Preparation of imine complexes of ruthenium and osmium stabilised by [MCl(η 6-p-cymene)(PR3)]+ fragments

Article abstract of DOI:10.1016/j.jorganchem.2009.11.008

Imine complexes [MCl(η ⁶-p-cymene){η¹-NH{double bond, long}C(H)Ar}(PR₃)]BPh₄ (1-3) [M = Ru, Os; PR₃ = PPh(OEt)₂, PPh₂OEt; Ar = Ph, p-tolyl] were prepared by reacting MCl₂

Full text of DOI:10.1016/j.jorganchem.2009.11.008

Journal of Organometallic Chemistry 695 (2010) 574–579
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Preparation of imine complexes of ruthenium and osmium stabilised
by [MCl(
g
6-p-cymene)(PR3)]+ fragments
a
b
Gabriele Albertin a, , Stefano Antoniutti , Jesús Castro
*
a Dipartimento di Chimica, Università Ca’ Foscari Venezia, Dorsoduro 2137, 30123 Venezia, Italy
b Departamento de Química Inorgánica, Universidade de Vigo, Facultade de Química, Edificio de Ciencias Experimentais, 36310 Vigo (Galicia), Spain
a r t i c l e i n f o
a b s t r a c t
g g
6-p-cymene){
1-NH@C(H)Ar}(PR3)]BPh4 (1–3) [M = Ru, Os; PR3 = PPh(OEt)2,
6-p-cymene)(PR3) precursors with benzyl
6-p-cymene){g1
NH@CPh2}(PR3)]BPh4 (4–6) [M = Ru, Os; PR3 = PPh(OEt)2, PPh2OEt] were also prepared by allowing
MCl2(
6-p-cymene)(PR3) to react with Ph2C@NH in the presence of NaBPh4. The complexes were char-
acterised spectroscopically (IR, 1H, 13C, 31P, 15N NMR) and by X-ray crystal structure determination of
[RuCl(g 6-p-cymene){ 1-NH@C(H)-p-tolyl}{PPh(OEt)2}]BPh4 (1b).
Ó 2009 Elsevier B.V. All rights reserved.
Article history:
Received 16 October 2009
Received in revised form 6 November 2009
Accepted 9 November 2009
Available online 14 November 2009
Imine complexes [MCl(
PPh2OEt; Ar = Ph, p-tolyl] were prepared by reacting MCl2(
azide ArCH2N3 in the presence of NaBPh4. Benzophenone-imine complexes [MCl(
g
g
-
g
Keywords:
g
Imine complexes
p-Cymene
Ruthenium
Osmium
Phosphite
1. Introduction
complexes of ruthenium and osmium, in order to test the behav-
iour of organic azide towards this class of compounds. The results,
which allowed the synthesis of unprecedented N-protio imine
complexes stabilised by p-cymene metal fragments, are reported
here.
Reaction of organic azides RN3 toward transition metal com-
plexes have attracted considerable attention in recent years due
to the rich chemistry of these systems and the variety of complexes
which can be obtained [1–8]. In the first step of the interaction
between RN3 and the metal fragment, organic azide is believed
2. Experimental
to
g
1-coordinate to the metal centre and, in some cases, the corre-
sponding complexes have been isolated and characterised [6–8].
Extrusion of N2 from these intermediates gave terminal metal imi-
do complexes, a common final product from reactions of organic
azide with transition metal complexes [1,2d,4a,d,6]. Metal imine
species [M]–NH@C(H)Ar have also recently been obtained from
coordinate benzyl azide [M]–N3CH2Ar [9], after loss of N2. Insertion
of azide into a metal-hydride bond to give stable triazenide [M]–
N(H)NNR derivatives has been observed in tungsten and hafnium
complexes [2a,4c], and the insertion of RN3 into M–CO bonds to
give isocyanate is also known [1d,2d,f]. Lastly, tetraazabutadiene
[M]–RN@N–N@NR complexes have been prepared from reaction
of a metal fragment and an excess of organic azide [2c,3a,b,4a,b].
We are interested in the chemistry of ‘‘diazo” and ‘‘triazo” com-
plexes of transition metals [10] and have recently reported the
reactivity of Mn, Re, and Ir derivatives toward organic azides,
which yielded azide, imine, and tetraazabutadiene complexes [9].
