Solution calorimetric investigation of oxidative addition of HEAr (E = O, S, Se; Ar = C6H4X, X = CH3, H, Cl, NO2) to (PMe3)4Ru(C2H4): Relationship between HEAr acidity and enthalpy of reaction

Article abstract of DOI:10.1021/om980253p

The enthalpies of reactions of (PMe₃)₄Ru(C₂H₄) (1) with a series of HEAr compounds (E = O, S, Se; Ar = aryl) leading to the formation of (PMe₃)₄Ru(H)(EAr) complexes, have been measured by anaerobic solution calorimetry in C₆H₆ at 30.0°C. These reactions are rapid and quantitative under the calorimetry conditions. The measured reaction enthalpies span a range of some 35 kcal/mol. The relative stability scale established is as follows: PMe₃)₄-Ru(H)(OC₆H₄-pCH₃) < (PMe₃)₄Ru(H)(OC₆H₅) (PMe₃)₄Ru(H)(OC₆H₄-p-Cl) < (PMe₃)₄Ru-(H)(OC₆H₄-p-NO ₂) < (PMe₃)₄Ru(H)(SC₆H₄-p-CH₃ < (PMe₃)₄Ru(H)(SC₆H₅) < (PMe₃)₄Ru(H)-(SC₆H₄-p-Cl) ≈ (PMe₃)₄Ru(H)(SeC₆H₅) < (PMe₃)₄Ru(H)(SC₆H₄-p-NO ₂). A single-crystal X-ray structure of one of these complexes, (PMe₃)₄Ru(SC₆H₅)H (7), is reported. The measured enthalpies of reaction display a dependence on the acidity ot HEAr.

Full text of DOI:10.1021/om980253p

3516
Organometallics 1998, 17, 3516-3521
Solu tion Ca lor im etr ic In vestiga tion of Oxid a tive
Ad d ition of HEAr (E ) O, S, Se; Ar ) C6H4X, X ) CH3, H,
Cl, NO2) to (P Me3)4Ru (C2H4): Rela tion sh ip betw een HEAr
Acid ity a n d En th a lp y of Rea ction †
J inkun Huang, Chunbang Li, 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 26506-6045
Received April 2, 1998
The enthalpies of reactions of (PMe3)4Ru(C2H4) (1) with a series of HEAr compounds (E )
O, S, Se; Ar ) aryl), leading to the formation of (PMe3)4Ru(H)(EAr) complexes, have been
measured by anaerobic solution calorimetry in C6H6 at 30.0 °C. These reactions are rapid
and quantitative under the calorimetry conditions. The measured reaction enthalpies span
a range of some 35 kcal/mol. The relative stability scale established is as follows: (PMe3)4-
Ru(H)(OC6H4-p-CH3) < (PMe3)4Ru(H)(OC6H5) < (PMe3)4Ru(H)(OC6H4-p-Cl) < (PMe3)4Ru-
(H)(OC6H4-p-NO2) < (PMe3)4Ru(H)(SC6H4-p-CH3) < (PMe3)4Ru(H)(SC6H5) < (PMe3)4Ru(H)-
(SC6H4-p-Cl) ≈ (PMe3)4Ru(H)(SeC6H5) < (PMe3)4Ru(H)(SC6H4-p-NO2). A single-crystal X-ray
structure of one of these complexes, (PMe3)4Ru(SC6H5)H (7), is reported. The measured
enthalpies of reaction display a dependence on the acidity of HEAr.
In tr od u ction
halide (or equivalent) and an alkali metal salt of the
heteroatom-containing anion. A recent example of this
metathesis route is shown in eq 1.10
Oxidative addition and reductive elimination reac-
tions are critical processes in the catalytic and stoichio-
metric applications of transition-metal reagents in
organic synthesis.1 The oxidative addition of C-H
bonds across a metal center has been the focus of much
attention in view of the interest in alkane activation and
functionalization.2 Much less is known of the activation
of E-H bonds, where E is a heteroatom (O, S, Se, N,
P). Transition-metal complexes bearing anionic oxygen
and nitrogen ligands represent important intermediates
in industrial3,4 and biological processes.5 Recent devel-
opments in this area have lead to the formation of novel
metal alkoxides,6 arylamides,7 thiolates,8 and phos-
phides.9 The major synthetic route employed to form
these complexes has been the metathesis of a metal
Cp*Ni(PEt3)(OTf) + LiNTol f
Cp*Ni(PEt3)(NTol) + LiOTf (1)
Cp* ) C5Me5; Tol ) p-MeC6H4
An alternative strategy has been presented by Berg-
man and co-workers in which oxidative addition of HX
to a Ru(0) center yields a series of interesting Ru(II)
complexes (eq 2 and 3).11 Although these systems have
(PMe3)4Ru(C2H4) + HEAr f
(PMe3)4Ru(H)(EAr) + C2H4 (2)
† This contribution is dedicated to Professor Carl Hoff, friend and
mentor, on the occasion of his 50th birthday.
E ) O, S; Ar ) p-MeC6H4
‡ E-mail: spncm@uno.edu.
