Versatile Reactivity of Bridged Pentelidene Complexes toward

Jun 3, 2013 - The 31P{1H} NMR spectrum of 3 shows a mixture of A2H (74%, no coupling ... In these reactions the elimination of a W(CO)5 group was not ...
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Versatile Reactivity of Bridged Pentelidene Complexes toward Secondary and Tertiary Phosphines Markus Stubenhofer,† Christian Kuntz,† Michael Bodensteiner,† Alexey Y. Timoshkin,‡ and Manfred Scheer*,† †

Department of Inorganic Chemistry, University of Regensburg, 93053 Regensburg, Germany Department of Chemistry, St. Petersburg State University, University pr. 26, Old Peterhoff, 198504 St. Petersburg, Russia

‡

S Supporting Information *

ABSTRACT: The reaction of the phosphinidene complex [Cp*P{W(CO) 5 } 2 ] (1a) with secondary and tertiary phosphines, respectively, proceeds via W(CO)5 elimination to form the phosphoranylidene complexes [{W(CO)5}(Cp*)P-P(H)iPr2] (2), [{W(CO)5}(Cp*)P-PMeiPr2] (7), and [{W(CO)5}(Cp*)P-PEt3] (9). Other novel types of products, the phosphine-coordinated bridged parent phosphinidene complexes [{W(CO) 5} 2(H)P-PMeiPr2] (6a) and [{W(CO)5}2(H)P-PEt3] (8a), are obtained by elimination of 1,2,3,4-tetramethylfulvene. The latter reaction path is predominantly found for the arsinidene complex [Cp*As{W(CO)5}2] (1b) to yield [{W(CO)5}2(H)As-PHiPr2] (4) upon reaction with HPiPr2 and, with tertiary phosphines, the products [{W(CO)5}2(H)As-PMeiPr2] (6b) and [{W(CO)5}2(H)As-PEt3] (8b). If a secondary phosphine coordinates to a bridged parent pentelidene complex, Cp*H elimination occurs to form either HP[PiPr2{W(CO)5}]2 (3) or the phosphine-substituted diarsene complex W(CO)5[AsPiPr2{W(CO)5}]2 (5). Each of the new products has been characterized by X-ray structure analysis, NMR, and mass spectroscopy. In each case as a first step the Lewis acid/base adducts are formed, which was monitored by 31P NMR spectroscopy. The different reaction pathways of the electrophilic pentelidene complexes [Cp*E{W(CO)5}2] (E = P, As) have been emphasized by extended DFT calculations.

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INTRODUCTION In contrast to the case for their organic homologues, metal− carbene complexes, which represent an important class of compounds for many different applications,1 the chemistry and use of phosphinidene complexes have been less developed. They are characterized by the coordinated PR unit at a transition-metal moiety in a terminal or bridging manner. Whereas the chemistry of terminal phosphinidene complexes of the type LnMPR is well-developed,2 the chemistry and especially the reactivity of bridged compounds of the type LnM{μ-P(R)}MLn have been less explored.3 Recently, however, μ-phosphinidene chemistry has been developed by Ruiz4 and by us, the latter with reports on the reactivity of Cp*-containing bridged pentelidene complexes of the formula [Cp*E{W(CO)5}2] (E = P (1a), As (1b)).5 The use of Cp* as a substituent at the pentel atom opens multiple reaction channels for these molecules and makes them unique building blocks for subsequent reactions. Thus, by Cp* migration to the transition metal highly reactive species containing a pentel−tungsten triple bond are formed, which can be trapped by reactive compounds to yield metallo-heterocycles and cage compounds.6 In addition, the Cp* substituent can shift to an incoming substrate such as a nitrile to form P-containing heterocycles.7 Moreover, a Cp* radical elimination occurs under photolytic conditions and the remaining pentel radical [E{W(CO)5}2] can be trapped by reactive compounds © XXXX American Chemical Society

containing multiple bonds to yield, for example, stable triphospha or arsadiphospha radicals.8 However, the most important reactivity feature represents the electrophilicity of these starting materials, which leads to a nucleophilic attack of an incoming substrate at the pentelidene atom, as exemplified by reactions with primary phosphines. Hereby, after the formation of the adduct A an intramolecular hydrophosphination reaction occurs leading to B (Scheme 1). After rearrangement to C, a Cp*H elimination results. After reaction with another 1 equiv of the phosphine, a stereoselective formation of triphosphines and 2-arsadiphosphines (D) coordinated by W(CO) 5 was observed, for which a diphosphene or arsaphosphene intermediate was proposed.9 If Cp*PH2 is used as a primary phosphine, this reaction proceeds further via a new sequence of hydrophosphination, subsequent Cp* elimination, and retro-Diels−Alder reaction.10 In light of these initial results, the reactivity of the pentelidene complexes 1a,b with secondary and tertiary phosphines was of special interest. We are reporting herein the differences and similarities of the reaction pathways in comparison to the reactions with primary phosphines. Moreover, between the phosphinidene and arsinidene starting materials different reaction channels are observed. Received: April 24, 2013

