Unusual ruthenium hydride complexes supported by the [N(2-PPh 2-4-Me-C6H3)2] pincer ligand

Article abstract of DOI:10.1016/j.ica.2010.07.040

Complexes of Ru(II) containing the pincer ligand [^-N(2-PPh ₂-4-Me-C₆H₃)₂] (PNP^Ph) were prepared. The complex (PNP^PhH)RuCl₂ (1) was treated with 2 equiv AgOTf to produc

Full text of DOI:10.1016/j.ica.2010.07.040

Inorganica Chimica Acta 364 (2010) 246–250
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Unusual ruthenium hydride complexes supported by the [N(2-PPh2-4-Me-C6H3)2]
pincer ligand
*
Meg E. Fasulo, T. Don Tilley
Department of Chemistry, University of California, Berkeley, CA 94720, USA
a r t i c l e i n f o
a b s t r a c t
Complexes of Ru(II) containing the pincer ligand [ꢀN(2-PPh2-4-Me-C6H3)2] (PNPPh) were prepared. The
Article history:
Available online 16 August 2010
complex (PNPPhH)RuCl2 (1) was treated with
2 equiv AgOTf to produce the triflate complex
(PNPPhH)Ru(OTf)2 (2). Complex 1 was also treated with an excess of NaBH4 to give a bimetallic complex
[(PNPPh)RuH3]2 (3). A number of methods, including X-ray crystallography, NMR spectroscopy, and com-
putational studies, were used to probe the structure of 3. Addition of Lewis bases to 3 resulted in octa-
hedral complexes containing a hydride ligand trans to a dihydrogen ligand.
Dedicated to Professor Arnold L. Rheingold
on the occasion of his 70th birthday.
Keywords:
Ó 2010 Elsevier B.V. All rights reserved.
Ruthenium compounds
Dihydrogen complexes
PNP pincer ligand
1. Introduction
a much smaller number of dinuclear species have been observed
[19–24]. Herein we report the synthesis and characterization of this
Transition metal complexes supported by multiple hydride and
dihydrogen ligands have been of considerable interest since stable
non-classical hydrides were first isolated by Kubas et al. [1–6]. A
number of such complexes have been synthesized, with a particu-
lar focus on the Group 8 metals [7]. The characterization of dihy-
drogen complexes can be based on a variety of experiments,
including T1 measurements, determination of JH–D coupling con-
stants, and neutron diffraction [8–11]. However, a continuum of
possible structures exist, ranging from dihydrogen ligands to dihy-
drides, making exact classification and determination both difficult
and subjective [4,7]. Additionally, recent calculations suggest that
many dihydrogen structures are nearly equal in energy to dihy-
dride structures, with a very low energy barrier between the two,
which can make it difficult to assign a definitive structure [12,13].
This group has long been interested in silyl and silylene ligands
on transition metal complexes [14]. Recent success with PNP pincer
ligands on Ir and Rh sparked an interest in exploration of related
chemistry on Ru, a metal that has supported a number of
interesting silylene complexes [15–17]. Within these contexts, we
envisioned a (PNPPh)RuH(H2) (PNPPh = [ꢀN(2-PPh2-4-Me-C6H3)2])
complex, analogous to the (PNPiPr)RuH(H2) complex reported by
Ozerov and co-workers [18], to be a suitable starting material for
reactions with organosilanes. However, we found that attempts to
prepare a ruthenium hydride complex supported by PNPPh resulted
in an unusual bimetallic complex with non-classical H2/(H)2 li-
gands. While a large number of H2 complexes have been reported,
dimer and its reactions with Lewis bases.
2. Experimental section
2.1. General procedures
All experiments were carried out under a nitrogen atmosphere
using standard Schlenk techniques or an inert atmosphere (N2)
glovebox. Olefin impurities were removed from pentane by treat-
ment with concentrated H2SO4, 0.5 N KMnO4 in 3 M H2SO4, and
NaHCO3. Pentane was then dried over MgSO4 and stored over acti-
vated 4 Å molecular sieves, and dried over alumina. Thiophene
impurities were removed from benzene and toluene by treatment
with H2SO4 and saturated NaHCO3. Benzene, toluene, tetrahydrofu-
ran, diethyl ether, dichloromethane, hexanes, and pentane were
dried using a VAC Atmospheres solvent purification system. Ben-
zene-d6 was dried by vacuum distillation from Na/K alloy. Dichlo-
romethane-d2 was dried by vacuum distillation from CaH2. PNPPh
[25] and [(COD)RuCl]n [26] were prepared according to literature
methods. All other chemicals were purchased from commercial
sources, and used without further purification.
