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.     

Facile and Reversible Formation of Iron(III)–Oxo–Cerium(IV) Adducts from Nonheme Oxoiron(IV) Complexes and Cerium(III)

Ceric ammonium nitrate (CAN) or Ce^IV(NH₄)₂(NO₃)₆ is often used in artificial water oxidation and generally considered to be an outer‐sphere oxidant. Herein we report the spectroscopic and crystallographic characterization of [(N4Py)Fe^III‐O‐Ce^IV(OH₂)(NO₃)₄]⁺ ( 3 ), a complex obtained from the reaction of [(N4Py)Fe^II(NCMe)]²⁺ with 2 equiv CAN or [(N4Py)Fe^IV=O]²⁺ ( 2 ) with Ce^III(NO₃)₃ in MeCN. Surprisingly, the formation of 3 is reversible, the position of the equilibrium being dependent on the MeCN/water ratio of the solvent. These results suggest that the Fe^IV and Ce^IV centers have comparable reduction potentials. Moreover, the equilibrium entails a change in iron spin state, from S =1 Fe^IV in 2 to S =5/2 in 3 , which is found to be facile despite the formal spin‐forbidden nature of this process. This observation suggests that Fe^IV=O complexes may avail of reaction pathways involving multiple spin states having little or no barrier.     

Synthese und Struktur der Nitrido‐Komplexe [(n‐Bu)4N]2[{(L)Cl4Re≡N}2PtCl2] (L = THF und H2O) und [(n‐Bu)4N]2[(H2O)Cl4Re≡N‐PtCl(μ‐Cl)]2

Synthesis and Crystal Structure of the Nitrido Complexes [(n‐Bu)₄N]₂[{(L)Cl₄Re≡N}₂PtCl₂] (L = THF und H₂O) and [(n‐Bu)₄N]₂[(H₂O)Cl₄Re≡N‐PtCl(μ‐Cl)]₂ The threenuclear complex [(n‐Bu)₄N]₂[{(THF)Cl₄Re≡N}_2—PtCl₂] ( 1a ) is obtained by the reaction of [(n‐Bu)₄N][ReNCl₄] with [PtCl₂(C₆H₅CN)₂] in THF/CH₂Cl₂. It forms red crystals with the composition 1a · 2 CH₂Cl₂ crystallizing in the tetragonal space group I4₁/a with a = 3186.7(2); c = 1311.2(1) pm and Z = 8. If the reaction of the educts is carried out without THF, however under exposure to air the compound [(n‐Bu)₄N]₂[{(H₂O)Cl₄Re≡N}₂PtCl₂] ( 1b ) is obtained as red trigonal crystals with the space group R3 and a = 3628.3(3), c = 1231.4(1) pm and Z = 9. In the centrosymmetric complex anions [{(L)Cl₄Re≡N}₂PtCl₂]^2— a linear PtCl₂moiety is connected in a trans arrangement with two complex fragments [(L)Cl₄Re≡N]^— via asymmetric nitrido bridges Re≡dqN‐Pt. For Pt^II such results a square‐planar coordination PtCl₂N₂. The linear nitrido bridges are characterized by distances Re‐N = 169.5 pm and Pt‐N = 188.8 pm ( 1a ), respectively, Re‐N = 165.6 pm and Pt‐N = 194.1 pm ( 1b ). By the reaction of [(n‐Bu)₄N][ReNCl₄] with PtCl₄ in CH₂Cl₂ platinum is reduced forming the heterometallic Re^VI/Pt^II complex, [(n‐Bu)₄N]₂[(H₂O)Cl₄Re≡N‐PtCl(μ‐Cl)]₂ ( 2 ). It crystallizes in the monoclinic space group C2/c with a = 2012.9(1); b = 1109.0(2); c = 2687.4(4) pm; β = 111.65(1)° and Z = 4. In the central unit ClPt(μ‐Cl)₂PtCl of the anionic complex [(H₂O)Cl₄Re≡N‐PtCl(μ‐Cl)]₂^2— with the symmetry C₂ the coordination of the Pt atoms is completed by two nitrido bridges Re≡N‐Pt to nitrido complex fragments [(H₂O)Cl₄Re≡N] ^— forming a square‐planar arrangement for the Pt atoms. The distances in the linear nitrido bridges are Re‐N = 165.9 pm and Pt‐N = 190.1 pm.     

