Catalytic Carbophilic Activation: Catalysis by Platinum and Gold π Acids

Abstract

The ability of platinum and gold catalysts to effect powerful atom-economic transformations has led to a marked increase in their utilization. The quite remarkable correlation of their catalytic behavior with the available structural data, coordination chemistry, and organometallic reactivity patterns, including relativistic effects, allows the underlying principles of catalytic carbophilic activation by pi acids to be formulated. The spectrum of reactivity extends beyond their utility as catalytic and benign alternatives to conventional stoichiometric pi acids. The resulting reactivity profile allows this entire field of catalysis to be rationalized, and brings together the apparently disparate electrophilic metal carbene and nonclassical carbocation explanations. The advances in coupling, cycloisomerization, and structural reorganization--from the design of new transformations to the improvement to known reactions--are highlighted in this Review. The application of platinum- and gold-catalyzed transformations in natural product synthesis is also discussed.

Allene formation by gold catalyzed cross-coupling of masked carbenes and vinylidenes

“…and Fürstner and Davies (27), the representation of the carbene ligand of 13 as a gold-stabilized carbocation is perfectly valid and in this case helps to avoid the uncommon Au(V) oxidation state. Reductive coupling of the carbene and vinylidene produces allenes 7 and regenerates the catalyst 3.…”

“…In the last few years there have been amazing developments in gold catalysis (25)(26)(27)(28). Once thought to be a noble metal with little synthetic utility, gold has recently demonstrated its unique and exciting catalytic properties.…”

Oxidative Coupling Reactions with Gold

“…[25] The dimerization of a nucleobase mediated by stoichiometric amounts of NaAuCl 4 was reported by Lippert and co workers (Scheme 2). [26] He supported the mechanism via C-H bond insertion by iso lating an Au complex which is structurally very close to the proposed intermediate by using K[Au(CN) 2 Cl 2 ] instead of NaAuCl 4 . The complex, trans K[Au(CN) 2 Cl(1,3 DimeU -C 5 )] (Fig.…”

“…[3] One of the most interesting features is the ability to act as a mild, relatively carbophilic π Lewis acid. [4] π Bonds activated by gold can undergo a variety of reactions such as the addition of nucleophiles, migration of propargyl and other esters, 1,2 migrations, [5] or cyclo isomerizations of enynes for example. [6] Redox reactions under homogeneous conditions are less frequently disclosed compared to the vast number of Au cata lyzed reactions.…”

Silver-free Gold(I) Catalysts for Organic Transformations

“…The identity and structure of these intermediates has been confirmed by several detailed analytical, spectroscopic and structural studies [11]. In the course of a slippage movement [10] of the [(L)Au] + electrophile away from the center of the multiple bond concerned, one of the carbon atoms can subsequently be attacked by a Scheme 53. nucleophile, followed by the cleavage of the (L)Au-C bond by protonation or alkylation etc. (Scheme 53) [2 -10] or by geminal di-auration (Scheme 16a) [65b].…”