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
2002-11-01T00:00:00Z (GMT) by
1,3-Bis(imino)lbenzenes [1,3-C<sub>6</sub>H<sub>4</sub>(CHNR)<sub>2</sub>], obtained from condensation of 1,3-isophthalaldehyde with primary amines (R = <sup>t</sup>Bu, Cy, Bu, Bn, Ph), were heated with K<sub>2</sub>PtCl<sub>4</sub> at reflux for 48 h in glacial acetic acid to give ((2,6-bis(<i>N</i>-R-substituted)imino)phenyl)platinum(II) chloride complexes (15−52% yield). X-ray crystal structures of the R = <sup>t</sup>Bu and R = Ph complexes are reported. The byproducts were found to be 1,3-isophthalaldehyde and <i>N</i>-acetylamines. Quantitative chloride abstraction with AgBF<sub>4</sub> (R = <sup>t</sup>Bu) or AgOTf (R = <sup>t</sup>Bu, Cy) provided the corresponding cationic complexes containing water coordinated to platinum, as established by an X-ray crystal structure of ((2,6-bis(<i>N</i>-<i>tert</i>-butyl)imino)phenyl)aquoplatinum(II) trifluoromethanesulfonate. Use of 4−5 mol % of ((2,6-bis(<i>N</i>-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.