Thermally Stable Diazoalkane Derivatives of the Unsaturated

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Thermally Stable Diazoalkane Derivatives of the Unsaturated Ditungsten Hydride [W2Cp2(H)(μ-PCy2)(CO)2] M. Angeles Alvarez, M. Esther García, Daniel García-Vivó,* Estefanía Huergo, Miguel A. Ruiz,* and M. Fernanda Vega Departamento de Química Orgánica e Inorgánica/IUQOEM, Universidad de Oviedo, E-33071 Oviedo, Spain S Supporting Information *

ABSTRACT: The title compound reacted rapidly with N2CH(SiMe3) at room temperature to give the electron-precise hydride [W2Cp2(H)(μPCy2)(CO)2{N-N2CH(SiMe3)}] (W−W = 2.9907(5) Å), in which the diazoalkane molecule is N-bound strongly to one of the metal centers, formally acting as an imido-like four-electron donor. Reaction with N2CPh2 led instead to a mixture of two products, the analogous diphenyldiazomethane complex [W 2 Cp 2 (H)(μ-PCy 2 )(CO) 2 (NN2CPh2)] and the bis(diazoalkane) derivative [W2Cp2(H)(μ-PCy2)(CO)2(N-N2CPh2)2], the latter having no metal−metal bond and bearing two inequivalent diazoalkane ligands bound to the same metal center (W−N = 1.78(1), 1.82(1) Å), whereas its dicarbonyl metal fragment displays a transoid geometry in the crystal, but a cisoid one in solution. These two compounds follow from competitive reaction pathways, since independent experiments revealed that the above mono(diazoalkane) complexes did not add a second diazoalkane molecule even under thermal activation. In contrast, the title compound reacted with excess N2CH2 to yield two new methyl derivatives requiring the participation of two molecules of reagent, the diazomethane complex [W2Cp2(CH3)(μ-PCy2)(CO)2(N-N2CH2)] and the 30-electron phosphinomethyl-bridged complex [W2Cp2(CH3)(μ-C:P-CH2PCy2)(μ-CO)(CO)], along with small amounts of the known methyl-bridged complex [W2Cp2(μ-CH3)(μ-PCy2)(CO)2]. The two new complexes follow from denitrogenation of one diazomethane molecule followed by insertion of methylene into the W−H bond to yield a methyl ligand, while the second diazomethane molecule either remains bound through its nitrogen atom or undergoes denitrogenation followed by insertion of methylene into a W−P bond, to yield a phosphinomethyl ligand. Once more, no denitrogenation of the coordinated diazomethane ligand in the first complex was observed even under thermal or photochemical activation.

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INTRODUCTION Organometallic complexes having metal−metal multiple bonds in combination with hydride ligands are a particularly attractive family of compounds for the study of fundamental transformations of unsaturated organic substrates in the coordination sphere of metals that involve transfer of hydrogen atoms. Within this area of work, some time ago our group developed an efficient synthetic route to the 30-electron hydride-bridged complex [Mo2Cp2(μ-H)(μ-PCy2)(CO)2],1 which was followed by a systematic and extensive study of its chemical behavior toward a wide variety of organic molecules, transition metal complexes, and p-block compounds.2 Aiming to test the influence that the metal center (W instead of Mo) would have on all this chemistry, we developed more recently a high-yield route to the analogous ditungsten hydride [W2Cp2(H)(μPCy2)(CO)2] (1) (Chart 1).3,4 Interestingly, our initial studies revealed remarkable differences in the structure and chemical behavior of the ditungsten complex. To begin with, compound 1 exists in solution as an equilibrium mixture of two isomers having either a bridging hydride ligand (B, major isomer) or a terminal hydride and a semibridging carbonyl (T, minor isomer), an unexpected structural feature since the analogous © XXXX American Chemical Society

Chart 1

dimolybdenum complex displays exclusively a H-bridged structure.1a,5 The chemical behavior of 1 also departs significantly from that of its Mo2 analogue. For instance, reactions of 1 with different unsaturated organic molecules such as alkynes or isocyanides revealed its ability to add two molecules of these reagents, eventually promoting different C−C or C−N coupling reactions at room temperature,6,7 whereas the Mo2 hydride typically adds just one molecule of these reagents.8 In a similar way, reactions of 1 with some transition metal complexes yielded new tetranuclear clusters,9 rather than the Received: May 30, 2015

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DOI: 10.1021/acs.organomet.5b00466 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

yielding isolable derivatives upon reaction with diazoalkanes but also to check if the high electronic unsaturation of this compound (equivalent to four electrons) would allow for the incorporation of more than one molecule of these reagents, with these being the main purposes of this paper. As it will be discussed below, compound 1 indeed reacts with different diazoalkanes to give isolable products, with several outcomes depending on the diazoalkane used: (a) formation of simple addition products with either one or two molecules of diazoalkane N-bound to one metal center and (b) formation of products derived from N2 loss followed by insertion of the resulting methylene fragment into either W−H or W−P bonds, to yield new methyl or phosphinomethyl ligands, respectively.

trinuclear derivatives formed under the same conditions when using the Mo2 hydride.10 Finally, a critical stabilizing effect of the tungsten atom (vs Mo) was also observed in some cases. For instance, the Mo2 hydride reacted with acids to yield intractable mixtures of products, while protonation of 1 led selectively to cationic dihydrides of formula [W2Cp2(H)2(μPCy2)(CO)2]+, which remained stable to dehydrogenation in the absence of coordinating counteranions.11 In order to further explore the potential differences in chemical reactivity of these unsaturated compounds, we have now examined reactions of 1 with different diazoalkanes. Our previous studies had shown that the Mo2 hydride just induces decomposition of these unsaturated molecules, but no new organometallic compounds could be isolated or even detected in the course of the corresponding reactions.8a Such a reluctance to form new organometallic species was indeed a surprise at the time, since diazoalkanes are known to react with a wide variety of unsaturated organometallic compounds with at least two well-established outcomes: (a) formation of simple addition products, with diazoalkanes being able to bind one or several metal atoms in different coordination modes, or (b) formation of carbene complexes following from loss of N2.12 A nice example of these processes was actually observed in reactions of the archetypal triply bonded complex [Mo2Cp2(CO)4] with different aryl diazoalkanes, these first yielding the corresponding diazoalkane complexes, which, upon moderate thermal (or photochemical) treatment, further evolved by releasing N 2 , to eventually yield carbene derivatives.13 Reactions of diazoalkanes with organometallic complexes featuring unsaturated M2(μ-H)x cores have been studied in a limited number of systems, such as the 46-electron triosmium cluster [Os3(μ-H)2(CO)10]14 or the 32-electron dirhenium dihydride [Re2(μ-H)2(CO)8].15 Although the outcome of these reactions depends strongly on the particular diazoalkane, we must note that formation of simple addition products was never observed for these unsaturated hydrides. In fact, in most cases these reactions take place with dinitrogen elimination to give the corresponding carbenes (not always observed), which then evolve typically through insertion into a M−H bond to eventually yield alkyl derivatives. However, some remarkable exceptions to this general trend have been reported. For instance, the above dihydride complexes reacted with N2CPh2 to give products containing a hydrazonate ligand (NHNCPh2),14c,15a this following from insertion of the diazo group into a M−H bond. More recently, a most unusual transformation was observed in the reaction of dinuclear tantalum complex [Ta2(μ-H)3L2]− (L2 = cyclometalated C,O,O,O-donor) with N2CH(SiMe3) to give the nitrido- and imido-bridged derivative [Ta 2 (μ-N)(μ-NCH 2 SiMe 3 )(LH)2]−,16 this following from complete cleavage of the N−N bond in the diazoalkane molecule. Finally, it is worth noting that all these unsaturated hydrides generally react with just one diazoalkane molecule. Reaction with two diazoalkane molecules appears to have been observed only in two previous cases, both involving incorporation of two CH2 fragments from the highly reactive diazomethane molecule.17 This limitation might be imposed by a modest electron deficiency of just two electrons in most of the above hydride complexes, so that addition of one molecule of diazoalkane leads to saturated compounds that therefore are not prone to incorporate a second molecule of reagent. Thus, it was of interest not only to test if ditungsten complex 1 could behave differently from its Mo2 analogue by

