Palladium complexes bearing novel strongly bent trans-spanning diphosphine ligands: Synthesis, characterization, and catalytic activity

Article abstract of DOI:10.1021/om050906j

The new air-stable chelating diphosphine ligands 1,8- bis(diisopropylphosphino)triptycene (2) and 1-(diisopropylphosphino)-8- (diphenylphosphino)triptycene (3) were synthesized in 51-73% yield from readily available starting materials. The examination of their coordination modes in the palladium(II) complexes [PdCl₂(2)] (4) and [PdCl₂(3)] (5) by means of ¹H, ¹³C, and ³¹P NMR is consistent with the formation of trans-spanned complexes. X-ray analysis of 4 and 5 confirmed the structure but disclosed a strong distortion of the palladium centers from the expected square-planar geometry toward a butterfly-like environment. Further investigation revealed that 2 can also behave as a binucleating ligand, forming the quasi-closed halogen-bridged dipalladium complex 6, featuring an unusual nonplanar Pd₂(μ-Cl) ₂Cl₂ core. The catalytic activity of the new ligands and complexes was tested in palladium-catalyzed cross-coupling reactions of aryl chlorides with phenylboronic acid.