Ab initio molecular orbital study of the electronic structure and the rotational barrier of benzene in the helicopter complex Os3(CO)9(C6H6)

Abstract

A theoretical analysis is presented on the structure, bonding nature, and rotational barrier of the Os3(CO)9(CeH6) complex, which has a benzene molecule in a new face-capping u3-y2'-v2'-V2 coordination mode. Using RHF geometry optimization and MP2 calculations, we have estimated the interaction energy between the Os3(CO)9 fragment and the benzene molecule, as well as the benzene rotational barrier with respect to the OS3 triangle (15.9 kcal/mol). An MO analysis leads to an interpretation of the interaction between Os3(CO)9 and benzene in terms of donation and back-donation which are enhanced by the CH bending. The origin of the KekulS distortion of benzene has been attributed to an increase in the back-donation and a decrease in exchange repulsion due to benzene x electrons. The rotational barrier is caused by a decrease in the back-donation and an increase in exchange repulsion due to benzene a electrons. A comparison has been made among the interactions of this polymetallic compound with benzene and ethylene as well as those of a model monometallic fragment with ethylene and benzene.

Organometallic Cluster Complexes with Face-Capping Arene Ligands. 8. Nucleophilic Reactivity of Cluster Complexes with Face-Capping Arene Ligands: Metal vs Ligand Protonation

“…Some of us have previously investigated the interaction of benzene with the (CpCo) 3 cluster, using the approximate Fenske−Hall SCF method . Our results have later been confirmed by several extended Hückel, Fenske−Hall, and ab initio studies on the valence isoelectronic derivatives [{(CO) 3 M} 3 (μ 3 -C 6 H 6 )] (M = Ru, Os) . There is an electronic preference for a staggered conformation of the benzene relative to the metal triangle and for an alternation of stronger (shorter) and weaker (longer) bonds in the ring, the shorter bonds eclipsing the metal atoms.…”

Theoretical Studies of [Os3(CO)10(α-Diimine)]: Structures, Frontier Orbitals and Bonding

“…Morokuma and co-workers studied the bonding in Os 3 -(CO) 9 (C 6 H 6 ) using single-point MP2 energy calculations on HF-optimized structures, and EH for orbital analysis. [5] Some of us qualitatively analyzed the bonding of orthometallated α-diimines to HOs 3 (CO) 9 . [6a] In this work, DFT calculations [7] performed under different conditions and on models of three Os 3 (CO) 10 (α-diimine) clusters are described, and the reliability of extended Hückel [8] calculations on these systems is discussed.…”

Spectroscopic and Computational Investigations of Stable Radical Anions of Triosmium Benzoheterocycle Clusters

“…This is also the case for 1 after exhaustive electrolysis for which we observe a uniform sharpening of the 1 H NMR resonances for the small amount of unreduced cluster as the temperature is decreased Density functional theory calculations and spectral simulations: The density functional theory (DFT) approach has proven to be a very useful method for understanding chemical bonding in transition-metal and polymetallic complexes. [17,18] DFT methods have been previously successfully applied to calculations of triosmium clusters: Morokuma and co-workers studied the bonding in [Os 3 (CO) 9 (C 6 H 6 )], [19] and Calhorda et al studied in detail structures, frontier orbitals, and bonding of [Os 3 (CO) 10 (a-diimine)] clusters. [20] The most important features of the molecular-orbital description of 1 are the characteristics of the HOMO and LUMO orbitals.…”