Base-catalysed cleavage of silyl-substituted polyynes. Attenuation of hydrocarbon acidity and transmission of substituent electrical effects in long-chain conjugated polyacetylenes

Iron(II) and iron(III) complexes containing ethynyl thiophene fragments

“…As the number of carbon atoms in the p-system increases, the C a signals are shifted downfield from (d, ppm) 146.3 for 1 to 152.9-153.2 for 2a-c and to 155.9-156.2 for 3a-c. This observation is in accordance with the increase of the electron-withdrawing effect of the organic carbon-rich ligand with the extension of its p-system [32]. In organometallic complexes, as the length of a carbon-rich ligand increases, its electron-withdrawing effect on the metal increases and induces a stronger p-back-bonding response from the metal center, the intensity of which being also related to how electron rich the metal is.…”

Trapping of Terminal Platinapolyynes by Copper(I) Catalyzed Click Cycloadditions; Probes of Labile Intermediates in Syntheses of Complexes with Extended sp Carbon Chains, and Crystallographic Studies

“…In a related series of platinum complexes in which the pentafluorophenyl groups have been replaced by p-tolyl ligands, [5b] protodesilylation rates have been shown to increase with sp chain lengths, probably for reasons connected to the Brønsted acidity trends of terminal polyynes noted above. [19] Qualitative observations suggest parallel behavior in Schemes 3 and 4, and the possibility of more efficient click trapping reactions at lower temperatures. In preliminary efforts, analogous coupling reactions involving PtC x SiR 3 and the tetraynes HC 8 SiR 3 have been investigated.…”

“…[18] Although it may not be directly relevant to this trend, the Brønsted acidities of terminal polyynes also increase with chain length. [19] Accordingly, the platinum complexes employed in this study were accessed by the chain extension reactions in Scheme 3. These use PtC 6 TES [5a] and PtC 8 TES, [5a] which are themselves substrates for the title reaction, as springboards.…”

Synthesis and reactivity of new heterodinuclear iron/rhenium Cx complexes of the formula (η5-C5Me5)Re(NO)(PPh3)(CC)n(η2-dppe)Fe(η5-C5Me5) (n = 3, 4): Redox properties and a dicobalt hexacarbonyl adduct

“…First, upon extension of the sp carbon chain, the increasingly remote iron center becomes a less effective donor. Second, longer polyynes are also more electron withdrawing, as evidenced by the progressively decreasing pK a values of H(C^C) n R species [38]. NMR spectroscopy ( 1 H, 31 P and 13 C) also supports the assigned structures.…”