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

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.