A new multicomponent reaction catalyzed by a [Lewis Acid](+)[Co(CO)(4)](-) catalyst: stereospecific synthesis of 1,3-oxazinane-2,4-diones from epoxides, isocyanates, and CO

The use of mechanistic information to develop a new, catalytic multicomponent reaction is described. The complex [(salph)Al(THF)2]+[Co(CO)4]- (1, salph = N,N'-o-phenylenebis(3,5-di-tert-butylsalicylideneimine), THF = tetrahydrofuran), which is known to carbonylate epoxides, aziridines, and beta-lactones, was used to catalyze the synthesis of 1,3-oxazinane-2,4-diones from epoxides, isocyanates, and CO. Under optimized conditions, the reaction was both selective and high-yielding. 1,3-Oxazinane-2,4-diones were synthesized from a variety of epoxides and isocyanates, including some epoxides that do not undergo simple ring-expansion carbonylation. The best results were obtained using highly electrophilic isocyanates. The mechanism of the multicomponent reaction was investigated using labeling and stereochemistry, and the data obtained were consistent with the 1-catalyzed formation of beta-lactone and 1,3-oxazinane-2,4-dione from a common intermediate.     

The mechanism of epoxide carbonylation by [Lewis Acid]+[Co(CO)4]- catalysts

A detailed mechanistic investigation of epoxide carbonylation by the catalyst [(salph)Al(THF)2]+ [Co(CO)4]- (1, salph = N,N'-o-phenylenebis(3,5-di-tert-butylsalicylideneimine), THF = tetrahydrofuran) is reported. When the carbonylation of 1,2-epoxybutane (EB) to beta-valerolactone is performed in 1,2-dimethoxyethane solution, the reaction rate is independent of the epoxide concentration and the carbon monoxide pressure but first order in 1. The rate of lactone formation varies considerably in different solvents and depends primarily on the coordinating ability of the solvent. In mixtures of THF and cis/trans-2,5-dimethyltetrahydrofuran, the reaction is first order in THF. From spectroscopic and kinetic data, the catalyst resting state was assigned to be the neutral (beta-aluminoxy)acylcobalt species (salph)AlOCH(Et)CH2COCo(CO)4 (3a), which was successfully trapped with isocyanates. As the formation of 3a from EB, CO, and 1 is rapid, lactone ring closing is rate-determining. The favorable impact of donating solvents was attributed to the necessity of stabilizing the aluminum cation formed upon generation of the lactone.     

Chromium(III) octaethylporphyrinato tetracarbonylcobaltate: a highly active, selective, and versatile catalyst for epoxide carbonylation

The development of a highly active and selective porphyrin-based epoxide carbonylation catalyst, [(OEP)Cr(THF)2][Co(CO)4] (1; OEP = octaethylporphyrinato; THF = tetrahydrofuran), is detailed. Complex 1 is a separated ion pair composed of a tetracarbonylcobaltate anion and an octahedral chromium porphyrin complex axially ligated by two THF ligands. Regarding the carbonylation of epoxides to beta-lactones, catalyst 1 exhibits excellent turnover numbers (up to 10,000) and turnover frequencies (up to 1670 h(-1)), with regioselective carbonyl insertion occurring between the oxygen and the sterically less hindered carbon of the epoxide substrate. Complex 1 is highly tolerant of nonprotic functional groups, carbonylating an array of aliphatic and cycloaliphatic epoxides, as well as epoxides with pendant ethers, esters, and amides. With careful control of reaction conditions in the carbonylation of glycidyl esters, the exclusive production of either the beta- or gamma-lactone isomer was achieved. Through analysis of reaction stereochemistry, a mechanism for the formation of gamma-lactone products was proposed. Overall, a broad array of synthetically useful lactones has been synthesized in a rapid and selective fashion by catalytic carbonylation using [(OEP)Cr(THF)2][Co(CO)4].     

