(Dimethylamino)borylene and Related Complexes of Electron-Rich Metal Fragments: Generation of Nucleophile-Resistant Cations by Spontaneous Halide Ejection

David A. Addy, Nicholas Phillips, Glesni A. Pierce, Dragoslav Vidovic, Tobias Kraemer, Dibyendu Mallick, Eluvathingal D. Jemmis, Gill Reid, Simon Aldridge

Research output: Contribution to journalArticle

Abstract

Spontaneous halide ejection from a three-coordinate Lewis acid has been shown to offer a remarkable new route to cationic metal complexes featuring a linear, multiply bonded boron-donor Ligand. The exploitation of electron-rich [CpM(PR3)(2)] fragments within boryl systems of the type LnMB(hal)NR2 leads to the spontaneous formation in polar solvents of chemically robust borylene complexes, [LnM(BNR2)](+), with exceptionally low electrophilicity and short M-B bonds. This is reflected by M-B distances (ca. 1.80 angstrom for FeB systems) which are more akin to alkyl-/aryl-substituted borylene complexes and, perhaps most strikingly, by the very low exothermicity associated with the binding of pyridine to the two-coordinate boron center (Delta H = -7.4 kcal mol(-1), cf. -40.7 kcal mol(-1) for BCl3). Despite the strong pi electron release from the metal fragment implied by this suppressed reactivity and by such short M-B bonds, the barrier to rotation about the Fe=B bond in the unsymmetrical variant [CpFe(dmpe)(BN{C6H4OMe-4}Me)](+) is found to be very small (ca. 2.9 kcal mol(-1)). This apparent contradiction is rationalized by the orthogonal orientations of the HOMO and HOMO-2 orbitals of the [CpML2](+) fragment, which mean that the M-B pi interaction does not fall to zero even in the highest energy conformation.

Original languageEnglish
Pages (from-to)1092-1102
Number of pages11
JournalOrganometallics
Volume31
Issue number3
DOIs
Publication statusPublished - 13 Feb 2012

Keywords

  • TERMINAL BORYLENE COMPLEXES
  • C-H ACTIVATION
  • REACTION CHEMISTRY
  • DOUBLE-BONDS
  • AMINOBORYLENE COMPLEXES
  • ABSTRACTION CHEMISTRY
  • METATHESIS CHEMISTRY
  • SILYLENE COMPLEXES
  • TRANSITION-METALS
  • LIGAND SYSTEMS

Cite this

Addy, D. A., Phillips, N., Pierce, G. A., Vidovic, D., Kraemer, T., Mallick, D., Jemmis, E. D., Reid, G., & Aldridge, S. (2012). (Dimethylamino)borylene and Related Complexes of Electron-Rich Metal Fragments: Generation of Nucleophile-Resistant Cations by Spontaneous Halide Ejection. Organometallics, 31(3), 1092-1102. https://doi.org/10.1021/om201144e