SYNTHESIS, STRUCTURES, AND POLYMERIZATION BEHAVIOR OF DISILANE-BRIDGED AND BIS(DISILANE)-BRIDGED [2]RUTHENOCENOPHANES

The disilane-bridged [2]ruthenocenophane RU(eta-C(5)H(4)SiMe(2))(2) (6) was synthesized via the reaction of cis-RuCl2(DMSO)(4) with the dilithium salt Li-2[C(5)H(4)SiMe(2)](2) in THF. In order to investigate the strain present in 6 the molecular structure was determined by single crystal X-ray diffraction. The tilt angle between the planes of the cyclopentadienyl ligands in 6 (7.8(5)degrees) indicated that the degree of strain present is significantly less than for other [n]-metallocenophanes which undergo ring-opening polymerization where the tilt angles are generally 19 degrees or greater. Significantly, the Si-Si bond in 6 was elongated to a value of 2.370(2) Angstrom compared to a typical Si-Si bond length of 2.34 Angstrom and this appears to provide a mechanism for the relief of strain. Compound 6 was found to be resistant to thermal ring-opening polymerization up to 350 degrees C. This behavior contrasts with that of hydrocarbon-bridged [2]ruthenocenophane which readily thermally polymerize. The analogous bis(silane)-bridged [2][2]ruthenocenophane Ru{eta-C5H3(SiMe(2))(2)}(2) (7) was prepared in a manner similar to that for 6 using Li-2[C5H3(SiMe(2))(2)](2). An X-ray diffraction study of 7 indicated that this compound is significantly more strained than 6, with a tilt angle of 12.9(2)degrees. The Si-Si bond in 7 (2.363(1) Angstrom) is also elongated relative to a typical Si-Si bond, but less so than in 6. Even though compound 7 was more strained than 6, this species was also found to be resistant to thermal ring-opening polymerization. Crystals of 6 are monoclinic, space group P2(1)/n, with a = 12.5407(12) Angstrom,b = 8.3877(8) Angstrom, c = 14.9848(9) Angstrom, beta = 109.197(6)degrees, V = 1488.6(2) Angstrom(3), and Z = 4. Crystals of 7 are monoclinic, space group C2/c, with a 10.908(2) Angstrom, b = 13.605(3) Angstrom, c = 14.859(3) Angstrom, beta = 109.89(2)degrees, V = 2073.6(10) Angstrom(3), and Z = 4.