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The reaction of the six-vertex amido-substituted silicon cluster Si 6 {N(SiMe 3 )Ph} 6 1 with two equiv. of KC 8 results in the abstraction of K{N(SiMe 3 )Ph} and leads to the contact ion pair 2 including an anionic silicon cluster with two unsubstituted pyramidal vertices. Facile functionalization of 2 was achieved with MeI, SiCl 4 and SiBr 4 and results in neutral two-fold functionalized silicon clusters.

The synthesis of mixed silicon and germanium clusters Si x Ge 6- x {N(SiMe 3 )Dipp} 4 1-3 ( x = 3.7, 3.1, 2.1) with amido-substituents and two unsubstituted germanium atoms was achieved in co-reductions using the tribromosilane {N(SiMe 3 )Dipp}SiBr 3 and the tribromogermane {N(SiMe 3 )Dipp}GeBr 3 in three different ratios. The ratio of Si and Ge used for the synthesis of 1-3 approximately corresponds to that in the final products. All compounds were characterized by single crystal X-ray diffraction and EI mass spectrometry. In addition, 1 and 2 were characterized by solid-state 29 Si{ 1 H} CP/MAS NMR spectroscopy and multinuclear NMR spectroscopy in solution.

The reductive debromination of {N(SiMe 3 )Ph}SiBr 3 1 with Rieke magnesium yields the six-vertex amido-substituted silicon cluster 2 with zwitterionic character that represents an unprecedented isomer of hexasilabenzene. The topology of Si1 and Si2 in 2 has bonding features of a highly twisted disilene and resembles that of a buckled dimer of Si(100)2 × 1 reconstructed surfaces. Cluster 2 forms the adducts 3 and 4 with NHC Me4 and DMAP, respectively. The NHC adduct 4 additionally coordinates to BH 3 which affords the saturated cluster BH 3 NHC Me4 Si 6 {N(SiMe 3 )Ph} 6 (5). Furthermore, 2 undergoes addition with MeI and iodine to form the halogenated silicon clusters 6 and 7, respectively.

Bis-NHC precursors composed of an azolium and a 2-halogenoazole group connected by different linkers have been site-selectively metallated to give heterobimetallic complexes from a single-frame bis-NHC ligand. The azolium group reacts with a base and oxidized metal centers to give NHC complexes with no participation of the halogenoazole, while the halogenoazole reacts in an oxidative addition with low-valent transition metals to give azolato complexes with no participation of the azolium group.

The NHC-coordinated trisilacyclopropylidene (A) is shown to behave as the basic component of an FLP used in combination with the Lewis acid B(C6F4H)3 (i.e. B(2,3,5,6-C6F4H)3). This FLP cleaves dihydrogen highly selectively at room temperature giving rise to the ionic compound [(NHC)SiH(Mes2SiSiMes2)][HB(C6F4H)3] 1 in 90% isolated yield. Further reaction of the FLP with Ph2NH and acetone yielded compounds [(NHC)SiH(Mes2SiSiMes2)][Ph2NB(C6F4H)3] 2 and [(NHC)SiH(Mes2SiSiMes2)][MeC(CH2)OB(C6F4H)3] 3 in 75% and 80% yield, respectively. Reaction of the FLP with N2O results in the oxidation of the silylene center affording [((NHC)SiOB(C6F4H)3)(Mes2SiSiMes2)] 4 in 53% yield. These products are spectroscopically characterized and an X-ray structure of 4 is reported.

The unsaturated metalloid germanium cluster Ge 6 {N(SiMe 3 )Dipp} 4 2 with two ligand-free germanium atoms and only four amine substituents was obtained starting from the base-coordinated germylene {N(SiMe 3 )Dipp}GeCl·DMAP 1 in 50% yield (DMAP = 4-(dimethylamino)-pyridine). This cluster reacts as a masked digermyne in cycloadditions with ethylene, diphenylacetylene and 2,3-dimethyl-1,3-butadiene in toluene at 100 °C to yield 3-5.

