Determination of the π-Accepting Properties of Borate-, Aluminate-, and Gallate-Functionalized N-Heterocyclic Carbenes by ⁷⁷Se NMR Spectroscopy

Abstract

Anionic N-heterocyclic carbenes with weakly coordinating borate, aluminate, and gallate moieties of the type [(F 5 C 6 ) 3 E-NHC] − (E = B, Al, Ga) were isolated as lithium salts by the lithiation of 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene (IMes) or 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene (IDipp) followed by the addition of E(C 6 F 5 ) 3 (E = B, Al, Ga). Treatment with elemental selenium afforded the lithium salts of the corresponding anionic selenourea derivatives [{(F 5 C 6 ) 3 E-NHC}Se] − (NHC = IMes, E = B; NHC = IDipp, E = B, Al, Ga), which were examined, among other things, by means of 77 Se{ 1 H} NMR spectroscopy to assess the π-accepting properties of the WCA-NHC ligands in comparison with their neutral NHC congeners.

Rhodium and Iridium Complexes of Anionic Thione and Selone Ligands Derived from Anionic N‐Heterocyclic Carbenes

“…All yields were calculated based on the WCA-IDipp containing substrate. [Rh(COD)Cl] 2 , [34] [Ir(COD)Cl] 2 , [35] [(η 5 -C 5 Me 5 )RhCl 2 ] 2 , [36] [(η 5 -C 5 Me 5 )IrCl 2 ] 2 , [37] [{(WCA-IDipp)S}Li(toluene)] [17] and [{(WCA-IDipp)Se} Li(toluene)] [18] were prepared according to literature procedures.…”

“…[17] Furthermore, the 77 Se NMR spectra of the selenides [{(WCA-NHC)Se}Li(toluene)] were studied to determine the πaccepting properties of the WCA-NHCs, revealing that the counter cation does not exert any significant influence, if it is fully separated from the selenium atom by solvation, for example, in THF-d 8 . [18] In this context, we envisaged that the lithium salts [{(WCA-IDipp)E}Li(toluene)] (1: E = S; 2: E = Se) or, similarly to I, the trimethylsilyl derivatives (WCA-IDipp)ESiMe 3 (3: E = S; 4: E = Se) might serve as suitable reagents for the transfer of the anionic (WCA-IDipp)E À ligand (III, Figure 1). The resulting metal complexes of the type [{(WCA-IDipp)E}ML n ] (E = S, Se) will have an identical total charge as the corresponding NHC-phosphinidenide complexes [{(IDipp)P}ML n ] and therefore allow the comparison of the phosphorus-metal and chalcogen-metal bonds, while preserving the overall structural and electronic properties.…”

Chalcogen‐Pnictogen Complexes of Anionic N‐Heterocyclic Carbenes with a Weakly Coordinating Borate Moiety

“…All solvents were stored over molecular sieves (4 Å) in argon atmosphere prior to use. [{(WCA‐IDipp)S}Li(toluene)], [20] [{(WCA‐IDipp)Se}Li(toluene)], [17] (WCA‐IDipp)SSiMe 3 [21] and (WCA‐IDipp)SeSiMe 3 [21] were prepared according to literature procedures. For crystallographic details, see the Supporting Information.…”

“…The resulting anionic N‐heterocyclic carbenes (WCA‐NHC) [13] were introduced as ancillary ligands for transition metal complexes and homogeneous catalysts [14–16] . Concurrently, the main group element chemistry with the WCA‐NHC ligands witnessed a similar extensive development [17–19] . The isolation of anionic chalcogen complexes VI bearing the WCA‐IDipp ligand is particularly important in the context of this work, and it has been demonstrated that these species can be converted into WCA‐IDipp‐stabilized disulfide and diselenide compounds VII under oxidative conditions [20] .…”

Heterobimetallic Coinage Metal‐Ruthenium Complexes Supported by Anionic N‐Heterocyclic Carbenes

“…[12] Related anionic analogues of NHCs in which the borate unit is attached to the heterocycle via a methylene (CH 2 ) spacer were also used in transition metal chemistry. [13] Lately, the lithium salts 1 were employed for the preparation of WCA-NHC complexes of the heavier p-block elements, covering groups 13, [14] 15, [15] 16, [16] and 17. [17] In search for alternative transmetalation reagents, sodium and potassium salts of WCA-NHCs were recently introduced, however, their synthesis through deprotonation of IDipp with It should be noted that formal charges are shown here to illustrate the anionic nature of the N-heterocyclic carbene ligands; in the following, however, formal charges will be omitted to avoid the assignment of awkward charges in transition metal complexes.…”