Synthesis, structure, and deprotonation of a mesitylphosphido-bridged cyclopentadienylnickel(II) dimer

Article abstract of DOI:10.1021/om950982u

The bridging phosphido complex [NiCp(μ-PHMes)]₂ (1, Mes=2,4,6-Me₃C₆H₂) was prepared from NiCp₂ and PH₂Mes. Deprotonation and methylation of 1 yields (NiCp)₂(μ-PHMes)(μ-PMeMes) (4) and [NiCp(μ-PMeMeS)]₂ (6) via observable anionic phosphinidene intermediates. NMR spectroscopy was used to characterize syn and anti isomers of 1, 4, and 6, and the structures of anti-1a and syn-6b were determined by X-ray crystallography.

Full text of DOI:10.1021/om950982u

Organometallics 1996, 15, 2483-2488
2483
Syn th esis, Str u ctu r e, a n d Dep r oton a tion of a
Mesitylp h osp h id o-Br id ged Cyclop en ta d ien yln ick el(II)
Dim er
Stanislav V. Maslennikov and David S. Glueck*
6128 Burke Laboratory, Department of Chemistry, Dartmouth College,
Hanover, New Hampshire 03755
Glenn P. A. Yap and Arnold L. Rheingold
Department of Chemistry, University of Delaware, Newark, Delaware 19716
Received December 27, 1995X
The bridging phosphido complex [NiCp(µ-PHMes)]2 (1, Mes ) 2,4,6-Me3C6H2) was prepared
from NiCp2 and PH2Mes. Deprotonation and methylation of 1 yields (NiCp)2(µ-PHMes)(µ-
PMeMes) (4) and [NiCp(µ-PMeMes)]2 (6) via observable anionic phosphinidene intermediates.
NMR spectroscopy was used to characterize syn and anti isomers of 1, 4, and 6, and the
structures of anti-1a and syn-6b were determined by X-ray crystallography.
Sch em e 1
In tr od u ction
Many dinuclear metal complexes with bridging sec-
ondary phosphido (µ-PR2) ligands are known,1 but the
corresponding µ-PHR primary derivatives are less com-
mon.2 Such complexes contain reactive P-H bonds and
may be used as precursors to phosphinidene ligands.3
We report here the preparation of a mesitylphosphido-
bridged Ni(II) cyclopentadienyl complex and its depro-
tonation to generate anionic µ-phosphinidene species,
which are characterized by 31P NMR and by their
reactions with methyl iodide.
pentene.4 We did not, however, attempt to characterize
these byproducts further.
Complex 1a was characterized spectroscopically. The
31P NMR spectrum (CD2Cl2) shows an 8-line pattern at
δ -237. Spectral simulation of the AA′XX′ spin system5
Resu lts a n d Discu ssion
2
1
3
gives J PP ) 432.6 Hz, J PH ) 318.3 Hz, J PH ) -20.5
Treatment of nickelocene with PH2Mes (Mes ) 2,4,6-
Me3C6H2) in petroleum ether gives a brown solution
which deposits [NiCp(µ-PHMes)]2 (1a ) as shiny brown
air-stable crystals in 70-80% yield (Scheme 1). Several
other phosphorus-containing products are formed. The
major one, which shows a 31P NMR signal at δ -68.6
4
Hz, and J HH ) 5.3 Hz. These coupling constants are
similar to those reported6 for [NiCp(µ-PH2)]2, which are
shown along with 31P NMR data for other complexes
reported here in Table 1. The P-H protons give rise to
an identical pattern (δ 3.62, CD2Cl2) in the 1H NMR
spectrum, but only the more intense four middle lines
are observed. The presence of P-H bonds is also
evident from the IR spectrum (νPH ) 2323 cm-1, KBr).
Deuterium-labeled 1D was prepared from PD2Mes. Its
2H NMR spectrum could be simulated using coupling
constants (Table 1) obtained from the results for 1a and
the gyromagnetic ratios7 γH/γD ) 6.5144. The IR
spectrum of 1D shows νPD ) 1688 cm-1 (νPH/νPD ) 1.38).
1
(d, J PH ) 211 Hz), may be a (mesitylphosphino)-
cyclopentene derivative, since NiCp2 and HP(CF3)2 give
the analogous secondary phosphido complex [NiCp{µ-
P(CF3)2}]2 and bis((trifluoromethyl)phosphino)cyclo-
X Abstract published in Advance ACS Abstracts, April 15, 1996.
(1) Carty, A. J .; MacLaughlin, S. A.; Nucciarone, D. In Phosphorus-
31 NMR Spectroscopy in Stereochemical Analysis; Verkade, J . G., Quin,
L. D., Ed.; VCH: Deerfield Beach, FL, 1987; pp 559-619.
(2) For some recent examples and leading references, see: (a)
Bleeke, J . R.; Rohde, A. M.; Robinson, K. D. Organometallics 1994,
13, 401-403. (b) Bleeke, J . R.; Rohde, A. M.; Robinson, K. D.
Organometallics 1995, 14, 1674-1680. (c) Haupt, H.-J .; Schwefer, M.;
Florke, U. Inorg. Chem. 1995, 34, 292-297. (d) Hey-Hawkins, E.; Kurz,
S.; Sieler, J .; Baum, G. J . Organomet. Chem. 1995, 486, 229-235. (e)
Kourkine, I. V.; Chapman, M. B.; Glueck, D. S.; Eichele, K.; Wasyl-
ishen, R. E.; Yap, G. P. A.; Liable-Sands, L. M.; Rheingold, A. L. Inorg.
