Synthesis and structures of chromium tricarbonyl complexes of benzylic halides and benzylic alcohols

Abstract

Chromium tricarbonyl complexes of mono-, bis- and tris-(hydroxymethyl) substituted benzene have been prepared via direct thermolysis of the alcohol and chromium hexacarbonyl in dibutyl ether–THF. Conversion into the corresponding benzyl halide complexes has been carried out using either PBr₃, HBr (aq), HBr in glacial acetic acid or BX₃ (X = Cl, Br or I). A comparative study showed that PBr₃ and BBr₃ give similar yields and purity and are superior to HBr. Crystallographic studies have been carried out on three benzyl alcohol complexes [Cr{η⁶-C₆H₄(CH₂OH)₂-1,4}(CO)₃], [Cr{η⁶-C₆Me₄(CH₂OH)₂-1,4}(CO)₃] and [Cr{η⁶-C₆H₃(CH₂OH)₃-1,3,5}(CO)₃] and on two benzyl bromide complexes [Cr(η⁶-C₆H₅CH₂Br)(CO)₃] and [Cr{η⁶-C₆H₄(CH₂Br)₂-1,4}(CO)₃].