Living Ring-Opening Metathesis Polymerisation of 2,3-Difunctionalized 7-Oxanorbornenes and 7-Oxanorbornadienes by Mo(CHCMe2R)(N-2,6-C6H3-i-Pr2)(O-t-Bu)2 and Mo(CHCMe2R)(N-2,6-C6H3-i-Pr2)(OCMe2CF3)2

Article abstract of DOI:10.1021/ja00018a028

7-Oxabenzonorbornadiene (9), 2,3-endo-cis-diacetoxy-7-oxanorbornene, and 2,3-endo-cis-(isopropylidenedioxy)-7-oxanorbornene can be polymerized by Mo(CHCMe2R)(NAr)(O-t-Bu)2 (Ar = 2,6-C6H3-i-Pr2; R = CH3, C6H5) ((CHCMe2R)) to give polymers with narrow molecular weight distributions (PDI < 1.17).However, 2,3-bis(trifluoromethyl)-7-oxoanorbornadiene (1), 2,3-dicarbomethoxy-7-oxanorbornadiene (4), and 2,3-trans-dicyano-7-oxanorborn-5-ene (12) form stable metallacycles upon addition to (CHCMe2R).The rate of reaction of 1 with (CHCMe2R) has been determined qualitatively to be comparable to that of norbornene in competition experiments, a result that implies that the lone pair on the oxygen in the 7-position is accelerating metallacycle formation.The metallacycle that results from addition of 1 to (CHCMe2Ph) is square pyramidal with the imido ligand in the apical position. (Crystal data for 2b: a = 12.420 (3) Angstroem, b = 15.466 (4) Angstroem, c = 20.856 (6) Angstroem, V = 3852 (2) Angstroem³, β = 105.97 (2) deg, space group = P2₁/n, Z = 4, M_r = 779.76, ρ = 1.345 g/cm³, μ = 3.9 cm^-1, R₁ = 0.049, R₂ = 0.068.) The MoC3 ring is planar with the CMe2Ph group pointed toward the imido ligand and the C7 frame of the monomer pointed away from it (a trans metallacyclic ring).The oxygen in the 7-position of the norbornene moiety is located 3.332 (4) Angstroem from the metal.Electronic and steric factors that influence first-order breakup of the metallacycle have been studied for monomers 1 and 4.The more reactive catalyst, Mo(CHCMePh)(NAr)(OCMe2CF3)2, can polymerize 1, 4, and 12 to give polymers with narrow molecular weight distributions (PDI < 1.15).