SYNTHETIC STRATEGIES FOR N2S2O-PENTACOORDINATE NICKEL(II) BASED ON THE HIGHLY STERICALLY ENCUMBERED LIGAND N,N′-BIS(2-MERCAPTO-2-METHYLPROPANE)-1,5-DIAZACYCLOOCTANE

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Abstract
An attempt to prepare a square pyramidal pentacoordinate Ni(II) complex was made by increasing steric hindrance in a N2S2O macrocyclic ligand derived from (bme-daco), N,N′-bis(2-mercaptoethyl)-1,5-diazacyclooctane. Thus two methyl groups were added to each carbon in a position α to sulfur atoms of the macrocycle. The resulting complex, 3,3,11,11-tetramethyl-7-oxa-4,10-dithia-bicyclo[11.3.3]nonadecanenickel(II) iodide or [Ni(bmmp-ether)]I2 or 2∗I2, shows a greater steric rigidity and a severe steric block of one side of the NiN2S2 pseudo-square plane. Neither iodide nor the ethereal oxygen bind to nickel. The 2∗I2 complex crystallizes in the monoclinic P21/n(No. 14) space group with a = 11.193(3) Å, b = 11.408(3) Å, c = 20.129(5) Å, β = 91.44(2)°, V = 2569.5(12) Å3, and Z = 4. The preparation and crystal structure of its precursor, N,N′-bis(2-mercapto-2-methylpropane)-1,5-diaza-cyclooctanenickel(II) or [(bmmp-daco)Ni] or 1∗, is also reported. Square planar complex 1∗ crystallizes in orthorhombic Pnma space group with a = 11.307(2) Å, b = 19.579(3) Å, c = 7.4790(10) Å, V = 1655.7(4) Å3, and Z = 4.