Metal-free synthesis of ynones from acyl chlorides and potassium alkynyltrifluoroborate salts

Soft Heteroleptic N-Heterocyclic Carbene Palladium(II) Species for Efficient Catalytic Routes to Alkynones via Carbonylative Sonogashira Coupling

N,N'-Substituted di-isopropyl (NHC-1), benzyl-isopropyl (NHC-2), and adamantyl-isopropyl (NHC-3) benzimidazolium salts react with palladium(II) bromide in pyridine to afford the corresponding trans-dibromidopyridinepalladium(II) complexes Pd-C1, Pd-C2, and Pd-C3 in high yields. A distorted square planar geometry for Pd-C2 and Pd-C3 was confirmed by single-crystal X-ray diffraction. The palladium(II) complexes show a remarkably higher catalytic activity and selectivity, compared to the literature data, in carbonylative Sonogashira coupling reactions of aryl iodides and aryl diiodides with aryl alkynes, alkyl alkynes, and dialkynes. Excellent yields with as low as 0.03 mol % loading of the catalyst were obtained. In the series of benzimidazolium (NHC) precursors, the ¹H NMR signals of the α hydrogen show a consistent probing of the N-substituent donor strength. The density functional theory (DFT) quantum mechanical descriptors of the frontier orbitals were calculated. A linear correlation of the calculated absolute softness of the complexes versus the calculated percent buried volume (%V _bur) of their corresponding ligands was obtained. The catalytic activity experimental data are consistent with the hard soft acid base (HSAB)-predicted high affinity of the softest Pd-C3 complex for soft substrates, such as aryl iodides.

Phosphinito palladium(ii) complexes as catalysts for the synthesis of 1,3-enynes, aromatic alkynes and ynones

An air-stable phosphinito palladium(ii) complex has been found to be an efficient catalyst in the formation of C–C bonds.