Two series of structurally related alkoxy-tethered NHC iron(II) complexes have been developed as catalysts for the regioselective hydroboration of alkenes. Significantly, Markonikov selective alkene hydroboration with HBpin has been controllably achieved using an iron catalyst (11 examples 35-90% isolated yield) with up to 37:1 branched:linear selectivity. anti-Markovnikov selective alkene hydroboration was also achieved using HBcat and modification of the ligand backbone (6 examples, 44-71% yields). In both cases, ligand design has enabled activator-free low oxidation-state iron catalysis.

Four-membered rings with a P BCh core (Ch=S, Se) have been synthesized by the reaction of phosphinidene chalcogenide (Ar*P=Ch) and phosphaborene (Mes*P=BNR ). The mechanistic pathways towards these rings are explained by detailed computational work that confirmed the preference for the formation of P-P, not P-B, bonded systems, which seems counterintuitive given that both phosphorus atoms contain bulky ligands. The reactivity of the newly synthesized heterocycles, as well as that of the known (RPCh) rings (n=2, 3), was probed by the addition of N-heterocyclic carbenes, which revealed that all investigated compounds can act as sources of low-coordinate phosphorus species.

Dimeric aminoboranes, [H 2 BNR 2 ] 2 (R = Me or CH 2 CH 2 ) containing B 2 N 2 cores, can be activated by I 2 , HNTf 2 (NTf 2 = [N(SO 2 CF 3 ) 2 ]), or [Ph 3 C][B(C 6 F 5 ) 4 ] to form isolable H 2 B(μ-NR 2 ) 2 BHX (for X = I or NTf 2 ). For X = [B(C 6 F 5 ) 4 ] − further reactivity, presumably between [H 2 B(μ-NMe 2 ) 2 BH][B(C 6 F 5 ) 4 ] and aminoborane, forms a B 3 N 3 -based monocation containing a three-center two electron B-(μ-H)-B moiety. The structures of H 2 B(μ-NMe 2 ) 2 BH(I) and [(μ-NMe 2 )BH(NTf 2 )] 2 indicated a sterically crowded environment around boron, and this leads to the less common O-bound mode of NTf 2 binding. While the iodide congener reacted very slowly with alkynes, the NTf 2 analogues were more reactive, with hydroboration of internal alkynes forming (vinyl) 2 BNR 2 species and R 2 NBH(NTf 2 ) as the major products. Further studies indicated that the B 2 N 2 core is maintained during the first hydroboration, and that it is during subsequent steps that B 2 N 2 dissociation occurs. In the mono-boron systems, for example, i Pr 2 NBH(NTf 2 ), NTf 2 is N-bound; thus, they have less steric crowding around boron relative to the B 2 N 2 systems. Notably, the monoboron systems are much less reactive in alkyne hydroboration than the B 2 N 2 -based bis-boranes, despite the former being three coordinate at boron while the latter are four coordinate at boron. Finally, these B 2 N 2 electrophiles are much more prone to dissociate into mono-borane species than pyrazabole [H 2 B(μ-N 2 C 3 H 3 )] 2 analogues, making them less useful for the dir...

Two templates used in meta-directed CÀ H functionalisation under metal catalysis do not direct meta-CÀ H borylation under electrophilic borylation conditions. Using BCl 3 only Lewis adduct formation with Lewis basic sites in the template is observed. While combining BBr 3 and the template containing an amide linker only led to amide directed ortho CÀ H borylation, with no pyridyl directed meta borylation. The amide directed borylation is selective for the ortho borylation of the aniline derived unit in the template, with no ortho borylation of the phenylacetyl ring -which would also form a six membered boracycle -observed. In the absence of other aromatics amide directed ortho borylation on to phenylacetyl rings can be achieved. The absence of meta-borylation using two templates indicates a higher barrier to pyridyl directed meta borylation relative to amide directed ortho borylation and suggests that bespoke templates for enabling meta-directed electrophilic borylation may be required.

Amide directed C-H borylation using two equiv. of BBr3 forms borenium cations containing a R2N(R’)C=O→B(Ar)Br unit which has significant Lewis acidity at the carbonyl carbon. This enables reduction of the...