Article pubs.acs.org/Organometallics
C−N Coupling of Isocyanide Ligands Promoted by Acetylide Addition to Diiron Aminocarbyne Complexes Fabio Marchetti,*,† Stefano Zacchini,‡ and Valerio Zanotti‡ †
Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Via Moruzzi 13, I-56124 Pisa, Italy Dipartimento di Chimica Industriale “Toso Montanari”, Università di Bologna, Viale Risorgimento 4, 40136 Bologna, Italy
‡
S Supporting Information *
ABSTRACT: The bis-isocyanide aminocarbyne diiron complexes [Fe2{μ-CN(Me)(R)}(μ-CO)(CNR′)2(Cp)2][SO3CF3] (R = R′ = Xyl, 1a; R = Me, R′ = Xyl, 1b; R = Xyl, R′ = tBu, 1c; Xyl = 2,6-C6H3Me2) and the analogous thiocarbyne complex [Fe2{μ-CS(Me)}(μ-CO)(CNXyl)2(Cp)2][SO3CF3], 2, were prepared in high yields from [Fe2{μ-C(E)}(μ-CO)(CO)2(Cp)2][SO3CF3] [E = N(Me)(R) or SMe, respectively], by reaction with Me3NO in the presence of the appropriate isocyanide. The addition of LiCCR′′ to 1a−b promoted intramolecular C−N coupling between the two isocyanide moieties, resulting in the formation of [Fe2(μCO){μ-CN(Me)(R)}{μ-C(NXyl)N(Xyl)C(CCR′′)}(Cp)2] (R = Xyl, R″ = Ph, 3a; R = Xyl, R″ = Tol, 3b; R = Me, R″ = Ph, 3c; Tol = 4-C6H5Me), in ca. 60% yields. The reaction of 1a with LiCCSiMe3 proceeded with coupling between two dinuclear units, to give the tetranuclear complex C2[Fe2(μ-CO)(Cp)2{μCN(Me)(Xyl)}{μ-C(NXyl)N(Xyl)C}]2, 4, in 65% yield. The reaction of 2 with LiCCTol resulted in the formation of a mixture of nonidentified products. The new complexes were purified by alumina chromatography and fully characterized by analytical techniques, IR and NMR spectroscopy. The molecular structures of 3b and 4 were ascertained by X-ray diffraction studies.
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Scheme 1. Isocyanide Coupling Reactions in Diiron μAminocarbyne Complex
INTRODUCTION Diiron complexes have emerged as interesting scaffolds for the design and the development of new synthetic pathways,1 due to their capability of mimicking biological systems,2 the advantages related to the use of a nontoxic and economic metal element,3 and the opportunities offered by the presence of a couple of metal centers. In general, two adjacent metal centers hold the potential to provide cooperative effects and to stabilize multisite coordination of bridging ligands, thus resulting in reactivity patterns not commonly observed with mononuclear species.4 Isocyanides represent an important class of versatile building blocks as C1 synthons for organic synthesis, and their chemistry has seen a tremendous progress in the past two decades.5 Although isocyanides have been largely employed as robust ligands in transition-metal complexes, they may become susceptible to a rich variety of metal directed reactions, which have been recently surveyed in an excellent review.6 Metaldirected reactions of isocyanides include isocyanide insertion into different metal−element bonds and, depending on the electronic properties of the metal center(s), nucleophilic and electrophilic additions to isocyanide ligands.6,7 In the framework of our interest in functionalization reactions of hydrocarbyl ligands within diiron complexes,1f,8 we have recently presented the synthesis of uncommon ligands by intramolecular combination of one isocyanide with, respectively, carbonyl or aminocarbyne units, promoted by the addition of nucleophiles (Scheme 1).9 © XXXX American Chemical Society
A number of C−C coupling reactions of isocyanide units (reductive coupling) have been reported in the literature to take place by the mediation of transition-metal complexes,10 whereas the C−N bond formation process is less common.10c,11 Received: June 15, 2015
A
DOI: 10.1021/acs.organomet.5b00515 Organometallics XXXX, XXX, XXX−XXX
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Organometallics Examples of combination of isocyanide moieties within iron complexes still remain rather sparse, regarding most exclusively the C−C coupling mode.10a We report herein on the synthesis of new bis-isocyanide diiron complexes, and the subsequent, straightforward C−N coupling reaction between the two isocyanide units, initiated by the addition of lithium acetylides. The reaction gives an entry into aminocarbene-N-iminoacyl ligands bearing an unusual coordination mode.
