Characteristics of Nickel(0), Nickel(I), and Nickel(II) in Phosphino Thioether Complexes:  Molecular Structure andS-Dealkylation of (Ph₂P(o-C₆H₄)SCH₃)₂Ni⁰

The molecular structure of a nickel(0) complex with P,S-donor atom ligands has been characterized by X-ray crystallography. Complex 1, (Ph 2 P( o -C 6 H 4 )SCH 3 ) 2 Ni 0, prepared by Na/Hg amalgam reduction of the Ni II complex [(Ph 2 P( o -C 6 H 4 )SCH 3 ) 2 Ni](BF 4 ) 2 ([ 2 ](BF 4 ) 2 ), degrades photochemically with loss of CH 3 radicals to yield complex 3, (Ph 2 P( o -C 6 H 4 )S) 2 Ni II . Crystallographic parameters for the three compounds are as follows: 1, monoclinic space group C 2/ c with a = 11.467(2) Å, b = 17.613(3) Å, c = 15.733(2) Å, β = 96.450(10)°, V = 3157.5(9) Å 3, and Z = 4; [ 2 ](BF 4 ) 2, monoclinic space group P2 1 / c with a = 9.417(4) Å, b = 14.822(9) Å, c = 13.773(2) Å, β = 98.55(3)°, V = 9101(14) Å 3, and Z = 2; and 3, monoclinic space group P 2 1 / c with a = 9.651(2) Å, b = 12.971(8) Å, c = 12.540(2) Å, β = 110.46(2)°, V = 1470.7(11) Å 3, and Z = 2. While complex 1 has a distorted tetrahedral geometry, complexes [ 2 ](BF 4 ) 2 and 3 are square planar with trans stereochemistry. The cyclic voltammogram of [ 2 ](BF 4 ) 2 in CH 3 CN shows two redox events assigned to Ni II/I and Ni I/0, whereas the thiolate 3 reveals only one reversible wave assigned to Ni II/III . The chemical reduction of [ 2 ](BF 4 ) 2 with Cp 2 Co provided a Ni I species, [(Ph 2 P( o -C 6 H 4 )SCH 3 ) 2 Ni I ] +, characterized at 100 K by an axial EPR signal with g x = g y = 2.10 and g z = 1.96. Hyperfine spectral features resulting from coupling to two 31 P nuclei suggests a retention of substantially square planar geometry. In contrast the isotropic character of the EPR signal of [(Ph 2 P( o -C 6 H 4 )SCH 3 )(Ph 2 P( o -C 6 H 4 )S)Ni I ], presumed to be the first product of the photochemical demethylation of 1 ultimately yielding the doubly demethylated complex 3, suggested the intervening thioether/thiolate Ni I species to be pseudotetrahedral. Protonation of the nickel(0) species 1 produced a five-coordinate nickel hydride complex, [(H)(arom-PSMe) 2 Ni]BF 4, 4 .