One-electron reduction of [Mo(NCMe)(η²-McC₂Me)₂(η⁵-C₉H₇)][BF₄] with sodium or magnesium amalgam in thf affords the three-alkyne ‘fly-over’ complex [Mo₂{µ-(ση³:η³,σ-C₆Me₅)}(η⁵-C₉H₇)₂](1). The structure of (1) has been established by X-ray crystallography. The dinuclear complex contains two molybdenum atoms at an interatomic distance consistent with the presence of a triple bond [Mo(1)–Mo(2) 2.305(2)Å]. Each molybdenum carries an η⁵-bonded indenyl ligand, and is also bonded (σ and η³) to a C₆Me₅ fragment in a ‘fly-over’ mode beginning and ending with different molybdenum atoms. The mechanism of formation of (1) is discussed. It is interesting that (1) does not react with an excess of but-2-yne. However, treatment of the 30-electron species with CO at room temperature leads to the rapid formation of the 34-electron dicarbonyl species [Mo₂{µ-(σ,η³:η³,σ-C₆Me₆)}(CO)₂(η⁵-C₉H₇)₂](2) whose structure was established by X-ray crystallography. The effect of the addition of two carbonyl ligands is to lengthen the Mo–Mo distance to 2.933(1)Å, a length compatible with a bond order of unity. The increase in the Mo–Mo distance spanned by the C₆Me₅ fragment is accompanied by an uncoiling of the ‘fly-over’ unit. An isomeric dicarbonyl species (3) with higher symmetry (C₂ instead of C₁) is formed in refluxing hexane, suggesting that (2) is the kinetically controlled product. In contrast, 2,6-xylyl isocyanide reacts at room temperature with (1) to form [Mo₂{µ-(σ,η³:η³,σ-C₆Me₆)}(CNC₆H₃Me₂-2,6)₂(η⁵-C₉H₇)₂](4), which is isostructrual with (3), i.e. the thermodynamically controlled product. The formation of these molecules is discussed in the context of related species obtained on the thermal reaction of alkynes with the dinuclear complex [Mo₂(µ-alkyne)(CO)₄(η-C₅H₅)₂].