Synthesis and Reactivity of Phosphinocarbyne Complexes

Article pubs.acs.org/Organometallics

Synthesis and Reactivity of Phosphinocarbyne Complexes Annie L. Colebatch, Anthony F. Hill,* and Manab Sharma Research School of Chemistry, The Australian National University, Canberra, ACT 0200, Australia S Supporting Information *

ABSTRACT: The successive treatment of [W(CBr)(CO)2(Tp*)] (Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate) with nBuLi and ClPPh2 affords the phosphinocarbyne complex [W(CPPh2 )(CO)2(Tp*)] (1), DFT interrogation of which suggests that reactions with electrophiles may involve both the phosphorus atom and/or the metal−carbon multiple bond. This is borne out in reactions of 1 with a variety of electrophilic reagents. With iodomethane or dimethylsulfide borane, electrophilic attack occurs exclusively at phosphorus to afford the compounds [W(CPMePh2)(CO)2(Tp*)]I ([2]I) and [W{ CP(BH3)Ph2}(CO)2(Tp*)] (3). The reaction of 1 with sulfur affords both the thiophosphorylcarbyne complex [W{CP(S)Ph 2 }(CO)2(Tp*)] (4) and the thioacyl complex [W{η2-SCP(S)Ph2}(CO)2(Tp*)] (5), though 4 fails to react with sulfur to provide 5. In a similar manner, the complexes 2 and 3 also fail to react with sulfur, indicating that increasing the valance of the phosphorus center of 1 deactivates the WC bond toward further attack. Addition of selenium to 1 occurs exclusively at phosphorus to afford [W{CP(Se)Ph2}(CO)2(Tp*)] (6) with no indication of selenoacyl formation. Reversible protonation of 1 with HBF4 in diethyl ether precipitates the phosphoniocarbyne salt [W(CPHPh2)(CO)2(Tp*)]BF4, [8]BF4, which, however, on dissolution in dichloromethane rearranges irreversibly to the thermodynamic (ΔGcacld = 22.4 kJmol−1) phosphinocarbene isomer [W(η2CHPPh2)(CO)2(Tp*)]BF4, [9]BF4.

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INTRODUCTION The chemistry of carbyne (alkylidyne) complexes1 has been dominated in recent times by investigations into their use as mediators for alkyne metathesis.2 Despite the significant role they played3 in Lappert’s early substantiation of the Chauvin− Hérrison mechanism for alkene metathesis,4 interest in aminocarbenes faded somewhat until they re-emerged as coligands of choice for, inter alia, various generations of the Grubbs alkene metathesis mediators.5 The single reason for both the evanescence and renaissance of interest in aminocarbenes lies in the deactivation of the metal−carbon “multiple” bond that arises from the presence of positively mesomeric (+M) nitrogen substituents (Chart 1a). A similar deactivation of the metal carbon multiple bond characterizes aminocarbyne ligands and, to a lesser extent, those

involving other less effective +M substituents (OR, SR, SeR, etc., Chart 1b). Thus, aminocarbynes (LnMCNR2) typically display trigonal planar geometry at nitrogen, short C−N bonds, and longer MC bonds relative to hydrocarbyl-substituted analogues, leading to their occasional descriptions as 2azavinylidenes.6 Aminocarbynes are available via conventional Fischer protocols involving alkoxide abstraction from amino-alkoxy carbenes7 or Fischer−Mayr oxide abstraction from carbamoylate precursors (Scheme 1).8 In either case, the precursor carbene or carbamoylate arises from nucleophilic attack by an amide at coordinated CO, a reaction that is not readily extendable to the synthesis of phosphorus or heavier chalcogen analogues due to the reduced nucleophilicity of the required phosphide or organochalcogenolate anions. An alternative route to aminocarbynes involves the addition of electrophiles to the nitrogen atom of electronrich isonitriles;9 however, given the rarity of corresponding phosphaisonitrile complexes,10,11 this does not yet present an attractive general route to the synthesis of phosphinocarbynes. In contrast to carbynes bearing nitrogen substituents, for which aminocarbynes are most prevalent, in the case of phosphorus the exotic variants (Chart 2) far outnumber simple

Chart 1. Valence Bond Descriptions of Amino (a) Carbenes and (b) Carbynes

Special Issue: Mike Lappert Memorial Issue Received: August 16, 2014 Published XXXX by the American Chemical Society

A

dx.doi.org/10.1021/om500833n | Organometallics XXXX, XXX, XXX−XXX

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Scheme 2. Synthesis of Phosphinocarbynes12,13a

Scheme 1. Conventional Synthetic Routes to Aminocarbyne Complexes [AX2 = OSCl2, Br2PPh3, Cl2PPh3, (OCBr)2, (CF3CO)2O]

Chart 2. Exotic Carbyne Complexes Bearing Phosphorus Substituents a NR2 = NtBu(C6H5Me2-3,5): (i) KCH2Ph; (ii) Cl2PR′ (R′ = Cl, Ph); (iii) nBuLi; (iv) ClPPh2.

complexes.25 Among these, the phosphinocarbyne [Mo( CPPh2)(CO)2(Tp*)]13 could be readily obtained from [Mo(CBr)(CO)2(Tp*)], reflecting the Cummins approach, though no subsequent chemistry has been reported. Herein, we wish to report the synthesis of the corresponding tungsten derivative [W(CPPh2)(CO)2(Tp*)] (1), chosen for chemical investigation of the phosphinocarbyne linkage due to the additional spectroscopic information provided by incorporation of spin-active tungsten-183.

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RESULTS AND DISCUSSION Before discussing the synthesis and reactivity of 1, it is perhaps useful to first consider the bonding characteristics of phosphinocarbyne ligands compared with aminocarbynes and how these might be manifest in reactivity patterns. Phosphaisonitrile (phosphaisocyanide) complexes (LnMCPR), though long sought,10 remain rare,11,12 and only the hypothetical model [Mo(CPPh)(NH2)3]− has been the subject of computational studies.11,26 We therefore considered it an appropriate juncture to also consider the bonding characteristics of phosphaisonitrile compared with isoelectronic isonitrile and thiocarbonyl ligands. A detailed analysis of the bonding of 1 will follow; however for illustrative purposes, the simple model complexes shown in Chart 3 were chosen, so as to focus on the W−C−X (X = N, P, S) spine of interest. From the outset, we should emphasize that we have chosen a metal−ligand fragment, “W(CO)5”, which lies at the extreme of the “Fischer-type” regime of metal carbon multiple bonding; that is to say, the coordinatively saturated metal center is in a low oxidation state, coligated by π-acidic ligands. Cummins’ phosphaisonitrile complex and its hypothetical model [Mo(CPPh)(NH2)3]− represent the alternative “Schrock-type” scenario in which the coordinatively unsaturated metal center is in a high oxidation state coligated by strong (+M) π-donor ligands. If and when this field develops, we may anticipate intermediate examples. The thiocarbonyl and isonitrile complexes WCS and WCNMe are real; indeed the latter is obtained by treating the former with methylamine.26 More importantly, WCS played a key role in the development of heteroatomfunctionalized carbyne chemistry.1f While WCNMe2 and WCSMe are unknown, the thermolabile aminocarbyne salt [W(CNEt2)(CO)5]BCl4 has been described by Fischer.27

phosphinocarbynes.12,13 The largest group involves phosphoniocarbynes (LnMCPR3, Chart 2b),14,15 which have become increasingly observed as the products of high-valent metal centers with phosphorus ylides.15 The corresponding ammoniocarbynes (LnMCNR3) are unknown, though a range of pyridinium carbyne complexes have been described.16 Perhaps the most intriguing class of phosphorus-substituted carbyne complexes are those reported by Weber involving the phosphavinyl PC(NR2)2 (R = Me, Et) substituent.17 In the interim numerous examples of main-group compounds have emerged in which, as a result of N-heterocyclic carbene (NHC) substitution, atypical geometries and coordination numbers have been observed,18 including the diphosphorus compound (NHC)PP(NHC).19 In this context, Weber’s complexes [Mo{CPC(NR2)2}(CO)2(Tp*)] (Tp* = hydrotris(3,5dimethylpyrazol-1-yl)borate)17a might now be viewed as aminocarbene-stabilized cyaphide (CP)20 complexes. Turning to phosphinocarbynes, the focus of this report, the first examples were reported by Cummins to arise via the reactions of an anionic carbido complex with chlorophosphines (Scheme 2).12 Suitably nucleophilic carbido complexes remain rare;21 however we have observed that the compounds [M{ CLi(thf)x}(CO)2(Tp*)] (M = Mo, W)22,23 may be conveniently prepared in situ via lithium/halogen exchange between n BuLi and the bromocarbyne complexes [M(CBr)(CO)2(Tp*)] (M = Mo, W)24 at low temperatures. These lithiated carbynes react with a range of main-group and transition metal electrophiles to afford novel carbyne B


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Chart 3. Model Complexes Chosen for Studya

(i.e., the energy of the σ-symmetric HOMO) of both isonitriles and carbon monosulfide exceeds that of CO, and while clMePC is comparable to MeNC, the bent geometry of fo-MePC increases this capacity considerably, though the orbital also comprises significant phosphorus “lone pair” character. Isonitriles are poorer π-acceptor ligands than CO, while CS is an extremely potent π-acid. The acceptor orbitals of both clMePC and fo-MePC are intermediate in energy between those of CO and CS, though it should be noted that bending at phosphorus lifts their degeneracy, such that orientational preferences might be anticipated when coordinated to a retrodative metal center. Thus, it may be presumed that, as a ligand, fo-MePC should be a stronger σ-donor (with an attendant trans influence) and more potent π-acceptor than either CO or isonitriles. The frontier orbitals of the cationic31 Me2NC+ and MeSC+ carbyne ligands relevant to binding to “W(CO)5”32 are shown in Figure 2. These comprise an occupied σ-dative orbital in

a Complexes in blue are known26 or an analogue of a known complex.27

Computational studies on thiocarbonyl complexes are already available;28 however WCS was re-evaluated here at the same level of theory as the other models for consistency. It is first appropriate to consider the frontier orbitals of the “free” ligands themselves, before addressing how these might combine with those of a monovacant d6-octahedral fragment such as “W(CO)5” (LUMO = empty σ-acceptor straddled by two occupied π-retrodative orbitals HOMO−1 and HOMO− 2). The frontier orbitals (RHF: 6-311+G**) for CPMe29 in both linearly constrained (cl-MePC) and freely optimized ( foMePC) geometries are presented in Figure 1 alongside those for the more familiar ligands CO, CNMe, and CS for comparative purposes. Commencing with cl-MePC, geometry optimization results in the considerably more stable bent geometry (C−P−C = 89.72°) of fo-MePC. The σ-dative ability

Figure 2. Frontier orbitals relevant to metal coordination for the series [Me2NC]+, optimized trigonal trig-[Me2PC]+, constrained pyramidal pyr-[Me2PC]+, and [MeSC]+.

