Hydridostannylene Derivatives of Magnesium and Calcium.

Reactions of a m-terphenylhydridostannylene with β-diketiminato magnesium and calcium hydrides provide bis-μ-hydrido species, the heterobimetallic constitutions of which are maintained after the addition of THF donor solvent. In both cases, reactions with hex-1-ene result in the formation of tetravalent organostannyl alkaline earth derivatives. Whereas the magnesium reagent undergoes facile twofold addition, the calcium-centered process is arrested after a single alkene reduction event.

Nucleophilic Triphenylgermanides of Magnesium and Calcium.

The dimeric calcium and magnesium hydrides, [(BDI)AeH] [BDI=HC{(Me)CNDipp}, Dipp=2,6-i-PrCH; Ae=Mg or Ca] do not react with PhGeH in non-coordinating solvent. Addition of THF, however, induces deprotonation and access to monomeric Ae-germanide complexes, [(BDI)Ae{GePh}(THF)], both of which have been structurally characterized. Although this process is facile when Ae=Ca, the analogous magnesium-based reaction requires heating to temperatures >100 °C, under which conditions germanide formation is complicated by THF ring opening and the generation of an alkaline earth germyl-C-terminated n-butoxide, [(BDI)Mg{μ-O(CH)GePh}].

Trends in Structure and Ethylene Polymerization Reactivity of Transition-Metal Permethylindenyl-phenoxy (PHENI*) Complexes.

A family of -permethylindenyl-phenoxy (PHENI*) transition-metal chloride complexes has been synthesized and characterized (; {(η-CMe)Me(R″)Si(2-R-4-R'-CHO)}MCl; R,R' = Me, Bu, Cumyl (CMePh); R″ = Me, Pr, Ph; M = Ti, Zr, Hf). The ancillary chloride ligands could readily be exchanged with halides, alkyls, alkoxides, aryloxides, or amides to form PHENI* complexes [L]TiX (; X = Br, I, Me, CHSiMe, CHPh, NMe, OEt, ODipp). The solid-state crystal structures of these PHENI* complexes indicate that one of two conformations may be preferred, parametrized by a characteristic torsion angle (TA'), in which the η system is either disposed away from the metal center or toward it.

Towards designer polyolefins: highly tuneable olefin copolymerisation using a single permethylindenyl post-metallocene catalyst.

Using a highly active permethylindenyl-phenoxy (PHENI*) titanium catalyst, high to ultra-high molecular weight ethylene-linear-α-olefin (E/LAO) copolymers are prepared in high yields under mild conditions (2 bar, 30-90 °C). Controllable, efficient, and predictable comonomer enchainment provides access to a continuum of copolymer compositions and a vast range of material properties using a single monomer-agnostic catalyst. Multivariate statistical tools are employed that combine the tuneability of this system with the analytical and predictive power of data-derived models, this enables the targeting of polyolefins with designer properties directly through predictive alteration of reaction conditions.

Fully tuneable ethylene-propylene elastomers using a supported permethylindenyl-phenoxy (PHENI*) catalyst.

Using a highly active supported permethylindenyl-phenoxy (PHENI*) titanium catalyst, high molecular weight ethylene-propylene (EPM) and ethylene-propylene-diene (EPDM) elastomers are prepared using slurry-phase catalysis. Final copolymer composition was found to reflect the monomer feed ratio in a linear fashion, to access a continuum of material properties with a single catalyst. Post-polymerisation crosslinking of EPDM was also demonstrated in a model sulfur vulcanisation system.

Hydrogen-bonding and resonance stabilisation effects in cationic bis(iminium) phenoxide diacids.

The synthesis and characterisation of a bis(iminium)phenoxide diacid cation [4-Bu-CH-2,6-(HCN(H)Dipp)-1-O] ([HL]), is discussed. [HL][BF] (1) and [HL][HN{B(CF)}] (2) were synthesised in high yields protonation of the bis(imino)phenol conjugate base with ethereal HBF or Bochmann's acid ([H(OEt)][HN{B(CF)}]). Both species were fully characterised using NMR and IR spectroscopy as well as X-ray crystallography.

Hydroboration and Deoxygenation of CO Mediated by a Gallium(I) Cation.

