Dong-Liang Wang

Efficient and recyclable Ir(I)-catalysts with the involvement of π-acceptor phosphines for N-alkylation of aryl amines with alcohols

Mono-phosphines (L1 and L2) and diphosphines (L3 and L4) with typical π-acceptor character were prepared and applied in Ir(I)-catalyzed N-alkylation of amines with alcohols. It was found that the π-acceptor character of the applied phosphines is closely correlated to the catalytic efficiency of the [Ir(COD)Cl]2 complex for this green reaction. Compared to PPh3 as the typical σ-donor (i.e. with poor π-acceptor character), L1–L4 all resulted in the efficient N-alkylation of aniline to benzyl-aniline. While L1–L4 coordinated to the Ir(I)-catalyst, the consolidated Ir–P linkages due to π-backdonation could well protect the Ir-catalyst against deactivation, giving rise to the N-alkylation of aniline. On the other hand, the stabilized Ir-catalyst with the involvement of L2 could be recycled successfully for at least 4 runs in the ionic liquid of [MePh3P]Br without the detectable leaching of Ir and P elements in the organic products.

Ionic palladium complex as an efficient and recyclable catalyst for the carbonylative Sonogashira reaction

Abstract The neutral palladium(II) complex bis-[1-(5’-diphenylphosphinothiazol-2’-yl)-imidazolyl] dichloropalladium(II) (1A) ligated by thiazolylimidazolyl-based phosphine (L1) in which thiazolylimidazolyl acted as an S- and N-donor provider with weak coordinating nature, and the ionic complex bis-[1-(5’-diphenylphosphinothiazol-2’-yl)-3-methylimidazolium] dichloropalladium(II) trifluoromethanesulfonate (2A) ligated by thiazolylimidazolium-based phosphine (L2) after quaternization of L1 using methyl trifluoromethanesulphonate were synthesized. It was found that the introduced positive charges and strong electron-withdrawing effect in 2A not only led to changes in the configuration and structural stability of the complex, but also lowered its catalytic performance in carbonylative Sonogashira reactions. These effects reveal the important role of the N-donor in 1A. In addition, as an ionic palladium complex, 2A combined with the room-temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate could be recycled eight times as the catalyst in carbonylative Sonogashira reactions without detectable metal leaching.

Aminocarbonylation of Aryl Halides to Produce Primary Amides by Using NH4HCO3 Dually as Ammonia Surrogate and Base

An efficient and clean protocol was developed for rapid production of primary aromatic amides by aminocarbonylation with NH4HCO3. Without addition of auxiliary base, the use of solid and cheap NH4HCO3 dually as ammonia surrogate and base not only promoted aminocarbonylation over subsequent dehydration and hydrolysis of amides owing to its weak basicity, and it also made the reaction manipulation clean and simplified without the presence of stinky NH3 or organic amines. The Xantphos ligand with relatively intensive π‐acceptor character (1J31P–77Se=758 Hz) and wide natural bite angle (βn=111°) was found to be indispensable for the high efficiency of this reaction.

Co-catalysis over a bi-functional ligand-based Pd-catalyst for tandem bis-alkoxycarbonylation of terminal alkynes

A bi-functional ligand (L1) containing a diphosphino fragment and sulfonic acid group (–SO3H) enabled PdCl2(MeCN)2 to efficiently catalyze the tandem bis-alkoxycarbonylation of terminal alkynes to produce aryl-/alkyl-substituted succinate (α,ω-diesters). It was found that the –SO3H incorporated in L1 indispensably assisted the Pd-catalyst in accomplishing this tandem reaction via intramolecular synergic effects. Co-catalysis over the L1-based Pd-catalyst was not due to the physical mixture of Xantphos and MeSO3H. In situ FTIR analysis verified that the formation and stability of Pd–H active species were facilitated by the presence of L1. The formation of stabilized diacylpalladium intermediate (F) was the critical driving force for the second-step methoxycarbonylation. DFT calculation was carried out to optimize the geometric structure of F, which indicated that the developed intramolecular O⋯H hydrogen bonds were an important structural feature to stabilize F. In addition, the L1-based Pd-catalyst could be recycled successfully for at least 3 runs in the ionic liquid [Bmim]NTf2 without obvious activity loss and detectable metal leaching.

Hydroaminocarbonylation of Alkynes to Produce Primary α,β‐Unsaturated Amides Using NH4HCO3 Dually as Ammonia Surrogate and Brønsted Acid Additive

By using NH4HCO3 dually as ammonia surrogate and Brønsted acid additive, the production of primary α,β‐unsaturated amides via hydroaminocarbonylation of alkynes was accomplished efficiently. The advantages of using the solid and inexpensive NH4HCO3 included: (1) the facile and clean manipulation without presence of stinky gaseous NH3 or liquids organic amines, (2) the inhibition of the subsequent dehydration and hydrolysis of amides due to its weak basicity, and (3) the facilitated formation of Pd−H catalytic active species by the released H2CO3 serving as a weak Brønsted acid additive. In addition, the diphopshine of Dppp with the natural bite angle (βn) of 91° was found indispensable to spur the performance of the palladium catalyst for this reaction. Both terminal and internal phenylacetylene derivatives could be used as the substrates, affording the corresponding primary α,β‐unsaturated amides in good yields along with excellent regio‐selectivities to the branched ones.