The chemistry of high valent tungsten chlorides with N-substituted ureas, including urea self-protonation reactions triggered by WCl6

The reactions of WCl6, WCl5 and WOCl4 with a selection of N-substituted ureas (tetramethylurea = tmu; tetraethylurea = teu; 1,3-diphenylurea = dpu; 1,3-dimethylurea = dmu) were performed in chlorinated solvents and then elucidated by means of analytical, spectroscopic and DFT results. The 1 : 2 molar reactions of WCl6 with, respectively, tmu and dpu proceeded with electron interchange and afforded the salts [(O-H-O)-(tmu)(2)(mu-H)][WCl6], 1a (40% yield), and [(O-H-O)-(dpu)(2)(mu-H)][WCl6], 1b (65%). Based on X-ray analyses, the cations in 1a,b consist of a O-protonated urea forming H-bond with a second urea unit. [dpu(O-H)][WCl6], 2, was obtained (68% yield) from WCl6/dpu (1 : 1 molar ratio). Dpu itself was identified as the presumably main source of protonation leading to 1b and 2, via N-H bond activation and possible involvement of the solvent (dichloromethane). The complexes WCl5(urea) (urea = dmu, 3a; tmu, 3b; teu, 3c) were isolated in moderate yields by allowing WCl6 to react with the appropriate organic reactant under different experimental conditions. The same complexes 3a-c were obtained in 40-50% yields from the combinations WCl5/urea, and few crystals of WOCl4(teuH), 4, were afforded from WCl5/tmu as a result of adventitious hydrolysis. The reactions of WOCl4 with ureas were not selective in general, although WOCl4(dmu), 5, was isolated in 66% yield. The X-ray structures determined for 3a and 3b constitute the first examples of crystallographic characterization of complexes of tungsten pentachloride with a neutral ligand.