Manganese‐σ‐Borane Complexes from Dihaloboranes

The hydride complex K[(η⁵‐C₅H₅)Mn(CO)₂H] reacted with a range of dihalo(organyl)boranes X₂BR (X = Cl, Br; R = tBu,Mes, Ferrocenyl) to give the corresponding borane complexes[(η⁵‐C₅H₅)Mn(CO)₂(HB(X)R)]., The presence of a hydride in bridging position between manganese and boron was deduced from ¹¹B decoupled ¹H NMR spectra. Additionally, the structure of the tert‐butyl borane complex was confirmed by single‐crystal X‐ray diffraction.     

Catalytic Asymmetric Epoxidation of α,β‐Unsaturated Esters with Chiral Yttrium–Biaryldiol Complexes

The full details of the asymmetric epoxidation of α,β‐unsaturated esters catalyzed by yttrium complexes with biaryldiol ligands are described. An yttrium–biphenyldiol catalyst, generated from Y(OiPr)₃–biphenyldiol ligand–triphenylarsine oxide (1:1:1), is suitable for the epoxidation of various α,β‐unsaturated esters. With this catalyst, β‐aryl α,β‐unsaturated esters gave high enantioselectivities and good yields (≤99 % ee). The reactivity of this catalyst is good, and the catalyst loading could be decreased to as little as 0.5–2 mol % (the turnover number was up to 116), while high enantiomeric excesses were maintained. For β‐alkyl α,β‐unsaturated esters, an yttrium–binol catalyst, generated from Y(OiPr)₃–binol ligand–triphenylphosphine oxide (1:1:2), gave the best enantioselectivities (≤97 % ee). The utility of the epoxidation reaction was demonstrated in an efficient synthesis of (?)‐ragaglitazar, a potential antidiabetes agent.     

Syntheses,Structures, and Polymorphism of β‐Diketonato Complexes – Co(thd)3

Oxidation of Co(thd)₂ dissolved in different solvents has been investigated in air and oxygen atmosphere. In oxygen atmosphere and at the boiling point of the solvents this treatment leads to oxidation of Co^II to Co^III, but also to degradation of some of the thd ligands and formation of a new mixed‐ligand complex. Three pure‐cultivated crystalline Co(thd)₃ phases are reported: 1 (room‐temperature phase), 2 (low‐temperature phase), and 3 (metastable phase) and in addition there exists an amorphous Co(thd)₃ phase ( 4 ) with approximate composition Co(thd)₃·xH(thd); x = 0.06. Reaction of metal(II) oxides (MO, M = Mn, Fe, and Co) with H(thd) under air or O₂ atmosphere is an easy direct route to M(thd)₃ complexes. Structure determinations are reported for Co(thd)₃ ( 1 – 3 ) based on single‐crystal X‐ray diffraction data. Modification 1 crystallizes in space group with a = b = 18.8100(10), c = 18.815(2) Å at 295 K; R(wR2) = 0.180, modification 2 in space group C2/c with a = 28.007(12), b = 18.482(8), c = 21.356(9) Å, β = 97.999(5)° at 100 K; R(wR2) =0.211, and modification 3 in space group Pnma with a = 19.2394(15), b = 18.8795(15), c = 10.7808(8) Å at 100 K; R(wR2) = 0.193. The molecular structures of 1 – 3 all comprise a central Co atom octahedrally co‐ordinated by the ketonato O atoms of three thd ligands. The transformation between modifications 1 and 2 is of a fully reversible second‐order character. Modifications 1 and 3 are, on the other hand, related by a quasi‐reversible cycle. Heat treatment (specifically sublimation) of 1 leads to 3 whereas re‐crystallization or prolonged storage at room temperature is required to regenerate 1 . Co(thd)₃ has sufficient thermal stability to permit sublimation without degradation. The various forms of Co(thd)₃ are all diamagnetic, viz. a confirmation of the Co^III valence state.     

