Protonation of Metal-Metal Bonds in Cp2Ru2(CO)3(PR3) and Cp2Mo2(CO)4(PR3)2

Article abstract of DOI:10.1021/ic971516v

Despite the much higher basicity expected for the Ru bearing the PR₃ ligand in Cp(PR₃)Ru(μ-CO)₂Ru(CO)Cp, NMR studies demonstrate that protonation of this complex with CF₃SO₃H occurs at the Ru-Ru bond,

Full text of DOI:10.1021/ic971516v

Inorg. Chem. 1998, 37, 2975-2983
2975
†
Protonation of Metal-Metal Bonds in Cp2Ru2(CO)3(PR3) and Cp2Mo2(CO)4(PR3)2
Chip Nataro and Robert J. Angelici*
Department of Chemistry, Iowa State University, Ames, Iowa 50011
ReceiVed December 3, 1997
Despite the much higher basicity expected for the Ru bearing the PR3 ligand in Cp(PR3)Ru(µ-CO)2Ru(CO)Cp,
NMR studies demonstrate that protonation of this complex with CF3SO3H occurs at the Ru-Ru bond, rather than
at the more basic Ru. As determined by calorimetric titration at 25.0 °C in 1,2-dichloroethane solvent, the enthalpy
of protonation (∆HMHM) of the Ru-Ru bond is higher in Cp2Ru2(CO)3(PMe3) (-30.0(4) kcal/mol) than in its
carbonyl analogue Cp2Ru2(CO)4 (-18.4(1) kcal/mol). Enthalpies (∆HMHM) for protonation of the Mo-Mo bond
in the dinuclear Mo complexes Cp2Mo2(CO)4(PR3)2 show that the PMe3 complex (-27.4(2) kcal/mol) is
dramatically more basic than its PMe2Ph analogue (-18.9(5) kcal/mol). Considering the ∆HMHM values as measures
of the basicities of the complexes, these results show that the basicities of metal-metal bonds are highly sensitive
to the nature of their associated ligands. In addition, evidence indicates that Ru-Ru bonds are more basic than
Ru in comparable mononuclear complexes. The structures, as determined by X-ray crystallographic studies, of
-
Cp2Ru2(CO)3(PMe3) and its protonated derivative Cp2Ru2(CO)3(PMe3)(µ-H)+CF3SO3 are also discussed.
Introduction
each Cp′2Ru2(CO)4 complex is given in parentheses): (C5Me4-
CF3)2 (12.0, b) < (indenyl)2 (14.1, b) < fulvalene (16.1, nb) <
The tendency of a transition metal complex to undergo acid
protonation at the metal is defined as its basicity. Quantitative
measures of the basicity of a metal complex are pKa and ∆HHM
Cp2(CH2)2 (16.9, b) < Cp2 (18.4, 50% nb) < (C5Me5)2 (19.2,
b) < Cp2CH2 (21.0, 90% nb). An analysis of these data
suggested that two factors were primarily responsible for the
trend. The first is the donor ability of the Cp′2 ligands; the
more strongly donating the Cp′2 ligands, the more basic the Ru-
Ru bond. The second factor is the energy (∆Hb) required to
convert (eq 2) a CO-bridged isomer to its nonbridged isomer.
1
.
Most basicities have been reported2-9 for mononuclear com-
plexes although there are a few quantitative studies of di- or
polynuclear compounds in which protonation occurs at a metal-
metal bond to give a bridging hydride product. Recently, we
reported results of a titration calorimetry study10 of the heats
of protonation (∆HMHM) of a series of dinuclear Cp′2Ru2(CO)4
complexes (eq 1). The -∆HMHM values, measured in 1,2-
For bridged Cp′2Ru2(CO)4 complexes, the overall ∆HMHM value
may be considered as the sum of ∆Hb and ∆Ha. For two
complexes that have Cp′2 ligands with similar donor abilities,
∆Ha will be similar, but if one of the complexes is CO-bridged,
an endothermic ∆Hb term will cause its -∆HMHM to be less
positive than that of the other Cp′2Ru2(CO)4 complex with no
bridging CO groups. Thus, bridging CO groups reduce the
basicity of the Ru-Ru bond as compared with those of
analogous complexes that are nonbridged.
In the present study, we sought to determine the basicity
(-∆HMHM) of the phosphine-substituted CO-bridged complexes
Cp2Ru2(CO)3(PR3) by the reaction in eq 3. These complexes
were of particular interest because the Ru atom bonded to the
PR3 ligand is expected to be much more basic than the Ru
coordinated to a terminal CO.1-9 The magnitude of this
expected difference is suggested by the -∆HHM values for
Cp*Ir(CO)(PMe3) (38.0(2) kcal/mol) and Cp*Ir(CO)(PPh3)
(37.1(2) kcal/mol) as compared with that of Cp*Ir(CO)2 (21.4-
(1) kcal/mol).11 If the PR3-substituted Ru in Cp2Ru2(CO)3(PR3)
were 15.7-16.6 kcal/mol more basic than the CO-substituted
dichloroethane(DCE) solvent, increased with variations in the
Cp′2 ligands in the following order (-∆HMHM values given in
kcal/mol; the CO-bridged (b) or nonbridged (nb) structure of
† Dedicated to Professor Warren R. Roper on the occasion of his 60th
birthday.
(1) Angelici, R. J. Acc. Chem. Res. 1995, 28, 51.
(2) Pearson, R. G. Chem. ReV. 1985, 85, 41.
(3) Martinho Simo˜es, J. A.; Beauchamp, J. L. Chem. ReV. 1990, 90, 629.
(4) Kristja´nsdo´ttir, S. S.; Norton, J. R. In Transition Metal Hydrides:
Recent AdVances in Theory and Experiment; Dedieu, A., Ed.; VCH:
New York, 1991; Chapter 10.
(5) Bullock, R. M. Comments Inorg. Chem. 1991, 12, 1.
(6) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles
and Applications of Organotransition Metal Chemistry; University
Science Books: Mill Valley, CA, 1987.
(7) Jessop, P. G.; Morris, R. H. Coord. Chem. ReV. 1992, 121, 155.
(8) Heinekey, D. M.; Oldham, W. J., Jr. Chem. ReV. 1993, 93, 913.
(9) Kramarz, K.; Norton, J. R. Prog. Inorg. Chem. 1994, 42, 1.
(10) Nataro, C.; Thomas, L. M.; Angelici, R. J. Inorg. Chem. 1997, 36,
6000.
S0020-1669(97)01516-4 CCC: $15.00 © 1998 American Chemical Society
Published on Web 06/15/1998

2976 Inorganic Chemistry, Vol. 37, No. 12, 1998
Nataro and Angelici
(-∆HMHM) of Cp2Mo2(CO)4(PR3)2 (PR3 ) PMe3, PMe2Ph) are
compared with those of related dinuclear complexes.
Experimental Section
General Procedures. All preparative reactions, chromatography,
and manipulations were carried out under an atmosphere of nitrogen
or argon using standard Schlenk techniques. Solvents were purified
under nitrogen using standard methods12 as described below. Hexanes,
heptanes, toluene, and methylene chloride were refluxed over CaH2
and then distilled. Diglyme was refluxed over CaH2 and vacuum-
distilled. Diethyl ether was distilled from sodium benzophenone. CD2-
Cl2 was stored over molecular sieves under nitrogen. 1,2-Dichloro-
ethane (DCE) was purified by washing successively with concentrated
sulfuric acid, distilled deionized water, 5% NaOH, and again with water.
The solvent was then predried over anhydrous MgSO4 and stored in
amber bottles over molecular sieves (4 Å). The DCE was distilled
from P4O10 under argon immediately before use. Triflic acid (CF3-
SO3H) was purchased from 3M Co. and purified by fractional
distillation under argon prior to use. Neutral Al2O3 (Brockmann,
activity I) used for chromatography was deoxygenated at room
temperature under vacuum for 12 h, deactivated with N2-saturated water
(3% w/w for ruthenium compounds and 5% w/w for molybdenum
compounds), and stored under N2.
Ru, one would expect protonation to occur at the PR3-substituted
Ru as in A. On the other hand, if the electron density provided
The compounds Cp2Ru2(CO)4,13 Cp2Ru2(CO)2(COC2Ph2),14,15 Cp2-
Mo2(CO)6,16 and Cp2Mo2(CO)416 were prepared by literature methods.
