Versatile Reactivity of Bridged Pentelidene Complexes toward Secondary and Tertiary Phosphines

The reaction of the phosphinidene complex [Cp*P­{W­(CO)₅}₂] (<b>1a</b>) with secondary and tertiary phosphines, respectively, proceeds via W­(CO)₅ elimination to form the phosphoranylidene complexes [{W­(CO)₅}­(Cp*)­P-P­(H)^<i>i</i>Pr₂] (<b>2</b>), [{W­(CO)₅}­(Cp*)­P-PMe^<i>i</i>Pr₂] (<b>7</b>), and [{W­(CO)₅}­(Cp*)­P-PEt₃] (<b>9</b>). Other novel types of products, the phosphine-coordinated bridged parent phosphinidene complexes [{W­(CO)₅}₂(H)­P-PMe^<i>i</i>Pr₂] (<b>6a</b>) and [{W­(CO)₅}₂(H)­P-PEt₃] (<b>8a</b>), are obtained by elimination of 1,2,3,4-tetramethylfulvene. The latter reaction path is predominantly found for the arsinidene complex [Cp*As­{W­(CO)₅}₂] (<b>1b</b>) to yield [{W­(CO)₅}₂(H)­As-PH^<i>i</i>Pr₂] (<b>4</b>) upon reaction with HP^<i>i</i>Pr₂ and, with tertiary phosphines, the products [{W­(CO)₅}₂(H)­As-PMe^<i>i</i>Pr₂] (<b>6b</b>) and [{W­(CO)₅}₂(H)­As-PEt₃] (<b>8b</b>). If a secondary phosphine coordinates to a bridged parent pentelidene complex, Cp*H elimination occurs to form either HP­[P^<i>i</i>Pr₂{W­(CO)₅}]₂ (<b>3</b>) or the phosphine-substituted diarsene complex W­(CO)₅[AsP^<i>i</i>Pr₂{W­(CO)₅}]₂ (<b>5</b>). Each of the new products has been characterized by X-ray structure analysis, NMR, and mass spectroscopy. In each case as a first step the Lewis acid/base adducts are formed, which was monitored by ³¹P NMR spectroscopy. The different reaction pathways of the electrophilic pentelidene complexes [Cp*E­{W­(CO)₅}₂] (E = P, As) have been emphasized by extended DFT calculations