Doctor of Philosophy
Paul J. Ragogna
Chelating nitrogen based ligands are well known for their use with transition metals while their chemistry with p-block elements has been relatively underdeveloped. This thesis examines the structure, bonding and reactivity of group 15 elements supported by a pyridyl tethered 1,2-bis(imino)acenaphthene (“clamshell”) and various homo- and heteroleptic guanidinate frameworks.
The unique “clamshell” ligand contains a pendant Lewis base and has been used to support N-heterocyclic phosphenium and arsenium cations. Reactivity studies with the phosphorus analogue demonstrate the ability of the ligand to act as a Lewis base, while the phosphorus centre provides a Lewis acidic site, showing the amphoteric nature of such a molecule. Cobaltocene has been used as a new one-electron reductant in the facile, high yielding synthesis of a diaminochloroarsine supported by the “clamshell” ligand. Unfortunately this method was not suitable for all Group 15 elements and resulted in low yields for phosphorus and insoluble black material for antimony and bismuth. In the absence of a reductant the “clamshell” ligand can be used to form hypervalent donor-acceptor complexes with heavy main group elements (Sn, Sb and Bi). The addition of a salt metathesis reagent to the hypervalent Sb and Bi complexes results in base-stabilized SbCl2+ and BiCl2+ cations.
A series of diaminochlorophosphines has been synthesized with various dianionic guanidinate ligands, and their reluctancy to release a chloride ion using halide abstracting reagents has been noted. A comprehensive study of their reactivity has been completed and the following were observed: (i) that the chloride ion could be removed with the addition of a chelating base; (ii) that carbodiimide can be eliminated chemically and thermally from the four-membered ring; and, (iii) that a rare ring expansion by the insertion of a chloro(imino)phosphine into a P–N bond of the P–N–C–N framework takes place. The analogous chemistry with heavier pnictogens to form diaminochloropnictines does not occur; rather the products are diaminodichloropnictines where the guanidinate ligand is monoanionic. Halide abstraction from these molecules is facile for As and Sb and the addition of a chelating base allows for the removal of the second chloride ion to give base-stabilized dicationic species.
Brazeau, Allison L., "The Synthesis and Reactivity of New Pnictogen(III) Cations" (2012). Electronic Thesis and Dissertation Repository. 576.