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The chemistry of platinum complexes and hydrosilation.

Chan, Danny (1999) The chemistry of platinum complexes and hydrosilation. PhD thesis, University of York.

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Abstract

This thesis describes the study of a series of platinum complexes, with particular emphasis towards hydrosilation. Platinum bis(phosphine) azodicarbonyl complexes Pt(PRI 3)2(R20CNNCOR2) (RI = Ph, Me; R2 = Ph, Me, OEt, Pri) were synthesised and studied. Multinuclear NMR spectroscopy on Pt(PRI3)2(R20CNNCOR2) revealed that the dicarbonyl substituted azo ligand is co-ordinated asymmetrically, consistent with a five membered, Pt-N-N-C-O ring. The crystal structure of Pt(PPh3)2(Pri02CNNC02Pri) shows that the co-ordination sphere of platinum is essentially square planar and co-planar with the five-membered, Pt(1)-0(1)-C(5)-N(2)-N(1) ring. The Pt(PRI 3)lR20CNNCOR2) complexes show sensitivity towards chlorinated solvents (CH2CI2, CHCI3) under photolysis conditions forming the corresponding platinum bis(phosphine) dichloride complexes; the same products are formed in a slower thermal reaction but only for complexes with azodicarboxylate ligands. Complexes with azodicarboxylate ligands also react photochemically with ethylene in ds-THF yielding Pt(PPh3)2(C2H4) but the azodiacyl analogues are inert in this respect. Azodicarboxylate compounds R02CNNC02R (R = Et, Pri, But) are inhibitors of the catalytic activity of [(Pt {174 _(CH2=CHSiMe2hO }h {.u-( CH2=CHSiMe2)20}] for the hydrosilation reaction. The inhibited species can be decomposed thermally or photoch~mically to give active hydrosilation catalysts. It was found that the bulky azo compound But02CNNC02But was the least effective inhibitor of [(Pt{ 174 - '(CH2=CHSiMe2hO} )2(P-( CH2=CHSiMe2)20)]. The photochemistry of platinum bis(phosphine) malonates and phthalates was found to be limited, and their reactivities were much lower compared to the analogous oxalate complexes. Silyl hydride complexes, cis-Pt(PCY3)2(H)(SiR3), were synthesised from the reaction of Pt(PCY3)2 and the corresponding silane. These complexes were undergo dynamic exchange in solution. Two exchange processes were identified; the first involves mutual phosphine exchange, i.e. positional interchange between the hydride and the silyl ligands. The second process occurs at higher temperatures (above 290 K) and involves the elimination and re-addition of the silane ligand HSiR3. Thermodynamic and activation parameters are obtained for cis-Pt(PCY3)2(SiR3) (R = Ph, SiR3 = SiMe2CH2CH=CH2, SiMe2Et). The reaction of Pt(PCY3)2 with the disilane HSiMe2(l,2-C6~)SiMe2H is thought to form a Pt(IV) bis(silyl) dihydride trigonal bipyramidal species of the form, Pt(PCY3)(H)2[SiMe2(1,2-C6~)SiMe2]' where the hydride ligands are in the axial positions. All of the platinum silyl hydride complexes studied degrade thermally to form trans-Pt(PCY3)2(H)2 at, or above, room temperature.

Item Type: Thesis (PhD)
Keywords: Silicon hydrides; Azo complexes; Dynamic NMR
Academic Units: The University of York > Chemistry (York)
Identification Number/EthosID: uk.bl.ethos.301683
Depositing User: EThOS Import (York)
Date Deposited: 09 Nov 2016 15:00
Last Modified: 09 Nov 2016 15:00
URI: http://etheses.whiterose.ac.uk/id/eprint/14173

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