Molecular structures of tris(1-tert-butyl-2-mercaptoimidazolyl)hydroborate complexes of titanium, zirconium and hafnium

Abstract

Cyclopentadienyl and tris(pyrazolyl)hydroborate have found much use as supporting ligands in the chemistry of titanium, zirconium and hafnium, especially with respect to applications involving olefin polymerization catalysis. In contrast, closely related tris(1-alkyl-2-mercaptoimidazolyl)hydroborate, [Tm], ligands have so far found little application to the chemistry of these elements, despite the fact that such ligands are currently used extensively in coordination chemistry. In view of the fact that a substituent in the 2-position exerts a direct influence on the steric environment of the metal center, we report here the application of the sterically demanding tris(1-tert-butyl-2-mercaptoimidazolyl)hydroborate [Tm] ligand to these metals. Dichlorido(η-cyclopentadienyl)[tris(1-tert-butyl-2-sulfanylidene-2,3-dihydro-1H-imidazol-3-yl)borato-κS,S',H]zirconium(IV) benzene hemisolvate, [Zr(CHBNS)(CH)Cl]·0.5CH, (I), dichlorido(η-cyclopentadienyl)[tris(1-tert-butyl-2-sulfanylidene-2,3-dihydro-1H-imidazol-3-yl)borato-κS,S',H]titanium(IV) benzene hemisolvate, [Ti(CHBNS)(CH)Cl]·0.5CH, (II), [bis(1-tert-butyl-2-sulfanylidene-2,3-dihydro-1H-imidazol-3-yl)borato-κS,S',H]dichlorido(η-cyclopentadienyl)zirconium(IV), [Zr(CHBNS)(CH)Cl], (III), (1-tert-butyl-2,3-dihydro-1H-imidazole-2-thione-κS)(1-tert-butyl-2-sulfanylidene-1H-imidazol-3-ido-κN,S)dichlorido(η-cyclopentadienyl)zirconium(IV) benzene monosolvate, [Zr(CHNS)(CHNS)(CH)Cl]·CH, (IV), and tribenzyl[tris(1-tert-butyl-2-sulfanylidene-2,3-dihydro-1H-imidazol-3-yl)borato-κS,S',S'']hafnium(IV) benzene tetrasolvate, [Hf(CH)(CHBNS)]·4CH, (V), have been structurally characterized by X-ray diffraction. The [Tm] ligand coordinates to Ti and Zr in Cp[κS,H-Tm]MCl [M = Zr, (I), and Ti, (II)] in a κS,H mode, while the benzyl compounds [Tm]M(CHPh) [M = Zr and Hf, (V)] exhibit κS coordination.

Organometallic Zirconium Compounds in an Oxygen-Rich Coordination Environment: Synthesis and Structural Characterization of Tris(oxoimidazolyl)hydroboratozirconium Compounds

“…The fact that the methylene groups appear as a singlet is, nevertheless, rationalized by facile enantiomer interconversion due to propeller inversion of the [To RBenz ] ligand, as noted above for Cp­[To MeBenz ]­ZrCl 2 . In this regard, it is pertinent to note that the methylene hydrogen atoms of the mercaptoimidazolyl counterpart [Tm Bu t ]­Zr­(CH 2 Ph) 3 appear as two doublets in the 1 H NMR spectrum . As such, the result is in accord with the spectral differences noted above for Cp­[To MeBenz ]­ZrCl 2 and Cp­[Tm Me ]­ZrCl 2 , which also indicate that the oxoimidazolyl system is more flexible than the sulfur counterpart.…”

“…For example, we previously reported that thallium compounds of the type [Tp R,R′ ]Tl are effective reagents for the synthesis of [Tp R,R′ ]­MR x –1 derivatives (e.g., M = Mg, Zn, Al) via reactions with MR x , , because decomposition of the incipient TlR byproduct provides an effective driving force for the reaction . Accordingly, the benzyl compounds [To R ]­Zr­(CH 2 Ph) 3 may be conveniently obtained by the metathesis of Zr­(CH 2 Ph) 4 with the corresponding thallium reagent [To R ]Tl (Scheme ), an approach that has also been employed for [Tm Bu t ]­M­(CH 2 Ph) 3 (M = Zr, Hf) and [Tp Ms* ]­Hf­(CH 2 Ph) 3 . , …”