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Title: Transition metal cyaphides : synthesis, reactivity, and electrochemistry
Author: Leech, Matthew Christopher
ISNI:       0000 0004 7657 6903
Awarding Body: University of Sussex
Current Institution: University of Sussex
Date of Award: 2019
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This thesis describes the synthesis, characterisation, and electrochemical behaviour of a series of transition metal cyaphide complexes, with the aim of understanding how the introduction of low-coordinate phosphorus fragments into through-conjugated organometallic systems affects their electronic structure. Formation of mono-metallic ruthenium cyaphide complexes, trans-[Ru(C≡P)(C≡CR)(dppe)2], via the corresponding η1-coordinated phosphaalkyne complexes, was achieved alongside the synthesis of the analogous carbocentric mixed acetylide complexes trans- [Ru(C≡CH)(C≡CR)(dppe)2]. This allowed the first direct comparison of ligated cyaphide and acetylide, revealing contrasting effects on the electrochemical behaviour when compared to their parent chloride complexes. This was supplemented by the synthesis of the systems trans- [RuH(C≡E)(dppe)2] (E = P, CH, N), facilitating the exploration of the isolobal analogy between carbon and phosphorus, alongside the relationship between multiply-bonded pnictogens. Multimetallic cyaphide complexes were also prepared, featuring either one or two cyaphide fragments. The electronic structure of these hetero- and homo-bimetallic complexes was explored using both computational and experimental investigations, with the latter achieved using UV-Vis spectroscopy and cyclic voltammetry. It was found that introduction of cyaphide greatly reduced the stability of the mixed-valence state resulting from mono-oxidation, however, complete destabilisation of this species was not observed. Furthermore, DFT calculations revealed that the HOMOs still exhibited the expected out-of-phase mixing of the ligand and metal π-orbitals. The synthesis of transition metal cyaphide complexes featuring less sterically-encumbering ancillary ligand sets was also pursued. This resulted in the successful synthesis of the complexes [MCpR'(dppe)(η1-P≡CSiMe3)]+ (M = Ru, Fe; R' = H, Me), with variable temperature NMR, and X- ray diffraction studies used to ascertain the coordination mode of the phosphaalkyne. Attempts to convert to the corresponding cyaphide complexes were undertaken using a variety of desilylating reagents, however, the identity of the final product appeared to be dependent on the base used. Attempts to oxidise the phosphorus centre of the ligated cyaphide from P(III) to P(V) using different chalcogen sources were undertaken, however, only sources of oxygen or sulfur were observed to undergo reactivity. Lastly, reactions with BR''3, X2 (X = Br, I), and PhICl2 have shown some evidence that reactivity of the C≡P moiety via either the lone pair or C≡P π-system is possible, opening up new avenues for further cyaphide chemistry.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD0411 Organometallic chemistry and compounds