An Approach to Mixed PnAsm Ligand Complexes

The reaction of a P₄ butterfly complex with yellow arsenic yields the largest mixed P_nAs_m ligand complexes synthesized to date. [{Cp′′′Fe(CO)₂}₂(μ,η^1:1‐P₄)] reacts with As₄ to yield [{Cp′′′Fe}₂(μ,η^4:4‐P_nAs_4‐n)] and [Cp′′′Fe(η⁵‐P_nAs_5‐n)]. Mass spectrometry together with NMR spectroscopy and X‐ray crystallography give clear evidence about the arrangement of the E positions within the cyclo‐E₅ and E₄ moieties of the products. Moreover, the results of DFT calculations agree well with the experimental determined outcomes. By coordinating the E₄ complex [{Cp′′′Fe}₂(μ,η^4:4‐P_nAs_4‐n)] with CuCl, a rearrangement of the E positions occurs in favor with a preferred phosphorus coordination towards copper atoms in the resulting 1D polymeric chain.     

Selective Formation and Unusual Reactivity of Tetraarsabicyclo[1.1.0]butane Complexes

The selective formation of the dinuclear butterfly complexes [{Cp′′′Fe(CO)₂}₂(μ,η^1:1‐E₄)] (E=P ( 1 a ), As ( 1 b )) and [{Cp*Cr(CO)₃}₂(μ,η^1:1‐E₄)] (E=P ( 2 a ), As ( 2 b )) as new representatives of this rare class of compounds was found by reaction of E₄ with the corresponding dimeric carbonyl complexes. Complexes 1 b and 2 b are the first As₄ butterfly compounds with a bridging coordination mode. Moreover, first studies regarding the reactivity of 1 b and 2 b are presented, revealing the formation of the unprecedented As₈ cuneane complexes [{Cp′′′Fe(CO)₂}₂{Cp′′′Fe(CO)}₂(μ₄,η^1:1:2:2‐As₈)] ( 3 b ) and [{Cp*Cr(CO)₃}₄(μ₄,η^1:1:1:1‐As₈)] ( 4 ). The compounds are fully characterized by NMR and IR spectroscopy as well as by X‐ray structure analysis. In addition, DFT calculations give insight into the transformation pathway from the E₄ butterfly to the corresponding cuneane structural motif.     

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.     

Functionalization of a cyclo‐P5 Ligand by Main‐Group Element Nucleophiles

Unprecedented functionalized products with an η⁴‐P₅ ring are obtained by the reaction of [Cp*Fe(η⁵‐P₅)] ( 1 ; Cp*=η⁵‐C₅Me₅) with different nucleophiles. With LiCH₂SiMe₃ and LiNMe₂, the monoanionic products [Cp*Fe(η⁴‐P₅CH₂SiMe₃)]^? and [Cp*Fe(η⁴‐P₅NMe₂)]^?, respectively, are formed. The reaction of 1 with NaNH₂ leads to the formation of the trianionic compound [{Cp*Fe(η⁴‐P₅)}₂N]^3?, whereas the reaction with LiPH₂ yields [Cp*Fe(η⁴‐P₅PH₂)]^? as the main product, with {[Cp*Fe(η⁴‐P₅)]₂PH}^2? as a byproduct. The calculated energy profile of the reactions provides a rationale for the formation of the different products.     

Dreiecksdodekaedrische Heterotri‐ und ‐tetrametall‐Eisen–Ruthenium‐Cluster mit CpR‐ und Pn‐Liganden (n = 5, 4)

Triangulated Dodecahedral Heterotrimetallic‐ and ‐tetrametallic Iron–Ruthenium Clusters with Cp^R and P_n Ligands (n = 5, 4) The cothermolysis of [Cp*Fe(η⁵‐P₅)] ( 1 ) and [{Cp″(OC)₂Ru}₂](Ru–Ru) ( 2 ), Cp″ = C₅H₃But₂‐1,3, affords low yields of [Cp″Ru(η⁵‐P₅)] ( 3 ) and [{Cp″Ru}₂P₄] ( 4 ) as well as the triangulated dodecahedral hetero‐ and homotrimetallic clusters [{Cp″Ru}₂{Cp*Fe}P₅] ( 5 ), [{Cp″Ru}₃P₅] ( 6 ), [{Cp*Fe}₂{Cp″Ru}P₅] ( 7 ) and the tetranuclear compound [{Cp″Ru}₃{Cp*Fe}P₄] ( 8 ). X‐ray crystallographic studies show that the P₅ ligand in the distorted M₂M′P₅‐triangulated dodecahedra of 5 and 7 offers an unusual novel coordination mode derived from the educt 1 .     

