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Borylation of cyclic aryl–alkyl sulfones gives boronate esters by selective cleavage of C(sp2)–SO2 or C(sp3)–SO2 bonds via Cu-mediated or Cu-free processes.

The use of transition metals to catalyse the addition of hydridoboranes to unsaturated organic molecules was initially realised several decades ago. Although this area of chemistry received considerable attention at the time, interest in this reaction and its use in organic synthesis waned for several years. Like a phoenix rising from the ashes, this amazing catalytic reaction has grown to include the use of earth-abundant metal catalysts and a much wider range of organic substrates. Indeed, it is now commonly utilised as a diagnostic tool to assess the reactivity and catalytic ability of newly generated transition metal and main group complexes. As this field is progressing so rapidly, this review highlights some important advances up to the end of 2021 and into early 2022. Excluded from this review are 'hydroboration' reactions using diboron sources.

The uncatalyzed addition of catecholborane to α-diimines has been examined. Reactions proceed smoothly at room temperature in the absence of a catalyst or additive, providing bis-hydroboration products with 3-coordinate boron centres or mono-hydroboration products with 4-coordinate boron centres, depending on the nature of the diimine reagent.

This investigation examines the reactivity of phosphinoboronate esters Ph2PBpin (pin = 1,2-O2C2Me4) and Ph2PBcat (cat = 1,2-O2C6H4), as well as other phosphinoboron species, with various aryl and aliphatic acyl chlorides. These reactions proceed smoothly to give acyl phosphines of the type RC(O)PR'2 along with loss of a boron-chloride compound. In some cases, a second equivalent of the phosphinoboron species can add to the C[double bond, length as m-dash]O double bond at elevated temperatures to give the corresponding diphosphines RC(OBR''2)(PR'2)2. These ambiphilic diphosphines behave like substituted (1,1-bis(diphenylphosphino)methane) derivatives in a reaction of PhC(OBpin)(PPh2)2 (2a) with (η5-C9H7)Rh(η2-coe)2 (coe = cis-cyclooctene) affording the indenyl rhodium complex (η5-C9H7)Rh(PhC(OBpin)(PPh2)2) (3a) where the phosphines are bound to the metal centre in a κ2-P,P bidentate manner.

A series of borylated conjugated trienes and skipped dienes is prepared by Ru-catalysed cross-dimerisation using alkynyl-, dienyl-, and vinyl boronates. These products are used as synthetic building blocks for polyene substructures by subsequent Pd-catalysed cross-coupling in a one-pot vessel without deprotection.

The reactions of the phosphinoboranes Ph2PBMes2, Ph2PBpin, and Ph2PBcat with the diazomethanes Ph2CN2, C12H8CN2, and EtO2CCHN2 are shown to give products of 1,1-phosphinoboration. The products (1–6) are shown to have PNB linkages with three-coordinate boron centers, whereas the products (EtOOC)CNN(PR2)(Bpin) (R = Ph 7, tBu 8) form zwitterionic heterocycles resulting from chelation of the ester carbonyl to boron. DFT calculations show that the reactions are initiated by N-to-B addition followed by 1,2-phosphinyl shift.

The stereoselective anti-addition of selenoboranes to α,β-acetylenic esters and amides was achieved in a transition metal-free context using catalytic amounts of PCy3. The reaction provides anti-3,4-selenoboration with concomitant delivery of α-vinyl selenides by protodeboronation with MeOH. Interestingly, in the absence of phosphine the selenoboration switches towards the formation of β-vinyl selenides. Theoretical calculations rationalize the regio- and stereoselectivity of the reaction by discovering a new mechanism for the anti-3,4-selenoboration. While the selenoborane is activated via the “push–pull” effect of B, the phosphine interacts with the β position of the alkynoate switching the polarity of the triple bond and favoring 1,3-selenoboration which provides the α-addition of the selenyl group. Then, the autocatalytic action of a second selenoborane reagent, which coordinates to the phosphorus ylide intermediate, determines the stereoselectivity and completes the catalytic process. Finally, the comparison of selenoborane reagents with diboranes and silaboranes, which have exhibited analogous reactivity, shows that the selenium moiety has a larger nucleophilic character favoring the performance of the reaction under mild conditions.

