The crystallographic observation of molecular lithium oxide: synthesis and solid-state structure of [Me2AlN(2-C5H4N)Ph]2(O)Li2·2THF†

Abstract

The reaction of Me 2 Al[N(2-C 5 H 4 N)Ph], 1, with 1 equiv. (Me 3 Si) 2 NLi affords the lithium aluminate Me 2 Al[N(SiMe 3 ) 2 ][N(2-C 5 H 4 N)Ph]Li, 2, which exhibits solvent dependent reactivity towards oxygen. In toluene 2 appears to resist oxygenation but in the presence of THF it reacts to afford the new complex [Me 2 AlN(2-C 5 H 4 N)-Ph] 2 (O)Li 2 ؒ2THF, 3. X-Ray diffraction data reveal that 3 has a butterfly-type Al 2 Li 2 bimetallic core with two equivalents of reformed 1 stabilising discrete, molecular lithium oxide. The structures of 1-3 are probed theoretically.

Ligand and Metal Effects on the Formation of Main‐Group Polyhedral Clusters

“…Evidently, the (known) reductive addition of LiH to pyridines16 does not represent a required intermediate step in hydride capture of the type noted here. Moreover, previously published data that strongly suggest t BuLi to be the lithium hydride source in the preparation of complexes such as 2 point to the role of t BuLi differing in the two syntheses reported here 10. 17 That this dichotomy gives a structural congener of 9 that incorporates not a hydride but a core void introduces the possibility of a truly polyhedral structural chemistry for alkali metals.…”

“…To date, attempts to significantly alter the composition of such hydride‐yielding systems have met with little success; the employment of, for example, N,N ′‐diphenylbenzamidine gives the hydride‐free superlithiate [Li 4 {PhNC(Ph)NPh} 3 ] + [Li(Me 2 AlMe t Bu) 2 ] − ( 8 ) 9. In seeking to probe the generality of cage–cluster formation and hydride entrapment, two variations on the methodology that yields 2 and 3 (and also 4 – 7 ) have been deployed; 1) N ‐2‐pridylaniline has been replaced by a non‐aromatic guanidine ligand, and 2) while the use of MeLi and HMDSLi (HMDS=hexamethyldisilazide) has circumstantially established the importance of β‐hydrogen‐containing t BuLi in hydride encapsulation chemistry10 the Group 13 organometallic substrate is now replaced by a Group 12 analogue. We report herein that a hydride‐entrapment cluster can be generated by using bicyclic 1,3,4,6,7,8‐hexahydro‐2 H ‐pyrimido[1,2‐ a ]pyrimidine (hppH) in tandem with ZnMe 2 and t BuLi.…”

Encapsulation of hydride by molecular main group metal clusters: manipulating the source and coordination sphere of the interstitial ion

“…21 In this context, amidoalane Ph(2-C 5 H 4 N)NAlMe 2 1 has been reported to undergo straightforward aluminate formation in the presence of hexamethyldisilamidolithium (hmdsLi), with the product, hmds{Ph(2-C 5 H 4 N)N}AlMe 2 Li 2, adopting a polymeric structure in the solid state. 26 Likewise, treatment of 1 with MeLi results in formation of the aluminate complex Ph(2-C 5 H 4 N)NAlMe 3 Li•thf 3 (Fig. 1 and Table 1), in which the generation of an Al(l-Me) 2 Li motif incurs the elongation of (bridging) C12-Al1 and C13-Al1 bonds (2.025(2) and 2.017(2) A ˚, respectively) relative to (terminal) C14-Al1 (1.971(2) A ˚) and renders the lithium centre four-coordinate (C12-Li1 2.281(5), C13-Li1 2.364(5), N2-Li1 1.987(4), O1-Li1 1.875(4) A ˚).…”

Ligand and Metal Effects on the Formation of Main‐Group Polyhedral Clusters

“…Moreover, previously published data that strongly suggest tBuLi to be the lithium hydride source in the preparation of complexes such as 2 point to the role of tBuLi differing in the two syntheses reported here. [10,17] That this dichotomy gives a structural congener of 9 that incorporates not a hydride but a core void introduces the possibility of a truly polyhedral structural chemistry for alkali metals.…”

“…[9] In seeking to probe the generality of cage-cluster formation and hydride entrapment, two variations on the methodology that yields 2 and 3 (and also 4-7) have been deployed; 1) N-2-pridylaniline has been replaced by a nonaromatic guanidine ligand, and 2) while the use of MeLi and HMDSLi (HMDS = hexamethyldisilazide) has circumstantially established the importance of b-hydrogen-containing tBuLi in hydride encapsulation chemistry [10] the Group 13 organometallic substrate is now replaced by a Group 12 analogue. We report herein that a hydride-entrapment cluster can be generated by using bicyclic 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (hppH) in tandem with ZnMe 2 and tBuLi.…”