Phosphaalkynes from Acid Chlorides via P for O(Cl) Metathesis:  A Recyclable Niobium Phosphide (P^3-) Reagent that Effects C−P Triple-Bond Formation

Abstract

Reported herein is a new, metathetical P for O(Cl) exchange mediated by an anionic niobium phosphide complex that furnished phosphaalkynes (RCP) from acid chlorides (RC(O)Cl) under mild conditions. The niobaziridine hydride complex, Nb(H)(tBu(H)C=NAr)(N[Np]Ar)2 (1, Np = neopentyl, Ar = 3,5-Me2C6H3), has been shown previously to react with elemental phosphorus (P4), affording the mu-diphosphide complex, (mu2:eta2,eta2-P2)[Nb(N[Np]Ar)3]2, (2), which can be subsequently reduced by sodium amalgam to the anonic, terminal phosphide complex, [Na][PNb(N[Np]Ar)3] (3). It is now shown that treatment of 3 with either pivaloyl (t-BuC(O)Cl) or 1-adamantoyl (1-AdC(O)Cl) chloride provides the thermally unstable niobacyles, (t-BuC(O)P)Nb(N[Np]Ar)3 (4-t-Bu) and (1-AdC(O)P)Nb(N[Np]Ar)3 (4-1-Ad), which are intermediates along the pathway to ejection of the known phosphaalkynes t-BuCP (5-t-Bu) and 1-AdCP(5-1-Ad). Phosphaalkyne ejection from 4-t-Bu and 4-1-Ad proceeds with formation of the niobium(V) oxo complex ONb(N[Np]Ar)3 (6) as a stable byproduct. Preliminary kinetic measurements for fragmentation of 4-t-Bu to 5-t-Bu and 6 in C6D6 solution are consistent with a first-order process, yielding the thermodynamic parameters DeltaH = 24.9 +/- 1.4 kcal mol-1 and DeltaS = 2.4 +/- 4.3 cal mol-1 K-1 over the temperature range 308-338 K. Separation of volatile 5-t-Bu from 6 after thermolysis has been readily achieved by vacuum transfer in yields of 90%. Pure 6 is recovered after vacuum transfer and can be treated with 1.0 equiv of triflic anhydride (Tf2O, Tf = O2SCF3) to afford the bistriflate complex, Nb(OTf)2(N[Np]Ar)3 (7), in high yield. Complex 7 provides direct access to 1 upon reduction with magnesium anthracene, thus completing a cycle of element activation, small-molecule generation via metathetical P-atom transfer, and deoxygenative recycling of the final niobium(V) oxo product.

Early-Transition-Metal-Mediated Activation and Transformation of White Phosphorus

“…As such, this reaction progression forms a closed synthetic cycle for the formation of a C − − − P bond in only a few synthetic steps from P 4 . 86 The anionic terminal phosphide complex 63 was also shown to add to Mes*N=PCl to afford a diphosphaazide complex, (η 2 -Mes*N=P=P)Nb(N[CH 2 t Bu]Ar) 3 that loses the P 2 unit upon gentle thermolysis, or upon coordination of W(CO) 5 . Therefore, this molecule serves as a synthon for diphosphorus or the W(CO) 5 complex of P 2 , allowing P 2 to be transferred to a variety of compounds including other terminal phosphide complexes which may themselves be derived from P 4 activation, organic dienes, and low-valent metal centers.…”

Terminal, Anionic Carbide, Nitride, and Phosphide Transition‐Metal Complexes as Synthetic Entries to Low‐Coordinate Phosphorus Derivatives

“…While the metal-ligand multiple-bond chemistry of singleatom ligands to date has featured most prominently the terminal oxo and nitrido functional groups, [1] recent developments have added terminal carbide [2][3][4][5][6][7][8] and phosphide [9][10][11][12][13][14][15][16][17][18] (alternatively carbido, phosphido) functional groups to the list of such available units. Terminal arsenic complexes were added to this list through the independent contributions of Schrock and Scheer.…”

The Versatile Chemistry of Disilenides: Disila Analogues of Vinyl Anions as Synthons in Low-valent Silicon Chemistry

“…64 Interestingly, this reactivity of disilenides 10 and 14a is completely analogous to the reaction of Cummins's isolobal terminal phosphide complex of niobium with carboxylic acid chlorides, which yielded a four-membered niobium cycle with a P=C double bond. 66 In view of the smooth reactions of 10 with aryl iodides, it was reasonable to expect that disilenides should be compatible with vinyl bromides as electrophiles as well. Indeed, the reaction of 10 and 14a with various vinyl bromides yielded the donorfree four-membered cyclic silenes 45a45e in good isolated yields (Scheme 17).…”