James E. Radcliffe

N-methyl-benzothiazolium salts as carbon Lewis acids for Si-H σ bond activation and catalytic (de)hydrosilylation.

Abstract N−Me‐Benzothiazolium salts are introduced as a new family of Lewis acids able to activate Si−H σ bonds. These carbon‐centred Lewis acids were demonstrated to have comparable Lewis acidity towards hydride as found for the triarylboranes widely used in Si−H σ‐bond activation. However, they display low Lewis acidity towards hard Lewis bases such as Et3PO and H2O in contrast to triarylboranes. The N−Me‐benzothiazolium salts are effective catalysts for a range of hydrosilylation and dehydrosilylation reactions. Judicious selection of the C2 aryl substituent in these cations enables tuning of the steric and electronic environment around the electrophilic centre to generate more active catalysts. Finally, related benzoxazolium and benzimidazolium salts were found also to be active for Si−H bond activation and as catalysts for the hydrosilylation of imines.

Frustrated Lewis Pair mediated 1,2-hydrocarbation of alkynes

Abstract Frustrated Lewis pair (FLP) chemistry enables a rare example of alkyne 1,2‐hydrocarbation with N‐methylacridinium salts as the carbon Lewis acid. This 1,2‐hydrocarbation process does not proceed through a concerted mechanism as in alkyne syn‐hydroboration, or through an intramolecular 1,3‐hydride migration as operates in the only other reported alkyne 1,2‐hydrocarbation reaction. Instead, in this study, alkyne 1,2‐hydrocarbation proceeds by a novel mechanism involving alkyne dehydrocarbation with a carbon Lewis acid based FLP to form the new C−C bond. Subsequently, intermolecular hydride transfer occurs, with the Lewis acid component of the FLP acting as a hydride shuttle that enables alkyne 1,2‐hydrocarbation.

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.

Synthesis, Characterization, and Functionalization of 1‐Boraphenalenes

Abstract 1‐Boraphenalenes have been synthesized by reaction of BBr3 with 1‐(aryl‐ethynyl)naphthalenes, 1‐ethynylnaphthalene, and 1‐(pent‐1‐yn‐1‐yl)naphthalene and they can be selectively functionalized at boron or carbon to form bench‐stable products. All of these 1‐boraphenalenes have LUMOs localized on the planar C12B core that are closely comparable in character to isoelectronic phenalenyl cations. In contrast to the comparable LUMOs, the aromatic stabilization of the C5B ring in 1‐boraphenalenes is dramatically lower than the C6 rings in phenalenyl cations. This is due to the occupied orbitals of π symmetry being less delocalised in the 1‐boraphenalenes.