Stability of trivalent vanadium alkyl and hydride supported by a chelating phosphinimido ligand

Article abstract of DOI:10.1021/om0101588

Reaction of [(Me₃Si)N=P(Ph)₂C(H)P(Ph)₂=N(SiMe₃)] VCl₂ (1) with 2 equiv of MeLi yielded the corresponding trivalent vanadium derivative [(Me₃Si)N=P(Ph)₂C(H)P(Ph)₂=N(SiMe₃)] -VMe₂ (3). Subsequent hydrogenolysis afforded the dinuclear hydride complex {[(Me₃Si)N=P(Ph)₂C(H)P(Ph)₂= N(SiMe₃)]V}₂(μ-H)₂ (4), where reduction of the metal center to the divalent state had occurred. Hydrogenolysis of solutions of 1 previously treated with lower than stoichiometric amounts of MeLi afforded the two mixed-valent V(II)/V(III) hydrides {[(Me₃-Si) N=P(Ph)₂C(H)P(Ph)₂=N(SiMe₃)]V}₂ (μ-Cl)₂(μ-H) (6) and {[(Me₃Si)N=P(Ph)₂ C(H)P(Ph)₂=N(SiMe₃)]V}₂(μ-Cl) (μ-H)₂ (7). Hydrolysis of the divalent 4 afforded the trivalent and dinuclear {[(Me₃Si)N=P(Ph)₂C(H)P(Ph)₂= (μ-N)]V(OSiMe₃)}₂ (5), featuring migration of the Me₃Si group from the N to the O atom of one incoming molecule of water.

Full text of DOI:10.1021/om0101588

2616
Organometallics 2001, 20, 2616-2622
Sta bility of Tr iva len t Va n a d iu m Alk yl a n d Hyd r id e
Su p p or ted by a Ch ela tin g P h osp h in im id o Liga n d
Ghazar Aharonian, Khalil Feghali, Sandro Gambarotta,* and Glenn P. A. Yap
Department of Chemistry, University of Ottawa, Ottawa, Ontario, Canada
Received February 27, 2001
Reaction of [(Me3Si)NdP(Ph)2C(H)P(Ph)2dN(SiMe3)]VCl2 (1) with 2 equiv of MeLi yielded
the corresponding trivalent vanadium derivative [(Me3Si)NdP(Ph)2C(H)P(Ph)2dN(SiMe3)]-
VMe2 (3). Subsequent hydrogenolysis afforded the dinuclear hydride complex {[(Me3Si)Nd
P(Ph)2C(H)P(Ph)2dN(SiMe3)]V}2(µ-H)2 (4), where reduction of the metal center to the divalent
state had occurred. Hydrogenolysis of solutions of 1 previously treated with lower than
stoichiometric amounts of MeLi afforded the two mixed-valent V(II)/V(III) hydrides {[(Me3-
Si)NdP(Ph)2C(H)P(Ph)2dN(SiMe3)]V}2(µ-Cl)2(µ-H) (6) and {[(Me3Si)NdP(Ph)2C(H)P(Ph)2d
N(SiMe3)]V}2(µ-Cl)(µ-H)2 (7). Hydrolysis of the divalent 4 afforded the trivalent and dinuclear
{[(Me3Si)NdP(Ph)2C(H)P(Ph)2d(µ-N)]V(OSiMe3)}2 (5), featuring migration of the Me3Si group
from the N to the O atom of one incoming molecule of water.
In tr od u ction
which is responsible for catalyst failure and deactiva-
tion, is believed to occur via â-hydrogen elimination of
the growing chain and consequent formation of unstable
vanadium hydrides. Therefore, identifying the factors
which affect the stability of mid-valent vanadium hy-
drides may have some important implications for cata-
lyst design and improvement.
A few years ago we reported the hydrogenolysis of a
cyclometalated trivalent vanadium silazanate species in
the presence of phosphine.9 The reaction afforded a
cationic divalent vanadium polyhydride. This result
indicates that trivalent vanadium hydride, supported
by monodentate amide and generated in the early stage
of the hydrogenolysis, may possess some intrinsic
instability. On the other hand, the successful charac-
terization by Cloke of a stable trivalent hydrido-bridged
vanadium complex10 stabilized by tridentate amide
ligand, also silylated, strongly suggests that ligand
Binary vanadium hydrides in medium-valent oxida-
tion states are important compounds, displaying a wide
range of useful applications in solid-state chemistry,1
electrochemistry,2 hydrogen storage devices,3 etc. Thus,
a wealth of reactivity can reasonably be expected for
molecular vanadium hydrides also in view of the re-
markable behavior displayed by the heavier Nb and Ta
congeners.4 Nevertheless, medium-valent vanadium hy-
drides remain rare,5 despite the promising behavior
displayed by some of the few existing examples.5,6
There is another point of interest that makes the
availability of di- and trivalent vanadium hydrides
particularly desirable. Trivalent vanadium complexes
are used as catalysts for the commercial production of
elastomers.7 One of the problems encountered during
the polymerization reaction is the reduction of the metal
center to the inactive divalent state.8 This reaction,
(5) (a) J onas, K.; Wiskamp, V.; Tsay, Y. H.; Kruger, C. J . Am. Chem.
Soc. 1983, 105, 5480. (b) Bansemer, R. L.; Huffman, J . C.; Caulton, K.
G. J . Am. Chem. Soc. 1983, 105, 6163. (c) Greiser, T.; Puttfarcken, U.;
Rehder, D.; Transition Met. Chem. 1979, 4, 168. (d) Herrmann, W. A.;
Biersack, H.; Balbach, B.; Wulknitz, P.; Ziegler, M. L. Chem. Ber. 1984,
117, 79. (e) Hessen, B.; Van Bolhuis, F.; Teuben, J . H.; Peterson, J . L.
J . Am. Chem. Soc. 1988, 110, 295. (f) Hessen, B.; Meetsma, A.; Teuben,
J . H. J . Am. Chem. Soc. 1989, 111, 5977. (g) Hessen, B.; Buijink, J . K.
F.; Meetsma, A.; Teuben, J . H.; Helgesson, G.; Hakansson, M.; J agner,
S. Organometallics 1993, 12, 2268. (h) Gardner, T. G.; Girolami, G. S.
Organometallics 1987, 6, 2551. (i) Arrieta, J . M. Polyhedron 1992, 11,
3045.
(1) See for example: (a) Dus, R.; Nowicka, E.; Wolfram, Z. Langmuir
1998, 14, 5487. (b) Paniago, R.; Schmid, S.; Metzger, T. H.; Chow, P.
