Reaction of sterically encumbered phenols, TEMPO-H, and organocarbonyl insertion reactions with L-AlH2 (L = HC(MeCNDipp)2, Dipp = 2,6-diisopropylphenyl)

Abstract

The reaction of L-AlH₂ (L = HC(MeCNDipp)₂, Dipp = 2,6-diisopropylphenyl) with sterically bulky phenols (2,4,6-trimethylphenol, MesOH; 2,6-diisopropylphenol, DippOH) and an N-hydroxylamine (1-hydroxy-2,2,6,6-tetramethyl-piperidine, TEMPO-H) forms an Al–O bond with concomitant loss of hydrogen gas to give L-Al(H)OMes, L-Al(H)ODipp and L-Al(H)TEMPO, respectively. Reaction with 1 or 2 equivalents of benzaldehyde or 1 equivalent of benzophenone results in insertion of carbonyl into the Al–H bond(s) to give the related benzylate and diphenylmethoxide products. Compounds L-Al(H)OMes, L-Al(H)ODipp, L-Al(H)TEMPO, L-Al(H)OBn, L-Al(OBn)₂, and L-Al(H)OCHPh₂ have been characterized by NMR spectroscopy, elemental analysis, infrared spectroscopy and single crystal X-ray diffraction. The reaction of L-Al(H)OBn with pinacol borane gives a complex mixture of unidentifiable products, providing evidence of the importance of the triflate group in the known aldehyde and ketone hydroboration catalyst L-Al(H)OTf (OTf = CF₃SO₃⁻).