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Andreas Stasch

Publications and source records attributed to Andreas Stasch.

18 recordsLinked to original sources
PubMed2007

Homo- and heteroleptic complexes of four-membered group 13 metal(I) N-heterocyclic carbene analogues with group 10 metal(0) fragments.

A series of complexes between recently developed four-membered group 13 metal(I) heterocycles and group 10 metal(0) fragments have been prepared and structurally characterized. One prepared complex, [Pt{Ga[N(Ar)]2CNCy2}3] (Ar = C6H3Pri2-2,6; Cy = cyclohexyl), possesses the shortest Pt-Ga bonds yet reported, the covalent components of which are suggested by theoretical studies to have significant pi character.

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PubMed2007

Base-stabilized amidodiarsenes: synthesis, structure, and theoretical studies.

The guanidinato- or amidinato-bridged diarsenes [As2{mu-(ArN)2CR}2] (Ar = C6H3Pri2-2,6; R = N(C6H11)2, NPri2, or But) have been prepared by reduction of the corresponding As(III) precursors, [Cl2As{kappa2-N,N'-(ArN)2CR}]. Theoretical studies suggest that the As-As bonds of the dimers have significant double-bond character, the sigma and pi components of which are derived mainly from As p orbital overlaps.

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PubMed2006

Synthesis and characterisation of complexes of Group 13 metal amidinate heterocycles with the CpFe(CO)2 fragment.

The first examples of complexes between a 4-membered amidinato-Group 13 metal(III) heterocycle and a transition metal fragment are formed in salt elimination reactions between Na[CpFe(CO)2] and [MX2(amid)], M=Al, Ga or In; X=Cl or Br; amid-=[(RN)2CBut]-; R=Pri or cyclohexyl (Cy). The formed complexes, [CpFe(CO)2M(X)(amid)] (4 examples) have been crystallographically characterised and subject to halide abstraction reactions. In one case, the cationic complex, [CpFe(CO)2Ga(OEt2){(CyN)2CBut}][BArf4], was isolated and crystallographically characterised. A hydrolysis product of this complex, [{CpFe(CO)2Ga[(CyN)2CBut]}2(micro-OH)][BArf4], was also isolated in low yield from this reaction and structurally characterised.

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PubMed2006

Synthetic, structural and theoretical studies of amidinate and guanidinate stabilised germanium(I) dimers.

The neutral germanium(i) dimers, [{Ge(Piso)}(2)] and [{Ge(Giso)}(2)], Piso = [(ArN)(2)CBu(t)](-), Giso = [(ArN)(2)CNPr(i)(2)](-), Ar = C(6)H(3)Pr(i)(2)-2,6, which are stabilised by bulky amidinate and guanidinate ligands respectively, have been prepared by reduction of the corresponding germanium(ii) chlorides, [Ge(Piso)Cl] and [Ge(Giso)Cl]; theoretical studies suggest that the Ge-Ge bonds of [{Ge(Piso)}(2)] and [{Ge(Giso)}(2)] are associated with their HOMOs, whilst their LUMOs have substantial Ge-Ge pi-bonding character.

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PubMed2006

Complexes of an anionic gallium(I) N-heterocyclic carbene analogue with group 14 element(II) fragments: synthetic, structural and theoretical studies.

The reactions of the anionic gallium(I) N-heterocyclic carbene (NHC) analogue, [K(tmeda)][:Ga{[N(Ar)C(H)]2}], Ar = C6H3Pri2-2,6, with the heavier group 14 alkene analogues, R2E=ER2, E = Ge or Sn, R = -CH(SiMe3)2, have been carried out. In 2:1 stoichiometries, these lead to the ionic [K(tmeda)][R2EGa{[N(Ar)C(H)]2}] complexes which exhibit long E-Ga bonds. The nature of these bonds has been probed by DFT calculations, and the complexes have been compared to neutral NHC adducts of group 14 dialkyls. The 4:1 reaction of [K(tmeda)][:Ga{[N(Ar)C(H)]2}] with R2Sn=SnR2 leads to the digallyl stannate complex, [K(tmeda)][RSn[Ga{[N(Ar)C(H)]2}]2], presumably via elimination of KR. In contrast, the reaction of the gallium heterocycle with PbR2 affords the digallane4, [Ga{[N(Ar)C(H)]2}]2, via an oxidative coupling reaction. For sake of comparison, the reactions of [K(tmeda)][:Ga{[N(Ar)C(H)]2}] with Ar'2E=EAr'2, E = Ge, Sn or Pb, Ar' = C6H2Pri3-2,4,6, were carried out and led to either no reaction (E = Ge), the formation of [K(tmeda)][Ar'2SnGa{[N(Ar)C(H)]2}] (E = Sn), or the gallium(III) heterocycle, [Ar'Ga{[N(Ar)C(H)]2}] (E = Pb). Salt elimination reactions between [K(tmeda)][:Ga{[N(Ar)C(H)]2}] and the guanidinato group 14 complexes [(Giso)ECl], E = Ge or Sn, Giso = [Pri2NC{N(Ar)}2]-, gave the neutral [(Giso)EGa{[N(Ar)C(H)]2}] complexes. All complexes have been characterized by NMR spectroscopy and X-ray crystallographic studies.

