Synthesis and Characterization of 5‐Coordinate Tungsten Hydride Anions: [( t Bu 3 SiNH)( t Bu 3 SiN=) 2 HWR]M

Treatment of (tBu3SiNH)(tBu3SiN=)2WH (1‐H) with small alkyl anions (RM) afforded tungsten alkyl hydride anions [(tBu3SiNH)(tBu3SiN=)2HWR)]M (3‐(R)M: R=CH3, M=Li; R=nBu, M=Li; R=neoPe, M=Li; R=CH2Ph (Bn), M=K (two isomers); R=CCH, M=Na; R=CH=CH2 (Vy), M=Li). The saturated alkyl anions 3‐(R)M (3‐(R)M: R=CH3, M=Li; R=nBu, M=Li; R=neoPe, M=Li; R=CH2Ph (Bn), M=K) degraded via apparent 1,2‐RH‐elimination to produce the known [(tBu3SiN=)3WH]M (2‐HM), but the acetylide (3‐(C2H)Na) and vinyl (3‐(Vy)Li) anions converted to their hydrogenated isomers, [(tBu3SiN=)3WVy]Na (2‐VyNa) and [(tBu3SiN=)3WEt]Li (2‐EtLi), respectively. The structure of 3‐(nBu)Li is reported, and a discussion of tungsten‐hydride coupling constants in tBu3SiX‐ligated (X=O, NH, N) systems is given.

Tungsten; hydride; anion; amide; imide; complex

The deprotonation of (tBu3SiNH)(tBu3SiN=)2WH (1‐H)[1] ,[2] at the silamide position, typically with hindered alkyl anions, is a reasonable route to tungsten hydride anions, [(tBu3SiN=)3WH]M (2‐HM; M=Li, Na, K) (2‐HM).[3] ,[4] Under certain conditions, the reactions of various 2‐HM with alkyl halides generated products consistent with CH‐bond activation[1] ,[4] ‐[23] of intermediate alkane complexes,[1] ,[4] ,[24] according to labeling and product distribution studies, as Scheme [NaN] illustrates. Byproducts from this process include halide anions [(tBu3SiN=)3WX]M (2‐HM; M=Li, Na, K; X=Cl, Br, I) (2‐XM), solvent adducts such as (tBu3SiN=)3WL (2‐L, L=Et2O, THF), and solvent‐activated (e. g. C6D6) species such as (tBu3SiND)(tBu3SiN=)2WC6D5 (1‐ND‐C6D5). During the course of examining this chemistry, attempted deprotonations of 1‐H with smaller bases often led to complex mixtures, but in certain instances a related class of five‐coordinate tungsten hydride anions, [(tBu3SiN=)3HWR]M (3‐H(R)M) M=Li, Na, K) could be isolated, or at least identified via NMR and IR spectroscopies. Herein these findings are reported, including an assessment of 1JWH coupling constants.[25] ‐[27]

