A new rhodium(I) hexapentaene complex prepared from a precursor containing a RhC5 chain

Article abstract of DOI:10.1021/om970734t

The metallacumulene [RhCl(=C=C=C=C= CPh₂)(PiPr₃)₂] (6) was prepared stepwise from [RhCl-(PiPr₃)₂]₂ (1) and HC≡CC≡CCPh₂OSiMe₃ via the π-alkyne complex 2, the diynylhydridorhodium(III) species 3, and the vinylidenerhodium(I) compound 4 as intermediates. The reaction of 6 with CH₂N₂ affords two isomers (A and B) of the square-planar rhodium(I) complex 7, in which the hitherto unknown hexapentaene H₂C=C=C=C=C=CPh₂ is π-coordinated to the RhCl-(PiPr₃)₂ fragment.

Full text of DOI:10.1021/om970734t

Organometallics 1997, 16, 5607-5609
5607
A New Rh od iu m (I) Hexa p en ta en e Com p lex P r ep a r ed
fr om a P r ecu r sor Con ta in in g a Rh C5 Ch a in
Ivan Kovacik, Matthias Laubender, and Helmut Werner*
Institut fu¨r Anorganische Chemie der Universita¨t Wu¨rzburg, Am Hubland,
D-97074 Wu¨rzburg, Germany
Received August 18, 1997X
Summary: The metallacumulene [RhCl(dCdCdCdCd
CPh2)(PiPr3)2] (6) was prepared stepwise from [RhCl-
(PiPr3)2]2 (1) and HCtCCtCCPh2OSiMe3 via the
π-alkyne complex 2, the diynylhydridorhodium(III) spe-
cies 3, and the vinylidenerhodium(I) compound 4 as
intermediates. The reaction of 6 with CH2N2 affords two
isomers (A and B) of the square-planar rhodium(I)
complex 7, in which the hitherto unknown hexapentaene
H2CdCdCdCdCdCPh2 is π-coordinated to the RhCl-
(PiPr3)2 fragment.
the diynylhydridorhodium(III) intermediate 3 and then
the isomeric vinylidenerhodium(I) complex 4. While 3
1
could only be characterized by its H and 31P NMR data
(for comparison with the related compound [RhH-
(CtCCtCPh)Cl(PiPr3)2], see ref 10), 4 was isolated as
a red-violet, almost air-stable solid.11 The most typical
spectroscopic features of 4 are the resonance of the
RhdCdCH proton at δ 0.83 and the low-field signals
at δ 291.3 and 90.4 (both doublets of triplets) for the
R-C and â-C vinylidene carbon atoms, respectively.
The reaction of 2 with pyridine in benzene led,
probably via 3 as an intermediate, to the formation of
a stable off-white solid which according to elemental
analysis and IR and NMR spectroscopy is the octahedral
complex 5. Treatment of 5 in toluene at -78 °C with 2
equiv of Tf2O (Tf dCF3SO2), followed by addition of an
excess of NEt3 when the mixture reached room temper-
ature, gave a deep violet solution. From this solution
upon chromatography on Al2O3 (first with toluene at
-50 °C and then with pentane at -20 °C) and removal
of the solvent the deep violet viscous product 6 was
obtained in ca. 60% yield. The preparation of 6 could
also be achieved by treatment of the vinylidene com-
pound 4 with an equimolar amount of Tf2O in toluene
at -78 °C, followed by addition of NEt3 at room
temperature. Although we failed to obtain 6 as a
crystalline material, the IR and NMR spectroscopic data
are in good agreement with the structure proposed in
Scheme 1.12 By analogy to the iridium counterpart
trans-[IrCl(dCdCdCdCdCPh2)(PiPr3)2],3 the IR spec-
trum of 6 displays two bands at 1962 and 1860 cm-1
which are assigned to the C-C-C stretching frequen-
cies of the RhC5 unit. In the 13C NMR spectrum, the
five carbon atoms of the metallacumulene chain give
rise to five signals between δ 246 and 141, of which
In contrast to the large number of vinylidene and
allenylidene transition-metal complexes containing a
linear MdCdC or MdCdCdC fragment,1 related com-
pounds with a MC4 or MC5 unit are still quite rare.
