Synthesis and Characterization of Tris(trimethylsilyl)siloxide

Jul 6, 2018 - (1−5) When these materials are doped with lanthanide (Ln) cations, the ..... Calcd for n = 0 C28H76HfO4Si8 (MW = 880.08): % C, 38.21; ...
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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

Synthesis and Characterization of Tris(trimethylsilyl)siloxide Derivatives of Early Transition Metal Alkoxides That Thermally Convert to Varied Ceramic−Silica Architecture Materials Timothy J. Boyle,*,† Jeremiah M. Sears,†,∥ Diana Perales,† Roger E. Cramer,†,‡ Ping Lu,§ Rana O. Chan,† and Bernadette A. Hernandez-Sanchez†

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Advanced Materials Laboratory, Sandia National Laboratories, 1001 University Boulevard, SE, Albuquerque, New Mexico 87106, United States ‡ Department of Chemistry, University of HawaiiManoa, 2545 McCarthy Mall, Honolulu, Hawaii 96822-2275, United States § Sandia National Laboratories, P.O. Box 5800, Albuquerque, New Mexico 87185-1411, United States S Supporting Information *

ABSTRACT: In an effort to generate single-source precursors for the production of metal−siloxide (MSiOx) materials, the tris(trimethylsilyl)silanol (H-SST or H-OSi(SiMe3)3 (1) ligand was reacted with a series of group 4 and 5 metal alkoxides. The group 4 products were crystallographically characterized as [Ti(SST)2(OR)2] (OR = OPri (2), OBut (3), ONep (4)); [Ti(SST)3(OBun)] (5); [Zr(SST)2(OBut)2(py)] (6); [Zr(SST)3(OR)] (OR = OBut (7), ONep, (8)); [Hf(SST)2(OBut)2] (9); and [Hf(SST)2(ONep)2(py)n] (n = 1 (10), n = 2 (10a)) where OPri = OCH(CH3)2, OBut = OC(CH3)3, OBun = O(CH2)3CH3, ONep = OCH2C(CH3)3, py = pyridine. The crystal structures revealed varied SST substitutions for: monomeric Ti species that adopted a tetrahedral (T-4) geometry; monomeric Zr compounds with coordination that varied from T-4 to trigonal bipyramidal (TBPY-5); and monomeric Hf complexes isolated in a TBPY-5 geometry. For the group 5 species, the following derivatives were structurally identified as [V(SST)3(py)2] (11), [Nb(SST)3(OEt)2] (12), [Nb(O)(SST)3(py)] (13), 2[H][(Nb(μ-O)2(SST))6(μ6-O)] (14), [Nb8O10(OEt)18(SST)2·1/ 5Na2O] (15), [Ta(SST)(μ-OEt)(OEt)3]2 (16), and [Ta(SST)3(OEt)2] (17) where OEt = OCH2CH3. The group 5 monomeric complexes were solved in a TBPY-5 arrangement, whereas the Ta of the dinculear 16 was solved in an octahedral coordination environment. Thermal analyses of these precursors revealed a stepwise loss of ligand, which indicated their potential utility for generating the MSiOx materials. The complexes were thermally processed (350−1100 °C, 4 h, ambient atmosphere), but instead of the desired MSiOx, transmission electron microscopy analyses revealed that fractions of the group 4 and group 5 precursors had formed unusual metal oxide silica architectures.

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INTRODUCTION Metal silica-based (MSiOx) materials have found utility in scintillator applications due to their intense luminescent response upon exposure to radiation sources.1−5 When these materials are doped with lanthanide (Ln) cations, the resultant MSiOx:Ln materials (i.e., M = barium,6 bismuth,7,8 rare earths9−12) are particularly sensitive and luminescent. In addition, a number of naturally occurring fluorescent MSiOx ceramics demonstrate bright emissions, such as zircon (ZrSiO4), benitoite (BaTiSi3O9), and baghdadite (Ca3(Zr, Ti)Si2O9).13 Because of these properties, it was of interest to synthesize doped group 4−6 silicate nanomaterials for potential scintillator applications. The production of MSiOx has been widely investigated using a variety of synthetic pathways.14−19 For routes that employ metal alkoxides ([M(OR)x]), the MSiOx products are reportedly generated from the reaction of the desired metal precursor with a Si(OR)420−24 or via metal siloxide [M(OSiR3)x]25−28 or metal trialkoxysiloxy28 precursors. © XXXX American Chemical Society

