The well-defined NHC-copper phosphides [(NHC)CuPPh2](3) (1, NHC = 1,3-diisopropy1-4,5-dimethyli- midazol-2-ylidene (I'Pr); 2, NHC = N,N-di-tert-butylimidazol-2-ylidene ((IBu)-Bu-t)) have been prepared by the reaction of simple copper halides with HPPh2 in the presence of N-heterocyclic carbenes (NHCs). Complexes 1 and 2 enabled catalytic double hydrophosphination of alkyl and aryl terminal alkynes to yield 1,2-diphosphinoethanes selectively in good yields. On the basis of these results, the most efficient and pratical in situ CuCl2/NHC catalyst has been developed. It catalyzes the selective double hydrophosphination of the alkynes with high efficiency and a wide substrate scope and exhibits even better performance than the well-defined NHC-Cu phosphides. The mechanistic studies disclosed that the formation of a copper acetylide in the catalytic cycle played an important role in the acceleration of the catalytic process.
The first catalytic double hydrophosphination of alkynes was achieved by reaction with diarylphosphines in the presence of an iron catalyst. The double hydrophosphination proceeded regioselectively and effectively for various secondary arylphosphines and terminalalkynes to give 1,2-bisphosphinoethane derivatives.
Double hydrophosphination of alkynes promoted by rhodium: the key role of an N-heterocyclic carbene ligand
作者:Andrea Di Giuseppe、Roberto De Luca、Ricardo Castarlenas、Jesús J. Pérez-Torrente、Marcello Crucianelli、Luis A. Oro
DOI:10.1039/c5cc09156j
日期:——
The stereoelectronic properties of the NHC ligand make possible the rhodium-catalysed double hydrophosphination of alkynes avoiding the catalyst deactivation by the diphosphine product.