Reactions of a Cationic Geminal Zr⁺/P Pair with Small Molecules

Abstract

The metallocene cation complex [Cp*₂ZrCH₃]⁺[B­(C₆F₅)₄]⁻ inserts the phosphino-substituted alkyne Ph–CC–PPh₂ into the [Zr]-CH₃ bond to form the internally phosphane-stabilized cation [Cp*₂Zr–C­(CMePh)­PPh₂]⁺ (<b>10</b>). Complex <b>10</b> adds alkyl isocyanides as well as pivalonitrile at a lateral site at the bent metallocene wedge with retention of the Zr–P bond. Complex <b>10</b> acts as a reactive frustrated Lewis pair toward heterocumulenes, undergoing Zr⁺/P addition reactions to the carbonyl groups of an alkyl isocyanate and of carbon dioxide to form the respective five-membered metallaheterocyclic adducts <b>13</b> and <b>14</b>. With mesityl azide complex <b>10</b> undergoes a Zr⁺/P FLP N,N-addition reaction at the terminal azide nitrogen atom to form the four-membered FLP cycloadduct <b>15</b>. The Zr⁺/P FLP is a reactive hydrogen activator. In a stoichiometric reaction it generates a hydridozirconocene cation that subsequently serves as a hydrogenation catalyst for various olefinic or acetylenic substrates. The Zr⁺/P pair <b>10</b> undergoes selective 1,4-addition reactions to conjugated enones and to a conjugated ynone to give the corresponding seven-membered metallacyclic Zr⁺/P FLP addition products. Many compounds of this study were characterized by X-ray diffraction