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Rapid, Reversible, Solid−Gas and Solution-Phase Insertion of CO2 into In−P Bonds Diane A. Dickie,† Madeline T. Barker,#,† Michael A. Land,‡ Kira E. Hughes,⊥,† Jason A. C. Clyburne,‡ and Richard A. Kemp*,†,§ †

Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, United States The Atlantic Centre for Green Chemistry, Department of Chemistry, Saint Mary’s University, Halifax, Nova Scotia B3H 3C3, Canada § Advanced Materials Laboratory, Sandia National Laboratories, Albuquerque, New Mexico 87106, United States ‡

S Supporting Information *

ABSTRACT: The P,P-chelated heteroleptic complex bis[bis(diisopropylphosphino)amido]indium chloride [(iPr2P)2N]2InCl was prepared in high yield by treating InCl3 with 2 equiv of (i-Pr2P)2NLi in Et2O/tetrahydrofuran solution. Samples of [(i-Pr2P)2N]2InCl in a pentane slurry, a CH2Cl2 solution, or in the solid state were exposed to CO2, resulting in the insertion of CO2 into two of the four M−P bonds to produce [O2CP(i-Pr2)NP(i-Pr2)]2InCl in each case. Compounds were characterized by multinuclear NMR and IR spectroscopy, as well as single-crystal X-ray diffraction. ReactIR solution studies show that the reaction is complete in less than 1 min at room temperature in solution and in less than 2 h in the solid−gas reaction. The CO2 complex is stable up to at least 60 °C under vacuum, but the starting material is regenerated with concomitant loss of carbon dioxide upon heating above 75 °C. The compound [(i-Pr2P)2N]2InCl also reacts with CS2 to give a complicated mixture of products, one of which was identified as the CS2 cleavage product [SP(i-Pr2)NP(i-Pr2)]2InCl]2(μ-Cl)[μ-(iPr2P)2N)].

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INTRODUCTION Carbon dioxide is often considered inert and unreactive, but the polarized bonds of CO2 are primed to undergo certain types of reactions. Recently our groups reviewed1 the area of CO2 reactivity and identified a number of modes of reactivity. One of those modes is the well-known insertion of CO2 into metalC, N, or O bonds to give carboxylates, carbamates, or carbonates, respectively. Examples of CO2 insertion into metalP bonds were also described.1 Despite the ubiquity of phosphorus-based ligands, this type of reactivity was rarely reported prior to the introduction of the “frustrated” Lewis pair (FLP) concept2 for the activation of CO2 and other small molecules. Although many are not truly insertion reactions because the metal and phosphorus atoms were not always bonded due to the “frustration”, a search of the Cambridge Structural Database (CSD)3 reveals 47 crystallographically characterized examples of CO2 simultaneously coordinated to a metal via its nucleophilic oxygen and to a phosphorus atom through its electrophilic carbon. Approximately 85% of these structures were published in the last five years, coinciding with the dramatic rise in FLP chemistry. The metals paired with phosphorus in these CO2 adducts include titanium,4 zirconium5 and hafnium,6 molybdenum7 and tungsten,7b ruthenium,8 zinc,9 tin,10 and even uranium.11 However, the most common are the group 13 elements aluminum4,12 and boron,13 that together make 70% of the © 2015 American Chemical Society

structurally characterized examples to date. To the best of our knowledge, indium, a much softer Lewis acid than the lighter group 13 elements that currently dominate CO2 activation, has not been previously reported to react with CO2 as part of a discrete ligand-based complex. However, inorganic InP electrodes have been shown to photochemically reduce CO214 and indium-containing metal−organic frameworks have been shown to adsorb CO2 and separate it from gas mixtures.15 Indium has a diagonal relationship with zinc, which we have recently shown forms complexes with P-based ligands −N(SiMe3)(i-Pr2P) and −N(i-Pr2P)2 that react readily with CO2 and its heavier analogue CS2.9 The related P,P-chelate complex of indium’s soft divalent group 14 neighbor tin, specifically [(iPr2P)2N]2Sn, reacts similarly to zinc,10 suggesting that hard Lewis acidic metals are not essential for CO2 activation and in fact may not be ideal for reversible CO2 capture. Therefore, we were motivated to prepare an indium analogue of the Zn and Sn complexes of −N(i-Pr2P)2 and examine its reactivity with CO2, as well as the heavier analogue CS2, which is known16 to form an adduct with the free ligand (i-Pr2P)2NH and which often shows surprising and very different reactivity from CO2.9b,17 Received: June 5, 2015 Published: November 17, 2015 11121

