No abstract

By using a zerovalent, electron-rich ruthenium complex bearing a tetradentate phosphine ligand, a fivemembered ruthenalactone was generated by oxidative cyclization of ethylene and CO 2 . This ruthenalactone underwent thermal, reversible β-H elimination to afford an acrylato(hydrido)ruthenium(II) complex, which liberated acrylate salt on treatment with a base. The reaction was successfully applied to the first ruthenium-catalyzed synthesis of an acrylate salt from ethylene and CO 2 . This study demonstrated the feasibility of the electron-rich ruthenium(0) complex as a catalyst in CO 2 -fixation chemistry.

Poly(2,5-pyridinediyl) was prepared by dehalogenation polycondensation of 2,5-dibromopyridine with Ni(0)-complexes. The polymer was soluble in formic acid, and the solution showed λmax at about 370 nm and large degree of depolarization.

Dehydrogenative borylation of alkenes and 1,3-dienes was realized by carrying out the reaction in the presence of bis(pinacolato)diboron (B 2 pin 2 ) and a catalytic amount of PSiP-pincer palladium complex. This protocol has the following notable features. 1) Monoanionic nature of the PSiP-pincer ligand prevents the formation of boryl(hydrido)-or dihydridopalladium species, enabling synthesis of various vinyl-or dienylboronic esters in good yield from a 1:1 mixture of B 2 pin 2 and alkenes or 1,3-dienes without forming hydroboration or hydrogenation products. 2) Due to the strong trans influence of the silicon atom, PSiP-pincer palladium complex showed high activity toward migratory insertion. 3) Suppression of these side-reactions and the high reactivity of the PSiP-pincer palladium complex enabled an efficient, successive dehydrogenative borylation to give 1,1-or 1,2-diborylated products depending on the kind of substituent on alkenes by using more than 2 equivalents of B 2 pin 2 . Mechanistic study revealed that PSiP-pincer borylpalladium complex was generated from hydridopalladium complex and B 2 pin 2 , and this complex underwent alkene insertion followed by ¢-hydride elimination to give alkenylboronic ester with regeneration of the hydridopalladium complex.