Tania Pape

Self-Assembly of Molecular Cylinders from Polycarbene Ligands and AgI or AuI

Tris- and tetrakis(imidazolium) salts react with Ag(2)O to give cylindrical polynuclear silver(I) complexes such as the tetrasilver derivative [Ag(4)(1)(2)](PF(6))(4). The silver(I) complexes undergo transmetalation with [AuCl(SMe(2))] to yield homonuclear gold(I) complexes with retention of the metallosupramolecular assembly.

Synthesis of Silver(I) and Gold(I) Complexes with Cyclic Tetra- and Hexacarbene Ligands

Cyclic polyimidazolium salts have been investigated with respect to their function as anion receptors and cyclophanelike tetraimidazolium tetracations have been shown to bind anions inside the ring cavity. Cyclic polyimidazolium cations can also serve as precursors for N-heterocyclic carbenes (NHCs) and their complexes. Complexes of cyclic di-NHC ligands have been generated from bisazolium cyclophanes like A. However, such dicarbene ligands coordinate in a cisfashion to the metal center. They act as classical bidentate ligands rather than encapsulating the metal in a manner typical for macrocyclic ligands. Only one cyclic tetradentate dicarbene ligand is known to form a saddle-shaped macrocyclic complex B with nickel(II). We have described the first complex with a macrocyclic tetracarbene ligand C. The rhenium complex of a tridentate, facially coordinated [11]ane-P2C NHC macrocycle has also been reported. Since the preparation of complex C in a metal-template controlled domino-reaction is cumbersome we became interested in the preparation of complexes with macrocyclic poly-NHC ligands from cyclic polyimidazolium cations. This approach has previously been applied successfully for the preparation of some mono (Pd) and dinuclear (Cu, Ag) carbene complexes from the cyclic tetraimidazolium salt D. We became particularly interested in the lutidine-bridged tetraimidazolium salt H4-1 ACHTUNGTRENNUNG(Br4)[8] which upon C deprotonation would yield a potentially hexadentate ligand possessing two C-N-C pincer-type binding sites. Here we describe the mono and dinuclear silver(I) complexes with the carbene ligands derived from H4-1(Br)4 and the transfer of the carbene ligand to yield the mono and dinuclear gold(I) complexes (Scheme 1). A slight modification in the synthesis protocol employed for the preparation of H4-1(Br)4 yields the cyclic hexaimidazolium salt H6-6Br ACHTUNGTRENNUNG(BPh4)5 (Scheme 2). The preparation and molecular structure of the hexanuclear silver(I)-NHC complex derived from this ligand is also ACHTUNGTRENNUNGdescribed. The tetraimidazolium salt H4-1(Br)4 is soluble in water. [8]

Metal template controlled formation of [11]ane-P2CNHC macrocycles

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.

Stepwise preparation of a molecular square from NR,NR- and NH,O-substituted dicarbene building blocks.

