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).

Palladium and platinum complexes of a benzannulated N-heterocyclic plumbylene with an unusual bonding mode.

Reaction of the N,N'-diisobutyl-substituted benzannulated N-heterocyclic plumbylene (NHPb) 1 with [Pd(PPh(3))(4)] and [Pt(PPh(3))(4)] gave the complexes [M(NHPb)(PPh(3))(3)] (M = Pd [2], Pt [3]). X-ray diffraction studies of both complexes showed an angle of ~125° between the plumbylene plane and the transition-metal-Pb axis, indicating coordination of the transition metal to the empty π orbital of the plumbylene Pb atom. The experimentally determined metric parameters of complexes [2] and [3] are discussed on the basis of DFT calculations.

Stepwise formation of a molecular square with bridging NH,O-substituted dicarbene building blocks.

The ß,ß'-bis(triisopropylsiloxy)phenyl-1,4-diisocyanide 3 and [Ir(Cp*)Cl(2)](2) were used for the stepwise assembly of the [Ir(Cp*)Cl] cornered molecular square [6](Cl)(4). Synthesis of the tetrakis(diisocyanide) bridged molecular square [Ir(Cp*)Cl(3)](4)(BF(4))(4) [5](BF(4))(4) followed by cleavage of the O-Si(i-Pr)(3) bonds of the diisocyanide bridges with HCl/i-PrOH led to an intramolecular attack of the liberated hydroxyl groups at the isocyanide carbon atoms with formation of molecular square [6](Cl)(4) featuring four dicarbene linkers.

Self-assembly of molecular cylinders from polycarbene ligands and Ag(I) or Au(I).

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.

Metal template controlled formation of [11]ane-P2C(NHC) 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.

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.

pi-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.

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.

Acetylenedithiolate: alkyne complex formation renders it a dithiolate chelate ligand.

The isostructural complexes [{Tp'W(CO)(2)(eta(2)-C(2)S(2))}(2)M] (M = Ni, Pd, Pt) show that the eta(2)-C,C'-alkyne complexes of acetylenedithiolate at [Tp'W(CO)(2)](+) can generally act as dithiolate chelate ligands, leading to dithiolene type complexes.

Template synthesis of tungsten complexes with saturated N-heterocyclic carbene ligands.

Tungsten complex with a coordinated 2-azidoethyl isocyanide ligand reacts with PMe3 at the azido function to give a complex with a coordinated iminophosphorane which upon hydrolysis of the P=N bond yields a complex with an NH,NH-stabilized N-heterocyclic carbene ligand, 7; alkylation of the carbene ring nitrogen atoms gives a complex with an N,N'-dialkylated imidazolidin-2-ylidene ligand, 8 .

Molecular rectangles from platinum(II) and bridging dicarbene, diisocyanide and 4,4'-bipyridine ligands.

A series of benzobisimidazolium salts have been prepared and treated with [PtCl2(dppe)] or [PtCl2(dmpe)] in the presence of sodium acetate to yield dinuclear dicarbene-bridged complexes of the type [(P^P)(X)Pt(benzodicarbene)Pt(X)(P^P)](X)2 [5]Br2-[11]I2. The reaction of compounds [7]Br2 and [11]I2 with AgPF6 in acetonitrile led to the exchange of the metal-bound bromo or iodo ligands for acetonitrile and the formation of complexes [(dmpe)(MeCN)Pt(benzodicarbene)Pt(MeCN)(dmpe)](PF6)4 [12](PF6)4 and [13](PF6)4. The dinuclear complex [13](PF6)4 reacts with 4,4'-bipyridine (4,4'-bipy) to give the molecular rectangle [15](PF6)8 featuring two bridging dicarbene and two bridging 4,4'-bipy ligands. Complex [13](PF6)4 also reacts with ß,ß'-bis(triisopropylsiloxy)phenyl-1,4-diisocyanide 16 followed by hydrolysis of the Si-O bonds and intramolecular carbene formation to yield the molecular square [18](BF4)8 featuring bridging NR,NR- and NH,O-substituted dicarbene ligands. Reaction of the dinuclear complex [12](PF6)4 containing a sterically demanding N,N',N'',N'''-substituted dicarbene ligand under otherwise identical reaction conditions did not lead to any molecular rectangles. The molecular square [19](BF4)8 was synthesized from ß,ß'-bis(triisopropylsiloxy)phenyl-1,4-diisocyanide 16 and [PtCl2(dmpe)] in the presence of AgBF4. It reacts to yield the molecular square [20](BF4)8 with four NH,O-substituted dicarbene ligands by Si-O bond cleavage and subsequent intramolecular cyclization.

