Diruthenium complexes

Matsumoto et al. reported some reactions of diruthenium complexes containing a bridging disulfide ligand with unsaturated compounds such as olefins and ketones [135]. These diruthenium complexes show unique reactivities towards double-bond systems since the S-S bond has some double bond character from the contribution of the canonical structure B in Scheme 36. 

Hidai et al. have reported the reaction of a diruthenium complex, (RuCp )2(yU-Si-Pr)2(//-S2), with zerovalent complexes of group 10 metals, [M(PPh3)4] (M=Pd, Pt) (Scheme 65) [146]. The reaction with the Pt complex... 

In addition, the reaction of the diruthenium complex [Ru2Cp 2S4] with [RhCp (MeCN)3](Pp6)2 has been reported to afford the trinuclear cluster [RhRu2Cp 3S4(MeCN)](PF6)2 in 85% yield (Scheme 66) [147],... 

After succeeding in the asymmetric reductive acylation of ketones, we ventured to see if enol acetates can be used as acyl donors and precursors of ketones at the same time through deacylation and keto-enol tautomerization (Scheme 8). The overall reaction thus corresponds to the asymmetric reduction of enol acetate. For example, 1-phenylvinyl acetate was transformed to (f )-l-phenylethyl acetate by CALB and diruthenium complex 1 in the presence of 2,6-dimethyl-4-heptanol with 89% yield and 98% ee. Molecular hydrogen (1 atm) was almost equally effective for the transformation. A broad range of enol acetates were prepared from ketones and were successfully transformed into their corresponding (7 )-acetates under 1 atm H2 (Table 19). From unsymmetrical aliphatic ketones, enol acetates were obtained as the mixtures of regio- and geometrical isomers. Notably, however, the efficiency of the process was little affected by the isomeric composition of the enol acetates. 

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 reaction of 3,6-diaryl-l,2,4,5-tetrazines (aryl = phenyl, 2-furyl or 2-thienyl) with 2 equivalents of Ru(acac)2(CH3CN)2 resulted in reductive tetrazine ring opening to yield diruthenium complexes <06IC821>. 

A pinacol-type silylative dimerization of various aromatic aldehydes promoted by a cationic thiolate-bridged diruthenium complex has been reported by Flidai and co-workers (Equation (28)).344 l,2-Diaryl-l,2-disiloxyethanes 153 were isolated as the major products along with the corresponding arylmethyl silyl ethers as minor products. 

The stoichiometric reaction of (PhS)2 with Cp RuCl(cod) gives a thiolate-bridged diruthenium complex, which also shows a high catalytic activity for the addition to alkenes (Equation (73)). 

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. 

The structural and photophysical properties of [Ru(bp 2(dafo)] PF6]2 (dafo = 93) have been reported the emission lifetime of the complex is 420 ns the study has been extended to the properties of the series of complexes [Ru(bpy) (dafo)3 J +. The nonplanar ligands (94) have been prepared, and form complexes of type [Ru(bpy)2(94)] for = 2, 3 or 4, and l Ru(bpy)2 2(94)]" for = 3 or 4. By using deuterated bpy ligands, more easily interpretable H NMR spectra are obtained. For the diruthenium complexes, there is limited inter-metal communication. ... 

Significantly improved DKR was reported by Backvall et al. who used diruthenium complex 1 together with CALB [8]. This work demonstrated for the first time the superiority of PCPA as the acyl donor over popular acyl donors such as vinyl and isopropenyl acetate. The DKR of 1-phenylethanol by this procedure afforded optically pure (R)-l-phenylethyl acetate in a high yield (Scheme 1.9) [8b]. 

The reaction was carried out with CALB and diruthenium complex 1 in the presence of 2,6-dimethyl-4-heptanol or molecular hydrogen (latm). In the case of 1-phenylvinyl acetate, (R)-l-phenylethyl acetate was obtained in 89% yield and 98% ee (Scheme 1.14) [15a]. 

Until now, hexapentaenylidene complexes are unknown, however, a hexapentaenylidene complex has been proposed as an intermediate in the formation of a Cg-bridged diruthenium complex (Scheme 3.20) [35]. 

Scheme 3.20 Postulated hexapentaenylidene complex as intermediate in the synthesis of a Cg-bridged diruthenium complex.

Scheme 3.28 Formation of a C7-bridged diruthenium complex with a central cyclobutenylidene unit.

Cycloaddition of the terminal C = C bond in [Cp (dppe)Ru-C = CC = C-SiMe3] to the C3=C4 bond in cationic [Cp (dppe)Ru=C=C=C=CH2] gave a diruthenium-complex containing a C7-bridge with a central cyclobutenylidene unit (Scheme 3.28) [51]. The complex was characterized by an X-ray structure analysis. A similar bis-[Ru(dppe)2Cl] complex was already obtained earlier by oxidation of the diynyl complex [RuCl2(dppe)2] with [FeCp2]PF6 [35, 50, 54]. 

Scheme 7.4 The first thiolate-bridged diruthenium complexes.

In the presence of a catalytic amount of methanethiolate-bridged diruthenium complex (la abbreviated as met-DIRUX), reactions of propargylic alcohols (2) with a variety of heteroatom-centered nucleophiles such as alcohols, thiols, amines, amides, and diphenylphosphine oxide gave the corresponding propargylic substituted... 

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