Preparation of 2‐Azarhodacyclobutanes by Rhodium(I)–Olefin Oxidation

Abstract

Erstaunliche Metallacyclen: Zwei Azarhodacyclobutane wurde durch Oxidation des RhI‐Olefin‐Komplexes 1 hergestellt (siehe Schema; Ts=p‐Toluolsulfonyl). Beide Isomere 2 a und 2 b wurden isoliert und durch NMR‐Spektroskopie und Massenspektrometrie charakterisiert; ihre Konfigurationen wurden in NOE‐Experimenten zweifelsfrei festgestellt.

Formation of Substituted Oxa‐ and Azarhodacyclobutanes

“…It is noteworthy that only complexes 14 and 15 , which have comparable geometry to complex 4 , were generated (Table 4). PhINTs oxidation of complex 1 under the same reaction conditions generated a 1:1.5 mixture of isomers 3 and 4 47. Whereas we were able to obtain complex 3 selectively using a protic solvent, under no circumstances were we ever able to obtain isomer 4 exclusively.…”

“…Oxidation with PhINTs : Having established that H 2 O 2 oxidation proceeds with excellent selectivity, we next explored the reactions of olefin complexes 6 and 7 with PhINTs. With ethylene as the olefinic ligand, we had previously shown that two isomers, 3 and 4 , were formed in aprotic solvents, but that only 3 was formed in protic solvents 47. As such, we selected MeOD as the solvent, anticipating that the reaction would be more selective than using an aprotic solvent.…”

“…PhINTs oxidation of complex 1 under the same reaction conditions generated a 1:1.5 mixture of isomers 3 and 4. [47] Whereas we were able to obtain complex 3 selectively using a protic solvent, under no circumstances were we ever able to obtain isomer 4 exclusively. To date, the basis for this selectivity with substituted olefins is unclear.…”

“…With ethylene as the olefinic ligand, we had previously shown that two isomers, 3 and 4, were formed in aprotic solvents, but that only 3 was formed in protic solvents. [47] As such, we selected MeOD as the solvent, anticipating that the reaction would be more selective than using an aprotic solvent. Unfortunately, the oxidation was not successful in MeOD and led to a complex mixture of unidentified products.…”

“…We also recently reported the isolation and characterization of the first 2‐azarhodacyclobutanes ( 3 and 4 ), by oxidation of TPA–Rh(ethylene) complex 1 with [ N ‐( p ‐toluenesulfonyl)imino]phenyliodinane (PhINTs) 47. The use of protic solvents led to the exclusive formation of isomer 3 , whereas aprotic solvents provided mixtures of 3 and 4 in varying ratios.…”