Synthesis, Structure, and Electronic Communication in Complexes Derived from RC₂Co₂(CO)₆C₂Co₂(CO)₆R

The loss of a Co 2 (CO) 6 fragment and the formation of compounds of the type RC⋮CC 2 Co 2 (CO) 6 - n [P(OMe) 3 ] n R ( n =1−3) is the main consequence of thermally-initiated substitution reactions of the diyne complexes RC 2 Co 2 (CO) 6 C 2 Co 2 (CO) 6 R [R = Ph, Fc; Fc = (η 5 -C 5 H 4 )Fe(η 5 -C 5 H 5 )] with P(OMe) 3 . Unstable RC 2 Co 2 (CO) 6 - n [P(OMe) 3 ] n C 2 Co 2 (CO) 6 - m [P(OMe) 3 ] m R ( n = 0−2, m = 0, 1) complexes are isolated in low yield, under mild reaction conditions, or in electron transfer catalyzed (ETC) substitution reactions. Thermal reactions with bis(diphenylphosphino)methane (dppm) gave RC⋮CC 2 Co 2 (CO) 4 (dppm)R (R = Ph, Fc) and PhC 2 Co 2 (CO) 4 (dppm)C 2 Co 2 (CO) 4 (dppm)Ph ( 9a ). These results highlight the steric requirements for these modules if they are to be incorporated in molecular arrays. The crystal and molecular structure of 9a has been determined from X-ray data. The dppm ligands adopt μ-η 2 configurations, bridging both Co−Co bonds, and bind at equatorial sites. Square-wave, conventional oxidative voltammetry and spectroscopic data provide evidence for communication between the ferrocene and C 2 Co 2 redox centers and, in 9a, the first example of delocalization between individual C 2 Co 2 redox centers in a phosphine derivative. 9a + and 9a 2+ have been characterized.