C.; Reichert, H.; Moss, S. C.; Peisl, J .; Liang, K. S. Physica B 1996,
221, 210. (c) Maitre, P.; Bauschlicher, C. W., J r. J . Phys. Chem. 1995,
99, 6836.
(2) See for example: (a) Tsukahara, M.; Takahashi, K.; Mishima,
T.; Miyamura, H.; Sakai, T.; Kuriyama, N.; Uehara, I. J . Alloys Compd.
1995, 231, 616. (b) Tsukahara, M.; Takahashi, K.; Mishima, T.; Sakai,
T.; Miyamura, H.;. Kuriyama, N.; Uehara, I. J . Alloys Compd. 1995,
231, 226. (c) Yang, H. W.; Wang, Y. Y.; Wan, C. C. J . Electrochem.
Soc. 1996, 143, 429. (d) Zuettel, A.; Meli, F.; Chartouni, D.; Schlapbach,
L.; Lichtenberg, F.; Friedrich, B. J . Alloys Compd. 1996, 239, 175.
(3) See for example: (a) Gao, X. P.; Zhang, W.; Yang, H. B.; Song,
D. Y.; Zhang, Y. S.; Zhou, Z. X.; Shen, P. W. J . Alloys Compd. 1996,
235, 225. (b) Iwakura, C.; Choi, W. K.; Miyauchi, R.; Inoue, H. J .
Electrochem. Soc. 2000, 147, 2503. (c) Tsukahara, M.; Kamiya, T.;
Takahashi, K.; Kawabata, A.; Sakurai, S.; Shi, J .; Takeshita, H. T.;
Kuriyama, N.; Sakai, T. J . Electrochem. Soc. 2000, 147, 2941.
(4) See for example: (a) Fryzuk, M. D.; J ohnson, S. A.; Rettig, S.
Organometallics 2000, 19, 3931. (b) Mulford, D. R.; Clark, J . R.;
Schweiger, S. W.; Fanwick, P. E.; Rothwell, I. P. Organometallics 1999,
18, 4448. (c) Fryzuk, M. D.; J ohnson, S. A.; Rettig, S. J . Am. Chem.
Soc. 1998, 120, 11024. (d) Parkin, B. C.; Clark, J . R.; Viscigllo, V. M.;
Fanwick, P. E.; Rothwell, I. P. Organometallics 1995, 14, 3002. (e)
Tayebani, M.; Gambarotta, S.; Yap, G. Organometallics 1998, 17, 3639.
(f) Tayebani, M.; Feghali, K.; Gambarotta, S.; Yap, G. Organometallics
1998, 17, 4282. (g) Berno, P.; Gambarotta, S. Organometallics 1995,
14, 2159.
(6) Sussmilch, F.; Olbrich, F.; Rehder, D. J . Organomet. Chem. 1994,
481, 125.
(7) See for example: (a) Desmangles, N.; Gambarotta, S.; Bensimon,
C.; Davis, S.; Zahalka, H. J . Organomet. Chem. 1997, 562, 53. (b) Kim,
W. K.; Fevola, M. J .; Liable-Sands, L. M.; Rheingold, A. L.; Theopold,
K. H. I. Organometallics 1998, 17, 4541. (c) Davis, S. C.; Van Hellens,
W.; Zahalka, H. In Polymer Material Encyclopedia; Salamone, J . C.,
Ed.; CRC Press: Boca Raton, FL, 1996; Vol. 3. (d) Adisson, E. J . Polym.
Sci., A: Polym. Chem. 1994, 32, 1033. (e) Gumboldt, A.; Helberg, J .;
Schleitzer, G. Makromol. Chem. 1967, 101, 229. (f) Ouzumi, T.; Soga,
K. Makromol. Chem. 1992, 193, 823. (g) Doi, Y.; Suzuki, S.; Soga, K.
Macromolecules 1986, 19, 2896.
(8) See for example: Reardon, D.; Conan, F.; Gambarotta, S.; Yap,
G.; Wang, Q. J . Am. Chem. Soc. 1999, 121, 9318 and references cited
therein.
(9) Berno, P.; Gambarotta, S. Angew. Chem., Int. Ed. Engl. 1995,
34, 822.
10.1021/om0101588 CCC: $20.00 © 2001 American Chemical Society
Publication on Web 05/17/2001

Trivalent Vanadium Alkyl and Hydride
Organometallics, Vol. 20, No. 12, 2001 2617
1027 (w), 999 (w), 954 (s, sh), 844 (s, br), 786 (m), 769 (m),
denticity rather than electronic factors affects the
stability of trivalent vanadium hydrides.
743 (m), 715 (m), 694 (m), 664 (m), 630 (w), 551 (m). µeff
2.86 µB/mol.
)
Herein, we describe the preparation and character-
ization of three rare examples of divalent and mixed-
valence vanadium hydrides as well as of a trivalent
alkyl. The ligand system selected for this work was the
pincer-type bis-phosphinimide anion (Me3Si)NdP(Ph)2-
CHP(Ph)2dN(SiMe3)11 because of its tridentate and
tripodal-like bonding mode and the electronic flexibility
provided by the delocalization of the negative charge
between the deprotonated carbon and the two nitrogen
atoms. Also desirable was the presence of the PdN
function, which is well known to support both a very
high level of catalytic activity12 and to stabilize a large
variety of metal complexes and oxidation states.13
Meth od B. Isola tion of 1‚1.5(tolu en e) a n d of [VCl4-
(TMEDA)]2[H2(TMEDA)] (2). A solution of VCl3(THF)3 (6.3
g, 16.7 mmol) in THF (70 mL) was treated with [CH2(PPh2-
NSiMe3)2] (4.7 g, 8.4 mmol) and TMEDA (1.9 mL, 12.6 mmol).
The solution turned red-purple and was stirred for 24 h. After
removal of THF in vacuo, the residual solid was redissolved
in warm toluene (150 mL) and the solution filtered. The purple
filtrate was allowed to stand at -30 °C for 1 day, upon which
blue-purple crystals of 1‚1.5(toluene) separated (1.2 g, 1.5
mmol, 17.5%). Anal. Calcd (found) for C41.5H51Cl2N2P2Si2V: C,
60.95 (60.83); H, 6.29 (6.15); N, 3.43 (3.39). µeff ) 2.83 µB.
The toluene-insoluble residue was redissolved in THF (70
mL), and the solution was filtered, concentrated (20 mL), and
allowed to stand at room temperature overnight, upon which
red-purple crystals of 2 separated (1.8 g, 2.5 mmol, 58%) Anal.
