Article pubs.acs.org/Organometallics
Ferrocenes Containing a Pendant Propargylic Chain Obtained via Addition of Propargyl Alcohol to μ-Vinyliminium Ligands in Diiron Complexes† Luigi Busetto,* Rita Mazzoni, Mauro Salmi, Stefano Zacchini, and Valerio Zanotti* Dipartimento di Chimica Fisica e Inorganica, Università di Bologna, Viale Risorgimento 4, I-40136 Bologna, Italy S Supporting Information *
ABSTRACT: The diiron bridging vinyliminium complexes [Fe 2 {μ-η 1 :η 3 -CN(Me) 2 C(R′)C(R″)}(μ-CO)(CO)(Cp)2][SO3CF3] (R′ = H, R″ = SiMe3, 3a; R′ = H, R″ = Tol =4-MeC6H4, 3b; R′ = Me, R″ = Me, 3c; R′ = SPh, R″ = Me, 3d; R′ = H, R″ = Fc = [Fe(C5H4)(Cp)], 6e) react with propargyl alcohol (HCCCH2OH), in refluxing toluene, affording the polysubstituted ferrocenes as mixtures of two isomeric forms: [1-NMe2-2-R′-3-R″-5-CH2OCH2CCH-Fc] (R′ = H, R″ = SiMe3, 6a; R′ = H, R″ = Tol, 6b; R′ = Me, R″ = Me, 6c; R′ = SPh, R″ = Me, 6d, R′ = H, R″ = Fc, 6e) and [1-NMe2-2-R′-3-R″-4-CH2OCH2CCH-Fc] (R′ = H, R″ = SiMe3, 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 C3 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-NMe22-CH2OCH2-N3(C6H4Ph)C2H-4-SiMe3-Fc] (12). Moreover, 6a reacts with Co2(CO)8, affording the complex [Co2{μ-η2-HC CR}(CO)6] (13), (HCCR = 6a), where the alkyne adopts a η2 coordination to a dicobalt hexacarbonyl fragment. The molecular structure of 7a has been determined by X-ray diffraction studies.
■
INTRODUCTION Transition-metal-mediated cycloaddition reactions are emerging as powerful synthetic tools for the construction of molecular architectures through the assembly of readily accessible building blocks. Alkynes are commonly involved in these reactions, such as in copper-catalyzed azide−alkyne cycloaddition (CuAAC),1 which corresponds well to the “nearperfect” bond-forming reactions condition required for a rapid combination of molecules according to the synthetic concepts developed by Sharpless.2 Indeed, the number of transitionmetal-promoted cycloadditions involving alkynes is much broader, and many of these reactions, although far from achieving the status of “click reactions”, have been developed in useful synthetic protocols: for example, for the construction of heterocycles.3 Conversely, there are few examples of cycloaddition reactions involving alkynes and hydrocarbyl fragments acting as bridging ligands, in spite of the fact that there is a large variety of dinuclear complexes with unsaturated bridging ligands potentially able to undergo cycloadditions.4 We have recently reported on [3 + 2] cycloadditions of alkynes with bridging C3 ligands in diiron complexes.5,6 One example, shown in Scheme 1, illustrates the [3 + 2] cycloaddition of a bridging vinylaminoalkylidene ligand with PhCCPh. The reaction results in the formation of a © 2011 American Chemical Society
Scheme 1
polysubstituted ciclopentadienyl ligand and directly affords the ferrocene product 2.5 The substituents present on the parent C3 and C2 fragments are retained in the resulting functionalized Cp ring of the ferrocene product. Conversely, the dinuclear complex undergoes fragmentation, with elimination of one iron fragment that formally corresponds to [Fe(H)(CO)2Cp]. The second example (Scheme 2) shows a similar cycloaddition involving a cationic vinyliminium ligand in place of a vinylalkylidene.6 Once more, the reaction affords, as the major Special Issue: F. GordonA. Stone Commemorative Issue Received: September 28, 2011 Published: November 22, 2011 2667
dx.doi.org/10.1021/om200904s | Organometallics 2012, 31, 2667−2674
Organometallics
Article
Scheme 2
Scheme 3
product, a ferrocene containing a polysubstituted Cp ring, which results from the assembly of the bridging C3 ligand with an alkyne. However, in this case, an additional product is formed resulting from a [3 + 2 + 1] cycloaddition where a CO is incorporated, affording the cyclohexadienyloxo derivative 5. The incorporation of CO makes the cycloaddition more similar to the classic Dötz benzannulation, which typically involves vinylcarbenes (α,β-unsaturated carbene ligands), alkynes, and CO.7 Despite the different natures of the parent complexes, a common feature of the two reactions is the direct access to ferrocenes in which only one cyclopentadienyl ring contains different functionalities. However, the cycloaddition of bridging vinylalkylidene ligands with alkynes (Scheme 1) has a general character, whereas those shown in Scheme 2, published in the form of a preliminary communication,6 are restricted to a limited number of propargyls and diiron vinyliminium complexes. Therefore, since a variety of diiron μ-vinyliminium complexes bearing different functional groups and substituents are readily available by simple synthetic procedures,8 we decided to extend our studies and specifically investigate the reactions of vinyliminium complexes with the propargyl alcohol, with the aim of increasing the library of polysubstituted Cp ferrocenes also containing hydroxymethyl functions.
