Synthesis and reactivity of a coordinatively unsaturated ruthenium(II) parent amido complex: Studies of X-H activation (X = H or C)

Article abstract of DOI:10.1021/om049836r

The five-coordinate parent amido complex (PCP)Ru(CO)(NH₂) (2) (PCP = 2,6-(CH₂P^tBu₂)₂C ₆H₃) has been prepared by two independent routes that involve deprotonation of Ru(II) ammine complexes. Complex 2 reacts with phenylacetylene to yield the Ru(II) acetylide complex (PCP)Ru(CO)(C≡CPh) (5) and ammonia. In addition, complex 2 rapidly activates dihydrogen at room temperature to yield ammonia and the previously reported hydride complex (PCP)Ru(CO)(H). The ability of the amido complex 2 to cleave the H-H bond is attributed to the combination of a vacant coordination site for binding/activation of dihydrogen and a basic amido ligand. Complex 2 also undergoes an intramolecular C-H activation of a methyl group on the PCP ligand to yield ammonia and a cyclometalated complex. The reaction of (PCP)Ru(CO)(Cl) with MeLi allows the isolation of (PCP)Ru(CO)-(Me) (8), and complex 8 undergoes an intramolecular C-H activation analogous to the amido complex 2 to produce methane and the cyclometalated complex. Determination of activation parameters for the intramolecular C-H activation transformations of 2 and 8 reveal identical δH^? {18(1) kcal/mol} with δS ^? = -23(4) eu and -18(4) eu, respectively. Density functional theory has been applied to the study of intermolecular activation of methane and dihydrogen by (PCP′)Ru(CO)(NH₂) to yield (PCP′)Ru(CO) (NH₃)(X) (X = Me or H; PCP′ = 2,6-(CH₂-PH ₂)₂C₆H₃). The results indicate that the activation of dihydrogen is both exoergic and exothermic. In contrast, the addition of a C-H bond of methane across the Ru-NH₂ bond has been calculated to be endoergic and endothermic. The surprising endoergic nature of the methane C-H activation has been attributed to a large and unfavorable change in Ru-N bond dissociation energy upon conversion from Ru-amido to Ru-ammine.

Full text of DOI:10.1021/om049836r

2724
Organometallics 2004, 23, 2724-2733
Syn th esis a n d Rea ctivity of a Coor d in a tively
Un sa tu r a ted Ru th en iu m (II) P a r en t Am id o Com p lex:
Stu d ies of X-H Activa tion (X ) H or C)
David Conner,† K. N. J ayaprakash,† Thomas R. Cundari,‡ and
T. Brent Gunnoe*,†
Department of Chemistry, North Carolina State University,
Raleigh, North Carolina 27695-8204, and Department of Chemistry, University of
North Texas, Box 305070, Denton, Texas 76203-5070
Received March 4, 2004
The five-coordinate parent amido complex (PCP)Ru(CO)(NH2) (2) (PCP ) 2,6-(CH2P-
tBu2)2C6H3) has been prepared by two independent routes that involve deprotonation of Ru-
(II) ammine complexes. Complex 2 reacts with phenylacetylene to yield the Ru(II) acetylide
complex (PCP)Ru(CO)(CtCPh) (5) and ammonia. In addition, complex 2 rapidly activates
dihydrogen at room temperature to yield ammonia and the previously reported hydride
complex (PCP)Ru(CO)(H). The ability of the amido complex 2 to cleave the H-H bond is
attributed to the combination of a vacant coordination site for binding/activation of
dihydrogen and a basic amido ligand. Complex 2 also undergoes an intramolecular C-H
activation of a methyl group on the PCP ligand to yield ammonia and a cyclometalated
complex. The reaction of (PCP)Ru(CO)(Cl) with MeLi allows the isolation of (PCP)Ru(CO)-
(Me) (8), and complex 8 undergoes an intramolecular C-H activation analogous to the amido
complex 2 to produce methane and the cyclometalated complex. Determination of activation
parameters for the intramolecular C-H activation transformations of 2 and 8 reveal identical
∆Hq {18(1) kcal/mol} with ∆Sq ) -23(4) eu and -18(4) eu, respectively. Density functional
theory has been applied to the study of intermolecular activation of methane and dihydrogen
by (PCP′)Ru(CO)(NH2) to yield (PCP′)Ru(CO)(NH3)(X) (X ) Me or H; PCP′ ) 2,6-(CH2-
PH2)2C6H3). The results indicate that the activation of dihydrogen is both exoergic and
exothermic. In contrast, the addition of a C-H bond of methane across the Ru-NH2 bond
has been calculated to be endoergic and endothermic. The surprising endoergic nature of
the methane C-H activation has been attributed to a large and unfavorable change in Ru-N
bond dissociation energy upon conversion from Ru-amido to Ru-ammine.
In tr od u ction
metal centers with high d-electron counts can exhibit
unique reactivity patterns.3,7,8,10,11,14 For example, amido
ligands bound to transition metal centers that possess
filled dπ manifolds exhibit reactivity consistent with the
localization of significant negative charge density on the
amido nitrogen.11,13,15-22 The highly reactive nature of
such complexes has been attributed to the disruption
of amido-to-metal π-donation (i.e., π-conflict) as well as
the polar nature of the metal-amido bond.7,8,11,23
Late transition metal amido complexes have been
implicated as important species in catalytic processes.1-6
Until recently, isolable examples of late transition metal
complexes that possess nondative ligands were rare
compared with early and middle transition elements in
high oxidation states.7-10 However, an increased inter-
est in late metal systems has resulted in the preparation
and detailed reactivity studies of amido complexes of
ruthenium, rhodium, iridium, nickel, platinum, osmium,
and copper.3,11-13 Reactivity studies of such complexes
have revealed that amido and related ligands bound to
(12) Blue, E. D.; Davis, A.; Conner, D.; Gunnoe, T. B.; Boyle, P. D.;
White, P. S. J . Am. Chem. Soc. 2003, 125, 9435-9441.
(13) Flood, T. C.; Lim, J . K.; Deming, M. A.; Keung, W. Organome-
tallics 2000, 19, 1166-1174.
(14) Sharp, P. R. J . Chem. Soc., Dalton Trans. 2000, 2647-2657.
(15) Macgregor, S. A.; MacQueen, D. Inorg. Chem. 1999, 38, 4868-
4876.
* Corresponding author. E-mail: brent_gunnoe@ncsu.edu.
† North Carolina State University.
‡ University of North Texas.
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10.1021/om049836r CCC: $27.50 © 2004 American Chemical Society
Publication on Web 04/27/2004

Ruthenium(II) Parent Amido Complex
Organometallics, Vol. 23, No. 11, 2004 2725
Sch em e 1. P r op osed P a th w a y for th e Activa tion
of Non p ola r X-H (X ) H or C) Bon d s tow a r d
In tr a m olecu la r Dep r oton a tion
since the inability of the nondative ligand to π-donate
(due to pπ-dπ conflict) should yield highly polarized
M-N bonds. In addition, due to the greater redox
flexibility of metals in the mid to late portion of the
transition series, accessing 1,2-additions across ruthe-
nium-nitrogen bonds could afford synthetic opportuni-
ties not available with early transition metal systems.
Herein, we report on efforts to access a coordinatively
unsaturated ruthenium complex that possesses a parent
amido ligand, including a combined experimental and
computational study of its reactivity toward dihydrogen
and carbon-hydrogen bonds.
A potential synthetic application of nondative ligands
bound to metal centers that possess high d-electron
counts is the cleavage of carbon-hydrogen bonds.
