Borate ruthenium

The vast majority of tris(pyrazolyl)borate ruthenium complexes prepared until now contains the parent Tp ligand. In contrast to other transition metals, ruthenium compounds which bear bulky Tp ligands remain still rare and are, thus far, limited to Tp, Tp Tp and Tp as shown in Chart 1. 

Caramori GF, Kunitz AG, Coimbra DF, Garcia LC, Fonseca DEP. The Ru—NO bonding in nitrosyl-[poly(l-pyrazolyl)borate] ruthenium complexes a theoretical insight based on EDA. J Braz Chem Soc. 2013 24 1487-1496. 

Liu, R.-S. (2008) Catalytic transformations of terminal alkynes by cationic tris(l-pyrazolyl) borate ruthenium catalysts versatile chemistry via catalytic allenylidene, vinylidene, and Ti-alkyne intermediates. Synlett, (6), 801-812. 

An unprecedented carbene insertion reaction was observed on reaction of the cationic re-arene ruthenium amidinates with trimethylsilyldiazo-methane (Scheme 145, TFPB = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate). 

Hydridotris(pyrazolyl)borate (N,N,N)-containing ruthenium(ll) complexes activate benzene in stoichiometric amounts to give the isolable complex B. A catalytic hydroarylation of ethylene led to ethylbenzene and a ca. 1 1 mixture of branched and linear alkylbenzenes was obtained when employing propylene (Equation (62)).63,63a... 

The hydroarylation of olefins is also achieved by using a ruthenium catalyst, TpRu(CO)(NCMe)(Ph) (Tp = hydridotris(pyrazolyl)borate) (Equation (34)).39 The reaction of benzene with ethene is catalyzed by the ruthenium complex to give ethylbenzene (TN = 51, TOF = 3.5 x 10 3mol 1 s-1 at 90 °G for 4h). The ruthenium-catalyzed reaction of benzene with propene gives the hydroarylation products with a 1.6 1.0 ratio of -propyl to isopropylbenzene, with 14 catalytic turnovers after 19 h. 

The ruthenium cluster [Ru4H4(//6-C6H6)4]2+ was also employed for the hydrogenation of arenes in a biphasic water/l-butyl-3-methylimidazolium tetrafluoro-borate biphasic system. At 90°C and 60 bar H2, benzene was reduced to cyclohexane with a TOF of 364. 

The ruthenium-catalyzed direct addition of saturated aliphatic alcohols to non-activated alkynes remains a challenge. Only ally alcohol has been successfully involved in the intermolecular addition to phenylacetylene to produce an ether and the enal resulting from Claisen rearrangement (Equation 10.7) [24]. Thus, in refluxing toluene, in the presence of a catalytic amount of RuCl(tris(pyrazolyl) borate) (pyridine)2, a 1 1 mixture of ally P-styryl ether and 2-phenylpent-4-enal was obtained in 72% overall yield. 

The formation of a ruthenium vinylidene is proposed as the key intermediate in the regioselective addition of hydrazine to terminal alkynes [55]. This reaction, which proceeds via addition of the primary amino group of a 1,1-disubstituted hydrazine followed by deamination, provides an unprecedented access to a variety of aromatic and aliphatic nitriles. The tris(pyrazolyl)borate complex RuCl(Tp)(PPh3)2 gave the best catalytic activity in the absence of any chloride abstractor (Scheme 10.17). 

H14B4K, Borate(l -), tetradecahydronona-potassium, 26 1 HgBrOvRujC,sHv, Ruthenium,... 

The first base-free silylene ruthenium complexes without a 7r-donor stabilization were prepared by Tilley and coworkers by displacement of a triflate ion by a noncoordinating lithium perfluorotetraphenyl borate (equation 34). The base-free silylene... 

Very recently, new ruthenium catalysts, for example RuCl2(triazol-5-ylidene) (p-cymene) [11] and the catalytic system generated in situ from [RuCl2(p-cym-ene)]2, tris(p-chlorophenyl)phosphine, and 4-dimethylaminopyridine [12], have provided efficient catalysts for synthesis of the same type of enol ester. The regio-selective cyclization of acetylenic acids containing a terminal triple bond to give unsaturated lactones was performed in the presence of catalytic amounts of Ru(tris(pyrazolyl)borate)(PhC=C(Ph)C CPh)(PMe2iPr2) [13],... 

The regioselective anti-Markovnikov addition of benzoic acid to phenyl-acetylene has also been carried out with success at 111 °C in the presence of ruthenium complexes containing a tris(pyrazolyl)borate (Tp) ligand [RuCl(Tp)(cod), RuCl(Tp)(pyridine), RuCl(Tp)(N,N,Ar,AT-tetramethylethyl-enediamine )] with a stereoselectivity in favour of the (E)-enol ester isomer [22]. The o-enynyl complex Ru(Tp)[PhC=C(Ph)C=CPh](PMe/-Pr2) (C) efficiently catalyses the regioselective cyclization of a,cu-alkynoic acids to give en-docyclic enol lactones [23] (Eq. 2). 

Catalytic transformations involving the C-H bonds of thiophene are rare, but recently there has been a report on the catalytic addition of the C(2)-H bond of thiophene across ethylene to form 2-ethylthiophene <20040M5514>. Reaction of the ruthenium complex TpRu(CO)(NCMe)(Me) (where Tp = hydrido tris(pyrazolyl)borate) with thiophene produces the 2-thienyl complex 249 and methane. This complex catalyzes the formation of 2-ethylthiophene from a solution of thiophene and ethylene (Equation 121). The mechanism of this reaction has been explored. 

---