previous findings (see Scheme 2) except for the CO incorporation, which is not observed: therefore, cyclohexadienone complexes are not formed in this case. Another unique feature is the incorporation of a second propargyl unit which originates the pendant chain on the ferrocenyl products. This point will be further discussed in detail, since we will first describe the cycloaddition reaction. The [3 + 2] cycloaddition is not regiospecific: a mixture of two isomers (compounds 6 and 7) are generally obtained, corresponding to the two possible modes in which the propargyl alcohol can be incorporated into the five-membered Cp ring. Usually, the regioisomer of type 6 is largely predominant and, in the case of 6d, it is the only product formed. Conversely, the reaction with 3e is less selective and 6e and 7e are obtained in comparable amounts. The different regioselectivity observed can be associated with the nature of the substituents R′ and R″ on the bridging C3 frame; however, it is not apparent whether the selectivity depends on steric arguments or is the consequence of a more complex balance of steric and electronic effects. Separation of the isomeric mixture by column chromatography (on alumina) was only partially achieved for 6a−7a, 6b− 7b, and 6c−7c, respectively. Nevertheless, assignments of the NMR resonances to each isomer was possible by NOE experiments and by consideration of the fact that one isomer is largely prevalent. For example, complexes of type 6 where the propargyl substituent and the amino group are in adjacent positions exhibit NOE effects between the NMe2 group and the protons of the −CH2OCH2CCH substituent, whereas no significant effect can be observed between the R″ substituent and the propargyl ether. Among the products shown in Scheme 3 the isomers 6e and 7e deserve more attention for their biferrocene character (Chart 1). As recently reported, the [3 + 2] cycloaddition of alkynes with bridging C3 ligands containing a ferrocenyl provides a general synthetic route to biferrocene complexes with unusual substitution patterns.9 This approach also applies to the reaction of 3e with propargyl alcohol. Indeed, common synthetic methods make it possible to obtain 1′,1‴disubstituted biferrocene compounds or similar centrosymmetric compounds which are, by far, the most investigated biferrocenes.10 Conversely, 6e and 7e are disubstituted-1,1″-
■
RESULTS AND DISCUSSION The diiron bridging vinyliminium complexes 3a−e react with propargyl alcohol (HCCCH2OH), in refluxing toluene, affording the corresponding polysubstituted ferrocenes as mixtures of two isomeric forms: 6a−e and 7a−c,e in overall yields of about 55−65% (Scheme 3). Compounds 6a−e and 7a−c,e have been characterized by NMR spectroscopy and elemental analysis. The molecular structure of 7e has been determined by X-ray diffraction (see below). The reaction leads to the [3 + 2] cycloaddition of the bridging C3 ligand and the alkyne to form a cyclopentadienyl ligand, consequently affording functionalized ferrocenes. In Scheme 3, the carbon atoms of the bridging C3 ligand and those of functionalized Cp have been numbered in order to make clearer which part of the cyclopentadienyl derives from the bridging vinyliminium (C1, C2, and C3) and which originates from the alkyne (C4 and C5). The result is consistent with 2668
dx.doi.org/10.1021/om200904s | Organometallics 2012, 31, 2667−2674
Organometallics
Article
Chart 1
Table 1. Selected Bond Lengths (Å) and Angles (deg) for 7a Fe(1)− 2.012(3)−2.111(3), av Cp(1)a 2.049(7) Fe(1)− 2.016(4)−2.034(4), av Cp(2)b 2.028(9) Fe(2)− 2.031(3)−2.059(3), av c Cp(3) 2.041(7) Fe(2)− 2.034(3)−2.041(3), av Cp(4)d 2.037(7) C(3)− 1.467(4) C(14) N(1)− 1.455(4) C(21) C(4)− 1.497(4) C(23) O(1)− 1.403(3) C(24) C(25)− 1.167(5) C(26) sum of angles at Cp(1)a 539.9(4) sum of angles at Cp(3)c 539.9(7) C(1)−N(1)−C(21) 115.5(2) C(21)−N(1)−C(22) 114.0(3) C(23)−O(1)−C(24) 112.1(2) C(24)−C(25)−C(26) 179.3(4)
biferrocenes with substitution patterns normally unavailable by usual substitution methods or by coupling of ferrocenyl units. As mentioned above, the molecular structure of 7e has been determined by X-ray diffraction (Figure 1 and Table 1) and can
C−C Cp(1)a C−C Cp(2)b C−C Cp(3)c C−C Cp(4)d C(1)− N(1) N(1)− C(22) C(23)− O(1) C(24)− C(25)
1.414(4)−1.427(3), 1.424(7) 1.413(4)−1.434(4), 1.426(9) 1.412(6)−1.439(4), 1.423(10) 1.395(5)−1.423(5), 1.406(11) 1.397(3)
av av av av
1.444(4) 1.434(3) 1.453(4)
sum of angles at Cp(2)b sum of angles at Cp(4)d C(1)−N(1)−C(22) C(4)−C(23)−O(1) O(1)−C(24)−C(25)
539.9(9) 540.2(7) 115.4(3) 113.6(2) 109.8(3)
a
Cp(1) is defined by atoms C(1), C(2), C(3), C(4), and C(5). Cp(2) is defined by atoms C(6), C(7), C(8), C(9), and C(10). c Cp(3) is defined by atoms C(11), C(12), C(13), C(14), and C(15). d Cp(4) is defined by atoms C(16), C(17), C(18), C(19), and C(20). b
the products 6 and 7: one is a constituent of the five-membered ring, while the second propargyl unit gives rise to the CH2OCH2CHCCCH pendant chain. We do not have direct evidence for the reaction mechanism; however, a reasonable possibility is a two-step process with the ferrocene intermediate I (Scheme 4). An alternative explanation based on the coupling of two HCCCH2OH molecules to form the dipropargyl ether which, in turn, undergoes [3 + 2] cycloaddition with 3 has to be excluded in that 3a was found unreactive upon treatment with dipropargyl ether. On the other hand, any attempt to isolate the intermediate I was unsuccessful, including the use of an equimolar amount of propargyl alcohol. Even in this case the reaction afforded the ferrocenes 6 and 7, although in lower yields. Therefore, the addition of the second propargyl unit must be very fast under the reaction conditions, which is unexpected, in that etherification of alcohols is not a prompt process unless it is catalyzed. The formation of the propargyl ether pendant substituent might occur by OH desplacement either at the propargyl alcohol or at the ferrocenylmethanol. Both possibilities are well documented in the literature. Propargylic substitution is generally promoted by transitionmetal complexes; for example, the use of Co2(CO)9 (Nicholas reaction)11 provides an effective tool for the substitution of propargyl alcohols with a variety of nucleophiles, including alcohols. More recently, ruthenium-catalyzed propargylic substitution has emerged as a most effective approach for the transformation of alkynols into valuable products. Examples include the thiolate-bridged diruthenium complexes developed by Nishibayashi et al.12 and the mononuclear ruthenium complexes developed by Gimeno and co-workers13 and the Rennes group.14 For these ruthenium catalysts the role of allenylidene intermediates has been proposed. In addition, Lewis acids, such as BiCl3,15 InBr3,16 CuBr2,17 and FeCl3,18 behave as catalysts in the propargylic substitution.
