Solvento complexes salts

McNeese and Mueller have shown35 that [VCKSchiff Base)] complexes lose halide in reactions with thallium tetrafluoroborate in acetone. The corresponding solvento-complexes are generated along with thallium chloride. The use of silver salts in such reactions could lead to oxidation of the starting material. 

Silver salts containing anions of strong adds are suitable reagents for synthesis of solvento-complexes by metal oxidation in non-aqueous solvents. Metallic gold in acetonitrile reacts with silver perchlorate to produce [Au(MeCN)4][C104], Eq. 4.3 ... 

The preparation of homoleptic solvento-complexes by metal oxidation with ArN2 or Ph3C+ salts in acetonitrile has been proposed.27 However, such procedures are not recommended as routine preparative methods. 

Synthesis of solvento-complexes by dissolution of salts in non-aqueous solvents... 

In certain cases, homoleptic solvento-complexes containing halides as counterions have been prepared (see Table 4.2). In general, preparation of such homoleptic solvento-complexes is of limited use due to the difficulties inherent in the preparation of the necessary anhydrous salts. In recent years it has been found that trifluoromethanesulfonate salts are easily prepared in anhydrous form. The CF3S03 ion only rarely fomas isolable complexes in which it is coordinated to a metal ion and is normally a weaker donor than the perchlorate anion. Unlike the common perchlorate salts, metal trifluoromethanesulfonates are not typically explosive under normal laboratory conditions. Thus, anhydrous met trifluoromethanesulfonates are very useful precursors in the preparation of homoleptic solvento-complexes. 

Synthesis of solvento-complexes by dehydration of aqua-complexes and hydrated salts... 

Many metal salts contain water of crystallization or coordinated water molecules. The interaction of such salts with non-aqueous solvents is a complex process involving competition for the metal ion between the solvent molecules, water, and the anion. To prepare homoleptic solvento-complexes, salts of strong acids, whose anions are poor electron donors, e.g, HCIO4, HBF4, HPF6, HSO3CF3, HS03Ar etc., are employed. This essentially eliminates competition from the X- anion for coordination sites at the metal center. 

Acid anhydrides have commonly been neglected as dehydrating agents in the synthesis of homoleptic solvento-compIexes. Applications of acid anhydrides in the synthesis of anhydrous salts or complexes with different ligands 2-44 aj-g more typical. 

Synthesis of solvento-complexes by halide abstraction from salts and complexes... 

In Chapter 3 we considered methods of formation of solvento-complexes and illustrated the various ways these compounds are prepared. Halide abstraction techniques that utilize silver salts are commonly employed in the synthesis of mixed-ligand solvento-complexes and such techniques are used also for the transformation of halide complexes into homoleptic solvento-complexes. 

There are many examples of the synthesis of homoleptic solvento-complexes by halide abstraction from compounds containing both coordinated halides and solvento-ligands. Palladium chloride is known to dissolve in nitriles, dimethylformamide, and dimethyl sulfoxide with the formation of complexes of the type [PdCl2(solv)2] which can be isolated as solids.3 The reaction of [PdCl2(RCN)2] with an excess of silver ions s is a convenient method for the synthesis of [Pd(RCN)4]2+. The tetra(acetonitrile)-platinum(II) and tetra(propionitrile)platinum(II) salts have been prepared in this way (Scheme 4.6). Wayland and Schramm have synthesized homoleptic palladium(II) complexes with DMSO, DMF, and DMAA in a similar manner. 

Because carboxylate anions are hard Lewis bases, they have low affinities for soft metal ions such as platinum(II). Conversely, the relatively soft bromide ion has a high affinity for this metal and yet halide abstraction by Ag+, with concomitant formation of the sparingly soluble salt, AgBr, results in substitution of bromide by the carboxylate anion. The use of dichloromethane, a poor ligand for platinum(II), as the solvent for this reaction prevents any competitive formation of a solvento-complex, although such species may be involved as short-lived intermediates in the reaction. 

It has been established34 that the reaction of the nortricydic compound, A, with a silver salt in MeCN results in the formation of a solvento-complex containing a coordinated acetonitrile ligand. In acetone solution, halide abstraction is followed by isomerization of the ligand, ring-dosure, and the formation of the norbomadiene complex, B, Figure 6.2. 

Preparation of anhydrous salts, metal halide complexes, and solvento-complexes... 

Nitrosonium salts containing weak donor anions are employed for the oxidation of metals in the preparation of both metal salts and homoleptic solvento-complexes. Thus, one of the first syntheses in which a nitrosonium salt was employed as the oxidant was reported by Seel in 1950, Eq. 8.5 ... 

More recently the oxidation of metals by nitrosonium salts in acetonitrile has been used to synthesize homoleptic solvento-complexes. Thus, the complexes, [Cu(MeCN)4]X (X = BF4, C104), l have been obtained by oxidation of metallic copper in acetonitrile with NOX the perchlorate, NOCIO4, in MeCN oxidizes metallic gold to form [Au(MeCN)4][C104], 3 Eq. 8.6 ... 

Examples of the oxidation of metal complexes ly thionitrosonium salts, NSX, are uncommon but some useful reactions have been reported. Thus, the reaction between [ReBrfCOls] and NSSbFg leads to formation of [Re(CO)5(NS)][SbF6] in low yield.4l In addition, interaction between [Ct(CO)3(C H6)] and NSPFs results in formation Z of the solvento-complex, [Cr(MeCN)5(NS)P+. 

The tetrafluoroborate complex, [Cr(BF4)(NO)2(T -Cp)], is converted into the more stable salt, [Cr(NO)2(MeCN)(Ti5-Cp)][BF4L on treatment with MeCN. 5 Similarly, the interaction of the isoelectroniccomplex, [Fe(CO)2(Ti5-Cp)l2, with p-toluenesulphonic add in acetonitrile leads to oxidative deavage of the Fe-Fe bond and formation of the acetonitrile solvento-complex, [Fe(CO)2(MeCN)(Ti5-Cp)][C)3SC6H4Me].8 For this reaction it was reported that the protic add was responsible for oxidation of the complex. However, the evolution of molecular hydrogen was not observed. 

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