An opened route to 1,3-dimethylenecyclobutanes via sequential ruthenium-catalyzed [2 + 2] cycloaddition of allenyl boronate and palladium Suzuki coupling

The regioselective head-to-head [2 + 2] cyclodimerization of allenyl boronate catalyzed by the ruthenium catalyst [Cp*RuCl(COD)] leads to a novel diboronated 1,3-dimethylenecyclobutane. Consecutive palladium-catalyzed C-C couplings open a route to novel disubstituted 1,3-dimethylenecyclobutane species. The X-ray crystalline structure of the phenyl-substituted 1,3-dimethylenecyclobutane is provided.     

Materials analysis using confocal Raman microscopy

The recent development of Raman microscopes with high optical throughput and very sensitive CCD cameras has led to Raman spectroscopy again competing effectively with FTIR methods for materials analysis. Modern Raman instruments, designed to operate confocally without serious alignment or energy trade-off problems, allow depth profiling of optically transparent polymers and polymer matrices to be routinely obtained with a spatial resolution of 1–2 μm. The use of such an instrument is illustrated by describing recent work on polymeric material problems including, 1 The distribution and redistribution of small molecules in polymeric matrices. 2 The monitoring of adhesion primer diffusion at a polymer/silica interface. 3 The determination of the extent of interdiffusion and interaction at a polymer/polymer interface. 4 A comparison of confocal and micotoming approaches to polymer laminate analysis. The range of possible applications is increasing rapidly. It is clear that Raman microscopy will become a very important tool for future materials analysis, both in the polymer area and many other areas.     

The Kynurenine Pathway and Kynurenine 3-Monooxygenase Inhibitors

Under normal physiological conditions, the kynurenine pathway (KP) plays a critical role in generating cellular energy and catabolizing tryptophan. Under inflammatory conditions, however, there is an upregulation of the KP enzymes, particularly kynurenine 3-monooxygenase (KMO). KMO has garnered much attention due to its production of toxic metabolites that have been implicated in many diseases and disorders. With many of these illnesses having an inadequate or modest treatment, there exists a need to develop KMO inhibitors that reduce the production of these toxic metabolites. Though prior efforts to find an appropriate KMO inhibitor were unpromising, the development of a KMO crystal structure has provided the opportunity for a rational structure-based design in the development of inhibitors. Therefore, the purpose of this review is to describe the kynurenine pathway, the kynurenine 3-monooxygenase enzyme, and KMO inhibitors and their potential candidacy for clinical use.     

Microstructures and structural properties of sol-gel silica foams

Silica xerogels were synthesized and annealed at 1000 degrees C for different durations to yield stable silica materials. The samples were prepared through base-catalyzed hydrolysis and condensation of tetramethyl orthosilicate in methanol. After aging and drying steps, clear and solid xerogels exhibiting a narrow pore size distribution were achieved. The annealing treatment of these xerogels was performed at 1000 degrees C and proved in the present study to lead to a monolithic glass when a progressive heat-treatment procedure was employed to attain 1000 degrees C. In addition to the expected glass, silica foams and ordered phases were observed when the samples were instantaneously heat-treated at 1000 degrees C. Raman spectra of the foamed materials exhibit the classical features of amorphous silica, whereas transmission electronic microscopy pictures reveal the presence of crystallized domains within the vitreous matrix. These crystallites are prone to nucleation and growth processes, which jeopardize the believed stability of the silica foam. The assessment of the hydroxyl content by IR spectroscopy reveals the role played by the latter polycondensation of silanols. The occurrence of foaming process was thus found to result from two competitive phenomena occurring at 1000 degrees C: evacuation of water-related species and viscous sintering.     

Charge Effects in PCP Pincer Complexes of NiII bearing Phosphinite and Imidazol(i)ophosphine Coordinating Jaws: From Synthesis to Catalysis through Bonding Analysis