(1) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Priciples and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987.
(2) Arndtsen, B. A.; Bergman, R. G. Science 1995, 270, 1970-1973
and references cited.
(3) Roundhill, D. M. Chem. Rev. 1992, 92, 1-27.
(4) Bryndza, H. E.; Tam, W. Chem. Rev. 1988, 88, 1163-1188.
(5) Holm, R. H.; Kennepohl, P.; Solomon, E. I. Chem. Rev. 1996,
96, 2239-2314 and other articles in this issue.
(6) Glueck, D. S.; Winslow, L. N.; Bergman, R. G. Organometallics
1991, 10, 1462-1479.
(7) (a) Driver, M. S.; Hartwig, J . F. J . Am. Chem. Soc. 1996, 118,
7217-7218. (b) Mann, G.; Hartwig, J . F. J . Am. Chem. Soc. 1996, 118,
13109-13110. (c) Woffe, J . P.; Wagaw, S.; Buckwald, S. L. J . Am.
Chem. Soc. 1996, 118, 7215-7216.
(8) Milstein, D.; Calabrese, J . C.; Williams, I. D. J . Am. Chem. Soc.
1986, 108, 6387-6389.
(9) Bohle, D. S.; J ones, T. C.; Rickard, C. E. F.; Roper, W. R. J . Chem.
Soc., Chem. Commun. 1984, 865-867.
L4Ru(C2H4) + HX f L4Ru(H)(X) + C2H4
X ) NHPh, PHPh, OAr, SAr;
(3)
L4 ) (PMe3)4, (DMPE)2
been fully characterized and the thermodynamic driving
forces behind important ligand-exchange processes have
been qualitatively addressed, no quantitative thermo-
dynamic information is available on these processes.
(10) Holland, P. L.; Andersen, R. A.; Bergman, R. G.; Huang, J .;
Nolan, S. P. J . Am. Chem. Soc. 1997, 119, 12800-12814.
(11) (a) Burn, M. J .; Fickes, M. G.; Hollander, F. J .; Bergman, R. G.
Organometallics 1995, 14, 137-150. (b) Hartwig, J . F.; Andersen, R.
A.; Bergman, R. G. Organometallics 1991, 10, 1875-1887.
S0276-7333(98)00253-2 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 07/10/1998

Oxidative Addition of HEAr to (PMe3)4Ru(C2H4)
Organometallics, Vol. 17, No. 16, 1998 3517
Ta ble 1. Solu tion En th a lp ies of Rea ction (k ca l/
m ol) for
C6H6
(PMe3)4Ru(C2H4) + HEC6H4(p-X) 30 °C 8
(PMe3)4Ru(H)[EC6H4(p-X)] + C2H4
a
complex
E
X
-∆Hrxn
2
3
4
5
6
7
8
9
10
O
O
O
O
S
S
S
S
Se
CH3
H
Cl
NO2
CH3
H
Cl
NO2
H
4.1(2)
6.1(2)
7.0(3)
13.2(2)
28.3(4)
30.6(3)
32.0(2)
39.0(2)
32.5(3)
a
Enthalpy values are reported with 95% confidence limits.
Elaborating on our earlier ruthenium thermochemical
studies,12 we present in this paper a solution calorimet-
ric investigation of the oxidative addition to an electron-
rich ruthenium(0) center.
F igu r e 1. Hammett σp parameter versus enthalpies of
reaction (kcal/mol) for the (PMe3)4Ru(H)(OC6H4X) system;
slope ) -0.10, R ) 0.99.
Resu lts a n d Discu ssion
Th er m och em istr y. A solution calorimetric inves-
tigation of the oxidative addition of a number of weak
proton-donor electrophiles is made possible by the rapid
displacement of ethylene from (PMe3)4Ru(C2H4) (1), eq
4. The electronic properties of HEAr can be modulated
(PMe3)4Ru(C2H4) + HEAr f
(PMe3)4Ru(H)(EAr) + C2H4 (4)
E ) O, S, Se
by varying E as well as the substituents on the Ar group.
To quantify the enthalpic effects associated with these
electronic variations, anaerobic solution calorimetry
measurements involving 1 and a series of HEAr com-
pounds were performed in benzene at 30 °C. All
reactions investigated proved rapid and quantitative
under calorimetric conditions. The utilization of 1 as a
thermochemical anchor point permits the construction
of a relative stability scale which includes 10 ruthenium
complexes. Enthalpy data are presented in Table 1.
Th er m och em ica l Effects of Electr on ic Va r ia -
tion s w ith in th e HEC6H4X Ser ies (E ) O, X ) CH3
(2), H (3), Cl (4), NO2 (5); E ) S, X ) CH3 (6), H (7),
Cl (8), NO2 (9)). A number of variations are brought
about in this series by affecting the electronic donation
F igu r e 2. Hammett σp parameter versus enthalpies of
reaction (kcal/mol) for the (PMe3)4Ru(H)(SC6H4X) system;
slope ) -0.09, R ) 0.99.
of the aryl moiety by selecting substrates with varying
substituent electronic properties in the trans position
to the heteroatom. This effect spans a range of 9 kcal/
mol for the phenols and 11 kcal/mol within the thiophe-
nol series. This para-substituent effect can be thought
of in terms of the Hammett parameter σp.13 A simple
thermochemical relationship can be established between
the enthalpies of reaction and the Hammett parameter
characterizing the inductive effect at play. Such rela-
tionships for the phenols and thiophenols are presented
in Figures 1 and 2. Both relationships display similar
slopes and span a similar range, indicating that similar
influences are felt at the metal binding site.
