Preparation of half-sandwich alkoxycarbene complexes of osmium(II)

Article abstract of DOI:10.1021/om101105s

Alkoxy-alkylcarbene complexes [OsCl{=C(OR′)CH ₂R′′}(η⁶-p-cymene)L]BPh₄ (1-4) [R′ = Me, Et; R′′ = Ph, p-tolyl, Bu^t; L = P(OMe)₃, P(OEt)₃, PPh(OEt)₂, PPh ₂OEt] were prepared by allowing dichloro compounds OsCl ₂(η⁶-p-cymene)L to react with terminal alkyne R′′C=CH in alcohol. Ethoxy-methylcarbene [OsCl{=C(OEt)CH ₃}(η⁶-p-cymene)L]BPh₄ (5) was also prepared from reaction with trimethylsilyl acetylene. A reaction path for the formation of compounds 1-5, involving the nucleophilic attack of alcohol on intermediate vinylidene complexes, is discussed. Acetylide derivatives OsCl(C=CAr) (η⁶-p-cymene)L (6, 7) [Ar = Ph, p-tolyl; L = P(OMe)₃, P(OEt)₃, PPh(OEt)₂] were prepared by reacting dichloro compounds OsCl₂(η⁶-p-cymene)L with lithium acetylide (Li⁺[ArC=C]^-) in thf. Protonation reaction with Bronsted acids of 6 and 7 led to vinylidene cations [OsCl{=C=C(H)Ar} (η⁶-p-cymene)L]⁺. Complexes OsCl₂(η ⁶-p-cymene)L also reacted with both PhC=CH and (CH₃) ₃SiC=CH in the presence of H₂O to give alkyl-carbonyl derivatives [Os(η¹-CH₂Ph)(CO)(η⁶-p- cymene)L]BPh₄ (8) and [Os(η¹-CH₃)(CO) (η⁶-p-cymene)L]BPh₄ (9). The complexes were characterized spectroscopically (IR and ¹H, ¹³C, ³¹P NMR) and by X-ray crystal structure determinations of [OsCl{=C(OEt)CH₂Ph}(η⁶-p-cymene){PPh(OEt) ₂}]BPh₄ (1c), [OsCl{=C(OEt)CH₂Ph} (η⁶-p-cymene)(PPh₂OEt)]BPh₄ (1d), and [Os(η¹-CH₂Ph)(CO)(η⁶-p-cymene){PPh(OEt) ₂}]BPh₄ (8c).

Full text of DOI:10.1021/om101105s

ARTICLE
pubs.acs.org/Organometallics
Preparation of Half-Sandwich Alkoxycarbene
Complexes of Osmium(II)
Gabriele Albertin,*,† Stefano Antoniutti,† and Jesꢀus Castro‡
†Dipartimento di Scienze Molecolari e Nanosistemi, Universitꢁa Ca' Foscari Venezia, Dorsoduro 2137, 30123 Venezia, Italy
‡Departamento de Química Inorgꢀanica, Universidade de Vigo, Facultade de Química, Edificio de Ciencias Experimentais,
36310 Vigo (Galicia), Spain
S Supporting Information
b
ABSTRACT: Alkoxy-alkylcarbene complexes [OsCl{d
C(OR0)CH2R00}(η6-p-cymene)L]BPh4 (1-4) [R0 = Me, Et;
R00 = Ph, p-tolyl, But; L = P(OMe)3, P(OEt)3, PPh(OEt)2,
PPh2OEt] were prepared by allowing dichloro compounds
OsCl2(η6-p-cymene)L to react with terminal alkyne R00CtCH
in alcohol. Ethoxy-methylcarbene [OsCl{dC(OEt)CH3}(η6-
p-cymene)L]BPh4 (5) was also prepared from reaction with
trimethylsilyl acetylene. A reaction path for the formation of
compounds 1-5, involving the nucleophilic attack of alcohol
on intermediate vinylidene complexes, is discussed. Acetylide
derivatives OsCl(CtCAr)(η6-p-cymene)L (6, 7) [Ar = Ph, p-
tolyl; L = P(OMe)3, P(OEt)3, PPh(OEt)2] were prepared by
reacting dichloro compounds OsCl2(η6-p-cymene)L with
lithium acetylide (Liþ[ArCtC]-) in thf. Protonation reaction
with Brønsted acids of 6 and 7 led to vinylidene cations
[OsCl{dCdC(H)Ar}(η6-p-cymene)L]þ. Complexes OsCl2(η6-p-cymene)L also reacted with both PhCtCH and
(CH3)3SiCtCH in the presence of H2O to give alkyl-carbonyl derivatives [Os(η1-CH2Ph)(CO)(η6-p-cymene)L]BPh4 (8) and
1
[Os(η1-CH3)(CO)(η6-p-cymene)L]BPh4 (9). The complexes were characterized spectroscopically (IR and H, 13C, 31P NMR)
and by X-ray crystal structure determinations of [OsCl{dC(OEt)CH2Ph}(η6-p-cymene){PPh(OEt)2}]BPh4 (1c),
[OsCl{dC(OEt)CH2Ph}(η6-p-cymene)(PPh2OEt)]BPh4 (1d), and [Os(η1-CH2Ph)(CO)(η6-p-cymene){PPh(OEt)2}]BPh4 (8c).
’ INTRODUCTION
compounds OsCl2(p-cymene)L (L = phosphite, phosphonite, or
phosphinite) react with terminal alkynes RCtCH in alcohol to
give novel alkoxycarbene derivatives. The results of these studies,
which include the synthesis and characterization of new alkoxy-
alkylcarbene, acetylide, and η1-alkyl derivatives of osmium(II),
are reported here.
Transition metal carbene complexes1 are an important class of
compounds that continue to be extensively studied, both for their
chemical reactivity and for catalytic applications in several
processes, including olefin metathesis and carbon-carbon and
carbon-heteroatom coupling reactions.2
A large number of carbene complexes were thus prepared for
several metals,1 although third-row transition metals have tradi-
tionally been considered of no practical use in catalysis, because
they form bonds stronger than their 3d and 4d homologues with
the ligands typically involved in catalytic transformations.3 In the
iron triad, for example, osmium has been used to prepare stable
models of reactive intermediates, proposed in catalytic transfor-
mations with ruthenium.4 Nevertheless, the carbene chemistry of
osmium has been extensively developed in recent years, and a
large number of osmium(0) and osmium(II) complexes contain-
ing either OsdCR2 or OsdC(H)R units have been prepared.5
Instead, less attention has been paid to Fisher-type carbene
complexes containing heteroatoms, and the alkoxycarbene
OsdC(OR0)R00 are quite rare.6
’ EXPERIMENTAL SECTION
General Comments. All synthetic work was carried out under
argon using standard Schlenk techniques or an inert atmosphere drybox.
Once isolated, the complexes were found to be relatively stable in air, but
were stored at -25 °C. All solvents were dried over appropriate drying
agents, degassed on a vacuum line, and distilled into vacuum-tight
storage flasks. OsO4 was a Pressure Chemical Co. (USA) product, used
as received. Phosphonite PPh(OEt)2 and phosphinite PPh2OEt were
prepared by the method of Rabinowitz and Pellon,8 while P(OEt)3 and
P(OMe)3 were Aldrich products, purified by distillation under nitrogen.
Other reagents were purchased from commercial sources in the highest
available purity and used as received. Infrared spectra were recorded on a
In the course of our investigations on half-sandwich arene
Received: November 25, 2010
Published: February 22, 2011
complexes of the iron triad,7 we have now found that the dichloro
r
2011 American Chemical Society
1558
dx.doi.org/10.1021/om101105s Organometallics 2011, 30, 1558–1568
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Organometallics
ARTICLE
Chart 1
2H, dC(OCH2CH3)], 4.11, 3.98 (m, 4H, CH2 phos), 2.59 (m, 1H,
CH), 1.98 (s, 3H, p-CH3 p-cym), 1.47, 1.42 (t, 6H, CH3 phos, JHH = 7.0
Hz), 1.38 [t, 3H, dC(OCH2CH3), JHH = 7.0 Hz], 1.16, 1.14 (d, 6H,
CH3 iPr, JHH = 7.1 Hz) ppm. 31P{1H} NMR (CD2Cl2, 25 °C) δ: 95.7
(s) ppm. 13C{1H} NMR (CD2Cl2, 25 °C) δ: 286.5 (d, OsdC, JCP
=
15.9 Hz), 165-122 (m, Ph), 119.24 (d, br, C1 p-cym, JCP = 1.4 Hz),
105.21 (br, C4 p-cym), 93.01 (d, C3 p-cym, JCP = 3.4 Hz), 88.31 (d, C6
p-cym, JCP = 3.1 Hz), 86.91 (d, C2 p-cym, JCP = 5.9 Hz), 86.38 (s, br, C5
p-cym), 76.58 [s, dC(OCH2CH3)], 65.1, 64.5 (d, CH2 phos, JCP = 9.9,
JCP = 7.3 Hz), 54.3 [br, dC(CH2Ph)], 31.1 (s, CH), 22.25, 21.96 (s,
Perkin-Elmer Spectrum-One FT-IR spectrophotometer. NMR spectra
(1H, 13C, 31P) were obtained on an AVANCE 300 Bruker spectrometer
at temperatures between -90 and þ30 °C, unless otherwise noted. 1H
and 13C spectra are referred to internal tetramethylsilane; assignments
are referred to Chart 1. 31P{1H} chemical shifts are reported with respect
to 85% H3PO4, with downfield shifts considered positive. COSY,
HMQC, and HMBC NMR experiments were performed with standard
programs. The SwaN-MR and iNMR software packages9 were used to
treat NMR data. The conductivity of 10-3 mol dm-3 solutions of the
complexes in CH3NO2 at 25 °C was measured on a CDM 83 radio-
meter. Elemental analyses were determined in the Microanalytical
Laboratory of the Dipartimento di Scienze Farmaceutiche, University
of Padova (Italy).
