A comparative study of the coordination behavior of cyclo-P5 and cyclo-As5 ligand complexes towards the trinuclear Lewis acid complex (perfluoro-ortho-phenylene)mercury

Reactions of the cyclo-E₅ sandwich complexes [Cp*Fe(η⁵-P₅)] (1) and [Cp*Fe(η⁵-As₅)] (2) with the planar Lewis acid trimeric (perfluoro-ortho-phenylene)mercury [(o-C₆F₄Hg)₃] (3) afford compounds that show distinctly different assemblies in the solid state. The phosphorus containing ligand 1 forms dimeric coordination units with two molecules of 3, with one P atom of each cyclo-P₅ ligand positioned in close proximity to the center of a molecule of 3. In contrast to the coordination behavior of 1, the arsenic analog 2 shows simultaneous interaction of three As atoms with the Hg atoms of 3. A DFT study and subsequent AIM analyses of the products suggest that electrostatic forces are prevalent over donor–acceptor interactions in these adducts, and may play a role in the differences in the observed coordination behavior. Subsequently, a series of [Cp^RFe(η⁵-P₅)] (Cp^R = C₅H_5–n tBu_n, n = 1–3, 6a–c) sandwich complexes was prepared and also reacted with [(o-C₆F₄Hg)₃]. In the solid state the obtained products 7a–c with increasing steric demand of the Cp^R ligands show no significant change in their assembly compared to the Cp* analog 4. All of the products were characterized by single crystal X-ray structure analysis, mass spectrometry and elemental analysis as well as NMR spectroscopy and IR spectrometry.     

A General Pathway to Heterobimetallic Triple-Decker Complexes

A systematic study on the reactivity of the triple-decker complex [(Cp’’’Co)₂(μ,η⁴:η⁴-C₇H₈)] ( A ) (Cp’’’=1,2,4-tritertbutyl-cyclopentadienyl) towards sandwich complexes containing cyclo-P₃, cyclo-P₄, and cyclo-P₅ ligands under mild conditions is presented. The heterobimetallic triple-decker sandwich complexes [(Cp*Fe)(Cp’’’Co)(μ,η⁵:η⁴-P₅)] ( 1 ) and [(Cp’’’Co)(Cp’’’Ni)(μ,η³:η³-P₃)] ( 3 ) (Cp*=1,2,3,4,5-pentamethylcyclopentadienyl) were synthesized and fully characterized. In solution, these complexes exhibit a unique fluxional behavior, which was investigated by variable temperature NMR spectroscopy. The dynamic processes can be blocked by coordination to {W(CO)₅} fragments, leading to the complexes [(Cp*Fe)(Cp’’’Co)(μ₃,η⁵:η⁴:η¹-P₅){W(CO)₅}] ( 2 a ), [(Cp*Fe)(Cp’’’Co)(μ₄,η⁵:η⁴:η¹:η¹-P₅){(W(CO)₅)₂}] ( 2 b ), and [(Cp’’’Co)(Cp’’’Ni)(μ₃,η³:η²:η¹-P₃){W(CO)₅}] ( 4 ), respectively. The thermolysis of 3 leads to the tetrahedrane complex [(Cp’’’Ni)₂(μ,η²:η²-P₂)] ( 5 ). All compounds were fully characterized using single-crystal X-ray structure analysis, NMR spectroscopy, mass spectrometry, and elemental analysis.     

Photochemical substitution of benzene in the iron cyclohexadienyl complex [(η<Superscript>5</Superscript>-C<Subscript>6</Subscript>H<Subscript>7</Subscript>)Fe(η-C<Subscript>6</Subscript>H<Subscript>6</Subscript>)]<Superscript>+</Superscript>

The visible light irradiation of the [(η⁵-C₆H₇)Fe(η-C₆H₆)]⁺ cation (1) in acetonitrile resulted in the substitution of the benzene ligand to form the labile acetonitrile species [(η⁵-C₆H₇)Fe(MeCN)₃]⁺ (2). The reaction of 1 with Bu^tNC in MeCN produced the stable isonitrile complex [(η⁵-C₆H₇)Fe(Bu^tNC)₃]⁺ (3). The photochemical reaction of cation 1 with pentaphosphaferrocene Cp*Fe(η-cyclo-P₅) afforded the triple-decker cation with the bridging pentaphospholyl ligand, [(η⁵-C₆H₇)Fe(μ-η:η-cyclo-P₅)FeCp*]⁺ (4). The latter complex was also synthesized by the reaction of cation 2 with Cp*Fe(η-cyclo-P₅). The structure of the complex [3]PF₆ was established by X-ray diffraction. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2088–2091, November, 2007.     