Higher oxidation states apparently increase the predi-
lection toward hydrogen atom abstraction due to the
favorable nature of metal-centered reduction, while
increased ligand basicity can promote acid-base trans-
formations for systems in lower oxidation states.22,24-37
For example, octahedral Ru(II) (d6) amido complexes
possess sufficient basicity to deprotonate relatively weak
acids, including some C-H bonds.22,36-38 The ability of
coordinatively and electronically saturated Ru(II) amido
complexes to deprotonate C-H bonds suggests the
possibility of activating more inert bonds. Thus, by
accessing Ru(II) complexes that possess an open coor-
dination site and a nondative nitrogen-based ligand, it
might be feasible to transiently bind nonpolar X-H (e.g.,
H-H or C-H) bonds to the metal center, thereby
activating the substrate toward intramolecular depro-
tonation (Scheme 1). Similar transformations have been
observed for early transition metal imido complexes.39-42
A recent computational study of C-H addition across
TidNR bonds suggests that increasing the Ti-N bond
polarization increases the propensity toward C-H
activation.43 Complexes with nondative ligands and high
d-electron counts are candidates for analogous reactions
Resu lts a n d Discu ssion
We have previously reported that TpRu(L)(L′)(NHR)
(L ) L′ ) P(OMe)3, PMe3 or L ) CO and L′ ) PPh3)
systems react to deprotonate C-H bonds. For example,
TpRu(L)(L′)(NHPh) complexes exhibit acid-base equi-
libria with malononitrile, while TpRu(L)(L′)(NHR)
(R ) H or tBu) complexes form ion pairs due to
deprotonation of phenylacetylene.22,38,44 However, the
activation of more inert bonds (e.g., C-H bonds of
alkanes/arenes or dihydrogen) by these TpRu complexes
has not been attained. One possible limitation for the
activation of nonpolar bonds using TpRu(L)(L′)(NHR)
and related complexes is the coordinative saturation of
the metal center. The Ru(II) complex (PCP)Ru(CO)(Cl)
(PCP ) 2,6-(CH2PtBu2)2C6H3) provides a precursor to a
five-coordinate Ru(II) amido complex.45 The reaction of
(PCP)Ru(CO)(Cl) with ammonia yields (PCP)Ru(CO)-
(Cl)(NH3) (1) (as indicated by IR and NMR spectroscopy)
(eq 1); however, the lability of the ammonia ligand
(23) Holland, P. L.; Andersen, R. A.; Bergman, R. G. Comments
Inorg. Chem. 1999, 21, 115-129.
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prevents the isolation of complex 1, and quantitative
reversion of 1 to (PCP)Ru(CO)(Cl) is observed upon
solvent removal under reduced pressure or purging the
reaction solution with dinitrogen. The precipitation of
complex 1 followed by drying in the solid state under
reduced pressure also results in conversion to (PCP)-
Ru(CO)(Cl). As delineated below, weakly coordinated
ammonia is a general feature for the series of octahedral
(PCP)Ru(CO)(X)(NH3) systems reported herein.
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The in situ reaction of the ammonia complex 1 with
[Na][N(SiMe3)2] yields (PCP)Ru(CO)(NH2) (2) (eq 2).
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2726 Organometallics, Vol. 23, No. 11, 2004
Conner et al.
Sch em e 2. Alter n a tive P a th w a y for th e Syn th esis
of (P CP )Ru (CO)(NH2) (2)
Sch em e 3. Rea ction of (P CP )Ru (CO)(NH2) (2) a n d
P h en yla cetylen e or (P CP )Ru (CO)(Cl) w ith
[Li][C2P h ] Yield in g (P CP )Ru (CO)(C2P h ) (5)
Complex 2 is characterized by a resonance at 72.9 ppm
(31P NMR) due to equivalent phosphine fragments and
a triplet at 4.36 ppm (1H NMR) due to the amido protons
(3J PH ) 9 Hz). The assignment of the resonance at 4.36
ppm as due to the amido hydrogens is confirmed by the
Placing a benzene solution of 2 under dihydrogen
pressure yields the previously reported hydride complex
(PCP)Ru(CO)(H) after workup (eq 3).47 Prior to workup,
1
absence of this resonance in the H NMR spectrum of
(PCP)Ru(CO)(ND2) (2-d2) that is synthesized by substi-
tuting ND3 for NH3. The IR spectrum of 2 exhibits
νCO ) 1890 cm-1 as well as symmetric/asymmetric NH
stretches at 3396 and 3306 cm-1. The IR spectrum of
(PCP)Ru(CO)(Cl) reveals νCO ) 1923 cm-1, while the
ammonia complex 1 displays νCO ) 1900 cm-1. Thus,
the {(PCP)Ru(NH2)} system is more π-basic than the
{(PCP)Ru(Cl)} and {(PCP)Ru(NH3)}+ fragments. The
instability of complex 2 (see below) precludes satisfac-
tory elemental analysis; however, high-resolution FAB
mass spectrometry of 2 reveals a parent ion peak
consistent with the theoretical molecular weight in
addition to anticipated peaks due to molecular frag-
mentation. The reaction of (PCP)Ru(CO)(Cl) with TM-
SOTf produces (PCP)Ru(CO)(OTf) (3), and the bisam-
mine complex [(PCP)Ru(CO)(NH3)2][OTf] (4) is formed
upon combination of 3 and ammonia. The observation
of two resonances due to bound ammonia ligands in the
1H NMR spectrum (2.50 and 2.45 ppm) of 4 indicates a
cis orientation of the ammine ligands. When complex 4
is synthesized using ND3, the resonances at 2.50 and
two CO absorptions are observed in the reaction mixture
(1925 and 1900 cm-1). The low-energy absorption at
1900 cm-1 is consistent with the formation of the
hydride complex (PCP)Ru(CO)(H). Dissolution of (PCP)-
Ru(CO)(H) in benzene and addition of H2 result in a new
CO absorption at 1925 cm-1, and the high-energy CO
stretching frequency is likely due to (PCP)Ru(H)3(CO).
This complex was not isolated pure, and the nature of
the three hydrogen atoms is unknown.
The pKa of dihydrogen is ∼49 in THF;48 however,
coordination to transition metal centers has been dem-
onstrated to increase the acidity of dihydrogen.49,50 For
example, ruthenium-bound dihydrogen complexes ex-
hibit pKa values as low as -5.51 Thus, we projected that
the five-coordinate Ru(II) amido complex might facilitate
intramolecular H-H bond breaking due to the acces-
sibility of an open coordination site, and the observed
H-H bond cleavage likely proceeds via transient metal
coordination with subsequent activation of the H-H
bond (Scheme 4). In contrast, under identical reaction
1
2.45 ppm are absent in the H NMR spectrum. Similar
to the reaction of complex 1 with strong base, the
treatment of 4 with [Na][N(SiMe3)2] results in the
formation of the amido complex 2 after workup (Scheme
2).
t
The reaction of TpRu(L)(L′)(NHR) (R ) H or Bu) or
trans-(DMPE)Ru(H)(NH2) systems with phenylacety-
lene results in alkyne deprotonation to form the ion
pairs [TpRu(L)(L′)(NH2R)][PhC2] and [trans-(DMPE)-
Ru(H)(NH3)][PhC2], respectively.22,36,44 The combination
of amido complex 2 with phenylacetylene rapidly pro-
duces (PCP)Ru(CO)(CtCPh) (5) and NH3 (Scheme 3).
Complex 5 has also been prepared by the reaction of
(PCP)Ru(CO)(Cl) with [Li][PhC2] (Scheme 3). The for-
mation of 5 from the amido complex 2 and phenylacety-
lene could proceed through the initial formation of
(PCP)Ru(CO)(NH3)(CtCPh); however, intermediates
are not observed by NMR spectroscopy while monitoring
the reaction of the amido complex 2 with phenylacety-
lene at low temperature (-78 °C).
(46) Na, Y.; Park, S.; Han, S. B.; Han, H.; Ko, S.; Chang, S. J . Am.
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5467-5476.

