In Z-type ligands the electrons for the coordination bond are formally provided by the metal. They represent an important addition to the much more extensively used L- and X-type σ-donor ligands for the development of transition metal complexes with new reactivities. We report here a new boron Z-type ligand with three tethering thiopyridazinyl donors forming exclusively complexes that feature a metal boron bond. Rational substitution pattern in the backbone of the pyridazinyl heterocycle led to a well-behaved ligand system that allowed preparation of a series of copper boratrane complexes in high yields. They are found to be more soluble in common organic solvents allowing reactivity studies in contrast to previous complexes with this type of ligand. Thus, copper complexes [Cu{B(Pn(Me,tBu))3}X] with X = Cl, OTf, N3, and κN-NCS are reported. Solution behavior was explored, and the molecular structures were determined by single-crystal X-ray diffraction analyses. The thiocyanate ligand is found to coordinate via its nitrogen atom pointing to a high oxidation state of the copper. Density functional theory calculations indicate a high positive charge on copper and a strong copper-boron interaction. Thus, here reported complexes deliver synthetic evidence for the Z-type nature of the ligand. These findings are important for further dissemination of these types of ligands in coordination chemistry.

The terminal zinc hydride complex [Tntm]ZnH (2; Tntm=tris(6-tert-butyl-3-thiopyridazinyl)methanide) is an efficient hydrosilylation catalyst of CO at room temperature without the need of Lewis acidic additives. The inherent electrophilicity of the system leads to selective formation of the monosilylated product (MeO) SiO CH (at room temperature with a TOF of 22.2 h and at 45 °C with a TOF of 66.7 h ). In absence of silanes, the intermediate formate complex [Tntm]Zn(O CH) (3) is quantitatively formed within 5 min. All complexes were fully characterized by H and C NMR spectroscopy and single-crystal X-ray diffraction analyses. Density functional theory (DFT) calculations reveal a high positive charge on zinc and the increased preference of the ligand to adopt a κ -coordination mode.

The soft scorpionate ligand hydrotris(6-tert-butyl-3-thiopyridazinyl)borate (Tn) was found to exhibit pronounced photoreactivity. Full elucidation of this process revealed the formation of 6-tert-butylpyridazine-3-thione (PnH) and 4,5-dihydro-6-tert-butylpyridazine-3-thione (H2PnH). Under exclusion of light, no solvolytic reactions occur, allowing the development of high-yield preparation protocols for the sodium, potassium, and thallium salts and improving the yield for their derived copper boratrane complex. The photoreactivity is relevant for all future studies with electron-deficient scorpionate ligands.

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The ligand tris(6-tert-butyl-3-thiopyridazinyl)methane ([Tntm]H) was synthesized by the reaction of 6-tertbutyl-3-thiopyridazine with bromoform and reacted with zinc bis(trimethylsilylamide) (Zn(N{SiMe 3 } 2 ) 2 ) to form [Tntm]-Zn(N{SiMe 3 } 2 ) (1). This complex further reacts with protic and acidic substrates, generating the zinc thiolate complex [Tntm]Zn(StBu) (2) and zinc benzoate complex [Tntm]Zn-(O 2 C-Me 2 C 6 H 3 ) (3a). In all compounds [Tntm] was found to have tridentate coordination to the metal center in a κ 3 -C,N,N fashion, as established by single-crystal X-ray diffraction analyses. In solution, rapid dynamic κ 3 /κ 4 equilibrium occurs at room temperature, while 1 H NMR spectroscopy at −30 °C confirms the asymmetric solid-state structure. Furthermore, complex 3a shows a rearrangement reaction in solution where the ligand isomerizes to give a κ 4 -C,N,N,S (3b) and a κ 4 -C,N,S,S isomer (3c), respectively. Density functional theory (DFT) calculations reveal 3b and 3c to be 13.7 and 15.6 kJ/mol more stable in methylene chloride than 3a, respectively. All compounds were fully characterized via 1 H, 13 C, and variable temperature NMR spectroscopy, as well as elemental and single-crystal X-ray diffraction analysis.

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A novel selenium-containing pyridazinyl-based soft scorpionate ligand (KTnse) was synthesized. It reacts with CoCl and NiCl, yielding the first metallaboratrane complexes with selenium in their donor positions. Further substitution with Ag(OTf) or NaN allows isolation of the respective triflate or azide complexes. Reaction with Ag(OTf) leads in the case of nickel to a dinuclear, dicationic complex with a short Ni-Ni distance, while cobalt gave a mononuclear cationic species. Substitution of the chloride by azide yields with both metals the respective azide complexes. All compounds were characterized via single-crystal X-ray diffraction analysis. Density functional theory calculations on the chloride species point to oxidized cobalt(III) and nickel(III) centers.

Scorpionate ligands with three soft sulfur donor sites have become very important in coordination chemistry. Despite its ability to form highly electrophilic species, electron-deficient thiopyridazines have rarely been used, whereas the chemistry of electron-rich thioheterocycles has been explored rather intensively. Here, the unusual chemical behavior of a thiopyridazine (6-tert-butylpyridazine-3-thione, HtBuPn) based scorpionate ligand towards zinc is reported. Thus, the reaction of zinc halides with tris(6-tert-butyl-3-thiopyridazinyl)borate Na[TntBu] leads to the formation of discrete torus-shaped hexameric zinc complexes [TntBuZnX]6 (X = Br, I) with uncommonly long zinc halide bonds. In contrast, reaction of the sterically more demanding ligand K[TnMe,tBu] leads to decomposition, forming Zn(HPnMe,tBu)2X2 (X = Br, I). The latter can be prepared independently by reaction of the respective zinc halides and two equiv of HPnMe,tBu. The bromide compound was used as precursor which further reacts with K[TnMe,tBu] forming the mononuclear complex [TnMe,tBu]ZnBr(HPnMe,tBu). The molecular structures of all compounds were elucidated by single-crystal X-ray diffraction analysis. Characterization in solution was performed by means of 1H, 13C and DOSY NMR spectroscopy which revealed the hexameric constitution of [TntBuZnBr]6 to be predominant. In contrast, [TnMe,tBu]ZnBr(HPnMe,tBu) was found to be dynamic in solution.