Metal Complexes of Small Cycloalkynes and Arynes

Abstract

Cyclooctyne is the smallest unsubstituted cycloalkyne that can be isolated in the free state and it is more reactive than acyclic alkynes towards transition metal complexes. Smaller cycloalkynes such as cycloheptyne, cyclohexyne, benzyne and cyclopentyne, which are transient molecules in the free state, can be stabilized by coordination either to mononuclear, electron-rich, transition metal-containing fragments, e.g. [ZrCp,(PMe,)] and M(PR,), (M = Ni, Pt), or by formation of dinuclear or polynuclear metal complexes, e.g.[Os,H,(CO), (C,H,)] and [Pt,(p-PPh,)(p-C,H,)(PPh3)3]. The alkynes can donate between two and four n-electrons to the metal centers, the higher number being favored for the early transition metals. The metal-cycloalkyne and metal-aryne bonds in the mononuclear complexes readily insert molecules containing C = 0 , C = C, C = C and C = N bonds, a feature that may be useful in organic synthesis. The highly unsaturated species 1,4-benzdiyne acts as a bridging ligand between two metal centers in [{Ni(Cy,PCH,CH,PCy,)J,(I.I-C,H,)I.

Palladium-Catalyzed Cycloaddition Reactions of Arynes

“…The evolution of the chemistry of late transition metal complexes is due principally to the efforts of Bennett and co-workers [6,7], and runs parallel to that sketched above for early transition metals. Figure 4 shows some representative examples of aryne complexes of late transition metals that have been characterized by X-ray diffraction studies.…”

“…Since then, complexes of arynes with a wide array of transition metals have been prepared, but in most cases only for structural studies [5][6][7][8][9] (Fig. 2).…”

“…Figure 3 shows some representative examples of aryne complexes of early transition metals that have been characterized by X-ray diffraction studies. The most useful procedure for the preparation of early transition metal complexes of type 13 is the thermal elimination of benzene or methane from diphenyl or arylmethyl compounds, respectively (12 and 14 in Scheme 1) [5][6][7][8][9]. At the end of the 1960s, the first studies of the reactivity of such a complex, specifically the aryne-titanocene complex 15, showed that it reacts with species such as alkynes, CO 2 , N 2 or selenium to form titanacycles [7].…”

Insertions of Unsymmetric Alkynes into the Metal−Carbon Bonds of Nickelacycles: What Determines the Regiochemistry?

“…It arises from sequential insertion of C 2 F 4 and DMAD into the 2,3h-naphthalyne complex [Ni(h 2 -C 10 H 6 )(dcpe)]. The product, [Ni{C(CO 2 Me)C(CO 2 -Me)C 10 H 6 CF 2 CF 2 -kC,C}(dcpe)] (35), results from insertion of the alkyne into the NiÀAr bond of the first insertion product, [Ni(o-C 10 H 6 CF 2 CF 2 -kC,C)(dcpe)] (34) [61]. The nickelaindene complex [Ni{o-C 6 H 4 C(CO 2 Me)C(CO 2 Me)-kC,C}(dcpe)] (30) reacts cleanly with the electrophilic alkynes YCCCO 2 R (Y H, Me, R Me; Y Ph, REt) to give exclusively the naphthalene-1,2,3-triesters 31 ± 33 (Scheme 5; Table 3, Entries 5 ± 7) (see [60] and Exper.…”

Structure and Bonding of Ni(C6H4-nFn)(CO)2(C6H4=benzyne, n=1-4) Complexes

“…3,[7][8] Since the first attempt for making metal complexes using benzyne by by Wittig and Bickelhaupt in 1958, 9 many benzyne complexes have been successfully prepared, [10][11][12][13] for example, M. A. Bennett et al 14 synthesized organometallic compounds, NiL 2 (C 6 H 4 )(L = PCy 3 , P i Pr 3 ; Cy = cyclohexyl, i Pr = isopropyl). K. R. Deaton and M. S. Gin studied the reactions of nickel(0)-benzyne complexes with symmetrically substituted 1,3-diynes in the presence of triethylphosphine, which lead to the regioselective formation of 2,3-dialkynyl naphthalenes 15 .…”