Carbodicarbenes: Divalent Carbon(0) Compounds

Abstract

carbenes · carbodicarbenes · carbodiphosphoranes · divalent carbonIsitpossibletocoordinatetwodonorligandsLtoacarbon (0) atom, and what would be the properties of such a carbon atom? These questions have been of interest to chemists for many years. First answers to this question have been obtained with the synthesis [1] and structural characterization [2] of carbodiphosphoranes (CDPs) A using donor ligands of type L = R 3 P.[3] Carbodiphosphoranes can be formulated as bisphosphine complexes of a naked carbon atom (Aa). Alternatively, a heterocumulene R 3 P=C=PR 3 (Ab) resonance structure and the description as a carbenoid species (Ac) are possible. The bonding parameters and reactivity of the carbodiphosphoranes indicate that the electronic situation of these compounds is reasonably described by a polar structure with two electron lone pairs at the central carbon atom (Aa, Scheme 1).The related carbodiarsoranes [4] as well as a series of cyclic carbodiphosphoranes [2f, 5] have also been described. Carbodiphosphoranes are all strong bases and nucleophiles. The high degree of charge excess at the ylidic carbon atom, which is not compensated by the phosphorus centers, makes them good donor ligands. The electronic situation found in carbodiphosphoranes differs however from that in diphosphino-or diaminocarbenes. A comparison of cyclic derivatives of these three types of donor ligands (Scheme 2) illustrates these differences. The carbene carbon atoms of N-heterocylic carbenes (NHCs) [6] or P-heterocyclic carbenes (PHCs)

Divalent Silicon(0) Compounds

“…Following the publication of the paper online, the groups of Bertrand [3] and Fürstner [4] independently synthesized substituted carbodicarbenes, which represent the first isolated examples of this new class of compounds. [5] In the meantime two theoretical papers [6] have reported the electronic structure of carbones CL 2 for various L, and divalent carbon(0) compounds with cyclic moieties have been synthesized. [7] There is no doubt that divalent carbon(0) chemistry is presently a topic of intense experimental and theoretical research.…”

New structural motifs of silver and gold complexes of pyridine-functionalized benzimidazolylidene ligands

“…The organometallic chemistry of N-heterocyclic carbene (NHCs) has been extensively studied in the recent decade [1][2][3][4][5][6][7]. The metal-NHC complexes exhibit excellent catalytic activity for many practically useful organic transformation especially for olefin metathesis [8][9][10][11][12][13], C-C [14][15][16][17][18][19], and C-N [20][21][22][23][24] bond formation reactions.…”

“…The achievement such as their synthetic routes, structural features, and applications of Ag-NHC complexes has been summarized by Youngs and coworkers [31,32] and Lin et al [33][34][35], respectively. These complexes are normally prepared according to three different procedures: (1) reaction of free NHC with silver salts [36]; (2) reaction of azolium salts with silver bases such Ag 2 O, Ag 2 CO 3 , and AgOAc [35,[37][38][39]; (3) reaction of azolium salts with silver salts under basic phase transfer conditions [33][34][35]. Among these approaches, route (2) is more convenient and most frequently used.…”

“…Heteroarene functionalized N-heterocyclic carbene ligands have proven to be good donating ligands for the assemblage of new metal clusters [63][64][65][66][67][68][69][70] 2 ](PF 6 ) 2 , (L1 = 1,3-bis(picolyl)benzimidazolylidene, L2 = 1-benzyl-3-picolylbenzimidazolylidene, L3 = 1,4-di(Nbenzylbenzimidazoliumyl)but-2-yne) containing bidentate or tridentate functionalized benzimidazolin-2-ylidene ligands. Seven silver and gold complexes were analyzed by X-ray single-crystal diffraction.…”

Carbenes As Catalysts for Transformations of Organometallic Iron Complexes

“…These pioneering studies paved the way for the current revolution in carbene chemistry, which has rapidly developed over the past two decades (4–7). Although fundamental interest has contributed, the primary driving force for the explosion of research in this area is that NHCs and related species (8, 9) have great synthetic utility.…”