ISSN:1042-7163    

DOI:10.1002/hc.520040203

出版商:VCH Publishers, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractDicationic 10‐C‐5 species14, formally two‐electron oxidation products of 1,8‐bis(arylthio)‐9‐(2,6‐dimethoxyaryl)‐10‐phenylanthracenes, are prepared and characterized by NMR spectroscopy. Evidence is presented for a bis‐sulfonium structure containing a hypervalent trigonal bipyramidal (TBP) carbon atom. Dicationic species14, prepared by the reaction of the appropriate diol with strong acid in liquid sulfur dioxide or sulfurylchlorofluoride, are stable for indefinite periods at room temperature in these solutions. Structural features common to these compounds which stabilize the TBP geometry sufficiently to allow their direct observation are as follows: (a) electronegative apical ligands (sulfonium sulfur atoms), (b) five‐membered rings linking each apical position to an equatorial position, (c) geometric constraints built into the tridentate ligand in a pattern designed to stabilize TBP, relative to tetrahedral carbon, (d) three relatively electropositive (sigma‐donor) equatorial ligands, which decrease the effective electronegativity of the central carbon atom of the threecenter bond, (e) a strain‐free, bidentate π‐acceptor equatorial ligand with its π‐axis parallel with the electron‐rich three‐center four‐electron bond axis, and (f) possible residual aromaticity (bis‐ipso‐aromaticity) in the equatorial six‐membered ring incorporating the hypervalent carbon atom.A low‐temperature19F NMR study of14bsets an upper limit for ΔG≠−100°Cof ca. 4 kcal/mol for a hypothetical process which would interconvert unsymmetrical species30and30′ if such a tautomeric mixture were to represent the structure of14. Evidence against such a tautomeric equilibrium is adduced from the upfield shift of 0.65 ppm observed for the proton meta to the two methoxyl substituents of dication14arelative to the comparable proton in21a, the model dication lacking one of the two arylthio substituents of14a. This is most easily explained by postulating a nucleophilic interaction of the second

ISSN:1042-7163    

DOI:10.1002/hc.520040204

出版商:VCH Publishers, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractRemoval of two electrons from 1,8‐bis(4‐methylphenylthio)‐9‐(2, 6‐dimethoxyphenyl‐1‐13C)‐10‐phenylanthracene(2)provides stable dication1. Isotopic enrichment (85%) of13C at the labeled site of the aromatic carbon, between the two sulfurs, makes possible the observation of spin‐spin coupling constants between this13C‐carbon and the directly bonded equatorial ligand carbons. The magnitudes of these coupling constants (two1JC1′C2′= 61.9 Hz and one1JC1′C9= 56.3 Hz) suggest that this carbon is sp2hybridized, with the postulated trigonal bipyramidal (TBP) geometry about this carbon center. The13C NMR chemical shifts for the 10‐C‐5 carbon (δ109.3) and for other carbons provide strong evidence against alternative structures for this dication. The data are consistent with the 10‐C‐5 species, with apical sulfonium ligands and equatorial carbons of

ISSN:1042-7163    

DOI:10.1002/hc.520040205

出版商:VCH Publishers, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe electrochemical oxidation of 1,8‐bis(4‐methylphenylthio)‐9‐(2, 6‐dimethoxyphenyl)‐10‐phenylanthracene (2) is discussed. It undergoes facile, reversible two‐electron electrooxidation in two closely spaced one‐electron steps at E 01′ = 0.98 V and E 02′ = 1.02 V (vs. SCE). This behavior is discussed in terms of relief of three‐center antibonding interaction involving the 1‐, 8‐, and 9‐substituents of2with two sulfurs and a carbon of the 2,6‐dimethoxyphenyl group, which becomes a stabilized three‐center bonding interaction in dication1. The central atom in the three‐center bond is a hypervalent pentacoordinate carbon atom.A related two‐center antibonding interaction present in 1‐(4‐methylphenylthio)‐9‐(2,6‐dimethoxyphenyl)‐10‐phenylanthracene (5) is relieved by facile one‐electron oxidation (Ep= 1.14 V vs. SCE) forming7. Removal of a second electron (Ep= 1.34 V vs. SCE) from anthracene5results in an unstable dication,8.Other analogous anthracene derivatives lacking both thioaryl groups (4) or the 9‐aryl group (4) prove much more difficult to oxidize, both showing oneelectron reversible oxidation potentials of 1.27 V (vs. SCE) similar to 9‐phenylanthracene (1.34 V vs. SCE) and 9,10‐diphenylanthracene (1.22 V vs. SCE).These results provide strong evidence for the postulated structure of dication2which incorpor

