Reactions of ruthenium cyclopropenyl complexes with trimethylsilyl azide

Article abstract of DOI:10.1039/a802199f

Treatment of three cyclopropenyl complexes [Ru]-C=C(Ph)CHR ([Ru] = (η⁵-C₅H₅)(PPh₃)₂Ru; R = Ph la, CN 1b, CH=CH₂ 1c} with Me₃SiN₃ afforded the nitrile complex 3a, the zwitterionic tetrazolate complex 6, and 7, respectively; for 1c, the triazole 8 was also obtained. c yclin@mail.ch.ntu.edu.tw.

Full text of DOI:10.1039/a802199f

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Reactions of ruthenium cyclopropenyl complexes with trimethylsilyl azide
Ku-Hsien Chang and Ying-Chih Lin*
Department of Chemistry, National Taiwan University Taipei, Taiwan 106, Republic of China
Treatment of three cyclopropenyl complexes [Ru]–
displays a singlet resonance at d 42.5. However, in the 31P NMR
5
CNC(Ph)CHR {[Ru] = (h -C5H5)(PPh3)2Ru; R = Ph 1a,
spectrum of 3a two doublet resonances at d 41.7 and 41.2 with
JPP 35.3 Hz indicate the presence of a diastereotopic center in
the N-coordinated nitrile ligand and, in the 1H NMR spectrum,
two resonances at 3.15 (JHH 16.6, 6.5 Hz) and 3.00 (JHH 16.6,
10.0 Hz) are assigned to the CH2 group. The parent peak of the
mass spectrum of 3a clearly indicates addition of one nitrogen
atom to 2a.
CN 1b, CHNCH2 1c} with Me3SiN3 afforded the nitrile
complex 3a, the zwitterionic tetrazolate complex 6, and 7,
respectively; for 1c, the triazole 8 was also obtained.
Organic cyclopropene is highly strained and its estimated strain
energy is > 50 kcal mol21 (1 cal = 4.184 J).1 This molecule
has played a crucial role in the development of important
concepts such as aromaticity and chemical reactivities.2 A few
recent papers focused on applications of various cyclopropenes
in organic synthesis.3 In organometallic systems, deprotonation
of a number of vinylidene complexes {[Ru]NCNC(Ph)CH2R}I
Treatment of 1b with TMSN3 at room temperature caused
addition of four nitrogen atoms to 1b and afforded the yellow
tetrazolate complex 6‡ in high yield and 7‡ in ca. 5% yield,
Scheme 1. Complex 6 is stable at room temperature, and in the
course of the reaction only a deep red color attributed to a
vinylidene intermediate 2b was observed. The intermediate 2b
5
{[Ru] = (h -C5H5)(PPh3)2Ru; R = CN, Ph, CHNCH2} readily
afforded ruthenium cyclopropenyl complexes.4 Protonation
opens the three-membered rings of these Ru complexes to give
back the vinylidene moiety. Nevertheless, in the ruthenium
system, the cyclopropenyl and the vinylidene complexes
display distinctive reactivities. We carried out reactions of
cyclopropenyl complexes with various organic substrates.
Herein we report the reaction of Me3SiN3 (TMSN3) with a
number of ruthenium cyclopropenyl complexes containing
different substituents at the cyclopropenyl ring to yield various
products.
could be isolated at 0 °C. In the H NMR spectrum of 6, a dd
1
resonance at d 4.32 (JHH 7.4, 7.7 Hz) is assigned to the methyne
proton and two multiplet resonances displaying doublets of an
AB pattern at d 2.66 (JHH 16.6, 7.4 Hz) and 2.44 (JHH 16.6, 7.7
Hz) are assigned to two methylene protons. In the 31P NMR
spectrum of 6, two doublet resonances at d 43.8 and 41.7 with
JPP 38.0 Hz are assigned to the two PPh3 ligands owing to the
presence of a diastereotopic center. The proton source of the
reactions of 1a and 1b is believed to come from water in TMSN3
(no attempt was made to dry TMSN3 due to potential hazards)
and protons are incorporated into the product through hydroly-
sis of the TMS substituents. TMSOH was distilled off with THF
solvent from the reaction mixture and identified by mass
spectrometry. In both reactions, addition of D2O to THF led to
incorporation of two deuterium atoms at two vicinal carbon
atoms of both 5 and 6. No reaction was observed between
{[Ru]NCNC(Ph)CH2CH}PF6 and TMSN3 possibly owing to the
covalent character of the Si–N bond in TMSN3 and weak
nucleophilicity of the cationic vinylidene complex to cleave the
Si–N bond.
Upon addition of a fivefold excess of TMSN3 to 1a in THF at
room temperature, the solution displayed color changes during
the course of the reaction. The light yellow solution of 1a turned
to deep red at the initial stage then became light orange in ca. 3
h and, after 5 h, turned yellow again. We thus carried out the
reaction at 210 °C and, while the solution was deep red,
isolated 2a‡ as the major product and the N-coordinated nitrile
complex 3a‡ as the minor product, Scheme 1. From the light
orange solution of the same reaction at room temperature, 3a
could be isolated in high yield. Finally with a 5 h reaction time
the reaction gave 45 and 5.6‡ As a precursor of 3a, 2a is unstable
at room temperature.
The reaction of 1a with TMSN3 may proceed by an
electrophilic addition of a TMS group followed by hydrolysis to
2
Complex 3a is also unstable and decomposes to give 4 and 5.
Exchange of the N32 counter anion with PF62 made 2a and 3a
more stable. In the 1H NMR spectrum of 2a, a singlet resonance
at d 3.50 is assigned to the CH2 group. The 31P NMR spectrum
afford 2a. Further nucleophilic addition of N3 at Ca and
electrophilic addition of a second TMS group at Cb followed by
loss of N2 gives the N-coordinated nitrile complex 3a,5 Scheme
1. In the reaction of 1b with TMSN3, formation of 6 is
Ph
+
[Ru]
NC
R = Ph
–
[Ru]
N
N3
[Ru] N3
+
+ Me3SiN3
H
R
Ph
R
1a R = Ph
b R = CN
3a R = Ph
4
5
Me3SiN3
H2O
R = Ph
[Ru]
Ru
PPh3
Ph
N
N
–
+
[Ru]
Ph3P
+
R = CN
C
–
N3
N
[Ru] CN
+
[Ru]
N
R
CN
2a R = Ph
b R = CN
6
7
Scheme 1
Chem. Commun., 1998
1441