Determination of Enantiomer Purity of β‐ and γ‐Amino Acids by NMR Analysis of Diastereoisomeric Palladium Complexes

Like α‐amino acids, β‐ and γ‐amino acids form spirobicyclic complexes (see 2 and 3 ) by reaction with the chiral di‐μ‐chlorobis{2‐[1‐dimethylamino‐ϰN)‐ethyl]phenyl‐ϰC}dipalladium complexes 1 under basic conditions (Scheme 1 and X‐ray structures in Fig. 1). The diastereoisomeric complexes formed with mixtures of enantiomers of either the amino acids or the dichloro‐dipalladium complexes give rise to marked chemical‐shift differences in the ¹H‐ and ¹³C‐NMR spectra (Figs. 2 – 4) to allow determination of the enantiomer purities. A simple procedure is described by which β‐ and γ‐amino acids (which may be generated in situ from Boc‐ or Fmoc‐protected precursors) are converted to the Pd complexes and subjected to NMR measurements. The effects of solvent, temperature, and variation of the aryl group in the chiral derivatizing Pd reagent are described (Figs. 4 and 5). The methyl esters of β‐amino acids can also be employed, forming diastereoisomeric chloro[(amino‐ϰN)aryl‐ϰC][(amino‐ϰN)alkanoate]palladium complexes 6 for determining enantiomer ratios (Scheme 6). The new method has great scope, as demonstrated for β²‐, β³‐, β^2,3‐, β^2,2,3‐, γ²‐, γ³‐, γ⁴‐, and γ^2,3,4‐amino acid derivatives.     

Dinuclear Rare‐Earth Metal Alkyl Complexes Supported by Indolyl Ligands in μ‐η2:η1:η1 Hapticities and their High Catalytic Activity for Isoprene 1,4‐cis‐Polymerization

Two series of new dinuclear rare‐earth metal alkyl complexes supported by indolyl ligands in novel μ‐η²:η¹:η¹ hapticities are synthesized and characterized. Treatment of [RE(CH₂SiMe₃)₃(thf)₂] with 1 equivalent of 3‐(tBuN?CH)C₈H₅NH ( L₁ ) in THF gives the dinuclear rare‐earth metal alkyl complexes trans‐[(μ‐η²:η¹:η¹‐3‐{tBuNCH(CH₂SiMe₃)}Ind)RE(thf)(CH₂SiMe₃)]₂ (Ind=indolyl, RE=Y, Dy, or Yb) in good yields. In the process, the indole unit of L₁ is deprotonated by the metal alkyl species and the imino C?N group is transferred to the amido group by alkyl CH₂SiMe₃ insertion, affording a new dianionic ligand that bridges two metal alkyl units in μ‐η²:η¹:η¹ bonding modes, forming the dinuclear rare‐earth metal alkyl complexes. When L₁ is reduced to 3‐(tBuNHCH₂)C₈H₅NH ( L₂ ), the reaction of [Yb(CH₂SiMe₃)₃(thf)₂] with 1 equivalent of L₂ in THF, interestingly, generated the trans‐[(μ‐η²:η¹:η¹‐3‐{tBuNCH₂}Ind)Yb(thf)(CH₂SiMe₃)]₂ (major) and cis‐[(μ‐η²:η¹:η¹‐3‐{tBuNCH₂}Ind)Yb(thf)(CH₂SiMe₃)]₂ (minor) complexes. The catalytic activities of these dinuclear rare‐earth metal alkyl complexes for isoprene polymerization were investigated; the yttrium and dysprosium complexes exhibited high catalytic activities and high regio‐ and stereoselectivities for isoprene 1,4‐cis‐polymerization.     

