Ruthenium hydrogenation catalysts with P-N-N-P ligands derived from 1,3-diaminopropane and the formation of a β-diiminate complex by a base-induced isomerization

Article abstract of DOI:10.1016/j.ica.2007.12.003

The complexes RuHCl{PPh₂(2-C₆H₄)CH{double bond, long}NCH₂CH₂CH₂N{double bond, long}CH(2-C₆H₄)PPh₂} (RuHCl{prP₂N₂}, 7) and RuHCl{PPh₂(2-C₆H₄)CH₂NHCH₂CH₂CH₂NHCH₂(2-C₆H₄)PPh₂} (RuHCl{prP₂(NH)₂}, 8) are prepared by reaction of RuHCl(PPh₃)₃ with a ligand derived from 1,3-diaminopropane and ortho-diphenylphosphinobenzaldehyde. They are active precatalysts for the hydrogenation of acetophenone and are moderately active for the hydrogenation of benzonitrile and imines. The related complex RuHCl{ethP₂(NH)₂} with a ligand derived from 1,2-diaminoethane provides a more active catalyst. Complexes 7 and 8 undergo an unusual base-promoted isomerization reaction that produces a ruthenium complex containing a novel β-diiminato ligand.

Full text of DOI:10.1016/j.ica.2007.12.003

Available online at www.sciencedirect.com
Inorganica Chimica Acta 361 (2008) 3149–3158
www.elsevier.com/locate/ica
Ruthenium hydrogenation catalysts with P–N–N–P ligands
derived from 1,3-diaminopropane and the formation of a
b-diiminate complex by a base-induced isomerization
F. Nipa Haque, Alan J. Lough, Robert H. Morris *
Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ont., Canada M5S 3H6
Received 30 October 2007; accepted 2 December 2007
Available online 8 December 2007
Dedicated to Professor Robert Angelici on the occasion of his 70th birthday.
Abstract
The complexes RuHCl{PPh2(2-C6H4)CH@NCH2CH2CH2N@CH(2-C6H4)PPh2} (RuHCl{prP2N2}, 7) and RuHCl{PPh2(2-
C6H4)CH2NHCH2CH2CH2NHCH2(2-C6H4)PPh2} (RuHCl{prP2(NH)2}, 8) are prepared by reaction of RuHCl(PPh3)3 with a ligand
derived from 1,3-diaminopropane and ortho-diphenylphosphinobenzaldehyde. They are active precatalysts for the hydrogenation of ace-
tophenone and are moderately active for the hydrogenation of benzonitrile and imines. The related complex RuHCl{ethP2(NH)2} with a
ligand derived from 1,2-diaminoethane provides a more active catalyst. Complexes 7 and 8 undergo an unusual base-promoted isomer-
ization reaction that produces a ruthenium complex containing a novel b-diiminato ligand.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Ruthenium hydride; Tetradentate ligand; Ketone; Imine; Nitrile hydrogenation
1. Introduction
which is activated by base for the asymmetric transfer
hydrogenation of aryl ketones to optically active alcohols
[10]. Rautenstrauch et al. later reported that complex 1,
the hydride 2, and complex 3 with the ethP2(NH)2 ligand
(ethP2(NH)2 = {PPh2(2-C6H4)CH2NH2CH2–}2) are also
very active precatalysts for the H2-hydrogenation of
ketones [12]. Further work from our group showed that
the dihydrido complex trans-RuH2{tmeP2N2} [13]
(tmeP2N2 = {PPh2(2-C6H4)CH@NCMe2–}2) (5) and the
amidohydrido complex 6 are active catalysts without the
addition of base [13]. More recently we reported that
the complex RuHCl{ethP2(NH)2} (4) is a precatalyst for
the hydrogenation of benzonitrile to benzylamine under
mild conditions [16].
Ruthenium complexes are often the catalysts of choice
for the hydrogenation of the polar bonds of ketones, imines
and nitriles [1–9]. Ruthenium(II) complexes with tetraden-
tate P–N–N–P ligands are useful precatalysts for the trans-
fer hydrogenation and H2-hydrogenation of ketones to
alcohols and imines to amines [10–14]. Typically, diphos-
phinediimine ligands P–N–N–P are conveniently prepared
by the Schiff base condensation of a diamine with 2 equiv.
of 2-diphenylphosphinobenzaldehyde [15]. These P–N–N–
P ligands can be readily reduced to the diaminediphosphine
ligands P–NH–NH–P. Gao et al. showed that the use of
enantiopure (R,R)-1,2-diaminocyclohexane leads to the
synthesis of ligand cyP2(NH)2 and this can be used to pre-
pare the precatalyst trans-RuCl2{cyP2(NH)2} (1, Chart 1),
For this class of ruthenium complexes, the effect on
catalytic properties of the ring sizes of the chelating groups
in their tetradentate ligands has not yet been examined.