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H
Notes and References
Ph
N
xs. Me3SiN3
N
N
† E-mail: yclin@mail.ch.ntu.edu.tw
[Ru]
[Ru] CN
+
Ph
‡ Selected spectroscopic data: 1H and 13C-{1H} NMR were recorded in
CDCl3 relative to SiMe4 and 31P NMR data with H3PO4 as external standard
in CDCl3. 2a: 1H NMR, d 7.41–6.80 (m, 45 H, Ph), 5.21 (s, 5 H, Cp), 3.56
7
H
(s, 2 H, CH2); 31P NMR, d 42.5 (s). FAB MS: m/z 883 (M+), 691 (M+
2
8
CCPhCH2Ph). 2b: 1H NMR, d 7.50–6.96 (m, 35 H, Ph), 5.21 (s, 5 H, Cp),
3.22 (s, 2 H, CH2). 3a: 1H NMR (253 K), d 7.43–6.85 (m, 45 H, Ph), 4.50
(t, JHH 10.0, 6.5 Hz, 1 H, CH), 4.33 (s, 5 H, Cp), 3.15, (JHH 16.6, 6.5 Hz, 1
H, CH2), 3.00 (JHH 16.6, 10.0 Hz, 1 H, CH2). 13C NMR (253 K), d
136.4–127.2 (Ph), 83.6 (Cp), 41.3 (CH), 40.0 (CH2). 31P NMR, d 41.7, 41.2
(two d, JPP 35.3 Hz). FAB MS: m/z 898 (M+), 691 (M+ 2 NCCHPhCH2Ph).
4: 1H NMR, d 7.68–7.07 (m, 30 H, Ph), 4.18 (s, 5 H, Cp); 13C NMR, d
138.4–127.4 (Ph), 81.3 (Cp); 31P NMR, d 41.8 (s). FAB MS: m/z 733.1
(M+); 705.0 (M+ 2 N2). Anal. Calc. for C41H35N3P2Ru: C, 67.20; H, 4.81;
N, 5.73. Found: C, 67.92; H, 4.95; N, 4.91%. 5: 1H NMR, d 7.43–7.09 (m,
10 H, Ph), 3.98 (dd, JHH 8.4, 6.7 Hz, 1 H, CH), 3.17, (dd, JHH 13.7, 6.7 Hz,
1 H, CH2) 3.11 (dd, JHH 13.7, 8.4 Hz, 1 H, CH2). HRMS: m/z 207.1050
(M+). Anal. Calc. for C15H13N: C, 86.92; H, 6.32; N, 6.76. Found: C. 87.01;
H, 6.30; N, 6.65%. 6: 1H NMR (C6D6), d 7.59–6.81 (m, 35 H, Ph), 4.45 (dd,
Me3SiN3
1c
Ph
N3
N3
+
[Ru]
+
C
H2O
–
Me3SiN3
[Ru]
[Ru]
Ph
Ph
–
N3
N3
Me3Si
A
B
C
Scheme 2
J
HH 7.4, 7.7 Hz, 1 H, CH), 4.30 (s, 5 H, Cp), 2.66, (JHH 16.6, 7.4 Hz, 1 H,
CH), 2.44 (JHH 16.6, 7.7 Hz, 1 H, CH2); 13C NMR, d 164.1 (CNN, Ca),
140.2 (Cipso), 138.3–127.1 (Ph), 118.6 (CN), 83.1 (Cp), 39.9 (CH), 23.5
(CH2). 31P NMR, d 43.8, 41.7 (two d, JPP 38.0 Hz). FABMS: m/z 889.2 (M+
rationalized by a [3 + 2] cycloaddition of the CN bond with a
second N32.7 As early as 1958, formation of tetrazolate ring
structure has been observed in the [3 + 2] cycloaddition reaction
of a nitrile group with azide.8 Metal-coordinated azide ligands
undergo 1,3-dipolar cycloaddition reactions with carbon–
carbon and carbon–heteroatom multiple bonds. Among others,
this chemistry has been investigated by the group of Beck. The
metals involved are most often palladium(ii),9 platinum(ii)10
and cobalt(iii)11 although a whole range of other transition
metals12 has been used. These metal azido complexes react with
nitrile to give various tetrazolate complexes.13 Formation of the
tetrazolate ring in 6 is derived from the reaction of nitrile with
