Synthesis and isomerism of neutral and cationic dimethylplatinum(IV) complexes. Crystal structure of the bis(pyrazol-1-yl)(thien-2-yl)methane complex PtI2Me2{(pz)2(thi)CH-N,N’}

Abstract

The reaction of [PtMe2(SEt2)]2 with tripodal nitrogen donor ligands and iodine in dichloromethane gives diiododimethylplatinum(IV) complexes, PtI2Me2{(pz)2(L) CH-N,N’}, in which the N,N’-bidentate ligands are trans to the cis-PtMe2 group and have one uncoordinated donor group. The bis(pyrazol-l-yl)(thien-2-yl)methane complex, PtI2Me2{(pz)2(thi)CH-N,N’}, has Pt-I bond lengths of 2.6199(7) and 2.6649(6) A for the trans-PtI2 group, and Pt-C bond lengths of 2.070(7) and 2.097(9) A, and Pt-N bond lengths of 2.181(5) and 2.192(6) A. Complexes of (pz)2(L)CH [L = N-methylimidazol-2-yl (mim), pyridin-2-yl (py)] exist as a mixture of isomers, with an isomer ratio as expected for a random distribution of coordinated pz and L donor groups, 2:1 for 2pz:(pz + L) coordination. The complexes of (pz)3CH, (pz)2(mim)CH, and (pz)2(py)CH are converted into [PtIMe2{(pz)2(L)CH-N,N’,N”}]I on heating, and the cations of the unsymmetrical tridentate ligands (pz)2(L)CH (L = py, mim) also exist as isomers. The isomers have the donor group L trans to a methyl or iodo group, where the ratio (L trans to Me)(L tram to I) is 2:1 for L = py (as expected for a random distribution of isomers) and 1: 1 for L=mim.