Molecular Polyarsenides of the Rare‐Earth Elements

Reduction of [Cp*Fe(η⁵‐As₅)] with [Cp′′₂Sm(thf)] (Cp′′=η⁵‐1,3‐(tBu)₂C₅H₃) under various conditions led to [(Cp′′₂Sm)(μ,η⁴:η⁴‐As₄)(Cp*Fe)] and [(Cp′′₂Sm)₂As₇(Cp*Fe)]. Both compounds are the first polyarsenides of the rare‐earth metals. [(Cp′′₂Sm)(μ,η⁴:η⁴‐As₄)(Cp*Fe)] is also the first d/f‐triple decker sandwich complex with a purely inorganic planar middle deck. The central As₄^2? unit is isolobal with the 6π‐aromatic cyclobutadiene dianion (CH)₄^2?. [(Cp′′₂Sm)₂As₇(Cp*Fe)] contains an As₇^3? cage, which has a norbornadiene‐like structure with two short As?As bonds in the scaffold. DFT calculations confirm all the structural observations. The As?As bond order inside the cyclo As₄ ligand in [(Cp′′₂Sm)(μ,η⁴:η⁴‐As₄)(Cp*Fe)] was estimated to be in between an As?As single bond and a formally aromatic As₄^2? system.     

Mehrkernige Eisen/Tantal‐ und Tantal‐Komplexe mit Asn‐Liganden

Polynuclear Iron/Tantalum and Tantalum Complexes with As_n Ligands Starting with [Cp@Ta(CO)₄] ( 1 ) (Cp@ = C₅H₃^tBu₂‐1,3) and As₄ or (^tBuAs)₄ ( 2 ) its thermolysis at 190 °C in decalin gives [{Cp@Ta}₂(μ‐η⁴ : η⁴‐As₈)] ( 3 ), which is also formed according to equation (2) in addition to [{Cp@Ta}₃As₆] ( 5 ). The reaction of 1 or [{Cp*(OC)₂Fe}₂] ( 6 ) with 3 affords 5 or [{Cp*Fe}{Cp@Ta}As₅] ( 8 ) demonstrating the use of 3 as As_n source. 8 can also be synthesized from 1 and [Cp*Fe(η⁵‐As₅)] ( 7 ) for which the cothermolysis of 2 and 6 gives a better yield.     

E4 Butterfly Complexes (E=P,As) as Chelating Ligands

The coordination properties of new types of bidentate phosphane and arsane ligands with a narrow bite angle are reported. The reactions of [{Cp′′′Fe(CO)₂}₂(μ,η^1:1‐P₄)] ( 1 a ) with the copper salt [Cu(CH₃CN)₄][BF₄] leads, depending on the stoichiometry, to the formation of the spiro compound [{{Cp′′′Fe(CO)₂}₂(μ₃,η^1:1:1:1‐P₄)}₂Cu]⁺[BF₄]^? ( 2 ) or the monoadduct [{Cp′′′Fe(CO)₂}₂(μ₃,η^1:1:2‐P₄){Cu(MeCN)}]⁺[BF₄]^? ( 3 ). Similarly, the arsane ligand [{Cp′′′Fe(CO)₂}₂(μ,η^1:1‐As₄)] ( 1 b ) reacts with [Cu(CH₃CN)₄][BF₄] to give [{{Cp′′′Fe(CO)₂}₂(μ₃,η^1:1:1:1‐As₄)}₂Cu]⁺[BF₄]^? ( 5 ). Protonation of 1 a occurs at the “wing tip” phosphorus atoms, which is in line with the results of DFT calculations. The compounds are characterized by spectroscopic methods (heteronuclear NMR spectroscopy and IR spectrometry) and by single‐crystal X‐ray diffraction studies.     

