Azobenzene as an Effective Ligand in Europium Chemistry-A Synthetic and Theoretical Study.

The preparation and characterization of two novel europium-azobenzene complexes that demonstrate the effectiveness of this ligand for stabilizing reactive, redox-active metals are reported. With the family of rare earth metals receiving attention due to their potential as catalysts, critical components in electronic devices, and, more recently, in biomedical applications, a detailed understanding of factors contributing to their coordination chemistry is of great importance for customizing their stability and reactivity. This study introduces azobenzene as an effective nonprotic ligand system that provides novel insights into rare earth metal coordination preferences, including factors contributing to the coordinative saturation of the large, divalent europium centers.

A Modern Twist to a Classic Synthetic Route: PhBi-Based Redox Transmetalation Protolysis (RTP) for the Preparation of Barium Metalorganic Species.

This paper reports advances in redox transmetalation/protolysis (RTP) utilizing the readily available PhBi for the synthesis of a series of barium metal-organic species. On the basis of easily available starting materials, an easy one-pot procedure, and workup, we have obtained BaL compounds (L = bis(trimethylsilyl)amide, phenyl(trimethylsilyl)amide, pentamethylcyclopentadienide, fluorenide, 2,6-di-isopropylphenolate, and 3,5-diphenylpyrazolate) quantitatively by sonication of an excess of barium metal with triphenylbismuth and HL in perdeuterotetrahydrofuran, as established by NMR measurements. Rates of conversion are affected by both pK and bulk of HL.

M-F interactions and heterobimetallics: furthering the understanding of heterobimetallic stabilization.

Heterobimetallic complexes containing alkali, alkaline-earth, and divalent europium metals utilizing the perfluoro-tert-butoxide (PFTB) ligand following the general formula, [AM(PFTB)3(co-ligand)x] (A=Na, K; M=Mg, Sr, Ba, Eu; co-ligand=THF, toluene), have been isolated. These compounds sublime at low temperatures with low residual weight indicating their potential as metal-organic chemical-vapor deposition (MOCVD) precursors. The complexes have unique molecular architectures that are strongly influenced by M-F interactions, as was verified in the solid state by using X-ray crystallography.

s-Block organometallics: analysis of ion-association and noncovalent interactions on structure and function in benzyl-based compounds.

The organometallic chemistry of alkali and alkaline-earth metals has been marred by synthetic setbacks because of their high reactivity. Advances in their synthesis and a better understanding of the stabilization effects of ligands and coligands have resulted in the revolution of s-block organometallics. Among those, benzyl-based derivatives have played a key role in developing this chemistry because factors such as the ligand size, charge delocalization, and introduction of electronic parameters along with metal effects can be analyzed.

Synthesis and characterization of cyano-substituted carborane-based compounds. Molecular structure of [1-(4-C7H7)-12-(C5H3-3-(CN)-3,4-(CH3)2)-C2B10H10].

The reaction of cyanogen chloride with [1-(4-C(7)H(7))-12-(C(5)H(3)-3,4-(CH(3))(2))-C(2)B(10)H(10)] (7) was found to yield two new C(5)-substituted carborane cluster-based compounds, [1-(4-C(7)H(7))-12-(C(5)H(2)-3-(CN)-3,4-(CH(3))(2))-C(2)B(10)H(10)] (8) and [1-(4-C(7)H(7))-12-(C(5)H-2,4-(CN)(2)-3,4-(CH(3))(2))-C(2)B(10)H(10)] (9). This cyano-substitution pattern is in contrast to the known substitution for the analogous organic quinarene[5.6.

Highly volatile alkaline earth metal fluoroalkoxides.

The synthetic strategies, structural comparison, and thermal gravimetric analyses for a novel family of alkaline earth metal perfluoro-tert-butoxides (PFTB) are presented. The isolated complexes follow the general formula, [Ae(PFTB)(2)(d)(x)]; (1a, Ae = Mg, d = THF, x = 2; 1b, Ae = Ca, d = THF, x = 4; 1c, Ae = Sr, d = THF, x = 4; 1d, Ae = Ba, d = THF, x = 4; 2a, Ae = Mg, d = DME, x = 1; 2b, Ae = Ca, d = DME, x = 2; 2c, Ae = Sr, d = DME, x = 2; 2d, Ae = Ba, d = DME, x = 3; 3a, Ae = Mg, d = diglyme, x = 1; 3b, Ae = Ca, d = diglyme, x = 2; 3c, Ae = Sr, d = diglyme, x = 2; 3d, Ae = Ba, d = diglyme, x = 2; THF = tetrahydrofuran, DME = 1,2-dimethoxyethane) where the crystallographically characterized compounds display either a cis or trans conformations in octahedral or pseudo-octahedral environments. Alkane elimination (Mg), direct metalation via ammonia activation (Ca, Sr, Ba), and transamination (Ca, Sr, Ba) methods yielded the target compounds in moderate to good yields.

