Catalytic synthesis of vinylphosphanes via calcium-mediated intermolecular hydrophosphanylation of alkynes and butadiynes

The calcium complex [(thf)4Ca(PPh2)2] (1) is a very effective catalyst for the hydrophosphanylation of substituted alkynes of the type R–CC–R (R = Me, Ph) yielding (E)-1,2-diphenyl-1-diphenylphosphanylethene (2a) and (Z)-1-phenyl-2-diphenylphosphanyl-1-propene (2b). The calcium-mediated hydrophosphanylation of butadiynes of the type R–CC–CC-R (R = Me, SiMe3, Ph, Mes, tBu) proceeds less selectively and diverse products are obtained such as 1,4-substituted 1,4-bis(diphenylphosphanyl)-1,3-butadienes (3), 1,4-diphenyl-1,2-bis(diphenylphosphanyl)-1,3-butadiene (4), and 1,4-di(tert-butyl)-1,4-bis(diphenylphosphanyl)buta-1,2-diene (5). Besides these regioisomers also several configuration isomers with respect to the C=C double bonds [(E)/(Z) isomerism] are obtained. A catalytic cycle can be formulated with the first addition of a Ca–P bond of the catalyst 1 to a CC triple bond always leading to the formation of an intermediate with the newly formed C–P bond in 1-position whereas the remaining phosphanido calcium fragment binds to the carbon in 2-position. The addition of a second diphenylphosphane is much faster and therefore, only two-fold hydrophosphanylated butadiynes are observed. Neither addition products with only one HPPh2 group nor those with more than two PPh2 substituents are obtained.

Graphical abstractButadiynes are easily hydrophosphanylated in THF by catalytic amounts of [(thf)4Ca(PPh2)2] yielding the appropriate 1,4-diorganyl-1,4-bis(diphenylphosphanyl)-1,3-butadienes (NUPHOS) and constitution isomers thereof. No hydrophosphanylation of these vinylphosphanes is observed.Figure optionsDownload full-size imageDownload as PowerPoint slide