Effect of ancillary ligation on the relative bond disruption enthalpies of Ru-H and Ru-Cl bonds in Cp(PR3)2RuX (PR3 = PMe3, PMe2Ph, PMePh2, PPh3; X = H, Cl)

Article abstract of DOI:10.1021/om000420x

The ruthenium chloride and hydride complexes Cp(PR₃)₂RuH {X = Cl; PR₃ = PMe₃ (1), PMe₂Ph (2), PMePh₂ (3), PPh₃ (4); X = H; PR₃ = PMe₃ (5), PMe₂Ph (6), PMePh₂ (7), PPh₃ (8)} were studied by spectroscopy and solution calorimetry. The structures of 2 and 3 are reported and complete the structural characterization of the series 1-4. In this series, the Ru-Cl distance (2.449 ± 0.007 A?) remains constant, while the Ru-PR₃ distance increases in the order 1 < 2 < 3 < 4. The ruthenium hydrides 5-8 were prepared from the reaction of the corresponding ruthenium chloride with KOMe in methanol.

Full text of DOI:10.1021/om000420x

4828
Organometallics 2000, 19, 4828-4833
Effect of An cilla r y Liga tion on th e Rela tive Bon d
Disr u p tion En th a lp ies of Ru -H a n d Ru -Cl Bon d s in
Cp (P R3)2Ru X (P R3 ) P Me3, P Me2P h , P MeP h 2, P P h 3; X )
H, Cl)
Samuel T. N. Freeman and Frederick R. Lemke*
Department of Chemistry and Biochemistry, Ohio University, Athens, Ohio 45701-2979
Christopher M. Haar and Steven P. Nolan
Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148
J effrey L. Petersen
Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506
Received May 18, 2000
The ruthenium chloride and hydride complexes Cp(PR3)2RuH {X ) Cl; PR3 ) PMe3 (1),
PMe2Ph (2), PMePh2 (3), PPh3 (4); X = H; PR3 ) PMe3 (5), PMe2Ph (6), PMePh2 (7), PPh3
(8)} were studied by spectroscopy and solution calorimetry. The structures of 2 and 3 are
reported and complete the structural characterization of the series 1-4. In this series, the
Ru-Cl distance (2.449 ( 0.007 Å) remains constant, while the Ru-PR3 distance increases
in the order 1 < 2 < 3 < 4. The ruthenium hydrides 5-8 were prepared from the reaction
of the corresponding ruthenium chloride with KOMe in methanol. Spectroscopic data on
hydrides 5-8 indicated that the ruthenium hydride interaction decreases in the order 5 >
6 > 7 > 8. Enthalpies of reaction for the hydride/chloride metatheses of 5-8 with
chlorocarbons (CHCl3 or CCl4) were studied by solution calorimetry and allowed for the
determination of Ru-Cl bond disruption enthalpies (BDEs) relative to the corresponding
Ru-H BDEs. [BDE(Ru-Cl) - BDE(Ru-H)] values covered a 6 kcal/mol range with an
average of 21.4 ( 2.5 kcal/mol. The magnitude of [BDE(Ru-Cl) - BDE(Ru-H)] correlated
with the number of methyl groups on the phosphine and was dependent on the electronic
and steric properties of the phosphine.
In tr od u ction
to evaluate the effect of ancillary ligation on the Ru-H
and Ru-Cl bonds.
Transition metal hydrides are involved in many
stoichiometric and catalytic processes.1-3 Thus, knowl-
edge of the bond strength between hydrogen and a
transition metal system is important to gain a funda-
mental understanding of these processes. Recently, we
reported the formation of ruthenium silyl complexes
from the reaction of ruthenium hydrides with chlorosi-
lanes4,5 and the RuCl2(PPh3)3-catalyzed hydrosilylation
of phenylacetylene.6 In both of these processes, the
making and/or breaking of Ru-H, Ru-Cl, and Ru-Si
bonds was observed to be dependent on the substituents
attached to ruthenium and silicon. As part of our
ongoing interest in substituent effects, the ruthenium
complexes Cp(PR3)2RuX (PR3 ) PMe3, PMe2Ph, PMe-
Ph2, PPh3; X ) H, Cl) were studied. This paper presents
thermochemical data on the hydride/chloride metathesis
reaction, as well as spectroscopic and structural data,
Resu lts a n d Discu ssion
Str u ctu r es of Cp (P R3)2Ru Cl (P R3 ) P Me2P h (2),
P MeP h 2 (3)). The crystal structures of Cp(PMe2-
Ph)2RuCl (2) and Cp(PMePh2)2RuCl (3) have been
determined by X-ray diffraction at 295 K. Perspective
views of 2 and 3 are shown in Figures 1 and 2,
respectively. The geometry of 2 and 3 can be described
in terms of a “three-legged piano stool”, with the legs
comprising the phosphine and chloride ligands. The
structures of 2 and 3, in combination with the reported
structures of Cp(PMe3)2RuCl (1)7 and Cp(PPh3)2RuCl
(4),7 complete the crystallographic characterization of
this class of complexes. Pertinent interatomic distances
and angles for ruthenium chloride complexes 1-4 are
presented in Table 1.