Ruthenium(II) Parent Amido Complex
Organometallics, Vol. 23, No. 11, 2004 2727
Sch em e 4. P r op osed Rea ction P a th w a y for th e
Con ver sion of (P CP )Ru (CO)(NH2) (2) a n d H2 to
(P CP )Ru (CO)(H) a n d NH3
F igu r e 1. Kinetic plots for the conversions of (PCP)Ru-
(CO)(Me) (8) (() and (PCP)Ru(CO)(NH2) (2) (9) to the
cyclometalated complex 7 at 50 °C.
supporting experimental evidence is not reported, the
catalytic hydrogenation of carbon dioxide with a Ru(II)
catalyst has been proposed to involve the addition of
the H-H bond across a Ru-OH bond.56 Siegbahn and
Crabtree have reported computational studies that
suggest the addition of the C-H bond of methane across
a nondative Pt-Cl bond is a key step in the mechanism
of the Shilov reaction.57
conditions the coordinatively saturated complex TpRu-
(PMe3)2(NH2) fails to react with dihydrogen (eq 4). The
In C6D6, (PCP)Ru(CO)(NH2) (2) undergoes intramo-
lecular C-H activation of a methyl group of a tBu
moiety to form the cyclometalated complex 7 after
workup (eq 5). A related iridium hydride complex that
dissolution of (PCP)Ru(CO)(H) and NH3 in C6D6 yields
(PCP)Ru(CO)(H)(NH3) (6) as determined by NMR and
IR spectroscopy. Complex 6 cannot be isolated pure due
to facile loss of the coordinated ammonia; however, the
formation of 6 is indicated by a new doublet in the
proton-coupled 31P NMR spectrum (95.7 ppm, J PH ) 21
Hz) and a new hydride resonance at -16.17 ppm
(triplet, J PH ) 21 Hz). The hydride resonance of (PCP)-
Ru(CO)(H) is observed at -27.9 ppm.47 The removal of
volatiles under vacuum results in the facile conversion
of 6 to (PCP)Ru(CO)(H). The reaction of (PCP)Ru(CO)-
(NH2) (2) with dihydrogen at low temperature (-78 °C)
in a sealed NMR tube allows the observation of complex
6 as a reaction intermediate by 1H and 31P NMR
spectroscopy.
These results suggest that the coordination of dihy-
drogen by Ru(II) activates the H-H moiety toward
intramolecular bond cleavage to yield (PCP)Ru(CO)(H)-
(NH3) (6), and dissociation of ammonia from 6 results
in the isolation of (PCP)Ru(CO)(H) upon workup. It is
also possible that oxidative addition of dihydrogen to
form the Ru(IV) dihydride complex (PCP)Ru(H)2(CO)-
(NH2) followed by reductive N-H bond formation yields
(PCP)Ru(CO)(NH3)(H) (6). Although examples are rare,
eliminations of amine N-H bonds from d6 metal centers
have been reported.52,53 Morris et al. have demonstrated
that the reaction of a Ru(II) amido complex with
dihydrogen yields a complex in which the H-H bond is
intermediate between protic-hydridic and dihydrogen
bonding,54 and the chelating amido ligand of Ru(Cl)-
(PPh3)[N(SiMe2CH2PPh2)2] deprotonates dihydrogen to
yield Ru(Cl)(H)(PPh3)[NH(SiMe2CH2PPh2)2].55 Although
possesses a PCP “pincer” ligand has been observed in
equilibrium with dihydrogen and a cyclometalated
complex similar to complex 7.58 Monitoring the conver-
1
sion of 2 to 7 by H NMR spectroscopy reveals that the
transformation is first-order in complex 2 (kobs ) 6.0(3)
× 10-5 s-1 at 50 °C; Figure 1). The reaction mixture
prior to workup contains a mixture of 7 and a small
amount of another complex that is likely due to am-
monia coordination to 7. The isolation of 7 and addition
of ammonia confirms that the second product is the
ammonia complex. Placing the reaction solution under
1
vacuum removes all ammonia, and H NMR spectros-
copy of the isolated solid reveals nearly quantitative
formation of 7. Complex 7 decomposes to produce
uncharacterized products after approximately 2 days in
the solid state under an atmosphere of dinitrogen.
The reaction of (PCP)Ru(CO)(Cl) with MeLi yields
(PCP)Ru(CO)(Me) (8) (Scheme 5). Complex 8 has been
characterized by multinuclear NMR and IR spectros-
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2728 Organometallics, Vol. 23, No. 11, 2004
Conner et al.
Sch em e 5. Rea ction of (P CP )Ru (CO)(Cl) a n d MeLi
Yield s (P CP )Ru (CO)(Me) (8), a n d Com p lex 8
Con ver ts to CH4 a n d Com p lex 7
F igu r e 3. B3LYP/SBK(d) optimized geometry of (PCP′)-
Ru(CO)(NH2) (2′) model reactant showing pertinent bond
lengths and bond angles.
intramolecular pathway would yield NH3. However, a
control experiment revealed that the reaction of (PCP)-
Ru(CO)(NH2) (2) with CD4 could not be used to dif-
ferentiate between the two possible reaction pathways.
Monitoring a solution of the cyclometalated complex 7
in the presence of a mixture of CH4 and ND3 reveals
significant isotopic scrambling to produce CH3D/ND2H/
CH4/NH3 in approximate 1:1:1:1 ratio (as determined
by mass spectrometry). Therefore, production of NH2D
from the reaction of the amido complex 2 with CD4
would not allow differentiation between direct produc-
tion of NH2D and isotopic scrambling between NH3 and
CD4 to produce NH2D. However, it can be stated that
the lack of observation of (PCP)Ru(CO)(Me) (8) in the
conversion of (PCP)Ru(CO)(NH2) (2) and methane to
complex 7 likely indicates that intramolecular C-H
activation dominates at 50 psi of methane.
copy. Similar to the amido complex 2, complex 8
decomposes to release methane (observed by H NMR
1
spectroscopy) and form the cyclometalated complex 7
(Scheme 5). The formation of methane has been con-
firmed using GC-MS. The rate of conversion of the
methyl complex 8 to 7 is approximately 5 times faster
(kobs ) 3.2(1) × 10-4 s-1 at 50 °C; Figure 1) than the
analogous conversion with the amido complex 2 (kobs
)
6.0(3) × 10-5 s-1 at 50 °C; Figure 1). The determination
of kobs at variable temperatures for the conversions
(PCP)Ru(CO)(NH2) (2) and (PCP)Ru(CO)(Me) (8) to the
cyclometalated complex 7 has allowed the extraction of
activation parameters. Eyring plots were made over a
30 °C temperature range for both complexes (Figure 2).
The ∆Hq for both reactions is 18(1) kcal/mol. The ∆Sq
for the conversion of complex 2 to complex 7 and
ammonia is -23(4) eu, while the ∆Sq for the production
of 7 and methane from the methyl complex 8 is -18(4)
eu.
The observations of H-H activation by complex 2 and
intramolecular C-H activation with failure to achieve
intermolecular C-H activation of methane prompted us
to incorporate DFT (density functional theory; B3LYP/
SBK(d) level of theory) studies to compare the energetics
of X-H activation (X ) H or CH3) by (PCP′)Ru(CO)-
(NH2) (2′). PCP′ is a model of the full PCP ligand that
The observed intramolecular C-H activation indi-
cated the possibility of accessing intermolecular C-H
addition across the Ru-amido bond of complex 2.