Synthesis and stabilization-advances in organoalkaline earth metal chemistry.

The last decade has seen an impressive growth in alkaline earth metal chemistry, with applications ranging from synthetic organic and polymer chemistry to materials science. As a consequence, alkaline earth metal chemistry has made a leap from obscurity into the spotlight of modern organometallic chemistry. Much of this rapid development was made possible by the establishment of novel synthetic procedures that allowed facile access to the target compounds, as many conventional synthetic routes posed and continue to pose significant limitations.

Heavy alkali metal amides: role of secondary interactions in metal stabilization.

The coordination chemistry of the bis(diphenylmethylsilyl)amine ligand, HN(SiMePh(2))(2), with the heavy alkali metals potassium and rubidium has been investigated to study its effect on the structure of the resulting compounds. The compounds exhibit extensive intra- and intermolecular M-pi interactions, creating 1-D coordination polymers, [K{N(SiMePh(2))(2)}](infinity) (1) and [Rb{N(SiMePh(2))(2)}](infinity) (3). This motif is maintained in the presence of tetrahydrofuran (THF), as seen in [K{N(SiMePh(2))(2)}thf](infinity) (2).

When VSEPR fails: experimental and theoretical investigations of the behavior of alkaline-earth-metal acetylides.

The synthesis, structural, and spectral characterization as well as a theoretical study of a family of alkaline-earth-metal acetylides provides insights into synthetic access and the structural and bonding characteristics of this group of highly reactive compounds. Based on our earlier communication that reported unusual geometry for a family of triphenylsilyl-substituted alkaline-earth-metal acetylides, we herein present our studies on an expanded family of target derivatives, providing experimental and theoretical data to offer new insights into the intensively debated theme of structural chemistry in heavy alkaline-earth-metal chemistry.

Metal based synthetic routes to heavy alkaline earth aryloxo complexes involving ligands of moderate steric bulk.

Treatment of an alkaline earth metal (Ca, Sr, Ba) with 2,4,6-trimethylphenol (HOmes) at elevated temperatures in the presence of mercury under solvent-free conditions, followed by extraction of the reaction mixture with 1,2-dimethoxyethane (dme), afforded dinuclear alkaline earth aryloxo complexes [Ae2(Omes)4(dme)4] (Ae = Ca 1, Sr 3, Ba 6). Extraction of the Ca metal and HOmes reaction mixture with thf afforded [Ca3(Omes)6(thf)] 2. In contrast, redox transmetallation ligand exchange reactions between an alkaline earth metal, diphenylmercury and HOmes in dme yielded solely 1 for Ca metal, a mixture of 3 and the methoxide bridged cage [Sr5(Omes)5(OMe)5(dme)4] x 2dme 4 for Sr metal, and solely [Ba5(Omes)5(OMe)5(dme)4] x dme 7 for Ba metal.

Charge-separated and molecular heterobimetallic rare earth-rare earth and alkaline earth-rare earth aryloxo complexes featuring intramolecular metal-pi-arene interactions.

Treatment of a rare earth metal (Ln) and a potential divalent rare earth metal (Ln') or an alkaline earth metal (Ae) with 2,6-diphenylphenol (HOdpp) at elevated temperatures (200-250 degrees C) afforded heterobimetallic aryloxo complexes, which were structurally characterised. A charge-separated species [(Ln'/Ae)(2)(Odpp)(3)][Ln(Odpp)(4)] was obtained for a range of metals, demonstrating the similarities between the chemistry of the divalent rare earth metals and the alkaline earth metals. The [(Ln'/Ae)(2)(Odpp)(3)](+) cation in the heterobimetallic structures is unusual in that it consists solely of bridging aryloxide ligands.

BiPh3--a convenient synthon for heavy alkaline-earth metal amides.

Environmentally friendly, commercially available BiPh3 reacts with heavy alkaline-earth metals (Ae) and bulky trimethylsilylamines to give the corresponding amides [Ae{N(SiMe3)(R)}2(thf)n] (R=SiMe3, 2,4,6-Me3C6H2, 2,6-iPr2C6H3) in good yields, providing proof of concept for a general synthetic method.

