Condensation Reactions of Chlorophosphanes with Chalcogenides

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Condensation Reactions of Chlorophosphanes with Chalcogenides Sivathmeehan Yogendra,† Saurabh S. Chitnis,‡ Felix Hennersdorf,† Michael Bodensteiner,§ Roland Fischer,∥ Neil Burford,*,‡ and Jan J. Weigand*,† †

Department of Chemistry and Food Chemistry, TU Dresden 01062 Dresden, Germany Department of Chemistry, University of Victoria, Victoria, British Columbia, Canada V8W 3V6 § University of Regensburg, 93053 Regensburg, Germany ∥ Department of Inorganic Chemistry, TU Graz, 8010 Graz, Austria ‡

S Supporting Information *

ABSTRACT: A high-yielding and facile synthesis for diphosphane monochalcogenides (1Ch(R)) and their constitutional isomers, diphosphanylchalcoganes (2Ch(R)), was developed, featuring a condensation reaction between chlorophosphanes (R2PCl) and sodium chalcogenides (Na2Ch, Ch = S, Se, (Te)). The optimized protocol selectively yields either 1Ch(R) (R2(Ch)PPR2) or 2Ch(R) (Ch(PR2)2) depending upon the steric demand of the substituents R. Reaction pathways consistent with the distinct reaction outcomes are proposed. The application of 1Ch(R) and 2Ch(R) as an interesting class of ligands is exemplarily demonstrated by the preparation of selected transition metal complexes.

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INTRODUCTION The demand for halogen-free, phosphorus-based flame retardants is increasing with emphasis on lower toxicity compared to halogencontaining alternatives.1 Organophosphorus chalcogenides that contain P−P bonds are especially sought-after since they show good performance as flame retardants.2 In this context, diphosphane monosulfides 1S(R) (Chart 1) are considered as suitable derivatives;

Chivers et al. via the careful oxidation of the corresponding diphosphane with elemental sulfur and selenium, respectively (Ch = S, Se, Chart 1).7 Furthermore, Morris et al. presented in 2014 a convenient approach for the preparation of 1S(R) (R = Ph, Cy) by reacting the corresponding R2PCl with Li2S.8 The subsequent isomerization of 1S(Ph) and 1S(Cy) in the presence of [RuCl(Cp*)(cod)] yields ruthenium complexes of type 4 (Chart 1), which feature diphosphanylsulfanes (2S(R)) as ligands. There are only few reports on the isomerization of 1S(R) to their constitutional isomers 2S(R),6 and to the best of our knowledge, synthetic protocols for acyclic diphosphane monoselenides (1Se(R)), and monotellurides (1Te(R)) have not been reported. A reported synthesis of the diphosphanylsulfane 2S(N(iPr)2) (Chart 1) involves oxidation of the diphosphane (P2(N(iPr)2)4) with elemental sulfur; however, the reaction also produces significant amounts of side products.9 Phosphane (CF3)2PCl can be converted to the corresponding diphosphanylsulfanes 2S(CF3) by the reaction with either H2S or Ag2S as sulfide sources under harsh conditions and after long reaction times (100 °C, 19 days).10 Derivatives of diphosphanylselanes- and tellanes11 (2Ch(R); R = tBu, N(iPr)2; Ch = Se, Te) are prepared in a similar manner to the sulfur derivative 2S(N(iPr)2)12 or via chalcogenation of persistent phosphanyl radicals.13,14 In this context, we present a versatile and high-yielding protocol for the selective synthesis of 1Ch(R) and 2Ch(R) via a facile condensation reaction of monochlorophosphanes (R2PCl) with sodium chalcogenides (Na2Ch, Ch = S, Se, Te). The

Chart 1. Diphosphane Monochalcogenides (1Ch(R)), Diphosphanylchalcogenanes (2Ch(R)), Cyclic Derivatives of Diphosphane Monochalcogenides (3Ch), and a Ruthenium Complex (4)

however, access to these compounds on a large scale is restricted due to the lack of convenient, industrial-scale synthetic protocols. Reported syntheses are based on desulfurization of diphosphane disulfides,3 oxidation reactions of diphosphanes with elemental sulfur,4,5 or comproportionation reactions of diphosphanes and diphosphane disulfides.4 As an example, sodium thiophosphinites react with R2PCl to give compounds of type 1S(R).6 Most of the reactions are nonselective and low-yielding, and some require harsh reaction conditions. Recently, two derivatives of cyclic diphosphane monochalcogenides of type 3Ch were prepared by © XXXX American Chemical Society

Received: November 26, 2015

A

DOI: 10.1021/acs.inorgchem.5b02723 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry formation of either 1Ch(R) or 2Ch(R) strongly depends on the steric requirement of the organic substituents in R2PCl. Derivatives 1Ch(R) and 2Ch(R) are interesting ligands, as exemplified by the formation of selected transition metal complexes.

