Azametallacyclobutanes have been invoked as intermediates in a number of catalytic reactions. For example, Alper et al. postulated the formation of a transient azarhodacyclobutane intermediate in the rhodium-catalyzed conversion of aziridines to b-lactams. Bergman proposed the intermediacy of azazirconacyclobutenes and azazirconacyclobutanes in the hydroamination of alkynes and olefins, respectively. Reductive elimination from an azaferracyclobutane was postulated by Halfen in the iron-catalyzed aziridination of olefins. Only a few azametallacyclobutanes have been isolated and characterized. The Bergman group prepared an azairidacyclobutane by C H activation, ligand displacement, and subsequent deprotonation on an iridium complex. Hillhouse and co-workers discovered that nickel bipyridyl complexes underwent oxidative addition to aziridines, inserting into the least hindered C N bond. The isolation and complete characterization of these novel azanickelacyclobutanes were reported. Likewise, Wolfe and co-workers demonstrated that azapalladacyclobutanes are intermediates in the isomerization of aziridines to ketimines. Recently, the Hillhouse group reported the intermediacy of an azanickelacyclobutane in a formal [2+2] addition of ethylene to a nickel nitrene complex. Subsequent b-hydride elimination and reductive elimination gave the nitrene insertion product. We have become interested in the synthesis and reactivity of heteroatom-containing metallacycles, anticipating that these complexes can serve as intermediates in novel chemical transformations. We recently reported that rhodaoxetanes (2) undergo transmetalation with organoboronic acids, with the goal of developing catalytic carbohydroxylation. The rhodaoxetanes were originally reported by de Bruin et al. and are easily prepared by oxidation of cationic Rh–ethylene complexes with H2O2 (Scheme 1, conversion of 1 into 2). [10] We hypothesized that by changing the oxidant 2-azarhodacyclobutanes could be synthesized from the same Rh–ethylene complex. Key to the success of this strategy would be the identification of an appropriate N-based oxidant. We report herein the first examples of isolable azarhodacyclobutanes using N-(p-toluenesulfonyl)iminophenyliodinane (PhINTs) as the oxidant. Complex 1 was exposed to one equivalent of PhINTs in methanol at room temperature. The reaction mixture darkened within minutes from a green to a deep rust-colored, almost black, solution. The ESI mass spectrum of the crude product mixture showed a signal at 590 m/z, which corresponded to the expected mass of azarhodacyclobutane 3, consistent with the incorporation of the N-tosyl (tosyl= ptoluenesulfonyl) fragment. We anticipated that azarhodacyclobutane 3 would exhibit a similar H NMR spectrum to rhodaoxetane 2. However, the crude H NMR spectrum of 3 was considerably more complicated than that of 2. Nonetheless, we were able to identify features in the H NMR spectrum of the crude reaction mixture that closely resembled signals found in the H NMR spectrum of 2. Specifically, we observed a doublet of triplets in 3 at approximately 2 ppm with a JRh-H coupling of about 2 Hz. Rhodaoxetane 2 exhibits a doublet of triplets with a similar chemical shift and coupling constants. We also observed a triplet in 3 at about 4 ppm. Rhodaoxetane 2 shows a triplet, again with a similar shift, but slightly farther downfield. The signals in complex 2 correspond to H1 and H2, respectively, in the oxametallacycle (Figure 1). Based on this information, we believed that we had prepared azarhodacyclobutane 3, as well as a number of by-products. Attempts to purify the crude material by crystallization, as complexes with Cl , BPh4 , or PF6 counterions, as well as by substitution of tris(2-pyridylmethyl)amine (TPA) for MeTPA as an auxiliary ligand were all unsuccessful. Liquid extraction methods and silica gel column chromatography also failed to purify the product. Gratifyingly, separation by HPLC on a C18 reverse-phase column was effective (14% yield by NMR using 1,3,5-trimethoxybenzene and tetramethylsilane as internal standards, 5% yield of isolated product after Scheme 1. Proposed formation of azarhodacyclobutane 3.