Selective diphosphine ligand chelation and π bond coordination in CoRu(CO)7(μ-PPh2): Kinetics and X-ray structure of CoRu(CO)4(μ-bma)(μ-PPh2)

Article abstract of DOI:10.1021/ic991279r

Thermolysis of CoRu(CO)₇(μ-PPh₂) (1) in refluxing 1,2-dichloroethane in the presence of the diphosphine ligands 2,3-bis(diphenylphosphino)maleic anhydride (bma) and 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) furnishes the new mixed-metal complexes CoRu(CO)₄(μ-P-P)(μ-PPh₂) [where P-P = bma (3a), bpcd (3b)] along with trace amounts of the known complex CoRu(CO)₆(PPh₃)(μ-PPh₂) (4). The requisite pentacarbonyl intermediates CoRu(CO)₅(μ-P-P)(μ-PPh₂)[where P-P = bma (2a), bpcd (2b)] have been prepared by separate routes (mild thermolysis and Me₃NO activation) and studied for their conversion to CoRu(CO)₄(μ-P-P)(μ-PPh₂). The penta- and tetracarbonyl complexes have been isolated and fully characterized in solution by IR and NMR spectroscopy. The kinetics for the conversion of 2a → 3a and of 2b → 3b were measured by IR spectroscopy in chlorobenzene solvent. On the basis of the first-order rate constants, CO inhibition, and the activation parameters (2a → 3a, ΔH? = 29.2 ± 1.4 kcal mol^-1 and ΔS? = 8.2 ± 3.8 eu; 2b → 3b, ΔH? = 27.7 ± 0.6 kcal mol^-1 and ΔS? = 1.4 ± 1.6 eu), a mechanism involving dissociative CO loss as the rate-limiting step is proposed. The solid-state structure of CoRu(CO)₄(μ-bma)(μ-PPh₂) (3a), as determined by X-ray crystallography, reveals that the two PPh₂ groups are bound to the ruthenium center while the maleic anhydride π bond is coordinated to the cobalt atom.

Full text of DOI:10.1021/ic991279r

Inorg. Chem. 2000, 39, 6051-6055
6051
Selective Diphosphine Ligand Chelation and π Bond Coordination in CoRu(CO)7(µ-PPh2):
Kinetics and X-ray Structure of CoRu(CO)4(µ-bma)(µ-PPh2)
Simon G. Bott*
Department of Chemistry, University of Houston, Houston, Texas 77204
Kaiyuan Yang, Jian Cheng Wang, and Michael G. Richmond*
Department of Chemistry, University of North Texas, Denton, Texas 76203
ReceiVed NoVember 1, 1999
Thermolysis of CoRu(CO)7(µ-PPh2) (1) in refluxing 1,2-dichloroethane in the presence of the diphosphine ligands
2,3-bis(diphenylphosphino)maleic anhydride (bma) and 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd)
furnishes the new mixed-metal complexes CoRu(CO)4(µ-P-P)(µ-PPh2) [where P-P ) bma (3a), bpcd (3b)]
along with trace amounts of the known complex CoRu(CO)6(PPh3)(µ-PPh2) (4). The requisite pentacarbonyl
intermediates CoRu(CO)5(µ-P-P)(µ-PPh2) [where P-P ) bma (2a), bpcd (2b)] have been prepared by separate
routes (mild thermolysis and Me3NO activation) and studied for their conversion to CoRu(CO)4(µ-P-P)(µ-PPh2).
The penta- and tetracarbonyl complexes have been isolated and fully characterized in solution by IR and NMR
spectroscopy. The kinetics for the conversion of 2a f 3a and of 2b f 3b were measured by IR spectroscopy in
chlorobenzene solvent. On the basis of the first-order rate constants, CO inhibition, and the activation parameters
(2a f 3a, ∆Hq ) 29.2 ( 1.4 kcal mol-1 and ∆Sq ) 8.2 ( 3.8 eu; 2b f 3b, ∆Hq ) 27.7 ( 0.6 kcal mol-1 and
∆Sq ) 1.4 ( 1.6 eu), a mechanism involving dissociative CO loss as the rate-limiting step is proposed. The
solid-state structure of CoRu(CO)4(µ-bma)(µ-PPh2) (3a), as determined by X-ray crystallography, reveals that
the two PPh2 groups are bound to the ruthenium center while the maleic anhydride π bond is coordinated to the
cobalt atom.