Developments in heterobimetallic s-block systems: synthesis and structural survey of molecular M/Ae (M=Li, Na, K, Cs; Ae=Ca, Sr) aryloxo complexes.

A series of novel heterobimetallic group 1/strontium and group 1/calcium aryloxo complexes having the composition [MAe(Odpp)3] [Ae=Sr and M=Na (1), K (2, 3), Cs (4); Ae=Ca and M=Na (5), K (6), Cs (7)] or [M2Ae(Odpp)4] [M=Li and Ae=Sr (9), Ca (10)] have been prepared using 2,6-diphenylphenol (HOdpp) as the ligand. Through the use of solid-state direct metalation, these compounds were obtained either directly from the reaction vessel or after workup in toluene. The Lewis base adduct [KCa(Odpp)3(thf)] (8) was obtained by treatment of [KCa(Odpp)3] (6) with tetrahydrofuran (thf).

A unique heterobimetallic benzyl calciate--an organometallic mixed-metal species involving a heavy alkaline-earth metal.

A co-complexation reaction utilizing homometallic benzylcalcium and benzyllithium affords a rare example of a heterobimetallic benzyl calciate.

Porphyrin complexes containing coordinated BOB groups: synthesis, chemical reactivity and the structure of [BOB(tpClpp)]2+.

The reactions of boron halides with free base porphyrins under conditions where partial hydrolysis of the boron halides can occur give diboron porphyrin complexes containing BOB moieties in which each boron is bonded to two porphyrin nitrogen atoms. BF(3).OEt(2) with H(2)(por) gives B(2)OF(2)(por) (por = tpp, ttp, tpClpp, oep) which has an asymmetric structure in which one boron lies in the porphyrin plane (B(ip)) while the other lies above it (B(oop)).

Lithium aryloxo magnesiates: an examination of ligand size and donor effects.

The combination of equimolar amounts of LiOAr and Mg(OAr)2 (OAr=aryloxide) in polar media afforded several lithium aryloxomagnesiates. Factors influencing the structural chemistry of the compounds, such as the degree of ligand bulk, type of Lewis base donors, and crystallization solvent, are examined. Structural characterization reveals a discrete, solvent-separated species, [Li(thf)4][Mg(BHT)3].

Alkali metal diphenylmethanides: synthetic, computational and structural studies.

In search of new synthetic precursors for the preparation of alkaline earth organometallic compounds, we investigated the application of a powerful desilylation reaction to cleanly afford a variety of contact and charge-separated alkali metal derivatives without the difficulties commonly encountered in other methods. The resulting diphenylmethanides display both contact molecules and separated ion pairs. Analysis of the structural data demonstrates that simple electrostatic models are insufficient for predicting and explaining the solid-state structures of these complexes.

Temperature-dependent coordination of phosphine to five-coordinate alkenylruthenium complexes.

The red, five-coordinate complexes Ru(CO)Cl(PPh(3))2(CH=CHPh) and [Ru(CO)Cl(PPh(3))2]2(mu-CH=CHC(6)H(4)CH=CH) undergo reversible coordination of PPh(3) at low temperature to produce the pale yellow, six-coordinate complexes Ru(CO)Cl(PPh(3))3(CH=CHPh) and [Ru(CO)Cl(PPh(3))3]2(mu-CH=CHC(6)H(4)CH=CH). X-ray crystal structures of the latter complex and of the hydride complex RuH(CO)Cl(PPh(3))3 were obtained. 1H and 31P NMR spectra between 20 and -70 degrees C exhibit large changes in both equilibrium constants and dynamic effects.

New structural features in heavy alkaline earth-metal chemistry--molecular heterobimetallic group 1, Ba complexes.

The preparation of heterobimetallic complexes consisting of alkali and heavy alkaline earth metals remains a challenge due to limited available synthetic strategies. Here we present a new class of group 1, Ba compounds of the type [M(n){Ba(Odpp)(2+n)}] (M=Na(n=1) (1), K(n=1) (2), Cs(n=1) (3), Li(n=2) (4); HOdpp=2,6-diphenylphenol) and the Lewis base adducts [Li(2)(thf)(2){Ba(Odpp)(4)}]PhMe (5) and [K{Ba(Odpp)(3)(diglyme)}] (6) (diglyme=[bis(2-methoxy)ethyl ether]) as the first representatives of heterobimetallic group 1, Ba species of low nuclearity. The compounds display a significant degree of metal-arene interaction, believed to be a key factor in stabilizing these highly reactive species.

Role of donor and secondary interactions in the structures and thermal properties of alkaline-earth and rare-earth metal pyrazolates.