Reduction of a Cerium(III) Siloxide Complex To Afford a Quadruple‐Decker Arene‐Bridged Cerium(II) Sandwich

Organometallic multi‐decker sandwich complexes containing f‐elements remain rare, despite their attractive magnetic and electronic properties. The reduction of the Ce^III siloxide complex, [KCeL₄] ( 1 ; L=OSi(OtBu)₃), with excess potassium in a THF/toluene mixture afforded a quadruple‐decker arene‐bridged complex, [K(2.2.2‐crypt)]₂[{(KL₃Ce)(μ‐η⁶:η⁶‐C₇H₈)}₂Ce] ( 3 ). The structure of 3 features a [Ce(C₇H₈)₂] sandwich capped by [KL₃Ce] moieties with a linear arrangement of the Ce ions. Structural parameters, UV/Vis/NIR data, and DFT studies indicate the presence of Ce^II ions involved in δ bonding between the Ce cations and toluene dianions. Complex 3 is a rare lanthanide multi‐decker complex and the first containing non‐classical divalent lanthanide ions. Moreover, oxidation of 1 by AgOTf (OTf=O₃SCF₃) yielded the Ce^IV complex, [CeL₄] ( 2 ), showing that siloxide ligands can stabilize Ce in three oxidation states.     

Synthese und Struktur der Komplexe [(n‐Bu)4N]2[{(THF)Cl4Re≡N}2PdCl2], [Ph4P]2[(THF)Cl4Re≡N‐PdCl(μ‐Cl)]2 und [(n‐Bu)4N]2[Pd3Cl8]

Synthesis and Crystal Structure of the Complexes [(n‐Bu)₄N]₂[{(THF)Cl₄Re≡N}₂PdCl₂], [Ph₄P]₂[(THF)Cl₄Re≡N‐PdCl(μ‐Cl)]₂ and [(n‐Bu)₄N]₂[Pd₃Cl₈] The threenuclear complex [(n‐Bu)₄N]₂[{(THF)Cl₄Re≡N}₂ PdCl₂] ( 1 ) is obtained in THF by the reaction of PdCl₂(NCC₆H₅)₂ with [(n‐Bu)₄N][ReNCl₄] in the molar ration 1:2. It forms orange crystals with the composition 1· THF crystallizing in the monoclinic space group C2/c with a = 2973.3(2); b = 1486.63(7); c = 1662.67(8)pm; β = 120.036(5)° and Z = 4. If the reaction is carried out with PdCl₂ instead of PdCl₂(NCC₆H₅)₂, orange crystals of hitherto unknown [(n‐Bu)₄N]₂[Pd₃Cl₈] ( 3 ) are obtained besides some crystals of 1· THF. 3 crystallizes with the space group P1¯ and a = 1141.50(8), b = 1401.2(1), c = 1665.9(1)pm, α = 67.529(8)°, β = 81.960(9)°, γ = 66.813(8)° and Z = 2. In the centrosymmetric complex anion [{(THF)Cl₄Re≡N}₂PdCl₂]^2— a linear PdCl₂ moiety is connected in trans arrangement with two complex fragments [(THF)Cl₄Re≡N]^— via asymmetric nitrido bridges Re≡N‐Pd. For Pd(II) thereby results a square‐planar coordination PdCl₂N₂. The linear nitrido bridges are characterized by distances Re‐N = 163.8(7)pm and Pd‐N = 194.1(7)pm. The crystal structure of 3 contains two symmetry independent, planar complexes [Pd₃Cl₈]^2— with the symmetry 1¯, in which the Pd atoms are connected by slightly asymmetric chloro bridges. By the reaction of equimolar amounts of [Ph₄P][ReNCl₄] and PdCl₂(NCC₆H₅)₂ in THF brown crystals of the heterometallic complex, [Ph₄P]₂[(THF)Cl₄Re≡N‐PdCl(μ‐Cl)]₂ ( 2 ) result. 2 crystallizes in the monoclinic space group P2₁/n with a = 979.55(9); b = 2221.5(1); c = 1523.1(2)pm; β = 100.33(1)° and Z = 2. In the central unit ClPd(μ‐Cl)₂PdCl of the centrosymmetric anionic complex [(THF)Cl₄Re≡N‐PdCl(μ‐Cl)]₂^2— the coordination of the Pd atoms is completed by two nitrido bridges Re≡N‐Pd to nitrido complex fragments [(THF)Cl₄Re≡N]^— forming a square‐planar arrangement for Pd(II). The distances in the linear nitrido bridges are Re‐N = 163.8(9)pm and Pd‐N = 191.5(9)pm.     

