Intuitive Quantifiers of Charge Flows in Coordinate Bonding

摘要

ETS-NOCV charge and bond energy analyses have been carried out for a broad range of transition-metal carbonyl complexes L-[M], comprising different ligand classes, transition metals, and coordination geometries. The resulting electronic redistributions are visually assigned to sigma donation, pi backbonding, and related interactions. We propose a Hirshfeld partitioning of these electronic redistributions to afford the corresponding charge flow contributions Delta(go), Delta(g pi), etc. Taken together, a detailed picture of the dative bonding arises, in terms of both energetics and the extent of sigma-electron donation and pi-rcelectron backbonding. The charge flows Delta(q sigma), and Delta(q pi); appropriately quantify trends in the ligand sigma-donor and pi-acceptor abilities and are transferable across the transition-metal complexes studied and thus promise to be suitable descriptors for ligand knowledge bases. As a case in point, the TEP is well reproduced: by the calculated nu(CO)(A(1)) frequencies and is 3 times more strongly affected by Delta(q sigma), than by Delta(q pi), with an additional modest steric influence. Further, empirical relationships are derived among the charge flows Delta(g pi) and Agit, the (L)W(CO)5 carbonyl stretching frequencies, and the ligand's steric volume %V-bur which allow estimating the a-donor and pi-acceptor abilities of phosphines from experimental observables. On the other hand, direct Cl: -> L-sigma* interactions are identified in several cis-(L)Ir(CO)(2)Cl complexes, which compromises the use of these species as experimental probes for ligand parameters.