DOI: 10.1021/acs.inorgchem.5b02031 Inorg. Chem. 2015, 54, 11121−11126

Article

Inorganic Chemistry Scheme 1. Preparation of Indium Complexes 1 and 2

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RESULTS AND DISCUSSION In our previous work with the divalent metals Sn10 and Zn,9 we were able to capture 2 equiv of CO2 by preparing homoleptic complexes in which CO2 inserted into one M−P bond per ligand. Therefore, we hoped that by moving to the trivalent group 13 metal indium we would be able to trap three CO2 equivalents. Surprisingly to us, we were unable to find conditions that would give the trisubstituted complex, despite precedent from Ellermann et al., who made the somewhat less bulky tris[bis(diphenylphosphino)amido]indium complex.18 Instead, the reaction of 2 equiv of (i-Pr2P)2NLi with InCl3 in a 3:1 mixture of Et2O and tetrahydrofuran (THF) produces the heteroleptic bis[bis(diisopropylphosphino)amido]indium chloride 1 in excellent yield (Scheme 1). The 2 equiv of LiCl are easily removed by filtration, and there is no evidence of indium reduction. The 31P{1H} NMR spectrum of 1 dissolved in C6D6 consisted simply of a singlet at 122 ppm, significantly downfield from the lithiated ligand that exhibits a resonance at 85 ppm. The 1H NMR spectrum of 1 was complicated due to coupling to 31P nuclei, but the 1H{31P} spectrum was consistent with a single isopropyl environment. The spectrum displayed a septet at 2.16 ppm for the methine protons and doublets at 1.29 and 1.22 ppm for inequivalent CH3 groups. The corresponding signals in the 13C{1H} spectrum were at 29.8, 18.5, and 17.8 ppm, respectively. Confirmation of the structure of 1 was needed and was obtained by single-crystal X-ray diffraction (Figure 1). For this analysis, colorless block-like crystals were grown from a saturated pentane solution, but 1 also crystallizes readily from other solvents including THF and CH2Cl2 . Two bis-

(diisopropylphosphino)amido ligands chelate the indium center through their phosphorus atoms. The geometry at indium is distorted trigonal bipyramidal with the Cl1, P2, and P4 in the equatorial positions. The equatorial In−P bonds are very close to the mean In−P bond distance of 2.658 Å reported in the CSD.3 The axial In−P bonds in 1 are ∼0.1 Å longer than the equatorial ones. This effect was also seen in the axial/ equatorial Sn−P bonds of the related [(i-Pr2P)2N]2Sn complex, but the difference was not as great as it is in 1, and in both cases, the P atoms are equivalent by NMR in solution.10 In contrast, the tetrahedral Zn center of [(i-Pr2P)2N]2Zn showed no significant differences in the Zn−P bonds.9a The P−N bonds of each ligand in 1 differ by only ∼0.02 Å, with the longer P−N bond associated with the phosphorus that also has the longer P−In bond. Within the free ligand bis(diisopropylphosphino)amine, the P−N−P bond angle is 121°, as is often seen in three-coordinate nitrogen bound to atoms that can engage in dative π-bonding with the nitrogen lone pair. To chelate the indium metal in 1, this angle is reduced by ∼10° to 111.75(6) and 111.96(6)°. These strained four-membered InP2N rings prime 1 for further reactivity. CO2 was bubbled through a slurry of 1 in pentane for 10 min, giving complete conversion to the CO2 addition product 2 (Scheme 1). The 1H NMR spectrum was not particularly helpful for characterizing 2 due to extensive peakbroadening and overlap, even in the decoupled 1H{31P} spectrum. The 31P{1H} spectrum displayed two distinct signals, one a broad peak at 54 ppm, and the other a sharp singlet at 31 ppm. This pattern is consistent with insertion of CO2 into only one In−P bond of each ligand, and it is similar to what we have seen previously for the related Sn and Zn complexes.9a,10 The clearest evidence for CO2 insertion was in the 13C{1H} NMR spectrum, with a doublet at 168.4 ppm (1JCP = 93 Hz) and signals for two distinct isopropyl environments. Single crystals of 2 were grown from a concentrated toluene solution, and the structure is shown in Figure 2. As in 1, there is distorted trigonal bipyramidal geometry at indium, with Cl1, P2, and P4 in the equatorial positions. The oxygen atoms O1 and O3 occupy the axial positions. Although the N−P bonds are not equal, the differences between them are approximately the same as they were in 1, strongly suggesting that the anionic charge of the ligand is delocalized around the P−N−P fragment. The C−O bond lengths show greater differences than the N−P bonds, with the indium-bound O1 and O3 atoms being longer ones, but again the differences are fairly small, once more indicating significant delocalization. The most useful spectroscopic tool for confirming CO2 insertion, besides the 13C{1H} NMR previously mentioned, is IR spectroscopy. The IR spectrum of 2 showed a very strong CO stretch at 1628 cm−1. This distinctive IR stretch, which is very similar to the CO2 adducts of the related Zn and Sn complexes,9a,10 suggested that this reaction would be a good candidate for in situ ReactIR analysis to qualitatively assess the rate of CO2 uptake. Neither 1 nor 2 are highly soluble in pentane, and therefore this experiment was performed in