Figure 1. ORTEP diagram of 7e. All the hydrogens have been omitted for clarity. Thermal ellipsoids are drawn at 30% probability level.
be described as a 1,3,5-trisubstituted ferrocene, where the 1substituent is a ferrocenyl group. The two Cp rings Cp(1) (defined by atoms C(1), C(2), C(3), C(4), and C(5)) and Cp(2) (C(6), C(7), C(8), C(9), and C(10)) bonded to Fe(1), as well as Cp(3) (C(11), C(12), C(13), C(14), and C(15)) and Cp(4) (C(16), C(17), C(18), C(19), and C(20)) bonded to Fe(2), are almost parallel (angles between the least-squares mean planes of the five-membered rings are 3.8° and 1.3°, respectively). The C−C-bonded Cp(1) and Cp(3) rings are almost coplanar (mean deviation from the least-squares plane 0.0799 Å) and the inter-Cp contact (C(3)−C(14) = 1.467(4) Å) is essentially a single bond. The Fe−C interactions with the two substituted C5 rings (average Fe(1)−Cp(1) = 2.049(7) Å and Fe(2)−Cp(3) = 2.041(7) Å) are sensibly longer than those with the unsubstuted Cp rings (average Fe(1)−Cp(2) = 2.028(9) Å and Fe(2)−Cp(4) = 2.037(7) Å) and increase in the order Fe− Cp(unsubstituted) < Fe−Cp(monosubstituted) < Fe−Cp(trisubstituted). The N(1) atom is essentially sp3 hybridized, displaying a strong pyramidalization (sum of angles 344.9(5)°), whereas C(24)−C(25)−C(26) (179.3(4)°) is nearly perfectly linear, in agreement with the acetylenic nature of the C(25)−C(26) triple bond (1.167(5) Å). The most peculiar and unprecedented feature of the reactions shown in Scheme 3 is that two propargyl units are incorporated in the functionalized cyclopentadienyl ligand of 2669
dx.doi.org/10.1021/om200904s | Organometallics 2012, 31, 2667−2674
Organometallics
Article
Scheme 4
primary or secondary and tertiary propargyls can behave quite differently with respect to propargylic substitution. We have also investigated the reaction of propargyl alcohol with the diiron vinylalkylidene complex 10 (Scheme 6).
On the other hand, ferrocenylmethylation of propargyl alcohol, via formation of the stabilized ferrocenylmethylidene cation, might also explain the formation of the propargyl ether pendant chain. Desplacement of OH in ferrocenyl alcohols also requires a suitable catalytic system, usually provided by Brønsted acids, Lewis acids, or transition-metal compounds.19 On the basis of these considerations, it is realistic to assume the role of the parent diiron complexes in promoting the second step in the reaction sequence shown in Scheme 4. In order to prove this possibility, we have investigated the reaction of hydroxymethylferrocene, [Fc-CH2OH] (8), with propargyl alcohol in the presence of catalytic amounts (0.1 equiv) of the vinyliminium complex 3a (Scheme 5).
Scheme 6
Scheme 5 Also in this case a [3 + 2] cycloaddition between the bridging vinylalkylidene ligand and the propargyl alcohol takes place, leading to the formation of the functionalized ferrocene 11. Complex 11 contains a hydroxymethyl substituent which does not undergo addition of a further alkynol unit. Therefore, only vinyliminium−diiron complexes (compounds of type 3), and not neutral vinylalkylidene complexes, are able to promote OH substitution. Considerations on the possible catalytic role of our diiron complexes should also include the observation that, in some cases, the catalytic properties attributed to polynuclear complexes are actually due to mononuclear species generated by fragmentation of the parent complexes. This possibility is particularly realistic in our case, in that vinyliminium complexes 3 undoubtedly undergo fragmentation in order to form the observed ferrocene products. The fragment released formally correspond to [Fe(CO)2Cp]+ (usually indicated as Fp+), which is known to behave as a Lewis acid and can coordinate alkynes by η2 coordination.23 Therefore, Fp+ might activate the propargyl alcohol and catalyze propargylic substitution. Nevertheless, the ferrocenylmethylation reaction cannot be excluded. In any case the catalytic role of Fp+ is clearly demonstrated by running the same reaction shown in Scheme 5, except for the fact that [Fp][SO3CF3] was used in the place of the dinuclear complex 3a. The results were quite similar, and compound 9 was obtained in comparable yields, indicating that Fp+ might be also the effective catalyst in the etherification step of the reaction, leading to the ferrocene complexes 6 and 7. This hypothesis should also explain the absence of catalytic activity in the case of the vinyl alkylidene complex 10. The fragmentation of 10, occurring in the reaction shown in Scheme 6, is expected to eliminate the neutral mononuclear iron fragment HFp, which does not have the acidic character of Fp+. Ferrocenes Containing Pendant Propargylic Substituents and Their Reactions. So far our attention has been almost exclusively directed to the reaction sequence, [3 + 2]
Under these conditions, etherification takes place, yielding 9, whereas no reaction occurs under the same conditions in the absence of the diiron complex 3a. Nevertheless, it is not obvious how 3a can catalyze the reaction. Some structural similarities with the Nishibayashi diruthenium catalysts should be envisaged, but this is certainly not enough to hypothesize a similar propargylic activation. Iron-bound propargyl units can be transformed into vinylidene and allenylidene complexes,20 but iron is apparently less effective than ruthenium in the activation of propargyl alcohol. Moreover, dinuclear complexes exhibit some distinct features. To the best of our knowledge, none of the numerous diiron complexes containing unsaturated C3 ligands, including bridging allenylidene complexes, can properly account for the possible involvement of 3a in catalytic propargylic substitution.21 As an example, no propargylic susbstitution is observed in the reaction of alkynols and MeOH with Fe3(CO)12, in spite of the formation of bridging allenylidene intermediates; the result is a rather complex rearrangement of the bridging ligand with incorporation of a CO.22 At this point it should be evident what is reported above in Scheme 2: the reaction of 3a with the diphenyl propargylic alcohol affords the ferrocene complexes 4 as the major product, which, in spite of the presence of a hydroxymethyl substituent and of the diiron species 3a (expected to act as catalyst), does not undergo OH substitution. In this case, the absence of reactivity should be associated with the different nature of the alkynol: HCCCPh2OH in place of HCCCH2OH. Indeed, 2670
dx.doi.org/10.1021/om200904s | Organometallics 2012, 31, 2667−2674
Organometallics
Article
Scheme 7
The choice of a rather unusual azide (4-biphenyl azide)27 was aimed at obtaining adjacent triazole and biphenyl rings, which might produce interesting properties that go beyond the scope of this report. Compound 12 was characterized by NMR spectroscopy and elemental analysis. In particular, the NMR spectrum shows a single set of resonances, thus indicating that the reaction leads to the formation of a single product. Indeed, the cycloaddition of the azide is regioselective, affording the 1,4-disubstituted 1,2,3-triazole product in excellent yields and near-perfect regioselectivity. The presence of a pendant propargylic chain in complexes 6 and 7 should be also exploited to connect the ferrocene unit to metal fragments through η2 coordination of the alkyne unit. We have investigated the reaction of 3a with Co2(CO)8 in order to obtain the corresponding dicobalt hexacarbonyl complex. Substitution of two carbonyl groups in Co2(CO)8 by acetylenic molecules has been known for a long time28 and can generate stable alkyne complexes and also opens possible applications and useful protocols in organic synthesis.29 Compound 13 was characterized by NMR spectroscopy and elemental analysis. Spectroscopic data are consistent with dicobalt hexacarbonyl alkyne complexes, including those obtained by transition-metal propargyl compounds.30 In particular, in the 1H NMR spectra, the resonance of the alkyne proton is shifted downfield in comparison with the signal for the parent compound 6a (6a shows a triplet at 2.46 ppm, while for 13 it is shifted to 6.05 ppm). Likewise, in the 13C NMR spectrum, the resonances due to the carbon atoms of the alkyne (at 91.6 and 70.3 ppm for the quaternary carbon and the CH carbon, respectively) are consistent with typical values for alkyne complexes with dicobalt hexacarbonyls.
