Alkylation of Cp*Cr(THF)Cl2 with 1 or 2 equiv of LiCH2SiMe3 yielded the paramagnetic chromium alkyls [Cp*Cr(μ-Cl)(CH2SiMe3)]2 (1), Cp*Cr(CH2SiMe3)2 (2), and Cp*Cr(L)(CH2SiMe3)2 (3a, L = py; 3b, L = THF). Compound 2 is a coordinatively unsaturated, pseudo-five-coordinate CrIII complex with a 13-electron configuration, and it catalyzes the polymerization of ethylene. The thermal decomposition of 2 in noncoordinating solvents proceeded via an intermediate, namely the bis(μ-alkylidene) complex [Cp*Cr(μ-CHSi(CH3)3)]2 (4). Compound 4 suffered reductive elimination to yield the dinuclear CrII alkyl Cp*2Cr2(μ-CH2Si(CH3)2CH2-μ-CHSi(CH3)3) (5). In contrast, the decomposition of 2 in THF, i.e., 3b, yielded the metallacycles Cp*Cr(L)(CH2)2Si(CH3)3) (6a, L = py; 6b, L = THF). Compounds 1, 2, 3b, 4, and 5 have been structurally characterized by X-ray diffraction. The reactions of 2 are rationalized in terms of competing α- and γ-hydrogen elimination processes yielding terminal alkylidene and metallacyclobutane intermediates existing in equilibrium.

[CpCr(mu-Cl)Cl](2) reacted with dioxygen (O(2)) to produce CpCr(O)Cl(2) (1), which has been structurally characterized. Although 1 oxidized PPh(3) and 1,4-cyclohexadiene catalytically, it did not epoxidize olefins. DFT calculations have been performed on the system to characterize the potential energy surface for the epoxidation of ethylene and, in particular, the consequences of the crossing from the doublet surface of the starting materials to the quartet surface of the product (i.e. a chromium(III) epoxide adduct). These calculations suggested that "spin-blocking" was not a significant problem and that the reaction of CpCr(O)Cl(2) (3) with ethylene should have a lower activation barrier. On the basis of this computational prediction, 3 was prepared; it was found to epoxidize olefins stoichiometrically.

Reactions of a new imido phosphido complex, Cp 2 Nb(dNBu t )(PPh 2 ) (1), with olefin complexes of rhodium afford two types of compounds. With [(μ-Cl)Rh(C 2 H 4 ) 2 ] 2 , an imido/phosphido-bridged complex, Cp(Cl)Nb(μ-NBu t )(μ-PPh 2 )RhCp (2), characterized by NMR and X-ray diffraction, was prepared. Formation of 2 represents a rare example of a Cp/Cl exchange reaction in organometallic chemistry. When 1 reacts with [(μ-Cl)Rh(COD)] 2 , the target phosphido-bridged bimetallic complex Cp 2 Nb(dNBu t )(μ-PPh 2 )Rh(Cl)(COD) ( 4) is formed. The structure of this product was established by NMR and an X-ray diffraction study. Both 2 and 4 are catalyst precursors for hydrosilylation of benzaldehyde and acetophenone. The activity of the neutral complex 4 exceeds that of the cation [Cp 2 Nb(NBu t )(PPh 2 )Rh(COD)] þ derived from 4 by chloride anion abstraction.

A left-handed homochiral [CuCl 2 (L1)] n (1) and two solvated heterochiral [CuCl 2 (L1)] n 3 n(H 2 O) (2) and [CuBr 2 (L1)] n 3 n(MeOH) (3) one-dimensional helical copper(II) coordination polymers have been self-assembled from Cu(II) with an achiral functionalized 1,2,3-triazoleThey have been characterized by single-crystal X-ray diffraction (XRD) analysis. Complexes 2 and 3 have been further analyzed by powder XRD, thermogravimetric analysis, and electron paramagnetic resonance. Different conformational twists of the ligand skeleton result in different chiral organizationsa large torsional twist (C-C-O-N) of ∼59.4°in 1 results in a large screw-pitch of ∼45.2 A ˚, whereas a small twist of ∼6.2°in 2 and 6.7°in 3 results in a short screw-pitch of ∼7.6 and 8.1 A ˚, respectively. The effect of the lattice solvates (H 2 O and MeOH) on the change of helical structures has also been described. † This paper is dedicated to the memory of Prof. Robert Bau (1944.

