FLP-type nitrile activation and cyclic ether ring-opening by halo-borane nonagermanide-cluster Lewis acid-base pairs

A Series of Cyclopentadienyl Lanthanum Complexes with Metalloid Germanium Clusters

A series of cyclopentadienyllanthanum complexes with the disilylated metalloid germanium cluster [Ge9(Hyp)2]2- [Hyp = Si(SiMe3)3] has been prepared and fully characterized. The synthetic procedure is based on the salt metathesis reaction of two different cyclopentadienyllanthanum diiodides CpLaI2 (Cp: Cp*, pentamethylcyclopentadienyl; Cpttt, 1,2,4-tri-tert-butylcyclopentadienyl) with K2[Ge9(Hyp)2] in tetrahydrofuran (THF) with a subsequent extraction with n-hexane. The composition of the obtained compounds and the mode of coordination of the germanium cluster to the rare-earth metal are strongly influenced by the steric demand of the cyclopentadienyl ligands and the crystallization conditions. The centrosymmetric dimeric compounds with the common formula [CpLa(solv)(η2,3-Ge9(Hyp)2)]2 [1, Cp = Cp*, solv-THF; 2, Cp = Cpttt, solv-NCCH2C(Me)NSiMe3] have been isolated by the slow evaporation of a n-hexane solution, while a mononuclear complex [CptttLa(THF)2(η3-Ge9(Hyp)2)] (4) was found by crystallization from THF. The repeated recrystallization of 1 from n-hexane afforded the asymmetric dimer [Cp*La(THF)(η2,3-Ge9(Hyp)2)][Cp*La(η2,3-Ge9(Hyp)2)] (3) with only one coordinated THF molecule.

Zintl Clusters as a Platform for Lewis Acid Catalysis

Clusters of the main group elements phosphorus and arsenic, commonly categorized as Zintl clusters, have been known for over a century. And, only now is the application of these systems as catalysts for organic synthesis being investigated. In this work, boranes are tethered via an aliphatic linker to Zintl-based clusters and their Lewis acidity is examined experimentally, by the Gutmann-Beckett test and competency in the hydroborative reduction of six organic substrates, as well as computationally, by fluoride ion affinity and hydride ion affinity methods. The effects of tuning the aliphatic linker length, substituents at the boron, and changing the cluster from a seven-atom phosphorus system to a seven-atom arsenic system on reactivity are studied.

Significantly enhanced catalytic performance of Pd nanocatalyst on AlOOH featuring abundant solid surface frustrated Lewis pair for improved hydrogen activation

The catalytic performance of a catalyst is significantly influenced by its ability to activate hydrogen. Constructing frustrated Lewis pairs (FLPs) with the capacity for hydrogen dissociation on non-reducible supports remains a formidable challenge. Herein, we employed a straightforward method to synthesize a layered AlOOH featuring abundant OH defects suitable for constructing solid surface frustrated Lewis pair (ssFLP). The results indicated that the AlOOH-80 (synthesized at 80 °C) possessed an appropriate crystalline structure conducive to generating numerous OH defects, which facilitated the formation of ssFLP. This was further evidenced by the minimal water adsorption in the AlOOH-80, inversely correlated with the quantity of defects in the catalyst. As expected, the Pd loaded onto AlOOH (Pd/AlOOH-80) exhibited excellent catalytic activity in hydrogenation reactions, attributed to abundant defects available for constructing ssFLP. Remarkably, the Pd/AlOOH-80 catalyst, with larger-sized Pd nanoparticles, displayed notably superior activity compared to commercial Pd/Al2O3 and Pd/C, both featuring smaller-sized Pd nanoparticles. Evidently, under the influence of ssFLP, the size effect of Pd nanoparticles did not dominate, highlighting the pivotal role of ssFLP in enhancing catalytic performance. This catalyst also exhibited exceptionally high stability, indicating its potential for industrial applications.

Zintl Ions and Phases Promote the Catalytic Hydrophosphination of Alkynes, Alkenes, and Imines

Although Zintl ions and phases have been known for more than a century, their application as tools to build organic molecules is underdeveloped. Here, a range of Zintl ions and phases were surveyed in the hydrophosphination of alkynes, alkenes, and imines with diphenylphosphine to afford useful organophosphine products. Further investigations with diphenylphosphine in the absence of the unsaturated organic substrates revealed the formation of the diphenylphosphide anion, allowing for the conclusion that the role of the Zintl species is as an initiator in these transformations.

[(thf)5Ln(Ge9{Si(SiMe3)3}2)] (Ln = Eu, Sm, Yb): Capping Metalloid Germanium Cluster with Lanthanides

We report the synthesis of three neutral complexes with different coordination modes of a di-silylated metalloid germanium cluster to divalent lanthanides [(thf)₅Ln(ηⁿ-Ge₉(Hyp)₂)] (Ln = Yb (1, n = 1); Eu (2, n = 2, 3), Sm (3, n = 2, 3); Hyp = Si(SiMe₃)₃) by the salt metathesis of LnI₂ with K₂[Ge₉(Hyp)₂] in THF. The complexes were characterized by elemental analysis, nuclear magnetic resonance and UV-vis-NIR spectroscopy, and single-crystal X-ray diffraction. In thf solution, the formation of contact or solvate-separated ion pairs depending on the concentration is assumed. Compound 2 exhibits a blue luminescence typical for Eu²⁺. The solid-state magnetic measurements of compounds 2 and 3 confirm the presence of divalent europium and samarium, respectively.