Introduction
ligands with polynuclear metal complexes. In earlier reports we
provided evidence showing the ease by which these ligands
undergo P-C bond cleavage reactions when tethered to dimetal
and trimetal clusters (eq 1).7,8,9 While far from unequivocal at
this point, it is our thinking that any type of diphosphine ligand
activation occurs after the coordination of the π bond of the
carbocyclic ring to a metal center(s). The driving force in our
P-C bond activations is presumably facilitated by the electron-
withdrawing behavior of the ancillary maleic anhydride or dione
rings.10
While our previous studies have involved homometallic
systems, we wished to extend our substitution and reactivity
studies using the bma and bpcd ligands with heterometallic
complexes. This would allow us the opportunity to explore any
site selectivity that might be associated with the initial coordina-
tion and subsequent activation of the diphosphine ligand. Herein
The reactivity and physical properties of mononuclear transi-
tion-metal complexes containing the diphosphine ligands 2,3-
bis(diphenylphosphino)maleic anhydride (bma) and 4,5-bis-
(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) have been
extensively studied over the last two decades.1,2 The presence
of a readily accessible π* LUMO on the unsaturated diphosphine
ligand has been shown to be instrumental in stabilizing electron
counts in excess of 18 electrons. The chemistry of such 18 +
δ complexes has been thoroughly investigated by Tyler and
Rieger.3-6
Our initial interest in the bma and bpcd ligand systems
stemmed from the absence of any reported chemistry of these
(1) (a) Fenske, D.; Becher, H. J. Chem. Ber. 1975, 108, 2115. (b) Fenske,
D. Angew. Chem., Int. Ed. Engl. 1976, 15, 381. (c) Becher, H. J.;
Bensmann, W.; Fenske, D. Chem. Ber. 1977, 110, 315. (d) Bensmann,
W.; Fenske, D. Angew. Chem., Int. Ed. Engl. 1978, 17, 462. (e) Fenske,
D. Chem. Ber. 1979, 112, 363. (f) Fenske, D.; Christidis, A. Angew.
Chem., Int. Ed. Engl. 1981, 20, 129.
(7) (a) Yang, K.; Bott, S. G.; Richmond, M. G. Organometallics 1994,
13, 3788, 4977. (b) Yang, K.; Martin, J. A.; Bott, S. G.; Richmond,
M. G. Organometallics 1996, 15, 2227. (c) Yang, K.; Bott, S. G.;
Richmond, M. G. J. Organomet. Chem. 1996, 516, 65.
(2) Lewis, J. S.; Heath, S. L.; Powell, A. K.; Zweit, J.; Blower, P. J. J.
Chem. Soc., Dalton Trans. 1997, 855.
(3) Tyler, D. R. Acc. Chem. Res. 1991, 24, 325.
(8) (a) Yang, K.; Smith, J. M.; Bott, S. G.; Richmond, M. G. Organo-
metallics 1993, 12, 4779. (b) Yang, K.; Bott, S. G.; Richmond, M. G.
Organometallics 1995, 14, 919. (c) Shen, H.; Bott, S. G.; Richmond,
M. G. Organometallics 1995, 14, 4625. (d) Shen, H.; Williams, T. J.;
Bott, S. G.; Richmond, M. G. J. Organonmet. Chem. 1995, 505, 1.
(e) Shen, H.; Bott, S. G.; Richmond, M. G. Inorg. Chim. Acta 1996,
250, 195.
(9) For the reaction of a Co4 cluster with bma, see: Xia, C.-G.; Yang,
K.; Bott, S. G.; Richmond, M. G. Organometallics 1996, 15, 4480.
(10) (a) Dubois, R. A.; Garrou, P. E. Organometallics 1986, 5, 466. (b)
Garrou, P. E. Chem. ReV. 1985, 85, 171. (c) Garrou, P. E.; Jung, C.
W. CHEMTECH 1985, 15, 123. (d) Abatjoglou, A. G.; Billing, E.;
Bryant, D. R.; Nelson, J. R. ACS Symp. Ser. 1992, No. 486, 229.
(4) Tyler, D. R.; Mao, F. Coord. Chem. ReV. 1990, 97, 119.
(5) (a) Mao, F.; Tyler, D. R.; Keszler, D. J. Am. Chem. Soc. 1989, 111,
130. (b) Mao, F.; Philbin, C. E.; Weakley, T. J., R.; Tyler, D. R.
Organometallics 1990, 9, 1510. (c) Fei, M.; Sur, S. K.; Tyler, D. R.
Organometallics 1991, 10, 419. (d) Mao, F.; Tyler, D. R.; Bruce, M.
R. M.; Bruce, A. E.; Rieger, A. L.; Rieger, P. H. J. Am. Chem. Soc.
1992, 114, 6418. (e) Meyer, R.; Schut, D. M.; Keana, Tyler, D. R.
Inorg. Chim. Acta 1995, 240, 405. (f) Schut, D. M.; Keana, K. J.;
Tyler, D. R.; Rieger, P. H. J. Am. Chem. Soc. 1995, 117, 8939.
(6) See also: Duffy, N. W.; Nelson, R. R.; Richmond, M. G.; Rieger, A.
L.; Rieger, P. H.; Robinson, B. H.; Tyler, D. R.; Wang, J. C.; Yang,
K. Inorg. Chem. 1998, 37, 4849.
10.1021/ic991279r CCC: $19.00 © 2000 American Chemical Society
Published on Web 11/28/2000

6052 Inorganic Chemistry, Vol. 39, No. 26, 2000
Bott et al.