The transition metal-free addition of phosphinoboronate ester Ph2PBpin (pin = 1,2-O2C2Me4) to heterocumulenes including carbodiimides, isocyanates, isothiocyanates and carbon dioxide has been investigated. The corresponding 1,2-addition products were readily prepared at room temperature without the need of a catalyst or added base. Addition of methanol to the compounds derived from addition of Ph2PBpin to carbodiimides, isocyanates, and isothiocyanates resulted in traditional hydrophosphination products. The methodology developed in this study provides a simple and elegant route for the generation of a wide range of functionalized phosphines. The phosphinoboronate ester Ph2PBpin also selectively and reversibly adds to CO2 at room temperature in a 1,2-manner.

The effect of transition metals as components of the mobile phase on the retention of 2-aminophenol in high-performance liquid chromatography was studied on both ODS-silica and porous polymer columns. 2-Aminophenol formed charged 1 : 1 complexes with the metal ions to give a reduction in retention through a mechanism analogous to ion-pair chromatography. Different metal ions and a range of concentrations and eluent pHs were investigated.

Addition of boranes to N-aryl-salicylaldimines takes place initially at the reactive phenolic O-H bond to give an activated boron-containing imine and dihydrogen. In some cases a subsequent intramolecular hydrogenation step is observed and the C=N imine bond is reduced to the corresponding amine. Reactions with dimesitylborane in THF are unique in that the reduced amine product is the major product observed in solution.

The rhodium catalysed addition of pinacolborane to aminopropyl vinyl ethers gave selective formation of the corresponding alkenylboronate esters while palladium or platinum complexes catalysed the hydroamination of aminopropyl vinyl ether to give tetrahydro-2-methyl-1,3-oxazine.

Metal-catalysed addition of B2cat′2 (cat′ = 4-But-1,2-O2C6H3) to ketimines affords N-borylenamines and HBcat′. Analogous catalysed reactions of ketimines with HBcat′ in tetrahydrofuran afford multiply borated products, providing the first examples of metal-catalysed hydroboration of enamines.

Addition of catecholatoborane (HBcat), 1, to [RhCl(N2)(PPri3)2] gives the first structurally characterised, unsaturated boryl complex, [RhHCl(Bcat)(PPri3)2], whereas reaction of [{(Pri2PCH2)2}Rh(η3-2-Me-allyl)] with 2 equiv. of 1 affords [{(Pri2PCH2)2Rh{(η6-cat)Bcat}]via B-substituent redistribution; both complexes catalyse the hydroboration of oct-1-ene with 1

The synthesis and non-linear optical properties of a series of Icosahedral carboranes are described. The carboranes are substituted on both carbon atoms, with a series of electron-donating and electron-withdrawing substituents. The single-crystal X-ray structure of two of the series 1,2-bis(3-nitrophenyl)-1,2-dicarba-closo-dodecaborane(12), 1, and 1-(3-nitrophenyl)-2-(4-nitrophenyl)-1,2-dicarba-closo-dodecaborane, 3, are presented. 3 crystallises in the space group P, with four molecules per unit cell with cell dimensions of a= 9.706(1)A, b= 13.798(2)A, c= 17.99(2)A, α= 109.17(1)°, β= 100.86(1)° and γ= 101.78(1)°. 1 crystallises in the space group P, with two molecules per unit cell with cell dimensions of a= 7.585(2)A, b= 11.032(3)A, c= 12.252(4)A, α= 105.29(3)°, β= 90.30(3)° and γ= 96.46(2)°. The second-harmonic generation (SHG) properties of all of the compounds prepared are described, and are related to the ZINDO-SOS calculations of molecular polarisibility, β, computed for selected examples.

A model has been developed for predicting the effect of transition metals as components of the mobile phase in high-performance liquid chromatography on the retention of an analyte containing a chelating group. It takes into account the secondary chemical equilibria in solution, including the formation constants of the complexes, the pH of the mobile phase and the concentration of the metal ions. The model was tested by comparison with data determined for the retention of 2-aminophenol on a porous polystyrene-divinylbenzene polymer column in the presence of metal ions.