UC Davis

The purpose of the first part of this thesis is to describe how dispersion energy donor ligands derived from 1-bromo-2,4,6-tricyclohexylbenzene (BrC6H2-2,4,6-Cy3) can effect the stabilization of low-valent transition metal and main group compounds. Thus, reactions of 2,4,6-tricyclohexylphenol with [M{N(SiMe3)2}2]2 (M = Mn(II), Fe(II), Co(II)) at room temperature in hexanes afforded the dimeric species [M(OC6H2-2,4,6-Cy3)2]2 (M= Mn(II), Fe(II), Co(II)) in high yield as crystalline species. Use of the sterically similar ligand HOC6H3-2,6-Pri2 (Pri = isopropyl) gave trimeric species [M(OC6H3-2,6-Pri2)2]3 (M = Fe(II), Co(II)) and implicates the dispersion energy donor capabilities of the phenol HOC6H2-2,4,6-Cy3 as the driving force for the formation of dimeric rather than trimeric species. While the Mn(II) and Fe(II) aryloxides are thermally stable, the corresponding Co(II) derivative rearranges to form a dimeric Co(II) semiquinone complex when heated under dynamic vacuum to temperatures above ca. 180 oC. Analogous reactions of HOC6H2-2,4,6-Cy3 with main group bis(trimethylsilyl)amides M{N(SiMe3)2}2 (M = Ge(II), Sn(II), and Pb(II)) gave the dimeric tetrel(II) aryloxides [M(OC6H2-2,4,6-Cy3)2]2. For Ge(II), stirring the reaction for longer than ca. 30 minutes at room temperature in hexane allows the isolation of the rearranged Ge6O8 cluster [Ge6(μ3-O)4(μ2-OC6H2-2,4,6-Cy3)4](NH3)0.5 which traps in situ generated ammonia in non-coordinating positions through the dispersion energy donor interactions provided by the cyclohexyl groups of -OC6H2-2,4,6-Cy3.The arylthiolates [M(SC6H2-2,4,6-Cy3)2]2 (M = Ge(II), Sn(II), Pb(II)) were synthesized in an analogous manner to the tetrel(II) aryloxides by the addition of HSC6H2-2,4,6-Cy3 to the M(II) bis(trimethylsilyl)amides. They are the first examples of dimeric M(II) arylthiolates of Ge(II) and Sn(II). Also, the Pb(II) species is the first arylthiolate isolable in the absence of donor ligands or Lewis bases. Previous attempts to obtain a Ge(II) arylthiolate using the thiol HSC6H2-2,4,6-Pri3 gave the Ge(IV) hydride HGe(SC6H2-2,4,6-Pri3)3. DFT calculations revealed that an increase in the dispersion energy stabilization provided by -SC6H2-2,4,6-Cy3 in the species [Ge(SC6H2-2,4,6-Cy3)2]2 prevents the formation of a Ge(IV) hydride analogous to that observed when the thiolato ligand -SC6H2-2,4,6-Pri3 was used. A concentration dependent monomer-dimer equilibrium is evident in benzene solutions of [Ge(SC6H2-2,4,6-Cy3)2]2, despite the large increase in dispersion energy stabilization. The Ge(II) and Sn(II) arylthiolates are not isostructural with their aryloxo congeners and have a cis arrangement of the ligands in the solid state. In contrast, the Pb(II) thiolate is isostructural with the Pb(II) aryloxo congener and crystallizes with a trans arrangement of the -SC6H2-2,4,6-Cy3 ligands. The final section of this thesis provides detail on the synthesis and isolation of Ni(I) and Ni(II) bis(trimethylsilyl)amides that were isolated during pursuit of the solid-state structure of the highly unstable species Ni{N(SiMe3)2}2. The use of the bis(trimethylsilyl)amide K{N(SiMe3)2} as transfer agent was reported to give intractable solids when reacted with NiCl2 in diethyl ether. This prompted a reinvestigation of the use of this transfer agent in the synthesis and isolation of new Ni(II) bis(trimethylsilyl)amides. The reaction of K{N(SiMe3)2} with NiI2 in Et2O gave the three new complexes [K][Ni{N(SiMe3)2}3], [K][Ni{N(SiMe3)2}2], and [K(THF)2][Ni{N(SiMe3)2}3]. The use of NiCl2(DME) (DME = 1,2-dimethoxyethane) instead of NiI2 as the nickel source gave [K(DME)][Ni2{N(SiMe3)2}3]. The isolation of the Ni(I) complexes [K][Ni{N(SiMe3)2}2] and [K(DME)][Ni2{N(SiMe3)2}3] highlights both the tendency for K{N(SiMe3)2} to function as a reducing agent and the sensitivity and unpredictable nature of the Ni(II) bis(trimethylsilyl)amido derivatives. Introduction of adventitious O2 to solutions of [K][Ni{N(SiMe3)2}2] gave the first nickel inverse crown ether (ICE) species [K2][O(Ni{N(SiMe3)2}2)2], which is one of just four known ICE complexes of the 3d metals. While the Ni(I) species can be isolated as crystalline solids from the disproportionation of the Ni(II) species, the corresponding Ni(III) products were not readily isolable under the employed reaction conditions.