Further Evidence for ‘Extended’ Cumulene Complexes: Derivatives from Reactions with Halide Anions and Water

Reactions of [Ru{C=C(H)-1,4-C₆H₄C≡CH}(PPh₃)₂Cp]BF₄ ([ 1 a ]BF₄) with hydrohalic acids, HX, results in the formation of [Ru{C≡C-1,4-C₆H₄-C(X)=CH₂}(PPh₃)₂Cp] [X=Cl ( 2 a-Cl ), Br ( 2 a-Br )], arising from facile Markovnikov addition of halide anions to the putative quinoidal cumulene cation [Ru(=C=C=C₆H₄=C=CH₂)(PPh₃)₂Cp]⁺. Similarly, [M{C=C(H)-1,4-C₆H₄-C≡CH}(LL)Cp ]BF₄ [M(LL)Cp’=Ru(PPh₃)₂Cp ([ 1 a ]BF₄); Ru(dppe)Cp* ([ 1 b ]BF₄); Fe(dppe)Cp ([ 1 c ]BF₄); Fe(dppe)Cp* ([ 1 d ]BF₄)] react with H⁺/H₂O to give the acyl-functionalised phenylacetylide complexes [M{C≡C-1,4-C₆H₄-C(=O)CH₃}(LL)Cp’] ( 3 a – d ) after workup. The Markovnikov addition of the nucleophile to the remote alkyne in the cations [ 1 a–d ]⁺ is difficult to rationalise from the vinylidene form of the precursor and is much more satisfactorily explained from initial isomerisation to the quinoidal cumulene complexes [M(=C=C=C₆H₄=C=CH₂)(LL)Cp’]⁺ prior to attack at the more exposed, remote quaternary carbon. Thus, whilst representative acetylide complexes [Ru(C≡C-1,4-C₆H₄-C≡CH)(PPh₃)₂Cp] ( 4 a ) and [Ru(C≡C-1,4-C₆H₄-C≡CH)(dppe)Cp*] ( 4 b ) reacted with the relatively small electrophiles [CN]⁺ and [C₇H₇]⁺ at the β-carbon to give the expected vinylidene complexes, the bulky trityl ([CPh₃]⁺) electrophile reacted with [M(C≡C-1,4-C₆H₄-C≡CH)(LL)Cp’] [M(LL)Cp’=Ru(PPh₃)₂Cp ( 4 a ); Ru(dppe)Cp* ( 4 b ); Fe(dppe)Cp ( 4 c ); Fe(dppe)Cp* ( 4 d )] at the more exposed remote end of the carbon-rich ligand to give the putative quinoidal cumulene complexes [M{C=C=C₆H₄=C=C(H)CPh₃}(LL)Cp’]⁺, which were isolated as the water adducts [M{C≡C-1,4-C₆H₄-C(=O)CH₂CPh₃}(LL)Cp’] ( 6 a–d ). Evincing the scope of the formation of such extended cumulenes from ethynyl-substituted arylvinylene precursors, the rather reactive half-sandwich (5-ethynyl-2-thienyl)vinylidene complexes [M{C=C(H)-2,5-^cC₄H₂S-C≡CH}(LL)Cp’]BF₄ ([ 7 a – d ]BF₄ add water readily to give [M{C≡C-2,5-^cC₄H₂S-C(=O)CH₃}(LL)Cp’] ( 8 a – d )].     

Darstellung und Kristallstruktur des Azavinylidenderivates Cp*2Ti(CH=CH2)(N=CPh2) ausgehend vom thermisch gebildeten Titanaallenintermediat [Cp*2Ti=C=CH2]

Preparation and Crystal Structure of the Azavinylidene Derivative Cp*₂Ti(CH=CH₂)(N=CPh₂) derived from the Thermally Generated Titanaallene Intermediate [Cp*₂Ti=C=CH₂] The title complex 4 was synthesized by reaction of Benzophenonimin with the titanaallene fragment [Cp*₂Ti=C=CH₂] ( 3 ). Complex 4 was characterized by ¹H and ¹³C NMR spectra and by X-ray structure analysis, respectively.     

