Abstract
[RuCl2(PPh3)2(amine)x]-type complexes, with NH2Ph (1; x = 2), NH2Bz (2; x = 2) and NHBuPh (3; x = 1) in the presence of ethyldiazoacetate (EDA), were investigated for ring opening metathesis polymerization (ROMP) of norbornene (NBE), norbornadiene (NBD) and dicyclopentadiene (DCPD). Quantitative yields of polyNBE were obtained at 50 °C for 30 min with 1 and for 5 min with 2, whereas this occurred at 25 °C for 5 min with 3. Polydispersity index (PDI) values ranged from 3.5 to 1.6 (M w = 10 4 -10 5 g mol -1 ). Complex 3 was active for ROMP of NBD and DCPD, as well as for copolymerizations of NBE with either NBD or DCPD. The high σ-donor character of NH2Bz favored the reactivity of the six-coordinated complex 2, contrary to complex 1. The large cone angle of NHBuPh defined the fivecoordination in 3 and the best reactivity for ROMP, in spite of the low σ-donor character as in NH2Ph.
Highlights
We focus on the development of Rubased catalysts combining the phosphine PPh3 with amines of the type NHR1R2 to act as ancillary ligands, where the amine substituents R1 and R2 permute their characteristics considering the electronic nature and steric hindrance
The active metal species was poisoned with excess of EDA, decreasing the propagation rate, or the monomer concentration decreased by cyclopropanation occurrence, as possible reasons to explain that event.[33]
It is important to observe the absence of signals associated with binuclear species in the solution, as promptly occurred when dissolving the fivecoordinated [RuCl2(PPh3)3] complex in CHCl3.29 In the latter case, the displacement of one PPh3 molecule occurred owing to the large steric hindrance around the coordination sphere
Summary
Cycloalkenes undergo ring-opening metathesis polymerization (ROMP) catalyzed by a transition metalcarbene complex to result in a polymer with the carboncarbon double bond retained.[1,2,3,4,5] ROMP is a practical method to produce copolymers and can be combined either with different olefin metathesis (OM) procedures or other polymerization methods.[6,7,8,9]A diversity of catalysts have been tested from complexes of Ru, W, Mo, Ti, Ta, Nb, V, Re, Ni, etc.[1,10,11,12,13,14,15] Besides the electronic nature of the metal center to select an olefin instead of an oxo-compound in the medium,[16] the success of ROMP is strongly influenced by ancillary ligands.[17,18] These ligands directly influence the reaction mechanism via an intramolecular interaction between a coordinated olefinUsually, the ancillary ligands in OM with Ru-based complex are bulky and good σ-donors.[20]. Reactions for 5 min with 1 as a function of [NBE]/[Ru] molar ratio in the range from 1000 to 5000 showed polyNBE yield increased either at 25 or 50 °C (Figure 2). In the case of 2, good yields were obtained for molar ratio of [NBE]/[Ru] = 10000, with PDI below 1.9 (Table 2).
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