Cp* as a removable protecting group: low valent Zn(i) compounds by reductive elimination, protolytic and oxidative cleavage of Zn–Cp*

Abstract

Zn-Cp* bond cleavage reactions leading to novel monovalent cationic zinc species are presented (Cp* = pentamethylcyclopentadienyl). The treatment of [Zn2Cp*2] with two equiv. of [H(Et2O)2][BAr4(F)] (BAr4(F) = B{C6H3(CF3)2}4) yields the triple-decker complex [Cp*3Zn4(Et2O)2][BAr4(F)] (1) via protolytic removal of a Cp* ligand as Cp*H, whereas the reaction with an equimolar amount of [FeCp2][BAr4(F)] (Cp = cyclopentadienyl) results in the formation of [Cp*Zn2(Et2O)3][BAr4(F)] (2) under oxidative cleavage of a Cp* ring giving decamethylfulvalene, (Cp*)2, and [FeCp2] as by-products. The molecular structures of compounds 1 and 2 are established by single-crystal X-ray diffraction studies. A new synthetic pathway for the formation of [Zn2Cp*2] based on the reductive elimination of Cp*H from in situ formed Cp*ZnH is presented.

Zincocene and Dizincocene N‐Heterocyclic Carbene Complexes and Catalytic Hydrogenation of Imines and Ketones

“…This mechanistic scenario was intimated by Power and co‐workers25a and was demonstrated for the cadmium homologue 25d. In support of this view, a sample of 1 pressurized with HD gave 2 , H 2 , D 2 , Cp*H, and Cp*D. A similar mechanistic proposal was recently reported by Fischer and co‐workers, in which the formation of 2 from 1 and ZnH 2 was explained by in situ formation of [Cp*ZnH] and reductive elimination upon reaction with another equivalent of 1 27. The intermediacy of [Cp*ZnH] 1−2 was further supported by our recent report of [Cp*ZnH(NHC)] (NHC=SIMes), which can be regarded as the NHC‐stabilized intermediate.…”

“…[25d] In support of this view, a sample of 1 pressurized with HD gave 2, H 2 , D 2 , Cp*H, and Cp*D. A similar mechanistic proposal was recently reported by Fischer and co-workers, in which the formation of 2 from 1 and ZnH 2 was explained by in situ formation of [Cp*ZnH] and reductive elimination upon reaction with another equivalent of 1. [27] [9b, 12] This implies that soluble zinc hydrides can undergo reductive elimination under reducing conditions.…”

Cyclic(Alkyl)(Amino)Carbene (CAAC)‐Supported Zn Alkyls: Synthesis, Structure and Reactivity in Hydrosilylation Catalysis

“…In particular, the LUMO energy level of such Lewis acids may correlate to their reactivity/electrophilicity . The LUMO of cations 5 + and 7 + (−5.53 and −5.86 eV, respectively; Figure ) features a π‐bonding interaction between the C CAAC atom and one of the empty p‐orbitals on Zn II , and is significantly lower in energy than that of the NHC analogue (IDipp)ZnR + (−4.61 and −4.91 eV for R=Me, C 6 F 5 , respectively) . The latter reflects the stronger π ‐ accepting character of CAAC (versus NHC ligand) and should enhance the reactivity of such cations.…”

Atompräzise organometallische Zinkcluster

“…Inspiriert durch die zuvor zitierten Arbeiten von Schnöckel haben wir die Möglichkeit untersucht, dieses Konzept auf ligandenstabilisierte Zn‐Cluster unter Verwendung von [Zn 2 ](Cp*) 2 als vorrangige Zinkquelle, mit entfernbaren Cp* als Schutzgruppe, zu übertragen. Insbesondere das semi‐geschützte [Cp*Zn 2 (Et 2 O) 3 ] + kann bei Raumtemperatur durch oxidative Zn‐Cp*‐Bindungsspaltung isoliert werden und neigt zu Disproportionierung . Diese Spezies kann als Zinkquelle genutzt werden, wobei die Reaktivität von {[Cp*Zn 2 ](L′ n )} + durch die Wahl der schwach koordinierenden Coliganden L′ modifiziert werden kann.…”