Molybdenum Tricarbonyl Complexes of 1-Substituted Borepins

The reaction of 1-substituted borepins C<INF>6</INF>H<INF>6</INF>BX, where X = Me, Ph, and Cl, with Py<INF>3</INF>Mo(CO)<INF>3</INF> and BF<INF>3</INF>·OEt<INF>2</INF> affords the corresponding borepin molybdenum tricarbonyl complexes. Similar reaction of 1-methoxyborepin affords (C<INF>6</INF>H<INF>6</INF>BF)Mo(CO)<INF>3</INF>. The reaction of (C<INF>6</INF>H<INF>6</INF>BCl)Mo(CO)<INF>3</INF> with appropriate nucleophiles affords the boron-substituted complexes (C<INF>6</INF>H<INF>6</INF>BX)Mo(CO)<INF>3</INF>, where X = H, OCH<INF>3</INF>, OH, O<INF>1/2</INF>, N(iPr)<INF>2</INF>, N(CH<INF>2</INF>)<INF>5</INF>, N(c-C<INF>6</INF>H<INF>11</INF>)<INF>2</INF>, and NBnMe. All complexes (C<INF>6</INF>H<INF>6</INF>BX)Mo(CO)<INF>3</INF> have been compared using ¹H NMR, ¹¹B NMR, and ¹³C NMR spectroscopies. The X-ray structure of (C<INF>6</INF>H<INF>6</INF>BN(iPr)<INF>2</INF>)Mo(CO)<INF>3</INF> shows that Mo is η⁶-coordinated to the ring carbon atoms but not to B. Rates of rotation about the B−N bonds of (C<INF>6</INF>H<INF>6</INF>BN(iPr)<INF>2</INF>)Mo(CO)<INF>3</INF> and (C<INF>6</INF>H<INF>6</INF>BNBnMe)Mo(CO)<INF>3</INF> have been measured using variable-temperature NMR spectroscopy.