Amido compounds of gallium and indium

Aluminium and Gallium Silylimides as Nitride Sources

Terminal aluminium and gallium imides of the type K[(NON)M(NR)], bearing heteroatom substituents at R, have been synthesised via reactions of anionic aluminium(I) and gallium(I) reagents with silyl and boryl azides (NON=4,5-bis(2,6-diisopropyl-anilido)-2,7-di-tert-butyl-9,9-dimethyl-xanthene). These systems vary significantly in their lability in solution: the N(Sii Pr3 ) and N(Boryl) complexes are very labile, on account of the high basicity at nitrogen. Phenylsilylimido derivatives provide greater stabilization through the π-acceptor capabilities of the SiR3 group. K[(NON)AlN(Sit BuPh2 )] offers a workable compromise between stability and solubility, and has been completely characterized by spectroscopic, analytical and crystallographic methods. The silylimide species examined feature minimal π-bonding between the imide ligand and aluminium/gallium, with the HOMO and HOMO-1 orbitals effectively comprising orthogonal lone pairs centred at N. Reactivity-wise, both aluminium and gallium silylimides can act as viable sources of nitride, [N]3- , with systems derived from either metal reacting with CO to afford cyanide complexes. By contrast, only the gallium system K[(NON)Ga{N(SiPh3 )}] is capable of effecting a similar transformation with N2 O to yield azide, N3 - , via formal oxide/nitride metathesis. The aluminium systems instead generate RN3 via transfer of the imide fragment [RN]2- .

Ligand-stabilized heteronuclear diatomics of group 13 and 15

A theoretical investigation of ligand-stabilized MX diatomics (M = group 13, X = group 15 element) with N-heterocyclic carbene (NHC) ligands has been carried out to assess bonding and electronic structure. Binding of two ligands in the form L-MX-L is generally preferred over binding of a single ligand as L-MX or MX-L. Binding of carbene donor ligands is predicted to be thermodynamically favorable for all the systems, and is very favorable for the lighter group 15 systems (nitrogen and phosphorus). Detailed analysis of the bonding in these complexes has been carried out with energy decomposition analysis (EDA). In all cases, the carbene to boron and carbene to nitrogen bonding is described as an electron-sharing double bond with both σ and π bonding interactions. For the heavier elements, bonding to C (except for PC interactions) is best described as a donor-acceptor σ single bond.

A Monomeric Aluminum Imide (Iminoalane) with Al-N Triple-Bonding: Bonding Analysis and Dispersion Energy Stabilization

The reaction of :AlAriPr8 (AriPr8 = C6H-2,6-(C6H2-2,4,6-iPr3)2-3,5-iPr2) with ArMe6N3 (ArMe6 = C6H3-2,6-(C6H2-2,4,6-Me3)2) in hexanes at ambient temperature gave the aluminum imide AriPr8AlNArMe6 (1). Its crystal structure displayed short Al-N distances of 1.625(4) and 1.628(3) Å with linear (C-Al-N-C = 180°) or almost linear (C-Al-N = 172.4(2)°; Al-N-C = 172.5(3)°) geometries. DFT calculations confirm linear geometry with an Al-N distance of 1.635 Å. According to energy decomposition analysis, the Al-N bond has three orbital components totaling -1350 kJ mol-1 and instantaneous interaction energy of -551 kJ mol-1 with respect to :AlAriPr8 and ArMe6N̈:. Dispersion accounts for -89 kJ mol-1, which is similar in strength to one Al-N π-interaction. The electronic spectrum has an intense transition at 290 nm which tails into the visible region. In the IR spectrum, the Al-N stretching band is calculated to appear at ca. 1100 cm-1. In contrast, reaction of :AlAriPr8 with 1-AdN3 or Me3SiN3 gave transient imides that immediately reacted with a second equivalent of the azide to give AriPr8Al[(NAd)2N2] (2) or AriPr8Al(N3){N(SiMe3)2} (3).

