Ferrocenes Containing a Pendant Propargylic Chain Obtained via Addition of Propargyl Alcohol to μ-Vinyliminium Ligands in Diiron Complexes

Abstract

The diiron bridging vinyliminium complexes [Fe 2 {μ-η 1 :η 3 -CN(Me) 2 C(R′)C(R″)}(μ-CO)(CO)-(Cp) 2 ][SO 3 CF 3 ] (R′ = H, R″ = SiMe 3 , 3a; R′ = H, R″ = Tol =4-MeC 6 H 4 , 3b; R′ = Me, R″ = Me, 3c; R′ = SPh, R″ = Me, 3d; R′ = H, R″ = Fc = [Fe(C 5 H 4 )(Cp)], 6e) react with propargyl alcohol (HCCCH 2 OH), in refluxing toluene, affording the polysubstituted ferrocenes as mixtures of two isomeric forms: [1-NMe 2 -2-R′-3-R″-5-CH 2 OCH 2 CCH-Fc] (R′ = H, R″ = SiMe 3 , 6a; R′ = H, R″ = Tol, 6b; R′ = Me, R″ = Me, 6c; R′ = SPh, R″ = Me, 6d, R′ = H, R″ = Fc, 6e) and [1-NMe 2 -2-R′-3-R″-4-CH 2 OCH 2 CCH-Fc] (R′ = H, R″ = SiMe 3 , 7a; R′ = H, R″ = Tol, 7b; R′ = Me, R″ = Me, 7c; R′ = SPh, R″ = Me, 7d) in overall yields of about 55−65%. Formation of the functionalized cyclopentadienyl in the ferrocene products takes place through the assembly of two propargyl units with the bridging vinyliminium ligand: one alkynol is incorporated by a [3 + 2] cycloaddition with the bridging C 3 ligand; a second alkynol unit gives rise to a pendant chain through −OH substitution. Investigations show that the substitution step is catalyzed by the parent diiron complex itself or by a mononuclear iron fragment (likely the Fp + complex). The pendant propargyl chain has been exploited to connect the ferrocene to other molecular fragments: in particular, the reaction of 6a with 4-biphenyl azide, by copper-catalyzed azide−alkyne cycloaddition (CuAAC), leads to the formation of the triazole-functionalized ferrocene [1-NMe 2 -2-CH 2 OCH 2 -N 3 (C 6 H 4 Ph)C 2 H-4-SiMe 3 -Fc] (12). Moreover, 6a reacts with Co 2 (CO) 8 , affording the complex [Co 2 {μ-η 2 -HC CR}(CO) 6 ] (13), (HCCR = 6a), where the alkyne adopts a η 2 coordination to a dicobalt hexacarbonyl fragment. The molecular structure of 7a has been determined by X-ray diffraction studies.

Constructing Organometallic Architectures from Aminoalkylidyne Diiron Complexes

“…The formation of 76 is the result of [3+2+1] cycloaddition involving the bridging vinyliminium, the alkyne and one carbonyl ligand,[106a] and might be viewed as a dinuclear version of the Dötz reaction (Scheme a) . On the other hand, amino‐ferrocenes 77 contain a pendant alkynyl chain and are obtained in moderate yields using two equivalents of propargyl alcohol (Scheme b) . Notably, this synthetic procedure allows the access to ferrocenes multi‐functionalized exclusively at the (C 1 –C 2 –C 3 )‐derived five‐membered ring, including N‐ and S‐substituted ferrocenes, which are quite rare .…”

“…(a) R′ = SiMe 3 , R′′ = H . (b) R′ = SiMe 3 , 4‐C 6 H 4 Me or Fc, R′′ = H; R′ = R′′ = Me; R′ = Me, R′′ = SPh …”

5-Ferrocenylmethyl-2,2-dimethyl-5-(prop-2-ynyl)-1,3-dioxane-4,6-dione

“…Interactions involving cyclopentadienide anions as hydrogen-bond acceptors have been reluctantly identified as hydrogen bonds (Harder, 1999). Using the query 'C C-HÁ Á ÁCg(ferrocene) non-bonded contact with HÁ Á ÁCg distance 2.7 Å 0 , several related structures have been found in the Cambridge Structure Database (Groom & Allen, 2014), see: Lin et al (1996); Buchmeiser et al (1998); Wong et al (2001); Li et al (2006); Busetto et al (2012). Although not explicitly described as such by the respective authors, these structures exhibited the C C-HÁ Á Á interactions mentioned, and the corresponding CÁ Á ÁCg distances are 3.58 Å with C-HÁ Á ÁCg angles ranging from 152 to 176 .…”

Iron(ii) catalyzed dehydrative etherification of alcohols: a convenient route to ferrocenylmethanol-ethers

“…2 In a related reaction, more recently reported, the bridging vinyliminium complexes of type 1 were found to react with propargyl alcohol to form ferrocene complexes containing a propargylic pendant chain (Scheme 2). 3 In this case two propargyl units are involved: one undergoes the [3 + 2] cycloaddition with the bridging vinyliminium ligand, whereas a second alkynol gives rise to the pendant propargyl chain, by -OH substitution. The reaction has been proposed to occur according to the sequence shown in Scheme 2, with I as intermediate species.…”

“…The reaction has been proposed to occur according to the sequence shown in Scheme 2, with I as intermediate species. 3 It was evidenced that ferrocenylmethanolpropargyl alcohol etherification step is catalyzed by the complex [Fp][OTf] (Fp + L[Fe(CO) 2 (Cp)] + and OTf 2 LSO 3 CF 3…”