Nenad M. Kostic

Molecular orbital study of bonding and conformations in dinuclear cyclopentadienyldicarbonyl complexes of manganese and chromium containing germanium, sulfide, dinitrogen or phosphinidene bridges

Abstract We carried out nonempirical molecular orbital calculations on syn , gauche and anti conformations of four dinuclear complexes of Mn and Cr with various bridging ligands: [CpM(CO) 2 ] 2 (μ 2 -L) where M is Mn, L is C (as a model for Ge), N 2 or PPh; and M is Cr, L is S. Contrary to a recent claim, [CpMn(CO) 2 ] 2 Ge does not seem to contain Mn Ge double bonds and is not analogous to allenes. The Mn Ge bonds are partially triple so that internal rotation about the Mnz.sbnd;Ge Mn axis is facile, in accord with the infrared spectra. Bonding in [CpCr(CO) 2 ] 2 S and in [CpMn(CO) 2 ] 2 N 2 is very similar to that in the Ge-containing complex. We explain the observed nonrigidity of the Cr complex. Reported infrared data lead to mutually inconsistent conclusions about conformation of the N 2 -containing complex in solution. On the basis of calculations, we suggest that these complex molecules are not centrosymmetric in solution. The N 2 -bridged dinuclear molecules are better viewed as containing an N 2 molecule rather than two N atoms. The π-antibonding orbitals of N 2 are crucial for its bonding to metals; the filled π-bonding orbitals do not seem to donate electrons to the metal atoms. The calculations show substantial Mn P π-bonding in [CpMn(CO) 2 ] 2 PPh and this molecule is best viewed as a three-center, four-electron system. We critically examine several other qualitative and intuitive explanations of bonding in these and similar complexes and discuss conclusions and predictions based on such explanations.

Xα SW study of bonding, photoelectron spectra and photoionization transition states of (cyclobutadiene)iron tricarbonyl

Abstract We report Xα SW MO calculations on (η 2 -C 4 H 4 )Fe(CO) 3 and its five transition states, formed by removing a half of an electron from each of the five uppermost filled MO s . Eigenvalues in the transition states depend only slightly upon the MO from which the “high-ionization” occurs. The MOs are more polarized in the transition states than in the ground state. The C 4 H 4 -Fe bonding is highly covalent.

Phosphorus-containing analogues of hydrocarbon ligands. Molecular orbital study of structure and bonding in potential transition-metal complexes containing phosphoranium ions as л ligands

Abstract Structures of phosphoranium ions C(PR3)32+ and CR(PR3)2+ reveal partial л character of the PC bonds and molecular orbital calculations confirm that. These two ions are structurally and orbitally similar to well-known trimethylenemethane and allyl species, respectively. We cautiously suggest that possibility of л coordination of phosphoranium ions to transition metals be explored. We carried out molecular orbital calculations on various conformations of two hypothetical complexes, (CO)3Co[C(PH3)3]+ and (PH3)2Pd[CH(PH3)2]+. In the former molecule, Co(CO)3− and C(PH3)32+ groups tend to be staggered, and the P atoms tend to bend toward the Co atom. In the latter molecule, the Pd(PH3)2 group tends to slip toward the phosphoranium P atoms and to stay perpendicular to the mirror plane of CH(PH3)2+; the ligand plane tends to tilt so that the CH group moves away from the Pd atom. In both molecules, the substituents at the phosphoranium P atoms tend to bend away from the metal atom. These predictions agree with structures of various known complexes of transition metals with unsaturated organic ligands.