Steering S-H and N-H bond activation by a stable N-heterocyclic silylene: Different addition of H2S, NH3, and organoamines on a Silicon(II) ligand versus its Si(II)→Ni(CO)3 complex

Article abstract of DOI:10.1021/ja910305p

The strikingly different behavior of the ylide-like, N-heterocyclic silylene LSI: (5: L = CH[(C=CH₂)CMe(NAr)₂]; Ar = 2,6- ⁱPrC₆H₃) versus its LSi→Ni(CO)₃ complex 13 to activate E-H bonds (E = S, N) of small molecules is reported. Remarkably, conversion of 5 with hydrogen sulfide leads exclusively to the first isolable silathioformamide, L′Si(=S)H (16: L′ ) CH[C(Me)NAr]2; Ar ) 2,6-ⁱPrC₆H₃) with a donorsupported Si=S double bond and four-coordinate silicon. The latter result demonstrates the unusual ambivalent reactivity of 5 by combining two modes of reactivity involving S-H bond activation and subsequent 1,4- and 1,1-addition, respectively. In addition, 5 can serve as a ligand with well-balanced σ-donor and π-acceptor capabilities toward transition metals. This has been demonstrated by the isolable [Ni⁰(arene)] complexes 12a-e (arene ) Me_nC ₆H₆-n, n = 0-3), which are ideal precursors for the formation of the corresponding Ni(CO)₃ complex 13. The latter activates a S-H bond in hydrogen sulfide, too, but the presence of the Ni(CO)₃ moiety governs the formation of the complex 17, bearing an unprecedented β-diketiminate silicon(II) thiol ligand: L′Si(SH): (L′ ) CH[C(Me)NAr]2; Ar ) 2,6-ⁱPrC₆H₃). Likewise, the Si(II)→Ni(CO)₃ coordination in 13 steers exclusively 1,4-addition of ammonia, isopropylamine, and phenylhydrazine onto the silylene ligand 5, leading to the corresponding β-diketiminate silicon(II) amide or hydrazide complexes L′Si(NHR)→Ni(CO)₃ (23a-c: R ) H, ⁱPr, N(H)Ph). IR measurements reveal that the carbonyl stretching frequencies of the Ni(CO)₃ moiety in 23a-c are shifted to even lower wavenumbers in comparison to those of NHCs or phosphines. In other words, the β-diketiminate silicon(II) amide ligands in 23a-c represent the strongest donors in the series of N-heterocyclic silylenes reported as yet.

Full text of DOI:10.1021/ja910305p

Published on Web 02/11/2010
Steering S-H and N-H Bond Activation by a Stable
N-Heterocyclic Silylene: Different Addition of H2S, NH3, and
Organoamines on a Silicon(II) Ligand versus Its Si(II)fNi(CO)3
Complex
Antje Meltzer, Shigeyoshi Inoue, Carsten Pra¨sang, and Matthias Driess*
Institute of Chemistry, Metalorganics and Inorganic Materials, Technische UniVersita¨t Berlin,
Strasse des 17. Juni 135, Sekr. C2, D-10623 Berlin, Germany
Received December 18, 2009; E-mail: matthias.driess@tu-berlin.de
Abstract: The strikingly different behavior of the ylide-like, N-heterocyclic silylene LSi: (5: L )
CH[(CdCH2)CMe(NAr)2]; Ar ) 2,6-iPrC6H3) versus its LSifNi(CO)3 complex 13 to activate E-H bonds (E
) S, N) of small molecules is reported. Remarkably, conversion of 5 with hydrogen sulfide leads exclusively
to the first isolable silathioformamide, L′Si(dS)H (16: L′ ) CH[C(Me)NAr]2; Ar ) 2,6-iPrC6H3) with a donor-
supported SidS double bond and four-coordinate silicon. The latter result demonstrates the unusual
ambivalent reactivity of 5 by combining two modes of reactivity involving S-H bond activation and
subsequent 1,4- and 1,1-addition, respectively. In addition, 5 can serve as a ligand with well-balanced
σ-donor and π-acceptor capabilities toward transition metals. This has been demonstrated by the isolable
[Ni0(arene)] complexes 12a-e (arene ) MenC6H6-n, n ) 0-3), which are ideal precursors for the formation
of the corresponding Ni(CO)3 complex 13. The latter activates a S-H bond in hydrogen sulfide, too, but
the presence of the Ni(CO)3 moiety governs the formation of the complex 17, bearing an unprecedented
ꢀ-diketiminate silicon(II) thiol ligand: L′Si(SH): (L′ ) CH[C(Me)NAr]2; Ar ) 2,6-iPrC6H3). Likewise, the
Si(II)fNi(CO)3 coordination in 13 steers exclusively 1,4-addition of ammonia, isopropylamine, and
phenylhydrazine onto the silylene ligand 5, leading to the corresponding ꢀ-diketiminate silicon(II) amide or
hydrazide complexes L′Si(NHR)fNi(CO)3 (23a-c: R ) H, iPr, N(H)Ph). IR measurements reveal that the
carbonyl stretching frequencies of the Ni(CO)3 moiety in 23a-c are shifted to even lower wavenumbers in
comparison to those of NHCs or phosphines. In other words, the ꢀ-diketiminate silicon(II) amide ligands in
23a-c represent the strongest donors in the series of N-heterocyclic silylenes reported as yet.
applications in catalysis and materials synthesis.6,7 NHSis are
also known to form complexes with various transition metals,
but the inherent reactivity of the metal-silicon bond has
prevented any application to date. Some recently reported,
catalytically active silylene complexes8 feature either NHSi8a,d
or terminal silylene ligands.8c-f
Catalytic systems in which the ligands participate directly in
a given reaction hold a great deal of potential. The ability of
main-group compounds to activate key substrates such as
hydrogen and ammonia under mild conditions has only been
realized very recently.9 This has been achieved with systems
which exhibit cooperating Lewis acid and Lewis base sites. The
Introduction
The first stable N-heterocyclic silylene (NHSi)1 was reported
only 3 years after Arduengo et al. published their initial com-
munication on an isolable N-heterocyclic carbene (NHC).2 Even
though derivatives of both classes have been utilized as ligands
in transition-metal complexes from an early stage, their chem-
istry has developed quite differently. In particular, NHCs have
been shown to be extremely fruitful ligands for the synthesis
of homogeneous transition-metal catalysts.3a-c Thus, NHCs are
well-established and indispensable ligands for the stabilization
of, for example, low-coordinate metal centers and low-valent
main group compounds,4,5 and they have also found numerous
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3038 J. AM. CHEM. SOC. 2010, 132, 3038–3046
10.1021/ja910305p  2010 American Chemical Society

Steering S-H and N-H Bond Activation
A R T I C L E S
Figure 2. 1,4- and 1,1-addition products of germylene 4 and silylene 5
with ammonia (6, 7a), hydrazine (7b), and methylhydrazine (7c): 7b, R′ )
H; 7c, R′ ) CH3; R ) 2,6-iPr2C6H3.
