Structural and NMR studies of indenyl hapticity and rotational barriers in the complexes (η-1-R-indenyl)Ni(PPh3)(X) (R = H, Me; X = Cl, Me)

Article abstract of DOI:10.1021/om970715j

The relative trans influences of Cl and Me in the complexes (1-Me-indenyl)Ni(PPh₃)Cl and (1-Me-indenyl)Ni(PPh₃)Me lead to different solid state hapticities for the 1-Me-indenyl ligands. Comparing the solution NMR data for these compl

Full text of DOI:10.1021/om970715j

Organometallics 1997, 16, 5811-5815
5811
Str u ctu r a l a n d NMR Stu d ies of In d en yl Ha p ticity a n d
Rota tion a l Ba r r ier s in th e Com p lexes
(η-1-R-In d en yl)Ni(P P h 3)(X) (R ) H, Me; X ) Cl, Me)
Trisha A. Huber, Malken Bayrakdarian, Sylvain Dion, Isabelle Dubuc,
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 August 12, 1997X
The relative trans influences of Cl and Me in the complexes (1-Me-indenyl)Ni(PPh3)Cl
and (1-Me-indenyl)Ni(PPh3)Me lead to different solid state hapticities for the 1-Me-indenyl
ligands. Comparing the solution NMR data for these complexes and the energy barriers to
the rotation of the indenyl ligands in their unsubstituted analogues demonstrates that solid
state hapticities are preserved in solution.
ates by the relatively facile “ring slippage” of the Ind
ligands (i.e., their more flexible hapticity). It has also
been suggested that, in some cases, the indenyl effect
is due to less stable ground states in Ind complexes
relative to their Cp analogues.5
In comparison to their Cp analogues, many transition
metal Ind complexes (Ind ) indenyl and its substituted
derivatives) possess enhanced reactivities in various
stoichiometric reactions, notably ligand substitution.1,2
This feature has been recognized as potentially advan-
tageous in catalytic systems where ligand substitution
rates play a determining role in the overall catalytic
cycle, and a few reactions are reported to be more
efficiently catalyzed by Ind complexes relative to their
Cp counterparts.1r,3,4 The difference in the reactivities
of these closely related compounds, the so-called “inde-
nyl effect”, is commonly attributed to the better stabi-
lization of transition states and/or reaction intermedi-
To date, most of the structural and reactivity studies
of late metal Ind complexes have focused on group 8 and
group 9 metals, while group 10 metal Ind complexes
have received little attention.6 We have begun inves-
tigating the preparation and reactivities of these com-
pounds and have found that the solid state hapticity of
the Ind ligand in the complex (Ind)Ni(PPh3)Cl (1) is
significantly distorted toward an unsymmetrical and
partially localized mode, i.e., (η3 T η1,η2)-Ind.6g More-
over, the solution NMR studies of this complex indicated
a considerable energy barrier to the rotation of the Ind
ligand around the Ind-Ni axis. We proposed that both
of these effects were caused by the relatively large
difference in the trans influences of the ancillary ligands
PPh3 and Cl. This assertion was indirectly supported
by the observation that replacing the Cl ligand in 1 by
the higher trans influence ligand Me resulted in a more
symmetrically coordinated Ind ligand, as inferred from
1H NMR spectroscopy (vide infra). Unfortunately,
however, the poor quality of the crystals obtained for
the methyl derivative (Ind)Ni(PPh3)Me (2) precluded a
solid state structure determination and prevented a
direct comparison of the indenyl hapticities in 1 and 2.
Therefore, we set out to prepare new derivatives of 1
and 2 and determine their solid state structures in order
to unequivocally establish the influence of the ancillary
X Abstract published in Advance ACS Abstracts, December 1, 1997.
(1) (a) Hart-Davis, A. J .; Mawby, R. J . Chem. Soc. A. 1969, 2403.
(b) White, C.; Mawby, R. J . Inorg. Chim. Acta 1970, 4, 261. (c) White,
C.; Mawby, R. J .; Hart-Davis, A. J . Inorg. Chim. Acta 1970, 4, 441. (d)
J ones, D. J .; Mawby, R. J . Inorg. Chim. Acta 1972, 6, 157. (e) Caddy,
P.; Green, M.; O’Brien, E.; Smart, L. E.; Woodward, P. Angew. Chem.,
Int. Ed. Engl. 1977, 16, 648. (f) Caddy, P.; Green, M.; O’Brien, E.;
Smart, L. E.; Woodward, P. J . Chem. Soc., Dalton Trans. 1980, 962.
