A comparative structural and spectroscopic study of diiron and diruthenium isocyanide and aminocarbyne complexes

The chemistry of [Fe2Cp2(CO)4] (1-Fe; Cp = η5-C5H5) has been widely investigated, and straightforward carbonyl/isocyanide substitution, followed by isocyanide alkylation, provides access to a variety of aminocarbyne complexes, displaying a rich and versatile reactivity. On the other hand, the parallel chemistry of [Ru2Cp2(CO)4] (1-Ru) has been much less developed, and relevant structural/bonding aspects scarcely elucidated. We report an IR study on 1-Ru in different solvents and in the solid state. The IR data of [M2Cp2(CO)3(CNR)] (M = Ru, R = 2,6-C6H3Me2 = Xyl, 2a-Ru; M = Ru, R = CH2Ph = Bn, 2b-Ru; M = Ru, R = Me, 2c-Ru; M = Fe, R = Xyl, 2a-Fe; M = Fe, R = Bn, 2b-Fe; M = Fe, R = Me, 2c-Fe) and [M2Cp2(CO)3{μ-CNR(Me)}]CF3SO3 (M = Ru, R = Xyl, 4a-Ru; M = Ru, R = Bn, 4b-Ru; M = Ru, R = Me, 4c-Ru; M = Fe, R = Xyl, 4a-Fe; M = Fe, R = Bn, 4b-Fe; M = Fe, R = Me, 4c-Fe) are comparatively presented, and the back-donation from the dimetallic core to π-acceptor ligands in complexes 4 is discussed. A new synthetic procedure to access 2a-Ru is reported, affording [Ru2Cp2(CO)2(CNXyl)2] (3) as by-product, as well as the single crystal X-ray structures of 2b-Ru and 4b-Ru. DFT calculations were carried out to elucidate the relative stability of isomeric forms within the series of isocyanide adducts 2-Ru and 3.