addition to two nondegenerate empty π-acceptor orbitals, the energetic inequivalence being most pronounced for Me2NC+. Thus, the acceptor orbital orthogonal to the trigonal plane, which conjugates with nitrogen, is less π-acidic than that which lies in the plane. Taken together, these suggest that an aminocarbyne is a stronger σ-donor than a thiocarbyne but a poorer π-acceptor (vide inf ra). This is borne out when considering infrared data (νCO) for otherwise analogous carbonyl-ligated amino compared with thiolato carbyne complexes.1a Two possible geometries are depicted for the singlet cationic Me2PC+ fragment.33 Beginning with an idealized tetrahedral geometry (pyr-Me2PC+), or indeed one in which all C−P angles are 90°, optimization leads to a

Figure 1. Frontier orbitals relevant to metal coordination for the series CO, CS, CNMe, constrained linear cl-CPMe, and freely optimized foCPMe. C


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Table 1. Atomic Chargesa for the Complexes (a) (OC)5WCY (Y = NMe, PMe, S) and (b) [(OC)5W(CYMe)]+ atoms complex

W −0.41 −0.33 −0.30 −0.22 −0.16 −0.10

(CO)5WCNMe (CO)5WCPMe (CO)5WCS (CO)5WCNMe2+ (CO)5WCPMe2+ (CO)5WCSMe+ a

C

(0.02/0.47) (+0.07/0.51) (0.04/0.49) (0.10/0.54) (0.13/0.57) (0.12/0.56)

0.21 −0.12 −0.08 0.22 −0.13 −0.17

(0.01/0.06) (−0.30/−0.17) (−0.07/−0.17) (0.02/0.10) (−0.13/−0.27) (−0.07/−0.19)

−0.23 0.18 0.05 −0.33 0.46 0.37

(−0.07/−0.59) (0.07/0.07) (0.02/0.04) (−0.01/−0.28) (0.27/0.21) (0.21/0.20)

Mulliken (Hirshfeld/CM5 in parentheses) charges.

Table 3. Calculated Geometriesa for the Complexes [(OC)5W(CYMe)]+ (Y = NMe, PMe, S)

geometry in which the phosphorus is trigonal (cf. Me2NC+) in the f ree state. While the trig-Me2PC+ geometry does indeed present a set of valence orbitals similar, but energetically better matched for synergic bonding, to those of Me2NC+, it should be noted that pyramidalization actually improves the match.34 While the σ-donor orbital of pyr-Me2PC+ is close in energy to that of the trigonal geometry, the energies of the acceptor orbitals both drop and become almost degenerate. Thus, pyramidalization should be expected to significantly enhance retrodonation from a metal and be favored by π-basic metal centers. For the complexes of these ligands, geometries were optimized at the BP86 level of theory (Tables 1−3) and

Bonds (Å) W−C1 W−C2 C−Y Angle (deg) C1−W−C2 W−C1−Y C1−Y−C3 C3−Y−C4 C1−Y−C4

a

Table 2. Calculated Geometries for the Complexes (OC)5WCY (Y = NMe, PMe, S)

a

Bonds (Å) W−C1 W−C2 C1−Y Angle (deg) C1−W−C2 W−C1−Y C1−Y−C3 a

Y

(OC)5WCNMe Y=N

(OC)5WCPMe Y=P

(OC)5WCS Y=S

2.13 2.05 1.19

2.02 2.11 1.66

2.04 2.10 1.57

179.9 179.9 179.9

179.9 173.3 101.8

180.0 180.0

(OC)5WCNMe2+ Y = NMe

(OC)5WCPMe2+ Y = PMe

(OC)5WCSMe+ Y=S

1.95 2.17 1.29

1.92 2.24 1.75

1.92 2.21 1.66

180.0 180.0 121.5 116.9 121.5

179.2 169.6 106.1 107.3 106.2

177.5 173.4 103.9

BP86/BS1.

interest. First, while the isocyanide ligand in WCNMe is exactly linear, the phosphaisonitrile ligand in WCPMe is clearly bent (CPC = 101.8°), consistent with the development of a “lone pair” (primarily HOMO−2, Figure 2) at phosphorus. This bending lifts the degeneracy of the two acceptor orbitals on the CPMe ligand. The CPPh ligand in [Mo(CPPh)(NH2)3]− was also calculated to coordinate in a bent form (CPC = 104.7°).11 It should be noted that while the CNMe ligand in WCNMe is linear, it is not uncommon for isonitriles to undergo bending at nitrogen when coordinated to especially π-basic metal centers. Such systems are often the most prone to electrophilic attack at nitrogen, affirming the conceptual connection between WCNMe and WCNMe2. Despite intentionally commencing with a geometry for WCPMe2 in which the phosphorus is trigonal, geometry optimization results in that shown, wherein the phosphorus is clearly pyramidalized (angle sum = 320°). Although this makes the ligand a slightly poorer σ-donor (Figure 2), pyramidalization lowers the energies of both π-acceptor orbitals, making them essentially degenerate. Thus, pyramidal Me2PC is both a stronger σ-donor and π-acceptor than trigonal Me2NC but less so than CSMe, and the net acceptor ability is reflected in the Mulliken charges on the tungsten (Table 1). The Me2PC ligand exerts the strongest trans influence upon the trans carbonyl, while the Me2NC ligand shows the least, with MeSC being intermediate. A corollary of pyramidalization of the phosphorus is that the devlopment of lone pair character means that in

BP86/BS1.

molecular orbitals were generated following calculations at the BP86 level of theory. Consistent with the relative σ-dative/πretrodative capacities inferred from calculations for the free ligands, we find that the metal−carbon multiple bond contracts in the heterocarbonyl series WCNMe (2.13) > WCS (2.04) > WCPMe (2.02 Å), and this pattern is replicated in the carbyne series WCNMe2 (1.95) > WCSMe (1.90) > WCPMe2 (1.88 Å). In both cases we might attribute this to the sequential decrease in effective pπ−pπ overlap being compensated for by increased W−C multiple bonding. The CS and CPMe ligands exert comparable trans influences upon the unique carbonyl ligand, which is more pronounced than for CNMe. This feature is similarly reflected in the cationic carbyne series and experimentally confirmed for 1 (vide inf ra). The geometry at phosphorus for WCPMe and WCPMe2 is the key point of D


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principle the phosphorus could be prone to electrophilic attack, a feature not observed in aminocarbyne chemistry where the trigonal sp2-nitrogen is deactivated toward electrophiles. The synthesis of complex 1 proceeds in a similar manner to that of the molybdenum analogue.13 Thus, treating [W( CBr)(CO)2(Tp*)] in THF with nBuLi at −78 °C followed by chlorodiphenylphosphine affords the orange phosphinocarbyne complex [W(CPPh2)(CO)2(Tp*)] (1) in 90% yield. Infrared data (Table 4) may be compared with those for Table 4. Selected Infrared (νCO) and NMR Data for Complexes [W(CR)(CO)2(Tp*)] ν1

ν2

kCOa

R

cm−1

cm−1

N m−1

ppm

Hz

PC(NMe2)217a OMe38 Me35 Ph36 SMe14e PPh2 SiMe2Ph37 SnMe340 H14i Br24 + PPh314e

1936 1935 1958 1968 1969 1975 1982 1982 1979 1992 1994 2026

1833 1848 1862 1867 1876 1880 1891 1889 1902 1903 1905 1940

14.35 14.46 14.74 14.86 14.93 14.99 15.13 15.14 15.19 15.32 15.36 15.89

248.6 318.3 228.2 289.0 277.9 264.4c 292.6 339.0 343.4 280.6 198.0 242.1

208 101 235 n.r.b n.r. n.r. 188d 160 241 192 n.r. 212

NEt239

δWC

Figure 3. Molecular structure of [W(CPPh2)(CO)2(Tp*)] (1) (hydrogen atoms omitted, 70% displacement ellipsoids, phenyl and pyrazolyl groups simplified). Selected bond lengths (Å) and angles (deg): W1−C1 1.827(2), C1−P1 1.783(3), P1−C41 1.833(3), P1− C51 1.829(3), W1−C1−P1 166.62(15), C1−P1−C41 101.52(12), C1−P1−C51 106.02(12).

1

JWC

(W1−N11 = 2.320(2)Å) relative to those trans to carbonyl ligands (2.208(2), 2.206(2) Å). (v) Within the crystal the complex has no element of symmetry; however, given the appearance of a single carbonyl resonance in the 13C{1H} NMR spectrum it may be assumed that free rotation occurs about the C1−P1 bond in solution (vide inf ra). All these observations correlate with the expectations that follow from the theoretical analysis of the simple model complex [(OC)5WCPMe2]+. Those calculations, however, suggested that the phosphorus might display some nucleophilic character, though this would be curtailed somewhat by the cationic charge and poor π-basicity of the [W(CO)5] metal/ ligand set compared with the neutral complex 1. Accordingly, complex 1 was interrogated using DFT methods. The experimentally determined geometry was satisfactorily reproduced at the BS86/BS1 level of theory (Supporting Information). The derived molecular orbital most relevant to the chemistry that follows is the HOMO−1 depicted in Figure 4a (the HOMO corresponds to W−CO π-bonding). This orbital is essentially composed of both a “lone pair” on phosphorus and one of the tungsten−carbyne π-bonds, the orthogonal π-bond being primarily HOMO−2 (Figure 4b). Accordingly, it may be anticipated that both sites will be prone to electrophilic attack in frontier orbital controlled reactions, though the steric bulk of the Tp* coligand affords the WC bond some kinetic protection relative to the more protrusive phosphorus lobe. Relevant to charge-controlled events, the most negatively charged atom of the WCP spine is the carbyne carbon (Mulliken: −0.27 (W), +0.32 (P)). Moreover, NBO analysis indicates the natural atomic orbital occupancies for the carbyne carbon to be 2s1.272px0.872py0.882pz1.24, while the phosphorus atom has 3s1.353px1.283py0.693pz0.74 (z-axis along the W−C−P spine, “lone pair” in xz-plane). The issue of rotation about the carbyne−phosphorus bond arose above when the conformation observed in the solid state had lower symmetry than that inferred (Cs) from solution 13C NMR data. Three gas-phase conformers (Figure 5) were located, one of which corresponds to the geometry found in the solid state. Although this is not the lowest in energy in the gas phase, as noted above the presence of C−H···π interactions in the solid state between phenyl groups in adjacent molecules most likely favors this geometry. It might be expected that barriers to phosphinocarbyne rotation and ground-state conformational preferences would be lower than those for

a

Cotton−Kraihanzel force constant. bn.r. = not reported. cNot reported, value given for [W(CSMe)(CO)2{HB(pz)3}].41 d1JPC = 74.5 Hz.