Anions↗
PubMed2006

The first complexes and cyclodimerisations of methylphosphaalkyne (P[triple bond]CMe).

The first complexes and cyclodimerisations of methylphosphaalkyne, P[triple bond]CMe, are reported to arise from its reactions with a range of platinum(0) complexes and [W(CO)5(THF)]. A number of differences between the chemistry of this phosphaalkyne and that of its bulkier analogues have been highlighted and explained on steric grounds.

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PubMed2006

Four-membered group 13 metal(I) N-heterocyclic carbene analogues: synthesis, characterization, and theoretical studies.

The synthesis, spectroscopic and structural characterization of the monomeric, four-membered group 13 metal(I) heterocycles ([:M{eta2-N,N'-(Ar)NC(NCy2)N(Ar)}], M = Ga or In, Ar = C6H3Pri2-2,6) and an isomeric thallium complex are reported. Theoretical studies on these complexes, which are analogues of four-membered N-heterocyclic carbenes, suggest they should act as good sigma-donor ligands.

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PubMed2006

Syntheses, characterization, and X-ray crystal structures of beta-diketiminate group 13 hydrides, chlorides, and fluorides.

A series of organometallic compounds of group 13 metals supported by the sterically encumbered beta-diketiminate ligand containing hydrides, fluorides, chlorides, and bromide have been synthesized and structurally characterized. The synthetic strategy applied utilizes halide metathesis and reduction of metal chlorides to the corresponding hydrides. Thus, the reaction of LLi.OEt2 with MeMCl2 affords LM(Me)Cl (M = Al (1), Ga (2), In (3)) and LGaBr2 (4) with GaBr3. Reduction of LGa(Me)Cl with LiH.BEt3 leads to the formation of LGa(Me)H (10). Synthesis of LGaH(2) (12) has been accomplished by reacting LGaI2 (8) with LiH.BEt3. LAl(Me)Cl (1) and LAlH2 (6) have been converted to LAl(Me)F (5) and LAlF2 (7), respectively. The former was obtained in a reaction of LAl(Me)Cl with Me3SnF while the latter was isolated in a reaction of LAlH2 with BF3.OEt2. Similarly reaction of LGaI2 (8) with Me3SnF affords LGaF2 (9). Compounds reported herein have been characterized by elemental analyses, IR, NMR, EI-MS, and single-crystal X-ray diffraction techniques.

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PubMed2005

Aluminum hydride cations stabilized by weakly coordinating carbaalanates.

The reactions of t-BuCCLi with a mixture of AlH(3).NMe(3) and ClAlH(2).NMe(3) in boiling toluene with the addition of [t-BuCH(2)(Bzl)NMe(2)]Cl, or a bulky beta-diketimine instead, and [n-Bu(4)N]Cl led to the carbaalanates [H(2)Al(NMe(3))(2)](2)[(AlH)(8)(CCH(2)t-Bu)(6)], 3, and [n-Bu(4)N](2)[(AlH)(8)(CCH(2)t-Bu)(6)], 4, respectively. The reaction of Me(3)N.Al(CCt-Bu)(3) 5 and AlH(3).NMe(3) in boiling toluene yielded [H(n-Bu)Al(NMe(3))(2)][(AlH)(7)(AlNMe(3))(CCH(2)t-Bu)(6)], 6, in trace amounts. The single-crystal X-ray structures of 3 and 6 are reported. The compounds 3, 4, and 6 consist of well-separated ion pairs introducing carbaalanates as weakly coordinating anions and stabilizing aluminum hydride cations.

