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)

Abstract

The [NBuⁿ₄]⁺ and [P(CH₂Ph)Ph₃]⁺ salts of the tetranuclear tungstate [W₄O₄Cl₁₀(NBu^t)₄]^2– have been prepared from WOCl₄ and NH₂Bu^t 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(NBu^t)₄]^2– with bipy gives [WOCl₂(NBu^t)(bipy)], whereas [WCl₂(NBu^t)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 NBu^t). 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.