Abstract
This thesis comprises four chapters derived from publications and a final body of research which is as yet unpublished, all centred on the chemistry of N-heterocyclic carbene (NHC) supported copper(I) p-block element complexes, with particular emphasis on the use of ringexpanded NHCs (RE-NHCs).Chapter one summarises the isolated and, in some cases, structurally characterised copper(I) stannanide complexes, along with all reported examples of copper(I) germanide complexes. This chapter establishes the wider context of the research presented in chapters two and three.
Chapter two details the characterisation of three RE-NHC supported copper(I) triphenylstannanides, (RE-NHC)CuSnPh3 (RE-NHC = 6-Mes, 6-Dipp, 7-Dipp), which were synthesised from the reaction between (RE-NHC)CuOtBu and Ph3SnH. Reactions of (6-Mes)CuSnPh3 with di-p-tolyl carbodiimide, phenyl isocyanate and phenyl isothiocyanate, generated the corresponding copper(I) benzamidinate, benzamide, and phenyl isothiocyanate, respectively, with concomitant elimination of (SnPh2)n. Attempts to extend this phenylation reactivity into a catalytic regime were unsuccessful. Instead, copper(I) catalysed dismutation of Ph3SnH was observed, resulting in the formation of various perphenylated tin oligomers, H2, and a metallic material postulated to be Sn(0). Using in situ NMR spectroscopy and mass spectrometry, mechanistic insight into this phenylation reaction was provided.
In chapter three, four NHC-copper(I) triphenylgermanide complexes, (NHC)CuGePh3 (NHC = SIMes, IPr, 6-Mes, 6-Dipp) were synthesised from the reaction between (NHC)CuX (X = OMe, OtBu, Mes) and Ph3GeH. Computational analysis of (IPr)CuGePh3 indicated nucleophilicity of the [GePh3] group. This nucleophilicity was observed in reactions of (IPr)CuGePh3 with p-block halides, resulting in the formation of new Ge–Sn and Ge–P bonded compounds. Additionally, π-bond insertions of (IPr)CuGePh3 with tBuNCS, CS2, and PhNCO resulted in the isolation of three new germyl-substituted carboxylate derivatives, (IPr)CuXC(Y)GePh3 (X = S, NPh; Y = S, NtBu, O). π-Bond insertions of (IPr)CuGePh3 with phenyl acetylene resulted in the formation of both the Markovnikov and anti-Markovnikov insertion products. The selectivity of this reaction was investigated using NMR spectroscopy and computational analysis. Finally, using triphenyl germane and a
catalytic amount of (SIMes)CuOtBu, a series of tin/germanium cross-couplings with tin(IV) alkoxides and hydrogermylation reactions of Michael acceptors and activated alkenes were successfully carried out.
Chapter four presents the characterisation of a copper(I) complex which features a terminal acyclic boryl ligand, (6-Dipp)CuB(OMe)2. This complex was synthesised from the σ-bond metathesis between (6-Dipp)CuOtBu and B2(OMe)4. Reaction of (6-Dipp)CuB(OMe)2 with CO2 resulted in the formation of (6-Dipp)CuOB(OMe)2 with concomitant elimination of CO. The catalytic deoxygenation of CO2 was achieved using 10 mol% (6-Dipp)CuB(OMe)2. πBond insertions of (6-Dipp)CuB(OMe)2 with ethene and diphenyl acetylene were reported, resulting in the formation of the corresponding insertion products, (6-Dipp)CuC(R)C(R)B(OMe)2 (R = H2, Ph). Reaction of (6-Dipp)CuB(OMe)2 with LiNMe2 resulted in salt metathesis at boron, yielding a second copper(I) complex featuring an acyclic boryl ligand, (6-Dipp)CuB(OMe)(NMe2). π-Bond insertion of this complex with diphenyl acetylene generated the corresponding copper(I) vinyl product, (6-Dipp)CuC(Ph)=C(Ph)B(OMe)(NMe2). Notably, this complex was also synthesised from the salt metathesis between (6-Dipp)CuC(Ph)C(Ph)B(OMe)2 and LiNMe2. Computational analysis revealed the electronic structures of (6-Dipp)CuB(OMe)2 and (6-
Dipp)CuB(OMe)(NMe2) are similar to (6-Dipp)CuBpin.
In chapter five, a ring-expanded copper(I) bis(trimethylsilyl)phosphide complex, (6-Dipp)CuP(SiMe3)2, was synthesised from the reaction between (6-Dipp)CuOtBu and P(SiMe3)3. Reaction of this complex with CO2, resulted in the formation of a copper(I) phosphaethynolate, (6-Dipp)Cu(PCO), through the elimination of (Me3Si)2O. The reaction between (6-Dipp)CuP(SiMe3)2 and 13CO2 was monitored using in situ NMR spectroscopy. Observation of an insertion intermediate in this reaction, (6-Dipp)CuP(SiMe3) 13C(O)OSiMe3, provided mechanistic insight. Similar insertion intermediates were observed in reactions of (6-Dipp)CuP(SiMe3)2 with isocyanates, (6-Dipp)CuP(SiMe3)C(NR)OSiMe3 (R = Ph, tBu, iPr). In the reactions with PhNCO and tBuNCO, spontaneous elimination of (Me3Si)2O from the corresponding insertion intermediates in the presence of excess isocyanate led to the formation of the corresponding [2+2] cycloaddition products, (6-Dipp)CuP{C(O)N(R)C(R)} (R = Ph, tBu). Thermolysis of (6-Dipp)CuP(SiMe3)C(NiPr)OSiMe3 suggested reversibility in the insertion of iPrNCO, through the formation of (6-Dipp)CuP{C(O)N(iPr)C(iPr)} and [iPrNCO]3. Finally, the reactivity of (6-Dipp)Cu(PCO) was explored in a reaction with P(SiMe3)3.
| Date of Award | 11 Dec 2024 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | David Liptrot (Supervisor) & Michael Whittlesey (Supervisor) |
Keywords
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