The ligands of Chart 1 make two six membered rings and
one five membered ring (a 6,5,6 combination) with the
*
Corresponding author. Tel./fax: +1 416 978 6962.
E-mail address: rmorris@chem.utoronto.ca (R.H. Morris).
0020-1693/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.12.003

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F.N. Haque et al. / Inorganica Chimica Acta 361 (2008) 3149–3158
H
H
H
H
H
H
Cl
N
N
N
N
Ru
Ru
P
P
P
P
Ph2
Ph2
Ph2
Ph2
Cl
Cl
1
2
H
H
H
H
Cl
N
N
N
N
Ru
Ru
P
P
P
P
Ph2
Ph2
Ph2
Ph2
Cl
Cl
4
3
H
H
H
H
N
N
H
N
N
Ru
Ru
P
P
P
P
Ph2
Ph2
Ph2
Ph2
H
6
5
Chart 1.
ruthenium. Gao et al. have reported the synthesis of
the complex trans-RuCl2{prP2N2} with a 6,6,6 combina-
tion of ring sizes where prP2N2 is PPh2(2-C6H4)HC
@NCH2CH2CH2N@ CH(2-C6H4)PPh2, but did not discuss
its catalytic activity [17]. In this study, we examine the cat-
alytic properties imparted by the prP2N2 ligand and its
hydrogenated form, prP2(NH)2.
enylphosphinobenzaldehyde, as reported previously
[15,17]. The reduced ligand, prP2(NH)2 is prepared by reac-
tion of prP2N2 with lithium aluminum hydride (Scheme 1).
The complexes RuHCl{prP2N2} (7) and RuHCl
{prP2(NH)2} (8) were prepared by reacting RuHCl(PPh3)3
with the respective ligand as in Scheme 1.
The red complex 7 and the yellow complex 8 were char-
1
acterized by H, 13C and 31P NMR spectroscopy and IR
2. Results and discussion
spectroscopy. The 31P{1H} NMR spectrum of 7 in CDCl3
shows two very broad signals at 64.5 and 57.2 ppm, while
the hydride resonance is a triplet with 2JPH 27.8 Hz, typical
of a cis hydride–phosphorus coupling. These features
The ligand prP2N2 is readily prepared through the con-
densation reaction of 1,3-diaminopropane and ortho-diph-
LiAlH4
prP2N2
prP2(NH)2
RuHCl(PPh3)3
-3 PPh3
RuHCl(PPh3)3
reflux, THF, 1.75 h
-3 PPh3
reflux, THF, 3.5 h
H
H
H
H
N
N
N
N
Ru
Ru
P
P
P
P
Ph2
Ph2
Ph2
Ph2
Cl
Cl
7
8
Scheme 1. Preparation of complexes 7 and 8.

F.N. Haque et al. / Inorganica Chimica Acta 361 (2008) 3149–3158
3151
indicate either a trans geometry with both P trans to N or a
cis-b geometry [18–21] with one P trans to N and one to Cl.
The H NMR spectrum is more consistent with the trans
[13]. The propylene backbone of the prP2N2 ligand in 9 is
in a skewed conformation [19,21,22]. In both 9 and
RuCl2{ethP2N2}, the Cl–Ru–Cl bond deviates from 180°
to 171.85(4)° and 170.0(1)°, respectively. The P–Ru–P
angles in each compound are similar: 101.83(4)° and
100.3(1)°, respectively. However the N–Ru–N angle in
1
configuration since only one imine resonance is observed
at 8.4 ppm. The 31P nuclei are diastereotopic because of
the skewed CH2CH2CH2 backbone of the ligand (see
below) and their resonances are broad due to backbone
dynamics (from skew to boat) [19,21,22]. The features of
the spectra of complex 8 are similar. In this case the
31P{1H} NMR spectrum in CDCl3 shows two sharp dou-
RuCl2{prP2N2}
(85.6(1)°)
is
greater
than
in
RuCl2{ethP2N2} (80.8(3)°) due to the longer three-carbon
backbone forming a six-membered ring instead of a five-
membered ring. This angle is accommodated in the struc-
ture of 9 by a pushing of the P atoms to above and below
the RuN2P2 plane.
2
blets at 66.6 and 60.2 ppm with a JPP coupling of
29.2 Hz, characteristic of cis-phosphorus donors on
ruthenium(II).
Both complexes are soluble in dichloromethane and
chloroform. However, 7 and 8 slowly react in chloroform
to produce the known complex trans-RuCl2{prP2N2} (9)
[23] and the new complex trans-RuCl2{prP2(NH)2} (10),
respectively. In this reaction, the hydrides are replaced by
chlorides producing the dichloro complexes and dichloro-
methane. Complex 9 was alternatively prepared by reacting
the prP2N2 ligand with RuCl2(PPh3)3.
