Preparation and characterization of cationic nickel indenyl complexes [(1-methylindenyl)NiLL′]+

Article abstract of DOI:10.1021/om970169u

The cationic complexes [(1-Me-Ind)Ni(PPh₃)-(L)]⁺ (1-Me-Ind = 1-methylindenyl; L = PPh₃, PMe₃, or MeCN) have been prepared and characterized spectroscopically and by means of single-crystal X-ray structural analy

Full text of DOI:10.1021/om970169u

4762
Organometallics 1997, 16, 4762-4764
P r ep a r a tion a n d Ch a r a cter iza tion of Ca tion ic Nick el
In d en yl Com p lexes [(1-m eth ylin d en yl)NiLL′]+
Rainer Vollmerhaus, Francine Be´langer-Garie´py, and Davit Zargarian*
De´partement de Chimie, Universite´ de Montre´al, Montre´al, Que´bec, Canada H3C 3J 7
Received March 3, 1997X
Sch em e 1
Summary: The cationic complexes [(1-Me-Ind)Ni(PPh3)-
(L)]+ (1-Me-Ind ) 1-methylindenyl; L ) PPh3, PMe3, or
MeCN) have been prepared and characterized spectro-
scopically and by means of single-crystal X-ray struc-
tural analysis in the case of [(1-Me-Ind)Ni(PPh3)(PMe3)]-
AlCl4. The in-situ-generated cations dimerize ethylene.
Recent reports have shown that metal-centered cat-
ionic species catalyze a number of important reactions1
and can promote a variety of others, such as C-H bond
activation,2 ligand substitution and insertion,3 and
â-alkyl elimination.4 Thus, the presence of a positive
charge on certain transition metal complexes seems to
confer to these species interesting patterns of reactivity.
In conjunction with our ongoing investigations into the
chemistry of neutral nickel indenyl complexes,5 we were
interested in studying the influence of a positive charge
on the structural features and reactivities of these
compounds. Although cationic Cp complexes of nickel
have been reported,6 little is known about their struc-
tural features and reactivities with olefins. Therefore,
we set out to prepare cationic nickel indenyl complexes
and report here the preparation, characterization, and
some reactivities of the cationic species [(1-Me-Ind)-
NiLL′]+.
31P{1H} NMR spectrum of complex 28 shows two mutu-
ally coupled doublets reflecting the inequivalence of the
PPh3 groups due to the absence of a plane of symmetry
in the complex. The 31P{1H} NMR spectrum of 39 shows
an AX + A′X′ spin system, with two doublets in the PPh3
chemical shift region and two in the PMe3 region. We
have attributed these signals to the two rotamers 3a
and 3b (Scheme 1), which arise from the hindered
rotation of the indenyl ligand around the Ni-(1-Me-Ind)
axis. The presence of the 1-Me substituent on the
indenyl renders these rotamers inequivalent, and so
their individual signals can be observed by NMR below
the coalescence temperature (ca. 273 K).10
When equimolar quantities of (1-Me-Ind)Ni(PPh3)Cl,
1,5 AgBF4, and PPh3 are stirred in CH2Cl2, the bis-
(phosphine) cationic species [(1-Me-Ind)Ni(PPh3)2]+, 2,
is obtained in 90% yield (eq 1). This methodology can
The isolation of suitable single crystals of 3 allowed
us to study its solid state structure in order to determine
whether the indenyl hapticity increases on going from
a neutral species to a cation; such an increase in the
also be used to prepare cationic complexes bearing
different phosphine ligands, such as [(1-Me-Ind)Ni-
(PPh3)(PMe3)]+, 3.7 These compounds have been char-
acterized by NMR spectroscopy.8,9 For example, the
(7) AlCl3 can also be used instead of AgBF4, but in some cases the
Cl- abstraction appears to be reversible and reforms 1, presumably
due to the slow formation of the AlCl3‚PR3 adduct.
(8) 2: 1H NMR (δ, CDCl3) ca. 7.9-6.96 (complex multiplets, PPh3,
H5 and H6), 6.91 (d, 3J H-H ) ca. 2.8, H2), 6.22 (m, H4 or H7), 6.06 (m,
X Abstract published in Advance ACS Abstracts, October 1, 1997.
(1) (a) J ohnson, L. K.; Killian, C. M.; Brookhart, M. J . Am. Chem.
