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Stereospecific Diphosphination of Activated Acetylenes:  A General Route to Backbone-Functionalized, Chelating 1,2-Diphosphinoethenes

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posted on 04.12.2006, 00:00 by Deborah L. Dodds, Mairi F. Haddow, A. Guy Orpen, Paul G. Pringle, Gary Woodward
The symmetrical diphosphanes R2P−PR2 {where R = Ph (1a), Cy (1b), or But (1c)} are made by the reaction of R2PLi with R2PCl. The unsymmetrical diphosphanes R2P−PR‘2 {where R = But and R‘ = Ph (2a); R = But and R‘ = o-Tol (2b); R = Cy and R‘ = Ph (2c); R = Cy and R‘ = o-Tol (2d); R = Cy and R‘ = But (2e)} are made by the reaction of R2P(BH3)Li with R‘2PCl followed by deprotection with Et2NH. Diphosphanes 1a,b and 2ad react with ZC⋮CZ (Z = CO2Me) to give the corresponding R2PCZCZPR2 (3a,b) or R2PCZCZPR‘2 (4ad). The reaction of 2a,b with HC⋮CZ give the corresponding R2PCHCZPR2 (5a,b). A mechanism is proposed that accounts for the cis stereospecificity and the regioselectivity of these diphosphinations. Treatment of [PtCl2(1,5-cod)] or [PdCl2(NCPh)2] with a selection of the diphosphines (35) gave the expected chelate complexes, four of which, [PtCl2(3b)], [PtCl2(4a)], [PtCl2(4c)], and [PdCl2(4a)], have had their crystal structures determined.