On the isomerization of a trans-dichloro to a cis-dichloro amide-chelated ruthenium benzylidene complex and the catalytic scope of these species in olefin metathesis

Abstract

Upon comparative NMR spectroscopy studies, the isomerization of newly disclosed dichloro [j 2 (C,O)-2-(N-propylaminocarbonyl)benzylidene][1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene]ruthenium from trans-dichloro configuration (SPY-5-31) to its thermodynamically more favored cis-dichloro derivative (with SPY-5-34 stereochemistry) was found to proceed via dissociation of one chloride ligand to form an intermediate cationic species. Furthermore, the performance of the trans-and the cis-dichloro derivatives as catalysts in ringclosing metathesis and as initiators in ring-opening metathesis polymerization was studied.

Ruthenium–Triazene Complexes as Latent Catalysts for UV‐Induced ROMP

“…The preference for highly selective formation of this five‐membered chelate can be explained by the resonance stabilization in this structure (see Figure 2 below), which is not possible in the corresponding six‐membered chelate. Furthermore, in view of recently reported structural data of Ru–alkylidenes with a cis arrangement of the two Cl ligands,59 and of the low propensity of N‐ and O‐donor ligands to assume a cis configuration,60,61 we consider such a cis arrangement less probable (though not impossible) and tentatively attribute the second, minor alkylidene signal to an isomeric form of 2 , i.e., one in which the triazene ligand forms a six‐membered chelate ring.…”

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

“…Table 1, entry 1). Those values are typical for a fast and complete initiation [19][20][21][22][23][24]. In contrast, slowly initiating M2 gave, under the same conditions, a polymer characterized by an M n value of Fig.…”

“…Additionally, two reference initiators, namely M31 and M2 were used for comparison. Compound M31 is a fast and fully initiating species allowing for controlled ROMP at room temperature in CH 2 Cl 2 (or toluene) [19][20][21][22][23][24][25], while M2 is an example for a rather slowly initiating initiator [19][20][21][22][23][24]. Accordingly, initiation of the polymerization of 9 with M31 at 25°C in CH 2 Cl 2 released a polymer characterized by an average number molecular mass (M n ) of 54,000 g/mol and a polydispersity index (PDI) of 1.08 (cf.…”

“…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).…”

“…Br Cl mass distributions are, above all, only dependent on the concentration of the actual active 14 electron species in the reaction mixture [19][20][21][22][23][24].…”