Kinetics of phosphine substitution in CpRu(PPh3)2X (X = Cl, Br, I, N3, and NCO)

Article abstract of DOI:10.1039/c7ra02793a

The kinetics of phosphine substitution in CpRu(PPh₃)₂X (X = Br, 1b, X = I, 1c, X = N₃, 1d, and X = NCO, 1e) have been measured under pseudo-first order conditions in THF solution and compared with data for CpRu(PPh₃)₂X (1a). The relative rate of substitution is found to be 1a > 1d > 1b > 1e > 1c. Substitution rates decrease in the presence of added PPh₃ and are independent of added X consistent with a dissociative process. Activation parameters for 1a-1c (ΔH^? = 113-135 kJ mol^-1, ΔS^? = 21-102 J mol^-1 K^-1) and DFT calculations support a dissociative or dissociative interchange pathway even though negative activation entropies (ΔS^? = -48 ± 16 to -105 ± 5 J mol^-1 K^-1) are observed for 1d-e. Differences in Ru-ligand bond angles in 1d-e point to different π-acceptor properties of the pseudohalide ligands, contributing to the faster rate of substitution for the azide complexes, 1d relative to the cyanate derivative 1e. Substitution is not observed when X = F, 1f, X = H, 1g, X = SnF₃, 1h, or X = SnCl₃, 1i. Compounds 1b-1e also react with chloroform to yield 1a. The rates of halide exchange are comparable to phosphine substitution for 1c and 1d. The latter reaction is inhibited by excess triphenylphosphine and is unaffected by both radical inhibitors and radical traps suggesting that a radical mechanism is unlikely.

Full text of DOI:10.1039/c7ra02793a

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Kinetics of phosphine substitution in CpRu(PPh3)2X
(X ¼ Cl, Br, I, N3, and NCO)†
Cite this: RSC Adv., 2017, 7, 34425
David Hill,a Connor Delaney,a Miles Clark,a Mathew Eaton,a Bakar Hassan,a
Olivia Hendricks,b Duy Khoi Danga and Rein U. Kirss
*
a
The kinetics of phosphine substitution in CpRu(PPh3)2X (X ¼ Br, 1b, X ¼ I, 1c, X ¼ N3, 1d, and X ¼ NCO, 1e)
have been measured under pseudo-first order conditions in THF solution and compared with data for
CpRu(PPh3)2X (1a). The relative rate of substitution is found to be 1a > 1d > 1b > 1e > 1c. Substitution
rates decrease in the presence of added PPh3 and are independent of added X consistent with
a dissociative process. Activation parameters for 1a–1c (DH† ¼ 113–135 kJ molꢀ1, DS† ¼ 21–102 J molꢀ1
K
ꢀ1) and DFT calculations support a dissociative or dissociative interchange pathway even though
negative activation entropies (DS† ¼ ꢀ48 ꢁ 16 to ꢀ105 ꢁ 5 J molꢀ1
K
ꢀ1) are observed for 1d–e.
Differences in Ru–ligand bond angles in 1d–e point to different p-acceptor properties of the
pseudohalide ligands, contributing to the faster rate of substitution for the azide complexes, 1d relative
to the cyanate derivative 1e. Substitution is not observed when X ¼ F, 1f, X ¼ H, 1g, X ¼ SnF3, 1h, or X ¼
SnCl3, 1i. Compounds 1b–1e also react with chloroform to yield 1a. The rates of halide exchange are
comparable to phosphine substitution for 1c and 1d. The latter reaction is inhibited by excess
triphenylphosphine and is unaffected by both radical inhibitors and radical traps suggesting that a radical
mechanism is unlikely.
Received 7th March 2017
Accepted 15th June 2017
DOI: 10.1039/c7ra02793a
rsc.li/rsc-advances
and SnBr3) follows the order: X ¼ SnF3 > SnCl3 z SnBr3 > F > Cl
z Br.5 In this case, dissociation of chloride is thought to be
Introduction
counterproductive to efficient catalysis with the greater activity
of CpRu(PPh3)2SnF3 attributed to phosphine dissociation. The
kinetics of phosphine substitution in CpRu(PAr3)2Cl6,7 and the
rate of solvolysis of the halide in CpRu(PR2R0)2X (R ¼ Ph, Me, X
¼ Cl, Br, I)8 have both been measured but the effect of X on the
rate of phosphine substitution (eqn (1)) has not been extensively
explored. Only for the related Cp*Ru(PMe3)2X9 has the effect of
the ancillary X ligand on the rate of phosphine substitution
been systematically investigated. The data for the latter were
consistent with a dissociative mechanism with a marked
increase in rate for better p-donor X ligands. In the present
study we report on the phosphine substitution in CpRu(PPh3)2X
(eqn (1), 1b–i where X ¼ Br, I, N3, NCO, H, F, SnCl3, and SnF3) in
THF as well as on the unexpected halide exchange reaction
between 1b–e and CDCl3. The results provide some insight into
the relative importance of Ru–P dissociation in catalytic reac-
tions involving 1a–i.
Cyclopentadienyl ruthenium bis(triphenylphosphine) chloride,
CpRu(PPh3)2Cl (1a), is a versatile catalyst for a range of useful
transformations.1 Changing the halide ligand in CpRu(PPh3)2Cl
for other halides or pseudohalides affects both the reactivity
and selectivity in these processes.2 For example, CpRu(PPh3)2I
(generated in situ) is reported to be more effective than
CpRu(PPh3)2Cl in catalyzing the cycloaddition of norbornene
and norbornadiene.3 A mechanism based on faster phosphine
dissociation is proposed as the explanation for the increased
catalytic activity of CpRu(PPh3)2I. On the other hand,
CpRu(PPh3)2X catalyzed conversion of cyclohexylamine and
methanol to CyNMe2 is nearly quantitative aer 6 hours at
100 ꢂC for X ¼ Cl while only 40% conversion to 2.4 : 2.8 : 1 ratio
of cyclohexylimine, methylcyclohexylamine and CyNMe2 is
observed for X ¼ I.4 In this case, the ionization of the Ru–X bond
is proposed as the key step the reaction mechanism. The
conversion rate of methanol to methyl acetate in the presence of
catalytic amounts of CpRu(PPh3)2X (X ¼ F, Cl, Br, SnF3, SnCl3
Experimental
aDepartment of Chemistry and Chemical Biology, Northeastern University, Boston, MA
02115, USA. E-mail: r.kirss@neu.edu
All compounds described in this work were handled using
Schlenk techniques or a M. I. Braun glove box under puried
nitrogen atmospheres.10 RuCl3$xH2O was purchased from
Pressure Chemical, Inc. Tertiary phosphines, PMePh2 and
PPh3, were obtained from Strem Chemical, Inc. and used as
bDepartment of Chemistry, Wellesley College, Wellesley, MA 02481, USA
† Electronic supplementary information (ESI) available: Representative plots ln
[CpRu(PPh3)2X] vs. t for phosphine substitution and halide exchange, Eyring
plots, and coordinates for the optimized geometries for 1a–e. See DOI:
10.1039/c7ra02793a
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 34425–34434 | 34425

View Article Online
RSC Advances
Paper
(1)
received. Solvents were puried by reuxing over Na/
benzophenone (toluene, tetrahydrofuran, benzene, hexane,
pentane), P2O5 (dichloromethane) or MgSO4 (ethanol) and
distilled prior to use. Chloroform-d1 and benzene-d6 (Cam-
bridge Isotope Laboratories) were puried by distillation
from CaH2 and Na/benzophenone, respectively. Ruth-
enium(II) compounds CpRu(PPh3)2Cl (1a),11 CpRu(PPh3)2Br
Synthesis of CpRu(PPh3)(PMePh2)X (X ¼ Br, I, NCO, N3, SCN,
and SnCl3)
General procedure. A slurry of CpRu(PPh3)(PMePh2) Cl (2a)
and a 5–10 fold excess of KX (X ¼ Br, I, N3, NCO, SCN) was
reuxed in 25 mL absolute ethanol for 16–18 h under nitrogen.
