Infrared Photodissociation Spectroscopy of Mass-Selected Dinuclear Transition Metal Boride Carbonyl Cluster Cations

Abstract

The transition-metal−boron bonding interactions and geometric structures of heterodinuclear transition metal carbonyl cluster cations BM(CO) n + (M = Co, Ni, and Cu) are studied by a combination of the infrared photodissociation spectroscopy and density functional theory calculations at the B3LYP/def2-TZVP level. The BCu(CO) 5 + and BCo(CO) 6 + cations are characterized as an (CO) 2 B−M(CO) 3/4 + structure involving an σ-type (OC) 2 B → M(CO) 3,4+ dative bonding with end-on carbonyls, while for BNi(CO) 5,6+ complexes with a bridged carbonyl, a 3c−2e bond involving the 5σ electrons of the bridged carbonyl and an electron-sharing bond between the B(CO) 2 fragment and the Ni(CO) 2,3 + subunits were revealed. Moreover, the fundamental driving force of the exclusive existence of a bridged carbonyl group in the boron−nickel complexes has been demonstrated to stem from the desire of the B and Ni centers for the favorable 8-and 18-electron structures.

Formation of Delocalized Linear M–B–M Covalent Bonds: A Combined Experimental and Theoretical Study of BM2(CO)8+ (M = Co, Rh, Ir) Complexes

“…Four well-resolved absorption bands centered at 2062, 2112, 2142, and 2146 cm –1 for the BRh­(CO) 7 + cation were detected, indicating that the carbonyl ligands in this complex should be terminally bonded. Similar results for the photofragmentation mass spectra (Figures S7 and S8) and infrared photodissociation spectra (Figure S9) of the BIr­(CO) 7,8 + complexes were obtained, as in the case of BCo­(CO) 7,8 + in our previous work …”

“…According to the calculations, the experimentally observed BIr­(CO) 6 + complex was determined to be a mimic of BRh­(CO) 6 + , with the same geometric symmetry and electronic state (Figure S17). Both BRh­(CO) 6 + and BIr­(CO) 6 + can be viewed as a combination of the B­(CO) 2 and M­(CO) 4 fragments, analogous to previously reported BCo­(CO) 6 + …”

“…The elucidation of the three delocalized bonds (21e u , 22e u , and 16a 2u ) in BCo 2 (CO) 8 + suggests that the formal bond index of the Co–B–Co link should be 1.5, which is in good agreement with the calculated Wiberg bond index (1.33). For comparison, the B–Co bond index of BCo­(CO) 6 + is estimated to be 0.85, corresponding to the previously revealed single dative bond . This is consistent with the fact that the predicted B–Co distance in BCo 2 (CO) 8 + (1.846 Å) is appreciably shortened relative to that of BCo­(CO) 6 + (2.049 Å).…”

“…This bonding scheme is also presented in BIr­(CO) 6 + , which has the same geometric and electronic parameters as BRh­(CO) 6 + (C s , 2 A′), conferring the iridium center the favored 18-electron configuration. In contrast, the saturated BCo­(CO) 6 + was disclosed to be a B­(CO) 2 → Co­(CO) 4 + coordination assembly with slight geometric distortions, leading to a departure from the C s symmetry . The unpaired electron of BCo­(CO) 6 + originates from a nonbonding orbital of the fragment B­(CO) 2 and hence fails to establish the weak covalent bonding interaction as in BRh­(CO) 6 + and BIr­(CO) 6 + .…”