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Synthesis and Characterization of Amine Complexes of the Cyclopentadienyliron + Dicarbonyl Complex Cation, [Cp(CO)2Fe] ⇑ Cyprian M

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Synthesis and Characterization of Amine Complexes of the Cyclopentadienyliron + Dicarbonyl Complex Cation, [Cp(CO)2Fe] ⇑ Cyprian M Inorganica Chimica Acta 366 (2011) 105–115 Contents lists available at ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica Synthesis and characterization of amine complexes of the cyclopentadienyliron + dicarbonyl complex cation, [Cp(CO)2Fe] ⇑ Cyprian M. M’thiruaine a, Holger B. Friedrich a, , Evans O. Changamu b, Muhammad D. Bala a a School of Chemistry, University of KwaZulu-Natal, Private Bag X54001, Durban 4000, South Africa b Chemistry Department, Kenyatta University, P.O. Box 43844, Nairobi, Kenya article info abstract + À 5 Article history: The organometallic Lewis acid, [CpFe(CO)2] BF4 (Cp = g -C5H5) reacts with excess dry diethyl ether at Received 6 July 2010 + À low temperatures to form the labile complex [CpFe(CO)2(Et2O)] [BF4] (1) which is stable at low temper- Received in revised form 11 October 2010 atures and has been fully characterized. Complex 1 in turn reacts with 1-aminoalkanes and a,x-diam- Accepted 14 October 2010 inoalkanes to form new complexes of the type [CpFe(CO) NH (CH ) CH ]BF (n = 2–6) (2) and Available online 16 November 2010 2 2 2 n 3 4 [{CpFe(CO)2}2l-(NH2(CH2)nNH2)](BF4)2 (n = 2–4) (3), respectively. These complexes have been fully char- acterized and the mass spectral patterns of complexes 2 are reported. The structures of compounds 2a Keywords: (n = 2) and 2b (n = 3) have been confirmed by single crystal X-ray crystallography. The single crystal a,x-Diaminoalkanes X-ray diffraction data show that complex 2a, [CpFe(CO) NH (CH ) CH ]BF , crystallizes in a triclinic P1 Diethyl ether complex 2 2 2 2 3 4 1-Aminoalkanes space group while 2b, [CpFe(CO)2NH2(CH2)3CH3]BF4, crystallizes in an orthorhombic Pca21 space group Cyclopentadienyliron dicarbonyl with two crystallographically independent molecular cations in the asymmetric unit. Furthermore, the reaction of 1 with 1-alkenes gives the g2-alkene complexes in high yield. Ó 2010 Elsevier B.V. All rights reserved. 0 0 1. Introduction the phosphine complex, [CpFe(CO)(PPh3)(Et2O)][BAr 4] (Ar = 3,5- (CF3)2C6H3) has been synthesized by protonation of [CpFe(CO)- + 0 The cationic complexes of type, [CpFe(CO)2L] (L = labile ligand) (PPh3)CH3] using H(OEt2)BAr 4 at À80 °C [44]. The dimethyl ether [1–4] are an important class of transition metal compounds that complex, [CpFe(CO)2(OMe2)]BF4, and its reaction with acetonitrile have been extensively utilized in synthesis [2,4–21] and catalysis to give [CpFe(CO)2(NCCH3)]BF4 has also been reported [1]. [CpFe(- [3,14,22–33]. A particular example is the ethereal complex, [CpFe- CO)2(OMe2)]BF4 degraded within a few hours even when stored (CO)2(THF)]BF4 [34] in which the labile tetrahydrofuran (THF) is under vacuum at À20 °C. This thermal instability made the com- coordinated to the metal centre through the oxygen atom. This plex difficult to handle, leading to its limited application as a start- complex has been proven to be an essential precursor in the syn- ing material for CpFe(CO)2 complexes. Diethyl ether complexes of thesis of various cyclopentadienyliron complexes [4,10–13,15– other cyclopentadienylmetal carbonyls such as Mn [45],Re[45], 20,35], as well as catalysts in various organic syntheses such as Mo [46], and W [46] are known. the [2+2] cycloaddition of alkenes [36], Diels–Alder reactions There have been very few reports on aminoalkane complexes of [37,38], cyclopropanation [27,31–33], epoxidation [29,30] and cyclopentadienyliron dicarbonyl in which the aminoalkane is coor- aziridination [25–28], among others [3,22–24,27,29,39]. In all dinated to the metal via the nitrogen atom. Reported cases include 2 these reactions THF is easily displaced by the desired substrate a reaction between [CpFe(CO)2(g -Et-C„C-Et)]BF4 and 2-amino- i i + to form either the desired intermediate or desired end product. propane, (NH2Pr ), to yield the black solid [CpFe(CO)2(NH2Pr )] + [CpFe(CO)2(acetone)] is another complex with an oxygen-bonded [47]. This is in sharp contrast to the yellow solid complex [CpFe(- n + ligand which has also been extensively used in the synthesis of CO)2(NH2Pr )] reported herein. The reaction between [CpFe(- 2 both neutral and cationic complexes based on the CpFe(CO)2 moi- CO)2(g -Ph-C„C-Ph)]BF4 and 2-amino-2-methylpropane to give t + ety [2,5–9,21,40,41]. [CpFe(CO)2(NH2Bu )] was also reported [47] but no physical or Although diethyl ether has a higher donor number (0.49) than analytical details were given. acetone (0.44) [42,43], the analogous diethyl ether complex, Cyclopentadienyliron dicarbonyl complexes of secondary [48], + [CpFe(CO)2(OEt2] has not been previously reported. However, tertiary [35] and cyclic [49] amines are established. Reaction of + the acetone complex [CpFe(CO)2(acetone)] with half a molar equivalent of either di(tertiary phosphine) [9,50], 2,5-dithiahexane ⇑ Corresponding author. Tel.: +27 312603107; fax: +27 312603091. or pyrazine [9] have been reported to yield bimetallic complexes in E-mail address: [email protected] (H.B. Friedrich). which the ligand acts as a bridge between two metal centers. 