Rodrigo S. Bitzer

A novel oxidative addition product from [Pt2(dba)3]: synthesis and spectroscopic characterization of a bimetallic Pt-eta2-tetracyanoethylene complex containing 2,3,5,6-tetrakis(alpha-pyridyl)pyrazine

{[Pt(h2-TCNE)]2(µ-TPP)} (1) has been prepared from the Pt(0) compound [Pt2(dba)3] (dba = dibenzylideneacetone), tetracyanoethylene (TCNE), and 2,3,5,6-tetrakis(a-pyridyl)pyrazine (TPP) in the 1:2:1 stoichiometric ratio, respectively. 1 has been characterized by elemental analysis, infrared spectroscopy, solution 1H NMR and solid-state 13C (CP/MAS) NMR spectroscopy. According to the NMR spectra of 1, TPP binds to each metal through two pyridine nitrogen atoms. In addition to the signals assigned to the TPP carbon atoms (d 128-155) and to the nitrile carbon atoms (d 115.1), the 13C-CP/MAS NMR spectrum of 1 exhibits a double doublet [d1 -2.6, 1J(195Pt-13 C) = 223 Hz and d2 1.6, 1J(195Pt-13 C) = 188 Hz] in the low frequency region. These signals are assigned to the ethylenic TCNE carbon atoms attached to platinum and confirm that the bonding at the Pt-h2-TCNE moieties is best described according to the metalacyclopropane model.

Synthesis and spectroscopic characterization of tin(II) and tin(IV) complexes containing 2,3,5,6-tetrakis(alpha-pyridyl)pyrazine as a bridging ligand

Neste trabalho foram investigadas as reacoes entre o ligante heterociclico nitrogenado 2,3,5,6-tetraquis(a-piridil)pirazina, TPP, e seis precursores de estanho, a saber: SnCl2, SnX4 (X = Cl ou Br), SnRCl3 (R = Ph ou Me) e SnPh2Cl2. Os produtos foram caracterizados por microanalise (C, H, N e Sn), espectroscopia no infravermelho (4000-200 cm-1), RMN de 1H, 13C{1H}, 13C-CP/MAS, 119Sn e 119Sn-MAS, bem como por espectroscopia Mossbauer de 119Sn. Todas as reacoes levaram ao isolamento de complexos bimetalicos, nos quais o TPP se comportou como um ligante bis-bidentado em ponte, ligando-se a cada centro metalico atraves de dois atomos de nitrogenio piridinicos. Este modo de coordenacao e ainda raro na literatura e, pela primeira vez, e observado em complexos de TPP com um metal representativo.

Supramolecular Cd(II) complexes with (E)-N,N′-bis(2-pyridyl)iminoisoindoline (2-pyimiso): synthesis, X-ray structures, Hirshfeld surface analyses, and DFT study of [CdX2(2-pyimiso)2] (X = Cl or NCS)*

Abstract The paucity of coordination entities bearing (E)-N,N′-bis(heteroaryl)iminoisoindolines has prompted us to investigate coordination modes and supramolecular features of (E)-N,N′-bis(2-pyridyl)iminoisoindoline (2-pyimiso), a versatile iminobis(pyridyl) ligand. In this article we report the synthesis, spectroscopic characterization and crystal structure analysis of two Cd(II) : 2-pyimiso (1 : 2) bis-adducts, [CdX2(2-pyimiso)2] [X = Cl (1) or NCS (2)]. Our X-ray structural results reveal that 1 exhibits distorted tetrahedral coordination (four-coordinate geometry index τ4 = 0.92), whereas 2 displays six-coordinate Cd(II) and two four-membered chelate rings (bite angles = 52.5°), each comprising one Cd–Npy [2.247(2) Å] bond and one Cd⋯Nimine [2.809(21) Å] secondary interaction. Remarkably, in 2 each 2-pyimiso unit binds to Cd(II) according to an unusual bidentate coordination. The contributions of the Cd–N and Cd–Cl bond valences to the total metal valence for both 1 and 2 have been evaluated to confirm the coordination modes of 2-pyimiso, which can be interpreted in terms of Jørgensen’s principle of symbiosis. X-ray structure and Hirshfeld surface analyses have shown that the crystal structure of 1 is determined by two perpendicular 1-D chains formed by weak hydrogen bonds along the a- and c-axes, whereas the supramolecular architecture of 2 exhibits 2-D sheets parallel to the ab-plane interconnected by C–H⋯π interactions along the c-axis. A vibrational analysis of both products has been conducted at the DFT B3LYP-D3/LACV3P** level of calculation.

Molecular and supramolecular properties of a Hg(II) complex with (E)-N,N′-bis(2-pyridyl)iminoisoindoline: synthesis, spectroscopy, X-ray structure and Hirshfeld surface analyses, and DFT calculations

Abstract A scarcity of metal complexes containing (E)-N,N′-bis(heteroaryl)iminoisoindolines has prompted us to investigate the coordinating ability and supramolecular behavior of (E)-N,N′-bis(2-pyridyl)iminoisoindoline (2-pyimiso), a versatile iminobis(pyridyl) ligand. The 1:1 reaction of HgCl2 with 2-pyimiso in MeOH afforded a dinuclear complex, [{HgCl(2-pyimiso)}2(μ-Cl)2] (1). The complex has been characterized by elemental microanalysis, vibrational spectroscopy (FTIR and FT-Raman) and 1H NMR spectroscopy. DFT calculations at the B3LYP-D3/LACV3P** level have been used in support of our vibrational analysis. Single-crystal X-ray diffraction data have shown that the coordination geometry of 1 is intermediate between the trigonal pyramidal and seesaw shapes insofar as each Hg(II) is four-coordinate and 2-pyimiso is a monodentate ligand. X-ray structure and Hirshfeld surface analyses have revealed that the supramolecular arrangement of 1 comprises perpendicular 1-D chains along the [011] direction assembled by nonclassical C–H⋯Cl–Hg and C–H⋯π hydrogen bonds. Moreover, adjacent sheets parallel to the bc-plane are interconnected by C–H⋯Npy, π–πpy stacking, and Hg⋯πpy interactions.

Synthesis and Application of Bimetallic Zinc(II) Phenoxy-Imine Complexes as Initiators for Production of Lactide Polymers

This article reports the synthesis of two bimetallic zinc(II) complexes containing phenoxyimine ligands and their application as initiators of ring opening polymerization (ROP) of L-lactide (LA). The phenoxy-imine ligands were obtained from salicylaldehyde derivatives and 2,3,5,6-tetramethylphenylenediamine, yielding two bidentate regions per ligand. The reactions of both phenoxy-imine ligands with ZnEt2 in the presence of n-BuOH afforded [Zn2(L1)(OBu)2] and [Zn2(L2)(OBu)2], which were characterized by elemental analysis, Fourier transform infrared (FTIR) and H nuclear magnetic resonance (NMR) spectroscopy. In addition, the geometries of both complexes were investigated by DFT (B3LYP/LACVP**) calculations. [Zn2(L1)(OBu)2] and [Zn2(L2)(OBu)2] were tested as initiators of ROP of LA at 180 °C using different LA/Zn molar ratios, namely 500, 1000 and 2500. Both complexes showed good activity, resulting in conversions up to 96% in 2 h. The poly-LLA exhibited average molecular weight (Mw) ranging from 45,000-92,000, relatively low polydispersity (Mw/Mn = 1.6-2.0) and high stereoregularity with melting temperature Tm = 164 °C.