Terminal and four-coordinate vanadium(IV) phosphinidene complexes. A pseudo Jahn-Teller effect of second order stabilizing the V-P multiple bond

Treatment of the four-coordinate vanadium neopentylidene (Nacnac)V=CHtBu(I) (Nacnac- = [Ar]NC(Me)CHC(Me)N[Ar], Ar = 2,6-iPr2C6H3) with a bulky primary lithium phosphide LiPHR (R = 2,4,6-iPr3C6H2, 2,4,6-tBu3C6H2) leads to alpha-hydrogen migration concomitant with the formation of a four-coordinate vanadium complex containing a terminal phosphinidene functionality (Nacnac)V=PR(CH2tBu). The crystal structures for the vanadium phosphinidene complexes prepared herein were determined by single-crystal X-ray diffraction methods. Solution EPR and magnetic measurements of the vanadium phosphinidenes are also in accordance with such systems containing a V(IV) metal center, and DFT calculations indicate the V=P bond to be stabilized through a pseudo Jahn-Teller effect of second order.