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 = ^tBu, 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 = ^tBu) 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-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.