Scheme 3. Coupling of Isocyanide Ligands Promoted by Acetylide Addition
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RESULTS AND DISCUSSION The bis-isocyanide diiron complexes 1a−c and 2, containing a bridging carbyne ligand, were prepared in 80−90% yields from the respective tris-carbonyl precursors, by treatment with a 2fold molar excess of both isocyanide and Me3NO in THF solution at room temperature (Scheme 2).
to one isocyanide ligand, followed by C−N intramolecular coupling with the second isocyanide. X-ray quality crystals of 3b could be obtained from a CH2Cl2/hexane mixture. The ORTEP molecular diagram is shown in Figure 1, whereas relevant bond distances and angles are reported in Table 1.
Scheme 2. Synthesis of Bis-isocyanide Diiron Carbyne Complexes
Figure 1. Molecular structure of 3b, with key atoms labeled (all H atoms have been omitted for clarity). Displacement ellipsoids are at the 30% probability level. Only the main image of the disordered Cp ligand bonded to Fe(2) is reported.
The IR spectra of 1a−c (in CH2Cl2 solution) exhibit diagnostic absorptions accounting for the presence of the isocyanides (ca. 2100 cm−1),12 the bridging carbonyl (ca. 1800 cm−1), and the bridging aminocarbyne moiety9,13 (e.g., at 1575 cm−1 in the case of 1b). The IR spectrum of 2 displays strong bands at 2131, 2091 (CNXyl), and 1818 (μ-CO) cm−1. In the NMR spectra (recorded in CDCl3), the resonances of the carbyne nuclei have been found at typically low fields (δ = 327.4−337.3 ppm for 1a−c, δ = 410.8 ppm for 2).13,14 Because of the asymmetry of the carbyne ligand in 1a, 1c, and 2, these complexes exhibit two distinct 13C resonances for the [CN] units (e.g., at 172.1 and 171.5 ppm in the case of 1a). The reactions of 1a−b with an excess of 4-tolylacetylide and phenylacetylide, performed in THF at −50 °C, took place straightforwardly to give the new complexes [Fe2(μ-CO){μCN(Me)(R)}{μ-Cα(NXyl)N(Xyl)Cβ(CCR′′)}(Cp)2] (R = Xyl, R″ = Ph, 3a; R = Xyl, R″ = Tol, 3b; R = Me, R″ = Ph, 3c; Tol = 4-C6H5Me), in approximately 60% yields (Scheme 3). To the best of our knowledge, 3a−c comprise the first examples of structurally characterized κ(C,C′)-aminocarbene-N-iminoacyl ligands; these may be viewed as the result of acetylide addition
The molecular structure of 3b consists of an Fe2{μCN(Me)(Xyl)}(μ-CO)(Cp)2 core to which a bridging ligand [C(NXyl)N(Xyl)C(CCXyl)] is coordinated through the iminoacyl (C22) and the aminocarbene (C23) carbons, respectively. The Fe(2)−C(23) distance [1.862(4) Å] in 3b is considerably shorter than a pure σ Fe−C bond, thus suggesting the presence of a strong π-interaction. Conversely the Fe(1)−C(22) distance [1.962(4) Å] manifests a weak πinteraction; accordingly, C(22)−N(3) [1.278(5) Å] is an almost pure double bond. The bridging carbon monoxide ligand shows a marked asymmetry [Fe(1)−C(11) 1.861(5) Å, Fe(2)−C(11) 1.949(5) Å], as a consequence of the different electron densities on Fe(1) and Fe(2). Fe(1) displays the strongest interaction with μ-CO because it is bound to a good σ-donor (iminoacyl), whereas Fe(2) interacts with the more acidic aminocarbene C(23) (see above). Even the bridging aminocarbyne ligand shows asymmetry, albeit with a minor degree [Fe(1)−C(12) 1.833(4) Å, Fe(2)−C(12) 1.855(4) Å]. The aminocarbyne N-substituents are oriented with the bulkier xylyl on the same side with respect to the alkynyl group, B
DOI: 10.1021/acs.organomet.5b00515 Organometallics XXXX, XXX, XXX−XXX