However, placing the amido complex (PCP)Ru(CO)(NH2)
(2) under methane pressure (50 psi) at various temper-
atures results in clean conversion to the cyclometalated
complex 7. The formation of 7 could occur directly from
2 (i.e., intramolecular C-H activation) or from an
intermolecular reaction with methane to produce (PCP)-
Ru(CO)(NH3)(Me) followed by ammonia dissociation and
conversion of (PCP)Ru(CO)(Me) (8) to complex 7. The
reaction of complex 2 with CD4 could allow the dif-
ferentiation between these two possibilities since the
activation of methane would produce NH2D, while the
t
is generated by the replacement of the phosphine Bu
substituents with hydrogen atoms. A variety of coordi-
nation isomers were investigated for the (PCP′)Ru(CO)-
(NH2) complex. In all cases (both square pyramidal and
trigonal bipyramidal geometries) the bound carbon and
phosphorus atoms of the PCP′ ligand were assumed to
be meridonal (i.e., the P-C-P fragment is roughly
coplanar with Ru). Two isomeric (PCP′)Ru(CO)(NH2)
minima were found, both of which had square pyramidal
geometry. Consistent with the structures of (PCP′)Ru-
(CO)(NH2) determined by these computational studies,
the complexes (PCP)M(CO)(Cl) (M ) Ru or Os) exhibit
square pyramidal structures in the solid state.45,59 The
higher energy isomer of (PCP′)Ru(CO)(NH2) has CO
trans to the aryl ring of the PCP′ ligand and is 15.6 kcal/
mol higher in energy (∆G) than the lowest energy
minimum found for (PCP′)Ru(CO)(NH2) (2′), in which
the coordination site trans to the aryl ring of the PCP′
ligand is vacant (Figure 3). The lower energy minimum
was used in the calculation of all subsequent thermo-
dynamic quantities.
F igu r e 2. Eyring plots for the conversions of (PCP)Ru-
(CO)(Me) (8) (2) and (PCP)Ru(CO)(NH2) (2) (9) to the
cyclometalated complex 7 and methane or ammonia,
respectively.
(59) Gusev, D. G.; Dolgushin, F. M.; Antipin, M. Y. Organometallics
2001, 20, 1001-1007.

Ruthenium(II) Parent Amido Complex
Organometallics, Vol. 23, No. 11, 2004 2729
Sch em e 6. DF T Ca lcu la tion s Revea l th a t th e
En d oth er m ic Na tu r e of th e Rea ction betw een
(P CP )Ru (CO)(NH2) a n d CH4 Is a Resu lt of Ch a n ge
in Ru -N BDE u p on Con ver sion fr om Non d a tive
Am id o Liga n d to Da tive Am m on ia Liga n d
([P ] ) P H2)
Calculations of the energies of the dihydrogen and
methane activation reactions shown in eq 6 (X ) H or
Me) were performed. As with the calculations for 2′, a
Sch em e 7. Equ ilibr iu m betw een Com p lex 8 a n d
(P CP )Ru (CO)(NH3)(Me) Lea d s to Mor e Ra p id
Con ver sion to Com p lex 7 a n d CH4 Com p a r ed w ith
th e Dir ect Con ver sion of Com p lex 8 to CH4 a n d 7
variety of coordination isomers of the product (PCP′)-
Ru(CO)(NH3)(X) were investigated at the B3LYP/SBK-
(d) level of theory for both X ) methyl and hydrogen.
The most stable isomers found were used in the calcula-
tion of reaction enthalpies and reaction free energies.
For dihydrogen activation, the reaction in eq 6 is
exothermic by 16.9 kcal/mol and exoergic by 8.9 kcal/
mol. The corresponding C-H activation of methane is
strikingly different, being endothermic by 3.7 and
endoergic by 13.6 kcal/mol. Hence, the calculations are
in qualitative agreement with experimental observa-
tions; that is, (PCP)Ru(CO)(NH2) (2) will activate dihy-
drogen but not methane. In comparison to the attempted
activation of methane, the entropy change for the
intramolecular C-H activation to yield the metallacycle
7 should be more favorable.
Perhaps the most interesting aspect of the computa-
tional comparison of dihydrogen versus methane activa-
tion is that the methane activation is endothermic
rather than just less exothermic than the dihydrogen
activation. To understand the calculated endothermic
nature of the methane activation (eq 6), further calcula-
tions were carried out. First, the bond dissociation
energies of dihydrogen and Me-H were calculated as
an internal check. The enthalpies of the reactions are
105.3 kcal/mol (for H-H cleavage) and 101.9 kcal/mol
(for C-H cleavage of methane). These numbers are in
reasonable agreement with the experimental values in
light of the small, double-ú basis set used for hydrogen.
One can estimate the enthalpy of eq 6 in terms of the
appropriate bond enthalpies as shown in eq 7. Calcula-
tion of the Ru-H bond enthalpy of (PCP′)Ru(CO)(NH3)-
(H) yields a value of 71.6 kcal/mol.
relevant B3LYP/SBK(d) bond enthalpies. The only other
potential source of a significant change in enthalpy is
the conversion of the ruthenium-nitrogen linkage from
a nondative amido to a dative ammine bond {although
minor perturbations might be anticipated, the ∆H’s due
to the Ru-phosphine, Ru-aryl, and Ru-CO bonds in
eq 6 are unlikely to be substantial since both reactants
and products are Ru(II)}. Clearly, if a change in en-
thalpy of the ruthenium-nitrogen bond is substantial
and unfavorable, it is anticipated that methane activa-
tion would be prohibited. Indeed, calculation of the
BDEs for RurNH3 and Ru-NH2 indicates that the
difference is significant: BDERu-NH2 ) 52.5 kcal/mol;
BDERurNH3 ) 12.6 kcal/mol; ∆BDE ) 39.9 kcal/mol
(Scheme 6). The calculations of a small BDE for the Ru-
NH3 linkage is consistent with the general experimental
observation that ammonia is weakly coordinated to the
(PCP)RuII(CO)(X)(NH3) systems reported herein. The
loss of approximately 40 kcal/mol upon converting from
an amide to ammine linkage more than cancels the
approximately 32 kcal/mol gain due to breaking the
methane C-H bond and forming Ru-CH3 and N-H
bonds and provides an explanation for the calculated
endothermic nature of the methane activation.
∆H ≈ BDERu-NH2 + BDEX-H - BDERu-NH3
-
BDEN-H - BDERu-X (7)
Consistent with known differences in metal-alkyl
versus metal-hydride bond dissociation energies, the
corresponding Ru-CH3 bond enthalpy (47.5 kcal/mol)
is 24.1 kcal/mol weaker than the ruthenium-hydride
bond enthalpy. This Ru-H/Ru-Me bond enthalpy dif-
ference is consistent with the difference in enthalpies
for the reactions in eq 6 (∆∆H ) 20.7 kcal/mol).
More relevant in the context of the present research
to identify novel hydrocarbon functionalization systems
is the root cause of the surprising endothermicity of
methane activation by (PCP′)Ru(CO)(NH2) (2′). Return-
ing to eq 6, a significant enthalpic gain is expected by
replacing a single C-H bond of methane with the N-H
and Ru-C bonds of the (PCP)Ru(CO)(Me)(NH3) product.
This gain is estimated to be 31.8 kcal/mol from the
The DFT calculations suggest that (PCP)Ru(CO)-
(NH3)(Me) should convert to (PCP)Ru(CO)(NH2) and
methane. Experimentally, the addition of ammonia to
(PCP)Ru(CO)(Me) (8) forms an equilibrium between
(PCP)Ru(CO)(Me)(NH3) and (PCP)Ru(CO)(Me)/NH3, and
the mixture converts to methane and the cyclometalated
complex 7 (Scheme 7). However, whether the formation
of 7 and methane is derived from complex 8 or (PCP)-
Ru(CO)(Me)(NH3) cannot be definitively determined.

2730 Organometallics, Vol. 23, No. 11, 2004
Conner et al.
lar C-H activation and intermolecular H-H activation
indicates that such reactions are accessible with late
transition metal systems. The results of DFT studies
indicate that the activation of dihydrogen by complex 2
is both exoergic and exothermic, while the addition of a
C-H bond of methane across the Ru-NH2 bond has
been calculated to be endoergic and endothermic. The
endoergic nature of the methane C-H activation has
been attributed to a large and unfavorable change in
Ru-N bond dissociation energy upon conversion from
Ru-amido to Ru-ammine. It is also possible that the
steric bulk of the PCP fragment contributes to the
inability to achieve intermolecular C-H activation.