Calcd (found) for C18H50N6Cl8V2: C, 29.37 (29.86); H, 6.85
(7.03); N, 11.42 (11.27). IR (Nujol mull, cm-1): ν 3674 (w), 1345
(w), 1261 (m), 1098 (m), 1009 (s), 950 (m), 923 (w), 849 (s),
801 (s), 723 (w), 681 (w). µeff ) 4.23 µB/mol.
P r ep a r a tion of [CH(P P h 2NSiMe3)2]V(CH3)2 (3). A solu-
tion of MeLi in ether (9.1 mL, 1.4 M, 12.7 mmol) was added to
a purple solution of 1‚2THF (5.2 g, 6.3 mmol) in THF (150
mL) cooled to 0 °C. The color rapidly changed upon mixing
from purple to burgundy red, and the solution was slowly
warmed to room temperature. After the mixture was stirred
for 24 h, THF was removed in vacuo and the residual solid
redissolved in ether (80 mL). A small amount of pale-colored
solid was removed by centrifugation. Concentration of the
ether solution to small volume (20 mL) and further standing
at room temperature for 48 h afforded dark red crystals of 3
(yield: 3.3 g, 5.2 mmol, 82%). Anal. Calcd (found) for C33H45N2P2-
Si2V: C, 62.05 (61.86); H, 7.10 (7.23); N, 4.39 (4.27). IR (Nujol
mull, cm-1): ν 2853 (vs), 1589 (w), 1437 (s), 1304 (w), 1261
(sh), 1247 (s), 1173 (sh), 1110 (s), 1076 (s), 1056 (s), 1025 (s),
962 (s), 840 (s), 800 (m), 766 (m), 740 (m), 712 (m), 689 (m),
663 (m), 624 (m), 552 (m). µeff ) 2.76 µB/mol.
Exp er im en ta l Section
All operations were performed under an inert atmosphere
by using standard Schlenk-type techniques. VCl3(THF)314 and
15
H2C(PPh2NSiMe3)2 were prepared according to published
procedures. Methyllithium (1.4 M solution in ether) was
obtained from Aldrich and was used as received. Infrared
spectra were recorded on Mattson 9000 and Nicolet 750-Magna
FTIR instruments from Nujol mulls prepared in a drybox.
Samples for magnetic susceptibility measurements were
weighed inside a drybox equipped with an analytical balance
and sealed into calibrated tubes. Magnetic measurements were
carried out with a Gouy balance (J ohnson Matthey) at room
temperature. Magnetic moments were calculated following
standard methods,16 and corrections for underlying diamag-
netism were applied to the data.17 Elemental analyses were
carried out with a Perkin-Elmer 2400 CHN analyzer. Data for
X-ray crystal structure determination were obtained with a
Bruker diffractometer equipped with a Smart CCD area
detector.
P r ep a r a tion of [CH(P P h 2NSiMe3)2]VCl2‚(solven t) (1).
Meth od A (Solven t ) 2THF ). A solution of Li[CH(PPh2-
NSiMe3)2] was prepared by addition of a solution of MeLi in
ether (15.2 mL, 1.4 M, 21.3 mmol) to a solution of (Me3Si)Nd
P(Ph)2CHP(Ph)2dN(SiMe3) (11.9 g, 21.3 mmol) in THF (150
mL) at 0 °C. The resulting solution was added to a suspension
of VCl3(THF)3 (7.9 g, 21.3 mmol) in THF (150 mL). A rapid
color change took place, resulting in the formation of a dark
brown-red solution by the end of the addition. After a further
24 h of stirring at room temperature, the solution was purple,
and stirring was continued for an additional 24 h. Since no
further color change was observed, the purple solution was
concentrated (50 mL) and cooled to -30 °C, upon which purple
crystals of 1‚2THF separated (yield: 12.7 g, 15.4 mmol, 72%).
Anal. Calcd (found) for C39H54Cl2N2O2P2Si2V: C, 56.93 (57.03);
H, 6.62 (6.71); N, 3.40 (3.37). IR (Nujol mull, cm-1): ν 1588
(w), 1440 (s), 1312 (w), 1252 (s), 1170 (s), 1113 (s), 1062 (s),
P r ep a r a tion of [CH(P P h 2NSiMe3)2]2V2(µ-H)2 (4). A bur-
gundy red solution of 3 (0.4 g, 0.6 mmol) in toluene (80 mL)
was pressurized in an autoclave with hydrogen (60 atm) for
24 h and at room temperature. The color changed to dark
brown-red. The solvent was removed in vacuo and the solid
residue redissolved in ether (80 mL). Concentration of the
resulting brown-red ether solution (20 mL) and standing for
24 h at room temperature afforded brown crystals of 4 (0.2 g,
0.16 mmol, 52%). Anal. Calcd (found) for C62H80N4P4Si4V2: C,
61.07 (61.41); H, 6.61 (6.81); N, 4.59 (4.83). IR (Nujol mull,
cm-1): ν 1950 (w), 1896 (w), 1773 (w), 1589 (w), 1306 (w), 1261
(m), 1154 (s), 1107 (s, br), 1024 (s), 947 (m), 830 (s, br), 741
(m), 717 (m), 691 (m, sh), 653 (m), 605 (m, sh), 548 (w). µeff
1.82 µB/mol.
)
P r ep a r a tion of [HC(P P h 2N)(P P h 2NSiMe3)V(OSiMe3)]2‚
2Et2O (5). The addition of water (10 µL, 0.6 mmol) to a dark
brown solution of 4 (0.4 g, 0.3 mmol) in toluene (50 mL)
changed the color to dark red upon mixing. The solvent was
removed in vacuo, and the remaining residue was redissolved
in ether (60 mL). Dark red crystals of 5 separated (0.14 g, 0.1
mmol, 33%) upon concentration and standing overnight at
room temperature. Anal. Calcd (found) for C35H49N2P2Si2O2V:
C, 63.04 (63.46); H, 7.41 (7.52); N, 4.20 (4.02). IR (Nujol mull,
cm-1): ν 1588 (w), 1482 (m), 1436 (s), 1377 (s), 1310 (m), 1246
(s), 1173 (s), 1111 (s), 1085 (s), 1046 (m), 1026 (m), 987 (s, br),
790 (w), 771 (m), 742 (m), 723 (m), 694 (m), 667 (m, sh), 617
(m), 555 (m), 533 (w). µeff ) 2.21 µB/mol.
(10) Clancy, G. P.; Clark, H. C. S.; Clentsmith, G. K. B.; Cloke, F.
G. N.; Hitchcock, P. B. J . Chem. Soc., Dalton Trans. 1999, 19, 3345.
(11) Ong, C. M.; Mckarns, P.; Stephan, D. M. Organometallics 1999,
18, 4197.
