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The Reactivity of Germanium Phosphanides with Chalcogens Lisa M. Harris,† Eric C. Y. Tam,† Struan J. W. Cummins,‡ Martyn P. Coles,†,§ and J. Robin Fulton*,†,§ †

Department of Chemistry, University of Sussex, Falmer, Brighton BN1 9QJ, United Kingdom School of Chemical and Physical Sciences, Victoria University of Wellington, P.O. Box 600, Wellington 6012, New Zealand

‡

S Supporting Information *

ABSTRACT: The reactivity of germanium phosphanido complexes with elemental chalcogens is reported. Addition of sulfur to [(BDI)GePCy2] (BDI = CH{(CH3)CN-2,6-iPr2C6H3}2) results in oxidation at germanium to form germanium(IV) sulfide [(BDI)Ge(S)PCy2] and oxidation at both germanium and phosphorus to form germanium(IV) sulfide dicylohexylphosphinodithioate complex [(BDI)Ge(S)SP(S)Cy2], whereas addition of tellurium to [(BDI)GePCy2] only gives the chalcogen inserted product, [(BDI)GeTePCy2]. This reactivity is different from that observed between [(BDI)GePCy2] and selenium. Addition of selenium to the diphenylphosphanido germanium complex, [(BDI)GePPh2], results in insertion of selenium into the Ge−P bond to form [(BDI)GeSePCy2] as well as the oxidation at phosphorus to give [(BDI)GeSeP(Se)Ph2]. In contrast, addition of selenium to the bis(trimethylsilyl)phosphanido germanium complex, [(BDI)GeP(SiMe3)2], yields the germanium(IV) selenide [(BDI)Ge(Se)P(SiMe3)2].

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INTRODUCTION Group 14/16 nanomaterials have a wide range of applications, from photovoltaic devices to phase change memory materials.1−4 The synthesis of these nanomaterials traditionally involves the treatment of a metal halide source, such as (e.g., GeI4, SnCl2, or PbCl2) with trioctylphosphine chalcogenide (TOP-E, E = S, Se, Te) in the presence of a surfactant (e.g., oleylamine) to facilitate nanoparticle growth.5−7 Metal phosphanido complexes have been postulated as important intermediates in the nucleation event in nanoparticle growth.8,9 However, the oxidative reactivity of metal phosphanido complexes with chalcogens has received little attention,10−20 especially when a redox-active metal center bears the phosphanido ligand.20,21 When only the phosphanido ligand is capable of undergoing oxidation, two different oxidation products are generally observed, the formation of the phosphinochalcogenoite ligand, [R2PE]−,10−16 or the double addition to the phosphinodichalcoganoate ligand, [R2PE2]−.10,17,20 Chalcogens have also been shown to oxidize germanium(II) complexes.22−25 With both germanium and phosphorus capable of undergoing oxidation with chalcogens,22,26,27 we were interested in determining the relative preference of chalcogens toward molecules containing a germanium−phosphorus bond. We have reported the reactivity of elemental selenium with β-diketiminatogermanium(II) dicyclohexyl phosphanide, [(BDI)GePCy 2 ] (1-Cy) (BDI = CH{(CH 3 )CN-2,6iPr2C6H3}2).21 Depending upon the conditions, three different products could be obtained (Scheme 1). Addition of 1 equiv of selenium yielded the phosphinoselenoito complex [(BDI)GeSePCy2] (2-Cy-Se), in which the phosphinoselenoito anion binds to selenium in a rare −κSe bonding mode. © XXXX American Chemical Society

Scheme 1. Reactivity of 1-Cy with Selenium

Addition of excess selenium led to the formation of phosphinodiselenoato complex [(BDI)GeSeP(Se)PCy2] (4Cy-Se). However, upon crystallization of this compound, yellow crystals of a second product were found interspersed with the orange crystals of 4-Cy-Se. The yellow crystals were identified as germanium(IV) selenide [(BDI)Ge(Se)PCy2] (3Cy-Se), an isomer of 2-Cy-Se in which the selenium is terminally bonded to the germanium. This latter compound was not observed spectroscopically prior to the crystallization process, even upon standing 3-Cy-Se for 3 weeks at room temperature. Thus, it is inferred that selenium is transferred from phosphorus to germanium during the crystallization process. Both 3-Cy-Se and 4-Cy-Se were identified by 1H, 31P, and 77Se NMR spectroscopies after manual separation of the crystals. Although attempts at generating 3-Cy-Se independently were unsuccessful, its formation suggested the thermoReceived: January 8, 2017

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DOI: 10.1021/acs.inorgchem.6b03109 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry neutrality of these three compounds. Density functional theory (DFT) calculations found isomer 3-Cy-Se to be 13.2 kcal mol−1 less stable than isomer 2-Cy-Se. To ascertain factors governing the relative stability of complexes of the type 2, 3, and 4, our investigations were expanded to include other chalcogens (sulfur and tellurium) and as well as other βdiketiminato germanium phosphanido complexes including [(BDI)GePPh2], 1-Ph and [(BDI)GeP(SiMe3)2], 1-SiMe3.28,29

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RESULTS AND DISCUSSION Reactivity between 1-Cy and Sulfur or Tellurium. Treatment of the germanium(II) dicyclohexylphosphanide (1Cy) with 1 equiv of elemental sulfur results in the formation of a mixture of products, with three new resonances at δP = −3.3, 97.7, and 104.0 ppm, in addition to a resonance corresponding to 1-Cy, observed in the 31P{1H} NMR spectrum. When 1-Cy is exposed to excess sulfur, a germanium(IV) sulfide dicylohexylphosphinodithioate complex is exclusively formed ([(BDI)Ge(S)SP(S)Cy2], 5-Cy-S), the product of the net

Figure 1. ORTEP diagram of germanium(IV) sulfide dicyclohexylphosphinodithioate, 5-Cy-S. H atoms omitted and BDI C atoms minimized for clarity. The ellipsoid probability is shown at 30%.