Arsenic-Rich Polyarsenides Stabilized by Cp*Fe Fragments

The redox chemistry of [Cp*Fe(η⁵-As₅)] ( 1 , Cp*=η⁵-C₅Me₅) 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, ¹H 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⁻.     

Ring Contraction by NHC‐Induced Pnictogen Abstraction

The reaction of [Cp′′′Co(η⁴‐P₄)] ( 1 ) (Cp′′′=1,2,4‐tBu₃C₅H₂) with ^MeNHC (^MeNHC=1,3,4,5‐tetramethylimidazol‐2‐ylidene) leads through NHC‐induced phosphorus cation abstraction to the ring contraction product [(^MeNHC)₂P][Cp′′′Co(η³‐P₃)] ( 2 ), which represents the first example of an anionic CoP₃ complex. Such NHC‐induced ring contraction reactions are also applicable for triple‐decker sandwich complexes. The complexes [(Cp*Mo)₂(μ,η^6:6‐E₆)] ( 3 a , 3 b ) (Cp*=C₅Me₅; E=P, As) can be transformed to the complexes [(^MeNHC)₂E][(Cp*M)₂(μ,η^3:3‐E₃)(μ,η^2:2‐E₂)] ( 4 a , 4 b ), with 4 b representing the first structurally characterized example of an NHC‐substituted As^I cation. Further, the reaction of the vanadium complex [(Cp*V)₂(μ,η^6:6‐P₆)] ( 5 ) with ^MeNHC results in the formation of the unprecedented complexes [(^MeNHC)₂P][(Cp*V)₂(μ,η^6:6‐P₆)] ( 6 ), [(^MeNHC)₂P][(Cp*V)₂(μ,η^5:5‐P₅)] ( 7 ) and [(Cp*V)₂(μ,η^3:3‐P₃)(μ,η^1:1‐P{^MeNHC})] ( 8 ).     

Structures and Properties of Spherical 90‐Vertex Fullerene‐Like Nanoballs

By applying the proper stoichiometry of 1:2 to [Cp^RFe(η⁵‐P₅)] and CuX (X=Cl, Br) and dilution conditions in mixtures of CH₃CN and solvents like CH₂Cl₂, 1,2‐Cl₂C₆H₄, toluene, and THF, nine spherical giant molecules having the simplified general formula [Cp^RFe(η⁵‐P₅)]@[{Cp^RFe(η⁵‐P₅)}₁₂{CuX}₂₅(CH₃CN)₁₀] (Cp^R=η⁵‐C₅Me₅ (Cp*); η⁵‐C₅Me₄Et (Cp^Et); X=Cl, Br) have been synthesized and structurally characterized. The products consist of 90‐vertex frameworks consisting of non‐carbon atoms and forming fullerene‐like structural motifs. Besides the mostly neutral products, some charged derivatives have been isolated. These spherical giant molecules show an outer diameter of 2.24 (X=Cl) to 2.26 nm (X=Br) and have inner cavities of 1.28 (X=Cl) and 1.20 nm (X=Br) in size. In most instances the inner voids of these nanoballs encapsulate one molecule of [Cp*Fe(η⁵‐P₅)], which reveals preferred orientations of π–π stacking between the cyclo‐P₅ rings of the guest and those of the host molecules. Moreover, π–π and σ–π interactions are also found in the packing motifs of the balls in the crystal lattice. Electrochemical investigations of these soluble molecules reveal one irreversible multi‐electron oxidation at E_p=0.615 V and two reduction steps (?1.10 and ?2.0 V), the first of which corresponds to about 12 electrons. Density functional calculations reveal that during oxidation and reduction the electrons are withdrawn or added to the surface of the spherical nanomolecules, and no Cu²⁺ species are involved.     

