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.     

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 .     

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.     

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.     

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.     

One‐Dimensional Polymers Based on Silver(I) Cations and Organometallic cyclo‐P3 Ligand Complexes

The synthesis and characterization of the first supramolecular aggregates incorporating the organometallic cyclo‐P₃ ligand complexes [Cp^RMo(CO)₂(η³‐P₃)] (Cp^R=Cp (C₅H₅; 1a ), Cp* (C₅(CH₃)₅; 1b )) as linking units is described. The reaction of the Cp derivative 1a with AgX (X=CF₃SO₃, Al{OC(CF₃)₃}₄) yields the one‐dimensional (1D) coordination polymers [Ag{CpMo(CO)₂(μ,η³:η¹:η¹‐P₃)}₂]_n[Al{OC(CF₃)₃}₄]_n ( 2 ) and [Ag{CpMo(CO)₂(μ,η³:η¹:η¹‐P₃)}₃]_n[X]_n (X=CF₃SO₃ ( 3a ), Al{OC(CF₃)₃}₄ ( 3b )). The solid‐state structures of these polymers were revealed by X‐ray crystallography and shown to comprise polycationic chains well‐separated from the weakly coordinating anions. If AgCF₃SO₃ is used, polymer 3a is obtained regardless of reactant stoichiometry whereas in the case of Ag[Al{OC(CF₃)₃}₄], reactant stoichiometry plays a decisive role in determining the structure and composition of the resulting product. Moreover, polymers 3a, b are the first examples of homoleptic silver complexes in which Ag^I centers are found octahedrally coordinated to six phosphorus atoms. The Cp* derivative 1b reacts with Ag[Al{OC(CF₃)₃}₄] to yield the 1D polymer [Ag{Cp*Mo(CO)₂(μ,η³:η²:η¹‐P₃)}₂]_n[Al{OC(CF₃)₃}₄]_n ( 4 ), the crystal structure of which differs from that of polymer 2 in the coordination mode of the cyclo‐P₃ ligands: in 2 , the Ag⁺ cations are bridged by the cyclo‐P₃ ligands in a η¹:η¹ (edge bridging) fashion whereas in 4 , they are bridged exclusively in a η²:η¹ mode (face bridging). Thus, one third of the phosphorus atoms in 2 are not coordinated to silver while in 4 , all phosphorus atoms are engaged in coordination with silver. Comprehensive spectroscopic and analytical measurements revealed that the polymers 2 , 3a , b , and 4 depolymerize extensively upon dissolution and display dynamic behavior in solution, as evidenced in particular by variable temperature ³¹P NMR spectroscopy. Solid‐state ³¹P magic angle spinning (MAS) NMR measurements, performed on the polymers 2 , 3b , and 4 , demonstrated that the polymers 2 and 3b also display dynamic behavior in the solid state at room temperature. The X‐ray crystallographic characterisation of 1b is also reported.     

Zincocene and Dizincocene N‐Heterocyclic Carbene Complexes and Catalytic Hydrogenation of Imines and Ketones

The N‐heterocyclic carbene (NHC) adducts Zn(Cp^R)₂(NHC)] (Cp^R=C₅HMe₄, C₅H₄SiMe₃; NHC=ItBu, IDipp (Dipp=2,6‐diisopropylphenyl), IMes (Mes=mesityl), SIMes) were prepared and shown to be active catalysts for the hydrogenation of imines, whereas decamethylzincocene [ZnCp*₂] is highly active for the hydrogenation of ketones in the presence of noncoordinating NHCs. The abnormal carbene complex [Zn(OCHPh₂)₂(aItBu)]₂ was formed from spontaneous rearrangement of the ItBu ligand during incomplete hydrogenation of benzophenone. Two isolated Zn^I adducts [Zn₂Cp*₂(NHC)] (NHC=ItBu, SIMes) are presented and characterized as weak adducts on the basis of ¹³C NMR spectroscopic and X‐ray diffraction experiments. A mechanistic proposal for the reduction of [ZnCp*₂] with H₂ to give [Zn₂Cp*₂] is discussed.     

Distibanes and Distibenes from Reduction of Sb(NONR)Cl by using MgI Reagents

The bis(amidodimethyl)disiloxane antimony chlorides Sb(NON^R)Cl (NON^R=[O(SiMe₂NR)₂]²⁻; R=tBu, Ph, 2,6-Me₂C₆H₃=Dmp, 2,6-iPr₂C₆H₃=Dipp, 2,6-(CHPh₂)₂-4-tBuC₆H₂=tBu-Bhp) are reduced to Sb^II and Sb^I species by using Mg^I reagents, [Mg(BDI^R′)]₂ (BDI=[HC{C(Me)NR′}₂]⁻; R′=2,4,6-Me₃C₆H₂=Mes, Dipp). Stoichiometric reactions with Sb(NON^R)Cl (R=tBu, Ph) form dimeric Sb^II stibanes [Sb(NON^R)]₂, shown crystallographically to contain Sb−Sb single bonds. The analogous distibane with R=Dmp substituents has an exceptionally long Sb−Sb interaction and exhibits spectroscopic and reactivity properties consistent with radical character in solution. When R=Dipp, reductions with Mg^I reagents directly give distibenes [Sb(μ-NON^Dipp)Mg(BDI^R′)(THF)_n]₂ (R′=Mes, n=1; R′=Dipp, n=0). Crystallographic analysis shows a trans-substitution of the Sb=Sb double bond, with bridging NON^Dipp-ligands between the Sb^I and Mg^II centres. An attempt to access the NON^Ph-analogue using the same protocol afforded the polystibide cluster Sb₈[μ₄,η^2:2:2:2-Mg(BDI^Mes)]₄, which co-crystallized with the ligand transfer product, [Mg(BDI^Mes)]₂(μ-NON^Ph).     