2.2. Catalytic hydrogenation of acetophenone to 1-
phenylethanol
The hydridochloro complexes 7 and 8 are active precat-
alysts with similar activity for the hydrogenation of aceto-
phenone in iPrOH (Scheme 2, Table 3). Complex 8
provides a somewhat less active system than that produced
by trans-RuCl2{ethP2(NH)2} (3) [12] and RuHCl{ethP2-
(NH)2} (4) [24] (Table 3).
2.1. Structure of RuCl2{prP2N2} (9)
The significant difference between the rates of conver-
sion when the solvent used is benzene and when it is isopro-
panol has also been observed previously with other
catalytic systems for the hydrogenation of ketones [12,25].
Crystals of 9 and 10 were analyzed by X-ray diffraction.
The quality of the structure determination for 10 was poor,
but verified the trans-configuration. The structure of 9
(Fig. 1, Tables 1 and 2) in the crystal is in agreement with
that derived from the interpretation of the NMR data for 9
[17]. The structural features of 9 are very similar to those of
trans-RuCl2{ethP2N2} (3) [23] and trans-RuHCl{tmeP2N2}
2.3. Hydrogenation of benzonitrile to benzylamine
Complex 7 catalyzes the conversion of benzonitrile to
benzylamine in toluene to 74% conversion in 45 h while
Fig. 1. Crystal structure of trans-RuCl2{prP2N2}, 9.

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F.N. Haque et al. / Inorganica Chimica Acta 361 (2008) 3149–3158
Table 1
N
H2, catalyst, KOtBu
toluene
Crystallographic data for RuCl2{prP2N2} ꢁ CHCl3 (9 ꢁ CHCl3)
Formula
Formula weight
Crystal system
Space group
NH2
C42H37Cl5N2P2Ru
910.00
monoclinic
P21/c
Scheme 3.
Unit cell dimensions
˚
a (A)
14.2050(4)
12.8371(3)
22.0581(6)
90
97.6860(14)
90
3986.18(18)
4
1.516
˚
2.4. Hydrogenation of imines to amines
b (A)
˚
c (A)
a (°)
b (°)
c (°)
Complexes 7 and 8 in benzene with excess base catalyzed
the incomplete hydrogenation of the imine N-(1-phenyleth-
ylidene)-benzeneamine (Scheme 4) to the racemic amine.
Other ruthenium tetradentate systems have been reported
that hydrogenate imines [11].
3
˚
Volume (A )
Z
qcalc. (g/cm3)
T (K)
150(2)
There is no conversion of the imine when isopropanol is
the solvent (Table 5).
˚
k (A)
0.71073
0.45 ꢂ 0.34 ꢂ 0.04
0.0544
Crystal size (mm)
R1
wR2
7 was also used in the catalytic hydrogenation of
ethP2N2 to ethP2(NH)2 in C6D6 (Scheme 5). A conversion
of 97.2% was obtained after hydrogenation for 6 days at
room temperature under 6 atm H2 pressure (S:C:B ratio
was 37:1:5).
0.1206
Table 2
Selected bond lengths and angles for 9
˚
Bond lengths (A)
2.5. Observation of dihydride complexes
Ru(1)–N(1)
Ru(1)–N(2)
Ru(1)–P(1)
Ru(1)–P(2)
Ru(1)–Cl(1)
2.118(4)
2.126(4)
2.309(1)
2.293(1)
2.449(1)
Ru(1)–Cl(2)
N(1)–C(4)
N(2)–C(5)
N(1)–(C1)
N(2)–(C3)
2.414(1)
1.275(6)
1.282(6)
1.474(6)
1.473(5)
On the basis of mechanistic investigation of the
RuHCl{cyP2(NH)2}2 and RuHCl(tmeP2(NH)2) systems,
the expected catalysts produced in the mixtures of 7 and
KOtBu or 8 and KOtBu are thought to be the hydrido
amido complex RuH{PPh2(2-C6H4)CH2NCH2CH2CH2-
NHCH2(2-C6H4)PPh2} (11) and the trans-dihydride com-
plex RuH2{prP2(NH)2} (12) (Scheme 6). The imine groups
in 7 are hydrogenated first to amine groups to produce the
active catalyst in a similar fashion to the conversion of
RuHCl{tmeP2N2} into RuH2{tmeP2(NH)2} by treatment
with base and dihydrogen [13].
