(μ-η~2:η~2-Disulfido)dinickel(II) complexes supported by 6-methyl-TPA ligands

摘要

A series of (μ-η~2:η~2 -disulfido)dinickel(II) complexes 2~n have been synthesized by the reaction of Na2S2and nickel(II) complexes 1~n supported by tris[(pyridin-2-yl)methyl]amine (TPA; 1~0) [(6-methylpyridin-2-yl)methyl]bis[(pyridin-2-yl)methyl]amine (Me_1TPA; 1~1), bis[(6-methylpyridin-2-yl)methyl][(pyridin-2-yl)methyl]amine (Me_2TPA; 1~2) and tris[(6-methylpyridin-2-yl)methyl]amine (Me_3TPA; 1~3), respectively,and characterised by UV-vis and resonance Raman spectroscopy. X-ray crystallographic analyses on 2~2and 2~3supported by Me_2TPA and Me_3TPA, respectively, have revealed that the Ni_2S_2core is largelybent (-30°) along the S-S axis, being in sharp contrast to the planar Ni_2S_2core structure of the(μ-η~2:η~2-disulfido)dinickel(II) complexes reported so far. The UV-vis spectra of 2~0 and 2~1 supported byTPA and Me_1TPA, respectively, exhibiting an intense absorption band at ~360 nm together with ashoulder around 400 nm and a weak and broad absorption band around 450-600 nm, are very close tothose of 2~2and 2~3,suggesting that 2~0 and 2~1 also exhibit a similar distorted Ni_2S_2core structure.Resonance Raman spectra of 2~nshowed a characteristic S-S stretching vibration mode at -450 cm~(-1)with an isotope shift Δv(~(32)S-~(34)S)=10-15 cm~(-1).The reactionof 2~nwith (p-Me-C_6H_4)_3P gave(p-Me-C_6H_4)_3P=Squantitatively based on 2~n.Hammett analysison the sulfur atom transfer processfrom r to the phosphine derivatives [(p-X-C_6H_4)P; X = OMe,Me, H and Cl] has indicated that thereaction involves an electrophilic ionic mechanism. Moreover, the order of reactivity of 2~n toward PPh_3has been found as 2~0>2~3 > 2~1 >2~2. Onthe basis of these results, the ligand effects of Me_nTPA on thestructure and reactivity of the nickel(II) complexes have been discussed.