A new tetratungstate, [W4O4Cl10(NBut)4]2–, and its degradation to the mononuclear complex [WOCl2(NBut)-(bipy)] or [WCl2(NBut)2(bipy)](bipy = 2,2′-bipyridine)
The [NBun4]+ and [P(CH2Ph)Ph3]+ salts of the tetranuclear tungstate [W4O4Cl10(NBut)4]2– have been prepared from WOCl4 and NH2But in the presence of chloride ions. The crystal structure of the phosphonium salt has been determined and shows bridging oxo ligands [W-O 1.88 Å(av.) and WOW 159.6°(av.)] and terminal tert-butylimido groups [W–N 1.70 Å(av.) and WNC 174.9°(av.)]. Two µ-chloro ligands occupy positions trans to the imido groups [W–Cl 2.66 Å(av.) and WCIW 115.6°(av.)] while the remaining chlorides are terminal [W–Cl 2.41 Å(av.)]. The structure is stable towards 1,2-dimethoxyethane but is degraded on addition of 2,2′-bipyridine (bipy). At lower temperatures, treatment of [W4O4Cl10(NBut)4]2– with bipy gives [WOCl2(NBut)(bipy)], whereas [WCl2(NBut)2(bipy)] is crystallised from a similar reaction carried out in refluxing toluene. In the oxo complex W–N 1.741(6), W–O 1.716(5) and W–N(bipy) 2.313(5)(trans to O) and 2.335(5)Å(trans to NBut). In the bis(imido) complex W–N 1.754(5) and 1.747(5) and W–N(bipy) 2.373(5) and 2.370(5)Å. These results are compared with crystal structures of related complexes in an effort to understand the bond-length variations in terms of the trans influences and steric properties of the π-bonding imido and oxo ligands.