Nano structures of group 13-15 mixed heptamer clusters: a computational study

The structural and thermodynamic characteristics of lowest-energy structures of group 13-15 mixed heptamers in two distinct series [(HM)(k)(HM')(l)(NH)(7)] (M, M' = B, Al, Ga and k + l = 7) and [(HGa)(7)(YH)(m)(Y'H)(n)] (Y,Y' = N, P, As and m + n = 7) have been systematically investigated using the density functional approach. Our main goal is to get knowledge of the preferential bonding patterns of the first three rows of group 13-15 elements for the construction of mixed heptameric clusters. Structural parameters, thermodynamic properties of oligomerization reaction, band gaps, and dipole moments of the 18 lowest-energy structures of the studied heptamers in each series are compared to their corresponding binary parents, that is, [(HM)(7)(NH)(7)] and [(HGa)(7)(YH)(7)]. The stability of different isomer structures is discussed to reveal the competitiveness of group 13 and 15 bonding. Mixed heptamers are predicted to be thermodynamically more stable compared to a mixture of monomers. However, the favorability for the generation of mixed heptamers strongly depends on the nature of inserted metal and nonmetal pairs of group 13-15. Moreover, it is found that among all studied heptamers the smaller band gaps correspond to arsenic containing species which are close to the semiconducting regime, around 4.62-4.98 eV.

Synthetic and structural studies of donor-functionalized alkoxy derivatives of gallium

The synthesis of a range of alkyl/chloro-gallium alkoxide and amido/alkoxide compounds was achieved via a series of protonolysis and alcoholysis steps. The initial reaction involved the synthesis of [Me(Cl)Ga{N(SiMe(3))(2)}](2) (1) via methyl group transfer from the reaction of GaCl(3) with two equivalents of LiN(SiMe(3))(2). Reaction of 1 with varying amounts of ROH resulted in the formation of [Me(Cl)Ga(OR)](2) (2, R = CH(2)CH(2)OMe; 3, CH(CH(3))CH(2)NMe(2)), [Me(Cl)Ga{N(SiMe(3))(2)}(μ(2)-OR)Ga(Cl)Me] (4, R = CH(2)CH(2)NMe(2)), or [MeGa(OR)(2)] (5, R = CH(CH(3))CH(2)NMe(2)). Compound 4 represents an intermediate in the formation of dimeric complexes, of the type [Me(Cl)Ga(OR)](2), when formed from compound [Me(Cl)Ga{N(SiMe(3))(2)}](2). A methylgallium amido/alkoxide complex [MeGa{N(SiMe(3))(2)}(OCH(2)CH(2)OMe)](2) (6) was isolated when 2 was further reacted with LiN(SiMe(3))(2). In addition, reaction of 2 with HO(t)Bu resulted in a simple alcohol/alkoxide exchange and formation of [Me(Cl)Ga(O(t)Bu)](2) (7). In contrast to the formation of 1, the in situ reaction of GaCl(3) with one equivalent of LiN(SiMe(3))(2) yielded [Cl(2)Ga{N(SiMe(3))(2)}](2) in low yield, where no methyl group transfer has occurred. Reaction of alcohol with [Cl(2)Ga{N(SiMe(3))(2)}](2) was then found to yield [Cl(2)Ga(OR)](2) (8, R = CH(2)CH(2)NMe(2)), and further reaction of 8 with LiN(SiMe(3))(2) yielded the gallium amido alkoxide complex, [ClGa{N(SiMe(3))(2)}(OR)](2) (9, R = CH(2)CH(2)NMe(2)), similar to 6. The structures of compounds 4, 5, 7, and 8 have been determined by single-crystal X-ray diffraction.

Dense passivating poly(ethylene glycol) films on indium tin oxide substrates

We describe the formation and characterization of surface-passivating poly(ethylene glycol) (PEG) films on indium tin oxide (ITO) glass substrates. PEG chains with a molecular weight of 2000 and 5000 D were covalently attached to the substrates in a systematic approach using different coupling schemes. The coupling strategies included the direct grafting with PEG-silane, PEG-methacrylate, and PEG-bis(amine), as well as the two-step functionalization with aldehyde-bearing silane films and subsequent coupling with PEG-bis(amine). Elemental analysis by X-ray photoelectron spectroscopy (XPS) confirmed the successful surface modification, and XPS and ellipsometry provided values for film thicknesses. XPS and ellipsometry thickness values were almost identical for PEG-silane films but differed by up to 400% for the other PEG layers, suggesting a homogeneous layer for PEG-silane but an inhomogeneous distribution for other PEG coatings on the molecularly rough ITO substrates. Atomic force microscopy (AFM) and water contact angle goniometry confirmed the different degrees of surface homogeneity of the polymer films, with PEG-silane reducing the AFM rms surface roughness by 50% and the water contact angle hysteresis by 75% compared to uncoated ITO. The ability of the PEG layers to passivate the substrate against the nonspecific adsorption of biopolymers was tested using fluorescence-labeled immunoglobulin G and DNA oligonucleotides in combination with fluorescence microscopy. The results indicate a positive relationship between film density and homogeneity on one hand and the ability to passivate against biopolymer adhesion on the other hand. The most homogeneous layers prepared with PEG-silane reduced the nonspecific adsorption of fluorescence-labeled DNA by a factor of 300 compared to uncoated ITO. In addition, the study finds that the ratio of film thicknesses derived by ellipsometry and XPS is a useful parameter to quantify the structural integrity of PEG layers on molecularly rough ITO surfaces. The findings may be applied to characterize PEG or other polymeric films on similarly coarse substrates.

