Complexes of Sterically Hindered

Complexes of Sterically Hindered Thiolate Ligands J. R. Dilworth and J. Hu... 

Indoles, pyrroles, and carbazoles themselves are suitable substrates for palladium-catalyzed coupling with aryl halides. Initially, these reactions occurred readily with electron-poor aryl halides in the presence of palladium and DPPF, but reactions of unactivated aryl bromides were long, even at 120 °C. Complexes of sterically hindered alkylmonophosphines have been shown to be more active catalysts (Equation (25)). 8 102 103 In the presence of these more active catalysts, reactions of electron-poor or electron-rich aryl bromides and electron-poor or electron-neutral aryl chlorides occurred at 60-120 °C. Reactions catalyzed by complexes of most of the /-butylphosphines generated a mixture of 1- and 3-substituted indoles. In addition, 2- and 7-substituted indoles reacted with unhindered aryl halides at both the N1 and C3 positions. The 2-naphthyl di-t-butylphosphinobenzene ligand in Equation (25), however, generated a catalyst that formed predominantly the product from A-arylation in these cases. 

Figure 4 Isolated palladium(O) complexes of sterically hindered alkylphosphines used in C-X coupling.

Transition metal complexes of sterically hindered thiolate ligands have been reviewed. " These ligands give rise to unusual geometries and oxidation states, and low coordination numbers in their complexes. 

Complexes of Sterically Hindered Thio-late Ligands... 

Mononuclear octahedral complexes have been obtained for carbonyl-bound acetic acid, and five-coordinate complexes of sterically hindered phenoxides of the type [V(py)3(C6H3Ph2-2,6)2]. A more hindered phenol gave a four-coordinate complex, [V (C6H3Pr2-2,6)4 Li(thf) 2] in which two pairs of cfr-phenolates were linked by a single Li(thf)+ unit. A binuclear complex of a substituted acetylacetone has the stmcture shown in(l). 

Figure 13 Structure of the aluminum complex of sterically hindered sulfur-bridged bisphenols.

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