Interactions of hafnocene and zirconocene dihydrides with acetylenes. Synthesis of the first acetylene complex of hafnium

The first acetylene complex of hafnium, Cp₂Hf[Me₃SiC=CHf(H)Cp₂], was synthesized by the reaction of hafnocene dihydride Cp₂HfH₂ with bis(trimethylsilyl)acetylene in benzene. The reaction is accompanied by elimination of the Me₃Si group from the molecule of the initial acetylene, as a result of which the acetylenide derivative of hafnium Cp₂Hf(C=CSiMe₃)(H) acts as an acetylene ligand in the complex. Under analogous conditions, the reaction of zirconocene dihydride Cp₂ZrH₂ with bis(trimethylsilyl)acetylene affords an analogous acetylene complex of zirconium Cp₂Zr(M₃SiC=CZr(H)Cp₂]. Reactions of Cp₂HfH₂ with tolane and 3-hexyne proceed differently than the reaction with bis(trimethylsilyl)acetylene. Here the corresponding hafnacyclopentadiene metallacycles are the final products. For preliminary communication, see Ref. 3. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 853–856, April, 1997.     

Synthesis, properties, and the crystal structure of the complex Cp2Yb(DAD)

The diazadiene complex of trivalent ytterbium, Cp₂Yb(DAD) (1) (DAD=Bu^t−N=CH−CH=N−Bu^t) was prepared according to three different procedures, namely, by oxidation of Cp₂Yb(THF)₂ with diazadiene in THF, by the reaction of Cp₂YbCl with DAD²⁻Na⁺ ₂ taken in a ratio of 2∶1, and by the reaction of Cp₂YbCl(THF) with DAD²⁻Na⁺ ₂ taken in a ratio of 1∶1. Complex1 was characterized by microanalysis, IR spectroscopy, magnetochemistry, and X-ray diffraction analysis. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 384–386, February, 1999.     

Vibrational spectra and structure of zirconium and hafnium cyclopentadienyl hydrides

Raman and IR spectra (4000-50 cm^–1) of solid cyclopentadienyl zirconium and hafnium hydrides Cp₂MH₂, Cp₂MD₂, Cp₂Zr(H)X, and Cp₂Zr(D)X (Cp = ⁵-C₅H₅; M = Zr, Hf; X = Cl, Br) have been studied. The vibrational modes of MH groups, Cp-rings, and metal-ligand bonds are discussed and the band assignments are proposed. In the solid state, these complexes form polymers with linear hydride bridges of the M-H-M type. The force constants of the M-H and M-Cp bonds increase on going from Zr to Hf.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1604–1609, September, 1994.     

Four‐Membered Heterometallacyclic d0 and d1 Complexes of Group 4 Metallocenes with Amidato Ligands

A study of the coordination chemistry of different amidato ligands [(R)N?C(Ph)O] (R=Ph, 2,6‐diisopropylphenyl (Dipp)) at Group 4 metallocenes is presented. The heterometallacyclic complexes [Cp₂M(Cl){κ²‐N,O‐(R)N?C(Ph)O}] M=Zr, R=Dipp ( 1 a ), Ph ( 1 b ); M=Hf, R=Ph ( 2 )) were synthesized by reaction of [Cp₂MCl₂] with the corresponding deprotonated amides. Complex 1 a was also prepared by direct deprotonation of the amide with Schwartz reagent [Cp₂Zr(H)Cl]. Salt metathesis reaction of [Cp₂Zr(H)Cl] with deprotonated amide [(Dipp)N?C(Ph)O] gave the zirconocene hydrido complex [Cp₂M(H){κ²‐N,O‐(Dipp)N?C(Ph)O}] ( 3 ). Reaction of 1 a with Mg did not result in the desired Zr(III) complex but in formation of Mg complex [(py)₃Mg(Cl) {κ²‐N,O‐(Dipp)N?C(Ph)O}] ( 4 ; py=pyridine). The paramagnetic complexes [Cp′₂Ti{κ²‐N,O‐(R)N?C(Ph)O}] (Cp′=Cp, R=Ph ( 7 a ); Cp′=Cp, R=Dipp ( 7 b ); Cp′=Cp*, R=Ph ( 8 )) were prepared by the reaction of the known titanocene alkyne complexes [Cp₂′Ti(η²‐Me₃SiC₂SiMe₃)] (Cp′=Cp ( 5 ), Cp′=Cp* ( 6 )) with the corresponding amides. Complexes 1 a , 2 , 3 , 4 , 7 a , 7 b , and 8 were characterized by X‐ray crystallography. The structure and bonding of complexes 7 a and 8 were also characterized by EPR spectroscopy.     

