Unusual degradation of the rhenium silyl ester Cp(NO)(PPh3)ReCO2SiMe2Ph to the bimetallic μ-η1(C(Re)):η1(O,O′(Re)) carbon dioxide complex Cp(NO)(PPh3)ReCO2Re(NO)(CO)(PPh3)OSiMe 2Ph

Article abstract of DOI:10.1021/om970831m

The silyl esters Cp(PPh₃)(NO)ReCO₂SiR₃ (2) are produced from treatment of Cp(PPh₃)(NO)ReCOBF₄ with the silanolates R₃SiONa (R₃Si = PhMe₂Si, Et₃Si) in CH₂Cl₂ (0 °C) or of Cp(PPh₃)(NO)ReCO₂K with R₃-SiCl in THF. Upon handling, 2 degraded to the bimetallocarboxylates Cp(PPh₃)(NO)ReCO₂Re(CO)(NO)-(PPh₃)(OSiR ₃) (3), one of which (SiR₃ = SiMe₂Ph) was characterized by X-ray crystallography as a μ-η¹(C(Re₁)): η²(O,O′(Re₂)) bimetallocarboxylate.

Full text of DOI:10.1021/om970831m

Organometallics 1998, 17, 1925-1927
1925
Un u su a l Degr a d a tion of th e Rh en iu m Silyl Ester
Cp (NO)(P P h 3)ReCO2SiMe2P h to th e Bim eta llic
µ-η1(C(Re)):η1(O,O′(Re)) Ca r bon Dioxid e Com p lex
Cp (NO)(P P h 3)ReCO2Re(NO)(CO)(P P h 3)OSiMe2P h
Stephen M. Tetrick, Marisa DiBiase Cavanaugh, Fook S. Tham, and
Alan R. Cutler*
Department of Chemistry, Rensselaer Polytechnic Institute, Troy, New York 12180
Received September 22, 1997
Sch em e 1
Summary: The silyl esters Cp(PPh3)(NO)ReCO2SiR3 (2)
are produced from treatment of Cp(PPh3)(NO)ReCOBF4
with the silanolates R3SiONa (R3Si ) PhMe2Si, Et3Si)
in CH2Cl2 (0 °C) or of Cp(PPh3)(NO)ReCO2K with R3-
SiCl in THF. Upon handling, 2 degraded to the bimet-
allocarboxylates
Cp(PPh3)(NO)ReCO2Re(CO)(NO)-
(PPh3)(OSiR3) (3), one of which (SiR3 ) SiMe2Ph) was
characterized by X-ray crystallography as a µ-η1(C(Re1)):
η2(O,O′(Re2)) bimetallocarboxylate.
Several tetrametallic bis(carbon dioxide) complexes
[(η5-C5R5)(L)(L′)M(CO2)Rh(η4-COD)]2 (C5R5 ) Cp* (R )
Me), M ) Fe, Ru (L, L′ ) CO) and Re (L ) NO, L′ )
CO); C5R5 ) Cp (R ) H), M ) Re (L ) NO, L′ ) PPh3)
(1)) recently have been reported.1 An X-ray crystal-
lographic structure determination of [Cp*(CO)(NO)Re-
(CO2)Rh(η4-COD)]2 and spectroscopic data for the others
established a M2Rh2(µ3-CO2)2 structural motif in which
each µ3-η1(C(Re)):η1(O(Rh)):η1(O′(Rh′)) carboxylate ligand
bridges two RhI (η4-COD) moieties.1a The resulting
“open-book” structure resembles that of the catalytically
active Rh(I) carboxylates [(RCO2)Rh(diene)]2.2 In pre-
liminary studies on the reactions of hydrosilanes with
1, the most stable and least reactive of the M2Rh2(µ3-
CO2)2 complexes, we have observed that the initially
formed rhenium silyl esters Cp(PPh3)(NO)ReCO2SiR3
experience an unexpected reaction chemistry.