i
CH3 Pr), 17.97 (s, p-CH3 p-cym), 16.29, 16.28 (d, CH3 phos, JCP = 7.3
Hz), 14.59 [s, dC(OCH2CH3)] ppm. Anal. Calcd for
C54H61BClO3OsP: C, 63.24; H, 6.00; Cl, 3.46. Found: C, 63.39; H,
6.07; Cl, 3.52.
1d: 1H NMR (CD2Cl2, 25 °C) δ: 6.86-5.76 (m, 35H, Ph), 5.28 (d,
HA p-cym, JAB = 6.2, JAC = 0.4, JAD = 0.8 Hz), 5.00 (d, HB p-cym, JBC
=
0.8, JBD = 0.4 Hz), 5.16 (d, HC p-cym, JCD = 6.2 Hz), 5.14 (d, HD p-
cym), 5.21, 3.63 [d, 2H, dC(CH2Ph), JHH = 12.8 Hz], 4.63 [m, 2H,
dC(OCH2CH3)], 3.74, 3.58 (m, 2H, CH2 phos), 2.57 (m, 1H, CH),
1.96 (s, 3H, p-CH3 p-cym), 1.42 [t, 3H, dC(OCH2CH3), JHH = 7.0 Hz],
i
1.25, 1.24 (t, 3H, CH3 phos, JHH = 7.0 Hz), 1.14, 1.12 (d, 6H, CH3 Pr,
JHH = 7.1 Hz) ppm. 31P{1H} NMR (CD2Cl2, 25 °C) δ: 81.3 (s) ppm.
13C{1H} NMR (CD2Cl2, 25 °C) δ: 291.8 (d, OsdC, JCP = 15.0 Hz),
165-122 (m, Ph), 116.17 (s, br, C1 p-cym), 99.95 (s, br, C4 p-cym),
93.00 (s, br, C5 p-cym), 87.82 (s, br, C3 p-cym), 86.65 (s, br, C2 p-cym),
85.14 (d, C6 p-cym, JCP = 6.4 Hz), 76.71 [s, dC(OCH2CH3)], 66.07 (d,
Synthesis of Complexes. Compounds [OsCl(μ-Cl)(η6-p-cym-
ene)]2 and OsCl2(η6-p-cymene)L [L = P(OMe)3, P(OEt)3, PPh-
(OEt)2, PPh2OEt] were prepared following the reported methods.7b,c,10
[OsCl{dC(OEt)CH2Ar}(η6-p-cymene)L]BPh4 (1, 2) [Ar = Ph
(1), p-tolyl (2); L = P(OMe)3 (a), P(OEt)3 (b), PPh(OEt)2 (c),
PPh2OEt (d)]. In a 25 mL three-necked round-bottomed flask were
placed 0.2 mmol of the appropriate chloro complex OsCl2(η6-p-
cymene)L, 137 mg (0.4 mmol) of NaBPh4, and 3.5 mL of ethanol. An
excess of the appropriate alkyne ArCtCH (0.6 mmol) was added to the
resulting mixture, which was stirred for 3 h. A yellow solid slowly
separated out, which was filtered and crystallized from CH2Cl2 and
ethanol; yield g75%.
CH2 phos, JCP = 12.3 Hz), 54.8 [br, dC(CH2Ph)], 30.89 (s, CH), 22.43,
i
21.63 (s, CH3 Pr), 17.60 (s, p-CH3 p-cym), 16.17 (d, CH3 phos, JCP
=
7.5 Hz), 14.43 [s, dC(OCH2CH3)] ppm. Anal. Calcd for
C58H61BClO2OsP: C, 65.87; H, 5.81; Cl, 3.35. Found: C, 66.00; H,
5.95; Cl, 3.48.
2c: 1H NMR (CD2Cl2, 25 °C) δ: 7.56-6.86 (m, 29H, Ph), 5.47 (d,
HA p-cym, JAB = 6.4, JAC = 0.4, JAD = 0.8 Hz), 5.40 (d, HB p-cym, JBC
=
0.8, JBD = 0.4 Hz), 5.39 (d, HC p-cym, JCD = 6.4 Hz), 5.30 (d, HD p-
cym), 5.30, 2.91 [d, 2H, dC(CH2Ar), JHH = 12.9 Hz], 4.42, 4.27 [m, 2H,
dC(OCH2CH3)], 4.09, 3.97 (m, 4H, CH2 phos), 2.59 (m, 1H, CH),
2.33 (s, 3H, CH3 p-tolyl), 1.96 (s, 3H, p-CH3 p-cym), 1.43 [t, 3H,
dC(OCH2CH3), JHH = 7.0 Hz], 1.40, 1.37 (t, 6H, CH3 phos, JHH = 7.0
Hz), 1.15, 1.14 (d, 6H, CH3 iPr, JHH = 7.1 Hz) ppm. 31P{1H} NMR
(CD2Cl2, 25 °C) δ: 95.9 (s) ppm. Anal. Calcd for C55H63BClO3OsP: C,
63.55; H, 6.11; Cl, 3.41. Found: C, 63.71; H, 6.02; Cl, 3.63.
1a: 1H NMR (CD2Cl2, 25 °C) δ: 7.41-6.86 (m, 25H, Ph), 5.39 (d,
HA p-cym, JAB = 6.1, JAC = 1.0, JAD = 0.6 Hz), 5.32 (d, HB p-cym, JBC
=
0.6, JBD = 1.0 Hz), 5.24 (d, HC p-cym, JCD = 6.0 Hz), 5.15 (d, HD p-
cym), 5.09, 4.29 [d, 2H, dC(CH2Ph), JHH = 13.4 Hz], 4.73 [q, 2H,
dC(OCH2CH3), JHH = 7.1 Hz], 3.69 (d, 9H, CH3 phos, JPH = 11.5 Hz),
2.61 (m, 1H, CH), 2.00 (s, 3H, p-CH3 p-cym), 1.51 [t, 3H, dC-
i
(OCH2CH3), JHH = 7.1 Hz], 1.22, 1.18 (d, 6H, CH3 Pr, JHH = 7.1 Hz)
[OsCl{dC(OMe)CH2Ph}(η6-p-cymene){PPh(OEt)2}]BPh4
(3c). This complex was prepared exactly like the related ethoxy
derivatives 1 and 2 using methanol instead of ethanol as a solvent; yield
72%. 1H NMR (CD2Cl2, 25 °C) δ: 7.55-6.86 (m, 30H, Ph), 5.47 (d,
ppm. 31P{1H} NMR (CD2Cl2, 25 °C) δ: 76.5 (br) ppm. 13C{1H} NMR
(CD2Cl2, 25 °C) δ: 290.3 (d, OsdC, JCP = 18 Hz), 165-122 (m, Ph),
117.85 (s, C1 p-cym), 103.20 (s, C4 p-cym), 89.21 (s, C5 p-cym), 88.39
(s, C3 p-cym), 85.88 (s, C6 p-cym), 85.77 (s, C2 p-cym), 78.5 [s,
dC(OCH2CH3)], 55.15 (d, CH3 phos, JCP = 7.8 Hz), 54.6 [br,
dC(CH2Ph)], 31.14 (s, CH), 22.42, 21.91 (s, CH3 iPr), 18.38 (s, p-
CH3 p-cym), 14.74 [s, dC(OCH2CH3)] ppm. Anal. Calcd for
C47H55BClO4OsP: C, 59.33; H, 5.83; Cl, 3.73. Found: C, 59.54; H,
5.91; Cl, 3.58.
