Complexes containing unbridged dative metal-metal bonds and the strong acceptor Ru(CO)3(SiCl3)2 moiety.: Comments on the transition metal to silicon bond

Complexes of formula (R3P)(OC)(4)MRu(CO)(3)(SiCl3)(2) (M = Ru, Os) and (OC)3((BuNC)-N-t)(2)MRu(CO)(3)(SiCl3)(2) (M = Fe, Ru, Os) have been prepared from the reaction of cis-Ru(CO)(4)(SiCl3)(2) and the appropriate donor molecule in solution at room temperature. The characterization of the complexes included the crystal structures of (Me3P)(OC)(4)MRu(CO)(3)(SiCl3)(2) (M = RU, 1Ru; Os, 10s) and the three M(CO)(3)(CNBut)(2) derivatives (3Fe, 3Ru, 3Os). All five structures reveal molecules with unbridged metal-metal bonds. The PMe3 ligand is trans to the metal bond in 1M, whereas the isocyanide ligands are cis to this bond in 3M. The (BuNC)-N-t substituents have a cis configuration in 3Fe and 3Ru, but a trans arrangement in 3(as. Complexes 3Fe, 1Ru, and 3Ru are rare examples of structurally characterized compounds in which a first-row or second-row transition metal acts as the donor atom in a molecule containing an unbridged dative bond between two transition metals. The (OC)(3)((BuNC)-N-t)(2)FeRu(CO)(3)(SiCl3)(2) derivative is unstable both in solution and the solid state and attempts to prepare similar complexes in which Fe acts as the donor atom were unsuccessful. In contrast to previous studies, the Ru(CO)(4)(PR3) derivatives were reasonably stable. The RuSi lengths trans to the dative metal-metal bond (range 2.338(3)-2.357(2) Angstrom) are considerably shorter than the RuSi lengths trans to the carbonyl ligand (range 2.399(5)-2.420(4) Angstrom), whereas there is no significant difference between the SiCl lengths in the two types of SiCl3 ligands in the five structures. These results are interpreted in terms of the trichlorosilyl ligand acting as a pi acceptor ligand principally via the Si 3d orbitals.