cyclo-P4 Building Blocks: Achieving Non-Classical Fullerene Topology and Beyond

Potential of Mixed Dipnictogen Molybdenum Complexes in the Self-Assembly of Thallium Coordination Compounds

The coordination chemistry of the homo- and heterodipnictogen tetrahedrane complexes [{CpMo(CO)2}2(μ,η2:2-EE')] (E, E' = P, As, Sb) (A-F) toward Tl[BArF24] ([BArF24]- = [B(3,5-C6H3(CF3)2)4]-) was studied. Controlled by the used tetrahedranes A-F, and thus depending on the respective pnictogen atoms, the monomers [Tl(η2-A)][BArF24] ([A]Tl) and [Tl(η2-B)][BArF24] ([B]Tl), the double substituted [Tl(η1-C)2][BArF24] ([C]2Tl) or the even higher aggregated compounds [Tl2(η2-D)3(μ,η2:1-D)(μ,η1:1-D)][BArF24]2 ([D]5Tl2), [Tl2(η2-E)2(μ,η2:1-E)3] [BArF24]2 ([E]5Tl2) and [Tl2(η2-F)3(μ,η2:1-F)3][BArF24]2 ([F]6Tl2) were obtained. Utilization of [BArF24]- promises additional stabilization of TlI via η6-coordination of two of its aryl rings as found in compounds [A]Tl, [B]Tl and [C]2Tl. Within the series of reactivity of A-F, the heavier congeners D, E and F tend to form larger aggregates in which σ(E-E') bond contributions to the coordination behavior were observed. Interatomic distances suggest the presence of Tl···Tl interactions in [E]5Tl2 and [F]6Tl2. The features of the respective coordination compounds were studied in the solid-state as well as in solution. For the latter at least a partial dissociation of the assemblies in solution was indicated. The isolated solid-state aggregates are the first examples of heterodipnictogen units as ligands in self-assembled TlI-based coordination compounds.

Cu(I) Complexes Comprising tetrahedral Mo2 E2 or Mo2 PE units (E=P, As, Sb) as Chelating Ligands

Novel isomorphous tetranuclear complexes, [(dppf)Cu(μ3 ,η2 : 2 : 2 -E2 {CpMo(CO)2 }2 ]BF4 [E=P (1), As (4), Sb (5), (dppf=1,1'-bis-(diphenylphosphino)-ferrocene)] and [(dppf)Cu(μ3 ,η2 : 2 : 2 -PE{CpMo(CO)2 }2 ]BF4 [E=As (2), Sb(3)] were synthesized from the reactions between [(dppf)Cu(MeCN)2 ][BF4 ] and tetrahedral molybdenum complexes containing unsubstituted homo- and hetero-diatomic group-15 elements [(μ,η2 : 2 -E2 {CpMo(CO)2 }2 ] [E=P (A), As (D), Sb (E)] and [(μ,η2 : 2 -PE{CpMo(CO)2 }2 ] [E=As (B), Sb (C)], respectively. In all these products, the {Mo2 E2 } or {Mo2 PE} moieties coordinate the Cu(I) center via a rare side-on η2 -coordination mode. The X-ray structure analyses of [(dppf)Cu(μ3 ,η2 : 2 : 1 -PSb{CpMo(CO)2 }2 ][BF4 ] demonstrate, for the first time, the utilization of an η1 -coordination mode for the ligand complex C to coordinate to the Cu(I) center. All the products were characterized by X-ray crystallography, NMR and IR spectroscopy, mass spectrometry and elemental analysis. Electrochemical studies also revealed the formation of 1-5, and, further, to understand the structure and bonding of the products, theoretical calculations using density functional theory (DFT) were conducted.