Highly Strained Heterometallacycles of Group 4 Metallocenes with Bis(diphenylphosphino)amide Ligands

A study regarding coordination chemistry of the bis(diphenylphosphino)amide ligand Ph₂P‐N‐PPh₂ at Group 4 metallocenes is presented herein. Coordination of N,N‐bis(diphenylphosphino)amine ( 1 ) to [(Cp₂TiCl)₂] (Cp=η⁵‐cyclopentadienyl) generated [Cp₂Ti(Cl)P(Ph₂)N(H)PPh₂] ( 2 ). The heterometallacyclic complex [Cp₂Ti(κ²‐P,P‐Ph₂P‐N‐PPh₂)] ( 3 Ti ) can be prepared by reaction of 2 with n‐butyllithium as well as from the reaction of the known titanocene–alkyne complex [Cp₂Ti(η²‐Me₃SiC₂SiMe₃)] with the amine 1 . Reactions of the lithium amide [(thf)₃Li{N(PPh₂)₂}] with [Cp₂MCl₂] (M=Zr, Hf) yielded the corresponding zirconocene and hafnocene complexes [Cp₂M(Cl){κ²‐N,P‐N(PPh₂)₂}] ( 4 Zr and 4 Hf ). Reduction of 4 Zr with magnesium gave the highly strained heterometallacycle [Cp₂Zr(κ²‐P,P‐Ph₂P‐N‐PPh₂)] ( 3 Zr ). Complexes 2 , 3 Ti , 4 Hf , and 3 Zr were characterized by X‐ray crystallography. The structures and bondings of all complexes were investigated by DFT calculations.     

Molecular and Crystal Structures of Cp2YbX(THF) (X = Cl,Br)

Cp₂YbCl(THF) crystallizes in the orthorhombic space group Pnma (Z = 4, a = 13.109(5), b = 11.851(4), c = 9.377(3) Å, R1 = 0.0412, wR2 = 0.0482), while Cp₂YbBr(THF) is monoclinic (P2₁/n, Z = 4, a = 8.149(2), b = 12.997(2), c = 14.388(3) Å, β = 105.73(2)°, R1 = 0.0425, wR2 = 0.0436). The ligand arrangements around the formally eight coordinate Yb atoms are pseudo tetrahedral. These two determinations complete the first series of [Cp₂LnX(L)] (X = F, Cl, Br, I) structures covering all halogens for one lanthanoid and cyclopentadienyl group.     

Synthesis of Unprecedented 4d/4f-Polypnictogens

A series of 4d/4f-polyarsenides, -polyarsines and -polystibines was obtained by reduction of the Mo-pnictide precursor complexes [{Cp^tMo(CO)₂}₂(μ,η^2:2-E₂)] (E=As, Sb; Cp^t=tBu substituted cyclopentadienyl) with two different divalent samarocenes [Cp*₂Sm] and [(Cp^Me4nPr)₂Sm]. For the reductive conversion of the Mo-stibide only one product was isolated, featuring a planar tetrastibacyclobutadiene moiety as an unprecedented ligand for organometallic compounds. For the corresponding Mo-arsenide a tetraarsacyclobutadiene and a second species with a side-on coordinated As₂²⁻ anion was isolated. The latter can be considered as reaction intermediate for the formation of the tetraarsacyclobutadiene.     