The aryl-substituted derivatives 1S(Ph) and 1S(Tol) are best prepared using Na2S as chalcogenide source and a catalytic amount of Me3SiCl (10 mol %). The addition of Me3SiCl significantly reduces side reactions and reaction time to give the products within 12 h at room temperature by acting as a phase-transfer catalyst and reacting with Na2S in situ to give (Me3Si)2S. According to the proposed catalytic cycle depicted in Scheme 3,

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RESULTS AND DISCUSSION Synthesis and Characterization of Diphosphane Monochalcogenides. Reactions of dialkyl-, diaryl-, or dialkoxychlorophosphanes R2PCl (R = Me, Et, EtO, Ph, p-Tol) with sodium chalcogenides (Na2Ch; Ch = S, Se) or bis(trimethylsilyl)chalcogenides ((Me3Si)2Ch; Ch = S, Se) give the corresponding diphosphane monochalcogenides 1Ch(R) in good to excellent yields (Scheme 1, Ch = S, Se; R = Me, Et, EtO, Ph,

Scheme 3. Proposed Mechanism for Catalytic Activity of Me3SiCl

Scheme 1. Syntheses of Various Diphosphane Monochalcogenides 1Ch(R) (Ch = S, Se; R = Me, Et, OEt, Ph, p-Tol; E = Na, Me3Si) (Me3Si)2S subsequently reacts with R2PCl to give the desired product and regenerates Me3SiCl. This protocol is readily scalable, demonstrated by the isolation of 20 g of 1S(Ph). Preparations of aryl-substituted diphosphane monoselenides 1Se(Ph) and 1Se(Tol) using (Me3Si)2Se are contaminated with small amounts of the corresponding diphosphane (R4P2, ∼6−7%, quantified by 31 P NMR spectroscopy). The use of Na2Se as a selenide source results in formation of larger amounts of the diphosphane (e.g., Ph4P2: 23%, quantified by 31P NMR spectroscopy). Separation of these mixtures has not been successful yet. We propose that Na2Se and (Me3Si)2Se are also capable of reducing R2PCl to the corresponding diphosphanes R4P2 by elimination of elemental selenium. Accordingly, the reaction of Ph2PCl with (Me3Si)2Te gives quantitative amounts of diphosphane Ph4P2 (determined by 31P NMR spectroscopy) and the deposition of elemental tellurium is observed. All derivatives of 1Ch(R) display the expected AX spin systems 1 ( JPP = 219−342 Hz, Table 1) in their 31P{1H} NMR spectra

a Isolated yields. bContains 7% impurities[*]. cYield[*]. dContains 6% Ph4P2[*]. eContains 7% p-Tol4P2[*]. quantification by 31P NMR spectroscopy is marked with [*].16

Table 1. Selected 31P and 77Se NMR Data for 1Ch(R)c

p-Tol). In most cases, Na2Ch,15 as inexpensive chalcogenide sources, are preferred over (Me3Si)2Ch. In the reactions of volatile alkyl-substituted R2PCl (R = Me, Et) and (Me3Si)2Ch, isolation of the analytically pure products involves simple removal of all volatiles in vacuo. When using Na2Ch instead, the pure products are obtained after filtration of concomitantly formed NaCl and subsequent removal of all volatiles in vacuo. The reaction of (EtO)2PCl with (Me3Si)2Ch is less selective, but gives mainly 1S(EtO) or 1Se(EtO). Small amounts of unidentified side products may be due to Arbuzovtype17 reactions.16 The reaction of (EtO)2PCl with Na2Ch as chalcogenide source is more selective but requires the addition of 15-crown-5 (10 mol %) to reduce the reaction time and to increase the yields. Distillation of the crude products is not possible due to isomerization at elevated temperatures, resulting in the formation of 2S(EtO) (78 °C; Scheme 2, vide supra).16 Scheme 2. Temperature-Induced Isomerization of 1Ch 2Ch(EtO) (Ch = S, Se)16

(EtO)

δ 31P{1H} (ppm) 1S(Me) 1Se(Me) 1S(Et) 1Se(Et) 1S(EtO) 1Se(EtO) 1S(Ph) 1Se(Ph)

to

1S(Tol) 1Se(Tol)

37.5(X) −56.5(A) 21.6(X) −56.6(A) 54.9(X) −34.7(A) 44.2(X) −35.2(A) 159.0(X) 98.9(A) 158.0(X) 102.9(A) 44.7(X) −13.2(A) 34.0(X) −12.5(A) 42.9(X) −16.0(A) 33.8(X) −14.6(A)

1

JPP (Hz)

δ 77Se (ppm)

1

JSeP (Hz)

2

JSeP (Hz)

−219.5 −228.0

−371.1

−694

21

−371.4

−691

22

−249.6 −257.4 −320.1 −342.4

a

b

−252.4 −260.9

−335.5

−750

29

−329.4

−741

28

−253.6 −260.9

a77

Se NMR spectrum was not recorded. bNot observed in the 31P{1H} NMR spectrum. cDesignation of the spin systems is by convention.26 The furthest downfield resonance is denoted by “X” and the furthest upfield by “A”. B