Diphenylacetylene was purchased from Eastman-Kodak, and Ru3(CO)12
was purchased from Strem. Dicyclopentadiene was purchased from
Aldrich and cracked over iron filings prior to use.13 The phosphines
PPh3, PMePh2, PMe2Ph, and PMe3 (1.0 M in toluene) were purchased
from Aldrich. The 13CO (13C, 99%) was purchased from Cambridge
Isotopes. The 1H NMR spectra were obtained at ambient temperature
unless indicated otherwise on samples dissolved in CD2Cl2 on a Nicolet
NT 300-MHz or a Bruker AC 200-MHz spectrometer with TMS (δ )
0.00 ppm) as the internal reference. 31P{H} NMR spectra were obtained
in CD2Cl2 on a Bruker AC 200-MHz spectrometer with H3PO4 (δ )
0.00 ppm) as the reference. The 13C NMR spectra were obtained at
room temperature in CD2Cl2 on a Bruker AC 200-MHz spectrometer
with the solvent (δ ) 53.8 ppm) as the internal reference. The 13C
NMR spectra at 100.6 MHz were obtained on a Bruker DRX 400-
MHz spectrometer. Solution infrared spectra were recorded on a
Nicolet 710 FT-IR spectrometer using sodium chloride cells with 0.1-
mm spacers. Electron ionization mass spectra (EIMS) were run on a
Finnigan 4000 spectrometer. Elemental microanalyses were performed
on a Perkin-Elmer 2400 Series II CHNS/O analyzer.
by the phosphine were distributed into the Ru-Ru bond, the
proton might bridge the two Ru atoms as in B. NMR and X-ray
diffraction studies provide evidence for the location of the
-
-
hydrogen in 1H+CF3SO3 and 4H+CF3SO3
. In addition,
∆HMHM for Cp2Ru2(CO)3(PMe3) has been measured and com-
pared with those for Cp2Ru2(CO)4 and related complexes.
Protonation reactions (eq 4) of four Cp2Mo2(CO)4(PR3)2
complexes have also been examined. NMR studies indicate
Cp2Ru2(CO)3(PR3). In a typical reaction, approximately 0.1 g (0.2
mmol) of Cp2Ru2(CO)2(COC2Ph2) and 1 equiv of the desired phosphine
were heated to reflux in 20 mL of toluene. The solution changed from
orange-red to bright yellow. Monitoring by IR spectroscopy indicated
that the reaction was complete within 30 min. Upon cooling and
vacuum removal of solvent, the compounds were chromatographed on
an alumina column (1.5 × 30 cm); the yellow product band was eluted
with a 3:2 (v/v) mixture of CH2Cl2 and hexanes. Solvent was removed,
and the compounds were crystallized at -20 °C from ether. Isolated
yields of the complexes were greater than 90% in all cases. IR data
for compounds 1-4 and 5-8 are presented in Tables 1 and 2,
respectively. 1H NMR and IR data for compound 4 are essentially the
same as those reported previously for this compound.17
Cp2Ru2(CO)3(PMe3) (1). 1H NMR (CD2Cl2): δ 5.23 (s, 5H, Cp),
5.00 (s, 5H, Cp), 1.23 (d 2JP-H 10.0 Hz, 9H, Me). 31P NMR (CD2Cl2):
δ 9.95 (s). IR (toluene): ν(CO) (cm-1) 1929 (m), 1742 (s). Anal.
(12) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of
Laboratory Chemicals, 2nd ed.; Pergamon: New York, 1980.
(13) Doherty, N. M.; Knox, S. A. R.; Morris, M. J. Inorg. Synth. 1990, 28,
189.
(14) Davies, D. L.; Dyke, A. F.; Knox, S. A. R.; Morris, M. J. J. Organomet.
Chem. 1981, 215, C30.
(15) Doherty, N. M.; Knox, S. A. R. Inorg. Synth. 1989, 25, 179.
(16) Curtis, M. D.; Hay, M. S. Inorg. Synth. 1990, 28, 150.
(17) Davies, D. L.; Knox, S. A. R.; Mead, K. A.; Morris, M. J.; Woodward,
P. J. Chem. Soc., Dalton Trans. 1984, 2293.
that the proton bridges the Mo-Mo bond in the product, as
expected for these symmetric structures. Measured basicities
(11) Sowa, J. R., Jr.; Zanotti, V.; Facchin, G.; Angelici, R. J. J. Am. Chem.
Soc. 1991, 113, 9185.

Protonation of Metal-Metal Bonds
Inorganic Chemistry, Vol. 37, No. 12, 1998 2977
Table 1. IR Data for Cp2Ru2(CO)3(PR3) and
Cp2Ru2(CO)3(PR3)(µ-H)+ in CH2Cl2 Solvent
(s). MS: m/e 446 (M+), 418 (M+ - CO), 390 (M+ - 2CO), 361 (M+
- 2CO - 13CO).
Cp2Ru2(CO)(13CO)(COC2Ph2) (6). In a quartz photolysis vessel,
121.6 mg (0.2042 mmol) of 5 and 152.3 mg (0.8545 mmol) of
diphenylacetylene were dissolved in 10 mL of toluene. The solution
was irradiated with 366 nm light under a slow N2 purge and monitored
by IR spectroscopy. The reaction was complete after 40 h of photolysis.
Solvent was removed, and the solid was chromatographed on alumina.
The red-orange product band was eluted with a 20:1 (v/v) mixture of
CH2Cl2/acetone. Solvent was removed under vacuum, and the product
was used without further purification. Yield: 55.9 mg (34%).
ν(CO), cm-1
terminal
complex
bridging
1728 (s)
1a
1929 (s)
2043 (s)
1932 (s)
2045 (s)
1937 (s)
2045 (s)
1947 (s)
2046 (s)
1H+ a
2b
1995 (s)
1996 (s)
1998 (s)
2000 (s)
1964 (m)
1965 (m)
1966 (m)
1969 (m)
1727 (s)
1727 (s)
1725 (s)
2H+ b
3c
3H+ c
4d
Cp2Ru2(CO)2(13CO)(PMe3) (7). With 6 as the starting material, 7
4H+ d
was prepared using the same methods as in the preparation of 1. 1H
2
a PR3 ) PMe3. b PR3 ) PMe2Ph. c PR3 ) PMePh2. d PR3 ) PPh3.
NMR (CD2Cl2): δ 5.24 (s, 5H, Cp), 5.01 (s, 5H, Cp), 1.23 (d, JP-H
10.0 Hz, 9H, Me). 13C NMR (CD2Cl2): δ 89.1 (s), 88.7 (s), 19.8 (d,
2
Table 2. IR Data for Cp2Ru2(CO)4, Cp2Ru2(CO)2(COC2Ph2),
Cp2Ru2(CO)3(PMe3), Cp2Ru2(CO)3(PPh3), and Their 13CO-Labeled
Analogues in CH2Cl2 Solvent
1JP-C 31.6 Hz). 13C NMR (CD2Cl2, -78 °C): δ 246.3 (d, JP-C 11.0
1
Hz), 205.2 (s), 89.1 (s), 88.7 (s), 19.8 (d, JP-C 31.6 Hz).
Cp2Ru2(CO)2(13CO)(PPh3) (8). With 6 as the starting material, 8
was prepared using the same methods as in the preparation of 4. 1H
NMR (CD2Cl2): δ 7.40 (m, 15H, Ph), 4.94 (s, 5H, Cp), 4.71 (s, 5H,
Cp). 13C NMR (CD2Cl2): δ 134.3 (d, JP-C 45.2 Hz), 132.8 (d, JP-C
10.0 Hz), 128.7 (d, JP-C 2.5 Hz), 126.8 (d, JP-C 10.0 Hz), 89.0 (s),
ν(CO), cm-1
complex
Cp2Ru2(CO)4
2003 1966 1934
1999 1956 1927 1897 1772 1742
1771
Cp2Ru2(CO)3(13CO), 5
calcd (13CO)a
1958 1921 1891
1803
1731
2
88.0 (s). 13C NMR (CD2Cl2, -78 °C): δ 245.6 (d, JP-C 10.0 Hz),
Cp2Ru2(CO)2(COC2Ph2)
1980
1733
200.7 (s), 134.3 (d, JP-C 45.2 Hz), 132.8 (d, JP-C 10.0 Hz), 128.7 (d,
JP-C 2.5 Hz), 126.8 (d, JP-C 10.0 Hz), 89.0 (s), 88.0 (s).
Cp2Ru2(CO)(13CO)(COC2Ph2), 6 1979 1934 1802 1772 1730 1700
calcd (13CO)a
1935
1762
1694
CpRu(13CO)(PPh3)H. The 13CO enrichment (45-65%) of Ru3-
(CO)12 was performed as described in the literature.18 The Ru3(13CO)12
was used to prepare CpRu(13CO)(PPh3)H by a modification of a
previously reported procedure.19 Ru3(13CO)12 (0.0443 g, 0.0687 mmol),
cyclopentadiene (0.45 mL), and heptanes (67 mL) were heated to reflux
for 1 h, during which the solution changed color from orange-red to
pale yellow. Then, PPh3 (0.0544 g, 0.207 mmol) was added and the
solution was refluxed an additional 20 min, during which the color
changed to bright yellow. Solvent was removed, and the residue was
recrystallized from a 10:1 (v/v) mixture of hexanes/CH2Cl2 to give
0.0075 g (72%) of the product. IR data for Ru3(13CO)12 and CpRu-
(13CO)(PPh3)H are presented in Table 2. 1H NMR (CD2Cl2) for
CpRu(13CO)(PPh3)H: δ 7.46 (m, 15H, Ph), 4.93 (s, 5H, Cp), -11.67
Cp2Ru2(CO)3(PMe3), 1
Cp2Ru2(CO)2(13CO)(PMe3), 7
calcd (13CO)a
1929
1929 1884 1729 1701
1886 1689
1728
Cp2Ru2(CO)3(PPh3), 4
Cp2Ru2(CO)2(13CO)(PPh3), 8
calcd (13CO)a
1947
1725
1947 1925 1725 1699
1903
1686
Ru3(CO)12
2060 2028 2010
2048 2021 1982 1938
2014 1982 1965
Ru3(13CO)12
calcd (13CO)a
CpRu(CO)(PPh3)Hb
CpRu(13CO)(PPh3)H
calcd (13CO)a
1937
1920 1876
1877
2
(d, JP-H 32.0 Hz, 1H, Ru-H). 31P NMR (CD2Cl2): δ 69.8 (s). 13C
a See text. b In hexanes, see ref 19.