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Organometallics Table 1. Selected Bond Lengths (Å) and Angles (deg) for 3b Fe(1)−Fe(2) Fe(1)−C(11) Fe(2)−C(11) Fe(1)−C(12) Fe(2)−C(12) Fe(1)−C(22) Fe(2)−C(23) N(3)−C(41) Fe(1)−C(22)−N(2) Fe(1)−C(22)−N(3) N(3)−C(22)−N(2) C(22)−N(2)−C(23) C(33)−N(2)−C(23) C(22)−N(2)−C(33)
2.4760(10) 1.861(5) 1.949(5) 1.833(4) 1.855(4) 1.962(4) 1.862(4) 1.398(5) 114.7(3) 135.9(3) 109.3(3) 120.8(3) 119.9(3) 118.6(3)
C(12)−N(1) C(22)−N(3) C(22)−N(2) N(2)−C(23) N(2)−C(33) C(23)−C(24) C(24)−C(25) C(25)−C(26) N(2)−C(23)−Fe(2) N(2)−C(23)−C(24) C(24)−C(23)−Fe(2) C(23)−C(24)−C(25) C(24)−C(25)−C(26) C(22)−N(3)−C(41)
1.333(5) 1.278(5) 1.468(5) 1.366(5) 1.450(5) 1.430(6) 1.188(6) 1.451(6) 124.8(3) 112.2(4) 122.9(3) 178.3(5) 168.0(5) 127.2(4)
Scheme 4. Synthesis of Dimeric Complex Bridged by an Alkyne Moiety
Figure 2. Molecular structure of 4, with key atoms labeled (all H atoms have been omitted for clarity). Displacement ellipsoids are at the 30% probability level. The second half of the molecule is generated by a 2-fold axis located in the middle of C(24)−C(24_2). Symmetry transformations used to generate equivalent atoms: −x, y, −z + 1/2.
fragment is usually either metal coordinated through the nitrogen atom15 or not involved in the coordination.16 The spectroscopic data collected for 3a−c are consistent with the X-ray features of 3b. The NMR spectra (in CDCl3) display single sets of resonances, thus suggesting that the pathway leading to the products is highly stereoselective. Cα and Cβ (see Scheme 3) resonate at ca. 200 and 240 ppm, in agreement with their imidoyl9b and aminocarbene character,17 respectively. The aminocarbyne carbon manifests itself by a 13C resonance falling in within the 342.5−348.8 ppm interval. The IR spectra of 3a− c (in CH2Cl2) show the absorptions due to the alkynyl unit (at
apparently to minimize steric repulsions with the other two xylyl groups. A ligand situation similar to that of 3b was reported for the ditungsten complex [W2Cp2(μ-C,N:C,C′-HCN(4-C6H4OMe)C{N(4-C6H4OMe)})(μ-PCy2)(CO)2], with the aminocarbeneN-iminoacyl ligand displaying a coordination mode slightly different from that found in 3b.11a Such a complex was obtained by addition of an excess of isocyanide to a ditungsten μ-hydride precursor, thus resulting in a C−N coupling reaction. Further examples of Fischer aminocarbene ligands functionalized with an N-bound imidoyl moiety are available in the literature; in contrast with what is observed in 3b, the imidoyl C
DOI: 10.1021/acs.organomet.5b00515 Organometallics XXXX, XXX, XXX−XXX
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Organometallics Table 2. Selected Bond Lengths (Å) and Angles (deg) for 4a Fe(1)−Fe(2) Fe(1)−C(11) Fe(2)−C(11) Fe(1)−C(12) Fe(2)−C(12) Fe(1)−C(22) Fe(2)−C(23) C(12)−N(1) Fe(1)−C(22)−N(2) Fe(1)−C(22)−N(3) N(3)−C(22)−N(2) C(22)−N(2)−C(23) C(25)−N(2)−C(23) C(22)−N(2)−C(25) a
2.4701(9) 1.868(4) 1.927(4) 1.834(4) 1.861(3) 1.963(4) 1.884(3) 1.325(5) 115.1(2) 135.0(3) 109.8(3) 121.1(3) 121.1(3) 117.2(3)
C(22)−N(3) N(3)−C(33) C(22)−N(2) N(2)−C(25) N(2)−C(23) C(23)−C(24) C(24)−C(24_2) C(11)−O(11) N(2)−C(23)−Fe(2) N(2)−C(23)−C(24) C(24)−C(23)−Fe(2) C(23)−C(24)−C(24_2) C(22)−N(3)−C(33) Fe(1)−C(12)−Fe(2)
1.279(5) 1.411(5) 1.482(4) 1.454(4) 1.352(4) 1.430(4) 1.215(6) 1.191(4) 123.7(3) 115.7(3) 120.5(2) 172.5(5) 127.2(3) 83.91(16)
Symmetry transformations used to generate equivalent atoms: −x, y, −z + 1/2.