Different N3-substituted derivatives of the new ligand 3H-imidazo[4,5-f]quinolin-5-ol were synthesized. The three pKa values of its nucleoside derivative 1 were determined as 2.72 ± 0.09, 5.2 ± 0.2 and 9.7 ± 0.2. Sophisticated computational methods were used to explain these experimental acidity constants. The artificial nucleoside analogue 1 containing the new ligand was introduced into various DNA duplexes. Upon the addition of Cu(ii) ions to the DNA, highly stabilizing 1-Cu(ii)-1 base pairs were formed, with an increase in the DNA melting temperature upon Cu(ii) insertion of up to 38 °C. The ligand represents the largest artificial nucleobase used for Cu(ii)-mediated base pairing. It was also applied in Cu(ii)-mediated base pairing with the smallest Cu(ii)-binding nucleoside 2, involving the ligand 4-carboxyimidazole. The thermal duplex stabilization upon 2-Cu(ii)-1 base pair formation is smaller than that of 1-Cu(ii)-1 and comes close to that of the previously reported 2-Cu(ii)-2. Important design principles for Cu(ii)-mediated base pairs can be derived by comparing the homoleptic complexes of the largest and the smallest Cu(ii)-binding nucleosides with the heteroleptic complexes comprising both nucleosides.

Hydroalumination of R-P(H)-C[triple bond, length as m-dash]C-tBu with bulky H-Al[CH(SiMe3)2]2 afforded the new P-H functionalized Al/P-based frustrated Lewis pair R-P(H)-C[[double bond, length as m-dash]C(H)-tBu]-AlR2 [R = CH(SiMe3)2; FLP 7]. A weak adduct of 7 with benzonitrile (8) was detected by NMR spectroscopy, but could not be isolated. tert-Butyl isocyanide afforded a similar, but isolable adduct (9), in which the isocyanide C atom was coordinated to aluminium. The unique reactivity of 7 became evident from its reactions with the heteroatom substituted nitriles PhO-C[triple bond, length as m-dash]N, PhCH2S-C[triple bond, length as m-dash]N and H8C4N-C[triple bond, length as m-dash]N. Hydrophosphination of the C[triple bond, length as m-dash]N triple bonds afforded imines at room temperature which were coordinated to the FLP by Al-N and P-C bonds to yield AlCPCN heterocycles (10 to 12). These processes depend on substrate activation by the FLP. Diphenylcyclopropenone and its sulphur derivative reacted with 7 by addition of the P-H bond to a C-C bond of the strained C3 ring and ring opening to afford the fragment (Z)-Ph-C(H)[double bond, length as m-dash]C(Ph)-C-X-Al (X = O, S). The C-O or C-S groups were coordinated to the FLP to yield AlCPCX heterocycles (13 and 14). The thiocarbonyl derived compound 14 contains an internally stabilized phosphenium cation with a localized P[double bond, length as m-dash]C bond, a trigonal planar coordinated P atom and a short P[double bond, length as m-dash]C distance (168.9 pm). Insight into formation mechanisms, the structural and energetic properties of FLP 7 and compounds 13 and 14 was gained by quantum chemical DFT calculations.

Treatment of alkynyl-arylchlorogermanes ArylnGe(Cl)(C[triple bond, length as m-dash]C-(t)Bu)3-n (n = 1, 2) with HM(t)Bu2 (M = Al, Ga) yielded mixed Al or Ga alkenyl-alkynylchlorogermanes via hydrometallation reactions. Intramolecular interactions between the Lewis-basic Cl atoms and the Lewis-acidic Al or Ga atoms afforded MCGeCl heterocycles. The endocyclic M-Cl distances were significantly lengthened compared to the starting compounds and indicated Ge-Cl bond activation. Dual hydrometallation succeeded only with HGa(t)Bu2. One Ga atom of the product was involved in a Ga-Cl bond, while the second one had an interaction to a C-H bond of a phenyl group. In two cases treatment of chlorogermanes with two equivalents of HAl(t)Bu2 resulted in hydroalumination of one alkynyl group and formation of unprecedented Ge-H functionalized germanes, Aryl-Ge(H)(C[triple bond, length as m-dash]C-(t)Bu)[C(Al(t)Bu2)[double bond, length as m-dash]C(H)-(t)Bu] (Aryl = mesityl, triisopropylphenyl). The Al atoms of these compounds interacted with the α-C atoms of the alkynyl groups. Ph(Cl)Ge(C[triple bond, length as m-dash]C-(t)Bu)[C(Al(t)Bu2}[double bond, length as m-dash]C(H)-(t)Bu] reacted in an unusual Cl/(t)Bu exchange to yield the tert-butylgermane Ph((t)Bu)Ge(C[triple bond, length as m-dash]C-(t)Bu)[C{Al((t)Bu)(Cl)}[double bond, length as m-dash]C(H)-(t)Bu]. Quantum chemical calculations suggested the formation of a germyl cation as a transient intermediate.

