Preparation of the octahedral d6 amido complex TpRu(CO)(PPh3)(NHPh) (Tp = hydridotris(pyrazolyl)borate): Solid-state structural characterization and reactivity

Article abstract of DOI:10.1021/ic010785p

The reaction of TpRu(CO)(PPh₃)(OTf) (2) with LiNHPh affords the amido complex TpRu(CO)(PPh₃)(NHPh) (3) in 88% isolated yield. The amido complex 3 has been characterized by ¹H NMR, ¹³C NMR, ³¹P NMR, elemental analysis, cyclic voltammetry, and a solid-state X-ray diffraction study. Variable temperature NMR studies have revealed a rotational barrier around the ruthenium-amido nitrogen bond of 3 of 12 kcal/mol (transformation of the major isomer to the minor isomer). The solid-state structure of 3 discloses a pyramidal amido moiety. Heating benzene solutions of the amido complex 3 and 1,4-cyclohexadiene or 9,10-dihydroanthracene results in no observable reaction. Reaction of complex 2 with excess aniline yields [TpRu(CO)(PPh₃)(NH₂Ph)][OTf] (4).

Full text of DOI:10.1021/ic010785p

Inorg. Chem. 2001, 40, 6481-6486
6481
Preparation of the Octahedral d6 Amido Complex TpRu(CO)(PPh3)(NHPh) (Tp )
Hydridotris(pyrazolyl)borate): Solid-State Structural Characterization and Reactivity
K. N. Jayaprakash, T. Brent Gunnoe,* and Paul D. Boyle
Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204
ReceiVed July 23, 2001
The reaction of TpRu(CO)(PPh3)(OTf) (2) with LiNHPh affords the amido complex TpRu(CO)(PPh3)(NHPh)
(3) in 88% isolated yield. The amido complex 3 has been characterized by 1H NMR, 13C NMR, 31P NMR, elemental
analysis, cyclic voltammetry, and a solid-state X-ray diffraction study. Variable temperature NMR studies have
revealed a rotational barrier around the ruthenium-amido nitrogen bond of 3 of 12 kcal/mol (transformation of
the major isomer to the minor isomer). The solid-state structure of 3 discloses a pyramidal amido moiety. Heating
benzene solutions of the amido complex 3 and 1,4-cyclohexadiene or 9,10-dihydroanthracene results in no
observable reaction. Reaction of complex 2 with excess aniline yields [TpRu(CO)(PPh3)(NH2Ph)][OTf] (4).
Introduction
(PR3)2(amido) and (η6-arene)Ru(PMe3)(Ph)(amido) com-
plexes.29-31 Whereas complexes with lower coordination num-
Transition metal amido moieties have been implicated in
important synthetic transformations including olefin and alkyne
hydroaminations as well as amination of arene and aryl halide/
triflate compounds.1-6 While numerous examples of transition
metal amido complexes have been reported, examples of late
metal complexes in low oxidation states are relatively rare.7-15
Of particular relevance here are reports of monomeric octahedral
amido complexes with d6 electron counts at the metal center,16-28
and most germane to the chemistry discussed herein are CpRu-
bers or electron counts can stabilize the amido moiety via
π-bonding (Scheme 1), octahedral/d6 systems formally offer no
such stabilization. In fact, it has been suggested that the presence
of dπ electrons on a metal center in close proximity to ligand
heteroatom lone electron pair(s) results in π-electron conflict
that increases the reactivity of the heteroatom moiety (Scheme
2).32,33 The E-C theory of bonding has also been used to
rationalize enhanced reactivity of late metal-heteroatom moi-
eties.34 We report herein the synthesis, characterization, and
preliminary reactivity of TpRu(CO)(PPh3)(NHPh), including
solid-state structural details.
* E-mail: brent_gunnoe@ncsu.edu. Fax: (919) 515-8909.
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Experimental Section
General Methods. All procedures were performed under inert
atmosphere (nitrogen) in an Innovative Technologies glovebox or using
standard Schlenk techniques. The glovebox atmosphere was maintained
by periodic nitrogen purges and monitored by an oxygen analyzer (O2(g)
< 15 ppm for all reactions). Methylene chloride, toluene, diethyl ether,
and hexanes were purified by passage through a column of activated
alumina.35 THF was purified by passage through a column of activated
alumina followed by distillation from sodium/benzophenone and storage
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10.1021/ic010785p CCC: $20.00 © 2001 American Chemical Society
Published on Web 11/07/2001

6482 Inorganic Chemistry, Vol. 40, No. 25, 2001
Jayaprakash et al.
according to a published procedure.36 KTp was prepared according to
a published procedure.37 LiNHPh was prepared by addition of BuLi to
a benzene solution of aniline. The resulting white LiNHPh salt
precipitated and was isolated by vacuum filtration. All other reagents
were used as purchased from commercial sources.