Treatment of 1 with 1.1-8.0 equiv of PhMe2SiH in
C6D6 at room temperature produced complex reaction
mixtures in which the predominant Cp(PPh3)(NO)Re-
containing product was identified as Cp(PPh3)(NO)-
ReCO2SiMe2Ph (2a ; 75% yield with 4.0 equiv of PhMe2-
SiH) (Scheme 1). The chemistry at the rhodium appears
to be dominated by the formation and subsequent
reactions of (COD)Rh(H)2SiMe2Ph.3,4 In the presence
of only 1.1-2.0 equiv of PhMe2SiH with respect to 1,
however, the initially formed 2a degraded to another
compound, 3a (28% conversion, 1 h for 2.0 equiv of
1
silane). IR and H, 13C, 31P, and 29Si NMR spectral data
for 3a indicated the presence of two rhenium centers
that are ligated by a total of one Cp, two PPh3, two NO,
one terminal CO, and one OSiMe2Ph.5 To further
characterize 3a and to document its origin, we inde-
pendently synthesized its silyl ester precursor 2a as well
as Cp(PPh3)(NO)ReCO2SiEt3 (2b) using synthetic pro-
cedures that were reported for several examples of Cp*-
(CO)(NO)ReCO2SiR3.6
Treatment of Gladysz’s Cp(PPh3)(NO)ReCO2K7 with
PhMe2SiCl or Et3SiCl quantitatively generated 2a and
2b, as judged by IR spectral monitoring (Scheme 2).5
Evaporation of solvent followed by either concentration
of ether extracts and precipitation (-78 °C) or evapora-
tion using a Schlenk line produced varying mixtures
of 2 and 3 (15-50% 3) as yellow solids. Similar re-
sults were obtained for the reaction of Cp(PPh3)(NO)-
(CO)ReBF4 and 1.1 equiv of NaOSiMe2Ph in CH2Cl2 (0
°C). This degradation of 2 to 3 is attributed to the
(5) Selected spectroscopic data are as follows: Cp(PPh3)(NO)ReCO2-
(1) (a) Tetrick, S. M.; Tham, F. S.; Cutler, A. R. J . Am. Chem. Soc.
1997, 119, 6193. (b) Tetrick, S. M.; Xu, C.; Pinkes, J . R.; Tham, F. S.;
Cutler, A. R. Organometallics, in press.
(2) (a) Rh(I)-catalyzed hydrogenation of CO2 to formic acid: Leitner,
W. Angew. Chem., Int. Ed. Engl. 1995, 34, 2207. Fornika, R.; Dinjus,
E.; Go¨rls, H.; Leitner, W. J . Organomet. Chem. 1996, 511, 145. (b)
Hydroformylation catalysis: Su¨ss-Fink, G.; Soulie, J .-M.; Rheinwald,
G.; Stoeckli-Evans, H.; Sasaki, Y. Organometallics 1996, 15, 3416. (c)
Mieczynska, E.; Trzeciak, A. M.; Zio´lkowski, J . J .; Lis, T. J . Chem.
Soc., Dalton Trans. 1995, 105.
(3) Marciniec, B.; Krzyzanowski, P. J . Organomet. Chem. 1995, 493,
261.
(4) Cavanaugh, M. D.; Tetrick, S. M.; Cutler, A. R., manuscript in
preparation.
SiMe2Ph (2a ): IR (CH2Cl2) ν(NO) 1682, ν(CdO) 1563 (br) cm-1 1H
;
NMR (500 MHz, C6D6) δ 7.6-7.0 (Ph), 4.81 (Cp), 0.48, 0.34 (SiMe2);
13C{1H} NMR (C6D6) δ 140-130 (Ph), 92.42 (Cp), 0.52,-0.073 (SiMe2);
31P{1H} NMR (C6D6) δ 19.83; 29Si{1H, DEPT} NMR (C6D6) δ 1.54.