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ca. 2170 cm−1), the bridging carbonyl ligand (at ca. 1760 cm−1), and the CαN moiety (at ca. 1560 cm−1). The reaction of 1a with an excess of LiCCSiMe3 led to a singular, reproducible outcome: the tetranuclear complex C2[Fe2(μ-CO)(Cp)2{μ-CN(Me)(Xyl)}{μ-Cα(NXyl)N(Xyl)Cβ}]2, 4, was isolated in 65% yield after work up (Scheme 4). Crystals of 4 were collected from a CH2Cl2/hexane mixture and permitted X-ray characterization: the ORTEP molecular diagram of 4 is shown in Figure 2, with main bonding parameters reported in Table 2. The asymmetric unit of 4 contains only half of the molecule, since the remaining part has been generated by symmetry. The two identical [Fe2(μ-CO)(Cp)2{μ-CN(Me)(Xyl)}{μ-Cα( NXyl)N(Xyl)CβC}] fragments are joined by an acetylenic CC bond [C(24)−C(24_2) 1.215(6) Å]. The stereochemistry as well as the geometric features within each fragment closely resemble what is discussed above for 3b. The salient IR and NMR data of 4 resemble those of complexes 3a−b. The main difference is given by the fact that no IR absorption has been observed for the [CC] moiety in 4, as expected for a symmetrically substituted alkyne. Our attempts to clearly identify any possible intermediate during the synthesis of 4 were not successful. However, the preliminary formation of a dinuclear complex analogous to 3a− c and containing the [CCSiMe3] moiety seems plausible, followed by a self-metathesis reaction (eq 1, [Fe2] = Fe2(μCO){μ-CN(Me)(Xyl)}{μ-Cα(NXyl)N(Xyl)Cβ}(Cp)2]). Both the excess of acetylide reactant and the alumina required for purification are likely to play a role in the transformation leading to the violet complex 4. It is worth mentioning that the clean conversion of Me3SiCCH into Me3SiCCSiMe3 and HCCH was previously achieved by means of alumina loaded with potassium fluoride as catalyst.18
CONCLUDING REMARKS Isocyanides are valuable building blocks for synthetic chemistry, and transition-metal complexes represent effective scaffolds for their transformations. Herein, we have presented a rare example of a C−N coupling reaction between two isocyanide units, made possible by the cooperativity effects of a diiron frame. Dinuclear and tetranuclear complexes have been generated, to which aminocarbene-N-iminoacyl ligands are anchored through a rare coordination mode. The reaction is initiated by the addition of lithium acetylides and appears to require fine-tuning of the electronic properties of the ancillary bridging carbyne ligand, the reaction proceeding straightforwardly in the presence of an aminocarbyne rather than a thiocarbyne ligand.
