摘要:

The reports in Volume 99 ofAnnual Reports Section Aonce again demonstrate the vibrancy of all sections of inorganic chemistry. To emphasise this we have asked all authors to begin their chapter with their own assessment of theHighlightsof the work on which they have reported. We, as editors, are therefore not highlighting any specific developments in thisIntroductionand simply would assert that the following pages validate the imaginative approach of inorganic chemists and the wide variety of areas in which their contributions continue to reap success.One change in structure from Volume 98 is the conflation of the chapters on macrocyclic and supramolecular coordination chemistry. Developments in polyoxometallate chemistry are revealing new kinds of macrocyclic and supramolecular compounds and we also felt that it would be informative to combine reports on polyoxometallates with those on supramolecular and macrocyclic systems. In drawing these topics together we would hope to help stimulate thinking across boundaries although, as this year's reports show, inorganic chemists need no prompting in this regard.

ISSN:0260-1818    

DOI:10.1039/b211628f

出版商:RSC    

年代:2003

数据来源: RSC

摘要:

1IntroductionThis chapter follows the usual pattern with emphasis on the organometallic and coordination chemistry of Groups 1 and 2 published in 2001.Reviews which contain material relevant to s-block chemistry have appeared on the chemistry of compounds containing the tris(trimethylsilyl)methyl or related groups,11-azaallyl complexes,2imido analogues of oxo anions,3tetraorganodichalcogenoimidodiphosphorus acids and their derivatives,4metal inverse crowns, based on combinations of alkali metal and magnesium (or zinc) amides,5the oxygen-scavenging properties of alkali metal-containing organometallic compounds,6the use of macrocyclic polyethers with aromatic side-chains to study alkali metal cation–π interactions,7the emerging use of magnesium bis(amides) as reagents in organic synthesis,8Ziegler–Natta heterogeneous catalysts, especially those basedon alkoxymagnesium species,9and the aqueous coordination chemistry of beryllium with a focus on aqua, fluoro, hydroxo, oxo and peroxo complexes as well as various carboxylates, carbonates, phenolates, enolates and polyolates in a bioinorganic context.10Group 1 metallation of 2-trimethylsilylaminopyridine (LH) in the presence of 12-crown-4 ether affords [LiL(12-crown-4)], the unusual ate complex [Na(12-crown-4)2][NaL2(thf)](thf) and [ML(12-crown-4)]2·nC6H5Me, (M = K,n= 2; M = Rb,n= 0; M = Cs,n= 1). X-Ray crystallography showed that the pyridine ligand bonds through both nitrogen atoms and bridges through both nitrogen atoms in the dimers. The structure of [Cs(NH-2-py)(12-crown-4)]∞was also reported.11The structure and reactivity of MCH2OMe (M = Li, Na, K) have been investigated usingab initiomethods. The MCO angle was found to be acute due to strong M–O interactions and the intermolecularmethylene transfer reaction to give MOCH2CH2OMe was found to occur more readily than methylene transfer to MMe or α-elimination of CH2. The important interaction takes place between σ(M–C) in the nucleophile and σ*(C–O) in the electrophile; electrophilic character decreases from Li to K.12The conformations of α-alanine and those of the eight most stable adducts that it forms with M+(M = Li, Na or K) have been studied using density functional theory. The lowest energy structures are either N,O-bicoordinate systems (M = Li or Na) or O-monocoordinate species (M = K).13The structural, electronic and vibrational properties of MCp (M = Li, Na or K) and MCp* (M = Li or Na) have been studied, using both spectroscopic and density functional techniques, with a view to investigatethe influence of methyl groups on spectral features, M–C force constants and change in ionic character of the M–C bond for different metals.14The enthalpies of formation of MCp (M = Li, Na, K or Tl) have been determined and those for M = Rb or Cs estimated.15Several cyclic and acyclic oligo(dimethylsilylene)phenylene species have been found to form cation–π complexes with alkali metal cations using electrospray mass spectrometry. The ability of the trimethylsilyl group to enhance the interaction was demonstrated usingab initiocalculations.16Reactivity studies and two crystal structures have been reported for [MSiX(SiBut3)2] (M = Li, Na or K; X = H, Me, Ph, F, Cl or Br).17The lithium and sodium salts of (dimethylfluorenylsilyl)cyclopentadieneform polymeric chains.18A crystallographic study of a series of alkali metal complexes of [(2-py)(SiMe3)CH2] (R1H) and [(6-Me-2-py)(SiMe3)CH2] (R2H), [MR1(pmdien)]2(M = Na or K), [NaR1(tmen)]2, [LiR2(pmdien)] and the magnesium complex [MgR12(hmpa)2] revealed that all are metal enamides in the solid state. The preference for the enamide, rather than the carbanion or azaallyl formulation was addressed byab initiocalculations.19The crystal structures of some organometallic compounds of lithium and magnesium containing the bulky ligands C(SiMe3)2(SiMe2X) (X= Me, Ph, NMe2or 2-py) have been reported.20The solid state structures of sodium and calcium complexes of sulfonated azo dyes [O3SC6H4NNC6H3R1R2]−(R1= H, R2= OH or NH2; R1= R2= OH) form a series of supramolecular arrays with one-, two- and three-dimensional frameworks. Sodium forms close linked sheets, chains and cages similar to many inorganic minerals whilst calcium adopts ring-ladder structures resembling those found in s-block amide chemistry.21The preparations of [M(μ-Cl)(η5-C4Et4E)(thf)n]2(M = Mg,n= 1; M = Ca,n= 2; E = P, As or Sb) and [M(η5-C4Et4E)2(thf)n] (M= Sr,n= 1; M = Ba,n= 0) have appeared. The structure of the barium compound shows molecules linked into chainsviaBa⋯P interactions.22A series of new alkaline earth metallocenes and their adducts with the carbene 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene have been described.23A simple, cheap and safe method of disposal for sodium and potassium has been published. A ceramic flower pot is half-filled with fine-ground sand, the residues are added and the pot is filled with sand and then placed in a tray of water. Capillary action then draws water into the sand and destroys the metal. The sand can be washed and used again.24

