Application of palladium complexes bearing acyclic amino(hydrazido)carbene ligands as catalysts for copper-free Sonogashira cross-coupling.

Metal-mediated coupling of one isocyanide in cis -[PdCl 2 (CNR 1 ) 2 ] (R 1 = C 6 H 11 (Cy) 1 , t Bu 2 , 2,6-Me 2 C 6 H 3 (Xyl) 3 , 2-Cl-6-MeC 6 H 3 4 ) and various carbohydrazides R 2 CONHNH 2 [R 2 = Ph 5 , 4-ClC 6 H 4 6 , 3-NO 2 C 6 H 4 7 , 4-NO 2 C 6 H 4 8 , 4-CH 3 C 6 H 4 9 , 3,4-(MeO) 2 C 6 H 3 10 , naphth-1-yl 11 , fur-2-yl 12 , 4-NO 2 C 6 H 4 CH 2 13 , Cy 14 , 1-(4-fluorophenyl)-5-oxopyrrolidine-3-yl 15 , (pyrrolidin-1-yl)C(O) 16 , 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propane-1-yl 17 , EtNHC(O) 18 ] or sulfohydrazides R 3 SO 2 NHNH 2 [R 3 = Ph 19 , 4-MeC 6 H 4 20 ] led to a series of (hydrazido)(amino)carbene complexes cis -[PdCl 2 { C (NHNHX) N(H)R 1 }(CNR 1 )]; X = COR 2 , SO 2 R 3 ( 21 – 48 , isolated yields 60–96%). All prepared species were characterized by elemental analyses (C, H, N), HR ESI + -MS, IR, 1 H and 13 C{ 1 H} NMR spectroscopy, and by a single-crystal X-ray diffraction for 38 . Complexes 21 – 48 demonstrated excellent activity as catalysts in copper-free Sonogashira coupling of aryl iodides and a variety of aromatic terminal alkynes. Catalytic system runs in environmentally benign EtOH ensuring product yields of up to 75–96% and TONs of up to 10 4 . Mechanism of the copper-free Sonogashira catalytic cycle involving 21 – 48 as catalysts was proposed upon identification of key intermediates using HRESI-mass. [ABSTRACT FROM AUTHOR]