Chem. 1996, 35, 1478-1485. See also: (f) J ones, R. A.; Norman, N.
C.; Seeberger, M. H.; Atwood, J . L.; Hunter, W. E. Organometallics
1983, 2, 1629-1634. (g) J ones, R. A.; Seeberger, M. H. Inorg. Synth.
1989, 25, 173-177.
(3) (a) Lorenz, I.-P.; Pohl, W.; Noth, H.; Schmidt, M. J . Organomet.
Chem. 1994, 475, 211-221. (b) Ho, J .; Drake, R. J .; Stephan, D. W.
Organometallics 1993, 115, 3792-3793. (c) Hirth, U.-A.; Malisch, W.
J . Organomet. Chem. 1992, 439, C16-C19. (d) Seyferth, D.; Wood, T.
G.; Henderson, R. S. J . Organomet. Chem. 1987, 336, 163-182. (e)
Bartsch, R.; Hietkamp, S.; Morton, S.; Stelzer, O. J . Organomet. Chem.
1981, 222, 263-273. (f) Treichel, P. M.; Douglas, W. M.; Dean, W. K.
Inorg. Chem. 1972, 11, 1615-1618.
The anti configuration of the mesityl groups in 1a ,
expected sterically, was confirmed by X-ray crystal-
lography (Figure 1). Crystal, data collection, and re-
finement parameters are given in Table 2. Atomic
coordinates and equivalent isotropic displacement coef-
(4) Dobbie, R. C.; Green, M. A.; Stone, F. G. A. J . Chem. Soc. A 1969,
1881-1882.
(5) For analysis of related NMR spin systems involving P-H bonds,
see: (a) Palmer, R. A.; Whitcomb, D. R. J . Magn. Reson. 1980, 39, 371-
379. (b) Pasquali, M.; Marchetti, F.; Leoni, P.; Beringhelli, T.; D’Alfonso,
G. Gazz. Chim. Ital. 1993, 123, 659-664.
(6) Schafer, H.; Zipfel, J .; Migula, B.; Binder, D. Z. Anorg. Allg.
Chem. 1983, 501, 111-120.
(7) Sergeyev, N. M. In Isotope Effects in NMR Spectroscopy; Diehl,
P., Fluck, E., Gu¨nther, H., Kosfeld, R., Selig, J ., Eds.; Springer
Verlag: Berlin, 1990; p 42.
S0276-7333(95)00982-4 CCC: $12.00 © 1996 American Chemical Society

2484 Organometallics, Vol. 15, No. 10, 1996
Maslennikov et al.
Ta ble 1. 31P NMR Da ta for Nick el µ-P h osp h id o a n d µ-P h osp h in id en e Dim er sa
compd
δ(31P)
2J PP
1J PH (1J PD
)
b
[NiCp(µ-PH2)]2
-305
-237
440
303
318.3 (48.9)
326.8
anti-[NiCp(µ-PHMes)]2 (1a )c
432.6
364.9
198
syn-[NiCp(µ-PHMes)]2 (1b)d
-220.2
[M][(NiCp)2(µ-PHMes)(µ-PMes)] (2)e
Li2[NiCp(µ-PMes)]2 (3)g
-94.2, -150.8f
13.8
296 (45.8)
anti-(NiCp)2(µ-PHMes)(µ-PMeMes) (4a )h
syn-(NiCp)2(µ-PHMes)(µ-PMeMes) (4b)i
[M][(NiCp)2(µ-PMes)(µ-PMeMes)] (5)e
anti-[NiCp(µ-PMeMes)]2 (6a )i
-168.4, -223.6f
-153.7, -212.2f
-56.9, -99.3
-168
425.6
373.8
198
315 (48.4)
318 (48.9)
syn-[NiCp(µ-PMeMes)]2 (6b)i
-154.6
a
b 3
Chemical shifts are reported in ppm (85% H3PO4 external reference) and coupling constants in Hz.
J
) -18: Schafer, H.; Zipfel,
PH
J .; Migula, B.; Binder, D. Z. Anorg. Allg. Chem. 1983, 501, 111-120. c In CD2Cl2; 3J PH ) -20.5; 4J HH ) 5.3. For 1D, 3J PD ) -3.1 and J DD
4
) 0.8. In CD2Cl2; J PH ) -9.4; J HH ) 3.0. e In THF, M ) Na or Li. f Peak showing J PH (1J PD). In THF. In C6D6; | J PH| ) 17. In
d
3
4
1
g
h
3
i
C6D6.
8
similar to those in [NiCp(µ-PPh2)]2 [for this complex,
Ni-P ) 2.15(0.7) Å, Ni-P′ ) 2.16(0.8) Å, and the PNiP
angle is 77.6(2)°] despite the different cone angles of
PH2Mes and PHPh2 (110 and 128°, respectively).9 The
P-H protons were located and refined. The phosphido
P atom is roughly tetrahedral; the relevant angles are
Ni-P-H 105.7(6)°, H-P-C(Mes) 106.3(6)°, Ni-P-Ni
101.6(1)°, and Ni-P-C(Mes) 121.4(2)°. The last of
these values is presumably larger for steric reasons.