Scheme 1. Illustration of Amido to Metal π-Donation To
Form a Trigonal Amido and Metal-Nitrogen Double Bond
TpRu(CO)(PPh3)(OTf) (2). To a yellow solution (1:1 v/v THF/
CH2Cl2, 30 mL) of TpRu(CO)(PPh3)(Cl) (1) (0.6401 g, 1.016 mmol)
was added a solution of AgOTf (0.261 g, 1.016 mmol dissolved in
THF). The solution was stirred at room temperature for approximately
36 h, during which time the formation of a white precipitate (AgCl)
was noted. The resulting pale yellow slurry was vacuum-filtered through
a fine-porosity frit in order to remove the precipitate, and the volatiles
were removed from the filtrate in vacuo. The resulting yellow solid
was washed with diethyl ether and hexanes, dried in vacuo, and isolated
(95% yield, 0.725 g). IR (thin film on KBr plate): νCO ) 1986 cm-1
.
1H NMR (benzene-d6, δ): 8.99, 7.41, 7.37, 7.19, 7.06, 6.43 (each 1H,
each a d, Tp CH 3 and 5 position), 5.78, 5.64, 5.25 (each 1H, each a
t, Tp CH 4 position), 7.33, 6.95 (15H, each a m, P(C6H5)3). 13C{1H}
Scheme 2. Qualitative Molecular Orbital Diagram of
TpRu(CO)(PPh3)(NHPh) (3) Illustrating the π-Conflict
between the Amido Ligand and Metal Center
2
NMR (benzene-d6, δ): 203.6 (d, JPC ) 15 Hz, CO), 147.9, 146.8,
144.1 (each a s, Tp CH’s), 137.5, 136.6, 135.7, 134.7, 134.5, 131.8,
131.2, 131.0, 129.1, 129.0 (resonances due to PPh3, and Tp CH’s, with
JPC to ispo, ortho, and meta PPh3 carbons would expect a total of 10
lines due to 7 resonances), 107.5, 106.9 (2:1, coincidental overlap for
first resonance, Tp 4 position CH’s). 31P{1H} NMR (CD2Cl2, δ): 39.0.
CV (CH3CN, TBAH, 100 mV/s): E1/2 ) 1.75 V {Ru(III/II)}. Anal.
Calcd for C29H25BF3N6O4PRuS: C, 46.23; H, 3.34; N, 11.15. Found:
C, 46.27; H, 3.47; N, 11.12.
TpRu(CO)(PPh3)(NHPh) (3). To a yellow solution (THF, 10 mL)
of TpRu(CO)(PPh3)(OTf) (2) (0.1151 g, 0.153 mmol) was added
dropwise a THF solution (5 mL) of LiNHPh (0.30 g, 0.306 mmol).
The solution was stirred at room temperature for approximately 30 min,
during which time the formation of a white precipitate (LiOTf) was
noted and the color changed from yellow to brown. After 30 min, the
volatiles were removed under reduced pressure, and the residue was
extracted with toluene and filtered through a fine-porosity frit (ap-
proximately 50 mL of toluene used). The volatiles were removed in
vacuo from the resulting filtrate to give a yellow-brown solid.
Recrystallization by layering a toluene solution of the product with
pentane yielded yellow crystals in 88% yield (0.094 g). IR (thin film
on KBr plate): νCO ) 1954 cm-1; νNH ) 3350 cm-1. 1H NMR (25 °C,
THF-d8, δ): 7.85, 7.72, 7.66, 7.54, 6.83, 6.38 (each 1H, each a d, Tp
CH 3 and 5 position), 6.13, 5.95, 5.82 (each 1H, each a t, Tp CH 4
position), 7.35, 7.22 (15H, each a m, P(C6H5)3), 6.52 (2H, t, 3JHH ) 7
over 4 Å molecular sieves. Acetonitrile was purified by passage through
a column of activated alumina followed by distillation from CaH2. All
solvents were purged with nitrogen for at least 10 min prior to use.
