Lithium-Aluminate-Catalyzed Hydrophosphination Applications

Abstract

Synthesized, isolated, and characterized by X-ray crystallography and NMR spectroscopic studies, lithium phosphidoaluminate iBu₃ AlPPh₂ Li(THF)₃ has been tested as a catalyst for hydrophosphination of alkynes, alkenes, and carbodiimides. Based on the collective evidence of stoichiometric reactions, NMR monitoring studies, kinetic analysis, and DFT calculations, a mechanism involving deprotonation, alkyne insertion, and protonolysis is proposed for the [iBu₃ AlHLi]₂ aluminate catalyzed hydrophosphination of alkynes with diphenylphosphine. This study enhances further the development of transition-metal-free, atom-economical homogeneous catalysis using common sustainable main-group metals.

Keywords: aluminate; homogeneous catalysis; hydrophosphination; lithium; phosphines.

Figure 1

a) Synthesis of iBu₃AlPPh₂Li(THF)₃, 2; b) Molecular structure of 2, H atoms and disordered THF molecules omitted for clarity, thermal ellipsoids drawn at 40 % probability; c) Depiction of E‐, Z‐stereoisomers and α‐regioisomers arising from hydrophosphination of alkyne substrates.

Figure 2

Molecular structure of iBu₃AlHLi(PMDETA). Ellipsoids are set at 40 % probability, and disordered iBu groups, disordered PMDETA, and hydrogen atoms except hydride are omitted for clarity.

Scheme 1

Proposed reaction mechanism for hydrophosphination of diphenylacetylene by pre‐catalyst 1, showing formation of active species 2.

Figure 3

Variable time normalization analysis (VTNA) plots illustrating the order in a) catalyst (first order); b) phosphine (inverse first order); c) diphenylacetylene (first order).