(g) Rerek, M. E.; J i, L.-N.; Basolo, F. J . Chem. Soc., Chem. Commun.
1983, 1208. (h) J i, L.-N.; Rerek, M. E.; Basolo, F. Organometallics 1984,
3, 740. (i) Rerek, M. E.; Basolo, F. J . Am. Chem. Soc. 1984, 106, 5908.
( j) O’Connor, J . M.; Casey, C. P. Organometallics 1985, 4, 384. (k)
O’Connor, J . M.; Casey, C. P. Chem. Rev. 1987, 87, 307 and references
therein. (l) Marder, T. B.; Williams, I. D. J . Chem. Soc., Chem.
Commun. 1987, 1478. (m) Turaki, N. N.; Huggins, J . M.; Lebioda, L.
Inorg. Chem. 1988, 27, 424. (n) Habib, A.; Tanke, R. S.; Holt, E. M.;
Crabtree, R. H. Organometallics 1989, 8, 1225. (o) Kakkar, A. K.;
Taylor, N. J .; Marder, T. B. Organometallics 1989, 8, 1765. (p) Kakkar,
A. K.; Taylor, N. J .; Marder, T. B.; Shen, J . K.; Hallinan, N.; Basolo,
F. Inorg. Chim. Acta 1992, 198-200, 219. (q) Bang, H.; Lynch, T. J .;
Basolo, Organometallics 1992, 11, 40. (r) Szajek, L. P.; Shapley, J . R.
Organometallics 1994, 13, 1395.
(2) A recent report has suggested that substitution rates in 19-
electron complexes are in fact slower for Ind than for Cp, the so-called
“inverse indenyl effect”: Pevear, K. A.; Banaszak Holl, M. M.;
Carpenter, G. B.; Rieger, A. L.; Rieger, P. H.; Sweigart, D. A.
Organometallics 1995, 14, 512.
(3) (a) Caddy, P.; Green, M.; Smart, L. E.; Smart, L. E. J . Chem.
Soc., Chem. Commun. 1978, 839. (b) Borrini, A.; Diversi, P.; Ingrosso,
G.; Lucherini, A.; Serra, G. J . Mol. Catal. 1985, 30, 181. (c) Bonneman,
H. Angew. Chem., Int. Ed. Engl. 1985, 24, 248. (d) Bonneman, H.;
Brijoux, W. In Aspects of Homogeneous Catalysis, Vol. 5; Ugo, R., Ed.;
D. Reidel: Dordrecht, 1984; p 75. (e) Marder, T. B.; Roe, D. C.; Milstein,
D. Organometallics 1988, 7, 1451. (f) Tanke, R. S.; Crabtree, R. H. J .
Am. Chem. Soc. 1990, 112, 7984. (g) Ceccon, A.; Gambaro, A.; Santi,
S.; Venzo, A. J . Mol. Catal. 1991, 69, L1. (h) Lee, B. Y.; Chung, Y. K.;
J eong, N.; Lee, Y.; Hwang, S. H. J . Am. Chem. Soc. 1994, 116, 8793.
(i) Mantovani, L.; Ceccon, A.; Gambaro, A.; Santi, S.; Ganis, P.; Venzo,
A. Organometallics 1997, 16, 2682.
(5) Kubas, G. J .; Kiss, G.; Hoff, C. D. Organometallics 1991, 10, 2870.
(6) The following are, to our knowledge, the only other group 10
metal Ind complexes reported to date: (a) Fritz, H. B.; Ko¨hler, F. H.;
Schwarzhans, K. E. J . Organomet. Chem. 1969, 19, 449 (synthesis of
Ni(Ind)2). (b) Westcott, S. A.; Kakkar, A. K.; Stringer, G.; Taylor, N.
J .; Marder, T. B. J . Organomet. Chem. 1990, 394, 777 (solid state
structure of Ni(Ind)2). (c) Nakasuji, K.; Yamaguchi, M.; Murata, I.;
Tatsumi, K.; Nakamura, A. Organometallics 1984, 3, 1257 (synthesis
of Pd2Cl2(Ind)2). (d) O’Hare, D. Organometallics 1987, 6, 1766 (syn-
thesis of [Pt(Ind)(COD)]+). (e) Lehmkuhl, H.; Na¨ser, J .; Mehler, G.;
Keil, T.; Danowski, F.; Benn, R.; Mynott, R.; Schroth, G.; Gabor, B.;
Kru¨ger, C.; Betz, P. Chem. Ber. 1991, 124, 441 (synthesis of Ni(Ind)-
(η3-allyl)). (f) Tanase, T.; Nomura, T.; Fukushima, T.; Yamamoto, Y.;
Kobayashi, K. Inorg. Chem. 1993, 32, 4578 (synthesis and solid state
structure of Pd2(µ-Ind)2(CNR)2). (g) Huber, T. A.; Be´langer-Garie´py,
F.; Zargarian, D. Organometallics 1995, 14, 4997 (synthesis and solid
state structure of (Ind)Ni(PPh3)Cl). (h) Vollmerhaus, R.; Be´langer-
Garie´py, F.; Zargarian, D. Organometallics 1997, 16, 4762. (synthesis
and solid state structure of [(1-Me-Ind)Ni(PPh3)(PMe3)]+[AlCl4]-).
