C‐N‐Bindungsspaltung und Ringerweiterung N‐heterocyclischer Carbene durch Hydrosilane

Abstract

Ringerweiterung von NHCs! Die Reaktion N‐heterocyclischer Carbene (NHCs) mit Hydrosilanen Ph4−nSiHn (n=1, 2, 3) führt zu einem vollständigen Aufbrechen des Heterocyclus unter Silyleninsertion in eine der C‐N‐Bindungen des Carbens (siehe Schema; R=Alkyl, Aryl).

Zinc‐Catalyzed Borylation of Primary, Secondary and Tertiary Alkyl Halides with Alkoxy Diboron Reagents at Room Temperature

“…In this regard, we note three recent examples involving Be, [23] B, [24] or Si, [25] for which ring expansion took place at elevated temperatures (80-120 8C), and very recent theoretical studies [26] on the mechanism of the ring expansion of NHCs. In this regard, we note three recent examples involving Be, [23] B, [24] or Si, [25] for which ring expansion took place at elevated temperatures (80-120 8C), and very recent theoretical studies [26] on the mechanism of the ring expansion of NHCs.…”

Insertion of Group 12–16 Hydrides into NHCs: A Theoretical Investigation

“…Activationo ft he CÀNb ond and ring expansionb y non-metalsw as first observed in 2012 by Hill [5] and Radius. [6] Radius described the insertion of hydrosilane (PhSiH 3 )i nto NHC iPr (notation refers to iPr substituent on each N), while Hill reported the insertion of ab eryllium hydride into the NHC (Figure 1). Around the same time, Rivard [7] independently observed similar phenomena of ring insertion using the same NHC iPr with boron hydrides.…”

Systematic Investigation of the Ring‐Expansion Reaction of N‐Heterocyclic Carbenes with an Iminoborane Dihydride

“…Remarkably, we did not observe the NHC complex of the iminoborane dihydride 2 Ac and 2 Bc, respectively; instead, the reaction resulted in nearly quantitative transfor-mation to the ring-expanded products 3 Ac and 3 Bc as well as the dihydrogenated NHC at room temperature (entries Ac and Bc, Figure 3). [3] Interestingly, when 1 B is reacted with only one equivalent of H 2 L Mes half-conversion occurs and a distinct 1:1:1 mixture of 1 B, 3 Bc, and H 2 L Mes is obtained. An apparent explanation can be found in the particular canonical structures of the iminoborane carbene complexes, as argued for the reactivity of the related L Dipp BH 3 .…”

“…[1] In 2012, the extensive study of main group metal N-heterocyclic carbene (NHC) complexes resulted in reports on the hydride-mediated ring-expansion reaction (RER) of respective beryllium, [2] silicon, [3] and boron [4] compounds in which the metal atom inserts into the adjacent CÀN bond of the carbene ligand (I-V, Scheme 1). [1] In 2012, the extensive study of main group metal N-heterocyclic carbene (NHC) complexes resulted in reports on the hydride-mediated ring-expansion reaction (RER) of respective beryllium, [2] silicon, [3] and boron [4] compounds in which the metal atom inserts into the adjacent CÀN bond of the carbene ligand (I-V, Scheme 1).…”

“…Thus, we converted L Mes (NH)BH 3 (1 A) as well as L Dipp (NH)BH 3 (1 B) with two equivalents of the mesityl-substituted imidazolidine H 2 L Mes (saturated at the ligand backbone). Thus, we converted L Mes (NH)BH 3 (1 A) as well as L Dipp (NH)BH 3 (1 B) with two equivalents of the mesityl-substituted imidazolidine H 2 L Mes (saturated at the ligand backbone).…”