Structural motifs in phenylbismuth heterocyclic carboxylates--secondary interactions leading to oligomers

The reaction of triphenylbismuth [BiPh(3)] with several heterocyclic carboxylic acids was explored. Seven crystalline compounds, [PhBi(2-O(2)C-3-(OH)C(5)H(3)N)(2)(2-O(2)C-3-(OH)C(5)H(3)NH)] (5), [(Bi(2-O(2)C-3-(OH)C(5)H(3)N)(4))(C(5)H(5)NH)(C(5)H(5)N)] (7), [PhBi(2-O(2)C-C(4)H(3)N(2))(2)(2-O(2)C-C(4)H(4)N(2))·H(2)O] (8), [PhBi(2-O(2)C-C(9)H(6)N)(2)·H(2)O] (9), [Ph(2)Bi(O(2)C-C(4)H(3)O)] (10), [Ph(2)Bi(O(2)C-C(4)H(3)S)] (11) and [PhBi(O(2)C-C(4)H(3)S)(2)](2) (12), were prepared by simple reactions using BiPh(3) and the corresponding acids, 3-hydroxypicolinic acid, pyrazine-2-carboxylic acid, quinoline-2-carboxylic (quinaldic) acid, furan-2-carboxylic acid and thiophene-2-carboxylic acid. Compound 5 primarily exhibits a coordination number of six with pentagonal pyramidal geometry at bismuth, but an additional weak Bi···O interaction in the direction of the lone pair of electrons is present. This feature leads to a weakly bound dimer. The use of pyridine as the solvent in a similar reaction, however, led to 7, in which all of the Bi-Ph bonds are cleaved. In this compound, bismuth exhibits a coordination number of eight and distorted dodecahedral geometry. In compound 8, the geometry around bismuth is primarily a pentagonal pyramid, however, clear-cut but weak secondary Bi···N interactions leading to a dimeric formulation are discernible in the structure. The quinaldate compound 9 exhibits a lower formal coordination number of five for bismuth, with square pyramidal geometry, but again two secondary Bi···O interactions for each bismuth in the direction of the lone pair lead to a dimer. A similar secondary Bi···O interaction involving furan oxygen is present in the furoate compound 10, which is a polymeric chain (one dimensional coordination polymer). Although the thiophene carboxylate 11 is also a polymeric chain, no Bi···S interactions are present. Unlike the previously reported tetrameric biscarboxylate [PhBi(2-O(2)C-C(5)H(3)N)(2)](4), the thiophene carboxylate [PhBi(O(2)C-C(4)H(3)S)(2)](2) (12) is a dimer considering only primary interactions. However, these dimers are arranged in such a way that there are secondary Bi···S interactions in the structure in the expected direction of the lone pair of electrons on bismuth. Thus, these studies suggest that the stereochemical activity (or inactivity) of the bismuth lone pair of electrons need to be judged more cautiously. TGA studies are consistent with the presence of Bi-Ph groups in all of the compounds, except 7, as indicated by their formulae.     

The possibility of the decomposition of 2'-deoxyribose moiety of thymidine induced by the low energy electron attachment

To evaluate the possibility of the decomposition of 2-deoxyribose moiety of thymidine induced by low energy electrons (LEE) attachment, the transition states and the energy barriers of the bond breaking processes of the ribose of the nucleoside have been studied theoretically by applying the density functional theory with the double zeta basis sets (DZP++). The energy barriers for the breakage of the C-C bonds (C(1')-C(2'), C(2')-C(3'), C(3')-C(4'), and C(4')-C(5')) of the ribose group of the radical anion of thymidine are found to be high (ca. 42-57 kcal/mol). The total energies of the C-C bond-broken products are significantly higher than that of the radical anion dT(*-). The decomposition of dT(*-) through the C-C bond rupture is unlikely to take place. The rupture of the C(1')-O(4') bond of dT(*-) needs an activation energy as low as 10.4 kcal/mol. However, the reversed reaction (C(1')-O(4') bond formation) needs the activation energy low as 0.3 kcal/mol. Therefore, the intermediate product LM1(C1')-(O4') is unlikely to be stable and the C(1')-O(4') bond-broken is not favored. The activation energy of the C(4')-O(4') bond rupture process amounts to 20.5 kcal/mol. The total energy of the C(4')-O(4') bond broken product is about 6.5 kcal/mol lower than that of the reactant dT(*-). The subsequent N1-glycosidic bond breaking process is found to have a very low energy barrier. Therefore, the LEE-induced base release through the C(4')-O(4') bond rupture might be a possible pathway.     