0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2010.10.018 106 C.M. M’thiruaine et al. / Inorganica Chimica Acta 366 (2011) 105–115 However, to our knowledge, there are no reports on diaminoalkane ethyl groups in coordinated diethyl ether, respectively. Separate complexes of iron in which the diaminoalkane links two iron resonance peaks corresponding to the protons of the methylene centers. and methyl groups of uncoordinated diethyl ether were observed Hence, in this paper we report the synthesis and characteriza- at 3.39 and 1.10 ppm, respectively. The uncoordinated diethyl + À tion of [CpFe(CO)2(Et2O)] [BF4] 1 and its reactions with a series ether in this case had been displaced from the coordination center of 1-aminoalkanes, and a,x-diaminoalkanes to form new com- by acetone, leading to the known acetone complex, [Cp(CO)2- + plexes, [CpFe(CO)2NH2(CH2)nCH3]BF4 (n = 2–6) (2) and [{CpFe(- Fe(OCMe2)] [52]. The chemical shift due to the Cp protons of the CO)2}2l-(NH2(CH2)nNH2)](BF4)2 (n = 2–4) (3), respectively. etherate complex was observed at 5.78 ppm, while a separate res- onance peak assignable to the Cp protons of the acetone complex was observed at 5.71 ppm. When wet acetone-d6 was used, a peak 2. Results and discussion + due to the Cp protons of the aqua complex, [Cp(CO)2Fe(OH2)] , was observed at 5.23 ppm. 2.1. Synthesis of [CpFe(CO) (Et O)]BF (1) 2 2 4 The intensity of the peaks at 5.78, 3.67 and 1.16 ppm corre- sponding to the etherate complex diminished as the temperature Reaction of [CpFe(CO) ]BF with a large excess of diethyl ether 2 4 was raised from À30 to À10 °C and eventually disappeared at high- at low temperatures results in the immediate formation of the er temperature. Conversely, the intensity of the resonance peaks at diethyl ether complex 1 in excellent yield. The product precipitates 5.71, 3.39 and 1.10 corresponding to the acetone complex in- and is easily isolated by filtration under inert atmosphere. Reaction creased and dominated at À5 °C. In general, the proton NMR spec- of [CpFe(CO) ]BF with two equivalents of diethyl ether in CH Cl 2 4 2 2 trum of compound 1 shows that diethyl ether is coordinated to the gave low yields (20%) of 1 and was difficult to isolate in pure form. metal centre in the coordination sphere and is not just a solvent It thus appears that the rate of reaction is partially dictated by the molecule trapped within the crystal lattice. amount of diethyl ether present. Compound 1 is a moisture sensitive red powder, insoluble in 2.2. Reaction studies hexane, sparingly soluble in chloroform, but very soluble in ace- tone and dichloromethane. The complex can be stored in anhy- The poor electron donating nature of diethyl ether makes com- drous atmosphere at À6 °C for at least three months without any plex 1 very electrophilic and thus it reacts with a wide range of degradation. nucleophiles. 2.1.1. Characterization 2.2.1. Reactions of 1 with n-aminoalkanes The IR spectrum of the complex 1 shows two carbonyl absorp- Equimolar quantities of 1 and 1-aminoalkanes react smoothly À1 tion peaks at 2063 and 2010 cm . These suggest a weak synergic at room temperature in CH2Cl2 to give a series of the new com- interaction between the iron center and the carbonyl due to re- plexes, 2, via displacement of diethyl ether according to Scheme 1. duced electron density on the metal centre which is as a result of The reaction time of 1 with 1-aminoalkanes at room tempera- the coordination of the ethereal group. A medium and two weak ture is chain length dependent. The longer aminoalkanes, though intensity bands due to the symmetrical and asymmetrical C–H stronger Lewis bases than the shorter ones, required longer reac- stretching modes were observed in the region between 2990 and tion times, probably due to steric effects. For example, while the 2850 cmÀ1. Two other medium intensity bands due to C–H rocking reactions of 1 with 1-aminopropane and 1-aminobutane took less and C–O stretching were observed at 1392 and 1286 cmÀ1, than 2 h, its reaction with longer aminoalkanes took 3–6 h.
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