Syntheses, characterization and DFT studies of two new (π-allyl) palladium(II) complexes of β-8,9-dihydrohimachalene

Abstract

Catalytic hydrogenation of β-himachalene, the main constituent of Atlas cedar’s essential oil, led to the formation of β-8,9-dihydrohimachalene (2,6,6,9-tetramethylbicyclo[5.4.0]undeca-1-ene). This latter when treated with palladium(II) chloride gives neutral bis(chloro)-bridged cyclopalladated dimers, [Pd2C12(C15H25)2] (di-μ-chloro-bis{[(1,2,15-η)-2,6,6,9-tetramethylbicyclo[5.4.0]undeca-1-ene]palladium), with a high regio- and stereoselectivity, which is stable under air and moisture. Its reaction with triphenylphosphine provided a monomer (π-allyl-β-8,9-dihydrohimachalene) palladium(triphenylphosphine) complex. Both complexes were characterized by 1H and 13C NMR spectroscopy and single crystal X-ray diffraction. DFT calculations were conducted on both compounds in order to predict their optimized structures, the frontier molecular orbitals and the global reactivity descriptors. A good correlation of bond lengths and angles with the experimental data was found at the B3LYP/6-31 +G(d,p) basis set. Moreover, Hirshfeld surface (HS) and 2D fingerprint analyses revealed an intermolecular hydrogen bond of 2.56 Å for the monomer palladium complex, which is close to the experimental value, along with an intramolecular close contact dominated by H-H interactions in both compounds.