Binding, Release and Functionalization of Intact Pnictogen Tetrahedra Coordinated to Dicopper Complexes

Polyphosphorus Ligand Complexes of Coinage Metals for Multiple Capturing of Intact P4 Tetrahedra

Two- and three-component self-assembly reactions of [CpRFe(η5-P5)] (CpR = C5(CH3)5 (Cp*, 1a), C5(4-EtC6H4)5) (CpPEt, 1b)) with the coinage metal salts [Cu(CH3CN)4][SbF6] or AgSbF6 were investigated to study the prerequisites for the potential coordination of white phosphorus by using a sterically encumbered CpR ligand and noncoordinating anions. In the self-assembly reactions with white phosphorus, either 0D or 1D coordination complexes are formed, all of which feature coordinated intact P4 tetrahedra and thus comprise an unprecedented class of mixed polyphosphorus ligand complexes capable of complete release of P4 in solution confirmed by NMR studies. The bulkiness of the used CpR ligand and the correctly chosen solvent allowed for obtaining more beneficial structural motifs, the first discrete tetra- and penta-coordinated cyclo-P5 ligand complexes, that provide the maximal content of coordinated P4 molecules per species known so far. All products are characterized by single-crystal X-ray diffraction, NMR spectroscopy, and mass spectrometry.

Stabilization of Sb4 Tetrahedra in Paramagnetic Transition Metal Carbonyl Complexes

We present a straightforward synthetic route to the novel chromium carbonyl-stabilized paramagnetic Sb4-based cluster [Et4N]4[Sb4Cr6(CO)28] ([Et4N]4[1]), which represented a rare example of the intact Sb4 tetrahedron structurally characterized in the solid state. Complex 1 exhibited versatile reactivities toward groups 7-9 metal carbonyls, dioxygen, or [Cu(MeCN)4][BF4] to form selective orbital-controlled Sb4-based products, including transmetalated paramagnetic complexes [Et4N]4[Sb4Cr5Mn(CO)28]Br ([Et4N]4[1-Mn]Br), [Et4N]4[Sb4Cr2Fe6(CO)30] ([Et4N]4[1-Fe]), and [Et4N]2[Sb4Cr4Co4(CO)31] ([Et4N]2[1-Co]), the dioxygen-activated paramagnetic cluster [Et4N]4[O2Sb4Cr6(CO)28] ([Et4N]4[1-O2]), or the spin-quenched complex [Et4N]2[Sb4Cr6(CO)28] ([Et4N]2[2]), respectively. The structural nature, bonding properties, paramagnetism, and semiconductivity of these unprecedented transition metal carbonyl-protected Sb4-based clusters were further realized with DFT calculations.

Nucleophilic Functionalization of Activated P4 in [CpFe(CO)2-(η1-P4)][Al(ORF)4] with Alcohols R-OH

The bonding situation in [Fp-P4][Al(ORF)4] (1) (Fp = (CO)2CpFe, RF = C(CF3)3) gives rise to an Umpolung of the P4 fragment, which should make it accessible for nucleophiles. To investigate this projected reactivity, the complex was combined with a series of hydroxy-nucleophiles - that all do not react with free P4 - leading to a variety of P1 building blocks. With excess of R-OH (R = Me, Et, Ph), the thermodynamically more stable complex salts [Fp-P(H)x(OR)3-x)][Al(ORF)4] (x=2,1,0) (2b-2d) are formed and show that the phosphonium type pathway is accessible. Quantum chemical calculations display a variety of reaction pathways that all lead very rapidly to the P1 building blocks. With stoichiometric amounts of R-OH, [Fp-PH3][Al(ORF)4] (2 a) as well as [HP(OR)3][Al(ORF)4] (2 f) were observed as products. Hence, activation of the P4-cage in complex 1 was confirmed.

