Tetra- and Dinuclear Palladium Complexes Based on a Ligand of 2,8-Di-2-pyridinylanthyridine: Preparation, Characterization, and Catalytic Activity

Abstract

Complexation of L [L = 5-phenyl-2,8-di-2-pyridinyl-anthyridine] with [Pd(CH 3 CN) 4 ](BF 4 ) 2 and [Pd(CH 3 CN) 3 Cl](BF 4 ) in a molar ratio of 1:2 rendered the corresponding dinuclear complexes [Pd 2 L (CH 3 CN) 4 ](BF 4 ) 4 (1) and [Pd 2 L (CH 3 CN) 2 Cl 2 ](BF 4 ) 2 ( 2), respectively. However, treatment of L with (COD)PdCl 2 followed by anion exchange yielded a tetranuclear complex [Pd 4 L 3 Cl 4 ](PF 6 ) 4 (4a). Structures of these complexes are characterized by both spectroscopy and X-ray crystallography. Interconversion of these three complexes was studied via the manipulation of stoichiometric ratio of ligand to metal precursor. The catalytic activity of these complexes for carbonylative Suzuki− Miyaura cross-coupling was investigated. Complex 2 shows an excellent catalytic activity on the reaction of aryl iodide with arylboronic acid in the presence of atmospheric pressure of CO to give the corresponding benzophenones.

An Anthyridine-Based Pentanitrogen Donor Switches from Mono- to Tetradentate with Pd(II) Ions

“…The average Pd–N bond length is about 2.1 Å, and the through-space distance of Pd···Pd is 5.1094(8) Å, indicating no metal–metal interaction (Table ). Similar lyto the structure of 2 , the entire molecule (cationic portion) of 5 does not maintain a planar geometry due to the steric congestion of metal ions associated with their surrounding donors . Thus, the N(6)···N(7) distance (two acetonitrile ligands) is 3.252(4) Å for the steric relief of the surrounding ligands, as represented by the side view of the crystal structure (Figure ).…”

“…With the characterization data of complex 1a , b in hand, we further explored the coordination chemistry difference between mono- and dinuclear complexes and their transformation. Complexes 2 and 3 were obtained according to our previously reported methods . Treatment of 2 and 3 with 1 equiv of L and 4 equiv of PPh 3 in acetonitrile readily gave 1a , b in high yields, respectively (Scheme ).…”

“…In previous work, we found that complex 2 has an excellent catalytic activity in carbonylative Suzuki–Miyaura coupling for the reaction of aryl iodide with arylboronic acid in the presence of an atmospheric pressure of CO to give the corresponding benzophenones. For comparison, we screened the catalytic activity of all newly prepared complexes in this coupling reaction under the conditions reported previously . Typically, a mixture of phenyl iodide, tolueneboronic acid, the palladium complex, and K 2 CO 3 in xylene in the presence of an atmospheric pressure of CO was heated at 50 °C and then the reaction mixture was then diluted with H 2 O and extracted with CH 2 Cl 2 .…”

“…Chemical shifts are given in parts per million relative to Me 4 Si for 1 H and 13 C NMR. Ligand L , and 2 , 3 , and Pd 4 L 3 were prepared according to our reported methods, whereas (COD)­PdMeCl was prepared from the reaction of (COD)­PdCl 2 with Me 4 Sn …”

“…5-Phenyl-2,8-bis­(2-pyridinyl)­anthyridine ( L ) is a pentanitrogen donor system, containing two bipyridinyl moieties that are suitable for the construction of bimetallic systems via bis-chelation or ortho cyclometalation (Scheme , I and II ). Indeed, the related dimetallic complexes have been disclosed in our previous works. , Interestingly, the reaction of L with (COD)­PdCl 2 followed by anion exchange yielded the tetranuclear complex Pd 4 L 3 , in which one ligand L acts a monodentate ligand with four nitrogen donors bound to four different palladium centers (denoted in red in Pd 4 L 3 , Scheme ). Nevertheless, in all these cases, the nitrogen atom (N (10) ) at the 10-position of the anthyridine remains as a free site.…”