A

dx.doi.org/10.1021/om400357y | Organometallics XXXX, XXX, XXX−XXX

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2 two doublets of an AM spin system at δ 42.8 and −67.7 ppm are detected. The observed 1JP,P coupling constant (298 Hz) compares well with that of [Cp*P{W(CO)5}2{H2P-BH2NMe3} (1JP,P = 276 Hz), which also represents a coordinative P−P bond.12 The signal at δ −67.7 ppm splits into a doublet of doublets in the 31P NMR spectrum, revealing the hydrogen atom at the phosphine unit (1JP,H = 297 Hz). The 31P{1H} NMR spectrum of 3 shows a mixture of A2H (74%, no coupling with 183W, 3′a), A2HX (12%, one coupling with 183W, 3′b), A2HX (12%, one coupling with 183W, 3′c) and A2HX2 (2%, two coupling with 183W, 3′d) spin systems with the terminal phosphorus atoms as a doublet at δ 64.3 ppm (1JP,P = 326 Hz) containing additionally four pairs of tungsten satellites with coupling constants of 27 Hz (2JP,W, 3′b + 3′c), 202 Hz (1JP,W, 3′b), 230 Hz (1JP,W, 3′d), and 256 Hz (1JP,W, 3′c). (For a simulation of the 31P NMR spectrum, see the Supporting Information) The central phosphorus atom displays a doublet of doublets which in the 31P NMR spectrum splits into a further doublet (1JP,H = 259 Hz). Compounds 4 and 5 show only singlets in the 31P{1H} NMR at δ 28.0 ppm (4) and δ 48.0 ppm (5). Reactivity toward Tertiary Phosphines. In comparison to secondary phosphines the tertiary phosphine PMe(iPr)2 reacts with the phosphinidene complex 1a to give 6a, a bridged phosphinidene complex coordinated by a phosphine (Scheme 3). During the reaction, 1,2,3,4-tetramethylfulvene is eliminated

Scheme 1. Reaction Sequence of the Pentelidene Complexes 1a,b with Primary Phosphines

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RESULTS AND DISCUSSION Reactivity toward Secondary Phosphines. Treatment of 1a with 2 equiv of HPiPr2 in toluene at −78 °C results in the formation of the corresponding pentacarbonyltungsten complex of the phosphoranylidenephosphine 2 by elimination of one W(CO)5 fragment. Additionally, the W(CO)5-stabilized triphosphine 3 is formed via Cp*H elimination. Only 3 could be isolated in an analytically pure yield of 18% (Scheme 2), while the remaining solution contains the major product 2. The ratio of 3 and 2 in the reaction solution is about 1:4. Compound 2 precipitates from n-hexane containing traces of 3, which could not be completely removed. Complexed triphosphines can alternatively be synthesized by the reaction of MP(SiMe 3 ) 2 (M = Li, Na, K) with complexed chlorophosphines or by reactions of PCl3 with complexed phosphines in the presence of NEt3.11 In contrast, the analogous reaction of the arsinidene complex 1b results in the formation of the phosphine-stabilized compound 4 in 48% isolated yield via fulvene elimination (monitored by 1H NMR). A change in the polarity of the solvent from toluene to CH2Cl2 leads to the formation of 5, featuring a side-on coordinated AsAs double bond with phosphanyl substituents. The corresponding reaction of the phosphinidene complex 1a in CH2Cl2 yields the same products as in toluene, but the phosphorus derivative of 5 was not observed. Compounds 2−4 are readily soluble in CH2Cl2 but dissolve only moderately in toluene. In contrast, 5 is less soluble in CH2Cl2. In the IR spectra of the products, stretching frequencies for terminal CO units are observed, and in the EI mass spectra the corresponding molecular ion peaks of 3−5 are detected. In contrast, the mass spectrum of 2 shows only characteristic fragment ions. In the 31P{1H} NMR spectrum of

Scheme 3. Reaction of Pentelidene Complexes with Tertiary Phosphines

(monitored by 1H NMR). Only a few parent (μ2-PH) phosphinidene complexes are known: e.g., [HP{(iPr4C5H)Re(CO) 2 } 2 ], [HP{Cp*Re(CO) 2 } 2 ], 13 and [HP{Cp*Mn(CO)2}2].14 Huttner et al. reported further examples of organic-substituted phosphinidene complexes coordinated by Lewis bases.15 The phosphoranylidene phosphine complex 7 is the main product of this reaction, but both compounds cocrystallize in an overall yield of 46%. Similar results are obtained by using PEt3 as the tertiary phosphine, due to its similar steric properties. The product ratio is similar, with the phosphoranylidene phosphine complex 9 as the main product.

Scheme 2. Reaction of Pentelidene Complexes with Secondary Phosphines

B

dx.doi.org/10.1021/om400357y | Organometallics XXXX, XXX, XXX−XXX

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Figure 1. Molecular structure of 3. Thermal ellipsoids are drawn at the 50% probability level; carbon-bound hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): W(1)−P(1) = 2.5468(7), P(1)−P(2) = 2.230(2); W(1)−P(1)−P(2) = 101.11(5), P(1)−P(2)−P(1′) = 129.95(7).

Figure 3. Molecular structure of 8a. Thermal ellipsoids are drawn at the 50% probability level; carbon-bound hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): W(1)−P(1) = 2.592(5), W(2)−P(1) = 2.585(6), P(1)−P(2) = 2.181(9); W(1)− P(1)−W(2) = 125.0(2), W(1)−P(1)−P(2) = 110.3(3), W(2)−P(1)− P(2) = 114.8(3).