Increasing the π–π Interactions in Trinuclear NiII3 Triplesalophen Complexes

The new triplesalophen ligand H₆kruse^Br was synthesized as a variation of the triplesalophen ligands H₆baron^R by replacing a phenyl by a methyl group at the terminal ketimine in order to allow closer contacts of trinuclear complexes due to less steric hindrance by the smaller methyl group. The ligand H₆kruse^Br was used to synthesize the trinuclear complex [(kruse^Br)Ni^II₃], which is insoluble in organic solvents despite the coordinating solvent pyridine. Recrystallization from pyridine results in the complex [(kruse^Br){Ni₂(Ni(py)₂)}], which was characterized by single‐crystal X‐ray diffraction. Two Ni^II ions are four‐coordinate by the salophen‐like subunits while the third Ni^II ion is six‐coordinate by two additional pyridine donors. The analysis of the molecular and crystal structure in comparison to that of Ni^II₃ complexes of (baron^R)^6– reveals that the methyl group in [(kruse^Br){Ni₂(Ni(py)₂)}] results in less ligand folding and in closer contact distance of two Ni^II₃ complexes by π–π interactions of 3.2 Å. This indicates that trinuclear complexes of H₆kruse^Br are more suitable than complexes of H₆baron^R as molecular building blocks for the anticipated synthesis of nonanuclear single‐molecule magnets.     

On the Reactivity of Platina‐β‐diketones – Synthesis and Characterization of Acylplatinum(II) Complexes

The platina‐β‐diketones [Pt₂{(COR)₂H}₂(μ‐Cl)₂] ( 1 , R = Me a , Et b ) react with phosphines L in a molar ratio of 1 : 4 through cleavage of acetaldehyde to give acylplatinum(II) complexes trans‐[Pt(COR)Cl(L)₂] ( 2 ) (R/L = Me/P(p‐FC₆H₄)₃ a , Me/P(p‐CH₂=CHC₆H₄)Ph₂ b , Me/P(n‐Bu)₃ c , Et/P(p‐MeOC₆H₄)₃ d ). 1 a reacts with Ph₂As(CH₂)₂PPh₂ (dadpe) in a molar ratio of 1 : 2 through cleavage of acetaldehyde yielding [Pt(COMe)Cl(dadpe)] ( 3 a ) (configuration index: SP‐4‐4) and [Pt(COMe)Cl(dadpe)] (configuration index: SP‐4‐2) ( 3 b ) in a ratio of about 9 : 1. All acyl complexes were characterized by ¹H, ¹³C and ³¹P NMR spectroscopy. The molecular structures of 2 a and 3 a were determined by single‐crystal X‐ray diffraction. The geometries at the platinum centers are close to square planar. In both complexes the plane of the acyl ligand is nearly perpendicular to the plane of the complex (88(2)° 2 a , 81.2(5)° 3 a ).     

Atomic integrals containing rrr with λ, μ, ν ≥ −2

In this paper, the efficient evaluation of the atomic integrals I =∫rrrrrre^{?αr1?βr2?γr3}dτ with one or two factors r is described. These integrals are necessary for a lower-bound calculation for Li-like systems using the method of variance minimization or Temple's formula. © 1993 John Wiley & Sons, Inc.     

Boryl‐Functionalized σ‐Alkynyl and Vinylidene Rhodium Complexes: Synthesis and Electronic Properties

The synthesis, reactivity, and properties of boryl‐functionalized σ‐alkynyl and vinylidene rhodium complexes such as trans‐[RhCl(?C?CHBMes₂)(PiPr₃)₂] and trans‐[Rh(C?CBMes₂)(IMe)(PiPr₃)₂] are reported. An equilibrium was found to exist between rhodium vinylidene complexes and the corresponding hydrido σ‐alkynyl complexes in solution. The complex trans‐[Rh(C?CBMes₂)(IMe)(PiPr₃)₂] (IMe=1,3‐dimethylimidazol‐2‐ylidene) was found to exhibit solvatochromism and can be quasireversibly oxidized and reduced electrochemically. Density functional calculations were performed to determine the reaction mechanism and to help rationalize the photophysical properties of trans‐[Rh(C?CBMes₂)(IMe)(PiPr₃)₂].     

