Transition-metal complexes [(PMe(3))(2)Cl(2)M(E)] and [(PMe(3))(2)(CO)(2)M(E)] with naked group 14 atoms (E=C-Sn) as ligands; part 1: parent compounds.
The equilibrium geometries and bond dissociation energies of 16-valence-electron(VE) complexes [(PMe(3))(2)Cl(2)M(E)] and 18-VE complexes [(PMe(3))(2)(CO)(2)M(E)] with M=Fe, Ru, Os and E=C, Si, Ge, Sn were calculated by using density functional theory at the BP86/TZ2P level. The nature of the M--E bond was analyzed with the NBO charge decomposition analysis and the EDA energy-decomposition analysis. The theoretical results predict that the heavier Group 14 complexes [(PMe(3))(2)Cl(2)M(E)] and [(PMe(3))(2)(CO)(2)M(E)] with E=Si, Ge, Sn have C(2v) equilibrium geometries in which the PMe(3) ligands are in the axial positions. The complexes have strong M--E bonds which are slightly stronger in the 16-VE species 1ME than in the 18-VE complexes 2ME. The calculated bond dissociation energies show that the M--E bonds become weaker in both series in the order C>Si>Ge>Sn; the bond strength increases in the order Fe<Ru<Os for 1ME, whereas a U-shaped trend Ru<Os<Fe is found for 2ME. The M--E bonding analysis suggests that the 16-VE complexes 1ME have two electron-sharing bonds with sigma and pi symmetry and one donor-acceptor pi bond like the carbon complex. Thus, the bonding situation is intermediate between a typical Fischer complex and a Schrock complex. In contrast, the 18-VE complexes 2ME have donor-acceptor bonds, as suggested by the Dewar-Chatt-Duncanson model, with one M<--E sigma donor bond and two M-->E pi-acceptor bonds, which are not degenerate. The shape of the frontier orbitals reveals that the HOMO-2 sigma MO and the LUMO and LUMO+1 pi* MOs of 1ME are very similar to the frontier orbitals of CO.
Parameswaran
Pattiyil
P
Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Strasse, 35032 Marburg, Germany.
Frenking
Gernot
G