Reactivity studies of (tBu3SiNH)(tBu 3SiN=)2WH including anionic derivatives featuring the tris-tri- tert -butylsilylimide tungsten core

Article abstract of DOI:10.1021/om200597z

Treatment of (^tBu₃SiNH)(^tBu ₃SiN=)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, C ₃H₆, methylenecyclopentane, butadiene, propyne, HCC ^tBu, p-tolunitrile, and tert-butylisocyanide gave insertion products 1-R (R = Et, ⁿPr, CH₂^cPe, E-CH ₂CH=CHMe, CH=CHMe, CH=CH^tBu), 1-N=CHtol, and 1-CH=N ^tBu, respectively. Thermolysis of 1-CH=N^tBu 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 D ₂ 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.

Full text of DOI:10.1021/om200597z

Article
pubs.acs.org/Organometallics
Reactivity Studies of (tBu3SiNH)(tBu3SiN)2WH Including Anionic
Derivatives Featuring the Tris-tri-tert-butylsilylimide Tungsten Core
Daniel F. Schafer, II, Peter T. Wolczanski,* and Emil B. Lobkovsky
Department of Chemistry & Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, United States
S
* Supporting Information
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.
t
Two equivalents of BuLi 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-
n
c
butylisocyanide gave insertion products 1-R (R = Et, Pr, CH2 Pe, 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.
employed limited the accuracy of the calculations, reasonable
agreement was found. The ease of 1,2-MeH elimination
diminishes from first- to second- to third-row transition
INTRODUCTION
■
A multiyear investigation of the activation of carbon−hydrogen
bonds by d0 imido complexes1−12 culminated in the study of
1,2-RH elimination reactions of (silox)2(tBu3SiNH)TiR and
corresponding 1,2-RH addition reactions to the purported d0
transient (silox)2TiNSitBu3.8 Kinetics and thermodynamics
studies established a linear free energy relationship (LFER)
between the ease of CH bond activation and the strength of the
titanium−carbon bond formed. A geometric factor involving
compression of the reaction coordinate explained the greater
propensity for sp2 versus sp3 C−H bond activation in
conjunction with the LFER.
While the foundation for understanding concerted bond
activations by d0 imido functionalities was provided by the
titanium cases and related 1,2-RH eliminations from
(tBu3SiNH)3ZrR,2−4 the role of alkaneor, more generally,
hydrocarboncomplexes in the context of CH activation
remained opaque to experimental observations, and pertinent
periodic trends were not well established. As Scheme 1 shows,
calculations by Cundari et al.13−18 were used to augment the
experimental findings,1−12,19,20 and while the simple models
element as the corresponding enthalpy of reaction (ΔH°add
)
corresponding to the addition of methane to the putative three-
coordinate imide becomes more favorable.
The transition states for the second-row transition metal
transient imido species are somewhat higher than either their
first- or third-row congeners for groups 5 and 6, but otherwise
the trends are as expected. A more favorable ΔH°add is
calculated when descending a column, as the exchange of a
MN π-bond for NH and MR σ-bonds becomes more
favorable due to an increase in bond strengths, and the energy
of the transient three-coordinate imido species rises. While the
ΔΔH°add are about the same from the first to third rows for
groups 4−6 (∼20 kcal/mol), the enthalpies of addition become
progressively larger until ΔH°add is calculated to be enormous
(−60.3 kcal/mol) for the tris-imido (HN)3W.15,16 It may
Received: July 6, 2011
Published: November 30, 2011
© 2011 American Chemical Society
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Article
Scheme 1
seem that (HN)3W is an 18 e− complex, assuming each
imide contributes 4 e− (3 × 4 e− + d6 = 18), and is therefore
less prone to react with RH, but the calculations suggest the
opposite. First, one pair of electrons pertaining to the tris-imido
group is intrinsically nonbonding due to symmetry consid-
erations,21 and second, competition for the d-orbitals among
several π-donor ligands weakens the π-bonds from groups 4 to
5 to 6, and the three-coordinate transient species become
progressively higher in energy.21−25 Experimentally, 1,2-MeH
elimination data obtained directly or indirectly as MeH loss
from (tBu3NH)3HfMe,8 (tBu3SiNH)2(tBu3SiN)VMe,19 and
(tBu3SiNH)2(tBu3SiN)TaMe5,26 complexes in addition to
the Ti6−10,27 and Zr systems2−4,28 are in line with the
calculations, leaving verification of group 6.29
(tBu3SiNH)(tBu3SiN)2WR. Herein is described the gener-
ation of tungsten complexes pertinent to Scheme 1 and anionic
derivatives that permitted the indirect evaluation of alkane
complexes as intermediates toward CH-bond activation. The
preparation of (tBu3SiNH)(tBu3SiN)2WH (1-H) was pre-
viously reported42 as occurring via the addition of 6 equiv of
LiNHSitBu3 to Na(THF)3[W2Cl7(THF)],43 as illustrated in
Scheme 2. An intermediate [(tBu3SiNH)2ClW]2 complex42,44
containing a tungsten−tungsten triple bond45,46 was isolated
and shown to be a precursor to 1-H via the addition of 2 equiv
t
of Bu3SiNHLi. Precedent for anionic derivatives of tris-imido
tungsten22 and molybdenum23 was established by Wigley et al.,
via the utilization of 2,6-diisopropyl arylimido ligands.
RESULTS
■
Although the calculations suggested that 1,2-RH elimination
Metathetical Routes to (tBu3SiNH)(tBu3SiN)2
WX/R. 1. (tBu3SiNH)(tBu3SiN)2WX (1-X, X = Cl, Br, I). The
most straightforward route to neutral tungsten alkyl derivatives
required starting materials that could be subjected to metathesis
by RM. With (tBu3SiNH)(tBu3SiN)2WH (1-H)42 in hand
as the primary starting material, its conversion to halides
(tBu3SiNH)(tBu3SiN)2WX (1-X, X = Cl, Br, I) was
accomplished via treatment with CX4 in hexanes (X = Cl) or
benzene (X = Br, I) at 23 °C, as shown in eq 1. The chloride,
bromide, and iodide complexes were isolated in 74%, 67%,
and 75% yields, respectively, as yellow microcrystals upon
precipitation from hexane or hexanes. Pertinent spectral
parameters for the halides and all other complexes are listed
in Table 1.
from (tBu3SiNH)(tBu3SiN)2WR could not be achieved
(ΔH‡
for (H2H)(HN)2WMe = 61.6 kcal/mol), the
elim
system was still intriguing because the enthalpy of binding for
MeH to (HN)3W was substantial (−15.6 kcal/mol);15,16
hence even the free energy for binding was favorable (ΔG°bind
=
−8.4 kcal/mol). Three-coordinate imido species were also
pyramidalized in the second and third rows in groups 5 and 6
due to ndz2/(n+1)p/(n+1)s mixing, a geometric distortion
favorable toward binding.
The detection of a methane complex of rhodium, [{2,6-
(tBu2PO)C5H3N}Rh(CH4)]BArF ],30 cyclopentane,31 and cy-
4
clohexane32 adducts of rhenium, CpRe(CO)2(cAlkH), the time-
resolved implication of {η2-HB(3,5-dimethylpyrazolyl)3}Rh-
(CO)(CyH)33 and related species by IR spectroscopy,34,35
and X-ray crystal structures of n-heptane bound within the
pocket of an iron porphyrin36 and various cyclic alkanes bound
to [κ-O3,N3-(2,4-(tBu)C6H2O(6-CH2)tacn]U(RH)37 provide
direct evidence of alkane binding to d8, d6, and f3 metal centers.
Previously, dynamic evidence, such as the interconversion of
hydride and methyl resonances in tungsten,38 rhenium,39 and
2. (tBu3SiNH)(tBu3SiN)2WR (1-R, CH3 (CD3), Ph, 3-tolyl,
4-tolyl, CH2Ph). Treatment of a cold diethyl ether solution of
(tBu3SiNH)(tBu3SiN)2WCl (1-Cl) with a slight excess (∼1.1
equiv) of MeLi (or CD3Li) afforded the colorless methyl
derivative (tBu3SiNH)(tBu3SiN)2WCH3 (1-CH3 (or 1-NH-
CD3)) in modest yield (eq 2, 51%). The methyl group
1
osmium40 methyl-hydride species by H NMR spectroscopy
1
resonated at δ 1.43 in the H NMR spectrum and displayed a
2JWH of 11 Hz, and its δ 21.62 signal in the 13C{1H} NMR
and chain walking in Cp*Rh(PMe3)R(H) species41 high-
lighted alkane intermediates in oxidative addition/reductive
elimination sequences. In a preliminary study, alkane
complexes of the type (tBu3SiN)3W(RH) were indirectly
implicated as a component of the free energy surface for alkane
activation in group 6 through the addition of RX to
[(tBu3SiN)3WH]K.11,12
1
spectrum exhibited a JWH of 138 Hz.
Competing pathways limited the scope and purity of other
tungsten alkyls generated by metathetical procedures. For
example, treatment of (tBu3SiNH)(tBu3SiN)2WCl (1-Cl)
with a slight excess of PhLi (∼1.3 equiv) in diethyl ether
resulted in the formation of (tBu3SiNH)(tBu3SiN)2WPh
(1-Ph) contaminated with [(tBu3SiN)3WPh]Li (2-Li-Ph) in
a 7:3 ratio (eq 3). A slight excess of alkyllithium reagent was
typically needed for conversion of the halide precursor, but if
Prior to investigating the chemistry of transient alkane
complexes of the (tBu3SiN)3W core, a viable synthetic path
to these complexes was developed, including the preparation of
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Article
Scheme 2
(tBu3SiN)3W(toluene) (2-tolH) is unlikely to be an
intermediate in the alkylation.11,12
Exposure of (tBu3SiNH)(tBu3SiN)2WCl (1-Cl) to potas-
sium benzyl47 in THF-d8 in an NMR tube experiment
produced the tris-imido tungsten chloride adduct
K(tBu3SiN)3WCl (2-K-Cl), in near quantitative yield (eq 5).
Since the objective was to generate some (tBu3SiNH)-
(tBu3SiN)2WCH2Ph (1-Bn) for spectral comparison, con-
ditions were varied. A THF solution of excess PhCH2K was
slowly added to a diethyl ether solution of (tBu3SiNH)-
(tBu3SiN)2WI (1-I) over the course of 5 min, producing
1-Bn as 40% of an inseparable mixture with K(tBu3SiN)3WH
(2-K-H, 28%) and other unidentified products (eq 6). The
distinguishing 1H NMR spectral feature of 1-Bn was the
CH2 group at δ 3.57, which possessed tungsten satellites
(2JWH = 15 Hz). When the addition of 2.5 equiv of PhCH2K
to 1-I occurred in THF, the reaction was optimized for the
formation of 2-K-H, which was isolated as a white powder in
64% yield (eq 7). An NMR tube scale experiment in C6D6
of 1-I and PhCH2K confirmed the presence of 2-K-H as
the sole organometallic product and bibenzyl as the organic
byproduct.
the halide was completely consumed, 2-Li-Ph invariably
appeared. The metathesis was not optimized to sufficient
purity for elemental analysis of 1-Ph.
The attempted arylations, and the benzylations with
PhCH2K gave products, i.e., K(tBu3SiN)3WH (2-K-H) and
bibenzyl, that were consistent with electron transfer and
possible hydrogen atom transfer processes. To further examine
this possibility, reactions of (tBu3SiNH)(tBu3SiN)2WCl
Related results were obtained from tolyllithiums designed to
highlight any potential rearrangements. Treatment of (tBu3-
SiNH)(tBu3SiN)2WCl (1-Cl) with 4-Me-C6H4Li in Et2O
afforded a mixture of (tBu3SiNH)(tBu3SiN)2W(C6H4-4-Me)
(1-C6H4-4-Me), Li(tBu3SiN)3W(C6H4-4-Me) (2-Li-C6H4-4-
Me), and Li(tBu3SiN)3WH (2-Li-H) in a ∼5:2:3 ratio
(eq 4). A similar reaction of (tBu3SiNH)(tBu3SiN)2WI
(1-I) with 3-Me-C6H4Li in Et2O provided a mixture of
(tBu3SiNH)(tBu3SiN)2W(C6H4-3-Me) (1-C6H4-3-Me),
Li(tBu3SiN)3W(C6H4-3-Me) (2-Li-C6H4-3-Me), and
Li(tBu3SiN)3WH (2-Li-H) in essentially the same ratio.
During the course of the reaction, no isomerization of the
tolyl fragment occurred. As subsequent studies showed,
the results suggested that an alkane complex of the type
t
(1-Cl) and BuLi were employed. In C6D6, thermolysis of 1-Cl
t
and 1 equiv of BuLi at 100 °C for ∼6 h produced half
an equivalent of Li(tBu3SiN)3WH (2-Li-H), isobutane, and
isobutylene; half an equivalent of 1-Cl remained. As
t
eq 8 illustrates, the use of 2 equiv of BuLi caused a near
quantitative conversion to 2-Li-H, which was accompanied by
isobutene and isobutylene in a 1:1 ratio. (tBu3SiNH)-
(tBu3SiN)2WH (1-H, ∼5%) is present at the end of the
reaction, suggesting that the tBuLi functioned as a 1e− reductant,
and the incipient W(V) species (tBu3SiNH)(tBu3SiN)2W
t
abstracted a hydrogen atom from the resulting Bu radical to
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a
1
Table 1. H and 13C{1H} NMR Spectral Assignments for (tBu3SiNH)(tBu3SiN)2WX/R (1-X/R)
1H NMR (δ (J (Hz)), assign.)
