Solution thermochemical and structural studies of ligand substitution of N-pyrrolyl phosphine ligands in the (p-cymene)RuCl2(PR3) system

Article abstract of DOI:10.1021/om970809t

The enthalpies of reaction of [(p-cymene)RuCl₂]₂ (p-cymene = (CH₃)₂CHC₆H₄CH₃) with a series of N-substituted tertiary phosphine ligands, leading to the formation of (p-cymene)-RuCl₂(PR₃) complexes (PR₃ = tertiary phosphine) have been measured by solution calorimetry in CH₂Cl₂ at 30°C. The overall relative order of stability, within this series, is as follows: P(NC₄H₄)₃ < P(NC₄H₄)₂(C₆H₅) < P(NC₄H₄)(C₆H₅)₂ < P(NC₄H₈)₃. Structural studies have been performed on three complexes in the (p-cymene)RuCl₂(PR3) system, PR₃ = P(NC₄H₄)₃, P(NC₄H₄)₂(C₆H₅), and PBz₃. Thermochemical and structural data are compared to provide an understanding of the bonding involving these N-pyrrolyl-substituted phosphine ligands.

Full text of DOI:10.1021/om970809t

104
Organometallics 1998, 17, 104-110
Solu tion Th er m och em ica l a n d Str u ctu r a l Stu d ies of
Liga n d Su bstitu tion of N-P yr r olyl P h osp h in e Liga n d s in
th e (p-cym en e)Ru Cl2(P R3) System
Scafford Serron and Steven P. Nolan*,†
Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148
Yuri A. Abramov and Lee Brammer
Department of Chemistry, University of MissourisSt. Louis, St. Louis, Missouri 63121-4499
J effrey L. Petersen
Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506-6045
Received September 12, 1997X
The enthalpies of reaction of [(p-cymene)RuCl2]2 (p-cymene ) (CH3)2CHC6H4CH3) with a
series of N-substituted tertiary phosphine ligands, leading to the formation of (p-cymene)-
RuCl2(PR3) complexes (PR3 ) tertiary phosphine) have been measured by solution calorimetry
in CH2Cl2 at 30 °C. The overall relative order of stability, within this series, is as follows:
P(NC4H4)3 < P(NC4H4)2(C6H5) < P(NC4H4)(C6H5)2 < P(NC4H8)3. Structural studies have
been performed on three complexes in the (p-cymene)RuCl2(PR3) system, PR3 ) P(NC4H4)3,
P(NC4H4)2(C6H5), and PBz3. Thermochemical and structural data are compared to provide
an understanding of the bonding involving these N-pyrrolyl-substituted phosphine ligands.
In tr od u ction
Cp*Ru(COD)Cl + 2PR3 f Cp*Ru(PR3)2Cl + COD
(1)
The utilization of tertiary phosphine ligands in orga-
nometallic chemistry and catalysis is widespread.1,2 In
spite of the vast amount of information focusing on
PR3-transition-metal complexes,3 few thermodynamic
data regarding heats of binding of these ligands to metal
centers exist, eqs 1-5.4-8 Interesting catalytic develop-
ments involving organoruthenium complexes would
CpRu(COD)Cl + 2PR3 f CpRu(PR3)2Cl + COD (2)
(BDA)Fe(CO)3 + 2PR3 f
trans-(PR3)2Fe(CO)3 + BDA (3)
Rh(acac)(CO)2 + PR3 f Rh(acac)(CO)(PR3) + COD
† Email: spncm@uno.edu.
X Abstract published in Advance ACS Abstracts, December 15, 1997.
(1) (a) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry, 2nd
ed.; University Science: Mill Valley, CA, 1987. (b) Parshall, G. W.;
Ittel, S. D. Homogeneous Catalysis Wiley Interscience: New York,
1992.
(4)
[RhCl(CO)2]2 + 4PR3 f 2RhCl(CO)(PR3)2 + 2 CO
(5)
(2) Homogeneous Catalysis with Metal Phosphine Complexes;
Pignolet, L. H., Ed.; Plenum: New York, 1983.
(3) (a) Noyori, R. Asymmetric Catalysis in Organic Synthesis Wiley
and Sons, Inc.: New York, 1994 and references cited therein. (b) Burk,
M. J .; Harper, G. P.; Kalberg, C. S. J . Am. Chem. Soc. 1995, 117, 4423-
4424 and references cited.
Cp ) C5H5; Cp* ) C5Me5;
BDA ) PhCHdCHCOMe;
PR3 ) P(NC4H4)3-xPhx (x ) 0-2)
(4) For leading references in this area, see: (a) Nolan, S. P. Bonding
Energetics of Organometallic Compounds. In Encyclopedia of Inorganic
Chemistry; J . Wiley and Sons: New York, 1994. (b) Hoff, C. D. Prog.