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PubMed2005

Synthesis and characterization of thermally robust amidinato group 13 hydride complexes.

The reactivity of two sterically bulky amidines, ArNC(R)N(H)Ar (Ar=2,6-diisopropylphenyl; R=H (HFiso); tBu, (HPiso)) towards LiMH4, M=Al or Ga, [AlH3(NMe3)], and [GaH3(quin)] (quin=quinuclidine) has been examined. This has given rise to a variety of very thermally stable aluminum and gallium hydride complexes. The structural motif adopted by the prepared complexes has been found to be dependent upon both the amidinate ligand and the metal involved. The 1:1 reaction of HFiso with LiAlH4 yielded dimeric [{AlH3(mu-Fiso)Li(OEt2)}2]. Amidine HFiso reacts in a 1:1 ratio with [AlH3(NMe3)] to give the unusual hydride-bridging dimeric complex, [{AlH2(Fiso)}2], in which the Fiso- ligand is nonchelating. The equivalent reaction with the bulkier amidine, HPiso, yielded a related hydride-bridging complex, [{AlH2(Piso)}2], in which the Piso- ligand is chelating. In contrast, the treatment of [GaH3(quin)] with one equivalent of HFiso afforded the four-coordinate complex [GaH2(quin)(Fiso)], in which the Fiso- ligand acts as a localized monodentate amido-imine ligand. The 2:1 reactions of HFiso with [AlH3(NMe3)] or [GaH3(quin)] gave the monomeric complexes [MH(Fiso)2], which are thermally robust and which exhibit chelating amidinate ligands. In contrast, HPiso did not give 2:1 complexes in its reactions with either of the Group 13 trihydride precursors. For sake of comparison, the reactions of [AlH3(NMe3)] and [GaH3(quin)] with the bulky carbodiimide ArN=C=NAr and the thiourea Ar(H)NC(=S)N(H)Ar were examined. These last reactions afforded the five-coordinate thioureido complexes, [MH{N(Ar)C[N(H)(Ar)]S}2], M=Al or Ga.

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PubMed2005

Synthesis, characterisation and theoretical studies of amidinato-indium(I) and thallium(I) complexes: isomers of neutral group 13 metal(I) carbene analogues.

The synthesis and characterisation of the monomeric amidinato-indium(I) and thallium(I) complexes, [M(Piso)].PisoH, M = In or Tl, Piso- = [ArNC(Bu(t))NAr]-, Ar = C6H3Pr(i)2-2,6, are reported. These complexes, in which the metal centre is chelated by the amidinate ligand in an N,eta3-arene-fashion, can be considered as isomers of four-membered group 13 metal(I) carbene analogues. Theoretical studies have compared the relative energies of both isomeric forms of a model complex, [In{PhNC(H)NPh}].

Amidines↗
PubMed2004

Synthesis of carbaalane halogen derivatives.

The carbaalane halogen derivatives [(AlX)(6)(AlNMe(3))(2)(CCH(2)CH(2)SiMe(3))(6)] (X = F (9), Cl (7), Br (10), I (11)) were prepared in toluene from [(AlH)(6)(AlNMe(3))(2)(CCH(2)CH(2)SiMe(3))(6)] (6) and BF(3).OEt(2), BX(3) (X = Br, I), Me(3)SnF, and Me(3)SiX (X = Cl, Br, I), respectively. A partially halogenated product [(AlH)(2)(AlX)(4)(AlNMe(3))(2)(CCH(2)CH(2)SiMe(3))(6)] (12) (X = Cl (approximately 40%), Br (approximately 60%)) was obtained from 5 and impure BBr(3). [(AlH)(6)(AlNMe(3))(2)(CCH(2)Ph)(6)] (5) was converted to [(AlX)(6)(AlNMe(3))(2)(CCH(2)Ph)(6)] (X = F (13), Cl (14), Br (15), I (16)) using BF(3).OEt(2) and Me(3)SiX (X = Cl, Br, I), respectively. The X-ray single-crystal structures of 11.C(6)H(6), 12.3C(7)H(8), 13.6C(7)H(8), and 15.4C(7)H(8) were determined. Compounds 7 and 9-11 are soluble in benzene/toluene and could be well characterized by NMR spectroscopy and MS (EI) spectrometry. The results demonstrate the facile substitution of the hydridic hydrogen atoms in 5 and 6 by the halides with different reagents.

