Enthalpies of reaction of Cp′Ru(COD)Cl (Cp′ = C5H5, C5Me5; COD = cyclooctadiene) with π-acceptor chelating phosphine ligands

Article abstract of DOI:10.1021/om980174d

The enthalpies of reaction of Cp′Ru(COD)Cl (Cp′ = C₅H₅, C₅Me₅; COD = 1,5- cyclooctadiene) with a series of π-acceptor bidentate phosphines, leading to the formation of Cp′Ru(PP)Cl complexes, have been measured by anaerobic calorimetry in THF at 30°C. These reactions are rapid and quantitative. Structural studies have been carried out on two complexes in this series. The overall relative order of stability established for these complexes in both Cp and Cp* systems is (PhO)₂PNMeNMeP(OPh)₂ > Ph₂PNMeNMeP Ph₂ ≈ (C₄H₄N)₂PCH₂-CH₂P(NC ₄H₄)₂ > ((EtO₂C)₂C₄H₂N)₂PCH ₂CH₂P(NC₄H₂(CO₂ Et)₂)₂. Present thermochemical data are discussed in terms of the nature of the bonding involved in the present complexes.

Full text of DOI:10.1021/om980174d

3000
Organometallics 1998, 17, 3000-3005
En th a lp ies of Rea ction of Cp ′Ru (COD)Cl (Cp ′ ) C5H5,
C5Me5; COD ) Cycloocta d ien e) w ith π-Accep tor
Ch ela tin g P h osp h in e Liga n d s
J inyu Shen, Edwin D. Stevens, and Steven P. Nolan*,†
Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148
Received March 9, 1998
The enthalpies of reaction of Cp′Ru(COD)Cl (Cp′ ) C5H5, C5Me5; COD ) 1,5- cyclooctadiene)
with a series of π-acceptor bidentate phosphines, leading to the formation of Cp′Ru(PP)Cl
complexes, have been measured by anaerobic calorimetry in THF at 30 °C. These reactions
are rapid and quantitative. Structural studies have been carried out on two complexes in
this series. The overall relative order of stability established for these complexes in both
Cp and Cp* systems is (PhO)2PNMeNMeP(OPh)2 > Ph2PNMeNMeP Ph2 ≈ (C4H4N)2PCH2-
CH2P(NC4H4)2 > ((EtO2C)2C4H2N)2PCH2CH2P(NC4H2(CO2 Et)2)2. Present thermochemical
data are discussed in terms of the nature of the bonding involved in the present complexes.
In tr od u ction
higher selectivity is obtained in some catalytic systems
modified with stronger π-acceptor and weak σ-donor
ligands.7 With the development of the coordination
chemistry of π-acceptor chelates, a study focusing on
their binding to transition metals would improve the
understanding of the reactivity and selectivity imparted
by these ancillary ligands.
Solution calorimetric studies have been useful in
providing insight into bonding and reactivity patterns8-10
and in directing the design of new metal-catalyzed
transformations.11 We have been involved in mapping
out the thermochemical surface of organometallic sys-
tems bearing phosphine ligands. Researchers have been
involved in describing metal-ligand systems in terms
of steric and electronic contributions using a variety of
methods. We have been interested in clarifying the
exact partitioning of these effects in tertiary phosphine-
based systems by means of solution calorimetry.12,13 We
have already achieved this in part for some ruthenium-
based organometallic systems (eqs 1 and 2).13
Chelating diphosphine ligands have been widely used
in organometallic chemistry. Kinetic, catalytic, and
structural studies have been performed on organome-
tallic systems incorporating this type of ligand.1 One
dramatic example of the use of diphosphine ligands is
illustrated in the different linear to branched product
ratios obtained when monodentate versus bidentate
phosphine ligands are bound to metals used to mediate
the oxo process.2 Recently, diphosphine compounds
with weak σ-donor and strong π-acceptor character, e.g.,
fluoroalkylphosphine chelate (CxFy)2PCH2CH2P(CxFy)2,3
bisphosphanyl hydrazides R2PN(Me)N(Me)PR2,4 and
N-pyrrolyl-substituted diphosphines,5,6 have attracted
some attention, largely because of their potential use
as ligands. Furthermore, it has been revealed that
† E-mail: spncm@uno.edu.
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Kawabata, Y.; Flowers, L. I. J . Chem. Soc., Chem. Commun. 1982,
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S0276-7333(98)00174-5 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 06/13/1998

Enthalpies of Reaction of Cp′Ru(COD)Cl
Organometallics, Vol. 17, No. 14, 1998 3001
Syn th esis. CpRu(COD)Cl (1),17 Cp*Ru(COD)Cl (2),18 and
all chelating diphosphines4,5d,6 were synthesized according to
literature procedures. All new complexes synthesized were
isolated using the procedure described for complex 3.
Cp Ru (P h 2P NMeNMeP P h 2)Cl (3). A 50 mL Schlenk tube
was charged with 62 mg (0.20 mmol) of CpRu(COD)Cl, 85 mg
(0.20 mmol) of Ph2PNMeNMePPh2, and 2 mL of dry THF.
After the mixture was stirred for 2 h at room temperature,
the resulting yellow precipitate was collected on a glass frit,
washed with hexane several times, and dried in a vacuum,
giving a yield of 51 mg (40%). 1H NMR (CD2Cl2): 2.75 (t, 6H,
J HP ) 4.0 Hz, NMe), 4.37 (s, 5H, Cp), 7.05 (m, 4H, Ph), 7.18
(m, 8H, Ph), 7.34 (m, 4H, Ph), 7.87 (m, 4H, Ph). 31P{1H} NMR
(CD2Cl2): 138.1. Anal. Calcd for C31H31ClN2P2Ru: C, 59.10;
H, 4.96; N, 4.45. Found: C, 59.23; H, 4.87; N, 4.35.