Inorg. Chem. 1992, 40, 503-561. (c) Martinho Simo˜es, J . A.; Beau-
champ, J . L. Chem. Rev. 1990, 90, 629-688. (d) Bonding Energetics
In Organometallic Compounds, Marks, T. J ., Ed. ACS Symposium
Series 428; American Chemical Society: Washington, DC, 1990. (e)
Marks, T. J ., Ed. Metal-Ligand Bonding Energetics in Organotransition
Metal Compounds; Polyhedron Symposium-in-Print, 1988, 7. (f) Skin-
ner, H. A.; Connor J . A. In Molecular Structure and Energetics;
Liebman, J . F., Greenberg, A., Eds; VCH: New York, 1987; Vol. 2,
Chapter 6. (g) Skinner, H. A.; Connor, J . A. Pure Appl. Chem. 1985,
57, 79-88. (h) Pearson, R. G. Chem. Rev. 1985, 85, 41-59. (i) Mondal,
J . U.; Blake, D. M. Coord. Chem. Rev. 1983, 47, 204-238. (j) Mansson,
M. Pure Appl. Chem. 1983, 55, 417-426. (k) Pilcher, G.; Skinner, H.
A. In The Chemistry of the Metal-Carbon Bond; Harley, F. R., Patai,
S., Eds.; Wiley: New York, 1982; pp 43-90. (l) Connor, J . A. Top. Curr.
Chem. 1977, 71, 71-110.
surely benefit from a better understanding of ligand
binding affinity/thermochemical studies. Enthalpies of
reaction involving a variety of phosphine ligands and
(5) For a recent review of the energetics of phosphorus(III) ligands
to transition-metal centers, see: Dias, P. B.; Minas de Piedade, M. E.;
Martinho Simo˜es, J . A. Coord. Chem. Rev. 1994, 135/ 136, 737-807.
(6) Nolan, S. P.; Lopez de la Vega, R.; Hoff, C. D. Organometallics
1986, 5, 2529-2537.
(7) (a) Manzer, L. E.; Tolman, C. A. J . Am. Chem. Soc. 1975, 97,
1955-1986. (b) Tolman, C. A.; Reutter, D. W.; Seidel, W. C. J .
Organomet.Chem. 1976, 117, C30-C33.
(8) (a) Nolan, S. P.; Hoff, C. D. J . Organomet. Chem. 1985, 290, 365-
373. (b) Mukerjee, S. L.; Nolan, S. P.; Hoff, C. D.; de la Vega, R. Inorg.
Chem. 1988, 27, 81-85.15.
S0276-7333(97)00809-1 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 01/05/1998

Substitution of N-Pyrrolyl Phosphine Ligands
Organometallics, Vol. 17, No. 1, 1998 105
ruthenium,9 iron,10 and rhodium11 systems have been
investigated. We have recently focused our thermo-
chemical research efforts in the direction of a new class
of pyrrolyl-substituted tertiary phosphine ligands. These
ligands bind to metal centers with variable degrees of
σ- and π-interactions.12 In the hope of delineating the
relative σ and π contributions, we present in this paper
a combination of thermochemical and structural data
probing the role of these ligands in the [(p-cymene)-
RuCl2(PR3)] system.
Ta ble 1. En th a lp ies of Su bstitu tion (k ca l/m ol) in
th e Rea ction
CH2Cl2
[RuCl2(p-cymene)]2(soln) + 2L(soln)
8
30 °C
2RuCl2(p-cymene)(PR3)(soln)
a,b
L
complex
-∆Hrxn
P(NC4H4)3
RuCl2(p-cymene)(P(NC4H4)3))
30.3 ( 0.3c
P(C6H5)(NC4H4)2 RuCl2(p-cymene)(PPh(NC4H4)2)
P(p-CF3C6H4)3
P(C6H5)2(NC4H4) RuCl2(p-cymene)(PPh2(NC4H4))
PCy3
PCy2Ph
P(p-ClC6H4)3
P(OPh)3
PiPr3
31.1 ( 0.3c
RuCl2(p-cymene)(P(p-CF3C6H4)3) 33.4 ( 0.1
34.4 ( 0.1c
34.4 ( 0.2
34.6 ( 0.1
34.8 ( 0.2
35.5 ( 0.3
35.6 ( 0.2
36.3 ( 0.1
36.5 ( 0.3
37.6 ( 0.3
38.8 ( 0.4
RuCl2(p-cymene)(PCy3)
RuCl2(p-cymene)(PCy2Ph)
RuCl2(p-cymene)(P(p-ClC6H4)3)
RuCl2(p-cymene)(P(OPh)3)
RuCl2(p-cymene)(PiPr3)
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations involving
organoruthenium complexes were performed under inert
atmospheres of argon or nitrogen using standard high-vacuum
or Schlenk tube techniques or in a Vacuum Atmospheres
glovebox containing less than 1 ppm of oxygen and water.
Methylene chloride was distilled from P2O5 into flame-dried
glassware prior to use. Only materials of high purity, as
indicated by NMR spectroscopy, were used in the calorimetric
experiments. NMR spectra were recorded using a Varian
Gemini 300 MHz spectrometer. Calorimetric measurements
were performed using a Calvet calorimeter (Setaram C-80)
which was periodically calibrated using the TRIS reaction13
or the enthalpy of solution of KCl in water.14 The experimen-
tally-determined enthalpies for these two standard calibration
reactions are the same within experimental error to literature
values. This calorimeter has been previously described,15 and
typical procedures are described below. Experimental en-
thalpy data are reported with 95% confidence limits.