Diantimony Complexes [CpR 2 Mo2 (CO)4 (μ,η2 -Sb2 )] (CpR =C5 H5 , C5 H4 t Bu) as Unexpected Ligands Stabilizing Silver(I)n (n=1-4) Monomers, Dimers and Chains

Synthesis and reactivity of transition metal compounds bearing "naked" pnictogen atoms is an active research area with remarkable bonding patterns observed in the formed compounds. Within this field, intense investigations on the coordination behavior of complexes possessing Pn and Asn (2≤n≤5) moieties have been conducted. However, studies on heavier analogues have been ignored so far due to arduous challenges related to low yields and moderate air stability. Herein, we present the first in-depth study addressing the reactivity of organometallic complexes containing Sb-donor atoms with several AgI salts. These reactions afforded twelve unprecedented aggregates as monomers, dimers as well as three- and four-membered chains of AgI ions claimed in the literature to be inaccessible. Interatomic distances as well as computational evidence obtained with help of several different methods suggest the presence of Ag⋅⋅⋅Ag interactions in all complexes containing more than one AgI ion.

Platonic and Archimedean solids in discrete metal-containing clusters

Metal-containing clusters have attracted increasing attention over the past 2-3 decades. This intense interest can be attributed to the fact that these discrete metal aggregates, whose atomically precise structures are resolved by single-crystal X-ray diffraction (SCXRD), often possess intriguing geometrical features (high symmetry, aesthetically pleasing shapes and architectures) and fascinating physical properties, providing invaluable opportunities for the intersection of different disciplines including chemistry, physics, mathematical geometry and materials science. In this review, we attempt to reinterpret and connect these fascinating clusters from the perspective of Platonic and Archimedean solid characteristics, focusing on highly symmetrical and complex metal-containing (metal = Al, Ti, V, Mo, W, U, Mn, Fe, Co, Ni, Pd, Pt, Cu, Ag, Au, lanthanoids (Ln), and actinoids) high-nuclearity clusters, including metal-oxo/hydroxide/chalcogenide clusters and metal clusters (with metal-metal binding) protected by surface organic ligands, such as thiolate, phosphine, alkynyl, carbonyl and nitrogen/oxygen donor ligands. Furthermore, we present the symmetrical beauty of metal cluster structures and the geometrical similarity of different types of clusters and provide a large number of examples to show how to accurately describe the metal clusters from the perspective of highly symmetrical polyhedra. Finally, knowledge and further insights into the design and synthesis of unknown metal clusters are put forward by summarizing these "star" molecules.

Structural Chemistry of Giant Metal Based Supramolecules

The review presents a bird-eye view on the state of research in the field of giant nonbiological discrete metal complexes and ions of nanometer size, which are structurally characterized by means of single-crystal X-ray diffraction, using the crystal structure as a common key feature. The discussion is focused on the main structural features of the metal clusters, the clusters containing compact metal oxide/hydroxide/chalcogenide core, ligand-based metal-organic cages, and supramolecules as well as on the aspects related to the packing of the molecules or ions in the crystal and the methodological aspects of the single-crystal neutron and X-ray diffraction of these compounds.

Substituted aromatic pentaphosphole ligands - a journey across the p-block

The functionalization of pentaphosphaferrocene [Cp*Fe(η5-P5)] (1) with cationic group 13-17 electrophiles is shown to be a general synthetic strategy towards P-E bond formation of unprecedented diversity. The products of these reactions are dinuclear [{Cp*Fe}2{μ,η5:5-(P5)2EX2}][TEF] (EX2 = BBr2 (2), GaI2 (3), [TEF]- = [Al{OC(CF3)3}4]-) or mononuclear [Cp*Fe(η5-P5E)][X] (E = CH2Ph (4), CHPh2 (5), SiHPh2 (6), AsCy2 (7), SePh (9), TeMes (10), Cl (11), Br (12), I (13)) complexes of hetero-bis-pentaphosphole ((cyclo-P5)2R) or hetero-pentaphosphole ligands (cyclo-P5R), the aromatic all-phosphorus analogs of prototypical cyclopentadienes. Further, modifying the steric and electronic properties of the electrophile has a drastic impact on its reactivity and leads to the formation of [Cp*Fe(μ,η5:2-P5)SbICp'''][TEF] (8) which possesses a triple-decker-like structure. X-ray crystallographic characterization reveals the slightly twisted conformation of the cyclo-P5R ligands in these compounds and multinuclear NMR spectroscopy confirms their integrity in solution. DFT calculations shed light on the bonding situation of these compounds and confirm the aromatic character of the pentaphosphole ligands on a journey across the p-block.