Cp(PPh3)(NO)ReCO2Re(CO)(NO)(PPh3)(OSiMe2Ph) (3a ): IR (THF)
ν(CO) 1972, ν(NO) 1703, 1683, ν(OCO)asym 1287, υ(OCO)asym 1248 cm-1
;
1H NMR δ 8.0-7.0 (Ph), 4.86 (Cp, major), 0.68, 0.41 (SiMe2), 4.79 (Cp,
minor), 0.47, 0.34 (SiMe2); 13C{1H} NMR δ 145-130 (Ph), 93.16 (Cp,
major), 3.25 (SiMe2, 2 degenerate absorptions by HMQC), 92.72 (Cp,
minor), 3.41, 2.85 (SiMe2, verified by HMQC); 31P{1H} NMR (C6D6) δ
21.51, 15.28 (major), 20.41, 17.69 (minor); 29Si{1H, DEPT} NMR δ
-4.01 (major), -5.28 (minor).
(6) Cavanaugh, M. D.; Tetrick, S. M.; Masi, C. J .; Cutler, A. R. J .
Organomet. Chem. 1997, 538, 41.
S0276-7333(97)00831-5 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 04/23/1998

1926 Organometallics, Vol. 17, No. 10, 1998
Communications
Sch em e 2
Sch em e 3
F igu r e 1. Ball and stick view of Cp(PPh3)(NO)ReCO2Re-
(CO)(NO)(PPh3)(SiMe2Ph) (3a ). Selected interatomic dis-
tances (Å) and angles (deg): Re(1)-C(1) ) 2.063(5), C(1)-
O(1) ) 1.306(5), C(1)-O(2) ) 1.302(5), Re(2)-O(1) )
2.153(3), Re(2)-O(2) ) 2.104(3), Re(2)-O(3) ) 1.979(3),
O(3)-Si ) 1.609(4); O(1)-C(1)-O(2) ) 112.0(4), O(1)-Re-
(2)-O(2) ) 61.04(13), O(3)-Re(2)-N(2) ) 178.1(2), C(2)-
Re(2)-P(2) ) 92.9(2), O(2)-Re(2)-P(2) ) 97.60(10), C(2)-
Re(2)-O(1) ) 107.8(2), C(1)-Re(1)-P(1) ) 92.05(13), N(1)-
Re(1)-C(1) ) 93.5(2), P(1)-Re(1)-Re(2)-N(2) ) -12.32(15),
Re(1)-O(1)-O(2) and Re(2)-O(1)-O(2) ) 9.2(1), Re(2)-
O(1)-O(2) and C(1)-O(1)-O(2) ) 6.7(7), Re(1)-O(1)-O(2)
and C(1)-O(1)-O(2) ) 2.5(6).
presence of traces of moisture (vide infra), which is in
contrast with the relative ease of handling Cp*(CO)-
(NO)ReCO2SiR3.6 By silanizing all glassware used, we
procured 10:1 mixtures of 2 (30-48% NMR spectro-
scopic yields) and 3. Compounds 2a and 2b displayed
1
single 31P and 29Si NMR spectral resonances; their H
and 13C NMR spectra revealed single Cp resonances
plus two absorptions each for the diastereotopic methyl
(2a ) or methylene hydrogens (2b).5 The presence of the
silyl ester ligand on these products is consistent with
their medium-intensity IR ν(CdO) absorptions at 1563
cm-1 (CH2Cl2), analogous to the 1593 cm-1 (THF) acyl
absorption for Cp(PPh3)(NO)ReCO2CH3.8
Sch em e 4
Compounds 3a and 3b also were synthesized inde-
pendently by combining Cp(PPh3)(NO)ReCO2K and Cp-
(PPh3)(NO)(CO)ReBF48b in THF, followed by treatment
with PhMe2SiOH or Et3SiOH,6 respectively (Scheme 3).