ISSN:0260-1818    

DOI:10.1039/b109552h

出版商:RSC    

年代:2002

数据来源: RSC

摘要:

2LithiumCarbon-donor ligandsTreatment of 6-dimethylaminofulvene with LiR (R = C&z.tbd6;CCH3, Bun, Ph or C6H4Me-4) results in nucleophilic addition at the fulvene carbon to give [LiC5H4CH(R)NMe2]. Crystallographic studies show that all contain polymeric chains with η5rings and NMe2groups linking to the adjacent metal; structures vary in coordination geometry and degree of interaction of the metal with the opposite side of the ring.29The preparation and structure of 2-[ethyl(2-methallyl)amino]indenyllithium has been reported. The compound has an oligomeric structure with a linear string of alternating μ-η5∶η5-indenyl anions and lithium cations along which substituents lie in a helical arrangement.30The η3-ansa-bis(allyllithium) compounds [{Li(tmen)}2{3-(η3-C3H3SiR13-1)2}SiR22](R1= R2= Me or Ph; R1= Me, R2= Ph; R1= Ph, R2= Me; R13= Me2But, R2= Me) have been obtained from theansa-bis(propene) and LiBun. Lithium can be substituted for potassium in the dimethyl compound by reaction with KOBut.31The structures and barriers to rotation of some methyl-substituted allylic lithium complexes with tmen have been established using NMR methods.32Reduction of3(R = H) in diethyl ether or4(R = Me) in thf with lithium yielded the corresponding tetraanions. X-Ray diffraction shows the lithium salt of3to be monomeric with two [Li(OEt2)]+ions located above and below the alkene double bond; an Si–H⋯Li interaction is present in both the solid state and solution. A dianion with ananalogous structure was prepared and a more extensively delocalized tetraanion made up of five- and seven-membered rings in which the cations migrate around the π system in solution has also been synthesized.33The key step in the manufacture of the HIV reverse transcriptase inhibitor, efavirenz (Sustiva), involves addition of a 2∶2 tetrameric complex (formed from lithium cyclopropylacetylide and the chiral mediator lithium (1R,2S)-N-pyrrolidinylnorephedrate) to a keto-aniline in 95% yield and 98% enantioselectivity. Studies of the asymmetric addition involving this tetramer provide conclusive evidence for formation of a 2∶1∶1 tetramer containing product alkoxide. Crystal structures of a 4∶2 hexamer crystallized from a solution of the 2∶2 tetramer and a 3∶1 tetramer were also reported.34A new structure of an alkyllithium, a central (LiC)2ring in a dimeric ladder, has been observed in the mixed aggregate formed from LiBunand Ph2Si(CH2Li)CH2N(CH2CH2OMe)2; the aggregate showed an enhanced reactivity relative to its components in the lithiation of benzene.35Vacuum sublimation of [Li(thf)4][Li{C(SiMe3)3}2] at 180 °C provides a low yield synthesis of [Li(thf)3- Li{C(SiMe3)3}2] with agostic interactions between the solvated lithium and a methyl group. Reaction of [LiC(SiMe3)3] with oxygen in toluene yields the red ketone (Me3Si)2C&z.dbd6;O which forms a 1∶1 adduct with [LiC(SiMe3)3].36A photoelectron spectroscopic investigation of the electronic structures of some alkyllithium clusters showed that LiR (R = Pri, Busor But) form only tetramers while, for R = Et, Prn, Bunor Bui, mixtures of tetramers and hexamers are observed.37Lithiumatom exchange has been shown to occur in solid LiButusing7Li NMR spectroscopy.38The kinetics of the reactions of Lewis base complexed primary and secondary σ-alkyllithium compounds with Ph3CH exhibit non-unity orders in line with reactionviaunidentified 1∶1 complexes formed in an equilibrium between aggregated LiR and Ph3CH. A major role in the observed reactivity enhancement owing to base-induced conversion of tetramers to dimers was ascribed to increased base participation in base-rich transition states. Amine and ether complexes have equal reactivities and lithiation of Ph3CH by dimeric LiCH2R was retarded by a factor of 24000 if a silyl group is linked to the α-carbon.39New organometallic compounds containing diphenylphosphino-substituted alkyl groups have been prepared and characterized by X-ray diffraction. A tricyclic structure with the metal bound to the carbanionic centre and to the three phosphorus atoms was observed in [&z.ub1s;LiC(SiMe2CH2P&z.ub1e;Ph2)3]; [&z.ub1s;Li(thf)C(SiMe3)2{CHSiMe2[Li(thf)2]P&z.ub1e;Ph2}] and [MC(SiMe3)2(SiMe2PPh2)] (M = Li) are fluxional in solution, and for M = Na the metal is bound intramolecularly to the carbanionic centre and to phenyl and intermolecularly to phenyl and phosphorus to form chains.40Metallation of PhSCH3with LiBun–pmdien yields [LiCH2SPh(pmdien)]; a toluene solution decomposes to give [LiSPh(pmdien)] and methane (in daylight) or ethene (reflux).41The crystal structures of [(LiC6H2Ph2-2,6)2(thf)] and [Li{(2,6-di(1-naphthyl)phenyl}(thf)2]have been reported. Both contain trigonal planar lithium with the former also possessing a formally two-coordinate metal centre with additional interactions to theorthocarbon atoms on two phenyl groups.42Rate studies of the lithiation of benzene and related alkoxy-substituted species using LiBun–tmen suggest all occur with similar mechanisms in which the proton transfers are rate-limiting with [(LiBun)2(tmen)2(ArH)]‡(ArH = C6H6, C6H5OMe, C6H4(OMe)2-m, C6H5OCH2OCH3or C6H5OCH2CH2NMe2) as transition structures.43Multinuclear NMR investigations into the important role of chiral non-racemic organolithium species in carbon–carbon bond forming reactionswith configurational stability and varying reactivity have shown that lithiopyrrolidines are dimeric in solution whereas lithiopiperidines are monomeric.44Multinuclear NMR techniques showed [LiSiPh(NEt2)2], [LiSiPh2(NEt2)] and [LiSiMePh(NEt2)] to be monomeric in thf; [Li{SiPh2(NPh2)}(thf)3] is monomeric in the solid state.45Nitrogen- and phosphorus-donor ligandsThe interest in chiral species continues. The high selectivities of chiral lithium amides in aldol reactions is thought likely to arise from mixed amide–enolate aggregates and it is in this context that the preparation and structure of a 2∶1 lithium amide–lithium enolate mixed aggregate trimer have been reported. The amide was derived from (S)-N-isopropyl-O-triisopropylsilylvalinol and the enolate from 3-pentanone.46Multinuclear and multidimensional NMR studies on enantiomerically pure lithium (S)-methyl(1-phenyl-2-pyrrolidinoethyl)[15N]amide and both racemic and enantiomerically pure lithium (1-isopropyl-2-pyrrolidinoethyl)methyl[15N]amide have shown that these compounds form trimers as well as symmetrically and unsymmetrically solvated dimers, depending on the solvent used. The magnitude of the6Li,15N coupling constant was found to be a sensitive tool for probing changes in the coordination number of lithium;T1relaxation rates were sensitive to aggregation state.47The activation parameters for the exchange of an ether ligand in a chiral lithium amide have been determined from full bandshape analysis of the dynamic NMR spectra and ligand dissociation was also modelled using semi-empirical and density functional calculations. The results showed that the greater coordinating ability of thf relative to diethyl ether is due, in part, to the greater loss in vibrational entropy for diethyl ether; enthalpic contributions are equal. An SN1-type dissociative mechanism that proceeds through an intermediate unsolvated lithium amide dimer was proposed.48Two chiral lithium amide complexes derived from α-(methylbenzyl)benzylamine have been prepared and characterized by X-ray diffraction. Complexation of (S)-{[Ph(Me)CH][PhCH2]NLi}nwith thf results in formation of (S)-{[Ph(Me)CH][PhCH2]NLi(thf)}2which contains a central (LiN)2ring withcis-benzyl substituents. Reaction of the (R)-polymer with pmdien gave (R)-{[Ph(Me)CH][PhCH2]NLi(pmdien)} which, when heated in either the solid state or in solution, loses hydrogen at the benzylic carbons to give an aza-allyl complex.49The two chiral lithium amides prepared from (R)-(2-N,N-dimethylaminoethyl)(1-phenyl-2-pyrrolidin-1-y lethyl)amine and (R)-(2-methoxyethyl)(1-phenyl-2-pyrrolidin-1- ylethyl)amine formed symmetrically solvated dimers in diethyl ether. Addition of other bases did not disrupt the very strong internal coordination. The reactivity as chiral bases was low due to the entropy-driven internal coordination, however mixed-ligand complexes were formed with LiBunwith at least one freecoordination site at lithium and these could alkylate PhCHO with 30–40% enantiomeric excess (ee) to give (S)-1-phenyl-1-pentanol.50Ab initiocalculations on possible transition states for the enanioselective deprotonation ofN-tert-butyloxycarbonylpyrrolidine with isopropyllithium/(−)-sparteine have appeared.51The complex interplay between solvation and aggregation in the reactivity of lithium complexes is borne out by studies of LiNPri2-mediated ester enolizaton in four different solvents. In experiments designed to exclude mixed aggregate effects, four different mechanisms but nearly identical rates were observed with disolvated monomers in thf, monosolvated dimers in ButOMe, both monosolvated monomers and tetrasolvated dimers in hmpa–thf and mono- and di-solvated monomers in dmpu–thf. These results show that strongly coordinated ligands do not necessarily promote higher reactivity and that similar reaction rates do not always imply similar mechanisms.52In related work in which aggregate formation was maximized, it was shown that the rates of enolization in the presence of these mixed aggregates are much lower and solvent dependent.53The prominent influence of entropyon the basicity of lithiumN-(3,6-dimethyl-3,6-diazaheptyl)-N-methylamide, lithium bis(N,N-dimethyl-2-aminoethyl)amide and lithiumN-(N,N-dimethyl-2-aminoethyl)-N-methylamide toward Ph3CH has been demonstrated. The results suggest that ΔpKLi,thfprovides an approximate value of the difference in relative enthalpies within a family of lithium amides of the same aggregation and complexation type.54NMR studies of the structures of lithiated phenylacetonitrile and 1-naphthylacetonitrile have revealed contact ion pairs in thf and either hmpa-solvated monomeric and dimeric contact ion pairs or hmpa-solvated separated ion pairs, depending on the hmpa concentration, in hmpa–thf.55The use of the weakly solvating dmp to partially disrupt the structure of solvent-free