Switchable Haptotropic Migrations of Tricarbonylchromium Complexes of 1,2-Dihydro-2-phenyl-1,2-azaborine

1,2-Dihydro-2-phenyl-1,2-azaborine ( 5 ) reacts with Cr(CO) 3 (CH 3 CN) 3 in THF at 50 °C to form the Cr(CO) 3 complex 7 in which the chromium is η 6 -bound to the heterocyclic ring. Heating 7 in THF to 101 °C causes it to isomerize to complex 8, in which the chromium is η 6 -bound to the phenyl ring. The Cr(CO) 3 group of 8 may be switched back to the heterocyclic ring by base conversion to the anion 9, followed by thermal isomerization to anion 10 . Protonation of 10 re-forms 7 . The X-ray structure of 8 shows that the uncoordinated 1,2-dihydro-1,2 azaborine ring is aromatic.