A direct route to platinum NCN-pincer complexes derived from 1,3-bis(imino)benzenes and an investigation into their activity as catalysts for carbon-carbon bond formation

1,3-Bis(imino)lbenzenes [1,3-C6H4(CH=NR)(2)], obtained from condensation of 1,3-isophthalaldehyde with primary amines (R = Bu-t, Cy, Bu, Bn, Ph), were heated with K2PtCl4 at reflux for 48 h in glacial acetic acid to give ((2,6-bis(N-R-substituted)imino)phenyl)platinum-(II) chloride complexes (15-52% yield). X-ray crystal structures of the R tBu and R = Ph complexes are reported. The byproducts were found to be 1,3-isophthalaldehyde and N-acetylamines. Quantitative chloride abstraction with AgBF4 (R = Bu-t) or AgOTf (R = tBu, Cy) provided the corresponding cationic complexes containing water coordinated to platinum, as established by an X-ray crystal structure of ((2,6-bis(N-tert-butyl)imino)phenyl)aquoplatinum(II) trifluoromethanesulfonate. Use of 4-5 mol % of ((2,6-bis(N-cyclohekyI)imino)phenyl)aquoplatinum(II) trifluoromethanesulfonate accelerated the rate of the Michael reaction between ethyl alpha-cyanoacetate and methyl vinyl ketone and the Diels-Aider reaction between acrylonitrile and cyclopentadiene.