Cationic and neutral phosphido-bridged pentamethylcyclopentadienyl-chromium dimers

Article abstract of DOI:10.1021/om0209881

The species [(Cp*Cr)₂(μ-Cl)₃]X (X = [AlCl₄] (3), [GaCl₄] (4), [B(C₆F₅)₄] (5)) were generated from (Cp*CrCl(μ-Cl))₂ (1) via reaction with a chloride abstraction reagent. Using a similar synthetic route, the reaction of 1, generated in situ, with MeLi and the borane B(C₆F₅)₃ gave crystals of the salt [(Cp*Cr)₂(μ-Cl)₃][MeB(C₆ F₅)₃] (6), while the complex [(Cp*Cr)₂(μ-Cl)₃][Me₂B(C₆ F₅)₂] (7) was obtained, albeit in low yield, from the reaction of [Cp*CrMe(μ-Cl)]₂ with HB(C₆F₅)₂. Monoalkylation of 5 with MeLi gave [(Cp*Cr(μ-Cl))₂(μ-Me)][B(C₆ F₅)₄] (8), while the related mono(phosphide)-bridged cationic species [(Cp*Cr)₂(μ-PPh₂) (μ-Cl)₂]-[B(C₆F₅)₄] (9) was derived from 5 via reaction with Ph₂PLi. The bis(phosphide)-bridged species [(Cp*Cr(μ-PPh₂))₂(μ-Cl)] [AlMe₃Cl] (10) was derived from reaction mixtures of 1, Ph₂PLi, and AlMe₃, while monoalkylation of 1 with MeLi followed by treatment with Ph₂PLi and AlMe₃ yielded [(Cp*Cr(μ-PPh₂))₂(μ-Me)][(Me₃ Al)₂(μ-Cl)] (11). The neutral phosphide-bridged species (Cp*Cr(μ-PPh₂))₂(μ-CH₂) (12) and (Cp*Cr)₂(μ-PPh₂)(μ-Cl)(μ-CH₂) (13) were obtained from reactions of 1, MeLi, and Ph₂PLi. X-ray structural data are reported from compounds 5-13. The synthetic routes and the structural data are discussed.

Full text of DOI:10.1021/om0209881

1712
Organometallics 2003, 22, 1712-1717
Ca tion ic a n d Neu tr a l P h osp h id o-Br id ged
P en ta m eth ylcyclop en ta d ien yl-Ch r om iu m Dim er s
Pingrong Wei and Douglas W. Stephan*
School of Physical Sciences, Chemistry and Biochemistry, University of Windsor, Windsor,
Ontario, Canada N9B 3P4
Received December 4, 2002
The species [(Cp*Cr)2(µ-Cl)3]X (X ) [AlCl4] (3), [GaCl4] (4), [B(C6F5)4] (5)) were generated
from (Cp*CrCl(µ-Cl))2 (1) via reaction with a chloride abstraction reagent. Using a similar
synthetic route, the reaction of 1, generated in situ, with MeLi and the borane B(C6F5)3
gave crystals of the salt [(Cp*Cr)2(µ-Cl)3][MeB(C6F5)3] (6), while the complex [(Cp*Cr)2(µ-
Cl)3][Me2B(C6F5)2] (7) was obtained, albeit in low yield, from the reaction of [Cp*CrMe(µ-
Cl)]2 with HB(C6F5)2. Monoalkylation of 5 with MeLi gave [(Cp*Cr(µ-Cl))2(µ-Me)][B(C6F5)4]
(8), while the related mono(phosphide)-bridged cationic species [(Cp*Cr)2(µ-PPh2)(µ-Cl)2]-
[B(C6F5)4] (9) was derived from 5 via reaction with Ph2PLi. The bis(phosphide)-bridged species
[(Cp*Cr(µ-PPh2))2(µ-Cl)][AlMe3Cl] (10) was derived from reaction mixtures of 1, Ph2PLi, and
AlMe3, while monoalkylation of 1 with MeLi followed by treatment with Ph2PLi and AlMe3
yielded [(Cp*Cr(µ-PPh2))2(µ-Me)][(Me3Al)2(µ-Cl)] (11). The neutral phosphide-bridged species
(Cp*Cr(µ-PPh2))2(µ-CH2) (12) and (Cp*Cr)2(µ-PPh2)(µ-Cl)(µ-CH2) (13) were obtained from
reactions of 1, MeLi, and Ph2PLi. X-ray structural data are reported from compounds 5-13.
The synthetic routes and the structural data are discussed.
In tr od u ction
oxo and sulfido complexes.23-29 In exploring alternative
ligand sets for Cr, amido derivatives have garnered
recent attention.9,18,30,31 While constrained-geometry18
and diimine30 Cr complexes have been shown to offer
new polymerization catalysts, the variety of structural
types of Cp*CrIII amides has been explored and shown
to depend on the nature of the amido substituents.9 In
seeking development of Cr(III) chemistry employing
phosphido ligands, we report herein a series of diphen-
ylphosphido-bridged dinuclear Cr(III) salts. The nature
of these species is described, and the implications of this
chemistry are considered.
The chemistry of Cr(III) is particularly difficult to
study, as a result of its paramagnetic nature. Nonethe-
less, the research groups of Theopold,1-4 and more
recently Poli5-7 and others,8-11 have made extensive
progress in developing an understanding of the struc-
ture, magnetic properties,12-14 and reactivity of Cr(III).
While much of this work has been focused on the
organometallic chemistry of Cr alkyls with olefin po-
lymerization catalysis as the principal motiva-
tion,2,3,11,13,15-22 other work has focused on the funda-
mental structural and reactivity questions around Cr
(1) Theopold, K. H. Acc. Chem. Res. 1990, 23, 263-270.
