Stereoselective addition reactions of diphenylphosphine to pyridyl and pyrimidylalkynes: chiral 1,2-diheteroaryl-1,2-bis(diphenylphosphino)ethanes and their group 6 metal carbonyl complexes

The base-catalysed addition of diphenylphosphine to the diarylethynes RC dr op CR' (R = R' = 2-pyridyl 1; R = R' = 3-pyridyl 2; R = 2-pyridyl, R' = 3-p yridyl 3; R = phenyl, R' = 2-pyridyl 4, 3-pyridyl 5, 2-pyrimidyl 6) yield d iphosphines of general formula Ph2PCH(R)CH(R')PPh2 together with alkene by- products Ph2PC(R)=CHR' and HC(R)=C(R')PPh2 in all cases except 1. Selected P,P'-coordinated M(CO)(4) complexes (M = Mo, W) of the diphosphines have be en prepared and their H-1-, C-13- and P-31-NMR data are presented. The patt ern of (CO)-C-13-NMR signals for the tetracarbonyl complexes was used unamb iguously to determine the stereochemistry of the parent diphosphine. At mod erately elevated temperatures, nitrogen coordination of 2-pyridyl and 2-pyr imidyl groups occurred for tetracarbonyl complexes of meso - or erythro-ste reochemistry, but not for complexes of rac- or three-form, to yield corresp onding fac-tricarbonyl complexes. At 162 degrees C the complex cis-rac-(CO) (4)W{P,P'-Ph2PCH(R)CH(R)PPh2} (R = R' = 2-pyridyl) is converted quantitativ ely into fac-erythro-(CO)(3)W{P,P',N-Ph2PCH(R)CH(R)PPh2} via an inversion/N -coordination pathway. (C) 1999 Elsevier Science S.A. All rights reserved.