Veasy, Agata
(2024)
Working towards the isolation of stable organometallic alkane
complexes.
PhD thesis, University of Nottingham.
Abstract
Chapter 1
An introduction to the photochemistry of organometallic alkane and noble gas complexes, which have been the subject of this Thesis is outlined here. Time-resolved spectrometry and computational methods are also briefly described.
Chapter 2
This Chapter looks at the photochemical reactions of [Fe(CO)2(NO)2] in n-heptane, utilising time-resolved infrared spectroscopy (TRIR) with 266 nm excitation wavelength, spanning both nanosecond and picosecond timescales. On the nanosecond timescale, compelling evidence for the formation of [Fe(CO)(NO)2(heptane)] is presented. The alkane complex was found to decay with a lifetime of ca. 600-700 ns. The spectroscopic data confirming the formation of a secondary dimeric structure, [Fe2(CO)4(NO)3] in an eclipsed conformation, is also described here. The spectroscopic data obtained on the picosecond timescale is discussed. However, the formation of [Fe(CO)(NO)2(heptane)] was less evident here due to multiple overlapping species.
Chapter 3
A computational invesƟgaƟon of metal-alkane bond dissociation energies (BDEs) in cationic complexes, [CpM(CO)2(alkane)]+, where M = Fe, Ru and Os, and [CpM(CO (NO)(alkane)]+, where M = Mn or Re is described. Our findings highlighted several interesting trends in these complexes. The introduction of functional groups onto the cyclopentadienyl (Cp) ligand resulted in weaker metal-alkane interactions in both group 7 and group 8 complexes. Ruthenium alkane complexes were also found to have the lowest bond dissociation energies in all group 8 complexes, which deviates from reported trends.
[CpRe(CO)(NO)(cyclopentane)]+ was found to have the highest BDE of 110 kJ mol-1, which is a remarkable increase in comparison to its neutral analogue[CpRe(CO)2(cyclopentane)]. We have also synthesised a range of cationic precursor complexes as part of this Chapter.
Chapter 4
This Chapter delves into the investigation of the structural optimisation and metal-alkane bond dissociation energies (BDEs) using Density Functional Theory (DFT) in a series on group 5, 6, 7, 8, and 9 complexes, with a particular focus on the impact of nitrosyl ligand introduction on the strength of metal-alkane interaction. The introduction of the nitrosyl ligand generally strengthens the metal-alkane interaction, leading to higher BDE values across all investigated nitrosyl complexes, with increases ranging from 13 to 76 kJ mol-1. Trends seen in complexes within group 5 to 9 were identified. An equation was also derived to predict rate constants in CO-substitution of organometallic alkane complexes based on their calculated BDEs.
Chapter 5
A concise overview of the findings obtained in this Thesis is provided in this Chapter. Additionally, the summary of the implications of these findings for future directions is summarised here.
Chapter 6
An overview of the experimental methodologies, spectroscopic apparatus and analytical techniques employed throughout this Thesis is provided.
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