Now we have extended these studies to include half-sandwich
2.1. General comments
All synthetic work was carried out in an appropriate atmo-
sphere (Ar, N2) using standard Schlenk techniques or a vacuum
atmosphere dry-box. Once isolated, the complexes were found to
be relatively stable in air, but were stored in an inert atmosphere
at ꢀ25 °C. All solvents were dried over appropriate drying agents,
degassed on a vacuum line, and distilled into vacuum-tight storage
flasks. RuCl3ꢁ3H2O and (NH4)2OsCl6 salts were Pressure Chemical
Co. (USA) products, used as received. Phosphites PPh(OEt)2 and
PPh2OEt were prepared by the method of Rabinowitz and Pellon
[11]. Benzyl and phenyl azides [12] were prepared following meth-
ods previously reported. The labelled C6H5CH215N3 azide was pre-
pared following the same method, by reacting Na[15NNN] (98%
enriched, CIL) with benzyl bromide, C6H5CH2Br. Equimolar mix-
tures of C6H5CH215NNN and C6H5CH2NN15N were obtained. Other
reagents were purchased from commercial sources in the highest
available purity and used as received. Infrared spectra were re-
corded on Perkin–Elmer Spectrum One FT-IR spectrophotometer.
NMR spectra (1H, 31P, 13C, 15N) were obtained on AC200 or AVANCE
* Corresponding author. Fax: +39 041 234 8917.
E-mail address: albertin@unive.it (G. Albertin).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.11.008

G. Albertin et al. / Journal of Organometallic Chemistry 695 (2010) 574–579
575
300 Bruker spectrometers at temperatures between ꢀ80
and +30 °C, unless otherwise noted. 1H and 13C{1H} spectra are re-
ferred to internal tetramethylsilane; 31P{1H} chemical shifts are re-
ported with respect to 85% H3PO4, while 15N with respect to
CH315NO2, in both cases with downfield shifts considered positive.
The COSY, HMQC and HMBC NMR experiments were performed
using their standard programs. The SwaNMR and iNMR software
packages [13] were used to treat NMR data. The conductivity of
10ꢀ3 mol dmꢀ3 solutions of the complexes in CH3NO2 at 25 °C were
measured with a Radiometer CDM 83. Elemental analyses were
determined in the Microanalytical Laboratory of the Dipartimento
di Scienze Farmaceutiche of the University of Padua, Italy.
2.3.2. [RuCl(g -
6-p-cymene){g1 15NH@C(H)C6H5}{PPh(OEt)2}]BPh4
(1a1)
This complex was prepared exactly like the related unlabelled
compound 1a, using C6H5CH215N3 as a reagent; yield 215 mg
(60%). IR (KBr pellet)
m .
NH: 3242 (m) cmꢀ1 1H NMR (CD2Cl2,
25 °C) d: ABXY spin system (A = 31P, B = 15N, X, Y = 1H), dX 8.71
(1H, NH), dY 8.15 (1H, @CH), JAB = 7.8, JAX = 2.3, JAY = 0.1,
JBX = 72.7, JBY = 0.94, JXY = 21.8 Hz, 7.57–6.87 (m, 30H, Ph), 5.58,
5.56, 5.48, 5.23 (d, 4H, Ph p-cym), 4.18, 4.05, 4.00 (m, 4H, CH2),
2.72 (m, 1H, CH p-cym), 2.06 (s, 3H, CH3 p-cym), 1.42, 1.41 (t,
6H, CH3 phos), 1.26, 1.24 (d, 6H, CH3 iPr) ppm. 31P{1H} NMR
(CD2Cl2, 25 °C) d: AB spin system, dA 147.1 ppm, JAB = 7.8 Hz.
13C{1H} NMR (CD2Cl2, 25 °C) d: 177.0 (d, J
¼ 72:5 Hz, @CH),
13C15N
165–122 (m, Ph), 115.34 (s, C1), 106.15 (s, C4), 92.48, 92.34,
89.01 (s, C3), 89.97, 89.91, 88.61, 88.50 (s, C2), 65.35, 64.8 (d,
CH2), 31.23 (s, CH p-cym), 22.4, 22.3 (s, CH3 iPr), 18.6 (s, CH3 p-
cym), 16.4 (d, CH3 phos) ppm. 15N NMR (CD2Cl2, 25 °C) d: ꢀ177.6
2.2. Synthesis of precursor complexes
Complexes MCl2(g6-p-cymene)(PR3) [M = Ru, Os; PR3 =
PPh(OEt)2, PPh2OEt] were prepared following the reported method
[14].
