The tripodal compounds [(TMG3trphen)MII–solv](PF6)2 (M = Mn, Fe, Co;
solv = MeCN, DMF) and bipodal
analogues [(TMG2biphen)MII(NCMe)
x
](PF6)2 (x = 3 for Mn, Fe; x = 2 for Co) and [(TMG2biphen)MIICl2] have been synthesized with ligands
that feature a triaryl- or diarylmethyl-amine framework and superbasic
tetramethylguanidinyl residues (TMG). The dicationic M(II) sites mediate
catalytic nitrene-transfer reactions between the imidoiodinane PhINTs
(Ts = tosyl) and a panel of styrenes in MeCN to afford aziridines
and low yields of imidazolines (upon MeCN insertion) with an order
of productivity that favors the bipodal over the tripodal reagents
and a metal preference of Fe > Co ≥ Mn. In CH2Cl2, the more acidic Fe(II) sites favor formation of 2,4-diaryl-N-tosylpyrrolidines by means of an in situ (3 + 2) cycloaddition
of the initially generated 2-aryl-N-tosylaziridine
with residual styrene. In the presence of ketone, 1,3-oxazolidines
can be formed in practicable yields, involving a single-pot cycloaddition
reaction of alkene, nitrene, and ketone (2 + 1 + 2). Mechanistic studies
indicate that the most productive bipodal Fe(II) site mediates stepwise
addition of nitrene to olefins to generate aziridines with good retention
of stereochemistry and further enables aziridine ring opening to unmask
a 1,3-zwitterion that can undergo cycloaddition with dipolarophiles
(MeCN, alkene, ketone) to afford five-membered N-heterocycles.