Stabilizing Heterobimetallic Complexes Containing Unsupported Ti−M Bonds (M = Fe, Ru, Co): The Nature of Ti−M Donor−Acceptor Bonds

Abstract

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 H(3)CC(CH(2)NSiMe(3))(3)TiX (1) and C(6)H(5)C(CH(2)NSiMe(3))(3)TiX (2) as well as HC{SiMe(2)N(4-CH(3)C(6)H(4))}(3)TiX (3) (X = Cl, a; Br, 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 H(3)CC(CH(2)NSiMe(3))(3)Ti-M(CO)(2)Cp (M = Fe, 6; Ru, 7) and HC{SiMe(2)N(4-CH(3)C(6)H(4))}(3)Ti-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) Å, b = 12.983(3) Å, c = 29.219(3) Å, beta = 104.52(2) degrees, Z = 8, V = 5690.71 Å(3), R = 0.070. 7: monoclinic, P2(1)/c, a = 12.977(3) Å, b = 12.084(3) Å, c = 18.217(3) Å, beta = 91.33(2) degrees, Z = 4, V = 2855.91 Å(3), R = 0.048. 12: monoclinic, I2/c, a = 24.660(4) Å, b = 15.452(3) Å, c = 20.631(4) Å, beta = 103.64(3) degrees, Z = 8, V = 7639.65 Å(3), R = 0.079. 13: monoclinic, I2/c, a = 24.473(3) Å, b = 15.417(3) Å, c = 20.783(4) Å, beta = 104.20(2) degrees, Z = 8, V = 7601.84 Å(3), R = 0.066. (1)H- and (13)C-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(CH(2)NH)(3)Ti-Fe(CO)(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(CH(2)NH)(3)Sn-Fe(CO)(2)Cp (15x) in which an N-Sn sigma-orbital may act as pi-acceptor orbital.