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 drop CR' (R = R' = 2-pyridyl 1; R = R' = 3-pyridyl 2; R = 2-pyridyl, R' = 3-pyridyl 3; R = phenyl, R' = 2-pyridyl 4, 3-pyridyl 5, 2-pyrimidyl 6) yield diphosphines 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 been prepared and their H-1-, C-13- and P-31-NMR data are presented. The pattern of (CO)-C-13-NMR signals for the tetracarbonyl complexes was used unambiguously to determine the stereochemistry of the parent diphosphine. At moderately elevated temperatures, nitrogen coordination of 2-pyridyl and 2-pyrimidyl groups occurred for tetracarbonyl complexes of meso - or erythro-stereochemistry, but not for complexes of rac- or three-form, to yield corresponding 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 quantitatively 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.