Durch Cp*Fe-Fragmente stabilisierte, Arsen-reiche Polyarsenide

Synthesis and Characterization of [Fe3 (As3 )3 (As4 )]3- , a Binary Fe/As Zintl Cluster With an Fe3 Core

We report here the synthesis and structural characterization of the first binary iron arsenide cluster anion, [Fe₃ (As₃ )₃ (As₄ )]^3- , present in both [K([2.2.2]crypt)]₃ [Fe₃ (As₃ )₃ (As₄ )] (1) and [K(18-crown-6)]₃ [Fe₃ (As₃ )₃ (As₄ )]⋅en (2). The cluster contains an Fe₃ triangle with three short Fe-Fe bond lengths (2.494(1) Å, 2.459(1) Å and 2.668(2) Å for 1, 2.471(1) Å, 2.473(1) Å and 2.660(1) Å for 2), bridged by a 2-butene-like As₄ unit. An analysis of the electronic structure using DFT reveals a triplet ground state with direct Fe-Fe bonds stabilizing the Fe₃ core.

Redox Chemistry of Heterobimetallic Polypnictogen Triple-Decker Complexes - Rearrangement, Fragmentation and Transfer

The redox chemistry of the heterobimetallic triple‐decker complexes [(Cp*Fe)(Cp′′′Co)(μ,η⁵:η⁴‐E₅)] (E=P (1), As (2), Cp*=1,2,3,4,5‐pentamethyl‐cyclopentadienyl, Cp′′′=1,2,4‐tri‐tertbutyl‐cyclopentadienyl) and [(Cp′′′Co)(Cp′′′Ni)(μ,η³:η³‐E₃)] (E=P (10), As (11)) was investigated. Compound 1 and 2 could be oxidized to the monocations 3 and 4 and further to the dications 5 and 6, while the initially folded cyclo‐E₅ ligand planarizes upon oxidation. The reduction leads to an opposite change in the geometry of the middle deck, which is now folded stronger into the direction of the other metal fragment (formation of monoanions 7 and 8). For the arsenic compound 8, a different behavior is found since a fragmentation into an As₆ (9) and As₃ ligand complex occurs. The Co and Ni triple‐decker complexes 10 and 11 can be oxidized initially to the heterometallic monocations 12 and 13, which are not stable in solution and convert selectively into the homometallic nickel complexes 14 and 15 and the cobalt complexes 16 and 17. This behavior was further proven by the oxidation of [(Cp′′′Co)(Cp′′Ni)(μ,η³:η²‐P₃)] (19, Cp′′=1,3‐di‐tertbutyl‐cyclopentadienyl) comprising two different Cp ligands. The transfer of {Cp^RM} fragments can be suppressed when a {W(CO)₅} unit is coordinated to the P₃ ligand (20) prior to the oxidation and the mixed cobalt and nickel cation 21 can be isolated. The reduction of 10 and 11 yields the heterometallic monoanions 22 and 23, where no transfer of the {Cp^RM} fragments is observed.

d/f-Polypnictides Derived by Non-Classical Ln2+ Compounds: Synthesis, Small Molecule Activation and Optical Properties

Reduction chemistry induced by divalent lanthanides has been primarily focused on samarium so far. In light of the rich physical properties of the lanthanides, this limitation to one element is a drawback. Since molecular divalent compounds of almost all lanthanides have been available for some time, we used one known and two new non‐classical reducing agents of the early lanthanides to establish a sophisticated reduction chemistry. As a result, six new d/f‐polyphosphides or d/f‐polyarsenides, [K(18‐crown‐6)] [Cp′′₂Ln(E₅)FeCp*] (Ln=La, Ce, Nd; E=P, As) were obtained. Their reactivity was studied by activation of P₄, resulting in a selective expansion of the P₅ rings. The obtained compounds [K(18‐crown‐6)] [Cp′′₂Ln(P₇)FeCp*] (Ln=La, Nd) are the first examples of an activation of P₄ by a f‐element‐polypnictide complex. Additionally, the first systematic femtosecond (fs)‐spectroscopy investigations of d/f‐polypnictides are presented to showcase the advantages of having access to a broader series of lanthanide compounds.

Cationic Functionalisation by Phosphenium Ion Insertion

The reaction of [Cp'''Ni(η3 -P3 )] (1) with in situ generated phosphenium ions [RR'P]+ yields the unprecedented polyphosphorus cations of the type [Cp'''Ni(η3 -P4 R2 )][X] (R=Ph (2 a), Mes (2 b), Cy (2 c), 2,2'-biphen (2 d), Me (2 e); [X]- =[OTf]- , [SbF6 ]- , [GaCl4 ]- , [BArF ]- , [TEF]- ) and [Cp'''Ni(η3 -P4 RCl)][TEF] (R=Ph (2 f), tBu (2 g)). In the reaction of 1 with [Br2 P]+ , an analogous compound is observed only as an intermediate and the final product is an unexpected dinuclear complex [{Cp'''Ni}2 (μ,η3 :η1 :η1 -P4 Br3 )][TEF] (3 a). A similar product [{Cp'''Ni}2 (μ,η3 :η1 :η1 -P4 (2,2'-biphen)Cl)][GaCl4 ] (3 b) is obtained, when 2 d[GaCl4 ] is kept in solution for prolonged times. Although the central structural motif of 2 a-g consists of a "butterfly-like" folded P4 ring attached to a {Cp'''Ni} fragment, the structures of 3 a and 3 b exhibit a unique asymmetrically substituted and distorted P4 chain stabilised by two {Cp'''Ni} fragments. Additional DFT calculations shed light on the reaction pathway for the formation of 2 a-2 g and the bonding situation in 3 a.

Iodination of cyclo-E5 -Complexes (E=P, As)

In a high‐yield one‐pot synthesis, the reactions of [Cp*M(η⁵‐P₅)] (M=Fe (1), Ru (2)) with I₂ resulted in the selective formation of [Cp*MP₆I₆]⁺ salts (3, 4). The products comprise unprecedented all‐cis tripodal triphosphino‐cyclotriphosphine ligands. The iodination of [Cp*Fe(η⁵‐As₅)] (6) gave, in addition to [Fe(CH₃CN)₆]²⁺ salts of the rare [As₆I₈]²⁻ (in 7) and [As₄I₁₄]²⁻ (in 8) anions, the first di‐cationic Fe‐As triple decker complex [(Cp*Fe)₂(μ,η^5:5‐As₅)][As₆I₈] (9). In contrast, the iodination of [Cp*Ru(η⁵‐As₅)] (10) did not result in the full cleavage of the M−As bonds. Instead, a number of dinuclear complexes were obtained: [(Cp*Ru)₂(μ,η^5:5‐As₅)][As₆I₈]_0.5 (11) represents the first Ru‐As₅ triple decker complex, thus completing the series of monocationic complexes [(Cp^RM)₂(μ,η^5:5‐E₅)]⁺ (M=Fe, Ru; E=P, As). [(Cp*Ru)₂As₈I₆] (12) crystallizes as a racemic mixture of both enantiomers, while [(Cp*Ru)₂As₄I₄] (13) crystallizes as a symmetric and an asymmetric isomer and features a unique tetramer of {AsI} arsinidene units as a middle deck.

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.

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.