Formation of New η5-Rhodium(III) Complexes from η5-Rh(I) Rhodacarborane-Containing Charge-Compensated Ligands

A series of new Rh(I) half-sandwich complexes of formula [3,3-(PPh 3 ) 2 -8-L- closo -3,1,2-RhC 2 B 9 H 10 )] (L = SMe 2 ( 2a ), SEt 2 ( 2b ), S(CH 2 ) 4 ( 2c ), SEtPh ( 2d )) and [1-Me-3,3-(PPh 3 ) 2 -8-L- closo -3,1,2-RhC 2 B 9 H 9 )] (L = SMe 2 ( 2e ), SEt 2 ( 2f )) have been prepared by reaction of the respective monoanionic charge-compensated ligands [10-L- nido -7,8-C 2 B 9 H 10 ] - and [7-Me-10-L-7,8-C 2 B 9 H 9 ] - with [RhCl(PPh 3 ) 3 ]. Complex [3,3-(cod)-8-SMe 2 - closo -3,1,2-RhC 2 B 9 H 10 ] ( 3 ) has also been prepared by reaction of K[10-SMe 2 - nido -7,8-C 2 B 9 H 10 ] with [RhCl(cod)] 2 . Rh(I) complexes 2a − d may be easily oxidized to the corresponding Rh(III) complexes 4a − d under N 2 atmosphere in some halogenated solvents such as CCl 4 and CHCl 3 . The complexes have been fully characterized by IR and NMR spectroscopy, and the crystal structures of 2a, 3, and 4a have been elucidated by single-crystal X-ray diffraction analysis. An EPR spectrum analysis clearly evidences the formation of free radicals as intermediates in the evolution of 2a − d to 4a − d complexes. The capacity to stabilize both Rh(I) and Rh(III) oxidation states by the [10-SMe 2 - nido -7,8-C 2 B 9 H 10 ] - system may be attributed to its donor capacity together with the presence of labile ligands in the molecule.