A comparison of the structural data for ruthenium
chloride complexes 1-4 indicated that these complexes
were surprisingly similar. There was essentially no
change in the Ru-Cl (2.449 ( 0.007 Å) and the Ru-Cp
(1.849 ( 0.002 Å) distances over the range of phosphine
ligands. A similar insensitivity in the Ru-Cl (2.453 (
(1) Transition Metal Hydrides; Dedieu, A., Ed.; VCH Publishers:
New York, 1992; p 399.
(2) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis, 2nd ed.; J ohn
Wiley & Sons: New York, 1992; p 342.
(3) Comprehensive Handbook on Hydrosilylation; Marciniec, B., Ed.;
Pergamon Press: New York, 1992.
(4) Lemke, F. R. J . Am. Chem. Soc. 1994, 116, 11183-11184.
(5) Lemke, F. R.; Galat, K. J .; Youngs, W. J . Organometallics 1999,
18, 1419-1429.
(7) Bruce, M. I.; Wong, F. S.; Skelton, B. W.; White, A. H. J . Chem.
Soc., Dalton Trans. 1981, 1398-1405.
(6) Yardy, N. M.; Lemke, F. R. Main Group Chem. 2000, in press.
10.1021/om000420x CCC: $19.00 © 2000 American Chemical Society
Publication on Web 10/12/2000

Bond Disruption Enthalpies of Ru-H and Ru-Cl Bonds
Organometallics, Vol. 19, No. 23, 2000 4829
F igu r e 1. Perspective view of the molecular structure of
one of the independent molecules of Cp(PMe2Ph)2RuCl (2)
with atom labels provided for all unique non-hydrogen
atoms. The thermal ellipsoids are scaled to enclose 30%
probability. In this molecule, the C(8)-P(1)‚‚‚P(2)-C(16)
torsion angle was 24.9°. In the other independent molecule
in the unit cell, one PMe2Ph group was rotated about the
Ru-P bond by ∼150°, so the corresponding C(8)-P(1)‚‚‚
P(2)-C(16) torsion angle was 175.2°.
2
F igu r e 3. J PH versus the RuH 1H NMR chemical shift
for ruthenium hydride complexes Cp(PR3)2RuH (5-8):
slope ) -1.37 ( 0.13 Hz per ppm, R ) 0.991.
tance. The average P-Ru-Cl angle remained constant
(90.0 ( 0.8°) even though the number of phenyl groups
and the steric demand of the phosphines significantly
increased from 1 (with PMe3, θ ) 118°) to 4 (with PPh3,
θ ) 145°).9 The P1-Ru-P2 angle was essentially
constant in complexes 1-3 (95.2 ( 0.6°) but increased
dramatically in the PPh3 complex 4 (103.99°); an op-
posite trend was observed in the average Cp-Ru-P
angles (124.5 ( 0.7° for 1-3 versus 121.5 ( 0.1° for 4).
The most significant structural change was observed in
the Ru-P distance, which gradually increased with the
number of phenyl groups on phosphorus: 1 (2.28 Å) <
2 (2.29 Å) < 3 (2.30 Å) < 4 (2.34 Å). Overall, the
coordination environment around the ruthenium center
was not significantly affected by changes in the sub-
stituents on phosphorus.
F igu r e 2. Perspective view of the molecular structure of
Cp(PMePh2)2RuCl (3) with atom labels provided for all
unique non-hydrogen atoms. The thermal ellipsoids are
scaled to enclose 30% probability.
Ru th en iu m Hyd r id e Com p lexes. Ruthenium hy-
drides 5-8 were prepared in high yields by a modifica-
tion of the â-hydride elimination method involving the
reaction of ruthenium chlorides 1-4 with KOMe in
refluxing MeOH (eq 1).10 Hydrides 6 and 7 were new
Ta ble 1. Selected In ter a tom ic Dista n ces (Å) a n d
Bon d An gles (d eg) for Cp (P R3)2Ru Cl Com p lexes
1-4
1a,b
2a
3
4b
avc
Ru-Cl
Ru-P1
Ru-P2
Ru-Cpd
2.451(6) 2.455(2) 2.456(1) 2.453(2) 2.449(7)
2.440(5) 2.436(2)
2.273(5) 2.292(2) 2.295(1) 2.337(1) 2.293(18)
2.280(6) 2.283(2)
2.275(6) 2.277(2) 2.302(1) 2.335(1) 2.292(19)
2.273(6) 2.288(2)
1.850
1.849
1.846
1.852
1.849
1.847
1.849(2)
P1-Ru-P2 94.7(2) 94.47(6) 95.58(3) 103.99(4) 96.6(29)
95.0(2) 96.14(6)
P1-Ru-Cl 89.7(2) 90.83(6) 89.23(3) 89.05(3) 90.1(7)
90.6(2) 91.34(6)
P2-Ru-Cl 90.1(2) 90.70(5) 92.22(3) 90.41(4) 89.8(16)
compounds and were characterized by elemental analy-
sis as well as NMR (1H and 31P) and IR spectroscopies.