Catalytic carbonylation of beta-lactones to succinic anhydrides

A well-defined, highly active and selective catalyst for the synthesis of succinic anhydrides from CO and beta-lactones is reported. At 200 psi of CO, the catalyst [(N,N'-bis(3,5-di-tert-butylsalicylidene)phenylenediamino)Al(THF)2][Co(CO)4] carbonylates beta-propiolactones to succinic anhydrides in high yield. (R)-beta-Butyrolactone is carbonylated to (S)-methylsuccinic anhydride with clean inversion of stereochemistry, while cis-2,3-dimethyl-beta-propiolactone yields exclusively trans-2,3-dimethylsuccinic anhydride. These data are consistent with a mechanism involving nucleophilic attack by [Co(CO)4]- on the beta carbon of the lactone, followed by CO insertion and anhydride formation.     

1,1,3,3-四烷基胍羰基钴离子液体:高效可循环利用的环氧化合物羰基化反应催化新材料

离子液体因其所独有的物理化学性质如蒸气压低、热稳定性好以及结构和性能的可调性等优点而备受关注.四羰基钴阴离子是多种重要均相催化反应的催化活性物种,含有四羰基钴阴离子的金属有机离子液体有效结合了羰基金属和离子液体各自的特点和优势,作为一类新颖而且重要的功能化离子液体,受到国内外研究者的青睐.2001年,Dyson等首次报道了一种室温下为液态的羰基钴金属有机离子液体[bmim][Co(CO)4],为四羰基钴阴离子离子液体的研究开创了先河.此后,有关羰基钴金属有机离子液体的催化应用研究也相继报道.目前[CnPy][Co(CO)4]以及[bmim][Co(CO)4]在环氧化合物的羰基化反应中已有报道,但该类催化剂的催化活性特别是循环使用性能有待进一步提高.胍盐具有阳离子电荷分散程度高、热稳定性和化学稳定性高、三个氮原子上的基团可以调节等特点,使得胍盐离子液体的设计、合成和应用研究受到国内外学者关注.由于其自身结构特点,氮原子上有取代氢可以和含F,O,N底物作用形成氢键,并且氮原子上取代烷基之间作用使阳离子的平面结构发生变化,使得与三个氮原子相连的碳原子处于缺电子状态,使阳离子表现出Lewis酸性.所以其在环氧化合物氢酯基化反应中可起到稳定四羰基钴阴离子以及活化环氧化合物的作用.基于此,本文以较高收率合成了四种新型的1,1,3,3-四烷基胍羰基钴金属有机离子液体:1,1-二甲基-3,3-二乙基胍羰基钴(3a),1,1-二甲基-3,3-二正丁基胍羰基钴(3b),1,1-二甲基-3,3-四亚甲基胍羰基钴(3c),1,1-二甲基-3,3-五亚甲基胍羰基钴(3d).通过红外光谱、紫外-可见光谱、1H核磁共振谱、13C核磁共振谱、高分辨质谱、差示量热扫描仪和热重分析对该类化合物进行了结构确认及性质研究.这四种催化剂,特别是3a,在环氧化合物的氢酯基化反应中表现出优异的催化性能,在无需任何助剂的情况下具有较好的催化活性及底物适用性.此外,以不同构型的环氧丙烷为反应底物,氢酯基化反应结果显示:在该催化体系作用下,产物的构型与底物保持一致,没有发生消旋.尤其值得指出的是,催化剂3a在环氧丙烷的氢酯基化反应中表现出了优异的循环稳定性能,在循环使用6次后依然可以获得较好的转化率(91%)和选择性(94%).     

Coordination copolymerization of tetrahydrofuran and oxepane with oxetanes and epoxides

