Spin-Coupled Model of the Bonding in First-Row Transition Metal Methylene Monocations

Abstract

The ab initio spin-coupled model, which is one of the most useful formulations of modern valence bond theory, has been used to study the general characteristics of, and the variations in, the chemical bonding in MCH 2 + (M ) Sc-Co) systems. The covalent metal-methylene interaction, characteristic of Schrock complexes, exhibits simultaneously a metal to ligand σ electron donation and a ligand to metal π electron donation. The degree of σ donation decreases and that of π donation increases monotonically from ScCH 2 + to CoCH 2 + in parallel with the decreasing dipole moment of the system and the increasing electronegativity of the M + center. The metal-methylene interactions are found to be well described by a balance between two resonant Lewis structures: a dominant doubly bonded closed-shell + MdCH 2 form and a much less important diradical-like, singly bonded form, + M • s • CH 2 . The importance of this last, which accounts for the triplet character in the π (and σ) interaction(s), grows with the number of unpaired nonbonding electrons on the metal. Such trends may be easily understood in terms of the preservation of intraatomic exchange energy and are consistent with a general decrease in the intrinsic bond strength from ScCH 2 + to MnCH 2 + , and vice versa from MnCH 2 + to CoCH 2 + . In addition, the sequential filling of nonbonding orbitals across the series is found to originate from a compromise between the minimization of repulsive electrostatic interactions between them and with bonding pairs, and the maximization of the intraatomic exchange energy.

Electronic spectroscopy of intermediates involved in the conversion of methane to methanol by FeO+

“…36,[39][40][41] However, only its ground state has been extensively studied and few attempts have been made to characterize excited states. During the past two decades FeCH 2 ϩ has been the subject of numerous experimental and theoretical studies.…”

Valence Bond Concepts Applied to the Molecular Mechanics Description of Molecular Shapes. 4. Transition Metals with π-Bonds

“…The ground triplet state of VO + is described as triple bond, similar to that of Cl 4 CrO, whereas the ground quartet state of RuO + involves a covalent σ-bond and two three-electron π-bonds, similar to the bonding in O 2 . With respect to MCH 2 bonding numerous descriptions of “naked” complexes have been provided. , Metal complexes with saturated valences and MC bonds are our primary concern. Goddard and Carter 30 described a VB analysis of ClRu(CH 2 )H with an emphasis on two conformers: one with the C−Ru−H plane orthogonal to the H−C−H plane and one with the two planes parallel.…”