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PubMed2003

Neutral and ionic aluminum, gallium, and indium compounds carrying two or three terminal ethynyl groups.

The syntheses of the ionic compounds [Li(+).2 dioxane (2,6-iPr(2)C(6)H(3)N(SiMe(3))Al(C triplebond CSiMe(3))(3))(-)].0.75 dioxane (1), [(Li(+))(2).(dioxane)(7)](0.5) [2,6-iPr(2)C(6)H(3)N(SiMe(3))Ga(C triplebond CSiMe(3))(3)(-)].1.5 dioxane (2), and [(Li(+))(2).(dioxane)(7)](0.5) [2,6-iPr(2)C(6)H(3)N(SiMe(3))In(C triplebond CSiMe(3))(3)(-)].1.5 dioxane (3) by the reaction of the corresponding organo metal chloride with LiC triplebond CSiMe(3) are reported. The neutral ethynyl compounds Br-Al(C triplebond CtBu)(2).2 THF (4), Cl-Ga(C triplebond CtBu)(2).THF (5), Cl-In(C triplebond CtBu)(2).2 THF (6), Al(C triplebond CtBu)(3).C[N(Me)CMe](2) (7), Ga(C triplebond CtBu)(3).dioxane (8), and In(C triplebond CtBu)(3).NEt(3) (9) have been obtained in good yields from the reaction of AlBr(3), GaCl(3), and InCl(3) with LiC triplebond CtBu in the presence of a Lewis base. Compound 7 is the first heterocyclic carbene substituted ethynyl derivative. Aluminum and gallium compounds with three terminal ethynyl groups Al(C triplebond CPh)(3).NMe(3) (10) and Ga(C triplebond CPh)(3).NMe(3) (11) have been prepared by the reaction of AlH(3).NMe(3) or GaH(3).NMe(3) with three equivalents of phenylethyne. All the above-mentioned compounds have been structurally studied. In compound 1 the lithium ion is coordinated to the three terminal ethynyl groups, whereas in compounds 2 and 3 the lithium is coordinated to the solvent (dioxane). Compound 8 crystallizes as a coordination polymer with dioxane molecules bridging the individual gallium units.

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PubMed2002

Syntheses, structures, and surface aromaticity of the new carbaalane [(AlH)(6)(AlNMe(3))(2)(CCH(2)R)(6)] (R = Ph, CH(2)SiMe(3)) and a stepwise functionalization of the inner and outer sphere of the cluster.

The reaction of the acetylene RC triple bond CH (R = Ph, CH(2)SiMe(3)) with an excess of AlH(3).NMe(3) in boiling toluene leads to the carbaalane [(AlH)(6)(AlNMe(3))(2)(CCH(2)R)(6)] (R = Ph 1, CH(2)SiMe(3) 2) in good yield. Treatment of 2 with BCl(3) under varying conditions gives the chlorinated products [(AlCl)(6)(AlNMe(3))(2)(CCH(2)CH(2)SiMe(3))(6)] 3 and [(AlCl)(6)(AlNMe(3))(2)(CCH(2)CH(2)SiMe(2)Cl)(6)] 4, respectively. The latter clearly demonstrates that the cluster can be stepwise functionalized within the inner and outer sphere. The X-ray single-crystal structures of 1, 2, and 4 have been determined. All compounds have in common that the central core consists of a cluster having eight aluminum and six carbon atoms. The bonding properties in this cluster are described as a new manifestation of three-dimensional surface aromaticity. Each Al(4)C fragment of the cube is formed by four bonds with three electron pairs, thus leading to a strong delocalization of the electrons. A phenomenological modeling using a three-dimensional Hückel scheme with fitted parameters to reproduce the energies from ab initio calculations revealed that the orbital scheme localized at one Al(4)C fragment possesses an orbital sextet with a large HOMO-LUMO gap. This is in line with the criteria of aromaticity. The idea of aromaticity was sustained also by qualitative valence bond reasons enumerating the different resonance structures by means of graph theoretical methods.

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