LIGAND-INDUCED FRAGMENTATION OF METHYLNICKEL PHENOLATES CONTAINING A 2-ALDEHYDE FUNCTION - STRUCTURE OF YL-5-METHYL-2-OXOBENZOYL)-TRIS(TRIMETHYLPHOSPHINE) NICKEL

O-bridging salicylaldehyde derivatives in dimeric methylnickel compoun ds NiMe(OR)(PMe3) showing equilibria of cis and trans forms (OR = 2-ox obenzaldehyde (1), 3-tert-butyl-5-methyl-2-oxobenzaldehyde (2), 3,5-di -tert-butyl-2-oxobenzaldehyde (3), 2-oxonaphthaldehyde (4)) spontaneou sly undergo, upon addition of trimethylphosphine, a fragmentation reac tion forming 2-oxobenzoyl-C,O chelating ligands in 18-electron mononuc lear complexes Ni(OC=O)(PMe3)3 (OC=O = 2-oxobenzoYl (5), 3-tert-butyl- 5-methyl-2-oxobenzoyl (6), 3,5-di-tert-butyl-2-oxobenzoYl (7), 2-oxona phthoyl (8)). The molecular structure of 6 contains pentacoordinate ni ckel with a chelate bite angle C-Ni-O = 85.5(1)-degrees. Dissociation of phosphine ligands in 5 gives Ni(OC=O)(PMe3)2 (9) and [Ni(OC)(PMe3)] 2 (10), but no mobilization of carbonyl ligands could be observed in t he presence of Ni(PMe3)4 as CO acceptor.