Bond angles (°)
N(1)–Ru(1)–N(2)
N(1)–Ru(1)–P(2)
N(2)–Ru(1)–P(2)
N(1)–Ru(1)–P(1)
N(2)–Ru(1)–P(1)
P(2)–Ru(1)–P(1)
N(1)–Ru(1)–Cl(2)
N(2)–Ru(1)–Cl(2)
85.6(1)
171.1(1)
86.1(1)
P(2)–Ru(1)–Cl(2)
P(1)–Ru(1)–Cl(2)
N(1)–Ru(1)–Cl(1)
N(2)–Ru(1)–Cl(1)
P(2)–Ru(1)–Cl(1)
P(1)–Ru(1)–Cl(1)
Cl(2)–Ru(1)–Cl(1)
C(1)–C(2)–C(3)
95.35(4)
86.88(4)
90.8(1)
86.7(1)
85.1(1)
170.3(1)
101.83(4)
87.4(1)
85.30(4)
100.95(4)
171.85(4)
114.4(4)
86.8(1)
There is good evidence for the formation of dihydrides
in this system. When complex 8 is reacted with excess
KOtBu under H2 in C6D6, a mixture of cis (13) and trans
(12) dihydrides is produced in a 3:1 ratio (Scheme 7). Other
species are produced in small amount including the novel
complex RuH(diimP2) (14) that is described below. The
O
H
OH
H2, catalyst, KOtBu
CH3
CH3
solvent
1
cis-dihydride displays in the H NMR spectrum hydride
Scheme 2.
peaks at ꢀ5.04 ppm (dd) and ꢀ16.85 ppm (br s), and in
the 31P{1H} NMR spectrum peaks at 75.62 and
75.08 ppm. The couplings are consistent with one P trans
to H and one P trans to N. The trans species produces a
the catalyst system with complex 8 deactivated after 14%
conversion (Scheme 3, Table 4). The activity is lower than
that of the ethP2(NH)2 system, 4 [16].
1
triplet in the H spectrum for the hydride at ꢀ6.22 ppm
Table 3
Results for the hydrogenation of acetophenone
Substrate (mmol) Catalyst (lmol) KOtBu (mmol) S:C:B ratio Solvent Temperature (°C) Pressure (atm) Time (min) Conv. (%)
7
7
7
8
0.84
0.84
0.87
0.83
1.00
1.00
0.40
0.40
0.053
0.053
0.037
0.037
836:1:53
836:1:53
2181:1:93
2106:1:94
C6H6
19
19
20
20
6.0
6.0
6.0
6.0
2752
15
25
20
40
99.1
98.5
86.1
88.6
99.3
99.4
iPrOH
iPrOH
iPrOH
4
0.832
0.40
0.036
2075:1:89
iPrOH
20
6.0
20

F.N. Haque et al. / Inorganica Chimica Acta 361 (2008) 3149–3158
3153
Table 4
Results for the hydrogenation of benzonitrile
Substrate (mmol)
Catalyst (lmol)
KOtBu (mmol)
S:C:B ratio
Solvent
Temperature (°C)
Pressure (atm)
Time (h)
Conv. (%)
7
8
4
0.44
0.78
0.89
2.2
3.9
4.5
0.027
0.036
0.045
197:1:12
199:1:9
198:1:10
Toluene
Toluene
Toluene
19
23.5
23.5
14
14
14
45
17
1.4
74
14
61
and a singlet in the 31P NMR spectrum at 70.44 ppm. Sim-
ilar patterns are observed upon reacting 6 with excess base
under H2 and the chemical shifts and couplings are similar
to those observed for the cis dihydride, cis phosphine iso-
mer of RuH2(PPh3)2(dach) and the trans-dihydride isomer
of RuH2(PPh3)2(dach), dach = (R,R)-1,2-diaminocyclo-
hexane [25].
H
H2, catalyst, KOtBu
benzene
N
N
H
It is interesting that complex 7 also reacts with base
under H2 to produce the same cis and trans-dihydrides, this
Scheme 4.
Table 5
Results for the hydrogenation of N-(1-phenylethylidene)-benzeneamine
Substrate (mmol)
Catalyst (lmol)
KOtBu (mmol)
S:C:B ratio
Solvent
Temperature (°C)
Pressure (atm)
Time (h)
Conv. (%)
7
7
8
1.67
1.67
1.67
1.01
1.01
1.19
0.071
0.058
0.037
1662:1:71
1662:1:57
1404:1:31
iPrOH
C6H6
C6D6
22.5
22.5
22.5
6.0
6.0
6.0
41.5
71.5
72
0
25
14
H
H
N
H
N
H
H
N
H2, 7, KOtBu
N
H
H
H
PPh2
PPh2
Ph2P
Ph2P
benzene
Scheme 5.
H
H
H
N
N
Ru
P
P
Ph2
Ph2
H
O
12
Ph
+ H2
Ph
‡
O
H
H
H
H
N
N
N
N
Ru
Ru
H
P
P
P
Ph2
P
Ph
2 H
11
Ph2
Ph2
Ph
OH
H
Scheme 6.

