Synthesis, Reactivity and DFT Investigation of a Cationic Zirconocene Benzyl Compound with an Appended Phenyl Group

Abstract

The reaction of [η5‐C5H5‐(η5‐C5H4CMe2C6H4Me)Zr(CH2Ph)2](1) with the cation generating agent B(C6F5)3 was studied by means of multinuclear NMR and density functional theory (DFT) methods. The clean reaction in CD2Cl2 at –60 °C yielded the cationic compound [η5‐C5H5‐(η5:η1‐C5H4‐CR2C6H4R)Zr(η2‐CH2Ph)] (R = Me: 2, R = H: 3), with a tolyl moiety coordinated to the cationic zirconium centre, in addition to the expected η2‐coordination of the benzyl moiety. Both coordinations were unambiguously assigned by multinuclear one‐ and two‐dimensional NMR spectroscopy. Detailed DFT calculations of congener 3 at the B3LYP level of theory explain the unusual chemical shift of the coordinated atom of the tolyl moiety. Furthermore, detailed electronic analysis (Bader and NBO analysis) were undertaken to ascertain the type of coordination (agostic versus electrostatic) that the tolyl moiety adopts. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Characterization of agostic interactions in theory and computation

“…Either in the ground state structure of the catalyst itself or in transition states during the reaction. These include arylpalladium halide complexes [70], molybdenum and tungsten catalysts used in olefin metathesis [71], salicyladiminato palladium and nickel complexes [72] and zirconocene benzyl complexes for propylene polymerization [73], hydro-gen binding ruthenium complexes which are reported to bind sp 3 and sp 2 C-H agostic ligands [74] and unsaturated hydride-and hydrocarbyl-molybdenum complexes [75]. In a recent study on CH bond activation by thorium and uranium complexes an interesting 5 centered agostic transition state was found [76].…”

Electronic or steric effects: Detailed DFT investigations of titanium amino based Kaminsky type olefin catalysts

“…We reasoned that probably and most likely, the remaining benzyl group will coordinate in the familiar η 3 mode to the cationic titanium centre, similar to that previously observed for cationic titanocene and zirconocene compounds. 41,42 Hence, we positioned the remaining benzyl group perpendicular to the pyridine ring as we reasoned that would be the least sterically hindered quadrant, i.e. we started off from geometry similar to 1-cat2 but with C 5' coordinated instead of C 5 .…”

“…This kind of coordination mode has been reported before, most notably for gas phase calculations of cationic zirconocene benzyl compounds. 41,42 The short C 5 -Ti bond distance of 2.33 Å concomitant with the acute Ti-CH 2 -C ipso angle of 81.8° is significant for an η 3 coordination mode of the benzyl group. This is further corroborated by Bader and NBO analyses: We obtain a bond path between Ti and C 5 with a bond critical point of ρ(r) = 0.0505 a.u.…”

“…We now have a better, more detailed understanding of the role of the ligand, the anion and the solvent. [34][35][36][37][38][39][40][41][42][43][44] To this end, we have been interested for some time now in the structure-reactivity relationship of organometallic compounds. 42,[45][46][47][48][49][50][51][52][53][54] In particular, the use of synergistic effects between spectroscopic data, reactivity and molecular modelling has been exploited.…”

“…[34][35][36][37][38][39][40][41][42][43][44] To this end, we have been interested for some time now in the structure-reactivity relationship of organometallic compounds. 42,[45][46][47][48][49][50][51][52][53][54] In particular, the use of synergistic effects between spectroscopic data, reactivity and molecular modelling has been exploited. 40-42, 47-50, 52 With this in mind we were quite interested in the reported amino phenoxy based dibenzylic titanium compound by Chan which serves as a precursor for ethene polymerisation.…”