The coordination chemistry of the bidentate P,N hybrid ligand 2-(2'-pyridyl)-4,6-diphenylphosphinine (1) towards Pd(II) and Pt(II) has been investigated. The molecular structures of the complexes [PdCl(2)(1)] and [PtCl(2)(1)] were determined by X-ray diffraction, representing the first crystallographically characterized λ(3)-phosphinine-Pd(II) and -Pt(II) complexes. Both complexes reacted with methanol at the P=C double bond at an elevated temperature, leading to the corresponding products [MCl(2)(1H·OCH(3))]. The molecular structure of [PdCl(2)(1H·OCH(3))] was determined crystallographically and revealed that the reaction with methanol proceeds selectively by syn addition and exclusively to one of the P=C double bonds. Strikingly, the reaction of [PdCl(2)(1H·OCH(3))] with the chelating diphosphine DPEphos at room temperature in CH(2)Cl(2) led quantitatively to [PdCl(2)(DPEphos)] and phosphinine 1 by elimination of CH(3)OH and rearomatization of the phosphorus heterocycle.
New dicationic and monocationic palladium complexes with 2,2'-bipyridine ligands bearing perfluorinated ponytails have been prepared and used as catalysts for CO/4-tert-butylstyrene (TBS) and CO/styrene (ST) copolymerization in supercritical carbon dioxide (scCO2) and in CO2-expanded liquids. Best catalytic performances were achieved carrying out the copolymerization in carbon dioxide expanded substrates in the presence of 2,2,2-trifluoroethanol (TFE). The dicationic systems with 5,5’-substituted ligands [Pd(N-N)2][X]2 generated the most active and productive catalysts with up to 532 g copolymer CP/g Pd•h for CO/TBS and led to polyketones with high molecular weight and narrow polydispersity (molecular weight up to Mw = 692000 for CO/ST; Mw/Mn = 1.2-3.3). MALDI-TOF mass spectrometry analysis of copolymer end groups revealed that the main initiation and termination steps involved the insertion of the alkene into the Pd-H bond and the -H-elimination on the Pd-alkyl bond, respectively
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