related carbyne complexes of the form [W(CR)(CO)2(Tp*)], by which it may be seen that the CPPh2 carbyne ligand is a substantially stronger π-acceptor than the analogous aminocarbyne and even the methylthiolatocarbyne. The most conspicuous resonance in the 13C NMR spectrum corresponds to the carbyne carbon (δWC = 292.6), which appears as a doublet due to coupling to phosphorus (1JPC = 74.5 Hz) and is straddled by 183W satellite resonances (1JWC = 188 Hz). The single resonance in the 31P{1H} NMR spectrum at 32.0 ppm is also flanked by 183W satellites (2JWP = 69.0 Hz). The characterization of 1 included a crystal structure determination, the results of which are summarized in Figure 3. The molybdenum analogue has been previously reported,13 and the structural features are similar. Key features of note include (i) a short tungsten−carbyne separation (1.872(2) Å) compared with 1.842(9) and 1.859(9) Å for the aminocarbyne complex [W(CNiPr2)(CO)2{HB(mt)3}] (mt = mercaptoimidazolyl).42 This is comparable to those found for [Mo( CPPh2)(CO)2(Tp*)] (1.802(2) Å)13 and the phospha-alkenylsubstituted carbyne [W{CPC(NEt 2) 2 }(CO) 2(Tp*)] (1.838(6) Å) and its cationic P-alkylation product [W{ CP(Me)C(NEt2)2}(CO)2(Tp*)]+ (1.840(8) Å).17 (ii) The phosphorus is clearly pyramidal with an angle sum of 311.9° and P1−C1 length of 1.783(3) Å. This may be compared with those for the simple alkyne HCCPPh2 (304.0° and 1.775 Å, respectively),43 in which the PPh2 group is also bound to an sphybridized carbon. (iii) The W1−C1−P1 spine is somewhat bent; however carbyne bending is not uncommon1a,44 and in this case may be attributed to a pair of complementary C−H···π interactions between phenyl groups on adjacent molecules (not shown). (iv) The phosphinocarbyne exerts a pronounced trans influence (57 esd, TR25e = 1.05) on the trans pyrazolyl group E


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Scheme 3. Synthesis of Phosphoniocarbynes

A resonance is observed at δP = 12.2 ppm, and consistent with the high s-character of the W−C−P linkage, a large coupling is seen to tungsten (2JWP = 161.6 Hz, cf. 147 Hz for [W(CPMe3)(CO)2(Tp*)]PF614e). Interestingly, the carbyne carbon appears as a singlet in the 13C{1H} NMR spectrum at 242.8 ppm with 1JWC = 206.2 Hz. The absence of resolvable 1 JPC coupling seems counterintuitive, but is consistent with what is observed for other phosphoniocarbynes14 with the exception of [W(CPCy 3 )(CO) 2(Tp*)]PF6 ,14f [Re( CPPh3)(SR)(NtBu)2] (R = adamantyl, tBu),15b,c and [Ta(CPPh3)(CHPPh3)Cl(Cp*)],15f which display very small carbon−phosphorus coupling constants between 7.5 and 15 Hz. Phosphine-borane adducts are commonly used reagents in synthetic chemistry. Boranes are useful protecting groups for phosphines, and in turn phosphines are often used to stabilize boranes.45 However, in parallel with alkyne hydroboration Stone and Wadepohl46 have shown that WC bonds may also be hydroborated (Scheme 4). In the case of [W(CR)(CO)2(η-C5H5)] (R = Me, C6H4Me-4), the reaction with BH3· THF affords binuclear boratoalkyne complexes [W2(μRCBHCH2R)(CO)4(η-C5H5)2], while the sterically more encumbered complexes [M(CR)(CO)2(Tp*)] (M = Mo,

Figure 4. (a) HOMO−1 (−5.42 eV) and (b) HOMO−2 (−6.04 eV) calculated for complex 1 (H atoms omitted).

Figure 5. Free energies (kJ mol−1)of rotational conformers of 1(BP86/BS1).

Scheme 4. Reactions of Carbyne Complexes with Boranes

(trigonal at nitrogen) amino carbynes given the greater disparity between the energies of the π-acceptor orbitals for trigonal [CNMe2 ]+ compared with pyramidal-[CPMe 2 ]+ (Figure 2). To explore the possible nucleophilicity of phosphorus and/or the WC bond in 1, reactions with a range of electrophilic reagents were investigated. Templeton has synthesized a number of phosphoniocarbyne complexes [W(CPR3)(CO)2(Tp*)]PF6 (R3 = Me3, Et3, Cy3, Ph3, Me2Ph) by treating the thiocarbyne [W(CSMe)(CO)2(Tp*)] with excess PR3 and NH4PF614e or by treating the chlorocarbyne [W( CCl)(CO)2(Tp*)] with PR3 and KPF6 (Scheme 3).14i Treatment of complex 1 with methyl iodide affords the methyldiphenylphosphonio analogue of Templeton’s complexes [W(CPMePh2)(CO)2(Tp*)]I ([2]I, Scheme 3). F


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R = C6H4Me-4; M = W, R = Me, C6H4Me-4) react with “Et4B2H2” to provide σ-boryl derivatives [M(κ2-H,B-BEtR)(CO)2(Tp*)], in which an ethyl group presents a β-agostic C− H···W interaction (Scheme 4). Intramolecular hydroboration of a carbyne ligand by a dihydrobis(pyrazolyl)borate coligand has also been observed.47 The reaction of 1 with BH3SMe2 affords the simple phosphine-borane adduct [W(CPPh2BH3)(CO)2(Tp*)] (3), in which the WC bond remains intact, as indicated by the appearance of a doublet resonance at δC = 271.2 (1JPC = 21.1, 1JWC = 199.2 Hz). The carbonyl absorbances are shifted to higher frequency (CH2Cl2: 2003, 1915 cm−1) relative to those of 1 (CH2Cl2: 1982, 1891 cm−1). The resonance in the 31P{1H} NMR spectrum (δP = 32.0) is broadened, consistent with coordination to quadrupolar 11B, such that coupling to 183W is not resolved. No evidence of a reaction between BH3 and the WC bond was observed under ambient conditions, in contrast to Stone and Wadepohl’s work. Complex 3 was heated in an attempt to encourage borane migration to the WC bond (d8-toluene: 140 h at 55 °C, 70 h at 80 °C); however no change in the 1H or 31P{1H} NMR spectra was observed other than decomposition of 3 to regenerate 1 via loss of BH3. No peaks that might correspond to BH3 migration to WC were observed. The molecular structure of 3 is depicted in Figure 6, which confirms the site of borane coordination and the retention of

Figure 7. Optimized geometries (BP86/BS1) and relative thermodynamics (M06/BS2//BP86/BS1) for the borane adducts of 1 and PPh3.

somewhat poorer Lewis σ-base, i.e., that the “Tp*(CO)2W C−” phosphine substituent is electron-withrawing in a manner akin to other sp-C-hybridized groups, e.g., NC and RCC. This is also supported by the dissociation of BH3 when 3 is heated (vide supra). Phosphines are readily oxidized by elemental sulfur or selenium; however metal−carbon triple bonds are also prone to addition of chalcogens to afford either chalcoacyls or dichalcocarboxylates (Scheme 5).50−61 It transpires that the reaction of 1 with elemental sulfur (1/8 S8) takes both courses. After stirring 1 with one equivalent of sulfur for 16 h the IR spectrum revealed two new pairs of CO absorptions (THF: 2003, 1917 and 1996, 1908 cm−1). Cryostatic chromatography (−30 °C) provided a purple band (minor product) and an orange band as the major product. The orange band had two CO absorptions in its infrared spectrum at 2004 and 1916 cm−1 in CH2Cl2. The mass spectrum and microanalytical data supported addition of one equivalent of sulfur. 1H NMR spectroscopy showed the presence of the Tp* ligand with the typical 2:1 ratio of peaks, as well as the presence of the phenyl rings. The 31P{1H} NMR spectrum shows a singlet at 41.1 ppm with 183W satellites 2JWP = 150.9 Hz. The 183W−31P coupling constant of 150.9 Hz is similar to that seen for four-coordinate phosphorus and supports formation of the phosphine sulfide complex [W(CPSPh2)(CO)2(Tp*)] (4) (Scheme 5). The carbyne resonance appears in the 13C{1H} NMR spectrum at 270.1 ppm with a 1JPC value of 4.9 Hz. This very small coupling constant is again indicative of a four-coordinate phosphorus carbyne, while the large 1JWC coupling seen for the carbyne resonance of 198.4 Hz is consistent with retention of a WC triple bond. IR spectroscopy of the purple fraction revealed two carbonyl bands at 1995 and 1907 cm−1 in CH2Cl2. The ESI(+) mass spectrum was consistent with the addition of two sulfur atoms. The 1H NMR spectrum showed the typical 2:1 ratio of Tp* peaks and the presence of the PPh2 group, while the 31P{1H} NMR spectrum consisted of a single peak at 52.9 ppm (CDCl3) without any visible 183W satellites. The absence of W−P coupling led us to initially suspect it may be the dithiocarboxylate complex [W(κ2-S2CPPh2)(CO)2(Tp*)].51 The 13C{1H} NMR spectrum shows a doublet at δC 250.1 (1JPC = 42.0 Hz) with 183W satellites (JWC = 42.8 Hz). This resonance was assigned to the C-PPh2 carbon because of the diagnostic phosphorus−carbon coupling. The chemical shift, while slightly downfield from what is typically seen for

Figure 6. Molecular structure of [W(CPPh2BH3)(CO)2(Tp*)] (3) (70% displacement ellipsoids, most hydrogen atoms omitted, phenyl and pyrazolyl groups simplified). Selected bond lengths (Å) and angles (deg): W1−C1 1.824(4), C1−P1 1.782(4), P1−B2 1.935(5), W1− C1−P1 164.1(2), C1−P1−B2 115.5(2).

the WC multiple bond. The structural features of the Tp*(CO)2WC fragment are unremarkable other than to note that coordination of borane does not lead to a significant change in the WC bond length, and the trans influence of the carbyne ligand remains effective. The geometry about phosphorus is tetrahedral, with the most obtuse angle being that of C1−P1−B2 (115.5(2)°). The P1−B2 bond length of 1.935(5) Å is similar to that in the related compounds (S,S){P(CCPh)(tBu)(BH3)}2C2H4 (average P−B distance 1.918 Å)48 and Ph3PBH3 (P−B distance 1.917 Å).49 The geometry of 3 could be computationally reproduced at the BP86/BS1 level of theory (Figure 7), and a comparison of the associated thermodynamic data relative to 1 and the compounds Ph3P and Ph3P→BH3 suggests that 1 is a G


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Scheme 5. Addition of Chalcogens to Carbyne Complexes (R = C6H4Me-4)50

Figure 8. Molecular structure of [W(CPSPh2)(CO)2(Tp*)] (4) (H atoms omitted, 70% displacement ellipsoids, phenyl and pyrazolyl groups simplified). Selected bond lengths (Å) and angles (deg): W1− C1 1.829(4), C1−P1 1.785(4), P1−S1 1.9568(16), W1−C1−P1 160.5(3), C1−P1−S1 114.0(2).

Figure 9. Molecular structure of [W(η2-SCPSPh2)(CO)2(Tp*)] (5) (70% displacement ellipsoids, hydrogen atoms omitted, phenyl and pyrazolyl groups simplified). Selected bond lengths (Å) and angles (deg): W1−C1 2.003(13), W1−S1 2.561(3), C1−S1 1.707(14), C1− P1 1.770(14), P1−S2 1.970(5), W1−N11 2.206(9), W1−N21 2.203(9), W1−N31 2.218(10), W1−C1−P1 145.4(7), W1−C1−S1 86.9(6), C1−W1−S1 41.7(4), W1−S1−C1 51.4(4), C1−P1−S2 113.2(4).