(12) Al-Benna, S.; Sarsfield, M. J .; Thornton-Pett, M.; Ormsby, D.
L.; Maddox, P. J .; Bre`s, P.; Bochmann, M. J . Chem. Soc., Dalton Trans.
2000, 23, 3345.
(13) See for example: (a) Kasani, A.; McDonald, R.; Cavell, R. G.
Organometallics 1999, 18, 3775. (b) Kasani, A.; McDonald, R.; Fergu-
son, M.; Cavell, R. G. Organometallics 1999, 18, 4241. (c) Kasani, A.;
McDonald, R.; Cavell, R. G. Chem. Commun. 1999, 19, 1993.
(14) Manzer, L. E. Inorg. Synth. 1982, 21, 138.
(15) Appel, V. R.; Ruppert, I. Z. Anorg. Allg. Chem. 1974, 406, 131.
(16) Mabbs, M. B.; Machin, D. Magnetism and Transition Metal
Complexes; Chapman and Hall: London, 1973.
P r ep a r a t ion of [CH (P P h 2NSiMe3)2]2V2(µ-Cl)2(µ-H )‚1/
2Et2O (6). A solution of MeLi in ether (1.1 mL, 1.4 M, 1.5
mmol) was added to a purple solution of 1‚2THF (1.3 g, 1.6
mmol) in THF (70 mL) at 0 °C. At the end of the addition the
color was red-purple. The solution was warmed slowly to room
(17) Foese, G.; Gorter, C. J .; Smits, L. J .; Constantes Se´lectionne´es
Diamagne´tisme, Paramagne´tisme, Relaxation Paramagne´tique; Mas-
son: Paris, 1957.

2618 Organometallics, Vol. 20, No. 12, 2001
Ta ble 1. Cr ysta l Da ta a n d Str u ctu r e An a lysis Resu lts
Aharonian et al.
3
4
5
6
7
formula
fw
space group
a (Å)
b (Å)
c (Å)
â (deg)
V (Å3)
Z
C
33H45N2P2Si2V
C62H80N4P4Si4V2
1219.42
C70H98N4O4P4Si4V2
1397.64
C64H84Cl2N4O0.5P4Si4V2
1326.37
C66H90ClN4OP4Si4V2
1328.99
orthorhombic, Pccn
12.120(1)
22.416(3)
27.168(3)
90
638.77
monoclinic, P21/c
12.205(2)
20.914(3)
14.899(2)
112.785(3)
3506.2(2)
4
orthorhombic, Pbca
15.7893(12)
17.8846(14)
22.6540(18)
90
monoclinic, P21/n
15.336(2)
12.965(1)
19.537(2)
104.225(2)
3765.6(6)
2
monoclinic, P21/n
16.872(3)
20.390(3)
22.209(4)
100.758(3)
7506(2)
6397.2(9)
4
7381(1)
4
4
radiation (K, Å)
T (K)
0.710 73
203(2)
1.210
4.66
1352
0.710 73
203(2)
1.266
5.08
2568
0.710 73
203(2)
1.233
4.44
1480
0.710 73
203(2)
1.174
5.07
2784
0.710 73
203(2)
1.196
4.81
2804
Dcalcd (g cm-3
)
Fcalcd (cm-1
)
F000
a
R, Rw
0.0422, 0.0866
1.015
0.0392, 0.0857
1.030
0.0479, 0.1022
1.014
0.0809, 0.2128
1.016
0.0518, 0.1565
1.072
GOF
a
2 1/2
R ) ∑Fo - Fc/∑Fo; Rw ) [∑(Fo - Fc)2/∑wFo
] .
temperature and allowed to stand at room temperature for 24
h, The solvent was removed in vacuo and the residue redis-
solved in toluene (80 mL). A small amount of pale-colored
insoluble material was removed by centrifugation and the
purple-red solution placed in an autoclave and pressurized
with H2 gas (60 atm) for 24 h at room temperature. The
solution changed to dark brown-red. The solvent was removed
in vacuo, and ether (80 mL) was added to the remaining dark
brown residue. After centrifugation, the dark brown-red solu-
tion was concentrated to a small volume (20 mL) and allowed
to stand for 24 h at room temperature, upon which yellowish
brown crystals of 6 formed (yield: 0.65 g, 0.5 mmol, 62%). Anal.
Calcd (found) for C64H84Cl2N4P4Si4V2O0.5: C, 57.95 (58.12); H,
6.38 (6.53); N, 4.22 (4.14). IR (Nujol mull, cm-1): ν 1960 (w),
1944 (w), 1895 (w), 1602 (w), 1589 (w), 1573 (w), 1308 (m),
1243 (s), 1069 (s), 1027 (m, sh), 999 (m, sh), 929 (s), 856 (s),
796 (m, sh), 762 (m, br), 710 (m, br), 656 (m), 627 (m), 600
(m), 548 (m), 507 (m). µeff ) 1.95 µB/mol.
P r ep a r a tion of [CH(P P h 2NSiMe3)2]2V2(µ-Cl)(µ-H)2‚Et2O
(7). A solution of MeLi in ether (1 mL, 1.4 M, 1.4 mmol) was
added to a purple solution of 1‚2THF (0.8 g, 0.97 mmol) in
THF (70 mL) at 0 °C. At the end of the addition, the color was
red-purple. The solution was warmed slowly to room temper-
ature, and stirring was continued for 24 h. The solvent was
removed in vacuo, and toluene (80 mL) was added to the
residue. A small amount of pale-colored solid was separated
by centrifugation, and the purple-red solution was placed in
an autoclave and pressurized with H2 gas (60 atm) for 24 h at
room temperature. The solution changed to dark brown-red.
The solvent was removed in vacuo and the residue redissolved
in ether (80 mL). After centrifugation, the dark brown-red
solution was concentrated to a small volume (20 mL) and
allowed to stand for 24 h at room temperature, upon which
yellowish brown crystals of 7 separated (yield: 0.36 g, 0.3
mmol, 56%). Anal. Calcd (found) for C66H90ClN4P4Si4V2O: C,
59.65 (60.23); H, 6.83 (6.92); N, 4.22 (4.17). IR (Nujol mull,
cm-1): ν 1962 (w), 1890 (w), 1582 (w), 1256 (sh), 1245 (sh),
1146 (s, br), 1100 (s, br), 1027 (w, sh), 924 (w, sh), 839 (s), 796
ported space groups. The structures were solved by direct
methods, completed with difference Fourier syntheses, and
refined with full-matrix least-squares procedures based on F .
