Methyl(2-phosphanylphenolatol[P,O])nickel(II) complexes - Synthesis, structure, and activity as ethene oligomerization catalysts

Reactions of various substituted 2-phosphanylphenols 1a-f with half-molar a mounts of cis-[MeNi(mu-OMe)(PMe3)](2) have been found to yield square-plana r methyl(2-phosphanylphenolato) (trimethylphosphane)nickel(II) complexes 2a -f. (2)J(PP) coupling constants of 305-316 Hz at low temperature indicate a trans-configuration for the products, while broad P-31-NMR signals at room temperature can be attributed to rapid dissociation of PMe3. Reaction with excess 1 gave rigid bis(2-phosphanylphenolato)nickel(II) complexes as exem plified by 3e, whereas addition of PMe3 to 2a led to the pentacoordinate me thyl(2-phosphanylphenolato)bis(trimethylphosphane)nickel(II) complex 4a. Hi gher yields of 4a and 4d were obtained by reactions of 1a and 1d with Me2Ni (PMe3)(3). Single-crystal X-ray diffraction analyses of 3e and 4a have reve aled the structures as square-planar trans-bis- and trigonal-bipyramidal mo no(2-phosphanylphenolato)nickel(II) (PO)-O-boolean AND-chelate complexes, r espectively. The methylnickel complexes 2 and 4 have been found to be effec tive one-component catalysts for the oligomerization of ethene. High conver sions (> 96%) were achieved with the P-basic derivatives 2e, 2f, and 4d bea ring one or two branched alkyl groups (isopropyl, tert-butyl), whereas the diphenylphosphanyl derivatives were less active; 4d gave shorter oligomers than 2e or 2f.