Stabilizing Metal-Alanes and Metal-Metal Multiple Bonds to Effect Small Molecule Transformations

Abstract

The objective of this dissertation is to synthesize a double-decker ligand framework, N(o-(NHCH2P(iPr)2)C6H4)3, capable of supporting various bimetallic species wherein one metal site is protected and trans to the open coordination site on the second. By systematically varying both metal sites, intrinsic properties of different metal-metal bonds can be elucidated and used to activate small molecule substrates. In the second chapter, this ligand is shown to support a series of metallalumatranes with inverse dative bonds between aluminum and nickel, cobalt, or iron. The cobalt- and iron-alane complexes also bind and modestly activate dinitrogen. In the third chapter, the zerovalent iron and cobalt centers are shown to be amenable to one-electron reduction, yielding subvalent iron(1-) and cobalt(1-) centers. Furthermore, the anionic iron-alane is shown to undergo a four-electron reduction at dinitrogen in the presence of the silylating reagent 1,2-bis(chlorodimethylsilyl)ethane, demonstrating multi-electron reduction of terminally ligated dinitrogen at a single iron site. In the fourth chapter, investigations of iron- chromium complexes show the first isolable example of metal-metal multiple bonding between different first row transition metals. In the fifth chapter, manganese-chromium and dichromium complexes are shown to engage in triple to quintuple bonding, generating extremely short metal-metal bonds. A series of isoelectronic complexes is prepared that contain Cr2, MnCr, and FeCr cores. Investigation into these complexes shows that the strength of the isoelectronic chromium-metal interaction increases as the paired metals become more similar, i.e., FeCr < MnCr < CrCr.