A different polynorbornene backbone by combination of two polymer growth pathways: vinylic addition and ring opening via β-C elimination

A new polynorbornene skeleton has been found that contains bicyclic norbornane units and cyclohexenyl methyl linkages. The polymers have been synthesized using a nickel catalyst in the presence of a controlled amount of ligands with low or moderate coordination ability. The backbone structure is the result of a vinylic addition polymerization, via sequential insertions of norbornene into a Ni–C bond (bicyclic units) combined with an unusual ring opening of the norbornene structure by a b-C elimination (cyclohexenyl methyl units) to give a new Ni–C(alkyl) bond that continues the polymerization. The ring opening events are favored when the rate of propagation of the vinylic addition polymerization decreases, and this can be modulated by making the coordination of norbornene to the metal center less favorable using additional ligands.Ministerio de Ciencia e Innovación/AEI; Grant PID2019-111406GB-I00Junta de Castilla y León-FEDER; Grant VA224P2

Palladium mono-N-protected amino acid complexes: experimental validation of the ligand cooperation model in C–H activation

Producción CientíficaMechanistic proposals for the C–H activation reaction enabled by mono-N-protected amino acid ligands (MPAAs) have been supported by DFT calculations. The direct experimental observation of the ligand- assisted C–H activation has not yet been reported due to the lack of well-defined isolated palladium complexes with MPAAs that can serve as models. In this work, palladium complexes bearing chelating MPAAs (NBu4)[Pd(k2-N,O–AcN–CHR–COO)(C6F5)py] (Ac = MeC(O); R = H, Me) and [Pd(k2-N,O–MeNH– CH2–COO)(C6F5)py] have been isolated and characterized. Their evolution in a solution containing toluene leads to the C–H activation of the arene and the formation of the C6F5–C6H4Me coupling products. This process takes place only for the ligands with an acyl protecting group, showing the cooperating role of this group in a complex with a chelating MPAA, therefore experimentally validating this working model. The carboxylate group is inefficient in this C–H activation.Ministerio de Ciencia e Innovación/AEI; Grant PID2019-111406GB-I00Junta de Castilla y León-FEDER; Grant VA224P20European Union / Ministerio de Ciencia e Innovación/Junta de Castilla y León; Grant C17.I01.P01.S21, H2MetAmo

Palladium-Catalyzed Ortho C-H Arylation of Unprotected Anilines : Chemo- and Regioselectivity Enabled by the Cooperating Ligand [2,2'-Bipyridin]-6(1 H)-one

Metal-catalyzed C-H functionalizations on the aryl ring of anilines usually need cumbersome N-protection-deprotection strategies to ensure chemoselectivity. We describe here the Pd-catalyzed direct C-H arylation of unprotected anilines with no competition of the N-arylation product. The ligand [2,2'-bipyridin]-6(1 H)-one drives the chemoselectivity by kinetic differentiation in the product-forming step, while playing a cooperating role in the C-H cleavage step. The latter is favored in an anionic intermediate where the NH moiety is deprotonated, driving the regioselectivity of the reaction toward ortho substitution