Reactivity Studies of (^tBu₃SiNH)(^tBu₃SiN═)₂WH Including Anionic Derivatives Featuring the Tris-tri-tert-butylsilylimide Tungsten Core

Abstract

Treatment of (tBu3SiNH)­(tBu3SiN)2WH (1-H) with CX4 (X = Cl, Br, I) afforded (tBu3SiNH)­(tBu3SiN)2WX (1-X, X = Cl, Br, I), but metatheses of 1-X with R– equivalents gave mixed results. With MeLi, (tBu3SiNH)­(tBu3SiN)2WR (1-R, R = CH3) was produced, but ArLi gave 1-Ar along with [(tBu3SiN)3WAr]Li (2-Li-Ar) and [(tBu3SiN)3WH]­M (2-M-H, M = Li). Alkylation attempts with BnK and 1-X cause deprotonation (X = Cl) to provide [(tBu3SiN)3WX]­M (2-M-X, M = K, X = Cl) and apparent electron transfer when X = I to give 1-Bn, 2-K-H, and bibenzyl. Two equivalents of tBuLi and 1-Cl afforded 2-Li-H via deprotonation of 1-H and byproducts likely derived from electron transfer. Exposure of 1-H to C2H4, C3H6, methylenecyclopentane, butadiene, propyne, HCCtBu, p-tolunitrile, and tert-butylisocyanide gave insertion products 1-R (R = Et, nPr, CH2 cPe, E-CH2CHCHMe, CHCHMe, CHCHtBu), 1-NCHtol, and 1-CHNtBu, respectively. Thermolysis of 1-CHNtBu gave the cyanide complex 1-CN. 1-H and 1-Me resisted dihydrogen and methane elimination in nondonor solvents at 200 °C, but in pyridine, 1-H lost H2 in a second-order process to give (tBu3SiN)3Wpy (ΔG°414K = 4.5 kcal/mol). Thermolysis of 2-py under D2 in C6D6 provided α-deuterated py. 2-M-H (M = Li, Na, K) and 2-K-R (R = Me, Et, nPr) were generated by deprotonation of 1-H and 1-R, respectively, and various 1-M-X were synthesized similarly and via exposure of 1-Li-H to alkyl halides. Treatment of 2-Li-H with CH3I provided 2-Li-I, but byproducts 1-CH3 and 1-I suggested the potential intermediacy of a methane complex. X-ray crystal structures of 2-py, 2-H-K­(OEt2)3, 2-H-K­(crypt-2.2.2), the dimer [2-H]2(μ-K)2 (i.e., 2-K-H), and the trimer [2-I]3(μ-K)3 (i.e., 2-K-I) revealed similar tris-imido cores. Discussion of the general reactivity of 1-H, structural features, and plausible mechanisms of 2-py formation are included.

Synthesis and Characterization of 5‐Coordinate Tungsten Hydride Anions: [(tBu3SiNH)(tBu3SiN=)2HWR]M

“…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(CH 3 )Li for 12 h afforded a number of species, including 1 ‐H, ( t Bu 3 SiNH)( t Bu 3 SiN=) 2 WCH 3 ( 1 ‐CH 3 ),, t Bu 3 SiNH 2 , Bu 3 SiNHLi, and unidentified products, but only a trace of [( t Bu 3 SiN=) 3 WH]Li ( 2 ‐HLi) …”

“…The deprotonation of ( t Bu 3 SiNH)( t Bu 3 SiN=) 2 WH ( 1 ‐H), at the silamide position, typically with hindered alkyl anions, is a reasonable route to tungsten hydride anions, [( t Bu 3 SiN=) 3 WH]M ( 2 ‐HM; M=Li, Na, K) ( 2 ‐HM) ,. Under certain conditions, the reactions of various 2 ‐HM with alkyl halides generated products consistent with CH‐bond activation,‐ of intermediate alkane complexes,,, according to labeling and product distribution studies, as Scheme illustrates.…”

Lewis Bases Trigger Intramolecular CH–Bond Activation: (tBu3SiO)2W=NtBu [rlhar2] (tBu3SiO)(κO,κC‐tBu2SiOCMe2CH2)HW=NtBu

“…The base comprises the cyclometalated unit [O1-W1-C6 = 79.14(10)°], the two siloxy units adjacent [O1-W1-O2 = 102.92(9)°] to one another, and the methylene group opposing the siloxy oxygen atom, albeit with a rather small angle [(O2-W1-C2) = 129.98(10)°]; the hydride is likely to be in between, according to both its estimated position and calculations (vide infra). [27,[31][32][33][34][35] The W1-N1 bond length of 1.721(2) Å is typical for a high valent imido group, [36,37] and it is accompanied by a nearly linear W1-N1-C1 angle of Figure 2 illustrates the geometries of 1 and 2 obtained from ONIOM(M06:UFF) calculations. The geometry of pseudotrigonal 1 corresponds well with the structure obtained by X-ray crystallography, [29] and the T-shaped distortion is derived from the strong trans influence of the imido group, as described previously.…”

“…[16] It is likely that the same electronic factors govern the cyclometalation behavior of (silox) 3 M (M = V, Nb, Ta). As Scheme 1 illustrates, (silox) 3 V does not cyclometalate, presumably because it is not thermodynamically favorable, and (silox) 3 Ta cyclometalates to (silox) 2 (κO,κC-OSi t Bu 2 CMe 2 CH 2 )TaH with ΔG ‡ = 24.4 kcal/mol [ΔH ‡ = 19.9 (27) kcal/mol, ΔS ‡ = -15(4) eu]. [22] In contrast, (silox) 3 -Nb cannot be isolated, but has been trapped by 4-picoline (4-pic) and PMe 3 to afford S = 0 (silox) 3 Nb(η 2 -N,C-4-pic) and S = 1 (silox) 3 NbPMe 3 .…”

“…are found in the reactions of [( t Bu 3 SiN=) 3 WH]K [27] with RX, where isotopic labeling experiments have revealed the intermediacy of ( t Bu 3 SiN=) 3 W(RH). [28] For the cyclometalation to occur for (silox) 3 M (M = Nb, Ta), an electrophilic site at the metal center must be generated; hence, a promotional energy must be paid for removal of electrons from d z 2.…”