Rate of interconversion of syn and anti rotamers of Mo(CHCMe2Ph)(NAr)(OR)2 and relative reactivity toward 2,3-bis(trifluoromethyl)norbornadiene

Abstract

Abstract : Anti rotamers of Mo(CHCMe2Ph)(NAr)(OR)2 complexes (Ar = 2,6-C6H3-i- Pr2; OR = OCMe2(CF3), OCMe(CF3)2, and OC(CF3)2(CF2CF2CF3)) can be generated at -80 deg in toluene by photolysis at 366 nm and the rate of conversion of anti to syn rotamers determined by NMR methods. At equilibrium the anti rotamers can be observed by high field proton NMR at 25 deg after many transients and values for Keq(syn/anti) thereby determined. Keq can be determined at O deg when OR = OCMe3 and k anti/syn estimated. The rate of conversion of the anti to the syn rotamer in toluene is found to vary by at least five orders of magnitude as the alkoxide is changed from t-butoxide to OC(CF3)2(CF2CF2CF3). The results in THF are analogous, although the rates of rotamer interconversion are much slower for any given alkoxide. Addition of 2,3-bis(trifluoromethyl)norbornadiene to mixtures containing both anti and syn Mo(CHCMe2Ph)(NAr)OCMe(CF3)2)2 showed that in both toluene and THF the anti rotamer was orders of magnitude more reactive than the syn rotamer.