Treatment of (tBu3SiNH)(tBu3SiN=)2WH (1‐H)[1] ,[2] with MeLi in diethyl ether afforded the anion [(tBu3SiNH)(tBu3SiN=)2HW(CH3)]Li (3‐(CH3)Li) as a colorless powder in 38 % isolated yield, as indicated in Scheme [NaN] . The 1H NMR spectrum (Table [NaN] ) of 3‐(CH3)Li exhibits a hydride resonance at δ 15.40 (dq) coupled to the amide hydrogen (δ 2.21, 3J=7 Hz), and to the tungsten‐methyl (δ 1.13, 3J=3.5 Hz), as confirmed by decoupling experiments (Table [NaN] ). Tungsten satellites are observed with the appropriate intensity (14 %), and reveal 1JWH=152 Hz coupling to the hydride and 2JWH=10 Hz coupling to the W‐CH3 group, whose 13C{1H} NMR spectroscopic resonance at δ 34.39 also shows a 1JWH=82 Hz. A broad absorption at 1892 cm−1 in the infrared spectrum is assigned to the ν(WH). The tBu3Si resonances at δ 1.19 and δ 1.28 are in a 27 : 54 ratio corresponding to the amide and imide groups, respectively, and are consistent with of mirror (Cs) symmetry. While the disposition of the lithium is unknown, it is most certainly intimately bound, as only trace amounts of ether are ever observed in NMR spectra of 3‐(CH3)Li. Although it is tempting to place the Li on a mirror plane, the fluxionality common for five‐coordinate species obviates a structural assignment. The compound is drawn as a pseudo‐tbp based on sterics, but as structural evidence on a the related n‐butyl molecule will indicate, some structural ambiguity persists. As a consequence, the alkyl‐hydride anions are generically depicted without placement of the cation, even though it is most certainly chelated by the nitrogens. Thermolysis of 3‐H(CH3)Li for 12 h afforded a number of species, including 1‐H, (tBu3SiNH)(tBu3SiN=)2WCH3 (1‐CH3),[3] ,[4] tBu3SiNH2,[28] Bu3SiNHLi, and unidentified products, but only a trace of [(tBu3SiN=)3WH]Li (2‐HLi).[3]

1 H and 13 C{ 1 H} NMR Spectral Parameters for [( t Bu 3 SiNH)( t Bu 3 SiN=) 2 HWR]M ( 3 ‐(R)M), [( t Bu 3 SiN=) 3 WVy]Na ( 2 ‐VyNa), and [( t Bu 3 SiN=) 3 WEt]Li ( 2 ‐EtLi).

1 a Amide tBu3SiNH‐ listed first, imide tBu3SiN= listed second. b Referenced to C6D6 at δ 7.15 (1H) and δ 128.00 (13C{1H}). c 13C resonances could not be positively identified. d Neopentyl tBu group obscured. e Quaternary amide resonance obscured by solvent. f Referenced to THF‐d8 at δ 3.58 (1H) and δ 67.57 (13C{1H}). g Two aryl resonances not observed.

When (tBu3SiNH)(tBu3SiN=)2WH (1‐H) was exposed to nBuLi in hexanes, [(tBu3SiNH)(tBu3SiN=)2 HW(nBu)]Li (3‐(nBu)Li) was prepared, and it was isolated as a white powder upon precipitation from bis‐trimethylsilylether. The use of this unusual solvent was predicated on the extreme solubility of the five‐coordinate species in which the “counterion” is actually incorporated in the coordination sphere. Like the previous methyl derivative, the hydride is observed at δ 15.20 in the 1H NMR as a doublet of triplets with 3J=8 Hz coupling to the amide hydrogen (δ 2.3), and 3J=4 Hz coupling to the tungsten methylene. The hydride coupling to 183W was 1JWH=156 Hz, suggestive of a structure related to 1‐H(CH3)Li, but the tungsten couplings to the CH2 group could not be unambiguously determined. A broad feature in the infrared spectrum at 1910 cm−1 was attributed to ν(WH).

As previously reported,[3] thermolysis of neoPeLi[29] and (tBu3SiNH)(tBu3SiN=)2WH (1‐H) for 6 h in benzene led to the formation of [(tBu3SiN=)3WH]Li (2‐HLi) in modest yield, but the isolation of 3‐(R)Li (R=Me, nBu) prompted a spectroscopic investigation of the process (Scheme [NaN] ). In C6D6, a 1H NMR spectrum taken after 10 min of mixing revealed the presence of [(tBu3SiNH)(tBu3SiN=)2HWneoPe]Li (3‐(neoPe)Li, ∼60 %), tentatively identified via a hydride resonance at δ 15.64 (dt, 3J=6.7 Hz, 3J=3.4 Hz, 1JWH=171 Hz). While the tert‐butyl resonance of the neoPe group could not assigned, a methylene at δ 1.85 (d, 3J=3.4 Hz) and appropriate tBu3Si resonances integrated relative to the hydride. An unidentified hydride‐containing material (δ 19.25, d, 4 Hz, 1JWH=84 Hz) was also present, in addition to 2‐HLi, and since conversion of 3‐(neoPe)Li to 2‐HLi occurred during acquisition of the 13C{1H} NMR spectrum, additional spectral information could not be determined with confidence. The mixture was cleanly converted to 2‐HLi upon heating for 2 h at 60 °C.

