Versatile Reactivity of a Lithium Tris(aryl)plumbate(II) Towards Organolanthanoid Compounds: Stable Lead-Lanthanoid-Metal Bonds or Redox Processes

Highly Adaptive Nature of Group 15 Tris(quinolyl) Ligands─Studies with Coinage Metals

The substitution of heavier, more metallic atoms into classical organic ligand frameworks provides an important strategy for tuning ligand properties, such as ligand bite and donor character, and is the basis for the emerging area of main-group supramolecular chemistry. In this paper, we explore two new ligands [E(2-Me-8-qy)₃] [E = Sb (1), Bi (2); qy = quinolyl], allowing a fundamental comparison of their coordination behavior with classical tris(2-pyridyl) ligands of the type [E'(2-py)₃] (E = a range of bridgehead atoms and groups, py = pyridyl). A range of new coordination modes to Cu⁺, Ag⁺, and Au⁺ is seen for 1 and 2, in the absence of steric constraints at the bridgehead and with their more remote N-donor atoms. A particular feature is the adaptive nature of these new ligands, with the ability to adjust coordination mode in response to the hard-soft character of coordinated metal ions, influenced also by the character of the bridgehead atom (Sb or Bi). These features can be seen in a comparison between [Cu₂{Sb(2-Me-8-qy)₃}₂](PF₆)₂ (1·CuPF₆) and [Cu{Bi(2-Me-8-qy)₃}](PF₆) (2·CuPF₆), the first containing a dimeric cation in which 1 adopts an unprecedented intramolecular N,N,Sb-coordination mode while in the second, 2 adopts an unusual N,N,(π-)C coordination mode. In contrast, the previously reported analogous ligands [E(6-Me-2-py)₃] (E = Sb, Bi; 2-py = 2-pyridyl) show a tris-chelating mode in their complexes with CuPF₆, which is typical for the extensive tris(2-pyridyl) family with a range of metals. The greater polarity of the Bi-C bond in 2 results in ligand transfer reactions with Au(I). Although this reactivity is not in itself unusual, the characterization of several products by single-crystal X-ray diffraction provides snapshots of the ligand transfer reaction involved, with one of the products (the bimetallic complex [(BiCl){ClAu₂(2-Me-8-qy)₃}] (8)) containing a Au₂Bi core in which the shortest Au → Bi donor-acceptor bond to date is observed.

Introduction of plumbole to f-element chemistry

Herein, we present the synthesis and characterization of heteroleptic lanthanide complexes bearing a dianionic η5-plumbole ligand in their coordination sphere. The reaction proceeds via a salt elimination reaction between the dilithioplumbole ([Li(thf)]2[1,4-bis-tert-butyl-dimethylsilyl-2,3-bis-phenyl-plumbolyl] = [Li2(thf)2(η5-LPb)]) and specifically designed [Ln(η8-COTTIPS)BH4] precursors (Ln = lanthanide, La, Ce, Sm, Er; COTTIPS = 1,4-bis-triisopropylsilyl-cyclooctatetraenyl), that are capable of stabilizing a planar plumbole moiety in the coordination sphere of different trivalent lanthanide ions. In-depth ab initio calculations show that the aromaticity of the dianionic plumbole is retained upon coordination. Electron delocalization occurs from the plumbole HOMO to an orbital of mainly d-character at the lanthanide ion. The magnetic properties of the erbium congener were investigated in detail, leading to the observation of magnetic hysteresis up to 5 K (200 Oe s-1), an unequivocal proof for single molecule magnet behavior in this system. The magnetic behavior of the erbium species can be modulated by manipulating the position of the lithium cation in the complex, which directly influences the bonding metrics in the central [(η5-LPb)Er(η8-COTTIPS)]- fragment. This allowed us to assess a fundamental magneto-structural correlation in an otherwise identical inner coordination sphere.

