Molecular solid-gas organometallic chemistry. Catalytic and stoichiometric iridium-assisted C-C bond-forming reactions involving ethyne and ethene

Article abstract of DOI:10.1021/om00016a020

Treatment of crystals of the (η²-ethene)dihydride complex [(triphos)Ir(H)₂(C₂H₄)]BPh₄ (1; triphos = MeC(CH₂PPh₂)₃) with ethyne (4 atm) at 70°C for 3 h results in evolution of ethene and but-2-ene and formation of five different organometallic products, namely the η⁴-benzene complex [(triphos)Ir(η⁴-C₆H₆)]BPh₄ (2), the η⁴-buta-1,3-diene complex [(triphos)Ir(η⁴-C₄H₆)]BPh₄ (3), the η⁴-cyclohexa-1,3-diene complex [(triphos)Ir(η⁴-C₆H₈)]BPh₄ (4), and the crotyl hydride isomers [(triphos)Ir(H)(η³-MeC₃H₄)]BPh₄ (5-anti and 5-syn) in a kinetic product ratio of 35:5:23:28:9. At 100°C, the solid-gas reaction produces catalytic amounts of benzene, the catalyst precursor being the η⁴-benzene complex 2. Temperature-programmed reactions carried out in a flow reactor and the use of isolated complexes in independent solid-gas reactions permit mechanistic conclusions which account for the varied organic and organometallic products. The ethene ligand in 1 is an essential ingredient for both cyclotrimerization and cooligomerization reactions of ethyne, which are traversed by η³-crotyl complexes. Conversely, the ethene ligand is a competitive inhibitor for the reductive dimerization of ethyne to buta-1,3-diene, for which the two hydride ligands are mandatory. Comparison with fluid solution-phase systems provides evidence for the control exerted by the constraining environment of the crystal lattice on the solid-gas reactions.