Synthesis and reactivity of group 13 phosphaethynolate complexes

Thesis

This thesis describes the synthesis and reactivity of group 13 coordination complexes of the 2-phosphaethynolate anion (PCO–). The synthesis and characterization of a stable phosphaethynolatoborane, [B]OCP ([B] = N,N′-bis(2,6-diisopropylphenyl)-2,3-dihydro-1H-1,3,2-diazaboryl), is described. This compound represents the first main-group, oxygen-bound isomer of the 2-phosphaethynolate anion to be structurally authenticated. The subsequent cyclisation chemistry of this compound was explored.

The reactivity of [B]OCP with a number of neutral and anionic nucleophiles was explored, the reaction outcome was found to be dependent on the properties of the nucleophile employed. Addition of catalytic amounts of tbutyl-isocyanide induced isomerisation to yield the linkage isomer, [B]PCO. The mechanism of this conversion was explored experimentally and computationally.

The nucleophilicity of [B]OCP was also explored, its steric properties allow access to a series of tungsten trisphosphaalkyne carbonyl complexes. The reaction of [B]OCP with tris(pentafluorophenyl)borane demonstrated an increase in nucleophilicity with respect to the alkyl-substituted tert-butyl phosphaalkyne. In an attempt to access the cyaphide anion, CP–, the reduction chemistry of [B]OCP was explored with the aim to selectively cleave the O–C bond. The reaction outcome is dependent on the reducing agent employed, however selectivity for the desired bond was poor, giving rise to complex product mixtures. It was possible to isolate and partially characterise a magnesium cyaphide complex.

Next, a series of gallium phosphaketenes were synthesised. Both photolytic and chemical decarbonylation processes were explored, allowing access to base stabilised phosphinidenes. The ligand displacement methodology was expanded on to allow access to a compound with a gallium phosphorus double bond.

Authors: Wilson, D

• DOI: 10.5287/ora-1zzjkkzv5
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: boron; low-valent; main group chemistry; phosphorus
• Subjects: Chemistry, Inorganic