(4) The reports cited in ref 3 do not include examples of reactions
catalyzed by Ind complexes of early metals (e.g., olefin and silane
polymerizations) because the ring slippage aptitude of the Ind ligand
is not believed to be a factor in these, normally unsaturated, complexes.
S0276-7333(97)00715-2 CCC: $14.00 © 1997 American Chemical Society

5812 Organometallics, Vol. 16, No. 26, 1997
Huber et al.
Ta ble 1. X-r a y Cr ysta llogr a p h ic Da ta for 3 a n d 4
3
4
formula, mol wt
crystal color and habit orange-red,
parallelepiped
C28H24ClNiP, 485.60 C29H27NiP, 465.19
dark red,
parallelepiped
cryst dimens, mm
cell setting and
space group
a, Å
b, Å
c, Å
0.39 × 0.14 × 0.05
0.22 × 0.17 × 0.07
triclinic, P1h
monoclinic, P21/n
9.086(3)
10.455(3)
13.466(4)
84.65(3)
88.09(3)
64.40(3)
1148.6(6)
2
1.404
1.545 06
220(2)
Nonius CAD-4
140
8.891(2)
28.089(9)
10.379(2)
90
113.92
90
2369.4(10)
4
1.304
1.540 56
293(2)
Nonius CAD-4
140
ω/2θ
4492
R, deg
â, deg
γ, deg
V, Å3
Z
D (calc), g cm-1
λ (Cu KR), cm-1
temp, K
F igu r e 1. ORTEP plot of 3 with atom numbering scheme.
diffractometer
2θmax, deg
data coll method
no. of reflns used
(I > 2σ (I))
R, Rw
ω/2θ
4341
0.0458, 0.1245
1.066
0.0383, 0.0819
0.213
max residual, e Å-3
Ta ble 2. Selected Bon d Dista n ces (Å) a n d
Str u ctu r a l P a r a m eter sa for 1,b 3, a n d 4
1
3
4
Ni-P
2.1835(7)
2.1822(7)
2.094(2)
2.061(2)
2.042(2)
2.318(2)
2.344(2)
1.399(4)
1.417(4)
1.449(3)
1.422(3)
1.459(3)
2.1782(11)
2.1865(10)
2.137(2)
2.072(2)
2.026(3)
2.308(2)
2.351(2)
1.403(4)
1.421(4)
1.451(4)
1.417(4)
1.457(4)
2.1213(13)
1.991(3)
2.089(4)
2.072(4)
2.082(4)
2.275(4)
2.273(4)
1.407(5)
1.404(5)
1.430(5)
1.424(5)
1.438(5)
8.1
Ni-Cl/C9
Ni-C1
Ni-C2
Ni-C3
Ni-C3a
Ni-C7a
C1-C2
C2-C3
C3-C3a
C3a-C7a
C7a-C1
HA (deg)
FA (deg)
∆M-C (Å)
F igu r e 2. ORTEP plot of 4 with atom numbering scheme.
10.9
11.7
0.26
11.0
11.8
0.25
The nickel center in both complexes is pentacoordi-
nate: the atoms P, Cl/C9, C1, C2, and C3 are within
expected bonding distance from Ni, while C3a and C7a
are considerably farther away. The geometry around
the Ni center is quite irregular but may be described
as either distorted square planar, with the C1dC2
occupying a single coordination site, or highly distorted
square pyramidal, with P, Cl/C9, C1, and C3 in the basal
plane and C2 above it. The planes formed by the atoms
P, Ni, and Cl/C9 on the one hand, and C1, C2, C3, C3a,
and C7a on the other, are nearly perpendicular to each
other (ca. 88°).7
Inspection of the C-C and Ni-C bond distances for
3 revealed that there are two types of hapticity distor-
tions in this complex. The first type is an allyl-ene
distortion reflected in the substantially longer Ni-C
bonds to the ring junction carbon atoms, i.e., Ni-C(3a,-
7a) > Ni-C(1-3), as well as the C-C bond lengths
inside the five-membered ring moiety, i.e., C1-C7a, C3-
C3a > C1-C2, C2-C3 (Table 2). Varying degrees of
such distortions (or “slippage”) also occur in most η-Ind
complexes;8 in the present case, they can be attributed
7.5
0.19
a
b
See text for definitions. Taken from ref 6g.
ligands vis a` vis the coordination of the Ind ligand to
the Ni center in these complexes.
