51752-50-2Relevant articles and documents
Triarylphosphine ligands with hemilabile alkoxy groups: Ligands for nickel(II)-catalyzed olefin dimerization reactions. hydrovinylation of vinylarenes, 1,3-dienes, and cycloisomerization of 1,6-dienes
Biswas, Souvagya,Zhang, Aibin,Raya, Balaram,Rajanbabu
, p. 2281 - 2292 (2014/07/21)
Substitution of one of the phenyl groups of triphenylphosphine with a 2-benzyloxy-, 2-benzyloxymethyl- or 2-benzyloxyethyl-phenyl moiety results in a set of simple ligands, which exhibit strikingly different behaviour in various nickel(II)-catalyzed olefin dimerization reactions. Complexes of ligands with 2-benzyloxyphenyl- and 2-benzyloxymethylphenyldiphenylphosphine (L5 and L6, respectively) are most active for hydrovinylation (HV) of vinylarenes, with the former leading to extensive isomerization of the primary 3-aryl-1-butenes into the conjugated 2-aryl-2-butenes even at -55 °C. However, 2-benzyloxymethyl-substituted ligand L6 is slightly less active, affording up to quantitative yields of the primary products of HV at ambient temperature with no trace of isomerization, thus providing the best option for a practical synthesis of these compounds. In sharp contrast, hydrovinylation of a variety of 1,3-dienes is best catalyzed by nickel(II) complexes of 2- benzyloxyphenyldiphenylphosphine, L5. The other two ligands, 2-benzyloxymethyl- (L6) and 2-benzyloxyethyldiphenylphosphine (L7) are much less effective in the HV of 1,3-dienes. Nickel(II)-catalyzed cycloisomerization of 1,6-dienes into methylenecyclopentanes, a reaction mechanistically related to the other hydrovinylation reactions, is also uniquely effected by nickel(II) complexes of L5, but not of L6 or L7. In an attempt to prepare authentic samples of the methylencyclohexane products, nickel(II) complexes of N-heterocyclic carbene ligands were examined. In sharp contrast to the phosphines, which give the methylenecyclopentanes, methylenecyclohexanes are the major products in the (N-heterocyclic carbene)nickel(II)-mediated reactions.
Stereogenic-at-metal Zn- and Al-based N-Heterocyclic Carbene (NHC) complexes as bifunctional catalysts in Cu-free enantioselective allylic alkylations
Lee, Yunmi,Li, Bo,Hoveyda, Amir H.
supporting information; body text, p. 11625 - 11633 (2011/02/26)
Investigations detailed herein demonstrate the ability of chiral bidentate N-heterocyclic carbenes to promote directly - without the need for a Cu salt - site- and enantioselective C-C bond forming reactions. Within this context, catalytic allylic alkylat
Tunable phosphoramidite ligands for asymmetric hydrovinylation: Ligands par excellence for generation of all-carbon quaternary centers
Smith, Craig R.,Hwan, Jung Lim,Zhang, Aibin,RajanBabu
experimental part, p. 2089 - 2100 (2010/02/28)
α-Alkylstyrenes undergo efficient hydrovinylation (addition of ethene) in the presence of a nickel catalyst prepared from [(allyl)NiBr] 2, Na+[BAr4]- [Ar = 3,5-bis(trifluoromethyl)phenyl], and a phosphoramidite ligand giving products in excellent yields and enantioselectivities. In many cases phosphoramidites derived from achiral 2,2′-biphenol are almost as good as ligands derived from the more expensive enantiopure 1,1′-bi(2-naphthol)s. The hydrovinylation products, which carry two versatile latent functionalities, an aryl and a vinyl group, are potentially useful for the synthesis of several important natural products containing benzylic all-carbon quaternary centers. Georg Thieme Verlag Stuttgart.
