The reaction of either [RhCl(C 8 H 14 ) 2 ] 2 or [RhCl(C 2 H 4 ) 2 ] 2 with tBu 2 PCH 2 CH 2 C 6 H 5 (3) affords at room temperature the five-coordinate arylhydridorhodium(III) complex 4, the molecular structure of which has been determined by X-ray crystallography. The C-H metalation is completely reversible, as is shown by the formation of trans-[RhCl(CO)(3) 2 ] from 4 and CO. Compound 4 also reacts with PhCtCH, H 2 , and AgPF 6 to give products 7-9 containing the intact phosphine ligand 3.