSO2CF3)]2 (Figure 6). Compound 12 is also
a dimer in which two phosphinimide ligands bridge two Al
centers. However, in addition to one hydride, a triflate group
is coordinated through O to Al. The disposition of the triflate
groups is pseudo-cis; that is, the two triflate groups are
positioned on the same side of the Al2N2 core. This
orientation presumably is viewed as a steric compromise,
yielding lesser triflate-phosphinimide steric conflicts. Be-
cause there are two molecules in the asymmetric unit, Al-O
distances in 12 were found to range between 1.787(5) and
1.828(4) Å, while the Al-N bond lengths fall in between
1.870(5) and 1.889(5) Å. The O-Al-N angles are ap-
proximately tetrahedral, ranging from 107.7(2)° to 110.3(2)°.
The Al2N2 cores are approximately square, with N-Al-N
angles falling in the narrow range of 90.8(2)-91.0(2)°, while
the Al-N-Al angles fall between 88.4(2)° and 89.1(2)°.
These core metrics result in an average Al‚‚‚Al′ distance of
2.624(3) Å. The P-N distances in 12 are longer than those
in 11, ranging from 1.607(5) to 1.625(5) Å, while the
corresponding P-N-Al angles were found to vary from
132.9(3)° to 135.1(3)°. The observation of longer P-N bonds
and shorter Al-N distances in 12 compared to 10 supports
the notion of a more electron-deficient Al center in 12.
An alternative strategy to complexes containing phosphin-
imide ligands involves the reactions of the lithium salt 13.9
Reaction of 13 with BCl3 proceeds smoothly to give a white
solid 14 in 78% yield (Scheme 3). Coordination of phos-
phinimide to the B center is indicated by the shift of the
31P{1H} NMR signal to 41.7 ppm and the observation of
the 11B NMR resonance at 20.3 ppm. This latter point
suggests that 14 contains a three-coordinate B center, while
elemental analysis was consistent with the formulation of
14 as t-Bu3PNBCl2. Derivatization of 14 was accomplished
Reaction of 13 in a 2:1 ratio with BCl3 in toluene affords
after refluxing for 12 h and subsequent isolation a crystalline
solid 17 in 72% yield. Compound 17 in CD2Cl2 shows a
31P{1H} NMR resonance at 55.7 ppm, and a broad 11B NMR
resonance was observed at 11.9 ppm. While these data
1
together with the H and 13C NMR spectra confirmed that
17 was distinct from 14, the nature of 17 could only be
confirmed by X-ray crystallography (Figure 7).20 This study
showed 17 to be [(t-Bu3PN)2B]Cl. As previously com-
municated, this compound is comprised of the -3 symmetric
cation [(t-Bu3PN)2B]+ in which the crystallographic sym-
metry imposes linearity on the N-B-N and P-N-B angles.
The Cl- anion sits 7.30 Å from the B center. The B-N
distance in 17 is 1.258(5) Å. This is significantly shorter
than those seen in B(NPPh3)3 [1.446(8) Å],17 [Fc2B2(Br)(µ-
Inorganic Chemistry, Vol. 46, No. 9, 2007 3629

Courtenay et al.
Figure 7. POV-ray drawing of the cation of 17. Color code: C, black; N,
light blue; B, rich blue; P, orange. H atoms are omitted for clarity. Selected
distances (Å) and angles (deg): P-N 1.531(5), B-N 1.258(5), N-B-N
180.0(4), B-N-P 180.0(2).
Figure 8. POV-ray drawing of 21. Color code: C, black; N, light blue;
B, blue; F, pink; P, orange. H atoms are omitted for clarity. Selected
distances (Å) and angles (deg): P(1)-N(1) 1.597(5), N(1)-B(1) 1.544(16),
B(1)-N(1)-P(1) 136.9(5), B(1)-N(1)-P(1) 137.3(6), N(1)-B(1)-N(1)
94.2(8), F(1)-B(1)-F(1) 104.7(16).
Scheme 4
In a similar fashion, abstraction of methyl or hydride from
18 or 6 with [Ph3C][PF6] afforded the analogous salt 20
(Scheme 3). In contrast, while the analogous reaction of 18
or 6 with [Ph3C][BF4] also affords Ph3CMe or Ph3CH,
respectively, the new product 21 was isolated in these cases.
The 11B{1H} NMR spectrum exhibited a single broad
resonance at 11.8 ppm, and the 19F NMR spectrum showed
a resonance at -75.5 ppm, inconsistent with the presence
of a [BF4]- anion. A crystallographic analysis of 21 revealed
that 21 is correctly formulated as [t-Bu3PNBF2]2 (Figure 8
and Scheme 3). Thus, the phosphinimide ligand bridges two
BF2 units. Crystallographic -3 symmetry is imposed, and
thus disorder of BF2 fragments is evident. As a result of this
disorder, detailed comments on the metric parameters are
inappropriate; however, the B-N bonds in 21 were found
to be 1.544(16) Å, which is slightly elongated in comparison
to 17 and 19. The formation of 21 presumably proceeds
through a transient formation of the salt [(t-Bu3PN)2B][BF4],
which rapidly undergoes fluoride abstraction and ligand
redistribution to form 21.
