CYCLOMETALLATION OF POLYDENTATE LIGANDS CONTAINING PYRAZOLE GROUPS, INCLUDING THE SYNTHESIS OF PLATINUM(IV) COMPLEXES WITH TRIPODAL [N-C-N]- LIGAND SYSTEMS

Dimethylplatinum(II) complexes, PtR2(L), have been made by reaction of [PtR2(μ-SEt2)]2 with a range of polydentate nitrogen donor ligands containing one or more pyrazol-1-yl (pz) donor groups, including the new ligand bis(pyrazol-1-yl)(thien-2-yl)methane. The complexes give cis-PtMe2(py)2 when dissolved in pyridine at ambient temperature, except for PtMe2(L) (L = (pz)2CH2, (pz)2C(H)Ph, (pz)3CH, or (pz)2(mim)CH (mim = N-methylimidazol-2-yl)), which undergo cyclometallation at a C(5) position of one pyrazol-1-yl ring. The cyclometallated ligands have been examined as 'isoelectronic' analogues of nitrogen donor poly(pyrazol-1-yl)alkane and poly(pyrazol-1-yl)borate ligands. A carbon monoxide derivative, PtMe(pz)2(C3H2N2)CH-N,C(CO) (1d) and a series of phosphine complexes have been prepared. The complex PtMe(pz)2(C3H2N2)CH-N,C(py) (1a) and polymeric [PtMe(pz)2(C3H2N2)CH]n (2) undergo oxidative addition reactions with organohalides to give the platinum(IV) complexes [fac-PtMe(R)(pz)2(C3H2N2)CH- N,N′,C(py)]X (7a-d) and fac-PtXMe(R)(pz)2(C3H2N2)CH- N,N′,C (8a,b), respectively. The new reagent 1-bromo-2-(pyrazol-1-yl)ethane forms [fac-PtMe(pz)2(C3H2N2)CH-N,N ′,C(pzCH2CH2-N,C)]Br (10), containing both [NCN]- and [NC]- ligands. Reaction of MeI or PhCH2Br with PtMe2(pz)3CH gives fac-PtXMe(R)(pz)2(C3H2N2)CH- N,N′,C B71 (8a,b) directly, and PtMe2(pz)4C undergoes a similar cyclometallation/oxidative addition in iodomethane to form fac-PtIMe2(pz)3(C3H2N 2)CH-N,N′,C (13). © 1990.