A Copper(I) Platform for One-Pot P–H Bond Formation and Hydrophosphination of Heterocumulenes

Abstract

The reaction of phosphorus­(III) esters with pinacolborane generates phosphines via the action of an NHC-copper­(I) catalyst. This gives access, within minutes, to 12 P–H bonded species, including secondary and primary phosphines as well as PH3, in excellent conversions. These phosphines can be subsequently applied in the copper­(I)-catalyzed hydrophosphination of heterocumulenes in a telescoped, one-pot fashion. This approach yielded 12 phosphaureas, 3 phosphaguanidines, and 2 phosphathioureas in moderate to excellent yields without the need to handle toxic, pyrophoric, or gaseous P–H bond containing compounds. The crystal structures of two of the phosphaureas, PhP­(C­(O)­NHPh)2 and P­(C­(O)­NHPh)3, are presented.

Broken Promises? On the Continued Challenges Faced in Catalytic Hydrophosphination

“…In 2022, Liptrot and co-workers reported the formation of secondary and primary phosphines, including PH 3 , from reduction of the corresponding phosphorus(III) esters with pinacolborane mediated by a Cu(I) precatalyst. 127 Subsequent HP of heterocumulenes was achieved using these phosphines generated in situ with the same precatalyst to give the single-addition products in moderate to good yields.…”

“…130−134 Of course, the field has been expanded to included alkynes and other hetero-unsaturated species, which allows for some increased diversity in product formation, and indeed some of the products are unique and warrant additional focus (vide supra). 115,127 For example, the vinylphosphines generated from HP of alkynes can potentially be further functionalized by HP, but the products of this transformation are ultimately usually limited to functionalized 1,2-bis(diphenylphosphino)ethane (dppe) derivatives. 81,135,136 To build truly diverse HP products and construct molecular complexity from simple molecules, we need more potent catalysts, including catalysts that can facilitate HP of even the most unactivated substrates.…”

Taming PH3: State of the Art and Future Directions in Synthesis

“…PH 3 was generated in 89% conversion on a 0.1 mmol scale. The in situ generated PH 3 was then directly implemented in the quantitative catalytic hydrophosphination of phenyl isocyanate in a two-pot procedure …”

Divergent Mechanistic Pathways for Copper(I) Hydrophosphination Catalysis: Understanding that Allows for Diastereoselective Hydrophosphination of a Tri-substituted Styrene

“…For example, 1-hexene is unlikely to be subject to nucleophilic attack. 38 Precedent for an insertion pathway with copper comes from Cui and Liptrot who have previously proposed insertion of terminal alkynes 50 and heterocumulenes, 16,45 respectively, into the Cu-P bond of NHCcopper phosphido compounds. Therefore, an initial hypothesis for this divergence, a combination of nucleophilic and insertion steps, was formed.…”

“…One articulated challenge is the absence of variety in the phosphorus substituents where Ph2PH, and more recently PhPH2, are the most commonly reported substrates. 12,17,31,69,70 For copper, preliminary data and a recent report from the Liptrot lab 45 indicate more diverse phosphine substrates are viable. Treatment of styrene with 2 equiv.…”