A Structural Diversity of Molecular Alkaline-Earth-Metal Polyphosphides: From Supramolecular Wheel to Zintl Ion

A series of molecular group 2 polyphosphides has been synthesized by using air-stable [Cp*Fe(η⁵-P₅)] (Cp*=C₅Me₅) or white phosphorus as polyphosphorus precursors. Different types of group 2 reagents such as organo-magnesium, mono-valent magnesium, and molecular calcium hydride complexes have been investigated to activate these polyphosphorus sources. The organo-magnesium complex [(^DippBDI−Mg(CH₃))₂] (^DippBDI={[2,6-ⁱPr₂C₆H₃NCMe]₂CH}⁻) reacts with [Cp*Fe(η⁵-P₅)] to give an unprecedented Mg/Fe-supramolecular wheel. Kinetically controlled activation of [Cp*Fe(η⁵-P₅)] by different mono-valent magnesium complexes allowed the isolation of Mg-coordinated formally mono- and di-reduced products of [Cp*Fe(η⁵-P₅)]. To obtain the first examples of molecular calcium-polyphosphides, a molecular calcium hydride complex was used to reduce the aromatic cyclo-P₅ ring of [Cp*Fe(η⁵-P₅)]. The Ca-Fe-polyphosphide is also characterized by quantum chemical calculations and compared with the corresponding Mg complex. Moreover, a calcium coordinated Zintl ion (P₇)³⁻ was obtained by molecular calcium hydride mediated P₄ reduction.     

Ring Expansions of Nonpolar Polyphosphorus Rings

The reaction of the phosphinidene complex [Cp*P{W(CO)₅}₂] ( 1 a ) (Cp*=C₅Me₅) with the anionic cyclo-P_n ligand complex [(η³-P₃)Nb(ODipp)₃]⁻ ( 2 , Dipp=2,6-diisopropylphenyl) resulted in the formation of [{W(CO)₅}₂{μ₃,η^3:1:1-P₄Cp*}Nb(ODipp)₃]⁻ ( 3 ), which represents an unprecedented example of a ring expansion of a polyphosphorus-ligand complex initiated by a phosphinidene complex. Furthermore, the reaction of the pnictinidene complexes [Cp*E{W(CO)₅}₂] (E=P: 1 a , As: 1 b ) with the neutral complex [Cp′′′Co(η⁴-P₄)] (Cp′′′=1,2,4-tBu₃C₅H₂) led to a cyclo-P₄E ring (E=P, As) through the insertion of the pentel atom into the cyclo-P₄ ligand. Starting from 1 a , the two isomers [Cp′′′Co(μ₃,η^4:1:1-P₅Cp*){W(CO)₅}₂] ( 5 a , b ), and from 1 b , the three isomers [Cp′′′Co(μ₃,η^4:1:1-AsP₄Cp*){W(CO)₅}₂] ( 6 a – c ) with unprecedented cyclo-P₄E ligands (E=P, As) were isolated. The complexes 6 a – c represent unique examples of ring expansions which lead to new mixed five-membered cyclo-P₄As ligands. The possible reaction pathways for the formation of 5 a , b and 6 a – c were investigated by a combination of temperature-dependent ³¹P{¹H} NMR studies and DFT calculations.     