Low-oxidation state cobalt-magnesium complexes: ion-pairing and reactivity

Magnesium cobaltates (Arnacnac)MgCo(COD)2 (1-3) were synthesised by reacting (Arnacnac)MgI(OEt2) with K[Co(η4-COD)2] (COD = 1,5-cyclooctadiene) [Arnacnac = CH(ArNCMe)2; Ar = 2,4,6-Me3-C6H2 (Mes), 2,6-Et2-C6H3 (Dep), 2,6-iPr2-C6H3Mes (Dipp)]. Compounds 1-3 form contact ion-pairs in toluene, while solvent separated ion-pairs are formed in THF. The effect of ion-pairing on the reactivity is illustrated by reaction of 2 with tert-butylphosphaalkyne, which affords distinct 1,3-diphosphacyclobutadiene complexes. The heteroleptic sandwich complex [(Depnacnac)MgCo(P2C2tBu2)]2 (4) is selectively formed in toluene, while the homoleptic bis(1,3-diphosphacyclobutadiene) complex [(Depnacnac)Mg(THF)3][Co(P2C2tBu2)2] (5) is obtained in THF. Complex 4 is a precursor to further unusual phosphaorganometallic compounds. Substitution of the labile COD ligand in 4 by white phosphorus (P4) enabled the synthesis of the phosphorus-rich sandwich compound [(Depnacnac)MgCoP4(P2C2tBu2)]2 (6). The heterobimetallic complex (Cp*NiP2C2tBu2)Co(COD) (7) was isolated after treatment of 4 with Cp*Ni(acac) (Cp* = C5Me5, acac = acetylacetonate).

Linking of CuI Units by Tetrahedral Mo2 E2 Complexes (E=P, As)

The reaction of [Cp2 Mo2 (CO)4 (μ,η2:2 -E2 )] (A: E=P, B: E=As, Cp=C5 H5 ) with the WCA-containing CuI salts ([Cu(CH3 CN)4 ][Al{OC(CF3 )3 }4 ] (CuTEF, C), [Cu(CH3 CN)4 ][BF4 ] (D) and [Cu(CH3 CN)3.5 ][FAl{OC6 F10 (C6 F5 )}3 ] (CuFAl, E)) affords seven unprecedented coordination compounds. Depending on the E2 ligand complex, the counter anion of the copper salt and the stoichiometry, four dinuclear copper dimers and three trinuclear copper compounds are accessible. The latter complexes reveal first linear Cu3 arrays linked by E2 units (E=P, As) coordinated in an η2:1:1 coordination mode. All compounds were characterized by X-ray crystallography, NMR and IR spectroscopy, mass spectrometry and elemental analysis. To define the nature of the Cu⋅⋅⋅Cu⋅⋅⋅Cu interactions, DFT calculations were performed.

Reappraising Schmidpeter's bis(iminophosphoranyl)phosphides: coordination to transition metals and bonding analysis

The synthesis and characterization of a range of bis(iminophosphoranyl)phosphide (BIPP) group 4 and coinage metals complexes is reported. BIPP ligands bind group 4 metals in a pseudo fac-fashion, and the central phosphorus atom enables the formation of d0-d10 heterobimetallic complexes. Various DFT computational tools (including AIM, ELF and NCI) show that the phosphorus-metal interaction is either electrostatic (Ti) or dative (Au, Cu). A bridged homobimetallic Cu-Cu complex was also prepared and its spectroscopic properties were investigated. The theoretical analysis of the P-P bond in BIPP complexes reveals that (i) BIPP are closely related to ambiphilic triphosphenium (TP) cations; (ii) the P-P bonds are normal covalent (i.e. not dative) in both BIPP and TP.