Treatment of the new alkynyl-chlorophosphine, Mes-P(Cl)-C ≡ C-CMe3, with LiNR2 afforded various unprecedented aminophosphines, Mes-P(NR2)-C ≡ C-CMe3, which showed a fascinating diversity in their reactivity towards H-Al(t)Bu2. NMe2 and NEt2 derivatives yielded the hydroalumination products Mes-P(NR2)-C(Al(t)Bu2) = C(H)-CMe3 which have an Al-N and an activated P-N bond. Elimination of aluminium amide yielded the transient 3H-phosphaallene, Mes-P = C = C(H)-CMe3, which finally afforded a five-membered AlP2C2 heterocycle with an Al-P bond and two exocyclic C = C bonds. This heterocycle is directly formed with the sterically shielded (i)Pr2N- and dimethylpiperidinophosphines. A unique R2AlH adduct resulted from the NPh2 and N(SiMe3)2 substituted phosphines. It may be viewed as an Al/P-based frustrated Lewis pair (FLP) which coordinates an R2AlH moiety. The heterocyclic AlP2C2 compound is formed in the final step of this reaction. Hydroalumination with Et2AlH yielded [Mes-P(H)-C(AlEt2) = C(H)-CMe3]2 which features an Al2P2C2 heterocycle and two Al-P bonds. This dimer resembles the class of hidden or masked FLPs which show a reactivity similar to uncoordinated FLPs. Its unique structural motif is a P-H bond which may result in a new type of FLP chemistry.

Hydroalumination of dialkynylphosphines, aryl-P(C≡C-(t)Bu)2 (aryl = 2,4,6-Me3C6H2 (1), Ph (2)), with the bulky dialkylaluminium hydride H-Al[CH(SiMe3)2]2 afforded mixed alkenyl-alkynyl phosphines (3 and 4) with aluminium atoms in geminal positions to phosphorus. These compounds contain coordinatively unsaturated aluminium and phosphorus atoms and may be applicable as alkynyl functionalised frustrated Lewis pairs. Their unique constitution with dialkylaluminium and alkynyl groups in close proximity favours unusual secondary reactions with the elimination of an aluminium alkynide and formation of reactive 3H-phosphaallenes, aryl-P=C=C(H)-(t)Bu (5 and 6), which depending on the steric shielding by the aryl groups, oligomerize at room temperature over days or weeks. The mesityl derivative 5 is formed in a very selective reaction, but the relatively unstable phenyl compound 6 was only detected in a mixture of several components. One of these (7) was isolated as orange-red crystals and identified as a heterocyclic zwitterionic compound with a central AlC2P2 ring. One of its phosphorus atoms is bonded to a terminal alkynyl group.

The DNA lesion 1,N(6)-ethenoadenine (εA) has been investigated with respect to its metal-binding properties. A synthetic DNA duplex comprising an εA : εA mispair readily forms doubly silver(I)-mediated base pairs εA-Ag(I)2-εA, representing the first example for a dinuclear metal-mediated homo base pair of a purine derivative. It also constitutes the first example for a Hoogsteen-type metal-mediated homo base pair within a B-DNA duplex.