Benzene-d6 was purified by distillation from CaH2, degassed, and stored
over 4 Å molecular sieves. CDCl3, CD2Cl2, and THF-d8 were degassed
3
Hz, phenyl meta protons), 6.38 (2H, d, JHH ) 7 Hz, phenyl ortho
protons), 5.88 (1H, t, 3JHH ) 7 Hz, phenyl para proton). 13C{1H} NMR
2
(25 °C, THF-d8, δ): 207.9 (d, JPC ) 15 Hz, CO), 163.9 (s, amido
phenyl ipso carbon), 146.3, 144.1, 143.9 (each a s, Tp CH’s), 137.0,
136.0, 135.7, 135.6, 135.5, 131.1, 129.6, 129.3, 129.1 (Tp CH’s, PPh3
resonances, and meta carbon of amido phenyl), 117.7 (s, amido phenyl
ortho carbon), 116.2 (s, amido phenyl para carbon), 107.0, 106.9, 106.8
(each a s, Tp 4 position CH’s). 31P{1H} NMR (25 °C, THF-d8, δ):
42.5. CV (CH3CN, TBAH, 100 mV/s): Ep,a ) 0.11 V {Ru(III/II)}.
Anal. Calcd for C34H31BN7O1PRu-C7H8 (note: one molecule of toluene
observed in the solid-state structure of complex 3 as well as in the 1H
NMR of the solid used for analysis): C, 62.44; H, 4.98; N, 12.43.
Found: C, 62.88; H, 5.15; N, 12.08.
1
and stored over 4 Å molecular sieves. H and 13C NMR spectra were
recorded on a General Electric 300 MHz spectrometer. All 1H and 13
C
NMR chemical shifts are reported in ppm and are referenced to
tetramethylsilane using residual proton signals or to the 13C signals of
the deuterated solvents. 31P NMR spectra were recorded on a General
Electric 300 MHz instrument and are referenced against external 85%
phosphoric acid. The phosphoric acid standard was referenced by adding
the 85% phosphoric acid to a 2 mm insert tube contained within a
standard 5 mm NMR tube with the appropriate sample (purchased from
[TpRu(CO)(PPh3)(NH2Ph)][OTf] (4). To a solution of TpRu(CO)-
(PPh3)(OTf) (2) (0.24 g, 0.32 mmol) in THF (20 mL) was added aniline
(0.148 g, 1.59 mmol) with stirring. The stirring was continued for
approximately 24 h, and the solvent was subsequently removed under
reduced pressure. The residue was redissolved in THF and precipitated
with hexanes. The solid was collected via vacuum filtration through a
fine frit and dried under vacuum. The solid product was collected in
1
Wilmad). Peaks in the H NMR spectra due to pyrazolyl resonances
are listed by chemical shift and multiplicity only (all coupling constants
are 2 Hz). Unless otherwise noted, infrared spectra were recorded on
a Mattson Genesis-II spectrometer as thin films on KBr plates.
Electrochemical experiments were performed under a nitrogen atmos-
phere using a BAS Epsilon potentiostat. Cyclic voltammograms were
recorded in a standard three-electrode cell from + 2.00 to -2.00 V
with a glassy carbon working electrode and tetrabutylammonium
hexafluorophosphate (TBAH) as supporting electrolyte. All potentials
are reported versus NHE (normal hydrogen electrode) using cobalto-
cenium hexafluorophosphate (E1/2 ) -0.78 V) as internal standard.
Mass spectra were acquired on a JEOL JMS SX-102 mass spectrometer
(Duke University). Elemental analyses were performed by Atlantic
Microlabs, Inc., Norcross, GA. TpRu(CO)(PPh3)(Cl) was prepared
91% yield (0.24 g). IR (thin film on KBr plate): νCO ) 1981 cm-1
;
1
νNH ) 3473 cm-1. H NMR (CDCl3, δ): 7.72, 7.67, 7.56, 7.02, 6.15
(each 1H, each a d, Tp CH 3 and 5 position), 6.05, 6.00, 5.78 (each
1H, each a t, Tp CH 4 position), 7.35, 7.16 (16H, each a m, one Tp
(36) Sun, N.-Y.; Simpson, S. J. J. Organomet. Chem. 1992, 434, 341-
349.
(37) Trofimenko, S. J. Am. Chem. Soc. 1967, 89, 3070-3077.

