A stable ring-expanded NHC-supported copper boryl and its reactivity towards heterocumulenes

Abstract

Reaction of bis(pinacolato)diboron with (6-Dipp)CuOtBu generates a ring-expanded N-heterocyclic carbene supported copper(I) boryl, (6-Dipp)CuBpin. This compound showed remarkable stability and was characterised by NMR spectroscopy and X-ray crystallography. (6-Dipp)CuBpin readily...

The structures of ring-expanded NHC supported copper(i) triphenylstannyls and their phenyl transfer reactivity towards heterocumulenes

“…27 We also recently described the formation of (6-Dipp)CuBpin which showed profoundly greater stability than (IPr)CuBpin. 28 In order to explore the effect of RE-NHC ligands on copper (I) systems more thoroughly, and with the hope of gaining additional insight into the reactivity of copper(I)-triphenylstannyl systems, we set out to synthesise a range of systems of the form (RE-NHC)CuSnPh 3 .…”

Ring‐Expanded N‐Heterocyclic Copper(I) Boryl Complexes: The Structures of [(6‐Dipp)CuBcat], [(6‐Dipp)CuBneop], and [(6‐Dipp)CuBhex]

“…Such close approaches are absent in the structure of compound 1, but equivalent intramolecular contacts are present in our previously reported structure of [(6-Dipp)CuBpin]. [23] The metric parameters of the CÀ Cu-B core of this compound ([(6-Dipp)CuBpin]: C1À Cu1 1.9587 (12); Cu1À B1 2.0017(15) Å; C1À Cu1À B1 164.24(6)°) were similar to those of 3 suggesting that the Bhex and Bpin ligands share a similar steric demand despite their divergent OÀ BÀ O angles (O1À B1À O2: 3, 117.58 (16); [(6-Dipp)CuBpin], 108.32(11)°).…”

“…The presence of these short contacts may imply that ligand‐boryl interactions contribute to the decrease in the C−Cu‐B angle, or may instead simply reflect the consequence of forcing this angle away from linearity which must, by its nature, bring the carbene and boryl ligands closer together. Such close approaches are absent in the structure of compound 1 , but equivalent intramolecular contacts are present in our previously reported structure of [(6‐Dipp)CuBpin] [23] . The metric parameters of the C−Cu‐B core of this compound ([(6‐Dipp)CuBpin]: C1−Cu1 1.9587(12); Cu1−B1 2.0017(15) Å; C1−Cu1−B1 164.24(6)°) were similar to those of 3 suggesting that the Bhex and Bpin ligands share a similar steric demand despite their divergent O−B−O angles (O1−B1−O2: 3 , 117.58(16); [(6‐Dipp)CuBpin], 108.32(11)°).…”

“…We reported that ring‐expanded NHCs (RE‐NHCs) could also confer additional stability on copper boryl systems; the electronic and steric divergence of 6‐Dipp from its five‐membered cousin, IPr, allowed us to isolate [(6‐Dipp)CuBpin] which persisted in solution for weeks at room temperature. In contrast, [(IPr)CuBpin] decomposes within hours [23] . Diaminoborane derivatives have also been extensively explored by Kleeberg and co‐workers who reported a range of NHC‐copper diaminoboryls where the varying substitution on both the NHC and boron resulted in either monomeric or, in the case of smaller substituents, dimeric μ‐boryl systems [21,24] .…”

“…In contrast, [(IPr)CuBpin] decomposes within hours. [23] Diaminoborane derivatives have also been extensively explored by Kleeberg and co-workers who reported a range of NHC-copper diaminoboryls where the varying substitution on both the NHC and boron resulted in either monomeric or, in the case of smaller substituents, dimeric μ-boryl systems. [21,24] Following the significant effects on stability introduced by the relatively minor substitution of the IPr for 6-Dipp ligand in a (NHC)CuBpin complex that we recently reported, we set out investigate whether the 6-Dipp ligand could support a wider range of dialkoxyboryl fragments at copper.…”