Hydrometallation of a pyrrolidyl functionalised trialkynylsilane, H8C4N-Si(C≡C-CMe3)3, with equimolar quantities of H-M(CMe3)2 (M = Al, Ga) resulted in the formation of mixed alkenyl-dialkynylsilanes (3a, 3b) which have a Lewis-acidic Al or Ga atom in the geminal position to the Si atom and form four-membered M-N-Si-C heterocycles by a strong interaction of the amine N atoms with the Lewis-acidic metal atoms. This interaction results in a concomitant lengthening and weakening of the Si-N bonds. Dual hydrometallation afforded alkynyl-dialkenylsilanes (4a, 4b) with two Lewis-acidic metal atoms. Al-N and Ga-N interactions to one of the Lewis-acidic centres led again to the formation of M-N-Si-C heterocycles. The second Al atom of 4a interacted with C-H bonds of the vinylic tert-butyl group, while the Ga atom of 4b was coordinated to the α-C atom of the remaining alkynyl substituent. Dual hydrometallation of the corresponding pyrrolyl-trialkynylsilane resulted in compounds with different structures (5a, 5b) due to the delocalisation of the lone pair of electrons at nitrogen in the aromatic ring. One metal atom is coordinated to the α-C atom of the alkynyl group, and the other has close contact to a C-H bond of the pyrrole ring. The synthesis of 4b gave an unprecedented bicyclic by-product (6) which has a Ga-H-Ga 3c-2e bond. It was formally formed by hydrogallation of the trialkyne with the sesquihydride [H2Ga-CMe3]2[H-Ga(CMe3)2]2 and was also obtained by the selective reaction with this starting material.

The artificial nucleobases 6-(2'-thienyl)-purine (6TP) and 6-(2'-furyl)-purine (6FP) have been investigated in terms of their applicability in metal-mediated base pairs. In principle, these nucleobases should be capable of providing an S,N- and O,N-coordination environment, respectively. Two metal complexes have been synthesized and structurally characterized, using the N9-methylated derivatives of 6TP and 6FP as model nucleobases. The silver(I) complex [Ag(9-Me6TP)(CH3CN)(NO3)]n is of polymeric nature. The thienyl substituent is not involved in metal binding. In contrast, the dinuclear copper(II) complex [Cu(9-Me6FP)Cl2(OH2)]2 clearly shows that the furyl substituent can participate in the coordination of the metal ion. Oligonucleotide double helices comprising a 6TP:6TP or a 6FP:6FP mispair are slightly stabilized in the presence of silver(I). However, a distinction between the formation of a metal-mediated base pair and an unspecific binding event cannot be finally made. Based on these studies, it is proposed that the formation of Hoogsteen-type metal-mediated base pairs should be the more promising alternative compared with the originally anticipated Watson-Crick-type metal-mediated base pairs.

Hydroalumination of aryldialkynylphosphines RP(C≡C-(t)Bu)(2) (R = Ph, Mes) with equimolar quantities of diethylaluminum hydride afforded mixed alkenyl-alkynyl cyclic dimers in which the dative aluminum-phosphorus bonds are geminal to the exocyclic alkenyl groups. Addition of triethylaluminum to isolated 1 (R = Ph) or to the in situ generated species (R = Mes) caused diethylaluminum ethynide elimination to yield the arylethylphosphorus dimers 2 and 3. These possess a chair-like Al(2)C(2)P(2) heterocycle with intermolecular Al-P interactions. The boat conformation (4) was obtained by the reaction of (t)Bu-P(C≡C-(t)Bu)(2) with di(tert-butyl)aluminum hydride. Despite being dimeric, 2 behaves as a frustrated Lewis pair and activates small molecules. The reaction with carbon dioxide gave cis/trans isomeric AlPC(2)O heterocycles that differ only by the configuration of the exocyclic alkenyl unit. Four isomers resulted from the reaction with phenyl isocyanate. This is caused by cis/trans isomerization of the initial C=O adduct and subsequent rearrangement to the AlPC(2)N heterocycle, being the C=N adduct.

