Fraser S. Pick

Anions are important hydrogen bond acceptors in a range of biological, chemical, environmental and medical molecular recognition processes. These interactions have been exploited for the design and synthesis of ditopic resorcinarenes as the hydrogen bond strength can be tuned through the modification of the substituent at the 2-position. However, many potentially useful compounds, especially those incorporating electron-withdrawing functionalities, have not been prepared due to the challenge of their synthesis: their incorporation slows resorcinarene formation that is accessed by electrophilic aromatic substitution. As part of our broader campaign to employ resorcinarenes as selective recognition elements, we need access to these specialized materials. In this article, we report a straightforward synthetic pathway for obtaining a 2-(carboxymethyl)-resorcinarene, and resorcinarene esters in general. We discuss the unusual conformation it adopts and propose that this arises from the electron-withdrawing nature of the ester substituents that renders them better hydrogen bond acceptors than the phenols, ensuring that each of them acts as a donor only. Density Functional Theory (DFT) calculations show that this conformation arises as a consequence of the unusual configurational isomerism of this compound and interruption of the archetypal hydrogen bonding by the ester functionality.

Anions are important hydrogen bond acceptors in a range of biological, chemical, environmental and medical molecular recognition processes. These interactions have been exploited for the design and synthesis of ditopic resorcinarenes as the hydrogen bond strength can be tuned through the modification of the substituent at the 2-position. However, many potentially useful compounds, especially those incorporating electron-withdrawing functionalities, have not been prepared due to the challenge of their synthesis: their incorporation slows resorcinarene formation that is accessed by electrophic aromatic substitution. As part of our broader campaign to employ resorcinarenes as selective recognition elements, we need access to these specialized materials, and in this article we report a straightforward synthetic pathway for obtaining a 2-(carboxymethyl)-resorcinarene, and resorcinarene esters in general. We discuss the unusual conformation it adopts, and propose that this arises from the electron-withdrawing nature of the ester substituents that renders them better hydrogen bond acceptors than the phenols, ensuring that each of those acts as a donor only. DFT calculations show that this conformation arises as a consequence of the unusual configurational isomerism of this compound and interruption of the archetypal hydrogen bonding by the ester functionality.

The redox behaviour of the dimeric tetrairon complex, ([fc(NPⁱPr₂)₂]Fe)₂ (where fc(NPⁱPr₂)₂ = 1,1′-(C₅H₄NPⁱPr₂)₂Fe) has been investigated.

A low-coordinate iron hydride complex bearing an unsymmetrical NpN (enamido–phosphinimine) ligand scaffold was synthesized and fully characterized. Insertion reactivity with azobenzene, 3-hexyne, and 1-azidoadamantane was explored, and the isolated products were analogous to previously reported β-diketiminate iron hydride insertion products. Surprisingly, the NpN iron hydride displays unprecedented reactivity toward hexafluorobenzene, affording an NpN iron fluoride complex and pentafluorobenzene as products. The NpN iron hydride is a precatalyst for catalytic hydro-defluorination of perfluorinated aromatics in the presence of silane. Kinetic studies indicated that the rate-determining step during catalysis involved silane.

The synthesis of enantiomerically pure pyridine-bridged phosphaalkene-oxazolines ArP═C(Ph)(2,6-C₅H₃NOx) (1, Ar = Mes/Mes*, Ox = CNOCH(i-Pr)CH₂/CNOCH(CH₂Ph)CH₂) is reported. This new ligand forms a κ(P), κ²(NN) dimeric complex with copper(I) (7) that dissociates into a cationic κ³(PNN) monomeric complex upon addition of a neutral ligand {[1a·CuL]OTf (8a–e): L = PPh₃ (a), P(OPh)₃ (b), 2,6-lutidine (c), 4-DMAP (d), 1-methylimidazole (e)}. The P–Cu bond lengths in 8 are influenced by the π-accepting/σ-donating properties of L, and this can be observed by changes in the δ³¹P_P═C NMR shift. The donor–acceptor properties in complexes of type 8 have also been investigated by UV/vis spectroscopy and density functional theory calculations.

A ferrocene-based bis(phosphinoamine) fc(NHPⁱPr₂)₂ has been deprotonated and used in salt metathesis reactions to form dimeric complexes ([fc(NPⁱPr₂)₂]M)₂ (M = Fe, Co). A novel coordination environment for Co(II) is observed including a weak but significant Fe–Co interaction, which was characterized using X-ray crystallography, Mössbauer spectroscopy, and VT-magnetometry. Density functional theory (DFT) calculations including natural bond order analysis provides further support for the interaction and suggests a combination of Fe → Co and Co → Fe interactions.

The reaction of 1 equiv of carbon dioxide with the dinuclear tetrahydride complex ([NPN]Ta)₂(μ-H)₄ [where NPN = PhP(CH₂SiMe₂NPh)₂] results in the formation of ([NPN]Ta)₂(μ-OCH₂O)(μ-H)₂ via a combination of migratory insertion and reductive elimination. The identity of the ditantalum complex containing a methylene diolate fragment was confirmed by single-crystal X-ray analysis, NMR analysis, and isotopic labeling studies. Density functional theory calculations were performed to provide information on the structure of the initial adduct formed and likely transition states and intermediates for the process.