Reaction of a Triruthenium μ₃‑Borylene Complex with Benzonitrile: Formation of a μ₃‑η³‑BCN Ring on a Cationic Ru₃ Plane via Photo-Induced Intramolecular Borylene Transfer

A μ3-η2(||)-iminobenzoyl complex supported by a μ3-borylene ligand, [(Cp*Ru)3(μ3-BH)­(μ3-η2-PhCNH)­(μ-H)2] (5a; Cp* = η5-C5Me5), was synthesized as an equilibrated mixture with its isomer, 5b, by the reaction of a μ3-borylene complex, [{Cp*Ru­(μ-H)}3(μ3-BH)] (1), with benzonitrile. Although the structure of 5a is very similar to that of the previously reported μ3-η2(||)-phenylacetylene complex, [(Cp*Ru)3(μ3-BH)­(μ3-η2-PhCCH)­(μ-H)3] (2), the reactivity of 5a is different from that of 2. While the thermolysis of 2 resulted in the reductive elimination of dihydrogen, a μ3-2-amino-2-bora­ruthenacyclo­pentenyl complex, [{Cp*Ru­(μ-H)}2{Cp*Ru­(−C6H4–CH-BNH2−)}] (6), was obtained by the thermolysis of 5a at 140 °C without hydrogen elimination. In contrast, a cationic μ3-η2(||)-iminobenzoyl complex, [(Cp*Ru)3(μ3-BH)­(μ3-η2-PhCNH)­(μ-H)3]+ (9), which was obtained by the protonation of 5a, showed reactivity similar to that of 2. Irradiation of 10 at a wavelength of 436 nm induced an intramolecular borylene transfer to the μ3-η2(||)-iminobenzoyl moiety and a cationic complex containing a μ3-η3-BCN ring, [{Cp*Ru­(μ-H)}3{μ3-η3-B­(H)­N­(H)­C­(Ph)−}]+ (10), was obtained. The crystal structure of 10 showed long B–N (1.634(6) Å) and B–C (1.719(6) Å) bonds in the μ3-η3-BCN skeleton, which are consistent with the small bond indices of 0.539 and 0.433, respectively, and suggest the unsupported nature of these bonds. Time-dependent density functional theory calculations of 2, 5a, and 9 suggested the importance of a μ-hydride at the Ru–Ru edge where the borylene ligand migrates upon irradiation.