NewC2-Chiral Bidentate Ligands Bridging the gap between donor phosphine and acceptor carbonyl ligands

Synthesis and characterisation of novel o-xylene-based P,E ligands

A range of novel hybrid ligands of the type, o-C6H4(CH2PBu(t)2)(CH2E) (E = P(C6F5)2, SBu(t), SPh, S(O)Bu(t), NR2, SiPh2H), have been synthesised in two or three steps from the common substrate, o-C6H4{CH2PBu(t)2(BH3)}(CH2Cl). The initial step involved treatment of the substrate with the appropriate nucleophilic reagent, or preparation of a Grignard reagent from o-C6H4{CH2PBu(t)2(BH3)}(CH2Cl) and reaction with the appropriate electrophile. In most cases, this versatile strategy produced air-stable crystalline ligand precursors. Phosphine deprotection was achieved via one of three methods, dependent upon the properties of the second functional group. An alternative synthesis of the known ligand, o-C6H4(CH2PBu(t)2)(CH2PPh2), is also presented.

[CpRu((R)-Binop-F)(H2O)][SbF6], a new fluxional chiral Lewis acid catalyst: synthesis, dynamic nmr, asymmetric catalysis, and theoretical studies

The C(2)-symmetric electron-poor ligand (R)-BINOP-F (4) was prepared by reaction of (R)-BINOL with bis(pentafluorophenyl)-phosphorus bromide in the presence of triethylamine. The iodo complex [CpRu((R)-BINOP-F)(I)] ((R)-6) was obtained by substitution of two carbonyl ligands by (R)-4 in the in situ-prepared [CpRu(CO)(2)H] complex followed by reaction with iodoform. Complex 6 was reacted with [Ag(SbF(6))] in acetone to yield [CpRu((R)-BINOP-F)(acetone)][SbF(6)] ((R)-7). X-ray structures were obtained for both (R)-6 and (R)-7. The chiral one-point binding Lewis acid [CpRu((R)-BINOP-F)][SbF(6)] derived from either (R)-7 or the corresponding aquo complex (R)-8 activates methacrolein and catalyzes the Diels-Alder reaction with cyclopentadiene to give the [4 + 2] cycloadduct with an exo/endo ratio of 99:1 and an ee of 92% of the exo product. Addition occurs predominantly to the methacrolein C(alpha)-Re face. In solution, water in (R)-8 exchanges readily. Moreover, a second exchange process renders the diastereotopic BINOP-F phosphorus atoms equivalent. These processes were studied by the application of variable-temperature (1)H, (31)P, and (17)O NMR spectroscopy, variable-pressure (31)P and(17)O NMR spectroscopy, and, using a simpler model complex, density functional theory (DFT) calculations. The results point to a dissociative mechanism of the aquo ligand and a pendular motion of the BINOP-F ligand. NMR experiments show an energy barrier of 50.7 kJ mol(-1) (12.2 kcal mol(-1)) for the inversion of the pseudo-chirality at the ruthenium center.

Synthesis and Characterization of New Binuclear Co(0) Complexes with Diphosphinoamine Ligands. A Potential Approach for Asymmetric Pauson-Khand Reactions

The synthesis of P-N-P bidentate ligands and the evaluation, based on IR and X-ray data, of their pi-acceptor properties in the complexes derived from phenylacetylene-dicobalt hexacarbonyl have been carried out. In addition, the reactivity of these complexes in the Pauson-Khand reaction has been examined.