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The C–C bond reduction and metathesis are fundamentally important in organic synthesis. However, homogeneously reducible C–C bonds are currently limited to either strained rings or to specific and prefunctionalized sites; and there are no practical methods for tandem C–C reduction and intramolecular C(sp3)–C(sp3) metathesis. Here we report a versatile approach for selective reduction of unstrained C(sp3)–C(sp3) bond of ketones, including hydrogenolytic retro-[2+2+2]-cycloreversion of 2,4-diaroylcyclohexanols, without requiring protecting groups. We have also established an unprecedented intramolecular C(sp3)–C(sp3) metathesis, thus enabling the cyclizative degradation of poly(vinylketone). The present C–C cleavage occurs via a bimetallic pathway and nucleophile trapping of resulting enone is crucial for C–C cleavage relay. These results would open new prospect for deconstruction of organic molecules.

A series of guanidinate rare-earth metal complexes [(PhCH2)2NC(NC6H4iPr2-2,6)2]RE(CH2C6H4NMe2-o)2 (RE = Y (2a), La (2b), Dy (2c), Lu (2d)) were synthesized by the acid–base reaction of RE(CH2C6H4NMe2-o)3 with (PhCH2)2N[C(NHR)(NR)] (R = 2,6-iPr2-C6H3) (1) in THF. Treatment of complexes 2 with two equivalents of carbon dioxide, sulfur and phenyl isothiocyanate gave the corresponding insertion products {[(PhCH2)2NC(NC6H4iPr2-2,6)2]RE(μ-η2:η1-O2CCH2C6H4NMe2-o)(μ-η1:η1-O2CCH2C6H4NMe2-o)}2 (RE = Y (3a), La (3b), Dy (3c), Lu (3d)), {[(PhCH2)2NC(NC6H4iPr2-2,6)2]RE[μ-S(CH2C6H4NMe2-o)]2}2 (RE = Y (4a), La (4b), Dy (4c), Lu (4d)) and {[(PhCH2)2NC(NC6H4iPr2-2,6)2]RE{SC(CH2C6H4NMe2-o)NPh}2 (RE = Y (5a), La (5b), Dy (5c), Lu (5d)) in good yields, respectively. All new complexes were fully characterized by NMR spectroscopy and elemental analysis. The structures of 1, 2d, 3, 4a, 4c–d, 5a, and 5c–d were established by X-ray diffraction studies. Complexes 2 were found to have a high activity and excellent 3,4-selectivity for isoprene polymerization in the presence of [Ph3C][B(C6F5)4].

[Cp2Ln(μ-OH)(THF)]2 react with 2 equiv of CyNCNCy (Cy = cyclohexyl) to form [Cp2Ln(μ-OC(NHCy)NCy)]2 (Ln = Er (1-Er), Y (1-Y)), while treatment of [Cp2Ln(μ-OH)]2(μ3-O)LnCp(THF) with CyNCNCy affords the addition/rearrangement products [Cp2Ln(μ3-O)(μ-OC(NHCy)NCy)LnCp]2 (Ln = Yb (3-Yb), Er (3-Er)). Compounds [(Cp2Ln)2(μ3-CO3)(THF)]2 (Ln = Yb (4-Yb), Er (4-Er)) can be obtained by treatment of [Cp2Ln(μ-OH)(THF)]2 with CO2 immediately followed by the reaction with the corresponding Cp3Ln. Complexes 1–4 were characterized by elemental analysis, spectroscopic properties and X-ray single crystal diffraction analysis.

A highly efficient air-initiated hydrosilylation of unactivated alkynes and alkenes and dehalogenation of halohydrocarbons with tris(trimethylsilyl)silane ((TMS)3SiH) as a reducing agent has been established under solvent-free conditions. These observations demonstrate that the potential and versatility of air to function as a competent initiator for Si–H bond activations. It can rival organic initiators and metal catalysts in its efficiency and is a superior initiating system from economic, environmentally sound and practical perspectives.

