An Enamine/HB(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub> Adduct as a Dormant State in Frustrated Lewis Pair Chemistry
dataset
posted on 2013-11-25, 00:00 authored by Bao-Hua Xu, Kathrin Bussmann, Roland Fröhlich, Constantin G. Daniliuc, Jan Gerit Brandenburg, Stefan Grimme, Gerald Kehr, Gerhard ErkerThe
enamine piperidinocyclopentene reacts with HB(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub> by formation of the C-Lewis base/B-Lewis
acid adduct <b>10</b>. It shows a zwitterionic iminium ion/hydridoborate
structure. However, this adduct formation is apparently reversible
and may generate the “invisible” frustrated Lewis pair <b>11</b> as a reactive intermediate by hydroboration of the enamine
CC bond in an equilibrium situation at room temperature. Consequently,
the FLP <b>11</b> was trapped by typical FLP reactions, namely
by the reaction with dihydrogen to give the ammonium/hydridoborate <b>12</b>, the acetylene deprotonation products <b>13</b> and <b>14</b>, and simple borane adducts with pyridine (<b>15</b>) and with an isonitrile (<b>17</b>). The products <b>10</b> and <b>12</b>–<b>15</b> and the isonitrile adduct <b>17</b> were characterized by X-ray diffraction. A DFT study determined
the thermodynamic features of the <b>10</b> ⇄ <b>11</b> equilibrium and of a previously discussed reference system (<b>18</b> ⇄ <b>19</b>) derived by reacting piperidinocyclohexene
with HB(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub>.
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