Synthesis of arsenic-rich As n ligand complexes from yellow arsenic

Dipnictogen Radical Chemistry: A Dithorium-Supported Distibene Radical Trianion

Although two examples of σ-bonded trans-bent [RSbSbR]•- (R = bulky organo- or Ga-groups) that formally contain the Sb2•3- radical trianion moiety are known in p-block chemistry, d- or f-element Sb2•3- radical trianion complexes, with or without R-substituents, have remained elusive. Here, we report that reduction of a 77:23 mix of [{Th(TrenTIPS)}2(μ-η2:η2-Sb2)] (3a, TrenTIPS = {N(CH2CH2NSiPri3)3}3-):[{Th(TrenTIPS)}2(μ-SbH)] (3b) with 1.5 equiv of KC8 in the presence of 1.1 equiv of 2.2.2-cryptand yields the emerald green Sb2•3- radical complex [K(2.2.2-cryptand)][{Th(TrenTIPS)}2(μ-η2:η2-Sb2)] (4), providing an f-block Sb2•3- radical trianion complex, and the heaviest actinide-N2 radical analogue. When the recrystallization conditions are modified, a small crop of red crystals determined to be [K(2.2.2-cryptand)]3[{Th(TrenTIPS)(μ-η3:η3-Sb3)}2(μ-K)] (5) were also isolated, highlighting the complexity of heavy group 15 homodiatomic reduction chemistry. SQUID magnetometry and EPR spectroscopy suggest that the Sb2•3- radical trianion in 4 is fairly well isolated, due to electrostatic binding to Th, with pseudoaxial g-values reflecting the distinctive Sb2•3- radical trianion side-on bridging π-bonded coordination mode. Spectroscopically validated computational analysis of 3a and 4 confirms the stronger donating capability, and weaker Sb-Sb bond, of Sb2•3- radical trianion compared to the Sb22- dianion form.

Synthesis and Redox Chemistry of Co3E4 (E=P, As) Clusters

The synthesis of the cluster complexes [(Cp'''Co)3(μ3,η2:η2:η2-E3)(μ3-E)] (E=P (3), As (4)) starting from the anionic triple-decker complexes [K(18cr6)(dme)2][(Cp'''Co)2(μ,η4:η4-E4)] (E=P (1), As (2)) by electrophilic quenching with the Co dimer [(Cp'''CoCl)2] is reported. Both complexes show a distinct redox chemistry, which was first investigated by cyclic voltammetry. Subsequently, the monoanions [K(L)(sol)n][(Cp'''Co)3(μ3,η2:η2:η2-E3)(μ3-E)] (E=P, L=18cr6, sol=dme, n=2 (5), E=As, L=2,2,2-crypt, n=0 (6)), the monocations [(Cp'''Co)3(μ3,η2:η2:η2-E3)(μ3-E)][FAl] (E=P (7), As (8)) and the dications [(Cp'''Co)3(μ3,η3:η3:η3-E4)][TEF]2 (E=P (9), As (10)) could be realized experimentally and isolated in moderate to good yields. All compounds were characterized by single crystal X-ray structure analysis, NMR and EPR spectroscopy, mass spectrometry and elemental analysis.

Synthesis and Characterization of Novel Cobalt Carbonyl Phosphorus and Arsenic Clusters

Phosphorus- and arsenic-containing cobalt clusters are an interesting class of compounds that continue to provide new structures with captivating bonding patterns. Although the first members of this family were reported 45 years ago, the number of such species is still limited within the broad family of transition metal complexes bearing pnictogen atoms. Herein, we present the reaction of Co2(CO)8 as a cobalt source with a number of phosphorus- and arsenic-containing compounds under variable reaction conditions. These reactions result in various known and novel cobalt phosphorus and cobalt arsenic clusters in which different nuclearity ratios between P/As and Co exist. All those clusters were characterized by X-ray structural analysis and partly by IR, 31P{1H} NMR, EI-MS and elemental analysis. This comprehensive study is the first detailed study in this field that reveals the richness of compounds that could be obtained only by modifying the ratio of used reactants and the involved reaction conditions.

