Intramolecular B−N Coordination in Boratabenzene Complexes

The reaction of 1-chloro-1-boracyclohexa-2,5-diene with (3-(dimethylamino)propyl)magnesium chloride followed by reaction with tert-butyllithium in ether affords lithium 1-(3-(dimethylamino)propyl)boratabenzene (8). The reaction of 8 with Mn(CO)3(CH3CN)3PF6 affords tricarbonyl[1-(3-(dimethylamino)propyl)boratabenzene]manganese(I) (15B). The crystal structure of 15B shows that it exists in the intramolecularly B−N-coordinated form with a B−N bond distance of 1.716(5) Å. However in toluene-d 8 solution 15B is in mobile equilibrium with its ring-opened isomer 15A. Using 11B NMR spectroscopy the equilibrium constants for 15B → 15A have been measured over the temperature range −35 to 48 °C, allowing evaluation of ΔH° (6.0 kcal/mol) and ΔS° (23 cal/mol K).