Synthesis and reactivity of fluoro complexes. Part 1. Cyclooctadiene rhodium(I) complexes

Article abstract of DOI:10.1021/ic015526e

The systhesis of [RhF(COD)]_n and its triphenylphosphine adduct 2, and a preliminary study of the reactivity of 2 are reported. The reactivity of the Rh-F-bond is illustrated by the reactions that lead to compounds 5 and 6. Compound 5 is the first triflouromethyl Rh(1) complex characterized by monocrystal X-ray diffraction. Both compounds 2 and 6 are initiators of the polymerization of phenylacetylene.

Full text of DOI:10.1021/ic015526e

2636
Inorg. Chem. 2001, 40, 2636-2637
Synthesis and Reactivity of Fluoro Complexes. Part 1. Cyclooctadiene Rhodium(I) Complexes
Jose´ Vicente,*,† Juan Gil-Rubio,† and Delia Bautista‡
Grupo de Qu´ımica Organometa´lica, Departamento de Qu´ımica Inorga´nica, Facultad de Qu´ımica, Universidad de Murcia, Apartado 4021,
Murcia, 30071 Spain, and SACE, Universidad de Murcia, Apartado 4021, Murcia, 30071 Spain
ReceiVed March 22, 2001
There is a growing interest in the study of transition metal
organometallic fluoro complexes.1 The unique properties of
fluorine impart an unusual reactivity to the metal-fluorine bond
which can be exploited in preparative organometallic chemistry2
or in catalysis.3 In addition, the development of transition metal
mediated C-F bond formation processes is still a virtually
unexplored field.4
Scheme 1
The number of rhodium(I) fluoro complexes is still scarce, and
very few studies on their reactivity have been reported.5 To the
best of our knowledge, only two Rh(I) fluoro complexes without
phosphine, arsine, or stibine ligands have been prepared. The first,
temptatively formulated as [Rh(µ-F)(cyclooctene)2]2, was obtained
by reacting [Rh(µ-Cl)(cyclooctene)2]2 with AgF.5c The second was
the tetramer [Rh(µ3-F)(C2H4)(C2F4)]4, which was prepared by the
successive treatment of [Rh(µ-Cl)(C2H4)(C2F4)]2 with AgBF4 and
the fluoride donor reagent [(Me2N)3S]+[Me3SiF2]-.5f
Herein, we report the synthesis of two novel rhodium(I) fluoro
complexes containing cyclooctadiene (COD) and a preliminary
study of the reactivity of the Rh-F bond, which is shown to be
substantially different from that of the other Rh-halogen bonds.
Treatment of [Rh(µ-OH)(COD)]26 with 73% hydrofluoric acid
in THF gave compound 1 as a yellow microcristalline precipitate
in 82% yield (Scheme 1). The NMR spectra of 1 were of poor
quality because, in contrast to [Rh(µ-X)(COD)]2 (X ) Cl, OH),
it is only sparingly soluble in organic solvents, which impeded
determination of its structure in solution.7 We were unable to grow
single crystals of 1 for X-ray structure determination, however,
we are currently attempting the preparation of more soluble fluoro
complexes containing different dienes for its structural charac-
terization.
The main product of the reaction of compound 1 with 1 equiv
of triphenylphosphine in THF is 2, which was isolated in 59%
yield. The crystal structure of 2 was determined by X-ray dif-
fraction analysis8 and shows a distorted square-planar coordination
geometry (Figure 1). As expected from the greater trans influence
of PPh3 with respect to F-, the Rh-C(5) and Rh-C(6) distances
are longer than the Rh-C(1) and Rh-C(2) ones (Figure 1).
In the 19F NMR spectrum of 2, a broad singlet was observed
at high field (δ -256.9 ppm in d8-toluene) characteristic of Rh-
(I)-bound fluorine.5j The room temperature 31P{1H} NMR spec-
trum displays a broad singlet at at δ 23.0 ppm which splits into
* To whom communication should be addressed.
† Grupo de Qu´ımica Organometa´lica, Departamento de Qu´ımica Inorga´nica,
Facultad de Qu´ımica, Universidad de Murcia.
