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Methanol as a Hydrogen Source in the Pd II −Bis( N ‐Heterocyclic Carbene)‐Mediated Catalytic Semireduction of Alkynes Under Mild Reaction Conditions
Author(s) -
Prabusankar Ganesan,
Sathyanarayana Arruri,
Raju Gembali,
Nagababu Chatla
Publication year - 2017
Publication title -
asian journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.846
H-Index - 44
eISSN - 2193-5815
pISSN - 2193-5807
DOI - 10.1002/ajoc.201700326
Subject(s) - chemistry , carbene , catalysis , medicinal chemistry , hydrogen halide , diphenylacetylene , ligand (biochemistry) , acridine , molecule , photochemistry , halogen , organic chemistry , alkyl , biochemistry , receptor
A series of six new mono‐organopalladium complexes of the form [LPdX 2 ] (L=1,2‐bis[( N ‐methylimidazol‐2‐ylidene)methyl]ethane ( 6 ), 1,2‐bis[( N ‐vinylimidazol‐2‐ylidene)methyl]ethane ( 7 ), 1,2‐bis[( N ‐isopropylimidazol‐2‐ylidene)methyl]ethane ( 8 ), 1,2‐bis[( N ‐2,6‐dimethylphenylimidazol‐2‐ylidene)methyl]ethane ( 9 ), 1,2‐bis[( N ‐4‐ethyl benzoate imidazol‐2‐ylidene)methyl]ethane ( 10 ), 4,5‐bis[( N ‐isopropylimidazol‐2‐ylidene)methyl]acridine ( 11 ); X=Br for complexes 6 – 9 and 11 , X=Cl for complex 10 ) were synthesized and characterized by using FTIR spectroscopy, 1 H and 13 C NMR spectroscopy, elemental analysis, and X‐ray crystallography. In the solid state, complexes 6 – 11 were of neutral charge and each contained one bis(NHC) ligand (L) and two halide ligands in an almost‐ideal square‐planar geometry. These molecules were catalytically competent for the semihydrogenation of diphenylacetylene. Notably, MeOH was used as a hydrogen source in catalytic processes for the first time. Among these six new catalysts, the acridine‐bridged palladium−bis( N ‐heterocyclic carbene) complex gave excellent selectivity for the formation of Z alkenes from internal alkynes. A range of 15 different alkynes were tested under our optimized conditions and the reactions all proceeded with very high diastereoselectivities under mild conditions.