Abstract
Nonsymmetrical nickel PCN pincer complexes [Ni(iPrPCNX)Cl] (X = NMe, CH2) are obtained by metalation of the benzene–pyridine-based pincer ligand iPrPCNX (X = NMe, CH2) with [Ni(dme)Cl2] (dme = 1,2-dimethoxyethane). These nickel species afforded the respective borohydride and ethyl complexes [Ni(iPrPCNX)L] (L = BH4, Et) upon treatment with NaBH4 and EtMgBr (or Et2Mg), respectively. Reacting [Ni(iPrPCNX)(κ2-BH4)] with CO2 gave the formate complexes [Ni(iPrPCNX)(OCHO)]. Treatment of [Ni(iPrPCNX)Cl] with the nitrosyl salt NOBF4 led to the formation of the unusual cationic square-pyramidal nickel nitrosyl pincer complexes [Ni(iPrPCNX)(NO)Cl]+ featuring a strongly bent NO ligand (∠Ni–N–O 128.5°). These systems can be described as {NiNO}10 according to the Enemark–Feltham convention. Despite of the bent nature of the NO ligand the νNO is observed at 1849 cm–1 which is more typical for a linear Ni–N–O arrangement. The structure of these complexes is rationalized by means of DFT calculations. The molecular structures of representative complexes are presented.
Highlights
Pincer complexes[1] have received considerable attention in the last few decades.[2]. Their high stability and their facile modifiability make them attractive compounds in transitionmetal chemistry as well as for the examination of stoichiometric and catalytic reactions.[2]
Nonsymmetrical PCN pincer ligands[4−7] became available, with nickel analogues appearing in the literature (Chart 1).[7−20] These kinds of pincer ligands offer new possibilities due to the incorporation of a soft phosphorus and a hard nitrogen donor
On the basis of our previous work with PCP pincer complexes,[21−23] we report here on the synthesis and reactivity of nickel PCN pincer complexes featuring a nonsymmetrical
Summary
Pincer complexes[1] have received considerable attention in the last few decades.[2]. On consideration of nonprecious first-row transition metals, the scientific landscape of nickel pincer complexes is quite comprehensive and is generally dominated by symmetrical monoanionic ECE as well as ENE pincer, ligands with E being two identical donor groups that feature an aromatic anionic benzene or neutral pyridine backbone, repsectively.[2,3] In the past decade, nonsymmetrical PCN pincer ligands[4−7] became available, with nickel analogues appearing in the literature (Chart 1).[7−20] These kinds of pincer ligands offer new possibilities due to the incorporation of a soft phosphorus and a hard nitrogen donor. A higher probability for the nitrogen donor to dissociate from the metal center has been reported, resulting in a vacant coordination site, making this ligand an interesting counterpart to its symmetrical relatives for homogeneous catalysis.[5,6]
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