The present paper reports the solid state structures
of the 1-methylindenyl analogues of 1 and 2, namely
(1-Me-Ind)Ni(PPh3)Cl (3) and (1-Me-Ind)Ni(PPh3)Me (4),
as well as the energy barrier for the rotation of the Ind
ligand in 2. Comparison of the structural data for 1, 3,
and 4 on the one hand, and the rotational energy
barriers for 1 and 2 on the other, demonstrates that (a)
the hapticity of the Ind ligand is very sensitive to the
electronic nature of the ancillary ligands and (b) the rate
of rotation of the Ind ligand varies considerably with
its hapticity.
Resu lts a n d Discu ssion
Reacting 1-Me-IndLi with (PPh3)2NiCl2 yields a mix-
ture of products from which the dark-red complex 3 can
be isolated as the major species in ca. 60% yield; the
subsequent reaction of 3 with MeLi gave 4 in 65% yield.
Suitable crystals of 3 and 4 were grown from cold
hexane/Et2O solutions and were subjected to X-ray
diffraction studies. X-ray crystallographic data (Table
1), selected bond distances (Table 2), and ORTEP views
(Figures 1 and 2) for these compounds are presented.
(7) This feature is also present in the following structures: (a) 1-Me-
CpNi(PPh3)I (Ballester, L.; Perez, S.; Gutierrez, A.; Perpinan, M. F.;
Gutierrez-Puebla, E.; Monge, A.; Ruiz, C. J . Organomet. Chem. 1991,
414, 411); (b) CpNi(PPh3)Ph (Churchill, M. R.; O’Brien, T. A. J . Chem.
Soc. (A) 1970, 161); (c) Cp*Ni(acac) (Smith, M. E.; Andersen, R. A. J .
Am. Chem. Soc. 1996, 118, 11119); and (d) Cp*Ni(PEt3)X for X ) Br,
CH2Ph, Me, OMe, SAr (Holland, P. L.; Smith, M. E.; Andersen, R. A.;
Bergman, R. G. J . Am. Chem. Soc., in press).
(8) Baker, R. T.; Tulip, T. H. Organometallics 1986, 5, 839.

Indenyl Hapticity and Rotational Barriers
Organometallics, Vol. 16, No. 26, 1997 5813
Ch a r t 1
quently for quantifying the degree of slip-fold distor-
tions in η-Ind complexes.11 In 3, HA ) 10.9°, FA )
11.8°, and ∆M-C ) 0.25 Å (Table 2), almost exactly the
same as the values found for 1.6g In 4, however, HA )
8.1°, FA ) 7.5°, and ∆M-C ) 0.19 Å (Table 2),
indicating significantly less slip-fold distortion in 4
compared to that in 3. In addition, the Ni-P distance
is significantly shorter in 4 (2.1213(13) Å) than in 1
(2.1835(7)) and 3 (2.1782(11)). Stronger Ni-Ind and
Ni-P interactions in 4 may serve to compensate for a
reduction in the overall electron density at the Ni center
in going from 3 to 4.12 However, a reduction in the
electron richness of the Ni center resulting from replac-
ing the Cl by the Me ligand, a better σ-donor, seems
counterintuitive unless Cl f Ni π-donation is an im-
portant component of the overall Ni-Cl interaction in
1 and 3. In this case, σ + π donation from Cl would
place more electron density on Ni than would σ-donation
from Me. Cl f Ni π-donation would also contribute to
the observed weakening of the Ni-C1 interaction in 1
and 3 (i.e., the distortion toward η1,η2-Ind), since these
types of interactions are believed to cause strong cis-
labilizing effects.13 It should be noted, however, that
Cl f M π-donation is more prevalent in unsaturated,
d6 complexes and would be highly repulsive and desta-
bilizing in these d8 complexes. Alternatively, stronger
Ni-P and Ni-Ind interactions may be attributed to the
tendency of “soft” ligands such as PPh3 and Ind to bind
more strongly with a soft metal center such as the Ni
in the methyl complex 4 than with the hard Ni center
in the chloro complexes 1 and 3.14 Our results cannot
determine which of these phenomena, if any, is respon-
sible for the above structural observations.
