To probe whether the formation of 11 is caused by the peculiar ligand framework, in which the three arms carrying the tertiary alcohol substituents are tied back onto a rigidifying arene linker, 1 was reacted with ordinary tertbutanol (Scheme 2). Once again, the corresponding heterodimer 12 was formed. It shows the same distinctive structural features, namely a very long MoMo bond (2.2944(2) Å) and small torsional angles (O-Mo-Mo-N: 32.57, 33.35, 34.72°) even further away from the ideal 60° that one might intuitively expect to find in such a crowded ligand environment (Figure ); the barrier to rotation about the NAr bond was determined to be on the order of 12.5 kcalmol 1 (for details, see the Supporting Information). Perplexed by the ease with which these unorthodox heterodimers are formed, the alcoholysis of 1 was repeated with tert-butanol in excess. Although a mixture was obtained in this case, the heterodimer 12 was still the major species in the crude product, whereas the homoleptic dimer [Mo2(OtBu)6] (13) was minor. Similarly instructive was another control experiment, in which purified heterodimer 12 was treated with tert-butanol; the recorded spectra showed no sign of formation of 13 even when the temperature was raised to 60°C for 15 h. This result is all the more surprising if one considers that the alcoholysis of [Mo2(NMe2)6] with tert-butanol in a hydrocarbon solvent is the standard method for the preparation of [Mo2(OtBu)6] (13). Moreover, [Mo2(OtBu)6] is the final product of and thermodynamic sink in many different reactions starting from various molybdenum sources. The remarkable preference for the formation of the heterodimer 12 is therefore likely kinetic in origin: putative [(tBuO)3Mo] (or a mixed species [(tBuO)n[(tBu)(Ar)N]mMo], n+m = 3) in statu nascendi is so "hot" that it instantly traps any remaining 1 with formation of 12. Once formed, the crowded ligand sphere precludes protonolysis of the remaining MoN bonds, at least by an encumbered partner such as tert-butanol.