The chelate catalyst, as typified by the Et₃Al-0.5 H₂O-0.5 acetylacetone product, usually prepared with Et₂O or tetrahydrofuran (THF) present, has all the known characteristics of a coordination catalyst for polymerizing epoxides and uniquely for oxetanes. We have found that the chelate catalyst gives fairly good copolymerization of THF (54% in monomer charge) with 3-(trimethylsilyloxy) oxetane which, after hydrolysis, is a water-soluble, moderate molecular weight copolymer of THF (36%) with 3-hydroxyoxetane (HO). This apparent coordination copolymerization of THF has been extended to trimethylene oxide (TMO), 3,3-bis(trimethylsilyoxymethyl) oxetane, 3,3-bis(chloromethyl)oxetane (BCMO), trans-2,3-epoxybutane (TBO), and propylene oxide, listed in order of decreasing copolymerizability with THF. Presumably, this is the first known coordination copolymerization of THF which hitherto has only been polymerized with cationic catalysts. Oxepane also copolymerizes coordinately with TMO and BCMO, but less readily than THF, with the chelate catalyst. TBO polymerizes slowly with the chelate catalyst to form stereoregular polymer which can be separated into an acetone-insoluble, highly stereoregular fraction and an acetone-soluble, somewhat less stereoregular fraction. The soluble fraction can be eliminated by using 1.0 acetyl acetone per Al in the catalyst or by adding a small amount of a very strong base (0.09 quinuclidine per Al). The copolymerization of TBO with THF (39%) gives insoluble stereoregular homopolymer and soluble copolymer containing about 23% THF, reflecting the varied steric hindrance of the sites. Some anomalous results appear to be related to the mechanism: (1) steric and electronic factors of the monomers and of the polymerization site. For example, the fourth coordination position of Al is needed to achieve homopolymerization of BCMO and TMO-THF copolymerization. (2) The aggregation state of the catalyst, since a nonpolar diluent as toluene is unfavorable for coordination copolymerization of THF. (3) The greater ring strain of epoxides causes a greater ease of polymerization, compared to oxetanes. Thus, Et₂O often present in the chelate catalyst lowers the molecular weight of the polymer considerably with oxetanes compared to epoxides where Et₂O has little or no effect.     

Novel pyridinium based cobalt carbonyl ionic liquids: synthesis, full characterization, crystal structure and application in catalysis

Through an optimized synthetic strategy, a series of novel alkylpyridinium cobalt tetracarbonyl salts, [C(1)Py][Co(CO)(4)] (), [C(4)Py][Co(CO)(4)] () and [C(16)Py][Co(CO)(4)] () (C(n)Py = N-C(n)H(2n+1)-pyridinium), were successfully prepared in good yields, using a water-organic biphasic system. All the three compounds melt well below 100 degrees C and could be classified as ionic liquids. The compounds were fully characterized using IR, UV-Vis, (1)H NMR, (13)C NMR, ESI-MS and elemental analysis, and was structurally characterized by X-ray single crystal analysis. Compound has been found to be an efficient and reusable catalyst for the alkoxycarbonylation of propylene oxide without the aid of a base additive.     

Catalytic double carbonylation of epoxides to succinic anhydrides: catalyst discovery, reaction scope, and mechanism

The first catalytic method for the efficient conversion of epoxides to succinic anhydrides via one-pot double carbonylation is reported. This reaction occurs in two stages: first, the epoxide is carbonylated to a beta-lactone, and then the beta-lactone is subsequently carbonylated to a succinic anhydride. This reaction is made possible by the bimetallic catalyst [(ClTPP)Al(THF)2]+[Co(CO)4]- (1; ClTPP = meso-tetra(4-chlorophenyl)porphyrinato; THF = tetrahydrofuran), which is highly active and selective for both epoxide and lactone carbonylation, and by the identification of a solvent that facilitates both stages. The catalysis is compatible with substituted epoxides having aliphatic, aromatic, alkene, ether, ester, alcohol, nitrile, and amide functional groups. Disubstituted and enantiomerically pure anhydrides are synthesized from epoxides with excellent retention of stereochemical purity. The mechanism of epoxide double carbonylation with 1 was investigated by in situ IR spectroscopy, which reveals that the two carbonylation stages are sequential and non-overlapping, such that epoxide carbonylation goes to completion before any of the intermediate beta-lactone is consumed. The rates of both epoxide and lactone carbonylation are independent of carbon monoxide pressure and are first-order in the concentration of 1. The stages differ in that the rate of epoxide carbonylation is independent of substrate concentration and first-order in donor solvent, whereas the rate of lactone carbonylation is first-order in lactone and inversely dependent on the concentration of donor solvent. The opposite solvent effects and substrate order for these two stages are rationalized in terms of different resting states and rate-determining steps for each carbonylation reaction.     