New synthetic route for organic polyoxometallic clusters: synthetic and structural investigations on the first dumb-bell shaped polyoxozirconium hydroxide with the [Zr9(mu5-O)2(mu3-O)4(mu-O)4(mu-OH)8] core structure

A new route for organic polyoxometallic clusters describes the first dumb-bell-like organic polyoxozirconium hydroxide [[(Cp*Zr)4(mu5-O)(mu3-O)2(mu-OH)4]2Zr(mu-O)4] x 2C7H8 (2; Cp* = C5Me5) involving the treatment of the Br?nsted acidic organozirconium hydroxide [(Cp*Zr)6(mu4-O)(mu-O)4(mu-OH)8] x 2C7H8 (1) with organozirconium compounds.     

Synthesis, structure, and magnetic properties of (6-9)-nuclear Ni(II) trimethylacetates and their heterospin complexes with nitroxides

New polynuclear nickel trimethylacetates [Ni6(OH)4(C5H9O2)8(C5H10O2)4] (6), [Ni7(OH)7(C5H9O2)7(C5H10O2)6(H2O)] x 0.5 C6H14 x 0.5 H2O (7), [Ni8(OH)4(H2O)2(C5H9O2)12] (8), and [Ni9(OH)6(C5H9O2)12(C5H10O2)4] x C5H10O2 x 3 H2O (9), where C5H9O2 is trimethylacetate and C5H10O2 is trimethylacetic acid, have been found. Their structures were determined by X-ray crystallography. Because of their high solubility in low-polarity organic solvents, compounds 6-9 reacted with stable organic radicals to form the first heterospin compounds based on polynuclear Ni(II) trimethylacetate and nitronyl nitroxides containing pyrazole (L(1)-L(3)), methyl (L(4)), or imidazole (L(5)) substituent groups, respectively, in side chain [Ni7(OH)5(C5H9O2)9(C5H10O2)2(L(1))2(H2O)] x 0.5 C6H14 x H2O (6+1a), [Ni7(OH)5(C5H9O2)9(C5H10O2)2(L2)2(H2O)] x H2O (6+1b), [Ni7(OH)5(C5H9O2)9(C5H10O2)2(L(3))2(H2O)] x H2O (6+1c), [Ni6(OH)3(C5H9O2)9(C5H10O2)4(L(4))] x 1.5 C6H14 (6'), and [Ni4OH)3(C5H9O2)5(C5H10O2)4(L(5))] x 1.5 C7H8 (4). Their structures were also determined by X-ray crystallography. Although Ni(II) trimethylacetates may have varying nuclearity and can change their nuclearity during recrystallization or interactions with nitroxides, this family of compounds is easy to study because of its topological relationship. For any of these complexes, the polynuclear framework may be derived from the [Ni6] polynuclear fragment {Ni6(mu4-OH)2(mu3-OH)2(mu2-C5H9O2-O,O')6(mu2-C5H9O2-O,O)(mu4-C5H9O2-O,O,O',O')(C5H10O2)4}, which is shaped like an open book. On the basis of this fragment, the structure of 7-nuclear compounds (7 and 6+1a-c) is conveniently represented as the result of symmetric addition of other mononuclear fragments to the four Ni(II) ions lying at the vertexes of the [Ni6] open book. The 9-nuclear complex is formed by the addition of trinuclear fragments to two Ni(II) ions lying on one of the lateral edges of the [Ni6] open book. This wing of the 9-nuclear complex preserves its structure in another type of 6-nuclear complex (6') with the boat configuration. If, however, two edge-sharing Ni(II) ions are removed from [Ni6] (one of these lies at a vertex of the open book and the other, on the book-cover line), we obtain a 4-nuclear fragment recorded in the molecular structure of 4. Twinning of this 4-nuclear fragment forms highly symmetric molecule 8, which is a new chemical version of cubane.     