The 1H NMR spectrum of 1a provides evidence for
restricted rotation about the P-C bonds at room tem-
perature. The two ortho methyls of a mesityl group are
inequivalent and appear as broad signals at 3.29 and
2.43 ppm (CD2Cl2). The aryl protons give two broad,
overlapping signals from 6.84 to 6.75 ppm. At -20 °C
these peaks are sharp and well-resolved, and the 13C-
F igu r e 1. ORTEP diagram of 1a , with thermal ellipsoids
at 35% probability. Selected bond lengths (Å): Ni-P
2.158(2); Ni-Pa 2.152(2); Nia-P 2.152(2); Ni‚‚‚Nia 3.340(2);
Ni-Cnt 1.740(5); P-H 1.257(44); P-C(6) 1.827(6). Selected
bond angles (deg): P-Ni-Pa 78.4(1); Ni-P-C(6) 121.4(2);
Ni-P-Nia 101.6(1); C(6)-P-Nia 114.8(2); Ni-P-H 105.7(6);
H-P-C(6) 106.3(6).
{1H} NMR spectrum shows six different signals for the
mesityl ring carbons, consistent with slow rotation about
the P-C bond on the NMR time scale at this temper-
1
ature. In toluene-d8 the H NMR Ar signals coalesce
at ∼30 °C and the o-Me ones at ∼60 °C. More precise
data could not be obtained because of isomerization of
1a on warming (see below); these observations give a
rotational barrier of ∼15 kcal/mol.10 Related restricted
rotations about N-C bonds in [Ni(C5Me4R′)(µ-NHR)]2
complexes were reported very recently.11
Ta ble 2. Cr ysta llogr a p h ic Da ta for
a n ti-[NiCp (µ-P HMes)]2 (1a ) a n d
syn -[NiCp (µ-P MeMes)]2‚0.5(p en ta n e) (6b‚0.5C5H12
)
1a
6b‚0.5C5H12
On standing in solution, 1a undergoes partial isomer-
ization to syn-[NiCp(µ-PHMes)]2 (1b); an apparent equi-
librium mixture of ∼5:1 1a :1b is formed in THF or
CD2Cl2 (Chart 1).12 Complex 1b is characterized by its
31P NMR spectrum (Table 1), which is similar to that
formula
fw
space group
a, Å
b, Å
c, Å
C28H34Ni2P2
539.8
P21/c
11.831(6)
13.353(5)
8.613(4)
104.27(4)
1319(1)
2
C35H50Ni2P2
650.1
C2/c
16.724(3)
13.576(2)
27.494(4)
92.55(1)
6236(2)
8
brown
1.384
13.33
243
2
of 1a but with a reduced J PP and a less shielded 31P
â, deg
1
V, Å3
chemical shift. The expected P-H H NMR signal for
1b can also be observed (δ 4.20 in CD2Cl2), as can a new
signal from its Cp protons (δ 4.73). However, the
chemical shifts of its mesityl protons and methyl groups
cannot be distinguished from those of 1a at room
temperature.
Z
cryst color
D(calc), g cm-3
µ(Mo KR), cm-1
temp, K
radiation
R(F), %
R(wF), %
red-brown
1.385
15.62
296
Mo KR (λ ) 0.710 73 Å)
5.38a
6.62a
6.67b
16.24b,c
(9) (a) Tolman, C. A. Chem. Rev. 1977, 77, 313-348. (b) The cone
angle of PH2Mes was measured using Tolman’s method for unsym-
metrical phosphines.
(10) Friebolin, H. Basic One- and Two-Dimensional NMR Spectros-
copy; VCH: New York, 1991; pp 263-275.
(11) Holland, P. L.; Andersen, R. A.; Bergman, R. G. J . Am. Chem.
Soc. 1996, 118, 1092-1104.
Quantity minimized ) ∑w∆2; R ) ∑∆/∑(Fo); R(w) ) ∑∆w1/2
/
a
∑(Fow1/2), ∆ ) |(Fo - Fc)|. Quantity minimized ) R(wF2) )
b
∑[w(Fo - Fc2)2]/∑[(wFo2)2]1/2; R ) ∑∆/∑(Fo), ∆ ) |(Fo - Fc)|.
2
c R(wF2), %.
(12) For related reports of isomerism in bridged primary phosphido
complexes, see ref 2a,b,e and: (a) Clegg, W.; Morton, S. Inorg. Chem.
1979, 18, 1189-1192. (b) Brown, M. P.; Buckett, J .; Harding, M. M.;
Lynden-Bell, R. M.; Mays, M. J .; Woulfe, K. W. J . Chem. Soc., Dalton
Trans. 1991, 3097-3102. (c) Manojlovic-Muir, L.; Muir, K. W.; J en-
nings, M. C.; Mays, M. J .; Solan, G. A.; Woulfe, K. W. J . Organomet.
Chem. 1995, 491, 255-262.
ficients are given in the Supporting Information. Se-
lected bond lengths and angles appear in the figure
caption; full listings are available as Supporting Infor-
mation. The Ni-P bond lengths and PNiP angles are
(8) Coleman, J . M.; Dahl, L. F. J . Am. Chem. Soc. 1967, 89, 542-
552.
(13) Ho, J .; Hou, Z.; Drake, R. J .; Stephan, D. W. Organometallics
1993, 12, 3145-3157.

A Cyclopentadienylnickel(II) Dimer
Organometallics, Vol. 15, No. 10, 1996 2485
Ch a r t 1
and syn (4b) isomers (Chart 1), which were isolated as
a brown petroleum-ether-soluble solid whose IR spec-
trum shows a P-H stretch at 2303 cm-1 (KBr). The
inequivalent P nuclei in 4a give rise to two doublets
(2J PP ) 425.6 Hz) at δ -168.4 and -223.6; the latter
1
shows an additional J PH of 315 Hz, while the former
shows an unresolved multiplet due to coupling with the
P-H and the P-Me protons. Related observations are
made for 4b, with chemical shift and coupling constant
differences between syn and anti isomers similar to
those observed for 1a /b. (Table 1). Methylation of 2D
gives isomers 4D.