Table 1. Selected Bond Lengths (Å) and Angles (deg) for Compound 5-Cy-S Ge−N(1) Ge−N(2) Ge−S(1) Ge−S(2) S(2)−P P−S(3) P−C(30) P−C(36) Ge−NCCCN planea

Scheme 2. Reactivity of 1-Cy with Sulfur and Tellurium

1.9298(12) 1.9343(12) 2.0676(4) 2.2345(4) 2.1038(5) 1.9597(5) 1.8347(15) 1.8466(15) 0.656

N(1)−Ge−N(2) N(1)−Ge−S(1) N(2)−Ge−S(1) N(1)−Ge−S(2) N(2)−Ge−S(2) S(1)−Ge−S(2) Ge−S(2)−P S(2)−P−S(3)

94.97(5) 116.51(4) 115.91(4) 101.88(4) 102.71(4) 120.828(15) 111.525(18) 103.87(2)

a

Distance between Ge and the plane defined by the BDI-backbone (N−C−C−C−N plane).

Table 2. Selected Spectroscopic Data for [(BDI)GePR2] (1), [(BDI)GeEPR2] (2), [(BDI)Ge(E)PR2] (3), [(BDI)GeEP(X)R2] (4), and [(BDI)Ge(E)EP(E)R2] (5) (R = PPh2, PCy2, P{SiMe3}2; E = S, Se Te)a

oxidation of both germanium and phosphorus (Scheme 2). The 31 1 P{ H} NMR spectrum of 5-Cy-S contains a singlet at δP 104.0 ppm, significantly downfield to that of both 1-Cy and 4Cy-Se, consistent with a fully oxidized phosphorus center. This reactivity is similar to that previously observed between βdiketiminato germanium(II) complexes and elemental sulfur,22,23,25 as well as phosphorus with sulfur.11,20,30 The germanium center in 5-Cy-S is tetrahedral, with the Ge−N bonds shorter than that of 1-Cy (ΔGe−N(ave) = 0.12 Å). The Ge−S(1) bond length of 2.0676(4) Å is significantly shorter than the Ge−S(2) bond length of 2.2345(4), indicative of multiple bonding in the former bond (Figure 1, Table 1) (2.06 Å).31 The germanium−sulfur double bond is similar in length to that of [(BDI)Ge(S)SH] (2.0641(4) Å) and [(BDI)Ge(S)Me] (2.104(7) Å).22,23 Similarly, the P−S(2) bond length of 2.1038(5) Å is longer than the P−S(3) bond length of 1.9597(5) Å, highlighting the contrast in bond order.11 Closer examination of the product mixture of 1 equiv of sulfur and 1-Cy revealed that 5-Cy-S is formed under these conditions, albeit in low conversion. When the reaction mixture was allowed to stand at −30 °C, a small amount of crystals corresponding to a single addition of sulfur to germanium (3Cy-S) was found. It is presumed that this compound gives the signal at δP −3.3 ppm in the 31P{1H} NMR spectrum as this resonance is slightly downfield to that of the precursor 1-Cy (δP −14.1 ppm) but in a range similar to that of 3-Cy-Se (δP = 0.7 ppm). See Table 2 for a comparison of selected spectroscopic data for compounds discussed within this Article.

31

1-Cy 1-Ph44 1-SiMe329 2-Cy-Se21 2-Ph-Se 2-Cy-Te 3-Cy-Se21 3-SiMe3-Se 3-Cy-S 4-Cy-Se21 4-Ph-Se 5-Cy-S 44

P

−14.1 −36.0 −192.7 41.9 11.1 26.1 0.7 −172.6 −3.3 63.7 26.3 (19.1) 104.0

77

Se/125Te

−19.3 136.5 −296.8 −91 −129 −18 not detected

|JPE| (E = Se, Te)

198 219 407 0.7 49 551 579 (201)

a

Italicized values reported elsewhere. Chemical shift/ppm; coupling constants/Hz.