Treatment of (tBu3SiNH)(tBu3SiN=)2WH (1‐H) with one equiv. of potassium benzyl in THF‐d8 (Scheme [NaN] ) led to the formation of a 6 : 1 ratio of two isomers of benzyl hydride anion [(tBu3SiNH)(tBu3SiN=)2HWBn]K (3‐(Bn)K). 1H NMR spectroscopy revealed a dt at δ 16.00 (A, 3J=6 Hz, 3J=3 Hz, 1JWH=159 Hz) attributed to the major hydride and a related dt at δ 14.39 (B, 3J=11 Hz, 3J=2.7 Hz, 1JWH=159 Hz) assigned to the minor species. Corresponding methylene resonances at δ 2.52 (d, 3J=3 Hz) and δ 2.74 (d, 3J=2.7 Hz) were not diastereotopic, suggesting static structures containing a mirror plane, or fluxional species. NMR spectroscopic monitoring of the reaction mixture showed a slow conversion to the second isomer (B) over 8 h at room temperature, while prolonged thermolysis (24 h, 100 °C) produced [(tBu3SiN=)3WH]K (2‐HK).[3] Scale‐up of the reaction in THF (23 °C, 18 h) led to the isolation of isomer B of 3‐(Bn)K as a white powder in ∼31 % yield, but it was contaminated with [(tBu3SiN=)3WH]K (2‐HK, ∼20 %). Note that isomers are found for this potassium‐based alkyl‐hydride species, but single species are generated for the remaining lithium and sodium complexes in this study.

Additional five‐coordinate hydride anions containing unsaturated alkyls were sought for comparison, but related syntheses incurred a number of byproducts. As Scheme [NaN] illustrates, thermolysis of (tBu3SiNH)(tBu3SiN=)2WH (1‐H) with excess NaCCH in THF for 2 d at 60 °C afforded [(tBu3SiN=)3WCH=CH2]Na (2‐VyNa), which was isolated as a white powder in ∼32 % yield accompanied by a small amount of [(tBu3SiN=)3WH]Na (2‐HNa, ∼5 %).[3] Vinyl complex 2‐VyNa manifested a characteristic ABX pattern in its 1H NMR spectrum, consisting of resonances at δ 6.41 and δ 6.54 corresponding to the cis (dd, J=20, 5 Hz, 3JWH=11 Hz) and trans (dd, J=14, 5 Hz, 3JWH=23 Hz) hydrogens, respectively, relative to the tungsten, and the gem hydrogen at δ 8.25 (dd, J=20, 14 Hz, 2JWH=4 Hz).

When the addition of NaCCH was monitored by 1H NMR spectroscopy in THF‐d8, the formation of three species was noted over the course of an hour; [(tBu3SiN=)3WH]Na (2‐HNa),[3] [(tBu3SiNH)(tBu3SiN=)2HW(CCH)]Na (3‐(CCH)Na), and an unknown (1‐H(NaC2H)) were generated in a 24 : 17 : 59 ratio. Over two days at 23 °C, 3‐(CCH)Na was converted to the unknown material while the 2‐HNa remained constant, and extended thermolysis (60 °C, 3 d) generated [(tBu3SiN=)3WCH=CH2]Na (2‐VyNa). Complex 3‐(CCH)Na is tentatively formulated as the acetylide hydride based on a hydride resonance in its 1H NMR spectrum at δ 15.90 (d, J=11 Hz, 1JWH=141 Hz), with coupling to the amide hydrogen at δ 3.53 (J=11 Hz), but not to the acetylide hydrogen at δ 2.15 (3J=4 Hz). The mixture prevented further analysis by 13C{1H} NMR spectroscopy as several of the features could not be positively identified.

