REACTIONS OF THE UNSATURATED ALKYNE CLUSTER 7)(MU(3)-ETA(2)(PERPENDICULAR-TO)-PHC(2)PH)(DPPM)] WITH P-DONORS - CRYSTAL-STRUCTURES OF [OS-3(CO)(6)(PHC(2)PH)(DPPM)(P(OME)(3))] AND 2 ISOMERS OF [OS-3(CO)(7)(PHC(2)PH)(DPPM)(PBU(3))] (DPPM=PH(2)PCH(2)PPH(2))

Treatment of the unsaturated cluster [Os-3(CO)(7)(PhC(2)Ph)(dppm)] 1 ( dppm = Ph(2)PCH(2)PPh(2)) with P-donors gave the saturated monoadducts [Os-3(CO)(7)(PhC(2)Ph)(dppm)L] [L = PBu(3) 2, PPh(3) 3, PMe(2)Ph4 or P(OMe)(3) 5]. Spectroscopic studies have established that these adduct s exist in three isomeric forms the ratio of which depends on the pola rity of the solvent used in the reaction. X-Ray crystallographic deter minations of two isomers of the PBu, adduct, 2a and 2c, showed the pho sphine to be co-ordinated to different metal centres in the two isomer s. The P(OMe)(3) adducts 5b and 5c underwent a facile decarbonylation reaction to give the unsaturated cluster [Os-3(CO)(6)(PhC(2)Ph)(dppm){ P(OMe)(3)}] 6, which has been structurally characterised by X-ray crys tallography. Attempts to decarbonylate the monoadducts 24 have been un successful.