Chemical reactivity and electrochemistry of metal-metal-bonded zincocenes.

Attempts to prepare mixed-ligand zinc-zinc-bonded compounds that contain bulky C(5)Me(5) and terphenyl groups, [Zn(2)(C(5)Me(5))(Ar')], lead to disproportionation. The resulting half-sandwich Zn(II) complexes [(η(5)-C(5)Me(5))ZnAr'] (Ar' = 2,6-(2,6-(i)Pr(2)C(6)H(3))(2)-C(6)H(3), 2; 2,6-(2,6-Me(2)C(6)H(3))(2)-C(6)H(3), 3) can also be obtained from the reaction of [Zn(C(5)Me(5))(2)] with the corresponding LiAr'. In the presence of pyr-py (4-pyrrolidinopyridine) or DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), [Zn(2)(η(5)-C(5)Me(5))(2)] reacts with C(5)Me(5)OH to afford the tetrametallic complexes [Zn(2)(η(5)-C(5)Me(5))L(µ-OC(5)Me(5))](2) (L = pyr-py, 6; DBU, 8), respectively. The bulkier terphenyloxide Ar(Mes)O(-) group (Ar(Mes) = 2,6-(2,4,6-Me(3)C(6)H(2))(2)-C(6)H(3)) gives instead the dimetallic compound [Zn(2)(η(5)-C(5)Me(5))(OAr(Mes))(pyr-py)(2)], 7, that features a terminal Zn-OAr(Mes) bond. DFT calculations on models of 6-8 and also on the Zn-Zn-bonded complexes [Zn(2)(η(5)-C(5)H(5))(OC(5)H(5))(py)(2)] and [(η(5)-C(5)H(5))ZnZn(py)(3)](+) have been performed and reveal the nonsymmetric nature of the Zn-Zn bond with lower charge and higher participation of the s orbital of the zinc atom coordinated to the cyclopentadienyl ligand with respect to the metal within the pseudo-ZnL(3) fragment. Cyclic voltammetric studies on [Zn(2)(η(5)-C(5)Me(5))(2)] have been also carried out and the results compared with the behavior of [Zn(C(5)Me(5))(2)] and related magnesium and calcium metallocenes.

Structural analysis of zincocenes with substituted cyclopentadienyl rings.

New zincocenes [ZnCp'(2)] (2-5) with substituted cyclopentadienyl ligands C(5)Me(4)H, C(5)Me(4)tBu, C(5)Me(4)SiMe(2)tBu and C(5)Me(4)SiMe(3), respectively, have been prepared by the reaction of ZnCl(2) with the appropriate Cp'-transfer reagent. For a comparative structural study, the known [Zn(C(5)H(4)SiMe(3))(2)] (1), has also been investigated, along with the mixed-ring zincocenes [Zn(C(5)Me(5))(C(5)Me(4)SiMe(3))] (6) and [Zn(C(5)Me(5))(C(5)H(4)SiMe(3))] (7), the last two obtained by conproportionation of [Zn(C(5)Me(5))(2)] with 5 or 1, as appropriate. All new compounds were characterised by NMR spectroscopy, and by X-ray methods, with the exception of 7, which yields a side-product (C) upon attempted crystallisation. Compounds 5 and 6 were also investigated by (13)C CPMAS NMR spectroscopy. Zincocenes 1 and 2 have infinite chain structures with bridging Cp' ligands, while 3 and 4 exhibit slipped-sandwich geometries. Compounds 5 and 6 have rigid, eta(5)/eta(1)(sigma) structures, in which the monohapto C(5)Me(4)SiMe(3) ligand is bound to zinc through the silyl-bearing carbon atom, forming a Zn--C bond of comparable strength to the Zn--Me bond in ZnMe(2). Zincocene 5 has dynamic behaviour in solution, but a rigid eta(5)/eta(1)(sigma) structure in the solid state, as revealed by (13)C CPMAS NMR studies, whereas for 6 the different nature of the Cp' ligands and of the ring substituents of the eta(1)-Cp' group (Me and SiMe(3)) have permitted observation for the first time of the rigid eta(5)/eta(1) solution structure. Iminoacyl compounds of composition [Zn(eta(5)-C(5)Me(4)R)(eta(1)-C(NXyl)C(5)Me(4)R)] resulting from the reactions of some of the above zincocenes and CNXyl (Xyl=2,6-dimethylphenylisocyanide) have also been obtained and characterised.

IR and Raman characterization of the zincocenes (eta(5)-C5Me5)2Zn2 and (eta(5)-C5Me5)(eta(1)-C5Me5)Zn.

