Conformational flexibility of dibenzobarrelene-based PC(sp3)P pincer iridium hydride complexes: The role of hemilabile functional groups and external coordinating solvents

Gleb A. Silantyev, Oleg A. Filippov, Sanaa Musa, Dmitri Gelman, Natalia V. Belkova*, Klaus Weisz, Lina M. Epstein, Elena S. Shubina

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

32 Scopus citations

Abstract

Bifunctional dibenzobarrelene-based PC(sp3)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 (1H, 31P) 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 P-Ir-P angle of ca. 100°. 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 (CH3CN, DMSO, or CO, but not Et3N). The process is reversible for CH3CN but irreversible for DMSO and CO, in agreement with the Lewis basicity of these molecules.

Original languageAmerican English
Pages (from-to)5964-5973
Number of pages10
JournalOrganometallics
Volume33
Issue number21
DOIs
StatePublished - 10 Nov 2014

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© 2014 American Chemical Society.

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