Insights into the Reactivity of the Ring-Opening Reaction of Tetrahydrofuran by Intramolecular Group-13/P- and Al/Group-15-Based Frustrated Lewis Pairs

A theoretical study concerning key factors affecting activation energies for ring-opening reactions of tetrahydrofuran (THF) by G13/P-based (G13 = B, Al, Ga, In, and Tl) and Al/G15-based (G15 = N, P, As, Sb, and Bi) frustrated Lewis pairs (FLPs) featuring the dimethylxanthene scaffold was performed using density functional theory. Our theoretical findings indicate that only dimethylxanthene backbone Al/P-Rea (Rea = reactant) FLP-type molecules can be energetically favorable to undergo the ring-opening reaction with THF. Our theoretical evidence reveals that the shorter the separating distance between Lewis acidic (LA) and Lewis basic (LB) centers of the dimethylxanthene backbone FLP-type molecules, the greater the orbital overlaps between the FLP and THF and the lower the activation barrier for such a ring-opening reaction. Energy decomposition analysis (EDA) evidence suggests that the bonding interaction for such a ring-opening reaction is predominated by the donor-acceptor interaction (singlet-singlet interaction) compared to the electron-sharing interaction (triplet-triplet interaction). In addition, the natural orbitals for chemical valence (NOCV) evidence demonstrate that the bonding situations of such ring-opening reactions can be best described as FLP-to-THF forward bonding (the lone pair (G15) → the empty σ*(C-O)) and THF-to-FLP back bonding (the empty σ*(G13) ← filled p-π(O)). The EDA-NOCV observations show that the former plays a predominant role and the latter plays a minor role in such bonding conditions. The activation strain model reveals that the deformation energy of THF is the key factor in determining the activation energy of their ring-opening reactions. Comparing the geometrical structures of the transition states with their corresponding reactants, a linear relationship between them can be rationally explained by the Hammond postulate combined with the respective activation barriers calculated in this work.

Crystal structure of (1,4,7,10,13,16-hexaoxacyclooctadecane-κ 6O6)potassium(2-methylphenylamino)ethyl-2-methylphenylamide ammoniate (1/3.5), [K(18-crown-6)](o-CH3C6H4)NH(CH2)2N(o-CH3C6H4) 3.5 NH3, C28H53.5KN5.5O6

C28H53.5KN5.5O6, monoclinic, Pc (no. 7), a = 18.7986(12) Å, b = 8.3431(6) Å, c = 22.4638(16) Å, β = 100.554(5)°, V = 3463.6(4) Å3, Z = 4, Rgt (F) = 0.0712, wRref (F 2) = 0.2226, T = 150 K.

Assembly of metallo-macrocycles through reductive C-C coupling of alkylnitriles by an Mg-Mg-bonded compound

Low-valent metal complexes have attracted much research interest owing to their novel reactivities toward small molecules. Herein the reactivity of the α-diimine-ligated, Mg-Mg-bonded compound [K(THF)₃]₂[LMg-MgL] (1, L = [(2,6-iPr₂C₆H₃)NC(Me)]₂^2-) with aliphatic nitriles has been studied. Complex 1 readily activates n-alkylnitriles (RCN; R = propyl, butyl, and pentyl) to afford the unique trinuclear magnesium metallo-macrocyclic complexes, [LMg(μ-{(NC-C(R)C(CH₂R)-NH})]₃[K₃(Solv)₆] (2-4: R = -(CH₂)_nCH₃, n = 2, 3, or 4; Solv = THF/DME), through a reductive deprotonation of the α-H of one nitrile molecule and C-C coupling between this α-carbon and the cyanide (CN) group of another nitrile, followed by a 1,3-H shift. The results demonstrate the possibility of assembling supramolecular architectures based on the α-diimine [LMg] fragment through small molecule activation.

Heteroallene Capture and Exchange at Functionalised Heptaphosphane Clusters

Despite being known for decades the chemical reactivity of homoatomic seven-atom phosphorus clusters towards small molecules remains largely unexplored. Here, we report that neutral tris(silyl) functionalised heptaphosphane (P7 (SiR3 )3 ) cages are capable of heteroallene capture between the P-Si bonds of the cluster. A range of isocyanates and an isothiocyanate were investigated. In the case of isocyanates, silyl bonding at oxygen or nitrogen is regioselectively directed by the functional group on the isocyanate and substituents on the silyl moiety. Above all, we find that captured isothiocyanate molecules can be exchanged for isocyanate molecules, indicative of small molecule catch and release. Small molecule catch and release at these Zintl-derived clusters reveals their potential application as chemical storage materials or as reusable probes.

Substitution of Hyp (Hyp = Si(SiMe3)3) at metalloid [Ge9(Hyp)3]- clusters using phosphine stabilized Au(I)Cl

We present two new intermetalloid cluster compounds [(nBu3P)AuGe9(Hyp)2Au(PnBu3)]2 (1) and [Au(iPr2POC6H4OPiPr2)AuGe9(Hyp)2]2 (2) which are obtained from the reaction of KGe9(Hyp)3 (Hyp = Si(SiMe3)3) with respective Au(I) phosphine precursors. The products...