Cycloaddition of Coordinated Diazoalkanes to Ethene To Yield 3H‑Pyrazole Derivatives

Diazoalkane complexes [Ru­(η⁵-C₅H₅)­(N₂CAr1Ar2)­(PPh₃)­L]­BPh₄ (1, 2; Ar1 = Ph, Ar2 = p-tolyl; Ar1Ar2 = C₁₂H₈; L = P­(OMe)₃, P­(OEt)₃) were prepared by allowing compounds RuCl­(η⁵-C₅H₅)­(PPh₃)­L to react with diazoalkane in ethanol. Treatment of complexes 1 and 2 with ethylene under mild conditions (1 atm, room temperature) led not only to the ethylene complexes [Ru­(η⁵-C₅H₅)­(η²-CH₂CH₂)­(PPh₃)­L]­BPh₄ (5, 6) but also to dipolar (3 + 2) cycloaddition, affording the 3H-pyrazole derivatives [Ru­(η⁵-C₅H₅)­{η¹-NNC­(Ar1Ar2)­CH₂CH₂}­(PPh₃)­L]­BPh₄ (3, 4). The propylene complexes [Ru­(η⁵-C₅H₅)­(η²-CH₃CHCH₂)­(PPh₃)­L]­BPh₄ (7, 8) were also prepared. The compounds were characterized by spectroscopy and by X-ray crystal structure determinations of 2a, 3b, and 7.