Different Coordination Modes of the Ph2PCsp3PPh2 Pincer Ligand in Rhodium Complexes as a Consequence of Csp3–H Metal Interaction

Abstract

Starting from commercially available 4,4′-di-tert-butyldiphenylmethane the pincer ligand bis(4-tert-butyl-2-(diphenylphosphino)phenyl)methane (PCP) was prepared in two steps in moderate yield. Treatment of a solution of RhCl3·3H2O in a mixture of isopropyl alcohol and toluene with equimolar amounts of PCP gave the dimeric rhodium complex 1. In an electrophilic metalation a facially coordinated pincer complex is formed. When PCP is treated with [CODRhCl]2 in a solution of pyridine, the square-pyramidal complex 2 is generated where the bis-phosphine PCP acts as bidentate ligand that coordinates in a cis fashion. SnCl2 inserts into the Rh–Cl bond of 2, which results in an oxidative addition of one of the methylene C–H bonds to form the Rh(III) complex 3, where the PCP ligand coordinates in a meridional way. A 2 equiv portion of PCP reacts with 1 equiv of [CODRhCl]2 in the presence of the electron-donating ligands HPhPC6H4NMe2, PPh2Py, and PPh3, respectively, as well as with stanna- and germa-closo-dodecabora...