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Inorganic Chemistry

1S(Ph): 2.2263(5) Å;24 3Se: 2.223(2), 2.216(1) Å7). The P−Se bond lengths of 1Se(Me) and 1Se(Ph) (1Se(Me): 2.1193(7) Å; 1Se(Ph): 2.1075(5) Å) are comparable with those observed in 3Se (2.116(1), 2.114(1) Å7). The C1−P1 bond length in 1Se(Me) is slightly shorter than the C2−P2 bond length as a result of the higher coordination number (CN) of P1(CN = 4) compared to P2(CN = 3). The CN dependency of the C−P bond lengths is also observed in the sulfur congener 1S(Me) (P(CN = 4)−C: 1.803(1) Å; P(CN = 3)−C: 1.830(1)/ 1.834(1) Å)23 and the phosphanyl-phosphonium cation [Me3PPMe2]+ (P(CN = 4)−C: 1.790(2)/1.786 Å; P(CN = 3)−C: 1.833(2) Å).25 The phenyl derivative 1Se(Ph) displays equal bond lengths for all C−P bonds, indicating no CN dependency of the P−C bond length. Synthesis and Characterization of Diphosphanylchalcoganes. Condensation reactions of chlorophosphanes with sterically demanding substituents (R2PCl, R = tBu, Mes (2,4,6-trimethylphenyl), N(iPr)2) or electron-withdrawing substituents (e.g., R = C6F5) and E2Ch (E = Na, Me3Si; Ch = S, Se) give derivatives of 2Ch(R) quantitatively (Scheme 4).

Figure 1. (a) 31P{1H} NMR spectrum, showing the AX-spin system, (b) Px-part (tetracoordinated P atom) of the 31P{1H} NMR spectrum, and (c) 77Se NMR spectrum of 1Se(Et) (CD2Cl2, 300 K). Trace amounts of Et2P(S)P(S)Et2 are marked with [*].

Scheme 4. Synthesis of Various Diphosphanylchalcoganes 2Ch(R) (Ch = S, Se, Te; R = tBu, Mes, N(iPr)2, C6F5; E = Na, Me3Si)

(Figure 1a).18,19 For the selenium substituted derivatives 1Se(R) (R = Me, Et, EtO, Ph, p-Tol), satellites are observed due to the 77 Se isotopologues (spin 1/2, natural isotopic abundance 7.6%)20 with common coupling constants of 1JPSe = −691 to −750 Hz (Figure 1b) for terminal P−Se bonds.21 The corresponding coupling patterns are also observed in the 77Se NMR spectra, displaying a doublet of doublets as a result of the additional 2 JSeP of 21−29 Hz (Figure 1c). Selected NMR data of 1Ch(R) are listed in Table 1.16 The solid state molecular structures of the selenium substituted derivatives 1Se(Me) and 1Se(Ph) are depicted in Figure 2, confirming their identities as the first crystallographically

Figure 2. Molecular structures of 1Se(Me) and 1Se(Ph) (hydrogen atoms are omitted for clarity, thermal ellipsoids are displayed at 50% probability, and atoms related by symmetry are marked with [‘]); selected bond lengths (in Å) and angles (in deg): 1Se(Me): P1−P2 2.1914(9), P1−Se1 2.1193(7), P1−C1 1.802(2), P2−C2 1.825(2); C1−P1−C1′ 104.81(9), C1−P1−Se1 113.28, Se1−P1−P2 117.36, C2−P2−C2′ 100.1(1), C2−P2−P1 98.22(7); 1Se(Ph) : P1−P2 2.2299(6), P1−Se1 2.1075(5), P1−C1 1.823(2), P1−C7 1.823(2), P2−C19 1.827(2), P2−C13 1.828(2); C1−P1−C7 106.39(8), C13− P2−C19 106.55(8), C1−P1−Se1 113.10(6), C7−P1−Se1 112.21(6), Se1−P1−P2 118.16(2), C7−P1−P2 102.77(6).

a Isolated yields. bDetermined by isolated.16

31

P{1H} NMR spectroscopy, not

Analogously, diphosphanyltellanes 2Te(Mes) and 2Te(N(iPr)2) are prepared by reacting chlorophosphanes R2PCl (R = Mes, N(iPr)2) with Na2Te.27 The reaction of (C6F5)2PCl and Na2Te results in the quantitative formation of (C6F5)4P2 together with formation of elemental Te. The increased steric demand at the phosphorus atom with R = Mes and N(iPr)2 might provide a kinetic barrier to reductive coupling, enabling isolation of diphosphanyltellanes rather than diphosphanes.28 Nevertheless, 2Te(Mes) slowly decomposes in solution (stable for ∼12 h, rt, in toluene) with formation of (Mes)4P2, accompanied by the deposition of elemental tellurium. This process is significantly accelerated

characterized examples of acyclic diphosphane monoselenides. The P−P bond lengths (1Se(Me): 2.1914(9) Å; 1Se(Ph): 2.2299(6) Å) are in the typical range of P−P single bonds18,19,22 and similar to values reported for tetramethyl-, and tetraphenyldiphosphane monosulfide as well as the cyclic derivative 3Se (1S(Me): 2.202(1) Å;23 C