lithium anilide resulted in the isolation of [{LiN(H)Ph]5(dmp)2}(C6H5Me)2- (dmp)0.5]∞in which (LiN)5units are linked by bridging dmp ligands. Interestingly, the final rung is bonded to the edge of the ladder, rather than to the penultimate rung, and this suggestion of multidirectional laddering may explain the amorphous nature of lithium anilide.56A series of lithium anilides, [Li(py)2(NHPh)]2, [Li(4-Me-py)2(NHPh)]2and [(LiNHPh)4(4-But-py)6] has been prepared and shown to adopt three different structures. The py complex has an [LiN(anilido)]2ring withtransamido groups, the 4-Me-py complex is similar withcisamido groups and the 4-But-pycompound has a centraltransring separating two mixed ligand [(anilido)N–Li(py)N–Li] rings containing rare bridging pyridine molecules.57The polyfunctional lithium amides [(2-C5H4N)CMe{CH2N(Li)SiMe2R}2]2(R = Me or But) have been found by X-ray diffraction to contain Li–N ladders in which the form of aggregation and the folding of the ladder is influenced by the steric demand of the N-bonded silyl groups. A mixed metal amide [(2-C5H4N)CMe{CH2N(Li)SiMe3}{CH2N(Tl)SiMe3}]2was also prepared.58Lithiation of 2-amino-6-methylpyridine in diethyl ether or hexane–thf affords the highly moisture sensitive [Li(C5H3NMeNH)Ln[ (L = Et2O,n= 0.5;L = tmen,n= 1) which yield {Li8(C5H3NMeNH)6(O)L2] on exposure to limited amounts of water. Both structures are based on O-centred Li6octahedra with one tmen being monodentate. Treatment with (Me2SiO)∞gives [Li(C5H3NMeNHSiMe2O)]4which contains an Li4O4cube.59The crystal structures of 2-Li(SiMe3)NC6H4CH2N(SiMe3)Li and its mono-thf adduct show an arched four-rung ladder in both compounds but that the arch is much flatter, the ladder is more twisted and the Li–C(benzyl) interactions are much weaker, with thf bound to the outer lithium atoms.60Trilithiation of Si(NHPri)4affords {Li3(thf)[Si(NPri)3(NHPri)]}2which contains a bis-thf solvated Li6(NPri)6cyclic ladder bicapped with two SiNHPriunits.61Crystallization of the lithium salt of 1H-pyrido[2,3-b]indole (α-carboline) from thf yields a tetranuclear species based on a distorted tetrahedron of lithium centres each of which is also coordinated to thf; when the salt is crystallized from toluene each lithium is three-coordinate.62The preparation and crystal structure of [Li{N(SiMe3)C(Ph)N(CH2)3NMe2}]2have been reported; each amidinato ligand is chelating with respect to one of the lithium atoms and bridging by virtue of its pendant γ-tertiary nitrogen atom to the second lithium centre. Ligand transfer reactions to aluminium, gallium, lanthanum and cerium were described.63The boraamidinate complexes [Li2{RB(NBut)2}]n(R = Bun,n= 2; R = Me,n= 3) have been prepared from LiR and B(NHBut)3. The structure of the dimer is based on a highly distorted Li4N4cube whereas the trimer contains a distorted Li6N6hexagonal prism.64Reaction of LiN(SiMe3)2with Mg(tmp)2is accompanied by an unexpected, sterically promoted, hydrogen transfer/amine elimination to give (R,R/S,S)-[LiMg(tmp){CH2SiMe2- N(SiMe3)}]2, the structure of which reveals LiNMgN rings with pendant Me2SiCH2groups intramolecularly bonded to Mgviathe CH2carbon. These units dimerize through intermolecular bonds from CH2to the magnesium of the other unit as shown in5. Theformally two-coordinate lithium atoms are involved in agostic interactions with tmp and SiMe3methyl groups. The most interesting feature of the structure is the chiral nature of the N(SiMe3) nitrogen centres.65The reactions of LiCH(SiMe3)2and related lithium alkyls with α-hydrogen-free nitriles to give either a 1-azaallyl, a β-diketiminato- or a 1,3-diazaallyl-lithium compound depending on the nature of the alkyl groups on lithium or the nitrile, the stoichiometry and the absence or presence of a neutral co-ligand have been presented together with eleven crystal structures of the products.66A series of dilithiumo-,m- andp-bis(1-azaallyl) compounds [{Li2(tmen)2}{N(SiMe3)C(R) C(H)}2C6H4}] (o, R = Butor Ph,mandp, R = But) have been prepared by addition of the relevant [{Li2(tmen)2}{(CHSiMe3)2C6H4}] to RCN (R = Butor Ph) followed by a 1,3-SiMe3shift. Use of ButNC with theorthocompound with 1,2-SiMe3migration yielded [{Li2(tmen)2}{o-{N(But)C(SiMe3)C(H)}2C6H4}]. Several compounds were crystallographically characterized and potassium derivatives were also prepared.67The preparations and structures of [Li(tacn-Pri2)]2and [MC5Me4SiMe2(tacn-Pri2)] (M = Li, Na or K) have been reported; the cyclopentadienyl compounds are fluxional in solution.68The analogous lithium compound with a dimethylene, rather than a dimethylsilyl bridge, has also been prepared.69The syntheses of [LiPHR]4, [LiPHR]6, [Li2PR] and [Li2PR·LiOBut]4(R = SiBut3) have been reported; the structure of the butoxide is based on a polyhedron made up of four- and five-membered rings capped by OButand PSiBut3groups, respectively.70Reaction of LiPHCy with PhCN followed by deprotonation of the presumed intermediate anion [CyPC(Ph)NH]−with LiBunyielded a cage complex, [{{Li2[NC(Ph)PCy]}{Li3[H(PhCN)3(PCy)2]}(thf)3}2] containing not only the desired dianion [CyPC(Ph)N]2−but also the