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)

Abstract

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 C_i. 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.