Synthesis of polynuclear Ag(I) and Au(I) complexes from macrocyclic tetraimidazolium salts.

The synthesis of the macrocyclic tetraimidazolium salt (H4-1)(Br)4 and the anion exchange to (H4-1)(PF6)4 have been explored. Deprotonation of (H4-1)(PF6)4 with Ag2O yields the mono- and dinuclear silver(I) complexes [Ag(H2-1)](PF6)3 and [Ag2(1)](PF6)2. Transmetallation of the dicarbene and tetracarbene ligands to gold(I) yields the mono- and dinuclear gold(I) complexes [Au(H2-1)](PF6)3 and [Au2(1)](PF6)2. The monosilver complex [Ag(H2-1)](PF6)3, featuring two imidazolium moieties, has been deprotonated and used for the synthesis of the tetranuclear silver(I) octacarbene complex [{Ag(1)}2Ag2](PF6)4.

A planar chiral [2.2]paracyclophane derived N-heterocyclic stannylene.

The reaction of pseudo-ortho-4,12-N,N'-diphenyldiamino-[2.2]paracyclophane ((±)-3) with Sn[N(SiMe(3))(2)](2) results in the formation of the monomeric planar chiral N-heterocyclic stannylene (±)-4, featuring a unique [2.2]paracyclophane backbone, which has been characterized by an X-ray diffraction study.

Synthesis of complexes bearing NH,NMe-substituted NHCs by oxidative addition of 2-halogenato-N-methylbenzimidazoles to Ni(0).

Reaction of 2-X-N-methylbenzimidazole (X = chloro, iodo) with Ni(0) complexes in the presence of dppe or PEt(3) and an external proton source yielded via an oxidative addition reaction nickel(II) complexes bearing NH,NMe-functionalized NHC ligands.

Organozinc hydroxylamides: on the bulk-dependent interplay of nuclearity, structure and dynamics.

The reactions of zinc dialkyls, R(2)Zn (1a-d; R = Me (a), Et (b), iPr (c) and tBu (d)), with N,N-dialkylhydroxylamines, HO-NR'(2) (2a-c; R' = Me (a), Et (b) and iPr (c)), afford organozinc hydroxylamides under alkane extrusion. Species of different nuclearity are observed, depending on the hydroxylamine 2 employed. The smaller 2a and 2b give pentanuclear complexes of the general formula Zn(RZn)(4)O-NR'(2))(6) (R = Me, Et, iPr and tBu; R' = Me and Et), whereas the derivatives of 2c are tetramers of the general formula (RZn)(4)(O-NR'(2))(4) (R = Me, Et and iPr; R' = iPr) as governed by bulk issues about the N-donor. Due to the ability of the double-donor unit O-NR(2) to change its bridging mode, two coordination isomers exist for both types of compounds. The pentanuclear species crystallise either in a heterofenestrane or an octahedroid motif. For these species, the central Zn atom exhibits either coordination number 4 or 6; in solution, a rapid change between coordination isomers is observed. Due to the absence of a central Zn atom in the tetranuclear species, these aggregate in heterocubane geometries or such derived thereof. They display the O-N units in either κ(3)O or κ(2)O;κ(1)N mode. The tetranuclear species are also yielded with the less sterically encumbered precursors under thermodynamic conditions (i.e. reflux), as exemplified by the reaction of Me(2)Zn (1a) with HO-NEt(2) (2b). They are non-dynamic in solution, showing that a central cation is mandatory for the fluxional behaviour observed for the pentanuclear derivatives. DFT studies on the O-NMe(2) series reveal that the relative energies of the pentazinc isomers become more similar with increasing RZn group size; possible conversions of these to their tetrazinc counterparts were also scrutinised. Two κ(3)O-bridged degradation products of hydroxylamide complexes could be structurally characterised. They were formed either by partial product hydrolysis, or by in situ oxygenation of the starting zinc dialkyl.