Ni(II), Pd(II), and Pt(II) complexes [M(Y-terpy)X] (X = Cl or Br) containing the tridentate N^C^N-cyclometalating 2,3′:5′,2″and 2,2′:4′,2″ stereoisomers of the well-known tridentate N^N^N ligand 2,2′:6′,2″-terpyridine (terpy) were synthesised in moderate to good yields through C–H activation. For the Pt complexes, the phenyl ethynide derivatives [Pt(Y-terpy)(C≡CPh)] were also obtained under Sonogashira conditions. In contrast to this, C^N^N cyclometalated complexes using the 2,2′:6′,3″- and 2,2′:6′4″-terpy isomers were not obtained. Comparison of the N^C^N complexes of the cyclometalated 2,3′:5′,2″- and 2,2′:4′,2″-terpy ligands with complexes [M(dpb)Cl] of the prototypical N^C^N cyclometalating ligand dpb− (Hdpb = 2,6-diphenyl-pyridine) showed higher potentials for the terpy complexes for the ligand-centred reductions in line with the superior π-accepting properties of the terpy ligands compared with dpb. Metal-centred oxidations were facilitated by the dpb ligand carrying a central σ-donating phenyl group instead of a metalated pyridine moiety. The same trends were found for the long-wavelength absorptions and the derived electrochemical and optical band gaps. The lower σ-donating capacities of the cyclometalated terpy derivatives is also confirmed by a reduced trans influence in the structure of [Ni(2,3′:5′,2″-terpy)Br0.14/OAc0.86]. Attempts to re-crystallise some poorly soluble Pd(II) and Pt(II) complexes of this series under solvothermal conditions (HOAc) gave two structures with N-protonated cyclometalated pyridine moieties, [Pt(2,3′:5′,2″-terpyH)Cl].Cl and [Pd(2,3′:5′,2″-terpyH)Cl2].

From the two organonickel(II) scaffolds [Ni(Phbpy)]+ and [Ni(PyPhPy)]+ (HPhbpy = 6-phenyl-2,2′-bipyridineHC∧N∧N and Py(HPh)Py = 2,6-di-2-pyridyl-benzeneN∧(HC)∧N) the hydrido complexes [Ni(C∧N∧N)H] and [Ni(N∧C∧N)H] were studied in a combined experimental/theoretical approach. The hydrido complexes were prepared via the reaction of the halido derivatives [Ni(C∧N∧N)X] and [Ni(N∧C∧N)X] (X = Cl, Br) with Li(Et3BH) (superhydride). The C∧N∧N complex undergoes rapid reductive elimination (RE) yielding HPhbpy and Ni particles even at the lowest temperatures, while the PyPhPy derivative is more stable. Low-temperature 1H nuclear magnetic resonance (NMR) spectroscopy allowed detection of a signal at δ = −2.86 ppm assignable to the hydrido ligand. The different stabilities can be directly correlated to the cis (Phbpy) and trans (PyPhPy) orientations of the carbanionic phen-2-ide group with the hydrido ligand, and rapid RE occurs from the cis position which is also supported by the density functional theory (DFT) calculations which are presented. A further TD-DFT/UV–vis absorption study is also reported to rationalize and confirm the fleeting existence of the Ni–H moiety, and proposals are made on the route of its decomposition.

A sulfonated poly-4-vinyl pyridinium (PVPy-IL-B-SO3H) containing an acidic pyridinium/HSO3− ionic liquid moiety was prepared and used as a catalyst for the three-component reaction of malononitrile with 1-alkylindoline-2,3-diones and 1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione or methyl 5-hydroxy-1H-pyrazole-3-carboxylate, leading to methyl 6′-amino-5′-cyano-2-oxo-2′H-spiro[indoline-3,4′-pyrano[2,3-c]pyrazole]-3′-carboxylates or -3,4′-pyrano[2,3-d]pyrimidine]-6′-carbonitrile derivatives under ultrasonic irradiation conditions. The solid catalyst allows easy separation, is cheap, produces high yields under mild conditions, and does not require column chromatography for product isolation and purification.