Osmium complexes structure

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

Terminal methylene complexes are relatively rare—less than 10 such compounds have been isolated and about as many again have been characterized by spectroscopic techniques only. The methylene complexes previously reported fall into two groups, (i) neutral complexes of the early transition metals (e.g., Ti, Ta) and (ii) cationic complexes of the later transition metals (e.g., Re, Fe). The osmium complex 47 is important, then, as it is a new example extending the neutral group to the later transition metals. Compound 47 is the prototype for the series Os(=CHR)Cl(NO)(PPh3)2 and is one of only three terminal methylene complexes to be structurally characterized by X-ray crystallography (see Section IV,B). 

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,... 

A similar range of reactions has also been reported for the ruthenium carbonyl-triphenylphosphine systems (148). In these systems, a high percentage of the products were dinuclear, reflecting the weaker bonding in the ruthenium system, and as for some of the osmium complexes discussed above, some contain orthometallated phenylphos-phine groups (see Fig. 29, structures I, IV, X). 

The osmium complexes undergo ready reaction with a variety of donor ligands for the ethylene adduct, the X-ray structure has been obtained and clearly indicates the folding back of the SR ligand and... 

The pentanuclear carbido species Ms(CO)lsC (M = Fe, Ru, Os) have been prepared. The iron compound has been known for some considerable time (209), but the ruthenium and osmium complexes were prepared recently by pyrolysis reactions (210). The ruthenium adduct was only isolated in low yield (—1%), while the osmium complex was obtained in higher yield (—40%). The infrared spectrum and mass spectral breakdown pattern indicate a common structure to these compounds. The molecular structure of the iron complex is shown in Fig. 46. 

The infrared, NMR, and electronic absorption spectra of the two complexes H2FeRu2Os(CO)i3 and H2FeRuOs2(CO)13 have been taken to indicate a structure for these compounds similar to H2FeRu3(CO)13. However, the infrared and low-temperature proton NMR spectra of both compounds indicate that they exist as a mixture of isomers the two projected isomers for H2FeRu2Os(CO)13 are shown in Fig. 58 (247). The mixed manganese and rhenium-osmium complexes, H3MOs3(CO)13, have been prepared by acidification of the reaction mix-... 

Ruthenium(IV) and osmium(IV) phosphoraniminato complexes are formed by nucleophilic attack of phosphines on the nitrido ligand of ruthenium(VI) or osmium(VI). The first examples of this type of complexes are [Os (NPR3)(PR3)2(Cl)3] and [Ru (NPEt2Ph)(Cl)3(PEt2Ph)2], which have been documented in CCC (1987). While there are quite a few osmium complexes of this class, there appears to be only one structurally characterized ruthenium complex. 

In [59] the authors reported the structure of a tri-osmium complex containing a hydride and clearly stated that a low temperature X-ray diffraction experiment would not be useful to locate the hydride if an accurate absorption correction is not carried out. Curiously, a few years before they had contacted Prof A. Sironi and myself at the University of Milan proposing a low temperature data collection on that compound, with the purpose of locating the not so clearly visible hydride. As evident from [59], we were able to convince them on the real problems connected with the location of hydrogens close to heavy metals. 

Fig. 16.56 Structures of osmium complexes which hove seven pairs of skeletul electrons. Each copped triangular face adds twelve electrons to the total electron count, but the number of skeletal pairs remains seven. Likewise removing OstCOlj deletes twelve electrons without changing the number of skeletal pairs. The diagonal lines show alternate geometries with the same total number of electrons [From McPanlm. M Poh-kednm IWM.J. 2 9 Reproduced with permission.)...

In addition to those complexes summarized in Tables I—III, X-ray structural analyses of some bi- and trinuclear complexes with a supporting metal-metal bond,1 -115 a trinuclear complex without a metal-metal bond supporting the bridge,3839 116 and two trinuclear osmium complexes with a terminal diphenylthioketone ligand117 have been reported. 

More recently a tetraimido osmium(VIII) compound has been formed by the reaction outlined in equation (90).236 The osmium complex subsequently formed in the further reaction with dimethyl-fumarate has been structurally characterized by a single crystal X-ray diffraction study (Figure 8).237 The structure conforms to the proposed general intermediate (8). 

Many osmyl complexes with group VI ligands have been reported. The purple diamagnetic potassium osmate K2[0s(0H)4(0)2] is the best known and is a useful starting material for the preparation of other osmyl or osmium complexes. It is best prepared from the reaction of 0s04 with excess KOH. The X-ray crystal structure of K2[0s(0H)4(0)2] shows that the complex has the trans-dioxo unit, with a d(0s=0) of 1.77 A and a 0=0s=0 angle of 180° (238,239). The acid dissociation constants of H2[0s02(0H)4] have been determined. 

The example considered is the redox polymer, [Os(bpy)2(PVP)ioCl]Cl, where PVP is poly(4-vinylpyridine) and 10 signifies the ratio of pyridine monomer units to metal centers. Figure 5.66 illustrates the structure of this metallopolymer. As discussed previously in Chapter 4, thin films of this material on electrode surfaces can be prepared by solvent evaporation or spin-coating. The voltammetric properties of the polymer-modified electrodes made by using this material are well-defined and are consistent with electrochemically reversible processes [90,91]. The redox properties of these polymers are based on the presence of the pendent redox-active groups, typically those associated with the Os(n/m) couple, since the polymer backbone is not redox-active. In sensing applications, the redox-active site, the osmium complex in this present example, acts as a mediator between a redox-active substrate in solution and the electrode. In this way, such redox-active layers can be used as electrocatalysts, thus giving them widespread use in biosensors. 

Similar nucleophic addition is observed with the analogous osmium complex 147 (Scheme 21). X-Ray structural analysis of 247 (R = n-C4H9) shows that the n-butyl group occupies the exo position (152). Complexes of type 247 react smoothly with trityl cation in acetone to give the arene... 

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. 

The complex Os(SCl0Hl3)4(CNMe) is made from OsCl3, the lithium salt of 2,3,5,6-tetramethyl-benzenethiolate and 2,3,5,6-tetramethylphenyl sulfide it is green-yellow. The X-ray crystal structure of the ruthenium salt shows it to be trigonal bipyramidal, with the acetonitrile in the axial position. The osmium complex is isomorphous it would seem therefore to be the only example so far reported of a trigonal bipyramidal osmium(IV) complex. In an attempt to make a complex of lower coordination number 2,4,6-triisopropylbenzenethiolate (SC15H23) was used but the complex was still pentacoordinate, i.e. Os(S15H23)4(MeCN).719... 

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