Sch em e 2
The mixture of isomers 4a ,b is most easily differenti-
ated in the 1H NMR spectrum by their P-Me reso-
nances, which show coupling to one or both of the P
nuclei. The P-H resonance could be seen for 4a (δ 4.16,
1
3
dd, J PH ) 314, | J PH| ) 17 Hz in toluene-d8), but the
corresponding peak for 4b was not observed due to its
low intensity. At 22 °C in toluene-d8, 4b shows two
resonances (δ 3.00, 2.82) due to the ortho methyl protons
of its Mes groups, while 4a shows only one at δ 3.04
(6H). At -60 °C, new ortho-Me signals due to 4a [δ 3.32
(3H), 2.43 (3H)] which are unobserved at room temper-
ature, grow in, along with new peaks due to the Mes
ring protons [δ 6.76 (1H), 6.54 (1H)]. The spectrum of
4b is unaffected by these temperature changes. From
these observations, it appears that, as in 1a , there is
restricted rotation about the P-C bond in anti isomer
4a .
Deprotonations of µ-PHR groups have been reported
for a variety of metal complexes,3,12bc,13 and similar
results were observed for 1 (Scheme 2). Reaction of 1a
or a mixture of 1a /b with n-BuLi or t-BuLi in THF at
room temperature generates Li[(NiCp)2(µ-PHMes)(µ-
PMes)] (2). Its 31P NMR spectrum shows two doublet
signals at δ -94.2 and -150.8 (2J PP ) 198 Hz); the latter
peak shows an additional 1J PH of 296 Hz and is assigned
Further deprotonation of 4a /b with n-BuLi or Na/18-
crown-6 gives the anion M[(NiCp)2(µ-PMeMes)(µ-PMes)]
2
(5; M ) Li, Na; Table 1). The J PP of 198 Hz in 5 is
identical to that in anion 2, and the changes in 31P
chemical shifts on deprotonation are also consistent with
the results for 1 and 2. As with 2 and 3, complex 5 was
not further characterized or isolated. Treatment with
MeI (Scheme 2) gives the symmetrical dimer [NiCp(µ-
PMeMes)]2 (6), which is also formed (in low yield) in
the direct reaction of dianion 3 with methyl iodide.
Analysis of reaction mixtures by 31P NMR (Table 1)
suggests that both anti and syn isomers 6a ,b (Chart 1)
are formed (the assignments were made on the basis of
the chemical shift trends observed for 1a /b and 4a /b),
but this mixture converts to pure 6b over the course of
1 day.
3
to the phosphido P, while no J PH is observed for the
2
phosphinidene P. The reduced J PP observed on forma-
tion of 2 from 1 can be rationalized by increased s
character in the P lone pair orbital of 2; similar changes
in 31P chemical shifts and coupling constants have been
reported for related anions.14 Deprotonation of 1D gave
1
2D, which shows J PD ) 45.8 Hz.
With an excess of base and longer reaction times, a
signal at 13.8 ppm, which shows no P-H coupling, is
observed; this peak is assigned to the dianion Li2[NiCp-
(µ-PMes)]2 (3). Complex 3 could be generated selec-
tively, free of 2, by deprotonation of 1a in THF with an
excess of n-BuLi in the presence of 12-crown-4.
No P-H resonance is observed in the IR spectrum of
isolated 6b. In the 1H NMR spectrum, the P-Me
protons give rise to a triplet at 1.01 ppm (C6D6). Such
apparent triplet splitting has been reported previously16
for complexes with bridging methylphosphido groups
and attributed to strong P-P coupling, as observed for
1 and 4. The peak separation gives the average P-H
coupling of the methyl protons to the two phosphorus
nuclei. The observed value of 6 Hz is consistent with
the average of these couplings directly measured for 4b
Treatment of 1a with an excess of sodium metal and
18-crown-6 in THF (the reaction was slower without the
crown ether) selectively gives anion 2. We assume that
this reaction proceeds, as reported15 for [NiCp(µ-PPh2)]2,
by formation of a radical anion, which loses a hydrogen
atom to yield the observed product.
We did not attempt to isolate or further characterize
spectroscopically anions 2 or 3; instead their reactions
with methyl iodide were investigated. Anion 2 could
be selectively methylated to form (NiCp)2(µ-PHMes)(µ-
PMeMes) (4, Scheme 2) as an ∼4:1 mixture of anti (4a )
4
(2J PH ) 10.2, J PH ) 2 Hz).
Hindered rotation of a mesityl group is characteristic
of the anti isomers 1a and 4a . Because this phenom-
enon is not observed in the 1H NMR spectrum of 6b,
the isomer observed in solution is likely to be the syn
one, consistent with the assignment based on the 31P
NMR chemical shift discussed above. The crystal
structure of 6b (Figure 2) confirms this geometry in the
(14) (a) Bautista, M. T.; J ordan, M. R.; White, P. S.; Schauer, C. K.
Inorg. Chem. 1993, 32, 5429-5430 and references therein. (b) Moser,
E.; Fischer, E. O. J . Organomet. Chem. 1968, 15, 157-163. (c) See
also: Deeming, A. J .; Doherty, S.; Marshall, J . E.; Powell, J . L.; Senior,
A. M. J . Chem. Soc., Dalton Trans. 1993, 1093-1100.
(15) Dessy, R. E.; Kornmann, R.; Smith, C.; Hayter, R. J . Am. Chem.
Soc. 1968, 90, 2001-2004.
