Synthesis and Hydrolysis of Cationic Palladium(II) 2,6-Diacetylpyridine Dimethyl Ketal Complexes. Cyclopalladation of 2,6-Diacetylpyridine. Palladium-Catalyzed Synthesis of a 1,5-Benzodiazepine

Abstract

The complex [Pd­(<i>O</i>¹,<i>N</i>¹,<i>C</i>¹-L)­(OClO₃)] (L = monoanionic ligand resulting from deprotonation of the acetyl group of the dimethyl monoketal of 2,6-diacetylpyridine) reacts with neutral ligands L¹ (phosphines, isocyanides, CO, N-donor ligands) to give the complexes [Pd­(<i>O</i>¹,<i>N</i>¹,<i>C</i>¹-L)­L¹]­ClO₄, [Pd­(<i>N</i>¹,<i>C</i>¹-L)­L¹₂]­ClO₄, and [Pd­(<i>C</i>¹-L)­L¹₃]­ClO₄. The complex [Pd­(<i>N</i>¹,<i>C</i>¹-L)­(pda)]­ClO₄ (pda = NH₂C₆H₄NH₂-2) can be used as a catalyst for the synthesis of 2′,2′,4′-trimethyl-2′,3′-dihydro-1<i>H</i>-1′,5′-benzodiazepine (Bzdiaz) from pda and acetone. The intermediate [Pd­(<i>O</i>¹,<i>N</i>¹,<i>C</i>¹-L)­(Bzdiaz)]­ClO₄ has been isolated from an acetone solution of [Pd­(<i>N</i>¹,<i>C</i>¹-L)­(pda)]­ClO₄. The ligand L in some of the above complexes hydrolyzes to give [Pd­(<i>O</i>¹,<i>N</i>¹,<i>C</i>¹-L′)­L¹]­ClO₄ (L′ = monoanionic ligand resulting from the deprotonation of one acetyl group of 2,6-diacetylpyridine, L¹ = MeCN, ^<i>t</i>BuNC). These complexes are best prepared by reacting L¹ with [Pd­(<i>O</i>¹,<i>N</i>¹,<i>C</i>¹-L′)­(NCMe)]­ClO₄, which, in turn, can be obtained from 2,6-diacetylpyridinium perchlorate and Pd­(OAc)₂ in MeCN. When THF is used as solvent, [Pd­(<i>O</i>¹,<i>N</i>¹,<i>C</i>¹-L′)­(OH₂)]­ClO₄ can be isolated. The crystal structures of [Pd­(<i>O</i>¹,<i>N</i>¹,<i>C</i>¹-L′)­(NCMe)]­ClO₄ and [Pd­(<i>O</i>¹,<i>N</i>¹,<i>C</i>^<i>1</i>-L)­(CNXy)]­ClO₄ have been determined