Polymerization of Racemic 2,2′-Dialkyl-Sila[1]ferrocenophanes: DFT‑Assisted Polymer Analysis by ²⁹Si NMR Spectroscopy Using Model Compounds

The described research aimed at the preparation of racemic, C2 symmetric sila[1]ferrocenophanes with alkyl groups in 2,2′-positions to complement their known enantiopure counterparts. As the synthetic approach, the well-known Ugi amine chemistry was chosen to introduce planar chirality into the ferrocene framework. The challenge in this multistep process is the separation of a rac and meso mixture of diols obtained through the reduction of 1,1′-dialkanoylferrocenes by LiAlH4 or NaBH4. From the three tested alkanoyl groups, only one led to a significant excess of the rac diol, which could be separated by crystallizations and converted to rac-2,2′-diisobutyl-dimethylsila[1]ferrocene. Thermal ring-opening polymerization of this new monomer gave a poly(ferrocenylsilane) that consists of two types of diads, as revealed by two sets of peaks in its 29Si NMR spectrum centered at −5.66 and −7.74 ppm. 29Si NMR chemical shifts could be predicted with density functional theory (DFT) methods for planar-chiral bis(ferrocenyl)dimethylsilanes that were used to model these meso and racemo diads of the polymer. These calculations realistically predict that silicon atoms of racemo diads are higher shielded than those of meso diads. Surprisingly, the 29Si NMR peaks of both diads are split into a set of peaks, revealing a sensitivity of δ values beyond diads

Polymerization of Racemic 2,2′-Dialkyl-Sila[1]ferrocenophanes: DFT‑Assisted Polymer Analysis by ²⁹Si NMR Spectroscopy Using Model Compounds

The described research aimed at the preparation of racemic, C2 symmetric sila[1]ferrocenophanes with alkyl groups in 2,2′-positions to complement their known enantiopure counterparts. As the synthetic approach, the well-known Ugi amine chemistry was chosen to introduce planar chirality into the ferrocene framework. The challenge in this multistep process is the separation of a rac and meso mixture of diols obtained through the reduction of 1,1′-dialkanoylferrocenes by LiAlH4 or NaBH4. From the three tested alkanoyl groups, only one led to a significant excess of the rac diol, which could be separated by crystallizations and converted to rac-2,2′-diisobutyl-dimethylsila[1]ferrocene. Thermal ring-opening polymerization of this new monomer gave a poly(ferrocenylsilane) that consists of two types of diads, as revealed by two sets of peaks in its 29Si NMR spectrum centered at −5.66 and −7.74 ppm. 29Si NMR chemical shifts could be predicted with density functional theory (DFT) methods for planar-chiral bis(ferrocenyl)dimethylsilanes that were used to model these meso and racemo diads of the polymer. These calculations realistically predict that silicon atoms of racemo diads are higher shielded than those of meso diads. Surprisingly, the 29Si NMR peaks of both diads are split into a set of peaks, revealing a sensitivity of δ values beyond diads

Olefin Metathesis and Stereoselective Ring-Opening Metathesis Polymerization with Neutral and Cationic Molybdenum(VI) Imido and Tungsten(VI) Oxo Alkylidene Complexes Containing N‑Chelating N‑Heterocyclic Carbenes

