Catalytic Dimerization of Alkynes via C–H Bond Cleavage by a Platinum–Silylene Complex

Abstract

The cyclodimerization of diphenylacetylene derivatives catalyzed by a platinum-silylene complex is reported. The reaction proceeds via the cleavage of a carbon-hydrogen bond at the ortho-position of an alkynyl group and no additives are needed. Platinum complexes bearing other common ligands, such as phosphines and NHCs, failed to promote this reaction, highlighting the utility of the silylene ligand in this reaction.

Cyclometallation of Heavier Tetrylenes: Reported Complexes and Applications in Catalysis

“…[17a] The iron(II) complex 28, which features two coordination variants of ligand E, is an efficient catalyst for the hydroboration of carbonyl compounds at room temperature. [19] Table 4 shows the catalytic results for the hydroboration of ketones (entries 1-16) and aldehydes (entries [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] with HBpin in THF (other solvents were found to be less efficient). [19] Complex 28 was able to hydroborate a plethora of para-and meta-substituted acetophenones (entries 1-12), rendering conversions close to or higher than 90 %, except for substrates featuring strong electron donating groups (entries 5 and 12).…”

“…[7,8] On the other hand, heavier tetrylenes (HTs) have been used as ligands in transition metal chemistry [9,10] since the 1970s. [9i-k,11] Recently, new generations of HTs, particularly those donorstabilized by amidinato and other chelating moieties, have been recognized as versatile ligands in homogeneous catalysis, [10] capable to promote processes such as (a) Suzuki, [12a] Heck, [12a] Kumada, [12b,c,e] Neghishi [12c] and Sonogashira [12d] couplings, (b) alkene hydrosilylations, [13] (c) ketone hydrosilylations, [14] (d) alkyne-azide "click" cycloadditions, [15] (e) olefin metathesis, [16] (f) ketone hydrogenations, [17] (g) arene and heterocycle borylations, [18] (h) H/D exchange reactions, [17a,18a] (i) ketone hydroborations, [19] (j) N 2 silylation, [20] (k) amide reductions, [21] (l) carbonyl cyanosilylations, [22] (m) [2 + 2 + 2] cycloadditions, [23] (n) alkene hydroformylations, [24] (o) Buchwald-Hartwig aminations, [25] (p) alkene [26a,b] and alkyne [26c] hydrogenations, (q) CÀ H functionalization of arylpyridines, [12e,27] (r) glycosidation reactions, [28] (s) lactide [29a] and lactone [29b] polymerizations, (t) cyclodimerization of alkynes, [30] etc. Noteworthy, some of these donor-stabilized HTs have demonstrated to be very strong electron-donating ligands, [31,32] even stronger than alkyl phosphanes and many NHCs, [32] a property that is crucial to develop effective and stable catalysts.…”

KOtBu-Catalyzed Synthesis of Isoindole Derivatives from N-Benzyl Amides Bearing an Ortho Alkynyl Group via 1,2-Acyl Shift

“…Our group recently reported on the nickel-catalyzed transformations of amides via the cleavage of the C­(acyl)–N bond . Building upon these studies, we hypothesized that amides bearing an alkynyl group (i.e., 1 ) would undergo cyclization if alkyne-directed oxidative addition of the C­(acyl)–N bond of amides and subsequent alkyne insertion were to occur (Scheme a). Based on this hypothesis, we initially examined the reaction of the o -alkynyl benzylamide 1a in the presence of [Pd­(allyl)­Cl] 2 (5.0 mol %), IPr·HCl (10 mol %), and KO t Bu (1.0 equiv) at 120 °C for 1.0 h, with the hope that an addition product 2a would be formed (Scheme b).…”

Reactivity of Pt(0) bromosilylene complexes towards ethylene

“…28 Related compounds were synthesised by Iwamoto and Kato, respectively and studied regarding their catalytic activity in hydrosilylation and isomerisation reactions. [29][30][31][32][33] A homoleptic platinum(0) complex containing two bis(guanidinato) silylene ligands was obtained by Tacke via reduction of a Pt(II) precursor. 34 The first complexes of base-free halosilylenes were reported by Sasamori and Tokitoh who prepared sterically congested 1,2-dibromodisilenes which, upon treatment with Pt (PCy 3 ) 2 dissociated and formed the bromosilylene platinum complex [Bbt(Br)SivPt(PCy 3 ) 2 ] (V) (Bbt = 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl).…”