Exploitation of a Chemically Non-innocent Acetate Ligand in the Synthesis and Reactivity of Ruthenium Vinylidene Complexes

Abstract

Reaction of the ruthenium bis-acetate complex cis-Ru(κ2-OAc)2(PPh3)2 with a range of terminal alkynes HCCR (R = Ph, CO2Me, C{OH}Ph2, C{OH}Me2) results in the formation of the vinylidene complexes Ru(κ2-OAc)(κ1-OAc)(CCHR)(PPh3)2. The acetate ligands in these species are fluxional and, in the case where R = Ph, are undergoing fast exchange on the NMR time scale even at 195 K. In the case of the hydroxy-substituted complex Ru(κ2-OAc)(κ1-OAc)(CCHC{OH}Ph2)(PPh3)2 a hydrogen bond exists between the OH group on the γ-position of the vinylidene and the κ1-OAc ligand. This hydrogen bond inhibits the exchange of the OAc ligands, which now becomes slow on the NMR time scale at 215 K. In addition, and in contrast to the Cl-substituted analogues, elimination of water from the hydroxy vinylidene complex does not readily occur, possibly due to the presence of this hydrogen-bonding interaction. Instead, a slow reaction to form Ru(κ2-OAc)(κ1-OAc)(CO)(PPh3)2 is observed with the concomitant formation of H2CCPh2. An analogous process with Ru(κ2-OAc)(κ1-OAc)(CCHC{OH}Me2)(PPh3)2 affords H2CCMe2 and Ru(κ2-OAc)(κ1-OAc)(CO)(PPh3)2.

Ruthenium carboxylate complexes as easily prepared and efficient catalysts for the synthesis of β-oxopropyl esters

“…The 13 C{ 1 H} NMR spectra also showed the presence of a single carbonyl resonance for the O 2 CPh groups, consistent with exchange of k 1 -and k 2 -bound benzoate which is fast on the NMR timescale. A similar observation was made for the acetate-containing analogues [16].…”

“…In addition, we have also demonstrated that hydroxy-substituted vinylidene complexes such as 5b convert to [Ru(k 2 -O 2 CMe)(k 1 -O 2 CMe)(CO)(PPh 3 ) 2 ], 10a and H 2 C]CMe 2 which provides an alternative source of CO in the reaction mixture [16]. These pathways are all plausible routes to the observed carbonyl complexes obtained from the catalytic reaction mixtures.…”

“…A 31 P{ 1 H} NMR spectrum of the reaction mixture exhibited two very broad resonances in the region d 66, at a chemical shift similar to that observed for pure 1a and for cis-[Ru (k 2 -O 2 CPh) 2 (PPh 3 ) 2 ], 1b (q.v.). Related complexes possessing mutually trans-phosphine ligand typically exhibit resonances in the 31 P{ 1 H} spectrum between d 40 and 30 [16,17]. We therefore concluded that rapid exchange of acetate and benzoate ligands was occurring, even at room temperature.…”

“…We have recently demonstrated that cis-[Ru(k 2 -O 2 CMe) 2 (PPh 3 ) 2 ], 1a, is a highly selective precursor for the formation of complexes containing vinylidene ligands [16]. Reaction with, for example, HC^CPh, 2, results in the rapid formation of [Ru(k 2 -O 2 CMe)(k 1 -O 2 CMe)(]C]CHPh)(PPh 3 ) 2 ], 3a.…”

Arene‐Ligand‐Free Ruthenium(II/III) Manifold for meta‐C−H Alkylation: Remote Purine Diversification

“…Ru ( [Ru(OAc) 2 (PPh 3 ) 2 ]( 4) [16] emerged as most effective (entries 1-9), interestingly,f eaturing the first arene-ligand-free remote CÀH alkylation [17] by ruthenium catalysis. Control experimentsv erified the essential role of the ruthenium catalyst and the base (entries 10 and 11).…”