Osmium complexes unsubstituted

Several modes of reactions were observed when heterocarbonyl complexes were exposed to oxidizing or reducing agents. The oxidation of the thioformaldehyde ligand in the osmium complex [OsCl(NO)(i72-S = CH2) (PPh3)2]53 with m-chloroperbenzoic acid afforded the rf-S,C complex of the unsubstituted sulfine H2C=S = 0, a molecule that is unknown in the uncoordinated form.226,227... 

As a tridentate conjugated ligand this would be expected, like 2,2 -bipyridyl and 1,10-phenanth-roline, to stabilize osmium(II) and this is indeed the case, with most of the reported complexes containing divalent osmium. The unsubstituted bis complex [Os(terpy)2]2+ is remarkably stable. It seems likely that terpyridyl complexes of osmium(II) are good candidates for further investigation as photosensitizers, having so far received less attention than the corresponding bipyridyl or phenanthroline species. 

The 7] -osmium complexes of a-unsubstituted thiophenes undergo Lewis acid-promoted addition with acetals at C-2 to give the thiophenium complexes in good yields <19990M2988>. These can be deprotonated to give the 2-substituted thiophene complexes. The electrophile attacks the substrate on the rivn-face (Scheme 83). 

Eor ferrocene sites at the end of long alkanethiols self-organized at gold electrodes and diluted with unsubstituted thiols with the redox moiety in contact with the electrolyte (Fig. 4a), Chidsey has reported [34] curved Tafel plots (Fig. 4b), which could be fitted by equations derived from Marcus theory with values of k = 0.85 eV and Z = 6.73 x 10 s"l eV" for a reaction rate of A = 2.5 s at in Fig. 4(b). Similar curvature in Tafel plots has been reported by Faulkner and coworkers [35] for adsorbed osmium complexes at ultramicro-electrodes (UME). The temperature dependence of the rate coefficient could also be fitted from Marcus equation and electron states in the metal and coupling factors given by quantum mechanics. 

The redox polymers, POs-EA, was polyvinylpyridine partially N-complexed with [osmium bis(bipyridine) chloride]+ 2+ and quaternized with bromoethylamine. The synthesis followed the published procedures (i). The structure and the composition of POs-EA is shown in Fig. 1. The elemental analysis and UV-VIS spectroscopy showed that the repeating unit of the POs-EA had 1.1 ethylamine pendant functions and 1.8 unsubstituted pyridine rings per osmium complexed pyridine. 

Ammonia forms a number of complexes with osmium (see Table 5), though the only fully established unsubstituted osmium ammine which has been isolated is the hexaammine [Os(NH3)6]3+ there is, however, electrochemical evidence for the existence both of [Os(NH3)6]2+ and of [Os(NH3)6]4+. Amongst the substituted ammines which have been isolated and characterized are several of osmium(II), all with supporting (or stabilizing) ir-acceptor ligands, e.g. [Os(N-H3)sCO]2 [Os(NH3)s(NO)]3+ and [Os(NH3)5(N2)]2+. 

Osmium(II). The unsubstituted complex [Os(terpy)2]Cl2 was made in 1937 by fusion of the ligand with a mixture of K2[OsC1J and osmium metal, and is singularly unreactive towards either acids or alkalis.191 The green chloride gives a red solution. For its redox and spectroscopic properties see below. 

There seem to be no unsubstituted complexes of biguanide with osmium, though a few tris species of substituted biguanides have been reported. 

No unsubstituted aqua complexes of osmium seem to have been reported, though we have already referred to a number of species in which H20 is a ligand. Species such as [0s(H20)6]3+ and [0s(H20)6]4+ would be expected to exist. 

Nitrato and nitro complexes There are very few of these for osmium, and no unsubstituted ones. 

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.—Diene ligands in complexes [Os3(CO)io(diene)] can either bridge two osmium atoms as in [Os(CO)io( y-t/ aAw-C4H6)] where the butadiene occupies two equatorial positions of unsubstituted [Osa(CO)x2] or can bond to one osmium atom, when one axial and one equatorial site are occupied (44), e.g. when diene= -cw-butadiene, cyclohexa-1,3-diene, or norbornadiene. The complex (44) (diene=... 

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