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.

本工作报道了一项结合合成、机理与密度泛函理论(DFT)计算的研究，针对新型二酰胺-胺负载钛硼亚胺配合物的合成，及其与TolCCH和ArFCCH的反应（其中Tol=4-C6H4Me，ArF=C6F5）。Ti{NB(NAr'CH)2}Cl2(py)3（Ar'=2,6-C6H3iPr2）与Li2N2RNMe（N2RNMe=MeN(CH2CH2NR)2）或Li2N2Npy（N2Npy=(2-C5H4N)CMe(CH2NSiMe3)2）反应，得到硼亚胺配合物Ti(N2RNMe){NB(NAr'CH)2}(py)（R=SiMe3（9）、ArF（10）或iPr（11））与Ti(N2Npy){NB(NAr'CH)2}(py)（21）。配合物9和10可与ArCCH（Ar=Tol或ArF）通过[2+2]环加成反应生成氮杂钛环丁烯类化合物Ti(N2RNMe){N{B(NAr'CH)2}C(H)C(Ar)}。当R=ArF时，该类产物会进一步发生分子内C-F键断裂与C-C偶联过程。配合物11与21分别与TolCCH反应也可生成氮杂钛环丁烯，而ArFCCH则通过C-H键活化过程生成硼酰胺-炔基化物；对于TolCCH而言，该C-H键活化过程为吸能过程。加热条件下，这些动力学产物可通过炔烃消除过程发生重排，生成相应的氮杂钛环丁烯，即为热力学主导产物。