Metal−Carbon and Carbon−Oxygen Related Reactivity in Tantalum p-tert-Butylcalix[4]arene Complexes Undergoing Organic Functionalization

[(Calix[4]OMe)TaCl<INF>2</INF>] (<BO>2</BO>), formed from [calix[4](OMe)<INF>2</INF>] (<BO>1</BO>) and TaCl<INF>5</INF> via a demethylation reaction, undergoes exhaustive alkylation to [(calix[4]OMe)TaR<INF>2</INF>] (<BO>3</BO>−<BO>5</BO>), which give photochemically or thermally induced concerted dealkylation at the metal and at the methoxy group, to give [calix[4]TaR] (<BO>6</BO>−<BO>8</BO>). Double migration of alkyl groups has been observed in the reaction of <BO>3</BO>−<BO>5</BO> with CO and Bu<BO>^t</BO>NC to form the corresponding η²-ketones [(calix[4]OMe)Ta(η²-COR<INF>2</INF>)] (<BO>9</BO>−<BO>11</BO>) and η²-imines [(calix[4]OMe)Ta{η²-N(Bu^t)CR<INF>2</INF>}] (<BO>12</BO>−<BO>14</BO>).