The unknown material (1‐H(NaC2H)) could be generated in ∼30 % yield (based on a 1 : 1 stoichiometry) with 5–10 % 2‐HNa as an impurity, and no obvious hydride resonance or tungsten‐hydride stretching frequency could be observed in 1H NMR and IR spectra, respectively. Three 1H resonances were observed at δ 3.04 (J=3 Hz), δ 10.55 (J=4 Hz, JWH=8 Hz), and δ 10.98 (J=3, 4 Hz). While the former signal is likely an SiNH, given its broadness in THF‐d8 δ 2.06 (br d, J=2.5 Hz), it may be part of an NH‐CH‐CH unit given the coupling pattern. Unfortunately, 13C{1H} NMR spectra could not be obtained and assigned without significant conversion to 2‐VyNa, and repeated attempts to produce X‐ray quality crystals failed.

Stirring [(tBu3SiN=)3WH]Li (2‐HLi)[3] and freshly prepared Li(CH=CH2)[32] in Et2O for 1 h produced the ethyl anion, [(tBu3SiN=)3WCH2CH3]Li (2‐EtLi), which was isolated in 33 % yield as a colorless powder (Scheme [NaN] ). Monitoring the reaction by 1H NMR spectroscopy in C6D6 permitted observation of the vinyl hydride anion, [(tBu3SiNH)(tBu3SiN=)2HW(CHCH2)]Li (3‐(Vy)Li), which exhibited a hydride at δ 14.55 (d, J=11 Hz, 1JWH=137 Hz) coupled to an amide proton at δ 2.53 (d, J=11 Hz), but not to the CH of the vinyl group. Upon heating, 3‐(Vy)Li converted to 2‐EtLi.

The molecular structure of [(tBu3SiNH)(tBu3SiN=)2HWnBu]Li (3‐H(nBuLi) is illustrated in Figure [NaN] , and selected metric parameters are given in the caption. The complex is best described as a distorted square pyramid with an apical imide (N1) linked to a basal amide (N2) at a 97.6(2)° angle via bonding to lithium. At late stages of refinement, a peak in the difference fourier map was in a reasonable position for the hydride at a d(WH) of 1.60(9) Å, a value consistent with related tungsten hydrides and the sum of covalent radii (1.62 Å). While the lithium is similarly bound to the amide (2.05(2) Å) and imide (2.01(2) Å) nitrogens, ligand anionic character appears to be transposed from the alkyl to the amide. Tungsten‐nitrogen distances for the imides (1.791(6), 1.810(6) Å) are considerably shorter than the corresponding amide distance of 2.106(6) Å. The former are somewhat long compared to neutral species containing like ligands (∼1.75 Å), but comparable to other anions.[3] The amide is considerably longer than typical 1.90–1.95 Å distances found in tBu3SiNH‐containing neutral species,[2] ,[4] but the d(W−C) of 2.185(8) Å is normal.

The basal ligands are bent back from the apical imide (/N1‐W−N2,C1,N3,H=97.6(2)°, 109.3(3)°, 115.6(3)°, 98(3)°), but comprise a relatively ordered base, as /N2‐W−N3=144.0(2)° and /C1‐W‐H=142(3)°. The variation from a square pyramid stems mainly from the hydride, which leans toward the amide nitrogen (/N2‐W‐H=65(3)°), perhaps a further indication that N2 possesses considerable anionic character. The remaining basal angles (/N2‐W−C1=83.9(3), /N3‐W−C1=97.0(3), /N3‐W‐H=95(3)) are in concert with this observation.