Octahedral d6 Amido Complex TpRu(CO)(PPh3)(NHPh)
Inorganic Chemistry, Vol. 40, No. 25, 2001 6483
CH 3 or 5 position and P(C6H5)3), 6.90, 6.10 (5H, m, phenyl para,
meta, and ortho protons overlap), 5.35 (1H, d, NH(H), 2JHH ) 12 Hz),
4.73 (1H, d, NH(H), 2JHH ) 12 Hz). 13C{1H} NMR (CDCl3, δ): 202.2
(d, 2JPC ) 12 Hz, CO), 145.7, 145.0, 143.9 (each a s, Tp CH’s), 142.4
(s, amine phenyl ipso carbon), 137.7, 136.6, 136.5, 133.7, 133.6, 131.5,
129.7, 129.6, 128.9, 128.6 (Tp CH’s, PPh3 resonances, and meta carbon
of amine phenyl), 125.8, 122.0 (s, amine phenyl carbons), 107.2, 107.1,
106.2 (each a s, Tp 4 position CH’s). 31P{1H} NMR (CD2Cl2, δ): 42.6.
CV (CH3CN, TBAH, 100 mV/s): Ep,a ) 1.14 V {Ru(III/II)}. Anal.
Calcd for C35H32BF3N7O4PSRu: C, 49.65; H, 3.81; N, 11.58. Found:
C, 49.64; H, 3.79; N, 11.72. FAB-MS: m/z [TpRu(CO)(PPh3)(NH2-
Ph)]+ calcd exact mass 698.1536, obsd 698.3041; [TpRu(CO)(PPh3)]+
calcd 605.0957, obsd 605.2192.
Crystal Structure of TpRu(CO)(PPh3)(NHPh) (3). Yellow crystals
were grown by slow diffusion of pentane into a toluene solution of
complex 3. A suitable crystal (0.38 × 0.30 × 0.30 mm3) was selected
and mounted on the end of a glass fiber using a small amount of silicon
grease and transferred to an Enraf-Nonius CAD4-MACH diffractometer.
The sample was maintained at a temperature of -125 °C using a
nitrogen cold stream. The unit cell dimensions were determined by a
fit of 25 well centered reflections and their Friedel pairs with 34° <
2θ < 36°. A quadrant of unique data was collected using the ω scan
mode in a nonbisecting geometry. The adoption of a nonbisecting scan
mode was accomplished by offsetting ψ by 20.00° for each data point
collected. This was done to minimize the interaction of the goniometer
head with the cold stream. Three standard reflections were measured
every 4800 s of X-ray exposure time. The intensity data were corrected
for Lorentz and polarization effects. Data were corrected for absorption
using an empirical correction based on ψ scan data for several
reflections.
Structure Solution and Refinement. The data were reduced using
routines from the NRCVAX set of programs.38 The structure was solved
using SIR92.39 Most non-hydrogen atom positions were recovered from
the initial E-map. The remaining non-hydrogen atom positions were
recovered from subsequent difference Fourier maps. All carbon bound
hydrogen atoms were placed at idealized positions and were allowed
to ride on the parent carbon. A difference map contained peaks
suggestive of hydrogen atom positions in the vicinity of atoms B and
N(7). The peak in the vicinity of atom B was constrained to an idealized
B-H bond length and allowed to ride on the parent B atom. As the
hybridization of N(7) is important to the present work, the difference
Fourier maps were analyzed in some detail. To increase confidence
that the peak in the vicinity of N(7) was indicative of a hydrogen atom
position, a series of difference Fourier map calculations were performed
following the method developed by Ibers and LaPlaca and used by
others.40,41 The peak position remained in the same position relative to
N(7) (see Supporting Information for full details). The peak was
included as H(7n) in the refinement model, and the N(7)-H(7n) bond
distance was constrained to be 0.86 Å. H(7n) was allowed to ride on
the parent N(7) atom. Refinement of the structure was performed using
full matrix least-squares based on F. All non-H atoms were allowed to
refine with anisotropic displacement parameters (ADPs).
AgOTf (OTf ) trifluoromethanesulfonate) in 1:1 CH2Cl2/THF
for approximately 36 h results in the formation of a precipitate
(presumably AgCl). After filtration and workup of the yellow
filtrate, TpRu(CO)(PPh3)(OTf) (2) can be isolated in high yield
(95%). The triflate complex 2 has been characterized by
elemental analysis and cyclic voltammetry, as well as 1H, 13C,
31P, and infrared spectroscopy. The chloride complex 1 exhibits
a CO stretching frequency at 1964 cm-1 in its infrared spectrum,
while complex 2 shows a CO stretching frequency at 1986 cm-1
.
The 22 cm-1 increase upon substituting triflate for chloride is
consistent with the weaker donating ability of triflate.55 The 1H
NMR spectrum of complex 2 (as well as all other complexes
reported herein) exhibits Tp resonances indicative of an asym-
metric metal center. The cyclic voltammogram of 2 exhibits
E1/2 ) 1.75 V {Ru(III/II), versus NHE}, while chloride complex
1 displays a reversible wave at 1.43 V.
