RESUMO
The mechanisms by which directed ortho metalation (DoM) and postmetalation processes occur when aromatic compounds are treated with mixed alkylamido aluminate i-Bu3Al(TMP)Li (TMP-aluminate 1; TMP = 2,2,6,6-tetramethylpiperidide) have been investigated by computation and X-ray diffraction. Sequential reaction of ArC(=O)N(i-Pr)2 (Ar = phenyl, 1-naphthyl) with t-BuLi and i-Bu3Al in tetrahydrofuran affords [2-(i-Bu3Al)C(m)H(n)C(=O)N(i-Pr)2]Li x 3 THF (m = 6, n = 4, 7; m = 10, n = 6, 8). These data advance the structural evidence for ortho-aluminated functionalized aromatics and represent model intermediates in DoM chemistry. Both 7 and 8 are found to resist reaction with HTMP, suggesting that ortho-aluminated aromatics are incapable of exhibiting stepwise deprotonative reactivity of the type recently shown to pertain to the related field of ortho zincation chemistry. Density functional theory calculations corroborate this view and reveal the existence of substantial kinetic barriers both to one-step alkyl exchange and to amido-alkyl exchange after an initial amido deprotonation reaction by aluminate bases. Rationalization of this dichotomy comes from an evaluation of the inherent Lewis acidities of the Al and Zn centers. As a representative synthetic application of this high kinetic reactivity of the TMP-aluminate, the highly regioselective deprotonative functionalization of unsymmetrical ketones both under mild conditions and at elevated temperatures is also presented.
Assuntos
Alumínio/química , Amidas/química , Alquilação , Cristalografia por Raios X , Isomerismo , Cinética , Modelos Moleculares , Estrutura MolecularRESUMO
Treatment of N-lithiopyridylketimide derivatives Li[R(C=N)py] (R=Ph, py) with ECl(2) (E=S, Se) affords the fused thiadiazolium and selenadiazolium salts [RC(6)H(4)N(2)E]Cl [1]Cl and [2]Cl containing a bridgehead N atom through intramolecular coordination.
Assuntos
Nitrogênio/química , Selênio/química , Tiadiazóis/síntese química , Ciclização , Tiadiazóis/químicaRESUMO
The hydrolysis of [ClP(mu-NtBu)]2 with H2O-Et3N in thf, followed by in situ lithiation with nBuLi gives the Li13 cage [[[O-P(mu-NtBu)]2Li2]3(LiCl)6Li(Cl/OnBu)0.5(thf)7], containing a [O-P(mu-NtBu)]2(2-) dianion that is isoelectronic with ligands of the type [(RN)P(mu-NR)]2(2-).
RESUMO
Stable dark red (M = Al) or dark green (M = Ga) neutral radicals {[PhB(mu-NtBu)2]2M} are obtained by the oxidation of their corresponding anions with iodine, and EPR spectra supported by DFT calculations show that the spin density is equally delocalized over all four nitrogen atoms in these spiroconjugated systems.
RESUMO
The silver(I) coordination networks [Ag2(mu-O2CCF3)2(mu-NN)2](infinity) exist as a polymer of macrocycles or a double-stranded polymer when NN = 1,2-C6H4[NHC(O)-4-C5H4N]2 or 1,2-C6H4[NHC(O)-3-C5H4N]2, respectively. Crystal engineering of the polymers is achieved through interchain hydrogen bonds.
RESUMO
The first polymeric organometallic double helix has been synthesized by self-assembly through hydrogen bonding by using a biomimetic strategy and a new side-by-side structural motif.
RESUMO
The equilibrium between digold and tetragold rings and a ring-opened oligomer and polymer is established by NMR and ESI-MS studies in solution and by structure determinations in the solid state; the polymer containing amide-derivatized ligands undergoes self-assembly through hydrogen bonding to give an ordered network.
