Transition-metal cation complexes with 1,3,5,7-cyclooctatetraene of the form M~+(C_8H_8)_(1,2)(M=V,Fe,Ni,and Ag)are produced by laser vaporization in a pulsed nozzle cluster source.The clusters are mass-selected and photodissociated using the second and third harmonics of an Nd:YAG laser(532 and 355 nm).The first-row transition-metal complexes undergo retro-cyclotrimerization to produce M~+(benzene).The photo-dissociation of V~+(C_8H_8)also produces a significant amount of V~+(C_5H_5).This is attributed to the ability of V~+to donate electron density to stabilize a cyclopentadienyl anion.Dissociation of Ag~+(C_8H_8)exhibits a photoinduced charge-transfer pathway allowing an upper limit of 2.6 eV to be placed on the binding energy in this system.Complexes with two C_8H_8 molecules primarily dissociate by loss of intact C_8H_8 molecules with some fragmentation to M~+(C_(10)H_(10))for M~+=V and Fe.Fragmentation of these M~+(C_(10)H_(10))species indicates a structure that is not ferrocene-like in nature.Mixed sandwich complexes are produced with both COT and benzene as ligands,and these dissociate by eliminating benzene,indicating that COT is more strongly bound to these transition-metal ions.The results of these experiments shed new insight on the bonding and photochemistry of these organometallic systems.
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