Cp Ru ((P h O)2P NMeNMeP (OP h )2)Cl (4). 4 was isolated
as a yellow microcrystalline solid in 82% yield. 1H NMR (CD2-
Cl2): 3.09 (t, 6H, J HP ) 3.9 Hz, NMe), 4.25 (t, 5H, J HP ) 1.2
Hz, Cp), 7.15-7.45 (m, 20H, Ph). 31P{1H} NMR (CD2Cl2):
171.2. Anal. Calcd for C31H31ClN2O4P2Ru: C, 53.65; H, 4.50;
N, 4.04. Found: C, 53.28; H, 4.77; N, 3.95.
Cp Ru ((C4H4N)2P CH2CH2P (NC4H4)2)Cl (5). 5 was iso-
lated as a yellow microcrystalline solid in 75% yield. 1H NMR
(CD2Cl2): 2.90 (m, 4H, CH2CH2), 4.92 (s, 5H, Cp), 6.29 (s, 4H,
NC4H4), 6.41 (s, 8H, NC4H4), 7.37 (s, 4H, NC4H4). 31P{1H}
NMR (CD2Cl2): 152.2. Anal. Calcd for C23H25ClN4P2Ru: C,
49.69; H, 4.53; N, 10.08. Found: C, 49.29; H, 4.58; N, 9.91.
Cp R u (((E t O2C)2C4H 2N)2P CH2CH 2P (NC4H 2(CO2E t )2)2)-
Cl (6). 6 was isolated as a yellow microcrystalline solid in
67% yield. 1H NMR (CD2Cl2): 1.23 (m, 24H, OCH2CH3), 2.96
(m, 4H, CH2CH2), 4.19 (m, 16H, OCH2CH3), 5.09 (s, 5H, Cp),
6.87 (s, 4H, NC4H2), 7.62 (s, 4H, NC4H2). 31P{1H} NMR (CD2-
Cl2): 158.9. Anal. Calcd for C47H57ClN4O16P2Ru: C, 49.85;
H, 5.07; N, 4.95. Found: C, 50.18; H, 5.34; N, 4.91.
THF
CpRu(COD)Cl(soln) + 2PR3(soln)
8
30 °C
CpRu(PR3)2Cl(soln) + COD(soln) (1)
THF
Cp*Ru(COD)Cl(soln) + 2PR3(soln)
8
30 °C
Cp*Ru(PR3)2Cl(soln) + COD(soln) (2)
Cp ) C5H5; Cp* ) C5Me5; PR3 ) tertiary phosphine
Recently, we have also studied the solution thermo-
chemistry of reactions involving CpRu(COD)Cl and
Cp*Ru(COD)Cl with some bidentate phosphine lig-
ands.12c,13d We now wish to expand on our solution
thermochemical studies of organoruthenium complexes
by focusing on quantitatively addressing the binding
ability of a series of interesting π-acceptor diphosphine
ligands to the CpRuCl and Cp*RuCl fragments and
examine how these ligands compare to more classical
chelating diphosphines.
Exp er im en ta l Section
Gen er a l Con sid er a tion . All manipulations involving
organoruthenium complexes were performed under an inert
atmosphere of argon or nitrogen using standard high-vacuum
or Schlenk-tube techniques or in a MBraun glovebox contain-
ing less than 1 ppm of oxygen and water. Tetrahydrofuran
was stored over sodium wire, distilled from sodium benzophe-
none ketyl, stored over Na/K alloy, and vacuum transferred
into flame-dried glassware prior to use. NMR spectra were
recorded using either a Varian Gemini 300 or 400 MHz
spectrometer. Calorimetric measurements were performed
using a Calvet calorimeter (Setaram C-80), which was periodi-
cally calibrated using the TRIS reaction14 or the enthalpy of
solution of KCl in water.15 The experimental enthalpies for
these two standard reactions compare very closely to literature
values. This calorimeter has been previously described,16 and
typical procedures are described below. Only materials of high
purity, as indicated by NMR spectroscopy, were used in the
calorimetric experiments. Experimental enthalpy data are
reported with 95% confidence limits. Elemental analyses were
performed by Desert Analytics, Tucson, AZ.
Cp *Ru (P h 2P NMeNMeP P h 2)Cl (7). 7 was isolated as a
yellow microcrystalline solid in 57% yield. 1H NMR (CD2Cl2):
1.37 (s, 15H, Cp*), 2.78 (t, J HP ) 3.9 Hz, 6H, NMe), 7.10-7.80
(m, 20H, Ph). 31P{1H} NMR (CD2Cl2): 137.7. Anal. Calcd
for C36H41ClN2P2Ru: C, 61.75; H, 5.90; N, 4.00. Found: C,
61.58; H, 5.97; N, 3.92.
Cp *Ru ((P h O)2P NMeNMeP (OP h )2)Cl (8). 8 was isolated
as a yellow microcrystalline solid in 40% yield. 1H NMR (CD2-
Cl2): 1.24 (t, 15H, J HP ) 2.7 Hz, Cp*), 2.97 (t, 6H, J HP ) 3.6
Hz, NMe), 7.12-7.60 (m, 20H, Ph). 31P{1H} NMR (CD2Cl2):
166.7. Anal. Calcd for C36H41ClN2O4P2Ru: C, 56.58; H, 5.41;
N, 3.67. Found: C, 56.31; H, 5.90; N, 3.46.