E4 Transfer (E=P, As) to Ni Complexes

The use of [Cp''2 Zr(η1:1 -E4 )] (E=P (1 a), As (1 b), Cp''=1,3-di-tert-butyl-cyclopentadienyl) as phosphorus or arsenic source, respectively, gives access to novel stable polypnictogen transition metal complexes at ambient temperatures. The reaction of 1 a/1 b with [CpR NiBr]2 (CpR =CpBn (1,2,3,4,5-pentabenzyl-cyclopentadienyl), Cp''' (1,2,4-tri-tert-butyl-cyclopentadienyl)) was studied, to yield novel complexes depending on steric effects and stoichiometric ratios. Besides the transfer of the complete En unit, a degradation as well as aggregation can be observed. Thus, the prismane derivatives [(Cp'''Ni)2 (μ,η3:3 -E4 )] (2 a (E=P); 2 b (E=As)) or the arsenic containing cubane [(Cp'''Ni)3 (μ3 -As)(As4 )] (5) are formed. Furthermore, the bromine bridged cubanes of the type [(CpR Ni)3 {Ni(μ-Br)}(μ3 -E)4 ]2 (CpR =Cp''': 6 a (E=P), 6 b (E=As), CpR =CpBn : 8 a (E=P), 8 b (E=As)) can be isolated. Here, a stepwise transfer of En units is possible, with a cyclo-E4 2- ligand being introduced and unprecedented triple-decker compounds of the type [{(CpR Ni)3 Ni(μ3 -E)4 }2 (μ,η4:4 -E'4 )] (CpR =CpBn , Cp'''; E/E'=P, As) are obtained.

Element-Element Bond Formation upon Oxidation and Reduction

The redox chemistry of [(Cp′′′Co)₂(μ,η²:η²‐E₂)₂] (E=P (1), As (2); Cp′′′=1,2,4‐tri(tert‐butyl)cyclopentadienyl) was investigated. Both compounds can be oxidized and reduced twice. That way, the monocations [(Cp′′′Co)₂(μ,η⁴:η⁴‐E₄)][X] (E=P, X=BF₄ (3 a), [FAl] (3 b); E=As, X=BF₄ (4 a), [FAl] (4 b)), the dications [(Cp′′′Co)₂(μ,η⁴:η⁴‐E₄)][TEF]₂ (E=P (5), As (6)), and the monoanions [K(18‐c‐6)(dme)₂][(Cp′′′Co)₂(μ,η⁴:η⁴‐E₄)] (E=P (7), As (8)) were isolated. Further reduction of 7 leads to the dianionic complex [K(18‐c‐6)(dme)₂][K(18‐c‐6)][(Cp′′′Co)₂(μ,η³:η³‐P₄)] (9), in which the cyclo‐P₄ ligand has rearranged to a chain‐like P₄ ligand. Further reduction of 8 can be achieved with an excess of potassium under the formation of [K(dme)₄][(Cp′′′Co)₂(μ,η³:η³‐As₃)] (10) and the elimination of an As₁ unit. Compound 10 represents the first example of an allylic As₃ ligand incorporated into a triple‐decker complex.

Iron β-diiminate complexes with As2-, As4- and As8-ligands

Depending on the sterics of the flanking group at the β-diiminate ligand at Fe(i) a tetramerisation or dimerisation of As₄ units is observed; for the latter case the ligand conformation was influenced by the crystallization temperature.

The Chemistry of Yellow Arsenic

The generation and handling of the light-sensitive and metastable yellow arsenic (As₄) is extremely challenging. In view of recent breakthroughs in synthesizing As₄ storage materials and transfer reagents, the more intensive use of yellow arsenic as a source for further reactions can be expected. Given these aspects, the current stage of knowledge of the direct use of As₄ is comprehensively summarized in the present review, which lists the activation of As₄ by main group elements as well as transition metal compounds (including the f-block elements). Moreover, it also partly compares the reaction outcomes in relation to the corresponding reactions of P₄. The possibility of using alternative sources for generating arsenic moieties and compounds is also discussed. The release of As₄ molecules from precursor compounds and the use of transfer reagents for polyarsenic entities open up new synthetic pathways to avoid the direct generation of yellow arsenic solutions and to ensure its smooth usage for subsequent reactions.

