Vinylidene and pentatetraenediyl rhodium complexes obtained from a bulky rhodium(i) dimer and a functionalized 1,3-diyne

Article abstract of DOI:10.1039/c1nj20392d

The vinylidene complex trans-[RhCl(CCHCCCPh₂OSiMe ₃)(PiPr₃)₂] (5), prepared from [RhCl(PiPr ₃)₂]₂ (1) and HCCCCCPh₂OSiMe ₃ (2), is in equilibrium with the p

Full text of DOI:10.1039/c1nj20392d

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LETTER
Vinylidene and pentatetraenediyl rhodium complexes obtained from a
bulky rhodium(I) dimer and a functionalized 1,3-diynew
Ivan Kovacik and Helmut Werner*
Received (in Victoria, Australia) 5th May 2011, Accepted 9th May 2011
DOI: 10.1039/c1nj20392d
Q Q
R
The vinylidene complex trans-[RhCl( CHC CCPh2O-
SiMe3)(PiPr3)2] (5), prepared from [RhCl(PiPr3)2]2 (1) and
C
in benzene or toluene at room temperature to give the
diynyl(hydrido) and vinylidene isomers 4 and 5 (Scheme 1).
The 31P NMR spectrum of the labile intermediate 4 displays a
doublet at d 50.2 with J(Rh,P) 97.4 Hz, which is in excellent
agreement with the data for trans-[RhH(Cl)(CRCCR
CPh)(PiPr3)2] (d 49.9, J(Rh,P) 96.0 Hz).6
R
HC CC CCPh2OSiMe3 (2), is in equilibrium with
the pentatetraenediyl isomer trans-[RhCl(
R
Q Q Q Q
C
C
C
CHCPh2OSiMe3)(PiPr3)2] (6) in benzene solution. The reaction
R
R
of the diynyl(hydrido) compound [RhH(Cl)(C CC
CCPh2OSiMe3)(PiPr3)2(py)] (7) with triflic acid in THF/water
afforded the functionalized rhodium(I) vinylidene trans-
The vinylidene complex 5, which had been isolated under
carefully controlled conditions,5 is significantly more labile
than the related iridium(I) compound trans-[IrCl(QCQCHCR
CCPh2OH)(PiPr3)2],3 and in benzene or toluene partly
isomerizes to the RhC4 cumulene 6. After 12 h at 22 1C in
C6D6, about equal amounts of 5 and 6 are formed. Changing
the reaction conditions (solvent, temperature, time of reaction)
has almost no effect on the equilibrium. Typical spectroscopic
features of 6 are the singlet at d 5.73 for the QCH proton in
the 1H NMR spectrum and the four distinct signals for the
carbon atoms of the RhC4 chain in the 13C NMR spectrum.
These signals exhibit quite different 13C–103Rh and 13C–31P
coupling constants. It is worth mentioning that the chemical
shifts of the resonances for the cumulene carbon atoms in a-,
b- and g-position (d 237.3, 161.1 and 173.1) are rather similar
to those of the IrC4 counterpart trans-[IrCl(QCQCQ
CQCPh2)(PiPr3)2] (d 225.7, 164.1 and 174.6).3 Moreover, we
note that prior to the synthesis of trans-[IrCl(QCQCQ
CRCPh2)(PiPr3)2],3 Selegue and Lomprey,7 Bruce et al.,8
Winter and Hornung,9 and Dixneuf et al.10 reported the
in situ formation of cationic ruthenium(II) complexes containing
the fragment RuQCQCQCQCH2, and they supported the
presence of those species in solution by trapping experiments
with nucleophiles such as NHPh2, PPh3, water and imines.
