Base-stabilized [BP3iPr](H)2CoSiH2(DMAP) (1, [BP3iPr] = PhB(CH2PiPr2)3-; DMAP = 4-dimethylaminopyridine) is a rare instance of a synthon for the simplest parent silylene complex (LM═SiH2). Complex 1 was accessed in high yields via double Si-H bond activation in SiH4 by [BP3iPr]Co(DMAP), and in solution, it undergoes rapid exchange between bound and free DMAP by an associative mechanism (as determined by variable-temperature 1H NMR dynamic studies). The DMAP ligand of 1 is readily displaced by metal-based fragments that bind silicon and cleave the Si-H bonds of the SiH2 moiety to produce bimetallic [Co═Si═M] (M = Co, Fe) molecular silicides. Thus, treatment of 1 with 0.5 equiv of (LCoI)2(μ-N2) (L = a tripodal ligand) resulted in the spontaneous formation of [BP3iPr](H)2Co═Si═Co(H)2L (L = [BP2tBuPz], PhB(CH2PtBu2)2(pyrazolyl)- (3); Tp″, HB(3,5-diisopropylpyrazolyl)3- (4)) with the concomitant release of DMAP. The symmetrical silicide [BP3iPr](H)2Co═Si═Co(H)2[BP3iPr] (5) was prepared by treatment of a mixture of 1 and [BP3iPr]Co(DMAP) with 2 equiv of Ph3B, which in this case is required to sequester DMAP as the elimination product Ph3B-DMAP. A heterobimetallic silicide, [BP3iPr](H)2Co═Si═Fe(H)2[SiP3iPr] (7; [SiP3iPr] = PhSi(CH2PiPr2)3), was obtained via in situ KC8 reduction of [SiP3iPr]FeCl and subsequent addition of 1 and Ph3B. These transformations involving a metal-SiH2 derivative demonstrate a fundamentally new type of reactivity for silylene complexes and provide a unique synthetic method for construction of molecular silicide complexes.

The synthesis of bimetallic molecular silicide complexes is reported, based on the use of multiple Si-H bond activations in SiH₄ at the metal centers of 14-electron LCo^I fragments (L = Tp″, HB(3,5-diisopropylpyrazolyl)₃^-; [BP₂^tBuPz], PhB(CH₂P^tBu₂)₂(pyrazolyl)). Upon exposure of (Tp″Co)₂(μ-N₂) (1) to SiH₄, a mixture of (Tp″Co)₂(μ-H) (2) and (Tp″Co)₂(μ-H)₂ (3) was formed and no evidence for Si-H oxidative addition products was observed. In contrast, [BP₂^tBuPz]-supported Co complexes led to Si-H oxidative additions with the generation of silylene and silicide complexes as products. Notably, the reaction of ([BP₂^tBuPz]Co)₂(μ-N₂) (5) with SiH₄ gave the dicobalt silicide complex [BP₂^tBuPz](H)₂Co═Si═Co(H)₂[BP₂^tBuPz] (8) in high yield, representing the first direct route to a symmetrical bimetallic silicide. The effect of the [BP₂^tBuPz] ligand on Co-Si bonding in 7 and 8 was explored by analysis of solid-state molecular structures and density functional theory (DFT) investigations. Upon exposure to CO or DMAP (DMAP = 4-dimethylaminopyridine), 8 converted to the corresponding [BP₂^tBuPz]Co(L)_x adducts (L = CO, x = 2; L = DMAP, x = 1) with concomitant loss of SiH₄, despite the lack of significant Si-H interactions in the starting complex. On heating to 60 °C, 8 underwent reaction with MeCl to produce small quantities of Me_xSiH_4-x (x = 1-3), demonstrating functionalization of the μ-silicon atom in a molecular silicide to form organosilanes.

Reactions of a dicopper(I) tert-butoxide complex with alkynes possessing boryl or silyl capping groups resulted in formation of unprecedented tetracopper(I) μ-acetylide/diyne complexes that were characterized by NMR and UV/Vis spectroscopy, mass spectrometry and single-crystal X-ray diffraction. These compounds possess an unusual μ₄ -η¹ :η¹ :η¹ :η¹ coordination mode for the bridging organic fragment, enforced by the rigid and dinucleating nature of the ligand utilized. Thus, the central π system remains unperturbed and accessible for subsequent reactivity and modification. This has been corroborated by addition of a fifth copper atom, giving rise to a pentacopper acetylide complex. This work may provide a new approach by which metal-metal cooperativity can be exploited in the transformation of acetylide and diyne groups to a variety of substrates, or as a starting point for the controlled synthesis of copper(I) alkyne-containing clusters.

