Novel Pyridazine Based Scorpionate Ligands in Cobalt and Nickel Boratrane Compounds

Abstract

Heating of 6-methylpyridazine-3-thione (HPn(Me)) and 6-tert-butylpyridazine-3-thione (HPn(tBu)) with potassium borohydride in diphenylmethane in a 3:1 ratio gave two new scorpionate ligands K[HB(Pn(Me))(3)] and K[HB(Pn(tBu))(3)]. Single crystal X-ray diffraction analysis of the methyl derivative K[HB(Pn(Me))(3)] revealed a dimeric species with one potassium atom coordinated by six sulfur atoms of two scorpionate ligands and a second potassium atom coordinated by three nitrogen atoms of one of the two ligands as well as by three water molecules. The reaction of K[HB(Pn(tBu))(3)] with nickel(II) chloride or cobalt(II) chloride in CH(2)Cl(2) led to the new boratrane compounds [M{B(Pn(tBu))(3)}Cl] (M = Ni 1, Co 3) where a formal reduction of the metal ions to Ni(I) and Co(I), respectively, and activation of the B-H bond occurred. Similar reactivity was observed by employing K[HB(Pn(R))(3)] (R = Me, tBu) and nickel(II) chloride in water. Reaction with cobalt(II) chloride in water also gave boratrane compounds [Co{B(Pn(R))(3)}(Pn(R))] (R = tBu 4, Ph 5), but instead of a chloride a bidentate pyridazinethionate ligand from a defragmentated scorpionate is found in the molecules. The molecular structures of all nickel and cobalt compounds were determined by single crystal X-ray diffraction analyses confirming the formation of boratranes in compounds 1-5. Magnetic measurements confirm the reduced oxidation states and the paramagnetic character of the Ni(I) and Co(I) complexes. Supportive DFT studies were carried out for a better understanding of the electronic nature of the metal-boron bond of the boratrane complexes.

Benzannulated tris(2-mercapto-1-imidazolyl)hydroborato ligands: tetradentate κ4-S3H binding and access to monomeric monovalent thallium in an [S3] coordination environment

“…17 Despite the dearth of compounds that feature [κ 4 – S 3 H- Tm R ] ligands, κ 4 – S 3 H coordination modes have, nevertheless, been reported for other ligand systems. 18,19,20 Such complexes, however, do not exist as discrete mononuclear species, but are either dinuclear or polymeric. Bond lengths associated with these M[S 3 HB] moieties are summarized in Table 3, from which it is evident that [Tm MeBenz ]K(OCMe 2 ) 3 possesses K–S and K•••H–B interactions that are comparable to those of the other potassium compounds that feature κ 4 – S 3 H interactions.…”

Cooperative Interactions in the Second Coordination Sphere of Pyridazine/Pyridine Containing Polyazaheterocyclic Iron(II) Complexes Favor Protonation

“…However, for first row transition metals, this generally requires that the pyridazine is part of a larger ligand scaffold or macrocycle functionalized with additional pendant donor sites. In the absence of this cooperation and notably in higher valent metals, pyridazines typically coordinate in a monodentate fashion through a single nitrogen . This is likely due to the initial coordination with the first nitrogen decreasing the basicity of remaining site for interaction with an additional metal.…”

Zinc Scorpionate Complexes with a Hybrid (Thiopyridazinyl)(thiomethimidazolyl)borate Ligand

“…Since then, numerous soft scorpionate ligands have been synthesized, varying in their substitution or their heterocycle backbone. Thus, not only differently substituted thiomethimidazoles (Tm), but also benzoimidazoles, thiadiazoles, benzothiadiazoles, thiazolidines,, triazoles, tetrazoles, pyridines, and pyridazines, have been introduced into soft scorpionate ligands (Figure ). In contrast to the nitrogen‐based scorpionate ligands, they form eight‐membered chelate rings (compared with six), which allows for more flexibility in their metal complexes leading to unusual structures and reactivities.…”

“…We have recently begun to explore a new class of scorpionate ligands (Tn R ) that contain electron‐deficient thiopyridazine heterocycles, Na[HB{Pn R } 3 ] (R = Me, t Bu) (Figure ) , , . They were found to exhibit a high tendency to form boratrane complexes with direct metal–boron bonds, such as [M I {B(Pn R )}Cl] (M = Cu, Ni, Co).…”

“…They were found to exhibit a high tendency to form boratrane complexes with direct metal–boron bonds, such as [M I {B(Pn R )}Cl] (M = Cu, Ni, Co). During their synthesis, the hydride on the boron was abstracted thereby reducing the metal center . Furthermore, the greater flexibility also led to compounds with inverted boron centers, with the hydride involved in B–H–M bonding interactions …”