A New Family of Halogen‐Chelated Hoveyda–Grubbs‐Type Metathesis Catalysts

Abstract

Coordination, not insertion: New ruthenium benzylidenes with a chelating halogen atom were easily prepared and showed excellent stability and activity as metathesis catalysts (see figure). Structure-activity studies reveal that strength of the ruthenium-halogen interaction can be tuned across a wide range to set up a family of latent to active catalysts.

Key processes in ruthenium-catalysed olefin metathesis

“…DFT studies suggested that the pathway in which the nitrogen remained bound to the ruthenium during this isomerisation was lowest in energy; however, there was a small difference between this pathway and the one in which the Ru-N bond is disrupted and re-formed. 63 Sulfur-and halide-chelated complexes also exhibit isomerisation from the trans-to the cisconfiguration, 64,65 although such processes have not been studied in as much detail for these systems. 66 For some complexes, the intermediate trans-isomer is not observable.…”

Initiation efficacy of halo-chelated cis-dichloro-configured ruthenium-based second-generation benzylidene complexes in ring-opening metathesis polymerization

“…Further, it is quite obvious that the trans isomer is formed rapidly and is readily extracted from the chemical balance by entering the polymerization cycle. Regrettably, the poor solubility of some of the pre-initiators in toluene at 25°C permitted a corresponding comparative study under these conditions [14].…”

“…Table 1, entries 2 and 11), M n values decrease in case of the halo-chelated pre-initiators (cf. Table 1, entries [12][13][14][15][16][17][18][19]. Still 1 is the pre-initiator with the highest initiation efficacy but variations of the M n value of different poly9 became smaller than at room temperature as the decrease in M n is bigger in case of using electronically modified initiators 3, 5, 6, and 7 (decrease by the factor of 1.8-2.6) than in case of the unsubstituted congeners 1, 2, 4, and 8 (decrease by the factor of 1.4-1.5).…”

“…Starting materials M2 and M31 were obtained from Umicore. Initiators 1-8 were prepared according to literature [14,[16][17][18]. Benchmark monomer dimethyl bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate (9) was synthesized via a Diels-Alder reaction according to literature procedure [31].…”

“…These complexes feature a rare RuÁÁÁX-R (X = Br, I; R = aromatic moiety) coordination and display appealing catalytic performance in a variety of olefin metathesis reactions [14]. Of particular interest is that these compounds feature the cisdichloro geometry, but nevertheless exhibit pronounced catalytic activity at room temperature [14].…”