Reaction of Cp 2 LnNH n Bu with 1 equiv. of Ph 2 CCO in toluene affords dimeric complexes [Cp 2 Ln(OC(CHPh 2 )N n Bu)] 2 [Ln = Yb ( 1 ), Dy ( 2 )], derived from a formal insertion of the C C bond of the ketene into the N–H bond. Treatment of CpErCl 2 with 2 equiv. of LiNH n Bu followed by reacting with Ph 2 CCO affords a rearrangement product [Cp 2 Er(OC(CHPh 2 )N n Bu)] 2 ( 3 ). Treatment of [Cp 2 Ln(μ-Im)] 3 (Im = imidazolate) with PhRCCO gives [Cp 2 Ln(μ-OC(Im) CPhR)] 2 [R = Et, Ln = Yb ( 4 ); R = Ph, Ln = Yb ( 5 ), Er ( 6 )]. In contrast to the previous observations that [Cp 2 ErN i Pr 2 ] 2 and [Cp 2 ErNHEt] 2 react with ketenes to give di-insertion products, in the present cases the presence of excess of ketenes has no influence on the final product even with prolonged heating and only monoinsertion products are isolated. All these complexes were characterized by elemental analysis, IR and mass spectroscopies. The structures of complexes 1 and 3 – 6 were also determined through X-ray single crystal diffraction analysis.

A mild, versatile, and efficient method for the one-step synthesis of substituted dihydro- and tetrahydroisoquinolines has been developed by the FeCl3.6H2O catalyzed intramolecular allenylation/cyclization reaction of benzylamino-substituted propargylic alcohols, representing the first example of the intramolecular Friedel-Crafts reaction of propargylic alcohols.

The focus of this review concerns the reactivity patterns of metal–cyclopentadienyl (indenyl, fluorenyl and cycloheptatrienyl) bonds. The advances in the metal–carbon(η5) insertion chemistry have demonstrated that the π-bonding character provides additional reaction opportunities which are not shown by metal–alkyl compounds and these differences are highlighted.

The synthesis and reactivity of new lanthanocene complexes incorporating phenothiazine ligand are described. The reaction of phenothiazine (HPtz) with nBuLi in THF and subsequently with 1 equiv. of (C5H5)2LnCl(THF) gave the original complexes (C5H5)2LnPtz(THF) (Ln = Yb(1), Er(2), Dy(3), Y(4)). Treatment of complexes 1–4 with N,N′-diisopropylcarbodiimide results in mono-insertion of carbodiimide into the Ln–N(Ptz)-bond to yield the corresponding guanidinates (C5H5)2Ln[(iPrN)2C(Ptz)] (Ln = Yb (5), Er (6), Dy (7), Y(8)). Further investigations indicate that phenyl isothiocyanate react with complexes 1 and 4, giving the correspondent insertion products (C5H5)2Ln[SC(Ptz)NPh](THF) (Ln = Yb(9), Y(10)). All these complexes were characterized by elemental analysis and spectroscopic properties. The structures of complexes 2, 5 and 9 were also determined by the X-ray single crystal diffraction analysis. All these reactions provide a new strategy for introducing a functional substituent at the nitrogen atom of phenothiazine via forming a new C–N(ring) bond.

Treatment of mesoporous silicate SBA-15 with Sm[N(SiMe3)2]3 led to the formation of a novel organolanthanide/inorganic hybrid material [SBA-15]Sm[N(SiMe3)2]x via abstraction of N(SiMe3)2 by terminal silanol groups and subsequent surface silylation. The hybrid material was characterized by elemental analyses, IR spectroscopy, X-ray diffraction, and nitrogen sorption, indicating a successful tailoring inside the silicate SBA-15 and the maintenance of the well-ordered mesostructure. This hybrid material is a promising heterogeneous catalyst for the Tishchenko reaction, where it is superior to the homogeneous correspondent in deactivation behavior, reusability and relative tolerance to oxygen, particularly in the control of selectivity of mixed Tishchenko reaction due to the steric hindrance and the diffusion control derived from the surface confinement.

Two new one-dimensional coordination polymers, viz. the title compounds, [Co[C(CN)(3)](2)(C(6)H(5)N(3))(2)](n), (I), and [Mn[C(CN)(3)](2)(C(5)H(8)N(2))(2)](n), (II), have been synthesized and characterized by X-ray diffraction. Both complexes consist of linear chains with double 1,5-tricyanomethanide bridges between neighbouring divalent metal ions. The Co and Mn atoms are located on centres of inversion. In (I), the coordination environment of the Co(II) atom is that of an elongated octahedron. The Co(II) atom is coordinated in the equatorial plane by four nitrile N atoms of four bridging tricyanomethanide ions, with Co-N distances of 2.106 (2) and 2.110 (2) A, and in the apical positions by two N atoms from the benzotriazole ligands, with a Co-N distance of 2.149 (2) A. The [Co[C(CN)(3)](2)(C(6)H(5)N(3))(2)] units form infinite chains extending along the a axis. These chains are crosslinked via a hydrogen bond between the uncoordinated nitrile N atom of a tricyanomethanide anion and the H atom on the uncoordinated N atom of a benzotriazole ligand from an adjacent chain, thus forming a three-dimensional network structure. In (II), the Mn(II) atom also adopts a slightly distorted octahedral geometry, with four nitrile N atoms of tricyanomethanide ligands [Mn-N = 2.226 (2) and 2.227 (2) A] in equatorial positions and two N atoms of the monodentate 3,5-dimethylpyrazole ligands [Mn-N = 2.231 (2) A] in the axial sites. In (II), one-dimensional polymeric chains extending along the b axis are formed, with tricyanomethanide anions acting as bidentate bridging ligands. A hydrogen bond between the uncoordinated nitrile N atom of the tricyanomethanide ligand and the H atom on the uncoordinated N atom of a 3,5-dimethylpyrazole group from a neighbouring chain links the molecule into a two-dimensional layered structure.