trianion [H(PhCN)3(CyP)2]3−, with a C–C bond between the two PhCN molecules (rather than the usual ‘head-to-tail’ coupling).The formation of two different anions is thought to result from competing nucleophilic and single electron transfer (SET) mechanisms.71The reaction of [(ButNH)P(μ-NBut)2PCl] with LiPCy and LiBunaffords [Li2(thf)(NBut)P(μ-NBut)2P( PCy)]2which contains two Li2P3N3cubes linked by a central Li2P2ring.72A series of P–H functionalized phosphanyl alcohols, RHPCH2CHMeOH and 2-PHR-1-OH-cyclo-C6H10) (R = Ph, mes or trip) have been dilithiated and the crystal structure of [Li2(thf)0.5{(CR, CR/CS,CS)-2-Pt rip-1-O-cyclo-C6H10}]4shows that eight lithium atoms form two trigonal prisms which share a square face and are twisted by 90°; four triangular faces are capped by phosphorus atoms and four square faces by oxygen atoms with four lithium centres also bonded to thf.73Oxygen- and sulfur-donor ligandsAs part of continuing studies on chiral syntheses involving LiBun, reaction of (1R,2R,4S)-2-endo-hydroxy-2-exo-(2-methoxy-3-trimethylsilylphenyl)-1,3,3-trimethylbicyclo[2.2.1]hept ane with LiBunaffords the chiral mixed aggregate, the structure of which is based on a Li4C2O2cubane core. This complex increases the enantioselectivity of LiBunaddition to PhCHO, relative to the unsilylated species.74The use of H2binol as a chiral auxiliary in metal-based enantioselective catalysts and reagents prompted a study of its lithiated derivatives, [Li(rac-Hbinol)], [Li{(R)-Hbinol}], [Li2(rac-binol)] and [Li2{(R)-binol}] with crystal structures of all but the last reported. The monolithiated species both crystallize from thf as helical polymeric chains withHbinol units linked by [Li(thf)2]+bridges. The dilithiated species is aC2-symmetric chiral cluster [Li6{(R)-binol}2{(S)-binol}(thf)8] (the unit cell contains twoRRSand twoSSRclusters). The chiral central Li4O4fragment resembles a section of a spiral staircase.75The crystal structure of dimeric lithium (1R,2R,4S)-exo-2-[o-(dimethyl aminomethyl)phenyl]-1,3,3-trimethylbicyclo[2.2.1]heptan-endo-2-ol eate shows the three-coordinate cations to be pyramidal.Ab initiocalculations suggest that electrostatic interactions disfavour this geometry which is attributed to repulsion between methylamino groups and bicycloheptane moieties.76A series of lithium phenoxides [Li(OAr)Lx]n(L = thf;x= 1;n= 4, Ar = Ph, C6H4Me-2, C6H3Me2-2,6 or C6H4Pri-2;n= 3, Ar = C6H3Pri2-2,6;n= 2, Ar = C6H3But2-2,6;x= 2,n= 2, Ar = C6H4But-2; L = py;x= 2;n= 2, Ar = Ph, C6H4Me-2, C6H3Me2-2,6, C6H4Pri-2, C6H3Pri2-2,6 or C6H4But-2;x= 1;n= 2; Ar = C6H3But2-2,6) have been characterized using X-ray diffraction and multinuclear NMR (solid state and solution) techniques.77The tetrameric unit [Li4(μ-OMe)4(μ-MeOH)2(MeOH)4]·2MeOH present in the crystal structure of [LiOMe(MeOH)2] is best described as two distorted squares [Li2(μ-OMe)(MeOH)] linked by bridging methoxy groups and two hydrogen bonds.78The crystal structure of [Li7(OBut)6]+can be thought of as an (LiOBut)6hexagonal antiprism with one hexagonal face capped by a lithium cation.79The synthesis and crystal structure of [Li4Zn(μ3,η2-ddbfo)2( μ,η2-ddbfo)3Cl(MeCN)2] revealed tetrahedral metal centres linked by μ- and μ3-bridging aryloxides whereas [Na4(μ3,η2-ddbfo)4(MeCN )4] forms centrosymmetric cubes.80Depending on the bulkiness of the substituents and the solvent, lithium salts ofN,O-bis(silyl)hydroxylamines crystallize as dimeric, trimeric or tetrameric lithiumN,N-bis(silyl)hydroxylamides,e.g.[(ButSiMe2)2NOLi(thf)]2, [(ButSiMe2)2NOLi]3and [(ButSiMe2)(SiMe3)NOLi]4. Lithiation of ButSiMe2ONHSiMe2Butin the presence of tmen results in cleavage of the N–O bond and formation of (ButSiMe2OLi)6.81An X-ray diffraction study revealed a rare example of an (LiO)4ladder in the structure of {[PhC(O)N(Me)Al(Me)(But)OMe]Li[PhC(O)N(Me)Al(Me)(OBut)OMe]Li}2.82Reaction of α-cyanophosphonates (RO)2P(O)CH2CN(R = Et or Pri) with LiNPri2in thf has yielded the Wittig-type reagents [N&z.tbd6;CCH(RO)2P(O)Li(thf)]∞the structures of which are based on Li2O2rings which link up through inter-dimer associationviathe nitrile group to form cross-linked polymeric networks. In solution the dimer units probably remain intact but the nitrile chelates to the metalviaintra-dimer association.83Halogen-donor ligandsX-Ray structural analysis of [{Li(diox)2.5TaCl4S}n]·0.5ndiox and [{Li2(diox)3Cl}n][TaCl6]nreveals diox molecules linking the cations to form layers of puckered hexagonal nets; in the latter compound the layers are linked by almost linear Li–Cl–Li units to form a three-dimensional structure.84The crystal structure of [HC(CHNPh)2]AlCl(Me)·2[Li{B(C6F5)4}]·C6H6reveals one lithium cation coordinated to six halogen atoms (Cl + 5 F) in a distorted trigonal prismatic arrangement. The other lithium is surrounded by η6-C6H6and four fluorines, two of which are involved in the shortest Li⋯F(C) contacts observed so far (1.895(3)and 1.956(3) Å).85The crystal structure of [LiI(NEt3)]4revealed a cubane core. The energetics of formation and stability with respect to LiI were rationalized using density functional calculations.86

