Reactions of Five-Membered Metallacyclocumulenes Cp₂M(η⁴-t-Bu-C₄-t-Bu) (M = Ti, Zr) with Diisobutylaluminum Hydride

Abstract

Reactions of the five-membered metallacyclocumulenes Cp2M(η4-t-Bu-C4-t-Bu) (M = Ti, Zr) with the Lewis Acid i-Bu2AlH were studied. Cp2Ti(η4-t-Bu-C4-t-Bu) (1) reacts with i-Bu2AlH to give a heterobimetallic complex which was isolated as the THF adduct Cp2Ti[μ-η1:η2-t-BuCC−CHC-t-Bu)(μ-H)(i-BuAl)(THF)] (4). The reaction of the corresponding zirconocene compound Cp2Zr(η4-t-Bu-C4-t-Bu) (2) with i-Bu2AlH results in a cleavage of the central CC bond of the metallacyclocumulene C4 chain and formation of the dinuclear complex 6 and the dinuclear acetylide [(Cp2Zr)2(μ-CC-t-Bu)2]. In addition to the formation of 6 and the acetylide species an elimination of the butadiyne takes place, which gives in the subsequent interaction with i-Bu2AlH the zwitterionic aluminum cluster 7. Alternatively, complex 7 is also formed in the direct reaction of the butadiyne with a 3-fold excess of i-Bu2AlH. The molecular structures of 4 and 7 were confirmed by X-ray analysis.

Molecular Main Group Metal Hydrides

“…The blank reaction of Cp 2 ZrCl 2 with a ten-fold excess of aluminum hydride was shown to afford [( Mes Nacnac)­AlH­(μ-H) 2 Zr­(H)­Cp 2 ] ( 584 ), as a likely catalyst resting state . Titanocene and zirconocene alkyne and cumulene complexes, Cp 2 M­(RCCR) and Cp 2 M­(RCCCCR) (M = Ti, Zr) have long been known to react with aluminum hydrides (such as HAl i Bu 2 , DIBAL-H) to give various heterocycles bearing M–H–Al bridging units, and several reports in the past two decades have continued this work. − In a more unusual reaction, when the decamethyl­ziroconocene complex Cp* 2 Zr­(Me 3 SiCCSiMe 3 ) was combined with HAl i Bu 2 , compound 586 was observed, arising from an intramolecular C–H bond activation . Ruthenium and iron also known to form bridging aluminates akin to the Group 3/4 metals. − …”

Boron, aluminium, gallium, indium and thallium

“…228 The Lewis acid i Bu 2 AlH has been shown to react with the five-membered metallacyclocumulenes Cp 2 Ti(Z 4-t Bu-C 4 -t Bu) to give the heterobimetallic complex Cp 2 Ti[m-Z 1 :Z 2-t BuCCCHC-t Bu)(m-H)( i BuAl)(THF)] which was isolated as the THF adduct and structurally characterised. 229 Dialkylaluminium hydrides have also been reacted with dipheny-diethynyl-lsilyl to afford the corresponding dialkenylsilanes by hydroalumination. 230 The aluminium borohydride system Al(BH 4 ) 3 Á6NH 3 has been investigated as a potential hydrogen storage candidate material.…”