Probing the Extremes of Covalency in M−Al bonds: Lithium and Zinc Aluminyl Compounds

Abstract

Synthetic routes to lithium, magnesium, and zinc aluminyl complexes are reported, allowing for the first structural characterization of an unsupported lithium-aluminium bond. Crystallographic and quantum-chemical studies are consistent with the presence of ah ighly polar Li À Al interaction, characterized by al ow bond order and relatively little charge transfer from Al to Li. Comparison with magnesium and zinc aluminyl systems reveals changes to both the MÀAl bond and the (NON)Al fragment (where NON = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene), consistent with am ore covalent character,w ith the latter complex being shown to react with CO 2 via ap athway that implies that the zinc centre acts as the nucleophilic partner.

Reductive Dimerization of CO by a Na/Mg(I) Diamide

“…In contrast to the unsupported Mg–Mg bonds of compounds 1 – 3 and 6 , a notable feature of compound 4 is the presence of bridging Na–aryl contacts, which presumably play a significant role in the stability of the dimeric molecule . We, and others, have recently observed that similarly persistent Na– and K–aryl interactions provide a defining feature in a number of dimeric potassium diamidoalumanyl derivatives. − In these cases, the integrity of the formal Al­(I) centers is maintained by a sterically demanding diamide ligand, such as in the seven-membered cyclic species, [{SiN Dipp }­AlK] 2 ­[{SiN Dipp } = {CH 2 SiMe 2 N­(Dipp)} 2 ; Dipp = 2,6- i- Pr 2 C 6 H 3 ] ( 7 ) . Prompted by the robust nature of compounds 4 and 7 , in this contribution we show that the thermodynamic preference for heavier group 1 element–aryl interactions , can provide a strategy to access dinuclear low oxidation state alkaline earth species that circumvents conventional salt elimination.…”

Controlling Al–M Interactions in Group 1 Metal Aluminyls (M = Li, Na, and K). Facile Conversion of Dimers to Monomeric and Separated Ion Pairs

“…This is in contrast to the previously reported potassium CDP [II-K] 2 , for which a symmetrical CDP with equivalent Al−K interactions is observed (WBIs [II-K] 2 = 0.130/0.130). 26 A subsequent article reported that the attempted reduction of the aluminum iodide I-I with either lithium or sodium metal failed to access the aluminyls "I-Li" and "I-Na", 35 highlighting the importance of the supporting ligand framework in this area of chemistry. Furthermore, we determined that [II-Li] 2 and [II-Na] 2 provide a facile route to the MIPs II-Li(Et 2 O) 2 and II-Na(Et 2 O) 2 , which can be accessed by simply dissolving the CDPs in diethyl ether solvent.…”

“…In an alternative approach, the corresponding MIP system I-Li(Et 2 O) 2 was isolated in low yield by cation exchange from [I-K] 2 using lithium iodide in diethyl ether. 35 In this contribution, we report the synthesis and structure of a full series of monomeric ion pairs and separated ion pairs for the aluminyl anion [Al(NON Dipp )] − with the group 1 metals lithium, sodium, and potassium. The results demonstrate our ability to mediate the position of the group 1 cation and provide a platform for studying the role that the group 1 metals contribute to the reactivity of this system.…”

Probing the Extremes of Covalency in M−Al bonds: Lithium and Zinc Aluminyl Compounds

“…Comparison with related magnesium and zinc systems reveals changes to both the MÀAl bond and the (NON)Al fragment consistent with greater covalent character, with the latter complex being shown to react with CO 2 via ap athway that implies that the zinc centre is sufficiently electron rich to formally act as the nucleophilic partner. [32] Figure 5. DFT-calculatednatural charges for naked aluminyl anion [(NON)Al] À ,a nd the corresponding complexeso flithium, magnesium, aluminium and zinc;( inset) predominant resonances tructure proposed by Schoeller and co-workers for amodel aluminyl system.…”