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 RCCR′ (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 1H-, 13C- and 31P-NMR data are presented. The pattern of 13CO-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 threo-form, to yield corresponding fac-tricarbonyl complexes. At 162°C the complex cis-rac-(CO)4W{P,P′-Ph2PCH(R)CH(R)PPh2} (R=R′=2-pyridyl) is converted quantitatively into fac-erythro-(CO)3W{P,P′,N-Ph2PCH(R)CH(R)PPh 2} via an inversion/N-coordination pathway.