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.

The oxidative addition of some alkyl halides to dimethylplatinum(II) complexes [PtMe2(NN)] (NN = bpy, phen, or bu2bpy) has been investigated. The formation of mono or binuclear organoplatinum(IV) complexes in the reaction of organoplatinum(II) complexes with dibromo or tetrabromoalkane depends upon the nature of diimine ligand. The reaction of organoplatinum(II) complexes [PtR2(NN)] (R2 = (CH2)4, NN = bpy, or phen; R = Me; NN = bpy) with 1,3-dibromobutane took place by an SN2 mechanism from the less sterically hindered C-Br side to afford the complexes trans-[PtR2Br{(CH2)2CHBrCH3)}(NN)] in which the platinacycle complexes reacted faster as compared to the related dimethyl analogue. The crystal structure of fac-[PtMe3Br(bpy)] is reported.Figure optionsDownload as PowerPoint slideHighlights
► New alkyl and haloalkyl organoplatinum(IV) complexes.
► Formation of mono or dinuclear Pt(IV) complexes depend upon the nature of diimine.
► Oxidative addition of 1,3-dibromobutane with Pt(II) complexes by an SN2 mechanism.
► Activation effect of the platinum falls off as the alkyl chain length increases.
► The crystal structure of fac-[PtMe3Br(bpy)] is reported.