Thus, access to intermolecular C-H activations might
be possible for systems that undergo reactions in which
the reactive metal-ligand bond remains nondative (e.g.,
conversion of imido to amido or oxo to oxide as observed
with early transition metal complexes).
F igu r e 4. Kinetic plots for the conversion of (PCP)Ru(CO)-
(Me) (8) and 1.5 equiv of NH3 (9) to complex 7 and CH4 as
well as for the conversion of (PCP)Ru(CO)(Me) (8) to CH4
in the absence of NH3 (().
Isotopic labeling studies are not useful due to H/D
scrambling as described above. The experimental ob-
servation that the rate of formation of 7 and methane
upon addition of NH3 to the methyl complex 8 (1.5 equiv
based NMR spectroscopy) is more rapid (kobs ) 1.2 ×
10-4 s-1 at 30 °C) than in the absence of ammonia
(kobs ) 5.5 × 10-5 s-1 at 30 °C; Figure 4) suggests the
possibility of a direct conversion of (PCP)Ru(CO)(Me)-
(NH3) to complex 7 and methane. Such a pathway would
require the initial formation of (PCP)Ru(CO)(NH2) (2)
and methane with subsequent conversion of complex 2
to ammonia and complex 7. However, the lack of
observation of the amido complex 2 as an intermediate
in this reaction precludes a definitive conclusion on the
feasibility of this pathway.
It has been suggested that the observation of unex-
pectedly strong bonding between nondative ligands and
late transition metals can be explained by a large ionic
contribution (versus covalent) to the overall M-X bond-
ing (X ) amido, oxide, etc.).23,53 This scenario also
accounts for the observed high reactivity due to the
localization of significant charge density on the nonda-
tive ligand. Although metal-amine bond dissociation
energies can be large, the significant and unfavorable
change in enthalpy upon conversion of a nondative Ru-
amido bond to a dative Ru-ammine bond supports the
suggestion that ionic contributions to metal-ligand
bonding can dominate for these systems. Therefore, the
unfavorable change in enthalpy upon conversion of the
amido ligand to an ammine ligand can be explained by
the loss of strong ionic bonding in the latter.
Exp er im en ta l Section
Gen er a l Meth od s. All reactions and procedures were
performed under anaerobic conditions in a nitrogen-filled
glovebox or by using standard Schlenk techniques. Glovebox
purity was maintained by periodic nitrogen purges and
monitored by an oxygen analyzer {O2(g) < 15 ppm, for all
reactions}. Toluene was dried by passage through a column
of activated alumina. THF and benzene were dried by distil-
lation over sodium/benzophenone. Pentane and cyclopentane
were dried by distillation over P2O5. Benzene-d6 was purified
by distillation from CaH2, degassed, and stored over 4 Å sieves.
CDCl3, toluene-d8, and CD2Cl2 were degassed via three freeze-
pump-thaw cycles and stored over 4 Å sieves. Room-temper-
ature 1H and 13C NMR spectra were obtained on a Varian
1
Mercury 400 or 300 MHz spectrometer. All H and 13C NMR
spectra were referenced against tetramethylsilane using re-
sidual proton signals (1H NMR) or the 13C resonances of the
deuterated solvent (13C NMR). 31P NMR spectra were obtained
on a Varian 300 MHz (observed frequency 161 MHz) spec-
trometer and referenced against external 85% H3PO4. All
variable-temperature NMR experiments were performed on
a Varian 400 MHz spectrometer. IR spectra were obtained on
a Mattson Genesis II spectrometer either as thin films on a
KBr plate or in a solution using a NaCl solution plate.
Elemental analyses were performed by Atlantic Microlabs, Inc.
The syntheses of TpRu(PMe3)2(NH2), (PCP)Ru(CO)Cl, and
(PCP)Ru(CO)(H) have been previously reported.44,45,47 [Li][C2-
Ph] was prepared by addition of butyllithium to a benzene
solution of phenylacetylene. The resulting white precipitate
was collected via vacuum filtration and washed with hexanes.
All other reagents were used as purchased from commercial
sources.
Su m m a r y a n d Con clu sion s
(P CP )Ru (CO)(NH3)(Cl) (1). A screw cap NMR tube was
charged with approximately 0.025 g of (PCP)Ru(CO)Cl in 1
mL of CDCl3. Ammonia was bubbled through the solution until
it turned from orange to pale yellow. The solution was shaken,
then vented to relieve excess pressure, and NMR and IR
spectra were acquired. Quantitative conversion to (PCP)Ru-
(CO)(NH3)Cl (1) was observed by 1H, 13C, and 31P NMR and
IR; however, removal of excess NH3 by purging or placing the
solution under reduced pressure results in rapid and quantita-
tive formation of the starting material (PCP)Ru(CO)(Cl). IR
A coordinatively unsaturated Ru(II) parent amido
complex has been prepared in anticipation that the
combination of an open coordination site and a highly
nucleophilic amido fragment would allow the activation
of nonpolar bonds. Accordingly, complex 2 cleaves
dihydrogen and activates an alkyl C-H bond in an
intramolecular C-H activation process. The C-H ac-
tivation of alkane and arene compounds has been
observed at high temperatures with highly electrophilic
complexes with imido ligands bound to early transition
metal centers.40,42,60-63 The observation of intramolecu-
(solution cell CDCl3): νCO ) 1900 cm-1 1H NMR (CDCl3, δ):
.
(61) Schaller, C. P.; Wolczanski, P. T. Inorg. Chem. 1993, 32, 131-
144.
(62) Schaller, C. P.; Cummins, C. C.; Wolczanski, P. T. J . Am. Chem.
Soc. 1996, 118, 591-611.
(63) Bennett, J . L.; Wolczanski, P. T. J . Am. Chem. Soc. 1994, 116,
2179-2180.
(60) Cummins, C. C.; Schaller, C. P.; Van Duyne, G. D.; Wolczanski,
P. T.; Chan, A. W. E.; Hoffman, R. J . Am. Chem. Soc. 1991, 113, 2985-
2994.

Ruthenium(II) Parent Amido Complex
Organometallics, Vol. 23, No. 11, 2004 2731
3
2
6.76 (2H, d, J HH ) 7 Hz, phenyl 3/5 position), 6.60 (1H, t,
position), 3.35 (2H, dt, J HH ) 16 Hz, J PH ) 7 Hz, CH2), 3.23
3J HH ) 7 Hz, phenyl 4 position), 3.14 (4H, m, CH2), 2.85 (3H,
bs, NH3), 1.17, 1.14 (each 18 H, each a vt, N ) 12 Hz, CH3).
(2H, dt, J HH ) 16 Hz, J PH ) 7 Hz, CH2), 2.50 (3H, bs, NH3),
2
2.45 (3H, bs, NH3), 1.33 (18H, vt, N ) 13 Hz, CH3), 1.26 (18H,
13C{1H} NMR (CDCl3, δ): 207.4 (t, J PC ) 13 Hz, CO), 147.7
vt, N ) 12 Hz, CH3). 13C{1H} NMR (CDCl3, δ): 207.4 (t,
2
2
2
(t, J PC ) 12 Hz, PCP phenyl), 128.4, 123.9 (each a s, PCP
2J PC ) 13 Hz, CO), 164.2 (s, PCP 4 position), 147.7 (t, J PC
)
phenyl), 122.5 (vt, N ) 13 Hz, PCP phenyl), 37.4, (vt, N ) 14
Hz, PC), 36.8 (vt, N ) 10 Hz, PC), 36.3 (vt, N ) 20 Hz, CH2),
31.7, 31.2 (each a vt, N ) 4 Hz, CH3). 31P{1H} NMR (CDCl3,
δ): 78.3.