Hydroboration of CO to formoxy borane occurs under ambient conditions in acetonitrile using pinacolborane HBpin in the presence of gallium(I) cation [(MeTACD)Ga][BAr] (; MeTACD = ,',″,'''-tetramethyl-1,4,7,10-tetraazacyclododecane; Ar = CH-3,5-Me). Slow turnover was accompanied by side reactions including ligand scrambling of HBpin to give BH(CHCN) and crystalline Bpin. When was reacted with CO alone, the formation of the gallium(III) carbonato complex [(MeTACD)Ga(κ-OCO)][BAr] () along with CO was observed.

Solvent-Dependent Oxidative Addition and Reductive Elimination of H Across a Gallium-Zinc Bond.

H adds reversibly across the metal-metal bond of [(BDI)Ga(H)-Zn(tmeda)(thf)][BAr ] (BDI=[HC{C(CH )N(2,6-iPr -C H )} ] , TMEDA=N,N,N',N'-tetramethylethylenediamine, BAr =[B(C H -3,5-(CF ) ) ] ). Due to the stabilising effect of solvent coordination, hydrogenation products [(BDI)GaH ] and [(tmeda)ZnH(thf)][BAr ] are favoured in THF solution, but THF-free mixtures of [(BDI)GaH ] and [(tmeda)ZnH(OEt )][BAr ] are predisposed towards entropically driven dehydrogenation to [(BDI)Ga(H)-Zn(tmeda)][BAr ] in fluorobenzene solution.

Reversible Oxidative Addition of Zinc Hydride at a Gallium(I)-Centre: Labile Mono- and Bis(hydridogallyl)zinc Complexes.

In the presence of TMEDA (N,N,N',N'-tetramethylethylenediamine), partially deaggregated zinc dihydride as hydrocarbon suspensions react with the gallium(I) compound [(BDI)Ga] (I, BDI={HC(C(CH )N(2,6-iPr -C H )) } ) by formal oxidative addition of a Zn-H bond to the gallium(I) centre. Dissociation of the labile TMEDA ligand in the resulting complex [(BDI)Ga(H)-(H)Zn(tmeda)] (1) facilitates insertion of a second equiv. of I into the remaining Zn-H to form a thermally sensitive trinuclear species [{(BDI)Ga(H)} Zn] (2).

A Brønsted Acidic Gallium Hydride: Facile Interconversion of NNNN-Macrocycle Supported [Ga ] and [Ga H].

Protonolysis of [Cp*M] (M=Ga, In, Tl) with [(Me TACD)H][BAr ] (Me TACD=N,N',N'',N'''-tetramethyl-1,4,7,10-tetraazacyclododecane; [BAr ] =[B{C H -3,5-(CH ) } ] ) provided monovalent salts [(Me TACD)M][BAr ], whereas [Cp*Al] yielded trivalent [(Me TACD)AlH][BAr ] . Protonation of [(Me TACD)Ga][BAr ] with [Et NH][BAr ] gave an unusually acidic (pK (CH CN)=24.5) gallium(III) hydride dication [(Me TACD)GaH][BAr ] .

Deaggregation of Zinc Dihydride by Lewis Acids Including Carbon Dioxide in the Presence of Nitrogen Donors.

Thermally sensitive polymeric zinc dihydride [ZnH] can conveniently be prepared by the reaction of ZnEt with [AlH(NEt)]. When reacted with CO (1 bar) in the presence of chelating N-donor ligands L = ,,','-tetramethylethylenediamine (TMEDA), ,,','-tetramethyl-1,3-propanediamine (TMPDA), -pentamethyldiethylenetriamine (PMDTA), and 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane (MeTACD), insertion into the Zn-H bond readily occurred. Depending on the denticity , formates [(L)Zn(OCHO)] were isolated and structurally characterized, either as a molecule (L = TMEDA, TMPDA, PMDTA) or a charge-separated ion pair [(L)Zn(OCHO)][OCHO] (L = MeTACD).

Reductive elimination of [AlH] from a cationic Ga-Al dihydride.

Oxidative addition of TMEDA-supported [AlH] to [{BDI}Ga] (BDI = {HC(C(CH)(2,6-iPr-CH))}) provides [{BDI}Ga(H)-Al(H)(tmeda)][B(CH-3,5-Me)] (TMEDA = ,,''-tetramethylethylenediamine) with a covalent metal-metal bond. The reaction is readily reversed by substituting TMEDA for an N-heterocyclic carbene or dissolving in THF.

Phosphinoborane interception at magnesium by borane-assisted phosphine-borane dehydrogenation.

