Different Coordination Modes of the (Ph2PCspPPh2)-P-3 Pincer Ligand in Rhodium Complexes as a Consequence of C-sp(3)-H Metal Interaction

摘要

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 center dot 3H(2)O 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 RhCl 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-dodecaborate to give the octahedral Rh(III) complexes 4-8. Attempts to remove the HCl with (KOBu)-Bu-t from complexes 4-6 produces the planar Rh(I) compounds 9 and 10. No carbene formation has been observed.