Trans-chelating Diphosphine Ligand Research Articles

Moderately Flexible Trans-Chelating Diphosphine Ligands Consisting of a Triazine Unit Showing High Ligand Acceleration Effect for Heck Reaction

Abstract Originally designed trans-chelating diphosphine ligands with moderate flexibility that allows trans- to cis-isomerization and bidentate to monodentate complex form were developed. The novel ligand shows high ligand acceleration effect (LAE) for Heck reaction. The catalyst loading was decreased to 0.0001 mol%, and the turnover number (TON) reached 970,000. The catalytic cycle was evaluated by DFT calculations. The calculations revealed the following: 1) the insertion step in monodentate pathway was the rate-determining step, 2) the high LAE effect of the novel ligand was due to a facile change of conformation from trans to cis form and flexibility to avoid steric repulsion between substrate and catalyst in the insertion step as well.

Addition of Water Across Si−Ir Bonds in Iridium Complexes with κ-P,P,Si (biPSi) Pincer Ligands

Electrophiles such as Me(+), Ag(+), or protons react with the five-coordinate Ir(III) complex [IrClH(biPSi)] (biPSi = κ-P,P,Si-Si(Me){(CH(2))(3)PPh(2)}(2)) by abstracting its chloride ligand. The resulting species can be stabilized by a variety of L ligands to give the cationic complexes [IrH(biPSi)L(2)](+). The derivative [IrH(biPSi)(NCMe)(2)](+) has been subjected to a kinetic study regarding the facile dissociations of its acetonitrile ligands. The presence of water changes the course of the reaction producing dihydride complexes that contain the silanol ligand κ-O,P,P-HOSi(Me){(CH(2))(3)PPh(2)}(2) (biPSiOH). The water activation product [IrH(2)(biPSiOH)(NCMe)](CF(3)SO(3)) undergoes insertion reactions with ethylene and phenylacetylene. The use of hydrolyzable fluorinated counterions such as PF(6)(-) or BF(4)(-) further modifies the reaction by provoking the incorporation of fluoride at the silicon atom of the former biPSi ligand. The dihydride resulting after such a process, [IrH(2)(biPSiF)(NCMe)(2)]BF(4) (biPSiF = κ-P(2)-FSi(Me){(CH(2))(3)PPh(2)}(2)), displays a trans-chelating diphosphine ligand. When dehydrogenating the Ir center, spontaneously or using ethylene as hydrogen acceptor, the diphosphine backbone undergoes a Si-C bond cleavage leading to a new Ir(III) species with κ-P,Si and κ-C,P chelate ligands.

ChemInform Abstract: Design and Synthesis of Optically Active Trans-Chelating Diphosphine Ligands. Application for Catalytic Asymmetric Synthesis

New chiral diphosphines 2,2“-bis[1-(disubstituted phosphino)ethyl]-1,1”-biferrocene, having both central and planar elements of chirality, was designed for a trans-chelating chiral diphosphine ligand (TRAP) for transition metals and synthesized form optically active N,N-dimethyl-1-ferrocenyl ethylamine. Some transition-metal complexes with the TRAP ligands were prepared and utilized as a chiral catalyst for asymmetric synthetic reactions.

Ferrocenyl-Aryl Based trans-Chelating Diphosphine Ligands: Synthesis, Molecular Structure and Application in Enantioselective Hydrogenation

Potentially trans-chelating diphosphine ligands based on a ferrocenyl-aryl backbone were synthesised in a four-step sequence and the molecular structures in the solid state of two representatives were determined by X-ray diffraction. High throughput screening of these ligands in rhodium-, ruthenium- and iridium-mediated hydrogenations of a variety of alkenes and ketones revealed that these ligands can deliver high enantioselectivity for alkenes (up to 98% ee) but are less selective when ketones are used as the substrates. The coordination behaviour of one ligand in its square planar palladium and platinum dichloride complexes was studied by 31 P NMR and only trans-chelated complexes, together with oligomeric by-products, were observed. Reaction with the (p-cymene)ruthenium dichloride dimer, [RuCl 2 (p-cymene)] 2 , resulted in a mixture of diastereomeric complexes.

Design and Synthesis of Optically Active Trans-Chelating Diphosphine Ligands. Application for Catalytic Asymmetric Synthesis

New chiral diphosphines 2,2“-bis[1-(disubstituted phosphino)ethyl]-1,1”-biferrocene, having both central and planar elements of chirality, was designed for a trans-chelating chiral diphosphine ligand (TRAP) for transition metals and synthesized form optically active N,N-dimethyl-1-ferrocenyl ethylamine. Some transition-metal complexes with the TRAP ligands were prepared and utilized as a chiral catalyst for asymmetric synthetic reactions.

Design and Synthesis of Optically Active Trans-Chelating Diphosphine Ligands. Application for Catalytic Asymmetric Synthesis

Design and Synthesis of Optically Active Trans-Chelating Diphosphine Ligands. Application for Catalytic Asymmetric Synthesis