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

TY - JOUR

T1 - Rhodium(III) and Iridium(III) Complexes of a NHC-Based Macrocycle

T2 - Persistent Weak Agostic Interactions and Reactions with Dihydrogen

AU - Gyton, Matthew R.

AU - Leforestier, Baptiste

AU - Chaplin, Adrian B.

N1 - Funding Information: We thank the European Research Council (ERC, grant agreement 637313) and Royal Society (UF100592, UF150675, A.B.C.) for financial support. High-resolution mass spectrometry data were collected using instruments purchased through support from Advantage West Midlands and the European Regional Development Fund. Crystallographic data were collected using an instrument that received funding from the ERC under the European Union’s Horizon 2020 research and innovation program (grant agreement No. 637313). We thank Dr. C. André Ohlin for access to specialist computational resources. Publisher Copyright: © 2018 American Chemical Society.

PY - 2018/11/12

Y1 - 2018/11/12

N2 - The synthesis and characterization of five-coordinate rhodium(III) and iridium(III) 2,2′-biphenyl complexes [M(CNC-12)(biph)][BArF 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 ϵ-agostic interactions that are characterized by M···H-C contacts of ca. 3.0 Å by X-ray crystallography and ν(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][BArF 4] (2a″) and [Ir(CNC-12)H2(H2)][BArF 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.

AB - The synthesis and characterization of five-coordinate rhodium(III) and iridium(III) 2,2′-biphenyl complexes [M(CNC-12)(biph)][BArF 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 ϵ-agostic interactions that are characterized by M···H-C contacts of ca. 3.0 Å by X-ray crystallography and ν(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][BArF 4] (2a″) and [Ir(CNC-12)H2(H2)][BArF 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.

UR - http://www.scopus.com/inward/record.url?scp=85054838420&partnerID=8YFLogxK

U2 - 10.1021/acs.organomet.8b00595

DO - 10.1021/acs.organomet.8b00595

M3 - Article

AN - SCOPUS:85054838420

SN - 0276-7333

VL - 37

SP - 3963

EP - 3971

JO - Organometallics

JF - Organometallics

IS - 21

ER -