Two new complexes, [Cu(C(2)N(3))(2)(dien)] (dien is diethylenetriamine, C(4)H(13)N(3)), (I), and [Cu(C(2)N(3))(trien)](C(2)N(3)) (trien is triethylenetetramine, C(6)H(18)N(4)), (II), have been characterized by single-crystal X-ray diffraction. Both complexes display a distorted tetragonal-pyramidal geometry. In (I), the Cu atom is coordinated in the basal plane by three diethylenetriamine N atoms [Cu-N = 2.000 (2), 2.004 (2) and 2.025 (2) A] and one terminal N atom [Cu-N = 1.974 (2) A] from one monodentate dicyanamide group, and in the apical position by one terminal N atom [Cu-N = 2.280 (2) A] from the other monodentate dicyanamide group. In (II), the Cu atom is surrounded by four triethylenetetramine N atoms [Cu-N = 2.012 (2), 2.014 (2), 2.019 (2) and 2.031 (2) A in the basal plane] and a terminal N atom [Cu-N = 2.130 (2) A in the apical site] from one monodentate dicyanamide group. The other dicyanamide anion is not directly coordinated to the metal atom. In both (I) and (II), hydrogen-bond interactions between the uncoordinated terminal N atoms of two dicyanamide ions and the amine H atoms lead to the formation of three-dimensional networks.

The synthesis and structures of three new lanthanide complexes incorporating tetra-substituted guanidinate ligand [iPrN∴C(NiPr2)∴NiPr] are described. Treatment of Cp2LnNiPr2(THF) (Ln=Yb, Dy, Gd) with N,N′-di-isopropyl-carbodiimide results in mono-insertion of carbodiimide into the LnN σ-bond to yield Cp2Ln[iPrN∴C(NiPr2)∴NiPr] (Ln=Yb(1), Dy(2), Gd(3)), providing an efficient method for the synthesis of organolanthanide guanidinate complexes. It was found that an excess of N,N′-di-isopropyl-carbodiimide did not affect the nature of the final product. Complexes 1–3 were characterized by elemental analysis, IR and mass spectroscopies. Complexes 1 and 2 were determined by the X-ray single crystal diffraction analysis.

Reactions of anhydrous lanthanide trichloride with one or two equivalent of tert -butyldimethylsilylcyclopentadienyl (Cp t ) potassium salt in THF afford mono( tert -butyldimethylsilylcyclopentadienyl)lanthanide dichloride complexes Cp t LnCl 2 (THF) 3 [Ln=Y( 1 ), Er( 2 )] and bis( tert -butyldimethylsilylcyclopentadienyl)lanthanide chlorides [Cp t 2 Ln(μ-Cl)] 2 [Ln=Gd( 3 ), Er( 4 ), Yb( 5 )], respectively. DyCl 3 reacts with KCp t in THF, followed by the treatment with two equivalents of C 5 H 5 Na to form the mixed-ring complex Cp t Cp 2 Dy(THF) ( 6 ). Reaction of 4 with LiNPr i 2 and subsequently with one equivalent of PhNCO in THF give the PhNCO insertion product Cp t 2 Er[OC(NPr i 2 )NPh](THF) ( 7 ). Complex 4 reacts with one equivalent of sodium benzothiazole-2-thiolate (NaSBT) to yield Cp t 2 Er(SBT)(THF) ( 8 ). Complexes 1 – 8 have been characterized by elemental analyses, infrared, 1 H-NMR and mass spectroscopies. The molecular structures of 3 and 8 were determined by single crystal X-ray diffraction.

Insertions of small molecules into lanthanide–ligand bonds have led to a number of new organolanthanide derivatives. Many attractive catalytic transformations are also based on these insertion reactions. The focus of this review concerns these important stoichiometric and catalytic transformations.