Scheme 1. Reaction Pathways of Germylene 4 and Silylene 5 with
HXa
Figure 1. NHCs and some heavier homologues of group 14 elements.
Dashed lines represent structural variations of known compounds, e.g.
saturated and unsaturated NHCs (1) or cyclic and acyclic alkyl(amino)car-
benes (2). R ) 2,6-iPrC6H3.
a Legend: (a) 1,4-addition of HX to 4, 5; (b) isomerization to 1,1-addition
product. 4, 5: E ) Si, Ge; R ) 2,6-iPr2C6H3.
activation usually proceeds via a heterolytic bond cleavage by
main-group elements in low oxidation states. In some cases,
the increased contribution of triplet character in the electronic
ground state might also be of importance as shown for
diarylstannylenes, a digermyne, and a distannyne studied by
Power et al.10 Stephan et al. were able to show that hydrogen
can be activated and even cleaved heterolytically by combining
an electron-poor borane (Lewis acid) with a bulky phosphine,
amine or carbene (Lewis base) that do not form stable adducts
(so-called “frustrated Lewis acid/base pairs”).11 In fact, such
systems can serve as active catalysts for the hydrogenation of
imines.12 While NHCs 113 with two nitrogen donors next to
the carbon(II) center are inert toward ammonia and hydrogen
(Figure 1), related alkyl(amino)carbenes 2,14 which are better
σ-donors and π-acceptors than carbenes of type 1, do add
hydrogen and ammonia readily in a 1,1-mode via the heterolytic
cleavage of the H-H or N-H bond, respectively.15 The
chemistry of the heavier carbene analogues of group 14 ele-
mentsssilylenes, germylenes, stannylenes, and plumbyleness
has been a prominent topic in main-group chemistry for
decades.16 The five- and six-membered NHC analogues of group
14 elements 3a,b17 cannot be employed for hydrogen or
ammonia activation, even though they are more Lewis acidic
and have a smaller singlet-triplet gap compared to the
corresponding carbenes. On the other hand, germylene 418 and
silylene 5,19 which feature a modified ꢀ-diketiminate backbone,
can undergo facile addition of ammonia (4, 5) and hydrazines
(5) to give the 1,4- and 1,1-insertion products 6 and 7a-c20,21
(Figure 2), respectively.
This can be explained by the significant electron-withdrawing
effect of the butadiene backbone allowing for the necessary
simultaneous interaction of the substrate with the reactant′s lone
pair and formally empty valence p orbital, as represented by
their resonance structures (Figure 1). Thus, addition of elec-
trophiles onto the germylene 4 leads exclusively to the 1,4-
adducts A as final products (Scheme 1).22
In contrast, the 1,4-adducts A are only the primary products
from the addition of small HX molecules (X ) OSO2CF3,
halide) or related organic halides onto silylene 5, which
subsequently undergoes isomerization to give the thermody-
namically favored 1,1-adduct B (Scheme 1).
Accordingly, the reaction of silylene 5 with other eletrophiles
such as trimethylsilyl triflate yields the ꢀ-diketiminate silicon(II)
triflate 8 as the kinetic product via 1,4-addition (Scheme 2).19
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A R T I C L E S
Meltzer et al.
Scheme 2. Conversion of Silylene 5a
Scheme 5. Formation of the Silathioformamide 16 via the
Proposed Intermediates 15a,ba
a 1,4-Addition: (a) Me3SiOTf. 1,1-Addition: (b) CH2Cl2, R′ ) CH2Cl;
(b) HSiCl3, R′ ) SiHCl2. R ) 2,6-iPr2C6H3.
a R ) 2,6-iPr2C6H3. Model systems 5′, 15a′, 15b′, and 16′ with R ) Ph.
Scheme 3. Synthesis of Siloxysilylene 11 via the Intermediates
10a,ba
facile formation of the first isolable N-donor-stabilized silathio-
formamide 16 from addition of H2S onto 5. Furthermore, we
describe the remarkable reactivity of the Ni(CO)3 complex 13
toward H2S, NH3, iPrNH2, and H2N-NH(Ph), which demon-
strates the particular steering role of the silylene ligand 5 in the
Si(II)fNi(CO)3 moiety.
a Legend: (a) H2O; (b) 5. R ) 2,6-iPr2C6H3.
Results
The reaction of silylene 5 with 1 equiv of H2S gas at low
temperature resulted in the surprisingly simple formation of the
donor-stabilized silathioformamide 16 (Scheme 5).
Scheme 4. Nickel(0) Complexes of Silylene 5, Including
η6-Coordinated Arenes: Toluene (12a), p-Xylene (12b), Mesitylene
(12c), Benzene (12d), C6D6 (12e)a
Analogous to the reaction of silylene 5 with water (Scheme
3), two possible intermediates might be envisaged. The silathio-
formamide 16 could result from an 1,1-insertion of the silicon(II)
center into an S-H bond to give the proposed intermediate 15a
followed by migration of an H atom to the exocyclic methylene
group. A second reasonable reaction path could proceed via the
donor-stabilized amino(mercapto)silylene 15b with subsequent
protonation of the silicon(II) lone pair.
a 14a,b: X ) OH, OTf. R ) 2,6-iPr2C6H3.
Remarkably, halocarbons or chlorosilanes such as dichloro-
methane and trichlorosilane allow for the isolation of the
corresponding 1,1-insertion products 9a,b (Scheme 2).23
The addition of water onto the silylene 5 deserves particular
attention, because the process affords the donor-stabilized
siloxysilylene (mixed-valent disiloxane) 11 (Scheme 3).24 Al-
though the mechanism is still unknown, we reason that the
conversion could either proceed via 1,4-addition to give
the elusive hydroxosilylene 10a or via 1,1-addition to give the
silanol 10b.
We have also shown recently that the silylene 5 can also serve
as a stabilizing ligand for the Ni(arene) complexes 12,25 which
can be easily transformed into the more robust Ni(CO)3 complex
13 (Scheme 4).26 Strikingly, the silylene ligand 5 in the latter
is still capable of activating H-X bonds of HX substrates (X
) OTf, OH) to give merely the ꢀ-diketiminate silicon(II)
nickel(0) complexes 14a,b; that is, the presence of the Ni(CO)3
moiety steers the progress of the reaction in a way that 1,4-
addition is now thermodynamically preferred.
Interestingly, it is possible to tune the σ-donor and π-acceptor
abilities of the new silicon(II) ligands generated in the coordina-
tion sphere of nickel(0) over a wide range.26 The possibility to
control 1,4- over 1,1-addition by Ni0 coordination to the Si(II)
atom inspired us to extend our studies to the activation of N-H-
and S-H-containing substrates, which results in 1,4-addition.