Synthesis,Structure, and Reactivity of a Tetranuclear Cerium(IV) Oxo Cluster Supported by the Kläui Tripodal Ligand [Co(η5‐C5H5){P(O)(OEt)2}3]−

A tetranuclear Ce^IV oxo cluster compound containing the Kläui tripodal ligand [Co(η⁵‐C₅H₅){P(O)(OEt)₂}₃]^? (L_OEt^?) has been synthesized and its reactions with H₂O₂, CO₂, NO, and Brønsted acids have been studied. The treatment of [Ce(L_OEt)(NO₃)₃] with Et₄NOH in acetonitrile afforded the tetranuclear Ce^IV oxo cluster [Ce₄(L_OEt)₄O₇H₂] ( 1 ) containing an adamantane‐like {Ce₄(μ₂‐O)₆} core with a μ₄‐oxo ligand at the center. The reaction of 1 with H₂O₂ resulted in the formation of the peroxo cluster [Ce₄(L_OEt)₄(μ₄‐O)(μ₂‐O₂)₄(μ₂‐OH)₂] ( 2 ). The treatment of 1 with CO₂ and NO led to isolation of [Ce(L_OEt)₂(CO₃)] and [Ce(L_OEt)(NO₃)₃], respectively. The protonation of 1 with HCl, ROH (R=2,4,6‐trichlorophenyl), and Ph₃SiOH yielded [Ce(L_OEt)Cl₃] ( 3 ), [Ce(L_OEt)(OR)₃] ( 4 ), and [Ce(L_OEt)(OSiPh₃)₃] ( 5 ), respectively. The chloride ligands in 3 are labile and can be abstracted by silver(I) salts. The treatment of 3 with AgOTs (OTs^?=tosylate) and Ag₂O afforded [Ce(L_OEt)(OTs)₃] ( 6 ) and 1 , respectively. The electrochemistry of the Ce‐L_OEt complexes has been studied by using cyclic voltammetry. The crystal structures of complexes 1 – 5 have been determined.     

Cerium‐Complex‐Catalyzed Oxidation of Arylmethanols under Atmospheric Pressure of Dioxygen and Its Mechanism through a Side‐On μ‐Peroxo Dicerium(IV) Complex

A new Ce^IV complex [Ce{NH(CH₂CH₂N=CHC₆H₂‐3,5‐(tBu)₂‐2‐O)₂}(NO₃)₂] ( 1 ), bearing a dianionic pentadentate ligand with an N₃O₂ donor set, has been prepared by treating (NH₄)₂Ce(NO₃)₆ with the sodium salt of ligand L1 . Complex 1 in the presence of TEMPO and 4 Å molecular sieves (MS4 A) has been found to serve as a catalyst for the oxidation of arylmethanols using dioxygen as an oxidant. We propose an oxidation mechanism based on the isolation and reactivity study of a trivalent cerium complex [Ce{NH(CH₂CH₂N=CHC₆H₂‐3,5‐(tBu)₂‐2‐O)₂}(NO₃)(THF)] ( 2 ), its side‐on μ‐O₂ adduct [Ce{NH(CH₂CH₂N=CHC₆H₂‐3,5‐(tBu)₂‐2‐O)₂}(NO₃)]₂(μ‐η²:η²‐O₂) ( 3 ), and the hydroxo‐bridged Ce^IV complex [Ce{NH(CH₂CH₂N=CHC₆H₂‐3,5‐(tBu)₂‐2‐O)₂}(NO₃)]₂(μ‐OH)₂ ( 4 ) as key intermediates during the catalytic cycle. Complex 2 was synthesized by reduction of 1 with 2,5‐dimethyl‐1,4‐bis(trimethylsilyl)‐1,4‐diazacyclohexadiene. Bubbling O₂ into a solution of 2 resulted in formation of the peroxo complex 3 . This provides the first direct evidence for cerium‐catalyzed oxidation of alcohols under an O₂ atmosphere.     

