Solution studies of complexes of the types trans-PtCl2L(1,4-diazine) and trans-Lcl2Pt(.mu.-1,4-diazine)PtCl2L (L = phosphine, C2H4). X-ray structures of Pt2Cl4L2(ppz) (L = C2H4, PEt3; ppz - 2,5-dimethylpyrazine) and the relative trans influence of alkene and tertiary phosphine ligands

Solution studies of the complexes PtCI,L( 1,4-diazine) and fruns-LCl,Pt( 1,4-diazine)PtCI,L (L = PEt,, PMe2Ph, PMePh,, P-n-Bu,, C2H4; diazine = pyrazine, 2-methylpyrazine, 2,3-, 2,5- and 2,6-dimethylpyrazine, 2,3,5-trimethylpyrazine, 2,3,5,6-tetramethylpyrazine, phenazine) have been carried out. It is shown that (a) coordination of the “PtCI,L” fragment does not significantly weaken the donor capacity of the still uncoordinated nitrogen atom of the heterocycle, (b) these complexes are dynamic in solution, the ethene complexes being more labile than the corresponding phosphine complexes, and (c) the presence of methyl substituents near the coordinated nitrogen atom slows down the dynamic process. The X-ray crystal structures of (C2H4)C12Pt(2,5-dimethylpyrazine)PtCI2(C2H4) (E2ppz) and (PEt3)CI,Pt(2,5-dimethylpyrazine)PtCl2(PEt3) (A2ppz) were determined. The crystals of E,ppz are monoclinic and belong to the space group P2,/n with unit cell dimensions u = 7.048 (3) A, b = 13.407 (3) A, c = 9.219 (2) A, /3 = 69.81 (3)O, V = 817.7 A’, and 2 = 2. The structure was refined to R = 0.044. The crystals of A2ppz are monoclinic and belong to the space group P2,/c with unit cell dimensions a = 12.149 (3) A, b = 8.231 (6) A, c = 15.464 (5) A, /3 = 108.95 (2)O, V = 1462.6 A’, and Z = 2. The structure was refined to R = 0.038. Each platinum atom shows normal square-planar geometry with bonding parameters that are typical of the complexes fruns-PtCI,L(N-ligand) (L = alkene, tertiary phosphine). The differences in Pt-N distances in the two complexes clearly show the higher trans influence of the phosphine relative to that of the alkene.