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

The complex [Pd­(O1,N1,C1-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(O1,N1,C1-L)­L1]­ClO4, [Pd­(N1,C1-L)­L12]­ClO4, and [Pd­(C1-L)­L13]­ClO4. The complex [Pd­(N1,C1-L)­(pda)]­ClO4 (pda = NH2C6H4NH2-2) can be used as a catalyst for the synthesis of 2′,2′,4′-trimethyl-2′,3′-dihydro-1H-1′,5′-benzodiazepine (Bzdiaz) from pda and acetone. The intermediate [Pd­(O1,N1,C1-L)­(Bzdiaz)]­ClO4 has been isolated from an acetone solution of [Pd­(N1,C1-L)­(pda)]­ClO4. The ligand L in some of the above complexes hydrolyzes to give [Pd­(O1,N1,C1-L′)­L1]­ClO4 (L′ = monoanionic ligand resulting from the deprotonation of one acetyl group of 2,6-diacetylpyridine, L1 = MeCN, tBuNC). These complexes are best prepared by reacting L1 with [Pd­(O1,N1,C1-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(O1,N1,C1-L′)­(OH2)]­ClO4 can be isolated. The crystal structures of [Pd­(O1,N1,C1-L′)­(NCMe)]­ClO4 and [Pd­(O1,N1,C1-L)­(CNXy)]­ClO4 have been determined.