Hood, Thomas M. (2020) Synthesis and organometallic chemistry of rhodium and iridium complexes of macrocyclic PNP and PONOP pincer ligands. PhD thesis, University of Warwick.

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Abstract

Rigid mer-tridentate ‘pincer’ ligands are a prominent ligand class in organometallic chemistry and catalysis, conferring thermal stability and enabling a wide range of metal-based reactivity. Phosphine pincer ligands are a particularly important class, with rhodium and iridium complexes finding notable application in the activation and functionalisation of nominally inert C–H bonds.

Inspired by Brookhart’s synthesis of a rhodium(I) σ-methane complex,1 the ultimate objective of this project was to prepare a macrocyclic variant featuring a mechanically-interlocked hydrocarbon substrate as a means to kinetically stabilise coordination of an alkane to the metal. Herein the synthesis of macrocyclic variants of commonly-employed phosphine-based pincer ligands derived from lutidine (PNP-14) and 2,6-dihydroxypyridine (PONOP-14) is reported. The rhodium(I/III) and iridium(I/III) coordination chemistry of these ligands has been explored, as well as that of acyclic analogues (PNP-tBu and PONOP-tBu) to gauge the impact of the macrocyclic tether. In the first instance, 2,2’-biphenyl (biph) adducts [M(pincer)(biph)][BArF 4] (M = Rh, Ir; ArF = 3,5-(CF3)2C6H3) were prepared and their dynamic behaviour and reactivity studied.

In the case of PNP-14, reaction with [M(COD)2][BArF 4] (M = Rh, Ir) demonstrates the flexibility of the ligand, forming products with a mer-coordination mode for rhodium, but a fac-coordination mode for iridium. Both resulting complexes have been employed in the homodimerisation of terminal alkynes and this reactivity studied in detail. Notably, rhodium complexes of interlocked enynes have been prepared and their subsequent reactivity examined. Using this methodology in combination with appropriate alkynes, a PNP-14-based rotaxane and catenane have been synthesised.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QD Chemistry
Library of Congress Subject Headings (LCSH):	Ligands (Biochemistry), Rhodium compounds, Iridium compounds, Organometallic chemistry
Official Date:	November 2020
Dates:	Date Event November 2020 UNSPECIFIED
Institution:	University of Warwick
Theses Department:	Department of Chemistry
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Chaplin, Adrian
Format of File:	pdf
Extent:	vii, 237 leaves : illustrations (some colour)
Language:	eng

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