Publication

Reactivity and fluxionality of late transition metal cluster compounds

Zoltan Beni
2004
Theses

Abstract

The first part of this work deals with oxidative addition reactions of the triangulo platinum cluster [Pt3(μ-CO)3(PCy3)3]. Reactions with the electrophilic molecules ICH2CN and X2 (X = I and Br) and with the weakly polar reagent Ph3SnH have been studied. All three reactants convert the starting cluster firstly to novel 44-electron clusters probably via a SN2 mechanism. In the case of ICH2CN the adduct [Pt3(μ-CO)3(PCy3)3(I)(CH2CN)] is the first example where a Pt(II)L3 moiety is bonded to two Pt(0)L units via direct metal-metal bonds. A similar adduct was observed in the oxidative addition of Ph3SnH to the starting cluster, e.g. [Pt3(SnPh3)(μ-CO)3(PCy3)3H] which is the first reported neutral hydrido Pt-Sn cluster. With elementary halogens oxidative addition is followed by nucleophilic substitution of a CO ligand giving adducts [Pt3X(μ-CO)2(μ-X)(PCy3)3] (X = I, Br). Excess of reactants led to fragmentation of these adducts giving Pt(I) dimers and Pt(II) monomers. The observed trends in the nuclear spin-spin coupling constants in Pt(I) dimers have been reproduced by computation at the DFT level. The second part reports novel synthetic routes for pentanuclear platinum cluster compounds starting from trinuclear ones. The first complete NMR characterization of these Pt5 phosphino-carbonyl clusters was achieved as well. The final part of our work deals with CO scrambling processes in tetranuclear iridium and rhodium carbonyl clusters as studied by variable pressure NMR. The two major processes are the 'merry-go-round' and the 'change of basal face' which may be distinguished by the sign of the activation volume, negative for the former, positive for the latter process. On the basis of a theoretical study at the DFT level, transition state structures of the 'change of basal face' were proposed in the case of Ir2Rh2(CO)12 and Ir4(μ-SO2)(CO)11. These transition state structures have larger molecular volumes compared to those of ground state geometries in accordance with the experimentally determined, positive values of activation volume for this fluxional process.

Official source

https://infoscience.epfl.ch/entities/publication/cf22181e-5624-4da9-925b-1d357b050332

Zoltan Beni
2004
Theses

Abstract

Official source

https://infoscience.epfl.ch/entities/publication/cf22181e-5624-4da9-925b-1d357b050332

Related concepts (32)

Nucleophilic substitution

In chemistry, a nucleophilic substitution is a class of chemical reactions in which an electron-rich chemical species (known as a nucleophile) replaces a functional group within another electron-deficient molecule (known as the electrophile). The molecule that contains the electrophile and the leaving functional group is called the substrate.R. A. Rossi, R. H. de Rossi, Aromatic Substitution by the SRN1 Mechanism, ACS Monograph Series No. 178, American Chemical Society, 1983. .

Nucleophilic aromatic substitution

A nucleophilic aromatic substitution is a substitution reaction in organic chemistry in which the nucleophile displaces a good leaving group, such as a halide, on an aromatic ring. Aromatic rings are usually nucleophilic, but some aromatic compounds do undergo nucleophilic substitution. Just as normally nucleophilic alkenes can be made to undergo conjugate substitution if they carry electron-withdrawing substituents, so normally nucleophilic aromatic rings also become electrophilic if they have the right substituents.

SN2 reaction

DISPLAYTITLE:SN2 reaction The SN2 reaction is a type of reaction mechanism that is common in organic chemistry. In this mechanism, one bond is broken and one bond is formed in a concerted way, i.e., in one step. The name SN2 refers to the Hughes-Ingold symbol of the mechanism: "SN" indicates that the reaction is a nucleophilic substitution, and "2" that it proceeds via a bi-molecular mechanism, which means both the reacting species are involved in the rate-determining step.

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