Elding, Lars I.;
Kellenberger, Bruno;
Venanzi, Luigi M.
Transition Metal Complexes with Bidentate Ligands Spanning trans‐Positions. XII. Steric effects in the kinetics and mechanism of substitutions at hydride and methyl bisphosphine platinum (II) complexes
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Medientyp:
E-Artikel
Titel:
Transition Metal Complexes with Bidentate Ligands Spanning trans‐Positions. XII. Steric effects in the kinetics and mechanism of substitutions at hydride and methyl bisphosphine platinum (II) complexes
Beteiligte:
Elding, Lars I.;
Kellenberger, Bruno;
Venanzi, Luigi M.
Erschienen:
Wiley, 1983
Erschienen in:
Helvetica Chimica Acta, 66 (1983) 6, Seite 1676-1690
Beschreibung:
<jats:title>Abstract</jats:title><jats:p>Ligand substitution reactions on square‐planar platinum (II) complexes of the types <jats:italic>trans</jats:italic>‐[PtRXL<jats:sub>2</jats:sub>], <jats:italic>trans</jats:italic>‐[PtR(4‐PADA)L<jats:sub>2</jats:sub>][BF<jats:sub>4</jats:sub>], <jats:italic>trans</jats:italic>‐[PtRX(<jats:chem-struct-wrap><jats:chem-struct><jats:graphic xmlns:xlink="http://www.w3.org/1999/xlink" mimetype="image/gif" position="anchor" specific-use="enlarged-web-image" xlink:href="graphic/must001.gif"><jats:alt-text>magnified image</jats:alt-text></jats:graphic></jats:chem-struct></jats:chem-struct-wrap>) and <jats:italic>trans</jats:italic>‐[PtR(4‐PADA)(<jats:chem-struct-wrap><jats:chem-struct><jats:graphic xmlns:xlink="http://www.w3.org/1999/xlink" mimetype="image/gif" position="anchor" specific-use="enlarged-web-image" xlink:href="graphic/must001.gif"><jats:alt-text>magnified image</jats:alt-text></jats:graphic></jats:chem-struct></jats:chem-struct-wrap>)][BF<jats:sub>4</jats:sub>] R=H, Me; X=Cl<jats:sup>−</jats:sup>, I<jats:sup>−</jats:sup>; L=PEt<jats:sub>3</jats:sub>, bis(3‐trifluoromethyl‐phenyl)benzylphosphine (<jats:bold>4</jats:bold>), <jats:chem-struct-wrap><jats:chem-struct><jats:graphic xmlns:xlink="http://www.w3.org/1999/xlink" mimetype="image/gif" position="anchor" specific-use="enlarged-web-image" xlink:href="graphic/must001.gif"><jats:alt-text>magnified image</jats:alt-text></jats:graphic></jats:chem-struct></jats:chem-struct-wrap>=the <jats:italic>trans</jats:italic>‐spanning 2,11‐bis[bis(3‐trifluoro‐methylphenyl)phosphinomethyl]benzo [<jats:italic>c</jats:italic>]phenanthrene (<jats:bold>3</jats:bold>); 4‐PADA (=pyridine‐4‐azo‐4′‐(<jats:italic>N</jats:italic>, <jats:italic>N</jats:italic>‐dimethyl)aniline have been studied at 30° using stopped‐flow and conventional spectrophotometry, methanol as solvent, and 2.5 × 10<jats:sup>−2</jats:sup> <jats:sc>M</jats:sc> ionic strength (LiClO<jats:sub>4</jats:sub> as supporting electrolyte). 4‐PADA was used as indicator ligand, as its absorption spectrum differs from those spectra where it is complexed.</jats:p><jats:p>The expected steric effects of the bulky ligands, especially of <jats:bold>3</jats:bold>, on the rates and mechanisms of all the reactions studied are small. All reactions take place by the usual two‐term rate law. Noteworthy, for the complexes with the bulky ligands <jats:bold>3</jats:bold> and <jats:bold>4</jats:bold>, the direct reaction path with the entering nucleophile is predominant. There is no preference for a solvent or dissociative path. The reactivity order for the hydride complexes is <jats:italic>trans</jats:italic>‐[PtHX (PEt<jats:sub>3</jats:sub>)<jats:sub>2</jats:sub>]<<jats:italic>trans</jats:italic>‐[PtHX(<jats:bold>4</jats:bold>)<jats:sub>2</jats:sub>]<<jats:italic>trans</jats:italic>‐[PtHX (<jats:bold>3</jats:bold>)]. However, for the corresponding methyl complexes, there is some retardation by ligand <jats:bold>3</jats:bold>, probably due to an interaction between the methyl group and the hydrocarbon moiety of <jats:bold>3</jats:bold>, which inhibits the fluxional behavior of this ligand. The results have some relevance for the understanding of olefin‐insertion reactions of hydride complexes containing these phosphine ligands.</jats:p>