Solvent was evaporated under vacuum and the product extrac-
ted with 2 ꢃ 25 mL CH2Cl2. Aer ltration to remove the
potassium salts, the ltrate was evaporated to dryness and the
crude product crystallized from CH2Cl2/hexane to yield
CpRu(PPh3)2X (1b–f). Chromatography on neutral alumina with
dichloromethane served as an additional purication method.
CpRu(PPh3)(PMePh2)Br (2b). Yellow-orange solid, 75% yield.
(1b),12
CpRu(PPh3)2I
(1c),12
CpRu(PPh3)2N3
(1d),13
CpRu(PPh3)2NCO (1e),12 CpRu(PPh3)2H (1f),12 CpRu(PPh3)2F
(1g),14 CpRu(PPh3)2SnF3 (1h),13 CpRu(PPh3)2SnCl3 (1i),13 and
CpRu(PPh3)(PPh2Me)Cl (2a),15 were prepared by literature
procedures. Melting points were determined in capillary
tubes using an Electrothermal 9110 melting point
apparatus and are uncorrected. Elemental analyses (C, H)
were performed by Columbia Analytical Services, Inc.
Tucson, AZ.
ꢂ
Mp turns dark brown without melting above 160 C.
Calculated for C36H33P2RuBr$CH2Cl2: 56.01% C, 4.45% H;
found: 56.53% C, 5.35% H.
1H (CDCl3) d 1.19 d (J ¼ 8.8 Hz, 3H, PCH3), 4.20 s (5H, Cp),
5.29 s (2H, CH2Cl2), 7.0–7.8 m (25 H, aryl).
NMR spectra were recorded at 400 MHz for 1H and 162 MHz
for 31P{1H} on a Mercury XL300 spectrometer. Proton chemical
shis are reported relative to residual protons in the solvent
(CD2HCl at d 7.24 ppm relative to TMS at 0.00 ppm). Phos-
phorus chemical shis are reported relative to 85% H3PO4 at
0.0 ppm.
Electrochemical measurements were made under
nitrogen on a BAS 100 B/W electrochemical workstation at
22 ꢂC using 1 ꢃ 10ꢀ3 M solutions in dry CH2Cl2, 0.1 M
nBu4NPF6 as supporting electrolyte at a scan rate of 100 mV
sꢀ1. The working electrode was a 3 mm Pt disk with a Pt wire
as auxiliary electrode. A silver wire was used as a pseudo-
reference electrode with ferrocene added as an internal
standard. All potentials for 1a–e, h and i (Table 1) are refer-
enced to ferrocene (E1/2 ¼ 0.00 V).
31P (CDCl3) d 42.9 d (JPP ¼ 43 Hz), 29.9 d (JPP ¼ 43 Hz).
CpRu(PPh3)(PMePh2)I (2c). Yellow-orange solꢂid, 51% yield. Mp
turns dark brown without melting above 140 C.
Calculated for C36H33P2RuI$CH2Cl2: 52.87% C, 4.20% H;
found: 53.08% C, 4.67% H.
1H (CDCl3) d 1.31 d (J ¼ 8.8 Hz, 3H, PCH3), 4.27 s (5H, Cp),
5.24 s (2H, CH2Cl2), 7.0–7.8 m (25 H, aryl).
31P (CDCl3) d 42.9 d (JPP ¼ 43 Hz), 30.0 d (JPP ¼ 43 Hz).
CpRu(PPh3)(PMePh2)N3 (2d). Yellow-orange solid, 15% yield.
ꢂ
Mp turns dark brown without melting above 163 C.
Calculated for C36H33N3P2Ru: 64.47% C, 4.96% H; found:
63.93% C, 5.31% H.
1H (CDCl3) d 1.17 d (J ¼ 8.8 Hz, 3H, PCH3), 4.23 s (5H, Cp),
7.21–7.46 m (25 H, aryl).
31P (CDCl3) d 41.3 d (JPP ¼ 43 Hz), 30.3 d (JPP ¼ 43 Hz).
CpRu(PPh3)(PMePh2)NCO (2e). Yellow-orangeꢂ solid, 74%
yield. Mp turns black without melting above 160 C.
Calculated for C37H33NOP2Ru: 66.26% C, 4.96% H; found:
66.45% C, 5.28% H.
Table
1 Electrochemical potentials for selected CpRu(PPh3)2X
complexesa
Compound
Eꢂ (mV)
Compound
Eꢂ (mV)
X ¼ Cl, 1a
X ¼ Br, 1b
X ¼ I, 1c
136
138
182
20
X ¼ NCO, 1e
X ¼ F, 1g
168
1H (CDCl3) d 1.06 d (J ¼ 8.8 Hz, 3H, PCH3), 4.15 s (5H, Cp),
7.18–7.3 m (25 H, aryl).
790
b
X ¼ SnF3, 1h
31P (CDCl3) d 39.5 d (JPP ¼ 43 Hz), 30.7 d (JPP ¼ 42 Hz).
CpRu(PPh3)(PMePh2)SnCl3 (2i). A solution of 172 mg (0.26
mmol) 2a and 54 mg (0.28 mmol) SnCl2 in 50 mL absolute ethanol
was reuxed for 90 minutes. The resulting precipitate was isolated
X ¼ N3, 1d
X ¼ SnCl3, 1i
730
a
1 ꢃ 10ꢀ3 M solutions in dry CH2Cl2, 0.1 M nBu4NPF6 as supporting
electrolyte at a scan rate of 100 mV sꢀ1 at 22 ꢂC vs. Fc/Fc+ at 0.00 mV.
b
1h is not sufficiently soluble for the experiment.
34426 | RSC Adv., 2017, 7, 34425–34434
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
by ltration, washed 2 ꢃ 5 mL methanol and dried under
vacuum. Compound 2i was isolated in 68% yield as an orange
solid. Mp. turns dark brown without melting 151–153 ꢂC.
Calculated for C36H33P2RuSnCl3: 50.65% C, 3.90% H; found:
50.83% C, 4.54% H.