The germanium center in 3-Cy-S adopts a distorted tetrahedral geometry (Figure 2, Table 4). As with the germanium(IV) selenide 5-Cy-Se, the Ge−N and Ge−P bonds 3-Cy-S are shorter than those in the germanium(II) dicyclohexylphosphanide 1-Cy precursor (ΔGe−N(ave) = 0.09 Å and ΔGe−P = 0.14 Å), with the Ge−S bond distance of 2.0954(8) Å slightly longer than that of 5-Cy-S. Although we were unable to assign the resonance at δP 97.7 ppm in the B

DOI: 10.1021/acs.inorgchem.6b03109 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Table 4. Selected Bond Lengths (Å) and Angles (deg) for Compounds 3-Cy-Se, 3-Cy-S, and 3-SiMe3-Se Ge−N(1) Ge−N(2) Ge−E Ge−P P−C(30) P−C(36) P−Si(1) P−Si(2) N(1)−Ge−E N(2)−Ge−E N(1)−Ge−N(2) N(1)−Ge−P N(2)−Ge−P E−Ge−P Ge−P−C(30) Ge−P−C(36) C(30)−P−C(36) Ge−P−Si(1) Ge−P−Si(2) Si(1)−P−Si(2) Ge−NCCCN planea DP (%)

Figure 2. ORTEP diagram of germanium(IV) sulfide, 3-Cy-S. H atoms omitted and BDI C atoms minimized for clarity. The ellipsoid probability is shown at 30%.

Table 3. Selected Bond Lengths (Å) and Angles (deg) for Compounds 2-Cy-Se, 2-Cy-Te, and 2-Ph-Se Ge−N(1) Ge−N(2) Ge−E E−P P−C(30) P−C(36) N(1)−Ge−E N(2)−Ge−E N(1)−Ge−N(2) Ge−E−P E−P−C(30) E−P−C(36) C(30)−P−C(36) Ge−NCCCN planea sum of angles around Ge DP (%)b

2-Cy-Se21

2-Cy-Te

2-Ph-Se

2.027(2) 2.027(2) 2.4498(5) 2.2609(9) 1.875(3) 1.877(3) 100.66(7) 96.98(7) 88.07(10) 94.07(3) 102.09(10) 100.32(10) 100.96(14) 0.927 285.71 82.5

2.019(4) 2.022(4) 2.6516(6) 2.4705(13) 1.875(5) 1.872(5) 101.67(12) 98.83(12) 87.67(15) 88.12(3) 100.88(17) 102.79(17) 102.8(2) 0.996 288.17 79.8

2.0108(18) 2.0224(19) 2.4490(4) 2.2524(7) 1.846(3) 1.841(3) 97.17(6) 100.54(5) 88.20(8) 90.27(2) 101.18(8) 104.68(10) 100.63(12) 0.986 285.9 82.3

3-Cy-Se5

3-Cy-S

1.975(3) 1.965(3) 2.2216(5) 2.3714(11) 1.880(4) 1.896(4)

1.956(2) 1.958(2) 2.0954(8) 2.3322(8) 1.883(3) 1.870(3)

110.22(9) 110.38(9) 92.37(13) 110.25(10) 108.12(9) 120.02(3) 100.42(14) 100.58(14) 101.15(19)

0.756 82.5

110.28(7) 110.50(7) 93.14(10) 103.26(7) 107.79(7) 126.56(3) 100.14(9) 103.46(10) 109.83(13)

0.831 79.8

3-SiMe3-Se 1.9174(18) 1.9923(18) 2.2163(3) 2.2976(7)

2.2415(9) 2.2525(9) 111.91(6) 116.22(5) 94.88(8) 114.97(6) 95.83(6) 119.388(19)

122.49(3) 106.77(3) 111.65(4) 0.637 82.3

a

Distance between Ge and the plane defined by the BDI-backbone (N−C−C−C−N plane).

a

Distance between Ge and the plane defined by the BDI-backbone (N−C−C−C−N plane). bDP = [(360 − {sum of the angles})/0.9].43

reaction mixture, we can assume it is due to a phosphorus(V) center, presumably of the type 4-Cy-S, or [(BDI)GeSP(S)Cy2]. In contrast to the reactivity observed with sulfur, addition of tellurium, either 1 equiv or excess, resulted only in insertion of tellurium into the Ge−P bond, forming βdiketiminatogermanium(II) dicyclohexylphosphinotelluroite [(BDI)GeTePCy2] (2-Cy-Te, Scheme 2). The 31P{1H} NMR spectrum shows a new resonance at δP 26.1 pm, upfield to that of the germanium dicyclohexylphosphinoselinoite complex 2Cy-Se (δP = 41.9 ppm). The tellurium satellites (|JTeP| = 407 Hz) have a smaller coupling than that observed in [Te{P(NiPr2)2}2] (562 Hz),32 and the 125Te NMR spectrum displays a doublet at −296.8 ppm (|JPTe| = 406 Hz). This reactivity is different from oxidative-addition chemistry generally observed between tellurium and germanium(II) complexes,31,33−37 including other β-diketiminato germanium complexes37 as well as aminotroponiminato germanium complexes.35 Complex 2-Cy-Te adopts a coordination geometry similar to that of 2-Cy-Se. A pyramidal geometry is observed at germanium, and the dialkylphosphinotelluroite ligand is found in the exo conformation (Figure 3, Table 3).38 The Ge−Te bond length of 2.6516(6) Å is longer that that reported for βdiketiminatogermanium(IV) tellurides (2.415−2.424 Å), and

Figure 3. ORTEP diagram of germanium(II) dicylohexylphosphinotelluroite, 2-Cy-Te. H atoms omitted and BDI C atoms minimized for clarity. The ellipsoid probability is shown at 30%.