2
2
NMR (CD2Cl2 at 100.6 MHz): δ 206.6 (dd, JP-C 23.1 Hz, JH-C
9.1 Hz). 13C{1H} NMR (CD2Cl2 at 400 MHz): δ 206.6 (d, JP-C
2
Calcd for C16H19O3PRu2: C, 39.03; H, 3.89. Found: C, 39.13; H, 4.03.
Orange crystals of 1 were obtained by cooling an ether solution of 1
to -20 °C for 3 days.
Cp2Ru2(CO)3(PMe2Ph) (2). 1H NMR (CD2Cl2): δ 7.44 (m, 5H,
23.1 Hz), 133.7 (d, JP-C 11.1 Hz), 129.9 (s), 128.3 (d, JP-C 9.0 Hz),
84.4 (s).
Cp2Mo2(CO)4(PR3)2. The synthesis of these compounds follows
the method developed by Riera20-22 for Cp2Mo2(CO)4(dppm). Ap-
proximately 0.2 g (0.4 mmol) of Cp2Mo2(CO)6 and 5 mL of diglyme
were used to prepare Cp2Mo2(CO)4 in situ according to the literature
procedure.16 In a separate flask, 2 equiv of the desired phosphine were
dissolved in 5 mL of CH2Cl2. The phosphine solution was added to
the solution of Cp2Mo2(CO)4, and the reaction mixture was allowed to
stir at room temperature for 1 h. The resulting precipitate was filtered
from the reaction solution, and the collected product was washed with
3 × 5 mL of hexanes. Upon drying, no further purification of the
compounds was necessary. The compounds all have a very deep, brick-
red color. Because halocarbon solutions of these compounds decom-
pose rapidly upon exposure to light, care was taken to limit the exposure
of all solutions to light. IR data for compounds 9-12 are presented in
Table 3.
2
Ph), 5.25 (s, 5H, Cp), 4.75 (s, 5H, Cp), 1.40 (d, JP-H 10.0 Hz, 6H,
Me). 31P NMR (CD2Cl2): δ 24.3 (s). IR (toluene): ν(CO) (cm-1
)
1933 (s), 1739 (s).
Cp2Ru2(CO)3(PMePh2) (3). 1H NMR (CD2Cl2): δ 7.41 (m, 10H,
2
Ph), 5.20 (s, 5H, Cp), 4.80 (s, 5H, Cp), 1.64 (d, JP-H 8.0 Hz, 3H,
Me). 31P NMR (CD2Cl2): δ 39.6 (s). IR (toluene): ν(CO) (cm-1
)
1936 (m), 1739 (s).
Cp2Ru2(CO)3(PPh3) (4). 1H NMR (CD2Cl2): δ 7.37 (m, 15H, Ph),
4.94 (s, 5H, Cp), 4.80 (s, 5H, Cp). 31P (CD2Cl2): δ 48.6 (s). IR
(toluene): ν(CO) (cm-1) 1939 (m), 1737 (s).
Cp2Ru2(CO)3(13CO) (5). Cp2Ru2(CO)2(COC2Ph2) (0.3134 g, 0.5271
mmol) was placed in a Fischer-Porter bottle and dissolved in 20 mL
of toluene. After two freeze-pump-thaw cycles, the solution was
cooled to -100 °C and degassed under vacuum. Gaseous 13CO was
then introduced into the reaction vessel, which was allowed to warm
to room temperature. The reaction mixture was heated to 90 °C for
20 min, during which it changed from red-orange to bright yellow.
After cooling, the solution was transferred to a Schlenk flask and solvent
was removed under vacuum. The residue was chromatographed on
alumina, and the yellow product band was eluted with 1:1 (v/v) hexanes/
CH2Cl2. Solvent was removed, and the product was recrystallized by
layering a CH2Cl2 solution of the product with a 10-fold excess of ether
and allowing the solvents to slowly mix at room temperature. Yield:
0.218 g (93%). 1H NMR (CD2Cl2): δ 5.30 (s, 5H, Cp). 13C NMR
(CD2Cl2): δ 217.7 (s), 89.8 (s). 13C NMR (CD2Cl2, -78 °C): δ 89.8
Cp2Mo2(CO)4(PMe3)2 (9). From 0.222 g (0.453 mmol) of Cp2Mo2-
(CO)6 in the above synthesis was collected 0.212 g (0.402 mmol) of 9
2
(80% yield). 1H NMR (CD2Cl2): δ 4.87 (s, 10H, Cp), 1.57 (d, JP-H
(18) Aime, S.; Gambino, O.; Milone, L.; Sappa, E. Inorg. Chim. Acta 1975,
15, 53.
(19) Humphries, A. P.; Knox, S. A. R. J. Chem. Soc., Dalton Trans. 1975,
1710.
(20) Riera, V.; Ruiz, M. A.; Villafan˜e, F. Organometallics 1992, 11, 2854.
(21) Riera, V.; Ruiz, M. A.; Villafan˜e, F.; Bois, C.; Jeannin, Y. J.
Organomet. Chem. 1990, 382, 407.
(22) Riera, V.; Ruiz, M. A.; Villafan˜e, F.; Jeannin, Y.; Bois, C. J.
Organomet. Chem. 1988, 345, C4.

2978 Inorganic Chemistry, Vol. 37, No. 12, 1998
Nataro and Angelici
Table 3. IR Data for Cp2Mo2(CO)4(PR3)2 and
Cp2Mo2(CO)4(PR3)2(µ-H)+ in CH2Cl2 Solvent
[Cp2Ru2(CO)3(PMe2Ph)(µ-H)]+CF3SO3- (2H+CF3SO3-). 1H NMR
(CD2Cl2): δ 7.57 (m, 5H, Ph), 5.51 (s, 5H, Cp), 5.19 (s, 5H, Cp), 2.1
2
2
(d, JP-H 10.0 Hz, 6H, Me), -18.57 (d, JP-H 20.0 Hz, 1H, µ-H). 31P
ν(CO), cm-1
complex
NMR (CD2Cl2): δ 28.4 (s).
[Cp2Ru2(CO)3(PMePh2)(µ-H)]+CF3SO3- (3H+CF3SO3-). 1H NMR
(CD2Cl2): δ 7.37 (m, 10H, Ph), 5.40 (s, 5H, Cp), 5.24 (s, 5H, Cp),
2.30 (d, 2JP-H 10.0 Hz, 3H, Me), -18.68 (d, 2JP-H 22.0 Hz, 1H, µ-H).
31P NMR (CD2Cl2): δ 42.9 (s).
9a
1839 (sh)
1979 (m)
1842 (sh)
1980 (m)
1844 (sh)
1982 (m)
1851 (sh)
1818 (s)
1954 (m)
1820 (s)
1966 (m)
1826 (s)
1966 (m)
1832 (s)
9H+ a
10b
1894 (s)
1896 (s)
1898 (s)
10H+ b
11c
[Cp2Ru2(CO)3(PPh3)(µ-H)]+CF3SO3 (4H+CF3SO3-). 1H NMR
-
11H+ c
12d
(CD2Cl2): δ 7.59 (m, 15H, Ph), 5.64 (s, 5H, Cp), 5.52 (s, 5H, Cp),
2
-18.75 (d, JP-H 21.6 Hz, 1H, µ-H). 31P NMR (CD2Cl2): δ 51.3 (s).
[Ru2Cp2(CO)3(13CO)(µ-H)]+CF3SO3 (5H+CF3SO3-). 1H NMR
-
a PR3 ) PMe3. b PR3 ) PMe2Ph. c PR3 ) PMePh2. d PR3 ) PPh3.
2
(CD2Cl2): δ 5.60 (s, 10H, Cp), -19.12 (d, JC-H 4.0 Hz, 1H, µ-H).
Table 4. IR Data for Cp2Ru2(CO)4(µ-H)+,
13C{1H} NMR (CD2Cl2): δ 195.4 (s), 87.6 (s).
