Synthesis of a hafnocene disilene complex

Reaction of the magnesium transmetalation product of a 1,2-dipotassiodisilane with hafnocene dichloride gives a disilene hafnocene complex. X-ray crystallography of the respective trimethylphosphane adduct provides structural proof for this assignment.     

A Germylene Stabilized by Homoconjugation

The synthesis of a bicyclic germylene from the reaction of a germole dianion with hafnocene dichloride is reported. This germylene is stabilized by a homoconjugative interaction of the dicoordinated germanium atom with a remote C=C double bond. First reactivity studies revealed its nucleophilic character and resulted in the synthesis of bimetallic hafnium/iron and hafnium/tungsten complexes with a germylene group linker.     

The preparation of HfC/C ceramics via molecular design

Polymer derived ceramics have received lots of attention throughout the last few decades. Unfortunately, only a few precursor systems have been developed, focusing on silicon based polymers and ceramics, respectively. Herein, the synthesis of novel hafnium containing organometallic polymers by two different approaches is reported. Dialkenyl substituted hafnocene monomers were synthesized and subsequently polymerized via a free radical mechanism. Salt metathesis reactions of hafnocene dichloride with bifunctional linkers led to the formation of polymeric materials. NMR spectroscopic methods--in solution as well as in the solid state--were used to characterize the organometallic polymers. Ceramics were finally obtained after cross-linking and thermal treatment under argon (T(max) = 1800 °C). SEM investigations, elemental analyses, Raman spectroscopy and XRD investigations identified the pyrolyzed products as partially crystalline HfC/C mixed phases.     

Palladium‐Catalyzed Reductive Coupling Reaction of Terminal Alkynes with Aryl Iodides Utilizing Hafnocene Difluoride as a Hafnium Hydride Precursor Leading to trans‐Alkenes

Herein, we describe a reductive cross‐coupling of alkynes and aryl iodides by using a novel catalytic system composed of a catalytic amount of palladium dichloride and a promoter precursor, hafnocene difluoride (Cp₂HfF₂, Cp=cyclopentadienyl anion), in the presence of a mild reducing reagent, a hydrosilane, leading to a one‐pot preparation of trans‐alkenes. In this process, a series of coupling reactions efficiently proceeds through the following three steps: (i) an initial formation of hafnocene hydride from hafnocene difluoride and the hydrosilane, (ii) a subsequent hydrohafnation toward alkynes, and (iii) a final transmetalation of the alkenyl hafnium species to a palladium complex. This reductive coupling could be chemoselectively applied to the preparation of trans‐alkenes with various functional groups, such as an alkyl group, a halogen, an ester, a nitro group, a heterocycle, a boronic ester, and an internal alkyne.     

Activation of hafnocene catalyzed polymerization of 1-hexene with MAO and borate

A study of 1-hexene polymerization with ethylene-bis(9-fluorenyl) hafnium dichloride has been carried out using two different cocatalyst systems, methyl-aluminoxane/trimethylaluminum (MAO/TMA) and tris-isobutyl-aluminum/N,N-dimethylanilinium tetrakis(pentafluorophenyl) borate (TIBA/borate). When MAO/TMA was used, 1-hexene polymerized into a low molar mass poly(1-hexene) with low catalytic activity. Activation with TIBA/borate increased polymerization activity drastically as well as the molar mass of the polymers. In order to analyze differences in the activity profiles, UV-Vis spectroscopy was employed to investigate ligand to metal charge transitions (LMCT) of the hafnocene dichloride during the activation process. The low catalytic activity and the fast chain transfer to the cocatalyst with MAO/TMA may originate from strong bonding between the metallocene cation and the MAO/TMA species thus obstructing monomer coordination and insertion.     

Studies into the mechanism of CO-induced N2 cleavage promoted by an ansa-hafnocene complex and C-C bond formation from an observed intermediate

Carbonylation of the hafnocene dinitrogen complex, [Me(2)Si(η(5)-C(5)Me(4))(η(5)-C(5)H(3)-(t)Bu)Hf](2)(μ(2), η(2), η(2)-N(2)), yields the corresponding hafnocene oxamidide compound, arising from N(2) cleavage with concomitant C-C and C-N bond formation. Monitoring the addition of 4 atm of CO by NMR spectroscopy allowed observation of an intermediate hafnocene complex with terminal and bridging isocyanates and a terminal carbonyl. (13)C labeling studies revealed that the carbonyl is the most substitutionally labile ligand in the intermediate and that N-C bond formation in the bridging isocyanate is reversible. No exchange was observed with the terminal isocyanate. Kinetic data established that the conversion of the intermediate to the hafnocene oxamidide was not appreciably inhibited by carbon monoxide and support a pathway involving rate-determining C-C coupling of the isocyanate ligands. Addition of methyl iodide to the intermediate hafnocene resulted in additional carbon-carbon bond formation arising from CO homologation following nitrogen methylation. Similar reactivity with (t)BuNCO was observed where C-C coupling occurred upon cycloaddition of the heterocumulene. By contrast, treatment of the intermediate hafnocene with CO(2) resulted in formation of a μ-oxo hafnocene with two terminal isocyanate ligands.     

