Ruthenium(II) chemistry of phosphorus-based ligands, Ph2PN(R)PPh2 (R=Me or Ph) and Ph2PN(Ph)P(E) Ph2 (E=S or Se). Solution thermochemical study of ligand substitution reactions in the Cp′RuCl(COD) (Cp′=Cp, Cp* C

Article abstract of DOI:10.1016/S0022-328X(99)00758-5

The enthalpies of reactions of Cp′RuCl(COD) (Cp′=Cp, Cp* COD=cyclooctadiene) with bis(phosphino)amines of the type Ph₂PN(R) PPh₂(R=Me 1 or R=Ph 2) and the monochalcogen derivatives Ph₂PN(Ph)P(E)Ph₂(E=S 3 or Se 4

Full text of DOI:10.1016/S0022-328X(99)00758-5

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 599 (2000) 159–165
Ruthenium(II) chemistry of phosphorus-based ligands,
Ph2PN(R)PPh2 (R=Me or Ph) and Ph2PN(Ph)P(E) Ph2 (E=S or
Se). Solution thermochemical study of ligand substitution reactions
in the Cp%RuCl(COD) (Cp%=Cp, Cp*; COD=cyclooctadiene)
system
Maravanji S. Balakrishna a,*1, Rashmishree Panda a, Dale C. Smith Jr. b,
Amy Klaman b, Steven P. Nolan b,*2
a Department of Chemistry, Indian Institute of Technology, Bombay, Powai, Mumbai 400 076, India
b Department of Chemistry, Uni6ersity of New Orleans, New Orleans, LA 70148, USA
Received 18 October 1999; received in revised form 26 November 1999
Dedicated to Professor S.S. Krishnamurthy on the occasion of his 60th birthday.
Abstract
The enthalpies of reactions of Cp%RuCl(COD) (Cp%=Cp, Cp*; COD=cyclooctadiene) with bis(phosphino)amines of the type
Ph2PN(R)PPh2(R=Me 1 or R=Ph 2) and the monochalcogen derivatives Ph2PN(Ph)P(E)Ph2(E=S 3 or Se 4) leading to the
formation of Cp%RuCl(PNP) and Cp%RuCl{PNP(E)} complexes, respectively, have been measured by anaerobic solution
calorimetry in THF at 30°C. These reactions are clean and quantitative. The synthesis and characterization of new organoruthe-
nium complexes is reported. Comparisons with enthalpy data in this two related organoruthenium systems and other similar
organometallic systems are also presented. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Thermochemistry; Bis(phosphino)amines; Ruthenium(II) complexes; Enthalpy; Mononuclear
phino)amines display their versatility by exhibiting dif-
ferent coordination behavior when the donor–acceptor
properties are altered by incorporating different sub-
stituents at both the phosphorus centers and at the
bridging nitrogen center [15].
1. Introduction
The use of chelating bis(phosphine) ligands is wide-
spread in organometallic chemistry and in homoge-
neous catalysis [1] as these ligands can be used to fine
tune the metal reactivity and selectivity. The ruthenium
complexes incorporating this ligand type are of consid-
erable interest because of their potential use in pro-
cesses such as reductive elimination and oxidative
addition for making and breaking CꢀH bonds [2–8],
formation and cleavage of NꢀH and OꢀH bonds [9].
Also their extensive use in classical catalytic processes
such as hydrogenation, isomerisation, decarbonylation,
etc. [10–14] cannot be ignored. In this context, bis(phos-
In homogeneous catalytic processes, the factors play-
ing a major role in understanding the exact ligand effect
at the metal sites are: (i) the entropy of the system and
(ii) the metalꢀligand bond disruption enthalpy value.
This bond disruption enthalpy (BDE) value is a net
effect of the stabilizing metal–phosphorus interaction
and the destabilizing strain energy caused by the forma-
tion of metallacyclic fragment in chelating systems.
Solution calorimetric studies have been useful in
providing bonding and reactivity pattern information
[16–18] that gives insight to design new catalysts for
various organic transformations. Nolan and co-workers
have previously examined, using solution calorimetric
1 *Corresponding author. Fax: +91-22-576152; e-mail: kr-
ishna@chem.iitb.ernet.in
2 *Corresponding author.
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00758-5

160
M.S. Balakrishna et al. / Journal of Organometallic Chemistry 599 (2000) 159–165
techniques, the enthalpy of reaction associated with
ligand displacement in related organoruthenium sys-
tems [19].