The reaction of 2 with LiNHPh at room temperature results
in a slow color change from yellow to brown and the
concomitant formation of a precipitate. The appearance of a
new CO stretching frequency at 1954 cm-1 and the dissipation
of the CO stretching frequency at 1986 cm-1 accompany this
reaction. In addition, the new product exhibits νNH ) 3350 cm-1
.
Workup of the brown filtrate results in isolation of TpRu(CO)-
(PPh3)(NHPh) (3) in 88% yield (eq 1). Complex 3 has been
1
characterized by H NMR, 13C NMR, 31P NMR, and infrared
spectroscopy and cyclic voltammetry, elemental analysis, and
a solid-state X-ray diffraction study (see in a following section).
The cyclic voltammogram of 3 exhibits Ep,a ) 0.11 V {Ru(III/
II), versus NHE}, and the irreversibility indicates that the
ruthenium (III) amido [TpRu(CO)(PPh3)(NHPh)]+ is unstable
on the time scale of the cyclic voltammetry experiment.
Restricted rotation of the amido ligand allows the possibility
of rotational isomers, and the observation of a single isomer at
elevated temperatures (80 °C) is the result of rapid rotation
around the Ru-amido nitrogen bond on the time scale of the
1H NMR experiment (see in a following section). A benzene
solution of the phenylamido complex 3 shows no signs of
decomposition after 48 h at room temperature.
Reaction of TpRu(CO)(PPh3)(OTf) (2) with excess aniline
Results and Discussion
(5 equiv) allows isolation of the cationic amine complex [TpRu-
{TpRu(L)(L′)} fragments have received significant recent
attention.42-54 The reaction of TpRu(CO)(PPh3)(Cl) (1) with
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Organometallics 1996, 15, 5275-5277.
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4532-4536.
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6484 Inorganic Chemistry, Vol. 40, No. 25, 2001
Jayaprakash et al.
Table 1. Selected Bond Distances (Å) and Angles (deg) for
TpRu(CO)(PPh3)(NHPh) (3)
bond distances
Ru-P
2.3518(9)
2.117(3)
2.117(3)
1.152(4)
1.420(5)
1.393(7)
1.381(5)
0.861(3)
Ru-C1
1.847(3)
2.151(3)
2.076(3)
1.411(5)
1.387(5)
1.379(7)
1.372(4)
Ru-N1
Ru-N3
Ru-N5
C1-O1
C11-C16
C13-C14
C15-C16
N7-H7n
Ru-N7
C11-C12
C12-C13
C14-C15
N7-C11
bond angles
Ru-N7-C11
C11-N7-H7
P-Ru-N1
130.7(2)
109.1(3)
95.44(7)
Ru-N7-H7
106.7(2)
93.40(10)
92.47(7)
P-Ru-C1
P-Ru-N3
P-Ru-N7
C1-Ru-N3
C1-Ru-N7
N1-Ru-N5
N3-Ru-N5
N5-Ru-N7
P-Ru-N5
176.80(7)
89.75(12)
89.78(12)
86.60(10)
168.48(11)
85.96(10)
174.6(3)
93.66(8)
C1-Ru-N1
C1-Ru-N5
N1-Ru-N3
N1-Ru-N7
N3-Ru-N7
Ru-C1-O1
173.36(12)
96.76(13)
84.97(10)
84.39(10)
85.56(10)
Figure 1. ORTEP diagram of TpRu(CO)(PPh3)(NHPh) (3).