raphy over silica gel, the desired product was isolated by an extraction
procedure. The solvent was removed under vacuum, and the residue
was dissolved in a minimum amount of CH2Cl2, followed by treatment
with 100 mL of petroleum ether. This initial precipitate was separated
from the mother liquor by filtration and discarded, as it contained
unreacted 1 and minor amounts of 2a and 3a. The CH2Cl2/petroleum
ether solution was concentrated to 20 mL and then cooled to 0 °C for
0.5-1.0 h. The resulting precipitate was collected and dried under
vacuum. Analytically pure CoRu(CO)5(µ-bma)(µ-PPh2) was obtained
after recrystallization from a mixture of CH2Cl2/hexane (2:8). Yield:
0.45 g (64%). IR (CH2Cl2): ν(CO) 2043 (w), 1993 (vs), 1933 (m),
1
1844 (w, asymm bma CdO), 1776 (m, symm bma CdO) cm-1. H
NMR (CDCl3, 298 K): δ 7.15-8.00 (m, phenyl groups). 31P NMR
(THF, 273 K): δ 171.4 (d, phosphido, JP-P ) 124 Hz), 58.0 (d, PPh2,
JP-P ) 124 Hz), 54.5 (s, PPh2). Anal. Calcd (found) for C45H30CoO8P3-
Ru: C, 56.80 (56.76); H 3.18 (3.21).
Synthesis of CoRu(CO)5(µ-bpcd)(µ-PPh2) (2b). A 0.40 g (0.74
mmol) amount of CoRu(CO)7(µ-PPh2) and 0.41 g (0.80 mmol) of bpcd
were charged to a large Schlenk flask under argon, after which 35 mL
of 1,2-dichloroethane was added. The solution was stirred overnight,
maintaining the reaction temperature from 65 to 70 °C. Both IR and
TLC analyses revealed that 2b was present as the major product
(>85%). The solvent was removed under vacuum, and the crude
material was purified by chromatography over silica gel using CH2-
Cl2/petroleum ether (1:1) as the eluent. Recrystallization of 2b from
CH2Cl2/hexane (1:1) afforded 0.45 g of red-brown 2b (yield: 64%).
IR (CH2Cl2): ν(CO) 2047 (w), 1987 (vs), 1925 (m), 1750 (w, asymm
bpcd CdO), 1719 (m, symm bpcd CdO) cm-1. 1H NMR (CDCl3, 298
K): δ 6.70-7.80 (m, phenyl groups), 3.63 (s, 2H, methylene group).
31P NMR (THF, 273 K): δ 167.2 (d, phosphido, JP-P ) 124 Hz), 56.5
(d, PPh2, JP-P ) 124 Hz), 51.2 (s, PPh2). Anal. Calcd (found) for C46H32-
CoO8P3Ru: C, 58.20 (57.93); H 3.40 (3.45).
Synthesis of CoRu(CO)4(µ-bma)(µ-PPh2) (3a). A 1,2-dichloro-
ethane solution containing 0.20 g (0.37 mmol) of CoRu(CO)7(µ-PPh2)
and 0.18 g (0.39 mmol) of bma was heated overnight at reflux under
an argon atmosphere. The solution was cooled to room temperature
and examined by IR and TLC analyses, both of which revealed the
presence of two new compounds, in addition to some unreacted starting
material. The solvent was removed under vacuum, and purification was
effected by column chromatography over silica gel. Unreacted 1 (<5%)
was obtained as the first eluted band when an 8:2 mixture of petroleum
ether/CH2Cl2 was employed as the eluent, while changing the solvent
system to a 1:1 mixture of petroleum ether/CH2Cl2 afforded a minor
amount of the known compound CoRu(CO)6(PPh3)(µ-PPh2) (0.05 g)
(yield: 17%). The tetracarbonyl complex 3a was obtained from the
column as the third band when CH2Cl2 was used as the eluting solvent.
The analytical sample and single crystals suitable for X-ray diffraction
analysis were from a CH2Cl2 solution of 3a that had been layered with
heptane. Yield: 0.17 g (48%). IR (CH2Cl2): ν(CO) 2043 (m), 2017
(vs), 1993 (s), 1953 (s), 1789 (m, asymm bma CdO), 1738 (m, symm
bma CdO) cm-1. 1H NMR (CDCl3, 298 K): δ 6.90-7.85 (m, phenyl
groups). 31P NMR (THF, 273 K): δ 168.0 (s, phosphido), 31.2 (s, PPh2),
30.6 (s, PPh2). Anal. Calcd (found) for C44H30CoO7P3Ru: C, 57.16
(57.06); H 3.25 (3.33).
we report our data on the substitution chemistry and structural
characterization of the products formed from the reaction
between the ligands bma and bpcd and the phosphido-bridged
complex CoRu(CO)7(µ-PPh2). This particular heterometallic
dimer was chosen, in part, due to the well-documented behavior
of CoRu(CO)7(µ-PPh2) toward a variety of two-electron donor
ligands,11 coupled with the possibility of the ruthenium center
in promoting the oxidative cleavage of a P-Ph bond as opposed
to the cleavage of the P-C bond belonging to the redox-active
carbocyclic ring. This latter bond activation process has been,
to date, the predominant mode of ligand activation found by
us.