1H NMR Titr a tion s. Prior to every set of calorimetric
experiments involving a new ligand, 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
CD2Cl2 was subsequently added. The solution was titrated
with a solution of the ligand of interest by injecting the latter
in aliquots through the septum with a microsyringe, followed
by vigorous shaking. The reactions were monitored by 1H
NMR spectroscopy, and the reactions were found to be rapid,
clean, and quantitative under experimental calorimetric condi-
tions. These conditions are necessary for accurate and mean-
PPh3
RuCl2(p-cymene)(PPh3)
P(p-FC6H4)3
P(p-MeC6H4)3
PCyPh2
RuCl2(p-cymene)(P(p-FC6H4)3)
RuCl2(p-cymene)(P(p-MeC6H4)3)
RuCl2(p-cymene)(PCyPh2)
P(p-MeOC6H4)3 RuCl2(p-cymene)(P(p-MeOC6H4)3) 39.0 ( 0.5
PiBu3
PBz3
RuCl2(p-cymene)(PiBu3)
RuCl2(p-cymene)(PBz3)
RuCl2(p-cymene)(P(NC4H8)3)
RuCl2(p-cymene)(PEtPh2)
RuCl2(p-cymene)(PPh2Me)
RuCl2(p-cymene)(P(OMe)3)
RuCl2(p-cymene)(PEt3)
39.6 ( 0.1
40.7 ( 0.3
44.0 ( 0.2c
45.2 ( 0.2
45.6 ( 0.3
45.9 ( 0.4
51.3 ( 0.3
52.5 ( 0.3
55.3 ( 0.2
P(NC4H8)3
PEtPh2
PPh2Me
P(OMe)3
PEt3
PPhMe2
PMe3
RuCl2(p-cymene)(PPhMe2)
RuCl2(p-cymene)(PMe3)
ingful calorimetric results and were satisfied for all organoru-
thenium reactions investigated. Only reactants and products
were observed in the course of the NMR titration.
Ca lor im etr ic Mea su r em en t of Rea ction betw een [(p-
cym en e)Ru Cl2]2 (1) a n d P (NC4H4)3. 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 [(p-cymene)RuCl2]2 was accurately weighed into the
lower vessel, and it was closed and sealed with 1.5 mL of
mercury. Four milliliters of a 25% stock solution of the tris-
(pyrrolyl)phosphine (1 g of P(NC4H4)3 in 25 mL of CH2Cl2) 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 (about 2 h), it was inverted, thereby
allowing the reactants to mix. The reaction was considered
complete after the calorimeter had once again reached thermal
equilibrium. The vessels were then removed from the calo-
rimeter, taken into the glovebox, opened, and analyzed using
1H NMR spectrocopy. Conversion to (p-cymene)RuCl2(P(NC4-
H4)3) was found to be quantitative under these reaction
conditions. The enthalpy of reaction, -25.2 ( 0.3 kcal/mol,
represents the average of five individual calorimetric deter-
minations. The enthalpy of solution of [(p-cymene)RuCl2]2 was
then added to this value to obtain a value of -30.3 ( 0.3 kcal/
mol for all species in solution. All enthalpy data measured
for this study are presented in Table 1.
(9) For organoruthenium systems, see: (a) Nolan, S. P.; Martin, K.
L.; Stevens, E. D.; Fagan, P. J . Organometallics 1992, 11, 3947-3953.
(b) Luo, L.; Fagan, P. J .; 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.; Serron, S. A.; Nolan,
S. P.; Petersen, J . L. Organometallics 1996, 15, 4020-4029. (k) Li, C.;
Ogasawa, M.; Nolan, S. P.; Caulton, K. G. Organometallics 1996, 15,
4900-4903.
(10) For organoiron systems, see: (a) Luo, L; Nolan, S. P. Organo-
metallics 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. (e)Serron, S. A.; Nolan, S. P. Inorg. Chim. Acta
1996, 252, 107-113.
(11) For organorhodium systems, see: (a) Serron, S. A.; Nolan, S.
P.; Moloy, K. G. Organometallics 1996, 15, 4301-4306. (b) Huang, A.;
Marcone, J . E.; Mason, K. L.; Marshall, W. J .; Moloy, K. G.; Serron, S.
A.; Nolan, S. P. Organometallics 1997, 16, 3377-3380.
(12) Moloy; K. G.; Petersen, J . L. J . Am. Chem. Soc. 1995, 117,
7696-7710.
(13) Ojelund, G.; Wadso¨, I. Acta Chem. Scand. 1968, 22, 1691-1699.
(14) Kilday, M. V. J . Res. Natl. Bur. Stand. (U.S.) 1980, 85, 467-
481.
Ca lor im etr ic Mea su r em en t of En th a lp y of Solu tion of
[(p-cym en e)Ru Cl2]2 (1) in CH2Cl2. In order to consider all
species in solution, the enthalpies of solution of [(p-cymene)-
RuCl2]2 had to be directly measured. This was performed by
using a similar procedure to the one described above with the
exception that no ligand was added to the reaction cell. This
enthalpy of solution represents the average of five individual
determinations, +5.1 ( 0.1 kcal/mol.
Syn th esis. The compound [(p-cymene)RuCl2]2 (1) was
synthesized according to the literature procedure.16 The
synthesis of (p-cymene)RuCl2(P(CH2C6H5)3) has been previ-
(15) Nolan, S. P.; Hoff, C. D. J . Organomet. Chem. 1985, 282, 357-
362.

