Synthesis and Characterization of Zirconium and Iron Complexes Containing Substituted Indenyl Ligands:  Evaluation of Steric and Electronic Parameters

Abstract

Evaluation of the steric and electronic influence of a family of silyl-and alkyl-substituted indenyl ligands on zirconium and iron centers has been accomplished by a combination of X-ray diffraction, IR spectroscopy, solution NMR dynamics, and electrochemical measurements. Three tetrasubstituted, bis-indenyl zirconocene dichloride complexes have been characterized by X-ray diffraction and adopt a gauche ligand conformation such that the interactions between tertiary substituents on adjacent rings are minimized. Similar solid state conformations were also observed in two of the corresponding iron compounds. Evaluation of the electronic environment about each zirconium center was achieved by measurement of the CO stretching frequencies of the dicarbonyl derivatives. Simple inductive effects govern the electronic properties of each zirconocene where silyl groups are relatively electron withdrawing and alkyl groups electron donating. For the most hindered zirconocene dicarbonyl derivatives, population of three vibrationally distinct rotamers has been detected by IR spectroscopy. Independent assessment of these stereoelectronic parameters by variabletemperature NMR spectroscopy and electrochemistry with the analogous series of iron complexes provided the same relative ordering of the indenyl ligands.

Novel sandwich complexes of zirconium [C9H5(SiMe3)2](C5Me4R)ZrCl2 (R=CH3, CH2CH2NMe2): Synthesis and reduction behavior

“…Such a conformation was not observed previously for mixed (cyclopentadienyl)(indenyl)zirconocenedichlorides [5,6,8,9]. The metrical parameters of 1 (Table 1) are close to those found for other silyl-substituted indenyl zirconium sandwiches [1].…”

“…Halfsandwich 3 was obtained previously [1] as an adduct with Et 2 O and LiCl by the reaction of Ind Si2 Li with ZrCl 4 in ether. We developed an alternative two-step synthesis of 3 starting from indene.…”

“…From this viewpoint, the choice of an appropriate ligand environment that could provide a compromise between the thermal stability and reactivity of the Zr(II) species appears to be one of the possible solutions of the problem. Among the known alternatives, the sterically hindered indenyl ligands [1,2] seem to be good candidates due to their ability to reversibly stabilize Zr(II) center by ''toggling" between g 5 , g 6 and g 9 coordination modes (see Scheme 1). Like other Zr(II) derivatives, these complexes are able to activate C-H bonds [3].…”

Chiral Indenes and Group‐4 Metallocene Dichlorides Containing α‐ and β‐Pinenyl‐Derived Ligand Substituents: Synthesis and Catalytic Applications in Polymerization and Carboalumination Reactions

“…In our previous communication, [28] we also described the preparation of the ethylene-bridged bis(indenyl) ligand analogues of 1 and 4a/4b (compounds 18 and 19), as well as the 1,3-chirally disubstituted indene analogue 20 ( Figure 3 any formation of the desired bis(indenyl)metallocene complex. Considering that the analogous 1,3-bis(trimethylsilyl)-indenyl and other 1,3-bis(trialkyl/arylsilyl)indenyl-derived anions were recently successfully complexed with zirconium and iron in moderately high yields by Chirik and coworkers, [34,35] the observation here is quite surprising and hardly explained by steric factors only. Other examples of both 1,2-and 1,3-trimethylsilyl-substituted bis(indenyl)-iron(ii) complexes have also been reported recently.…”

New 1,3-disubstituted side-chain functionalized indenyl ligands and zirconium complexes derived from them

“…All solvents, includ ing deuterated solvents, were purified according to standard procedures, degassed, and recondensed under high vacuum (10 -3 Torr) directly into a reaction vessel or an NMR tube. Magnesium amalgam, 5 isopropylindene, 15 1 isopropyl 3 (iso propylidene)indene, 15 and Cp * ZrCl 3 16 were synthesized accord ing to procedures described in the literature.…”