Transition metal complexes with pyrazole and bulky salen ligands, catalysis, spectroscopic properties and bioactivity

Abstract

2,6-Bis[(4S, 7R)-7, 8, 8-trimethyl-4, 5, 6, 7-tetrahydro-4, 7-methano-1-indazoly]pyridine (PPz*) is a pincer ligand rarely used by chemists in the synthesis of transition metal complexes since its preparation is difficult. In this work, a new synthetic route to the compound was developed with safer and milder conditions. Iridium(III), palladium(II), platinum(II), cobalt(II) and silver(I) complexes supported with the PPz* ligand have been synthesized. Their luminescent and catalytic properties have been investigated. The iridium(III) carbene PPz* complex has been synthesized and studied by ESI-MS. The silver PPz* complex was found to catalyze cyclopropanation of styrenes and ethyl phenyldiazoacetate in good yields. A new methylated palladium(II) complex has been synthesized. (+)-(Z)-3-(hydroxymethylene)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-one (HPz*), one of the starting materials for the synthesis of PPz*, bears a pyrazole ring, which can be also used as a ligand. The coinage metals, copper, silver and gold have been chosen to complex with HPz*. Their catalytic activities and anti-cancer properties have been investigated. The silver(I) HPz* complex was found to be an effective catalyst for intermolecular alkene cyclopropanation and sp3 C-H insertion to give corresponding products in good yields. Furthermore, it gives a better performance than cis-platin in killing cancer in cell line A2780, human ovarian carcinoma with IC50 7.21±0.29 μM. Salen is one of the most common ligands used in transition metal catalysis. A novel bulky iron salen complex [FeIII(salen)Cl] (salen = N,N’-bis(2-CPh3-4-tBu-salicylidene)-1,2-cyclohexenediamine dianion) was synthesized by the reaction of the corresponding H2salen ligand and FeCl3. The complex structure was characterized by FAB-MS. Its catalytic activities toward carbene and nitrene transfer reactions were examined but it was found ineffective for these reactions. The Lewis acid catalysis with this complex is now being studied.