Phenyl backbone-derived P,O- and P,N-ligands for palladium/ligand-catalyzed aminations of aryl bromides, iodides, and chlorides.: Syntheses and structures of (P,O)n-palladium(II)aryl(Br) complexes

The phenyl backbone-derived P,O- and P,N-compounds 1-10 were investigated for their utility as ligands in palladium/ligand-catalyzed aryl aminations. The P,O-ligands 2-(2'-diphenylphosphinophenyl)-2-methyl- 1,3-dioxolane (1) and 2-(2'-dicyclohexylphosphinophenyl)-2-methyl-1,3-dioxolane (6) in combination with Pd(dba)(2) afford active catalysts for general aminations of aryl bromides, iodides, and chlorides. The Pd/ligand 6 catalyst, in particular, is efficient for general aminations of aryl chlorides. But the structurally related ligand 2-(2'-diphenylphosphinophenyl)- 1,3-dioxolane (2) and other P,O- or P,N-ligands were less effective. The reactions of Pd(dba)(2) with excess 4-Bu-t-C6H4Br and excess ligand (1, 6, 2) or the ligand displacement reactions of {Pd[P(o-toluyl)(3])(4-Bu-t-C6H4)(mu-Br)}(2) with ligands 1, 6, and 2 afford the potential catalytic intermediates of Pd/L-catalyzed (L = 1, 6, 2) aryl aminations, viz., LPd(4-Bu-t-C6H4)(Br) (11, L = 1; 12, L = 6) and L2Pd(4-Bu-t-C6H4)(Br) (13, L = 2), respectively. The X-ray crystallographic studies establish that ligands 1 and 6 function as P,O-chelating ligands in complexes 11 and 12, respectively, while ligand 2 functions as a monodentate P-ligand in complex 13. The NMR spectroscopic studies indicate that complexes 11-13 retain their solid-state structures in solution. The higher efficiency of ligands 1 and 6 in comparison with ligand 2 and other P,O- or P,N-ligands in Pd/L-catalyzed aryl aminations most likely results from the formation of the P,O-chelating Pd/L complexes, which appear to be most suitable for aryl aminations involving this class of ligands.