Versatile Reactivity of Bridged Pentelidene Complexes toward Secondary and Tertiary Phosphines

The
reaction of the phosphinidene complex [Cp*P­{W­(CO)5}2] (1a) with secondary and tertiary phosphines,
respectively, proceeds via W­(CO)5 elimination to form the
phosphoranylidene complexes [{W­(CO)5}­(Cp*)­P-P­(H)iPr2] (2), [{W­(CO)5}­(Cp*)­P-PMeiPr2] (7), and [{W­(CO)5}­(Cp*)­P-PEt3] (9). Other novel types of products, the phosphine-coordinated bridged
parent phosphinidene complexes [{W­(CO)5}2(H)­P-PMeiPr2] (6a) and [{W­(CO)5}2(H)­P-PEt3] (8a), 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] (1b) to yield [{W­(CO)5}2(H)­As-PHiPr2]
(4) upon reaction with HPiPr2 and, with tertiary phosphines, the products [{W­(CO)5}2(H)­As-PMeiPr2] (6b) and [{W­(CO)5}2(H)­As-PEt3] (8b). If a secondary phosphine coordinates
to a bridged parent pentelidene complex, Cp*H elimination occurs to
form either HP­[PiPr2{W­(CO)5}]2 (3) or the phosphine-substituted
diarsene complex W­(CO)5[AsPiPr2{W­(CO)5}]2 (5).
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.