Complexation between MOTf (M = Li and Na) and N-Phosphine Oxide-substituted Imidazolylidenes via Coordination of the N-Phosphoryl Groups

Abstract

A reaction between an N-phosphine oxide-substituted imidazolylidene (PoxIm) and MOTf (M = Li or Na) in THF afforded the complexes [(PoxIm) x (MOTf) y (THF) z ] through the coordination of the N-phosphoryl group to Na + or Li + , which was unambiguously confirmed by 13 C and 31 P NMR spectroscopy and single-crystal X-ray diffraction analyses. These measurements confirmed that the carbene moieties in these complexes remain intact. In solution, PoxIm and MOTf might form the complexes in a 3:2 ratio (i.e., x = 3, y = 2), while ratios of 1:1 (M = Li; x = 1, y = 1) and 2:1 (M = Na; x = 2, y = 1) were observed in the solid state.

Palladium(II) Complexes with N-Phosphine Oxide-Substituted Imidazolylidenes (PoxIms): Coordination Chemistry and Catalysis

“…We have included in our study carbene precursors 1 , 2 , and 5 , previously reported by Hoshimoto (Scheme ). The preparation of these precursors is straightforward and is accomplished by oxidation with hydrogen peroxide of the known parent N -phosphanyl imidazolium or N , N ′-diphosphanyl-imidazolium salt to yield 1 , 2 , and 5 as air- and moisture-stable compounds. Subsequent deprotonation of the precursors at C-2 with KHDMS furnishes the free carbenes 3 , 4 , and 6 , which can be isolated and characterized.…”

“…All solvents were purified and dried by standard methods. Ligand precursors 1 , 2 , and 5 as well as starting complex [PdCl 2 ­(BN) 2 ] were prepared according to standard procedures. NMR spectra were recorded on Bruker Avance spectrometers working at 300 MHz (300.1 MHz for 1 H, 75.5 MHz for 13 C, 282.2 MHz for 19 F, and 121.5 MHz for 31 P); chemical shifts (δ) are reported in units of ppm relative to the residual solvent signals and to external 85% H 3 PO 4 (for 31 P).…”

“…In 2015, the group of Hoshimoto reported on yet another class of functional NHCs featuring an N–P bond, namely, N -phosphine oxide-substituted imidazolylidenes, which were termed PoxIms (Chart ). Such carbenes appear particularly useful as ligands, since the two coordination sites (the carbene carbon and the oxide) possess widely different properties, e.g., the former being a soft donor (with some acceptor character as well), the latter a hard donor. Interestingly, to the best of our knowledge, there are just two examples on the use of PoxIms as ligands, i.e., one by the group of Nozaki concerning PoxIm chelate coordination to palladium­(II) and the other by the group of Hoshimoto concerning weak complexes with alkaline metal ions in which PoxIms act as monodentate ligands through the phosphanyl oxide group .…”

Room-Temperature Reversible Chemisorption of Carbon Monoxide on Nickel(0) Complexes

“…2A) (25,26). To date, (S)PoxIms have demonstrated various coordination modes toward metals, including coordination by only the carbene atom (-C) (27,28), by only the N-phosphinoyl oxygen atom (-O) (29,30), and by both the carbene and oxygen atoms (-C,O) (31,32); however, dynamic coordination exchange between the -C and -C,O modes remains unknown.…”

Axial Chirality around N–P Bonds Induced by Complexation between E(C6F5)3 (E = B, Al) and an N-Phosphine Oxide-Substituted Imidazolinylidene: A Key Intermediate in the Catalytic Phosphinoylation of CO2

“…Recently, we have proposed a concept of multifunctional multipurpose carbenes, i.e., carbenes that include functional groups applicable to a variety of purposes beyond additional coordination sites. In this context, N -phosphine oxide-substituted imidazolylidene (PoxIm) and the corresponding imidazolinylidene (SPoxIm) represent pioneering examples (Figure A).…”