Unsymmetrical organodiplatinum(II) and organodiplatinum(IV) complexes containing bis(diphenylphosphino)methane as bridging ligand: general approaches for synthesis and characterization by multinuclear NMR studies

Reaction of cis-[PtR2(SMe2)2] (R=Ph or p-MeC6H4) with [PtMe2(dppm)] or [Pt{(CH2)4}(dppm)] (dppm=Ph2PCH2PPh2) gave the unsymmetrical cis,cis-diaryl-dialkyl diplatinum(II) complexes cis,cis-[R2Pt(μ-SMe2)(μ-dppm)PtMe2], 1a and 2a, or cis,cis-[R2Pt(μ-SMe2)(μ-dppm)Pt{(CH2)4}], 1b and 2b, respectively. Complexes 1a and 2a were also prepared by reaction of [Pt2Me4(μ-SMe2)2] with [PtR2(dppm)]. The unsymmetrical complex cis,cis-[Me2Pt(μ-SMe2)(μ-dppm)Pt{(CH2)}4] (3b) was prepared by the same method using [Pt{(CH2)4}(dppm)] and [Pt2Me4(μ-SMe2)2]. The symmetrical complex cis,cis-[Me2Pt(μ-SMe2)(μ-dppm)PtMe2] (3a) was prepared by reaction of [Pt2Me4(μ-SMe2)2] with either one equivalent of dppm or [PtMe2(dppm)]. The complexes 2 and 3 reacted with MeI to give the unsymmetrical diplatinum(IV) complexes fac,fac-[R2MePt(μ-I)2(μ-dppm)PtMeR′2] (4a, R=R′=Me; 4b, R=Me, R′2=(CH2)4; 5a, R=p-MeC6H4, R′=Me; 5b, R=p-MeC6H4, R′2=(CH2)4). The reactions probably occurred by a SN2-type mechanism and the entering Me groups stereoselectively remained in the equatorial positions (PtP taken as axial direction), unless for fac-PtMe3 moiety that Me scrambling was taken place. Reaction of cis,cis-dialkyl-dialkyl diplatinum(II) complexes 3 with one equivalent of dppm gave bis(dppm-bridged) complexes cis,cis-[R2Pt(μ-dppm)2PtR′2] (6a, R=R′=Me; 6b, R=Me, R′2=(CH2)4). The complexes were fully characterized using multinuclear (1H-, 13C{1H}-, 31P{1H}-, 195Pt{1H}-) NMR spectroscopy.