Stannylalkynes as Starting Materials for the Synthesis of Vinylidene Rhodium Complexes and of Heterodimetallic Compounds Containing a Rh—Hg or Rh—Sn Bond

Abstract

(2 e ) and [ Rh( C=CCH20Me) (HgPh) C1( PiPr3) (6d) have been determined.Currently, there is much interest in the chemistry of vinylidene transition-metal complexes[*], which are key species in the transformation of two-carbon ligands and play an important role in organometallic as well as in organic synthesisL31. After we had discovered that not only terminal alkynes H C 4 R but also trimethylsilyl and triphenylsilyl derivatives, RC=CSiMe3 and RC=CSiPh3, can be converted in the coordination sphere of rhodium to the corresponding vinylidenes :C=C(R)SiR'3[41, we set out to investigate whether a similar rearrangement proceeds with stannyl-substituted acetylenes, too. We expected that due to the decrease in bond strength along the series C-Si > C-Ge > C-Sn['] a 1,2-SnR3 shift should be less activated than a 1,2-SiR3 shift. However, due to the reduced bond strength and the higher electrophilicity of tetravalent tin, an increased tendency to undergo side reactions was also expected. In this context, we note that Lewis et a1.L61 have recently shown that mono-, oligo-, and polymeric alkynylrhodium(II1) complexes are obtained on treatment of [Rh(PMe3)4]C1 with SnR3-substituted alkynes, one of the driving forces in these processes being the formation of R3SnCl.In the present paper we report that with [RhC1(PiPr3)z], (1) and RC=CSnPh3 as starting materials square-planar vinylidenerhodium(1) complexes bearing a SnPh3 group at the P-carbon atom of the vinylidene ligand can be prepared. They readily react not only with proton sources by C-Sn bond cleavage but also with PhHgCl to give a novel type of Rh-Hg dimetallic products. Vinylidenerhodium Complexes from RC=CSnPh3Since we had found that trimethylsilyl-substituted alkynes are more reactive toward 1 than the SiPh3-substituted we began our studies with alkynes RC=CSnMe3 (R = H, tBu, Ph, C02Me) as substrates. However all attempts to coordinate these alkynes to the [RhC1(PiPr3 A clean reaction occurs by adding triphenylstannyl-substituted alkynes RC=CSnPh3 (R = H, Me, Ph) to a solution of 1 in THF at -50 to -78°C. After slow warming to room temperature, red to violet microcrystalline solids are isolated which according to the spectroscopic data are not the alkyne but the isomeric vinylidene complexes 2a-c. Diagnostic, in particular[2a], are the two signals at low field in the I3C-NMR spectra in the range of 6 = 270-290 and 80-110 which are both split into doublets of triplets due to Rh-C and P-C coupling. The absence of a C=C stretching frequency in the IR spectra at about 1800-1850 cm-' further supports the proposed coordination of a vinylidene instead of an alkyne ligand.[RhC1(PiPrJz], 1

Mechanistic aspects regarding the formation of metal vinylidenes from alkynes and related reactions

“…Often, the backword reaction is also observed (Scheme 1). The most common migrating species is hydrogen, but regarding the alkyne to vinylidene isomerization, migration of SiR 3 [18][19][20][21][22], SnPh 3 [23], SMe [24], and iodine [25] have also been known. The irreversible isomerization of vinylidene ligand in [CpFe(CO) 2 (‚C‚CR 1 R 2 )] + (R 1 , R 2 = Me, Ph) to form the corresponding g 2 -alkyne complex [CpFe(CO) 2 (R 1 C"CR 2 )] + was observed by means of NMR spectroscopy above À50°C, where the higher migrating ability of the Ph than Me group was noted [26].…”

Metal Vinylidenes and Allenylidenes in Catalysis: Applications in Anti‐Markovnikov Additions to Terminal Alkynes and Alkene Metathesis

“…[29,30] Internal alkynes bearing a labile substituent are also prone to form vinylidene derivatives. Trialkylsilyl, [31][32][33][34][35][36][37] alkylthiol, [38] triphenylstannane, [39] and iodide [40,41] are able to migrate and generate functionalized vinylidene metal complexes, and some of them have been involved in catalytic reactions.…”

Reactions of Alkenyl Fischer Carbene Complexes with Ketene Acetals: Formation of Alkynes

“…However, the reverse process has been investigated to some extent as a method for the preparation of alkynes 14. Other than terminal alkynes (Z = H), the formation of vinylidene complexes has been observed with alkynes where Z is trialkylsilyl,15 trialkyltin,16 thioethers,17 iodide18 and an ester 19…”