(2) Theopold, K. H. CHEMTECH 1997, 27, 26-32.
(3) Theopold, K. H. Eur. J . Inorg. Chem. 1998, 15-24.
(4) Pariya, C.; Theopold, K. H. Curr. Sci. 2000, 78, 1345-1351.
(5) Mattamana, S. P.; Poli, R. Organometallics 1997, 16, 2427-2433.
(6) Fettinger, J . C.; Mattamana, S. P.; Poli, R.; Rogers, R. D.
Organometallics 1996, 15, 4211-4222.
(19) White, P. A.; Calabrese, J .; Theopold, K. H. Organometallics
1996, 15, 5473-5475.
(20) Kim, W.-K.; Fevola, M. J .; Liable-Sands, L. M.; Rheingold, A.
L.; Theopold, K. H. Organometallics 1998, 17, 4541-4543.
(21) Tani, K.; Mashima, K.; Oshiki, T.; Urata, T. (Mitsubishi
Chemical Industries Ltd., J apan) J pn. Kokai Tokkyo Koho, 1998; p
15ff.
(22) Andell, O.; Maaranen, J .; Hoikka, J .; Vanne, T.; Rautio, S.
(Borealis Technology Oy, Finland; Campbell, Neil) PCT Int. Appl.,
2002, p 55ff.
(23) Qin, K.; Incarvito, C. D.; Rheingold, A. L.; Theopold, K. H.
Angew. Chem., Int. Ed. 2002, 41, 2333-2335.
(24) Hess, A.; Horz, M. R.; Liable-Sands, L. M.; Lindner, D. C.;
Rheingold, A. L.; Theopold, K. H. Angew. Chem., Int. Ed. 1999, 38,
166-168.
(25) Noh, S. K.; Heintz, R. A.; Haggerty, B. S.; Rheingold, A. L.;
Theopold, K. H. J . Am. Chem. Soc. 1992, 114, 1892-1893.
(26) Hubbard, J . L.; McVicar, W. K. Inorg. Chem. 1992, 31, 910-
913.
(27) Hess, J . S.; Leelasubcharoen, S.; Rheingold, A. L.; Doren, D.
J .; Theopold, K. H. J . Am. Chem. Soc. 2002, 124, 2454-2455.
(28) Morse, D. B.; Rauchfuss, T. B.; Wilson, S. R. J . Am. Chem. Soc.
1988, 110, 8234-8235.
(7) Bender-Gresse, M.; Collange, E.; Poli, R.; Mattamana, S. Poly-
hedron 1998, 17, 1115-1119.
(8) Bazan, G. C.; Rogers, J . S.; Fang, C. C. Organometallics 2001,
20, 2059-2064.
(9) Danopoulos, A. A.; Wilkinson, G.; Sweet, T. K. N.; Hursthouse,
M. B. J . Chem. Soc., Dalton Trans. 1996, 271-281.
(10) Herrmann, W. A.; Thiel, W. R.; Herdtweck, E. J . Organomet.
Chem. 1988, 353, 323-336.
(11) Peucker, U.; Heitz, W. Macromolecular Rapid Communications
1998, 19, 159-162.
(12) J aniak, C.; Silvestre, J .; Theopold, K. H. Chem. Ber. 1993, 126,
631-643.
(13) Bhandari, G.; Rheingold, A. L.; Theopold, K. H. Chem. Eur. J .
1995, 1, 199-203.
(14) Bluemel, J .; Herker, M.; Hiller, W.; Koehler, F. H. Organome-
tallics 1996, 15, 3474-3476.
(15) Thomas, B. J .; Theopold, K. H. J . Am. Chem. Soc. 1988, 110,
5902-5903.
(29) Brunner, H.; Kauermann, H.; Pfauntsch, J .; Wachter, J .;
Enemark, J . H.; Young, C. G. J . Organomet. Chem. 1987, 331, 45-52.
(30) Theopold, K. H.; Kim, W.-K.; Power, J . M.; Mora, J . M.; Masino,
A. P. (University of Delaware, Chevron Chemical Co.) PCT Int. Appl,
2001, p 112ff.
(31) Danopoulos, A. A.; Hankin, D. M.; Wilkinson, G.; Cafferkey, S.
M.; Sweet, T. K. N.; Hursthouse, M. B. Polyhedron 1997, 16, 3879-
3892.
(16) Dawkins, G. M. (BP Chemicals Ltd.) Eur. Pat. Appl. Ep, 1991;
p 8ff.
(17) Bhandari, G.; Kim, Y.; McFarland, J . M.; Rheingold, A. L.;
Theopold, K. H. Organometallics 1995, 14, 738-745.
(18) Liang, Y.; Yap, G. P. A.; Rheingold, A. L.; Theopold, K. H.
Organometallics 1996, 15, 5284-5286.
10.1021/om0209881 CCC: $25.00 © 2003 American Chemical Society
Publication on Web 03/21/2003

Phosphido-Bridged Chromium Dimers
Organometallics, Vol. 22, No. 8, 2003 1713
Cp*). 11B NMR: δ -20.7. 19F NMR: δ -132.7, -162.7, -166.4.
X-ray unit cell data: monoclinic, a ) 18.93(1) Å, b ) 34.05(2)
Å, c ) 14.970(8) Å, â ) 99.76(1)°, V ) 9507(1) Å3.