The NMR data for the salts 17 and 19 show a marked
solvent dependence. The 31P NMR resonance for 17 shifts
from 55.7 ppm in CD2Cl2 to 28.5 ppm in C6D6, whereas the
analogous signals for 19 are observed at 55.8 and 55.0 ppm,
respectively. The addition of AlCl3 to a benzene solution of
17 sequesters the chloride ion, forming [AlCl4]-, and the
31P NMR resonance shifts from 28.5 to 55.8 ppm. These
data infer that 17 forms a tight ion pair in nonpolar solvents,
while in polar solvents, salvation of the ions results in ion-
pair separation. These results also suggest that the energy
difference between a tight ion pair and the corresponding
salt of 17 is small. This view is further supported by the
observation that crystals of 17 in which ion-pair separation
is confirmed crystallographically were grown from toluene.
This suggests that, despite the ion pairing in solution, crystal-
packing forces favor the salt. These views are also supported
by theoretical predictions of the 31P NMR chemical shifts,
as previously communicated.20
NPEt3)2][Br] [Fc ) ferrocenyl; 1.44(1) and 1.57(1) Å],28
[H3B3(NPEt3)3Cl2][Br] [1.47(1) Å],29 [HBNPEt3]3[I]3 [1.43(1)
Å],30
[Bn(Me3C)N)2B][AlCl4]
[1.33(3)
Å],
and
[(Me2N)B(NC5H6Me4)]+ [1.30(4) and 1.42(4) Å],31 consistent
with the cationic nature of 17. The P-N bond length in 17
is 1.531(5) Å, typical of main-group phosphinimide deriva-
tives.
The formation of 17 exclusively occurs even in the
presence of excess 13. Smaller phosphinimides have been
shown to result in trisubstitution, as is the case in the
formation of B(NPPh3)3.17 The steric demands present in 17
result in the spontaneous dissociation of halide from the B
center. Although bulky amidoborinium ions were reviewed
by Ko¨lle and No¨th31 two decades ago, the linear geometry
of the PNBNP atoms in the cation of 17 is, to our knowledge,
the first example of a borinium ion formed spontaneously
instead of via halide abstraction with a Lewis acid. The
stability of this linear cationic arrangement of five atoms is
undoubtedly related to resonance forms that distribute the
cationic charge onto the N atoms (Scheme 4).
Compound 17 reacts with MeLi to form a species
formulation (t-Bu3PN)2BMe (18) in 69% yield (Scheme 3).
This species, as well as 6, reacts with [Ph3C][B(C6F5)4] to
abstract methyl or hydride, affording the borinium salt 19
(Scheme 3). This species was also characterized crystallo-
graphically.20 The geometries of the cations of 17 and 19
are very similar, although in the latter case, lesser crystal-
lographic symmetry is imposed, and thus, while a linear
geometry at B is required, the geometry at N distorts slightly
with a P-N-B angle of 162.1(3)°. The cation and anion in
19 are well-separated. The B-B distance is 10.43 Å.
DFT calculations were performed for the models [(Me3-
PN)2M]+ (M ) B, Al) using the B3LYP/6-31g(d) basis set.
These models were constructed based on the crystallographic
data described herein for 14. Geometry optimizations and
molecular orbital calculations were performed. In both cases,
the highest occupied molecular orbital (HOMO; Figure 9a,c)
(28) Mohlen, M.; Neumuller, B.; Pebler, J.; Dehnicke, K. Z. Anorg. Allg.
Chem. 2001, 627, 1508.
(29) Mohlen, M.; Neumuller, B.; Dashti-Mommertz, A.; Muller, C.; Massa,
W.; Dehnicke, K. Z. Anorg. Allg. Chem. 1999, 625, 1631.
(30) Mohlen, M.; Neumuller, B.; Harms, K.; Krautscheid, H.; Fenske, D.;
Diedenhofen, M.; Frenking, G.; Dehnicke, K. Z. Anorg. Allg. Chem.
1998, 624, 1105.
(31) Ko¨lle, P.; No¨th, H. Chem. ReV. 1985, 85, 399.
3630 Inorganic Chemistry, Vol. 46, No. 9, 2007

Sterically Demanding Phosphinimines and Phosphinimides
the lowest unoccupied molecular orbital (LUMO; Figure 9b)
is comprised of a B-based p orbital mixed with an N-P π
orbital. This is consistent with the delocalization of the formal
positive charge over the entire P-N-B-N-P chain. In
contrast, the LUMO for the hypothetical Al model is based
primarily on an Al-based d orbital (Figure 9d). This
localization of the positive charge on Al in this model is
consistent with the observed propensity of aluminum phos-
phinimides for dimerization as well as the inability to
experimentally synthesize a direct Al analogue of 14.
Summary
The chemistry described herein presents several strategies
for the formation of boron and aluminum phosphinimine and
phosphinimide complexes. In general, sterically demanding
phosphinimide ligands result in the formation of monomeric
B species, whereas in the related Al compounds, the
phosphinimide ligands bridge Al centers, resulting in dimeric
products. The chemistry of main-group phosphinimides
continues to be a subject of study in our laboratories.
Acknowledgment. Financial support from NSERC of
Canada is gratefully acknowledged.
Figure 9. Gaussview depictions of molecular orbitals for the model
compounds [(Me3PN)2M]+ (M ) B, Al). M ) B: (a) HOMO; (b) LUMO.
M ) Al: (c) HOMO; (d) LUMO.
Supporting Information Available: Crystallographic data in
CIF format. This material is available free of charge via the Internet
at http://pubs.acs.org.
is comprised primarily of the interaction of the N-based p
orbital with the P-based d orbital. In the case of the B species,
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