Article

Inorganic Chemistry when 2Te(Mes) is heated to 110 °C in fluorobenzene, showing quantitative conversion to the diphosphane after 30 min. Derivatives of 2Ch(R) show singlet resonances in the 31P{1H} NMR spectra. The selane derivatives 2Se(R) (R = tBu, Mes, N(iPr)2, C6F5) display characteristic satellites of the 77Se isotopologues with typical 1JPSe coupling constants (1JPSe = 185−264 Hz) for the P−Se−P fragments.9,12 The 77Se NMR spectra of 2Se(R) (R = tBu, Mes, N(iPr)2) show the expected triplet resonances (e.g., 2Se(tBu): Figure 3a). In the case of

(Table 2) are comparable to those reported in the literature (cf. 2S(N(iPr)2),9 2Te(N(iPr)2),9 2Ch(CH(SiMe3)2)13 (see Table 2), and 2Te((CH2)2(NDipp)2) (P−Te 2.584(7) Å, 2.587(8) Å)14). As expected, in all derivatives, the P−Ch bond length increases with higher atomic number of the Ch atom. Consistently, in terms of periodic trends, the P−Ch−P angles decrease as the atomic number of Ch increases. An exception is observed when comparing the P−Ch−P angles of 2Se(Mes) and 2Te(Mes). Postulated Reaction Pathways. Two distinct reaction pathways are possible that give either compounds 1Ch(R) or 2Ch(R). Their formation can be understood as a substitution reaction via intermediate 5 (Scheme 5). 5 is formed in situ by the nucleophilic attack of the chalcogenide in E2Ch (E = Na, Me3Si; Ch = S, Se, (Te)) on R2PCl via ECl elimination and has previously been studied (with E = Me3Si; Ch = S) by NMR spectroscopy.30 Depending on the basicity and steric requirements of the substituents R in 5, either the P or the Ch atom acts as a nucleophile in a subsequent substitution reaction with the second equivalent of R2PCl. With sterically less demanding substituents (R = Me, Et, EtO, Ph, p-Tol), derivatives 1Ch(R) are formed, induced by nucleophilic attack of the more basic P atom (pathway I). Sterically more demanding (R = tBu, Mes, N(iPr)2) or electron-withdrawing substituents (R = C6F5) on R2PCl lead to a decreased nucleophilicity of the P atom in 5. Consequently, the Ch atom acts as the nucleophile (pathway II), yielding derivatives of 2Ch(R). Consistently, the reaction of iPr2PCl, representing a substituent with moderate steric demand, and (Me3Si)2S results in the formation of both constitutional isomers 1S(iPr) and 2S(iPr).31 The reaction mixture displays a product distribution of 85:15 (1S(iPr):2S(iPr)) in the 31P{1H} NMR spectrum, indicating a slight preference for reaction pathway I.16 A thermally induced isomerization of 1Ch(R) to 2Ch(R) is observed when heating, e.g., 1S(EtO) to 100 °C for 2 h.16 Further heating to 120 °C for 2 h did not complete isomerization to 2S(EtO), presumably due to the reversibility of this reaction (cf. Scheme 2). In contrast, the phenyl derivative 1S(Ph) shows no thermally induced isomerization at 82 °C after 1 h. Reactivity and Coordination Chemistry of 1Ch(R) and 2Ch(R). A wide variety of phosphanes are used as ligands to form complexes with either transition metals or main group elements. Derivatives of 1Ch(R) are suitable ligands for coordination

Figure 3. 77Se NMR spectrum of (a) 2Se(tBu) and (b) 2Se(C6F5) (CD2Cl2, 300 K); 31P{1H} NMR spectrum (c), and 125Te NMR spectrum (d) of 2Te(Mes) (C6D6, 300 K).

2Se(C6F5), a triplet of nonets is observed as a result of the additional 4JSeF coupling (Figure 3b). The 31P{1H} NMR spectra of the tellane derivatives (2Te(Mes), 2Te(N(iPr)2)) display two sets of satellites due to the two 123Te and 125Te isotopologues (123Te: spin 1/2, natural isotopic abundance 0.9%; 125Te: spin 1/2, natural isotopic abundance 7.1%;29 e.g., 2Te(Mes): 1JPTe(123) = 344 Hz, 1JPTe(125) = 413 Hz; Figure 3c). The 125Te NMR spectrum of 2Te(Mes) shows a triplet resonance as a result of the 1 JTe(125)P coupling (Figure 3d). The molecular structures of the crystallographically characterized diphosphanylchalcoganes 2Ch(R) are depicted in Figure 4. The P−Ch bond lengths

Figure 4. Molecular structures of 2S(R) (R = tBu, Mes, C6F5), 2Se(R) (R = tBu, Mes, C6F5, N(iPr)2), and 2Te(Mes) (hydrogen atoms are omitted for clarity, thermal ellipsoids are displayed at 50% probability, and atoms related by symmetry are marked with [‘]). D


