Coordination Chemistry of N‐Heterocyclic Nitrenium‐Based Ligands

Abstract

Comprehensive studies on the coordination properties of tridentate nitrenium-based ligands are presented. N-heterocyclic nitrenium ions demonstrate general and versatile binding abilities to various transition metals, as exemplified by the synthesis and characterization of Rh(I) , Rh(III) , Mo(0) , Ru(0) , Ru(II) , Pd(II) , Pt(II) , Pt(IV) , and Ag(I) complexes based on these unusual ligands. Formation of nitrenium-metal bonds is unambiguously confirmed both in solution by selective (15) N-labeling experiments and in the solid state by X-ray crystallography. The generality of N-heterocyclic nitrenium as a ligand is also validated by a systematic DFT study of its affinity towards all second-row transition and post-transition metals (Y-Cd) in terms of the corresponding bond-dissociation energies.

Nitrogen‐Based Lewis Acids Derived from Phosphonium Diazo Cations

“…[21] Structural optimization and computation of the LUMOs of compound 3 and 4 as well as the NBO computations were dominated by the p*component of the NÀNb ond (about 53-55 %) with minor contributions from the p*o rbitals from the N-bound aryl substituent (Figure 4). These features account for the Lewis acidity at the nitrogen adjacent the aryl substituent and are similar to features reported for the diazonium-carbene species of the form, [ArN 2 (NHC)] + described by Severin, et al [17] As af urther measure of Lewis acidity the GEI values [22] for 3 and 4 were calculated to be 2.69 eV and 2.27 eV,respectively, inferring that 3 is more Lewis acidic than 4.I nterestingly, these are both significantly less acidic than the model cyclic triazenium cation [11] [C 6 H 4 (NMe) 2 N] + (3.06 eV) and the cyclic (amino)(aryl)nitrenium cation derived from spiro[fluorene-9,3'-indazole] [14] (3.03 eV; see the Supporting Information).…”

“…[9] Recently,weand others have turned our attention to the potential of nitrogen-based Lewis acids.Although N-containing compounds are usually considered basic due to the typical presence of alone pair of electrons,afew classes of nitrogen compounds are known to be N-centered electrophiles (Figure 1). [10] In what is best described as seminal work, Gandelman and co-workers [11] described several examples of the incorporation of triazolium cations into multidentate ligands where the nitreniums serve as donors,coordinating to transition metal centers.T his group has also demonstrated that such nitrenium cations behave as Lewis acids,f orming donor-acceptor adducts with ar ange of phosphines. [12] More recently we have described astrategy exploiting the analogy between CAACs( cyclic alkyl amino-carbenes) and CAAN (cyclic diazenium cations-cyclic (alkyl)-(amino)nitrenium cations) to enhance the Lewis acidity at nitrogen (Figure 1).…”

Electronic Influences on the Stability and Kinetics of Cp* Rhodium(III) Azide Complexes in the iClick Reaction with Electron‐Poor Alkynes

“…This is a shift of about 8 ppm to higher field compared to the signal of alkyne 7 , which shows the CF 3 resonance in the 19 F NMR spectrum at –52.3 ppm . Only two series of rhodium complexes with triazolate or triazolium ligands have been structurally characterized so far, both of which, however, feature Rh I centers carrying additional donor groups at the 4‐ and 5‐ or 1‐ and 3‐positions of the five‐membered ring , . Our own attempts have so far failed to provide single crystals suitable for X‐ray structure analysis for the two title compounds 8 and 9 , but by comparison with our recently reported manganese(I) compound and literature reports, for example on [Rh(Cp*)(triazolate CF3,CF3 )(PPh 3 )],, it is assumed that the triazolate is symmetrically coordinated via the N2 nitrogen atom.…”

The Reactivity of Isomeric Nitrenium Lewis Acids with Phosphines, Carbenes, and Phosphide

“…In seminal work, Gandelman showed that a triazinium salt ( N ‐heterocyclic nitrenium (NHN)) can form classic Lewis acid/base adducts with phosphines (Figure 1). Gandelman and co‐workers have also expanded the range of triazolium salts, demonstrating access to a wide variety of N‐based Lewis acids [24–27] . More recently, Mehta and Goicoechia [28] as well as Gandelman [29] have exploited the Lewis acidity of triazinium salts for Lewis acid catalysis and FLP Si−H activation.…”

“…Gandelman and co-workers have also expanded the range of triazolium salts, demonstrating access to aw ide variety of N-based Lewis acids. [24][25][26][27] More recently,M ehta and Goicoechia [28] as well as Gandelman [29] have exploited the Lewis acidity of triazinium salts for Lewis acid catalysis and FLP SiÀHa ctivation.…”