The Dewar–Chatt–Duncanson model reversed — Bonding analysis of group-10 complexes [(PMe3)2M–EX3] (M = Ni, Pd, Pt; E = B, Al, Ga, In, Tl; X = H, F, Cl, Br, I)

Abstract

Quantum chemical calculations using BP86 with TZ2P basis sets were carried out to elucidate the structures and the bond–bond dissociation energies of the donor–acceptor complexes [(PMe3)2M–EX3] with X = H, F, Cl, Br, I; E = B, Al, Ga, In, Tl; and M = Ni, Pd, Pt. The nature of the metal–ligand bond was investigated with an energy decomposition analysis. The geometry optimizations gave for most compounds T-shaped structures with nearly linear P–M–P angles where the EX3 ligand has either a staggered or eclipsed conformation with respect to the PMP plane. The energy differences between the conformations are very small which means that there is nearly free rotation about the M–EX3 axis. The equilibrium structures of eight nickel compounds have a distorted geometry where one E–X bond is engaged in attractive interactions with the metal atom which yields a distorted square-planar arrangement of the metal atom. The complex [(PMe3)2Ni–TlI3] exhibits two attractive interactions between Tl–I bonds and the metal which features a five-coordinated metal atom. The calculated bond dissociation energies show that the boron complexes exhibit a different trend for the De values than the heavier group-13 homologues. The results for the Pd and Pt complexes suggest that the [(PMe3)2M–BX3] bond strength increases with F < Cl < Br < I < H which means that the BH3 ligands are the most strongly bonded Lewis acids and BF3 is the most weakly bonded species . The trend for the heavier group-13 complexes [(PMe3)2M–EX3] where E = Al, Ga, In, Tl follows the opposite order F > Cl > Br > I > H. The energy decomposition analysis of the M–EX3 bonds indicates a substantial π contribution of between 12.7% and 30.3% to the total orbital interactions. There is no direct correlation between the strength of the orbital interactions or any of the other energy terms ΔEelstat or ΔEPauli which correlates with the total interaction energy. The bond dissociation energy of the EX3 ligands after breaking the M–EX3 bonds is quite large. It is shown that the intrinsic strength of the M–EX3 bonds is much larger than the BDEs and that the trends of ΔEint and De are not always the same. The EX3 ligands in [(PMe3)2M–BX3] always carry a large negative charge.