Synthesis Of Functionalized Phosphine Ligands And Their Application To Cross-coupling Reactions

Transition metal-mediated cross-coupling reactions are one of the most efficient methods for the construction of C(aryl)-C(aryl), C(aryl)-N,C(aryl)-Obonds and have found widespread use in organic synthesis. Its importance in organic synthesis is evident from its application in a number of areas, ranging from natural product synthesis to materials chemistry. The development of phosphane ligands has had a huge impact in transition-metal-catalyzed reactions. Much recent work has been directed toward the development of new catalyst systems that efficiently process challenging substrates. In this paper, synthesis of functionalized phosphine ligands and their application to cross-coupling reactions have been studied.(1) 1- 3-( diphenylphosphono)propyl-2,2'-biimidazole was synthesized by nucleophilic substitution reaction between 2,2'-biimidazole and 3-bromine propyl diphenylphosphono in high yields. 1- 3-( diphenylphosphono)propyl-2,2'-biimidazole were deoxidized by LiAlH4 to yield 1,1'-di[3-(diphenylphosphino)propyl]-2,2'-biimidazole(L1) . 1- 3-( Phosphorodithioic)propyl-2,2'-biimidazole(L2) was efficiently synthesized by Sulfur oxidationin of 1,1'-di[3-(diphenylphosphino)propyl]-2,2'-biimidazole in good yields.(2) 1,1'-di[3-( diphenylphosphono)propyl]-2,2'-biimidazole was synthesized by nucleophilic substitution reaction between 2,2'-biimidazole and 3-bromine propyl diphenylphosphono in high yields. 1,1'-di[3-( diphenylphosphono)propyl]-2,2'-biimidazole were deoxidized by LiAlH4 to yield 1,1'-di[3-(diphenylphosphino)propyl]-2,2'-biimidazole (L3). 1,1'-di[3-( Phosphorodithioic)propyl]-2,2'-biimidazole(L4) was efficiently synthesized by Sulfur oxidationin of 1,1'-di[3-(diphenylphosphino)propyl]-2,2'-biimidazole in good yields.(3) 1,1'-dibutyl-2,2'-biimidazole was synthesized by nucleophilic substitution reaction between 2,2'-biimidazole and 1-butyl iodide in high yields. Biimidazole-Phosphine salt was yielded by subsitutution reaction between 1,1'-dibutyl-2,2'-biimidazole and 3-bromine propyl diphenylphosphono in good yields.(4) The ligands L1, L2, L3, and L4 were used in palladium-catalyzed Suzuki and Heck cross-coupling reaction, the experimental results showed that ligand L3 had excellent catalytic activity and selectivity in Suzuki reaction and Heck reaction, ligand L1 showed moderate activity in Suzuki reaction, while the poor catalytic activity in Heck reaction. Ligand L4 provied to be a highly effective catalyst in Suzuki reaction, while ligand L2 was not good catalyst for Suzuki reaction. Ligands L2 and L4 ligands were unsuccessful under a very general Heck coupling system.