In the 1H NMR spectra (CD2Cl2), the hydride resonances
for 5-8 were observed as characteristic triplets (2J PH
) 33-37 Hz) over the -11.5 to -14 ppm region.
A linear inverse relationship was observed between
88.9(2) 86.40(5)
Cp-Ru-P1d 122.7
123.8
125.2
126.1
123.8
124.3
122.4
121.9
124.6
123.5
122.5
121.5
121.4
122.5
124.0(13)
124.0(13)
122.8(6)
Cp-Ru-P2d 126.3
124.7
Cp-Ru-Cld 123.3
124.0
1
2J PH and RuH H chemical shift (Figure 3). The hydride
a
b
Two independent molecules per unit cell. Structural data
from ref 7. c Average interatomic distances and angles for 1-4.
Values in parentheses represent the 95% confidence limits in the
2
resonances moved upfield and the magnitude of J PH
increased as the number of methyl groups on the
d
last digits. Cp refers to the centroid of the cyclopentadienyl ring.
(8) Smith, D. C., J r.; Haar, C. M.; Luo, L.; Li, C.; Cucullu, M. E.;
Mahler, C. H.; Nolan, S. P.; Marshall, W. J .; J ones, N. L.; Fagan, P. J .
Organometallics 1999, 18, 2357-2361.
(9) Tolman, C. A. Chem. Rev. 1977, 77, 313-348.
(10) Lemke, F. R.; Brammer, L. Organometallics 1995, 14, 3980-
3987.
0.002 Å) distance was observed in the structures of the
related Cp*(PR3)2RuCl complexes,8 and it is interesting
to note that changing the Cp group to the more electron-
donating Cp* group had no effect on the Ru-Cl dis-

4830 Organometallics, Vol. 19, No. 23, 2000
Freeman et al.
Ta ble 2. Hyd r id e/Ch lor id e Meta th esis Rea ction En th a lp ies a n d Rela tive BDE(Ru -H) Va lu es (k ca l/m ol) for
Cp (P R3)2Ru H
CH2Cl2
Cp(PR3)2RuH(soln) + R - Cl(soln)
8 Cp(PR3)2RuCl(soln) + R - H(soln)
30 °C
BDE(R-Cl) -
BDE(R-H)b
BDE(Ru-Cl) -
BDE(Ru-H)c
a
d
PR3
R-Cl
-∆Hrxn
ød
θe
PMe3
HCl2C-Cl
HCl2C-Cl
HCl2C-Cl
Cl3C-Cl
45.7(0.3)
43.8(0.4)
41.2(0.2)
43.7(0.3)
-21.3(0.1)
-21.3(0.1)
-21.3(0.1)
-24.8 (0.1)
24.4(0.3)
22.5(0.4)
19.9(0.2)
18.9(0.3)
8.55
10.60
12.10
13.25
118
122
136
145
PMe2Ph
PMePh2
PPh3
a
b
Corrected for the enthalpy of solution of the corresponding ruthenium hydride in CH2Cl2. [BDE(R-Cl) - BDE(R-H)] values derived
from ∆Hf° gas-phase data for RH, RCl, H•, and Cl• taken from ref 33. c [BDE(Ru-Cl) - BDE(Ru-H)] ) -∆Hrxn + [BDE(R-Cl) - BDE(R-
H)]. PR3 σ-donicity from ref 15. e PR3 cone angle from ref 9.
d
phosphine increased. A similar inverse relationship was
unique products under the calorimetric conditions as
determined by NMR spectroscopy.
