(H)(L) Complexes (L = Lewis Base) - ACS Publications - American

Dec 14, 2016 - ... Chemistry of Cp*W(NO)(CH2CMe3)(H)(L) Complexes (L = Lewis Base) ... been established by single-crystal X-ray crystallographic analy...
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Thermal Chemistry of Cp*W(NO)(CH2CMe3)(H)(L) Complexes (L = Lewis Base) Diana Fabulyak,† Rex C. Handford,† Aaron S. Holmes,† Taleah M. Levesque,† Russell J. Wakeham,† Brian O. Patrick,† Peter Legzdins,*,† and Devon C. Rosenfeld‡ †

Department of Chemistry, The University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1 The Dow Chemical Company, 2301 North Brazosport Boulevard, Freeport, Texas 77541, United States

‡

S Supporting Information *

ABSTRACT: The complexes trans-Cp*W(NO)(CH2CMe3)(H)(L) (Cp* = η5-C5Me5) result from the treatment of Cp*W(NO)(CH2CMe3)2 in n-pentane with H2 (∼1 atm) in the presence of a Lewis base, L. The designation of a particular geometrical isomer as cis or trans indicates the relative positions of the alkyl and hydrido ligands in the base of a four-legged piano-stool molecular structure. The thermal behavior of these complexes is markedly dependent on the nature of L. Some of them can be isolated at ambient temperatures [e.g., L = P(OMe) 3 , P(OPh) 3 , or P(OCH2)3CMe]. Others undergo reductive elimination of CMe4 via trans to cis isomerization to generate the 16e reactive intermediates Cp*W(NO)(L). These intermediates can intramolecularly activate a C−H bond of L to form 18e cis complexes that may convert to the thermodynamically more stable trans isomers [e.g., Cp*W(NO)(PPh3) initially forms cis-Cp*W(NO)(H)(κ2-PPh2C6H4) that upon being warmed in n-pentane at 80 °C isomerizes to trans-Cp*W(NO)(H)(κ2-PPh2C6H4)]. Alternatively, the Cp*W(NO)(L) intermediates can effect the intermolecular activation of a substrate R-H to form trans-Cp*W(NO)(R)(H)(L) complexes [e.g., L = P(OMe)3 or P(OCH2)3CMe; R-H = C6H6 or Me4Si] probably via their cis isomers. These latter activations are also accompanied by the formation of some Cp*W(NO)(L)2 disproportionation products. An added complication in the L = P(OMe)3 system is that thermolysis of trans-Cp*W(NO)(CH2CMe3)(H)(P(OMe)3) results in it undergoing an Arbuzov-like rearrangement and being converted mainly into [Cp*W(NO)(Me)(PO(OMe)2)]2, which exists as a mixture of two isomers. All new complexes have been characterized by conventional and spectroscopic methods, and the solid-state molecular structures of most of them have been established by single-crystal X-ray crystallographic analyses.

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INTRODUCTION One of our longer-term research goals has been the development of Group 6 cyclopentadienyl nitrosyl complexes as initiators of hydrocarbon C−H activation and functionalization processes.1 In that vein, one family of these compounds that attracted our renewed interest recently consists of the hydrido complexes, trans-Cp*W(NO)(CH2SiMe3)(H)(L) [Cp* = η5-C5Me5; L = Lewis base].2 Our designation of a particular geometrical isomer as cis or trans indicates the relative positions of the alkyl and hydrido ligands in the base of a fourlegged piano-stool molecular structure. These compounds are conveniently prepared by exposing Cp*W(NO)(CH2SiMe3)2 to low pressures of dihydrogen in the presence of a variety of Lewis bases. The reaction involving PMe3 as the Lewis base is particularly instructive in that it affords trans-Cp*W(NO)(CH2SiMe3)(H)(PMe3) that subsequently activates C6H6 and forms cis-Cp*W(NO)(H)(C6H5)(PMe3).3 Kinetic, mechanistic, and theoretical investigations of this benzene C−H activation process are consistent with the probable mechanism summarized in Scheme 1 in which R = CH2SiMe3 and R′ = © 2016 American Chemical Society

Scheme 1. Probable Mechanism for the Activation of C6H6 by trans-Cp*W(NO)(CH2SiMe3)(H)(PMe3)

C6H5.3 Initial trans to cis isomerization of the reactant is followed by intramolecular reductive elimination of SiMe4 to Received: October 11, 2016 Published: December 14, 2016 573

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the trans-Cp*W(NO)(CH2CMe3)(H)(L) complexes (A in Scheme 3) can be isolated at ambient temperatures. Others are less thermally stable and undergo reductive elimination of CMe4 via trans to cis isomerization to generate the 16e reactive intermediates Cp*W(NO)(L) (cf. Scheme 1). These intermediates can then effect one of two types of C−H activation. They can intramolecularly activate a C−H bond of L to form cis complexes of type B in Scheme 3 that may or may not be converted to their thermodynamically more stable trans isomers C. Alternatively, they can effect the intermolecular C−H activation of an incoming substrate, R-H, to form cis complexes of type D in Scheme 3 that again may or may not isomerize to their E forms. One final point involving the trans to cis isomerizations of complexes A merits mention. These isomerizations are probably facilitated by the initial loss of L from the metals’ coordination spheres, a process that can result in some decomposition of the organometallic reactants and/or some formation of the Cp*W(NO)(L)2 complexes designated as F in Scheme 3. As outlined in detail in the following paragraphs, the nature of L determines just which transformations are dominant for a particular trans-Cp*W(NO)(CH2CMe3)(H)(L) complex. L = PMe3. This proligand is a relatively small and strong Lewis base, having a Tolman cone angle7 of 118° and a pKa of 8.65.8 Nevertheless, our efforts to extend the C−H activation chemistry of trans-Cp*W(NO)(CH2CMe3)(H)(PMe3) beyond that reported previously3 have been unsuccessful to date. Thus, thermolyses of the complex in n-pentane under various conditions do not afford cis-Cp*W(NO)(C5H11)(H)(PMe3) but rather produce the disproportionation product Cp*W(NO)(PMe3)2 (i.e., F in Scheme 3) as the only tractable organometallic complex. Because cis-Cp*W(NO)(CH2SiMe3)(H)(PMe3) can be prepared in this manner by C(sp3)−H bond activation of Me4Si by trans-Cp*W(NO)(CH2CMe3)(H)(PMe3),3 it appears that the failure of n-pentane to produce a similar product is probably a manifestation of the thermal instability of cis-Cp*W(NO)(C5H11)(H)(PMe3). L = PPh3. PPh3, with a Tolman cone angle7 of 145° and a pKa of 2.73,8 as a Lewis base is larger and weaker than PMe3 is. The overnight reaction at ambient temperatures of Cp*W(NO)(CH2CMe3)2 in n-pentane with PPh3 under 1 atm of H2 results in a complete conversion of the starting material to the known5 cis-Cp*W(NO)(H)(κ2-PPh2C6H4) (i.e., B in Scheme 3). It has also been previously reported that thermolysis of cisCp*W(NO)(H)(κ2-PPh2C6H4) in benzene at 50 °C for 24 h affords the hydrido phenyl complex cis-Cp*W(NO)(H)(Ph)(PPh3) (i.e., D in Scheme 3).6 We have now discovered that overnight thermolysis of cis-Cp*W(NO)(H)(κ2-PPh2C6H4) in n-pentane at 80 °C results in it isomerizing to transCp*W(NO)(H)(κ2-PPh2C6H4) (i.e., C in Scheme 3) with no concomitant C−H activation of n-pentane. The cis and trans isomers of this and related complexes discussed later in this Article are readily distinguishable by the 2JHP or 2JPH coupling constants evident in their 1H or 31P NMR spectra, respectively. The trans isomers in which the phosphorus-containing and hydrido ligands are cis to one another invariably exhibit 2JHP or 2 JPH values significantly larger than those of their cis counterparts. The effect of replacing the Cp* ligand with the η5-C5H4iPr group on the chemistry of the PPh3 system has also been investigated because we have previously demonstrated that such a substitution in other Cp*W(NO)-containing complexes causes them to initiate C−H activations at a markedly faster

form the 16e Cp*W(NO)(PMe3) intermediate. Subsequent intermolecular oxidative addition of the incoming C6H6 substrate to this coordinatively unsaturated intermediate produces the final cis hydrido phenyl complex. In a complementary manner, exposure of Cp*W(NO)(CH2SiMe3)2 to H2 in the presence of PPh3 affords the orthometalated complex cis-Cp*W(NO)(H)(κ2-PPh2C6H4)4 [probably via cis-Cp*W(NO)(CH2SiMe3)(H)(PPh3)]5 that also effects the intermolecular activation of benzene via the Cp*W(NO)(PPh3) intermediate complex (Scheme 2).6 Scheme 2. Formation of cis-Cp*W(NO)(H)[κ2-PPh2C6H4] and Its Activation of C6H6