(11) (a) Nolan, S. P.; Stern, D.; Hedden, D.; Marks, T. J . In ref 8c,
pp 159-174. (b) Nolan, S. P.; Lopez de la Vega, R.; Mukerjee, S. L.;
Gonzalez, A. A.; Hoff, C. D. In ref 8b, pp 1491-1498. (c) Schock, L. E.;
Marks, T. J . J . Am. Chem. Chem. Soc. 1988, 110, 7701-7715. (d)
Marks, T. J .; Gagne´, M. R.; Nolan, S. P.; Schock, L. E.; Seyam, A. M.;
Stern, D. L. Pure Appl. Chem. 1989, 61, 1665-1672.
Cp *Ru ((C4H4N)2P CH2CH2P (NC4H4))2)Cl (9). 9 was iso-
lated as a yellow microcrystalline solid in 77% yield. 1H NMR
(CD2Cl2): 1.54 (t, 15H, J HP ) 3.0 Hz, Cp*), 2.60 (m, 2H, CH2-
CH2), 2.90 (m, 2H, CH2CH2), 6.30 (s, 4H, NC4H4), 6.37 (s, 8H,
NC4H4), 7.08 (d, 4H, NC4H4). 31P{1H} NMR (CD2Cl2): 152.5.
Anal. Calcd for C28H35ClN4P2Ru: C, 53.72; H, 5.63; N, 8.95.
Found: C, 53.42; H, 5.59; N, 8.82.
(12) (a) Nolan, S. P.; Martin, K. L.; Stevens, E. D.; Fagan, P. J .
Organometallics 1992, 11, 3947-3953. (b) Luo, L.; Fagan, P. L.; Nolan,
S. P. Organometallics 1993, 12, 4305-4311. (c) Luo, L.; Zhu, N.; Zhu,
N.-J .; Stevens, E. D.; Nolan, S. P.; Fagan, P. J . Organometallics 1994,
13, 669-675. (d) Li, C.; Cucullu, M. E.; McIntyre, R. A.; Stevens, E.
D.; Nolan, S. P. Organometallics 1994, 13, 3621-3627. (e) Luo, L.;
Nolan, S. P. Organometallics 1994, 13, 4781-4786. (f) Cucullu, M. E.;
Luo, L.; Nolan, S. P.; Fagan, P. J .; J ones, N. L.; Calabrese, J . C.
Organometallics 1995, 14, 289-296. (g) Luo, L.; Li, C.; Cucullu, M.
E.; Nolan, S. P. Organometallics 1995, 14, 1333-1338. (h) Serron, S.
A.; Nolan, S. P. Organometallics 1995, 14, 4611-4616. (i) Serron, S.
A.; Luo, L.; Li, C.; Cucullu, M. E.; Nolan, S. P. Organometallics 1995,
14, 5290-5297. (j) Li, C.; Ogasawa, M.; Nolan, S. P.; Caulton, K. G.
Organometallics 1996, 15, 4900-4903. (k) Serron, S. A.; Luo, L.;
Stevens, E. D.; Nolan, S. P.; J ones, N. L.; Fagan, P. J . Organometallics
1996, 15, 5209-5215.
(13) (a) Luo, L.; Nolan, S. P. Organometallics 1992, 11, 3483-3486.-
(b) Luo, L.; Nolan, S. P. Inorg. Chem. 1993, 32, 2410-2415. (c) Li, C.;
Nolan, S. P. Organometallics 1995, 14, 1327-1332. (d) Li, C.; Stevens,
E. D.; Nolan, S. P. Organometallics 1995, 14, 3791-3797.
(14) Ojelund, G.; Wadso¨, I. Acta Chem. Scand. 1968, 22, 927-937.
(15) Kilday, M. V. J . Res. Natl. Bur. Stand. (U.S.) 1980, 85, 467-
481.
Cp *Ru (((EtO2C)2C4H2N)2P CH2CH2P (NC4H2(CO2Et)2)2)-
Cl (10). 10 was isolated as a yellow microcrystalline solid in
87% yield. 1H NMR (CD2Cl2): 1.31 (m, 24H, OCH2CH3), 1.67
(s, 15H, Cp*), 2.85 (m, 2H, CH2CH2), 3.05 (m, 2H, CH2CH2),
4.26 (m, 16H, OCH2CH3), 6.95 (s, 4H, NC4H2), 7.55 (s, 4H,
NC4H2). 31P{1H} NMR (CD2Cl2): 156.9. Anal. Calcd for C52
67ClN4O16P2Ru: C, 51.94; H, 5.62; N, 4.66. Found: C, 51.46;
H, 6.13; N, 4.60.
-
H
NMR Titr a tion . Prior to every set of calorimetric experi-
ments involving a new reaction, an accurately weighed amount
(( 0.1 mg) of the organoruthenium complex was placed in a
Wilmad screw-capped NMR tube fitted with a septum, and
THF-d8 was subsequently added. The solution was titrated
(17) Albers, M. O.; Robinson, D. J .; Shaver, A.; Singleton, E.
Organometallics 1986, 5, 2199-2205.
(18) Fagan, P. J .; Mahoney, W. S.; Calabrese, J . C.; Williams, I. D.
Organometallics 1990, 9, 1843-1852.
(16) Nolan, S. P.; Hoff, C. D. J . Organomet. Chem. 1985, 282, 357-
362.

3002 Organometallics, Vol. 17, No. 14, 1998
Shen et al.