The measured Raman and IR spectra of solid, polycrystalline bis(pentamethylcyclopentadienyl)dizinc, (eta(5)-C5Me5)2Zn2, 1, and bis(pentamethylcyclopentadienyl)monozinc, (eta(5)-C5Me5)(eta(1)-C5Me5)Zn, 8, are reported in some detail. The IR spectra of the vapors of 1 and 8 each trapped in a solid Ar matrix at 12 K confirm the essentially molecular character of the solids. The experimental results have been interpreted with particular reference (i) to the corresponding spectra of (68)Zn-enriched samples of the compounds, and (ii) to the spectra simulated by density functional theory (DFT) calculations at the B3LYP level. The marked differences of structure of 1 and 8 contrast with the relatively close similarity of their vibrational spectra, disparities being revealed only on detailed scrutiny, including the effects of (68)Zn enrichment, and primarily at wavenumbers below 1000 cm(-1). The Zn-Zn stretching motion of 1 features not as a single, well-defined mode identifiable with intense Raman scattering but in several normal modes which respond in varying degrees to (68)Zn substitution. A stretching force constant of 1.42 mdyne A(-1) has been estimated for the Zn-Zn bond of 1.

White phosphorus as single source of "P" in the synthesis of nickel phosphide.

White phosphorus, P4, was reacted in a stoichiometric manner with Ni(0) complexes or particles to produce nanoparticles of nickel phosphide.

Low-temperature NMR studies of Zn tautomerism and hindered rotations in solid zincocene derivatives.

Using a combination of NMR methods we have detected and studied fluxional motions in the slip-sandwich structure of solid decamethylzincocene (I, [(eta5-C5Me5)Zn(eta1-C5Me5)]). For comparison, we have also studied the solid iminoacyl derivative [(eta5-C5Me5)Zn(eta1-C(NXyl)C5Me5)] (II). The variable temperature 13C CPMAS NMR spectra of I indicate fast rotations of both Cp* rings in the molecule down to 156 K as well as the presence of an order-disorder phase transition around 210 K. The disorder is shown to be dynamic arising from a fast combined Zn tautomerism and eta1/eta5 reorganization of the Cp* rings between two degenerate states A and B related by a molecular inversion. In the ordered phase, the degeneracy of A and B is lifted; that is, the two rings X and Y are inequivalent, where X exhibits a larger fraction of time in the eta5 state than Y. However, the interconversion is still fast and characterized by a reaction enthalpy of DeltaH = 2.4 kJ mol-1 and a reaction entropy of DeltaS = 4.9 J K-1 mol-1. In order to obtain quantitative kinetic information, variable temperature 2H NMR experiments were performed on static samples of I-d6 and II-d6 between 300 and 100 K, where in each ring one CH3 is replaced by one CD3 group. For II-d6, the 2H NMR line shapes indicate fast CD3 group rotations and a fast "eta5 rotation", corresponding to 72 degrees rotational jumps of the eta5 coordinated Cp* ring. The latter motion becomes slow around 130 K. By line shape analysis, an activation energy of the eta5 rotation of about 21 kJ mol-1 was obtained. 2H NMR line shapes analysis of I-d6 indicates fast CD3 group rotations at all temperatures. Moreover, between 100 and 150 K, a transition from the slow to the fast exchange regime is observed for the 5-fold rotational jumps of both Cp* rings, exhibiting an activation energy of 18 kJ mol-1. This value was corroborated by 2H NMR relaxometry from which additionally the activation energies 6.3 kJ mol-1 and 11.2 kJ mol-1 for the CD3 rotation and the molecular inversion process were determined.

Experimental and theoretical characterization of the Zn-Zn bond in [Zn2(eta5-C5Me5)2].

The existence and characterization of a bond between the Zn atoms in the recently synthesized complex [Zn(2)(eta(5)-C(5)Me(5))(2)], as well as between Zn and ligand C atoms is firmly based on neutron diffraction and low-temperature X-ray synchrotron diffraction experiments. The multipolar analysis of the experimental electron density and its topological analysis by means of the 'Atoms in Molecules' (AIM) approach reveals details of the Zn-Zn bond, such as its open-shell intermediate character (the results are consistent with a typical metal-metal single bond), as well as many other topological properties of the compound. Experimental results are also compared with theoretical ab initio calculations of the DFT (density functional theory) and MP2 (Møller-Plesset perturbation theory) electron densities, giving a coherent view of the bonding in the complex. For instance, charges calculated from the AIM approach applied to the atomic basin of each Zn atom are, on average, +0.72 e from both the experimental and the theoretical electron density, showing a moderate charge transfer from the metal, confirmed by the calculated topological indexes.

