Alkyne-Induced Facile C–C Bond Formation of Two η²-Alkynes on Dinuclear Tantalum Bis(alkyne) Complexes To Give Dinuclear Tantalacyclopentadienes

Abstract

The dinuclear tantalum–alkyne complexes [(η2-RCCR)­TaCl2]2(μ-OMe)2(μ-thf) (2a, R = Et; 2b, R = n Pr) were synthesized by treating the mononuclear tantalum–alkyne complexes (η2-RCCR)­TaCl3(dme) (1a, R = Et; 1b, R = n Pr) with 1 equiv of NaOMe in THF. We found that adding a catalytic amount (20 mol %) of 3-hexyne to 2a induced the spontaneous formation of Ta2Cl4(OMe)2(μ-C4Et4)­(thf) (4a). Similarly, Ta2Cl4(OMe)2(μ-C4 n Pr4)­(thf) (4b) was obtained by treatment of 2b with a catalytic amount (20 mol %) of 4-octyne. Reaction of 4a,b with 4-dimethylaminopyridine gave 4-dimethylaminopyridine-coordinated complexes 6a,b, whose structures were elucidated by the X-ray structure of 6a. We conducted a control experiment in which 10 equiv of 4-octyne was added to 2a to give Ta2Cl4(OMe)2(μ-C4-2,3- n Pr2-4,5-Et2)­(thf) (7) in 90% yield, indicating that free 4-octyne reacted with the tantalacyclopropene moiety of 2a to form a dissymmetric tantalacyclopentadiene, followed by the release of 3-hexyne. The catalytic activity of 4a–6a for [2 + 2 + 2] cyclotrimerization of 3-hexyne was examined, and we found that their activities were in the order 5a > 4a ≫ 6a.

Nickel-Catalyzed Alkyne Cyclotrimerization Assisted by a Hemilabile Acceptor Ligand: A Computational Study

“…From the bis­(acetylene) complex Ph 1-[I2] , several closed-shell or open-shell pathways have been considered for the coupling of two acetylene fragments (Figure ). First, the most stable intermediate is the pentacoordinate metallacyclopentadiene Ph 1-[I3] , arising from the oxidative coupling from Ph 1-[I2] , with concerted formation of one σ­(C–C) and two σ­(Ni–C) bonds. Ph 1-[I3] adopts a trigonal-bipyramidal geometry in which the CO moiety from Ph L1 is η 2 bound.…”

Synthesis and Characterization of Heterobimetallic Tantalum–Rhodium and Tantalum–Iridium Complexes Connected by a Tantalacyclopentadiene Fragment

“…[13] Because of the high coordination number for the Ta atom in complex 3 compared with that of 2 , the bond lengths of Ta–C(1) and Ta–C(4) (2.225(11) and 2.186(12) Å) are longer than those of complex 2 , while they are consistent with other metallacyclopentadiene‐bridged dinuclear Ta complexes. [14] The bond lengths of the C‐atom linkages in the tantalacyclopentadiene, C(1)–C(2), C(2)–C(3), and C(3)–C(4) bonds, are similar, and equalization of the C–C bonds agree with other dinuclear metallacyclopentadiene complexes …”

“…Although the molecular structure of complex 5 was not clear due to difficulties obtaining single crystals, we presumed that the Ir center in complex 5 would strongly interact with the tantalacyclopentadiene moiety by deforming the flat five‐membered metallacycle, whose deformation was previously observed for a dinuclear tantalacyclopentadiene complex. [14] Loss of cyclooctadiene from the Ir center suggested the construction of a chloride‐bridged tetranuclear Ta 2 Ir 2 structure similar to complex 4 .…”

Transmetalation Reactions of Aromatic Dilithionickelole: Synthesis of Heterobimetallic Complexes Featuring Metalloles as Diene Ligands

“…On the other hand, bimetallic complexes bearing a metallacyclopentadiene as π ligand are most commonly synthesized through metal-mediated oxidative cyclometallation of alkynes, [7,8] which requires variable oxidation states of the metal centers and thus is not feasible for main-group and rare-earth metals. As a result, metallacyclopentadienes of Mg, Sc and Lu have never been employed as π ligands for transition metals.…”