Cyclometallation of polydentate ligands containing pyrazole groups, including the synthesis of platinum(IV) complexes with tripodal - ligand systems

Article abstract of DOI:10.1016/0022-328X(90)80028-X

Dimethylplatinum(II) complexes, PtR2(L), have been made by reaction of 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 >n (2) undergo oxidative addition reactions with organohalides to give the platinum(IV) complexes (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 (pzCH2CH2-N,C)>Br (10), containing both ^- and ^- ligands.Reaction of MeI or PhCH2Br with PtMe2<(pz)3CH>> gives fac-PtXMe(R)<(pz)2(C3H2N2)CH-N,N',C> (8a,b) directly, and PtMe2<(pz)4C> undergoes a similar cyclometallation/oxidative addition in iodomethane to form fac-PtIMe2<(pz)3(C3H2N2)CH-N,N',C> (13).