Neutral and cationic molybdenum(VI) imido and tungsten(VI) oxo alkylidene complexes containing an N-chelating N-heterocyclic carbene, [Mo(N-2,6-Me2-C6H3)I(3-(2-(2,6-diisopropylphen-1-ylamido)phen-1-yl)-1-methylimidazol-2-ylidene)(CHCMe2Ph)] (Mo1), [Mo(N-2-tBu-C6H4)I(3-(2-(2,6-diisopropylphen-1-ylamido)phen-1-yl)-1-methylimidazol-2-ylidene)(CHCMe2Ph)] (Mo2), [Mo(N-2,6-Me2-C6H3)(3-(2-(2,6-diisopropylphen-1-ylamido)phen-1-yl)-1-methylimidazol-2-ylidene)(CHCMe2Ph)(L)][B(ArF)4] (Mo3: L = none, Mo4: L = CH3CN), [Mo(N-2-tBu-C6H4)(3-(2-(2,6-diisopropylphen-1-ylamido)phen-1-yl)-1-methylimidazol-2-ylidene)(CHCMe2Ph)][B(ArF)4] (Mo5), [W(O)(B(C6F5)3)Cl(1-methyl-3′-(2-N-(2,6-iPr2-C6H4)-1-C6H4)imidazol-2-ylidene)(CHCMe2Ph)] (W1), and [W(O)(1-methyl-3′-(2-N-(2,6-iPr2-C6H4)-1-C6H4)imidazol-2-ylidene)(CHCMe2Ph)][B(ArF)4] (W2) have been prepared. Catalysts Mo2, Mo4, W1, and W2 were characterized by single-crystal X-ray analysis. Catalysts Mo4 and W2 were benchmarked in homo-, cross-, ring-closing metathesis (RCM) as well as in ring-opening cross-metathesis (ROCM) reactions. In the ring-opening metathesis polymerization (ROMP) of endo,exo-2,3-dicarbomethoxynorborn-5-ene (DCMNBE), methyl-N-(S)-(−)-α-methylbenzyl-2-azabicyclo[2.2.1]hept-5-ene-3-carboxylate, exo-N-(R)-(+)-α-methylbenzyl-5-norbornene-2,3-dicarboximide, and 2,3-bis((menthyloxy)carbonyl)norbornadiene Mo4 and W2 offered access to trans-isotactic and cis-syndiotactic polymers, respectively

Olefin Metathesis and Stereoselective Ring-Opening Metathesis Polymerization with Neutral and Cationic Molybdenum(VI) Imido and Tungsten(VI) Oxo Alkylidene Complexes Containing N‑Chelating N‑Heterocyclic Carbenes

Neutral and cationic molybdenum(VI) imido and tungsten(VI) oxo alkylidene complexes containing an N-chelating N-heterocyclic carbene, [Mo(N-2,6-Me2-C6H3)I(3-(2-(2,6-diisopropylphen-1-ylamido)phen-1-yl)-1-methylimidazol-2-ylidene)(CHCMe2Ph)] (Mo1), [Mo(N-2-tBu-C6H4)I(3-(2-(2,6-diisopropylphen-1-ylamido)phen-1-yl)-1-methylimidazol-2-ylidene)(CHCMe2Ph)] (Mo2), [Mo(N-2,6-Me2-C6H3)(3-(2-(2,6-diisopropylphen-1-ylamido)phen-1-yl)-1-methylimidazol-2-ylidene)(CHCMe2Ph)(L)][B(ArF)4] (Mo3: L = none, Mo4: L = CH3CN), [Mo(N-2-tBu-C6H4)(3-(2-(2,6-diisopropylphen-1-ylamido)phen-1-yl)-1-methylimidazol-2-ylidene)(CHCMe2Ph)][B(ArF)4] (Mo5), [W(O)(B(C6F5)3)Cl(1-methyl-3′-(2-N-(2,6-iPr2-C6H4)-1-C6H4)imidazol-2-ylidene)(CHCMe2Ph)] (W1), and [W(O)(1-methyl-3′-(2-N-(2,6-iPr2-C6H4)-1-C6H4)imidazol-2-ylidene)(CHCMe2Ph)][B(ArF)4] (W2) have been prepared. Catalysts Mo2, Mo4, W1, and W2 were characterized by single-crystal X-ray analysis. Catalysts Mo4 and W2 were benchmarked in homo-, cross-, ring-closing metathesis (RCM) as well as in ring-opening cross-metathesis (ROCM) reactions. In the ring-opening metathesis polymerization (ROMP) of endo,exo-2,3-dicarbomethoxynorborn-5-ene (DCMNBE), methyl-N-(S)-(−)-α-methylbenzyl-2-azabicyclo[2.2.1]hept-5-ene-3-carboxylate, exo-N-(R)-(+)-α-methylbenzyl-5-norbornene-2,3-dicarboximide, and 2,3-bis((menthyloxy)carbonyl)norbornadiene Mo4 and W2 offered access to trans-isotactic and cis-syndiotactic polymers, respectively

