Bharatam V. Prasad

Theoretical studies of (μ-CR) bridging complexes

Abstract Scrambling of substituents on the C3R3 bridging ligands in L2W(μ-C3R3)(μ- CR)WL2 is studied using Extended Huckel calculations by two pathways: deinsertion and cyclopropenium ring formation. The reaction of L2W(μ-CR)2WL2 with allenes to give L2W(μ-CHC(CR2)2)(μ-CR)WL2 is also studied. The electronic structure of CpMeW(μ- CMe)2WMeCp is compared to that of L2W(μ-CR)2WL2.

To tilt or not to tilt? The dilemma of μ-C3R3 ligands in binuclear complexes

Abstract The symmetrical or tilted positioning of μ-C 3 R 3 groups that straddle an otherwise symmetrical metalmetal bond is dictated by the geometric flexibility available to the terminal ligands of the metal. The C 3 Cl 3 in [(OC)Ni(μ-C 3 Cl 3 )Ni(CO)] 2 Cl 2 is symmetrical because the Ni(CO)Cl groups are free to pyramidalize around the metal so that both metals can bond simultaneously with the bridging ligand. The additional bridging CR group in L 2 W(μ-CR)(μ-C 3 R 3 )WL 2 prevents substantial pyramidalization at the WL 2 centre. In unsymmetrical metal environments the middle carbon of the C 3 R 3 group tilts toward the ML n fragment that provides the more diffuse frontier orbitals. For example, (η 5 -C 5 (C 6 R 5 ) 2 )Ni(μ-C 3 (C 6 H 5 ) 2 )Ni(η 4 - C 4 (C 6 H 5 ) 4 ) has the middle CR group tilted towards (η 4 -C 4 (C 6 H 5 ) 4 )NI.

Ab initio MO studies on the isomers of Si2BH3

Abstract Ab initio molecular orbital calculations at the QCISD(T)/6-31 G* level on the isomers of Si 2 BH 3 indicate the global minimum to be a hydrogen-bridged structure with 2π electron delocalization and planar tetra coordination around boron. Disilaborirene, analogous to borirene, lies slightly higher in energy than the global minimum. In contrast to borylethyne, disilaborylethyne was found to be a higher-order stationary point. Cyclic delocalization and divalency on silicon tend to stabilize the isomers, while multiple bonding involving silicon is not favoured. Isomers predicted using the diagonal relationship between boron and silicon retain similar relative energies.

Theoretical studies on (μ-S2CR) bridged cyclopentadienyl molybdenum dimers

The electronic structures of CpMo(μ-S2C2H2)(μ S2CS)MoCp, (1), CpMo(μ-S2C2H2)(μ-S2CSMe)- MoCp+ (2) and CpMo(μ-S2C2H2)(μ-S2CCH3)MoCp+ (3) are studied. Electronic factors control the unsymmetrical bridging nature of the η3 bridging units in 2 and 3.

Isolobal analogy between trivalent boron and divalent silicon

Singlet organosilylenes with a lone pair and an emptyp orbital are isolobal to trivalent borane if a B-H is equated to the lone pair on Si. Using this analogy, a particular isomer of CSi2H2 (24) is predicted to be a stable structure. MNDO calculations on24 and many of its possible isomers suggest that24 is at global minimum on the potential energy surface of CSi2H2.Ab initio calculations using a, minimal STO-3G basis set, on some selected structures also support these results.

The fragment molecular orbital approach in organometallic reactivity. Reactions of the binuclear complexes

The fragment molecular orbital approach has emerged as a framework model in theoretical organometallic chemistry. This provides an understanding of the electronic structure and bonding in polynuclear complexes in terms of their constituent fragments that are well understood. Symmetry properties of the frontier molecular orbitals of organometallic complexes help in explaining their reactivity towards various reagents.