2
observed between J PH and NiH 1H chemical shift in
the complexes trans-HNi(X)(PCy3)2 (X ) Ph, Me, I, Br,
Cl, etc.).11 The upfield chemical shifts indicated greater
electronic shielding of the hydrogen (the hydrogen is
“buried” in the ruthenium’s electron cloud), which
suggested stronger ruthenium-hydrogen interaction. In
5-8, stronger ruthenium-hydrogen interaction was
also supported by increased communication between
The hydride/chloride metathesis reaction of hydrides
5-7 with CHCl3 (eq 2) became more exothermic (i.e.,
-∆Hrxn increased) as the number of methyl groups on
phosphorus increased: 7 (41.2 kcal/mol) < 6 (43.8 kcal/
mol) < 5 (45.7 kcal/mol). This trend in the enthalpies
of reaction was attributed to the change in electronic
properties of the phosphine ligands and paralleled the
2
phosphorus and hydrogen in the form of larger J PH
σ-donor ability15 of the phosphine ligands (PMePh2
<
values: 5 (36.8 Hz) > 6 (35.6 Hz) > 7 (34.9 Hz) > 8
(33.6 Hz).
PMe2Ph < PMe3). The greater σ-donor and poorer
π-acceptor ability of PPh3 compared to CO also ex-
plained why the hydride/chloride metathesis reaction
of hydride 8 with CCl4 (eq 3, ∆H ) -43.7 kcal/mol) was
more exothermic than the hydride/chloride metathesis
reaction of Cp*(CO)2RuH with CCl4 (eq 4).14
Hyd r id e/Ch lor id e Meta th esis Stu d ies. Halogenat-
ing agents have been used in organometallic thermo-
chemistry to determine metal-hydride and metal-
halide bond disruption enthalpy (BDE) values and
trends.12-14 In the present study, we have found that
ruthenium hydrides 5-7 readily underwent hydride/
chloride metathesis with CHCl3 (eq 2). Hydride 8, on
the other hand, did not readily react with CHCl3, but
rapid hydride/chloride metathesis was observed with
CCl4 (eq 3). This set of hydride/chloride metathesis
BDE(Ru-Cl) was greater than BDE(Ru-H) for each
chloride/hydride pair studied; consistent with previously
investigated ruthenium,14 molybdenum,16,17 and iri-
dium18 systems. The [BDE(Ru-Cl) - BDE(Ru-H)] dif-
ferences covered a 6 kcal/mol range with an average of
21.4 ( 2.5 kcal/mol. This [BDE(Ru-Cl) - BDE(Ru-H)]
difference was significantly larger than the [BDE(Ru-
Cl) - BDE(Ru-H)] differences observed for Cp*(CO)2RuX
(15.7 kcal/mol)14 and Cp*(dppe)RuX (15.0 kcal/mol)14
and reflects the greater σ-donicity of the monodentate
phosphines PMe3-nPhn compared to CO and dppe.
A definite trend in the [BDE(Ru-Cl) - BDE(Ru-H)]
difference data was also observed. A plot of [BDE(Ru-
Cl) - BDE(Ru-H)] as a function of the number of
methyl groups in the chloride/hydride pairs exhibited
a linear relationship (Figure 4). Replacing a phenyl
group with a methyl group changed the electronic as
well as the steric properties of the phosphines. A
QALE15 analysis was used to evaluate the dependence
of [BDE(Ru-Cl) - BDE(Ru-H)] on the electronic (σ-
donicity, ød) and steric (cone angle, θ) properties of the
phosphines (eq 5). This analysis indicated that both the
reactions provided direct solution calorimetric access to
enthalpy of reactions which allowed for determination
of ruthenium-chloride BDE values relative to the
corresponding ruthenium-hydride BDE, [BDE(Ru-Cl)
- BDE(Ru-H)].
Enthalpies of reaction with the appropriate chlorinat-
ing agents are reported in Table 2. All reported enthal-
pies of reaction were solution phase values and took into
account the enthalpy of solution of the appropriate
ruthenium hydride complex. The reactions described in
eqs 2-3 were examined by NMR spectroscopy prior to
performing the calorimetric experiments and were
determined to be rapid and quantitative under calori-
metric conditions. All reactions investigated led to
(15) Liu, H.-Y.; Eriks, K.; Prock, A.; Giering, W. P. Organometallics
1990, 9, 1758-1766.
(11) Darensbourg, M. Y.; Ludwig, M.; Riordan, C. G. Inorg. Chem.
1989, 28, 1630-1634.
(16) Nolan, S. P.; de la Vega, R. L.; Hoff, C. D. J . Organomet. Chem.
1986, 315, 187-199.
(12) Simo˜es, J . A. M.; Beauchanp, J . L. Chem. Rev. 1990, 90, 629-
688.
(17) Calado, J . C. G.; Dias, A. R.; Simo˜es, J . A. M. J . Organomet.
Chem. 1979, 174, 77-80.
(18) Nolan, S. P.; Hoff, C. D.; Stoutland, P. O.; Newman, L. J .;
Buchanan, J . M.; Bergman, R. G. J . Am. Chem. Soc. 1987, 109, 3143-
3145.
(13) Nolan, S. P.; Stern, D.; Marks, T. J . J . Am. Chem. Soc. 1989,
111, 7844-7853.
