Jay J. Dunsford

Direct C(sp2)C(sp3) Cross‐Coupling of Diaryl Zinc Reagents with Benzylic, Primary, Secondary, and Tertiary Alkyl Halides

The direct C(sp(2) )-C(sp(3) ) cross-coupling of diaryl zinc reagents with benzylic, primary, secondary, and tertiary alkyl halides proceeded in the absence of coordinating ethereal solvents at ambient temperature without the addition of a catalyst. The C(sp(2) )-C(sp(3) ) cross-coupling showed excellent functional-group tolerance, and products were isolated in high yields, generally without the requirement for purification by chromatography. This process represents an expedient, operationally simple method for the construction of new C(sp(2) )-C(sp(3) ) bonds.

E–H (E = R3Si or H) bond activation by B(C6F5)3 and heteroarenes; competitive dehydrosilylation, hydrosilylation and hydrogenation

In the presence of B(C6F5)3 five-membered heteroarenes undergo dehydrosilylation and hydrosilylation with silanes. The former, favoured on addition of a weak base, produces H2 as a by-product making the process catalytic in B(C6F5)3 but also enabling competitive heteroarene hydrogenation.

A Zinc Catalyzed C(sp3)−C(sp2) Suzuki–Miyaura Cross-Coupling Reaction Mediated by Aryl-Zincates

Abstract The Suzuki–Miyaura (SM) reaction is one of the most important methods for C−C bond formation in chemical synthesis. In this communication, we show for the first time that the low toxicity, inexpensive element zinc is able to catalyze SM reactions. The cross‐coupling of benzyl bromides with aryl borates is catalyzed by ZnBr2, in a process that is free from added ligand, and is compatible with a range of functionalized benzyl bromides and arylboronic acid pinacol esters. Initial mechanistic investigations indicate that the selective in situ formation of triaryl zincates is crucial to promote selective cross‐coupling reactivity, which is facilitated by employing an arylborate of optimal nucleophilicity.

Highly nucleophilic dipropanolamine chelated boron reagents for aryl-transmetallation to iron complexes

New aryl- and heteroarylboronate esters chelated by dipropanolamine are synthesised directly from boronic acids. The corresponding anionic borates are readily accessible by deprotonation and demonstrate an increase in hydrocarbyl nucleophilicity in comparison to other common borates. The new borates proved competent for magnesium or zinc additive-free, direct boron-to-iron hydrocarbyl transmetallations with well-defined iron(II) (pre)catalysts. The application of the new borate reagents in representative Csp(2)-Csp(3) cross-coupling led to almost exclusive homocoupling unless coupling is performed in the presence of a zinc additive.

N-Heterocycle-Ligated Borocations as Highly Tunable Carbon Lewis Acids

The relative (to BEt3) hydride ion affinity (HIA) of a series of acridine borenium salts has been calculated, with some HIAs found to be similar to that for [Ph3C]+. The HIA at the acridine C9 position is controlled by both acridine and the boron substituents, the latter presumably affecting the strength of the B=N bond in the acridane-BY2 products from hydride transfer. Through a range of hydride abstraction benchmarking reactions against organic hydride donors the experimental HIA of [F5acr-BCat]+ (cat = catechol, F5acr = 1,2,3,4,7-pentafluoroacridine) has been confirmed to be extremely high and closely comparable to that of [Ph3C]+. The high HIA of [F5acr-BCat]+ enables H2 and alkene activation in a FLP with 2,6-di-tert-butylpyridine. Finally, the HIA of pyridine and quinoline borenium cations has been determined, with the HIA at boron in [PinB(amine)]+ (pin = pinacol, amine = pyridine or quinoline) found to be relatively low. This enabled the hydroboration of pyridine and quinoline by HBPin to be achieved through the addition of 5–10 mol % of bench-stable cationic carbon Lewis acids such as 2-phenyl-N,N-dimethylimidazolium salts.

CCDC 1836436: Experimental Crystal Structure Determination

Related Article: Daniel L. Crossley, Pakapol Kulapichitr, James E. Radcliffe, Jay J. Dunsford, Inigo Vitorica‐Yrezabal, Rachel J. Kahan, Adam W. Woodward, Michael L. Turner, Joseph J. W. McDouall, Michael J. Ingleson|2018|Chem.-Eur.J.|24|10521|doi:10.1002/chem.201801799

CCDC 1836437: Experimental Crystal Structure Determination

Related Article: Daniel L. Crossley, Pakapol Kulapichitr, James E. Radcliffe, Jay J. Dunsford, Inigo Vitorica‐Yrezabal, Rachel J. Kahan, Adam W. Woodward, Michael L. Turner, Joseph J. W. McDouall, Michael J. Ingleson|2018|Chem.-Eur.J.|24|10521|doi:10.1002/chem.201801799

CCDC 1836439: Experimental Crystal Structure Determination

Related Article: Daniel L. Crossley, Pakapol Kulapichitr, James E. Radcliffe, Jay J. Dunsford, Inigo Vitorica‐Yrezabal, Rachel J. Kahan, Adam W. Woodward, Michael L. Turner, Joseph J. W. McDouall, Michael J. Ingleson|2018|Chem.-Eur.J.|24|10521|doi:10.1002/chem.201801799

C-H Borylation / Cross Coupling Forms Twisted Donor-Acceptor Compounds Exhibiting Donor Dependent Delayed Emission.

Abstract Benzothiadiazole (BT) directed C−H borylation using BCl3, followed by B−Cl hydrolysis and Suzuki–Miyaura cross‐coupling enables facile access to twisted donor–acceptor compounds. A subsequent second C−H borylation step provides, on arylation of boron, access to borylated highly twisted D−A compounds with a reduced bandgap, or on B−Cl hydrolysis/cross‐coupling to twisted D‐A‐D compounds. Photophysical studies revealed that in this series there is long lifetime emission only when the donor is triphenylamine. Computational studies indicated that the key factor in observing the donor dependent long lifetime emission is the energy gap between the S1/T2 excited states, which are predominantly intramolecular charge‐transfer states, and the T1 excited state, which is predominantly a local excited state on the BT acceptor moiety.

Ring-expanded N-heterocyclic carbenes for copper-mediated azide-alkyne Click cycloaddition reactions

A series of well‐defined copper(I) complexes bearing ring‐expanded N‐heterocyclic carbene (NHC) ligands has been applied to the azide–alkyne cycloaddition reaction. The obtained results notably showed that the six‐membered NHC ligands outperform well‐established five‐membered ones. [CuI(Mes‐6)] displayed a remarkable catalytic activity while respecting the strict criteria for click reactions.