Visiting the Limits between a Highly Strained 1‐Zirconacyclobuta‐2,3‐diene and Chemically Robust Dizirconacyclooctatetraene

Abstract

The reaction of the allene precursor Li (Me SiC SiMe ) with [Cp ZrCl ] (Cp=cyclopentadienyl) was examined. The selective formation of hitherto unknown linear, allene-bridged dizirconocene complexes [(Cp ZrCl) {-μ-(Me Si)C (SiMe )-}] and [(Cp Zr) {-μ-(Me Si)C (SiMe )-} ] was observed. Upon σ coordination of the allenediyl unit to {Cp Zr}, pyrophoric Li (Me SiC SiMe ) is tamed stepwise to yield a surprisingly robust 1,5-dizirconacyclooctatetra-2,3,6,7-ene with cumulated double bonds. This complex is unexpectedly inert against moisture, air, water and acetone. Surprisingly, it degrades under MS conditions to give the highly strained 1-zirconacyclobuta-2,3-diene. All compounds isolated have been fully characterised and the molecular structures are discussed. The stability and reactivity of these complexes are rationalised by DFT computations.

1-Titanacyclobuta-2,3-diene – an elusive four-membered cyclic allene

“…To evaluate the influence of the metal centre we first adapted our previously reported procedure18 and reacted [Cp 2 TiCl 2 ] with [Li 2 (Me 3 SiC 3 SiMe 3 )]. 1 H NMR analysis of an aliquot taken after a reaction time of 16 hours at room temperature shows the formation of several Cp containing products along with a large number of resonances in the SiMe 3 region of the spectrum, out of which we identified the coupling product 1 ( cf.…”

“…We have thus revisited and optimised the synthesis of a previously reported 1,3-dilithioallene precursor [Li 2 (Me 3 SiC 3 SiMe 3 )]17 and reacted this with [Cp 2 ZrCl 2 ]. To our surprise, we obtained two unusual allenediide bridged dizirconocene complexes [Cp 2 Zr(RC 3 R) 2 ZrCp 2 ] and [Cp 2 Zr(Cl)RC 3 R(Cl)ZrCp 2 ] (R = SiMe 3 ),18 the latter being a promising precatalyst for amine borane dehydropolymerisation 19. Interestingly, we were able to show that the dizirconacyclooctatetraene [Cp 2 Zr(RC 3 R) 2 ZrCp 2 ] degrades under mass spectrometry conditions into the desired mononuclear 1-zirconacyclobuta-2,3-diene compound.…”

Take a “Snapshot” of New Syntheses, Reactions, and Characterizations from Unusual Unsaturated Ring Strained Group 4 Metallacycles

“…It is of interest that the later in this paper mentioned theoretical prediction for the existence of 4‐menbered matalla‐cycloallenes of Group 4 metals was realized in 2019 by Reiss, Beweries and coworkers in a paper under the title “1‐Titanacyclobuta‐2,3‐diene ‐ an elusive fourmembered cyclic allene” . For the synthesis of a highly strained 1‐metalla‐cyclobuta‐2,3‐diene of a Group 4 metal, firstly the reaction of the allene precursor Li 2 (Me 3 Si‐C=C=C‐SiMe 3 ) with Cp 2 ZrCl 2 was investigated [12] . As products of this reaction were only the linear allene‐bridged dizirconocene complexes (Cp 2 ZrCl) 2 [‐μ‐(Me 3 Si)C 3 (SiMe 3 )‐] and (Cp 2 Zr) 2 [‐μ‐(Me 3 Si)C 3 (SiMe 3 )‐] 2 obtained.…”

A Ghost Trapped: Realization of the 1‐Titanacyclobuta‐2,3‐diene as the First Four‐Membered Group 4 Metallacycloallene

“…After revisiting and optimising the synthesis and isolation of the known SiMe 3 substituted 1,3‐dilithioallene [Li 2 (Me 3 SiC 3 SiMe 3 )] this compound was used by Reiß, Beweries and co‐workers as a precursor for the synthesis of all‐C ‐metallacyclooallenes. In reactions of the Li salt with Cp 2 ZrCl 2 an unusual dinuclear zirconocene complex Cp 2 Zr[η 2 ‐C(SiMe 3 )=C=C(SiMe 3 )] 2 ZrCp 2 was found in which two allenediide‐ligands ‐C(SiMe 3 )=C=C(SiMe 3 )‐ bridge two zirconocene units (Scheme ).…”

“…In reactions of the Li salt with Cp 2 ZrCl 2 an unusual dinuclear zirconocene complex Cp 2 Zr[η 2 ‐C(SiMe 3 )=C=C(SiMe 3 )] 2 ZrCp 2 was found in which two allenediide‐ligands ‐C(SiMe 3 )=C=C(SiMe 3 )‐ bridge two zirconocene units (Scheme ). This complex turned out to be air and water stable and decomposes under mass spectrometric conditions selectively to the desired 1‐zirconacyclobuta‐2,3‐diene …”