Osmium binuclear complexes

Recently, we have studied such a photoredox reaction (6) that proceeds in analogy to the photolysis of the binuclear osmium complex Eq. (23) ... 

We have undertaken the detailed study of the binuclear symmetric osmium complexes with the view of addressing the following questions ... 

Aspects of this area have been reviewed by Creutz/ A number of new binuclear ruthenium and osmium complexes which can exist in mixed-valence form have been reported/ " The ligand 2,2, 3,3 -tetra-2-pyridyl-6,6 -biquinoxaline allows attachment of up to four Ru(II)(bipy)2 fragments. The molecule appears to act as two independent subunits which can exist in mixed-valence forms. Intervalence transfer (IT) bands detected for these mixed-valence subunits allow calculation of an electron transfer rate of 1 X 10 s" between the metal centers 6.8 A apart. 

This tetrahydridoborate complex reacts with Lewis bases L such as CO, P(OMe)3, PMe3, and P Pr3 to form dihydride-osmium(II) complexes OsH2(CO) L(P Pr3 )2, whereas the reactions with electrophiles afford monohydride derivatives (Scheme 35). The reaction with HBF4-OEt2 leads to the binuclear complex [(P Pr3 )2 (CO)HOs(p,-r 4-H2BH2)OsH(CO)(PI Pr3 )2]BF4, consisting of two OsH... 

Dihydrogen complexes, osmium, 37 3(X)-301 Dihydroxo-bridged complexes acid-base equilibria, 32 108-110 quantitative considerations, 32 115-118 binuclear, 32 66-67 crystallographic data, 32 61, 63 stability complexes, 32 103-104... 

Binding energy, pentacarbonyliron, 6, 3 Binuclear complexes bis-Cp titanium halides, 4, 522 with Ni-M and Ni-C cr-bonds heterometallic clusters, 8, 115 homometallic clusters, 8, 111 Binuclear dicarbonyl(cyclopentadienyl)hydridoiron complexes, with rand C5 ligands, 6, 178 Binuclear iridium hydrides, characteristics, 7, 410 Binuclear monoindenyl complexes, with Ti(IV), 4, 397 Binuclear nickel(I) carbonyl complexes, characteristics, 8, 13 Binuclear osmium compounds, with hydrocarbon bridges without M-M bonds, 6, 619... 

A binuclear bis(/z-germylene) osmium carbonyl complex [(OC)4Os(GeMe2)]2 on photolysis or thermolysis yields a mixture of an interesting series of (/z-germylene) osmium clusters36. Bis(metalcarbonyl)germacyclopentene complexes on photolysis or thermolysis... 

Barigelletti F et al (1993) Luminescence properties of rigid rod-like binuclear ruthenium(II)-osmium(II) terpyridine complexes - electronic interaction through phenyl bridges. JCS Chem Commun 942-944... 

A new class of binuclear nitrido complexes of tetravalent osmium and ruthenium is described in which the metal atoms are symmetrically bridged by a nitride ligand to give a linear M-N—M unit They have the stoichiometries M2NX8(H20)2]3 and [M2N(NH3)8Y2]3+ (M = Os, Ru X = Cl, Br Y = Cl, Br, etc.). Studies are reported on their vibrational spectra, structures, and bonding. Preliminary studies are reported also on trinuclear complexes of osmium and iridium. Finally, the use of vibrational spectroscopy in the study of metal-nitrido and metal-oxo complexes is discussed briefly. 

Table III. Binuclear Osmium and Ruthenium Nitrido Complexes...

In contrast to the cocondensation of osmium atoms with benzene which gives the osmium(O) derivative 322, cocondensation of osmium atoms with mesitylene affords the binuclear complex 329 as the major product (10%) and a second minor product 330 (1%). The structure of 330 has been... 

Osmium forms a number of complexes with pyridine (Table 7), mostly of the II oxidation state although there are examples of osmium(III) and osmium(IV) pyridine complexes. The important osmium(VI) species 0s206py4, a binuclear pp -oxo osmyl species, is considered on p. 595. There is also some important recent chemistry of osmium nicotinic and isonicotinic acid complexes (the 3- and 4-pyridinecarboxylic adds respectively). 

The osmium(V) species 0s02(terpy)(0H) has also been detected electrochemically at pH 13, from reduction of [0s02(terpy)(0H)]+ the latter is made from trans-K2[0s02(0H)4] and terpy.194 Binuclear complexes. For [0s20(terpy)2(bipy)2]4+ and [Os20(terpy)2(bipy)2]2+, see p. 594.192... 

The arrangement of this large section on osmium oxo complexes follows the pattern of other sections in this chapter. We consider mononuclear complexes first, by increasing oxidation state and, within each oxidation state, we consider those complexes with the largest number of oxo ligands first. The same procedure is then followed for binuclear species. For convenience, however, mononuclear and polynuclear oxo esters are considered together. 

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. 

Few triazenide complexes reported to date are paramagnetic. Examples studied by ESR are restricted to the low-spin osmium(III) complexes OsX2(PhNNNPh)(PPh3)2 (3), the binuclear mixed-valence rhodium salts [ Rh(/z-ArNNNAr)(CO)(PPh3) 2][PFe] (43), and the low-spin d cobalt(II) species Co(ArNNNAr)(C5H5)L (178). 

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