Synthesis of Cationic Molybdenum Imido 2‑Adamantylidene Complexes from Bispyrrolides via Cationic Pyrrolenine Complexes

Mo­(N-t-Bu)­(Adene)­(Me2Pyr)2 (2a) (Adene = 2-Adamantylidene, Me2Pyr = 2,5-dimethylpyrrolide) and Mo­(NAr)­(Adene)­(Me2Pyr)2 (2b) (Ar = 2,6-diisopropylphenyl) were prepared through addition of LiMe2Pyr to Mo­(N-t-Bu)­(Adene)­(Triflate)2(dme) and Mo­(NAr)­(Adene)­(Triflate)2(dme) complexes, respectively. Addition of 1 equiv of [Me2PhNH]­[BArF4] (ArF = 3,5-(CF3)2C6H3) and more than 2 equiv of pivalonitrile to Mo­(NC6F5)­(Adene)­(Me2Pyr)2, followed by 1 equiv of HMTOH (2,6-Mesityl2C6H3OH), led to isolation of yellow crystalline Mo­(NC6F5)­(Adene)­(OHMT)­(Piv)2(BArF4) (3, Piv = pivalonitrile). Reactions analogous to that for 3 were found to produce Mo­(NC6F5)­(Adene)­[OC­(CF3)3]­(Piv)2(BArF4) (4), Mo­(NC6F5)­(Adene)­(OHMT)­(PhF6CN)2(BArF4) (5; PhF6CN = 3,5-(CF3)2C6H3CN ), Mo­(NAr)­(Adene)­(OHMT)­(PhF6CN)2(BArF4) (6), Mo­(NAr)­(Adene)­[OC­(CF3)3]­(Piv)2(BArF4) (7), and Mo­(N-t-Bu)­(Adene)­(OHMT)­(PhF6CN)2(BArF4) (8). Compounds 3, 6, and 7 were found to have basically square pyramidal structures with trans nitriles in two basal positions. The bisnitrile complexes are active metathesis catalysts in the presence of 1 equiv of B­(C6F5)3, consistent with the 14e monononitrile cationic complexes being the active species. The 14e complex required for metathesis is accessed most readily in bis PhF6CN complexes