Fast atom bombardment mass spectrometry of non-volatile organometallic compounds. Rhodium,iridium and platinum complexes containing a cumulene ligand

Fast atom bombardment (FAB) mass spectrometry has been used to examine a series of rhodium, iridium and platinum organimetallic complexes, in which a cumulene ligand is attached to the metal in either σ-or π-bonding fashion. The most intense ion formed in the rhodium and platinum series is the metal-bis(triphenylphosphine) ion, while the [Ir(P(C₆H₅)₃)₂CO]⁺ ion is most intense for the iridium series. The platinum complexes show the most intense molecular ion peaks (up to 35% relative intensity), while the rhodium complexes show the least intense molecular ion peaks. The primary fragmentations of all these complexes occur at the metal-ligand bonds. The cumulenic ligand is lost as an impact unit in all cases. The FAB mass spectra of Rh(P(C₆H₅)₃)₃Cl (Wilkinson's catalyst), Ir(P(C₆H₅)₃)₂COCl (Vaska's compound), Rh(P(C₆H₅)₃)₂COCl and Pt(P(C₆H₅)₃)₂(C₂H₄)–synthetic precursors or related compounds to the organometallic complexes examined here–are included for comparison.     

Bidentate ligands capable of variable bond angles in the self-assembly of discrete supramolecules

Flexible donor ligands like 1,2-bis(3-pyridyl)ethyne or 1,4-bis(3-pyridyl)-1,3-butadiyne self-assemble into discrete supramolecules instead of infinite networks upon combination with organoplatinum 90, 120, and 180 degree acceptor units. These systems are unique examples of versatile pyridine donors adjusting their bonding directionality to accommodate rigid platinum acceptors in the formation of closed macrocycles.     

Bildung von Mischkristallen bei Verbindungen vom Huréaulith-Typ

We investigated to what an extent mixed crystals of phosphates (arsenates) of Mn and Cd, [M₅(HPO₄)₂(PO₄)₂ · 4 H₂O], with Fe(II), Co, Ni, Zn and Cu can be formed.     

Supramolecular chemistry: Self-assembly of titanium based molecular squares

The interaction of Cp₂TiCl₂ with LiC₅H₅N and LiC₁₁H₈N provides Cp₂Ti(Cl)(C₅H₅N) and Cp₂Ti(Cl)(C₁₁H₈N), respectively. Reaction of these species with AgOSO₂CF₃ results in self-assembly of the respective cationic, tetranuclear molecular squares where the required 90° bond angles, demanded by a rectangle, is provided by the distorted tetrahedral bond angles of the coordinated Ti.     

Synthesis of novel symmetrical and nonsymmetrical 6-membered heterocycles with pendant electron-rich organoiron substituents

The functionalized complexes [(dppe)Cp^*Fe(CC)]₂-(Py) (Py=2,6-C₅H₃N and 3,5-C₅H₃N (dppe=1,2-bis(diphenylphosphino)ethane) were isolated in good yields from reaction of the chloro complex (dppe)Cp^*FeCl with the protected bis-acetylenic heterocyclic precursor. These electron-rich pyridyl ligands constitute interesting examples of organometallic heterocycles bearing redox-active substituents. Attempts to find an alternative route starting from the alkynyl complex [(dppe)Cp^*Fe(CCH)] and the corresponding dibromopyridines using a Sonogashira cross-coupling reaction are also described. By this route, the monofunctionalized products [(dppe)Cp^*Fe(CC)]-2,6-Py-Br and [(dppe)Cp^*Fe(CC)]-3,5-Py-Br could be cleanly isolated. These compounds open the way to the generation of heteroaromatics featuring nonequivalent alkyne substituents such as [(dppe)Cp^*Fe(CC)]-2,6-Py-[(CC)SiMe₃] or [(dppe)Cp^*Fe(CC)]-3,5-Py-[(CC)SiMe₃] by further coupling.In commemoriation of the centenary of Academician A. N. Nesmeyanov.UMR CNRS 6509 Organométalliques et catalyse: Chimie et Electrochimie Moléculaires, Université de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1207–1218, September, 1999.     

The synthesis of new 60 degrees organometallic subunits and self-assembly of three-dimensional M3L2 trigonal-bipyramidal cages

By employing the coupling reaction of trans-PtI2(Et3)2 with C-H bonds in alkynes as the key step, two new 60 degrees organometallic subunits with different size from 3,6-dibromophenanthrene were prepared in reasonable yields. The X-ray structures of both di-Pt(II) diiodide complexes showed that they were indeed suitable candidates for 60 degrees building units. By utilizing these novel linkers as ditopic acceptor subunits, three M3L2 trigonal-bipyramidal (TBP) cages were formed. All three TBP cages were characterized with multinuclear NMR and electrospray ionization mass spectrometry (ESI-MS) along with element analysis.     