Solu tion Ha p ticities of th e In d Liga n d s in 1-4.
Since the nature of M-Ind interactions in the solution
can influence substantially the reactivity of Ind com-
plexes, it is important that Ind hapticities in solution
be known. Baker and Tulip8 and Marder’s group6b have
suggested that, to a large extent, solid state hapticities
are maintained in solution, while Ceccon et al.3g,i,15 have
proposed that the solution hapticity of Ind complexes
involves a fast equilibrium between η3- and η5-bound
species, regardless of the solid state hapticity. We have
relied on the solution NMR spectra (1H, 13C{1H}, and
31P{1H}) of our complexes to conclude that their solid
state structures are maintained in the solution, as
described below.
to the tendency of Ni(II) to avoid forming 18-electron
complexes. The second and more unusual type of
distortion found in 3 is evident from the unsymmetric
nature of the Ni-C bonds, i.e., Ni-C1 > Ni-C2 > Ni-
C3 and Ni-C7a > Ni-C3a (Table 2). Thus, the Ind
hapticity in this complex is very similar to that found
in the solid state structure of 16g and seems to arise from
a combination of tilting of the Ind ring and its “sideways
slippage”. The net result of these distortions is a partial
localization of bonding in the allyl moiety of the Ind
ligand (i.e., η1,η2 distortion), which is reflected in a
nominally shorter C1-C2 bond relative to C2-C3
(Table 2) and in the 1H and 13C{1H} NMR chemical
shifts of this complex (vide infra).
In contrast to 3, there is no sideways slippage in the
solid state structure of 4, as the Ind ligand is virtually
symmetrically coordinated to Ni, i.e., Ni-C1 ) Ni-C3
and Ni-C3a ) Ni-C7a (Table 2). These types of
symmetrical Ind hapticities are commonly found in
complexes (Ind)RhL2 (L ) PR3, CO, C2H4), which have
identical ligands L on either side of the mirror plane
bisecting the Ind ligand and incorporating the metal and
the C2 atoms.1p,9 We attribute the differences in the
hapticity of the Ind ligands in 3 and 4 to the relative
trans influences of the ancillary ligands PPh3 and X in
these complexes. The role of ancillary ligand trans
influence differences in controlling the conformation of
η-Ind complexes has been discussed previously,10 but
their effect on the hapticity of the Ind ligand has not
been addressed. The present results demonstrate that,
in complexes of the type IndMLX, wherein the ancillary
ligands L and X are positioned pseudotrans in relation
to the Ind carbon atoms C1 and C3, the M-Ind
interaction is strongly influenced by the electronic
natures of the ligands L and X in the following manner.
When L and X possess comparable trans influences, as
in 4, the Ind hapticity is symmetrical; when the trans
influences of L and X are sufficiently different, however,
significant perturbations are observed in the normally
symmetrical coordination of the Ind ligand, as observed
in 1 and 3 (Chart 1).
Solution hapticities of Ind ligands are believed to
correlate with the ease of their rotations: the less
distorted the Ind ligand, the more facile its rotation.12b,16
(11) HA and FA represent the bending of the Ind ligand at C1/C3
and C3a/C7a, respectively, and ∆M-C ) [1/2(M-C3a + M-C7a) -
1/2(M-C1 + M-C3)] (ref 6b).
(12) (a) Marder et al. (ref 9b) have shown that, in most cases, the
Ind hapticity increases (i.e., ring slippage decreases) as the overall
electron density at the metal center decreases, but they have also noted
some exceptions to this phenomenon (ref 12b). (b) Kakkar, A. K.;
Taylor, N. J .; Calabrese, J . C.; Nugent, W. A.; Roe, D. C.; Connaway,
E. A.; Marder, T. B. J . Chem. Soc., Chem. Commun. 1989, 990.
(13) (a) Caulton, K. G. New J . Chem. 1994, 18, 25. (b) Poulton, J .
T.; Folting, K.; Sreib, W. E.; Caulton, K. G. Inorg. Chem. 1992, 31,
3190.
(14) The influence of charge polarization in Ni-X bonds on bond
lengths and ligand labilities has been discussed recently by Bergman
and co-workers in the context of a generalized electrostatic-covalent
bonding model (ref 7d).
The Ni-Ind interactions in 3 and 4 can also be
compared in more quantitative terms by calculating the
parameters such as the hinge and fold angles (HA and
FA) and the slip value (∆M-C), which are used fre-
(9) (a) Mlekuz, M.; Bougeard, P.; Sayer, B. G.; McGlinchey, M. J .;
Rodger, C. A.; Churchill, M. R.; Ziller, J . W.; Kang, S.-K.; Albright, T.