In our hands, after processing the [M(OSiR3)x] precursors, phase separated nano-oxides were isolated instead of the desired MSiOx. This led us to investigate tris(trimethylsilyl)silanol (HOSi(Si(CH3)3)3 or H-SST; Figure 1a) modified [M(OR)4] as a potential single-source precursor to MSiOx. The H-SST ligand became of interest due to the different internal bond strengths where the Si−Si bond strength (326.8 kJ/mol) is less than the Si−C bond strength (435 kJ/mol) and much less than the Si−O bonds (798.7 kJ/mol).29 Further, upon complexation to a group 4 metal [Ti−O (661.9 kJ/mol), Zr−O (759.8 kJ/mol), Hf−O (794.1 kJ/mol), V−O (644 kJ/mol), Nb−O (753 kJ/mol), Ta− O (805.0 kJ/mol)], the Si−Si bond still remains the weakest link.29 It was anticipated that, with proper processing of a “[M(SST)n(OR)x−n]” compound, the oxide could be avoided Received: March 9, 2018

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DOI: 10.1021/acs.inorgchem.8b00630 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

oxide silica architectures were observed. Details of these investigations are discussed. [M(OR)x ] + nH ‐ SST → ′[M(SST)n (OR)x ‐ n ]′ + nH ‐ OR

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EXPERIMENTAL SECTION

All complexes described below were handled with rigorous exclusion of air and water using standard Schlenk line and glovebox techniques. All reactions were conducted under an argon atmosphere in a glovebox. All solvents were stored under argon and used as received (Aldrich) in Sure Seal bottles, including hexanes (hex), toluene (tol), chloroform (CHCl3), carbon tetrachloride (CCl4), and diethyl ether (OEt2). The following chemicals were used as received (Aldrich and Alfa Aesar): tris(trimethylsilyl)silane (H−Si(Si(CH3)3)3), triethylamine (N(Et)3), sodium sulfate (Na2SO4), neo-pentanol (H-ONep), titanium isopropoxide ([Ti(OPri)4]), titanium n-butoxide ([Ti(OBun)4]), metal tert-butoxides [M(OBut)4] (M = Ti, Zr, Hf)], vanadium oxo isopropoxide ([V(O)(OPri)3]), vanadium oxo chloride ([V(O)(Cl)3]), niobium ethoxide ([Nb(OEt)5], and tantalum ethoxide ([Ta(OEt)5]). The metal ONep derivatives {[Ti(μ-ONep)(ONep)3]2 (referred to as [Ti(ONep)4])39 and [M2(ONep)8(OBut)]2 (M = Zr, Hf; referred to as [Zr(ONep)4], [Hf(ONep)4], respectively)40} were synthesized according to literature procedures. In-house deionized (DI) water (Millipore) was used without further purification. All samples used for analytical analyses were dried and handled under an argon atmosphere. FTIR spectral data were collected on a Bruker Vector 22 MIR spectrometer under an atmosphere of flowing nitrogen using NaCl salt plates for 1 and KBr pellets for all other reported FTIR spectra. Elemental analyses were performed on a PerkinElmer 2400 CHN-S/O elemental analyzer. TGA/DSC analyses were undertaken under a flowing argon atmosphere from room temperature to 550 °C at 5 °C/min using a Mettler Toledo TGA/DSC 1 STARe System. 1H NMR spectra were collected on a Bruker Avance 500 MHz NMR spectrometer referencing against the residual protons in toluene-d8 (told8) or deuterated chloroform (CDCl3) under standard experimental conditions: 1H analyses were performed with a 4 s recycle delay at 16 scans; 29Si analyses were performed with a 240 s delay at a minimum of 192 scans using a 5 mm broad-band probe. H-OSi(Si(CH3)3)3 (1). The H-SST ligand was synthesized according to the literature preparative routes with minor modifications noted below.36−38 In general, H−Si(Si(CH3)3)3 (20.0 g, 80.4 mmol) was stirred with heating in CHCl3/CCl4 (100:25 mL) at reflux temperatures for 4 h, allowed to cool to room temperature, and dried in vacuo. The resulting pale-yellow gel was redissolved in hexanes; a mixture of water and N(Et)3 (75:50 mL) was added and stirred for an additional 24 h. The organic fraction was separated from the aqueous, dried over NaSO4 (∼10 g), filtered, vacuum distilled to an oil, and stored over dried molecular sieves for 24 h prior to use. Yield 1: 96.9% (25.8 g). FTIR (NaCl plate) v̅max (cm−1): 3670 (m, sh), 3649 (m, sh), 3433 (m), 2949 (s), 2893 (s, sh), 1437 (w, sh), 1395 (w), 1309 (w), 1244 (s), 1032 (w), 835 (s), 761 (m, sh), 743 (s), 687 (m), 623 (m). 1H (500.1 MHz, tol-d8) δ 0.18 (H-OSi(Si(CH3)3)3). 29Si NMR (99.325 MHz, told8) δ −3.52 (s, H−OSi(Si(CH3)3)3), −16.34 (s, H−OSi(Si(CH3)3)3). From one incompletely washed reaction mixture, crystals were isolated as 3(H-SST)·HN(CH2CH3)3+·Cl− (1a, Figure 1b). Analytical data were not collected on this complex, but the crystal parameter data are supplied in Table S1 in the Supporting Information to allow for rapid identification. General Inorganic Precursor Preparation. In a vial, stoichiometric amounts of H-SST were added to a stirring solution of the appropriate M(OR)x dissolved in the desired solvent. After 12 h, the reaction was set aside to allow the volatile components to slowly evaporate until crystals grew. After this time, the mother liquor was decanted off. Crystals were removed for single crystal analysis and the remaining crystals dried in vacuo and used for all additional analyses. Yields were not optimized.

