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A ligand field molecular mechanics (LFMM) force field has been constructed for the spin states of [Fe(bpp)2 ]2+ (bpp=2,6-di(pyrazol-1-yl)pyridine) and related complexes. A new charge scheme is employed which interpolates between partial charges for neutral bpp and protonated [H3 bpp]3+ to achieve a target metal charge. The LFMM angular overlap model (AOM) parameters are fitted to fully ab initio d orbital energies. However, several AOM parameter sets are possible. The ambiguity is resolved by calculating the Jahn-Teller distortion mode for high spin, which indicates that in [Fe(bpp)2 ]2+ pyridine is a π-acceptor and pyrazole a weak π-donor. The alternative fit, assumed previously, where both ligands act as π-donors leads to an inconsistent distortion. LFMM optimisations in the presence of [BF4 ]- or [PF6 ]- anions are in good agreement with experiment and the model also correctly predicts the spin state energetics for 3-pyrazolyl substituents where the interactions are mainly steric. However, for 4-pyridyl or 4-pyrazolyl substituents, LFMM only treats the electrostatic contribution which, for the pyridyl substituents, generates a fair correlation with the spin crossover transition temperatures, T1/2 , but in the reverse sense to the dominant electronic effect. Thus, LFMM generates its smallest spin state energy difference for the substituent with the highest T1/2 . One parameter set for all substituted bpp ligands is insufficient and further LFMM development will be required.

At temperatures below 150 K, the photoactivated metastable endo‐nitrito linkage isomer [Ni(Et4dien)(η2‐O,ON)(η1‐ONO)] (Et4dien=N,N,N′,N′‐tetraethyldiethylenetriamine) can be generated with 100 % conversion from the ground state nitro‐(η1‐NO2) isomer on irradiation with 500 nm light, in the single crystal by steady‐state photocrystallographic techniques. Kinetic studies show the system is no longer metastable above 150 K, decaying back to the ground state nitro‐(η1‐NO2) arrangement over several hours at 150 K. Variable‐temperature kinetic measurements in the range of 150–160 K show that the rate of endo‐nitrito decay is highly dependent on temperature, and an activation energy of Eact=+48.6(4) kJ mol−1 is calculated for the decay process. Pseudo‐steady‐state experiments, where the crystal is continually pumped by the light source for the duration of the X‐ray experiment, show the production of a previously unobserved, exo‐nitrito‐(η1‐ONO) linkage isomer only at temperatures close to the metastable limit (ca. 140–190 K). This exo isomer is considered to be a transient excited‐state species, as it is only observed in data collected by pseudo‐steady‐state methods.

Spin transitions are a spectacular example of molecular switching that can provoke extreme electronic and structural reorganizations in coordination compounds. A new 3D cyanoheterometallic framework, [Fe(pz)(Au(CN)2)2], has been synthesized in which a highly cooperative spin crossover has been observed at 367 and 349 K in heating and cooling modes, respectively. Mössbauer spectroscopy revealed a complete transition between the diamagnetic and paramagnetic states of the iron centres. The low-spin-to-high-spin transition induced a drastic structural distortion involving a large one-directional expansion (ca. 10.6%) and contraction (ca. 9.6%) of the lattice. Negative thermal expansion along the c axis was detected below and above the transition temperature.

The crystal structures of phenylpropylpyridine-N-oxide and N-methyl-phenylpropylpyridinium iodide are compared, revealing that hydrogen bonding with the solvent molecule plays an important role in the N-oxide compound, whilst electrostatic interactions are predominant in controlling the solid-state orientation of the N-methylated compound. Fluorescence spectroscopy and NOESY indicate that in contrast to the previously reported pyridinium iodide, the N-oxide is not subject to intramolecular pi-stacking, as judged by excimer emission and a lack of corresponding cross peaks, respectively.

The importance of C–H bond activation in a simple molecule to form a molecule with enhanced functionality can be easily understood from a study of biological processes at a molecular level where, for example, a specific enzyme selectively activates a chemically inert C–H bond and functionalizes it to a useful product. This strategy is now being used for large scale industrial processes and has both social and environmental benefits. C–H bond functionalization is also of major importance in catalysis because of the possibility of constructing complex structural motifs from relatively simple precursors. However, functionalization of a chemically inert C–H bond needs specific catalysts or reaction conditions that can selectively activate a particular C–H bond, leaving others intact. To achieve this target, various metal catalyzed or mediated reactions have been employed. Keeping the growing importance of this emerging field in mind, we now present recent advances in the field of C–H activation and functionalization using group 10 transition metal catalysts. Attempts have also been made to discuss the future of group 10 transition metals in catalysis.