15N31
(dd) ppm, J
P = 7.8, J15N1H = 72.7 Hz.
2.3.3. [OsCl(p-cymene){g
1-NH@C(H)C6H4-4-CH3}{PPh(OEt)2}]BPh4
2.3. Synthesis of complexes
(3b)
An excess of 4-CH3C6H4CH2N3 (0.74 mmol, 0.62 mL of a 1.2 M
solution in ethanol) was added to solution of complex
2.3.1. [RuCl(
g
6-p-cymene){
g
1-NH@C(H)Ar}(PR3)]BPh4 (1, 2)
a
[PR3 = PPh(OEt)2 (1), PPh2OEt (2); Ar = C6H5 (a), 4-CH3C6H4 (b)]
An excess of the benzyl azide ArCH2N3 (1.2 mmol, 0.8 mL of a
1.5 M solution in ethanol) was added to a solution of the appropri-
OsCl2(g6-p-cymene)[PPh(OEt)2] (0.15 g, 0.25 mmol) in 5 mL of eth-
anol containing an excess of NaBPh4 (0.35 mmol, 0.12 g). The reac-
tion mixture was stirred for 36 h and then the solvent removed
under reduced pressure to about 2.5 mL. By slow cooling to
ꢀ25 °C of the resulting solution, a yellow solid separated out which
was filtered and crystallised from CH2Cl2 and ethanol; yield
ate complex RuCl2(
g
6-p-cymene)(PR3) (0.4 mmol) in ethanol
(10 mL) containing a slight excess of NaBPh4 (0.6 mmol, 0.205 g).
The reaction mixture was stirred for 24 h and then the solution
concentrated to about 4 mL by evaporation of the solvent under re-
duced pressure. By slow cooling to ꢀ25 °C of the resulting solution,
a yellow solid separated out which was filtered and crystallised
from CH2Cl2 and ethanol. Suitable crystals for X-ray analysis of
1b were obtained by slow diffusion of ethanol into a CH2Cl2 solu-
tion of the complex. Yield: 236 mg (66%) for 1a, 258 mg (71%) for
1b, 255 mg (68%) for 2b.
162 mg (65%). IR (KBr pellet) m
NH: 3253 (m) cmꢀ1. 1H NMR (CD2Cl2,
25 °C) d: 9.16 (d, br, 1H, NH), 8.04 (d, 1H, @CH), 7.55–6.87 (m, 29H,
Ph), 5.81, 5.75, 5.73, 5.52 (d, 4H, Ph p-cym), 4.16, 4.01, 3.98, 3.92
(m, 4H, CH2), 2.69 (m, 1H, CH p-cym), 2.44 (s, 3H, CH3 p-tol),
2.20 (s, 3H, CH3 p-cym), 1.43, 1.38 (t, 6H, CH3 phos), 1.29, 1.27
(d, 6H, CH3 iPr) ppm. 31P{1H} NMR (CD2Cl2, 25 °C) d: 99.2 ppm.
KM = 49.6
X
ꢀ1 molꢀ1 cm2. Anal. Calc. for C52H58BClNO2OsP
Compound 1a: IR (KBr pellet)
m
NH: 3252 (m) cmꢀ1
.
1H NMR
(996.49): C, 62.68; H, 5.87; Cl, 3.56; N, 1.41. Found: C, 62.50; H,
5.99; Cl, 3.37; N, 1.34%.
