Osmium II

The photochemistry of the complexes [Os(II)(terpy)LL ] , with L = Ph2PCH2CH2PPh2 or Ph2PCH=CHPPh2 and L = CF, py, MeCN, or CO, has been examined in acetonitrile solution. All except the chloro complexes 

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Pyridazines form complexes with iodine, iodine monochloride, bromine, nickel(II) ethyl xanthate, iron carbonyls, iron carbonyl and triphenylphosphine, boron trihalides, silver salts, mercury(I) salts, iridium and ruthenium salts, chromium carbonyl and transition metals, and pentammine complexes of osmium(II) and osmium(III) (79ACS(A)125). Pyridazine N- oxide and its methyl and phenyl substituted derivatives form copper complexes (78TL1979). 

This is the second of the common oxidation states for iron and is familiar for ruthenium, particularly with Group 15-donor ligands (Ru probably forms more nitrosyl complexes than any other metal). Osmium(II) also produces a considerable number of complexes but is usually more strongly reducing than Ru". 

Osmium(II) forms no hexaaquo complex and [Os(NH3)g] +, which may possibly be present in potassium/liquid NH3 solutions, is also unstable. [Os(NH3)5N2] and other dinitrogen complexes are known but only ligands with good 7r-acceptor properties, such as CN, bipy, phen, phosphines and arsines, really stabilize Os , and these form complexes similar to their Ru analogues. 

Many of the ammine complexes are osmium(III) compounds the +2 state is less stable than with ruthenium, as expected, and osmium(II) compounds... 

Some bis(dinitrogen) complexes exist, generally as m-isomers (presumably this minimizes competition for the metal t2g electron density in 7r-bonding). Unlike ruthenium, osmium(III) dinitrogen complexes do exist, showing osmium(III) to be a better 7r-donor not surprisingly, they are more labile than the osmium(II) species. 

The pattern of behaviour in osmium nitrosyls seems to be similar to that seen with ruthenium, though fewer data are available. The most common type of complex has octahedrally coordinated osmium(II) with linear Os-N-O linkage. Some syntheses are shown in Figure 1.67. 

The change in formal oxidation state from osmium(VI) to osmium(II) is noteworthy [192],... 

Eichler and Wahl have attempted an isotopic study ( Os and Os) of the exchange reaction between Os(dipy)3 and Os(dipy)3 using a direct injection technique so that reaction times 7 x 10 sec were possible. With total osmium 10" M in aqueous sulphate media at 0 °C complete exchange was observed. The separation methods used were, (a) perchlorate precipitation (in presence of iron(II) carrier) and (6) extraction with p-toluenesulphonic acid in nitromethane, of the osmium(II) complex. A lower limit of 1 x 10 l.mole. sec was placed on the rate coefficient (0 °C, 3.0 M H2SO4). Dietrich and Wahl using the line broadening effect produced by Os(dipy)3 on the nmr spectrum of Os(dipy)3 have been able to propose a value of > 5x 10" l.mole . sec at 6 °C in D2O (0.14 M [Cr] and 5x10 M [D- ]). 

The rate of oxidation of tris(2,2 -bipyridine)osmium(II) by octacyanomo-lybdate(V)... 

The formation of the first osmium hydrido(alkoxo) complex, a yellow air-stable and thermally stable hydrido(methoxo)osmium(II) complex, trans-[OsH(OMe)(Cl) (NO) (P Pr3)2] (72), by the oxidative addition of MeOH to a 16-electron complex, trans-[OsCl(NO)(P Pr3)2] (71) was briefly reported (Eq. 6.22) [51]. 

Hanif, M., Nazarov, A. A., Hartinger, C. G., Kandioller, W., Jakupec, M. A., Arion, V. B., Dyson, P. J. Keppler, B. K. Osmium(ii)-versus ruthenium(ii)-arene carbohydrate-based anticancer compounds similarities and differences. Dalton... 

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... 

Treatment of OsT rf-T BT XCOXP Pr with ethanol under reflux does not lead to the formation of OsH2(CO)2(P Pr3)2 but instead gives the hydride-methyl osmium(II) compound OsHMe(CO)2(P Pr3)2 in good yield. 2-Methoxyethanol behaves in a manner similar to ethanol, and the reaction with the tetrahydridoborate complex yields OsH(CH2OMe)(CO)2(P Pr3)2 (Scheme 38).79... 

Esteruelas, Miguel, A., and Oro, Luis, A., The Chemical and Catalytic Reactions of Hydrido-chloro-carbonylbis (triisopropylphosphine) osmium(II) and... 

The intense colors in 2,2/-bipyridyl complexes of iron(II), ruthenium(II), and osmium(II) are due to excitation of an electron from metal t2g orbitals to an empty, low-lying ir orbital of a conjugated 2,2 bipyridyl ligand. The photoexcitation of this MLCT excited state can lead to emission as the excited state collapses back to the ground state. However, not all complexes are... 

IV. Osmium(II)-Arenes A Cytotoxic Family of the Heavier Congener 51... 

Fig. 25. (a) General aqueous reactivity of osmium(II)-arenes the formation of an hydroxido-bridged dimer can play a major role in the aqueous chemistry of osmium(II)-arenes, especially if the chelate XY is an 0,0-bidentate ligand (b) molecular structures of the osmium-arene anticancer agents 26-30. 

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