The chemistry summarized in Schemes 1 and 2 has been extended previously to include only Cp*W(NO)(CH2CMe3)2 as the initial organometallic reactant and SiMe4 as a substrate that has been activated.3 It therefore appeared to us that this class of dialkyl compounds presented an excellent opportunity to investigate the effects of a variety of Lewis bases on the C−H activating abilities of the Cp*W(NO)(L) intermediate complexes and to extend these studies to encompass the activation and possible functionalization of a range of C(sp2)− H and C(sp3)−H bonds. This Article reports the results of our investigations in this regard that originated with Cp*W(NO)(CH2CMe3)2.

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RESULTS AND DISCUSSION The thermal chemistry of the various trans-Cp*W(NO)(CH2CMe3)(H)(L) complexes established during this study is summarized in Scheme 3 in which fully characterized Scheme 3. Summary of the Thermal Chemistry of transCp*W(NO)(CH2CMe3)(H)(L) Complexes [[W]* = Cp*W(NO)]

complexes are designated by uppercase letters and the one invoked intermediate is enclosed in square brackets. All the compounds result from the treatment of Cp*W(NO)(CH2CMe3)2 in n-pentane with H2 (∼1 atm) in the presence of a Lewis base, L. In some cases, prolonged reaction times result in the production of trans-Cp*W(NO)(H)2(L). Some of 574

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Figure 1. 1H NMR spectra of trans-(η5-C5H4iPr)W(NO)(H)(κ2-PPh2C6H4) and trans-Cp*W(NO)(H)(κ2-PPh2C6H4) in the hydride region.

rate.9 In this system, however, this is not the case. Thus, the reaction of (η5-C5H4iPr)W(NO)(CH2CMe3)2 with PPh3 and H2 under experimental conditions identical to those employed for the Cp* analogue (vide supra) results not in the preparation of the expected cis-(η5-C5H4iPr)W(NO)(H)(κ2-PPh2C6H4) (i.e., B in Scheme 3) but rather in the exclusive formation of trans-(η 5 -C 5H 4 i Pr)W(NO)(H)(κ 2 -PPh 2 C 6 H 4 ) (i.e., C in Scheme 3). This latter complex has been fully characterized both in solution and in the solid state. As expected, its 1H and 31 P NMR spectra in C6D6 closely resemble those exhibited by trans-Cp*W(NO)(H)(κ2-PPh2C6H4) (Figure 1). While the conversion from the cis to the trans isomer in the Cp* system occurs upon thermolysis at 80 °C, in the case of η5-C5H4iPr this transformation occurs readily at room temperature, and there is no evidence of the cis isomer being present in the final reaction mixture. In other words, replacement of Cp* with the η5C5H4iPr ligand in this system enhances the rate of cis to trans isomerization (i.e., B to C in Scheme 3) rather than facilitating intermolecular C−H activations by the cis isomer. Recrystallization of trans-(η 5 -C 5 H 4 i Pr)W(NO)(H)(κ 2 PPh2C6H4) from CH2Cl2/hexanes at −30 °C affords yellow crystals suitable for a single-crystal X-ray diffraction analysis, the results of which are shown in Figure 2. The complex is a fourlegged piano-stool molecule capped by a η5-C5H4iPr ligand with the hydride ligand situated cis to the phosphorus atom. The nitrosyl ligand is linear, and the W(1)−P(1) bond length is similar to those found in related molecules.10 The complex trans-(η5-C5H4iPr)W(NO)(H)(κ2-PPh2C6H4) is an air- and moisture-stable solid that is also quite thermally stable. For instance, heating of a C6D6 solution of the complex at 80 °C for several days results in only minimal decomposition of the organometallic complex and no activation of the solvent as determined by NMR spectroscopy. L = P(OMe)3. P(OMe)3, with a Tolman cone angle7 of 107° and a pKa of 2.60,8 is comparable in size to PMe3 but as a Lewis base is weaker than its trimethyl analogue. It was chosen for this study to contrast how a phosphite ligand affects the chemical properties of the complexes of interest in comparison to the phosphine complexes described in the preceding paragraphs. As expected, reaction of Cp*W(NO)(CH2CMe3)2 with 1.1 equiv of P(OMe)3 under a dihydrogen atmosphere (1 atm) in npentane results in the conversion of the starting material into trans-Cp*W(NO)(CH 2 CMe 3 )(H)(P(OMe)3 ) (i.e., A in Scheme 3), which can be readily purified by column chromatography on basic alumina. The complex is a forest-

Figure 2. Solid-state molecular structure of trans-(η5-C5H4iPr)W(NO)(H)(κ2-PPh2C6H4) with 50% probability thermal ellipsoids. Some hydrogen atoms have been omitted for the sake of clarity. Selected bond lengths (angstroms) and angles (degrees): W(1)− H(1A) = 1.64(2), W(1)−P(1) = 2.4892(5), W(1)−C(9) = 2.2134(18), P(1)−C(14) = 1.7870(19), P(1)−C(15) = 1.823(2), P(1)−C(21) = 1.8124(19), W(1)−N(1) = 1.7837(17), N(1)−O(1) = 1.226(2), C(9)−C(14) = 1.406(3), W(1)−N(1)−O(1) = 173.21(14), C(9)−W(1)−P(1) = 62.34(5), W(1)−C(9)−C(14) = 110.52(13), P(1)−C(14)−C(9) = 99.27(13), and W(1)−P(1)−C(14) = 87.87(6).

green solid, and its 1H NMR spectrum in C6D6 (Figure 3) exhibits a hydride signal that is an apparent doublet of triplets with 183W satellites reflecting coupling to phosphorus and the two inequivalent methylene protons of the neopentyl ligand (Figure 3). Similar spectral features have been reported previously for related hydrido complexes.10 A single-crystal X-ray crystallographic analysis has established the solid-state molecular structure of trans-Cp*W(NO)(CH2CMe3)(H)(P(OMe)3) (Figure 4). As anticipated, the complex is a four-legged piano-stool molecule having an essentially linear NO ligand [W(1)−N(1)−O(1) = 170.9(9)°]. Even though the hydride ligand was not located, the analysis has revealed a “vacant” coordination slot between the phosphite and nitrosyl ligands at which it probably coordinates to the tungsten center. As evidenced by the diagnostic hydride signals in the 1H NMR spectra of the final reaction mixtures, thermolyses of 575

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Scheme 4. Thermolyses of transCp*W(NO)(CH2CMe3)(H)(P(OMe)3) in C6H6 and Me4Si

product results from an Arbuzov-like rearrangement that probably occurs in the manner shown in Scheme 5. Initial

Figure 3. 1H NMR spectra of trans-Cp*W(NO)(CH2CMe3)(H)(P(OMe)3) in the hydride region.