Recently, Dixneuf et al. described the synthesis of a
cationic ruthenium complex of composition [RuCl-
(dCdCdCdCdCPh2)(dppe)2]+ (dppe ) Ph2PCH2CH2-
PPh2),2 and shortly thereafter we reported the isolation
and structural characterization of the first neutral
species trans-[IrCl(dCdCdCdCdCPh2)(PiPr3)2], having
a linear MC5 chain.3 In the meantime, a paper describ-
ing the preparation of the corresponding octahedral
derivatives [M(dCdCdCdCdC(NMe2)2)(CO)5] (M ) Cr,
W) has also appeared.4
The unexpected thermodynamic stability of the IrC5
complex prompted us to prepare also the analogous
RhC5 compound trans-[RhCl(dCdCdCdCdCPh2)(Pi-
Pr3)2] (6) with the particular aim of comparing the
reactivity of this metallacumulene with that of the
structurally similar RhC3 species trans-[RhCl(dCdCd
CPh2)(PiPr3)2].5 The methodology to obtain 6 is outlined
in Scheme 1. Treatment of the labile dimer 16 with the
substituted pentadiyne HCtCCtCCPh2OSiMe37 in pen-
tane at -78 °C afforded, after warming up to room
temperature, the π-alkyne complex 2 as an orange solid
in 63% yield.8,9 The couplings of the CtCH proton and
of the respective alkyne carbon atoms to 103Rh support
the assumption that it is the terminal triple bond which
is coordinated to the metal center.
(9) Werner, H.; Gevert, O.; Steinert, P.; Wolf, J . Organometallics
1995, 14, 1786-1791.
(10) Selected spectroscopic data for 2: IR (KBr) ν(CtC)uncoord 2210,
ν(CtC)coord 1805 cm-1 1H NMR (C6D6, 200 MHz) δ 4.12 (d, J H-Rh
; )
2.2 Hz, 1H, tCH), 0.21 (s, 9H, OSiMe3); 13C NMR (toluene-d8, 50.3
MHz, -20 °C) δ 92.9 (s, tCCPh2OSiMe3), 85.6 (d, J C-Rh ) 15.3 Hz,
CtCH), 80.4 (s, CtCCPh2OSiMe3), 77.6 (s, CPh2OSiMe3), 55.4 (d, J C-Rh
) 15.3 Hz, CtCH), 1.7 (s, OSiMe3); 31P NMR (C6D6, 81.0 MHz) δ 34.8
(d, J P-Rh ) 114.8 Hz).
Thermal rearrangement of 2 in toluene, which was
carefully monitored by 31P NMR spectroscopy, gave first
X Abstract published in Advance ACS Abstracts, December 1, 1997.
(1) (a) Bruce, M. I. Chem. Rev. 1991, 91, 197-257. (b) Werner, H.
Nachr. Chem.-Tech. Lab. 1992, 40, 435-444.
(2) Touchard, D.; Haquette, P.; Daridor, A.; Toupet, L.; Dixneuf, P.
H. J . Am. Chem. Soc. 1994, 116, 11157-11158.
(3) Lass, R. W.; Steinert, P.; Wolf, J .; Werner, H. Chem. Eur. J . 1996,
2, 19-23.
(4) Roth, G.; Fischer, H. Organometallics 1996, 15, 1139-1145.
(5) (a) Werner, H.; Rappert, T. Chem. Ber. 1993, 126, 669-678. (b)
Werner, H. J . Chem. Soc., Chem. Commun. 1997, 903-910.
(6) (a) Isolation: Werner, H.; Wolf, J .; Ho¨hn, A. J . Organomet. Chem.
1985, 287, 395-407. (b) X-ray crystal structure: Binger, P.; Haas, J .;
Glaser, G.; Goddard, R.; Kru¨ger, C. Chem. Ber. 1994, 127, 1927-1929.
(7) Brandsma, L. Preparative Acetylenic Chemistry, 2nd ed.; Elsevi-
er: Amsterdam, 1988; p 179.
(11) Selected spectroscopic data for the isomers 3 and 4 are as
follows: 3: 1H NMR (C6D6, 200 MHz) δ -16.42 (dt, J H-Rh ) 44, J H-P
) 13 Hz, 1H, RhH); 31P NMR (C6D6, 81.0 MHz) δ 50.2 (d, J P-Rh ) 97.4
Hz). 4: IR (KBr) ν(CtC) 2195, ν(CdC) 1606 cm-1; 1H NMR (C6D6, 200
MHz) δ 0.83 (dt, J H-Rh ) 0.6, J H-P ) 2.9 Hz, 1H, Rh)CdCH); 13C NMR
(C6D6, 100.6 MHz) δ 291.3 (dt, J C-Rh ) 62.3, J C-P ) 15.9 Hz, RhdC),
101.5 (s, CtCCPh2OSiMe3), 90.4 (dt, J C-Rh ) 17.8, J C-P ) 6.4 Hz,
RhdCdC), 77.0 (s, CPh2OSiMe3), 66.3 (t, J C-P ) 3.5 Hz, CtCCPh2-
OSiMe3), 1.8 (s, OSiMe3); 31P NMR (C6D6, 162.0 MHz) δ 43.1 (d, J P-Rh
) 132.3 Hz).
