Synthesis and Structural Characterization of Novel Organometallic Dehydroannulenes with Fused CpCo-Cyclobutadiene and Ferrocene Units Including a Cyclic Fullerenyne Segment

Abstract

The synthesis of fused organometallic dehydroannulenes containing cyclobutadiene(cyclopentadienyl)cobalt or ferrocene units separated by butadiyne linkers is presented. Starting from the corresponding 1,2-diethynylated sandwich complexes, either Eglinton, Hay, or Vögtle-type coupling furnishes the desired dehydroannulenes. The choice of the coupling variant is critical for the success of this reaction. It was found that for diethynylferrocene a variant of the classic Eglinton system utilizing a Cu2Cl2/CuCl2 mixture in pyridine works successfully, while for the case of the cyclobutadiene(cyclopentadienyl)cobalt complexes the Vögtle coupling utilizing Cu(OAc)2 in acetonitrile gave the most impressive results, leading to a 87% yield of cyclized material. To obtain perethynylated organometallic dehydroannulenes, a novel synthesis of tetraethynylated cyclobutadiene complexes was developed. Flash vacuum pyrolysis of a bisbutadiynylated CpCo-ligated cyclobutadiene furnishes the desired tetraethynylated cyclobutadiene complex via a Bergman-type rearrangement. The two TMS and two TIPS substituents of the cyclobutadiene complex are oriented pairwise ortho with respect to each other. Removal of the TMS groups accesses a monomer, which under the conditions of the Vögtle coupling cyclizes to novel trimeric and tetrameric, perethynylated, cyclobutadieno fused, organometallic dehydroannulenes.

Concave Butterfly-Shaped Organometallic Hydrocarbons?

“…[16] The extension of this concept towards larger systems of higher unsaturation may lead to the formation of fullerenes from cyclobutadienecontaining precursors under appropriate matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) conditions, similar to the coalescence of suitable cyclophynes elegantly demonstrated independently by Rubin et al [16] and Tobe et al [17] Experimental Section 4 b: A round-bottom flask was charged [11] with 5 a (0.098 g, 0.11 mmol), tetramethylammonium fluoride (0.300 g, 10.9 mmol), DMSO (5 mL), and diethyl ether (10 mL). The resulting mixture was stirred at 25 8C for 2 h. Aqueous workup (diethyl ether) followed by removal of the solvent in vacuo yielded 5 b as a dark red oil.…”

“…Vollhardt, Youngs et al [7] have developed a powerful method to assemble dehydrobenzo [14]annulenes, [8±10] which is suitable for preparing the butterfly complexes 4. Starting from 1 a, [11] fourfold Pd-catalyzed coupling with 2 a furnishes 3 a after chromatography and removal of the trimethylsilyl groups by K 2 CO 3 in methanol in an overall yield of 16 % (64 % per coupling step; Scheme 1). Treatment of 3 a with Cu(OAc) 2 in acetonitrile/THF under conditions described by Vögtle and Berscheid [9] and recently utilized by us [10] leads to 4 a as sole product in 94 % yield ( Table 1).…”

Concave Butterfly-Shaped Organometallic Hydrocarbons?

“…[16] When d-Val is used as AA1, the sense of enantioselection is reversed, indicating that the stereochemical identity of AA1 is critical to the sense of stereochemical induction and that the d,l-ligand may deliver lower levels of enantioselectivity than the l,l isomer. Starting from 1 a, [11] fourfold Pd-catalyzed coupling with 2 a furnishes 3 a after chromatography and removal of the trimethylsilyl groups by K 2 CO 3 in methanol in an overall yield of 16 % (64 % per coupling step; Scheme 1). Topologies of type 4 are attractive because related species featuring the tetraethynylcylobutadiene motif have been suggested by Jarrold et al [6] to play an important role in the formation of fullerenes such as C 60 .…”

New carbon-rich organometallic architectures based on cyclobutadienecyclopentadienylcobalt and ferrocene modules

“…R0/methyl or butyl. route, significantly restricting the amount of material that could be made [48]. Scheme 4 shows the solutionphase approach [51,52].…”