Synthesis and reactions of mono- and dipalladium complexes containing 2-thienyl and 2,5 (or 2,5′) -bridged thienylene (or dithienylene) ligand: new dipalladium complex formation connected by thioketene part via CS bond cleavage of thiophene

Abstract

Oxidative addition reactions of 2-iodothiophene, 2-bromothiophene, and 2,5-dibromothiophene with equimolar Pd(CH2CHPh)L2 (LPMe3 and PEt3) at room temperature in THF produce mononuclear s-thienyl palladium(II) complexes trans-(2-C4H3S)PdX(PMe3)2 (XI, 1 ;X Br, 2) and trans-(5-Br(2-C4H2S))PdBrL2 (L PMe3, 3 ;L PEt3, 4). Reactions using 2,5-dibromothiophene, 2,5-diiodothiophene, and 5,5-dibromo-2,2%-bithiophene under 2:1 molar ratio in THF give thienylene (or dithienylene) bridged dipalladium complexes trans,trans-L2XPd(m-2,5-C4H2S)PdXL2 (L PMe3 ;X I, 5; Br, 6 ;L PEt3 ;X Br, 7) and trans,trans-(Me3P)2BrPd(m-2,5%-C4H2S-C4H2S)PdBr(PMe3)2 (8), in high yields. However, the equimolar reaction of 2,5-dibromothiophene with the Pd(0) complex results in formation of a dinuclear complex cis,trans-[(Me3P)2Pd(h 2 SCCHCHCBr)PdBr(PMe3)2 (9), in 56% yield via CS bond cleavage of the thiophene ring. All the complexes provided satisfactory IR and NMR ( 1 H, 31 P{ 1 H}, and 13 C{ 1 H}) spectra as well as elemental analyses. Molecular structures of 1, 7, and 9 were confirmed by X-ray crystallography. Treatment of 5 and 7 with CO (1 atm) results in CO insertion into one of the PdC bonds to give trans,trans-(Me3P)2IPdC(O)C4H2SPdI(PMe3)2 (10) in 94% and trans,trans-(Et3P)2BrPdC(O)C4H2SPdBr(PEt3)2 (11) in 23%, respectively. Also, treatments of 5 with n-butyl, tert-butyl, and cyclohexyl isocyanides result in its insertion into both of the PdC bonds to form iminoacyl Pd complexes trans,trans-(Me3P)2IPdC(NR)C4H2SC(NR)PdI(PMe3)2 (R n-Bu, 12; t-Bu, 13; cyclohexyl, 14), respectively. © 1999 Elsevier Science S.A. All rights reserved.