However, the lower solubility of the coordinated phosphinidene allows 8a to be isolated as yellow prisms in moderate yields of 11%. In contrast to the case for 1a, the arsinidene complex 1b reacts with PMe(iPr)2 to give 6b and with PEt3 to give 8b under fulvene elimination as the only products. Both compounds have been isolated as orange solids in yields of over 70%. In these reactions the elimination of a W(CO)5 group was not observed. Compounds 6a,b, 7, 8a,b, and 9 are poorly soluble in hexane and moderately soluble in toluene but have good solubility in CH2Cl2. In the IR spectra, typical stretching frequencies for terminal CO ligands are observed. The molecular ion peaks of 6a,b, 7, and 8a are detected in the EI mass spectra. Additionally, the mass spectra of 6a,b and 8a reveal a characteristic fragmentation pattern of successive CO eliminations. The 31 1 P{ H} NMR spectrum of 7 shows two doublets of an AM spin system at δ 40.8 and −99.8 ppm, which is similar to those of 2 (δ 42.8 and −67.7 ppm), since the only difference is one methyl group at the phosphine ligand. However, the 1JP,P coupling constant of 490 Hz is much larger for 7 in comparison to that for 2 (298 Hz). Phosphoranylidene phosphine complexes of this type were already synthesized by Mathey et al. by reacting phosphorus norbornadiene derivatives with tertiary phosphines.16 The reported chemical shifts of the phosphinidene unit (−100 to −145 ppm) and the phosphine entity (+31 to +40 ppm) as well as large 1JP,P coupling constants (370 to 440 Hz) agree well with the data found for 7. The chemical shifts of 9 (+35.2 and −104.5 ppm) and the 1JP,P coupling constant of 476 Hz are also in good agreement. In comparison to 7 and 9, compounds 6a and 8a reveal smaller

1

JP,P coupling constants of 267 Hz (6a) and 260 Hz (8a), caused by the absence of the double-bond character. The 31 1 P{ H} NMR spectrum displays an AM spin system (6a, δ 40.3 and −182.3 ppm; 8a, δ 37.3 and −190.7 ppm). The assignment of the phosphorus atoms is unambiguous, because the signals at −182.3 and −190.7 ppm bear two pairs of tungsten satellites. The related arsenic-containing compounds 6b and 8b show only singlets at 28.2 ppm (6b) and 24.7 ppm (8b), as expected for the tertiary substituted phosphines. Crystal Structure Analysis. The main feature of 3 (Figure 1) is a triphosphine unit coordinated by two W(CO)5 fragments. The central phosphorus atom is disordered over two positions with equal occupancy. The H substituent could be located by residual electron density. The P−P bond length (2.230(2) Å) represents a slightly elongated single bond. In comparison to the calculated bond angle in the parent compound P3H5 (104.5°),17 the angle in compound 3 is significantly widened to 129.95(7)°, due to the steric demand of four isopropyl groups and two W(CO)5 fragments. Formally, the structures of 4 and 6b (Figure 2) can be viewed as the parent hydrogen-substituted arsinidene complexes both coordinated by a phosphine ligand. The structures consist of an arsenic atom in a distorted-tetrahedral environment coordinated by two W(CO)5 fragments. The hydrogen atom at the As1 site was located by a difference Fourier map. The arsenic−phosphorus bond distances of 2.306(3) Å (4) and

Figure 2. Molecular structures of 4 (left) and 6b (right): Thermal ellipsoids are drawn at the 50% probability level; organic hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg) are as follows. 4: W(1)−As(1) = 2.6747(11), W(2)−As(1) = 2.6522(10), P(1)− As(1) = 2.306(3); W(1)−As(1)−P(1) = 114.84(7), W(1)−As(1)−W(2) = 127.62(4), W(2)−As(1)−P(1) = 107.07(7). 6b: W(1)−As(1) = 2.6573(4) W(2)−As(1) = 2.6665(4), P(1)−As(1) = 2.3295(9); W(1)−As(1)−P(1) = 117.12(2), W(1)−As(1)−W(2) = 124.22(1), W(2)−As(1)− P(1) = 105.77(3). C

dx.doi.org/10.1021/om400357y | Organometallics XXXX, XXX, XXX−XXX

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2.3295(9) Å (6b) are in the range of P−As single bonds. The slight lengthening of the latter bond is most likely due to steric reasons. The As−W distances are elongated in comparison to those of the Cp*-substituted arsinidene complex 1b (2.5390(16) and 2.5562(16) Å)18 due to the inhibition of the π back-bonding from the two tungsten atoms by donation of the phosphines in the acceptor orbital at the pentelidene atom. Figure 3 shows the hydrogen-substituted phosphinidene complex 8a coordinated by a phosphine ligand, revealing a distorted-tetrahedral phosphorus atom. The P(1)−P(2) bond distance (2.181(9) Å) represents a slightly shortened P−P single bond. Compound 5 (Figure 4) is a unique example of a phosphinesubstituted diarsene complex side-on coordinated at a W(CO)5

Figure 5. Molecular structure of 7. Thermal ellipsoids are drawn at the 50% probability level; hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): W(1)−P(1) = 2.6363(11), P(1)− P(2) = 2.1631(16), P(1)−C(6) = 1.929(4); W(1)−P(1)−P(2) = 111.39(5), W(1)−P(1)−C(6) = 117.31(14), P(2)−P(1)−C(6) = 103.10(14).