the Te−P bond of 2.4705(13) Å is between that of a single bond of [Te(PSiMe3)2] (2.505−2.552 Å) and double bond of [TePCy3] (2.3632(7) Å).26,37,39 The Ge−Te−P bond angle of 88.12(3)° is significantly more acute than the Ge−Se−P bond angle of 2-Cy-Se (94.07(3)°). Complex 2-Cy-Te is not only a rare example of a phosphinochalcogenoite ligand (R2PE¯) ligand,21,40 but it is the first example of a dialkylphosphinotelluroite ligand. The insertion of tellurium into the germanium−phosphorus bond is similar to that observed between selected diphosphines or digermanes and tellurium41,42 and is the result either of a direct insertion of tellurium across the Ge−P bond or of initial oxidation of germanium or phosphorus by tellurium followed by rearrangement to form 2-Cy-Te, although we were unable to obtain any spectroscopic evidence for either mechanism. This reactivity with tellurium is only observed with 1-Cy as both 1-Ph or 1SiMe3 are inert toward tellurium, even at elevated temperatures over a prolonged period of time. C

DOI: 10.1021/acs.inorgchem.6b03109 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Reactivity between 1-Ph or 1-SiMe3 and Selenium. Addition of 1 equiv of selenium to germanium(II) diphenylphospanide [(BDI)GePPh2] (1-Ph) resulted in insertion of selenium into the Ge−P bond to form germanium(II) diphenylphosphinoselenoite [(BDI)GeSePPh2] (2-Ph-Se) in analogy to reactivity observed with 1-Cy (Scheme 3).

in 2-Ph-Se is also smaller than that observed in 2-Cy-Se (94.07(3)°). Germanium diphenylphosphinodiselenoate, 4-Ph-Se, is formed upon addition of 5 equiv of selenium to 1-Ph (Scheme 3). Yellow crystals suitable for an X-ray diffraction study were grown from a concentrated solution of the filtered product at −30 °C, confirming the connectivity (Figure 5, Table 5). The

Scheme 3. Reactivity of 1-Ph and 1-SiMe3 with Selenium

Figure 5. ORTEP diagram of germanium(II) diphenylphosphinodiselenoate 4-Ph-Se. H atoms omitted and BDI C atoms minimized for clarity. The ellipsoid probability is shown at 30%.

Table 5. Selected Bond Lengths (Å) and Angles (deg) for Compounds 4-Cy-Se and 4-Ph-Se

Complex 2-Ph-Se is unstable; tetraphenyldiphosphine, Ph2PPPh2 (6), is also found within the reaction mixture, and increases in concentration upon standing 2-Ph-Se in solution, regardless of temperature reduction to −27 °C or restrictions to light exposure. Thus, two resonances are observed in the 31P NMR spectrum, an upfield resonance at δP −14.9 ppm, corresponding to 6, and a downfield resonance at δP 11.1 ppm, corresponding to 2-Ph-Se (|JSeP| = 219 Hz). This latter differs from those of 1-Ph (δP = −36.0 ppm) and 2-Cy-Se (δP = 42 ppm, |JSeP| = 198 Hz).21,44 The identity of the diphenylphosphine dimer 6 was confirmed through the similarity of the 31P chemical shift to the literature value,45,46 along with a unit cell check of isolated crystals of 6.44 The solid-state structure of 2-Ph-Se is similar to that of 2Cy-Se and 2-Cy-Te (Figure 4, Table 3). The germanium− selenium bond length of 2.4490(4) Å is comparable to that of 2-Cy-Se (2.4498(5) Å), and the selenium−phosphorus bond of 2.2524(7) Å is slightly shorter than the analogous bond in 2Cy-Se (2.2602(9) Å). The Ge−Se−P bond angle of 90.27(2)°

Ge−N(1) Ge−N(2) Ge−Se(1) Se(1)−P P−Se(2) P−C(30) P−C(36) N(1)−Ge−Se(1) N(2)−Ge−Se(1) N(1)−Ge−N(2) Ge−Se(1)−P Se(1)−P−Se(2) Se(1)−P−C(30) Se(1)−P−C(36) Se(2)−P−C(30) Se(2)−P−C(36) Ge−NCCCN planea sum of angles around Ge DP (%)b

4-Cy-Se5

4-Ph-Se

2.020(2) 2.0320(19) 2.4613(4) 2.2208(7) 2.1114(7) 1.849(3) 1.837(3) 94.84(6) 94.20(6) 88.72(8) 100.77(2) 117.92(3) 103.01(9) 102.00(9) 112.52(9) 113.29(10) 0.987 277.8 91.4

2.004(3) 2.006(3) 2.5390(5) 2.2209(10) 2.1172(10) 1.822(3) 1.820(3) 95.96(8) 95.75(8) 91.17(11) 100.00(3) 115.48(4) 104.89(11) 106.57(12) 111.56(11) 112.78(12) 0.020 282.9 85.7

a

Distance between Ge and the plane defined by the BDI-backbone (N−C−C−C−N plane). bDP = [(360 − {sum of the angles})/0.9].43

geometry at germanium for 4-Ph-Se is reminiscent of a βdiketiminato germanium(II) cation; that is, the germanium lies essentially in the NCCCN plane (Ge−NCCCN plane: 0.020 Å).47,48 The Ge−Se(1) bond length of 2.5390(5) Å is significantly longer than that of 4-Cy-Se (2.4613(4) Å), although the P−Se(1) and P−Se(2) distances (2.2209(10) and 2.1172(10) Å, respectively) are very similar to the P−Se bond lengths of 4-Cy-Se. The elongated Ge−Se(1) bond length is potentially a reflection of the ionic nature of 4-CySe; this compound is significantly less soluble in hydrocarbon solvents than the cyclohexane analogue. The [PSe2Ph2] anion is