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RESULTS AND DISCUSSION Reactions of Compound 1 with Diazoalkanes. The outcome of these reactions was critically dependent on the particular reagent used, although rapid reactions at room temperature occurred in all cases upon addition of a slight excess of diazoalkane. Reaction of 1 with commercially available N2CH(SiMe3) gives instantaneously the electron-precise hydride [W2Cp2(H)(μ-PCy2)(CO)2{N-N2CH(SiMe3)}] (2a) (Chart 2), in which the added diazoalkane molecule remains Chart 2

intact and is coordinated to the metal in a N-bound terminal fashion, acting as an imido-like ligand. In contrast, reaction with N2CPh2 yields two products in comparable amounts, the diphenyldiazomethane complex [W 2 Cp 2 (H)(μ-PCy 2 )(CO)2(N-N2CPh2)] (2b), analogous to 2a, and the doubleaddition product [W2Cp2(H)(μ-PCy2)(CO)2(N-N2CPh2)2] (3) (Chart 2). Independent experiments indicated that compounds 2a,b do not react with additional molecules of the corresponding diazoalkane at room temperature or even upon moderate heating. Therefore, it must be concluded that compound 3 is formed via an undetected intermediate different from 2b (perhaps an isomer of it). It is worth noting here that all the above diazoalkane complexes are relatively stable (i.e., they can be conveniently purified by column chromatography), and they do not undergo dinitrogen elimination even under thermal or photochemical (irradiation with visible−UV light) treatment. In fact, prolonged heating of solutions of compounds 2a,b in refluxing toluene led only to gradual formation of the saturated hydride [W2Cp2(μ-H)(μ-PCy2)(CO)4] (actually a precursor of 1), with this rather pointing to a complete dissociation of the B


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methyl-bridged complex [W2Cp2(μ-CH3)(μ-PCy2)(CO)2]. These observations suggest that reaction of 1 with diazomethane is initiated with the terminal N-coordination of a molecule of the latter reagent to yield intermediate A, which then evolves differently depending on reaction conditions: in the absence of excess reagent, A preferentially would evolve via N 2 loss to render the methyl-bridged complex, thus reproducing the classical reactions of dihydrides [Os3(μH)2(CO)10] and [Re2(μ-H)2(CO)8] with the same reagent.14b,15b However, in the presence of enough reagent, coordination of a second diazomethane molecule would be favored, and two independent pathways would become then available to yield compounds 4 and 5 in comparable amounts, although proposing a plausible sequence of events for these multistep processes might be highly speculative at present. Besides this, we cannot rule out that compound 4 could also be formed to some extent through reaction of the methyl-bridged complex with excess reagent, although this should initially lead to an isomer of 4 having the methyl and diazoalkane ligands bound to different metal atoms. In any case, it is remarkable that the diazomethane ligand present in 4 does not further evolve through N2 loss. N-Bound terminal diazomethane ligands are very rare species; actually we are aware of only two other reported examples, the cations trans-[MX(NN2CH2){P,P′-Ph2P(CH2)2PPh2}2]+ (MX = WBr, MoF), which, however, were not prepared from diazomethane itself, but from the corresponding hydrazido(2−) precursors.21 We can also quote a few complexes displaying thermally stable diazomethane ligands bridging two metal atoms in either the μN:N- or μ-C:N- coordination modes.22 It is finally worth noting that all products obtained in reactions of 1 with diazoalkanes display either W(CO)2 or W(CO)(μ-CO) fragments. It is then tempting to assume that formation of all these products would follow more easily through addition of diazoalkanes to the minor isomer T of compound 1, a hypothesis that would be consistent with the failure of the Mo2 hydride (which exclusively displays a Hbridged structure in solution) to give stable products. Yet we cannot fully exclude participation of the hydride-bridged isomer B of compound 1 in all the above processes. Structural Characterization of Diazoalkane Complexes 2a,b and 3. The molecule of 2a in the crystal (Figure 1 and Table 1) is built from two WCp fragments arranged in a transoid disposition and bridged symmetrically by a PCy2 ligand. The coordination sphere of the metals is then

diazoalkane ligand upon heating, to give back the parent compound 1, which is known to decompose upon heating to give the mentioned tetracarbonyl complex. Given the reluctance of these diazoalkane complexes to evolve through dinitrogen elimination, we resorted to test if more activated diazoalkanes could do it more easily. First we tried commercially available ethyl diazoacetate, but this yielded a mixture of two products (one of them likely analogous to complexes 2a,b), which could not be separated nor properly characterized. In contrast, diazomethane rapidly reacted with 1 to give a mixture of two new and isolable methyl derivatives, the diazomethane complex [W2Cp2(CH3)(μ-PCy2)(CO)2(NN 2 CH 2 )] (4) and the phosphinomethyl complex [W2Cp2(CH3)(μ-C:P-CH2PCy2)(μ-CO)(CO)] (5) (Chart 2), along with small amounts of the methyl-bridged complex [W2Cp2(μ-CH3)(μ-PCy2)(CO)2], a compound previously described by us.18 Formation of the major products obviously requires participation of two molecules of diazomethane, one of them being invariably transformed into a terminal methyl group, likely following from N2 loss of a metal-bound diazomethane molecule, and subsequent insertion of the sogenerated methylene into a W−H bond. However, the fate of the second diazomethane molecule differs substantially in these two compounds; it remaining intact and terminally bound in 4, whereas in 5 it underwent N2 elimination and methylene insertion, now into a W−P bond, to generate a new bridging phosphinomethyl group (CH2PCy2). Although methylene insertion into M−P bonds of phosphide ligands is not as common as insertion into metal−hydride bonds, there are precedents of such a process.19 Even if compounds 4 and 5 are formally related by a denitrogenation step, we should stress that 4 is not a precursor of 5, since no net transformation between these compounds was observed after prolonged stirring of a mixture of these species at room temperature. In order to identify potential intermediates in the necessarily multistep reactions leading to compounds 4 and 5, we also carried out low-temperature reactions of 1 with defect diazomethane. Under these conditions we managed to detect (by IR and NMR) the formation of an initial intermediate retaining a terminal hydride ligand, which we tentatively have identified as the diazomethane analogue of compounds 2a,b on the basis of their spectroscopic similitude (A in Scheme 1).20 However, increasing the reaction time or temperature at this point led only to the formation of the final products 4 and 5, along with increased amounts of the Scheme 1

Figure 1. ORTEP diagram (30% probability) of compound 2a with H atoms and Cy groups (except their C1 atoms) omitted. C


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Table 2. Selected IRa and 31P{1H} NMR Datab for New Compounds

Table 1. Selected Bond Lengths (Å) and Angles (deg) for Compound 2a W1−W2 W1−P W2−P W1−C1 W1−C2 W2−N1 W2−H1 N1−N2 N2−C3 C1−O1 C2−O2