cycloaddition and propargylic substitution, in order to provide a reasonable picture of transformations that occur in the synthesis of the ferrocene isomers 6 and 7 and, in particular, to account for the OH substitution step. However, the structure of these functionalized ferrocenes deserve some comment. Some peculiar features of the substitution pattern in the biferrocene complexes 6e and 7e have already been outlined. The ferrocene products 6 and 7 display, as a characteristic feature, one cyclopentadienyl ring containing different functionalities. Since ferrocenes with a single polysubstituted Cp ligand are difficult to obtain by common synthetic methods,24 the cycloadditions described above might provide a valuble synthetic approach, in that the “one pot” synthesis would largely compensate the synthetic effort for the construction of bridging C3 ligands containing appropriate functionalities. Moreover, ferrocenes provided with a pendant propargylic chain and heteroatom-containing functionalities have potential applications as organometallic ligands or functional building blocks for the construction of more complex molecular architectures. This point is of particular importance in view of the increasing interest in the use of ferrocene derivatives as selective and sensitive multichannel chemical probes with applications spanning from biomolecules to nanomaterials and sensors.25 The pendant propargylic chain might be used to connect the ferrocenyl unit to a variety of molecular fragments via covalent or coordination bonds. In order to investigate these possibilities, we have studied a classic copper-catalyzed azide−alkyne cycloaddition. In particular, we have investigated the reaction of 6a with 4-biphenyl azide and have observed the formation of the expected triazole derivative 12 in high yield (Scheme 7). It should be remarked that, in spite of careful alumina column chromatography, samples of 6a used in these experiments contained trace amounts of the isomeric form 7a. These were too limited to allow the formation of the corresponding products of type 12 (or 13; see later) in detectable amounts. The synthesis follows a literature procedure that takes advantage of the in situ reduction of Cu(II) by sodium ascorbate, to give Cu(I), which catalyzes the [3 + 2] cycloaddition between the terminal alkyne and the azide.26
■
CONCLUSIONS The assembly of propagyl alcohol with bridging vinyliminium ligands in diiron complexes led to to the formation of ferrocene containing a pendant propargyl chain. In comparison to previous results concerning the analogous reaction with tertiary propargyl alcohols, the reactions with HCCCH2OH exhibit some distinct and unprecedented features. In particular, two 2671
dx.doi.org/10.1021/om200904s | Organometallics 2012, 31, 2667−2674
Organometallics
Article
Scheme 8
Synthesis of 6a and 7a. Compound 3a (400 mg, 0.883 mmol) was dissolved in toluene (30 mL); then HCCCH2OH (0.5 mL, 8.9 mmol) was added. The resulting mixture was stirred at reflux overnight and then was cooled to room temperature and filtered on a Celite pad. Solvent removal and chromatography of the residue on an alumina column with petroleum ether (bp 40−60 °C) as eluent first gave a yellow fraction, corresponding to nonsubstituted ferrocene (FeCp2). Two orange fractions, not fully separated, corresponding to a mixture of the isomers 6a and 7a were collected by using a mixture of petroleum ether and diethyl ether (1/1, v/v) as eluent. Yield: 201 mg, 62%. Anal. Calcd for C19H27FeNOSi: C, 61.78; H, 7.37. Found: C, 61.64; H, 7.46. Data for 6a are as follows. 1H NMR (CDCl3): δ 4.73, 4.31 (d, 2H, 2 JHH = 10.6 Hz, C5-CH2O−); 4.23, 4.16 (dd, 2H, 2JHH = 15.8 Hz, 4JHH = 2.4 Hz, −CH2OCH2−); 4.11 (s, 5H, Cp); 3.98 (d, 1H, 4JHH = 1.4 Hz, C4H); 3.81 (d, 1H, 4JHH = 1.4 Hz, C2H); 2.66 (s, 6H, NMe2); 2.46 (t, 1H, 4JHH = 2.4 Hz, −OCH2CCH); 0.19 (s, 9H, SiMe3). 13C NMR (CDCl3): δ 117.3 (C1); 80.2 (CCH); 77.5 (C5); 74.6 (C CH); 73.0 (C4); 68.9 (Cp); 67.3 (C5-CH2O−); 66.7 (C3); 60.9 (C2); 57.3 (−OCH2−CCH); 45.0 (NMe2); 0.3 (SiMe3). Data for 7a are as follows. 1H NMR (CDCl3): δ 4.49, 4.20 (d, 2H, 2 JHH = 10.6 Hz, C4-CH2O−); 4.11, 4.04 (dd, 2H, 2JHH = 15.8 Hz, 4JHH = 2.4 Hz, −CH2OCH2−); 4.19 (s, 5H, Cp); 4.02 (d, 1H, 4JHH = 1.6 Hz, C5H); 3.67 (d, 1H, 4JHH = 1.6 Hz, C2H); 2.59 (s, 6H, NMe2); 2.42 (t, 1H, 4JHH = 2.40 Hz, −OCH2CCH); 0.2 (s, 9H, SiMe3). Isomer ratio 6a/7a: 10/1. Synthesis of Complexes 6b−e and 7b,c,e. Complexes 6b−e and 7b,c,e were prepared following the same procedure abovedescribed by reacting 3b−e, respectively, with HCCCH2OH. 6b and 7b: overall yield 55%. Anal. Calcd for C23H25FeNO: C, 71.33; H, 6.51. Found: C, 71.44; H, 6.46. Data for 6b are as follows. 