Palladacycle versus coordination complex of palladium(II) with a bulky organophosphorus (P,N) ligand: Application in catalysis of allylation of aldehydes

Abstract

Palladacyclic complex 1 [Pd(L1)Cl] [L1: anthracene–9-yl–CH = N(CH2)2–PPh2 behaving as (P, N, C−) ligand] has been prepared, and characterized using multi-nuclei NMR spectroscopic, high resolution mass spectrometric (HRMS) and single-crystal X-ray diffraction (SC-XRD) techniques. This palladacycle 1 and the 2 [i.e., Pd(L1)Cl2, a square planar Pd(II) complex of the same ligand] have anthracene core, imine functionality and P,N donors. Both the 1 and 2 have been explored as potential catalysts for allylation of aldehydes with allyltributylstannnane. Both the complexes show good efficiency towards this CC coupling reaction. Various aldehydes such as 4–bromobenzaldehyde, 4–chlorobenzaldehyde, 2–bromobenzaldehyde, 2–chlorobenzaldehyde, 4–methoxybenzaldehyde, 4–methylbenzal dehyde, 4–nitrobenzaldehyde pyridine–2–carboxaldehyde and furfural have been explored for this reaction. Effect of presence of Pd–C bond is noticed on the catalytic performance. The palladacyclic complex 1 is more efficient than coordination complex 2 as the Pd-C bond of metallacyclic complex increases the rate of dissociation of Pd-Cl bond and therefore helping in easy participation and increased efficiency of complex 1 in catalysis.