Cationic Platinum(II) σ‐SiH Complexes in Carbon Dioxide Hydrosilation

The low‐electron‐count cationic platinum complex [Pt(ItBu’)(ItBu)][BAr^F], 1 , interacts with primary and secondary silanes to form the corresponding σ‐SiH complexes. According to DFT calculations, the most stable coordination mode is the uncommon η¹‐SiH. The reaction of 1 with Et₂SiH₂ leads to the X‐ray structurally characterized 14‐electron Pt^II species [Pt(SiEt₂H)(ItBu)₂][BAr^F], 2 , which is stabilized by an agostic interaction. Complexes 1 , 2 , and the hydride [Pt(H)(ItBu)₂][BAr^F], 3 , catalyze the hydrosilation of CO₂, leading to the exclusive formation of the corresponding silyl formates at room temperature.     

Transfer Hydrogenation of Ethyl Levulinate to γ‐Valerolactone Catalyzed by Iron Complexes

Conversion of biomass‐derived ethyl levulinate to γ‐valerolactone is realized by using homogeneous iron‐catalyzed transfer hydrogenation (CTH). By utilizing Casey's catalyst and cheap isopropanol as hydrogen source, γ‐valerolactone can be generated in 95% yield. Addition of catalytic amount of base is important to achieve good yield.     

Poly[(μ3‐1,1‐dioxo‐1,2‐benzoisothiazole‐3‐thiolato‐κ3N:S3:S3)silver(I)]

The centrosymmetric title compound, [Ag(C₇H₄NO₂S₂)]_n, consists of dinuclear units in which two thiosaccharinate anions each bridge two Ag atoms via an endocyclic N atom and an exocyclic S atom across a crystallographic centre of inversion midway between the Ag atoms. The dimeric units are connected via Ag—S_exo interactions to create two‐dimensional networks. The thiosaccharinate anions bridge in a μ₃‐S:S:N manner. The Ag...Ag distance can be considered a strong argentophilic interaction.     

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.     

Photoregulated Sol‐Gel Transition of Novel Azobenzene‐Functionalized Hydroxypropyl Methylcellulose and Its α‐Cyclodextrin Complexes

Summary: Novel azobenzene‐functionalized hydroxypropyl methylcellulose (AZO‐HPMC) polymers and their α‐cyclodextrin (α‐CD) complexes have been prepared. These polymers show interesting sol‐gel transition behavior in aqueous solutions. In the absence of α‐CD, the gelation temperature increases after UV irradiation, while in the presence of α‐CD, the gelation temperature decreases after UV irradiation. The difference in the gelation temperatures between the trans and cis samples of AZO‐HPMC opens a wide operating window for reversible regulation of the sol‐gel transition behavior by photoirradiation.

The UV‐induced cis/trans isomerism of azobenzene‐functionalized hydroxypropyl methylcellulose and its α‐cyclodextrin complexes.     

Stepwise Strategy to Cyclometallated PtII Complexes with N‐Heterocyclic Carbene Ligands: A Luminescence Study on New β‐Diketonate Complexes

The imidazolium salt 3‐methyl‐1‐(naphthalen‐2‐yl)‐1H‐imidazolium iodide ( 2 ) has been treated with silver(I) oxide and [{Pt(μ‐Cl)(η³‐2‐Me‐C₃H₄)}₂] (η³‐2‐Me‐C₃H₄=η³‐2‐methylallyl) to give the intermediate N‐heterocyclic carbene complex [PtCl(η³‐2‐Me‐C₃H₄)(H$\widehat{CC}$ *‐κC*)] ( 3 ) (H$\widehat{CC}$ *‐κC*=3‐methyl‐1‐(naphthalen‐2‐yl)‐1H‐imidazol‐2‐ylidene). Compound 3 undergoes regiospecific cyclometallation at the naphthyl ring of the NHC ligand to give the five‐membered platinacycle compound [{Pt(μ‐Cl)($\widehat{CC}$ *)}₂] ( 4 ). Chlorine abstraction from 4 with β‐diketonate Tl derivatives rendered the corresponding neutral compounds [Pt($\widehat{CC}$ *)(L‐O,O′)] {L=acac (HL=acetylacetone) 5 , phacac (HL=1,3‐diphenyl‐1,3‐propanedione) 6 , hfacac (HL=hexafluoroacetylacetone) 7 }. All of the compounds ( 3 – 7 ) were fully characterized by standard spectroscopic and analytical methods. X‐ray diffraction studies were performed on 5 – 7 , revealing short Pt?Pt and π–π interactions in the solid‐state structure. The influence of the R‐substituents of the β‐diketonate ligand on the photophysical properties and the use of the most efficient emitter, 5 , as phosphor converter has also been studied.     

