Synthetic routes to zinc beta-diiminate complexes are reported. The synthesis of 11 beta-diimine [(BDI)-H] ligands, with varying N-aryl substituents and bridging structures, is described. These ligands are converted to (BDI)ZnX complexes (X = OAc, Et, N(SiMe3)2, Br, Cl, OH, OMe, O(i)Pr). X-ray structural data revealed that all zinc complexes examined exist as micro-X-bridged dimers in the solid state, with the exception of the zinc ethyl and amido complexes which were monomeric. Complexes of the form (BDI)ZnOR (R = alkyl, acyl) and (BDI)ZnN(SiMe3)2 are highly active catalysts for the alternating copolymerization of epoxides and CO2. Copolymerizations of cyclohexene oxide (CHO) and CO2 with (BDI-1)ZnX [(BDI-1) = 2-((2,6-diisopropylphenyl)amido)-4-((2,6-diisopropylphenyl)imino)-2-pentene)] and (BDI-2)ZnX [(BDI-2) = 2-((2,6-diethylphenyl)amido)-4-((2,6-diethylphenyl)imino)-2-pentene)], where X = OAc, Et, N(SiMe3)2, Br, Cl, OH, OMe, O(i)Pr, were attempted at 50 degrees C and 100 psi CO2. Complexes with X = OAc, N(SiMe3)2, OMe, O(i)Pr all produced polycarbonate by the alternated insertion of CHO and CO2 with similar catalytic activities, comparable molecular weights, and narrow molecular weight distributions (MWD approximately 1.1), indicating the copolymerizations are living. Furthermore, ligand effects were shown to dramatically influence the polymerization activity as minor steric changes accelerated or terminated the polymerization activity.

Abstract:Developing nontraditional approaches to the synthesis and characterization of multivalent compounds is critical to our efforts to study and interface with biological systems and to build new noncovalent materials. This paper demonstrates a biomimetic approach to the construction of discrete, modular, multivalent receptors via molecular self-assembly in aqueous solution. Scaffolds presenting 1-3 viologen groups recruit a respective 1-3 copies of the synthetic host, cucurbit [8]

1:1 molar mixtures of electron rich dialkoxynapthalene (Dan) and electron deficient 1,4,5,8-napthalenetetracarboxylic diimide (Ndi) derivatives form highly tunable, columnar mesophases with a dark red color due to a charge transfer absorbance derived from alternating face-centered stacking. Certain Dan-Ndi mixtures undergo a dramatic color change from dark red to an almost colorless material upon crystallizing from the mesophase. Macroscopic morphology of the solid is not changed during this process. In order to investigate the origins of this interesting thermochromic behavior, Dan and Ndi side chains were systematically altered and their 1:1 mixtures studied. We have previously speculated that the presence or absence of steric interactions due to side chain branching on the aromatic units controlled the level of color change associated with crystallization. Results from the present study further refine this conclusion including a key crystal structure that provides a structural rationale for the observed results.

Derivatives of relatively electron rich 1,5-dialkoxynaphthalene (Dan) donors and relatively electron deficient 1,4,5,8-naphthalenetetracarboxylic diimide (Ndi) acceptors have been exploited in the folding and self-assembly of a variety of complex molecular systems in solution. Here, we report the use of Dan and Ndi derivatives to direct assembly of extended columns with alternating face-centered stacked structure in the solid state. A variety of 1:1 Dan:Ndi mixtures produced mesophases that were found to be stable over temperature ranges extending up to 110 degrees C. Analysis of these mesophases indicates mixtures with soft/plastic crystal phases and a few mixtures with the thermodynamic properties of true liquid crystals, all composed of alternating donor-acceptor columns within. Importantly, a correspondence was found between the clearing and crystallization points of the mesophase mixtures and the melting/clearing points of the component Ndi and Dan units, respectively. This correspondence enables the predictable tuning of mesophase phase transition temperatures. The study of sterically hindered derivatives led to a set of mixtures in which a dramatic and sudden color change (deep red to yellow) was observed upon crystallization of the mesophase due to a phase separation of the component donor and acceptor units.