(14) Luo, L.; Li, C.; Cucullu, M. E.; Nolan, S. P. Organometallics
1995, 14, 1333-1338.

Bond Disruption Enthalpies of Ru-H and Ru-Cl Bonds
Organometallics, Vol. 19, No. 23, 2000 4831
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations of oxygen- or
water-sensitive compounds were carried out either under an
atmosphere of argon by using Schlenk or vacuum-line tech-
niques or under an argon atmosphere in a MBraun drybox.20
1H NMR (400 and 250 MHz) spectra were recorded on a Varian
VXR 400S and a Bru¨ker AC-250 spectrometer, respectively.
1
The H chemical shifts were referenced to the residual proton
peak of the solvent (CDHCl2, δ 5.32). IR spectra were recorded
on a Perkin-Elmer 1600 Series FT-IR spectrometer. Elemental
analyses were carried out by Oneida Research Services.
Calorimetric measurements were performed using a Calvet
calorimeter (Setaram C-80), which was periodically calibrated
using the TRIS reaction21 or the enthalpy of solution of KCl
in water.22 The experimental enthalpies for these two standard
reactions compared very closely to literature values. This
calorimeter has been previously described,23,24 and typical
procedures are described below. Only materials of high purity,
as indicated by IR and NMR spectroscopies, were used in the
calorimetric experiments.
F igu r e 4. [BDE(Ru-Cl) - BDE(Ru-H)] versus number
of methyl groups in the Cp(PR3)2RuX complexes 1-8: slope
) 0.96 ( 0.11 kcal/mol per methyl group, R ) 0.987.
steric and electronic contributions of the phosphines
were significant in determining [BDE(Ru-Cl) - BDE-
(Ru-H)]. No apparent steric threshold was observed,
and the magnitude of the electronic contribution was
larger than the steric contribution in determining [BDE-
(Ru-Cl) - BDE(Ru-H)].
Ma ter ia ls. Cp(PR3)2RuCl (PR3 ) PMe3,7,25 PMe2Ph,26 PMe-
Ph2,26 PPh3),27 Cp(PMe3)2RuH,10 and Cp(PPh3)2RuH28 were
prepared according to literature procedures. All solvents were
transferred under vacuum. Hexane was distilled from sodium/
benzophenone and stored over [Cp2TiCl]2ZnCl2.29 Dichlo-
romethane was distilled from and stored over CaH2. Methanol
was dried and stored over Mg. Dichloromethane-d2 was dried
over P2O5 and stored over CaH2. KOMe was prepared by
reacting solid K with excess MeOH in Et2O, collecting the solid
by filtration, and drying the white solid under vacuum.
Cp (P MeP h 2)2Ru H (3). This method was adapted from the
literature preparation of Cp(PMe3)2RuH.10 MeOH (30 mL) was
added by vacuum transfer to a flask charged with Cp-
(PMePh2)2RuCl (1.0 g, 1.66 mmol) and KOMe (500 mg, 7.13
mmol). The orange reaction mixture was heated to reflux for
4-5 h, after which time the now yellow reaction mixture was
evaporated to dryness under vacuum. The reaction residue was
extracted with Et2O, until the extracts were colorless, and
filtered through Celite. The yellow filtrate was evaporated to
dryness under vacuum to give Cp(PMePh2)2RuH as a pale
yellow solid (794 mg, 79%; typical yields were 75-85%). 1H
NMR (250 MHz, CD2Cl2): δ 7.32 (m, 20H, Ph), 4.34 (s, 5H,
[BDE(Ru-Cl) - BDE(Ru-H)] (in kcal/mol) )
-[0.84 ( 0.40]ød - [0.06 ( 0.06]θ + (39.15 ( 4.39)
(5)
n ) 4; R2 ) 0.973
The [BDE(Ru-Cl) - BDE(Ru-H)] data in Table 2
and Figure 4 were consistent with three scenarios. (1)
Based on the constancy of the Ru-Cl bond lengths,
absolute BDE(Ru-Cl) may be constant regardless of the
PMe3-nPhn ligation. Absolute BDE(Ru-H) would then
decrease with increasing number of phosphine methyl
2
groups, a trend inconsistent with the J PH data and the
2
4
σ-donicity of the phosphines. (2) On the other hand,
absolute BDE(Ru-H) may be constant regardless of
PMe3-nPhn ligation, consistent with the observation that
BDE(Cr-H) did not change when PPh3 was replaced
with PEt3 in Cp(CO)2(PR3)CrH complexes.19 Absolute
BDE(Ru-Cl) would then increase with the number of
phosphine methyl groups, a trend inconsistent with the
Ru-Cl bond length data. (3) Alternatively, absolute
values of both BDE(Ru-Cl) and BDE(Ru-H) may
increase with the number of phosphine methyl groups,
but with BDE(Ru-Cl) increasing at a faster rate than
BDE(Ru-H).
