NO Bond (no + bond)

Distribution by Scientific Domains

Selected Abstracts

Metal Nitrosyl Reactivity: Acetonitrile-Promoted Insertion of an Alkylidene into a Nitrosyl Ligand with Fission of the NO Bond

C. M. Frech Dr.
Abstract Treatment of the complexes [Re(NO)2(PR3)2][BArF4] (R = Cy, 1,a; R = iPr, 1,b) with phenyldiazomethane gave the cationic benzylidene species [Re{CH(C6H5)}(NO)2(PR3)2][BArF4] (2,a and 2,b) in good yields. Upon reaction of 2,a and 2,b with acetonitrile, the consecutive formation of [Re(NCCH3)(NCPh)(NO)(OC(CH3)NH)(PR3)][BArF4] (3,a and 3,b) and [Re(NCCH3)(OC{CH3}NH{C6H5})(NO)(PR3)2][BArF4] (4,a and 4,b) was observed. The proposed reaction sequence involves the coupling of coordinated NO, carbene and acetonitrile molecules to yield the (1Z)- N -[imino(phenyl)methyl]ethanimidate ligand. The coupling of the nitrosyl and the benzylidene is anticipated to occur first, forming an oximate species. The subsequent acetonitrile addition can be envisaged as a heteroene reaction of the oximate and the acetonitrile ligand yielding 3,a and 3,b, which in turn can cyclise and undergo a prototropic shift initiated by an internal attack of the ethaneimidate ligand on the benzonitrile moiety to afford 4,a and 4,b. [source]

Deactivation reactions in the modeled 2,2,6,6-tetramethyl-1-piperidinyloxy-mediated free-radical polymerization of styrene: A comparative study with the 2,2,6,6-tetramethyl-1-piperidinyloxy/acrylonitrile system

Andrzej Kaim
Abstract The competitiveness of the combination and disproportionation reactions between a 1-phenylpropyl radical, standing for a growing polystyryl macroradical, and a 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) radical in the nitroxide-mediated free-radical polymerization of styrene was quantitatively evaluated by the study of the transition geometry and the potential energy profiles for the competing reactions with the use of quantum-mechanical calculations at the density functional theory (DFT) UB3-LYP/6-311+G(3df, 2p)//(unrestricted) Austin Model 1 level of theory. The search for transition geometries resulted in six and two transition structures for the radical combination and disproportionation reactions, respectively. The former transition structures, mainly differing in the out-of-plane angle of the NO bond in the transition structure TEMPO molecule, were correlated with the activation energy, which was determined to be in the range of 8.4,19.4 kcal mol,1 from a single-point calculation at the DFT UB3-LYP/6-311+G(3df, 2p)//unrestricted Austin Model 1 level. The calculated activation energy for the disproportionation reaction was less favorable by a value of more than 30 kcal mol,1 in comparison with that for the combination reaction. The approximate barrier difference for the TEMPO addition and disproportionation reaction was slightly smaller for the styrene polymerization system than for the acrylonitrile polymerization system, thus indicating that a ,-proton abstraction through a TEMPO radical from the polymer backbone could diminish control over the radical polymerization of styrene with the nitroxide even more than in the latter system. 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 232,241, 2007 [source]

Thermally induced intramolecular oxygen migration of N -oxides in atmospheric pressure chemical ionization mass spectrometry

Xin Wang
N -Oxides are known to undergo three main thermal degradation reactions, namely deoxygenation, Cope elimination (for N -oxides containing a ,-hydrogen) and Meisenheimer rearrangement, in atmospheric pressure chemical ionization mass spectrometry (APCI-MS). The ions corresponding to these thermal degradants observed in the ensuing APCI mass spectra have been used to identify N -oxides as well as to determine the N -oxidation site when the analyte contains multiple tertiary amine groups. In this paper, we report a thermally induced oxygen migration from one N -oxide amine to another tert -amine group present in the same molecule through a six-membered ring transition state during APCI-MS analysis. The observed intramolecular oxygen migration resulted in the formation of a new isomeric N -oxide, rendering the results of the APCI-MS analysis more difficult to interpret and potentially misleading. In addition, we observed novel degradation behavior that happened after the Meisenheimer rearrangement of the newly formed N -oxide: a homolytic cleavage of the NO bond instead of elimination of an aldehyde or a ketone that usually follows the rearrangement. Understanding of these unusual degradation pathways, which have not been reported previously, should facilitate structural elucidation of N -oxides using APCI-MS analysis. Copyright 2010 John Wiley & Sons, Ltd. [source]

