Three-Fold-Symmetric Selenium-Donor Metallaboratranes of Cobalt and Nickel

Abstract

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.

Synthesis and Structural Characterization of Copper Complexes Containing “R-Substituted” Bis-7-Azaindolyl Borate Ligands

“…In 2008, we suggested that this new set of ligands be termed “flexible scorpionates” [ 6 , 7 ] since the consequences of this extra atom in each of the heterocycles change their properties and potential reactivity quite significantly [ 8 , 9 , 10 ]. A range of heterocycles has now been utilized to generate flexible scorpionate ligands based on sulfur [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ], nitrogen [ 17 , 18 , 19 , 20 , 21 ], phosphine [ 22 , 23 ], oxygen [ 24 , 25 ] and other donors [ 26 , 27 ]. To the best of our knowledge, there are only a small number of complexes reported containing nitrogen-based flexible scorpionate ligands.…”

Quantifying the Donor Strength of Ligand-Stabilized Main Group Fragments

“…In recent years, it has been a matter of particular interest as to whether neutral, tricoordinate boron compounds can serve as electron-donating ligands rather than pure acceptor ligands, as they are commonly viewed. Notably, a majority of tricoordinate boron compounds of the type BR 3 are known to act as Lewis acids and σ-accepting or Z-type ligands in transition-metal complexes. − By manipulation of the R substituents in BR 3 , it is possible to cause a dramatic change in these properties: formally anionic substituents, such as hydrides, alkyls, aryls, halogenides, and most anionic N-heterocycles lead to classical Lewis acids or Z-type ligands. ,− In these cases, the vacant p z -orbital of the trigonal planar boron compound is stabilized either by π-donation of the substituents or by dimerization and the formation of two-electron, three-center bonds. Replacing one of the substituents R on boron by a neutral σ-donating and π-accepting substituent L formally results in a partially filled p z -orbital at the boron atom in BR 2 L. This ligand-stabilized boryl ligand acts as an X-type ligand and contributes one electron to a covalent bond.…”

Thiopyridazine-Based Palladium and Platinum Boratrane Complexes

“…The respective metal complexes are generally referred to as metallatranes and specifically with boron as metallaboratranes. Many borane ligands with various structural motifs capable for boratrane formation were developed including nitrogen, sulfur, selenium, or phosphorus donor sites. ,− Typically, such metallaboratrane complexes can either be formed by direct reaction of the respective neutral borane [Me 2 P­(CH 2 ) 2 ] 3 B or [ o -(R 2 P)­C 6 H 4 ] 3 B with a metal precursor or via the more general reaction of a hydroborate ligand HB­(Het) 3 ¯ (Het = 2-thiomethimidazole, 7-azaindol, 2-thiopyridine, 5-thiotriazol, 6- tert -butyl-3-thiopyridazine) ,,, with a metal precursor under elimination of the hydride at boron (Figure ).…”

“…49 We have recently developed thiopyridazine-based borate ligands K[HB(Pn R,tBu ) 3 ] (KTn R,tBu ) which form boratrane complexes with metal halide precursors (as shown in Scheme 1). 27,30,34,35,41,50 Thiopyridazine belongs to the electrondeficient heterocycles and is thus expected to promote a strong Z-type interaction. Our observed high tendency for boratrane formation goes along with this expectation.…”

“…Here we present the synthesis and characterization of a palladium and platinum boratrane complexes of the general formula [M{B(Pn Me,tBu In contrast to 1 where a C 3 symmetric product is obtained, reaction of KTn Me,tBu with [PtCl 2 (PPh 3 ) 2 ] led to the isolation Scheme 1. Thiopyridazine-Based Borate Ligand K[HB(Pn R,tBu ) 3 ] (KTn R,tBu ) and Boratrane Formation 27,30,34,35,41 . This is also supported by the IR spectrum where a band for the Pt−H stretching frequency at 2147 cm −1 is prominently observed, which is in perfect agreement with the calculated IR spectrum (Figure S26).…”