13C{1H} NMR (δ, (assign.), J (Hz))
b
b
b
compound
(tBu3SiNH)(tBu3SiN)2WH (1-H)
tBu
NH and R
7.41 (NH)
SiCMe3 SiC(CH3)3
R
1.18
1.34
1.22
1.35
1.22
1.35
1.22
1.36
1.19
1.33
1.20
1.34
22.72
23.95
23.72
24.88
23.71
24.85
23.64
24.77
23.38
24.55
23.31
24.42
30.53
31.11
30.82
31.29
30.83
31.29
30.83
31.33
30.72
31.26
30.72
31.22
13.34 (JWH = 356)
(tBu3SiNH)(tBu3SiN)2WCl (1-Cl)
(tBu3SiNH)(tBu3SiN)2WBr (1-Br)
(tBu3SiNH)(tBu3SiN)2WI (1-I)
7.18 (NH)
7.34 (NH)
7.50 (NH)
(tBu3SiNH)(tBu3SiN)2WCH3 (1-CH3)
(tBu3SiNH)(tBu3SiN)2WEt (1-Et)
6.59 (NH)
21.62 (1JWC = 138)
1.43 (JWH = 11, CH3)
6.51 (NH)
19.67 (CH3)
39.01 (1JWC = 137,
2.06 (t, 7, CH3)
WCH2)
c
2.36 (q, 7, CH2)
(tBu3SiNH)(tBu3SiN)2WnPr (1-nPr)
1.21
1.34
6.54 (NH)
23.34
24.44
30.72
31.23
21.38 (CH3)
28.99 (CH2)
39.01 (1JWC =136,
1.05 (t, 7, CH3)
2.24−2.44 (m, (CH2)2)
c
WCH2)
(tBu3SiNH)(tBu3SiN)2W(E-CH2CHCHMe) (1-E-CH2CH
1.21
1.34
6.58 (NH)
23.36
24.44
30.71
31.18
17.72 (CH3)
48.49 (WCH2)
123.44 (CH)
135.39 (CH)
c
CHMe)
1.85 (d, 6, CH3)
3.05 (d, 7, CH2)
5.25 (dq, 15, 6, CH)
6.17 (dt, 15, 7, CH)
6.90 (NH)
d
(tBu3SiNH)(tBu3SiN)2WPh (1-Ph)
1.19
1.36
23.56
24.57
30.88
31.30
129.16 (CH)
143.44 (CH)
174.50 (1JWC = 181,
7.02 (t, 7, CH4)
7.22 (m, CH3,5
)
WC1)
8.45 (d, 7, CH2,6
6.85 (NH)
)
c,d
(tBu3SiNH)(tBu3SiN)2WC6H4-3-Me (1-C6H4-3-Me)
1.21
1.37
23.58
24.58
30.79
31.29
21.12 (CH3)
128.78 (CH)
129.95 (CH)
136.87 (C3)
140.13 (CH)
144.42 (CH)
171.90 (WC1)
21.49 (CH3)
139.03 (CH)
143.62 (CH)
174.43 (C1)
2.17 (CH3)
6.87 (d, 8, CH4)
7.18 (t, 8, CH5)
8.26 (d, 8, CH6)
8.35 (CH2)
c,f
(tBu3SiNH)(tBu3SiN)2WC6H4-4-Me (1-C6H4-4-Me)
1.22
6.83 (NH)
23.58
24.58
30.81
31.32
1.38 (CH3) 1.93
7.02 (d, 8, CH3,5
)
)
8.39 (d, 8, CH2,6
6.74 (NH)
d,e
(tBu3SiNH)(tBu3SiN)2WCH2Ph (1-Bn)
1.21
1.29
3.57 (JWH = 15, CH2)
6.88 (t, 7, CH4)
7.31 (d, 7, CH2)
6.63 (NH)
c,e
(tBu3SiNH)(tBu3SiN)2W(E-CHCHMe) (1-E-CHCHMe)
1.23
1.37
23.54
24.53
30.78
31.26
24.42 (CH3)
153.46 (CH)
167.63 (CH)
1.70 (dd, 6, 1.5, CH3)
8.01 (dq, 15, 1.5, WCH)
6.75 (NH)
e
(tBu3SiNH)(tBu3SiN)2W(Z-CHCHMe) (1-Z-CHCHMe)
1.23
1.37
2.06 (dd, 6, 1.5, CH3)
7.11 (m, CH)
8.10 (dq, 11, 1.5, WCH)
e
(tBu3SiNH)(tBu3SiN)2W(E-CHCHtBu) (1-E-CHCHtBu)
1.23
1.37
6.61 (NH)
1.05 (tBu)
23.65
24.59
30.81
31.26
29.02 (CMe3)
36.86 ((CH3)3)
7.20 (d, 18, JWH = 10,
WCH)
159.67 (1JWC = 182,
WCH)
7.95 (d, 18, CH)
4.03 (NH)
167.74 (CH)
21.49 (CH3)
129.67 (CH)
129.73 (CH)
135.16 (C)
(tBu3SiNH)(tBu3SiN)2W(NC(H)-C6H4-4-Me) (1-NCHtol) 1.38
23.83
24.55
31.22
31.35
1.36
1.93 (CH3)
6.92 (d, 8, CH)
7.51 (d, 8, CH)
10.29 (NCH)
143.83 (C)
176.05 (WNC)
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Table 1. continued
1H NMR (δ (J (Hz)), assign.)
13C{1H} NMR (δ, (assign.), J (Hz))
b
tBu
b
b
compound
NH and R
SiCMe3 SiC(CH3)3
R
(tBu3SiNH)(tBu3SiN)2WCHNtBu (1-CHNtBu)
1.35
1.33
4.60 (NH)
23.79
24.50
31.33
31.24
29.29 (Me3)
1.13 (tBu)
61.89 (NCMe3)
11.34 (JWH = 21, CH)
214.18 (1JWC = 159,
WC)
(tBu3SiNH)(tBu3N)2WCN (1-CN)
1.31
8.24 (NH)
23.20
24.49
30.52
31.03
149.44 (1JWC = 243,
c
WC)
1.16
1.31
1.31
(tBu3SiNH)(tBu3N)2WCHNMe (1-CHNMe)
3.36 (NH)
3.07 (CH3)
10.72 (JWH = 19, CH)
(tBu3SiN)3Wpy (2-py)
1.41
6.61 (m, C3,5
)
24.61
31.56
125.33
140.92
155.25
6.44 (t, 7, C4)
9.04 (d, 7, C2,6
)
Li(tBu3SiN)3WH (2-Li-H)
Na(tBu3SiN)3WH (2-Na-H)
K(tBu3SiN)3WH (2−K-H)
1.26
1.42
1.45
1.16
12.14 (JWH = 338)
7.20 (JWH = 314)
7.11 (JWH = 313)
2.58 (t, 5, CH2N)
2.58 (s, CH2O)
23.43
23.87
23.95
24.59
31.02
31.52
31.63
32.31
g
[K-crypt 2.2.2][tBu3SiN)3WH] (2-H-Kc)
54.97 (CH2)
68.69 (CH2)
71.52 (CH2)
3.57 (t, 5, CH2O)
10.06 (JWH = 329)
Li(tBu3SiN)3WCl (2-Li-Cl)
Na(tBu3SiN)3WCl (2-Na-Cl)
K(tBu3SiN)3WCl (2-K-Cl)
Na(tBu3SiN)3WBr (2-Na-Br)
K(tBu3SiN)3WBr (2-K-Br)
Li(tBu3SiN)3WI (2-Li-I)
K(tBu3SiN)3WI (2-K-I)
1.28
1.47
1.52
1.51
1.52
1.28
1.53
1.15
24.52
24.88
24.99
24.90
24.94
24.33
24.81
25.31
31.70
31.71
31.87
31.79
31.88
31.22
31.95
32.37
g
ch
,
K(tBu3SiN)3WCH3 (2-K-CH3)
0.65 (2JWH = 12)
10.85 (WC)
g
c
K(tBu3SiN)3WCH2CH3 (2-K-Et)
1.42
1.38
0.62 (q, 8, CH2)
1.87 (t, 8, CH3)
1.81 (m, CH2)
2.10 (m, CH2)
24.75
24.77
31.87
31.83
20.23
27.98
g,i
K(tBu3SiN)3WCH2CH2CH3 (2-K-nPr)
20.50 (CH2)
29.05 (CH2)
c
40.25 (WC)
144.41 (CH)
172.91 (C1H)
dj
,
Li(tBu3SiN)3WPh (2-Li-Ph)
1.27
1.28
7.03 (t, 7, CH4)
24.21
24.24
31.23
31.23
7.21 (t, 7, CH3,5
)
8.41 (d, 7, CH2,6
)
Li(tBu3SiN)3W(C6H4-3-Me) (2-Li-C6H4-3-Me)
2.20 (s, CH3)
21.20 (CH3)
127.41 (CH)
136.30 (C3)
141.46 (CH)
159.45 (CH)
172.78 (C1H)
21.48 (CH3)
133.56 (CH)
144.57 (CH)
6.87 (d, 7, CH4)
7.17 (t, 7, CH5)
8.19 (d, 7, CH6)
8.31 (s, CH2)
f
Li(tBu3SiN)3W(C6H4-4-Me) (2-Li-C6H4-4-Me)
1.29
2.01 (s, CH3)
24.23
31.25
7.02 (d, 7, CH3,5
8.34 (d, 7, CH2,6
)
)
a
Benzene-d6 unless otherwise noted; all JWH reported were obtained from W satellites that integrated to ∼14% intensity, indicative of one tungsten
b
c
d
e
center. Amide listed first, imide second. Tungsten satellites could not be confidently assigned. CHn, n = 1−6 phenyl positions. Aryl position(s)
obscured by C6D5H. Aryl carbon not observed. THF-d8. Tentative assignment. Me resonance obscured by Bu. Aryl resonance(s) obscured by
f
g
h
i
j
t
residual solvent.
t
form isobutylene. The second equiv of BuLi deprotonates 1-H,
as the experiment in eq 9 proved plausible.
can be construed as an 18e− complex, an evaluation of insertion
reactions appeared warranted. Exposure to olefinstypically in
excessand related unsaturated substrates met with reasonable
success, as illustrated in Scheme 3. Treatment of 1-H with
ethylene (16 equiv), propylene (16 equiv), and methylenecy-
clopentane (10 equiv) led to the isolation of (tBu3SiNH)(tBu3-
SiN)2WEt (1-Et) and the propyl derivative (tBu3SiNH)-
(tBu3SiN)2WnPr (1-nPr) and disappearance of the hydride
Insertion Routes to (tBu3SiNH)(tBu3SiN)2WX/R. Me-
tathesis procedures toward the preparation of (tBu3SiNH)-
(tBu3SiN)2WR (1-R) that featured the displacement of
halide by alkyl anion equivalents proved limited due to
competing reduction and deprotonation events. Despite the
saturated nature of (tBu3SiNH)(tBu3SiN)2WH (1-H), which
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more difficult the insertion process, as evidenced by the 150 °C,
c
3 d conditions that pertain to 1-CH2 Pe versus the room-
temperature conditions that led to ethylene capture. During the
c
formation of 1-CH2 Pe, ∼35% of the excess methylenecyclo-
pentane underwent isomerization to 1-methylcyclopentene.
Given the rather harsh conditions, it is uncertain whether the
isomerization is derived from a 2,1-insertion event followed by
β-H elimination or whether the reaction is catalyzed by a
spurious impurity.
The most curious consequence of examining various
insertion substrates was the case of butadiene, which afforded
only one regioisomer in both the crude (∼90%) and isolated
resonance, consistent with formation of the cyclopentylmethyl
species (tBu3SiNH)(tBu3SiN)2WCH2 Pe (1-CH2 Pe) under
c
c
varied conditions. The majority of the resonances for putative
1-CH2 Pe were obscured by the substrate; hence its tentative
c
formulation is largely inferred. The larger the substrate, the
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the other to an aryl-based mode. The imino proton
1
resonated at δ 10.29 in the H NMR spectrum, and its
corresponding carbon was assigned to a resonance at δ
176.05 in the 13C{1H} NMR spectrum.
tert-Butylisocyanide underwent an immediate 1,1-insertion
with 1-H to provide the light yellow formimidoyl (tBu3SiNH)-
(tBu3SiN)2WCHNtBu (1-CHNtBu) in 62% isolated
yield. The characteristic formimidoyl53 proton resonated at δ
1
2
11.34 in the H NMR spectrum with a JWH = 21 Hz, and
its corresponding carbon was located at δ 214.18 (1JCH
=
159 Hz) in the 13C{1H} NMR with accompanying tungsten
satellites (1JWC = 159 Hz). The IR spectrum of 1-CHNtBu
exhibited two νCN of 1559 and 1595 cm−1, which may be
indicative of two rotomers of the molecule; one with the
imine group between the imides and another where the imine
resides between the imide and amide. Thermolysis of 1-CH
NtBu in hexanes at 100 °C for 3 d cleanly produced the
cyanide complex (tBu3SiNH)(tBu3SiN)2WCN (1-CN),
which was formulated on the basis of a resonance at δ
149.44 in the 13C{1H} NMR possessing a tungsten−carbon
coupling (1J) of 243 Hz and a weak νCN = 2146 cm−1 in the IR
spectrum. An NMR tube reaction confirmed the quantitative
nature of the conversion and revealed isobutene as an organic
byproduct.
Use of methyl isocyanide afforded a purple-colored solution
in C6D6 at 23 °C and resonances consistent with the generation
of (tBu3SiNH)(tBu3SiN)2WCHNMe (1-CHNMe).
The compound subsequently decomposed over the course of
12 h to a number of unknown products with concomitant
bleaching of the solution. Most early transition metal
formimidoyl species adopt an η2-coordination mode,53 but
none of the spectral parameters can consistently distinguish
between it and an η1-CHNR species. Closely related
structurally characterized complexes that differ in coordination
of the formimidoyl show only a slightly increased νCN and
downfield 13C NMR spectroscopic chemical shift for the η2-
mode.54 The colored solution of 1-CHNMe may be
indicative of a different coordination, but an η2-CHNR
must compete with the π-donation from the imides and amide.