Cp2Ru2(CO)3(PMe3)(µ-H)+, Cp2Ru2(CO)3(PPh3)(µ-H)+, and Their
13CO-Labeled Analogues in CH2Cl2 Solvent
[Cp2Ru2(CO)2(13CO)(PMe3)(µ-H)]+CF3SO3- (7H+CF3SO3-). 1H
2
NMR (CD2Cl2): δ 5.61 (s, 5H, Cp), 5.33 (s, 5H, Cp), 1.79 (d, JP-H
10.0 Hz, 9H, Me), -18.41 (dd, 2JP-H 20.0 Hz 2JC-H 4.0 Hz, 1H, µ-H).
ν(CO), cm-1
complex
2
13C{1H} NMR (CD2Cl2 at 50.33 MHz): δ 200.0 (d, JP-C 19.1 Hz),
Cp2Ru2(CO)4(µ-H)+
Cp2Ru2(CO)3(13CO)(µ-H)+, 5H+
calcd (13CO)a
2073 2049 2017
2064 2036 2011 1981 1960
2026 2003 1972
2
197.3 (s), 196.6 (s), 86.7 (s), 85.5 (s), 21.8 (d, JP-C 37.2 Hz). 13C
2
2
NMR (CD2Cl2 at 100.6 MHz): δ 200.6 (dd, JP-C 19.3 Hz, JH-C 3.1
3
2
3
Hz), 197.7 (dd, JP-C 8.2 Hz, JH-C 3.5 Hz), 196.9 (dd, JP-C 8.1 Hz,
Cp2Ru2(CO)3(PMe3)(µ-H)+, 1H+
2043 1995 1964
2JH-C 3.5 Hz). 13C{1H} NMR (CD2Cl2 at 400 MHz): δ 200.6 (d, 2JP-C
Cp2Ru2(CO)2(13CO)(PMe3)(µ-H)+, 2043 1996 1966 1921
3
3
19.3 Hz), 197.7 (d, JP-C 8.2 Hz), 196.9 (d, JP-C 8.1 Hz), 86.7 (s),
7H+
2
85.5 (s), 21.8 (d, JP-C 37.2 Hz).
calcd (13CO)a
1997 1950 1920
[Cp2Ru2(CO)2(13CO)(PPh3)(µ-H)]+CF3SO3- (8H+CF3SO3-). 1H
NMR (CD2Cl2): δ 7.37 (m, 15H, Ph), 5.35 (s, 5H, Cp), 5.15 (s, 5H,
Cp2Ru2(CO)3(PPh3)(µ-H)+, 4H+
2046 2000 1969
Cp2Ru2(CO)2(13CO)(PPh3)(µ-H)+, 2045 2000 1972 1925
Cp), -18.75 (dd, JP-H 20.0 Hz, JC-H 4.0 Hz, 1H, µ-H). 13C{1H}
2
2
8H+
2
NMR (CD2Cl2 at 50.33 MHz): δ 200.7 (d, JP-C 17.6 Hz), 196.6 (s),
calcd (13CO)a
a See text.
2000 1955 1925
196.1 (s), 134.3 (d, JP-C 50.2 Hz), 132.8 (d, JP-C 10.0 Hz), 131.0 (d,
JP-C 2.5 Hz), 128.7 (d, JP-C 10.0 Hz), 86.9 (s), 85.8 (s). 13C NMR
2
2
(CD2Cl2 at 100.6 MHz): δ 201.1 (dd, JP-C 18.4 Hz, JH-C 2.9 Hz),
197.0 (dd, 3JP-C 6.9 Hz, 2JH-C 3.8 Hz), 196.4 (dd, 3JP-C 6.7 Hz, 2JH-C
3.1 Hz). 13C{1H} NMR (CD2Cl2 at 400 MHz): δ 201.1 (d, 2JP-C 18.4
Hz), 197.0 (d, 3JP-C 6.9 Hz), δ 196.4 (d, 3JP-C 6.7 Hz), 134.3 (d, JP-C
50.2 Hz), 132.8 (d, JP-C 10.0 Hz), 131.0 (d, JP-C 2.5 Hz), 128.7 (d,
JP-C 10.0 Hz), 86.9 (s), 85.8 (s).
8.9 Hz, 18H, Me). 31P NMR (CD2Cl2): δ 32.9 (s). Anal. Calcd for
C20H28Mo2O4P2: C, 40.97; H, 4.81. Found: C, 40.63; H, 4.80.
Cp2Mo2(CO)4(PMe2Ph)2 (10). From 0.223 g (0.454 mmol) of Cp2-
Mo2(CO)6 in the above preparation was obtained 0.289 g (0.409 mmol)
of 10 (90% yield). 1H NMR (CD2Cl2): δ 7.58 (m, 10H, Ph), 4.68 (d,
[Cp2Mo2(CO)4(PMe3)2(µ-H)]+CF3SO3- (9H+CF3SO3-). 1H NMR
2
3JP-H 1.8 Hz, 10H, Cp), 1.88 (d, JP-H 8.5 Hz, 12H, Me). 31P NMR
(CD2Cl2): δ 5.27 (s, 10H, Cp), 1.71 (d, 2JP-H 9.8 Hz, 18H, Me), -19.75
(CD2Cl2): δ 42.6 (s).
2
(t, JP-H 11.9 Hz, 1H, µ-H). 31P NMR (CD2Cl2): δ 21.7 (s).
Cp2Mo2(CO)4(PMePh2)2 (11). Using 0.223 g (0.454 mmol) of Cp2-
Mo2(CO)6 in the above procedure resulted in the formation of 0.289 g
(0.345 mmol) of 11 (76% yield). 1H NMR (CD2Cl2): δ 7.51 (m, 20H,
-
[Cp2Mo2(CO)4(PMe2Ph)2(µ-H)]+CF3SO3 (10H+CF3SO3-). 1H
NMR (CD2Cl2): δ 7.60 (m, 10 H, Ph), 5.21 (s, 10H, Cp), 2.04 (d,
2JP-H 9.8 Hz, 12H, Me), -20.23 (t, 2JP-H 9.7 Hz, 1H, µ-H). 31P NMR
(CD2Cl2): δ 27.9 (s).
3
2
Ph), 4.64 (d, JP-H 1.5 Hz, 10H, Cp), 2.17 (d, JP-H 8.1 Hz, 6H, Me).
31P NMR (CD2Cl2): δ 61.2 (s).
[Cp2Mo2(CO)4(PMePh2)2(µ-H)]+CF3SO3 (11H+CF3SO3-). 1H
-
Cp2Mo2(CO)4(PPh3)2 (12). From 0.239 g (0.488 mmol) of Cp2-
Mo2(CO)6 was obtained 0.400 g (0.449 mmol) of 12 (92% yield). H
NMR (CD2Cl2): δ 7.52 (m, 20H, Ph), 5.09 (s, 10H, Cp), 2.28 (d, 2JP-H
9.9 Hz, 6H, Me), -20.86 (t, 2JP-H 9.1 Hz, 1H, µ-H). 31P NMR (CD2-
Cl2): δ 45.4 (s).
1
3
NMR (CD2Cl2): δ 7.48 (m, 30H, Ph), 4.56 (d, JP-H 1.6 Hz, 10H,
Cp). 31P NMR (CD2Cl2): δ 79.1 (s).
Calorimetric Studies. Heats of protonation (∆HMHM) of the Cp2-
Ru2(CO)3(PR3) and Cp2Mo2(CO)4(PR3)2 complexes were measured
using a Tronac model 458 isoperibol titration calorimeter as originally
described23 and then modified.24 A typical calorimetric run consisted
of three sections:25 initial heat capacity calibration, titration, and final
heat capacity calibration. Each section was preceded by a baseline
acquisition period. During the titration, 1.2 mL of a 0.1 M CF3SO3H
solution (standardized to a precision of (0.0002 M) in DCE was added
at a rate of 0.3962 mL/min to 50 mL of a 2.6 mM solution of the
complex (5-10% excess) in DCE at 25.0 °C. Infrared spectra of the
titrated solutions exhibited ν(CO) bands for the Cp2Ru2(CO)3(PR3)(µ-
H)+ or Cp2Mo2(CO)4(PR3)2(µ-H)+ products, as well as small bands for
the excess starting complexes. Two different standardized acid
solutions were used for determining the ∆HMHM of each complex. The
reported values are an average of at least four titrations and as many
as five. The reaction enthalpies were corrected for the heat of dilution
(∆Hdil) of the acid in DCE (-0.2 kcal/mol).24 The reported error in
∆HMHM is the average deviation from the mean of all of the
Protonation Reactions. Compounds 1-5 and 7-12 were proto-
nated for characterization of either the [Cp2Ru2(CO)3(L)(µ-H)]+CF3-
-
-
SO3 (L ) CO, PR3) or the [Cp2Mo2(CO)4(PR3)2(µ-H)]+CF3SO3
products by dissolving approximately 10 mg of the complex in 0.50
mL of either CD2Cl2 (for NMR) or CH2Cl2 (for IR) in an NMR tube
under nitrogen. To the solution was added 1 equiv of CF3SO3H with
a gastight microliter syringe through the rubber septum. Solutions of
the ruthenium compounds turned from yellow to yellow-orange. Yields
of the protonated ruthenium compounds were determined to be
quantitative by IR and NMR spectroscopy of the solutions. The
molybdenum complex solutions turned from a deep red to dark orange
with the exception of 12, which produced a precipitate, and an IR
spectrum of the solution showed that 12H+CF3SO3 was not formed.
