A Family of Four‐Coordinate Iron(II) Complexes Bearing the Sterically Hindered Tris(pyrazolyl)borato Ligand Tp^tBu,Me

Abstract

A new family of 14-electron, four-coordinate iron(II) complexes of the general formula [Tp(tBu,Me)FeX] (Tp(tBu,Me) is the sterically hindered hydrotris(3-tert-butyl-5-methyl-pyrazolyl) borate ligand and X=Cl (1), Br, I) were synthesized by salt metathesis of FeX(2) with Tp(tBu,Me)K. The related fluoride complex was prepared by reaction of 1 with AgBF(4). Chloride 1 proved to be a good precursor for ligand substitution reactions, generating a series of four-coordinate iron(II) complexes with carbon, oxygen, and sulphur ligands. All of these complexes were fully characterized by conventional spectroscopic methods and most were characterized by single-crystal X-ray crystallographic analysis. Magnetic measurements for all complexes agreed with a high-spin (d(6), S=2) electronic configuration. The halide series enabled the estimation of the covalent radius of iron in these complexes as 1.24 Å.

Four‐Coordinate Trispyrazolylboratomanganese and ‐iron Complexes with a Pyrazolato Co‐ligand: Syntheses and Properties as Oxidation Catalysts

“…[13] Compounds 1 a-c and 2 a-c are very unreactive. They can be crystallised in contact with air, and they are also inert towards water for longer periods of time.…”

“…Potassium hydrotris(3,5-dimethylpyrazolyl)-borate and 3,5-diisopropylpyrazole were purchased from Aldrich; 3,5-methylphenylpyrazole, [37] [(Tp iPr,iPr )Mn(Cl)] [8] and [(Tp Ph,Me )Mn(Cl)] [10] were synthesised as described earlier. The syntheses of the alkali metal hydrotrispyrazolylborate [38] compounds of 3,5-diisopropylpyrazole, 3,5-tert-butylmethylpyrazole and 3,5-phenylmethylpyrazole, as well as 3,5-tert-butylmethylpyrazole, [39] [(Tp iPr,iPr )Fe(Cl)] [12] and [(Tp Me,tBu )Fe(Cl)] [13] , corresponded to published procedures. …”

Methyl Complexes of the Transition Metals

“…Bulky tris(pyrazolyl)borate ligands (Tp) have also been used to stabilise 14-electron tetracoordinated complexes, including TpFeCH3 (Scheme 11). 80,81 Another example of low electron count Fe(II)-methyl complex is square planar (IMes)2FeMe2 that was prepared by Glorius and collaborators by reacting Fe(N(SiMe3)2)2 with IMesCl (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and treating the resulting (IMes)2FeCl2 with LiMe. The geometric change from the dichloride to the dimethyl complex was attributed by the authors to both the steric properties of the IMes ligands and the strong ligand field created by the -donor character of the carbene and the methyl ligands.…”

Scorpionato Halide Complexes [(TpPh,Me)Ni–X] [X = Cl, Br, I; TpPh,Me = Hydrotris(3‐phenyl‐5‐methyl‐1‐pyrazolyl)borate]: Structures, Spectroscopy, and Pyrazole Adducts

“…M-X] are particularly valuable as synthetic precursors, since a wide range of co-ligands can be introduced by metathesis or halide abstraction, [5][6][7][8][9][10][11] thereby enabling biomimetic chemistry and catalysis. [8][9][10][11][12][13] We recently reported several arylthiolate complexes [(Tp R,Me )Ni-SAr] (R = Me, Ph), which were readily obtained by reaction of [(Tp R,Me )Ni-Cl] with NaSAr.…”