Ta ble 1. En th a lp ies of Su bstitu tion (k ca l/m ol) in
th e Rea ction a
Ta ble 2. En th a lp ies of Su bstitu tion (k ca l/m ol) in
th e Rea ction a
THF
THF
CpRu(COD)Cl(soln) + PP(soln)
8 CpRu(PP)Cl(soln) + COD(soln)
Cp*Ru(COD)Cl(soln) + PP(soln)
8 Cp*Ru(PP)Cl + COD(soln)
30 °C
30 °C
b
b
PP
-∆Hreacn
PP
-∆Hreacn
((EtO2C)2C4H2N)2PCH2CH2P(NC4H2(CO2Et)2)2
(C4H4N)2PCH2CH2P(NC4H4)2
Ph2PNMeNMePPh2
24.0(0.4)c
29.1(0.1)c
29.7(0.4)c
30.5(0.2)d
32.4(0.3)c
32.7(0.2)d
39.4(0.3)d
39.7(0.3)d
((EtO2C)2C4H2N)2PCH2CH2P(NC4H2(CO2Et)2)2
Ph2PNMeNMePPh2
19.4(0.2)c
22.6(0.2)c
23.2(0.4)c
26.4(0.2)c
29.8(0.2)d
31.3(0.2)d
34.8(0.2)d
35.6(0.3)d
(C4H4N)2PCH2CH2P(NC4H4)2
(PhO)2PNMeNMeP(OPh)2
Ph2PCH2CH2PPh2
Ph2PCH2CH2PPh2
(PhO)2PNMeNMeP(OPh)2
Ph2PCHCHPPh2
Ph2PCHCHPPh2
Et2PCH2CH2PEt2
Me2PCH2CH2PMe2
Me2PCH2CH2PMe2
Et2PCH2CH2PEt2
a
b
a
b
Cp* ) C5Me5; PP ) chelating diphosphine. Enthalpy values
Cp ) C5H5; PP ) chelating diphosphine. Enthalpy values
are reported with 95% confidence limits. c This work. Taken from
ref 12c.
d
are reported with 95% confidence limits. c This work. Taken from
ref 12d.
d
diffusion of diethyl ether into a CH2Cl2 solution of 8. A single
crystal having approximate dimensions 0.18 × 0.30 × 0.16 mm
was placed in a capillary tube and mounted on a Siemens
X-ray diffractometer fitted with a CCD area detector. Data
were collected using Mo KR radiation at 113 K. Cell dimen-
sions were determined by least-squares refinement of the
measured setting angles of 25 reflections with 30° < 2θ < 46°.
The structure was solved using direct methods (MULTAN80)
and refined by full-matrix least-squares techniques. Crystal
data for 8 are summarized in Table 3, and selected bond
distances and angles are listed in Table 5. Figure 2 presents
an ORTEP drawing of this molecule.
with a solution of the reactant of interest by injecting the latter
in aliquots through the septum with a microsyringe, followed
by vigorous shaking. The reactions were monitored by 1H and
31P NMR spectroscopy, and the reactions were found to be
rapid and quantitative, conditions necessary for accurate and
meaningful calorimetric results. These criteria were satisfied
for all organoruthenium reactions investigated.
Solu tion Ca lor im etr y. Ca lor im etr ic Mea su r em en t for
Reaction between CpRu (COD)Cl an d P h 2P NMeNMeP P h 2.
The mixing vessels of the Setaram C-80 were cleaned, dried
in an oven maintained at 120 °C, and then taken into the
glovebox. A 20-30 mg sample of recrystallized CpRu(COD)-
Cl (1) was accurately weighed into the lower vessel, which was
then closed and sealed with 1.5 mL of mercury. A 4 mL
amount of a stock solution of Ph2PNMeNMePPh2 (350 mg of
Ph2PNMeNMePPh2 in 25 mL of THF) was added, and the
remainder of the cell was assembled, removed from the
glovebox, and inserted in the calorimeter. The reference vessel
was loaded in an identical fashion with the exception that no
organoruthenium complex was added to the lower vessel.
After the calorimeter had reached thermal equilibrium at 30.0
°C (ca. 2 h), the calorimeter was inverted, thereby allowing
the reactants to mix. After the reaction had reached comple-
tion and the calorimeter had once again reached thermal
equilibrium (ca. 2 h), the vessels were removed from the
calorimeter. Conversion to CpRu(Ph2PNMeNMePPh2)Cl was
found to be quantitative under these reaction conditions. The
enthalpy of reaction, -25.8 ( 0.3 kcal/mol, represents the
average of three individual calorimetric determinations. The
final enthalpy value listed in Table 1 (-29.7 ( 0.4 kcal/mol)
represents the enthalpy of ligand substitution with all species
in solution. The enthalpy of solution of 1 (3.9 ( 0.1 kcal/mol)
has, therefore, been subtracted from the -25.8 ( 0.3 kcal/mol
value. This methodology represents a typical procedure
involving all organometallic compounds and all reactions
investigated in the present study. A compilation of enthalpies
of reaction for all ligands investigated in the study is presented
in Tables 1 and 2.
Str u ctu r e Deter m in ation of CpRu ((P h O)2P NMeNMeP -
(OP h )2)Cl (4). Yellow crystals of 4 were obtained by slow
diffusion of diethyl ether into a CH2Cl2 solution of 4. A single
crystal having approximate dimensions 0.24 × 0.35 × 0.20 mm
was placed in a capillary tube and mounted on a Siemens
X-ray diffractometer fitted with a CCD area detector. Data
were collected using Mo KR radiation at 110 K. Cell dimen-
sions were determined by least-squares refinement of the
measured setting angles of 25 reflections with 30° < 2θ < 46°.
The structure was solved using direct methods (MULTAN80)
and refined by full-matrix least-squares techniques. Crystal
data for 4 are summarized in Table 3, and selected bond
distances and angles are listed in Table 4. Figure 1 presents
an ORTEP of this molecule.
