Rare‐Earth Catalyzed C−H Bond Alumination of Terminal Alkynes

Abstract

Organoaluminum reagents' application in catalytic CÀHbond functionalization is limited by competitive side reactions, such as carboalumination andh ydroalumination. Herein, rare-earth tetramethylaluminate complexes are shown to catalyzet he exclusive CÀHb ond metalation of terminal alkynes with the commodity reagents trimethyl-, triethyl-, and triisobutylaluminum.K inetic experiments probing alkyl-group exchange between rare-earth aluminates and trialkylaluminum, CÀHb ond metalation of alkynes,a nd catalytic conversionsr eveal distinct pathways of catalytic aluminationsw ith triethylaluminum versus trimethylaluminum. Most significantly,k inetic data point to reversible formation of au nique [Ln](AlR 4 ) 2 ·AlR 3 adduct, followed by turnover-limiting alkyne metalation. That is, CÀHb ond activation occurs from am ore associated organometallic species, rather than the expected coordinatively unsaturated species. These mechanistic conclusions allude to an ew general strategy for catalytic CÀHb ond alumination thatm ake use of highly electrophilic metal catalysts. representsanonlinear least-squares fit to the equation d[tBuCCAlEt 2 ] = dt = A[AlEt 3 ] = {[AlEt 3 ]+ +B}, where A = k 2 [1 Y ][tBuCCH] and B = (k -1 + +k 2 [tBuC CH]) = k 1 .[ AlEt 3 ] = 0.194-1.419 m;[tBuCCH] = 0.096 m;[1 Y ] = 0.012 M.All manipulations were carried out under inert conditions, either using Schlenk techniques or in gloveboxes under an itrogen at-Caution:T rialkylaluminum and alkynyldialkylaluminum compounds are pyrophoric liquids and must be handled under inert atmospheres. The terminal alkyne and trialkylaluminum reactants were added via syringe to as olution of the catalyst (3 mol %) in [D 6 ]benzene at room temperature, and the reaction mixture was placed in aT eflon-sealed JY oung-style NMR tube. The NMR tube 1 HNMR ([D 6 ]benzene): d = 7.40 (m, 2H, m-C 6 H 5 ), 6.91 (vt, 3 J HH = 7.5, 1H, p-C 6 H 5 ), 6.81 (vt, 3 J HH = 7.5, 2H, o-C 6 H 5 ), 1.50 (t, 3 J HH = 8.1 Hz, 6H,A lCH 2 CH 3 ), 0.64 (q, 3 J HH = 8.1 Hz, 4H,A lCH 2 CH 3 ). 13 C{ 1 H} NMR

Structural Similarity in a Series of Alkali Metal Aluminates with Heteroleptic tert‐Butoxide–Isobutyl Ligand Sets

“…The development and fundamental study of well-defined organoaluminium compounds is therefore currently undergoing a resurgence. [8,[16][17][18][19][20][21][22] Our specific interest in this resurgence overlaps with our general interest in alkali-metal-mediated synergistic effects in polar main group organometallic chemistry, the subject of a recent review article. [23] This work has resulted in the synthesis of bimetallic lithium organoaluminate complexes that have PMDETA.…”

Solution Structure and Dynamics of Hf–Al and Hf–Zn Heterobimetallic Adducts Mimicking Relevant Intermediates in Chain Transfer Reactions

“…Heterobimetallic adducts featuring bridging alkyl/hydride/chloride moieties are usually proposed as catalyst resting states or intermediates in these transformations. − Although several heterobimetallic adducts having hydride, methyl, or chloride bridges have been intercepted and characterized, ,,− very few studies examine systems with alkyl bridges longer than methyl or systems with inequivalent alkyl bridges − critical to olefin polymerization, CCTP, and CSP processes.…”