H
1H, 2H, 31P{1H}, and 13C{1H} NMR spectra were recorded using
Bruker AVB 400, AV-500 or AV-600 spectrometers equipped with
a 5 mm BB probe. Spectra were recorded at room temperature and
referenced to the residual protonated solvent for 1H. 31P{1H} NMR
spectra were referenced relative to 85% H3PO4 external standard
(d = 0). 13C{1H} NMR spectra were calibrated internally with the res-
onance for the solvent relative to tetramethylsilane. For 13C{1H}
* Corresponding author.
E-mail address: tdtilley@berkeley.edu (T. Don Tilley).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.07.040

M.E. Fasulo, T. Don Tilley / Inorganica Chimica Acta 364 (2010) 246–250
247
NMR spectra, resonances obscured by the solvent signal are omit-
ted. Elemental analyses were performed by the College of Chemistry
Microanalytical Laboratory at the University of California, Berkeley.
Infrared spectra were recorded on a Nicolet Nexus 6700 FTIR spec-
trometer with a liquid-nitrogen-cooled MCT-B detector. Measure-
ments were made at a resolution of 4.0 cmꢀ1. Solution molecular
weights were obtained by the Signer method [27].
toluene and the resulting solution was stirred for 20 h. The reaction
mixture was filtered and dried under vacuum to give 4 as a brown
solid (0.096 g, 87% yield). 1H NMR (C6D6, 400.0 MHz): d 8.15 (m,
4H, ArH), 8.02 (m, 2H, ArH), 7.83 (d, 2H, JHH = 8.5 Hz, ArH), 7.30
(m, 2H, ArH), 7.06 (ov m, 6H, ArH), 6.94 (m, 6H, ArH), 6.74 (d, 2H,
JHH = 8.5 Hz, ArH), 6.69 (m, 3H, ArH), 1.94 (s, 6H, ArCH3), 1.90 (s,
6H, ArCH3), -4.38 (br s, 2H, Ru-H2) , ꢀ8.80 (t, 1H, JHP = 20.6 Hz,
Ru-H). 13C{1H} NMR (C6D6, 125.9 MHz): d 169.0, 136.6, 133.5,
131.8, 129.7, 129.1, 128.9, 124.6, 123.8, 123.0, 108.1, 19.9, 18.5.
2.2. (PNPPhH)RuCl2 (1)
31P{1H} NMR (C6D6, 161.9 MHz): d 55.6. IR (cmꢀ1):
2010; (Ru-H2) 1586. Anal. Calc. for C47H44N2P2Ru: C, 70.57; H,
m(Ru-H) 2040,
A
Teflon-stopped flask was charged with PNPPh
H
(1.00 g,
m
1.77 mmol) and [(COD)RuCl2]n (0.495 g, 1.77 mmol) followed by
25 mL of toluene. The reaction was heated at 110 °C for 24 h. The
orange precipitate was collected by filtration and dried under vac-
uum to give 1 as an orange solid (1.10 g, 85% yield). 1H NMR (CD2Cl2,
500.0 MHz): d 9.51 (s, 1H, NH), 8.16 (d, JHH = 8.2, 2H, ArH), 7.44 (br s,
4H, ArH), 7.37 (d, JHH = 8.2, 2H, ArH), 7.19 (t, JHH = 7.6, 2H, ArH), 7.04
(br s, 2H, ArH), 7.00–6.95 (ov m, 6H, ArH), 6.84 (br s, 4H, ArH), 6.66 (t,
JHH = 7.6, 4H, ArH), 2.24 (s, 6H, ArCH3). 13C{1H} NMR (CD2Cl2,
125.9 MHz): d 154.9, 136.7, 135.3, 132.4, 131.8, 130.6, 128.9,
127.9, 127.2, 126.7, 20.5. 31P{1H} NMR (CD2Cl2, 161.9 MHz): d
5.54; N, 3.50. Found: C, 69.59; H, 5.56; N, 3.57%.
2.6. (PNPPh)RuH(H2)(PPh3) (5)
A solution of triphenylphosphine (0.037 g, 0.14 mmol) in 1 mL
of toluene was added to a solution of 3 (0.092 g, 0.07 mmol) in
1 mL of toluene and the resulting solution was stirred for 24 h.