Since (tBu3SiNH)(tBu3SiN)2WR (1-R) behave more like
18e− compounds, the bulkier, lightly colored 1-CHNtBu is
formulated as an η1-species. For comparison, 1-H was stable to
an excess of CO (3 atm) until heated to 130 °C, when
decomposition was evident.
(17%) samples: (tBu3SiNH)(tBu3SiN)2W(E-CH2CH
complex is likely derived from 2,1-insertion of butadiene,48,49
followed by rearrangement via the η3-allyl, lending credence to
the postulation that 2,1-insertion may be operational in the
preceding isomerization discussion.
3
CHMe) (1-E-CH2CHCHMe, JHH = 15 Hz). This σ-allyl
Propyne and 3,3-dimethylbutyne undergo insertion to afford
the vinyl complexes (tBu3SiNH)(tBu3SiN)2W(CH
CHMe) (1-CHCHMe) and (tBu3SiNH)(tBu3SiN)2W-
(CHCHtBu) (1-CHCHtBu), which are both observed as
mixtures of their E- and Z-isomers, with the E-isomer favored.
It was later found that these compounds were light sensitive;
hence the unexpected appearance of the Z-isomers, which
should not arise from a standard 1,2-insertion event,50 was
rationalized on that basis. In the NMR tube experiment with
excess propyne, a dark purple precipitate was also noted and
was believed to be composed of substrate oligomers. In support
of this hypothesis, the reaction of 1-H with acetylene
immediately generated a solid consistent with the formation
of acetylene oligomers.
A few nonolefinic substrates were assayed, and treatment of
(tBu3SiNH)(tBu3SiN)2WH (1-H) with p-tolunitrile provided
the p-tolylimino species (tBu3SiNH)(tBu3SiN)2WN
C(H)C6H4-4-Me (1-NCHtol), produced from hydride
reduction of the cyano group. The IR spectrum of 1-N
CHtol revealed a νNH at 3280 cm−1 and two absorptions at
1604 and 1662 cm−1 in the region expected for νNC (1600−
1700 cm−1),51,52 one of which is assigned to the imine and
Thermolyses of (tBu3SiNH)(tBu3SiN)2WR (1-R, R = H,
CH3). Calculations by Cundari et al.16 suggested that 1,2-RH
elimination from (tBu3SiNH)(tBu3SiN)2WR (1-R, R = H,
CH3) would have very high activation energies (Scheme 1).
With 1-H and 1-CH3 and labeled derivatives available, extended
thermolyses were conducted, and the results supported the
calculations. As Scheme 4 reveals, thermolysis of 1-H for
1 week at 200 °C in C6D6 with D2 incurred no label incorpo-
ration in the starting material, thereby ruling out several label
scrambling paths under these conditions; no evidence of
σ-bond metathesis,55 1,2-D2 addition, or 1,2-H2 elimination was
obtained, nor was any solvent incorporation,56 e.g.,
formation of (tBu3SiND)(tBu3SiN)2W(C6D5) (1-ND-
C6D5), implicated. Similarly, thermolysis of 1-CD3 for
1 week at 200 °C revealed no label scrambling between amide
and methyl sites,38−40 nor was any solvent (arene) activa-
tion and incorporation detected. Since the 1,2-elimination
of dihydrogen and methane has typical, modest barriers in
related systems (Scheme 1), the thermolyses clearly showed
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Scheme 3
that such events were not plausible for (tBu3SiNH)-
(tBu3SiN)2WR, supporting studies with related arylimido
species.22 Extended thermolyses of 1-H and 1-CH3 in C6D6 at
200 °C for 30 d revealed no exchange with solvent and no
decomposition.
2-py + H2 is disfavored relative to 1-H and py. Under pseudo-
first-order conditions, the loss of 1-H was monitored with
various concentrations of py present, and plots of ln[1-H]
versus time were found to be linear; the data are given in
Scheme 5. Due to the approach to equilibrium, observations of
the disappearance of 1-H were limited to 2−3 half-lives. From a
plot of kobs versus [py], a second-order rate constant of 5.9(2) ×
Pyridine-Induced 1,2-H2-Elimination from (tBu3SiNH)-
(tBu3SiN)2WH (1-H). 1. Synthesis of (tBu3SiN)3Wpy
(2-py). While inert toward 1,2-H2-elimination in nondonating
solvents, (tBu3SiNH)(tBu3SiN)2WH (1-H) was heated in
pyridine at 140 °C for 36 h with occasional degassing of H2 to
afford orange (tBu3SiN)3Wpy (2-py) in 56% yield. Pyridine
adduct 2-py is extremely stable and does not decompose upon
extended thermolysis at 200 °C in C6D6. In contrast,
dissolution of 2-py in py-d5 resulted in displacement of py
within seconds at 23 °C, as assessed by 1H NMR spectroscopy.
The apparent associative exchange of py in 2-py prompted
consideration of a related mechanism for 1,2-H2 elimination
from 1-H.
10−6 M−1 s−1, corresponding to ΔG‡ = 34.4 kcal/mol, was
for
obtained. The expected observation of a second-order process
was consistent with an associative path, where a five-coordinate
intermediate of the type (tBu3SiNH)(tBu3SiN)2WH(py)
(1-H-py) is likely. An alternative interchange pathway, where
1-H-py constitutes an activated complex where py enters as the
H−H bond is being formed, cannot be distinguished on the
basis of the kinetics data.
Another path involving deprotonation of the amide by
pyridine, followed by loss of H2 via dihydrogen loss from the
complex ion [(tBu3SiN)3WH][pyH] (2-H-pyH), is also a
possibility, but deprotonation of the amide typically requires a
much stronger base. Nonetheless the pKa difference between
[pyH]+ (∼3.4) and that of the amide (est. 20−30) is not too
different than the activation energy for dihydrogen loss; the
difficulty with this path is envisoning the microscopic reverse. It
would seemingly require a displacement of py by H2 that would
enable complex ion formation by subsequent deprotonation of
a dihydrogen complex.58 Since 1,2-H2 addition to an imide
The conditions of neat pyridine and dihydrogen degassing in
the conversion of (tBu3SiNH)(tBu3SiN)2WH (1-H) to
(tBu3SiN)3Wpy (2-py) prompted measurement of the
equilibrium constant. A sealed NMR tube containing roughly
2 equiv of dihydrogen and 2-py in C6D6 was heated at 141 °C
for 4 d until no changes in concentration were noted.57 The
equilibrium constant, as defined by 1-H + py ⇄ 2-py + H2, was
4.4 × 10−3, which corresponds to ΔG° = 4.5 kcal/mol; that is,
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Scheme 4
from a dihydrogen complex is expected to be rapid, the proton
transfer path is deemed less plausible. The contrast between the
equilibrium in the tungsten case versus previous observations in
the related titanium imide system is remarkable. Equilibrium
studies have shown that (silox)2(tBu3SiN)Tipy + H2 is
8.6 kcal/mol more stable than (silox)2(tBu3SiNH)TiH + py.8 The
origin of this ΔΔG° of 13.1 kcal/mol is not clear, but several
factors may be contributing. The metal−hydride bond strength is
expected to be stronger for the group 6 element,59 and the
corresponding imide π-bond that is lost upon 1,2-H2 addition is
likely to be weaker for tungsten versus titanium; similar, more
detailed arguments were presented in the Introduction. It is
also conceivable that the smaller size of tungsten (cov. rad. W =
1.30 Å;60 cov. rad. Ti = 1.32 Å), in combination with the shorter
multiple imide ligands compared to the siloxide, sterically favors
the amide-hydride over the pyridine adduct. In addition, the
reduced electrophilicity of tungsten may lower the interaction
energy of the pyridine.
thermolysis illustrated in Scheme 4. An alternative possibility
embraces the involvement of (tBu3SiND)(tBu3SiN)2-
W(N-pyridyl-α-D) (1-ND-α-pdyl), as illustrated by eq 10.
Thermolysis of (tBu3SiN)3Wpy (2-py) with D2 (∼10
equiv) at 180 °C for 20 h in C6D6 revealed deuterium
incorporation (∼80%) in the α-positions of the released
pyridine61 and some hydrogen in the amide (∼80% D) and
hydride (∼83% D) positions. No incorporation into the
remaining position of pyridine was noted, and HD and H2 were
observed in a ∼3:1 ratio. A reversible CH bond activation at the
α-position of a bound pyridine requires an additional step for
deuterium incorporation. While σ-bond metathesis is an
obvious candidate,55 note that the process was not observed
for (tBu3SiNH)(tBu3SiN)2WH (1-H) and D2, nor was any
reversible activation of C6D6 revealed during the 200 °C
The pyridyl transient would be created via a 1,2-insertion of the
pyridine into a W−D bond,61−69 and it generates hydrogen for
the hydride and amide positions via β-H elimination. Equation
10 provides a rationale for the generation of HD, deuteration of
the pyridine α-positions, and the presence of H in the amide-
hydride.
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Scheme 5
2. Structure of (tBu3SiN)3Wpy (2-py). An X-ray crystal
structure determination of (tBu3SiN)3Wpy (2-py) was
conducted, and a molecular view is presented in Figure 1.
Selected details of the data collection and refinement are given
in Table 2, and pertinent metric parameters are listed in Table 3.
The asymmetric unit is comprised of two independent and
almost identical distorted tetrahedral molecules, with ∠Nim−
W−Nim angles averaging 115.4(9)° and a ∠Nim−W−Npy
average angle of 102.6(13)°. The tungsten-imide distances
average 1.820(19) Å, the pyridine is bound at a W−N distance
of 2.148(2) Å, and the imides are nearly linear, with an average
∠W−Nim−Si) angle of 174.1(26)°. The metric parameters
are not particularly striking, except that the imide distances are
somewhat long for W(VI). For example, a rough average of
d(WN) in d0 bis-imido tungsten complexes is 1.74(3) Å.24,70
Recall that the C3v symmetry of the WN3 core renders one pair
of the 12 N(pπ) electrons nonbonding by virtue of their a2
symmetry, which has no match on the metal.21 In addition,
competition among all three imides for metal receptor orbitals
renders the π-bonding modestly attenuated in this system, as
discussed in the Introduction.21−25
Syntheses and Characterizations of M[(tBu3SiN)WH/
X/R]. 1. M[(tBu3SiN)3WH. Deprotonation of (tBu3SiNH)-
t
(tBu3SiN)2WH (1-H) was effected by BuLi to produce
Li(tBu3SiN)3WH (2-Li-H) according to eq 9, but a scale-up
of the deprotonation reaction utilized neoPeLi, as indicated in
eq 11. Sodium and potassium analogues were produced via the
use of MH (M = Na, K) to afford M(tBu3SiN)3WH (2-M-H,
M = Na, K) in modest (unoptimized) yields as given in eq 12.71
The neutral hydride, 1-H, possesses a hydride resonance at δ
13.34 in its 1H NMR spectrum, with a 1JWH of 356 Hz, and this
is accompanied by a ν(WH) of 1910 cm−1 in its IR
spectrum.11,42 The LiH species, 2-Li-H, also has a downfield
1
1
resonance at δ 12.14 with a similar JWH of 338 Hz in its H
NMR spectrum, and its IR spectrum manifested a ν(WH) of
1907 cm−1, which is remarkably similar to the neutral complex.
In modest contrast, the hydride shifts of Na(tBu3SiN)3-
WH (2-Na-H) and K(tBu3SiN)3WH (2-K-H) appear more
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regarding the data collection and refinement may be found in
Table 2, while Table 3 contains pertinent metric information.
As Figure 2a illustrates, 2-H-K(OEt2)3 is a pseudotetrahedral
molecule with the potassium bound to the hydride at 2.71(7) Å
and to three ether molecules with d(K−O)av = 2.744(14) Å
that are staggered with respect to the tungsten core.74 The
W−H−K bridge angle is 153(2)°, and the tungsten−hydride
distance is 1.72(6) Å,75 slightly longer than the sum of covalent
radii (1.62 Å)59 and about the mean of a rather wide spectrum
of d(WH) determined from X-ray studies.42,60,76−78 The
tungsten−imido bonds average 1.806(4) Å, and the N−W−N
angles are somewhat splayed from a tetrahedral value at
116.1(2)°, presumably reflecting the demonstrably greater
steric influences among the imides versus the hydride. The
N−W−H angles are correspondingly smaller, averaging
101.6(11)°, and the W−N−Si linkages are 166.9(23)°.
Few structures with a comparable W−H−M′ (M′ = alkali
metal) connection have been reported;77 hence the structure of
Cp2Mo(μ-H)K(18-crown-6)74 is the most apt comparison,
with a d(Mo−H) of 1.66 Å and a d(K−H) of 2.80 Å. Tungsten-
bridging hydride distances have been measured by neutron
diffraction studies on [(Me3P)3H2W](μ-H)3[M′(crown)]
(M′(crown) = K(18-c-6), Na(15-c-5)), and their values of
1.77(2) Å do not differ from the terminal distances of 1.77(2) Å.78
3. Structure of [(tBu3SiN)3WH][K(crypt-2.2.2)] (2-H-Kc). The
molecular structure of [(tBu3SiN)3WH][K(crypt-2.2.2)]
(2-H-Kc) was also determined by X-ray crystallography, and
two discrete ionsthe [(tBu3SiN)3WH]− anion and the [K-
(crypt-2.2.2)]+ cationare clearly separated in the structure.