Figure 4. ORTEP diagram of germanium(II) diphenylphosphinoselenoite, 2-Ph-Se. H atoms omitted and BDI C atoms minimized for clarity. The ellipsoid probability is shown at 30%. D

DOI: 10.1021/acs.inorgchem.6b03109 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry less basic than the [PSe2Cy2]; thus the former would have a higher propensity to behave as an anion and the latter would be better stabilized by covalent bonding. The 31P NMR spectrum of a freshly prepared solution of 4Ph-Se crystals reveals a signal at δP 26.3 ppm (|JSeP| = 579 Hz). The Se−P coupling is consistent with that observed in 4-Cy-Se (|JSeP| = 551 Hz) as well as other isolated compounds bearing a [Se2PPh2] ligand.10,17,21,40,49,50 A second resonance, in an approximate 1:1 ratio with 4-Cy-Se, also appears at δP 19.1 ppm (|JSeP| = 201 Hz) after 30 min at room temperature (compound A). The phosphorus−selenium coupling of this compound is consistent with a P−Se single bond.50 The 1H NMR spectrum of this solution revealed two sets of signals in a 1:1 ratio, with the proton for the γ-H atoms found at δ 5.00 and 4.76 ppm for compounds 4-Ph-Se and A, respectively. The reaction mixture is homogeneous, with no evidence of a precipitate. Upon reduction of solvent, crystals of 4-Ph-Se were formed. The identity of compound A was never confirmed but could be an isomer of 4-Ph-Se in which preferential oxidation of germanium over phosphorus has occurred to form [(BDI)Ge(Se)SePPh2] (eq 1). This complex would be consistent with

Figure 6. ORTEP diagram of germanium(IV) selenide, 3-SiMe3-Se. H atoms omitted and BDI C atoms minimized for clarity. The ellipsoid probability is shown at 30%.

phosphanido complexes, 1-Cy or 1-Ph, can be partially explained by a stronger Ge−P bond of 1-SiMe3, as evidenced by the shorter Ge−P bond (2.3912(8) Å) relative to that of 1Cy (2.4746(11) Å) or 1-Ph (2.4724(8) Å).28,44 In addition, the planar phosphorus in 1-SiMe3, as opposed to the pyramidal phosphorus in both 1-Cy and 1-Ph, implies an sp2 hybridized phosphorus in 1-SiMe3, which would both increase the Ge−P bond strength and reduce the nucleophilicity of the phosphorus center.11

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the observed phosphorus−selenium single bond coupling observed in the 31P NMR spectrum. An equilibrium constant (Keq = 1.3) was measured, revealing that isomer A is slightly more stable in solution than 4-Ph-Se. Although never observed in the dicyclohexylphosphanide system, [(BDI)Ge(Se)SePCy2] was predicted to be only minimally higher in energy than 4-CySe.21 In addition, direct oxidation of germanium with selenium has been observed with other β-diketiminato germanium complexes.24,51,52 Unfortunately, we were unable to find a signal in the 77Se NMR spectrum for either product. In contrast to both 1-Cy and 1-Ph, addition of selenium to germanium bis(trimethylsilyl)phosphanide 1-SiMe3 resulted in the oxidative addition of selenium on germanium to form germanium(IV) selenide, 3-SiMe3-Se, as the only product, even when excess selenium was added (Scheme 3). A single resonance at δP −176.2 ppm, with selenium and silicon satellites (|JSeP| = 52 Hz and |JPSi| = 26 Hz), is found in the 31 1 P{ H} NMR spectrum. This signal is downfield from that in the precursor 1-SiMe3 (δP = −192.8 ppm). The 77Se NMR spectrum of 3-SiMe3-Se shows a doublet centered at δSe −129 ppm, with selenium−phosphorus coupling at |JSeP| = 49 Hz. The solid-state structure of 3-SiMe3-Se revealed a different conformation preference for the phosphanido and selenido ligands, as compared to 3-Cy-Se and 3-Cy-S, in which the selenium of 3-SiMe3-Se is found as the exo ligand and the phosphanide is located as the endo ligand (Figure 6, Table 4).38 The Ge−N bond lengths (1.9174(18) and 1.9923(18) Å) and the Ge−P bond length (2.2976(7) Å) of 3-SiMe3-Se are shorter than those of the 1-SiMe3 precursor (Ge−N = 2.006(2) and 2.046(2) Å; Ge−P = 2.3912(8) Å). The Ge = Se bond distance of 2.2163(3) Å is slightly shorter than that found for 3Cy-Se (2.2216(5) Å). The phosphorus atom adopts a pseudoplanar geometry (DPP = 21.21%) and is slightly more pyramidal than the precursor 1-SiMe3 (DPP = 5.3%).43 The difference in reactivity of selenium with 1-SiMe3 and the other