Article

Inorganic Chemistry Table 2. Selected Geometrical Parameters for Crystallographically Characterized Derivatives of 2Ch(R) 2Ch(tBu) 2Ch(Mes) 2Ch(C6F5) 2Ch(N(iPr)2) 2Ch(CH(SiMe3)2) a

P−S (Å)

P−Se (Å)

2.131(2) 2.135(2) 2.118(1) 2.126(1) 2.1272(5) 2.163(1)b 2.162(1)b 2.182(2)c 2.141(2)c

2.2765(7) 2.2807(5) 2.3067(5) 2.2807(5) 2.2688(4) 2.3162(4) 2.333(2)c 2.295(2)c

P−Te (Å)

2.5102(6)− 2.5140(8)a 2.559(1)b 2.576(2)b 2.505(2)c 2.552(2)c

P−S−P (deg)

P−Se−P (deg)

103.28(8)

92.58(2)

P−Te−P (deg)

95.57(5)

92.58(2)

93.71(3) 100.1(1)b

90.93(2) 96.61(2)

94.4(1)b

98.36(6)c

96.65(6)c

94.87(8)c

98.94(2) 99.47(2)a

Two independent molecules in asymmetric unit. bReference 12. cReference 13.

yielding complex 7 almost quantitatively.33 The IR spectrum of 7 shows distinct carbonyl stretching frequencies (2045(m), 1973(w), and 1931(vs) cm−1), which are reminiscent of the two a1 and e stretching vibrations of the C3v symmetric Fe(CO)4.34 The 13C{1H} NMR spectrum displays a doublet of doublets (δ = 212.7 ppm; 2JCP = 15.5 Hz; 3JCP = 3.2 Hz) for the carbonyl functionalities as a consequence of coupling to both P atoms.35 The 31P{1H} NMR spectrum reveals an AM spin system, in which the iron substituted P atom is downfield shifted, compared to the tricoordinated P atom of 1S(Ph) (Δ(δ) = 92.1 ppm). The sulfur substituted P atom is only slightly downfield shifted (Δ(δ) = 4.1 ppm), compared to the corresponding P atom in 1S(Ph). A coupling constant of 1 JPP = −138.9 Hz is observed, which is a typical value for bis(tetracoordinated) diphosphorus compounds.19 The molecular structure of 7 is depicted in Figure 5, showing a typical

Scheme 5. Postulated Reaction Pathways for the Condensation Reaction of R2PCl with E2Ch (E = Na, Me3Si; Ch = S, Se), Yielding Either 1Ch(R) or 2Ch(R) (I: R = Me, Et, EtO, Ph, p-Tol; II: R = tBu, Mes, N(iPr)2, C6F5)

chemistry, exhibiting possible donor sites at the Ch and the tricoordinated P atom. To investigate the Lewis basic properties of 1Ch(R), (Me) 1S was reacted with MeOTf to yield the known32 salt 6[OTf] quantitatively (Scheme 6), illustrating a preference for Scheme 6. (I) Reaction of 1S(Me) with MeOTf, Yielding 6[OTf] (rt, CH2Cl2, Quantitative by 31P{1H} NMR Spectroscopy);16 (II) Reaction of 1S(Ph) with Fe2CO9, Yielding Complex 7 (rt, CH2Cl2, 71%33); (III) Reaction of 1S(tBu) with AgOTf, Yielding Complex 8[OTf]2 (rt, CH2Cl2, 82%)

Figure 5. Top: Molecular structure of 7 and 8[OTf]2 (hydrogen atoms are omitted for clarity, thermal ellipsoids are displayed at 50% probability, and atoms related by symmetry are marked with [‘]); selected bond lengths (in Å) and angles (in deg): 7: P1−P2 2.2704(8), P2−S1 1.9457(9), P1−Fe1 2.2527(6); 8[OTf]2: 8[OTf]2 crystallizes with two unique molecules. Selected bond lengths (in Å) and angles (in deg) of only one molecule are given due to negligible differences. P1−S1 1.120(1), P2−S1 2.1184(6), P1−Ag1 2.4727(7), P2−Ag1′ 2.4713(6), Ag1−O(OTf) 2.685(4), Ag1−Ag2 2.9719(6); P1−S1−P2 108.37(3), S1−P1−Ag1 116.53(3), P1−Ag1−P2′ 151.26(2), S1−P1− Ag1−Ag1′ 29.85(3), S1−P2−Ag1′−Ag1 29.24(3). Bottom: Newman projection of 1S(Ph) and 7.

methylation at the tricoordinate phosphorus site rather than the sulfur atom. To demonstrate transition metal coordination with 1Ch(R), compound 1S(Ph) was reacted with Fe2(CO)9 (Scheme 6),

P−Fe bond length (2.2427(6) Å).36 A gauche conformation of the phenyl substituents is observed, as a consequence of the sterically demanding Fe(CO)4 fragment. In contrast, E