C-H键选择性直接电氧化研究

C-H键是有机化合物中最基本的化学键,C-H键的活化和直接转化避免了反应物的预先官能化,是最终实现烷烃类化合物转化为不同种类有机化合物最直接、高效的转换方式,通过C-H键构建C-X键（X=O、C、N）是非常重要和具有挑战性的研究. C-H键直接电氧化活化过程中以“电子”参与反应,不需要加入额外的催化剂,并可通过选择合适的电极材料、支持电解质、溶剂和反应温度,通过恒电流或者恒电位电解,进行具有特定的反应选择性和区域选择性的C-H键电氧化活化,从而获得含其他活性基团的目标产物.     

Transition metal-catalyzed carbon-carbon bond activation

This tutorial review deals with recent developments in the activation of C-C bonds in organic molecules that have been catalyzed by transition metal complexes. Many chemists have devised a variety of strategies for C-C bond activation and significant progress has been made in this field over the past few decades. However, there remain only a few examples of the catalytic activation of C-C bonds, in spite of the potential use in organic synthesis, and most of the previously published reviews have dwelt mainly on the stoichiometric reactions. Consequently, this review will focus mainly on the catalytic reaction of C-C bond cleavage by homogeneous transition metal catalysts. The contents include cleavage of C-C bonds in strained and unstrained molecules, and cleavage of multiple C-C bonds such as C[triple bond]C triple bonds in alkynes. Multiple bond metathesis and heterogeneous systems are beyond the scope of this review, though they are also fascinating areas of C-C bond activation. In this review, the strategies and tactics for C-C bond activation will be explained.     

Carbon-silicon and carbon-carbon bond formation by elimination reactions at metal N-heterocyclic carbene complexes

Two functional groups can be delivered at once to organo-rare earth complexes, (L)MR(2) and (L)(2)MR (M = Sc, Y; L = ({1-C(NDippCH(2)CH(2)N)}CH(2)CMe(2)O), Dipp = 2,6-(i)Pr(2)-C(6)H(3); R = CH(2)SiMe(3), CH(2)CMe(3)), via the addition of E-X across the metal-carbene bond to form a zwitterionic imidazolinium-metal complex, (L(E))MR(2)X, where L(E) = {1-EC(NDippCH(2)CH(2)N)}CH(2)CMe(2)O, E is a p-block functional group such as SiR(3), PR(2), or SnR(3), and X is a halide. The "ate" complex (L(Li))ScR(3) is readily accessible and is best described as a Li carbene adduct, ({1-Li(THF)C(NDippCH(2)CH(2)N)}CH(2)CMe(2)O)Sc(CH(2)SiMe(3))(3), since structural characterization shows the alkoxide ligand bridging the two metals and the carbene Li-bound with the shortest yet recorded Li-C bond distance. This can be converted via lithium halide-eliminating salt metathesis reactions to alkylated or silylated imidazolinium derivatives, (L(E))ScR(3) (E = SiMe(3) or CPh(3)). All the E-functionalized imidazolinium complexes spontaneously eliminate functionalized hydrocarbyl compounds upon warming to room temperature or slightly above, forming new organic products ER, i.e., forming C-Si, C-P, and C-Sn bonds, and re-forming the inorganic metal carbene (L)MR(X) or (L)(2)MX complex, respectively. Warming the tris(alkyl) complexes (L(E))MR(3) forms organic products arising from C-C or C-Si bond formation, which appears to proceed via the same elimination route. Treatment of (L)(2)Sc(CH(2)SiMe(3)) with iodopentafluorobenzene results in the "reverse sense" addition, which upon thermolysis forms the metal aryl complex (L)(2)Sc(C(6)F(5)) and releases the iodoalkane Me(3)SiCH(2)I, again facilitated by the reversible functionalization of the N-heterocyclic carbene group in these tethered systems.     

