Oxidative addition of some mono, di or tetra haloalkanes to organoplatinum(II) complexes

Dimethylplatinum(II) complexes [PtMe2(NN)] {NN = bpy (2,2′-bipyridine), phen (1,10-phenanthroline) or bu2bpy (4,4′-di-tert-butyl-2,2′-bipyridine)} were reacted with alkyl halides (RX = EtI or EtBr, NN = bu2bpy; RX = nBuBr, NN = bpy; RX = CHPh2Br, NN = bpy, phen, or bu2bpy) to yield the Pt(IV) complexes [PtMe2RX(NN)]. On the basis of NMR data, the Pt(IV) product of each reaction contains almost exclusively the kinetic trans isomer, and only in a few cases, very small traces of the thermodynamic cis isomers are observed. The binuclear complexes [Pt2Me4Br2{μ-(CH2)2}(NN)2] (NN = bpy, phen) were obtained from reaction of [PtMe2(NN)] with 1,2-dibromoethane. Notably, the mononuclear complex fac-[PtMe3Br(bpy)], obtained as a byproduct during the reaction of [PtMe2(bpy)] with 1,2-dibromoethane, was characterized by X-ray crystallography from the reaction of [PtMe2(bpy)] with 1,2-dibromoethane. On the other hand, the reaction of [PtMe2(bu2bpy)] with 1,2-dibromoethane resulted in formation of the mononuclear complex trans-[PtMe2Br{(CH2)2Br}(bu2bpy)]. The reaction of [PtMe2(NN)] with 1,2-bis(dibromomethyl)xylene in a 1:1 or 2:1 mol ratio afforded the mononuclear complexes [PtMe2(CHBr-o-C6H4CHBr2)Br(NN)] (NN = bpy, phen, or bu2bpy) or binuclear complexes [Pt2Me4Br2{μ-o-(CHBr)2C6H4}(NN)2] (NN = bpy, or phen), respectively. Finally, 1,3-dibromobutane was oxidatively added to the organoplatinum(II) complexes [PtR2(NN)] (R2 = (CH2)4, NN = bpy, or phen; R = Me; NN = bpy) via an SN2 mechanism from the less sterically hindered C–Br side to yield the complexes trans-[PtR2Br{(CH2)2CHBrCH3}(NN)]. The products were fully characterized by 1H and 13C NMR spectroscopy and elemental analysis. The platinacycle complex [Pt(CH2)4(bpy)] was shown to react faster, as compared to the dimethyl analogue complex [PtMe2(bpy)], by a factor of 3.8–4.2. The reactions of [Pt(CH2)4(bpy)] or [Pt(CH2)4(phen)] with 1,3-dibromobutane were faster as compared to those with 1,4-dibromobutane, due to the activation effect of the platinum.