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

Abstract

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