Transition metal–carbon bonds. Part 51. Action of amines on buta-1,3-diene complexes of type cis,cis-[Pt2Cl4(PR3)2(µ-C4H6)] : crystal structures of [ Pt2Cl4(PMe2Ph)2(µ-C4H6)](meso isomer) and [(Et3P)ClPt(Me2NCH2CHCHCH2NMe2)PtCl(PEt3)](two trans-fused five-membered rings)

Treatment of chloro-bridged complexes [Pt2Cl4(PR3)2](PR3= PMe2Ph, PEt3, or PPrn3) with buta-1,3-diene over several days gives the µ-butadiene complexes cis,cis-[Pt2Cl4(PR3)2(µ-C4H6)]; such complexes have not previously been fully characterized. Buta-1,3-diene is prochiral and the product is shown to be the meso isomer for PR3= PMe2Ph, by X-ray crystallography. A low-temperature study in CDCl3 shows that at –30 °C buta-1,3- diene reacts rapidly and reversibly with [Pt2Cl4(PPrn3)2] to give trans-[PtCl2(PPrn3)(C4H6)]; a very small amount of cis-[PtCl2(PPrn3)(C4H6)], in which the butadiene is monodentate, was also probably formed. Treatment of [NBun4]2[Pt2X6] with buta-1,3-diene gave the µ-butadiene complexes [NBun4]2[Pt2X6(µ-C4H6)](X = Cl or Br). Treatment of [Pt2Cl4(PMe2Ph)2] with isoprene at –60 °C reversibly gives a new species, probably trans-[Pt2Cl2(PMe2Ph)(isoprene)], and at room temperature probably cis-[PtCl2(PMe2Ph)(isoprene)], although we could not separate this cis species from the bridged complex. Treatment of cis,cis-[Pt2Cl4(PMe2Ph)2(µ-C4H6)] with an excess of dimethylamine (even at –78 °C) rapidly gave [(PhMe2P)Cl[graphic omitted]tCl(PMe2Ph)](5a); a similar reaction gave the PEt3 complex (5d), the crystal structure of which shows the presence of two trans-fused five-membered rings. Treatment of cis,cis-[Pt2Cl4(PPrn3)2(µ-C4H6)] with methylamine similarly gave [(Prn3P)Cl[graphic omitted]tCl(PPrn3)] as a mixture of three isomers due to the positioning of the N–Me groups; one isomer was isolated pure. Proton, 13C, 31P, and 195Pt n.m.r. and i.r. data are given. Crystals of both the title compounds are monoclinic, space group P21/n, with Z= 2 and molecular symmetry Ci. Those of [Pt2Cl4(PMe2Ph)2(µ-C4H6)] have a= 1.9658(4), b= 0.9741(3), c= 0.6557(1) nm, and β= 94.24(2)°. Those of (5d) have a= 0.8015(3), b= 1.3461(3), c= 1.3070(3) nm, and β= 97.56(3)°. Final R factors were 0.042 for 1 391 and 0.040 for 1 584 observed reflections, respectively.