Treasure complexes: Lutidine‐bridged tetraimidazolium salts form macrocyclic mono‐ and dinuclear silver(I) and gold(I) carbene complexes, whereas the lutidine‐bridged hexakis(imidazolin‐2‐ylidene) ligand reacts with silver(I) to yield complex [1]+, which contains six silver(I) atoms arranged in a hexagon and sandwiched in between two hexacarbene ligands.

The synthesis of cylinder-type carbene complexes from polycarbene ligands and coinage metal ions via metal-controlled self-assembly has been explored. Imidazole reacts with 1,2,4,5-tetrabromobenzene or 1,3,5-tribromobenzene to give 1,2,4,5-tetrakis(1-imidazolyl)benzene (1) and 1,3,5-tris(1-imidazolyl)benzene (3), respectively. The tetrakisimidazolium salts of type H4-2a,b(Br)4 and the trisimidazolium salts of type H3-4a,b(Br)3 have been prepared by alkylation of the remaining free imines of the tetrakis- and trisimidazoles (H4-2a 4+, H3-4a 3+: R = n-butyl; H4-2b 4+, H3-4b 3+: R = ethyl). Polyimidazolium salts H4-2a,b(PF6)4 and H3-4a,b(PF6)3 have been synthesized by anion exchange from H4-2a,b(Br)4 and H3-4a,b(Br)3. Two equivalents of tetraimidazolium salt H4-2a(Br)4 or H4-2a,b(PF6)4 reacts with four equivalents of Ag2O to yield via self-assembly molecular cylinders of type [Ag4(2a)2]Y4 (Y− = [AgBr2]− and/or Br−) or [Ag4(2a,b)2](PF6)4, respectively. Similarly, reaction of two equivalents of trisimidazolium salts H3-4a(Br)3 or H3-4a,b)(PF6)3 with three equivalents of Ag2O yields the molecular cylinder [Ag3(4a)2](Y)3 (Y− = [AgBr2]− and/or Br−) or [Ag3(4a,b)2](PF6)3, respectively. Transmetalation of [Ag4(2a,b)2](PF6)4 with four equivalents of [AuCl(SMe2)] leads to the formation of the tetranuclear gold(I) complex [Au4(2a,b)2](PF6)4 with retention of the metallosupramolecular assembly. Analogously, transmetalation of [Ag3(4a,b)2](PF6)3 with three equivalents of [AuCl(SMe2)] or CuBr yields the trinuclear gold(I) complexes [Au3(4a,b)2](PF6)3 or the copper(I) complexes [Cu3(4a,b)2](PF6)3, respectively. Contrary to the metallosupramolecular assemblies of type [M4(2a)2]4+ (M = Ag+, Au+), tetrakisimidazolium salt H4-2a(Br)4 reacts with K2PtCl4 in the presence of NaOAc to yield the square-planar dinuclear complex [Pt2(2a)Br4].

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.

The monomeric aluminium hydrazide H10 C5 NN(AltBu2 )Ad (4; Ad=adamantyl, NC5 H10 =piperidinyl) was obtained in high yield by hydroalumination of the corresponding hydrazone derivative 1. Compound 4 has a strained AlN2 heterocycle formed by a donor-acceptor bond between the β-nitrogen atom of the hydrazide group and the aluminium atom. Opening of this bond resulted in the formation of an active Lewis pair that was able to cooperatively activate carbon dioxide or isocyanates. Insertion of the heterocumulenes into the AlN bond selectively afforded a carbamate and two urea derivatives in high yield. In the first step, phenyl isocyanate gave the adduct 6, which has the oxygen atom coordinated to the aluminium atom and its central carbon atom bound to the nitrogen atom of the piperidine moiety. Adduct 6 represents a reasonable intermediate state for these activation processes. The applicability of hydroaluminated compounds, such as 4, in organic synthesis was demonstrated by the reaction with an imidoyl chloride, which gave the corresponding amidrazone derivative 9.