Exp er im en ta l Section
Gen er a l Da ta . All preparations were done under an
atmosphere of dry, O2-free N2 employing both Schlenk line
techniques and Innovative Technologies, MBraun, or Vacuum
Atmospheres inert-atmosphere gloveboxes. Solvents were
purified employing Grubbs’ type column systems manufac-
tured by Innovative Technology. All organic reagents were
purified by conventional methods. 1H,31P{1H},11B{1H}, and 19F
NMR spectra were recorded on Bruker Avance 300 or 500
spectrometers. All NMR spectra were recorded in CDCl3. Trace
amounts of protonated solvents were used as references for
the 1H NMR data, and chemical shifts are reported relative
to SiMe4. 31P, 19F, and 11B NMR spectra are referenced to 85%
H3PO4, CFCl3, and NaBH4, respectively. Magnetic susceptibil-
ity was determined by the Evans method.32 Guelph Chemical
Laboratories or in-house elemental analysis services were
employed to perform combustion analyses. The species
(Cp*CrCl(µ-Cl))2 (1) and (Cp*CrMe(µ-Cl))2 (2) were generated
as previously described in the literature.15,33
Syn th esis of [(Cp *Cr )2(µ-P P h 2)(µ-Cl)2][B(C6F 5)4] (9). To
stirred toluene solution of 5 (0.125 mmol) which was
a
prepared in situ was added Ph2PLi (0.024 g, 0.125 mmol). The
solution was stirred for 2 days and filtered through Celite.
Crystallization from toluene/CH2Cl2/hexane gave dark crystals.
Yield: 0.055 g, 34%. Anal. Calcd (found) for C56H40F20PBCr2-
Cl2: C, 51.36 (50.89); H, 3.08 (2.71). 1H NMR: δ 7.72, 7.37,
7.19, 7.12 (br, Ph H), -5.00 (br, Cp*). 31P NMR: silent. 11B
NMR: δ -21.0. 19F NMR: δ -132.3, -163.1, -166.7.
Syn th esis of [(Cp *Cr (µ-P P h 2))2(µ-Cl)][AlMe3Cl] (10). To
a stirred THF suspension of CrCl3‚3THF (0.094 g, 0.25 mmol)
was added Cp*Li (0.036 g, 0.25 mmol) in THF. The mixture
was stirred for 1 h at room temperature. To the solution was
added Ph2PLi (0.048 g, 0.25 mmol) in THF. The resulting
solution was stirred for 2 days. After the volatiles were
removed under vacuum, to the residue was added benzene
following AlMe3 (0.045 g, 0.626 mmol). The resulting solution
was stirred for 2 days and filtered through Celite. Crystal-
lization from benzene/hexane gave dark crystals, Yield: 0.015
g, 13%. Anal. Calcd (found) for C47H59P2Cr2AlCl2‚0.5C6H6: C,
64.79 (64.32); H, 6.74 (6.45). 1H NMR: δ 7.63, 7.45, 7.14, 7.07
(br, Ph H), Cp* not observed. 31P NMR: silent.
Syn th esis of [(Cp *Cr )2(µ-Cl)3]X (X ) [AlCl4] (3), [Ga Cl4]
(4), [B(C6F 5)4] (5)). These compounds were prepared in a
similar manner using AlCl3, GaCl3, and [Ph3C][B(C6F5)4],
respectively. To a stirred THF suspension of CrCl3‚3THF
(0.108 g, 0.29 mmol) was added Cp*Li (0.041 g, 0.29 mmol) in
THF. The mixture was stirred for 1 h at 25 °C, and the
volatiles were removed under vacuum. To the residue was
added CH2Cl2 followed by AlCl3 (0.020 g, 0.145 mmol). The
solution was stirred for 2 days and filtered through Celite. The
addition of hexane gave dark blue crystals. 3: yield 0.040 g,
43%. Anal. Calcd (found) for C20H30Cr2AlCl7: C, 36.98 (37.20);
H, 4.65 (5.12). 1H NMR: δ -12.10 (br, Cp*). X-ray unit cell
data: orthorhombic, a ) 12.630(7) Å, b ) 20.85(1) Å, c ) 23.07-
(1) Å, V ) 6078(1) Å3, 4: yield 0.045 g, 46%. Anal. Calcd (found)
for C20H30Cr2GaCl7: C, 34.70 (34.50); H, 4.37 (3.61). 1H NMR:
δ -12.30 (br, Cp*). X-ray unit cell data: orthorhombic, a )
20.81(1) Å, b ) 12.661(7) Å, c ) 23.08(1) Å, V ) 6082 (1) Å3. 5:
yield 0.066 g, 40%. Anal. Calcd (found) for C44H30F20Cr2BCl3:
Syn th esis of [(Cp *Cr (µ-P P h 2))2(µ-Me)][(Me3Al)2(µ-Cl)]
(11). To a stirred THF suspension of CrCl3 (0.040 g, 0.25 mmol)
was added Cp*Li (0.036 g, 0.25 mmol) in THF. The mixture
was stirred overnight at room temperature. To the solution
was added MeLi (1.4 M; 0.09 mL, 0.125 mmol) followed by Ph2-
PLi (0.048 g, 0.25 mmol) in THF. The resulting solution was
stirred for 2 days. After the volatiles were removed under
vacuum, AlMe3 (0.054 g, 0.750 mmol) was added to the residue.
The resulting solution was stirred a further 2 days and filtered
through Celite. Removal of the solvent and recrystallization
of the residue from benzene/hexane gave dark crystals of 11.
Yield: 0.030 g, 25%. Anal. Calcd (found) for C51H71P2Cr2Al2-
Cl: C, 65.20 (64.78); H, 7.62 (7.15). µ ) 3.42 µB. 1H NMR: δ
7.64, 7.37, 7.16, 6.92 (br, Ph H), Cp* not observed. 31P NMR:
silent.
1
C, 45.57 (45.80); H, 2.61 (2.49). H NMR: δ -12.0 (br, Cp*).