CONCLUSIONS In this series of germanium phosphanido complexes, we have examined both the trends in reactivity with chalcogens as well as the effect of different substituents on the phosphanido ligand. With regards to periodic trends, sulfur shows a preference toward germanium over phosphorus in phosphanide 1-Cy; however, both germanium and phosphorus will react if sulfur is not limiting. In contrast, tellurium only inserts into the Ge−P bond, even though both germanium(II) and phosphorus(III) compounds are known to oxidatively react with tellurium. The reactivity of 1-Cy with selenium is similar to that of sulfur, although the stoichiometric control of selenium to give defined products is easier to manipulate. Interestingly, addition of 1 equiv of chalcogen only resulted in either insertion of the chalcogen into the Ge−P bond or oxidation at germanium. The third alternative, oxidation at phosphorus, was never observed, implying that in this system, germanium is slightly more reactive than phosphorus with chalcogens. There is little difference between 1-Cy and 1-Ph in terms of reactivity with selenium. However, some tentative clues about the accessibility of isomers of either 2-Cy or 4-Ph were observed, with 3-Cy isolated in the solid state upon crystallization of 4-Cy, and spectroscopic evidence of an equilibrium between 4-Ph and potentially the germanium(IV) complex, [(BDI)Ge(Se)SePPh2]. The formation of these different isomers highlights the thermoneutrality of transferring selenium from phosphorus to germanium. The one exception to this is with the bis(trimethylsilyl)phosphanido complex, 1SiMe3, in which the phosphido ligand was found to be unreactive toward selenium, potentially due to both the decrease in nucleophilicity of the planar phosphorus atom and the stronger Ge−P bond in 1-SiMe3. Together, these observations imply that chalcogens do not have a strong E

DOI: 10.1021/acs.inorgchem.6b03109 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Celite after 20 h. Volatiles were removed from the filtrate under vacuum. The residue was washed with n-hexane (3 × ∼5 mL). Yellow crystals of [(BDI)Ge(Se)P(SiMe3)2] (3-SiMe3-Se) were obtained from a minimum amount of toluene at −30 °C (0.25 g, 61%). 1H NMR (C6D6, 303 K): δ 7.18 (s, 6H, ArH), 4.90 (s, 1H, γ-CH), 3.60 (septet, J = 6.8 Hz, 4H, CHMe2), 1.59 (d, J = 6.4 Hz, 12H, CHMe2), 1.56 (s, 6H, NCMe), 1.22 (d, J = 6.8 Hz, 6H, CHMe2), 1.06 (d, J = 6.8 Hz, 6H, CHMe2), 0.50 (d, J = 6.0 Hz, 6H, SiMe3), 0.42 (d, J = 6.0 Hz, 6H, SiMe3). 31P{1H} NMR (161.72 MHz, C6D6, 303 K): δ −172.6 (JPSe = 52 Hz, JPSi = 26 Hz). 