Reactivity of [Re(η 2-H 2)(CO) 2P 3] + cations with alkynes: preparation of vinylidene and propadienylidene complexes

Abstract

Treatment of [Re(η 2-H 2)(CO) 2P 3] + cations with phenylacetylene leads to the displacement of H 2 and the formation of vinylidene [Re{CC(H)Ph}(CO) 2P 3] + ( 1– 3) [P=P(OEt) 3, PPh(OEt) 2 or PPh 2OEt] derivatives. Infrared and NMR data support equilibrium in solution [Re(CO) 2P 3] ++PhCCH⇄[Re{CC(H)Ph}(CO) 2P 3] + 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-C 6H 4CCH)}(CO) 2P 3]BF 4 [P=P(OEt) 3 or PPh(OEt) 2] vinylidene derivatives. Vinylidene complexes 1– 3 are deprotonated easily by NEt 3 to give acetylides Re(CCR)(CO) 2P 3 ( 4– 6) (R=Ph or 1,4-C 6H 4CCH), which may in turn be reprotonated with HBF 4·Et 2O to reform vinylidenes 1– 3. Acetylide complexes 4– 6 were also prepared by reacting unsaturated cations [Re(CO) 2P 3] + with lithium acetylide. Binuclear complexes {Re(CO) 2P 3} 2(μ-1,4-CCC 6H 4CC) ( 7, 8) [P=PPh(OEt) 2 or PPh 2OEt] were obtained by sequential treatment of [Re(CO) 2P 3] + cations, first with 1,4-HCCC 6H 4CCH and then with an excess of NEt 3. Propadienylidene complexes [Re(CCCPh 2)(CO) 2P 3]BF 4 ( 9, 10) [P=PPh(OEt) 2 or PPh 2OEt] were prepared by allowing [Re(η 2-H 2)(CO) 2P 3] + cations or unsaturated species [Re(CO) 2P 3] + to react with HCCC(Ph 2)OH at room temperature. The characterisation of all new complexes by IR and 1H-, 31P{ 1H}- and 13C{ 1H}-NMR spectra is also discussed.