2
The compound molecule in 7 was located at a 2-fold axis, while
each compound molecule in 5 and 4 was located at an inversion
center. One cocrystallized diethyl ether solvent molecule was
found in each asymmetric unit of 5, half-occupied in 6, and
disordered over a 2-fold axis in 7. Hydride ligands for 7 and 6
were initially located from the difference map and refined with
a riding model. All other hydrogen atoms were treated as
idealized contributions. A hydride ligand and a chloride ligand
were each found to be disordered by a 2-fold axis in 7. All non-
hydrogen atoms were refined with anisotropic displacement
parameters. All scattering factors and anomalous dispersion
factors are contained in the SHELXTL 5.10 program library.19
Crystal data and relevant bond distances and angles are given
in Tables 1 and 2.
Com p lex 3. The complex shows the ligand connected to the
metal center via the two nitrogen atoms (V-N(1) ) 2.054(3)
Å, V-N(2) ) 2.048(3) Å) (Figure 1). The carbon atom located
between the two phosphorus forms a long V-C distance (V-
C(18) ) 2.524(3) Å), which may be considered as at the edge
of the bonding range. The ligand adopted with the metal center
a butterfly type of conformation folded along the V-C vector.
The coordination geometry around the vanadium center is
distorted trigonal bipyramidal, with the two nitrogen donor
atoms and one carbon of one of the two terminally bonded
methyl groups (V-C(2) ) 2.070(4) Å) defining the trigonal
equatorial plane (N(1)-V-N(2) ) 116.07(11)°, N(1)-V-C(2)
) 116.46(13)°, N(2)-V-C(2) ) 117.60(13)°). The ligand carbon
donor atom and the second methyl group (V-C(1) ) 2.120(3)
Å) occupy the axial positions (C(1)-V-C(18) ) 162.90(13)°).
Com p lex 4. The dimeric structure consists of two identical
[(Me3Si)NdP(Ph)2C(H)P(Ph)2dN(SiMe3)]V units where the
ligand adopted the usual geometry folded along the V-Cligand
vector (V(1)-C(16) ) 2.381(2) Å) (Figure 2). The structure was
of sufficient quality to allow location with a reasonable degree
of confidence the positions of the hydrogen atoms, including
those of the two bridging hydrides. The two hydrides bridge
the two vanadium atoms (V(1)-H(1) ) 1.74(2) Å, V(1)-H(1a)
) 2.180(2) Å), forming a planar V2H2 core (torsion angle V(1)-
H(1)-V(1a)-H(1a) ) 0°) with a rather short V-V distance
(V(1)-V(1a) ) 2.4569(7) Å). The coordination geometry around
each vanadium center is severely distorted trigonal bipyra-
midal. The equatorial plane is defined by the two nitrogen
donor atoms (V(1)-N(1) ) 2.141(2) Å; V(1)-N(2) ) 2.186(2)
Å) and one hydride, forming a distorted trigonal plane with
the vanadium atom (N(1)-V(1)-N(2) ) 107.13(7)°, N(1)-
V(1)-H(1a) ) 133.87(7)°, N(2)-V(1)-H(1a) ) 108.32(7)°). The
two axial positions are occupied by the ligand carbon atom and
(w), 760 (m), 741 (m), 722 (m), 709 (m), 658 (w), 597 (w). µeff
1.88 µB/mol.
)
X-r a y Cr ysta llogr a p h y. Str u ctu r a l Deter m in a tion of
3-7. Suitable crystals were selected, mounted on thin, glass
fibers using paraffin oil, and cooled to the data collection
temperature. Data were collected on a Bruker AX SMART 1K
CCD diffractometer using 0.3° ω-scans at 0, 90, and 180° in
φ. Unit-cell parameters were determined from 60 data frames
collected at different sections of the Ewald sphere. Semiem-
pirical absorption corrections based on equivalent reflections
were applied.18 Systematic absences in the diffraction data and
unit-cell parameters were uniquely consistent with the re-
(18) Blessing, R. Acta Crystallogr. 1995, A51, 33.
(19) Sheldrick, G. M. Bruker AXS, Madison, WI, 1997.

Trivalent Vanadium Alkyl and Hydride
Organometallics, Vol. 20, No. 12, 2001 2619
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles (d eg)
Compound 3
V-N(2)
V-N(1)
V-C(2)
2.045(3)
2.048(3)
2.070(4)
V-C(1)
V-C(18)
2.120(3)
V-P(1)
2.8118(11) P(1)-N(1)
2.8201(11) P(1)-C(18)
1.618(3)
1.726(3)
2.524(3)
V-P(2)
N(2)-V-N(1)
N(2)-V-C(2)
N(1)-V-C(2)
116.07(11)
117.60(13)
116.46(13)
N(2)-V-C(1)
N(1)-V-C(1)
C(2)-V-C(1)
100.93(13)
100.21(12)
100.60(15)
N(2)-V-C(18)
N(1)-V-C(18)
71.58(11)
71.82(11)
C(2)-V-C(18)
C(1)-V-C(18)
95.50(13)
163.90(13)
Compound 4
V(1)-H(1)
V(1)A-H(1)
V(1)-N(1)
1.741(2)
1.802(2)
V(1)-N(2)
V(1)-C(16)
2.1859(18) V(1)-P(1l)
2.7743(7)
2.8174(7)
1.5926(18)
P(1)-C(16)
P(1)-C(9)
1.743(2)
1.822(2)
2.381(2)
V(1)-P(2)
