89970-02-5Relevant academic research and scientific papers
Structure-activity relationship analysis of Pd-PEPPSI complexes in cross-couplings: A close inspection of the catalytic cycle and the precatalyst activation model
Nasielski, Joanna,Hadei, Nilofaur,Achonduh, George,Kantchev, Eric Assen B.,O'Brien, Christopher J.,Lough, Alan,Organ, Michael G.
supporting information; scheme or table, p. 10844 - 10853 (2010/12/19)
A series of Pd-N-heterocyclic carbene (Pd-NHC) complexes with various NHC, halide and pyridine ligands (PEPPSI (pyridine, enhanced, precatalyst, preparation, stabilisation and initiation) precatalysts) were prepared, and the effects of these ligands on catalyst activation and performance were studied in the Kumada-TamaoCorriu (KTC), Negishi, and Suzuki-Miyaura cross-coupling reactions. The lowered reactivity of more hindered 2,6-dimethylpyridyl complex 4 in the Negishi and KTC reactions is consistent with slow reductive dimerisation of the organometallic reaction partner during precatalyst activation. Comparative rate studies of complexes 1, 4 and 5 in the KTC and Suzuki-Miyaura reactions verify that 4 activated more slowly than the others. A potential on/ off mechanism of pyridine coordination to NHC-Pd0 is also plausible, in which the more basic pyridine stays bound for longer.
Versatile catalysts for the Suzuki cross-coupling of arylboronic acids with aryl and vinyl halides and triflates under mild conditions
Littke, Adam F.,Dai, Chaoyang,Fu, Gregory C.
, p. 4020 - 4028 (2007/10/03)
Through the use of Pd2(dba)3/P(t-Bu)3 as a catalyst, a wide range of aryl and vinyl halides, including chlorides, undergo Suzuki cross-coupling with arylboronic acids in very good yield, typically at room temperature; through use of Pd(OAc)2/PCy3, a diverse array of aryl and vinyl triflates react cleanly at room temperature. Together, these two catalyst systems cover a broad spectrum of commonly encountered substrates for Suzuki couplings. Furthermore, they display novel reactivity patterns, such as the selective cross-coupling by Pd2(dba)3/P(t-Bu)3 of an aryl chloride in preference to an aryl triflate, and they can be used at low loading, even for reactions of aryl chlorides. Preliminary mechanistic work indicates that a palladium monophosphine complex is the active catalyst in the cross-coupling of aryl halides.
DECOMPOSITION OF (NiRR'L2) COMPLEXES INDUCED BY BROMINE OR ANODIC OXIDATION
Coronas, Juan M.,Muller, Guillermo,Rocamora, Mercedes
, p. 227 - 236 (2007/10/02)
A study has been made of the decomposition of the compounds t-(NiRR'L2) (L=PMe2Ph and PEt3; R=aryl or vinyl groups) and (Ni(mes)(o-tol)bipy) (mes=mesityl) oxidatively induced either by electrochemical means or by bromine.No organometallic compound of Ni(III) was isolated in the above reactions, but a pentacoordinate intermediate of Ni(III) is postulated.Breakdown takes place readily after the Ni(III) intermediate is formed.If the decomposition is induced is induced electrochemically, the intermediate decomposes giving only the coupling product R-R'.When bromine is used as the oxidizing agent, the Ni(III) intermediate is only formed if coordination to the central atom is allowed by the volume of the ligands.Thus, (Ni(C2Cl3)(mes)(PMe2Ph)2) dos not decompose at all, and only (Ni(C2Cl3(mesBr2)(PMe2Ph)2) is obtained.The intermediate ' Ni(III)RR'BrL2' undergoes reductive elimination to give R-R', RBr and R'Br.The formation of the products R-R'is increasingly favoured the greater the electronegativity of the organic ligands.The reductive elimination giving RBr takes place more readily the greater the electronegativity of the organic ligand R.The product of the reductive elimination reaction is 'Ni(I)Br', 'Ni(I)R', or 'Ni(I)R'', which in the presence of bromine give Ni(2+), (NiBr(RBr)L2), phosphonium salts, RBr, and R'Br.