(CO)(PPh3)(NH2Ph)][OTf] (4) in 91% yield after workup (eq
2). Complex 4 is characterized by a CO stretching frequency at
1981 cm-1 in the IR spectrum and diastereotopic amine protons
with resonances (two doublets with geminal JHH ) 12 Hz) at
Table 2. Selected Crystallographic Data and Collection Parameters
for TpRu(CO)(PPh3)(NHPh) (3)
formula
mol wt
cryst syst
space group
a, Å
b, Å
c, Å
C44.5H43BN7OPRu
834.72
monoclinic
P21/c
12.0038(14)
22.169(2)
14.9766(19)
99.292(15)
3933.2(8)
4
1
5.35 and 4.73 ppm in its H NMR spectrum. In addition, a
resonance at 42.6 ppm is observed in the 31P NMR spectrum
of 4, and the cyclic voltammogram reveals Ep,a ) 1.14 V. While
the basicity of the amido ligand of 3 has not been quantitatively
determined, the formation of 4 in the presence of excess aniline
indicates that 3 is at least more basic than the free amine (pKa
≈ 4.6 in water and 3.2 in dimethyl sulfoxide for PhNH3+).56 In
contrast, the amine ligand of the d4 and octahedral complex
[Tp*W(CO)(PhC2Me)(NH2Ph)][OTf] (Tp* ) hydridotris(3,5-
dimethyl)pyrazolylborate) is deprotonated in the presence of
aniline.57
â, deg
V, Å3
Z
D
calcd, g cm-3
1.410
total no. of reflns
unique reflns
6880
6880
R
0.037
Rw
0.039
osmium and the amido nitrogen compared with the osmium-
pyrazolyl nitrogen bond distances.58 The osmium(IV) amido
complex has an empty dπ-orbital available for π-bonding with
the amido ligand. In analogy, the Ru-N(7) bond distance of
complex 3 is shorter than the Ru-pyrazolyl nitrogen {N(1),
N(3), and N(5)} bond distances; however, the effect is less
pronounced for complex 3 compared with TpOs(NHPh)(Cl)2.
The difference between an average of the Os-pyrazolyl nitrogen
bond distances and the osmium amido bond distance is
0.105(16) Å, while the analogous difference for complex 3 is
0.052(6) Å.
The ORTEP diagram in Figure 1 shows the pyramidal nature
of the amido moiety, and the pyramidal character of the amido
ligand is indicated by inspection of the bond angles around the
N-atom which sum to 346.5(4)°. The position of hydrogen atoms
is often difficult to determine by X-ray structure analyses;
however, the primary error in the position of hydrogen atoms
in X-ray structure analysis is typically along the internuclear
vector.59,60 That is, atom-H bond lengths are systematically
shorter because of polarization of the hydrogen’s electron into
a bonding orbital. Because the argument of pyramidalization
relies primarily on the bond angles around N(7), the argument
Solid-State X-ray Diffraction Study of TpRu(CO)(PPh3)-
(NHPh) (3). Recrystallization of 3 from toluene and pentane
yields yellow crystals, and an X-ray diffraction study was
performed. An ORTEP diagram is presented in Figure 1,
selected bond distances and angles are shown in Table 1, and
data collection parameters are shown in Table 2. The Ru-amido
nitrogen {N(7)} bond distance is 2.076(3) Å. The Ru-amido
nitrogen bond distances of trans-(DMPE)2Ru(H)(NH2) and cis-
(PMe3)4Ru(H)(NHPh) are 2.191(6) Å and 2.160(4) Å, respec-
tively.16,25 The Ru-N bond distance of (η6-C6Me6)Ru(Ph)-
(PMe3)(NHPh) is 2.121(3) Å.29 In comparison to the amido
complexes, the Ru-amine nitrogen bond distance of [CpRu-
(PPh3)2(NH3)][OTf] is 2.172(3) Å.30
Mayer et al. have recently discussed the multiple bonding
between the amido ligand and Os(IV) metal center of TpOs-
(NHPh)(Cl)2 in terms of the shorter bond distance between
(58) Soper, J. D.; Bennett, B. K.; Lovell, S.; Mayer, J. M. Inorg. Chem.
2001, 40, 1888-1893.
(59) Jeffrey, G. A. Accurate Crystal Structure Analysis by Neutron
Diffraction; Domenicano, A., Hargittai, I., Eds.; Oxford University
Press: New York, 1992; pp 270-298.
(56) Isaacs, N. S. Physical Organic Chemistry; John Wiley and Sons: New
York, 1987.
(57) Gunnoe, T. B.; White, P. S.; Templeton, J. L. J. Am. Chem. Soc. 1996,
118, 6916-6923.
(60) Allinger, N. L. Molecular Mechanics; Domenicano, A., Hargittai, I.,
Eds.; Oxford University Press: New York, 1992; pp 336-354.

Octahedral d6 Amido Complex TpRu(CO)(PPh3)(NHPh)
Inorganic Chemistry, Vol. 40, No. 25, 2001 6485
Table 3. Inverse Correlation between Ru-Namido and Namido-Cipso
Bond Distances for Octahedral Ruthenium(II) Phenylamido
Complexes
a
a
complex
Ru-Namido
Namido-Cispo
TpRu(CO)(PPh3)(NHPh) (3)
(η6-C6Me6)Ru(PMe3)(Ph)(NHPh)b
cis-(PMe3)4Ru(H)(NHPh)c
anilined
2.076(3)
2.121(3)
2.160(4)
N/A
1.372(4)
1.360(5)
1.340(9)
1.398
a In Å. b See ref 29. c See ref 25. d See ref 61.
