Steric and Electronic Effects of Carbene Substitution in Grubbs First-Generation Catalysts

Abstract

The relative energies of the carbene species in a variety of metathesis reactions catalyzed by Grubbs first-generation catalyst (Cy3P)2Cl2RuCHC6H5 have been determined. High-quality equilibrium data are obtainable by 1H NMR methods. In the case of para-substituted aromatic derivatives (Cy3P)2Cl2RuCH(p-C6H4X), the carbenes are stabilized by donor substituents, and energies may be determined indirectly by use of either NMR data or Hammett correlations, because only electronic effects are operative. Four systems have been characterized by X-ray crystallography. The energies of alkyl-substituted carbenes (Cy3P)2Cl2RuCHR are almost entirely dependent on steric interactions.

Alkyl group-tagged ruthenium indenylidene complexes: Synthesis, characterization and metathesis activity

“…For 6a, the 3-isopropyl-1-indenylidene moiety is completely disordered over two positions, turned over about 175.8 with respect to each other. Complexes 6a-c feature a slightly distorted square-pyramidal geometry around the ruthenium atom, similar to complexes 1a [27] and 3a [28], with the indenylidene moieties in the axial position.…”

Ring-closing metathesis within chromium-coordination sphere: Facile access to phosphine-chelate (π-arene)chromium complexes

“…With a shorter alkenyl substituent (vinyl group) on the h 6 -arene in 1a and 1b, the probability of meeting the two olefinic termini becomes higher leading to the higher yields of 2a and 2b than 2c. Alternatively, the higher yields of 2a/2b could be explained by the greater reactivity of the h 6 -styrene moieties in 1a and 1b than the h 6 -allylbenzene in 1c [13,14].…”

“…1 H NMR (at 400 MHz) and 13 17] were prepared according to the reported methods. All the other chemicals were obtained from commercial sources.…”

“…(d,J ¼ 6.8 Hz,2H),4.10e4.14 (m,1H),4.22e4.23 (m,2H),4.37e4.41 (m,2H),4.88e4.94 (m,2H),5.44 (td,17.8 and 1.7 Hz,1H),5.56 (ddd,J ¼ 35.7,11.8,and 1.7 Hz,1H),5.79 (ddt,J ¼ 17.8,9.6,and 6.8 Hz,1H),6.54 (ddd,J ¼ 17.8,17.2,and 11.8 Hz, 1H), 6.99e7.10 (m, 6H), 7.53e7.58 (m, 4H). 13 1, 17.4, and 11.9 Hz, 1H), 6.99e7.10 (m, 6H), 7.54e7.58 (m, 4H). T ¼ 296 K, R 1 ¼ 0.0547 (I > 2s (I)), wR 2 ¼ 0.1865 (I > 2s(I)), S ¼ 1.018, number of collected data ¼ 18502, number of refined parameters ¼ 245.…”

“…H NMR (C 6 D 6 ): d 2.56 (ddd, J ¼ 8.9, 5.8, and 1.7 Hz, 2H),4.01e4.04 (m, 2H), 4.32e4.36 (m, 1H), 4.71e4.75 (m, 2H), 5.39 (ddt, J ¼ 13.1, 11.0, and 5.8 Hz, 1H), 6.03 (ddt, J ¼ 11.0, 3.0, and 1.7 Hz, 1H), 6.99e7.04 (m, 2H), 7.06e7.11 (m, 4H), 7.47e7.52 (m, 4H) 13. C{ 1 H} NMR (C 6 D 6 ): d 30.8 (d, J PC ¼ 14.1 Hz), 80.8 (d, J PC ¼ 0.9 Hz), 85.6 (s), 91.0 (d, J PC ¼ 1.1 Hz), 100.4 (d, J PC ¼ 3.0 Hz), 128.2 (d, J PC ¼ 9.1 Hz), 128.6 (d, J PC ¼ 12.6 Hz), 128.8 (s), 129.1 (d, J PC ¼ 2.1 Hz), 132.2 (d, J PC ¼ 10.0 Hz), 140.4 (d, J PC ¼ 35.0 Hz), 238.5, (d, J PC ¼ 18.9 Hz).…”