Structurally Defined Allyl Compounds of Main Group Metals: Coordination and Reactivity

Abstract

Organometallic allyl compounds are important as allylation reagents in organic synthesis, as polymerization catalysts, and as volatile metal precursors in material science. Whereas the allyl chemistry of synthetically relevant transition metals such as palladium and of the lanthanoids is well-established, that of main group metals has been lagging behind. Recent progress on allyl complexes of Groups 1, 2, and 12-16 now provides a more complete picture. This is based on a fundamental understanding of metal-allyl bonding interactions in solution and in the solid state. Furthermore, reactivity trends have been rationalized and new types of allyl-specific reactivity patterns have been uncovered. Key features include 1) the exploitation of the different types of metal-allyl bonding (highly ionic to predominantly covalent), 2) the use of synergistic effects in heterobimetallic compounds, and 3) the adjustment of Lewis acidity by variation of the charge of allyl compounds.

η3‐Allyl Coordination at Tin(II)—Reactivity towards Alkynes and Benzonitrile

“…The A 4 X coupling pattern is consistent with an h 3 ground state (A 2 B 2 X pattern) in a fluxional situation (A 4 X pattern) but would also match a fluxional h 1 coordination. [2] Temperature-dependent 1 H NMR measurements in [D 8 ]toluene showed no significant changes in the spectrum up to 100 8C. Towards À80 8C, a broadening of the doublet followed by its complete disappearance into the baseline was observed.…”

“…[1] In case of tetravalent tin, the allyl substituent binds in the h 1 coordination mode whereas complexes of several other main-group elements feature the allyl ligand in the h 3 coordination mode. [2] Switching the oxidation state of the tin atom from IV to II in allyl tin compounds may result in new coordination modes and reactivity as unoccupied binding sites will then be available at the tin atom. [3] In 2010, Power et al reported the binding of a tin compound to a hydrocarbon moiety in an h 3 fashion.…”

η3‐Allylkoordination an Zinn(II) – Reaktivität gegenüber Alkinen und Benzonitril

“…[2] Ein Wechsel des Oxidationszustandes am Zinnatom von IV nach II in Allylzinnverbindungen kçnnte zu neuen Koordinationsmodi und Reaktivitäten führen, da unbesetzte Koordinationsstellen am Zinnatom verfügbar sind. [3] 2010 berichteten Power et al von einer h 3 -Koordination eines Zinnfragmentes durch ein Cyclooctatetraenmolekül (COT).…”

“…[3] 2010 berichteten Power et al von einer h 3 -Koordination eines Zinnfragmentes durch ein Cyclooctatetraenmolekül (COT). [4] Bei Reaktion eines Distannins mit COT wurden die Spaltung der Sn Sn-Bindung und im Festkçrper eine h 2 :h 3 -Koordination zweier Ar-Sn-Fragmente an das entstehende,m it zehn Elektronen p-aromatische [COT] 2À beobachtet ([(ArSn) 2 (m 2 -h 2 :h 3 -cot)] (A); Ar = C 6 H 3 -2,6-(C 6 H 3 -2,6-iPr 2 ) 2 ). [4] Wirs tellen hier die Synthese einer allylsubstituierten Zinn(II)-Verbindung (1)v or, die eine unseres Wissens zuvor unbekannte h 3 -C 3 H 5 -Koordination am Zinnatom aufweist.…”

“…Dieses A 4 X-Kopplungsmuster ist im Einklang mit einem h 3 -Grundzustand (A 2 B 2 X) unter dynamischen Bedingungen (A 4 X), würde aber auch zu einer dynamischen h 1 -Koordination passen. [2] Te mperaturabhängige 1 H-NMR-Messungen in [D 8 ]Toluol zeigten keine signifikante ¾nderung im Spektrum bis 100 8 8C. In Richtung À80 8 8Cwurde eine Verbreiterung des Dubletts,g efolgt von komplettem Verschmelzen mit der Basislinie,b eobachtet.…”