Treatment of trimethylsilylethynylbenzene derivatives with HGaCl(2) afforded products, [C(6)H(6-x){C(H)=C(SiMe(3))GaCl(2)}(x)], in which by a very fast cis/trans-rearrangement the Ga and H atoms occupied opposite sides of the resulting C=C double bonds. The stability of the cis-forms considerably increased upon application of 1,3-dibromo- and pentafluorophenylalkyne derivatives. Two pairs of cis/trans-isomers could be characterized by crystal structure determinations and allow the direct comparison of structural parameters. For the first time an equilibrium was detected between cis- and trans-forms in solution. Treatment of 1,4-di(tert-butylalkynyl)benzene with HAlR(2) (R = CMe(3), CH(2)CMe(3)) afforded cyclophane-type molecules by the release of AlR(3). Only the neopentyl derivative could be isolated and characterized by crystal structure determination. In contrast, the dibromo compound, 1,4-Br(2)-2,5-(Me(3)CC[triple bond]C)(2)C(6)H(2), yielded the simple addition product, C(6)H(2)Br(2){C(AlR(2))=C(H)CMe(3)}(2) (R = CMe(3)). Condensation was hindered in this case by intramolecular Al-Br interactions. Surprisingly, the simple addition product was also isolated from the reaction of 1,4-(Me(3)CC[triple bond]C)(2)C(6)H(4) with the relatively small hydride HAlEt(2). Solid-state NMR spectra of the product revealed strong intermolecular Al-C interactions involving the negatively charged terminal vinylic carbon atoms, to give one-dimensional coordination polymers.

The aminoalcohols MeNH(CH(2))(2)OH (), (t)BuNH(CH(2))(2)OH (), MeNH(CH(2))(3)OH (), (t)BuNH(CH(2))(3)OH () and MeNHCH(2)CMe(2)CH(2)OAlMe(2) () have been reacted with AlMe(3) to give the five corresponding aminoalkoxides of the general formula RNH-X-AlMe(2)- (X = organic spacer between N and O). (t)BuNHCH(2)CMe(2)CH(2)OH () reacts with AlMe(3) to give [(t)BuNHCH(2)CMe(2)CH(2)OAlMe(2)].AlMe(3) (.AlMe(3)). Analogous reactions of the aminoalcohols , , and with Al(t)Bu(3), GaMe(3) and Ga(t)Bu(3) afforded the corresponding aminoalkoxides of the general formula RNH-X-MR'(2)- (MR'(2) = Al(t)Bu(2)), - (MR'(2) = GaMe(2)) and - (MR'(2) = Ga(t)Bu(2)). The compounds were characterised by NMR spectroscopy, elemental analyses and mass spectrometry. Crystal structures were determined for , , .AlMe(3), , , and . Compounds and dimerise via Al(2)O(2) rings, while the amino-functions form intramolecular Al-N bonds. Compounds and form monomers with intramolecular Ga-N bonds. Compounds and are dimers via Ga(2)O(2) rings but in contrast to and without formation of intramolecular Ga-N bonds. .AlMe(3) also forms a monomeric compound with intramolecular AlN bond and a further AlMe(3) unit bonded to the O atom. The dynamic behaviour of and was investigated by variable-temperature NMR spectroscopy. Some compounds have different aggregation in solid and fluid phases.

The rare-earth metal hydroxylamide compound Y[N(SiHMe2)2]2[ONBn2][THF] (1) was prepared by the silylamide elimination pathway from the reaction of N,N-dibenzylhydroxylamine, Bn2NOH (Bn = CH2C6H5), with Y[N(SiHMe2)2]3[THF]2 and was characterised by multinuclear NMR spectroscopy and elemental analysis. The compounds [Cp2Y(ONBn2)]2 (2a) [Cp2Sm(ONBn2)]2 (2b) were obtained by the reactions of MCp3 (M = Y, Sm) with Bn2NOH. The trinuclear compound Cp5Y3[ON(Me)CH2CH2(Me)NO]2 (3) was obtained by the reaction of YCp3 and the bishydroxylamine HON(Me)CH2CH2(Me)NOH. 2a, 2b and 3 were characterised by NMR spectroscopy, single-crystal X-ray diffraction and elemental analysis. In all these complexes side-on-coordination of the hydroxylamide units was observed. The compounds are of dynamic nature in solution.