(CD2Cl2, 25 °C) d: 8.72 (d, br, 1H, NH), 8.15 (d, 1H, @CH), 7.58–
6.85 (m, 30H, Ph), 5.58, 5.56, 5.47, 5.23 (d, 4H, Ph p-cym), 4.18,
4.04, 4.00 (m, 4H, CH2), 2.72 (m, 1H, CH p-cym), 2.06 (s, 3H, CH3
p-cym), 1.42, 1.41 (t, 6H, CH3 phos), 1.26, 1.24 (d, 6H, CH3 iPr)
ppm. 31P{1H} NMR (CD2Cl2, 25 °C) d: 147.0 ppm. KM = 53.8
2.3.4. [RuCl(g g
6-p-cymene)( 1-NH@CPh2)(PR3)]BPh4 (4, 5)
[PR3 = PPh(OEt)2 (4), PPh2OEt (5)]
In a 25-mL three-necked round-bottomed flask were placed
X
ꢀ1 molꢀ1 cm2. Anal. Calc. for C51H56BClNO2PRu (893.30): C,
0.25 mmol of RuCl2(
(0.4 mmol, 137 mg), and 4 mL of ethanol. An excess of benzophe-
none-imine Ph2C@NH (0.5 mmol, 84 L) was added to the result-
ing suspension, which was stirred for 24 h. yellow solid
g
6-p-cymene)(PR3), an excess of NaBPh4
68.57; H, 6.32; Cl, 3.97; N, 1.57. Found: C, 68.49; H, 6.42; Cl,
3.75; N, 1.69%. Compound 1b: IR (KBr pellet) NH: 3247 (m)
cmꢀ1 1H NMR (CD2Cl2, 25 °C) d: 8.51 (d, br, 1H, NH), 8.08 (d, 1H,
m
l
.
A
JHH = 21 Hz, @CH), 7.58–6.86 (m, 29H, Ph), 5.59, 5.54, 5.44, 5.23
(d, 4H, Ph p-cym), 4.18, 4.01 (m, 4H, CH2), 2.69 (m, 1H, CH p-
cym), 2.41 (s, 3H, CH3 p-tol), 2.04 (s, 3H, CH3 p-cym), 1.41, 1.40
(t, 6H, CH3 phos), 1.25, 1.23 (d, 6H, CH3 iPr) ppm. 31P{1H} NMR
(CD2Cl2, 25 °C) d: 147.1 ppm. 13C{1H} NMR (CD2Cl2, 25 °C) d:
176.2 (s, @CH), 165–122 (m, Ph), 115.3 (s, C1), 106.2 (s, C4),
92.39, 92.32, 89.09 (s, C3), 90.12, 90.09, 88.69 (s, C2), 65.2, 64.7
(d, CH2), 31.24 (s, CH p-cym), 22.3, 22.2 (s, CH3 iPr), 21.89 (d,
CH3 p-tol), 18.64 (s, CH3 p-cym), 16.4 (d, CH3 phos) ppm.
separated out, which was filtered and crystallised from CH2Cl2
and ethanol. Yield: 213 mg (88%) for 4, 218 mg (87%) for 5.
Compound 4: IR (KBr pellet)
m .
NH: 3239 (m) cmꢀ1 1H NMR
(CD2Cl2, 25 °C) d: 8.80 (s, br, 1H, NH), 7.72–6.86 (m, 35H, Ph),
5.22, 5.21, 5.06, 5.05 (d, 4H, Ph p-cym), 4.25, 4.13 (m, 4H, CH2),
2.63 (m, 1H, CH p-cym), 1.98 (s, 3H, CH3 p-cym), 1.47, 1.46 (t,
6H, CH3 phos), 1.15, 1.14 (d, 6H, CH3 iPr) ppm. 31P{1H} NMR
(CD2Cl2, 25 °C) d: 145.2 ppm. 13C{1H} NMR (CD2Cl2, 25 °C) d:
185.24 (s, @CH), 165–118 (m, Ph), 118.09 (s, C1), 104.43 (s, C4),
91.34, 91.25, 89.36 (s, C3), 89.97, 89.94, 88.08 (s, C2), 65.96,
65.76 (d, CH2), 31.3 (s, CH p-cym), 22.69, 21.57 (s, CH3 iPr), 18.72
KM = 52.5
(907.33): C, 68.83; H, 6.44; Cl, 3.91; N, 1.54. Found: C, 68.66; H,
6.36; Cl, 3.72; N, 1.39%. Compound 2b: IR (KBr pellet) NH: 3269
(m) cm-1 1H NMR (CD2Cl2, 25 °C) d: 10.06 (d, br, 1H, NH), 8.61
X
ꢀ1 molꢀ1 cm2. Anal. calc. for C52H58BClNO2PRu
m
(s, CH3 p-cym), 16.5 (d, CH3 phos) ppm. KM = 52.5 X
ꢀ1 molꢀ1 cm2.
.