Synthesis and Characterization of Multiferrocenyl‐Substituted Group 4 Metallocene Complexes

The reaction of different metallocene fragments [Cp₂M] (Cp=η⁵‐cyclopentadienyl, M=Ti, Zr) with diferrocenylacetylene and 1,4‐diferrocenylbuta‐1,3‐diyne is described. The titanocene complexes form the highly strained three‐ and five‐membered ring systems [Cp₂Ti(η²‐FcC₂Fc)] ( 1 ) and [Cp₂Ti(η⁴‐FcC₄Fc)] ( 2 ) (Fc=[Fe(η⁵‐C₅H₄)(η⁵‐C₅H₅)]) by addition of the appropriate alkyne or diyne to Cp₂Ti. Zirconocene precursors react with diferrocenyl‐ and ferrocenylphenylacetylene under C? C bond coupling to yield the metallacyclopentadienes [Cp₂Zr(C₄Fc₄)] ( 3 ) and [Cp₂Zr(C₄Fc₂Ph₂)] ( 5 ), respectively. The exchange of the zirconocene unit in 3 by hydrogen atoms opens the route to the super‐crowded ferrocenyl‐substituted compound tetraferrocenylbutadiene ( 4 ). On the other hand, the reaction of 1,4‐diferrocenylbuta‐1,3‐diyne with zirconocene complexes afforded a cleavage of the central C? C bond, and thus, dinuclear [{Cp₂Zr(μ‐η¹:η²‐C?CFc)}₂] ( 6 ) that consists of two zirconocene acetylide groups was formed. Most of the complexes were characterized by single‐crystal X‐ray crystallography, showing attractive multinuclear molecules. The redox properties of 3 , 5 , and 6 were studied by cyclic voltammetry. Upon oxidation to 3 ⁿ⁺, 5 ⁿ⁺, and 6 ⁿ⁺ (n=1–3), decomposition occured with in situ formation of new species. The follow‐up products from 3 and 5 possess two or four reversible redox events pointing to butadiene‐based molecules. However, the dinuclear complex 6 afforded ethynylferrocene under the measurement conditions.     

Highly Strained Heterometallacycles of Group 4 Metallocenes with Bis(diphenylphosphino)methanide Ligands

A study of the coordination chemistry of different bis(diphenylphosphino)methanide ligands [Ph₂PC(X)PPh₂] (X=H, SiMe₃) with Group 4 metallocenes is presented. The paramagnetic complexes [Cp₂Ti{κ²‐P,P‐Ph₂PC(X)PPh₂}] (X=H ( 3 a ), X=SiMe₃ ( 3 b )) have been prepared by the reactions of [(Cp₂TiCl)₂] with [Li{C(X)PPh₂}₂(thf)₃]. Complex 3 b could also be synthesized by reaction of the known titanocene alkyne complex [Cp₂Ti(η²‐Me₃SiC₂SiMe₃)] with Ph₂PC(H)(SiMe₃)PPh₂ ( 2 b ). The heterometallacyclic complex [Cp₂Zr(H){κ²‐P,P‐Ph₂PC(H)PPh₂}] ( 4 aH ) has been prepared by reaction of the Schwartz reagent with [Li{C(H)PPh₂}₂(thf)₃]. Reactions of [Cp₂HfCl₂] with [Li{C(X)PPh₂}₂(thf)₃] gave the highly strained corresponding metallacycles [Cp₂M(Cl){κ²‐P,P‐Ph₂PC(X)PPh₂}] ( 5 aCl and 5 bCl ) in very good yields. Complexes 3 a , 4 aH , and 5 aCl have been characterized by X‐ray crystallography. Complex 3 a has also been characterized by EPR spectroscopy. The structure and bonding of the complexes has been investigated by DFT analysis. Reactions of complexes 4 aH , 5 aCl , and 5 bCl did not give the corresponding more unsaturated heterometallacyclobuta‐2,3‐dienes.     

