Guanidine–Guanidinium Cooperation in Bifunctional Artificial Phosphodiesterases Based on Diphenylmethane Spacers; <i>gem</i>-Dialkyl Effect on Catalytic Efficiency

Diphenylmethane derivatives <b>1</b>–<b>3</b>, decorated with two guanidine units, are effective catalysts of HPNP transesterification. Substitution of the methylene group of the parent diphenylmethane spacer with cyclohexylidene and adamantylidene moieties enhances catalytic efficency, with <i>gem</i>-dialkyl effect accelerations of 4.5 and 9.1, respectively. Activation parameters and DFT calculations of the rotational barriers around the C–Ar bonds indicate that a major contribution to the driving force for enhanced catalysis is entropic in nature

Substituent Effects on the Catalytic Activity of Bipyrrolidine-Based Iron Complexes

The catalytic activity and the selectivity of the new bipyrrolidine-based Fe­(II) complexes <b>2</b><b>·</b><b>Fe</b>(OTf)₂ and <b>3</b><b>·</b><b>Fe</b>(OTf)₂ in the oxidation of a series of alkyl and alkenyl hydrocarbons as well as of an aromatic sulfide with H₂O₂ were tested and compared with the catalytic efficiency of White’s parent complex <b>1·Fe</b>(OTf)₂ in order to evaluate the sensitivity of the reaction to electronic effects

Ribonuclease Activity of an Artificial Catalyst That Combines a Ligated Cu^II Ion and a Guanidinium Group at the Upper Rim of a <i>cone</i>-Calix[4]arene Platform

A <i>cone</i>-calix­[4]­arene derivative, featuring a guanidinium group and a Cu^II ion ligated to a 1,4,7-triazacyclononane (TACN) ligand at the 1,3-distal positions of the upper rim, effectively catalyzes the cleavage of 2-hydroxypropyl <i>p</i>-nitrophenyl phosphate (HPNP) and a number of diribonucleoside 3′,5′-monophosphates (<i>N</i>p<i>N</i>′). Kinetic and potentiometric measurements support the operation of a general-base/general-acid mechanism and demonstrate that the hydroxo form of the ligated Cu^II ion is the sole catalytically active species. Rate enhancements relative to the background hydrolysis reaction at 1 mM catalyst concentration are 6 × 10⁵-fold for HPNP and cluster around 10⁷-fold with the most favorable catalyst–<i>N</i>p<i>N</i>′ combinations

Ring-Opening Metathesis Polymerization of a Diolefinic [2]-Catenane–Copper(I) Complex: An Easy Route to Polycatenanes

A dilute (30 mM) dichloromethane solution of the copper­(I) complex <b>1</b>·Cu⁺ of a [2]-catenane composed of two identical 28-membered macrocyclic alkenes featuring a phenanthroline moiety in the backbone was subjected to ring-opening metathesis polymerization (ROMP) with second-generation Grubbs catalyst. Shortly after mixing of reactants, the dark red solution transformed into a gel. The bis­(phenanthroline)­copper­(I) units were effectively preserved during ROMP, as evinced by spectroscopic analysis. This implies that the putative metal alkylidene pseudorotaxane intermediates did not undergo dethreading processes but were involved in ring–chain equilibria strongly biased toward the ring products at the low monomer concentration employed in the ROMP reactions. MALDI-TOF mass spectra of the reaction mixtures obtained at an early stage of the reaction revealed a distribution of interlocked oligomers (<b>1</b>·Cu⁺)_<i>n</i>(PF₆^–)_<i>n</i>−1 with <i>n</i> up to 7, with no traces of peaks ascribable to open chain species. Rheological and mechanical analyses of the gel products provided independent evidence in support of the conclusion that the fraction of linear species in the polymer is negligible. Indications were obtained that the major portion of the polymeric material is composed of fully interlocked species