The novel nitrosyl-bridged complex W2Cp2(μ-P t Bu2)(μ-κ:η-NO)(CO)(NO)(BAr4) Ar = 3,5-C6H3(CF3)2 was prepared in a multistep procedure starting from the hydride W2Cp2(μ-H)(μ-P t Bu2)(CO)4 and ...involving the new complexes W2Cp2(μ-P t Bu2)(CO)4(BF4), W2Cp2(μ-P t Bu2)(CO)2(NO)2(BAr4), and W2(μ-κ:η5-C5H4)Cp(μ-P t Bu2)(CO)(NO)2 as intermediates, which follow from reactions with HBF4·OEt2, NO, and Me3NO·2H2O, respectively. The nitrosyl-bridged cation easily added chloride upon reaction with N(PPh3)2Cl, with concomitant NO rearrangement into the terminal coordination mode, to give W2ClCp2(μ-P t Bu2)(CO)(NO)2, and underwent N–O and W–W bond cleavages upon the addition of CN t Bu to give the mononuclear phosphinoimido complex WCp(NP t Bu2)(CN t Bu)2(BAr4). Another N–O bond cleavage was induced upon photochemical decarbonylation at 243 K, which gave the oxo- and phosphinito-bridged nitrido complex W2Cp2(N)(μ-O)(μ-OP t Bu2)(NO)(BAr4), likely resulting from a N–O bond cleavage step following decarbonylation.
The reaction of amido-substituted stannylenes with phospha-Wittig reagents (Me3PPR) results in release of hexamethyldisilazane and tethering of the resulting −CH2PMe2PR fragment to the tin center to ...give P-donor stabilized stannylenes featuring four-membered Sn,C,P,P heterocycles. Through systematic increases in steric loading, the structures of these systems in the solid state can be tuned, leading to successive P–P bond lengthening and Sn–P contraction and, in the most encumbered case, to complete P-to-Sn transfer of the phosphinidene fragment. The resulting stannaphosphene features a polar SnP double bond as determined by structural and computational studies. The reversibility of phosphinidene transfer can be established by solution phase measurements and reactivity studies.
Four halopyridinium salts, 3-chloro- and 3-bromopyridinium chlorides and bromides, have been successfully cocrystallized with two ditopic perfluorinated iodobenzenes, 1,4-diiodotetrafluorobenzene and ...1,2-diiodotetrafluorobenzene. These halogen bond donor molecules were chosen because the different positionings of halogen bond donor atoms can lead to different supramolecular architectures. In this work, we present insight into the halogen bond acceptor potential of chloride and bromide ions, as well as the halogen bond donor potential of chlorine and bromine atoms substituted on the pyridinium ring when combined with the expectedly very strong hydrogen bonds between halopyridinium ions and free halogenide anions. A series of eight cocrystals were obtained in which three pairs of isostructural cocrystals were formed. Dominant interactions in the obtained cocrystals were charge-assisted hydrogen bonds between halopyridinium cations and halogenide ions as well as halogen bonds between halogen atoms on the pyridinium ring and halogenide ions.
Chiral cis-MoO2(acac)2 racemizes via four pathways that agree with and extend upon Muetterties’ topological analysis for dynamic MX2(chel)2 complexes. Textbook Ray–Dutt and Bailar twists are the ...least favored with barriers of 27.5 and 28.7 kcal/mol, respectively. Rotating both acac ligands of the Bailar structure by 90° gives the lower Conte–Hippler twist (20.0 kcal/mol), which represents a valley–ridge inflection that invokes the trans isomer. The most favorable is a new twist that was found by 90° rotation of only one acac ligand of the Bailar structure. The gas-phase barrier of 17.4 kcal/mol for this Dhimba–Muller–Lammertsma twist further decreases upon inclusion of the effects of solvents to 16.3 kcal/mol (benzene), 16.2 kcal/mol (toluene), and 15.4 kcal/mol (chloroform), which are in excellent agreement with the reported experimental values.