Experimental Section
General Methods. (p-cymene)RuCl2(PPh2H) used in the synthesis
of CoRu(CO)7(µ-PPh2)12 was prepared from hydrated RuCl3 according
to the published procedures.13 The chemicals Co2(CO)8 and R-phel-
landrene were purchased from Strem Chemical Co. and Lancaster
Chemicals, respectively, and were used as received. The ligands bma
and bpcd were prepared according to published procedures.1a,5b All
solvents were distilled from an appropriate drying agent under argon
and were transferred to Schlenk storage vessels using inert-atmosphere
techniques.14 All combustion analyses were performed by Atlantic
Microlabs, Norcross, GA.
Infrared spectra were recorded on a Nicolet 20 SXB FT-IR
spectrometer in 0.1 mm NaCl cells, using PC control and OMNIC
software. The 1H NMR and 31P spectra were recorded at 300 and 121
MHz, respectively, on a Varian 300-VXR spectrometer. Positive 31P
chemical shifts are to low field of external H3PO4, whose chemical
shift is taken to have δ ) 0.
Synthesis of CoRu(CO)5(µ-bma)(µ-PPh2) (2a). To a Schlenk tube
containing 0.40 g (0.74 mmol) of CoRu(CO)7(µ-PPh2) and 0.40 g (0.86
mmol) of bma was added 35 mL of 1,2-dichloroethane by syringe,
after which the solution was heated overnight at 65-70 °C. IR analysis
at this point showed that the major product was CoRu(CO)5(µ-bma)-
(µ-PPh2) (∼80%). Since 2a decomposes extensively upon chromatog-
Synthesis of CoRu(CO)4(µ-bpcd)(µ-PPh2) (3b). The procedure
used to synthesize 3b was identical to that used with 3a and will not
be described in detail. The compound was isolated by chromatography,
which yielded a trace amount of starting material (<2% of 1) and 0.04
g of CoRu(CO)6(PPh3)(µ-PPh2) (yield: 14%). CoRu(CO)4(µ-bpcd)(µ-
PPh2) was isolated as the third eluted band from the column using CH2-
Cl2 and was recrystallized from a 1:1 mixture of CH2Cl2/heptane to
give 0.20 g (yield: 59%). IR (CH2Cl2): ν(CO) 2035 (s), 2009 (vs),
1981 (s), 1948 (s), 1708 (m, asymm bpcd CdO), 1675 (m, symm bpcd
(11) (a) Regragui, R.; Dixneuf, P. H.; Taylor, N. J.; Carty, A. J.
Organometallics 1984, 3, 814. (b) Guesmi, S.; Su¨ss-Fink, G.; Dixneuf,
P. H.; Taylor, N. J.; Carty, A. J. J. Chem. Soc., Chem. Commun. 1984,
1606. (c) Regragui, R.; Dixneuf, P. H.; Taylor, N. J.; Carty, A. J.
Organometallics 1986, 5, 1; 1964; 1990, 9, 2234 (d) Guesmi, S.;
Dixneuf, P. H.; Su¨ss-Fink, G.; Taylor, N. J.; Carty, A. J. Organome-
tallics 1989, 8, 307. (e) Regragui, R.; Dixneuf, P. H.; Taylor, N. J.;
Carty, A. J. J. Organomet. Chem. 1987, 328, 193.
(12) Regragui, R.; Dixneuf, P. H.; Taylor, N. J.; Carty, A. J. Organo-
metallics 1984, 3, 1020.
(13) (a) Baird, M. C.; Zelonka, R. A. Can. J. Chem. 1972, 50, 3063. (b)
Bennett, M. A.; Smith, K. A. J. Chem. Soc., Dalton Trans. 1974, 233.
(14) Shriver, D. F. The Manipulation of Air-SensitiVe Compounds; McGraw-
Hill: New York, 1969.
CdO) cm-1 1H NMR (CDCl3, 298 K): δ 6.70-7.80 (m, phenyl
.
groups), 3.66 (2H, AB quartet, JH-H ) 22 Hz). 31P NMR (THF, 273
K): δ 169.4 (s, phosphido), 33.1 (s, PPh2), 32.8 (s, PPh2). Anal. Calcd
(found) for C45H32CoO8P3Ru: C, 58.62 (58.33); H 3.50 (3.95).
X-ray Diffraction Structure of CoRu(CO)4(µ-bma)( µ-PPh2) (3a).
Single crystals of CoRu(CO)4(µ-bma)(µ-PPh2) suitable for X-ray
diffraction analysis were grown from a CH2Cl2 solution containing
CoRu(CO)4(µ-bma)(µ-PPh2) that had been layered with heptane. A

Selective Diphosphine Ligand Chelation
Inorganic Chemistry, Vol. 39, No. 26, 2000 6053
Scheme 1
Me3N on the anhydride ring of the ligand. Given the higher
yields of 2a by the thermolysis route, the reaction using Me3-
NO was abandoned.
Both 2a and 2b were subsequently isolated and characterized
in solution by IR and NMR spectroscopy. Attempted chroma-
tography of 2a over silica gel led to extensive decomposition,
as observed by us in other bma-substituted complexes.16 Here
the pendant anhydride ring of the ligand is readily hydrolyzed
on the adsorbent. Changing the chromatographic support to
either alumina or Florisil or carrying out the separation at low-
temperature did little to improve the situation. Accordingly,
compound 2a was isolated via an extraction/recrystallization
sequence, as outlined in the Experimental Section. Compound
2b with its 1,3-dione ring is stable to silica gel and was purified
by column chromatography.