The approach to 4d/4f-polyphosphides

The first 4d/4f polyphosphides were obtained by reaction of the divalent metallocenes [Cp*₂Ln(thf)₂] (Ln = Sm, Yb) with [{CpMo(CO)₂}₂(μ,η^2:2-P₂)] or [Cp*Mo(CO)₂(η³-P₃)]. Treatment of [Cp*₂Ln(thf)₂] (Ln = Sm, Yb) with [{CpMo(CO)₂}₂(μ,η^2:2-P₂)] gave the 16-membered bicyclic compounds [(Cp₂*Ln)₂P₂(CpMo(CO)₂)₄] (Ln = Sm, Yb) as the major products. From the reaction involving samarocene, the cyclic P₄ complex [(Cp*₂Sm)₂P₄(CpMo(CO)₂)₂] and the cyclic P₅ complex [(Cp*₂Sm)₃P₅(CpMo(CO)₂)₃] were also obtained as minor products. In each reaction, the P₂ unit is reduced and a rearrangement occurred. In dedicated cases, a P–P bond formation takes place, which results in a new aggregation of the central phosphorus scaffold. In the reactions of [Cp*₂Ln(thf)₂] (Ln = Sm, Yb) with [Cp*Mo(CO)₂P₃] a new P–P bond is formed by reductive dimerization and the 4d/4f hexaphosphides [(Cp*₂Ln)₂P₆(Cp*Mo(CO)₂)₂] (Ln = Sm, Yb) were obtained.     

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.     

Synthesis and Reactivity of a Cyclooctatetraene-Like Polyphosphorus Ligand Complex [Cyclo-P8]

The thermolysis of Cp′′′Ta(CO)₄ with white phosphorus (P₄) gives access to [{Cp′′′Ta}₂(μ,η^{2 : 2 : 2 : 2 : 1 : 1}-P₈)] ( A ), representing the first complex containing a cyclooctatetraene-like (COT) cyclo-P₈ ligand. While ring sizes of n >6 have remained elusive for cyclo-P_n structural motifs, the choice of the transition metal, co-ligand and reaction conditions allowed the isolation of A . Reactivity investigations reveal its versatile coordination behaviour as well as its redox properties. Oxidation leads to dimerization to afford [{Cp′′′Ta}₄(μ₄,η^{2 : 2 : 2 : 2 : 2 : 2 : 2 : 2 : 1 : 1 : 1 : 1}-P₁₆)][TEF]₂ ( 4 , TEF=[Al(OC{CF₃}₃)₄]⁻). Reduction, however, leads to the fission of one P−P bond in A followed by rapid dimerization to form [K@[2.2.2]cryptand]₂[{Cp′′′Ta}₄(μ₄,η^{2 : 2 : 2 : 2 : 2 : 2 : 2 : 2 : 1 : 1 : 1 : 1}-P₁₆)] ( 5 ), which features an unprecedented chain-type P₁₆ ligand. Lastly, A serves as a P₂ synthon, via ring contraction to the triple-decker complex [{Cp′′′Ta}₂(μ,η^{6 : 6}-P₆)] ( B ).     

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.     

Size-determining dependencies in supramolecular organometallic host-guest chemistry

Treatment of the pentaphosphaferrocene [Cp*Fe(η⁵‐P₅)] with Cu^I halides in the presence of different templates leads to novel fullerene‐like spherical molecules that serve as hosts for the templates. If ferrocene is used as the template the 80‐vertex ball [Cp₂Fe]@[{Cp*Fe(η⁵‐P₅)}₁₂{CuCl}₂₀] ( 4 ), with an overall icosahedral C₈₀ topological symmetry, is obtained. This result shows the ability of ferrocene to compete successfully with the internal template of the reaction system [Cp*Fe(η⁵‐P₅)], although the 90‐vertex ball [{Cp*Fe(η⁵:η¹:η¹:η¹:η¹:η¹‐P₅)}₁₂(CuCl)₁₀(Cu₂Cl₃)₅{Cu(CH₃CN)₂}₅] ( 2 a ) containing pentaphosphaferrocene as a guest is also formed as a byproduct. With use of the triple‐decker sandwich complex [(CpCr)₂(μ,η⁵‐As₅)] as a template the reaction between [Cp*Fe(η⁵‐P₅)] and CuBr leads to the 90‐vertex ball [(CpCr)₂(μ,η⁵‐As₅)]@[{Cp*Fe(η⁵‐P₅)}₁₂{CuBr}₁₀{Cu₂Br₃}₅{Cu(CH₃CN)₂}₅] ( 6 ), in which the complete molecule acts as a template. However, if the corresponding reaction is instead carried out with CuCl, cleavage of the triple‐decker complex is found and the 80‐vertex ball [CpCr(η⁵‐As₅)]@[{Cp*Fe(η⁵‐P₅)}₁₂{CuCl}₂₀] ( 5 ) is obtained. This accommodates as its guest [CpCr(η⁵‐As₅)], which has only 16 valence electrons in a triplet ground state and is not known as a free molecule. The triple‐decker sandwich complex [(CpCr)₂(μ,η⁵‐As₅)] requires 53.1 kcal mol^?1 to undergo cleavage (as calculated by DFT methods) and therefore this reaction is clearly endothermic. All new products have been characterized by single‐crystal X‐ray crystallography. A favoured orientation of the guest molecules inside the host cages has been identified, which shows π???π stacking of the five‐membered rings (Cp and cyclo‐As₅) of the guests and the cyclo‐P₅ rings of the nanoballs of the hosts.     

