Activation of the GaI Cation for Bond Activation: from Oxidative Additions into C-Cl and H-P Bonds to Reversible Insertion into P4.

Although the discovery of the GaI complex salt [Ga(PhF)2-3 ][Al(ORF )4 ] (RF =C(CF3 )3 , PhF=C6 H5 F) invoked the preparation of a diverse library of cationic Ga(I) coordination complexes and clusters, studies on small molecule activation with low-valent GaI cations are scarce. Herein, a first experimental study on the reactivity of a monomeric Ga(I) cation activated with a pyridine-diimine pincer ligand (in [Ga(PDIdipp )][Al(ORF )4 ]) towards small-molecules is reported. First controlled oxidative additions of the GaI cation into C-Cl, H-P and P-P bonds are presented. Moreover, the [4+1]cycloaddition to butadienes was achieved. Intriguingly, the isolated, blue insertion product into the P-P bond of P4 allows for the quantitative release of the P4 molecule upon reaction with AlEt3 and butadienes. Reversible P4 insertion of main-group metals has previously been reported for Ge and Sn, respectively. The experimental study is supported by high-level computational analysis of the in-part reversible oxidative additions at the DLPNO-CCSD(T)/def2-TZVPP//PBEh-3c/def2-mSVP level of theory with COSMO-RS solvation in 1,2-difluorobenzene.

Low-Valent Mx Al3 Cluster Salts with Tetrahedral [SiAl3 ]+ and Trigonal-Bipyramidal [M2 Al3 ]2+ Cores (M=Si/Ge).

Schnöckel's [(AlCp*)4 ] and Jutzi's [SiCp*][B(C6 F5 )4 ] (Cp*=C5 Me5 ) are landmarks in modern main-group chemistry with diverse applications in synthesis and catalysis. Despite the isoelectronic relationship between the AlCp* and the [SiCp*]+ fragments, their mutual reactivity is hitherto unknown. Here, we report on their reaction giving the complex salts [Cp*Si(AlCp*)3 ][WCA] ([WCA]- =[Al(ORF )4 ]- and [F{Al(ORF )3 }2 ]- ; RF =C(CF3 )3 ). The tetrahedral [SiAl3 ]+ core not only represents a rare example of a low-valent silicon-doped aluminium-cluster, but also-due to its facile accessibility and high stability-provides a convenient preparative entry towards low-valent Si-Al clusters in general. For example, an elusive binuclear [Si2 (AlCp*)5 ]2+ with extremely short Al-Si bonds and a high negative partial charge at the Si atoms was structurally characterised and its bonding situation analysed by DFT. Crystals of the isostructural [Ge2 (AlCp*)5 ]2+ dication were also obtained and represent the first mixed Al-Ge cluster.

Cationic dialanes with fluxional π-bridged cyclopentadienyl ligands.

Unique π-cyclopentadienyl bridged dialanes are synthesized as complex salts with aluminate anions by comproportionation of aluminocenium cations [AlIII(Cp)(Cp*)]+/[AlIIICp2]+ with [(AlICp*)4]. Very short Al-Al bond lengths occur in positively charged Al24+ fragments. Intriguingly, the prepared asymmetric dialane shows a unique fluxional coordination of the cyclopentadienyl ligands.

From mixed group 13 cations [M(AlCp*)3]+ (M = Ga/In/Tl) to an Al4 + cluster.

AlCp*-complexes with transition metals have shown to be highly reactive and enable C-H or Si-H bond activation. Yet, complexes of AlCp* with low-valent main-group metals are scarce. Here, we report the syntheses of [M(AlCp*)3][Al(ORF)4] (RF = C(CF3)3) with M = Ga, In, Tl, which include the first covalent Al-In and Al-Tl bonds. For M = Ga, AlCp*-coordination induced the formation of the dication [Ga2(AlCp*)6]2+ in the solid state, which exhibits a solvent and temperature dependent monomer-dimer equilibrium in solution. By contrast, the In and Tl complexes are monomeric and prone to reduction to the metal by the electron-rich AlCp*-moieties. The QTAIM analysis suggests that the metal centres are already highly reduced in the complexes, while the positive charge is distributed onto the AlCp* units. Addition of Me3TACN (1,4,7-trimethyl-1,4,7-triazacyclononane) to the Ga- and Tl-complex salts resulted in an isomerization to the novel low-valent Al4 + cation [(Me3TACN)Al(AlCp*)3][Al(ORF)4]. Intermittently formed tetrahedral GaAl3 + clusters could be structurally characterized. From a detailed mechanistic study of this isomerization, the very high yield and clean preparation of [(Me3TACN)Al(AlCp*)3][Al(ORF)4] was devised from [M(Me3TACN)][Al(ORF)4] (M = Ga, Tl) and [(AlCp*)4].

Synthesis of a low-valent Al4+ cluster cation salt.

Low-valent aluminium compounds are very reactive main-group species and have therefore been widely investigated. Since the isolation of a stable molecular Al(I) compound in 1991, [(AlCp*)4] (Cp* = [C5Me5]-), a variety of highly reactive neutral or anionic low-valent aluminium complexes have been developed. By contrast, their cationic counterparts have remained difficult to access. Here, we report the synthesis of [Al(AlCp*)3]+[Al(ORF)4]- (RF = C(CF3)3) through a simple metathesis reaction between [(AlCp*)4] and Li[Al(ORF)4]. Unexpectedly, the [Al(AlCp*)3]+ salt forms a dimer in the solid state and concentrated solutions. Addition of Lewis bases results in monomerization and coordination to the unique formal Al+ atom, giving [(L)xAl(AlCp*)3]+ salts where L is hexaphenylcarbodiphosphorane (x = 1), tetramethylethylenediamine (x = 1) or 4-dimethylaminopyridine (x = 3). The Al+-AlCp* bonds in the resulting [(L)xAl(AlCp*)3]+ cluster cations can be finely tuned between very strong (with no ligand L) to very weak and approaching isolated [Al(L)3]+ ions (when L is dimethylaminopyridine).

A Highly Lewis Acidic Strontium ansa-Arene Complex for Lewis Acid Catalysis and Isobutylene Polymerization.

The potential of a dicationic strontium ansa-arene complex for Lewis acid catalysis has been explored. The key to its synthesis was a simple salt metathesis from SrI2 and 2 Ag[Al(ORF )4 ], giving the base-free strontium-perfluoroalkoxyaluminate Sr[Al(ORF )4 ]2 (ORF =OC(CF3 )3 ). Addition of an ansa-arene yielded the highly Lewis acidic, dicationic strontium ansa-arene complex. In preliminary experiments, the complex was successfully applied as a catalyst in CO2 -reduction to CH4 and a surprisingly controlled isobutylene polymerization reaction.