C-H vs C-C bond activation of acetonitrile and benzonitrile via oxidative addition: rhodium vs nickel and Cp* vs Tp' (Tp' = hydrotris(3,5-dimethylpyrazol-1-yl)borate, Cp* = η(5)-pentamethylcyclopentadienyl)

The photochemical reaction of (C(5)Me(5))Rh(PMe(3))H(2) (1) in neat acetonitrile leads to formation of the C-H activation product, (C(5)Me(5))Rh(PMe(3))(CH(2)CN)H (2). Thermolysis of this product in acetonitrile or benzene leads to thermal rearrangement to the C-C activation product, (C(5)Me(5))Rh(PMe(3))(CH(3))(CN) (4). Similar results were observed for the reaction of 1 with benzonitrile. The photolysis of 1 in neat benzonitrile results in C-H activation at the ortho, meta, and para positions. Thermolysis of the mixture in neat benzonitrile results in clean conversion to the C-C activation product, (C(5)Me(5))Rh(PMe(3))(C(6)H(5))(CN) (5). DFT calculations on the acetonitrile system show the barrier to C-H activation to be 4.3 kcal mol(-1) lower than the barrier to C-C activation. A high-energy intermediate was also located and found to connect the transition states leading to C-H and C-C activation. This intermediate has an agostic hydrogen interaction with the rhodium center. Reactions of acetonitrile and benzonitrile with the fragment [Tp'Rh(CNneopentyl)] show only C-H and no C-C activation. These reactions with rhodium are compared and contrasted to related reactions with [Ni(dippe)H](2), which show only C-CN bond cleavage.     

C-H Bond activation and C-C bond formation in the reaction of 2,5-dimethylthiophene with TpMe2Ir compounds

The bulky 2,5-dimethylthiophene (2,5-Me2T) reacts at 60 degrees C with TpMe2Ir(C2H4)2 to give a mixture of two TpMe2Ir(III) hydride products, 3 and 4, that contain in addition a thienyl (3) or a thienyl-derived ligand (4). For the generation of 3 only sp2 C-H activation is needed, but the formation of 4 requires also the activation of an sp3 C-H bond and the formation of a new C-C bond (between vinyl and thienyl fragments). In the presence of 2,5-Me2T, compound 4 reacts further to produce a complex thiophenic structure (5, characterized by X-ray methods) that derives formally from two molecules of 2,5-Me2T and a vinyl fragment. Compounds 3-5 can be readily protonated by [H(OEt2)2][BAr'4](Ar'= 3,5-C6H3(CF3)2), with initial generation of carbene ligands (in the case of 3 and 5) as a consequence of H+ attack at the beta-carbon of the Ir-thienyl unit. Free, substituted thiophenes, derived from the original 2,5-Me2T, may be isolated in this way.     

Molecular structure and internal rotation in 2,3,5,6-tetrafluoroanisole as studied by gas-phase electron diffraction and quantum chemical calculations

The geometric structure of 2,3,5,6-tetrafluoroanisole and the potential function for internal rotation around the C(sp2)-O bond were determined by gas electron diffraction (GED) and quantum chemical calculations. Analysis of the GED intensities with a static model resulted in near-perpendicular orientation of the O-CH3 bond relative to the benzene plane with a torsional angle around the C(sp2)-O bond of tau(C-O) = 67(15) degrees. With a dynamic model, a wide single-minimum potential for internal rotation around the C(sp2)-O bond with perpendicular orientation of the methoxy group [tau(C-O) = 90 degrees] and a barrier of 2.7 +/- 1.6 kcal/mol at planar orientation [tau(C-O) = 0 degrees] was derived. Calculated potential functions depend strongly on the computational method (HF, MP2, or B3LYP) and converge adequately only if large basis sets are used. The electronic energy curves show internal structure, with local minima appearing because of the interplay between electron delocalization, changes in the hybridization around the oxygen atom, and the attraction between the positively polarized hydrogen atoms in the methyl group and the fluorine atom at the ortho position. The internal structure of the electronic energy curves mostly disappears if zero-point energies and thermal corrections are added. The calculated free energy barrier at 298 K is 2.0 +/- 1.0 kcal/mol, in good agreement with the experimental determination.     