2.9907(5) 2.382(2) 2.417(2) 1.949(8) 1.968(8) 1.759(6) 1.64(8) 1.337(9) 1.28(1) 1.16(1) 1.15(1)

W2−W1−C1 W2−W1−C2 C1−W1−P C2−W1−P N1−W2−P N1−W2−W1 H1−W2−W1 H1−W2−P H1−W2−N1 W2−N1−N2 N1−N2−C3 C2−W1−C1

87.0(2) 124.2(2) 102.8(2) 77.0(2) 98.3(2) 96.5(2) 120(3) 69(3) 97(3) 160.0(5) 120.1(7) 83.5(3)

compound [W2Cp2(H)(μ-PCy2){NN2CH(SiMe3)}(CO)2] (2a) [W2Cp2(H)(μ-PCy2)(N-N2CPh2) (CO)2] (2b) [W2Cp2(H)(μ-PCy2)(NN2CPh2)2(CO)2] (3) [W2Cp2(CH3)(μ-PCy2)(N-N2CH2) (CO)2] (4) [W2Cp2(CH3)(μ-C:P-CH2PCy2)(μCO)(CO)] (5)

ν(CO) 1889 (vs), 1798 (s) 1889 (vs), 1796 (s) 1902 (vs), 1804 (s) 1890 (vs), 1799 (s) 1804 (vs), 1692 (s)

δP (JPW) 174.7 (222, 179) 174.2c 7.5 (312, 200)d 168.4 (219, 206)d −36.1 (396, 49)d

a Recorded in dichloromethane solution, with C−O stretching bands [ν(CO)] in cm−1. bRecorded in CD2Cl2 at 162.01 MHz and 295 K unless otherwise stated, with 31P−183W coupling constants (JPW) in Hz. cP−W couplings could not be measured due to broadness of the resonance. dRecorded at 233 K.

completed either with two terminal carbonyls (on W1) or with a hydride and a N-bound diazoalkane molecule (on W2). The hydride and one of the carbonyl ligands are placed very close to the W2P plane, a conformation also found in the related alkyl complexes [Mo2Cp2(CH2R)(μ-PCy2)(CO)(NO)2] (R = H, Ph)23 and [W2Cp2{CH2(p-tol)}(O)(μ-PCy2)(CO)2].6 The metric parameters of the coordinated diazoalkane are indicative of a strong imido-like (four-electron donor) coordination of this group (SB1 in Chart 3),12d this implying the presence of

terminal coordination of the hydride ligands in solution is clearly denoted by their poorly shielded resonances (δH ca. −0.5 ppm). These hydrides expectedly display a high P−H coupling of 33 Hz, consistent with the cisoid arrangement of the corresponding atoms (ca. 70° in the crystal),27 but their onebond H−W coupling of ca. 125 Hz is unexpectedly large. For comparison, the corresponding coupling in isomer T of compound 1 is lower (99 Hz).3,11 In the absence of additional information, we tend to link this large coupling to the presence of the highly electronegative N atom in the coordination sphere of the same metal atom.27a Spectroscopic data in solution for compound 3 suggest coordination of two diazoalkane molecules, instead of one, indicated by the appearance of resonances in the aromatic region of its 1H NMR spectrum corresponding to a total of 20H atoms and the observation of two broad resonances at 134.8 and 133.2 ppm in the 13C{1H} NMR spectrum corresponding to the N-bound C atoms, with chemical shifts very close to the value of 136.5 ppm reported for the crystallographically characterized complex [Mo2Cp2{μ-C(Ph)CO}(μ-PCy2)(CO)(N-N2CPh2)].25b On the other hand, coordination of two carbonyl ligands to the same metal center, as found in compounds 2, is denoted by the appearance of two strong C−O stretching bands separated by ca. 90 cm−1 in the IR spectrum, with relative intensities corresponding to a cisoid W(CO)2 oscillator, and this asymmetric coordination of carbonyls should be likely balanced by coordination of both diazoalkane ligands at the other metal center. The molecule bears a terminal hydride, as denoted by the moderate shielding of the corresponding resonance in the 1H spectra (−6.1 ppm), while its large 31P−1H coupling of 60 Hz indicates an acute cisoid disposition with respect to the bridging phosphide ligand, to yield a local environment comparable to that in the mononuclear phosphine complex cis-[WCp(H)(PMe3)(CO)2] (δH −7.95 ppm, JHP = 68 Hz).27b The bridging ligand gives rise to an anomalously shielded 31P NMR resonance (δP 8.6 ppm), which can be explained only by assuming the absence of a direct metal−metal bond.28 The latter in turn requires that electron donation from the two diazoalkane ligands is close to a total of six electrons, a circumstance that might be fulfilled by assuming that one molecule is coordinated in the imido-like fashion found in 2a (four-electron donor), while the second molecule would act as a two-electron donor, a coordination mode itself having some structural variants.12d In any case, the coordination numbers of the metal centers in the structure of 3

Chart 3

essentially triple W−N [1.759(6) Å], single N−N [1.337(9) Å], and double N−C [1.28(1) Å] bonds, a situation further supported by the proximity of the values of the angles W−N− N [160.0(5)°] and N−N−C [120.1(7)°] to the ideal figures of 180° and 120°, respectively. Similar bond lengths and angles have been observed for a number of mononuclear tungsten complexes bearing terminal N-bound diazoalkanes12c,d,24 and also in the binuclear compounds [W2Cp2(μ-PPh2)2(NN2 CPh 2)(CO)] and [Mo2 Cp 2(μ-PCy 2){μ-C(CO)Ph}(NN2CPh2)(CO)].25 A four-electron donation of the diazoalkane ligand in turn implies that compound 2a might be considered a 34-electron complex; therefore a single metal−metal bond should be formulated for this molecule according to the 18electron rule, which is fully consistent with the intermetallic separation of 2.9907(5) Å, a figure comparable to those determined in the mentioned PCy2-bridged alkyl complexes (in the range 2.95−3.10 Å), which also are 34-electron species.6,23 Spectroscopic data in solution for compounds 2a,b (Table 2) are quite similar to each other and fully consistent with the solid-state structure of 2a. In particular, both compounds show two characteristically strong C−O stretching bands in the corresponding IR spectra, which are separated by ca. 100 cm−1, as expected for compounds having two carbonyl ligands placed on the same metal atom and conforming to C−W−C angles lower than 90° (83.5° in the crystal).26 The 31P NMR resonances of these complexes (ca. 174 ppm) fall in the region expected for compounds having single metal−metal bonds (cf. 170.9 ppm in [W2Cp2{CH2(p-tol)}(O)(μ-PCy2)(CO)2])6 and display two sets of similar, medium-strength W−P couplings in accordance with the presence of two different metal centers with the same coordination numbers. Finally, retention of D