Solid-state structures and solution studies of novel cyclopentadienyl mercury compounds.

New mercury cyclopentadienyl complexes Hg(eta1-Cp')Cl have been prepared by the reaction of HgCl2 and the appropriate KCp' salts or by the transmetalation of HgCl2 with ZnCp'2 (Cp'=C5Me4H, 1; C5Me4But, 2; C5Me4SiMe3, 3; C5H4SiMe3, 4). By contrast, only the SiMe3-substituted bis(cyclopentadienyl) derivatives, Hg(C5Me4SiMe3)2 (5) and Hg(C5H4SiMe3)2 (6), can be isolated by the above synthetic procedures and the appropriate ratio of reagents or from HgCp'Cl and KCp'. Solution NMR studies reveal nonfluxional behavior of the SiMe3-substituted complexes 3, 5, and 6. X-ray studies of the solid-state structures show that the six compounds contain eta1-Cp' ligands, with linear or almost linear C-Hg-Cl or C-Hg-C coordination environments. The two HgCp'2 compounds, 5 and 6, have the expected insular structures, but the HgCp'Cl derivatives show supramolecular associations by means of weak secondary Hg...Cl interactions. Thus, the HgCp'Cl compounds 1, 3, and 4 form three different polymeric chain structures with typically two Hg...Cl interactions of 3.04-3.46 A per mercury. By contrast, 2 forms a tetramer, [Hg(C5Me4SiMe3)Cl]4, with a cubelike arrangement of four Hg and four Cl atoms. Density functional theory has been used to investigate the electronic structure of the compounds.

Zinc-zinc bonded zincocene structures. Synthesis and characterization of Zn2(eta5-C5Me5)2 and Zn2(eta5-C5Me4Et)2.

While, in general, decamethylzincocene, Zn(C5Me5)2, and other zincocenes, Zn(C5Me4R)2 (R = H, But, SiMe3), react with dialkyl and diaryl derivatives, ZnR'2, to give the half-sandwich compounds (eta5-C5Me4R)ZnR', under certain conditions the reactions of Zn(C5Me5)2 with ZnEt2 or ZnPh2 produce unexpectedly the dizincocene Zn2(eta5-C5Me5)2 (1) in low yields, most likely as a result of the coupling of two (eta5-C5Me5)Zn* radicals. An improved, large scale (ca. 2 g) synthesis of 1 has been achieved by reduction of equimolar mixtures of Zn(C5Me5)2 and ZnCl2 with KH in tetrahydrofuran. The analogous reduction of Zn(C5Me4R)2 (R = H, SiMe3, But) yields only decomposition products, but the isotopically labeled dimetallocene 68Zn2(eta5-C5Me5)2 and the related compound Zn2(eta5-C5Me4Et)2 (2) have been obtained by this procedure. Compound 2 has lower thermal stability than 1, but it has been unequivocally characterized by low-temperature X-ray diffraction studies. As for 1 a combination of structural characterization techniques has provided unambiguous evidence for its formulation as the Zn-Zn bonded dimer Zn2(eta5-C5Me4Et)2, with a short Zn-Zn bond of 2.295(3) A indicative of a strong Zn-Zn bonding interaction. The electronic structure and the bonding properties of 1 and those of related dizincocenes Zn2(eta5-Cp')2 have been studied by DFT methods (B3LYP level), with computed bond distances and angles for dizincocene 1 very similar to the experimental values. The Zn-Zn bond is strong (ca. 62 kcal.mol-1 for 1) and resides in the HOMO-4, that has a contribution of Zn orbitals close to 60%, consisting mostly of the Zn 4s orbitals (more than 96%).

Decamethyldizincocene, a stable compound of Zn(I) with a Zn-Zn bond.

Unlike mercury, which has an extensive +1 oxidation state chemistry, zinc usually adopts the +2 oxidation state. Decamethyldizincocene, Zn2(eta5-C5Me5)2, an organometallic compound of Zn(I) formally derived from the dimetallic [Zn-Zn]2+ unit, has been isolated from the low-temperature (-10 degrees C) reaction of Zn(C5Me5)2 and Zn(C2H5)2 in diethyl ether. X-ray studies show that it contains two eclipsed Zn(eta5-C5Me5) fragments with a Zn-Zn distance (+/- standard deviation) of 2.305(+/-3) angstroms, indicative of a metal-metal bonding interaction.