Anal. Calc. for C57H60BClNO2PRu (969.40): C, 70.62; H, 6.24; Cl,
3.66; N, 1.44. Found: C, 70.44; H, 6.35; Cl, 3.37; N, 1.56%. Com-
(d, 1H, JHH = 21 Hz, @CH), 7.65–6.87 (m, 34H, Ph), 5.77, 5.65,
5.45, 5.39 (d, 4H, Ph p-cym), 3.90–3.75 (m, 2H, CH2), 2.62 (m, 1H,
CH p-cym), 2.45 (s, 3H, CH3 p-tol), 2.07 (s, 3H, CH3 p-cym), 1.29,
1.26 (t, 3H, CH3 phos), 1.24, 1.21 (d, 6H, CH3 iPr) ppm. 31P{1H}
pound 5: IR (KBr pellet)
m .
NH: 3244 (m) cmꢀ1 1H NMR (CD2Cl2,
25 °C) d: 8.64 (s, br, 1H, NH), 7.67–6.87 (m, 40H, Ph), 5.42, 5.37,
4.99, 4.36 (d, 4H, Ph p-cym), 4.09, 3.77 (m, 2H, CH2), 2.67 (m, 1H,
CH p-cym), 2.12 (s, 3H, CH3 p-cym), 1.43 (t, 3H, CH3 phos), 1.23,
1.19 (d, 6H, CH3 iPr) ppm. 31P{1H} NMR (CD2Cl2, 25 °C) d: 128.3
NMR (CD2Cl2, 25 °C) d: 123.4 ppm. KM = 55.0
X
ꢀ1 molꢀ1 cm2. Anal.
Calc. for C56H58BClNOPRu (939.37): C, 71.60; H, 6.22; Cl, 3.77; N,
1.49. Found: C, 71.73; H, 6.12; Cl, 3.59; N, 1.40%.
ppm. KM = 53.6
X
ꢀ1 molꢀ1 cm2. Anal. Calc. for C61H60BClNOPRu

576
G. Albertin et al. / Journal of Organometallic Chemistry 695 (2010) 574–579
(1001.44): C, 73.16; H, 6.04; Cl, 3.54; N, 1.40. Found: C, 72.97; H,
6.13; Cl, 3.68; N, 1.31%.
3. Results and discussion
p-Cymene complexes MCl2(g6-p-cymene)(PR3) react with ben-
zyl azide, ArCH2N3, in the presence of NaBPh4, to give yellow solids
which were characterised as the imine derivatives [MCl(g6-p-cym-
2.3.5. [OsCl(g g
6-p-cymene)( 1-NH@CPh2){PPh(OEt)2}]BPh4 (6)
This complex was prepared exactly like the related ruthenium
ene){g
1-NH@C(H)Ar}(PR3)]BPh4 (1–3) (Scheme 1).
complexes 4, 5 and was crystallised from CH2Cl2 and ethanol; yield
214 mg (81%). IR (KBr pellet) m
NH: 3216 (m) cmꢀ1. 1H NMR (CD2Cl2,
The formation of imine complexes was somewhat unexpected,
but may be explained as due to the initial coordination of the ben-
zyl azide with the metal centre [9], to give an unstable azide deriv-
ative [A] (Scheme 2).
25 °C) d: 9.78 (s, br, 1H, NH), 7.64–6.87 (m, 35H, Ph), 5.88, 5.79,
5.23, 5.20 (d, 4H, Ph p-cym), 4.13, 4.09 (m, 4H, CH2), 2.54 (m, 1H,
CH p-cym), 2.11 (s, 3H, CH3 p-cym), 1.45 (t, 6H, CH3 phos),
1.18, 1.10 (d, 6H, CH3 iPr) ppm. 31P{1H} NMR (CD2Cl2,
Extrusion of N2 in the coordinate azide species [A] may give the
benzyl imido intermediate [B], which undergoes tautomerisation
(1,2-H shift) to afford the final imine derivatives 1–3. In order to
support the pathway of Scheme 2, we attempted either to isolate
the azide intermediate [A] or, at least, to obtain spectroscopic data
supporting its formation. Unfortunately, no evidence of coordina-
tion of ArCH2N3 was obtained by monitoring the progress of the
reaction by NMR spectra, and the only signals observed, in the case
of ruthenium, were those of the final imine complexes 1 and 2. In-
stead, in the case of osmium, when the reaction was carried out at
0 °C, we did isolate a raw product, the IR spectrum of which
25 °C) d: 99.5 ppm. KM = 50.1
X
ꢀ1 molꢀ1 cm2. Anal. Calc. for
C57H60BClNO2OsP (1058.56): C, 64.67; H, 5.71; Cl, 3.35; N, 1.32.