6 Hz, RuC), 124.3 (s, PCP 5 and 5 positions), 122.9 (vt, N )
13 Hz, PCP 2 and 6 positions), 37.3 (vt, N ) 15 Hz, PC), 36.6
(vt, N ) 11 Hz, PC), 36.0 (vt, N ) 20 Hz, P-CH2), 31.3 (vt,
N ) 5 Hz, CH3), 31.0 (vt, N ) 5 Hz, CH3). 31P{1H} NMR
(CDCl3, δ): 78.2. Note: Elemental analysis could not be
obtained because drying under reduced pressure for a pro-
longed period of time results in the dissociation of ammonia.
(P CP )Ru (CO)(CtCP h ) (5). Meth od A. (PCP)Ru(CO)(Cl)
(0.1096 g, 0.1964 mmol) was dissolved in approximately 30
mL of THF. Approximately 10 mL of a saturated solution of
NH3 in THF were added. Upon addition of the ammonia
solution, a color change from dark orange to yellow was
observed. Sodium bis(trimethylsilyl)amide (0.216 mmol, 1.0 M
in THF) was added dropwise using a microsyringe, and a
change in color to dark orange was observed. The solution was
filtered through a fine porosity frit, and the volatiles were
removed under reduced pressure. Approximately 25 mL of
THF was added to dissolve all solids. Phenylacetylene (24 µL,
0.219 mmol) was added using a microsyringe. Upon addition,
a color change to dark red orange was observed. The volatiles
were removed under reduced pressure to yield a dark red
product (0.1112 g, 0.1781 mmol, 91%).
(P CP )Ru (CO)(NH2) (2). (PCP)Ru(CO)(Cl) (0.0969 g, 0.1736
mmol) was dissolved in approximately 30 mL of THF. Ap-
proximately 10 mL of a saturated solution of NH3 in THF was
added. Upon combination of the two solutions, a color change
from dark orange to yellow was observed. Sodium bis(tri-
methylsilyl)amide (0.190 mmol, 1.0 M in THF) was added
dropwise using a microsyringe. Upon addition of the amide, a
color change to dark orange was observed. The solution was
filtered through a fine porosity frit, and the volatiles were
removed under reduced pressure (0.0771 g, 0.143 mmol, 82%).
Orange microcrystalline product was obtained upon recrys-
tallization from pentane at -20 °C (isolated yield of the
recrystallization is approximately 50%). IR (solution cell
THF): νCO ) 1890 cm-1, νNH ) 3396, 3306 cm-1
.
1H NMR
3
(C6D6, δ): 7.06 (2H, d, J HH ) 8 Hz, phenyl 3/5 position), 6.98
3
3
(1H, t, J HH ) 8 Hz, phenyl 4 position), 4.36 (2H, br t, J PH
)
9 Hz, NH2), 3.19 (2H, dt, 2J HH ) 17 Hz, J PH ) 7 Hz, CH2), 3.09
(2H, dt, 2J HH ) 17 Hz, J PH ) 9 Hz, CH2), 1.26, 1.14 (each 18H,
each vt, N ) 12 Hz, CH3). 13C{1H} NMR (C6D6, δ): 212.5 (t,
Meth od B. (PCP)Ru(CO)(Cl) (0.0977 g, 0.1750 mmol) was
dissolved in approximately 30 mL of toluene. The solution was
cooled to -78 °C. The salt [Li][C2Ph] (0.021 g, 0.194 mmol)
was added to the solution of (PCP)Ru(CO)(Cl). A color change
to dark red-orange was observed upon addition of the lithium
acetylide salt. The volatiles were removed under reduced
pressure, and the product was extracted with cyclopentane and
filtered through a fine porosity frit. Removal of volatiles from
the resulting filtrate allowed the isolation of a dark red solid
(0.0850 g, 0.1362 mmol, 78%). This procedure yields product
that is pure by NMR spectroscopy; however, additional puri-
fication can be achieved by column chromatography on silica
gel with THF as eluent. IR (solution cell THF): νCO ) 1915
cm-1. 1H NMR (CD2Cl2, δ): 7.29 (2H, t, 3J HH ) 8 Hz, acetylide
phenyl meta position), 7.23-7.17 (4H, m, overlapping PCP and
2
2J PC ) 11 Hz, CO), 169.1 (PCP phenyl), 149.1 (t, J PC ) 7 Hz,
PCP phenyl), 121.8 (s, PCP phenyl), 121.5 (vt, N ) 14 Hz, PCP
phenyl), 36.4 (vt, N ) 22 Hz, P-CH2), 36.3 (vt, N ) 13 Hz,
PC), 36.2 (vt, N ) 13 Hz, PC), 30.1-29.9 (m, CH3). 31P{1H}
NMR (C6D6, δ): 72.9. High-resolution FAB-MS: 539.2 (PCP)-
Ru(CO)(NH2), 523.2 (PCP)Ru(CO). Note: Elemental analysis
could not be obtained due to instability of the product. This
complex undergoes intramolecular elimination of ammonia to
form the cyclometalated complex 7 in approximately 24 h.
(P CP )Ru (CO)(OTf) (3). In a 100 mL round-bottom flask,
(PCP)Ru(CO)Cl (0.0675 g, 0.1209 mmol) was dissolved in
approximately 40 mL of cyclopentane. Approximately 1 mL of
trimethylsilyltriflate was added dropwise at room temperature.
After 30 min the formation of an orange solid was observed.
The reaction was stirred for 1 h. After removal of volatiles
under reduced pressure, the resulting solids were dissolved
in approximately 10 mL of THF, and the products were
precipitated upon addition of 30 mL of cyclopentane. Orange
crystals were isolated by filtration through a medium porosity
frit (0.0690 g, 0.1027 mmol, 85%). IR (solution cell THF):
3
acetylide phenyl), 7.09 (1H, t, J HH ) 8 Hz, phenyl para/4
3
position), 6.95 (1H, t, J HH ) 8 Hz, phenyl para/4 position),
3.63 (4H, vt, N ) 8 Hz, PCP CH2), 1.53, 1.18 (each 18H, each
a vt, N ) 14 Hz, CH3). 13C{1H} NMR (CD2Cl2, δ): 209.0 (t,
2
2J PC ) 13 Hz, CO), 179.4 (t, J PC ) 3 Hz, ipso phenyl), 152.5
(vt, N ) 15 Hz, PCP 3,5 or 2,6 position), 131.7 (t, 2J PC ) 11 Hz
CCPh), 130.3 (t, N )1.4 Hz, PCP 4 or Ph o, m, p), 129.8 (t,
4J PC ) 0.8 Hz, Ph ipso), 128.1 (s, PCP 4 or Ph o, m, p), 127.8
1
3
νCO ) 1936 cm-1. H NMR (CDCl3, δ): 7.09 (2H, d, J HH ) 7
3
Hz, phenyl 3/5 position), 6.93 (1H, t, J HH ) 7 Hz, phenyl 4
3
position), 3.37 (4H, vt, N ) 8 Hz, CH2), 1.50 (18 H, vt, N ) 14
(t, J PC ) 1.1 Hz, CCPh), 124.5 (s, PCP 4 or Ph o, m, p), 124.4
Hz, CH3), 1.17 (18 H, vt, N ) 13 Hz, CH3). 13C{1H} NMR
(s, PCP 4 or Ph o, m, p), 121.8 (vt, N ) 15 Hz, PCP 3,5- or
2,6-position), 37.9 (vt, N ) 23 Hz, CH2), 37.8 (vt, N ) 15 Hz,
PC), 37.0 (vt, N ) 17 Hz, PC), 30.0, 29.8 (each a vt, N ) 5 Hz,
2
(CDCl3, δ): 204.9 (t, J PC ) 12 Hz, CO), 157.2 (s, phenyl 4
position), 152.7 (t, J PC ) 7 Hz, phenyl ipso), 125.4 (s, phenyl
2
3/5 positions), 123.3 (vt, N ) 16 Hz, phenyl 2/6 positions), 38.0
(vt, N ) 14 Hz, PC), 36.7 (vt, N ) 16 Hz, PC), 33.7 (vt, N ) 22
Hz, CH2), 30.1 (vt, N ) 4 Hz, CH3), 29.4 (vt, N ) 4 Hz, CH3).