11B NMR: δ -20.7. 19F NMR: δ -132.8, -163.3, -167.0.
Syn th esis of [(Cp *Cr )2(µ-Cl)3][MeB(C6F 5)3] (6). To a
stirred THF suspension of CrCl3‚3THF (0.094 g, 0.25 mmol)
was added Cp*Li (0.036 g, 0.25 mmol) in THF. The mixture
was stirred for 1 h at 25 °C. MeLi (1.4 M; 0.080 mL, 0.125
mmol) was added. After the volatiles were removed under
vacuum, to the residue was added CH2Cl2 followed by B(C6F5)3
(0.064 g, 0.125 mmol). The solution was stirred for 2 days and
filtered through Celite. The addition of hexane gave dark blue
Syn th esis of (Cp*Cr (µ-P P h 2))2(µ-CH2) (12) an d (Cp*Cr )2-
(µ-P P h 2)(µ-Cl)(µ-CH2) (13). To a stirred THF suspension of
CrCl3‚3THF (0.108 g, 0.29 mmol) was added Cp*Li (0.041 g,
0.29 mmol) in THF. The mixture was stirred for 1 h at room
temperature. To the solution was added MeLi (1.4 M; 0.207
mL, 0.29 mmol) followed by Ph2PLi (0.056 g, 0.29 mmol) in
THF. The resulting solution was stirred for 2 days and then
filtered through Celite. Crystallization from benzene gave dark
crystals of 12. Yield: 0.055 g, 50%. Upon standing for extended
period of time, 13 was obtained in very low yield (<6%). 12:
crystals. Yield: 0.045 g, 37%. Anal. Calcd (found) for C39H33
-
F
15Cr2BCl3‚0.5C6H6: C, 48.19 (47.78); H, 3.47 (3.31). 1H
NMR: δ 0.5 (br, Me-B), -12.03 (br, Cp*). 11B NMR: δ -19.0.
19F NMR: δ -133.2, -165.2, -167.6.
1
µ ) 4.09 µB; H NMR δ 7.90, 7.57, 6.89, 6.76 (br, Ph H), Cp*
Syn th esis of [(Cp *Cr )2(µ-Cl)3][Me2B(C6F 5)2] (7). To a
stirred CH2Cl2 solution of 2 (0.035 g, 0.147 mmol) was added
HB(C6F5)2 (0.051 g, 0.147 mmol) in CH2Cl2. The resulting
solution was stirred for 2 days at room temperature. Crystal-
lization from benzene/hexane gave dark crystals. Yield: 0.020
g, 16%. Anal. Calcd (found) for C34H36F10BCr2Cl3: C, 47.72
(47.28); H, 4.24 (3.87). 1H NMR: δ -12.10 (br, Cp*). 11B
NMR: δ -19.1. 19F NMR: δ -132.4, -164.2, -167.1.
silent; 31P NMR silent. Anal. Calcd (found) for C45H52Cr2P2:
C, 71.23 (70.80); H, 6.91 (7.15). 13: yield 0.006 g, 6%; 1H NMR
δ 7.61, 7.43, 7.17, 6.92 (br, Ph H), Cp* silent; 31P NMR silent.
Anal. Calcd (found) for C33H42Cr2PCl: C, 65.07 (64.59); H, 6.95
(6.47).
X-r a y Da ta Collection a n d Red u ction . The crystals were
manipulated and mounted in capillaries in a glovebox, thus
maintaining a dry, O2-free environment for each crystal.
Diffraction experiments were performed on a Siemens SMART
System CCD diffractometer. The data were collected for a
hemisphere of data in 1329 frames with 10 s exposure times.
Crystal data are summarized in Table 1. The observed
extinctions were consistent with the space groups in each case.
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. An empirical absorption
correction based on redundant data was applied to each data
Syn th esis of [(Cp *Cr (µ-Cl))2(µ-Me)][B(C6F 5)4] (8). To a
stirred THF solution of 5 (0.125 mmol) which was prepared
in situ was added MeLi (1.4 M; 0.267 mL, 0.375 mmol). The
solution was stirred for 2 days and filtered through Celite.
Crystallization from CH2Cl2/hexane gave dark purple crystals.
Yield: 0.040 g, 30%. Anal. Calcd (found) for C45H33F20BCr2-
1
Cl2: C, 47.44 (47.90); H, 2.92 (3.20). H NMR: δ -12.01 (br,
(32) Evans., D. F. J . Chem. Soc. 1959, 2003.
(33) Noh, S. K.; Sendlinger, S. C.; J aniak, C.; Theopold, K. H. J .
Am. Chem. Soc. 1989, 111, 9127-9129.