Soc. 1995, 117, 6414. (b) Collins, S.; Ward, D. G. Ibid. 1992, 114, 5460
and references therein.
(2) (a) Yi, C. S.; Wodka, D.; Rheingold, A. L.; Yap, G. P. A.
Organometallics 1996, 15, 2. (b) Arndtsen, B. A.; Bergman, R. G.
Science 1995, 270, 1970.
(3) Mecking, S.; Keim, W. Organometallics 1996, 15, 2650.
(4) Horton, A. D. Organometallics 1996, 15, 2675.
(5) (a) Huber, T. A.; Be´langer-Garie´py, F.; Zargarian, D. Organo-
metallics 1995, 14, 4997. (b) Bayrakdarian, M.; Davis, M. J .; Reber,
C.; Zargarian, D. Can. J . Chem. 1996, 74, 2194. (c) Huber, T. A.;
Bayrakdarian, M.; Dion, S.; Dubuc, I.; Be´langer-Garie´py, F.; Zargarian,
D. Manuscript in preparation.
(6) (a) Kuhn, N.; Heuser, N.; Winter, M. J . Organomet. Chem. 1984,
267, 221. (b) Kuhn, N.; Winter, M. Ibid. 1982, 239, C31. (c) Majima,
T.; Kurosawa, H. Ibid. 1977, 134, C45. (d) Salzer, A.; Court, T. L.;
Werner, H. Ibid. 1972, 54, 325. (e) Yamamoto, Y.; Yamazaki, H.;
Hagihara, N. Ibid. 1969, 18, 189. (f) Kuhn, N.; Werner, H. Synth. React.
Inorg. Met-Org. Chem. 1978, 8, 249. (g) Treichel, P. M.; Shubkin, R.
L. Inorg. Chim. Acta 1968, 2, 485.
3
H7 or H4), 5.01 (m, H3), 1.00 (dd, J P-H ) ca. 5.6, 3.3 Hz, CH3); 31P-
2
2
{1H} NMR (δ, CDCl3) 35.8 (d, J P-P ) 25 Hz), 32.5 (d, J P-P ) 25 Hz).
Although this compound appeared pure on the basis of its spectra,
satisfactory analyses were not obtained.
(9) 3a : H NMR (δ, CDCl3, 273 K) 7.9-7.1 (m, PPh3), 7.52 (m, H7),
3
3
7.38 (m, H6), 7.25 (t, J H-H ) 8.0 Hz, H5), 6.58 (d, J H-H ) 7.9 Hz,
H4), 6.39 (d, 3J H-H ) 3.1 Hz, H2), 4.43 (ddd, 3J PPh
) 3.7 Hz, 3J PMe
) 6.1 Hz, J PMe
3-H
3-H
3
4
4
) 3.7 Hz, J H-H ) 3.4 Hz, H3), 2.04 (dd, J PPh
)
3-H
3-H
2.8 Hz, CH3-Ind), 0.87 (d, J P-H ) 9.4); 31P{1H} NMR (δ, CDCl3, 273
K) 40.9 (d, 2J P-P ) 41.5, PPh3), -15.3 (d, 2J P-P ) 41.5 Hz, PMe3). [3b]+:
1H NMR (δ, CDCl3, 273 K) 7.9-7.1 (m, PPh3), 7.39 (m, H4), 7.26 (m,
H5), 7.23 (t, 3J H-H ) 8.0 Hz, H6), 6.38 (d, 3J H-H ) 7.9 Hz, H7), 6.35 (d,
2
3J H-H ) 2.7 Hz, H2), 5.60 (ddd, J PMe
) 6.4 Hz, J PPh
) 2.8 Hz,
3-H
4
3
3
3-H
3J H-H ) 2.7 Hz), 0.98 (d, J P-H ) 9.7 Hz, P(CH3)3), 0.75 (dd, J PMe
2
3-H
4
) 6.0 Hz, J PPh
) 1.9 Hz, CH3-Ind); 31P{1H} NMR (δ, CDCl3, 273
3-H
K) 41.2 (d, 2J P-P ) 42 Hz, PPh3), -10.1 (d, 2J P-P) 42 Hz, PMe3). Anal.
Calcd for C31H33P2NiAlCl4: C, 53.57; H, 4.79. Found: C, 53.81; H, 4.75.
(10) We are studying the dynamic processes arising from the
hindered rotation of the indenyl ligands in these and related complexes
and will report our results in greater detail in due course.