Results
Kinetics of phosphine exchange
The substitution of one PPh3 in 1b–e by PPh2Me (10–15 equiv-
alents, pseudo rst order conditions) was followed by 31P NMR
in both CDCl3 and THF/10% C6D6 (v/v) solution between 25 and
60 ꢂC. The singlet resonance for the starting material is replaced
by a pair of doublets assigned to the mono-substituted prod-
ucts, CpRu(PPh3)(PPh2Me)X (2b–e) with concurrent appearance
of resonances for PPh3 (d ꢀ 4.4 ppm in CDCl3, ꢀ4.6 ppm in
THF/10% C6D6). The 31P chemical shis of the products were
veried by comparison with independently synthesized and
characterized samples of 2b–f. Formation of CpRu(PPh2Me)2X
(i.e. di-substitution) is not observed during the reaction period
even in the presence of z10 equivalents of PMePh2. Formation
of 1b–c from reactions between 2b–c and PPh3 is not observed.
Qualitatively, the rate of reaction at 40 ꢂC is found to be 1a > 1d >
1b z 1e > 1c.
1H (CDCl3) d 1.19 d (J ¼ 8.8 Hz, 3H, PCH3), 4.19 s (5H, Cp),
6.9–7.7 m (28 H, aryl).
31P (CDCl3) d 43.4 d (JPP ¼ 44 Hz), 30.4 d (JPP ¼ 44 Hz).
Kinetic measurements
Reactions of 1b–e with PMePh2. The collection of kinetic data
for reactions between 1b–e with PMePh2 followed procedures
described for reactions between CpRu(PAr3)2Cl and PMePh2.6
Stock solutions of 1b–e (10.0 mL) were prepared in volumetric
asks by dissolving an appropriate amount of 1b–e and a 10–15
fold excess of PMePh2 in CDCl3 or THF containing 10% C6D6.
Samples for the kinetic experiments were prepared by transferring
600 mL of the stock solution to 5 mm NMR tubes attached to 14/20
ground glass joints. The tubes were ame-sealed sealed under
Reactions between CpRu(PPh3)2X and PMePh2 in THF solu-
tion follow rst order kinetics over several half-lives. Rate
constants, half-lives and activation parameters for reactions in
THF/C6D6 mixtures are summarized in Fig. 1 and Table 2. The
reaction rates are largely independent of the [PMePh2], up to 60
equivalents (Fig. 2 and Table S3†). By comparison, the reaction
rate decreases dramatically in the presence of added PPh3. In
addition, the reaction rates are unaffected by the addition of
ꢂ
vacuum. Samples were stored at ꢀ20 C until needed and then
heated in thermostated block heaters. The rate of substitution of
PPh3 by PMe2Ph was measured by monitoring the decrease in the
singlet for CpRu (PPh3)2X (1b–e) over time relative to the doublets
for CpRu(PPh3)(PMePh2)X (2b–e). Three independent measure-
ments of the substitution rate were made at each temperature to
determine the rate constants for the reaction.
n
excess Bu4NX in all four cases.18 The rates of phosphine
To assess the effect of excess PPh3 and Xꢀ, additional
experiments were carried out by adding 600 mL of the stock
solution to weighed amounts of PPh3 (3–10 equivalents) or
nBu4NX (z10 equivalents). The resulting solutions were trans-
ferred to NMR tubes and sealed as described above. These
experiments were typically limited to a single measurement of
the substitution rate at one temperature.
substitution in 1a in both CDCl3 and in THF are known.6,7 The
remaining complexes, 1f–g and 1i fail to react with excess
PMePh2 in THF/C6D6, dioxane/C6D6 or other solvent mixtures
up to the boiling point of the solvents even aer 30 days or
more. Compound 1h has minimal solubility in THF and
dioxane hampering comparable studies, however, phosphine
substitution was not observed.
Activation parameters were determined using the Eyring
equation by plotting ln(kobs/T) vs. 1/T where the slope ¼ ꢀDH‡/R
and the intercept ¼ DS‡/R + ln kB/h as described in our prior
work.6 The activation entropies and enthalpies were also
calculated from the slope and intercept of a plot of T ln(k/T) vs.
T, respectively.16 The same values for DH‡ and DS‡ were ob-
tained using each method within error. Errors in DS‡ and DH‡
were calculated using the statistical packages in Excel and by
procedures described in standard analytical chemistry texts.17
Reactions of 1c–d with CDCl3. Flame sealed tubes containing
10–15 mM solutions of 1c–d were prepared as described for the
reactions with PMePh2. The rate of the halide exchange reaction
was determined by integration of the singlets assigned to 1a and
1c–d in the 31P NMR spectra. Additional tubes containing PPh3
(6–21 eq.), 9,10-dihydroanthraene (3–16 eq.) and duroquinone
(2–24 eq.) were prepared by adding 600 mL of the stock solution
to weighed amounts of these reagents.
The activation parameters reveal different trends for the
halide complexes 1a–c and the pseudohalide complexes 1d–e.
Activation enthalpies for the former are generally larger and
the activation entropies are positive. The activation entropies
for 1d and 1e, however, are negative. The free energies of
activation (DG‡) calculated at 25 ꢂC (298 K) for 1a–e are similar
Computational methods
All calculations were conducted using density functional theory
(DFT) as implemented in the Gaussian09 Revision B.01 suite of
ab initio quantum chemistry programs as described for phos-
Fig. 1 Eyring plots of ln(kobs/T) vs. 1/T for 1b–e in THF containing 10%
phine substitution in 1a and related CpRu(PAr3)2Cl complexes.6 v/v C6D6.
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 34425–34434 | 34427

View Article Online
RSC Advances
Paper
a
Table 2 Rate constants, half-lives, and activation parameters for the substitution of PPh3 by PMePh2 in 1a–e in THF containing 10% (v/v) C6D6
X
k30,THF (ꢃ106 sꢀ1
)
t1/2 (h)
DH‡ (kJ molꢀ1
)
DS‡ (J molꢀ1 Kꢀ1
)
DG‡ (kJ molꢀ1
)
1a, Clꢀ
1b, Brꢀ
1c, Iꢀ
29 ꢁ 2b
0.66
24
77
7.8
12
121 ꢁ 4b
135 ꢁ 7
113 ꢁ 4
86 ꢁ 5
71 ꢁ 8b
100
105
107
100
101
7.89 ꢁ 0.79
2.49 ꢁ 0.3
24.6 ꢁ 1.5
16.1 ꢁ 3.6
102 ꢁ 23
21 ꢁ 12
ꢀ
1d, N3
ꢀ48 ꢁ 16
1e, NCOꢀ
70 ꢁ 7
ꢀ105 ꢁ 23
a
Concentrations of 1b–e ranged from 8 to 17 mM with a z 10–15 fold excess of PMePh2. Benzene-d6 is added to lock and shim the spectrometer.
From ref. 7.
b
in these reactions is suppressed in the presence of added
nBu4NX. The rate of substitution, however, remains unaf-
fected by the presence of excess Xꢀ. Comparison of the values
for ksubs,THF with ksubs,CDCl for 1a–e indicate that reactions
3
are between 1.5 and 5 times faster in THF solution.