Figure 1. Schematic representation of (a) tris(trimethylsilyl)silanol (HSST, 1) and (b) structure plot of 1a. The heavy atom thermal ellipsoids are drawn at the 30% level, with C atoms drawn as ball and stick, and most of the H atoms are not shown for clarity.

and the desired MSiOx generated. Therefore, the utility of SSTmodified group 4 and 5 [M(OR)n] complexes as precursors to MSiOx materials was explored. A search of the structure literature30 indicates that there are only a handful of SST ligated metal complexes that have been crystallographically characterized.31−35 Since there were no structure reports disseminated for SST derivatives of the group 4 or 5 metals, the synthesis of a series of SST-modified [M(OR)x] was undertaken. The initial efforts focused on the synthesis of the H-SST ligand (1, schematic in Figure 1a), following slightly modified literature procedures36−38 to isolate the pure oil. The coordination behavior of the pure H-SST with a series of group 4 and 5 [M(OR)n] species at room temperature was undertaken following eq 1. The products isolated from eq 1 were crystallographically characterized as [Ti(SST)2(OR)2] (OR = OPri (2), OBut (3), ONep (4)), [Ti(SST)3(OBun)] (5), [Zr(SST)2(OBut)2(py)] (6), [Zr(SST)3(OR)] (OR = OBut (7); ONep, (8)), [Hf(SST)2(OBut) 2] (9), [Hf(SST)2(ONep)2(py)n] (n = 1 (10); n = 2 (10a)), [V(SST)3(py)2] (11), [Nb(SST)3(OEt)2] (12), [Nb(O)(SST)3(py)] (13), 2[H][(Nb(μ-O)2(SST))6(μ6-O)] (14), [Nb8O 10(OEt)18(SST)2·1/5Na2O] (15), [Ta(SST)(μ-OEt)(OEt)3]2 (16), and [Ta(SST)3(OEt)2] (17) where OEt = OCH2CH3, OPri = OCH(CH3)2, OBut = OC(CH3)3, OBun = O(CH2)3CH3, ONep = OCH2C(CH3)3, py = pyridine. On the basis of the thermal analysis of the isolated powders, attempts were made to convert these precursors into silicate-based group 4 materials. However, instead of the desired MSiOx species, unusual metal B

