INTRAMOLECULAR B-N COORDINATION IN BORATABENZENE COMPLEXES

The reaction of 1-chloro-1-boracyclohexa-2,5-diene with (3-(dimethylam ino)propyl)magnesium chloride followed by reaction with tert-butyllith ium in ether affords lithium 1-(3-(dimethylamino)pro pyl)boratabenzene (8). The reaction of 8 with Mn(CO)(3)(CH3CN)(3)PF6 affords 3-(dimethy lamino)propyl)boratabenzene]manganese(I) (15B). The crystal structure of 15B shows that it exists in the intramolecularly B-N-coordinated fo rm with a B-N bond distance of 1.716(5) Angstrom. However in toluene-d (s) solution 15B is in mobile equilibrium with its ring-opened isomer 15A. Using B-11 NMR spectroscopy the equilibrium constants for 15B --> 15A have been measured over the temperature range -35 to 48 degrees C , allowing evaluation of Delta H degrees (6.0 kcal/mol) and Delta S de grees (23 cal/mol K).