The Influence of β-diiminato Ligands on As4 Activation by Cobalt Complexes

In a systematic study of the activation of As₄, three [LCo(tol)] (L=β‐diiminato) complexes have revealed different steric and electronic influences. 2,6‐Diisopropylphenyl (Dipp) and 2,6‐dimethylphenyl (dmp) flanking groups were used, one of the ligands with H backbone substituents (β‐dialdiminate L⁰) and two with Me substituents (β‐diketiminates L³ and L¹). In the reaction with As₄, different dinuclear products [(LCo)₂As₄] (LM=L⁰ (1), L¹ (2), L³ (3)) were isolated, with all showing differently shaped [Co₂As₄] cores in the solid state: octahedral in 1, prismatic in 2, and asterane‐like in 3. Thermal treatment of 3 leads to the abstraction of one arsenic atom to yield [(L³Co)₂As₃] (4). All products were comprehensively characterized by single‐crystal X‐ray diffraction, FD‐MS, and ¹H NMR spectroscopy. A rational explanation for the different reactivity is also proposed and DFT calculations shed light on the nature of the highly flexible [Co₂As₄] cores.

Transfer Reagent for Bonding Isomers of Iron Complexes

The cothermolysis of As₄ and [Cp″₂Zr(CO)₂] (Cp″ = η⁵-C₅H₃tBu₂) results in the formation of [Cp″₂Zr(η^1:1-As₄)] (1) in high yields and the arsenic-rich complex [(Cp″₂Zr)(Cp″Zr)(μ,η^2:2:1-As₅)] (2) as a minor product. In contrast to yellow arsenic, 1 is a light-stable, weighable and storable arsenic source for subsequent reactions. The transfer reaction of 1 with [Cp‴Fe(μ-Br)]₂ (Cp‴ = η⁵-C₅H₂tBu₃) yields the unprecedented bond isomeric complexes [(Cp‴Fe)₂(μ,η^4:4-As₄)] (3a) and [(Cp‴Fe)₂(μ,η^4:4-cyclo-As₄)] (3b). In contrast, the analogous reaction with the Cp^Bn derivative [Cp^BnFe(μ-Br)]₂ (Cp^Bn = η⁵-C₅(CH₂(C₆H₅)₅) leads exclusively to the triple decker complex [(Cp^BnFe)₂(μ,η^4:4-As₄)] (4) possessing the tetraarsabutadiene-type ligand analogous to 3a. To elucidate the stability of the bonding isomers 3a and 3b, DFT calculations were performed. The oxidation of 4 with AgBF₄ affords [(Cp^BnFe)₂(μ,η^5:5-As₅)][BF₄] (5), which is a product expanded by one arsenic atom, instead of the expected complex [(Cp^BnFe)₂(μ,η^4:4-cyclo-As₄)]⁺.

Coordination Behavior of [Cp''2 Zr(η1:1 -P4 )] towards Different Lewis Acids

A detailed method for the preparation of [Cp''₂ Zr(η^1:1 -P₄ )] (1) is presented. The coordination behavior of 1 towards Lewis acidic transition metal complexes of tungsten, manganese, and iron, respectively, and main group compounds (AlMe₃ , AlEt₃ ) was investigated in detail by computational and experimental studies. In doing so, a series of unprecedented complexes with different coordination modes and multiple coordination numbers of the tetraphosphabicyclo[1.1.0]butane framework were synthesized. All products, as well as the starting materials, were comprehensively characterized by NMR spectroscopy, mass spectrometry, elemental analysis, and single crystal X-ray structural analysis.