P(1)-N(1)
2.1410(19) V(1)-V(1)A
2.4569(7)
V(1)-H(1)-V(1)A
N(1)-V(1)-N(2)
N(1)-V(1)-C(16)
N(2)-V(1)-C(16)
87.80(7)
107.13(7)
73.46(7)
71.26(7)
N(1)-V(1)-V(1)A
N(2)-V(1)-V(1)A
C(16)-V(1)-V(1)A 143.34(5)
126.74(5)
N(1)-V(1)-P(1)
N(2)-V(1)-P(1)
C(16)-V(1)-P(1)
34.89(5)
90.26(5)
38.57(5)
V(1)A-V(1)-P(1)
N(1)-V(1)-P(2)
N(2)-V(1)-P(2)
149.90(3)
96.78(5)
34.27(5)
119.54(5)
Compound 5
V(1)-O(1)
V(1)-N(2)
V(1)-N(2)A
1.860(3)
1.946(4)
2.011(4)
V(1)-N(1)
V(1)-C(16)
V(1)-P(1)
2.036(4)
2.485(5)
V(1)-V(1)A
2.7828(16) P(1)-C(16)
2.7968(16) P(1)-C(22)
1.727(5)
1.800(5)
2.011(4)
V(1)-P(2)
2.7142(16) P(1)-N(2)
1.593(4)
V(1)A-N(2)
O(1)-V(1)-N(2)
121.36(15)
N(2)A-V(1)-N(1)
O(1)-V(1)-C(16)
N(2)-V(1)-C(16)
103.75(15)
97.41(15)
73.66(16)
O(1)-V(1)-P(1)
N(2)-V(1)-P(1)
111.94(11)
35.35(11)
O(1)-V(1)-V(1)A
N(2)-V(1)-V(1)A
N(2)A-V(1)-V(1)A
N(1)-V(1)-V(1)A
121.37(11)
46.28(11)
44.37(11)
117.55(12)
O(1)-V(1)-N(2)A 102.52(15)
N(2)-V(1)-N(2)A
O(1)-V(1)-N(1)
N(2)-V(1)-N(1)
90.64(15)
116.89(15)
114.57(16)
N(2)A-V(1)-P(1) 125.47(12)
N(2)A-V(1)-C(16) 159.17(16)
N(1)-V(1)-P(1)
C(16)-V(1)-P(1)
96.87(11)
38.48(11)
N(1)-V(1)-C(16)
71.90(16)
Compound 6
V(1)-H(1)
V(1)-N(2)
V(1)-N(1)
V(1)-C(13)
1.902(10)
2.193(8)
2.277(8)
2.353(11)
V(1)-Cl(2)
V(1)-Cl(1)
V(1)-V(2)
V(1)-P(2)
2.434(4)
2.474(3)
2.754(3)
2.800(3)
V(1)-P(1)
V(2)-N(3)
V(2)-N(4)
V(2)-C(44)
2.840(3)
2.055(9)
2.147(8)
2.332(10)
V(2)-Cl(1)
V(2)-Cl(2)
V(2)-P(3)
V(2)-P(4)
2.386(3)
2.414(4)
2.756(3)
2.789(3)
V(1)-H(1)-V(2)
N(2)-V(1)-N(1)
N(2)-V(1)-C(13)
N(1)-V(1)-C(13)
92.8(3)
93.8(3)
72.4(3)
70.6(3)
N(2)-V(1)-Cl(2)
N(1)-V(1)-Cl(2)
C(13)-V(1)-Cl(2)
N(2)-V(1)-Cl(1)
96.6(2)
107.6(2)
168.6(3)
172.2(3)
N(1)-V(1)-Cl(1)
91.9(2)
N(1)-V(1)-V(2)
C(13)-V(1)-V(2)
Cl(2)-V(1)-V(2)
139.0(2)
133.7(3)
55.04(9)
C(13)-V(1)-Cl(1) 104.4(3)
Cl(2)-V(1)-Cl(1)
N(2)-V(1)-V(2)
86.85(11)
122.8(2)
Compound 7
V(1)-H(1)
V(1)-H(2)
V(1)A-H(2)
V(1)-N(2)
1.647(2)
1.684(2)
1.676(2)
2.155(2)
V(1)-N(1)
V(1)-C(16)
V(1)A-Cl
V(1)-Cl
2.227(2)
2.338(2)
V(1)-V(1)A
2.6518(8)
2.8012(8)
2.8045(8)
Cl-V(1)A
P(1)-N(1)
P(1)-C(16)
2.3878(11)
1.588(2)
1.744(3)
V(1)-P(2)
2.3878(11) V(1)-P(1)
2.4532(12)
V(1)-H(1)-V(1)A 107.26(10)
V(1)-H(2)-V(1)A 104.22(10)
N(2)-V(1)A-Cl
N(1)-V(1)A-Cl
C(16)-V(1)A-Cl
N(2)-V(1)-Cl
96.62(6)
103.18(7)
166.63(6)
172.12(7)
N(1)-V(1)-Cl
90.21(6)
102.40(6)
89.16(5)
N(1)-V(1)-V(1)A
C(16)-V(1)-V(1)A
ClA-V(1)-V(1)A
Cl-V(1)-V(1)A
138.02(6)
134.53(6)
57.98(3)
55.61(3)
C(16)-V(1)-Cl
Cl-V(1)A-Cl
N(2)-V(1)-N(1)
N(2)-V(1)-C(16)
N(1)-V(1)-C(16)
93.67(8)
72.57(8)
70.48(8)
N(2)-V(1)-V(1)A 123.55(6)
F igu r e 2. Thermal ellipsoid plot of 4. Thermal ellipsoids
are drawn at the 30% probability level.
particular nitrogen atom bridges the vanadium atom of an
identical unit, assembling a dimeric structure (N(2)-V(1)-
N(2a) ) 90.64(15)°, V(1)-N(2)-V(1a) ) 89.36(20)°) with a
planar V2N2 core (torsion angle V(1)-N(2)-V(1)A-N(2a) ) 0°).
Conversely, the silane group is found attached to an oxygen
atom of a terminally bonded trimethylsilanolate group (V(1)-
O(1) ) 1.860(3) Å). The coordination geometry around each
vanadium atom is trigonal bipyramidal, as a common feature
among these derivatives. The equatorial plane is defined by
one terminally bonded N atom (V(1)-N(1) ) 2.036(4) Å) of the
Me3SiN group, one bridging desilylated N atom (V(1)-N(2) )
1.946(4) Å), and the oxygen atom of the silanolate group (O(1)-
F igu r e 1. Partial thermal ellipsoid plot of 3. Thermal
ellipsoids are drawn at the 30% probability level.
by the second bridging hydride, featuring a bent H-V-C array
(C(16)-V(1)-H(1a) ) 170.95(7)°). The V-H distances are
slightly different, as a possible result of the asymmetric
arrangement of the two hydrides, each occupying an equatorial
position with respect to one vanadium and an axial position
with respect to the second one.
Com p lex 5. The complex is a dimer formed by two vana-
dium moieties attached to the ligand, where one of the two
nitrogen atoms no longer bears the silyl group (Figure 3). This

2620 Organometallics, Vol. 20, No. 12, 2001
Aharonian et al.
F igu r e 5. Thermal ellipsoid plot of 7. Thermal ellipsoids
are drawn at the 30% probability level.
F igu r e 3. Thermal ellipsoid plot of 5. Thermal ellipsoids
are drawn at the 30% probability level.
Sch em e 1
F igu r e 4. Thermal ellipsoid plot of 6. Thermal ellipsoids
are drawn at the 30% probability level.
