Reactivity of [Re(η2-H2)(CO)2P3]+ cations with alkynes: preparation of vinylidene and propadienylidene complexes

Treatment of [Re(η2-H2)(CO)2P3]+ cations with phenylacetylene leads to the displacement of H2 and the formation of vinylidene [Re{CC(H)Ph}(CO)2P3]+ (1–3) [P=P(OEt)3, PPh(OEt)2 or PPh2OEt] derivatives. Infrared and NMR data support equilibrium in solution [Re(CO)2P3]++PhCCH⇄[Re{CC(H)Ph}(CO)2P3]+ involving the unsaturated complex, free alkyne and vinylidene derivative. 1,4-Diethynylbenzene also tautomerises to the Re(I) centre, affording the [Re{CC(H)(1,4-C6H4CCH)}(CO)2P3]BF4 [P=P(OEt)3 or PPh(OEt)2] vinylidene derivatives. Vinylidene complexes 1–3 are deprotonated easily by NEt3 to give acetylides Re(CCR)(CO)2P3 (4–6) (R=Ph or 1,4-C6H4CCH), which may in turn be reprotonated with HBF4·Et2O to reform vinylidenes 1–3. Acetylide complexes 4–6 were also prepared by reacting unsaturated cations [Re(CO)2P3]+ with lithium acetylide. Binuclear complexes {Re(CO)2P3}2(μ-1,4-CCC6H4CC) (7, 8) [P=PPh(OEt)2 or PPh2OEt] were obtained by sequential treatment of [Re(CO)2P3]+ cations, first with 1,4-HCCC6H4CCH and then with an excess of NEt3. Propadienylidene complexes [Re(CCCPh2)(CO)2P3]BF4 (9, 10) [P=PPh(OEt)2 or PPh2OEt] were prepared by allowing [Re(η2-H2)(CO)2P3]+ cations or unsaturated species [Re(CO)2P3]+ to react with HCCC(Ph2)OH at room temperature. The characterisation of all new complexes by IR and 1H-, 31P{1H}- and 13C{1H}-NMR spectra is also discussed.