Recent Advances in the Synthesis of Borinic Acid Derivatives

Borinic acids [R2B(OH)] and their chelate derivatives are a subclass of organoborane compounds used in cross-coupling reactions, catalysis, medicinal chemistry, polymer or optoelectronics materials. In this paper, we review the recent advances in the synthesis of diarylborinic acids and their four-coordinated analogs. The main strategies to build up borinic acids rely either on the addition of organometallic reagents to boranes (B(OR)3, BX3, aminoborane, arylboronic esters) or the reaction of triarylboranes with a ligand (diol, amino alcohol, etc.). After general practical considerations of borinic acids, an overview of the main synthetic methods, their scope and limitations is provided. We also discuss some mechanistic aspects.

(2Sp,4R,8Sp)-4-Methyl-1-phenyl-diferroceno-5-Z-ethylene-1-phosphinoxide

We present a synthesis of the title compound, a homochiral diferroceno cycle intended for use in asymmetric catalysis. We present a hydrovinylation protocol, which allows the production of the title compound in two steps from a known diferrocenyl precursor. We obtained one of two possible diastereomers selectively and propose a plausible regio- and stereoselective reaction mechanism.

Frustrated Lewis pairs incorporating the bifunctional Lewis acid 1,1'-fc{B(C6F5)2}2: reactivity towards small molecules

Applications of the bifunctional ferrocenediyl Lewis acid 1,1'-fc{B(C₆F₅)₂}₂ in frustrated Lewis pair (FLP) chemistry are described. The coordination (or otherwise) of a range of sterically encumbered C-, N- and P-centred Lewis bases has been investigated, with lutidine, tetramethylpiperidine, PPh₃, P^tBu₃ and the expanded ring carbene 6Dipp being found to be sterically incapable of coordinate bond formation. The chemistry of a range of these FLPs in the presence of H₂O, NH₃, CO₂ and cyclohexylisocyanate (CyNCO) has been investigated, with the patterns of reactivity identified including simple coordination chemistry, E-H bond cleavage and C-B insertion.

Extension of conjugation: probing anion binding strength and reporter mechanisms in (phenyl)cyclopentadienyl and indenyl receptors

Two families of novel organo-iron functionalized boranes have been developed for anion binding/detection. Synthetically simple phenylferrocene systems, while stable to air and moisture, possess similar binding affinities to FcBMes2 and no workable discrimination between F(-) and CN(-). In addition, reduced electronic communication between receptor and reporter sites brought about by a lack of conformational rigidity means that photochemical and electrochemical responses to anion binding are intrinsically weak. Receptors based on a more rigid indenyl framework are available in two steps from organic precursors (in ca. 50% yield), and feature intrinsically higher binding constants for F(-) and especially CN(-), consistent with the lower LUMO energies implied by extended conjugation. One such system, (4-dimesitylboryl-indenyl)cyclopentadienyl-iron(ii), can be shown to bind cyanide in protic media with an accompanying green to red/pink colour change. Extremely high selectivity over fluoride and hydroxide and a detection limit of ca. 10 ppm represent a highly desirable combination among borane derived cyanide receptors.

MALDI-TOFMS analysis of coordination and organometallic complexes: a nic(h)e area to work in

A mini-review of the characterisation of metal-containing compounds by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS) is presented. Organometallic and coordination compounds have many varied applications, most notably in industrial catalytic processes and also in the electronics and healthcare sectors. In general, the compounds discussed, be they small or large molecules, have a high percentage metal content, rather than simply containing 'a metal atom'. A brief history of the field is given, but the main scope over the last 5 years is covered in some detail. How MALDI-TOFMS compliments electrospray for metal-containing compounds is highlighted. Perspectives on recent advances, such as solvent-free and air/moisture-sensitive sample preparation, and potential future challenges and developments, such as nanomaterials and metallodrug/metallometabolite imaging, are given.

Extending pi-conjugation of triarylborons with a 2,2-bpy core: impact of donor-acceptor geometry on luminescence, anion sensing, and metal ion binding

Four new 2,2'-bipyridine-based molecules functionalized by either BMes(2)-phenyl (Mes = mesityl) or NPh(2)-phenyl--5,5'-(p-BMes(2)-phenyl)(2)-2,2'-bpy (5,5'-BP2bpy, 1), 4,4'-(p-BMes(2)-phenyl)(2)-2,2'-bpy (4,4'-BP2bpy, 2), 4-(p-BMes(2)-phenyl)-4'-(p-NPh(2)-phenyl)-2,2'-bipy (4,4'-BPNPbpy, 4), and 4,4'-(p-NPh(2)-phenyl)(2)-2,2'-bpy (4,4'-NP2bpy, 5)--have been synthesized. Their complexes with PtPh(2) have been synthesized and fully characterized. The electronic and photophysical properties of the new molecules have been examined by electrochemical, absorption, and luminescence spectroscopic analysis and DFT calculations, which show significant differences from those of the related but smaller 2,2'-bpy derivatives functionalized directly by either BMes(2) or NPh(2) groups that we reported previously. Molecules 1, 2, and 4 and their Pt(II) complexes respond to fluoride ions in both absorption and emission modes. The donor-acceptor molecule 4 and its Pt(II) complex have a distinct fluorescence/phosphorescence turn-on response toward fluoride or cyanide ions. Molecules 1, 2, 4, and 5 also respond to Zn(II) ions in both absorption and emission modes. The diboryl molecules 1 and 2 have a distinct and contrasting fluorescence response toward Zn(II) ion--turn-off for 1 and turn-on for 2--demonstrating the significant impact of molecular geometry on metal ion binding and fluorescence.