The conversion of 1 to 4 does not significantly affect the WC bond length (1.829(4) Å), though the W1−C1−P1 spine is further distorted from linearity (160.5(3)°). The angles about P1 are close to tetrahedral (104.4(2)−114.0(2)°), the largest of these being between the sulfur and carbyne carbon. The C1− P1 bond (1.785(4) Å) is not significantly different from that found for 1 despite the increased coordination number at P1. Structural data are not available for mononuclear group 6 metal thioacyls; however a large number of thiocarbamoyl complexes have been structurally characterized52,62 in addition to a small number of alkoxythiocarbonyls63 and metallacyclic derivatives.64 The single most relevant structural study however involves the bimetallic bridging thiotoluyl complex [WRu(μSCC6H4Me-4)(CO)4(Tp)(Cb)] (Cb = η5-C2B9H11),65 which may be viewed as a Lewis acid (“Ru(CO)2(Cb)”) adduct of the thiotoluyl complex [W(η2-SCC6H4Me-4)(CO)2(Tp)] akin to 5. The complexes [MRu(μ-ECC6H4Me-4)(CO)4(Tp)(Cb)] (M = Mo, W; E = S, Se) arise from the addition of elemental chalcogens to the bridging carbynes [MRu(μCC6H4Me-4)(CO)4(Tp)(Cb)],66 and the thioacyl resonances (E = S) occur

dithiocarboxylates, could be consistent with either a dithiocarboxylate or a thioacyl group. Mayr has reported the complex [W(κ2-S2CNEt2)(η2-SCNEt2)(η2-SCHPh)(CO)], which contains both a dithiocarbamate and a thiocarbamoyl group.52 In the 13C{1H} NMR spectrum (CDCl3) of this compound the η2-SCNEt2 carbon appears at δC 256.9 with 183W satellites (1JWC = 111 Hz), while the κ2-S2CNEt2 carbon appears at δC 214.6 with no visible 183W coupling. The thiotoluyl complex [Mo(η2SCC6H4OMe-4)(CO)2(Tp)] has δC = 278.0, while the dithiocarboxylate [Mo(κ2-S2CC6H4OMe-4)(CO)2(Tp)] has δC = 250.4.50b Because too few examples exist of authenticated group 6 thioacyl complexes, the identity of the purple product could not be conclusively determined based simply on a comparison of the 1JWC coupling constants or chemical shifts observed; however the complex was unequivocally identified crystallographically. Figures 8 and 9 summarize, respectively, the results of crystallographic studies on the phosphine sulfide complex [W(CPSPh2)(CO)2(Tp*)] (4) and the second compound, its thioacyl derivative [W(η 2 -SCPSPh 2 )(CO)2(Tp*)] (5). H


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at δC = 270.0 (M = Mo) and 252.1 (M = W), cf. δC = 250.1 for 5 and 278.0 for [Mo(η2-SCC6H4OMe-4)(CO)2(Tp)].50b Both the positively mesomeric effect of amino substituents on thiocarbamoyls (Chart 4)67 and the coordination of a

simple benzylidynes, which preferentially form dithiobenzoates with elemental sulfur,50c thiobenzoyls being isolable only when methylthiirane is used to selectively deliver a single sulfur atom.50b On the basis of the computed energies for 4 relative to the putative complex [W(η2-SCPPh2)(CO)2(Tp*)] (Figure 10),

Chart 4. Limiting Valence Bond Descriptions: (a) Thioacyl; (b) Metallathiirene; (c) Thiocarbamoyl

second metal center to the sulfur atom might be expected to have a significant effect on the metallathiirene geometry given that substituent mesomeric effects play a role in both the facility and the thermodynamics of thiocarbonyl migratory insertion processes.68 In practice, the geometric features of the MCS ring in 5, [WRu(μ-SCC6H4Me-4)(CO)4(Tp)(Cb)], and the most closely related thiocarbamoyl derivative [Mo(η2-SCNMe2)(CO)2(Qp)] (Qp = tetrakis(pyrazol-1-yl)borate)62f,69 are remarkably similar. The M−C−S angles are all close to 90° (84.6−86.9°). Both mononuclear complexes have comparable M−S bond lengths, somewhat longer than observed in the binuclear thiotoluyl derivative, while the W−C bond length in 5 (2.003(13) Å) is intermediate between the longer thiocarbamoyl example (2.076(3) Å) and the shorter thiotoluyl comparitor (1.970(4) Å). Thus, coordination of the Lewisacidic “CbRu(CO)2” unit appears to result in a modest contraction of the WCS metallacycle. Although the thioacyl complex 5 is conceptually related to 4 by the simple addition of one atom of sulfur across the WC bond, as, for example, observed in the reactions of [M( CC6H4OMe-4)(CO)2(Tp)] (M = Mo, W) with methylthiirane,50b in practice this proves to not be the case. The reaction of 1 with methylthiirane (a monatomic sulfur source) leads to the formation of small amounts of 4, but no 5 is observed. Heating 4 with one equivalent of sulfur in toluene under reflux for 7 days fails to produce spectroscopically observable amounts of 5. In the original reaction between 1 and elemental sulfur there is some minor variation in the proportion of 4 to 5 formed depending on solvent and the amount of sulfur used. Thus, when an excess of sulfur (10 equiv) is used, the yield of mono-addition product 4 reaches 98% with only 0.5% of 5 being formed. At no stage were we able to detect the putative thioacyl [W(η2-SCPPh2)(CO)2(Tp*)] that might be formed by single addition of sulfur directly to the WC of 1. We might therefore conclude that when this species forms, the phosphino group conjugates less with the resulting metallathiirene becoming more prone to rapid oxidation by further sulfur to afford 5. In contrast it would appear that competitive initial oxidation of the phosphino group in 1 by sulfur deactivates the WC bond of 4 to preclude conversion to 5. To test the supposition that electrophilic attack at phosphorus deactivates the WC bond, the reactivity of [W(CPMePh 2 )(CO) 2 (Tp*)]I ([2]I) and [W( CPPh2BH3)(CO)2(Tp*)] (3) toward sulfur was explored; however no metallathiirene formation was observed over 6 days (CDCl3, 25 °C). In all of the reactions of 1 with elemental sulfur or methylthiirane, no evidence of dithiocarboxylate complex formation, [W(κ2-S2CPPh2)(CO)2(Tp*)] or [W(κ2S2CPSPh2)(CO)2(Tp*)], was seen. This is in contrast to

Figure 10. Relative thermodynamic information (bp686/BS2/B3LYP/ BS1) for rotational conformers of the complexes [W{CP(S)Ph2}(CO)2(Tp*)] (4) and hypothetical [W(η2-SCPPh2)(CO)2(Tp*)] (in red).

we may conclude that the thioacyl is viable, lying some 12 kJ mol−1 above 4 (depending on the rotational conformers), and that the failure to isolate it manifests a kinetic phenomenon. Unfortunately, the mechanisms by which elemental sulfur reacts are typically complex (nucleophilic, electrophilic, or biradical),70 and polysulfur assemblies readily redistribute in solution70e and are therefore not readily ammenable to computational interrogation. The results of the computational analyses are provided in the Supporting Information and include an investigation of the conformations of the WCPSPh2 spine of 4. This was considered useful given that while in dichloromethane solution two νCO absorptions are observed (2004, 1916 cm−1), in tetrahydrofuran four bands are observed (2004, 1997, 1918, 1908 cm−1), suggesting the presence of two rotational conformers. The relative energies of these are depicted in Figure 11, with that corresponding most closely to the solid state structure (SPWC(O) dihedral angle 34°) lying some 2.3 kJ mol−1 higher in energy (i.e., well within the magnitude of crystal packing effects) than the lowest conformer, which has the PS bond bisecting the intercarbonyl angle. While these calculations relate to the gas phase, even in solution it may be assumed that an equilibrium will develop between these low-energy conformers and that the barrier to interconversion (ca. 17.8 kJ I


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Figure 12. Molecular structure of 6 in a crystal of 6·CHCl3 (70% displacement ellipsoids, hydrogen atoms and CHCl3 omitted). Selected bond lengths (Å) and angles (deg): W1−C1 1.823(4), C1−P1 1.784(4), P1−Se1 2.1120(11), W1−C1−P1 164.6(2), C1− P1−Se1 114.25(12).

Figure 11. Rotational conformers of the complex [W(CPSPPh2)(CO)2(Tp*)] (4) with associated relative energies (BP86/BS2/ B3LYP/BS1, θ = 250−25° generated by symmetry).

phosphorus in these systems; however the chemical shift value of 19.9 ppm is shifted slightly upf ield relative to 1. This is unexpected for tertiary phosphines, as typically oxidation of the phosphorus leads to a 20−30 ppm downfield shift in the 31 1 P{ H} NMR spectrum. The simplest electrophile (H+) has been left until last because its behavior proved least simple. For hydrocarbyl carbyne complexes, the initial site of charge-controlled protonation may be open to interpretation because the ultimate residence of the proton reflects the thermodynamic preferences imbued by the metal center and associated ligands. The possible outcomes of protonation at the metal center (to afford a hydride ligand), the carbyne carbon (to afford a carbene), and the metal−carbon bond (to afford an agostic carbene) are all in principle in equilibrium via low-energy α-elimination/insertion processes (Chart 5).

mol−1) via higher energy conformers (phenyl and pyrazole groups eclispsed) is easily surmountable, thereby accounting for the disparity between solution and solid-state infrared data. While the complex [W(CC6H4Me-4)(CO)2(η-C5H5)] reacts with elemental selenium to afford a diselenocarboxylate [W(κ2-Se2CC6H4Me-4)(CO)2(η-C5H5)],50c the corresponding reaction of [Mo(CC4H2S-2)(CO)2(Tp)] with the single selenium atom transfer agent SeCNC6H2Me3-2,4,6 affords the selenoacyl complexes [Mo(η2-SeCC4H2S-2)(CO)2(Tp)] and [Mo(η2-SeCC4H2S-2)(CO)(CNC6H2Me3-2,4,6)(Tp)].50g Accordingly, the reaction of 1 with gray selenium was investigated and found to provide, after chromatography, the phosphine selenide complex [W(CPSePh2)(CO)2(Tp*)] (6) in 92% yield, with no evidence for the formation of diselenocarboxylate or selenoacyl species, even when an excess of selenium was employed. The 1H and 13C{1H} NMR spectra of 6 are unremarkable. The carbyne resonance occurs within the typical range at δC 265.2 (1JPC = 13.6 Hz, 1JWC = 201.4 Hz). The small phosphorus−carbon coupling constant is indicative of the four-coordinate nature of the phosphorus, and the large tungsten−carbon coupling constant is characteristic of a W C triple bond. The 31P{1H} NMR chemical shift is essentially unchanged (δP = 31.9, cf. 32.0 for 1), but the presence of 77Se satellites (I = 1/2, 7.6% natural abundance, 1JSeP = 711.8 Hz) supports the formulation of 6. The characterization of 6 included a crystallographic study (Figure 12), which revealed geometric features comparable to those of 5, which call for little comment. In comparison to the rapid reactions of 1 with sulfur and selenium, 1 is relatively stable in air. Formation of the phosphine oxide [W(CPOPh2)(CO)2(Tp*)] (7) at room temperature is slow; a solution of 1 in CH2Cl2 shows only 43% conversion to 7 after 14 days in air. Deliberate formation of 7 can be achieved by treatment of 1 with 30% H2O2, heating 1 in refluxing toluene in air for 8 h, or by treating [W( CBr)(CO) 2(Tp*)] with nBuLi and ClP(O)Ph2. The spectroscopic characterization of 7 is largely unremarkable, with the exception of the 31P{1H} NMR spectrum, which shows a singlet at 19.9 ppm with 2JWP = 145.2 Hz. This large 183 W−31P coupling constant is typical of a four-coordinate