Both 2a and 2b exhibit three terminal carbonyl bands [2043
(w), 1993 (vs), 1933 (m) cm-1 for 2a; 2047 (w), 1987 (vs),
1925 (m) cm-1 for 2b] and two ν(CO) bands that are assigned
to the anhydride ring and the 1,3-dione ring of 2a,b, respectively.
The 31P{1H} NMR spectrum of CoRu(CO)5(µ-bma)(µ-PPh2)
(2a) at 273 K reveals the presence of the expected low-field
µ-phosphido moiety at δ 171.4.17,18 Coupling of the µ-PPh2
ligand to a trans PPh2 group associated with the bma ligand
leads to the observed phosphido doublet with 2JP-P ) 124 Hz.
The bma ligand exhibits two inequivalent PPh2 groups because
of their differing orientations relative to the bridging phosphido
moiety, as depicted in the structure of CoRu(CO)5(µ-bma)(µ-
PPh2) shown below. Assuming a distorted octahedral geometry
at the ruthenium center, the PPh2 singlet found at δ 54.5 and
the doublet resonance at δ 58.0 are assigned to Pa and Pb,
respectively, on the basis of their cis and trans relationship to
the µ-PPh2 group. The bpcd-substituted complex 2b shows an
analogous pattern for the 31P chemical shifts and indicates that
compounds 2a,b possess identical structures.
black crystal of dimensions 0.07 × 0.09 × 0.44 mm3 was selected and
sealed inside a Lindemann capillary tube, followed by mounting on
the goniometer of an Enraf-Nonius CAD-4 diffractometer. The Mo KR
radiation used was monochromatized by a crystal of graphite. Cell
constants were obtained from a least-squares refinement of 25 reflec-
tions with 2θ > 30°. Intensity data in the range of 2.0 < θ < 44.0°
were collected at 298 K using the ω-scan technique in the variable-
scan speed mode. The crystal structure was solved by using SHELX-
86, and all of the non-hydrogen atoms were located with difference
Fourier maps and refined by using full-matrix least-squares methods.
Excluding the carbon atoms, all non-hydrogen atoms were refined
anisotropically. Refinement converged at R ) 0.0633 and Rw ) 0.0768
for 2320 unique reflections with I > 3σ(I).
Results and Discussion
Synthesis and Spectral Characterization. The reaction
between CoRu(CO)7(µ-PPh2) (1) and the diphosphine ligands
bma and bpcd proceeds readily over the temperature range of
65-70 °C in 1,2-dichloroethane to afford the disubstituted
complexes CoRu(CO)5(µ-bma)(µ-PPh2) (2a) and CoRu(CO)5-
(µ-bpcd)(µ-PPh2) (2b) as the major product in each reaction.
The minor byproducts found were unreacted 1 and small
amounts of 3a,b (vide infra). Scheme 1 depicts the course of
reactivity between 1 and the diphosphine ligands bma and bpcd.
In compounds 2a,b the diphosphine ligands are bound at the
ruthenium center in a chelating fashion as verified by 31P NMR
spectroscopy. The site of bma and bpcd ligand substitution in
compounds 2a,b is analogous to the reaction of CoRu(CO)7-
(µ-PPh2) with dppm.11c,e The only major difference between our
results and those of Dixneuf and Carty is the absence of any
sign of a bridged-bma or -bpcd isomer. In the case of the
reaction with dppm, both the chelating and bridging isomers of
CoRu(CO)5(dppm)(µ-PPh2) were observed depending upon the
reaction conditions.
Compound CoRu(CO)5(µ-bpcd)(µ-PPh2) (2b) could be ob-
tained free of CoRu(CO)4(µ-bpcd)(µ-PPh2) (3b) when the
reaction between CoRu(CO)7(µ-PPh2) and bpcd was carried out
at room temperature using the oxidative-decarbonylation
reagent Me3NO.15 The ligand substitution was rapid and the
only product found was 2b. Treatment of CoRu(CO)7(µ-PPh2)
and bma with Me3NO also led to an immediate reaction and
the production of 2a, as ascertained by IR analysis; however,
under these conditions compound 2a decomposed almost as
quickly as it was formed presumably by attack of the liberated
Thermolysis of CoRu(CO)7(µ-PPh2) with added bma or bpcd
in refluxing 1,2-dichloroethane affords the new compounds
CoRu(CO)4(µ-bma)(µ-PPh2) (3a) and CoRu(CO)4(µ-bpcd)(µ-
PPh2) (3b) in moderate to high yields. Besides the tetracarbonyl
compounds, we observed the presence of the pentacarbonyl
precursors 2a,b (for the appropriate ligand), in addition to
production of the known PPh3-substituted compound CoRu-
(CO)6(PPh3)(µ-PPh2) (4).11c,19Compound 4 was routinely iso-
lated in yields of ca. 15% and was unequivocally characterized
in solution by IR and 31P NMR spectroscopy and by comparison
to independently prepared samples of CoRu(CO)6(PPh3)(µ-
(16) Yang, K.; Bott, S. G.; Richmond, M. G. Organometallics 1995, 14,
2387.