The resulting mustard yellow solids after recrystalli-
zation from benzene-pentane (1:3) were characterized
as analytically pure Cp(PPh3)(NO)ReCO2Re(CO)(NO)-
(PPh3)(OSiR3) (SiR3 ) SiMe2Ph (3a ), SiEt3 (3b)), in 78-
80% yields. Both 3a and 3b crystallize or precipitate
as a mixture of two diastereomers in 1:1 to 1:2 ratios,
as established by multinuclear NMR spectroscopy. The
diastereomeric ratio of these isolated complexes was
invariant with time and handling; exchange between
1
the diastereomers for 3a was not detected by H NMR
EXSY experiments. IR spectra of these compounds
exhibit medium-intensity ν(OCO)asym and ν(OCO)sym
bands at 1287 and 1248 cm-1 (THF), albeit with an very
small ∆ν ) ν(OCO)asym - ν(OCO)sym value of 39 cm-1 9
.
An X-ray crystallographic structure determination of
3a confirmed the presence of the Re2(µ2-η3-CO2) bridging
carboxylate (Figure 1).10 Re(1) on the pseudooctahedral
Cp(PPh3)(NO)Re moiety11 connects to the carboxylate
carbon, and the carboxylate oxygens chelate Re(2) in a
facial array with the silanolate ligand. Remaining
ligands on Re(2) include PPh3 and CO trans to the
metallocarboxylate O’s and NO trans to the silanolate.
The µ-η1(C(Re1)):η2(O,O′(Re2)) carboxylate ligand on 3
has Re-C ) 2.063(5) Å, which, although relatively short
for a µ2-η3-CO2 bimetallocarboxylate,7,9 is reasonable for
an acyl complex Cp(PPh3)(NO)ReCOR.11b The sym-
(7) Senn, D. R.; Emerson, K.; Larsen, R. D.; Gladysz, J . A. Inorg.
Chem. 1987, 26, 2737.
(8) (a) Merrifield, J . H.; Strouse, C. E.; Gladysz, J . A. Organome-
tallics 1982, 1, 1204. (b) Agbossou, F.; O’Connor, E. J .; Garner, C. M.;
Me´ndez, N. Q.; Ferna´ndez, J . M.; Patton, A. T.; Ramsden, J . A.;
Gladysz, J . A. Inorg. Synth. 1992, 29, 210.
(9) Gibson, D. H. Chem. Rev. 1996, 96, 2063.

Communications
Organometallics, Vol. 17, No. 10, 1998 1927
metrical chelation of the carboxylate oxygens to Re(2)
resembles that observed in Gibson’s Cp*(CO)(NO)Re-
(CO2)Re(PPh3)(CO)3,12 although unsymmetrical chela-
tion was noted for Gladysz’s Cp(PPh3)(NO)ReCO2-
SnPh3.7 Solid-state structural data also have been
reported for several examples of Cp*(CO)(NO)Re-
(CO2)MLx (Lx ) Mo(CO)2Cp, ZrClCp2, WCp2+, SnMe3,
and SnPh3) as well as for Cp(CO)(PPh3)Fe(CO2)Re(CO)3-
[P(OEt3)].9
to 4 followed by “silanolysis” yields the observed 3. In
support of this mechanism, treatment of 2b with either
1.0 equiv of 6 or 0.5 equiv of water gave 93% 3b, as
1
quantified by H NMR spectroscopy.18
Most examples of bimetallic µ-CO2 complexes have
resulted from metalation of either metal-CO2 adducts
or metallocarboxylic acids with the appropriate metal
electrophile, usually under carefully controlled reac-
tion conditions.9 The clean transformation of rhenium
silyl esters 2 to the Re2(µ2-η3-CO2) compounds 3, in
contrast, represents a mechanistically unique example
of degradation of a metallocarboxylic derivative into a
stable bimetallic µ-CO2 complex.19 Studies in progress
address (a) the metallocarboxylate ligand promoted η5-
η1 Cp ring slippage and (b) the intermediacy of the
putative metalloanhydride 5 during the transformation
of 2 to 3.
A plausible pathway for the synthesis of 3 from Cp-
(PPh3)(NO)ReCO2K and Cp(PPh3)(NO)(CO)ReBF4 also
appears in Scheme 3. The key intermediate postulated
in this reaction is 4, which results from an η5-η1 Cp
ring shift13 commensurate with O,O′-chelation of the
rhenium carboxylate group. Examples of Cp ligand slip-
page have been documented for other Re(I) com-
pounds.13b-g The silanol present presumably traps 4,
with or without ionization of the η1-Cp as Cp-,13c and
provides 3 plus C5H6 (which also was detected, 85%).
