Olefin coordination versus weak agostic C[sbnd]H[sbnd]M interactions in Sandwich-Type complexes of the split (3 + 2) Five-Electron donor hydrocarbon ligand Tricyclo[5.2.1.0]-deca-3,8-dien-5-yl (dicp) related to cyclopentadiene dimer

Abstract

Sandwich-type complexes (dicp)MCp (M = Ti, V, Cr, Mn, Fe, Co, Ni; Cp = cyclopentadienyl) of the split (3 + 2) five-electron donor ligand tricyclo[5.2.1.0]-deca-3,8-dien-5-yl (dicp) related to cyclopentadiene dimer have been investigated by density functional theory. In the low-energy structures of the transition metal complexes (dicp)MCp (M = Ti, V, Cr, Mn, Fe), all of the split (3 + 2) five electrons from the dicp ligand are donated to the central transition metal atom leading to 14-, 15-, 16-, 17, and 18-electron configurations for the singlet (dicp)TiCp, quartet (dicp)VCp, triplet (dicp)CrCp, doublet (dicp)MnCp, and singlet (dicp)FeCp structures. For the late transition metals Co and Ni, only the allyl unit of the dicp ligand is strongly coordinated to the transition metal atom, in contrast to the Cp2Co and Cp2Ni in which all ten carbon atoms of the two cyclopentadienyl ligands are coordinated to the central metal atom. The potential energy surface for the manganese complex (dicp)MnCp is much more complicated than that of manganocene Cp2Mn, in which the doublet, quartet, and sextet structures are nearly degenerate in energy, with the quartet and sextet low-energy structures having only have part of the allyl or olefin unit coordinated to the central manganese atom. Weak agostic CHM interactions between the dicp ligand and the metal atoms, typically with M—H distances of ∼2.7 Å, are found in many of the (dicp)MCp complexes in contrast to the Cp2M (M = Ti, V, Cr, Mn, Fe, Co, Ni).