Direct Sp3α-C-H activation and functionalization of alcohol and ether

Seven kinds of sp(3)α-C-H activation/C-C formation reactions of alcohols and ethers have been reviewed in this tutorial review, from the viewpoint of both methodology and synthetic application, towards the efficiency, chemo-, regio- and stereoselectivity, catalytic system, substrate scope and mechanistic study. Section 2 describes radical-mediated α-C-H activation and addition/elimination of ethers with unsaturated (C=C and C[triple bond]C) species. Sections 3-8 discuss the α-C-H activation and additions of alcohols and/or ethers with unsaturated (C=C, C[triple bond]C, C=O and C=N) compounds, which involve the key processes of radical mediation, carbenoid insertion, 1,5-H-migration, oxidative dehydrogenation coupling, transfer hydrogenative coupling, and metal-mediated C=C insertion into the C-H bond.     

木质素模化物键离解能的理论研究

采用密度泛函理论B3P86方法,在6-31G(d,p)基组水平上,对木质素结构中的6种连接方式(β-O-4、α-O-4、4-O-5、β-1、α-1、5-5)的63个木质素模化物的醚键(C-O)和C-C键的键离解能E_B进行了理论计算研究。分析了不同取代基对键离解能的影响以及键长与键离解能的相关性。计算结果表明,C-O键的键离解能通常比C-C键的小,在各种醚键中C_α-O键的平均键离解能最小,为182.7 kJ/mol;其次是β-O-4连接中的C_β-O键,苯环和烷烃基上的取代基对醚键的键离解能有较强的弱化作用,C-O键的键长和键离解能的相关性较差。与C-O键相比,C-C键的键离解能受苯环上取代基的影响很小,而烷烃基上的取代基对C-C键的键离解能有较大的影响,C-C键的键离解能和键长之间存在较强的线性关系,C-C键的键长越长,其键离解能越小。     

Reversible intramolecular C-C bond formation/breaking and color switching mediated by a N,C-chelate in (2-ph-py)BMes2 and (5-BMes2-2-ph-py)BMes2

A diboron compound with both 3-coordinate boron and 4-coordinate boron centers, (5-BMes2-2-ph-py)BMes2 (1) and its monoboron analogue, (2-ph-py)BMes2 (2) have been synthesized. Both compounds are luminescent but have a high sensitivity toward light. UV and ambient light cause both compounds to isomerize to 1a and 2a, respectively, via the formation of a C-C bond between a mesityl and the phenyl group, accompanied by a drastic color change from yellow or colorless to dark olive green or dark blue. The structures of 1a and 2a were established by 2D NMR experiments and geometry optimization by DFT calculations. Both 1a and 2a can thermally reverse back to 1 and 2 via the breaking of a C-C bond, with the activation barrier being 107 and 110 kJ/mol, respectively. The N,C-chelate ligands in 1 and 2 were found to play a key role in promoting this unusual and reversible photo-thermal isomerization process on a tetrahedral boron center. Reactions with oxygen molecules convert 1a and 2a to 5-BMes2-2-[(2-Mes)-ph]-pyridine (1b) and 2-(2-Mes)-ph-pyridine (2b), respectively.     

Unusual group migration and C(sp3)-H activation leading to stable metallacycles in the reactions of Cp*IrS2C2B10H10 and aryl azides

The thermal or photochemical reactions of Cp*IrS(2)C(2)B(10)H(10) (1) and aryl azides lead to C-C coupling via C(sp(3))-H activation in 2 as well as the formation of C-S bonds and new-type SSN pincer ligands in 3-8 through ortho-substituted electron-withdrawing group migration over an aryl ring.     

