Subporphyrinato Boron(III) Hydrides

Subporphyrinato boron­(III)
hydrides were prepared by reduction
of subpor­phyrinato boron­(III) methoxides with diisobutyl­aluminum
hydride (DIBAL-H) in good yields. The authenticity of the B–H
bond has been unambiguously confirmed by a 1H NMR signal
that appears as a broad quartet at −2.27 ppm with a large coupling
constant with the central 11B, characteristic B–H
infrared stretching frequencies, and single crystal X-ray diffraction
analysis. Red shifts in the corresponding absorption and fluorescence
profiles are accounted for in terms of the electron-donating nature
of the B-hydride. The hydridic character of subpor­phyrinato
boron­(III) hydrides has been demonstrated by the production of H2 via reaction with water or HCl, and controlled reductions
of aromatic aldehydes and imines in the presence of a catalytic amount
of Ph3C­[B­(C6F5)4].