New routes to 1- and 2-adamantyl anion equivalents are described, starting from commercially available 1- and 2-adamantylzinc bromides and employing reducing metals (Mg; Li). Adamantylmagnesium bromides (both 1-AdMgBr and 2-AdMgBr) can reliably be produced via reaction of the corresponding adamantylzinc bromides with excess magnesium metal. Reactions of adamantylzinc bromides with stoichiometic lithium biphenylide or lithium 2,2'-bipyridylide afford the new diadamantylzinc species, 1-AdZn and 2-AdZn, isolable free of solvent and salt impurities. Addition of 2,2'-bipyridine (bipy) leads to the crystalline adducts 1-AdZn(bipy) and 2-AdZn(bipy), which were structurally characterized. The resulting adamantyl anions were used in order to generate the first adamantyl complexes of mercury (1- and 2-AdHg), gold (1- and 2-AdAu(PPh), 1- and 2-AdAu(PCy)) and bismuth (2-AdBiBr), of which 1- and 2-AdHg, 2-AdAu(PPh), 2-AdAu(PCy), and 2-AdBiBr were isolated. These include the first structurally characterized unsupported 2-adamantyl metal complexes.

Dedicated to the memory of Paul von Ragué Schleyer, who made modern adamantyl chemistry possible.Abstract: The first adamantyl platinum complexes were isolated and characterized, namely [(COD)Pt(2-Ad)Cl], [(dppe)Pt(2-Ad)Cl], [(COD)Pt(2-Ad)Me] and, [(dppe)Pt(2-Ad)Me] {COD = 1,5cyclooctadiene, dppe = 1,2-bis(diphenylphosphino)ethane, Ad = adamantyl}. These complexes show considerable stability, including resistance to heating to 125°C in solution for several days. It is therefore concluded that previously existing road Adamantane, the simplest diamondoid molecule, has great potential for use in advanced materials, [1] drug development, [2] and ligands for organometallic catalysis. [3] Due to adamantane's innate chemical stability, the synthetic tool kit for the functionalization of the adamantyl group is still quite limited, in contrast to the situation for other alkyls. The exceptional donating ability of the adamantyl group at both the 1-adamantyl (bridgehead) and 2-adamantyl (bridge) positions makes transformations that involve carbocations rather straightforward. Conversely, many transformations involving carbanions, which are routine for other alkyls, are very difficult for adamantyls. [4] Arguably, efficient future procedures for functionalization of adamantane will be transition metal mediated, in particular for the bridge position, which in comparison to the bridgehead position, is much less accessible through radical pathways. [5] Despite substantial initial interest in adamantane within the organometallic community, largely due to adamantane's resistance to -elimination, progress in adamantyl metal chemistry over the last several decades has been very slow. [6] The reason for this is twofold; first, the synthesis of adamantyl anions, specifically lithium and Grignard compounds, is fraught with highly erratic yields and side reactions, [7] and reliable zinc chemistry has only recently been developed. [7b,7c] Second, homoleptic metal adamantyl complexes [8] have proven to be extremely insoluble, [a]

The 2-adamantyl (2-Ad) group is a particularly challenging alkyl to install on a transition metal, with the only reported 2-adamantyl complexes of platinum being those of Pt(II). The question of whether 2-adamantyl complexes with platinum in the oxidation state +IV can be made and whether they are stable is answered here. The Pt(IV) compound trans-[(bpy)PtMe2(2-Ad)I] (bpy= 2,2’-bipyridine) was synthesized via oxidative addition of iodomethane to [(COD)PtMe(2-Ad)] (COD=1,5-cyclooctadiene) in the presence of bpy. Iodide abstraction with silver triflate (triflate anion, OTf-=CF3SO3-) produced trans-[(bpy)PtMe2(2-Ad)(OTf)]. Both complexes were unambiguously characterized by 1D NMR (1H, 13C) spectroscopy and X-ray crystallography. Both show evidence for the large steric bulk of the 2-adamantyl group (through the conformation of the complex adopted) and also for its exceptionally pronounced trans-influence (very long bonds to iodide/triflate trans to adamantyl). Both of the new platinum(IV) adamantyl complexes were extremely stable, even to prolonged heating.

Selective synthetic modifications on diamondoids (well‐defined molecular nano‐diamonds) are difficult. Group IV organometallic complexes are promising systems for CH bond activation. We study the CH bond activation of the hard‐to‐activate CH2 positions of the adamantyl group (the smallest diamondoid) using density functional theory. As a platform for activation, we tether the adamantyl group to the cyclopentadienyl in a substituted bis‐cyclopentadienyl group IV metal diphenyl complex. The mechanism proposed in the experimental paper reporting the activation of C(Me)2‐Ph or t‐Bu groups using Zr(IV) involves an η2‐benzyne complex intermediate. Our computational work confirms the two‐step mechanism proposed for activation of C(Me)2‐Ph or t‐Bu using Zr(IV) and further extends it to Ti(IV) and Hf(IV). The first step forms the benzyne complex. In the second step, the cyclopentadienyl‐bound group is activated through a mechanism that closely resembles a σ‐bond metathesis when the benzyne complex is described as a metallacyclopropene We demonstrate through computations that the two‐step reaction can be successfully applied to the adamantyl group. CH bond activation of adamantyl is found to be thermodynamically and kinetically feasible. The important question of regioselectivity is addressed. We predict that α‐CH bond activation will be achievable with Ti (thermodynamic control), and selective γ‐CH bond activation with Zr (kinetic or thermodynamic control).