Synthetic and X-ray structural studies of complexes formed by metallation of tri(1-pyrazolyl)methane by dimethylplatinum(II)

Abstract

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)[graphic omitted]. 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 PPh₃ortho-metallated to give two cyclometallated ligands bound to Pt^II, [graphic omitted], 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 PPh₃trans 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 P2₁/n, a= 15.67(1), b= 9.193(5), c= 12.082(8)Å, β= 90.22(5)°, and Z= 4; (5), triclinic, space group P, a= 14.526(9), b= 12.133(7), c= 11.560(6)Å, α= 89.88(5), β= 87.35(5), γ= 87.66(5)°, and Z= 2.