In the present study, we report a thermochemical
study used to examine quantitatively the binding ability
of the ligands 1–4 in two related organoruthenium
systems. Furthermore, the synthesis and characteriza-
tion of new organoruthenium complexes 5–13 are
presented.
sealed with 1.5 ml of mercury. A solution of
Ph2PN(Me)PPh2 (108.0 mg, 270.4 mmol) in THF (4 ml)
was added, and the remainder of the cell was assem-
bled, removed from the glove box, and inserted into the
calorimeter. The reference vessel was loaded in an
identical fashion with the exception that no
organometallic complex was added to the lower vessel.
After the calorimeter had reached thermal equilibrium
at 30°C (ca. 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 (ca. 2.5 h). Control reactions with Hg and
phosphine show no reaction enthalpy contribution. The
enthalpy of ligand substitution (−19.9+0.2 kcal
mol−1) listed in Table 2 represents the average of at
least three individual calorimetric determinations with
all species in solution. All calorimetric results (in solu-
tion) are presented in Table 2. These values include the
enthalpy of solution of CpRuCl(COD) (+3.9+0.1
kcal mol−1) or Cp*RuCl(COD) (+4.9+0.1 kcal
mol−1) in THF.
Reactions with Ph2PN(Ph)P(Se)Ph2 showed reactivity
with Hg and an alternative calorimetric method was
utilized. For reactions forming 8 and 12, the mixing
vessels of the Setaram C-80 were cleaned, dried in an
oven maintained at 120°C, and then taken into the
glove box. A sample of Cp*RuCl(COD) (20.5 mg, 54.0
mmol) was dissolved in THF (2 ml) and syringed into
the inner vessel. A solution of Ph2PN(Ph)P(Se)Ph2 (61.8
mg, 114.4 mmol) was dissolved in THF (2 ml) was
added to the outer vessel, and the remainder of the cell
was assembled, removed from the glove box, and in-
serted into the calorimeter. The reference vessel was
loaded in an identical fashion with the exception that
no organometallic complex was added to the lower
vessel. After the calorimeter had reached thermal equi-
librium at 30°C (ca. 2 h), it was inverted, thereby
allowing the reactants to mix. The reaction was consid-
ered complete after the calorimeter had once again
reached thermal equilibrium (ca. 2.5 h).
2. Experimental
2.1. General considerations
All experimental manipulations were performed un-
der an inert atmosphere of dry nitrogen or argon, using
standard Schlenk techniques. Solvents, including
deuterated solvents for NMR analysis, were dried by
standard methods and vacuum transferred before use.
Multinuclear NMR spectra were recorded using VXR
300S or Varian Unity 400 MHz spectrometers operat-
ing at the appropriate frequencies using TMS and 85%
H3PO4 as internal and external references, respectively.
CDCl3 was used as both solvent and internal lock.
Positive shifts are downfield in all cases. Microanalyses
were carried out in the Department of Chemistry, IIT,
Bombay. Calorimetric measurements were performed
using a Calvet calorimeter (Setaram C-80), which was
periodically calibrated using the Tris reaction [20] or
the enthalpy of solution of KCl in water [21]. This
calorimeter has been previously described [22] and typi-
cal procedures are described below. Experimental en-
thalpy data are reported with 95% confidence limits.
2.2. NMR titrations
Prior to every set of calorimetric experiments involv-
ing each new ligand, a precisely measured amount
(+0.1 mg) of CpRuCl(COD) or Cp*RuCl(COD) was
placed in an NMR tube along with THF-d8 and \1.2
equivalents of ligand. Both 1H- and 31P{1H}-NMR
spectra were measured within 1.5 h of mixing; both
indicated the reactions were clean and quantitative.
These conditions are necessary for accurate and mean-
ingful calorimetric results and were satisfied for all
reactions investigated.
2.4. Syntheses
The ligands 1–4 [23–25] and the compounds
CpRuCl(PPh3)2 [26], CpRuCl(COD) [27] and
Cp*RuCl(COD) [28] were synthesized according to lit-
erature procedures. Experimental details leading to the
isolation of complexes 5–12 are reported below.