Article

Inorganic Chemistry precursor 1S(Ph) shows an anti conformation of the phenyl groups. (Figure 5, bottom). Diphosphanylchalcoganes 2Ch(R) are related to the wellestablished bis(phosphanyl)methylene (e.g., dppm)37 and bis(phosphanyl)amine (e.g., dppa),38 which represent small bite angle chelating ligands for transition metals and are often used for catalytic applications. In this context, we reacted 2S(tBu) with 1 equiv of AgOTf, yielding the dinuclear Ag complex 82+ (Scheme 6). The 31P{1H} NMR spectrum of 8[OTf]2 reveals two pseudo-triplets at δ = 123.3 and 120.1 ppm (Figure 6a),

into a spin system of higher order as a consequence of the AA′BB′XY′ spin system40 (Figure 6c). Single crystals were obtained by cooling a saturated solution of 7[OTf]2 in a mixture of fluorobenzene and CH2Cl2 to −30 °C. The molecular structure of complex 8[OTf]2 shows the centrosymmetric dimer, where two diphosphanylsulfanes 1S(tBu) bridge two silver ions. The Ag···Ag distance of 2.9719(6) Å indicates a small argentophilic interaction.41 The P1−Ag1−P2′ angle of 151.26(2)° displays bent coordination of the Ag1 atom by the P atoms. As a consequence, the Ag atoms are located out of the P1··S1··P2··P1′··S1′··P2′ plane (distance between Ag atoms and the P1··S1··P2··P1′··S1′··P2′ plane: 0.519 Å). Each Ag atom is coordinated by an oxygen atom of the [OTf]− anion (Ag1−O(OTf) 2.685(4) Å). The P−S bond lengths (P1−S1 1.120(1) Å, P2−S1 2.1184(6) Å) are comparable with those observed in the noncoordinated ligand 2S(tBu), whereas the P1−S1−P2 angle in 8[OTf]2 is slightly widened (8[OTf]2: P1−S1−P2 108.37(3)°; 2S(tBu): 103.28(8)°). In addition, a large S1−P1−Ag1 angle of 116.53° is observed, which differs from the ideal tetrahedral angle of 109.5°.

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CONCLUSION The condensation reactions of sterically less demanding R2PCl (R = Me, Et, EtO, Ph, p-Tol) with chalcogenides (Na2Ch, (Me3Si)2Ch; Ch = S, Se) result in the formation of diphosphane monochalcogenides 1Ch(R) in high yields, demonstrated by the synthesis of ten derivatives. A different reaction outcome is obtained, when sterically more demanding R2PCl (R = tBu, Mes, N(iPr)2)- or R2PCl with the electron-withdrawing substituent -C6F5 are reacted with chalcogenides (Ch = S, Se, Te), yielding the diphosphanylchalcoganes 2Ch(R). Ten different derivatives of 2Ch(R) were synthesized in high yields. The reaction conditions were optimized by using, e.g., Me3SiCl or 15-crown-5, leading to higher selectivity and reduced reaction times. The characteristic 31 P, 77Se, and 125Te NMR spectra of 1Ch(R) and 2Ch(R) are given, providing a comprehensive solution NMR data set for these compounds. Compounds 1Ch(R) and 2Ch(R) are suitable ligands for transition metals, demonstrated by the formation of the iron complex 7 and the dinuclear silver complex 8[OTf]2.

Figure 6. 31P{1H} NMR spectrum of 8[OTf]2; 9[OTf] is marked with [°]; (CD2Cl2, (a)) at 300 K; (b) at 265 K; (c) at 200 K).

caused by the presence of Ag isotopologues, giving A4X2-, A4Y2-, and AA′BB′XY spin systems (A = 31P (bonded to107Ag); B = 31P (bonded to 109Ag); X = 107Ag; Y = 109Ag). Centered between the pseudo-triplets, a broad resonance at δ = 121.6 ppm is observed. The broad resonance indicates the known39,40 rearrangement equilibrium between the dinuclear structure 8[OTf]2 and the isomeric mononuclear structure 9[OTf], involving a dynamic dissociation/association reaction of the ligand at 300 K (Scheme 7). 9[OTf] is identified in the 31P{1H} Scheme 7. Rearrangement Equilibrium between the Dinuclear Structure 8[OTf]2 and the Isomeric Mononuclear Structure 9[OTf] at 300 K

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.5b02723. Crystallographic data for 1Se(Me) (CIF) Crystallographic data for 1Se(Ph) (CIF) Crystallographic data for 2S(C6F5) (CIF) Crystallographic data for 2S(Mes) (CIF) Crystallographic data for 2S(tBu) (CIF) Crystallographic data for 2Se(N(iPr)2) (CIF) Crystallographic data for 2Se(C6F5) (CIF) Crystallographic data for 2Se(tBu) (CIF) Crystallographic data for 2Te(Mes) (CIF) Crystallographic data for 6 (CIF) Crystallographic data for 7[OTf]2 (CIF) Materials and methods, syntheses and spectroscopic data, and crystallographic details (PDF)

