Tuning Main Group Redox Chemistry through Steric Loading: Subvalent Group 13 Metal Complexes of Carbazolyl Ligands

Dehydrogenation of dimethylamine-borane mediated by Group 1 pincer complexes

Alkali metal carbazolido complexes are precatalysts for the dehydrogenation of Me₂NH·BH₃, where the cation plays a vital role in the reaction outcome.

Metal-Catalyzed Cyclization Reactions of 2,3,4-Trien-1-ols: A Joint Experimental-Computational Study

Controlled preparation of tri- and tetrasubstituted furans, as well as carbazoles has been achieved through chemo- and regioselective metal-catalyzed cyclization reactions of cumulenic alcohols. The gold- and palladium-catalyzed cycloisomerization reactions of cumulenols, including indole-tethered 2,3,4-trien-1-ols, to trisubstituted furans was effective, due to a 5-endo-dig oxycyclization by attack of the hydroxy group onto the central cumulene double bond. In contrast, palladium-catalyzed heterocyclization/coupling reactions with 3-bromoprop-1-enes furnished tetrasubstituted furans. Also studied was the palladium-catalyzed cyclization/coupling sequence involving protected indole-tethered 2,3,4-trien-1-ols and 3-bromoprop-1-enes that exclusively generated trisubstituted carbazole derivatives. These results could be explained through a selective 6-endo-dig cumulenic hydroarylation, followed by aromatization. DFT calculations were carried out to understand this difference in reactivity.

Extremely bulky amide ligands in main group chemistry

The development of extremely sterically demanding, monodentate amide ligands facilitates the isolation of main group species with new and highly reactive coordination modes. An outstanding feature of these ligands is the ability to tune their steric demands. Reactivity investigations highlight the potential for small molecule activation chemistry and catalysis for these compounds.

Tuning coordination in s-block carbazol-9-yl complexes

1,3,6,8-Tetra-tert-butylcarbazol-9-yl and 1,8-diaryl-3,6-di(tert-butyl)carbazol-9-yl ligands have been utilized in the synthesis of potassium and magnesium complexes. The potassium complexes (1,3,6,8-tBu4carb)K(THF)4 (1; carb = C12H4N), [(1,8-Xyl2-3,6-tBu2carb)K(THF)]2 (2; Xyl = 3,5-Me2C6H3) and (1,8-Mes2-3,6-tBu2carb)K(THF)2 (3; Mes = 2,4,6-Me3C6H2) were reacted with MgI2 to give the Hauser bases 1,3,6,8-tBu4carbMgI(THF)2 (4) and 1,8-Ar2-3,6-tBu2carbMgI(THF) (Ar = Xyl 5, Ar = Mes 6). Structural investigations of the potassium and magnesium derivatives highlight significant differences in the coordination motifs, which depend on the nature of the 1- and 8-substituents: 1,8-di(tert-butyl)-substituted ligands gave π-type compounds (1 and 4), in which the carbazolyl ligand acts as a multi-hapto donor, with the metal cations positioned below the coordination plane in a half-sandwich conformation, whereas the use of 1,8-diaryl substituted ligands gave σ-type complexes (2 and 6). Space-filling diagrams and percent buried volume calculations indicated that aryl-substituted carbazolyl ligands offer a steric cleft better suited to stabilization of low-coordinate magnesium complexes.

Divalent heteroleptic ytterbium complexes--effective catalysts for intermolecular styrene hydrophosphination and hydroamination

New heteroleptic Yb(II)-amide species supported by amidinate and 1,3,6,8-tetra-tert-butylcarbazol-9-yl ligands [2-MeOC6H4NC(tBu)N(C6H3-iPr2-2,6)]YbN(SiMe3)2(THF) (6) and [1,3,6,8-tBu4C12H4N]Yb[N(SiMe3)2](THF)n (n = 1 (7), 2 (8)) were synthesized using the amine elimination approach. Complex 6 features an unusual κ(1)-N,κ(2)-O,η(6)-arene coordination mode of the amidinate ligand onto Yb(II). Complexes 7 and 8 represent the first examples of lanthanide complexes with π-coordination of carbazol-9-yl ligands. Complexes 6 and 7, as well as the amidinate-Yb(II)-amide [tBuC(NC6H3-iPr2-2,6)2]YbN(SiMe3)2(THF) (5), are efficient precatalysts for the intermolecular hydrophosphination and hydroamination of styrene with diphenylphosphine, phenylphosphine, and pyrrolidine to give exclusively the anti-Markovnikov monoaddition product. For both types of reaction, the best performances were observed with carbazol-9-yl complex 7 (TONs up to 92 and 48 mol/mol at 60 °C, respectively).