Binuclear dimethylaminoborole iron carbonyls: iron–iron multiple bonding versus nitrogen → iron dative bonding
Theoretical studies show that pendant dimethylamino groups can play a significant role in the chemistry of unsaturated binuclear dimethylaminoborole iron carbonyls. For [C4H4BN(CH3)2]2Fe2(CO)5, the lowest energy structures have single CO bridges and Fe–Fe single bonds of lengths ~2.8 Å. The lowest energy [C4H4BN(CH3)2]2Fe2(CO) n (n = 4, 3) structures have two bridging CO groups with Fe=Fe double bonds of lengths ~2.5 Å for n = 4 and three bridging CO groups with Fe≡Fe triple bonds of lengths ~2.2 Å for n = 3. These structures are similar to structures previously found for the corresponding methylborole derivatives (C4H4BCH3)Fe2(CO) n . However, slightly higher energy [C4H4BN(CH3)2]2Fe2(CO) n (n = 4, 3) structures are found in which dimethylaminoborole is a six-electron donor bridging ligand using electron pairs from the nitrogen atom as well as from the two C=C double bonds. For the more highly unsaturated [C4H4BN(CH3)2]2Fe2(CO) n (n = 2, 1), low energy singlet (n = 2) and triplet (n = 1) perpendicular structures are also found with similar bridging six-electron donor dimethylaminoborole ligands. In addition, highly unsaturated [C4H4BN(CH3)2]2Fe2(CO) n (n = 3, 2, 1) structures are found with agostic hydrogen atoms bridging an iron–carbon bond.
KeywordsIron Boroles Metal carbonyls Dimethylaminoborole Metal–metal bonding Nitrogen–iron dative bonding Density functional theory
The research was supported by the Program for New Century Excellent Talents in University (Grand No. NCET-10-0949) China, the Scientific Research Fund of the Key Laboratory of the Education Department of Sichuan Province (Grant No. 10ZX012) and the Research Fund of Key Disciplines of Atomic and Molecular Physics, Xihua University, China, as well as the US National Science Foundation (Grants CHE-0716718, CHE-0749868, CHE-1057466, and CHE-1054286) for the support of this research.
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