Berke et al. described a different approach to the generation of
the pentatetraenediyl ligand CQCQCQCH2 at manganese(I)
as the metal atom using the stannyl-substituted derivatives
[(C5H4R)Mn{QCQCQCQC(SnPh3)2}(R02PCH2CH2PR02)]
(R = H, Me; R0 = Me, Et) as the precursors.11 While
the latter were stable under ambient conditions, the
MnC4H2 compounds [(C5H4R)Mn(QCQCQCQCH2)-
(R02PCH2CH2PR02)] decomposed above ꢀ5 1C and were
Q Q
[RhCl(
Q
C
CHC(O)CH CPh2)(PiPr3)2] (9), which was also
Q Q Q
obtained from the metallacumulene trans-[RhCl(
Q Q
CPh2)(PiPr3)2] (8) under analogous conditions.
C
C
C
C
Following our work on the chemistry of vinylidene rhodium(I)
and iridium(I) complexes of the general composition trans-
[MCl(QCQCRR0)(PiPr3)2] and their allenylidene analogues
trans-[MCl(QCQCQCRR0)(PiPr3)2] (M = Rh, Ir; R, R0 = H,
alkyl, aryl),1,2 we recently reported the synthesis and molecular
structure of the pentatetraenediyl and hexapentaenediyl
iridium(I) compounds trans-[IrCl(QCQCQCQCPh2)(PiPr3)2]
and trans-[IrCl(QCQCQCQCQCPh2)(PiPr3)2], respectively.3,4
While the hexapentaenediyl rhodium(I) complex trans-
[RhCl(QCQCQCQCQCPh2)(PiPr3)2] could also be generated
and trapped with diazomethane to give two isomers of the metal
hexapentaene trans-[RhCl(H2CQCQCQCQCQCPh2)(PiPr3)2],5
previous attempts to obtain a RhC4 cumulene, related to
trans-[IrCl(QCQCQCQCPh2)(PiPr3)2], remained unsuccessful.
In this letter we disclose the spectroscopic data of the
RhC4 cumulene trans-[RhCl(QCQCQCQCHR)(PiPr3)2]
(R = CPh2OSiMe3) and report about the reactivity of the
RhC5 counterpart trans-[RhCl(QCQCQCQCQCPh2)(PiPr3)2]
towards phenyl azide and triflic acid in the presence of water.
The rhodium(I) dimer 1, which had already been used to
prepare the above-mentioned vinylidene and allenylidene
rhodium(I) compounds,1 reacts with the diyne 2 to give the
square-planar complex 3, in which the terminal triple bond is
linked to the metal atom.5 Compound 3 rearranges stepwise
characterized by NMR spectroscopy. Most recently,
a
Institut fur Anorganische Chemie der Universitat Wurzburg,
¨
¨
Am Hubland, D-97074 Wurzburg, Germany.
¨
¨
similar synthetic protocol to that used for the MnC4(SnPh3)2
derivatives was disclosed also by Berke’s group for the
tungsten(0) compounds [W(CO){QCQCQCQC(R)C6H4tBu}-
(Ph2PCH2CH2PPh2)2] (R = H, SnMe3).12
E-mail: helmut.werner@mail.uni-wuerzburg.de
w Dedicated to Professor Didier Astruc in recognition of his important
contributions to inorganic and organometallic chemistry.
c
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Scheme 1 L: PiPr3, 2: HCRCCRCCPh2OSiMe3, Tf: CF3SO2.
The reaction of the five-coordinate diynyl(hydrido) complex
4 with pyridine leads to the octahedral 1 : 1 adduct 7, which
on treatment with triflic acid anhydride and triethylamine
gives the RhC5 cumulene 8.5 Whereas diazomethane reacts
with 8 to furnish two isomers of the hexapentaene complex
trans-[RhCl(H2CQCQCQCQCRCPh2)(PiPr3)2],5 treatment
of 8 with phenylazide under the same conditions affords a
mixture of products, among which trans-[RhCl(N2)(PiPr3)2]
is the dominating species. It has been characterized by
the mass spectrum and by reference to the IR and NMR
spectroscopic data.13 Reaction of either 7 or 8 with triflic
acid in the presence of an equimolar amount of water gives
the rhodium(I) vinylidene complex 9 (Scheme 2) as an
orange solid, which for short periods of time can be handled
in air. The IR spectrum of 9 shows a strong band at
1640 cmꢀ1, assigned to the CQO stretching mode of the
ketone unit. Typical NMR spectroscopic features of 9
are the broadened triplet for RhQCQCH proton at
d 1.78 and the doublets-of-triplets resonances for the vinyl-
idene carbon atoms at d 288.5 (a-C) and d 117.8 (b-C).
