Heteroleptic Four-Coordinate Tris(oxazolinyl)borato Iron(II) Compounds

Abstract

The reaction of FeBr 2 and 1 equiv. of thallium tris(4,4-dimethyl-2oxazolinyl)phenylborate (TlTo M ) in THF provides To M FeBr (1), whereas FeBr 2 and 2 equiv. of TlTo M react to give (To M ) 2 Fe (2). Two ν CN bands at 1604 and 1548 cm -1 indicated bidentate coordination of To M to iron in 2. Homoleptic 2 and FeBr 2 react in THF overnight through an unusual comproportionation process to give compound 1, which is apparently the thermodynamic product. The salt metathesis reaction of 1 and KCH 2 Ph affords To M FeCH 2 Ph (3).The effective magnetic moments of compounds 1 -3 range from 4.9 to 5.4  B , and these values are consistent with high-spin iron(II) (S = 2). A single 1 H NMR signal assigned to the methyl groups of the To M ligand suggested tridentate coordination of the To M ligand to iron in 1 and 3.X-ray crystallography studies of 1 -3 establish their structure as four-coordinated tetrahedral iron complexes. To M FeBn and CO (1 atm) react to afford isolable To M Fe{C(=O)Bn}(CO) 2 (4) as a yellow solid. Complex 4 is diamagnetic (S = 0), and the three distinct methyl signals in the 1 H

Selective Pathway toward Heteroleptic Spin-Crossover Iron(II) Complexes with Pyridine-Based N-Donor Ligands

“…The proposed "one-pot" approach to heteroleptic complexes, including those inaccessible by other synthesis pathways, is applicable to other types of N-donor ligands, such as nonplanar scorpionate 96 or bidentate 97 ligands. It expands even further the "toolkit" for molecular design of SCO compounds to tailor the SCO behaviors for practical applications by a proper choice of co-ligands�and by modifications to these ligands�that have a different (opposite) effect on the spin state of the metal ion or even produce SCO-inactive homoleptic complexes.…”