Unfortunately, while the hydride pertaining to the anion was
determined by a difference Fourier map and successfully
refined, its d(WH) of 1.93(9) Å and H−W−N angles (118(2)°,
92(2)°, 90(2)°) likely reflect an inaccuracy in the
model.42,60,76−78 Refinement and data collection parameters
are given in Table 2 and the metrics of the molecule are listed
Figure 1. Molecular view of (tBu3SiN)3Wpy (2-py).
upfield at δ 7.20 (1JWH = 314 Hz) and δ 7.11 (313 Hz),
1
respectively, with JWH values that are somewhat attenuated. In
addition, the ν(WH) values for 2-Na-H and 2-K-H are lower at
1855 and 1858 cm−1, respectively. In general, the solubilities of
M(tBu3SiN)3WH (2-M-H) were consistent with neutral
complexes; that is, they possessed solubilities that were not very
different from (tBu3SiNH)(tBu3SiN)2WR (1-R), and there
was little difficulty in obtaining NMR spectra in benzene-d6,
perhaps due to alkalai metal−benzene interactions.72,73
2. Structure of (tBu3SiN)3WHK(OEt2)3 (2-H-K(OEt2)3). When
crystallized with diethyl ether present, K(tBu3SiN)3WH
(2-K-H) coordinated three ether molecules to afford
(tBu3SiN)3WHK(OEt2)3 (2-H-K(OEt2)3), whose structure
was determined by X-ray crystallography. Selected details
Table 2. Selected Crystallographic and Refinement Data for (tBu3SiN)3Wpy (2-py), (tBu3SiN)3WHK(OEt2)3 (2-H-
K(OEt2)3), [(tBu3SiN)3WH][K(crypt-2.2.2)] (2-H-Kc), (tBu3SiN)3WHK (2-K-H), and (tBu3SiN)3WIK (2-I-K)
a
b
c
2-py
2-H-K(OEt2)3
2-H-Kc
2-K-H
2-I-K
formula
C41H86N4Si3W
903.26
C48H111N3O3Si3KW
1085.62
C56H128N5O6.5Si3KW
1282.85
C36H82N3Si3KW
864.27
C111H245N3K3I3W
3011.07
fw
space group
Pbca
P21/n
P1
̅
P1
P1
̅
̅
Z
16
4
2
2
2
a, Å
17.948(4)
26.404(5)
42.901(9)
90
13.2546(2)
22.01670(10)
20.8776(3)
90
12.168(2)
17.080(3)
18.459(4)
88.37(3)
88.41(3)
69.99(3)
3602.4(12)
1.183
12.941(1)
13.103(1)
16.293(1)
70.85(4)
71.47(4)
62.55(4)
2269.3(3)
1.265
19.065(4)
20.937(4)
23.744(5)
67.569(5)
66.668(7)
63/299(6)
7531.3(26)
1.328
b, Å
c, Å
α, deg
β, deg
90
95.6070(10)
90
γ, deg
V, Å3
ρcalc, g·cm−3
μ, mm−1
temp, K
λ, Å
90
20330.7(71)
1.180
6063.40(13)
1.189
2.371
2.069
1.755
2.741
3.079
293(2)
165(1)
173(2)
295(2)
293(2)
0.91000
R1 = 0.0651
wR2 = 0.1861
R1 = 0.0674
wR2 = 0.1919
0.71073
0.71073
0.71073
0.71073
de
,
R indices [I > 2σ(I)]
R1 = 0.0427
wR2 = 0.1331
R1 = 0.0788
wR2 = 0.01685
1.045
R1 = 0.0519
wR2 = 0.1285
R1 = 0.0909
wR2 = 0.1820
1.079
R1 = 0.0581
wR2 = 0.1500
R1 = 0.0671
wR2 = 0.1661
R1 = 0.1055
wR2 = 0.2398
R1 = 0.1771
wR2 = 0.2705
1.088
de
,
R indices (all data)
f
GOF
1.006
1.041
a
b
c
d
e
Two molecules per asymmetric unit. Half of the dimer is the asymmetric unit. The trimer is the asymmetric unit. R1 = ∑||Fo| − |Fc||/∑|Fo|. wR2 =
f
[∑w(|Fo| − |Fc|)2/∑wFo ]1/2. GOF (all data) = [∑w(|Fo| − |Fc|)2/(n − p)]1/2, n = number of independent reflections, p = number of parameters.
2
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Table 3. Selected Interatomic Bond Distances (Å) and Angles (deg) for (tBu3SiN)3Wpy (2-py), (tBu3SiN)3WHK(OEt2)3
(2-H-K(OEt2)3), [(tBu3SiN)3WH][K(crypt-2.2.2)] (2-H-Kc), (tBu3SiN)3WHK (2-K-H), and (tBu3SiN)3WIK (2-I-K)
a
b
c
2-py
2-H-K(OEt2)3
2-H-Kc
2-K-H
2-I-K
W1N1
1.821(6), 1.842(8)
1.816(6), 1.795(7)
1.842(7), 1.804(6)
2.148(7), 2.147(8)
1.736(12)
1.803(5)
1.810(5)
1.805(5)
1.72(6)
1.809(4)
1.802(4)
1.783(4)
1.793(5)
1.799(4)
1.75(4)
1.737(3)
2.64(4)
2.43(4)
4.249(4)
2.77(5)
1.68(3), 1.62(2), 1.56(2)
1.75(3), 1.79(2), 1.79(2)
1.82(2), 1.84(2), 1.84(2)
2.724(2), 2.727(3), 2.726(3)
1.78(10)
W1N2
W1N3
1.802(4)
b
W1−X
N−Siav
K1−H1, I
K1−H1′
K1···K1′
H1···H1′
1.716(7)
2.71(7)
1.704(6)
3.52(5)av
K1−O1
K1−O2
K1−O3
K1−O4
K1−O5
K1−O6
2.756(4)
2.747(4)
2.728(6)
2.828(5)
2.825(5)
2.787(5)
2.784(5)
2.859(4)
2.802(4)
117.0(2)
117.3(2)
N1−W1−N2
N1−W1−N3
N2−W1−N3
N1−W1−X
N2−W1−X
N3−W1−X
W1−N1−Si1
W1−N2−Si2
W1−N3−Si3
K1−H−K1′
H−K1−H′
O1−K1−O2
O1−K1−O3
O2−K1−O3
O−K−O
114.6(3), 114.6(3)
115.9(3), 116.8(3)
115.5(3), 114.8(3)
100.8(3), 101.5(3)
103.8(3), 102.1(3)
103.4(3), 103.9(3)
171.2(5), 172.9(4)
175.1(4), 177.9(5)
171.7(5), 175.9(4)
116.1(2)
116.2(2)
115.9(2)
101.8(17)
100.4(16)
102.5(18)
168.2(3)
168.3(3)
164.2(3)
114.3(2)
118.8(2)
117.8(2)
106.2(11)
88.9(14)
104.7(13)
174.2((3)
165.6(3)
167.4(3)
113.9(15)
66.1(15)
110.1(12), 110.5(8), 110.3(9)
113.4(11), 115.4(8), 113.8(11)
116.8(12), 115.5(10), 116.7(10)
102.8(6), 103.4(7), 101.8(8)
105.2(6), 105.1(7), 105.4(7)
107.2(8), 105.5(7), 107.7(8)
170.3(20), 173.4(12), 173.0(12)
174.6(12), 176.6(14), 176.3(16)
178.8(14), 177.6(11), 177.1(13)
116.2(2)
b
b
b
175.4(3)
175.7(3)
175.0(3)
d
99.52(14)
119.1(2)
89.8(2)
60.1(4)
d
97.4(16)
d
d
123.7(23)
133.6(21)
O1−K1−H/N
O2−K1−H/N
O3−K1−H/N
136.3(11)
101.1(10)
99.1(11)
a
b
Two molecules per asymmetric unit; chemically equivalent parameters listed together. Hydride refined, but d(WC) = 1.93(9) Å and H−W−N
angles of 118(2)°, 92(2)°, and 90(2)° appear unreasonable. Trimer is the asymmetric unit. Chemically equivalent parameters listed together;
∠I−K−I = 83(2)°, 105(2)°, and 105(2)°; ∠K−I−K = 118(2)°, 121(2)°, and 121(2)°; ∠W−I−K = 97.4(6)av°. Fifteen O−K−O angles in the crypt
2.2.2 are in four groups averaged as indicated.
c
d
Figure 2. Molecular views of (tBu3SiN)3WHK(OEt2)3 (2-H-K(OEt2)3 (a)) and the [(tBu3SiN)3WH] anion of [(tBu3SiN)3WH][K(crypt-
2.2.2)] (2-H-Kc (b); its hydride has been tentatively located).
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Figure 3. Molecular (a) and core (b) views of (tBu3SiN)3WHK
(2-H-K, as [2-H]2(μ-K)2).
the series of hydrides, averaging 1.792(8) Å, and the N−W−N
angles have slightly greater variance than the previous examples,
averaging 117.0(27)°. The H−W−N1, −N2, and −N3 angles
are 106.2(11)°, 88.9(14)°, and 104.7(13)°, respectively. The
hydride is bound to the tungsten at 1.75(4) Å, and it is slightly
asymmetric, with W−H1−K1 and W−H1−K1′ angles of
117(2)° and 124(2)°.
in Table 3. The core of the [(tBu3SiN)3WH]− anion that is
illustrated in Figure 2b is very similar to the previous cases, with
d(WN)av = 1.804(4) Å, N−W−N angles that average 116.8(6)°,
and W−N−Si linkages that are nearly linear (175.4(4)°av).
4. Structure of K(tBu3SiN)3WH (2-K-H). The most
interesting of the hydride anion structures is the unsolvated
version of K(tBu3SiN)3WH (2-K-H), whose structure was
determined by X-ray crystallography to be dimeric (i.e., [2-H]2-
(μ-K)2) in the solid state. Data collection and refinement
information is listed in Table 2, while selected interatomic
distances and angles are given in Table 3. The dimer shown in
Figure 3 possesses a center of inversion about a planar K2H2
diamond core (∠H1−K1−H1′ = 66(2)°, ∠K1−H1−HK′ =
113(2)°; d(K1···K1′) = 4.249(4), d(H1···H1′) = 2.77(5)), with
two symmetry-equivalent, flanking pseudotetrahedral tris-imido
tungsten moieties. In addition to the two hydrides bound to
each potassium, six ligand carbon atoms are within 3.23−
3.93 Å, providing corresponding calculated CH···K contacts of
2.66−3.00 Å. This secondary coordination sphere is similar to
that reported for {(Me3Si)2N]2V[N(SiMe3)SiMe2CH2]}2{K-
(THF)2}2,79 which is composed of two almost identical
vanadium monomers bridged by two separate K(THF)2
units, and manifests H···K contacts of 3.01−3.52 Å that
derive from the SiMe3 groups. The d(WN) are the shortest in
5. K(tBu3SiN)3WR (2-K-R). The appearance of [(tBu3-
SiN)3WPh]Li (2-Li-Ph), Li(tBu3SiN)3W(C6H4-3-Me) (2-
Li-C6H4-3-Me), and Li(tBu3SiN)3W(C6H4-4-Me) (2-Li-
C6H4-4-Me) in the arylation attempts illustrated by eqs 3 and
4 prompted a brief survey of anion generation71 via KH and
n
(tBu3SiNH)(tBu3SiN)2WR (1-R, R = Me, Et, Pr). As eq 13
reveals, deprotonation of 1-Me, 1-Et, and1-nPr with KH was
conducted in THF (or THF-d8) with heating to produce the
desired potassium tungsten alkyl compounds K(tBu3-
SiN)3WR (2-K-R, R = Me, Et, nPr). Only the methyl
derivative was isolated (50%), while the others were prepared
1
quantitatively according to H NMR assays.
6. M(tBu3SiN)3WX (2-M-X). The production of K-
(tBu3SiN)3WCl (2-K-Cl) upon treatment of (tBu3SiNH)(tBu3-
SiN)2WCl (1-Cl) with potassium benzyl in THF-d8 (eq 5) was
likely a product of a simple acid−base reaction, prompting efforts
at generalizing the process.22 As a consequence, (tBu3SiNH)-
(tBu3SiN)2WX (1-X, X = Cl, Br, I) were treated with KH in
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THF and heated to afford the corresponding potassium tungsten
halide complexes K(tBu3SiN)3WX (2-K-X, X = Cl, Br, I) in
reasonable yields, as indicated by eq 14.
used to describe the results in eqs 15 and 16, but what would
happen if CH3I were the substrate?
Exposure of Li(tBu3SiN)3WH (2-Li-H) to 1 equiv of CH3I
in C6D6 yielded the LiI complex Li(tBu3SiN)3WI (2-Li-I) in
80% yield, but two unexpected products were also identified.
The neutral methyl derivative, (tBu3SiNH)(tBu3SiN)2WCH3
(1-CH3), was detected in 12% yield, and the related iodide
species, (tBu3SiNH)(tBu3SiN)2WI (1-I), was also present
(8%). While radical paths can describe how these products
formed, aspects of those reactions prompted additional investi-
gations. This study, which invokes the intermediacy of alkane
complexes in several reactions of M(tBu3SiN)3WH (2-M-H)
and RX,11,12 will be fully described in a subsequent article.
7. Structure of K(tBu3SiN)3WI (2-K-I). An X-ray crystallo-
graphic study of K(tBu3SiN)3WI (1-K-I) that was crystallized
from hexane revealed its solid-state structure to be a trimer, in
contrast to cryoscopic molecular weight measurements that
revealed 1-K-I as a monomer in benzene. Data collection and
refinement information is given in Table 2, and various metrics
are listed in Table 3, but the latter parameters show large
variation due to poor data. Nonetheless, the structure shown in
Figure 4 features a six-membered K3I3 ring, with the usual
pseudotetrahedral tris-imido tungsten cores attached to the
iodine atoms. The K3I3 ring has potassium−iodine distances
Alternative routes to the alkali halide derivatives were
explored, and alkyl halides were used as a source of X.