DOI: 10.1021/acs.inorgchem.8b00630 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry [Ti(SST)2(OPri)2] (2). This synthesis used Ti(OPri)4 (0.269 g, 0.946 mmol) and H-SST (0.500 g, 1.89 mmol) in ∼10 mL of toluene. Yield: 73.7% (0.484 g). FTIR (KBr, pellet) v̅max (cm−1): 2950 (s), 2893 (s, sh), 2347 (w), 1439 (w), 1394 (w), 1377 (w), 1363 (w), 1332 (w), 1242 (s), 1168 (m, sh), 1120 (m), 1003 (m), 953 (s, sh), 919 (s), 840 (s, b), 688 (m), 623 (m), 505 (w), 471 (w) cm−1. 1H NMR (500.1 MHz, told8) δ 4.54 (1H, sept, OCH(CH3)2, JH−H = 5 Hz), 1.25 (6H, d, OCH(CH3)2, JH−H = 5 Hz), 0.34 (27H, s, OSi(Si(CH3)3)3). 29Si NMR (99.325 MHz, tol-d8) δ 7.26 (H−OSi(Si(CH3)3)3), −16.53 (OSi(Si(CH3)3)3). Anal. Calcd for C24H68O4Si8Ti (MW = 693.35): % C, 41.58; % H, 9.89. Found: % C, 41.03; % H, 9.49. [Ti(SST)2(OBut)2] (3). This synthesis used [Ti(OBut)4] (0.322 g, 0.946 mmol) and H-SST (0.500 g, 1.89 mmol) in ∼10 mL of toluene. Yield: 79.4% (0.543 g). FTIR (KBr, pellet) v̅max (cm−1): 3437 (m, b), 2973 (s), 2895 (s, sh), 2366 (w), 1926 (w), 1466 (w), 1438 (w), 1394 (w), 1361 (m), 1310 (w), 1243 (s), 1198 (m), 1173 (m, sh), 1046 (m, sh), 996 (s), 943 (s, sh), 917 (s), 846 (s, b), 744 (w), 688 (m), 624 (m), 599 (w), 470 (w) cm−1. 1H NMR (500.1 MHz, tol-d8) δ 1.36 (9H, s, OC(CH3)3) 0.35 (27H, s, OSi(Si(CH3)3)3. 29Si NMR (99.325 MHz, tol-d8) δ 6.90 (OSi(Si(CH3)3)3), −16.26 (OSi(Si(CH3)3)3). Anal. Calcd for C26H72O4Si8Ti (MW = 721.41): % C, 43.29; % H, 10.06. Found: % C, 43.50; % H, 10.37. [Ti(SST)2(ONep)2] (4). This synthesis used [Ti(ONep)4] (0.374 g, 0.946 mmol) and H-SST (0.500 g, 1.89 mmol) in ∼10 mL of toluene. Yield: 74.6% (0.530 g). FTIR (KBr, pellet) v̅max (cm−1): 3670 (m), 3650 (m), 3448 (m, b), 2953 (s), 2894 (s, sh), 2362 (m), 2343 (m, sh), 1437 (w), 1395 (w), 1364 (w), 1244 (s), 1085 (m, b), 1026 (w), 982 (m), 950 (m), 916 (s), 837 (s, b) 750 (w), 688 (m), 624 (w), 471 (w) cm−1. 1H NMR (500.1 MHz, tol-d8) δ 4.10 (2H, s, OCH2C(CH3)3), 0.98 (9H, s, OCH2C(CH3)3), 0.31 (27H, s, OSi(Si(CH3)3)3). 