Regioselective Double Cycloplatination of 9,10-Bis(diphenylphosphino)anthracene

Double cyclometalation of 9,10-bis(diphenylphosphino)anthracene (PAnP) by Pt(L)(OTf)2 (L = diphosphines, OTf = CF3SO3) gives rise to the geometrical isomers syn- and anti-[Pt2(L)2(PAnP-H2)](OTf)2 (Pt2). The reaction is regioselective, with the syn-isomer being the kinetic product. The cyclomelation is reversible, and thermodynamic product distribution is obtained after prolonged standing. The ratio of the isomers is subject to the influence of solvents and ancillary diphosphines. Protonolysis of the Pt−C leads to a monocyclometalated intermediate. A mechanistic postulate that invokes a preferential electrophilic attack of the Pt ions at the C−H bonds of the anthracenyl ring is proposed to explain the regioselectivity.