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A series of nickel pincer complexes of the type [4-Z-2,6-(R 2 PO) 2 C 6 H 2 ]NiX (R = t Bu, i Pr, Ph; Z = H, CO 2 Me; X = NCS, N 3 ) have been synthesized from the reactions of the corresponding nickel chloride complexes [4-Z-2,6-(R 2 PO) 2 C 6 H 2 ]NiCl and potassium thiocyanate or sodium azide. X-ray structure determinations of these complexes have shown that the thiocyanate ion binds to the nickel center through the nitrogen. A comparable Ni-N bond length (approx. 1.87 Å for the isothiocyanate complexes and 1.91 Å for the azide complexes) and an almost identical Ni-C ipso bond length (approx. 1.89 Å) have been observed for these complexes. Metathesis reactivity of [4-Z-2,6-(R 2 PO) 2 C 6 H 2 ]NiCl and ligand exchange reactions between the nickel isothiocyanate and nickel azide complexes have been investigated. The metathesis reactions with thiocyanate/azide complexes are faster with a less electron rich and more sterically accessible nickel center. The thermodynamic stability of these nickel complexes has been rationalized using the hard-soft acid-base theory (HSAB theory); a harder ligand prefers a less electron rich nickel center. These © 2015. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ 2 experimental results have been supported by quantum chemical analysis of the coordinating nitrogen atoms in SCNand N 3 -.

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