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coordination of diazoalkane ligands in 3, we note that these ligands are indeed distinctly bound to the tungsten atom, but differences are less prominent than suspected. The one displaying the stronger binding to the metal atom (W2−N1 = 1.78(1), N1−N3 = 1.32(2) Å; W2−N1−N3 = 172(1)°) is also the closest one to an extreme singly bent, imido-like coordination mode of the ligand (SB1 in Chart 3),12d yet the W−N1 distance seems to be a bit longer than the one found in compound 2a. The second diazoalkane molecule, in contrast, displays a somewhat longer W2−N2 bond (1.82(1) Å), shorter N2−N4 bond (1.27(2) Å), and a significantly larger bending at the N2 atom (W−N2−N4 = 158(1)°). We note here that, for N-bound diazoalkane ligands having N−N−C angles close to 120°, two other extreme coordination modes are possible, these formally implying a two-electron contribution to the metal center (SB2 and DB in Chart 3) and therefore being expected to yield longer M−N lengths. A large bending at the N2 atom in 3 can be explained only by introducing some participation of doubly bent form DB in the actual coordination of the ligand, but this should not imply a significant reduction of the N−N separation. Since, however, this distance for the second diazoalkane molecule in 3 seems to be some 0.05 Å shorter, then we suspect a significant contribution also of the singly bent form SB2 (actually a resonant form of SB1), although the low precision of our interatomic distances prevents us from making more definitive conclusions. In agreement with the above analysis, however, we note that the W−N length of this second diazoalkane molecule in 3 is close to the values of ca. 1.83 Å determined for related Mo complexes having two threeelectron-donor diazenyl ligands.30 Structural Characterization of Diazomethane Derivatives 4 and 5. Spectroscopic data available for compound 4 reveal a close structural relationship with compounds 2a,b, with the major difference being the replacement of the hydride ligand in the latter compounds with a methyl group in 4. Indeed its IR spectrum displays C−O stretches almost identical to those of 2a, and its 31P{1H} NMR spectrum at 233 K displays a resonance with a chemical shift and P−W couplings comparable to those of 2a (Table 2). The transformation of the former hydride ligand into a methyl group is fully supported by the absence of any resonance in the negative region of the 1H spectrum, which is replaced by a moderately shielded resonance at 1.44 ppm (3JHP = 6 Hz) with intensity corresponding to 3H atoms. Coordination of this group to a tungsten atom is further supported by the strong shielding of its 13C nucleus (δC −13.1 ppm). Finally, the coordinated diazomethane molecule gives rise to two deshielded and strongly coupled 1H NMR resonances (δH 7.10, 7.36 ppm; 2JHH = 14 Hz), while the corresponding C atom gives rise to a 13C NMR resonance at 141.6 ppm. These spectroscopic parameters are not far from those of 2a and also compare well with those measured for the diazomethane-bridged complex [Mo2Cp*2(μ-CH2)(CO)4(μN2CH2)] (δH 6.91, 7.47 ppm; 2JHH =11 Hz; δC 146.8 ppm).22b The IR spectrum of compound 5 in dichloromethane solution displays two strong C−O stretching bands at 1804 and 1692 cm−1. The low frequency of the second band is indicative of the presence of a bridging carbonyl ligand, further corroborated by the observation of a highly deshielded resonance in the corresponding 13C NMR spectrum at 305.8 ppm. When recorded in petroleum ether solution, however, the IR spectrum of 5 displays four bands at 1829 (m), 1809 (vs), 1743 (s), and 1729 (m), which is indicative of the coexistence in solution of two similar dicarbonyl species. Yet, all NMR

would differ by one, which is consistent with the observation of quite different 183W−31P couplings of 200 and 312 Hz for this complex (cf. 230 Hz in the mentioned mononuclear complex). Eventually we could obtain crystals of 3 suitable for an X-ray diffraction study. Although the quality of the diffraction data was not very high, it was enough to depict the essential structural features of the complex, even if precision in the geometrical parameters is only modest (Figure 2 and Table 3).

Figure 2. ORTEP diagram (30% probability) of compound 3 with H atoms and Ph and Cy groups (except their C1 atoms) omitted.

Table 3. Selected Bond Lengths (Å) and Angles (deg) for Compound 3 W1−P1 W1−C1 W1−C2 W1−H1 W2−P1 W2−N1 W2−N2 N1−N3 N3−C3 N2−N4 N4−C4

2.530(4) 1.95(2) 1.98(2) 1.7(1) 2.589(4) 1.78(1) 1.82(1) 1.32(2) 1.28(2) 1.27(2) 1.29(2)

H1−W1−P1 C1−W1−C2 C1−W1−P1 C2−W1−P1 N1−W2−P1 N2−W2−P1 N1−W2−N1 W2−N1−N3 N1−N3−C3 W2−N2−N4 N2−N4−C4

132(9) 103.4(7) 84.0(4) 79.4(5) 91.6(4) 96.3(4) 105.9(6) 172(1) 123(1) 158(1) 125(1)

As expected, the molecule is built from WCp(CO)2H and WCp(N-N2CPh2)2 fragments bridged asymmetrically by a PCy2 ligand, with the P−W(CO)2 length being substantially shorter (2.530(4) vs 2.589(4) Å), a difference consistent with the formal description of these bonds as single-dative and single bonds, respectively (Chart 2). However, the arrangement of ligands at the W(CO)2 fragment is of the transoid type (C−W− C = 103.4(7)°, H−W−P = 132(9)°), as opposed to the cisoid arrangement displayed in solution. Indeed, an IR spectrum of the X-ray crystals in Nujol mull displayed C−O stretching bands at 1907 (s) and 1811 (vs) cm−1, with their relative intensity (strong and very strong, in order of decreasing frequencies) corresponding to a transoid M(CO)2 oscillator defining a C−M−C angle somewhat larger than 90°.26 However, when these crystals were dissolved in dichloromethane, a single species was observed by IR or NMR, with the spectroscopic properties discussed above, that is, those corresponding to the cis isomer. Thus, it is concluded that compound 3 exists in solution as its cis isomer, whereas the trans isomer prevails in the crystal lattice. The geometrical parameters involving the WCp(CO)2H moiety are comparable to those of other complexes of type trans-[WCpH(CO)2(PR3)] crystallographically characterized previously29 and deserve no particular comments. As for the E


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spectra of 5 (31P, 1H, 13C) were consistent with the presence of just one species in solution, even at temperatures as low as 178 K. Then, it must be concluded that compound 5 displays in solution two similar isomers interconverting rapidly on the NMR time scale. The averaged NMR data of 5 indicate that this complex contains a Me ligand, identified by NMR resonances (δH 0.24 ppm, δC −15.9 ppm) comparable to those of 4. There is also a methylene group inserted in one of the W−P bonds of the former PCy2 ligand, therefore transforming it into a phosphinomethyl ligand. The first indication of such insertion comes from the huge shielding of some 200 ppm operating on the 31P NMR resonance of 5 (δP −35.0 ppm), which now appears in the region expected for a coordinated phosphine ligand. Such a shielding effect when going from phosphide to phosphinomethyl ligands is nicely exemplified by complex [W2Cp2(μ-C:P-CH2PPh2)(O)(μPPh2)(CO)], for which the phosphide and phosphinomethyl resonances differ by ca. 140 ppm (δP 138.5 and −2.0 ppm, respectively).31 Moreover, the 31P resonance of 5 displays two sets of quite different 183W satellites, 49 and 396 Hz, as expected for two- and one-bond couplings, respectively (66 and 315 Hz in the mentioned oxo complex); additionally, the high value of the one-bond coupling denotes a low coordination number in the corresponding metal center, it being similar to that measured in the 30-electron complex [W2Cp2(CO)2(μPh2PCH2PPh2)] (421 Hz).31 As expected, the methylene resonances also appear quite shielded as a result of its coordination to the tungsten atom (δH 0.51 and −0.33 ppm; δC 7.4 ppm), as usually found in related phosphinomethylbridged complexes.31,32 In all, the structure proposed for 5 is based on that crystallographically determined for the isoelectronic (30electron) cation [Mo2Cp2(H)(μ-PCy2)2(CO)]+ 33 and the one computed for isomer T of the starting hydride 1 (Chart 1).3,11 This would be built on a W2PC2 central ring likely to be somewhat puckered, thus allowing for the existence in solution of the conformers detected by IR spectroscopy. Apart from this, two distinct isomers (C and D in Chart 4) might be drawn