Chart 5. Alternative Sites of Metal−Carbyne Protonation: (a) Metal; (b) Metal−Carbon Bond (“Face” Protonation); (c) Carbyne Carbon

Attack at any of these sites is expected to be comparatively slow because, in contrast to the protonation of heteroatom bases (O, N, F, S, P) bearing electron lone pairs, structural rearrangement is necessary for both metal- and carbon-centered bases.71,72 As indicated in Figure 4a, the HOMO−1 has both phosphorus “lone” pair and WC character; that is, fronitier orbital controlled protonation could occur at either site. The calculated Mulliken/Hirschfeld charges associated with tungsten (+0.36/+0.23), the carbyne carbon (−0.27/−0.21), and the phosphorus (+0.31/+0.14) would however suggest that charge-controlled kinetic protonation would occur at carbon J


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formulation as the dihapto phosphinocarbene salt [W{η2-C,PC(H)PPh2}(CO)2(Tp*)]BF4 ([9]BF4, Scheme 6), an isomer of [8]BF4. While crystallographic grade crystals were not forthcoming, sufficient precedent exists75−77 from related complexes to substantiate the assignment. Most notably, the 1 H NMR spectrum includes a doublet resonance for which both the significantly downfield chemical shift (δH = 14.78) and the associated scalar couplings (2JPH = 4.8, 2JWH = 13.8 Hz) attest to the proton residing on a carbene ligand. This resonance correlates with a resonance at δC = 237.1 (1JCH = 199.0, 1JPC = 46.3, 1JWC = 21.5 Hz), while the associated single CO resonance (δC = 214.8, 1JWC = 134.3 Hz) and the ratio of pyrazolyl environments (2:1) suggests that either the HCPW metallacycle lies in the plane between the two CO ligands or traverses such a geometry in a fluxional process that is rapid on the 1H and 13C NMR time scales. The 31P{1H} NMR spectrum of [9]BF4 comprises a singlet resonance (δP = −101.3) straddled by a doublet, the splitting of which (1JWP = 138.5 Hz) is suggestive of a direct W−P interaction and may be compared with those observed for the related salts [W(η2-CPhPPh2)(CO)2(Tp)]BPh4 (δP = −96.8, 1JWP = 117 Hz)75 and [W{η2C(H)PC(NEt2)2}(CO)2(Tp*)]OTf (δP = −148.86, 1JWP not given).76 The former arises from the reaction of [W( CPh)(CO)2(Tp)] with ClPPh2 and Tl[PF6]75 (vide inf ra), while the latter is more directly analogous to the formation of [9]BF4, being obtained from the protonation of [W{ CPC(NEt2)2}(CO)2(Tp*)], which under appropriate conditions was also found to afford an intermediate involving kinetic protonation at phosphorus (Scheme 7).76

(steric factors not withstanding). By employing a solvent (Et2O) from which an ionic product might be expected to rapidly precipitate, it was possible to isolate the product of kinetic protonation of 1 with HBF4, which on the basis of limited spectroscopic data would appear to occur at phosphorus, viz., [W(CPHPh2)(CO)2(Tp*)]BF4 ([8]BF4, Scheme 6). Scheme 6. Kinetic and Thermodynamic Protonation of Phosphinocarbyne 1

The data are limited because disolution in a range of solvents (CH2Cl2, CHCl3, MeCN) results in spontaneous isomerization to the thermodynamic product (vide inf ra). Consistent with protonation at phosphorus (i.e., a heteroatom), washing precipitated [8]BF4 with diethyl ether regenerates the starting complex 1, indicating that protonation at phosphorus is reversible. The solid-state infrared spectrum of [8]BF4 includes four absorptions of note. First, the CO-associated absorptions (Nujol: 2022, 1937 cm−1, kCK = 15.81 N cm−1) appear close to those of the related phosphoniocarbyne salt [2]I (2015, 1925 cm−1, kCK = 15.66 N cm−1) when the relative basicities of PMePh2 and PHPh2 are taken into account (Tolman electronic parameters:73 PMePh2 = 2067.3, PHPh2 = 2073.0 cm−1). In addition to the characteristic νBH absorption at 2578 cm−1, an additional albeit weak absorption was observed at 2457 cm−1. Given this appears above the range associated with νWH absorptions for terminal hydride ligands, we tentatively assign it to the νPH mode by comparison with that observed (2415 cm−1) for [HPPh3][WOCl4(OPPh3)].74 Furthermore, the values calculated (νPH = 2402, νCO = 2004, 1946 cm−1, kCK = 15.73 N cm−1, vide inf ra) agree well, given the caveats associated with comparisons between experimental solid-state and calculated gas-phase data for ionic species. Within 2 min of dissolution in CH2Cl2, infrared spectroscopy indicated approximately 80% conversion to a thermodynamic product (absorptions for [8]+ were fleetingly observed in solution at 2022, 1937 cm−1), precluding the acquisition of useful NMR data for [8] + . The reaction of 1 with trifluoromethanesulfonic acid (HOTf) proceeds in a similar manner to that with HBF4·Et2O though not as cleanly, and the products [8]OTf and [9]OTf are less stable than the corresponding fluoroborate salts. After overnight at room temperature [9]OTf is present, but the 1H NMR spectrum in CD3CN indicates the presence of a significant number of other unidentified species. The spectroscopic, mass spectrometric, and elemental microanalytical data for the product are all consistent with its

Scheme 7. Kinetic and Thermodynamic Protonation of a Phospha-alkenyl Carbyne76

Given the lack of experimentally derived structural data for either [8]+ or [9]+, the geometries of both were computationally optimized at the BP86/BS1 level of theory and are depicted in Figure 13a and b, respectively. The relative energies of the two different isomers (ΔG[8]→[9] = −22.4 kJ mol−1 (gas phase) account for the irreversible isomerism. Among the factors that contribute to the thermodynamic preference for the formation of a phosphinocarbene ligand, the development of a direct W− P bond alleviates the otherwise coordinative unsaturation at tungsten (HOMO−7, Figure 14). While solvent-mediated P-deprotonation/C-protonation may not be excluded, given the reversibility of P-protonation, direct P−C prototropy was also considered. A trajectory for the isomerism is presented in Figure 15, which includes the identification of an intermediate PCHW, in which the tungsten is partially stabilized by an agostic C−H−W interaction (ΔGCHW = +16.5 kJ mol−1). However, this is separated from K


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Figure 13. Calculated geometries (BP86/BS1) for (a) phosphoniocarbyne [8]+ (HPCW). Selected bond lengths (Å) and angles (deg): W−C 1.860, C−P 1.757, P−H 1.421, W−C−P 170.0, C−P−H 108.9. (b) Phosphinocarbene [9]+ (HCPW). Selected bond lengths (Å) and angles (deg): W−C 1.999, W−P 2.544, C−P 1.730, C−H 1.093, W− C−H 140.6, H−C−P 133.6, W−C−P 85.7, C−P−W 51.6, P−W−C 42.7.

Figure 15. Prototropic trajectory for the isomerism of [8]+ (HPCW) to [9]+ (HCPW) via intermediate PCHW. Energies in the gas phase.

transfer to and from the solvent, i.e., a rapid but reversible protonation of phosphorus followed by a slow but irreversible direct protonation at carbon. Support for the intermediacy of PCHW is provided by the complex [W(CH2)(CO)2(Tp*)]+ described by Templeton,78 in which one methylidene C−H bond agostically associates with the tungsten center. Such interactions are typically weak, and, accordingly, in the case of PCHW this is replaced by the more favorable P−W interaction in HCPW (ΔGHCPW = −22.4 kJ mol−1). The protonation of 1 to afford [9]+ (via [8]+) has direct analogy with that of [W(CSMe)(CO)2(Tp)], reported by Angelici to afford [W{η2-C(H)SMe}(CO)2(Tp)]+, though no intermediate corresponding to [8]+ was observed.79 Alternatively, related bidentate thiolatocarbenes may be obtained via either the alkylation of thioacyl ligands50a,b or the reaction of carbyne complexes with [MeSSMe2]BF4.50a,b,80 Angelici’s thiolato carbene reacts with nucleophiles (HNu) in one (or more) of four ways: (i) coordination of the nucleophile to the carbene carbon to afford [W{η2-C(SMe)NuH}(CO)2(Tp)]BF4; (ii) deprotonation of the C−H group to regenerate [W(CSMe)(CO)2(Tp)]; (iii) formation of a new carbyne complex [W(CNu)(CO)2(Tp)] for selected monobasic nucleophiles; (iv) disproportionation to afford both [W{η2CH(SMe)2}(CO)2(Tp)] and [W(CSMe)(CO)2(Tp)]. In many cases outcomes (iii) and (iv) were found to compete. The salt [9]BF4, however, behaves quite differently. First, it is not observed to form upon treatment of [W(CH)(CO)2(Tp*)] with ClPPh2 and NaPF6, in contrast to the formation of [W(η2-CPhPPh2)(CO)2(Tp)]BPh4.75 Second, in contrast to [8]BF4, which spontaneously deprotonates in THF or Et2O solution, and [W{η2-C(H)SMe}(CO)2(Tp)]+, which is deprotonated by a range of bases, all attempts to deprotonate [9]BF4 resulted in either no reaction or a plethora of unidentified products (by 31P NMR specroscopy).

Figure 14. Frontier orbitals of interest associated with the WPC metallacycle of [8]+ (HCPW): (a) HOMO−7; (b) HOMO−11.