Scheme 5. Arbuzov-like Rearrangement of transCp*W(NO)(CH2CMe3)(H)(P(OMe)3)

Figure 4. Solid-state molecular structure of trans-Cp*W(NO)(CH2CMe3)(H)(P(OMe)3) with 50% probability thermal ellipsoids. Hydrogen atoms have been omitted for the sake of clarity. Selected bond lengths (angstroms) and angles (degrees): W(1)−C(11) = 2.250(11), W(1)−N(1) = 1.782(10), W(1)−P(1) = 2.426(3), N(1)− O(1) = 1.227(13), P(1)−O(2) = 1.596(8), P(1)−O(3) = 1.607(8), P(1)−O(4) = 1.585(8), O(2)−C(16) = 1.433(14), O(3)−C(17) = 1.423(14), O(4)−C(18) = 1.441(14), W(1)−N(1)−O(1) = 170.9(9), N(1)−W(1)−C(11) = 94.8(4), C(11)−W(1)−P(1) = 81.4(3), and P(1)−W(1)−N(1) = 103.2(3).

reductive elimination of CMe4 from the cis form of the complex followed by the intramolecular oxidative addition of an O−Me bond to the tungsten center results in the formation of 16e Cp*W(NO)(Me)(P(O)(OMe)2) that then dimerizes so that the tungsten centers can attain the favored 18e configuration. Most interestingly, the product of this rearrangement is unlike those of previously reported Arbuzov rearrangements in that both the Me group and the resulting phosphonate ligand remain attached to the same metal center.11−16 When the thermolysis of trans-Cp*W(NO)(CH2CMe3)(H)(P(OMe)3) is conducted in n-pentane, [Cp*W(NO)(Me)(PO(OMe)2)]2 deposits as a yellow precipitate. Recrystallization of this precipitate from Et2O/THF has afforded single crystals suitable for an X-ray diffraction analysis. The complex crystallizes as a pseudomerohedral twin; the solid-state molecular structure of one of the twins is shown in Figure 5. The structure of the other twin is quite similar to that depicted in Figure 5, differing only slightly in the orientations of its Cp*

trans-Cp*W(NO)(CH2CMe3)(H)(P(OMe)3) in C6H6 or Me4Si do result in some single C−H activations of the solvents to form trans complexes (i.e., E in Scheme 3). Both signals are upfield of TMS, display coupling to phosphorus, and have 183W satellites (cf. Figure S1).10 In addition, the benzene activation occurs more readily than does tetramethylsilane activation. However, all attempts to isolate the organometallic products of these activations (shown in Scheme 4) have been unsuccessful to date, primarily because the major product of these reactions is the one resulting from trans-Cp*W(NO)(CH2CMe3)(H)(P(OMe)3) undergoing an Arbuzov-type rearrangement.11 Dissolution of trans-Cp*W(NO)(CH 2 CMe 3 )(H)(P(OMe)3) in benzene, n-pentane, or tetramethylsilane results in it being converted mainly into [Cp*W(NO)(Me)(PO(OMe)2)]2, slowly at room temperature and more rapidly at higher temperatures. The [Cp*W(NO)(Me)(PO(OMe)2)]2 576

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Figure 5. Solid-state molecular structure of one of the “boat” isomers of [Cp*W(NO)(Me)(PO(OMe)2]2 with 50% probability thermal ellipsoids. Hydrogen atoms have been omitted for the sake of clarity. Selected bond lengths (angstroms) and angles (degrees): W(1)−N(1) = 1.997(12), W(1)−C(21) = 2.051(4), W(1)−O(2) = 2.126(17), W(1)−P(1) = 2.490(7), N(1)−O(1) = 1.273(14), P(1)−O(6) = 1.51(2), W(2)−N(2) = 1.897(12), W(2)−C(24) = 2.060(6), W(2)− O(6) = 2.24(2), W(2)−P(2) = 2.692(7), N(2)−O(5) = 1.223(14), P(2)−O(2) = 1.576(18), W(1)−N(1)−O(1) = 169(2), and W(2)− N(2)−O(5) = 160.2(18).

Figure 6. Solid-state molecular structure of trans-Cp*W(NO)(CH2CMe3)(H)(P(OCH2)3CMe) with 50% probability thermal ellipsoids. Most hydrogen atoms have been omitted for the sake of clarity. Selected bond lengths (angstroms) and angles (degrees): W(1)−C(11) = 2.2654(18), W(1)−N(1) = 1.7886(17), W(1)−P(1) = 2.4138(5), N(1)−O(1) = 1.219(2), P(1)−O(2) = 1.6141(14), P(1)−O(3) = 1.6063(14), P(1)−O(4) = 1.6138(14), O(2)−C(16) = 1.457(2), O(3)−C(17) = 1.462(2), O(4)−C(18) = 1.452(2), W(1)− H(1) = 1.59(2), W(1)−N(1)−O(1) = 171.37(15), N(1)−W(1)− C(11) = 95.95(7), C(11)−W(1)−P(1) = 81.39(5), and P(1)−W(1)− N(1) = 99.05(6).

ligands. The principal structural feature of these two molecular structures is the central W2P2O2 six-membered ring that exists in a boat conformation. When the thermolysis of trans-Cp*W(NO)(CH2CMe3)(H)(P(OMe)3) is conducted in Me4Si, [Cp*W(NO)(Me)(PO(OMe)2)]2 is deposited as a mixture of two isomers, one of which is the boat isomer (cf. Figure 5). Because the two isomers in C6D6 exhibit similar 1H NMR spectra, the molecular structure of the other isomer is probably one having the central W2P2O2 ring in a chair conformation. Monitoring of all the thermolyses of trans-Cp*W(NO)(CH2CMe3)(H)(P(OMe)3) by 1H NMR spectroscopy indicates that the boat conformer is always formed in smaller amounts. However, because it is less soluble than the chair conformer, it constitutes a larger percentage of the precipitates formed. Nevertheless, there is no evidence of the two isomers of [Cp*W(NO)(Me)(PO(OMe)2)]2 interconverting in solution. L = P(OCH2)3CMe. This proligand, with a Tolman cone angle7 of 101° and a pKa probably similar to that of P(OMe)3, closely resembles P(OMe)3 in its steric and electronic properties. Hence, it was chosen for investigation with the expectation that trans-Cp*W(NO)(CH 2 CMe 3 )(H)(P(OCH2)3CMe) would exhibit C−H activation chemistry similar to that of its P(OMe)3 analogue but would not undergo an Arbuzov-like rearrangement upon thermolysis. The desired hydrido neopentyl complex deposits as a yellow precipitate in reasonable yield when an n-pentane solution of Cp*W(NO)(CH2CMe3)2 is treated with H2 in the presence of P(OCH2)3CMe. Recrystallization of this precipitate from Et2O at −30 °C produces yellow prisms of trans-Cp*W(NO)(CH2CMe3)(H)(P(OCH2)3CMe) as its monoether solvate suitable for an X-ray crystallographic analysis. The solid-state molecular structure of this complex as it occurs in these crystals is shown in Figure 6. Not surprisingly, the metrical parameters defining the tungsten atom’s coordination sphere in this structure closely resemble those extant in the structure of transCp*W(NO)(CH2CMe3)(H)(P(OMe)3) (Figure 4). As shown in Scheme 6, thermolysis of a benzene solution of trans-Cp*W(NO)(CH2CMe3)(H)(P(OCH2)3CMe) at 50 °C

