Synthesis and Comparison of Transition Metal Complexes of Abnormal and Normal Tetrazolylidenes: A Neglected Ligand Species

Abstract

To date, only few examples of tetrazolylidene carbenes coordinated to transition metal complexes have been described. A direct comparison of "normal" tetrazolylidenes (1,4-substitution pattern) and "abnormal" tetrazolylidenes (also referred to as "mesoionic carbenes"; 1,3-substitution pattern) has not been performed at all. In this work, we describe coordination of both ligand types to a row of transition metals. For example, the first examples of tetrazolylidene Mo, Ag, or Ir complexes have been isolated and fully characterized. The mesoionic tetrazolylidene Ag compound 2d is shown to be a viable carbene transfer reagent. By means of NMR, IR, and Raman spectroscopy, as well as X-ray crystallography and computational results, the pronounced differences between the two ligand substitution patterns are highlighted. It is shown that simply changing the position of a methyl group from N3 to N4 in the heterocycle can cause enormous differences in ligand characteristics.

N-heterocyclic carbene complexes of Group 6 metals

“…The crystal structures of Mo-44(a,b) shows that one acetonitrile molecule coordinates to the Mo centre with a Mo-N distance of 2.172 (2) with abnormal tetrazolylidene and 1,2,3-triazolylidene as spectator ligands [146,147]. These complexes can be also synthesized through a transmetallation route from the corresponding silver carbene with CpMo(CO) 3 Table 3.1 in Supplementary Information).…”

“…CpMo(II) complexes with tetrazolylidene and 1,2,3-triazolylidene ligand[146,147].Molybdenocene NHC complexes with saturated and unsaturated NHC ligands have been reported by Yamaguchi et al[148].Complexes Mo-47(a-c) (Figure 3.7) are synthesized by a free carbene method from [Cp 2 Mo(H)(OTs)]. They can be also prepared by treatment of [Cp 2 Mo(H)Li] 4 with the corresponding imidazolium salt in THF under photo-conditions.…”

Novel tetrazol‐5‐germavinylidenes with triplet monomeric, normal, and abnormal forms studied using DFT method

“…Kühn et al also have reported that variation of substitution pattern in normal and abnormal isomers has an effect on σ–donor capacities of the species. It is found that the abnormal tetrazolylidene with 1,3‐substitutions is considered a better electron donor than its corresponding normal isomer …”

Synthesis and properties of heteroaromatic carbenes of the imidazole and triazole series and their fused analogues

“…In contrast, the tetrazolylidenes themselves are probably stable, and two types of isomeric compounds have been obtained in complexes, namely, normal 65D and mesoionic 65E. 300 To the best of our knowledge, comparable studies of carbenes of other azole series have not yet been undertaken. Recently, a related decomposition was detected for a non-aromatic 1,3-p-tolyl-4,5-dihydroimidazol-2-ylidene at 110 C in toluene.…”