2.3. Solution calorimetry
2.5. [CpRuCl{p2-Ph2PN(R)PPh2}] (R=Me 5, R=Ph
6)
The mixing vessels of the Setaram C-80 were cleaned,
dried in an oven maintained at 120°C, and then taken
into the glove box. For the reactions forming 5, 6, 7, 9,
10, and 11 a representative experimental trial involved
weighing a sample of Cp*RuCl(COD) (17.3 mg, 45.5
mmol) into the lower vessel, which was closed and
A solution of Ph2PN(R)PPh2 (0.028 g, 0.069 mmol
R=Me 1; 0.032 g, 0.069 mmol R=Ph 2) in toluene (8
ml) was added to a solution of CpRuCl(PPh3)2 (0.05 g,
0.069 mmol) also in toluene (8 ml) and the reaction

M.S. Balakrishna et al. / Journal of Organometallic Chemistry 599 (2000) 159–165
161
mixture was stirred at room temperature (r.t.) for 3 h.
During that period a yellow crystalline product was
separated from the reaction mixture. The solution was
cooled to r.t. and the product was isolated by filtration
and dried under vacuum.
filtrate was kept at low temperature to get orange
crystals, which were isolated by filtration and dried
under vacuum.
Complex 9, orange crystals, yield 90% (0.057 g), m.p.
160°C (decomposes). Anal. Found: C, 62.69; H, 5.79;
N, 1.89. Calc. for C35H38NP2ClRu: C, 62.63; H, 5.71;
N, 2.08%. 1H-NMR (CDCl3): l 7.24–7.75 (m, 20H,
When the above reaction was carried out in toluene
at 60°C for 6 h, the analytically pure cationic product
[CpRuPPh3{h2-Ph2PN(R)PPh2}]Cl (R=Me 13, R=Ph
14) precipitated as yellow microcrystalline material.
Complex 5, light yellow crystals, yield 93% (0.038 g),
m.p.\250°C (decomposes). Anal. Found: C, 60.16; H,
4.91; N, 2.20. Calc. for C30H28NP2ClRu: C, 59.94; H,
4.69; N, 2.33%. 1H-NMR (CDCl3): l 7.08–7.41 (m,
3
Ph), l 1.49 (s, 15H, Cp*), d 2.73 (t, JPꢀH=8.99 Hz,
3H, NꢀMe).
Complex 10, orange crystals, yield 97% (0.067 g),
m.p. 168°C (decomposes). Anal. Found: C, 65.29; H,
5.47; N, 1.79. Calc. for C40H40NP2ClRu: C, 65.51; H,
5.50; N, 1.91%. 1H-NMR (CDCl3): l 7.21–7.41 (m,
25H, Ph), l 1.50 (s, 15H, Cp*).
3
20H, Ph), l 4.66 (s, 5H, Cp), l 3.00 (t, JPꢀH=9.89 Hz,
3H, NꢀMe).
Complex 6, light yellow crystals, yield 86% (0.039 g),
m.p. 220°C (decomposes). Anal. Found: C, 63.17; H,
4.43; N, 1.99. Calc. for C35H30NP2ClRu: C, 63.30; H,
4.56; N, 2.11%. 1H-NMR (CDCl3): l 7.32–7.50 (m,
25H, Ph), l 4.41 (s, 5H, Cp).
2.8. [Cp*RuCl{p2-Ph2PN(R)P(E)Ph2}] (E=S 11,
E=Se 12)
A solution of Ph2PN(R)P(E)Ph2 (0.047 g, 0.095
mmol E=S 3; 0.051 g, 0.095 mmol E=Se 4) in THF
(8
ml)
was
added
to
a
solution
of
2.6. [CpRuCl{p2-Ph2PN(R)P(E)Ph2}] (E=S 7, E=Se
8)
Cp*RuCl(COD)(0.036 g, 0.095 mmol) also in THF (8
ml) and the reaction mixture was stirred at r.t. for 3 h.
During that period a brick-red solution was obtained.
The solvent and volatile were removed under vacuum
and 5 ml of THF was added to the solid product,
stirred for 15 min, filtered and 2 ml of hexane was
added to the filtrate. A brick-red crystalline product
was precipitated at low temperature, which was isolated
by filtration and dried under vacuum.
Complex 11, brick-red crystals, yield 87% (0.063 g),
m.p. 146°C (decomposes). Anal. Found: C, 62.82; H,
5.39; N, 1.92. Calc. for C40H40SNP2ClRu: C, 62.77; H,
5.27; N, 1.83%. 1H-NMR (CDCl3): l 7.13–7.58 (m,
25H, Ph), l 1.39 (s, 15H, Cp*).