Kinetics of halide exchange between 1c–d and CDCl3
The rates of the halide exchange reactions between 1c and 1d
with CDCl3 were measured independently by integration of the
31P resonances for reactants (1c–d) and product (1a) in CDCl3 at
ꢂ
30 C. Linear plots of ln[CpRu(PPh3)2X] vs. time are observed
for both compounds, with rst order rate constants for the
reaction (kCDCl ) being listed in Table 3. The rate of reaction
3
with CDCl3 reects the same order observed for phosphine
substitution: 1d > 1c. The reaction rates of 1c–d in CDCl3 were
Fig. 2 Plots of kobs as a function of [PMePh2] and [PPh3] for the
reaction between CpRu(PPh3)2X (1b–e) and excess PMePh2 in THF.
The data are for reactions at 30 ꢂC except for X ¼ N3 (1d) which was
collected at 35 ꢂC.
further investigated in the presence of excess PPh3, (6–21 eq.),
a radical initiator, 9,10-dihydroanthracene, (3–16 eq.), and
a radical trap, duroquinone, (2–24 eq.). Fig. 3 reveals that the
reaction rates are essentially independent of radical initiators
and traps but are slowed signicantly by the presence of PPh3.
The ksubs,CDCl /kCDCl ratio in Table 3 reveals that the rate of
to those reported for Cp*Ru(PMe3)2X: 109 kJ molꢀ1, 106 kJ
molꢀ1 and 113 kJ molꢀ1 for X ¼ Cl, Br, and I, respectively.9
Pseudohalide derivatives in the Cp*Ru(PMe3)2X series were
not studied.
3
3
reaction with CDCl3 is competitive with the rate of phosphine
substitution for 1c–d.
Reactions between 1b–e and PMePh2 were also investi-
gated in CDCl3 but were complicated by the appearance of 1a
Computational studies
(d 39.9 ppm) and 2a as the reaction progressed. The forma- DFT calculations were initially used to optimize the structures
tion of 1a is the result of reaction between the starting of 1a–e (Table 4). The calculated values for bond distances and
materials and the solvent since the starting materials were bond angles for 1a–b and 1d compare favorably with the pub-
pure by 31P NMR at the outset of the reaction. Thus the nal lished structures determined by X-ray crystallography: the
reaction mixtures in CDCl3 contain 2b–e and 2a. Neverthe- calculated bond distances are only slightly longer than the
less, the rate of reaction between excess PMePh2 (10–15 observed values.19
equivalents, i.e. pseudo rst order conditions in PMePh2) and
Computational chemistry was then applied to the calcula-
1b–e at early reactions times could be measured by integra- tion of the relative energies of potential intermediates in
tion of the 31P resonances for reactant and product before a dissociation of PPh3 in 1a–e. The free energies for the 16-
halide exchange led to measurable quantities of 1a. Quali- electron intermediate that results from PPh3 dissociation from
tatively, the order of the rates for the reaction of 1b–e with 1a–e (second column in Table 5) are quite similar to each other
PMePh2 in CDCl3 is the same as in THF: 1a > 1d > 1b > 1e > 1c. and lower than the energies for intermediates resulting from
Reasonable estimates of rst order rate constants (ksubs,CDCl
)
halide dissociation and coordination of THF (third column in
3
for the substitution reactions in CDCl3 at early reaction Table 5). The calculated free energy changes for the overall
times, when less than 5% of 1a (and no 2a) is observed in the conversion of 1a–e to 2a–e are listed in the fourth column of
solution, are summarized in Table 3. The substitution is Table 5 indicating a fairly narrow range of value for DG of about
slowed by the addition of excess PPh3 and the formation of 1a 12 kJ molꢀ1
.
34428 | RSC Adv., 2017, 7, 34425–34434
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
Table 3 Estimated first order rate constants for substitution of PPh3 by PMePh2 in 1a–e in CDCl3a and first order rate constants for the reaction of
1c–d with CDCl3
X
k30,susb,CDCl (ꢃ106 sꢀ1
)
k30,THF/k30,susb,CDCl
k30,CDCl (ꢃ106 sꢀ1
)
k30,susb,CDCl /k30,CDCl
3
3
3
3
3
1a, Cl
1b, Br
1c, I
1d, N3
1e, NCO
13b
2.2b
1.6
1.4
4.0
4.6
—
—
—
3
1
—
5.0 ꢁ 0.3
1.8 ꢁ 0.2
6.1 ꢁ 0.1
3.5 ꢁ 0.5
0.54 ꢁ 0.2
6.6 ꢁ 0.4
—
a
Concentrations of 1a–e ranged from 12 to 18 mM in CDCl3 with a z 10 fold excess of PMePh2. b From data in ref. 6 and 7.
(2)
The energies of the transition states for the two steps in eqn
(2) were also calculated (Table 6). The data indicate that the
activation energy for the dissociation of PPh3 is greater than for
the reaction of the 16 eꢀ intermediate, CpRu(PPh3)X, with
PMePh2, consistent with the kinetic measurements. The calcu-
lated values of DG for the transitions states of 1a–e are also quite
close in energy, covering a range of <4 kJ molꢀ1 for the rate-
determining step and about 8–12 kJ molꢀ1 less than the
values of DG‡ from experiment.
Discussion
The effect of the X group on phosphine substitution rates in 1a–
e is qualitatively similar to those reported previously for
Cp*Ru(PMe3)2X for the same set of X ligands. An increase in the
rate of substitution in Cp*Ru(PMe3)2X is observed for X ligands
with lone pairs of electrons on the donor atom, e.g. X ¼ Cl, Br, I,
NPh2, NHPh, OPh, OH, and SH relative to such s-donor ligands
such as H, CH3, CH2Ph, Ph and CH2SiMe3.9 Kinetic data for
phosphine exchange between Cp*Ru(PMe3)2X and PMe3 in
aromatic hydrocarbon solution are consistent with
Fig. 3 Plot of ln[CpRu(PPh3)2I] vs. time (s) for halide exchange in CDCl3
solution at 30 ꢂC. (a) 1c in the presence of 9,10-dihydroanthracene
(DHA, 3 eq.), duroquinone (DQ, 7 eq.) and PPh3 (21 eq.) and (b) 1d in the
presence of 9,10-dihydroanthracene (DHA, 2 eq.), duroquinone (DQ, 3
eq.) and PPh3 (6 eq.).
Table 4 Calculateda and observedb bond distances and bond angles for 1a–e
(ꢂ)
Ru–X
˚
˚
˚
˚
Compound
dRu–X (A)
dRu–P1 (A)
dRu–P2 (A)
dRu–Cp,centroid (A)
:
1a
1b
2.513
2.448b
2.648
2.568b
2.842
2.196
2.135b
2.136
2.401
2.323b
2.406
2.323b
2.416
2.401
2.329b
2.400
2.396
2.329b
2.411
2.329b
2.413
2.400
2.330b
2.3999
2.27
—
—
—
—
—
118.5
124.5b
153.5
2.20b
2.27
2.214b
2.275
2.275
1.843b
2.27
1c
1d
1e
a
The isocyanate ligand is treated as N bonded. Calculations use the B3LYP functional and the DGDZVP basis set on the Gaussian 09 suite. Normal
b
convergence conditions were applied and geometries were determined to be of a minimal through a frequency calculation. From X-ray
crystallography see ref. 19. This value seems abnormally short for a Cp–Ru bond.
