Heavy Alkali Metal Manganate Complexes: Synthesis, Structures and Solvent‐Induced Dissociation Effects

Abstract

Rare examples of heavier alkali metal manganates [{(AM)Mn(CH 2 SiMe 3 )(N 'Ar ) 2 } ∞ ] (AM = K, Rb, or Cs) [N 'Ar = N-(SiMe 3 )(Dipp), where Dipp = 2,6-iPr 2 -C 6 H 3 ] have been synthesised with the Rb and Cs examples crystallographically characterised. These heaviest manganates crystallise as polymeric zig-zag chains propagated by AM•••π-arene interactions. Key to their preparation is to avoid Lewis base donor solvents. In contrast, using multidentate nitrogen donors encourages ligand scrambling leading to redistribution of these bimetallic manganate compounds into their corresponding homometallic species as witnessed for the complete Li -Cs series. Adding to the few known crystallographically characterised unsolvated and solvated rubidium and caesium s-block metal amides, six new derivatives ([{AM(N 'Ar )} ∞ ], [{AM(N 'Ar )•TMEDA} ∞ ], and [{AM(N 'Ar )•PMDETA} ∞ ] where AM = Rb or Cs) have been structurally authenticated. Utilising monodentate diethyl ether as a donor, it was also possible to isolate and crystallographically characterise sodium manganate [(Et 2 O) 2 Na-( n Bu)Mn[(N 'Ar ) 2 ], a monomeric, dinuclear structure prevented from aggregating by two blocking ether ligands bound to sodium.

Application of Bis(amido)alkyl Magnesiates toward the Synthesis of Molecular Rubidium and Cesium Hydrido-magnesiates

“…For this study, we decided to utilize the secondary heteroamido ligand – N­(SiMe 3 )­(Dipp) (which we will refer to as N′; Dipp = 2,6-diisopropylphenyl), that is, replacing one of the SiMe 3 groups of HMDS by an aromatic group with its π-surface. The alkali metal chemistry of this ligand is quite well-established, and crucially to this pursuit, the infinite supramolecular structure of unsolvated CsN­(SiMe 3 )­(Dipp) propagates in the solid state via multihapto Cs–C 6 (π) interactions, while its anionic nitrogen is naked in the sense that it does not form a bond to cesium, suggesting that it is potentially well-suited to our needs described above. Furthermore, the Dipp entity is a common feature of a wide variety of subvalent aluminum dimers which appear stitched together by heavy alkali metal cations engaging intramolecularly with N -bound Dipp groups at the periphery of the discrete molecules .…”

“…Starting materials and research chemicals were obtained from commercial suppliers where appropriate and used without further purification. MgN′ 2 , 11 n BuMg N ′, 11 Rb(CH 2 SiMe 3 ), 13c Cs(CH 2 SiMe 3 ), 13c RbN′, 9 and CsN′ 9 were synthesized according to literature procedures. Hexane was dried by heating to reflux over sodium benzophenone ketyl and then distilled under nitrogen prior to use.…”

Cooperative activation of carbon–hydrogen bonds by heterobimetallic systems

“…125 More generally, alkali-metal reagents have been shown to be powerful additives in a great number of dehydrometalations, enabling chemical transformations that could not be accomplished by a single, less electropositive metal center. Mulvey and coworkers developed a series of alkali-metalmediated metalations (AMMMs), 126,127 among them magnesiations (AMMMg), 128 zincations (AMMZn) 129 and manganations (AMMMn II ), 130,131 which rely on the formation of a heterobimetallic alkyl amide of the general composition [(TMEDA)A I (μ-TMP)(μ-R)M II (R,TMP)] (A I = Li, Na; M II = Mg II , Zn II , Mn II ; R = n Bu, t Bu, CH 2 SiMe 3 ; TMEDA = N,N,N′,N′-tetramethylethylenediamine, TMP = 2,2,6,6-tetramethylpiperidine) (Fig. 36).…”