NH2(C2H4)2O]MX5: a new family of morpholinium nonlinear optical materials among halogenoantimonate(III) and halogenobismuthate(III) compounds. Structural characterization, dielectric and piezoelectric properties

This paper presents the structural features of ionic complexes formed by morpholine and metal ions which belong to group VA, namely Sb(III) and Bi(III). A series of target inorganic-organic hybrid compounds of the general formula [NH(2)(C(2)H(4))(2)O](2)MX(5) (where M = Sb, Bi; X = Cl, Br) has been synthesized by incorporating the organic component (morpholine) into the highly polarizable one-dimensional halogenoantimonate(III)/halogenobismuthate(III) chain network. Among the studied compounds, four were found to crystallize in the room temperature phase in the piezoelectric, orthorhombic space group P2(1)2(1)2(1), Z = 4, the feature being confirmed by the powder second harmonic generation of light and piezoelectric measurements. Dielectric dispersion studies between 200 Hz and 2 MHz disclosed a relaxation process below room temperature well described by the Cole-Cole equation. Based on crystal structures available in Cambridge Structural Database (version 5.32, November 2010) we attempt to show a relationship between the acentric symmetry of compounds and the type of anionic network within the R(2)MX(5)-subgroup (where R denotes organic cation) of halogenoantimonates(III) and halogenobismuthates(III).     

Olefin epoxidation by peroxo complexes of cr, mo, and W. A comparative density functional study

The epoxidation of olefins by peroxo complexes of Cr(VI), Mo(VI) and W(VI) was investigated using the B3LYP hybrid density functional method. For the mono- and bisperoxo model complexes with the structures (NH(3))(L)M(O)(2)(-)(n)()(eta(2)-O(2))(1+)(n)() (n = 0, 1; L = none, NH(3); M = Cr, Mo, W) and ethylene as model olefin, two reaction mechanism were considered, direct oxygen transfer and a two-step insertion into the metal-peroxo bond. The calculations reveal that direct attack of the nucleophilic olefin on an electrophilic peroxo oxygen center via a transition state of spiro structure is preferred as significantly higher activation barriers were calculated for the insertion mechanism than for the direct mechanism. W complexes are the most active in the series investigated with the calculated activation barriers of direct oxygen transfer to ethylene decreasing in the order Cr > Mo > W. Barriers of bisperoxo species are lower than those of the corresponding monoperoxo species. Coordination of a second NH(3) base ligand to the mono-coordinated species, (NH(3))M(O)(2)(eta(2)-O(2)) and (NH(3))MO(eta(2)-O(2))(2), results in a significant increase of the activation barrier which deactivates the complex. Finally, based on a molecular orbital analysis, we discuss factors that govern the activity of the metal peroxo group M(eta(2)-O(2)), in particular the role of metal center.     

Reactivity of niobium(v) and tantalum(v) halides with carbonyl compounds: synthesis of simple coordination adducts, C-H bond activation, C=O protonation, and halide transfer

The metal halides of Group 5 MX(5) (M = Nb, Ta; X = F, Cl, Br) react with ketones and acetylacetones affording the octahedral complexes [MX(5)(ketone)] () and [TaX(4){kappa(2)(O)-OC(Me)C(R)C(Me)O}] (R = H, Me, ), respectively. The adducts [MX(5)(acetone)] are still reactive towards acetone, acetophenone or benzophenone, giving the aldolate species [MX(4){kappa(2)(O)-OC(Me)CH(2)C(R)(R')O}] (). The syntheses of (M = Ta, X = F, R = R' = Ph) and (M = Ta, X = Cl, R = Me, R' = Ph) take place with concomitant formation of [(Ph(2)CO)(2)-H][TaF(6)], and [(MePhCO)(2)-H][TaCl(6)], respectively. The compounds [acacH(2)][TaF(6)], and [TaF{OC(Me)C(Me)C(Me)O}(3)][TaF(6)], have been isolated as by-products in the reactions of TaF(5) with acacH and 3-methyl-2,4-pentanedione, respectively. The molecular structures of, and have been ascertained by single crystal X-ray diffraction studies.     