Scheme 4. Possible Reaction Pathways of the Reactions with Secondary and Tertiary Phosphines

Figure 4. Molecular structure of 5. Thermal ellipsoids are drawn at the 50% probability level; hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): W(1)−P(1) = 2.5882(13), W(2)−P(2) = 2.5782(13), P(1)−As(1) = 2.3855(13), P(2)−As(2) = 2.3821(14), As(1)−W(3) = 2.7589(5), As(2)−W(3) = 2.7406(6), As(1)−As(2) = 2.3314(7); W(1)−P(1)−As(1) = 123.49(5), W(2)− P(2)−As(2) = 122.35(5), P(1)−As(1)−As(2) = 96.04(4), P(2)− As(2)−As(1) = 101.03(4), P(1)−As(1)−W(3) = 108.21(4), P(2)− As(2)−W(3) = 108.12(3), As(1)−W(3)−As(2) = 50.17(2), W(3)− As(2)−As(1) = 65.32(2), W(3)−As(2)−As(1) = 65.32(2).

fragment. The As−As distance (2.3314(7) Å) is shorter than a single bond and is comparable with that in the trans complex [(CO)4Fe(2,3-η-PhAsAsPh)] (As−As = 2.365(2) Å),19 but longer than the AsAs bond in sMes-AsAs-sMes (2.2634(7) Å).20 Hitherto, only examples of analogous diphosphorus compounds substituted by phosphine substituents have been reported,21 in addition to side-on and end-on coordinated diphosphenes and diarsenes by metal fragments.22 Compound 7 (Figure 5) reveals a shortened P−P bond (2.1631(16) Å), which can be regarded as a polar covalent P−P single bond. The P−C bond lengths at the phosphine substituent are in the range of single bonds, while the P−C distance toward the Cp* ligand is elongated to 1.929(4) Å. Computational Studies of the Reaction Mechanisms. To obtain insight into the energies of the different reaction pathways of 1a,b, DFT studies have been carried out. Computed energetic parameters for all considered reactions of 1a,b with secondary phosphine PHiPr2 and tertiary phosphines PMeiPr2 and PEt3 are summarized in Table 1. We propose the mechanistic pathway given in Scheme 4 for the formation of experimentally observed products. The first step is the formation of a Lewis acid/base adduct A between the phosphine and the pentelidene complex.12 Formation of A can be monitored by 31P NMR spectroscopy in solution at low

temperatures.23 Intermediate A is destabilized due to the bulky substituents at the pentelidene complex as well as at the phosphine ligand. In case of the tertiary phosphine two reaction pathways are possible to reduce the steric demands of the intermediate A. It can either eliminate a W(CO)5 fragment (formation of 7 and 9) or a fulvene moiety by leaving a H-substituted pentel atom (formation of 6a,b and 8a,b). All reactions leading to 6a,b− 9a,b are predicted to be exothermic in the gas phase. Thus, both proposed pathways (Scheme 3) are viable from an energetic point of view. The estimated Gibbs energy values in D

dx.doi.org/10.1021/om400357y | Organometallics XXXX, XXX, XXX−XXX

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phosphino−arsinidene species B (E = As) are formed. As a next step a W(CO)5 fragment shifts from the pentelidene atom to the phosphine substituent with formation of intermediate C. At this stage the phosphinidene complex C (E = P) reacts with another phosphine ligand to form intermediate D, and finally 3 is formed after some rearrangements. In contrast, the arsinidene complex intermediate C (E = As) undergoes a dimerization (product E), which after W(CO)5HPR2 elimination and rearrangement forms diarsene 5. The energetic profile for the reactions of 1a,b with the secondary phosphine PHiPr2 is shown in Figure 6. Reactions leading to 2a,b−5a,b are all energetically favorable, and estimations of the Gibbs energies show that all processes are exergonic in solution and therefore thermodynamically allowed (Table 1). In the gas phase the most favorable products are 3a (per mole of 1a) and 3b (per mole of 1b). The formation of 5a,b is slightly less favorable, followed by 2a,b and finally 4a,b as the energetically least favorable products. Note that the reactions leading to 3b and 5b are close in energy. In solution, the formation of 3a is favored over that of 5a by 23 kJ mol−1. In contrast, the formation of 5b and 3b is predicted to be competitive in solution from a thermodynamic point of view; 5b is only slightly (by 1.6 kJ mol−1) favored over 3b. Thus, the observed different reactivities of phosphorus (1a) and arsenic (1b) derivatives arises rather from kinetic rather than from thermodynamic reasons.

Figure 6. Computed energetic profile for the reactions shown in Schemes 2 and 4 with respect to 1a (E = P, blue) and 1b (E = As, red). Lines are drawn to guide the eye only.

solution for reactions leading to 6 and 7 differ less than 7 kJ mol−1 both for the P and As derivatives, which is consistent with the experimentally observed formation of both 6a and 7a in the reaction with PMeiPr2 (Table 1). The reactions leading to 9 are more energetically favorable than for 8, in agreement with the experimental finding of 9 as the major product. In the case of the secondary phosphines the presence of a hydrogen atom plays an important role in the subsequent reactivity of the initially formed intermediate A, since it allows a Cp*H elimination. We propose that after Cp*H elimination the phosphine−phosphinidene species B (E = P) and the

Table 1. Gas Phase Reaction Energies ΔE°0, Standard Enthalpies ΔH°298, and Gibbs energies ΔG°298 in kJ mol−1, Standard Entropies ΔS°298 in J mol−1 K−1, and Estimated Gibbs Energies in Solution ΔG°298(soln) in kJ mol−1 Computed at the B3LYP/ 6-31G* (LANL2DZ ECP on W) Level of Theory process

ΔE°0

ΔH°298

ΔS°298

ΔG°298

ΔG°298(soln)

