Controlled CO labilization of tungsten carbonyl precursors for the low-temperature synthesis of tungsten diselenide nanocrystals

We report a low-temperature colloidal synthesis of WSe 2 nanocrystals from tungsten hexacarbonyl and diphenyl diselenide in trioctylphosphine oxide (TOPO). We identify TOPO-substituted intermediates, W(CO) 5 TOPO and cis- W(CO) 4 (TOPO) 2 by infrared spectroscopy. To confirm these assignments, we synthesize aryl analogues of phosphine-oxide-substituted intermediates, W(CO) 5 TPPO (synthesized previously, TPPO = triphenylphosphine oxide) and cis- W(CO) 4 (TPPO) 2 and fac- W(CO) 3 (TPPO) 3 (new structures reported herein). Ligation of the tungsten carbonyl by either the alkyl or aryl phosphine oxides results in facile labilization of the remaining CO, enabling low-temperature decomposition to nucleate WSe 2 nanocrystals. The reactivity in phosphine oxides is contrasted with syntheses containing phosphine ligands, where substitution results in decreased CO labilization and higher temperatures are required to induce nanocrystal nucleation.