31P{1H} NMR (CDCl3, δ): 70.0. Anal. Calcd for C26H43F3O4P2-
RuS: C 46.42, H 6.45. Found: C 46.28, H 6.58.
CH3). 31P{1H} NMR (CD2Cl2, δ): 80.0. Anal. Calcd for C33H48
-
OP2Ru: C 63.54, H 7.76. Found: C 63.52, H 7.74.
(P CP )Ru (CO)(NH3)(H) (6). A screw cap NMR tube was
charged with approximately 0.025 g of (PCP)Ru(CO)(H) and
1 mL of C6D6. Ammonia was gently bubbled through the
solution until it turned from orange to pale yellow. The solution
was vigorously mixed and vented to relieve excess pressure,
and NMR and IR spectra were acquired. Quantitative conver-
sion to (PCP)Ru(CO)(NH3)(H) (6) was observed by 1H, 13C, and
31P NMR and IR spectroscopy; however, removal of excess
ammonia by purging the solution with dinitrogen or placing
the solution under reduced pressure results in the rapid
formation of the starting material (PCP)Ru(CO)(H). IR (solu-
tion cell THF): νCO ) 1905 cm-1. 1H NMR (C6D6, δ): 7.07 (2H,
[(P CP )Ru (CO)(NH3)2][OTf] (4). In a 50 mL round-bottom
flask, 0.0816 g (0.121 mmol) of (PCP)Ru(CO)(OTf) (3) was
dissolved in approximately 15 mL of THF. A THF solution of
ammonia was added until the solution turned from orange to
colorless. The volatiles were removed under reduced pressure.
The solids were dissolved in approximately 5 mL of THF, and
the product was precipitated with approximately 30 mL of
cyclopentane. Pale yellow crystals were isolated by filtration
through a fine porosity frit (0.0439 g, 0.0621 mmol, 51%). IR
(solution cell THF): νCO ) 1923 cm-1, νNH ) 3415, 3358, 3292,
d, J HH ) 9 Hz, phenyl 3/5 position), 6.98 (1H, t, J HH ) 9 Hz,
3
3
3
2
3203 cm-1
.
1H NMR (CDCl3, δ): 6.95 (2H, d, J HH ) 8 Hz,
phenyl 4 position), 3.26 (2H, dt, J HH ) 16 Hz, J PH ) 8 Hz,
3
phenyl 3/5 positions), 6.80 (1H, t, J HH ) 8 Hz, phenyl 4
CH2), 3.19 (2H, dt, 2J HH ) 17 Hz, J PH ) 6 Hz, CH2), 1.18, 1.06

2732 Organometallics, Vol. 23, No. 11, 2004
Conner et al.
2
(each 18 H, each a vt, N ) 12 Hz, CH3), -16.17 (1H, t, J PH
)
was precooled to -50 °C. 1H and 31P NMR spectra were
acquired at regular time intervals, allowing the observation
of the formation of (PCP)Ru(CO)(H)(NH3) as a reaction inter-
mediate.
21 Hz). The resonance due to bound NH3 is not observed
possibly due to overlap with a Bu resonance. 13C{1H} NMR
t
2
2
(C6D6, δ): 208.1 (t, J PC ) 13 Hz, CO), 149.9 (t, J PC ) 11 Hz,
PCP phenyl), 123.4 (s, PCP phenyl), 122.5 (vt, N ) 16 Hz, PCP
phenyl), 39.4, (vt, N ) 14 Hz, PC), 36.8 (vt, N ) 9 Hz, PC),
36.5 (vt, N ) 21 Hz, CH2), 30.0-29.7 (m, overlapping CH3);
note: missing one PCP phenyl resonance possibly due to
coincidental overlap. 31P NMR (hydrogen coupled; C6D6, δ):
Rea ction of (P CP )Ru (CO)(NH2) (2) w ith P h CtCH a t
-78 °C. A screw cap NMR tube was charged with (PCP)Ru-
(CO)(NH2) (0.0311 g, 0.0577 mmol) in 1 mL of toluene-d8. The
solution was cooled to -78 °C in a dry ice/acetone bath.
Phenylacetylene (7 µL, 0.0637 mmol) was added via micro-
syringe. The tube was kept at -78 °C until transferred to the
NMR probe which was precooled to -80 °C. Conversion to
(PCP)Ru(CO)(CtCPh) (5) and NH3 was observed in 1H and
31P NMR without observation of reaction intermediates.
Rea ction of Tp Ru (P Me3)2(NH2) w ith H2. In a 50 mL
round-bottom flask, TpRu(PMe3)2(NH2) was dissolved in ap-
proximately 20 mL of THF. Dihydrogen was bubbled through
the solution for 2 h. The volatiles were removed under reduced
pressure, and the resulting solids were dissolved in C6D6 to
2
95.7 (d, J PH ) 21 Hz).
Ru (CO){C6H3-2-(CH2P tBu 2)-6-(CH2P (tBu )(CMe2CH2} (7).
In a 100 mL round-bottom flask, (PCP)Ru(CO)Cl (0.3837 g,
0.6876 mmol) was dissolved in approximately 50 mL of THF.
Methyllithium (1.6 M in THF, 0.907 mmol) was added drop-
wise using a microsyringe. The volatiles were removed under
reduced pressure, and the solids were dissolved in benzene.
The solution was allowed to stir at room temperature for 48
h. Filtration of the solution through a fine porosity frit and
removal of the volatiles under reduced pressure yielded a
brown solid (0.3337 g, 0.6404 mmol, 93%). IR (solution cell
1
give a homogeneous solution. H NMR spectroscopy revealed
the presence of only TpRu(PMe3)2(NH2).
benzene): νCO ) 1897 cm-1. H NMR (C6D6, δ): 7.37 (1H, d,
1
Kin etic Stu d ies for th e Cyclom eta la tion of (P CP )Ru -
(CO)(NH2) (2) or (P CP )Ru (CO)(Me) (8). The general pro-
cedures for all kinetic analyses of cyclometalation reactions
for (PCP)Ru(CO)(Me) (8) and (PCP)Ru(CO)(NH2) (2) were
similar. A representative procedure is provided: In a reaction
vial, (PCP)Ru(CO)(Me) (8) (0.1251 g, 0.2320 mmol) was dis-
solved in 2.96 g of C6D6. A small amount of Cp2Fe was added
as an internal standard. The solution was transferred into
three screw cap NMR tubes, and 1H NMR spectra were
acquired with the delay time set to 10 s. The solutions were
then heated in an oil bath. The disappearance of complex 8
was monitored at regular time intervals using 1H NMR
spectroscopy. The formation of complex 7 and methane was
observed. In addition, the formation of methane and ammonia
(for reactions with complex 2) was confirmed by GC/MS
analysis.
Com p u ta tion a l Meth od s. Quantum calculations were
carried out using the Gaussian 98 package.64 The B3LYP
hybrid functional was employed for all calculations.65 Heavy
atoms were described with the Stevens relativistic effective
core potentials (ECPs) and valence basis sets (VBSs).66,67 The
valence basis sets of main group elements were augmented
with a d polarization function. This ECP/VBS combination,
termed SBK(d), has been validated for the calculation of a wide
variety of transition metal properties in previous studies.43,68-70
All stationary points were fully optimized without symmetry
constraint. All species investigated are closed-shell singlets.
