A Paramagnetic NMR Spectroscopy Toolbox for the Characterisation of Paramagnetic/Spin‐Crossover Coordination Complexes and Metal–Organic Cages

Abstract

The large paramagnetic shifts and short relaxation times resulting from the presence of ap aramagnetic centre complicate NMR data acquisition and interpretation in solution. As aresult, NMR analysis of paramagnetic complexes is limited in comparison to diamagnetic compounds and often relies on theoretical models.W er eport at oolbox of 1D (1 H, proton-coupled 13 C, selective 1 H-decoupling 13 C, steady-state NOE) and 2D (COSY,NOESY,HMQC) paramagnetic NMR methods that enables unprecedented structural characterisation and in some cases,p rovides more structural information than would be observable for ad iamagnetic analogue.W ed emonstrate the toolboxsb road versatility for fields from coordination chemistry and spin-crossover complexes to supramolecular chemistry through the characterisation of Co II and highspin Fe II mononuclear complexes as well as aC o 4 L 6 cage.

Copper‐Free One‐Pot Sonogashira‐Type Coupling for the Efficient Preparation of Symmetric Diarylalkyne Ligands for Metal‐Organic Cages**

“…Cage 4b was prepared in situ only, whereas cages 3b, 3c and 4a were isolated by precipitation with diethyl ether. Characterisation using our recently reported paramagnetic NMR spectroscopy toolbox 13 and mass spectrometry was consistent with tetrahedral Co4L6 cages ( Figures S55-81). Further investigation of these cages and their properties will be the focus of future work.…”

“…Palladium catalysed cross-coupling reactions are powerful synthetic methods for carbon-carbon bond formation in modern organic chemistry. 1 In particular, Sonogashira cross-coupling reactions [2][3][4] have been used extensively for the synthesis of diarylalkynes in natural products, 5 conjugated oligomers/polymers in materials science 6,7 and ligands/building blocks [8][9][10][11][12][13][14][15][16][17][18][19][20] in coordination chemistry and supramolecular chemistry due to their typically high yields and tolerance of a wide range of functional groups.…”

“…Symmetric diarylalkynes find application in diverse fields since they are precursors in the synthesis of hexaarylbenzene derivatives, 21,22 building blocks for lightemitting materials 23 and inorganic heterocycles 24 as well as building blocks in supramolecular architectures. 9,10,13 However, their preparation is typically a multi-step synthesis, often involving long reaction times and multiple purification steps, resulting in overall lower yields and making scale-up for applications difficult (black route, Scheme 1). 23 Glaser coupling [25][26][27] can also take place in the presence of the copper co-catalyst with traces of oxygen, leading to side-product formation 2,28 and difficult purifications.…”

“…We recently reported that the synthesis of ligand 1a [39][40][41] could be reduced from three to two steps using TBAF for the in situ deprotection of the TMS protected alkyne (first step in black route, Scheme 2). 13 However, the Glaser byproduct was also obtained in the final Sonogashira coupling using copper(I) iodide in some instances. Mori 37 and Li 38 reported copper-and amine-free Sonogashira couplings between terminal alkynes and aryl halides, including aryl chlorides, with short reaction times and good to excellent yields using TBAF as an activator.…”

“…38 Therefore, we envisaged TBAF could play the role of not only a deprotection reagent but also activator and base in a one-pot procedure while preventing the formation of Glaser by-products. Firstly, we investigated the applicability of the Sonogashira-type coupling using TBAF to heterocyclic diarylalkynes by reacting 5a with 6 13 (second step in black route, Scheme 2). The previously reported Sonogashira coupling 13 reaction conditions for 1a were initially adapted replacing the copper(I) iodide and amine with a commercially available TBAF solution in THF.…”