Jörg Rust

Probing Metal Complexation, Structure, Ligand Lability and Dissociative Ligand‐Exchange Mechanism in the Slipped Triple‐Decker Complexes [{(η5‐CpR)Co}2‐μ‐{η4:η4‐arene}] (R=Me5, 1,2,4‐tri‐tert‐butyl; arene=toluene, benzene)

Triple-deckers 1 and 3 are extremely labile with respect to an exchange of their bridging arene middle deck. Crossover exchange experiments between 1, 3, benzene, and azulene have unraveled for the first time a dissociative mechanism for ligand exchange in organometallic triple-decker complexes. Further preparative utility of this high exchange lability can be foreseen and is herein exemplified by the synthesis of a new class of structurally characterized dinuclear Co complexes containing bridging azulenes.

New carbene and vinylidene chelate complexes of cyclopentadienylcobalt bearing a phosphorus tether

Abstract The {η 5 [2-(di- tert -butylphosphanyl- P )ethyl]cyclopentadienyl}cobalt chelate was treated with trimethylsilylethyne to give the corresponding alkyne complex along with the trimethylsilylvinylidene complex. In a similar way, the bis(trimethylsilyl)ethyne complex was obtained. Silyl migration to give the bis(trimethylsilyl)vinylidene complex was observed at elevated temperature and represents the first cobalt example of this reaction. As the first cobalt vinylidene complex the bis(trimethylsilyl)vinylidene complex was characterized by an X-ray structure analysis. Reaction of the cobalt chelate with an Arduengo type carbene unexpectedly gave a non-chelated cobalt complex bearing the carbene ligand and ethene at the same metal atom. This complex was also structurally characterized.

New reaction of ethenetetracarbonitrile with N-arylisoindolines

N-Arylisoindolines 1a - i react with ethenetetracarbonitrile 2 in aerated benzene by formation of (3-(2-aryl-3-dicyanomethylene- 2,3-dihydro-1H-isoindol-1-ylidene)-2-aryl-2,3-dihydro-1H-isoindol-1-ylidene)propanedinitriles 8a- i (20 - 36%), N-aryl-3-dicyano- methylene-isoindol-2-ones 9a - i (15 - 21%) and N-arylphthalimides 10a- i (4- 9%) as well as 1,1,2,2-tetracyanoethane 11 (35 - 55%). The structure of 8d has been unambiguously confirmed by a single crystal X-ray structure analysis. A rationale for the formation of products 8 - 11 is presented. q 2003 Elsevier Science Ltd. All rights reserved.

Synthesis and reactivity of metal complexes with acyclic (amino)(ylide)carbene ligands.

No cycle required: The straightforward synthesis of acyclic (amino)(ylide)carbene gold complexes was achieved by reaction of isocyanide gold complexes with phosphorus and arsenic ylides as well as electron-rich olefins. Their ability to form bimetallic species and to act as ligand-transfer reagents has also been established.

Synthesis, crystal structure, and NMR investigation of methyl α,α-dimethyl acetate-substituted π-allylpalladium complexes

Abstract The dimeric, trifluoroacetate-bridged π-allylpalladium complex 6 and the cationic allyl complex 8 were prepared and characterized by NMR spectroscopy as well as crystal structure analyses. The carbonyl group of the carboxylic ester moiety does not form a chelate with the metal atom. The activation enthalpy of a π–σ–π conversion could be determined to be 14.6 kcal mol −1 based on the dynamic NMR spectroscopy of the allylpalladium complex 8 .

Bis[(dialkylamino)cyclopropenimine]‐Stabilized PIII‐ and PV‐Centered Dications

The treatment of bis[(dialkylamino)cyclopropenimines] with dihalophosphines in the presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf) to form diimine-stabilized P(III) -centered dications is reported. The structures of the new compounds were determined by using X-ray diffraction analysis and their donor abilities as ligands evaluated through electrochemical methods. Despite the two positive charges that they bear, these compounds depict intermediate behavior between that of phosphines and phosphites. The coordination of the [L2 PR](2+) moiety to Au(I) and Ag(I) is also reported. Even more surprisingly, these phosphorus centers can be oxidized to the corresponding P(V) dications in the presence of strong oxidants such as peroxides or XeF2 .

