Preparation of diazoalkane complexes of ruthenium and their cyclization reactions with alkenes and alkynes

Article abstract of DOI:10.1021/om500481d

The diazoalkane complexes [Ru(η⁵-C₅H ₅)(N₂CAr1Ar2)(PPh₃)(L)]BPh₄ (1-5: Ar1 = Ar2 = Ph (a), Ar1 = Ph and Ar2 = p-tolyl (b), Ar1Ar2 = C ₁₂H₈ (c), Ar1 = Ph and Ar2 = PhCO (d); L = PPh₃ (1), P(OMe)₃ (2), P(OEt)₃ (3), PPh(OEt)₂ (4), Bu^tNC (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-CH ₂=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-C ₅H₅){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-C₅H ₅)(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-C ₅H₅){η¹-N=NC(Ar1Ar2)CH=CH}(PPh ₃){P(OMe)₃}]BPh₄ (24), whereas reactions with the terminal alkynes PhC≡CH and Bu^tC≡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-C₅H ₅){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}]BPh ₄ (19b), [Ru(η⁵-C₅H₅) {η²-CH=CHCO(O)CO}(PPh₃){P(OMe)₃}]BPh ₄ (21), and [Ru(η⁵-C₅H₅) {η¹-N=NC(C₁₂H₈)CH=CH}(PPh ₃){P(OMe)₃}]BPh₄ (24c).