Rhodium complexes, nitrosyl

Although rhodium forms far fewer Nitrosyl Complexes than its neighbor in the Periodic Table, ruthenium, over 50 nitrosyl rhodium complexes are known, in addition to some ill-characterized ternary halorhodiinn nitrosyls. Three main... 

Although rhodium forms far fewer Nitrosyl Complexes than its neighbor in the Periodic Table, ruthenium, over 50 nitrosyl rhodium complexes are known, in addition to some ill-characterized ternary halorhodium nitrosyls. Three main series of complexes exist, with general formulas [Rh(NO)L3], [RhX2(NO)L2], and [Rh(NO)L4]X. There are also a few dinitrosyls of the type [Rh(NO)2L2]X. 

Interestingly, solvents of strrMig coordinating abiUties turned out to be beneficial to the oxidization process from the nitrosyl to the nitro complex. While the dicationic rhodium(I) nitrosyl complex 47 undergoes oxidation with molecular oxygen, the neutral Rh(l) nitrosyl derivative [(MeCN)Cl2Rh(NO)] (48) appears to... 

For ruthenium, electrolytes based on ruthenium sulphamate or nitrosyl-sulphamate have been described, but the most useful solutions currently available are based on the anionic complex (H2 0 Cl4 Ru N Ru-Cl4-OH2) . The latter solutions operate with relatively high cathode efficiency to furnish bright deposits up to a thickness of about 0-005 0 mm, which are similar in physical characteristics to electrodeposited rhodium and have shown promise in applications for which the latter more costly metal is commonly employed. Particularly interesting is the potential application of ruthenium as an alternative to gold or rhodium plating on the contact members of sealed-reed relay switches. 

Figure 2.101 Synthesis of some rhodium nitrosyl complexes.

Table 2.15 Structural data for rhodium nitrosyl complexes...

In a logical continuation of this work, carbene addition to an iron-iron double bond has also been exploited for the simple synthesis of the first /. -methylene complex in the nitrosyl series. The readily available /x-nitrosyliron complex [(Tj5-C5H5)Fe(/u.-NO)]2 (26) exhibits the same structural features as the rhodium dimer 21 (157) and reacts with diazomethane in the temperature range -80-25°C to give the expected /z-methylene derivative 27 (Scheme 14) as a black, air-stable compound in... 

The complexes of rhodium will primarily be considered in order of increasing oxidation state. However, complexes in which the oxidation state of the metal is uncertain (e.g. nitrosyls) or dinuclear complexes of mixed oxidation state will be dealt with last. 

The reaction between rhodium trichloride and nitric oxide forms another ternary nitrosyl whose formulation is unknown.1294 However, nitric oxide ligates rhodium(II) acetate (equation 293).1295 The ternary complexes have been used to prepare other complexes, but these derivatives are commonly prepared from more accessible starting materials. 

If nitrosyl bromide is allowed to react with hydrated rhodium trichloride and PPh3 in ethanol, the mixed chlorobromo complex is obtained (equation 301).13 3 When [RhCl(PPh3)3] is the substrate the dibromo complex is formed (equation 302). This complex can also be obtained from rhodium tribromide, JV-methyl-JV-nitrosotoluene-p-sulfonamide and PPh3. Replacement of PPh3 by other tertiary phosphines permits analogous dibromo complexes to be prepared (cf. equation 299). Another source of the triphenylphosphine complex is [Rh(NO)2Br] . The diiodo complex can be obtained from a similar reaction mixture containing Lil (equation 304).1293... 

They are more usually prepared by the action of nitrosyl compounds on rhodium(I) complexes containing labile ligands.1336"1339 It has also proved possible in one instance to prepare this type of complex by anion metathesis (equations 318 to 320).1340... 

The crystal structure of the dinitrosyl cation (139) has been determined.1344 This cation can be prepared from other rhodium nitrosyl complexes (equations 323 and 324).1SU304... 

There are a few thionitrosyl complexes of rhodium, many of which contain thionitrosyl bridges. They have been prepared by allowing [NSC1]3 to react with sundry rhodium nitrosyl complexes (equations 327 and 328). 

Analogs of the dichloro complex are prepared by a variety of methods, many of which are specific for single compounds. The dibromo complexes can be prepared using nitrosyl bromide or from A-methyl-iV-nitrosotoluene-4-sulfonamide and rhodium tribromide. Replacement of the tribromide by the trichloride and an alkali metal iodide gives diiodo complexes (equations 50 and 51). 

Both mono and dinitrosyl cations may be prepared. Salts of the tetrahedral dinitrosyl cation can be prepared either from rhodium nitrosyls (equation 56) or by addition of nitric oxide to ionic rhodium(I) complexes (equation 57). Both nitrosyl groups in complex (47) are bent. The action of dppe upon the i)A(triphenylphosphine) complex produces N2O. Penta- and hexacoordinate mononitrosyl cations are more common and are usually prepared by the action of NOPFe or NOBF4 on rhodium(I) complexes in organonitrile solvents (equation 58). The principal reactions of the complexes are substitutions of the nitrile ligands (equations 59-61). A noteworthy feature of (48), [Rh(NO)(MeCN)3(PPh3)2]+, is that the MeCN ligand trans to the bent nitrosyl group is said to be bent. 

The rhodium nitrosyl complex is a deep-red crystalline solid which is moderately stable in the air but decomposes rapidly in solution in the presence of oxygen. It is soluble in chloroform, dichloromethane, and benzene and is insoluble in ether, methanol, and ethanol. The compound is a homogeneous hydrogenation catalyst for unsaturated organic compounds. > ... 

M = Rh, 1626 cm M = Ir, 1545 cm ) led to the incorrect conclusion that different solid-state structures are adopted by the two compounds (60). However, X-ray powder data showed the rhodium material to be isomorphous with the structurally characterized iridium complex, which in the solid state has a square-pyramidal geometry and a bent apical nitrosyl ligand (61). 

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