Acetylenic derivatives of metal carbonyls I. Substitution reactions of CO2(CO)6C2RR′ complexes

Synthesis, Characterization, Structures and Comparative Electrochemical Study of 2,4‐Bis(trimethylsilylethynyl)thiophene Coordinated Carbonylcobalt Units

“…Then, the preference of the Co 2 (CO) 4 X [X = (CO) 2 or dppm] moieties to coordinate the alkyne in position 2 can be explained by electronic factors. In agreement with this, the electron density on the triple bond of the alkyne in position 4 is higher than on the alkyne in position 2, as judged by the 13 C NMR shifts for the alkyne C atoms; this situation should disfavor the attachment of the Co atoms to the CϵC group in position 4, since back-donation from the Co d-orbitals to the π*-MO of an electron-poor ligand is the stabilizing factor in the bonding. [13] However, Diederich et al obtained in the reaction of Co 2 (CO) 8 with 1,6-bis(triisopropylsilyl)hexa-1,3,5-triyne the exclusive formation of the compound in which the carbonylcobalt fragment is coordinated to the central CϵC triple bond, which was attributed to the presence of the bulky triisopropylsilyl end-caps.…”

“…Figure 1 presents a molecular diagram of 2Ј. Supporting Information (see footnote on the first page of this article): IR, UV/Vis, MS, 1 H, 13 C, 31 P NMR spectra and elemental analysis of 1-9, 1Ј-2Ј, 2,4T and 2,4TЈ.…”

“…35 ppm) with respect to that of the free ligand because of the coordination. [7d] and by using the 13 C NMR spectra of 4 and 5 in the same solvent in addition to HMQC and HMBC spectroscopy (these experiments have also been performed for the rest of the complexes) ( Figure 2). …”

“…13 C NMR (500 MHz, CDCl 3 , 25°C, ppm) data for the compounds 1-9 and 2,4T. [a] 97.7 (s br) [a] 139.0 (s) [a] 134.2 (s) [a] 125.9 (s) [a] 124.6 (s) [a] 96.9 (s) [a] 100.1(s) [a] 94.5 (s br) [a] 143.1 (s) [a] 130.8 (s) [a] 125.2 (s) [a] 139.9 (s) [a] 97.7 (s br) [a] 80.0 (s br) [ …”

Synthetic Routes to the Cyclo[n]carbons

“…Hexacarbonyl dicobalt fragments [24] [25] were used as protecting groups to allow geometrically disfavored cyclization reactions by bending an alkyne moiety [26] or to stabilize strained alkynes [27]. The p-(hexacarbony1)dicobalt units in 13 and 14 should be readily removable either by oxidation [28], alkyne-ligand exchange [29], or flash-vacuum pyrolysis [30]. From the general retrosynthetic scheme, we set out to prepare the precursor 16 from 1,6-bis(triisopropylsilyl)hexa-1,3,5-triyne via 15 [22] [31].…”