1714 Organometallics, Vol. 22, No. 8, 2003
Ta ble 1. Cr ysta llogr a p h ic Da ta a
Wei and Stephan
5
6
7
9
formula
fw
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
cryst syst
V (Å3)
C
88H60B2Cl6Cr4F40
C
42H36BCl3Cr2F15
C
34H36BCl3Cr2F10
C56H40BCl2Cr2F20P
1309.56
31.57(5)
11.852(19)
30.80(5)
2319.68
1046.87
11.815(6)
12.065(6)
17.292(9)
87.968(10)
70.213(10)
78.280(10)
triclinic
2270(2)
P1h
1.532
2
0.747
9863
6496
589
855.79
11.251(8)
12.519(9)
14.347(10)
98.905(13)
102.621(13)
90.142(13)
triclinic
1947(2)
P1h
1.460
2
0.913
8197
5550
451
18.914(9)
34.087(17)
15.051(7)
100.407(10)
103.54(4)
monoclinic
9544(8)
P21/c
1.614
4
monoclinic
11204(32)
C2/c
1.553
8
0.616
20 107
8287
space group
δ(calcd) (g cm-3
Z
)
abs coeff, µ (cm-1
)
0.734
no. of data collected
13 609
13 609
1282
no. of data, Fo2 > 3σ(Fo
)
2
no. of variables
697
R
Rw
GOF
0.0424
0.0822
0.763
0.0571
0.1322
0.895
0.0608
0.1084
1.044
0.0748
0.1609
1.014
10
50H62AlCl2Cr2P2
11
51H71Al2ClCr2P2
12
45H51CrP
13
formula
fw
a (Å)
b (Å)
c (Å)
C
C
C
C33H40ClCr2P
607.07
11.266(6)
12.028(6)
12.536(7)
86.238(10)
80.103(9)
71.857(9)
triclinic
1590.1(14)
P1h
926.82
939.43
11.136(5)
15.005(7)
16.986(8)
88.346(10)
73.993(9)
81.270(10)
triclinic
2696(2)
P1h
378.90
11.114(6)
28.983(15)
16.187(8)
19.770(8)
10.659(4)
20.997(9)
R (deg)
â (deg)
γ (deg)
cryst syst
V (Å3)
space group
101.902(12)
116.384(7)
monoclinic
5102(5)
P21/c
1.207
4
0.641
21 842
7327
monoclinic
3964(3)
C2/c
1.270
4
0.659
6839
2791
δ(calcd) (g cm-3
)
1.157
1.317
2
0.921
6906
4534
352
Z
2
abs coeff, µ (cm-1
)
0.575
11 611
7703
no. of data collected
no. of data, Fo2 > 3σ(Fo
)
2
no. of variables
514
535
222
R
Rw
GOF
0.0664
0.1714
0.898
0.0389
0.0783
0.802
0.0567
0.1357
0.758
0.0348
0.0847
0.817
All data collected at 24 °C with Mo KR radiation (λ ) 0.710 69 Å), R ) ∑||Fo| - |Fc||/∑|Fo|, Rw ) [∑[w(Fo - Fc2)2]/∑[w(Fo2)2]]0.5
.
a
2
set. Subsequent solution and refinement was performed using
the SHELXTL solution package.
Resu lts a n d Discu ssion
The species (Cp*CrCl(µ-Cl))2 was generated and
reacted with a chloride abstraction reagent such as
AlCl3, GaCl3, or [Ph3C][B(C6F5)4]. Subsequent workup
and recrystallization gave the salts formulated as
[(Cp*Cr)2(µ-Cl)3]X (X ) [AlCl4] (3), [GaCl4] (4), [B(C6F5)4]
(5)). The formulations of these compounds were consis-
tent with the observation of a single resonance in the
1H NMR spectra. In the last case, 11B and 19F NMR
confirmed the presence of the perfluorinated borate
anion. Recrystallization of these species gave dark blue
crystals in each case. Crystallographic data were ob-
tained for each of these species. In the case of 3 and 4,
initial solutions were consistent with the formulations;
however, disorder issues were evident in both the anions
and cations. Extensive attempts to model the disorders
were problematic. In the case of 5, a satisfactory solution
was obtained and refined where the asymmetric unit
contained two anions and cations. The borate anions
were as expected. The cations were formulated as
[(Cp*Cr)2(µ-Cl)3]+ with the two Cp* rings oriented in a
parallel fashion perpendicular to the Cr-Cr vector
(Figure 1). For one of the cations in the asymmetric unit
it was necessary to model a 4-fold disorder of the
bridging chloride atoms. On the other hand, the second
St r u ct u r e Solu t ion a n d R efin em en t . Non-hydrogen
atomic scattering factors were taken from the literature
tabulations.34 The heavy-atom positions were determined using
direct methods. The remaining non-hydrogen atoms were
located from successive difference Fourier map calculations.
The refinements were carried out by using full-matrix least-
squares techniques on F, minimizing the function w(|Fo| -
|Fc|)2 where the weight w is defined as 4Fo2/2σ(Fo2) and Fo and
Fc are the observed and calculated structure factor amplitudes.
In the final cycles of each refinement, all non-hydrogen atoms
were assigned anisotropic temperature factors. In cases where
disorder was implied by the difference maps or the thermal
parameters, attempts to model the disorder were undertaken.
Such a model was deemed acceptable if the thermal param-
eters were typical and the geometry was chemically reason-
able. In such cases the disordered atoms were treated isotro-
pically. Carbon-bound hydrogen atom positions were calculated
and allowed to ride on the carbon to which they are bonded,
assuming a C-H bond length of 0.95 Å. Hydrogen atom
temperature factors were fixed at 1.10 times the isotropic
temperature factor of the carbon atom to which they are
bonded. The hydrogen atom contributions were calculated but
not refined.
(34) Cromer, D. T.; Mann, J . B. Acta Crystallogr., Sect. A 1968, A24,
321-324.

Phosphido-Bridged Chromium Dimers
Organometallics, Vol. 22, No. 8, 2003 1715
F igu r e 1. ORTEP drawing of one of the two cations of 5
in the asymmetric unit. Thermal ellipsoids are shown at
the 30% level. Hydrogen atoms have been omitted for
clarity. Selected bond distances (Å) and angles (deg):
Cr(1)-Cl(2) ) 2.3392(18), Cr(1)-Cl(1) ) 2.3526(18), Cr(1)-
Cl(3) ) 2.3563(17), Cr(2)-Cl(1) ) 2.3534(18), Cr(2)-
Cl(2) ) 2.3550(17), Cr(2)-Cl(3) ) 2.3582(19), Cr(1)-
Cr(2) ) 2.8157(13); Cl(1)-Cr(2)-Cl(2) ) 87.41(7), Cl(1)-
Cr(2)-Cl(3) ) 88.37(6), Cl(2)-Cr(2)-Cl(3) ) 87.38(7),
Cr(1)-Cl(1)-Cr(2) ) 73.50(5), Cr(1)-Cl(2)-Cr(2) ) 73.71-
(5), Cr(1)-Cl(3)-Cr(2) ) 73.35(5).
