Iridium(i) complexes bearing hemilabile coumarin-functionalised N-heterocyclic carbene ligands with application as alkyne hydrosilylation catalysts. Issue 32 (2nd August 2021)

• Record Type: Journal Article
• Authors: Karataş, Mert Olgun; Alıcı, Bülent; Passarelli, Vincenzo; Özdemir, Ismail; Pérez-Torrente, Jesús J.; Castarlenas, Ricardo
• Is Part Of: Dalton transactions. Volume 50:Issue 32(2021)
• Page Start: 11206
• Page End: 11215
• Publication Date: 2021-08-02
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/d1dt01946e
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : Pentacoordinated iridium(i )-cyclooctadiene complexes featuring a coumarin-functionalised imidazoline– or benzimidazoline–NHC ligand exhibit fluxional behavior as a consequence of the hemilability of the pyrone ring in the coumarin wingtip. Abstract : A set of iridium(i ) complexes of formula IrCl(κ C, η 2 -I R Cou R′ )(cod) or IrCl(κ C, η 2 -BzI R Cou R′ )(cod) (cod = 1, 5-cyclooctadiene; Cou = coumarin; I = imidazolin-2-carbene; BzI = benzimidazolin-2-carbene) have beeen prepared from the corresponding azolium salt and [Ir(μ-OMe)(cod)]2 in THF at room temperature. The crystalline structures of 4b and 5b show a distorted trigonal bipyramidal configuration in the solid state with a coordinated coumarin moiety. In contrast, an equilibrium between this pentacoordinated structure and the related square planar isomer is observed in solution as a consequence of the hemilability of the pyrone ring. Characterization of both species by NMR was achieved at the low and high temperature limits, respectively. In addition, the thermodynamic parameters of the equilibrium, Δ H R and Δ S R, were obtained by VT 1 H NMR spectroscopy and fall in the range 22–33 kJ mol −1 and 72–113 J mol −1 K −1, respectively. Carbonylation of IrCl(κ C, η 2 -BzI Tol Cou 7, 8-Me2 )(cod) resulted in the formation of a bis-CO derivative showing no hemilabile behaviour. The newly synthesised complexes efficiently catalyze the hydrosilylation of alkynes at room temperature with a preference for the β-( Z ) vinylsilane isomer.