V(1)-N(1) ) 116.89(15)°, O(1)-V(1)-N(2) ) 121.36(15)°,
N(1)-V(1)-N(2) ) 114.57(16)°). The ligand carbon atom
(V(1)-C(16) ) 2.485(5) Å) and the desilylated N atom of a
second unit occupy the axial positions, forming a bent N-V-C
vector (N(2)A-V(1)-C(16) ) 159.17(16)°). The desilylated N
atoms display with the two vanadium atoms and the phos-
phorus a curious planar T-shaped type of geometry (P(1)-
N(2)-V(1a) ) 167.14(16)°, P(1)-N(2)-V(1) ) 99.67(16)°, V(1)-
N(2)-V(1a) ) 89.36(20)°).
with respect to one N donor atom of one vanadium atom and
trans to the Cligand atom of the second vanadium-containing
moiety.
Com p lexes 6 a n d 7. The crystal structures of 6 and 7 show
the same dinuclear arrangement, with the ligand around each
vanadium atom adopting the usual tridentate bonding mode
with a folded-butterfly type of conformation (6, V(1)-N(1) )
2.277(8) Å, V(1)-N(2) ) 2.193(8) Å; 7, V(1)-N(1) ) 2.227(2)
Å, V(1)-N2 ) 2.155(2) Å) (Figures 4 and 5). Different from 4,
the overall coordination geometry around each vanadium atom
in both compounds is octahedral, with three coordination sites
occupied by the two nitrogen and carbon atoms (6, V(1)-C(13)
) 2.353(11) Å; 7, V(1)-C(16) ) 2.338(2) Å) and the other three
occupied by the bridging chlorine (6, V(1)-Cl(1) ) 2.474(3) Å;
7, V(1)-Cl(1) ) 2.434(2) Å) and hydride atoms (6, V(1)-H(1)
) 1.902(10) Å; 7, V(1)-H(1) ) 1.647(2) Å). In the case of 6,
the two metals are bridged by one hydride (V(1)-H(1)-V(2)
) 92.8(2)°) and two chlorine atoms (V(1)-Cl(1)-V(2) ) 69.00-
(20)°, V(1)-Cl(2)-V(2) ) 69.21(19)°), while two bridging
hydrides (V(1)-H(1)-V(1a) ) 107.26(20)°, V(1)-H(2)-V(1a)
) 104.22(18)°) and one chlorine atom (V(1)-Cl(1)-V(1a) )
66.41(20)°) are present in the case of 7. The divanadium units
thus adopt in both compounds a face-sharing bioctahedral
structure. In complex 7 the chlorine atom appears to be trans
Resu lts a n d Discu ssion
Reaction of VCl3(THF)3 with the diphosphine diimine
ligand [(Me3Si)NdP(Ph)2C(H)2P(Ph)2dN(SiMe3)] in its
neutral form and in the presence of TMEDA afforded
the violet [(Me3Si)NdP(Ph)2C(H)P(Ph)2dN(SiMe3)]VCl2‚
(toluene) (1‚(toluene)) and the red-purple [(TMEDA)-
VCl4]2[H2(TMEDA)] (2) (Scheme 1). Both compounds
were isolated in pure form from the same reaction
mixture via fractional crystallization from THF and
toluene. Analytical data consistent with the proposed
formulation were obtained for both compounds and their
structures elucidated by X-ray crystallography (see the
Supporting Information). The two complexes are para-
magnetic and display magnetic moments consistent
with a d 2 electronic configuration. Complex 1 was
prepared in substantially higher yield (72%) as a THF
solvate (1‚2THF) via direct reaction of the VCl3(THF)3
starting material with the monolithium phosphinoimi-
nato anion12 prepared in situ via treatment of [(Me3-

Trivalent Vanadium Alkyl and Hydride
Organometallics, Vol. 20, No. 12, 2001 2621
Sch em e 2
Si)NdP(Ph)2C(H)2P(Ph)2dN(SiMe3)] with 1 equiv of
MeLi in ether. The bond distances and angles of the two
solvate forms of 1 are identical within the esd values
(see the Supporting Information).
P(1) ) 80.46(13)°, V-C(18)-P(2) ) 80.74(12)°). How-
ever, given that very similar distortions are observed
in 1, which contains a much shorter V-Cligand distance,
the longer V-Cligand distance of 3 is likely to be instead
the result of trans influence or of an enhanced contribu-
tion of the amido-type resonance structure.
The hydrogenolysis of 3 was performed at room
temperature and under pressure (60 atm). The reaction
afforded the extremely air-sensitive, divalent, and di-
nuclear hydride complex {[(Me3Si)NdP(Ph)2C(H)P-
(Ph)2dN(SiMe3)]V}2(µ-H)2 (4) (Figure 2), which was
isolated as brown crystals in 57% yield. The identity of
the product was established by a combination of X-ray
crystal structure, elemental analysis, and chemical
degradation carried out with anhydrous HCl in a sealed
vessel connected to a Toepler pump, which afforded 96%
of the expected amount of H2 gas. The magnetic moment
(1.82 µB/mol) is considerably low for a dinuclear d3
system and is presumably indicative of some direct V-V
interaction.
The divalent hydride 4 is a highly reactive species,
whose handling has proven to be unusually difficult. We
also observed that exposure of either solid samples or
solutions of 4 to air turned the samples intensely red.
As shown in Scheme 2, reaction of 4 with 2 equiv of
water released 87% of the expected 3 equiv of hydrogen
gas, affording the new dinuclear and trivalent species
{[(Me3Si)NdP(Ph)2C(H)P (Ph)2d(µ-N)]V(OSiMe3)}2 (5),
isolated as dark red crystals. Its X-ray crystal structure
revealed a dinuclear complex where the ligand was
deprived of one of the two SiMe3 groups attached to the
N atom, forming a terminally bonded silanolate group
(Figure 3). The complex displayed a rather low para-
magnetism (µeff ) 2.21 µB/mol), which is consistent with
the fairly short V-V distance (V(1)-V(1)A ) 2.783(2)
Å).
Metal complexes of the deprotonated phosphinoimine
derivatives are organometallic species only from the
formal point of view, given that resonance structures
with the negative charge localized on the nitrogen
rather than on the carbon atom are likely to be the most
important. Nonetheless, the coexistence in the reaction
mixture of a V(III) species, presumably containing
reactive V-N and V-C bonds, with a fairly strong acid
such as the ammonium salt of TMEDA is rather
surprising and reiterates the unique stability of the
derivatives of the pincer-type ligand system.13 On the
other hand, the ammonium acidic protons are tightly
coordinated in complex 2 between TMEDA and two
VCl3(TMEDA) units bridging the TMEDA nitrogen atom
and one of the four chlorine atoms bound to the
vanadium center. The strong hydrogen bonding may
well be responsible for quenching the acidity of the
ammonium cation.