overnight results in the formation of the product resulting from the C−H activation of the solvent, namely trans-Cp*W(NO)(C6H5)(H)(P(OCH2)3CMe) (i.e., E in Scheme 3), as well as the product resulting from the disproportionation of the original reactant, namely Cp*W(NO)(P(OCH2)3CMe)2 (i.e., F in Scheme 3). The thermolysis is also accompanied by the formation of considerable amounts of intractable decomposition products. Consequently, replacement of P(OMe)3 in the tungsten’s coordination sphere with P(OCH2)3CMe does not produce more beneficial C−H activation results (cf. Scheme 4). L = P(OPh)3. P(OPh)3 has a Tolman cone angle7 of 128° and a pKa of −2.008 and thus has steric properties intermediate between those of P(OMe)3 and PPh3 but differs from them in its ability to function as a pure σ donor. It was hoped that incorporation of a P(OPh)3 ligand into the tungsten’s coordination sphere would result in the complex favoring intermolecular C−H activations rather than the intermolecular activations exhibited by the analogous PPh3 compound (vide supra). As with the other Lewis bases that have been studied, reaction of Cp*W(NO)(CH2CMe3)2 in n-pentane with 1.2 equiv of P(OPh)3 under 1 atm of H2 at ambient temperatures affords yellow trans-Cp*W(NO)(CH2CMe3)(H)(P(OPh)3) as the major product in the reaction mixture after 1 h. The hydride resonance in the 1H NMR spectrum of transCp*W(NO)(CH2CMe3)(H)(P(OPh)3) in C6D6 exhibits a large 2JPH coupling constant of 117.4 Hz indicative of the organometallic complex existing in a trans configuration. This fact agrees with similar observations found for the other Lewis base systems reported in this Article. No evidence of the formation of the cis isomer of this complex has been found. The solid-state molecular structure of trans-Cp*W(NO)(CH2CMe3)(H)(P(OPh)3) is shown in Figure 7, and it is a Cp*-capped four-legged piano stool whose intramolecular dimensions are again quite comparable to those extant in the structure of trans-Cp*W(NO)(CH2CMe3)(H)(P(OMe)3) (Figure 4). Thermolysis of trans-Cp*W(NO)(CH 2 CMe 3 )(H)(P(OPh)3) at 50 °C for 1 h in n-pentane results in the evolution of neopentane and the subsequent decomposition of the 577

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Inorganic Chemistry Scheme 6. Thermolysis of trans-Cp*W(NO)(CH2CMe3)(H)(P(OCH2)3CMe) in C6H6

such transformations include (1) the isomerization of active cisCp*W(NO)(H)(κ2-PPh2C6H4) to inactive trans-Cp*W(NO)(H)(κ2-PPh2C6H4) when L = PPh3, (2) the disproportionation of trans-Cp*W(NO)(CH2CMe3)(H)(L) to Cp*W(NO)(L)2 especially at higher temperatures [e.g., L = PMe3 and P(OCH2)3CMe], and (3) the intramolecular rearrangement of L [e.g., L = P(OMe)3]. Future investigations with this family of trans-Cp*W(NO)(CH2CMe3)(H)(L) compounds will be directed at identifying L’s that provide more thermally stable molecular scaffolds that favor the desired C−H activations and subsequent functionalizations.

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EXPERIMENTAL SECTION

General Methods. All reactions and subsequent manipulations involving organometallic reagents were performed under anhydrous and anaerobic conditions except where noted. All inert gases were purified by being passed through a column containing MnO and then through a column of activated 4 Å molecular sieves. High-vacuum and inert-atmosphere techniques were performed using double-manifold lines or in Innovative Technologies LabMaster 100 and MS-130 BG dual-station gloveboxes equipped with freezers maintained at −30 °C. Preparative scale reactions were performed with Schlenk or roundbottom flasks; reactions were performed in thick-walled glass reaction flasks (larger scale) or J. Young NMR tubes (smaller scale), both of which were typically sealed with Kontes greaseless stopcocks. THF was dried over sodium/benzophenone ketyl and freshly distilled prior to use; all other solvents were dried according to standard procedures.17 All binary magnesium reagents used were prepared from the corresponding Grignard reagents.18 Complexes Cp*W(NO)Cl2,19 Cp*W(NO)(CH2CMe3)2,20 and (η5-C5H4iPr)W(NO)I29 and the proligand P(OCH2)3CMe21 were prepared according to the published procedures. Pentamethylcyclopentadiene was obtained from the Boulder Scientific Co. All other chemicals and reagents were ordered from commercial suppliers and used as received. Unless otherwise specified, all IR samples were prepared as Nujol mulls sandwiched between NaCl plates, and their spectra were recorded on a Thermo Nicolet model 4700 FT-IR spectrometer. Except where noted, all NMR spectra were recorded at room temperature on Bruker AV-300 and AV-400 instruments (direct and indirect probes), and all chemical shifts are reported in parts per million and coupling constants in hertz. 1H NMR spectra were referenced to the residual protio isotopomer present in C6D6 (7.16 ppm). 13C NMR spectra were referenced to C6D6 (128.39 ppm). 31P NMR spectra were externally referenced to 85% H3PO4. For the characterization of most complexes, two-dimensional NMR experiments, {1H−1H} COSY, {1H−13C} HSQC, {1H−31P} HMBC, and {1H−13C} HMBC, were performed to correlate and assign 1H, 13C, and 31P NMR signals and establish atom connectivity. Low- and highresolution mass spectra (EI, 70 eV) and MALDI-TOF spectra were recorded by M. Lapawa of the University of British Columbia (UBC) mass spectrometry facility using a Kratos MS-50 spectrometer and a Bruker Autoflex spectrometer, respectively. M. Yung recorded ESI mass spectra on a Bruker HCT spectrometer, and elemental analyses were performed by D. Smith of the UBC microanalytical facility. X-ray crystallographic data collection, solution, and refinement were performed at the UBC X-ray crystallography facility.

Figure 7. Solid-state molecular structure of trans-Cp*W(NO)(CH2CMe3)(H)(P(OPh)3) with 50% probability thermal ellipsoids. Hydrogen atoms have been omitted for the sake of clarity. Selected bond lengths (angstroms) and angles (degrees): W(1)−N(1) = 1.783(3), W(1)−P(1) = 2.4216(9), W(1)−C(11) = 2.274(4), N(1)− O(1) = 1.225(4), P(1)−O(2) = 1.611(3), P(1)−O(3) = 1.611(3), P(1)−O(4) = 1.626(3), W(1)−N(1)−O(1) = 169.9(3), N(1)− W(1)−C(11) = 94.77(14), C(11)−N(1)−P(1) = 82.55(9), and N(1)−W(1)−P(1) = 95.43(10).

remaining organometallic fragment. Even in solution at ambient temperatures, the complex slowly evolves neopentane and decomposes into intractable products. Interestingly, when allowed to proceed for 22 h rather than just 1 h, the reaction of Cp*W(NO)(CH2CMe3)2 with P(OPh)3 and H2 results in the formation of trans-Cp*W(NO)(H)2(P(OPh)3). This complex probably is formed via further hydrogenation of the initially produced trans-Cp*W(NO)(CH2CMe3)(H)(P(OPh)3). The hydride resonance in the 1H NMR spectrum of the dihydrido complex in C6D6 exhibits a 2JPH of 85.9 Hz, reflecting the fact that the hydride ligands are trans to one another. Consistently, in the 1H{31P} NMR spectrum of this compound, the hydride resonance is a sharp singlet of relative intensity 2 with 183W satellites.

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EPILOGUE This study has demonstrated that some, but not all, of the structurally similar Cp′W(NO)(CH2CMe3)(H)(L) complexes (Cp′ = Cp* or η5-C5H4iPr) that have been investigated can effect inter- and/or intramolecular activations of some hydrocarbon C(sp2)−H and C(sp3)−H bonds under relatively gentle conditions. However, attempts to extend this activation chemistry to encompass linear alkanes such as n-pentane have not been successful. The activations are also accompanied by various side reactions that are primarily reflective of the steric and electronic properties of L that determine its tendency to dissociate from the tungsten’s coordination sphere. Examples of 578

DOI: 10.1021/acs.inorgchem.6b02431 Inorg. Chem. 2017, 56, 573−582

Article

Inorganic Chemistry Preparation of cis-Cp*W(NO)(H)(κ2-PPh2(C6H4)). In a glovebox, a thick-walled flask with a Kontes greaseless stopcock was charged with Cp*W(NO)(CH2CMe3)2 (0.495 g, 1.010 mmol) and a magnetic stir bar. The flask was charged with PPh3 (0.320 g, 1.220 mmol) and npentane (∼50 mL) to obtain a dark red solution. H2 was bubbled through the reaction mixture for 5 min, and the flask was then sealed under 1 atm of H2. The reaction mixture was stirred at room temperature overnight, whereupon it developed a green color, and a yellow precipitate was deposited. The solvent was removed from the final reaction mixture by cannulation, and the remaining precipitate was washed with n-pentane (10 × 10 mL) before being dried in vacuo to yield cis-Cp*W(NO)(H)(κ2-PPh2(C6H4)) as a yellow solid (0.249 g, 40% yield).

