Norbornadiene complexes of molybdenum(II) and their transformation to a catalyst for ring-opening metathesis polymerization: DFT calculations – X-ray crystal structure of a new norbornadiene complex [MoCl(GeCl3)(CO)3(η4-nbd)]

Ring Opening Metathesis Polymerization of Norbornene and Derivatives by the Triply Bonded Ditungsten Complex Na[W2(µ-Cl)3Cl4(THF)2]·(THF)3

“…Evidently, our findings are remarkably similar to those reported by Szymańska-Buzar et al on the polymerization of NBE and NBD by 5, 5' and 6 [35,42,[45][46][47]. However, the NBD-to-carbene transformation in this system is more facile than those occurring in 5a, and 6/NBD, as this is reflected in the stabilities of the relevant adducts (4a stable and isolable; 1a or 1'a unstable) and the polymerization reaction rates, respectively (5 or 5a/NBD/CHCl 3 or CHCl 3 /CH 2 Cl 2 slow; 1/NBD/CH 2 Cl 2 vigorous).…”

“…In relation to this work, worth noting in some detail are the results reported by Szymańska-Buzar et al (9) taking into account extra important intermediate steps [44], which lower the activation energies by half, favor the mechanism first hypothesized by Handzlik et al [42] (oxidative coupling to form metallacyclopentane, followed by a 1,4-H-shift between the two α-bonded carbons across the face of the metal atom (Scheme S2).…”

“…Instead, at t = 0-1 h, multiple broad unresolved high field peaks in the region 9.80-13.80 ppm, characteristic of the propagating tungsten alkylidene PNBD chains [2,48,49] appear simultaneously with peaks at 6.18, 5.90, 3.78 and 2.92 ppm, and one at 3.92 ppm, which could be assigned to the formation of exo-2-chloronorborn-5-ene and exo-3-chloronortricyclane, respectively [42]. As the reaction progresses, the intensity of the above peaks increases, along with parallel and increasing formation of PNBD.…”

Stannylation of unsaturated carbon–carbon bonds by tin tetrachloride

“…The proton signal at 4.24 ppm correlates with the carbon signal at 58.6 ppm but in the 2D 1 He 1 H COSY spectrum it correlates with the proton signal at 3. (d H 4.24 ppm) and the carbon signal (d C 58.6 ppm) assigned to the HClC unit compare well with the chemical shift reported for exo-5-chloro-bicyclo[2.2.1]-hept-2-ene (d H 3.77, d C 59.0) [32]. The proper assignment of the carbon signals to the norbornenyl moiety was confirmed by the 2D 1 He 13 C HMBC NMR spectra.…”

Carbonyl Complexes of Molybdenum and their Catalytic Activity

“…The detailed reaction mechanism for the formation of carbene catalysts from carbonyl complexes of Mo or W in low oxidation states remains unclear, although, without a doubt, the carbene species are formed due to the rearrangement of olefin coordinated to the metal atom. DFT studies of the potential routes to the formation of carbene from olefin have been carried out by various researchers [19,24,25], but none of the rearrangement pathways found has an activation barrier as low as could be expected for a process carried out experimentally at very mild conditions. One piece of direct evidence for the 1,2-hydrogen shift and the formation of norborn- ylidene ligand from nbe is the detection of 2,2´-binorbornylidene, which can be regarded as the product of the coupling of two norbornylidene ligands, in reactions of nbe initiated by Mo and W seven-coordinate complexes (Scheme 4) [18,20].…”