A new phosphaazaallene Mes*PCNAr (Mes*=2,4,6- t Bu 3 C 6 H 2 , Ar= p -ClC 6 H 4 ) ( 1 ) has been synthesized. Complex 1 reacts with Mes*PHSiMe 2 t Bu to form the phosphaazaallene insertion product Mes*PC(PHMes*)NAr(SiMe 2 t Bu) ( 2 ). The treatment of 1 with an excess amount of YCl 3 in THF leads to the isolation of the symmetrical dimer Mes*P(μ-CNAr) 2 PMes* ( 3 ), indicating both of the PC and CN bonds of 1 are reactive sites. X-ray structure analysis of 1 indicates that the distance of the PC bond, 1.642(5) A, is markedly shorter than those of isolated PC bonds (1.66–1.72 A), and the NCP unit slightly deviates from linearity with the PCN angle of 170.8(4)°. The structure determination of 2 revealed the molecule adopts a planar conformation about PC bond and the mutual orientation of two bulky Mes* moieties is almost orthogonal (92.8°). Complex 3 is a symmetrical four-membered ring structure in which the Mes* rings lie nearly perpendicular to the planes of the Ar ring and the P 2 C 2 ring (84.8 and 75.6°, respectively), while the Ar ring is almost parallel to the plane of the P 2 C 2 ring (25.2°).

Reaction of (C 5 H 4 Me) 3 Ln and TzH (5-phenyl-1H-tetrazole) in THF affords complexes [(C 5 H 4 Me) 2 LnTz] 2 [Ln=Yb ( 1 ), Er ( 2 )]. 1 crystallized in the space group C 2/ c , with unit cell dimensions a =25.596(2), b =8.342(1), c =21.573(2) A, β =129.322(9)°. V =3563.5(8) A 3 and Z =8 for D c =1.776 g cm −3 . Least-squares refinement of the model based on 2700 reflections converged to a final R =0.031. The molecule is centrosymmetric dimer in which each ytterbium atom is coordinated by two methylcyclopentadienyl groups and three nitrogen atoms of the bridging Tz ligands to form a distorted trigonal-bipyramidal geometry. When there is a small amount of (C 5 H 4 Me) 2 Ln(C 5 H 5 ) in (C 5 H 4 Me) 3 Ln, the 1:1 complexes [{(C 5 H 4 Me)(C 5 H 5 )LnTz} 2 ][{(C 5 H 4 Me) 2 LnTz} 2 ] (Ln=Dy ( 3 ), Gd ( 4 )) were obtained in crystalline form. 3 and 4 crystallize as isomorphous crystals of space group P 1 with the following unit cell parameters ( 3 / 4 ): a =9.374(2)/9.420(4), b =13.048(2)/13.215(4), c =16.542(4)/16.677(5) A, a =86.95(2)/87.24(2), β =74.61(1)/74.50(3), γ =77.31(1)/77.08(3)°, Y =1903(1)/1950(1) A 3 , Z =2, D c =1.602/1.545 g cm −3 , R =0.046/0.051. Crystallographic data for 3 and 4 show that there are two disconnected structural units [(C 5 H 4 Me)(C 5 H 5 )Ln( μ - η 1 : η 2 -Tz)] 2 and [(C 5 H 4 Me) 2 Ln( μ - η 1 : η 2 -Tz)] 2 , crystallizing in one asymmetrical unit, each of which is tetrazolate-bridged dimer and has an inversion center. The bridging unit Ln 2 N 6 is planar. All three structures reveal an unusual bonding mode of the tetrazolate ligand, in which the tetrazolate group acts as both a bridging and chelating ligand, with the nitrogen atoms at 1, 2 and 3-position taking part in bonding.