(16) (a) Hayter, R. G. J . Am. Chem. Soc. 1963, 85, 3120-3124. (b)
Reference 12b and references therein.

2486 Organometallics, Vol. 15, No. 10, 1996
Maslennikov et al.
solution and solid-state structures of 1, 4, and 6,
established by NMR spectroscopy and X-ray crystal-
lography, show the small differences in energy between
syn and anti isomers in this system. These observations
suggest that the deprotonation of dicationic [LnM(µ-
PHR)]22+ complexes will yield cationic or neutral µ-phos-
phinidene complexes, and we are currently exploring
this possibility.
Exp er im en ta l Section
Gen er a l Exp er im en ta l Deta ils. All manipulations were
carried out under a nitrogen atmosphere using either standard
Schlenk apparatus or a glovebox. Solvents were distilled from
sodium and benzophenone (toluene, THF, ether, petroleum
ether) or from CaH2 (methylene chloride) and stored under
nitrogen. NMR spectra were obtained at the following fre-
F igu r e 2. ORTEP diagram of 6b, with thermal ellipsoids
at 35% probability. Selected bond lengths (Å): Ni(1)-P(1)
2.168(2); Ni(1)-P(2) 2.164(3); Ni(2)-P(1) 2.161(3); Ni(2)-
P(2) 2.167(2); Ni(1)‚‚‚Ni(2) 2.975(2); Ni(1)-CntA 1.763(10);
Ni(2)-CntB 1.769(11); P(1)-C(20) 1.859(8); P(2)-C(30)
1.836(9); P(1)-C(16) 1.849(8); P(2)-C(26) 1.857(8). Selected
bond angles (deg): P(2)-Ni(1)-P(1) 77.94(9); P(1)-Ni(2)-
P(2) 78.02(9); P(2)-Ni(1)-Ni(2) 46.67(6); P(1)-Ni(1)-Ni(2)
46.49(7); P(1)-Ni(2)-Ni(1) 46.69(7); P(2)-Ni(2)-Ni(1)
46.57(7); C(20)-P(1)-C(16) 103.1(4); C(20)-P(1)-Ni(2)
114.0(4); C(16)-P(1)-Ni(2) 120.2(2); C(20)-P(1)-Ni(1)
115.9 (3); C(16)-P(1)-Ni(1) 117.2(3); Ni(2)-P(1)-Ni(1)
86.82(10); C(30)-P(2)-C(26) 103.1(4); C(30)-P(2)-Ni(1)
113.1(4); C(26)-P(2)-Ni(1) 120.0(3); C(30)-P(2)-Ni(2)
115.2(3); C(26)-P(2)-Ni(2) 118.9(3); Ni(1)-P(2)-Ni(2)
86.76(9).
1
quencies (MHz): 31P, 121.4; 13C, 75.4; H, 299.9. Elemental
analyses were done by Schwarzkopf Labs, Woodside, NY, or
by QTI, Whitehouse, NJ . Mesitylphosphine was prepared by
the literature procedure.17 Methyl iodide was stored over
copper wire in the dark.
a n ti-[NiCp (µ-P HMes)]2 (1a ). To a slurry of nickelocene
(600 mg, 3.18 mmol) in 10 mL of petroleum ether was added
PH2Mes (705 mg, 4.64 mmol). The dark green solution was
allowed to stand overnight. The resulting dark brown solution
was decanted from a mass of shiny brown-black crystals, which
were washed with three 1-mL portions of petroleum ether and
dried in vacuo to give 551 mg of the product. A second crop of
crystals (90 mg, total yield 641 mg, 73%) was deposited from
the mother liquor after 1 more day. Brown crystals suitable
for X-ray crystallography were obtained from a saturated THF
solution (ca. 50 mg of the compound in 1 mL of THF) at -20
solid state. Crystal, data collection, and refinement
parameters are given in Table 2. Atomic coordinates,
equivalent isotropic displacement coefficients, and com-
plete lists of bond lengths and angles are in the
supporting information, while selected bond lengths and
angles are in the figure caption. In contrast to the
planar Ni2P2 ring in anti 1a (torsion angle Ni-P‚‚‚P(A)-
Ni(A) ) 180°), the ring in 6b is now puckered (torsion
angle Ni(1)-P(1)‚‚‚P(2)-Ni(2) ) 124°). Consequently,
the NiCp fragments are closer together (Ni-Ni distance
3.340(2) Å vs 2.975(2) Å). This ring puckering, which
presumably also occurs in 1b and 4b, is a distortion of
the generic syn isomer structure shown in Chart 1.
The relative energies of syn and anti isomers in 1, 4,
and 6 are presumably controlled by steric interactions
of the phosphido groups with the Cp ligands and with
each other. The observation in all cases of both isomers
shows that the energy differences are small. The anti
geometry favored in 1 and 4, which avoids placing two
bulky Mes groups syn to each other, might also be
expected in 6, which contains sterically more demanding
phosphido ligands. In this case, however, it is energeti-
cally more favorable to pucker the Ni2P2 ring, avoiding
phosphido-Cp interactions in the anti isomer. Isomer-
ism in the recently reported11 amido dimers [Ni(C5-
Me4R′)(µ-NHR)]2 was also suggested to be controlled by
steric effects, but direct comparison with these results
is difficult because of the difference in size of the
cyclopentadienyl ligands in the two systems.
°C. In a similar experiment, the
31P NMR spectrum of the
mother liquor was recorded. 31P{1H} NMR (petroleum ether,
δ): 0.4; -31.1; -36.6; -68.6; -84.4; -153.9; -221.3; -238.5.