S0276-7333(97)00169-6 CCC: $14.00 © 1997 American Chemical Society

Communications
Organometallics, Vol. 16, No. 22, 1997 4763
(PPh3)(MeCN)]+, 4, on the basis of its NMR and IR
spectra (eq 2).13 The presence of a coordinated MeCN
is supported by the increase in the value of ν(CN)
resulting from a transfer of electron density from MeCN
to the electrophilic Ni+ center. A similar observation
has been made for cationic Pt complexes bearing coor-
dinated isocyanide ligands.14 Although the coordinated
MeCN in 4 can be displaced readily by stronger ligands
such as phosphines (eq 2), weaker ligands such as
olefins do not compete effectively with MeCN for coor-
dination to Ni. Complex 4 is relatively unstable in
solution and decomposes over several minutes at room
temperature to produce an insoluble white solid and
other unidentified products.
Evidently, the MeCN adduct 4 is not a suitable
precursor to cationic complexes bearing weaker ligands
(e.g., olefins, alkynes, etc.) which may exhibit interesting
reactivities. In an attempt to prepare the MeCN-free,
“naked” cation [(1-Me-Ind)Ni(PPh3)]+, 5, we reacted 1
with AgBF4 in CH2Cl2 in the absence of any added donor
ligand; interestingly, the only species detected in this
reaction was 2 (ca. 30% yield). Thus, abstraction of Cl-
from 1 initially forms the nonstabilized, coordinatively
unsaturated, cationic intermediate 5, which is highly
electrophilic and, in the absence of an added donor such
as MeCN, coordinates any residual PPh3 from the
reaction medium forming 2.15 In order to suppress the
formation of 2, we carried out the abstraction of Cl- in
the presence of an excess of 1-hexene, which led, once
again, to the formation of 2. However, when 1 was
reacted with AgBF4 under a 5 atm pressure of ethylene
in a semibatch type reactor, rapid uptake of ethylene
began after a brief induction period and lasted during
the entire experiment (20-30 min); the temperature of
the reactor also rose significantly during the reaction.
The apparent turnover (TO) frequency of this system
is estimated to be ca. 100-500 TO/s, corresponding to
an ethylene consumption rate of ca. 11 000 kg‚(mol
Ni)-1‚h-1. GC/MS analyses of the final reaction mix-
tures showed only 1-butene, indicating that â-H elimi-
nation from the putative Ni-Bu intermediate is too
rapid to allow chain propagation.
F igu r e 1. ORTEP view of complex 3b and selected bond
lengths (Å): Ni-P(1) ) 2.1794(10), Ni-P(2) ) 2.1909(11),
Ni-C(1) ) 2.160(2), Ni-C(2) ) 2.096(2), Ni-C(3) ) 2.033-
(2), Ni-C(3A) ) 2.249(2), Ni-C(7A) ) 2.305(2), C(1)-C(2)
) 1.400(3), C(2)-C(3) ) 1.416(3), C(3)-C(3A) ) 1.459(3),
C(3A)-C(7A) ) 1.419(3), C(1)-C(7A) ) 1.465(3).
hapticity would serve to transfer more electron density
to the electrophilic Ni center, thereby stabilizing it.
Figure 1 shows the ORTEP view of [(1-Me-Ind)Ni(PPh3)-
(PMe3)][AlCl4]11 along with some pertinent bond dis-
tances. Indenyl hapticities can be determined conve-
niently by calculating the slip value, ∆M-C,12 which is
found to be 0.18 Å for 3; comparing this to the ∆M-C
of 0.26 Å for 15c confirms the significant increase in the
indenyl hapticity upon cation formation.
It is interesting to note that the rotamer that crystal-
lizes from the solution is that with the Me group on top
of the PPh3 ligand, 3b, which might appear to be the
more sterically crowded one of the two rotamers ob-
served in solution until one notes that the coordination
of 1-Me-Ind to Ni is quite nonsymmetrical (i.e., Ni-C1
> Ni-C2 > Ni-C3). Such nonsymmetrical Ni-Ind
interactions, which seem to result in a “tilting” of the
indenyl ligand, have also been observed in 15c and the
related complex (Ind)Ni(PPh3)Cl.5a In the latter com-
pounds, this “sideways slippage” has been shown to be
caused by the unequal trans influences of the pseudo-
trans ligands PPh3 and Cl. By analogy, we propose that
the large trans influence of PMe3 is responsible for the
nonsymmetrical coordination of the 1-Me-Ind ligand in
complex 3.