-
The molybdenum complexes 9-11 also protonated quantitatively. NMR
(1H and 31P) spectral data for the protonated dinuclear complexes are
given below. IR data for compounds 1H+-4H+ are presented in Table
1, for compounds 5H+, 7H+, and 8H+ in Table 4, and for compounds
9H+-11H+ in Table 3.
[Cp2Ru2(CO)3(PMe3)(µ-H)]+CF3SO3- (1H+CF3SO3-). 1H NMR
(CD2Cl2): δ 5.67 (s, 5H, Cp), 5.35 (s, 5H, Cp), 1.81 (d, 2JP-H 10.0 Hz,
9H, Me), -18.51 (d, 2JP-H 20.0 Hz, 1H, µ-H). 31P NMR (CD2Cl2): δ
(23) Bush, R. C.; Angelici, R. J. Inorg. Chem. 1988, 27, 681.
(24) Sowa, J. R., Jr.; Angelici, R. J. J. Am. Chem. Soc. 1991, 113, 2537.
(25) Eatough, D. J.; Christensen, J. J.; Izatt, R. M. Experiments in
Thermometric and Titration Calorimetry; Brigham Young Univer-
sity: Provo, UT, 1974.
14.7 (s). Orange crystals of 1H+CF3SO3 were obtained by slowly
-
cooling an NMR sample to -78 °C.

Protonation of Metal-Metal Bonds
Inorganic Chemistry, Vol. 37, No. 12, 1998 2979
Table 7. Selected Bond Distances (Å) and Angles (deg)a for
Table 5. Crystal and Data Collection Parameters for
Cp2Ru2(CO)3(PMe3) (1) and [Cp2Ru2(CO)3(PMe3)(µ-H)]+CF3SO3
[Cp2Ru2(CO)3(PMe3)(µ-H)]+CF3SO3 (1H+CF3SO3
)
-
-
-
(1H+CF3SO3
)
-
Distances
-
1
1H+CF3SO3
Ru(1)-Ru(2) 3.0271(6) Ru(1)-H(1) 1.67(3) Ru(2)-H(1) 1.75(3)
b
Ru(1)-P(1) 2.299(2) Ru(1)-C(9) 1.866(7) Ru(1)-Cpc 1.891
empirical formula
space group
a, Å
b, Å
c, Å
C16H19O3PRu2
P21/c
C17H20F3O6PRu2S
P21/c
P(1)-C(6)
C(9)-O(1)
1.801(7) P-C(7)
1.805(7) P-C(8)
1.794(6)
1.139(8) Ru(2)-C(15) 1.854(6) Ru(2)-C(16) 1.885(7)
7.997(5)
14.40(1)
15.46(1)
101.18(6)
1746(2)
4
1.873
18.28
Mo KR (λ )
0.710 73 Å)
20(1)
12.760(1)
11.288(1)
16.691(2)
111.93(1)
2230.1(4)
4
b
Ru(2)-Cpc 1.880
C(15)-O(2) 1.162(7) C(16)-O(3) 1.146(7)
Angles
Ru(2)-Ru(1)-C(9)
Ru(1)-Ru(2)-C(15)
Ru(1)-C(9)-O(1)
Ru(2)-C(16)-O(3)
C(15)-Ru(2)-C(16)
Cpc-Ru(1)-Ru(2)-Cpc
88.5(2) Ru(2)-Ru(1)-P(1)
96.7(2) Ru(1)-Ru(2)-C(16)
176.8(6) Ru(2)-C(15)-O(2)
176.4(5) P-Ru(1)-C(9)
90.2(3) Ru(1)-H(1)-Ru(2)
62.9
101.15(4)
74.8(2)
174.8(6)
88.2(2)
124.8
â, deg
V, Å3
Z
d
calc, g/cm3
1.914
130.41
µ, cm-1
b
radiation (monochromated
in incident beam)
Cu KR (λ )
1.541 78 Å)
-60(2)
0.0410
0.0439
a Numbers in parentheses are estimated standard deviations in the
temp, °C
least significant digits. b Cpc ) centroid of Cp ring.
Ra
Rw
0.0558
0.1956
b
2
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) [∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2; w
) 1/σ2(|Fo|).
Table 6. Selected Bond Distances (Å) and Angles (deg)a for
Cp2Ru2(CO)3(PMe3) (1)
Distances
b
Ru(1)-Ru(2) 2.722(2) Ru(1)-Cpc 1.924
Ru(1)-P
2.291(3)
1.781(12)
P-C(13)
1.793(10) P-C(14)
1.745(12) P-C(15)
Ru(1)-C(1) 1.994(10) C(1)-O(1) 1.173(10) Ru(1)-C(2) 1.985(9)
b
C(2)-O(2) 1.184(8) Ru(2) -Cpc 1.930
Ru(2)-C(1) 2.071(1)
Ru(2)-C(2) 2.089(8) Ru(2)-C(16) 1.855(9) C(16)-O(3) 1.130(9)
Angles
Ru(1)-C(1)-Ru(2)
Ru(1)-Ru(2)-C(16)
Ru(1)-P-C(13)
84.1(4) Ru(1)-C(2)-Ru(2)
103.9(3) Ru(2)-Ru(1)-P
115.8(4) Ru(1)-P-C(14)
117.5(4) C(1)-Ru(1)-P
89.7(2) C(1)-Ru(2)-C(16)
91.3(3) O(1)-C(1)-Ru(1)
83.8(3)
104.04(8)
119.1(4)
90.8(3)
90.9(4)
140.4(9)
Ru(1)-P-C(15)
C(2)-Ru(1)-P
Figure 1. Thermal ellipsoid drawing of Cp2Ru2(CO)3(PMe3) (1)
showing the atom numbering scheme (50% probability ellipsoids).
Hydrogen atoms have been omitted for clarity.
C(2)-Ru(2)-C(16)
O(2)-C(2)-Ru(1)
Cpc-Ru(1)-Ru(2)-Cpc
143.4(6) O(3)-C(16)-Ru(2) 175.4(9)
b
2.4
a Numbers in parentheses are estimated standard deviations in the
least significant digits. b Cpc ) centroid of Cp ring.
determinations. Titrations of 1,3-diphenylguanidine (GFS Chemicals)
with CF3SO3H in DCE (-37.0 ( 0.3 kcal/mol; literature value -37.2
( 0.4 kcal/mol23) were used to monitor the accuracy of the calorimeter
before each set of determinations. Titrations of complexes 2-4 and
11 failed to give reproducible ∆HMHM values for reasons that are not
known at this time.
X-ray Diffraction Studies. The crystals were mounted on glass
fibers and transferred to a Siemens P4RA diffractometer. Data were
collected at 20 ( 1 °C for 1 and at -60 ( 2 °C for 1H+CF3SO3-. Cell
constants for 1 and 1H+CF3SO3- were determined from reflections in
360° rotation photographs. Pertinent data collection and reduction
details are given in Table 5. Lorentz and polarization corrections were
applied. Nonlinear corrections based on decay in the standard
reflections were applied to the data for both 1 and 1H+CF3SO3-. Series
of azimuthal reflections were also collected for both. No absorption
correction was applied to 1. A semiempirical absorption correction
based on the azimuthal scan was applied to 1H+CF3SO3-. The space
groups were determined by systematic absences and intensity statistics,
and the structures were solved by direct methods.26 All non-hydrogen
atoms were placed directly from the E map and refined with anisotropic
displacement parameters. Hydrogen atoms were treated as riding atoms
with individual isotropic displacement parameters, except for atom H
in 1H+CF3SO3-. Atom H is the bridging hydrogen between Ru(1) and
Ru(2) and was found from the difference map; its coordinates were
refined. Selected bond distances and angles are listed in Table 6 for
1 and in Table 7 for 1H+. The ORTEP drawing of 1 is shown in Figure
1 and that of 1H+ in Figure 2.
Figure 2. Thermal ellipsoid drawing of Cp2Ru2(CO)3(PMe3)(µ-H)+
(1H+) showing the atom numbering scheme (50% probability el-
lipsoids). Hydrogen atoms have been omitted for clarity.
Results
Cp2Ru2(CO)3(PR3) Syntheses. Refluxing Cp2Ru2(CO)2-
(COC2Ph2) and the desired phosphine in toluene for ap-
proximately 30 min results in nearly quantitative formation of
the phosphine-substituted complexes Cp2Ru2(CO)3(PR3). Knox
reported14 that the reaction of Cp2Ru2(CO)2(COC2Ph2) with
P(OMe)3 in refluxing toluene occurs quickly to give Cp2Ru2-
(CO)3[P(OMe)3] in very high yield; however, details of the
reaction conditions and product isolation were not provided.
(26) SHELXTL-PLUS; Siemens Analytical X-ray, Inc.: Madison, WI, 1989.

2980 Inorganic Chemistry, Vol. 37, No. 12, 1998
Nataro and Angelici
The IR spectrum of the complex in CH2Cl2 shows ν(CO)
bands at 1953(s) and 1733(s) cm-1 14
Knox also reported
.