Reactions of B(C6F5)3 with the β-diketiminato (BDI) alkaline-earth phosphidoborane complexes, 1a [(BDI)Ca(H3B·PPh2)] and 1b [(BDI)Mg(H3B·PPh2)]2 (BDI = [HC{C(CH3)N(2,6-iPr-C6H3)}2]-) result in the formation of phosphinodiboronate complexes 4a [(BDI)Ca(η6-toluene){H3B·PPh2·B(C6F5)3}] and 4b [(BDI)Mg{H3B·PPh2·B(C6F5)3}]. Calcium complex 4a is stable in aromatic solvents at room temperature and does not display well-defined onward reactivity at elevated temperatures. Magnesium complex 4b undergoes a room temperature transformation to provide the known hydridoborate derivative 3b [(BDI)Mg{HB(C6F5)3}] and an N,P,N'-ligated species, 5 [{HC(C(CH3)N(2,6-iPr-C6H3))2(H2BPPh2)}Mg{H3B·PPh2·B(C6F5)3}] that results from interception of the putative phosphinoborane, H2B = PPh2, by the BDI ligand backbone following B(C6F5)3-mediated hydride abstraction.

Nucleophilic Magnesium Silanide and Silaamidinate Derivatives.

Density functional theory (DFT) calculations demonstrate that the previously reported reaction of [(BDI)Mg--Bu] (BDI = HC{(Me)CN-Dipp}; Dipp = 2,6-diisopropylphenyl) with the silaborane MePhSi-Bpin provides the magnesium silanide derivative [(BDI)MgSiMePh], through the intermediacy of a short-lived silyl-pinacolato-organoborate species. The nucleophilic character of the resultant silanide anion is assayed through a series of reactions with RN═C═NR (R = i-Pr, Cy, -Bu) and -tolN═C═N--tol. When they are performed in a strict 1:1 stoichiometry, all four reactions result in silyl addition to the carbodiimide carbon center and formation of the corresponding β-diketiminato magnesium silaamidinate complexes.

Synthesis and reactivity of alkaline-earth stannanide complexes by hydride-mediated distannane metathesis and organostannane dehydrogenation.

The synthesis of heteroleptic complexes with calcium- and magnesium-tin bonds is described. The dimeric β-diketiminato calcium hydride complex, [(BDI)Ca(μ-H)]2 (ICa) reacts with Ph3Sn-SnPh3 to provide the previously reported μ2-H bridged calcium stannanide dimer, [(BDI)2Ca2(SnPh3)(μ-H)] (3). Computational assessment of this reaction supports a mechanism involving a hypervalent stannate intermediate formed by nucleophilic attack of hydride on the distannane.

Heavier Alkaline-Earth Catalyzed Dehydrocoupling of Silanes and Alcohols for the Synthesis of Metallo-Polysilylethers.

The dehydrocoupling of silanes and alcohols mediated by heavier alkaline-earth catalysts, [Ae{N(SiMe ) } ⋅(THF) ] (I-III) and [Ae{CH(SiMe ) } ⋅(THF) ], (IV-VI) (Ae=Ca, Sr, Ba) is described. Primary, secondary, and tertiary alcohols were coupled to phenylsilane or diphenylsilane, whereas tertiary silanes are less tolerant towards bulky substrates. Some control over reaction selectivity towards mono-, di-, or tri-substituted silylether products was achieved through alteration of reaction stoichiometry, conditions, and catalyst.

Calcium stannyl formation by organostannane dehydrogenation.

Reaction of the dimeric calcium hydride, [(BDI)CaH]2 (1), with Ph3SnH ensues with elimination of H2 to provide [(BDI)Ca-μ2-H-(SnPh3)Ca(BDI)] (3) and [(BDI)Ca(SnPh3)]2 (4) alongside dismutation to Ph4Sn, H2 and Sn(0). DFT analysis indicates that stannyl anion formation occurs through deprotonation of Ph3SnH and with retention of dinuclear species throughout the reactions.

Effect of Ba Content on the Activity of La Ba MnO Towards the Oxygen Reduction Reaction.

The electrocatalytic activity of La Ba MnO nanoparticles towards the oxygen reduction reaction (ORR) is investigated as a function of the A-site composition. Phase-pure oxide nanoparticles with a diameter in the range of 40 to 70 nm were prepared by using an ionic liquid route and deposited onto mesoporous carbon films. The structure and surface composition of the nanoparticles are probed by XRD, TEM, EDX, and XPS.