Low Valent Magnesium Chemistry with a Super Bulky ß-Diketiminate Ligand.

The steric bulk of the well-known DIPP BDI ligand (CH[C(CH3 )N-DIPP]2 , DIPP=2,6-diisopropylphenyl) was increased by replacing isopropyl for isopentyl groups. This very bulky DIPeP BDI ligand could not stabilize the radical species (DIPeP BDI)Mg. : reduction of (DIPeP BDI)MgI with Na gave (DIPeP BDI)2 Mg2 with a rather long Mg-Mg bond of 3.0513(8) Å. Addition of TMEDA prior to reduction gave complex (DIPeP BDI)2 Mg2 (C6 H6 ), which could also be obtained as its THF adduct. It is speculated that combination of a bulky spectator ligand and TMEDA prevents dimerization of the intermediate MgI radical, which then reacts with the benzene solvent. Complex (DIPeP BDI)2 Mg2 (C6 H6 ), which formally contains the anti-aromatic anion C6 H6 2- , reacted with tBuOH as a Brønsted base to 1,3- and 1,4-cyclohexadiene and with H2 as a two electron donor to (DIPeP BDI)2 Mg2 H2 and C6 H6 . It also reductively cleaved the C-F bond in fluorobenzene and gave (DIPeP BDI)MgPh, (DIPeP BDI)MgF, and C6 H6 .

Nucleophilic Aromatic Substitution at Benzene with Powerful Strontium Hydride and Alkyl Complexes.

Key to the isolation of the first alkyl strontium complex was the synthesis of a strontium hydride complex that is stable towards ligand exchange reactions. This goal was achieved by using the super bulky ß-diketiminate ligand DIPeP BDI (CH[C(Me)N-DIPeP]2 , DIPeP=2,6-diisopentylphenyl). Reaction of DIPeP BDI-H with Sr[N(SiMe3 )2 ]2 gave (DIPeP BDI)SrN(SiMe3 )2 , which was converted with PhSiH3 into [(DIPeP BDI)SrH]2 . Dissolved in C6 D6 , the strontium hydride complex is stable up to 70 °C. At 60 °C, H-D isotope exchange gave full conversion into [(DIPeP BDI)SrD]2 and C6 D5 H. Since H-D exchange with D2 is facile, the strontium hydride complex served as a catalyst for the deuteration of C6 H6 by D2 . Reaction of [(DIPeP BDI)SrH]2 with ethylene gave [(DIPeP BDI)SrEt]2 . The high reactivity of this alkyl strontium complex is demonstrated by facile ethylene polymerization and nucleophilic aromatic substitution with C6 D6 , giving alkylated aromatic products and [(DIPeP BDI)SrD]2 .

A combined gas-phase dissociative ionization, dissociative electron attachment and deposition study on the potential FEBID precursor [Au(CH3)2Cl]2.

Motivated by the potential of focused-electron-beam-induced deposition (FEBID) in the fabrication of functional gold nanostructures for application in plasmonic and detector technology, we conducted a comprehensive study on [Au(CH3)2Cl]2 as a potential precursor for such depositions. Fundamental electron-induced dissociation processes were studied under single collision conditions, and the composition and morphology of FEBID deposits fabricated in an ultrahigh-vacuum (UHV) chamber were explored on different surfaces and at varied beam currents. In the gas phase, dissociative ionization was found to lead to significant carbon loss from this precursor, and about 50% of the chlorine was on average removed per dissociative ionization incident. On the other hand, in dissociative electron attachment, no chlorine was removed from the parent molecule. Contrary to these observations, FEBID in the UHV setup was found to yield a quantitative loss and desorption of the chlorine from the deposits, an effect that we attribute to electron-induced secondary and tertiary reactions in the deposition process. We find this precursor to be stable at ambient conditions and to have sufficient vapor pressure to be suitable for use in HV instruments. More importantly, in the UHV setup, FEBID with [Au(CH3)2Cl]2 yielded deposits with high gold content, ranging from 45 to 61 atom % depending on the beam current and on the cleanliness of the substrates surface.

On the Electron-Induced Reactions of (CH3)AuP(CH3)3: A Combined UHV Surface Science and Gas-Phase Study.

Focused-electron-beam-induced deposition (FEBID) is a powerful nanopatterning technique where electrons trigger the local dissociation of precursor molecules, leaving a deposit of non-volatile dissociation products. The fabrication of high-purity gold deposits via FEBID has significant potential to expand the scope of this method. For this, gold precursors that are stable under ambient conditions but fragment selectively under electron exposure are essential. Here, we investigated the potential gold precursor (CH3)AuP(CH3)3 using FEBID under ultra-high vacuum (UHV) and spectroscopic characterization of the corresponding metal-containing deposits. For a detailed insight into electron-induced fragmentation, the deposit's composition was compared with the fragmentation pathways of this compound through dissociative ionization (DI) under single-collision conditions using quantum chemical calculations to aid the interpretation of these data. Further comparison was made with a previous high-vacuum (HV) FEBID study of this precursor. The average loss of about 2 carbon and 0.8 phosphor per incident was found in DI, which agreed well with the carbon content of the UHV FEBID deposits. However, the UHV deposits were found to be as good as free of phosphor, indicating that the trimethyl phosphate is a good leaving group. Differently, the HV FEBID experiments showed significant phosphor content in the deposits.

Mg-Mg bond polarization induced by a superbulky ß-diketiminate ligand.

The bulk of a recently reported superbulky ß-diketiminate ligand was further increased by introducing tBu substituents in the ligand backbone. Attempts to isolate free Mg radicals with this extremely bulky ligand failed. Instead, a dinuclear Mg(i) complex with one chelating and one monodentate ß-diketiminate ligand was isolated. Asymmetry in metal coordination results in a polarized Mg-Mg bond.