Synthesis and Study of New Late Metal Complexes Featuring N-Phosphinoamidinate Ligands

Abstract

N-Phosphinoamidine/amidinate (P,N) ligands have recently been shown to be highly effective for the selective chromium-catalyzed tri-/tetramerization of ethylene. Since this initial report, a joint collaboration between the Chevron-Phillips Chemical Company (CPChem) and the Stradiotto/Turculet research groups at Dalhousie University has reported on the iron-catalyzed hydrosilyation of carbonyl compounds and the cobalt-catalyzed hydroboration of alkenes using (P,N)M(N(SiMe3)2) complexes (M = Fe, Co).

These monoanionic, bidentate P,N-chelating ligands offer a mix of hard and soft donors and the anionic charge promotes tight binding to facilitate the isolation of unusual low-coordinate late metal complexes. The propensity of such species to exhibit unusual bonding motifs, unprecedented reactivity, and their applications in catalysis is the focus of this work. Futhermore, the chemistry of monoanionic P,N-ligands in general is surprisingly underexplored.

Encouraged by the exceptional reactivity of the first-row transition metal complexes mentioned above, the initial goals of this thesis were to explore the synthesis and reactivity of low-coordinate second and third-row transition metal complexes. Coordinatively unsaturated Cp*RuLn complexes have a well-established track record of exhibiting new and unusual metal-centered reactivity with diverse applications in organic synthesis. As such, considerable focus continues to be directed toward developing new and isolable classes of such complexes and exploring their stoichiometric reactivity. In this regard, the synthesis and reactivity of 16-electron Cp*Ru(II) (Cp* = η5-C5Me5) complexes supported by N-phosphinoamidinates is detailed herein.

Intrigued by the ability of related (nacnac)Pt species in supporting low-coordinate reactive complexes, structurally and electronically unique low-coordinate Pt(II) complexes supported by N-phosphinoamidinate ligands were developed in pursuit of unusual bonding motifs and reactivity. The synthesis and reactivity of an isolable, three-coordinate, neutral, 14-electron Pt(II) species along with the synthesis and reactivity of a Pt(II)-η3-benzyl complex that undergoes an unprecedented benzylic borylation reaction is also detailed herein.

Within the spirit of moving toward the use of relatively abundant and inexpensive metals in catalysis, and building on the previous advances in this area by the CPChem/Turculet/Stradiotto team, this thesis also examines the development of the manganese complex (P,N)Mn(N(SiMe3)2). The remarkable ability of this complex to reduce amides, ketones, aldehydes, and esters under mild conditions is described herein.