Search

A computational mechanistic study was performed to investigate the transfer hydrogenation of styrene catalysed by a potassium tris‐hexamethyldisilazide magnesiate in the presence of 1,4‐cyclohexadiene. Exploiting cooperative effects between Mg and K centres present in this tris(amide) complex results in the selective formation of the desired product ethylbenzene. The calculations demonstrate the synergy of the metal centres within the bimetallic complex, since neither the monometallic potassium amide K(HMDS) nor the magnesium amide Mg(HMDS)2 on their own can efficiently execute this transformation under the experimental conditions. Several distinct mechanistic pathways have been explored, leading to the identification of the most plausible sequence in which both metal centres act in a synchronised manner. [ABSTRACT FROM AUTHOR]

While organoelement compounds of lithium, sodium and potassium have been much studied for decades and consequently have found forests of applications, those of the heavier alkali metals, rubidium and caesium would barely manage to fill a tree. However, recently the literature has seen some little growth spurts with these metals, hinting at a possible fertile future in areas such as homogeneous catalysis provided more work is put into their fundamental development. Here we report the synthesis and crystal structures of lithium, rubidium and caesium derivatives of the ureaphosphane Ph2PCH2CH2NHC(=O)NHPh, chosen because it offers O, N, P, and π‐coordination sites. Though one may expect such alkali metal compounds to be essentially similar, the caesium complex has novel features where Cs+ engages in a side‐on coordination to the C=O bond and in a weak bond to the P centre, both of which are absent in the Rb structure. Less surprisingly, the lithium derivative is tetrameric in contrast to the infinite networks of the rubidium and caesium structures. All alkali metal derivatives were made with deprotonating the ureaphosphane by a suitable base, including the sodium and potassium complexes though these two complexes could not be obtained in a crystalline form. [ABSTRACT FROM AUTHOR]

A widely utilised class of ligands in synthesis and catalysis, β‐diketiminate (BDI) or NacNac compounds were initially considered innocent in the sense that they remained intact in all their applications. That changed when the γ‐C−H unit of their NCCCN backbone was found to engage in reactions with electrophiles. Here, we show that this special reactivity can be used advantageously to prepare tripodal modifications of the common NacNac ligand derived from 2,6‐diisopropylphenyl‐β‐methyldiketimine [NacNacH (Me, Dipp)]. Lithiation to give NacNacLi, followed by reactions with isocyanates, isothiocyanates and a carbodiimide, have afforded a series of tripodal NacNac variants having N,N,N,O; N,N,N,S; or N,N,N,N potential dentation sites, many of which have been crystallographically characterised. Distinct ligating modes of these new ligands have been elucidated through the crystal structures of their lithiated derivatives. [ABSTRACT FROM AUTHOR]

Light alkali metal (Li, Na, K) amides have a long history of synthetic utility, but heavier (Rb, Cs) congeners have barely been studied. This study reveals remarkable structurally complex outcomes of reacting AM(HMDS) (AM = Rb, Cs; HMDS = hexamethyldisilazide) with benzaldehyde and acetophenone. Though complicated, reactions give a diversity of eye-catching isolated products, an enolate with a hexagonal prismatic network, two dienolates with distinct extended ladder motifs, and two β-imino-alkoxides comprising zig-zag chains of metal–oxygen bonds in infinite cages. [ABSTRACT FROM AUTHOR]

Three distinct routes are reported to the soluble, dihydridoaluminate compounds, AM[Al(NONDipp)(H)2] (AM=Li, Na, K, Rb, Cs; [NONDipp]2−=[O(SiMe2NDipp)2]2−; Dipp=2,6‐iPr2C6H3) starting from the alkali metal aluminyls, AM[Al(NONDipp)]. Direct H2 hydrogenation of the heavier analogues (AM=Rb, Cs) produced the first examples of structurally characterized rubidium and caesium dihydridoaluminates, although harsh conditions were required for complete conversion. Using 1,4‐cyclohexadiene (1,4‐CHD) as an alternative hydrogen source in transfer hydrogenation reactions provided a lower energy pathway to the full series of products for AM=Li−Cs. A further moderation in conditions was noted for the thermal decomposition of the (silyl)(hydrido)aluminates, AM[Al(NONDipp)(H)(SiH2Ph)]. Probing the reaction of Cs[Al(NONDipp)] with 1,4‐CHD provided access to a novel inverse sandwich complex, [{Cs(Et2O)}2{Al(NONDipp)(H)}2(C6H6)], containing the 1,4‐dialuminated [C6H6]2− dianion and representing the first time that an intermediate in the commonly utilized oxidation process of 1,4‐CHD to benzene has been trapped. The synthetic utility of the newly installed Al−H bonds has been demonstrated by their ability to reduce CO2 under mild conditions to form the bis‐formate AM[Al(NONDipp)(O2CH)2] compounds, which exhibit a diverse series of eyecatching bimetallacyclic structures. [ABSTRACT FROM AUTHOR]

Co‐complexation of equimolar amounts of 1‐alkali‐metal‐2‐tertbutyldihydropyridines with AlMe3 in the presence of a polydentate N‐donor ligand has delivered four crystallographically verified alkali‐metal aluminates [donor⋅AM(μ‐tBuDHP)AlMe3]n (1, AM=Li, donor=TMEDA, n=1; 2, AM=Na, donor=PMDETA, n=1; 3, AM=K, donor=PMDETA, n=2; 4, AM=Cs, donor=PMDETA, n=∞; TMEDA=N,N,N′,N′‐tetramethylethylenediamine; PMDETA=N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine). While the monomeric complexes (1, 2) and the polymeric complex (4) are thermally stable, the dimeric complex (3) undergoes a disproportionation process yielding the known ion‐separated homoanionic complex [K ⋅ (PMDETA)2]+ [AlMe4]− (3 a). Utilizing TMEDA as the N‐donor resulted in the same disproportionation, but gave rise to two distinct solid‐state aggregated forms of aluminate [K ⋅ (TMEDA)2]+ [AlMe4]−, namely monomeric (3 b) and polymeric (3 b′) polymorphs, in which the anionic moiety acts as a bidentate chelator or monodentate bridge respectively to the potassium cationic moieties. [ABSTRACT FROM AUTHOR]

Ferrocence, ruthenocene, or osmocene to the synergic amide base sodium-magnesium tris(diisopropylamide) affords a unique homologous series of metallocence derivatives of general formula where M=Fe(1), Ru (2), or Os(3). Variable temperature NMR soectorscopic studies indicate that 1,2 and 3 each exist as two distinct interconverting conformers in arene solution.