Organometallics 1996, 14, 1087-1088
1087
Formation of Indenyl Dihydride Complexes from an Iridium Polyhydride Complex: Molecular Structures of (q6-C9H7)IrH2(PPr'3) and the q3-IndenylIntermediate ( q3-C9H7)IrH2(PPri3)2 Trang Le Husebo and Craig M. Jensen" Department of Chemistry, University of Hawaii, Honolulu, Hawaii 96822 Received November 21, 1994@ Summary: The reaction of IrHs(PP&h and indene at 60 "C leads to the formation of (q3-C&17)IrHdPP&& and (v5-C&17)IrHdPPrQ. The molecular structures of these products have been determined by single crystal X-ray difiaction studies. The $-indeny1 complex is stable only in the solid state and converts to the y5-indenyl complex product upon dissolution. Recently, Jones reported that the polyhydride complex ReH~(PPh312 reacts with indene to produce hydrido v5indenyl and v5-indanyl complexes.' We have found that the iridium polyhydride complex IrHs(PPr'3)z (1) also reacts with indene to produce a hydrido v5-indenyl complex. However, unlike the rhenium system, a hydrido q3-indenyl complex is also obtained. We wish to report the synthesis and molecular structures of the iridium indenyl hydride complexes. The title complexes are obtained in major yield upon heating 1 (0.600 g, 1.2 mmol) with excess indene (2.7 mL, 23 mmol) in benzene (50 mL) at 60 "C for 4 days as seen in Scheme 1. Recrystallization of the crude reaction mixture from pentane gave rise to a mixture of distinctively different, red crystals of (v3-CgH7)IrHz(PPri3)z(2) and orange crystals of (7;15-CgH7)IrH~(PPri3) (3). Both types of crystals were suitable for X-ray difiaction. Diagrams of the determined molecular structures2 and selected bond distances for the compounds are presented in Figures 1and 2, respectively. Although the hydride ligands could not be reliably located, their position can be inferred from the observed molecular geometries. The presence of the hydride ligands was confirmed through solid state infrared spectroscopy of KBr pellets of the complexes. Ir-H stretches were observed at 2213 and 2174 cm-l for 2 and at 2230 and 2159 cm-l for 3. The structures determined for 2 and 3 allow the comparison of a pair of highly related q3- and q5coordinated indenyl complexes. The q3-indenyl ligand of 2 is coordinated in an v3-allyl fashion, as the Ir-C(2) bond length is significantly shorter than the Ir-C(l) and Ir-C(3) bond distances. Similar coordination was found Abstract published in Advance ACS Abstracts, February 15,1995. (l)Rosini, G. P.; Jones, W. D. J. Am. Chem. SOC.1993,115, 965. (2)(a) Crystallographic data for 2: monoclinic, P21/n, 2 = 8 (2 symmetry-independentmolecules of 2 er asymmetric unit), a = 8.515(8) A, b = 34.73(2) A, c = 19.044(11) 8, = 91.45(4)",V = 5630(5) A3, gcalc= 1.479 g/cm3;Nicolet P3 difii-actometer, Mo Ka radiation ( I = 0.710 73 A); 6099 independent reflections with 4" < 28 < 40" collected, 5310 reflections used in refinement with I > 3 d 0 ; R = 0.047, R, = 0.057, GOF = 1.62. T w o of the carbons of one of the symmetryindependent molecules of 2 could not be refined anisotropically. (b) Crystallographic data for 3: triclinic, P1, 2 = 4 (2 symmet independent molecules of 3 per asymmetric per unit), a = 9.355(2)3, b = 14.012(3) A, c = 15.535(3) A, a = 63.45(3)",,8 = 89.20(3Y', y = 88.49(3)"= 1821.0(7)A3,g d c= 1.705 g/cm3;Nicolet P3 difiactameter, Mo Ka radiation (I = 0.71073 A); 3689 independent reflections with 3" < 28 < 40" collected, 3408 reflections used in refinement with I > 3130; R = 0.028, R, = 0.037, GOF = 1.24. @
dI
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0276-7333l95/2314-1087$09.0Ol0
Figure 1. Projection of (v3-CgH7)IrHz(PPri3)~ (2)with the thermal ellipsoids at 50% probability. Selected bond lengths (A): Ir(l)-C(l) = 2.266(2), Ir(l)-C(2) = 2.121(3),Ir(1)C(3) = 2.286(2). The hydrogen atoms have been omitted for clarity. Scheme 1 IrH5(PPri3)2 1
+
xs Indene
6OoC c6%
-
+
-
2
3
by Merola for the q3-indenyl ligand of (q3-CgH7)Ir(PM~s)~ The . ~ q5-coordination of the five-membered indenyl ring of 3 entails extensive ring slippage, as depicted in Figure 3. The Ir-C bonds involving the carbons also contained in the six-membered ring are pronouncedly lengthened. This is similar to the bonding situation found4 for [(v5-CgH7)IrH(PPh3)z1+.However, unlike the case for the monohydride complex, the hydride trans influence in 3 also results in a significant lengthening of the Ir(l)-C(3) bond. The observed orientation of the indenyl and phosphine ligands in 3 is not in accordance with the general trends (3) Merola, J. S.;Kacmarcik, R. T.; Van Engen, D. J.Am. Chem. SOC.1988,108,329.