(12) Selected spectroscopic data for 6: IR (hexane) ν(CdCdC) 1962,
1860 cm-1 13C NMR (C6D6, 100.6 MHz) δ 246.1 (dt, J C-Rh ) 16.5, J C-P
;
) 6.4 Hz, RhdCdC), 205.3 (dt, J C-Rh ) 67.4, J C-P ) 17.8 Hz, RhdC),
197.8 (dt, J C-Rh ) 1.3, J C-P ) 3.8 Hz, RhdCdCdC), 156.1 (t, J C-P
)
(8) Correct elemental analyses have been obtained for complexes 2,
4, 5 and 7.
1.9 Hz, CPh2), 141.4 (t, J C-P ) 3.5 Hz, CdCPh2); 31P NMR (C6D6, 162.0
MHz) δ 34.5 (d, J P-Rh ) 128.8 Hz).
S0276-7333(97)00734-6 CCC: $14.00 © 1997 American Chemical Society

5608 Organometallics, Vol. 16, No. 26, 1997
Communications
Sch em e 1a
a
L ) PiPr3.
three (R-C, â-C, γ-C) are split into doublets of triplets
and two into triplets. The 31P NMR spectrum of 6
displays one doublet resonance at δ 34.5, indicating that
the phosphine ligands are equivalent and are in a trans
arrangement.
proximately 1:1.14 When a solution of the isomeric
mixture in toluene was stirred at 80 °C for 4 h, the ratio
A:B changed from 1:1 to 2:3; however, continuous
heating caused decomposition. Quite unexpectedly, a
1:4 mixture of A and B was obtained upon storing a solid
sample of 7 for 2 weeks at -60 °C. The more abundant
isomer B, which was the same as that isolated upon
fractional crystallization of the 2:3 isomeric mixture
from diethyl ether, was investigated by X-ray crystal-
lography.15 The structural analysis (see Scheme 1)
reveals a square-planar coordination sphere around the
metal center with the two phosphines in a trans disposi-
Like the allenylidene complex trans-[RhCl(dCdCd
CPh2)(PiPr3)2],13 compound 6 reacted with excess dia-
zomethane at 25 °C within a few minutes. The reaction
was accompanied by an evolution of gas (N2) and a
change of color from violet to orange. After removal of
the solvent and addition of 1 mL of pentane to the
viscous residue, orange-yellow, slightly air-sensitive
crystals of 7 were isolated in 63% yield. While the
elemental analysis and the mass spectra (EI, 170 °C)
confirmed the composition of a four-coordinated rhod-
ium(I) complex with π-bonded H2CdCdCdCdCdCPh2,
the 1H, 13C, and 31P NMR spectra of 7 revealed the
presence of two isomers A and B in a ratio of ap-
(14) Selected spectroscopic data of isomers A and B of compound 7
are as follows: Isomer A: 1H NMR (C6D6, 200 MHz) δ 2.75 (s, br, 2H,
dCH2); 13C NMR (C6D6, 100.6 MHz) δ 199.4 (s, dCd), 158.2 (dt, J C-Rh
) 24.1, J C-P ) 5.1 Hz, CdCH2), 121.4, 117.4 (both s, dCd), 113.0 (s,
CPh2), 15.5 (d, J C-Rh ) 12.7 Hz, dCH2); 31P NMR (C6D6, 81.0 MHz) δ
35.5 (d, J P-Rh ) 117 Hz). Isomer B: 1H NMR (C6D6, 200 MHz) δ 5.57
(t, J H-P ) 2.6 Hz, 1H of dCH2), 5.33 (s, br, 1H of dCH2); 13C NMR
(C6D6, 100.6 MHz) δ 167.5 (dt, J C-Rh ) 1.9, J C-P ) 3.8 Hz, CdCPh2),
138.2 (dt, J C-Rh ) 18.4, J C-P ) 4.5 Hz, Rh-C), 135.4 (dt, J C-Rh ) 3.2,
J C-P ) 5.7 Hz, CdCdCPh2), 120.2 (dt, J C-Rh ) 15.9, J C-P ) 5.1 Hz,
Rh-C), 117.5 (s, br, CPh2), 101.4 (d, J C-Rh ) 1.9 Hz, dCH2); 31P NMR
(C6D6, 81.0 MHz) δ 33.1 (d, J P-Rh ) 117 Hz); MS (70 eV) m/ z 687 (M+).
(13) Werner, H.; Laubender, M.; Wiedemann, R.; Windmu¨ller, B.
Angew. Chem. 1996, 108, 1330-1332; Angew. Chem., Int. Ed. Engl.
1996, 35, 1237-1239.

