This thesis describes the chemistry of heavier analogues of alkenes, including their synthesis, properties, and reactivity.
Chapter 1. The chemistry of heavy alkenes (i.e. containing a double bond between elements with a principal quantum number n > 2) is introduced and compared to their ubiquitous carbon analogues. Using the isolobal analogy, the substitution of carbon for a pnictogen element in alkenes is discussed. Finally, the synthetic routes to compounds with E=Pn double bonds are described and their reactivity compared.
Chapter 2. The reactivity of Ge=P and Sn=P double bonds towards substrates containing E–H bonds (E = N, O, Si) is compared. The hydroelementation reaction products are fully characterised and the trends in reactivity rationalised. The observation of reactivity as base-stabilised phosphinidenes is probed in detail, targeting phosphinidene metathesis and transfer reactions towards a range of substrates.
Chapter 3. Improved methods are described for the synthesis of low-valent nucleophiles commonly used in main-group chemistry. For the gallium(I) carbenoid Ga(DippNacNac), “GaCp” solutions are used as an alternative source of gallium(I) ions, while the alkyl tetrylenes E[CH(SiMe3)2]2 (E = Ge, Sn) are prepared by salt metathesis with a magnesium alkyl in toluene or Et2O, respectively. The synthetic challenges of previous methods are examined and compared to the modified procedures, which provide more consistent access to these useful compounds.
Chapter 4. A trigonal planar zinc phosphaketene complex can be rapidly prepared by salt metathesis with [Na(diox)0.32][PCO]. Nucleophiles with a small steric profile (e.g. PMe3) react to form Lewis adducts via coordination to the zinc centre. Under photolytic conditions, decarbonylation proceeds with E[CH(SiMe3)2]2 (E = Ge, Sn) via a transient zinc phosphinidene to afford novel zinc phosphatetrylenes. The propensity of phosphaketenes to decarbonylate under chemical or photolytic conditions is investigated by examination of solid-state bond metrics.
Chapter 5. The cobalt phosphaketene complex (DippPDI)Co(PCO) reacts with Sn[CH(SiMe3)2]2 to afford a novel cobalt phosphastannene complex which is unstable at room temperature. The presence of a carbonyl moiety at the cobalt centre enables base-stabilised phosphinidene reactivity towards metal halides by phosphaketene transfer. With amines, addition across the Sn=P bond was observed followed by Co–P bond cleavage.
Chapter 6. The synthesis of phosphaketene complexes using the group 10 elements was investigated. A platinum phosphaketene could be observed spectroscopically but was prone to rapid decarbonylation at room temperature and could not be isolated. Careful modification of the metal-
bound ligand was used to enable the isolation of a stable palladium phosphaketene (6.5), which was shown to react with Ge[CH(SiMe3)2]2 under photolytic conditions to afford an isolable phosphagermene.
germanium
,phosphinidene
,transition metal
,amine
,multiple bond
,tin
,gallium
,phosphorus
