Mixed Guanidinato/Alkylimido/Azido Tungsten(VI) Complexes: Synthesis and Structural Characterization

A series of structurally characterized new examples of pentacoordinated heteroleptic tungsten(VI)−guanidinates
complexes are described. Starting out from [WCl2(Nt-Bu)2py2] (1) (py = pyridine) and the guanidinato transfer
reagents (TMEDA)Li[(Ni-Pr)2CNi-Pr2] (2a) (TMEDA = N,N,N‘,N‘-tetramethylethylendiamine) and [Li(NC(NMe2)2)]x
(2b), the title compounds [WCl(Nt-Bu)2{(Ni-Pr)2CNi-Pr2}] (3) and [W(Nt-Bu)2Cl{NC(NMe2)2}]2 (6) were selectively
formed by the elimination of one mole equivalent of lithium chloride. The isopropyl-substituted guanidinato ligand
{(Ni-Pr)2CNi-Pr2} of monomeric 3 is N1,N3-bonded to the tungsten center. The introduction of the sterically less-demanding tetramethyl guanidinato ligand {NC(NMe2)2} expectedly leads to dimeric 6 exhibiting a planar W2N2
ring with the guanidinato group bridging the two tungsten centers via the deprotonated imino N-atom. The remaining
chloro ligand of 3 is labile and can be substituted by sterically less-crowded groups such as dimethylamido or
azido that yield the presumably monomeric compounds 4 and 5, respectively. A similar treatment of 6 with sodium
azide yields the dimeric azido derivative 7. Reacting [WCl2(Nt-Bu)2py2] directly with an excess of sodium azide
leads to the dimeric bis-azide species [{W(Nt-Bu)2(N3)(μ2-N3)py}2]. The new compounds were fully characterized
by single-crystal X-ray diffractometry (except 2, 4, and 5), NMR, IR, and mass-spectroscopy as well as elemental
analysis. Compound 5, [W(N3)(Nt-Bu)2{(Ni-Pr)2CNi-Pr2}], can be sublimed at 80 °C, 1 Pa.