H₂ activation using the first 1 : 1 : 1 hetero-tri(aryl)borane

Abstract

The first 1 : 1 : 1 hetero-tri(aryl)borane cleaves H2 with various Lewis bases, and its electrochemistry is studied.

Halogenated triarylboranes: synthesis, properties and applications in catalysis

“…74 The first halogenated triarylborane with three different aryl rings, B(C6F5)(C6Cl5)(3,5-(CF3)2C6H3), was prepared from borane dimethylsulfide through a five-step synthesis Scheme 12). 116 First, a single equivalent of Li(C6F5) was generated at -78 °C and was reacted with borane diimethylsulfide to form [[H3B(C6F5)] -. The excess hydride was abstracted with TMSCl to afford H2B(C6F5).…”

“…Finally, the bromoborane was reacted with half an equivalent of Zn(C6Cl5)2 to install the final aryl ring. 116 Heteroleptic boranes have also been formed as a result of decomposition in catalytic reactions. Whilst these may have been unwanted at the time, they may inspire novel methods of producing new complexes.…”

“…119 Scheme 12: Synthesis of B(C6F5)(C6Cl5)(3,5-(CF3)2C6H3). 116 Scheme 13: Decomposition routes to produce halogenated triarylboranes. [117][118][119]…”

Electrochemical Reduction of Homo– and Hetero–tri(aryl)borohydrides

“…These were characterised by multi-nuclear NMR spectroscopy ( Figure S1). 35 In all cases the borohydride is irreversibly oxidised at peak potentials (at 100 mV.…”

“…Our studies of the homo-and hetero-tri(aryl)borohydrides [HB(C 6 F 5 ) x {m,m-(CF 3 ) 2 C 6 H 3 } y (C 6 Cl 5 ) z ] −[H1] − -[H10] − , together with our previous studies of their parent boranes,35,36 allow for a complete assessment of the potential of the electrochemically coupled -frustrated Lewis pair concept 34. While each separate step occurs under appropriately mild conditions for at least one of thetri(aryl)boranes of interest: rapid heterolytic cleavage of H 2 in conjunction with a Lewis base to give a redox active borohydride for 1 -3 (for the entire series under less mild conditions and/or at There are no single species which will readily perform all steps under the conditions studied; leaving the NHC-stabilised borenium cation [( i PrN) 2 H 2 C 3 BC 9 H 14 ] + , as the only species which clearly acts as the Lewis acidic component of an electrochemically coupled -frustrated Lewis pair.…”