Formation of a [ONN(allyl)O]⁻ Anion via NO Insertion and Coupling Using Yttrium and Lanthanide Allyl Metallocenes

Nitric oxide (NO) reacts with (C5Me5)2Ln(η3-CH2CHCH2)(THF) to form the first crystallographically characterized group 3 and organolanthanide NO insertion products, namely, {(C5Me5)2Ln[μ-ONN(CH2CHCH2)O]}2 (Ln = Y, La, Sm). The [ONN(allyl)O]− anions adopt an unusual trans geometry and presumably arise from insertion of NO into the Ln−C(allyl) bond followed by coupling of the (allyl-NO) radical anion with a second molecule of NO. Heating a solution of the yttrium product at 110 °C for 20 h affords (C5Me5)2Y[ONN(CH2CHCH2)O-κ2O,O′], resulting from cleavage of the dimer and formation of the monomer as the thermodynamic product. The NN, N−O, and Ln−O bond distances suggest that a zwitterionic (−)O−NN(+)(R)−O(−) resonance structure is a main contributor to the bonding of these N-allyl-N-nitrosohydroxylaminato ligands.