Synthesis and analysis of low-valent NHC supported nickel complexes

This thesis focuses on the synthesis of N-heterocyclice carbene (NHC) supported nickel complexes and their reactivity in bond-breaking and bond forming reactions. The body of this work discusses isolation of (NHC)Nickel(I) alkoxides and their subsequent chemical transformations into different (NHC)Nickel complexes. First, we demonstrate that (IDipp)Ni(I) hexamethyldisilazide (IDipp = 1,3-bis(2,6- diisopropylphenyl)-imidazole-2-ylidene) cleanly deprotonates neopentyl and methyl alcohols to form the corresponding (IDipp)Ni(I) alkoxides. Both alkoxides form dimeric solid-state structures. Abstraction of one alkoxide fragment forms the corresponding alkoxy-bridged dinickel cation species with an inner sphere bridging triflate. Abstraction of both neopentoxide fragments result in formation of (IDipp)Ni(OTf)(Et2O), a synthetic equivalent of (IDipp)Ni(I)+. Next, we show that the reaction of [(IDipp)Ni)]2(μ-ONp)(μ-OTf) with pentamethyldisiloxane results in isolation of {[(IDipp)Ni]2(μ-H)}[OTf]. Deprotonation of this hydride complex results in formation of [(IDipp)Ni]2, further supporting the interpretation of {[(IDipp)Ni]2(μ-H)}+ as proton bridging two (IDipp)Ni(0) fragments. The reactivity of {[(IDipp)Ni]2(μ-H)}[OTf] with alkyl nitriles was further studied by 1H NMR. [(IDipp)Ni(CN)2]4, a product of the reaction between {[(IDipp)Ni]2(μ-H)}+ with alkyl nitriles, can be synthesized by the reaction of [(IDipp)Ni(Cl)]2(μ-Cl)2 with trimethylsilyl cyanide. Subsequently, we show that the mixed valent complex, {[(IDipp)Ni]2}+ [OTf]− can be synthesized by combining synthetic equivalents of (IDipp)Ni(0) and (IDipp)Ni(I)+. Computational studies of this complex classify it as Robin-Day Class II. Cyclic voltammetry shows that the [Ni2]2+/+ and [Ni2]+/0 couples are reversible. The reactions of {[(IDipp)Ni]2}+ [OTf]− with CO and NO form mononuclear products and the reaction of {[(IDipp)Ni]2}+ [OTf]− with aryl bromide leads to predominant C-arylation of IDipp. Lastly, we show our pursuit of the first reported (NHC)Ni(I) fluoride. The reaction of [(IDipp)Ni)]2(μ-ONp)(μ-OTf) with benzoyl fluoride resulted in isolation of crystals of {[(IDipp)Ni]2(μ-F)(μ-C7H8)}[OTf] suitable for study by X-ray diffraction. Despite varying synthetic attempts, bulk isolation of {[(IDipp)Ni]2(μ-F)(μ-C7H8)}[OTf] was ultimately unsuccessful. Next, we show that {[(IDipp)Ni]2(μ-PPh2)}[OTf] can be isolated from the reaction of [(IDipp)Ni)]2(μ-OMe)(μ-OTf) with (trimethylsilyl)diphenylphosphine. We also show that (IDipp)Ni(C6H6) reacts with acyl fluorides to form the corresponding [(IDipp)Ni(R)(μ-F)]2 complexes. Lastly, we show that sodium naphthalenide can reduce [(IDipp)Ni(μ-Cl)]2 to form a synthetic equivalent of (IDipp)Ni(0).

Level thesis:degree_level

Doctoral

Department dc:contributor.department

Chemistry and Biochemistry

Grantor dc:publisher

Georgia Institute of Technology

Year dc:date.issued

2023

Author dc:creator

• Dodd, Neil Alexander

Advisor dc:contributor.advisor

• Sadighi, Joseph P.

Committee members dc:contributor.committeemember

• Soper, Jake D.
• France, Stefan
• La Pierre, Henry
• Walton, Krista

• NHC
• Nickel
• organometallic
• inorganic
• low-valent
• alkoxide
• hydride
• mixed-valent

Language dc:language.iso

en_US

Handle dc:identifier.uri

https://hdl.handle.net/1853/73199

OAI identifier oai:identifier

oai:repository.gatech.edu:1853/73199