Resu lts
A facile entryway into the thermochemistry of Cp′Ru
(PP)Cl (Cp′ ) C5H5 and C5Me5) complexes is made
possible by the rapid and quantitative reaction of Cp′Ru-
(COD)Cl with the bidentate phosphine ligand (eq 3).
THF
Cp′Ru(COD)Cl(soln) + PP(soln)
8
30 °C
Cp′Ru(PP)Cl(soln) + COD(soln) (3)
Cp′ ) C5H5, C5Me5; PP ) chelating diphosphine
This type of bidentate phosphine binding reaction
appears to be general and was found to be rapid and
quantitative for all ligands calorimetrically investigated
at 30.0 °C in tetrahydrofuran. All reaction enthalpy
data shown in Tables 1 and 2 refer to solution-phase
values and include the enthalpy of solution of Cp′Ru-
(COD)Cl.
Discu ssion
Solu tion Th er m och em istr y. Recent work on Cp′Ru-
(COD)Cl (Cp′ ) Cp, Cp*) has shown that cyclooctadiene
(COD) is very weakly bound to the Cp′RuCl moiety. The
labile nature of these ruthenium-diene bonds has
already been exploited in the investigation of phosphine
substitution reactions as shown in eqs 1 and 2.6a,12i,f This
same approach was also tested with some bidentate
ligands (eq 4) for which conversion of Cp′Ru(COD)Cl to
Cp′Ru(PP)Cl complexes was also found to be quan-
titative.12c,d The donor properties of tertiary phos-
THF
Cp′Ru(COD)Cl(soln) + PP(soln)
8
30 °C
Cp′Ru(PP)Cl(soln) + COD(soln) (4)
PP )
dppm, dmpm, dppb, dppe, dppp, dppv, depe, dmpe
Str u ctu r e Deter m in ation of Cp*Ru ((P h O)2P NMeNMeP -
(OP h )2)Cl (8). Yellow crystals of 8 were obtained by slow

Enthalpies of Reaction of Cp′Ru(COD)Cl
Organometallics, Vol. 17, No. 14, 1998 3003
Ta ble 3. Cr ysta llogr a p h ic Da ta for 4 a n d 8
empirical formula
fw
temp, K
C31H31ClN2O4P2Ru
694.04
110(2)
C36H41ClN2O4P2Ru
764.17
113(2)
wavelength, Å
cryst syst
space group
unit cell dimens
a, Å
0.710 73
monoclinic
P21
0.710 73
triclinic
P1h
15.5617(5)
12.1883(4)
b, Å
c, Å
9.9700(3)
20.3622(7)
16.9193(6)
18.7914(6)
R, deg
90
79.970(1)
75.140(1)
69.541(1)
3493.9(2)
â, deg
108.562(1)
90
2994.9(2)
γ, deg
V, Å3
Z
4
4
D(calcd), g/cm3
abs coeff, cm-1
F(000)
1.539
0.759
1416
1.453
0.658
1576
cryst size, mm
θ range for data collcn, deg
index ranges
no. of collcd reflns
no. of indep reflns
refinement method
data/restraints/params
goodness of fit on F2
final R index [I > 2σ(I)]
R indices (all data)
largest diff peak and hole, e Å-3
0.24 × 0.35 × 0.20
0.16 × 0.18 × 0.30
1.05-35.87
1.13-35.67
-25 e h e 22, -16 e k e 16, -32 e l e 33
49 044
25 744 (Rint ) 0.1535)
full-matrix least-squareson F2
25744/1/744
-7 e h e 7, -26 e k e 27, 0 e l e 30
63 310
14 830 (Rint ) 0.0851)
full-matrix least-squares on F2
14830/996/938
0.488
1.219
R1 ) 0.0444, wR2 ) 0.1346
R1 ) 0.0452, wR2 ) 0.1377
2.079 and -1.941
R1 ) 0.1066, wR2 ) 0.2328
R1 ) 0.1376, wR2 ) 0.2533
2.849 and -2.159
Ta ble 4. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for 4
Ta ble 5. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for 8
Bond Lengths
Bond Lengths
Ru(1)-Cl(1)
Ru(1)-P(1)
Ru(1)-P(2)
P(1)-O(1)
P(1)-O(2)
P(2)-O(3)
Ru(1)-Cp(c)
2.4304(6)
2.2129(6)
2.1905(6)
1.633(2)
1.631(2)
1.613(2)
1.879(2)
P(1)-N(1)
P(2)-N(2)
N(1)-C(59)
P(2)-O(4)
N(1)-N(2)
N(2)-C(60)
1.668(2)
1.725(2)
1.463(3)
1.613(2)
1.433(3)
1.473(3)
Ru(1)-Cl(1)
Ru(1)-P(1)
Ru(1)-P(2)
P(1)-O(1)
2.438(2)
2.221(2)
2.213(3)
1.633(6)
1.637(7)
1.611(8)
1.890(4)
P(1)-N(1)
P(2)-N(2)
N(1)-C(25)
P(2)-O(4)
N(1)-N(2)
N(2)-C(26)
1.657(9)
1.736(6)
1.470(10)
1.622(5)
1.414(12)
1.499(10)
P(1)-O(2)
P(2)-O(3)
Ru(1)-Cp*(c)
Bond Angles
Bond Angles
P(1)-Ru(1)-P(2)
N(1)-N(2)-P(2)
Ru(1)-P(2)-N(2)
O(1)-P(1)-N(1)
O(1)-P(1)-Ru(1)
P(1)-N(1)-C(59)
O(4)-P(2)-Ru(1)
P(2)-N(2)-C(60)
N(2)-N(1)-C(59)
C(13)-O(3)-P(2)
C(19)-O(4)-P(2)
P(2)-Ru(1)-Cl(1)
80.39(2)
106.2(2)
113.50(7)
103.28(10)
122.82(7)
125.4(2)
110.71(7)
118.1(2)
115.2(2)
122.0(2)
127.8(2)
90.99(2)
P(1)-N(1)-N(2)
Ru(1)-P(1)-N(1)
O(1)-P(1)-O(2)
O(2)-P(1)-N(1)
O(2)-P(1)-Ru(1)
O(3)-P(2)-Ru(1)
O(3)-P(2)-O(4)