Stereochemistry of Formation of the β‐Ring of Lycopene: Biosynthesis of (1R,1′R)‐β,β‐[16,16,16,16′,16′,16′‐2H6]Carotene from [16,16,16,16′,16′,16′‐2H6]Lycopene in Flavobacterium R 1560

Incubation of deuteriated precursors in cultures of Flavobacterium produced specifically deuteriated carotenoids. Analysis of these led to several conclusions: i) Lycopene is a direct precursor of β,β‐carotene. ii) Its terminal Me groups retain their integrity during cyclization: there is a stereospecific folding of the 1,5‐diene. The Me(16,16′) groups of lycopene become the Me(16,16′) of β,β‐carotene. Consequently, the folding must follow the C₂(E,E) mode. iii) Incorporation of deuterium was sufficiently extensive to permit CD measurements on the isolated β,β‐carotene, allowing its centers of chirality to be assigned as (1S,1′S). iv) The same chirality resulted from incorporation of [²H₃]mevalonate into zeaxanthin. The syntheses of specifically deuteriated [²H₃]GPP, [²H₃]FPP, and [²H₃]GG are described.     

Monomeric Magnesium and Calcium Complexes containing the Rigid,Dianionic 1, 2‐Bis[(2, 5‐di‐tert‐butylphenyl)imino]acenaphthene (dtb‐BIAN) and 1, 2‐Bis[(2‐biphenyl)imino]acenaphthene (bph‐BIAN) Ligands

The new rigid bidentate nitrogen ligands 1, 2‐bis[(2, 5‐di‐tert‐butylphenyl)imino]acenaphthene ( 1 ) (dtb‐BIAN) and 1, 2‐bis[(2‐biphenyl)imino]acenaphthene ( 2 ) (bph‐BIAN) have been synthesized by condensation of 1, 2‐acenaphthylenedione with 2, 5‐di‐tert‐butylaniline and 2‐aminobiphenyl, respectively. Reduction of 1 and 2 with magnesium and calcium results in the formation of the monomeric metal complexes [(dtb‐BIAN)Mg(THF)₂] ( 3 ), [(bph‐BIAN)Mg(DME)₂] ( 4 ), and [(bph‐BIAN)Ca(THF)₃] ( 5 ). Compounds 1 — 5 have been characterized by C/H analyses, IR, ¹H NMR, and ¹³C NMR spectra, the structures of 2 , 3 , and 5 have been estimated by single crystal X‐ray diffraction.     

Catalytic Water Oxidation by Ruthenium(II) Quaterpyridine (qpy) Complexes: Evidence for Ruthenium(III) qpy‐N,N′′′‐dioxide as the Real Catalysts

Polypyridyl and related ligands have been widely used for the development of water oxidation catalysts. Supposedly these ligands are oxidation‐resistant and can stabilize high‐oxidation‐state intermediates. In this work a series of ruthenium(II) complexes [Ru(qpy)(L)₂]²⁺ (qpy=2,2′:6′,2′′:6′′,2′′′‐quaterpyridine; L=substituted pyridine) have been synthesized and found to catalyze Ce^IV‐driven water oxidation, with turnover numbers of up to 2100. However, these ruthenium complexes are found to function only as precatalysts; first, they have to be oxidized to the qpy‐N,N′′′‐dioxide (ONNO) complexes [Ru(ONNO)(L)₂]³⁺ which are the real catalysts for water oxidation.     

N,N,N′,N′-Tetramethylethylendiamin-di(tert-butyl)aluminium-Kationen — Molekülstruktur des [(Me3C)2Al · TMEDA]⊕[(Me3C)2AlBr2]⊖

(N,N,N′,N′ -tetramethylethylendiamine) di(tert-butyl)aluminium Cations — Molecular Structure of [(Me₃C)₂Al(TMEDA)]^⊕[(Me₃C)₂AlBr₂]^? Dimeric di(tert-butyl)aluminium halides (Me₃C)₂AlX (X = Cl, Br) react with N,N,N′,N′ -tetramethylethylendiamine (TMEDA) to give three compounds: the salt-like [(Me₃C)₂Al(TMEDA)]^⊕[(Me₃C)₂AlX₂]^? 1 , characterized by crystal structure determination, and [(Me₃C)₂Al(TMEDA)]^⊕X^? 3 both with chelating amine, and the more covalent, pentane soluble (Me₃C)₂AlX(TMEDA) 2 with TMEDA bound by only one nitrogen atom. The reaction resembles the symmetrical and unsymmetrical cleavage of diborane(6). 3 (X = Cl) is also formed by treatment of 1 with boiling n-hexane in the presence of TMEDA over a period of 24 hours, while for X = Br the more covalent 2 is the main product under similar conditions. In solution 2 decomposes slowly yielding different products in dependency of the solvent: in benzene 3 and in n-pentane 1 are formed.     