Synthesis, Characterization and Structural Properties of Some Heterobimetallic Carbonyl Clusters Derived from Diethynylsilane and Diethynyldisilane Ligands

We report the synthesis of some heterobimetallic carbonyl clusters of groups 8 and 9 derived from diethynylsilane and diethynyldisilane ligands. The triosmium carbonyl clusters containing a pendant acetylene unit [(μ-CO)Os₃(CO)₉(μ₃-η²-HC≡C-E-C≡CH)] [E = Si(CH₃)₂, Si(CH₃)₂–Si(CH₃)₂ and SiPh₂] were prepared and subsequently used for mixed-metal cluster formation. New diyne complexes of the type [{(μ-CO)Os₃(CO)₉}{Co₂(CO)₆}(μ₃-η²:η²-diyne)] and [{(μ-CO)Os₃(CO)₉}{(μ-H)Ru₃(CO)₉}(μ₃-η²:μ₃-η², η²-diyne)] [diyne = HC≡CSi(CH₃)₂C≡CH, HC≡CSi(CH₃)₂–Si(CH₃)₂C≡CH or HC≡CSi(Ph)₂C≡CH] have been prepared in good yields from the reaction of [(μ-CO)Os₃(CO)₉(μ₃-η²-HC≡C-E-C≡CH)] with a molar equivalent of [Co₂(CO)₈] and [Ru₃(CO)₁₂], respectively. All the new heterobimetallic compounds have been characterized by IR and ¹H NMR spectroscopy and mass spectrometry. The X-ray crystal structures and computational analyses based on density functional theory of these three molecules have been studied. Structurally, the dicobalt species adopts a pseudo-tetrahedral Co₂C₂ core with the alkyne bond which lies essentially perpendicular to the Co–Co vector. For the mixed osmium–ruthenium analogue, the hexanuclear carbonyl cluster consist of two trinuclear metal cores with the μ₃-(η²-||) bonding mode for the acetylene group in the former case and the μ₃-η², η² bonding mode in the latter one.     

Reactions of Group 4 Metallocenes with Monosubstituted Acetonitriles: Keteniminate Formation versus CC Coupling

The reactions of the Group 4 metallocene dichlorides [Cp′₂MCl₂] ( 1 a : M=Ti, Cp′=Cp*=η⁵‐pentamethylcyclopentadienyl, 1 b : M=Zr, Cp′=Cp=η⁵‐cyclopentadienyl) with lithiated MesCH₂?C?N gave [Cp*₂TiCl(N=C=C(HMes))] ( 3 ; Mes=mesityl) in the case of 1 a . For compound 1 b , a nitrile–nitrile coupling resulted in a five‐membered bridge in 4 . The reaction of the metallocene alkyne complex [Cp*₂Zr(η²‐Me₃SiC₂SiMe₃)] ( 2 ) with PhCH₂?C?N led in the first step to the unstable product [Cp*₂Zr(η²‐Me₃SiC₂SiMe₃)(NC?CH₂Ph)] ( 5 ). After the elimination of the alkyne, a mixture of products was formed. By variation of the solvent and the reaction temperature, three compounds were isolated: a diazadiene complex 6 , a bis(keteniminate) complex 7 , and 8 with a keteniminate ligand and a five‐membered metallacycle. Subsequent variation of the Cp ligand and the metal center by using [Cp₂Zr] and [Cp*₂Ti] with Me₃SiC₂SiMe₃ in the reactions with PhCH₂?C?N gave complex mixtures.     

Zur Reaktivität von Titanocenkomplexen [Ti(Cp′)2(η2‐Me3SiC≡CSiMe3)] (Cp′ = Cp,Cp*) gegenüber Benzoldicarbonsäuren

On the Reactivity of Titanocene Complexes [Ti(Cp′)₂(η²‐Me₃SiC≡CSiMe₃)] (Cp′ = Cp, Cp*) towards Benzenedicarboxylic Acids Titanocene complexes [Ti(Cp′)₂(BTMSA)] ( 1a , Cp′ = Cp = η⁵‐C₅H₅; 1b , Cp′ = Cp* = η⁵‐C₅Me₅; BTMSA = Me₃SiC≡CSiMe₃) were found to react with iodine and methyl iodide yielding [Ti(Cp′)₂(μ‐I)₂] ( 2a / b ; a refers to Cp′ = Cp and b to Cp′ = Cp*), [Ti(Cp′)₂I₂] ( 3a / b ) and [Ti(Cp′)₂(Me)I] ( 4a / b ), respectively. In contrast to 2a , complex 2b proved to be highly moisture sensitive yielding with cleavage of HCp* [{Ti(Cp*)I}₂(μ‐O)] ( 7 ). The corresponding reactions of 1a / b with p‐cresol and thiophenol resulted in the formation of [Ti(Cp′)₂{O(p‐Tol)}₂] ( 5a / b ) and [Ti(Cp′)₂(SPh)₂] ( 6a / b ), respectively. Reactions of 1a and 1b with 1,n‐benzenedicarboxylic acids (n = 2–4) resulted in the formation of dinuclear titanium(III) complexes of the type [{Ti(Cp′)₂}₂{μ‐1,n‐(O₂C)₂C₆H₄}] (n = 2, 8a / b ; n = 3, 9a / b ; n = 4, 10a / b ). All complexes were fully characterized analytically and spectroscopically. Furthermore, complexes 7 , 8b , 9a ·THF, 10a / b were also be characterized by single‐crystal X‐ray diffraction analyses.     

