Ring Structure Formation in Transition-Metal Nitrido Chlorides by Donor−Acceptor Formation

Abstract

According to quantum chemical calculations, nitrido chlorides constituted from d6 transition metals form ring structures which are best described as weak donor−acceptor complexes between the lone pair at nitrogen and the empty d orbitals at the transition metal. The stabilities of the ring structures increase in the order Cr < Mo < W. The transition metal Cr forms only endothermic ring systems, and these in turn decompose into monomers. A comparison of several homologous oligomers of NMoCl3 shows maximum stability for the tetramer, in agreement with the experimental findings. This particular stability of the tetramer is due to a perfect alignment of the nitrogens between two metal centers. The vibrational analyses reveal that the character of the monomers is nearly conserved in the ring systems. An analysis of the electron densities on the basis of Bader's method of atoms in molecules as well as of the natural bond orbitals (NBO) substantiates the weak ring stabilities.

Unusually stable tungstenacyclobutadienes featuring an ONO trianionic pincer-type ligand

“…1 H} NMR spectra of the reaction mixture may represent several multi-nuclear species; it is well-known for Wnitrido complexes to exist as dimers, 20,76-79 trimers, [77][78][79][80] and larger oligomers. 77,78 Most importantly, complex 7 and the free 4,4-dimethyl-2-pentyne indicate retro-[2 + 2]-cycloaddition occurred. In fact, retro-[2 + 2]-cycloaddition must occur swiftly because 7 is the product of alkylidyne 5 and free 4,4-dimethyl-2-pentyne.…”

Nitrido Dimers and Trimers of Tungsten Supported by tBuMe2SiO and CF3Me2CO Ligands, Respectively. Factors Influencing the Reductive Cleavage of Nitriles by Tungsten-Tungsten Triple Bonds and An Analysis of the Structure of the Cyclotrimer

“…DFT calculations show that [W 3 N 3 Cl 9 ] is formed from three weakly interacting WCl 3 N units and has a structure similar to [W 3 N 3 (OR 3 ) 9 ] with unequal WÀN bonds. [23] With these arguments in mind, it is easy to understand why equivalent TaÀN bond distances are observed for the first two metal-nitride trimers prepared. Each tantalum center is located in a pseudotetrahedral environment, if the cyclo- pentadienyl (Cp) rings are considered to occupy one coordination site about the metal.…”

“…The optimized structure of the monomer WN(OH) 3 (WÀN 1.670 , WÀO 1.9121 , OÀWÀN 103.38) is very similar to that calculated for WNCl 3 . [23] The bonding interaction in the trinuclear system is calculated to be 25.6 kcal mol…”

Electronic Structure of Metallacyclophosphazene and Metallacyclothiazene Complexes

“…A similar connectivity has been found in the cyclic nitrido complexes of these transition metals. − In this case, a strong asymmetry in the M−N bonds is observed. Each transition metal center forms one very strong M−N bond of almost triple bond character; the other M−N bond is only a weak donor−acceptor interaction between the nitrogen and the transition metal atom …”