A series of pyrazole-based potential ligands bearing polydentate amine substituents in the 3-and 5-positions of the heterocycle has been synthesized [3,5-bis(R2NCH2)-pyzH; R2N = Me2N(CH2)3NMe (2aH), (Me2N(CH2)3)2N (2bH), (Et2NCH2CH2)2N (2cH)l. Upon reaction with two equivalents of CoC1, they form complexes LCo2C13 (3a-c; L = 2a-c, respectively) which are shown crystallographically to contain a dinuclear metal core bridged by both the pyrazolate unit and a chlorine atom, with each cobalt center carrying a further terminal chlorine atom. Two of the ligand side arms in 3b, c are dangling, thus leading to five-coordination of the cobalt(I1) centers in all cases. Addition of two equivalents of NaBPh, to solutions of 3b, c induced coordination of the formerly dangling side arms to the metal centers by substitution of the terminal chlorine atoms. The resulting compounds [ L C O~C~] ( B P~~)~ (4b, c, respectively) were characterized by X-ray structure analyses. They can be viewed as dinuclear linked versions of tran-type complexes [(tran = tris(aminoalkyl)amine] with distorted trigonal-bipyramidal coordination spheres around cobalt(I1). Conformational analyses employing force-field calculations were carried out for 4b, c in order to rationalize the conformations observed in the solid state with regard to the accessible conformational space.

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The conformational space spanned by tripod metal templates CH3C(CH2Ph&M is analysed on the basis of the solid-state structures of 82 tripodCo templates in compounds tripodCoL, and tripodCoL3. Systematic analysis, including the techniques of conformational space group scatter graphs, principalcomponent analysis, and partial least squares, reveals a series of basic regularities: The torsion of the phenyl groups is strongly linked to the torsional skew of the bicyclooctanetype framework of the chelate cage. For one sense of this skew there are two classes of low-energy conformation that differ by the helicity of the phenyl arrangement and by the degree of torsional skew in the chelate backbone. From the scatter graphs it is evident that a change in helicity may ocworks / Factor analysis cur by one-or by two-ring flip mechanisms. The basic regularities found by the above methods are also evident from the analysis of the same data by a neural network approach. The fact that these regularities are found for tripodCoL, and tripodCoL3, irrespective of the widely different coligands L and crystal environments, means that the conformation of the tripod metal templates is governed by the forces acting within them and not so much by the forces imposed on them by their individual chemical or crystal environment. It is shown that the classifications, although derived from a data basis only containing Co compounds, are characteristic for tripod metal templates irrespective of the specific metal involved.In most cases specificity in coordination chemistry is dominated by a specific choice of the ligands surrounding the metal. Homogenous catalysisr'*'] and. even more so, the subset of enantioselective catalysis [7] are clear illustrations of this statement.Part of this specificity will arise from steric interactions. In order to be able to predict specificity a thorough knowledge of these steric interactions is therefore needed. One basis for acquiring such a knowledge is currently available in many cases: A considerable amount of information exists on solid-state structures (determined by X-ray analysis), most of it deposited in an orderly and easily retrievable way in internationally available databasesr41. The wealth of information contained in these data fles is, as yet, far from having been systematically exploited.The current paper deals with the systematic analysis of all such structural data describing the solid-state conformation of tripodCo templates [tripod = CH7C(CH'PPh2)7] for compounds tripodCoL, and tripodCoI+ The interest in this analysis stems from a research programme aiming at an understanding of the chemical reactivity of a subsel of ligand metal templates in which the ligand is a neopentanebased tripodal entity. The programme involves the three following steps: 1) synthesis of a library of neopentane-based tripod ligands RCH2C(CH2X)(CH2Y)(CH2Z) (X, Y, Z = donor groups), 2) understanding and modelling the shape of tripod metal templates tril,odM, 3) correlating the results Catalysis mediated by tripod metal t...

NMR‐NOE analysis of the three compounds (RRS/SSR)‐CH3C(CH2PPhBz)3Mo(CO)3 (1), (RRR/SSS)‐CH3C(CH2PPhBz)3Mo(CO)3 (2), and (RRR/SSS)‐CH3C[CH2P(m‐Xyl)Bz]3Mo(CO)3 (3), leads to experimental values for a number of intramolecular H···H contacts in each case. By the very nature of the NOE method, and with the type of molecules studied here, these values have to be understood as a Boltzmann weighted average over all the conformations accessible to the molecules in solution. – A Boltzmann weighted force field approach is used to predict these values on the basis of sets of force field parameters derived earlier for this class of compounds. The agreement between observed and calculated NOE distances is highly satisfactory in each case (rms = 0.2 Å to 0.3 Å). By a statistical analysis it is shown that the predictions made by applying this Boltzmann weighted force field approach are highly significant. There is only a chance of 3 in 100 000 that this quality of prediction might be obtained by chance. This is taken as a validation, albeit indirect, of the energy scale reproduced by the force field parameters as developed. The methods described give a detailed insight into the conformational flexibility of molecules of the type studied. Solid state structures of the molecules are also correctly modelled by the force field used.

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