A solution of Ph2PN(R)P(E)Ph2 (0.021 g, 0.041
mmol E=S 3; 0.023 g, 0.041 mmol E=Se 4) in THF
(8 ml) was added to a solution of CpRuCl(PPh3)2
(0.030 g, 0.041 mmol) also in THF (8 ml) and the
reaction mixture was stirred at r.t. for 24 h. During that
period a clear red solution was obtained to which 3 ml
of n-hexane was added. A red product was isolated by
filtration and dried under vacuum.
Complex 7, red crystals, yield 72% (0.021 g), m.p.
218°C (decomposes). Anal. Found: C, 60.23; H, 4.18;
N, 2.21. Calc. for C35H30SNP2ClRu: C, 60.46; H, 4.35;
N, 2.02%. 1H-NMR (CDCl3): l 7.19–7.75 (m, 25H,
Ph), l 4.39 (s, 5H, Cp).
Complex 12, brick-red crystals, yield 89% (0.069 g),
m.p. 140°C (decomposes). Anal. Found: C, 59.01; H,
4.83; N, 1.69. Calc. for C40H40SeNP2ClRu: C, 59.15; H,
4.96; N, 1.72%. 1H-NMR (CDCl3): l 7.21–7.41 (m,
25H, Ph), l 1.42 (s, 15H, Cp*).
Complex 8, red crystals, yield 68% (0.021 g), m.p.
240°C (decomposes). Anal. Found: C, 56.61; H, 4.12;
N, 1.78. Calc. for C35H30SeNP2ClRu: C, 56.64; H, 4.07;
N, 1.89%. 1H-NMR (CDCl3): l 7.21–7.41 (m, 25H,
Ph), l 4.41 (s, 5H, Cp).
3. Results and discussion
2.7. [Cp*RuCl{p2-Ph2PN(R)PPh2}] (R=Me 9, R=Ph
10)
Following our previous studies [15d, 29], we prepared
a series of ruthenium complexes 5–12 either via the
displacement of COD or 2 moles of PPh3, respectively
from Cp*RuCl(COD) and CpRuCl(PPh3)2 with the
chelate ligands 1–4 as shown in Schemes 1 and 2.
The synthesis and the spectroscopic characterization
of the above compounds are provided in Section 2. The
31P{1H}-NMR spectroscopic data are listed in Table 1.
Reactions of CpRuCl(PPh3)2 with Ph2PN(R)-
PPh2(R=Me 1, R=Ph 2) in toluene in a ratio of 1:1 at
r.t. for 3 h gave a yellow insoluble micro crystalline
A solution of Ph2PN(R)PPh2 (0.038 g, 0.095 mmol
R=Me 1; 0.044 g, 0.095 mmol R=Ph 2) in THF (8
ml) was added to a solution of Cp*RuCl(COD) (0.036
g, 0.095 mmol) also in THF (8 ml) and the reaction
mixture was stirred at r.t. for 3 h. During that period
an orange–red solution was obtained. The solvent and
volatile were removed under vacuum and 8 ml solvent
mixture hexane and THF (2:6) was vacuum transferred
to the cooled (−78°C) solid product. This solution was
warmed to r.t., stirred for 15 min and filtered. The
precipitate of neutral complexes
5
and 6,

162
M.S. Balakrishna et al. / Journal of Organometallic Chemistry 599 (2000) 159–165
respectively. The 31P{1H}-NMR spectrum shows single
peaks at 54.0 ppm for 5 and 49.0 ppm for 6, respec-
tively indicating that both PPh3 ligands are replaced by
Ph2PN(R)PPh2, which is acting as a bidentate chelating
ligand. The same reactions when carried out at 60°C for
6 h gave cationic complexes 13 and 14 [29] as the major
products. The 31P{1H}-NMR spectrum of the product
excess of bis(phosphino)amine ligand. The 31P{1H}-
NMR spectra of the complexes 9 and 10 show singlets
at 87.9 and 90.8 ppm, respectively indicating that the
diene (COD) has been replaced by the bidentate chelat-
ing bis(phosphino)amines. The reactions of 3 and 4
with Cp*RuCl(COD) in equimolar quantities afforded
the mononuclear neutral complexes 11 and 12, respec-
tively. The 31P{1H}-NMR spectrum of 11 shows two
sharp doublets as expected [25] at 117.9 ppm and 76.2
13 shows
Ph2PN(R)PPh2 and a triplet at 45.2 ppm for PPh3 with
2JPꢀP value of 34.9 Hz. The reaction of
a doublet at 80.5 ppm for chelating
2
a
ppm, respectively, for PIII and PV centers with a JIPVII
Ph2PN(R)PPh2(R=Me 1, R=Ph 2) with Cp*RuCl-
(COD) afforded only the neutral complexes 9 and 10,
respectively in good yield even in the presence of an
value of 70.0 Hz. The 31P{1H}-NMR spectrum of 12
also shows two sharp doublets at 121.8 and 62.5 ppm
with a 2JPIVII coupling of 80.9 Hz with the latter (PV
Scheme 1.