We have no information at present on the (nonobliga-
Ack n ow led gm en t. Support from the Department
of Energy, Office of Basic Energy Science, and from the
National Science Foundation (Grant CHE-9108591) is
gratefully acknowledged.
tory) intermediacy of the metalloanhydride 5.14
A
similar Fp-based metalloanhydride was postulated by
Cooper and Lee during their studies on the reaction
between Cp(CO)2FeCO2Na and FpCOBF4.14d
The rearrangement of 2 to 3 also could entail tran-
sience of intermediates 4 and 5 (Scheme 4). This re-
arrangement could be initiated by adventitious water,
hydrolyzing 2 to the rhenium acid Cp(PPh3)(NO)Re-
CO2H (6)15 and silanol.16 Subsequent addition of 6 to
2, perhaps via the depicted tetrahedral intermediate 7,17
then provides 5 plus more silanol. Rearrangement of 5
Su p p or tin g In for m a tion Ava ila ble: Text giving spec-
troscopic and characterization data for all compounds and
tables of crystallographic parameters, hydrogen atom param-
eters, thermal parameters, and bond distances and angles and
figures giving additional views of 3a (22 pages). Ordering
information is given on any current masthead page.
OM970831M
(15) Tam, W.; Lin, G.-Y.; Wong, W.-K.; Kiel, W. A.; Wong, V. K.;
Gladysz, J . A. J . Am. Chem. Soc. 1982, 104, 141.
(10) Crystal data for 3a : C51H46N2O6P2Re2Si‚0.5C6H6, Mr ) 1284.38,
triclinic, P1h (No. 2); a ) 9.1251(5) Å, b ) 14.4101(8) Å, c ) 19.8446(9)
Å; R ) 85.392(4), â ) 87.004(4), γ ) 81.382(4)°, V ) 2541.3 Å3; Z ) 2;
Dc ) 1.678 g/cm3; yellow prism (0.06 × 0.16 × 0.48 mm); 9720
reflections (7996 independent); 198 K; Siemens P4 diffractometer (ω-
2θ scan, 3.4 e 2θ e 48°). The full-matrix least-squares refinement was
based on 7996 reflections (I > 2σ(I)) and 604 parameters and converged
with R ) 0.0282 (Rw ) 0.0642). Data were processed using the
SHELXTL version 5.03 package (Siemens). Only the diastereomer
depicted was observed in the crystal examined.
(11) (a) Georgiou, S.; Gladysz, J . A. Tetrahedron 1986, 42, 1109. (b)
Bodner, G. S.; Patton, A. T.; Smith, D. E.; Georgiou, S.; Tam, W.; Wong,
W.-K.; Strouse, C. E.; Gladysz, J . A. Organometallics 1987, 6, 1954.
(c) Blackburn, B. K.; Davies, S. G.; Whittaker, M. In Stereochemistry
of Organometallic and Inorganic Compounds; Bernal, I., Ed.; Elsevi-
er: Amsterdam, 1989; Vol. 3, Chapter 2.
(16) (a) Analogous alcoholysis reactions occur for Cp*(CO)(NO)-
ReCO2SiR3.6 (b) Related transesterification reactions of metallocar-
boxylic acids and esters16d-e are well-known. (c) Treatment of Cp-
(PPh3)(NO)ReCO2H with 4 equiv of methanol in CDCl3 promptly
yielded a 3:2 mixture of Cp(PPh3)(NO)ReCO2CH3 and starting acid,
as determined by NMR spectroscopy. (d) Ford, P. C.; Rokicki, A. Adv.
Organomet. Chem. 1988, 28, 139. (e) Brunner, H. Adv. Organomet.
Chem. 1980, 18, 151.