固相β-环糊精包结物诱导7-羟基-2-甲氧基-2-甲基色满的不对称合成

研究了室温下间苯二酚和甲基乙烯基酮分别与β-环糊精（ β-CD）形成包结物后的几种不同固相反应,结果表明包结物A（间苯二酚/β-CD）与包结物B（甲基乙烯基酮/β-CD）反应能够很好地得到目的产物,产率及ee值分别为82.8%和78.4%;间苯二酚与包结物B反应仅得到低光学活性产物（ee值为19.5%）;包结物A与甲基乙烯基酮反应却没有得到手性目的产物。以熔点、X-粉末衍射、固相核磁碳谱及ROESY多种方法对所形成的包结物进行了表征,包结物中主客体的比例（1：1）通过¹H NMR (400 MHz)得以确定,文章对固相环加成反应的机制也进行了初步探讨。     

Base‐Catalyzed Highly Stereoselective Conversion of γ‐Hydroxy‐α,β‐acetylenic Esters to γ‐Acetoxy Dienoates

A convenient route with high stereo control to γ‐acetoxy dienoates is provided by the reaction of methyl propiolate with aldehydes in the presence of ZnEt₂ and N‐methylimidazole at room temperature, followed by the catalytic conversion of the resulting γ‐hydroxy‐α,β‐acetylenic esters with p‐N,N‐dimethylaminopyridine (DMAP) in acetic anhydride (see scheme).

     

Magnesium Complexes Bearing η2-Pyrazolato Ligands

Despite the small size of the magnesium ion , η²-bound pyrazolato ligands are found in complexes 1 – 3 . These complexes provide new insight into the design of volatile Group 2 metal complexes for use in chemical vapor deposition processes.     

Mixed‐Ligand Complexes of Copper(II) with α‐Hydroxycarboxylic Acids and 1,10‐Phenanthroline

Eight new two‐ligand complexes of copper(II) with 1,10‐phenanthroline and one of four different α‐hydroxy‐carboxylic acids (glycolic, lactic, mandelic and benzylic) were prepared. The complexes of general formula [Cu(HL)₂(phen)] · nH₂O (HL = monodeprotonated acid) ( 1 – 4 ) were characterized by elemental analysis, IR, electronic and EPR spectroscopy, magnetic measurements and thermo‐gravimetric analysis. The complexes of general formulae [Cu(HL)(phen)₂](HL) · H₂L · nSolv [ 1 a (HL = HGLYO^–, n = 1, Solv = MeCN) and 3 a (HL = HMANO^–, n = 0)] and [Cu(L)(phen)(OH₂)] · nH₂O [ 2 a (L = LACO^2–, n = 4) and 4 a (L = BENO^2–, n = 2)] were characterized by X‐ray diffractometry. In all these latter a pentacoordinated copper atom has a basically square pyramidal coordination polyhedron, the distortion of which towards a trigonal bipyramidal configuration has been evaluated in terms of the parameter τ. In 1 a and 3 a there are three forms of α‐hydroxycarboxylic acid: a monodentate monoanion, a monoanionic counterion, and a neutral molecule lying in the outer coordination sphere; in 2 a and 4 a the α‐hydroxycarboxylic acid is a bidentate dianion coordinating through carboxyl and hydroxyl oxygens.