A. Organometallics 1986, 5, 1656. (b) Marder, T. B.; Calabrese, J . C.;
Roe, D. C.; Tulip, T. H. Organometallics 1987, 6, 2012.
(10) (a) Faller, J . W.; Chen, C.-C.; Mattina, M. J .; J akubowski, A.
J . Organomet. Chem. 1973, 52, 361. (b) Faller, J . W.; J ohnson, B. V.
J . Organomet. Chem. 1975, 88, 101. (c) Faller, J . W.; Crabtree, R. H.;
Habib, A. Organometallics 1985, 4, 929. d) Kakkar, A. K.; Stringer,
G.; Taylor, N. J .; Marder, T. B. Can. J . Chem. 1995, 73, 981. (e) Husebo,
T. L.; J ensen, C. M. Organometallics 1995, 14, 1087.
(15) (a) Ceccon, A.; Elsevier, C. J .; Ernsting, J . M.; Gambaro, A.;
Santi, S.; Venzo, A. Inorg. Chim. Acta 1993, 204, 15. (b) Bonifaci, C.;
Carta, G.; Ceccon, A.; Gambaro, A.; Santi, S.; Ganis, P.; Venzo, A.
Organometallics 1996, 15, 1630.

5814 Organometallics, Vol. 16, No. 26, 1997
Huber et al.
Complexes 1 and 2 possess C1 symmetry in their ground
state structures but can attain Cs symmetry as a result
of the rapid rotation of the Ind ligand in solution;
derivatives. These results also support the suggestions
of Baker and Tulip8 and Marder and co-workers6b that
there is a strong correlation between the ∆δavC value
for a complex and the degree of slip-fold distortion
observed in its solid state structure.
Finally, the maintenance of the solid state structures
of these complexes in solution is also supported by the
solution 31P{1H} NMR spectra of 1-4, which show a
downfield shift in the 31P{1H} resonances on going from
free PPh3 (ca. -5 ppm in C6D6) to the Ni-Cl compounds
1 and 3 (28.2 and 31.1 ppm, respectively) and the Ni-
Me derivatives 2 and 4 (47.1 and 47.7 ppm, respec-
tively). This trend reflects the increasing P f Ni
σ-donation in 4 and 2 compared to that in 3 and 1, which
is consistent with the shorter Ni-P bond length ob-
served in the solid state structure of 4 relative to that
in 3.
1
therefore, they exhibit temperature-dependent H and
13C{1H} NMR spectra which can yield the energy
barriers to indenyl rotations in these complexes. For
instance, the H1 and H3 signals for 1 and 2 appear at
ca. 5.4-5.9 and ca. 3.3-4.1 ppm, respectively, at below
the coalescence temperature and merge into a singlet
at ca. 4.5-4.7 ppm above the coalescence temperature.
We conclude, therefore, that 1 and 2 undergo the same
dynamic behavior, with the main difference being the
coalescence temperature, which is significantly higher
for 1 than for 2.17 The calculated energy barriers for
the rotation of the Ind rings in 1 and 2 are ca. 16.0 and
10.1 kcal/mol, respectively; such a large difference be-
tween rotational energy barriers indicates that the Ind
ligand is significantly more distorted in 1 than in 2.18
In summary, the solid state structures of 1 and 3 show
a “sideways slippage” of Ni which has resulted in η5Tη3
distortions and a partial localization of bonding inside
the 1-Me-Ind ligand (η1,η2). In contrast, the η5Tη3
distortions found in the solid state structure of 4 are
symmetric, this difference arising from the different
trans influences of the ligands Cl and Me, i.e., Me ≈
PPh3 > Cl. In the case of the unsubstituted 1 and 2,
replacing Cl in 1 by Me effectively accelerates the rate
of rotation of the Ind ligand, presumably because of the
more symmetric coordination of the Ind ligand in 2. In
the absence of a solid state structure for 2, we have
relied on the similarities between the solid state struc-
tures and the NMR spectra of 1 and 3 on the one hand,
and the similarities in the NMR spectra of 2 and 4 on
the other, to argue that the solid state structure of 2
must be very similar to that of 4, and that in all
complexes the solid state Ind hapticity is maintained
in the solution. The direct correlation observed here
between structural and solution NMR data allow us to
In contrast to 1 and 2, the ground state C1 symmetry
of 3 and 4 is not affected by Ind rotations because the
unsymmetrically substituted 1-Me-Ind ligand is prochiral,
which renders 3 and 4 dissymmetric (chiral at the Ni
center) and their 1H NMR spectra independent of
temperature. In spite of this basic difference, pairwise
1
comparisons of the H NMR spectra of these complexes
(i.e., 1/3 and 2/4) are very informative in terms of the
solution hapticity of their Ind ligands. For example, the
H3 resonance in 3 at ambient temperature (3.37 ppm)
is very close to the corresponding resonance for 1 at 188
K (ca. 3.3 ppm); likewise, in 4, the H3 resonance at
ambient temperature (4.17 ppm) is very close to the
corresponding resonance for 2 at 188 K (ca. 4.1 ppm).