106 Organometallics, Vol. 17, No. 1, 1998
Ta ble 2. Cr ysta llogr a p h ic Da ta for th e X-r a y Diffr a ction An a lyses of 2, 4, a n d 6
Serron et al.
empirical formula
fw
C22H26Cl2N3PRu (2)
535.40
C24H27Cl2N2PRu (4)
546.42
C31H35Cl2PRu (6)
610.53
temp
wavelength
cryst syst
208(2) K
0.710 73Å
monoclinic
208(2) K
0.710 73 Å
monoclinic
295(2) K
0.710 73 Å
triclinic
space group
unit cell dimens
P21/c
P21/c
P1h
a, 17.158(4) Å R, 90°
b, 8.851(2) Å â, 99.394(4)°
c, 14.626(4) Å γ, 90°
2191.3(9) Å3, 4
1.623 g/cm3
a, 17.206(4) Å R, 90°
b, 8.811(2) Å â, 97.758(4)°
c, 14.857(3) Å γ, 90°
2231.9(9) Å3, 4
1.626 g/cm3
a, 9.381(2) Å R, 93.70(1)°
b, 10.046(1) Å â, 96.44(1)°
c, 15.181(1) Å γ, 93.60(2)°
1415.3(3) Å3, 2
volume, Z
calcd density
abs coeff
1.433 g/cm3
1.047 mm-1
1.028 mm-1
0.817 mm-1
F(000)
1088
1112
628
cryst dimens
θ range for data collection
index ranges
0.33 × 0.25 × 0.10 mm
0.30 × 0.18 × 0.08 mm
0.16 × 0.22 × 0.48 mm
2.41-30.00°
2.39-30.06°
2.04-25.00°
-23 e h e 23, -11 e k e 12,
-20 e l e 20
31 754
6018 (Rint ) 0.1342)
full-matrix least-squares on F2
6018/0/262
-24 e h e -23, -12 e k e 12,
-20 e l e 20
33 478
6223 (Rint ) 0.0867)
full-matrix least-squares on F2
6223/0/271
0 e h e 11, -11 e k e 11,
-18 e l e 17
5276
4949 (Rint ) 0.0295)
Full-matrix least-squares on F2
4636/0/319
no of reflns collected
no. of indep reflns
refinement method
data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
1.038
0.956
1.027
R1 ) 0.0692, wR2 ) 0.1398
R1 ) 0.1363, wR2 ) 0.1675
1.723, -1.193 e Å-3
R1 ) 0.0417, wR2 ) 0.0882
R1 ) 0.0844, wR2 ) 0.1022
1.602, -1.007 e Å-3
R1 ) 0.0384, wR2 ) 0.0856
R1 ) 0.0590, wR2 ) 0.0946
0.748, -0.347 e Å-3
largest diff peak and hole
ously reported.9h Ligands were synthesized as reported in the
literature.12 Experimental synthetic procedures, leading to
isolation of previously unreported complexes, are described
below.
were repeated at the end to check for crystal decay. In both
cases, examination revealed a small twin component, the
orientation of which could not be determined. Integration of
the three-dimensional intensity profiles was, therefore, based
upon a well-defined orientation matrix for the major (90%)
component and yielded 33, 748 and 31, 754 reflections for 2
and 4, respectively, providing reciprocal space coverage to
resolution d g 0.71 Å of 93.9% and 94.6%, respectively.
Intensity data were corrected for the effects of absorption by
an empirical method using repeated and symmetry-equivalent
reflections and based on the method of Blessing.17 Slightly
elevated residual densities and Rint values are a result of a
failure to account for the minor component of the twin but in
our view do not significantly detract from the accuracy of the
structure determinations. The structures were solved by direct
methods; all non-hydrogen atoms were refined using aniso-
tropic displacement parameters, hydrogen atoms were in-
cluded in calculated positions with fixed isotropic displacement
parameters, and refined according to a riding model. All
calculations were performed using the Siemens/SHELXTL
suite of crystallographic programs.18 The refined lattice
parameters and other pertinent crystallographic information
are summarized in Table 2. The refined positional parameters
with equivalent isotropic displacement parameters for 2 and
4 are provided in the Supporting Information, and the inter-
atomic distances and bond angles are listed in Tables 3 and
4, respectively. ORTEP diagrams of 2 and 4 are presented in
Figures 1 and 2.
Cr ysta l Str u ctu r e Deter m in a tion of (p-cym en e)Ru Cl2-
(P (CH 2C6H 5)3) (6). A red crystal of (p-cymene)RuCl2P-
(CH2C6H5)3 (6) was sealed in a capillary tube and then optically
aligned on the goniostat of a Siemens P4 automated X-ray
diffractometer. The reflections that were used for the deter-
mination of the dimensions of the triclinic unit cell were
located and indexed by the automatic peak search routine
XSCANS.19 The corresponding lattice parameters and orien-
tation matrix were provided from a nonlinear least-squares
fit of the orientation angles of 38 reflections (10° < 2θ < 24°)
at 22 °C. The refined lattice parameters and other pertinent
crystallographic information are summarized in Table 2.
(p-cym en e)Ru Cl2(P (NC4H4)3) (2). A 50 mL flask was
charged with 188 mg (0.82 mmol) of P(pyrrole)3, 250 mg (0.41
mmol) of [RuCl2(p-cymene)]2, and 15 mL of CH2Cl2. The clear
wine-red solution was stirred at room temperature for 15 min,
after which the solvent was removed under vacuum. The
residue was washed with ca. 50 mL of hexane, filtered, and
dried under vacuum, which afforded 370 mg of the product
(yield 85%). 1H NMR (300 MHz, CDCl3, 25 °C): 1.25 (d, 6H,
2CH3), 1.99 (s, 3H, -CH3), 2.95 (sp, 1H, -CH), 5.27 (d, 2H,
-C6H4), 5.57 (d, 2H, -C6H4), 6.31 (s, 6H, pyrrole), 7.02 (s, 6H,
pyrrole). Anal. Calcd for C22H26RuCl2PN3: C, 49.35; H, 4.89;
N, 7.85. Found: C, 49.70; H, 5.13; N, 7.61.
