Substitution and Hydrogenation Reactions on Rhodium(I)-Ethylene Complexes of the Hydrotris(pyrazolyl)borate Ligands Tp′ (Tp′ ) Tp, Tp Me2 ) ² M. Carmen Nicasio, ‡,§ Margarita Paneque,* ,‡ Pedro J. Pe ´ rez, ‡,§ Antonio Pizzano, ‡ Manuel L. Poveda,* ,‡ Luis Rey, ‡ Sabine Sirol, ‡ Soraya Taboada, ‡,| Marianela Trujillo, ‡ Angeles Monge, ⊥ Caridad Ruiz, ⊥ and Ernesto Carmona* ,‡ Instituto de Investigaciones Quı ´micas, Departamento de Quı ´mica Inorga ´nica, Consejo Superior de Investigaciones Cientı ´ficas, Universidad de Sevilla, Avda. Ame ´rico Vespucio s/n, Isla de la Cartuja, 41092 Sevilla, Spain, and Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientı ´ficas, Campus de Cantoblanco, 28049 Madrid, Spain ReceiVed April 16, 1999 The bis(ethylene) Rh species Tp Me2 Rh(C 2 H 4 ) 2 (1*) (Tp Me2 ) tris(3,5-dimethyl-1-pyrazol-1-yl)hydroborate) has been obtained from [RhCl(C 2 H 4 ) 2 ] 2 and KTp Me2 . Complex 1* easily decomposes in solution to give mainly the butadiene species Tp Me2 Rh(η 4 -C 4 H 6 ). In the solid state its thermal decomposition follows a different course and the allyl Tp Me2 RhH(syn-C 3 H 4 Me) is cleanly obtained as a mixture of exo and endo isomers. The complexes Tp′Rh- (C 2 H 4 ) 2 (Tp′ ) Tp, Tp Me2 ) afford the monosubstituted species Tp′Rh(C 2 H 4 )(PR 3 ) upon reaction with PR 3 but react differently with L ) CO or CNR: the Tp compound gives dinuclear [TpRh] 2 (µ-L) 3 complexes, while, in the case of 1*, Tp Me2 Rh(C 2 H 4 )(L) species are obtained. The ethylene ligand of complexes Tp Me2 Rh(C 2 H 4 )(PR 3 ) is labile, and several peroxo compounds of composition Tp Me2 Rh(O 2 )(PR 3 ) have been isolated by their reaction with O 2 . All the mononuclear Rh(I) complexes are formulated as 18e - trigonal bipyramidal species on the basis of IR and NMR spectroscopic studies. A series of dihydride complexes of Rh(III) of formulation Tp′RhH 2 (PR 3 ) have been prepared by the hydrogenation of the corresponding ethylene derivatives. Complexes [TpRh] 2 (µ-CNCy) 3 , Tp Me2 Rh(C 2 H 4 )(PEt 3 ), and Tp Me2 Rh(O 2 )(PEt 3 ) have been further characterized by X-ray diffraction studies. Introduction The hydrotris(pyrazolyl)borate anions, Tp′, have become very useful and versatile ligands in transition metal coordination and organometallic chemistry. 1-3 Despite their consideration as cyclopentadienyl analogues, their complexes with transition elements often exhibit unusual reactivity patterns, which in many instances find no precedent in the related Cp′ systems. In recent years, a number of studies on complexes of these ligands with the G9 elements, particularly Rh and Ir, have become available.Whereas in the oxidation state III the κ 3 binding mode is the commonest by far, both bidentate and tridentate coordination can be encountered in Rh(I) and Ir(I) complexes. The propensity of Rh(I) to adopt a square-planar geometry explains the relative abundance of the κ 2 -Tp′ coor- dination mode in compounds of composition Tp′RhL 2 4-15 and also the frequent observation of the κ 2 -κ 3 isomerism of the ligand. 