1H NMR (CDCl3): δ 7.49−7.06 (m, 4H, C6H4Me); 4.83, 4.76 (d, 2H, 2JHH = 11.0 Hz, C5-CH2O−); 4.65 (d, 1H, 4JHH = 1.4 Hz, C4H); 4.33, 4.26 (dd, 2H, 2JHH = 16.1 Hz, 4JHH = 2.2 Hz, −CH2OCH2−); 4.21 (s, 5H, Cp); 4.12 (d, 1H, 4JHH = 1.4 Hz, C2H); 2.79 (s, 6H, NMe2); 2.53 (t, 1H, 4JHH = 2.2 Hz, −OCH2C CH); 2.42 (s, 3H, C6H4Me). 13C NMR (CDCl3): δ 135.7−125.7 (C6H4Me); 115.0 (C1); 84.0 (C3); 80.3 (CCH); 75.0 (C5); 74.7 (CCH); 71.2 (C4); 70.4 (Cp); 67.6 (C5-CH2O−); 58.3 (C2); 57.1 (−OCH2CCH); 45.2 (NMe2); 21.1 (C6H4Me). Data for 7b are as follows. 1H NMR (CDCl3): δ 7.49−7.06 (m, 4H, C6H4Me); 4.51 (d, 1H, 4JHH = 1.5 Hz, C5H); 4.49, 4.45 (d, 2H, 2JHH = 11.0 Hz, C4−CH2O−); 4.24 (d, 1H, 4JHH = 1.5 Hz, C2H); 4.09 (s, 5H, Cp); 4.16−4.05 (m, 2H, −CH2OCH2−); 2.68 (s, 6H, NMe2); 2.55 (t, 1H, 4JHH = 2.2 Hz, -OCH2CCH); 2.40 (s, 3H, C6H4Me). 13C NMR (CDCl3): δ 114.8 (C1); 80.5 (CCH); 74.5 (CCH); 69.2 (Cp);
propargyl units are involved in the assembly with the bridging C3 ligand: one alkynol unit undergoes [3 + 2] cycloaddition with the vinyliminium ligand, whereas a second alkynol gives rise to the pendant propargyl chain by −OH substitution. We have evidenced that this second step is catalyzed: the parent diiron complex itself or a mononuclear fragment (likely the Fp+ complex) is able to promote the formation of propargyl ferrocenylmethyl ethers. These results are interesting for the presence on the polysubstituted Cp of a propargyl pendant chain functionality whose reactivity could open routes to new ferrocenes with unusual substitution patterns. We have described a couple of reactions in which the pendant alkynyl has been connected by formation of a covalent bond in a copper-catalyzed azide−alkyne cycloaddition (CuAAC) and, in another example, by η2 coordination to a dicobalt carbonyl fragment. Finally, having found iron complexes which can produce catalytic activation of alcohols will prompt us to further investigate the subject, which is certainly of general interest; so far, it has been almost completely dominated by the more expensive and toxic ruthenium derivatives.
■
EXPERIMENTAL SECTION
General Data. All reactions were routinely carried out under a nitrogen atmosphere, using standard Schlenk techniques. Solvents were distilled immediately before use under nitrogen from appropriate drying agents. Chromatography separations were carried out on columns of deactivated alumina (4% w/w water). Glassware was ovendried before use. Infrared spectra were recorded at 298 K on a PerkinElmer Spectrum 2000 FT-IR spectrophotometer, and elemental analyses were performed on a ThermoQuest Flash 1112 Series EA Instrument. All NMR measurements were performed on a Varian Mercury Plus 400 instrument. Unless otherwise stated, NMR spectra were recorded at 298 K. Chemical shifts for 1H and 13C were referenced to internal TMS. Spectra were fully assigned via DEPT experiments and 1H,13C correlation measured through gs-HSQC and gs-HMBC experiments. NOE measurements were recorded using the DPFGSE-NOE sequence. For the isomers 6 and 7, not fully separated by chromatography, yields have been determined by integration of the NMR signals. NMR resonances are indicated according to the numbering shown in Scheme 8. All the reagents were commercial products (Aldrich) of the highest purity available and used as received. [Fe2(CO)4(Cp)2] was purchased from Strem and used as received. Compounds 3a−c,31 3d,32 3e,33 and 1034 were prepared by published methods. 2672
dx.doi.org/10.1021/om200904s | Organometallics 2012, 31, 2667−2674
Organometallics
Article
67.1 (C4-CH2O); 66.0 (C5); 56.9 (-OCH2CCH); 55.8 (C2); 42.4 (NMe2); 21.4 (C6H4Me). Isomer ratio 6b/7b: 6/1. 6c and 7c: yield 60%. Anal. Calcd for C18H23FeNO: C, 66.47; H, 7.13. Found: C, 66.44; H, 7.22. Data for 6c are as follows. 1H NMR (CDCl3): δ 4.66, 4.12 (d, 2H, 2 JHH = 11.0 Hz, C5-CH2O−); 4.15 (dd, 2H, 2JHH = 15.8 Hz, 4JHH = 2.4 Hz, −CH2OCH2−; 3.98 (s, 5H, Cp); 3.95 (s, 1H, C4H); 2.76 (s, 6H, NMe2); 2.42 (t, 1H, 4JHH = 2.4 Hz, −OCH2CCH); 1.96 (s, 3H, Me); 1.88 (s, 3H, Me). 13C NMR (CDCl3): 110.9 (C1); 81.0 (C CH); 80.4 (C3); 80.0 (C2); 74.5 (CCH); 74.3 (CCH); 72.8 (C5); 70.6 (Cp); 67.5 (C4); 67.4 (C5-CH2O−); 56.5 (−OCH2CCH); 45.6 (NMe2); 13.4 (Me); 11.7 (Me). Data for 7c are as follows. 1H NMR (CDCl3): δ 4.55, 4.25 (d, 2H, 2 JHH = 11.0 Hz, C4-CH2O−); 4.07 (dd, 2H, 2JHH = 15.8 Hz, 4JHH = 2.4 Hz, −CH2OCH2−); 3.89 (br s, 5H + 1H, Cp and C5H); 2.56 (s, 6H, NMe2); 2.45 (t, 1H, 4JHH = 2.4 Hz, −OCH2CCH); 2.01 (s, 3H, Me); 1.83 (s, 3H, Me). 