Rhodium Complexes with the New Anionic Diphosphine [7,8-(PPh2)2-7,8-C2B9H10]-Ligand

New rhodium complexes with the eclipsed anionic diphosphine [7,8-(PPh 2 ) 2 -7,8-C 2 B 9 H 10 ] - are described. These were prepared from the neutral cod complex [Rh{ 7,8-(PPh 2 ) 2 -7,8- C 2 B 9 H 10 }(cod)] either directly or via the complex [Rh{ 7,8- (PPh 2 ) 2 -7,8-C 2 B 9 H 10 }(CO) 2 ], which was obtained by bubbling CO through a suspension of [Rh{ 7,8-(PPh 2 ) 2 -7,8-C 2 B 9 H 10 }(cod)] in deoxygenated methanol. The CO ligands may be readily replaced by monophosphines, chelating diphosphines, monoamines, and chelating diamines. CO substitution by monophosphines depends on the phosphine cone angle more than the phosphine basicity. Both CO ligands can be replaced in [Rh{ 7,8-(PPh 2 ) 2 -7,8-C 2 B 9 H 10 }(CO) 2 ] by monophosphines with small cone angles, while monophosphines with large cone angles are only able to displace one CO ligand. Thus [Rh{ 7,8- (PPh 2 ) 2 -7,8-C 2 B 9 H 10 }(CO)(phosphine)] and [Rh{ 7,8-(PPh 2 ) 2 - 7,8-C 2 B 9 H 10 }(phosphine) 2 ] can be obtained. By contrast, with chelating diamines, carbamoyl complexes have been obtained.