Monomeric complexes NiL with tetradentate ligands [R2P(S)N-R '-NP(S)R-2](2-) (= L) [1]

Metathesis of [NiCl2(PPh3)(2)] with Li salts of the potentially tetradentat e ligands [R2P(S)N-R'-NP(S)R-2](2-) (= L) affords monomeric complexes NiL c ontaining the chromophore NiN2S2 (1: R = Et; a, b: R' = Me2C-(CH2)(2)-CMe2, o-Phenylen; 2: R = t-Bu, R' = (CH2)(n); a-c: n = 2, 3, 4). According to th e results of magnetic measurements and VIS as well as NMR spectroscopy (H-1 , P-31) these complexes are planar except la that is tetrahedral. In case o f 1a and 2c this was confirmed by the results of crystal structure analyses . In toluene, however, 1a and 2c form an equilibrium of planar (diamagnetic ) and tetrahedral (paramagnetic) conformers. VT-H-1-NMR including H-1,H-1-C OSY showed a hindered Delta,Lambda-inversion of 1a below 330 K. Only with 1 b a pentacoordinate adduct 1b.PPh3 was obtained that completely dissociates in its components on dissolving in benzene. 1a and 2c crystallize in the m onoclinic space group P2(1)/c containing 4 molecules in the unit cell of th e dimensions la: a = 8.774(1), b = 12.335(2), c = 21.339(3) Angstrom, beta = 92.33(1)degrees and 2c: a = 13.374(8), b = 16.197(8), c = 12.814(6) Angst rom, beta = 109.20(4)degrees. The coordination of the Ni atom yields in 1a a dihedral angle epsilon of 41.7(1)degrees and thus a geometry intermediate between planar and tetrahedral while in 2c the angle of 4.5(1)degrees reve als a nearly planar chromophore NiN2S2.