Monomeric Nickel(II) Amido Complexes. Synthesis, Reactivity, and Dynamics

Article abstract of DOI:10.1021/ic00125a035

Addition of KNHAr to trans-Ni(PMe3)2(Ar')Cl (Ar = Ph, 2,6-(i)Pr2C6H3; Ar' = Ph, 2,4,6-Me3C6H2) results in the formation of monomeric Ni(II) amide complexes of the type trans-Ni(PMe3)2(NHAr)(Ar') in good yield, with the exception of the amide complex trans-Ni(PMe3)2(NHPh)(Ph), 1a, which is initially formed as a mixture of monomer, 1a, and dimeric compounds (which form upon loss of PMe3), 1b. The monomer and dimers can be readilyinterconverted by the addition or removal of PMe3. The compounds trans-Ni(PMe3)2(NHAr')(2,4,6-Me3C6H2) react readily with H2O to form the binuclear hydroxide compound [Ni(μ-OH)(PMe3)(Mes)]2, 5. The compound trans-Ni(PMe3)2(NHPh)(Mes), 3, reacts with a variety of small electrophilic molecules resulting in insertion into either the Ni-N bond or the N-H bond. A single-crystal X-ray diffraction study of trans-Ni(PMe3)2(Mes)[N(Ph)C(O)CHPh2], 8, which resulted from the addition of diphenylketene to 3,reveals that it crystallizes in the space group P21/c with a = 9.379(1)?, b = 19.561(2) ?, c = 18.793(2) ? β = 103.07(1)°, V = 3358.5(6) ?**3, and Z = 4. A short N-Ccarbonyl bond length of 1.354(3) ? reveals that nitrogen's lone pair of electrons is delocalized onto the carbonyl, stabilizing the complex. All but one of the insertion or addition products of 3 exhibit a hindered rotation about theNi-R bond in the compounds trans-Ni(PMe3)2(Mes)R. The ΔG(.++.) for rotation of the Ni-R bonds in these compounds was measured using variable-temperature NMR experiments and can be correlated with the steric bulk of the R group.