NMR spectrum at 300 K, diplaying two doublets at δ = 120.1 ppm, due to the two isotopologues (1JPAg(107) = 214 Hz; 1 JPAg(109) = 247 Hz; Figure 6a); marked with [°]). Low temperature NMR analysis was performed to clarify this dynamic behavior, showing reduced intensity culminating in the total loss of the broad central resonance (Figure 6b) consistent with inhibition of the rearrangement equilibrium upon cooling. At lower temperatures (e.g., 200 K), the two pseudo-triplets split

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (N.B.). *E-mail: [email protected] (J.J.W.). F


Article

Inorganic Chemistry Notes

(25) Chitnis, S. S.; MacDonald, E.; Burford, N.; Werner-Zwanziger, U.; McDonald, R. Chem. Commun. 2012, 48, 7359−7361. (26) (a) Pavia, D. L.; Lampman, G. M.; Kriz, G. S.; Vyvvan, J. R. Introduction to Spectroscopy, 5th ed.; Brooks and Cole: Belmont, CA, 2008; pp 269ff. (b) Hesse, M.; Meier, H.; Zeeh, B. Spektroskopische Methoden in der organischen Chemie, 8th ed.; Thieme: Stuttgart, Germany, 2012; pp 92ff. (c) Kalsi, P. S. Spectroscopy of Organic Compounds, 6th ed.; New Age International: New Dehli, India, 2005; pp 270ff. (27) The tetra-tert-butyldiphosphanyltellane (2Te(tBu)) was prepared analogously and is presented in ref: Du Mont, W.-W. Angew. Chem. 1980, 92, 562−563. (28) The benefit of sterical demanding substituents at the phosphorus atom for the stabilization of heterocyclic organophosphorus(III) tellurides is illustrated in ref: Nordheider, A.; Chivers, T.; Schön, O.; Karaghiosoff, K.; Arachchige, K. S. A.; Slawin, A. M. Z.; Woollins, J. D. Chem.Eur. J. 2014, 20, 704−712. (29) Schroeder, T. B.; Job, C.; Brown, M. F.; Glass, R. S.; You, N.; Block, E. Magn. Reson. Chem. 1997, 35, 752−756. (30) Fritz, G.; Hanke, D. Z. Anorg. Allg. Chem. 1986, 537, 17−30. (31) 31P NMR shifts of 1S(iPr) and 2S(iPr) are consistent with that presented in ref: Foss, V. L.; Khukhmisterov, P. L.; Lutsenko, F. I. Zh. Obshch. Khim. 1982, 52, 1063−1067. (32) Weigand, J. J.; Burford, N.; Mahnke, D.; Decken, A. Inorg. Chem. 2007, 46, 7689−7691. (33) 31 P{ 1 H} NMR analysis of 7 (isolated material after recrystallization: yield 71%) shows purity of ∼95% (by 31P{1H} NMR spectroscopy), accompanied by minor unidentified side products, which cannot be separated by recrystallization. (34) Clifford, A. F.; Mukherjee, A. K. Inorg. Chem. 1963, 2, 151−153. (35) Sarmah, C.; Borah, M.; Das, P. Appl. Organomet. Chem. 2011, 25, 552−558. (36) Riley, P. E.; Davis, R. E. Inorg. Chem. 1980, 19, 159−165. (37) See, e.g.: (a) Puddephatt, R. J. Chem. Soc. Rev. 1983, 12, 99− 127. (b) Kabir, S. E.; Hogarth, G. Coord. Chem. Rev. 2009, 253, 1285− 1315. (c) Freixa, Z.; van Leeuwen, P. W. N. M. Dalton Trans. 2003, 34, 1089−1901. (38) See, e.g.: (a) Song, K.; Gao, H.; Liu, F.; Pan, J.; Guo, L.; Zai, S.; Wu, Q. Eur. J. Inorg. Chem. 2009, 2009, 3016−3024. (b) Elowe, P. R.; McCann, C.; Pringle, P. G.; Spitzmesser, S. K.; Bercaw, J. E. Organometallics 2006, 25, 5255−5260. (c) Balakrishna, M. S.; Reddy, V. S.; Krishnamurthy, S. S.; Nixon, J. F.; Burckett St. Laurent, J. C. T. R. Coord. Chem. Rev. 1994, 129, 1−90. (39) (a) Rosa, V.; Fliedel, C.; Ghisolfi, A.; Pattacini, R.; Aviles, T.; Braunstein, P. Dalton Trans. 2013, 42, 12109−12119. (b) Hong, M.; Wu, D.; Liu, H.; Mak, T. C. W.; Zhou, Z.; Wu, D.; Li, S. Polyhedron 1997, 11, 1957−1962. (c) Dean, P. A. W.; Bittal, J. J.; Srivastava, R. S. Can. J. Chem. 1987, 65, 2628−2633. (40) Effendy; Hanna, J. V.; Marchetti, F.; Martini, D.; Pettinari, C.; Pettinari, R.; Skelton, B. W.; White, A. H. Inorg. Chim. Acta 2004, 357, 1523−1537. (41) (a) Schmidbaur, H.; Schier, A. Angew. Chem., Int. Ed. 2015, 54, 746−784. (b) Sculfort, S.; Braunstein, P. Chem. Soc. Rev. 2011, 40, 2741−2760.