Communications
Organometallics, Vol. 16, No. 26, 1997 5609
tion. The rhodium is bound to the double bond between
C2 and C3, in close analogy to the situation found in
trans-[RhCl(η2-Ph2CdCdCdCdCdCPh2)L2] (L ) PPh3,16
PiPr317). While the Rh-P bond lengths are almost
identical, the Rh-C2 and Rh-C3 distances differ by
about 0.05 Å. The P-Rh-P axis is not exactly linear,
possibly due to the unsymmetric bonding situation of
the cumulene unit. The C6 chain is bent, in agreement
with previous findings, possessing C-C-C angles that
are similar to those in related rhodium hexapentaene
and butatriene complexes.16-18 It is important to note,
however, that in contrast to stable Ph2CdCdCdCd
CdCPh2 (which is the ligand in the above-mentioned
Rh(I) compounds16,17), the 1,1-disubstituted hexapen-
taene H2CdCdCdCdCdCPh2, generated during the
formation of 7, is an unknown species like other hexa-
pentaenes with CH2 as the terminal unit.19 With regard
to isomer A of complex 7, we assume that in this
molecule the C6 ligand is coordinated via the terminal
CdCH2 bond. Some of the spectroscopic data (e.g. the
position of the signal of the dCH2 protons in the 1H
NMR and that of the phosphine resonance in the 31P
NMR spectrum)14 are quite similar to those of trans-
[RhCl(η2-H2CdCdCdCPh2)(PiPr3)2], the structure of
which was determined by X-ray crystal structure analy-
sis.13
In conclusion, the results reported here illustrate that
derivatives of the readily accessible diynol HCtCCt
CCPh2OH20 can be converted stepwise, in the coordina-
tion sphere of rhodium, to the highly unsaturated car-
bene :CdCdCdCdCPh2. The corresponding metallacu-
mulene 6 is an appropriate starting material for the
generation of the coordinated hexapentaene H2CdCd
CdCdCdCPh2, which due to its high lability has not
been generated up to now in the free state.
Ack n ow led gm en t. We are grateful for financial
support of this work from the Deutsche Forschungsge-
meinschaft (SFB 347) and the Alexander-von-Humboldt
Stiftung (Max-Planck-Forschungspreis to H.W.). We
also thank Dr. W. Buchner and Mrs. R. Schedl for NMR
and DTA measurements and Dr. G. Lange and Mr. F.
Dadrich for recording the mass spectra.
(15) Principal bond lengths (Å) and interbond angles (deg) for isomer
B of 7: Rh-Cl 2.348(1); Rh-P1, 2.367(1); Rh-P2, 2.369(1); Rh-C2,
1.992(5); Rh-C3, 2.040(4); C1-C2, 1.321(8); C2-C3, 1.357(6); C3-
C4, 1.302(6); C4-C5, 1.261(6); C5-C6, 1.337(7); P1-Rh-P2, 171.25(5);
P1-Rh-Cl, 87.75(5); P2-Rh-Cl, 87.09(5); Cl-Rh-C2, 151.0(2); Cl-
Rh-C3, 169.6(1); C1-C2-C3, 149.2(6); C2-C3-C4, 152.6(5); C3-C4-
C5, 177.1(5); C4-C5-C6, 175.3(5); C2-Rh-C3, 39.3(2); Rh-C2-C1,
138.5(5); Rh-C3-C4, 138.9(4).
Su p p or tin g In for m a tion Ava ila ble: Text giving syn-
thetic details and characterization data for 2 and 5-7 and
tables giving experimental details and data of the X-ray crystal
structure analysis, bond lengths and bond angles, and atomic
positional and anisotropic thermal parameters and an ORTEP
drawing for 7 (isomer B) (12 pages). Ordering information is
given on any current masthead page.
(16) Song, L.; Arif, A. M.; Stang. P. J . J . Organomet. Chem. 1990,
395, 219-226.
(17) Werner, H.; Wiedemann, R.; Mahr, N.; Steinert, P.; Wolf, J .
Chem. Eur. J . 1996, 2, 561-569.
(18) Stang, P. J .; White, M. R.; Maas, G. Organometallics 1983, 2,
720-725.
(19) (a) Hopf, H. In The Chemistry of Ketenes, Allenes and Related
Compounds; Patai, S., Ed.; Wiley: Chichester, New York, Brisbane,
Toronto, 1980; Chapter 20, p 867. (b) Fisher, H. In The Chemistry of
Alkenes; Patai, S., Ed.; Interscience: London, New York, Sydney, 1964;
Chapter 13, p 1108.
OM970734T
(20) Armitage, J . B.; J ones, E. R. H.; Whiting, M. C. J . Chem. Soc.
1952, 1993-1998.