Treatment of Li(tBu3SiN)3WH (2-Li-H) with 1 equiv of
CCl4 quantitatively converts the hydride into the chloride,
Li(tBu3SiN)3WCl (2-Li-Cl), and byproduct chloroform, as
indicated by eq 15. Although the reaction looks like a simple
displacement, electron transfer events are more common with
CCl4. Another substrate that is unlikely to undergo an SN2-like
displacement is neoPeCl, where abackside attack is known to be
prohibitively inhibited by sterics. With 7 equiv of neoPeCl,
Na(tBu3SiN)3WH (2-Na-H) was slowly converted to
Na(tBu3SiN)3WCl (2-Na-Cl) with concomitant neopentane
at 150 °C over 36 h, as shown in eq 16. Radical paths can be
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Scheme 6 summarizes the problems encountered during this
approach. Displacement typically occurs more favorably for X =
Cl > Br > I, since the softer halides tend to encourage
reduction, but the evidence in this study is limited, and at times
counterintuitive. (tBu3SiNH)(tBu3SiN)2WCH3 (1-CH3) is
readily formed from 1-Cl (eq 2), yet KCH2Ph deprotonates
1-Cl, but does transfer benzyl anion to 1-I to a modest extent.
Metathetical reactions of this type are subject to the vagaries of
the particular conditions employed, and no systematic study
was made to segregate the various influences.
Substantial amounts of metathesis products 1-Me, 1-Bn,
1-Ph, 1-C6H43-Me, and 1-C6H4-4-Me were generated, and
electron transfer processes were suggested by the nature of the
byproducts in several of these cases. In particular, the
production of M(tBu3SiN)3WH (2-M-H, M = Li, K) in
eqs 4, 6, and 7 implicated electron transfer events that often
occur with ArLi and BnK reagents. One possible subsequent
reaction is H-atom transfer,80,81 but only in the case of BuLi
t
and 1-Cl is this substantiated (eqs 8, 9); (tBu3SiNH)(tBu3-
SiN)2WH (1-H) appears to be the initial product that is then
deprotonated to generate M(tBu3SiN)3WH (2-M-H). No
1-H was detected in other instances in which electron transfer is
likely to play a role, and the final 2-M-H product was likely
formed from a subsequent second electron transfer from excess
reducing agent. In the case of potassium benzyl (eq 7), dibenzyl
was observed consistent with the generation of benzyl radical
upon electron transfer. In this case, C6D6 was the solvent when
the reaction was carried out on the NMR tube scale, and it is
likely that excess KBn reduced the intermediate W(V) product
formed upon reduction/halide loss to directly afford 2-M-H.
Insertion Routes to (tBu3SiNH)(tBu3SiN)2WR (1-R).
Steric factors appear to govern the conditions necessary to
effect olefin insertion routes to various alkyl complexes in
Scheme 3. The only reaction that is particularly strange is the
formation of (tBu3SiNH)(tBu3SiN)2W(E-CH2CHCHMe)
1
(1-E-CH2CHCHMe) (>95%, H NMR) upon reaction of
butadiene with (tBu3SiNH)(tBu3SiN)2WH (1-H). It is
difficult to reconcile this product without invoking a 2,1-
insertion of C4H6,48,49 followed by rearrangement via an η3-
allyl, at a metal center that is significantly encumbered by its
imide ligands. Two other reactions support this observation:
(1) methylenecyclopentane is isomerized to 1-Me-cyclo-
pentene in the course of insertion efforts, and (2) in the likely
absence of σ-bond metathesis paths, deuteration of the α-
positions of the pyridine in eq 10 requires an insertion of
pyridine into the tungsten−deuteride(hydride) bond. Alter-
natively, a bis-amide imide W(IV) species could conceivably
mediate both formation of the 1-E-CH2CHCHMe product
from butadiene and the scrambling in the pyridine deuteration
studies via related NH abstraction82−84 and metalla-ene
rearrangements that are illustrated in Scheme 7. The three-
coordinate W(IV) intermediate85 cannot be ruled out by the
experiments presented, but the exchange of the W−H bond
and WN π-bonds for an NH bond is likely to be substantially
endothermic.
Figure 4. Molecular view of the trimer of K(tBu3SiN)3WI (2-K-I, as
[2-I]3(μ-K)3); ball and stick presentation due to data quality.
that average 3.52(5) Å, I−K−I angles of 83(2)°, 105(2)°, and
105(2)°, fairly regular K−I−K angles of 118°(2), 121°(2), and
121(2)°, and W−I−K angles that average 97.4(6)°. The
tungsten core parameters are comparable to the previous
examples, yet reflect the limited resolution of the model,
with d(WN) = 1.74(10) Å, N−W−N angles that average
113.6(27)°, and N−W−I angles averaging 104.9(19)°.
Thermal Stability of (tBu3NH)(tBu3SiN)2WH/R (1-H/R).
As calculated, and as predicted on the basis of known trends,
1,2-H2 and 1,2-MeH elimination from (tBu3SiNH)(tBu3-
SiN)2WH (1-H) and (tBu3SiNH)(tBu3SiN)2WCH3 (1-CH3),
respectively, are not observable according to Scheme 4.11,12,22
In the case of 1-H, the addition of pyridine permits
exchange of the amide hydrogen and hydride positions with
deuterium from D2 (Scheme 5, eq 10). Unfortunately, since
DISCUSSION
■
Metathetical Routes to (tBu3SiNH)(tBu3SiN)2WR (1-R).
Metathetical procedures employing (tBu3SiNH)(tBu3-
SiN)2WX (1-X) proved complicated due to side reactions
that were not unexpected, but counterproductive nonetheless.
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Scheme 6
Scheme 7
this process is associative in character, according to the
kinetics study, several mechanisms, three of which are
illustrated in Scheme 5 and a less likely one implicated in
Scheme 7, cannot be easily ruled out.
crystallization conditions, and three different species were
identified, two with W−H−K connectivity and one without.
While a discussion of hydride metric parameters is intrinsically
problematic due to a lack of confidence in correctly locating
the position of the hydride, other metrics show the
tris-imido tungsten hydride core to be relatively constant.24
The tungsten−imido bond lengths and core angles among
Solution versus Solid -State Structures of M(tBu3SiN)3-
WH (2-M-H). Solid-state structures of K(tBu3SiN)3WH
(2-K-H) were determined under three separate sets of
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(tBu3SiN)3WHK(OEt2)3 (2-H-K(OEt2)3), [(tBu3SiN)3WH]-
[K(crypt-2.2.2)] (2-H-Kc), and (tBu3SiN)3WHK (2-H-K) are
very similar, despite the separated anion [(tBu3SiN)3WH]
and cation [K(crypt-2.2.2)] pair in 2-H-K. For comparison,
the pyridine in (tBu3SiN)3Wpy (2-py) appears to render
the metal center more electron rich, as its WN distances
are slightly longer, but even this judgment must be tempered
by the ∼0.02 Å difference with respect to the hydrides,
a small factor that might simply reflect added steric
influences.
It is more interesting to speculate on what structure the
hydrides possess in solution. A scale of solvent donicity has
been developed,86 and a brief NMR spectroscopic study of
K(tBu3SiN)3WH (2-K-H) in various media revealed some
correlations, as shown in Table 4. Nondonor and poor donor
in 2-Li-H.87 The larger Na and K substituents may be
coordinated to the hydride and solvent or imide ligands within
t
2-M-H (M = Na, K). Note that the Bu chemical shifts are at δ
1.42 and 1.46 for the Na and K derivatives, respectively,
compared to a δ 1.26 pertaining to 2-Li-H, when taken in C6D6.
The tBu chemical shift differences between Li and Na or K exist
for the halide derivatives M(tBu3SiN)3WX (2-M-X) as well
as the hydrides. These are very large shift differences for the
silimide groups and may reflect differing solution geometries;
alternatively, the data may simply be a consequence of the
greater covalency of lithium in its coordination.
CONCLUSIONS
■
Approaches to the synthesis of (tBu3SiNH)(tBu3SiN)2WX/R
(1-X/R) and M(tBu3SiN)3WH/X/R (2-M-H/X/R) have
been explored herein, including metatheses, insertions, various
halogenations, and deprotonations. None are general, yet each
one is efficient for certain transformations. As expected from
calculations and previous results, the thermal stability of
(tBu3SiNH)(tBu3SiN)2WH/R (1-H/R) with respect to
dihydrogen and hydrocarbon loss is remarkable. The structures
of (tBu3SiN)3Wpy (2-py), (tBu3SiN)3WHK(OEt2)3 (2-H-
K(OEt2)3), [(tBu3SiN)3WH][K(crypt-2.2.2)] (2-H-Kc), (tBu3-
SiN)3WHK (2-H-K, as [2-H]2(μ-K)2), and K(tBu3SiN)3WI
(2-K-I, as [2-I]3(μ-K)3) have been elucidated by X-ray
crystallography, and their tris-imido cores have been found to
be very similar. The reaction of 2-Li-H and MeI provided
products that hint at the formation of an intermediate methane
complex;11,12 this subject will be featured subsequently.
Table 4. Hydride Chemical Shifts (1H NMR) for
K(tBu3SiN)3WH (2-K-H) and [(tBu3SiN)3WH]
[K(crypt-2.2.2)] (2-H-Kc) in Various Solvents at 23 °C
a
compound
solvent
C6D6
solvent donicity
δ(WH)
1JWH (Hz)
2-K-H
2-K-H
2-K-H
2-K-H
2-K-H
2-H-Kc
2-K-H
2-K-H
0.003
0.003
0.026
0.495
0.483
0.515
0.515
0.853
7.20
7.23
313
314
313
304
327
329
329
324
toluene-d8
CD2Cl2
7.27
Et2O-d10
acetone-d6
THF-d8
7.58
9.97
10.06
10.09
10.61
THF-d8
pyridine-d5
a
See ref 86.
solvents afford hydride chemical shifts in the 7.2−7.6 ppm
region, whereas good donors cause a change to 10.0−10.6 ppm.
EXPERIMENTAL SECTION
■
1
General Considerations. All manipulations were performed
using either glovebox or high vacuum line techniques. All glassware
was oven-dried. THF and ether were distilled under nitrogen from
purple sodium benzophenone ketyl and vacuum transferred from the
same prior to use. Hydrocarbon solvents were treated in the same
manner with the addition of 1−2 mL/L tetraglyme. Benzene-d6 and
toluene-d8 were dried over sodium, vacuum transferred, and stored
over activated 4 Å molecular sieves. THF-d8 was dried over sodium
and vacuum transferred from sodium benzophenone ketyl prior to use.
All glassware was base-washed and oven-dried. NMR tubes for sealed
tube experiments were flame-dried under dynamic vacuum prior to
use. Organic reagents and solutions of alkyllithiums were obtained
from Aldrich Chemical. Ethylene, propene, and dihydrogen
(Matheson) were passed through a −78 °C trap prior to use.
Methyl-substituted aryl lithium reagents were prepared by the
transmetalation of aryl iodides with nBuLi. (tBu3SiNH)-
(tBu3SiN)2WH (1-H)42 and potassium benzyl47 were prepared
according to literature procedures. All other chemicals were
commercially available and used as received.
Likewise, the JWH values change from ∼304−314 Hz to 324−
329 Hz in concert with the shift changes. When crypt-2.2.2 is
incorporated in the synthesis described by eq 11, the hydride
shift in THF-d8 appears to be that of the corresponding anion,
[(tBu3SiN)3WH]−, because it is the same as 2-K-H taken in
the same solvent. The shift is at δ 10.06, with a 1JWH of 329 Hz
and a corresponding ν(WH) = 1925 cm−1.
Since the structural study of 2-H-Kc shows separation of
[K(crypt-2.2.2] from the tungsten anion, the chemical shift and
IR stretching values may signify structural differences depend-
ing on solvation and alkali metal ion. Specifically, in strong
donors the spectral parameters are likely to be those of the free
anion, [(tBu3SiN)3WH]−. While shifts and WH coupling
pertaining to the Na and K hydrides are quite similar, those of
Li(tBu3SiN)3WH (2-Li-H) show greater similarity to the
neutral hydride, (tBu3SiNH) (tBu3SiN)2WH (1-H), prompt-
ing speculation that the lithium is coordinated by the nitrogens
Figure 5. Plausible solution structures for M(tBu3SiN)3WH (2-M-H) rationalizing apparent NMR spectroscopic differences between M = Li and
M = Na, K.
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1H, 13C{1H}, and 2H{1H} NMR spectra were obtained using Varian
XL-200, XL-400, and Unity-500 spectrometers. Chemical shifts are
reported relative to benzene-d6 (1H, δ 7.15; 13C, δ 128.00) or THF-d8
(1H, δ 3.58; 13C, δ 67.57). Infrared spectra were recorded on a Nicolet
Impact 410 spectrophotometer interfaced to a Gateway PC.
Combustion analyses were conducted by Oneida Research Services
(Whitesboro, NY, USA) or Robertson Microlit Laboratories
(Madison, NJ, USA). The Center for High Energy Synchrotron
Studies (CHESS) at Cornell University was used for the X-ray
crystallographic study of (tBu3SiN)3Wpy (2-py).
argon counterflow at 0 °C. The yellow solution was allowed to stir 2 h
at 0 °C and 12 h at 23 °C. After removal of volatile materials and
filtration in pentane, the solution volume was reduced to 3 mL and
cooled to −78 °C, precipitating a light yellow powder, collected by
1
filtration. H and 13C{1H} NMR spectroscopy indicated a mixture of
(tBu3SiNH)(tBu3SiN)2WPh (1-Ph, 70%) and Li(tBu3SiN)3WPh (2-
Li-Ph, 30%).
