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Ligands Based on Phosphine-Stabilized Aluminum(I), Boron(I) and Carbon(0).

Research paper by Lisa L Vondung, Paul P Jerabek, Robert R Langer

Indexed on: 20 Dec '18Published on: 20 Dec '18Published in: Chemistry - A European Journal



Abstract

We report a systematic quantum chemical study of the bonding in d⁶ transition metal complexes, containing phosphine-stabilized main group element fragments (R₃P)₂E as ligands (E = AlH, BH, CH+, C). Using energy decomposition analysis it is demonstrated that a strong M-E bond is accompanied by weak P-E bonds and vice versa. Although the Al-M bond is for example found to be very strong, the weak Al-P bond suggests that the corresponding metal complexes will not be stable towards phosphine dissociation. The interaction energies for the boron(I)-based ligand are lower, but still higher than for the two carbon-based ligands. For neutral ligands the electrostatic interactions are the dominating contributions to metal-ligand-bonding, while for the cationic ligand a significant destabilisation with weak orbital and even weaker electrostatic metal ligand interactions are observed. Finally, we demonstrate for iron complexes that different reactivity patterns are expected for the four donor groups: the experimentally observed reversible E-H-reductive elimination of the borylene-based ligand (E=BH) exhibits significantly higher barriers for the protonated CDP-ligand (E=CH) and would proceed via different intermediates and transition states. For aluminum, such reaction pathways are not feasible (E = AlH). Moreover, we demonstrate that the metal hydrido complexes with CDP-ligands might not be stable towards reduction and isomerisation to a protonated CDP-ligand and a reduced metal centre. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.