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 34425–34434 | 34429

View Article Online
RSC Advances
Paper
Table 5 Calculated Gibbs free energies (kJ molꢀ1) for PPh3 dissociation, halide dissociation and the overall phosphine substitution reactions of
1a–ea
DG
DG
DG
(kJ molꢀ1
)
(kJ molꢀ1
)
(kJ molꢀ1
)
CpRu(PPh3)2X 0
CpRu(PPh3)X + PPh3
CpRu(PPh3)2X + THF 0
CpRu(PPh3)2X + PMePh2 0
CpRu(PMePh2)(PPh3)X + PPh3
CpRu(PPh3)2X
CpRu(PPh3)2(THF)+ + Xꢀ
1a, X ¼ Cl
1b, X ¼ Br
1c, X ¼ I
43.5
40.7
43.6
47.2
43.9
70.9
59.0
47.2
105.1
108.8
ꢀ35.8
ꢀ40.8
ꢀ45.2
ꢀ32.6
ꢀ31.9
1d, X ¼ N3
1e, X ¼ NCO
a
Geometry optimizations were optimized in the gas phase using the B3LYP exchange–correlation functional and DGDZVP basis set followed by
a single point energy calculation using a polarizable continuum model (PCM) for THF solvation.
Table 6 Calculated Gibbs free energies (kJ molꢀ1) for transition states for PPh3 dissociation and the subsequent phosphine substitution reactions
of 1a–ea
DG‡TS1 (kJ molꢀ1
)
DG‡TS2 (kJ molꢀ1
)
CpRu(PPh3)2X
CpRu(PPh3)2X 0 [CpRu(PPh3)X/PPh3]‡
CpRu(PPh3)2X + PMePh2 0 [CpRu(PMePh2)(PPh3)X]‡
1a, X ¼ Cl
1b, X ¼ Br
1c, X ¼ I
92.1
93.2
91.1
89.6
91.1
73.7
75.7
80.0
79.9
79.5
1d, X ¼ N3
1e, X ¼ NCO
a
The transition state optimization was performed using the synchronous transit and quasi-Newton methods (STQN). The guess structure used was
the maximum of a relaxed PES scan along the Ru–P bond. They were conrmed as rst order saddle points by harmonic frequency analysis.
a dissociative process through 16-electron Cp*Ru(PMe3)X independence of the rate on PMePh2 concentration and the
intermediates.9 The relative rates of substitution in observed positive activation entropies. Closer examination of
Cp*Ru(PMe3)2X were judged to reect both ground state and the effect of added PPh3 on the substitution rate reveals that the
transition state effects of X.9 The observation that 1g–i (X ¼ H, effect is not the same across the series 1b–e.
SnF3, and SnCl3) do not react at all with PMePh2 under the
Ionization of Ru–X bonds in CpRu(PR2R0)2X (R ¼ Ph, Me, X ¼
reaction conditions is consistent with the observations for Cl, Br, I) systems in Lewis basic solvents such as alcohols,
Cp*Ru(PMe3)2X: good s-donors lead to slower reaction. The acetonitrile, or dimethylsulfoxide is well established but does
corresponding indenyl complex, (h5-C9H7)Ru(PPh3)2H, is also not seem to play a signicant role in the substitution reactꢀions
known to be inert toward phosphine substitution.20 The effect of in THF.21 The absence of any signicant effect of added X on
s-donor, p-donor, and possibly p-acceptor properties of the the rate suggests that formation of [CpRu(PPh3)2(THF)]+ and Xꢀ
ligands on both ground state and transition state energies are ions in THF solution is unlikely to be the rate determining step;
likely to be relevant to interpretations of the rate data for 1a–e. one would expect a decrease in rate if dissociation of Xꢀ was the
We start by considering the halide derivatives 1a–c. The rate determining step. With the exception of 1c calculations of
observed order of substitution rates in 1a–c are the same as for the relative energies of CpRu(PPh3)X and [CpRu(PPh3)2(-
Cp*Ru(PMe3)2X: Cl > Br > I. The substitution rates in 1a–c span THF)]+[X]ꢀ conrm that the latter is signicantly higher in
a relatively small range; kobs for 1a (X ¼ Cl) is z 50 times greater energy than the former. Even in the case of CpRu(PPh3)2I (1c),
than for 1c (X ¼ I) in THF, a slightly broader range of kobs values the 16 eꢀ intermediate is 3–4 kJ molꢀ1 lower in energy than
for 1a–c than for Cp*Ru(PMe3)2X for the same X ligands. A [CpRu(PPh3)2(THF)]+[I]ꢀ (in the gas phase).
dissociative mechanism for phosphine substitution has been
The absence of signicant differences in the Ru–P or Ru–Cp
suggested for reactions of 1a with PMePh2 in both THF and bond distances in 1a–c in either the crystal structures or in the
CDCl3.6,7 The kinetic data for substitution in 1b and 1c in Table calculated structures (Table 4) suggests that only small differ-
1 in THF are also consistent with a dissociative or dissociative ences exist in the ground state energies of 1a–c. Despite
interchange mechanism with the loss of PPh3 as the rate- a signicantly larger ionic radius and a longer Ru–X bond
determining step.6 This conclusion is supported by the distance, the iodide (1c), reacts slower than the chloride (1a).
observed decrease in rate in the presence of added PPh3, the Increasing the size of X (X ¼ I > Br > Cl) does not increase the
34430 | RSC Adv., 2017, 7, 34425–34434
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
rate of the reaction suggesting that transition state effects also the rate of substitution in CpRu(CO)2Cl with P(OPh)3 is faster
contribute to the order of substitution rates for 1a–c.9,22 The than for the bromide and iodide. A dissociative process is
electrochemical potentials of CpRu(PPh3)2X (Table 1) reveal proposed for all three CpRu(CO)2X compounds.
surprisingly similar Eꢂ values for 1a–c. The Eꢂ values for 1a–c are
Finally, the calculated transition state energies (DG‡) for the
essentially indistinguishable: 136 vs. 138 mV vs. Fc/Fc+ for 1a reactions of 1a–c with PMePh2 support the interpretation of the
and 1b, respectively and less than a 50 mV difference in Eꢂ experimental data. The rst step, dissociation of PPh3, is the
between the chloride and iodide complexes. Although 1c does rate determining step with subsequent reaction of the coor-
react slower than 1a–b, the small difference in Eꢂ values dinatively unsaturated CpRu(PPh3)X intermediate with
remains consistent with minimal contribution from ground PMePh2: DG‡TS1 > DGT‡S2. The difference between DGT‡S1 and DG‡
state effects to the substitution reaction. Further support for (Table 2) is small. The range of values for DG‡TS1 is quite narrow
small ground state effects of chloride, bromide and iodide is and mirrors the trend for DG‡ in Table 2 suggesting that only
seen in the nCO for CpRu(CO)2X (nCO X ¼ Cl > Br > I) which differ small differences in the transition state contribute to the
by only 11 cmꢀ1
.