The latter conversions would allow access for the first time to
unique ꢀ-diketiminate silicon(II) amines and thiols in the
coordination sphere of Ni(0). At first, we report the unexpected
The intramolecular stabilization of the intermediate by
hydrogen migration is obviously faster than the reaction with
another 1 equiv of silylene 5, as has been observed in the case
of the hydrolysis (Scheme 3). The acidity of the SH proton,
which is several magnitudes higher (pKa values in aqueous
solution: H2O, 16; H2S, 7) compared to OH, could play a key
role in the intramolecular stabilization of 15a,b. DFT calcula-
tions (B3LYP with 6-31G(d) basis set; see the Supporting
Information) of the respective model systems (Scheme 5) in
which the bulky aryl groups R at nitrogen were replaced by
phenyl groups revealed that the postulated intermediates 15a′
(Erel ) 0 kcal mol-1) and 15b′ (Erel ) -0.2 kcal mol-1) are
practically isoenergetic, while its tautomer 16′ is favored by
-23 kcal mol-1. Attempts to observe an intermediate by
monitoring the conversion of 5 with H2S at -78 °C in an NMR
1
tube by means of H NMR spectroscopy were unsuccessful.
Since the formation of 16 is still very fast under the latter
conditions in solution, we monitored the heterogeneous reaction
of solid 5 with gaseous H2S at ambient temperature by means
of solid-state MAS 29Si NMR spectroscopy. After a sample of
silylene 5 had been in contact with an approximately 20-fold
excess of gaseous H2S for 3 days, only the resonances of silylene
5 and silathioformamide 16 in the ratio of 4:6 (1H NMR) could
be observed (see the Supporting Information and Experimental
Section for further details). It is astonishing that the tautomer-
ization reaction of the initial products to give 16 is remarkably
fast even without a solvent.
Although stable species containing a SidS double bond are
already known (silanethiones),27,28 compound 16 is the first
isolable silathioformamide to be stabilized by intramolecular
donor stabilization. Its composition has been proven by elemen-
tal analysis, and the structure is evident from 1H and 29Si NMR
spectroscopy. In the 1H NMR spectrum the characteristic signals
of the exocyclic methylene and methyl groups of precursor 5
(23) Xiong, Y.; Yao, S.; Driess, M. Organometallics 2009, 28, 1927–1933.
(24) Yao, S.; Xiong, Y.; Brym, M.; Driess, M. J. Am. Chem. Soc. 2007,
129, 7268–7269.
(25) Meltzer, A.; Praesang, C.; Milsmann, C.; Driess, M. Angew. Chem.,
Int. Ed. 2009, 48, 3170–3173.
(26) Meltzer, A.; Praesang, C.; Driess, M. J. Am. Chem. Soc. 2009, 131,
7232–7233.
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Steering S-H and N-H Bond Activation
A R T I C L E S
parison of the X-ray crystallographic data of “free” silylene
5 with those of complex 12a and the newly reported
complexes 12c,d (Figure 4) reveals only small changes within
the ligand moieties. Common features are, for example, the
short Si-N (5, 173.5 pm; 12a,c,d, 173-174 pm) and N-Cring
distances (5, 141.6 pm; 12a,c,d, 140.8-141.2 pm), acute
N-Si-N angles (5, 99.3°; 12a,c,d, 99.3 and 100°), and the
virtually planar six-membered SiC3N2 ring skeleton. Accord-
ingly, the Ni and Si centers of 12a,c,d are positioned almost
within the mean plane of the C3N2 ligand backbone (12c:
C3N2-Si, 10 pm; C3N2-Ni, 23 pm).
Silylene complex 12a turned out to be an ideal starting
material for the preparation of complex 13 (Scheme 4), which
was utilized to synthesize several ꢀ-diketiminate silicon(II)
ligands with variable donor strengths.26 Interestingly, this has
been realized while the silicon center remains coordinated
to the Ni(CO)3 moiety. Because of this, the silicon lone pair
cannot participate in any reaction directly and the corre-
sponding substrates were compelled to react at the Lewis
basic methylene group and the Lewis acidic silicon center
instead.
In other words, 13 is still capable of reacting with H2S even
in the presence of the Ni(CO)3 moiety. Thus, the resulting
compound 17 was obtained by reaction of 13 with stochiometric
amounts of H2S and isolated after crystallization from toluene
in 27% yield (Scheme 6). A small amount (ca. 5%) of the side
product 16 was detected by 1H NMR spectroscopy in the crude
reaction mixture. Similar to the reaction with water, H2S adds
in a 1,4-fashion to the silylene center and the ligand backbone.
Apparently, a possible second 1,4-addition between product 17
and another 1 equiv of complex 13 is prevented for steric
reasons.
The reactivity of transition-metal-silylene complexes toward
Brønsted acids has been studied quite extensively over the last
few decades.32 The resonance structures of complexes of type
18 (Scheme 6) offer a good description of the electronic
polarization (ylide-like character) of the Si(II)-metal bond,
which generally undergoes a 1,2-addtion if reacted with
substrates of sufficient acidity. The corresponding products, silyl
metal hydrides 19, have been isolated and characterized, even
from the reaction of an NHSi molybdenum complex with water
to give 22.33 The direct and stepwise rupture of the Si-metal
bond has also been observed. In these cases, the silylene ligands
were converted to alkoxysilanes 20 and dialkoxysilanes 21,
respectively.
Figure 3. Molecular structure of 16 with thermal ellipsoids drawn at the
50% probability level. Hydrogen atoms are omitted for clarity, except those
of C1, C3, C5, and Si1. Selected bond distances (pm) and angles (deg) of
16: Si1-S1, 198.54(9); Si1-N1, 181.0(2); Si1-N2, 180.0(2); N1-C2,
133.4(3); N2-C4, 134.6(3); C1-C2, 149.8(3); C2-C3, 139.3(3); C3-C4,
138.4(3); C4-C5, 150.2(3); N1-Si1-N2, 97.63(9); S1-Si1-N1,
116.90(7).
are replaced by a single resonance at δ 1.91 ppm corresponding
to six protons. Additionally, the proton of the Si-H group
resonates as a singlet at δ 6.09 with 29Si satellites (1JSiH ) 255
Hz). The 29Si chemical shift of 16 (δ -16.8 ppm) is in the range
for tetracoordinate silicon and is comparable to that of related
donor-stabilized compounds with a SidS bond (chemical shift
range +23.3 to -41.3 ppm).27 The structure of 16 was
confirmed by single crystal X-ray diffraction analysis (Figure
3). The SidS distance of 198.5 pm is between those of related
donor-stabilized silanethiones (201 pm)27 versus unsupported
ones (195-196 pm)28 but significantly shorter than Si-S single
bonds (ca. 214 pm).29
We have already reported some Ni0 complexes of silylene 5
in order to investigate its capability to add small molecules
containing EsH bonds and to compare the σ-donor/π-acceptor
properties of the resulting silicon(II)-nickel complexes with
related NHSi-Ni0 complexes that are known in the literature.25,26,30
Isolable (η6-arene)-Ni0 complexes are very rare,31 and the
surprising stability of compounds 12a-e can be explained
by increased back-bonding from the electron-rich metal atom
to the electron-deficient silicon center, facilitated by the
electronic influence of the butadiene backbone.26 A com-
The 1H and 13C NMR spectra of complex 17 reflect its higher
symmetry compared to the starting material 13; the SH
resonance was detected at 1.30 ppm as a somewhat broadened
singlet. Single crystals suitable for X-ray analysis were obtained
from toluene at -20 °C.