HPCW by a transition state (TS1) in which the proton traverses the P−C bond (ΔG⧧ = 171.5 kJ mol−1), which would not be accessible under the reaction conditions. We must therefore conclude that the prototropy from phosphorus to carbon is not a concerted process, but rather an intermolecular L


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The solvation energies were calculated using BS2 on gas-phaseoptimized geometries with the CPCM solvation model89 using dichloromethane and acetonitrile as solvents. Single-point calculations were also carried out at the M06/BS2, B97D/BS2, and B3LYP/BS2 level of theories. Synthesis of [W(CPPh2)(CO)2(Tp*)] (1). A solution of [W( CBr)(CO)2(Tp*)] (5.001 g, 7.951 mmol) in THF (100 mL) was cooled to −78 °C in a dry ice/acetone bath and treated with nBuLi (4.7 mL, 1.7 M in hexanes, 8.0 mmol). The resulting light brown solution was stirred for 45 min and then treated with PClPh2 (1.45 mL, 8.08 mmol). The solution instantly turned dark red and was left in the dry ice/acetone bath to warm to room temperature overnight. The solvent was removed under reduced pressure, and the residue was chromatographed on silica gel using CH2Cl2 as the eluent. The first orange band (containing the product) was collected. Ethanol was added, and the solution was concentrated on the rotary evaporator to afford 1 as an orange powder, which was isolated by filtration. Crystals suitable for crystallographic analysis were obtained by slow diffusion of n hexane into a solution of 1 in CH2Cl2. Yield: 5.228 g (7.120 mmol, 90%). IR (Nujol) ν/cm−1: 2548 w (BH), 2001 m, 1974 s, 1912 m, 1883 s (CO, solid state splitting). IR (CH2Cl2) ν/cm−1: 2554 w (BH), 1982 vs, 1891 vs (CO). IR (THF) ν/cm−1: 2550 w (BH), 1981 s, 1893 vs (CO). 1H NMR (CDCl3) δ/ppm: 7.62−7.56 (m, 4 H, C6H5), 7.36−7.31 (m, 6 H, C6H5), 5.85 (s, 2 H, pzH), 5.74 (s, 1 H, pzH), 2.38 (s, 3 H, pzCH3), 2.37 (s, 6 H, pzCH3), 2.31 (s, 3 H, pzCH3), 2.26 (s, 6 H, pzCH3). 13C{1H} NMR (CDCl3) δ/ppm: 292.6 (d, WC, 1 JPC = 74.5, 1JWC = 187.9), 225.3 (s, CO, 1JWC = 168.9), 152.6 (1 C), 152.2 (2 C), 145.3 (1 C), 144.6 (2 C) [C3,5(pz)], 136.5 [d, C1(C6H5), 1 JPC = 9.4], 133.5 [d, C2,3,5,6(PPh), JPC = 19.7], 128.6 [s, C4(C6H5)], 128.5 [d, C2,3,5,6(PPh), JPC = 7.2], 106.8 (1 C), 106.6 (2 C) [C4(pz)], 16.6 (2 C), 15.3 (1 C), 12.9 (2 C), 12.7 (1 C) (pzCH3). 31P{1H} NMR (CDCl3) δ/ppm: 32.0 (s, 2JWP = 69.0). MS-ESI(+): m/z 734.7 [M]+, 619.8 [M − 2CO + MeCN]+, 679.5 [M − 2CO + H]+. Accurate mass: found 735.2006 [M + H]+, calcd for C30H33BN6O2P184W 735.2005. Anal. Found: C, 48.48; H, 4.65; N, 11.42. Calcd for C30H32BN6O2PW: C, 49.07; H, 4.39; N, 11.45.90 Crystals suitable for X-ray diffraction were obtained by slow diffusion of n-hexane into a solution of 2 in CH2Cl2. Crystal data for C30H32BN6O2PW: Mw = 734.26, triclinic, P1̅ (No. 2), a = 8.1714(1) Å, b = 10.1587(1) Å, c = 18.9544(2) Å, α = 76.1227(8)°, β = 87.1138(8)°, γ = 81.0287(7)°, V = 1508.67(3) Å3, Z = 2, ρcalcd = 1.616 Mg m−3, μ(Mo Kα) = 3.92 mm−1, T = 200(2) K, orange plate, 0.23 × 0.14 × 0.05 mm, 8792 independent reflections. F2 refinement, R = 0.025, wR = 0.055 for 7926 reflections (I > 2σ(I), 2θmax = 60°), 371 parameters. Synthesis of [W(CPMePh2)(CO)2(Tp*)]I ([2]I). Methyl iodide (0.3 mL, excess) was added to a solution of [W(CPPh2)(CO)2(Tp*)] (1: 0.300 g, 0.409 mmol) in CH2Cl2 (20 mL) and stirred for 3 days. The orange solution gradually became red, and IR monitoring showed the formation of the product (2022, 1937 cm−1). The solution was filtered through diatomaceous earth and then chromatographed on neutral alumina using 2:1 CH2Cl2/MeCN as the eluent. The bright pink band was collected and the solvent removed by rotary evaporation, affording the product as a red microcrystalline solid. Yield: 0.268 g (0.306 mmol, 75%). IR (Nujol) ν/cm−1: 2556 w (BH), 2015 s, 1925 s (CO). IR (CH2Cl2) ν/cm−1: 2560 w (BH), 2022 s, 1937 vs (CO). IR (THF) ν/cm−1: 2557 w (BH), 2018 vs, 1932 vs (CO). 1H NMR (CDCl3) δ/ppm: 7.90−7.83 (m, 4 H, C6H5); 7.77− 7.73 (m, 2 H, C6H5); 7.69−7.62 (m, 4 H, C6H5); 6.00 (s, 2 H, pzH); 5.82 (s, 1 H, pzH); 2.79 (d, 3 H, PCH3, 2JPH = 12.9); 2.41 (s, 6 H, pzCH3); 2.35 (s, 3 H, pzCH3); 2.31 (s, 3 H, pzCH3); 2.18 (s, 6 H, pzCH3). 13C{1H} NMR (CDCl3) δ/ppm: 242.8 (s, WC, 1JWC = 206.2), 221.8 (d, W-CO, 3JPC = 2.8, 1JWC = 158.3), 152.1 (1 C), 150.2 (2 C), 146.1 (1 C), 145.3 (2 C) [C3,5(pz)], 133.8 [d, C4(C6H5), 4JPC = 1.9], 131.4, [d, C2,3,5,6(PPh), JPC = 11.1], 129.4 [d, C2,3,5,6(C6H5), JPC = 12.8], 120.1 [d, C1(C6H5), 1JPC = 89.3], 107.1 (1 C), 106.6 (2 C) [C4(pz)], 16.0 (2 C), 14.4 (1 C), 12.0 (1 C), 11.9 (2 C) (pzCH3), 11.1 (d, PCH3, 1JPC = 57.0). 31P{1H} NMR (CDCl3) δ/ppm: 12.2 (s, 2 JWP = 161.6). MS-ESI(+): m/z 762.6 [M + MeCN − CO − I]+, 749.5 [M − I]+, 721.5 [M − CO − I]+, 693.6 [M − 2CO − I]+. Accurate

CONCLUDING REMARKS A convenient synthesis of the first phosphinocarbyne complex of tungsten 1 has allowed an integrated experimental and computational study of the bonding and reactivity of this rare class of carbyne ligand with a variety of electrophiles. Three outcomes were encountered (Scheme 8), in which the Scheme 8. Regioselectivity of Electrophilic (E) Attack at the Phosphinocarbyne Complex 1

electrophile was ultimately found to reside on the phosphorus, on the carbon, or across the WC multiple bond. It remains to be seen where metal-based electrophiles might attack the WCP spine.81

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EXPERIMENTAL SECTION

General Considerations. All manipulations of air-sensitive compounds were carried out under a dry and oxygen-free nitrogen atmosphere using standard Schlenk, vacuum line, and inert atmosphere (argon) drybox techniques with dried and degassed solvents. NMR spectra were recorded at 25 °C on a Varian Mercury 300 (1H at 300.1 MHz, 31P at 121.5 MHz), Varian Inova 300 (1H at 299.9 MHz, 13C at 75.47 MHz, 31P at 121.5 MHz), Varian Mercury 400 (1H at 399.9 MHz, 13C at 100.5 MHz, 31P at 161.9 MHz), Varian Inova 500 (1H at 500.0 MHz, 13C at 125.7 MHz, 31P at 202.4 MHz), or Bruker Avance 600 (1H at 600.0 MHz, 13C at 150.9 MHz) spectrometers. Chemical shifts (δ) are reported in ppm and referenced to the solvent peak (1H, 13C) or external 85% H3PO4 (31P) with coupling constants given in Hz. While 13C{1H} signals for ortho and meta carbon nuclei of PPh2 groups could be routinely observed, their narrow spectral range and comparable JPC values often precluded unequivocal assignment, in which case they are designated as “C2,3,5,6(PPh)”. Infrared spectra were obtained from solution and in the solid state (Nujol) using a PerkinElmer Spectrum One FT-IR spectrometer. Elemental microanalytical data were obtained from the ANU Research School of Chemistry microanalytical service. Electrospray ionization mass spectrometry (ESI-MS) was performed by the ANU Research School of Chemistry mass spectrometry service with acetonitrile as the matrix. Data for X-ray crystallography were collected with a Nonius Kappa CCD diffractometer. The compound [W( CBr)(CO)2(Tp*)]22 was prepared according to published procedures. All other reagents were obtained from commercial sources. Computational Details. All computational works were performed by using the Gaussian 09 suite of programs.82 The geometries of all complexes have been optimized at the DFT level of theory using the exchange functional of Becke83 in conjunction with the correlation functional of Perdew84,85 (BP86). The Stuttgart basis set in combination with the 60-core−electron relativistic effective core potential (SDD)86 was used for W; 6-31G(d)87 basis sets were used for all other atoms. This basis set combination is referred to as BS1. Frequency calculations were performed to confirm that optimized structures were minimal or saddle points using the BP86/BS1 level of theory. Single-point energy calculations for all the optimized structures were carried out with a larger basis set (BS2). BS2 utilizes the quadruple-ζ valence def2-QZVP88 basis set on W along with the corresponding ECP and the 6-311+G(2d,p) basis set on other atoms. M