A dual catalytic
manifold that enables site-selective functionalization
of unactivated
sp
3
C–O
bonds in cyclic acetals with aryl and alkyl halides is reported. The
reaction is triggered by an ...appropriate σ*–p orbital
overlap prior to
sp
3
C–O
cleavage, thus highlighting the importance of conformational flexibility
in both reactivity and site selectivity. The protocol is characterized
by its excellent chemoselectivity profile, thus offering new vistas
for activating strong
σ sp
3
C–O linkages.
The absence of residual solvent in metal precursors can be of key importance for the successful preparation of metal complexes or materials. Herein, we describe methods for the quantitation of ...residual coordinated tetrahydrofuran (THF) that binds to FeN(SiMe3)22, a commonly used iron synthon, when prepared according to common literature procedures. A simple method for quantitation of the amount of residual coordinated THF using 1H NMR spectroscopy is highlighted. Finally, a detailed synthetic procedure is described for the synthesis of THF-free FeN(SiMe3)22.
C–H bond activation at cationic (η5-C5Me5)Ir(PMe2Ar′) centers is described, where PMe2Ar′ are the terphenyl phosphine ligands PMe2ArXyl 2 and PMe2ArDipp 2. Different pathways are defined for the ...conversion of the five-coordinate complexes (η5-C5Me5)IrCl(PMe2Ar′)+, 2(Xyl)+ and 2(Dipp)+ , into the corresponding pseudoallyls 3(Xyl)+ and 3(Dipp)+ . In the absence of an external Brønsted base, electrophilic, remote ζ C–H activation takes place, for which the participation of dicationic species, (η5-C5Me5)Ir(PMe2Ar′)2+, is proposed. When NEt3 is present, the PMe2ArDipp 2 system is shown to proceed via 4(Dipp)+ as an intermediate en route to the thermodynamic, isomeric product 3(Dipp)+ . This complex interconversion involves a non-innocent C5Me5 ligand, which participates in C–H and C–C bond formation and cleavage. Remarkably, the conversion of 4(Dipp)+ to 3(Dipp)+ also proceeds in the solid state.
Network Routing: Algorithms, Protocols, and Architectures, Second Edition explores network routing and how it can be broadly categorized into Internet routing, PSTN routing, and telecommunication ...transport network routing. The book systematically considers these routing paradigms, as well as their interoperability, discussing how algorithms, protocols, analysis, and operational deployment impact these approaches and addressing both macro-state and micro-state in routing. Readers will learn about the evolution of network routing, the role of IP and E.164 addressing and traffic engineering in routing, the impact on router and switching architectures and their design, deployment of network routing protocols, and lessons learned from implementation and operational experience. Numerous real-world examples bring the material alive.
Bridges the gap between theory and practice in network routing, including the fine points of implementation and operational experienceRouting in a multitude of technologies discussed in practical detail, including, IP/MPLS, PSTN, and optical networkingPresents routing protocols such as OSPF, IS-IS, BGP in detailDetails various router and switch architecturesDiscusses algorithms on IP-lookup and packet classificationAccessible to a wide audience with a vendor-neutral approach
An enantiopure ligand with four bidentate metal-binding sites and four (S)-carbon stereocenters self-assembles with octahedral ZnII or CoII to produce O-symmetric M8L6 coordination cages. The Λ- or ...Δ-handedness of the metal centers forming the corners of these cages is determined by the solvent environment: the same (S)-ligand produces one diastereomer, (S)24-Λ8-M8L6, in acetonitrile but another with opposite metal-center handedness, (S)24-Δ8-M8L6, in nitromethane. Van ’t Hoff analysis revealed the Δ stereochemical configuration to be entropically favored but enthalpically disfavored, consistent with a loosening of the coordination sphere and an increase in conformational freedom following Λ-to-Δ transition. The binding of 4,4′-dipyridyl naphthalenediimide and tetrapyridyl Zn-porphyrin guests did not interfere with the solvent-driven stereoselectivity of self-assembly, suggesting applications where either a Λ- or Δ-handed framework may enable chiral separations or catalysis.
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