Use of a cyclo-P4 building block - a way to networks of host-guest assemblies

Despite the proven ability to form supramolecular assemblies via coordination to copper halides, organometallic building blocks based on four-membered cyclo-P4 ligands find only very rare application in supramolecular chemistry. To date, only three types of supramolecular aggregates were obtained based on the polyphosphorus end-deck complexes CpRTa(CO)2(η4-P4) (1a: CpR = Cp''; 1b: CpR = Cp'''), with none of them, however, possessing a guest-accessible void. To achieve this target, the use of silver salts of the weakly coordinating anion SbF6 - was investigated as to their self-assembly in the absence and in the presence of the template molecule P3Se4. The two-component self-assembly of the building block 1a and the coinage-metal salt AgSbF6 leads to the formation of 1D or 3D coordination polymers. However, when the template-driven self-assembly was attempted in the presence of an aliphatic dinitrile, the unprecedented barrel-like supramolecular host-guest assembly P3Se4@[{(Cp''Ta(CO)2(η4-P4))Ag}8]8+ of 2.49 nm in size was formed. Moreover, cyclo-P4-based supramolecules are connected in a 2D coordination network by dinitrile linkers. The obtained compounds were characterised by mass-spectrometry, 1H and 31P NMR spectroscopy and X-ray structure analysis.

Transformations of the cyclo-P4 ligand in [Cp'''Co(η4-P4)]

The reactivity of the cyclo-P₄ ligand complex [Cp′′′Co(η⁴-P₄)] (1) (Cp′′′ = 1,2,4-tri-tert-butyl-cyclopentadienyl) towards reduction and main group nucleophiles was investigated. By using K[CpFe(CO)₂], a selective reduction to the dianionic complex [(Cp′′′Co)₂(μ,η³:η³-P₈)]²⁻ (2) was achieved. The reaction of 1 with ^tBuLi and LiCH₂SiMe₃ as carbon-based nucleophiles yielded [Cp′′′Co(η³-P₄R)]⁻ (R = ^tBu (4), CH₂SiMe₃ (7)), which, depending on the reaction conditions, undergo subsequent reactions with another equivalent of 1 to form [(Cp′′′Co)₂(μ,η³:η³-P₈R)]⁻ (R = ^tBu (5), CH₂SiMe₃ (8)). In the case of 4, a different pathway was observed, namely a dimerisation followed by a fragmentation into [Cp′′′Co(η³-P₅^tBu₂)]⁻ (6) and [Cp′′′Co(η³-P₃)]⁻ (3). With OH⁻ as an oxygen-based nucleophile, the synthesis of [Cp′′′Co(η³-P₄(O)H)]⁻ (9) was achieved. All compounds were characterized by X-ray crystal structure analysis, NMR spectroscopy and mass spectrometry. Their electronic structures and reaction behavior were elucidated by DFT calculations.

The reactivity of the cyclo-P₄ ligand complex [Cp′′′Co(η⁴-P₄)] (1) (Cp′′′ = 1,2,4-tri-tert-butyl-cyclopentadienyl) towards reduction and main group nucleophiles was investigated.

The reaction behavior of [Cp2Mo2(CO)4(μ,η2:2-P2)] and [Cp′′Ta(CO)2(η4-P4)] towards hydroxide and tert-butyl nucleophiles

The reaction behavior of [Cp₂Mo₂(CO)₄(μ,η^2:2-P₂)] (1) and [Cp′′Ta(CO)₂(η⁴-P₄)] (2), respectively, towards the anions OH⁻ and ^tBu⁻ are reported, which leads to a selective functionalisation of one P atom.

From nano-balls to nano-bowls

Pentaphosphaferrocene [Cp*Fe(η5-P5)] in combination with Cu(i) halides is capable of a template-directed synthesis of fullerene-like spheres. Herein, we present the use of a triple decker complex as template that leads to the formation of unprecedented 'nano-bowls'. These spherical domes resemble the truncated fullerenes I h-C80 and represent a novel spherical arrangement in the chemistry of spherical molecules.

