MONOMERIC NICKEL(II) AMIDO COMPLEXES - SYNTHESIS, REACTIVITY, AND DYNAMICS

Addition of KNHAr to trans-Ni(PMe(3))(2)(Ar')Cl (Ar = Ph, 2,6-(Pr2C6H3 )-Pr-i; Ar' = Ph, 2,4,6-Me(3)C(6)H(2)) results in the formation of mon omeric Ni(II) amide complexes of the type trans-Ni(PMe(3))(2)(NHAr)(Ar ') in good yield, with the exception of the amide complex trans-Ni(PMe (3))(2)(NHPh)(Ph), 1a, which is initially formed as a mixture of monom er, 1a, and dimeric compounds (which form upon loss of PMe(3)), 1b. Th e monomer and dimers can be readily interconverted by the addition or removal of PMe(3). The compounds trans-Ni(PMe(3))(2)(NHAr')(2,4,6-Me(3 )C(6)H(2)) react readily with H2O to form the binuclear hydroxide comp ound [Ni(mu-OH)(PMe(3))(Mes)](2), 5. The compound trans-Ni(PMe(3))(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 si ngle-crystal X-ray diffraction study of trans-Ni(PMe(3))(2)(Mes)-[N(Ph )C(O)CHPh(2)], 8, which resulted from the addition of diphenylketene t o 3, reveals that it crystallizes in the space group P2(1)/c with a 9. 379(1) Angstrom, b = 19.561(2) Angstrom, c = 18.793(2) Angstrom, beta = 103.07(1)degrees, V = 3358.5(6) Angstrom(3), and Z = 4. A short N-C- carbonyl bond length of 1.354(3) Angstrom reveals that nitrogen's lone pair of electrons is delocalized onto the carbonyl, stabilizing the c omplex. Al but one of the insertion or addition products of 3 exhibit a hindered rotation about the Ni-R bond in the compounds trans-Ni(PMe( 3))(2)(Mes)R. The Delta G(double dagger) for rotation of the Ni-R bond s in these compounds was measured using variable-temperature NMR exper iments and can be correlated with the steric bulk of the R group.