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the Natural Sciences and Engineering Research Council (NSERC) of Canada, the Vanier Canada Graduate Scholarships Program, the Fonds der Chemischen Industrie (FCI, scholarship for F.H.), and the European research council (ERC, SynPhos 307616) for funding.

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REFERENCES

(1) (a) Döring, M., Diederichs, J., Eds. Innovative Flame Retardants in E&E Applications, 3rd ed.; Pinfa: Brussels, Belgium, 2010. (b) Rakotomalala, M.; Wagner, S.; Döring, M. Materials 2010, 3, 4300−4327. (c) Lu, S.-Y.; Hamerton, I. Prog. Polym. Sci. 2002, 27, 1661−1712. (d) Harley, K. G.; Marks, A. R.; Chevrier, J.; Bradman, A.; Sjödin, A.; Eskenazi, B. Environ. Health Perspect. 2010, 118, 699−707. (2) (a) Hahn, K.; Kriha, O.; Bellin, I.; Spies, P.; Fuchs, S.; Degelmann, P.; Klemens, K.; Denecke, H.; Fleckenstein, C.; Janssens, G. PCT Int. Appl. WO 2011029901A1, 2011. (b) Denecke, H.; Tishkov, A.; Gutfrucht, N.; Maase, M. PCT Int. Appl. WO 2009112349, 2009. (3) Maier, L. J. Inorg. Nucl. Chem. 1962, 24, 275−283. (4) Maier, L. Helv. Chim. Acta 1962, 45, 2381−2383. (5) Matschiner, H.; Krech, F.; Steinert, A. Z. Anorg. Allg. Chem. 1969, 371, 256−262. (6) Foss, V. L.; Veits, A. Y.; Khukhmisterov, P. L.; Lutsenko, F. I. Zh. Obshch. Khim. 1977, 47, 478−479. (7) Elder, P. J. W.; Chivers, T. Inorg. Chem. 2013, 52, 7791−7804. (8) Sues, P. E.; Lough, A. J.; Morris, R. H. Chem. Commun. 2014, 50, 4707−4710. (9) Du Mont, W. W.; Hensel, R.; McFarlane, W.; Colquhoun, I. J.; Ziegler, M. L.; Serhadli, O. Chem. Ber. 1989, 122, 37−41. (10) (a) Burg, A. B.; Gosling, K. J. Am. Chem. Soc. 1965, 87, 2113− 2116. (b) Dobbie, R. C.; Hopkinson, M. J. J. Fluorine Chem. 1974, 3, 367−374. (11) An overview of organophosphorus tellurides is given in a review: Nordheider, A.; Woollins, J. D.; Chivers, T. Chem. Rev. 2015, 115, 10378−10406. (12) Westerman, H.; Nieger, M.; Niecke, E. Chem. Ber. 1991, 124, 13−16. (13) Hill, N. J.; Reeske, G.; Cowley, A. H. Main Group Chem. 2010, 9, 5−10. (14) Giffin, N. A.; Hendsbee, A. D.; Roemmele, T. L.; Lumsden, M. D.; Pye, C. C.; Masuda, J. D. Inorg. Chem. 2012, 51, 11837−11850. (15) (a) DeGroot, M. W.; Taylor, N. J.; Corrigan, J. F. J. Mater. Chem. 2004, 14, 654−660. (b) So, J.-H.; Boudjouk, P. Synthesis 1989, 1989, 306−307. (16) For experimental details, see the Supporting Information. (17) (a) Arbusow, B. A. Pure Appl. Chem. 1964, 9, 307−336. (b) Bhattacharya, A. K.; Thyagarajan, G. Chem. Rev. 1981, 81, 415− 430. (18) Burford, N.; Herbert, D. E.; Ragogna, P. J.; McDonald, R.; Ferguson, M. J. J. Am. Chem. Soc. 2004, 126, 17067−17073. (19) Weigand, J. J.; Riegel, S. D.; Burford, N.; Decken, A. J. Am. Chem. Soc. 2007, 129, 7969−7976. (20) (a) Lardon, M. J. Am. Chem. Soc. 1970, 92, 5063−5066. (b) Eggert, H.; Nielsen, O.; Henriksen, L. J. Am. Chem. Soc. 1986, 108, 1725−1730. (21) Montilla, F.; Galindo, A.; Rosa, V.; Avilés, T. Dalton Trans. 2004, 16, 2588−2592. (22) Mundt, O.; Riffel, H.; Becker, G.; Simon, A. Z. Naturforsch., B: J. Chem. Sci. 1988, 43, 952−958. (23) Gruber, M.; Jones, P. G.; Schmutzler, R. Chem. Ber. 1990, 585, 177−188. (24) Aluri, B. R.; Peitz, S.; Wöhl, A.; Peulecke, N.; Müller, B. H.; Spannenberg, A.; Rosenthal, U. Acta Crystallogr., Sect. E: Struct. Rep. Online 2009, 65, o404. G


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