(12) (a) Nolan, S. P.; Martin, K. L.; Stevens, E. D.; Fagan, P. J .
Organometallics 1992, 11, 3947-3953. (b) Luo, L.; Fagan, P. L.; Nolan,
S. P. Organometallics 1993, 12, 4305-4311. (c) Luo, L.; Zhu, N.; Zhu,
N.-J .; Stevens, E. D.; Nolan, S. P.; Fagan, P. J . Organometallics 1994,
13, 669-675. (d) Li, C.; Cucullu, M. E.; McIntyre, R. A.; Stevens, E.
D.; Nolan, S. P. Organometallics 1994, 13, 3621-3627. (e) Luo, L.;
Nolan, S. P. Organometallics 1994, 13, 4781-4786. (f) Cucullu, M. E.;
Luo, L.; Nolan, S. P.; Fagan, P. J .; J ones, N. L.; Calabrese, J . C.
Organometallics 1995, 14, 289-296. (g) Luo, L.; Li, C.; Cucullu, M.
E.; Nolan, S. P. Organometallics 1995, 14, 1333-1338. (h) Serron, S.
A.; Nolan, S. P. Organometallics 1995, 14, 4611-4616. (i) Serron, S.
A.; Luo, L.; Li, C.; Cucullu, M. E.; Nolan, S. P. Organometallics 1995,
14, 5290-5297. (j) Li, C.; Ogasawa, M.; Nolan, S. P.; Caulton, K. G.
Organometallics 1996, 15, 4900-4903. (k) Serron, S. A.; Luo, L.;
Stevens, E. D.; Nolan, S. P.; J ones, N. L.; Fagan, P. J . Organometallics
1996, 15, 5209-5215. (l) Li, C.; Olivan, M.; Nolan, S. P.; Caulton, K.
G. Organometallics 1997, 16, 4223-4225. (m) Serron, S. A.; Nolan, S,
P.; Abramov, Y. A.; Brammer, L.; Petersen, J . L.Organometallics 1998,
17, 104-110.
A second property of the acidic reactants which is
influenced by the inductive effects of the para-substitu-
ent is their pKa.14 In view of this relationship and since
the Hammett σp parameter and pKa correlate linearly,
(13) Hammett σp values are taken from Isaacs, N. Physical Organic
Chemistry, 2nd ed.; Longman Scientifc & Technical: England, 1995;
pp 152-153.

3518 Organometallics, Vol. 17, No. 16, 1998
Huang et al.
a simple relationship between enthalpy of reaction and
pKa of the acidic HEC6H4X compounds can be estab-
lished for both phenol and thiophenol systems. Both
relationships display excellent linear fits (R ) 0.99 for
each).
pies of deprotonation and pKa values.19,20 Using these
pKa values, a relationship can be established between
the acidity constants and the enthalpies of oxidative
addition. The relationship displays a remarkable linear
fit (R ) 0.95) in view of pKa solvent dependence.
We have recently performed a solution calorimetric
study of a late-transition-metal system where similar
chalcogenide moieties were bound to the metal center,
eq 5.10 In the present system, a similar reaction
It has been suggested previously that oxidative ad-
dition reactions are principally driven by the acidity
function of the incoming reagent, the feasibility of the
oxidative addition depending on both this acidity func-
tion and the acid-base behavior/character of the metal
center.15 The exothermicity of the oxidative addition
at the electron-rich metal center can be modulated by
as much as 10 kcal/mol by simply making subtle
electronic variations.
Cp*Ni(PEt3)OTol + TolSH f
Cp*Ni(PEt3)STol + TolOH (5)
∆Hrxn ) -14.0 kcal/mol
This para-substituent effect is two-fold. The case of
the electron-withdrawing NO2 substituent is analyzed
as a specific example. In the acid form, the electron-
withdrawing character of the NO2 fragment draws
electron density from the H-E bond, weakening this
bond compared to the unsubstituted parent acid (phenol
or thiophenol). In the complex, the electron-withdraw-
ing character of the substituents facilitate back-donation
from the electron-rich metal center, leading to a stronger
metal-heteroatom bond than in the unsubstituted
parent. The measured enthalpy of reaction is therefore
the most exothermic for the -NO2-substituted aryl-
containing moieties since weaker bonds are broken and
stronger bonds are formed.