Molecular and Crystal Structures of CpSmX2(THF)3 (X = Br,I)

The reaction of Cp₂Sm(THF) with 1,2-dibromoethane or 1,2-diiodoethane leads to an equimolar mixture of Cp₃Sm(THF) and CpSmX₂(THF)₃ (X = Br, I). CpSmBr₂(THF)₃ crystallizes in the monoclinic system (P2₁, Z = 2, a = 804.6(1), b = 1507.6(2), c = 913.8(1) pm, β = 107.36(1)°, R₁ = 0.0327, wR₂ = 0.0578), while CpSmI₂(THF)₃ is orthorhombic (Pna2₁, Z = 4, a = 1950.6(3), b = 1377.1(2), c = 831.93(9) pm, R₁ = 0.0438, wR₂ = 0.0412). The ligand arrangement around the formally eight coordinate Sm atom is a distorted octahedron with the centroid of the Cp-ring and one THF-molecule in the apical positions, whilst the halides are transoid in the equatorial plane.     

Synthesis and molecular structure of [1, 3-(Me3Si)2C5H3]2Lu(μ-Cl)2

Cp^* ₂Lu(-Cl)₂ (1) was isolated following the reaction of Cp^*Na (Cp^* = 1, 3-(Me₃Si)₂C₅H₃) with LuCl₃ in THF and subsequent treatment with toluene at 80°C. An X-ray structural investigation of1 was performed (MoK radiation, 2933 reflections,R = 0.020). The crystals are triclinic,a = 10.744(3) Å,b=11.821(2) Å, c=12.966(3) Å, a=71.54(1)°, =85.32(2)°, =74.83(1)°,Z = 2, space groupP-1. Two Lu atoms withdistorted tetrahedral coordination are linked by two chloride bridges with a mean Lu-Cl distance equal to 2.62 Å.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 568–570, March, 1993.     

The Influence of the Ligands Cp*(η5‐C5Me5) and Cp(η5‐C5H5) on the Stability and Reactivity of Titanocene and Zirconocene Complexes: Reactions of the Bis(trimethylsilyl)acetylene Permethylmetallocene Complexes (η5‐C5Me5)2M(η2‐Me3SiC2SiMe3), M = Ti,Zr, with H2O and CO2

The reactions of the bis(trimethylsilyl)acetylene permethylmetallocene complexes CpM(η²‐Me₃SiC₂SiMe₃) (M = Ti ( 1 ), M = Zr ( 2 )) with H₂O and CO₂ were studied and compared to those of the corresponding metallocene complexes Cp₂M(L)(η²‐Me₃SiC₂SiMe₃) (M = Ti ( 3 ), L = – ; M = Zr, L = THF ( 4 )) to understand the influence of the ligands Cp(η⁵‐C₅H₅) and Cp*(η⁵‐C₅Me₅) as well as the metals titanium and zirconium on the reaction pathways and the obtained products. In the reaction of the permethyltitanocene complex 1 with water the dihydroxy complex CpTi(OH)₂ ( 5 ) was formed. This product differs from the well‐known titanoxane Cp₂TiOTiCp₂ which was obtained by the reaction of the corresponding titanocene complex 3 with water. The reaction of the permethylzirconocene complex 2 with water gives the mononuclear alkenyl zirconocene hydroxide 6 . An analogous product was assumed as the first step in the reaction of the corresponding zirconocene complex 4 with water which ends up in a dinuclear zirconoxane. In the conversion of the permethylzirconocene complex 2 with carbon dioxide the mononuclear insertion product 7 was formed by coupling of carbon dioxide and the acetylene. In contrast, the corresponding zirconocene complex 4 affords, by an analogous reaction, a dinuclear complex. In additional experiments the known complex CpZr(η²‐PhC₂SiMe₃) ( 8 ) was prepared, starting from CpZrCl₂ and Mg in the presence of PhC≡CSiMe₃. This complex reacts with carbon dioxide resulting in a mixture of the regioisomeric zirconafuranones 9 a and 9 b . From these in the complex 9 a , having the SiMe₃ group in β‐position to the metal, the Zr–C bond was quickly hydrolyzed by water to give the complex CpZr(OH)OC(=O)–C(SiMe₃)=CHPh ( 10 a ) compared to complex ( 9 b ) which gives slowly the complex CpZr(OH)OC(=O)–CPh=CH(SiMe₃) ( 10 b ).     