(17) Carty, A. J.; MacLaughlin, S. A.; Nucciarone, D. In Phosphorus-31
NMR Spectroscopy in Stereochemical Analysis; Verkade, J. G., Quin,
L. D., Eds.; VCH Publishers: Deerfield Beach, FL, 1987; Chapter
16.
(18) All 31P NMR data were collected at 273 K to minimize the undesirable
effects of 59Co quadrupolar broadening on the 31P resonance. See:
Yuan, P.; Richmond, M. G.; Schwartz, M. Inorg. Chem. 1991, 30,
679 and references therein.
(15) (a) Koelle, U. J. Organomet. Chem. 1977, 133, 53. (b) Albers, M. O.;
Coville, N. Coord. Chem. ReV. 1984, 53, 227.
(19) See also: Foley, H. C.; Finch, W. C.; Pierpont, C. G.; Geoffroy, G.
L. Organometallics 1982, 1, 1379.

6054 Inorganic Chemistry, Vol. 39, No. 26, 2000
Bott et al.
and 1718 cm-1, respectively. The effect of added CO on the
reaction of 2a f 3b and 2b f 3b is shown by entries 4 and 9,
respectively, in Table 1. In the case of the reaction of 2a f 3b
the presence of 1 atm of CO leads to a significant drop in the
reaction rate by a factor of ca. 32. While the effect of added
CO on the reaction of 2b f 3b is less dramatic than in the
bma derivative, a rate retardation of ca. 1.6 was found for the
conversion of 2b to 3b. The activation parameters for 2a f 3a
(∆Hq ) 29.2 ( 1.4 kcal mol-1 and ∆Sq ) 8.2 ( 3.8 eu) and
2b f 3b (∆Hq ) 27.7 ( 0.6 kcal mol-1 and ∆Sq ) 1.4 ( 1.6
eu),20 coupled with the rate retardation in the presence of added
CO, support a unimolecular process involving CO loss as the
rate-limiting step and which obeys the following general rate
law:21,22
Table 1. Experimental Rate Constants for the Transformation of 2a
f 3a and 2b f 3ba
entry no.
T, °C
104kobsd, s-1
2a f 3a
77.2
83.0
88.0
88.0
93.2
98.1
1
2
3
4
5
6
2.37 ( 0.11
7.30 ( 0.68
10.14 ( 0.59
0.32 ( 0.02b
20.35 ( 1.41
30.29 ( 0.91
2b f 3b
83.3
88.3
88.3
93.3
98.2
103.3
7
8
9
10
11
12
1.53 ( 0.05
2.60 ( 0.10
1.66 ( 0.07b
4.04 ( 0.24
8.35 ( 0.34
12.07 ( 0.49
k1k2[RuCo(CO)5(P-P)(PPh2)]
a From ca. 10-2 M CoRu(CO)5(µ-bma)(µ-PPh2) (2a) and CoRu-
(CO)5(µ-bpcd)(µ-PPh2) (2b) in chlorobenzene solvent by following the
disappearance of the ν(CO) band at 1775 and 1718 cm-1, respectively.
b In the presence of 1 atm of CO.
rate )
k-1[CO] + k2
Finally, the presence of minor amounts of CoRu(CO)6(PPh3)-
(µ-PPh2) was verified in all kinetic experiments by TLC analysis.
What may be concluded at this time is that the observed
byproduct 4 does not originate from the chelated diphosphine
compounds CoRu(CO)4(µ-bma)(µ-PPh2) (2b) and CoRu(CO)4-
(µ-bpcd)(µ-PPh2) (3b). No evidence (TLC and IR) was obtained
for the formation of CoRu(CO)6(PPh3)(µ-PPh2) when indepen-
dent theromlysis reactions were carried out with isolated samples
of 2b and 3b at 85 °C overnight. Under these conditions only
the slow decomposition of 2b and 3b was observed.
X-ray Diffraction Data. The structure of CoRu(CO)4(µ-
bma)(µ-PPh2) (3a) was determined by single-crystal X-ray
diffraction analysis in order to establish the coordination mode
exhibited by the ancillary bma ligand. Single crystals of CoRu-
(CO)4(µ-bma)(µ-PPh2) were grown (see Experimental Section
for the exact conditions), and CoRu(CO)4(µ-bma)(µ-PPh2) was
found to exist in the unit cell with no unusually short inter- or
intramolecular contacts. The X-ray data collection and process-
ing parameters for CoRu(CO)4(µ-bma)(µ-PPh2) are given in
Table 2 with selected bond distances and angles listed in Table
3.
PPh2). The path by which CoRu(CO)6(PPh3)(µ-PPh2) arises is
not known, but it is clear that a formal transfer of a phenyl
group to a PPh2 ligand has taken place. The source of the PPh3
group in 4 could be either the phosphido moiety or a PPh2 group
from the bma or bpcd ligands.
Proof of the involvement of 2a f 3a and 2b f 3b was
established by conducting independent experiments using
isolated samples of 2a,b at temperatures in excess of 75 °C, as
shown in eq 2. The expected tetracarbonyl complex was formed
in each as the major product, along with small amounts of CoRu-
(CO)6(PPh3)(µ-PPh2) (4) (vide supra).
