A series of novel sandwich complexes: MQ(η4-E4)2 (M = Be or Mg; Q = C or Si; E = P, As, Sb or Bi) with donor–acceptor bonds

Abstract

A series of sandwich-like compounds MQ(η4-E4)2 (M=Be or Mg; Q=C or Si; E=P, As, Sb, or Bi) with centered donor–acceptor bond Q–M are investigated at the B3LYP/6-311+G(d)/SDD and M06-2x/6-311+G(d)/SDD levels of theory. The C4v staggered conformations are predicted to be more stable than the eclipsed ones. Wiberg bond index, electron density and Laplacian of electron density were computed, which can provide an indication of the strength and the character of the bonds. The results indicate that the donor–acceptor Q–M bonds in these complexes (with Wiberg bond index values 0.153–0.203, small electron density values less than 0.1 au and positive Laplacian of electron density) are all ionic, and the C–Be bonds with relatively larger electron density are stronger than the Si–Mg bonds. The bonds between M and E42− are ionic, whereas the Q-ligand bonds are covalent. The dissociation reactions show that these complexes are stable, and BeC(η4-E4)2 with C–Be bond dissociation energies (DE) close to the Zn–Zn bond DE in the synthesized Zn2(η5-C5Me5)2, may be synthesized in future experiments. Nucleus-independent chemical shift values suggest that the rings bonded to the donor atom have strong π aromaticity.