It has been long known that certain transition metal sulfides dissolve in aqueous ammonium polysulfide. Although it was assumed that they thereby formed metal polysulfides, attention was first paid to such compounds only a few years ago. In recent years a host of new complexes with polysulfido chelate ligands have been isolated and characterized. The complexes are of interest not only regarding their structure and reactivity but also in view of their potential uses; they can be used for the directed preparation of sulfur rings of a given size, and there are indications that they will find applications in catalysis.

Transition Metal Polysulfides: Coordination Compounds with Purely Inorganic Chelate Ligands

In this Communication, we describe the first highly enantioselective cyanosilylation of ketones catalyzed by simple chiral amino acid salt. A broad range of aromatic, α,β-unsaturated, heterocyclic ketones catalyzed by l-phenylglycine sodium salt gave the corresponding trimethylsilyl ethers of cyanohydrins in 75−96% yields with 86−97% enantioselectivities. A catalytic cycle based on experimental phenomena and studies has been proposed to explain the origin of this activation. The reaction employed commercially available and fully recyclable catalysts and involves a simple experimental procedure.

Catalytic Asymmetric Cyanosilylation of Ketones by a Chiral Amino Acid Salt

A straightforward to assemble catalytic system for the intermolecular hydroacylation reaction of beta-S-substituted aldehydes with activated and unactivated alkenes and alkynes is reported. These catalysts promote the hydroacylation reaction between beta-S-substituted aldehydes and challenging substrates, such as internal alkynes and 1-octene. The catalysts are based upon [Rh(cod)(DPEphos)][ClO(4)] (DPEphos=bis(2-diphenylphosphinophenyl)ether, cod=cyclooctadiene) and were designed to make use of the hemilabile capabilities of the DPEphos ligand to stabilise key acyl-hydrido intermediates against reductive decarbonylation, which results in catalyst death. Studies on the stoichiometric addition of aldehyde (either ortho-HCOCH(2)CH(2)SMe or ortho-HCOC(6)H(4)SMe) and methylacrylate to precursor acetone complexes [Rh(acetone)(2)(DPEphos)][X] [X=closo-CB(11)H(6)Cl(6) or [BAr(F) (4)] (Ar(F)=3,5-(CF(3))(2)C(6)H(3))] reveal the role of the hemilabile DPEphos ligand. The crystal structure of [Rh(acetone)(2)(DPEphos)][X] shows a cis-coordinated diphosphine ligand with the oxygen atom of the DPEphos distal from the rhodium. Addition of aldehyde forms the acyl hydride complexes [Rh(DPEphos)(COCH(2)CH(2)SMe)H][X] or [Rh(DPEphos)(COC(6)H(4)SMe)H][X], which have a trans-spanning DPEphos ligand and a coordinated ether group. Compared to analogous complexes prepared with dppe (dppe=1,2-bis(diphenylphosphino)ethane), these DPEphos complexes show significantly increased resistance towards reductive decarbonylation. The crystal structure of the reductive decarbonylation product [Rh(CO)(DPEphos)(EtSMe)][closo-CB(11)H(6)I(6)] is reported. Addition of alkene (methylacrylate) to the acyl-hydrido complexes forms the final complexes [Rh(DPEphos)(eta(1)-MeSC(2)H(4)-eta(1)-COC(2)H(4)CO(2)Me)][X] and [Rh(DPEphos)(eta(1)-MeSC(6)H(4)-eta(1)-COC(2)H(4)CO(2)Me)][X], which have been identified spectroscopically and by ESIMS/MS. Intermediate species in this transformation have been observed and tentatively characterised as the alkyl-acyl complexes [Rh(CH(2)CH(2)CO(2)Me)(COC(2)H(4)SMe)(DPEphos)][X] and [Rh(CH(2)CH(2)CO(2)Me)(COC(6)H(4)SMe)(DPEphos)][X]. In these complexes, the DPEphos ligand is now cis chelating. A model for the (unobserved) transient alkene complex that would result from addition of alkene to the acyl-hydrido complexes comes from formation of the MeCN adducts [Rh(DPEphos)(MeSC(2)H(4)CO)H(MeCN)][X] and [Rh(DPEphos)(MeSC(6)H(4)CO)H(MeCN)][X]. Changing the ligand from DPEphos to one with a CH(2) linkage, [Ph(2)P(C(6)H(4))](2)CH(2), gave only decomposition on addition of aldehyde to the acetone precursor, which demonstrated the importance of the hemiabile ether group in DPEphos. With [Ph(2)P(C(6)H(4))](2)S, the sulfur atom has the opposite effect and binds too strongly to the metal centre to allow access to productive acetone intermediates.