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F.N. Haque et al. / Inorganica Chimica Acta 361 (2008) 3149–3158
H
H
H
H
N
N
18 %
Ru
P
P
Ph2
Ph2
H
12
H
H
H
KOtBu, H2
C6D6
N
N
Ru
P
P
H
Ph2
Ph2
H
Cl
N
P
N
H
63 %
Ru
8
Ph2
P
Ph2
13
Scheme 7.
time in a 37:27 ratio, along with minor amounts of the
complex RuH(diimP2) and other unidentified species that
give small peaks in the 31P NMR spectrum in the region
42.20–40.18 ppm. Therefore, under catalysis conditions,
both precursors 7 and 8 lead to the same dihydride cata-
lysts. The fact that the activation of 7 leads to a higher ratio
of the trans-dihydride could explain the slightly higher
activity of 7 over that of 8 since it is the trans-dihydride
that is the most active ketone hydrogenation catalyst by
the outer sphere hydrogenation mechanism (Scheme 6).
Attempts to isolate the dihydride species in a pure state
failed.
hydrido complex RuH(PPh2(2-C6H4)CH2NCHCHCH-
NCH2(2-C6H4)PPh2) (14) containing a b-diiminato ligand
(Scheme 8).
The 31P{1H} NMR spectrum of the product 14, a sharp
singlet at 58.72 ppm, indicates there is only one species
1
present with both P nuclei equivalent. The H NMR spec-
trum shows that this is a hydride species with a chemical
2
shift that lies far upfield at ꢀ25.55 ppm (t, JPH
=
34.07 Hz). Square pyramidal hydridoruthenium complexes
with a hydride in the apical position such as RuHCl(CO)-
(PiPr3)2 [26], [RuH(isopropanol)2(P–P)]BF4 (P–P = 6,60-
dimethoxybiphenyl-2,20-(diyl)bis[3,5-di(tert-butyl)phenyl-
phosphine]) [27], [RuH(R,R0-Me-DuPHOS)2]PF6 [28], and
[RuH(dcpe)2][BPh4] [29] have hydride chemical shifts in
this high field region. The RuNCHCHCHN ring of 14
has similar NMR characteristics to that of the diiminate
ring in the oxidized form of the complex [3,30-(1,3-propane-
diamino)bis(3-methyl-2-butanoneoxime)] nickel(II) [30,31]
2.6. Formation of a b-diiminate complex
The reaction of a red dispersion of 7 with excess KOtBu
in C6D6 was carried out on an NMR scale under N2 to see
how this precatalyst would behave in the absence of a
hydrogen source (H2 gas). Instantly, a dark brown solution
was produced containing a well defined complex. This
complex either completely or partially decomposed during
our several attempts to crystallize or precipitate it out of
i
and in the complex Zn(BDI-11)Et (BDI = (2,6-C6H3 Pr2)-
i
NCHCHCHN(2,6-C6H3 Pr2)) [32]. The b-proton of 14 pro-
duces a triplet at 5.13 ppm, a similar chemical shift to those
reported for the Ni(II) and Zn(II) complexes. The two
a-protons are reported to show up furthest downfield in
the aromatic region as a doublet for the Zn(BDI-11)Et
complex at 7.19 ppm and for the Ni(II) complex at
1
1
1
solution. However, H, 13C, 31P{1H}, H–1H and H–13C
correlation NMR studies of this brown solution produce
spectra that are all consistent with the formation of the
Hβ
C1
H
H
H
Hα
C2
H
α
H
H
H
C2
H
C3
H
C3
excess KOtBu
N2, C6D6
H
H
H
H
N
N
N
N
H
H
Ru
Ru
- KCl
P
P
P
P
- HOtBu
Ph2
Ph2
Ph2
Ph2
Cl
14
7
Scheme 8.

F.N. Haque et al. / Inorganica Chimica Acta 361 (2008) 3149–3158
3155
7.04 ppm [32]. This corresponds well with our finding of a
carbons in the Ni(II) and Rh(I) complexes. C3 appears as a
1
multiplet at 7.83 ppm for the a-protons in complex 14.
triplet at 72.49 ppm for 14. Finally, H–13C heteronuclear
1
Furthermore, H–1H correlation 2D NMR data (COSY)
correlation 2D NMR data (GHSQ-CAD) further confirms
our assignments.
shows that the protons corresponding to these two peaks
at 5.13 and 7.83 ppm couple to each other. The benzylic
protons in 14 generate a resonance at 4.74 ppm. The
13C{1H} NMR spectrum of 14 provides further support
for our structural determination. The signal corresponding
to C1 (see the numbering in Scheme 8) appears at
90.58 ppm in our spectrum. This is similar to the reported
values for the corresponding carbon in the diiminate com-
plex of Ni(II) mentioned above [23] and in those reported
for diiminate complexes of Rh(I) [33]. C2 appears at
152.96 ppm, also similar to the signals of the corresponding
We hypothesize that a base-catalyzed imine isomerization
occurs in 7 to initiate the reaction leading to the formation of
14(Scheme 9). Jaeger et al. have reported that intramolecular
rearrangement of imines may occur in the presence of KOtBu
[34]. The ruthenium hydride complexes RuH2(N2)(PPh3)3
and RuH2(PPh3)4 are known to catalyze the isomerization
of imines via [1,3]-hydrogen shifts [35]. Therefore, 14 can
form by the successive base-catalyzed transfer of protons
from the propylene ring to the benzylic positions followed
by deprotonation of an acidic b proton (Scheme 9).