31P NMR (petroleum ether, δ): 0.4 (m); -31.1 (d, J PH ) 317);
-36.6 (d, J PH ) 305); -68.6 (d, J PH ) 211); -84.4 (d, J PH
)
201); -153.9 (t, J PH ) 198, PH2Mes); -221.3 (m, 1b); -238.5
(m, 1a ). 31P NMR (CD2Cl2, δ): -237.0 (8-line pattern; see Table
1). The spectrum did not change at -40 or 80 °C in toluene-
d8. 1H NMR (CD2Cl2, 21 °C, δ): 6.84-6.75 (broad, 2 overlap-
2
ping peaks, 4H, Ar); 4.75 (10H, Cp); 3.62 (m, J PP ) 432.6 Hz,
3
4
1J PH ) 318.3 Hz, J PH ) -20.5 Hz, J HH ) 5.3 Hz, 2H, P-H);
3.29 (6H, broad, o-Me); 2.43 (6H, broad, o-Me); 2.24 (6H, p-Me).
1H NMR (CD2Cl2, -20 °C, δ): 6.84 (2H, Ar); 6.73 (2H, Ar);
4.73 (10H, Cp); 3.56 (m, 2H, P-H); 3.27 (6H, o-Me); 2.41 (6H,
o-Me); 2.22 (6H, p-Me). 1H NMR (toluene-d8, -20 °C, δ): 6.82
(2H, Ar); 6.60 (2H, Ar); 4.77 (10H, Cp); 3.80 (m, 2H, P-H);
3.54 (6H, o-Me); 2.37 (6H, o-Me); 2.11 (6H, p-Me). 1H NMR
(toluene-d8, 80 °C, δ): 6.71 (4H, Ar); 4.76 (10H, Cp); 3.82 (m,
2H, P-H); 2.87 (very broad, 12H, o-Me); 2.10 (6H, p-Me).
13C{1H} NMR (CD2Cl2, -20 °C, δ): 141.7 (m, ortho Ar); 139.4
(ortho Ar); 136.7 (para Ar); 130.3 (m, ipso Ar); 129.6 (meta
Ar); 128.4 (meta Ar); 89.5 (Cp); 23.3 (broad, ortho Me); 20.9
(para Me). IR (KBr): 2915, 2323, 1766, 1711, 1650, 1601,
1549, 1463, 1440, 1404, 1375, 1342, 1290, 1242, 1029, 1011,
984, 945, 871, 846, 830, 780, 683, 615, 576, 551, 458, 410 cm-1
.
Anal. Calcd for C28H34Ni2P2: C, 61.15; H, 6.23. Found
(Schwarzkopf): C, 61.30; H, 6.39.
syn -[NiCp (µ-P HMes)]2 (1b). On standing in solution or,
more quickly, on warming, complex 1a isomerizes to 1b, which
was observed by NMR as an ∼1:5 mixture with 1a . 31P NMR
(CD2Cl2, δ): -220.2 (8-line pattern). 1H NMR (CD2Cl2, 21 °C,
1
δ): 4.73 (10H, Cp); 4.20 (4-line pattern; 2J PP ) 364.9 Hz, J PH
3
4
) 326.8 Hz, J PH ) -9.4 Hz, J HH ) 3.0 Hz; 2H, PH).
[NiCp (µ-P DMes)]2 (1D) was prepared as for 1a using PD2-
Mes, which was prepared from PCl2Mes and LiAlD4.2e NMR
Con clu sion
The P-H bonds in 1 provide both a useful spectro-
scopic probe and a reactive center which allows simple
generation of phosphinidene anions 2, 3, and 5. The
(17) Bartlett, R. A.; Olmstead, M. M.; Power, P. P.; Sigel, G. A. Inorg.
Chem. 1987, 26, 1941-1946.

A Cyclopentadienylnickel(II) Dimer
Organometallics, Vol. 15, No. 10, 1996 2487
analysis showed the labeled phosphine was about 80% PD2-
Mes, 15% PHDMes, and 5% PH2Mes. IR (KBr): 2916, 2325,
1765, 1688, 1650, 1601, 1556, 1454, 1404, 1378, 1342, 1290,
1028, 1010, 984, 881, 868, 846, 836, 778, 660, 614, 560, 523
(d, 2J PH ) 9 Hz, 3H, P-Me*); 2.27 (d, 2J PH ) 9 Hz, 3H, P-Me);
2.05 (para Me, 4a ,b, overlaps solvent peak). 13C{1H} NMR
(C6D6, 22 °C, δ): 141.3; 141.0 (d, J ) 7.2); 137.4 (m); 137.1 (m);
135.4 (d, J ) 4); 134.2; 131.6 (d, J ) 10.5); 130.8 (d, J ) 7.2,
meta Mes); 130.6 (d, J ) 6.6, meta Mes); 129.9 (d, J ) 6.6);
90.5 (Cp*); 90.3 (Cp); 26.5 (m); 26.0; 25.9; 25.8; 24.2; 24.1; 24.0;
23.9; 23.2; 23.1; 21.4 (para Me); 21.1 (para Me). IR (KBr):
2958, 2910, 2725, 2303, 1762, 1624, 1601 (s), 1544, 1452(s),
1403, 1374, 1343, 1286, 1272, 1241, 1148, 1098, 1012, 985, 944
cm-1. Anal. Calcd for C29H36Ni2P2: C, 61.75; H, 6.44. Found
(QTI): C, 60.15; H, 6.23. Several attempts gave analytical
results low in carbon.
