4997
Organometallics 1996,14, 4997-4999
Preparation and Characterization of [(q-indenyl)Ni(PPhs) Cl]+ Trisha A. Huber, Francine BBlanger-GariBpy, and Davit Zargarian" Departement de chimie, Universite de Montreal, Montrial (Quebec), Canada H3C 3J7 Received July 21, 1995@ Summary: The complex [(rpin&enyl)Ni(PPhdCll has been synthesized and characterized by single-crystal X-ray 13C, 31P)spectroscopy. structural analysis and NMR (IH, The energy barrier to indenyl ring rotation is ca. 16 kcall mol. Although p I n d complexes (Ind = indenyl or its substituted derivatives) of many transition metals are known to display enhanced reactivities in various stoichiometric and catalytic reactions compared t o their q-Cp analogues,l the chemistry of group 10 metal indenyl complexes remains virtually unexplored. We are studying this class of compounds and report herein the preparation and characterization of (q-Ind)Ni(PPh& C1, along with a discussion of the solution- and solidstate hapticity of the Ind ligand. The reaction of IndLi with (PPh312NiC12 (1) results in a mixture of the title compound (r-Ind)Ni(PPhs)Cl (21, the Ni(1) species (PPh3)3NiCI(31,and 1,l'-biindene (eq 1). The relative proportions of these species in the IndLi 1 - 2 + 3 + 1,l'-biindene
final reaction mixture vary with the reaction scale, temperature, solvent, concentration, and rate of addition of IndLi. Preliminary studies of the effects of these variables have allowed us to optimize the conditions for the formation of 2, which can be prepared in 40-60% yield by the dropwise addition of a dilute Et20 solution of IndLi to a suspension of 1 in Et20 at room temperature. Even under these conditions, however, the byproducts 3 and 1,l'-biindene form in small amounts. We propose that 2, 3,and 1,l'-biindene originate from the common intermediate (y1-Ind)Ni(PPh3)2C1via two competing pathways (Scheme 1): loss of a PPh3 and concomitant indenyl ring slippage gives 2, whereas reaction with a second equivalent of IndLi, followed by reductive elimination, produces 1,l'-biindene and Ni(PPh3),; the latter is known2 to undergo a disproportionation reaction with 1 to give 3. Complex 33 and 1,l'-biindene4 are known species and were identified on the basis of comparisons to literature data; complex 2 is a new compound and has been fully + Dedicated to Prof. Stephen Hanessian on the occasion of his 60th birthday. Abstract published in Aduance ACS Abstracts, October 1, 1995. (1)Westcott, S. A.; Kakkar, A. K.; Stringer, G.; Taylor, N. J.;Marder, T. B. J. Organomet. Chem. 1990,394, 777. (2) D'hiello, M. J.;Barefield, K. J.Am. Chem. Soc. 1978,100,1474. (3) Mealli, C.; Dapporto, P.; Sriyunyongwat, V.; Albright, T. A. Acta Crystallogr. 1983,C39, 995. (4) Nicolet, P.; Sanchez, J.-Y.; Benaboura, A.; Abadie, M. J. M. Synthesis 1987,202. @
0276-7333/95/2314-4997$09.00/0
Scheme 1 IndLi
1
- - - .- - - +
(q'-Ind)Ni(PPhz)zC1 IndLi
- PPh3
-------- -
2
j
t (ql-Ind) ,Ni(PPh,), PPh3
1 !---* Ni(PPh3), .---+ 3
? 1,I'-biindene
characterized by X-ray crystallography5and NMR spectroscopy.6 Inspection of C-C and Ni-C bond distances (Figure 1) reveals that (a) Cl-C7a and C3-C3a =- C1C2 and C2-C3, (b) Ni-C3a,7a > Ni-C(1-3), and (c) Ni-C1 > Ni-C2 > Ni-C3 and Ni-C7a > Ni-C3a. Therefore, the hapticity of the Ind ligand is significantly distorted away from an idealized v5 mode toward an unsymmetrical v3 mode (vide infra). The main parameters for measuring the degree of hapticity distortions in pInd complexes are (a) hinge and fold angles (HA and FA) representing the bending of the Ind ligand a t C1/C3 and C3a/C7a, respectively, and (b) the slip value represented by AM-C = [M-Cadfor C3a,7a)l- [M-C,(for Cl,3)I.l In complex 2, HA = 10.9', FA = 11.7', and AM-C = 0.26 A. The only other structurally characterized q-Ind nickel complex is Ni(Ind)z, for which HA and FA are ca. 13-14' for both Ind ligands and AM-C = 0.42 A.1 Evidently, the slip-fold distortion toward an v3 mode is more pronounced