Figure 1. Structure of 1. Thermal ellipsoids are shown at 50% probability and hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): In1−Cl1 = 2.4480(3); In1−P1 = 2.7404(4); In1−P2 = 2.6354(3); In1−P3 = 2.7402(3); In1−P4 = 2.6512(3); N1−P1 = 1.6470(11); N1−P2 = 1.6213(11); N2−P3 = 1.6456(12); N2−P4 = 1.6265(11); P1−N1−P2 = 111.75(6); P3− N2−P4 = 111.96(6); P1−In1−P3 = 168.327(10); P1−In1−Cl1 = 96.441(10); P2−In1−Cl1 = 106.785(11); P3−In1−Cl1 = 95.232(11); P4−In1−Cl1 = 105.332(11). 11122

DOI: 10.1021/acs.inorgchem.5b02031 Inorg. Chem. 2015, 54, 11121−11126

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Inorganic Chemistry

the same CO stretch at 1628 cm−1 as the solution-state preparations of 2. Further characterization by 31P{1H} NMR confirmed the formation of 2. After CO2 flowed for 2 h, there was no signal at 122 ppm in the 31P{1H} NMR, indicating that 1 had been completely consumed. With shorter reaction times of 30 or 60 min, mixtures of 1 and 2 were present, along with a third set of peaksa doublet at 133.3 ppm (J = 43 Hz), a broad triplet at 49.7 ppm (J = 43 Hz), and a sharp singlet at 27.4 ppm. We speculate that these signals correspond to an intermediate in which CO2 inserted into one ligand but not the other. We were not able to detect this intermediate in the solution-phase synthesis (vide supra). Finally, we note that the reaction time in the solid state is dependent on the particle size. If the crystalline sample of 1 was not crushed, the ratio of 1:2 after 2 h of CO2 exposure was approximately the same as after 30 min of reaction as a powder. To determine if the CO2 addition was reversible, thermal gravimetric analysis (TGA) of 2 was performed. A representative plot is shown in Figure 4. Across three runs,

Figure 2. Structure of 2. Thermal ellipsoids are shown at 50% probability, hydrogen atoms are omitted for clarity, and only the major position of the disordered O2 is shown. Selected bond lengths (Å) and angles (deg): In1−O1 = 2.2494(12); In1−O3 = 2.2841(11); In1−P2 = 2.5284(4); In1−P4 = 2.5375(4); N1−P1 = 1.5803(13); N1−P2 = 1.6051(13); N2−P3 = 1.5806(12); N2−P4 = 1.6053(12); P1−C25 = 1.8615(17); P3−C26 = 1.8771(15); C25−O1 = 1.261(2); C25−O2 = 1.247(6); C26−O3 = 1.2707(18); C26−O4 = 1.2236(18); O1−C25− O2 = 126.4(2); O3−C26−O4 = 127.88(14); P1−N1−P2 = 135.26(8); P3−N2−P4 = 135.94(8).