13C NMR (CDCl3) δ 112.4 (C1); 81.3 (C CH); 80.3 (C3); 78.8 (C2); 75.1 (C4); 70.3 (Cp); 67.1 (C4-CH2O−); 56.9 (−OCH2CCH); 56.1 (C2); 45.1 (NMe2); 12.1 (Me); 11.4 (Me). Isomer ratio 6c/7c: 7/1. 6d: yield 55%. Anal. Calcd for C23H25FeNOS: C, 65.87; H, 6.01. Found: C, 65.94; H, 6.12. Data for 6d are as follows. 1H NMR (CDCl3): δ 7.20−6.95 (m, 5H, SPh); 4.63, 4.26 (d, 2H, 2JHH = 10.6 Hz, C5-CH2O−); 4.35 (s, 1H, C4H); 4.23−4.19 (m, 2H, −CH2OCH2−); 4.15 (s, 5H, Cp); 2.75 (s, 6H, NMe2); 2.47 (t, 1H, 4JHH = 2.4 Hz, −OCH2CCH); 1.94 (s, 3H, C3Me). 13C NMR (CDCl3): δ 140.8, 128.9, 125.3, 124.6 (Carom); 114.0 (C1); 85.9 (C2); 80.1 (CCH); 77.3 (C5); 74.7 (CCH); 71.5 (Cp); 71.0 (C3); 69.5 (C4); 67.1 (C5-CH2O−); 57.4 (-OCH2C CH); 45.9 (NMe2); 13.2 (C3Me). Isomers 6e and 7e were separated by chromatography. Crystals of 7e suitable for X-ray diffraction were obtained by slow evaporation from a CH2Cl2 solution. 6e: yield 36%. Anal. Calcd for C26H27Fe2NO: C, 64.89; H, 5.66. Found: C, 64.94; H, 5.57. Data for 6e are as follows. 1H NMR (CDCl3): δ 4.53, 4.32 (d, 2H, 2 JHH = 11.0 Hz, C5-CH2O−); 4.36 (d, 1H, 4JHH = 1.5 Hz, C4H); 4.29 (m, 2H, −CH2OCH2−); 4.19 (s, 5H, Cp); 4.01 (s, 5H, Cp); 4.06− 3.95 (br m, 4H, C5H4); (d, 1H, 4JHH = 1.5 Hz, C2H); 2.71 (s, 6H, NMe2); 2.50 (t, 1H, 4JHH = 2.4 Hz, −OCH2CCH). 13C NMR (CDCl3): δ 115.1 (C1); 86.4 (C3); 74.0 (CCH); 70.0, (Cp); 69.3 (Cp); 88.1 72.0, 71.4, 69.9, 68.9, 68.0, 66.9 (C2, C4, and C5H4); 67.0 (C5-CH2O−); 57.5 (−OCH2CCH); 43.4 (NMe2). 7e: yield 24%. Anal. Calcd for C26H27Fe2NO: C, 64.89; H, 5.66. Found: C, 64.80; H, 5.71. Data for 7e are as follows. 1H NMR (CDCl3): δ 4.65, 4.36 (d, 2H, 2 JHH = 11.0 Hz, C4-CH2O−); 4.25 (m, 2H, −CH2OCH2−); 4.13 (d, 1H, 4JHH = 1.5 Hz, C2H); 4.06 (s, 5H, Cp); 3.99 (s, 5H, Cp); 3.95− 3.92 (m, 4H, C5H4 and C5H); 2.60 (s, 6H, NMe2); 2.38 (t, 1H, 4JHH = 2.4 Hz, −OCH2CCH). 13C NMR (CDCl3): δ 114.6 (C1); 74.3 (CCH); 69.2 (Cp), 68.0 (Cp); 89.0, 87.1, 73.1, 71.8, 69.5, 67.7, 66.2, 65.9 (C2, C5, and C5H4); 66.4 (C4-CH2O−); 55.4 (−OCH2C CH); 41.9 (NMe2). Synthesis of 11. Complex 11 was prepared by following the same procedure described for 6a, by reacting the complex 10 with HC CCH2OH (yield 55%). Anal. Calcd for C14H20FeOSi: C, 58.34; H, 6.99. Found: C, 58.26; H, 7.06. 1H NMR (CDCl3): δ 4.41−4.37 (m, 3H, −CH2OH and C5H); 4.17 (t, 4JHH = 1.40 Hz, C2H); 4.14 (s, 5H, Cp); 4.09 (dd, 3JHH = 2.2 Hz, 4JHH = 1.4 Hz, C4H); 1.57 (t, 1H, 3JHH = 5.8 Hz, −CH2OH); 0.22 (s, 9H, SiMe3). 13C NMR (CDCl3): δ 90.9 (C3); 73.1 (C2); 72.9 (C1); 72.6 (C5); 70.6 (C4); 68.5 (Cp); 60.9 (−CH2OH); −0.3 (SiMe3). Synthesis of 12. Compound 6a (183 mg, 0.5 mmol) and diphenyl azide (Ph2N3) (98 mg, 0.5 mmol) were suspended in a 1:1 mixture of water and tert-butyl alcohol (10 mL). Sodium ascorbate (0.05 mmol, 0.5 mL of a freshly prepared 0.1 M solution in water) was added, followed by copper(II) sulfate pentahydrate (5 mg, 0.02 mmol,
in 0.5 mL of water). The heterogeneous mixture was stirred overnight; then, it was diluted with water (50 mL) and cooled in ice, and the yellow precipitate was collected by filtration. After the precipitate was washed with cold water (three 25 mL portions), it was dried under vacuum to afford a yellow powder. Yield: 255 mg, 91%. Anal. Calcd for C31H36FeN4OSi: C, 65.95; H, 6.43. Found: C, 66.02; H, 6.56. 1H NMR (CDCl3): δ 8.01−7.07 (m, 10H, Ph); 4.81, 4.38 (d, 2H, 2JHH = 10.8 Hz, C5-CH2O−); 4.79, 4.72 (d, 2H, 2JHH = 15.6 Hz, −CH2OCH2−); 4.12 (s, 5H, Cp); 4.01 (d, 1H, 4JHH = 1.2 Hz, C4H); 3.84 (d, 1H, 4JHH = 1.24 Hz, C2H); 2.69 (s, 6H, NMe2); 0.2 (s, 9H, SiMe3). 13C NMR (CDCl3): δ 146.2 (−CH2CCHtriazole); 141.8, 139.4, 138.9, 130.4−119.5 (Carom); 121.0 (−CH2CCHtriazole); 116.8 (C1); 77.4 (C5); 73.2 (C4); 68.8 (Cp); 68.4 (C5-CH2O−); 66.0 (C3); 63.5 (−OCH2CCH); 61.2 (C2); 44.8 (NMe2); −0.4 (SiMe3). Synthesis of 13. Compound 6a (183 mg, 0.5 mmol) was dissolved in CH2Cl2 (20 mL). Then, Co2(CO)8 (171 mg, 0.5 mmol) was added. The resulting solution was stirred at room temperature for 2 h, and then it was filtered on a Celite pad. Solvent removal afforded a dark red solid, corresponding to 6. Yield: 291 mg, 89%. Anal. Calcd for C25H27Co2FeNO7Si: C, 45.82; H, 4.15. Found: C, 45.93; H, 4.16. IR (CH2Cl2): ν(CO) 2084 (vs), 2025 (vs) cm−1. 1H NMR (CDCl3): δ 6.05 (br s, 1H, HCC−); 4.80, 4.43 (d, 2H, 2JHH = 11.2 Hz, C5-CH2O−); 4.38−4.25 (m, 2H, −CH2OCH2−); 4.10 (s, 5H, Cp); 3.95 (d, 1H, 4JHH = 1.2 Hz, C4H); 3.82 (d, 1H, 4JHH = 1.2 Hz, C2H); 2.66 (s, 6H, NMe2); 0.2 (s, 9H, SiMe3). 13C NMR (CDCl3): δ 200.2−199.4 (CO); 117.2 (C1); 91.6 (HCC−); 78.2 (C5); 72.6 (C4); 70.3 (HCC−); 69.0 (Cp); 68.3 (C5-CH2O−); 66.5 (C3); 64.5 (−OCH2CCH); 60.8 (C2); 45.0 (NMe2); 1.2 (SiMe3). X-ray Crystallography. Crystal data and collection details for 7e are reported in Table 2. The diffraction experiments were carried out
