Reactions of a Cyclopentadienyl–Amidinate Titanium Benzimidamido Complex

We report the first reactivity study of a transition-metal benzimidamido complex, namely Cp*Ti­{PhC­(NiPr)2}­{NC­(ArF5)­NOtBu} (5, ArF5 = C6F5). Reaction with CO2 and tBuNCO gave the cycloaddition products Cp*Ti­{PhC­(NiPr)2}­{OC­(O)­N­(C­{ArF5}­NOtBu)} and Cp*Ti­{PhC­(NiPr)2}­{OC­(NtBu)­N­(C­{ArF5}­NOtBu)} (10), respectively, whereas with CS2 slow extrusion of ArF5CN from 5 occurred to ultimately form Cp*Ti­{PhC­(NiPr)2}­{SC­(S)­N­(OtBu)}. Reaction of 5 with ArC(O)H (Ar = Ph, 4-C6H4Me, 4-C6H4tBu, 4-C6H4OMe, 4-C6H4NMe2, 4-C6H4CF3) also gave the isolable metallacyclic complexes Cp*Ti­{PhC­(NiPr)2}­{N­(C­{ArF5}­NOtBu)­C­(Ar)­(H)­O} (13) via reversible [2 + 2] cycloaddition reactions. In contrast, reaction with HC­(O)­NMe2 formed Me2N­{NC­(ArF5)­NOtBu}H (16) within 1 h at room temperature. Upon heating, 10 and 13 also underwent retrocyclization, forming the organic products tBuNCNC­(ArF5)­NOtBu and ArC­{NC­(ArF5)­NOtBu}­H (14), respectively. Selected examples of 14 and 16 were studied by DFT and UV–visible spectroscopy. Addition of isonitriles tBuNC and XylNC (Xyl = 2,6-C6H3Me2) to Cp*Ti­{PhC­(NiPr)2}­{NC­(Ar)­NOtBu} (Ar = ArF5 (5), 2,6-C6H3F2 (ArF2)) afforded the σ adducts Cp*Ti­{PhC­(NiPr)2}­{NC­(Ar)­NOtBu}­(CNR) (Ar = ArF5, R = tBu, Xyl (19); Ar = ArF2, R = Xyl). Subsequently, 19 formed Cp*Ti­{PhC­(NiPr)2}­{NC­(NOtBu)­C6F4N­(Xyl)­C}­(F) (20) via C–F bond activation. Reaction of 5 with 2 equiv of B­(ArF5)3 gave Cp*Ti­{PhC­(NiPr)2}­{ON­(B­{ArF5}3)­C­(ArF5)­N­(H)­(B­{ArF5}3)} with elimination of 2-methylpropene.