The Thermal [2+2] Cyclodimerisation of (E,Z)-Cycloocta-1,3-diene Revisited − Chemical Trapping and Properties of the Intermediate 1,4-Diradicals

The thermal [2+2] cyclodimerisation of (E,Z)-cycloocta-1,3-diene (9), which is known to afford the cyclobutane dimers 11, 12, and 13, has been investigated in the presence of the nitroxyls 17 and 18 and of atmospheric dioxygen, all of which are known to be efficient trapping agents for carbon-centred free radicals. The nitroxyls have been found to divert the reaction from formation of the dimers to formation of 2:2 adducts of two molecules of 9 and two molecules of nitroxyl. The rate constant for the formation of the overall sum of the dimers plus the 2:2 adducts in the presence of nitroxyl has been found to equal the rate constant for the formation of dimers in the absence of nitroxyl. This and the molecular structures of the 2:2 adducts prove that two molecules of 9 combine irreversibly to produce the two epimeric bis(allylic) 1,4-diradicals 14 and 15 (meso and rac, respectively) which undergo two competing reactions: ring-closure to dimers 11, 12, and 13, and trapping by nitroxyl to form the 2:2 adducts. Dioxygen, too, was found to trap 14 and 15 efficiently. From the kinetics of the latter trapping reaction, studied at six temperatures between 5 and 55 °C, the heights of the activation barriers separating 14 from 11 and 15 from 12 + 13 were estimated at 11.1 ± 1.5 and 10.2 ± 1.5 kcal·mol−1, respectively, corresponding to diradical lifetimes of ca. 0.5 μs. These unexpectedly high barriers have been verified by MM3 force-field calculations and by an investigation of the kinetics of the gas-phase thermolysis of 12 (to give 13 and 16 which is an epimer of 12 and 13) and of 13 (to give 12 and 16). When the cyclodimerisation of 9 was carried out in the presence of spin = 1/2 transition metal complexes, no trapping was observed, but a shift in the 12/13 ratio, resulting from a catalysed conversion of 15 from its singlet to its triplet spin state, was seen. Since nitroxyl also catalysed the singlet-to-triplet conversion (dioxygen did not) in competition with trapping, the kinetics of trapping by nitroxyl was complex, but it did show that 14 and 15 were jeopardised to trapping twice in their lifetimes, meaning that 14 and 15 were generated in their anti conformations, which had to change to the gauche conformations by crossing the barriers referred to above before they could ring-close to dimers; all the anti and the triplet gauche conformations are trappable, but the singlet gauche conformations are not. The same conclusion was reached for 15 from independent experimental evidence. In addition, there is a minor path from 9 to dimers 11, 12, and 13, which is not subject to trapping and which involves the direct formation of the singlet gauche conformers of 14 and 15 from 9. The gauche conformer formed in the smallest amount along this minor pathway is the one giving rise to 12, which is the one with its two radical p-orbitals pointing towards each other most strongly, thus causing adverse Woodward−Hoffmann effects. The direct formation of the principal gauche conformer (which gives rise to 13) from 9 requires 2.75 ± 0.44 and 2.57 ± 0.42 kcal·mol−1 more activation energy than required for the formation of the anti conformers of 14 and 15, respectively.

Ethylenebis(phosphonic acid)

The as yet structurally uncharacterized title compound, C 2 H 8 O 4 P 2 , was isolated as a by-product of the synthesis of 1,2-bis(dimethylphosphino)ethane (dmpe) from 1,2-bis(dichlorophosphino)ethane. In the crystal structure, which is characterized by strong intermolecular O-H…Osp 2 hydrogen bonds, only the R * ,S * diastereomer is found. The molecule is located on a center of inversion intersecting the central C-C bond, thereby preserving the molecular C i symmetry.

On the reactivity of tetrakis(trifluoromethyl)cyclopentadienone towards carbon-based Lewis bases.

The reactivitiy of tetrakis(trifluoromethyl)cyclopentadienone towards different C-based Lewis bases, such as N-heterocyclic carbenes (NHC), ylides and isonitriles, are reported. While sterically not hindered carbenes were found to yield kinetic adducts by regiospecific nucleophilic attack at the position adjacent to the carbonyl group of the ketone, bulkier nucleophiles afforded the thermodynamically more stable O-bridged zwitterions. Interestingly, isonitriles were found to dimerize and trimerize under the same reaction conditions, forming bicyclic products that evolve differently depending on the nature of the substituents.