Rhodium(III) and Iridium(III) Complexes of a NHC-Based Macrocycle: Persistent Weak Agostic Interactions and Reactions with Dihydrogen.

ABSTRACT: The synthesis and characterization of five-coordinate rhodium(III) and iridium(III) 2,2'-biphenyl complexes [M(CNC-12)(biph)][BAr^F ₄] (M = Rh (1a), Ir (1b)), featuring the macrocyclic lutidine- and NHC-based pincer ligand CNC-12 are reported. In the solid state these complexes are notable for the adoption of weak ?-agostic interactions that are characterized by M···H-C contacts of ca. 3.0 Å by X-ray crystallography and ?(CH) bands of reduced wavenumber by ATR IR spectroscopy. Remarkably, these interactions persist on dissolution and were observed at room temperature using NMR spectroscopy (CD₂Cl₂) and solution-phase IR spectroscopy (CCl₄). The associated metrics point toward a stronger M···H-C interaction in the iridium congener, and this conclusion is borne out on interrogation of 1 in silico using DFT-based NBO and QTAIM analyses. Reaction of 1 with dihydrogen resulted in hydrogenolysis of the biaryl and formation of fluxional hydride complexes, whose ground state formulations as [Rh(CNC-12)H₂][BAr^F ₄] (2a?) and [Ir(CNC-12)H₂(H₂)][BAr^F ₄] (2b?) are proposed on the basis of inversion recovery and variable-temperature NMR experiments, alongside a computational analysis. Reactions of 1 and 2 with carbon monoxide help support their respective structural properties.

SUBMITTER: Gyton MR 

PROVIDER: S-EPMC6234485 | biostudies-literature | 2018 Nov

REPOSITORIES: biostudies-literature