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].