1
a broad doublet at T < -20 °C with JRhP ) 159.3 Hz.9 The
‡ SACE, Universidad de Murcia.
31P-19F and 103Rh-19F couplings were not resolved even at -90
°C. This suggests that, although 2 is the main species present in
solution, fast Rh-F and Rh-P bond dissociations take place to
give products whose nature is still not clear. Complex 2 is the
first fluoro complex of Rh(I) with only one phosphine ligand.
(1) (a) Doherty, N. M.; Hoffman, N. W. Chem. ReV. 1991, 91, 553-573.
(b) Murphy, E. F.; Murugavel, R.; Roesky, H. W. Chem. ReV. 1997, 97,
3425-3468.
(2) (a) Veltheer, J. E.; Burger, P.; Bergman, R. G. J. Am. Chem. Soc. 1995,
117, 12478-12488. (b) Grushin, V. V. Angew. Chem., Int. Ed. Engl.
1998, 37, 994-996. (c) Archibald, S. J.; Braun, T.; Gaunt, J. A.; Hobson,
J. E.; Perutz, R. N. J. Chem. Soc., Dalton Trans. 2000, 2013-2018.
(3) Pagenkopf, B. L.; Carreira, E. M. Chem. Eur. J. 1999, 5, 3437-3442.
(4) Barthazy, P.; Stoop, R. M.; Wo¨rle, M.; Togni, A.; Mezzetti, A.
Organometallics 2000, 19, 2844-2852.
(7) Broad signals assignable to the COD ligand were observed in the 1H
and 13C{1H} NMR spectra of 1 (d8-THF) at room temperature. No signals
were observed in the 19F NMR spectrum (d8-THF) in the +20 to -380
ppm range (relative to external CFCl3) at temperatures from +60 to -80
°C.
(5) (a) Grinberg, A. A.; Singkh, M. M.; Varshavskii, Yu. S. Russ. J. Inorg.
Chem. 1968, 13, 1399-1401. (b) Vaska, L.; Peone, J., Jr. J. Chem. Soc.,
Chem. Commun. 1971, 418-419. (c) van Gaal, H. L. M.; van den
Bekerom, F. L. A.; Verlaan, J. P. J. J. Organomet. Chem. 1976, 114,
C35-C37. (d) van Gaal, H. L. M.; van den Bekerom, F. L. A. J.
Organomet. Chem. 1977, 134, 237-248. (e) Goswami, K.; Singh, M.
M. J. Indian Chem. Soc. 1979, 56, 477-482. (f) Burch, R. R.; Harlow,
R. L.; Ittel, S. D. Organometallics, 1987, 6, 982-987. (g) Araghizadeh,
F.; Branan, D. M.; Hoffman, N. W.; Jones, J. H.; McElroy, E. A.; Miller,
N. C.; Ramage, D. L.; Battaglia Salazar, A.; Young, S. H. Inorg. Chem.
1988, 27, 3752-3755. (h) Fryzuk, M. D.; Piers, W. E. Polyhedron 1988,
7, 1001-1014. (i) Sakakura, T.; Sodeyama, T.; Sasaki, K.; Wada, K.;
Tanaka, M. J. Am. Chem. Soc. 1990, 112, 7221-7229. (j) Gil-Rubio,
J.; Weberndo¨rfer, B.; Werner, H. J. Chem. Soc., Dalton Trans. 2000,
1437-1444. (k) Gil-Rubio, J.; Weberndo¨rfer, B.; Werner, H. Angew.
Chem., Int. Ed. 2000, 39, 786-789.