Metal-Free and PdII -Promoted [2+3] Cycloadditions of a Cyclic Nitrone to Phthalonitriles: Syntheses of Oxadiazolines as well as Phthalamide,PdII and Dihydropyrrolyl-iminoisoindolinone,PdII Complexes with High Catalytic Activity in Suzuki,Miyaura Cross-Coupling Reactions

Jamal Lasri Dr.
Abstract The previously unknown reactions between phthalonitriles, 1,2-(CN)2(C6)R1R2R3R41 (1,a, R1=R2=R3=R4=H; 1,b, R1=R2=R4=H, R3=CH3; 1,c, R1=R4=H, R2=R3=Cl; 1,d, R1=R2=R3=R4=Cl; 1,e, R1=R2=R3=R4=F), and a cyclic nitrone, ,O+NCHCH2CH2CMe22, proceed under heating in a sealed tube to give phthalimides 3, 2-oxadiazolyl-benzonitriles 4 or ortho -bis(oxadiazolyl)tetrafluorobenzene 4,e,. In the presence of palladium(II) chloride, phthalonitriles 1 react with 2 at room temperature, to give bis(pyrrolidin-2-ylidene)phthalamide PdII complexes 5 via metal-promoted rupture of the NO bond of the oxadiazoline ring. The ketoimine ligands thus generated can be liberated from the metal by displacement with a diphosphine. Although the first [2+3] cycloaddition of 2 to 1 can occur in the absence of the metal to give the mono-cycloadducts 4, the second [2+3] coupling at the still-unreacted cyano group requires its activation by coordination to PdII, affording complexes 6 containing two ligated oxadiazolyl-benzonitriles. These ligands undergo either i) further cycloaddition with 2 to afford ultimately (upon rearrangement) the bis(pyrrolidinylidene)phthalamide complexes 5 or ii) NO bond cleavage in the oxadiazoline ring with intramolecular attack of the imine nitrogen on the cyano carbon and bridging to a second PdII center to afford dimeric palladium(II) complexes 7, with chloride bridges, that bear a dihydropyrrolyl-iminoisoindolinone, a new type of ligand. The compounds were characterized by IR, 1H, and 13C,NMR spectroscopy, ESI MS or FAB+ MS, elemental analyses and, in the case of 4,c, 5,a, 5,c, and 7,c, also by X-ray diffraction analysis. Complexes 5,a and 7,c show high catalytic activity for the Suzuki,Miyaura cross-coupling reaction of bromobenzene and phenylboronic acid and give biphenyl in high yields with turnover frequencies (TOFs) of up to 9.0105,h,1. [source]

Chiral ureas with two electronegative substituents at 1-N: An unusual case of coexisting pyramidal and almost planar 1-N atoms in the same crystal,

CHIRALITY, Issue 7 2009
Oleg V. Shishkin
Abstract XRD studies of structure of N -acetoxy- N -methoxyurea and N,N -bis(methoxycarbonyl)- N -methoxyimide have revealed that in N -methoxy- N -X-ureas (X = OAc, Cl, OMe, N+C5H5) the additional shortening of NOMe bond took place, which arising from an nO(Me) -,*NX anomeric orbital interaction. XRD studies of N -chloro- N -ethoxyurea crystal have revealed the presence of two kinds of anomeric nitrogen configuration in the ONCl group in the form of a pyramidal configuration and a planar configuration for same 1-N nitrogen atom. XRD studies of N -4-chlorobenzoyloxy- N -ethoxyurea have revealed that the degree of pyramidality of the 1-N nitrogen in N -aroyloxy- N -alkoxyureas is tuned by orientation of benzoyl group with respect to the NO bond, which in turn depends of size of N -alkoxy group. Chirality, 2009. 2008 Wiley-Liss, Inc. [source]