Reactions of cyclopentadienylmolybdenum compounds with bismuth alkoxides

Dimetalloylene (M-E-M) Complexes of Heavier Main Group Elements Ge, Sn, Pb, Bi via Cleavage of E-X Bonds (X=N(SiMe3 )2 , OtBu) with an Iridium Hydride

Reactions of the IrV hydride [Me BDIDipp ]IrH4 {BDI=(Dipp)NC(Me)CH(Me)CN(Dipp); Dipp=2,6-iPr2 C6 H3 } with E[N(SiMe3 )2 ]2 (E=Sn, Pb) afforded the unusual dimeric dimetallotetrylenes ([Me BDIDipp ]IrH)2 (μ2 -E)2 in good yields. Moreover, ([Me BDIDipp ]IrH)2 (μ2 -Ge)2 was formed in situ from thermal decomposition of [Me BDIDipp ]Ir(H)2 Ge[N(SiMe3 )2 ]2 . These reactions are accompanied by liberation of HN(SiMe3 )2 and H2 through the apparent cleavage of an E-N(SiMe3 )2 bond by Ir-H. In a reversal of this process, ([Me BDIDipp ]IrH)2 (μ2 -E)2 reacted with excess H2 to regenerate [Me BDIDipp ]IrH4 . Varying the concentrations of reactants led to formation of the trimeric ([Me BDIDipp ]IrH2 )3 (μ2 -E)3 . The further scope of this synthetic route was investigated with group 15 amides, and ([Me BDIDipp ]IrH)2 (μ2 -Bi)2 was prepared by the reaction of [Me BDIDipp ]IrH4 with Bi(NMe2 )3 or Bi(OtBu)3 to afford the first example of a "naked" two-coordinate Bi atom bound exclusively to transition metals. A viable mechanism that accounts for the formation of these products is proposed. Computational investigations of the Ir2 E2 (E=Sn, Pb) compounds characterized them as open-shell singlets with confined nonbonding lone pairs at the E centers. In contrast, Ir2 Bi2 is characterized as having a closed-shell singlet ground state.

Bismuth species in the coordination sphere of transition metals: synthesis, bonding, coordination chemistry, and reactivity of molecular complexes

This contribution is focused on bismuth species in the coordination sphere of transition metals. In molecular transition metal complexes, three types of Bi-M bonding are considered, namely dative Bi→M interactions (with Bi acting as a donor), dative Bi←M interactions (with Bi acting as an acceptor) and covalent Bi-M interactions (M = transition metal). Synthetic routes to all three classes of compounds are outlined, the Bi-M bonding situation is discussed, trends in the geometric parameters and in the coordination chemistry of the compounds are addressed, and common spectroscopic properties are summarized. As an important part of this contribution, the reactivity of bismuth species in the coordination sphere of transition metal complexes in stoichiometric and catalytic reactions is highlighted.

Simple soluble Bi(iii) salts as efficient catalysts for the oxidation of alkanes with H2O2

Simple soluble Bi(iii) salts exhibit pronounced catalytic activity in the oxidation of inert alkanes with H₂O₂via a radical mechanism with participation of the HO˙ radicals.

A molecular Mo4Bi4 framework composed exclusively of unsupported metal-metal bonds

Reaction of [Cp(2)MoH(2)] with bismuth allyloxide, [Bi{OCH(CH(3))CH==CH(2)}(3)], gave rise to an extended octanuclear complex wherein two cyclic Mo(2)Bi(2) units composed of four Mo-Bi bonds are linked by a Bi-Bi bond. The fact that the construction of such an assembly could be accomplished only in the case of a monomethylation of the parent allyl residue demonstrates a subtle substituent effect.