Bis(arylimido) Molybdenum(VI) Amidinate and Guanidinate Complexes; Molecular Structures of [(ArN)2MoMe{N(Cy)C[N(i‐Pr)2]N(Cy)}] (Ar = 2,6‐i‐Pr2C6H3; Cy = Cyclohexyl) and [(2,6‐i‐Pr2C6H3N)2MoCl2] · [NH=C(C6H5)CH(SiMe3)2]

The reaction of [(ArN)₂MoCl₂] · DME (Ar = 2,6‐i‐Pr₂C₆H₃) ( 1 ) with lithium amidinates or guanidinates resulted in molybdenum(VI) complexes [(ArN)₂MoCl{N(R¹)C(R²)N(R¹)}] (R¹ = Cy (cyclohexyl), R² = Me ( 2 ); R¹ = Cy, R² = N(i‐Pr)₂ ( 3 ); R¹ = Cy, R² = N(SiMe₃)₂ ( 4 ); R¹ = SiMe₃, R² = C₆H₅ ( 5 )) with five coordinated molybdenum atoms. Methylation of these compounds was exemplified by the reactions of 2 and 3 with MeLi affording the corresponding methylates [(ArN)₂MoMe{N(R¹)C(R²)N(R¹)}] (R¹ = Cy, R² = Me ( 6 ); R¹ = Cy, R² = N(i‐Pr)₂ ( 7 )). The analogous reaction of 1 with bulky [N(SiMe₃)C(C₆H₅)C(SiMe₃)₂]Li · THF did not give the corresponding metathesis product, but a Schiff base adduct [(ArN)₂MoCl₂] · [NH=C(C₆H₅)CH(SiMe₃)₂] ( 8 ) in low yield. The molecular structures of 7 and 8 are established by the X‐ray single crystal structural analysis.     

Synthesis and Structure of a New Vanadium(IV)‐Cadmium(II) Compound with the Nitrilotriacetate Ligand: {(NH4)2[(VIVO)2(μ2‐O)(nta)2Cd(H2O)2]·H2O}n

A polymeric V^IV‐Cd compound, {(NH₄)₂[(V^IVO)₂(μ₂‐O)(nta)₂Cd(H₂O)₂]·H₂O}_n (H₃nta = nitrilotriacetic acid), has been prepared and characterized by single‐crystal X‐ray diffraction. The compound crystallizes in the monoclinic space group C2/c with a = 17.3760(2) Å, b = 8.0488(1) Å, c = 17.3380(2) Å, β = 107.9690(10)°, V = 2306.55(5) ų, Z = 4, and R₁ = 0.0303 for 1958 observed reflections. The structure exhibits a heterometallic three‐dimensional network formed by polymeric [(V^IVO)₂(μ₂‐O)(nta)₂Cd(H₂O)₂]^2? anions.     