Several conformations of the different ligands were investi-
gated by torsion about the appropriate metal-ligand bonds;
3J HH ) 7 Hz, phenyl 3/5 position), 7.34 (1H, d, J HH ) 7 Hz,
3
3
phenyl 3/5 position), 7.22 (1H, t, J HH ) 7 Hz, phenyl 4
2
2
position), 3.67 (2H, d, J PH ) 8 Hz CH2), 3.47 (1H, dd, J HH
)
2
2
17 Hz, J PH ) 10 Hz, P-CH2), 3.37 (1H, dd, J HH ) 17 Hz,
2J PH ) 6 Hz CH2), 1.37 (3H, d, J PH ) 13 Hz, PC(CH3)2), 1.19
3
3
3
(9H, d, J PH ) 13 Hz, PC(CH3)3), 1.00 (9H, d, J PH ) 13 Hz,
3
PC(CH3)3), 0.90 (3H, d, J PH ) 12 Hz, PC(CH3)2), 0.71 (9H, d,
3J PH ) 12 Hz, PC(CH3)3), 0.49 (1H, d, 2J HH ) 16 Hz, Ru-CH2),
0.44 (1H, d, J HH ) 16 Hz, Ru-CH2). 13C{1H} NMR (C6D6, δ):
2
2
2
207.4 (t, J PC ) 13 Hz, CO), 147.7 (t, J PC ) 12 Hz, phenyl
ipso), 128.4 (s, phenyl 3/5 position), 123.9 (s, phenyl 4 position),
122.5 (vt, N ) 12 Hz, phenyl 2/6 position), 37.4, (vt, N ) 14
Hz, PC), 36.8 (vt, N ) 10 Hz, PC), 36.3 (vt, N ) 20 Hz, CH2),
31.7, 31.2 (vt, N ) 4 Hz, CH3). 31P{1H} NMR (C6D6, δ): 82.7
(d, 2J PP ) 245 Hz, PtBu2), 46.3 {d, 2J PP ) 244 Hz, P(tBu)(CMe2-
CH2)}. Note: Elemental analysis could not be obtained due to
instability of the product. This complex reacts to form an
unidentified product in approximately 48 h at room temper-
ature.
(P CP )Ru (CO)(CH3) (8). In a 100 mL round-bottom flask,
(PCP)Ru(CO)Cl (0.0557 g, 0.0997 mmol) was dissolved in
approximately 50 mL of THF. Methyllithium (1.6 M in the,
0.136 mmol) was added dropwise using a microsyringe. The
volatiles were removed under reduced pressure, and the solids
were dissolved in benzene. The solution was filtered through
a fine porosity frit, and the volatiles were removed under
reduced pressure to yield a brown solid (0.0471 g, 0.0877 mmol,
88%). Orange microcrystals were obtained upon recrystalli-
zation from pentane at -40 °C. IR (solution cell THF): νCO
)
1893 cm-1. 1H NMR (C6D6, δ): 7.29 (2H, d, 3J HH ) 8 Hz, phenyl
(64) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J . R.; Zakrzewski, V. G.; J r., J . A. M.;
Stratmann, R. E.; Burant, J . C.; Dapprich, S.; Millam, J . M.; Daniels,
A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J .; Barone, V.;
Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford,
S.; Ochterski, J .; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma,
K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J . B.;
Cioslowski, J .; Ortiz, J . V.; Baboul, A. G.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.;
Fox, D. J .; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Challacombe, M.; Gill, P. M. W.; J ohnson, B.; Chen, W.; Wong, M. W.;
Andres, J . L.; Gonzalez, C.; Head-Gordon, M.; Replogle, E. S.; Pople,
J . A. Gaussian 98, Revision A.9; Pittsburgh, PA, 1998.
(65) Becke, A. D. J . Chem. Phys. 1993, 98, 5648-5652.
(66) Stevens, W. J .; Basch, H.; Krauss, M. J . Chem. Phys. 1984, 81,
6026-6033.
(67) Stevens, W. J .; Krauss, M.; Basch, H.; J asien, P. G. Can. J .
Chem. 1992, 70, 612-613.
(68) Holland, P. L.; Cundari, T. R.; Perez, L. L.; Eckert, N. A.;
Lachicotte, R. J . J . Am. Chem. Soc. 2002, 124, 14416-14424.
(69) Veige, A. S.; Slaughter, L. M.; Wolczanski, P. T.; Matsunaga,
N.; Decker, S. A.; Cundari, T. R. J . Am. Chem. Soc. 2001, 123, 6419-
6420.
3/5 position), 7.15 (1H, t, 3J HH ) 8 Hz, phenyl 4 position), 3.43
2
(2H, dt, J HH ) 17 Hz, J PH ) 7 Hz, P-CH2), 3.32 (2H, dt,
2J HH ) 17 Hz, J PH ) 9 Hz, P-CH2), 1.20, 0.84 (each 18 H,
each a vt, N ) 12 Hz, CH3), 0.24 (3H, t, J PH ) 4 Hz). 13C{1H}
3
2
2
NMR (CDCl3, δ): 208.7 (t, J PC ) 9 Hz, CO), 151.9 (t, J PC
)
11 Hz, RuC), 124.2 (s, PCP 4 position), 123.9 (s, PCP 3 and 5
position), 120.9 (vt, N ) 17 Hz, PCP 2 and 6 position), 38.0
(vt, N ) 15 Hz, PC), 37.6 (vt, N ) 18 Hz, CH2), 36.3 (vt, N )
13 Hz, PC), 31.2, 30.1 (each a vt, N ) 5 Hz, CH3). 31P{1H}
NMR (C6D6, δ): 84.9. Note: Elemental analysis could not be
obtained due to instability of the product. This complex
undergoes intramolecular elimination to form the cyclometa-
lated complex 7 in approximately 24 h.
Rea ction of (P CP )Ru (CO)(NH2) (2) w ith H2 a t -78 °C.
A screw cap NMR tube was charged with approximately 0.025
g of (PCP)Ru(CO)(NH2) (2) in 1 mL of toluene-d8. The solution
was cooled to -78 °C in a dry ice/acetone bath. Dihydrogen
was bubbled through the solution until the solution changed
from orange to light yellow (approximately 5 min). The tube
was kept at -78 °C until transferred to the NMR probe which
(70) Bergman, R. G.; Cundari, T. R.; Gillespie, A. M.; Gunnoe, T.
B.; Harman, W. D.; Klinckman, T. R.; Temple, M. D.; White, D. P.
Organometallics 2003, 22, 2331-2337.

Ruthenium(II) Parent Amido Complex
Organometallics, Vol. 23, No. 11, 2004 2733
the lowest energy conformers found were used in the analyses
given below. The energy Hessian was calculated at all station-
ary points to characterize them as minima (no imaginary
frequencies). The quoted energies include zero-point, enthalpy,
and entropic corrections determined from unscaled vibrational
frequencies calculated at the B3LYP/SBK(d) level of theory.
All energetic determinations were done at 298.15 K and 1 atm.
funding for the facility was obtained from the North
Carolina Biotechnology Center and the National Science
Foundation. T.R.C. wishes to acknowledge the U.S.
Department of Energy for support of this research
through grant DOE-FG02-97ER14811.
Su p p or tin g In for m a tion Ava ila ble: Cartesian coordi-
nates for all optimized minima are given. 1H and 31P NMR
spectra of complexes 1, 2, 4, and 6-8 are provided. This
material is available free of charge via the Internet at
http://pubs.acs.org.
Ack n ow led gm en t. T.B.G. acknowledges the Na-
tional Science Foundation (CAREER Award; CHE
0238167) for support of this research. Mass spectra were
obtained at the Mass Spectrometry Facility for Biotech-
nology (D.C. thanks Marty Lail for assistance). Partial
OM049836R