Found: C, 64.45; H, 5.61; Cl, 3.16; N, 1.44%.
2.4. X-ray crystallography
Crystallographic data were collected on a Bruker Smart 1000
CCD diffractometer at CACTI (Universidade de Vigo) using graphite
monochromated Mo Ka radiation (k = 0.71073 Å), and were cor-
rected for Lorentz and polarisation effects. The software SMART
[15] was used for collecting frames of data, indexing reflections,
and the determination of lattice parameters, SAINT [16] for integra-
tion of intensity of reflections and scaling, and SADABS [17] for
empirical absorption correction.
The structure was solved and refined with the Oscail program
[18] by direct methods and refined by a full-matrix least-squares
based on F2 [19]. Non-hydrogen atoms were refined with aniso-
tropic displacement parameters. Hydrogen atoms were included
in idealised positions and refined with isotropic displacement
parameters. Details of crystal data and structural refinement are
given in Table 1.
showed a band at 2190 cm-1, attributable to the mN of the coordi-
3
nate azide [9a]. The 1H NMR spectrum in CD2Cl2 revealed the pres-
ence not only of imine complex 3 as major product, but also of a
new species, slowly transforming into the imine, which may be
the hypothesised azide intermediate [A].
We also studied the reaction of MCl2(g
6-p-cymene)(PR3) with
phenyl azide, C6H5N3, but no stable complex could be isolated.
Phenyl azide, like benzyl, is probably not stabilised by the
+
ArCH2N3
NaBPh4, EtOH
Table 1
—
BPh4
M
M
PR3
Cl
PR
Crystal data and structure refinement for 1b.
3 H
Cl
Cl
N
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å3)
Crystal system
C52H58BClNO2PRu
907.29
293(2)
C
H
0.71073
Ar
1 - 3
Triclinic
ꢀ
Space group
P1
Scheme 1. M = Ru (1, 2), Os (3); PR3 = PPh(OEt)2 (1, 3), PPh2OEt (2); Ar = Ph (a), p-
tolyl (b).
Unit cell dimensions
a = 9.9778(10) Å
b = 11.1865(11) Å
c = 12.1480(12) Å
a
= 90.174(2)°
b = 106.724(2)°
= 112.967(2)°
+
c
Volume (Å3)
Z
Dcalc.
Absorption coefficient
F(0 0 0)
1185.4(2)
1
— N2
ArCH2N3
— Cl—
M
M
1.271 Mg/m3
PR3
Cl
PR3
N
0.460 mmꢀ1
Cl
Cl
N
N
474
Crystal size
h range for data collection
Index ranges
0.21 ꢂ 0.19 ꢂ 0.16 mm
1.77 to 28.06°
ꢀ13 6 h 6 13; ꢀ14 6 k 6 14;
ꢀ815 6 l 6 16
10 803
C
H
Ar
H
[ A ]
Reflections collected
Independent reflections
Reflections observed (>2
9683 [R(int) = 0.0282]
5542
+
+
r)
Data completeness
0.971
Absorption correction
Max. and min. transmission
Refinement method
Semi-empirical from equivalents
1.000 and 0.828
Full-matrix least-squares on F2
9683/3/538
M
M
PR3
N
PR
3 H
Cl
Cl
N
Ar
H
Data/restraints/parameters
Goodness-of-fit on F2
0.870
C
C
H
Final i indices [I > 2
r
(I)]
R1 = 0.0496 wR2 = 0.0723
R1 = 0.1043 wR2 = 0.0861
ꢀ0.03(2)
Ar
H
R indices (all data)
1 - 3
Absolute structure parameter
Largest diff. peak and hole
[ B ]
0.527 and ꢀ0.547
(e Åꢀ3
)
Scheme 2.

G. Albertin et al. / Journal of Organometallic Chemistry 695 (2010) 574–579
577
p-cymene fragment [MCl(g6-p-cymene)(PR3)]+ and, as in this case
imine formation is prevented, it does not give isolable complexes.