Homo‐ and Heterovalent Polynuclear Cerium and Cerium/Manganese Aggregates

Reactions of Ce^III(NO₃)₃?6 H₂O or (NH₄)₂[Ce^IV(NO₃)₆] with Mn‐containing starting materials result in seven novel polynuclear Ce or Ce/Mn complexes with pivalato (^tBuCO ) and, in most cases, auxiliary N,O‐ or N,O,O‐donor ligands. With nuclearities ranging from 6–14, the compounds present aesthetically pleasing structures. Complexes [Ce^IV₆(μ₃‐O)₄(μ₃‐OH)₄(μ‐O₂C^tBu)₁₂] ( 1 ), [Ce^IV₆Mn^III₄(μ₄‐O)₄(μ₃‐O)₄(O₂C^tBu)₁₂(ea)₄(OAc)₄]?4 H₂O?4 MeCN (ea^?=2‐aminoethanolato; 2 ), [Ce^IV₆Mn^III₈(μ₄‐O)₄(μ₃‐O)₈(pye)₄(O₂C^tBu)₁₈]₂[Ce^IV₆(μ₃‐O)₄(μ₃‐OH)₄(O₂C^tBu)₁₀(NO₃)₄] [Ce^III(NO₃)₅(H₂O)]?21 MeCN (pye^?=pyridine‐2‐ethanolato; 3 ), and [Ce^IV₆Ce^III₂Mn^III₂(μ₄‐O)₄(μ₃‐O)₄(^tbdea)₂(O₂C^tBu)₁₂(NO₃)₂(OAc)₂]?4 CH₂Cl₂ (^tbdea^2?=2,2′‐(tert‐butylimino]bis[ethanolato]; 4 ) all contain structures based on an octahedral {Ce^IV₆(μ₃‐O)₈} core, in which many of the O‐atoms are either protonated to give (μ₃‐OH)^? hydroxo ligands or coordinate to further metal centers (Mn^III or Ce^III) to give interstitial (μ₄‐O)^2? oxo bridges. The decanuclear complex [Ce^IV₈Ce^IIIMn^III(μ₄‐O)₃(μ₃‐O)₃(μ₃‐OH)₂(μ‐OH)(bdea)₄(O₂C^tBu)_9.5(NO₃)_3.5(OAc)₂]?1.5 MeCN (bdea^2?=2,2′‐(butylimino]bis[ethanolato]; 5 ) contains a rather compact Ce^IV₇ core with the Ce^III and Mn^III centers well‐separated from each other on the periphery. The aggregate in [Ce^IV₄Mn^IV₂(μ₃‐O)₄(bdea)₂(O₂C^tBu)₁₀(NO₃)₂]?4 MeCN ( 6 ) is based on a quasi‐planar {Mn^IV₂Ce^IV₄(μ₃‐O)₄} core made up of four edge‐sharing {Mn^IVCe^IV₂(μ₃‐O)} or {Ce^IV₃(μ₃‐O)} triangles. The structure of [Ce^IV₃Mn^IV₄Mn^III(μ₄‐O)₂(μ₃‐O)₇(O₂C^tBu)₁₂(NO₃)(furan)]?6 H₂O ( 7 ?6 H₂O) can be considered as {Mn^IV₂Ce^IV₂O₄} and distorted {Mn^IV₂Mn^IIICe^IVO₄} cubane units linked through a central (μ₄‐O) bridge. The Ce₆Mn₈ equals the highest nuclearity yet reported for a heterometallic Ce/Mn aggregate. In contrast to most of the previously reported heterometallic Ce/Mn systems, which contain only Ce^IV and either Mn^IV or Mn^III, some of the aggregates presented here show mixed valency, either Mn^IV/Mn^III (see 7 ) or Ce^IV/Ce^III (see 4 and 5 ). Interestingly, some of the compounds, including the heterovalent Ce^IV/Ce^III 4 , could be obtained from either Ce^III(NO₃)₃?6 H₂O or (NH₄)₂[Ce^IV(NO₃)₆] as starting material.     

Reaktion von (R,R)‐(N,N′)‐Diisopropylcyclohexyl‐1,2‐diamin mit Me2MCl (M = Ga,In)

Reaction of (R,R)‐(N,N′)‐Diisopropylcyclohexyl‐1,2‐diamine with Me₂MCl (M = Ga, In) (R,R)‐(N,N′)‐Diisopropylcyclohexyl‐1,2‐diamine (H₂L) was reacted with Me₂GaCl and Me₂InCl in boiling toluene, respectively. In both cases the salt [Me₂M(H₂L)][Me₂MCl₂] [M = Ga ( 1 ), In ( 2 )] was formed. 1 and 2 were characterized by NMR and vibrational spectroscopy. In addition, an X‐ray structure determination was applied on 2 . According to the spectroscopical and structural findings 1 and 2 consist of cations [Me₂M(H₂L)]⁺ and anions [Me₂MCl₂]^?.     