77Se NMR (76.19 MHz, C6D6, 303 K): δ −129 (d, JSeP = 49 Hz). Anal. Calcd for C35H59GeN2PSeSi2 (746.54): C, 56.30; H, 7.97; N, 3.75. Found: C, 56.25; H, 7.92; N, 3.79. [CH{(CH3)CN-2,6-iPr2C6H3}2GeSeP(Se)(C6H5)2] (4-Ph-Se). Excess selenium (0.15 g, 1.9 mmol), finely suspended in toluene, was added dropwise to a solution of [(BDI)GePPh2] (1-Ph) (0.25 g, 0.37 mmol) in toluene (5 mL), and the mixture was stirred vigorously for 24 h at room temperature resulting in the color changing from purple to yellow. The solution was filtered, the solvent evaporated under reduced pressure, and ether was added to the residue. The solution was stored at −27 °C for 24 h, yielding [(BDI)Ge(Se)SeP(C6H5)2] as yellow crystals. 4-Ph-Se, 1H NMR (C6D6, 293 K): δ 7.46 (t, 2H, J = 7.3 Hz, m-H), 7.14 (d, J = 7.3 Hz, 1H, ArH), 7.09−7.06 (m, 2H, ArH), 7.02 (d, 2H, J = 7.6 Hz, ArH), 7.00 (d, 2H, J = 7.6 Hz, ArH), 6.97− 6.82 (m, 2H, ArH), 5.00 (s, 1 H, γ-CH), 3.90 (septet, 2H, J = 6.8 Hz, CHMe2), 3.45 (septet, 2H, J = 6.8 Hz, CHMe2), 1.55 (d, 6H, J = 6.4 Hz, CHMe2), 1.51 (s, 6H, NCMe), 1.26 (d, 6H, J = 6.8 Hz, CHMe2), 1.09 (d, 6H, J = 6.8 Hz, CHMe2), 0.90 (d, 6H, J = 6.8 Hz, CHMe2). Unknown, 1H NMR (C6D6, 293 K): δ 7.83−7.77 (2H, m, ArH), 7.16−7.09 (m, 7H, ArH), 6.84 (2H, m, ArH), 4.76 (s, 1H, γ-CH), 3.44 (broad s, 2H, CHMe2), 3.23 (broad s, 2H, CHMe2), 1.48 (s 6H, NCMe), 1.34 (d, 6H, J = 6.8 Hz, CHMe2), 1.06 (broad, 6H, CHMe2). 4-Ph-Se, 13C{1H} NMR (C6D6, 293 K, note, overlapping aryl resonances prevent full assignment): δ 166.9 (NCMe), 146.7, 145.9, 140.2, 139.9, 139.6, 137.8, 133.8 (d, 1JPC = 22 Hz)), 129.3, 128.8 128.4, 128.4, 128.3, 125.5 and 125.0, 101.7 (γ-C), 29.6 (CHMe2), 29.3 (J = 3 Hz, CHMe2), 26.9 (CHMe2), 26.1, and 25.2 (CHMe2), 24.8 (d, J = 2 Hz, CHMe2), 24.3 (CHMe2). Unknown, 13C{1H} NMR (C6D6, 293 K, note, overlapping aryl resonances prevent full assignment): 166.82, 139.8, 139.6, 139.1, 137.9, 131.9 (d, 1JPC = 12 Hz) 129.9 (d, 1 JPC = 3 Hz), 125.7, 98.4 (γ-C), 28.9, 28.8, 26.3, 25.9 (br), 25.7 (br), 23.6, 15.6. 31P{1H} NMR (C6D6, 293 K): δ 26.3 (JSeP = 579 Hz, 4-PhSe), 19.1 (JSeP = 201 Hz, unknown). Anal. Calcd for C41H51N2PSe2Ge: C, 59.09; H, 6.17; N, 3.36. Found: C, 59.15; H, 6.23; N, 3.19. [CH{(CH3)CN-2,6-iPr2C6H3}2Ge(S)SP(S)(C6H11)2] (5-Cy-S). Sulfur (0.028 g, 0.87 mmol), suspended in toluene, was added dropwise to a solution of [(BDI)GePCy2] (1-Cy) (0.20 g, 0.29 mmol) in toluene (5 mL), and the mixture was stirred for 24 h at room temperature. The solvent was filtered, concentrated in vacuo, and stored at −27 °C for 24 h to give yellow crystals of 5-Cy-S (0.61 g, 27%, first crop). 1H NMR (C6D6, 293 K): 7.10−7.05 (m, 6H, ArH), 4.63 (s, 1H, γ-H), 3.81 (septet, J = 6.6 Hz, 2H, CHMe2), 3.17 (septet, J = 6.7 Hz, 2H, CHMe2), 2.83 (m, 2H, Cy−CH), 1.70 (d, J = 6.5 Hz, 6 H, CHMe2), 1.59 (d, J = 6.7 Hz, 6 H, CHMe2), 1.43−1.38 (m, 6H, PCy), 1.41 (s, 6H, NCMe), 1.10 (d, J = 6.5 Hz, 6 H, CHMe2), 1.09−1.03 (m, 4H, PCy), 0.97−0.91 (m, 2H, PCy), 0.91 (d, J = 6.8 Hz, 6 H, CHMe2). 13 C{1H} NMR (C6D6, 293 K): δ 168.6 (NCMe), 146.7, 145.0, 136.5, 128.7, 125.9, 124.2 (ArC), 97.4 (γ-C), 42.3 (PCy), 42.0 (PCy), 30.02, 28.5, 27.5, 26.5 (PCy), 25.0, 23.8, 23.6. 31P{1H} NMR (C6D6, 293 K): δ 104.0.

