Journal of the American Chemical Society
Journal of the American Chemical Society
5 years ago

New Scandium Borylimido Chemistry: Synthesis, Bonding, and Reactivity

New Scandium Borylimido Chemistry: Synthesis, Bonding, and Reactivity
Simona Mellino, Benjamin A. Clough, Philip Mountford, Eric Clot
We report a combined synthetic, mechanistic, and theoretical study of the first borylimido complex of a rare earth metal, (NacNacNMe2)Sc{NB(NAr′CH)2} (25, Ar′ = 2,6-C6H3iPr2, NacNacNMe2 = Ar′NC(Me)CHC(Me)NCH2CH2NMe2). Thermolysis of the methyl-borylamide (NacNacNMe2)Sc(Me){NHB(NAr′CH)2} (18) generated transient imide 25 via rate-determining, first-order methane elimination (KIE ≈ 8.7). In the absence of external substrate, 25 underwent a reversible cyclometalation reaction (sp3 C–H bond addition to Sc═Nimide) with a methyl group of the NacNacNMe2 ligand forming {MeC(NC6H3iPrCH(Me)CH2)CHC(Me)NCH2CH2NMe2}Sc{NHB(NAr′CH)2} (21). In the presence of pyridine or DMAP, reversible sp2 C–H bond activation occurred, forming orthometalated complexes (NacNacNMe2)Sc{NHB(NAr′CH)2}(η2-4-NC5H3R) (R = H or NMe2). In situ reaction of 25 with HCCTol gives irreversible sp C–H bond activation under kinetic control, and with MeCCPh [2+2] cycloaddition to Sc═Nimide takes place. These reactions represent the first substrate activation processes for any metal-bound borylimide. The bonding in 25 and the mechanism and thermodynamics of the reactions have been studied using density functional theory (DFT), supported by quantum theory of atoms in molecules and natural bond orbital analysis. Although the borylimido and arylimido dianions studied here are formally isoelectronic and possess comparable frontier molecular orbitals, the borylimido ligand is both a better π-donor and σ-donor, forming stronger and shorter metal–nitrogen bonds with somewhat reduced ionicity. Despite this, reactions of these types of borylimides with C–H or C≡C bonds are all more exothermic and more strongly activating than for the corresponding arylimides. DFT calculations on model systems of differing steric bulk unpicked the underlying thermodynamic factors controlling the reactions of 25 and its reaction partners, and a detailed comparison was made with the previously described arylimido homologues.

Publisher URL: http://dx.doi.org/10.1021/jacs.7b05405

DOI: 10.1021/jacs.7b05405

You might also like
Discover & Discuss Important Research

Keeping up-to-date with research can feel impossible, with papers being published faster than you'll ever be able to read them. That's where Researcher comes in: we're simplifying discovery and making important discussions happen. With over 19,000 sources, including peer-reviewed journals, preprints, blogs, universities, podcasts and Live events across 10 research areas, you'll never miss what's important to you. It's like social media, but better. Oh, and we should mention - it's free.

  • Download from Google Play
  • Download from App Store
  • Download from AppInChina

Researcher displays publicly available abstracts and doesn’t host any full article content. If the content is open access, we will direct clicks from the abstracts to the publisher website and display the PDF copy on our platform. Clicks to view the full text will be directed to the publisher website, where only users with subscriptions or access through their institution are able to view the full article.