The 7‐bromo derivative of 2‐amino‐2′‐deoxytubercidin fluorinated at the sugar moiety

The title compound, 2,4‐diamino‐5‐bromo‐7‐(2‐deoxy‐2‐fluoro‐β‐d ‐arabinofuranosyl)‐7H‐pyrrolo[2,3‐d]pyrimidine, C₁₁H₁₃BrFN₅O₃, shows two conformations of the exocyclic C4′—C5′ bond, with the torsion angle γ (O5′—C5′—C4′—C3′) being 170.1 (3)° for conformer 1 (occupancy 0.69) and 60.7 (7)° for conformer 2 (occupancy 0.31). The N‐glycosylic bond exhibits an anti conformation, with χ = −114.8 (4)°. The sugar pucker is N‐type (C3′‐endo; ³T₄), with P = 23.3 (4)° and τ_m = 36.5 (2)°. The compound forms a three‐dimensional network that is stabilized by several intermolecular hydrogen bonds (N—H...O, O—H...N and N—H...Br).     

Darstellung,Charakterisierung und Reaktionsverhalten von Natrium‐ und Kaliumhydridosilylamiden R2(H)Si—N(M)R′ (M = Na,K) — Kristallstruktur von [(Me3C)2(H)Si—N(K)SiMe3]2·THF

Preparation, Characterization and Reaction Behaviour of Sodium and Potassium Hydridosilylamides R₂(H)Si—N(M)R′ (M = Na, K) — Crystal Structure of [(Me₃C)₂(H)Si—N(K)SiMe₃]₂ · THF The alkali metal hydridosilylamides R₂(H)Si—N(M)R′ 1a‐Na — 1d—Na and 1a‐K — 1d‐K ( a : R = Me, R′ = CMe₃; b : R = Me, R′ = SiMe₃; c : R = Me, R′ = Si(H)Me₂; d : R = CMe₃, R′= SiMe₃) have been prepared by reaction of the corresponding hydridosilylamines 1a — 1d with alkali metal M (M = Na, K) in presence of styrene or with alkali metal hydrides MH (M = Na, K). With NaNH₂ in toluene Me₂(H)Si—NHCMe₃ ( 1a ) reacted not under metalation but under nucleophilic substitution of the H(Si) atom to give Me₂(NaNH)Si—NHCMe₃ ( 5 ). In the reaction of Me₂(H)Si—NHSiMe₃ ( 1b ) with NaNH₂ intoluene a mixture of Me₂(NaNH)Si—NHSiMe₃ and Me₂(H)Si—N(Na)SiMe₃ ( 1b‐Na ) was obtained. The hydridosilylamides have been characterized spectroscopically. The spectroscopic data of these amides and of the corresponding lithium derivatives are discussed. The ²⁹Si‐NMR‐chemical shifts and the ²⁹Si—¹H coupling constants of homologous alkali metal hydridosilylamides R₂(H)Si—N(M)R′ (M = Li, Na, K) are depending on the alkali metal. With increasing of the ionic character of the M—N bond M = K > Na > Li the ²⁹Si‐NMR‐signals are shifted upfield and the ²⁹Si—¹H coupling constants except for compounds (Me₃C)(H)Si—N(M)SiMe₃ are decreased. The reaction behaviour of the amides 1a‐Na — 1c‐Na and 1a‐K — 1c‐K was investigated toward chlorotrimethylsilane in tetrahydrofuran (THF) and in n‐pentane. In THF the amides produced just like the analogous lithium amides the corresponding N‐silylation products Me₂(H)Si—N(SiMe₃)R′ ( 2a — 2c ) in high yields. The reaction of the sodium amides with chlorotrimethylsilane in nonpolar solvent n‐pentane produced from 1a‐Na the cyclodisilazane [Me₂Si—NCMe₃]₂ ( 8a ), from 1b‐Na and 1‐Na mixtures of cyclodisilazane [Me₂Si—NR′]₂ ( 8b , 8c ) and N‐silylation product 2b , 2c . In contrast to 1b‐Na and 1c‐Na and to the analogous lithium amides the reaction of 1b‐K and 1c‐K with chlorotrimethylsilane afforded the N‐silylation products Me₂(H)Si—N(SiMe₃)R′ ( 2b , 2c ) in high yields. The amide [(Me₃C)₂(H)Si—N(K)SiMe₃]₂·THF ( 9 ) crystallizes in the space group C2/c with Z = 4. The central part of the molecule is a planar four‐membered K₂N₂ ring. One potassium atom is coordinated by two nitrogen atoms and the other one by two nitrogen atoms and one oxygen atom. Furthermore K···H(Si) and K···CH₃ contacts exist in 9 . The K—N distances in the K₂N₂ ring differ marginally.     

