Synthesis and Supramolecular Association of NCN-Pincer Pd-Complex-bound Norvaline Derivatives toward Fabrication of Controlled Metal Array

Abstract

Novel NCN-pincer Pd-complex-bound norvaline derivatives were synthesized. The N- and C-termini-alkylated Pd–norvalines spontaneously assemble into fibrous aggregates to form supramolecular gels, in which the NCN-pincer Pd complex moieties assemble in a highly oriented manner.

Synthesis and Self‐Assembly of NCN‐Pincer Pd‐Complex‐Bound Norvalines

“…However, there have been almost no investigations into amino‐acid‐based metal assembly except as detailed in our previous reports 35b. 37 We found that the N ‐ and C ‐alkylated Pd‐bound norvalines L ‐ 2 37a and L ‐ 4 showed excellent self‐assembly in various aromatic solvents to afford supramolecular gels. Figure 5 shows the typical gelation experiment for L ‐ 4 .…”

“…This occurs because the intermolecular π–π interactions dominate the assembly of 1 and L ‐ 2 in DMF solution, where the formation of hydrogen bonds is suppressed. Indeed, in the crystalline state of 1 , the β‐sheet‐type self‐assembled structure found in the supramolecular gel of L ‐ 2 was not observed 37a. In contrast, for L ‐ 2 , a unique dimeric structure wrapped with undecyl alkyl chains was found, in which the π–π interaction between two PdCl(dpb) units binds up two molecules of L ‐ 2 and the dimer units are connected to each other through hydrogen bonding to form a chain‐like aggregate.…”

“…The X‐ray structures of metallocene‐bound amino acids such as ferrocenylalanine11b, 48 and Fe‐, Co‐, Rh‐, and Ti‐cyclopentadienyl‐complex‐bound valine‐derived diketopiperazine derivatives14b were also obtained, from which the configurations of amino acid moieties could not clearly be assessed. We previously reported an X‐ray crystal structure of Pd‐bound norvaline L ‐ 1 with an adequately small Flack parameter, from which the absolute stereochemistry was determined as an S configuration of the norvaline moiety 37a…”

“…Significant changes in and enhancement of the original properties, functions, and performance can be induced by cooperative interactions of arrayed functionalities in well‐ordered nanosized hierarchical architectures. In practice, arrayed functional groups fabricated from functionalized amino acids and peptides bearing conjugated with photoactive,54 electronically active,55 and catalytically active37b, 56 auxiliaries have been reported as examples of such advanced supramolecular functional materials that show enhanced performance or emergent properties not accessible by unimolecular systems. Metalated amino acids and peptides that conjugate with functional organometallics have potent abilities as such supramolecular materials; however, little research on such peptides has been reported as yet.…”

Macrocyclic Metal Complexes Bearing Rigid Polyaromatic Ligands: Synthesis and Catalytic Activity

“…The geometrical parameters around the metal centres in these complexes, summarised in Table , are mostly unexceptional. One notable feature is the significant deviation from typical square‐planar coordination of the palladium(II) and platinum(II) centre, as shown in the side views (Figure S3) along with the small C6‐M‐Cl angles (155.3(2)–157.4(3)°). The deformation may be ascribed to steric repulsion between the chlorine atom and the two phenyl rings .…”