3 years ago

Intuitive Quantifiers of Charge Flows in Coordinate Bonding

Intuitive Quantifiers of Charge Flows in Coordinate Bonding
Yu-Ying Lai, Erik P. A. Couzijn, Peter Chen, Armin Limacher
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 σ donation, π backbonding, and related interactions. We propose a Hirshfeld partitioning of these electronic redistributions to afford the corresponding charge flow contributions Δqσ, Δqπ, etc. Taken together, a detailed picture of the dative bonding arises, in terms of both energetics and the extent of σ-electron donation and π-electron backbonding. The charge flows Δqσ and Δqπ appropriately quantify trends in the ligand σ-donor and π-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 νCO(A1) frequencies and is 3 times more strongly affected by Δqσ than by Δqπ, with an additional modest steric influence. Further, empirical relationships are derived among the charge flows Δqσ and Δqπ, the (L)W(CO)5 carbonyl stretching frequencies, and the ligand’s steric volume %Vbur, which allow estimating the σ-donor and π-acceptor abilities of phosphines from experimental observables. On the other hand, direct Cl:→L−σ* interactions are identified in several cis-(L)Ir(CO)2Cl complexes, which compromises the use of these species as experimental probes for ligand parameters.

Publisher URL: http://dx.doi.org/10.1021/acs.organomet.7b00365

DOI: 10.1021/acs.organomet.7b00365

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