An Efficient Synthetic Approach to trans‐(NHC)₂Pd(R)Br Type Complexes and Their Use in Suzuki–Miyaura Cross‐Coupling Reactions

Abstract

Mixed organohalidopalladium complexes of the type trans‐(NHC)2Pd(R)Br were conveniently obtained from trans‐(NHC)2PdBr2 type complexes by a ligand‐substitution reaction. In particular, the trans‐[1‐(1S)‐menthyl‐4‐(R1)‐1,2,4‐triazol‐5‐ylidene]2Pd(R2)Br [R1 = Et, R2 = CH2Ph (3a1); R1 = Et, R2 = o‐OMeC6H4 (3a2); R1 = R2 = CH2Ph (3b1); R1 = CH2Ph, R2 = o‐OMeC6H4 (3b2)] complexes were obtained from the corresponding palladium(II) precursor complexes, 2a,b, by reaction with the respective Grignard reagents, in good to excellent yields (74–93 %). Three of the four mixed organohalidopalladium complexes, 3a1,a2,b1, have been structurally characterized by single‐crystal X‐ray diffraction, which revealed the trans disposition of the NHC ligands around the palladium center. The use of these mixed organohalidopalladium complexes in the Suzuki–Miyaura cross‐coupling reaction was established for all of the complexes, 3a1–b2, which yielded the desired cross‐coupled products upon treatment with various ArB(OH)2 [Ar = 1‐naphthyl, 4‐(1,1′‐biphenyl), 9‐phenanthrenyl, 4‐FC6H4, and 2,6‐Me2C6H3] compounds, in the presence of NaOH as a base, in CH3CN, in three hours, under reflux conditions.

Potent Anticancer Activity with High Selectivity of a Chiral Palladium N-Heterocyclic Carbene Complex

“…The Pd – C carbene distance of ca. 2.008(6) − 2.049(11) Å observed in the bromo derivatives, (1 S ,2 S ,5 R )- 2b and (1 R ,2 R ,5 S )-( 1–3 ) b , compare well with the range of 1.999(10) − 2.022(11) Å observed in two of earlier reported bromide enantiomers, (1 S ,2 S ,5 R )- 1b and (1 S ,2 S ,5 R )- 3b , 22 and also with that of 2.020(8) − 2.047(11) Å of the trifluoroacetate derivatives (1 S ,2 S ,5 R )-( 1c , 3c ) and (1 R ,2 R ,5 S )-( 1c , 3c ).…”

“…Five enantiomeric pairs of the palladium N-heterocyclic carbene complexes, centered on a chiral menthyl moiety, were constructed by a sequence of reactions starting from the enantiomers of 1-menthyl-1,2,4-triazoles, (1 S ,2 S ,5 R )- A 22 and (1 R ,2 R ,5 S )- A , based on our earlier reported protocol for the (1 S ,2 S ,5 R )- 1b 22 and (1 S ,2 S ,5 R )- 3b 22 complexes. The direct alkylation reaction with alkyl bromides yielded the respective 1,2,4-triazolium bromide salts (1 S ,2 S ,5 R )-( 1 – 3 ) a and (1 R ,2 R ,5 S )-( 1 – 3 ) a ( Scheme 1 ).…”

“…(1 R ,2 S ,5 R )-2-isopropyl-5-methylcyclohexyl p -toluenesulfonate 22 and (1 S ,2 R ,5 S )-2-isopropyl-5-methylcyclohexyl p -toluenesulfonate were synthesized by following modified literature procedures. 22 The ligand precursors (1 S ,2 S ,5 R )- 1a and (1 S ,2 S ,5 R ) -3a and the palladium N-heterocyclic carbene complexes (1 S ,2 S ,5 R )- 1b and (1 S ,2 S ,5 R )- 3b were prepared according to a literature procedure reported by us. 22 Bruker 400 and 500 MHz NMR spectrometers were used for recording the 1 H NMR, 13 C{ 1 H} NMR, and 19 F{ 1 H} NMR spectra.…”

Palladium Acyclic Diaminocarbene (ADC) Triflate Complexes as Effective Precatalysts for the Hiyama Alkynylation/Cyclization Reaction Yielding Benzofuran Compounds: Probing the Influence of the Triflate Co‐Ligand in the One‐Pot Tandem Reaction

“…With our interest lying in exploring the potential of transition metal N‐heterocyclic carbene complexes in homogeneous catalysis and in biomedical applications, we have explored the utility of various type of singlet carbene ligand scaffolds namely, the imidazole, benzimidazole, 1,2,4‐triazole based ones,, abnormal carbenes, bicyclic and the tricyclic carbene systems . In this connection, we became interested in another new motif, particularly that of the acyclic diaminocarbene ligands, for their utility in time efficient tandem reactions ,.…”

Synthesis of the First Resorcin[4]arene-Functionalized Triazolium Salts and Their Use in Suzuki–Miyaura Cross-Coupling Reactions

“…Their precursors, namely 1,2,3-triazoles, are easily accessible through copper-catalyzed Huisgen [3 + 2] click-type cycloaddition of azides and alkynes (CuAAC) [6,7], followed by N3-quaternarization. The resulting 1,2,3-triazolium salts can then be converted to transition metal complexes that, i.a., are suitable for Suzuki-Miyaura [8][9][10][11][12][13][14][15][16][17][18], Mizoroki-Heck [19,20], and Sonogashira coupling reactions [19,21], as well as for various reduction or oxidation reactions [22][23][24][25][26][27], and C-heteroatom bond forming reactions [28][29][30][31][32].…”