H), 7.94 (m, 2H, aryl H). 13C NMR (100 MHz, C6D6): δ 11.1 (s, C5Me5), 106.1 (s, C5Me5), 125.4 (d, JCP = 8.3, aryl C), 129.9 (d, JCP = 9.2, aryl C), 129.2 (aryl C), 130.0 (d, 3JCP = 1.8, m-aryl C), 131.2 (d, 3 JCP = 2.8, m-aryl C), 132.2 (d, 4JCP = 4.6, p-aryl C), 132.65 (d, JCP = 10.1, aryl C), 134.2 (d, 1JCP = 41.4, ipso-aryl C), 135.2 (d, JCP = 11.9, aryl C), 139.1 (d, 2JCP = 27.6, o-aryl C), 151.5 (s, ipso-aryl C), 167.8 (d, 1 JCP = 14.7, ipso-aryl C). 31P NMR (162 MHz, C6D6): δ −39.5 (1JPW = 148.5, C6H4PPh2). Preparation of (η5-C5H4iPr)W(NO)(CH2CMe3)2. In a glovebox, two Schlenk flasks were charged with (η5-C5H4iPr)W(NO)I2 (5.062 g, 8.806 mmol) and Mg(CH2CMe3)2 (titer of 179 g/mol, 3.158 g, 17.64 mmol). Et2O (150 mL) was cannulated into both flasks that were then placed into a dry ice/acetone bath at −78 °C. The contents of the second Schlenk flask containing the binary magnesium reagent were slowly cannulated into the Schlenk flask containing (η5-C5H4iPr)W(NO)I2. Upon addition, the color of the reaction mixture changed from dark green to light red. The reaction Schlenk flask was removed from the dry ice/acetone bath and left to warm to room temperature for 20 min while its contents were being stirred. The volume of the reaction mixture was then reduced in vacuo and transferred to the top of a basic alumina column (4 cm × 2 cm). Elution of the column with Et2O as an eluant produced a bright red band that was collected. Removal of the solvent from the eluate in vacuo afforded (η5C5H4iPr)W(NO)(CH2CMe3)2 as a red solid (0.985 g, 24% yield). Characterization data for (η5-C5H4iPr)W(NO)(CH2CMe3)2. IR (cm−1): 1594 (s, υNO). MS (LREI, m/z, probe temperature of 150 °C): 463 [M+, 184W]. HRMS-EI m/z: [M+, 182W] calcd for C18H33NO182W, 461.20444; found, 461.20414. 1H NMR (400 MHz, C6D6): δ −1.43 (d, 2JHH = 11.9, 2H, CH2CMe3), 0.96 (d,3JHH = 6.9, 6H, iPr CH3), 1.34 (s, 18H, CH2CMe3), 2.49 (sept, 3JHH = 6.9, 1H, iPr CH), 3.80 (d, 2JHH = 11.9, 2H, CH2CMe3), 5.08 [s, 4H, C5H4(iPr)]. 13 C APT NMR (100 MHz, C6D6): δ 23.7 (iPr CH3), 27.6 (iPr CH), 34.7 (CH2CMe3), 39.8 (CH2CMe3), 92.8 (CH2CMe3), 100.5 [C5H4(iPr)], 102.3 [C5H4(iPr)], 122.9 [ipso-C5H4(iPr)]. Preparation of trans-(η5-C5H4iPr)W(NO)(H)(κ2-PPh2C6H4). In a glovebox, a thick-walled flask equipped with a Kontes stopcock was loaded with (η5-C5H4iPr)W(NO)(CH2CMe3)2 (0.200 g, 0.432 mmol), PPh3 (0.118 g, 0.450 mmol), and n-pentane (20 mL) to produce a burgundy-colored solution. The reaction vessel was then charged with H2 (1 atm), and the contents were stirred for 16 h at room temperature, whereupon the color of the reaction mixture changed to brown and a light yellow precipitate formed. The solvent was removed from the final mixture in vacuo to yield a yellow solid that was purified by column chromatography using a flash silica support. A yellow band was eluted from the column with a 20:80 mixture of ethyl acetate and hexanes, and removal of the solvent from the eluate in vacuo afforded trans-(η5-C5H4iPr)W(NO)(H)(κ2-PPh2C6H4) as an analytically pure, bright yellow solid (0.081 g, 32% yield). Recrystallization of this solid from a 50:50 mixture of CH2Cl2 and hexanes at −30 °C for 1 week produced yellow crystals suitable for a single-crystal X-ray diffraction analysis.

Characterization data for cis-Cp*W(NO)(H)(κ2-PPh2(C6H4)). IR (cm−1): 1595 (s, υNO). 1H NMR (400 MHz, C6D6): δ 1.79 (s, 15H, C5Me5), 4.00 (d, 1JHW = 101.1, 2JHP = 10.8, 1H, W-H), 7.49 (t, 2JHH = 8.2, 1H, aryl H), 7.85 (m, 1H, aryl H), 7.95 (m, 2H, aryl H), 8.09 (d, 2 JHH = 7.2, 1H, aryl H). 31P{1H} NMR (162 MHz, C6D6): δ −48.58 (s, 1 JPW = 168.4, W-P). These data match previously reported spectroscopic data.5 Isomerization of cis-Cp*W(NO)(H)(κ2-PPh2(C6H4)). In a glovebox, a thick-walled flask with a Kontes greaseless stopcock was charged with cis-Cp*W(NO)(H)(κ2-PPh2(C6H4)) (0.064 g, 0.100 mmol), npentane (∼20 mL), and a magnetic stir bar to produce a dark yellow solution. The stirred reaction mixture was heated overnight at 80 °C, whereupon it became yellow-brown in color. The solvent was removed from the final reaction mixture in vacuo to produce a yellow solid whose 1H NMR spectrum in benzene-d6 showed it to consist of a 3:1 trans:cis mixture of isomers of Cp*W(NO)(H)(κ2-PPh2(C6H4)). An authentic sample of trans-Cp*W(NO)(H)(κ2-PPh2(C6H4)) was subsequently synthesized and isolated as described in the following paragraph. Preparation of trans-Cp*W(NO)(H)(κ2-PPh2C6H4). In a glovebox, a thick-walled flask equipped with a Kontes stopcock was loaded with Cp*W(NO)(η3-CH2CHCMe2)(Ph) (0.095 g, 0.192 mmol), benzene-d6 (∼5 mL), and an excess of PPh3 (0.059 g, 0.225 mmol) to produce a yellow mixture. The reaction flask was sealed, and its contents were heated for 8 days in an ethylene glycol bath at 70 °C, during which time the color of the solution changed to dark brown. Removal of solvent in vacuo produced a dark brown oil that was dissolved in a 1:1 Et2O/n-pentane mixture, and the solution was maintained at −30 °C for 14 h to induce the deposition of a light orange precipitate (0.046 g). The precipitate was removed by filtration, and the brown filtrate was left at room temperature for 10 min, whereupon a light yellow precipitate identified as trans-Cp*W(NO)(H)(κ2-PPh2C6H4) (0.008 g, 7%) was deposited.