Metallosupramolecular self-assembly has been a field of intensive research ever since Lehn et al. first demonstrated the spontaneous self-assembly of dinuclear helicates from bipyridine and copper(I). Thereafter, different metallosupramolecular structures have been synthesized. Some of these feature internal cavities suitable for the encapsulation of small molecules. Reactive intermediates have been stabilized in such cavities and selected catalytic transformations have been carried out and accelerated inside metallosupramolecular assemblies. The molecular square [A] (Scheme 1) by Fujita et al. built up from end-capped Pd ions and 4,4’-bipyridine building blocks was among the first metallosupramolecular structures to be studied in detail. Related molecular squares were subsequently studied by Stang and Olenyuk and other research groups. Complex [A] and most other metallosupramolecular assemblies described to date are derived from polydentate ligands featuring either nitrogen or oxygen donor atoms coordinating to the metal centers. Supramolecular assemblies built from polydentate ligands with carbon donors are quite rare, although some examples with bridging diisocyanide, acyclic diaminocarbene, remote-NHC, or a,w-dicarbanion ligands have been described. The preparation of the molecular rectangle [B], which features rigid linear dicarbenes and 4,4’-bipyridine linkers, as well as cylindrical structures synthesized from macrocyclic and other poly-NHC ligands, have only recently been reported, while N-heterocyclic carbenes have developed into an important class of ligands in organometallic chemistry over the last 30 years. Herein we introduce a novel molecular square that is built up from four platinum(II) corners that are held together by bonds formed between platinum and the carbon atoms of two classical bis(diaminocarbene) and two di(NH,O-NHC) ligands. In contrast to the known metallosupramolecular structures featuring bridging ligands that form M C bonds, only Pt Ccarbene bonds are employed for the formation of the molecular square. Previous studies have established that the reaction of square-planar platinum(II) with sterically demanding diphosphines and rigid linear dicarbenes, obtained by double deprotonation of benzobisimidazolium salts, yielded a mixture of dinuclear dicarbene-bridged syn (minor) and anti complexes (major). Once formed, these isomers do not interconvert with the anti isomer being geometrically unfit for the construction of a molecular square. We have now found that a reduction of the steric demand of the ligands at platinum(II) leads to a lower barrier of rotation about the Pt Ccarbene bond, thereby allowing the formation of the dinuclear complex with syn geometry by interconversion of the potential geometrical isomers. The tetramethyl-substituted benzobisimidazolium salt 1 I2 was reacted with NaOAc and [PtCl2(dmpe)] instead of the previously used [PtCl2(dppe)] [16] to yield complex [2]I2 (Scheme 2; see Supporting Information; dmpe = bis(dimethylphosphino)ethane, dppe = bis(diphenylphosphino)ethane). The complex was identified by the characteristic chemical shift for the carbene carbon atom at d = 183.9 ppm, which was recorded as a multiplet owing to coupling with the phosphorus atoms. The high-resolution mass spectrometry (ESI, positive ions) shows the mass of the cationic complex ion [2] as peak of highest intensity. Only one multiplet was observed in the P{H} NMR spectrum at d = 30.9 ppm for the two chemically different phosphorus atoms. Scheme 1. Molecular square [A] and molecular rectangle [B] (R=n-butyl).

Trapping of Tin(II) and Lead(II) Homologues of Carbon Monoxide by a Benzannulated Lutidine-Bridged Bisstannylene

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.

Synthesis of NHC Complexes by Oxidative Addition of 2-Chloro-N-methylbenzimidazole

The oxidative addition of 2-chloro-N-methylbenzimdazole to complexes of type [M(PPh(3))(4)] yields after N-protonation compounds with NH,NMe-substituted NHC ligands. For M = Pd complex compound trans-[3]BF(4) was obtained, while the oxidative addition for M = Pt yielded a mixture of cis-[4]BF(4) (major) and trans-[4]BF(4) (minor).

π‐Bonding in Complexes of Benzannulated Biscarbenes, ‐germylenes, and ‐stannylenes: An Experimental and Theoretical Study

Benzannulated bisstannylenes, exhibiting a CH(2)C(CH(3))(2)CH(2) linking unit and CH(2)tBu (1) or CH(2)CH(2)CH(2)NMe(2) (2) N-substituents, and their molybdenum tetacarbonyl complexes 3 and 4 have been prepared. The complexes 3 and 4 exhibit remarkably short Mo-E bond lengths compared to the related biscarbene and bisgermylene complexes. The experimentally determined bonding parameters of the molybdenum bisstannylene complexes are discussed based on DFT calculations.

