A synthetic, spectroscopic and structural examination of phosphorus, arsenic and antimony peri-substituted acenaphthenes

Abstract

Donor–acceptor complexes have been known for over a century and enjoy a long list of applications in chemistry. In this thesis, the dative interaction between phosphorus and its two heavier congeners, arsenic and antimony, are explored. Utilising peri-substitution atoms can be forced in close proximity to one another, resulting in a repulsive (nonbonding) interaction or an attractive (bonding) interaction. Hence, peri-substitution can be used to support traditionally ephemeral species. A range of phosphorus, arsenic and antimony containing peri-substituted compounds were synthesised and characterised using multi-nuclear NMR, mass spectrometry, elemental microanalysis and single crystal X-ray diffraction. The reduction of a peri-substituted dichloroarsine, led to the formation of a primary arsine, which underwent spontaneous elimination of hydrogen gas forming the first structurally characterised cyclic arsanylidene–σ⁴–phosphorane, the formation of which is essentially thermoneutral. With no sterically demanding groups shielding the arsenic atom, the reactivity and spectroscopic characteristics of this compound were explored through reactions with selected metal complexes. Reaction of the arsanylidene–phosphorane with a limited amount of oxygen reveals arsinidene–like reactivity via the formation of cycloarsines, supporting the formulation that the bonding can be described as a Lewis base–stabilised arsinidene R₃P→AsR. A series of phosphine–stibine and phosphine–stiborane peri-substituted acenaphthenes containing all permutations of pentavalent groups –SbCl[sub]nPh[sub](4-n) as well as trivalent groups –SbCl₂, –Sb(R)Cl, and –SbPh₂ (R = Ph, Mes), were synthesised and characterised by multi-nuclear NMR, MS, microanalysis and X-ray crystallography. The bonding in these species was studied by DFT computational methods. The P–Sb dative interactions range from strongly bonding to nonbonding as the Lewis acidity of the Sb acceptor is decreased. Unexpectedly, the phosphine–stiborane complexes represent the first examples of σ⁴P→σ⁶Sb structural motif. A study of unsymmetrical bis(phosphino)acenaphthenes showed the presence of a 3c–4e interaction, supported by the short P∙∙∙P distances and the large J[sub](PP) through-space couplings. Severely strained bis(sulfides) of the unsymmetrical phosphines experience pronounced displacements of the exocyclic peri-atoms. The resulting nonbonded intramolecular P∙∙∙P distances (ca. 4.05 Å) are among the largest ever reported peri-separations, independent of the heteroatoms involved. In addition, three metal complexes with square planar, tetrahedral and octahedral geometry are reported. In all three cases, the acenaphthene backbone is distorted to a greater extent than in the free bis(phosphine) but notably less than in the bis(sulfides).