Characterization data for trans-(η5 -C 5 H4 iPr)W(NO)(H)(κ2 PPh2C6H4). IR (cm−1): 1880 (w, νWH), 1579 (s, νNO). MS (LREI, m/z, probe temperature of 150 °C): 583 [M+, 184W], 553 [M+ − NO, 184 W]. 1H NMR (400 MHz, C6D6): δ 1.07 (d, 3JHH = 6.9, 3H, iPr CH3), 1.05 (d, 3JHH = 6.9, 3H, iPr CH3), 2.27 (d, 2JHP = 70.62, 1JHW = 58.3, WH), 2.64 (sept, 3JHH = 6.9, 1H, iPr CH), 4.80 (dd, 3JHH = 2.9, 1H, C5H4iPr), 5.06 (dd, 3JHH = 2.9, 1H, C5H4iPr), 5.26 (m, 1H, C5H4iPr), 5.44 (m, 1H, C5H4iPr), 6.94 (m, 1H, aryl H), 6.94 (m, 1H, m-aryl H), 7.01 (m, 5H, aryl H), 7.01 (m, 1H, m-aryl H), 7.27 (t, 3JHH = 7.4, p-aryl H), 7.52 (m, 2H, aryl H), 7.69 (dd, 3JHH = 7.4, 3JHP = 2.7, o-aryl H), 7.94 (dd, 3JHH = 7.0, 3JHP = 1.37, 2H, aryl H). 13C APT

Characterization data for trans-Cp*W(NO)(H)(κ2-PPh2C6H4). IR (cm−1): 1552 (s, υNO). MS (LREI, m/z, probe temperature of 150 °C): 611 [M+, 184W]. HR-MALDI-TOF (LDI, m/z): [M+, 184W] calcd for C28H30NOP184W, 611.15746; found, 611.15796. 1H NMR (400 MHz, C6D6): δ 1.75 (s, 15H, C5Me5), 2.29 (d, 2JHP = 70.4, 1JHW = 61.1, 1H, WH), 6.88 (m, 1H, aryl H), 6.93 (m, 1H, m-aryl H), 6.98−7.04 (m, 5H, aryl H), 7.01 (m, 1H, m-aryl H), 7.31 (t, 1H, 3JHH = 7.4, p-aryl H), 7.39 (m, 2H, aryl H), 7.79 (dd, 1H, 3JHH = 7.8, 3JHP = 3.1, o-aryl 579

DOI: 10.1021/acs.inorgchem.6b02431 Inorg. Chem. 2017, 56, 573−582

Article

Inorganic Chemistry NMR (100 MHz, C6D6): δ 23.9 (iPr CH3), 24.3 (iPr CH3), 28.2 (iPr CH), 91.3 (C5H4iPr), 91.7 (C5H4iPr), 95.3 (C5H4iPr), 97.9 (C5H4iPr), 123.8 (ipso-C5H4iPr), 129.1 (d, JCP = 9.6, aryl C), 129.2 (d, JCP = 9.6, aryl C), 129.4 (aryl C), 130.5 (d, 3JCP = 2.02, m-aryl C), 131.2 (m-aryl C), 132.1 (d, 4JCP = 4.6, p-aryl C), 132.8 (d, JCP = 10.6, aryl C), 133.7 (d, 1JCP = 41.9, ipso-aryl C), 134.4 (d, JCP = 11.6, aryl C), 134.7 (d, 1JCP = 39.4, ipso-aryl C), 140.1 (d, 2JCP = 27.3, o-aryl C), 152.5 (d, 1JCP = 50.0, ipso-aryl C), 160.4 (d, 2JCP = 17.7, ipso-aryl C). 31P{1H} NMR (162 MHz, C6D6): δ −41.65 (1JPW = 157.5). 31P NMR (162 MHz, C6D6): δ −41.65 (d, 2JPH = 71.9). Anal. Calcd for C26H26NOPW: C, 53.54; H, 4.49; N, 2.40. Found: C, 53.66; H, 4.50; N, 2.30. Preparation of trans-Cp*W(NO)(CH2CMe3)(H)(P(OMe)3). In a glovebox, Cp*W(NO)(CH2CMe3)2 (0.536 g, 1.091 mmol) and a stir bar were added to a thick-walled flask that was sealed with a Kontes greaseless stopcock and connected to a double manifold. n-Pentane (∼50 mL) and P(OMe)3 (0.13 mL, 1.10 mmol) were added to the flask, and the reaction mixture was stirred while H2 was bubbled through the solution for 2 h before the flask was sealed under a H2 atmosphere. The mixture was stirred at room temperature for an additional 20 h, whereupon the color of the solution changed from an initial wine red to a navy blue. The final mixture was cannulated on top of a basic alumina column (2 cm × 8 cm) made up in n-pentane. Elution of the column with a 20 to 100% Et2O gradient in n-pentane afforded a yellow eluate. The solvent was removed from the eluate in vacuo to produce trans-Cp*W(NO)(CH2CMe3)(H)(P(OMe)3) as an analytically pure forest-green powder (0.428 g, 72% yield). Crystals of the complex suitable for an X-ray diffraction analysis were grown over 3 days from an Et2O/n-pentane solution maintained at −30 °C.

C APT NMR (100 MHz, C6D6): δ 9.92 (C5Me5), 28.7 (d, 2JCP = 16.0, WMe), 48.9 [d, 2JCP = 11.8, P(OMe)2], 53.4 [d, 2JCP = 3.4, P(OMe)2], 108.6 (C5Me5). 31P{1H} NMR (162 MHz, C6D6): δ 119.67 (s, 1JPW = 337.1). Anal. Calcd for C26H48N2O8P2W2: C, 33.00; H, 5.11; N, 2.96. Found: C, 33.73; H, 5.05; N, 2.82. 13

Characterization data for the chair form of [Cp*W(NO)(Me)(PO(OMe)2)]2 (34%). 1H NMR (400 MHz, C6D6): δ 0.56 (d, 3JHP = 1.8, 6H, WCH3), 1.81 (s, 30H, C5Me5), 3.34 [d, 3JHP = 10.4, 6H, P(OMe)2], 3.64 [d, 3JHP = 10.8, 6H, P(OMe)2]. 13C APT NMR (100 MHz, C6D6): δ 10.2 (C5Me5), 26.7 (d, 2JCP = 18.4, WMe), 50.3 [d, 2JCP = 11.3, P(OMe)2], 52.8 [d, 2JCP = 4.6, P(OMe)2], 109.6 (C5Me5). 31 1 P{ H} NMR (162 MHz, C6D6): δ 110.8 (s, 1JPW = 338.3). Preparation of trans-Cp*W(NO)(CH2CMe3)(H)(P(OCH2)3CMe). In a glovebox, Cp*W(NO)(CH2CMe3)2 (0.244 g, 0.497 mmol) and a stir bar were loaded into a thick-walled flask that was sealed with a Kontes greaseless stopcock and connected to a double manifold. P(OCH2)3CMe (0.08 g, 0.54 mmol) was then added; the solids were dissolved in n-pentane (∼50 mL), and the contents were sealed under a H2 atmosphere. The resulting red solution was stirred at room temperature overnight, whereupon the solution turned dark blue and a yellow precipitate formed. The precipitate was washed with n-pentane until the washes were clear and colorless, and it was then dried in vacuo to yield trans-Cp*W(NO)(CH2CMe3)(H)(P(OCH2)3CMe) as a pale yellow solid (0.183 g, 64% yield). A large yellow prismatic crystal suitable for an X-ray diffraction analysis was grown by dissolving trans-Cp*W(NO)(CH2CMe3)(H)(P(OCH2)3CMe) in a minimal amount of Et2O and then maintaining the solution undisturbed over a weekend at −30 °C.