enthalpy can be calculated from the thermochemical
data, eq 6. The enthalpy difference between the two
(PMe3)4RuH(OTol) + TolSH f
(PMe3)4RuH(STol) + TolOH (6)
∆Hcalcd ) -24.2 kcal/mol
systems is 10 kcal/mol, favoring ruthenium. The nickel
system includes a π ligand (Cp*), therefore the overall
π-bonding interaction with the incoming fragment may
be decrease in view of this alternative pathway to
channel π-electron density. In the present ruthenium
system, this enthalpy difference between the alkoxide
and sulfide is 24 kcal/mol. The ancillary ligation is
comprised of excellent σ-donor ligands which do not
possess π-acceptor properties. This ruthenium system
is an excellent example of an electron-rich system that
is unable to behave as a π acceptor but more than likely
back-donates electron density into π orbitals of incoming
ligand fragments. Therefore, the moiety most capable
of accepting electron density from the metal center will
have the largest enthalpy of oxidative addition. This
is exactly what is observed since electron-withdrawing
groups on the aryl substituent make the chalcogen-
containing fragment more acidic, enabling electron
density to be channeled back into the incoming π
system. This preference for second-row main-group
elements has been observed by Bryndza and Bercaw21
and Glueck22 for the (DPPE)PtMeX system. This trend
appears slightly more accentuated for third-row main-
group elements, eq 7.
Th er m och em ica l Effects of Electr on ic Va r ia -
tion s w ith in th e HEC6H5 Ser ies (E ) O (3), S (7),
a n d Se (10)). The aryl substituent electronic effect is
of significant importance. The thermochemical data
allow us to examine the more obvious difference within
a series of compounds which differ at the heteroatom,
the effect on thermochemistry as a function of heteroa-
tom-metal binding. The enthalpies of reaction within
this series progress in the following order: phenol <
thiophenol < selenophenol. The range spans 24 kcal/
mol. The highest exothermicity measured within this
series is for the selenophenol (-32.5 kcal/mol) and can
be understood in terms of the acid-base concept. Arnett
and Small have reported on the enthalpy of deprotona-
tion of these compounds.16 The trend observed mimics
the present one for enthalpies of oxidative addition. In
Arnett’s study, the enhanced acidity order selenyl
>sulfhydryl > hydroxyl is also observed. This is
explained in terms of the decreasing H-E bond strength
as one goes down a group, which in turn may be related
to the more diffuse bonding orbitals of larger atoms. The
trend has also been quantified in the hard/soft concept
of acids and bases17 and in the E and C bonding
factorization of Drago.18 In a more quantitative fashion,
Arnett has highlighted a relationship between enthal-
(PMe3)4RuH(OPh) + PhSeH f
(PMe3)4RuH(SePh) + PhOH (7)
∆Hcalcd ) -26.4 kcal/mol
Str u ctu r al Deter m in ation of (P Me3)4Ru (SC6H5)H
(7). To gain insight into the bonding patterns at play
in this system, a structural determination of complex 7
(14) (a) For pKa value of phenols, see: The Chemistry of Functional
Groups: the Chemistry of the Hydroxyl Goup, part 1; Patai, S., Ed.;
Interscience Publishers: New York, 1971; pp 374-375. (b) For pKa
value of thiophenols, see: The Chemistry of Functional Groups: the
Chemistry of the Thiol Goup, part 1; Patai, S., Ed.; Interscience
Publishers: New York, 1971; p 401.
(19) Arnett, E. M.; Moriarity, T. C.; Small, L. E.; Rudolph, R. P.;
Quirk, R. P. J . Am. Chem. Soc. 1973, 95, 1492-1495.
(20) In the present case, the relationship is somewhat restrictive
since no pKa value has been reported for the selenol. A value can be
determined (4.6 in water) by extrapolation of the relationship discussed
in ref 19.
(21) Bryndza, H. E.; Fong, L. K.; Paciello, R. A.; Tam, W.; Bercaw,
J . E. J . Am. Chem. Soc. 1987, 109, 1444-1456.
(22) Wicht, D. K.; Paisner, S. N.; Lew, B. M.; Glueck, D. S.; Yap, G.
P. A.; Liable-Sands, L. M.; Rheingold, A. L.; Haar, C. M.; Nolan, S. P.
Organometallics 1998, 17, 652-660.
(15) Vaska, L. Acc. Chem. Res. 1968, 1, 335-344.
(16) Arnett, E. M.; Small, L. E. J . Am. Chem. Soc. 1977, 99, 808-
816.
(17) Pearson, R. G. In Advances in Linear Free Energy Relationships;
Chapman, N. B., Shorter, J ., Eds.; Plenum Press: New York, 1972.
(18) Drago, R. S. Applications of Electrostatic-Covalent Models in
Chemistry; Surfside: Gainesville, FL, 1994.

