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We report the first reactivity study of a transition-metal benzimidamido complex, namely Cp Ti{PhC(NiPr)2}{NC(ArF 5NOtBu} (5, ArF5= C6F5). Reaction with CO2 and tBuNCO gave the cycloaddition products CpTi{PhC(NiPr)2}{OC(O)N(C{ArF5}NO tBu)} and CpTi{PhC(NiPr)2}{OC(N tBu)N(C{ArF5}NOtBu)} (10), respectively, whereas with CS2 slow extrusion of ArF5CN from 5 occurred to ultimately form CpTi{PhC(NiPr)2}{SC(S)N(O tBu)}. Reaction of 5 with ArC(O)H (Ar = Ph, 4-C6H 4Me, 4-C6H4tBu, 4-C 6H4OMe, 4-C6H4NMe2, 4-C6H4CF3) also gave the isolable metallacyclic complexes CpTi{PhC(NiPr)2}{N(C{ArF5}NO tBu)C(Ar)(H)O} (13) via reversible [2 + 2] cycloaddition reactions. In contrast, reaction with HC(O)NMe2 formed Me 2N{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-C6H 3Me2) to CpTi{PhC(NiPr)2}{NC(Ar) NOtBu} (Ar = ArF5 (5), 2,6-C6H 3F2 (ArF2)) afforded the σ adducts CpTi{PhC(NiPr)2}{NC(Ar)NOtBu}(CNR) (Ar = ArF5, R = tBu, Xyl (19); Ar = ArF2, R = Xyl). Subsequently, 19 formed CpTi{PhC(NiPr)2}{NC(NO tBu)C6F4N(Xyl)C}(F) (20) via C-F bond activation. Reaction of 5 with 2 equiv of B(ArF5)3 gave CpTi{PhC(NiPr)2}{ON(B{ArF5}3) C(ArF5)N(H)(B{ArF5}3)} with elimination of 2-methylpropene. © 2014 American Chemical Society. |