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⁻.     

Remarkable Structural and Electronic Features of the Complex Formed by Trimeric Copper Pyrazolate with Pentaphosphaferrocene

According to spectroscopic (NMR, IR, UV/Vis) study, the interaction of pentaphosphaferrocene [Cp*Fe(η⁵‐P₅)] with trimeric copper pyrazolate [(Cu{3,5‐(CF₃)₂Pz})₃] yields a new compound that is astonishingly stable in solution. Single‐crystal X‐ray analysis reveals unprecedented structural changes in the interacting molecules and the unique type of coordination [Cp*Fe(μ₃‐η⁵:η²,η²‐P₅){Cu(3,5‐(CF₃)₂Pz)}₃]. As a result of the 90° macrocycle folding, the copper atoms are able to behave both as a Lewis acid and as a Lewis base in the interaction with the cyclo‐P₅ ligand.     

Insertion of Phosphenium Ions into a Bicyclo[1.1.0]Tetraphosphabutane Iron Complex

By reacting [{Cp‴Fe(CO)₂}₂(µ,η^1:1-P₄)] (1) with in situ generated phosphenium ions [Ph₂P][A] ([A]⁻ = [OTf]⁻ = [O₃SCF₃]⁻, [PF₆]⁻), a mixture of two main products of the composition [{Cp‴Fe(CO)₂}₂(µ,η^1:1-P₅(C₆H₅)₂)][PF₆] (2a and 3a) could be identified by extensive ³¹P NMR spectroscopic studies at 193 K. Compound 3a was also characterized by X-ray diffraction analysis, showing the rarely observed bicyclo[2.1.0]pentaphosphapentane unit. At room temperature, the novel compound [{Cp‴Fe}(µ,η^4:1-P₅Ph₂){Cp‴(CO)₂Fe}][PF₆] (4) is formed by decarbonylation. Reacting 1 with in situ generated diphenyl arsenium ions gives short-lived intermediates at 193 K which disproportionate at room temperature into tetraphenyldiarsine and [{Cp‴Fe(CO)₂}₄(µ₄,η^1:1:1:1-P₈)][OTf]₂ (5) containing a tetracyclo[3.3.0.0^2,7.0^3,6]octaphosphaoctane ligand.     

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.     

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 Cp^RTa(CO)₂(η⁴-P₄) (1a: Cp^R = Cp′′; 1b: Cp^R = 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.

A one-pot self-assembly template-controlled reaction is reported to result in a 2D coordination network of first host-guest assemblies P₃Se₄@[{(Cp′′Ta(CO)₂(η⁴-P₄))Ag}₈]⁸⁺ of 2.49 nm in size based on an organometallic complex with a cyclo-P₄ end-deck.     

