Hydrogen-halide versus alkyl-halide oxidative addition in dimethyl platinum(II) complexes: Crystal structure of [PtBr2(bpy)]

Dimethyl platinum(II) complexes [PtMe2(NN)] {NN = bu2bpy (4,4′-di-tert-butyl-2,2′-bipyridine) (1a), bpy (2,2′-bipyridine) (1b), phen (1,10-phenanthroline) (1c)} reacted with commercial 3-bromo-1-propanol in the presence of 1,3-propylene oxide to afford cis, trans- [PtBrMe2{(CH2)3OH}(NN)] (NN = bu2bpy (2a), bpy (2b), phen (2c)). On the other hand, [PtMe2(NN)] (1a)–(1b) reacted with the trace of HBr in commercial 3-bromo-1-propanol to give [PtBr2(NN)] (NN = bu2bpy (3a), bpy (3b)). The reaction pathways were monitored by 1H NMR at various temperatures. Treatment of 1a–1b with a large excess of 3-bromo-1-propanol at −80 °C gave the corresponding methyl(hydrido)platinum(IV) complexes [PtBr(H)Me2(NN)] (NN = bu2bpy (4a), bpy (4b)) via the oxidative addition of dimethyl platinum(II) complexes with HBr. The complexes [PtBr(H)Me2(NN)] decomposed by reductive elimination of methane above −20 °C for bu2bpy and from −20 to 0 °C for bpy analogue to give methane and platinum(II) complexes [PtBrMe(NN)] (5a)–(5b) and then decomposed at about 0 °C to yield [PtBr2(NN)] and methane. When the reactions were performed at a molar ratio of Pt:RX/1:10, the corresponding complexes [PtBrMe(NN)] (5a)–(5b) were also obtained. The crystal structure of the complex 3b shows that platinum adopts square planar geometry with a twofold axis through the platinum atom. The Pt…Pt distance (5.164 Å) is considerably larger than the interplanar spacing (3.400 Å) and there is no platinum–platinum interaction.