Transitions triflate catalysis

Nitrogen extrusion from diazo compounds can be induced photochemieally, thermally, or by transition-metal catalysis. Complex 2f is decomposed neither by eopper(I) triflate (CuOTf) nor by Rh2(OAc)4 at room temperature. The photochemical decomposition of 2f leads to simultanous nitrogen and earbonyl extrusion, but no product could be characterized. 

Numerous transition and rare earth metal triflates were screened as catalysts for the alkenylation of arenes with alkynes, a transformation that can be performed only with difficulty in conventional solvents, see Scheme 9.23. Particularly with electron deficient alkynes such as p-trifluormethylphenylacetylene and />-chlorophenylacetylene the presence of an ionic liquid was found to be mandatory to observe any catalysis. Highest activity was obtained with Hf(OTf)3, In(OTf)3 and Sc(OTf)3 and the reaction proceeded smoothly, even at relatively low catalyst loadings. It is proposed... 

J. F. Hartwig, Transition Metal Catalyzed Synthesis of Arylamines and Aryl Ethers from Aryl Halides and Triflates Scope and Mechanism, Angew. Chem. Int. Ed. 1998,37,2047. P. G. Jessop, T. Ikariya, and R. Noyori, Homogeneous Catalysis in Supercritical C02, Chem. Rev. 1995, 95, 259. 

A chiral bisphosphine such as 2,2 -h -(diphenylphosphino)-l,F-binaphthyl (BINAP) has been extensively used as a chiral chelator in asymmetric catalysis. When Stang et al. reacted the chiral metal complex 42 with 40, they synthesized a square box (Figure 25) and asymmetric induction was observed [79,82] with the formation of an excess of one of the preferred diastereoisomers as measured by NMR spectroscopy. The same reaction has been carried out with 42 and 6is-4-(4 -pyridyl)phenyl)iodonium triflate, but in this case the diaza ligands of the iodonium species possess rotational symmetry about their linkages. Consequently, the optical activity of the molecular squares obtained is due exclusively to the chiral transition metal auxiliary BINAP. 

Halide and triflate leaving groups are also involved with palladium catalysis in the most general of all these reactions with vinyl electrophiles. These use a main group rather than transition metal, chiefly boron or tin, in stoichiometric amounts to mark one molecule as nucleophilic and then... 

Kappe and Stadler have developed an MW procedure for rapid production of triaryl phosphines by coupling diphenylphospine with aryl halides and triflates [134]. Taking into account the importance of phosphine ligands in a variety of transition metal-catalyzed reactions, convenient procedures for their production is valuable. Both homogeneous Pd-Ni and heterogeneous Pd catalysts were explored and the more unusual substrate phenyl triflate could also be coupled swiftly by use of nickel catalysis (Scheme 15.68). Couplings with other aryl halides proceeded in 26-85% yield after 3-30 min microwave irradiation at 180-200 °C. 

Cycloisomerization of methyl-substituted 1,6-diene is also catalyzed by tin(rv) triflate (Equation (8.8)). DFT computations proposed that the mechanism does not involve the direct addition of the tin(IV) cation to a double bond because the catalyst regeneration step would be energetically unfeasible [24]. The active catalyst is a hydrated triflate salt where water molecule plays a decisive role to enable the smooth completion of the catalytic cycle. The diastereoselectivity observed in the cycloisomerization was associated with the transition-state geometries. DFT calculations also showed that protonation and deprotonation occur on a single face of the substrate. These considerations, correlated to the experiments, showed that Brpnsted superacids are not effective in Lewis superacid catalysis. 

There are also water-insensitive metals of which triflates were extensively studied in catalysis due to the very specific Lewis acid properties. Group 3b transition metals and rare earth metal triflates [RE(OTf)3] belong to this group of elements. They have been introduced and confirmed as promising mild, powerful, and selective Lewis add catalysts for a variety of functional group transformations. 

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