Regioselective Single and Double Hydrophosphination and Hydrophosphinylation of Unactivated Alkynes

Abstract

A lanthanum-based N,N-dimethylbenzylamine complex was used as a precatalyst for both hydrophosphination and hydrophosphinylation of alkynes under mild conditions. In the case of hydrophosphination, the catalyst induced monoaddition with high regiospecificity, yielding only the anti-Markovnikov product, and stereoselectivity that could be controlled on the basis of the reaction conditions. Undertaking the catalysis with excess phosphine yielded the E isomer as the major product; however, using excess alkyne, the Z isomer was instead isolated as the major product. A brief investigation into the catalytic cycle suggested that a dimeric form of the lanthanum phosphide active catalyst provided the Z isomers as kinetic products that then underwent isomerization to yield the final E isomers. In the case of hydrophosphinylation, the chemoselectivity depended on the nature of the alkyne used. Terminal alkynes gave only double addition products while both single and double addition products were successfully isolated in the case of internal alkynes. The hydrophosphinylation also showed high chemo- and regioselectivity as only the anti-Markovnikov products were isolated. Monohydrophosphinylation of internal alkynes gave almost exclusively the E isomer, and double hydrophosphinylation of all alkynes led to 1,2-addition products.

Hydrophosphinylation of Styrenes Catalysed by Well‐Defined s‐Block Bimetallics

“…[6,7] Although many transition-metal free methods for the hydrophosphination (i. e. P III -H addition) of unsaturated species have been reported, [8] the hydrophosphinylation reaction (i. e. P V -(O)À H addition) is considerably less explored. [9] Whilst catalyst-free methods have shown some success for the hydrophosphinylation of activated unsaturated substrates such as isocyanates, [10] there has been encouraging developments using s- [11][12][13][14][15][16][17] or f-block [18][19][20][21] organometallics to extend the scope of this reaction. Unlike transition-metal catalysis which relies on oxidative addition of the PÀ H bond or activation of the unsaturated substrate itself, [8,9] s-and f-block metal (pre)catalysts operate by deprotonation of HP(O)R 2 to generate a nucleophilic M-OPR 2 species which in turn can undergo insertion of the unsaturated organic substrate.…”

“…The double hydrophosphinylation of alkynes and nitriles using s-and f-block catalysts has also been explored. [14,19,20] A powerful strategy to upgrade the catalytic activity of lighter group 2 metals such as magnesium is through cocomplexation with a group 1 metal, affording heterobimetallic 'ate' complexes. [22,23] These heterobimetallics have been widely used for many stoichiometric transformations, [24] and this has more recently been expanded to catalytic regimes.…”

Heterogeneous Catalytic Method for the Copper(II)-Catalysed Addition of H-Phosphinates and Secondary Phosphine Oxides to Phenylacetylene

“…Radical conditions have also been applied for the selective synthesis of Z-alkenylphosphine oxides by Lei and co-workers [37]. Schmidt et al elaborated the hydrophosphinylation of alkynes under mild conditions in the presence of a lanthanum-based N,Ndimethylbenzylamine complex [38]. The earth abundant cobaloxime was used to convert the H-phosphine oxide into its reactive radical species under visible light irradiation [39].…”

Hydrophosphination using [GeCl{N(SiMe3)2}3] as a pre-catalyst

“…Naphthyl substituted phosphine 2n is formed in excellent yield (entry 14) and 1,1-diphenylethylene performs comparably well, albeit under slightly more forcing conditions (50 1C, 24 h, entry 15). Phenyl acetylene does not react, but internal alkynes (entries 16 to 19) react at RT: conditions that are highly competitive compared to the leading literature, for example Schmidt's RT, La-catalyzed process in pyridine solvent 30 and Cui's Ca-and Y-mediated chemistry that uses temperatures ranging from RT-75 1C. 31 Unfortunately, reactions of 2-and 4-vinylpyridine and acrylonitrile with 1 all result in the formation of unidentified polymers irrespective of order of addition of Ph 2 PH.…”