Phosphorus Coordination Chemistry in Catalysis: Air Stable P(III)-Dications as Lewis Acid Catalysts for the Allylation of C–F Bonds

Abstract

Modification of C−F bonds with main-group catalysts has typically employed electron-deficient Lewis superacids in high oxidation states, and the challenges of preparing and handling such species have prevented broader adoption of metal-free reduction protocols. Here, we show that a hemilabile ligand coordinated to an easily accessed P(III) center imparts air stability without sacrificing the ability to activate C−F bonds. Catalytic C−C coupling of benzyl fluorides with allylsilanes was achieved using a P(III) complex under benchtop conditions. This application of coordination chemistry principles to main-group Lewis acids reveals a new strategy for controlling catalysis.

Diiminepyridine‐Supported Phosphorus(I) and Phosphorus(III) Complexes: Synthesis, Characterization, and Electrochemistry

“…In addition to widespread application in late, first‐row transition metal mediated catalysis, they are also used for their simple ability to bind early transition metals,, rare earths, and main‐group elements in a tridentate, pincer‐like fashion . With respect to the p‐block, DIP complexes are known for Groups 13, 14,, 15 and 16, centres. Such complexes have found use, for example, in Lewis acid mediated catalysis including C–F bond allylation, although in such scenarios, hemi‐lability (chemical non‐innocence) of the supporting ligands rather than redox non‐innocence can be prized …”

Nitrenium Salts in Lewis Acid Catalysis

“…Finally,t he benchtop catalytic dehydrocoupling of alcohols with silanes to eliminate hydrogen gas and form an OÀSi bond was expanded on. Catalytic benchtop transformations of this nature are of importance because silanes are employed as protecting groups for alcohols and amines in organic laboratories.T his transformation has been previously reported with the more air-sensitive Lewis acid BCF by Piers,however they observed diminished reactivity with bulky silanes such as HSiBu 3 and HSi i Pr 3 . [53] We found that this reactivity could be expanded to HSiBu 3 with phenol to afford PhOSiBu 3 (6c) under ambient conditions with 5mol % 2,b ut not HSi i Pr 3 .…”

“…Traditional examples of main-group Lewis acid catalysts involve group 13 and 14 elements as the central locus of reactivity,a stheyf eature al ow-lying orbital for substrate activation. [1] Over the last decade there has been increasing interest in studying pnictogens,o ften considered Lewis basic given the availability of an energetically accessible lone pair, in this unconventional role.T his work has been expanded to include compounds of phosphorus, [2][3][4][5][6][7][8][9][10][11] arsenic, [12] antimony, [13][14][15][16][17][18][19][20] and bismuth. [21][22][23] By contrast, the reactivity of nitrogen-containing compounds as Lewis acids has been investigated to am uch lesser extent, largely due to the dearth of such species.C hloramines,n itrenes,d iazocarboxylates,azides,and diazonium salts have been shown to possess N-centered electrophilic behavior.…”

Nitrenium Salts in Lewis Acid Catalysis

“…Over the last decade there has been increasing interest in studying pnictogens, often considered Lewis basic given the availability of an energetically accessible lone pair, in this unconventional role. This work has been expanded to include compounds of phosphorus, arsenic, antimony, and bismuth . By contrast, the reactivity of nitrogen‐containing compounds as Lewis acids has been investigated to a much lesser extent, largely due to the dearth of such species.…”