4,5,16,17 For Ir(I), tridentate coordination appears to prevail but the steric effects associated with the pyrazolyl substituents may have an important influence on the hapticity of the ligand. 14,18-21 Another issue of interest in connection with this kind of complex concerns the relative stability of oxidation states I and III, notably in connection with the C-H bond activation of the ethylene ligand in Tp′M I -C 2 H 4 complexes. 22 In contrast with the Cp′ analogues, η 2 -ethene derivatives of Tp′Ir I systems are ² This paper is dedicated to Prof. Rene ´ Poilblanc on the occasion of his retirement. ‡ Instituto de Investigaciones Quı ´micas, Departamento de Quı ´mica Inorga ´nica, Sevilla, Spain. § Present address: Departamento de Quı ´mica y Ciencia de los Materiales, Universidad de Huelva, 21819 Palos de la Frontera, Huelva, Spain. | Present address: Universidad Central de Venezuela, Caracas, Venezuela. ⊥ Instituto de Ciencia de Materiales de Madrid. (1) Trofimenko, S. Chem. ReV. 1993, 93, 943. (2) Parkin, G. AdV. Inorg. Chem. 1995, 42, 291. (3) Kitajima, N.; Tolman, W. B. Prog. Inorg. Chem. 1995, 43, 418. (4) Akita, M.; Ohta, K.; Takahasi, Y.; Hikichi, S.; Moro-oka, Y. Organometallics 1997, 16, 4121. (5) Northcutt, T. O.; Lachicotte, R. J.; Jones, W. D. Organometallics 1998, 17, 5148. (6) Wick, D. D.; Northcutt, T. O.; Lachicotte, R. J.; Jones, W. D. Organometallics 1998, 17, 4484. (7) Jones, W. D.; Hessell, E. T. Inorg. Chem. 1991, 30, 778. (8) Jones, W. D.; Hessell, E. T. J. Am. Chem. Soc. 1992, 114, 6087. (9) Chauby, V.; Serra Le Berre, C.; Kalck, Ph.; Daran, J.-C.; Commenges, G. Inorg. Chem. 1996, 35, 6354. (10) Connelly, N. G.; Emslie, D. J. H.; Metz, B.; Orpen, A. G.; Quayle, M. J. J. Chem. Soc., Chem. Commun. 1996, 2289. (11) Hill, A. F.; White, A. J. P.; Williams, D. J.; Wilton-Ely, J. D. E. T. Organometallics 1998, 17, 3152. (12) Gosh, C. K.; Graham, W. A. G. J. Am. Chem. Soc. 1987, 109, 4726. (13) Ghosh, C. K.; Graham, W. A. G. J. Am. Chem. Soc. 1989, 111, 375. (14) Oldham, W. J., Jr.; Heinekey, D. M. Organometallics 1997, 16, 467. (15) Oldham, W. J., Jr.; Hinkley, A. S.; Heinekey, D. M. J. Am. Chem. Soc. 1997, 119, 11028. (16) Bucher, U. E.; Currao, A.; Nesper, R.; Ru ¨egger, H.; Venanzi, L. M.; Younger, E. Inorg. Chem. 1995, 34, 66. (17) Sanz, D.; Santamarı ´a, M. D.; Claramunt, R. M.; Cano, M.; Heras, J. V.; Campo, J. A.; Ruiz, F. A.; Pinilla, E.; Monge, A. J. Organomet. Chem. 1996, 526, 341. (18) Alvarado, Y.; Boutry, O.; Gutie ´rrez, E.; Monge, A.; Nicasio, M. C.; Pe ´rez, P. J.; Poveda, M. L.; Ruiz, C.; Bianchini, C.; Carmona, E. Chem. Eur. J. 1997, 3, 860. (19) Gutie ´rrez-Puebla, E.; Monge, A.; Nicasio, M. C.; Pe ´rez, P. J.; Poveda, M. L.; Rey, L.; Ruiz, C.; Carmona, E. Inorg. Chem. 1998, 37, 4538. (20) Ciriano, M. A.; Ferna ´ndez, M. J.; Modrego, J.; Rodrı ´guez, M. J.; Oro, L. A. J. Organomet. Chem. 1993, 443, 249. (21) Bovens, M.; Gerfin, T.; Gramlich, V.; Petter, W.; Venanzi, M. L.; Haward, M. T.; Jackson, S. A.; Eisenstein, O. New J. Chem. 1992, 16, 337. 180 Inorg. Chem. 2000, 39, 180-188 10.1021/ic990419u CCC: $19.00 © 2000 American Chemical Society Published on Web 12/23/1999