Catalytic performance of [Bmim][Co(CO)4] functional ionic liquids for preparation of 1,3-propanediol by coupling of hydroesterification-hydrogenation from ethylene oxide

In this paper, synthesis of 1,3-propanediol (1,3-PDO) through coupling of hydroesterification-hydrogenation from ethylene oxide (EO) catalyzed by 1-butyl-3-methylimidazolium cobalt tetracarbonyl [Bmim][Co(CO)₄] functional ionic liquid which was prepared by metathesis reaction between [Bmim]Cl and KCo(CO)₄ has been studied. The structure of [Bmim][Co(CO)₄] was characterized by FT-IR and ¹H NMR. Using [Bmim][Co(CO)₄] as catalyst and [Bmim]PF₆ as solvent, 1,3-PDO was prepared for the first time by coupling of hydroesterifaction of EO and hydrogenation of methyl 3-hydroxypropionate (3-HPM). The yield of 3-HPM can reach 90.8%, while the yield of 1,3-PDO up to 82.9%. The catalyst can be separated from the product mixture by extraction with deionized water and recycled several times without significant loss of catalytic efficiency. A possible reaction mechanism has also been proposed.     

Chiral (salen)Co(III) catalyst for the synthesis of cyclic carbonates

A catalyst system comprised of a Co(III)(salen) complex and a Lewis base is investigated for the reaction of CO2 and a variety of epoxides to form cyclic carbonates. Application of this catalyst system in the kinetic resolution of propylene oxide is also discussed.     

Carbonylative ring opening of terminal epoxides at atmospheric pressure

The carbonylative opening of terminal epoxides under mild conditions has been developed using Co2(CO)8 as the catalyst. Under 1 atm of carbon monoxide and at room temperature in methanol, propylene oxide is converted to methyl 3-hydroxybutanoate in up to 89% yield. This transformation is general for many terminal epoxides bearing alkyl, alkenyl, aryl, alkoxy, chloromethyl, phthalimido, and acetal functional groups. The opening takes place without epimerization at the secondary stereocenter.     

双金属氰化络合物及其催化的聚合反应

本文综述了双金属氰化络合物及其催化的环氧化物参与的聚合反应研究。双金属氰化络合物是由其内界金属M^Ⅱ通过氰基与外界金属M^Ⅰ连接形成的含 M^Ⅱ-C≡N-M^Ⅰ 桥键的三维网络状无机高分子(M^Ⅰ一般为Zn²⁺、Fe²⁺、Co²⁺和Ni²⁺等二价金属离子,M^Ⅱ一般为Fe²⁺、Fe³⁺、Co²⁺、Co³⁺和Ni²⁺等过渡金属离子)。外界金属M^Ⅰ一般被认为是催化反应的活性中心金属。该类催化剂早期被用于催化环氧化物开环聚合,并逐步发展成为合成中高分子量、低不饱和度聚醚多元醇的极高效催化剂。近年来该类催化剂被用来催化环氧化物/环状酸酐共聚、环氧化物/CX₂(X≡O,S)共聚和环氧化物/环状酸酐/CO₂三元共聚反应合成聚酯、聚碳酸酯、聚(醚-碳酸酯)、聚硫代碳酸酯和聚(碳酸酯-酯)等具有生物降解性的聚合物。尤其对氧化环己烯(CHO)与CO₂(或酸酐)共聚,锌-钴双金属氰化络合物表现出了极高的催化活性和选择性。结合本研究组十多年的研究结果,本文讨论了双金属氰化络合物催化活性中心的可能结构和催化机理,提出了双金属氰化络合物催化聚合的共性难题和解决这些问题的方向。     

Mechanism of the cycloaddition of carbon dioxide and epoxides catalyzed by cobalt-substituted 12-tungstenphosphate