The addition of neutral coligands to reduce the aggregation and improve the volatility of potential heavy alkaline-earth metal chemical vapor deposition (CVD) precursors has typically resulted in liberation of the coligand upon heating. A new series of dinuclear alkaline-earth and rare-earth metal pyrazolates, bis[bis(3,5-di-tert-butylpyrazolato)(tetrahydrofuran)calcium] (1), bis[bis(3,5-di-tert-butylpyrazolato)(tetrahydrofuran)strontium] (2), and bis[bis(3,5-di-tert-butylpyrazolato)bis(tetrahydrofuran)barium] (3), have been obtained from our previous donor-free oligonuclear complexes [{M(3,5-tBu2pz)2}n] (5, M = Ca, n = 3; 6, M = Sr, n = 4; 7, M = Ba, n = 6) by treatment with tetrahydrofuran (THF). Compounds 1-3, as well as the europium analogue bis[bis(3,5-di-tert-butylpyrazolato)(tetrahydrofuran)europium(II)] (4), can also be prepared by direct reaction of the metals and pyrazole in THF and anhydrous liquid ammonia.

Synthetic, structural, and theoretical investigations of alkali metal germanium hydrides--contact molecules and separated ions.

The preparation of a series of crown ether ligated alkali metal (M=K, Rb, Cs) germyl derivatives M(crown ether)nGeH3 through the hydrolysis of the respective tris(trimethylsilyl)germanides is reported. Depending on the alkali metal and the crown ether diameter, the hydrides display either contact molecules or separated ions in the solid state, providing a unique structural insight into the geometry of the obscure GeH3- ion. Germyl derivatives displaying M--Ge bonds in the solid state are of the general formula [M([18]crown-6)(thf)GeH3] with M=K (1) and M=Rb (4).

From monomers to solids: controlled hydrolysis to form novel, heteroleptic hydroxide-containing complexes.

Four novel alkaline earth metal tetranuclear aryloxide/pyrazolate hydroxides of the general formula M4(ligand)6(OH)2(donor)n have been prepared by either adding stoichiometric quantities of water to preformed alkaline earth metal aryloxides or in a direct metalation regime combining metal, ligand (alcohol, pyrazole), and donor with stoichiometric amounts of water. The compounds are considered as potential intermediates in the sol-gel process. A nonhydrolyzable magnesium aryloxide has also been obtained using the same reaction scheme.

Synthesis and structures of monomeric magnesium, calcium, strontium, and barium amides involving the N,N-(2,4,6-trimethylphenyl)(trimethylsilyl)amido ligand.

An extended family of aryl-substituted alkaline earth metal silylamides M{N(2,4,6-Me3C6H2)(SiMe3)}donor(n) was prepared using alkane elimination (Mg), salt elimination (Ca, Sr, Ba), and direct metalation (Sr, Ba). Three different donors, THF, TMEDA (TMEDA = N,N,N',N'-tetramethylethylenediamine), and PMDTA (PMDTA = N,N,N',N'',N''-pentamethyldiethylenetriamine) were employed to study their influence on the coordination chemistry of the target compounds, producing monomeric species with the composition M{N(2,4,6-Me3C6H2)(SiMe3)}2(THF)2 (M = Mg, Ca, Sr, Ba), M{N(2,4,6-Me3C6H2)(SiMe3)}2TMEDA (M = Ca, Ba), and M{N(2,4,6-Me3C6H2)(SiMe3)}2PMDTA (M = Sr, Ba). For the heavier metal analogues, varying degrees of agostic interactions are completing the coordination sphere of the metals.

Syntheses and structures of the first heavy-alkali-metal tris(trimethylsilyl)germanides.

The first heavy-alkali-metal tris(trimethylsilyl)germanides were obtained in high yield and purity by a simple one-pot reaction involving the treatment of tetrakis(trimethylsilyl)germane, Ge(SiMe3)4, with various alkali metal tert-butoxides. The addition of different sizes of crown ethers or the bidentate TMEDA (TMEDA=N,N,N',N'-tetramethylethylenediamine) provided either contact or separated species in the solid state, whereas in aromatic solvents the germanides dissociate into separated ions, as shown by 29Si NMR spectroscopic studies. Here we report on two series of germanides, one displaying M-Ge bonds in the solid state with the general formula [M(donor)n Ge(SiMe3)3] (M=K, donor=[18]crown-6, n=1, 1; Rb, donor=[18]crown-6, n=1, 4; and M=K, donor=TMEDA, n=2, 6).