MOLECULAR-SOLID GAS ORGANOMETALLIC CHEMISTRY - CATALYTIC AND STOICHIOMETRIC IRIDIUM-ASSISTED C-C BOND-FORMING REACTIONS INVOLVING ETHYNE AND ETHENE

Treatment of crystals of the (eta2-ethene)dihydride complex [(triphos)Ir(H)2(C2H4)]BPh4 (1; triphos = MeC(CH2PPh2)3) with ethyne (4 atm) at 70-degrees-C for 3 h results in evolution of ethene and but-2-ene and formation of five different organometallic products, namely the eta4-benzene complex [(triphos)Ir(eta4-C6H6)]BPh4 (2), the eta4-buta-1,3-diene complex [(triphos)Ir(eta4-C4H6)]BPh4 (3), the eta4-cyclohexa-1,3-diene complex [(triphos)Ir(eta4-C6H8)]BPh4 (4), and the crotyl hydride isomers [(triphos)Ir(H) (eta3-MeC3H4)]BPh4 (5-anti and 5-syn) in a kinetic product ratio of 35:5:23:28:9. At 100-degrees-C, the solid-gas reaction produces catalytic amounts of benzene, the catalyst precursor being the eta4-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 eta3-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.