Co(II)-substituted α-Keggin-type 12-tungstenphosphate [(n-C(4)H(9))(4)N](4)H[PW(11)Co(H(2)O)O(39)]-(PW(11)Co) is synthesized and used as a single-component, solvent-free catalyst in the cycloaddition reaction of CO(2) and epoxides to form cyclic carbonates. The mechanism of the cycloaddition reaction is investigated using DFT calculations, which provides the first computational study of the catalytic cycle of polyoxometalate-catalyzed CO(2) coupling reactions. The reaction occurs through a single-electron transfer from the doublet Co(II) catalyst to the epoxide and forms a doublet Co(III)-carbon radical intermediate. Subsequent CO(2) addition forms the cyclic carbonate product. The existence of radical intermediates is supported by free-radical termination experiments. Finally, it is exhilarating to observe that the calculated overall reaction barrier (30.5 kcal mol(-1)) is in good agreement with the real reaction rate (83 h(-1)) determined in the present experiments (at 15 °C).     

Hydroesterification of ethylene oxide catalyzed by 1-butyl-3-methylimidazolium cobalt tetracarbonyl ionic liquid

In this paper, functional ionic liquid 1-butyl-3-methylimidazolium cobalt tetracarbonyl [Bmim][Co(CO)₄] is prepared in a metathesis reaction between [Bmim]Cl and KCo(CO)₄. The structure of [Bmim]⁺ is illustrated by ¹H NMR, while [Co(CO)₄]⁻ is confirmed by IR(ν_CO) spectrum. Methyl 3-hydroxypropionate(3-HPM), an intermediate to 1,3-propanediol (1,3-PDO), can be prepared in high yield by hydroesterification of ethylene oxide in the presence of a [Bmim][Co(CO)₄] catalyst. Under a pressure of 3.7 MPa and at a temperature of 75 °C, the yield of 3-HPM can reach 90.8% in 10 h. Even after the catalyst is recycled three times, a yield of more than 80% can be obtained. A possible reaction mechanism has also been proposed.     

共沉淀法制备氧化铝负载Co-Mo双金属氮化物催化剂

采用硝酸铝和硝酸钴的乙醇溶液与钼酸铵的碳酸铵水溶液共沉淀制备了Al2O3负载Co-Mo双金属氧化物前驱体,结合氨程序升温还原法制得了氮化物催化剂Co-Mo-N/Al2O3.利用X射线衍射和N2物理吸附方法表征了制备的前驱体和钝化态Co-Mo-N/Al2O3催化剂的晶相和孔结构,用程序升温脱附、程序升温表面反应及扫描电子显微镜考察了共沉淀法和浸渍法制备的催化剂的晶格稳定性、活性中心和表面形貌,用氨分解反应表征了Co-Mo-N/Al2O3催化剂的活性.结果表明,焙烧温度对催化剂比表面积有较大影响,低温焙烧的样品中活性组分散性较好,673K焙烧制得催化剂的氨分解活性最高.与浸渍法制备的Co-Mo-N/Al2O3催化剂相比,共沉淀法制备的催化剂具有更高的晶格稳定性、更均匀的活性组分分布和更高的氨分解活性.     

Biodegradable Polycarbonate Synthesis by Copolymerization of Carbon Dioxide with Epoxides Using a Heterogeneous Zinc Complex

As a means for the chemical fixation of carbon dioxide and the synthesis of biodegradable polycarbonates, copolymerizations of carbon dioxide with various epoxides such as cyclohexene oxide (CHO), cyclopetene oxide, 4-vinyl-1-cyclohexene-1,2epoxide, phenyl glycidyl ether, allyl glycidyl ether, propylene oxide, butene oxide, hexene oxide, octene oxide, and 1-chloro-2,3-epoxypropane were investigated in the presence of a double metal cyanide catalyst (DMC). The DMC catalyst was prepared by reacting K₃Co(CN)₆ with ZnCl₂, together with tertiary butyl alcohol and poly(tetramethylene ether glycol) as complexing reagents and was characterized by various spectroscopic methods. The DMC catalyst showed high activity (526.2 g-polymer/g-Zn atom) for CHO/CO₂ (P_CO2 = 140 psi) copolymerization at 80 °C, to yield biodegradable aliphatic polycarbonates of narrow polydispersity (M_w/M_n = 1.67) and moderate molecular weight (M_n = 8900). The DMC catalyst also showed high activities with different CO₂ reactivities for other epoxides to yield various aliphatic polycarbonates with narrow polydispersity.     