Geminal 2JCCH spin-spin coupling constants as probes of the phi glycosidic torsion angle in oligosaccharides

Two-bond (13)C-(1)H NMR spin-spin coupling constants ((2)J(CCH)) between C2 and H1 of aldopyranosyl rings depend not only on the relative orientation of electronegative substituents on the C1-C2 fragment but also on the C-O torsions involving the same carbons. The latter dependencies were elucidated theoretically using density functional theory and appropriate model pyranosyl rings representing the four relative configurations at C1 and C2, and a 2-deoxy derivative, to probe the relationship between (2)J(C2,H1) magnitude and sign and the C1-O1 (phi, phi) and C2-O2 (alpha) torsion angles. Related calculations were also conducted for the reverse coupling pathway, (2)J(C1,H2). Computed J-couplings were validated by comparison to experimentally measured couplings. (2)J(CCH) displays a primary dependence on the C-O torsion involving the carbon bearing the coupled proton and a secondary dependence on the C-O torsion involving the coupled carbon. These dependencies appear to be caused mainly by the effects of oxygen lone pairs on the C-H and C-C bond lengths along the C-C-H coupling pathway. New parameterized equations are proposed to interpret (2)J(C1,H2) and (2)J(C2,H1) in aldopyranosyl rings. The equation for (2)J(C2,H1) has particular value as a potential NMR structure constraint for the C1-O1 torsion angle (phi) comprising the glycosidic linkages of oligosaccharides.     

交叉脱氢偶联反应*

发现高效高选择性的有机合成反应是有机合成化学研究中一个重要的发展方向。传统的有机合成化学是建立在官能团相互转化基础上的,又称官能团化学。非活泼化学键（如C-H键）的直接官能团化省去了一步甚至多步制备官能团化的反应底物,因此,非活泼化学键活化是提高有机合成反应效率的一个重要发展方向。交叉脱氢偶联（Cross-Dehydrogenative-Coupling,CDC）反应就是直接利用不同反应底物中的C-H键,在氧化条件下,进行脱氢偶联反应形成C-C键。交叉脱氢偶联反应实现了更短的合成路线和更高的原子利用效率,为直接利用简单的原料进行高效的复杂的有机合成任务提供了一种新的思路和手段。     

Methylene transfer from SnMe groups mediated by a rhodium(I) pincer complex: Sn-C, C-C, and C-H bond activation

The PCP-Rh(I) complex 1a based on the [1,3-phenylenebis(methylene)]bis(diisopropylphosphine) ligand reacts with [diazo(phenyl)methyl]trimethylstannane (2) at room temperature to give novel pincer-type phenyl(dimethylstannyl)methylene]hydrazinato complex 3a. The reaction sequence involves a unique combination of Sn-C bond cleavage, C-C bond formation, C-H activation and intramolecular deprotonation of a rhodium hydride intermediate, which results in methylene transfer from an SnMe group to the pincer system and PCP-chelate expansion. A methylene-transfer reaction was also demonstrated with tetramethyltin as the methylene source in the presence of KOC(CH(3))(3) at room temperature. The resulting unstable "chelate-expanded" Rh(I) complex [(C(10)H(5)(CH(2)PiPr(2))(2))(CH(2))Rh(L)] (L=N(2), THF; 4a) was isolated as its carbonyl derivative 5a. Heating 4a in benzene yielded an equimolar amount of toluene and 1a, which demonstrates the ability of the Rh(I) pincer complex to extract a methylene group from an unactivated alkyl tin substrate and transfer it, via C-C followed by C-H activation, to an arene. Use of fluorobenzene resulted in formation of fluorotoluene. Catalytic methylene-group transfer mediated by 1a was not possible, because of formation of o-xylylene complex 8 under the reaction conditions. Steric parameters play a decisive role in the reactivity with tin compounds; while iPrP derivative 1 a underwent facile reactions, tBuP complex 1b was inert.