Planar, Three-Coordinate Boron Monohydrides Ligated by Bis(3-methylindolyl)methanes

Abstract

Reactions of tris(3-methylindolyl)methane, bis(3-methylindolyl)-2-methoxyphenylmethane, and bis(3-methylindolyl)phenylmethane with THF·BH3 result in hydrogen elimination and yield the corresponding boron monohydride complexes (3-CH3C8H4NH)HC(3-CH3C8H4N)2BH (6), (2-CH3OC6H4)HC(3-CH3C8H4N)2BH (7), and PhHC(3-CH3C8H4N)2BH (8), respectively. Compositions and structures were confirmed by NMR (1H, 11B, 13C) and IR spectroscopy, elemental analysis, and X-ray crystallography. The molecular structures of 6–8 each possess a trigonal-planar boron atom which resides in the plane of a bidentate diindolylmethane ligand. This planarity, the lack of Lewis acid–base complexation in the presence of THF, and the short B–N distances suggest significant N→B π donation. Thermolysis of 6 did not produce the three-coordinate, pyramidal borane HC(3-CH3C8H4N)3B or a tripodal, four-coordinate acid–base complex, presumably due to the significant B–N π bonding in 6. The planarity of 6–8 and the isoelectronic relationship of BH to C: suggest that diindolylmethanes may be useful platforms for the preparation of a new family of N-heterocyclic carbenes.

Boron, aluminium, gallium, indium and thallium

“…158 (b-Diketiminate)BX 2 (X = F or Cl) complexes reacted with strong bases by deprotonation and subsequent cyclopropanation of a tBu substituent, 159 whilst one electron reduction with KC 8 led to a delocalised radical, with reactivity studies suggesting significant boryl radical character. 160 A number of cyclic-aza and -diazaboranes have been synthesised, [161][162][163] including pentaaryl-substituted diazaboroles. 164 The benzodiazaborolyl moiety was used as a p electron donor, with donor power calculated to be intermediate to that of dimethylamino-and methoxy-groups, with the -BMes 2 group used as the acceptor unit.…”

Synthesis and crystal structures of some bis(3-methyl-1H-indol-2-yl)(salicyl)methanes

“…Recently, 2,2 0 ,2 00 -TIMs [see (b) in Scheme 1] and 2,2 0 -BIMs [see (c) in Scheme 1] have attracted greater interest because of their potential as ligands (Mason, 2003;Bakthadoss et al, 2015). Structural data has been reported for poly(indol-2-yl)methanes bonded through the indole N atom to main-group elements from group 13 (B, Al, and Ga) (Fneich et al, 2018;Song et al, 2012;Kingsley et al, 2010), group 14 (Si) (Mason, 2003), and group 15 (P and Sb) (Mason, 2003;Mallov et al, 2012). Similar bonding patterns have been reported for group 4 metals (Ti and Zr) (Mason, Fneich et al, 2003;Mason, 2003;Mason et al, 2005).…”

Intramolecular Hydride Transfer Reactions in (Formazanate)Boron Dihydride Complexes

“…In 2004, Hey-Hawkins and co-workers reported a series of intramolecularly base-stabilized borane compounds with six- and seven-membered chelate rings ( A ) . In 2012, several three-coordinate boron monohydride complexes ligated by the bis­(3-methylindolyl)­methanes ( B ) were reported by Mason and co-workers . Piers and co-workers indicated the formation of an unstable dipyrrinato boron dihydride complex ( C ) by UV–vis absorption and emission spectroscopy .…”