Structure of a Reactive Gold Carbenoid

Abstract

A formal gold-for-chromium transmetalation allowed the gold carbenoid species [Cy₃PAuCAr₂]NTf₂ (11) (Ar=pMeOC₆H₄-) to be obtained in crystalline form. The structure in the solid state suggests that there is only little back donation of electron density from gold to the carbene center of 11 and hence very modest Au—C double-bond character; rather, it is the organic ligand framework that is responsible for stabilizing this species by resonance delocalization of the accumulated positive charge. Because 11 is capable of cyclopropanating p-methoxystyrene even at low temperature, the discussion of its structure is deemed relevant for a better understanding of the mechanisms of π-acid catalysis in general

Concise Total Synthesis of Enigmazole A

“…This conclusion, drawn from atotal synthesis project, invigorates our parallel efforts to contribute to adeeper mechanistic understanding of noblemetal catalysis in general. [41] …”

The chemistry of the carbon-transition metal double and triple bond: Annual survey covering the year 2014

“…Failure to form a discrete gold-carbon double-bonded species was suggested as evidence against a compound having a gold-carbon double bond. A mononuclear complex could be prepared from the analogous carbene complex 586, however the bulk of the stabilization of the carbenic center in resulting complex (588) was via the methoxy groups (favoring resonance form 588B) as shown by the X-ray structure and the barriers to rotation [931]. The photochemical reaction of Fischer carbene complexes (e.g.…”

“…This mechanism was supported through deuterium labeling studies. The reaction of cobalt(I) derivatives of general structure 929 (Scheme 76) with 2 eq of TMS-CF 3 (930) led to either the difluorocarbene complex (931) or the tetrafluoroethylene complex (932) carbene ligand was also reported [1047]. The iridium carbene complex 950 was prepared through reaction of the tridentate tris(pyrazolyl)ruthenium complex 949 with iridium complex 941 [1048].…”

General Conclusion and Perspective

“…A major difficulty is clearly the introduction of the second coupling partner. Typical transmetallation procedures require (Lewis-) basic additives, which are incompatible with the here employed [L 2 Au + ] fragment due to blocking of the empty coordination site required for oxidative addition. In this context, special attention should be paid to the influence of the bite angle of the diphosphine ligand.…”

“…For example, compounds featuring gold-carbon double bonds have eluded structural characterization so far and the existence of such compounds is matter of debate [2]. However, the influence of the increased backdonation of the bent diphosphine complexes described in Chap.…”