SCHEDULED MAINTENANCE
The chemistry of high valent tungsten chlorides with N-substituted ureas, including urea self-protonation reactions triggered by WCl6†
Abstract
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(μ-H)][WCl6], 1a (40% yield), and [(O–H–O)-(dpu)2(μ-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.
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