A series of structurally characterized new examples of pentacoordinated heteroleptic tungsten(Vi)-guanidinates complexes are described. Starting out from [WCl2(Nt-Bu)(2)py(2)] (1) (py = pyridine) and the guanidinato transfer reagents (TMEDA)Li[(Ni-Pr)(2)CNi-Pr-2] (2a) (TMEDA = N,N,N',N'-tetramethylethylendiamine) and [Li(NC(NMe2)(2))](x) (2b), the title compounds [WCl(Nt-Bu)(2){(Ni-Pr)(2)CNi-Pr-2}] (3) and [W(Nt-Bu)(2)Cl{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)(2)CNi-Pr-2} of monomeric 3 is N-1,N-3-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)(2)py(2)] directly with an excess of sodium azide leads to the dimeric bis-azide species [{W(Nt-Bu)(2)(N-3)(mu(2) -N-3)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(N-3)(Nt-Bu)(2){(Ni-Pr)(2)CNi-Pr-2}], can be sublimed at 80 degrees C, 1 Pa.