Quasi-Isomeric Gallium Amides and Imides GaNR2 and RGaNR (R = Organic Group): Reactions of the Digallene, Ar‘GaGaAr‘ (Ar‘ = C6H3-2,6-(C6H3-2,6-Pri2)2) with Unsaturated Nitrogen Compounds

Reactions of the "digallene" Ar'GaGaAr'(1) (Ar' = C(6)H(3)-2,6-(C(6)H(3)-2,6-Pr(i)(2))(2)), which dissociates to green :GaAr' monomers in solution, with unsaturated N-N-bonded molecules are described. Treatment of solutions of :GaAr' with the bulky azide N(3)Ar(#) (Ar(#) = C(6)H(3)-2,6-(C(6)H(2)-2,6-Me(2)-4-Bu(t))(2)), afforded the red imide Ar'GaNAr(#) (2). Addition of the azobenzenes, ArylNNAryl (Aryl = C(6)H(4)-4-Me (p-tolyl), mesityl, and C(6)H(3)-2,6-Et(2)) yielded the 1,2-Ga(2)N(2) ring compound Ar'GaN(p-tolyl)N(p-tolyl)GaA' (3) or the products MesN=NC(6)H(2)-2,4-Me(2)-6-Ga(Me)Ar' (4) and 2,6-Et(2)C(6)H(3)N=NC(6)H(3)-2-Et-6-Ga(Et)Ar' (5). Reaction of GaAr' with N(2)CPh(2) yielded the 1,3-Ga(2)N(2) ring compound Ar'Ga(mu:eta(1)-N(2)CPh(2))(2)GaAr' (6), which is quasi-isomeric to 3. Calculations on simple model isomers showed that the Ga(I) amide GaNR(2) (R = Me) is much more stable than the isomeric Ga(III) imide RGaNR. This led to the synthesis of the first stable monomeric Ga(I) amide, GaN(SiMe(3))Ar' ' (8) (Ar' ' = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-Me(3))(2) from the reaction of LiN(SiMe(3))Ar' ' (7) and "GaI". Compound 8 is also the first one-coordinate gallium species to be characterized in the solid state. The reaction of 8 with N(3)Ar' ' afforded the amido-imide derivative Ar' 'NGaN(SiMe(3))Ar' ' (9), a gallium nitrogen analogue of an allyl anion. All compounds were spectroscopically and structurally characterized. In addition, DFT calculations were performed on model compounds of the amide, imide, and cyclic 1,2- and 1,3-species to better understand their bonding. The pairs of compounds 2 and 8 as well as 3 and 6 are rare examples of quasi-isomeric heavier main group element compounds.

Hydrido and chloro gallium and aluminium complexes with the tridentate bis(2-dimethylaminoethyl)amide ligand

Five-coordinate gallium and aluminium dihydrides, H2Ga[N(CH2CH2NMe2)2] () and H2Al[N(CH2CH2NMe2)2] (), were synthesized and found to be volatile and thermally stable. and reacted with H3Ga(NMe3) and H3Al(NMe3), respectively, to form H2Ga[N(CH2CH2NMe2)2]GaH3 () and H2Al[N(CH2CH2NMe2)2]AlH3 (), in which the amido nitrogen bridged between the MH2 and MH3 groups (M=Ga or Al). A mixed metal complex, H2Al[N(CH2CH2NMe2)2]GaH3 () was obtained from the reaction of with H3Al(NMe3) or with H3Ga(NMe3), and a crystal consisting of a mixture of and was structurally characterized. The five-coordinate chloro derivative, Cl2Ga[N(CH2CH2NMe2)2] (), was synthesized and characterized.

Synthesis and structural characterization of the first metal organic thallium antimonide

The first metal organic thallium antimonide, the heterocycle [Me2TlSb(SiMe3)2]3, was synthesized by reaction of [Me2AlSb(SiMe3)2]3 with the Lewis acid-base adduct dmap-TlMe3 (dmap = 4-dimethylaminopyridine). The analogous TlBi heterocycle [Me2TlBi(SiMe3)2]3 couldn't be isolated due to its limited thermal stability in solution.