The reaction mixture was filtered and dried under vacuum to give
5 as a brown solid (0.098 g, 76% yield). 1H NMR (C6D6, 400.0 MHz):
d 7.86 (d, 2H, JHH = 8.3 Hz, ArH), 7.57 (m, 6H, ArH), 7.50 (t, 6H,
JHH = 8.3 Hz, ArH), 6.97 (m, 6H, ArH), 6.90 (t, 10H, ArH), 6.81 (t,
5H, JHH = 7.0 Hz, ArH), 6.69 (m, 6H, ArH), 1.82 (s, 6H, ArCH3),
ꢀ4.59 (s, 2H, Ru-H2), ꢀ9.73 (dt, 1H, JHP = 21.7, 22.4 Hz, Ru-H).
13C{1H} NMR (C6D6, 125.9 MHz): d 160.7, 139.6, 139.3, 134.6,
134.5, 134.4, 133.7, 133.2, 133.0, 133.9, 131.1, 129.0, 128.4,
126.8, 126.7, 122.9, 67.4, 25.4. 31P{1H} NMR (C6D6, 161.9 MHz): d
65.6. IR (cmꢀ1):
m(N–H) 3015. Anal. Calc. for C38H33NCl2P2Ru: C,
61.88; H, 4.51; N, 1.90. Found: C, 62.27; H, 4.72; N, 1.88%.
2.3. (PNPPhH)Ru(OTf)2 (2)
A flask covered with aluminum foil was charged with 1 (0.100 g,
0.136 mmol) and AgOTf (0.100 g, 2.64 mmol) followed by 10 mL of
C6H6. The reaction was stirred at room temperature for 5 h, then
the green-brown solution was filtered through Celite and evapo-
rated to dryness. The resulting yellow residue was recrystallized
from C6H6 at room temperature to give 3 as a yellow solid
(0.090 g, 65% yield).1H NMR (C6D6, 600.0 MHz): d 11.72 (s, 1H,
NH), 8.32 (d, JHH = 8.2, 2H, ArH), 7.47 (q, JHH = 7.0, 4H, ArH), 7.34
(t, JHH = 7.4, 4H, ArH), 7.08–7.00 (ov m, 8H, ArH), 6.92–6.91 (ov
m, 6H, ArH), 6.74 (br s, 2H, ArH), 1.68 (s, 6H, ArCH3). 13C{1H}
NMR (C6D6, 150.9 MHz): d 139.8, 134.5, 133.5, 132.3, 131.6,
131.4, 130.9, 129.6, 129.2, 19.9. 31P{1H} NMR (C6D6, 161.9 MHz):
71.13 (t, JPP = 29.4 Hz), 55.3 (d, JPP = 29.4 Hz). IR (cmꢀ1):
1957, 1913; (Ru-H2) 1579. Anal. Calc. for C56H50NP3Ru: C, 72.25;
m(Ru-H)
m
H, 5.41; N, 1.50. Found: C, 69.62; H, 5.61; N, 1.49%. The low value
observed for carbon may be due to incomplete combustion of the
complex during analysis; alternatively, it may reflect a small
amount of impurity that is not observed by NMR spectroscopy.
2.7. X-ray Structure determination
The X-ray analysis of 3 was carried out at UC Berkeley CHEXRAY
crystallographic facility. Measurements were made on an APEX-II
CCD area detector with a HELIOS multilayer mirrors monochro-
d 48.1. IR (cmꢀ1):
m(N–H) 3374. Anal. Calc. for C40H33NF6O6P2S2Ru:
C, 49.79; H, 3.45; N, 1.45. Found: C, 50.07; H, 3.36; N, 1.18%.
mating device using Cu K
a radiation (k = 1.54184 Å). Data was
integrated and empirical absorption corrections were made using
the APEX2 program package. The structure was solved by direct
methods and expanded using Fourier techniques. All calculations
were performed using the SHELXTL crystallographic package. Non-
hydrogen atoms were refined anisotropically and hydrogen atoms
were placed in calculated positions.
2.4. [(PNPPh)RuH3]2 (3)
A flask was charged with 1 (0.100 g, 0.136 mmol) and NaBH4
(0.100 g, 2.64 mmol) followed by 25 mL of THF. The reaction was
stirred at 80 °C for 3 h, then the brown solution was reduced in vacuo
and the resulting dark brownresidue was dissolved in 10 mL of C6H6.
