Ruthenium complexes, reactions dinuclear bridged

The reaction of the coordinatively unsaturated ruthenium amidinates with [Cp RuCl]4 tetramer or [CpRufMeCNlsJPFg provides access to novel amidinate-bridged dinuclear ruthenium complexes (Scheme 146), which in turn can be transformed into cationic complexes or hydride derivatives. In these complexes, a bridging amidinate ligand perpendicular to the metal-metal axis effectively stabilizes the highly reactive cationic diruthenium species. 

The use of Me3NO to induce substitution of dppm (bis(diphenylphosphino)-methane) for CO molecules on dinuclear iron complexes led to insertion of CO into C-C bonds of alkyne-derived metallacycles. Similar behavior was observed when [PPNJCl salts were used to favor the formation of alkyne-substituted triruthenium dppm-containing clusters.I This behavior should be compared with the insertion of CO into allenylidene and phosphido-bridging ligands occurring when dppm coordinates to binuclear ruthenium complexes as shown in Fig. 3. This reaction is a nucleophilic attack of the coordinated allenylidene and phosphido groups on a coordinated CO (see Section 2.8.2.2). 

Recently, a proposal has been put forth that a /raor-addition process may be possible through dinuclear ruthenium intermediates.34 As shown in Scheme 5, reaction of tetraruthenium aggregate A with phenylacetylene results in the fully characterized bridging dinuclear alkenyl complex B. The authors propose a direct /ra .r-dclivcry of hydride through a dinuclear intermediate may be active in the hydrosilylation catalyzed by A, though compound B itself is unreactive to Et3SiH. 

A few stable metal-metal bonded complexes (70) have been described. They are synthesized by reaction of a zirconium dichloride complex with an organometallate of iron or ruthenium (see following section). CO2 and CS2 insertion into the polar metal metal bond affords hetero dinuclear complexes of the second family (71) (Scheme 18). The /U.-OXO complexes are representative complexes of the (71) group. They are readily prepared by the smooth hydrolysis of most metallocenes. Arrangement (71) is also present in the methyl-bridged homo dinuclear species (77) formed by reaction of methylzirconocene cation with Cp2ZrMc2. 

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