Analysis of Spectroscopic, Reactivity, and Structural Differences Originating Uniquely from Differing Modes of .pi.-Facial Complexation. The Three Possible Stereoisomeric Bis(isodicyclopentadienyl)titanium Combinations

Abstract

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 ...

ansa-[(tert-Butylamino)(isodicyclopentadienyl)dimethylsilane]Zr(NMe2)2prepared by an amine-elimination reaction

“…As expected on the basis of experimental reaction conditions and prior results in this ®eld (Paquette et al, 1989;Sornay et al, 1991;Zaegel et al, 1995;Gobley et al, 1998;Gentil et al, 2000Gentil et al, , 2002, the molecular structure of (I) indicates that exo complexation of the isodicyclopentadienyl ligand to Zr has occurred. This structure exhibits the classical half-sandwich pseudo-tetrahedral geometry about the Zr atom.…”

A Silylene-Bridged (Isodicyclopentadienyl)(Fluorenyl) Complex of Zirconium for Homogeneous Olefin Polymerization

“…The methano 14 and ethano 13 bridge protons give rise to two sets of double multiplets between 1.01 and 2.51 ppm. The syn- methano bridge proton chemical shift at 2.51 ppm is observed to be 0.5 ppm more shielded than in classical nonbridged isodicyclopentadienyl complexes. − The corresponding chemicals shifts of the fluorenyl ligand protons are within the range of δ 7.23−8.23 ppm and appear as two sets of double triplets centered at δ 7.45 and 8.03 ppm and two sets of triple multiplets at 7.23 and 7.59 ppm.

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“…It has been assumed that even with a large centroid−metal−centroid angle, syndiospecificity can be realized when complexes contain a cyclopentadienyl ligand bulky enough to force the orientation of the methyl group of the incoming monomer unit to the open region of the flat fluorenyl ligand. Our investigations involving isodicyclopentadienyl ligand utilization for the synthesis of group 4 metallocene − complexes allowed us to anticipate that the presence of fluorenyl and isodicyclopentadienyl ligands in the same complex could lead to syndiotactic polypropylene when activated with MAO. We report below the synthesis, characterization, and polymerization behavior of complex 5 , the first isodicyclopentadienyl-bridged complex.…”

Stereoselective Access to New Half-Sandwich Complexes Containing an Isodicyclopentadienyl Ligand

“…Isodicyclopentadienide anion 1 was obtained by conventional reaction of isodicyclopentadiene with n -butyllithium in ether at −78 °C. ,, Reaction of 1 at −78 °C with a large excess of dichlorodimethylsilane in THF led to chloro(dimethyl)(isodicyclopentadienyl)silane ( 2 ) in 81% yield. In related published works, − the influence of reaction temperature on stereoselectivity was demonstrated. At −78 °C, the endo product is obtained nearly exclusively.…”