A first structural and theoretical comparison of pyridinylidene-type rNHC (remote N-heterocyclic carbene) and NHC complexes of Ni(II) obtained by oxidative substitution

摘要

A series of cationic pyridinylidene and quinolinylidene complexes of chlorobis(triphenylphosphine)-nickel(n) were prepared by oxidative substitution of Ni(PPh_3)_4 with methylated chloropyridines or chloroquinolines.NMR as well as X-ray crystallographic studies confirmed the trans arrangement of the two phosphines in the products.Calculations,using suitable model compounds at the BP86/TZVP level,clearly differentiate between a standard imidazolylidene complex and new complexes of the NHC-type on the one hand,and new complexes classified as rNHC-types-with the heteroatom distant from the carbene carbon-on the other.The latter form significantly stronger bonds-mainly of an electrostatic nature-with the metal.