This contribution reports on a new family of Ni^II pincer complexes featuring phosphinite and functional imidazolyl arms. The proligands ^RPIMC^HOP^R′ react at room temperature with Ni^II precursors to give the corresponding complexes [(^RPIMCOP^R′)NiBr], where ^RPIMCOP^R=κ^P,κ^C,κ^P‐{2‐(R′₂PO),6‐(R₂PC₃H₂N₂)C₆H₃}, R=iPr, R′=iPr ( 3 b , 84 %) or Ph ( 3 c , 45 %). Selective N‐methylation of the imidazole imine moiety in 3 b by MeOTf (OTf=OSO₂CF₃) gave the corresponding imidazoliophosphine [(^iPrPIMIOCOP^iPr)NiBr][OTf], 4 b , in 89 % yield (^iPrPIMIOCOP^iPr=κ^P,κ^C,κ^P‐{2‐(iPr₂PO),6‐(iPr₂PC₄H₅N₂)C₆H₃}). Treating 4 b with NaOEt led to the NHC derivative [(NHCCOP^iPr)NiBr], 5 b , in 47 % yield (NHCCOP^iPr=κ^P,κ^C,κ^C‐{2‐(iPr₂PO),6‐(C₄H₅N₂)C₆H₃)}). The bromo derivatives 3–5 were then treated with AgOTf in acetonitrile to give the corresponding cationic species [(^RPIMCOP^R)Ni(MeCN)][OTf] [R=Ph, 6 a (89 %) or iPr, 6 b (90 %)], [(^RPIMIOCOP^R)Ni(MeCN)][OTf]₂ [R=Ph, 7 a (79 %) or iPr, 7 b (88 %)], and [(NHCCOP^R)Ni(MeCN)][OTf] [R=Ph, 8 a (85 %) or iPr, 8 b (84 %)]. All new complexes have been characterized by NMR and IR spectroscopy, whereas 3 b , 3 c , 5 b , 6 b , and 8 a were also subjected to X‐ray diffraction studies. The acetonitrile adducts 6 – 8 were further studied by using various theoretical analysis tools. In the presence of excess nitrile and amine, the cationic acetonitrile adducts 6 – 8 catalyze hydroamination of nitriles to give unsymmetrical amidines with catalytic turnover numbers of up to 95.     

Two‐Coordinate Iron(I) Complex [Fe{N(SiMe3)2}2]−: Synthesis,Properties, and Redox Activity

First‐row two‐coordinate complexes are attracting much interest. Herein, we report the high‐yield isolation of the linear two‐coordinate iron(I) complex salt [K(L)][Fe{N(SiMe₃)₂}₂] (L=18‐crown‐6 or crypt‐222) through the reduction of either [Fe{N(SiMe₃)₂}₂] or its three‐coordinate phosphine adduct [Fe{N(SiMe₃)₂}₂(PCy₃)]. Detailed characterization is gained through X‐ray diffraction, variable‐temperature NMR spectroscopy, and magnetic susceptibility studies. One‐ and two‐electron oxidation through reaction with I₂ is further found to afford the corresponding iodo iron(II) and diiodo iron(III) complexes.     

Study of the luminescent and magnetic properties of a series of heterodinuclear [Zn(II)Ln(III)] complexes

Herein, we report the synthesis, structural investigation, and magnetic and photophysical properties of a series of 13 [Zn(II)Ln(III)] heterodinuclear complexes, which have been obtained employing a Schiff-base compartmental ligand derived from o-vanillin [H(2)valpn = 1,3-propanediylbis(2-iminomethylene-6-methoxy-phenol)]. The complexes have been synthesized starting from the [Zn(valpn)(H(2)O)] mononuclear compound and the corresponding lanthanide nitrates. The crystallographic investigation indicated two structural types: the first one, [Zn(H(2)O)(valpn)Ln(III)(O(2)NO)(3)], contains 10-coordinated Ln(III) ions, while in the second one, [Zn(ONO(2))(valpn)Ln(III)(H(2)O)(O(2)NO)(2)]·2H(2)O, the rare earth ions are nine-coordinated. The Zn(II) ions always display a square-pyramidal geometry. The first structural type encompasses the larger Ln ions (4f(0)-4f(9)), while the second is found for the smaller ions (4f(8)-4f(11)). The dysprosium derivative crystallizes in both forms. Luminescence studies for the heterodinuclear compounds containing Nd(III), Sm(III), Tb(III), Dy(III), and Yb(III) revealed that the [Zn(valpn)(H(2)O)] moiety acts as an antenna. The magnetic properties for the paramagnetic [Zn(II)Ln(III)] complexes have been investigated.     

Expanding the azaspiro[3.3]heptane family: synthesis of novel highly functionalized building blocks

The preparation of versatile azaspiro[3.3]heptanes carrying multiple exit vectors is disclosed. Expedient synthetic routes enable the straightforward access to these novel modules that are expected to have significance in drug discovery and design.     