New hybrid semiconductor materials based on viologen salts of bimetallic Fe-Pt and Fe-Au carbonyl clusters: first structural characterization of the diradical pi-dimer of the diethylviologen monocation and EPR evidence of its triplet state

The synthesis, structure, spectroscopic characterization and electrical resistivity of the [EtV](2)[Fe(4)Pt(CO)(16)], [EtV][Fe(3)Pt(3)(CO)(15)].THF, [EtV][Fe(4)Au(CO)(16)](2)2.THF (EtV=1,1'-diethyl-4,4'-bipyridilium cation) and [NEt(4)](2)[Fe(4)Au(CO)(16)] is reported. The crystal structure of [EtV](2)[Fe(4)Pt(CO)(16)] is based on infinite stacks of [(EtV)(*+)](2) pi-dimers rotated by 90 degrees and isolated [Fe(4)Pt(CO)(16)](2-) ions. Within each pi-dimer, the [EtV](*+) radical ions are perfectly eclipsed and the distance between their mean planes is 3.275 A. The EPR spectrum of the solid material at room temperature clearly indicates the presence of a significantly populated triplet state of the pi-dimer, by showing signals both at Deltam=1 and Deltam=2. The solid-state structure of [EtV][Fe(3)Pt(3)(CO)(15)].THF is based on the ionic packing of [EtV](2+) and [Fe(3)Pt(3)(CO)(15)](2-) ions, inferred from a comparison of their molecular parameters with literature data. Significant electron transfer could have been expected to give [EtV](*+)[Fe(3)Pt(3)(CO)(15)](*-) on the basis of their formal redox potentials. In spite of their different stoichiometries, the structures of [EtV][Fe(4)Au(CO)(16)](2).2 THF and [NEt(4)](2)[Fe(4)Au(CO)(16)] both contain an isomer of the monoanion [Fe(4)Au(CO)(16)](-) in solution (previously characterized in the solid state as a [NMe(3)CH(2)Ph](2)[Fe(4)Au(CO)(16)]Cl mixed salt). Resistivity measurements on pellets of powdered samples of the above compounds indicate that their tetrasubstituted ammonium salts, and complex [EtV][Fe(4)Au(CO)(16)](2)2.THF, largely behave as insulators. However, the [EtV](2)[Fe(4)Pt(CO)(16)] and [EtV][Fe(3)Pt(3)(CO)(15)].THF samples respectively display resistivities 3 and 4 orders of magnitude less than those of their corresponding ammonium salts and could be classified as semiconductor materials.     

Synthesis,characterization, and solution redox properties of (trimpsi)M(CO)(2)(NO) complexes [M = V,Nb, Ta; trimpsi = (t)BuSi(CH(2)PMe(2))(3)

