Heterometallic Complexes by Transmetalation of Alkynyl Groups from Copper or Silver to Allyl Palladium Complexes: Demetalation Studies and Alkynyl Homocoupling

Abstract

The reaction of [Pd­(η3-allyl)­ClL] (L = AsPh3, PPh3) with [M­(CCR)] n (M = Cu, Ag; R = nBu, Ph) leads to transmetalation of the alkynyl group from M to Pd. However, the group 11 metal stays η2-bound to the new Pd–alkynyl fragment and heterometallic Pd–M complexes are formed with different nuclearities depending on M: [{Pd­(η3-allyl)­(alkynyl)­L}­CuCl]2 (3, 4) or [{Pd­(η3-allyl)­(alkynyl)­L}2AgCl] (5, 6). The M-containing fragment can be eliminated to give the actual transmetalation complex [Pd­(η3-allyl)­(alkynyl)­L] by adding an excess of arsine or phosphine, whereas amines do not have this effect. Allyl–alkynyl reductive elimination is a slow process; therefore, complexes 3–6 cleanly decompose by dimerization (homocoupling) of the alkynyl group. In the decomposition process reversible alkynyl transmetalation from Pd to Cu has been observed.

Formal Gold‐to‐Gold Transmetalation of an Alkynyl Group Mediated by Palladium: A Bisalkynyl Gold Complex as a Ligand to Palladium

“…[8,9] After the transfer of the alkynyl group to palladium, the group 11 metal may remain coordinated to the Pd-alkynyl groups forming stable bimetallic intermediates. [9] Both features are important since they influence the formation of the [Pd(alkynyl)RL2] intermediate that eventually give, by reductive elimination, the coupling alkynyl-R derivative. We have previously studied the transmetalation reaction between copper or silver alkynyls and palladium allylic derivatives.…”

“…The reluctance of the allylic fragment to undergo reductive elimination in a [Pd(alkynyl)(allyl)L2] compound hampers the otherwise preferred coupling process and allows the detection of bimetallic intermediate complexes. [9] We report here the reaction of gold alkynyls with palladium allylic derivatives which turns out to be a complex process that involves multiple transmetalations between Au and Pd leading to a formal Au to Au alkynyl transfer. The impulse experienced by gold catalysis makes this metal an attractive candidate for the design of bimetallic catalysts, [2,10] and this has been realized both in alkynyl coupling as in the gold cocatalyzed version of the Sonogashira reaction, [11] or other PdAu catalyzed reactions.…”

“…This is supported by several independent experiments that show that gold to palladium alkynyl transmetalation is reversible and can lead to complex 3. from palladium to gold. The reverse transmetalation, from gold to palladium, occurs by the addition of an excess of PPh3 on complex 3, which leads to the formation of the monoalkynyl allyl palladium complex 9, [9] and gold derivatives 5 and [AuClPPh3]…”

Coinage Metal Complexes of Bis‐Alkynyl‐Functionalized N‐Heterocyclic Carbenes: Reactivity, Photophysical Properties, and Quantum Chemical Investigations

“…The second complex was tetranuclear[ {(NHC Di-Ph-Alkyne )Au(CCPh)} 2 Cu 2 X 2 ]( 12:X = Cl, 13:B r), in which two molecules of 11 trap aC u 2 X 2 unit by coordination to the AuCCPh moiety.C ompounds 12 and 13 are isostructural and were isolated,d epending on the applied startingc omplex 4 or 5,i ne qual yield. [79] The phenylacetylene acts as ab identate ligand with end-oncoordination to Au and side-on coordination to Cu. In each case, the gold atoms are coordinated in al inear fashionw ith C1-Au1-C22 bond angles of 1768.T he copper atoms exhibit trigonal-planar coordination with two m 2 -X ligands and one terminal alkynel igand.…”

“…The CuÀCd istances range from 2.025(4) to (14) and therefore are similart ot hose in, for example, [{Pd(h 3 -allyl)(alkynyl)PPh 3 }CuCl] 2 . [79] The phenylacetylene acts as ab identate ligand with end-oncoordination to Au and side-on coordination to Cu. Surprisingly,a ni nteraction with the alkynyl units of the NHC ligand was not observed, and this indicates that only the "activated" triple bond coordinatedt oA ua cts as suitable ligand for furthermetal ions.…”