Cation- and Anion-Mediated Supramolecular Assembly of Bismuth and Antimony Tris(3-pyridyl) Complexes

The use of antimony and bismuth in supramolecular chemistry has been largely overlooked in comparison to the lighter elements of Group 15, and the coordination chemistry of the tripodal ligands [Sb(3-py)₃] and [Bi(3-py)₃] (L) containing the heaviest p-block element bridgehead atoms has been unexplored. We show that these ligands form a common hybrid metal–organic framework (MOF) structure with Cu(I) and Ag(I) (M) salts of weakly coordinating anions (PF₆^–, SbF₆^–, and OTf^–), composed of a cationic substructure of rhombic cage (M)₄(L)₄ units linked by Sb/Bi–M bonding. The greater Lewis acidity of Bi compared to Sb can, however, allows anion···Bi interactions to overcome Bi–metal bonding in the case of BF₄^–, leading to collapse of the MOF structure (which is also seen where harder metals like Li⁺ are employed). This study therefore provides insight into the way in which the electronic effects of the bridgehead atom in these ligand systems can impact their supramolecular chemistry.

The Lewis acidity of the Group 15 bridgehead atoms (E = Sb vs Bi) proves to be a decisive structural directing factor in the coordination of tris(3-pyridyl) ligands E(3-py)₃, being responsible for promoting or disfavoring E−metal or E···anion interactions.

Synthesis of tris(3-pyridyl)aluminate ligand and its unexpected stability against hydrolysis: revealing cooperativity effects in heterobimetallic pyridyl aluminates

We report the elusive metallic anion [EtAl(3-py)₃]^- (3-py = 3-pyridyl) (1), the first member of the anionic tris(3-pyridyl) family. Unexpectedly, the lithium complex 1Li shows substantial protic stability against water and alcohols, unlike related tris(2-pyridyl)aluminate analogues. This stability appears to be related to the inability of the [EtAl(3-py)₃]^- anion to chelate Li⁺, which precludes a decomposition pathway involving Li/Al cooperativity.

Uncovering the Hidden Landscape of Tris(4-pyridyl) Ligands: Topological Complexity Derived from the Bridgehead

Supramolecular main group chemistry is a developing field which parallels the conventional domain of metallo-organic chemistry. Little explored building blocks in this area are main group metal-based ligands which have the appropriate donor symmetry to build desired molecular or extended arrangements. Tris(pyridyl) main group ligands (E(py)₃ , E=main group metal) are potentially highly versatile building blocks since shifting the N-donor arms from the 2- to the 3-positions and 4-positions provides a very simple way of changing the ligand character from mononuclear/chelating to multidentate/metal-bridging. Here, the coordination behaviour of the first main group metal tris(4-pyridyl) ligands, E(4-py)₃ (E=Sb, Bi, Ph-Sn) is explored, as well as their ability to build metal-organic frameworks (MOFs). The complicated topology of these MOFs shows a marked influence on the counter anion and on the ability of the E(4-py)₃ ligands to switch coordination mode, depending on the steric and donor character of the bridgehead. This structure-directing influence of the bridgehead provides a potential building strategy for future molecular and MOF design in this area.

f-Element silicon and heavy tetrel chemistry

The last three decades have seen a significant increase in the number of reports of f-element carbon chemistry, whilst the f-element chemistry of silicon, germanium, tin, and lead remain underdeveloped in comparison. Here, in this perspective we review complexes that contain chemical bonds between f-elements and silicon or the heavier tetrels since the birth of this field in 1985 to present day, with the intention of inspiring researchers to contribute to its development and explore the opportunities that it presents. For the purposes of this perspective, f-elements include lanthanides, actinides and group 3 metals. We focus on complexes that have been structurally authenticated by single-crystal X-ray diffraction, and horizon-scan for future opportunities and targets in the area.

Dysprosium complexes bearing unsupported DyIII-GeII/SnII metal-metal bonds as single-ion magnets

Two dysprosium complexes bearing unsupported Dy-Ge/Sn metal-metal bonds are reported here, wherein the Dy-Ge and Dy-Sn bonds both contain relatively large covalency. The complexes exhibit slow relaxation of magnetization at zero field with energy barriers of 485 and 620 K, respectively, and the blocking temperature of 6 K.

Deprotonation, insertion and isomerisation in the post-functionalisation of tris-pyridyl aluminates

Reactions of aluminate anions [EtAl(6-R-2-py)₃]⁻(6-R-2-py = 6-R-2-pyridyl, R = Me or Br) with aldehydes (RCHO) or carboxylic acids (RCO₂H) reveal how these species can be used to sense chirality and show a new aspect of isomerism in this area.

