Synthesis, formation constants and reactions of cationic rhodium(I) complexes of nitriles

Abstract

Reactions of Rh(ClO 4)(CO)(PPh 3) 2 with nitriles produce new cationic rhodium(I) complexes, [RhL(CO)(PPh 3) 2]ClO 4 [L = CH 3CN ( 1), CH 3CH 2CH 2CN ( 2) or C 6H 5CN ( 3)], whose spectral data suggest that the nitriles are coordinated through the nitrogen atom. Formation constants for the reaction Rh(ClO 4)(CO)(PPh 3) 2 + L ⇋ [RhL(CO)(PPh 3) 2]ClO 4, have been measured to be 1.01 × 10 5 M −1 (CH 3CN), 1.07 × 10 5 M −1 (CH 3CH 2CH 2CN) and 2.59 × 10 4 M −1 (C 6H 5CN) at 25°C in monochlorobenzene. The differences in the formation constants for the different nitriles seem to be predominantly due to differences in Δ H (not to differences in Δ S). The nitriles in 1–3 are readily replaced with nitrogen base ligands (unsaturated nitriles and pyridine) and PPh 3.