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Preparation of Diazoalkane Complexes of Ruthenium and Their Cyclization Reactions with Alkenes and Alkynes

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posted on 14.07.2014, 00:00 authored by Gabriele Albertin, Stefano Antoniutti, Alessandra Botter, Jesús Castro, Mattia Giacomello
The diazoalkane complexes [Ru­(η5-C5H5)­(N2CAr1Ar2)­(PPh3)­(L)]­BPh4 (15: Ar1 = Ar2 = Ph (a), Ar1 = Ph and Ar2 = p-tolyl (b), Ar1Ar2 = C12H8 (c), Ar1 = Ph and Ar2 = PhCO (d); L = PPh3 (1), P­(OMe)3 (2), P­(OEt)3 (3), PPh­(OEt)2 (4), ButNC (5)) were prepared by allowing the chloro compounds RuCl­(η5-C5H5)­(PPh3)­(L) to react with the diazoalkanes Ar1Ar2CN2 in ethanol. Treatment of complexes 15 with ethylene (CH2CH2) under mild conditions (1 atm, room temperature) led not only to the η2-ethylene complexes [Ru­(η5-C5H5)­(η2-CH2CH2)­(PPh3)­(L)]­BPh4 (1014) but also to dipolar (3 + 2) cycloaddition, affording the 4,5-dihydro-3H-pyrazole derivatives [Ru­(η5-C5H5)­{η1-NNC­(Ar1Ar2)­CH2CH2}­(PPh3)­(L)]­BPh4 (69). Acrylonitrile (CH2C­(H)­CN) reacted with diazoalkane complexes 2 and 3 to give the 1H-pyrazoline derivatives [Ru­(η5-C5H5)­{η1-NC­(CN)­CH2C­(Ar1Ar2)NH}­(PPh3)­(L)]­BPh4 (19, 20). However, reactions with propylene (CH2C­(H)­CH3), maleic anhydride (ma, CHCHCO­(O)CO) and dimethyl maleate (dmm, CH3OCOCHCHOCOCH3) led to the η2-alkene complexes [Ru­(η5-C5H5)­(η2-R1CHCHR2)­(PPh3)­(L)]­BPh4 (1722). Treatment of the diazoalkane complexes 1 and 2 with acetylene CHCH under mild conditions (1 atm, room temperature) led to dipolar cycloaddition, affording the 3H-pyrazole complexes [Ru­(η5-C5H5)­{η1-NNC­(Ar1Ar2)­CHCH}­(PPh3)­{P­(OMe)3}]­BPh4 (24), whereas reactions with the terminal alkynes PhCCH and ButCCH gave the vinylidene derivatives [Ru­(η5-C5H5)­{CC­(H)­R}­(PPh3)­{P­(OMe)3}]­BPh4 (25, 26). The alkyl propiolates HCCCOOR1 (R1 = Me, Et) also reacted with complexes 2 to give the 3H-pyrazole complexes [Ru­(η5-C5H5)­{η1-NNC­(Ar1Ar2)­C­(COOR1)CH}­(PPh3)­{P­(OMe)3}]­BPh4 (27, 28). The complexes were characterized by spectroscopy and by X-ray crystal structure determinations of [Ru­(η5-C5H5)­{η1-NC­(CN)­CH2C­(Ph)­(p-tolyl)NH}­(PPh3)­{P­(OMe)3}]­BPh4 (19b), [Ru­(η5-C5H5)­{η2-CHCHCO­(O)CO}­(PPh3)­{P­(OMe)3}]­BPh4 (21), and [Ru­(η5-C5H5)­{η1-NNC­(C12H8)­CHCH}­(PPh3)­{P­(OMe)3}]­BPh4 (24c).