Synthesis, Characterization and Crystal Structures of Some Linked Metal Carbonyl Clusters Derived from Diethynyl-Substituted Silane and Disilane Ligands

The use of diethynylsilane, diethynyldisilane and diethynyldisiloxane in the synthesis of some linked metal carbonyl clusters is demonstrated. New dimeric η²-diyne complexes of cobalt [{Co₂(CO)₆}₂(η²-diyne)], ruthenium [{(μ-H)Ru₃(CO)₉}₂(μ₃-η²,η²-diyne)] and osmium [{(μ-CO)Os₃(CO)₉}₂(μ₃-η²-diyne)] {diyne=HC≡CSi(CH₃)₂C≡CH, HC≡CSi(CH₃)₂–Si(CH₃)₂C≡CH, HC≡CSi(CH₃)₂–O–Si(CH₃)₂C≡CH or HC≡CSi(Ph)₂C≡CH} have been prepared in good yields from the reaction of [Co₂(CO)₈], [Ru₃(CO)₁₂] and [Os₃(CO)₁₀(NCMe)₂] with half an equivalent of the appropriate diyne ligand, respectively. All the twelve compounds have been characterized by IR and ¹H NMR spectroscopies and mass spectrometry. The molecular structures of eight of them have been determined by X-ray crystallography. Structurally, each of the tetracobalt species displays two Co₂C₂ cores adopting the pseudo-tetrahedral geometry with the alkyne bond lying essentially perpendicular to the Co–Co vector. For the group 8 ruthenium and osmium analogues, the hexanuclear carbonyl clusters consist of two trinuclear metal cores with the μ₃-η²,η² bonding mode for the acetylene groups in the former case and μ₃-(η²-||) bonding mode in the latter one. Density functional theory was employed to study the electronic structures of these molecules in terms of the nature of the silyl or disilyl unit and its substituents.     

Synthese und Eigenschaften Pentamethylcyclopentadienyl-substituierter PPC- bzw. AsPC-Dreiring-Systeme

Synthesis and Properties of Pentamethylcyclopentadienylsubstituted PPC and AsPC three-membered Rings Via the reaction of bis-(pentamethylcyclopentadienyl)diphosphene [Cp*P?PCp*, 1 ] and 1-(pentamethylcyclopentadienyl)-2-(2,4,6-tri^tbutylphenyl)- diphosphene [Cp*P?PMes*, 2 ] with the diazomethanes N₂CHR [R = H, Si(CH₃)₃] the four new diphosphiranes Cp*PPCp*CHSi(CH₃)₃, 4a , Cp*PPMes*CHSi(CH₃)₃, 4b , Cp*PPCp*CH₂, 5a , Cp*PPMes*CH₂, 5b , are obtained. The formation of 4a results via a 2 + 3-cyclo-addition product, which could be proved by nmr spectroscopy. The reaction of As-(pentamenthylcyclopentadienyl)-P-(2,4,6-tri^tbutylphenyl) arsaphosphene [Cp*As?PMes*, 3 ] with diazomethane leads to 1-(pentamethylcyclopentadienyl)-2-(2,4,6-tri^tbutylphenyl)-1-arsa-2 -phosphacyclopropane [phospharsiran, Cp*AsPMes*CH₂, 6 ]. Analysis of the structures by nmr spectroscopy gives clear evidence for a trans-orientation of the substituents at the El? P bond (El = As, P) in all of the three membered ring systems. For the diphosphirane Cp*PPCp*CH₂ ( 5a ) a Cp*-phosphorus bond cleavage by thermolysis cannot be observed. From the reaction of compound 5a with Cr(CO)₅thf one obtains 1-(pentacarbonylchrom)-1,2-bis(pentamethylcyclopentadienyl)-1,2- diphosphacyclo-propane, 7 .     