Oxidative Addition of HEAr to (PMe3)4Ru(C2H4)
Organometallics, Vol. 17, No. 16, 1998 3519
Ta ble 3. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for (P Me3)4Ru (SC6H5)H (7)
Bond Lengths
Ru-P(1)
2.2534(12)
2.3374(13)
2.4579(10)
1.757(3)
1.885(7)
1.827(5)
1.840(5)
1.856(6)
1.815(5)
1.865(5)
Ru-P(3)
2.3347(13)
2.3484(12)
1.84
1.773(8)
1.910(7)
1.823(6)
1.805(5)
1.819(5)
1.832(5)
Ru-P(4)
Ru-P(2)
Ru-S
S-C(1)
Ru-H
P(1)-C(7)
P(1)-C(9)
P(2)-C(11)
P(3)-C(13)
P(3)-C(15)
P(4)-C(17)
P(1)-C(8)
P(2)-C(10)
P(2)-C(12)
P(3)-C(14)
P(4)-C(16)
P(4)-C(18)
Bond Angles
P(1)-Ru-P(3)
P(1)-Ru-P(4)
P(1)-Ru-H
96.57(6)
95.85(6)
86.4
93.56(5)
173.6
82.97(4)
82.68(4)
81.8
128.0(3)
111.0(2)
117.8(2)
118.6(2)
117.1(2)
114.2(2)
116.9(2)
P(1)-Ru-P(2)
99.71(4)
168.08(4)
94.78(5)
92.20(4)
163.65(4)
82.5
P(1)-Ru-S
P(2)-Ru-P(3)
P(2)-Ru-S
F igu r e 3. ORTEP of (PMe3)4Ru(SC6H5)H (7). Ellipsoids
are drawn in with 50% probability.
P(2)-Ru-P(4)
P(2)-Ru-H
P(3)-Ru-P(4)
P(3)-Ru-H
P(3)-Ru-S
Ta ble 2. Cr ysta l Da ta a n d Deta ils of th e
Str u ctu r e Deter m in a tion of (P Me3)4Ru (SC6H5)H (7)
P(4)-Ru-S
P(4)-Ru-H
C(1)-S-Ru
87.7
S-Ru-H
117.27(10)
120.0(3)
120.0(2)
115.3(2)
122.5(2)
124.9(2)
C(7)-P(1)-Ru
C(9)-P(1)-Ru
C(10)-P(2)-Ru
C(12)-P(2)-Ru
C(15)-P(3)-Ru
C(16)-P(4)-Ru
C(18)-P(4)-Ru
C(8)-P(1)-Ru
C(11)-P(2)-Ru
C(13)-P(3)-Ru
C(14)-P(3)-Ru
C(17)-P(4)-Ru
empirical formula
fw
C18H42P4RuS
515.53
temp
295(2) K
wavelength
cryst system
space group
unit cell dimens
0.710 73 Å
monoclinic
P21/c
a ) 14.884(1) Å
b ) 13.113(1) Å
c ) 14.044(1) Å
R ) 90°
Ru-P bond lengths are longer in 7. As in the case of 7,
the Ru-P bond trans to the main-group atom in 2
displays a trans influence, making it shorter than the
other Ru-P length by 0.1 Å. The bond distance elonga-
tions observed in 7 (and discussed above) can be
explained in terms of increased back-donation into the
sulfur-containing moiety.
â ) 106.509(6)°
γ ) 90°
vol
2628.0(3) Å3
Z
4
density(calcd)
abs coeff
1.303 g/cm3
9.20 cm-1
F(000)
1080
The structural differences between 2 and 7 are also
apparent in the bond angles. The P(1)-Ru-E angle (E
) O, 176.96°; E ) S, 168.08°) shows a more linear
arrangement in 2. The E-Ru-H angles (E ) O,
101.15°; E ) S, 81.2°) show a closer distance between
the aryl fragment and the hydride in 7. The C(1)-E-
Ru angles (E ) O, 133.3°; E ) S, 117.2°) also display a
more linear arrangement in 2. These three pairs of
angles reflect a significant bending of the aryl moiety
toward the Ru-H fragment in 7. This “bend” could be
attributable to an effort to maximize the dπ-pπ interac-
tion and to minimize the electron lone-pair repulsions
in the complex.
It would be desirable to extract bond energy data from
the enthalpic information, yet as illustrated by the
variation in metrical parameters between 2 and 7,
reorganization energy24 renders such treatment impos-
sible. The enthalpies of reaction encompass all ener-
getic terms involved in the transformation (ethylene
displacement, oxidative addition, and reorganization
energy). The enthalpic terms are, however, a true gauge
of the relative stability of these electron-rich complexes.
cryst size
range for data collection
index ranges
0.32 × 0.36 × 0.48 mm
2.11-27.50°
-19 e h e18, 17 e k e 0,
0 e l e 17
6191
5946 (Rint ) 0.0180)
full-matrix least-squares on F2
5306/12/265
no. of reflns collected
no. of indep reflns
refinement method
data/restraints/params
goodness-of fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
ext coeff
1.033
R1 ) 0.0486, wR2 ) 0.1037
R1 ) 0.0858, wR2 ) 0.1213
0.00033(10)
largest diff peak and hole
1.047 and -0.704 e A-3
was undertaken. An ORTEP drawing of 7 is presented
in Figure 3. The most striking feature of this pseudo-
octahedral complex is the inequivalent Ru-P distances.
