The reactivity of the kinetically stabilized stannylene (MesTer)2Sn (1) (MesTer = –C6H3-2,6-(2,4,6-Me3-C6H2)2) toward N2O is revisited, yielding the terminal tin(IV) hydroxide 2 via formal intramolecular C(sp3)–H activation of a putative terminal stannanone intermediate. By switching to Eind ligation (Eind = 1,1,3,3,5,5,7,7-octaethyl-s-hydrindacen-4-yl) at the tin center, the synthesis and characterization of the crystalline lithium salt (Eind)Li(THF)2 (3) is reported, serving as a straightforward precursor for the clean generation of the corresponding stannylene (Eind)2Sn (4). Compound 4 can be further cleanly converted into the heteroleptic Eind/halide stannylene (Eind)SnCl (6). Both 4 and 6 serve as suitable precursors for the synthesis of the heteroleptic s-hydrindacene-/amido-substituted stannylene (Eind)Sn{N(SiMe3)2} (5).

Metal-organic frameworks (MOFs) are attractive platforms that merge concepts of homogeneous and heterogeneous catalysis. Catalyst design and optimization are enabled by an array of synthetic methods that offer independent control over the local chemical structure of lattice-embedded metal ions (i.e., ligand identity and geometry) and the long-range materials properties (i.e., porosity). Establishing the origin of catalytic activity in MOF-promoted reactions remains a significant challenge: The relative rates of catalyst turnover and substrate diffusion dictate the extent to which interstitial sites are accessible and operational in catalysis. To minimize the contributions of surface sites in catalysis, materials with large pore dimensions are often sought, however, the impact of pore expansion on the origins of catalytic activity is similarly challenging to establish. Here, we describe TAM-3, a Co(II) based MOF with accessible metal sites supported by a facially coordinating tris-tetrazole ligand set. TAM-3 features large channel-like pores (17 × 23 Å) and promotes aerobic C–H oxidation and olefin epoxidation. Using a set of simple kinetics experiments, based on the analysis of kinetic isotope effects and olefin oxidation diastereoselectivities, we demonstrate that despite the large pores, interstitial metal ions do not significantly contribute to the observed substrate oxidation. This study highlights the importance of conducting kinetic experiments to assess the origin of apparent catalytic activity with MOFs and the challenge of harnessing reactive oxidants with microporous catalyst materials.

Expanding the boundaries of synthetic tractability ─ of what molecules can be synthesized and isolated ─ is an eternal challenge for synthetic chemists. The development of new synthetic methods and strategies enables the properties and potential functions of novel molecular targets to be experimentally evaluated. In the context of catalysis, predictable synthetic strategies are often available to access kinetically persistent intermediates such as catalyst resting states. In contrast, synthesis and characterization of the reactive intermediates are often not possible due to the fleeting lifetimes of these species. In crystallo photochemistry combines single-crystal matrix isolation with cryogenic photochemistry to enable reactive intermediates to be synthesized under conditions in which they are persistent and can be (crystallographically) characterized. This Outlook highlights key achievements of in crystallo photochemistry as well as discusses opportunities and challenges that confront realization of the potential of in crystallo synthesis to redefine the boundaries of synthetic tractability.