Reactions of Alkynes with [RuCl(cyclopentadienyl)] Complexes: The Important First Steps

Cyclopentadienyl–ruthenium half‐sandwich complexes with η²‐bound alkyne ligands have been suggested as catalytic intermediates in the early stages of Ru‐catalyzed reactions with alkynes. We show that electronically unsaturated complexes of the formula [RuCl(Cp^)(η²‐RC≡CR′)] can be stabilized and crystallized by using the sterically demanding cyclopentadienyl ligand Cp^ (Cp^=η⁵‐1‐methoxy‐2,4‐tert‐butyl‐3‐neopentyl‐cyclopentadienyl). Furthermore we demonstrate that [RuCl₂(Cp^)]₂ is an active and regioselective catalyst for the [2+2+2] cyclotrimerization of alkynes. The first elementary steps of the reaction of mono(η²‐alkyne) complexes containing {RuCl(Cp*)} (Cp*=η⁵‐C₅Me₅) and {RuCl(Cp^)} fragments with alkynes were investigated by DFT calculations at the M06/6‐31G* level in combination with a continuum solvent model. Theoretical results are able to rationalize and complement the experimental findings. The presence of the sterically demanding Cp^ ligand increases the activation energy required for the formation of the corresponding di(η²‐alkyne) complexes, enhancing the initial regioselectivity, but avoiding the evolution of the system towards the expected cyclotrimerization product when bulky substituents are present. Theoretical results also show that the electronic structure and stability of a metallacyclic intermediate is strongly dependent on the nature of the substituents present in the alkyne.     

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 )).     

Latest News: Reactions of Group 4 Bis(trimethylsilyl)acetylene Metallocene Complexes and Applications of the Obtained Products

Recently published reactions of group 4 metallocene bis(trimethylsilyl)acetylene (btmsa) complexes from the last two years are reviewed. Complexes like Cp’₂Ti(η²-Me₃SiC₂SiMe₃) and Cp₂Zr(py)(η²-Me₃SiC₂SiMe₃) with Cp’ as Cp (cyclopentadienyl) and Cp* (pentamethylcyclopentadienyl) have been considered (py=pyridine). These complexes can liberate a reactive low-valent titanium or zirconium center by dissociation of the ligands and act as ‘‘masked’’ M^II complexes (M=Ti, Zr). They represent excellent sources for the clean generation of the reactive coordinatively and electronically unsaturated complex fragments [Cp’₂M]. This is the reason why they were used for many synthetic and catalytic reactions during the last years. As an update to several review articles on this topic, this contribution provides an update with recent examples of preparative organometallic and organic chemistry of these complexes, acting as reagents for a wide range of coordinating and coupling reactions. In addition, applications and investigations concerning reaction products derived from this chemistry are mentioned, too.     

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.     

Synthesis of high‐molecular‐weight elastomeric poly(propylene) with half‐titanocene/MAO catalyst

A novel catalyst precursor, (η⁵‐pentamethylcyclopentadienyl)titanium triallyloxide (Cp*Ti(OCH₂—CH=CH₂)₃), was prepared and employed in a study of propylene polymerization in the presence of methylaluminoxane (MAO). This work has revealed that the half‐titanocene catalyst is desirable for the production of elastomeric poly(propylene) with high molecular weight (M_w = 8–69×10⁴) as well as in good yields under typical polymerization conditions.     

Reactions of [Cp*Ru(H2O)(NBD)]+ with alkynes

Formal [2 + 2 + 2] addition reactions of [Cp*Ru(H₂O)(NBD)]BF₄ (NBD = norbornadiene) with PhC?CR (R = H, COOEt) give [Cp*Ru(η⁶‐C₆H₅? C₉H₈R)] BF₄ (1a, R = H; 2a, R = COOEt). Treatment of [Cp*Ru(H₂O)(NBD)]BF₄ with PhC?C? C?CPh does not give [2 + 2 + 2] addition product, but [Cp*Ru(η⁶‐C₆H₅? C?C? C?CPh)] BF₄(3a). Treatment of 1a, 2a, 3a with NaBPh₄ affords [Cp*Ru(η⁶‐C₆H₅? C₉H₈R)] BPh₄ (1b, R = H; 2b, R = COOEt) and [Cp*Ru(η⁶‐C₆H₅? C?C? C?CPh)] BPh₄(3b). The structures of 1b, 2b and 3b were determined by X‐ray crystallography. Copyright © 2007 John Wiley & Sons, Ltd.     

