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(CH2NSiMe3)3TiX (1) and C6H5C(CH2NSiMe3)3TiX (2) as well as HCSiMe2N(4-CH3C6H4)3TiX (3) (X = Cl, a; Br, b) with KM(CO)2Cp (M = Fe, Ru) and NaCo(CO)3(PR3) (R = Ph, Tol) gave the corresponding stable heterobimetallic complexes of which H3CC(CH2NSiMe3)3Ti-M(CO) 2Cp (M = Fe, 6; Ru, 7) and HC{SiMe2N(4-CH3C6H4)} 3-Ti-M(CO)2Cp (M = Fe, 12; Ru, 13) have been characterized by X-ray crystallography. 6: monoclinic, P21/n, a = 15.496(3) A , b = 12.983(3) A , c = 29.219(3) A , I²= 104.52(2)°, Z = 8, V = 5690.71 A 3, R = 0.070. 7: monoclinic, P21/c, a = 12.977(3) A , b = 12.084(3) A , c = 18.217(3) A , I²= 91.33(2)°, Z = 4, V= 2855.91 A 3, R = 0.048. 12: monoclinic, I2/c, a = 24.660(4) A , b = 15.452(3) A , c = 20.631(4) A , I²= 103.64(3)°, Z = 8, V = 7639.65 A 3, R = 0.079. 13: monoclinic, I2/c, a = 24.473(3) A , b = 15.417(3) A , c = 20.783(4) A , I²= 104.20(2)°, Z = 8, V = 7601.84 A 3, R = 0.066. 1H- and 13C-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)3Ti-Fe(CO)2Cp (6x) have revealed a significant degree of I�-donor-acceptor interaction between the two metal fragments reinforcing the Ti-Fe I�-bond. Due to the availability of energetically low-lying I�-acceptor orbitals at the Ti center this partial multiple bonding is more pronounced that in the tin analogue HC(CH2NH)3Sn-Fe(CO)2Cp (15x) in which an N-Sn I�*-orbital may act as I�-acceptor orbital.