Carbon-oxygen bond formation at metal(IV) centers: Reactivity of palladium(II) and platinum(II) complexes of the [2,6-(dimethylaminomethyl)phenyl-N,C,N](-)(pincer) ligand toward iodomethane and dibenzoyl peroxide; Structural studies of M(II) and M(IV

摘要

The presence of the [2,6-(dimethylaminomethyl)phenyl-N,C,N](-) (pincer) ligand (NCN) in platinum(II) complexes has been used to generate stable organoplatinum(IV) complexes that model possible intermediates and reactivity in metal-catalyzed C-O bond formation processes. The complexes M(O2CPh)(NCN) [M = Pd (1), Pt (2)] were obtained by metathesis reactions from the chloro analogues, and although I does not react with dibenzoyl peroxide, 2 does so to form Pt(O2CPh)(3)(NCN) (3) as a model intermediate for the acetoxylation of arenes by acetic acid in the presence of palladium(II) acetate and an oxidizing agent. The complex Pt(O2CPh)(NCN) (2) reacts with iodomethane in a complex manner to form PtI-(NCN) (6) and cis-Pt(O2CPh)(2)Me(NCN) (7). Complex 7 decomposes to form Pt(O2CPh)(NCN) (2) and MeO2CPh, probably via benzoate dissociation followed by nucleophilic attack by the benzoate ion at the Pt-IV-Me carbon atom. The Pd(II) analogue Pd(O2CPh)(NCN) (1) reacts with MeI to give PdI(NCN) (8) and MeO2CPh, for which the potential intermediacy of Pd-(IV) species could not confirmed by H-1 NMR spectroscopy. The complex PtTol(NCN) (4) (Tol = 4-tolyl) reacts with (PhCO2)(2) to form cis-Pt(O2CPh)(2)Tol(NCN) (5), but, unlike the (PtMe)-Me-IV analogue 7, the Pt(IV)Tol complex 5 does not undergo facile C-O bond formation. X-ray structural studies of the isostructural square-planar complexes M(O2CPh)(NCN) (1, 2) and of the octahedral Pt(IV) complexes as solvates 3(.)1/2Me(2)CO, 5(.)Me(2)CO, and 7(.)Me(2)CO(.)H(2)O are reported. Complexes 5 and 7 have cis-PtC2 and cis-Pt(O2CPh)(2) configurations.