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

Abstract

The diazoalkane complexes [Ru(η5-C5H5)(N2CAr1Ar2)(PPh3)(L)]BPh4 (1–5: 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 1–5 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 (10–14) 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 (6–9). 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 (17–22). 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).