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[Fe2]−CC−SiMe3 + [Fe2]−CC−SiMe3 → [Fe2]−CC−[Fe2] + Me3Si−CC−SiMe3 4
EXPERIMENTAL SECTION
General Experimental Details. All the reactions were routinely carried out under a nitrogen atmosphere, using standard Schlenk techniques. Solvents were distilled before use under nitrogen from appropriate drying agents. Once isolated, the metal products were conserved under nitrogen. Chromatography separations were carried out on columns of deactivated alumina (4% w/w water). The reaction vessels were oven-dried at 140 °C prior to use, evacuated (10−2 mmHg), and then filled with nitrogen. Infrared spectra were recorded on a PerkinElmer Spectrum 2000 FT-IR spectrophotometer. Elemental analyses were performed on a ThermoQuest Flash 1112 Series EA Instrument. NMR spectra were recorded on a Mercury Plus 400 instrument. The chemical shifts for 1H and 13C were referenced to the nondeuterated aliquot of the solvent. The 1H and 13C NMR spectra were assigned with assistance of 1H,13C correlation measured through gs-HSQC and gs-HMBC experiments.19 The organic reactants were commercial products (Sigma-Aldrich) of the highest purity available used as received. [Fe2(CO)4(Cp)2] was purchased from Strem and used as received; then, [Fe2{μ-C(E)}(μ-CO)(CO)2(Cp)2][SO3CF3] [E = NMe2,20 N(Me)(Xyl),21 SMe22] were prepared according to the literature. Synthesis of [Fe2{μ-CN(Me)(R)}(μ-CO)(CNR′)2(Cp)2][CF3SO3] (R = Xyl, R′ = Xyl, 1a; R = Me, R′ = Xyl, 1b; R = Xyl, R′ = tBu, 1c). The synthesis of 1a is described in detail; 1b−c were prepared by the same procedure from [Fe 2 {μ-CN(Me)2 }(μ-CO)(CO) 2 (Cp) 2 ][CF3SO3] and CNXyl/Me3NO and [Fe2{μ-CN(Me)(Xyl)}(μ-CO)(CO)2(Cp)2][CF3SO3] and CNtBu/Me3NO, respectively. A solution of [Fe2{μ-CN(Me)(Xyl)}(μ-CO)(CO)2(Cp)2][CF3SO3] (200 mg, 0.322 mmol), in THF (25 mL), was treated with CNXyl (86 mg, 0.66 mmol) and Me3NO (55 mg, 0.73 mmol). The resulting mixture was stirred for 18 h; then, the volatile materials were removed under vacuo. The residue was dissolved in CH2Cl2 (15 mL) and charged on an alumina column. A green band was collected by using neat MeOH as
(1)
The reaction of the thiocarbyne complex 2 with 4tolylacetylide resulted in the formation of a mixture of nonidentified products; according to IR and NMR spectra, the most prevalent product contained at least one intact isocyanide ligand. This result suggests that the presence of the aminocarbyne ligand, although apparently playing a spectator role, is crucial in order to make the C−N coupling reaction effectively working around the diiron frame. D
DOI: 10.1021/acs.organomet.5b00515 Organometallics XXXX, XXX, XXX−XXX
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Organometallics Table 3. Crystal Data and Experimental Details for 3b and 4 formula fw T, K λ, Å crystal system space group a, Å b, Å c, Å β, deg cell volume, Å3 Z Dc, g cm−3 μ, mm−1 F(000) crystal size, mm θ limits, deg reflections collected independent reflections data/restraints/parameters goodness on fit on F2 R1 (I > 2σ(I)) wR2 (all data) largest diff. peak and hole, e·Å−3
