Reactive Dicarbon as a Flexible Ligand for Transition-Metal Coordination and Catalysis

Abstract

Dicarbon is a reactive carbon allotrope that naturally exists only in the high-temperature medium of stellar space. We report the successful preparation of a series of bottleable phosphine-stabilized dicarbon (PDC) molecules. We explore the use of these molecules as a new complementary class of carbenelike ligands featuring strong σ-donor (>NHCs and CAAcs) but weak π-acceptor properties. Steric map analysis of PDC based on Cavallo's SambVca program reveals comparable steric volume bulk of 32.5%, similar to the conventional IMes carbene. However, our PDCs exhibit dynamic steric flexibility modulated by the nature of the metal complexes and catalytic reaction environment. We demonstrate the catalytic utility of the PDC framework by its successful implementation for Suzuki−Miyaura cross-coupling and the reductive coupling reaction of an aldehyde and alkyne. Detailed investigations of the reductive coupling reaction reveal an important secondary interaction between PDC and metal complexes, which plays a critical role in the catalytic system.

Counterintuitive Chemistry: Carbene Stabilization of Zero-Oxidation State Main Group Species

“…In contrast to the linear “cumulene” cores of 55 – 57 , a monoligated L:C 2 complex ( 58 ) [L: = (NHC Dipp =N) 2 (Me)­P] was recently synthesized by Ong, using a sterically demanding phosphine ligand (Scheme ). Notably, these phosphine-stabilized dicarbon complexes have been utilized as supporting ligands in transition-metal catalysis …”

“…111 Notably, these phosphine-stabilized dicarbon complexes have been utilized as supporting ligands in transitionmetal catalysis. 112 Following our discovery of carbene-stabilized disilicon (28), we extended the carbene-stabilization strategy to the group 15 elements. The potassium graphite reduction of NHC R :ECl 3 in THF gives the corresponding carbene-stabilized E 2 (0) species (E = P, R = Dipp, 59; E = P, R = Mes, 60; E = As, R = Dipp, 61) (Scheme 17).…”

%VBur index and steric maps: from predictive catalysis to machine learning

“…However, steric maps improved the latter analysis of the buried volume, uncovering distinct reactive pockets for NHCs with mesityl or 2,6-diisopropylphenyl N substituents. As %V Bur can be considered to a simple number, it is sometimes not sufficient to explain the reactivity of a catalyst, 207 or similarly to rule out on steric features that a catalyst is inefficient, for example comparing NHC-based catalysts ruthenium and iron. 208 5.5 The evolution of %V Bur to steric maps.…”