Decomposition of Monochlorogallane, [H2GaCl]n, and Adducts with Amine and Phosphine Bases: Formation of Cationic Gallane Derivatives

Thermal decomposition of monochlorogallane, [H2GaCl]n, at ambient temperatures results in the formation of subvalent gallium species. To Ga[HGaCl3], previously reported, has now been added a second mixed-valence solid, Ga4[HGaCl3]2[Ga2Cl6] (1), the crystal structure of which at 150 K shows a number of unusual features. Adducts of monochlorogallane, most readily prepared from the hydrochloride of the base and LiGaH4 in appropriate proportions, include not only the 1:1 molecular complex Me3P.GaH2Cl (2), but also 2:1 amine complexes which prove to be cationic gallane derivatives, [H2Ga(NH2R)2]+Cl-, where R = tBu (3a) or sBu (3b). All three of these complexes have been characterized crystallographically at 150 K.

Reactions of a Gallium(II)−Diazabutadiene Dimer, [{{[(H)C(But)N]2}GaI}2], with [ME(SiMe3)2] (M = Li or Na; E = N, P, or As): Structural, EPR, and ENDOR Characterization of Paramagnetic Gallium(III) Pnictide Complexes

The reactions of the paramagnetic gallium(II) complex [{(Bu(t)-DAB)GaI}2] (Bu(t)-DAB = {(Bu(t))NC(H)}2) with the alkali metal pnictides [ME(SiMe3)2] (M = Li or Na; E = N, P, or As) have been carried out under a range of stoichiometries. The 1:2 reactions have led to a series of paramagnetic gallium(III)-pnictide complexes, [(Bu(t)-DAB)Ga{E(SiMe3)2}I] (E = N, P, or As), while two of the 1:4 reactions afforded [(Bu(t)-DAB)Ga{E(SiMe3)2}2] (E = P or As). In contrast, treatment of [{(Bu(t)-DAB)GaI}2] with 4 equiv of [NaN(SiMe3)2] resulted in a novel gallium heterocycle coupling reaction and the formation of the diradical species [(Bu(t)-DAB)Ga{N(SiMe3)2}{[CC(H)N2(Bu(t))2]Ga[N(SiMe3)2]CH3}]. The mechanism of this unusual reaction has been explored, and evidence suggests it involves an intramolecular transmethylation reaction. The X-ray crystal structures of all prepared complexes are reported, and all have been characterized by EPR and ENDOR spectroscopies. The observed spin Hamiltonian parameters provide a detailed picture of the distribution of the unpaired spin density over the molecular frameworks of the complexes.

Oligomeric Rods of Alkyl- and Hydridogallium Imides

Reaction of [RGa(NMe(2))(2)](2), where R = Me, Et, Bu, and Hx, with ammonia at 150 degrees C in an autoclave produced insoluble white powders formulated as oligomers of [RGaNH](n). The analogous reaction between NH(3) and MeGa[N(SiMe(3))(2)](2) at low temperature (<25 degrees C) formed an isolable intermediate, [MeGa(mu-NH(2))N(SiMe(3))(2)](2), that was characterized using single-crystal X-ray diffraction. Infrared spectroscopy and X-ray diffraction of the oligomers were consistent with a rodlike structure comprised of six-membered, [RGaNH](3) rings stacked perpendicular to the long axis of the rod. The method of synthesis, formula, and diffraction results suggested a structural similarity between the alkyl, [RGaNH](n)(), and the previously reported hydride, [HGaNH](n). The structural and electronic properties of rods having the general formula H(3)[(HXYH)(3)](n)H(3) (XY = GaN, GeC; n = 1-9) were investigated using density functional theory. Atomic electronegativity differences between the group 13/15 and 14/14 systems were found to play important roles in the geometrical structures of the two rods and also caused significant differences in the electronic structures. Energetically, it was found to be increasingly favorable to add additional cyclotrigallazane rings to the GaN rods, while for the GeC rods, there was a roughly constant energy cost associated with each additional ring. The electric dipole moments of the GaN rods increased substantially with length; in the GeC rods, charge separation occurred to a much smaller extent and had a polarization opposite to that found in GaN. In addition, increased dipole moments correlated with smaller electronic excitation energies, as predicted by time-dependent density functional theory. All of the powders exhibited luminescence in the visible spectrum at room temperature. Structure observed in the photoluminescence spectra of [HGaNH](n) and [MeGaNH](n) was interpreted as arising from rods of different length.

