A tripodal aminothioether ligand scaffold: Synthesis and coordination to zirconium and hafnium

Abstract

The heptadentate ligand, tris-(2-(2-(methylthio)phenylamino)ethyl)amine (2), has been synthesized from the condensation of nitrilotriacetyl chloride with 2-(methylthio)aniline, to generate 2,2',2"-nitrilotris(N-(2-(methylthio)phenyl)acetamide) (1), followed by a lithium aluminum hydride reduction. The zirconium (3) and hafnium (4) complexes of this ligand were generated via transamination reactions. Both complexes are isostructural, exhibiting a hexadentate N 4 S 2 coordination from the ligand, with one diethylamido ligand also bound. The solid state structures of all compounds are reported.

A modular synthesis of tris(aryl)tren ligands: Synthesis, structure and lithiation chemistry

“…The structure of (2) is shown in Figure 1 the a-axis. This structure is very similar to the structure of (1), which we previously reported [21]. The solid state structure of (3) can be seen in Scheme 2.…”

“…The solid state structure of (3) can be seen in Scheme 2. Like 2 has been seen in other aryl substituted tren ligands [18,19,21,25].…”

“…The NTA is first treated with phosphorus pentachloride to yield nitrilotriacetyl chloride [22]. The acid chloride is then coupled with 2-(methylthio)aniline or 2-(phenylthio)aniline using trimethylamine as a sacrificial base to yield 2,2',2"-nitrilotris(N-(2-(methylthio)phenyl)acetamide (1), as previously reported [21], and 2,2',2"-nitrilotris(N-(2-(phenylthio)phenyl)acetamide (2). Following the same procedure with 2-chloroaniline generates a mixture (1:2) of 2,2',2"-nitrilotris(N-(2-chlorophenyl)acetamide (3) and N-2-chlorophenyl-3,5dioxo-1-piperazine-N-(2-chlorophenyl)acetamide (4) with an internal ring-closing favored over the substitution of the third arm [23].…”

“…The tris-amides can then be reduced to the desired tren ligands. The reduction of (1) and 2proceeds with excess lithium aluminum hydride to generate the desire tris-(2-(2-(methylthio)phenylamino)ethyl)amine (5), as we have previously reported [21], and tris-(2-(2-(phenylthio)phenylamino)ethyl)amine (6). For the reduction of (3), borane was used as the reductant, to generate tris-(2-(2-chlorophenylamino)ethyl)amine (7).…”

“…Our lab has begun to explore the inclusion of sulfur moieties in the secondary coordination sphere of metals bound by tris(amido)amine ligands [21]. In a previous report, we described the synthesis of tris(2-methylthio)phenylamino)ethyl)amine (5), which starts with the conversion of nitrilotriacetic acid to nitrilotriacetyl chloride, proceeds via a coupling with 2-(methylthio)aniline and a standard reduction to the desired tren ligand.…”