A Remarkable Solvent Effect on the Nuclearity of Neutral Titanium(IV)‐Based Helicate Assemblies

The spontaneous self‐assembly of a neutral circular trinuclear Ti^IV‐based helicate is described through the reaction of titanium(IV) isopropoxide with a rationally designed tetraphenolic ligand. The trimeric ring helicate was obtained after diffusion of n‐pentane into a solution with dichloromethane. The circular helicate has been characterized by using single‐crystal X‐ray diffraction study, ¹³C CP‐MAS NMR and ¹H NMR DOSY solution spectroscopic, and positive electrospray ionization mass‐spectrometric analysis. These analytical data were compared with those obtained from a previously reported double‐stranded helicate that crystallizes in toluene. The trimeric ring was unstable in a pure solution with dichloromethane and transformed into the double‐stranded helicate. Thermodynamic analysis by means of the PACHA software revealed that formation of the double‐stranded helicates was characterized by ΔH(toluene)=?30 kJ mol^?1 and ΔS(toluene)=+357 J K^?1 mol^?1, whereas these values were ΔH(CH₂Cl₂)=?75 kJ mol^?1 and ΔS(CH₂Cl₂)=?37 J K^?1 mol^?1 for the ring helicate. The transformation of the ring helicate into the double‐stranded helicate was a strongly endothermic process characterized by ΔH(CH₂Cl₂)=+127 kJ mol^?1 and ΔH(n‐pentane)=+644 kJ mol^?1 associated with a large positive entropy change ΔS=+1115 J K^?1?mol^?1. Consequently, the instability of the ring helicate in pure dichloromethane was attributed to the rather high dielectric constant and dipole moment of dichloromethane relative to n‐pentane. Suggestions for increasing the stability of the ring helicate are given.     

Crucial role of the counteranion on the templation of metallomacrocycles and a 3D network: synthesis,characterization, and structural analysis

Two novel supramolecular architectures, [[Ag(2)L(1)(2)][X](2)] with X = CF(3)SO(3)(-) (2a) or X = NO(3)(-) (2b) and [[AgL(1)(2)][X]](n) with X = BF(4)(-) (3), were constructed by self-assembly and obtained in quantitative yields, using AgX as a building block and L(1) as the bridging ligand (L(1) = 1,3-bis(benzimidazol-1-ylmethyl)benzene). The X-ray molecular structures of 2a and 3 are reported. Complex 2a was identified as a metallomacrocycle in which one ligating triflate anion is coordinated to each of the two unsaturated Ag(I) ions. 2a crystallizes in monoclinic unit cell P2(1)/n with a = 9.728(6) A, b = 17.303(4) A, c = 13.268(3) A, beta = 92.52(4) degrees, V = 2231(2) A(3), and Z = 2. Remarkably, the X-ray structure of 2a shows a layered network structure consisting of infinite metallomacrocycles held together through pi-pi interactions between benzimidazole rings. In dramatic contrast, the product 3 prepared from AgBF(4) and L(1) lacks metal-counterion bonding, leading to a supramolecular 3D network with the following three outstanding features: (i) in one dimension, metallomacrocycles containing two Ag centers and two bridging ligands form infinite, double-stranded chains; (ii) neighboring chains are arranged by two distinct pi-pi interactions, one between substituted benzene rings and the other between benzimidazole rings, leading to a 3D structure; (iii) cavities within the 3D network contain BF(4)(-) counteranions. 3 crystallizes in monoclinic unit cell C2/c with a = 25.33(3) A, b = 11.655(6) A, c = 18.466(8) A, beta = 123.00(8) degrees, V = 4572(8) A(3), and Z = 4. Interestingly, electrospray mass spectroscopy suggests in either case that the identified elemental subunit [AgL(1)(2)](+) is the key building block which self-assembles and subsequent anion templation provides either the macrocycles 2a, b or the inorganic polymer 3. Remarkably, in dichloromethane solvent ligand-to-metal stoichiometries of 2:1 in 3 and 1:1 in 2a, b are obtained even with excess ligand, showing the power of metal-anion interactions in determining the overall supramolecular structure. Anion metathesis, showing supramolecular structural rearrangements from 2a to 2b and more spectacularly from 3 to 2b, smoothly occurred. The crucial effect and the nature of coordinating counteranions (BF(4)(-), CF(3)SO(3)(-), NO(3)(-)) on the supermolecule design are presented and discussed.