Syntheses and Characterization of Copper(II) Carboxylate Dimers Formed from Enantiopure Ligands Containing a Strong π···π Stacking Synthon: Enantioselective Single-Crystal to Single-Crystal Gas/Solid-Mediated Transformations

Abstract

Tri- and tetrafunctional enantiopure ligands have been prepared from 1,8-naphthalic anhydride and the amino acids L-alanine, D-phenylglycine, and L-asparagine to produce (S)-2-(1,8-naphthalimido)propanoic acid (HL(ala)), (R)-2-(1,8-naphthalimido)-2-phenylacetic acid (HL(phg)), and (S)-4-amino-2-(1,8 naphthalimido)-4-oxobutanoic acid (HL(asn)), respectively. Reactions of L(ala)(-) with copper(II) acetate under a variety of solvent conditions has led to the formation and characterization by X-ray crystallography of three similar copper(II) paddlewheel complexes with different axial ligands, [Cu(2)(L(ala))(4)(THF)(2)] (1), [Cu(2)(L(ala))(4)(HL(ala))] (2), and [Cu(2)(L(ala))(4)(py)(THF)] (3). A similar reaction using THF and L(phg)(-) leads to the formation of [Cu(2)(L(phg))(4)(THF)(2)] (4). With the exception of a disordered component in the structure of 4, the naphthalimide groups in all of these compounds are arranged on the same side of the square, central paddlewheel unit, forming what is known as the chiral crown configuration. A variety of π···π stacking interactions of the 1,8-naphthalimide groups organize all of these complexes into supramolecular structures. The addition of the amide group functionality in the L(asn)(-) ligand leads to the formation of tetrameric [Cu(4)(L(asn))(8)(py)(MeOH)] (5), where reciprocal axial coordination of one of the amide carbonyl oxygen atoms between two dimers leads to the tetramer. Extensive supramolecular interactions in 5, mainly the π···π stacking interactions of the 1,8-naphthalimide supramolecular synthon, support an open three-dimensional structure containing large pores filled with solvent. When crystals of [Cu(4)(L(asn))(8)(py)(MeOH)] are exposed to (S)-ethyl lactate vapor, the coordinated methanol molecule is replaced by (S)-ethyl lactate, bonding to the copper ion through the carbonyl oxygen, yielding [Cu(4)(L(asn))(8)(py)((S)-ethyl lactate)] (6) without a loss of crystallinity. With the exception of the replacement of the one axial ligand, the molecular structures of 5 and 6 are very similar. In a similar experiment of 5 with vapors of (R)-ethyl lactate, again a change occurs without a loss of crystallinity, but in this case the (R)-ethyl lactate displaces only slightly more than half of the axial methanol molecules forming [Cu(4)(L(asn))(8)(py){((R)-ethyl lactate)(0.58)(MeOH)(0.42)}] (7). Importantly, in 7, the (R)-ethyl lactate coordinates through the hydroxyl group. When crystals of [Cu(4)(L(asn))(8)(py)(MeOH)] are exposed to vapors of racemic ethyl lactate, the coordinated methanol molecule is displaced without a loss of crystallinity exclusively by (S)-ethyl lactate, yielding a new form of the tetramer [Cu(4)(L(asn))(8)(py)((S)-ethyl lactate)], in which the ethyl lactate in the pocket bonds to the copper(II) ion through the carbonyl oxygen as with 6. Exposure of [Cu(4)(L(asn))(8)(py){((R)-ethyl lactate)(0.58)(MeOH)(0.42)}] to racemic ethyl lactate yields a third form of [Cu(4)(L(asn))(8)(py)((S)-ethyl lactate)], where the three forms of [Cu(4)(L(asn))(8)(py)(...

Structural and magnetic properties of dinuclear Cu(II) complexes featuring triazolyl-naphthalimide ligands

“…Bond lengths and angles are consistent with other axially elongated square-based pyramidal structures where the equatorial (square base) bond lengths average 1.985(2) Å whilst the axial bond to the carbonyl oxygen atom is 2.307(2) Å. The coordination of the carbonyl oxygen atoms in naphthalimides to transition metals is not a commonly observed occurrence and only three structures are reported in the CSD [19,41,42]. (Figure 7) with O···centroid distances of 2.881 Å and 2.852 Å for the two different interactions.…”

“…[1][2][3][4] In this, their π-deficient character has been exploited giving rise to systems where the extension of structure arises through π-based (π···π stacking, anion···π interactions and C=O···π interactions) contacts and results in frameworks constructed from less traditional weak non-covalent supramolecular interactions rather than the more typical charge assisted coordination bonds observed in coordination polymers and metal-organic frameworks (MOFs). Reger and coworkers have been instrumental in this field and have developed many 1,8-naphthalimide transition metal conjugates with a range of coordinating groups [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] whose structures were extended in the solid state by means of the naphthalimide groups acting as secondary building units through π-based interactions. Such self-assembled systems have applications in areas including molecular electronics, porous materials for sensing and gas storage, supramolecular spintronics and crystal engineering development.…”

1-Imidoalkylphosphonium salts with modulated Cα–P+ bond strength: synthesis and application as new active α-imidoalkylating agents

“…Synthesis of 2-(1,8-naphthalimido)propionic acid: The synthesis of 2-(1,8-naphthalimido)propionic acid was carried out based on the procedure described by Reger [ 35 ]. To a stirred aqueous solution of L-alanine (1.96 g, 22 mmol) potassium hydroxide (1.12 g, 20 mmol) was added.…”

Homochiral, Supramolecular Frameworks Built from a Zinc(II) Tetramer or Cadmium(II) Dimer Containing Enantiopure Carboxylate Ligands Functionalized with a Strong π···π Stacking Synthon

“…Ground solid samples were used in a 4 mm cell. The protonated form of the ligand, ( S )‐2‐(1,8‐naphthalimido)propanoic acid (H L ala ), was synthesized as previously reported 11i. Elemental analyses were performed by Robertson Microlit Laboratories (Ledgewood, NJ).…”

“…Although considerable effort has recently been dedicated to the syntheses of chiral framework structures because of a multitude of potential applications,12–14 the use of simple amino acids coupled to the strong π ··· π‐stacking naphthalimide group is a unique methodology aimed at the syntheses of homochiral SMOFs. In our earlier work, we have shown that trifunctional L ala – and tetrafunctional L asn – ligands (Scheme ), when incorporated into the paddlewheel Cu 2 (O 2 CR) 4 ‐type SBU core, led to homochiral solids with unique structures and interesting properties 11f,11i. In an effort to elaborate the molecular and supramolecular chemistry of these interesting ligands with d 10 group 12 metals, we report here the structural analysis and luminescent properties of zinc(II) and cadmium(II) complexes of the trifunctional L ala – ligand.…”