GENERATION OF SOLVENTO-COMPLEXES

Metal-solvent interactions can be conveniently considered in terms of the hard-soft acid-base (HSAB) principle (Chapter 1). For example, palladium(II) is a soft metal center and so the hard oxygen donor solvent, diethyl ether, interacts only poorly with it. Simple valence bond models have been presented that adequately explain such soft metal-hard base interactions. In this chapter complexes containing coordinated halocarbons are treated in a separate section (3.7) from those that contain other hard bases since such species have only been recognized as well-defined complexes in recent years and their potential for exploitation in coordination chemistry merits special attention. 

A process referred to as aging may occur when a complex in solution has been allowed to stand for some time. Ligand exchange reactions often occur more rapidly within an aged solution than when that solution is 

The pathway followed will depend upon the nature of the complex and the solvent. If the complex is coordinatively saturated, a dissociative pathway 

Abstraction of the last chloride ligand from [RhCl(DMS0)5lIC104]2 has been unsuccessful even with an excess of silver perchlorate.4 

Widely used in preparative coordination chemistry, labile solvento-complexes are generated by a number of different approaches. Aspects of the 

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The equilibrium generation of solvento-complexes is based on reaction between the solvent and the complex. Scheme 3.1 ... 

Chemical (Chapter 8), electrochemical (Chapter 7), thermal, and photochemical elimination of CO ligands from carbonyl-containing complexes are common methods for the generation of solvento-complexes and such reactions are discussed extensively in the literature. In 1968 a comprehensive account of the topic was published. Since then many examples have been reported along with studies of synthetic pathways and mechanisms. This section is confined to a description of several examples of decarbonylation based on thermal and photochemical means. More detailed discussions of these subjects are found elsewhere. - 14... 

In conclusion, the generation of solvento-complexes as reactive intermediates is extensively used in synthesis. Three distinct approaches have been developed to provide solvent-binding sites (i) conversion of ligands into products with low solubility or their transformation into volatile compounds, (ii) chemical transformations of coordinated ligands where the products of the reaction are poorer donors and are expelled from the coordination sphere of the complex, and (Hi) manipulation of the metal oxidation state to affect ligand-binding properties. 

Titanium(III) sulfate has been employed successfully to generate a solvento-complex of platinum(II) by reduction of the nitro ligand in [Ph3PCH2Ph]2[PtCl3(N02)]. The reaction, performed in a mixture of MeCN and H2O, produced the acetonitrile complex, [Ph3PCH2Ph][PtCl3(MeCN)I, in... 

The formation of solvento-complexes as a result of redox transformations of coordinated ligands is not r tricted to N-donor ligands reactions with other ligands are well known. For example, oxidation of the dimethyl sulfoxide ligand in [Co(NH3)5(DMSO)]3+ can be effected by treatment with KMn04 or CI2 in aqueous solution. The sulfoxide oxidizes to the sulfone which exhibits a much lower donor ability than Me2SO and, as a result of hydrolysis, is expelled from the complex generating the aqua-complex. 

Jackson, Jurisson, and O Leary have reported preparation of the [Co(MeS02)(NH3)5]2+ cation S containing O-coordinated methanesulfinate, MeS02 - This complex is formed by reaction of [Co(NH3)5(H20)]3+ with MeSOQ in the presence of 2,6-lutidine in trimethylphosphate solution. The [Co(MeS02)(NH3)5]2+ is alkylated by Mel in dimethyl sulfoxide to generate the solvento-complex, [Co(NH3)5(DMSO)]3+, and free dimethyl sulfone. No intermediates were detected for this reaction. 

Generally, synthetic procedures for silane complexes are similar to those that produce silyl hydride complexes16 and involve addition of silane to an unsaturated complex, often generated by photolytic or thermolytic dissociation of CO as for CpMn(CO)2(silane). Agostic, H2, or solvento complexes are also excellent precursors because silanes tend to bind as well or more strongly than H2 or weak donors such as THF. Addition of a primary or secondary silane to solutions of Mo(CO)(R2PC2H4PR2)2 forms yellow silane complexes [Eq. (11.4)].24 The less... 

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. 

Solvento-complexes also may be generated through redox transformations of other types of N-donor ligands. 2,63 poj. example, the reduction at an electrode of the arenediazenate ligand in the ruthenium(II) complex, [RuCl(bipy)2(N2C6H4Me)]2+, in MeCN solution leads to formation of [RuCl(bipy)2(MeCN)]+ in addition to toluene and dinitrogen. 

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