Highly Efficient Ru−Pseudohalide Catalysts for Olefin Metathesis

Abstract

Ruthenium alkylidene complexes containing one aryloxide "pseudohalide" ligand catalyze ring-closing metathesis of diene and ene-yne substrates with exceptionally high efficiency. Chromatographic removal of Ru residues is unexpectedly facile, offering a convenient means of isolating pure organic products in high yields.

Ruthenium‐Catalyzed Ring‐Closing Metathesis: Recent Advances, Limitations and Opportunities

“…Consistent with Jacobson-Stockmayer theory, however (vide supra), cyclooligomeric byproducts were observed at higher concentrations (10 mM), as also reported in other work [62]. Interestingly, new pseudohalide catalysts (Section 4.2) show complete conversion to the macrocycle within 15 minutes [65]. Whether this represents improved selectivity for RCM over ADMET, or simply faster backbiting, is as yet unclear.…”

“…In contrast to the metathesisinactive alkoxides C43, catalyst C50 effects up to 41,000 turnovers in RCM of DEDAM, at exceptionally low catalyst loadings (5 × 10 -4 mol % C50). In comparison, monoaryloxide complexes C51 exhibit lower total turnover numbers, though lifetimes still exceed those of C1/C2 ( Table 1,2) [65]. The decrease in total productivity is offset by heightened reactivity relative to C50.…”

“…RCM of 1 using C1a and related catalysts is reportedly incomplete even after 30 h [151][152][153][154], while NHC catalyst C2b effects 72-87% ring-closing within 2-4 h [80,151]. In comparison, C51b effects quantitative formation of this value-added target molecule within 15 minutes [65]. Parallel experiments with C2a showed that at similar dilutions (5 mM), ADMET was kinetically preferred over cyclization, but that quantitative RCM could be achieved on 1 h reaction time in refluxing CDCl 3 (see Section 2.2.2).…”

“…Thus, a single, routine, chromatographic pass afforded colourless oils in which the residual Ru content was below the ICP-AES detection limit (<100 ppm, or 0.1 µg/mg; ICP-AES = inductively coupled plasma atomic emission spectroscopy) [65].…”

Ring closing metathesis employing organometallic substrates and the templated synthesis of macrocycles

“…As well, olefin metathesis is now firmly entrenched in polymer chemistry [1,10]. In addition to the original catalysts, a number of research groups have actively ଝ A portion of this contribution was presented as a lecture at the 16th Interna- pursued the development of either derivative or novel systems that have opened new areas in this chemistry by improving activity, chemo-, regio-and stereo-selectivity as well as addressing important factors such as catalyst stability, ease of synthesis, recycling and functional group tolerance; [1][2][3][4][5][6][7][8][9][11][12][13][14][15][16] see Fig. 1 for a small selection of metathesis catalysts with some selected properties.…”