N(1)-N(2)-C(60)
C(1)-O(1)-P(1)
C(7)-O(2)-P(1)
P(1)-Ru(1)-Cl(1)
119.3(2)
P(1)-Ru(1)-P(2)
N(1)-N(2)-P(2)
Ru(1)-P(2)-N(2)
O(1)-P(1)-N(1)
O(1)-P(1)-Ru(1)
P(1)-N(1)-C(25)
O(4)-P(2)-Ru(1)
P(2)-N(2)-C(26)
N(2)-N(1)-C(25)
C(7)-O(3)-P(2)
C(13)-O(4)-P(2)
P(2)-Ru(1)-Cl(1)
80.03(10)
107.5(5)
112.8(4)
100.8(3)
122.8(2)
125.7(8)
110.9(3)
116.8(6)
114.4(8)
124.3(6)
128.9(6)
89.98(8)
P(1)-N(1)-N(2)
Ru(1)-P(1)-N(1)
O(1)-P(1)-O(2)
O(2)-P(1)-N(1)
O(2)-P(1)-Ru(1)
O(3)-P(2)-Ru(1)
O(3)-P(2)-O(4)
N(1)-N(2)-C(26)
C(1)-O(1)-P(1)
C(19)-O(2)-P(1)
P(1)-Ru(1)-Cl(1)
119.7(5)
111.8(3)
93.6(4)
111.02(8)
93.15(10)
102.53(10)
120.73(7)
125.75(7)
102.20(10)
111.6(2)
116.6(2)
123.4(2)
90.46(2)
102.6(4)
121.5(2)
126.6(2)
103.9(4)
112.1(7)
120.8(5)
128.0(7)
91.61(7)
F igu r e 2. ORTEP diagram of Cp*Ru((PhO)2PNMeNMeP-
(OPh)2)Cl (8). Ellipsoids are drawn in with 50% probability.
F igu r e 1. ORTEP diagram of CpRu((PhO)2PNMeNMeP-
(OPh)2)Cl (4). Ellipsoids are drawn in with 50% probability.
tallic chemistry is to examine such effects while main-
taining one of the two factors constant. Using this
method, we have found from calorimetric studies that
steric factors are the overwhelming component influenc-
ing the magnitude of the enthalpy of reaction in eqs 1
and 2.6a,12i,f In reaction 4, the displacement of COD by
bidentate phosphine ligands results in the incorporation
of the Cp′RuCl moiety into the chelate structures,
phine ligands can be modulated by electronic and steric
parameter variation. This is usually achieved by varia-
tion of the substituents bound to the phosphorus atom.
The binding affinities of specific phosphine ligands are
commonly explained in terms of steric and electronic
effects; yet these two factors are not easily separated.
A common approach in physical inorganic/organome-

3004 Organometallics, Vol. 17, No. 14, 1998
Shen et al.
producing metallacyclic rings. Enthalpies of this type
of reaction showed that ligand displacements involving
more basic alkyl-substituted phosphines prove to be
more exothermic.
To study the binding of a transition metal with
π-acceptor chelates and the relative importance of steric
versus electronic ligand effects in the reaction of Cp′Ru-
(COD)Cl with bidentate phosphine ligands, a thermo-
chemical study of ligand substitution involving the
newly reported ligands Ph2PNMeNMePPh2, (PhO)2-
PNMeNMeP(OPh)2, (C4H4N)2PCH2CH2P(NC4H4)2, and
((EtO2C)2C4H2N)2PCH2CH2P(NC4H2(CO2Et)2)2 was un-
dertaken (eq 5).
Ph2PNMeNMePPh2, (C4H4N)2PCH2CH2P(NC4H4)2, and
Ph2PCH2CH2PPh2 have similar steric but quite different
electronic characters. Steric effects appear to again
predominate, as illustrated by the reaction enthalpies
of CpRu(COD)Cl with (PhO)2PNMeNMeP(OPh)2, which
is less sterically demanding and more exothermic by 2.7
kcal/mol than Ph2PNMeNMePPh2 and (EtO2C)2C4H2N)2-
PCH2CH2P(NC4H2(CO2Et)2)2), which is more sterically
demanding and less exothermic by 5.7 kcal/mol than
Ph2PNMeNMePPh2. The previously demonstrated im-
portance of sterics in this system should not be con-
strued as stating that ligand electronics do not contrib-
ute to the magnitude of the enthalpy of reaction. The
electronic effects in the last two cases should not be
ignored. We have shown that phosphite ligands are
excellent binders to ruthenium in this system.12k We
also are aware that the carboalkoxy substituent on the
pyrrolyl ring bound to the phosphine has a net electron-
withdrawing effect. The observed effect must, therefore,
represent a combination of steric and electronic effects.
THF
Cp′Ru(COD)Cl(soln) + PP(soln)
8
30 °C
Cp′Ru(PP)Cl(soln) + COD(soln) (5)
PP ) Ph2PNMeNMePPh2,
(PhO)2PNMeNMeP(OPh)2,
(C4H4N)2PCH2CH2P(NC4H4)2,
In the Cp*-based system, the reaction enthalpies of
Cp*Ru(COD)Cl with Ph2PNMeNMePPh2 and (C4H4N)2-
PCH2CH2P(NC4H4)2 are almost identical but about 6
kcal/mol lower than that involving Ph2PCH2CH2PPh2.