3b
4
C48H47Fe2N3O 793.59 293(2) 0.71073 monoclinic P21/n 12.291(3) 17.124(3) 18.910(4) 96.62(3) 3953.7(14) 4 1.333 0.774 1664 0.23 × 0.21 × 0.15 1.61−25.03 24 578 6996 [Rint = 0.0834] 6996/292/491 1.036 0.0574 0.1626 0.675/−0.312
C80H80Fe4N6O2 1380.90 293(2) 0.71073 monoclinic C2/c 22.661(5) 12.612(3) 23.523(5) 95.04(3) 5144.6(18) 4 1.370 0.903 2888 0.22 × 0.18 × 0.11 1.74−26.37 32 857 6855 [Rint = 0.0883] 6855/0/422 0.997 0.0516 0.1392 0.587/−0.577
7.29−6.67 (6 H, C6H3Me2); 5.21, 5.13 (s, 10 H, Cp); 3.67 (s, 3 H, SMe); 1.93 ppm (s, 12 H, C6H3Me2). 13C{1H} NMR (CDCl3, 298 K): δ = 410.8 (μ-CS); 262.0 (μ-CO); 167.9, 167.7 (CN); 146.6 (ipsoC6H3Me2); 134.2, 128.4, 127.5 (C6H3Me2); 89.4, 88.8 (Cp); 35.9 (SMe); 18.0 ppm (C6H3Me2). Synthesis of [Fe2(μ-CO)(Cp)2{μ-CN(Me)(R)}{μ-C(NXyl)N(Xyl)C(CCR′′)}] (R = Xyl, R″ = Ph, 3a; R = Xyl, R″ = Tol, 3b; R = Me, R″ = Ph, 3c). The synthesis of 3a is described in detail; 3b−c were prepared by the same procedure from 1a/LiCCTol and 1b/LiC CPh, respectively. Crystals of 3b suitable for X-ray analysis were collected from a CH2Cl2 solution layered with hexane and settled aside at −20 °C for 72 h. A solution of 1a (200 mg, 0.242 mmol) in THF (20 mL) was cooled to −50 °C and then treated with a solution of LiCCPh in THF (3.5 mL, 0.36 mmol), freshly prepared from HCCPh and BuLi. The mixture was allowed to warm to room temperature and stirred for an additional 2 h. The final solution was filtered on a short alumina pad; hence, the volatiles were removed under vacuo. The residue was dissolved in CH2Cl2 (10 mL) and charged on an alumina column. The use of a mixture of CH2Cl2 and THF (3:1 v/v) as eluent allowed isolating a red band corresponding to 3a. Removal of the volatiles under vacuo afforded a microcrystalline dark-red powder. [Fe2(μ-CO)(Cp)2{μ-CN(Me)(Xyl)}{μ-C(NXyl)N(Xyl)C(CCPh)}], 3a. Yield 117 mg, 62%. Anal. Calcd for C47H45Fe2N3O: C, 72.41; H, 5.82; N, 5.39. Found: C, 72.30; H, 5.69; N, 5.43. IR (CH2Cl2): νCC = 2171w, νCO = 1762vs, νCαN = 1564s cm−1. 1H NMR (CDCl3, 298 K): δ = 7.43−6.78 (14 H, arom CH); 4.63, 4.37 (s, 10 H, Cp); 4.39 (s, 3 H, NMe); 2.55, 2.29, 2.15, 2.13, 2.07, 1.92 ppm (s, 18 H, C6H3Me2). 13 C{1H} NMR (CDCl3, 298 K): δ = 348.3 (μ-CN); 279.6 (μ-CO); 237.8 (Cβ); 198.8 (Cα); 150.3, 147.5, 147.3 (ipso-Me2C6H3); 135.4− 120.5 (arom CH); 116.5, 92.1 (CC); 91.4, 86.5 (Cp); 52.7 (NMe); 20.2, 19.6, 19.5, 19.0, 18.9, 18.8 ppm (C6H3Me2). See Scheme 3 for C atom labeling. [Fe 2 (μ-CO)(Cp) 2 {μ-CN(Me)(Xyl)}{μ-C(NXyl)N(Xyl)C(C CC6H4Me)}], 3b. Red solid, 64% yield. Anal. Calcd for C48H47Fe2N3O: C, 72.65; H, 5.97; N, 5.29. Found: C, 72.88; H, 5.90; N, 5.25. IR (CH2Cl2): νCC = 2169w, νCO = 1761vs, νCαN = 1565s cm−1. 1H NMR (CDCl3, 298 K): δ = 7.30−6.75 (13 H, arom CH); 4.62, 4.36 (s, 10 H, Cp); 4.39 (s, 3 H, NMe); 2.55, 2.29, 2.14, 2.13, 2.06, 1.91 (s, 18
