Isolation of Reactive Main Group Species by Anionic N-Heterocyclic Olefin and Terphenyl Ligands

• Author / Creator

  Baird, Samuel R.

• The work in this Thesis describes the preparation of a new vinylithium reagent, [(MeIPrCH)Li]2 (MeIPr = (MeCNDipp)2C:; Dipp = 2,6-iPr2C6H3), which was utilized as a general source for the anionic N-heterocyclic olefin (aNHO) [(MeIPrCH)]–, a potential 2σ, 2π-electron donor. Utilizing [(MeIPrCH)Li]2, a complete acyclic divinyltetrelene series (MeIPrCH)2E: (E = Si – Pb) was prepared with (MeIPrCH)2Si: being the first example of a stable two-coordinate acyclic diorganosilylene. Notably, (MeIPrCH)2Si: exhibits dual nucleophilic and electrophilic character at the Si(II) center. The efficacy of [(MeIPrCH)Li]2 to stabilize low-valent main group elements was extended to the Group 13 elements, with a tetrahedron-shaped indium(I) tetramer, [(MeIPrCH)In]4, supported by aNHOs being described. Scission of the indium(I) tetramer was possible upon the addition of a strong Lewis base affording monomeric units that exhibit both electrophilic and nucleophilic characteristics. This indium(I) tetramer was also found to be highly reactive with the activation of strong H–B bonds in boranes by the In(I) centers, while the steric profile of the aNHO allowed for the isolation of a rare neutral indium-imide, RInNR'. The synthesis of a related aNHO synthon, [(SIPrCH)Li]2 (SIPr = (H2CNDipp)2C:), is also described. Next, the preparation of a diborene (RB=BR) stabilized by aNHOs was explored. The precursor (SIPrCH)ClB-BCl(CHSIPr) was prepared in high yield by combining [(SIPrCH)Li]2 with Me2S•Cl2B-BCl2•SMe2. Unfortunately, attempts to reduce (SIPrCH)ClB-BCl(CHSIPr) gave exclusively decomposition/hydrolysis and, in one instance, a C-N ligand activation product which may have been formed by a transient diborene. Computationally, it was found that the theoretical diborene, (MeIPrCH)B=B(CHMeIPr) will likely exist in a triplet ground state. The synthesis of an aminoborane supported by a sterically demanding terphenyl ligand (an inorganic analogue to styrene), ArDippB(H)=NH2 (ArDipp = 2,6-Dipp2C6H3), was investigated. First, the terphenyl-supported amine-borane adduct ArDippBH2•NH3, was prepared in high yield in an efficient one-pot synthesis by combining ArDippLi and Me2S•BH3, followed by the addition of excess [NH4]Cl, liberating H2, LiCl and SMe2 as by-products. ArDippBH2•NH3 could be dehydrogenated further to give the target species ArDippB(H)=NH2 by using a catalytic amount of [Rh(COD)Cl]2 (COD = 1,5-cyclooctadiene). Unfortunately, attempts to dehydrogenate ArDippB(H)=NH2 further were unsuccessful, possibly due to the low hydridic character within the boron-bound hydrides. Lastly, the bulky N-heterocyclic carbene (NHC) MeITr (MeITr = (MeCNCPh3)2C:) was prepared by incorporating methyl groups in the backbone of the heterocyclic ring forcing the nitrogen-bound trityl groups forward to further protect the coordination pocket of the carbene. This arrangement raises the percent buried volume (%VBur) to an astounding 72.6 %, making MeITr the world’s bulkiest NHC to date.

• Subjects / Keywords

  • Main Group
  • Indium
  • N-Heterocyclic Olefin

• Graduation date

  Fall 2024

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-3h33-ax88

• License

  This thesis is made available by the University of Alberta Library with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.