1a + 2 PHiPr2 = 2a + W(CO)5PHiPr2 1b + 2 PHiPr2 = 2b + W(CO)5PHiPr2 1a + 2PHiPr2 = 3a + HCp* 1b + 2PHiPr2 = 3b + HCp* 1a + PHiPr2 = 4a + tmf 1b + PHiPr2 = 4b + tmf 2 1a + 3 PHiPr2 = 5a + W(CO)5PHiPr2 + 2 HCp* 2 1b + 3 PHiPr2 = 5b + W(CO)5PHiPr2 + 2 HCp*

−72.7 −64.4 −149.7 −128.4 −29.4 −10.9 −227.9 −237.9

−59.4 −51.3 −133.6 −113.5 −32.9 −16.2 −199.9 −208.9

−217.8 −229.3 −217.9 −235.2 −5.1 −13.2 −273.0 −308.9

5.5 17.0 −68.6 −43.3 −31.4 −12.2 −118.5 −116.8

−21.3 −9.8 −95.5 −70.2 −31.4 −12.2 −145.3 −143.6

1a + PMeiPr2 = 6a + tmf 1b + PMeiPr2 = 6b + tmf 1a + 2 PMeiPr2 = 7a + W(CO)5PMeiPr2 1b + 2 PMeiPr2 = 7b + W(CO)5PMeiPr2

−44.8 −27.4 −89.6 −84.5

−48.1 −32.0 −76.5 −71.8

−9.7 −19.4 −216.9 −229.7

−45.3 −26.3 −11.9 −3.3

−45.3 −26.3 −38.7 −30.1

1a + PEt3 = 8a + tmf 1b + PEt3 = 8b + tmf 1a + 2PEt3 = 9a + W(CO)5PEt3 1b + 2PEt3 = 9b + W(CO)5PEt3

−33.7 −18.0 −93.1 −86.7

−36.7 −22.7 −81.4 −74.9

−10.1 −19.9 −186.4 −197.9

−33.7 −16.8 −25.8 −15.9

−33.7 −16.8 −52.6 −42.7

39.6 11.2 −89.0 3.8 −26.6 −77.6 −55.2 −0.02 18.4 −168.2

52.4 23.1 −94.2 5.0 −17.6 −79.1 −59.0 1.6 27.2 −167.7

−249.5 −252.3 255.3 −16.0 −205.3 −2.3 244.0 −22.5 −240.4 −6.8

126.8 98.3 −170.3 9.7 43.6 −78.5 −131.7 8.4 98.9 −165.6

100.0 71.5 −143.4 9.7 16.7 −79.1 −104.9 8.4 72.0 −165.6

1a + PHiPr2 = A_P 1b + PHiPr2 = A_As A_P = B + Cp*H B_P = C_P C_P + PHiPr2 = D D = 3a A_As = Cp*H + B_As B_As = C_As 2 C_As = E E + PHiPr2 = 5b + W(CO)5PHiPr2