HA p-cym, JAB = 6.4, JAC = 0.4, JAD = 0.8 Hz), 5.41 (d, HB p-cym, JBC
=
0.8, JBD = 0.4 Hz), 5.41 (d, HC p-cym, JCD = 6.4 Hz), 5.31 (d, HD p-
cym), 5.27, 2.95 [d, 2H, dC(CH2Ph), JHH = 13.2 Hz], 4.08, 3.95 (m,
4H, CH2 phos), 4.01 [s, 3H, dC(OCH3)], 2.56 (m, 1H, CH), 1.98 (s,
3H, p-CH3 p-cym), 1.43, 1.37 (t, 6H, CH3 phos, JHH = 7.0 Hz), 1.14,
1.12 (d, 6H, CH3 iPr, JHH = 7.1 Hz) ppm. 31P{1H} NMR (CD2Cl2,
25 °C) δ: 95.8 (s) ppm. 13C{1H} NMR (CD2Cl2, 25 °C) δ: 288.1 (d,
OsdC, JCP = 16 Hz), 165-122 (m, Ph), 118.69 (s, C1 p-cym), 105.93
(s, br, C4 p-cym), 92.07 (d, C5 p-cym, JCP = 2.8 Hz), 88.24 (d, C6 p-cym,
JCP = 2.9 Hz), 87.35 (d, C2 p-cym, JCP = 5.2 Hz), 86.77 (s, br, C3 p-cym),
66.70 [s, dC(OCH3)], 65.60, 64.55 (d, CH2 phos, JCP = 9.9, JCP = 7.1
1b: 1H NMR (CD2Cl2, 25 °C) δ: 7.37-6.86 (m, 25H, Ph), 5.37 (d,
HA p-cym, JAB = 5.7, JAC = 0.4, JAD = 1.1 Hz), 5.35 (d, HB p-cym, JBC
=
1.1, JBD = 0.4 Hz), 5.16 (d, HC p-cym, JCD = 5.7 Hz), 5.11 (d, HD p-
cym), 5.04, 4.33 [d, 2H, dC(CH2Ph), JHH = 13.3 Hz], 4.34 [m, 2H,
dC(OCH2CH3)], 3.99, 3.84 (m, 6H, CH2 phos), 2.58 (m, 1H, CH),
2.00 (s, 3H, p-CH3 p-cym), 1.50 [t, 3H, dC(OCH2CH3), JHH = 7.0 Hz],
i
i
Hz), 53.40 [s, dC(CH2Ph)], 31.15 (s, CH), 22.29, 21.92 (s, CH3 Pr),
1.27 (t, 9H, CH3 phos, JHH = 7.0 Hz), 1.13, 1.10 (d, 6H, CH3 Pr, JHH
=
7.1 Hz) ppm. 31P{1H} NMR (CD2Cl2, -60 °C) δ: 75.2 (s) ppm. Anal.
Calcd for C50H61BClO4OsP: C, 60.45; H, 6.19; Cl, 3.57. Found: C,
60.64; H, 6.09; Cl, 3.49%.
18.21 (s, p-CH3 p-cym), 16.26, 16.16 (d, CH3 phos, JCP = 4.3, JCP = 5.7
Hz) ppm. Anal. Calcd for C53H59BClO3OsP: C, 62.93; H, 5.88; Cl, 3.50.
Found: C, 63.01; H, 5.99; Cl, 3.65.
[OsCl{dC(OEt)CH2But}(η6-p-cymene){P(OMe)3}]BPh4 (4a).
In a 25 mL three-necked round-bottomed flask were placed 100 mg
(0.19 mmol) of OsCl2(η6-p-cymene){P(OMe)3}, 130 mg (0.38 mmol)
of NaBPh4, and 2 mL of ethanol. An excess of tert-butyl acetylene,
1c: 1H NMR (CD2Cl2, 25 °C) δ: 7.56-6.87 (m, 30H, Ph), 5.48 (d,
HA p-cym, JAB = 6.7, JAC = 0.4, JAD = 0.8 Hz), 5.43 (d, HB p-cym, JBC
=
0.8, JBD = 0.4 Hz), 5.40 (d, HC p-cym, JCD = 6.7 Hz), 5.32 (d, HD p-
cym), 5.37, 2.97 [d, 2H, dC(CH2Ph), JHH = 13.2 Hz], 4.43, 4.31 [m,
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ARTICLE
HCtCBut, (68 μL, 0.54 mmol) was added to the resulting mixture,
which was stirred for 5 h. A yellow solid slowly separated out, which, after
cooling of the reaction mixture to complete the precipitation, was
filtered and crystallized from CH2Cl2 and ethanol; yield 65%. 1H
NMR (CD2Cl2, 25 °C) δ: 7.32-6.89 (m, 20H, Ph), 5.49 (d, HA p-
cym, JAB = 6.2, JAC = 0.6, JAD = 0.8, JHP = 1.9 Hz), 5.61 (d, HB p-cym, JBC
= 0.8, JBD = 0.8, JHP = 1.8 Hz), 5.42 (d, HC p-cym, JCD = 6.2, JHP = 1.3
Hz), 5.11 (d, HD p-cym, JHP = 0.5 Hz), 4.87 [m, 2H, dC(OCH2CH3)],
3.62, 2.97 [d, 2H, dC(CH2But), JHH = 19.0 Hz], 3.69 (d, 9H, CH3 phos,
phos), 2.80 (m, 1H, CH), 2.20 (s, 3H, p-CH3 p-cym), 1.31 (t, 9H, CH3
i
phos, JHH = 7.0 Hz), 1.24 (d, 6H, CH3 Pr, JHH = 7.1 Hz) ppm. 31P{1H}
NMR (CD2Cl2, 25 °C) δ: 70.4 (s) ppm. 13C{1H} NMR (CD2Cl2,
25 °C) δ: 132-125 (m, Ph), 128.7 (d, br, CR), 100.79 (d, C1 p-cym, JCP
= 2.7 Hz), 95.31 (d, C4 p-cym, JCP = 2.8 Hz), 81.64 (d, C2/C6 p-cym,
JCP = 5.3 Hz), 80.85 (d, C3/C5 p-cym, JCP = 6.2 Hz), 62.75 (d, CH2
i
phos, JCP = 6.0 Hz), 30.60 (s, CH), 22.38 (s, CH3 Pr), 18.04 (s, p-CH3 p-
cym), 16.30 (d, CH3 phos, JCP = 2.3 Hz) ppm. Anal. Calcd for
C24H34ClO3OsP: C, 45.96; H, 5.46; Cl, 5.65. Found: C, 46.12; H,
5.39; Cl, 6.80.
JHP = 11.4 Hz), 2.74 (m, 1H, CH), 2.11 (s, 3H, p-CH3 p-cym), 1.61 [t,
3H, dC(OCH2CH3), JHH = 7.0 Hz], 1.32, 1.24 (d, 6H, CH3 Pr, JHH
=
6c: IR (KBr) cm-1: νCtC 2086 (m). 1H NMR (CD2Cl2, 25 °C) δ:
7.66, 7.44 (m, 10H, Ph), 5.52 (d, 2H, HA, HA0 p-cym, JHH = 5.6 Hz),
5.39 (d, 2H, HB, HB0 p-cym, JHH = 5.6 Hz), 4.12, 3.97 (m, 4H, CH2
phos), 2.64 (m, 1H, CH), 2.06 (s, 3H, p-CH3 p-cym), 1.32 (t, 6H, CH3
i
7.1 Hz), 1.04 (s, 9H, CH3 But) ppm. 31P{1H} NMR (CD2Cl2, 25 °C) δ:
73.2 (s) ppm. 13C{1H} NMR (CD2Cl2, 25 °C) δ: 295.07 (br, OsdC),
165-122 (m, Ph), 121.7 (br, C1 p-cym), 100.3 (br, C4 p-cym), 88.74 (s,
C3 p-cym), 85.76 (s, C2 p-cym), 85.44 (s, C5 p-cym), 85.33 (s, C6 p-
cym), 80.68 [s, dC(OCH2CH3)], 73.7 [s, br, dC(CH2But)], 55.36 (d,
CH3 phos, JCP = 8.0 Hz), 33.84 (s, C But), 31.29 (s, CH), 30.22 (s, CH3
But), 23.18, 21.10 (s, CH3 iPr), 18.50 (s, p-CH3 p-cym), 14.97 [s,
dC(OCH2CH3)] ppm. Anal. Calcd for C45H59BClO4OsP: C, 58.03; H,
6.38; Cl, 3.81. Found: C, 58.16; H, 6.49; Cl, 3.97.
phos, JHH = 7.0 Hz), 1.16 (d, 6H, CH3 Pr, JHH = 7.1 Hz) ppm. 31P{1H}
i
NMR (CD2Cl2, 25 °C) δ: 93.2 (s) ppm. 13C{1H} NMR (CD2Cl2,
25 °C) δ: 136.87 (s, Cβ), 131-127 (m, Ph), 128.5 (d, CR, JCP = 5.6
Hz), 100.81 (d, C1 p-cym, JCP = 7.1 Hz), 93.50 (d, C4 p-cym, JCP = 1.9
Hz), 81.81 (d, C3/C5 p-cym, JCP = 5.5 Hz), 81.25 (d, C2/C6 p-cym, JCP
= 5.2 Hz), 63.66 (d, CH2 phos, JCP = 7.7 Hz), 30.4 (s, CH), 22.30 (s,
CH3 iPr), 17.7 (s, p-CH3 p-cym), 16.28 (d, CH3 phos, JCP = 6.9 Hz)
ppm. Anal. Calcd for C28H34ClO2OsP: C, 51.01; H, 5.20; Cl, 5.38.