0 1995 American Chemical Society
Communications
1088 Organometallics, Vol. 14, No. 3, 1995 Scheme 2
- PPr',
2
Figure 2. Projection of (q5-CgH,)IrHz(PPri3)(3) with the thermal ellipsoids at 50%probability. Selected bond lengths (A): Ir(1)-C(1) = 2.249(1),Ir(l)-C(2) = 2.244(1), Ir(1)C(3) = 2.304(1), Ir(l)-C(4) = 2.399(1), Ir(l)-C(9) = 2.380(1).The hydrogen atoms have been omitted for clarity. CIS1
P(1)
C(61
Cl21
C(8)
Figure 3. Projection of (q5-C9H,)IrH~(PPri3) (3) along the plane normal to the five-membered ring.
Expected
Observed
Figure 4. Schematic drawings of the expected and observed conformations of (q5-CgH7)IrH2(PPri3) (3). in the conformations of indenyl complexes outlined by Faller and C~-abtree.~ In view of the relative trans influence of hydride and phosphine ligands, the conformation illustrated in Figure 4, in which the phosphine eclipses the indenyl ligand and the hydrides are transoid t o the indenyl ligand, would be expected. As seen in Figure 3, the phosphine is found instead to be in a staggered orientation with regard to the indenyl ligand. Apparently, steric factors prevent 3 from assuming the electronically preferred conformation. In contrast to the case for the solid state, only one complex and free triisopropylphosphine are detected by 'H, 13C, and 31P NMR spectroscopy of the product mixture dissolved in cD~C12.~ The observed complex is readily identified as 3. The doublet resonance observed in the lH NMR spectrum for the hydride ligands at -21.9 ppm (JP-H= 26.0 Hz) establishes the monophosphine formulation, and the resonances observed for the (4) Faller, J. W.; Crabtree, R. H.; Habib, A. Organometallics 1986, 4, 929.
H
3
y5-indenyl ligand are very similar to those reported by Bergman for (y5-CsH7)IrHz(PMe3).6We do not observe any of the resonances which Merola has shown to be diagnostic of an iridium q3-indenyl complex3 or additional resonances in the hydride region. Infrared spectroscopy of the product mixture dissolved in pentane confirms that a single dihydride complex is present in solution, as only two Ir-H stretches are observed a t 2221 and 2142 cm-l. We conclude that 2 undergoes loss of phosphine and conversion to 3 as seen in Scheme 2 upon dissolution. Attempts to reverse this process by addition of excess triisopropylphosphine led instead to a complicated mixture of unidentified products. The microreverse of the process in Scheme 2, ring slippage followed by capture of a coordination site by an incoming ligand, has often been proposed to occur in the reactions of rhodium and iridium hydrido complexes containing q5-aromatic ligands. For example, Jones has proposed that such sequences occur during the displacement of CsMesH from (q5-C5Me5)RhHz(PMe& (4) by PMe3.7 Previous structural characterizations of q3-indenyl complexes3s8have lent support for such mechanisms. Our results provide more direct evidence for y3-indenyl intermediates in the reactions of rhodium and iridium hydrido complexes containing y5-aromatic ligands. Moreover, these results illustrate that the energetically preferred distribution of complexes containing y5- and y3-bonded aromatic ligands can be drastically different in solution than in the solid state.
Acknowledgment. The support of this research by the U.S. Department of Energy Hydrogen Program is gratefully acknowledged. Supplementary Material Available: Tables of crystal data, atomic positions, anisotropicthermal parameters, bond distances,bond angles, and hydrogen atom coordinates for (v3CgH7)IrH2(PPri&(2) and (v5-C9H,)IrH2(PPri3)(3)(12 pages). Ordering information is given on any current masthead page. OM9408876
27.9 (d, Jc-p = 31.5 Hz),20.0 (6). (6)Foo, T.; Bergman, R. G. organometallics 1992,11, 1801. (7) Jones, W. D.; Kuydendal,V. L.;Selmeczy, A. D.Organometallics 1991,10, 1577. (8)O'Connor. J. M.; Casev, C. P. Chem. Rev. 1987,87,307 and references therein.
