Chloride-Modulated Insertion Reactions of Dimethylallene across the Pd−C Bond in Palladium Methyl Complexes Bearing Potentially Terdentate Pyridylthioether Ligands

Abstract

Palladium methyl complexes with potentially terdentate pyridylthioether (S-N-S(R) ) 2,6-bis(R-thiomethyl)pyridine, R ) Me, t-Bu, Ph; N-S-N ) 2[(2-pyridylmethylthio)methyl]pyridine) ligands have been prepared and characterized. Both the bidentate chloride [Pd(Me)(S-N-S(R))]Cl and the terdentate chloride-free [Pd(Me)(S-N-S(R))] + species are present in solution and display a substantially different reactivity toward allene insertion across the Pd-C bond. The structures of the complexes [Pd(Me)(S-N-S(t-Bu))]OTf and [Pd(Me)(S-N-S(t-Bu))]Cl were determined by X-ray diffraction. The chloride methyl substrates [Pd(Me)(S-N-S(R))]Cl display an enhanced reactivity in solution with respect to the allene insertion, and this reactivity was traced back to the distortion of the main coordination plane induced by the presence of an uncoordinated -CH 2 -S-R group in position 6 of the coordinating pyridine. The equilibrium position between the terdentate and the bidentate species can be modulated by addition of chloride ion, which therefore controls the overall reactivity of the system.

Methyl Complexes of the Transition Metals

“…Migratory insertion is arguably the most common reaction found in TM-CH3 fragments. Insertion of a wide variety of metal-ligated groups into M-CH3 bonds has been reported over the years, including alkenes, 78,108c,112e,117,159 alkynes, 160 allenes, 161 isocyanides, 162 as well as small molecules such as CO, 163 CO2, 100j,164 or SO2. 165 .In fact, several of these insertion reactions constitute the basis of some of the most prevalent industrial chemical processes, such as olefin polymerization and carbonylation.…”

PNS-Type Ruthenium Pincer Complexes

“…Hence, we decided to synthesize the new PNS ligand 1 and the corresponding ruthenium PNS pincer complexes, analogous to ruthenium PNN and PNP pincer complexes. Like in the case of the amine “arm” of PNN complexes, the thioether “arm” of PNS complexes is expected to be hemilabile, − but, unlike the PNN ligand, it lacks the ability to serve as a base.…”

Pincer versus pseudopincer: isomerism in palladium(ii) complexes bearing κ3C,S,C ligands

“…As a result, highly active yet stable catalysts are obtained. 4 Frequently, the donor functionalities in the side chains of the pincer ligands are hemilabile sites, 5 but cases in which the central donor moiety exhibits hemilabile behaviour have also been reported. 6 However, to control hemilabile behaviour, the governing geometric and electronic factors still need to be understood.…”