Reactions of d0 tungsten alkylidyne complexes with O2 or H2O. Formation of an oxo siloxy complex through unusual silyl migrations

Article abstract of DOI:10.1039/c3cc46014b

(Me₃SiCH₂)₃(Me₃SiC) W←OPMe₃ (1), an adduct between (Me₃SiCH ₂)₃WCSiMe₃ (2) and OPMe₃, reacts with O₂ to give OW(OSiMe₃)(CH<

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Reactions of d0 tungsten alkylidyne complexes with O2 or H2O. Formation of an
oxo siloxy complex through unusual silyl migrations
Laurel A. Morton, Maozhong Miao, Tabitha M. Callaway, Tianniu Chen, Shu-Jian Chen, Albert A. Tuinman,
Xianghua Yu, Zheng Lu, and Zi-Ling Xue*
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
(Me3SiCH2)3(Me3SiC≡)W←O=PMe3 (1), an adduct between
(Me3SiCH2)3W≡CSiMe3 (2) and O=PMe3, reacts with O2 to
give O=W(OSiMe3)(CH2SiMe3)3 (3) and CO2. Reaction of 2
10 with H2O yields 3 and the trimer [(ꢀ-O)W(CH2SiMe3)2(=O)-
(THF)]3 (4). In the reaction of D2O with 2, 3-dn and methane
isotopologues CH2D2, CHD3 and CD4 have been observed.
Early transition metal complexes are often sensitive to O2 and
15 H2O.1,2 Reactions of O2 with d0 complexes are often unique,
leading to the oxidation of ligands.1 In comparison, reactions of
O2 with dn complexes usually involve the oxidation of metals.
Earlier studies showed O insertion into the M-Si and M-C bonds
of d0 complexes in their reactions with O2.1c-k The use of redox-
20 active ligands in a Zr(IV) complex leads to the isolation of a
bisperoxo complex.1a We have found that the reaction of O2 with
d0 silyl alkylidyne 5a and its bis-alkylidene tautomer 5b leads to
the formation of the oxo alkylidene compound 6 (Eq. 1).1r The
nature of reactions between early transition metal complexes and
25 H2O has also been of intense interest.2 The reaction of water with
d0 (ButCH2)3W≡CBut (7) was found to give CMe4 and
O[W(=O)(CH2But)3]2 (8, Eq. 2).2f We found earlier that
(ButCH2)3W≡CSiMe3 (9) reacted with D2O, through a rate-
determination process, to give the oxo 10-d4 which then
30 selectively loses the CD2SiMe3 ligands, yielding the trimer 11
Scheme 1. Reactions of 2. SiMe4 was observed by NMR.
40
the trimer 4, through O-H addition to the W≡CSiMe3 bond and
elimination of SiMe4. When 2 reacts with D2O, analysis by high-
resolution mass spectrometry (HRMS) reveals the formation of
the methane isotopologues CH2D2, CHD3 and CD4.
45
1 was prepared from 2 and O=PMe3.8 The 13C NMR peak of
327.39 ppm for C≡W in the 14e 1 is up-field shifted from 343.67
ppm in 12e 2. The W≡C bond length of 1.763(7) Å in 1 (Fig. 1) is
slightly longer than 1.739(8) Å in (ButCD2)3W≡CSiMe3 (9-d6).9
When 1 was exposed to O2, it was found to convert to
50 O=W(OSiMe3)(CH2SiMe3)3 (3).8 A quantitative MS analysis of
the gaseous products using 13CO2 revealed the formation of CO2,
and the molar ratio of 3 : CO2 is ca. 1.0 : 0.9 (Scheme 1).8 In
comparison, when 2 was exposed to O2 in the absence of
O=PMe3, it decomposed to unknown species. Addition of 2 to the
55 reaction mixture from 1 and O2 and crystallization gave crystals
of 12 as a 1:1 adduct between 3 and 2.8 The 29Si NMR peak of
OSiMe3 at 10.74 ppm is downfield shifted from those of C≡W-
CH2SiMe3 at –1.50 ppm, O=W-CH2SiMe3 at –2.97 ppm, and
≡CSiMe3 at –19.76 ppm in 12.8 The X-ray structure of 12 reveals
60 a C3 axis through the C≡W←O=W-O-Si bonds, giving thus a
linear W(2)-O(2)-Si(4) linkage (Fig. 1). 3 and 2 are bonded
3
(Eq. 3). Reactions of d0 complexes with O2 or H2O4 have been
used recently to make metal oxides as microelectronic insulating
materials, leading to significant drops in leakage currents in
transistors. We have found that the reaction of O2 with d0
1
35 surprisingly yields the oxo siloxide 3 and CO2 (Scheme 1). One
SiMe3 group in 1 undergoes an unusual migration to give the
OSiMe3 ligand in 3.5,6 Unexpectedly, 27 reacts with H2O to yield
3 as well. CH4 is generated in the reaction. Another product is
through a W=O→W dative bond [2.578(6)
distance of 1.775(11) Å in 12 is longer than those in 9-d6
[1.739(8) Å]9 and 1 [1.763(7)
], perhaps as a result of trans
Å]. The W≡C bond
Å
65 influence by 2. The W=O bond distance of 1.735(6) Å in 12 is
similar to those in other W oxo complexes.2f,5e,10
The pathway in the formation of 3 from 1 is not clear. The
alkylidyne carbon atom in 1 is the most electron-rich atom with a
formal -4 charge. It is thus not surprising that the W≡C bond in 1
70 is attacked by O2, an oxidant, yielding A in Scheme 2. Additional
attack by O2 and oxidation of the C atom give CO2. The unusual
silyl migration in B is perhaps driven by the oxophilicity of
silicon.
