Synthesis, Structure, and CO₂ Reactivity of a Two-Coordinate (Carbene)copper(I) Methyl Complex

Abstract

Two-coordinate copper(I) acetate and copper(I) methyl complexes, bearing an N-heterocyclic carbene (NHC) supporting ligand, have been synthesized and structurally characterized, and the stability of the monodentate acetate has been examined by DFT calculations. The methyl complex readily inserts carbon dioxide at ambient temperature and pressure, regenerating the acetate in near-quantitative yield.

Single-Electron Oxidation of Monomeric Copper(I) Alkyl Complexes: Evidence for Reductive Elimination through Bimolecular Formation of Alkanes

“…The complexes (SIPr)-Cu(OAc) (1) and (IMes)Cu(OAc) (2) (SIPr ) 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene; IMes ) 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) can be prepared in reactions analogous to the synthesis of (IPr)Cu(OAc). 30 Complexes 1 and 2 have been characterized by 1 H and 13 C NMR spectroscopy and elemental analysis. In addition, single-crystal X-ray diffraction studies of 1 and 2 have confirmed their identity (Figures 1 and 2 and Table 1).…”

“…Similar to (IPr)Cu(OAc), the acetate ligands of 1 and 2 both exhibit a κ 1 -coordination mode, and Sadighi et al have suggested the possibility that the preferred κ 1 -coordination mode (in preference to the κ 2 -coordination mode) is the result of an intermolecular interaction between the distal oxygen and a hydrogen of a second carbene ligand. 30 The distance between Cu and the distal oxygen is shorter for the IMes complex 2 (2.831 Å) than for the SIPr complex 1 (3.082 Å) but is similar to that of (IPr)Cu(OAc) {2.868(4) Å}. The similar bond distances of 2 and (IPr)Cu(OAc) suggest that electronic effects of the carbene ligand likely govern the interaction, a result supported by density functional calculations on (NHC)-Cu(acetate), which show conversion of the acetate ligand from κ 2 to κ 1 upon energy minimization, presumably driven by the stability of linear, two-coordinate geometries for d 10 -Cu(I).…”

“…The ligands IMes, SIPr, and dtbpe as well as the complexes (IPr)Cu-(OAc), (IPr)Cu(Me), (IPr)Cu(Et), and (IPr)Cu(OTf) were prepared according to literature procedures. 30,47,[52][53][54] (SIPr)Cu(OAc) (1) 0.059 g, 0.50 mmol), and toluene (15 mL), and the resulting solution was stirred for 2 h at room temperature. The solution was filtered through Celite, approximately half of the solvent was removed in vacuo, and hexanes were added to form a white precipitate.…”

“…[29][30][31][32] Copper systems that possess Cu-R (R ) alkyl or aryl) or Cu-H bonds are often highly reactive substrates. The reduction of Cu(II) halides with tetraalkyllead has been studied, which may involve Cu(II) alkyl systems.…”

“…36 Recently, Sadighi et al have reported the synthesis, isolation, and full characterization of the two-coordinate Cu(I) methyl complex (IPr)Cu(Me) (IPr ) 1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene). 30 Given the diversity of reactivity available for the Lewis acidic Cu(II) oxidation state, we became interested in exploring the possible preparation of Cu(II) alkyl complexes. To our knowledge, no isolable Cu(II) alkyl complexes have been reported.…”