in Ni(Ind)z, presumably because fully q6-Indligands would lead t o a 20-electron configuration in this complex but only an 18-electron configuration in complex 2. (5) Red crystals of 2 were grown from an EtzOhexane solution a t -20 "C. Crystallopa hic data for NiClPC27Hzz (M = 471.60): triclinic pi, a = 9.7128(10) b = 10.046(2) A, c = 13.098(2) A, a = 88.530(lo)", 5,' = 85.420(10)", y = 66.010(10Y, V = 1099.2 A3, 2 = 2, ~ ( C U Ka) = 3.18 mm-I, 1 = 1.540 56 A, 28" = 140.0", T = 230 K, 8193 reflections measured using the w/20 scan mode (Aw = (0.80 0.14 tan 0)"; 4164 independent, 3753 observed), refinement by blockdiagonal least squares gave RF = 0.0363 and R, = 0.0396. The ORTEP diamam is shown in Fieure 1 alone with Dertinent bond distances. (6) 'H NMR (6; tolu&e-ds): 2 9 l K , 7.64 (m, PPhs), 7.33 (br, H4/ H7), 7.0 (m, PPh3 and H5/H6), 6.45 (t, J e 3 Hz, H2), 6.15 (br, H4/ H7), 5.9 (br, Hl), 3.3 (br, H3); 380 K, 7.65 and 7.05 (br, PPhd, 6.86 (br, H5 and H6), 6.66 (br, H4 and H7), 6.48 (br, H2), 4.57 (br, H1 & H3); 220 K, 7.55 (m, PPh3), 7.41 (d, J = 7.8, H4/H7), 7.16 (t, J = 7.6, H5/H6), 6.9 (br, PPh3 and H5/H6), 6.44 (t, J = 3, H2), 6.04 (d, J = 8.2, H4/H7), 5.94 (br, Hl), 3.20 (br, H3); 183 K, 7.5 (br, PPh3 and H4/H7), 7.22 and 6.95 (t, J 7.5, H5 and H6), 6.9 (br, PPh& 6.44 (t, J = 3, H2), 6.0 (br, H1 and H4/H7), 3.15 (br, H3). 13C{1H}NMR (6; toluene&, 233 K): 134.5 (d, J = 11.4, 0-C of PPhs), 132.4 Ni-C3; vide supra),12which C1 = 2.094(2),Ni-C2 = 2.061(2),Ni-C3 = 2.042(2),Niis caused by a large difference between the ligand trans C3a = 2.318(2), Ni-C7a = 2.344(2), Cl-C2 = 1.399(4), effects of PPh3 and C1-. Thus, the Ni-C3 interaction C2-C3 = 1.417(4),C3-C3a = 1.449(3),C3a-C7a = 1.422(3), C7a-C1 = 1.459(3), C3a-C4 = 1.394(3),C4-C5 = can be viewed as stronger and more a-like, in contrast 1.382(4),C5-C6 = 1.381(5),C6-C7 = 1.385(4),C7-C7a to a weaker, n-type interaction between Ni and Cl-C2 = 1.398(4). (A in Chart 1). This picture of a partially localized bonding would require that C1 and C3 be quite different The ambient-temperature lH and 13C{lH} NMR specin terms of hybridization, which would explain the tra of complex 2 consist of both sharp and broad rather large chemical shift differences in the slowresonances which have been assigned by means of exchange regime between C 1 and C3 0 2 ' ( ppm) and inverse gated decoupling and low-temperature heteroH1 and H3 (>2.9 ppm).13 nuclear correlation through multiple quantum coherRelative ligand trans effects are known to influence ence (HMQC)experiments.6 NMR data are valuable in the conformation of r-Ind complexes,14but their effect assessing indenyl hapticity; for instance, the difference on the hapticity of the Ind ligand is unknown. If the in the 13C chemical shifts of the ring-junction carbons large trans effect difference between PPh3 and C1- in 2 in V-Ind complexes and NaInd has been shown to does distort the Ni-Ind bonding toward a localized ql: correlate well with the 7-Ind h a p t i ~ i t y .For ~ complex 2 r , 9 mode, replacing the C1- ligand by a stronger trans at 233 K, AdaV(C3a/C7a) -3, indicating7 that the effect ligand should reduce this distortion. We have intermediate hapticity of the Ind ligand observed in the prepared (r,~Ind)Ni(PPh3)Me'~ and note that its ambisolid state is maintained in solution a t ca. -40 "C. For lH NMR spectrum contains a single ent-temperature comparison, Ada,(C3a/C7a) is -43.7 for Fe($-Ind)z,' resonance for H1 and H3 at 4.76 ppm, very similar t o +3.6 for Ni(Ind)z,l and +25.7 for (~~-Ind)Ir(PMezPh)3.