ISSN:0260-1818    

DOI:10.1039/b103207k

出版商:RSC    

年代:2001

数据来源: RSC

摘要:

The breadth, strength and vitality of research in inorganic chemistry worldwide is demonstrated in this, the 105th Volume ofAnnual Reports,Section A, covering research literature published during 2008. As in previous years, the bulk of the referenced work in this compendium has been published in the “core” inorganic chemistry journals, but the growing significance and impact of inorganic chemistry in medicine, biology, materials science and engineering may be evidenced by the year-on-year increase in the breadth of scientific journals publishing inorganic chemistry.The format ofAnnual Reports, Section Aremains largely unchanged, with closely defined reviews organised by the Groups in the periodic table alongside cross-cutting (so-called) special topics in the areas of polymer science, bioinorganic chemistry and material science. In Volume 105, the feature article onHydrogen Storageby Duncan Gregory reviews the topical and burgeoning significance of inorganic compounds in this area. Each article, opening with the author’s own pick of the most important and significant advances in each field, is strictly page limited, ensuring that only the research of the highest quality and impact is included and leading to the most succinct summaries of research in inorganic chemistry published during 2008.However, the most significant value of this volume to research and teaching academics alike is its immediacy and accessibility to the community. Year-on-year, the authors, editorial and production teams have delivered step-change improvements in publication date. Volumes 103 and 104 each set new records for their dates of publication in 2007 and 2008, respectively, and Volume 105 will be published just as speedily, thereby delivering informative and authoritative review articles in the most timely fashion to our readers; indeed Cotton’s review of actinide chemistry published during 2008 was available electronically to subscribers just 4 weeks into 2009. As Editors, we are extremely grateful to the skill, dedication and commitment of the authors in achieving such high standards. We hope that the readers will share our appreciation. Perusal of the work reported here in Volume 105 will leave no one in doubt of the vitality of inorganic chemistry within its own discipline as well as its reach into other scientific subject areas.