Imine complexes of ruthenium and osmium are rare and, apart
from Taube’s pentaamine [Os(NH3)5{NH@C(H)CH3}]+ complex
[20a], only a few examples are known [20b,c] and none contains
a half-sandwich fragment. The reaction of benzyl azide with phos-
phite-containing p-cymene precursors MCl2(g6-p-cymene)(PR3)
(M = Ru, Os) allows the easy synthesis of stable mono-substituted
imine derivatives 1–3.
[14,23,24] and also show the different trans effect of the other li-
gands. Ru–C(4) and Ru–C(3), trans to the phosphorus atom, are
the longer ones. The Ru–C(1) bond involving the isopropyl-substi-
tuted carbon atom is also remarkably elongated. In any case, the
longer one corresponds to the methyl substituted carbon atom, a
feature described in the literature as the expected [25]. The dis-
tance from the ruthenium atom to the centroid of the benzene ring
of the cymene ligand (Ct) is 1.738(14) Å, virtually the same value as
that found between the best cymene plane and the metal atom,
1.737(2) Å. The rms value for this plane is 0.030, with maximum
deviation of C(2) by 0.040(4) Å. This atom, labelled as C(2), is a
non-substituted carbon atom, may be considered trans to the chlo-
ride atom, and is the shorter R–C bond found in the compound. The
orientation of the p-cymene ligand is such that the phosphorus and
chlorine atoms may be viewed as eclipsed with the Ru–C bonds
(see Fig. S1) and the P–Ru–Ct–C(6) and Cl–Ru–Ct–C(4) torsion an-
gles of 15.6(3)° and 16.4(3)°, respectively, and, consequently, the
Ru–P and Ru–Cl bonds are trans to Ru–C bonds. However, the
Ru–N are not eclipsed with Ru–C(2) bond, and the N–Ru–Ct–C(2)
and N–Ru–Ct–C(3) torsion angles are 25.4(3)° and ꢀ35.3(4)°,
respectively.
N-Protio imine complexes 1–3 were isolated as yellow solids,
stable in air and in solution of polar organic solvents, where they
behave as 1:1 electrolytes [21]. The complexes were characterised
spectroscopically (IR and 1H, 31P, 13C, 15N NMR) and by X-ray crys-
tal
structure
determination
of
[RuCl(g -
6-p-cymene){g1
NH@C(H)C6H4-4-CH3}{PPh(OEt)2}]BPh4 (1b), whose ORTEP is
shown in Fig. 1. The structure of the complex consists of a ruthe-
nium atom
g
6-coordinated to a p-cymene molecule, one chlorine
atom, one diethoxyphenylphosphine bonded through the phos-
phorus atom and one benzylideneamine (bonded through the
nitrogen atom:
g
1-NH@C(H)C6H5) leading to the formation of a
‘‘three-legged piano stool’’ structure.
The geometry of the complex is octahedral and marked by near
90° values for angles N(11)–Ru–P(3), 87.7(1); Cl–Ru–P(3), 85.22(6)
and N(11)–Ru–Cl; 81.2(1)°. This last value may be surprisingly
short, but there are more than twenty compounds in the CCDC
database (CSD version 5.30 with February 2009 updates) [22] con-
taining a RuCl(p-cymene)LL0 residue, where L and L0 are not chelat-
ing ligand, with Cl–Ru–L angles below 82°. In at least seven of
these, L is a monodentated N-donor ligand [23].
The Ru–N bond length is 2.059(5) Å, significantly shorter
than the values found, for example, for complexes RuCl2(p-cym-
ene)(p-NH2–C6H4–Cl), 2.173(2) Å [23c] or RuCl2(p-cymene)(p-
NH2–CH2C6H5), 2.144(2)
Å [23e]. Such values are found in
ruthenium-p-cymene complexes when the nitrogen atom is in-
volved in delocalised systems, such as azides or polypyridines
[26]. The C@N bond distance of the benzylideneamidate ligand,
1.260(7) Å, is the same as that found in an iridium complex
[9a] and slightly shorter than that found in a tungsten complex
[27]. For the time being, at the best of our knowledge, those
The average Ru–C bond distance is 2.235(7) Å (Table 2). These
bond lengths are close to those in other related complexes
two complexes are the only transition metal
g
1-benzylideneam-
idate complexes crystallographically described in the literature.