E

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Organometallics

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JP,P = 326 Hz, 2JP,W = 17 Hz, 1P), 64.3 (d, 1JP,P = 326 Hz, 1JP,W = 202 Hz, 1JP,W = 230 Hz, 1JP,W = 256 Hz, 3JP,W = 27 Hz, 2P); 31P NMR (CD2Cl2, 300 K) δ −103.7 (dm, 1JP,P = 326 Hz, 1P), 64.3 (ddd, 1JP,P = 326 Hz, 1JH,P = 256 Hz, 2P); EI MS m/z (%) 913.9 (2) [M+], 473.1 (100) [M+ − {P(iPr)2W(CO)5}], 443.1 (30) [M+ + H − {PP(iPr)2W(CO)5}]; IR (KBr, ν̃(CO), cm−1) 2068 (m), 1993 (m), 1915 (vs). Anal. Calcd for C22H19O10P3W2 (914.00 g/mol): C, 28.91; H, 3.20. Found: C, 28.81; H, 3.27. Synthesis of 4. To a stirred solution of [Cp*As{W(CO)5}2] (1b; 172 mg, 0.2 mmol) in toluene (20 mL) was slowly added 0.48 mL of a solution of 10% HPiPr2 (48 mg, 0.4 mmol) in n-hexane at −78 °C using a Teflon capillary. The mixture was stirred for 15 min at −78 °C, while the color changed from deep blue to red-brown. The mixture was warmed slowly to room temperature and stirred for a further 16 h. Subsequently, the solvent was reduced to 3 mL and stored at −30 °C. Brown crystals of 4 could be isolated after 2 days. Yield: 82 mg (48%). 4: 1H NMR (C6D6, 300 K) δ 0.53 (dd, 3JH,H = 7 Hz, 3JH,P = 18 Hz, 6H, iPr), 0.82 (dd, 3JH,H = 7 Hz, 3JH,P = 19 Hz, 6H, iPr), 1.74 (m, 2H, i Pr), 2.56 (d, 2JH,P = 6 Hz, 1H, AsH), 4.44 (dt, 1JH,P = 404 Hz, 3JH,H = 6 Hz, 1H, PH); 31P{1H} NMR (C6D6, 300 K) 28.0 (s, 1P); 31P NMR (C6D6, 300 K) 28.0 (dm, 1JH,P = 404 Hz, 1P); EI MS m/z (%) 841.1 (8) [M+]; IR (KBr, ν̃(CO), cm−1) 2075 (m), 2058 (s), 1980 (s), 1915 (vs). Anal. Calcd for C16H16AsO10PW2 (841.87 g/mol): C, 22.83; H, 1.92. Found: C, 22.91; H, 2.03. Synthesis of 5. To a stirred solution of [Cp*As{W(CO)5}2] (1b; 172 mg, 0.2 mmol) in CH2Cl2 (20 mL) was slowly added 0.48 mL of a solution of 10% HPiPr2 (24 mg, 0.2 mmol) in n-hexane at −78 °C using a Teflon capillary. The mixture was stirred for 15 min at −78 °C, while the color changed from deep blue to red-brown. The mixture was warmed slowly to room temperature and stirred for a further 16 h. Subsequently, the solvent was reduced to 3 mL and covered with a layer of n-hexane. Yield: 30 mg (16%). Crystals of 5 suitable for X-ray structure analysis were obtained from recrystallization in n-hexane/ toluene at −25 °C. 5: 1H NMR (CD2Cl2, 300 K) δ 1.40 (dd, 3JH,P = 13 Hz, 3JH,H = 7 Hz, 6H, iPr), 1.46 (dd, 3JH,P = 13 Hz, 3JH,H = 7 Hz, 6H, iPr), 1.51 (dd, 3 JH,P = 13 Hz, 3JH,H = 7 Hz, 6H, iPr), 1.59 (dd, 3JH,P = 13 Hz, 3JH,H = 7 Hz, 6H, iPr), 2.56 (dsept, 3JH,P = 13 Hz, 3JH,H = 7 Hz, 4H, iPr); 31 1 P{ H} NMR (CD2Cl2, 300 K) δ 48.0 (s); EI MS m/z (%) 1355.2 (2) [M+]. Synthesis of 6a and 7. A solution of PMeiPr2 (40 mg, 0.3 mmol) in toluene was added to a solution of [Cp*P{W(CO)5}2] (1a; 163 mg, 0.20 mmol) in toluene (20 mL) at −78 °C. After the reaction mixture was slowly warmed to room temperature and stirred for a further 16 h, the reaction mixture turned yellow-brown. The reaction mixture was concentrated to approximately 2 mL and layered with 2 mL of hexane. Compounds 6a and 7 (57 mg, 46%) crystallized as orange solids, which could not be obtained analytically pure. 6a: 1H NMR (CD2Cl2, 300 K) δ 1.43 (dd, 3JH,H = 1 Hz, 3JH,P = 7 Hz, 6H, iPr), 1.48 (dd, 3JH,H = 2 Hz, 3JH,P = 7 Hz, 6H, iPr), 1.76 (dd, 3 JH,H = 3 Hz, 2JH,P = 11 Hz, 3H, CH3), 2.72 (m, 2H, iPr), 3.69 (dd, 1 JH,P = 265 Hz, 2JH,P = 5 Hz, 3JH,W = 3 Hz, 1H, PH); 31P{1H} NMR (CD2Cl2, 300 K) δ 40.3 (d, 1JP,P = 267 Hz, 1P), −182.3 (d, 1JP,P = 267 Hz, 1JP,W = 156 Hz, 1P); 31P NMR (CD2Cl2, 300 K) δ 40.3 (d, 1JP,P = 267 Hz, 1P), −182.3 (dd, 1JP,P = 267 Hz, 1JP,H = 265 Hz, 1JP,W = 156 Hz, 1P); EI MS m/z (%) 811.7 (42) [M+], 783.6 (42) [M+ − CO], 755.7 (41) [M+ − 2CO]. 7: 1H NMR (CD2Cl2, 300 K) δ 1.05 (dd, 2JH,P = 3 Hz, 3JH,P = 19 Hz, 3H, CH3), 1.23 (m, 12H, iPr), 1.50 (d, 3JH,P = 12 Hz, 3H, Cp*), 1.77 (s, 6H, Cp*), 1.99 (s, 6H, Cp*), 2.25 (m, 2H, iPr); 31P{1H} NMR (CD2Cl2, 300 K) δ 40.8 (d, br, 1JP,P = 490 Hz, 1P), −99.8 (d, br, 1 JP,P = 490 Hz, 1P); 31P NMR (CD2Cl2, 300 K) δ 40.8 (d, br, 1JP,P = 490 Hz, 1P), −99.8 (d, br, 1JP,P = 490 Hz, 1P); EI MS m/z (%) 622.0 (65) [M+]. Synthesis of 6b. A solution of PMeiPr2 (27 mg, 0.2 mmol) in toluene was added to a solution of [Cp*As{W(CO)5}2] (1b; 172 mg, 0.2 mmol) in toluene (20 mL) at −78 °C. After the reaction mixture was slowly warmed to room temperature and stirred for 16 h, the reaction mixture turned yellowish brown. The reaction mixture was

We also considered the reaction energy profile for the proposed (Scheme 4) pathways of the formation of 3a and 5b. The results are also presented in Figure 6. The computations show that only the formation of the intermediate A is unfavorable (by 40 kJ mol−1 in the case of P and by 11 kJ mol−1 in the case of As); all other intermediates are formed exothermically with respect to 1a,b.

