Substituent effects on cyclometalation: N-benzylideneanilines

Highlights: • Electronic structures of N-benzylideneanilines were studied and related to cyclometalation. • Stability of complexes of Schiff bases with metals. • Effect of nitrogen lone pair orbital energy on rate of cyclometalation. The electronic structures of several derivatives of N-benzylidenaniline ligands (NBA) studied previously by HeI UV photoelectron spectroscopy (UPS) have been re-analyzed with outer valence Green's function (OVGF) and ionization-potential equation of motion coupled cluster method (IP-EOMCC) quantum chemical calculations. The calculations allowed us to clearly identify molecular orbitals with predominantly nitrogen lone pair character and correlate their ionization energies with the experimental kinetic data on the cyclopalladation of imines. We have also rationalized the stability (or the lack of it) for NBA complexes with d-block transition metals.