Substitution and hydrogenation reactions on rhodium(I)-ethylene complexes of the hydrotris(pyrazolyl)borate ligands Tp ' (Tp ' = Tp, Tp(Me2))

The bis(ethylene) Rh species Tp(Me2)Rh(C2H4)(2) (1*) (Tp(Me2) = tris(3,5-di methyl-1-pyrazol-1-yl)hydroborate) has been obtained from [RhCl(C2H4)(2)](2 ) and KTp(Me2). Complex 1* easily decomposes in solution to give mainly the butadiene species Tp(Me2)-Rh(eta(4)-C4H6). In the solid state its thermal decomposition follows a different course and the allyl Tp(Me2)RhH(syn-C3H4M e) is cleanly obtained as a mixture of exo and endo isomers. The complexes Tp'Rh(C2H4)(2) (Tp' = Tp, Tp(Me2)) afford the monosubstituted species Tp'Rh (C2H4)(PR3) upon reaction with PR3 but react differently with L = CO or CNR : the Tp compound gives dinuclear [TpRh](2)(mu-L)(3) complexes, while, in t he case of 1*, Tp(Me2)Rh(C2H4)(L) species are obtained. The ethylene ligand of complexes Tp(Me2)Rh(C2H4)(PR3) is labile, and several peroxo compounds of composition Tp(Me2)Rh(O-2)(PR3) have been isolated by their reaction wit h 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. s eries of dihydride complexes of Rh(III) of formulation Tp'RhH2(PR3) have be en prepared by the hydrogenation of the corresponding ethylene derivatives. Complexes [TpRh](2)(mu-CNCy)(3), Tp(Me2)Rh(C2H4)(PEt3), and Tp(Me2)-Rh(O-2 )(PEt3) have been further characterized by X-ray diffraction studies.