Since the first report on the tridentate pincer-type metal
complexes published thirty years ago [1], the development of
various tridentate pincer-type ligands for the cyclometallation
has become a hot and emerging topic in the modern organometallic
chemistry. This is mainly due to their advanced applications
in coordination, mechanistic, synthetic, supramolecular
chemistry and development of sensors and molecular switches
[2e7]. Most significantly, a unique and highly protective environment
provided by these ligands to the metal centre offers an
opportunity to fine tune the steric and electronic properties of
the metal atom in the catalytic reactions [8e11]. Typically, such
ligands comprise of an anionic aryl ring and ortho-disubstituted
donor heteroatom substituents (DCD: D ¼ NR2, PR2, SR and SeR)
which generally coordinate to the metal centre and support the
MeC s bond. The majority of investigations are carried out with
cyclopalladated pincer-type ligands containing symmetrically