(17) In the transformation of Cp(PPh3)(NO)ReCO2CH3 to other acyl
complexes Cp(PPh3)(NO)ReCOR, stronger nucleophiles (e.g., RMgCl)
presumably add to a rhenium alkoxycarbonyl ligand via tetrahedral
intermediates. (a) Buhro, W. E.; Wong, A.; Merrifield, J . H.; Lin, G.-
Y.; Constable, A. C.; Gladysz, J . A. Organometallics 1983, 2, 1852.
(18) The frequently discussed mechanism for transesterification of
metallocarboxylic acids and esters LxMCO2R involves metal-assisted
ionization19 to LxMCO+ and then association of the exchanging alcohol,
an overall SN1 process.16d,e We disfavor involvement of this pathway
in the conversion of Cp(PPh3)(NO)ReCO2H and 2 to 3 for two reasons.
(1) Ionization of 2 or Cp(PPh3)(NO)ReCO2H to Cp(PPh3)(NO)ReCO+
(12) Gibson, D. H.; Mehta, J . M.; Ming, Y.; Richardson, J . F.;
Mashuta, M. S. Organometallics 1994, 13, 1070.
(13) (a) O’Connor, J . M.; Casey, C. P. Chem. Rev. 1987, 87, 307. (b)
Casey, C. P.; O’Connor, J . M.; J ones, W. D.; Haller, K. J . Organome-
tallics 1983, 2, 535. (c) Casey, C. P.; O’Connor, J . M.; Haller, K. J . J .
Am. Chem. Soc. 1985, 107, 1241. (d) Young, K. M.; Miller, T. M.;
Wrighton, M. S. J . Am. Chem. Soc. 1990, 112, 1529. (e) Hubbard, J .
L.; Kimball, K. L.; Burns, R. M.; Sum, V. Inorg. Chem. 1992, 31, 1,
4224. (f) Casey, C. P.; Widenhoefer, R. A.; O’Connor, J . M. J .
Organomet. Chem. 1992, 428, 99. (g) Dahlenburg, L.; Hillman, G.;
Markus, E.; Moll, M.; Knoch, F. J . Organomet. Chem. 1996, 525, 115.
(14) Considerably more evidence is available for the transience of
η2(C,C′) metalloanhydride intermediates involving a single metal
center, LxMC(O)OC(O),14a-c as oppposed to those involving a bridging
metalloanhydride ligand:14d (a) Lee, G. R.; Cooper, N. J . Organome-
tallics 1985, 4, 794. (b) Cutler, A. R.; Hanna, P. K.; Vites, J . C. Chem.
Rev. 1988, 88, 1363. (c) Pinkes, J . R.; Masi, C. J .; Chiulli, R.; Steffey,
B. D.; Cutler, A. R. Inorg. Chem. 1997, 36, 70. (d) Lee, G. R.; Cooper,
N. J . Organometallics 1985, 4, 1467.
and OSiR3 or OH-, respectively, was not detected in dry THF, CH2-
-
Cl2, or dimethylformamide. (2) No reaction took place between Cp-
(PPh3)(NO)ReCO2H and Cp(PPh3)(NO)ReCO+ in the presence of 1
equiv of lutidine (which does not independently react with Cp(PPh3)-
(NO)ReCO+). These observations were the result of IR spectral
monitoring of reactions involving 1 equiv of potential base for at least
2 h.
(19) (a) Grice, N.; Kao, S. C.; Pettit, R. J . Am. Chem. Soc. 1979,
101, 1627. (b) Liu, L.-K.; Eke, U. B.; Mesubi, M. A. Organometallics
1995, 14, 3958.
(20) In a formally related degradation, Cp(NO)(CO)ReC(dO)OCH2-
CH2Mo(CO)3Cp extrudes CO plus ethylene and leaves the µ-η1(C(Re)):
η2(O,O′(Mo)) bimetallocarboxylate Cp(NO)(CO)ReCO2Mo(CO)2Cp: Gib-
son, D. H.; Franco, J . O.; Mehta, J . M.; Harris, M. T.; Ding, Y.;
Mashuta, M. S.; Richardson, J . F. Organometallics 1995, 14, 5073.