may be more confidently made than if it depended on the bond
distances. The full details of X-ray analysis and location of the
amido hydrogen are given in the Experimental Section and
Supporting Information. To our knowledge, this is only the
second example of a structurally characterized transition metal
amido complex with a pyramidal amido ligand.26,27
The bond distance (1.372(4) Å) from the amido nitrogen
{N(7)} to the phenyl ipso carbon {C(11)} of the amido moiety
is shorter than that of aniline by 0.026 Å ((0.01 Å).61 In
comparison, the analogous bond distances for (η6-C6Me6)Ru-
(PMe3)(Ph)(NHPh) and cis-(PMe3)4Ru(H)(NHPh) are 1.360(5)
Å and 1.340(9) Å, respectively, while that of CpRe(NO)(PPh3)-
(NHPh) is 1.379(9) Å.25,27,29 This is an inverse correlation
between Ru-Namido and Namido-Cipso (phenyl) bond distances
for the series of ruthenium (II) phenyl-amido complexes TpRu-
(CO)(PPh3)(NHPh) (3), cis-(PMe3)4Ru(H)(NHPh), and (η6-C6-
Me6)Ru(PMe3)(Ph)(NHPh) (Table 3).
Variable Temperature 1H NMR Studies. Rotational isomers
are possible for complex 3 because of restricted rotation around
the ruthenium-amido nitrogen bond. 1H NMR spectra of amido
complex 3 at elevated temperatures (80 °C and above) show
Tp, PPh3, and amido phenyl resonances consistent with a single
isomer. Cooling a THF-d8 solution of 3 to -90 °C reveals a
fluxional process. Thus, at low temperatures, resonances
consistent with the presence of two isomers are observed. For
example, in the range from 4 to 5 ppm, two new resonances
are observed (Figure 2), and these resonances have been
assigned as NH resonances for two rotational isomers (∼1.63:1
ratio at -90 °C). One of the resonances is a doublet, presumably
due to coupling with phosphorus (3JPH ) 9 Hz). As the
temperature of the NMR probe is warmed, broadening of these
resonances is observed. Line broadening of the resonance due
to the major isomer was used to calculate the exchange rate
(krotation ) 4.3 s-1) and rotational barrier (12 kcal/mol) at -60
°C. The rate constant and barrier to rotation correspond to the
rate of conversion from the major isomer to the minor isomer.
As the temperature of the solution is increased, the resonances
coalesce into a doublet with JPH ≈ 3 Hz (80 °C).
Figure 2. Variable temperature 1H NMR of TpRu(CO)(PPh3)(NHPh)
(3) from approximately 4.0 to 5.2 ppm. The resonances are due to the
amido proton of two rotational isomers (note: the vertical scale of the
spectra at -90 °C and 80 °C are decreased relative to the other spectra).
sponding rotational barrier of TpRu(CO)(PPh3)(NHPh) (3) is
12 kcal/mol (-60 °C, conversion of major isomer to minor
isomer). Given that one of the small CO ligands of the tungsten
complexes has been replaced by a bulky PPh3 in the ruthenium
system, the smaller barrier to rotation for the ruthenium complex
(cf. the tungsten systems) is likely due to the high d-electron
count of the ruthenium complex. However, the role of sterics
is complicated by the presence of the more sterically imposing
Tp* ligand of the Tp*W(CO)2(NHR) systems. In comparison,
the barrier to amido rotation for the isoelectronic CpRe(NO)-
(PPh3)(NMe2) (i.e., isoelectronic with 3) complex has been
determined to be 7.8 kcal/mol.27 The difference in activation
barriers to amido rotation of 3.7-3.9 kcal/mol between 3 and
CpRe(NO)(PPh3)(NMe2) is likely a result of the larger steric
profile of the Tp ligand versus the Cp ligand.63
Reactivity. Bergman et al.’s intriguing reports of deproto-
nation of 1,4-cyclohexadiene, 9,10-dihydroanthracene, and
toluene with trans-(DMPE)2Ru(NH2)(H) led us to consider the
generality of these reactions. That is, is the high basicity of the
amido ligand of trans-(DMPE)2Ru(NH2)(H) a general property
of octahedral ruthenium(II) amido complexes, and what factors
control the amido basicity? Heating benzene-d6 solutions (70
°C) of amido complex 3 with excess 1,4-cyclohexadiene or 9,10-
dihydroanthracene results in no reaction after 72 h. Thus,
complex 3 fails to demonstrate basicity similar to trans-
