Design of Sulfur Centred Ligands

Once we had pioneered a new synthetic route to sulfur triimide, most of our S-centred ligand design is either based on the sulfur diimde or sulfur triimide[1,2] (Fig. 1a and b, respectively).

The triimido sulfite S(NR)32– and the tetraimido sulfate S(NR)42– derive from the sulfite and sulfate dianions by isoelectronical replace of the oxygen atom by RN-groups. Consequently, they can be replaced by methylene R2C-groups as well to give polyimido sulfur ylides. (R2C)S(NR)22– [3] and (R2C)S(NR)32– [4] were syn- thesized and isolated as well (Fig. 2).

More recently we focus on heteroatomic-substituted multidentate ligand systems featuring two pendent arms and a second co- ordination site, which can also be referred to as claw ligands or scorpionates (Fig. 3). The additional Lewis basic centre is provided either by a R2P(CH2)n– oder R2N(CH2)n– group, connected to the sulfur atom. Our principal goal is to develop these ligands, which bear coordination sites for both hard and soft metal centres. If both coordination sites of the ligand point in opposite directions we have coined it a Janus head ligand. By these means, simultaneous coordination of catalytically active and co-catalytical metals in heterobimetallic complexes would be feasible, promoting their catalytic versatility[5]. This project is awarded a grant in the PhD program Catalysis for Sustainable Synthesis (CaSuS) funded by the Land Niedersachsen.

Metal complexes are accessible via salt elimination from e. g. the dimer [Li{Me2PCH2S(NR)2}]2 and metal amides. They can (N,N,P)- or (N,N,N)-coordinate in a facial fashion to various metals. To widen the route to ligands with even more donor sites TMMDA (Tetramethylmethylenediamine) was employed as a side arm at sulfur. This ligand provides a Li4 torus, organized and maintained by a polydentate S-centered N-donating ligand, capable to acco- mmodate thermodynamically unfavoured lithium peroxide[6]
(Fig. 4).

Those ligands are promising targets in hetero-bimetallic homo- genous, preferentially non-d-block, metal catalysis and even in electrolyte materials towards the lithium air battery.


[1] R. Fleischer, A. Rothenberger, D. Stalke Angew. Chem. 1997, 109, 1140; Angew.Chem. Int. Ed. Engl. 1997, 36, 1105.

[2] R. Fleischer, S. Freitag, D. Stalke J. Chem. Soc. Dalton Trans. 1998, 193.

[3] S. Deuerlein, D. Leusser, U. Flierler, H. Ott, D.Stalke Organometallics 2008, 27, 2306.

[4] B. Walfort, D.Stalke Angew. Chem. 2001, 113, 3965; Angew.Chem. Int. Ed. Engl. 2001, 40, 3846.

[5] M. M. Meinholz, S. M. Deuerlein, S. K. Pandey, D.Stalke Dalton Trans. 2011, 40, 1662 and front cover title.

[6] M. M. Meinholz, E. Carl, E. Kriemen, D.Stalke Chem. Commun. 2011, 47, 10948.