A
functionalized vinylidene ligand of the composition
CQCHC(O)CHPh2, related to that found in 9, was recently
generated at iridium(I) and ruthenium(II) from HCRCC(O)-
CHPh2 as the precursor.3,10
As confirmed by X-ray diffraction analysis,14 in compound
9 the rhodium atom is coordinated in a slightly distorted
square-planar fashion, with the two phosphine ligands trans
to each other and the chloride trans-disposed to the metal-
bound carbon atom. The RhQC distance is 1.784(6) A, which
is almost identical with the rhodium–carbon bond lengths in
the related complexes trans-[RhCl(QCQCHCH3)(PiPr3)2]
[1.775(6) A]15 and trans-[RhCl(QCQCHC(CH3)QCH2)-
(PiPr3)2] [1.78(1) A].16 The carbon atoms of the vinylidene
fragment RhQCQC and the ketonic unit C–C(O)–CHQC lie
essentially in the same plane, indicating that in the crystal this
conformation is preferred. The lengths of the two formal
CH–C(O) single bonds [1.456(6) and 1.471(6) A] are shorter
than expected, which is presumably due to conjugative effects.
With regard to the formation of 9 from 8, we propose a
stepwise mechanism with the initial step being either the
protonation at the b-carbon of the RhC5 chain or the attack
of the water molecule to the g-carbon atom. Theoretical
studies revealed that metallacumulenes of the general compo-
sition [M{QC(QC)nR2}(L)x] with
n = 1 to 4 react
preferentially with electrophiles at C2 or C4 and with
nucleophiles at C1, C3 or C5.17 The reactivities of the
square-planar rhodium(I) and iridium(I) complexes trans-
[MCl{QC(QC)nR2}(PiPr3)2] (M = Rh, n = 1, 2; M = Ir,
n = 1, 2, 3) are in perfect agreement with these results.
Scheme 2 L: PiPr3, Tf: CF3SO2.
c
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or fractional crystallization failed. Spectroscopic data of
6: NMR (C6D6): dH (200 MHz, 295 K) 7.52 [4 H, d, J(H,H)
8.0, ortho-H of C6H5], 7.22–6.95 (6 H, br m, meta- and para-H
of C6H5), 5.73 (1 H, s, QCH), 2.75 (6 H, m, PCHCH3), 1.29
[36 H, dvt, N 13.8, J(H,H) 6.9, PCHCH3], 0.11 (9 H, s,
OSiMe3); dC (100.6 MHz, 295 K) 237.3 [dt, J(Rh,C) 66.1,
J(P,C) 16.9, RhQC], 173.1 [dt, J(Rh,C) 3.8, J(P,C) 3.2,
RhQCQCQC], 161.1 [dt, J(Rh,C) 19.1, J(P,C) 6.7,
RhQCQC], 148.7, 148.5 (both s, ipso-C of C6H5), 128.1,
127.2, 127.0 (all s, C6H5), 88.0 [t, J(P,C) 3.5,
RhQCQCQCQCH], 72.3 [t, J(P,C) 3.5, CPh2], 24.0 (vt, N
20.3, PCHCH3), 20.7 (s, PCHCH3), 2.0 (s, SiCH3); dP
(162.0 Hz, 295 K) 41.1 [d, J(Rh,P) 128.9].
