3-Rhoda-1,2-diazacyclopentanes: a series of novel metallacycle complexes derived from C-N functionalization of ethylene

Rh-containing metallacycles, [(TPA)Rh(III)(κ(2)-(C,N)-CH2CH2(NR)2-]Cl; TPA = N,N,N,N-tris(2-pyridylmethyl)amine have been accessed through treatment of the Rh(I) ethylene complex, [(TPA)Rh(η(2)-CH2CH2)]Cl ([1]Cl) with substituted diazenes. We show this methodology to be tolerant of electron-deficient azo compounds including azo diesters (RCO2N=NCO2R; R = Et [3]Cl, R = iPr [4]Cl, R = tBu [5]Cl, and R = Bn [6]Cl) and a cyclic azo diamide: 4-phenyl-1,2,4-triazole-3,5-dione (PTAD), [7]Cl. The latter complex features two ortho-fused ring systems and constitutes the first 3-rhoda-1,2-diazabicyclo[3.3.0]octane. Preliminary evidence suggests that these complexes result from N-N coordination followed by insertion of ethylene into a [Rh]-N bond. In terms of reactivity, [3]Cl and [4]Cl successfully undergo ring-opening using p-toluenesulfonic acid, affording the Rh chlorides, [(TPA)Rh(III)(Cl)(κ(1)-(C)-CH2CH2(NCO2R)(NHCO2R)]OTs; [13]OTs and [14]OTs. Deprotection of [5]Cl using trifluoroacetic acid was also found to give an ethyl substituted, end-on coordinated diazene [(TPA)Rh(III)(κ(2)-(C,N)-CH2CH2(NH)2-](+) [16]Cl, a hitherto unreported motif. Treatment of [16]Cl with acetyl chloride resulted in the bisacetylated adduct [(TPA)Rh(III)(κ(2)-(C,N)-CH2CH2(NAc)2-](+), [17]Cl. Treatment of [1]Cl with AcN=NAc did not give the Rh-N insertion product, but instead the N,O-chelated complex [(TPA)Rh(I)(κ(2)-(O,N)-CH3(CO)(NH)(N=C(CH3)(OCH=CH2))]Cl [23]Cl, presumably through insertion of ethylene into a [Rh]-O bond.