Expanding the Concepts Trans Influence and Back-Donation: Hybrid and Side Donations in [Cp*M^III(L)XY] (M = Rh, Ir) Complexes with CO, CN^–, and CNR Ligands. A Window to Cis Influence

Abstract

Analysis of the bonding contributions in molecules [M III Cp*(L)XY] (M = Rh, Ir; Cp* = C 5 Me 5 ; L = CO, CN − , CNR) has uncovered a rich variety of types of interaction that seem to have escaped detection so far, in spite of the continuous popularity of cyclopentadienyl transition-metal complexes since the 1970s. At variance with the MCO bond in square-planar systems, which shows typical metal-to-CO π-back-donation, the nonorthogonal arrangement of the Cp* plane and RhCO fragment and the pseudooctahedral geometry lead to the observation of many direct lateral donations from other ligands that do not involve the metal orbitals, and we name side donations, for instance, Cp* → π*(CO), Cl → π*(CO), and F → π*(CO). Hybrid donations partially involving the metal, M−C aryl → π*(CO), are also observed. The summation of multiple contributions other than back-donation can easily account for about 20% of the electron donation to the π*(CO) orbitals.

Assessing the donor ability of boratabenzene and 9-borataphenanthrene anions through metal complexes with carbonyl ligands

“…16 For the anionic group 6 species, the cations and crown ethers were included. The calculated values with a 0.966 scaling factor applied (which is documented in similar calculations) 17 correlate well with the experimental values and obey the same trends. The group 6 complexes with L1 and L2 have three stretching frequencies while the Cp and mesitylene complexes have only two, due to higher symmetry.…”

Bond Strength of a Diatomic Acceptor Ligand: A Reliable Measure of Its Antibond Occupation and Its Charge?

“…As an example, the origin of the red‐shift of the C−O stretch in alkaline‐earth octacarbonyls is seen as a result of backbonding by the one group, or as a result of lateral CO⋅⋅⋅CO interactions by the other [17] . Moreover, new orbital‐based concepts in carbonyl and cyanide chemistry such as ‘side donation’ might be inspected with respect to electrostatic aspects [18] …”

“…[17] Moreover, new orbital-based concepts in carbonyl and cyanide chemistry such as 'side donation' might be inspected with respect to electrostatic aspects. [18] Bond strength measures…”

γ-Agostic interactions in (MesCCC)Fe–Mes(L) complexes

“…19 NBO analysis on 1-CO revealed an additional backdonation with important contribution of the CO ligand located cis (Fig. S23, ESI †), 20 which further contributes to the weakening of the C-H bond, thus increasing its subsequent reactivity as observed in experiments.…”