7
H
A
KOtBu-catalyzed
imine
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
isomerization
N
N
N
N
Ru
Cl
Ru
Cl
P
P
P
P
Ph2
Ph2
KOtBu-catalyzed
Ph2
Ph2
imine
isomerization
H
H
H
H
14
B
H
H
H
H
H
H
H
H
H
H
H
H
H
KOtBu
N
N
N
N
Ru
Cl
Ru
P
P
P
P
- HOtBu
- KCl
Ph2
Ph2
Ph2
Ph2
Scheme 9. Proposed mechanism for the formation of 14 by the base-promoted isomerization of the prP2N2 ligand via unobserved intermediates A and B.
8
C
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
NH
NH
excess KOtBu
NH
H
N
Ru
Cl
Ru
P
P
P
P
- HOtBu
- KCl
Ph2
Ph2
Ph2
Ph2
E
D
H
H
H
H
cis and trans
-
H
H
H
H
H
H
RuH2{prP2(NH)2}
H
H
H
H
H
H
H
H
C
N
NH
N
H
N
P
Ru
H
Ru
H
P
P
P
Ph2
Ph2
Ph2
Ph2
F
14
H
H
cis and trans
-
H
H
H
N
H
H
RuH2{prP2(NH)2}
H
H
H
H
H
H
H
H
H
C
H
N
N
N
P
Ru
Ru
H
P
P
P
Ph2
Ph2
Ph2
Ph2
Scheme 10. Proposed dehydrogenation of the prP2(NH)2 ligand via unobserved intermediates C–F.

3156
F.N. Haque et al. / Inorganica Chimica Acta 361 (2008) 3149–3158
In an attempt to observe the amido hydrido complex of
use of standard Schlenk, vacuum line and glove box tech-
niques in dry, oxygen-free solvents. Tetrahydrofuran
(THF), toluene, diethyl ether and hexanes were dried and
distilled from sodium benzophenone ketyl. Deuterated
solvents were degassed and dried over activated molecular
sieves. Potassium tert-butoxide and 2-(diphenylphos-
phino)benzaldehyde were supplied by the Aldrich Chemi-
cal Company. Benzonitrile was purchased in 99% pure,
anhydrous form from Aldrich, vacuum distilled under Ar
Scheme 6, we reacted complex 8 with KOtBu in C6D6
under N2. In a surprising development, instead of the
production of an amido complex similar to the known amido
complex RuH{tmeP2(N)(NH)}, the b-diiminato complex 14
was produced along with the cis and trans-dihydrides. It is
now clear that the dihydrogen that must be used to produce
the dihydride complexes is transferred from the ligand of
complex 8 by a mechanism like the one shown in Scheme
10. The diamine complex 8 can provide five hydrogen atoms
in the process of producing complex 14.
˚
and stored over 4 A molecular sieves under Ar. The com-
plex RuHCl(PPh3)3 was prepared by the literature method
[38]. The tetradentate ligands ethP2(NH)2 and prP2N2 were
prepared by the literature method [15]. NMR spectra were
recorded on a Varian Unity-500 (500 MHz for 1H), a
Varian Unity-400 (400 MHz for 1H, 100 MHz for 13C,
121.5 MHz for 31P), a Mercury 400 (400 MHz for 1H,
100 MHz for 13C), or on a Varian Gemini 300 MHz spec-
The conversion of the amine complex 8 to complex 14
requires dehydrohalogenation and dehydrogenation steps.
We assume that reaction of 8 with base under Ar or N2 gives
initially the amido complex C. Such amido complexes are
known to undergo b-hydride elimination. This would pro-
duce a dihydride complex D that can transfer an equivalent
of dihydrogen to another molecule C to produce a dihydride
complex (12, 13) and an unsaturated amido complex E.
Complex E might also undergo b-hydride elimination to pro-
duce the trans-dihydride F that transfers dihydrogen to C to
produce more of the dihydrides 12 and 13 and the b-diimi-
nate complex 14. Reference [36] provides a precedent for
the reverse of step F to 14 in Scheme 10.
These methods of synthesis of the b-diiminatometal
complex 14 appear to be unprecedented [37]. Thus far,
the synthesis of b-diiminate ligands has generally involved
condensation reactions between primary amines and b-
diketones or 1,1,3,3-tetraethoxypropane, or the reaction
of metal alkyls with 2 equiv. of a nitrile or of metal 1-aza-
allyls with 1 equiv. of a nitrile [37]. Yet other methods have
included deprotonation of the b-diiminate precursor using
BuLi, or oxidation of an aliphatic diamine ligand in a metal
complex to the b-diiminate in basic media using either O2
or other oxidizing agents [30,32].
