The structures of organolithium compounds in solution have been the subject of attention for four decades because of concerns regarding the mode of solvation, dynamic behavior, and reactivity of ion pairs. Chiefly as a consequence of their synthetic

The three diastereomeric (isodiCp)zTiClz complexes have been prepared in stereocontrolled fashion. The exo,exo isomer, on reaction with boron tribromide or with ethereal methyllithium, gives rise to the dibromo and dimethyl analogues which show reasonable stability.In contrast, the endo,endo and endo,exo dichlorides do not lead to stable products under analogous conditions. All three (isodiCp)zTiClz isomers do react well with pentafluorophenyllithium, leading to the air stable, crystalline (isodiCp)~Ti(CsF5)Cl triad, whose members are readily distinguished by their NMR spectra. An analysis of the notable trends reflected in these spectra is reported. X-ray crystallographic analysis of the three diastereomers reveals the three pentafluorophenyl complexes to have in common a solid-state spatial arrangement which differs notably from that adopted by the exo,exo dichloride and dimethyl derivatives.In recent years, considerable attention has been accorded to the complexation of cyclopentadienyl ligands endowed with diastereotopic faces to group 4 transition metals. h early example is the bis(~5-tricyclo[5.2.1.02~61deca-2,5-dienyl) or isodicyclopentadienyl anion ( 1h2 A wide variety of optically active anions of this generic class has subsequently been d e~e l o p e d .~-~ As a direct consequence of the inherent structural features of 1 and its congeners, the faces of these ligands feature distinctively different chemical environments. Their involvement in metalation reactions can lead to mixtures of metallocenes but often does not if proper controls are + Universite de Bourgogne. Gautheron, B.; Gugelchuk, M.; Meunier, P.; Paquette, L. A. Organometallics 1987, 6, 15. (3) (a) McLaughlin, M. L.; McKinney, J. A.; Paquette, L. A. Tetrahedron Lett. 1986, 27, 5595. (b) Paquette, L. A.; McKinney, J. A.; McLaughlin, M. L.; Rheingold, A. L. (5) (a) Burger, P.; Hund, H.-U.; Evertz, K.; Brintzinger, H.-H. J. Organomet. Chem. 1989,378,153. (b) Bhaduri, D.; Nelson, J. H.; Wang, T.; Jacobson, R. A. , J. A.; Green, M. L. H.; Gardner, I. M.; Prout, K. J. Chem. SOC., Dalton Trans. 1991, 2207. Q276-7333l95I2314-4576$09.QQlQexercised. The engagement of a single face is presently recognized to be subject to reasonable modulation by several factors, including nonbonded steric interactions: monomer-dimer preequilibrium complexation to lithium counter ion^,^ reaction temperature: and con~entration.~ Since each ligand can in principle serve as precursor to three diastereomeric metallocenes, we have been led to investigate those features that distinguish such a subset of closely related complexes. To our knowledge, no investigation of this type has previously been undertaken. The one potential limitation of this study, ready access to the stereoisomerically pure diastereomers without the need to accomplish difficult separations, was lifted by our earlier discovery that structurally defined trimethylsilyl-substituted ligands undergo complexation exclusively via net inversion of configuration.1° Results and DiscussionSynthesis and Spectroscopic ...

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The crystallographically determined structural features of Na(isodiCp)(15-crown-5) and [K-cryptand(2.2.2)]+(isodiCp)- are compared to those of the corresponding Li(TMEDA) complex and the sandwich dimer involving Li+ (cocrystallized with Li(12-crown-4)2). The features of the potassium salt are distinctively different from those of its congeners. As a consequence of the encapsulation of the K+ ion by the cryptand, no interaction occurs with the isodiCp anion, which is “naked”. Notwithstanding the complete dissociation that exists, the stand-alone isodiCp anion exhibits appreciable folding about the bond that it shares with the norbornyl framework. The dihedral angle is 8.3(1)° in a downward direction away from the exo surface. This unrivaled opportunity to observe the free isodicyclopentadienide anion is shown to be in agreement with the results of HF−SCF calculations.

The diastereomeric endo and exo isomers of the title complex, [TiCl3(C10H11)], have been synthesized by electrophilic attack of TiCl4 on the exo- or endo-trimethylsilyl derivative of isodiCp (isodiCp = isodicyclopentadiene). This reaction proceeds with net inversion of configuration to give exclusively either the endo- or exo-(isodiCp)TiCl3 compound. Although the two isomers have similar unit-cell constants, they crystallize in different space groups. The endo complex, (2), is in Pbcm with a crystallographic mirror plane, while the exo complex, (4), is in Pca2(1) with pseudo-mirror symmetry. Both molecules display a distorted tetrahedral geometry about the Ti atom. Each Ti atom is bonded in a eta(5) manner to the Cp ring of the isodiCp ligand, with Ti--ring centroid distances of 2.031 (2) and 2.013 (2) A for (2) and (4), respectively. A slight bending of the isodiCp ligand about the bond shared by the Cp ring and the norbornane fragment is observed in both structures. The determination of the absolute structure of (4) defines the directionality of the packing along the polar c axis.