Early Metal Di(pyridyl) Pyrrolide Complexes with Second Coordination Sphere Arene-π Interactions: Ligand Binding and Ethylene Polymerization

Synthesis, structural characterization, and bonding analysis of two-coordinate copper(I) and silver(I) complexes of pyrrole-based bis(phosphinimine): new metal-pyrrole ring π-interactions

The reaction between 2,5-bis(diphenylphosphinomethyl)pyrrole and Me3SiN3 gave the new pyrrole-based bis(phosphinimine) L1H in an excellent yield. L1H reacts with [CuCl(COD)]2, AgBF4, or AgOTf to give the corresponding two-coordinate mononuclear ionic complex formulated as [M{(L1H)-κ2N,N}]+[X]- where M = Cu and Ag; X = [CuCl2], BF4 or OTf. Their single crystal X-ray diffraction studies confirmed the two-coordinate geometry formed by the chelate bonding mode of L1H. These 10-membered metalacycles exhibit planar chirality and were also characterized by spectroscopic methods. In addition, in all three structures, there exists a hitherto unknown π-interaction between the pyrrole ring atoms and metal, represented as η2-(Cα-N) in the copper(i) complex, and η3-(Cα-N-Cα') in the silver(i) complexes. These weak interactions were supported by DFT calculations in terms of their electron densities, non-covalent interaction plots and the decrease in the aromaticity of the pyrrole ring.

Effect of Substituents of Cerium Pyrazolates and Pyrrolates on Carbon Dioxide Activation

Homoleptic ceric pyrazolates (pz) Ce(RR’pz)₄ (R = R’ = tBu; R = R’ = Ph; R = tBu, R’ = Me) were synthesized by the protonolysis reaction of Ce[N(SiHMe₂)₂]₄ with the corresponding pyrazole derivative. The resulting complexes were investigated in their reactivity toward CO₂, revealing a significant influence of the bulkiness of the substituents on the pyrazolato ligands. The efficiency of the CO₂ insertion was found to increase in the order of tBu₂pz < Ph₂pz < tBuMepz < Me₂pz. For comparison, the pyrrole-based ate complexes [Ce₂(pyr)₆(µ-pyr)₂(thf)₂][Li(thf)₄]₂ (pyr = pyrrolato) and [Ce(cbz)₄(thf)₂][Li(thf)₄] (cbz = carbazolato) were obtained via protonolysis of the cerous ate complex Ce[N(SiHMe₂)₂]₄Li(thf) with pyrrole and carbazole, respectively. Treatment of the pyrrolate/carbazolate complexes with CO₂ seemed promising, but any reversibility could not be observed.

Versatility of the bis(iminopyrrolylmethyl)amine ligand: tautomerism, protonation, helical chirality, and the secondary coordination sphere with halogen bonds in the formation of copper(II) and nickel(II) complexes

The reaction of N,N-di(2,6-bis(isopropyl)phenylimino-pyrrolyl-α-methyl)-N-methylamine H2L1 with copper(i) sources such as CuX (X = Cl (1), Br (2), and I (3)) afforded bis(chelated) ionic copper(ii) complexes of the type [CuL1H]X. A similar type of mononuclear structure was obtained with Cu(NO3)2·(H2O)3. Conversely, binuclear copper(ii) complexes [Cu2(μ-L1)(μ-OOCCH3)(μ-OH)](4) and [Cu2(μ-L1H)(μ-OOCPh)(μ-O)] (5) were obtained from the reaction of Cu(O2CR)2·H2O with H2L1. Notably, these reactions in the presence of a base yielded the neutral copper(ii) complex [CuL1] (6). This product was also obtained from the reaction of complex 2 or 4 with NaOH in methanol. All structures feature a dianionic imino-pyrrole motif and a protonated central amine function except 4. The reaction of H2L1 with NiCl2·DME gave the mononuclear complex [NiCl2(L1H2)], 7. In contrast to this, the reaction of the newly synthesized sterically less encumbered ligand N,N-di(phenylimino-pyrrolyl-α-methyl)-N-methylamine H2L2 with NiCl2·DME gave the binuclear complex [NiCl(L2H2)(HOMe)]2[Cl]2 (8). Both 7 and 8 show the amine-azafulvene ligand form and coordination of the central amine. The reaction of complex 7 with NaHBEt3 yielded a neutral complex [NiL1] (8) containing the imino-pyrrole form. In the molecular structures, interesting secondary coordination spheres incorporating guest molecules such as CHCl3 and MeOH in the crystal lattices and the presence of helical enantiomers were observed and analysed. In one case, CHCl3 was found inside an unusual cage-like structure supported by halogen bonds. Preliminary DFT calculations on the geometry of the nickel complex with H2L1 showed that the pentacoordinated tbp geometry is more stable than the square planar geometry.