The Missing Parent Compound [(C5H5)Fe(η5-P5)]: Synthesis,Characterization, Coordination Behavior and Encapsulation

The so far missing parent compound of the large family of pentaphosphaferrocenes [CpFe(η⁵-P₅)] ( 1 b ) was synthesized by the thermolysis of [CpFe(CO)₂]₂ with P₄ using the very high-boiling solvent diisopropylbenzene. It was comprehensively characterized by, inter alia, NMR spectroscopy, single crystal X-ray structure analysis, cyclic voltammetry and DFT computations. Moreover, its coordination behavior towards Cu^I halides was explored, revealing the unprecedented 2D polymeric networks [{CpFe(η^5:1:1:1:1-P₅)}Cu₂(μ-X)₂]_n ( 2 a : X=Cl, 2 b : X=Br) and [{CpFe(η^5:1:1-P₅)}Cu(μ-I)]_n ( 3 ) and even the first cyclo-P₅-containing 3D coordination polymer [{CpFe(η^5:1:1-P₅)}Cu(μ-I)]_n ( 4 ). The sandwich complex 1 b can also be incorporated in nano-sized supramolecules based on [Cp*Fe(η⁵-P₅)] ( 1 a ) and CuX (X=Cl, Br, I): [CpFe(η⁵-P₅)]@[{Cp*Fe(η⁵-P₅)}₁₂(CuX)_20-n] ( 5 a : X=Cl, n=2.4; 5 b : X=Br, n=2.4; 5 c : X=I, n=0.95). Thereby, the formation of the CuI-containing fullerene-like sphere 5 c is found for the first time.     

Ringkontraktion durch NHC‐induzierte Pnictogen‐Abstraktion

Die Reaktion von [Cp′′′Co(η⁴‐P₄)] ( 1 ) (Cp′′′=1,2,4‐tBu₃C₅H₂) mit ^MeNHC (^MeNHC=1,3,4,5‐tetramethylimidazol‐2‐ylidene) führt über eine NHC‐induzierte Phosphorkationen‐Abstraktion zum Ringkontraktionsprodukt [(^MeNHC)₂P][Cp′′′Co(η³‐P₃)] ( 2 ), welches das erste Beispiel eines anionischen CoP₃‐Komplexes repräsentiert. Solche von NHCs induzierten Ringkontraktionsreaktionen lassen sich ebenfalls auf Tripeldecker‐Sandwich‐Komplexe anwenden. So werden die Komplexe [(Cp*Mo)₂(μ,η^6:6‐E₆)] ( 3 a , 3 b ) (Cp*=C₅Me₅; E=P, As) zu den Komplexen [(^MeNHC)₂E][(Cp*M)₂(μ,η^3:3‐E₃)(μ,η^2:2‐E₂)] ( 4 a , 4 b ) transformiert, wobei 4 b das erste strukturell charakterisierte Beispiel eines NHC‐substituierten As^I‐Kations darstellt. Darüber hinaus führt die Reaktion des Vanadium‐Komplexes [(Cp*V)₂(μ,η^6:6‐P₆)] ( 5 ) mit ^MeNHC zur Bildung der neuartigen Komplexe [(^MeNHC)₂P][(Cp*V)₂(μ,η^6:6‐P₆)] ( 6 ), [(^MeNHC)₂P][(Cp*V)₂(μ,η^5:5‐P₅)] ( 7 ) bzw. [(Cp*V)₂(μ,η^3:3‐P₃)(μ,η^1:1‐P{^MeNHC})] ( 8 ).     

An Icosidodecahedral Supramolecule Based on Pentaphosphaferrocene: From a Disordered Average Structure to Individual Isomers

Pentaphosphaferrocenes [Cp^RFe(η⁵‐P₅)] ( 1 ) and Cu^I halides are excellent building blocks for the formation of discrete supramolecules. Herein, we demonstrate the potential of Cu(CF₃SO₃) for the construction of the novel 2D polymer [{Cp*Fe(μ₄,η^5:1:1:1‐P₅)}{Cu(CF₃SO₃)}]_n ( 2 ) and the unprecedented nanosphere (CH₂Cl₂)_1.4@[{Cp^BnFe(η⁵‐P₅)}₁₂{Cu(CF₃SO₃)}_19.6] ( 3 ). The supramolecule 3 has a unique scaffold beyond the fullerene topology, with 20 copper atoms statistically distributed over the 30 vertices of an icosidodecahedron. Combinatorics was used to interpret the average disordered structure of the supramolecules. In this case, only two pairs of enantiomers with D₅ and D₂ symmetry are possible for bidentate bridging coordination of the triflate ligands. DFT calculations showed that differences in the energies of the isomers are negligible. The benzyl ligands enhance the solubility of 3 , enabling NMR‐spectroscopic and mass‐spectrometric investigations.     