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CONCLUSION In summary, the pathway of the reaction of the pentelidene complexes 1a,b with secondary and tertiary phosphines differs decisively from that with primary phosphines. Only the initial formation of a Lewis acid/base adduct of the electrophilic pentelidene complex is a common starting point in all these reactions. Afterward, whereas in the latter reactions triphosphines and arsadiphosphines are produced, only for iPr2PH is the formation of a triphosphine 3 observed; however, it is generated by a different reaction mechanism. The process involving the secondary phosphines is dominated by the formation of phosphinopentelidene intermediates, which dimerize as in the case of the arsinidene starting material to form the unprecedented phosphine-substituted diarsene complex 5, side-on coordinated to a W(CO)5 unit. These processes are initiated by a Cp*H elimination. For tertiary phosphines W(CO)5 eliminations are preferred to form phosphoranylidene−phosphine complexes (formation of complexes 7 and 9), whereas the arsinidene complex prefers fulvene elimination (formation of complexes 6b and 8b). Only diisopropylphosphine follows the same discussed process of the tertiary phosphines to yield complexes 2 and 4, respectively. The transformations that we have described demonstrate the potential of bridged pentelidene complexes to form a large variety of polyphosphorus-containing products, which could become valuable building blocks in synthetic chemistry.

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EXPERIMENTAL SECTION

All manipulations were performed under an atmosphere of dry nitrogen using standard glovebox and Schlenk techniques. Solvents were purified and degassed by standard procedures. The starting materials 1a24 and 1b6c were prepared according to published methods. Solution NMR spectra were recorded on a Bruker AVANCE 400 spectrometer (1H, 400.13 MHz; 31P, 161.976 MHz; with δ (ppm) referenced to external SiMe4 (1H, 13C) and H3PO4 (31P)). Mass spectra were performed using a Finnigan MAT 95 instrument. IR spectra were recorded on a Varian FTS 2000, and elemental analyses were performed with an Elementar Vario EL III. Synthesis of 2 and 3. To a stirred solution of [Cp*P{W(CO)5}2] (1a; 163 mg, 0.2 mmol) in toluene (20 mL) was slowly asdded 0.48 mL of a solution of 10% HPiPr2 (48 mg, 0.4 mmol) in n-hexane at −78 °C using a Teflon capillary. Upon slow warming up to 20 °C a color change from deep blue to orange red was observed. Subsequently, the solvent was reduced to 5 mL and layered with n-hexane. Colorless crystals of 3 suitable for X-ray analysis were obtained from recrystallization in n-hexane/toluene at −25 °C (yield: 30 mg (18%)). By reducing the reaction mixture to 3 mL with subsequent layering of hexane, a yellow powder precipitated, containing a mixture of compound 2 with traces of 3. Yield: 35 mg (37%). 2: 31P NMR (C6D6, 300 K) δ 42.8 (d, 1JP,P = 298 Hz, 1JP,W = 221 Hz, 1P), −67.7 (d, 1JP,P = 298 Hz, 1P); 31P{1H} NMR (C6D6, 300 K) δ 42.8 (d, 1JP,P = 298 Hz, 1JP,W = 221 Hz, 1P), −67.7 (dd, br, 1JP,P = 298 Hz, 1JP,H = 297 Hz, 1P). 3: 1H NMR (CD2Cl2, 300 K) δ 1.36 (dd, 3JH,H = 7 Hz, 3JH,P = 16 Hz, 12H, iPr), 1.38 (dd, 3JH,H = 7 Hz, 3JH,P = 17 Hz, 12H, iPr), 2.56 (dsept, 3JH,P = 13 Hz, 3JH,H = 7 Hz, 4H, iPr), 3.86 (dt, 1JH,P = 256 Hz, 2 JH,P = 9 Hz, 1H, PH); 31P{1H} NMR (CD2Cl2, 300 K) δ −103.7 (dd, F

dx.doi.org/10.1021/om400357y | Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

