Synthetic and X-Ray Structural Studies of Complexes formed by Metallation of Tri(1-pyrazolyl)methane by Dimethylplatinum(II)

Dimethylplatinum(II) forms a complex [PtMe2(tpzm)](1) with tri(1-pyrazolyl)methane (tpzm), and on heating in pyridine metallation of one pyrazole ring occurs at C(5) to form [PtMe(tpzm-H)(py)](2), which has a cis-PtC2N2 moiety and tpzm-H present as a bidentate (cyclometallated) ligand with one unco-ordinated pyrazole group to give square-planar co-ordination, Me(py)PtCNCNN. Complexes (1) and (2) react with two equivalents of PPh3 in hot pyridine to form [PtMe(tpzm-H)(PPh3)2](3), which has PPh3 both cis and trans to the methyl group. On heating slowly to 185 C complex (3)forms [Pt(tpzm-H){PPh2(C6H4)}](4), which has PPh3 ortho-metallated to give two cyclometallated ligands bound to Pt(II), NNCNCPtCCP, one forming a six-membered ring and one forming a four-membered ring. Crystal structures of complex (2) and an impurity crystal of [PtMe(tpzm-H)(py)(PPh3)].2py (5), obtained from a sample of (3), are reported. The latter complex has a cis-PtC2NP moiety, with PPh3 trans to the methyl group and pyridine trans to tpzm-H, which is bound via C(5) of a pyrazole ring only. Crystal data: (2), monoclinic, space group P2,/n, a = 15.67(1), b = 9.193(5), c = 12.082(8) A, beta = 90.22(5), and Z = 4; (5), triclinic, space group P1 bar, a = 14.526(9), b = 12.133(7), c = 11.560(6) A, alpha = 89.88(5), beta = 87.35(5), gamma = 87.66(5), and z = 2.