Nitrosyl complexes, osmium

Al-Nitrosodiethanolamine, 2 449, 450 Nitroso dyes, 9 263-264 Nitro soluble dyes, 7 373t Nitroso soluble dyes, 7 373t Nitrosomonas, use in recirculating aquaculture biofiltration, 3 196 P-Nitrostyrenes, preparation by nitration of styrenes, 16 581 Nitrosyl chloride, 20 634 Nitrosyl complexes, osmium, 19 642 Nitrosyl perchlorate, 18 279 Nitrosyl tetrafluoroborate, 4 144t n-Nitrotoluene, 17 263... 

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". 

Figure 1.67 Syntheses of some osmium nitrosyl complexes.

Nitric oxide and iron nitrosyl complexes have been observed in the reduction of nitrite by bacterial nitrite reductases, which contain iron chlorin or iron isobac-terichlorin [151]. A specific nitric oxide reductase also exists to convert NO to nitrous oxide [9]. Iron complexes of chlorins, isobacteriochlorins, and porphyrins, as well as ruthenium and osmium polypyridines, and cobalt and nickel... 

The normal classification of material by oxidation state is inappropriate for nitrosyl complexes because the oxidation state concept is very much a formalism for them. Instead we shall use the generally accepted [M(NO)x] + classification in which x is the number of coordinated NO groups and n the number of metal d electrons, the latter being calculated on the basis that NO+ is the coordinated moiety. As will be apparent, osmium complexes within each such category do in fact show considerable similarities of structure and reactivity, and also with their ruthenium analogues. Osmium is unusual in forming an [M(NO)]5 type of complex. 

Since a far greater number of nitrosyl complexes have been isolated for ruthenium than for any other metal it might be expected that osmium should rival ruthenium in this respect. There seems no reason why this should not be so, and the present disparity in numbers of known osmium and ruthenium nitrosyls simply suggests that much less work has been carried out on the osmium systems. 

There are several recent and comprehensive reviews on metal nitrosyl complexes which give good coverage to the osmium complexes 198 a review on ruthenium nitrosyl complexes is particularly... 

Octaethylporphyrin (OEP) affords three osmium nitrosyl complexes Os(NO)(OMe)(OEP), made from Os(CO)py(OEP), methanol and NO 232 with HF this yields Os(NO)F(OEP)232 and with HC104 it gives 0s(N0)(0C103)(0EP).2SS The nitrosyl carbonyl complex [Os(NO)(CO)Cl2(PPh3)2]BF4 is made by reaction of Os(NO)(CO)Cl(PPh3)2 with HBF4.223... 

Osmium carbyne (see Carbyne Complexes) or aUcylidyne complexes have a triple bond between the metal and the carbon atom of the ligand. Carbyne complexes are related to singlet carbenes. They are analogous to linear nitrosyl (see Nitrosyl Complexes) complexes and the osmium is usually in a lower oxidation state. Alkylidyne complexes are related to triplet carbenes and the bonding between the osmium and the carbon atom is similar to the C-C bond in an alkyne. 

Until recently ammine complexes of osmium have been little studied compared with their ruthenium analogs. This appears to have been caused by the lack of suitable synthetic routes to them. The discovery of pentaammine(dini-trogen)osmium (II) opened convenient routes to pentaammines of osmium (III), and a convenient synthesis of hexaammineosmium(IIl)2 gave new routes to the previously unknown nitrosyls of osmium(II). Here are given the synthesis of [Os(NH3)s(N2)]l2 and its conversion to [Os(NH3)5l]l2 the synthesis of [Os(NH3)6]l3 and its conversion to [Os(NH3)5(NO)]X3 H20(X = Cl, Br, I) and the preparation of [OsX(NH3)4(NO)]2+(X = OH, Cl, Br, I) from [Os(NH3)5(NO)]3+. 

Pipes DW, Meyer TJ (1984) Comparisons between polypyridyl nitrosyl complexes of osmium (II) and ruthenium (II). Inorg Chem 23 2466-2472... 

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