Self-assembly of dendritic tris(crown ether) hexagons and their complexation with dibenzylammonium cations

The construction of a new series of dendritic tris(crown ether) hexagons via coordination-driven self-assembly is described. Combining 120° crown ether-containing diplatinum(II) acceptors with 120° dendritic dipyridyl donors in a 1:1 ratio allows for the formation of a new family of dendritic triple crown ether derivatives with a hexagonal cavity in quantitative yields. The number and the position of these pendant groups can be precisely controlled on the hexagonal metallacycle. The structures of all dendritic multiple crown ether hexgaons are confirmed by multinuclear NMR ((1)H and (31)P), ESI-MS and ESI-TOF-MS, and elemental analysis. The complexation of these dendritic trivalent receptors with dibenzylammonium cations was investigated by (1)H NMR titration experiments. The thermodynamic binding constants between the receptors and guests were established by using the nonlinear least-squares fit method based on (1)H NMR titration experiments. It was found that the association constants of each assembly decrease correspondingly upon the increase of the generation of the dendrons from [G0] to [G3], which might be caused by the steric effect of the dendrons on host-guest complexation.     

Dynamic equilibrium of a supramolecular dimeric rhomboid and trimeric hexagon and determination of its thermodynamic constants

A supramolecular dimeric rhomboid and its trimeric counterpart, a hexagon, are generated by design via the directional bonding methodology of self-assembly. The different-sized supramolecular macrocycles formed by Pt-coordination undergo a concentration- and temperature-dependent dynamic equilibrium. The two structures are characterized by multinuclear NMR and ESI-MS. Extensive study of the dynamic equilibrium of the two species in solution is performed to obtain its thermodynamic properties. By varying the ionic strength, mu, of the solutions, the true thermodynamic equilibrium constant, K, is determined at each experimental temperature (K(253) = 36 +/- 7, K(273) = 18 +/- 6, K(293) = 10 +/- 3, K(313) = 9 +/- 2, K(333) = 5 +/- 2, and K(353) = 3.0 +/- 0.2). By applying these values of true K at the respective temperatures to the van't Hoff equation extended with the entropy term, the standard enthalpy and entropy changes are determined for the equilibrium: with Delta H degrees = -18 +/- 1 kJ mol(-1) and Delta S degrees = -43 +/- 4 J mol(-1) K(-1), respectively, for the forward reaction (rhomboid to hexagon) of the equilibrium. The rhomboid is selectively crystallized, and its crystal structure is determined by X-ray diffraction. The structure reveals a significant amount of porosity as well as distortion of the rhomboid from planarity, leading to channels that can be observed from two viewing positions of the packing.     

Coordination-driven assembly of molecular rectangles via an organometallic "clip"

The combination of linear dipyridyl ligands with a new type of modular building unit, based upon a 1,8-platinum-functionalized anthracene, leads to the self-organization of rectangular frameworks. X-ray crystallography confirms the cyclic structure of the supramolecular cationic complexes. Spectral assignments were provided by 2D NOESY (1)H NMR experiments.     

Preparation, characterization, and X-ray crystal structures of helical and syndiotactic zinc-based coordination polymers

The reactions of (facac)2Zn.2H2O (facac = 1,1,1,5,5,5-hexafluoroacetylacetonate) with 2,5-bis(4-ethynylpyridyl)furan (1) and 1,2-bis(4-ethynylpyridyl)benzene (2) yield, upon crystallization, coordination polymers. The former polymer, ((facac)2Zn.1)n, has an isotactic, helical structure in the solid state [monoclinic space group P2(1)/n; a = 11.0374(3) A, b = 24.2179(10) A, c = 14.3970(4) A, beta = 92.880(2) degrees; Z = 4]. The latter polymer, ((facac)2Zn.2)n, adopts a syndiotactic structure in the solid state [monoclinic space group P2(1)/n; a = 9.1344(1) A, b = 21.7985(5) A, c = 16.0322(4) A, beta = 99.6680(11) degrees; Z = 4]. The solution structures of the corresponding oligomers have been studied by low-temperature 1H and 19F NMR spectroscopy. Chiral polymers were prepared using the fragment [(+)-tfc]2Zn ((+)-tfc = 3-((trifluoromethyl)hydroxymethylene)-(+)-camphorate). A linear, zigzag structure was found for ([(+)-tfc]2Zn.1)n [triclinic space group P1; a = 7.4833(2) A, b = 14.1563(5) A, c = 21.21230(5) A, alpha = 78.4440(15) degrees, beta = 81.5644(15) degrees, gamma = 76.4976(13) degrees; Z = 1]. Reaction with tris(4-pyridyl)methanol (3) yielded a homochiral, helical polymer, ([(+)-tfc]2Zn.3)n [monoclinic space group C2; a = 25.0633(12) A, b = 11.8768(7) A, c = 17.1205(9) A, alpha = 90 degrees, beta = 117.954(3) degrees, gamma = 90 degrees; Z = 4].