By variation of the zinc bonded alkyl group significantly different post-oxygenation products, the novel zinc alkylperoxide and the tetranuclear zinc oxo-encapsulated cluster, were derived from the controlled oxygenation of the corresponding alkylzinc complexes with a pyrrolylketiminate ligand.

O what a reaction: The oxygenation of Me2Zn⋅tBu‐DAB (tBu‐DAB=1,4‐di‐tert‐butyl‐1,4‐diazabutadiene) affords the unprecedented oxo(methylperoxide) cubane 1, the corresponding double cubic oxo(methoxide) 2, and the CC coupled dinuclear methoxide [(MeZn)2(tBu‐DAB‐DAB(H)‐tBu)(μ‐OMe)], the formation of which involves initial ZnOOMe bond homolysis.

The mechanisms of O 2 activation by main-group metal alkyl compounds and the character of reactive intermediate oxygen species, along with the origins of reaction outcomes, have been a challenge to understand since the Franklands pioneering studies.[1] For decades, these oxygenation reactions have been commonly considered as difficult to control owing to their radical-chain character.[2] Metal alkyl peroxide complexes have been proposed as intermediates in these reactions, [3,4] and the formation of the most commonly observable alkoxides as final products has traditionally been explained by s bond metathesis involving an alkyl peroxide intermediate and the starting metal alkyl complex. [2, 4a] Our recent systematic investigations have not only advanced a plausible hypothesis concerning the mechanism of O 2 activation by organometallic compounds, [4b,c,k,l, 5] but also convincingly demonstrated a high tendency of incipient zinc peroxide species to form relatively stable adducts with the parent zinc alkyl complex.[4m, 5] Moreover, we have revealed a long overlooked decomposition pathway of zinc alkyl peroxides via homolysis of the O À O bond, which is responsible for the formation of oxo complexes. [4l,m, 5] To date, the formation of alkyl peroxide (path a, Scheme 1), alkoxide (path b), and oxo species (path c) in the oxygenation of ZnÀR species has been well-documented. To our knowledge, homolytic MO À OR bond cleavage to give the corresponding metal carboxylate species (path d, scheme 1) has not been considered as a mode of decomposition of both zinc and other metal alkyl peroxides. [6] Our previous studies demonstrated that N,N-donor pyrroloimines, HL 1 , are versatile supporting ligands that can have diverse bonding modes to metal centers. [4m, 7] Moreover, the controlled oxygenation of [RZn(L 1 )] complexes provides a novel zinc alkyl peroxide or a zinc oxo-encapsulated cluster, the formation of which was mediated by the nature of the zinc-bonded alkyl substituents.[4m] Herein we present a novel extension of the latter investigations, which involves 2,5-bis[(2,6-diisopropylphenyl)aldimino]pyrrole (HL 2 ) as a N,N,N-donor supporting ligand, and the oxygenation of the corresponding ethylzinc derivative [EtZn (L 2 )] leading to the zinc acetate species.The reaction of Et 2 Zn with one equivalent of HL 2 in toluene affords the alkyl zinc complex [{EtZn(L 2 )} n ] (1) in quantitative yield. Although we were not able to obtain single crystals of 1, the 1 H NMR data (see below) are fully consistent with the anticipated formula. Molecular weight measurements revealed that 1 occurs predominantly as a dimeric species in a benzene solution. In the next step, a solution of 1 in toluene at À20 8C was treated with an excess of dry dioxygen, the reaction mixture was stirred for 10 minutes, and then the excess O 2 was removed. From this oxygenation reaction, we expected new zinc alkyl peroxide or oxo aggregates. To our surprise, colorless crystals of the zinc carboxylate [{(L 2 )Zn 2 (m-O 2 CMe) 3 } 2 ] (2) deposited...

O, was für eine Reaktion: Die Oxygenierung von Me2Zn⋅tBu‐DAB (tBu‐DAB= 1,4‐Di‐tert‐butyl‐1,4‐diazabutadien) liefert das neuartige Oxo(methylperoxid)‐Cuban 1, das entsprechende doppelt cubische Oxo(methoxid) 2 und das C‐C‐verknüpfte zweikernige Methoxid [(MeZn)2(tBu‐DAB‐DAB(H)‐tBu)(μ‐OMe)], dessen Bildung mit der Homolyse einer ZnO‐OMe‐Bindung beginnt.

The mechanisms of O 2 activation by main-group metal alkyl compounds and the character of reactive intermediate oxygen species, along with the origins of reaction outcomes, have been a challenge to understand since the Franklands pioneering studies. [1] For decades, these oxygenation reactions have been commonly considered as difficult to control owing to their radical-chain character. [2] Metal alkyl peroxide complexes have been proposed as intermediates in these reactions, [3,4] and the formation of the most commonly observable alkoxides as final products has traditionally been explained by s bond metathesis involving an alkyl peroxide intermediate and the starting metal alkyl complex. [2, 4a] Our recent systematic investigations have not only advanced a plausible hypothesis concerning the mechanism of O 2 activation by organometallic compounds, [4b,c,k,l, 5] but also convincingly demonstrated a high tendency of incipient zinc peroxide species to form relatively stable adducts with the parent zinc alkyl complex. [4m, 5] Moreover, we have revealed a long overlooked decomposition pathway of zinc alkyl peroxides via homolysis of the O À O bond, which is responsible for the formation of oxo complexes. [4l,m, 5] To date, the formation of alkyl peroxide (path a, Scheme 1), alkoxide (path b), and oxo species (path c) in the oxygenation of ZnÀR species has been well-documented. To our knowledge, homolytic MO À OR bond cleavage to give the corresponding metal carboxylate species (path d, scheme 1) has not been considered as a mode of decomposition of both zinc and other metal alkyl peroxides. [6] Our previous studies demonstrated that N,N-donor pyrroloimines, HL 1 , are versatile supporting ligands that can have diverse bonding modes to metal centers. [4m, 7] Moreover, the controlled oxygenation of [RZn(L 1 )] complexes provides a novel zinc alkyl peroxide or a zinc oxo-encapsulated cluster, the formation of which was mediated by the nature of the zinc-bonded alkyl substituents. [4m] Herein we present a novel extension of the latter investigations, which involves 2,5bis[(2,6-diisopropylphenyl)aldimino]pyrrole (HL 2 ) as a N,N,N-donor supporting ligand, and the oxygenation of the corresponding ethylzinc derivative [EtZn(L 2 )] leading to the zinc acetate species.The reaction of Et 2 Zn with one equivalent of HL 2 in toluene affords the alkyl zinc complex [{EtZn(L 2 )} n ] (1) in quantitative yield. Although we were not able to obtain single crystals of 1, the 1 H NMR data (see below) are fully consistent with the anticipated formula. Molecular weight measurements revealed that 1 occurs predominantly as a dimeric species in a benzene solution. In the next step, a solution of 1 in toluene at À20 8C was treated with an excess of dry dioxygen, the reaction mixture was stirred for 10 minutes, and then the excess O 2 was removed. From this oxygenation reaction, we expected new zinc alkyl peroxide or oxo aggregates. To our surprise, colorless crystals of the zinc carboxylate [{(L 2 )Zn 2 (m-O 2 CMe) 3 } 2 ] (2) deposite...