CONCLUSION When compared to its dimolybdenum analogue, the ditungsten hydride [W2 Cp 2 (H)(μ-PCy 2 )(CO)2 ] (1) behaves in a completely different way in reactions with diazoalkanes, which in this case takes place rapidly to give new and isolable organometallic species, even if the outcome of these reactions depends critically on the diazoalkane used. Substituted diazoalkanes N2CRR′ (R = H, R′ = SiMe3; R = R′ = Ph) give invariably addition products following from N-coordination of either one or two molecules of the reagent, this being in contrast with prior work on related unsaturated hydrides, for which this sort of product was never observed. In all these new complexes, the diazoalkanes are terminally bound to one of the metal centers acting preferentially as four-electron (imido-like) donors, except when this would lead to electronic oversaturation of the metal center, and are in any case reluctant to undergo dinitrogen loss even under moderate thermal or photochemical activation. Reaction of 1 with diazomethane seems to proceed initially in an analogous way to give a related diazomethane intermediate, [W2Cp2(H)(μ-PCy2)(CO)2(NN2CH2)], which, however, is thermally unstable and evolves differently depending on reaction conditions, but always involving loss of nitrogen. In the absence of more reagent, denitrogenation occurs to give the methyl-bridged complex [W2Cp2(μ-CH3)(μ-PCy2)(CO)2], but in the presence of additional reagent, a second molecule of diazomethane readily adds and further evolves along two independent reaction paths that eventually lead to two new products. Both of them have terminal methyl ligands, thus indicating that one of the diazomethane molecules evolves as usual, that is, through N2 elimination and insertion of methylene into a W−H bond. However, the second molecule of diazomethane is able to remain intact, as observed in the diazomethane complex [W2Cp2(CH3)(μ-PCy2)(N-N2CH2)(CO)2], or gives rise to a second methylene group now inserting into a W−P bond to yield a phosphinomethyl ligand, as found in the 30-electron complex [W2Cp2(CH3)(μ-C:P-CH2PCy2)(μ-CO)(CO)]. The presence of W(CO)2 or W(CO)(μ-CO) fragments in all these products might be taken as an indication of the preferential participation of the minor isomer T of compound 1 in these reactions and would be consistent with the fact that the Mo2 analogue of 1, which exists only in the H-bridged structure B, failed to give detectable organometallic products in analogous reactions.

Chart 4

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EXPERIMENTAL SECTION

General Procedures and Starting Materials. All manipulations and reactions were carried out under a nitrogen (99.995%) atmosphere using standard Schlenk techniques. Solvents were purified according to literature procedures and distilled prior to use.34 Diphenyldiazomethane,35 diethyl ether solutions of diazomethane,36 and compound [W2Cp2(H)(μ-PCy2)(CO)2] (1)11 were prepared as described previously, and all other reagents were obtained from the usual commercial suppliers and used as received, unless otherwise stated. Petroleum ether refers to that fraction distilling in the range 338−343 K. Photochemical experiments were performed using jacketed Pyrex Schlenk tubes, cooled by tap water (ca. 288 K). A 400 W mercury lamp placed ca. 1 cm away from the Schlenk tube was used for these experiments. Filtrations were carried out through diatomaceous earth unless otherwise stated. Chromatographic separations were carried out using jacketed columns refrigerated by tap water or by a closed 2-propanol circuit kept at the desired temperature with a cryostat. Commercial aluminum oxide (activity I, 70−290 mesh) was degassed under vacuum prior to use. The latter

depending on the relative arrangement of the phosphinomethyl ligand with respect to the methyl group, while keeping the transoid arrangement of the terminal ligands. However, based on the fact that the 13C NMR resonance at 242.0 ppm of the terminal carbonyl in 5 displays a measurable P−C coupling of 5 Hz, it seems more sensible proposing for this complex a structure of type C, where this carbonyl ligand and the P atom are bound to the same metal atom, even if this formally implies the presence of W(I) and W(III) metal centers (rather than W(II) centers) and consequently the formulation of a donor W(I) → W(III) interaction. Interestingly, the structure of the mentioned oxo ditungsten complex also corresponds to the most dissymmetric W(II)/W(IV) isomer, with the oxo and methylene donors bound to the same W atom. F