This difference must be an electronic effect since these
ligands are thought to be isosteric. On the other hand,
the reaction enthalpy of Cp*Ru(COD)Cl with the π-ac-
ceptor (PhO)2PNMeNMeP(OPh)2 is 3 kcal/mol higher
than that with Ph2PNMeNMePPh2 and 3 kcal/mol lower
than that with Ph2PCH2CH2PPh2. As already stated,
the phosphite functionality yields a better binder, the
presence of the OPh and N(Me) groups within the ligand
affords a phosphite which is less donating but still a
phosphite. These observations suggest that ligand
steric and electronic effects must both play a role in
dictating the magnitude of the enthalpy of this reaction.
A partitioning of the relative steric vs electronic param-
eters appears difficult in the present case. This is
further complicated by the presence of π effects dis-
played by these ligand types. We do not presume to
offer a definite answer as to the partitioning of σ and π
effects in the present system but simply report the
overall thermodynamic stability afforded by these ligands.
Efforts to partition such contributions are in progress.20
When the enthalpy data of the Cp and Cp* systems are
compared, a good linear fit (R ) 0.93) is obtained (Figure
3), suggesting similar effects at play in both systems.
((EtO2C)2C4H2N)2PCH2CH2P(NC4H2(CO2Et)2)2
Ph2PNMeNMePPh2 and (PhO)2PNMeNMeP(OPh)2
are two representatives of the bis(phosphanyl) hy-
drazide chelating ligand family, which have chain
lengths similar to Ph2PCH2CH2PPh2. However, their
coordination chemistry with molybdenum and tungsten
indicates that they are good π-acceptors.4 A variety of
spectroscopic, structural, and thermochemical measure-
ments have shown that N-pyrrolyl-substituted phos-
phines, which are isosteric with their phenylated coun-
terparts, are good π-acceptors.5,6 It has been demon-
strated that the substituent parameter Xi for the N-
pyrrolyl functionality is approximately 12. The π-ac-
ceptor character of these ligands is thus found to
exceed that of alkoxy/aryloxy- (-OPh, Xi ) 9.7) and
perfluoroaryl-substituted phosphines (-C6F5, Xi ) 11.2)
and approaches that found for fluoroalkylphosphines.19
On the basis of these observations, the diphosphine
(C4H4N)2PCH2CH2P(NC4H4)2 and its carboethoxy de-
rivative ((EtO2C)2C4H2N)2PCH2CH2P(NC4H2(CO2Et)2)2
were designed and expected to behave as good π-accep-
tor bidentate ligands. Moloy and co-workers have found
that the respective carbonyl stretching frequencies of
Mo(CO)4((E t O2C)2C4H 2N)2P CH 2CH 2P (NC4H 2(CO2-
Et)2)2) and Mo(CO)4((C4H4N)2PCH2CH2P(NC4H4)2) are
32 and 23 cm-1 higher than that of Mo(CO)4(Ph2PCH2-
CH2PPh2), clearly indicating that N-pyrrolyl-substituted
bidentate phosphine ligands are good π-acceptors.6 It
should also be mentioned that (C4H4N)2PCH2CH2P-
(NC4H4)2 and Ph2PNMeNMePPh2 are most likely isos-
teric with Ph2PCH2CH2PPh2.5 Enthalpy data are pre-
sented in Tables 1 and 2 for the CpRu(PP)Cl and
Cp*Ru(PP)Cl systems, along with selected data for
previously investigated chelating phosphine ligands12c,d
In the Cp system, the enthalpies of the reactions of
CpRu(COD)Cl with Ph2PNMeNMePPh2 and (C4H4N)2-
PCH2CH2P(NC4H4)2 are almost identical to that of Ph2-
PCH2CH2PPh2. This result suggests that electronic
effects have little influence over the magnitude of the
enthalpy of this reaction, given that chelating ligands
Comparison between the Cp and Cp* data affords a
look into the effects of electronic properties of the
ancillary ligand as it contributes to the enthalpy of
reaction. On average, there exists a difference between
the enthalpies of reaction involving the same phosphine
ligand of 6.4 kcal/mol, favoring the Cp system. Since
the Cp* is more electron donating than Cp, the Cp*
system accommodates less electron density from the
incoming two-electron donor,2c therefore leading to lower
enthalpies of ligand substitution. This point has been
described previously in our study on the CpRu(PR3)2Cl
and Cp*Ru(PR3)2Cl systems, where the average differ-
ence was 5.9 kcal/mol.12f
(20) Haar, C. M.; Nolan, S. P.; Fernandez, A.; Giering, W. Manu-
script in preparation.
(19) Tolman, C. A. Chem. Rev. 1977, 77, 313-348.

Enthalpies of Reaction of Cp′Ru(COD)Cl
Organometallics, Vol. 17, No. 14, 1998 3005
tances in 4 (Ru-P ) 2.2017(6) Å, Ru-Cp ) 1.879(2) Å)
are shorter than those found in 8 (Ru-P ) 2.217(3) Å,
Ru-Cp* ) 1.890(4) Å).
The average P-N distances obtained in 4 (1.697(2)
Å) and 8 (1.697(9) Å) are similar to that observed in
the complex Mo(CO)4((PhO)2PNMeNMeP(OPh)2) (1.698-
(4) Å)4b but shorter than typical P-N bonds (1.75-1.80
Å).4a,24 This is possibly due to the nitrogen-phosphorus
pπ-dπ interaction. It is also interesting to note that
unequal Ru-C (carbon of the Cp or Cp* rings) distances
are also found in 4 and 8, similar to those in CpRu(Ph2-
PCH2CH2PPh2)Cl21 and CpRu(Ph2CH2CH(CH3)PPh2)-
Cl.25 In each case, the shorter Ru-C distances are
found trans to the chloro ligand, with longer Ru-C
distances trans to P atoms, consistent with the differing
trans influences of Cl and P.