Treatment of [Et(4)N][M(CO)(6)] (M = Nb, Ta) with I(2) in DME at -78 degrees C produces solutions of the bimetallic anions [M(2micro-I)(3)(CO)(8)](-). Addition of the tripodal phosphine (t)BuSi(CH(2)PMe(2))(3) (trimpsi) followed by refluxing affords (trimpsi)M(CO)(3)I [M = Nb (1), Ta (2)], which are isolable in good yields as air-stable, orange-red microcrystalline solids. Reduction of these complexes with 2 equiv of Na/Hg, followed by treatment with Diazald in THF, results in the formation of (trimpsi)M(CO)(2)(NO) [M = Nb (3), Ta (4)] in high isolated yields. The congeneric vanadium complex, (trimpsi)V(CO)(2)(NO) (5), can be prepared by reacting [Et(4)N][V(CO)(6)] with [NO][BF(4)] in CH(2)Cl(2) to form V(CO)(5)(NO). These solutions are treated with 1 equiv of trimpsi to obtain (eta(2)-trimpsi)V(CO)(3)(NO). Refluxing orange THF solutions of this material affords 5 in moderate yields. Reaction of (trimpsi)VCl(3)(THF) (6) with 4 equiv of sodium naphthalenide in THF in the presence of excess CO provides [Et(4)N][(trimpsi)V(CO)(3)] (7), (trimpsi)V(CO)(3)H, and [(trimpsi)V(micro-Cl)(3)V(trimpsi)][(eta(2)-trimpsi)V(CO)(4)].3THF ([8][9].3THF). All new complexes have been characterized by conventional spectroscopic methods, and the solid-state molecular structures of 2.(1)/(2)THF, 3-5, and [8][9].3THF have been established by X-ray diffraction analyses. The solution redox properties of 3-5 have also been investigated by cyclic voltammetry. Cyclic voltammograms of 3 and 4 both exhibit an irreversible oxidation feature in CH(2)Cl(2) (E(p,a) = -0.71 V at 0.5 V/s for 3, while E(p,a) = -0.55 V at 0.5 V/s for 4), while cyclic voltammograms of 5 in CH(2)Cl(2) show a reversible oxidation feature (E(1/2) = -0.74 V) followed by an irreversible feature (0.61 V at 0.5 V/s). The reversible feature corresponds to the formation of the 17e cation [(trimpsi)V(CO)(2)(NO)](+) ([5](+)()), and the irreversible feature likely involves the oxidation of [5](+)() to an unstable 16e dication. Treatment of 5 with [Cp(2)Fe][BF(4)] in CH(2)Cl(2) generates [5][BF(4)], which slowly decomposes once formed. Nevertheless, [5][BF(4)] has been characterized by IR and ESR spectroscopies.     

Lanthanide-transition metal carbonyl complexes: condensation of solvent-separated ion-pair compounds into extended structures

New solvent-separated ion-pair compounds and extended structures containing ytterbium(II)-transition metal isocarbonyl linkages were synthesized. [Yb(THF)6][M(CO)5]2 (1, M = Mn; 2, M = Re) were prepared via transmetalation reactions between Yb metal and Hg[M(CO)5]2 in THF. Reflux of 1 in Et2O afforded {Yb(THF)2(Et2O)2[(mu-CO)2Mn(CO)3]2}infinity (3) which is a sheet-layer structure. In ether solution, 3 is converted to {Yb(THF)4[(mu-CO)2Mn(CO)3]2}infinity (4) which has a linear structure. In both 3 and 4, ytterbium is 8-coordinated (distorted square antiprism geometry), four coordination sites occupied by molecules of solvent and four more by oxygen atoms of isocarbonyl linkages. The [Mn(CO)5]- anion has trigonal bipyramidal geometry and is linked to ytterbium through two equatorial carbonyls. The formation of two minor products, (THF)2Mn3(CO)10 (5) and [(THF)5Yb(mu-CO)Mn3(CO)13][Mn3(CO)14] (6), was observed during condensation of 1 into 3 and 4.     

Tetrasilacyclobutadiene ((t)Bu(2)MeSi)(4)Si(4): a new ligand for transition-metal complexes

The anionic complex of [tetrakis(di-tert-butylmethylsilyl) tetrasilacyclobutadiene]dicarbonylcobalt, [(R4Si4)Co(CO)2]-.K+ (R = SiMetBu2) 2-.K+, was synthesized by the reaction of tetrasilacyclobutadiene dianion dipotassium salt [R4Si4]2-.2K+ 1 with an excess of CpCo(CO)2 in THF. X-ray analysis of 2-.[K+(diglyme)2(THF)] showed an almost planar Si4 ring of rectangular shape with an in-plane arrangement of the silyl substituents. 2- was also prepared as a free anion with the [K+[2.2.2]cryptand] counterion by complexation with [2.2.2]cryptand and as a dimer {2-.[K+(THF)3]}2 without complexing reagents in THF. Such a tetrasilacyclobutadiene fragment represents a new type of ligand for Co complexes, being the first example of a cyclobutadiene containing only heavier group 14 elements.