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Reaction of Cp2TaH3 (1) with ClPEt2 gives the insertion product [Cp2TaH2(PHEt2)]Cl (5), which upon deprotonation with LiN(SiMe3)2 affords the phosphido complex Cp2TaH2(PEt2) (6) as the kinetic product. The latter transforms by a first-order reaction during the course of 3.5 days to the phosphine complex Cp2TaH(PHEt2) (7). Repetition of this insertion/deprotonation sequence gives the compounds [Cp2Ta(PHEt2)2]Cl (8) and Cp2Ta(PEt2)(PHEt2) (9). Reaction of the latter with 0.5[(μ-Cl)Rh(η2-C2H4)]2 in the presence of LiN(SiMe3)2 gives the bimetallic complex Cp2Ta(μ-PEt2)2Rh(η2-C2H4) (10), which was studied by NMR and X-ray diffraction analysis. Complex 10 catalyses the hydrosilylation of acetophenone by PhMeSiH2.

Four new metal−organic frameworks (MOFs) based on 1,4-phenylenediacetic acid (1,4-H 2 phda), [Co(1,4-phda)(4,4′-bpa)] (1), [Co(1,4-phda)(4,4′-bpp)] (2), [Co(1,4-phda)(4,4′-bpa)(H 2 O) 2 ] (3), and [Co(1,4-phda)-(4,4′-bpa)] (3a) (4,4′-bpa = 1,2-bis(4-pyridyl)ethane and 4,4′-bpp = 1,3-bis(4-pyridyl)propane) were successfully synthesized. The various synthetic methods play an important role in the formation of diverse structural frameworks.Compound 1 shows a 3D framework, while 2, 3, and 3a exhibit 2D layered MOFs with different architectures. The irreversible thermally induced single-crystal-to-single-crystal transformation with chromotropism from 3 to 3a was observed, which was established by the breakage and reformation of coordination bonds around Co(II) centers. The orientation of coordinated 4,4′-bpa ligand and conformation of 1,4-phda ligand play a key role on pore opening in 3 and pore closing in 3a. Furthermore, the functional properties as heterogeneous catalysts of these MOFs including epoxidation of alkenes and photocatalytic performance for MB degradation have been investigated. The heterogeneous catalytic properties of 1, 2, and 3a exhibit high catalytic activity with good catalyst stability.

Attempts to trap a terminal chromium alkylidene by reactions of dialkyl Cp*Cr(CH2SiMe3)2 (Cp* = η5-C5Me5) or metallacycle Cp*(THF)Cr(CH2)2SiMe2 with the bidentate ligand 1,2-bis(dimethyphosphino)ethane (dmpe) lead to dinuclear paramagnetic chromium alkyls [Cp*Cr(CH2SiMe3)2]2(μ-η1:η1-dmpe) (1) and [Cp*Cr(CH2)2Si(CH3)2]2(μ-η1:η1-dmpe) (2), respectively. On the other hand, the unusual mononuclear chromium complex (η5-pentamethylcyclopentadienyl)(2-(2‘ ‘,2‘ ‘-dimethyl-2‘ ‘-silapropyl)-1,2-dihydro[2,2‘]bipyridine-1,3‘ ‘-diyl)chromium(III) (3) was obtained by a reaction of Cp*(THF)Cr(CH2)2SiMe2 with 1 equiv of 2,2‘-bipyridine (bipy). 3 is formed by carbon−carbon bond formation between one terminus of the metallacyle and the 2-position of the bipy ligand, at the expense of the aromaticity of a pyridyl group. Single-electron oxidation of 3 with ferricenium hexafluorophosphate ([Cp2Fe]PF6) yielded 4, a dicationic dimer of 3 linked via a carbon−carbon bond between the bipy backbones. 1−4 were structurally characterized by X-ray diffraction.