Experimental
All experiments were carried out under an atmosphere of
argon using Schlenk techniques. The starting materials 118
and 219 were prepared as described in the literature. The
preparative protocol for 3, 7 and 8 was already described.5
NMR spectra were recorded on Bruker AC 200 and AMX
400 instruments, and IR spectra on a Perkin-Elmer 1420
spectrometer. Melting points were determined by DTA.
Abbreviations used: s, singlet; d, doublet; t, triplet; vt, virtual
triplet; m, multiplet; br, broadened signal; coupling constants
J and N [N = 3J(P,H) + J(P,H) or J(P,C) + J(P,C) or
5
1
3
4
2J(P,C) + J(P,C)] in Hz.
Syntheses
Reaction of compound 8 with phenyl azide. A solution of 8
(80 mg, 0.12 mmol) in toluene (10 cm3) was treated with an
equimolar amount of PhN3 and stirred for 30 min at room
temperature. A change of color from deep violet to orange
occurred. The solution was concentrated in vacuo to ca. 2 cm3
and pentane (5 cm3) was added. After the mixture was stored
for 4 h at ꢀ20 1C, an orange solid precipitated. Based on the
31P NMR spectrum, it contained a mixture of two rhodium-
containing compounds in the ratio of ca. 6 : 1. Attempts to
separate the two compounds failed. The major product was
identified as trans-[RhCl(N2)(PiPr3)2] by mass spectrometry
(m/z 486), and IR and NMR spectroscopic data.
R R
[Rh(H)Cl(C CC CCPh2OSiMe3)-
Generation
of
(PiPr3)2], 4. A sample of 3 (54 mg, 0.07 mmol) was dissolved
in d8-toluene (0.5 cm3) at room temperature. The solution was
stirred for ca. 5 min and then cooled to ꢀ20 1C. The 1H
and 31P NMR spectra indicated the formation of the
alkynyl(hydrido) isomer 4 as well as of small amounts of the
vinylidene complex 5. Typical NMR data of 4: dH (C6D5CD3,
200 MHz, 253 K) ꢀ16.42 [dt, J(Rh,H) 44.0, J(P,H) 13.0,
RhH]; dP (C6D5CD3, 81.0 MHz, 253 K) 50.2 [d, J(Rh,P) 97.4].
Q Q
R
trans-[RhCl( CHC CCPh2OSiMe3)(PiPr3)2], 5. A
C
solution of 3 (110 mg, 0.14 mmol) in C6D6 (2 cm3) was stirred
at room temperature and the course of the reaction was
carefully monitored by 31P NMR spectroscopy. After 30 min
the spectrum revealed the presence of approximately 90% of
the vinylidene isomer. The solvent was quickly removed
in vacuo, and pentane (1 cm3) was added to the viscous residue.
After the mixture was stored for 1 h at ꢀ20 1C, a red-violet
solid was formed. It was separated from the mother liquor,
washed twice with 1 cm3 portions of pentane (ꢀ20 1C) and
dried in vacuo: yield 63 mg (57%); mp 71 1C (decomp). Anal.
found: C, 58.68; H, 8.22%. C38H62ClOP2RhSi requires: C,
Q Q
Q
trans-[RhCl( C CHC(O)CH CPh2)(PiPr3)2], 9.
A
solution of either 7 (300 mg, 0.36 mmol) or 8 (242 mg,
0.36 mmol) in tetrahydrofurane (3 cm3) was treated at
ꢀ78 1C first with an equimolar amount of water and then
with trifluoromethanesulfonic acid (0.64 cm3, 0.72 mmol).
Under continuous stirring the solution was slowly warmed
to room temperature, which led to a change of color from
off-white to orange. The solution was concentrated in vacuo to
ca. 2 cm3 and the concentrate was chromatographed on Al2O3
(acidic, activity grade I). With chilled toluene (ꢀ50 1C) an
orange fraction was eluted from which the solvent was
removed in vacuo. To the viscous residue pentane (1 cm3)
was added, and the mixture was stored for 6 h. An orange
solid precipitated, which was separated from the mother
liquor, washed twice with 1 cm3 portions of pentane (ꢀ20 1C)
and dried in vacuo: yield 120 mg (49%); mp 84 1C (decomp).