Stereoselectivity and nonmigratory insertion mechanism of dimethylacetylene dicarboxylate into metallocene-hydride of Cp2M(L)H [Cp = η5-C5H5; M = Nb,V; L = CO,P (OMe)3]: A DFT study

The insertion of an alkyne into transition metal–hydrogen bonds is a key elementary step in catalytic polymerization and hydrogenation processes. It was found that a (Z)- or (E)-type alkyenyl complex can be formed through trans/cis stereospecific processes. In this work, the reaction mechanism of Cp₂M(L)H [Cp = η⁵-C₅H₅; M = Nb, V; L = CO, P (OMe)₃] with dimethylacetylene dicarboxylate (DMAD), and the factors influencing the stereoselectivity have been investigated based on density functional theory calculations. The calculated results show that all of the reactions are exothermic. For L = CO, the Z-isomer product forms first even at low temperatures because of the low Gibbs free energy barrier (ΔG^#). Then the Z-pro converts to E-pro , while for L = P (OMe)₃, the exclusive product is the E-isomer. For different metal centers, the reaction mechanisms of the Cp₂M(CO)H + DMAD (M = Nb and V) reaction are similar, while their products are different at room temperature. For M = Nb, because the energy barrier of the isomerization from Z-pro to E-pro is low and the relative free energies of Z-pro and E-pro are almost equal, both Z-pro and E-pro can be obtained. While for the Cp₂V(CO)H + DMAD reaction, only the Z-pro can be obtained under mild conditions, E-pro can be obtained only at high temperatures. For the Cp₂M(CO)H+DMAD(M=V and Nb) reactions, the formation of E-isomer products proceeds via two five-membered ring transition states. The calculated results provide an reasonable explanation for the experimental results and predict a new insertion reaction.     

Living ring‐opening polymerization of ϵ‐caprolactone with Ti alkoxides derived from the Cp2TiCl‐catalyzed SET reduction of aldehydes

A series of substituted benzaldehydes were investigated as initiators for the living ring‐opening polymerization (LROP) of ε‐caprolactone (CL) mediated by titanium alkoxides obtained from the Cp₂TiCl‐catalyzed single electron transfer (SET) reduction of the carbonyl group following the in situ reduction of Cp₂TiCl₂ with Zn. The aldehyde initiation was demonstrated (NMR) by the presence of the initiator derived fragment on the polycaprolactone (PCL) chain end. The effect of the nature of the aldehyde functionality (R‐Ph‐CHO, R = H, Cl, PhCH₂O, NMe₂, CH₃O, NO₂, and CHO), reagent ratios ([CL]/[aldehyde] = 50/1 to 400/1, [aldehyde]/[Cp₂TiCl₂] = 1/1 to 1/4, and [Cp₂TiCl₂]/[Zn] = 1/0.5 to 1/2), and temperature (T = 75–120 °C) was investigated over a wide range of values to reveal a living polymerization in all cases with an optimum observed at 90 °C with typical stoichiometric ratios of [CL]/[aldehyde]/[Cp₂TiCl₂]/[Zn] = 100/1/1/2. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2869–2877, 2008     

Convenient method of synthesis of Cp2TaH3

Modified method for preparation of Cp₂TaH₃ by reaction between TaCl₅, CpNa, and LiAlH₄ in dimethoxyethane is described: The yield of Cp₂TaH₃ is 25 %.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2050–2051, October, 1995.     

Reaction of Nitrogen(I) Oxide with Nitrogen-fixing Systems on the Basis of Lithium,Chlorotrimethylsilane, and Transition Metal Compounds

Reaction of nitrogen(I) oxide with nitrogen-fixing systems Li/Me₃SiCl/MCl _n (MCl _4n = CrCl₃, CoCl₂, Cp₂TiCl₂, FeCl₃, CuCl₂). In these systems nitrogen(I) oxide, molecular nitrogen, and air nitrogen undergo reductive silylation to tris(trimethylsilyl)amine. The efficiency of the process was estimated by the molar ratio of the tris(trimethylsilyl)amine formed to metal chloride MCl _n n. The reaction of N₂O with the nitrogen-fixing systems including CoCl₂ and Cp₂TiCl₂ is not exhausted by the reduction of the former to molecular nitrogen and its subsequent fixation by transition metal complexes.     