~ the coalesced signal for Hl/H3, which resonates at ca. The variable-temperature lH NMR spectra for com4.6 ppm in the high-temperature spectrum of complex plex 26show that gradually increasing the temperature 2. Apparently, the smaller difference between the trans causes the six broad resonances present in the ambienteffects of PPh3 and Me- leads to a more symmetrical, temperature spectrum to disappear into the base line delocalized Ni-Ind bonding (Bin Chart 1)and conseand reappear as three coalesced resonances; lowering quently a smaller rotational barrier in the Ni-Me the temperature sharpens the broad resonances and derivative. These observations are consistent with our changes their chemical shifts. These results point t o proposal that at low temperatures the Ind ligand in the hindered rotation of the Ind ligand as the cause of complex 2 coordinates in a partially localized fashion. the resonance broadening observed in the ambientThis aspect of Ni-Ind bonding and the factors affecting temperature lH and 13C{lH} NMR ~ p e c t r a .Using ~ the Eyring equation for a two-site exchange process involv( l l ) ( a )Barr, R. D.; Green, M.; Marder, T. B.; Stone, F. G. A. J. ing a molecualr rotation,1° an average AG*T,value of ~~
(7) Baker, R. T.; Tulip, T. H. Organometallics 1986, 5 , 839-845. According to this procedure, when the average chemical shift of C3a/ C7a in the q-Ind complex is significantly upfield or downfield of the corresponding shift in NaInd, the Ind ligand is thought to be coordinated in a q5 or q3 fashion, respectively; if, on the other hand, the two shifts are not very different, an intermediate hapticity is assumed. (8) Merola, J . S.; Kacmarcik, R. T.; Van Engen, D. J. Am. Chem. SOC.1986, 108, 329. (9) The absence of a plane of symmetry in complex 2 means that rapid ring rotation is required in order for the halves of the Ind ligand (on either side of the plane containing C2 and the midpoints of C3aC7a and C5-C6) to appear equivalent in solution NMR spectra. If this rotation is slow on the NMR time scale, some broadening might be expected below the coalescence temperature. (10)Abraham, R. J.; LoRus, P. Proton and Carbon-13 NMR Spectroscopy; Wiley: New York, 1985; Chapter 7, pp 165-168, eq. 7.11. AG*IRT, = 22.96 + ln(T,/dv).
Chem. Soc., Dalton Trans. 1984, 1261. (b) Marder, T. B.; Calabrese, J. C.; Roe, D. C.; Tulip, T. H. Organometallics 1987, 6, 2012. (12) (a) A reviewer has suggested that the mechanism of the indenyl rotation might involve an (q1:q2)to 7' change of hapticity and, thus, the large energy barrier might imply that Cl=C2 is strongly coordinated to Ni. We agree with this possibility and have in fact put forth a similar scenario in an earlier presentation,lZbbut no evidence exists in support of these ideas. (b) Huber, T. A.; Zargarian, D. Late Metal IndenyUAmidoComplexes. CIC 78th CSC Annual Conference, Guelph, Ontario, Canada, May 28-June 1 1995; Abstract 959. (13) That these chemical shift differences are not due to the ring current effects of the PPh3 phenyl groups is supported by the observation that, in the PMe3 analogue of 2, in which no ring current effect can be invoked, a similar difference is observed, i.e. AS(Hl,H3) > 2.1 PPm). (14)(a) Faller, J. W.; Crabtree, R. H.; Habib, A. Organometallics 1985,4, 929. (b) Husebo, T. L.; Jensen, C. M. Organometallics 1995, 14, 1087. (15) Huber, T. A,; Dion, S.; Zargarian, D. Unpublished results.
Organometallics, Vol. 14, No. 11, 1995 4999
Communications
it will be probed further by studying the hapticities of analogous (rp1nd)NiLXcomplexes.
Acknowledgment. We thank the NSERC (Canada), the F C m (Qu6bec),and the Uiversite de Montreal for financial ~ o f e s s o r M. s J. ~ ~ G landi T, ~ B. Marder for valuable discussions and constructive criticisms, and S. Dion, I. Dubuc. and A. Gamon for contributions to our studies.
Supporting Information Available: Text giving procedures for the syntheses of complex 2 and its PMe3 and Me analogues, NMR data for 2, a . figures giving lH,13C, and 31P table giving the elemental analysis of2, and complete details on the X-ray analysis of 2, including tables of bond distances ~ and h angles, ~ ~ anisotropic thermal parameters, and atomic coordinates (39 pages). Ordering information is given on any current masthead page.
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OM9505571
