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Abstract

The chemistry of the macrocycle PhP(CH₂SiMe₂NSiMe₂CH₂)₂PPh (abbreviated as [P₂N₂] within this thesis) with niobium(III) is explored. The paramagnetic chloride compound NbCl[P₂N₂] (1) is used as a starting material for other derivatives, such as {[P₂N₂]Nb}₂ (µ-N₂) (2) , Nb(CH₂SiMe₃)[P₂N₂] (6), and Nb(CH₂Ph)[P₂N₂ ] (9). Compound 1 forms adducts with small molecules and solvents, including CO which causes the complex to become diamagnetic. NbCl[P₂N₂] (1) reacts with KC₈ under 1 atm of N₂ to give {[P₂N₂]Nb}₂(µ-N₂) (2). Complex 2, characterized by X-ray crystallography, is found to have an end-on bound dinitrogen ligand with an N-N bond length of 1.272 (5) A . This is only the fourth niobium dinitrogen species to be structurally characterized. Reaction of 2 with 2 equivalents of Me₃N-HCl gives the original chloride 1 and 0.31 equivalents of hydrazine. Nb(CH₂SiMe₃)[P₂N₂] (6) and Nb(CH₂Ph)[P₂N₂] (9) are synthesized by reaction of chloride 1 with LiCH₂SiMe₃ and KCH₂Ph respectively. Reaction of trimethylsilylmethyl 6 with H₂ in benzene results in the formation of a cyclohexadienyl ligand complex, Nb(ƞ⁵-C₆H₇)[P₂N₂] (8). Also, reaction of compound 6 with CO results in the CO insertion and rearrangement with the trimethylsilylmethyl ligand to give an enolate complex. Compound 9 is determined to have an ƞ⁵ bound benzyl ligand. Preliminary investigations in the reaction of compound 1 with LiN(SiMe₃)₂, Mel, and KC₈ while under Ar give Nb{N(SiMe₃)₂}[P₂N₂] (4), Nb(MeI)Cl[P₂N₂] (10), and {[P₂N₂]Nb}₂ (3) respectively. Molecular structure information is given for {[P₂N₂]Nb}₂(µ-N₂)(µ-Cl) (5); the first characterized side-on bridged dinitrogen niobium complex. Studies into the elemental determinations of {[P₂N₂]Nb(µ-N₂) (2) and Nb(CH₂Ph)[P₂N₂] (9) reveal limitations in microanalysis due to the formation of stable niobium nitrides and carbides. ¹H NMR spectroscopy is successfully used for identification of all paramagnetic complexes within this thesis.