Mono- and digallane complexes of a tridentate amido-diamine ligand

Bis(2-dimethylaminoethyl)amido gallane, H2GaN(CH2CH2NMe2)2, that melts at 27 degrees C and remains stable upon heating at 55 degrees C for two days, was synthesized either from the reaction of the quinuclidine adduct of monochlorogallane with the lithium salt of the corresponding amine, or from the reaction of trimethylamine gallane and the amine; the latter affords an unusual co-product with both GaH2 and GaH3 bonded to the same amido nitrogen.

Synthesis and structural characterisation of primary amine adducts of gallane, RH2N·GaH3, and of their decomposition products, [RHNGaH2]n(R = Me, n= 3; R =tBu, n= 2)

Primary amine-gallane adducts, RH(2)N.GaH(3)[R = Me (1) and (t)Bu (2)], have been isolated for the first time from the reaction of [RNH(3)]Cl with LiGaH(4) in Et(2)O solution at ca. 273 K and characterised by their vibrational and (1)H NMR spectra. The structures of single crystals, grown at low temperatures and determined by X-ray diffraction, reveal pseudo-polymeric arrays of RH(2)N.GaH(3) molecules with Ga-N distances of 2.0424(18) and 2.058(5)A for 1 and 2, respectively. The adducts decompose at or near ambient temperatures with the elimination of H(2) and formation of the corresponding monoalkylamido derivative [RHNGaH(2)](n). The crystal structures of these at 150 K consist of either [MeHNGaH(2)](3) molecules with a "skew-boat" conformation for the cyclic Ga(3)N(3) skeleton (3) or [(t)BuHNGaH(2)](2) molecules with a four-membered Ga(2)N(2) core (4), with Ga-N distances averaging 1.986(8) and 1.991(3)A for 3 and 4, respectively. The crystalline solids 1, 3 and 4 feature intermolecular N-H...H-Ga interactions with H...H distances estimated to fall in the range 2.1-2.3 A. The significance of these is discussed.

Pi Bonding and Negative Hyperconjugation in Mono-, Di-, and Triaminoborane, -alane, -gallane, and -indane

A systematic quantum chemical investigation of mono-, di-, and triaminoborane, -alane, -gallane, and -indane is carried out to determine quantitatively the effects of pi bonding and negative hyperconjugation on structures, energetics, and rotational barriers in these systems. Pi bonding plays a significant role in the aminoborane compounds, but becomes rapidly less significant in the aminoalanes, -gallanes, and -indanes. For each main-group metal X investigated, X-N rotational barriers are found to be essentially equal depending only on the number of remaining in-plane amino groups. The contribution of negative hyperconjugation to reducing rotational barriers, as assessed from natural bond orbital (NBO) delocalization energies, is independent of the pyramidalization of the out-of-plane amino group, and is also dependent only on the number of rotated groups. Optimized tris[bis(trimethylsilyl)amino]-substituted structures of boron, aluminum, gallium, and indium are found to compare quite well with available experimental structural data, and exhibit X-N torsion angles that are independent of the central metal atom.

Synthesis and structures of gallium amido imido phenyl clusters (PhGa)(4)(NH(i)Bu)(4)(N(i)Bu)(2) and (PhGa)(7)(NHMe)(4)(NMe)(5)

The phenylgallium-containing clusters constructed with bridging imido and amido ligands, (PhGa)(4)(NH(i)Bu)(4)(N(i)Bu)(2) (1) (51% yield) and (PhGa)(7)(NHMe)(4)(NMe)(5) (2) (31% yield), were synthesized from the room-temperature reactions of bis(dimethylamido)phenylgallium, [PhGa(NMe(2))(2)](2), with isobutylamine and methylamine, respectively. The reaction of [PhGa(NMe(2))(2)](2) in refluxing isobutylamine (85 degrees C) afforded (Ph(2)GaNH(i)Bu)(2) as one of the products, while the reaction of [PhGa(NMe(2))(2)](2) with methylamine at 150 degrees C afforded compound 2 in only 9% yield. Compound 1 possessed an admantane-like Ga(4)N(6) core, whereas compound 2 had a novel Ga(7)N(9) core constructed with both chair- and boat-shaped Ga(3)N(3) rings. The presence of several isomers of compounds 1 and 2 in solution is discussed along the structural similarities with other known gallium-nitrogen clusters and with gallium nitride.