1H NMR, IR, and elemental analysis data for compound 4,10
which was isolated as a side product from the reaction of
Cp2Ru2(CO)2(COC2Ph2) with H2CdPPh3.17 The analogous iron
complexes, Cp2Fe2(CO)3(PR3), have also been prepared; they
exist in only the CO-bridged form in solution.27 However, it
was not determined whether the Cp ligands are cis or trans to
each other. IR data for compounds 1-4 compare favorably
with those of the related iron complexes in number of bands
and relative intensities, indicating that compounds 1-4 also exist
solely as bridged isomers in solution. Although the cis/trans
relationship of the Cp ligands in 1 is not known in solution, the
compound adopts the cis geometry in the solid state (Figure 1).
The Cp ligands are eclipsed as indicated by the Cpcent-Ru-
Ru-Cpcent torsion angle of only 2.4°. The bridging CO groups
and ruthenium atoms are not planar, as indicated by the 155.5°
dihedral angle between the Ru(1)-C(1)-Ru(2) and Ru(1)-
C(2)-Ru(2) planes. This angle presumably results from the
bridging CO groups adopting positions that maximize the
overlap with the metal orbitals in the π* HOMO, as proposed
for Cp2Fe2(CO)4.28 The Ru-Ru bond distance is 2.722(2) Å,
which is slightly shorter than that in Cp2Ru2(CO)4 (2.735(2)
Å).29
Figure 3. Top-down views (Cp excluded for clarity) of cis and trans
CO ligand arrangements in Cp2Mo2(CO)4(PR3)2.
When a CD2Cl2 solution of 5 was cooled to -78 °C, no 13C
signals were observed in the carbonyl region, due to fluxionality
of the CO ligands. The 13C NMR spectra of 7 and 8 at room
temperature also show no signals in the carbonyl region. Upon
cooling to -78 °C, two signals are observed. The peak (∼δ
246 ppm) for the bridging CO groups is split into a doublet by
the phosphorus; however the peak (∼δ 203 ppm) for the
terminal CO’s is not split by phosphorus.
Cp2Mo2(CO)4(PR3)2 Syntheses. Compounds 9-12 were
prepared in greater than 75% yields by reacting phosphine (2
molar equiv) with Cp2Mo2(CO)4. Compound 12 was prepared
previously by two very different routes. By stirring Cp2Mo2-
(CO)4 and PPh3 together in toluene, Curtis and Klingler31
obtained 12 in 41% yield. Bruce et al. prepared 12 in 89%
yield by reaction of Mo(CO)3(PPh3)3 with CpH in refluxing
dibutyl ether.32 The relatively high ν(CO) values (Table 3)
suggest that all of the Cp2Mo2(CO)4(PR3)2 complexes have only
terminal CO ligands. IR studies of Cp2Mo2(CO)4(PR3)2 (R )
Ph, OMe)31 established that these complexes exist only as the
isomer in which the two CO groups are trans to each other
(Figure 3); this assignment was based on the relative intensities
of the ν(CO) bands for the symmetric and asymmetric vibra-
tional modes.
By the reaction of Cp2Ru2(CO)2(COC2Ph2) with 13CO (1 atm)
in toluene at 90 °C, diphenylacetylene was displaced to give
Cp2Ru2(CO)3(13CO) (5) in 93% yield. The mass spectrum of
5 showed that there was only one 13CO group in the complex.
Complex 6, Cp2Ru2(CO)(13CO)(COC2Ph2), easily prepared from
5, reacted with phosphines to give Cp2Ru2(CO)2(13CO)(PMe3)
(7) and Cp2Ru2(CO)2(13CO)(PPh3) (8). The IR spectrum (Table
2) of compound 5 consists of six ν(CO) bands, four in the
terminal carbonyl region and two in the bridging region. The
unlabeled complex, Cp2Ru2(CO)4, has four carbonyl bands, three
terminal and one bridging.10 To understand the spectrum of
the 13CO-labeled compound 5, the positions of its ν(CO) bands
were estimated by assuming that each of the four bands of Cp2-
Ru2(CO)4 could be approximated by calculating the 13CO isotope
effect using a diatomic vibrational model: [ν(13C)]2/[ν(12C)]2
) {m(12C)[m(13C) + m(O)]}/{m(13C)[m(12C) + m(O)]}, where
m values are masses of the indicated isotopes. The overall result
(Table 2) of this calculation is that the positions of each of the
four bands in Cp2Ru2(CO)4 shift 40-45 cm-1 to lower values
when the 13CO group is located in a terminal or bridging position
that directly affects the ν(CO) value. Two of these calculated
bands (1958 and 1921 cm-1) overlap bands from unlabeled CO
groups of 4. The two other calculated bands (1891 and 1731
cm-1) have wavenumber values similar to those observed in 5,
which supports this simplified method of estimating ν(CO)
values for 5. Compounds 6-8 also give IR spectra (Table 2)
that have ν(CO) bands that can be satisfactorily explained by
this method of estimating the ν(CO) values for the 13CO-labeled
complexes. These estimates also suggest that the 13CO occupies
both bridging and terminal positions in compounds 5-8.
At room temperature in the 13C NMR spectrum of 5, there is
only one singlet in the 13CO region. Gansow30 had previously
studied the low-temperature 13C NMR spectrum of Cp2Ru2(CO)4
and observed separate singlet signals for the terminal and
bridging CO groups at -118 °C in 95% CHFCl2/5% CS2.
Protonation Reactions. Quantitative formation of the hy-
dride-bridged dinuclear Ru complexes 1H+CF3SO3--5H+CF3-
-
SO3-, 7H+CF3SO3-, and 8H+CF3SO3 occurs (eq 3) upon
addition of 1 equiv of triflic acid to complexes 1-5, 7, and 8.
The CO-bridged structure of the reactants is converted to the
nonbridged structure of the products, which were characterized
1
by IR and H, 13C, and 31P NMR spectroscopy. The Ru-H-
1
Ru resonances in the H NMR spectra occur as doublets be-
tween δ -18.51 and -18.75 for compounds 1H+-4H+ due to
coupling with the phosphorus of the PR3 ligand. For compound
5H+, the hydride signal is a doublet, due to coupling with the
single labeled 13CO group. The hydride signals for compounds
7H+ and 8H+ are doublets of doublets, due to splitting by the
phosphorus and labeled carbonyl ligand. The 1H NMR signals
for the Cp groups in the protonated dimers are approximately
0.7 ppm downfield of those for 1-4.
The ν(CO) bands of the protonated dimers are higher than
those of 1-4, and there are no ν(CO) bands below 1850 cm-1
,
which indicates that there are no bridging CO groups (Table
1). Complex 5H+, Cp2Ru2(CO)3(13CO)(µ-H)+, exhibits five ν-
(CO) bands (Table 4) while the analogous unlabeled compound
Cp2Ru2(CO)4(µ-H)+ displays only three ν(CO) bands.10 Table
4 lists IR data for both of these compounds as well as estimated
wavenumbers for ν(CO) modes that involve the 13CO group;
these estimations were performed as described for 5 above. One
of the calculated bands (2026 cm-1) overlaps one of the bands
observed for the unlabeled complex. The remaining two
calculated bands (2003 and 1972 cm-1) are in reasonable
(27) Haines, R. J.; du Preez, A. L. Inorg. Chem. 1969, 8, 1459.
(28) Jemmis, E. D.; Pinhas, A. R.; Hoffmann, R. J. Am. Chem. Soc. 1980,
102, 2576 and references therein.
(29) Mills, D. S.; Nice, J. P. J. Organomet. Chem. 1967, 9, 339.
(30) Gansow, O. A.; Burke, A. R.; Vernon, W. D. J. Am. Chem. Soc. 1976,
98, 5817.
(31) Curtis, M. D.; Klingler, R. J. J. Organomet. Chem. 1978, 161, 23.
(32) Bruce, M. I.; Goodall, B. L.; Sharrocks, D. N.; Stone, F. G. A. J.
Organomet. Chem. 1972, 39, 139.

Protonation of Metal-Metal Bonds
Inorganic Chemistry, Vol. 37, No. 12, 1998 2981
Table 8. Heats of Protonation (∆HMHM) of Cp2Ru2(CO)3(PR3) and
agreement with the lowest wavenumber, isotopically shifted
bands observed for 5H+. Compounds 7H+ and 8H+ display
similar features in their IR spectra (Table 4).
Cp2Mo2(CO)4(PR3)2
metal complex
-∆HMHM,
a,b kcal/mol
The 13C NMR spectrum of compound 5H+ exhibits one peak
(δ 195.4) for the four equivalent terminal carbonyl groups. For
compounds 7H+ and 8H+, there are three peaks in the terminal
carbonyl region as expected for a structure (Figure 2) with only
terminal CO groups. When collected on the 200 MHz instru-
ment, these peaks were broad singlets. On the 400 MHz
instrument, the signals appeared as doublets due to coupling
with the phosphorus atom of the PR3 ligand. Two of the
doublets exhibited relatively small JP-C coupling constants (8.2
and 8.1 Hz for 7H+; 6.9 and 6.7 Hz for 8H+); these are assigned
to the two CO groups on the Ru(CO)2Cp end of the dimers.
