Synthesis and Structural Characterization of Organometallic Cyclynes: Novel Nanoscale, Carbon-Rich Topologies

Abstract

Dedicated to Professor G¸nther E. Szeimies ™Carbon-rich∫ defines an exciting area that spans the world of large arenes to that of highly alkynylated structures including carbon wires, peralkynylated p perimeters, graphdiyne segments, dehydroannulenes, and cyclophane derivatives. [1±9] Carbon-rich organometallic compounds are less explored than their organic counterparts, a tribute to the considerably increased effort in their synthetic access. [10±14] Aesthetic structures, exciting topologies on the nanometer scale, and their modular synthesis, however, make carbon-rich organometallic compounds attractive. Rewards are expected in materials properties that differ from their organic counterparts, such as electroactivity and potential nonlinear optics (NLO) activity. In addition, large carbon-rich organometallic molecules are often surprisingly soluble and form single crystals, which allows their structural characterization in the solid state, [13] a feature that is often elusive for their organic counterparts.Herein we report the synthesis and structural characterization of three novel organometallic cyclynes [10] with an expanded bicyclo[1.1.0]butane (A) and a [2.1.0.0 1,3 ]pentane (B) topology. In these structures, the CÀC single bonds of the small rings are replaced by alkyne or butadiyne bridges, while the carbon atoms are substituted by benzene rings, cyclobutadiene(cyclopentadienylcobalt) units, or ferrocene centers. Key steps in the synthesis of these targets are the selective ortho-metalation of organometallic acetals, [14] and the conversion of aldehydes into alkynes by the Ohira method. [15] Pd-catalyzed coupling of 1 [14] to the iodide 2 a furnishes 3 in 23 % (Scheme 1). The moderate yield of 3 is a result of the two meta-positioned alkyne groups in 2 a between which the iodide is sandwiched. Only the active Hartwig catalyst epoxide synthesis. A study of other ligands to expand the scope of the process and enhance asymmetric induction, as well as synthetic applications, is currently underway. Experimental SectionTypical procedure for lithiation ± electrophile trapping of cyclooctene oxide (1) in the presence of a diamine:The diamine (2.6 mmol) was added dropwise to a solution of RLi (1.4 m, 2.5 mmol) in Et 2 O (8 mL) at À 90 8C. This mixture was stirred for 1 h at À 90 8C. A solution of cyclooctene oxide (1; 2.0 mmol) in Et 2 O (2 mL), precooled to À 90 8C, was then added rapidly by cannula to the solution of ligand/RLi and the reaction mixture was then stirred at À 90 8C for 3 h. Neat electrophile (3.0 mmol) was added dropwise, and the mixture was then allowed to warm to room temperature over 5 h. After quenching with aqueous H 3 PO 4 (0.5 m, 25 mL), the organic phase was washed with saturated aqueous NaHCO 3 (25 mL) and brine (25 mL). The aqueous layers were extracted twice with Et 2 O (25 mL) and the combined organic phases were dried (MgSO 4 ) and evaporated under reduced pressure. Purification of the residue by column chromatography (SiO 2 , Et 2 O, petrol) gave the substituted epoxide.

An Intermolecular Double [2+2] Cyclodimerization of a Tetraalkyne

“…Bunz and co‐workers constructed a series of highly alkynated carbon‐rich derivatives 7. 8 Dinuclear [Co 2 (CO) 8 ] facilitates the Pauson–Khand reaction, a [2+2+1] cycloaddition affording extremely useful cyclopentenones 9. 10…”