Synthesis, characterisation and natural abundance 187Os NMR spectroscopy of hydride bridged triosmium clusters with chiral diphosphine ligands

Treatment of [Os3(μ-H)2(CO)10] with the chiral diphosphines BINAP, tolBINAP [(R)-2,2′-bis(di-4-tolylphosphino)-1,1′-binaphthyl], DIOP [(4R,5R)-(−)-O-isopropenylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane] affords [Os3(μ-H)2(CO)8(μ-L)] (L = BINAP (1), tolBINAP (2), DIOP (4)) in high yield. The X-ray structures for 1, 2 and 4 are reported, and structural and spectroscopic comparisons are made between these clusters and [Os3(μ-H)2(CO)8(μ-L)] (L = dppm (5), dppe (6), dppp (7)) which were synthesised similarly. Compounds 5 to 7 were previously synthesised by hydrogenation of 1,2-[Os3(CO)10(μ-L)] but the route from [Os3(μ-H)2(CO)10] is preferable. The H-bridged Os⋯Os distances are similar in 1, 2 and 4 indicating that these species are formally unsaturated 46-electron clusters. The P⋯P distances vary from 4.24 to 4.30 Å in 1 and 2, respectively, to 4.53 Å in 4 and there are related changes in the angles associated with the ligand set around the H-bridged osmium atoms. Introduction of the diphosphine ligands completely suppresses the ability to add CO, to insert acetylene to form a μ-η1,η2-vinyl compound, and to exchange hydride ligands with styrene-d8, which are reactions characteristic of [Os3(μ-H)2(CO)10]. Clusters 2 and 5–7 were also used to examine the potential of natural abundance 187Os NMR spectroscopy through techniques based on inverse detection by HMQC, HSQC and HMBC spectroscopy.