RESUMO
Reaction of Ph(2)C=O and py(2)C=O with Li[N(SiMe(3))(2)] and ArSCl (Ar = 2-O(2)NC(6)H(4), 2,4-(O(2)N)(2)C(6)H(3)) yielded Ph(2)C=NSAr (1a and 1b respectively) and py(2)C=NSAr (2a and 2b respectively). Reaction of fluorenone, C(12)H(8)C=O with Li[N(SiMe(3))(2)] and ArSCl under similar conditions afforded C(12)H(8)CNSAr (3a and 3b respectively). Whilst reaction of fluorenone with Li[N(SiMe(3))(2)] and SCl(2) in a 2 : 2 : 1 ratio afforded the sulfur-diimide, C(12)H(8)CNSNCC(12)H(8) (4), reaction of py(2)C=O with Li[N(SiMe(3))(2)] and SCl(2) under similar conditions afforded the thiazyl heterocycle [py(2)CNS]Cl (5) via intramolecular coordination. The structures of 1a, 1b, 2a, 2b, 3a, 3b and 4 are determined by X-ray diffraction. In the case of 4, bond lengths and DFT studies reveal greater π-delocalisation than in 1-3.
RESUMO
The ß-sheet structure associated with chlorinated aromatics (d(Cl···Cl)≈ 4.0 Å) has been implemented to drive formation of π-stacked structures of dithiadiazolyl radicals. Both title compounds exhibit an increase in paramagnetism above 150 K but solid-state EPR studies indicate that the origin of the paramagnetism in these two systems is different.
RESUMO
The chiral diphosphine ligand R,R-trans-1,2-C(6)H(10)(NHCOC(6)H(4)PPh(2))(2), 1, gives the fluxional trans-chelate complexes [M(1)]X, 2a-2c, M = Au or Ag. It is suggested that a similar trans-chelate conformation may be present in the catalytic intermediate [Pd(1)].
RESUMO
The conversion of 3,4-dialkoxy-benzenes into dialkoxy-benzo-1,3,2-dithiazolyls is described and representative examples (1 and 2) derived from benzodioxole and veratrol, respectively, are reported. Whilst 1 is a dimeric pi*-pi* dimer, the dimethoxy derivative 2 is monomeric in the solid state and exhibits antiferromagnetic interactions.
RESUMO
A series of tris-pyridyl complexes [RAl(2-py)(3)]Li.thf [2-py = 2-pyridyl; R = Et (1); (n)Bu (2); (s)Bu (3), (t)Bu (4)] were prepared by the sequential reaction of AlCl(3) with RLi then 2-Li-py in thf. The related complexes [MeAl{2-(3-Me)py}(3)]Li(mu-Br)Li(thf)(3) (5), [MeAl{2-(5-Me)py}(3)]Li.thf (6) and [MeAl{2-(6-Me)py}(3)]Li.thf (7) are obtained similarly from MeAlCl(2) and the appropriate lithio-pyridine (2-Li-py'). The synthetic approaches used provide the means for extensive elaboration of the [RAl(2-py')(3)](-) ligand frameworks, and potentially broad access to a large range of new anionic tris-pyridyl ligands of this type. Fundamental insights into how the ligand bites and coordination environments offered are modified by substituents at the Al bridgehead and pyridyl rings are given by the solid-state structures of 1-7 .
RESUMO
The in situ reaction of the dianion [O_P(micro-N(t)Bu)]2(2-) with the dimer [ClP(micro-N(t)Bu)]2 gives the O_bridged macrocycle [{P(micro-N(t)Bu)}2(micro-O)]4 (1), being the largest crown-like phosph(III)azane of its type to be reported and having a structure that is directly related to the ubiquitous 12-crown-4.
RESUMO
Dilithiation of 1,2-(PH2)2C6H4 with nBuLi followed by reaction with Sn(NMe2)2 in the presence of the Lewis base donor tmeda [Me2NCH2CH2NMe2] gives [(C6H4P2Sn)(Li.tmeda)2] , containing the phosphide-stabilised, 6pi stannylene dianion [C6H4P2Sn]2-.