The brown solution was filtered through Celite and the volatile
material was removed under vacuum to give 2 as a red-brown solid
(0.088 g, 96% yield). 1H NMR (C6D6, 400.0 MHz): d 7.93–7.88 (ov m,
4H, ArH), 7.77 (dt, JHH = 8.4, JHP = 2.4, 2H, ArH), 7.84–7.45 (ov m,
6H, ArH), 7.33–7.26 (ov m, 6H, ArH), 7.20 (ov m, 6H, ArH), 7.15 (d,
JHH = 8.4 Hz, 2H, ArH), 2.27 (s, 6H, ArCH3), ꢀ12.08 (s, 1H, Ru-H),
-13.17 (s, 1H, Ru-H), -15.55 (s, 1H, Ru-H). 13C{1H} NMR (CD2Cl2,
125.9 MHz): d 161.9 (t, JPC = 8.8), 137.0, 136.7 (t, JPC = 22.9), 136.3
(t, JPC = 3.0), 135.9 (t, JPC = 7.4), 135.5 (t, JPC = 21.7), 135.1 (t,
JPC = 5.5), 131.9, 131.8, 130.8, 130.1, 130.0 (t, JPC = 5.0), 129.4 (t,
JPC = 4.7), 124.0 (t, JPC = 4.9), 21.9. 31P{1H} NMR (C6D6, 161.9 MHz):
d 56.1. Anal. Calc. for C76H70N2P4Ru2: C, 68.25; H, 5.28; N, 2.09.
Found: C, 69.16; H, 5.49; N, 1.89%. Molecular weight in CH2Cl2:
1450 g/mol. Calculated for the dimer: 1337 g/mol.
*
2.8. Computational details of 3
All calculations were performed in the molecular graphics and
computing facility of the College of Chemistry, University of Cali-
fornia, Berkeley (NSF grant CHE-0233882). Calculations were per-
formed using the Gaussian ’03 suite of programs [28] at the
B3LYP/LANL2DZ level of theory with LANL2DZdp ECP polarization
functions for Ru [29]. Vibrational frequencies were calculated for
all converged structures and confirm that these structures lie on
a minimum. Graphical representations of the structures were gen-
erated using Mercury.
3. Results and discussion
2.5. (PNPPh)RuH(H2)(XylNC) (4)
3.1. Synthesis of Ru(II) complexes supported by PNPPh
H
A solution of xylylisocyanide (0.018 g, 0.14 mmol) in 1 mL of tol-
uene was added to a solution of 3 (0.092 g, 0.07 mmol) in 1 mL of
The reaction of 1 equiv of PNPPhH with 1 equiv of [(COD)RuCl2]n
in toluene at 110 °C for 24 h produced (PNPPhH)RuCl2 (1) as an

248
M.E. Fasulo, T. Don Tilley / Inorganica Chimica Acta 364 (2010) 246–250
orange solid in 85% yield (eq 1). The 1H NMR spectrum displays a
broad singlet at 9.51 ppm for the intact amine resonance and a sin-
gle methyl resonance at 2.24 ppm for the ligand. The 31P{1H} NMR
spectrum possesses a single resonance for the PNP ligand at
65.6 ppm, indicating the presence of equivalent phosphorus
groups. The infrared spectrum of the complex exhibits a broad
in both the solid state and in solution. The 1H and 31P{1H} NMR
spectra of 3 indicate that the PNPPh ligand lies on a plane of sym-
metry, with one methyl resonance observed at 2.27 ppm and only
one phosphorus resonance appearing at 56.1 ppm. Interestingly,
the 1H NMR spectrum of 3 possesses three chemically inequivalent
upfield hydride resonances at ꢀ12.08, ꢀ13.17, and ꢀ15.55 ppm,
each of which integrate to one with respect to the methyl groups
on the ligand. These hydride resonances are broad and exhibit no
splitting due to coupling to phosphorus nuclei. Additionally, H–H
coupling is not observed due to the broadness of the resonances
(width at half height = 34 Hz). The inequivalent resonances are sur-
prising because they seem to indicate that full oxidative addition of
an H2 ligand has taken place to give a Ru(IV) trihydride complex. In
contrast, (PNPiPr)RuH(H2) displays a single broad resonance in the
hydride region integrating to 3 and resulting from exchange of
the hydride and H2 ligand [25]. The 1H NMR spectra of 3 (Fig. 1) ob-
served at temperatures ranging from ꢀ90 °C to 80 °C exhibited nei-
ther sharpening nor coalescence of all three hydride resonances.
