Trimethylphosphine Complexes of Diorganonickel(IV) Moieties

When coordinated to 2-oxobenzoyl- C, O chelating ligands (O⌒C O) (⌒ = 3- tert -butyl-5-methylphenyl, 3,5-di- tert -butylphenyl, 3-methoxyphenyl, 3,4-benzocyclohexenyl, cyclohexenyl), 18 electron nickel(II) complexes Ni(O⌒C O)(PMe 3 ) 3 ( 1 − 5 ) oxidatively add iodomethane affording thermally labile Ni IV compounds trans-mer- Ni(Me)I(O⌒C O)(PMe 3 ) 2 ( 6 − 10 ) or react with iodine in a ligand dismutation reaction to form stable molecules of trans -Ni(O⌒C O) 2 (PMe 3 ) 2 ( 21 − 25 ), which contain cisoidal acylphenolato chelate rings. Acylphenolato compounds 1 − 5 react with larger electrophiles [C 2 H 5 I, (CH 3 ) 2 CHI, n -C 4 H 9 I, cyclo -C 6 H 11 I, CH 3 COCl, PhCOCl, (CH 3 ) 3 COCl] in different regioselectivities affording ketones or esters. The square pyramidal bis[ n -butyl 2-oxophenyl ketone]nickel(II) complex 16 crystallizes in the monoclinic space group C2/c, while the square planar chloro(phenyl)nickel(II) complex 19 with an ester group in the 2-position crystallizes in the triclinic space group P 1̄. Steric control of C,C-coupling reactions is demonstrated in three transformations, starting either from (acylphenolato)nickel(II) or from metastable diorganonickel(IV) compounds.