(p-cym en e)Ru Cl2(P P h 2(NC4H4)) (3). In a similar fashion
as described for 2, 3 was isolated in 81% yield. 1H NMR (300
MHz, CDCl3, 25 °C): 1.13 (d, 6H, 2CH3), 1.90 (s, 3H, -CH3),
2.85 (sp, 1H, -CH), 5.09 (d, 2H, -C6H4), 5.32 (d, 2H, -C6H4),
6.30 (s, 2H, -pyrrole), 7.12 (2H, -pyrrole), 7.38 (m, 6H, C6H5),
7.70 (m, 4H, C6H5). Anal. Calcd for C26H28RuCl2PN: C, 56.02;
H, 5.06; N, 2.51. Found: C, 55.75; H, 4.90; N, 2.42.
(p-cym en e)Ru Cl2(P P h (NC4H4)2) (4). In an analogous
manner, 4 is isolated in 79% yield. 1H NMR (300 MHz, CDCl3,
25 °C): 1.16 (d, 6H, 2CH3), 1.94 (s, 3H, -CH3), 2.87 (sp, 1H,
-CH), 5.21 (d, 2H, -C6H4), 5.43 (d, 2H, -C6H4), 6.28 (s, 4H,
-pyrrole), 7.08 (s, 4H, -pyrrole), 7.40 (m, 5H, C6H5). Anal.
Calcd for
C24H27RuCl2PN2: C, 52.72; H, 4.98; N, 5.13.
Found: C, 52.97; H, 4.90; N, 4.96.
(p-cym en e)Ru Cl2(P (NC4H8)3) (5). Following an identical
procedure, 5 is isolated in 88% yield. 1H NMR (300 MHz,
CDCl3, 25 °C): 1.33 (d, 6H, 2CH3), 1.74 (s, 12H, -pyrrolidinyl),
2.16 (s, 3H, -CH3), 3.21 (s, 12H, -pyrrolidinyl), 5.07 (d, 2H,
-C6H4), 5.50 (d, 2H, -C6H4). Anal. Calcd for C22H38RuCl2-
PN3: C, 48.26; H, 7.00; N, 7.67. Found: C, 48.20; H, 6.69; N,
7.32.
Cr ysta l Str u ctu r e Deter m in a tion of (p-cym en e)Ru Cl2-
(P (NC4H4)3) (2) a n d (p-cym en e)Ru Cl2(P P h (NC4H4)2) (4).
Data for these two red crystals, 2 and 4, were collected using
a Siemens SMART CCD area detector diffractometer. At each
series of four orientations about the φ angle, the crystal was
scanned in ω by 688 steps of 0.3° (frames). The first 50 frames
(17) Blessing, R. H. Acta Crystallogr. 1995, A51, 33-38.
(18) (a) SMART, SAINT; Siemens Analytical X-ray Instruments
Inc.: Madison, WI, 1996. (b) SHELXTL 5.0; Siemens Analytical X-ray
Instruments Inc.: Madison, WI, 1995.
(16) Bennett, M. A.; Huang, T.-N.; Matheson, T. W.; Smith, A. K.
Inorg. Synth. 1982, 21, 74-79.
(19) XSCANS, version 2.0; Siemens Analytical X-ray Instruments
Inc.: Madison, WI, 1991.

Substitution of N-Pyrrolyl Phosphine Ligands
Organometallics, Vol. 17, No. 1, 1998 107
Ta ble 3. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for (p-cym en e)Ru Cl2P (NC4H4)3 (2)
Bond Lengthsa
Ru-Cl(1)
Ru-P
2.396(2)
2.282(2)
1.696(5)
1.713(5)
1.382(7)
Ru-Cl(2)
Ru-Ar(c)b
P-N(2)
N(1)-C(11)
N(3)-C(34)
2.398(2)
1.723
1.692(5)
1.385(8)
1.369(8)
P-N(1)
P-N(3)
N(2)-C(24)
Bond Anglesa
P(1)-Ru(1)-Cl(1)
Cl(1)-Ru(1)-Cl(2)
N(2)-P(1)-N(3)
N(2)-P(1)-Ru(1)
N(3)-P(1)-Ru(1)
C(1)-Ru(1)-Cl(1)
C(2)-Ru(1)-Cl(2)
89.27(5) P(1)-Ru(1)-Cl(2)
91.48(5)
103.5(3)
99.1(3)
115.3(2)
112.8(2)
86.6(2)
88.72(6) N(2)-P(1)-N(1)
98.6(2)
121.4(2)
115.4(2)
157.8(2)
123.4(2)
N(1)-P(1)-N(3)
N(1)-P(1)-Ru(1)
C(1)-Ru(1)-P(1)
C(4)-Ru(1)-Cl(1)
C(5)-Ru(1)-Cl(2) 108.4(2)
a
Numbers in parentheses are the estimated standard devia-
b
tions. Ar(c) designates the centroid of the arene ring.
Ta ble 4. Selected Bon d Dista n ces (Å) a n d
Bon d An gles (d eg) for
F igu r e 2. ORTEP of (p-cymene)RuCl2(PPh(NC4H4)2) (4)
with ellipsoids drawn at 40% probability.