As Scheme [NaN] reveals, the reactivity of (tBu3SiNH)(tBu3SiN=)2WH (1‐H) with alkyl anion reagents shows two basic paths: deprotonation to afford of [(tBu3SiN=)3WH]M (2‐HM), and formation of the alkyl hydride anion, [(tBu3SiNH)(tBu3SiN=)2HWR]M (3‐(R)M). Anions 3‐(R)M were stable enough to be characterized, but eventually degraded upon thermolysis, with half‐lives and rates consistent with previous studies of 1,2‐RH‐elimination: R=neoPe (t1/2∼0.5 h, 60 °C)<nBu (t1/2∼1 h, 60 °C)1/2∼2 h, 60 °C). The counterion appears to factor into the stablity of 3‐(R)M, as 3‐(Bn)K degraded slower (t1/2∼4 h) than expected at a higher temperature (100 °C). While a reductive elimination of the RH from 3‐(R)M to give [(tBu3SiNH)(tBu3SiN=)2W]M, followed by α‐H‐migration to tungsten, is a plausible alternative process, the similar rates suggest 1,2‐RH‐elimination as the pathway. One can also invoke reversible formation of RM, and deprotonation as a means of RH and tris‐imido‐hydride (1‐HM) formation. Unfortunately, appropriately labeled 1‐H could not be synthesized for some mechanistic differentiation.

The activation energy for 1,2‐RH‐elimination from (tBu3SiNH)(tBu3SiN=)2WR (1‐R) is calculated to be prohibitively high (ΔH≠elim(MeH) from (H2N)(HN=)2WMe is 61.6 kcal/mol).[3] , If 1,2‐RH‐elimination from [(tBu3SiNH)(tBu3SiN=)2HWR]M (3‐(R)M) is the degradation path to 1‐HM, compression of the reaction coordinate would be a reasonable rationalization, as RH extrusion from a five‐coordinate species would necessarily render the alkyl and NH positions closer.

Competitive hydrogenation of unsaturated [(tBu3SiNH)(tBu3SiN=)2HWR]M (3‐(R)M; M=Li, R=Vy, CCH) to the tris‐imido ethyl and vinyl species, [(tBu3SiN=)3WR′]M (2‐R′M: M=Li, R′=Et; M=Na, R′=Vy), respectively, is observed relative to 1,2‐RH‐elimination. Scheme [NaN] illustrates possible paths for the formation of 2‐EtLi. Reversibility of adduct formation, rendered as RM dissociation, could lead to the insertion of LiVy to form a β‐lithioethyl species that can simply internally deprotonate the amide to produce the tris‐imido ethyl complex. Insertions of small olefins like ethylene have been observed in the chemistry of (tBu3SiNH)(tBu3SiN=)2WH (1‐H), hence this step has precedent. Depending on where the lithium is situated, or if it readily migrates as expected, an alternative α‐H‐migration to the vinyl group of 3‐(Vy)H can lead to the same β‐lithioethyl species. While this step has no precedent in the system, the reaction coordinate is similar to a reductive elimination, and has merit as a fundamental process. Related pathways can be envisaged for 3‐(CCH)Na, and the structurally unidentified 1‐H(NaC2H) is a likely intermediate; unfortunately, aside from recognizing a ‐HCCH‐ or HCCH‐NH component through examination of the coupling constants, the unusual chemical shifts obviate confidence in structural assignments.

For two coupled nuclei, the dominant interaction mediating the transmission of magnetic information between the nucleus and bonding electrons is the Fermi Contact term,[25] , [26] , [27] the strength of which correlates with amount of s‐character in the interaction. In tungsten‐hydrides, the magnitude of 1JWH will be predicated on the s‐character at tungsten, i. e. its hybridization.[25] Differences in ligand environment can also have a profound influence on hybridization and 1JWH, but there are enough tungsten hydrides that possess tBu3SiX (X=O, NH, N) ligands to provide a reasonable series for comparison, and they are listed in Table [NaN] .[2] ,[3] ,[38] ,[39]

Chemical Shift (δ), 1 J WH (Hz), and ν(WH) (cm −1 ) of Terminal Tunsten Hydrides Ligated by t Bu 3 SiX n (n=‐1, X=O, NH; n=‐2; X=N). a,b

2 a NMR spectroscopic data from C6D6 unless noted. b IR spectroscopic data from nujol mulls. c This work. d THF‐d8. e For a discussion of solvent dependent hydride shifts, see ref. 3.

