Zirconium complexes incorporated with asymmetrical tridentate pincer type mono- and di-anionic pyrrolyl ligands: mechanism and reactivity as catalytic precursors

Abstract

The reactions of Zr(NR(2))(4) (1, R = Me; 2, R = Et) with an asymmetrical tridentate pincer type pyrrole ligand precursor [C(4)H(2)NH(2-CH(2)NH(t)Bu)(5-CH(2)NMe(2))] and treatment of the derivatives with either PhNCS or PhNCO have been carried out and characterized. Reacting Zr(NR(2))(4) (1, R = Me; 2, R = Et) with [C(4)H(2)NH(2-CH(2)NH(t)Bu)(5-CH(2)NMe(2))] generates Zr[C(4)H(2)N(2-CH(2)N(t)Bu)(5-CH(2)NMe(2))](NR(2))(2) (3, R = Me; 4, R = Et) in high yield along with the elimination of 2 equiv of dimethylamine or diethylamine, respectively. Interestingly, while changing the solvent from Et(2)O to CH(2)Cl(2), the complex Zr[C(4)H(2)N(2-CH(2)N(t)Bu)(5-CH(2)NMe(2))][C(4)H(2)N(2-CH(2)NH(t)Bu)(5-CH(2)NMe(2))]Cl (5) is produced by undergoing C-Cl bond cleavage. Furthermore, reaction of either 3 or 4 with 1 or 2 equiv of PhNCS or PhNCO yields Zr[C(4)H(2)N(2-CH(2)N(t)Bu)(5-CH(2)NMe(2))](NMe(2))[PhNC(NMe(2))S] (6), Zr[C(4)H(2)N(2-CH(2)N(t)Bu)(5-CH(2)NMe(2))](NEt(2))[PhNC(NEt(2))O] (7) and Zr[C(4)H(2)N(2-CH(2)NH(t)Bu)(5-CH(2)NMe(2))][PhNC(NEt(2))O](3) (8), respectively. All the aforementioned complexes were characterized by (1)H and (13)C NMR spectrometry and the molecular structures of 5, 6, and 8 have been determined by single-crystal X-ray diffractometry. Complexes 4, 5, and 7 initiated the ethylene polymerization in the presence of MAO as the co-catalyst.

Synthesis, Characterization, and Catalytic Activity of Nickel(II) Alkyl Complexes Supported by Pyrrole–Diphosphine Ligands

“…Furthermore, chelating ligands based on pyrrole motifs have been shown to produce unique catalysts when paired with certain transition metals . In the context of PNP ligands, the role of the pyrrolide group in modulating the catalytic activity of pincer-supported transition-metal complexes remains a question. − …”

Coordination and Reactivity Study of Group 4 and 10 Transition Metal Complexes ofN-Imidazol-2-ylidene-N′-p-tolylureate and Thioureate Ligands

“…Considering the hardness of Ti(IV) and the softness of sulfur, we were quite surprised to conclude a coordination of the thioureate ligand through sulfur. However, out of all the thioureate transition metal complexes structurally characterized and registered with the Cambridge Structural Database, − only two cases with an N ∧ N coordination mode were found. , Our system thus provides further evidence of the shortcomings of the concept of hard and soft acids and bases, recently documented by Mayr . Multiple attempts to grow single crystals for X-ray diffraction studies using several solvent combinations were not successful.…”

Ag(I) and Tl(I) Precursors as Transfer Agents of a Pyrrole-Based Pincer Ligand to Late Transition Metals

“…The splitting of the methylene protons into a virtual triplet has been previously described 22,23,40 and is explained by the meridional coordination of the ligand, in which the methylene protons couple to equivalent phosphines (singlet resonance at 60.53 in the 31 P{ 1 H} NMR spectrum). Virtual triplets are also observed in the corresponding 13 C{ 1 H} NMR spectrum for the methine, methylene, and pyrroletertiary carbons for the same reason.…”

“…Compound [(PN pyr P)Tl] (8) was isolated in 96% yield and characterized crystallographically and by 1 H, 13 C{ 1 H}, 31 P{ 1 H} and 205 Tl NMR spectroscopy. The 1 H NMR spectrum is consistent with a tridentate metal complex, similar to the solution structure of [(PNP)Tl] (PNP = bis(2-di-isopropylphosphino)-4-methylphenyl)amide).…”