Molecular Recognition of Primary Amines by Three‐Point Binding with Boron‐Containing Host Molecules

Abstract

positions situated spatially nearby, thereby leading to synergistic effects.To test this concept experimentally we synthesized the boron-containing crown ethers ['] The corresponding ammonium ions RNH? are bound more strongly by suitable crown ethers, but generally the degree of selectivity here is also quite low.['] The latter is hardly surprising because the RNHf/crown ether complexes, which are held together by hydrogen bonds, are structurally so arranged that the groups R are too remote from the framework of the host m~l e c u l e . [~.~~ The formation of adducts with Lewis acids,[" for example with trialkyl boranes leading to reversible formation of adducts R,N. BR3,16] is a quite different type of amine complexation. The dissociation constants of these equilibria depend, among other factors, on the number and size of the groups R in the amine.We describe here a new concept in molecular recognition in which host molecules containing a Lewis acid metal centerrzb. 4 9 '1 and at least two donor sites selectively bind primary amines via three-point binding (Scheme l). If the amine RNH, forms a reversible dative bond with the metal center, it takes on the character of an ammonium ion. This should permit the formation of hydrogen bonds with the donor

A Structural Investigation of the N−B Interaction in an o-(N,N-Dialkylaminomethyl)arylboronate System

“…Further evidence for steric effects comes from Reetz. He reported a catechol phenylboronate structure with an N−B coordinating benzylamine . The coordination of boron with this primary amine affords an N−B bond length of 1.612 Å, shorter than that in compound 13 .…”

Highly Sensitive NH3 Detection Based on Organic Field-Effect Transistors with Tris(pentafluorophenyl)borane as Receptor

“…Boranes have frequently been used as complexation agents for Lewis bases − because of the strong interaction between boron atoms and lone pairs; furthermore, borane–amine complexes have also been widely used as light-emitting molecules and in fluorescent sensors . TPFB is frequently used as a strongly Lewis acidic cocatalyst in numerous reactions, such as dehydration, Friedel–Crafts reactions, ring-opening reactions, and syndiospecific living polymerization .…”

Using Intelligent/Random Library Screening To Design Focused Libraries for the Optimization of Homogeneous Catalysts: Ullmann Ether Formation

“…Incorporating molecular parameters important to most homogeneous catalyst functions was a natural way to cover ligand diversity space as completely as possible with a relatively small parent library . For our particular study, we considered the following as important parameters to vary when preparing the “intelligent” portion of the parent library: (1) electron-donating and -withdrawing abilities of the ligands (σ and π); (2) sterics around the donating atom on the ligands; (3) monodentate or multidentate donation, (4) for multidentate ligands, ligand bite angles; and (5) second coordination sphere effects (molecular recognition potential) . Taking these parameters into account, we attempted to maximize the chance of discovering the best ligand with a minimum set.…”