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-C 6 H 4 (CH NR) 2 ], obtained from condensation of 1,3-isophthalaldehyde with primary amines (R = t Bu, Cy, Bu, Bn, Ph), were heated with K 2 PtCl 4 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 = t Bu and R = Ph complexes are reported. The byproducts were found to be 1,3-isophthalaldehyde and N -acetylamines. Quantitative chloride abstraction with AgBF 4 (R = t Bu) or AgOTf (R = t Bu, 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 -cyclohexyl)imino)phenyl)aquoplatinum(II) trifluoromethanesulfonate accelerated the rate of the Michael reaction between ethyl α-cyanoacetate and methyl vinyl ketone and the Diels−Alder reaction between acrylonitrile and cyclopentadiene.