Article

Organometallics was mixed afterward under nitrogen with the appropriate amount of water to reach the activity desired (activity IV, unless otherwise stated). IR stretching frequencies of CO ligands were measured in solution (using CaF2 windows) or in Nujol mulls (using NaCl windows) and are referred to as ν(CO)(solvent) and ν(CO)(Nujol), respectively. Nuclear magnetic resonance (NMR) spectra were routinely recorded at 400.13 (1H), 162.00 (31P{1H}), or 100.63 MHz (13C{1H}), at 295 K in CD2Cl2 solution unless otherwise stated. Chemical shifts (δ) are given in ppm, relative to internal tetramethylsilane (1H, 13C) or external 85% aqueous H3PO4 (31P). Coupling constants (J) are given in hertz. Preparation of [W2Cp2(H)(μ-PCy2)(CO)2{N-N2CH(SiMe3)}] (2a). Compound 1 (0.035 g, 0.047 mmol) and N2CH(SiMe3) (50 μL of a 2 M solution in hexane, 0.10 mmol) were stirred in dichloromethane (4 mL) at room temperature for 5 min to give a purple solution. Solvent was then removed under vacuum, and the residue was extracted with dichloromethane−petroleum ether (1:9) and chromatographed through an alumina column at 288 K. Elution with the same solvent mixture gave a purple fraction, yielding, after removal of solvents, compound 2a as a deep purple, microcrystalline solid (0.037 g, 92%). The crystals used in the X-ray diffraction study were grown from a concentrated petroleum ether solution of the complex at 273 K. Anal. Calcd for C28H43N2O2PSiW2: C, 38.82; H, 5.00; N, 3.23. Found: C, 39.17; H, 4.61; N, 2.81. 1H NMR: δ 8.04 (s, 1H, CH), 5.77, 5.23 (2s, 2 × 5H, Cp), 2.70−0.40 (m, 22H, Cy), 0.08 (s, 9H, SiMe3), −0.38 (d, 2 JHP = 33, 1JHW = 123, 1H, W−H). 13C{1H} NMR: δ 227.9 (s, CO), 227.3 (d, 2JCP = 22, CO), 166.8 (s, N2CHSi), 96.5, 87.1 (2s, Cp), 46.1 [d, 1JCP = 20, C1(Cy)], 44.4 [d, 1JCP = 30, C1(Cy)], 34.4, 34.1, 33.6, 33.2 [4s, C2(Cy)], 28.3 [d, 3JCP = 11, C3(Cy)], 28.2, 28.1, 28.0 [3d, 3 JCP = 12, C3(Cy)], 27.0, 26.8 [2s, C4(Cy)], −3.2 (s, SiMe3). Reaction of Compound 1 with N2CPh2. Compound 1 (0.035 g, 0.047 mmol) and N2CPh2 (3 mL of a ca. 0.05 M solution in Et2O, 0.15 mmol) were stirred in dichloromethane (4 mL) at room temperature for 2 h to give a maroon solution containing an approximately equimolar mixture of compounds [W2Cp2(H)(μ-PCy2)(CO)2(NN2CPh2)] (2b) and [W2Cp2(H)(μ-PCy2)(CO)2(N-N2CPh2)2] (3). Solvent was then removed under vacuum, and the residue was chromatographed through an alumina column (activity II) at 253 K. Elution with dichloromethane−petroleum ether (2:1) gave a red fraction, yielding, after removal of solvents, compound 3 as a red, microcrystalline solid (0.021 g, 39%). Elution with the same solvent mixture gave a blue fraction, yielding, after removal of solvents, compound 2b as a blue, microcrystalline solid (0.017 g, 38%). The crystals of 3 used in the X-ray study were grown by the slow diffusion of a layer of petroleum ether into a concentrated dichloromethane solution of the complex at 253 K. Data for 2b: Anal. Calcd for C37H43N2O2PW2: C, 46.96; H, 4.58; N, 2.96. Found: C, 46.61; H, 4.61; N, 2.99. 1H NMR: δ 7.50 (m, 10H, Ph), 5.33, 5.23 (2s, 2 × 5H, Cp), 2.70−0.50 (m, 22H, Cy), −0.84 (s, 2JHP = 33, 1JHW = 127, 1H, W−H). Data for 3: Anal. Calcd for C50H53N4O2PW2: C, 52.65; H, 4.68; N, 4.91. Found: C, 52.31; H, 4.45; N, 4.68. IR ν(CO) (petroleum ether): 1915 (vs), 1828 (s). 1H NMR: δ 7.60−7.20 (m, br, 20H, Ph), 5.39, 5.38 (2s, 2 × 5H, Cp), 3.00−1.00 (m, 22H, Cy), −5.95 (d, br, 2JHP = 60, 1H, W−H). 1H NMR (233 K): δ 7.65−7.45 (m, 10H, Ph), 7.40−7.25 (m, 10H, Ph), 5.42, 5.32 (2s, 2 × 5H, Cp), 2.80−1.00 (m, 22H, Cy), −6.15 (d, 2JHP = 60, 1JHW = 45, 1H, W−H). 31 1 P{ H} NMR: δ 8.6 (s, br). 31P{1H} NMR (C6D6): δ 11.3 (s, 1JPW = 315, 204). 13C{1H} NMR (CD2Cl2, 213 K): δ 243.7, 237.9 (2s, br, CO), 146.7, 137.4 [2s, C1(Ph)], 134.8, 133.2 (2s, vbr, NCPh2), 129.4, 129.3, 128.7, 127.2 [4s, C2,3(Ph)], 129.1 [s, 2C4(Ph)], 106.8, 88.5 (2s, Cp), 46.4, 39.7 [2s, vbr, C1(Cy)], 31.6, 30.7 [2s, br, C2(Cy)], 28.3 [m, br, 2C3(Cy)], 27.0 [s, 2C4(Cy)]. Reaction of Compound 1 with N2CH2. Compound 1 (0.035 g, 0.047 mmol) and N2CH2 (2 mL of a ca. 0.7 M solution in Et2O, 1.40 mmol) were stirred in dichloromethane (4 mL) at room temperature for 2 h to give a reddish-brown solution. Caution! diazomethane is toxic and explosive; it should be generated and handled with glassware devoid of any sharp edges in a good hood with an adequate shield. Solvent was then removed under vacuum, and the residue was chromatographed through an alumina column. Elution with dichloromethane−

petroleum ether (1:2) gave a violet fraction, yielding, after removal of solvents, compound [W2Cp2(CH3)(μ-PCy2)(CO)2(N-N2CH2)] (4) as a violet, microcrystalline solid (0.008 g, 21%). Elution with dichloromethane gave a purple fraction, yielding, after removal of solvents, compound [W2Cp2(CH3)(μ-C:P-CH2PCy2)(μ-CO)(CO)] (5) as a purple, microcrystalline solid (0.025 g, 69%). Data for 4: Anal. Calcd for C26H37N2O2PW2: C, 38.64; H, 4.61; N, 3.47. Found: C, 39.04; H, 4.15; N, 2.98. 1H NMR: δ 7.35, 7.03 (2d, 2JHH = 14, 2 × 1H, NCH2), 5.83, 5.18 (2s, 2 × 5H, Cp), 1.44 (d, 3JHP = 6, 3H, WCH3), 3.00−0.50 (m, 22H, Cy). 1H NMR (233 K): δ 7.36, 7.10 (2d, 2JHH = 14, 2 × 1H, NCH2), 5.85, 5.20 (2s, 2 × 5H, Cp), 1.41 (d, 3JHP = 6, 3H, WCH3), 3.00−0.50 (m, 22H, Cy). 13C{1H} NMR (233 K): δ 229.5, 228.8 (2s, CO), 141.6 (s, NCH2), 102.5, 87.6 (2s, Cp), 42.6 [d, 1JCP = 16, C1(Cy)], 41.1 [d, 1JCP = 26, C1(Cy)], 33.5, 32.7, 31.2, 30.7 [4s, C2(Cy)], 28.2 [d, 3JCP = 11, 2C3(Cy)], 28.0 [d, 3JCP = 13, C3(Cy)], 27.7 [d, 3JCP = 12, C3(Cy)], 26.7, 26.6 [2s, C4(Cy)], −13.1 (d, 2JCP = 14, WCH3). 31P{1H} NMR: δ 168.3 (s, br). Data for 5: Anal. Calcd for C26H37O2PW2: C, 40.02; H, 4.78. Found: C, 39.93; H, 4.61. IR ν(CO) (petroleum ether): 1829 (m), 1809 (vs), 1743 (s), 1729 (m). 1H NMR: δ 5.37 (d, 3JHP = 1.5, 5H, Cp), 5.17 (s, 5H, Cp), 2.20−1.10 (m, 22H, Cy), 0.51 (dd, 2JHH = 11, 2JHP = 6, 1H, PCH2), 0.24 (s, 3H, WCH3), −0.33 (dd, 2JHH = 11, 2JHP = 9, 1H, PCH2). 31P{1H} NMR: δ −35.0 (s, br, 1JPW = 400). 31P{1H} NMR (233 K): δ −36.1 (s, 1JPW = 396, 2JPW = 49). 13C{1H} NMR (233 K): δ 305.8 (s, μ-CO), 242.0 (d, 2 JCP = 5, CO), 100.1, 92.1 (2s, Cp), 39.8 [d, 1JCP = 16, C1(Cy)], 38.7 [d, 1JCP = 20, C1(Cy)], 29.7, 29.5, 29.3, 29.2 [4s, C2(Cy)], 27.9 [d, 3JCP = 11, C3(Cy)], 27.7, 27.2 [2d, 3JCP = 12, C3(Cy)], 27.1 [d, 3JCP = 11, C3(Cy)], 26.7, 26.6 [2s, C4(Cy)], 7.4 (s, WCH2P), −15.9 (s, WCH3). X-ray Crystal Structure Determination for Compound 2a. The X-ray intensity data for 2a were collected on a Kappa-Appex-II Bruker diffractometer using graphite-monochromated Mo Kα radiation at 100 K. The software APEX37 was used for collecting frames with the ω/ϕ scans measurement method. The SAINT software was used for data reduction,38 and a multiscan absorption correction was applied with SADABS.39 Using the program suite WinGX,40 the structure was solved by Patterson interpretation and phase expansion using SHELXL9741 and refined with full-matrix leastsquares on F2 using SHELXL97. All positional parameters and anisotropic temperature factors of all non-H atoms were refined anisotropically, except for the carbon atom C17, which was refined isotropically to prevent its temperature factors from becoming nonpositive definite. All hydrogen atoms were geometrically placed and refined using a riding model, except for atoms H1 and H3, which were located in the Fourier maps and refined isotropically. Upon convergence, the strongest residual peak (7.74 e Å−3) was located around one of the tungsten atoms. X-ray Crystal Structure Determination for Compound 3. The X-ray intensity data were collected at 158 K on an Oxford Diffraction Xcalibur Nova single-crystal diffractometer, using Cu Kα radiation. Images were collected at a 62 mm fixed crystal−detector distance, using the oscillation method, with 1° oscillation and variable exposure time per image (10.0−65.9 s). The data collection strategy was calculated with the program CrysAlis Pro CCD.42 Data reduction and cell refinement were performed with the program CrysAlis Pro RED, and an empirical absorption correction was applied using the SCALE3 ABSPACK algorithm as implemented in that program.42 The structure was solved by Patterson interpretation and phase expansion using SHELXL2014 and refined with full-matrix least-squares on F2 using SHELXL2014.41 All positional parameters and anisotropic temperature factors for all non-H atoms could be refined anisotropically, a few of them in combination with the instructions DELU and SIMU. All hydrogen atoms were geometrically placed and refined using a riding model, except for H1, which was located in the Fourier maps and refined isotropically with a restraint in the W1−H1 distance to reach a satisfactory convergence. The compound was found to crystallize with a molecule of disordered solvent, which could not be identified. Therefore, the SQUEEZE procedure,43 as implemented in PLATON,44 was used. Upon squeeze application and convergence, the strongest residual peak (3.50 e Å−3) was close to one of the phenyl groups, but a number of other minor peaks were still present. G


