Synthesis and Properties of Ferrocenyl Allenylidene Complexes: X-ray Structure of [Ru(C═C═CHFc)(PPh₃)₂(η⁵-C₅H₅)][PF₆]·CH₂Cl₂

Abstract

Reactions of the transition metal halide complexes [MXL2(Cp)] (M = Fe, X = I, L2 = dppe; M = Ru, X = Cl, L = PPh3; M = Os, X = Br, L = PPh3; Cp = η-C5H5) with the alkynol HCCCH(OH)(Fc) (1) (Fc = ferrocenyl) in the presence of TlBF4 gave the monosubstituted allenylidene complexes [M(CCCHFc)L2(Cp)][BF4] (2a: M = Ru, L = PPh3; 3: M = Fe, L2 = dppe; 4: M = Os, L = PPh3). Similarly, the reaction of 1 with [RuCl(PPh3)2(Cp)] and NH4PF6 in methanol gave [Ru(CCCHFc)(PPh3)2(Cp)][PF6] (2b). These highly colored compounds were characterized by spectroscopic and electrochemical techniques and in the case of 2b by a single-crystal X-ray structure determination. Cyclic voltammetry in MeCN in the presence of [nBu4N][ClO4] at 100 mV·s−1 shows a reversible ferrocenyl-based one-electron oxidation, in addition to irreversible oxidation and reduction processes. The NMR spectra of 2b show complex behavior at low temperature, attributed to temperature-dependent chemical shifts and correlated motions of the allenylidene ligand and the ferrocenyl substituent.

Activation of Propargyl Alcohols by TpRu Complexes Bearing a Bidentate NHC Ligand

“…The signals observed at δ 305.9, 223.7, and 145.8 ppm in the 13 C­{ 1 H} NMR spectrum are respectively characteristic for the C α , C β , and C γ atoms of the allenylidene ligand. These spectral properties compare well with those found in other allenylidene complexes bearing tertiary phosphines as auxiliary ligands. ,− …”

“…The reaction of 1 with HCCC­(OH)­Ph 2 and NaBPh 4 in MeOH at 60 °C led to the deep purple allenylidene derivative [TpRuCCCPh 2 ( L )]­[BPh 4 ] ( 6 ) instead of the corresponding γ-methoxyvinylidene complex. As has been observed in the case of half-sandwich phosphine complexes, , this reaction is assumed to occur through the intermediacy of the γ-hydroxyvinylidene complex [TpRuCCHC­(OH)­Ph 2 ( L )]­[BPh 4 ] (not isolated in pure form), which undergoes spontaneous thermal dehydration, furnishing the final allenylidene product (Scheme ).…”

“…The relevance of ruthenium allenylidene complexes as key intermediates for propargylic substitution reactions has prompted many studies on the reactivity of allenylidene ligands attached to different ruthenium fragments. − Many of these studies have focused on the factors controlling the selectivity of the addition of nucleophiles to either the C α or C γ of the allenylidene ligand. − Thus, the electronic and steric properties of the metal fragment and the allenylidene substituents control the regioselectivity. On the other hand, whereas the α- and γ-carbons are electrophilic centers, the β-carbon exhibits a nucleophilic character, and protonation at this position leads to vinyl-carbyne species. , Our research group has broad experience with the chemistry of allenylidene complexes of ruthenium bearing monodentate, bidentate, and hemilabile phosphine ligands. ,, The electron richness of the metal center is tuned not only by the steric and electronic properties of the phosphine substituents but also by the nature of other supporting ligands such as hydrotris­(pyrazolyl)­borate (Tp), , Cp, ,, Cp* ,, and indenyl . Thus, the fragments {[Cp*Ru­(PR 3 ) 2 ] + } (PR 3 = PEt 3 , PMe i Pr 2 ) and {[Cp*Ru­(dippe)] + } (dippe = 1,2-bis­(diisopropylphosphino)­ethane) are electron rich, and nucleophilic addition reactions to the allenylidene ligand take place at the γ-carbon, yielding vinylidene or alkynyl derivatives. , At variance with this, fragments such as {[Cp*Ru­( i Pr 2 PNHPy) 2 ] + }, {[Cp*Ru­(CO)­(PMe i Pr 2 )] + }, {[CpRu­(CO)­(P i Pr 3 )] + }, and {[(η 6 -arene)­Ru­(PR 3 )] + } are more electron poor, and addition of nucleophiles to the allenylidene ligand occurs at the α-carbon, furnishing vinyl-carbene or σ-allenyl complexes.…”

Synthesis of Rhenium Vinylidene and Carbyne Complexes from Reactions of [Re(dppm)3]I with Terminal Alkynes and Alkynols

“…Reactions of d 6 metal complexes with terminal alkynes and alkynols have been widely explored to make interesting transition-metal complexes with a metal–carbon multiple bond, including vinylidene, allenylidene, and carbyne (when the reactions were carried out in the presence of an acid) complexes, especially for group 8 metals. − Although potentially useful, similar chemistry has been less explored for d 6 Re­(I) complexes. A literature survey shows that Re­(I) complexes which were reported to react with terminal alkynes or alkynols to give vinylidene or allenylidene complexes are usually those with CO or cyclopentadienyl ligands (Chart ).…”

Reactions of Ruthenium–Allenylidene Complexes Tethering a Cyclopropyl Group

“…In the reactions of various propargylic alcohols with [Ru]Cl, γ‐hydroxyvinylidene,5c, 8a vinylvinylidene,8b–c allenylidene,8d or phosphonium acetylide9e complexes were possible products. However, here, the allenylidene complex 2a is isolated as the only product and the γ‐hydroxyvinylidene species A is proposed as the intermediate.…”