Found: C, 50.88; H, 5.13; Cl, 5.52.
[OsCl{dC(OEt)CH3}(η6-p-cymene){PPh(OEt)2}]BPh4 (5c).
In a 25 mL three-necked round-bottomed flask were placed 100 mg
(0.17 mmol) of OsCl2(η6-p-cymene){PPh(OEt)2}, 116 mg (0.34
mmol) of NaBPh4, and 3 mL of ethanol. An excess of trimethylsilyl
acetylene, HCtCSi(CH3)3, (73.6 μL, 0.51 mmol) was added to the
resulting mixture, which was stirred for 5 h. By cooling the resulting
solution to -25 °C, a yellow solid slowly separated out, which was
filtered and crystallized from CH2Cl2 and ethanol; yield 55%. 1H NMR
7b: IR (KBr) cm-1: νCtC 2090 (m). 1H NMR (CD2Cl2, 25 °C) δ:
7.37-7.05 (m, 4H, Ph p-tolyl), 5.61 (d, 2H, HA, HA0 p-cym, JHH = 5.6
Hz), 5.47 (d, 2H, HB, HB0 p-cym, JHH = 5.6 Hz), 4.10 (qnt, 6H, CH2
phos), 2.80 (m, 1H, CH), 2.35 (s, 3H, CH3 p-tolyl), 2.20 (s, 3H, p-CH3
p-cym), 1.27 (t, 9H, CH3 phos, JHH = 7.0 Hz), 1.23 (d, 6H, CH3 iPr,
JHH = 7.1 Hz) ppm. 31P{1H} NMR (CD2Cl2, 25 °C) δ: 70.4 (s) ppm.
13C{1H} NMR (CD2Cl2, 25 °C) δ: 132-125 (m, Ph), 127.8 (d, CR,
JCP = 4.8 Hz), 100.80 (d, C1 p-cym, JCP = 2.7 Hz), 95.32 (d, C4 p-cym,
JCP = 2.8 Hz), 81.69 (d, C2/C6 p-cym, JCP = 5.2 Hz), 80.85 (d, C3/C5
p-cym, JCP = 6.2 Hz), 62.74 (d, CH2 phos, JCP = 6.0 Hz), 30.61 (s,
CH), 22.38 (s, CH3 iPr), 21.22 (s, CH3 p-tolyl), 18.05 (s, p-CH3 p-
cym), 16.30 (d, CH3 phos, JCP = 6.4 Hz) ppm. Anal. Calcd for
C25H36ClO3OsP: C, 46.83; H, 5.66; Cl, 5.53. Found: C, 47.01; H,
5.78; Cl, 5.70.
(CD2Cl2, 25 °C) δ: 7.80-6.88 (m, 25H, Ph), 5.50 (d, HA p-cym, JAB
=
6.4, JAC = 0.6, JAD = 0.6 Hz), 5.46 (d, HB p-cym, JBC = 0.6, JBD = 0.6 Hz),
5.50 (d, HC p-cym, JCD = 6.4 Hz), 5.42 (d, HD p-cym), 4.22, 4.04 [m,
2H, dC(OCH2CH3)], 4.06, 3.96, 3.88 (m, 4H, CH2 phos), 2.59 (m,
1H, CH), 2.23 [s, 3H, dC(CH3)], 2.07 (s, 3H, p-CH3 p-cym), 1.50 [t,
3H, dC(OCH2CH3), JHH = 7.0 Hz], 1.37, 1.34 (t, 6H, CH3 phos, JHH
=
i
7.0 Hz), 1.20, 1.14 (d, 6H, CH3 Pr, JHH = 7.1 Hz) ppm. 31P{1H} NMR
(CD2Cl2, 25 °C) δ: 96.53 (s) ppm. 13C{1H} NMR (CD2Cl2, 25 °C) δ:
285.1 (d, OsdC, JCP = 15.8 Hz), 164-122 (m, Ph), 119.54 (s, C1 p-
cym), 106.42 (s, C4 p-cym), 92.03 (d, C3 p-cym, JCP = 2.6 Hz), 89.44 (s,
C5 p-cym), 88.48 (s, C6 p-cym), 85.88 (d, C2 p-cym, JCP = 4.4 Hz),
[Os(η1-CH2Ph)(CO)(η6-p-cymene){PPh(OEt)2}]BPh4 (8c).
In a 25 mL three-necked round-bottomed flask were placed 100 mg (0.17
mmol) of OsCl2(η6-p-cymene)[PPh(OEt)2], 116 mg (0.34 mmol) of
NaBPh4, 4.5 mL of acetone, and 1 mL of H2O. An excess of phenylace-
tylene, PhCtCH (60 μL, 0.54 mmol), was added to the resulting mixture,
which was stirred for 3 h. The solvent was removedunderreduced pressure
to give an oil, which was triturated with ethanol (2 mL). A yellow solid
slowly separated out and was filtered and crystallized from CH2Cl2 and
ethanol; yield 65%. IR (KBr) cm-1: νCO 1970 (s). 1H NMR (CD2Cl2,
25 °C) δ: 7.62-6.84 (m, 30H, Ph), 5.53 (d, HAp-cym, JAB = 6.4, JAC = 0.4,
JAD = 0.5, JHP = 1.6 Hz), 5.15 (d, HB p-cym, JBC = 0.5, JBD = 0.4, JHP = 1.6
75.27 [s, dC(OCH2CH3)], 64.98, 64.37 (d, CH2 phos, JCP = 9.6, JCP
=
i
6.8 Hz), 39.11 [br, dC(CH3)], 31.12 (s, CH), 22.49, 21.95 (s, CH3 Pr),
18.18 (s, p-CH3 p-cym), 16.0 (t, CH3 phos, JCP apparent = 16.4 Hz), 14.45
[s, dC(OCH2CH3)] ppm. Anal. Calcd for C48H57BClO3OsP: C, 60.72;
H, 6.05; Cl, 3.73. Found: C, 60.59; H, 5.94; Cl, 3.81.
OsCl(CtCAr)(η6-p-cymene)L (6, 7) [Ar = Ph (6), p-tolyl (7);
L = P(OMe)3 (a), P(OEt)3 (b), PPh(OEt)2 (c)]. An excess of lithium
acetylide Liþ[ArCtC]- (0.68 mmol, 0.38 mL of a 1.8 M solution in thf)
was added to a solution of the appropriate complex OsCl2(η6-p-
cymene)L (0.17 mmol) in 10 mL of thf cooled to -196 °C. The
reaction mixture was allowed to reach room temperature and stirred for
3 h. The solvent was removed under reduced pressure to give an oil,
which was triturated with n-hexane (5 mL). A red-brown solid slowly
separated out and was filtered and crystallized from toluene and n-
hexane; yield g75%.
Hz), 5.46(d, HCp-cym, JCD = 6.4, JHP =1.6 Hz), 5.34 (d, HDp-cym, JHP
=
1.6 Hz), 3.91 (m, 4H, CH2 phos), ABX spin system (A, B = 1H, X = 31P),
δA 3.34, δB 3.11, JAB = 10.3, JAX = 6.8, JBX = 3.5 Hz (2H, CH2Ph), 2.35 (m,
1H, CH), 1.85 (s, 3H, p-CH3 p-cym), 1.43, 1.39 (t, 6H, CH3 phos, JHH
=
7.0 Hz), 1.04, 0.97 (d, 6H, CH3 Pr, JHH = 7.1 Hz) ppm. 31P{1H} NMR
(CD2Cl2, 25 °C) δ: 99.4 (s) ppm. 13C{1H} NMR (CD2Cl2, 25 °C) δ:
177.7 (d, CdO, JCP = 20.4 Hz), 165-122 (m, Ph), 121.82 (d, C1 p-cym,
JCP = 4.5 Hz), 113.62 (s, C4 p-cym), 100.78 (d, C5 p-cym, JCP = 2.4 Hz),
97.16 (d, C6 p-cym, JCP =6.6Hz), 96.30(d, C3p-cym, JCP =2.7Hz), 92.84
(s, br, C2 p-cym), 64.76 (m, CH2 phos), 32.04 (s, CH), 23.00, 22.84 (s,
CH3), 18.10 (s, p-CH3 p-cym), 16.03 (m, CH3 phos), -5.20 (d, CH2-Os,
JCP = 8.2 Hz) ppm. Anal. Calcd for C52H56BO3OsP: C, 64.99; H, 5.87.