(p-cym en e)Ru Cl2P (C6H5)(NC4H4)2 (4)
Ta ble 5. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for (p-cym en e)Ru Cl2P (CH2C6H5)3 (6)
Bond Lengthsa
Ru-Cl(1)
Ru-P
2.388(1)
2.292(1)
1.792(3)
1.706(3)
1.396(5)
Ru-Cl(2)
Ru-Ar(c)b
P-N(1)
N(1)-C(14)
N(2)-C(21)
N(2)-C(24)
2.392(1)
1.710
1.703(3)
1.378(5)
1.368(4)
1.381(4)
Bond Lengthsa
Ru-C(30)
P-N(2)
Ru-Cl(1)
Ru-P
P-C(11)
P-C(25)
C(1)-C(6)
2.416(1)
2.359(1)
1.848(4)
1.861(4)
1.433(6)
Ru-Cl(2)
Ru-Ar(c)b
P-C(18)
C(1)-C(2)
C(1)-C(7)
2.412(1)
1.708
1.839(4)
1.395(6)
1.507(6)
N(1)-C(11)
Bond Anglesa
91.65(3) Cl(1)-Ru-Cl(2)
Bond Anglesa
P(1)-Ru-Cl(2)
N(1)-P1-N(2)
N(2)-P(1)-C(30)
N(2)-P(1)-Ru
88.72(3)
102.9(2)
101.3(2)
120.9(1)
N(1)-P(1)-C(30)
N(1)-P(1)-Ru
102.4(2)
114.4(1)
112.6(1)
128.6(3)
P-Ru-Cl(1)
81.93(4)
134.9
111.3(1)
103.9(2)
101.9(2)
P-Ru-Cl(2)
83.45(4)
90.88(4)
106.0(2)
118.4(1)
114.1(1)
P-Ru-Ar(c)
C(11)-P-Ru
C(11)-P-C(25)
C(18)-P-C(25)
Cl(1)-Ru-Cl(2)
C(11)-P-C(18)
C(18)-P-Ru
C(25)-P-Ru
C(30)-P(1)-Ru
C(14)-N(1)-P(1)
C(14)-N(1)-C(11) 107.5(3)
C(11)-N(1)-P(1)
C(21)-N(2)-P(1)
122.7(2)
126.9(2)
C(21)-N(2)-C(24) 107.5(3)
C(24)-N(2)-P(1)
125.2(3)
a
Numbers in parentheses are the estimated standard devia-
a
b
Numbers in parentheses are the estimated standard devia-
tions. Ar(c) designates the centroid of the arene ring.
tions. Ar(c) designates the centroid of the arene ring.
b
0.783) based upon the ψ scans measured for six reflections (ø
≈ -90°, 2θ ) 13-31°) was applied.
The initial coordinates of the Ru atom were determined by
Patterson methods, and the coordinates for the remaining non-
hydrogen atoms were obtained from subsequent Fourier sum-
mations calculated with the algorithms provided by SHELXTL
IRIS operating on a Silicon Graphics IRIS Indigo workstation.
Hydrogen atoms were included in calculated positions with
fixed isotropic displacement parameters and refined according
to a riding model. The refined positional parameters with
equivalent isotropic displacement parameters 6 are provided
in the Supporting Informaiton, and the interatomic distances
and bond angles are listed in Table 5. An ORTEP of 6 is
presented in Figure 3.
Resu lts a n d Discu ssion
A facile entryway into the thermochemistry of (p-
cymene)Ru(PR3)Cl2 complexes is made possible by the
rapid and quantitative reaction of [(p-cymene)RuCl2]2
(1) with a variety of phosphine ligands, eq 6. This type
F igu r e 1. ORTEP of (p-cymene)RuCl2(P(NC4H4)3) (2) with
ellipsoids drawn at 40% probability.
Intensity data were measured with graphite-monochro-
mated Mo KR radiation (λ ) 0.710 73 Å) and variable ω scans
(4.0-10.0 deg/min). Background counts were measured at the
beginning and at the end of each scan with the crystal and
counter kept stationary. The intensities of three standard
reflections were measured periodically during data collection
and gave no indication of crystal decay or sample movement.
The data were corrected for Lorentz-polarization, and the
symmetry-equivalent reflections were averaged. An empirical
absorption correction (range of transmission coefficients: 0.708-
(6)
of phosphine binding reaction is rapid and quantitative
for all ligands calorimetrically investigated at 30.0 °C
in methylene chloride. We have previously examined

108 Organometallics, Vol. 17, No. 1, 1998
Serron et al.
the effect of placing a partial positive charge on the
nitrogen. This would be expected to reduce the basicity
of the adjacent phosphorus atom. Structure D suggests
that N-pyrrolyl phosphines will be poorer donors than
the corresponding phenyl phosphines since the more
electronegative nitrogen replaces carbon. Moloy12 has
shown these ligands to undergo quantitative binding to
the RhCl(CO) fragment, eq 8. The pyrrolyl moiety,
[RhCl(CO)2]2 + 4PR3 f 2RhCl(CO)(PR3)2 + 2CO
(8)
PR3 )
P(NC4H4)3; P(NC4H4)2Ph; P(NC4H4)Ph2; P(NC4H8)3
known for its π-involvement, has been shown by the
vibrational spectroscopic data obtained for a related
series of rhodium compounds to affect the binding ability
of the phosphine. The thermochemical information
subsequently gathered for this rhodium system quan-
titatively supports11 that the phosphine donor strength
decreases with increasing number of pyrrolyl substitu-
ents on phosphorus.