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Organometallics

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(9) Alvarez, M. A.; García, M. E.; Ruiz, M. A.; Toyos, A.; Vega, M. F. Inorg. Chem. 2013, 52, 7068−7077. (10) Alvarez, C. M.; Alvarez, M. A.; García, M. E.; Ramos, A.; Ruiz, M. A.; Graiff, C.; Tiripicchio, A. Organometallics 2007, 26, 321−331. (11) Alvarez, M. A.; García, M. E.; García-Vivó, D.; Ruiz, M. A.; Vega, M. F. Dalton Trans. 2014, 43, 16044−16055. (12) (a) Herrmann, W. A. Adv. Organomet. Chem. 1982, 20, 159− 263. (b) Curtis, M. D. Polyhedron 1987, 6, 759−782. (c) Mizobe, Y.; Ishii, Y.; Hidai, M. Coord. Chem. Rev. 1995, 139, 281−311. (d) Dartiguenave, M.; Menu, M. J.; Deydier, E.; Dartiguenave, Y.; Siebald, H. Coord. Chem. Rev. 1998, 178−180, 623−663. (13) (a) Messerle, L.; Curtis, M. D. J. Am. Chem. Soc. 1980, 102, 7789−7791. (b) Messerle, L.; Curtis, M. D. J. Am. Chem. Soc. 1982, 104, 889−891. (c) D’Errico, J. J.; Messerle, L.; Curtis, M. D. Inorg. Chem. 1983, 22, 849−851. (14) (a) Keister, J. B.; Shapley, J. R. J. Am. Chem. Soc. 1976, 98, 1056−1057. (b) Calvert, R. B.; Shapley, J. R. J. Am. Chem. Soc. 1977, 99, 5225−5226. (c) Burgess, K.; Johnson, B. F. G.; Lewis, J.; Raithby, P. R. J. Chem. Soc., Dalton Trans. 1982, 263−269. (15) (a) Carlucci, L.; Ciani, G.; Gudenberg, D. W. v.; D’Alfonso, G. J. Organomet. Chem. 1997, 534, 233−235. (b) Carlucci, L.; Proserpio, D. M.; D’Alfonso, G. Organometallics 1999, 18, 2091−2098. (16) Kurogi, T.; Ishida, Y.; Hatanaka, T.; Kawaguchi, H. Chem. Commun. 2012, 48, 6809−6811. (17) (a) Kabir, S. E.; Malik, K. M. A.; Mandal, H. S.; Mottalib, M. A.; Abedin, M. J.; Rosenberg, E. Organometallics 2002, 21, 2593−2595. (b) Mottalib, M. A.; Begum, N.; Abedin, S. M. T.; Akter, T.; Kabir, S. E.; Miah, M. A.; Rokhsana, D.; Rosenberg, E.; Hossain, G. M. G.; Hardcastle, K. I. Organometallics 2005, 24, 4747−4759. (18) Alvarez, M. A.; García, M. E.; García-Vivó, D.; Ruiz, M. A.; Vega, M. F. Organometallics 2015, 34, 870−878. (19) (a) Yu, Y. F.; Chau, C. N.; Wojcicki, A.; Calligaris, M.; Nardin, G.; Balducci, G. J. Am. Chem. Soc. 1984, 106, 3704−3705. (b) Yu, Y. F.; Gallucci, J.; Wojcicki, A. J. Chem. Soc., Chem. Commun. 1984, 653− 655. (c) Werner, H.; Zolk, R. Organometallics 1985, 4, 601−603. (20) Spectroscopic data available for this intermediate are quite limited due to its progressive transformation upon manipulation. IR ν(CO) (CH2Cl2): 1890 (vs), 1799 (s) cm−1. 31P{1H} NMR (162.00 MHz, 298 K, CD2Cl2): δ 170.3 ppm. 1H NMR (400.13 MHz, 298 K, CD2Cl2): δ 7.29, 6.97 (2d, 2JHH = 14, 2H, NCH2), 5.44, 5.23 (2s, 2 × 5H, Cp), −0.08 (d, 2JHP = 33, 1H, W−H). (21) (a) Ben-Shosham, R.; Chatt, J.; Leigh, G. J.; Hussain, W. J. Chem. Soc., Dalton Trans. 1980, 771−775. (b) Hidai, M.; Mizobe, Y.; Sato, M.; Kodama, K.; Uchida, Y. J. Am. Chem. Soc. 1978, 100, 5740− 5748. (22) (a) Clauss, A. D.; Shapley, J. R.; Wilson, S. R. J. Am. Chem. Soc. 1981, 103, 7387−7388. (b) Herrmann, W. A.; Bell, L. K. J. Organomet. Chem. 1982, 239, C4−C8. (c) Liu, X. Y.; Riera, V.; Ruiz, M. A.; Bois, C. Organometallics 2001, 20, 3007−3016. (23) Alvarez, M. A.; García, M. E.; Martínez, M. E.; Ramos, A.; Ruiz, M. A. Organometallics 2009, 28, 6293−6307. (24) For some representative examples, see for instance: (a) Head, R. A.; Hitchcock, P. B. J. Chem. Soc., Dalton Trans. 1980, 1150−1155. (b) Aoshima, T.; Tamura, T.; Mizobe, Y.; Hidai, M. J. Organomet. Chem. 1992, 435, 85−99. (c) Seino, H.; Watanabe, D.; Ohnishi, T.; Arita, C.; Mizobe, Y. Inorg. Chem. 2007, 46, 4784−4786. (d) Khosla, C.; Jackson, A. B.; White, P. S.; Templeton, J. L. Organometallics 2012, 31, 987−994. (25) (a) García, M. E.; García-Vivó, D.; Ruiz, M. A.; Herson, P. Organometallics 2008, 27, 3879−3891. (b) Alvarez, M. A.; García, M. E.; Menéndez, S.; Ruiz, M. A. Organometallics 2011, 30, 3694−3697. (26) Braterman, P. S. Metal Carbonyl Spectra; Academic Press: London, U.K., 1975. (27) A general trend established for 2JXY in complexes of the type [MCpXYL2] is that |Jcis| > |Jtrans|. See, for instance: (a) Jameson, C. J. In Phosphorus-31 NMR Spectroscopy in Stereochemical Analysis; Verkade, J. G., Quin, L. D., Eds.; VCH: Deerfield Beach, FL, 1987; Chapter 6. (b) Wrackmeyer, B.; Alt, H. G.; Maisel, H. E. J. Organomet. Chem. 1990, 399, 125−130.