The doublet with the large JP-C coupling constant (19.3 Hz for
7H+; 18.4 Hz for 8H+) is assigned to the CO on the Ru(CO)-
(PR3)Cp end of the dimers. When the 13C NMR spectrum was
taken with 1H coupling, each of the three 13CO signals became
Cp2Ru2(CO)3(PMe3) (1)
Cp2Ru2(CO)4
Cp2Mo2(CO)4(PMe3)2 (9)
Cp2Mo2(CO)4(PMe2Ph)2 (10)
30.0(4)
18.4(1)c
27.4(2)
18.9(5)
a For protonation with 0.1 M CF3SO3H in DCE solvent at 25.0 °C.
b Numbers in parentheses are average deviations from the mean of at
least four titrations. c Reference 10.
base diphenylguanidine. The resulting solution was passed
through an alumina column (1.5 × 30 cm) eluting with CH2-
Cl2. Isolation of the pure, unprotonated complexes (1, 8, 9)
was achieved by recrystallization of the complexes from CH2-
Cl2 by layering with hexanes.
Discussion
Protonation of Cp2Ru2(CO)3(PR3). Reactions of the CO-
bridged Cp2Ru2(CO)3(PR3) complexes (1-4) with CF3SO3H
proceed according to eq 3 to give products Cp2Ru2(CO)3(PR3)-
(H)+ in which all of the CO ligands are nonbridging. An X-ray
2
a doublet of doublets, and the JH-C coupling constants (3.1,
3.5, 3.5 Hz for 7H+; 2.9, 3.8, 3.1 Hz for 8H+) involving all
three CO ligands in each complex are about the same. This
suggests that the hydride ligand is not associated with one Ru
substantially more strongly than the other.
diffraction study of 1H+CF3SO3 supports this structural
-
assignment (Figure 2). The site of protonation in the Cp2Ru2-
(CO)3(PR3)(H)+ complexes was of particular interest because
the Ru bearing the PR3 ligand should be much more basic than
the other Ru with only CO ligands. As detailed in the
Introduction, the metal in Cp*Ir(CO)(PR3) complexes is 15.7-
16.6 kcal/mol more basic than that in Cp*Ir(CO)2.11,33 Assum-
ing that ∆S is the same for the protonation of all of these
complexes, the equilibrium constant (K) for protonation of the
Cp*Ir(CO)(PR3) complexes is estimated (∆G ) ∆HHM ) -RT
ln K) to be 5 × 1011 times greater than that for protonation of
Cp*Ir(CO)2.11,33 In a variety of other metal carbonyl complexes,
the basicities of the metals as measured by the equilibrium
constant (K) for protonation also increase many orders of
magnitude when a CO ligand in the complex is replaced by a
phosphine.4 Thus, in the Cp2Ru2(CO)3(PR3)(H)+ complexes,
one might expect the H ligand to be bonded to the Ru in the
relatively basic Cp(CO)(PR3)Ru unit as in A (see Introduction).
The other likely location of the hydride is bridging the Ru-Ru
bond as in B. With the goal of ascertaining the binding site of
the H ligand, 1H and 13C NMR studies of the mono-13CO-labeled
Cp2Ru2(CO)2(13CO)(PR3)(H)+ complexes, where PR3 ) PMe3
(7H+) or PPh3 (8H+), were performed. The 13CO ligand was
distributed among the three possible sites in the complex, which
gave rise to three 13C NMR signals; each was a doublet due to
coupling with the phosphorus (see Results for details). On the
basis of the larger JC-P coupling constant for the 13CO group
in the Cp(CO)(PR3)Ru unit than for the 13CO’s in the Cp-
(CO)2Ru moiety, each of the three 13CO signals were assigned
to the three different 13CO ligands. With these assignments, it
was possible to determine, from a proton-coupled 13C NMR
spectrum, JC-H coupling constants between each CO and the
hydride. In 7H+, JC-H for hydride coupling to the CO in Cp-
(CO)(PMe3)Ru was 3.1 Hz; JC-H values for hydride coupling
to the two inequivalent CO’s in Cp(CO)2Ru were both 3.5 Hz.
In 8H+, JC-H for the CO in Cp(CO)(PPh3)Ru was 2.9 Hz; JC-H
values for the two CO groups in Cp(CO)2Ru were 3.8 and 3.1
Hz. The fact that coupling constants between the hydride and
CO groups on both Ru atoms all fall within the narrow range
2.9-3.8 Hz suggests that the hydride ligand bridges the Ru-
Ru bond and couples nearly equally with CO groups on both
A comparison of the structures of 1 (Figure 1) and 1H+
(Figure 2) as determined by X-ray diffraction studies shows
that the Ru-Ru bond distance is longer in 1H+ (3.0271(6) Å)
than in 1 (2.722(2) Å). Similarly, the Ru-Ru bond in the
protonated dimer, Cp2Ru2(CO)4(µ-H)+, is longer (3.037 Å)3 than
that of Cp2Ru2(CO)4 (2.735(2) Å).29 The Ru-P bond length
does not change significantly upon protonation (2.299(2) Å in
1H+ vs 2.291(3) Å in 1), and neither does the Ru-C distance
to the terminal carbonyl groups (average 1.868 Å in 1H+ vs
1.855(9) Å in 1). This small change in the Ru-C distance to
the terminal carbonyl groups is also observed in the protona-
tion of Cp2Ru2(CO)4 (average 1.88 Å in Cp2Ru2(CO)4(µ-H)+
vs 1.86 Å in Cp2Ru2(CO)4).10,29 The bridging hydride in 1H+
was located, and it appears to be closer to the ruthenium atom
with the phosphine (Ru(1)-H 1.67(3) Å vs 1.75(3) Å for Ru-
(2)-H).
Quantitative formation of the hydride-bridged dinuclear Mo
-
complexes 9H+CF3SO3--11H+CF3SO3 occurs (eq 4) upon
addition of 1 equiv of triflic acid to complexes 9-11. The
products were characterized by IR and 1H and 31P NMR
spectroscopy. A triplet is observed for the hydride ligand at
approximately δ -20 ppm in the 1H NMR spectra of complexes
9H+-11H+. The chemical shift and equal coupling to both
phosphorus atoms is consistent with a bridging hydride in these
protonated dimers. The average positions of the ν(CO) bands
of the dimers 9-11 increase approximately 100 cm-1 upon
protonation. While there are no previous reports of the
protonation of 9-11, Cp2Mo2(CO)4(dppm) is known20 to react
with HBF4‚Et2O to give Cp2Mo2(CO)4(dppm)(µ-H)+BF4
,
-
which contains a bridging hydride. This complex, whose
structure was established by X-ray diffraction studies, has IR
and 1H NMR spectra21,22 that are similar to those of 9H+-11H+.
Calorimetry Studies. Heats of protonation (∆HMHM), de-
termined by calorimetric titration, of complexes 1, 8, and 9 with
CF3SO3H in DCE solvent at 25.0 °C according to eqs 3 and 4,
are presented in Table 8. Plots of temperature vs amount of
acid added were linear, indicating that the protonations occurred
rapidly and stoichiometrically.25 Normal pre- and post-titration
traces were evidence that no decomposition of the neutral or
protonated species occurred. The unprotonated dimers were
recovered from the titration solutions by adding 1 equiv of the
(33) Wang, D.; Angelici, R. J. Inorg. Chem. 1996, 35, 1321.

2982 Inorganic Chemistry, Vol. 37, No. 12, 1998
Nataro and Angelici
Ru atoms. That the JC-H values are reasonable for bridging
hydride-to-13CO coupling is supported by a JC-H value of 4.0
Hz for hydride coupling to the four equivalent 13CO ligands in
Cp2Ru2(CO)3(13CO)(µ-H)+, 5H+. If the proton were on the Ru
at the Cp(CO)(PR3)Ru end of the molecule (structure A), a
significantly larger JC-H value for coupling between the 13CO
and H on the same Ru would be expected. Such a configuration
of ligands is present in CpRu(13CO)(PPh3)H, and the JC-H
coupling constant (9.1 Hz) is indeed larger than that for the
bridging hydride complex Cp2Ru2(CO)3(13CO)(µ-H)+ 5H+), and
it is larger than those for 7H+ and 8H+. Thus, the NMR
evidence, as well as the X-ray diffraction study, strongly
supports structure B for the Cp2Ru2(CO)3(PR3)(µ-H)+ com-
plexes in which the hydride ligand bridges the Ru-Ru bond,
despite the presence of a strongly donating phosphine ligand
on one of the Ru atoms.
mononuclear complex. If CpRu(CO)(PMe3)Cl or CpRu(CO)2H
had been selected instead of CpRu(CO)(PMe3)H, the Ru-Ru
bond in Cp2Ru2(CO)3(PMe3) would have been relatively even
more basic than the Ru in these mononuclear complexes,
because CpRu(CO)(PMe3)Cl and CpRu(CO)2H are substantially
less basic than CpRu(CO)(PMe3)H.
