Ru-amido complex

When nitroalkenes were used as Michael acceptors, high yields and enantioselectivities of the desired Michael addition products were also obtained (Scheme 5.22). In these reactions, a well-defined chiral Ru amido complex (Figure 5.9) was an efficient catalyst. The mild reaction conditions and high reactivities and stereoselectivities allowed a large-scale reaction in the presence 1 mol% Ru catalyst. By using a chiral Pd(II) catalyst, an asymmetric allylic arylation was reported by Mikami and coworkers to give the cross-couphng product via the activation of both allylic C H and aryl C H bonds in moderate enantioselectivity (Scheme 5.23). ... 

Inspired by the reaction mechanism of Noyori s catalytic enantioslective transfer hydrogenation of ketones (32) using a chiral Ru-amido complex 31, Dcariya et al. reported that 31 can also function as a unique Bronsted base-Bronsted acid catalyst... 

Another mechanistically interesting example was reported by Ikariya et al. in 2003 (Scheme 10) [12], The authors focused on the basic character of the Ru-amido complex 21. The reaction of dimethyl malonate with 21 afforded a C-bound Ru-enolate, the structure of which was supported by X-ray analysis. It was considered that the N-H moiety plays a role in bringing the enones to the optimum position by hydrogen bonding, as shown in 22 C-C bond formation then occurs at relatively high reaction temperature, affording the desired adduct in 97 % ee. Before this report appeared, a related catalyst system had been examined by Suzuki et al. for the Type I reaction [4f]. 

Ito et al. developed an effective catalyst for racemization of chiral non-racemic secondary alcohols. Catalytic system, Cp RuCl(cod)/Ph2P(CH2)2NH2/tBuOK, effects extremely rapid racemization (Eq. 12.28). These authors proposed the in-situ formation of a coordinatively unsaturated (16 e) Cp Ru(amido) complex 68 as an active species [32]. 

PhNHC(NPh)2]2Ru(CO)(PPh3) The Ru(n) amido complex (PCP)Ru(CO) (PMesllNHPh) (PCP = CgH3(CH2PBu2)2-2,6) reacts with nitriles under formation... 

Scheme 3.12 Enantioselective hydrogenation of a ketone by transfer from iso-propanol catalyzed by the hydride complex RuH( 6-arene)(NH2CHPhCHPhNTs) and the amido complex Ru(r 6-arene)(NHCHPhCHPhNTs) [94].

Reaction of the ruthenium(II) amido complex [Ru (NHPh)(Tp)(CO)(PPh3)l with two equivalents of AgOTf in the presence of excess NEts or lutidine generates [Ru qNHPh)(Tp)(CO)-(PPh3)](OTf)2 (115d). The BAr 4 (AT = C6H3(CF3)2-3,5) salt was also prepared. ... 

Analogous heterobimetallic tripodal amido complexes 1275 (M = Fe, Ru) undergo highly selective reactions with heteroallenes X=C=Y (C02, CS2, OGNPh, SCNMe, SCNPh) to yield the insertion products 1276 (Equation (65)).962 Single crystal X-ray structures of the products (1276 M = Fe X = Y = S X = S, Y = NPh) established the mode of coordination of the substrates to the two metal centers as depicted in Equation (65). The Zr-Fe complex CpFe(CO)2Zr(OBut)Cp2 reacts with 1 equiv. of CS2 to form the analogous stable dithiocarboxylate complex.963... 

The ruthenium-catalyzed reduction of polar bonds using H gas, rather than a sacrificial reductant such as isopropanol, is an atom-economical reaction that has been thoroughly explored. A key discovery by our laboratory was that neutral, stmctur-ally characterized metal-amido complexes such as 11 (Scheme 7) could cleave H heterolytically to yield the fran -dihydride complex 12, and that these are crucial intermediates during catalysis.R - Once the H-N-Ru-H moiety is in place, proton and hydride can then be transferred to the substrate. Having methyl groups instead of hydrogens on carbons alpha to the amido group (beta to the ruthenium) in this case and in the case of 1 (Scheme 4) was important to allow the isolation of an amido... 

It was originally thought that the high basicity of the amido complex would make the reprotonation a dillusion controlled process so that fc.., was always much greater than fc2- This is indeed true for the majority of Co" systems examined and for all studied cases of Cr", Ru", Rh" and Ir complexes. Under these conditions, the expression for the rate constant reduced to feg = S n ki k2 /k-i or 2 K k2 where K is the equilibrium constant for the proton transfer process (1). With proton transfer as a rapid preequilibrium, such systems exhibit specific base catalysis. 

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