Hetero-Bimetallic Complexes Based on an Anthyridine Ligand Preparation and Catalytic Activity

Abstract

Complexation of anthyridine-based ligand L with [(η 6cymene)RuCl 2 ] 2 , [Cp*RhCl 2 ] 2 , and [Cp*IrCl 2 ] 2 yielded a mononuclear complex: [(N,N-L)Ru(η 6 -cymene)Cl]Cl (1), [(N,N-L)Rh(Cp*)Cl]Cl (2), and [(N,N-L)Ir(Cp*)Cl]Cl (3), respectively [L = 5-phenyl-2,8-di-2pyridinylanthyridine]. Upon treatment with (CH 3 CN)PdCl 2 , complexes 1−3 underwent o-metalation to yield heterobimetallic complexes Ru−Pd, Rh−Pd, and Ir−Pd, respectively.Complexes were all characterized by spectroscopic method, and some are further confirmed by X-ray crystallography. Complex Ru−Pd exhibits catalytic activities for the tandem reactions of Suzuki−Miyaura coupling/transfer hydrogenation of pbromoacetophenone with phenylboronic acid in isopropanol, whereas Ir− Pd shows a moderate activity. However, complex Rh−Pd does not behave the same way. Furthermore, catalytic activity of these heterobimetallic complexes toward debromination/transfer hydrogenation of p-bromoacetophenonewas also investigated. The catalytic pathways of these processes were studied and discussed. This study reveals the base used in the reactions plays an important role in the reaction pathway.

Synthesis and Characterization of RhIII–MII (M = Pt, Pd) Heterobimetallic Complexes Based on a Bisphosphine Ligand: Tandem Reactions Using Ethanol

“…Furthermore, the physical mixture of 1 and 2c improves the selectivity toward product C (TH/DH) but is still significantly less effective than 3c . This result supports cooperativity in the heterobimetallic catalyst. ,, …”

“…The catalytic activity of the synthesized mono- and heterobimetallic complexes were examined for TH/DH of different p -haloacetophenones. The three potential products A – C (see Table ) are expected, depending on the relative rates of TH versus DH . TH/DH reactions were performed under mildly basic conditions in the presence of Cs 2 CO 3 in EtOH solvent as a source of hydrogen transfer at 90 °C.…”

“…The enhanced catalytic activities of these air-stable complexes have been applied for three different tandem reactions: TH/DH, TH/Suzuki–Miyaura coupling, and coupling of nitrobenzenes with benzylic alcohols for imine synthesis. We used EtOH (instead of the previously reported i PrOH) , as an uncommon hydrogen source and solvent. , The scope of these tandem processes is very broad, covering electron-rich and electron-deficient p -haloacetophenones or nitroarenes. The Rh III –Pd II complex 3c shows higher activity in comparison the mono- and heterobimetallic complexes reported in this work.…”

“…Heterobimetallic compounds can be an option for tandem catalytic processes . In this regard, several catalytic systems such as Ir III –Pd II , ,, Rh III –Pd II , , Ru II –Pd II , , Ir III –Au I , Rh III –Au I , Pd II –Au I , , etc. have been described and their catalytic activities investigated in various tandem transformations (Chart ).…”

“…Interestingly, in our tandem reactions ethanol (having abundance, sustainability, and a safe nature) was used as a powerful and efficient hydrogen source for the tandem reactions. Although formic acid or i PrOH have been mainly used for TH reactions, , ethanol has rarely been applied for tandem processes. − This difficulty can be attributed to the fact that EtOH causes catalyst deactivation. , …”