Using the inversion recovery method, the average T1 relaxation
times were found to be 115 ms for each hydride, which is longer
than expected for a dihydrogen ligand [7]. 11B NMR spectroscopy
supports the absence of any borohydride ligands in 3.
m
(N–H) band at 3015 cmꢀ1. The analogous [(PNPiPrH)RuCl2]n com-
plex synthesized by Ozerov and co-workers was found to be an
insoluble coordination polymer [18], while 1 was found to be sol-
uble in halogenated solvents such as CHCl3, CH2Cl2, and C6H5F.
However, reactions of 1 with reagents such as MeLi, nBuLi, LiN(-
SiMe3)2, and LDA in THF resulted in multiple unidentifiable prod-
ucts. Complex 1 did not react with silanes such as PhSiH3,
Ph2SiH2, and Et3SiH at 80 °C for 2 days in C6D6 or C6D5Br.
ð1Þ
Treatment of 1 with 2 equiv of AgOTf in benzene in the absence
of light resulted in the formation of (PNPPhH)Ru(OTf)2 (2) as a light
yellow solid in 65% yield (eq 2). The 1H NMR spectrum displays a
broad singlet at a downfield resonance of 11.72 ppm for the amine,
ð3Þ
and a broad m
(N–H) band at 3374 cmꢀ1 was observed by infrared
spectroscopy. A single methyl resonance is observed for the ligand
backbone at 1.68 ppm, indicating a symmetric arrangement of the
ligand about the Ru center. The 31P{1H} NMR spectrum reveals an
upfield shift for the PNPPh ligand to 48.1 ppm. In contrast to 1,
complex 2 was found to be soluble in both polar and nonpolar sol-
vents, allowing for reactivity studies with various alkylating re-
agents and silanes. Reactions to derivatize 2 with reagents like
Bn2Mgꢁ(Et2O)n, MeLi, or LDA were found to be unproductive due
to rapid conversion of complex mixtures of unidentified products.
Reactions of the organosilanes MesSiH3 and Ph3SiH with 2 did not
proceed even with heating at 80 °C for 3 days.
The gross connectivity in 3 was determined by X-ray crystallog-
raphy, with dark red needles grown by vapor diffusion of heptane
into a toluene solution of 3 at room temperature over one week.
Due to poor crystallinity, the X-ray data is not of sufficient quality
to report accurate bond distances and angles; however, general
comments on the structure of 3 can be made. Complex 3 is a di-
meric species consisting of two Ru atoms, two PNP ligands, and
therefore six hydride-like ligands (not located crystallographi-
cally). The Ru–Ru distance of 2.6 Å is typical of two Ru atoms
bridged by hydride ligands. The pincer ligand is bound to the metal
in a facial arrangement rather than the more common meridinal
binding. The angles around the N atom of the ligand sum to
360°. An empty coordination site is located trans to the N atom
of each PNP ligand, presumably filled by a hydride ligand. Complex
3 was found to have a molecular weight of 1450 g/mol in CH2Cl2,
indicating that the dimer remains intact in solution [27].
ð2Þ
DFT studies at the B3LYP/LANL2DZ level of theory were under-
taken to provide further insight into the geometric structure of 3
and the optimized DFT structure is designated as 3 . The connec-
3.2. Synthesis and characterization of [(PNPPh)RuH3]2
*
tivity found via X-ray analysis was utilized as a starting point,
and different arrangements of the hydride ligands were examined.
No PNPPh ligand simplifications were made. The geometries of a
number of structures were optimized, and all converged to the
The reaction of 1 with an excess of NaBH4 in THF at 80 °C for 3 h
generated a new complex (3) in high yield as a red-brown solid (eq
3). Complex 3 exhibits good stability at room temperature under N2
Fig. 1. Upfield region of 1H NMR spectrum of 3 at 300 K.