Reliable Chemical Synthesis of Oligoribonucleotides (RNA) with 2′‐O‐[(Triisopropylsilyl)oxy]methyl(2′‐O‐tom)‐Protected Phosphoramidites

A method for the introduction of the 2′‐O‐[(triisopropylsilyl)oxy]methyl (=tom) group into N‐acetylated, 5′‐O‐dimethoxytritylated ribonucleosides is presented. The corresponding 2′‐O‐tom‐protected phosphoramidite building blocks were obtained in pure form and were successfully employed for the routine synthesis of oligoribonucleotides on DNA synthesizers. Under DNA coupling conditions (2.5 min coupling time for a 1.5‐μmol synthesis scale) and with 5‐(benzylthio)‐1H‐tetrazole (BTT) as activator, 2′‐O‐tom‐protected phosphoramidites exhibited average coupling yields >99.4%. The combination of N‐acetyl and 2′‐O‐tom protecting groups allowed a reliable and complete two‐step deprotection, first with MeNH₂ in EtOH/H₂O and then with Bu₄NF in THF, without concomitant destruction of the product RNA sequences.     

Synthesis,crystal structure and magnetic properties of (acetato‐κ2O,O′)bis(5,5′‐dimethyl‐2,2′‐bipyridine‐κ2N,N′)nickel(II) perchlorate monohydrate

The title hydrated ionic complex, [Ni(CH₃COO)(C₁₂H₁₂N₂)₂]ClO₄·H₂O or [Ni(ac)(5,5′‐dmbpy)₂]ClO₄·H₂O (where 5,5′‐dmbpy is 5,5′‐dimethyl‐2,2′‐bipyridine and ac is acetate), (1), was isolated as violet crystals from the aqueous ethanolic nickel acetate–5,5′‐dmbpy–KClO₄ system. Within the complex cation, the Ni^II atom is hexacoordinated by two chelating 5,5′‐dmbpy ligands and one chelating ac ligand. The mean Ni—N and Ni—O bond lengths are 2.0628 (17) and 2.1341 (15) Å, respectively. The water solvent molecule is disordered over two partially occupied positions and links two complex cations and two perchlorate anions into hydrogen‐bonded centrosymmetric dimers, which are further connected by π–π interactions. The magnetic properties of (1) at low temperatures are governed by the action of single‐ion anisotropy, D, which arises from the reduced local symmetry of the cis‐NiO₂N₄ chromophore. The fitting of the variable‐temperature magnetic data (2–300 K) gives g_iso = 2.134 and D/hc = 3.13 cm⁻¹.     

A Novel Coordination Polymer, [Ag4^1 （bpdc）（H2bpdc）（Hbpdc）2]n （bpdc = 2,2＇-bipyridyl-3,3＇-dicarboxylate）： Coordination Models of bpdc Ligands

A novel coordination polymer, [Ag₄ppdc)(H₂bpdc)(Hbpdc)₂] (bpdc = 2,2′‐bipyridyl‐3,3′‐dicarboxylate), was hydrothermally synthesized at 403 K and structurally characterized by single crystal X‐ray diffraction analysis. The compound crystalizes in the monoclinic space group C2/c with a=1.9516(4) nm, b=1.9503(4) nm. c=1.2566(3) nm, and β=112.48(3)°. In the two‐dimensional crystal structure, Ag^I center is coordinated, in a scarce coordination environment, double‐capped tetrahedron, by one bpdc ligand to form N‐Ag‐N chelate bond via two pyridyl N atoms, and other two bpdc ligands to form two O‐Ag‐O chelate bonds, respectively, via two carboxyl O atoms. The bpdc ligands are present in one non‐protonated form, bpdc, and two protonated forms, Hbpdc and H2bpdc, which all act as μ3‐ligand in a hexadentate fashion (N, N′; O, O′; O, O′) to coordinate with three Ag centers, respectively, through the three chelate bonds. This coordinated fashion of bpdc ligand is first found in the title compound. W‐Us‐NIR reflectance spectroscopy study revealed insulator nature for the crystal with an optical energy gap of 3.1 eV.