Borylene

A borylene is the boron analogue of an carbene. [1] [2] [3] The general structure is R-B: with R an organic residue and B a boron atom with two unshared electrons. Borylenes are of some academic interest in the field of chemistry. A singlet ground state is predominant with boron having two vacant sp2 orbitals and one doubly occupied one. With just one additional substituent the boron is more electron deficient than the carbon atom in a carbene. For this reason stable borylenes are more uncommon than stable carbenes. Some borylenes such as boron monofluoride and boron monohydride have been detected in microwave spectroscopy. Other borylenes exist as reactive intermediates and can only be inferred by chemical trapping.

The first stable borylene ((CO)5WBN(SiMe3)2) was reported in 1998. [4] [5] In this compound a borylene was coordinated to a transition metal as a ligand. Another way to stabilise borylenes is as mono Lewis base adduct with a NHC carbene, in one exploit the key intermediate was found to dimerise to the diborene with a double boron-boron bond [6]. Other strategies are the use of cyclic alkyl amino carbenes (CAAC) [7] and their use as bis-adducts. [8]

References

  1. ↑ Braunschweig, H. and Colling, M. (2003), The Chemistry of Borylene Complexes. Eur. J. Inorg. Chem., 2003: 393–403. doi:10.1002/ejic.200390054
  2. ↑ Soleilhavoup, M. and Bertrand, G. (2017), Borylenes: An Emerging Class of Compounds. Angew. Chem. Int. Ed.. doi:10.1002/anie.201705153
  3. ↑ Transition metal borylene complexes Holger Braunschweig, Rian D. Dewhurst and Viktoria H. Gessner Chem. Soc. Rev., 2013,42, 3197-3208 doi:10.1039/C3CS35510A
  4. ↑ Braunschweig, H., Kollann, C. and Englert, U. (1998), Synthesis and Structure of the First Terminal Borylene Complexes. Angew. Chem. Int. Ed., 37: 3179–3180. doi: 10.1002/(SICI)1521-3773(19981204)37:22<3179::AID-ANIE3179>3.0.CO;2-Z
  5. ↑ Reactivity of Transition-Metal Borylene Complexes: Recent Advances in B–C and B–B Bond Formation via Borylene Ligand Coupling Holger Braunschweig and Rong Shang Inorg. Chem., 2015, 54 (7), pp 3099–3106 doi:10.1021/acs.inorgchem.5b00091
  6. ↑ A Stable Neutral Diborene Containing a BB Double Bond Yuzhong Wang , Brandon Quillian , Pingrong Wei , Chaitanya S. Wannere , Yaoming Xie , R. Bruce King , Henry F. Schaefer , III, Paul v. R. Schleyer , and Gregory H. Robinson J. Am. Chem. Soc., 2007, 129 (41), pp 12412–12413 doi:10.1021/ja075932i
  7. ↑ Dahcheh, F., Martin, D., Stephan, D. W. and Bertrand, G. (2014), Synthesis and Reactivity of a CAAC–Aminoborylene Adduct: A Hetero-Allene or an Organoboron Isoelectronic with Singlet Carbenes. Angew. Chem. Int. Ed., 53: 13159–13163. doi:10.1002/anie.201408371
  8. ↑ Synthesis and Characterization of a Neutral Tricoordinate Organoboron Isoelectronic with Amines Rei Kinjo, Bruno Donnadieu, Mehmet Ali Celik, Gernot Frenking, Guy Bertrand Science 2011 Vol. 333, Issue 6042, pp. 610-613 doi:10.1126/science.1207573
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