Again, the C–N–metal angle, 138.7(4)°, and N–C–C angle,
128.6(6)°, are surprisingly large for an sp2-hybridised N atom,
but similar values have been found for the above-mentioned
complexes.
Cl
The Ru–Cl bond length is 2.393(2) Å, matching literature values
well [14,23,24], and does not require further comment. The Ru–P
bond length, 2.293(2) Å, is slightly shorter than lengths found for
other phosphine RuCl(p-cymene) complexes [24a,28], but longer
than that of the phosphito compound [Ru(g6-p-cymene)(-
P{OPh}3)Cl2], 2.2642(8) Å [29]. The disposition of the substituents
of the phosphorus atoms in the phosphonite ligand is such that
the phenyl ring is situated over the position occupied by the NH
group. The dihedral angle N(11)–Ru–P(3)–C(21) is only ꢀ10.2(3)°
(see Fig. S2).
Ru
N11
P3
C11
The IR spectra of imine complexes [RuCl(
NH@C(H)Ar}{PPh(OEt)2}]BPh4 (1–3) show
band at 3269–3247 cm-1, attributed to the
g
6-p-cymene){g1
medium-intensity
NH of the imine ligand.
-
a
Fig. 1. ORTEP drawn of the cation of 1b. Hydrogen atoms and the substituents on
the phosphorus atom are omitted for clarity. Thermal ellipsoids are drawn at 30%
probability level.
m
The 1H NMR spectra confirm the presence of this ligand, showing a
slightly broad doublet between 10.04 and 8.50 ppm, attributed to
the @NH imine proton, and a sharp doublet at 8.63–8.04 ppm due
to the @CH imine resonance. In the spectrum of the labelled
Table 2
complex [RuCl(g6-p-cymene){ 1 15NH@C(H)C6H5}{PPh(OEt)2}]BPh4
g -
Selected bond lengths [Å] and angles [°] for 1b.
(1a1) the NH broad doublet splits into a multiplet, due to coupling
with both 15N and 31P of the phosphite. The spectrum can be simu-
lated using an AXBY model (A = 31P, X = 1H, B = 15N, Y = CH) with the
parameters reported in the Section 2. The J15N1H value of 72.7 Hz is as
expected for imine, whereas J1H1H of 21.8 Hz suggests a trans
arrangement of the imine ligand, like those observed in the solid
state.
Ru–P(3)
Ru–N(11)
Ru–C(1)
Ru–C(3)
Ru–C(5)
2.2933(17)
2.059(5)
2.259(6)
2.252(7)
2.202(5)
Ru–Cl
2.3929(17)
1.738(14)
2.186(5)
2.298(5)
2.213(5)
Ru–Ct01
Ru–C(2)
Ru–C(4)
Ru–C(6)
N(11)–C(11)
N(11)–Ru–P(3)
N(11)–Ru–Cl
Ct01–Ru–Cl
1.260(7)
87.72(13)
81.19(14)
126.6(6)
138.7(4)
C(11)–C(12)
Cl–Ru–P(3)
Ct01–Ru–P(3)
Ct01–Ru–N(11)
N(11)–C(11)–C(12)
1.458(7)
85.22(6)
130.7(5)
129.0(7)
128.6(6)
Also diagnostic for the presence of the ArC(H)@15NH ligand is
the proton-coupled 15N NMR spectrum, which appears as a doublet
C(11)–N(11)–Ru
of doublets at ꢀ177.6 ppm, owing to coupling with both 1H and 31
P
Ct represents the centroid of the benzene ring of the p-cymene ligand.
nuclei, fitting the presence of the imine ligand.

578
G. Albertin et al. / Journal of Organometallic Chemistry 695 (2010) 574–579
Ph
Ph
+
article can be found, in the online version, at doi:10.1016/
j.jorganchem.2009.11.008.
C
NH
—
BPh4
M
M
PR3
Cl
PR
NaBPh4, EtOH
3 H
Cl
Cl
N
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4 - 6
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with dichloro precursors MCl2(
parameters of the N-protio imine complex of ruthenium
[RuCl( are
6-p-cymene){ 1-NH@C(H)-p-tolyl}{PPh(OEt)2}]BPh4
g
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g
g
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The financial support of MIUR (Rome)-PRIN 2008 is gratefully
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