29Si NMR (99.325 MHz, tol-d8) δ 8.29 (OSi(Si(CH3)3)3), −16.70 (OSi(Si(CH3)3)3). Anal. Calcd for C28H76O4Si8Ti (MW = 749.46): % C, 44.87; % H, 10.22. Found: % C, 44.72; % H, 10.86. [Ti(SST)3(OBun)] (5). This synthesis used [Ti(OBun)4] (0.214 g, 0.630 mmol) and H-SST (0.500 g, 1.89 mmol) in ∼10 mL of toluene. Yield: 75.0% (0.439 g). FTIR (KBr, pellet) v̅max (cm−1): 3677 (m), 3651 (m), 2952 (s), 2895 (s, sh), 2347 (m), 1439 (w), 1397 (w), 1313 (w), 1244 (s), 1124 (m), 1098 (w, sh), 955 (m), 908 (s), 837 (s, b), 814 (s, sh), 747 (w), 689 (m), 625 (m), 548 (w), 463 (w) cm−1. 1H NMR (500.1 MHz, tol-d8) δ 4.43(2H, t, (OCH2(CH2)2CH3) 1.66 (2H, mult, (OCH2(CH2)2CH3), 1.34 (5H, mult, (OCH2(CH2)2CH3), 0.36 (81H, s, OSi(Si(CH3)3)3). 29Si NMR (99.325 MHz, tol-d8) δ 8.30 (OSi(Si(CH3)3)3), −16.59 (OSi(Si(CH3)3)3). Anal. Calcd for C31H90O4Si12Ti (MW = 911.94): % C, 40.83; % H, 9.95. Found: % C, 40.34; % H, 10.74. [Zr(SST)2(OBut)2(py)] (6). This synthesis used [Zr(OBut)4] (0.364 g, 0.945 mmol) and H-SST (0.500 g, 1.89 mmol) in ∼10 mL of pyridine. Yield: 66.6% (0.533 g). FTIR (KBr, pellet) v̅max (cm−1): 3670 (s), 3651 (m), 2949 (s), 2894 (s), 2346 (w), 1438 (w), 1389 (w), 1361 (w), 1243 (s), 1205 (w), 1187 (w), 1047 (w, sh), 1003 (m), 936 (m, sh), 912 (s), 836 (s, b), 743 (w), 687 (m), 623 (m), 550 (w), 472 (w) cm−1. 1H NMR (500.1 MHz, CDCl3) δ 1.32 (9H, s, OC(CH3)3), 0.32 (27H, s, OSi(Si(CH3)3)3). 29Si NMR (99.325 MHz, CDCl3) δ −2.02 (OSi(Si(CH 3 )3) 3), −17.0 (OSi(Si(CH 3 )3) 3). Anal. Calcd for C31H77NO4Si8Zr (MW = 843.86): % C, 44.12; % H, 9.20; % N, 1.66. Calcd for C57H149NO8Si16Zr2 (MW = 1608.605; 6 − 1/2 py): % C, 42.56; % H, 9.34; % N, 0.87. Found: % C, 42.40; % H, 9.76; % N, 0.95. [Zr(SST)3(OBut)] (7). This synthesis used [Zr(OBut)4] (0.25 g, 0.653 mmol) and H-SST (0.517 g, 1.96 mmol) in ∼10 mL of toluene. Yield: 83.5% (0.521 g). FTIR (KBr, pellet) v̅max (cm−1): 3504 (w), 2950 (s), 2894 (s), 2821 (m), 1927 (w), 1863 (w), 1603 (w), 1493 (w), 1395 (w), 1361 (w), 1309 (w, sh), 1243 (s), 1193 (w), 1153 (w), 1034 (m), 949 (s, sh), 904 (s, sh), 836 (s), 743 (m), 687 (s), 624 (s), 549 (w), 484 (m). 1H NMR (500.1 MHz, CDCl3) δ 1.29 (3H, s, OC(CH)3)3), 0.20 (27H, s, OSi(Si(CH3)3)3). 29Si NMR (99.325 MHz, CDCl3) δ −2.88 (OSi(Si(CH3)3)3), −16.79 (OSi(Si(CH3)3)3). Anal. Calcd for C31H90O4Si12Zr (MW = 955.30): % C, 38.98; % H, 9.50. Calcd for C69H188O8Si24Zr2 (MW = 2002.74; 7 + 1/2 tol): % C, 41.38; % H, 9.46. Found: % C, 41.26; % H, 9.23.