In conclusion, cationic species of the type [(1-Me-Ind)-
Ni(PPh3)L]+ display interesting structural and spectro-
scopic features pertaining to the hapticity of the indenyl
ligand. The nonstabilized cationic species 5, which
could be generated in-situ but not isolated, dimerizes
ethylene at a very high rate, reminiscent of the reac-
The reaction of 1 with AgBF4 in MeCN without the
added PPh3 gave, after removal of the solvent, a yellow-
brown solid which was identified as [(1-Me-Ind)Ni-
(13) 4: 1H NMR (δ, CDCl3) 7.7-7.1 (PPh3, H6 and H7), 7.06 (t, H5,
J H-H ≈ 6 Hz), 6.47 (bs, H2), 6.00 (d, H4, J H-H ≈ 5 Hz), 4.16 (s, H3),
1.98 (b, CH3CN), 1.73 (s, CH3-Ind); 31P{1H} NMR (δ, CDCl3) 34.94 (s);
IR (cm-1, Nujol) 2335, 2310 (compared to 2300 and 2260 for neat
MeCN).
(14) Clark, H. C.; Manzer, L. E. Inorg. Chem. 1973, 12, 362.
(15) This can proceed in at least two different ways: (a) if the
phosphine coordination step is much faster than the removal of Cl-,
any initial amount of cation formed would abstract PPh3 from the
unreacted starting material 1 to form 2 and other materials; (b)
alternatively, all of the starting material may be converted to 5 in a
rapid step, followed by a slower redistribution step producing 2 and
[(Ind′)Ni]+, which would decompose readily. Experiments are currently
underway to determine which, if any, of these two mechanisms are at
work in this reaction.
(11) Orange-red crystals of [3b]+[AlCl4]- were grown from a CH2-
Cl2/hexane solution at -35 °C. Crystallographic data for NiP2Cl4-
AlC31H33 (M ) 695.04): Triclinic, P1h, unit cell dimensions of a )
9.780(4) Å, b ) 10.762(5) Å, c ) 16.061(6) Å, R ) 95.55(4)°, â ) 91.90-
(3)°, γ ) 97.40(3)°, V ) 1666.7(12) Å3, Z ) 2, µ(Cu KR) ) 3.18 mm-1
,
λ ) 1.540 56 Å, 2θmax ) 140.0°, T ) 223 K, 12 434 reflections measured
using the θ/2θ scan mode (6323 independent, 5791 observed), refine-
ment by block-diagonal least-squares gave RF ) 0.0326 and Rw
)
0.0351. The ORTEP diagram is shown in Figure 1 along with pertinent
bond distances.
1
1
(12) (a) ∆M-C )
/ (Ni-C7a + Ni-C3a) - / (Ni-C1 + Ni-C3);
2
2
∆M-C values close to zero indicate little distortion from η5 hapticity,
whereas values above ca. 0.5 Å indicate nearly η3 hapticity (ref 12b).
(b) Westcott, S. A.; Kakkar, A.; Stringer, G.; Taylor, N. J .; Marder, T.
B J . Organomet. Chem. 1990, 394, 777.
(16) Bogdanovic, B.; Spliethoff, B.; Wilke, G. Angew. Chem., Int. Ed.
Engl. 1980, 19, 622.

4764 Organometallics, Vol. 16, No. 22, 1997
Communications
tivities displayed by Wilke’s system of (π-allyl)Ni(PCy3)-
Br/EtAlCl2.16 We believe that the hapticity of the Ind
ligand plays an important role in the reactivity of these
cationic species. The dynamic behavior of these com-
plexes in solution and their reactivities with other
substrates are under investigation.
for helpful discussions as well as the use of the high-
pressure reactor for the ethylene experiments.
Su p p or tin g In for m a tion Ava ila ble: Experimental data
on the preparation and spectroscopic characterization of the
species 2, 3, and 4, tables of crystal data, collection, and
refinement parameters, positional parameters, bond distances
and angles, and anisotropic displacement parameters, and
NMR spectra (29 pages). Ordering information is given on
any current masthead page.
Ack n ow led gm en t. The authors are grateful to
NSERC (Canada), FCAR (Que´bec), and Universite´ de
Montre´al for financial support and to Prof. S. Collins
OM970169U