Nonlinear d¹⁰‐ML₂ Transition‐Metal Complexes

Abstract

We have investigated the molecular geometries of a series of dicoordinated d10-transition-metal complexes ML2 (M=Co−, Rh−, Ir−, Ni, Pd, Pt, Cu+, Ag+, Au+; L=NH3, PH3, CO) using relativistic density functional theory (DFT) at ZORA-BLYP/TZ2P. Not all complexes have the expected linear ligand–metal–ligand (L–M–L) angle: this angle varies from 180° to 128.6° as a function of the metal as well as the ligands. Our main objective is to present a detailed explanation why ML2 complexes can become bent. To this end, we have analyzed the bonding mechanism in ML2 as a function of the L–M–L angle using quantitative Kohn–Sham molecular orbital (MO) theory in combination with an energy decomposition analysis (EDA) scheme. The origin of bent L–M–L structures is π backdonation. In situations of strong π backdonation, smaller angles increase the overlap of the ligand’s acceptor orbital with a higher-energy donor orbital on the metal-ligand fragment, and therefore favor π backdonation, resulting in additional stabilization. The angle of the complexes thus depends on the balance between this additional stabilization and increased steric repulsion that occurs as the complexes are bent.

New Concepts for Designing d10‐M(L)n Catalysts: d Regime, s Regime and Intrinsic Bite‐Angle Flexibility

“…strong p backbonding). [29] Going from Pd(PH 3 ) 2 to Ag(PH 3 ) 2 + , we find a slightly more steeply increasing catalyst strain in an early stage of the reaction, despite the fact that both catalyst complexes have linear L-M-L angles in their equilibrium geometries. This shows that not the bite angle itself, but the intrinsic bite-angle flexibility of the catalyst is decisive for the reaction barrier.…”

“…We have recently elucidated the reason for this bending. [29] Our analyses showed that L-M-L bending is favorable for d 10 M(L) 2 complexes with strong p backbonding, because the increase in steric repulsion is outweighed by a more strongly increasing stabilization that occurs when one of the two ligand p* acceptor orbitals overlaps and interacts with a different metal d orbital that is not yet stabilized by backbonding to the other ligand and therefore at a higher orbital energy.…”

“…The concomitant deformation energy DE strain [cat] is smallest for Ni(PH 3 ) 2 and largest for Pt(PH 3 ) 2 , because a somewhat stronger p backbonding from the higher-energy nickel d orbitals causes this complex to have a reduced resistance against bending the ligands away. [29] Therefore, the energy profiles of Pd(PH 3 ) 2 and Pt(PH 3 ) 2 rise faster in an early stage of the reaction than for Ni(PH 3 ) 2 . Later on, however, the interaction energy curve starts to descend more steeply for Pt(PH 3 ) 2 than for Ni(PH 3 ) 2 and Pd(PH 3 ) 2 .…”

Origin of Inversion versus Retention in the Oxidative Addition of 3-Chloro-cyclopentene to Pd(0)Ln

“…Figure S2. Profiles of the total energy E, the interaction energy E int , and the distortion energies E d (1) (for PdL) and E d (2) (for the allylic fragment) in kcal/mol versus the C-Cl distance in Å. The grey vertical lines mark the transition state locations (dotted=syn; solid=anti).…”

“…E_SCF (1) a E_SCF (2) Table 3. Orbital overlaps, orbital energies, charge transfer, electron density and the laplacian of the electron density at the Pd-Cl bond critical point along the reaction coordinate.…”