Hypoelectronic 8–11-Vertex Irida- and Rhodaboranes

A series of novel <i>isocloso</i>-diiridaboranes [(Cp*Ir)₂B₆H₆], <b>1</b>, <b>2</b>; [1,7-(Cp*Ir)₂B₈H₈], <b>4</b>; [1,4-(Cp*Ir)₂B₈H₈], <b>5</b>; [(Cp*Ir)₂B₉H₉], <b>8</b>; <i>isonido-</i>[(Cp*Ir)₂B₇H₇], <b>3</b>; and 10-vertex cluster [5,7-(Cp*Ir)₂B₈H₁₂], <b>6</b> (Cp* = η⁵-C₅Me₅) have been isolated and structurally characterized from the pyrolysis of [Cp*IrCl₂]₂ and BH₃·thf. On the other hand, the corresponding rhodium system afforded 10- and 11-vertices clusters [5-(Cp*Rh)­B₉H₁₃)], <b>7</b>, and [(Cp*Rh)₂B₉H₉], <b>9</b>, respectively. Clusters <b>1</b> and <b>2</b> are topological isomers. The geometry of <b>1</b> is dodecahedral, similar to that of its parent borane [B₈H₈]^2–, in which two of the [BH] vertices are replaced by two [Cp*Ir] fragments. The geometry of <b>2</b> can be derived from a nine-vertex tricapped trigonal prism by removing one of the capped vertices. Compounds <b>4</b> and <b>5</b> are 10-vertex <i>isocloso</i> clusters based on a 10-vertex bicapped square antiprism structure. The only difference between them is the presence of a metal–metal bond in <b>5</b>. The solid-state structures of <b>8</b> and <b>9</b> attain an 11-vertex geometry in which a unique six-membered B₆H₆ moiety is bonded to the metal center. In addition, quantum-chemical calculations have been used to provide further insight into the electronic structure and stability of the clusters. All the compounds have been characterized by IR and ¹H, ¹¹B, and ¹³C NMR spectroscopy in solution, and the solid-state structures were established by X-ray crystallographic analysis

BRAIN Journal - Suicide: Neurochemical Approaches

<div><i>Abstract</i></div><div><br></div><div>Despite the devastating effect of suicide on numerous lives, there is still a dearth of knowledge concerning its neurochemical aspects. There is increasing evidence that brain-derived neurotrophic factor (BDNF) and Nerve growth factor (NGF) are involved in the pathophysiology and treatment of depression through binding and activating their cognate receptors trk B and trk A respectively. The present study was performed to examine whether the expression profiles of BDNF and/or trk B as well as NGF and/or trk A were altered in postmortem brain in subjects who commit suicide and whether these alterations were associated with specific psychopathologic conditions. These studies were performed in hippocampus obtained 21 suicide subjects and 19 non-psychiatric control subjects. The protein and mRNA levels of BDNF, trk B and NGF, trk A were determined with Sandwich ELISA, Western Blot and RT PCR respectively. Given the importance of BDNF and NGF along with their cognate receptors in mediating physiological functions, including cell survival and synaptic plasticity, our findings of reduced expression of BDNF, Trk B and NGF, Trk A in both protein and mRNA levels of postmortem brain in suicide subjects suggest that these molecules may play an important role in the pathophysiological aspects of suicidal behavior.</div><div><br></div><div><b>Find more at:</b></div><div><b>https://www.edusoft.ro/brain/index.php/brain/article/view/425</b><br></div