(8) Crystal data for 3 were recorded on a Siemens P4 difractometer, λ )
0.71073 Å, C26H27FPRh (492.36), monoclinic (P21/c) a ) 12.7652(7)
Å, b ) 11.3795(7) Å, c ) 14.6419(8) Å, â ) 95.728(4)°, V ) 2116.3-
(2) Å3, Z ) 4, Fcalc ) 1.545 Mg/m3, µ ) 0.901 mm-1, F(000) ) 1008,
T ) 173(2) K; θ range ) 3.08-25.00, -15 e h e 15, -13 e k e 1,
-17 e l e 0; reflect. collected, 3891; indep reflns, 3720 (Rint ) 0.0140),
abs corr ψ-scans, max and min transmission 0.79798 and 0.75555;
structure refinement full-matrix least squares on F2, data/restraints/
parameters 3720/208/262, GOF on F2 ) 1.057, final R indices [I > 2σ(I)],
R1 ) 0.0205, all data wR2 ) 0.0498; largest diff peak and hole 0.372
and -0.331 eÅ-3
.
(9) This value is similar to the ones found in [RhCl(COD)(PR3)] complexes;
see Naaktgeboren, A. J.; Nolte, R. J. M.; Drenth, W. J. Am. Chem. Soc.
1980, 102, 3350-3354.
(6) Uso´n, R.; Oro, L. A.; Cabeza, J. A. Inorg. Synth. 1985, 23, 126-130.
10.1021/ic015526e CCC: $20.00 © 2001 American Chemical Society
Published on Web 05/09/2001

Communications
Inorganic Chemistry, Vol. 40, No. 12, 2001 2637
Figure 1. Molecular structure of 2 with 50% probability ellipsoids and
the labeling scheme. Selected bond lengths (Å) and angles (deg): Rh-F
2.0214(12), Rh-C(1) 2.115(2), Rh-C(2) 2.097(2), Rh-C(5) 2.197(2),
Rh-C(6) 2.189(2), C(1)-C(2) 1.399(3), C(5)-C(6) 1.379(3), Rh-P
2.3229(5); F-Rh-C(5) 89.06(7), F-Rh-C(6) 87.24(7), C(1)-Rh-P
96.92(6), C(2)-Rh-P 92.86(6), F-Rh-P 89.40(4).
Figure 2. Molecular structure of 5 with 50% probability ellipsoids and
the labeling scheme. Only one of the two independent molecules is
displayed. Selected bond lengths (Å) and angles (deg): Rh(1)-C(9)
2.097(2), Rh(1)-C(1) 2.215(2), Rh(1)-C(2) 2.194(2), Rh(1)-C(5) 2.208-
(2), Rh(1)-C(6) 2.206(2), Rh(1)-P(1) 2.3245(5), C(1)-C(2) 1.381(3),
C(5)-C(6) 1.379(3); C(9)-Rh(1)-C(2) 87.60(9), C(9)-Rh(1)-C(1)
91.55(8), C(9)-Rh(1)-P(1) 91.13(6), C(6)-Rh(1)-P(1) 90.01(6), C(5)-
Rh(1)-P(1) 96.71(6).
Treatment of 2 with PPN+Cl- (PPN ) [Ph3P]2N) gave
quantitatively the chloro complex 3.10 The reaction of 2 with Me3-
1
SiO3SCF3 afforded Me3SiF, which was detected by H and 19F
NMR spectroscopy, and compound 4 in 87% yield. The triflate
4 can be also prepared by the reaction of 3 with AgCF3SO3.
The reaction of 2 with Me3SiCF3 afforded complex 5, which
was isolated in 76% yield, and Me3SiF. This synthethic method
has been previously used only for the preparation of Ru and Os
trifluoromethyl complexes.11 We were interested in testing this
method on Rh(I) fluoro complexes since only one Rh(I) trifluo-
romethyl complex is known.12 The crystal structure of 5 was
determined by X-ray diffraction (Figure 2).13 Two independent
molecules were found in the unit cell which show very small
differences in both bond distances and angles. In contrast to
complex 2, the Rh-C distances were similar for both Rh-olefin
bonds, which suggest that CF3 and PPh3 have similar trans
influences. This is the first crystal structure determination of a
Rh(I) trifluoromethyl complex. In C6D6 solution, the 31P{1H}
acetylene in the presence of Na2CO3, which neutralized the HF
formed in the reaction.5j It is noteworthy that [RhCl(COD)(PPh3)]
does not react appreciably with phenyl acetylene under the same
conditions. The presence of the alkynyl unit was confirmed by
the IR [ν(CtC) ) 2084 cm-1] and 13C NMR spectra, which
displayed two doublets at δ 121.5 ppm (1JRhC ) 48.6 Hz) and
120.8 ppm (2JRhC ) 12.2 Hz) for the R and â alkynyl carbons,
respectively. An exchange process involving dissociation of the
phosphine is likely responsible for the absence of the 13CR,â-31P
couplings and for the broad singlet observed in the 31P{1H} NMR
spectrum at room temperature. On cooling at -10 °C, this broad
singlet was transformed into a doublet (1JRhP ) 159.8 Hz).