Scheme 2.

M.S. Balakrishna et al. / Journal of Organometallic Chemistry 599 (2000) 159–165
163
Table 1
31P{1H}-NMR a spectroscopic data for ligands 1–4 and their complexes 5–13
Compounds
Chemical shifts
J (Hz)
l(PIII
)
l(PV)
Ph2PN(Me)PPh2(1)
Ph2PN(Ph)PPh2(2)
Ph2PN(Ph)P(S)Ph2(3)
Ph2PN(Ph)P(Se)Ph2(4)
73.6
69.1
54.5d
55.1d
72.4d
72.1d
2JPꢀP=104.6
2JPꢀP=104.6
1JPꢀSe=766.5
[CpRuCl{h2-Ph2PN(Me)PPh2}](5)
[CpRuCl{h2-Ph2PN(Ph)PPh2}](6)
[CpRuCl{h2-Ph2PN(Ph)P(S)Ph2}](7)
[CpRuCl{h2-Ph2PN(Ph)P(Se)Ph2}](8)
54.0
49.0
125.9d
126.0d
46.0d
42.9d
2JPꢀP=46.0
2JPꢀP=47.2
1JPꢀSe=710.2
[Cp*RuCl{h2-Ph2PN(Me)PPh2}](9)
[Cp*RuCl{h2-Ph2PN(Ph)P(Ph2}](10)
Cp*RuCl{h2-Ph2PN(Ph)P(S)Ph2}](11)
[Cp*RuCl{h2Ph2PN(Ph)P(Se)Ph2}](12)
87.9
90.8
117.9d
121.8d
76.2d
62.5d
2JPꢀP=70.0
2JPꢀP=80.9
1JPꢀSe=682.0
2JPꢀP=34.9
[CpRu(PPh3){h2Ph2PN(Me)PPh2}]Cl(13)
80.0d 45.2t
a All spectra in CDCl3; l in ppm vs 85% H3PO4; d=doublet; t=triplet.
1
center) also showing JPse coupling of 682.0 Hz. The
g]. The magnitude of the enthalpy of reaction can be
examined in terms of the basicity of the donor atoms
and that of the metal centers.
heterodifunctional ligands 3 and 4 also react with
CpRuCl(PPh3)2 to give the chelates 7 and 8, respec-
tively.31P{1H}-NMR data for these compounds (Table
1) are consistent with the proposed chelated structures.
The use of (Cp%RuCl(COD) (Cp%=Cp; Cp*; COD=
cyclooctadiene) system in this synthesis and solution
calorimetry study of the complexes 5–12 has been
possible by the rapid substitution of COD with the
chelate ligands. This type of bis(phosphino)amine bind-
ing reaction appears general and quantitative for all
ligands investigated by solution calorimetry at 30°C in
THF. A tabulation of the enthalpies (−DHrxn) for the
reaction of Cp%RuCl(COD) with chelate ligands 1–4 to
give complexes 5–12 is presented in Table 2. These
values include the enthalpy of solution of
Cp*RuCl(COD) (+4.990.1 kcal mol−1) or CpRu-
Cl(COD) (+3.990.1 kcal mol−1) in THF.
