Homoleptic and Heteroleptic Carbones L1-C-L2

Quantum chemical calculations using density functional theory at the BP86-D3(BJ)/def2-TZVPP level and ab initio theory at the CCSD(T)/def2-TZVPP level have been carried out for the heteroleptic carbones L1-C-L2 with the ligands L1, L2 = PPh₃, SPh₂, CO, CS, NHC^Me, CAAC^Me. The complexes L1-C-L2 have bent equilibrium structures, with the exception of N₂-C-CS and OC-C-CS, which have a linear geometry. Calculations of the bond dissociation energy suggest that all heteroleptic carbones, which are considered in this work, are stable enough to be experimentally observed. A comparison of the change of the bond strength and the bond length of the heteroleptic complexes compared with the homoleptic species shows that there is no direct correlation between the changes of the bond length and the carbon-ligand BDE, which is influenced by several factors. The detailed analysis of the carbon-ligand interactions using the EDA-NOCV approach shows that the Pauli repulsion often has a stronger effect on the carbon-ligand interactions than the attractive orbital interactions. In general, weaker carbon-ligand bonds in homoleptic complexes L1-C-L1 are strengthened in heteroleptic carbons L1─C─L2, while stronger bonds L2─C─L2 are weakened. However, the extent of bond weakening/bond strengthening is not quantitatively correlated, and mutual strengthening of the bonds may even occur.