Pseudo‐tetrahedral species exhibited the greatest 1JWH (313–391 Hz) and the values were substantially greater than the five coordinate complexes (131–171 Hz), with two outliers among the “six‐coordinate” species. Dimers (tBu3SiN=)2HW(μ‐Cl)(μ‐H)2W(=NSitBu3)L2 (L2=py2, DME) have 1JWH of 237 and 245 Hz, respectively, that reflect the loose association of the two bridging hydrides (L2=py2, δ(μ‐H) 7.79, 1JWH=139, 20 Hz; L2=DME, δ(μ‐H) 5.17, 1JWH=173, 17 Hz), whose coupling to the tungsten center containing the terminal hydride is minimal. The μ‐H‐associations appear weaker than that of py in (tBu3SiN=)2Cl(py)WH, since its 1JWH is smaller at 217 Hz. Note that there is essentially no correlation between ν(WH) and hybridization.

Within the five‐coordinate species, the magnitude of 1JWH can be construed as inversely proportional to the strength of the hydride/alkyl interaction (H>Vy>CCH>Me>nBu>CH2CMe2SitBu2O>Bn>neoPe) in the complex, a relationship that is roughly a trans‐influence, provided the hydride and R/H are anti in basal sites of a square pyramid, or axial in a tbp arrangement. Within the four‐coordinate species, the 1JWH for neutral complexes is much greater than that of the anions, which is probably an indication of the strength of the interaction, as indicated by d(WH), or a reflection of greater hydride character.[25]

The reaction of alkali metal alkyls, RM, with (tBu3SiNH)(tBu3SiN=)2WH (1‐H), formed five‐coordinate anions [(tBu3SiNH)(tBu3SiN=)2HWR]M (3‐(R)M). Thermal degradation of the anions afforded [(tBu3SiN=)3WH]M (2‐HM) as the predominant product. NMR spectroscopy of 3‐(R)M revealed mirror plane symmetry, consistent with either tbp or square pyramidal structures, and likely fluxional behavior.

All manipulations were performed using glovebox or high vacuum techniques. Hydrocarbon and ethereal solvents were dried over and vacuum transferred from purple sodium benzophenone ketyl (3–4 mL tetraglyme/L were added to hydrocarbons). Benzene‐d6 was sequentially dried over sodium and 4 Å molecular sieves, then stored over and vacuum transferred from sodium benzophenone ketyl. All glassware was base‐washed and oven dried. NMR tubes for sealed tube experiments were flame dried under dynamic vacuum prior to use. Solutions of alkyllithium reagents were purchased from Aldrich. Sodium acetylide was purchased from Aldrich as a suspension in xylenes/mineral oil and subsequently filtered, washed with hexanes, THF, hexanes again, and dried under vacuum. Vinyl lithium,[32] neopentyl lithium,[29] potassium benzyl, (tBu3SiNH)(tBu3SiN=)2WH (1‐H),[2] [(tBu3SiN=)3WH]M (M=Li, 2‐HLi; Na, 2‐HNa; K, 2‐HK)[3] were prepared according to published procedures.

1H and 13C{1H} NMR spectra were obtained using Varian XL‐200, XL‐400, and Unity‐500 spectrometers, with chemical shifts reported relative to benzene‐d6 (1H, d 7.15; 13C, d 128.00) or THF‐d8 (1H, d 3.58; 13C, d 67.57). Infrared spectra were recorded on a a Nicolet Impact 410 spectrophotometer interfaced to a Gateway PC. Combustion analyses were performed by Oneida Research Services, Whitesboro, NY, or Robertson Microlit Laboratories, Madison, NJ.

