Oxygen-Induced Dimerization of Alkyl-Manganese(II) 2,6-Bisiminopyridine Complexes: Selective Synthesis of a New Ditopic NNN-Pincer Ligand

Abstract

The outcome of the reaction of manganese(II) dialkyls with 2,6-bisiminopyridine (BIP) ligands is dramatically altered by the presence of very small amounts of oxygen (< 0.5 mol %), leading to binuclear species. These arise from the dimerization of the initial product, a Mn(II) 4-alkyl-2,6-bisiminodihydropyridinate alkyl complex. Cleavage of the binuclear Mn products with methanol affords the free dimeric bases, which can be regarded as a special type of ditopic NNN pincer ligand with an unusual tricyclic framework. The coordinative ability of the new ligands has been probed with the syntheses of Zn and Pd organometallic derivatives.

Building C(sp3) Molecular Complexity on 2,2′‐Bipyridine and 1,10‐Phenanthroline in Rhenium Tricarbonyl Complexes

“…The latter was formed by C−C coupling between the 3 positions and the 5 positions of 12‐C4 followed by protonation at the 6 positions. As previously found for the products from PDI dimerization, [33–35] the 3, 4, and 5 positions of the coupled rings defined a cyclohexane ring in a chair configuration. As a result of the selective 3–3 and 5–5 C−C bond formation, the tetradentate N‐chelate adopted a U‐shaped configuration.…”

“…Dimerization of pyridyldiimine (PDI) ligands triggered by intramolecular alkyl migration to the pyridyl ring has been reported in manganese(II), [33] aluminium(III), [34] and chromium(II) [35] alkyl complexes. An analogous transformation involving bipy was unknown and could be thought to be more energetically demanding as it involves the dearomatization of a second pyridyl ring.…”

Neutral Bis(imino)-1,4-dihydropyridinate and Cationic Bis(imino)pyridine σ-Alkylzinc(II) Complexes as Hydride Exchange Systems: Classic Organometallic Chemistry Meets Ligand-Centered, Biomimetic Reactivity

“…However, compound 1 reacts readily with weak acids and electrophiles, as summarized in Scheme 2. We have shown before that methanol attacks at the Zn center, 17 cleanly releasing the known 1,4-dihydropyridine base 4-Bn-H2 iPr BIP. In situ NMR investigation of a similar reaction of 1 with BnOH in C6D6 in nearly 1:1 ratio revealed that the Zn-bound benzyl group ends up as toluene but did not allow to ascertain the fate of the Zn atom.…”

“…More recently, we have shown that trace amounts of oxygen suffice to trigger the dimerization pathway also in this system, leading to the corresponding Mn(II) dimers of type B. 17 Alkyl migration to the pyridine ring has also been observed when BIP ligands react with organometallic derivatives of "non-redox" main group metals. For example, Budzelaar showed that the reaction of alkylaluminum derivatives with iPr BIP produces complicated mixtures arising from non-selective alkyl migration, amongst which the corresponding C4-alkylated products of type A were detected.…”

“…0.5 Å for 6 and 10). In contrast, and angles (deg): Zn1-C28 1.970(5); Zn1-N1, 2.069(4); Zn1-N2, 2.367(4); Zn1-N3, 2.243(5); C1-C6, 1.472(8); C5-C17, 1.483(8); C1-N1, 1.346(7); C5-N1, 1.337(7); C8-N2, 1.449(7); C17-N3, 1.434(7); C28-Zn1-N1, 158.0(2); N3-Zn1-N2, 141.88(15); N1-Zn1-N2, 72.15 (17); N1-Zn1-N3, 74.76 (17). Distance from Zn1 to the to the[N1-N2-N3] plane: 0.52 Å. a number of crystal structures of similar complexes containing smallsized X ligands [( iPr BIP)M-X] n+ (e. g., X = halogen or methyl; M = Mn, 39 Fe, 32,43 Co, 42a,44 Ni 45 or Cu 46 ; n varying from -1 to +1) all exhibit strictly flat geometries.…”