Table 2. Crystal Data and Experimental Details for 7e formula fw T, K λ, Å cryst syst space group a, Å b, Å c, Å α, deg β, deg γ, deg V, Å3 Z Dc, g cm−3 μ, mm−1 F(000) cryst size, mm θ limits, deg no. of rflns collected no. of indep rflns no. of data/restraints/params goodness on fit on F2 R1 (I > 2σ(I)) wR2 (all data) largest diff peak and hole, e Å−3
C26H27Fe2NO 481.19 295(2) 0.710 73 triclinic P1̅ 7.9265(11) 9.8809(13) 15.145(2) 105.555(2) 95.967(2) 101.465(2) 1104.3(3) 2 1.447 1.331 500 0.18 × 0.13 × 0.11 1.42−26.00 11 249 4289 (Rint = 0.0265) 4289/150/271 1.040 0.0362 0.1099 0.565/−0.250
on a Bruker APEX II diffractometer equipped with a CCD detector using Mo Kα radiation. Data were corrected for Lorentz−polarization and absorption effects (empirical absorption correction SADABS).35 Structures were solved by direct methods and refined by full-matrix least squares based on all data using F2.36 All hydrogen atoms were fixed at calculated positions and refined by a riding model. Similar U restraints (standard uncertainty 0.01) were applied to all C atoms. 2673
dx.doi.org/10.1021/om200904s | Organometallics 2012, 31, 2667−2674
Organometallics
■
Article
(16) Yadav, J. S.; Subba Reddy, B. V.; Raghavendra Rao, K. V.; Narayana Kumar, G. G. K. S. Synthesis 2007, 3205−3210. (17) Hui, H.-h.; Zhao, Q.; Yang, M.-y.; She, D.-b.; Chen, M.; Huang, G.-s. Synthesis 2008, 191−196. (18) Zhan, Z.-p.; Yu, J.-l.; Liu, H.-j.; Cui, Y.-y.; Yang, R.-f.; Yang, W.z.; Li, J.-p. J. Org. Chem. 2006, 71, 8298−8301. (19) See for example: (a) Jiang, R.; Zhang, Y.; Shen, Y. C.; Zhu, X.; Xu, X. P.; Ji, S. J. Tetrahedron Lett. 2010, 66, 473−1179. (b) Vicennati., P.; Cozzi, P. G. Eur. J. Org. Chem. 2007, 2248−2253. (20) (a) Venancio, A. I. F.; da Silva, M. F. C. G.; Martins, L. M. D. R. S.; Frausto da Silva, J. J. R.; Pombeiro, A. J. L. Organometallics 2005, 24, 4654−4665. and references therein. (b) Selegue, J. P. Coord. Chem. Rev. 2004, 248, 1543−1563. (c) Gauss, C.; Veghini, D.; Orama, O.; Berke, H. J. Organomet. Chem. 1997, 541, 19−38. (21) (a) Etienne, M.; Talarmin, J.; Toupet, L. Organometallics 1992, 11, 2058−2068. (b) Akita, M.; Kato, S.-i.; Terada, M.; Masaki, Y.; Tanaka, M.; Moro-oka, Y. Organometallics 1997, 16, 2392−2412. (22) Bertolotti, F.; Gervasio, G.; Marabello, D.; Sappa, E.; Secco, A. J. Organomet. Chem. 2008, 693, 2673−2678. (23) (a) Reger, D. L. Acc. Chem. Res. 1988, 21, 229−235. (b) Akita, M.; Kakuta, S.; Sugimoto, S.; Terada, M.; Tanaka, M.; Moro-oka, Y. Organometallics 2001, 20, 2736−2750. (24) (a) Metallinos, C.; Zaifman, J.; Dodge, L. Org. Lett. 2008, 10, 3527−3530. (b) Stoll, A. H.; Mayer, P.; Knochel, P. Organometallics 2007, 26, 6694−6697. (c) Wang, Y.; Weissensteiner, W.; Spindler, F.; Arion, V. B.; Mereiter, K. Organometallics 2007, 26, 3530−3540. (d) Christophe, P.; Odell, B.; Brown, J. M. Chem. Commun. 2004, 598−599. (e) Butler, D. C. D.; Richards, C. J. Organometallics 2002, 21, 5433−5436. (25) Ferrocenes-Ligands Materials and Biomolecules; Štěpnička, P., Ed.; Wiley: West Sussex, U.K., 2008. (26) Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B. Angew. Chem., Int. Ed. 2002, 41, 2596−2599. (27) Tsao, M.-L.; Gritsan, N.; James, T. R.; Platz, M. S.; Hrovat, D. A.; Borden, W. T. J. Am. Chem. Soc. 2003, 125, 9343−9358. (28) Dickson, R. S.; Fraser, P. J. Adv. Organomet. Chem. 1974, 12, 323−377. (29) (a) Chung, Y. K. Coord. Chem. Rev. 1999, 188, 297−341. (b) Went, M. J. Adv. Organomet. Chem. 1997, 41, 69−125. (c) Bonaga, L. V. R.; Krafft, M. E. Tetrahedron 2004, 60, 9795−9833. (30) Wido, T. M.; Young, G. H.; Wojcicki, A.; Calligaris, M.; Nardin, G. Organometallics 1988, 7, 452−458. (31) Albano, V. G.; Busetto, L.; Marchetti, F.; Monari, M.; Zacchini, S.; Zanotti, V. Organometallics 2003, 22, 1326−1331. (32) Busetto, L.; Marchetti, F.; Mazzoni, R.; Salmi, M.; Zacchini, S.; Zanotti, V. J. Organomet. Chem. 2008, 693, 3191−3196. (33) Busetto, L.; Mazzoni, R.; Salmi, M.; Zacchini, S.; Zanotti, V. J. Organomet. Chem. 2010, 695, 2519−2525. (34) Albano, V. G.; Busetto, L.; Marchetti, F.; Monari, M.; Zacchini, S.; Zanotti, V. Organometallics 2004, 23, 3348−3354. (35) Sheldrick, G. M. SADABS, Program for Empirical Absorption Correction; University of Göttingen, Göttingen, Germany, 1996. (36) Sheldrick, G. M. SHELX97, Program for Crystal Structure Determination; University of Göttingen, Göttingen, Germany, 1997.
