STRUCTURE OF THE [1.1]METALLOCENOPHANES OF FE AND RU - SINGLE-CRYSTAL X-RAY-DIFFRACTION ANALYSIS OF (C5H4-CH2-C5H4)2FE2, (C5H4-CH2-C5H4)2FERU, AND (C5H4-CH2-C5H4)2RU2

Single-crystal X-ray diffraction studies of the [1.1]metallocenophanes of Fe and Ru [(Cp-CH2-Cp)2MM', 1, M = M' = Fe; 2, M = Fe,M' = Ru; and 3, M = M' = Ru] clearly document that all three compounds exist only in a syn conformation which, in twisting by angles between 10-degrees and 28-degrees, can relieve the steric crowding of the inner alpha-Cp protons. The anti conformation, in which such strain relief is not possible because of structural rigidity, does not exist. The structures indicate the presence of two fully independent metallocenes in each of these systems and give no obvious indication of any metal-metal bonding: the metallocene halves show now sign of distortion, and the Cp rings in them are coplanar. However, the larger twist in [1.1]ruthenocenophane indicates a metal-metal interaction which, while leading to a net nonbonding situation for the Ru atoms, drastically lowers the redox potential of this compound. Crystal data. compounds 1-3 crystallize in the monoclinic space group P2(1)/c with Z = 4; (1) C20H20Fe2, a = 7.894 (3) angstrom, b = 10.530 (3) angstrom, c = 19.402 (6) angstrom, beta = 94.57 (3)-degrees; (2) C20H20FeRu2 a = 7.980 (2) angstrom, b = 10.724 (3) angstrom, c = 19.112 (5) angstrom, beta = 95.76 (2)-degrees; (3) C20H20Ru2, a = 6.003 (3) angstrom, b = 19.472 (7) angstrom, c = 14.196 (5) angstrom, beta = 92.55 (4)-degrees.