Synthesis of a rhodaazacyclopropane and characterization of its radical cation by EPR spectroscopy.

Cyclopropane and its derivatives (ER2)3 (E=C, Si, Ge, Sn), bicyclobutanes, and other strained hydrocarbons have remarkably low oxidation potentials when compared to their unstrained linear counterparts. Can this property be translated to transition-metal complexes, such that small rings incorporating the transition metal lead to more facile oxidation? With this question in mind, we characterized a d Rh complex that has a metal center incorporated in a three-membered ring. Furthermore, we report the results from high-resolution pulse EPR spectroscopy, which, in combination with density functional theory (DFT) calculations, allowed us to characterize in detail the electronic structure of the corresponding radical cation. In analogy to the preparation of trop2NH [4] (trop= tropylidenyl= 5Hdibenzo[a,d]cyclohepten-5-yl), we prepared the N-methyl derivative trop2NMe (1) from (Me3Si)2NMe and tropCl (Scheme 1). Subsequently, 1 was treated with [Rh2(m2Cl)2(cod)2] (cod= 1,5-cyclooctadiene) to yield [Rh2(m2-Cl)2(trop2NMe)2], which was treated with PPh3 to give [RhCl(trop2NMe)(PPh3)] (2). Addition of AgOTf (OTf = CF3SO3 ) led to the isolation of [Rh(trop2NMe)(PPh3)]OTf (3) as red needles in 78% overall yield (for details, see the Supporting Information). The Cand D3-labeled iodide complexes [C]5 and [D3]5 were prepared from the reactions of the rhodium(i)amide 4 with CH3I and CD3I, respectively. The NMR data indicate that 2 and 5 form trigonal bipyramidal 18-electron complexes in CDCl3 solution with the halide atoms and the C=Ctrop units in the equatorial