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-C6H3
iPr2) with Li2N2
RNMe (N2
RNMe = MeN(CH2CH2NR)2) or Li2N2Npy (N2Npy = (2-C5H4N)CMe(CH2NSiMe3)2) afforded the borylimides Ti(N2
RNMe){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(N2
RNMe){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.