Copper boryl species have been widely invoked as reactive intermediates in Cu-catalysed C-H borylation reactions, but their isolation and study have been challenging. Use of the robust dinucleating ligand DPFN (2,7-bis(fluoro-di(2-pyridyl)methyl)-1,8-naphthyridine) allowed for the isolation of two very thermally stable dicopper(i) boryl complexes, [(DPFN)Cu₂(μ-Bpin)][NTf₂] (2) and [(DPFN)Cu₂(μ-Bcat)][NTf₂] (4) (pin = 2,3-dimethylbutane-2,3-diol; cat = benzene-1,2-diol). These complexes were prepared by cleavage of the corresponding diborane via reaction with the alkoxide [(DPFN)Cu₂(μ-O ^t Bu)][NTf₂] (3). Reactivity studies illustrated the exceptional stability of these boryl complexes (thermal stability in solution up to 100 °C) and their role in the activation of C(sp)-H bonds. X-ray diffraction and computational studies provide a detailed description of the bonding and electronic structures in these complexes, and suggest that the dinucleating character of the naphthyridine-based ligand is largely responsible for their remarkable stability.

High-valent Ru^V-oxo intermediates have long been proposed in catalytic oxidation chemistry, but investigations into their electronic and chemical properties have been limited due to their reactive nature and rarity. The incorporation of Ru into the [Co₃O₄] subcluster via the single-step assembly reaction of Co^II(OAc)₂(H₂O)₄ (OAc = acetate), perruthenate (RuO₄^-), and pyridine (py) yielded an unprecedented Ru(O)Co₃(μ₃-O)₄(OAc)₄(py)₃ cubane featuring an isolable, yet reactive, Ru^V-oxo moiety. EPR, ENDOR, and DFT studies reveal a valence-localized [Ru^V(S = 1/2)Co^III₃(S = 0)O₄] configuration and non-negligible covalency in the cubane core. Significant oxyl radical character in the Ru^V-oxo unit is experimentally demonstrated by radical coupling reactions between the oxo cubane and both 2,4,6-tri-tert-butylphenoxyl and trityl radicals. The oxo cubane oxidizes organic substrates and, notably, reacts with water to form an isolable μ-oxo bis-cubane complex [(py)₃(OAc)₄Co₃(μ₃-O)₄Ru]-O-[RuCo₃(μ₃-O)₄(OAc)₄(py)₃]. Redox activity of the Ru^V-oxo fragment is easily tuned by the electron-donating ability of the distal pyridyl ligand set at the Co sites demonstrating strong electronic communication throughout the entire cubane cluster. Natural bond orbital calculations reveal cooperative orbital interactions of the [Co₃O₄] unit in supporting the Ru^V-oxo moiety via a strong π-electron donation.

High-valent RuV-oxo intermediates have long been proposed in catalytic oxidation chemistry, but investigations into their electronic and chemical properties have been limited due to their reactive nature and rarity. The incorporation of Ru into the [Co3O4] subcluster via the single-step assembly reaction of CoII(OAc)2(H2O)4 (OAc = acetate), perruthenate (RuO4-), and pyridine (py) yielded an unprecedented Ru(O)Co3(μ3-O)4(OAc)4(py)3 cubane featuring an isolable, yet reactive, RuV-oxo moiety. EPR, ENDOR, and DFT studies reveal a valence-localized [RuV(S = 1/2)CoIII3(S = 0)O4] configuration and non-negligible covalency in the cubane core. Significant oxyl radical character in the RuV-oxo unit is experimentally demonstrated by radical coupling reactions between the oxo cubane and both 2,4,6-tri-tert-butylphenoxyl and trityl radicals. The oxo cubane oxidizes organic substrates and, notably, reacts with water to form an isolable μ-oxo bis-cubane complex [(py)3(OAc)4Co3(μ3-O)4Ru]-O-[RuCo3(μ3-O)4(OAc)4(py)3]. Redox activity of the RuV-oxo fragment is easily tuned by the electron-donating ability of the distal pyridyl ligand set at the Co sites demonstrating strong electronic communication throughout the entire cubane cluster. Natural bond orbital calculations reveal cooperative orbital interactions of the [Co3O4] unit in supporting the RuV-oxo moiety via a strong π-electron donation.

The synthesis of polycyclic aromatic hydrocarbons (PAHs) and related nanographenes requires the selective and efficient fusion of multiple aromatic rings. For this purpose, the Diels-Alder cycloaddition has proven especially useful; however, this approach currently faces significant limitations, including the lack of versatile strategies to access annulated dienes, the instability of the most commonly used dienes, and difficulties with aromatization of the [4 + 2] adduct. In this report we address these limitations via the marriage of two powerful cycloaddition strategies. First, a formal Cp₂Zr-mediated [2 + 2 + 1] cycloaddition is used to generate a stannole-annulated PAH. Secondly, the stannoles are employed as diene components in a [4 + 2] cycloaddition/aromatization cascade with an aryne, enabling π-extension to afford a larger PAH. This discovery of stannoles as highly reactive - yet stable for handling - diene equivalents, and the development of a modular strategy for their synthesis, should significantly extend the structural scope of PAHs accessible by a [4 + 2] cycloaddition approach.