Characterization data for trans-Cp*W(NO)(CH2CMe3)(H)(P(OMe)3). IR (cm−1): 1849 (w, υWH), 1586 (s, υNO). MS (LREI, m/ z, probe temperature of 150 °C): 545 [M+, 184W]. 1H NMR (400 MHz, C6D6): δ −2.45 (pseudo dt, 3JHH = 7.2, 2JHP = 107.8, 1JHW = 49.8, 1H, WH), 0.74 (ddd, 3JHP = 14.3, 3JHH = 7.0, 2JHH = 12.7, 2JHW = 9.0, 1H, CH2CMe3), 1.54 (s, 9H, CH2CMe3), 1.81 (overlapping m, 1H, CH2CMe3), 1.83 (s, 15H, C5Me5), 3.36 [d, 3JHP = 10.6, 9H, P(OMe)3]. 13C APT NMR (100 MHz, C6D6): δ 10.9 (C5Me5), 30.0 (d, 2JCP = 20.7, CH2CMe3), 35.4 (CH2CMe3), 38.6 (CH2CMe3), 52.8 [d, 2JCP = 6.1, P(OMe)3], 95.9 (C5Me5). 31P{1H} NMR (162 MHz, C6D6): δ 141.6 (s, 1JPW = 350.5). Anal. Calcd for C18H36NO4PW: C, 39.65; H, 6.65; N, 2.57. Found: C, 39.46; H, 6.63; N, 2.57. Thermolysis of trans-Cp*W(NO)(CH2CMe3)(H)(P(OMe)3) in Me4Si: Preparation of [Cp*W(NO)(Me)(PO(OMe)2)]2. In a glovebox, trans-Cp*W(NO)(CH2CMe3)(H)(P(OMe)3) (0.158 g, 0.290 mmol), Me4Si (∼30 mL), and a stir bar were added to a thick-walled flask. The flask was sealed with a Kontes greaseless stopcock and heated at 50 °C for 16 h, whereupon a brown precipitate formed. The precipitate was isolated by removing the supernatant solution via a pipet and drying the residue in vacuo. In this manner, [Cp*W(NO)(Me)(PO(OMe)2)]2 (0.021 g, 15% yield) was obtained as an analytically pure solid that contained both isomers of the complex. A single isomer of the complex was isolated by performing the original thermolysis in n-pentane rather than in Me4Si and collecting the yellow precipitate that deposited. X-ray quality crystals of this isomer were grown by dissolving the precipitate in a 50:50 Et2O/THF mixture and leaving the resulting solution undisturbed at −30 °C for 2 days. Characterization data for the boat form of [Cp*W(NO)(Me)(PO(OMe)2)]2 (66%). IR (cm−1): 1571 (s, υNO). ESI(+)-MS (40 V, m/z): 969.1 for C26H48N2O8P2W2 , ([M + Na] +, 184W), 931.2 for C25H45N2O8P2W2, ([M − CH3]+, 184W). 1H NMR (400 MHz, C6D6): δ 0.93 (d, 3JHP = 2.1, 6H, WCH3), 1.73 (s, 30H, C5Me5), 3.28 [d, 3JHP = 10.4, 6H, P(OMe)2], 3.80 [d, 3JHP = 10.6, 6H, P(OMe)2].

Characterization data for trans-Cp*W(NO)(CH2CMe3)(H)(P(OCH2)3CMe) (64%). IR (cm−1): 1583 (s, υNO). MALDI-TOF (dctb, m/z): 568.2 for C20H35NO4PW, ([M − H]+, 184W). 1H NMR (400 MHz, C6D6): δ −2.10 (pseudo dt, 3JHH = 7.4, 2JHP = 109.7, 1JHW = 49.3, 1H, WH), −0.36 [s, 3H, P(OCH2)3CMe], 0.82 (ddd, 3JHP = 15.2, 2JHH = 12.8, 3JHH = 7.4, 1H, CH2CMe3), 1.65 (s, 9H, CH2CMe3), 1.90 (s, 15H, C5Me5), 1.98 (ddd, 3JHP = 27.4, 2JHH = 12.8, 3JHH = 7.4, 1H, CH2CMe3), 3.47 [m, 6H, P(OCH2)3CMe]. 13C APT NMR (100 MHz, C6 D6 ): δ 11.0 (C 5Me 5 ), 15.0 [P(OCH 2 )3 CMe], 28.4 (CH 2 CMe 3 ), 32.3 [P(OCH 2 ) 3 CMe], 35.4 (CH 2 CMe 3 ), 38.8 (CH2CMe3), 75.2 [2JCP = 7.1, P(OCH2)3CMe], 105.8 (d, 2JCP = 2.1, C5Me5). 31P{1H} NMR (162 MHz, C6D6): δ 115.9 (s, 1JPW = 359.6). Anal. Calcd for C20H36NO4PW: C, 42.19; H, 6.37; N, 2.46. Found: C, 42.33; H, 6.41; N, 2.36. 580

DOI: 10.1021/acs.inorgchem.6b02431 Inorg. Chem. 2017, 56, 573−582

Article

Inorganic Chemistry Thermolysis of trans-Cp*W(NO)(CH2CMe3)(H)(P(OCH2)3CMe) in Benzene. In a glovebox, trans-Cp*W(NO)(CH2CMe3)(H)(P(OCH2)3CMe) (0.167 g, 0.293 mmol) and benzene (∼5 mL) were added to a thick-walled flask equipped with a Kontes greaseless stopcock that was then sealed. The resulting yellow solution was heated at 50 °C for 14 h, whereupon it became a very dark browngreen color. The solvent was removed in vacuo to yield a green-black solid. The solid was purified by transferring it in n-pentane to the top of a basic alumina column (1 cm × 10 cm) made up in n-pentane. The product of benzene activation, namely trans-Cp*W(NO)(C6H5)(H)(P(OCH2)3CMe), was the minor component and eluted in a yellow solution with 15% THF in Et2O. Removal of solvent from the eluate in vacuo afforded the compound as an oily yellow solid.

Characterization data for Cp*W(NO)(CH2CMe3)(H)(P(OPh)3). IR (cm−1): 1878 (vw, υWH), 1590 (s, υNO). MS (LREI, m/z, probe temperature of 150 °C): 659 [M+ − CMe4, 184W]. MS (LRESI, m/z): 731.3 [M•+, 184W]. 1H NMR (400 MHz, C6D6): δ −2.42 (ddd, 2JHP = 117.4, 1JHW = 47.2, 3JHH = 8.2, 5.4, 1H, W-H), 0.78 (ddd, 2JHH = 12.9, 3 JHP = 11.7, 3JHH = 5.3, 1H, CH2Me3), 1.59 (s, 9H, CH2CMe3), 1.60 (s, 15H, C5Me5), 2.38 (ddd, 3JHP = 33.1, 2JHH = 13.3, 3JHH = 8.2, 1H, CH2CMe3), 6.82 (t, 3JHH = 7.4, 3H, p-aryl H), 7.00 (t, 3JHH = 7.6, 6H, m-aryl H), 7.28 (d, 3JHH = 8.4, 6H, o-aryl H). 13C APT NMR (100 MHz, C6D6): δ 10.8 (C5Me5), 27.9 (d, 2JCP = 20.4, CH2CMe3), 35.4 (CH2CMe3), 38.8 (d, 3JCP = 1.5, CH2CMe3), 106.6 (d, 2JCP = 2.3, C5Me5), 121.8 (d, 3JCP = 4.5, o-aryl), 124.8 (p-aryl) 130.1 (m-aryl), 153.0 (ipso C). 31P NMR (162 MHz, C6D6): δ 120.0 [ddd, 1JPW = 361.6, 2JPH = 116.9, 3JPH = 33.7, 11.4, P(OPh)3]. Preparation of trans-Cp*W(NO)(H)2(P(OPh)3). The reaction was performed as outlined for the preparation of trans-Cp*W(NO)(CH2CMe3)(H)(P(OPh)3). However, in this instance, the reaction mixture was stirred for 22 h at room temperature to produce a dark green solution with a green precipitate. The supernatant solution was removed by cannulation, and the precipitate was washed with cold npentane (4 × 10 mL) to yield trans-Cp*W(NO)(H)2(P(OPh)3) as a yellow-green solid (0.055 g, 16% yield). Attempts to effect further purification of this solid by column chromatography on basic alumina or by crystallization from Et2O or Et2O/n-pentane solutions were unsuccessful.