(Figure Presented) Give and take: A molecular cluster that readily takes up and stores two molecules of H2 also rapidly releases (milliseconds) the stored H2 by a simple redox process. This process represents a new method of hydrogen storage and release from a well-defined molecular material. © 2006 Wiley-VCH Verlag GmbH and Co. KGaA.

(Trimethylsilyl)diazomethane (1-H) reacts with nBuLi in THF at elevated temperature to afford (previously reported) 1-Li·3/2THF. However, reaction in hexane/TMEDA at low temperature affords instead the N-lithiate Me3SiCNNLi·TMEDA (9), which is a novel “open” pseudo-cubic tetramer in the solid state. Variable-temperature NMR spectroscopy suggests that N-metallated 9, apparently the kinetic product of the reaction, irreversibly rearranges at high temperature in solution to give the thermodynamically preferred C-lithiated isomer. These observations, supported by DFT calculations, influence our understanding of the reactivity of lithiated diazomethanes towards aryl isothiocyanates, suggesting as they do that previously observed product selectivity in these reactions is critically dependent on temperature control exercised during the process. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Complexation of the salt lithium triflamide [LiNTf2; NTf2 = N(SO2CF3)(2)], with a range of nitrogen donor ligands results in the formation of a series of coordination complexes [(Tf2N)Li.N(H)PPh2Me] (1), [(Tf2N)Li.N(H)PPh3] (2), [(Tf2N)Li.TMEDA] (3), [(Tf2N)Li.PMDTEA] (4) and [(Bz-TAC)(2)-Li][NTf2] (5). The molecular structures of 1, 3, 4 and 5 have been determined by single-crystal X-ray diffraction. The resulting solvated structures are discussed in terms of solvent-separated ion pairs, contact ion pairs and higher aggregates, with the degree of aggregation and ion contact being dependent on the relative coordinating abilities and steric demands of the donor ligand and the anion, and provide an insight into the possible structures of lithium aggregates present in complex systems such as polymer electrolytes and synthetic reaction media. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).

A systematic investigation into the relationship between the solid-state luminescence and the intermolecular AuAu interactions in a series of pyrazolate-based gold(I) trimers; tris(μ2-pyrazolato-N,N')-tri-gold(I) (1), tris(μ2-3,4,5- trimethylpyrazolato-N,N')-tri-gold(I) (2), tris(μ2-3-methyl-5- phenylpyrazolato-N,N')-tri-gold(I) (3) and tris(μ2-3,5-diphenylpyrazolato- N,N')-tri-gold(I) (4) has been carried out using variable temperature and high pressure X-ray crystallography, solid-state emission spectroscopy, Raman spectroscopy and computational techniques. Single-crystal X-ray studies show that there is a significant reduction in the intertrimer AuAu distances both with decreasing temperature and increasing pressure. In the four complexes, the reduction in temperature from 293 to 100 K is accompanied by a reduction in the shortest intermolecular AuAu contacts of between 0.04 and 0.08 The solid-state luminescent emission spectra of 1 and 2 display a red shift with decreasing temperature or increasing pressure. Compound 3 does not emit under ambient conditions but displays increasingly red-shifted luminescence upon cooling or compression. Compound 4 remains emissionless, consistent with the absence of intermolecular AuAu interactions. The largest pressure induced shift in emission is observed in 2 with a red shift of approximately 630 cm-1 per GPa between ambient and 3.80 GPa. The shifts in all the complexes can be correlated with changes in AuAu distance observed by diffraction.

Lithium cages containing hydride: The reaction of tBuLi with Me(2)AlN(2-Pyr)Ph in toluene gave [Li(8)(H){N(2-Pyr)Ph}(6)](+)[Li(Me(2)AltBu(2))(2)](-), whose cation is the first molecular main group metal species to contain interstitial hydride (the cluster core is shown in the picture). Treatment of the reaction mixture with THF gave the neutral hydride Li(7)(H)[N(2-Pyr)Ph](6), which has a capped octahedral (Li(+))(7) cluster core. 2-Pyr=2-pyridyl.

The photochemistry of M3(CO)12 [M = Ru (1a), Os (1b)] with pyrazole, 3,5-dimethylpyrazole, and 3,5-diphenylpyrazole is documented. With 1a, photolysis with pyrazole leads to the substitution product HRu3(CO)10(C3H3N2) (2a). In the case of 1b, the initial product is the ortho-metallated species HOs3(CO)10(C3H3N2) (3b), heating of which yields HOs3(CO)10(C3H3N2) (2b). Photolysis of 1a and 1b with 3,5-dimethylpyrazole yields HRu3(CO)10(C3HMe2N2) (4a) and HOs3(CO)10(C3HMe2N2) (4b), respectively. The molecular structure of 4b has been determined by X-ray crystallography. There is no reaction on photolysis of 1a and 1b with 3,5-diphenylpyrazole.