Complex 1 was converted into the corresponding
isostructural dimethyl derivative [(Me3Si)NdP(Ph)2C-
(H)P(Ph)2dN(SiMe3)]VMe2 (3) via simple treatment
with MeLi (Scheme 1) followed by crystallization from
ether. This species is also paramagnetic and displays a
magnetic moment consistent with a d2 electronic con-
figuration of a monomeric V(III) derivative. The chelat-
ing ligand in complex 3 displays the same geometry as
in 1 with comparable bond distances and angles (Figure
1). The most noticeable difference between the two
compounds arises from the V-Cligand distance (V-C(16)
) 2.334(2) Å (1) versus V-C(18) ) 2.524(3) Å (3)). This
can in principle be ascribed to steric compression of the
ligand, as indicated by the substantial distortions of the
bond angles around the carbon bridging the two phos-
phorus atoms (P(1)-C(18)-P(2) ) 127.4(3)°, V-C(18)-
The connectivity of 5, as yielded by the crystal
structure clearly attributes the oxidation state +3 to

2622 Organometallics, Vol. 20, No. 12, 2001
Aharonian et al.
Sch em e 3
each vanadium atom. Thus, the formation of 5 from the
divalent 4 involves not only an acid-base reaction but
also a one-electron oxidation of each of the two vana-
dium centers, releasing a total of 3 equiv of hydrogen
gas. The reaction can be conveniently rationalized by
assuming an initial acid-base reaction of 4 with one
molecule of water to afford an intermediate divalent oxo
derivative (Scheme 2). This step releases the first 2
equiv of hydrogen. Further reaction with a second
molecule of water forms a trivalent dioxo species upon
releasing the third equivalent of hydrogen gas. Migra-
tion of the oxophilic Me3Si group from nitrogen to the
oxygen atom affords 5. The displacement of the Me3Si
group is rather surprising in this case, in the view of
the fact that {[(Me3Si)2N]2V(µ-O)}2 is a perfectly stable
species.20
The formation of the divalent 4 from the trivalent 3
again poses questions about the stability of vanadium
hydrides. As briefly mentioned in the Introduction, an
intrinsic instability of intermediate vanadium alkyls
toward presumably unstable trivalent vanadium hy-
drides is believed to be responsible for polymer chain
termination and reduction of the vanadium catalytic site
to the inactive divalent state.8 This process is commonly
regarded as catalyst deactivation. To mitigate its nega-
tive impact, the current technology for elastomer manu-
facture employs halogenated organic substances. It is
also common belief that the role of this species is that
of reoxidizing the inactive divalent metal centers toward
the active trivalent state. This oxidation process implies
that a chloride anion is transferred to the vanadium
center. It is also well established from the patent
literature that the presence of chloride ions as a
component of the catalytic system is critical to the
performance of the catalytic cycle.8 These observations
prompted us to evaluate the stability of mixed hydride/
chloride vanadium species. For this purpose, we at-
tempted the preparation of a partially alkylated triva-
lent [(Me3Si)NdP(Ph)2C(H)P(Ph)2dN(SiMe3)]V(Cl)Me
species for further hydrogenolysis. Unfortunately, the
isolation of methyl/chloride precursors only afforded a
mixture of 1 and 3. Therefore, it was decided simply to
mix the starting dichloride 1 with the appropriate
amount of MeLi and to carry out the hydrogenolysis of
the resulting mixture under the usual reaction condi-
tions (60 atm, room temperature). This strategy proved
to be successful for the isolation in crystalline form of
two new mixed-valent vanadium hydride/chloride spe-
cies depending on the stoichiometric V/MeLi ratio
employed for the reaction.
2.754(3) Å; 7, V(1)-V(1a) ) 2.6518(8) Å), which obvi-
ously are exclusively determined by the number of
bridging chlorine atoms. The substantial variation of
intermetallic distances does not correspond to a signifi-
cant variation of the magnetic moments, which are
comparable in the two compounds and are in both cases
consistent with the presence of one unpaired electron
per dimeric unit.
The divalent state of vanadium in 4 is in striking
contrast with the mixed-valence nature of 6 and 7 and
clearly demonstrates the ability of the chlorine atom to
prevent complete reduction toward the divalent state.
Although the formation of the monohydride dichloride
6 could be regarded as the result of the direct reaction
of 1 with in situ generated 4, this obviously cannot be
the case for 7, which contains two hydrides and one
chloride. Furthermore, there is no apparent reason
complex 4 could not exist as a mixed-valence V(II)/V(III)
species with three bridging hydrides and a face-sharing
biocathedral structure similar to that of 6 and 7. Indeed,
the retention of chlorine is a factor preventing reduction
toward the divalent state.
Con clu sion s
The monoanionic “pincer”-type ligand [(Me3Si)Nd
P(Ph)2C(H)P(Ph)2dN(SiMe3)] afforded stabilization of
rare examples of trivalent vanadium dialkyls and
mixed-valence and divalent hydrides. The three hydride
derivatives 4, 6, and 7 have been obtained through
identical reactions, the only difference being the amount
of residual chlorine present in the reaction mixture.
Thus, the role of chlorine in terms of stabilizing higher
oxidation states and preventing reduction toward diva-
lent state becomes apparent. It is tempting at this stage
to speculate that the crucial role of chlorine in promoting
and optimizing the performance of vanadium as a
Ziegler-Natta catalyst relies on its ability to assemble
polymetallic structures where, similar to the case of 6
and 7, the preservation of the trivalent oxidation state
results in an extended catalyst life.
Reaction of 1 with either 1.0 or 1.5 equiv of MeLi
followed by hydrogenolysis of the resulting solutions
afforded the dinuclear and mixed-valence V(II)/V(III)
species {[(Me3Si)NdP(Ph)2C(H)P(Ph)2dN(SiMe3)]V}2(µ-
Cl)2(µ-H) (6) (Figure 4) and {[(Me3Si)NdP(Ph)2C(H)P-
(Ph)2dN(SiMe3)]V}2(µ-Cl)(µ-H)2 (7) (Figure 5), respec-
tively (Scheme 3). Both compounds were isolated in
analytically pure form as extremely air-sensitive brown
crystalline solids and released the expected amount of
hydrogen gas upon decomposition with gaseous HCl.
The most noticeable difference between the two com-
pounds consists of the V-V distances (6, V(1)-V(2) )
Ack n ow led gm en t. This work was supported by the
Natural Science and Engineering Council of Canada
(NSERC).
Su p p or tin g In for m a tion Ava ila ble: Complete listings
of structural parameters and crystal data for the complexes.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(20) Duan, Z.; Schmidt, M.; Young, V. G.; Xie, X.; McCarley, R. E.;
Verkade, J . G. J . Am. Chem. Soc. 1996, 118, 5302.
OM0101588