Phosphorylation of Isocyanates and Aldehydes Mediated by Multifunctional N-Phosphine Oxide-substituted Imidazolylidenes

Abstract

The direct syntheses of imidic-phosphinic mixed anhydrides and phosphinates were accomplished via phosphorylation of isocyanates or aldehydes with N-phosphine oxide-substituted imidazolylidenes (PoxIms) that are equipped with both nucleophilic carbene and electrophilic phosphorus moieties. In addition, the catalytic cyclotrimerization of phenyl isocyanate took place by employing a PoxIm having bis-N-phosphine oxide groups. The results presented in the current study demonstrate that judiciously designed multifunctional carbenes represent a promising potential for the phosphorylation of heterocumulenes and carbonyl compounds. Keywords: N-Heterocyclic carbene (NHC) | Phosphine oxide | PhosphorylationOver the past couple of decades, N-heterocyclic carbenes (NHCs) have found a multitude of applications in diverse research areas in organic, inorganic, and organometallic chemistry.1 The advancement of these research areas has largely benefitted from the advent of novel NHCs and other stable carbenes that exhibit unprecedented functionality.2 Among these examples, NHC derivatives containing a phosphorus-based functional group have been extensively employed as multidentate ligands for transition metals.3 However, there are only few reports on NHCs that contain a phosphine oxide moiety. 4,5 The reactivity of these carbenes should be of substantial interest as the phosphine oxide moiety could function as a hemi-labile coordination ligand, 4b,5c as well as an electron-withdrawing substituent. 4a We developed N-phosphine oxide-substituted imidazolylidenes (PoxIms) as a novel type of isolable NHCs, 5a that afforded carboxylic-phosphinic mixed anhydrides via direct phosphorylation of CO 2 (Scheme 1).5b The resulting mixed anhydride was subsequently transformed into a variety of unsymmetrical carbonyl compounds via the corresponding imidazolium salt followed by a sequential double substitution reaction. In this work, we envisioned that the direct syntheses of imidicphosphinic mixed anhydrides and phosphinates could be achieved by the treatment of PoxIms with isocyanates and aldehydes, respectively (Scheme 1). These unprecedented transformations should offer novel and efficient methods for phosphorylation of carbonyl compounds.6 Given the significant utility of these organophosphorus compounds that are frequently encountered in bioactive reagents as well as industrial commodities, 6a6d development of an efficient phosphorylation method should be noteworthy. Herein, we report the phosphorylation of isocyanates and aldehydes by using PoxIms.The reaction of phenyl isocyanate (2a) with PoxIm 1a in toluene at room temperature afforded mixed anhydride 3a in 95% yield through the formation of the oxygenphosphorous bond (Scheme 2), which was unambiguously confirmed by single-crystal X-ray diffraction analysis (Figure 1a). In the 13 C NMR spectrum, the resonances for C1 and C2 are observed at ¤ C 140.4 ( 2 J C,P = 12.0 Hz) and 129.2 ppm ( 3 J C,P = 12.0 Hz), respectively. In the 31 P NMR spectrum, the resonance for the phosphinate ...

N‐Phosphine Oxide‐Substituted Imidazolylidenes (PoxIms): Multifunctional Multipurpose Carbenes

“…In the succeeding study on the phosphorylation of isocyanates and aldehydes, bis‐phosphine oxide‐substituted 3 g was found to catalyze the cyclotrimerization of phenyl isocyanate, whereas phenyl isocyanate was efficiently phosphorylated by PoxIm 3 c (Figure ) . These results demonstrate the further utility of PoxIms as an efficient reagent for the transformation of heterocumulenes and carbonyls.…”

Complexation-Induced N‒P Axial Chirality in Sm(II) N-Phosphine-Oxide-Substituted Imidazolylidene and Imidazolinylidene Complexes

“…Given that the utility of the multifunctional NHCs reported so far has been limited to their use as multidentate ligands for the complexation of metals, the exploration of an unprecedented application of multifunctional NHCs would significantly advance the development of their chemistry. [7][8][9][10][11] Previously, we have proposed a concept of multifunctional multipurpose carbenes, [12][13][14][15][16][17][18][19][20][21][22] which are carbenes that include functional groups applicable to a variety of purposes beyond solely possessing additional coordination sites. In this context, the N-phosphine-oxidesubstituted imidazolylidene, PoxIm (Figure 1A), and the corresponding imidazolinylidene, SPoxIm, are pioneering examples.…”

Corrigendum: Strategic Utilization of Multifunctional Carbene for Direct Synthesis of Carboxylic—Phosphinic Mixed Anhydride from CO2

“…In Scheme 3 of this Communication, the structure of compound 2 g′ was erroneously depicted as oligomeric. According to a recent re‐investigation, compound 2 g′ is monomeric. This structure and the corresponding text paragraph (starting p. 16076, left column) must be corrected as shown below:…”