Modifying the donor properties of tris(pyridyl)aluminates in lanthanide(ii) sandwich compounds

Changing the substituents at the 6-position of the 2-pyridyl groups in the aluminate ligands [EtAl(2-py)₃]⁻ has a large electronic and steric effect on their coordination to lanthanide(ii) ions.

The coordination chemistry of the neutral tris-2-pyridyl silicon ligand [PhSi(6-Me-2-py)3]

The first transition metal complexes of Si(iv) tris(2-pyridyl) ligands are reported.

Electronic nature of zwitterionic alkali metal methanides, silanides and germanides - a combined experimental and computational approach

Zwitterionic group 14 complexes of the alkali metals of formula [C(SiMe2OCH2CH2OMe)3M], (M-1), [Si(SiMe2OCH2CH2OMe)3M], (M-2), [Ge(SiMe2OCH2CH2OMe)3M], (M-3), where M = Li, Na or K, have been prepared, structurally characterized and their electronic nature was investigated by computational methods. Zwitterions M-2 and M-3 were synthesized via reactions of [Si(SiMe2OCH2CH2OMe)4] (2) and [Ge(SiMe2OCH2CH2OMe)4] (3) with MOBu t (M = Li, Na or K), resp., in almost quantitative yields, while M-1 were prepared from deprotonation of [HC(SiMe2OCH2CH2OMe)3] (1) with LiBu t , NaCH2Ph and KCH2Ph, resp. X-ray crystallographic studies and DFT calculations in the gas-phase, including calculations of the NPA charges confirm the zwitterionic nature of these compounds, with the alkali metal cations being rigidly locked and charge separated from the anion by the internal OCH2CH2OMe donor groups. Natural bond orbital (NBO) analysis and the second order perturbation theory analysis of the NBOs reveal significant hyperconjugative interactions in M-1-M-3, primarily between the lone pair and the antibonding Si-O orbitals, the extent of which decreases in the order M-1 > M-2 > M-3. The experimental basicities and the calculated gas-phase basicities of M-1-M-3 reveal the zwitterionic alkali metal methanides M-1 to be significantly stronger bases than the analogous silanides M-2 and germanium M-3.

A non-chiral lithium aluminate reagent for the determination of enantiomeric excess of chiral alcohols

Here we illustrate a new method for the rapid determination of ee's of chiral alcohols using the thermally-stable, non-chiral lithium aluminate reagent [EtAl(6-Me-2-py)₃Li] (1).

On the reaction mechanism of redox transmetallation of elemental Yb with Hg(C6F5)2 and subsequent reactivity of Yb(C6F5)2 with pyrazole: a DFT investigation

DFT investigations of the redox transmetallation reaction of the diorganomercurial (Hg(C₆F₅)₂) with Yb metal, yielding Yb(C₆F₅)₂, allowed us to define a very low energy reaction mechanism via a C₆F₅Yb–HgC₆F₅ intermediate.

Rare earth–metal bonding in molecular compounds: recent advances, challenges, and perspectives

In this review, all structurally authenticated molecular compounds with direct bonds between rare earth metals and transition or main group metals are summarized. Novel aspects of their syntheses, properties and reactivities are highlighted.

A tetradentate metalloligand: synthesis and coordination behaviour of a 2-pyridyl-substituted cyclobutadiene iron complex

A novel cyclobutadiene iron complex with four 2-pyridyl-substitutents acts as a bis(bidentate) chelate ligand toward Zn²⁺ cations.

Direct synthesis of the Janus-head ligand (MePy)3Sn–Sn(MePy)3using an unusual pyridyl-transfer reaction (MePy = 6-methyl-2-pyridyl)

Thein situreaction of the tripodal anion [EtAl(^MePy)₃]⁻(^MePy = 6-Me-2-py) with SnCl₂gives the Janus-head ligand (^MePy)₃Sn–Sn(^MePy)₃, containing a Sn–Sn bond, through a novel, one-pot reaction involving a combination of pyridyl transfer and metal-oxidation.