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Scheme 3
by H2O through Path I, eliminating two molecules of SiMe4 to
give dioxo 4 containing two alkyl ligands. In other words, rates of
50 two competing paths here lead to two different products. Perhaps
in the reaction of 10-d4 with D2O (Eq. 3), attack by D2O is fast,
removing the CD2SiMe3 ligands before they undergo a migration.
When 2 in THF-d8 was added D2O (99.9% D, ca. 5 equiv),8,11
we were surprised to find that an HRMS analysis of the methane
55 isotopologues gave the following ratios of CH4 : CH3D : CH2D2 :
CHD3 : CD4 = 0 : 3 : 100 : 19 : 32(± 5)% (Fig. 3). CH2D2 and
CHD3 were unexpectedly major products in the reaction. 2H
NMR spectrum of the reaction of 2 with D2O (Fig. S1) revealed
the formation of SiMe4-dn and O=W(OSiMe3)(CH2-nDnSiMe3)3
60 (3-dn) containing partially deuterated ligands.8 It should be noted,
although the glassware was pre-dried (0.01 torr, >400 °C),8,11
silanol groups apparently remained. They may exchange with
D2O, leading to a higher H/D ratio.8 Thus, the above ratios of the
methane isotopologues are analysed qualitatively below.
Fig. 1 Structures of 1 (Left) and 12 (Right). Bond lengths (Å) and angles
(°): 1 C4-W1 1.763(7), O1-W1 2.307(7), C4-W1-O1 179.5(3), P1-O1-W1
178.5(5). 12 C1-W1 1.775(11), O1-W2 1.735(6), O2-W2 1.9246,
O1→W1 2.578(6), O2-Si4 1.630(6), C1-W-C3 100.45(15), O1-W2-C7
92.33(14), O2-W2-C7 87.67(14).
5
Scheme 2. Part of the proposed pathway in the reaction of 1 with
O2.
The alkyl alkylidyne 2 reacts with water, yielding CH4, SiMe4,
10 and two complexes (Scheme 1). One is trimer 4 which is similar
to 112n in Eq. 3. The crystal structure of 4 is given in Fig. 2. It is
surprising that O=W(OSiMe3)(CH2SiMe3)3 (3) was also isolated
from the reaction (Scheme 1), indicating a SiMe3 migration to a
W=O ligand in the reaction. When the reaction was conducted at
15 23 °C, the molar ratio of 3 : 4 is 0.7 : 1. The yield of 3 is higher at
-25 °C or below. When 2 reacted with H2O at -78 °C, the ratio
was 29 : 1. When powders of 2 were added H2O in THF at -25
°C, the yield of 3 was also higher with 3 : 4 = 13 : 1.
100
65
CX
2
80
CX
3
CX
4
60
40
MS analyses of the gaseous products using 13CH4 as the
20 calibration showed the formation of 0.62 equiv of CH4 when 1
reacts with 2 equiv of H2O.8 Since the yield of 3 is ca. 66%, the
ratio of CH4 and 3 in the reaction mixture is ca. 1:1. A
mechanism consistent with the observations is given in Path II in
Scheme 3. The ≡C- atom in 2 is basic. Addition of H2O to the
25 W≡C bond in 2 leads to the formation of the hydroxyl alkylidene
E and oxo F. The oxophilic SiMe3 group in one of the CH2SiMe3
ligands in F then undergoes a migration to the oxo ligand in Path
II, yielding the OSiMe3 and a methylene ligand in C. Addition of
a second H2O molecule gives 3 and CH4. F may also be attacked
30
70
20
0
15
16
17
18
19
20
Mass
Fig. 3 The HRMS for the methane isotopologues in the 15-20 Dalton
75 region. Isotopologues of methylene (CX2), methyl (CX3) and methane.