F igu r e 3. ORTEP drawing of the cation of 9. Thermal
ellipsoids are shown at the 30% level. Selected bond
distances (Å) and angles (deg): Cr(1)-Cl(2) ) 2.323(4),
Cr(1)-Cl(1) ) 2.340(4), Cr(1)-P(1) ) 2.390(5), Cr(1)-
Cr(2) ) 2.802(4), Cr(2)-Cl(1) ) 2.324(4), Cr(2)-Cl(2) )
2.340(4), Cr(2)-P(1) ) 2.404(4); Cl(2)-Cr(1)-Cl(1) ) 88.74-
(15), Cl(2)-Cr(1)-P(1) ) 87.90(11), Cl(1)-Cr(1)-P(1) )
88.16(11), Cl(1)-Cr(2)-Cl(2) ) 88.74(16), Cl(1)-Cr(2)-
P(1) ) 88.24(12), Cl(2)-Cr(2)-P(1) ) 87.20(10), Cr(2)-
Cl(1)-Cr(1) ) 73.86(14), Cr(1)-Cl(2)-Cr(2) ) 73.88(10),
Cr(1)-P(1)-Cr(2) ) 71.55(8).
F igu r e 2. ORTEP drawing of 7. Thermal ellipsoids are
shown at the 30% level. Hydrogen atoms have been omitted
for clarity.
was isolated as dark, purple crystals in 30% yield. The
bridging methyl resonances were not observed in the
1H NMR spectrum. Although crystallographic data were
obtained, a complete and satisfactory solution was not.
Nonetheless, the data appeared consistent with the
presence of the Cp*Cr fragments and the anion, al-
though the nature and positions of the bridging atoms
could not unambiguously be determined, as a result of
disorder. Nonetheless, one piece of preliminary metric
information that supports the above formulation was
the observed Cr-Cr distance of 2.59(1) Å. This distance
is markedly shorter than that seen in 5-7, while being
longer than that alluded to by Theopold et al. for
[(Cp*Cr)2(µ-Me)3][BF4] (2.42 Å).12 This, together with
elemental analyses, was consistent with monomethyl-
ation of the bridging positions.
Related phosphide-bridged cationic species were de-
rived from the reaction of 5 with the phosphide Ph2-
PLi. Following workup the species formulated as
[(Cp*Cr)2(µ-PPh2)(µ-Cl)2][B(C6F5)4] (9) was isolated in
34% yield. The X-ray structure (Figure 3) of 9 confirmed
the formulation, revealing a structure of the cation that
is analogous to that seen in 5-7, with a phosphide
replacing one of the bridging chloride atoms. The
bridging Cr-Cl and Cr-P distances averaged 2.332(5)
and 2.397(5) Å, respectively, while the Cr-Cl-Cr and
Cr-P-Cr angles at the bridging atoms were found to
be 73.87(14) and 71.55(8)°, respectively. The Cr-Cr
distance of 2.802(1) Å was slightly shorter than those
found in 5-7.
cation was refined without such a disorder. The latter
case offers a more reliable metric of the Cr-Cl distances,
which was found to be 2.3524(20) Å. On the other hand,
the Cr-Cr separations are very similar in the two
models (ordered cation, 2.8157(13) Å; disordered cation,
2.825(2) Å).
Using a similar synthetic route, the reaction of 1
generated in situ with MeLi and the borane B(C6F5)3
gave crystals of the salt [(Cp*Cr)2(µ-Cl)3][MeB(C6F5)3]
(6). X-ray crystallography revealed that this species also
crystallized in a disordered fashion. This disorder
involved a 4-fold disorder of the Cl. This was satisfac-
torily modeled with 12 partial Cl positions located in
the plane bisecting the Cr-Cr vector. The Cr-Cr
separation was found to be similar to that in 5 (2.820-
(5) Å). A completely ordered structure was obtained for
the complex [(Cp*Cr)2(µ-Cl)3][Me2B(C6F5)2] (7) (Figure
2). This species was derived, albeit in low yield, from
the reaction of [Cp*CrMe(µ-Cl)]2 with HB(C6F5)2 in CH2-
Cl2. In this case, the Cr-Cl distances and the Cl-Cr-
Cl angles averaged 2.363(4) Å and 74.4(1)°, respectively,
while the Cr-Cr separation was found to be 2.859(2)
Å, a metric similar to those seen in the previous salts.
The compound [(Cp*Cr)2(µ-Me)3][BF4],12 which rep-
resents the only previously known triply bridged di-
nuclear Cr salt, was generated via protonation of
(Cp*Cr(µ-Me))2(µ-CH2). Although crystallographic data
have not been published to our knowledge, the Cr-Cr
distance is described as 2.42 Å, significantly shorter
than those found in 5-7.