To a stirred solution of 1‐H (410 mg, 0.496 mmol) in Et2O at 0 °C was transferred 0.39 mL CH3Li (1.5 M in Et2O, 1.10 equiv) via syringe under Ar counterflow. The colorless solution was allowed to stir 2 h at 0 °C and an additional 2 h at 23 °C. After removal of the volatiles and filtration in pentane, the volume was reduced to 3 mL, precipitating a white powder (3‐(Me)Li) that was collected by filtration (160 mg, 38 %). IR (nujol, cm−1): 1892 (w, br, ν(WH)), 1467 (s), 1386 (s), 1365 (m), 1183 (w), 1122 (m), 1041 (s), 1007 (s), 935 (m), 818 (s), 665 (m), 619 (s), 581 (s). Anal. Calcd for C37H86N3LiSi3W: C, 52.40; H, 10.22; N, 4.95. Found: C, 52.04; H, 10.25; N, 4.97.

To a stirred solution of 1‐H (502 mg, 0.610 mmol) in hexanes was transferred 0.50 mL nBuLi (1.6 M in hexanes, 1.3 equiv) via syringe under Ar counterflow. The colorless solution was allowed to stir for 1 h at 23 °C, and the volatiles were removed. Bis‐trimethylsilylether (∼5 mL) was added, the solution was filtered, and the volume was reduced to 3 mL and cooled to −78 °C, producing colorless, microcrystalline 3‐(nBu)Li, which was collected by filtration (167 mg, 31 %). IR (nujol, cm−1): 1910 (w, br, ν(WH)), 1467 (s), 1386 (s), 1366 (m), 1148 (m), 1117 (m), 1032 (s), 1008 (s), 934 (m), 819 (s), 616 (s), 577 (s). Anal. Calcd for C40H92N3LiSi3W: C, 53.97; H, 10.42; N, 4.72. Found: C, 52.42; H, 10.09; N, 4.58.

To a flask loaded with 1‐H (350 mg, 0.420 mmol) and KBn (75 mg, 0.58 mmol, 1.3 equiv) was transferred 12 mL THF at −78 °C. The resulting orange solution was allowed to stir at 23 °C for 18 h, followed by removal of the volatiles. The solid was triturated with Et2O (3 x 5 mL) and filtered in 10 mL Et2O. The volume was reduced to 3 mL and cooled to −78 °C, producing 127 mg of a colorless precipitate. 1H NMR analysis indicated two isomers of 3‐(Bn)K contaminated by ∼20 % [(tBu3SiN=)3WH]K (2‐HK).[3] IR (nujol, cm−1): 1857 (m, br, ν(WH)), 1590 (m), 1467 (s), 1384 (s), 1215 (w), 1138 (m), 1040 (s), 1009 (s), 934 (m), 835 (s), 818 (s), 761 (m), 617 (s), 582 (m).

To a glass vessel loaded with 1‐H (300 mg, 0.360 mmol) and NaCCH (35 mg, 0.72 mmol, 2 equiv) was transferred 15 mL THF at −78 °C. The resulting solution was heated to 60 °C for 2 d, followed by removal of the volatiles. The resulting material was dissolved in 15 mL Et2O and filtered. The solution was reduced to 3 mL, and cooled to −78 °C, precipitating 2‐VyNa as a light yellow powder (105 mg, ∼33 %). The 1H NMR spectrum of the isolated material revealed contaminants 2‐HNa (∼5 %) and 4 (∼5 %). IR (nujol, cm−1): 1518 (w), 1467 (s), 1384 (s), 1107 (w), 1043 (s), 997 (s), 934 (m), 873 (m), 847 (s), 818 (s), 650 (s), 617 (s).