Organometallics

Article

mass: found 749.2168 [M − I]+, calcd for C31H35BN6O2P184W 749.2162. Anal. Found: C, 42.28; H, 4.20; N, 9.63. Calcd for C31H35BIN6O2PW: C, 42.49; H, 4.03; N, 9.59. Synthesis of [W(CPPh2BH3)(CO)2(Tp*)] (3). Dimethylsufide borane (Me2SBH3: 0.05 mL, 0.5 mmol) was added to a solution of [W(CPPh2)(CO)2(Tp*)] (1: 0.300 g, 0.409 mmol) in toluene (10 mL), and the reaction mixture was stirred overnight. The brown suspension was allowed to settle, and the supernatant was filtered off. The precipitate was washed with 2 × 2 mL of toluene, and the washings were combined with the filtrate. The solution was filtered through diatomaceous earth, and the solvent removed under reduced pressure. Et2O was added to the brown solid residue, and the mixture was ultrasonically triturated to provide the product as a brown powder, which was collected by vacuum filtration. Crystals suitable for X-ray diffraction were obtained from slow diffusion of n-hexane into a solution of 5 in CHCl3. Yield: 0.178 g (0.238 mmol, 58%). IR (Nujol) ν/cm−1: 2557 w (pzBH), 2359 br (BH3), 2001 s, 1911 s, (CO). IR (CH2Cl2) ν/cm−1: 2556 w (pzBH), 2359 br (BH3), 2003 s, 1915 s, (CO). IR (THF) ν/cm−1: 2552 w (pzBH), 2375 br (BH3), 2003 s, 1916 s, (CO). 1H NMR (CDCl3) δ/ppm: 7.84−7.77 (m, 4 H, C6H5), 7.47−7.41 (m, 6 H, C6H5), 5.89 (s, 2 H, pzH), 5.76 (s, 1 H, pzH), 2.38 (s, 9 H, pzCH3), 2.31 (s, 3 H, pzCH3), 2.23 (s, 6 H, pzCH3). 13 C{1H} NMR (CDCl3) δ/ppm: 271.2 (d, WC, 1JPC = 21.1, 1JWC = 199.2), 224.2 (s, W-CO, 1JWC = 164.5), 152.8 (1 C), 152.1 (2 C), 145.6 (1 C), 145.0 (2 C) [C3,5(pz)], 132.8 [d, C2,3,5,6(PPh), JPC = 10.6], 130.8 [s, C4(C6H5)], 130.3 [d, C1(C6H5), 1JPC = 57.3], 128.6 [d, C2,3,5,6(PPh), JPC = 10.6], 107.2 (1 C), 106.8 (2 C) [C4(pz)], 16.9 (2 C), 15.2 (1 C), 12.8 (2 C), 12.7 (1 C) (pzCH3). 31P{1H} NMR (CDCl3) δ/ppm: 32.0 (s, broad). 11B{1H} NMR (CDCl3) δ/ppm: −10.1 (s, BN3), −37.8 (s, BH3). MS-ESI(+): m/z 789.9 [M + MeCN + H]+, 770.8 [M + Na]+, 749.4 [M + H]+, 735.3 [M − BH2]+. Accurate mass: found 790.2601 [M + MeCN + H]+, calcd for C32H39B2N7O2P184W 790.2599; found 771.2151 [M + Na]+, Calcd for C30H35B2N6O2NaP184W 771.2152. Anal. Found: C, 47.88; H, 4.68; N, 11.35. Calcd for C30H35B2N6O2PW: C, 48.17; H, 4.72; N, 11.23. Crystal data for C30H35B2N6O2PW·CHCl3: Mw = 867.47, triclinic, P1̅ (No. 2), a = 10.2173(2) Å, b = 10.4412(2) Å, c = 17.5622(3) Å, α = 90.0224(10)°, β = 92.6882(10)°, γ = 105.8832(10)°, V = 1799.87(6) Å3, Z = 2, ρcalcd = 1.601 Mg m−3, μ(Mo Kα) = 3.51 mm−1, T = 200(2) K, orange block, 0.22 × 0.15 × 0.11 mm, 10 526 independent reflections. F2 refinement, R = 0.040, wR = 0.089 for 8636 reflections (I > 2σ(I), 2θmax = 60°), 415 parameters. Synthesis of [W(CPSPh2)(CO)2(Tp*)] (4) and [W(η2-SCPSPh2)(CO)2(Tp*)] (5). A solution of [W(CPPh2)(CO)2(Tp*)] (1: 0.500 g, 0.681 mmol) and elemental sulfur (0.022 g, 0.69 g-atom) in THF (30 mL) was stirred overnight. The volatiles were removed in vacuo, and the residue was chromatographed on silica gel at −30 °C with CH2Cl2 as the eluent. The second (purple) and fourth (orange) fractions were collected, containing [W(η2-SCPSPh2)(CO)2(Tp*)] (5) and [W(CPSPh2)(CO)2(Tp*)] (4), respectively. Complex 4 was isolated by concentration of a CH2Cl2/EtOH solution in vacuo to afford the product as an orange powder. Complex 5 was isolated by addition of Et2O and sonication to afford the product as a purple powder. Crystals of 4 suitable for X-ray diffraction were obtained from CH2Cl2/n-hexane. Crystals of 5 suitable for X-ray diffraction were obtained from CH2Cl2/MeOH. When the reaction is carried out in toluene, 4 and 5 are obtained in 80% and 16% yields, respectively. If the reaction is carried out with an excess of sulfur (10 equiv), then 4 is obtained in 98% yield. [W(CPSPh2)(CO)2(Tp*)] (4). Yield: 0.422 g (0.551 mmol, 81%). IR (Nujol) ν/cm−1: 2560 w, 2550 w (BH, solid-state splitting), 1996 s, 1924 s, 1909 s (CO, solid-state splitting). IR (CH2Cl2) ν/cm−1: 2556 w (BH), 2004 s, 1916 s (CO). IR (THF) ν/cm−1: 2552 w (BH), 2004 s, 1997 sh, 1918 s, 1908 sh (CO). 1H NMR (CDCl3) δ/ppm: 8.00− 7.95 (m, 4 H, C6H5), 7.47−7.43 (m, 6 H, C6H5), 5.88 (s, 2 H, pzH), 5.76 (s, 1 H, pzH), 2.38 (s, 9 H, pzCH3), 2.31 (s, 3 H, pzCH3), 2.27 (s, 6 H, pzCH3). 13C{1H} NMR (CDCl3) δ/ppm: 270.1 (d, WC, 1 JPC = 4.9, 1JWC = 198.4), 224.0 (s, W-CO, 1JWC = 162.5), 152.8 (1 C), 152.4 (2 C), 145.7 (1 C), 145.0 (2 C) [C3,5(pz)], 134.3 [d, C1(C6H5), 1 JPC = 86.7], 131.9 [d, C2,3,5,6(PPh), JPC = 11.0], 131.1 [d, C4(C6H5),

3

JPC = 2.4], 128.5 [d, C2,3,5,6(PPh), JPC = 12.2], 107.2 (1 C), 106.9 (2 C) [C4(pz)], 17.0 (2 C), 15.3 (1 C), 12.8 (2 C), 12.8 (1 C) (pzCH3). 31 1 P{ H} NMR (CDCl3) δ/ppm: 41.0 (s, 2JWP = 152.5). MS-ESI(+): m/z 789.5 [M + Na]+, 710.7 [M − 2CO]+, 454.6 [M − 2CO − Tp* + MeCN]+, 413.5 [M − 2CO − Tp*]+. Accurate mass: found 789.1545 [M + Na]+, calcd for C30H32BN6O2NaPS184W 789.1545. Anal. Found: C, 47.19; H, 4.47; N, 10.84. Calcd for C30H32BN6O2PSW: C, 47.02; H, 4.21; N, 10.97. Crystal data for C30H32BN6O2PSW: Mw = 766.32, triclinic, P1̅ (No. 2), a = 10.2968(2) Å, b = 10.4179(2) Å, c = 17.2038(4) Å, α = 98.7173(12)°, β = 106.0368(13)°, γ = 106.6702(11)°, V = 1644.85(6) Å3, Z = 2, ρcalcd = 1.547 Mg m−3, μ(Mo Kα) = 3.66 mm−1, T = 200(2) K, orange block, 0.20 × 0.18 × 0.11 mm, 9625 independent reflections. F2 refinement, R = 0.042, wR = 0.089 for 7233 reflections (I > 2σ(I), 2θmax = 60°), 379 parameters. [W(η2-SCPSPh2)(CO)2(Tp*)] (5). Yield: 0.047 g (0.059 mmol, 9%). IR (Nujol) ν/cm−1: 2552 w (BH), 1992 s, 1892 s (CO). IR (CH2Cl2) ν/cm−1: 2559 w (BH), 1995 s, 1907 s (CO). IR (THF) ν/cm−1: 1993 s, 1908 s (CO). 1H NMR (CDCl3) δ/ppm: 8.09−8.02 (m, 4 H, C6H5), 7.51−7.42 (m, 6 H, C6H5), 5.91 (s, 1 H, pzH), 5.80 (s, 2 H, pzH), 2.55 (s, 3 H, pzCH3), 2.37 (s, 6 H, pzCH3), 2.32 (s, 3 H, pzCH3), 1.93 (s, 6 H, pzCH3). 13C{1H} NMR (CDCl3) δ/ppm: 250.1 (d, WC, 1JPC = 42.0, 1JWC = 42.8), 224.5 (s, W-CO, 1JWC = 76.3), 153.8 (1 C), 152.9 (2 C), 145.3 (1 C), 144.4 (2 C) [C3,5(pz)], 132.7 [d, C1(C6H5), 1JPC = 87.3], 132.5 [d, C2,3,5,6(PPh), JPC = 11.0], 131.5 [s, C4(C6H5)], 128.3 [d, C2,3,5,6(PPh), JPC = 13.3], 108.2 (1 C), 107.5 (2 C) [C4(pz)], 16.3 (1 C), 13.7 (2 C), 13.2 (1 C), 12.6 (2 C) (pzCH3). 31P{1H} NMR (CDCl3) δ/ppm: 52.9 (s). MS-ESI(+): m/z 821.6 [M + Na]+, 798.7 [M]+, 743.4 [M − 2CO + H]+. Accurate mass: found 821.1268 [M + Na]+, calcd for C30H32BN6O2NaPS2184W 821.1266. Anal. Found: C, 44.41; H, 4.20; N, 10.42. Calcd for C30H32BN6O2PS2W: C, 45.13; H, 4.04; N, 10.53.90 The crystal structure determination revealed solvent-accessible void channels consistent with partial solvation (SQUEEZE protocol), which most likely accounts for the low percentage of carbon found in the elemental microanalytical data. Crystal data for C30H32BN6O2PS2W: Mw = 798.39, monoclinic, P21/c, a = 9.9675(2) Å, b = 15.4834(4) Å, c = 23.6677(6) Å, β = 92.4264(15)°, V = 3649.38(15) Å3, Z = 4, ρcalcd = 1.453 Mg m−3, μ(Mo Kα) = 3.36 mm−1, T = 200(2) K, purple lath, 0.30 × 0.09 × 0.04 mm, 8407 independent reflections. F2 refinement, R = 0.095, wR = 0.217 for 6295 reflections (I > 2σ(I), 2θmax = 55°), 388 parameters. Synthesis of [W(CPSePh2)(CO)2(Tp*)] (6). A mixture of [W( CPPh2)(CO)2(Tp*)] (1: 0.306 g, 0.417 mmol) and gray selenium (0.033 g, 0.42 g-atom) was stirred overnight in CH2Cl2 (15 mL). The solvent was removed in vacuo. The red residue was chromatographed on silica (4 × 10 cm) with 1:1 CH2Cl2/n-pentane as the eluent. The first yellow band to elute containing 1 was discarded, and the polarity increased to 3:1 CH2Cl2/n-pentane. The red fraction containing the product was collected, and the solvent was removed in vacuo. The orange residue was redissolved in CH2Cl2, EtOH was added, and the solution was concentrated in vacuo to afford the product as an orange microcrystalline powder. Yield: 0.313 g (0.385 mmol, 92%). Crystals of 6 suitable for X-ray diffraction were obtained by slow concentration of a saturated solution in CHCl3. IR (Nujol) ν/cm−1: 2553 w (BH), 2002 s, 1912 s (CO). IR (CH2Cl2) ν/cm−1: 2556 w (BH), 2005 vs, 1917 vs (CO). IR (THF) ν/cm−1: 2552 w (BH), 2004 vs, 1997 s, 1918 vs, 1907 s (CO). 1H NMR (CDCl3) δ/ppm: 8.02−7.95 (m, 4 H, C6H5), 7.44−7.41 (m, 6 H, C6H5), 5.90 (s, 2 H, pzH), 5.78 (s, 1 H, pzH), 2.40 (s, 6 H, pzCH3), 2.38 (s, 3 H, pzCH3), 2.32 (s, 3 H, pzCH3), 2.27 (s, 6 H, pzCH3). 13C{1H} NMR (CDCl3) δ/ppm: 265.2 (d, WC, 1JPC = 13.6, 1JWC = 201.4), 224.0 (d, W-CO, 3JPC = 3.0, 1 JWC = 164.4), 152.8 (1 C), 152.3 (2 C), 145.7 (1 C), 145.0 (2 C) [C3,5(pz)], 133.2 [d, C1(C6H5), 1JPC = 76.9], 132.2 [d, C2,3,5,6(PPh), JPC = 12.1], 131.1 [d, C4(C6H5), 3JPC = 3.0], 128.4 [d, C2,3,5,6(PPh), JPC = 13.6], 107.2 (1 C), 106.8 (2 C) [C4(pz)], 17.0 (2 C), 15.3 (1 C), 12.8 (2 C), 12.7 (1 C) (pzCH3). 31P{1H} NMR (CDCl3) δ/ppm: 31.9 (s, 2JWP = 152.6, 1JSeP = 711.8). MS-ESI(+): m/z 836.6 [M + Na]+, 813.3 [M − H]+, 787.4 [M − CO + H]+, 759.5 [M − 2CO + H]+. Accurate mass: found 814.1093, calcd for C30H32BN6O2P80Se184W 814.1092. Anal. Found: C, 44.59; H, 3.96; N, 10.77. Calcd for N