Found: C, 65.15; H, 6.03.
i
6a: IR (KBr) cm-1: νCtC 2095 (m). 1H NMR (CD2Cl2, 25 °C) δ:
7.34-7.12 (m, 5H, PhCtC), 5.63 (d, 2H, HA, HA0 p-cym, JHH = 5.6
Hz), 5.50 (d, 2H, HB, HB0 p-cym, JHH = 5.6 Hz), 3.73 (d, 9H, CH3 phos,
JHP = 9.8 Hz), 2.79 (m, 1H, CH), 2.21 (s, 3H, p-CH3 p-cym), 1.23 (d,
6H, CH3 iPr, JHH = 7.1 Hz) ppm. 31P{1H} NMR (CD2Cl2, 25 °C) δ:
74.9 (s) ppm. Anal. Calcd for C21H28ClO3OsP: C, 43.11; H, 4.82; Cl,
6.06. Found: C, 42.92; H, 4.99; Cl, 6.25.
6b: IR (KBr) cm-1: νCtC 2085 (m). 1H NMR (CD2Cl2, 25 °C) δ:
7.36-7.10 (m, 5H, PhCtC), 5.61 (d, 2H, HA, HA0 p-cym, JHH = 5.6
Hz), 5.47 (d, 2H, HB, HB0 p-cym, JHH = 5.6 Hz), 4.08 (qnt, 6H, CH2
[Os(η1-CH3)(CO)(η6-p-cymene){PPh(OEt)2}]BPh4 (9c).
This complex was prepared exactly like the related benzyl derivative
8c using trimethylsilyl acetylene, HCtCSi(CH3)3, as a reagent; yield
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Table 1. Crystal Data and Structure Refinement
1c
1d
8c
empirical formula
fw
C
54H61BClO3OsP
C58H61BClO2OsP
1057.50
C52H56BO3OsP
960.95
1025.46
temperature
wavelength
cryst syst
293(2) K
293(2) K
293(2) K
0.71073 Å
0.71073 Å
0.71073 Å
triclinic
monoclinic
monoclinic
space group
unit cell dimens
P1
P21/n
P21/c
a = 12.3115(10) Å
b = 14.1504(12) Å
c = 14.4752(12) Å
R = 75.418(2)°
β = 77.243(2)°
γ = 87.722(2)°
2380.0(3) Å3
2
a = 18.222(3) Å
b = 14.828(2) Å
c = 18.678(3) Å
a = 13.5866(10) Å
b = 13.5816(11) Å
c = 24.7454(18) Å
β = 101.077(3)°
β = 94.385(2)°
volume
4952.6(14) Å3
4
4552.8(6) Å3
4
Z
density (calcd)
absorp coeff
F(000)
1.431 Mg/m3
2.811 mm-1
1044
1.418 Mg/m3
2.703 mm-1
1.402 Mg/m3
2.877 mm-1
1952
2152
cryst size
0.40 ꢀ 0.21 ꢀ 0.15 mm
1.49 to 25.03°
-14 e h e 14
-16 e k e 16
-17 e l e 17
17 984
0.47 ꢀ 0.19 ꢀ 0.10 mm
1.43 to 25.01°
-21 e h e 21
-17 e k e 13
-22 e l e 22
25 716
0.26 ꢀ 0.18 ꢀ 0.10 mm
1.65 to 25.03°
-15 e h e 16
-16 e k e 13
-24 e l e 29
23 320
θ range for data collection
index ranges
reflns collected
indep reflns
8343 [R(int) = 0.0498]
6509
8689 [R(int) = 0.0762]
5114
7957 [R(int) = 0.0499]
5091
reflns obsd (>2σ)
data completeness
absorp corr
0.990 fc
0.996
0.989
semiempirical from equivalents
1.000 and 0.739
full-matrix least-squares on F2
8343/0/556
semiempirical from equivalents
1.000 and 0.602
full-matrix least-squares on F2
8689/0/582
semiempirical from equivalents
1.000 and 0.810
full-matrix least-squares on F2
7957/0/528
max. and min transmn
refinement method
data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
1.044
0.975
1.008
R1 = 0.0381
R1 = 0.0412
R1 = 0.0375
wR2 = 0.0729
R1 = 0.0607
wR2 = 0.0825
R1 = 0.0954
wR2 = 0.0817
R indices (all data)
R1 = 0.0818
wR2 = 0.0823
1.420 and -0.897 e Å-3
wR2 = 0.1125
1.260 and -1.515 e Å-3
wR2 = 0.1074
0.714 and -0.622 e Å-3
largest diff peak and hole
g60%. IR (KBr) cm-1: νCO 1977 (s). 1H NMR (CD2Cl2, 25 °C) δ: 7.57-
6.87 (m, 25H, Ph), 5.62 (d, HA p-cym, JAB =6.6,JAC =0.4,JAD =0.5,JHP =1.0
Hz), 5.22 (d, HB p-cym, JBC = 0.5, JBD = 0.4, JHP = 1.0 Hz), 5.36 (d, HC p-
cym, JCD =6.6, JHP =1.4Hz), 5.66(d, HDp-cym, JHP = 1.2 Hz), 3.85 (m, 4H,
CH2 phos), 2.44 (m, 1H, CH), 1.89 (s, 3H, p-CH3 p-cym), 1.38, 1.33 (t, 6H,
of acetone. An excess of phenylacetylene (34 μL, 0.30 mmol) was
added to the resulting solution, which was stirred for 4 h. The solvent
was removed under reduced pressure, leaving an oil, which was
characterized as such.
Method 2: In a 25 mL three-necked round-bottomed flask were placed
100 mg (0.17 mmol) of OsCl2(η6-p-cymene)[PPh(OEt)2], 44 mg (0.17
mmol) of silver triflate AgCF3SO3 (AgOTf), and 7 mL of dichloro-
methane. The reaction mixture was stirred for 24 h in the dark and
filtered to remove the solid AgCl, and then an excess of phenylacetylene
(57 μL, 0.51 mmol) was added. The resulting solution was stirred for 8 h,
and then the solvent removed under reduced pressure to give an oil,
which was characterized as such.
i
CH3 phos, JHH = 7.0 Hz), 1.17, 1.13 (d, 6H, CH3 Pr, JHH = 7.1 Hz), 0.66 (d,
CH3-Os, JHP = 6 Hz) ppm. 31P{1H} NMR (CD2Cl2, 25 °C) δ: 100.9 (s)
ppm. 13C{1H} NMR (CD2Cl2, 25 °C) δ: 177.1 (d, CdO, JCP = 18.9 Hz),
165-122 (m, Ph), 120.92 (d, C1 p-cym, JCP = 2.6 Hz), 115.82 (s, C4 p-cym),
94.74 (d, C5 p-cym, JCP = 5.6 Hz), 94.29 (d, C6 p-cym, JCP = 5.2 Hz), 94.16
(s, C2 p-cym), 93.81 (s, C3 p-cym), 64.32, 64.15 (d, CH2 phos, JCP = 8.9,
i
JCP = 7.8 Hz), 31.85 (s, CH), 23.75, 22.71 (s, CH3 Pr), 18.34 (s, p-CH3 p-
cym), 16.00, 15.90 (d, CH3 phos, JCP = 4.8, JCP = 5.2 Hz), -33.51 (d, CH3-
Os, JCP = 9.1 Hz) ppm. Anal. Calcd for C46H52BO3OsP: C, 62.43; H, 5.92.
Found: C, 62.35; H, 5.84.
Method 3: A solution of the complex OsCl(CtCPh)(η6-p-cymene)-
[PPh(OEt)2] (6c) (20 mg, 0.03 mmol) in 0.6 mL of CH2Cl2 was placed
in a 5 mm NMR tube, cooled to -80 °C, and treated with a slight excess
of either HBF4 (0.035 mmol, 5.0 μL of a 54% solution in Et2O) or HOTf
(0.035 mmol, 3.1 μL). The tube was inserted into the probe (precooled
to -80 °C) of the NMR instrument, and the spectra were recorded from
-80 to þ20 °C.
[OsCl{dCdC(H)Ph}(η6-p-cymene){PPh(OEt)2}]þY- [A] (Y =
BPh4, BF4, CF3SO3). Method 1: In a 25 mL three-necked round-
bottomed flask were placed 60 mg (0.10 mmol) of OsCl2(η6-p-
cymene)[PPh(OEt)2], 34 mg (0.10 mmol) of NaBPh4, and 10 mL
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Scheme 1a
Scheme 2
a Ar = Ph (1), p-tolyl (2); L = P(OMe)3 (a), P(OEt)3 (b), PPh(OEt)2
(c), PPh2OEt (d).
1H NMR (CD2Cl2, 25 °C) δ: 4.38 ppm (s, 1H, dCH). 31P{1H}
NMR (CD2Cl2, 25 °C) δ: 95.8 ppm (s). 13C{1H} NMR (CD2Cl2,
25 °C) δ: 278.0 ppm (d, CdOs, JCP = 10.5 Hz).
Crystal Structure Determination of [OsCl(η6-p-cymene){dC-
(OEt)CH2Ph}{PPh(OEt)2}]BPh4 (1c), [OsCl(η6-p-cymene){dC-
(OEt)CH2Ph}(PPh2OEt)]BPh4 (1d), and [Os(η1-CH2Ph)-(CO)(η6-
p-cymene){PPh(OEt)2}]BPh4 (8c). Crystallographic data were col-
lected on a Bruker Smart 1000 CCD diffractometer at CACTI
(Universidade de Vigo) using graphite-monochromated Mo KR radiation
(λ = 0.71073 Å) and were corrected for Lorentz and polarization effects.