Synthesis, Chemistry, and Electronic Structures of Group 9 Metallaboranes

Dimetallaoctaborane­(12) of Ru, Co, and Rh have been well-characterized by a range of spectroscopic techniques and X-ray diffraction studies. Thus, reinvestigation of the Ir-system became of interest. As a result, a slight modification in the reaction conditions enabled us to isolate the missing Ir analogue of octaborane(12), [(Cp*Ir)₂B₆H₁₀], <b>1</b>. Compound <b>1</b> adapts a geometry similar to that of its parent octaborane(12) and Ru, Co, and Rh analogues. In [M₂B₆H_10+<i>x</i>]­(M = Ru, <i>x</i> = 2; M = Co and Rh, <i>x</i> = 0), there exist two M–H–B protons. However, a significant difference observed in [(Cp*Ir)₂B₆H₁₀] is the presence of two Ir–H instead of Ir–H–B protons that eventually controls the reactivity of this molecule. For example, unlike [M₂B₆H₁₀]­(M = Co or Rh), the Ir-analogue does not react with metal carbonyl compounds or [Au­(PPh₃)­Cl]. Along with <b>1</b>, a <i>closo</i> trimetallic 8-vertex iridaborane [(Cp*Ir)₃B₅H₄Cl], <b>2</b> was also isolated. Additionally, from another reaction, 12-vertex <i>closo</i> iridaboranes [(Cp*Ir)₂B₁₀H_<i>y</i>(OH)_<i>z</i>], <b>3a</b> and <b>3b</b> (<b>3a</b>: <i>y</i> = 12, <i>z</i> = 0; <b>3b</b>: <i>y</i> = 8, <i>z</i> = 2), have also been isolated. Further, density functional theory calculations were performed to gain useful insight into the structure and stability of these compounds

Interconversion Rates and Reactivity of <i>Syn</i>- and <i>Anti</i>-rotamers of Neutral and Cationic Molybdenum and Tungsten Imido Alkylidene <i>N</i>‑Heterocyclic Carbene Complexes

The interconversion rates of the syn- and anti-isomers of the neutral molybdenum and tungsten imido alkylidene N-heterocyclic carbene (NHC) complexes of the general formula [M(NR)(CHCMe2R′)(NHC)(OR″)2] (M = Mo, W; R = adamantyl, 2,6-Me2-C6H3, 2,6-iPr2–C6H3, 2,6-Cl2–C6H3, 2-tBu-C6H4; NHC = 1,3-diisopropylimidazol-2-ylidene (IiPr), 1,3-dimethylimidazol-2-ylidene (IMe), 1,3-dicyclohexylimidazol-2-ylidene (ICy), and 1,3-dimesitylimidazol-2-ylidene (IMes); R′ = Me, Ph; R″ = CMe(CF3)2, CMe2(CF3), C(CF3)3, C6F5, SO2CF3) and of the cationic complex [Mo(N-2,6-Me2-C6H3)(CHCMe2Ph)(IMes)(SO3CF3)(CD3CN)+ B(3,5-(CF3)2C6H3)4–] were determined by irradiating solutions of the catalysts with 366 nm UV light followed by recording the back-isomerization of the anti- to the syn-isomer. Both the rate of anti to syn and syn to anti interconversion, ka/s and ks/a were found to be orders of magnitude lower than in tetracoordinated, neutral Schrock catalysts of the general formula [Mo(NR)(CHCMe2R′)(OR″)2]. Accordingly, the values for the Gibbs free energy of the transition state, ΔG‡, are significantly higher for both neutral and cationic molybdenum and tungsten imido alkylidene NHC complexes than for Schrock catalysts. NMR investigations strongly suggest that these higher ΔG‡ values are attributable to dissociation of an anionic ligand from a neutral pentacoordinated catalyst that precedes interconversion. As with Schrock catalysts, the anti-isomer proved to be the more reactive isomer, in both ring-opening metathesis polymerization and ring-closing metathesis (RCM) reactions, allowing for higher productivities, expressed as turnover numbers, in RCM