The reactions involving the ligands 1 and 2 prove to
be more exothermic where the donor atoms are phos-
phorus centers. However, the substitutions of the mixed
ligands 3 and 4 are ca. 10 kcal mol−1 less exothermic
than those for 1 and 2, resulting in less thermodynami-
cally stable complexes. In the latter case the donor
atom other than the phosphorus center is sulfur or
selenium, which is less basic, rendering the MꢀL bond
weaker and hence the low enthalpy of reaction. A
similar trend [19e] is observed in the reactions involving
alkyl-substituted phosphines and mixed phosphine–ar-
Table 2
Enthalpies of substitution (kcal mol−1
)
in the reaction
THF
Cp%RuCl(COD)(soln)+LꢀL(soln)ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢁCp%Ru(LꢀL)Cl(soln)
30°C
The labile nature and relative thermodynamic stabil-
ity of a number of metal–diene complexes are well
known [30]. In the case of Cp%RuCl(COD), the diene
ligand has been shown to be weakly bound to the metal
center. This reaction type was investigated by solution
calorimetry involving 2 moles of monodentate phosphi-
nes or with chelating bis(phosphine) ligands [19]. The
labile nature of the RuꢀCOD bond has also been
exploited in the present thermochemical study of bis-
(phosphino)amine substitution reactions. This exchange
reaction has been quite efficient in leading to quantita-
tive conversion of Cp%RuCl(COD) to complexes 5–12.
From the experimental data of the solution calorimetry,
important insights are offered by a comparison between
the present data and that of the Cp*RuCl(h2-PP)
(PP=bisphosphines with PCP backbone) system [19e–
(Cp´ =Cp,Cp*)
+COD(soln)
a
b
Complex
Ligands (LꢀL)
DHrnx (kcal mol−1
)
5
6
7
8
Ph2PN(Me)PPh2
Ph2PN(Ph)PPh2
Ph2PN(Ph)P(S)Ph2
Ph2PN(Ph)P(Se)Ph2
Ph2PN(Me)PPh2
Ph2PN(Ph)PPh2
−23.1(4)
−25.6(4)
−13.1(2)
−13.4(3)
−19.9(2)
−19.8(2)
−9.3(3)
9
10
11
12
Ph2PN(Ph)P(S)Ph2
Ph2PN(Ph)P(Se)Ph2
−9.7(2)
a 5–8 CpRu(h2-LꢀL)Cl; 9–12 Cp*Ru(h2-LꢀL)Cl.
b Enthalpy values are provided with 95% confidence limit.

164
M.S. Balakrishna et al. / Journal of Organometallic Chemistry 599 (2000) 159–165
Acknowledgements
sine ligands (arphos). The measured enthalpy of reac-
tion is 6.1 kcal mol−1 less exothermic for arphos than
for the symmetrical diphosphine dppe(bis(diphenyl-
phosphino)ethane). In the substitution involving the
monodentate ligands [19f] AsEt3 and PEt3, this trend
of arsenic-based ligands being weaker donors has also
been observed. A difference of 3.1 kcal mol−1 is
observed in the above case.
We are grateful to the Department of Atomic En-
ergy (DAE), India for funding. We also wish to thank
the Regional Sophisticated Instrument Center (RSIC),
IIT, Bombay for NMR spectroscopy. S.P.N. acknowl-
edges the National Science Foundation and the Board
of Regents of the State of Louisiana for partial
support of this research.
Further, the thermochemical data exhibit a differ-
ence in enthalpies of reaction between the Cp and
Cp* systems. For two sets of ligands, 1 and 2 having
two phosphorus centers (symmetrical) and 3 and 4
having one phosphorus and one sulfur or selenium,
significant enthalpy differences are observed. In both
Cp and Cp* systems, we can compare (Cp vs. Cp*)
the magnitude of enthalpy of reaction on the basis of
the effect of electronic properties of the ancillary
ligand as it contributes to the change in metal basicity
[30]. Since Cp* is more electron donating than Cp, it
renders the metal center more basic and hence less
electrophilic. As a consequence the metal center will
not be able to accommodate greater electron density
from the incoming ligand, resulting in lower enthalpy
of ligand substitution. Angelici and co-workers [31]
have also investigated a series of iridium complexes
and have observed a difference, in enthalpies of pro-
tonation, of 5.7 kcal mol−1 between CpIr(COD) and
Cp*Ir(COD) complexes. Hoff and co-workers [32]
first demonstrated this difference in metal basicity
between Cp and Cp* in their thermochemical investi-
gation of organomolybdenum complexes. In the
present study the enthalpy difference of 4 kcal mol−1
between the ligand substitution reactions reflects the
difference of metal basicity due to the change in
ancillary ligand. This difference is of the same order
of magnitude as Angelici’s enthalpies of protonation
and the average difference in enthalpy of ligand
substitution in the Cp versus Cp* organoruthenium
system.