F igu r e 3. ORTEP of (p-cymene)RuCl2(P(CH2C6H5)3) (6)
with ellipsoids drawn at 30% probability.
similar substitution reactions for a wide variety ofphos-
phine ligands. The present enthalpy of reaction data
along with that previously reported on this system are
compiled in Table 1.
In the present ruthenium study, this same phosphine
ligand series was examined. From the data in Table 1,
it is evident that the pyrrolyl-substituted phosphines
are in fact among the most weakly bound ligands
investigated in this system. The pyrrolyl- and pyrro-
lidinyl-substituted phosphines are isosteric, having a
cone angle of 145°.12,23 Therefore, any observed en-
thalpy difference can be essentially attributed to elec-
tronic effects. The reaction enthalpy data in Table 1
clearly show that these addition reactions become less
exothermic as the number of pyrrolyl substituents on
the phosphine increases. The observed trend has been
observed in other ruthenium systems.9j A stepwise
increase of this reaction enthalpy as a function of
pyrrolyl substitution is graphically represented in Fig-
ure 4.24 The totally saturated P(NC4H8)3 ligand is more
closely related to a trialkylphosphine than to its pyrrolyl
congener. This remark was previously supported by the
enthalpy data measured in other rhodium11a and
ruthenium9j systems, where enthalpies of reactions for
P(NC4H8)3 are closer to PEt3. The enthalpy scale trend
present in the (p-cymene)RuCl2(PR3) (PR3 ) P(NC4H4)3,
P(NC4H4)2(C6H5), P(NC4H4)(C6H5)2 and P(NC4H8)3) sys-
tem is, therefore, consistent with the thermochemical
data measured for these previously investigated sys-
tems.
The complex [(p-cymene)RuCl2]2 (1) and some of its
phosphine derivatives have been demonstrated as ef-
ficient catalyst/catalyst precursors. For example, Noels
and co-workers have shown 1 and some of its phosphine
derivatives to be efficient precursors for the ring-opening
metathesis polymerization of olefins.20 Grubbs and
Nguyen, in synthetic studies related to their investiga-
tions on ring-opening and ring-closing metathesis reac-
tions,21 have used 1 as a synthon, leading to the isolation
of catalytically active ruthenium carbene complexes,
(PR3)2Cl2Ru(CHdCHdCPh2), eq 7.22 In view of the
(7)
reactivity displayed by 1, thermochemical studies were
undertaken to obtain quantitative data about the en-
thalpic driving forces behind the fragmentation and
ligand binding trends for this dimeric complex.
The N-pyrrolyl-substituted phosphine series has been
shown to act as a potent electron-withdrawing group,
rendering the phosphine a poor σ donor and a good
π-acceptor.12 Pertinent resonance structures for the
N-pyrrolyl phosphines can be drawn as follows:
To determine the relative importance of the σ- and
π-bonding components of the phosphine ligand, single-
crystal X-ray diffraction studies were performed on
three complexes. Two of these compounds bear pyrrolyl
substituents, (p-cymene)RuCl2(P(NC4H4)3) (2) and (p-
cymene)RuCl2(P(NC4H4)2(C6H5) (4), on the phosphine,
Aromatic delocalization of the nitrogen lone pair into
the pyrrole ring, as depicted in structures B and C, has
(20) (a) Demonceau, A.; Noels, A. F.; Saive, E.; Hubert, A. J . J . Mol.
Catal. 1992, 76, 123-132. (b) Demonceau, A.; Stumpf, A. W.; Saive,
E.; Noels, A. F. Macromolecules 1997, 30, 3127-3136.
(21) (a) Nguyen, S. T.; J ohnson, L. K. Grubbs, R. H.: Ziller, J . W.
J . Am. Chem. Soc. 1992, 114, 3974-3975. (b) Fu, G. C.; Nguyen, S. T.;
Grubbs, R. H. J . Am. Chem. Soc. 1993, 115, 9856-9857. (c) Nguyen,
S. T.; Grubbs, R. H.: Ziller, J . W. J . Am. Chem. Soc. 1993, 115, 9858-
9859.
(23) Tolman, C. A. Chem. Rev. 1977, 77, 313-348.
(24) The electronic parameter used in this relationship is the one
determined in ref 12, which is the carbonyl stretching frequency of
Rh(CO)Cl(PR3)2.
(22) Nguyen, S. T.; Grubbs, R. H. Personnal communication.

Substitution of N-Pyrrolyl Phosphine Ligands
Organometallics, Vol. 17, No. 1, 1998 109
contrast, for the π-activated tris(pyrrolyl)phosphine in
2, its enhanced π-acceptor ability reduces the degree of
π-back-donation into the arene, thus leading to a longer
Ru-Ar(c) distance of 1.723 Å. The observed variation
in Ru-Cl bond distances appears to be consistent with
the π-donor character of the Cl ligand, with the longer
average Ru-Cl distance in 6 being associated with a
more electron-rich Ru center.
We have previously reported on the thermochemistry
and structural features of this ligand series within the
Cp*Ru(PR3)2Cl system.9j The enthalpy trend observed
in this system is P(NC4H4)(C6H5)2 < P(NC4H4)3
<
P(NC4H4)2(C6H5) < P(NC4H8)3. The structural trend in
that study shows an increase in the average Ru-P bond
length within this series, correlating with an increase
in reaction exothermicity, A trend that is counterintui-
tive if the bonding is solely considered in terms of σ
donation. It was, therefore, concluded that the bonding
in the pyrrolyl-substituted phosphines appeared to
involve some π-back-donation as well. In the present
F igu r e 4. Enthalpy of reaction (kcal/mol) vs phosphine
electronic factor in the [(p-cymene) RuCl2(PR3)] system.