eluent. The product was isolated in the solid state upon removal of the solvent under vacuo. [Fe2{μ-CN(Me)(Xyl)}(μ-CO)(CNXyl)2(Cp)2][CF3SO3], 1a. Yield 213 mg, 80% yield. Anal. Calcd for C40H40F3Fe2N3O4S: C, 58.06; H, 4.87; N, 5.08. Found: C, 57.95; H, 4.91; N, 5.10. IR (CH2Cl2): νCN = 2115vs, 2085vs-sh, νCO = 1805s, νμ‑CN = 1517m cm−1. 1H NMR (CDCl3, 298 K): δ = 7.38−6.82 (9 H, Me2C6H3); 5.21, 4.54 (s, 10 H, Cp); 4.60 (s, 3 H, NMe); 2.81, 2.09 (s, 6 H, μ-CNC6H3Me2); 2.17, 1.81 ppm (s, 12 H, t-CNC6H3Me2). 13C{1H} NMR (CDCl3, 298 K): δ = 336.2 (μ-CN); 265.0 (μ-CO); 172.1, 171.5 (t-CN); 147.6 (ipso-Me2C6H3); 134.3−127.6 (Me2C6H3); 88.3, 87.4 (Cp); 54.5 (NMe); 18.7, 18.2 (μ-CNC6H3Me2); 18.4, 17.8 ppm (t-CNC6H3Me2). [Fe2{μ-CN(Me)2}(μ-CO)(CNXyl)2(Cp)2][CF3SO3], 1b. Dark-green solid, 84% yield. Anal. Calcd for C33H34F3Fe2N3O4S: C, 53.75; H, 4.65; N, 5.70. Found: C, 53.83; H, 4.61; N, 5.65. IR (CH2Cl2): νCN = 2115vs, 2097vs-sh, νCO = 1802s, νμ‑CN = 1575m cm−1. 1H NMR (CDCl3, 298 K): δ = 7.05−6.67 (6 H, C6H3Me2); 5.07 (s, 10 H, Cp); 4.44 (s, 6 H, NMe); 1.95 ppm (s, 12 H, C6H3Me2). 13C{1H} NMR (CDCl3, 298 K): δ = 327.4 (μ-CN); 267.1 (μ-CO); 172.0 (CN); 133.8, 127.8, 127.3 (C6H3Me2); 87.6 (Cp); 53.3 (NMe); 18.0 ppm (C6H3Me2). [Fe2{μ-CN(Me)(Xyl)}(μ-CO)(CNtBu)2(Cp)2][CF3SO3], 1c. Green solid, 82% yield. Anal. Calcd for C32H40F3Fe2N3O4S: C, 52.55; H, 5.51; N, 5.74. Found: C, 52.90; H, 5.37; N, 5.65. IR (CH2Cl2): νCN = 2128vs, νCO = 1803s, νμ‑CN = 1505m cm−1. 1H NMR (CDCl3, 298 K): δ = 7.35−7.14 (3 H, C6H3Me2); 4.93, 4.29 (s, 10 H, Cp); 4.42 (s, 3 H, NMe); 2.68, 2.10 (s, 6 H, C6H3Me2); 1.34, 1.29 ppm (s, 18 H, CMe3). 13 C{1H} NMR (CDCl3, 298 K): δ = 337.3 (μ-CN); 267.3 (μ-CO); 160.9, 158.3 (CN); 147.9 (ipso-C6H3Me2); 133.2, 132.2, 129.5, 128.8, 128.7 (C6H3Me2); 87.4, 86.5 (Cp); 58.7, 58.6 (CMe3); 53.6 (NMe); 30.7, 30.6 (CMe3); 18.4, 18.2 ppm (C6H3Me2). Synthesis of [Fe2{μ-CS(Me)}(μ-CO)(CNXyl)2(Cp)2][CF3SO3], 2. This product was obtained as a dark-green solid by the same procedure described for the synthesis of 1a, starting from [Fe2{μCS(Me)}(μ-CO)(CO)2(Cp)2][SO3CF3] (110 mg, 0.206 mmol), CNXyl (55 mg, 0.42 mmol), and Me3NO (35 mg, 0.47 mmol). Yield: 137 mg, 90%. Anal. Calcd for C32H31F3Fe2N2O4S2: C, 51.91; H, 4.22; N, 3.78. Found: C, 52.01; H, 4.26; N, 3.76. IR (CH2Cl2): νCN = 2131vs, 2091vs-sh, νCO = 1818s cm−1. 1H NMR (CDCl3, 298 K): δ = E
DOI: 10.1021/acs.organomet.5b00515 Organometallics XXXX, XXX, XXX−XXX
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Organometallics H, C6H3Me2); 2.29 ppm (s, 3 H, C6H4Me). 13C{1H} NMR (CDCl3, 298 K): δ = 348.8 (μ-CN); 280.0 (μ-CO); 238.0 (Cβ); 198.9 (Cα); 150.5, 147.6, 147.4 (ipso-Me2C6H3); 139.5−120.5 (arom CH); 117.2, 92.0 (CC); 91.4, 86.5 (Cp); 52.7 (NMe); 21.6 (C6H4Me); 20.2, 19.5, 19.4, 19.0, 18.8, 18.7 ppm (C6H3Me2). See Scheme 3 for C atom labeling. [Fe2(μ-CO)(Cp)2{μ-CN(Me)2}{μ-C(NXyl)N(Xyl)C(CCPh)}], 3c. Dark-red solid, 60% yield. Anal. Calcd for C40H39Fe2N3O: C, 69.68; H, 5.70; N, 6.09. Found: C, 69.74; H, 5.62; N, 5.99. IR (CH2Cl2): νCC = 2170w, νCO = 1761vs, νCαN = 1554s, νμ‑CN = 1535m cm−1. 1 H NMR (CDCl3, 298 K): δ = 7.28−6.75 (8 H, arom CH); 4.89, 4.42 (s, 10 H, Cp); 4.17, 3.89 (s, 6 H, NMe); 2.23, 2.09, 1.94, 1.76 ppm (s, 12 H, C6H3Me2). 