LIGAND EFFECTS ON THE CHEMOSELECTIVITY OF ORTHO-METALATED RHODIUM(II)CATALYZED ALPHA-DIAZO KETONE TRANSFORMATIONS

Rh-2(OOCR)(2)(PC)(2) complexes (PC = orthometalated phosphines, OOCR = carboxylates) with very polarizable ligands, such as aromatic rings d irectly joined to the rhodium atoms, control chemoselectivity in compe titive metal carbene transformations of cc-diazo ketones. These cataly sts have a mixed set of ligands that allows choosing among a big selec tion of ligands to gradually affect the electronic and steric properti es of the catalyst. Their selectivity depends on the electrophilicity of the ligands and the polarizability of the metalated aromatic rings. Thus, Rh-2(OOCR)(2)(PC)(2) compounds [PC = (C6H4)P(CH3)(C6H5), (p-CH3 C6H3)P(pCH(3)C(6)H(4))(2), (C6H4)P(C6H5)(2); R = C3F7 or CF3] exhibit an exceptional selectivity for aliphatic C-H insertion over aromatic s ubstitution in catalytic decomposition of 1-diazo-5-methyl-3-phenyl-2- hexanone. Results obtained from these complexes in competitive intramo lecular cyclopropanation versus tertiary C-H insertion, cyclopropanati on versus aromatic substitution, and C-H insertion versus aromatic sub stitution are compared with those obtained for other rhodium(II) compo unds, such as rhodium(II) caprolactamate (Rh-2(cap)(4)), rhodium(II) p erfluorobutyrate, and rhodium(II) acetate.