Synthesis of Titanium Borylimido Compounds Supported by Diamide-Amine Ligands and Their Reactions with Alkynes

We report a combined synthetic, mechanistic, and computational (DFT) study of the synthesis of new diamide-amine-supported titanium borylimides and their reactions with TolCCH and ArFCCH (Tol = 4-C6H4Me, ArF = C6F5). Reaction of Ti­{NB­(NAr′CH)2}­Cl2(py)3 (Ar′ = 2,6-C6H3iPr2) with Li2N2RNMe (N2RNMe = MeN­(CH2CH2NR)2) or Li2N2Npy (N2Npy = (2-C5H4N)­CMe­(CH2NSiMe3)2) afforded the borylimides Ti­(N2RNMe)­{NB­(NAr′CH)2}­(py) (R = SiMe3 (9), ArF (10), or iPr (11)) and Ti­(N2Npy)­{NB­(NAr′CH)2}­(py) (21). Compounds 9 and 10 reacted with ArCCH (Ar = Tol or ArF) via [2 + 2] cycloaddition to form the azatitanacyclobutenes Ti­(N2RNMe)­{N­{B­(NAr′CH)2}­C­(H)­C­(Ar)}. In the case of R = ArF these underwent subsequent intramolecular C–F bond cleavage/C–C coupling processes. Reaction of 11 and 21 with TolCCH also formed azatitanacyclobutenes, whereas ArFCCH formed borylamide-acetylides via a C–H bond activation process which is endergonic in the case of TolCCH. On heating, these kinetic products rearranged via alkyne elimination to form the corresponding azatitanacyclobutenes as the thermodynamic outcomes.