(DMPE)2Ru(NH2)(H). However, the failure of aniline to depro-
tonate [TpRu(CO)(PPh3)(NH2Ph)][OTf] (4) in THF indicates
that TpRu(CO)(PPh3)(NHPh) (3) is basic enough to deprotonate
PhNH3+ (see previously). We have recently learned that parent
amido complexes of the type TpRu(L)(L′)(NH2) (L ) L′ )
PMe3, P(OMe)3 or L ) CO and L′ ) PPh3) react with 1,4-
cyclohexadiene to yield benzene, TpRu-hydride complexes, and
other uncharacterized TpRu complexes.64 In addition, the TpRu-
(L)(L′)(NH2) complexes deprotonate phenylacetylene (pKa ≈
Comparison of the barriers to rotation around the ruthenium-
amido nitrogen bond of complex 3 with Tp*W(CO)2(amido)
complexes provides a means to assess the impact of the filled
dπ manifold of the ruthenium complexes.62 The tungsten
complexes are structurally related to the ruthenium systems;
however, the tungsten(II) systems are d4 and have an empty
d-orbital of appropriate symmetry to undergo bonding with the
amido lone electron pair. Tp*W(CO)2(NH2) has been reported
to have a barrier to rotation (around the tungsten-amido nitrogen
bond) of 17 kcal/mol, while Tp*W(CO)2(NHPh) has barriers
to rotation of 23.0 and 24.2 kcal/mol. In contrast, the corre-
(61) Fukuyo, M.; Hirotsu, K.; Higuchi, T. Acta Crystallogr. Sect. B 1982,
38, 640-643.
(62) Powell, K. R.; Pe´rez, P. J.; Luan, L.; Feng, S. G.; White, P. S.;
Brookhart, M.; Templeton, J. L. Organometallics 1994, 13, 1851-
1864.
(63) Kitajima, N.; Tolman, W. B. Prog. Inorg. Chem. 1995, 43, 419-531.
(64) Jayaprakash, K. N.; Conner, D.; Gunnoe, T. B. Organometallics, in
press.

6486 Inorganic Chemistry, Vol. 40, No. 25, 2001
Jayaprakash et al.
23) at room temperature.65 These reactions are similar to those
reported for trans-(DMPE)2Ru(H)(NH2). Thus, the reactivity
differences between TpRu(CO)(PPh3)(NHPh) (3) and the oc-
tahedral ruthenium(II) parent amido complexes are attributed
to the presence of the amido phenyl ring. It is suggested that
the amido phenyl substituent mitigates the amido basicity via
delocalization of the amido lone electron pair, and the solid-
state structure of 3 supports this notion (see previously). We
are presently exploring the reactivity of a series of TpRu(L)-
(L′)(NHR) (R ) H, tBu or Ph; L, L′ ) CO, PPh3, P(OMe)3, or
PMe3) complexes to help delineate the factors which control
amido basicity including the extent of influence of amido
substituents and ancillary ligands.
complex TpRu(CO)(PPh3)(NHPh) (3). Complex 3 has been
structurally characterized by an X-ray diffraction study, and
evidence for the influence of the filled dπ manifold has been
observed. In addition, the lack of reactivity of 3 with 1,4-
cyclohexadiene or 9,10-dihydroanthracene has been discussed
in terms of the ability of the amido phenyl substituent to
delocalize the amido lone electron pair.
Acknowledgment. Acknowledgment is made to the donors
of the Petroleum Research Fund (administered by the American
Chemical Society) and to North Carolina State University for
support of this research. We also thank Professor George Dubay
(Duke University) for assistance with mass spectral analysis.
Summary
Supporting Information Available: Complete tables of crystal
data, collection and refinement data, atomic coordinates, bond distances
and angles, and anisotropic displacement coefficients for 3. This material
is available free of charge via the Internet at http://pubs.acs.org.
Because of the potential for novel structural patterns and
reactivity, interest in metal systems which simultaneously
possess π-donating ligands and high d-electron counts is
increasing.32-34,66-68 Along these lines, we have reported the
synthesis and characterization of the octahedral d6 amido
IC010785P
(66) Bergman, R. G. Polyhedron 1995, 14, 3227-3237.
(67) Sharp, P. R. Comments Inorg. Chem. 1999, 21, 85-114.
(68) Sharp, P. R. J. Chem. Soc., Dalton Trans. 2000, 1-11.
(65) Lowry, T. H.; Richardson, K. S. Mechanism and Theory in Organic
Chemistry, 3rd ed.; Harper Collins Publishers: New York, 1987.