RESUMEN
The earth-metal olefin complex [GaI (COD)2 ]+ [Al(ORF )4 ]- (COD=1,5-cyclooctadiene; RF =C(CF3 )3 ) constitutes the first homoleptic olefin complex of any main-group metal accessible as a bulk compound. It is straight forward to prepare in good yield and constitutes an olefin complex of a main-group metal that-similar to many transition-metals-may adopt the +1 and +3 oxidation states opening potential applications. Crystallographic-, vibrational- and computational investigations give an insight to the atypical bonding between an olefin and a main-group metal. They are compared to classical transition-metal relatives.
RESUMEN
The reaction of the Ga+ source [Ga(PhF)2 ]+ [Al(ORF )4 ]- with the neutral σ-donor ligand dmap (4-Me2 N-C6 H4 N) produces the unexpectedly large and fivefold positively charged cluster cation salt [Ga5 (dmap)10 ]5+ ([Al(ORF )4 ]- )5 . It includes a regular and planar Ga5 pentagon with strong metal-metal bonding. Additionally, the compound represents the first salt in which an ionic 1:5 packing is realized. We discuss the nature of this structure which results from the conversion of the non-bonding 4s2 lone-pair orbitals into fully Ga-Ga-bonding orbitals and the solid-state arrangement of the ions constituting the lattice as an almost orthohexagonal AX5 lattice, possibly the aristotype of any 5:1 salt.
RESUMEN
The univalent salt Ga(PhF)2 + [Al(ORF )4 ]- (RF =OC(CF3 )3 ) forms the strongly metal-metal bonded cluster tetracations [GaII 2 (L)4 ]4+ and [GaI 4 (L')8 ]4+ , when it reacts with innocent ligands like phenanthroline (L=phen) or t-butylisonitrile (L'=t Bu-NC). Their structures and energetics are discussed as a function of the employed ligands, supported by DFT calculations and Born-Fajans-Haber cycles.
RESUMEN
Already 1 mol% of subvalent [Ga(PhF)2]+[pf]- ([pf]- = [Al(ORF)4]-, RF = C(CF3)3) initiates the hydrosilylation of olefinic double bonds under mild conditions. Reactions with HSiMe3 and HSiEt3 as substrates efficiently yield anti-Markovnikov and anti-addition products, while bulkier substrates such as HSiiPr3 are less reactive. Investigating the underlying mechanism by gas chromatography and STEM analysis, we unexpectedly found that H2 and metallic Ga0 formed. Without the addition of olefins, the formation of R3Si-F-Al(ORF)3 (R = alkyl), a typical degradation product of the [pf]- anion in the presence of a small silylium ion, was observed. Electrochemical analysis revealed a surprisingly high oxidation potential of univalent [Ga(PhF)2]+[pf]- in weakly coordinating, but polar ortho-difluorobenzene of E 1/2(Ga+/Ga0; oDFB) = +0.26-0.37 V vs. Fc+/Fc (depending on the scan rate). Apparently, subvalent Ga+, mainly known as a reductant, initially oxidizes the silane and generates a highly electrophilic, silane-supported, silylium ion representing the actual catalyst. Consequently, the [Ga(PhF)2]+[pf]-/HSiEt3 system also hydrodefluorinates C(sp3)-F bonds in 1-fluoroadamantane, 1-fluorobutane and PhCF3 at room temperature. In addition, both catalytic reactions may be initiated using only 0.2 mol% of [Ph3C]+[pf]- as a silylium ion-generating initiator. These results indicate that silylium ion catalysis is possible with the straightforward accessible weakly coordinating [pf]- anion. Apparently, the kinetics of hydrosilylation and hydrodefluorination are faster than that of anion degradation under ambient conditions. These findings open up new windows for main group catalysis.