In attempts to isolate related neutral phosphide-
bridged species, the reaction of 1 with Ph2PLi was
undertaken. Although reaction was evident from the
observed color change, repeated attempts under various
Attempts to alkylate 5 with MeLi afforded the species
formulated as [(Cp*Cr(µ-Cl))2(µ-Me)][B(C6F5)4] (8), which

1716 Organometallics, Vol. 22, No. 8, 2003
Wei and Stephan
F igu r e 5. ORTEP drawing of 11. Thermal ellipsoids are
shown at the 30% level. Hydrogen atoms have been omitted
for clarity. Selected bond distances (Å) and angles (deg):
Cr(1)-C(45) ) 2.215(5), Cr(1)-P(2) ) 2.3559(14), Cr(1)-
P(1) ) 2.3672(14), Cr(1)-Cr(2) ) 2.6392(12), Cr(2)-
C(45) ) 2.238(5), Cr(2)-P(1) ) 2.3516(13), Cr(2)-P(2) )
2.3739(15), Al(1)-Cl(1) ) 2.382(2), Al(2)-Cl(1) ) 2.378-
(2); C(45)-Cr(1)-P(2) ) 87.25(14), C(45)-Cr(1)-P(1) )
87.99(16), P(2)-Cr(1)-P(1) ) 97.28(4), C(45)-Cr(2)-
P(1) ) 87.84(15), C(45)-Cr(2)-P(2) ) 86.28(15), P(1)-
Cr(2)-P(2) ) 97.21(4), P(1)-Cr(2)-Cr(1) ) 56.27(3), P(2)-
Cr(2)-Cr(1) ) 55.76(4), Al(2)-Cl(1)-Al(1) ) 116.02(7),
Cr(2)-P(1)-Cr(1) ) 68.01(4), Cr(1)-P(2)-Cr(2) ) 67.83-
(3), Cr(1)-C(45)-Cr(2) ) 72.68(12).
F igu r e 4. ORTEP drawing of the cation of 10. Thermal
ellipsoids are shown at the 30% level. Hydrogen atoms have
been omitted for clarity. Selected bond distances (Å) and
angles (deg): Cr(1)-Cl(1) ) 2.353(2), Cr(1)-P(1) ) 2.392-
(2), Cr(1)-P(2) ) 2.393(3), Cr(1)-Cr(2) ) 2.7984(19),
Cr(2)-Cl(1) ) 2.346(3), Cr(2)-P(1) ) 2.385(2), Cr(2)-
P(2) ) 2.398(2); Cl(1)-Cr(1)-P(1) ) 86.14(8), Cl(1)-Cr(1)-
P(2) ) 86.24(8), P(1)-Cr(1)-P(2) ) 93.78(7), Cl(1)-Cr(2)-
P(1) ) 86.45(9), Cl(1)-Cr(2)-P(2) ) 86.30(8), P(1)-Cr(2)-
P(2) ) 93.84(8), Cr(2)-Cl(1)-Cr(1) ) 73.09(7), Cr(2)-P(1)-
Cr(1) ) 71.73(7), Cr(1)-P(2)-Cr(2) ) 71.48(7).
Alkylation of 1 with MeLi in situ followed by treat-
ment with 2 equiv of Ph2PLi and subsequent excess
AlMe3 yielded [(Cp*Cr(µ-PPh2))2(µ-Me)][(Me3Al)2(µ-Cl)]-
(11) in 25% yield (Figure 5). The anion was found to
contain a chloride ion bridging two AlMe3 fragments
with an average Al-Cl distance of 2.380(2) Å. The cation
of 11 was similar to that seen in 10, with a methyl group
replacing the bridging chloride. The Cr-P distances
average 2.3586(16) Å, while the Cr-C bond lengths to
the bridging methyl group average 2.226(5) Å. The
corresponding Cr-C-Cr angle is 72.68(12)°. The result
of methyl replacing Cl appears to be a slightly shorter
Cr-Cr distance of 2.6392(12) Å in 11 and a decrease in
the Cr-P-Cr angle to 67.92(4)°.
Sch em e 1
The neutral phosphide- and methylene-bridged spe-
cies (Cp*Cr(µ-PPh2))2(µ-CH2) (12) was isolated from the
reaction of 2 with 2 equiv of Ph2PLi by elimination of
LiCl and methane in 50% yield (Figure 6, Scheme 1).
Although not determined quantitatively, a 1H NMR
resonance attributable to methane was observed. In
addition, an extremely small yield of a few crystals of
(Cp*Cr)2(µ-PPh2)(µ-Cl)(µ-CH2) (13) was also obtained
(Figure 7). Crystallographic data confirmed the neutral
formulations, although the data for 13 revealed a
disorder of the bridging Cl and CH2 ligands. In 12 the
bridging Cr-P and Cr-C distances were found to be
2.3148(13) and 2.253(3) Å, respectively. The correspond-
ing Cr-P distances in 13, averaging 2.3613(15) Å, are
slightly longer than in 12. The presence of the bridging
methylene group in these species resulted in relatively
short Cr-Cr separations of 2.5517(13) Å in 12 and
2.6134(11) Å in 13. The angles at the bridging P and
Cr centers (Cr-P-Cr: 12, 66.89(3)°; 13, 67.20(3)°) are
similar but smaller than those seen in 9 and 10.
The data presented above describe neutral and phos-
phido-bridged Cr dimers. The Cr-P bonds found in
conditions to isolate clean product from this reaction
were unsuccessful. Nonetheless, subsequent reaction of
what is presumed to be (Cp*Cr(µ-PPh2)Cl)2 with AlMe3
afforded the isolation of the bis(phosphide)-bridged salt
[(Cp*Cr(µ-PPh2))2(µ-Cl)][AlMe3Cl] (10) (Figure 4, Scheme
1). The anion was unexceptional, while the average
Cr-P and Cr-Cl distances in the cation of 10 were
found to be 2.392(2) and 2.350(2) Å, respectively. The
Cr-Cr distance in 10 is 2.7984(19) Å, slightly less than
that seen in 9, while the Cr-P-Cr angle of 71.50(9)° is
similar to that seen in 9.