The software SMART11 was used for collecting frames of data, indexing
reflections, and the determination of lattice parameters, SAINT12 for
integration of intensity of reflections and scaling, and SADABS13 for
empirical absorption correction. The crystallographic treatment of the
compound was performed with the Oscail program14 The structures were
solved by Patterson methods for 1d and by direct methods for 1c and 8c and
refined by a full-matrix least-squares based on F2.15 Non-hydrogen atoms
were refined with anisotropic displacement parameters. Hydrogen atoms
were included in idealized positions and refined with isotropic displacement
parameters. Details of crystal data and structural refinement are given in
Table 1. The three compounds possess a chiral center in the osmium atom,
although both enantiomers are present in the unit cell.
Scheme 3
’ RESULTS AND DISCUSSION
Unfortunately, the isolated product was a mixture containing
only traces of the hypothesized vinylidene species [A]. The
major compound present in the mixture was [Os(η1-CH2Ph)-
(CO)(η6-p-cymene)L]BPh4 (8), formed by hydrolysis of the
alkyne (see below) with the traces of H2O always present in
“anhydrous” acetone. We therefore used a different strategy to
prepare the vinylidene intermediate [A], involving the reaction
of the dichloro precursor first with silver triflate, to form the
triflate intermediate OsCl(κ1-OTf)(η6-p-cymene)L, and then
with an excess of phenylacetylene in dichloromethane as solvent
(Scheme 3).
Preparation of Carbene Complexes. Half-sandwich di-
chloro complexes OsCl2(η6-p-cymene)L react with terminal
alkynes ArCtCH (Ar = Ph, p-tolyl) in ethanol to give the
ethoxycarbene derivatives [OsCl{dC(OEt)CH2Ar}(η6-p-cym-
ene)L]BPh4 (1, 2), which were isolated as BPh4 salts (Scheme 1)
and characterized.
Crucial for successful synthesis is the presence of the salt
NaBPh4, which probably favors the substitution of the chloride
ligand in the starting complex, allowing final derivatives 1 and 2
to be obtained in good yields.
The formation of an ethoxycarbene from the reaction of
terminal alkynes with dichloro complexes OsCl2(η6-p-cymene)L
is somewhat surprising, but may be explained according to the
reaction path shown in Scheme 2, which involves the initial
formation of a vinylidene intermediate [A]. Nucleophilic attack
by the oxygen atom of ethanol on the CR of the vinylidene
followed by proton transfer gives the final ethoxy-benzyl carbene
complexes 1 and 2.
In order to support the proposed reaction path, we attempted
either to isolate the intermediate vinylidene complex [A] or, at
least, to identify its presence in the reaction mixture. At first, we
treated the dichloro complex OsCl2(η6-p-cymene)L, in the
presence of NaBPh4, with phenylacetylene in CH2Cl2, but no
reaction was observed, perhaps owing to the insolubility of
NaBPh4 in this solvent. We therefore changed to acetone and
did observe a reaction, resulting in a purplish-red solution.
The triflate intermediate quickly reacts with phenylacetylene
to give the purple solution, from which we were not able
to isolate a solid, but only an oily product. However, its NMR
spectra strongly suggest the presence of the vinylidene com-
plex [A], showing a doublet at 278.0 ppm (JCP = 10.5 Hz) in
the 13C spectrum, which is attributed to the CR carbon atom
of a vinylidene species. In an HMQC experiment, this 13C
signal was correlated with the singlet observed at 4.38 ppm
1
in the H NMR spectrum and attributed to the dCH(Ph)
proton of the vinylidene ligand, fitting the proposed formula-
tion.
The triflate ligand is labile in the complex OsCl(κ1-OTf)(η6-p-
cymene)L and may be substituted by the alkyne, which then
tautomerizes2h,16 on the metal center to give the vinylidene
intermediate. The fact that this vinylidene complex is really the
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Scheme 4
Scheme 5a
a Ar = Ph (6), p-tolyl (7).
proposed intermediate [A] of the reaction path (Scheme 2) is
confirmed by treatment with ethanol, which gives the ethoxy-
carbene final product 1 (Scheme 3). Furthermore, as expected,
the addition of methanol to a solution of [A] gives the methox-
ycarbene complex [OsCl{dC(OMe)CH2Ph}(η6-p-cyme-
ne)L]BPh4 (3), which can be isolated as a BPh4 salt and
characterized. The same methoxycarbene derivative 3 was also
prepared directly by treating the dichloro complex OsCl2(η6-p-
cymene)L with terminal alkyne ArCtCH, with methanol as a
solvent (see Scheme 1).
Scheme 6a
Nucleophilic attack of alcohol on the CR carbon atom of the
allenylidene17 ligand [Os]dCdCdCR0R00 has previously been
reportedinosmiumcomplexes,6a,e affording alkoxy-alkenyl carbene
derivatives [Os{dC(OR)CHdCR0R00}(CH3CN)4(IPr)(OTf)2]
[IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolylidene] and [Os
Cl(η6-mes)(PMe3){dC(OR)CHdCPh2}]PF6 (mes = 1,3,5-
trimethylbenzene). The reaction of our p-cymene osmium(II)
fragment containing phosphite, phosphonite, or phosphinite li-
gands highlights the fact that the vinylidene intermediate can also
undergo nucleophilic attack on the CR atom, yielding alkoxy-
alkylcarbene derivatives [Os]{dC(OR)CH2R} (1-3).
The reaction of dichloro precursors was also extended to other
terminal alkynes, such as tert-butyl and trimethylsilyl acetylene.
The results showed that, while with ButCtCH the expected
ethoxyneopentylcarbene complex [OsCl{dC(OEt)CH2But}-
(η6-p-cymene)L]BPh4 (4) could be isolated, the reaction with
trimethylsilyl acetylene gives the ethoxymethylcarbene derivative
[OsCl{dC(OEt)CH3}(η6-p-cymene)L]BPh4 (5), which was
isolated in good yields and characterized (Scheme 4).
a HY = HOTf, HBF4.
Unfortunately, we were not able to obtain the vinylidene com-
plex as a solid, but only as a rather unstable oil. However, NMR
data of the protonated solution of complex OsCl(CtCPh)(η6-
p-cymene)[PPh(OEt)2] (6c) with HOTf clearly support the
formation of the vinylidene complex [A]: the 13C NMR spec-
trum shows the characteristic signal of the CR carbenic carbon
atom of the vinylidene ligand at 278 ppm, and the proton spectra
of a singlet at 4.38 ppm, attributed to the dCH(Ph) vinylidene
proton (see above), matching the proposed formulation.
Protonated solutions of acetylide complexes 6 and 7 reacted
with ethanol to yield the ethoxycarbene derivatives 1 and 2, as
further support to the proposed reactivity of half-sandwich
complexes OsCl2(η6-p-cymene)L with terminal alkynes.
Good analytical data were obtained for complexes 1-7, which
were isolated as yellow or reddish-brown solids, stable in air and in
solution of common organic solvents, where they behave as either
1:1 (1-5) or nonelectrolytes21 (6, 7). IR and NMR (1H, 13C, 31P)
data confirmed the proposed formulations, which were further
supported by X-ray crystal structure determination of complexes
[OsCl(η6-p-cymene){dC(OEt)CH2Ph}{PPh(OEt)2}]BPh4 (1c)
and [OsCl(η6-p-cymene){dC(OEt)CH2Ph}(PPh2OEt)]BPh4
(1d), ORTEP representations of which are given in Figure 1, at a
probability level of 30%.
The structure of complexes 1c and 1d consists of a tetraphenyl
borate anion (not shown in the figures) and a cation formed by
an osmium atom η6-coordinated to a p-cymene molecule and to
three donor atoms, leading to the formation of a “three-legged
piano stool” structure. These ligands are a chloride ligand, a
Fisher-type carbene group, and a phosphorus-donor ligand. The
geometry of the complexes can be considered to be octahedral
and is marked by values for the angles C(11)-Os-P, Cl-Os-
P, and C(11)-Os-Cl, in any case not more than 2.3° from 90°.
The average Os-C bond distance for the p-cymene ligand is
2.272(7) Å in both compounds (Table 2). These bond lengths
are close to those of other related complexes7b,22,23 and also
show the different trans influence of the other ligands, since Os-
C(1) and Os-C(6), trans to the Fisher carbene ligand in each
The formation of complex 5, involving cleavage of the C-
Si(CH3)3 bond, is somewhat surprising, because the Si-C bond
is known to be quite inert to cleavage in many organometallic
complexes.18 However, a few examples of cleavage of the
trimethylsilyl group have been reported,19 one of which20
involves a trimethylsilyl vinylidene complex of Ru, very similar
to our probable vinylidene intermediate [A].