Reaction of Pentelidene Complexes with Diazoalkanes: Stabilization of Parent 2,3‐Dipnictabutadienes

The reaction of the phosphinidene complex [Cp*P{W(CO)₅}₂] ( 1 a ) with diphenyldiazomethane leads to [{W(CO)₅}Cp*P=NN{W(CO)₅}=CPh₂] ( 2 ). Compound 2 is a rare example of a phosphadiazadiene ligand (R‐P=N?N=CR′R′′) complex. At temperatures above 0 °C, 2 decomposes into the complex [{W(CO)₅}PCp*{N(H)N=CPh₂)₂] ( 3 ), among other species. The reaction of the pentelidene complexes [Cp*E{W(CO)₅}₂] (E=P, As) with diazomethane (CH₂NN) proceeds differently. For the arsinidene complex ( 1 b ), only the arsaalkene complex 4 b [{W(CO)₅}₂{η^1:2‐(Cp*)As=CH₂}] is formed. The reaction with the phosphinidene complex ( 1 a ) results in three products, the two phosphaalkene complexes [{W(CO)₅}₂{η^1:2‐(R)P=CH₂}] ( 4 a : R=Cp*, 5 : R=H) and the triazaphosphole derivative [{W(CO)₅}P(Cp*)‐CH₂‐N{W(CO)₅}=N‐N(N=CH₂)] ( 6 a ). The phosphaalkene complex ( 4 a ) and the arsaalkene complex ( 4 b ) are not stable at room temperature and decompose to the complexes [{W(CO)₅}₄(CH₂=E?E=CH₂)] ( 7 a : E=P, 7 b : E=As), which are the first examples of complexes with parent 2,3‐diphospha‐1,3‐butadiene and 2,3‐diarsa‐1,3‐butadiene ligands.     

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⁻.     

Katalysatordesaktivierungen bei der Acetylen-Polymerisation mit Titanocen- bzw. Zirconocen-Komplexen des Bis(trimethylsilyl)acetylens

Desactivation of Catalysts in the Polymerization of Acetylene by Bis(trimethylsilyl)acetylene Complexes of Titanocene or Zirconocene Unexpected inactive byproducts were observed in the catalytic polymerization of acetylene using metallocene alkyne complexes Cp₂M(L)(η²-Me₃SiC₂SiMe₃), 1 : M = Ti, without L; 2 : M = Zr, L = thf. The reaction of 1 was investigated in detail by NMR to give quantitatively at –20 °C the titanacyclopentadiene Cp₂Ti–CH=CH–C(SiMe₃)=C(SiMe₃) ( 3 ). Around 0 °C 3 starts to rearrange to yield the dihydroindenyl complex 4 via coupling of one Cp-ligand with the titanacyclopentadiene. In the reaction of 2 under analogous conditions a zirconacyclopentadiene Cp₂Zr–CH=CH–C(SiMe₃)=C(SiMe₃) ( 5 ) and the dimeric complex [Cp₂Zr(C(SiMe₃)=CH(SiMe₃)]₂[μ-σ(1,2)-C≡C] ( 6 ) were observed. Whereas 5 decomposes to a mixture of unidentified paramagnetic species, 6 was isolated and investigated by NMR spectroscopy and X-ray analysis. In the reaction of rac-(ebthi)Zr(η²-Me₃SiC₂SiMe₃) (ebthi = ethylenbistetrahydroindenyl) with 2-ethynyl-pyridine the complex rac-(ebthi)ZrC(SiMe₃)=CH(SiMe₃)](σ-C≡CPy) 7 was obtained, which was investigated by an X-ray analysis.     

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.     

