A new class of triarylmethane-based phosphines (L1−L4) and their Pd(II) and Rh(I) complexes were synthesized and subsequently characterized by NMR spectroscopy and X-ray diffraction analysis. The reactions of these phosphines with [PdCl(π-allyl)] 2 gave the square-planar Pd(II) complexes [PdCl(π-allyl)(L)] (L = L1−L4). The treatment of [PdCl(π-allyl)(L3)] and [PdCl(π-allyl)(L4)], which have CF 3 -substituted triarylmethane and 9-arylfluorene moieties, respectively, with LiOtBu afforded P,C(sp 3 )-chelated palladacycle complexes. Reversibility between a C(sp 3 )−M covalent bond and a C(sp 3 )−H•••M interaction was experimentally demonstrated using [RhCl(nbd)] 2 as a Rh(I) source. The triarylmethane-monophosphines L1−L4 were applied to the Pd-catalyzed 1,4-addition of arylboronic acids to enones. Article pubs.acs.org/Organometallics
A silica-supported triphenylphosphane (Silica-3p-TPP) with a Ph3P-type core, immobilized on a silica surface, was synthesized and characterized by nitrogen-absorption measurements and solid-state NMR spectroscopy. The tripodal immobilization constrains the mobility of the phosphane molecule and causes the lone pair on the phosphorus atom to face in the direction perpendicular to the support, resulting in the selective formation of a 1:1 metal-phosphane species that is free from unfavorable steric repulsions caused by the silica surface. Heterogeneous Pd catalysts created in this manner enabled room-temperature Suzuki-Miyaura cross-coupling reactions with unactivated chloroarenes, despite the moderate electronic and steric nature of the Ph3P-based ligands. These catalysts also showed potential in reactions with more challenging substrates under mild conditions. Tripodally immobilized and well-dispersed phosphanes on the silica surface were crucial for high catalytic activity.
Silica-supported tripod triarylphosphines that have a Ph3P-type core tripodally immobilized on a silica surface enabled the Pd-catalyzed borylation of chloroarenes with bis(pinacolato)diboron under mild conditions. The immobilization in tripod was crucial for the excellent performance of the Ph3P-based ligands.
An ordered network of tetrasodium tetra(4-sulphonatophenyl)porphyrin iron(III) chloride (FeTPPS 4 Na 4 ), which exhibited a higher catalytic activity for oxygen reduction than Co and Ir(CO)TPPS 4 Na 4 , was fabricated by complexation with alkaline-earth metal ions. Heat treatment of these complexes enhanced their catalytic activity with the 2 highest performance observed with Ba 2+ -FeTPPS 4 . The onset potential for oxygen reduction (E onset ) was 720 mV vs. Ag|AgCl, which is almost the same as that for Pt-impregnated carbon black. The number of electrons, n, transferred during oxygen reduction at a Ba 2+ -FeTPPS 4 -coated electrode, as determined by rotating ring-disc experiments, was 3.9 and suggests that oxygen was reduced to water. A neutral solution of FeTPPS 4 Na 4 was acidified by the addition of barium ion, and the elemental ratio
The new heterogeneous phosphane (POS), which is tripodally immobilized on a silica surface, selectively forms a 1:1 palladium-phosphane molecule. The latter can be used as an efficient catalyst for the coupling of unactivated aromatic chlorides and triflates with arylboronic acids under mild conditions. It can be easily removed and reused four times without loss of activity. The application of a tripodally immobilized and well-dispersed phosphane on silica surface (0,11 mmolg -1 ) is found to be important to achieve high catalytic activity. -(IWAI, T.; TANAKA, R.; HARADA, T.; SAWAMURA*, M.; Chem. -Eur. J. 20 (2014) 4, 1057-1065, http://dx.
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