Self‐Coupling of a 4‐H‐Butatrienylidene Tungsten Complex

Abstract

Tungsten tryst: A 4-H-butatrienylidene complex of tungsten was successfully isolated and structurally characterized. It undergoes a unique self-coupling, which leads to a dimer (see picture; P pink, O red) with a cross-conjugated pi system and with electrochemically and magnetically active metal centers.

Synthesis and Properties of 2,3‐Diethynyl‐1,3‐Butadienes

“…Substituted DEBDs are scattered through the literature,w ith single examples from the groups of Larock, [5] Gleiter, [6] Grigg, [7] and Suzuki, [8] three compounds from Faust, [9] and three from Hopf, [10] including the parent hydrocarbon 1.R u, Fe,a nd W complexes containing DEBDs,w hich display interesting electronic properties,h ave been studied by Bruce [11] and others. [12] Thec ontribution from the Hopf group uncovered almost everything that is known about the reactivity of DEBDs and identified interesting applications.H opf and co-workers reported the Diels-Alder reaction of their compounds with dienophiles to prepare cyclic Z-endiynes, [10] which found application in both Bergman cycloaromatizations [13] and in the synthesis of substituted phthalocyanines with potential in photodynamic therapy. [9] Hopf also reported the formation of 1,4-cyclooctadienes through the thermal [4+ +4]-cycloaddition dimerization of DEBDs.T his remarkable transformation represents af ormally disallowed process according to the Woodward-Hoffmann rules.…”

Oxidative Activation of Aryldiynyl–Iron Complexes: Regioselective Dimerization

“…It has been suggested that this reaction proceeds via a 1,2-bis(ethynyl)cyclobutenyl diradical intermediate which undergoes retro-electrocyclic ring opening. 27 A recent experimental and theoretical investigation on iron and ruthenium σ-polyynyl complexes has concluded that the iron(III) radicals bearing ligands with four and six sp carbon atoms are stable in solution for a few minutes at 20 °C and for an unlimited time below −20 °C. It was also suggested that the 17e iron radicals may react via a smooth chemical process, since the ESR signal disappeared cleanly, no traces of other radicals being detected.…”

“…Related to this chemistry is the earlier report of the dimerization of the butatrienylidene (dppe) 2 (CO)W{CCCCH(C 6 H 4 Bu t )} to give {(dppe) 2 (CO)W}{CC[CH(C 6 H 4 Bu t )]C[CH(C 6 H 4 Bu t )]CC}{W(CO)(dppe) 2 } by C γ –C γ coupling. It has been suggested that this reaction proceeds via a 1,2-bis(ethynyl)cyclobutenyl diradical intermediate which undergoes retro-electrocyclic ring opening …”

Vinylidene and pentatetraenediyl rhodium complexes obtained from a bulky rhodium(i) dimer and a functionalized 1,3-diyne

“…Typical spectroscopic features of 6 are the singlet at d 5.73 for the QCH proton in the 1 H NMR spectrum and the four distinct signals for the carbon atoms of the RhC 4 chain in the 13 C NMR spectrum. These signals exhibit quite different 13 C-103 Rh and 13 C-31 P coupling constants. It is worth mentioning that the chemical shifts of the resonances for the cumulene carbon atoms in a-, band g-position (d 237.3, 161.1 and 173.1) are rather similar to those of the IrC 4 counterpart trans-[IrCl(QCQCQ CQCPh 2 )(PiPr 3 ) 2 ] (d 225.7, 164.1 and 174.6).…”

“…It has been characterized by the mass spectrum and by reference to the IR and NMR spectroscopic data. 13 Reaction of either 7 or 8 with triflic acid in the presence of an equimolar amount of water gives the rhodium(I) vinylidene complex 9 (Scheme 2) as an orange solid, which for short periods of time can be handled in air. The IR spectrum of 9 shows a strong band at 1640 cm À1 , assigned to the CQO stretching mode of the ketone unit.…”