Anionic Platinum Complexes with 2-Pyridylphosphines as Ligands for Rhodium: Synthesis of Zwitterionic Pt−Rh Organometallic Compounds

Bimetallic zwitterionic platinum(II)−rhodium(I) complexes of the type [(C6F5)3Pt(μ-PPynPh3-n)Rh(CO)2)] and [(C6F5)3Pt(μ-PPynPh3-n)Rh(diene))] (n = 2, 3; Py = 2-pyridyl) have been prepared. The P end of the bridging ligands
(μ-PPynPh3-n) is always coordinated to the Pt center, while the N-donor ends chelate the Rh atom, giving
metallacycles comparable to pyrazolylborate−Rh complexes. These metallacycles can adopt two conformations,
either with the Pt complex in pseudoaxial position approaching the Rh center or with the Pt complex in a remote
position. The preferred conformation depends on the steric hindrance at the rhodium center. In less sterically
demanding Rh−carbonyl complexes the Pt moiety gets close to the Rh moiety as this brings closer the opposite
charges of the zwitterion. For diene complexes mixtures of conformers are obtained. The X-ray structures of [(C6F5)3Pt(μ-PPhPy2)Rh(COD)] (COD = 1,5-cyclooctadiene) and [(C6F5)3Pt(μ-PPhPy2)Rh(CO)2] are reported.