[Ru]–N3 since under our mild reaction condition, no such
reaction was observed. The reaction of the acetylide complex
[Ru]–C·CPh with an excess of TMSN3 afforded 4 and
PhCH2CN, identified by elemental analysis and high resolution
mass spectroscopy. Conversion of a vinylidene precursor to
N-coordinated nitrile by hydrazine, an organometallic Beck-
mann rearrangement, has been reported in an iron system.14
Interestingly, treatment of 1c with an excess of TMSN3
afforded 7 and 8,‡ Scheme 2. The organic product is identified
by elemental analysis and high resolution mass spectrometry.
Formation of 7 and 8 by cleavage of the CNC double bond of the
cyclopropenyl ring and transformation of the vinyl to an ethyl
group could be explained as followed. Addition of a TMS group
to the terminal carbon atom of the vinyl group accompanied by
opening of the three-membered ring resulted in formation of A,
Scheme 2. We previously reported that the reaction of TCNQ
with 1c gave similar addition at the terminal carbon of the vinyl
group.4 Subsequent nucleophilic addition of N32 at Ca followed
by hydrolysis gave B. Further addition of TMSN3 at Cd
followed by hydrolysis led to the formation of C. The single
bond character of the Ca–Cb in C facilitates its cleavage, which
is accompanied by a [3 + 2] cycloaddition of the Cb–Cg double
bond with N32 to give the triazole compound 8 and 7. The fact
that 7 is isolated in this reaction as the only organometallic
product suggests that it is not likely to have an intermediate with
a terminal N-coordinated nitrile ligand. Formation of 7 as a
minor product in the reaction of 1b with TMSN3 could proceed
through the same pathway. A detailed mechanism for these
processes is currently under investigation.
+ 1, Ru
=
104), 691 (M+ 2 N4C2HPhCH2CN), 429 (M+ 2 PPh3,
N4C2HPhCH2CN). Anal. Calc. for C51H43N5P2Ru: C, 68.91; H, 4.88; N,
7.88. Found: C, 69.20; H, 4.96; N, 7.96%. 7: 1H NMR, d 7.69–6.95 (m, 30
H, Ph, 4.36 (s, 5 H, Cp); 13C NMR, d 138.2–127.3 (Ph), 85.0 (Cp); 31P
NMR, d 50.3 (s). FABMS: m/z 717.0 (M+); 691.0 (M+ 2 CN). Anal. Calc.
for C42H35NP2Ru: C, 70.38; H, 4.92; N, 1.95. Found: C, 69.94; H, 4.85; N,
2.06%. 8: 1H NMR, d 7.31–7.19 (m, 5 H, Ph), 2.89 (q, JHH 7.6 Hz, 2 H,
CH2), 1.30 (t, JHH 7.6 Hz, 3 H, CH3). HRMS: m/z 173.0952 (M+). Anal.
Calc. for C10H11N3: C, 69.34; H, 6.40; N, 24.26. Found: C, 69.53; H, 6.21;
N, 23.98%.
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We are grateful for support of this work by the National
Science Council, Taiwan, the Republic of China.
Received in Cambridge, UK, 20th March 1998; 8/02199F
1442
Chem. Commun., 1998