Dep r ot on a t ion of 4. Gen er a t ion of [(NiCp )2(µ-
P MeMes)(µ-P Mes)]- (5). (a ) Li Cou n ter ion . Butyllithium
(15 µL of a 1.6 M hexane solution, 0.024 mmol) was added to
a brown solution of 4 (10 mg, 0.017 mmol) in 1 mL of THF.
After 30 min, 31P NMR of the reaction mixture showed that 5
had formed.
cm-1 2H NMR (toluene, δ): 3.84 (broad 3-line pattern, “J ” )
.
22 Hz). This spectrum was simulated using the results for
1
2
1a and the gyromagnetic ratios of H and 2H, to give J PP
)
432.6, J PD ) 48.9, J PD ) -3.1,and J DD ) 0.8 Hz. 31P NMR
(toluene, δ): -240.8 (5-line pattern, “J ” ) 22 Hz). After 1 d in
solution the minor isomer 1b was also observed: δ -223.7 (m).
Dep r oton a tion of 1. Gen er a tion of [(NiCp )2(µ-P HMes)-
(µ-P Mes)]- (2). (a ) Li Cou n ter ion . To a brown solution of
1 (25 mg, 0.046 mmol) in 1 mL of THF was added n-BuLi (50
µL of a 1.6 M solution in hexanes, 0.08 mmol). The solution
became darker brown. After 1 h, 31P NMR showed that 2 had
formed.
1
3
4
(b) Na Cou n ter ion . To a brown solution of 1 (25 mg, 0.046
mmol) and 18-crown-6 (12 mg, 0.045 mmol) in 1 mL of THF
was added an excess (10 mg, 0.43 mmol) of freshly cut sodium
metal. The solution became darker brown. After 3.5 h, the
solution was decanted, and 31P NMR showed that 2 had
formed.
(b) Na Cou n ter ion . A mixture of 4 (85 mg, 0.15 mmol),
18-crown-6 (45 mg, 0.17 mmol), and excess sodium metal in
10 mL of THF was allowed to stand overnight. The resulting
brown solution was decanted from the sodium, and 31P NMR
showed that 5 had formed.
Dep r ot on a t ion of 1D. Gen er a t ion of [(NiCp )2(µ-
P DMes)(µ-P Mes)]- (2D) a n d Its Meth yla tion To F or m 4D.
A sample of 1D (30 mg, 0.054 mmol) in THF (1 mL) was
treated with BuLi (50 µL of a 1.6 M solution in hexanes, 0.08
mmol). The solution became darker brown, and 31P NMR after
1 h showed an ∼4:1 mixture of 2D and 2. 31P{1H} NMR data
2-
Rea ction of [NiCp (µ-P Mes)]2 (3) w ith MeI. Complex
3 was prepared by the addition of BuLi (400 µL of a 1.6 M
hexane solution, 0.64 mmol) to a solution of 1a (30 mg, 0.055
mmol) and 12-crown-4 (30 mg, 0.17 mmol) in THF (5 mL).
After 20 h the dark brown solution was cooled to -20 °C and
added dropwise with stirring to a similarly cooled solution of
MeI (60 µL, 0.96 mmol) in THF (5 mL). The volatile materials
were immediately removed in vacuo. The brown residue was
extracted with five 2-mL portions of petroleum ether and
filtered through Celite. The 31P{1H} NMR spectrum of this
brown extract showed the presence of 6a /b, 4a /b, and several
other unidentified compounds. Adding MeI to a solution of 3
did not improve the yield or the selectivity of the alkylation.
Alkylation at -78 °C was also unsuccessful, even when a large
excess of MeI was used.
syn -[NiCp (µ-P MeMes)]2 (6b). To a solution of complexes
4a /b (100 mg, 0.177 mmol) in THF (20 mL) was added BuLi
(160 µL of 1.6 M hexane solution, 0.256 mmol). After 6 h, the
solution was cooled to -78 °C and MeI (160 µL, 2.57 mmol) in
5 mL of THF was added all at once. The solution was stirred
at -78 °C for 15 min and then allowed to warm to room
temperature while the solvent and excess MeI were removed
in vacuo. The brown residue was extracted with six 5-mL
portions of petroleum ether. After filtration through Celite,
the solvent was removed from the brown extract, yielding 63
mg of brown solid (62%). This compound is difficult to
crystallize, and brown impurity-containing oils are often
obtained by this procedure. However, brown needles suitable
for X-ray crystallography were grown from petroleum ether
at -20 °C. Both crystallography and the analytical data show
these are a pentane hemisolvate.
2
2
for 2D (THF, δ): - 96.1 (d, J PP ) 198 Hz); -153.4 (dt, J PP
)
1
198, J PD ) 45.8 Hz). After the sample was left standing
overnight, some scrambling occurred, and the ratio of 2D to 2
was ∼4:5. Methyl iodide (50 µL, 0.8 mmol) was added directly
to the tube containing this mixture, and the 31P NMR spectrum
showed that the desired mixture of 4D and 4, as a mixture of
isomers, had formed. 31P{1H} NMR data for 4D (THF, δ):
2
2
-155.6 (d, J PP ) 375 Hz, minor isomer b); -170.3 (d, J PP
)
2
1
429 Hz, major isomer a ); -215.7 (dt, J PP ) 375, J PD ) 48.9,
2
1
b); -227.1 (dt, J PP ) 429, J PD ) 48.4, a ).