The Ru-P(1) distance (2.2534 Å) is 0.09 Å shorter than
the average Ru-P(2-4) distance (2.3402 Å). This bond
shortening is a result of the trans influence23 of the
electron-withdrawing SPh group. This interaction is
presumably resulting from the dπ-pπ bonding mode.
Of further significance are the Ru-S distance of 2.4579
Å, the Ru-H bond distance of 1.84 Å, and the S-Ru-H
(81.2°), C(1)-S-Ru (117.2°), and P(1)-Ru-S (168.1°)
bond angles. All other crystallographic and bond dis-
tance and angle data are presented in Tables 2 and 3.
These data permit a comparison with the structural
parameters previously reported for 2.11b On going from
O to S, the Ru-E bond distance increases by 0.31 Å.
The Ru-H distance increases by 0.1 Å. The average
Con clu sion
The rapid and quantitative nature of the reactivity
of HEAr (E ) O, S, Se) with 1 makes the determination
of a relative stability scale possible for 10 ruthenium
complexes. The enthalpy trend can be explained in
terms of H-EAr acidity. The study of substituent
(23) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev.
1973, 10, 335-422.
(24) Huang, J .; Haar, C. M.; Nolan, S. P.; Marshall, W. J .; Moloy,
K. G. J . Am. Chem. Soc., in press.

3520 Organometallics, Vol. 17, No. 16, 1998
Huang et al.
(OC6H4-p-CH3) was found to be quantitative under these
reaction conditions. Control reactions with Hg and HEAr show
no reaction. The enthalpy of reaction, -0.5 ( 0.2 kcal/mol,
represents the average of five individual calorimetric deter-
minations. The final enthalpy value listed in Table 1 (-4.1 (
0.2 kcal/mol) represents the enthalpy of reaction with all
species in solution. The enthalpy of solution of 1 (3.6 ( 0.1
kcal/mol) has therefore been subtracted from the -0.5 kcal/
mol value. This methodology represents a typical procedure
involving all organometallic compounds and all reactions
investigated in the present study.
effects on HEAr allows for the construction of thermo-
chemcial relationships between enthalpies of reaction
and substituent Hammett parameters. Single-crystal
diffraction work on one complex (PMe3)4Ru(SC6H5)H (7)
permits comparisons between S-- and O--containing
complexes. In view of significant bond length and bond
angle variations between the two complexes, we wish
to stress that reorganization energy prohibits the direct
translation of reaction enthalpies into bond strengths
in the present system.
En th a lp y of Solu tion of (P Me3)4Ru (C2H4) (1). To con-
sider all species in solution, the enthalpy of solution of (PMe3)4-
Ru(C2H4) (1) had to be directly measured. This was performed
by using a similar procedure as the one described above, with
the exception that no HEAr was added to the reaction cell.
The enthalpy of solution, 3.6 ( 0.1 kcal/mol, represents the
average of five individual determinations.
Syn th esis. The compound (PMe3)4Ru(C2H4) (1) was syn-
thesized according to literature procedures.11b Other organ-
oruthenium complexes, (PMe3)4Ru(H)(OC6H4-p-CH3)29 (2),
(PMe3)4Ru(H)(OC6H5)11 (3), (PMe3)4Ru(H)(OC6H4-p-Cl)11 (4),
(PMe3)4Ru(H)(OC6H4-p-NO2)11 (5), and (PMe3)4Ru(H)(SC6H4-
p-CH3)11 (6) have been previously reported. Experimental
synthetic procedures, leading to the isolation of previously
unreported complexes, are described below.
(P Me3)4Ru (H)(SC6H5) (7). In the glovebox, 60.6 mg (0.140
mmol) of (PMe3)4Ru(C2H4) and 10 mL of pentane were charged
into a 50 mL flask. To this solution, 15.4 mg (0.140 mmol) of
HSC6H5 was added. The reaction mixture was stirred for 3
h, during which time a precipitate formed. The solution was
filtered and evacuated to dryness. The resulting yellow
powder was recrystallized from pentane/methylene chloride
to yield amber crystals, which were dried thoroughly under
vacuum. Yield: 41 mg (57%). 1H NMR (C6D6, mult, J ) Hz):
δ (ppm) 8.33 (d, J ) 8.1, 2 H, Ph), 7.21 (m, 2 H, Ph), 6.92 (t,
J ) 7.8, 1 H, Ph), 1.28 (t, J ) 3.0, 18 H, PMe3), 1.12 (d, J )
5.4, 9 H, PMe3), 1.08 (d, J ) 9.6, 9 H, PMe3), -8.67 (dt, J )
28.2, J ) 87.6, 1 H, Ru-H). 31P{1H} NMR (C6D6): δ (ppm)
2.56 (m, J ) 24.4, J ) 29.8), -7.55 (m, J ) 26.0), -17.91 (m).
