Oxidation of Half-Lantern Pt2(II,II) Compounds by Halocarbons. Evidence of Dioxygen Insertion into a Pt(III)-CH3 Bond

The half-lantern compound [{Pt(bzq)(mu-N<^>S)}(2)] (1) [bzq = benzo[h]quinoline, HN<^>S = 2-mercaptopyrimidine (C4H3N2HS)] reacts with CH3I and haloforms CHX3 (X = Cl; Br, I) to give the corresponding oxidized diplatinum(III) derivatives [{Pt(bzq)(mu-N<^>S)X}(2)] (X = Cl 2a, Br 2b, I 2c). These compounds exhibit half-lantern structures with short intermetallic distances (similar to 2.6 angstrom) due to Pt-Pt bond formation. The halogen abstraction mechanisms from the halocarbon molecules by the Pt-2(II,II) compound 1 were investigated. NMR spectroscopic evidence using labeled reagents support that in the case of (CH3I)-C-13 the reaction initiates with an oxidative addition through an S(N)2 mechanism giving rise to the intermediate species [I(bzq)Pt(mu-N<^>S)(2)Pt(bzq)((CH3)-C-13)}]. However, with haloforms the reactions proceed through a radical-like mechanism, thermally (CHBr3, CHI3) or photochemically (CHCl3) activated, giving rise to mixtures of species [X(bzq)Pt(mu-NAS)(2)Pt(bzq)R] (3a-c) and [X(bzq)Pt(mu-N<^>S)(2)Pt(bzq)X] (2a-c). In these cases the presence of O-2 favors the formation of species 2 over 3. Transformation of 3 into 2 was possible upon irradiation with UV light. In the case of [I(bzq)Pt(mu-N<^>S)(2)Pt(bzq)((CH3)-C-13)}] (3d), in the presence of O-2 the formation of the unusual methylperoxo derivative [I(bzq)Pt(mu-N<^>S)(2)Pt(bzq)(O-(OCH3)-C-13)}] (4d) wa detected, which in the presence of (CH3I)-C-13 rendered the final product [{Pt(bzq)(mu-N<^>S)I}(2)] (2c) and (CH3OH)-C-13.