Interaction of the Buchwald Seven-Membered Zirconacyclocumulene Complex with Carbonyl Compounds

Abstract

The interaction of the Buchwald seven-membered zirconacyclocumulene Cp 2 Zr[η 4 -Me 3 SiC 4 (SiMe 3 )− C(C 2 SiMe 3 )=CSiMe 3 ] (1) with a 2-fold excess of benzophenone in toluene at 100 °C for 20 h results in the formation of Me 3 SiCC−CCSiMe 3 and a nine-membered dioxazirconacycle Cp 2 Zr[η 2 -OC(Ph) 2 C(SiMe 3 )C 2 C(SiMe 3 )C(Ph) 2 O] (5) containing [3]cumulene group in the ring. Analogous metallacycle (6) is formed on heating of 1 with fluorenone in toluene at 100 °C. A treatment of 5 with HCl in dioxane at 20 °C affords Cp 2 ZrCl 2 and cis-[3]cumulenic diol Ph 2 (HO)C(Me 3 Si)-CC 2 C(SiMe 3 )C(OH)Ph 2 (7) in 85% yield. The reaction of 1 with benzil (PhCO) 2 at 80 °C in benzene proceeds differently than with benzophenone and fluorenone. In this case, a nine-membered dioxazirconacycle Cp 2 Zr[η 2 -Me 3 SiCC(C 2 SiMe 3 )− C(SiMe 3 )C(C 2 SiMe 3 )OC(Ph)C(Ph)O] ( 10) is produced. The nature of products formed in the interaction of 1 with acenaphthenequinone proved to be temperature dependent. Thus, on carrying out the reaction at 20 °C, an 11-membered trioxazirconacycle (11) containing three CC bonds in the ring was isolated from the mixture, whereas at 80 °C the reaction gave a ten-membered tetraoxadizirconacycle (12) and octasubstituted cyclooctatetraene [(Me 3 Si)CC(CCSiMe 3 )] 4 (13). The structures of 5−7 and 10−13 have been determined by X-ray diffraction. The mechanism of the reactions found is discussed.

A Seven‐Membered Zirconacyclocumulene Complex as a source of Cyclobutadiene: Trapping of Cyclobutadiene by the Diels‐Alder Reaction

“…These facts allowed one to suggest that there is a contribution of the resonance form of the corresponding fivemembered zirconacyclopentadiene, wherein the α-alkynyl group is coordinated with zirconium, to the electronic structure of these zirconacycles (Scheme 1). [4][5][6][7] During our recent work focused on studying the reactions of the seven-membered zirconacycle Cp 2 Zr[η 4 -Me 3 SiC 4 (SiMe 3 )-C(C 2 SiMe 3 ) = CSiMe 3 ] (1) with carbonyl compounds we found the reaction of 1 with acenaphthenequinone, which leads to a ten-membered tetraoxadizirconacycle (2) and SiMe 3 C � C-and SiMe 3 -substituted cyclooctatetraene (3) at 80 °C in benzene (see Scheme 2). [6] We assumed that in this reaction the interaction of initial compounds leads to the generation of the short-lived tetrasub-stituted cyclobutadiene [(Me 3 Si)C=C(C � CSiMe 3 )] 2 (4), that undergoes the fast dimerization via the intermediate Diels-Alder dimer (5) with the formation of cyclooctatetraene (Scheme 3).…”

Aromaticity of 5- and 7-Membered Metallacyclocumulenes of Group 4

“…Since the pioneered works of Buchwald’s, Burlakov and Rosenthal, − the two types of metallacycles containing [3]­cumulene fragments 1 an 2 are known for group 4 metallocenes (Figure ). ,− They have not only high stability but also unique chemical behavior and electronic structure. The group 4 metal atom incorporation leads to excited mesomerism/valence tautomerism in unsaturated metallacycles and new synthetic routes of other synthetically used systems. − …”

“…The structures 1 and 2 and related compounds 3 and 4 were studied earlier using various computational − and experimental methods. − Based on the bond distances, electron density distributions, vibrational spectra, and reactivity, cyclocumulenes 1 and 2 are usually considered by means of two resonance forms. − ,, For 1 , it is M-cyclocumulene and diacetylene complex (Scheme ), and for 2 , it is M-cyclocumulene and M-cyclopentadiene with a coordinated lateral alkyne branch (Scheme ). It is well known that frontier canonical molecular orbitals (CMOs) of the Cp 2 M moiety, , which are essentially d-orbitals of the metal, are located in the bisecting plane.…”

Protolysis of Seven-Membered Zirconacyclocumulene Complexes of Zirconocene

“…This latter fact allowed one to suggest that the electronic structure of these zirconacycles can be described as a resonance hybrid of the corresponding zirconacyclocumulene resonance form and the five-membered zirconacyclopentadiene one wherein the α-alkynyl group is coordinated with zirconium (Scheme ). ,− …”

“…The aforementioned resonance description of the electronic structure of seven-membered zirconacyclocumulene complexes explains satisfactorily not only the abnormally high thermal stability of these compounds but also the peculiarities of their reactivity. Thus, it turned out that in the interaction with acetylenes, nitriles, , diarylketones, and N -benzylideneaniline, , the Buchwald zirconacycle 1 reacts in its zirconacyclocumulene resonance form, whereas in the reactions with benzil, acenaphthenequinone, and S 2 Cl 2 , , the same zirconacycle behaves as if it was in the zirconacyclopentadiene resonance form.…”