THE QUEST FOR BRIDGING TRIFLUOROPHOSPHINE LIGANDS IN TRANSITION METAL COMPLEXES

Trifluorophosphine is a strong back-bonding ligand like the ubiquitous carbonyl ligand. In fact mononuclear zerovalent trifluorophosphine complexes such as M(PF3)(6) (M = Cr, Mo, W), M(PF3)(5) (M = Fe, Ru), and M(PF3)(4) (M = Ni, Pt) are even more stable than their well-known carbonyl analogues. However, metal complexes with bridging trifluorophosphine ligands are virtually unknown. We review theoretical studies on the Co-2(PF3)(8), Fe-2(PF3)(9), and Cp2Fe2(PF3)(n) (Cp = eta(5)-C5H5; n = 4, 3) systems analogous to the well-known metal carbonyls Co-2(CO)(6)(mu-CO)(2), Fe-2(CO)(6)(mu-CO)(3), Cp2Fe2(CO)(2)(mu-CO)(2), and Cp2Fe2 (mu-CO)(3) containing two or three bridging CO groups. In most cases structures having features other than bridging PF3 groups are energetically preferred.