Stabilizing heterobimetallic complexes containing unsupported Ti-M bonds (M=Fe, Ru, Co): The nature of Ti-M donor-acceptor bonds

The stabilization of unsupported Ti-M (M = Fe, Ru, Co) heterodinuclear complexes has been achieved by use of amidotitanium building blocks containing tripodal amido ligands. Salt metathesis of H3CC(CH(2)NSiMe(3))(3)TiX (1) and C6H6C(CH(2)NSiMe(3))3TiX (2) as well as HC(SiMe(2)N(4-CH3C6H4))(3)TiX (3) (X = Cl, a; Pr, b) with K[M(CO)(2)Cp] (M = Fe, Ru) and Na[Co(CO)(3)(PR(3))] (R = Ph, Tol) gave the corresponding stable heterobimetallic complexes of which H3CC(CH(2)NSiMe(3))3Ti-M(CO)(2)Cp (M = Fe, 6; Ru, 7) and HC{SiMe(2)N(4-CH3C6H4)}Ti-3-M(CO)(2)Cp (M = Fe, 12; Ru, 13) have been characterized by X-ray crystallography. 6: monoclinic, P2(1)/n, a = 15.496(3) Angstrom, b = 12.983(3) Angstrom, 29.219(3) Angstrom, beta = 104.52(2)degrees, Z = 8, V = 5690.71 Angstrom(3), R = 0.070. 7: monoclinic, P2(1)/c, a = 12.977(3) Angstrom, b = 12.084(3) Angstrom, c = 18.217(3) Angstrom, beta = 91.33(2)degrees, Z = 4, V = 2855.91 Angstrom(3), R = 0.048. 12: monoclinic, I2/c, a = 24.660(4) Angstrom, b = 15.452(3) Angstrom, c = 20.631(4) Angstrom, beta = 103.64(3)degrees, Z = 8, V = 7639.65 Angstrom(3), R = 0.079. 13: monoclinic, I2/c, a = 24.473(3) Angstrom, b = 15.417(3) Angstrom, c = 20.783(4) Angstrom, beta = 104.20(2)degrees, Z = 8, V = 7601.84 Angstrom(3), R = 0.066. H-1- and C-13-NMR studies in solution indicate free internal rotation of the molecular fragments around the Ti-M bonds. Fenske-Hall calculations performed on the idealized system HC(CH2NH)(3)Ti-Fe(O-C)(2)Cp (6x) have revealed a significant degree of pi-donor-acceptor interaction between the two metal fragments reinforcing the Ti-Fe sigma-bond. Due to the availability of energetically low-lying pi-acceptor orbitals at the Ti center this partial multiple bonding is more pronounced that in the tin analogue HC(CH2NH)(3)Sn-Fe(CO)(2)Cp (15x) in which an N-Sn sigma*-orbital may act as pi-acceptor orbital.