Abstract

Pincer ligands are monoanionic, tridentate binding molecules that have been used in coordination chemistry as efficient homogeneous and heterogeneous catalysts (i.e. as transition metal complexes). The focus of this work lies in the synthesis, characterization and coordination chemistry of a series of novel asymmetric potentially monoanionic NN'N", NN'C and NN'P type pincer ligands with amide functionality derived from the skeleton of 2-(2'-anilinyl)-4,4-dimethyl-2-oxazoline. Modular approach to this synthesis has been developed through an alkyl halide intermediate, in addition to the substrate-dependent alternative pincer syntheses, which are also described. The coordination chemistries of Pd and Ni, as well as the potential application of these pincer complexes in metal mediated catalysis of aldehyde allylation reactions will be explored. Moreover, a number of Pd(II) pincer complexes have been successfully synthesized and structurally characterized and these results are likewise described.

Highlights

  • The oxazoline, a subclass of oxazoles, is a five-membered heterocyclic organic compound with O and N atoms connected through an sp[2] hybridized C atom (Figure 1.3).[13]. It plays an important role in transition metal chemistry, since oxazoline-based ligands have been investigated extensively in recent years and show great number of applications in homogeneous catalysis.[22]

  • Metal complexes formed with oxazoline moieties, combined with phosphorus, nitrogen or oxygen as donor atoms, often showcase interesting electronic properties associated with catalysis.[22]

  • We previously showed that carboxylic group on the N,N-dimethylglycine can be transformed into the acyl chloride form using excess thionyl chloride under the neat conditions (Scheme 2.2).[54]

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Summary

PINCER LIGANDS AND COMPLEXES

Even though coordination compounds have existed for a long time, it was not until the late nineteenth century that Alfred Werner proposed the octahedral structures for Co(III) complexes, and as such pioneered this area of study. Pincers can be defined as tridentate ligands with one formal anionic coordinating atom and two neutral coordinating atoms binding to a central atom in typically a mer configuration.[13,14] Over the years, this definition has been broadened (Scheme 1.1), and the scope of pincer chemistry has been extended to encompass various coordinating atoms (e.g., P, N, S, O).[1]. The oxazoline, a subclass of oxazoles, is a five-membered heterocyclic organic compound with O and N atoms connected through an sp[2] hybridized C atom (Figure 1.3).[13] It plays an important role in transition metal chemistry, since oxazoline-based ligands have been investigated extensively in recent years and show great number of applications in homogeneous catalysis.[22]

N O1 2
Asymmetric pincer complexes in catalysis
O N Cu N
THESIS OBJECTIVE
MODULAR APPROACH
Synthesis of Pincers 3b-3j
Synthesis of 3k
Synthesis of 3m and 3m!oxide
Synthesis of 3n
NNC type pincer complex
NNP type pincer complex
NNN type pincer complexes
GENERAL
LIGANDS 2-Chloro-N-(2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)phenyl)acetamide (2)
H HN O N
PALLADIUM COMPLEXES Synthesis of 9a
CATALYSIS Allylatoin of aldehydes
C13 H15 Cl N2 O2
Findings
CHAPTER 8 – REFERENCES
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