Regiospecific reactions of cobalt-rhodium mixed-metal clusters. Unprecedented, facile and reversible tetranuclear-dinuclear transformations involving diphenylacetylene and/or carbon monoxide

Article abstract of DOI:10.1021/om00132a034

Co₂Rh₂(CO)₁₂ (1) reacts with alkynes (RC₂R, R = C₆F₅ (2a), R = Ph (2b)) via specific insertion into the cobalt-cobalt bond to give Co₂Rh₂(CO)₁₀(μ₄-η ²-RC₂R) (3a,b). 3a was characterized by a single-crystal X-ray diffraction analysis: space group P2₁/c (No. 14), a = 11.286 (8) A?, b = 17.37 (1) A?, c = 16.65 (1) A?, β= 126.32 (5)°, V = 2630 (5) A7ring;³, Z = 4, D_calcd, = 2.43 g/ cm³. A total of 2479 reflections (I ≥ 2σ) of 3215 reflections were used to give R_F = 5.2% and R_F2 = 5.6%. Reaction of 3a with CO and 2a results in regiospecific fragmentation to give CoRh(CO)₆(μ-η²-F₅C₆C ₂C₆F₅) (4a) exclusively. 3b undergoes facile, reversible, and regiospecific fragmentation when treated with PhC₂Ph (2b) and carbon monoxide to give CoRh(CO)₆(μ-η²-PhC₂Ph) (4b). Medium-pressure in situ IR studies have revealed that 3b reacts with carbon monoxide in a reversible and regiospecific reaction to give the 1:1 mixture of CoRh(CO)₇ (5) and 4b.