Infrared spectra (Table 1) of the Cp2Ru2(CO)3(PR3) com-
plexes in CH2Cl2 solvent show the expected decrease in ν(CO)
as the PMexPh3-x ligand donor strength increases. For example,
ν(CO) for the PPh3 complex is 1947 cm-1 while that for the
PMe3 complex is 1929 cm-1. In contrast, the ν(CdO) value
for the bridging CO groups increases slightly as the PMexPh3-x
donor strength increases. Thus, ν(CdO) is 1725 cm-1 for the
PPh3 complex, but it increases to 1728 cm-1 for the PMe3
complex. A similar trend is seen when the spectra are taken in
toluene solvent (see Experimental Section). Although the same
trend is observed in the analogous Cp2Fe2(CO)3(PR3) com-
plexes,27 a convincing explanation for these data is not apparent.
Protonation of Cp2Mo2(CO)4(PR3)2 Complexes. These
complexes have only terminal CO ligands both before and after
protonation (eq 4). The basicity (-∆HMHM) of Cp2Mo2(CO)4-
(PMe3)2 (27.4(2) kcal/mol) is substantially higher than that of
the closely related Cp2Mo2(CO)4(PMe2Ph)2 (18.9(5) kcal/mol).
The 8.5 kcal/mol difference is much larger than that observed
for the replacement of two PMe2Ph ligands by two PMe3 ligands
in Fe(CO)3(PR3)2 (2.1 kcal/mol) and in CpOs(PR3)2Br (3.2 kcal/
mol).36,37 It is even larger than that observed in fac-W(CO)3-
(PR3)3 (2.0 kcal/mol), where three PR3 ligands are replaced.38
Thus, the Mo-Mo bond basicity in these Cp2Mo2(CO)4(PR3)2
complexes is very sensitive to the donor ability of the PR3
ligands, much more so than in mononuclear complexes. The
position of the phosphine ligand trans to the Mo-Mo bond
(Figure 3) may account for the large effect of the PR3 ligands
on the Mo-Mo bond basicity. Poilblanc and co-workers39
studied the protonation in ethanol of the series of Fe2(CO)4(µ-
SMe)2L2 (L ) PMe3, PMe2Ph, PMePh2, PPh3) complexes where
the phosphine ligands are trans to the Fe-Fe bond. When L
) PMe3 or PMe2Ph, the compounds could be completely
protonated with an excess of aqueous HCl. However, when L
) PMePh2 and PPh3, excess HCl would give only partial
protonation of the Fe-Fe bond and the protonated complexes
could not be isolated. Poilblanc attributes this drastic difference
in basicity to the trans disposition of the phosphines.
The heat of protonation (-∆HMHM) of Cp2Ru2(CO)3(PMe3)
(1) according to eq 3 is 30.0(4) kcal/mol (Table 8) as compared
with only 18.4(1) kcal/mol for the carbonyl analogue Cp2Ru2-
(CO)4.10 The 11.6 kcal/mol higher basicity of 1 is easily
understandable in terms of the stronger electron-donor ability
of PMe3 as compared with CO. However, as noted in the
Introduction, the overall ∆HMHM value for this protonation may
be considered (eq 2) as the sum of ∆Hb for converting the CO-
bridged isomer to the nonbridged isomer and ∆Ha for proto-
nation of the nonbridged isomer. The ∆Hb for Cp2Ru2(CO)4 is
known30,34 to be approximately +2 kcal/mol; since Cp2Ru2(CO)4
is approximately 50% in the CO-bridged form, about +1 kcal
is required to convert the bridged isomer to the nonbridged form.
The ∆Ha value for Cp2Ru2(CO)4 is then -19.4 kcal/mol, roughly
+1 kcal/mol more exothermic than ∆HMHM
.
For Cp2Ru2(CO)3(PMe3) (1), the ∆Hb value is not known,
but since 1 exists completely in the bridged form, ∆Hb is likely
to be more endothermic for 1 than for Cp2Ru2(CO)4. Thus,
the energy required to convert 1 from the bridged to the
nonbridged form would make the overall ∆HMHM value less
exothermic than it would be if its ∆Hb were comparable to that
of Cp2Ru2(CO)4. Therefore, if Cp2Ru2(CO)4 and Cp2Ru2(CO)3-
(PMe3) (1) had the same ∆Hb values, 1 would be even more
basic than Cp2Ru2(CO)4; that is, there would be more than the
observed 11.6 kcal/mol difference in their ∆HMHM values.
Previously,10 we compared the basicity of the Ru-Ru bond
in the dinuclear Cp2Ru2(CO)4 with that of the single Ru atom
in mononuclear CpRu(CO)2H. Although this comparison relied
on an estimate of -∆HHM for CpRu(CO)2H, it was nevertheless
possible to state that the Ru-Ru bond in Cp2Ru2(CO)4 was
substantially more basic than the Ru in CpRu(CO)2H. In the
present studies, it would be desirable to compare -∆HMHM for
1 with -∆HHM for CpRu(CO)(PMe3)H. While the latter
complex is known,35 its basicity is not. However, it can be
estimated from -∆HHM (21.2(4) kcal/mol) for CpRu(PMe3)2-
Cl by replacing one PMe3 with a CO, which decreases the
basicity by approximately 16.6 kcal/mol (see above),1 and by
replacing Cl by H, which increases the basicity by approximately
The Cp2Mo2(CO)4(PR3)2 complexes are clearly more basic
than Cp2Mo2(CO)6, which requires 3 equiv of CF3SO3H in CD2-
Cl2 solvent for complete protonation. The Cp2Mo2(CO)6(µ-
H)+ product, which exhibits Cp and hydride signals at δ 5.88
1
and -20.55 ppm, respectively, in the H NMR spectrum, was
previously identified in 98% H2SO4.40 It has also been prepared
from the reaction of CpMo(CO)3H with CpMo(CO)3(BF4).41
When compared with the Cp2Ru2(CO)3(L) complexes, Cp2-
Mo2(CO)4(PMe3)2 has an intermediate basicity (-∆HMHM) in
the series Cp2Ru2(CO)3(PMe3) (30.0 kcal/mol) > Cp2Mo2-
(CO)4(PMe3)2 (27.4 kcal/mol) > Cp2Ru2(CO)4 (18.4kcal/mol).
Because of the differences in metals, ligands, and structures,
many factors may contribute to this trend.
17.6 kcal/mol.36,37 Thus, the overall estimated basicity (-∆HHM
)
of CpRu(CO)(PMe3)H is 22 kcal/mol. Therefore, the basicity
(-∆HMHM) of the Ru-Ru bond in Cp2Ru2(CO)3(PMe3) (30.0
kcal/mol) is greater than that of the Ru in CpRu(CO)(PMe3)H
(22 kcal/mol). Of course, such comparisons of di- and mono-
nuclear complex basicities depend on the choice of the compared
Summary
NMR studies lead to the interesting conclusion that the site
of protonation in the unsymmetrically substituted Cp(PMe3)Ru(µ-
(38) Sowa, J. R., Jr.; Zanotti, V.; Angelici, R. J. Inorg. Chem. 1993, 32,
848.
(39) Fauvel, K.; Mathieu, R.; Poilblanc, R. Inorg. Chem. 1976, 15, 976.
(40) Davison, A.; McFarlane, W.; Pratt, L.; Wilkinson, G. J. Chem. Soc.
1962, 3653.
(34) Novak, K. J. Organomet. Chem. 1967, 7, 151.
(35) Chinn, M. S.; Heinekey, D. M. J. Am. Chem. Soc. 1990, 112, 5166.
(36) Rottink, M. K.; Angelici, R. J. J. Am. Chem. Soc. 1992, 114, 8296.
(37) Rottink, M. K.; Angelici, R. J. J. Am. Chem. Soc. 1993, 115, 7267.
(41) Beck, W.; Schloter, K. Z. Naturforsch. 1978, 33B, 1214.

Protonation of Metal-Metal Bonds
Inorganic Chemistry, Vol. 37, No. 12, 1998 2983
CO)2Ru(CO)Cp (1) is the Ru-Ru bond rather than the Ru
bearing the strongly donating PMe3 ligand. The Ru-Ru bond
in Cp2Ru2(CO)3(PMe3) is 11.6 kcal/mol more basic than that
in Cp2Ru2(CO)4, as expected for the replacement of a CO ligand
by PMe3. The Ru-Ru bonds in Cp2Ru2(CO)3(PMe3) and Cp2-
Ru2(CO)4 are substantially more basic than the Ru in related
mononuclear complexes such as CpRu(CO)(PMe3)H and CpRu-
(CO)2H. The effect of changing the PR3 ligand in Cp2Mo2-
(CO)4(PR3)2 on the basicity of the Mo-Mo bond is much larger
than comparable effects on the basicities of mononuclear
complexes.
Acknowledgment. We thank the National Science Foun-
dation (Grant CHE-9414242) for support of this work, Dr.
Leonard Thomas for solving the crystal structures of 1 and
1H+CF3SO3-, and Johnson-Matthey for the generous loan of
RuCl3‚nH2O.
Supporting Information Available: X-ray crystallographic files,
in CIF format, for the structures of 1 and 1H+CF3SO3 are available
-
on the Internet only. Access information is given on any current
masthead page.
IC971516V