M.E. Fasulo, T. Don Tilley / Inorganica Chimica Acta 364 (2010) 246–250
249
1H NMR spectra of 4 and 5 display two new characteristic upfield
resonances: a broad peak integrating to two hydrogens (ꢀ4.38
and ꢀ4.59 ppm, respectively, for 4 and 5) and a sharp peak at
higher field corresponding to one hydrogen that exhibits fine cou-
pling. In the case of 4, this peak is a triplet (JHP = 20.6 Hz) at
ꢀ8.80 ppm. For complex 5,
a doublet of triplets (JHP = 21.7,
22.4 Hz) is observed at ꢀ9.73 ppm. The small coupling constants
to phosphorus indicate that this hydride ligand is cis to all P-atoms
in each complex. The 31P{1H} NMR spectrum of 4 displays a single
resonance at 55.6 ppm, while the spectrum of 5 possesses two res-
onances: a triplet at 71.1 ppm for the PPh3 ligand and a doublet at
55.3 ppm for the PNP ligand. The P–P coupling constant of 29.4 Hz
is indicative of a cis arrangement of the two types of phosphorus
donor atoms.
ð4Þ
The T1 times were measured for 4 and 5. In complex 4, the res-
onance at ꢀ4.38 ppm has a T1 of 100 ms, while the resonance at
ꢀ8.80 ppm has a T1 of 300 ms. The T1 times for 5 follow a similar
pattern: 90 ms (ꢀ4.59 ppm) and 650 ms (ꢀ9.73 ppm). These times
are consistent with the integrations, splitting patterns, and the
assignment of the downfield resonance (ꢂ4.5 ppm) to an H2 ligand
and the upfield resonance (ꢂ9 ppm) to a classical hydride ligand.
Both 4 and 5 react rapidly with 1 atm D2 gas at room temperature
to give (PNP)Ru(D)(D2)L. The 1H NMR spectra were obtained from
ꢀ30 °C to 60 °C, but JH–D was not observable for either complex.
However, a number of ruthenium complexes with a classical hy-
dride ligand trans to an H2 ligand have been documented, with a
narrow range of dH–H values (0.84–0.94 Å) [7]. The shorter T1 times
for 4 and 5, as compared to 3, indicate that the H–H distances in
these complexes are similar to those described in the literature
for related trans-(H2)(H) complexes.
*
Fig. 2. Optimized geometry of 3 .
Table 1
*
Selected bond distances of 3 (Å).
Ru(1)–P(1)
Ru(1)–P(2)
Ru(1)–N(1)
Ru(1)–H(1a)
Ru(1)–H(1b)
H(1a)–H(1b)
Ru(1)–H(3)
Ru(1)–H(4)
Ru(1)–Ru(2)
Ru(2)–P(3)
Ru(2)–P(4)
Ru(2)–N(2)
Ru(2)–H(2a)
Ru(2)–H(2b)
H(2a)–H(2b)
Ru(2)–H(3)
Ru(2)–H(4)
2.3595
2.3249
2.1372
1.7506
1.7570
0.842
1.8073
1.8442
2.824
2.3590
2.3274
2.1380
1.7564
1.7501
0.842
4. Conclusion
New Ru hydride complexes supported by a PNPPh pincer ligand
have been obtained. The exact structural nature of the hydride 3
has yet to be determined, but it has been shown to behave as a syn-
thon for the [(PNPPh)RuH3] fragment. The Ru dimer undergoes at-
tack by a Lewis base to give a monomeric species containing a
non-classical H2 ligand. These complexes represent the first Ru
complexes supported by the PNPPh ligand.
1.8108
1.8398
*
same structure, represented by 3 in Fig. 2. Rather than displaying
three hydrides, a non-classical dihydrogen ligand with an H–H
bond distance of 0.842 Å is observed. Other bond distances and
*
Acknowledgements
bond angles of 3 are consistent with the experimental data
(Table 1).
This work was supported by the National Science Foundation
under Grant No. CHE-0649583 and an NSF Predoctoral Fellowship
to M.E.F. The authors thank Drs. Fred Hollander and Antonio Di
Pasquale of the UC Berkeley CHEXRAY facility for assistance with
X-ray crystallography, Rudi Nunlist for assistance with NMR spec-
troscopy, and Drs. Kathleen Durkin and Jamin Krinsky for assis-
tance with DFT studies.
Thus, the computational studies suggest a structure that seems
inconsistent with the NMR data in that rapid exchange (e.g., by
rotation about the Ru–H2 bond) would be expected to give rise
to one hydride resonance for the H2 ligand. Although the detailed
structure of 3 is yet to be determined, it seems reasonable to con-
clude that it is a dimeric hydride of the type [(PNPPh)RuH3]2,
involving bridging hydrogen ligands.
3.3. Addition of Lewis Bases to [(PNPPh)RuH3]2
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