Hence, the solution hapticities of the Ind ligands in 1-4,
1
as reflected in their H NMR spectra, are pairwise very
similar.19
The above conclusion can also be reached from the
13C{1H} NMR data, which can be used for estimating
solution hapticities of Ind ligands according to the
formula ∆δavC ) δav(C3a,C7a of η-Ind) - δav(C3a,C7a
of Na+Ind-).8 The solution hapticity of the Ind ligand
is thought to be closer to η5 when ∆δavC , 0, closer to
η3 when ∆δavC . 0, and intermediate when ∆δavC ≈ 0.
The ∆δavC values for our complexes are ca. -2 ppm for
1 and 3 and ca. -10 ppm for 2 and 4, showing that, in
solution, as in the solid state, there is less slip-fold
distortion in the Ni-Me derivatives than in the Ni-Cl
1
use the H NMR resonances for the symmetry-related
pairs of protons (H1/H3, H4/H7, and H5/6) as a conve-
nient indicator of Ind hapticity. This is a very useful
tool not only for extracting solid state structural infor-
mation from solution spectra, but also for estimating
rotational energy barriers in the case of dissymmetric
complexes (e.g., 3 and 4), for which VT NMR spectros-
copy cannot be used to yield such data.
Exp er im en ta l Section
(16) Barr, R. D.; Green, M.; Marder, T. B.; Stone, F. G. A. J . Chem.
Soc., Dalton Trans. 1984, 1261.
(17) We have shown (ref 6g) that this dynamic process is not due to
phosphine exchange.
All manipulations and experiments were performed under
an inert atmosphere of nitrogen using standard Schlenk
techniques and/or in an argon-filled glovebox. Dry, oxygen-
free solvents were employed throughout. A Bruker AMX400
(18) The present results also provide further support for the notion
that solid state hapticities of Ind ligands correlate with their rotational
energy barriers. For example, the complexes 1 and Cp2Zr(µ-PPh2)2Rh-
(Ind) (ref 8) have similar energy barriers of 16.0 and 14.0 kcal/mol,
respectively, and exhibit similar solid state Ind hapticities evident from
∆M-C values of 0.26 and 0.23 Å, respectively. Moreover, complexes 2
and (1-Me-Ind)Rh(PMe3)2 (ref 9b) have similar energy barriers of 10.1
and 11.2 kcal/mol, respectively, and although the solid state hapticities
of these compounds are not known, their close analogues 4 and (Ind)-
Rh(PMe3)2 (ref 9b) have very similar ∆M-C values of 0.19 and 0.20
Å, respectively.
1
spectrometer was employed for recording H (400 MHz), 13C-
{1H} (100.56 MHz), and 31P{1H} (161.92 MHz) NMR spectra.
BuLi (2.5 M solution in hexanes), MeLi (1.4 M in Et2O), indene
(technical grade, distilled prior to use), PPh3, and MeI were
purchased from Aldrich and used as received. The preparation
of 1 and 2 has been reported elsewhere.6g
(1-Me-In d )Ni(P P h 3)Cl (3). An Et2O solution (100 mL) of
1-Me-IndLi (371 mg, 2.73 mmol) was added dropwise to a
stirring suspension of (PPh3)2NiCl2 (3.331 g, 5.09 mmol) in
Et2O (60 mL) at ambient temperature. The resultant dark
red mixture was stirred for approximately 15-30 min after
the addition, filtered, and evaporated to dryness. The residue
was washed with hexane (3 × ca. 20 mL) to remove PPh3 and
other byproducts and recrystallized from CH2Cl2/hexane at
-20 °C to give the product as a dark red solid (720 mg, 61%).
Recrystallization of a small portion of this solid from a cold
(19) Comparing 1H NMR chemical shifts for the protons in coordi-
nated Ind ligands and free indenes provides further support for the
assertion that solid state hapticities of the Ind ligands are largely
preserved in the solution. In 3, for example, the 1H resonances for H2
and H3 appear at ca. 6.3 and 3.4 ppm, respectively, compared to ca.