Reaction of stoichiometric amounts of the benzannulated bisstannylene with [Pt(nbe)(3)] in the presence of PPh(3) and OPPh(3) gave complex with an Sn(2)PtP(2) core and an O[double bond, length as m-dash]PPh(3) molecule coordinated to one of the stannylene donors according to an X-ray diffraction study. Complex was also obtained by substitution of two PPh(3) ligands in [Pt(PPh(3))(4)] by the bisstannylene in the presence of OPPh(3). The reaction of 2 equivalents of the bisstannylenes and exhibiting different spacers between the stannylene donors with one equivalent of [Pt(nbe)(3)] gave the intensely coloured homoleptic [Pt(bisstannylene)(2)] complexes and . Both complexes were characterized by X-ray diffraction studies which demonstrated the presence of four identical tin atoms for complex and two different types of tin atoms for complex . Temperature dependent (119)Sn NMR spectra for complex with the 1,3-(CH(2))(2)C(6)H(4) bridging unit between the stannylene donors indicate the presence of an equilibrium between complexes with three- and tetra-coordinated platinum atoms in solution.

Reactions of bishydroxylamines of the type HON(R)CH2CH2N(R)OH (R=Me, tBu) with trimethyl- and triisopropylgallium gave bicyclic metalla cages of the formula R'2GaO(R)NCH2CH2N(R)OGaR'2 [R'=Me, R=Me (), tBu (); R'=iPr, R=Me (), tBu ()] with six-membered Ga2O2N2-rings. While the complexes show the same core constitution in the solid state, NMR spectra reveal the steric influence of the isopropyl substituent of the compounds / on its behaviour in solution. The reaction of the sterically more demanding substituted tri-tert-butylgallium with HON(Me)CH2CH2N(Me)OH yielded a heterodimeric complex O'-[HON(Me)CH2CH2NH(Me)O(tBu2Ga)]-cyclo-(tBu2Ga)-O,N'-[ON(Me)CH2CH2N(Me)O] () with two gallium atoms of different surrounding and two different bishydroxylamine ligands, one doubly deprotonated and one protonated, but at one end in its tautomeric aminoxide form. Further condensation of was observed to give a tricyclic compound cyclo-[(tBuGa)ON(Me)CH2CH2N(Me)O]2 () with a central Ga2O2N2 ring resulting from two Ga-N donor-acceptor bonds.

The first homoleptic anions of hydroxylaminato ate-complexes of yttrium and samarium of the formulae K[M(ON(i)Pr(2))(4)] (M = Y, Sm) have been prepared and structurally characterised featuring variations of the hapticity of their ON(i)Pr(2) ligands leading to different chain connectivities in their solid state aggregates.

The reactions of bis- and tris(tert-butylethynyl)benzenes with dialkylgallium hydrides afforded two different types of products. 1,4-Di(tert-butylethynyl)benzene and dialkylgallium hydrides R(2)GaH bearing relatively small substituents (R = Et, nPr) gave the expected addition products with each C triple bond C triple bond inserted into a Ga-H bond. The intact GaR(2) groups are attached to those carbon atoms which are in alpha-position to the benzene rings, and intermolecular Ga-C interactions led to the formation of one-dimensional coordination polymers. In contrast secondary reactions with the release of the corresponding trialkylgallium derivatives GaR(3) (R = Et, nPr, iPr, CH(2)tBu, tBu) were observed for all hydrogallation reactions involving the trisalkyne 1,3,5-tris(tert-butylethynyl)benzene. A similar reaction was observed upon treatment of the 1,4-bisalkyne with a dialkylgallium hydride bearing a relatively bulky substituent (R = neopentyl). Cyclophane type molecules are formed in all these cases with two or three gallium atoms in the bridging positions between both benzene rings.