Reaction of MeCp 3 Ln(MeCp = COLLABCH 3 C 5 H 4 , Ln = Nd, Gd, Dy) with two equivalents of HPzMe 2 (HPzMe 2 = 3,5-dimethylpyrazole) in THF at room temperature yielded complexes [MeCpLn(PzMe 2 ) 2 ] [Ln-Nd( 1 ), Gd( 2 ), Dy( 3 )], which have been characterized by elemental analysis, IR and MS spectra. The new complexes react with dimethylsilicone grease to give the dimethylsilanone insertion products: [MeCpLn( η 2 -PzMe 2 )( μ-η 1 : η 2 -OSiMe 2 PzMe 2 )] 2 [Nd( 4 ), Gd( 5 ), Dy( 6 )]. The complex 6 has been structurally characterized by X-ray crystallography. 6 crystallizes in the space group P 2 1 / n with unit cell dimensions a =12.066(5), b =11.601(2), c =15.307(3) A, β = 105.84(3)°, V = 2061(1) A 3 , and Z =2 for D Caled =1.63 g cm −3 . Least-squares refinement on the basis of 2930 observed reflections were allowed to reach a final R value of 0.031. The molecule is centrosymmetric dimer in which each dysprosium is coordinated by one methylcyclopentadienyl group, two bridging oxygens, two nitrogens of the chelating PzMe 2 ligand and one nitrogen atom of the bridging PzMe 2 ligand to form a distorted octahedron. The Dy-N(bridging) and Si-N bond lengths are 2.454(5) and 1.803(5) A, respectively. The average Dy-C(ring), Dy-0 and Dy-N(chelating) distances are 2.684(16), 2.294(10), and 2.344(25) A, respectively.

Two new complexes, [Co(C 2 N 3 ) 2 (C 8 H 6 N 2 ) 2 ], (I), and [Cu(C 2 N 3 ) 2 (C 8 H 6 N 2 ) 2 ], (II), are reported. They are essentially isomorphous. Complex (I) displays distorted octahedral geometry, with the Co atom coordinated by four dicyanamide nitrile N atoms [Co-N = 2.098 (3) and 2.104 (3) A] in the basal plane, along with two monodentate quinoxaline N atoms [Co-N = 2.257 (2) A] in the apical positions. In complex (II), the Cu atom is surrounded by four dicyanamide nitrile N atoms [Cu-N = 2.003 (3) and 2.005 (3) A] in the equatorial plane and two monodentate quinoxaline N atoms [Cu-N = 2.479 (3) A] in the axial sites, to form a distorted tetragonal-bipyramidal geometry. The metal atoms reside on twofold axes of rotation. Neighbouring metal atoms are connected via double dicyanamide bridges to form one-dimensional infinite chains. Adjacent chains are then linked by π-π stacking interactions of the quinoxaline molecules, resulting in the formation of a three-dimensional structure.

In the title complex, [Co(C2N3)2(bentrz)2]n (bentrz is 1H-1,2,3-benzotriazole, C6H5N3), the Co atom occupies a special position with 2/m site symmetry and is coordinated in the equatorial plane by four dicyan­amide nitrile N atoms [Co—N = 2.110 (3) A], and in the apical positions by two monodentate 1,2,3-benzotriazole N atoms [Co—N = 2.157 (4) A], forming a slightly distorted octahedral geometry. The bentrz ligands lie on a mirror plane. Neighbouring Co atoms are connected via double dicyan­amide bridges to form a one-dimensional infinite chain; these chains are cross-linked via hydrogen-bond interactions between one dicyan­amide amide N atom and the H atom on the uncoordinated N atom of a 1,2,3-benzotriazole ligand from an adjacent chain, thus forming a three-dimensional network.

The centrosymmetric title complex, [Cu2(C7H5N4)4(C10H8N2)2], comprises two Cu atoms, four 5-phenyl­tetrazolate ligands and two 2,2′-bi­pyridine ligands. The five-coordinated Cu atom adopts a distorted tetragonal–pyramidal geometry.

Iron chloride has been found to be an efficient catalyst for the disproportionation of allylic alcohols, which provides a convenient method for selective transformation of allylic alcohols to alkenes and alpha,beta-unsaturated ketones. Furthermore, this catalytic system is also effective for highly selective allylic reduction of allylic alcohols, allylic ethers, and allylic acetates with benzyl alcohol under neutral and convenient reaction conditions.

The title compound, (benzophenone-O)tris­(η5-cylopentadienyl)dysprosium, [Dy(C5H5)3(C13H10O)], is a distorted tetrahedral coordination complex. The central dysprosium ion is η5-bonded to three cyclopentadienyl (Cp) groups and η1-bonded to one benzophenone molecule. The average Dy—O and Dy—C distances are 2.384 (3) and 2.733 (6) A, respectively. The Dy—O—C angle is 170.6 (3)°.

Reaction of NaCp′ (Cp′ = C5H4CH3) with YbCl3 and YbOCl in THF results in the formation of a new complex, Cp′3Yb4(μ-Cl)6(μ3-Cl)(μ4-O)(THF)3 (1). The X-ray crystal structure of 1 reveals an oxygen-centered tetrahedral arrangement of ytterbium atoms which has μ-Cl groups bridging each edge and a μ3-Cl ligand over the trianglar face composed of Yb atoms with Cp′ groups.