Arsine complexes osmium

Numerous phosphine and arsine complexes have been synthesized and characterized predominately with osmium in the +2, + 3 or +4 oxidation states. Examples include [OsCl2(dppm)2] [108341-10-2], [OsC13(P(CH3)2(C6H5)3] [20500-70-3], [0s2Cl6(dppm)2(0)] [87883-12-3], and [Os(AsC2Hb(C6Hb)2)4H2] [27498-19-7]. An example of an unusually low oxidation state is the Os(—2) complex K2[Os(PF3)4] [26876-74-4]. High coordination numbers and formal oxidation states are found in the phosphine hydrides, eg, [Os(P(CH3)(C(5HB)2)H6] [25895-55-0] and... 

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. 

The osmium(IV) complexes are only obtained by this route with fairly unreactive phosphines and arsines (e.g. PBu2Ph) but they are conveniently made by oxidation of mer-OsX3(QR3)3 (Q = P, As) with the halogen in CHC13, or CCI4 and refluxing. 

Considerable structural information is available on osmium complexes of tertiary phosphines, arsines and stibines (Table 1.13) [152, 157]. 

Considerable structural information is available on osmium complexes of tertiary phosphines, arsines and stibines (Table 1.13) [152, 157], Comparison with data (mainly obtained from EXAFS measurements) on osmium diarsine complexes (Table 1.14) shows that as the oxidation state increases, osmium-halogen bonds shorten whereas Os-P and Os-As bonds lengthen. Bond shortening is predicted for bonds with ionic character,... 

There are now a substantial number of nitrido complexes of osmium(VI) and osmium(IV) as well as the osmiamate ion [OsVII 03N]. In addition to the ammine and ethylenediamine complexes, much recent work has been carried out on the bipy, phen and terpy complexes, often in connection with research into the photodissociation of water. The nitrosyl chemistry of the element, though seemingly not as extensive as that of ruthenium, has received much attention, and there has been considerable work on the phosphine, arsine and stibine complexes. 

A number of osmium(IV) phosphineiminato complexes are known which also contain phosphine or arsine coligands they are prepared by nucleophilic attack of phosphines on the nitrido ligand in osmium(VI) species. There is also one example of a phosphiteiminato complex, one of a phosphineaminato species, both formally involving osmium(IV), and two examples of osmium(I) aroylphos-phineiminato complexes. 

Osmium pentacarbonyl is a convenient precursor to other osmium carbonyl complexes. Hydrogenation gives the dihydride OsH2(CO)4. This hydride is not acidic with a p/fa of 18.5 but it can be deprotonated by strong bases to give [OsH(CO)4] and reduced by sodium (Scheme 23). Substitution of CO on Os(CO)5 by trialkyl or triarylphosphines, arsines, or stibenes gives Os(CO)4L or Os(CO)3L2. Other carbonyl phosphine complexes result from the reduction of osmium halides by alcohols in the presence of the tertiary phosphine. 

Non-chromophoric ligand variations have been carried out in the series of osmium complexes [Os(phen)L ](L-pyridine, MeCN, phosphine, arsine) and emission energies, excited-state redox potentials, and radiative and non-radiative rate const2uits found to vary systematically with the potential of the ground-state Os(III/II) couple.Phosphorescence from [Os(TTP)(CO)MeOH] au d [Os(TTP)(CO)pytIdlne] is quenched by electron donors auid acceptors by a reversible electron transfer mechauiism. 

It is a singular circumstance that the known chemistry of the tertiary phosphite complexes of osmium differs quite significantly from that of the tertiary phosphines, arsines and stibines. The closest analogue to P(OR)3 in osmium coordination chemistry would seem to be PF3, but even here the similarities are not marked. The oxidation states found are 0, II, III and IV (there are no established zerovalent unsubstituted osmium phosphine complexes), and the phosphites form unsubstituted species of the type OsL and [OsL ] " which have no counterparts in phosphine chemistry. The reason for these differences must be associated in part at least with the different cone angles and basicities of P(OR)3 ligands as against PR3. Further similarities and differences between the chemistries of osmium phosphines, phosphites and phosphorus trihalide complexes would obviously constitute a worthwhile study. 

Osmium(III), d, compounds consist of the halide salts, except fluoride, and complexes involving halides, amines, and acetylacetonate, as well as some mixed ligand species involving phosphines and arsines. These complexes are... 

Ruthenium(III), d, is ruthenium s most stable oxidation state and resembles rhodium(III) and iridium(III) more than osmium(III). The salts inelude the halides, hydroxides, and oxides RuCls SHaO is most important because it is a good starting material for other compounds and reacts readily with olefins and phosphines. Complexes of this oxidation state are known with water, eyanide, oxygenated organies, sueh as diketones and earboxylates, pyridines, earbonyls, ey-elopentadienyls, phosphine, and arsine ligands. A notable differenee between ruthenium(II) and ruthenium(III) is the absenee of ruthenium(III) nitrosyl complexes. 

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