Organometallics

Article

Synthesis of [W{η2-C,P-C(H)PPh2}(CO)2(Tp*)]BF4 ([9]BF4). Dissolution of the precipitate of [8]BF4 obtained above in CH3CN, CHCl3, or CH2Cl2 afforded a dark purple solution. Removal of the solvent in vacuo afforded [9]BF4 as a purple solid. A sample for elemental microanalysis was obtained by washing the crude product with cold (−15 °C) diethyl ether (2 × 10 mL) and storage under high vacuum for 8 days. Yield: 0.179 g (0.218 mmol, 80%). IR (Nujol) ν/cm−1: 2563 w (BH), 2055 s, 1979 broad, vs, 1926 broad, m (CO). IR (CH2Cl2) ν/cm−1: 2567 w (BH), 2054 s, 1982 vs (CO). The IR spectrum could not be obtained in THF, as [9]BF4 is not stable in THF. 1H NMR (CDCl3) δ/ppm: 14.78 (d, 1 H, WCH, 2JPH = 4.8, 2 JWH = 13.8), 7.45−7.40 (m, 2 H, C6H5), 7.34−7.26 (m, 4 H, C6H5), 7.09−7.02 (m, 4 H, C6H5), 6.06 (s, 1 H, pzH), 5.89 (s, 2 H, pzH), 2.60 (s, 3 H, pzCH3), 2.51 (s, 6 H, pzCH3), 2.35 (s, 3 H, pzCH3), 1.42 (s, 6 H, pzCH3). 13C{1H} NMR (CDCl3) δ/ppm: 237.1 (d, WC, 1 JPC = 46.3, 1JWC = 21.5), 214.8 (s, W-CO, 1JWC = 134.3), 154.7 (1 C), 153.5 (2 C), 148.1 (1 C), 146.9 (2 C) [C3,5(pz)], 133.2 [d, C 2,3,5,6(C6H5 ), J PC = 12.1], 132.2 [s, C 4(C 6H5)], 129.5 [d, C2,3,5,6(C6H5), JPC = 13.6], 128.8 [d, C1(C6H5), 1JPC = 64.9], 109.6 (1 C), 109.0 (2 C) [C4(pz)], 16.3 (1 C), 15.5 (2 C), 13.1 (1 C), 12.8 (2 C) (pzCH3). 13C NMR (CDCl3) δ/ppm: 237.1 (dd, WC, 1JPC = 46.3, 1JCH = 199.0, 1JWC = 21.5). 31P{1H} NMR (CDCl3) δ/ppm: −101.3 (s, 1JWP = 138.5). MS-ESI(+): m/z 735.2 [M − BF4]+. Accurate mass: found 735.2005 [M − BF 4 ] + , calcd for C30H3311BN6O2P184W 735.2005. Anal. Found: C, 44.16; H, 4.34; N, 9.96. Calcd for C30H33B2F4N6O2PW: C, 43.83; H, 4.05; N, 10.22.

C30H32BN6O2PSeW: C, 44.31; H, 3.97; N, 10.33. Crystal data for C30H32BN6O2PSeW·CHCl3: Mw = 932.59, triclinic, P1̅ (No. 2), a = 10.2609(2) Å, b = 10.4116(1) Å, c = 17.5341(3) Å, α = 90.5897(11)°, β = 91.1982(9)°, γ = 106.3725(10)°, V = 1796.60(5) Å3, Z = 2, ρcalcd = 1.724 Mg m−3, μ(Mo Kα) = 4.53 mm−1, T = 200(2) K, orange plate, 0.26 × 0.24 × 0.12 mm, 10 523 independent reflections. F2 refinement, R = 0.041, wR = 0.092 for 8432 reflections (I > 2σ(I), 2θmax = 60°), 415 parameters. Synthesis of [W(CPOPh2)(CO)2(Tp*)] (7). Method A: A solution of [W(CPPh2)(CO)2(Tp*)] (1: 0.200 g, 0.272 mmol) in CH2Cl2 (20 mL) in air was treated with 30% aqueous H2O2 (1.0 mL, 9.8 mmol), and the mixture was stirred vigorously. After 75 min TLC showed the reaction was complete. The organic layer was washed with water (3 × 15 mL) and dried with MgSO4. The solvent was removed to afford crude 7 as an orange oil. The product was chromatographed on silica gel with 1:1 THF/hexane. An initial yellow band was discarded, and the second (major) orange band containing the product was collected. 1H and 31P{1H} NMR spectroscopy showed only a marginal improvement in purity as a result of chromatography (ca. 80% 7 by 31P{1H} NMR). Yield: 0.132 g (0.176 mmol, 65%). Method B: A solution of [W(CPPh2)(CO)2(Tp*)] (1: 0.100 g, 0.136 mmol) in toluene (9 mL) in air was heated to reflux. After 8 h IR spectroscopy indicated all the starting material had been consumed. The solvent was removed under reduced pressure. 1H and 31P{1H} NMR spectroscopy indicated 7 to be the major product (ca. 70% by 31 1 P{ H} NMR). Method C: A solution of [W(CBr)(CO)2(Tp*)] (0.020 g, 0.032 mmol) in THF (1 mL) was cooled to −78 °C and treated with nBuLi (0.07 mL, 0.45 M in hexanes, 0.03 mmol). The resulting dark yellow solution was stirred for 30 min and then treated with ClPOPh2 (0.31 mL, 0.10 M in THF/hexane, 0.032 mmol). The solution instantly turned orange and was stirred 40 min, then allowed to warm to room temperature and stirred for a further 40 min. The volatiles were removed under reduced pressure. 1H and 31P{1H} NMR spectroscopy indicated formation of 7 as the major product. IR (Nujol) ν/cm−1: 2550 w (BH), 2002 s, 1987 m, 1913 s, broad (CO). IR (CH2Cl2) ν/cm−1: 2556 w (BH), 2004 vs, 1983 m, 1915 vs, broad (CO). IR (THF) ν/cm−1: 2553 w (BH), 2001 vs, 1975 w, 1911 vs, broad (CO). 1H NMR (CDCl3) δ/ppm: 7.96−7.93 (m, 4 H, C6H5), 7.49−7.46 (m, 6 H, C6H5), 5.91 (s, 2 H, pzH), 5.78 (s, 1 H, pzH), 2.40 (s, 6 H, pzCH3), 2.38 (s, 3 H, pzCH3), 2.35 (s, 6 H, pzCH3), 2.33 (s, 3 H, pzCH3). 13C{1H} NMR (CDCl3) δ/ppm: 281.2 (d, WC, 1 JPC = 16.1, 1JWC = 190.6), 224.0 (d, W-CO, 1JWC = 164.4), 152.0 (1 C), 151.7 (2 C), 145.3 (1 C), 144.5 (2 C) [C3,5(pz)], 133.3 [d, C1(C6H5), 1JPC = 105.6], 131.0 [d, C2,3,5,6(C6H5), JPC = 10.0], 130.9 [d, C4(C6H5), 3JPC = 1.8], 127.9 [d, C2,3,5,6(C6H5), JPC = 12.1], 106.7 (1 C), 106.4 (2 C) [C4(pz)], 16.2 (2 C), 14.7 (1 C), 12.3 (2 C), 12.2 (1 C) (pzCH3). 31P{1H} NMR (CDCl3) δ/ppm: 19.9 (s, 2JWP = 145.2). MS-ESI(+): m/z 1523.4 [2 M + Na]+, 814.2 [M + Na + MeCN]+, 789.1 [M + K]+, 773.2 [M + Na]+, 751.2 [M + H]+. Accurate mass: found 751.1953 [M + H] + , calcd for C30H3311BN6O3P184W 751.1954; found 773.1777 [M + Na]+, calcd for C30H32BN623NaO3P184W 773.1774. Anal. Found: C, 47.48; H, 4.45; N, 11.06. Calcd for C30H32BN6O3PW: C, 48.03; H, 4.30; N, 11.20.90 NB: The observed data correspond more closely with those for a hemihydrate. Calcd for C30H32BN6O3PW·0.5H2O: C, 47.46; H, 4.38; N, 11.07. Synthesis of [W(CPHPh2)(CO)2(Tp*)]BF4 ([8]BF4). A suspension of [W(CPPh2)(CO)2(Tp*)] (1: 0.200 g, 0.272 mmol) in Et2O (12 mL) was cooled to −78 °C and treated with HBF4·Et2O (0.06 mL, 0.4 mmol) dropwise. The orange suspension was stirred at −78 °C for 1 h, then allowed to warm to room temperature and stirred for a further 45 min. Upon warming, the mixture became a pink suspension. The mixture was filtered, and the pink precipitate was washed with Et2O (2 × 3 mL) and npentane (2 × 3 mL) and dried under vacuum. IR spectroscopy revealed the precipitate to be [8]BF4. IR (Nujol) ν/ cm−1: 2578 w (BH), 2459 vw (PH, assignment substantiated by simulation at the BP86/BS1 level of theory), 2022 s, 1937 s (CO). IR (CH2Cl2) ν/cm−1: 2022 s, 1937 s (CO). The spectrum also contains bands attributable to small amounts of [9]BF4 and 1, so the BH and PH absorptions cannot be conclusively identified.

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ASSOCIATED CONTENT

S Supporting Information *

Crystallographic data for 1 (CCDC 995718), 3 (CCDC 995719), 4 (CCDC 995720), 5 (CCDC 995721), and 6 (CCDC 995722) in CIF format and computational details. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Australian Research Council (DP110101611). This research was undertaken with the assistance of resources provided at the NCI National Facility systems at the Australian National University through the National Computational Merit Allocation Scheme supported by the Australian Government and the Tasmanian Partnership for Advanced Computing.

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REFERENCES

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