References
[1] L.H. Pignolet (Ed.), Homogeneous Catalysis with Metal Phos-
phine Complexes, Plenum, New York, 1983.
[2] S.D. Ittel, C.A. Tolman, A.D. English, J.P. Jesson, J. Am.
Chem. Soc. 100 (1978) 7577.
[3] J.W. Rathke, E.L. Muetterties, J. Am. Chem. Soc. 97 (1975)
3272.
[4] H.H. Karsch, H.F. Klein, H. Schmidbaur, Angew. Chem. Int.
Ed. Engl. 14 (1975) 637.
[5] J.F. Hartwig, R.A. Anderson, R.G. Bergman, Organometallics
10 (1991) 1875.
[6] M. Antberg, L. Dahlenberg, Angew. Chem. Int. Ed. Engl. 25
(1986) 260.
[7] P.J. Desrosiers, R.S. Shinomoto, T.C. Flood, J. Am. Chem. Soc.
108 (1986) 1346.
[8] R.S. Shinomoto, P.J. Desrosiers, G.P. Harper, T.C. Flood, J.
Am. Chem. Soc. 110 (1988) 7915.
[9] J.F. Hartwig, R.A. Anderson, R.G. Bergman, Organometallics
10 (1991) 1710.
[10] B.R. James, R.S. McMillan, R.H. Moriss, D.K.W. Wang, Adv.
Chem. Ser. 167 (1978) 122.
[11] A.M. Joshi, I.S. Thorburn, S.J. Rettig, B.R. James, Inorg. Chim.
Acta 198 (1992) 283.
[12] D.E. Fogg, B.R. James, Inorg. Chem. 36 (1997) 1961.
[13] F.H. Jardine, Prog. Inorg. Chem. 31 (1984) 265.
[14] P.R. Hoffman, K.G. Caulton, J. Am. Chem. Soc. 97 (1975)
4221.
[15] (a) R.B. King, Acc. Chem. Res. 13 (1980) 243. (b) M.S. Balakr-
ishnna, S.S. Krishnamurthy, R. Murugavel, M. Netaji, I.I.
Mathews, J. Chem. Soc. Dalton Trans. (1994) 477. (c) M.S.
Balakrishnna, V.S.R. Reddy, S.S. Krishnamurthy, J.C.T.R. Bur-
ckette St. Lurent, J.F. Nixon, Coord. Chem. Rev. 129 (1994) 1,
and references cited therein. (d) M.S. Balakrishna, K. Ra-
maswamy, R.M. Abhyankar, J. Organomet. Chem. 560 (1998)
131.
[16] (a) C.D. Hoff, Prog. Inorg. Chem. 40 (1992) 503. (b) J.A.
Martinho Simoes, J.L. Beauchamp, Chem. Rev. 90 (1990) 629.
(c) R.G. Pearson, Chem. Rev. 85 (1985) 41. (d) J.A. Connor,
Top. Curr. Chem. 71 (1977) 71.
[17] (a) S.P. Nolan, C.D. Hoff, P.O. Stoutland, L.J. Newman, J.M.
Buchann, R.G. Bergman, G.K. Yang, K.G. Peters, J. Am.
Chem. Soc. 109 (1987) 314 and references therein. (b) S.P.
Nolan, de la Vega R. Lopez, C.D. Hoff, Organometallics 5
(1986) 2529.
[18] (a) S.P. Nolan, M. Porchia, T.J. Marks, Organometallics 10
(1991) 1450. (b) S.P. Nolan, D. Stern, T.J. Marks, J. Am. Chem.
Soc. 111 (1989) 7844.
[19] (a) S.P. Nolan, K. Martin, E.D. Stevens, P.J. Fagan,
Organometallics 11 (1992) 3947. (b) L. Luo, S.P. Nolan,
Organometallics 11 (1992) 3483. (c) L. Luo, S.P. Nolan, Inorg.