ASSOCIATED CONTENT

S Supporting Information *

A PDF file containing a table with crystal data for compounds 2a and 3 and a CIF file containing full crystallographic data for these compounds (CCDC 1049261 and 1403680). The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.5b00466.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (D. Garcı ́a-Vivo)́ . *E-mail: [email protected] (M. A. Ruiz). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the DGI of Spain for financial support (Project CTQ2012-33187) and grants (to E.H. and M.F.V.). We also thank the X-ray units of Universidad de Santiago de Compostela and Universidad de Oviedo for collection of diffraction data.

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REFERENCES

(1) (a) Alvarez, C. M.; Alvarez, M. A.; García, M. E.; Ramos, A.; Ruiz, M. A.; Lanfranchi, M.; Tiripicchio, A. Organometallics 2005, 24, 7−9. (b) García, M. E.; Melón, S.; Ramos, A.; Ruiz, M. A. Dalton Trans. 2009, 8171−8182. (2) García-Vivó, D.; Ramos, A.; Ruiz, M. A. Coord. Chem. Rev. 2013, 257, 2143−2191. (3) Alvarez, M. A.; García, M. E.; García-Vivó, D.; Ruiz, M. A.; Vega, M. F. Organometallics 2010, 29, 512−515. (4) We have adopted a “half-electron” counting convention for complexes displaying bridging hydrides or alkyls (if only bound through a single C atom), so these ligands (X) have been considered as one-electron donors. Then, complexes of the type [M2Cp2(μ-X)(μPCy2)(CO)2] (M = Mo, W) are regarded as having MM bonds. These “triple” bonds actually follow from the superimposition of two bicentric (M2) bonding interactions and a tricentric one (M2X). Yet, the electron density at the intermetallic bond critical points, structural features, and chemical behavior of these unsaturated complexes are comparable to those of 30-electron complexes having more conventional MM bonds such as the dimers [M2Cp2(CO)4] (see, for instance, ref 2). Other authors, however, recommend the adoption for these systems of a “half-arrow” convention. Under this convention, the corresponding intermetallic bond orders appearing in this paper should be reduced by one unit per bridging ligand X present in a molecule. In particular, the “half-arrow” convention implies that the 30-electron hydride complexes [M2Cp2(μ-H)(μ-PCy2)(CO)2] must be assimilated to the 32-electron complexes [M2Cp2(μ-Y)(μ-PCy2)(CO)2] (Y = Cl, PRR′, O2CR) and hence considered to have a double MM bond, a relationship that we consider of little use to interpret the strong differences separating the structure, spectroscopic properties, and reactivity of these molecules. See the following and references therein: Green, J. C.; Green, M. L. H.; Parkin, G. Chem. Commun. 2012, 48, 11481−11508. (5) García, M. E.; Ramos, A.; Ruiz, M. A.; Lanfranchi, M.; Marchiò, L. Organometallics 2007, 26, 6197−6212. (6) Alvarez, M. A.; García, M. E.; Ruiz, M. A.; Vega, M. F. Dalton Trans. 2011, 40, 8294−8297. (7) Alvarez, M. A.; García, M. E.; García-Vivó, D.; Ruiz, M. A.; Vega, M. F. Organometallics 2013, 32, 4543−4555. (8) (a) Alvarez, M. A.; García, M. E.; Ramos, A.; Ruiz, M. A. Organometallics 2007, 26, 1461−1472. (b) Alvarez, M. A.; García, M. E.; Ramos, A.; Ruiz, M. A.; Lanfranchi, M.; Tiripicchio, A. Organometallics 2007, 26, 5454−5467. H


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Organometallics (28) (a) Carty, A. J.; MacLaughlin, S. A.; Nucciarone, D. In Phosphorus-31 NMR Spectroscopy in Stereochemical Analysis; Verkade, J. G., Quin, L. D., Eds.; VCH: Deerfield Beach, FL, 1987; Chapter 16. (b) Garrou, P. E. Chem. Rev. 1981, 81, 229−266. (29) (a) Fischer, P. J.; Neary, M. C.; Avena, L.; Sullivan, K. P.; Hackbarth, K. C. Organometallics 2012, 31, 2437−2444. (b) Antunes, M. A.; Namorado, S.; de Azevedo, C. G.; Lemos, M. A.; Duarte, M. T.; Ascenso, J. R.; Martins, A. M. J. Organomet. Chem. 2010, 695, 1328− 1336. (c) Shafiq, F.; Szalda, D. J.; Creutz, C.; Bullock, R. M. Organometallics 2000, 19, 824−833. (30) (a) Ferguson, G.; Ruhl, B. L.; Parvez, M.; Lalor, F. J.; Deane, M. E. J. Organomet. Chem. 1990, 381, 357−377. (b) Lalor, F. J.; Condon, D.; Ferguson, G.; Khan, M. A. Inorg. Chem. 1981, 20, 2178−2181. (31) Alvarez, M. A.; García, M. E.; Riera, V.; Ruiz, M. A.; Falvello, L. R.; Bois, C. Organometallics 1997, 16, 354−364. (32) (a) García, G.; García, M. E.; Melón, S.; Riera, V.; Ruiz, M. A. Organometallics 1997, 16, 624−631. (b) Alvarez, C.; García, M. E.; Riera, V.; Ruiz, M. A. Organometallics 1997, 16, 1378−1383. (33) Alvarez, M. A.; García, M. E.; Martínez, M. E.; Ramos, A.; Ruiz, M. A.; Sáez, D. Inorg. Chem. 2006, 45, 6965−6978. (34) Armarego, W. L. F.; Chai, C. L. L. Purification of Laboratory Chemicals, 5th ed.; Butterworth-Heinemann: Oxford, UK, 2003. (35) Miller, J. B. J. Org. Chem. 1959, 24, 560−561. (36) Vogel, A. I. Textbook of Practical Organic Chemistry, 4th ed.; Longmans: London, U.K., 1978; p 291. (37) APEX 2, version 2.0-1; Bruker AXS Inc.: Madison, WI, 2005. (38) SMART & SAINT Software Reference Manuals, Version 5.051; Bruker Analytical X-ray Instruments: Madison WI, 1998. (39) Sheldrick, G. M. SADABS, Program for Empirical Absorption Correction; University of Göttingen: Göttingen, Germany, 1996. (40) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837−838. (41) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122. (42) CrysAlis Pro; Oxford Diffraction Limited, Ltd.: Oxford, U.K., 2006. (43) Van der Sluis, P.; Spek, A. L. Acta Crystallogr., Sect. A: Found. Crystallogr. 1990, 46, 194−201. (44) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool; Utrecht University: Utrecht, The Netherlands, 2010.

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