Intriguingly, despite the high thiophilicity of nickel, H2S reacts
with 13 exclusively by 1,4-addition to the silylene ligand. A
comparison of the structural data of complex 17 (Figure 5) with
those of complex 14a (Scheme 4) indicates a weaker interaction
of the ligand backbone with the silicon center, probably due to
the lower electronegativity of sulfur as compared to oxygen.
Thus, the N-Si bonds are longer (17, 184.2 pm;14a, 180.7 pm)
and the N-Cring bonds are slightly shorter (17, 134.7 pm; 14a,
135.8 pm). The Si-SH distance of 219.0 pm represents clearly
(27) (a) Arya, P.; Boyer, J.; Carre´, F.; Corriu, R.; Lanneau, G.; Lapasset,
J.; Perrot, M.; Priou, C. Angew. Chem., Int. Ed. Engl. 1989, 28, 1016–
1018. (b) So, C.-W.; Roesky, H. W.; Oswald, R. B.; Pal, A.; Jones,
P. G. Dalton Trans. 2007, 5241–5244. (c) Yao, S.; Xiong, Y.; Brym,
M.; Driess, M. Chem. Asian J. 2009, 3, 113–118. (d) Yao, S.; Xiong,
Y.; Driess, M. Chem. Eur. J. 2009, in press, DOI: 10.1002/
chem.200902467.
(28) (a) Suzuki, H.; Tokitoh, N.; Nagase, S.; Okazaki, R. J. Am. Chem.
Soc. 1994, 116, 11578–11579. (b) Iwamoto, T.; Sato, K.; Ishida, S.;
Kabuto, C.; Kira, M. J. Am. Chem. Soc. 2006, 128, 16914–16920.
(29) Kaftory, M.; Kapon, M.; Botoshansky, M. In The Chemistry of Organic
Silicon Compounds; Rappoport, Z., Apeloig, Y., Eds.; Wiley: New
York, 1998; Vol. 2, Part 1, pp 228-233.
(30) (a) Gehrhus, B.; Hitchcock, P. B.; Lappert, M. F.; Maciejewski, H.
Organometallics 1998, 17, 5599–5601. (b) Schmedake, T. A.; Haaf,
M.; Paradise, B. J.; Powell, D.; West, R. Organometallics 2000, 19,
3263–3265. (c) Avent, A. G.; Gehrhus, B.; Hitchcock, P. B.; Lappert,
M. F.; Maciejewski, H. J. Organomet. Chem. 2003, 686, 321–331.
(31) (a) Nickel, T.; Goddard, R.; Krueger, C.; Poerschke, K.-R. Angew.
Chem., Int. Ed. Engl. 1994, 33, 879–882. (b) Hoon, C. H.; Laitar,
D. S.; Mueller, P.; Sadighi, J. P. J. Am. Chem. Soc. 2007, 129, 13802–
13803.
(32) Okazaki, M.; Tobita, H.; Ogino, H. Dalton Trans. 2003, 493–506.
(33) Petri, S. H. A.; Eikenberg, D.; Neumann, B.; Stammler, H.-G.; Jutzi,
P. Organometallics 1999, 18, 2615–2618.
9
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Figure 4. Molecular structures of 12c (left) and 12d (right) with thermal ellipsoids drawn at the 50% probability level. Hydrogen atoms are omitted for
clarity, except those of C1-C5 and C31A-C36A (12d). Selected bond distances (pm) and angles (deg) of 12c: Si1-Ni1, 206.0(1); Si1-N1, 173.5(3);
Si1-N2, 174.0(2); C1-C2, 136.7(4); C2-C3, 143.0(4); C3-C4, 134.2(4); C4-C5, 150.4(4); Ni1-C(mesitylene, average), 213.1; Ni1-C(mesitylene, centroid),
160.7; N1-Si1-N2, 99.3(1); N1-Si1-Ni1, 129.73(9); N2-Si1-Ni1, 130.9(1). Selected bond distances (pm) and angles (deg) of 12d: Si1-Ni1, 206.47(6);
C1-C2, 139.9(3); C2-C3, 140.8(3); C3-C4, 138.4(3); C4-C5, 143.6(3); Ni1-C(benzene, average), 212.2; Ni1-C(benzene, centroid), 160.4; N1-Si1-N2,
99.31(9); N1-Si1-Ni1, 129.08(7); N2-Si1-Ni1, 131.61(7).
Scheme 6. 1,4-Addition of H2S to 13 vs Common Reactivity of
Transition-Metal-Silylene Complexes toward Brønsted Acids HXa
a R1,2 ) H, alkyl, Cl, H; R ) 2,6-iPr2C6H3.
Figure 5. Molecular structure of 17 with thermal ellipsoids drawn at the
50% probability level. Hydrogen atoms are omitted for clarity, except those
a single bond, about 10 pm (5%) longer than the partial SidS
double bond in 16 (198.5 pm).
of C1, C3, and S1. Selected bond distances (pm) and angles (deg) of 17:
Si1-Ni1, 224.66(6); Si1-S1, 219.01(9); Si1-N1, 184.0(2); Si1-N2,
184.4(2); N1-C2, 134.6(3); C1-C2, 150.2(4); C2-C3, 138.6(3); C3-C4,
138.9(3); C4-C5, 150.2(4); C4-N2, 134.7(3); Ni1-C(average), 178.5;
C-O(average), 114.1; N1-Si1-N2, 95.67(9); N1-Si1-Ni1, 120.88(7);
Ni1-Si1-S1, 113.50(3); N1-Si1-S1, 100.35(7).