Cp), 1.52 (filled-in-doublet, J PH + J PH ) 7.9 Hz, 6H, PMe),
-12.76 (t, 2J PH ) 34.9 Hz, 1H, RuH). 31P{1H} NMR (101 MHz,
CD2Cl2): δ 31.23 (s). IR (CH2Cl2): ν(Ru-H) 1896 (br) cm-1
.
Anal. Calcd for C31H32P2Ru: C, 65.60; H, 5.68. Found: C,
65.47; H, 5.38.
Cp(P Me2P h )2Ru H(2). Cp(PMe2Ph)2RuH was prepared from
the reaction of Cp(PMe2Ph)2RuCl (1.0 g, 2.1 mmol) with KOMe
(0.70 g, 10.0 mmol) in MeOH as described above for Cp-
(PMePh2)2RuH. Cp(PMe2Ph)2RuH was further purified by
sublimation at 100 °C (<0.01 mmHg) to yield 752 mg (82%) of
bright yellow, microcrystalline solid. Typical yields were 75-
1
85%. H NMR (250 MHz, CD2Cl2): δ 7.43 (m, 10H, Ph), 4.57
2
(s, 5H, Cp), 1.42 (filled-in-doublet, J PH + 4J PH ) 7.9 Hz, 12H,
Which scenario was active in 1-8 could not be
determined at this point due to a lack of absolute values
for either BDE(Ru-H) or BDE(Ru-Cl) as a function of
PMe3-nPhn ligation. BDE differences in solution were
the only reliable information obtainable from the ther-
mochemical experiments employed in this study. We
know that the energy difference, [BDE(Ru-Cl) - BDE-
(Ru-H)], increases with the number of phosphine
methyl groups, but we do not know at this time how
the energy scales for the Cp(PR3)2Ru moieties relate to
each other.
(20) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air-
Sensitive Compounds, 2nd ed.; Wiley-Interscience: New York, 1986.
(21) Ojelund, G.; Wadso¨, I. Acta Chem. Scand. 1968, 22, 1691-1699.
(22) Kilday, M. V. Res. Natl. Bur. Stand. (U.S.) 1980, 85, 467-481.
(23) Nolan, S. P.; Hoff, C. D.; Landrum, J . T. J . Organomet. Chem.
1985, 282, 357-362.
(24) Mukerjee, S. L.; Nolan, S. P.; Hoff, C. D.; de la Vega, R. Inorg.
Chem. 1988, 27, 81-85.
(25) Treichel, P. M.; Komar, D. A. Synth. React. Inorg. Met.-Org.
Chem. 1980, 10, 205-218.
(26) Lomprey, J . R.; Selegue, J . P. J . Am. Chem. Soc. 1992, 114,
5518-5523.
(27) Bruce, M. I.; Hameister, C.; Swincer, A. G.; Wallis, R. C. Inorg.
Synth. 1982, 21, 78-84.
(28) Davies, S. G.; Moon, S. D.; Simpson, S. J . J . Chem. Soc., Chem.
Commun. 1983, 1278-1279.
(19) Kiss, G.; Zhang, K.; Mukerjee, S. L.; Hoff, C. D.; Roper, G. C.
J . Am. Chem. Soc. 1990, 112, 5657-5658.
(29) Sekutowski, D. G.; Stucky, G. D. Inorg. Chem. 1975, 14, 2192-
2199.

4832 Organometallics, Vol. 19, No. 23, 2000
Freeman et al.