CH2Cl2, a solvent chosen because it has no IR absorptions in the 1600−1700 cm−1 range. The reaction flask was pressurized with 16 psig of CO2, and IR spectra were collected every 15 s. As Figure 3 shows, the reaction is extremely rapid, and no intermediate was observed. After only 15 s, the conversion of 1 to 2 is 71% complete, and by 1 min the reaction is finished. Figure 4. TGA plot showing the loss of CO2 from 2 when heated at 5 °C/min under an argon atmosphere.

an average weight loss of 10.2% was observed between 75 and 175 °C. The calculated weight loss for the elimination of two CO2 molecules from 2 is 12.0%. To confirm that the decrease in weight was due to loss of CO2 rather than to some other decomposition process, a sample of 2 was heated to 130 °C under vacuum for 1 h, and then the residue was analyzed by 31 1 P{ H} NMR. The spectrum matched that of 1, indicating that the CO2 had been completely released from 2. In contrast, samples that were held under vacuum at room temperature or at 60 °C for the same amount of time showed no loss of CO2 at all. Finally, the reactivity of 1 with CS2 was explored to serve as a complementary reaction (Scheme 2). As was the case for CO2, three conditions were tested, namely, as a pentane slurry, a CH2Cl2 solution, and as a solid/gas reaction. In each case, an immediate color change to dark greenish-brown was observed, and a brown oil was obtained upon workup of the solutions and directly from the solid-state reaction. 31P{1H} NMR spectra of each reaction showed a complex mixture of products. Numerous attempts at separation and recrystallization were made; however, these efforts were met with little success. In one case, a small quantity (several milligrams) of platelike yellow crystals coated in other oily products were isolated from the pentane slurry reaction and identified by single-crystal X-ray diffraction as [SP(i-Pr 2 )NP(i-Pr 2 )] 2 InCl] 2 (μ-Cl)[μ-(iPr2P)2N)] (3) (Figure 5). As Figure 5 shows, compound 3 is dinuclear, in contrast to the mononuclear 1 and 2. Each trigonal bipyramidal indium atom is bound by two P atoms and a terminal chloride in the

Figure 3. ReactIR plot showing the formation of 2 at 1628 cm−1 in CH2Cl2 solution.

The rapid solution-phase transformation of 1 into 2 prompted the question of whether 1 was reactive enough to undergo reaction in the solid state as well. By eliminating the volatile solvent, several principles of green chemistry are addressed. Specifically, less waste is generated in the reaction process, less energy is required to isolate the product because there is no solvent removal step, and the overall process is less hazardous. A crystalline sample of 1 was ground into a powder using a mortar and pestle, and then CO2 was flowed over it at 5 psig for periods of times up to 2 h. The reaction vessel was then purged with argon for 5 min before the powder was analyzed. The IR spectrum of the powder after CO2 exposure displayed 11123

DOI: 10.1021/acs.inorgchem.5b02031 Inorg. Chem. 2015, 54, 11121−11126

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Inorganic Chemistry Scheme 2. Synthesis of 3, Showing Two Equivalent Resonance Forms

we have been unable to conclusively determine the fate of the “CS” fragment, but it is clear from the numerous peaks in the 31 1 P{ H} NMR spectra of the crude reactions mixtures, and from the differences in metal−ligand stoichiometry between 1 and 3, that other products are formed, one or more of which likely contain this missing piece. The fragment “CS” is known from transition metal chemistry to be unstable and extremely reactive in solution; yet, it can act as a ligand in certain metal complexes.

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CONCLUSION We have shown that CO2 is inserted rapidly into the In−P bonds of the strained four-membered rings of the heteroleptic P,P-chelated complex [(i-Pr2P)2N]2InCl 1. This extends the number of main group metal−ligand bonds that can demonstrate CO2 insertion and activation. Under very mild conditions, the addition of gaseous CO2 to 1 to form 2 is complete in less than 1 min in solution and in less than 2 h in a solid/gas reaction. Interestingly, during the solid-state reaction it is possible to identify an intermediate, that, based upon 31 1 P{ H} NMR spectroscopic studies, we speculate is the monoCO 2 addition product [O 2 CP(i-Pr 2 )NP(i-Pr 2 )]InCl[(iPr2P)2N]. The CO2 complex [O2CP(i-Pr2)NP(i-Pr2)]2InCl 2 is stable up to at least 60 °C, even under vacuum, but CO2 is completely released at 130 °C to regenerate compound 1. This ability to quickly and reversibly capture and release CO2 may prove important as we continue our studies to chemically sequester and/or convert CO2 to more useful products using main group metal complexes. In contrast to the very clean CO2 reactivity, CS2 reacts with 1 under several different sets of conditions to give a mixture of products resulting from CS bond cleavage. We were able to identify one of these products

