Osmium complexes bidentate

Osmium complexes, 519-619 alkaloids, 569 alkoxo, 596 amido, 557 amines, 557 bidentate, 530 monodentate. 530 amino acids, 602... 

Osmium(VI) forms irons-0s02(malt)2 (98), while dioxouranium(VI) forms irons-U02(malt)2 (98) and many hydroxypyridinonate complexes, with bidentate and with tetradentate (177) ligands - trans-UO2L2 and UO2L, respectively. Several actinide elements form complexes with hexa- and octa-dentate hydrox5rpyridinonates (see Section IV.C.7 later). 

In this section we consider the complexes of mono-, di- and poly-carboxylato complexes. There appear to be marked differences from ruthenium carboxylato chemistry particularly in respect of the II/III and III states. A number of osmyl complexes are known with monodentate or bidentate carboxylates (p. 582) but apparently none of ruthenium(VT). On the other hand, the binuclear ruthenium species [Ru30(OCOR)6L3]"+, in which OCOR functions as a bidentate ligand, does not appear to have an osmium counterpart both elements form lantem -like species containing [M2(OCOR)4]"+ cores, but again with marked differences between ruthenium and osmium. This is clearly an interesting and rewarding field for further study. 

The crystal structure of yellow metallacyclic-osmium(iv) complex 9 was also reported <20030M414>. The distribution of ligands around the osmium atom can be described as a four-legged piano-stool geometry with the carbon atom C-5 of the metallated phenyl group disposed transoid to the hydride ligand. The bidentate carbon donor... 

Extension beyond the dimetallic stage for complexes constructed using 1 was accomplished with both a ruthenium(II)12 and an osmium(II) core in octahedral coordination.18 The peripheral metal sites in each complex (5 and 6) were occupied by ruthenium(II) species, each peripheral site capped by a pair of 2,2 -bipyridyl ligands. (In all of the preparations noted here, the bridges of the multinuclear complexes were formed by simple displacement of monodentate chloride or pyridine ligands by the bridging species which was bidentate in nature toward each metal center.) In addition to 2,2 -bipyridyl, o-phenanthroline (7) and 2,2 6, 2"-terpyrid-ine (8) were used. 

Bis(trifluoroacetato) complexes of ruthenium and osmium [M-(PPh3)2(C0)(CF3C02)2] show exchange between bidentate and uni-dentate trifluoroacetate linkage which is sufficiently slow at room temperature for the two CF3 groups to be resolved (77) fac-stereochemistry is indicated by the reactivity of the compounds. 

Scheme 15 Generation of bidentate osmium boryl complexes from reaction of 8.127 with diols...

There is evidence (NMR, IR, X-ray) that TMEDA forms a (reactive) bidentate complex with the osmium tetroxide whereby the diamine ligand increases the electron density on both the osmium center and also the outlying 0x0 ligands this in turn makes them more electron rich and better hydrogen bond acceptors and so leads to the selectivity observed. ... 

The first mixed-metal cluster of Os-Pd, [Os6Pd(bipy)(CO)i8], was reported in 1994, and since then a variety of mixed-metal cluster that contain various Os Pd ratios have been created. Palladium-pyridine complexes appear to be useful reagents in the synthesis of mixed-metal clusters with osmium carbonyl compounds. " The reaction of the coordinately unsaturated cluster [Os3(yu-H)2(CO)io] with [Pd(NH3)2l2] afforded a number of Os-Pd clusters with a high hydride content. " Both palladium phosphine and bidentate phosphine complexes are useful in the preparation of high-nuclearity mixed-metal clusters. The reaction of [Os3(/i-H)2(CO)io] with [Pd2(/i-dppm)2Cl2] gave 258 and 259, in addition to 260, with the same metal core, " in which the molecule contains a twofold symmetry axis. " " ... 

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