Different structures and reactivities have been observed with the unsymmetrical pincertype complex (5,6-POCOP´)Ni(II)Br and its various derivatives compared to their analogous symmetrical 5,5-POCOP systems, thus serving to establish the importance of the size and degree of flexibility in the metallacycle rings. AbstractThis report describes the synthesis and characterization of a family of unsymmetrical pincer complexes of nickel(II) featuring both 5-and 6-membered nickelacycles. The room temperature reaction of NiBr 2 (NCCH 3 ) x with the bis(phosphinite) ligand 1-(i-Pr 2 PO),3-(i-Pr 2 POCH 2 )-C 6 H 4 (POCHOP´) results in direct nickelation at the 2-position of the aromatic ring to give (5,6-POCOP´)NiBr (5,6-POCOP´ = {κ P ,κ C ,κ P´-2-(i-Pr 2 PO),6-(i-Pr 2 POCH 2 )-C 6 H 3 }). This complex undergoes salt metathesis reactions with M´X to give the corresponding charge neutral derivatives (5,6-POCOP´)NiX (X = OSO 2 CF 3 , OSO 2 (4-CH 3 -C 6 H 4 ), CH 3 , and C≡CCH 3 ), whereas abstraction of the bromide by AgBPh 4 in acetonitrile gave the cationic derivative [(5,6-POCOP´)Ni(NCCH 3 )][BPh 4 ]. The new complexes have been characterized by multinuclear NMR spectroscopy and X-ray diffraction studies. The reactivities of the new complexes (5,6-POCOP´)NiX (X= Br, OSO 2 CF 3 ) have been explored briefly to establish the nucleophilicity of the X ligand and the substitutional lability of the phosphinite moiety in the 6-membered cycle.