ISSN:1042-7163    

DOI:10.1002/hc.520040206

出版商:VCH Publishers, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractModified neglect of diatomic overlap (MNDO) calculations have been used to investigate the ground state properties of the 130 nonfully boron‐nitrogenalternating isomers of pentaazapentaboraazulene (PAPBAZ), N5B5H8. The two most stable of these nonfully boron‐nitrogen‐alternating isomers, 1,2,3a, 5,7‐pentaaza‐3,4,6,8,8a‐pentaboraazulene, (1,2,3a, 5,7‐PAPBAZ) (3), and 1,3,3a,5,7‐PAPBAZ (4) have strongly exothermic heats of formation (−142.5 and −142.4 kcal/mol, respectively), while the two least stable isomers, 1,6,7,8,8a‐PAPBAZ (131) and 1,2,3,3a,8a‐PAPBAZ (132), are calculated to have endothermic heats of formation (+95.43 and +96.31 kcal/mol, respectively). Each isomer optimized as a slightly to extremely nonplanar molecule, but each remained a bicyclic system containing a seven‐membered ring fused to a five‐membered ring. Thus, no ring‐opened structures were observed. An empirical relationship between the heat of formation and the number, position, and type of homonuclear (NN or BB) bonds present in the molecules could be established, but as the heat of formation for the molecules became more positive, the relationship became less strong. A general trend of diminishing energy difference between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) was observed as the heat of formation became more positive. In addition to a discussion of the structures of (3), (4), (131), and (132), the structures of 2,3a,4,6,8‐PAPBAZ (9), 2,3a,5,6,8‐PAPBAZ (11), 1,2,4,6,8‐PAPBAZ (15), 2,3a,4,7,8a‐PAPBAZ (19), 1,3a,4,5,8‐PAPBAZ (32), 1,2,3,5,7‐PAPBAZ (47), 1,3a,5,8,8a‐PAPBAZ (67), 1,3a,6,7,8a‐PAPBAZ (87), 3a,4,6,8,8a‐PAPBAZ (106), 1,2,3,5,6‐PAPBAZ (109), 1,2,3a,8,8a‐PAPBAZ (116), and 4,5,6,7,8‐PAPBAZ (130) are discussed in detail. Some of these molecules were chosen because they represent the minima and maxima, respectively, in heats of formation [(3), (4), (130), (131), and (132)], ionization potentials [(9) and (32)], differences in LUMO and HOMO energies [(106) and (32)], and dipole moments [(11) and (87)]. The remaining molecules were chosen because each represent the most stable system containing the following homonuclear chains: B‐B‐B (15), N‐N‐N (19),

ISSN:1042-7163    

DOI:10.1002/hc.520040207

出版商:VCH Publishers, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractA survey of selected novel hybrid organic‐inorganic polymers obtained by polymerization and copolymerzation of main group compounds containing vinyl groups is presented. Examples from groups 13 through 16 are discussed with an emphasis on synthesis and quantitative reactivity studie

ISSN:1042-7163    

DOI:10.1002/hc.520040208

出版商:VCH Publishers, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe reaction of a series of 4,4‐dimethyl‐3,5,5‐(R3, R2, R1)‐3‐hydroxy‐1,2‐dioxolanes1a–d[1a(R1= R2= R3= Me);1b(R1= R2= Me, R3= Ph);1c(R1= Ph, R2= R3= Me);1d(R1= R3= Ph, R2= Me)] with trimethyl phosphite or triphenylphosphine produced theβ‐hydroxy ketones,2a–d[(R1R2C(OH)CMe2‐COR3)], and the corresponding phosphoryl compounds in high yield. The reactions were slow (∼24 hours), requiring excess of the trivalent phosphorus compounds for optimum results. The reaction was found to be of the second order overall, first order in peroxide and in phosphorus reagent. Triphenylphosphine was found to be more reactive than trimethyl phosphite. Formal substitution of a phenyl group for a methyl group on the hemiperketals yielded a reduction of reactivity of ∼2.4‐fold at the 3‐position but an increase in reactivity (∼1.5‐fold) at the 5‐position. The rate constants for tautomerization of1cin benzene were determined. The activitation parameters for reaction of1cwith triphenylphosphine in benzened6were determined [ΔH‡= 15.0 ± 1.5 kcal/mol; ΔS‡= −21.7 eu; ΔG‡= 21.7 kcal/mol; k34°= 2.4 × 10−3M−1s−1]. The data are consistent with direct insertion of the phosphorus compounds into the peroxide bond to yield phosphorane intermediates. Rapid intramolecular hydrolysis of the intermediates woul

ISSN:1042-7163    

DOI:10.1002/hc.520040209

出版商:VCH Publishers, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractCascade molecules in which the branch points are phosphonium ion sites have been synthesized bearing phosphorus in a variety of oxidation states at the core. In addition to the previously reported phosphonium ion core species, these new cascade molecules include those bearing phosphine, phosphine oxide, and phosphorane cores.

ISSN:1042-7163    

DOI:10.1002/hc.520040210

出版商:VCH Publishers, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractTreatment of 2‐pyridyl 2‐thienyl sulfoxide with 2‐thienyllithium was found to give both 2‐(2‐pyridyl)thiophene2and 2,5‐(di‐2‐pyridyl)thiophene3. The reaction between 2‐thienyllithium and thionyl chloride was found to give 2,2′‐bithienyl8, a coupling product, which is also formed by the reaction between di‐2‐thienyl sulfo

ISSN:1042-7163    

DOI:10.1002/hc.520040211

出版商:VCH Publishers, Inc.    

年代:1993

数据来源: WILEY

摘要:

Abstract1,6‐Dihydrophosphinine 1‐oxides with 4‐chloro‐3(or 5)‐methyl substituents give cycloadducts with dimethyl acetylenedicarboxylate having the 2‐phosphabicyclo[2.2.2]octa‐5,7‐diene ring system that can be fragmented easily on irradiation with ultraviolet light (254 nm). The phosphorus‐containing bridge is released as a derivative of the 3‐coordinate methylene phosphine oxide species, RP(O)CH2. This species is too reactive to observe but is readily trapped by an addition reaction with alcohols to give phosphinates (R = alkyl or aryl) or phosphonates (R = O‐alkyl). These experiments constitute the first demonstration of the existence of ROP(O)CH2. Phosphoryl oxygen in the cycloadducts has been replaced by sulfur, and these sulfides fragment smoothly on irradiation. The 3‐coordinate species PhP(S)CH2has been generated by other workers, but the species ROP(S)CH2was generated here for the first time. The power of the bicyclic fragmentation route for the generation of a variety of 3‐coordinate P‐methylen

ISSN:1042-7163    

DOI:10.1002/hc.520040212

出版商:VCH Publishers, Inc.    

年代:1993

数据来源: WILEY