Conformational Flexibility of Dibenzobarrelene-Based PC(sp(3))P Pincer Iridium Hydride Complexes: The Role of Hemilabile Functional Groups and External Coordinating Solventsстатья
Статья опубликована в высокорейтинговом журнале
Информация о цитировании статьи получена из
Web of Science,
Scopus
Статья опубликована в журнале из списка Web of Science и/или Scopus
Дата последнего поиска статьи во внешних источниках: 18 марта 2017 г.
Аннотация:Bifunctional dibenzobarrelene-based PC(sp(3))P pincer iridium complex 1 is known as an efficient catalyst in acceptorless dehydrogenation of alcohols and hydrogenation/hydroformylation of alkenes. In order to shed light on the mechanism of the hydrogen formation/activation, we performed variable-temperature IR and NMR (H-1, P-31) analysis of intra- and intermolecular interactions involving a hydride ligand and hydroxymethyl cooperating group in 1 and its analogues. The results of the spectroscopic measurements in different media (dichloromethane, toluene, DMSO, and mixed solvents) were compared with the quantum chemical (DFT/M06 and B3PW91) calculations. The obtained data imply flexibility of the dibenzobarrelene-based scaffold, unprecedented for conventional pincer ligands. Both the CH2OH-substituted complex 1 and its COOEt analogue 3 prefer facial configuration of the PCP ligand with a PIrP angle of ca. 100 degrees. Such geometries are stabilized by Ir...O interaction with the dangling functional group and differ by the mutual arrangement of the H and Cl ligands. The complexes show dynamic equilibrium between the two most stable fac-isomers, which can be transformed into the meridional ones in the presence of coordinating additives ((CHCN)-C-3, DMSO, or CO, but not (EtN)-N-3). The process is reversible for CH3CN but irreversible for DMSO and CO, in agreement with the Lewis basicity of these molecules.