Ta ble 3. X-r a y Cr ysta llogr a p h ic Da ta for Cp Ru (P Me2P h )2Cl (2) a n d Cp Ru (P MeP h 2)2Cl (3)
2
3
empirical formula
cryst dimens, mm
cryst syst
space group
a, Å
C
21H27ClP2Ru
C31H31ClP2Ru
0.12 × 0.32 × 0.62
0.20 × 0.36 × 0.60
orthorhombic
monoclinic
Pbca
P21/c
9.244(1)
16.106(1)
b, Å
14.220(1)
15.079(2)
c, Å
37.378(4)
19.991(2)
R, deg
90
90
â, deg
90
94.377(8)
γ, deg
90
90
volume, Å3
Z
8560.8(1.3)
2778.3(5)
16
4
fw, amu
477.89
602.02
calc density, g/cm3
µ, cm-1
1.483
1.439
7.94
1232
10.09
F(000)
3904
temperature, K
scan type
scan rate, deg/min
2θ, deg
295 ( 2
295 ( 2
ω, variable
4.0-20.0
ω, variable
4.0-10.0
5.0-50.0
10-25
h (-1 e h e 19)
k (-1 e k e 16)
l (-44 e l e 1)
9040
7515 (Rint ) 0.0402)
4679
R1 ) 0.0456; wR2 ) 0.0746
R1 ) 0.1011; wR2 ) 0.0927
1.001
0.0280, 0.0000
460
3.4-50.0
14-25
h (-1 e h e 10)
k (-1 e k e 17)
l (-23 e l e 23)
6322
4871 (Rint ) 0.0175)
3837
R1 ) 0.0285; wR2 ) 0.0569
R1 ) 0.0470; wR2 ) 0.0641
1.039
0.0262, 0.2493
319
2θ, centered reflns
reflns sampled
no. of reflns collected
no. of unique data
no. of data, I > 2σ(I)
R indices, I > 2σ(I)
R indices, all data
σ1, GOF
weighting, a and b
no. of variables
max. diff peak and hole
0.438, -0.402
0.338, -0.265
PMe), -13.43 (t, 2J PH ) 35.6 Hz, 1H, RuH). 31P{1H} NMR (101
MHz, CD2Cl2): δ 29.04 (s). IR (CH2Cl2): ν(Ru-H) 1904 (br)
cm-1. Anal. Calcd for C21H28P2Ru: C, 56.88; H, 6.36. Found:
C, 56.66; H, 6.02.
all species in solution, the enthalpy of solution for the
ruthenium hydrides had to be directly measured. The calo-
rimeter cells were loaded in the exact fashion as in the example
described above with the exception that no CCl4 was intro-
duced into the reaction cell. The measured enthalpy of solution
for Cp(PPh3)2RuH is 6.7 ( 0.2 kcal/mol and represents seven
separate determinations. To ensure that no decomposition had
occurred during the thermal equilibration at 30 °C, a CH2Cl2
solution of Cp(PPh3)2RuH was maintained at 30 °C for 3 h;
the solvent was then removed and the residue examined by
NMR spectroscopy. No decomposition of the ruthenium hy-
drides in CH2Cl2 was observed during this time.
Ru th en iu m Hyd r id e/Ch lor id e Meta th esis: 1H NMR
Stu d ies. The H/Cl metathesis reactions were examined by 1H
NMR spectroscopy prior to every set of calorimetric experi-
ments. An excess of chlorocarbon (CHCl3 or CCl4) was added
to a CD2Cl2 solution of a ruthenium hydride. After vigorous
mixing, the reactions were monitored by 1H NMR spectroscopy
and were found to be rapid and quantitative, conditions
necessary for accurate and meaningful calorimetric results.
These criteria were satisfied for all of the hydride/chloride
metathesis reactions investigated.
X-r a y Cr ysta l Str u ctu r e Deter m in a tion s of Cp (P Me2-
P h )2Ru Cl (2) a n d Cp (P MeP h 2)2Ru Cl (3). Crystals suitable
for X-ray diffraction analysis were grown by vapor diffusion
of hexanes into saturated CH2Cl2 solutions of Cp(PMe2-
Ph)2RuCl and Cp(PMePh2)2RuCl. The same general procedures
were followed for the structural analyses of Cp(PMe2Ph)2RuCl
and Cp(PMePh2)2RuCl. A suitable crystal of each compound
was sealed under a nitrogen atmosphere in a glass capillary
tube and then optically aligned on the goniostat of a Siemens
P4 automated X-ray diffractometer. The reflections that were
used for the determination of the cell parameters were located
and indexed by the automatic peak search routine XSCANS.30
For CpRu(PMePh2)2Cl, the systematic absences were consis-
tent with the centrosymmetric monoclinic space group P21/c
(No. 14, C2h),5 whereas for CpRu(PMe2Ph)2Cl the systematic
absences were compatible with the centrosymmetric orthor-
Ru th en iu m Hyd r id e/Ch lor id e Meta th esis: Ca lor im et-
r ic Mea su r em en ts. 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
Cp(PPh3)2RuH was accurately weighed into the lower vessel,
and it was closed and sealed with 1.5 mL of mercury. Four
milliliters of a stock solution of CCl4 [5 mL in 25 mL of CH2-
Cl2] 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 ruthenium hydride complex was added
to the lower vessel. After the calorimeter had reached thermal
equilibrium at 30.0 °C (about 2 h), the reaction was initiated
by inverting the calorimeter. At the end of the reaction (1-2
h), the vessels were removed from the calorimeter, taken into
the glovebox, and opened, and an NMR tube was filled under
inert atmosphere. An NMR spectrum of each product was
recorded using this procedure. Conversion to Cp(PPh3)2RuCl
was found to be quantitative under these reaction conditions.