The behavior of half-sandwich complexes OsCl2(η6-p-cym-
ene)L toward terminal alkynes prompted us to extend the study
to acetylide. Results show that the reaction with an excess of lithium
acetylide proceeds in thf with the substitution of one chloride and
the formation of acetylide complexes OsCl(CtCAr)(η6-p-cym-
ene)L, which were isolated in good yields and characterized
(Scheme 5).
Substitution of both the chloride ligands in the OsCl2(η6-p-
cymene)L precursors to yield bis(acetylide) complexes was not
observed, either in the presence of a large excess of Liþ[ArCtC]-
or when long reaction times were applied, and monoacetylides 6
and 7 were the only isolated products. Refluxing conditions yielded
only decomposition products.
The acetylide complexes OsCl(CtCAr)(η6-p-cymene)L (6, 7)
react with Brønsted acids [HBF4 or CF3SO3H(HOTf)] at-80 °C
to give the vinylidene derivative [OsCl{dCdC(H)Ar}(η6-p-
cymene)L]þ [A], as shown in Scheme 6.
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Figure 1. Left: The cation of 1c. Right: The cation of 1d. In the phosphorus-donor ligands, ethoxy groups are represented only by the oxygen atoms, and
phenyl rings by simple spheres. The hydrogen atoms are omitted.
is 2.410(2) Å on average for both compounds, matching
literature values well.7b,22-25
Table 2. Selected Bond Lengths [Å] and Angles [deg] for
Compounds 1c and 1d
The Os-C(carbene) bond lengths are 1.982(7) and 1.983(5)
Å for both compounds, slightly longer than those found for other
Os-non-Fischer-carbene complexes6a,26 but similar to other
Fischer-carbene complexes,6f,27 in accordance with the usual
features for this kind of heteroatom-stabilized carbene
complexes.28 The sum of angles around the carbene C(11) atom
is 359.9°, showing the planarity of this atom (which is consistent
with sp2 hybridization). In addition, the distance from the
carbene carbon to the ethoxy oxygen, on average 1.303(1) Å,
is intermediate between that expected for carbon-oxygen single
and double bonds, reflecting intermediate bond order. This is a
value typically found in Fischer-type carbene complexes.27 In
each of compounds 1d and 1c, the dC(OEt)CH2Ph ligand is
oriented so that the phenyl groups are directed toward the p-
cymene ligand, as previously observed for Fe and Ru half-
sandwich complexes with similar ligands.29
1c
1d
Os-CT01
Os-C(11)
Os-Cl
1.7841(1)
1.981(5)
2.4149(14)
2.2869(15)
2.324(5)
2.289(5)
2.294(5)
2.234(5)
2.201(5)
2.303(5)
1.311(6)
1.7804(4)
1.982(7)
2.405(2)
2.314(2)
2.340(7)
2.277(7)
2.272(7)
2.230(7)
2.189(7)
2.324(7)
1.295(9)
Os-P
Os-C(1)
Os-C(2)
Os-C(3)
Os-C(4)
Os-C(5)
Os-C(6)
O(1)-C(11)
CT01-Os-C(11)
CT01-Os-Cl
CT01-Os-P
127.92(13)
128.2(2)
122.46(6)
126.08(5)
90.7(2)
123.78(4)
127.38(4)
88.72(15)
87.70(14)
88.87(6)
117.3(4)
118.7(4)
123.7(4)
As well as the signals of p-cymene, phosphorus-donor ligand,
and BPh4-, the 1H NMR spectra of carbene complexes
[OsCl{dC(OR0)CH2R00}(η6-p-cymene)L]BPh4 (1-4) (R0 =
Me, Et; R00 = Ph, p-tolyl, But) show the characteristic resonances
of the R0 and R00 substituents of the carbene. In particular, the
methyl or ethyl substituents of the alkoxy OR0 are singlets (3c) or
triplets and quartets (4c), respectively, whereas benzyl and
neopentyl protons CH2R00 appear as two doublets at 5.37-
3.62 and 4.33-2.91 ppm. The multiplicity of this signal is due to
the presence of a chiral center, which makes the two CH2R00
protons diastereotopic, with different values of chemical shift and
JHH values of 19.0-12.8 Hz. In addition, coupling between
benzyl and neopentyl protons and the P nucleus of the phos-
phorus-donor ligand was not observed, probably owing to the
small value of JHP. However, diagnostic for the presence of the
carbene ligand are the 13C NMR spectra, which show a doublet at
295.07-286.50 ppm (JCP = 15.0-18.0 Hz), characteristic of
carbene carbon resonance. The signals of substituents OR0 and
CH2R00, as well as those of the supporting ligands p-cymene and
phosphite, phosphonite, or phosphinite, are also present in the
spectra, and their attributions were confirmed by HMQC and
HMBC experiments.
C(11)-Os-Cl
C(11)-Os-P
89.5(2)
P-Os-Cl
88.18(8)
117.4(7)
119.6(5)
123.0(6)
O(1)-C(11)-C(12)
O(1)-C(11)-Os
C(12)-C(11)-Os
complex, are longer. The atom labeled as C(6) also corresponds
to the isopropyl-substituted carbon atom, and we found that this
is usually the longer metal-C bond in p-cymene complexes.7b,22
The distance Os-C(3), trans to the phosphorus donor ligand, is
also slightly longer than the other ones, in both compounds, and
causes a slight lack of planarity in the p-cymene ligand, showing
small differences between the compounds. The distances from
the osmium atom to the centroid of the benzene ring of the
cymene ligand are 1.780(4) and 1.784(1) Å, respectively. The
rms values for this plane are 0.0264 and 0.0276, respectively, with
maximum deviation for C(6) and C(3), for both compounds.
The Os-P bond length is slightly longer in the case of the
phosphonite PPh(OEt)2 ligand, 2.314(2) Å, than that of the
phosphinite PPh2(OEt), 2.287(2) Å.24 The Os-Cl bond length
The 1HNMRspectraofthecomplex[OsCl{dC(OEt)CH3}(η6-
p-cymene){PPh(OEt)2}]BPh4 (5c), obtained by reaction with
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Scheme 7a
Scheme 8
a L = PPh(OEt)2 (c).
(CH3)3SiCtCH, do not show the signal of the trimethylsilyl
substituent but a singlet at 2.23 ppm, correlated in a HMBC
experiment with the 13C carbene carbon resonance at 285.1 ppm (JCP
= 15.8 Hz) and attributed to the methyl substituent of the carbene
ligand. Instead, the signal of the ethoxy substituent appears as two
multiplets, at 4.22 and 4.04 ppm for the CH2 protons, and one triplet
at 1.50 ppm (JHH = 7.0 Hz) for theCH3 ones. The 13CNMR spectra
also support the presence of the carbene ligand dC(OEt)CH3,
showing a doublet at 285.1 ppm (JCP = 15.8 Hz) of the carbene
carbon atom, a singlet at 39.11 ppm of the methyl substituent, and
two singlets at 75.27 (CH2) and 14.45 ppm (CH3) of the ethoxy
group, fitting the proposed formulation for complex 5c.
Scheme 9a
The IR spectra of the acetylide complexes OsCl(CtCAr)(η6-p-
cymene)L (6, 7) show a medium-intensity band at 2085-2095
cm-1 due to the νCtC of the acetylide ligand. However, support for
the presence of this ligand comes from the 13CNMRspectra, which,
besides the signals of the p-cymene and phosphite or phosphonite
carbons, also show one doublet at 128.7-127.8 ppm (JCP = 5.6-
4.8 Hz), attributed to the CR carbon resonance, and one singlet at
136.8 ppm, due to the Cβ of the acetylide ligand. The 1H NMR
spectrum of complex OsCl(CtC-p-tolyl)(η6-p-cymene)[P-
(OEt)3] (7b) also shows a singlet at 2.35 ppm of the methyl
substituent of the p-tolyl, which, in an HMQC experiment, was
correlated with a singlet at 21.22 ppm in the 13C spectrum,
matching the proposed formulation for acetylide complexes 6and 7.
Hydrolysis of Alkyne. The facile reaction of the half-sandwich
vinylidene complex [OsCl{dCdC(H)Ar}(η6-p-cymene)L]þ [A]
with alcohols, leading to alkoxycarbene derivatives 1-5, prompted
us to study the reaction with other nucleophiles, such as water, to
test whether related carbenes could be obtained. Results show that
dichloro complexes OsCl2(η6-p-cymene)L do react with phenyla-
cetylene in the presence of H2O, but give alkyl-carbonyl derivatives
[Os(η1-CH2Ph)(CO)(η6-p-cymene)L]BPh4 (8), which were iso-
lated in good yields and characterized (Scheme 7).
The formation of benzyl-carbonyl complex 8, instead of the
expected hydroxycarbene [OsCl{dC(OH)(CH2Ph)}(η6-p-
cymene)L]BPh4, was somewhat surprising, but may be explained
as due to the instability of hydroxycarbene [B] (Scheme 8)
formed by nucleophilic attack of H2O on the vinylidene species
[A]. Deprotonation of the same oxycarbene [B] with an excess of
H2O gave acyl complex [C], which, by CO deinsertion of the acyl
ligand and concurrent loss of the Cl- ligand, afforded the final
carbonyl complex 8.
a L = PPh(OEt)2 (c).