Considering the pKa values of trifluoromethanesulfonic
acid, H2S, and water (in aqueous solution: -15, 7, and 16,
respectively) it is not surprising that the exocyclic methylene
group of 13 is also able to abstract a proton from H2S. Amines
and phosphines are primarily bases (and thus correspondingly
very weak acids), and the activation of N-H bonds by
transition-metal complexes is in competition with their
suitability to simply act as a ligand and coordinate to the
metal center with their lone pairs. It is therefore interesting
to learn that 13 is also capable of activating amines without
rupture of the Si-metal bond or ligand exchange at the Ni0
center. Moreover, the impact of a wider range of substituents
on the donor/acceptor capabilities of ꢀ-diketiminate silicon(II)
ligands in complexes of type 14 could be studied.
Scheme 7. Reaction of Complex 13 with Amines and a Hydrazinea
a R ) 2,6-iPr2C6H3.
In fact, reactions of complex 13 with ammonia, isopropyl-
amine, and phenylhydrazine in toluene yield the corresponding
ꢀ-diketiminate SiII-Ni(CO)3 complexes 23a-c (Scheme 7). No
significant byproduct except for small amounts (ca. 5%) of the
H2O adduct 14a were detected by 1H NMR in the crude reaction
mixtures. The 1H and 13C NMR spectra of 23a-c are consistent
with their expected Cs symmetry, with mirror planes perpen-
dicular to the silylene ligand backbone. The NH protons are
observed at δ 1.52 (23a), 1.49 (23b), and 3.98, 4.95 (23c) ppm
9
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Steering S-H and N-H Bond Activation
A R T I C L E S
a
Scheme 8. Proposed Intermediates during the Formation of 23a-c with Simultaneous Activation of Amines R′NH2
a R ) 2,6-iPr2C6H3.
Figure 6. Molecular structure of 23a with thermal ellipsoids drawn at the
50% probability level. Hydrogen atoms are omitted for clarity, except those
Figure 7. Molecular structure of 23b with thermal ellipsoids drawn at the
50% probability level. Hydrogen atoms are omitted for clarity, except those
of C1, C3, C5, and N3. Selected bond distances (pm) and angles (deg) of
23b: Si1-Ni1, 225.52(6); Si1-N1, 186.2(1); Si1-N2, 183.8(1); Si1-N3,
173.0(2); N1-C2, 133.7(2); C1-C2, 150.0(2); C2-C3, 139.4(2); C3-C4,
138.6(2); C4-C5, 150.6(3); N2-C4, 134.3(2); Ni1-C(average), 178.3;
C-O(average), 113.7; N1-Si1-N2, 94.11(6); N1-Si1-Ni1, 117.76(5);
N3-Si1-Ni1, 114.83(6); N1-Si1-N3, 104.11(7).
of C1, C3, and N3. Selected bond distances (pm) and angles (deg) of 23a:
Si1-Ni1, 225.5(1); Si1-N1, 185.2(2); Si1-N2, 171.1(4); N1-C2, 134.0(4);
C1-C2, 150.8(4); C2-C3, 138.8(3); Ni1-C(average), 178.6; C-O(average),
114.0; N1-Si1-N1, 94.06(9); N1-Si1-Ni1, 120.98(8); N3-Si1-Ni1,
100.5(2); N1-Si1-N3, 100.5(2).
as singlets corresponding to one or two protons (23a), respec-
tively. The 29Si NMR chemical shifts exhibit a upfield shift of
δ 110-116 ppm in comparison to complex 13 (δ 142.1), which
is consistent with the increase of the coordination number at
the silicon centers from 3 to 4 and comparable to the same effect
observed for 14a,b.
The mechanism is still unknown but the surprising ef-
fortlessness of the 1,4-additions of amines to 13 could be
explained by the initial formation of an acid-base pair such
as compound 25 (Scheme 8). The latter would cause an
increased acidity of the N-H protons as well as an increase
in basicity of the exocyclic methylene group. A second
molecule of complex 13 could then assist to deprotonate the
amine ligand; however, this process might also occur
simultaneously. This would yield two complexes: the anionic,
strongly basic intermediate 26, which could easily be
converted into the observed product by deprotonation of
another acid-base pair 25, and the cationic, Lewis acidic
complex 27, which has already been isolated and character-
ized.26 The resultant complexes 23a-c could then result
through (back) protonation of 26 with 27.
Single crystals suitable for X-ray analysis were obtained in
toluene (23a) (Figure 6) and hexane (23b,c) (Figures 7 and 8).
In all three cases, an N-H bond clearly reacted by 1,4-addition
to the ligand moiety. Similar to the case for the complexes 14a,b
and 17, the silicon centers of 23a-c are coordinated in a
distorted-tetrahedral fashion and the Si atom is out of the mean
plane of the ligand backbone by 64-74 pm. The increased
valence p character of all Si-N bonds can be derived from the
somewhat acute N-Si-N angles of 94-95° (ligand backbone)
and 101-104° (ligand N-exocyclic N). At the same time, the
Figure 8. Molecular structure of 23c with thermal ellipsoids drawn at the
50% probability level. Hydrogen atoms are omitted for clarity, except those
of C1, C3, C5, N3, and N4. Selected bond distances (pm) and angles (deg)
of 23c: Si1-Ni1, 223.6(1); Si1-N1, 185.4(4); Si1-N2, 181.9(4); Si1-N3,
174.8(5); N1-C2, 133.2(5); C1-C2, 150.9(7); C2-C3, 139.8(6); C3-C4,
137.9(7);C4-C5,151.0(6);N2-C4,135.1(5);N3-N4,141.5(6);Ni1-C(average),
177.4; C-O(average), 115.1; N1-Si1-N2, 94.8(2); N1-Si1-Ni1, 120.3(1);
N3-Si1-Ni1, 111.0(2); N1-Si1-N3, 102.7(7); Si1-N3-N4, 129.4(3).
larger Ni-Si-N angles (111-124°) point to an increasing s
character of the Si-Ni bond. The amine and hydrazine groups
act as strong donors toward the silicon center, in accordance
with the rather short Si-N distances (23a-c: Si-N, 171.2,
9
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Chart 1. Comparison of Ni(CO)3 Carbonyl Stretching Frequencies (A1 Mode) of Novel Complexes with Those of Analogous Phosphine and
NHC Systems and from Ref 26a
a
t
R ) 2,6-iPr2C6H3. 28: R3 ) 2,4,6-Me3C6H2. 29a: R2 ) Ph. 29b: R2 ) Bu.
173.0, and 176.8 pm; N-Si(backbone), 180.7, 185.0 (average),
Remarkably, the silylene ligand 5 is able to stabilize otherwise
quite elusive Ni0(arene) complexes, 6a-e, thanks to its ability
to act as a good σ-donor and π-acceptor simultaneously. The
latter are ideal precursors for the facile synthesis of the Ni(CO)3
complex 13. Remarkably, the silylene ligand in 13 is still capable
of activating S-H and N-H bonds of several substrates in the
presence of the Ni(CO)3 moiety without breaking of or addition
across the Si-Ni bond. Instead, addition proceeds exclusively
in a 1,4-fashion across the silylene ligand to yield unprecedented
ꢀ-diketiminate silicon(II)-thiol, -amide, and -hydrazide ligands
with striking σ-donor/π-acceptor capabilities comparable to
those of phosphines and NHCs.