Hydrogallation of 1,4-bis(trimethylsilylethynyl)benzene and 1,3,5-tris(trimethylsilylethynyl)benzene with dialkylgallium hydrides R2GaH (R = Et, nPr, iPr, neopentyl, tBu) afforded the corresponding addition products with intact GaR2 groups and two or three alkenyl substituents. In all products the gallium atoms attacked those carbon atoms that are attached to the trimethylsilyl groups. The expected cis arrangement of gallium and hydrogen atoms at the CC double bonds was detected only with di(tert-butyl)gallium residues. Smaller alkyl groups gave the spontaneous formation of the trans-addition products. Cis/trans isomerization is an inevitable step for the formation of effective chelating Lewis acids, and in particular the trisalkene derivatives form interesting chalice-like hollows containing three Lewis-acidic centers at their inner surfaces.

The reaction of the benzannulated bisstannylene ligand 2 with Sn O or Pb O generated in situ gave the pincer complexes 3 and 4. Both complexes have been characterized by X-ray diffraction and multinuclear NMR spectroscopy. A divalent state has been found by Mössbauer spectroscopy for the tin atoms in complexes 3 and 4.

Fluorobenzene solutions of RPCl2 and a Lewis acid such as ECl3 (E = Al, Ga) in a 1:1 ratio are used as reactive sources of chlorophosphenium cations [RPCl]+, which insert into P–P bonds of dissolved P4. This general protocol represents a powerful strategy for the synthesis of new cationic chloro-substituted organophosphorus [RP5Cl]+-cages as illustrated by the isolation of several monocations (21a-g +) in good to excellent yields. For singular reaction two possible reaction mechanisms are proposed on the basis of quantum chemical calculations. The intriguing NMR spectra and structures of the obtained cationic [RP5Cl]+-cages are discussed. Furthermore, the reactions of dichlorophosphanes and the Lewis acid GaCl3 in various stoichiometries are investigated to obtain a deeper understanding of the species involved in these reactions. The formation of intermediates such as RPCl2·GaCl3 (14) adducts, dichlorophosphanylchlorophosphonium cations [RPCl2–RPCl]+ (16 +) and [RPCl2–RPCl–GaCl3]+ (17 +) in reaction mixtures of RPCl2 and GaCl3 in fluorobenzene strongly depends on the basicity of the dichlorophosphane RPCl2 (R = tBu, Cy, iPr, Et, Me, Ph, C6F5) and the reaction stoichiometry.

The synthesis of N-heterocyclic carbene-diphosphine macrocycles by metal template assisted cyclization reactions has been explored. Attempts to prepare the facial tungsten tricarbonyl precursor complex containing an NH,NH-functionalized carbene and a suitable diphosphine resulted in displacement of the coordinated carbene and the isolation of the corresponding diphosphine tungsten tetracarbonyl [3]. The Re(I) chloro tetracarbonyl complex bearing an NH,NH-functionalized carbene ligand [5] can be prepared and is a suitable precursor for the subsequent formation of the carbene-diphosphine tricarbonyl intermediate [H(2)-6]Cl bearing reactive 2-fluoro substituents at the phosphine-phenyl groups. Two of these fluoro substituents are displaced by a nucleophilic attack upon deprotonation of the coordinated NH,NH-functionalized carbene resulting in new C-N bonds resulting in the partially coupled intermediate, [10], followed by the desired complex with the macrocyclic ligand [8]Cl. Compounds [H-7]Cl and [8]Cl are also formed during the synthesis of [H(2)-6]Cl as a result of spontaneous HF elimination. Complex [8](+) may be converted to the neutral dicarbonyl chloro analog [11] by action of Me(3)NO. Related chemistry with analogous manganese complexes is observed. Thus, from the NH,NH-functionalized carbene manganese bromo tetracarbonyl [12], the diphosphine manganese carbene tricarbonyl cation [H(2)-13] may be readily prepared which provides the macrocyclic carbene-diphosphine tricarbonyl cation [14](+) following base promoted nucleophilic intramolecular displacement of fluoride. Again, [14](+) is converted to the neutral bromo dicarbonyl upon reaction with Me(3)NO. All complexes with the exception of the reaction intermediate [10] have been characterized by spectroscopic and analytical methods in addition to X-ray crystallographic structure determinations for complexes [3], [5], [H(2)-6]Cl, [H(2)-6][9], [8]Cl, [10], [11], [12], and [14]Br.