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Synthesis of Electrophiles Derived from Dimeric Aminoboranes and Assessing Their Utility in the Borylation of π Nucleophiles.
- Source :
-
Organometallics [Organometallics] 2022 Sep 26; Vol. 41 (18), pp. 2638-2647. Date of Electronic Publication: 2022 Sep 14. - Publication Year :
- 2022
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Abstract
- Dimeric aminoboranes, [H <subscript>2</subscript> BNR <subscript>2</subscript> ] <subscript>2</subscript> (R = Me or CH <subscript>2</subscript> CH <subscript>2</subscript> ) containing B <subscript>2</subscript> N <subscript>2</subscript> cores, can be activated by I <subscript>2</subscript> , HNTf <subscript>2</subscript> (NTf <subscript>2</subscript> = [N(SO <subscript>2</subscript> CF <subscript>3</subscript> ) <subscript>2</subscript> ]), or [Ph <subscript>3</subscript> C][B(C <subscript>6</subscript> F <subscript>5</subscript> ) <subscript>4</subscript> ] to form isolable H <subscript>2</subscript> B(μ-NR <subscript>2</subscript> ) <subscript>2</subscript> BHX (for X = I or NTf <subscript>2</subscript> ). For X = [B(C <subscript>6</subscript> F <subscript>5</subscript> ) <subscript>4</subscript> ] <superscript>-</superscript> further reactivity, presumably between [H <subscript>2</subscript> B(μ-NMe <subscript>2</subscript> ) <subscript>2</subscript> BH][B(C <subscript>6</subscript> F <subscript>5</subscript> ) <subscript>4</subscript> ] and aminoborane, forms a B <subscript>3</subscript> N <subscript>3</subscript> -based monocation containing a three-center two electron B-(μ-H)-B moiety. The structures of H <subscript>2</subscript> B(μ-NMe <subscript>2</subscript> ) <subscript>2</subscript> BH(I) and [(μ-NMe <subscript>2</subscript> )BH(NTf <subscript>2</subscript> )] <subscript>2</subscript> indicated a sterically crowded environment around boron, and this leads to the less common O-bound mode of NTf <subscript>2</subscript> binding. While the iodide congener reacted very slowly with alkynes, the NTf <subscript>2</subscript> analogues were more reactive, with hydroboration of internal alkynes forming (vinyl) <subscript>2</subscript> BNR <subscript>2</subscript> species and R <subscript>2</subscript> NBH(NTf <subscript>2</subscript> ) as the major products. Further studies indicated that the B <subscript>2</subscript> N <subscript>2</subscript> core is maintained during the first hydroboration, and that it is during subsequent steps that B <subscript>2</subscript> N <subscript>2</subscript> dissociation occurs. In the mono-boron systems, for example, <superscript> i </superscript> Pr <subscript>2</subscript> NBH(NTf <subscript>2</subscript> ), NTf <subscript>2</subscript> is N-bound; thus, they have less steric crowding around boron relative to the B <subscript>2</subscript> N <subscript>2</subscript> systems. Notably, the monoboron systems are much less reactive in alkyne hydroboration than the B <subscript>2</subscript> N <subscript>2</subscript> -based bis-boranes, despite the former being three coordinate at boron while the latter are four coordinate at boron. Finally, these B <subscript>2</subscript> N <subscript>2</subscript> electrophiles are much more prone to dissociate into mono-borane species than pyrazabole [H <subscript>2</subscript> B(μ-N <subscript>2</subscript> C <subscript>3</subscript> H <subscript>3</subscript> )] <subscript>2</subscript> analogues, making them less useful for the directed diborylation of a single substrate.<br />Competing Interests: The authors declare no competing financial interest.<br /> (© 2022 The Authors. Published by American Chemical Society.)
Details
- Language :
- English
- ISSN :
- 0276-7333
- Volume :
- 41
- Issue :
- 18
- Database :
- MEDLINE
- Journal :
- Organometallics
- Publication Type :
- Academic Journal
- Accession number :
- 36185396
- Full Text :
- https://doi.org/10.1021/acs.organomet.2c00393