Scheme 10a
a L = PPh(OEt)2 (c).
that the alkyl-carbonyl complex [Os(η1-CH2Ph)(CO)(η6-p-cyme-
ne)L]BPh4 (8) was also obtained by treating ethoxycarbene com-
plexes [OsCl{dC(OEt)CH2Ph}(η6-p-cymene)L]BPh4 (1) with
an excess of LiOH in acetone (Scheme 9).
Substitution of the OEt group of the carbene by OH- should
take place, affording hydroxycarbene [B], which, in the presence
of an excess of LiOH, yields the final carbonyl compound 8.
Trimethylsilyl acetylene was also reacted with OsCl2(η6-p-
cymene)L in the presence of H2O, but the resulting compound
was the methyl-carbonyl derivative [Os(η1-CH3)(CO)(η6-p-
cymene)L]BPh4 (9) (Scheme 10).
The formation of the desilylated product 9 suggests that,
besides hydrolysis, also C-Si bond cleavage takes place with the
alkyne HCtCSi(CH3)3, as previously observed in the case of
carbene complex 5.
Good analytical data were obtained for carbonyl complexes
[Os(η1-CH2Ph)(CO)(η6-p-cymene){PPh(OEt)2}]BPh4 (8c)
and [Os(η1-CH3)(CO)(η6-p-cymene){PPh(OEt)2}]BPh4 (9c),
which were isolated as yellow solids stable in air and in solution of
polar organic solvents, where they behave as 1:1 electrolytes.21 IR
and NMR (1H, 31P, 13C) data support the proposed formulation,
which was further confirmed by X-ray crystal structure determina-
tion of complex 8c, an ORTEP representation of which is shown
in Figure 2. The structure of this complex also consists of a
tetraphenyl borate anion (not shown in the figure) and a cation
formed by an osmium atom η6 coordinated to a p-cymene
Therefore, the reaction entails hydrolysis of the terminal alkyne,
with CtC bond cleavage and formation of an alkyl-carbonyl
derivative. Metal-assisted hydrolysis of alkyne with H2O has pre-
viously been reported for some metals,30-32 and a pathway similar to
that of Scheme 8 has been proposed for ruthenium complexes.31a In
our case, the isolation of alkoxycarbene complexes like 1-5 strongly
supports the formation of the key intermediate [B], which makes
the reaction path of the type of Scheme 8 for CtC bond cleavage of
the terminal alkyne a very plausible proposition. It is worth noting
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Table 3. Selected Bond Lengths [Å] and Angles [deg] for 8c
Os-C(0)
Os-CT1
1.863(8)
1.8298(3)
2.358(6)
2.321(7)
2.292(8)
1.135(8
Os-C(1)
Os-C(3)
Os-C(5)
C(0)-O(1)
Os-C(21)
Os-P(1)
Os-C(2)
Os-C(4)
Os-C(6)
C(21)-C(22)
2.169(7)
2.282(2)
2.277(6)
2.318(7)
2.306(7)
1.497(10)
C(0)-Os-C(21)
C(21)-Os-P(1)
CT1-Os-C(21)
O(1)-C(0)-Os
C(0)-Os-P(1)
CT1-Os-C(0)
CT1-Os-P(1)
C(22)-C(21)-Os
87.4(3)
86.3(2)
Figure 2. ORTEP representation of the cation of 8c. The substituents
of the phosphonite ligand are not shown. The hydrogen atoms are
omitted.
123.0(2)
177.8(8)
86.4(3)
molecule and to three ligands, which are now a carbonyl group, a
η1-benzyl group, and a phosphonite PPh(OEt)2 ligand. Again, the
half-sandwich structure is of the typical “three-legged piano stool”
type. As is well known for this kind of half-sandwich complex, the
overallgeometry should beconsideredasoctahedral and is marked
by near-90° values for angles C(0)-Os-C(21), 87.4(3)°, C(0)-
Os-P(1), 86.4(3)°, and C(21)-Os-P(1), 86.3(2)°. The aver-
age Os-C bond distance for the p-cymene ligand is 2.312 (7) Å,
slightly longer than those found for the previous complexes, e.g.,
the distance from the osmium atom to the centroid of the benzene
ring, 1.8298(3) Å. Between these Os-C bond lengths, the longer
match with the atom labeled C(1), trans to the carbonyl group,
also correspondsto the isopropyl-substituted carbon atom, and we
found that this is usually the longer metal-C bond in p-cymene
complexes.7b,22
At this point, it is interesting to note that, in complexes 1d and
1c, the disposition of the p-cymene ligand is staggered, in such a
way that a carbon-carbon bond is trans to each monodentated
ligand. However, in alkyl complex 8c, the disposition of the η6-
ligand is almost perfectly eclipsed with the other ligands, so that
the C(1) [C(1)-CT-Os-C(0) torsion angle of 171.9(4)°] is
trans to the carbonyl ligand, the C(3) [C(3)-CT-Os-C(21)
torsion angle of 168.4(4)°] is trans to the alkyl ligand, and the
C(5) [C(5)-CT-Os-P(1) torsion angle of 165.6(4)°] is trans
to the phosphonite ligand.
Os-P and Os-C (carbonyl) bond lengths are 2.282(2) and
1.863(8) Å, respectively, but, as they are normal values, they are not
commented on further here. The Os-C(benzyl) bond length is
2.169(7) Å, clearly longer than that found for carbene-osmium
complexes [(η6-p-cymene)OsCl(dCHPh)(L)], 1.919(4) Å.33 To
our knowledge, there is no benzyl complex with Os deposited in the
CCDC,34 but some η1-alkyl complexes—for example, neopentyl
complexes—can be found in the literature with similar distances.35
The parameters of the ligand are similar to those found for other
benzyl complexes, with a C(22)-C(21)-Os angle of 115.6(5)°,
slightly more acute than those found in iridium complexes [IrCp*Cl
(η1-CH2Ph)(CO)], 117.7(4)°,36 or 117.8(4)° in the tungsten com-
plex [WCp*(NO)(η1-CH2Ph)(η3-CH2CHCHMe)].37
129.1(2)
130.42(4)
115.6(5)
6.8, JBX = 3.5 Hz)] attributed to the benzyl protons of the η1-CH2Ph
ligand. Owing to the chirality of the complexes, the two CH2R
protons are prochiral and are coupled with each other and with the
phosphorus nucleus of the phosphonite, giving the observed dd
pattern. In the 13C NMR spectra, the carbon resonance falls at-5.20
ppm, whereas the CO carbon signal appears as a doublet at 177.7
ppm (JCP = 20.4 Hz), fitting the formulation found in the solid state
by X-ray analysis. In the proton NMR spectrum of compound
[Os(η1-CH3)(CO)(η6-p-cymene){PPh(OEt)2}]BPh4 (9c), the
methyl resonance of the η1-CH3 ligand appears as a doublet at
0.66 ppm (JHP = 6 Hz), whereas the 13C spectrum, besides the
signals of p-cymene and phosphonite, also has a doublet at 177.1
ppm (JCP = 18.9 Hz), attributed to a carbonyl carbon resonance,
matching the formulation proposed for the complex.
’ CONCLUSIONS
Half-sandwich p-cymene fragments containing phosphorus donors
as supporting ligands are reported to be able to stabilize alkoxy-
alkylcarbene complexes of the type [OsCl{dC(OR0)CH2R00}(η6-p-
cymene)L]BPh4. The synthesis of the carbene derivatives involves a
highly reactive vinylidene intermediate, [OsCl{dCdC(H)R00}(η6-
p-cymene)L]þ, which can react either with alcohol R0OH to yield
alkoxycarbene or with H2O to afford alkyl-carbonyl derivatives
[Os(η1-CH2R)(CO)(η6-p-cymene)L]BPh4. The preparation of
half-sandwich acetylide derivatives OsCl(CtCAr)(η6-p-cymene)L
is also reported.
’ ASSOCIATED CONTENT
S
Supporting Information. Crystallographic data for com-
b
pounds 1c, 1d, and 8c (cif). This material is available free of
charge via the Internet at http://pubs.acs.org.
The IR spectra of complexes 8 and 9 show strong bands at 1970
(8c) or 1977 (9c) cm-1 attributed to the νCO of the carbonyl ligand.
As well as the signals characteristic of p-cymene and PPh(OEt)2, the
1H NMR spectrum of 8c shows two doublets of doublets at 3.34 and
’ AUTHOR INFORMATION
Corresponding Author
*Fax: þ39 041 234 8917. E-mail: albertin@unive.it.
3.11 ppm [ABX spin system (A, B = 1H, X = 31P) JAB = 10.3, JAX
=
1566
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Organometallics
ARTICLE
’ ACKNOWLEDGMENT
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