Anal. Calcd for C18H42P4SRu: C, 41.93; H, 8.21. Found: C,
41.90; H, 7.97
(P Me3)4Ru (H)(SC6H4-p-Cl) (8). In a manner analogous
to 7, 8 was isolated as amber crystals in 54% yield. 1H NMR
(C6D6, mult, J ) Hz): δ (ppm) 8.13 (d, J ) 8.4, 2 H, Ph), 7.13
(d, J ) 9.0, 2 H, Ph), 1.23 (t, J ) 2.7, 18 H, PMe3), 1.08 (d, J
) 4.8, 9 H, PMe3), 1.05 (d, J ) 6.9, 9 H, PMe3), -8.82 (dt, J )
33.1, J ) 81.0, 1 H, Ru-H). 31P{1H} NMR (C6D6): δ (ppm)
2.00 (m, J ) 19.1, J ) 24.3), -8.17 (m, J ) 25.3), -18.41 (m).
Anal. Calcd for C18H41ClP4SRu: C, 39.31; H, 7.51. Found:
C, 39.60; H, 7.38.
Exp er im en ta l Section
Gen er a l Con sid er a tion . All manipulations involving
organoruthenium complexes were performed under argon
using standard high-vacuum or Schlenk tube techniques or
in a MBraun glovebox containing less than 1 ppm of oxygen
and water. All phenols, thiophenols, and benzeneselenol were
purchased from Aldrich and recrystallized or redistilled before
use. Solvents were dried and distilled under argon before use
employing standard drying agents.25 Only materials of high
purity, as indicated by NMR spectroscopy, were used in the
calorimetric experiments. NMR spectra were recorded using
a Varian Gemini 300 MHz spectrometer. Calorimetric mea-
surements were performed using a Calvet calorimeter (Set-
aram C-80), which was periodically calibrated using the TRIS
reaction26 or the enthalpy of solution of KCl in water.27 The
experimental enthalpies for these two standard reactions
compared very closely to literature values. This calorimeter
has been previously described,28 and typical procedures are
described below. Experimental enthalpy data are reported
with 95% confidence limits.
NMR Titr a tion s. Prior to every set of calorimetric experi-
ments involving a new HEAr, an accurately weighed amount
((0.1 mg) of the organoruthenium complex was placed in a
Wilmad screw-capped NMR tube fitted with a septum and
C6D6 was subsequently added. The solution was titrated with
a solution of the HEAr of interest by injecting the latter in
aliquots through the septum with a microsyringe, followed by
vigorous shaking. The reactions were monitored by 31P and
1H NMR spectroscopy, and the reactions were found to be
rapid, clean, and quantitative. These conditions are necessary
for accurate and meaningful calorimetric results and were
satisfied for all organometallic reactions investigated.
Solu tion Ca lor im etr y. Ca lor im etr ic Mea su r em en t of
Reaction Between (P Me3)4Ru (C2H4) (1) an d p-CH3C6H4OH.
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 mg sample of (PMe3)4Ru(C2H4) was accurately
weighed into the lower vessel, which was closed and sealed
with 1.5 mL of mercury. Four milliliters of a stock solution of
p-CH3C6H4OH (30 mg of p-CH3C6H4OH in 20 mL of C6H6) was
added, and the remainder of the cell was assembled, removed
from the glovebox, and inserted in the calorimeter. The
reference vessel was loaded in an identical fashion with the
exception that no organoruthenium complex was added to the
lower vessel. After the calorimeter had reached thermal
equilibrium at 30.0 °C (about 2 h), the calorimeter was
inverted, thereby allowing the reactants to mix. After the
reaction had reached completion and the calorimeter had once
again reached thermal equilibrium (ca. 2 h), the vessels were
removed from the calorimeter. Conversion to (PMe3)4Ru(H)-
(P Me3)4Ru (H)(SC6H4-p-NO2) (9). In a manner analogous
to 7, 9 was isolated as purple microcrystals in 86% yield. 1H
NMR (C6D6, mult, J ) Hz): δ (ppm) 8.31 (m, 2 H, Ph), 7.41
(m, 2 H, Ph), 1.33 (t, J ) 3.0, 18 H, PMe3), 1.25 (d, J ) 4.5, 9
H, PMe3), 1.22 (d, J ) 7.5, 9 H, PMe3), -8.82 (dt, J ) 27.3, J
) 87.0, 1 H, Ru-H). 31P{1H} NMR (C6D6): δ (ppm) 2.64 (m,
J ) 31.6, J ) 19.4), -7.79 (m, J ) 40.1), -18.88 (m). Anal.
Calcd for
C18H41NO2P4SRu: C, 38.57; H, 7.37; N; 2.50.
Found: C, 38.54; H, 7.25; N, 2.73.
(P Me3)4Ru (H)(SeC6H5) (10). In a manner analogous to
7, 10 was isolated as amber crystals in 56% yield. 1H NMR
(C6D6, mult, J ) Hz): δ (ppm) 8.48 (d, J ) 7.8, 2 H, Ph), 7.10
(m, J ) 6.3, 2 H, Ph), 6.98 (t, J ) 6.0, 1 H, Ph), 1.28 (t, J )
3.0, 18 H, PMe3), 1.04 (d, J ) 5.4, 9 H, PMe3), 1.01 (d, J ) 9.6,
9 H, PMe3), -9.05 (dt, J ) 25.8, J ) 85.5, 1 H, Ru-H). 31P-
{1H} NMR (C6D6): δ (ppm) 2.59 (m, J ) 30.5), -10.40 (m,
(25) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3rd ed.; Pergamon Press: New York, 1988.