A most interesting structural comparison is with
CpRu(Ph2PCH2CH2PPh2)Cl,21 which does not contain
a fragment that could provide a π contribution to the
bonding. In 4, the Ru-Cp(centroid) distance is 1.879
Å, compared to 1.853 Å in the diphos complex. Signifi-
cant differences are also present in the Ru-P distances
(2.2129 and 2.2863 Å for 4 and the diphos complex,
respectively). Both variations in the metric parameters
illustrate the push-pull influence of the presence of
ligands with π-bonding capabilities.
Figu r e 3. Enthalpies of reaction (kcal/mol) of Cp*Ru(PP)Cl
versus CpRu(PP)Cl; slope ) 1.04, R ) 0.93.
Str u ctu r a l Stu d ies of Cp Ru ((P h O)2P NMeNMeP -
(OP h )2)Cl (4) a n d Cp *R u ((P h O)2P NMeNMeP (O-
P h )2)Cl (8). To help clarify the enthalpy trends ob-
served, a structural study was conducted on two related
complexes: CpRu((PhO)2PNMeNMeP(OPh)2)Cl (4) and
Cp*Ru((PhO)2PNMeNMeP(OPh)2)Cl (8). As seen in
Figures 1 and 2, the environment around the Ru atoms
in 4 and 8 corresponds to a general three-legged piano-
stool structure. The average Ru-P bond length in 4 is
2.2017(6) Å, clearly short when compared with that in
CpRu(Ph2PCH2CH2PPh2)Cl (2.2776 Å).21 The phosphite
donor property of the ligand appears to be attenuated
by the N(Me) acceptor property. The difference in the
Ru-P bond length qualitatively follows the reaction
enthalpy trend: the reaction enthalpy value of (Ph-
O)2PNMeNMeP(OPh)2 is 1.9 kcal/mol more exothermic
than that of Ph2PCH2CH2PPh2. Similarly, the average
Ru-P bond length (2.217(3) Å) in 8 is also much shorter
than those observed for classical tertiary phosphine,
which are usually in the range of 2.30-2.35 Å in
[Cp*Ru(PR3)2L] neutral or cationic complexes,12d,22 and
even shorter than those observed in Cp*Ru(P(NC4H4)3)2-
Cl (2.2598(11) Å)5a and Cp*Ru(tmbp)Cl (2.2425(2) Å,
tmbp ) 4,4′,5,5′-tetramethyl-2,2′-biphosphinine),23 which
contain the π-acceptors P(NC4H4)3 and tmbp, respec-
tively. The observed distance compares more closely to
the Ru-P distance found in Cp*Ru(P(OMe)3)2Cl (2.232
Å).12k In view of the metal basicity difference provided
by Cp and Cp*, the Ru-P and Ru-Cp′(centroid) dis-
Con clu sion
A relative enthalpy scale has been established for the
binding of π-acceptor chelating phosphine ligands to the
CpRuCl and Cp*RuCl moieties that enables thermo-
chemical comparisons with classical bidentate phos-
phine ligands. The labile nature of the COD ligand in
CpRu(COD)Cl and Cp*Ru(COD)Cl was used to gain
access into the thermochemistry of ligand substitution
for bidentate π-acceptor ligands and also shows these
reactions to be of synthetic use for isolation of these
compounds. A combination of thermochemistry and
X-ray diffraction investigations allows us to state that,
as in previously investigated systems, the ligands
investigated in this study display π-acceptor capabili-
ties.
Ack n ow led gm en t. The National Science Founda-
tion (Grant No. CHE-9631611) and Dupont (Educational
Aid Grant) are gratefully acknowledged for financial
support of this research.
Su p p or tin g In for m a tion Ava ila ble: Tables of anisotro-
pic thermal parameters, positional parameters, bond angles,
and bond lengths for 4 and 8 (29 pages). Ordering and
Internet access information are given on any current masthead
page.
(21) Pearson, W. H.; Shade, J . E.; Brown, J . E.; Bitterwolf, T. E.
Acta Crystallogr. 1996, C52, 1106-1110.
OM980174D
(22) See, for example: (a) Linder, E.; Haustein, M.; Fawzi, R.;
Steimann, M.; Wegner, P. Organometallics 1994, 13, 5021-5029. (b)
Le Lagadec, R.; Roman, E.; Toupet, L.; Muller, U.; Dixneuf, P. H.
Organometallics 1994, 13, 5030-5039. (c) Bruce, M. I.; Humphrey, M.
G.; Patrick, J . M.; White, A. H. Aust. J . Chem. 1983, 36, 2065-2072.
(23) Floch, P. Le.; Mansuy, S.; Ricard, L.; Mathey, F.; J utand, A.;
Amatore, C. Organometallics 1996, 15, 3267-3274.
(24) (a) Corbridge, D. E. C. Phosphorus, 3rd ed.; Elsevier: Amster-
dam, 1985. (b) Alcock, H. R. Phosphorus Nitrogen Compounds;
Academic Press: New York, 1972. (c) Keat, R. Top. Curr. Chem. 1982,
102, 89-116.
(25) Morandini, F.; Consiglio, G.; Straub, B.; Ciani, G.; Sironi, A. J .
Chem. Soc., Dalton Trans. 1983, 2293-2298.