The chemistry of Mo(+3) is dominated by the massive bias of [X3Mo] units to dimerize. It is the stability of the resulting  2  4 metal-metal triple bond between the two d electron fragments that provides a formidable thermodynamic driving force for the formation of homo-bimetallic complexes of the general type [X3MoMoX3] (X = alkyl, (pseudo)halide, alkoxy, silyloxy, dialkylamido etc.). Ever since the first such complex had been described by Wilkinson and coworkers in 1971, the field flourished, leading to a plethora of homoleptic representatives. 2,3 Some of them have been transformed into heteroleptic variants by partial ligand exchange via protonolysis or salt metathesis, whereby "symmetrical" ligand distributions ([X2YMoMoYX2], "1,2-pattern") were far more commonly attained than "unsymmetrical" ones ([XY2MoMoX3], "1,1-pattern"). Such isomers tend not to interconvert, suggesting that the barriers for group transfer between the two neighboring molybdenum centers under thermal conditions are high in most cases. Heteroleptic examples of the type [X2YMoMoX3] or [XY2MoMoX3] are exceedingly rare, and heterodimers of the general constitution [X3MoMoY3] seem to be unknown. The challenge to access a kinetically stable monomeric Mo(+3) complex was first met in 1995 by Cummins and coworkers, who disclosed the preparation, structure and stunning reactivity of the trigonal planar complex [(tBu)(Ar)N]3Mo (Ar = 3,5-dimethylphenyl) (1) (Figure ). This particular trisamidomolybdenum species and its siblings are capable of activating numerous small molecules under mild conditions, including substrates as unreactive as N2 or N2O. The serendipitous discovery in our laboratory that 1 also reacts with CH2Cl2 to generate alkyne metathesis catalysts in situ that proved highly chemoselective and therefore appropriate for applications to polyfunc-tionalized substrates opened an interface to advanced organic synthesis as well. In any case, the strongly -donating and very bulky amido ligands safeguard the Mo(+3) center so effectively that dimerization of 1 has never been observed, not even as a side reaction in any of the applications that this complex has found so far in the literature. Very few other monomeric Mo(+3) complexes were described ever since. Arguably most prominent are complexes such as 2 comprising a trisamidoamine ligand framework, which served as entry point for the reductive cleavage of N2 with formation of NH3 in a catalytic mode. Though much less -donating than amides, bulky silanolates were also shown to be adequate ligands, as witnessed by complex [(tBu3SiO)3Mo] (3), even though the structure of 3 proper is unknown and its monomeric nature was inferred from a crystalline phosphine adduct. Complex [[tBuO)3SiO]3Mo] (4) constitutes an interesting variation on that theme: by virtue of the additional lateral oxygen atoms, each siloxide engages in weak  2 binding; 4 is hence a coordinatively saturated octahedral entity, yet retains the prototypical reactivity of a monomeric Mo(+3) species towards N2 and other small molecules. A higher level of coordinative and electronic saturation also helps stabilize complex 5, in which two of the three 2,5-dimethylpyrrolide ligands are  5 -bound, thus rendering the bonding situation analogous to that of a bent metallocene. Scheme 1. A dumbbell dimer with two tripodal silanolate endcaps; Ar = 2,6-dimethylphenyl Intrigued by these reports, we wondered whether tripodal silanolates or alkoxides of the types recently used to support high-valent molybdenum or tungsten alkylidynes could serve similar purposes. For the excellent synergy between these ligands and the respective high-valent metal centers, catalysts such as 6 and 7 excel in alkyne metathesis for reasons that are now fairly well understood. When applied to Mo(+3), the phenyl ring forming the basal plane of the "canopy" ligand framework would effectively block one side of the hypothetical complex A, whereas the fence of upward-pointing substituents R on the tethers encircling the Mo(+3) atom potentially shields the opposite face.