Light induced sulfur-dealkylation of phosphino-thioether nickel(0) complexes
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abstract
The observation of homolytic S-CH3 bond cleavage in (Ph2P(o-C6H4)SCH3) 2Ni0 under photochemical conditions has prompted further investigation of nickel(0) complexes and their stability. Tetradentate P2S2 donor ligands (S = thioether type S donor) with aromatic rings incorporated into the P to S links, Ph2P(o-C6H4)S(CH2) 3S(o-C6H4)PPh2 (arom-PSSP), or the S to S links, Ph2P(CH2)2SCH2(o-C6H 4) CH2S (CH2)2PPh2 (PS-xy-SP), have been used to form four-coordinate, square planar nickel (II) complexes, [(arom-PSSP)Ni] (BF4)2 (2) and [(PS-xy-SP)Ni] (BF4)2 (3). The bidentate and tetradentate ligands, Ph2P(o-C6H4)SCH2CH3 (arom-PSEt) and Ph2P(CH2)2S(CH2) 3S(CH2)2PPh2 (PSSP), give similar complexes, [(arom-PSEt)2Ni] (BF4)2 (1) and [(PSSP)Ni] (BF4)2 (4), respectively. Cyclic voltammograms of the NiII complexes in CH3CN show two reversible redox events assigned to NiII/I and NiI/0. The one-electron reduction product produced by stoichiometric amounts of Cp2Co can be characterized by EPR. At 100 K rhombic signals show hyperfine coupling to two phosphorus atoms. Complete bulk chemical reduction of complexes 1, 2, 3 and 4 with Na/Hg amalgam provided the corresponding nickel(0) complexes 1R, 2R, 3R and 4R which were isolated as red solutions or solids and characterized by magnetic resonance properties and reaction products. Photolysis of these nickel(0) complexes leads to S-dealkylation to produce alkyl radicals and dithiolate nickel(II) complexes. Complex 3 crystallized in the monoclinic space group P21/c with a = 20.740(5), b = 9.879(3), c = 17.801(4) , = 92.59(2), V = 3644(2) 3 and Z=4; complex 4: P21 with a = 13.815(4), b = 13.815(4), c = 15.457(5) , = 104.89(2), V = 3365.4(14) 3 and Z = 4.
