Lone-Pair-Induced Topicity Observed in Macrobicyclic Tetra-thia Lactams and Cryptands: Synthesis, Spectral Identification, and Computational Assessment

Syntheses, homeomorphic and configurational isomerizations, and structures of macrocyclic aliphatic dibridgehead diphosphines; molecules that turn themselves inside out

The diphosphine complexes cis- or trans-[upper bond 1 start]PtCl₂(P((CH₂) _n )₃P[upper bond 1 end]) (n = b/12, c/14, d/16, e/18) are demetalated by MC[triple bond, length as m-dash]X nucleophiles to give the title compounds (P((CH₂) _n )₃)P (3b-e, 91-71%). These "empty cages" react with PdCl₂ or PtCl₂ sources to afford trans-[upper bond 1 start]MCl₂(P((CH₂) _n )₃P[upper bond 1 end]). Low temperature ³¹P NMR spectra of 3b and c show two rapidly equilibrating species (3b, 86 : 14; 3c, 97 : 3), assigned based upon computational data to in,in (major) and out,out isomers. These interconvert by homeomorphic isomerizations, akin to turning articles of clothing inside out (3b/c: ΔH ^‡ 7.3/8.2 kcal mol^-1, ΔS ^‡ -19.4/-11.8 eu, minor to major). At 150 °C, 3b, c, e epimerize to (60-51) : (40-49) mixtures of (in,in/out,out) : in,out isomers, which are separated via the bis(borane) adducts 3b, c, e·2BH₃. The configurational stabilities of in,out-3b, c, e preclude phosphorus inversion in the interconversion of in,in and out,out isomers. Low temperature ³¹P NMR spectra of in,out-3b, c reveal degenerate in,out/out,in homeomorphic isomerizations (ΔG ^‡ _Tc 12.1, 8.5 kcal mol^-1). When (in,in/out,out)-3b, c, e are crystallized, out,out isomers are obtained, despite the preference for in,in isomers in solution. The lattice structures are analyzed, and the D ₃ symmetry of out,out-3c enables a particularly favorable packing motif. Similarly, (in,in/out,out)-3c, e·2BH₃ crystallize in out,out conformations, the former with a cycloalkane solvent guest inside.

Synthesis and structural studies of copper(ii) complex with N2S2 based N-substituted pendant phosphonic acid arms

The synthesis of a heteromacrocyclic bifunctional chelator with phosphonic acid pendent arms is presented along copper(ii) complexation. Ligand N₂S₂-POH featuring N,N'-bis-substituted phosphonate pendent arms was isolated in respectable yields, characterized, and chelated to copper(ii). Implementation of both Moedritzer-Irani and Kabachnik-Fields conditions using aza-thia macrocycle 1,8-dithia-4,11-diazacyclotetradecane afforded 1,8-dithia-4,11-diazacyclotetradecane-4,11-diyl-bis-(methylene)-bis-(phosphonic acid) (N₂S₂-POH). Kinetic NMR studies provided four acid dissociation constants with respect to hydronium ion concentration. Benesi-Hildebrand binding experiment provided a conditional formation constant of 2.8 × 10⁴ M^-1. Heteromacrocycle N₂S₂-POH readily formed an encapsulated copper(ii) chelate at room temperature, which was examined through EPR analysis.

SC, Schrage BR, Ziegler CJ, Gao X, Wheeler SE. Topomeric aza/thia cryptands: synthesis and theoretical aspects of in/out isomerism using n-alkyl bridging

A series of heterobicyclic aza/thia-lactams and cryptands incorporating changes in n-alkyl bridging length have been synthesized, characterized, chelated to heavy metals and computationally assessed.

Synthesis, Characterization, and Copper(II) Chelates of 1,11-Dithia-4,8-diazacyclotetradecane

Synthesis of 1,11-dithia-4,8-diazacyclotetradecane (L1), a constitutional isomer of the macrocyclic [14]aneN₂S₂ series, is accompanied with reaction and method optimization. Chelation of L1 with copper(II) provided assessment of lattice packing, ring contortion, and evidence of conformational fluxionality in solution through two unique crystal structures: L1Cu(ClO4)₂ and [(L1Cu)₂μ-Cl](ClO₄)₃. Multiple synthetic approaches are presented, supplemented with reaction methodology and reagent screening to access [14]aneN₂S₂ L1. Reductive alkylation of bis-tosyl-cystamine was integrated into the synthetic route, eliminating the use and isolation of volatile thiols and streamlining the synthetic scale-up. Late-stage cleavage of protecting sulfonamides was addressed using reductive N-S cleavage to furnish macrocyclic freebase L1.