1
trometer (300 MHz for H, 121.5 MHz for 31P). All 31P
chemical shifts were measured relative to 85% H3PO4 as
an external reference. 1H chemical shifts were measured rel-
ative to partially deuterated solvent peaks but are reported
relative to tetramethylsilane. All infrared spectra were
obtained on a Nicolet 550 Magna-IR spectrometer. Micro-
analyses were performed at the University of Toronto;
however for each complex below the percent carbon was
low by 1–4% while the percent nitrogen and hydrogen were
acceptable. This appears to be a combustion problem, even
when V2O5 is added. X-ray data were collected on a Non-
ius Kappa-CCD diffractometer using Mo Ka radiation and
refined using SHELXTL 6.1 software.
Samples from catalytic tests were analyzed for conver-
sion using a Perkin–Elmer Autosystem XL gas chromato-
graph with a Chrompack capillary column ChirasilDex
CB (25 m ꢂ 0.25 mm). The carrier gas was H2 at a column
pressure of 5 psi, with an oven temperature of 130 °C,
injector temperature of 250 °C, and FID temperature of
275 °C. The injected sample volume was 1 lL.
3. Conclusions
Complexes 7 and 8 are active precatalysts for the hydroge-
nation of acetophenone and are moderately active for the
hydrogenation of nitriles and imines. The related complex
RuHCl{ethP2(NH)2} provides a more active catalyst. There-
fore the 6,5,6 combination of ring sizes appears to be supe-
rior to that of the 6,6,6 combination. A side reaction of
complexes 7 and 8 in the presence of base that may lead to
catalyst deactivation is the formation of the novel b-diimina-
to complex 14. See reference [36] for the other example of a
ruthenium diiminate complex. The proposed routes of
formation of this complex are unprecedented, but involve
reasonable isomerization and deprotonation events.
4.2. RuHCl{prP2N2} (7)
A solution of crude prP2N2 (382 mg) and RuHCl(PPh3)3
(540 mg, 0.53 mmol) in THF (18 mL) was refluxed under
Ar for 1.75 h. Filtration of the reaction mixture, repeated
washing with ether, and subsequent drying in vacuo pro-
1
duced a bright red powder. Yield: 276 mg, 69% yield. H
NMR (CD2Cl2, 400 MHz), d: 8.39 (d, N@C–H), 7.35–
6.90 (m, Ar–H), 4.68, 4.14 (broad s, N–CH2CH2CH2–N),
2.15 (m, N–CH2CH2CH2–N), ꢀ16.69 (t, Ru–H,
2JPH = 27.77 Hz). 13C{1H} NMR (CD2Cl2, 100 MHz), d:
2
164.17 (d, JC–P = 5.34 Hz, N@CH), 136.82 (s), 136.49
(s), 134.21 (broad s), 131.86 (s), 130.58 (d), 128.98 (s),
128.58 (s), 128.45 (s), 127.42 (d), 127.14 (d) (all Caromatic),
63.29 (broad s, CH2CH2CH2), 62.87 (broad s, CH2CH2
CH2), 29.52 (s, CH2CH2CH2). 31P{1H} NMR (CDCl3,
121.5 MHz), d: 64.49 (broad s, RuHCl{prP2N2}), 57.18
(broad s, RuHCl{prP2N2}), 44.74 (s, RuCl2 {prP2N2}).
IR (KBr, cmꢀ1): 1959 (m, m(Ru–H)), 1621 (m, m(C@N)).
4. Experimental
4.1. General
All preparations and manipulations were carried out
under hydrogen, nitrogen or argon atmospheres with the

F.N. Haque et al. / Inorganica Chimica Acta 361 (2008) 3149–3158
3157
Anal. Calc. for C41H37N2P2ClRu C, 65.12; H, 4.93; N,
3.70. Found: C, 61.06; H, 6.57; N, 4.47%.
(13). For the reaction with 7: 1H NMR (C6D6,
300 MHz), d: 8.67–6.84 (m, Ar–H), 5.84 (br s, Ar–H),
3.61, 2.92, 2.39 (br s, CH, NH), ꢀ5.02 (dd, Ru–H, 13),
ꢀ6.06 (t, Ru–H, 12), ꢀ16.60 (br s, Ru–H, 13). 31P NMR
(C6D6, 121.5 MHz), d: 76.40 (s, 13), 75.32 (s, 13), 69.79
(s, 12), 58.58 (s, 14), 42.20 (br s), 40.18 (s). For the reaction
with 8: 1H NMR (C6D6, 300 MHz), d: 8.71–6.55 (m, Ar–H,
N–CH2–Ar), 5.86 (br s, N–CH2–Ar), 2.84 (br s,
CH2CH2CH2, 13), 2.30 (br s, NH, 13), ꢀ5.04 (dd, Ru–H,
4.3. RuCl2{prP2N2} (9)
A solution of crude prP2N2 (130 mg) and RuCl2(PPh3)3
(198 mg, 0.206 mmol) in THF (25 mL) was refluxed under
Ar for 4.5 h. The reaction mixture was filtered to obtain a
dark red filtrate. The solvent was removed in vacuo from
the filtrate to leave a dark red sticky material. Crystals of
9 were obtained by recrystallizing this crude product from
chloroform. 31P{1H} NMR (CDCl3, 121.5 MHz), d: 44.77
(s). Anal. Calc. for C41H36N2P2Cl2Ru C, 62.28; H, 4.59;
N, 3.54. Found: C, 54.17; H, 4.08; N, 3.09%.