Reactivity and properties of [-O-Bi(III...)O=Mo-]n chains

A coordination polymer [Cp(O)2Mo-O-Bi(o-tolyl)2]n, II, containing Mo-O-Bi and Mo=O...Bi moieties was investigated with respect to its behavior in contact with OH- and Cp2MoH2 and as potential single source precursor in the polyol method. It turned out that hydroxide as a base breaks up the polymer to yield CpMoO3- and (o-tolyl)2BiOH. The latter polymerizes to give the coordination polymer [(o-tolyl)2BiOH]n, 1. Alternatively, 1 can be prepared by reacting [(o-tolyl)2Bi(hmpa)2]SO3CF3 with NBu4OH/H2O in thf/water. If, however, NBu4OH/MeOH is used in dichloromethane as the solvent, the (o-tolyl)2BiOH formed intermediately undergoes methanolysis, and finally, [(o-tolyl)2BiOMe]n, 3, is isolated. Although 1 and 3 are very similar compounds, their crystal structures differ significantly: while the structure of 1 is dominated by secondary bonding leading to seesaw-type coordination geometries around the Bi centers, the Bi atoms in 3 are coordinated in a distorted tetrahedral fashion, and secondary bonding plays only a minor role. If 1 is dissolved in a nonpolar, nonprotic solvent, condensation reactions occur immediately leading to [(o-tolyl)2BiOBi(o-tolyl)2], 2, which can be obtained on a preparative scale this way. Compound 3 which can be prepared in good yields may prove to be a useful starting material in bismuth chemistry. Here, it was shown to react with molybdocene dihydrides to provide stable Bi-substituted molybdocene monohydrides [(R)Cp2Mo(H)(Bi(o-tolyl)2)] (R = Me 4, R = H 5); compounds of that type were identified in solution before but had so far eluded isolation. Compound 4, whose crystal structure is discussed, also forms when II is treated with methylated molybdocene dihydride. This obviously leads to the formation of Mo-Bi bonds (--> 4), as well as Mo-OH units, which undergo condensation reactions leading to Mo-O-Mo moieties (i.e., [Cp2Mo2O5] is formed as a byproduct). The use of II as precursor in the polyol method successfully led to bismuthmolybdate nanoparticles (accompanied by crystallites); however, no single phase is obtained, but biphasic materials consisting of Bi(2)Mo2O9 and Bi2MoO6, whose ratio can be determined by the choice of the hydrolyzing reagent, are formed instead. One of these materials proved to be capable of sensing EtOH selectively at elevated temperatures.

“Bent Bonds” between Bismuth and Carbon Atoms as a Result of CH Activation in MoBi Complexes

The reaction of molybdocenedihydride with two equivalents of [Bi(OtBu)(3)] proceeds via alcohol elimination and provides the compound [Cp(2)Mo{Bi(OtBu)(2)}(2)] (1), which contains two Mo--Bi metal bonds, in good yields. If the two reagents are employed in a 1:1 ratio continuative condensation reactions occur. These initially lead to [{Cp(2)Mo}(2){mu-Bi(OtBu)}(2)] (2), which, however, is very unstable in solution and decomposes via additional alcohol elimination: Complex-induced proximity effects facilitate the cleavage of C--H bonds within the cyclopentadienyl ligands by the residual alkoxide ligands, so that spontaneously two further equivalents of alcohol are released, thereby yielding two isomeric compounds 3 and 4 with Cp ligands bridging Mo--Bi metal bonds: The first isomer (3) contains two mu(2)-eta(5):eta(1)-C(5)H(4) ligands, the second isomer (4) contains one bridging mu(3)-eta(5):eta(1):eta(1)-C(5)H(3) ligand. The binding of these ligands to molybdenum and bismuth atoms at the same time is made possible through "bent bonds" between the bismuth and certain carbon centres. These unusual bonding situations were analysed by means of calculations based on density functional theory (DFT), the atoms in molecules (AIM) theory, natural bond order (NBO) considerations and the electron localisation function (ELF). According to the results the bonds can be understood in terms of carbanionic centres interacting with bismuth cations (i.e. closed-shell interactions). The formation of these bonds and the thermodynamics/kinetics involved on going from 2 to 3 and 4 were also studied by theoretical methods, so that the product formation is rationalised. The crystal structures of all four new compounds were determined. These structures but also the properties and mechanisms of formation are discussed against the background of the corresponding results obtained while studying the system [(Me)Cp(2)MoH(2)]/[Bi(OtBu)(3)].