Enhancing the Reactivity of an Aromatic cyclo-P5 Ligand via Electrophilic Activation

Electrophilic activation of the aromatic cyclo-P5 ligand in [Cp*Fe(η5-P5)] is demonstrated to drastically enhance its reactivity towards weak nucleophiles. Unprecedented functionalized, contracted as well as complexly aggregated polyphosphorus compounds are accessed utilizing [Cp*Fe(η5-P5Me)][OTf] (A), highlighting the great potential of this underexplored mode of reactivity. Addition of carbenes to A affords novel 1,2- or 1,1-difunctionalized cyclo-P5 complexes [Cp*Fe(η4-P5(1-L)(2-Me)][OTf] (L=IDipp (1), EtCAAC (2), IiPr (3 b)) and [Cp*Fe(η4-P5(1-IiPr)(1-Me)][OTf] (3 a). For the first time, the much smaller IMe4 leads to the contraction of the cyclo-P5 ligand and formation of [Cp*Fe(η4-P4(1-IMe)(4-Me)] (4). DFT calculations shed light on the delicate mechanism of this type of reaction, which is reinforced by the experimental identification of key intermediates. Even the comparably weak nucleophile IDippCH2 reacts with A to form [Cp*Fe(η4-P5(1-IDippCH2)(1/2-Me)][OTf] (6 a/b), highlighting its explicitly more reactive nature. Moreover, exposure of A to IDippEH (E=N, P) leads to a unique aggregation reaction affording [{Cp*Fe}2{μ2,η4:3:1-P10Me2(IDippN)}][OTf] (8) and [{Cp*Fe}2{μ2,η4:1:1:1-P11Me2(IDipp)}][OTf] (9), respectively.

Controlling the Size of Molecular Copper Clusters Supported by a Multinucleating Macrocycle

The use of a nonrigid, pyridyldialdimine-derived macrocyclic ligand (3PDAI2) enabled the synthesis of well-defined mono-, di-, tri-, and tetra-nuclear Cu(I) complexes in good yields through rational synthetic means. Starting from mono- and diargentous 3PDAI2 complexes, transmetalation to Cu(I) proceeded smoothly with formation of AgX (X = Cl, I) salts to generate mono-, di-, and trinuclear copper complexes. Monodentate supporting ligands (MeCN, xylNC, PMe3, PPh3) were found to either transmetallate with or bind various di- and trinuclear clusters. The solution-phase dynamic behaviors of these species were studied through NMR spectroscopic investigations, and an in-depth study of the trinuclear systems revealed a rate dependence on the identity of the supporting ligand, indicating that ligand dissociation reactions were involved in the dynamic exchange processes. Synthetic investigations further found methods for the purposeful interconversion between the di- and trinuclear systems as well as the synthesis of a pseudotetrahedral tetracopper complex with two μ-Ph supporting ligands.

Understanding the Remarkable Stability of Well-Defined Dinuclear Copper(I) Carbene Complexes

The synthesis of a well-defined dicopper carbene complex supported by the PNNP (2,7-bis(di-tert-butylphosphaneyl)methyl-1,8-naphthyridine) expanded pincer ligand is reported. This carbene complex is remarkably stable, even in the presence of air and water. The reactivity of this complex was explored towards typical carbene transfer substrates and its electronic structure was investigated. Using a combination of experiments and DFT calculations, the principles that underly the stability of dinuclear carbene complexes are probed.

Structure and bonding of proximity-enforced main-group dimers stabilized by a rigid naphthyridine diimine ligand

The development of ligands capable of effectively stabilizing highly reactive main-group species has led to the experimental realization of a variety of systems with fascinating properties. In this work, we computationally investigate the electronic, structural, energetic, and bonding features of proximity-enforced group 13-15 homodimers stabilized by a rigid expanded pincer ligand based on the 1,8-naphthyridine (napy) core. We show that the redox-active naphthyridine diimine (NDI) ligand enables a wide variety of structural motifs and element-element interaction modes, the latter ranging from isolated, element-centered lone pairs (e.g., E = Si, Ge) to cases where through-space π bonds (E = Pb), element-element multiple bonds (E = P, As) and biradical ground states (E = N) are observed. Our results hint at the feasibility of NDI-E₂ species as viable synthetic targets, highlighting the versatility and potential applications of napy-based ligands in main-group chemistry.