Activation of Propargyl Alcohols by TpRu Complexes Bearing a Bidentate NHC Ligand

The complex [TpRuCl­(COD)] reacts with <b>L</b>·Ag₂Cl₂ (<b>L</b> = bis­(3-methylimidazol-2-ylidene)) in dichloroethane at 120 °C for a period of 20 h, furnishing the bis­(carbene) derivative [TpRuCl­(<b>L</b>)] (<b>1</b>). This compound reacts with NaBAr′₄ in FPh under dinitrogen to yield the cationic dinitrogen complexes [TpRu­(N₂)­(<b>L</b>)]­[BAr′₄] (<b>2</b>′) and [{TpRu­(<b>L</b>)}­(μ-N₂)]­[BAr′₄]₂ (<b>2</b>). The terminal dinitrogen complex <b>2</b>′ is labile and spontaneously converts into <b>2</b>, which was structurally characterized. The reaction of <b>2</b> with CO is slow and affords [TpRu­(CO)­(<b>L</b>)]­[BAr′₄] (<b>3</b>). The kinetics of the substitution of coordinated dinitrogen in <b>2</b> by CD₃CN has been studied. The value of 25 ± 4 kcal mol^–1 determined for Δ<i>G</i>^⧧₂₉₈ for the substitution reaction is consistent with the observation that the dinitrogen ligand is strongly bound to ruthenium in <b>2</b>. Complex <b>1</b> reacts with propargyl alcohols HCCC­(OH)­RR′ (RR′ = Me₂, (CH₂)₅, MePh, HPh) and NaBPh₄ in MeOH at 50–60 °C, yielding the corresponding γ-methoxyvinylidene complexes [TpRuCCHC­(OMe)­RR′(<b>L</b>)]­[BPh₄] (RR′ = Me₂ (<b>4a</b>), (CH₂)₅ (<b>4b</b>), MePh (<b>4c</b>), HPh (<b>4d</b>)). The reaction of <b>1</b> with HCCCH₂OH under the same conditions led to the γ-hydroxyvinylidene derivative [TpRuCCHCH₂OH­(<b>L</b>)]­[BPh₄] (<b>5</b>), whereas the reaction with HCCC­(OH)­Ph₂ resulted in the formation of the deep purple allenylidene complex [TpRuCCCPh₂(<b>L</b>)]­[BPh₄] (<b>6</b>). A series of N- and S-donor molecules such as pyrazole, piperidine, 2-pyridinethiol, and 1,3-benzenedithiol add to the C_α atom of the allenylidene ligand in <b>6</b> to yield the corresponding diphenylvinylcarbene species [TpRuC­(X)­CHCPh₂(<b>L</b>)]­[BPh₄] (X = C₃H₃N₂ (<b>7</b>), N­(CH₂)₄CH₂ (<b>8</b>), SC₅H₄N (<b>9</b>), SC₆H₄SH (<b>10</b>)), of which compound <b>7</b> was structurally characterized. The reaction of <b>6</b> with KOBu^t in acetone produced the neutral σ-alkynyl derivative [TpRuCCC­(CH₂COCH₃)­Ph₂(<b>L</b>)] (<b>11</b>), resulting from the addition of acetone enolate to the C_γ of the allenylidene ligand