Organometallic Polymers Assembled from Cation–π Interactions: Use of Ferrocene as a Ditopic Linker Within the Homologous Series [{(Me₃Si)₂NM}₂⋅(Cp₂Fe)]_∞ (M=Na, K, Rb, Cs; Cp=cyclopentadienyl)

Abstract

Addition of ferrocene to solutions of alkali metal hexamethyldisilazides M(HMDS) in arenes (in which M=Na, K, Rb, Cs) allows the subsequent crystallization of the homologous series of compounds [{(Me(3)Si)(2)NM}(2) (Cp(2)Fe)](infinity) (1-4). Similar reactions using LiHMDS led to the recrystallization of the starting materials. The crystal structures of 1-4 reveal the formation of one-dimensional chains composed of dimeric [{M(HMDS)}(2)] aggregates, which are bridged through neutral ferrocene molecules by eta(5)-cation-pi interactions. In addition, compounds 3 and 4 also contain interchain agostic M--C interactions, producing two-dimensional 4(4)-nets. Whereas 1 and 2 were prepared from toluene, the syntheses of 3 and 4 required the use of tert-butylbenzene as the reaction media. The attempted crystallization of 3 and 4 from toluene resulted in formation of the mixed toluene/ferrocene solvated complexes [{(Me(3)Si)(2)NM)(2)}(2) (Cp(2)Fe)(x)(Tol)(y)](infinity) (in which M=Rb, x=0.6, y=0.8, 5; M=Cs, x=0.5, y=1, 6). The extended solid-state structures of 5 and 6 are closely related to the 4(4)-sheets 3 and 4, but are now assembled from a combination of cation-pi, agostic, and pi-pi interactions. The charge-separated complex [K{(C(6)H(6))(2)Cr}(1.5)(Mes)][Mg(HMDS)(3)] (15) was also structurally characterized and found to adopt an anionic two-dimensional 6(3)-network through doubly eta(3)-coordinated bis(benzene)chromium molecules. DFT calculations at the B3 LYP/6-31G* level of theory indicate that the binding energies of both ferrocene and toluene to the M(HMDS) dimers increases in the sequence Li<Na<K. This pattern is a consequence of the larger metals allowing more open coordination spheres to support cation-pi contacts. By comparison, binding of the isolated metal cations to the aromatic groups follow the reverse order K<Na<Li. A combined analysis of theoretical and experimental data suggest that ferrocene is a stronger cation-pi donor than toluene for the lighter metals, but that this difference is eliminated on descending the group.

K[Al4(PPh2)7PPh]: An AlII Phosphanide / Phosphinidene Intermediate on the Path to AlP Formation

“…The chain can be viewed as a series of [Al 4 (PPh 2 ) 7 PPh] -units held together by a K-P coordinate bond and cation-π interactions between the potassium ion and phenyl rings ( Figure S2a). Similar alkali metal-π interactions are known in organometallic polymers prepared in arene solvents [18] as well as sodium-containing 'dialuminyne' species. [5] The [Al 4 (PPh 2 ) 7 PPh] -units are chiral and form homochiral chains that propagate along the 2 1 screw axis of the crystal lattice.…”

Exploring the solid state and solution structural chemistry of the utility amide potassium hexamethyldisilazide (KHMDS)

“…This motif is also observed when ferrocene is added to KHMDS, resulting in the isolation of the unusual polymeric [(KHMDS) 2 (ferrocene)] ∞ ( Fig. 1h), 42 where ferrocene π-coordinates to the potassium metal. When KHMDS is combined with alkaline earth metal amides forming mixed metallate species, [43][44][45] it is possible to isolate inverse crown species such as hydrido- 46 and oxo-variants 47,48 as well as simpler binuclear heterobimetallic amide formulations 49,50 also observed when the alkaline earth metal is replaced by lanthanides.…”

“…Both compounds, 10 and 11, crystallise from toluene solutions. The affinity of heavy alkali metals to engage π-interactions with arenes is well known; 42,[80][81][82][83][84][85][86] however, in the presence of the corresponding multidentate ligands TMDAE and TMEEA in 10 and 11, respectively, there is no interaction with the arene in the solid-state structures.…”

Exklusiver π‐Einschluss leichter Alkalimetallkationen durch ein neutrales Molekül

“…Während massenspektrometrische Daten von neutralen Molekülen existieren, welche Alkalimetallkationen ausschließlich durch Kation-p-Wechselwirkungen binden, [23] gibt es nur wenige strukturell belegte Beispiele.D iese sind Fullerene mit eingekapselten Kationen (I und II,A bbildung 1), [24] und vier Alkin-und Arenkomplexe von Kaliumund Caesiumkationen (III-VI,A bbildung 1). [25] Neben den Fullerenkomplexen I und II,indenen die Kationen kinetisch gefangen sind, sind keine Komplexe in kondensierter Phase beschrieben, in denen die leichteren Alkalimetallkationen Li + und Na + ausschließlich an neutrale p-Systeme gebunden sind. [26] Dies ist besonders deshalb überraschend, da Berechnungen im M + -Benzol-Modell ergeben, dass Kation-p-Wechselwirkungen der leichten Alkalimetalle gegenüber den schwereren Homologen energetisch bevorzugt sind.…”