Cu(i) complex bearing a PNP-pincer-type phosphaalkene ligand with a bulky fused-ring Eind group: properties and applications to FLP-type bond activation and catalytic CO2 reduction. Issue 11 (4th March 2020)

• Record Type: Journal Article
• Authors: Takeuchi, Katsuhiko; Tanaka, Yuto; Tanigawa, Ippei; Ozawa, Fumiyuki; Choi, Jun-Chul
• Is Part Of: Dalton transactions. Volume 49:Issue 11(2020)
• Page Start: 3630
• Page End: 3637
• Publication Date: 2020-03-04
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/d0dt00276c
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : A highly Lewis acidic Cu(i ) complex bearing a PNP-pincer-type phosphaalkene ligand with bulky fused-ring Eind groups activates hydrogen and phenylacetylene in an FLP-type manner, and catalyzes the hydrogenation and hydrosilylation of CO2 . Abstract : Herein, we report the synthesis of [Cu(Eind2 -BPEP)][PF6 ] (2 ) (Eind2 -BPEP = 2, 6-bis(2-Eind-2-phosphaethenyl)pyridine, Eind = 1, 1, 3, 3, 5, 5, 7, 7-octaethyl-1, 2, 3, 5, 6, 7-hexahydro- s -indacen-4-yl), a three-coordinated Cu(i ) complex bearing a PNP-pincer-type phosphaalkene ligand with bulky fused-ring Eind groups. The Gutmann–Beckett test revealed that complex 2 is highly Lewis acidic and comparable in strength to B(C6 F5 )3, which is a relatively strong Lewis acid. In addition, 2 is more Lewis acidic than [Cu(Mes*2 -BPEP)][PF6 ] (3 ), the analogous complex with less-bulky Mes* instead of Eind groups. DFT calculations using model compounds revealed that the higher Lewis acidity of 2 compared to 3 is not due to the electronic effects of the ligand, but due to a reduction in the LUMO energy caused by the steric effect of the bulky Eind groups. When combined with a tertiary amine, the highly Lewis acidic and bulky 2 exhibits the reactivity of a frustrated Lewis pair (FLP) and can activate hydrogen and phenylacetylene. Complexes 2 and 3 were found to catalyze the hydrogenation and hydrosilylation of CO2 in the presence of DBU under relatively mild conditions.