2
13, JPH = 25.5 Hz; 91.5 Hz), ꢀ6.22 (t, Ru–H, 12,
2JPH = 21 Hz), ꢀ16.85 (br s, Ru–H, 13). 31P NMR
(C6D6, 121.5 MHz), d: 75.62 (s, 13), 75.08 (s, 13), 70.44
(s, 12), 39.72 (br s).
4.7. RuH(diimP2) (14)
4.4. RuHCl{prP2(NH)2} (8)
Complex 7 (20 mg, 0.026 mmol) and KOtBu (6 mg,
0.053 mmol) were added to a NMR tube under N2. C6D6
(0.8 mL) was added and the tube shaken vigorously. The
mixture turned progressively darker to a very dark brown
colour. The mixture also increased in viscosity as a precip-
A mixture of prP2(NH)2 (200 mg, 0.321 mmol) and
RuHCl(PPh3)3 (329 mg, 0.324 mmol) in THF (12 mL)
was refluxed for 3.5 h under Ar. Filtration of the mixture
gave a yellow solid that was washed with ether and dried
in vacuo to give a bright yellow powder. Yield: 148 mg,
1
itate appeared. H NMR (C6D6, 400 MHz), d: 7.83 (m,
1
61%. H NMR (CD2Cl2, 400 MHz), d: 8.49–6.82 (m, Ar–
CH–CH–CH), 7.44, 7.07–6.71 (m, Ar–H), 5.13 (t, CH–
CH–CH, JHH = 6.77 Hz), 4.74 (m, CH2–NCHCHCHN–
H), 5.51 (broad s, Ar–H), 3.98 (broad s, HN–CH2), 3.92
(broad s, HN–CH2–Ar), 3.53–3.51 (s, HN–CH2–Ar),
3.19–2.76 (broad s, CH2–CH2–CH2), 2.02 (m, N–H), 1.84
2
CH2), ꢀ25.55 (t, Ru–H, JPH = 34.07 Hz). 31P NMR
(C6D6, 121.5 MHz), d: 58.72 (s). 13C NMR (C6D6,
100 MHz), d: 152.96 (s, C2), 134.87 (d), 129.43–128.37
(s), 127.25–126.82 (s) (Caromatic), 90.58 (s, C1), 72.49 (t,
(m, N–H), ꢀ18.75 (t, Ru–H, JPH = 28.96 Hz). 13C{1H}
2
NMR (CD2Cl2, 100 MHz), d: 140.62 (s), 140.27 (s),
137.81 (d), 135.56 (broad s), 130.36 (broad s), 127.76 (s),
127.52 (s), 127.32 (s), 126.96 (s), 126.06 (d) (Ar–CH2–
NH, Caromatic), 60.34 (broad s, CH2CH2CH2), 57.85 (broad
s,CH2CH2CH2), 29.60 (s, CH2CH2CH2). 31P NMR
3
C3, JPC = 8.5 Hz).
Acknowledgement
2
(CDCl3, 121.5 MHz), d: 66.64 (d, JPP = 29.2 Hz, RuHCl
An NSERC Discovery Grant to RHM supported this
work.
2
{prP2(NH)2}), 60.17 (d, JPP = 29.2 Hz, RuHCl{prP2
(NH)2}), 37.48 (broad s, RuCl2{prP2(NH)2}). 31P NMR
(CD2Cl2, 121.5 MHz), d: 67.74 (s), 61.21 (s). IR (KBr,
cmꢀ1): 1951 (m, m(Ru–H)), 2868 (m, m(N–H)). Anal. Calc.
for C41H41N2P2ClRu C, 64.77; H, 5.44; N, 3.68. Found:
C, 61.34; H, 5.40; N, 3.31%.
Appendix A. Supplementary material
CCDC 287142 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/
j.ica.2007.12.003.
4.5. RuCl2{prP2(NH)2} (10)
RuHCl{prP2(NH)2} (8) (50 mg) was dissolved in CHCl3
(1 mL) and the solution stirred for 2 h. Crystals of 10 were
then precipitated by vapour diffusion of diethyl ether. Anal.
Calc. for C41H40N2P2Cl2Ru C, 61.97; H, 5.07; N, 3.53.
Found: C, 59.16; H, 5.12; N, 3.28%.
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