Chem. 32 (1993) 2410. (d) L. Luo, S.P. Nolan, P.J. Fagan,
Organometallics 12 (1993) 4305. (e) L. Luo, N. Zhu, N.J. Zhu,
4. Conclusions
The enthalpy of ligand substitution reactions in the
case of heterodifunctional ligands has clearly indicated
that they have weaker MꢀE (E=S, Se) bonds. Al-
though these heterodifunctional ligands form stable
five-membered metallacycles, the MꢀE bonds can be
easily cleaved. This feature can be exploited in utiliz-
ing this class of ligands bound to suitable metals for
designing a variety of heterodinuclear or polynuclear
complexes and in a variety of metal-mediated organic
transformations. Research in this direction is in
progress.

M.S. Balakrishna et al. / Journal of Organometallic Chemistry 599 (2000) 159–165
165
[23] W.A. Kamil, M.R. Bond, J.M. Shreeve, Inorg. Chem. 26 (1987)
2015.
[24] W. Seidel, M. Alexiev, Z. Anorg. Allg. Chem. 438 (1978) 68.
[25] M.S. Balakrishna, R. Klein, S. Uhlenbrock, A.A. Pinkerton,
R.G. Cavell, Inorg. Chem. 32 (1993) 5676.
[26] M.I. Bruce, C. Hameister, A.G. Swincer, R.C. Wallis, Inorg.
Synth. 21 (1982) 79.
[27] M.O. Albers, D.J. Robinson, J.V. Caspar, A. Shaver, E. Single-
ton, Organometallics 5 (1986) 2199.
[28] P.J. Fagan, W.S. Maloney, J.C. Calabrese, I.D. Williams,
Organometallics (1990) 1843.
[29] M.S. Balakrishna, R.M. Abhyankar, J.J. Mague, J. Chem. Soc.
Dalton Trans. (1999) 1407.
[30] J.P. Collman, L.S. Hegedus, J.R. Norton, R.G. Finke, Principles
and Applications of Organotransition Metal Chemistry, 2nd
edition, University Science, Mill Valley, CA, 1987.
[31] (a) J.R. Sowa Jr, R.J. Angelici, J. Am. Chem. Soc. 113 (1991)
2537. (b) M.K. Rottink, R.J. Angelici, J. Am. Chem. Soc. 115
(1993) 7267.
[32] (a) S.P. Nolan, C.D. Hoff, J.T. Landrum, J. Organomet. Chem.
282 (1985) 357(b) S.P. Nolan, R. de la Vega Lopez, C.D. Hoff,
Inorg. Chem. 25 (1986) 4446
E.D. Stevens, S.P. Nolan, P.J. Fagan, Organometallics 13 (1994)
669. (f) C. Li, M.E. Cucullu, R.A. McIntyre, E.D. Stevens, S.P.
Nolan, Organometallics 13 (1994) 3621. (g) L. Luo, S.P. Nolan,
Organometallics 13 (1994) 4781. (h) M.E. Cucullu, L. Luo, S.P.
Nolan, P.J. Fagan, N.L. Jones, J.C. Calabrese, Organometallics
14 (1995) 289. (i) L. Luo, C. Li, M.E. Cucullu, S.P. Nolan,
Organometallics 14 (1995) 1333. (j) S.A. Serron, S.P. Nolan,
Organometallics 14 (1995) 4611. (k) S.A. Serron, L. Luo, C. Li,
M.E. Cucullu, S.P. Nolan, Organometallics 14 (1995) 5290. (l)
S.A. Serron, S.P. Nolan, K.G. Moloy, Organometallics 15 (1996)
4301. (m) S.A. Serron, S.P. Nolan, Inorg. Chim. Acta 252 (1996)
107. (n) C. Li, S.A. Serron, S.P. Nolan, J.L. Petersen,
Organometallics 15 (1996) 4020. (o) C. Li, L. Luo, S.P. Nolan,
W. Marshall, P.J. Fagan, N.L. Jones, Organometallics 15 (1996)
3456. (p) C. Li, M. Ogasawa, S.P. Nolan, K.G. Caulton,
Organometallics 15 (1996) 4900. (q) C. Li, M. Olivan, S.P.
Nolan, K.G. Caulton, Organometallics 16 (1997) 4233.
[20] G. Ojelund, I. Wadso, Acta Chem. Scand. 22 (1968) 691.
[21] M.V. Kilday, J. Res. Natl. Bur. Stand (US) 85 (1980) 467.
[22] S.P. Nolan, C.D. Hoff, J. Organomet. Chem. 282 (1985)
357.
.