[Pd(N,N-chelate)(olefin)] Complexes Containing Chiral Nitrogen Chelates Based on Carbohydrates – Enantioselectivity of Olefin Coordination

Abstract

Chiral N,N‐chelates of formula 6‐Me‐pyridine–2‐CH=N–R (1) and R–N=CH–CH=N–R (2) (R = 6‐deoxy‐α‐D‐glucoside or 6‐deoxy‐α‐D‐mannoside residue) and their palladium(0) complexes [Pd(N,N‐chelate)(olefin)] (I) were prepared. Symmetrical type 2 ligands induced higher enantioselectivity in the coordination of prochiral olefins. The ability of a type 1 chelate to promote a stereoselective process was also assessed, i.e. dimethylfumarate inserted into the Pd–Me bond formed upon methylation of a type I complex with 50% ee. Finally, a water‐soluble Pd0 complex was also prepared by deprotecting the alcoholic functions on the sugar residue, and its molecular structure determined through X‐ray diffractometry.

Palladium(0)-Alkene Bis(triarylphosphine) Complexes as Catalyst Precursors for the Methoxycarbonylation of Styrene

“…The Pd−N (2.153(5) Å) and Pd−C distances (2.045(5) Å) are also in agreement with previously reported values . The N(1)−Pd(1)−N(1)a bite angle of 76.32(12)° is somewhat smaller than values known in the literature for related complexes (values of 77.2−77.5° are reported − ). As expected, upon coordination of the alkene, an elongation of the CC bond distance (1.417(6) Å) when compared with the free ligand (1.249(10) Å) and a concomitant expected shortening of the C−CN bonds (1.435(7) Å) when compared with the free ligand (1.480(8) Å) are observed .…”

Hydrophilic Pd0 Complexes Based on Sugars for Efficient Suzuki–Miyaura Coupling in Aqueous Systems

“…Upon coordination to the Pd centre, the signals of the olefin undergo a large shift to lower frequencies. This behaviour has been reported previously7a,7c,8,9 and is attributed to the substantial degree of π back‐donation in the Pd 0 –olefin bond, which stabilizes the low oxidation state of the palladium centre. The consequent partial sp 2 →sp 3 rehybridization of the alkene carbon atoms shifts the corresponding signals towards the aliphatic region in both the 1 H and the 13 C NMR spectra.…”

“…The coordination bond lengths fall within the expected range for Pd–α‐diimine complexes12,13 and are similar to those found for [Pd(N,N‐chelate)(olefin)] complexes 7a. The length of the olefinic bond is evidence of the substantial rehybridization of the olefinic carbon atoms towards sp 3 upon coordination (1.41 and 1.47 Å for the two diastereomers vs. 1.34 Å for the free alkene).…”

Aqueous Organometallic Chemistry with Nitrogen Ligands: Synthesis of Hydrophilic Platinum(0) Olefin Complexes

“…However, the dimethyl fumarate complexes were found to be the least stable and started to slowly decompose to untraceable products after 1 h. However, even after 24 h significant amounts of the complexes remained in solution. In agreement with previous reports, the maleic anhydride complex displayed stability comparable to that of the fumaronitrile derivatives. Reaction of the symmetrical ligand 4 with Pt(η 2 -norbornene) 3 in the presence of fumaronitrile gave complex 11 in high yield.…”