2-
Dep r oton a tion of 1. Gen er a tion of [NiCp (µ-P Mes)]2
(3). To a brown solution of 1 (30 mg, 0.055 mmol) and 12-
crown-4 (30 mg, 0.17 mmol) in 1 mL of THF was added n-BuLi
(400 µL of a 1.6 M hexanes solution, 0.64 mmol). The solution
became darker brown/purple. After 45 min, 31P NMR showed
a mixture of monoanion 2 and dianion 3 in ∼3:7 ratio. After
the tube was stored overnight, only dianion 3 was observed
by 31P NMR.
(NiCp )2(µ-P HMes)(µ-P MeMes) (4). To a solution of 1a
(158 mg, 0.288 mmol) in 15 mL of THF was added n-BuLi (270
µL of a 1.6 M solution in hexanes, 0.43 mmol). The solution
became darker brown immediately. After 1 h, the solution was
cooled to -78 °C, and a solution of MeI (270 µL, 4.34 mmol)
in THF (5 mL) was added all at once with stirring. The
solution was stirred at -78 °C for 15 min and then allowed to
warm to room temperature while the solvent and excess MeI
were removed in vacuo. The brown residue was extracted with
five 5-mL portions of petroleum ether. After filtration through
Celite, the solvent was removed from the brown extract,
yielding 114 mg of brown crystalline solid (70%). Recrystal-
lization from petroleum ether at -20 °C gives small brown
crystals.
1H NMR (C6D6, δ): 6.43 (4H, Mes); 5.14 (10H, Cp); 2.88
(12H, ortho Me); 2.03 (6H; para Me); 1.01 (t, “J ” ) 6 Hz, 6H,
P-Me). 13C{1H} NMR (C6D6, δ): 143.0 (m, ortho Mes); 137.6
(para Mes); 129.1 (m, Mes); 128.4 (m, obscured by C6D6 peaks,
Mes); 92.1 (Cp); 34.8 (para Me); 30.6 (ortho Me); 25.3 (apparent
triplet, “J ” ) 5.5, P-Me). IR (KBr): 2919, 2849, 1734, 1602,
1452, 1263, 1028, 881, 835, 774, 697 cm-1. Anal. Calcd for
This complex exists in solution as an ∼4:1 mixture of anti
and syn isomers 4a ,b. Peaks assigned to minor isomer 4b are
labeled with an asterisk. 1H NMR (toluene-d8, 22 °C, δ): 6.69;
C
30H38Ni2P2‚0.5C5H12
: C, 63.56; H, 7.24. Found (QTI): C,
63.57; H, 6.97.
1
6.66 (Mes, 4a ,b); 4.75 (10H, Cp, 4a ,b); 4.16 (dd, J PH ) 314,
Cr yst a l St r u ct u r e Det er m in a t ion s for 1a a n d
6b‚0.5C5H12. Crystal, data collection, and refinement param-
eters are given in Table 2. The systematic absences in the
diffraction data are consistent with Cc and C2/c for 6b‚0.5C5H12
and uniquely consistent with P21/c for 1a . The centrosym-
metric space group chosen for 6b‚0.5C5H12 yielded chemically
reasonable and computationally stable results. No absorption
corrections were required because of the <10% variation in
the ψ-scan integrated intensities. The structures were solved
3
| J PH| ) 17 Hz, 1H, P-H); 3.04 (6H, ortho Me); 3.00 (6H, ortho
2
4
Me*); 2.82 (6H, ortho Me*); 2.42 (dd, J PH ) 10.2, J PH ) 2
1
Hz, 3H, P-Me*); 2.35 (d, J PH ) 10.8, 3 H, P-Me); 2.09 (para
Me, 4a ,b, overlaps solvent peak). 1H NMR (toluene-d8, - 60
°C, δ): 6.76 (1H, Mes); 6.65; 6.61 (4a ,b), 6.54 (1H, Mes); 4.74
1
3
(broad, 10H, Cp, 4a ,b); 4.16 (dd, J PH ) 314, | J PH| ) 17 Hz,
1H, P-H); 3.32 (3H, ortho Me); 3.05 (6H, ortho Me); 2.98 (6H,
ortho Me*); 2.83 (6H, ortho Me*); 2.43 (3H, ortho Me); 2.38

2488 Organometallics, Vol. 15, No. 10, 1996
Maslennikov et al.
using direct methods and refined by full-matrix least-squares
procedures. The molecule in 1a is located on an inversion
center. A half-molecule of pentane solvate was located on a
undergraduate research fellowship. We thank Profes-
sors Alan Cowley and J ohn Bleeke for helpful cor-
respondence and the latter for a preprint of ref 2b.
2-fold axis in 6b‚0.5C5H12
. All non-hydrogen atoms were
refined with anisotropic displacement coefficients. The hy-
drogen atom bonded to the phosphorus atom in 1a was located.
All other hydrogen atoms were treated as idealized contribu-
tions. All software and sources of the scattering factors are
contained in either the SHELXTL (5.3) or the SHELXTL PLUS
(4.2) program libraries (G. Sheldrick, Siemens XRD, Madison,
WI).
Su p p or tin g In for m a tion Ava ila ble: Details of the X-ray
structure determinations for 1a and 6b, including tables of
anisotropic displacement coefficients, complete atom coordi-
nates and isotropic displacement coefficients, and complete
bond lengths and angles (15 pages). This material is contained
in many libraries on microfiche, immediately follows this
article in the microfilm version of the journal, can be ordered
from the ACS, and can be downloaded from the Internet; see
any current masthead page for ordering information and
Internet access instructions.
Ack n ow led gm en t. We thank Dartmouth College
and the donors of the Petroleum Research Fund, ad-
ministered by the American Chemical Society, for
partial support. S.V.M. thanks NECUSE for a summer
OM950982U