concentrated to 3 mL. Compound 6b (123 mg, 72%) crystallized as an orange solid. 6b: 1H NMR (CD2Cl2, 300 K) δ 1.41 (dd, 3JH,H = 7 Hz, 3JH,P = 11 Hz, 6H, iPr), 1.45 (dd, 3JH,H = 7 Hz, 3JH,P = 12 Hz, 6H, iPr), 1.76 (d, 2 JH,P = 12 Hz, 3H, CH3), 2.62 (d, 2JH,P = 6 Hz, 1H, AsH), 2.63 (m, 2H, i Pr); 31P{1H} NMR (CD2Cl2, 300 K) δ 28.2 (s, 1P); 31P NMR (CD2Cl2, 300 K) δ 28.2 (m, 1P); 13C{1H} NMR (CD2Cl2, 300 K) δ 6.0 (d, 1JC,P = 33 Hz, 1C, CH3), 17.5 (d, 2JC,P = 4 Hz, 2C, iPr), 17.9 (d, 2 JC,P = 4 Hz, 2C, iPr), 26.0 (d, 1JC,P = 27 Hz, 2C, iPr), 199.2 (d, 3JC,P = 3 Hz, 8C, CO), 199.7 (d, 3JC,P = 2 Hz, 2C, CO); EI MS m/z (%) 855.9 (12) [M+], 827.9 (2) [M+ − CO], 800.0 (1) [M+ − 2CO], 716.0 (10) [M+ − PMeiPr2]; IR (KBr, ν̃(CO), cm−1) 2058 (s), 1975 (s), 1915 (vs). Anal. Calcd for C17H18AsO10PW2 (855.89 g/mol): C, 23.86; H, 2.12. Found: C, 23.88; H, 2.15. Synthesis of 8a and 9. A solution of PEt3 (26 mg, 0.2 mmol) in toluene was added to a solution of [Cp*P{W(CO)5}2] (1a; 163 mg, 0.20 mmol) in toluene (20 mL) at −78 °C. After the reaction mixture was slowly warmed to room temperature and stirred for a further 16 h, the reaction mixture turned yellowish brown. The reaction mixture was concentrated to 2 mL and layered with 2 mL of hexane. 8a (18 mg, 11%) crystallized in the form of yellow prisms. The mother liquor contained the main product 9 (determined by 31P NMR). 8a: 1H NMR (CD2Cl2, 300 K) δ 1.36 (td, 3JH,H = 15 Hz, 3JH,P = 8 Hz, 9H, Et), 2.25 (qdd, 3JH,H = 15 Hz, 2JH,P = 8 Hz, 3JH,P = 3 Hz, 6H, Et), 3.50 (dd, 1JH,P = 259 Hz, 2JH,P = 6 Hz, 2JH,W = 3 Hz, 1H, PH); 31 1 P{ H} NMR (CD2Cl2, 300 K) δ 37.4 (d, 1JP,P = 260 Hz, 1P), −190.7 (d, 1JP,P = 260 Hz, 1JP,W = 156 Hz, 1P); 31P NMR (CD2Cl2, 300 K) δ 37.4 (db, 1JP,P = 260 Hz, 1P), −190.7 (dd, 1JP,P = 260 Hz, 1JP,H = 260 Hz, 1JP,W = 156 Hz, 1P); 13C{1H} NMR (CD2Cl2; 300 K) δ 7.4 (d, 2 JC,P = 6 Hz, CH3), 17.1 (d, 1JC,P = 38 Hz, CH2), 198.9 (dd, 2JC,P = 3 Hz, 3JC,P = 3 Hz, 1JC,W = 126 Hz, 8 CO), 199.1 (dd, 2JC,P = 16 Hz, 3JC,P = 2 Hz, 2 CO); EI MS: m/z (%) 798.0 (35) [M+], 770.0 (40) [M+ − CO], 135.2 (35) [Cp*+]; IR (CH2Cl2, ν̃(CO), cm−1) 2075 (m), 2061 (m), 1980 (m), 1941 (vs), 1919 (vs). Anal. Calcd for C16H16O10P2W2 (797.91 g/mol): C, 24.08; H, 2.02. Found: C, 24.92; H, 2.28. 9: 31P{1H} NMR (C6D6, 300 K) δ 35.2 (d, br, JP,P = 476 Hz, 1P), −104.5 (d, br, JP,P = 476 Hz, 1P); 31P NMR (C6D6, 300 K) δ 35.2 (d, br, JP,P = 476 Hz, 1P), −104.5 (d, br, JP,P = 476 Hz, 1P). Synthesis of 8b. A solution of PEt3 (26 mg, 0.2 mmol) in toluene was added to a solution of [Cp*As{W(CO)5}2] (1b; 172 mg, 0.2 mmol) in toluene (20 mL) at −78 °C. After the reaction mixture was slowly warmed to room temperature and stirred for 16 h, the reaction mixture turned yellowish brown. The reaction mixture was concentrated to 3 mL. 8b (98 mg, 56%) crystallized as an orange solid. 1 H NMR (CD2Cl2, 300 K): δ 1.34 (td, 3JH,H = 18 Hz, 3JH,P = 8 Hz, 9H, Et), 2.21 (qd, 3JH,H = 15 Hz, 2JH,P = 8 Hz, 6H, Et), 2.30 (d, 2JH,P = 7 Hz, 1H, AsH); 31P{1H} NMR (CD2Cl2, 300 K) δ 24.7 (s); 31P NMR (CD2Cl2, 300 K) δ 24.7 (m). Crystal Structure Analysis. The crystal structure analyses were performed on an Oxford Diffraction Gemini R Ultra CCD. An analytical absorption correction from crystal faces was carried out for 4.25 For the other experiments semiempirical absorption corrections from equivalents (multiscan) were applied.26 The structures were solved by direct methods with the program SIR-97,27 and full-matrix least-squares refinement on F2 in SHELXL-9728 was performed with anisotropic displacements for non-H atoms. In 3, 4, and 6b the hydrogen atoms at the phosphorus and arsenic sites, respectively, were located by difference Fourier syntheses and refined isotropically. All other hydrogen atoms were located in idealized positions and refined isotropically according to the riding model. In 3 the phosphorus of the PH group is disordered over two positions with 50% occupancy. Further crystallographic details are summarized in Table 1S (Supporting Information). CCDC 930880 (3), 930881 (4), 930882 (5), 930883 (6b), 930884 (7), and 930885 (8a) contain supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge

CB2 1EZ, U.K. (fax, (+44)1223-336033; e-mail, [email protected]. uk). Computational Details. The geometries of the compounds have been fully optimized with gradient-corrected density functional theory (DFT) in form of Becke′s three-parameter hybrid method B3LYP29 with standard 6-31G* all-electron basis set as implemented in the Gaussian 03 program package.30 The ECP basis set of Hay and Wadt was used for W.31 All structures correspond to minima on their respective potential energy surfaces.

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ASSOCIATED CONTENT

S Supporting Information *

Text, figures, tables, and CIF files giving experimental and crystal data for 3−8a, NMR spectra of all new compounds, 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 for M.S.: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was comprehensively supported by the Deutsche Forschungsgemeinschaft and the Alexander von Humboldt Foundation (A.T. for a reinvitation fellowship). The COST action CM0802 PhoSciNet is gratefully acknowledged.

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REFERENCES

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