Figure 5. Structure of 3. Thermal ellipsoids are shown at 50% probability, and hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): In1−P1 = 2.5557(19); In1−P3 = 2.562(2); In1−S1 = 2.6224(19); In1−C11 = 2.4022(19); In1−Cl2 = 2.768(2); In2−Cl2 = 2.7168(19); In2−Cl3 = 2.4136(19); In2−P4 = 2.564(2); In2−P5 = 2.562(2); In2−S2 = 2.6308(19); N1−P1 = 1.626(6); N1−P2 = 1.586(6); N2−P3 = 1.593(6); N2−P4 = 1.602(6); N3−P5 = 1.603(5); N3−P6 = 1.602(6); S1−P2 = 2.047(3); S2−P6 = 2.027(3); P1−N1−P2 = 127.1(4); P3−N2−P4 = 141.4(4); P5−N3−P6 = 127.6(4).

equatorial positions and by a sulfur and bridging Cl in the axial positions. The S atoms come from cleavage of CS2 and formal insertion into an In−P bond. The formal cleavage of CS2 into the fragments “CS” and “S” is well-known for transition metal complexes,19 with reviews dating back as early as 1977,20 but to the best of our knowledge this is the first such example of this mode of reactivity with a main group element. To date, Table 1. Crystallographic Data for 1−3 empirical formula Fw T (K) cryst syst space group a, Å b, Å c, Å β, deg volume, Å3 Z calcd. density (g/cm3) μ, mm−1 crystal size (mm3) R1[I > 2σ(I)]a wR2[I > 2σ(I)]b a

1

2

3

C24H56ClInN2P4 646.88 100(2) monoclinic P21/n 11.2942(5) 18.3235(8) 15.8967(7) 99.0770(10) 3248.6(2) 4 1.323 1.022 0.264 × 0.624 × 0.685 0.0206 0.0474

C26H56ClInN2O4P4 734.87 100(2) monoclinic P21/c 18.9863(6) 12.2031(4) 15.6316(5) 102.349(2) 3537.9(2) 4 1.380 0.955 0.278 × 0.500 × 0.539 0.0229 0.0547

C36H84Cl3In2N3P6S2 1144.99 100(2) monoclinic P21/c 15.1370(6) 20.4781(9) 18.4774(9) 111.822(3) 5317.1(4) 4 1.430 1.305 0.082 × 0.127 × 0.152 0.0599 0.0975