The influence of the intramolecular hydrogen bond on the 1,3-N,S- and 1,5-O,S-coordination of N-phosphoryl-N′-(R)-thioureas with Ni(II) and Pd(II)

Reaction of the potassium salts of N-phosphorylated thioureas of common formula R1–N(H)–C(S)–N(H)–P(O)(OiPr)2 (HA) with NiII and PdII cations leads to [MA2] chelate complexes (M = NiII, R1 = p-MeOC6H4, p-BrC6H4, t-Bu, c-Hex; M = PdII, R = iPr). In both the NiII and PdII complexes, the metal center is found in a square-planar N2S2 environment formed by the CS sulfur atoms and the P–N nitrogen atoms of two deprotonated ligands A−. The PdII atoms in [PdB2] complexes with deprotonated thioureas of common formula R2–C(S)–N(H)–P(O)(OiPr)2 (HB) (R2 = Et2N, morpholine-N-yl) are coordinated in a square-planar fashion by the CS sulfur atoms and the PO oxygen atoms of two anionic ligands. Molecular structures of four complexes [M(A-N,S)2] (M = NiII, R1 = p-MeOC6H4, p-BrC6H4, t-Bu; M = PdII, R1 = iPr) and the palladium(II) 1,5-O,S-chelate of formula [Pd(B-O,S)2] (R2 = morpholine-N-yl) were elucidated by X-ray diffraction.

A dinuclear triple-stranded helicate with a bis(benzene-o-dithiolato) ligand

The bis(benzene-o-dithiol) ligand H4-1 reacts with Ti4+ in a self-assembly reaction to give the dinuclear triple-stranded helicate [Ti2(1)3]4- which is the first helicate build exclusively from benzene-o-dithiolato donor groups.

Strong Intramolecular Si−N Interactions in the Chlorosilanes Cl3−nHnSiOCH2CH2NMe2 (n = 1−3)

The compounds Cl 3SiOCH 2CH 2NMe 2 ( 1) and Cl 2HSiOCH 2CH 2NMe 2 ( 2) were prepared by reactions of lithium 2-(dimethylamino)ethanolate with SiCl 4 and HSiCl 3. The analogous reaction with H 2SiCl 2 gave ClH 2SiOCH 2CH 2NMe 2 ( 3), but only in a mixture with Cl 2HSiOCH 2CH 2NMe 2 ( 2), from which it could not be separated. All compounds were characterized by IR and NMR ( (1)H, (13)C, (29)Si) spectroscopy, 1 and 2 by elemental analyses and by determination of their crystal structures. Cl 3SiOCH 2CH 2NMe 2 ( 1) and Cl 2HSiOCH 2CH 2NMe 2 ( 2) crystallize as monomeric ring compounds with pentacoordinate silicon atoms participating in intramolecular Si-N bonds [2.060(2) A ( 1), 2.037(2) A ( 2)]. The dative bonds in 1 and 2 between the silicon and nitrogen atoms could also be proven to exist at low temperatures in solution in (1)H, (29)Si-HMBC-NMR experiments by detection of the scalar coupling between the (29)Si and the protons of the NCH 2 and NCH 3 groups. A function describing the chemical shift delta exp (29)Si dependent on the chemical shifts of the individual equilibrium components, the temperature, and the free enthalpy of reaction was worked out and fitted to the experimental VT-NMR data of 1 and 2. This provided values of the free reaction enthalpies of Delta G = -28.8 +/- 3.9 kJ x mol (-1) for 1 and Delta G = -22.3 +/- 0.4 kJ x mol (-1) for 2 and estimates for the chemical shifts of open-chain (index o) and ring conformers (index r) for 1 of delta r = -94 +/- 2 ppm and delta o = -36 +/- 5 ppm and for 2 of delta r = -82 +/- 1 ppm and delta o = -33 +/- 4 ppm. The value of delta r for 1 is very close to that obtained from a solid-state (29)Si MAS NMR spectrum. Quantumchemical calculations (up to MP2/TZVPP) gave largely differing geometries for 1 (with a Si...N distance of 3.072 A), but well reproduced the geometry of 2. These differences are due to Cl...H and Cl...C repulsions and solid state effects, which can be modeled by conductor-like screening model calculations and also rationalized in terms of the topology of the electron density, which was analyzed in terms of the quantum theory of atoms in molecules.