[Zr(SST)3(ONep)] (8). This synthesis used [Zr(ONep)4]2 (0.277 g, 0.630 mmol) and H-SST (0.500 g, 1.89 mmol) in ∼10 mL of toluene. Yield: 77.0% (0.472 g). FTIR (KBr, pellet) v̅max (cm−1): 3670 (m), 3651 (m), 3422 (m, b), 2951 (s), 2894 (s, sh), 2346 (m), 1439 (w), 1396 (w), 1363 (w), 1309 (w), 1244 (s), 1130 (w), 906 (m), 836 (s, b), 762 (w), 744 (w), 687 (m), 624 (w), 471 (w) cm−1. 1H NMR (500.1 MHz, tol-d8) δ 3.90 (2H, s, OCH2C(CH)3)3), 1.29 (9H, s, OCH2C(CH)3)3), 0.20 (81H, s, OSi(Si(CH3)3)3). 29Si NMR (99.325 MHz, tol-d8) δ −2.26 (OSi(Si(CH3)3)3), −16.66 (OSi(Si(CH3)3)3). Anal. Calcd for C32H92O4Si12Zr (MW = 969.33): % C, 39.65; % H, 9.57. Found: % C, 39.17; % H, 9.83. [Hf(SST)2(OBut)2] (9). This synthesis used [Hf(OBut)4] (0.446 g, 0.945 mmol) and H-SST (0.500 g, 1.89 mmol) in ∼10 mL of pyridine. Yield: 77.5% (0.682 g). FTIR (KBr, pellet) v̅max (cm−1): 3670 (s), 3657 (m), 2949 (s), 2894 (s, sh), 2375 (m), 2345 (m), 1243 (m), 1193 (w), 1014 (m), 954 (m), 920 (m), 837 (s, b), 743 (w), 687 (m), 624 (m), 469 (w) cm−1. 1H NMR (500.1 MHz, CDCl3) δ 1.57 (9H, s, OC(CH3)3), 0.33 (31H, s, OSi(Si(CH3)3)3). 29Si NMR (99.325 MHz, CDCl3) δ −1.99 (OSi(Si(CH3)3)3), −16.63 (OSi(Si(CH3)3)3). Anal. Calcd for C26H72HfO4Si8 (MW = 852.03): % C, 36.65; % H, 8.52; % N, 0.00. Found: % C, 36.36; % H, 9.06; % N, 0.06. [Hf(SST)2(ONep)2(py)n] (n = 1 (10); n = 2 (10a)). This synthesis used [Hf(ONep)4] (0.535 g, 0.945 mmol) and H-SST (0.500 g, 1.89 mmol) in ∼10 mL of pyridine. Yield: 75.8% (0.687 g). FTIR (KBr, pellet) v̅max (cm−1): 3670 (s), 3657 (s), 2951 (s), 2894 (s, sh), 2346 (m), 1244 (m), 1121 (m, b), 1025 (w), 911 (m), 837 (s), 744 (w), 687 (m), 624 (m), 467 (w) cm−1. 1H NMR (500.1 MHz, tol-d8) δ 3.92 (2H, s, OCH2C(CH3)3), 0.97 (9H, s, OCH2C(CH3)3), 0.33 (31H, s, OSi(Si(CH3)3)3). 29Si NMR (99.325 MHz, tol-d8) δ −2.10 (OSi(Si(CH3)3)3), −16.66 (OSi(Si(CH3)3)3). Anal. Calcd for n = 2 C38H86HfN2O4Si8 (10a, MW = 1038.29): % C, 43.96; % H, 8.35; % N, 2.70. Calcd for n = 1 C33H81HfNO4Si8 (10, MW = 959.18): % C, 41.32; % H, 8.51; % N, 1.46. Calcd for n = 0 C28H76HfO4Si8 (MW = 880.08): % C, 38.21; % H, 8.70; % N, 0.00. Found: % C, 39.55; % H, 8.8; % N, 2.45. [V(SST)3(py)2] (11). This synthesis used (O)VCl3 (2.00 g, 11.5 mmol) and H-SST (9.25 g, 37.2 mmol) in 200 mL of toluene, 3 mL of trimethylamine, and py (2 mL). This mixture was heated to 60 °C, filtered, and concentrated, and OEt2 (120 mL) was added. The reaction mixture was allowed to slowly evaporate until crystals formed. The yield was 72.7% (6.41 g). FTIR (KBr, pellet) v̅max (cm−1): 2954 (s), 2895 (s), 2827 (m), 1608 (w), 1491 (w), 1448 (w), 1400 (w), 1245 (s), 1033 (s), 839 (s), 754 (m), 689 (s), 623 (w), 570 (s), 498 (m). 1H NMR (500.1 MHz, tol-d8) δ 0.32 (s, OSi(Si(CH3)3)3). 29Si NMR (99.325 MHz, told8) δ 0.92 (OSi(Si(CH3)3)3) −16.69 (OSi(Si(CH3)3)3). Anal. Calcd for C37H91N2O3Si12V (MW = 1000.11): % C, 44.44; % H, 9.17; % N, 2.80. Calcd for C32H86NO3Si12V (MW = 921.01; 11 − py): % C, 41.73; % H, 9.41; % N, 1.52. Found: % C, 41.43; % H, 9.20; % N, 2.27. [Nb(SST)3(OEt)2] (12). This synthesis used [Nb(OEt)5] (0.100 g, 0.314 mmol) and H-SST (0.250 g, 0.942 mmol) in ∼10 mL of toluene. Yield: 90.2% (0.276 g). FTIR (KBr, pellet) v̅max (cm−1): 2950 (s), 2894 (s), 1439 (w), 1397 (w), 1375 (w), 1312 (w), 1245 (s), 1103 (w), 1067 (m), 902 (s), 837 (s), 809 (s, sh), 688 (m), 624 (w), 575 (w), 489 (w), 467 (w). 1H NMR (500.1 MHz, CDCl3) δ 2.54 (4H, q, OCH2CH3 JH−H = 7.0 Hz) 1.05 (6H, t, OCH2CH3, JH−H = 7.0 Hz), 0.16 (81H, s, OSi(Si(CH3)3)3). 29Si NMR (99.325 MHz, tol-d8) δ 0.88 (OSi(Si(CH3)3)3), −16.2 (OSi(Si(CH3)3)3). Anal. Calcd for C31H91NbO5Si12 (MW = 973.99): % C, 38.23; % H, 9.42; % N, 0.00. Found: % C, 38.46; % H, 9.37; % N, 0.08. [Nb(O)(SST)3(py)] (13). This synthesis used [Nb(OEt)5] (0.100 g, 0.314 mmol) and H-SST (0.250 g, 0.942 mmol) in ∼10 mL of toluene. Yield: 64.5% (0.198 g). FTIR (KBr, pellet) v̅max (cm−1): 3551 (m), 2949 (s), 2893 (s), 2824 (m), 1439 (w), 1398 (w), 1313 (w), 1245 (s), 1009 (w), 937 (s), 900 (w), 837 (s), 769 (s), 691 (s), 623 (w), 474 (w), 435 (w). 1H NMR (500.1 MHz, tol-d8) δ 0.25 (OSi(Si(CH3)3)3). 29Si NMR (99.325 MHz, tol-d8) δ 13.19, −16.1. Anal. Calcd for C32H86NNbO4Si12 (MW = 978.97): % C, 39.26; % H, 8.86; % N 1.43. Found: % C, 39.01; % H, 9.77; % N, 0.82. [Ta(SST)(μ-OEt)(OEt)3]2 (16). This synthesis used [Ta(OEt)5] (0.770 g, 1.89 mmol) and H-SST (0.500 g, 1.89 mmol) in ∼10 mL of C