R1 = [∑∥F0| − |Fc∥]/[∑|F0|]. bwR2 = {[∑w(F02 − Fc2)2]/[∑w(F02)2]}1/2. 11124

DOI: 10.1021/acs.inorgchem.5b02031 Inorg. Chem. 2015, 54, 11121−11126

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Inorganic Chemistry

removed under vacuum to give a brown oil. A small amount of yellow crystals identified as 3 were subsequently isolated by washing the oil with pentane followed by slow evaporation of the pentane extract. Further characterization was not obtained due to low isolated yield and the presence of other oily products mixed with the crystalline sample. In Situ Infrared Analysis. A sample of 1 (0.20 g, 0.31 mmol) was dissolved in 10 mL of CH2Cl2 in a 50 mL Schlenk flask equipped with a stir bar. The flask was continuously purged with nitrogen as the ReactIR probe was inserted into solution. The flask was then closed and was briefly placed under vacuum. After the flask was evacuated data collection commenced with the ReactIR system. The flask was pressurized with ca. 16 psig of CO2, sealed, and left to stir for 25 min, with spectra recorded at 15 s intervals. Solid−Gas Reaction of 1 with CO2. A sample of 1 (0.04 g, 0.06 mmol) was ground to a powder with a mortar and pestle and then placed in an argon-filled 50 mL Schlenk flask. The flask was evacuated, and then CO2 was flowed through the flask at ∼5 psig for 30, 60, or 120 min. After the CO2 addition was complete, the flask was purged with argon for 5 min before the powder was analyzed by IR and 31 1 P{ H} NMR spectroscopy. IR (KBr) ν 1628 (vs) cm−1. 31P{1H} (121 MHz, C6D6, 30 or 60 min reaction) δ 133.3 (d, JPP = 43 Hz, PNP), 49.7 (br t, JPP = 43 Hz, PNPCO2), 27.4 (s, PNPCO2) ppm and the same peaks previously assigned to 1 and 2. 120 min reaction showed only peaks corresponding to 2. Decarboxylation of 2. A sample of 2 (0.04 g, 0.05 mmol) was placed in an argon-filled 50 mL Schlenk flask. The flask was evacuated and then held under active vacuum for 1 h at ambient temperature, 60 °C, or 130 °C. The flask was then opened to an argon atmosphere, and the contents were dissolved in C6D6 for analysis by 31P{1H} NMR spectroscopy. The spectra showed no change from 2 for the two lower temperature samples. The 130 °C sample showed no peaks associated with 2, only the signal for 1.

by single-crystal X-ray diffraction as [S = P(i-Pr2)NP(iPr2)]2InCl]2(μ-Cl)[μ-(i-Pr2P)2N)].

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EXPERIMENTAL SECTION

General Experimental. All manipulations were performed in an argon-filled glovebox or by using standard Schlenk techniques unless otherwise noted. The ligand bis(diisopropylphosphino)amine was prepared according to literature procedures.21 Anhydrous solvents were stored in the glovebox over 4 Å molecular sieves prior to use. Caution! CS2 is both toxic and flammable, and appropriate caution should be used in handling. 1H and 13C{1H} spectra were referenced to residual solvent downfield of tetramethylsilane. 31P{1H} spectra were referenced to external 85% H3PO4. IR spectra were recorded as mineral oil mulls on KBr windows. A Mettler-Toledo ReactIR 15 spectrometer equipped with a silicon-tipped probe was employed for the in situ infrared analysis, and the data were processed and plotted using iC.IR 4.3 software and Microsoft Office Excel 2010, respectively. Single-crystal X-ray diffraction studies were performed on a Bruker Kappa Apex II CCD diffractometer. Crystals were coated in ParatoneN oil and mounted on a MiTeGen MicroLoop. The Bruker Apex2 software suite22 was used for data collection, structure solution, and refinement. Relevant parameters are summarized in Table 1. TGA studies were performed on a Mettler-Toledo TGA/DSC1 Stare system using 5−8 mg portions of 2 in sealed 100 μL aluminum crucibles under flowing argon with a heating rate of 5 °C/min. Elemental analyses were performed by ALS Global (Tucson, AZ). (i-Pr2P)2NLi. A solution of n-BuLi (3.8 mL, 1.6 M in hexanes) was added slowly to a solution of (i-Pr2P)2NH (1.37 g, 5.5 mmol) in ca. 15 mL of THF. The resulting thick white suspension was stirred at room temperature (rt) for 20 min, and then the product was isolated as a fine white powder by filtration and dried under vacuum. Yield = 1.24 g (88%), mp > 200 °C. 1H{31P} (300 MHz, deuterated dimethyl sulfoxide (DMSO-d6)) δ 1.14 (sept, 3JHH = 7 Hz, 1H, CH), 0.90 (d, 3 JHH = 7 Hz, 3H, CH3), 0.84 (d, 3JHH = 7 Hz, 3H, CH3) ppm. 13C{1H} (75 MHz, DMSO-d6) δ 29.2 (vt, CH), 20.1 (vt, CH3), 18.2 (vt, CH) ppm. 31P{1H} (121 MHz, DMSO-d6) δ 85.3 ppm. Anal. Calcd for C12H28LiNP2: C, 56.47; H, 11.06; N, 5.49. Found: C, 56.53; H, 11.93; N, 5.06%. [(i-Pr2P)2N]2InCl (1). A solution of Et2O (15 mL) and THF (5 mL) was added to solid InCl3 (0.22 g, 1.0 mmol) and (i-Pr2P)2NLi (0.51 g, 2.0 mmol). The resulting pale yellow mixture was stirred at rt for 2 h and then filtered to remove LiCl. Solvent was removed under vacuum to give 1 as a white to pale yellow powder. Yield = 0.59 g (91%), mp 140−141 °C. 1H{31P} (300 MHz, C6D6) δ 2.16 (sept, 3JHH = 7 Hz, 1H, CH), 1.29 (d, 3JHH = 7 Hz, 3H, CH3), 1.22 (d, 3JHH = 7 Hz, 3H, CH3) ppm. 13C{1H} (75 MHz, C6D6) δ 29.8 (vt, CH), 18.5 (s, CH3), 17.8 (s, CH3) ppm. 31P{1H} (121 MHz, C6D6) δ 122 ppm. Anal. Calcd for C24H56ClInN2P4: C, 44.56; H, 8.73; N, 4.33. Found: C, 44.29; H, 8.82; N, 4.29%. X-ray quality single crystals of 1 were grown from a saturated pentane solution at −25 °C. [O2CP(i-Pr2)NP(i-Pr2)]2InCl (2). Carbon dioxide was bubbled through a slurry of 1 (0.40 g, 0.62 mmol) in ca. 5 mL of pentane for 10 min. The mixture was then purged with argon, and the colorless supernatant was decanted from the white powder 2. Yield = 0.39 g (87%), mp 138 °C (dec). 1H{31P} (300 MHz, C6D6) δ 2.55 (br sept, 3 JHH = 7 Hz, 1H, CH), 2.37 (br sept, 3JHH = 7 Hz, 1H, CH), 2.00−2.13 (overlapping sept, 2H, CH), 0.97−1.42 (overlapping doublets, 24H, CH3) ppm. 13C{1H} (75 MHz, C6D6) δ 168.4 (d, 1JCP = 93 Hz, CO2), 27.3 (d, 1JCP = 56 Hz, CH), 25.5 (d, 1JCP = 67 Hz, CH), 17.1 (s, CH3), 16.6 1 (s, CH3), 16.2 1 (s, CH3), 15.7 1 (s, CH3) ppm. 31P{1H} (121 MHz, C6D6) δ 54 (br s, P-In), 31 (s, P-CO2) ppm. IR (KBr) ν 1628 (vs) cm−1. Anal. Calcd for C26H56ClInN2O4P4: C, 42.49; H, 7.68; N, 3.81. Found: C, 42.67; H, 8.12; N, 3.69%. X-ray quality single crystals were grown from concentrated toluene solutions at −25 °C. [S = P(i-Pr2)NP(i-Pr2)]2InCl]2(μ-Cl)[μ-(i-Pr2P)2N)] (3). Carbon disulfide (61 μL, 1.0 mmol) was added via syringe to a slurry of 1 (0.325 g, 0.5 mmol) in ca. 5 mL of pentane. An immediate color change from colorless through yellow to green-brown was observed. The mixture was allowed to stir at rt for 20 min, and then solvent was