preference toward either germanium or phosphorus, and subtle changes in the electronic properties of either center can play a significant role in determining the most thermodynamically stable product.

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EXPERIMENTAL SECTION

General. All manipulations were carried out under an inert atmosphere of dry nitrogen using standard Schlenk techniques or in an inert-atmosphere glovebox. Solvents were dried form the appropriate drying agent, distilled, degassed, and stored over 4 Å molecular sieves. The NMR spectra were recorded on Varian 400 and 500 MHz spectrometers or Bruker 300 and 600 MHz spectrometers. The 1H and 13C NMR chemical shifts are were measured relative to residual solvent peaks and reported relative to Me4Si; 31P and 77Se were externally referenced to H3PO4(aq) and Me2Se, respectively. The data for the X-ray structures of 2-Ph-Se, 3-Cy-S, 3-SiMe3-Se, and 4-Ph-Se were collected at 173 K on a Nonius Kappa CCD diffractometer [λ (Mo, Kα) 0.71073 Å], the data for the X-ray structure of 2-Cy-Te were collected AT 120 K on a Bruker AXS SMART diffractometer [λ (Mo, Kα) 0.71073 Å], and the data for 5-Cy-S were recorded on an Agilent SuperNova diffractometer [λ (Cu, Kα) 1.54184 Å]. The X-ray data for all complexes were refined using the SHELXL-97 software package.53 [(BDI)Ge(PCy2)] (1), [(BDI)Ge(PPh2)], and [(BDI)GeP(SiMe3)2] were made according to published procedures.29,44 [CH{(CH3)CN-2,6-iPr2C6H3}2GeTeP(C6H11)2] (2-Cy-Te). A slurry of tellurium (0.05 g, 0.4 mmol), finely suspended in toluene, was added dropwise to a solution of [(BDI)GePCy2] (1-Cy) (0.25 g, 0.36 mmol) in toluene (5 mL), and the mixture was stirred for 24 h at room temperature resulting in the color changing from purple to red. The solution was filtered, concentrated under reduced pressure, and stored at −27 °C for 24 h, yielding [(BDI)GeTeP(C6H11)2] as red crystals. 1H NMR (C6D6, 293 K): δ 7.10−7.06 (m, 4H, ArH), 7.03 (dd, J = 7.2 Hz, 2H, m-H), 4.70 (s, 1H, γ-CH), 3.62 (septet, J = 6.8 Hz, 2H, CHMe2), 3.28 (septet, J = 6.8 Hz, 2H, CHMe2), 1.68−1.66 (br, 4H, PCy), 1.61 (d, J = 6.8 Hz, 6H, CHMe2), 1.57−1.51 (m, 6H, PCy), 1.48 (s, 6H, NCMe), 1.42 (d, J = 6.8 Hz, 6H, CHMe2), 1.15 (d, J = 6.8 Hz, 6H, CHMe2), 1.12 (d, J = 6.8 Hz, 6H, CHMe2), 1.08−1.04 (br, 10H, PCy), 0.86−0.82 (br, 2H, PCy). 13C{1H} NMR (C6D6, 293 K): δ 166.4 (NCMe), 146.0, 143.2, and 141.5 (ArC), 127.1 (para-C), 124.7 and 124.5 (m-C), 96.8 (γ-CH), 33.6 and 33.4 (Cy-CH), 32.5 (d, JCP = 8 Hz, CHMe2), 31.3 (d, JCP = 17 Hz, PCH), 29.6 (CHMe2), 28.8, 27.8, 27.7, 27.7, and 27.7 (PCy), 27.2 (d, JCP = 3 Hz, CHMe2), 27.0 (PCy), 25.2, 24.9, and 24.8 (CHMe2), 23.4 (NCMe). 31P{1H} NMR (C6D6, 293 K): δ 26.1 (JPTe = 407 Hz). 125Te {1H} NMR (C6D6, 293 K): −296.8 (JPTe = 406 Hz). IR (Nujol, cm−1): 1558 (s), 1317 (s), 1260 (s), 1169 (s), 1100 (s), 1017 (s), 933 (s), 887 (s), 847 (s), 824 (s), 722 (s). [CH{(CH3)CN-2,6-iPr2C6H3}2GeSeP(C6H5)2] (2-Ph-Se). A slurry of selenium (0.03 g, 0.4 mmol), finely suspended in toluene, was added dropwise to a solution of [(BDI)GePPh2] (1-Ph) (0.25 g, 0.37 mmol) in toluene (5 mL), and the mixture was stirred for 10 days at room temperature resulting in the color changing from purple to orange. The solution was filtered, the solvent evaporated under reduced pressure, and ether was added to the residue. The solution was stored at −27 °C for 24 h, yielding [(BDI)GeSeP(C6H5)2] as orange crystals, interspersed with traces of diphenylphosphine. 1H NMR (C6D6, 293 K): δ 7.33−6.93 (m, 16 H, ArH), 4.80 (s, 1H, middle CH), 3.67 (septet, 2H, J = 6.8 Hz, CHMe2), 3.35 (septet, 2H, J = 6.8 Hz, CHMe2), 1.53 (s, 6H, NCMe), 1.42 (d, 6H, J = 6.8 Hz, CHMe2), 1.33 (d, 6H, J = 6.8 Hz, CHMe2), 1.16 (d, 6H, J = 8.0 Hz, CHMe2), 1.14 (d, 6H, J = 7.2 Hz, CHMe2). 31P{1H} NMR (C6D6, 293 K): δ 11.1 (JP−Se = 219 Hz). 77Se{1H} NMR (C6D6, 293 K): 136.5 (JSe−P = 217 Hz). Unable to obtain satisfactory combustion analysis due to the presence of Ph2PPPh2 (see text). [CH{(CH3)CN-2,6-iPr2C6H3}2Ge(Se)P(Si(CH3)3)2] (3-SiMe3-Se). [(BDI)GeP(SiMe3)2] (1-SiMe3) (0.37 g, 0.55 mmol) in diethyl ether (15 mL) was added to an excess of elemental selenium (0.13 g, 1.64 mmol) suspended in diethyl ether (5 mL). The mixture was stirred rapidly at room temperature and filtered through a pad of

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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.6b03109. Selected NMR data for compounds 2-Cy-Te, 2-Ph-Se, 4Ph-Se (and isomer A), and 5-Cy-S; data collection parameter tables and thermal ellipsoid plots of 2-Cy-Te, F

DOI: 10.1021/acs.inorgchem.6b03109 Inorg. Chem. XXXX, XXX, XXX−XXX

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2-Ph-Se, 3-Cy-S, 3-SiMe3-Se, 4-Ph-Se, and 5-Cy-S (PDF) X-ray crystallographic data 2-Cy-Te (CIF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

J. Robin Fulton: 0000-0002-6370-6452 Present Address §

School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington 6012, New Zealand. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge funding from the University of Sussex and the EPSRC UK National Crystallography Service at the University of Southampton for the structural determination of 2-Cy-Te.

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REFERENCES

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DOI: 10.1021/acs.inorgchem.6b03109 Inorg. Chem. XXXX, XXX, XXX−XXX