Acyclic Boryl Complexes of Copper(I)

Reaction of (6-Dipp)CuOtBu (6-Dipp=C{NDippCH2}2CH2, Dipp=2,6-iPr2C6H3) with B2(OMe)4 provided access to (6-Dipp)CuB(OMe)2 via sigma-bond metathesis. (6-Dipp)CuB(OMe)2 was characterised by NMR spectroscopy and X-ray crystallography and shown to be a monomeric acyclic boryl of copper. (6-Dipp)CuB(OMe)2 reacted with ethylene and diphenylacetylene to provide insertion compounds into the Cu-B bond which were characterised by NMR spectroscopy in both cases and X-ray crystallography in the latter. It was also competent in the rapid catalytic deoxygenation of CO2 in the presence of excess B2(OMe)4. Alongside pi-insertion, (6-Dipp)CuB(OMe)2 reacted with LiNMe2 to provide a salt metathesis reaction at boron, giving (6-Dipp)CuB(OMe)NMe2, a second monomeric acyclic boryl, which also cuproborated diphenylacetylene. Computational interrogation validated these acyclic boryl species to be electronically similar to (6-Dipp)CuBpin. A ring-expanded NHC, 6-Dipp ((6-Dipp=C{NDippCH2}2CH2, Dipp=2,6-iPr2C6H3)), has been shown to support two acyclic boryls. Reaction of (6-Dipp)CuOtBu with B2(OMe)4 provided access to (6-Dipp)CuB(OMe)2, the first acyclic boryl of copper, which was shown to react similarly to its cyclic cousins. Remarkably, however, it could also be subjected to salt metathesis to access (6-Dipp)CuB(OMe)NMe2, the second acyclic boryl of copper.image

Automated summary

In this study, two acyclic boryl complexes, (6-Dipp)CuB(OMe)2 and (6-Dipp)CuB(OMe)NMe2, were synthesized and their similar reactivities were demonstrated.