Phosphido-Bridged Chromium Dimers
Organometallics, Vol. 22, No. 8, 2003 1717
F igu r e 7. ORTEP drawing of 13. Thermal ellipsoids are
shown at the 30% level. Hydrogen atoms have been omitted
for clarity. Selected bond distances (Å) and angles (deg):
Cr(1)-C(33) ) 1.983(15), Cr(1)-C(33B) ) 2.11(3), Cr(1)-
Cl(1) ) 2.333(3), Cr(1)-P(1) ) 2.3620(12), Cr(1)-Cl(1A) )
2.393(7), Cr(1)-Cr(2) ) 2.6134(11), Cr(2)-C(33B) ) 2.01-
(3), Cr(2)-C(33) ) 2.08(2), Cr(2)-Cl(1) ) 2.350(3), Cr(2)-
Cl(1A) ) 2.353(9), Cr(2)-P(1) ) 2.3606(15); C(33)-Cr(1)-
C(33B) ) 78.5(8), C(33)-Cr(1)-Cl(1) ) 89.2(6), C(33)-
Cr(1)-P(1) ) 91.1(5), C(33B)-Cr(1)-P(1) ) 89.8(8), C(33B)-
Cr(1)-Cl(1A) ) 82.7(6), Cl(1)-Cr(1)-Cl(1A) ) 93.4(3),
P(1)-Cr(1)-Cl(1A) ) 93.2(2), C(33B)-Cr(2)-Cl(1) ) 8.6-
(8), C(33)-Cr(2)-Cl(1) ) 86.6(5), C(33B)-Cr(2)-Cl(1A) )
85.8(7), Cl(1)-Cr(2)-Cl(1A) ) 94.0(2), C(33B)-Cr(2)-
P(1) ) 92.4(8), C(33)-Cr(2)-P(1) ) 88.9(5), Cl(1)-Cr(2)-
P(1) ) 89.12(7), Cl(1A)-Cr(2)-P(1) ) 94.3(2), Cr(2)-P(1)-
Cr(1) ) 67.20(3), Cr(1)-Cl(1)-Cr(2) ) 67.84(8), Cr(2)-
Cl(1A)-Cr(1) ) 66.81(17), Cr(1)-C(33)-Cr(2) ) 80.1(5),
Cr(2)-C(33B)-Cr(1) ) 78.7(9).
F igu r e 6. ORTEP drawing of 12. Thermal ellipsoids are
shown at the 30% level. Hydrogen atoms have been omitted
for clarity. Selected bond distances (Å) and angles (deg):
Cr(1)-C(1) ) 2.253(3), Cr(1)-P(1) ) 2.3130(13), Cr(1)-
P(1) ) 2.3167(13), Cr(1)-Cr(1) ) 2.5517(13); C(1)-Cr(1)-
P(1) ) 91.36(6), C(1)-Cr(1)-P(1) ) 91.26(5), P(1)-Cr(1)-
P(1) ) 93.56(4), Cr(1)-P(1)-Cr(1) ) 66.89(3), Cr(1)-C(1)-
Cr(1) ) 68.98(12).
Ta ble 2. Cr -Cr Dista n ces (Å) in Tr ip ly Br id ged
Cr (III) Dim er s
compd
Cr-Cr
compd
Cr-Cr
5
6
7
9
10
11
2.8157(13)
2.820(2)
2.859(2)
2.802(1)
2.7984(19)
2.6392(12)
13
8
12
2.6134(11)
2.59(1)
triply bridged neutral species, containing three-center-
four-electron methylene donors, give rise to shorter Cr-
Cr distances than in the cationic species. In addition,
variation in the Cr-Cr distances among the triply
bridged cations appears to reflect the covalent radii of
the bridging atoms (Cl > P > Me). While the general
synthetic methods described herein provide only moder-
ate to low yields, suggesting alternate reaction path-
ways may be operative, efforts are continuing to develop
new synthetic strategies and to explore the chemistry
of Cr phosphide complexes.
2.5517(13)
[(Cp*Cr)2(µ-Me)3][BF4]
(Cp*Cr)2(µ-Me)2(µ-CH2)
2.4212
2.394(1)37
these dimers all fall in the narrow range between
2.3130(13) and 2.393(3) Å. Although no previous reports
of Cr(III) phosphides have appeared, these values can
be compared with the Cr-P distances of 2.389(1), 2.396-
(1), 2.343(1), and 2.449(2) Å found in the dialkylphos-
phide-bridged heterobimetallics (Me3P)(OC)4Cr(µ-PtBu2)-
Rh(COD), (Me3P)(OC)4Cr(µ-PtBu2)Co(CO)(PMe3),35 (Me3-
P)(OC)4Cr(µ-PtBu2)NiCl(PMe3), and (Me3P)(OC)4Cr(µ-
PtBu2)Rh(CO)(PMe3),36 respectively. In addition, the
structural data for dimeric Cr species show trends
(Table 2) consistent with previous observations.12 The
Ack n ow led gm en t . Financial support from the
NSERC of Canada and the ORDCF is gratefully ac-
knowledged. D.W.S. is grateful to the Alexander von
Humboldt Stiftung for the award of a Forschungpreis.
(35) Chandler, D. J .; J ones, R. A.; Stuart, A. L.; Wright, T. C.
Organometallics 1984, 3, 1830-1838.
(36) J ones, R. A.; Lasch, J . G.; Norman, N. C.; Stuart, A. L.; Wright,
T. C.; Whittlesey, B. R. Organometallics 1984, 3, 114-119.
(37) Noh, S. K.; Heintz, R. A.; J aniak, C.; Sendlinger, S. C.; Theopold,
K. H. Angew. Chem. 1990, 102, 805-807.
Su p p or tin g In for m a tion Ava ila ble: Tables giving crys-
tallographic data. This material is available free of charge via
the Internet at http://pubs.acs.org.
OM0209881