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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.5b02031. CIF files for 1−3. The CIF files were also deposited at the CCDC (1401832, 1401833, and 1419352). (CIF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Present Addresses #

Sandia National Laboratories, Albuquerque, NM, 87123. Department of Chemistry, University of Washington, Seattle, WA, 98195.

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Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the National Science Foundation (Grant No. CHE12-13529) and the Laboratory Directed Research and Development (LDRD) program at Sandia National Laboratories (LDRD 151300). J.A.C.C. thanks the Natural Sciences and Engineering Research Council of Canada (through the Discovery Grants Program) the Canada Research Chairs Program, the Canadian Foundation for Innovation, and the Nova Scotia Research and Innovation 11125

DOI: 10.1021/acs.inorgchem.5b02031 Inorg. Chem. 2015, 54, 11121−11126

Article

Inorganic Chemistry

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Trust Fund. We thank J. Sears and D. Bencoe of Sandia National Laboratories for assisting with TGA data collection and processing. The Bruker X-ray diffractometer was purchased via a National Science Foundation CRIF:MU award to the Univ. of New Mexico (CHE04-43580), and the NMR spectrometers were upgraded via grants from the NSF (CHE08-40523 and CHE09-46690). Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract No. DE-AC04-94AL85000.

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DOI: 10.1021/acs.inorgchem.5b02031 Inorg. Chem. 2015, 54, 11121−11126