Coordination chemistry of [Cp*Fe(η5-P3C2tBu2)] (Cp* = η5-C5Me5) with copper(I) halides – Formation of oligomeric and polymeric compounds

The reaction of the 1,2,4-triphosphaferrocene [Cp*Fe(η⁵-P₃C₂tBu₂)] (1) with CuX (X = Cl, Br, I) in a 1:1 stoichiometric ratio leads to the formation of the oligomeric compounds [{Cu(μ-X)}₆(μ₆-X)Cu(MeCN)₃{μ,η²-(Cp*Fe(η⁵-P₃C₂tBu₂))}₂{μ₃,η³-(Cp*Fe(η⁵-P₃C₂tBu₂))}] (X = Cl (2), Br (3)) and [{Cu(μ-I)}₃{Cu(μ₃-I)}₃Cu(μ₆-I){μ,η²-(Cp*Fe(η⁵-P₃C₂tBu₂))}₃{η¹-(Cp*Fe(η⁵-P₃C₂tBu₂))}] (4) revealing Cu(I) halide cages surrounded by 1,2,4-triphosphaferrocene moieties. The reaction of [Cp*Fe(η⁵-P₃C₂tBu₂)] with CuI in a 1:4 stoichiometry leads to the formation of the two-dimensional polymer [{Cu(μ-I)}₄{Cu(μ₃-I)(MeCN)}₂{μ₃,η³-(Cp*Fe(P₃C₂tBu₂))}]_n (5). The oligomeric compounds show dynamic behavior in solution monitored by ³¹P NMR spectroscopy. All compounds are additionally characterized by single crystal X-ray diffraction.     

Regioselective Insertion of Aluminum(I) in the cyclo‐P5 Ring of Pentaphosphaferrocene

A route to directly access mixed Al–Fe polyphosphide complexes was developed. The reactivity of pentaphosphaferrocene, [Cp*Fe(η⁵‐P₅)] (Cp*=C₅Me₅), with two different low‐valent aluminum compounds was investigated. The steric and electronic environment around the [Al^I] centre are found to be crucial for the formation of the resulting Al–Fe polyphosphides. Reaction with the sterically demanding [Dipp‐BDIAl^I] (Dipp‐BDI={[2,6‐ⁱPr₂C₆H₃NCMe]₂CH}^?) resulted in the first Al‐based neutral triple‐decker type polyphosphide complex. For [(Cp*Al^I)₄], an unprecedented regioselective insertion of three [Cp*Al^III]²⁺ moieties into two adjacent P?P bonds of the cyclo‐P₅ ring of [Cp*Fe(η⁵‐P₅)] was observed. The regioselectivity of the insertion reaction could be rationalized by isolating an analogue of the reaction intermediate stabilized by a strong σ‐donor carbene.     

Nucleophilic Attack at Pentaarsaferrocene [Cp*Fe(η5-As5)]—The Way to Larger Polyarsenide Ligands

By the reaction of [Cp*Fe(η⁵-As₅)] ( I ) (Cp*=C₅Me₅) with main group nucleophiles, unique functionalized products with η⁴-coordinated polyarsenide (As_n) units (n=5, 6, 20) are obtained. With carbon-based nucleophiles such as MeLi or KBn (Bn=CH₂Ph), the anionic organo-substituted polyarsenide complexes, [Li(2.2.2-cryptand)][Cp*Fe(η⁴-As₅Me)] ( 1 a ) and [K(2.2.2-cryptand)][Cp*Fe{η⁴-As₅(CH₂Ph)}] ( 1 b ), are accessible. The use of KAsPh₂ leads to a selective and controlled extension of the As₅ unit and the formation of the monoanionic compound [K(2.2.2-cryptand][Cp*Fe(η⁴-As₆Ph₂)] ( 2 ). When I is reacted with [M]As(SiMe₃)₂ (M=Li ⋅ THF; K), the formation of the largest known anionic polyarsenide unit in [M′(2.2.2-cryptand)]₂[(Cp*Fe)₄{μ₅-η⁴:η⁴:η³:η³:η¹:η¹-As₂₀}] ( 3 ) occurred (M′=Li ( 3 a ), K ( 3 b )).     

