Sterically demanding ligands and their effect on the structure and reactivity of main group metal complexes

Abstract

The effects of adding steric bulk to the ligands of main group organometallic complexes are examined in this dissertation. First, bulky allyl complexes of beryllium and magnesium, using the 1,3-bis(trimethylsilyl)allyl ligand, are explored, which results in the first structurally authenticated allyl complex of beryllium as well as the first structurally authenticated π-allyl complex of magnesium. In addition, spectroscopic and DFT investigations of these and related complexes are presented.

In addition, it was determined that a commonly used preparation of Ca[N(SiMe3)2]2 involving the reaction of potassium bis(trimethylsilyl)amide with CaI2 can produce material that contains substantial amounts of potassium, probably in the form of a calciate such as K[Ca{N(SiMe3)2}3]. This possibility was confirmed with density functional theory calculations and the potassium calciate was synthesized and structurally authenticated. Discussion of the 1H NMR spectrum of deliberately doped solutions of Ca[N(SiMe3)2]2 with potassium bis(trimethylsilyl)amide is presented in detail.

Furthermore, treatment of the phosphonium salt [Me(t-Bu)P(C5Me4H)2]I with 2 equiv of KH produces the coordination polymer {K[Me(t-Bu)P(C5Me4)2](thf)}∞. If the phosphonium salt reacts with a single equivalent of KH followed by Ca[N(SiMe3)2]2, the calcium complex [Me(t-Bu)P(C5Me4)2]CaN(SiMe3)2 is produced, which is structurally related to Cp′2LnX organolanthanides. Density functional theory studies of the H3E (E = C, Si, P)-substituted cyclopentadienyl ring indicate that the energy required for out-of-plane bending of the substituent decreases in the order H3C > H3Si > H3P. Preliminary work towards the synthesis of an allyl-containing phosphonium-bridged ansa complex is also presented.

Finally, arsenic and antimony triiodide react with three equiv of Na[C5Me4H] in THF to form the yellow tris(tetramethylcyclopentadienyl) derivatives M(C5Me4H)3. When equimolar amounts of SbI3 and Na[C5Me4H] react in THF, the orange diiodo species Sb(C5Me4H)I2 is produced. The effect on the complexes of the methylated cyclopentadienyl rings varies from minimal to substantial. A single crystal X-ray structure of M(C5Me4H)3 reveals three σ-bound rings with strongly localized bonding. The diiodo complex displays an η3-bound ring and forms a coordination polymer in the solid state, with ordering driven by intermolecular I…I´ and Me…Me´ van der Waals attractions. Spectroscopic and DFT investigations of the compounds are also presented.