Synthesis and characterisation of triosmium nitrite clusters containing phosphine ligands

The nitrite cluster [Os3(n-H)(CO)IO(u-r|J-NO2)] 1 reacted with trimethylamine W-oxide in CH2C12 to give a pair of isomers with formula [Os3(u-H)(CO)9(u-r|2-NO2)(NMej)] 2a and 2b in moderate yields. Reaction of 1 with PPh, and Me3NO in CH2C12 gave a pair of isomers [Osj(u-H)(CO)9(u-n2-NOj)(PPh3)] 3a and 3b and [Os3(u-H)(CO)8(u-nz-NO2)(PPh3)2] 4. With c-l,2-bis(diphenylphosphino)ethylene (dppen) and Me3NO in CH2C12,1 gave a pair of isomers [Os3(u-H)(CO)8(u-r|2-NO2)(dppen)] 5a and 5b, and [Os3(u-H)(CO)6(u-Ti2-NO2)(dppen)2] 6. Reaction of 1 with bis(diphenylphosphino)acetylene (dppa) and Me3NO in CH2C12 gave [Os3(u-H)(CO)8(u-T(J-NO2)(dppa)] 7 in good yield. The dppa co-ordinates to two Os atoms to form a six-membered ring suffering from severe angle strain in which the carbon-carbon triple bond is maintained. AH the products were characterised by IR, NMR and FAB mass spectroscopies. All these clusters contain an asymmetrically bridging NO2~ ligand along one Os-Os edge of the triosmium metal framework, as is evident from structural determinations of 2a, 2b, 3b, 4, 5a, 6 and 7.