(26) Ojelund, G.; Wadso¨, I. Acta Chem. Scand. 1968, 22, 1691-1699.
(27) Kilday, M. V. J . Res. Natl. Bur. Stand. U.S. 1980, 85, 467-
481.
(28) (a) Nolan, S. P.; Hoff, C. D.; Landrum, J . T. J . Organomet.
Chem. 1985, 282, 357-362. (b) Nolan, S. P.; Lopez de la Vega, R.; Hoff,
C. D. Inorg. Chem. 1986, 25, 4446-4448.
(29) This complex was first synthesized using (PMe3)4RuH2 and the
appropriate phenol, see: Osakada, K.; Ohshiro, K.; Yamamoto, A.
Organometallics 1991, 10, 404-410.

Oxidative Addition of HEAr to (PMe3)4Ru(C2H4)
Organometallics, Vol. 17, No. 16, 1998 3521
J ) 28.9), -17.77 (m). Anal. Calcd for C18H42P4SeRu: C,
38.44; H, 7.53. Found: C, 38.61; H, 7.94.
positions of C(7), C(8), and C(9) were refined using a two-site
model with the P-C and C-C distances restrained to 1.820
( 02 and 2.800 ( 02 Å, respectively. The refined occupancy
factor indicated that two disordered sites were present in a
60:40 ratio. The position of the hydride ligand was located
and refined isotropically. Full-matrix least-squares refine-
ment, based upon the minimization of ∑wi|Fo - Fc | , with
wi-1 ) σ2(Fo2) + (0.0430P)2 + 2.7585P], where P ) (Max(Fo2,0)
+ 2Fc2)/3,was performed with SHELXL-93.31 After conver-
gence, the final discrepancy indices were R1 ) 0.0486 and wR2
) 0.1037 for 4037 reflections with I > 2σ(I) and the overall
GOF value was 1.033. Selected interatomic distances and
angles are listed in Table 3. An ORTEP view of the complex
is presented in Figure 3.
Str u ctu r e Deter m in a tion of (P Me3)4Ru (H)(SC6H5) (7).
Crystals of (PMe3)4Ru(H)(SC6H5) suitable for X-ray crystal-
lography were grown in pentane. A crystal of (PMe3)4Ru(H)-
(SC6H5) was sealed in a capillary tube and then optically
aligned on the goniostat of a Siemens P4 automated X-ray
diffractometer. The reflections that were used for the unit cell
determination were located and indexed by the automatic peak
search routine XSCANS.30 The corresponding lattice param-
eters and orientation matrix were provided from a nonlinear
least-squares fit of the orientation angles of 54 centered
reflections (10° < 2θ < 25°) at 22 °C. The refined lattice
parameters and other pertinent crystallographic information
are summarized in Table 2.
2
2 2
Intensity data were measured with graphite-monochro-
mated Mo KR radiation (λ ) 0.710 73 Å) and variable ω scans
(4.0-20.0°/min). Background counts were measured at the
beginning and at the end of each scan with the crystal and
counter kept stationary. The intensities of three standard
reflections were measured after every 100 reflections. Their
combined intensity decreased by 2% during data collections.
The data were corrected for Lorentz-polarization and the
symmetry-equivalent reflections were averaged. An empirical
absorption correction (range of transmission coefficients: 0.736-
0.775) based upon the ψ scans measured for 8 reflections (ø ≈
90°, 2θ ) 6-36°) was applied.
Ack n ow led gm en t. S.P.N. acknowledges the Na-
tional Science Foundation (Grant No. CHE-9631611)
and Dupont (Educational Aid Grant) for financial sup-
port of this research. J .L.P acknowledges the financial
support provided by the Chemical Instrumentation
Program of the National Science Foundation (Grant No.
CHE-9120098) for the acquisition of a Siemens P4 X-ray
diffractometer by the Department of Chemistry at West
Virginia University.
The initial coordinates for the non-hydrogen atoms were
determined with a combination of direct methods and differ-
ence Fourier calculations performed with algorithms provided
by SHELXTL IRIS operating on a Silicon Graphics IRIS Indigo
workstation. During the course of the structural refinement,
it became evident that the three carbons of the trimethylphos-
phine ligand trans to the thiolate ligand were disordered. The
Su p p or tin g In for m a tion Ava ila ble: Tables of anisotro-
pic thermal parameters, positional parameters, bond angles,
and bond distances for 7 (7 pages). Ordering and Internet
access information are given on any current masthead page.
OM980253P
(31) SHELXL-93 is a FORTRAN-77 program (Prof. G. Sheldrick,
Institut fu¨r Anorganische Chemie, University of Go¨ttingen, D-37077,
Go¨ttingen, Germany) for single-crystal X-ray structural analysis.
(30) XSCANS (version 2.0) is
developed by Siemens Analytical X-ray Instruments, Madison, WI.
a diffractometer control system