Reactions of 7,7,8,8-Tetracyanoquinodimethane with Poly-ynyl Ruthenium and Iron Complexes

Abstract

The reaction of tetracyanoquinodimethane (TCNQ) with Ru(CCCCH)(dppe)Cp* (5) at the outer (from Ru) CC triple bond gives η 1 -(butadienyl)ethynyl Ru{CCC[CHC(CN) 2 ]C 6 H 4 C-(CN) 2 }(dppe)Cp (8), which reacts with a second equivalent of diynyl-Ru complex to give {Ru(dppe)Cp*}{CCC[C 6 H 4 C(CN) 2 ]CH CHC[C(CN) 2 ]CC}{Ru(dppe)Cp*} (9). The Ph-substituted complexes M{CCCCPh}(dppe)Cp* (M = Fe 6-Fe, Ru 6-Ru) and Ru{(CC) 3 Ph}(PPh 3 ) 2 Cp (7) react with TCNQ to give the η 1 11), respectively. Single-crystal X-ray diffraction molecular structure determinations for 8−11 have been carried out. In the Fe series, we suggest that the initial step of the mechanism involves electron transfer to form the [TCNQ] −• salt of the diynyl-iron cation, followed by C−C bond formation to give a zwitterionic intermediate. Isolated products can be rationalized by further reaction involving [2 + 2]-cycloaddition of one of the CC(CN) 2 groups of TCNQ to a CC triple bond of the metal poly-ynyl complex and a subsequent ring-opening reaction of the resulting (unobserved) cyclobutenyl intermediate. On the basis of X-ray diffraction data, redox potential determinations, and 57 Fe Mossbauer and UV−vis spectroscopies, the electronic structures of the new compounds contain significant contributions from polarized mesomers involving charge transfer from the electron-rich metal−ligand fragment to the cyanocarbon ligand via the conjugated unsaturated carbon linker.

From Molecular Wires to Molecular Resistors: TCNE, a Class-III/Class-II Mixed-Valence Chemical Switch

“…These bands are more intense and blue-shifted in the complex 2Ru than in the complex 2Fe, in accord with the colors of these compounds, which are yellow-brown and purple, respectively. As the visible spectra of the related mononuclear alkynyl derivatives have similar absorptions, 35,43,47 they are tentatively assigned to dπ(M) → π*(CC) metal-to-ligand charge transfer (MLCT) transitions. The spectrum of the heterobinuclear complex 2FeRu shows absorptions on the low-energy side that match well with those of 2Fe, while on the high-energy side its shape is close to that of the spectrum of 2Ru.…”

Reactivity of Polyynes: Complex Molecules from Simple Carbon Rods

“…For instance, reaction of symmetrical ruthenium end-capped octatetrayne 173 with an excess of TCNE results in formation of double adduct 174. [100] Interesting reactivity was observed by Lapinte and Bruce for a series of binuclear hexatriynes (184-186). However, the selectivity depends on the type of an end-group.…”

Electronic Interplay between TTF and Extended-TCNQ Electrophores along a Ruthenium Bis(acetylide) Linker

“…For each CC bond of the diyne bridges, the IR spectrum of 2 exhibits two stretching vibration bands at 2129 and 1993 cm −1 , while for 3 the stretching vibration of the C N, CC, and CC bonds are observed at 2202, 1932, and 1590 cm −1 , respectively. 11 The CC bond IR vibrations in 2 and 3 are at a lower energy than in the starting TTF 1 (2201 cm −1 ), which indicates a high degree of conjugation between the TTF and the Ru atom in 2 as well as between the DCNQ moieties and the Ru in 3.…”

“…In principle, the two triple bonds on both sides of the Ru atom can react with TCNQ for the [2 + 2] cycloaddition leading to a cyclobutenyl intermediate which undergo a ring opening (see the Supporting Information). − Due to the steric hindrance generated by the dppe ligands, the CC bonds closest to the TTFs are involved in the CA-RE reaction as demonstrated by X-ray crystallographic analysis (vide infra). This reactivity at the outer CC bond of a diynyl ligand has been observed in trans -bis­(buta-1,3-diynyl)­Pt complexes as well as in M­(−CC–CC–R)­(dppe)­Cp* (R = Ph, H and M = Ru, Fe). , It is worth mentioning that it is the first time that an alkyne bond connected to a TTF undergoes such a reaction with TCNQ .…”

“… − Due to the steric hindrance generated by the dppe ligands, the CC bonds closest to the TTFs are involved in the CA-RE reaction as demonstrated by X-ray crystallographic analysis (vide infra). This reactivity at the outer CC bond of a diynyl ligand has been observed in trans -bis­(buta-1,3-diynyl)­Pt complexes as well as in M­(−CC–CC–R)­(dppe)­Cp* (R = Ph, H and M = Ru, Fe). , It is worth mentioning that it is the first time that an alkyne bond connected to a TTF undergoes such a reaction with TCNQ . Moreover, the regioselectivity of the TCNQ addition to 2 leads to the dicyanoquinodimethane (DCNQ) moiety at the β-carbon atom of the linkers relative to the TTF core.…”