ASSOCIATED CONTENT S Supporting Information * A CIF file giving crystal data for 7e. This material is available free of charge via the Internet at http://pubs.acs.org.
■
AUTHOR INFORMATION Corresponding Author *Tel.: +39 0512093694. E-mail:
[email protected] (L.B.);
[email protected] (V.Z.).
■ ■
DEDICATION In memory of Professor F. G. A. Stone.
†
REFERENCES
(1) (a) Huisgen, R. In 1,3-Dipolar Cycloaddition Chemistry; Padwa, A., Ed.; Wiley: New York, 1984; pp 1−176. (b) Huisgen, R. Pure Appl. Chem. 1989, 61, 613−628. (c) Huisgen, R.; Szeimies, G.; Moebius, L. Chem. Ber. 1967, 100, 2494−2507. (2) (a) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew. Chem., Int. Ed. 2001, 40, 2004−2021. For recent reviews see: (b) Hein, J. E.; Fokin, V. V. Chem. Soc. Rev. 2010, 39, 1302−1315. (c) Holub, J. M.; Kirshenbaum, K. Chem. Soc. Rev. 2010, 39, 1325−1337. (d) Amblard, F.; Cho, J.-H.; Schinazi, R. F. Chem. Rev. 2009, 109, 4207−4220. (3) See for example: (a) Dötz, K. H.; Stendel, J. Jr. Chem. Rev. 2009, 109, 3227−3274. (b) De Meijere, A.; Schirmer, H.; Duetsch., M. Angew. Chem., Int. Ed. 2000, 39, 3964−4002. (c) Barluenga, J.; Santamaria, J.; Tomas, M. Chem. Rev. 2004, 104, 2259−2283. (d) Barluenga, J. Pure Appl. Chem. 2002, 74, 1317−1325. (4) (a) Ritleng, V.; Chetcuti, M. J. Chem. Rev. 2007, 107, 797−858. (b) Cowie, M. Can. J. Chem. 2005, 83, 1043−1055. (c) Busetto, L.; Maitlis, P. M.; Zanotti, V. Coord. Chem. Rev. 2010, 254, 470−486. (5) Busetto, L.; Marchetti, F.; Mazzoni, R.; Salmi, M.; Zacchini, S.; Zanotti, V. Organometallics 2009, 28, 3465−3472. (6) Busetto, L.; Marchetti, F.; Mazzoni, R.; Salmi, M.; Zacchini, S.; Zanotti, V. Chem. Commun. 2010, 46, 3327−3329. (7) (a) Dötz., K. H. Angew. Chem., Int. Ed. Engl. 1975, 14, 644−645. (b) Dötz, K. H.; Tomuschat, P. Chem. Soc. Rev. 1999, 28, 187−198. (8) Zanotti, V. Pure Appl. Chem. 2010, 7, 1555−1568. (9) Salmi, M.; Busetto, L.; Mazzoni, R.; Zacchini, S.; Zanotti, V. Organometallics 2011, 30, 1175−1181. (10) (a) Barlow, S.; O’Hare, D. Chem. Rev. 1997, 97, 637−669. (b) Dong, T.-Y.; Hendrickson, D. N.; Iwai, K.; Cohn, M. J.; Geib, S. J.; Rheingold, A. L.; Sano, H.; Motoyama, I.; Nakashima., S. J. Am. Chem. Soc. 1985, 107, 7996−8008. (c) Sinha, U.; Lowery, M. D.; Ley, W. W.; Drickamer, H. G.; Hendrickson, D. N. J. Am. Chem. Soc. 1988, 110, 2471−2477. (11) (a) Nicholas, K. M. Acc. Chem. Res. 1987, 20, 207−214. (b) Green, J. R. Curr. Org. Chem. 2001, 5, 809−826. (c) Teobald, B. J. Tetrahedron 2002, 58, 4133−4170. (12) Selected examples: (a) Nishibayashi, Y.; Yoshikawa, M.; Inada, Y.; Hidai, M.; Uemura, S. J. Am. Chem. Soc. 2002, 124, 11846−11847. (b) Nishibayashi, Y.; Imajima, H.; Onodera, G.; Hidai, M.; Uemura, S. Organometallics 2004, 23, 26−30. (c) Nishibayashi, Y.; Milton, M. D.; Inada, Y.; Yoshikawa, M.; Wakiji, I.; Hidai, M.; Uemura, S. Chem. Eur. J. 2005, 11, 1433−1451. (d) Inada, Y.; Nishibayashi, Y.; Uemura, S. Angew. Chem., Int. Ed. 2005, 44, 7715−7717. (e) Nishibayashi, Y.; Uemura, S. Curr. Org. Chem. 2006, 10, 135−150. (13) (a) Cadierno, V.; Dı ́ez, J.; Garcı ́a-Garrido, S. E.; Gimeno, J. Chem. Commun. 2004, 2716−2717. (b) Cadierno, V.; Garcı ́a-Garrido, S. E.; Gimeno, J.; Nebra, N. Inorg. Chim. Acta 2010, 363, 1912−1934, and references therein.. (14) (a) Bustelo, E.; Dixneuf, P. H. Adv. Synth. Catal. 2005, 347, 393−397. (b) Fischmeister, C.; Toupet, L.; Dixneuf, P. H. New J. Chem. 2005, 29, 765−768. (15) Zhan, Z.-p.; Yang, W.-z.; Yang, R.-f.; Yu, J.-l.; Li, J.-p.; Liu, H.-j. Chem. Commun. 2006, 3352−3354. 2674
dx.doi.org/10.1021/om200904s | Organometallics 2012, 31, 2667−2674