6. (tBu3SiNH)(tBu3SiN)2WCl (1-Cl) + LiC6H4-4-Me. A solution
consisting of 1-Cl (227 mg, 2.64 × 10−4 mol) and LiC6H4-4-Me
(41 mg, 3.96 × 10−4 mol, 1.5 equiv) in Et2O was stirred at 0 °C for 1 h
followed by 12 h at 23 °C. After removal of volatile materials and
Procedures. 1. (tBu3SiNH)(tBu3SiN)2WCl (1-Cl). To a stirred
solution of 1-H (3.36 g, 4.07 mmol) in 50 mL of hexane was vacuum
transferred 2.5 mL of CCl4 (0.026 mol, 6 equiv). The reaction
continued to stir for 10 h at 23 °C, and the original colorless solution
became yellow. After removal of all volatiles and filtration in hexane,
the solution volume was reduced to 20 mL and cooled to −78 °C,
producing 2.60 g of 1-Cl as yellow microcrystals that were collected by
filtration (74%). IR (Nujol, cm−1): 3261(m), 3245(m), 1468(s),
1387(s), 1131(s), 1041(s), 1008(s), 935(s), 841(s), 819(s), 622(s),
580. Anal. Calcd for C36H82N3ClSi3W: C, 50.24; H, 9.60; N, 4.88.
Found: C, 50.54; H, 10.11; N, 4.66.
1
filtration in hexanes, H and 13C{1H} NMR spectroscopy indicated a
mixture of (tBu3SiNH)(tBu3SiN)2W(C6H4-4-Me) (1-C6H4-4-Me,
50%), Li(tBu3SiN)3W(C6H4-4-Me) (2-Li-C6H4-4-Me, 18%), and
Li(tBu3SiN)3WH (2-Li-H, 32%).
7. (tBu3SiNH)(tBu3SiN)2WI (1-I) + LiC6H4-3-Me. A solution
consisting of 1-I (403 mg, 4.23 × 10−4 mol) and LiC6H4-3-Me
(65 mg, 6.62 × 10−4 mol, 1.6 equiv) in Et2O was stirred at 0 °C for 1 h
followed by 3 h at 23 °C. After removal of volatile materials and
filtration in hexanes, the solution volume was reduced to 3 mL and
cooled to −78 °C, precipitating 130 mg of a light yellow powder,
2. (tBu3SiNH)(tBu3SiN)2WBr (1-Br). 1-H (300 mg, 3.63 × 10−4
mol) and CBr4 (126 mg, 3.80 × 10−4 mol, 1.05 equiv) were combined
in a flask, 15 mL of benzene was added, and the solution was stirred
for 12 h at 23 °C. During this period, the original colorless solution
slowly became pale yellow. After removal of all the volatiles, the
remaining material was sublimed at 100 °C (10−3−10−4 Torr, 6 h).
The solids were dissolved in hexanes, the volume was reduced to 3
mL, and the solution was cooled to −78 °C, producing 220 mg of
yellow microcrystalline 1-Br (67%), collected by filtration. IR (Nujol,
cm−1): 3255(w), 3244(w), 1464(s), 1386(s), 1367(m), 1131(s),
1040(s), 1008(s), 935(m), 841(s), 820(s), 622(s), 580(s). Anal. Calcd
for C36H82N3BrSi3W: C, 47.47; H, 9.13; N, 4.64. Found: C, 47.27; H,
9.21; N, 4.70.
1
which was collected by filtration. H and 13C{1H} NMR spectroscopy
indicated a mixture of (tBu3SiNH)(tBu3SiN)2W(C6H4-3-Me) (1-
C6H4-3-Me, 51%), Li(tBu3SiN)3W(C6H4-3-Me) (2-Li-C6H4-3-Me,
18%), and Li(tBu3SiN)3WH (2-Li-H, 31%).
8. (tBu3SiNH)(tBu3SiN)2WI (1-I) + KCH2Ph. A solution of KBn
(138 mg, 1.060 × 10−3 mol, 2.07 equiv) in 8 mL of THF was slowly
added to a stirring solution of 1-I (506 mg, 5.31 × 10−4 mol) in 20 mL
of Et2O and allowed to react for 10 min, over which time a precipitate
1
(KI) was observed to form. After removal of all volatile materials, H
and 13C{1H} NMR analysis indicated a mixture consisting of 2-H-K
(28%), 1-Bn (40%), and unidentified tungsten-containing products.
9. (tBu3SiNH)(tBu3SiN)2WEt (1-Et). Ethylene (610 Torr in a
calibrated 283.1 mL gas bulb, 9.39 mmol, 16 equiv) was passed
through a trap at −78 °C and condensed into a glass reaction vessel
containing 1-H (480 mg, 5.80 × 10−4 mol) and 25 mL of hexanes. The
reaction was stirred at 60 °C for 18 h followed by removal of all
volatiles. The remaining material was slurried in 4 mL of THF and
cooled to −78 °C, and the resulting white powder of 1-Et was
collected by filtration (400, 81%). IR (Nujol, cm−1): 3243(w),
3234(w), 1464(s), 1385(s), 1365(s), 1143(s), 1130(s), 1048(s),
1010(s), 934(m), 848(s), 820(s), 620(s), 583(s). Anal. Calcd for
C38H87N3Si3W: C, 53.43; H, 10.27; N, 4.92. Found: C, 53.17; H,
10.10; N, 5.35.
3. (tBu3SiNH)(tBu3SiN)2WI (1-I). 1-H (3.56 g, 4.31 × 10−3 mol)
and CI4 (2.46 g, 4.73 × 10−3 mol, 1.1 equiv) were combined in a flask,
and 40 mL of benzene was added. The reaction mixture was stirred for
20 h at 23 °C, and the orange solution did not perceptively change
color. A small amount of brown, insoluble solid was filtered, and the
reaction mixture was sublimed at 100 °C for 1 h to remove unreacted
CI4 and byproduct HCI3. The remaining material was dissolved in
hexanes, the volume reduced to 25 mL, and the solution cooled to
−78 °C, yielding 2.65 g of a yellow precipitate. A second crop of 1-I of
420 mg gave a total yield of 75%. IR (Nujol, cm−1): 3241(m, NH),
1468(s), 1386(s), 1365(m), 1131(s), 1040(s), 1008(s), 934(m),
890(w), 841(s), 819(s), 622(s), 579(s). Anal. Calcd for
C36H82N3ISi3W: C, 45.42; H, 8.68; N, 4.41. Found: C, 44.70; H,
9.40; N, 4.41.
10. (tBu3SiNH)(tBu3SiN)2WnPr (1-nPr). Propene (560 Torr in a
calibrated 283.1 mL gas bulb, 16 equiv) was passed through a trap at
−78 °C and condensed into a glass reaction vessel containing 1-H
(490 mg, 5.93 × 10−4 mol) and 30 mL of hexanes. The reaction was
stirred at 60 °C for 48 h followed by removal of all volatiles. The
remaining material was slurried in 4 mL of THF and cooled to
−45 °C, and the resulting white powder was collected by filtration to
yield 350 mg of 1-nPr (68%). IR (Nujol, cm−1): 3239(m), 1469(s),
1386(s), 1364(m), 1185(w), 1158(m), 1133(s), 1050(s), 1009(s),
934(m), 848(s), 820(s), 779(w), 665(w), 621(s), 581(s). Anal. Calcd
for C39H89N3Si3W: C, 53.95; H, 10.33; N, 4.84. Found: C, 54.09; H,
10.32; N, 4.84.
4. (tBu3SiNH)(tBu3SiN)2WCH3 (1-CH3). a. 1-CH3. To a stirred
solution of 1-Cl (380 mg, 4.42 × 10−4 mol) in diethyl ether was
transferred 0.33 mL of CH3Li (1.5 M in OEt2, 1.1 equiv) via syringe
under argon counterflow at 0 °C. The yellow solution was stirred for
2 h at 0 °C, then for 4 h at 23 °C, and the color faded. After removal of
all volatiles and filtration in pentane, the solution volume was reduced
to 3 mL and cooled to −78 °C, yielding 0.188 g (51%) of 1-Me, which
was collected as a white powder by filtration. IR (Nujol, cm−1): 3249(m,
NH), 3241(w), 1465(s), 1385(s), 1364(m), 1184(w), 1147(s), 1129(s),
1050(s), 1009(s), 935(s), 850(s), 820(s), 621(s), 583(s). Anal. Calcd
for C37H85N3Si3W: C, 52.89; H, 10.20; N, 5.00. Found: C, 52.55; H,
10.30; N, 4.80. b. 1-NH-CD3 and thermolysis. 1-NH-CD3 was
11. (tBu3SiNH)(tBu3SiN)2W-E-CH2CHCHMe (1-E-CH2CH
CHMe). To a glass reaction vessel containing 1-H (700 mg, 8.47 ×
10−4 mol) in 15 mL of hexanes was vacuum transferred 2.3 mL of 1,3-
butadiene (2.77 × 10−2 mol, 33 equiv). The reaction was stirred at
90 °C for 21 h followed by removal of all volatiles. Analysis of the
reaction mixture by 1H NMR spectroscopy revealed complete
conversion to 1-E-CH2CHCHMe. The residue was dissolved in
toluene, its volume reduced to 4 mL, and the solution cooled to
−78 °C to yield 125 mg of white powder (17%). IR (Nujol, cm−1):
3231(m), 1479(s), 1469(s), 1386(s), 1364(m), 1138(s), 1080(w),
1044(s), 1009(s), 965(m), 935(m), 845(s), 820(s), 665(w), 622(s),
580(s). Anal. Calcd for C40H89N3Si3W: C, 54.58; H, 10.19; N, 4.77.
Found: C, 56.15; H, 10.25; N, 4.62.
2
similarly obtained by treatment of 1-Cl with LiCD3. H NMR analysis
revealed no D-incorporation at the amide position, and thermolysis of a
C6H6 solution of 1-NH-CD3 for 1 week at 200 °C in a sealed NMR
tube revealed no change (2H NMR spectroscopy). IR (Nujol, cm−1):
3250(m), 3242(w), 2215(w), 2210(w), 1476(s), 1385(s), 1364(s),
1148(s), 1130(s), 1050(s), 1010(s), 936(s), 849(s), 820(s), 620(s),
583(s).
5. (tBu3SiNH)(tBu3SiN)2WCl (1-Cl) + PhLi. To a stirred solution
of 1-Cl (490 mg, 5.69 × 10−4 mol) in ether was transferred 0.41 mL of
PhLi (1.8 M in cyclohexane/diethyl ether, 1.3 equiv) via syringe under
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12. (tBu3SiNH)(tBu3SiN)2WCHCHtBu (1-CHCHtBu). 1-H
935(m), 820(s), 621(s). Anal. Calcd for C36H82N3LiSi3W: C, 51.96;
H, 9.93; N, 5.05. Found: C, 51.74; H, 10.04; N, 4.81.
t
(0.698 g, 8.45 × 10−4 mol) and BuCCH (1.1 mL, 8.9 × 10−3 mol,
18. Na(tBu3SiN)3WH (2-Na-H). 1-H (510 mg, 6.17 × 10−4 mol)
and NaH (165 mg, 6.88 × 10−3 mol, 11 equiv) were loaded into a
bomb and stirred in 20 mL of THF for 24 h at 100 °C. After removal
of the volatile materials, the residue was triturated with hexanes (3 ×
5 mL), taken up in diethyl ether, and filtered. Reducing the solution
volume to 3 mL and cooling to −78 °C precipitated 2-NaH, which was
collected by filtration to yield 170 mg (28%). 1H NMR analysis
indicates 1 equiv of THF isolated per equiv of 2-Na-H. IR (Nujol,
cm−1): 1855(m, br, WH), 1460(s), 1377(s), 1365(s), 1305(w),
1160(m), 1055(s), 1023(s), 1006(s), 935(m), 890(w), 819(s),
722(w), 665(m), 613(s), 583(s). Anal. Calcd for C36H82N3NaSi3W:
C, 50.98; H, 9.74; N, 4.95. Found: C, 50.62; H, 10.04; N, 4.68.
19. K(tBu3SiN)3WH (2-K-H). a. To a stirred solution of 1-I (700 mg,
7.35 × 10−4 mol) in 20 mL of THF was transferred a KBz solution
(240 mg in 4 mL of THF, 1.84 × 10−3 mol, 2.5 equiv) via syringe
over the course of 10 min under argon counterflow at 0 °C. The
reaction was stirred for 15 min, and a precipitate was observed (KI).
After removal of all volatiles, the remaining material was sublimed at
90 °C under active vacuum. Subsequent dissolution in benzene,
filtration, and collection in hexanes yielded 405 mg of white 2-K-H
(64%). b. NMR tube scale. The preceding experiment was repeated
on the NMR tube scale. The quantitative formation of 2-KH as the
only tungsten-containing compound was confirmed along with the
formation of 1 molar equiv of bibenzyl as organic side product. c. 1-H
(2.00 g, 2.42 × 10−3 mol) and KH (388 mg, 9.67 × 10−3 mol, 4 equiv)
were combined in a flask and stirred in 50 mL of THF for 48 h at 23 °C,
over which time the originally colorless solution became light red. After
removal of the volatiles in vacuo, the remaining material was triturated
with hexanes (3 × 5 mL), taken up in diethyl ether, and filtered to
remove excess KH. The solvent volume was reduced to
8 mL, and the solution cooled to −78 °C, producing 1.64 g (79%) of
colorless, microcrystalline 2-KH, which was collected by filtration as a
THF-free white powder after being subjected to vacuum for 24 h. IR
(Nujol, cm−1): 1858(m, WH), 1465(s), 1384(s), 1365(m), 1150(w),
1036(s), 1006(s), 935(m), 820(s), 621(s), 579(s). Anal. Calcd for
C36H82N3Si3KW: C, 50.03; H, 9.56; N, 4.86. Found: C, 50.19; H, 10.03;
N, 4.69.