To a glass vessel loaded with 1‐H (379 mg, 0.459 mmol) and NaCCH (110 mg, 0.23 mmol, 5 equiv) was transferred 25 mL THF at −78 °C, and the resulting solution was stirred for 48 h at 23 °C, during which time the solution developed a red tinge. After removal of the volatiles, the solids were dissolved in Et2O and the solution was filtered. Removal of Et2O and the addition of hexanes precipitated 1‐H(NaC2H) (unknown structure), which was collected by filtration (140 mg, 32 %). The 1H NMR spectrum of 4 indicated the presence of 1 equiv. THF. 1H NMR (THF‐d8): δ 1.42 (s, 27H, tBu3SiNH), 1.27 (s, 54H, tBu3SiNH), 3.04 (d, 3, 1H, CH or NH), 10.55 (d, 4, JWH=8, CH), 10.98 (dd, 4, 3, CH). 13C{1H} NMR (THF‐d8): δ 24.60 (HNSiC), 25.32 (=NSiC), 31.58 (3 C(CH3)3) 31.89 (6 C(CH3)3); resonances arising from C2H could not be discerned. IR (nujol, cm−1): 3232 (m), 1538 (m), 1468 (s), 1385 (s), 1364 (m), 1137 (m), 1063 (m), 1044 (m), 1033 (m), 980 (m), 936 (m), 912 (m), 852 (s), 819 (s), 682 (m), 650 (s), 623 (s), 610 (s), 586 (m). Anal. Calcd for C38H84N3NaSi3W: C, 52.21; H, 9.69; N, 4.81. Found: C, 52.70; H, 8.84; N, 5.64.

To a 50 mL flask loaded with 1‐H (700 mg, 0.847 mmol) and LiCH=CH2 (35 mg, 1.03 mmol, 1.2 equiv) was transferred 30 mL Et2O at −78 °C. The solution was stirred for 1 h at 23 °C and the volatiles were removed. The remaining material was filtered in Et2O and the volume was reduced to 4 mL. The solution was cooled to −78 °C to afford 240 mg (33 %) of colorless 2‐EtLi upon filtration. IR (nujol, cm−1): 1466 (s), 1385 (s), 1366 (m), 1143 (m), 1037 (s), 1024 (s), 1005 (s), 934 (m), 820 (s), 621 (s), 583 (s). Anal. Calcd for C38H86N3LiSi3W: C, 53.06; H, 10.08; N, 4.89. Found: C, 52.85; H, 9.82; N, 4.66.

Flame‐dried NMR tubes, sealed to 14/20 ground glass joints, were charged with metal reagent (typically ∼10 mg, 10−2 mmol) and other solid substrates in the dry box, attached to needle valves, and moved to the vacuum line. The tubes were degassed, and after vacuum transfer of deuterated solvent, were flame sealed with a torch. Consult the text for particular reactions.

Crystal data for3‐(nBu)Li : C40H92N3LiSi3W.(0.5 C5H12) grown from pentane, M=926.30, monoclinic, P21/n, a=9.4710(10), b=25.655(3), c=21.827(2) Å, β=101.170(10)°, V=5203.0(9) Å3, D=1.183 g/cm3, T=293(2) K, λ = 0.71073 Å, Z=4, Rint=0.0344, 7190 reflections, 6716 independent, R1(all data)=0.0828, wR2=0.0903, GOF=1.011, P4 Siemens four‐circle diffractometer, SHELXS, macromolecular crystallographic routines (PHASES, CHAIN) were used to ultimately trace the C5H12, CCDC‐1535742.

Support from the National Science Foundation (CHE‐1402149 (PTW) and Cornell University is gratefully acknowledged.

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Graph: Molecular view of [(tBu3SiNH)(tBu3SiN=)2HWnBu]Li (3‐H(nBuLi). Selected interatomic distances (Å) and angles (°): W−H, 1.60(9); W−N1, 1.810(6); W−N2, 2.106(6); W−N3, 1.791(6); W−C1, 2.185(8); W−Li, 2.62(2); Li−N1, 2.05(2); Li−N2, 2.01(2); N1‐W−N2, 97.6(2); N1‐W−N3, 115.6(3); N2‐W−N3, 144.0(2); N1‐W−C1, 109.3(3); N2‐W−C1, 83.9(3); N3‐W−C1, 97.0(3); N1‐W−H, 98(3); N2‐W−H, 65(3); N3‐W−H, 95(3); C1‐W−H, 142(3); W−N1‐Si1, 164.7(4); W−N2‐Si2, 148.1(4); W−N3‐Si3, 167.2(4); W−N1‐Li, 85.3(5); W−N2‐Li, 79.2(5); N1‐Li−N2, 93.3(7).

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