Anal. found: C, 59.83; H, 7.71%. C35H54ClOP2Rh requires: C,
60.83; H, 7.88%. IR (KBr): n(CQO) 1640 cmꢀ1. NMR (C6D6,
295 K): dH (200 MHz) 7.35–6.95 (11 H, br m, C6H5 and
CHQCPh2), 2.65 (6 H, m, PCHCH3), 1.78 [1 H, t, J(P,H) 2.6,
RhQCQCH], 1.29 [36 H, dvt, N 13.2, J(H,H) 6.8, PCHCH3];
dC (100.6 MHz) 288.5 [dt, J(Rh,C) 61.0, J(P,C) 14.0,
RhQCQCH], 180.1 (s, CQO), 150.8 (s, CHQCPh2), 142.2,
140.1 (both s, ipso-C of C6H5), 130.1 (s, CHQCPh2), 129.1,
128.9, 128.5, 128.2 (all s, C6H5), 117.8 [dt, J(Rh,C) 15.3,
J(P,C) 5.1, RhQCQCH], 24.2 (vt, N 20.3, PCHCH3), 20.3
(s, PCHCH3); dP (162.0 Hz) 43.8 [d, J(Rh,P) 132.3].
59.79; H, 8.19%. IR (KBr): n(CRC) 2195, n(CQC) 1605 cmꢀ1
.
NMR (C6D6): dH (200 MHz, 295 K) 7.77 [4 H, d, J(H,H) 7.2,
ortho-H of C6H5], 7.22–6.95 (6 H, br m, meta- and para-H of
C6H5), 2.75 (6 H, m, PCHCH3), 1.28 [36 H, dvt,
N 13.8, J(H,H) 6.9, PCHCH3], 0.83 [1 H, dt, J(Rh,H) 0.6,
J(P,H) 2.9, RhQCQCH], 0.23 (9 H, s, OSiMe3); dC
(100.6 MHz, 295 K) 291.3 [dt, J(Rh,C) 62.3, J(P,C) 15.9,
RhQCQCH], 147.9 (s, ipso-C of C6H5), 127.9, 127.3, 126.7
(all s, C6H5), 101.5 (s, CRCCPh2), 90.4 [dt, J(Rh,C) 17.8,
J(P,C) 6.4, RhQCQCH], 77.0 (s, CRCCPh2), 66.3 [t, J(P,C)
3.5, CRCCPh2], 23.7 (vt,
N 20.3, PCHCH3), 20.3
(s, PCHCH3), 1.8 (s, SiCH3); dP (162.0 Hz, 295 K) 43.1
[d, J(Rh,P) 132.3]. Note: it is important to measure the
NMR spectra immediately after the solid sample is dissolved
in C6D6.
Q Q Q Q
Isomerization of 5 to trans-[RhCl( CHCPh2-
C
C
C
OSiMe3)(PiPr3)2], 6. A sample of 5 (38 mg, 0.05 mmol) was
dissolved in C6D6 (0.5 cm3) and the NMR spectra of the
solution were carefully monitored in time intervals of 30 min
at room temperature. After 12 h, the spectra revealed the
presence of approximately equal amounts of the isomers 5 and 6.
Attempts to separate the isomers by column chromatography
Acknowledgements
We gratefully acknowledge financial support from the
Deutsche Forschungsgemeinschaft, the Fonds der Chemischen
Industrie and the Humboldt Foundation. We also thank
c
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Mrs R. Schedl and Mr C. P. Kneis (DTA and elemental
analyses) and Dr G. Lange and Mr F. Dadrich (mass spectra).
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D. Touchard, J.-L. Fillaut, S. Golhen and P. H. Dixneuf, Angew.
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c
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