Organoplatinum: Some Reaction Modes

Young, George Brent (1975) Organoplatinum: Some Reaction Modes. PhD thesis, University of Glasgow.

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The thermal decomposition of organoplatinum(ll) complexes of the type cis-L2PtAr2 and (biL)PtAr2 [Ar =C6H5, 4-Me-C6H4; L = Ph3P, (4-Me-C6H4)3P, Ph2MeP; biL = Ph2PCH2PPh2 (dpm), Ph2PC2H4PPh2 (dpe), Me2PC2H4PMe2 (dmpe)] has been studied. In the condensed phase, the thermolyses have been examined by thermal analytical techniques (DSC and simultaneous TGA/DTA) and by product analysis (GLC). The results indicate that the complexes undergo thermal disruption via a predominant primary route which involves concerted reductive elimination of the platinum-bound aryl ligands as biaryl. This process is intramolecular, and no intermolecular exchange of aryls occurs prior to, or during, decomposition. Secondary reactions which produce quantities of arene and biaryl originating from the arylphosphine ligands, and whose operation is concurrent with, but essentially independent of, the primary reductive elimination, are also observed. These data are interpreted in terms of slower reactions (subsequent to the primary process) of the species L2Pto or (biL)Pto , involving aryl- or hydride-transfer to platinum, by oxidative insertion into P-C or C-H bonds, and ultimate reductive eliminations. Although their identities remain uncertain,analysis of the glassy, red-brown decomposition residues provides more evidence for these propositions. In the presence of an added equimolar amount of the appropriate phosphine, primary concerted reductive elimination of biaryl is facilitated. The effect is most marked for complexes of dpm in presence of free ligand. This general observation is in qualitative agreement with previous predictions and is discussed in terms of nucleophilic attack at Pt(ll) by a phosphorus donor. Secondary reactions are largely, if not altogether suppressed, and this is attributable to the diminished tendency of Pt(0) to undergo the oxidative insertion sequences in higher coordination number phospbine complexes. An exception is (dpm)2Pt(0) which appears to decompose under the conditions of its formation. In this case, an additional secondary process involves rupture of the P-C-P bridge, presumably again by oxidative insertion of Pt(0) into P-C (the first such example with P-alkyl). When a phosphine different to that already present is added, there is some evidence that exchange may occur prior to the Pt-C scission processes. The thermal decomposition of these systems was, additionally, followed in toluene solution. Product analyses served to corroborate the mechanistic conclusions drawn from the condensed-phase data. Primary, concerted, intramolecular reductive elimination is followed by the same slower secondary processes. Kinetic studies showed that the primary elimination is first-order in platinum complex and that, again, reductive elimination is facilitated by the presence of free phosphine. Only the complexes cis-(Ph3P)2PtAr2 displayed sufficient lability to be extensively studied under these conditions. Such activation parameters as were determined for these systems suggested that the enhanced lability of the 4-tolylplatinum species compared with its phenyl-analogue, and that of either system in the presence of Ph3P (relative to the complex alone) may be largely due to entropy effects, interpretations of which are discussed.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Organic chemistry, Inorganic chemistry
Date of Award: 1975
Depositing User: Enlighten Team
Unique ID: glathesis:1975-78705
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 15:00
Last Modified: 30 Jan 2020 15:00

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