Carbazole-bis(oxazolines) as Monoanionic, Tridentate Chelates in Lanthanide Chemistry: Synthesis and Structural Studies of Thermally Robust and Kinetically Stable Dialkyl and Dichloride Complexes

Synthesis and Magnetic Studies of Two Neutral, Bis-Ligand Fe(II) Complexes Containing Carbazole-Bis(tetrazole) Ligands

Previously reported carbazole-bis(tetrazole) (CzT^R) ligands (where R = iPr and CH₂-2,4,6-C₆H₂Me₃) were used to synthesize air-stable, six-coordinate, octahedral bis-ligand Fe(II) complexes (CzT^R)₂Fe. The synthesis and characterization of these complexes using ¹H nuclear magnetic resonance (NMR), X-ray crystallography, Mössbauer spectroscopy, and density functional theory (DFT) calculations are reported. Analysis of the magnetic properties revealed that the isopropyl derivative displays thermally induced spin crossover (SCO) over a temperature range of 150-350 K. This transition appears as an abrupt two-step transition in the solid state but simplifies to a smooth one-step transition in solution. The two-step transition in the solid state has been postulated to be due to lattice and solvation effects. In contrast, the slightly bulkier substituted CH₂-2,4,6-C₆H₂Me₃ (CH₂Mes) Fe complex displays dramatically different magnetic behavior with no SCO and magnetic data suggesting low-spin Fe(II) with a possible TIP contribution. DFT calculations support the postulate that the change in magnetic behavior is primarily due to the nature of the ligand substituents.

Synthesis and crystal structures of tetra-meric [2-(4,4-dimethyl-2-oxazolin-2-yl)anilido]sodium and tris-[2-(4,4-dimethyl-2-oxazolin-2-yl)anilido]ytterbium(III)

The reaction of 2-(4′,4′-dimethyl-2′-oxazolin­yl)aniline (H₂-L1) with Na[N(SiMe₃)₂] afforded colourless crystals of tetra­meric Na₄(H-L1)₄ (2). Reaction of either Na₄(H-L1)₄ (2) with YbCl₃ or reaction of H₂-L1 with Yb[N(SiMe₃)₂]₃ afforded yellow crystals of the highly distorted octa­hedral complex Yb(H-L1)₃ (3).

Reaction of 2-(4,4-dimethyl-2-oxazolin-2-yl)aniline (H₂-L1) with one equivalent of Na[N(SiMe₃)₂] in toluene afforded pale-yellow crystals of tetra­meric poly[bis­[μ₃-2-(4,4-dimethyl-2-oxazolin-2-yl)anilinido][μ₂-2-(4,4-dimethyl-2-oxa­zolin-2-yl)aniline]tetra­sodium(I)], [Na₄(C₁₁H₁₃N₂O)₄]_n or [Na₄(H-L1)₄]_n (2), in excellent yield. Subsequent reaction of [Na₄(H-L1)₄]_n (2) with 1.33 equivalents of anhydrous YbCl₃ in a 50:50 mixture of toluene–THF afforded yellow crystals of tris­[2-(4,4-dimethyl-2-oxazolin-2-yl)anilinido]ytterbium(III), [Yb(C₁₁H₁₃N₂O)₃] or Yb(H-L1)₃ (3) in moderate yield. Direct reaction of three equivalents of 2-(4′,4′-dimethyl-2′-oxazolin­yl)aniline (H₂-L1) with Yb[N(SiMe₃)₂]₃ in toluene resulted in elimination of hexa­methyl­disilazane, HN(SiMe₃)₂, and produced Yb(H-L1)₃ (3) in excellent yield. The structure of 2 consists of tetra­meric Na₄(H-L1)₄ subunits in which each Na⁺ cation is bound to two H-L1 bridging bidentate ligands and these subunits are connected into a polymeric chain by two of the four oxazoline O atoms bridging to Na⁺ cations in the adjacent tetra­mer. This results in two 4-coordinate and two 5-coordinate Na⁺ cations within each tetra­meric unit. The structure of 3 consists of a distorted octa­hedron where the bite angle of ligand L1 ranges between 74.72 (11) and 77.79 (11) degrees. The oxazoline (and anilide) N atoms occupy meridional sites such that for one ligand an anilide nitro­gen is trans to an oxazoline nitro­gen while for the other two oxazoline N atoms are trans to each other. This results in a significantly longer Yb—N(oxazoline) distance [2.468 (3) Å] for the bond trans to the anilide compared to those for the oxazoline N atoms trans to one another [2.376 (3), 2.390 (3) Å].

Water oxidation catalyzed by a charge-neutral mononuclear ruthenium(iii) complex

A new charge-neutral Ru(iii) complex RuL(pic)₃ (1) (H3L = 3,6-di-tert-butyl-9H-carbazole-1,8-dicarboxylic acid, pic = 4-picoline) was synthesized and fully characterized. This complex promoted chemical and photochemical water oxidation efficiently with turnover frequencies of 0.28 s^-1 and 5 min^-1, respectively. In particular, for photochemical water oxidation, complex 1 showed excellent stability and good activity. The X-ray crystal structure, electrochemical results, and the detection of the Ru^IV-OH intermediate by high-resolution mass spectrometry revealed that complex 1 exchanged its 4-picoline ligand with water at the Ru^III state to form the authentic water oxidation catalyst. The kinetics studies suggested a reaction mechanism involving nucleophilic attack by a water molecule.

Variable coordination of carbazolyl-bis(tetrazole) ligands in lanthanide chemistry

Lanthanide complexes of 1,8-bis(2′-isopropyltetrazo-5′-yl)-3,6-di-tert-butylcarbazolide adopt geometries that include planar, buckled and tetrazolyl-bridged tridentate, as well as bidentate, bonding modes.

Transition metal complexes bearing tridentate ligands for precise olefin polymerization

This review covers key developments in the design of post-metallocene transition metal complexes (precatalysts) bearing tridentate chelating ligands and their application in olefin polymerization.

Tetrahydropentalenyl-phosphazene constrained geometry complexes of rare-earth metal alkyls

A new sterically demanding rigid cyclopentadienyl chelate ligand facilitates NMR spectroscopic investigations and signal assignment of paramagnetic rare earth organometallics.

Thermally stable rare earth dialkyl complexes supported by a novel bis(phosphinimine)pyrrole ligand

A novel bis(phosphinimine)pyrrole based ligand (HL) and its synthesis are reported. Rare earth dialkyl complexes of the ligand, LLn(CH(2)SiMe(3))(2) (Ln = Er, Lu, Sc), have been prepared and found to exhibit high thermal stability in solution. The protio-ligand and dialkyl lanthanide complexes (Ln = Er, Lu) have been characterised by single crystal X-ray diffraction studies.