The stable benzyl azide (I) containing a boronate ester allows regioselective 1,3-dipolar cycloaddition with terminal olefins followed by a Cu-catalyzed Suzuki coupling of the resulting triazoles such as (IIIa).

A series of α′-diphenylphosphinoyl enones has been prepared and their s-cis or s-trans conformations correlated with 1H NMR and IR spectra and an X-ray crystal structure of the title compound. The effect of chelation to cerium(III) is correlated with the regio- and stereo-selectivity of reductions under the Luche conditions.

Monomers of Sb(N=CPh 2 ) 3 1, the first tris(imino) antimony compound characterised in the solid state, exhibit unusual packing in the crystal in which short aromatic meta-C-H... Sb intermonomer contacts are present

The development of transition metal cluster chemistry is traced from the early discoveries of metal-metal bonded systems through to some recent developments made in the area of high nuclearity osmium and rutherium cluster carbonyls. Emphasis is placed on developments made in the physical techniques used to establish the structures of the cluster complexes in the solid state and in solution. Recent developments in synthetic methods which lead to “rational” cluster synthesis are described, and the electron counting rules used to rationalise the observed structures of carbonyl clusters are reviewed. New high nuclearity cluster structures are described, and emphasis is placed on the ability of these systems to undergo reversible redox chemistry without the metal frameworks rearranging. This contrasts the situation observed for low nuclearity clusters, and illustrates the potential of the higher nuclearity clusters to act as electron sinks.

Functionalized pyrazolium salts 1 react with metal complex hydrides (LiAlH4 and NaBH4) to give pyrazolidines 2 with good-to-excellent levels of diastereoselectivity. The stereochemical course of the reduction is essentially anti, leading to trans,trans-pyrazolidines. The relative configuration of the crystalline pyrazolidine 2c has been determined by X-ray crystallographic analysis.

The determination of the structure of the title compound, C25H35NO4, confirms the R and S absolute configurations at the 5 position of the furanone ring and the α position of the hydroxybenzyl substituent, respectively, taking into account the known configuration of the menthyl moiety.

Lithiation of four different chiral phosphine oxides and reaction with seven different electrophiles has been carried out in order to discover what factors govern the sense and degree of asymmetric induction imparted by the resident chiral centre. Provided the groups at the chiral centre are significantly different in steric size (e.g. Ph and Me) and ketones, esters or Me3SiCl are used as the electrophile, surprisingly high levels of syn-diastereoselectivity are observed. Reactions with benzaldehyde or methyl iodide proved to be rather unselective. The stereochemistry of the reaction of lithiated 1-diphenylphosphinoyl-2-phenylpropane 9 with cyclohexanone was elucidated by conversion into (1R*,2S*,1′S*,2′R*)-1-(1′-diphenylphosphinoyl-2′-phenylpropyl)-2-phenylsulfanylcyclohexan-1-ol syn,syn,anti-39 and subsequent X-ray crystal structure analysis. The stereochemistry of the remainder of the compounds were determined by analogy and by using a reliable 13C NMR spectroscopy 3JPC coupling constant correlation. A detailed (and potentially general) mechanistic interpretation of the results which combines knowledge of the structure and configurational stability of lithiated phosphine oxides is discussed. In particular, it is suggested that a dynamic kinetic diastereoselection of rapidly equilibrating diastereomeric lithiated phosphine oxides explains the observed high levels of stereocontrol; a tentative transition state model is proposed to explain the syn-selectivity. Finally, the use of one of the addition products in the concise and stereoselective synthesis of an alkene with 1,4-disposed chiral centres is described.

The D-3-phosphorylated myo-inositol phospholipids PtdIns(3)P, PtdIns(3,4)P2, PtdIns(3,4,5)P3 and PtdIns(3,5)P2 were synthesised from myo-inositol orthoformate 8. Key transformations included the regioselective DIBAL- and trimethylaluminium-mediated cleavages of myo-inositol orthoformate intermediates and a resolution–protection protocol using the camphor acetals 17. The final reductive debenzylation was effected with Pearlman's catalyst [Pd(OH)2] in the presence of sodium hydrogen carbonate. The biological properties of the phospholipids were evaluated against various protein kinases (PKB and PDK-1) in which they played an important activation role.