Anionic Hosts for the Incorporation of Cationic Guests

Pentaphosphaferrocene [Cp*Fe(η5 -P5 )] (1 a) represents an excellent building block for the template-directed synthesis of spherical supramolecules. Here, the self-assembly of 1 a with CuI and CuII halides in the presence of the template complexes [FeCp2 ][PF6 ], [CoCp2 ][PF6 ] and [CoCp2 ] is reported, testifying to the redox behavior of the formed supramolecules. The oxidation or reduction capacity of these reactive complexes does not inhibit their template impact and, for the first time, the cationic metallocene [CoCp2 ]+ is enclosed in unprecedented anionic organometallic hosts. Furthermore, the large variety of structural motifs, as icosahedral, trigonal antiprismatic, cuboidal and tetragonal antiprismatic arrangements of 1 a units are realized in the supramolecules [FeCp2 ]@[{1 a}12 (CuBr)17.3 ] (3), [CoCp2 ]+3 {[CoCp2 ]+ @[{1 a}8 Cu24.25 Br28.25 (CH3 CN)6 ]4- } (4), {[Cp2 Co]+ @[{1 a}8 (CuI)28 (CH3 CN)9.8 ]}{[Cp2 Co]+ @[{1 a)}8 Cu24.4 I26.4 (CH3 CN)8 ]2- } (5), and [{1 a}3 {(1 a)2 NH}3 Cu16 I10 (CH3 CN)7 ] (6), respectively.

The Cobalt cyclo-P4 Sandwich Complex and Its Role in the Formation of Polyphosphorus Compounds

A synthetic approach to the sandwich complex [Cp′′′Co(η⁴‐P₄)] (2) containing a cyclo‐P₄ ligand as an end‐deck was developed. Complex 2 is the missing homologue in the series of first‐row cyclo‐P_n sandwich complexes, and shows a unique tendency to dimerize in solution to form two isomeric P₈ complexes [(Cp′′′Co)₂(μ,η⁴:η²:η¹‐P₈)] (3 and 4). Reactivity studies indicate that 2 and 3 react with further [Cp′′′Co] fragments to give [(Cp′′′Co)₂(μ,η²:η²‐P₂)₂] (5) and [(Cp′′′Co)₃P₈] (6), respectively. Furthermore, complexes 2, 3, and 4 thermally decompose forming 5, 6, and the P₁₂ complex [(Cp′′′Co)₃P₁₂] (7). DFT calculations on the P₄ activation process suggest a η³‐P₄ Co complex as the key intermediate in the synthesis of 2 as well as in the formation of larger polyphosphorus complexes via a unique oligomerization pathway.

Azido- and amido-substituted gallium hydrides supported by N-heterocyclic carbenes

The synthesis of azido- and amido-gallanes supported by hindered N-heterocyclic carbene donors is reported.

cyclo-P4 Building Blocks: Achieving Non-Classical Fullerene Topology and Beyond

The cyclo‐P₄ complexes [Cp^RTa(CO)₂(η⁴‐P₄)] (Cp^R: Cp′′=1,3‐C₅H₃tBu₂, Cp′′′=1,2,4‐C₅H₂tBu₃) turned out to be predestined for the formation of hollow spherical supramolecules with non‐classical fullerene‐like topology. The resulting assemblies constructed with CuX (X=Cl, Br) showed a highly symmetric 32‐vertex core of solely four‐ and six‐membered rings. In some supramolecules, the inner cavity was occupied by an additional CuX unit. On the other hand, using CuI, two different supramolecules with either peanut‐ or pear‐like shapes and outer diameters in the range of 2–2.5 nm were isolated. Furthermore, the spherical supramolecules containing Cp′′′ ligands at tantalum are soluble in CH₂Cl₂. NMR spectroscopic investigations in solution revealed the formation of isomeric supramolecules owing to the steric hindrance caused by the third tBu group on the Cp′′′ ligand. In addition, a 2D coordination polymer was obtained and structurally characterized.