10 equiv) were stirred for 6 d at 105 °C in 20 mL of benzene, over
which time the originally colorless solution changed to yellow. A
flocculent, white solid was also produced, presumably acetylene
oligomers. Following filtration the solvent was replaced with 4 mL of
pentane. Cooling to −78 °C and filtering yielded 0.225 g (30%) of
yellow 1-CHCHtBu. IR (Nujol, cm−1): 3247(m, NH), 1568(w,
CC), 1479(s), 1468(s), 1387(s), 1363(m), 1128(s), 1042(s), 1009(s),
979(w) 934(m), 844(s), 821(s), 620(s), 580(s). Anal. Calcd for
C36H93N3Si3W: C, 55.54; H, 10.32; N, 4.63. Found: C, 55.64; H,
10.55; N, 4.45.
13. (tBu3SiNH)(tBu3SiN)2WNC(H)C6H4CH3 (1-NC(H)tol). 1-H
(0.498 g, 6.03 × 10−4 mol) and p-tolunitrile (0.180 g, 1.54 × 10−3 mol,
2.5 equiv) were stirred for 24 h at 100 °C in 20 mL of benzene, over
which time the originally colorless solution changed to bright orange.
Following filtration the solvent was replaced with 4 mL of hexane.
Cooling to −78 °C and filtering yielded 0.245 g of orange 1-N
C(H)C6H4CH3. A second crop yielded a further 77 mg for an overall
yield of 57%. IR (Nujol, cm−1): 3280(w), 1662(s), 1604(m), 1468(s),
1386(s), 1361(m), 1304(w), 1292(w), 1173(m), 1136(s), 1114(m),
1047(s), 1008(s), 960(w), 935(m), 922(m), 821(s), 753(w), 689(m),
665(s), 619(s), 579(s). Anal. Calcd for C44H89N4Si3W: C, 56.08; H,
9.52; N, 5.95. Found: C, 56.39; H, 9.22; N, 5.87.
14. (tBu3SiNH)(tBu3SiN)2WCHNtBu (1-CHNtBu). To a stirred
benzene solution of tert-butylisocyanide (0.150 mL, 1.33 × 10−4 mol,
2.2 equiv) was added a benzene solution of 1-H (0.495 g, 5.99 × 10−4
mol). The resulting solution was allowed to stir for 1.5 h at 23 °C, and
the original colorless solution turned light yellow. After removal of all
volatiles and filtration in hexane, the solvent was replaced with 4 mL of
THF, cooled to −78 °C, and filtered to yield 0.350 g of yellow 1-
CHNtBu (62%). IR (Nujol, cm−1): 3248(m, NH), 1595(m),
1559(m), 1469(s), 1388(s), 1363(s), 1276(w), 1226(w), 1195(m),
1134(s), 1041(s), 1009(s), 936(s), 895(w), 855(s), 843(s), 821(s),
733(m), 620(s), 581(s). Anal. Calcd for C41H92N4Si3W: C, 54.16; H,
10.20; N, 6.16. Found: C, 54.30; H, 10.47; N, 6.08.
15. (tBu3SiNH)(tBu3SiN)2WCN (1-CN). A hexane solution of 1-
CHNtBu (215 mg, 2.36 × 10−4 mol) was heated to 100 °C for 3 d.
After removal of the volatiles, the remaining material was taken up in
2 mL of hexanes and cooled to −78 °C, which precipitated 97 mg
(48%) of yellow, microcrystalline 1-CN, which was collected by
filtration. An NMR tube scale reaction verified isobutane as an organic
coproduct. IR (Nujol, cm−1): 3241(w), 3228(w), 2146(w), 1475(s),
1387(s), 1366(m), 1125(s), 1038(s), 1008(s), 934(m), 840(s),
819(s), 622(s), 578(s). Anal. Calcd for C37H82N4Si3W: C, 52.21; H,
9.71; N, 6.58. Found: C, 51.91; H, 9.53; N, 6.30.
19. [(tBu3SiN)3WH][K(crypt-2.2.2)] (2-H-Kc). 2-KH (700 mg,
8.10 × 10−4 mol) in 15 mL of Et2O was exposed to crypt-2.2.2
(310 mg, 8.23 × 10−4 mol, 1.02 equiv) for 1 h at 23 °C. The solution
was filtered, reduced to 4 mL, and cooled to −78 °C, producing 0.575
mg of white 2-H-Kc, which was collected by filtration as a white
powder. Another crop gave 87 mg for a total yield of 66%. IR
(Nujol, cm−1): 1925(m, br, WH), 1466(s), 1382(s), 1360(s), 1354(s),
1298(m), 1261(s), 1238(w), 1174(w), 1134(s), 1106(s), 1060(s),
1011(s), 952(s), 933(s), 818(s), 754(w), 613(s). Anal. Calcd for
C54H118O6N5Si3KW: C, 52.27; H, 9.59; N, 5.46. Found: C, 52.05; H,
9.25; N, 5.56.
16. (tBu3SiN)3Wpy (2-py). A glass reaction vessel was charged with
1-H (2.00 g, 2.42 × 10−3 mol) followed by 40 mL of pyridine, the
solution was stirred at 145 °C for a total of 36 h, and it was periodically
degassed to remove H2 as it changed from colorless to orange. All
volatiles were removed, and the material was triturated with hexanes
(10 × 5 mL) to remove excess pyridine. Dissolving the material in
13 mL of hexanes and cooling to −78 °C produced 1.23 g of orange 2-
py (56%) after collection by filtration. IR (Nujol, cm−1): 1612(s),
1468(s), 1384(s), 1362(m), 1239(w), 1217(w), 1185(w), 1160(m),
1041(s), 1009(s), 934(s), 819(s), 756(s), 690(m), 656(w), 619(s),
580(s). Anal. Calcd for C41H86N4Si3W: C, 54.52; H, 9.60; N, 6.20.
Found: C, 54.81; H, 9.91; N, 6.14. 2-py-d5 was analogously obtained.
17. Li(tBu3SiN)3WH (2-Li-H). To a vessel loaded with 1-H (1.00 g,
1.21 × 10−3 mol) and neoPeLi (104 mg, 1.33 × 10−3 mol, 1.1 equiv)
was transferred 25 mL of benzene. The solution was heated at 70 °C
for 6 h, followed by removal of the volatiles. The solids were taken up
in 20 mL of hexanes and filtered, and the solution volume was reduced
to 3 mL. After addition of a small amount of THF, the solution was
cooled to −78 °C for 1 h, and 2-Li-H was collected by filtration as a
20. K(tBu3SiN)3WCH3 (2-K-Me). a. 1-Me (460 mg, 5.47 × 10−4
mol) and potassium hydride (45 mg, 1.12 × 10−3 mol, 2 equiv) were
combined in a flask with 18 mL of THF and heated to 60 °C for 36 h.
After removal of the volatiles in vacuo, the remaining material was
triturated with hexanes (3 × 5 mL), taken up in diethyl ether, and
filtered to remove excess KH. The solvent volume was reduced to
3 mL, and the solution cooled to −78 °C, depositing 240 mg (50%) of
2-K-Me, which was collected by filtration as a white powder. IR (Nujol,
cm−1): 1479(s), 1384(s), 1183(w), 1162(w), 1039(s), 1007(s), 932(m),
817(s), 617(s), 585(s). Anal. Calcd for C37H84N3Si3KW: C, 50.60; H,
9.64; N,4.78. Found: C, 49.88; H, 9.57; N, 4.33. b. K(tBu3SiN)3WCD3
(2-K-CD3). Utilizing 1-CD3 (111 mg, 1.32 × 10−4 mol) and KH (10 mg,
2.49 × 10−3 mol, 1.9 equiv), the above procedure produced 41 mg (35%)
of 2-KCD3. IR (Nujol, cm−1): 2213(w), 2203(w), 1456(s), 1365(m),
1157(w), 1047(s), 1034(s), 1015(m), 1006(s), 931(w), 818(s), 614(s).
21. K(tBu3SiN)3WCl (2-K-Cl). 1-Cl (438 mg, 5.09 × 10−4 mol) and
potassium hydride (82 mg, 2.04 × 10‑3 mol, 4 equiv) were combined
in a flask with 15 mL of THF and heated at 60 °C for 24 h as the
colorless solution became light yellow. After removal of the volatiles in
vacuo, the remaining material was triturated with hexanes (3 × 5 mL),
1
colorless precipitate (0.190 g, 17%). A H NMR spectrum in C6D6
indicated 1 equiv of THF per 2-Li-H. An analogous reaction that was
worked up in (Me3Si)2O yielded THF-free 2-Li-H in 21% yield. IR
(Nujol, cm−1): 1907(m), 1467(s), 1388(m), 1151(w), 1035(s), 1007(s),
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taken up in diethyl ether, and filtered to remove excess KH. The
solvent volume was reduced to 5 mL, and the solution cooled to
−40 °C, depositing large cubes of yellow 2-KCl. The material was
collected by filtration, yielding 245 mg (54%) of 2-K-Cl as a Et2O-free
yellow powder after exposure to vacuum for 12 h. IR (Nujol, cm−1):
1469(s), 1384(s), 1362(m), 1165(w), 1089(m), 1048(s), 1010(s),
936(m), 820(s), 621(s), 584(s). Anal. Calcd for C36H81N3ClKSi3W:
C, 48.11; H, 9.08; N, 4.68. Found: C, 47.93; H, 9.21; N, 4.39.
22. K(tBu3SiN)3WI (2-K-I). 1-I (230 mg, 2.42 × 10−4 mol) and KH
(62 mg, 1.55 × 10−3 mol, 6 equiv) were loaded into a bomb and
stirred in 15 mL of THF for 15 h at 60 °C. The initially yellow
solution did not perceptively change color. After removal of the
volatile materials, the remaining material was triturated with hexanes
three times, taken up in diethyl ether, and filtered, removing the excess
KH. Reduction of the solution volume to 2 mL of Et2O, followed by
addition of 2 mL of hexanes, precipitated 2-KI. Cooling to −78 °C and
filtering isolated 147 mg (61%) of 2-KI as a yellow powder after 24 h
under dynamic vacuum. IR (Nujol, cm−1): 1470(s), 1384(s), 1362(m),
1162(w), 1042(s), 1010(s), 935(m), 820(s), 620(s), 582(s). Anal.
Calcd for C36H81N3Si3KIW: C, 43.67; H, 8.25; N, 4.24. Found: C,
42.87; H, 8.56; N, 3.91. Mw(benzene cryoscopy): calcd, 990; found,
997(50).
upon warming from 77 K. The 1H NMR spectra indicated quantitative
formation of 1-CHNMe. Over the course of 24 h, the solution
bleaches as 1-CHNMe degrades, and unidentified compounds
appear.
30. (tBu3SiNH)(tBu3SiN)2WH (1-H) + py ⇄ (tBu3SiN)3Wpy (2-py) +
H2. 2-py (15 mg, 1.7 × 10−5 mol) and H2 (300 Torr at 77 K, ∼1.5 ×
10−4 mol, 8.8 equiv) were heated to 141 °C for 7 days in ∼0.6 mL of
C6D6. The headspace of the NMR tube was estimated to be ∼2.4 mL.
Equilibrium was established after 4 d, and the Keq value was measured
by integrating the resonances attributable to 2-py, 1-H, H2, and py in
the 1H NMR spectrum. A preacquisition delay of 60 s was used due to
the prolonged relaxation time of H2 (T1 = 5.8(6) s). The equilibrium
constant was adjusted for differences in H2 solubility between spectral
observation at 296 and 414 K. This required the temperature
dependence of the Henry’s law constant.57
31. (tBu3SiN)3Wpy (2-py) + D2 (excess). 2-Py (15 mg, 1.7 × 10−5
mol) and D2 (435 Torr at 77 K, ∼3 atm at 403 K) in C6D6 were
1
heated to 180 °C for 2 days. H NMR spectroscopy indicated ∼80%
deuterium incorporation at the hydride and amide sites of product
1-N(D/H)-D/H, ∼80% deuteration of the α-H positions of free
pyridine, H2, and HD. The percent label incorporation did not change
upon subsequent thermolysis. No label incorporation was detected at
the other pyridine sites.
NMR Tube Reactions. General. Flame-dried NMR tubes,
sealed to 14/20 ground glass joints, were charged with metal reagent
(typically 10 mg, ∼1 × 10−5 mol) in the drybox and removed to the
vacuum line on needle valve adapters. The NMR tube was degassed,
and after transfer of deuterated solvent, the volatile reagents were
introduced by vacuum transfer via a calibrated gas bulb at −196 °C.
The tubes were then sealed with a torch. Solid substrates were loaded
with the metal complex followed by solvent transfer on the vacuum
line and flame sealing.
32. (tBu3SiNH)(tBu3SiN)2WEt (1-Et) + KH (excess). 1-Et and
∼5 equiv of KH in THF-d8 were heated at 70 °C for 15 h to give a
colorless solution. 1H and 13C{1H} NMR spectra indicated
quantitative production of K(tBu3SiN)3WEt (2-K-Et) and H2.
33. (tBu3SiNH)(tBu3SiN)2WnPr (1-nPr) + KH (excess). 1-nPr and
∼5 equiv of KH in THF-d8 were heated at 70 °C for 15 h, resulting in
a colorless solution. 1H and 13C{1H} NMR spectra indicated
quantitative production of K(tBu3SiN)3WnPr (2-K-nPr) and H2.
34. (tBu3SiNH)(tBu3SiN)2WBr (1-Br) + KH (excess). 1-Br and
23. (tBu3SiNH)(tBu3SiN)2WCl (1-Cl) + PhCH2K. 1-Cl and 1 equiv
of PhCH2K were loaded into an NMR tube, and THF-d8 was
condensed in at 77 K. Once warmed, the solution turned from orange
(due to dissolved KBz) to light yellow over the course of 1 min. Initial
1H and 13C{1H} NMR spectra indicated the formation of 2-K-Cl and
toluene.
1
∼5 equiv of KH in THF-d8 were heated at 70 °C for 15 h. H and
13C{1H} NMR spectra indicated quantitative production of K-
(tBu3SiN)3WBr (2-K-Br) and H2.