Intermolecular Alkene and Alkyne Hydroacylation with β‐S‐Substituted Aldehydes: Mechanistic Insight into the Role of a Hemilabile P–O–P Ligand

Es ist schon sehr lange bekannt, das sich manche Ubergangsmetallsulfide in wasrigem Ammoniumpolysulfid losen. Obwohl anzunehmen war, das sich dabei Metallpolysulfide bilden, hat man sich diesem Verbindungstyp erst in den letzten Jahren intensiver zugewandt. Dabei konnte eine Fulle neuer Komplexe mit Polysulfido-Chelatliganden S (n=2,3,4…) isoliert und charakterisiert werden. Die Komplexe interessieren bezuglich ihrer Struktur und Reaktivitat, aber auch im Hinblick auf mogliche Anwendungen; mit ihnen konnen Schwefelringe definierter Grose gezielt hergestellt werden, und es deutet sich an, das sie auch in der Katalyse Verwendung finden konnten.

Übergangsmetallpolysulfide, Koordinationsverbindungen mit rein anorganischen Chelatliganden

Etudes des methodes RMN permettant d'etudier les comportements dynamiques de molecules plus particulierement l'inversion de S, Se et Te, ainsi que d'autres comportements fluxionnels de tels atomes. Discussion

The Stereodynamics of Metal Complexes of Sulfur-, Selenium-, and Tellurium-Containing Ligands

[3]Ferrocenophane bridge reversal barriers

[3]Ferrocenophane Bridge Reversal Barriers : II. Carbon, Oxygen and Sulphur Bridging Atoms

The inversion barrier of the TiS5 ring in DI(η5-cyclopentadienyl)titanium pentasulphide

The series of complexes trans-[MX2{[graphic omitted]H2)5}2](M = Pd; X = Cl, Br, or I; M = Pt; X = Cl) have been synthesised and, by accurate analysis of their variable-temperature 1H and 13C n.m.r. spectra using total band-shape fitting methods, energy barriers for ligand ring reversal and for sulphur inversion have been separated and calculated for the first time. The barriers to ring reversal in the complexes are similar to those already known for the unco-ordinated ligand, whereas those for sulphur inversion are also similar to values known for analogous non-cyclic ligand complexes. The power of 13C dynamic n.m.r. spectral analysis was demonstrated by the fact that no simplifications in the conformational analyses were needed in order to account for the 13C spectral line changes. This was in marked contrast to the 1H spectra, which, in order for their analyses to be possible, had to be attributed to the conformations of either six-membered heterocyclic ring rather than to total conformational structures of the complexes.

Determination of the separate barrier energies for six-membered ligand ring reversal and pyramidal sulphur inversion in complexes of palladium(II) and platinum(II). A dynamic hydrogen-1 and carbon-13 nuclear magnetic resonance study

The series of complexes trans-[MX2{[graphic omitted]R2)n}2](M = PdII or PtII; X = Cl, Br, or I; R = H and/or Me; n= 2–5) have been synthesised, and accurate analysis of their variable-temperature n.m.r. spectra by band-shape fitting methods has been used to determine the barrier to pyramidal inversion at the sulphur atom. Barrier energies in chloro-complexes are 2–3 kJ mol–1 higher than in the corresponding bromides, which are in turn 4–5 kJ mol–1 higher than in the iodo-complexes. The pyramidal inversion energies are very dependent upon ligand ring size; those for five- and six-membered rings are comparable with complexes of linear sulphides, but the complexes of four-membered rings show a considerable heightening of the pyramidal sulphur inversion barrier. For the complexes of the three-membered ring sulphides no inversion was detectable up to the temperature where decomposition commenced, this being the first reported example of such rigidity in dialkyl sulphide metal complexes.

Effect of variation in ligand ring size upon the inversion barrier at sulphur in complexes of palladium(II) and platinum(II). A dynamic hydrogen-1 nuclear magnetic resonance study

Martin Booth

Papers

[3]Ferrocenophane bridge reversal barriers

[3]Ferrocenophane Bridge Reversal Barriers : II. Carbon, Oxygen and Sulphur Bridging Atoms

The inversion barrier of the TiS5 ring in DI(η5-cyclopentadienyl)titanium pentasulphide

Determination of the separate barrier energies for six-membered ligand ring reversal and pyramidal sulphur inversion in complexes of palladium(II) and platinum(II). A dynamic hydrogen-1 and carbon-13 nuclear magnetic resonance study

Effect of variation in ligand ring size upon the inversion barrier at sulphur in complexes of palladium(II) and platinum(II). A dynamic hydrogen-1 nuclear magnetic resonance study