The enthalpy of reaction, -36.9 ( 0.1 kcal/mol, represents the
average of five individual calorimetric determinations. This
methodology represents a typical procedure involving all
organometallic compounds and all reactions investigated in
the present study.
hombic space group Pbca (No. 61, D2h)
15 with two independent
molecules in the asymmetric unit. The refined lattice param-
eters and orientation matrix were calculated from a nonlinear
least-squares fit of the orientation angles of at least 40
centered reflections at 22 °C. Pertinent crystallographic data
are summarized in Table 3.
Intensity data were measured with graphite-monochro-
mated Mo KR radiation (λ ) 0.71073 Å) and variable ω scans.
Background counts were measured at the beginning and at
Ca lor im etr ic Deter m in a tion of th e En th a lp y of Solu -
tion for th e Ru th en iu m Hyd r id es in CH2Cl2. To consider
(30) XSCANS (version 2.0) is
developed by Siemens Analytical X-ray Instruments, Madison, WI.
a diffractometer control system

Bond Disruption Enthalpies of Ru-H and Ru-Cl Bonds
Organometallics, Vol. 19, No. 23, 2000 4833
the end of each scan with the crystal and counter kept
stationary. The intensities of three standard reflections were
measured after every 100 reflections, and their combined
intensity did not decrease during data collection. The data
were corrected for Lorentz-polarization, and equivalent reflec-
tions were merged. For CpRu(PMePh2)2Cl, an empirical ab-
sorption correction (range of transmission coefficients: 0.890-
0.977) based upon the PSI scans measured for eight reflections
(ø ≈ 90°, 2θ ) 8-46°) was applied to the diffraction data. For
CpRu(PMe2Ph)2Cl, an empirical absorption correction (range
of transmission coefficients: 0.821-0.984) based upon the PSI
scans recorded for seven reflections (ø ≈ 90°, 2θ ) 8-40°) was
applied.
[σ2(Fo2) + (aP)2 + bP] where P ) (Max(Fo2,0) + 2Fc2)/3, was
performed with SHELXL-93.31 After convergence, the final
discrepancy indices32 for CpRu(PMePh2)2Cl were R1 ) 0.0285,
wR2 ) 0.0569 for 3837 reflections with I > 2σ(I). The
corresponding R-factors for CpRu(PMe2Ph)2Cl were R1 )
0.0456, wR2 ) 0.0746 for 4679 reflections with I > 2σ(I).
Ack n ow led gm en t. F.R.L. acknowledges the donors
of the Petroleum Research Fund, administered by the
American Chemical Society, for support of this research,
and J ohnson Matthey for the generous loan of RuCl3‚
nH2O. S.P.N. acknowledges the financial support pro-
vided by the National Science Foundation (Grant No.
CHE-9985213). J .L.P. acknowledges the financial sup-
port provided by the Chemical Instrumentation Pro-
gram of the National Science Foundation (Grant No.
CHE-9120098) to acquire a Siemens P4 X-ray diffrac-
tometer in the Department of Chemistry at West
Virginia University.
The positions of the non-hydrogen atoms were determined
by a combination of direct methods and difference Fourier
calculations, which were performed with algorithms provided
by SHELXTL IRIS operating on a Silicon Graphics IRIS Indigo
workstation. Idealized positions for the hydrogen atoms were
included as fixed contributions using a riding model with
isotropic temperature factors set at 1.2 times that of the
adjacent carbon. The positions of the methyl hydrogens were
optimized by a rigid rotating group refinement with idealized
tetrahedral angles. Full-matrix least-squares refinement,
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data collection and refinement parameters, positional and
anisotropic displacement parameters, and interatomic dis-
tances and angles for Cp(PMe2Ph)2RuCl (2) and Cp(PMePh2)2-
RuCl (3) and the perspective view of the other independent
molecule in the unit cell of 2. This material is available free
of charge via the Internet at http://pubs.acs.org.
2
2 2
based upon the minimization of ∑wi|Fo - Fc | , with wi-1
)
(31) SHELXL-93 is a FORTRAN-77 program (Professor G. Sheld-
rick, Institut fu¨r Anorganische Chemie, University of Go¨ttingen,
D-37077, Go¨ttingen, Germany) for single-crystal X-ray structural
analyses.
(32) The R-factors were calculated from the expressions R1 ) ∑||Fo|
- |Fc||/∑|Fo| and wR2 ) [∑(wi(Fo - Fc2)2]/∑[wi(Fo2)2)]1/2. The standard
2
OM000420X
2
deviation of an observation of unit weight (GOF) is equal to [∑(wi(Fo
- Fc2)2)/(n - p)]1/2, where n is the number of reflections and p is the
number of parameters that were varied during the last refinement
cycle.
(33) Chase, M. W., J r. J . Phys. Chem. Ref. Data, Monograph 9 1998,
1-1951.