Molekül‐ und Kristallstruktur von Bis[chloro(μ‐phenylimido)(η5‐pentamethylcyclopentadienyl)tantal(IV)](Ta–Ta), [{TaCl(μ‐NPh)Cp*}2]

Molecular and Crystal Structure of Bis[chloro(μ‐phenylimido)(η⁵‐pentamethylcyclopentadienyl)tantalum(IV)](Ta–Ta), [{TaCl(μ‐NPh)Cp*}₂] Despite the steric hindrance of the central atom in [TaCl₂(NPh)Cp*] (Ph = C₆H₅, Cp* = η⁵‐C₅(CH₃)₅), caused by the Cp* ligand, the imido‐ligand takes a change in bond structure when this educt is reduced to the binuclear complex [{TaCl(μ‐NPh)Cp*}₂] in which tantalum is stabilized in the unusual oxidation state +4.     

Phenylselenolato Complexes of Cyclopentadienylrhodium: Structural Variety in the Solid State and in Solution

Diphenyl diselenide reacts with [CpRh(CO)₂] ( 1 ) to give the dimer [CpRh(SePh)(μ-SePh)]₂ ( 2 ), the solid state structure of which has been determined by X-ray analysis; the dimeric structure is retained in solution. In contrast, [Cp*Rh(CO)₂] ( 4 ) gives the ionic product [Cp*Rh(μ-SePh)₃RhCp*][Cp*Rh(SePh)₃] ( 5 ), which dissolves as such in THF but as a monomeric 16-electron complex [Cp*Rh(SePh)₂] ( 6 ) in CDCl₃ or CD₂Cl₂. Upon UV irradiation in CDCl₃, ( 2 ) is converted into the ionic species [CpRh(μ-SePh)₃RhCp]Cl ( 3 ). The monomer ( 6 ) slowly decomposes in CH₂Cl₂, and single crystals of [Cp*Rh(μ-SePh)₃RhCp*][PhSeCl₂] ( 5 a ) have been obtained. The crystal structure of 5 a has been determined by X-ray diffraction methods. The structures in solution were proposed in particular on the basis of ⁷⁷Se NMR spectroscopy where the splitting due to ¹⁰³Rh–⁷⁷Se coupling makes it possible to distinguish between bridging and terminal PhSe groups.     

η4‐HBCC‐σ,π‐Borataallyl Complexes of Ruthenium Comprising an Agostic Interaction

Thermolysis of [Cp*Ru(PPh₂(CH₂)PPh₂)BH₂(L₂)] 1 (Cp*=η⁵‐C₅Me₅; L=C₇H₄NS₂), with terminal alkynes led to the formation of η⁴‐σ,π‐borataallyl complexes [Cp*Ru(μ‐H)B{R‐C=CH₂}(L)₂] ( 2 a – c ) and η²‐vinylborane complexes [Cp*Ru(R‐C=CH₂)BH(L)₂] ( 3 a – c ) ( 2 a , 3 a : R=Ph; 2 b , 3 b : R=COOCH₃; 2 c , 3 c : R=p‐CH₃‐C₆H₄; L=C₇H₄NS₂) through hydroboration reaction. Ruthenium and the HBCC unit of the vinylborane moiety in 2 a – c are linked by a unique η⁴‐interaction. Conversions of 1 into 3 a – c proceed through the formation of intermediates 2 a – c . Furthermore, in an attempt to expand the library of these novel complexes, chemistry of σ‐borane complex [Cp*RuCO(μ‐H)BH₂L] 4 (L=C₇H₄NS₂) was investigated with both internal and terminal alkynes. Interestingly, under photolytic conditions, 4 reacts with methyl propiolate to generate the η⁴‐σ,π‐borataallyl complexes [Cp*Ru(μ‐H)BH{R‐C=CH₂}(L)] 5 and [Cp*Ru(μ‐H)BH{HC=CH‐R}(L)] 6 (R=COOCH₃; L=C₇H₄NS₂) by Markovnikov and anti‐Markovnikov hydroboration. In an extension, photolysis of 4 in the presence of dimethyl acetylenedicarboxylate yielded η⁴‐σ,π‐borataallyl complex [Cp*Ru(μ‐H)BH{R‐C=CH‐R}(L)] 7 (R=COOCH₃; L=C₇H₄NS₂). An agostic interaction was also found to be present in 2 a – c and 5 – 7 , which is rare among the borataallyl complexes. All the new compounds have been characterized in solution by IR, ¹H, ¹¹B, ¹³C NMR spectroscopy, mass spectrometry and the structural types were unequivocally established by crystallographic analysis of 2 b , 3 a – c and 5 – 7 . DFT calculations were performed to evaluate possible bonding and electronic structures of the new compounds.