Ruthenium diruthenium complexes

Another method for reductive dimerization has been developed in hy-drosilylation. NiCl2-SEt2 is an effective catalyst in silylative dimerization of aromatic aldehydes with a hydrosilane (Scheme 12) [40]. A catalytic thiolate-bridged diruthenium complex [Cp RuCl(/ 2-SPrI)2RuCp ][OTf] also induces the conversion to 1,2-diaryl-1,2-disiloxyethane [41]. A dinuclear (siloxyben-zyl)ruthenium complex is considered to be formed, and the homolytic Ru - C bond fission leads to the siloxybenzyl radicals, which couple to the coupling product 14. 

The nature of the bridging thiolate ligands or the replacement of a terminal chloride ligand by water did not have much effect on the catalytic activity, complexes 105b-d and 106a,b being also operative in these transformations. In contrast, conventional monometallic ruthenium derivatives, as well as diruthenium complexes having no Ru-Ru bond, did not work at all. 

Propargylic alcohols bearing a terminal triple bond react with electron-rich aromatic compounds in the presence of thiolate-bridged diruthenium complexes to give the propargylated aromatic compounds.30 l-Phenylprop-2-yn-l-ol, for example, reacts with 2-methylfuran to form (15). Intramolecular examples of the reaction were also reported. The process is believed to involve electrophilic attack by the ruthenium-stabilized propargyl cation. 

Thiolate-bridged diruthenium complexes such as Cp RuCl(p2-SR)2RuCp Cl catalyze the propargylic substitution reaction of propargylic alcohol derivatives with various carbon-centered nucleophiles [118-120]. Ketones [119] (Eq. 88), aromatic compounds [120] (Eq. 89), or alkenes thus selectively afford the corresponding propargylated products with C-C bond formation. An allenylidene intermediate is proposed in these reactions. They are detailed in the chapter Ruthenium Vinylidenes and Allenylidenes in Catalysis of this volume. 

The double phosphinylation of propargylic alcohols with diphenylphos-phine oxide to form 2,3-bis(diphenylphosphinyl)-1-propenes is catalyzed by a thiolate-bridged diruthenium complex (Scheme 28) [69]. It has been shown that the reaction proceeds via three ruthenium-catalyzed transformations propargylation of the phosphine oxide, alkyne to allene isomerization, and addition of phosphine oxide to the allene structure. 

Ruthenium. In 1995, Hidai reported that a diruthenium complex can catalyze the silylative dimerization of a wide variety of aromatic aldehydes (Eq. 3.29) [49, 50]. The analogous reaction of acetophenone proceeds more slowly and furnishes only 33% of the desired coupling product. It is postulated that this ruthenium-catalyzed... 

A screening of ruthenium(II) carboxylates and several ruthenium(II) chloride complexes has identified tetrakis(trifluoroacetato)diruthenium as an excellent catalyst for the cyclo-propanation of cyclooctene with ethyl diazoacetate (60°C, excess of alkene, 0.75 mol% of catalyst yield of ethyl bicyclo[6.1,0]nonane-9-carboxylate 99% endojexo 1.65)." With several other ruthenium(II) complexes, ring-opening metathesis polymerization of cyclooctene competes strongly with the cyclopropanation reaction. 

Sizova OV, Sokolov AY et al (2007) Quantum chemical study of the bond orders in the ruthenium, diruthenium and diifaodium nitrosyl complexes. Polyhedron 26 4680-4690... 

The dimerisation of phenylacetylene to yield exclusively the head-to-tail coupling product has been achieved using the diruthenium complex 12 as catalyst (Scheme 7a) [31]. This was the first complex to display such selectivity and remains the only ruthenium complex to do so. Complex 12 contains two bridging... 

Ruthenium dihydride complex [Ru(H)2(CO)(PPh3)3], activated by treatment with st3rrene, catalyzes several hydrosilylation polymerization processes, such as the reaction of tereftaldehyde with 1,3-tetramethyldisiloxane and hydrosilylation of poly(l-hydrido-l,3,3,5,5-pentamethyltrisiloxane) with benzophenone (221,222). [Ru3(CO)i2] was found catalytically active in the hydrosilylation of acetophenone with HSi(OEt)3 (222). The same cluster and several ruthenium carbonyl complexes efficiently catalyze the reduction of linear and cyclic amides with trisubstituted silanes to give the corresponding amines (224). Activated diruthenium and triruthenium carbonyls catalyze the hydrosilylation of ketones, as well as that of aldehydes wdth different silanes (225). First-generation Grubbs... 

In 1999, Fiirstner [33] reported the reaction of the allenylidene ruthenium complex 3 with [RuCl2(p-cymene)]2, which led to the formation of a diruthenium complex bearing chloride bridges and mixed, arene-allenylidene ligands of... 

---