183.7 (average) pm) and IR spectroscopic data (vide infra).
IR Spectroscopy
Carbonyl stretching frequencies are a convenient probe to
judge the σ-donor/π-acceptor capabilities of a wide range of
ligands L in transition metal complexes of the general formula
LM(CO)n. We have shown recently26 that these properties of
complex 13 can be tuned over a wide range by either addition
of a Lewis acid to the exocyclic methylene group or 1,4-addition
of water or triflic acid to the ligand while the silylene ligand is
coordinated to a Ni(CO)3 moiety (complexes 27a,b (Chart 1)
and 14a,b (Scheme 4), respectively). The cationic and quasi-
cationic ligands of complexes 27a,b are quite similar to the
moderate σ-donor and good π-acceptor PF3 with regard to their
impact on the carbonyl stretching frequencies of the Ni(CO)3
metal complex fragment (Chart 1). Complexes 13 and 14b are
more similar to triphenylphosphine, a frequently used ligand in
transition-metal chemistry. All other silicon(II) ligands in the
complexes 14a, 17, and 23a-c are similar to trialkylphosphines
and NHCs: e.g. tri-tert-butylphosphine, 29b; N,N′-dimesityl-
substituted NHC, 28 (see Chart 1).34
Experimental Section
General Considerations. All experiments and manipulations
were carried out under a dry and oxygen-free atmosphere of nitrogen
using standard Schlenk techniques or in an MBraun inert-
atmosphere drybox containing an atmosphere of purified nitrogen.
Solvents were dried by standard methods and freshly distilled prior
to use. The complexes LSi-Ni(η6-toluene) (12a), LSi-Ni(η6-p-
xylene) (12b), and LSi-Ni(η6-mesitylene) (12c)25 and the starting
material LSi-Ni(CO)3 (13) as well as L′Si(OH)-Ni(CO)3 (14a),
L′Si(OTf)-Ni(CO)3 (14b), [(C6F5)4B][L′Si-Ni(CO)3] (27b), and
(C6F5)3B-LSi-Ni(CO)3 (27a)26 (L′ ) HC[C(Me)NAr]2; Ar ) 2,6-
iPr2C6H3) were prepared according to literature procedures.25
Solution NMR spectra were recorded with Bruker AM200 and
AM400 spectrometers and referenced to the residual solvent signals
as internal standard. Solid-state 29Si{1H} MAS cross-polarization
(CP) measurements were carried out on a Bruker Avance II
spectrometer at an external magnetic field of 9.4 T using a standard
Bruker 4 mm double-resonance H-X MAS probe operating at a
29Si resonance frequency of 79.4 MHz. The spectra were recorded
Varying the terminal substituents at nitrogen or interchanging
from saturated to unsaturated NHC frameworks has little effect
on the corresponding CO wavenumbers of the Ni(CO)3 moiety.34
The variances observed for Ni(CO)3 complexes with ligands
derived from silylene 5 are remarkable and cover a range of 52
cm-1, which is nearly as large as the difference between
trialkylphosphines and PF3 (55 cm-1).
Summary
1
with a cross-polarization time of 2 ms, and composite pulse H
The ylide-like silylene 5 undergoes a facile reaction with H2S
to form the first isolable N-donor-stabilized silathioformamide
16 with a SidS moiety and tetracoordinate silicon. DFT
calculations of the model system 16′, in which the bulky aryl
groups at nitrogen are replaced by phenyl, revealed that this
form is favored by 23 kcal mol-1 over the two possible
tautomers with a tetravalent Si(H)SH or divalent:Si(SH) subunit.
decoupling was applied during the acquisition. A total of 5000
transients were recorded with a relaxation delay of 2 s under MAS
conditions with a rotation frequency of 10 kHz. The spectra were
referenced to TMS (tetramethylsilane) using TKS (tetrakis(trim-
ethylsilyl)silane) as a secondary reference.
Single-Crystal X-ray Structure Determinations. Crystals were
each mounted on a glass capillary in perfluorinated oil and measured
under a cold N2 flow. The data for compounds 12c,d, 16, 17, and
23a-c were collected on an Oxford Diffraction Xcalibur S Sapphire
at 150 K (Mo KR radiation, λ ) 0.710 73 Å). The structures were
(34) Dorta, R.; Stevens, E. D.; Scott, N. M.; Costabile, C.; Cavallo, L.;
Hoff, C. D.; Nolan, S. P. J. Am. Chem. Soc. 2005, 127, 2485–2495.
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Steering S-H and N-H Bond Activation
A R T I C L E S
solved by direct methods and refined on F2 with the SHELX-9735
software package. The positions of the H atoms were calculated
and considered isotropically according to a riding model.
1H NMR (400 MHz, toluene-d8, 25 °C): δ 0.93, 1.17, 1.34, 1.42
(each d, 3JHH ) 6.8 Hz, 6H, CH(CH3)2), 1.30 (s, 1H, SH), 1.52 (s,
3
6H, CH3), 3.13, 4.11 (each sept, JHH ) 6.8 Hz, 2H, CH(CH3)2),
Synthesis of LSi-Ni(η6-C6H6) (12d). The synthesis of 12d
follows the same protocol as the synthesis of the related LSi-Ni(η6-
arene) complexes.25 A solution of silylene 5 (500 mg, 1.12 mmol)
in benzene (10 mL) was added to a suspension of [Ni(cod)2] (206
mg, 0.75 mmol) in benzene (10 mL) at -60 °C. The reaction
mixture was slowly warmed to room temperature overnight. All
volatiles were removed in vacuo, and n-hexane (15 mL) was added.
Filtration and cooling to -20 °C gave 252 mg of complex 12d
5.17 (s, 1H, γ-H), 6.9 - 7.2 (m, 6H, Haryl) ppm. 13C{1H} NMR
(101 MHz, toluene-d8, 25 °C): δ 24.0 (CH(CH3)2), 24.1 (CH3), 24.1,
25.9, 26.8 (CH(CH3)2), 28.9, 29.6 (CH(CH3)2), 103.8 (γ-C), 124.7,
125.9, 129.2, 139.9, 143.5, 147.0 (Caryl), 169.5 (NCCH3), 198.8
(CO) ppm. 29Si NMR (79.5 MHz, toluene-d8, 25 °C): δ 52.3 ppm.