observed order of reaction rates: 1a > 1b > 1c. For 1c, the similar
23
Interestingly CpRu(PPh3)2F (1f) has a signicantly larger energies
for
two
intermediates,
CpRu(PPh3)I
and
positive Eꢂ, 790 mV, which may help explain the lack of reac- [CpRu(PPh3)2(THF)]+[I]ꢀ in Table 5 may account for the greater
tivity toward PMePh2. Fluoride is a weaker s-donor and difference between DG‡TS1 and DG‡.
a stronger p-donor than Clꢀ, Brꢀ and Iꢀ.2 One not on might
The compounds with pseudohalide ligands (N3ꢀ and NCOꢀ),
expect greater p-donation to accelerate the substitution rate but 1d and 1e, introduce ligands with both p-donating and p-
the opposite is observed. The much greater electronegativity of accepting properties. Compounds 1d and e react with PMePh2
uoride as reected by Eꢂ, suggests that the Ru–PPh3 bond is as fast, or even faster, than 1b. Unlike 1a–c, the activation
signicantly stronger in 1f than in 1a–c contributing to the entropies for 1d and 1e are negative: DS‡ ¼ ꢀ48 ꢁ 16 and ꢀ105
failure of CpRu(PPh3)2F (1f) to react with PMePh2 under the ꢁ 23 J molꢀ1 Kꢀ1, respectively. This raises the possibility of
conditions of the experiment. No data is available for a change in mechanism from a dissociative interchange to an
Cp*Ru(PMe3)2F for CpRu(CO)2F making further comparisons associative interchange pathway. Nevertheless, the observation
difficult.
that the substitution rate in both 1d and 1e decreases in the
The calculated free energies of the 16-electron CpRu(PPh3)X presence of excess PPh3 and is unchanged when excess pseu-
fragments span a narrow range, about 10 kJ molꢀ1 (Table 5). It dohalide is added to the solution argues for a dissociative or
was previously shown that PPh3 dissociation from 1a yields dissociative interchange mechanism for 1a–e. The greatest
a lower energy intermediate than dissociation of Clꢀ to form effect of added PPh3 on rate is seen for 1d, the compound that
+
CpRu(PPh3)2 , the common intermediate from halide dissoci- reacts the fastest and the smallest effect is seen for 1c, which
ation from 1a–c.6 The computational results for the free ener- exhibits the slowest rate of phosphine substitution. One
gies of the CpRu(PPh3)X intermediate must be treated with possible explanation is that the halide complexes, 1b–c react by
caution when comparing calculations in the gas phase to the a dissociative interchange mechanism while substitution in 1d–
kinetic measurements in solution. As expected, the calculated e follows a more dissociative pathway.
free energy changes for substitution of one PPh3 by PMePh2 for
the halide compounds are exergonic (DG < 0, Table 5) and differ the rate determining step, then one expects a decrease in rate
by <15 kJ molꢀ1 as a function of the halide ligand. when excess N3ꢀ or NCOꢀ is added to the reaction mixture, yet
If ionization of the pseudohalide ligand in 1d–e represents
Support for the role of transition state effects on the reac- the rate is unchanged. Calculated values of DG for product of
tivity of 1a–c comes from decades-old studies of carbonyl substitution of N3ꢀ or NCOꢀ by THF, [CpRu(PPh3)2(THF)]+[X]ꢀ,
substitution reactions of M(CO)5X (M ¼ Re, Mn) and M(CO)5Xꢀ are more than double the DG for CpRu(PPh3)X, suggesting that
(M ¼ Cr, Mo, where X ¼ Cl, Br and I).24 Substitution cis to the X dissociation of Xꢀ also does not play a role in the reaction with
group is observed in all cases and kinetic data for these reac- PMePh2. Large negative values for DS‡ were also reported for
tions are consistent with a dissociative pathway. The rate of phosphine substitution in (h5-pentadienyl)Ru(PPh3)2Cl in what
substitution in the chloride complexes is between 15 and 250 appears to be a dissociative mechanism and have been observed
times the rate of substitution in the corresponding iodides. This in halide exchange reactions of CpRu(prophos)Cl.26 The large
effect was attributed to stabilization of the 16-electron inter- positive DS‡ values for substitution in Cp*Ru(PMe3)2X were
mediate or transition state by the stronger s-donation from the attributed to a late or product like transition state9 so one
halide ligand: Cl > Br > I.24 There are strong parallels between possible explanation for the differences in DS‡ values between
the substitution rates in these mononuclear metal carbonyl 1a–c and 1d–e is an earlier, more ordered transition state in 1d–
halides and 1a–c. The observed order of rates, Cl > Br > I, is the e than in 1a–c. For comparison, the activation entropy for
same and substitution in 1a–c also occurs cis to the X group if substitution in Re(CO)5NCO, DS‡ ¼ +8 J molꢀ1 Kꢀ1, is less
one considers the Cp ligand to occupy a fac geometry in positive than DS‡ ¼ +73 and +44 J molꢀ1 Kꢀ1 for substitution in
a pseudo-octahedral geometry. A stabilizing role for p-donation Re(CO)5Cl and Re(CO)5Br, respectively.27 The rate of substitu-
from X is less likely because the order of p-donation, I > Br > Cl, tion in the rhenium(I) series reveals that Re(CO)5NCO reacts
does not match the relative rates of phosphine substitution.1,22 slightly slower than Re(CO)5Cl but faster than the bromide
The kinetics of carbonyl substitution in CpRu(CO)2X provide an derivative similar to our observations for 1a–b and 1e.27 Detailed
even better comparison with the reactions of 1a–c.25 In xylene, calculations of the structure of the transition state for 1a–e are
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 34425–34434 | 34431

View Article Online
RSC Advances
Paper
in progress but the data for DG‡TS1 indicate a lower activation Cp*Ru(PMe3)2CH3 are 29–59 kcal molꢀ1 greater than for
energy for 1d and correlate well with the values for DG‡ in Table Cp*Ru(PMe3)2Cl. The lack of phosphine substitution in 1g–i is
2, as observed for 1a–c.