13C{1H} NMR (CDCl3, 298 K): δ = 342.5 (μ-CN); 280.5 (μ-CO); 236.8 (Cβ); 199.4 (Cα); 150.7, 147.4 (ipso-Me2C6H3); 135.2−120.6 (arom CH); 116.2, 90.5 (CC); 91.1, 85.5 (Cp); 51.5, 50.7 (NMe); 20.2, 19.3, 17.9, 17.0 ppm (C6H3Me2). See Scheme 3 for C atom labeling. Synthesis of C2[Fe2(μ-CO)(Cp)2{μ-CN(Me)(Xyl)}{μ-C(NXyl)N(Xyl)C}]2, 4. This product was obtained by a procedure analogous to that described for the synthesis of 3a, from 1a (200 mg, 0.242 mmol) and LiCCSiMe3 (0.46 mmol in 3.7 mL of THF). The final brown-red mixture was charged on an alumina column. A violet fraction was collected by using CH2Cl2/THF (9:1 v/v) as eluent. Thus, the product was isolated as a violet microcrystalline solid upon removal of the volatiles. Yield 109 mg, 65%. Crystals suitable for X-ray analysis were collected from a CH2Cl2 solution layered with hexane and settled aside at −20 °C for 72 h. Anal. Calcd for C80H80Fe4N6O2: C, 69.58; H, 5.84; N, 6.09. Found: C, 69.50; H, 5.78; N, 6.18. IR (CH2Cl2): νCO = 1770vs, νCN = 1564s cm−1. 1H NMR (CDCl3, 298 K): δ = 7.54−6.75 (9 H, C6H3Me2); 4.55, 3.83 (s, 10 H, Cp); 4.37 (s, 3 H, NMe); 2.56, 2.22, 2.20, 2.06, 1.89, 1.87 ppm (s, 18 H, C6H3Me2). 13 C{1H} NMR (CDCl3, 298 K): δ = 349.6 (μ-CN); 276.4 (μ-CO); 233.9 (Cβ); 197.8 (Cα); 150.1, 148.2, 147.0 (ipso-C6H3Me2); 136.0− 120.5 (C6H3Me2); 110.5 (CC); 90.7, 87.0 (Cp); 53.2 (NMe); 21.0, 20.6, 20.2, 19.6, 19.4, 18.8 ppm (C6H3Me2). See Scheme 4 for C atom labeling. X-ray Crystallography. Crystal data and collection details for 3b and 4 are reported in Table 3. The diffraction experiments were carried out on a Bruker SMART 2000 diffractometer, equipped with a CCD detector using Mo−Kα radiation. Data were corrected for Lorentz polarization and absorption effects (empirical absorption correction SADABS).23 Structures were solved by direct methods and refined by full-matrix least-squares based on all data using F2.24 Hydrogen atoms were fixed at calculated positions and refined by a riding model. All non-hydrogen atoms were refined with anisotropic displacement parameters, unless otherwise stated. The Cp ligand bonded to Fe(2) in 3b is disordered. Disordered atomic positions were split and refined isotropically using similar distances and similar U restraints and one occupancy parameter per disordered group.
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Notes
The authors declare no competing financial interests.
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ASSOCIATED CONTENT
S Supporting Information *
Figures S1−S16 show the 1H and 13C NMR spectra of the products. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/ acs.organomet.5b00515. CCDC reference numbers 1404832 (3b) and 1404833 (4) contain the supplementary crystallographic data for the X-ray studies reported in this paper. These data can be obtained free of charge at www.ccdc.cam.ac.uk/ conts/retrieving.html [or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, U.K.; Fax: (internat.) +44-1223/336-033; E-mail:
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DOI: 10.1021/acs.organomet.5b00515 Organometallics XXXX, XXX, XXX−XXX
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DOI: 10.1021/acs.organomet.5b00515 Organometallics XXXX, XXX, XXX−XXX