Characterization data for trans-Cp*W(NO)(H)(C 6 H 5 )(P(OCH2)3CMe). MALDI-TOF (LDI, m/z): 574.2 for C21H29NO4PW, ([M − H]+, 184W). 1H NMR (400 MHz, C6D6): δ −0.46 [s, 3H, P(OCH2)3CMe], 0.09 (d, 2JHP = 111.3, 1JHW = 55.8, 1H, WH), 1.82 (s, 15H, C5Me5), 3.39 [d, 3JHP = 4.7, 6H, P(OCH2)3CMe], 7.21 (dd, 3JHH = 7.3, 4JHH = 1.3, 1H, p-aryl H), 7.34 (t, 2JHH = 7.3, 2H, m-aryl H), 7.97 (br m, 2H, o-aryl H). 13C APT NMR (100 MHz, C 6 D 6 ): δ 11.0 (C 5 Me 5 ), 15.0 [P(OCH 2 ) 3 CMe], 32.1 [P(OCH2)3CMe], 75.5 [d, 2JCP = 7.1, P(OCH2)3CMe], 107.3 (d, 2JCP = 2.0, C5Me5), 124.7 (d, 5JCP = 2.7, p-aryl C), 127.6 (m-aryl C), 144.0 (d, 3JCP = 8.9, o-aryl C), 159.2 (ipso-aryl C). 31P{1H} NMR (162 MHz, C6D6): δ 116.2 (s, 1JPW = 352.6). Another product of the thermolysis, namely Cp*W(NO)(P(OCH2)3CMe)2, was eluted from the column as a yellow fraction in 100% THF. The solvent was removed from the eluate in vacuo to yield the complex as an oily yellow solid.

Characterization data for Cp*W(NO)(H)2(P(OPh)3). IR (cm−1): 1591 (s, υNO). MS (LREI, m/z, probe temperature of 150 °C): 659 [M+ − H2, 184W]. MS (HREI, m/z, 182W): calcd, 657.13947; found, 657.14009. 1H NMR (400 MHz, C6D6): δ −0.94 (d, 1JHW = 90.6, 2JHP = 85.9, 2H, W-H), 1.86 (s, 15H, C5Me5), 6.88 (t, 3JHH = 7.4, 3H, p-aryl H), 7.07 (t, 3JHH = 7.8, 6H, m-aryl H), 7.35 (d, 3JHH = 8.22, 6H, o-aryl H). 13C APT NMR (100 MHz, C6D6): δ 11.7 (C5Me5), 105.7 (C5Me5), 122.5 (d, 3JCP = 4.6, o-aryl C), 125.3 (p-aryl C), 130.5 (maryl C), 153.2 (ipso C). 31P NMR (162 MHz, C6D6): δ 142.7 [t, 1JPW = 281.9, 2JPH = 86.0, P(OPh)3]. X-ray Crystallography. Full details of all single-crystal X-ray diffraction analyses are presented in the Supporting Information.

Characterization data for Cp*W(NO)(P(OCH2)3CMe)2. MALDITOF (dithranol, m/z): 645.2 for C20H33NO7P2W, ([M]+•, 184W). 1H NMR (400 MHz, C6D6): δ −0.25 [s, 6H, P(OCH2)3CMe], 2.26 (s, 15H, C5Me5), 3.69 [br s, 12H, P(OCH2)3CMe]. 13C{1H} NMR (100 MHz, C6D6): δ 11.6 (C5Me5), 15.8 [P(OCH2)3CMe], 31.9 [P(OCH2)3CMe], 75.5 [t, 2JCP = 3.3, P(OCH2)3CMe], 102.0 (C5Me5). 31 1 P{ H} NMR (162 MHz, C6D6): δ 142.8 (s, 1JPW = 723.9). Preparation of trans-Cp*W(NO)(CH2CMe3)(H)(P(OPh)3). In a glovebox, a thick-walled flask was charged with Cp*W(NO)(CH2CMe3)2 (0.266 g, 0.519 mmol), n-pentane (∼20 mL), and a magnetic stir bar to produce a dark red solution. The reaction vessel was then sealed with a Kontes greaseless stopcock. P(OPh)3 (0.164 mL, 0.623 mmol) was added to the reaction vessel, and H2 was bubbled through the solution for 15 min before the vessel was sealed under 1 atm of H2. After being stirred at room temperature for 1 h, the reaction mixture consisted of a dark turquoise solution and a yellow precipitate. The supernatant solution was removed by cannulation, and the precipitate was washed with n-pentane (4 × 10 mL) to yield Cp*W(NO)(CH2CMe3)(H)(P(OPh)3) as a light yellow solid (0.100 g, 27% yield). X-ray quality crystals of the complex were obtained by maintaining an Et2O solution of the compound at −30 °C for several days.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b02431. Full details of the crystallographic analysis (TXT) Full details of the crystallographic analysis (TXT) Full details of the crystallographic analysis (TXT) Full details of the crystallographic analysis (TXT) Full details of the crystallographic analysis (TXT) Expansion of overlapping 1H and 1H{31P} NMR spectra (from −0.60 to −0.05 ppm) of the signal attributed to the W−H proton from benzene activation by transCp*W(NO)(CH2CMe3)(H)(P(OMe)3), experimental details of the single-crystal X-ray crystallographic analyses, and a table of X-ray crystallographic data for 581

DOI: 10.1021/acs.inorgchem.6b02431 Inorg. Chem. 2017, 56, 573−582

Article

Inorganic Chemistry

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the five complexes whose solid-state molecular structures are reported herein, and above-listed CIF files providing full details of the crystallographic analyses of all complexes (PDF)

(12) Kuksis, I.; Baird, M. C. New Examples of Arbuzov Rearrangements of Coordinated Phosphites Initiated by Metal-Centred Radicals. J. Organomet. Chem. 1996, 512, 253. (13) Towle, D. K.; Landon, S. J.; Brill, T. B.; Tulip, T. H. A Double Michaelis-Arbuzov Rearrangement Involving (η5-C5H5)CoI2(CO) and P(OCH3)3. Formation of the Cobalt ″Supersandwich″ Complex. Organometallics 1982, 1, 295. (14) Landon, S. J.; Brill, T. B. Steric and Electronic Control of the Arbuzov Reaction in Transition Metal Halides: Proton and Phosphorus-31 NMR Study of the Reaction of [CpCo(LL)X]+ complexes (LL = N, P, As chelate ligands; X− = Cl−, Br−, I−, CN−) with P(OMe)3. Inorg. Chem. 1984, 23, 1266. (15) Chen, Z.; Jablonski, C.; Bridson, J. Evidence for an Intramolecular Transition Metal Abuzov Reaction. Can. J. Chem. 1996, 74, 2083. (16) Leeuwen, P. W. N. M. v.; Kamer, P. C. J.; Claver, C.; Pàmies, O.; Diéguez, M. Phosphite-Containing Ligands for Asymmetric Catalysis. Chem. Rev. 2011, 111, 2077. (17) Armarego, W. L. F.; Chai, C. L. L. Purification of Laboratory Chemicals, 5th ed.; Elsevier: Amsterdam, 2003. (18) Pamplin, C. B.; Legzdins, P. Thermal Activation of Hydrocarbon C-H Bonds by Cp*M(NO) Complexes of Molybdenum and Tungsten. Acc. Chem. Res. 2003, 36, 223. (19) Dryden, N. H.; Legzdins, P.; Batchelor, R. J.; Einstein, F. W. B. Improved Syntheses of Cyclopentadienyl Dichloro Nitrosyl Complexes of Molybdenum and Tungsten. Utility of Phosphorus Pentachloride as a Chlorinating Agent. Organometallics 1991, 10, 2077. (20) Debad, J. D.; Legzdins, P.; Rettig, S. J.; Veltheer, J. E. Reactivity of the Lewis Acids Cp*M(NO) (CH2CMe3)Cl [M = Mo, W] and Related Complexes. Organometallics 1993, 12, 2714. (21) Cole, J. R.; Dellinger, M. E.; Johnson, T. J.; Reinecke, B. A.; Pike, R. D.; Pennington, W. T.; Krawiec, M.; Rheingold, A. L. Caged Phosphite Complexes of Copper(I) Halides. J. Chem. Crystallogr. 2003, 33, 341.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Rex C. Handford: 0000-0002-3693-1697 Peter Legzdins: 0000-0002-3914-3768 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful to The Dow Chemical Co. for continuing financial support of our work and to our colleagues Andy Arthur, Brian Kolthammer, and Monica Shree for assistance and helpful discussions.

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DOI: 10.1021/acs.inorgchem.6b02431 Inorg. Chem. 2017, 56, 573−582