Asymmetric Pentafulvene Carbometalation—Access to Enantiopure Titanocene Dichlorides of Biological Relevance

Unprecedented asymmetric copper‐catalyzed addition of ZnEt₂ (ZnBu₂) to the exocyclic C?C bond of pentafulvenes C₅H₄(?CHAr) (Ar=2‐MeOPh and related species) results in enantiomerically enriched (up to 93:7 e.r.) cyclopentadienyl ligands (C₅H₄CHEtAr; abbreviated Cp^R). Copper catalyst promotion with both chiral phosphoramidite ligands and a phosphate additive is vital in realizing both acceptable enantioselectivities and reaction rates. Enantiomeric Cp^R₂TiCl₂ complexes have been prepared; the (S,S) isomer is twice as active towards pancreatic, breast, and colon cancer cell lines as its (R,R) enantiomer at 24 h.     

Chemie der Isoblausäure. VIII. Protonierung eines ‚mobilen’︁ Cyanoliganden: cis-[(μ-CNH2)Fe2Cp2(CO)3]X (X = Cl,BF4, PF6, I)

Chemistry of Hydrogen Isocyanide. VIII. Protonation of a ‘Mobile’ Cyano Ligand: cis-[μ-CNH₂)Fe₂Cp₂(CO)₃]X (X = Cl, BF₄, PF₆, I) . Protonation of the terminal cyano ligand in the complex cis-Na[Fe₂(CN)Cp₂(CO)₃] affords the N-diprotonated produkt [Fe₂Cp₂(CO)₃(μ-CNH₂)]⁺ X^? (X = Cl, BF₄, PF₆, I) exclusively; the structure of the chloride has been determined by X-ray analysis.     

Synthesis and properties of dicyclopentadienyltantalum(III) carbonyl compounds

Reaction of Cp₂Ta(H)L (L = C₃H₆, C₄H₈, C₅H₁₀ and C₅H₈) with CO under mild conditions gives alkyltantalum carbonyl complexes Cp₂Ta(CO)R (R = C₃H₇, C₄H₉, C₅H₁₁ and C₅H₉, respectively). Depending upon the position of the olefin relative to the hydride ligand in the hydride-olefin complex, Cp₂Ta(CO)H is also formed during the carbonylation reaction. Reduction of Cp₂TaCl₂ by potassium or t-BuMgCl under one atmosphere of CO affords the very stable compound Cp₂Ta(CO)Cl in moderate yields. Reaction of Cp₂Ta(CO)Cl with RLi or RMgX does not give the Cp₂Ta(CO)R complex.     

Insertion Reactions of Neutral Phosphidozirconocene Complexes as a Convenient Entry into Frustrated Lewis Pair Territory

Neutral phosphidozirconocene complexes [Cp₂Zr(PR₂)Me] (Cp=cyclopentadienyl; 1a : R=cyclohexyl (Cy); 1b : R=mesityl (Mes); 1c : R=tBu) undergo insertion into the Zr?P bond by non‐enolisable carbonyl building blocks (O=CR′R′′), such as benzophenone, aldehydes, paraformaldehyde or CO₂, to give [Cp₂Zr(OCR′R′′PR₂)Me] ( 3 – 7 ). Depending on the steric bulk around P, complexes 3 – 7 react with B(C₆F₅)₃ to give O‐bridged cationic zirconocene dimers that display typical frustrated Lewis pair (FLP)/ambiphilic ligand behaviour. Thus, the reaction of {[Cp₂Zr(μ‐OCHPhPCy₂)][MeB(C₆F₅)₃]}₂ ( 10a ) with chalcone results in 1,4 addition of the Zr⁺/P FLP, whereas the reaction of {[Cp₂Zr(μ‐OCHFcPCy₂)][MeB(C₆F₅)₃]}₂ ( 11a ; Fc=(C₅H₄)CpFe) with [Pd(η³‐C₃H₅)Cl]₂ yields the unique Zr?Fe?Pd trimetallic complex 13a , which has been characterised by XRD analysis.