Maarten D. K. Boele

Fast Palladium Catalyzed Arylation of Alkenes Using Bulky Monodentate Phosphorus Ligands

Complex 1b shows an unprecedented high activity in the Heck reaction. Kinetic studies show that in this system not the oxidative addition but the alkene coordination/migratory insertion is the rate determining step.

Palladium‐Catalyzed Amination of Aryl Bromides and Aryl Triflates Using Diphosphane Ligands: A Kinetic Study

[Pd(P-O-P)(Ar)]+ complexes with ligands that have wide bite angles are active catalysts for the coupling of aniline derivatives with aryl triflates. Kinetic studies show that for these systems a fast equilibrium that involves coordination of the amine precedes the deprotonation, which is the rate-limiting step of the reaction. This reaction is faster for compounds with a smaller P-Pd-P angle. When halide salts are present, the base sodium tert-butoxide is activated and adds to the palladium complex. This rate-limiting step is preceded by a fast equilibrium that involves decoordination of the halide. The initial reaction rate is faster for compounds with a larger P-Pd-P angle. This is due to the closer proximity of the oxygen to the Pd center, and this assists in the dissociation of the halide.

103Rh-NMR spectroscopy of some hydridorhodiumbis(carbonyl)diphosphine compounds

Abstract The 103 Rh chemical shifts of a series of hydridorhodiumbis(carbonyl)diphosphine compounds 1 – 17 and one phosphine–phosphite analogue 18 , containing chelating bidentate P-ligands, have been obtained by inverse HMQC detection sequences 1 H-{ 103 Rh} and 31 P-{ 103 Rh, 1 H}. These active hydroformylation catalysts are stable only under pressure of H 2 /CO (synthesis gas) and hence 1 H-, 31 P- and 103 Rh-NMR spectra have been recorded in a sapphire high-pressure NMR tube. The compounds HRh(CO) 2 (PP) exist as a mixture of equatorial–equatorial and equatorial–axial five-coordinate isomers for 1 – 17 , which are in a dynamic equilibrium that could not be brought into the slow exchange regime on the proton, the phosphorus or the rhodium NMR time scales. A correlation ( R =0.980) was found between δ ( 103 Rh) and the Hammett σ p -constant of the para -substituents Y of the P(C 6 H 4 Y- p ) 2 groups in the thixantphos ligand for the series of compounds 4 , 8 – 13 (lower δ ( 103 Rh) for electron withdrawing substituents). Correlation of δ ( 103 Rh) with Tolman basicity parameters (higher δ ( 103 Rh) with higher basicity) also gave a good fit ( R =0.955). The finding that correlations exist for this series between the ligand basicity, the ratio of equatorial–equatorial/equatorial–axial trigonal bipyramidal isomers and the δ ( 103 Rh) indicates that small structural and electronic changes in the ligands in the vicinity of transition metal nuclei have a small but significant influence on δ ( 103 Rh). This, together with other knowledge, may in the future serve to use Rh-NMR as an analytical tool in coordination chemistry.

The coordination behaviour of large natural bite angle diphosphine ligands towards methyl and 4-cyanophenylpalladium(II) complexes

The structures of neutral and ionic 4-cyanophenylpalladium(II) and methylpalladium(II) complexes containing bidentate phosphine ligands were investigated in solution and in the solid state. Diphosphine ligands with a xanthene and a ferrocene backbone were used. New bis(dialkylphosphino) substituted Xantphos ligands were synthesised. 1H NMR and 31P NMR spectroscopy, conductivity measurements, UV-Vis spectroscopy, and X-ray crystallography were used to elucidate the structures of the complexes. Subtle changes of the phosphine ligands govern the coordination mode of the ligand. A variety of bidentate cis-, and trans-coordination and terdentate P–O–P, P–S–P and P–Fe–P coordination modes of the ligands were observed.