The Ru–P bond distances in the solid state structure of 1d19c hydride ligands that substantially greater Ru–P bond strength.
and the results of DFT calculations (Tables 4 and 5) for 1d–1e do The observation of halide exchange reactions between
therefore, most likely the result of a small, strong s-donor
not reveal any striking structural anomalies. The electro- CpRu(PPh3)2X and CDCl3 has not been previously reported28 for
chemical potential for 1e is again indistinguishable from the 1b–e although reaction between 1a and acetyl halides, CH3COX
values for 1a–1c suggesting similar ground state energies. The where X ¼ Br and I, was recently reported to yield 1b–c.29 An
electrochemistry of 1d, however, indicates that it is much easier increase in the rate of halide exchange was observed in the
to oxidize than 1a or 1b by about 160 mV. The signicance of presence of 9,10-dihydroanthracene (radical initiator) and
this Eꢂ value on the relative value of kobs is not entirely clear but a concomitant decrease in conversion when TEMPO (radical
may indicate a slightly higher energy for the ground state in 1d. trap) is added to the reaction mixture supporting a radical
Crystallography conrms that the azide ligand in 1d is bent mechanism. Computational chemistry suggested a pathway
with a Ru–N–N bond angle of 124.5ꢂ.19c DFT calculations are where phosphine dissociation is followed by halogen atom
consistent with this geometry yielding a calculated bond angle, abstraction from CH3COX and formation of a radical pair.29
:
¼ 118.5ꢂ. The calculated Ru–N–C bond angle in 1e Further support for radical intermediates in the chemistry of 1
Ru–N–N
(153.5ꢂ) reveals that the NCO ligand is more linear in 1e, is found in the catalytic activity of CpRu(PPh3)(PMe3)Cl in the
consistent with a greater contribution of resonance forms C and atom transfer radical addition (ATRA) reactions of CCl4 and
D in Fig. 4, while structures A andꢀB are likely to be the major styrene.30 There are also two reports of the reaction between 1a
contributors to the bonding of N3 in 1d. The importance of and excess iodomethane yielding 1c in situ and as a synthetic
structures C and D may make the linear NCO ligand a better p- method but the mechanism of the reaction was not explored.3
acceptor than the bent N3 ligand.
The reactions between 1c–d and CDCl3, however, are
Transition state stabilization and increased substitution inconsistent with radical mechanisms given the absence of any
rates for square planar complexes bearing ancillary p-acceptor noticeable effect of 1–16 equivalents of 9,10-dihydroanthracene
ligands is well established but the effect of p-acceptor ligands or duroquinone (Fig. 3).25a The addition of PPh3 signicantly
on substitution rates in octahedral complexes is less docu- reduces the rate of the halide exchange reaction. The latter
mented.22 Seminal studies on dissociative substitution reac- observation argues for phosphine substitution as the potential
tions of group 6 and group 7 carbonyls suggest that 16 eꢀ rate-limiting step in the halide exchange reaction. The relative
transition states are stabilized by electron donors and destabi- rates of halide exchange for 1c and 1d mimic the trend for the
lized by acceptor ligands.22,24,27 If this is true, than the bent N3 phosphine substitution rates in these two compounds. Both
ligand in 1d stabilizes the transition state and accounts for the the oxidative addition of C-halide bonds and concerted
faster reaction of 1d compared to 1e. Conversely, the better p- mechanisms (Fig. 5) must be considered for the conversion of
acceptor, linear NCO ligand may destabilize (raise the energy of) 1c–d to 1a.
the transition state decreasing the reaction rate. The linear p-
Limited evidence for both mechanisms can be found in the
accepting phenylacetylide ligand in Cp*Ru(PMe3)2CCPh literature. Oxidative addition of allyl chloride to
increases the Ru–PMe3 bond energy by about 38 kJ molꢀ1 and CpRu(PPh3)2Cl yields CpRu(C3H5)Cl2 (ref. 31) while a halo-
reduces the rate of phosphine dissociation.9 Signicantly slower carbon complex, [CpRu(PPh3)2(CH3I)][PF6] is isolated from
phosphine substitution was also observed in reactions of (h5- reaction of 1a with Ag+ and methyl iodide.32 A further mech-
C9H7)Ru(PPh3)2CCPh compared to (h5-C9H7)Ru(PPh3)2Cl.20
anistic proposal for the halide exchange reaction is the
In addition to 1f, phosphine substitution was also not formation of quaternary phosphonium salts by reaction
observed in 1g–i all of which contain good s-donors: hydride between the dissociated PPh3 and CDCl3 followed by dissoci-
and trihalotin (SnX3ꢀ, X ¼ Cl, F) ligands. To understand the lack ation of Clꢀ and subsequent halide exchange with 1b–e. The
of reaction, we turn to the studies of phosphine substitution latter pathway was proposed for the catalytic halogen exchange
that
include
Cp*Ru(PMe3)2Cl,
Cp*Ru(PMe3)2H,
and between MeI and CH2Cl2 catalyzed by a broad range of group 9
Cp*Ru(PMe3)2CH3.9 The data for the latter three compounds transition metal complexes.33 Although no new resonances are
suggests that the activation enthalpy, DH‡, for the reaction observed in the 31P NMR spectrum of PPh3 in CDCl3, the
closely approximates the Ru–PMe3 bond energies, leading to the possibility of halide exchange in 1b–e by this mechanism
conclusion that the Ru–PMe3 bonds in Cp*Ru(PMe3)2H and cannot be excluded at this time.
Fig. 4 Resonance forms for the pseudohalide ligands in 1d–e.
34432 | RSC Adv., 2017, 7, 34425–34434
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
Fig. 5 Possible mechanisms for halide exchange in 1c–d.
The rate data for phosphine substitution in 1a–i provide best catalyst but the position of the hydride complex, 1g, is
some insight into reaction mechanisms where 1a–i show cata- anomalous suggesting that more work is needed to understand
lytic activity. The assertion that faster phosphine dissociation the effect of different ligand environments on the reactivity of
accounts for higher yields in the cycloaddition of norbornene cyclopentadienyl ruthenium(II) complexes in carbon–carbon
and norbornadiene3 when 1c is used in place of 1a is incon- and carbon–nitrogen bond forming processes.
sistent with the relative rates of phosphine substitution re-
ported herein. In fact, our data suggest that any catalytic process
that relies on phosphine dissociation from 1a–e should proceed
References
fastest for X ¼ Cl with X ¼ N3 as the next most active catalyst
1 Ruthenium in Organic Synthesis, ed. S.-I. Murahashi, Wiley-
VCH, 2004.
2 For a review of halide effect in transition metal catalyzed
reactions see K. Fagnou and M. Lautens, Angew. Chem., Int.
precursor. The effect of 1b–e on the rate and selectivity of
ruthenium-catalyzed dimerization of alkynes34 and the 1,3-
dipolar addition of azides to alkynes35 represent potential future
studies of the effect of the X ligand on catalytic properties.
Ed., 2002, 41, 26–47.
Phosphine substitution in trihalotin ligands in 1h–i are clearly
3 (a) A. Tenaglia and L. Giordano, Synlett, 2003, 2333–2336; (b)
slow and consistent with the high temperatures required for
A. Tenaglia and M. Sylvain, J. Org. Chem., 2008, 73, 1397–
1402; (c) A. Tenaglia, L. Giordano, M. Sylvain and I. De
converting methanol to methylacetate5 in their presence.
Riggi, Angew. Chem. Int. Ed., 2011, 50, 9062–9065.
4 A. Del Zotto, W. Baratta, M. Sandri, G. Verardo and P. Rigo,
Eur. J. Inorg. Chem., 2004, 524–529.
Conclusions
The results of the kinetic study of phosphine substitution in
CpRu(PPh3)2X for ve halide and pseudohalide derivatives in
THF and CDCl3 solution reveals a likely dissociative or disso-
ciative interchange process. These data suggest that dissociative
substitution mechanisms reported for CpRu(PAr3)2Cl6 and
Cp*Ru(PMe3)2X complexes9 are a general reaction pathway for
18-electron, cyclopentadienyl ruthenium(II) derivatives. Differ-
ences in the rate of substitution in 1a–e are likely a combination
of ground state and transition state effects. Dissociation of
phosphine in 1b–e is a likely step in the exchange of Ru–X
bonds for Ru–Cl bonds when CpRu(PPh3)2X is dissolved in
CDCl3, however, further mechanistic studies are needed to
identify the likely mechanism.