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.     

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.     

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 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.     

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.     

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.     

Insight into Oxide‐Bridged Heterobimetallic Al/Zr Olefin Polymerization Catalysts

Reaction of (TBBP)AlMe ? THF with [Cp*₂Zr(Me)OH] gave [(TBBP)Al(THF)?O?Zr(Me)Cp*₂] (TBBP=3,3’,5,5’‐tetra‐tBu‐2,2'‐biphenolato). Reaction of [DIPPnacnacAl(Me)?O?Zr(Me)Cp₂] with [PhMe₂NH]⁺[B(C₆F₅)₄]^? gave a cationic Al/Zr complex that could be structurally characterized as its THF adduct [(DIPPnacnac)Al(Me)?O?Zr(THF)Cp₂]⁺[B(C₆F₅)₄]^? (DIPPnacnac=HC[(Me)C=N(2,6‐iPr₂?C₆H₃)]₂). The first complex polymerizes ethene in the presence of an alkylaluminum scavenger but in the absence of methylalumoxane (MAO). The adduct cation is inactive under these conditions. Theoretical calculations show very high energy barriers (ΔG=40–47 kcal mol^?1) for ethene insertion with a bridged AlOZr catalyst. This is due to an unfavorable six‐membered‐ring transition state, in which the methyl group bridges the metal and ethene with an obtuse metal‐Me‐C angle that prevents synchronized bond‐breaking and making. A more‐likely pathway is dissociation of the Al‐O‐Zr complex into an aluminate and the active polymerization catalyst [Cp*₂ZrMe]⁺.     

Dianionic Mononuclear Cyclo‐P4 Complexes of Zero‐Valent Molybdenum: Coordination of the Cyclo‐P4 Dianion in the Absence of Intramolecular Charge Transfer

Relative to other cyclic poly‐phosphorus species (that is, cyclo‐P_n), the planar cyclo‐P₄ group is unique in its requirement of two additional electrons to achieve aromaticity. These electrons are supplied from one or more metal centers. However, the degree of charge transfer is dependent on the nature of the metal fragment. Unique examples of dianionic mononuclear η⁴‐P₄ complexes are presented that can be viewed as the simple coordination of the [cyclo‐P₄]^2? dianion to a neutral metal fragment. Treatment of the neutral, molybdenum cyclo‐P₄ complexes Mo(η⁴‐P₄)I₂(CO)(CNAr^Dipp2)₂ and Mo(η⁴‐P₄)(CO)₂(CNAr^Dipp2)₂ with KC₈ produces the dianionic, three‐legged piano stool complexes, [Mo(η⁴‐P₄)(CO)(CNAr^Dipp2)₂]^2? and [Mo(η⁴‐P₄)(CO)₂(CNAr^Dipp2)]^2?, respectively. Structural, spectroscopic, and computational studies reveal a similarity to the classic η⁶‐benzene complex (η⁶‐C₆H₆)Mo(CO)₃ regarding the metal‐center valence state and electronic population of the planar‐cyclic ligand π system.     

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 ).     

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 ).     

Niob- und Tantalkomplexe mit P2- und P4-Liganden

Niobium and Tantalum Complexes with P₂ and P₄ Ligands The photolysis of [Cp″Ta(CO)₄] 1 (Cp″ = C₅H₃^tBu₂?1,3) and P₄ affords Cp″(CO)₂Ta(η⁴?P₄) 2 , [{Cp″(CO)Ta}₂(m??η^2:2?P₂)₂] 3 and [Cp₃″(CO)₃Ta₃(P₂)₂] 4 . In a photochemical reaction 2 and [Cp*Nb(CO)₄] 5 form [{Cp*(CO)Nb}{Cp″(CO)Ta}(m??η^2:2?P₂)₂] 6 and [{Cp*(CO)₂Nb} {Cp*Nb}{Cp″(CO)Ta}(m?₃?η^2:1:1?P₂)₂] 7 , a compound with the novel m?₃?η^2:2:1?P₂-coordination mode. The reaction of 2 and [Cp*Co(C₂H₄)₂] 8 leads to [{Cp*Co} {Cp″(CO)Ta}(m??η^2:2?P₂)₂] 9 , a heteronuclear complex with an ?early”? and a ?late”? transition metal. Complexes 2, 3, 7 and 9 have been further characterized by X-ray structure analyses.     

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 )).