(CX4) are given in black, red, and blue colours, respectively.8
H
OD
OD
W
Me3Si
Me3Si
Me3Si
SiMe3
H
D2O
SiMe3
D
Me3Si
Me3Si
Me3Si
Me3Si
W
SiMe3
W
D
SiMe3
I
2
J
SiMe3
O
O
D
H
Me3Si
SiMe3
D
SiMe3
Me3Si
Me3Si
SiMe3
D
W
W
D
H
Me3Si
K
L
SiMe3
SiMe3
SiMe3
SiMe3
SiMe3
H
D
+
H
Me3Si
D
Me3Si
O
O
O
O
Me3Si
Me3Si
Me3Si
H2C
SiMe3
D
SiMe3
D
W
W
CD2
W
W
CHD
H2C
H
D
Me3Si
SiMe3
D2O
SiMe3
SiMe3
D2O
M
N
O
SiMe3
D2O
P
D2O
CD4
35
3-d2
CH2D2
CH2D2
3-
d
2
CHD3
3-d1
+ 3
+
+
Scheme 4
The formation of CH2D2 and CHD3 and observation of
80 O=W(OSiMe3)(CH2-nDnSiMe3)3 (3-dn) are consistent with
exchanges of the α-H atoms between =CDSiMe3 and –CH2SiMe3
in I in Scheme 4 to yield J containing a W=CH– bond, after the
D–OD addition to the W≡C– bond in 2. Similar α-H migrations
have been reported.9,12 In addition to the α-H exchange, the
85 migration of the second D atom in W-OD to the W=CDSiMe3
40
Fig. 2 Structure of 4. Bond lengths (Å) and angles (°): W1-C11 2.167(4),
W1-C12 2.159(4), W1-O1 2.363(3), W1-O4 1.758(3), W1B-O4 2.239(3),
W1-O4A 2.239(3), W1-O5 1.711(3), O4-W1-O4A 89.0(2), O5-W1-O1
45 86.3(1), W1-O4-W1A 150.9(1), W1-C12-Si1 118.3(2).
2
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ligand affords the tetraalkyl W oxo intermediate K. In J,
65
70
subsequent D migration from W-OD to W=CH- yields L. The
SiMe3 group in one of these alkyl ligands in K and L undergoes
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give M/N and G/P, respectively, containing a methylene ligand
(W=CD2– in M, W=CH2– in N/O, or W=CHD– in P), which
subsequently reacts with D2O to yield the methane isotopologues.
The presence of HOD in the D2O-THF-d8 may lead to the
formation of 3(± 5)% CH3D.9,11
5
10
It is interesting to note that the reactions of H2O with
75
2. For reactions of H2O with d0 complexes or their moisture sensitivity,
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(ButCH2)3W≡CBut (7, an analog of 2, Eq. 2), and
(ButCH2)2Mo(=CHBut)(=NBut)
give
82f
and
[{Mo(=NBut)(CH2But)3}2(MoO4)],2g respectively. The alkylidene
intermediate (ButCH2)3W(=CDBut)(OD) in the reaction of 7 with
80
15 D2O does not undergo α-H migration.2f Reactions of H2O/O2 with
d4 Cp*M(NO)(CH2SiMe3)2 (M = Mo, W) afford Cp*M(=O)2-
(CH2SiMe3),2h with no SiMe3 migration to the oxo ligands.
The formation of the novel siloxide 3 demonstrates rich
chemistry in the reactions of d0 complexes with O2 or H2O. The
20 reactions of 1 with O2 and 2 with H2O are of different nature: The
former a redox reaction and the latter an acid-base reaction. Both,
however, involve the alkylidyne carbon atoms and yield the same
complex 3. At the oxidation state of -4, the ≡C- atoms in 1 and 2
are electron rich. Two molecules of O2, an oxidant, obtain a total
25 of 8 electrons from the ≡C atom in 1, oxidizing it to CO2 and
yielding 3. When 2 is exposed to H2O, the ≡C- atom in 2 acts as a
base, abstracting a total of four H+ ions from two H2O molecules,
yielding 3 and converting itself to CH4. Oxophilicity of silicon
and tungsten plays a critical role here, obtaining oxygen atoms
30 and driving the formation of CO2 and CH4 in the reactions.
We thank the US National Science Foundation (CHE-
1012173) for financial support, Profs. George M. Sheldrick and
Craig E. Barnes for help with the structure of 12, and Michael
Bleakley for assistance.
85
90
95
100
105
110
115
120
35 Notes and references
Department of Chemistry, University of Tennessee, Knoxville, Tennessee
37996, USA. Tel:+1-865-974-3443; E-mail: xue@utk.edu
† Electronic Supplementary Information (ESI) available: Experimental
section, aditional HDMS analysis, and cif files of X-ray crystal structures.
40 See DOI: 10.1039/b000000x/
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