Arsenic-Rich Polyarsenides Stabilized by Cp*Fe Fragments

The redox chemistry of [Cp*Fe(η⁵ -As₅ )] (1, Cp*=η⁵ -C₅ Me₅ ) has been investigated by cyclic voltammetry, revealing a redox behavior similar to that of its lighter congener [Cp*Fe(η⁵ -P₅ )]. However, the subsequent chemical reduction of 1 by KH led to the formation of a mixture of novel As_n scaffolds with n up to 18 that are stabilized only by [Cp*Fe] fragments. These include the arsenic-poor triple-decker complex [K(dme)₂ ][{Cp*Fe(μ,η^2:2 -As₂ )}₂ ] (2) and the arsenic-rich complexes [K(dme)₃ ]₂ [(Cp*Fe)₂ (μ,η^4:4 -As₁₀ )] (3), [K(dme)₂ ]₂ [(Cp*Fe)₂ (μ,η^2:2:2:2 -As₁₄ )] (4), and [K(dme)₃ ]₂ [(Cp*Fe)₄ (μ₄ ,η^{4:3:3:2:2:1:1} -As₁₈ )] (5). Compound 4 and the polyarsenide complex 5 are the largest anionic As_n ligand complexes reported thus far. Complexes 2-5 were characterized by single-crystal X-ray diffraction, ¹ H NMR spectroscopy, EPR spectroscopy (2), and mass spectrometry. Furthermore, DFT calculations showed that the intermediate [Cp*Fe(η⁵ -As₅ )]^- , which is presumably formed first, undergoes fast dimerization to the dianion [(Cp*Fe)₂ (μ,η^4:4 -As₁₀ )]^2- .

Different Reactivity of As4 towards Disilenes and Silylenes

The activation of yellow arsenic is possible with the silylene [PhC(NtBu)₂ SiN(SiMe₃ )₂ ] (1) and the disilene [(Me₃ Si)₂ N(η¹ -Me₅ C₅ )Si=Si(η¹ -Me₅ C₅ )N(SiMe₃ )₂ ] (3). The reaction of As₄ with 1 leads to the unprecedented As₁₀ cage compound [(LSiN(SiMe₃ )₂ )₃ As₁₀ ] (2; L=PhC(NtBu)₂ ) with an As₇ nortricyclane core stabilized by arsasilene moieties containing silicon(II)bis(trimethylsilyl)amide substituents. In contrast, the compound [Cp*{(SiMe₃ )₂ N}SiAs]₂ (4) containing a butterfly-like diarsadisilabicyclo[1.1.0]butane unit is formed by the reaction of As₄ with the disilene 3. Both compounds were characterized by single-crystal X-ray diffraction analysis, NMR spectroscopy, and mass spectrometry. The reaction outcomes demonstrate the different reaction behavior of yellow arsenic (As₄ ) compared to white phosphorus (P₄ ) in the reactions with the corresponding silylenes and disilenes.

Transformation of nortricyclane type cage compounds P4S3, P4Se3 and As4S3 by [Cp''2Zr(CO)2]

The complex [Cp''₂Zr(CO)₂] (Cp'' = C₅H₃tBu₂) was used to transform the nortricyclane type cage compounds E₄Q₃ (E = P, Q = S, Se; E = As, Q = S) resulting in unprecedented complexes [(Cp''₂Zr)₂(μ,η^1:1:1:1-E₂Q₄)] possessing bridging ligands that represent the anions of the so far unknown tetrachalcogenohypodiphosphorous acid (HQ)₂PP(QH)₂ and tetrathiohypodiarsenous acid (HS)₂AsAs(SH)₂, 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.

CpPEt2 As4 -An Organic-Substituted As4 Butterfly Compound

Cp^PEt₂ As₄ (Cp^PEt =C₅ (4-EtC₆ H₄ )₅ ) (1) is synthesized by the reaction of Cp^PEt. radicals with yellow arsenic (As₄ ). In solution an equilibrium of the starting materials and the product is found. However, 1 can be isolated and stored in the solid state without decomposition. As₄ can be easily released from 1 under thermal or photochemical conditions. From powder samples of Cp^PEt₂ As₄ , yellow arsenic can be sublimed under rather mild conditions (T=125 °C). A similar behavior for the P₄ -releasing agent was determined for the related phosphorus compound Cp^BIG₂ P₄ (2; Cp^BIG =C₅ (4-nBuC₆ H₄ )₅ ). DFT calculations show the importance of dispersion forces for the stability of the products.