A Nano‐sized Supramolecule Beyond the Fullerene Topology

The reaction of [Cp^BnFe(η⁵‐P₅)] ( 1 ) (Cp^Bn=η⁵‐C₅(CH₂Ph)₅) with CuI selectively yields a novel spherical supramolecule (CH₂Cl₂)_3.4@[(Cp^BnFeP₅)₁₂{CuI}₅₄(MeCN)_1.46] ( 2 ) showing a linkage of the scaffold atoms which is beyond the Fullerene topology. Its extended CuI framework reveals an outer diameter of 3.7 nm—a size that has not been reached before using five‐fold symmetric building blocks. Furthermore, 2 shows a remarkable solubility in CH₂Cl₂, and NMR spectroscopy reveals that the scaffold of the supramolecule remains intact in solution. In addition, a novel 2D polymer [{Cp^BnFe(η⁵‐P₅)}₂{Cu₆(μ‐I)₂(μ₃‐I)₄}]_n ( 3 ) with an uncommon structural motif was isolated. Its formation can be avoided by using a large excess of CuI in the reaction with 1 .     

Highly Dynamic Coordination Behavior of Pn Ligand Complexes towards “Naked” Cu+ Cations

Reactions of Cu⁺ containing the weakly coordinating anion [Al{OC(CF₃)₃}₄]^? with the polyphosphorus complexes [{CpMo(CO)₂}₂(μ,η²:η²‐P₂)] ( A ), [CpM(CO)₂(η³‐P₃)] (M=Cr( B1 ), Mo ( B2 )), and [Cp*Fe(η⁵‐P₅)] ( C ) are presented. The X‐ray structures of the products revealed mononuclear ( 4 ) and dinuclear ( 1 , 2 , 3 ) Cu^I complexes, as well as the one‐dimensional coordination polymer ( 5 a ) containing an unprecedented [Cu₂( C )₃]²⁺ paddle‐wheel building block. All products are readily soluble in CH₂Cl₂ and exhibit fast dynamic coordination behavior in solution indicated by variable temperature ³¹P{¹H} NMR spectroscopy.     

Rearrangement of a P4 Butterfly Complex—The Formation of a Homoleptic Phosphorus–Iron Sandwich Complex

The versatile coordination behavior of the P₄ butterfly complex [{Cp′′′Fe(CO)₂}₂(μ,η^1:1-P₄)] ( 1 , Cp′′′=η⁵-C₅H₂^tBu₃) towards different iron(II) compounds is presented. The reaction of 1 with [FeBr₂⋅dme] (dme=dimethoxyethane) leads to the chelate complex [{Cp′′′Fe(CO)₂}₂(μ₃,η^1:1:2-P₄){FeBr₂}] ( 2 ), whereas, in the reaction with [Fe(CH₃CN)₆][PF₆]₂, an unprecedented rearrangement of the P₄ butterfly structural motif leads to the cyclo-P₄ moiety in {(Cp′′′Fe(CO)₂)₂(μ₃,η^1:1:4-P₄)}₂Fe][PF₆]₂ ( 3 ). Complex 3 represents the first fully characterized “carbon-free” sandwich complex containing cyclo-P₄R₂ ligands in a homoleptic-like iron–phosphorus-containing molecule. Alternatively, 2 can be transformed into 3 by halogen abstraction and subsequent coordination of 1 . The additional isolated side products, [{Cp′′′Fe(CO)₂}₂(μ₃,η^1:1:2-P₄){Cp′′′Fe(CO)}][PF₆] ( 4 ) and [{Cp′′′Fe(CO)₂}₂(μ₃,η^1:1:4-P₄){Cp′′′Fe}][PF₆] ( 5 ), give insight into the stepwise activation of the P₄ butterfly moiety in 1 .