Slope ) 4.79; R ) 0.98
Ta ble 6. Selected Bon d Dista n ces (Å) a n d
En th a lp y of Liga n d Su bstitu tion (k ca l/m ol) for
[p-cym en eRu Cl2(P R3)] Com p lexes
system, the observed enthalpy trend is P(NC4H4)3
<
P(NC4H4)2(C6H5) < P(NC4H4)(C6H5)2 < P(NC4H8)3, more
along the lines of the π-bonding ability of the series. The
structural features of the first two complexes in this
series (2 and 4) show a slight shortening of the Ru-P
bond length on going from 2 to 4. The present system
appears to be much more sensitive to the electronic
π-back-donation. The two systems contain different
ancillary ligands, which will surely influence (in a
different manner) the amount of electron density avail-
able for back-donation. Furthermore, the Cp*Ru(PR3)2-
Cl system contains two phosphine ligands competing for
back-donation, compared to a single phosphine in the
(p-cymene)RuCl2PR3 system. In the case of the presence
of a unique phosphine ligand, a marked increase of the
π-back-donation from Ru into pyrrolyl substituent an-
tibonding orbitals should be expected. The trend of
increased pyrrolyl substitution accompanied by a shorter
Ru-P bond length and lower enthalpy values clearly
illustrates this effect.26
2 (P(NC4H4)3
4(PPh(NC4H4)2)
6 (PBz3)
Ru-P
2.282(2)
2.396(2)
2.398(2)
1.723
2.292(1)
2.388(1)
2.392(1)
1.710
2.359(1)
2.416(1)
2.412(1)
1.708
Ru-Cl(1)
Ru-Cl(2)
Ru-Ar(c)
-∆H
30.3(0.3)
31.1(0.3)
40.7(0.3)
and the third provides a standard for comparison due
to the presence of a simple trialkyl phosphine ligand in
(p-cymene)RuCl2(PCH2C6H5)3 (6). The pertinent crys-
tallographic bond distances and angles are summarized
in Table 6. From a comparison of the structural data
for 2 and 4, it is apparent that the replacement of a
pyrrolyl with a phenyl substituent on the phosphine
produces only a modest increase of 0.01 Å25 in the Ru-P
bond distance. However, a substantially larger increase
of 0.07 Å in the Ru-P distance is observed when the
three pyrrolyl groups of 2 are replaced by the three
benzyl substituents of 6. On the basis of the observed
variation in the Ru-P distances for these three com-
pounds, the least exothermic enthalpy of reaction cor-
responds to the Ru phosphine complex, 2, with the
shortest Ru-P bond. However, any reasonable inter-
pretation must also consider any reorganization energy
illustrated by changes in bond lengths between the
metal and the p-cymene and Cl ligands. It should be
kept in mind that the present enthalpy data does not
represent “bond strength” but is a sum of a number of
enthalpic contributions which include bond strength
differences and fragment relaxation enthalpies. This
relaxation enthalpy can be explained in terms of bond
length/bond strength reorganization resulting from dif-
fering π-bonding involved in the incoming phosphine
ligand. In the case of complex 6, which contains the
most basic phosphine ligand and the longest Ru-P
distance, one finds the shortest Ru-Ar(c) distance of
1.708 Å and the longest average Ru-Cl distance of 2.414
Å. Apparently, the weaker π-acceptor ability of the
tribenzylphosphine ligand in 6 is compensated by a
greater π-back-donation from the Ru to the arene. In
Con clu sion
The lability of the chloride bridges in [(p-cymene)-
RuCl2]2 (1) provides a suitable entry to probe the
thermochemistry associated with ligand binding for
pyrrolyl- and pyrrolidinyl-substituted phosphine ligands.
By holding the steric factor constant for the phosphines
examined within this Ru series, the observed trend in
the measured reaction enthalpies can be accounted for
by considering the differences in the relative σ-donor
and π -acceptor bonding contributions for these phos-
phine ligands. Further thermochemical, mechanistic,
and catalytic investigations focusing on this and related
ligand system are presently underway.
Ack n ow led gm en t. The National Science Founda-
tion (Grant No. CHE-963116 to S.P.N.; Chemical In-
stumentation Program Grant Nos. CHE-9120098 to
J .L.P. and CHE-9309690 to L.B. and collegues) and
DuPont (Educational-Aid-Grant to S.P.N.) are gratefully
acknowledged for support of this research. S.P.N. is
(25) This distance difference, although metrically real, may not be
chemically significant, see: Martin, A.; Orpen, A. G. J . Am. Chem.
Soc., 1996, 118, 1464-1470.
(26) It should also be stated that such a simple analysis does not
take into account the importance of steric repulsive effects in the
Cp*Ru(PR3)2Cl system.9j

110 Organometallics, Vol. 17, No. 1, 1998
Serron et al.
angles, anisotropic thermal displacement parameters, and
hydrogen bond distances for 2, 4, and 6 (18 pages). Ordering
information is given on any current masthead page.
indebted to J ohnson-Matthey/Aesar for the generous
loan of ruthenium salts.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
and intensity data, atomic coordinates, selected distances and
OM970809T