Recently, it has been reported that complexes of the general
composition [Rh(CtCAr)(Nbd)(PR3)] generated in situ are excel-
lent initiators for the controlled living polymerization of pheny-
lacetylenes.14 However, in contrast to 6, these species are too
unstable to be isolated. Preliminary experiments show that
polymerization of phenylacetylene takes place in the presence of
catalytic amounts of 2 or 6, both in the presence of Na2CO3, to
give polyphenylacetylene in a nearly quantitative yield.
1
NMR spectrum shows a doublet of quartets with JRhP ) 177.9
3
Hz and JPF ) 21.4 Hz.
The alkynyl complex [Rh(CtCPh)(COD)(PPh3)] (6) was
obtained in 79% yield by reaction of 2 with 1 equiv of phenyl
(10) Chatt, J.; Venanzi, L. M. J. Chem. Soc. 1957, 4735-4741.
(11) Huang, D.; Koren, P. R.; Folting, K.; Davidson, E. R.; Caulton, K. G. J.
Am. Chem. Soc. 2000, 122, 8916-8931.
(12) Trans-[Rh(CF3)(CO)(PPh3)2] was prepared by reacting trans-[RhH(CO)-
(PPh3)2] with the toxic Hg(CF3)2; see Burrell, A. K.; Clark, G. R.; Jeffrey,
J. G.; Rickard, C. E. F.; Roper, W. R. J. Organomet. Chem. 1990, 388,
391-408.
Acknowledgment. We thank the DGICYT (PB97-1047 and
a research contract to J.G.R.) and the European Commission
(Contract HPMF-CT1999-00116) for financial support.
Supporting Information Available: Synthetic procedures, spectral
and analytical data for 1-6, crystallographic files in CIF format for
compounds 3 and 5, and ORTEP plots of the two independent molecules
of 5. This material is available free of charge via the Internet at
http://pubs.acs.org.
(13) Crystal data for 5 were recorded on a Siemens P4 difractometer, λ )
0.71073 Å. C27H27F3Rh (542.37), triclinic (P-1), a ) 11.8239(5) Å, b
) 13.0316(7) Å, c ) 15.0851(9) Å, R ) 92.237(5)°, â ) 99.544(4)°, γ
) 90.658(4)°, V ) 2290.1(2) Å3, Z ) 4, Fcalc 1.573 Mg/m3, µ ) 0.853
mm-1, F(000) ) 1104, T ) 173(2) K; θ range ) 3.10-25.00, -14 e
h e 14, -15 e k e 15, -17 e l e 5; reflns collected, 11116; indep
reflns, 8040 (Rint ) 0.0145), abs corr ψ-scans, max and min transmission
0.78749 and 0.75721; structure refinement full-matrix least squares on
F2, data/restraints/parameters 8040/508/577, GOF on F2 ) 1.066, final
R indices [I > 2σ(I)], R1 ) 0.0211, all data wR2 ) 0.0520; largest diff
IC015526E
(14) (a) Kishimoto, Y.; Miyatake, T.; Ikariya, T.; Noyori, R. Macromolecules
1996, 29, 5054-5055. (b) Kishimoto, Y.; Eckerle, P.; Miyatake, T.;
Kainosho, M.; Ono, A.; Ikariya, T.; Noyori, R. J. Am. Chem. Soc. 1999,
121, 12035-12044.
peak and hole 0.318 and -0.313 eÅ-3
.