IR (toluene, cm-1): ν(CO) 1985, 2054. EI MS (70 eV): m/z (%)
536 (1) [M - 3CO]+, 478 (15) [M - Ni(CO)3]+, 463 (100) [M -
i
Ni(CO)3 - CH3]+, 435 (15) [M - Ni(CO)3 - Pr]+. Anal. Calcd
1
(39%) as red crystals. H NMR (400 MHz, C6D6, 25 °C): δ 1.18,
for C32H42N2O3SSiNi: C, 61.8; H, 6.8; N, 4.5. Found: C, 62.4; H,
6.7; N, 4.4.
3
1.37, 1.40, 1.44 (each d, JHH ) 6.8 Hz, 6H, CH(CH3)2), 1.43 (s,
3
3H, CH3), 3.30 (s, 1H, CHH′), 3.40, 3.54 (each sept, JHH ) 6.8
Synthesis of L′Si(NH2)-Ni(CO)3 (23a). NH3 was passed
through a Schlenk flask with a cooled solution (-60 °C) of complex
13 (176 mg, 0.30 mmol) in toluene (10 mL) for about 1 min. Then
the yellow reaction mixture was slowly warmed to room temper-
ature. All volatiles were removed in vacuo, and the residue was
recrystallized in toluene (114 mg, 63%). 1H NMR (400 MHz, C6D6,
Hz, 2H, CH(CH3)2), 3.91 (s, 1H, CHH′), 5.37 (s, 1H, γ-H), 6.9-7.3
(m, 12H, Haryl) ppm. 13C NMR (101 MHz, C6D6, 25 °C): δ 22.2
(CH3), 24.1, 24.3, 25.1, 25.5 (CH(CH3)2), 28.6, 28.7 (CH(CH3)2),
1
81.2 (CH2), 95.1 (t, JCD ) 26 Hz, η6-C6D6), 105.3 (γ-C), 123.5,
124.0, 127.5, 127.6, 138.5, 138.9 (Caryl), 140.4 (NCCH3), 148.0,
148.2 (Caryl), 148.7 (NCCH2) ppm. 29Si NMR (79.5 MHz, C6D6,
25 °C): δ 100.4 (C6D6 complex). IR (KBr, cm-1): ν 465 (w), 531
(w), 610 (w), 677 (w), 746 (w), 760 (w), 802 (w), 918 (w), 980
(w), 1057 (w), 1072 (w), 1103 (w), 1176 (w), 1203 (w), 1252 (w),
1321 (w), 1356 (m), 1383 (m), 1443 (w), 1464 (w), 1550 (w), 1640
(w), 2866 (w), 2926 (w), 2960 (m), 3062 (w). EI MS (70 eV): m/z
(%) 580 (1) [M+], 502 (3) [M+ - C6H6], 444 (5) [M+ - Ni(C6H6)],
429 (100) [M+ - Ni(C6H6) - CH3], 414 (7) [M+ - Ni(C6H6) -
3
25 °C): δ 0.98, 1.19, 1.37, 1.40 (each d, JHH ) 6.8 Hz, 6H,
CH(CH3)2), 1.48 (s, 6H, CH3), 1.52 (s, 2H, NH2), 3.17, 3.56 (each
3
sept, JHH ) 6.8 Hz, 2H, CH(CH3)2), 4.89 (s, 1H, γ-H), 7.0 -7.4
(m, 6H, Haryl) ppm. 13C{1H} NMR (101 MHz, C6D6, 25 °C): δ
23.8 (CH3), 23.8, 24.1, 24.7, 26.2 (CH(CH3)2), 28.5, 29.5
(CH(CH3)2), 100.0 (γ-C), 124.7, 125.3, 128.5, 140.6, 143.3, 145.9
(Caryl), 166.2 (NCCH3), 200.6 (CO) ppm. 29Si NMR (79.5 MHz,
C6D6, 25 °C): δ 32.6 ppm. IR (toluene, cm-1): ν(CO) 1965, 1978,
2046. EI MS (70 eV): m/z (%) 547 (0.3) [M - 2CO]+, 519 (3) [M
- 3CO]+, 461 (9) [M - Ni(CO)3]+, 446 (100) [M - Ni(CO)3 -
2CH3], 401 (12) [M+
C35H46N2SiNi: C, 72.3;, H, 7.3; N, 4.8. Found: C, 72.2;, H, 8.0; N,
4.7.
-
Ni(C6H6)-iPr]. Anal. Calcd for
CH3]+, 418 (24) [M - Ni(CO)3
-
iPr]. Anal. Calcd for
Synthesis of L′Si(S)H (16). A 22 mL portion of H2S (0.93 mmol)
was slowly added to a solution of silylene 5 (344 mg, 0.77 mmol)
in 15 mL of toluene at -78 °C. The reaction mixture was warmed
to ambient temperature and then kept at -30 °C for 2 days. All
volatile components were removed under vacuum, and the slightly
yellow residue was dissolved in toluene. Cooling to -30 °C
overnight yielded X-ray-quality crystals of silathioformamide 16
(199 mg, 54%). 1H NMR (200 MHz, CDCl3, 25 °C): δ 1.17, 1.27,
C32H43N3O3SiNi: C, 63.6; H, 7.2; N, 7.0. Found: C, 63.9; H, 7.4;
N, 6.6.
Synthesis of L′Si(NHiPr)-Ni(CO)3 (23b). Isopropylamine (5.7
µL) was added to a solution of complex 13 (39 mg, 0.066 mmol)
in toluene (3 mL) at -60 °C. The reaction mixture was slowly
warmed to room temperature overnight. All volatiles were removed
in vacuo, and the residue was crystallized in hexane (12 mg, 29%).
1H NMR (400 MHz, C6D6, 25 °C): δ 1.03, 1.05, 1.17, 1.34, 1.44
3
1.34, 1.43 (each d, JHH ) 6.8 Hz, 6H, CH(CH3)2), 1.91 (s, 6H,
3
3
(each d, JHH ) 6.8 Hz, 6H; CH(CH3)2), 1.48 (s, 6H, CH3), 1.49
CH3), 2.95, 8.38 (each sept, JHH ) 6.8 Hz, 2H, CH(CH3)2), 5.58
(s, 1H, γ-H), 6.09 (s, JSiH ) 255 Hz, 1H, SH), 7.1-7.4 (m, 6H,
(s, 1H, NH), 2.84 (sept, 3JHH ) 6.8 Hz, 1H, NH-CH(CH3)2), 3.00,
3.98 (each sept, 3JHH ) 6.8 Hz, 2H, CH(CH3)2), 5.05 (s, 1H, γ-H),
7.0-7.3 (m, 6H, Haryl) ppm. 13C{1H} NMR (101 MHz, C6D6, 25
°C): δ 23.9 (CH3), 24.6, 24.8, 25.1, 25.5, 26.4 (CH(CH3)2), 27.3,
29.1, 47.3 (CH(CH3)2), 102.6 (γ-C), 125.1, 125.5, 128.6, 141.2,
144.0, 146.3 (Caryl), 167.8 (NCCH3), 200.8 (CO) ppm. 29Si NMR
(79.5 MHz, C6D6, 25 °C): δ 28.3 ppm. IR (hexane, cm-1): ν(CO)
1968, 1981, 2048. EI MS (70 eV): m/z (%) 589 (1) [M - 2CO]+,
561 (5) [M - 3CO]+, 559 (5) [M - 2CO - CH3]+, 503 (17) [M
- Ni(CO)3]+, 488 (100) [M - Ni(CO)3 - CH3]+, 460 (28) [M -
Ni(CO)3 - iPr]+. Anal. Calcd for C35H49N3O3SiNi: C, 65.0; H, 7.6;
N, 6.5. Found: C, 65.7; H, 7.0; N, 6.0.