35. Li(tBu3SiN)3WH (2−Li-H) + CCl4 (excess). 2-Li-H and 1 equiv
of CCl4 in C6D6 immediately produced Li(tBu3SiN)3WCl (2-Li-Cl)
24. (tBu3SiNH)(tBu3SiN)2WCl (1-Cl) + 1 equiv of tBuLi. 1-Cl and
and HCCl3 according to an assay by H NMR (C6D6: δ 6.13).
1
1.3 equiv of solid tBuLi were loaded into an NMR tube and heated to
36. Na(tBu3SiN)3WH (2-Na-H) + neoPeCl (excess). 2-Na-H and
1
1
100 °C for 6 h in C6D6. The initial H NMR spectrum (10 min)
7 equiv of neoPeCl in C6D6 were heated to 150 °C for 36 h. H and
13C{1H} NMR spectra indicated quantitative production of Na-
(tBu3SiN)3WCl (2-Na-Cl) and neoPeH.
indicated the presence of only the two reagents. At 40 min the reaction
mixture contained unreacted 1-Cl, 2-Li-H (20% total W), 1-H (10%),
and a 1:1 mixture of isobutylene and isobutane. At 3 h, the 2-Li-H
concentration increased to 40%, and after 6 h the reaction is complete
with 60% 2-Li-H, 10% 1-H, and 30% unreacted 1-Cl.
37. Li(tBu3SiN)3WH (2-Li-H) + CH3I. 2-Li-H and 1 equiv of CH3I in
1
C6D6 were heated to 60 °C for 24 h. H and 13C{1H} NMR spectra
indicated formation of a mixture consisting of 2-Li-I (80%),
(tBu3SiNH)(tBu3SiN)2WCH3 (1-CH3, 12%), and (tBu3SiNH)-
(tBu3SiN)2WI (1-I, 8%).
25. (tBu3SiNH)(tBu3SiN)2WCl (1-Cl) + 2 equiv of tBuLi. 1-Cl and
2 equiv of tBuLi were heated at 100 °C for 6 h in C6D6. After 3 h the
1H NMR spectrum indicated a solution composition of 80% 2-Li-H,
10% 1-Cl, 10% 1-H, and a 1:1 mixture of isobutylene and isobutane.
The final spectrum shows 95% 2-Li-H with 5% 1-H.
Kinetics Procedures: 1-H + Excess Pyridine. Solutions of 1-H
and an appropriate amount of pyridine were prepared in C6D6 in 2 mL
volumetric flasks. Bis(trimethylsilyl) ether (∼0.5 μL) was added as an
internal integration standard. Three samples of 0.6 mL each were
transferred to flame-dried 5 mm NMR tubes joined to 14/20 joints
and attached to needle valves. The tubes were subjected to three
freeze−pump−thaw degas cycles prior to flame sealing under vacuum.
The three NMR tubes were simultaneously submerged in a 141.0 °C
polyethylene glycol bath with a Tamson immersion circulator. The
temperature was stable to ±0.3 °C. The rates of disappearance were
monitored measuring the integrated intensity of the hydride resonance
at selected time intervals. All runs were monitored for 3−4 half-lives to
determine the approach-to-equilibrium process; 2−3 half-lives were
assessed as being representative of the forward rate process. Rates and
uncertainties were obtained from nonlinear, nonweighted least-squares
fitting to the exponential form of the rate expression, averaged for the
three simultaneous runs.
t
26. (tBu3SiNH)(tBu3SiN)2WH (1-H) + 1 equiv of BuLi. 1-H and
1 equiv of tBuLi were heated at 100 °C in C6D6 for 6 h, producing 2-
LiH and isobutane.
27. (tBu3SiNH)(tBu3SiN)2WCH2 Pe (1-CH2 Pe). 1-H and 10 equiv
c
c
1
of methylenecyclopentane were heated at 150 °C for 3 days. The H
and 13C{1H} spectra revealed loss of 1-H and essentially one new
c
product (∼95%), consistent with the formation of 1-CH2 Pe, but its
alkyl resonances were obscured by the excess reagent. Over the course
of the reaction, resonances consistent with the formation of 1-
methylcyclopentene36 were observed.
28. (tBu3SiNH)(tBu3SiN)2W-E-CHCHMe (1-E-CHCHMe). 1-H
and 10 equiv of MeCCH were combined with C6D6 and sealed in an
NMR tube. Upon warming to 23 °C, a flocculent dark purple solid was
immediately produced and assumed to be propyne oligomers. The
initial spectrum indicated the presence of both reagents, so the mixture
Single-Crystal X-ray Diffraction Studies. 38. (tBu3-
SiN)3Wpy (2-py). An orange needle of 2-py, obtained by slow
evaporation of a saturated hexane solution, was cut to 0.2 ×
0.15 × 0.1 mm, mounted, and sealed in a glass capillary for data
collection. The data were collected at the Cornell High Energy
Synchrotron Source (CHESS). The X-ray wavelength was 0.91000 Å,
was heated at 70 °C for 6 d. The H and 13C{1H} NMR spectra
1
indicated quantitative formation of 1-CHCHMe in an E:Z ratio of
8:1. No effort was made to shield this reaction from light.
29. (tBu3SiNH)(tBu3SiN)2WCHNMe (1-CHNMe). 1-H and
1 equiv of MeNC in C6D6 immediately produced a purple solution
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Organometallics
Article
the crystal to detector distance was set to 42 mm, and a 2048 × 2048
pixel charge-coupled device was used to record the diffraction data.
Data were collected as 5 s, 10° rotations, with a total of 360° covered.
The first frame was indexed using the program DENZO,88 yielding an
orthorhombic crystal system. The data were indexed using DENZO
and scaled together with SCALEPACK.88 The structure was solved
(SHELXS)89 by direct methods and refined by full-matrix least-squares
on F2 using anisotropic thermal parameters for all non-hydrogen
atoms. Hydrogen atoms were introduced geometrically. A total of
9504 symmetry-independent reflections were collected, and 9123 were
greater than 2σ(I). A semiempirical absorption correction from
solution, was loaded into a glass capillary and placed on a Siemens
SMART CCD area detector system (see Table 2). The data were
subsequently processed with the Bruker SAINT program to yield 22
565 reflections, of which 17 259 were symmetry independent (Rint
=
0.0797) and 8486 were greater than 2σ(I). The structure was solved by
direct methods (SHELXS),89 completed by subsequent difference
Fourier syntheses, and refined by full-matrix least-squares procedures
(SHELXL).89 The refinement utilized w−1 = σ2(Fo ) + (0.1000p)2 +
2
2
0.0000p, where p = (Fo + 2Fc2)/3. All non-hydrogen atoms were
refined with anisotropic displacement parameters, and hydrogen atoms
were included at calculated positions. Constraints were applied to the
t
equivalents was applied, and the refinement utilized w−1 = σ2(Fo ) +
2
geometries of the Bu3Si fragments such that chemically equivalent
(0.1502p)2 + 23.7640p, where p = (Fo + 2Fc2)/3.
2
inter- and intra-atomic distances were constrained to equal the same
least-squares variables (e.g., all d(SiCq) are equivalent; all d(CqC) are
equivalent, etc.). In addition to the trimer, a diffusely formed and
positionally disordered small molecule was located near the center of
symmetry. This was treated and refined as three carbon atoms per
asymmetric unit.
39. (tBu3SiN)3WHK(OEt2)3 (2-H-K(OEt2)3. A colorless crystal
(0.4 × 0.25 × 0.1 mm) of 2-K-H, obtained by slow evaporation of a
saturated diethyl ether solution at −23 °C, was immersed in
polyisobutylene, extracted out with a glass fiber, placed on the
goniometer head under a 165 K nitrogen stream, and centered on a
Siemens SMART CCD area detector system (see Table 2).
Preliminary diffraction data revealed a monoclinic crystal system,
and a hemisphere routine was used for data collection. The data were
processed with the Bruker SAINT program to yield 35 914 reflections,
of which 13 553 were symmetry independent (Rint = 0.0486) and 8560
were greater than 2σ(I). The data were corrected for absorption with
ASSOCIATED CONTENT
■
S
* Supporting Information
CIF files for 2-py, 2-H-K(OEt2)3, 2-H-Kc, 2-K-H, and 2-K-I.
This material is available free of charge via the Internet at
http://pubs.acs.org.
SADABS, and the refinement utilized w−1 = σ2(Fo ) + (0.1000p)2 +
2
0.0000p, where p = (Fo2 + 2Fc2)/3. The structure was solved by direct
methods (SHELXS),89 completed by subsequent difference Fourier
syntheses, and refined by full-matrix least-squares procedures
(SHELXL).89 After an initial refinement with all non-hydrogen
atoms treated anisotropically, the difference Fourier map exhibited a
maximum with reasonable geometric parameters for a bridging
hydride. This atom subsequently underwent successful isotropic
refinement.
AUTHOR INFORMATION
■
Corresponding Author
*Fax: 607 255 4173. E-mail: ptw2@cornell.edu.
Biography
40. [(tBu3SiN)3WH][K(crypt-2.2.2)] (2-H-Kc). A colorless crystal
(0.5 × 0.23 × 0.25 mm) of 2-H-Kc, obtained by slow evaporation of a
saturated diethyl ether solution, was loaded into a glass capillary tube,
sealed, and placed on a Siemens SMART CCD area detector system
(see Table 2). A hemisphere routine35 was used for data collection.
The model includes one-half molecule of diethyl ether per asymmetric
unit, located on the center of symmetry. The data were processed with
the Bruker SAINT program to yield 21 561 reflections, of which 14
926 were symmetry independent (Rint = 0.0324) and 8807 were
greater than 2σ(I). The data were corrected for absorption by
SADABS, and the refinement utilized w−1 = σ2(Fo ) + (0.0668p)2 +
2
6.0095p, where p = (Fo2 + 2Fc2)/3. The structure was solved by direct
methods (SHELXS),89 completed by subsequent difference Fourier
syntheses, and refined by full-matrix least-squares procedures
(SHELXL).89 After an initial refinement with all non-hydrogen
atoms treated anisotropically, the difference Fourier map exhibited a
maximum with reasonable geometric parameters for a bridging
hydride. This atom subsequently underwent successful isotropic
refinement.
Photo provided by Peter T. Wolczanski.
Peter T. Wolczanski obtained his B.S. in Chemistry at the Massachusetts
Institute of Technology in 1976. There he helped Prof. Mark S.
Wrighton initiate studies on the photoelectrolysis of H2O with TiO2
and SrTiO3 photoelectrodes. Despite a mediocre GPA, his under-
graduate research and some temperance led to matriculation at the
California Institute of Technology, where he was a Fluor Fellow in Prof.
John E. Bercaw's group. Investigation of zirconium hydrides and the
reduction of CO and related molecules ensued, leading to his Ph.D. in
1981, and honors as a McKoy Award winner. After a 2 month
postdoctoral stint with Dr. William P. Schaefer at Caltech, designed to
permit participation in one last backpacking trip, he became an Assistant
Professor at Cornell University.
41. K(tBu3SiN)3WH (2-K-H). A colorless crystal (0.6 × 0.5 ×
0.4 mm) of 2-KH, obtained by slow evaporation of a saturated
benzene solution, was loaded in a glass capillary and placed on a
Siemens SMART CCD area detector system (see Table 2). The data
were subsequently processed with the Bruker SAINT program to yield
13 041 reflections, of which 9148 were symmetry independent (Rint
=
0.0356) and 7838 were greater than 2σ(I). The data were corrected for
absorption with SADABS, and the refinement utilized w−1 = σ2(Fo ) +
2
(0.1034p)2 + 5.9010p, where p = (Fo + 2Fc2)/3. The structure was
2
solved by direct methods (SHELXS),89 completed by subsequent
difference Fourier syntheses, and refined by full-matrix least-squares
procedures (SHELXL).89 After an initial refinement with all non-
hydrogen atoms treated anisotropically, the difference Fourier map
exhibited a maximum with reasonable geometric parameters for a
bridging hydride. This atom subsequently underwent successful
isotropic refinement.
Professor Wolczanski's research interests have included the synthesis
and reactivity of early-transition-metal complexes with small
molecules, such as dioxygen, carbon monoxide, carbon dioxide,
methane, and hydrocarbons, and the generation of solid state and
polymeric inorganic materials from molecular precursors. Studies
42. K(tBu3SiN)3WI (2-K-I). A light yellow crystal (0.4 × 0.3 ×
0.2 mm) of 2-K-I, obtained by slow evaporation of a saturated hexane
6559
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Article
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continue to emphasize the reactivity of low-coordinate molecules in
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in an effort to induce C-C bond forming processes and broaden their
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46, 5580−5582. (b) Hoyt, H. M.; Michael, F. E.; Bergman, R. G. J. Am.
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Professor Wolczanski is an Alfred P. Sloan Fellow, an American
Academy of Arts & Sciences Fellow, winner of the 2011 ACS Award in
Organometallic Chemistry, and the George W. & Grace L. Todd
Professor of Chemistry & Chemical Biology at Cornell. He was the
chair of the Organometallics Gordon Research Conference in 2002
and has served on the Organometallics and Inorganic Chemistry
advisory boards.
He married Elizabeth A. Wood in June of 1993, and lives with her,
their 14.6 year old son Alex, and 12.5 year old daughter Grace in a
wooded area, where they fight a never-ending battle against the evil
forces of nature (i.e., deer & weeds). Occasionally he escapes to the
golf course, thereby inducing further stress in this ulterior quest for
perfection. There he also attempts to teach his children while fighting
the urge to strangle them as they step in his line while 4-putting most
greens. Usually this is followed by an attack on his wine cellar in order
to lower his score. In the winter he can often be found in some frigid
building rooting on his hockey-playing children or helping coach
Grace while attempting to avoid pneumonia.
ACKNOWLEDGMENTS
■
P.T.W. thanks the NSF (CHE-9528914, CHE-1055505) and
Cornell University for financial support.
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