Thiopyridazine-Based Copper Boratrane Complexes Demonstrating the Z-type Nature of the Ligand

Abstract

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.

Adding to the Family of Copper Complexes Featuring Borohydride Ligands Based on 2-Mercaptopyridyl Units

“…It was this greater flexibility within the ligand structure that opened up the potential for activation at the boron bridgehead and formation of metal-borane (metallaboratrane) complexes [17][18][19][20][24][25][26][27], giving rise to reactivity not observed in the analogous polypyrazolylborate ligands [10][11][12][13][14][15][16]. Over the following twenty years since the first report of hydride migration from the boron center of a scorpionate ligand, a number of research groups have focused on new, more flexible borohydride ligands containing a range of supporting units based on nitrogen [28][29][30][31] and other sulfur heterocycles [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]. As part of our research, we have focused on providing new derivative ligand systems.…”

“…The first of the more flexible scorpionate ligands was [Tm] − [hydrotris(methylimidazolyl)borate] (Figure 1; middle) [23]. This new ligand had two major Over the following twenty years since the first report of hydride migration from the boron center of a scorpionate ligand, a number of research groups have focused on new, more flexible borohydride ligands containing a range of supporting units based on nitrogen [28][29][30][31] and other sulfur heterocycles [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]. As part of our research, we have focused on providing new derivative ligand systems.…”

(Acetamide-κO){2,2′,2′′-boranetriyltris[6-tert-butyl-4-methylpyridazine-3(2H)-thione]-κ4 B,S,S′,S′′}copper(I) trifluoromethanesulfonate chloroform disolvate

“…Their Z-type coordination mode provides an entry into electronically interesting metal atoms, which recently were successfully used in catalytic dinitrogen reduction (Anderson et al, 2013). Our group is focusing on thiopyridazine-based soft scorpionates and their related metallaboratrane complexes (Nuss et al, 2011a,b;Holler et al, 2016Holler et al, , 2017. In an attempted synthesis of the boratrane complex {2,2 0 ,2 00 -boranetriyltris[6-tert-butyl-4-methylpyridazine-3(2H)-thione]}(trifluoromethanesulfonato)copper(I) (= [Cu{B(Pn Me,tBu ) 3 }(OTf)]), described in the literature by our group (Holler et al, 2016), the title compound formed serendipitously by reaction with residual acetamide from the acetonitrile solvent.…”

Tris(6-tert-butyl-4-methylpyridazine-3-thiolato-κ2N,S)aluminium

“…To a solution of lithiumaluminium hydride in THF (12 ml, 0.15 M, 1.8 mmol) a solution of 6-(tert-butyl)-4-methylpyridazine-3(2H)-thione (1.00 g, 5.48 mmol), prepared by a reported procedure (Holler et al, 2016), in 5 ml THF was added dropwise using a syringe data reports under a nitrogen atmosphere over a period of 30 min, whereupon gas evolution was observed. After 1 h of stirring gas evolution ceased.…”