Three ferrocene analogues, D 5h (η5-CB5H5)2M (M = Fe2-, Co-, and Ni), with triplet aromatic CB5H5 ligands have been predicted at TPSSh/6-311+G(d,p) level. We find that the M atom interacts drastically with the two CB5H5 ligands through a nearly fully-filled 3d subshell, which is different from (η5-C5H5)2Fe. The natural population analyses suggest that (η5-CB5H5)2M have an unconventional charge distribution, i.e., the M atom is negatively charged, while the two boron rings are positively charged. The analyses of the electronic and dynamic stabilities indicate that (η5-CB5H5)2Co- is the most stable among (η5-CB5H5)2M. Thus, we theoretically confirm that the triplet aromatic CB5H5 cluster can be regarded as a potential new ligand. Our theoretical predictions are awaiting future experimental verification.
Keywords: Ferrocene analogue; Sandwich compound; Triplet aromaticity.