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.