5 P. A. Robles-Dutenhefner, E. M. Mora, G. J. Gama,
H. G. L. Siebald and E. V. Gusevskaya, J. Mol. Catal. A:
Chem., 2000, 164, 39–47.
6 (a) M. J. Verschoor-Kirss, O. Hendricks, L. Renna, D. Hill and
R. U. Kirss, Dalton Trans., 2014, 43, 15221–15227; (b) C. Peng
and H. B. Schlegel, Isr. J. Chem., 1993, 33, 449.
7 M. P. Gamasa, J. Gimeno, C. Gonzalz-Bernardo, B. M. Martin-
Vaca, D. Monti and M. Bassetti, Organometallics, 1996, 15,
302–308.
8 (a) R. J. Haines and A. L. DuPreez, J. Organomet. Chem., 1975,
84, 357–367; (b) P. M. Treichel and P. J. Vincenti, Inorg.
Chem., 1985, 24, 228–230.
9 H. E. Bryndza, P. J. Domaille, R. A. Paciello and J. E. Bercaw,
Organometallics, 1989, 8, 379–385.
For reactions where Ru–X bond ionization is important, the
data on phosphine substitution in 1a–e offer more limited 10 D. F. Shriver, Manipulation of Air Sensitive Compounds,
insight. Compounds 1a, 1c–d, 1g and 1i all catalyze the N- McGraw Hill, 1969.
methylation of cyclohexylamines4 to varying degrees in meth- 11 M. I. Bruce, C. Hameister, A. G. Swincer and R. C. Wallis,
anol solution. An order of relative rates, 1a > 1g > 1c $ 1d [ 1i Inorg. Synth., 1990, 28, 270.
(no reaction), can be inferred from the observed product ratios 12 T. Wilczewski, M. Bochenska and J. F. Biernat, J. Organomet.
of CyNMe2 : CyNHMe : CyNH2. Among these, 1a is by far the
Chem., 1981, 215, 87–96.
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 34425–34434 | 34433

View Article Online
RSC Advances
Paper
13 E. M. Moura, H. G. L. Siebald and G. M. de Lima, Polyhedron, 24 J. D. Atwood and T. L. Brown, J. Am. Chem. Soc., 1976, 98,
2002, 21, 2323–2331. 3160–3166.
14 (a) M. I. Bruce, C. Hameister, A. G. Swincer and R. C. Wallis, 25 (a) K. Tabataiana and K. White, Inorg. Chem., 1981, 20, 2020–
Inorg. Synth., 1982, 21, 78–84; (b) M. I. Bruce, R. C. F. Gardner
and F. G. A. Stone, J. Chem. Soc., Dalton Trans., 1976, 81–89.
2022; (b) D. A. Brown, H. J. Lyons and R. T. Sane, Inorg. Chim.
Acta, 1970, 4, 621–625.
15 P. M. Treichel and D. A. Komar, Synth. React. Inorg. Met.-Org. 26 (a) M. Daniels and R. U. Kirss, J. Organomet. Chem., 2007,
Chem., 1980, 10, 205–218.
16 G. Lente, I. Fabian and A. J. Poe, New J. Chem., 2005, 29, 759–
692, 1716–1725; (b) H. Brunner, M. Muschiol, T. Tsuno,
T. Takahashi and M. Zabel, Organometallics, 2008, 27,
3514–3525.
760.
17 D. A. Skoog, D. M. West and J. Holler, Analytical Chemistry: 27 R. J. Angelici and G. C. Faber, Inorg. Chem., 1971, 10, 514–
An Introduction, Saunders, 7th edn, 2000. 517.
18 See ESI† for plots of ln[Ru] vs. time, complete tables of rate 28 Halide exchange is also observed between 1c and
constants and Eyring plots for reactions of 1b–e with
PMePh2.
19 (a) M. I. Bruce, F. S. Wong, B. W. Skelton and A. H. White, J.
Chem. Soc., Dalton Trans., 1981, 1398–1405; (b) M. I. Bruce,
benzylbromide but not with bromobenzene.
29 H. Kuniyasu, A. Sanagawa, T. Nakajima, T. Iwasaki,
N. Kambe, K. Bobuatong and M. Ehara, J. Organomet.
Chem., 2014, 769, 34–39.
P. J. Low, B. W. Skelton, E. R. T. Tietink, A. Werth and 30 R. P. Nair, T. H. Kim and B. J. Frost, Organometallics, 2009,
A. H. White, Aust. J. Chem., 1995, 48, 1887–1892; (c) 28, 4681–4688.
M. M. T. Khan, M. M. Bhadbhade, M. R. H. Siddiqui and 31 H. Nagashima, K. Mukai, Y. Shiota, K. Yamaguchi, K.-I. Ara,
K. Venkatasubramanian, Acta Crystallogr., Sect. C: Cryst.
Struct. Commun., 1994, 50, 502–504.
T. Fukahori, H. Suzuki, M. Akita, Y. Moro-oka and K. Itoh,
Organometallics, 1990, 9, 799–807.
20 M. Bassetti, S. Marini, F. Tortorella, V. Cadierno, J. Diez, 32 (a) R. J. Kulawiec, J. W. Faller and R. H. Crabtree,
M. P. Gamasa and J. Gimeno, J. Organomet. Chem., 2000,
593–594, 292–298.
21 Rate constants for solvation for CpRu(PPh2OMe)2X and
CpRu(PPh2Me)2X in CD3CN comparable to the substitution
Organometallics, 1990, 9, 745–755; (b) A related complex,
[CpRu(PPh3)(CNtBu)(CH3I)]+ is also known: F. M. Conroy-
Lewis, A. D. Redhouse and S. J. Simpson, J. Organomet.
Chem., 1989, 366, 357–367.
rates for CpRu(PPh3)2X at 30 ꢂC require more than doubling 33 D. Forster, J. Chem. Soc., Chem. Commun., 1975, 917–918.
the reaction temperature to 67 ꢂC. Compound 1a–c do not 34 M. Daniels and R. U. Kirss, J. Organomet. Chem., 2007, 692,
dissolve sufficiently in CD3CN for a direct comparison. See ref. 8.
1716–1725.
22 J. M. Atwood, Inorganic and Organometallic Reaction 35 L. Zhang, X. Cheng, P. Xue, H. H. Y. Sun, I. D. Williams,
Mechanisms, Wiley-VCH, 2nd edn, 1997.
23 R. J. Haines and A. L. duPreez, J. Chem. Soc., Dalton Trans.,
1972, 944–948.
K. B. Sharpless, V. V. Fokin and G. Jia, J. Am. Chem. Soc.,
2005, 127, 15998–15999.
34434 | RSC Adv., 2017, 7, 34425–34434
This journal is © The Royal Society of Chemistry 2017