RHODAOXETANE - SYNTHESIS, STRUCTURE, AND THEORETICAL EVALUATION

Oxidative addition of Rh(PMe3)3Cl to HOCMe2CH2Br leads to the beta-hydroxy complex 4. Deprotonation of 4 with (Me3Si) 2 NK leads to the rhodaoxetane 5. 4 and 5 were crystallographically characterized, allowing direct evaluation of the structural consequences of ring closure. The oxetane ring in 5 is planar and it exhibits Rh-C [2.069(10) angstrom] and C-0 [1.416(12) angstrom], significantly shorter than the equivalent bonds in 4. The planarity of the oxetane ring was assigned to a minimization of repulsive interactions between filled orbitals of the metal and oxygen in this geometry, a result of a theoretical study based on extended Huckel calculations. 4 also shows a substantial Cl...H hydrogen bond. 5 can also be obtained by direct oxidative addition of Rh(PMe3)3Br to isobutyleneoxide, providing the first direct demonstration of oxidative addition of a metal complex to a simple epoxide to yield a metallaoxetane. Calculations were done in order to probe the reactivity of the metallacycle.