The ORTEP diagram presented in Figure 1 shows the
molecular structure of CoRu(CO)4(µ-bma)(µ-PPh2) and estab-
lishes the chelation of both of the maleic anhydride PPh2 groups
to ruthenium center and coordination of the maleic anhydride
π bond to the cobalt atom. Both the ruthenium and cobalt centers
in 3a may be described as having distorted octahedral geom-
etries, assuming that the cobalt-bound π bond is counted as a
two-coordinate ligand. The Ru-Co bond length of 2.674(3) Å
is consistent with its single-bond designation12,23 and is only
The identities of 3a,b were ascertained by spectroscopic
methods and X-ray diffraction analysis in the case of CoRu-
(CO)4(µ-bma)(µ-PPh2) (3a). Coordination of the π bond to the
cobalt center causes enough of an angular distortion between
the phosphido group and Pb so that all three phosphorus centers
appear as singlets in the 31P NMR spectrum of 3a,b. This fact
is also supported by the X-ray data on 3a (vide infra). In the
case of 3b, the methylene group in the dione ring appears as an
AB quartet centered at δ 3.66 due to the diastereotopic nature
of these protons.
The kinetics for the conversion of 2a f 3a and 2b f 3b
were measured in order to establish whether product formation
proceeded via a dissociative CO loss scheme or an associative
attack of the ancillary π bond on the cobalt center, coupled with
simultaneous CO expulsion. Each reaction was studied by IR
spectroscopy in chlorobenzene solution over the temperature
range of ca. 77-103 °C. All reactions followed first-order
kinetics over a period of at least 3 half-lives, as evidenced by
(20) For examples of rate-limiting dissociative CO loss in mono- and
polynuclear compounds exhibiting large, positive values of ∆Hq (25-
30 kcal/mol) and low, positive values of ∆Sq (0-10 eu), see: (a)
Covey, W. D.; Brown, T. L. Inorg. Chem. 1973, 12, 2820. (b)
Sonnenberger, D.; Atwood, J. D. Inorg. Chem. 1981, 20, 3243. (c)
Payne, M. W.; Leussing, D. L.; Shore, S. G. J. Am. Chem. Soc. 1987,
109, 616.
(21) (a) Atwood, J. D. Inorganic and Organometallic Reaction Mechanisms;
Brooks/Cole Publishing: Monterey, CA, 1985. (b) Jordan, R. B.
Reaction Mechanisms of Inorganic and Organometallic Systems;
Oxford University Press: New York, 1998.
(22) The rate law in the absence of added CO (k2 > k-1[CO]) reduces to
the simple first-order expression: rate ) k1[RuCo(CO)5(P-P)(PPh2)].
(23) (a) Rossi, S.; Pursiainen, J.; Pakkanen, T. A. J. Organomet. Chem.
1990, 397, 81. (b) Rossi, S.; Pursiainen, J.; Ahlgren, M.; Pakkanen,
T. A. J. Organomet. Chem. 1990, 393, 403. (c) Albiez, T.; Bernhardt,
W.; von Schnering, C.; Roland, E.; Bantel, H.; Vahrenkamp, H. Chem.
Ber. 1987, 120, 141. (d) Schacht, H.-T.; Vahrenkamp, H. Chem. Ber.
1989, 122, 2253.
linear plots of ln(At A∞) vs time. The slopes of such plots
-
afforded the reported first-order rate constants given in Table
1. The quoted rate constants were obtained by monitoring the
decrease in the absorbance of the bma and bpcd bands at 1775

Selective Diphosphine Ligand Chelation
Inorganic Chemistry, Vol. 39, No. 26, 2000 6055
Table 2. X-ray Crystallographic Data and Processing Parameters
for CoRu(CO)4(µ-bma)(µ-PPh2) (3a)
space group
a, Å
b, Å
c, Å
P21/c, monoclinic
21.318(3)
9.3693(9)
20.352(2)
91.88(1)
4062.8(8)
C44H30CoO7P3Ru
923.65
â, deg
V, Å3
mol formula
fw
formula units/cell (Z)
4
F, g‚cm-3
1.510
λ(Mo KR), Å
collcn range, deg
tot. no. of data collcd
no. of indep data, I > 3σ(I)
Ra
0.710 73
2.0 e θ e 44.0
5446
2320
0.0633
b
Rw
0.0768
GOFc
0.82
weights
[0.04F2 + (σ(F))2]-1
2
c
a R ) Σ||Fo| - |Fc||Σ|Fo|. b Rw ) [Σw(|Fo| - |Fc|)2/Σw|Fo| ]1/2. GOF
2
) Σw(|Fo| - |Fc| /N - NP.
Table 3. Selected Bond Distances (Å) and Angles (deg) in
CoRu(CO)4(µ-bma)(µ-PPh2) (3a)a
Bond Distances
Ru-Co
2.674(3)
2.366(5)
2.229(5)
2.04(2)
1.81(2)
1.37(2)
1.19(2)
1.45(2)
Ru-P(1)
2.354(5)
2.318(5)
2.05(2)
1.81(2)
1.19(2)
1.39(2)
1.47(2)
1.47(3)
Ru-P(2)
Ru-P(3)
Co-P(3)
Co-C(11)
Figure 1. ORTEP drawing of the non-hydrogen atoms of CoRu(CO)4-
(µ-bma)(µ-PPh2) (3a) showing the thermal ellipsoids at the 50%
probability level.