6.2 and 3.2 for the corresponding resonances in 3-alkylindenes which
have localized bonding in the five-membered ring. The similarity of
these shifts suggests that the partially localized, unsymmetric hapticity
of the Ind ligand observed in the solid state of 3 is largely preserved
in the solution.

Indenyl Hapticity and Rotational Barriers
Organometallics, Vol. 16, No. 26, 1997 5815
Et2O/hexane solution yielded crystals suitable for X-ray dif-
fraction studies and elemental analysis. 1H NMR (C6D6, 400
MHz): δ 7.63 (m, PPh3), 7.08 (t, J H-H ) 7.38 Hz, H6), 6.97 (m,
PPh3 and H7), 6.83 (t, J H-H ) 7.32 Hz, H5), 6.27 (br s, H2),
Ind-Me), -0.72 (d, J P-H ) 5.48 Hz, Ni-Me). 13C{1H} NMR
(C6D6, 100.56 MHz): δ 134.3 (d, J P-C ) 42.8 Hz, i-C), 133.8
(d, J P-C ) 11.9 Hz, o-C), 129.4 (p-C), 127.8 (d, J P-C ) ca. 9
Hz, m-C), 122.1 (C6), 122.0 (C5), 120.8 (C7a), 120.0 (C3a),
116.7 (C7), 115.9 (C4), 101.7 (C2), 89.0 (d, J P-C ) 12.5 Hz, C1),
74.5 (C3), 11.1 (Ind-Me), -16.8 (d, J P-C ) 22.9 Hz, Ni-Me).
6.06 (d, J H-H ) 7.8 Hz, H4), 3.37 (br s, H3), 1.54 (d, J P-H
)
5.49 Hz, Me). 13C {1H} NMR (acetone-d6, 100.56 MHz): δ
134.6 (d, J P-C ) 11.5 Hz, o-C), 132.6 (d, J P-C ) 44.1 Hz, i-C),
131.2 (p-C), 130.4 (C7a), 128.8 (d, J P-C ) ca. 10 Hz, m-C),
127.1 (C3a), 127.0 (C6), 126.8 (C5), 118.7 (C7), 117.6 (C4),
107.5 (C2), 103.4 (d, J P-C ) 14.8 Hz, C1), 67.2 (C3), 12.7 (Me).
31P {1H} NMR (C6D6, 162 MHz): δ 31.1 (s). Anal. Calcd for
31P NMR (C6D6, 162 MHz): δ 47.7 (s). Anal. Calcd for C29H27
-
NiP: C, 75.20; H, 5.87. Found: C, 74.49; H, 5.80.
Ack n ow led gm en t . We are grateful to NSERC
(Canada), FCAR (Que´bec), and Universite´ de Montre´al
for financial support, Prof. K. Caulton for valuable
discussions, and Profs. R. G. Bergman and R. A.
Andersen and Dr. P. L. Holland for sending us a copy
of their unpublished manuscript.
C
28H24NiPCl: C, 69.25; H, 4.98. Found: C, 68.56; H, 5.45.
(1-Me-In d )Ni(P P h 3)Me (4). MeLi (1.4 M solution in Et2O,
1.40 mL, 1.96 mmol) was added dropwise to an Et2O (65 mL)
solution of 3 (942 mg, 1.94 mmol) at 0 °C, and the mixture
was stirred for 1 h, filtered, and evaporated to dryness. The
residue was crystallized from a cold Et2O/hexane solution to
give the product as a green-brown solid (573 mg, 63%).
Recrystallization of a portion of this solid from Et2O/hexane
yielded crystals suitable for X-ray diffraction studies and
elemental analysis. 1H NMR (C6D6, 400 MHz): δ 7.31 (m,
PPh3), 7.22 (br, H5 or H6), 7.20 (br, H7 and H5 or H6), 6.99
(m, PPh3), 6.47 (d, J H-H ) 7.8 Hz, H4), 6.22 (d, J H-H ) 2.92
Hz, H2), 4.17 (t, J H-H ) 2.34 Hz, H3), 1.89 (d, J P-H ) 3.92 Hz,
Su p p or tin g In for m a tion Ava ila ble: Complete details on
the X-ray analyses of 3 and 4 and VT 1H NMR data used in
calculating the energy barrier for the rotation of the Ind in 2
(44 pages). Ordering information and Internet access instruc-
tions are given on any current masthead page.
OM970715J