1
Haryl). 13C{1H} NMR (50 MHz, CDCl3, 25 °C): δ 23.8 ppm, 24.3,
24.7, 25.0 (CH(CH3)2), 25.9 (CH3), 29.2, 29.2 (CH(CH3)2), 100.4
(γ-C); 124.6, 125.1, 128.0, 136.3, 145.2, 145.2 (Caryl), 171.4
(NCCH3). 29Si NMR (79.5 MHz, CDCl3, 25 °C): δ -16.8 ppm. IR
(KBr, cm-1): ν 2962 (s), 2927 (m), 2865 (m), 2127 (m, Si-H),
1544 (s), 1370 (s), 669 (m, SidS). EI MS (70 eV): m/z (%) 478
(10) [M]+, 463 (100) [M - CH3]+, 435 (11) [M - C3H7]+, 403 (7)
[M - C3H7 - S]+. Anal. Calcd for C32H42N2O3SSiNi: C, 72.75;
H, 8.84; N, 5.85. Found: C, 72.64; H, 8.90; N, 5.73.
Heterogeneous Reaction of Solid Silylene 5 with Gaseous
H2S. A 100 mg portion of silylene 5 (0,225 mmol) was placed in
a Schlenk tube with a Teflon-coated magnetic stirbar. The reaction
vessel was evacuated to 1 × 10-2 mbar and then filled with H2S to
standard pressure (approximately 100 mL, 4.5 mmol). The mixture
was stirred for 3 days, and then the hydrogen sulfide was replaced
by dry nitrogen. The resulting light yellow powder was analyzed
by solution 1H NMR as well as solid-state MAS 29Si NMR
spectroscopy. 29Si NMR (79.4 MHz, solid state, 25 °C): δ -17.9,
Synthesis of L′Si(NHNHPh)-Ni(CO)3 (23c). Phenylhydrazine
(6.2 µL, 0.063 mmol) was added to a solution of complex 13 (37
mg, 0.063 mmol) in toluene (3 mL) at -60 °C. The reaction mixture
was slowly warmed to room temperature overnight. All volatiles
were removed in vacuo, and the residue was crystallized in hexane
1
(17 mg, 39%). H NMR (400 MHz, C6D6, 25 °C): δ 0.94, 1.00,
3
1.38, 1.39 (each d, JHH ) 6.8 Hz, 6H, CH(CH3)2), 1.51 (s, 6H,
1
3
97.6. H NMR (200 MHz, C6D6, 25 °C): ratio of 5:16 4:6.
CH3), 3.12, 3.40 (each sept, JHH ) 6.8 Hz, 2H, CH(CH3)2), 3.98
Synthesis of L′Si(SH)-Ni(CO)3 (17). A 3 mL portion of
gaseous H2S was added via syringe to a solution of complex 13
(74 mg, 0.126 mmol) in toluene (3 mL) at -60 °C. The reaction
mixture was slowly warmed to room temperature overnight. The
yellow solution was removed, and the green precipitate was
recrystallized from toluene to give yellow crystals (21 mg, 27%).
(s, 1H, NH), 4.95 (s, 1H, NH), 5.13 (s, 1H, γ-H), 6.7-7.3 (m,
11H, Haryl) ppm. 13C{1H} NMR (101 MHz, C6D6, 25 °C): δ 23.8
(CH3), 24.1, 24.2, 24.8, 26.1 (CH(CH3)2), 27.7, 28.4 (CH(CH3)2),
101.5 (γ-C), 112.5, 119.5, 124.9, 125.5, 128.8, 129.5, 140.3, 143.5,
146.6, 150.2 (Caryl), 168.9 (NCCH3), 200.1 (CO) ppm. 29Si NMR
(79.5 MHz, C6D6, 25 °C): δ 25.7 ppm. IR (hexane, cm-1): ν(CO)
1973, 1985, 2051. EI MS (70 eV): m/z (%) 610 (1) [M - 3CO]+,
522 (41) [M - Ni(CO)3]+, 537 (100) [M - Ni(CO)3 - CH3]+,
522 (16) [M - Ni(CO)3 - 2CH3]+, 509 (45) [M - Ni(CO)3 -
(35) Sheldrick, G. M. SHELX-97 Program for Crystal Structure Determi-
nation; Universita¨t Go¨ttingen, Go¨ttingen, Germany1997.
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J. AM. CHEM. SOC. VOL. 132, NO. 9, 2010 3045

A R T I C L E S
Meltzer et al.
iPr]+. Anal. Calcd for C38H48N4O3SiNi: C, 65.6; H, 7.0; N, 8.0.
Found: C, 65.5; H, 6.4; N, 7.8.
Theoretical Calculations. DFT calculations were performed
employing the simplified model compounds 5′, 15a′, 15b′, and 16′
at the B3LYP level using 6-31G(d) basis sets of the GAUSSIAN-
03 program package. Optimized structures of model compounds
were obtained without symmetry constraints.
Jan-Dirk Epping (NMR Laboratories of the Institute of Chemistry,
TU Berlin) for solid-state MAS 29Si NMR measurements.
Supporting Information Available: Text, figures, tables, and
CIF files giving details of the X-ray crystal structure analyses
of 12c,d, 16, 17, and 23a-c, solid-state MAS 29Si NMR
spectrum of the product mixture from 5 and gaseous H2S, and
coordinates of the optimized model compounds 5′, 15a′, 15b′,
and 16′. This material is available free of charge via the Internet
at http://pubs.acs.org.
Acknowledgment. This work is dedicated to Prof. Herbert
Schumann (deceased, January 12, 2010). We are grateful to the
Cluster of Excellence “Unicat” (sponsored by the Deutsche Fors-
chungsgemeinschaft and administered by the TU Berlin) and to
the JSPS (fellowship for S.I.) for financial support. We thank Dr.
JA910305P
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3046 J. AM. CHEM. SOC. VOL. 132, NO. 9, 2010