TADDOLate as Ligand in Zirconium and Hafnium Chemistry

The enantiomeric pure TADDOLate complexes of the heavier group 4 metals [(η⁵‐C₅H₅)₂M{(S,S)‐TADDOLate}] (M = Zr, Hf) were prepared by treatment of (S,S)‐TADDOL with 2.5 equivalents of n‐butyl lithium followed by reaction with zirconocene and hafnocene dichloride, respectively. The new complexes have been characterized by standard analytical/spectroscopic techniques and the solid‐state structures of both compounds were established by single crystal X‐ray diffraction. The title compounds are the first fully characterized TADDOLate complexes of zirconium and hafnium.     

Hydridoorganostannylene Coordination: Group 4 Metallocene Dichloride Reduction in Reaction with Organodihydridostannate Anions

Organodihydridoelement anions of germanium and tin were reacted with metallocene dichlorides of Group 4 metals Ti, Zr and Hf. The germate anion [Ar*GeH₂]⁻ reacts with hafnocene dichloride under formation of the substitution product [Cp₂Hf(GeH₂Ar*)₂]. Reaction of the organodihydridostannate with metallocene dichlorides affords the reduction products [Cp₂M(SnHAr*)₂] (M=Ti, Zr, Hf). Abstraction of a hydride substituent from the titanium bis(hydridoorganostannylene) complex results in formation of cation [Cp₂M(SnAr*)(SnHAr*)]⁺ exhibiting a short Ti–Sn interaction. (Ar*=2,6-Trip₂C₆H₃, Trip=2,4,6-triisopropylphenyl).     

Synthesis, structure, and alpha-elimination chemistry of hafnocene triarylstannyl complexes

New hafnocene triarylstannyl complexes were prepared and were shown to undergo clean thermal decompositions via alpha-aryl-elimination to produce the corresponding stannylene and a hafnocene aryl complex. The rate of the decomposition is highly dependent on the nature of the ancillary ligand, with the stabilities of the CpCp*Hf(SnPh(3))X compounds following the order X = NMe(2) > Np (alpha-agostic) > OMe > Cl > Me. Mechanistic information suggests that alpha-aryl-elimination may be viewed as a concerted process involving nucleophilic attack of the migrating aryl group onto the electrophilic metal center.     

Supported metallocene catalysts—interactions of (n-BuCp)2HfCl2 with methylaluminoxane and silica

The species on supported olefin polymerisation catalysts consisting of (n-BuCp)₂HfCl₂, methylaluminoxane (MAO) and dehydroxylated silica were identified by EXAFS and UV-Vis spectroscopy. Whereas the reaction of (n-BuCp)₂HfCl₂ with silica leads to a product containing HfO and HfSi non-bonded interactions with concurrent loss of Hf---Cl bonds, the reaction of (n-BuCp)₂HfCl₂ with silica pretreated with methylaluminoxane yields a mixture of several hafnocene species. The bonding features of (n-BuCp)₂HfCl₂ and (n-BuCp)₂HfCl₂/SiO₂ are still present to some extent but with new interactions consistent with hafnocene cation formation. The relative proportions of these species depend strongly on the method of the catalyst preparation.     

N-C bond formation promoted by a hafnocene dinitrogen complex: comparison of zirconium and hafnium congeners

Nitrogen-carbon bond formation from coordinated dinitrogen has been observed upon addition of 2 equiv of PhNCO to the hafnocene dinitrogen complex, [(eta5-C5Me4H)2Hf]2(mu2,eta2,eta2-N2). The resulting product most likely arises from initial N=C cycloaddition of the first equivalent of heterocumulene, followed by carbonyl insertion of a second equivalent into the newly formed hafnium-nitrogen bond. The resulting product has considerable hafnium imido character, as evidenced by the metrical parameters determined from the solid-state structure as well as reactivity studies, whereby PhNCO, p-tolyl isocyanate, and t-BuCCH each undergo cycloaddition with the hafnium-nitrogen bond. The origin of the nitrogen-carbon-forming chemistry is likely derived from the reluctance of the hafnocene dinitrogen complex to undergo ligand-induced N2 isomerization, as was observed with the zirconium congener.     

大取代茂钛,锆,铪,铁化合物的合成与结构分析

通过芳基锂与6,6-二烷基富烯发生环外双键的加成反应,形成的取代环戊二烯基阴离子与FeCl_2、MCl_4(M=Ti,Zr,Hf)及(CpTiCl_2)_2络合,合成出16个含或不含手性碳取代茂金属化合物。对其~1H NMR光谱进行了研究。     

Dinitrogen functionalization with bis(cyclopentadienyl) complexes of zirconium and hafnium

The rich chemistry of substituted bis(cyclopentadienyl)zirconium and hafnium complexes bearing side-on coordinated dinitrogen ligands is highlighted in this Perspective. Our studies in this area were initially motivated by the desire to understand side-on vs. end-on dinitrogen coordination in bimetallic zirconocene and hafnocene N2 compounds. In the cases where eta2,eta2-dinitrogen compounds were isolated, both structural and computational data have established significant imido character in the metal-nitrogen bonds. This additional bonding interaction, which is diminished in end-on complexes bearing both terminal and bridging N2 ligands, facilitates dinitrogen functionalization by non-polar reagents including dihydrogen, carbon-hydrogen bonds and weak Br?nsted acids such as water and ethanol. In hafnocene chemistry, where unwanted side-on, end-on isomerization is suppressed, cycloaddition of phenylisocyanate to coordinated N2 has also been accomplished. For N-H bond forming reactions involving H2, kinetic measurements, in addition to isotopic labelling and computational studies, are consistent with dinitrogen functionalization by 1,2-addition involving a highly ordered, four-centred transition structure.     

