DFT Study on Alkyl‐ and Haloborylene Complexes of Manganese and Rhenium: Structure and Bonding Energy Analysis in [(η 5 ‐C 5 H 5 )(CO) 2 M(BR)] and [(η 5 ‐C 5 H 5 )(CO) 2 M(BX)] (M = Mn, Re; R = Me, Et, i Pr, t Bu; X = F, Cl, Br, I)

Electronic, molecular structures, and bonding analysis of the terminal neutral alkylborylene and haloborylene complexes of manganese and rhenium [(η 5 ‐C 5 H 5 )(CO) 2 M(BR)] and [(η 5 ‐C 5 H 5 )(CO) 2 M(BX)] (M = Mn, Re; R = Me, Et, i Pr, t Bu; X = F, Cl, Br, I) were investigated at the DFT/BP86/TZ2P level of theory. The calculated geometry of the manganese alkylborylene complex [(η 5 ‐C 5 H 5 )(CO) 2 Mn(B t Bu)] is in excellent agreement with the experimentally derived structural data. Pauling bond order of the optimized structures shows that the M–B bonds in these complexes are almost M=B double bonds, which is also supported by the performed energy decomposition analysis. The orbital interactions between the metal and boron arise mainly from M←BR σ donation, while the π bonding contribution is relatively small (22.6–25.8 % of total orbital contributions). The M–B π bond orbitals are highly polarized towards the metal atom and the contributions of boron are very small. In the BX ligands, σ bonding, interaction energies, electrostatic interactions and bond dissociation energies are smaller than those in the BR ligands. The contributions of the electrostatic interactionsΔ E elstat are significantly larger in all borylene complexes than the covalent bonding Δ E orb : the [M]=BR bonding in the alkylborylene and haloborylene complexes has a greater degree of ionic character (ca. 61.7 % for the complexes I – IV , ca. 65.7 % for the complexes V – VIII , 53.9–56.2 % for the complexes IX – XII and 58.5–60.4 % for the complexes XIII – XVI ). The chloroborylene complexes [(η 5 ‐C 5 H 5 )(CO) 2 M(BCl)] possess the highest electrostatic interactions, Δ E elstat of all haloborylene complexes [(η 5 ‐C 5 H 5 )(CO) 2 M(BX)], whereas the iodoborylene complexes [(η 5 ‐C 5 H 5 )(CO) 2 M(BI)] display the highest orbital interactions, Δ E orb . The dimerization of the terminal borylene complex [(η 5 ‐C 5 H 5 )(CO) 2 Mn(BCl)] to [{(η 5 ‐C 5 H 5 )(CO) 2 Mn} 2 (η:η:μ‐B 2 Cl 2 )] is a strongly exothermic process (21.04 kcal/mol below the starting monomers) and the energies are in favor of a dimerization reaction.