RESUMO
This critical review covers significant recent advances in the chemistry of pnictogen(III)-nitrogen ring systems, also known as cyclopnict(III)azanes. The synthetic methodologies and reactions of the heavier pnictogen systems are compared with the well-developed chemistry of cyclophosph(III)azanes. Particular attention is focused on ring-oligomerization processes and the use of four-membered E(2)N(2) rings as building blocks for the synthesis of macrocyclic molecules. Main-group element and transition-metal complexes are also discussed (95 references).
Assuntos
Aminas/química , Compostos Organometálicos/química , Compostos Organofosforados/química , Antimônio/química , Arsenicais/química , Bismuto/química , Ciclização , Estrutura Molecular , Compostos Organometálicos/síntese química , Compostos Organofosforados/síntese química , EstereoisomerismoRESUMO
A synthetic protocol for the tert-butyl-substituted dichalcogenoimidodiphosphinates [Na(tmeda){(EPtBu(2))(2)N}] (3 a, E=S; 3 b, E=Se; 3 c, E=Te) has been developed. The one-electron oxidation of the sodium complexes [Na(tmeda){(EPR(2))(2)N}] with iodine produces a series of neutral dimers (EPR(2)NPR(2)E--)(2) (4 b, E=Se, R=iPr; 4 c, E=Te, R=iPr; 5 a, E=S, R=tBu; 5 b, E=Se, R=tBu; 5 c, E=Te, R=tBu). Attempts to prepare 4 a (E=S, R=iPr) in a similar manner produced a mixture including HN(SPiPr(2)). Compounds 4 b, 4 c and 5 a-c were characterised by multinuclear NMR spectra and by X-ray crystallography, which revealed two alternative structures for these dimeric molecules. The derivatives 4 b, 4 c, 5 a and 5 b exhibit acyclic structures with a central chalcogen-chalcogen linkage that is elongated by approximately 2 % (E=S), 6 % (E=Se) and 8 % (E=Te) compared to typical single-bond values. By contrast, 5 c adopts an unique spirocyclic contact ion-pair structure in which a [(TePtBu(2))(2)N](-) ion is Te,Te' chelated to an incipient [(TePtBu(2))(2)N](+) cyclic ion. DFT calculations of the relative energies of the two structural isomers indicate a trend towards increasing stability for the contact ion pair relative to the corresponding dichalcogenide on going from S to Se to Te for both the isopropyl and tert-butyl series. The two-electron oxidation of [Na(tmeda){(EPtBu(2))(2)N}] (E=S, Se, Te) with iodine produced the salts [(EPtBu(2))(2)N](+)X(-) (7 a, E=S, X=I(3); 7 b, E=Se, X=I; 7 c, E=Te, X=I), which were characterised by X-ray crystallography. Compound 7 a exists as a monomeric, ion-separated complex with [d(S--S)=2.084(2) A]; 7 b and 7 c are dimeric [d(Se--Se)=2.502(1) A; d(Te--Te)=2.884(1) A].
RESUMO
The dichlorocyclodistib(III)azane [ClSb(mu-NtBu)]2 (1) has been shown to exist as the cis isomer in the solid state. A series of bis(1 degree-amino)cyclodistib(III)azanes [R'NHSb(mu-NtBu)]2 (2, R' = tBu; 3, R' = Dipp; 4, R' = Dmp) has been prepared by the reaction of 1 with 2 equiv. of LiNHR'. On the basis of NMR solution spectra, all three derivatives are formed as a mixture of cis and trans isomers. In the case of 3, the structures of both the cis and trans isomers have been determined by X-ray crystallography; cis-3 adopts an endo, endo arrangement for the amido protons of the DippNH groups. Isomerization of trans-3 into cis-3 occurs slowly in solution. Deprotonation of 2 with 2 equiv. of nBuNa or trans-3 with nBuLi produces [Na2Sb2(mu-NtBu)4] (5) and [Li2Sb2(mu-NtBu)2(mu-NDipp)2] (6), whose solvated cubane structures were established by X-ray crystallography. In contrast, the reaction of cis-3 with 2 equiv. of nBuLi produces the tricyclic compound [Li2Sb(mu-NtBu)2(mu-NDipp)(mu-NHDipp)] (7).