大取代环戊二烯基铪的合成与结构分析

芳基锂与6, 6-二烷基富烯发生加成反应, 生成含或不含手性碳的大位阻取代环戊二烯基负离子。用四氯化铪配合物, 合成了19个大取代茂铪化合物。讨论了其^1H NMR。化合物[(CH3)2C(C6H4-p-CH3)-C5H4]HfCl2经X射线衍射分析。晶体为单斜晶系, 空间群为I2/a, 晶胞参数a=2.2263(7), b=0.6674(2), c=2.5379(9)nm,β=135.13(3)°, R=0.058, Rw=0.069。结构研究表明, 取代基的引入, 使得茂环发生变型, 最大扭曲角为8.45°。     

Photolytic cyclopentadienyl ligand exchange between dicyclopentadienylzirconium dichloride and related systems.

Irradition of benzene solutions of zirconocene dichloride and zirconocene- d₁₀ dichloride with 313 nm light leads to the formation of zirconocene-d₅ dichloride with a quantum yield of 0.021 mol/Ei. The equilibrium constant is 2.8 Zirconocene dichloride exchanges a cyclopentadienyl ligand photolytically with bis(methylcyclopentadienyl)zirconium dichloride with the constant equal to 2.3.     

冠醚化合物的合成(ⅩⅩ)——桥链冠醚的合成

用不对称二苯并14-冠-4-双羟基冠醚的顺式异构体(Ⅰ、Ⅲ)和反式异构体(Ⅱ)分别与丙二酰氯、丁二酰氧和己二酰氯反应,合成了14种桥链冠醚,用IR、¹H NMR、MS和元素分析确证了它们的结构。结果表明,顺式异构体与丁二酰氧和己二酰氧反应可生成1:1和2:2缩合物,而与丙二酰氯反应则只生成2:2缩合物;反式异构体与3种脂肪二酰氯反应都生成2:2缩合物。     

Ethylene Polymerization with Cycloalkylidene‐Bridged Cyclopentadienyl Metallocene Catalysts

Ethylene was polymerized with cycloalkylidene‐bridged cyclopentadienyl metallocene catalysts 1 – 9 in the presence of methyl aluminoxane (MAO) as the cocatalyst. Unlike the normal titanocene catalysts, the cycloalkylidene‐bridged cyclopentadienyl titanocene catalysts show much higher activities than the corresponding zirconocene and hafnocene catalysts and show the highest activities at higher temperature. This indicates that the cycloalkylidene‐bridged cyclopentadienyl titanocene system is very thermally stable and maybe a very promising catalyst system for industrial application.     

Synthesis and characterization of polyesters from hindered biphenols and hydroquinones

Polyesters have been synthesized by polycondensation of terephthaloyl dichloride or isophthaloyl dichloride with hindered biphenols and hydroquinones which contain bulky substituents (methyl and phenyl) on the arylene ring. Polymers derived from isophthaloyl dichloride have better solubility and lower glass transition temperatures than the corresponding polymers obtained from terephthaloyl dichloride. © 1994 John Wiley & Sons, Inc.     

Sulfur-containing polymers by the reaction of diphenyl sulfide with sulfur chlorides

The electrophilic reaction of sulfur dichloride with diphenyl sulfide proceeds efficiently at room temperature to yield oligo(phenylene sulfide) in the presence of a catalytic amount of Fe powder. Sulfur dichloride shows higher reactivity than sulfur monochloride. The reaction is promoted through the activation of sulfur dichloride by Fe powder. The polymeric product contains a linear structure linked by disulfide and sulfide bonds.     

Photochemical reactions of bis(η5-cyclopentadienyl)- titanium dichloride

Irradiation of benzene solutions 10^?3M in both titanocene-d₁₀ dichloride and titanocene dichloride with light of wavelengths 313, 360, 400, and 520 nm leads to the formation of titanocene-d₅ dichloride with quantum yields of 0.02, 0.005, 0.01 and 0.007 mol Ei^?1, respectively. Photodecomposition of titanocene dichloride is negligible even at much longer photolysis times than those required for isotopic equilibration. Photolysis of benzene solutions 10^?2M in titanocene dichloride and 1.0 M in methanol leads to the formation of cyclopentadienyl(methoxo)titanium dichloride with a quantum yield of about 0.08 mol Ei^?1 when the irradiating wavelength is 313 nm.