Co-C(15)
P(2)-C(15)
O(13)-C(12)
O(14)-C(14)
C(11)-C(15)
P(1)-C(11)
O(12)-C(12)
O(13)-C(14)
C(11)-C(12)
C(14)-C(15)
is due to the tethering of the maleic anhydride moiety to the
cobalt atom in going from 2a to 3a. Here the substantial
diminution in the P(1)-Ru-P(3) bond angle from the idealized
180° bond angle at an octahedral center approaches the cis
relationship exhibited by P(2)-Ru-P(3) [89.4(2)°] and P(1)-
Ru-P(2) [80.4(2)°] and is expected to show a negligible or zero
phosphorus-phosphorus coupling.25 The coordination of the
maleic anhydride moiety to the cobalt center leads to a slight
elongation of the carbon-carbon π bond. The C(11)-C(15)
distance of 1.45(2) Å is ca. 0.11 Å longer than bma-substituted
complexes having a noncomplexed π bond.1b,7,8 The remaining
bond distances and angles are unexceptional and require no
comment.
Bond Angles
Co-Ru-P(1)
Co-Ru-P(3)
Co-Ru-C(2)
P(1)-Ru-P(3)
P(1)-Ru-C(2)
P(2)-Ru-C(1)
P(3)-Ru-C(1)
C(1)-Ru-C(2)
Ru-Co-C(4)
Ru-Co-C(15)
P(3)-Co-C(4)
Ru-P(3)-Co
70.3(1)
52.5(1)
96.2(5)
122.5(2)
90.3(5)
94.3(6)
121.2(6)
94.8(8)
157.0(6)
78.2(5)
103.8(7)
72.0(1)
Co-Ru-P(2)
75.5(1)
167.4(6)
80.4(2)
116.0(6)
89.4(2)
169.2(5)
90.9(5)
99.3(6)
80.3(4)
97.4(6)
41.3(6)
Co-Ru-C(1)
P(1)-Ru-P(2)
P(1)-Ru-C(1)
P(2)-Ru-P(3)
P(2)-Ru-C(2)
P(3)-Ru-C(2)
Ru-Co-C(3)
Ru-Co-C(11)
P(3)-Co-C(3)
C(11)-Co-C(15)
a Numbers in parentheses are estimated standard deviations in the
least significant digits.
Conclusions
The bidentate ligands bma and bpcd react with CoRu(CO)7-
(µ-PPh2) under thermolysis conditions and Me3NO activation
initially at the ruthenium center to afford CoRu(CO)5(diphos-
phine)(µ-PPh2). Thermolysis of these pentacarbonyl complexes
leads to the coordination of the π bond of the redox-active
diphosphine ligand to the cobalt center. The activation param-
eters and CO inhibition found for the reaction of 2a f 3b and
2b f 3b support a rate-limiting step involving dissociative CO
loss, followed by a rapid coordination of the maleic anhydride
and 1,3-dione π bonds.
slightly shorter than the 2.7858(7) Å (chelating) and 2.7580(9)
Å (bridging) Ru-Co bond distances reported in the isomeric
RuCo(CO)5(dppm)(µ-PPh2) complexes.11e The Ru-P(1) and
Ru-P(2) distances of 2.354(5) and 2.366(5) Å are not signifi-
cantly different unlike the two metal-phosphorus bond distances
associated with the phosphido moiety. The Ru-P(3) distance
of 2.318(5) and the Co-P(3) bond distance of 2.229(5) Å show
the asymmetric bonding of the three-electron donating PPh2
group to the Ru-Co vector, a feature that has been observed
in other phosphido-bridged metal-metal bonds.24
The near trans diaxial arrangement of P(1) and the phosphido
group P(3) is clearly seen in the ORTEP diagram, and the loss
of P-P coupling in the 31P NMR spectrum of 3a (vide supra)
is reflected by the P(1)-Ru-P(3) bond angle whose value is
122.5(2)°. This deviation from an idealized bond angle of 180°
Acknowledgment. Financial support from The Robert A.
Welch Foundation (Grant B-1039 to M.G.R.) is gratefully
acknowledged.
Supporting Information Available: Tables and figures of X-ray
crystallographic files that are not available in CIF format. This material
is available free of charge via the Internet at http://pubs.acs.org.
(24) (a) Krusic, P. J.; Baker, R. T.; Calabrese, J. C.; Morton, J. R.; Preston,
K. F.; Page, Y. L. J. Am. Chem. Soc. 1989, 111, 1262. (b) Powell, J.;
Sawyer, J. F.; Stainer, M. V. R. Inorg. Chem. 1989, 28, 4461. (c)
Davies, S. J.; Howard, J. A. K.; Pilotti, M. U.; Stone, F. G. A. J.
Chem. Soc., Chem. Commun. 1989, 190.
IC991279R
(25) Carty, A. J. AdV. Chem. Ser. 1982, No. 196, 163.