Reactivity Study of Unsymmetrical β-Diketiminato Copper(I) Complexes: Effect of the Chelating Ring

Abstract

β-Diketiminato copper(I) complexes play important roles in bioinspired catalytic chemistry and in applications to the materials industry. However, it has been observed that these complexes are very susceptible to disproportionation. Coordinating solvents or Lewis bases are typically used to prevent disproportionation and to block the coordination sites of the copper(I) center from further decomposition. Here, we incorporate this coordination protection directly into the molecule in order to increase the stability and reactivity of these complexes and to discover new copper(I) binding motifs. Here we describe the synthesis, structural characterization, and reactivity of a series of unsymmetrical N-aryl-N'-alkylpyridyl β-diketiminato copper(I) complexes and discuss the structures and reactivity of these complexes with respect to the length of the pyridyl arm. All of the aforementioned unsymmetrical ß-diketiminato copper(I) complexes bind CO reversibly and are stable to disproportionation. The binding ability of CO and the rate of pyridyl ligand decoordination of these copper(I) complexes are directly related to the competition between the degree of puckering of the chelate system and the steric demands of the N-aryl substituent.

Improved Synthesis of Unsymmetrical N‐Aryl‐N′‐alkylpyridyl ß‐Diketimines Using Molecular Sieves and their Lithium Complexes

“…In general, the chelating pyridylmethyl arms form five‐membered rings with anionic β‐diketiminato moieties L1 – and L3 – , and the pyridylethyl arms form six‐membered rings with the anionic β‐diketiminato moieties L2 – and L4 – . In a chelating ring stability study of corresponding Zn II and Cu I complexes,, we found that the five‐membered chelating ring (pyridylmethyl arm) has a stronger tendency to become a pendent arm than the six‐membered chelating ring (pyridylethyl arm) in solution. Therefore, the unusual dinuclear structure formation of Li L3 may result from the hemilabile nature of the pyridylmethyl arm during the crystallization packing process.…”

“…Recently, our group reported the synthesis of UNAADpy ligands H L1 –H L4 using catalytic quantities of TsOH. The reaction was monitored for two days using 1 H NMR spectroscopy (Table ) , . We found that using one equivalent of TsOH gave low product yields that required further purification.…”

“…Introducing hemilabile pendant pyridyl donors in unsymmetrical N ‐aryl‐ N′ ‐alkyl β‐diketimines (UNAAD) in the preparation of unsymmetrical N ‐aryl‐ N′ ‐alkylpyridyl β‐diketimines (UNAADpy) may introduce new electronic and steric binding features, which can aid in the stabilization and the ability to modulate the reactivity of unsaturated metalated complexes . In order to understand the coordination abilities of the pendant donor of UNAADpy, we recently reported several UNAADpy ligands and their corresponding Zn II and Cu I complexes , . However, the isolated yields of UNAADpy were low (≈50 %) and required several purification steps , .…”

Nitric oxide generation study of unsymmetrical β-diketiminato copper(ii) nitrite complexes

“…The Cu-N py bond distances of complexes L 1 CuCl [2.0431( 18) Å] and L 3 CuCl [2.0308( 19) Å] are significantly longer than those of L 2 CuCl [2.020(4) Å] and L 4 CuCl [2.0080(2) Å] (Table 1); a similar behavior has been observed in copper(I) analogoues. 32 Therefore, the difference in the molecular structures of the copper(II) complexes L 1 CuCl-L 4 CuCl clearly suggests the disparities due to the length of the pyridyl arm supporting the β-diketiminato ligands. Apart from this, the Cu-N py bond distance of complexes L 1 CuCl-L 4 CuCl falls within the range of the reported data for the copper(II) complexes containing a pyridyl ligand.…”

“…19,27 However, lacking in the literature is a thorough study of copper complexes supported by unsymmetrical N-aryl-N′-alkyl-substituted β-diketiminato ligands in comparison with N,N′aryl-substituted analogues. 32 Based on previous studies of symmetric N-aryl-N′-aryl-substituted type of β-diketiminato copper (I) and copper(II) nitrite 19,28 and our work on biomimetic copper(I)-nitrito complexes, 29,30,33 we decided to introduce unsymmetrical N-aryl-N′-alkyl-substituted β-diketiminato ligands 32,34,35 into copper-nitrite chemistry. Herein, we describe the synthesis and structural characterization of unsymmetrical N,N′-aryl-substituted β-diketiminato L 1 CuCl-L 4 CuCl complexes (Scheme 2) and their nitrite complexes L 1 Cu(O 2 N) and L 2 Cu(O 2 N).…”