Halogenation of the Hexaphosphabenzene Complex [(Cp*Mo)2(μ,η6:η6-P6)]: Snapshots on the Reaction Progress

The oxidation of [(Cp*Mo)₂(μ,η⁶:η⁶-P₆)] ( 1 ) with halogens or halogen sources was investigated. The iodination afforded the ionic complexes [(Cp*Mo)₂(μ,η³:η³-P₃)(μ,η¹:η¹:η¹:η¹-P₃I₃)][X] (X=I₃⁻, I⁻) ( 2 ) and [(Cp*Mo)₂(μ,η⁴:η⁴-P₄)(μ-PI₂)][I₃] ( 3 ), while the reaction with PBr₅ led to the complexes [(Cp*Mo)₂(μ,η³:η³-P₃)(μ-Br)₂][Cp*MoBr₄] ( 4 ) [(Cp*MoBr)₂(μ,η³:η³-P₃)(μ,η¹-P₂Br₃)] ( 5 ) and [(Cp*Mo)₂(μ-PBr₂)(μ-PHBr)(μ-Br)₂] ( 6 ). The reaction of 1 with the far stronger oxidizing agent PCl₅ was followed via time- and temperature-dependent ³¹P{¹H} NMR spectroscopy. One of the first intermediates detected at 193 K was [(Cp*Mo)₂(μ,η³:η³-P₃)(μ-PCl₂)₂][PCl₆] ( 8 ) which rearranges upon warming to [(Cp*Mo)₂(μ-PCl₂)₂(μ-Cl)₂] ( 9 ), [(Cp*MoCl)₂(μ,η³:η³-P₃)(μ-PCl₂)] ( 10 ) and [(Cp*Mo)₂(μ,η⁴:η⁴-P₄)(μ-PCl₂)][Cp*MoCl₄] ( 11 ), which could be isolated at room temperature. All complexes were characterized by single-crystal X-ray diffraction, NMR spectroscopy and their electronic structures were elucidated by DFT calculations.     

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-P₄R₂)][X] (R=Ph ( 2 a ), Mes ( 2 b ), Cy ( 2 c ), 2,2′-biphen ( 2 d ), Me ( 2 e ); [X]⁻=[OTf]⁻, [SbF₆]⁻, [GaCl₄]⁻, [BAr^F]⁻, [TEF]⁻) and [Cp′′′Ni(η³-P₄RCl)][TEF] (R=Ph ( 2 f ), tBu ( 2 g )). In the reaction of 1 with [Br₂P]⁺, 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-P₄Br₃)][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 .     

Heterometall-Komplexe mit E6-Liganden (E = P,As)

Heterometallic Complexes with E₆ Ligands (E = P, As) The reaction of [Cp*Co(μ-CO)]₂ 1 with the sandwich complexes [Cp*Fe(η⁵-E₅)] 2 a: E = P, 2 b: E = As in decalin at 190°C affords besides [CpCo₂E₄] 4: E = P, 7: E = As and [CpFe₂P₄] 5 the trinuclear complexes [(Cp*Fe)₂(Cp*Co)(μ-η²-P₂)(μ₃-η^1:2:1-P₂)₂] 3 as well as [(Cp*Fe)₂(Cp*Co)(μ₃-η^2:2:2-As₃)₂] 6 . With [Mo(CO)₅(thf)] 3 and 6 form in a build-up reaction the tetranuclear clusters [(Cp*Fe)₂(Cp*Co)E₆{Mo(CO)₃}] 10: E = P, 11: E = As. 3, 6 and 11 have been further characterized by an X-ray crystal structure determination.     

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 .     

NHCs as Neutral Donors towards Polyphosphorus Complexes

The first adducts of NHCs (=N-heterocyclic carbenes) with aromatic polyphosphorus complexes are reported. The reactions of [Cp*Fe(η⁵-P₅)] ( 1 ) (Cp*=pentamethyl-cyclopentadienyl) with IMe (=1,3,4,5-tetramethylimidazolin-2-ylidene), IMes (=1,3-bis(2,4,6-trimethylphenyl)-imidazolin-2-ylidene) and IDipp (=1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene) led to the corresponding neutral adducts which can be isolated in the solid state. However, in solution, they quickly undergo a dissociative equilibrium between the adduct and 1 including the corresponding NHC. The equilibrium is influenced by the bulkiness of the NHC. [Cp′′Ta(CO)₂(η⁴-P₄)] (Cp′′=1,3-di-tert-butylcyclopentadienyl) reacts with IMe under P atom abstraction to give an unprecedented cyclo-P₃-containing anionic tantalum complex. DFT calculations shed light onto the energetics of the reaction pathways.