Rhodaoxetane: Synthesis, structure, and theoretical evaluation

Oxidative addition of Rh(PMe₃)₃Cl to HOCMe₂CH₂Br leads to the β-hydroxy complex 4. Deprotonation of 4 with (Me₃Si)₂NK 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) Å] and C-O [1.416(12) Å], 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 Hückel calculations. 4 also shows a substantial Cl⋯H hydrogen bond. 5 can also be obtained by direct oxidative addition of Rh(PMe₃)₃Br to isobutylene oxide, 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.