DOI: 10.1021/acs.inorgchem.8b00630 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry toluene. Yield: 48.1% (0.567 g). FTIR (KBr, pellet) v̅max (cm−1): 3670 (s), 3651 (s), 2966 (s), 2347 (m), 1720 (s), 1638 (s), 1377 (s), 1244 (s), 1108 (m), 1072 (m), 917 (m), 840 (s), 688 (w), 624 (w), 468 (w) cm−1. 1H NMR (500.1 MHz, tol-d8) δ 4.57(6H, m, OCH2CH3), 4.44 (2H, m, OCH2CH3), 1.29 (12H, m, OCH2CH3), 0.39 (30H, s, OSi(Si(CH3)3)3). 29Si NMR (99.325 MHz, tol-d8) δ −2.17 (OSi(Si(CH 3 ) 3 ) 3 ), −17.00 (OSi(Si(CH 3 ) 3 ) 3 ). Anal. Calcd for C34H94O10Si8Ta2 (MW = 1249.69): % C, 32.68; % H, 7.58. Calcd for C73H193NO20Si16Ta4 (MW = 2578.49; 16 + 1/2 py): % C, 34.00; % H, 7.54; % N, 0.54. Found: % C, 33.4; % H, 8.66; % N, 0.53. [Ta(SST)3(OEt)2] (17). This synthesis used [Ta(OEt)5] (0.256 g, 0.630 mmol) and H-SST (0.500 g, 1.89 mmol) in ∼10 mL of toluene. Yield: 87.6% (0.589 g). FTIR (KBr, pellet) v̅max (cm−1): 2949 (s), 2893 (s), 1720 (m), 1638 (m), 1400 (m), 1244 (m), 1085 (m), 909 (m), 837 (s), 688 (w), 623 (w), 481 (w) cm−1. 1H NMR (500.1 MHz, CDCl3) δ 3.46 (4H, q, OCH2CH3 JH−H = 3.5 Hz) 1.18 (6H, t, OCH2CH3, JH−H = 7.1 Hz), 0.16 (81H, s, OSi(Si(CH3)3)3). 29Si NMR (99.325 MHz, CDCl3) δ −2.39 (OSi(Si(CH3)3)3), −16.60 (OSi(Si(CH3)3)3). Anal. Calcd for C31H91O5Si12Ta (MW = 1062.03): % C, 35.06; % H, 8.64. Calcd for C25H75O5Si10Ta (MW = 917.67 17 − 2 SiMe3): % C, 32.72; % H, 8.24. Found: % C, 32.22; % H, 9.1. General X-ray Crystal Structure Information. Single crystals were mounted onto a loop from a pool of Fluorolube or Parabar 10312 and immediately placed in a 100 K N2 vapor stream. A Bruker APEX-II CCD diffractometer with Mo or Cu Kα radiation (λ = 0.71070 or 1.54178 Å, respectively) was used to collect single crystal X-ray diffraction data. Structures were solved and refined using the Bruker SHELXTL41,42 software package within Apex343 and/or OLEX2.44 All final CIF files were checked using the CheckCIF program (http:// www.iucr.org/). Additional information concerning the data collection and final structural solutions (Table S1) of these complexes can be found in the Supporting Information or by accessing CIF files through the Cambridge Crystallographic Data Base. It is of note that crystal structures of [M(OR)x] are often plagued by weak diffraction and/or disorder within the atoms of the ligand chain, which leads to complicated structure solutions with higher final Rvalues than often reported for other materials. [M(OSiR3)x] complexes were expected to suffer from similar issues due to the low rotational barriers about the long Si−Si and Si−C bonds, low bond polarity, and weak intermolecular forces limited to van der Waals interactions (mostly between methyl groups). Not surprising then, it was common for these samples to present poor quality data sets with high thermal parameters and bond rotational disorder. Further complicating the structure solution is the frequent phenomenon of twinned crystals for this family of compounds. While the structure of these molecules is firmly established, the precision of the metrical data would be considered low; however, in each case the results for the best data set are reported. Specific structural issues are discussed below. Complete details for the structural solution experiments performed on each structure are available in the Supporting Information. The following is a brief presentation of the issues associated for the more complex structures. The final structural solutions of 1, 3, 5, and 15 suffer from weak diffraction, resulting in