ISSN:0260-1818    

DOI:10.1039/b818130f

出版商:RSC    

年代:2009

数据来源: RSC

摘要:

Introduction“Molecular magnetism” is a phrase that means different things to different people. Indeed historically the general nature of research carried out under this banner has changed in emphasis from studies of simple spin carriers and small clusters, through to the search for polymeric networks, which could be tuned to show high-temperature magnetically ordered phases. Most recently we have seen a renaissance in cluster chemistry due to the phenomena of “single molecule magnetism” (SMM) and a greater focus on model systems and multifunctional behaviour. We may try to rationalise the field by looking at it in the wider context of magnetism, and while molecular systems make a small proportion of magnetic materials being investigated, fundamentally the “molecular” part does not limit the breadth and diversity of magnetic behaviour that may be observed. For example while non-itinerant (localised or insulating) systems dominate molecular materials, there are equally examples of metallic1and even superconducting2molecular magnets. To imagine what role will exist for molecular magnetic materials in the future, we must look at likely uses and applications of non-molecular materials. It is difficult to see how molecular systems would surpass the useful properties of robust, inert and cheap materials such as transition metal oxides or intermetallics like samarium cobalt. Such materials will continue to be used in transducer and actuator applications. It is also abundantly clear that existing knowledge and developments in thin film technologies mean that magnetic data storage and read/write devices will continue to develop using simple atomic/ionic materials being engineered with ever more complex nanostructured architectures. Indeed virtually all research into the exciting field of spintronics is focused on non-molecular materials.So what is it that Molecular Materials can offer? In principle molecular systems can be engineered with specific arrangements of magnetic atoms. In reality chemistry isn’t always so kind, yet it is frequently the case that the magnetic atoms are linked up in some other interesting way, to form structures that are inconceivable in simple atomic or ionic compounds. For molecular systems we strive to control not just the relative positions of magnetic ions, but also the sign and strength of all coupling interactions between spin carriers. However, practically we can usually only hope to control some positions and some of the coupling interactions. That said, molecular systems offer two clear key advantages over conventional magnetic materials. (1) The structures that can be formed are more complex and more diverse than the sort of structures that you can see in conventional inorganic/ionic materials. It is also the case that molecular crystals can provide us with ensembles of identical structures and iso-orientated magnetic objects on which we can study physical behaviour. (2) Molecular systems often permit scope for the incorporation of other useful functionality. This may be a synergistic property that is not-coupled with the magnetism, or it may be a more definite coupling of different physical properties, such as a conventional second order ferroic material, or for example, the less conventional light-induced magnetic ordering in spin crossover Prussian blue phases.3The first type of materials will see much continued academic interest, as they offer model systems to test our theories on many body problems, and our rapidly expanding understanding of different macroscopic quantum phase behaviours, while the second group is more likely to find highly specific and novel applications.In view of the large amount of work reported under the umbrella of molecular magnetism, we have been very selective about the area on which we report. The quest for new magnetic materials is a problem for synthetic chemists, whether the aim is to construct a specific discrete molecular cluster, or to form a desirable extended network topology. The synthetic construction of coordination polymers (a rapidly expanding field itself) have been recently reviewed,4but it is worth to note that even the control of the strength of coupling interactions is challenging, especially if one aims for a strong magnetic interaction, since it not only relies upon the network of ions linked by superexchange interactions, but the relative orientation of bridging ligand and magnetic (metal based) orbitals is imperative. In addition anisotropy effects can be equally important in determining the magnetic behaviour of the system. In this respect it is clear that synthetically we have far to go before we are really making designer magnets.

ISSN:0260-1818    

DOI:10.1039/b612962p

出版商:RSC    

年代:2007

数据来源: RSC

摘要:

1.IntroductionAt the juncture of the 20th and 21st centuries it was realised that there was an urgent requirement for an alternative and sustainable energy vector as reserves of fossil fuels faded.1,2Moreover, if the adverse effects of global warming and consequent climate change is to be arrested then the utilisation of green and renewable energy sources is imperative. As Grochala and Edwards and later van den Berg and Areán note in their articles,3Jules Verne first brought these issues to the attention of the public in a work of fiction over 100 years ago: ‘…water will one day be employed as a fuel,that hydrogen and oxygen will constitute it,used singly or together,will furnish an inexhaustible source of heat and light’ and ‘water will be the coal of the future’ (“The Mysterious Island”, Jules Verne, 1874). Verne’s work was to presage with uncanny pertinence the role of hydrogen as the fuel of the future and predict the coming of the so-called ‘hydrogen economy’.An uninterrupted and secure energy supply for the developed nations and meeting the increasing energy demands of the rapidly developing nations are essential. The burgeoning need for energy coupled with the rapid depletion of fossil fuels pose serious threats for sustainable development. Before the potential for hydrogen as a future energy carrier can be realised, fundamental research including components of invention and discovery, subsequent implementation of new technology and socio-economic acceptance must occur. These are the key steps to thehydrogen energy transition.The greater hydrogen energy picture centres around theproductionandstorageof hydrogen, the two most important steps that currently represent a bottle neck to utilization of hydrogen more widely in fuel cell systems. It must be realized that unlike coal or oil, hydrogen is not naturally available. Thus, stable large-scale hydrogen production is necessary for the gradual switchover to the hydrogen economy. However a safe, efficient and economic storage medium is likely to be a crucial prerequisite before hydrogen would be globally acceptable as a fuel, particularly in mobile (automotive) applications. It should be emphasised here that while gaseous or liquid hydrogen is currently an option for prototype personal vehicles (cars) or larger commercial transport, solid state storage of hydrogen is potentially superior with regard to its storage capacity (both gravimetric and volumetric), energy efficiency and safety.2Nevertheless compact storage of hydrogen in a solid medium is the most demanding and challenging part of realising the hydrogen economy as far as mobile applications are concerned (Fig. 1).2bAlternatives for storage of 4 kg hydrogen, with volume relative to the size of a car. (Reprinted fromref. 2b, with permission from Macmillan Publishers Ltd.)Hydrogen storage is thus a key research area where considerable international effort is concentrated. Since this review is written from a materials perspective, current chemical research in hydrogen storage materials will be highlighted capturing the discoveries and developments over the past decade (1998–2009), the many opportunities that could be seized and the future pathways that could be taken. Although many of the materials classes meet the majority of the US Department of Energy (US-DoE) criteria for vehicular applications (e.g.hydrogen storage capacity; the amount of hydrogen stored per unit mass and per unit volume),4other factors such as non-reversibility, slow kinetics and sometimes thermodynamic barriers to hydrogen uptake-release limit or prevent their practical use. Holistic and systematic research towards understanding mechanism, structure and thermodynamics and their inter-relationships are crucial to innovation and materials development. This review illustrates the extent of emerging materials discovery and design and demonstrates how an improved chemical understanding of storage processes informs an evolving materials design strategy.

ISSN:0260-1818    

DOI:10.1039/b818951j

出版商:RSC    

年代:2009

数据来源: RSC

摘要:

IntroductionThis review covers the literature published in 2001. Due to space limitations it is not exhaustive, focusing on what this author considers to be significant contributions to the field in 2001. Descriptions of specific results are often kept to a minimum, with the reader directed to the original paper for more information. The overall approach of this section is similar to that used in previous years, with the inorganic and organometallic aspects of boron reviewed.Exo-substituted heteroboranes are included under a separate section, while complexes bearing tris(pyrazolyl)borate type ligands, boron complexes acting simply as innocent counter-ions and organoboron compounds, in general, have not been included.

ISSN:0260-1818    

DOI:10.1039/b109572m

出版商:RSC    

年代:2002

数据来源: RSC

摘要:

1IntroductionThis review covers the literature published in 2000, searched using Web of Science, CAS and the Cambridge Crystallographic Database. Owing to space limitations, descriptions of specific results are kept to a minimum, with the reader directed to the original paper for more information. The overall approach of this section is similar to that used in previous years, with the inorganic and organometallic aspects of boron reviewed.exoMetalla-substituted heteroboranes are included in the heteroborane section, while complexes bearing tris-pyrazolyl type borate ligands, boron complexes acting simply as innocent counter ions and organoboron compounds in general have not been included.

ISSN:0260-1818    

DOI:10.1039/b103229c

出版商:RSC    

年代:2001

数据来源: RSC

摘要:

HighlightsHighlights include the first molecular calcium hydride and calcium hydroxide, several reports detailing the synergic reactivity of heterometallic ‘ate’ complexes and the first example of a chiral main group metal based catalyst for asymmetric hydroamination/cyclisation reactions of aminoalkenes.

ISSN:0260-1818    

DOI:10.1039/b612595f

出版商:RSC    

年代:2007

数据来源: RSC

摘要:

The chemistry of metalloid cluster compounds for Al, Ga and In dominate current Group 13 chemistry; a review by Schnepf and Schnöckel summarizes the situation for Al and Ga.13bThe first direct observation of radicals by EPR in the activation of a Zeigler–Natta system is both interesting and important for our understanding of these catalysts.50bFor gallium and indium chemistry, a highlight very much in tune with the green chemistry movement, is the report of the first aqueous preparation of high yield, relatively monodisperse, well crystallized GaP and InP nanocrystallites, exhibiting pronounced quantum confinement.59Whilst they have had to be relegated to ESI, the increasing interest in indium for Barbier-Grignard type organic syntheses in aqueous media has a green complexion and there are the first signs of similar developments for aqueous gallium chemistry.110bNew work on the two-electron transfer for Tlaq3+/Tlaq+with electrochemical evidence for [Tl(ii)–Tl(ii)]4+is a major highlight for thallium chemistry.142The synthesis and structure of [In(ii)–In(ii)]4+is also notable.129

ISSN:0260-1818    

DOI:10.1039/b211506a

出版商:RSC    

年代:2003

数据来源: RSC