Binuclear titanium(III) complex derived from diphenylphosphanylmalononitrile, [μ2(N,N′)-Ph2PC(CN)2TiCp2]2: Synthesis, structure and properties

Article abstract of DOI:10.1016/j.jorganchem.2007.06.025

Diphenylphosphanyl malononitrile, Ph₂P-CH(CN)₂ (1) reacts with Cp₂TiCl in the presence of triethylamine in THF to give air sensitive Ti(III) complex [μ²(N,N′)-Ph₂PC(CN)₂TiCp₂]

Full text of DOI:10.1016/j.jorganchem.2007.06.025

Journal of Organometallic Chemistry 692 (2007) 4157–4160
www.elsevier.com/locate/jorganchem
Binuclear titanium(III) complex derived from
diphenylphosphanylmalononitrile, [l2(N,N0)-Ph2PC(CN)2TiCp2]2:
Synthesis, structure and properties
Yuriy A. Min’ko, Natalia V. Belina, Vyacheslav V. Sushev, Georgy K. Fukin,
*
Mikhail P. Bubnov, Alexander N. Kornev
Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences, 49 Tropinin Street, 603950 Nizhny Novgorod, Russia
Received 5 May 2007; received in revised form 7 June 2007; accepted 13 June 2007
Available online 23 June 2007
Abstract
Diphenylphosphanyl malononitrile, Ph2P–CH(CN)2 (1) reacts with Cp2TiCl in the presence of triethylamine in THF to give air sen-
sitive Ti(III) complex [l2(N,N0)-Ph2PC(CN)2TiCp2]2 (2), which is centrosymmetric dimer in the solid state, containing nearly planar 12-
member metallocycle. Solution of 2 (200 K) exhibits anisotropic EPR spectrum; every spectral component contains splitting on a single
phosphorus nucleus.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Transition metal complexes; Titanium; Metallocenes; Malononitrile; Phosphinoamides; Imido-complexes; X-ray diffraction
1. Introduction
This promising ligand may show so far multiple reactiv-
ity, using phosphorus-, carbon- and nitrogen-active cen-
ters. However equilibrium concentration of ylide form 1c
is negligibly small. It is known that for the raise the stabil-
ity of ylide form more bulky substituents at phosphorus
(e.g. t-Bu) are required [3]. Interestingly, IR spectrum of
1 contains absorption bands in the NH region (our data:
3400 (m), 3185 (w)), which may be assigned to associated
and non-associated forms, and two very strong absorptions
at 2170 and 2122 cmꢀ1 which may be explained by the
presence of both cyano (C„N) and ketimido-groups
(@C@N–). To that note, that 1H NMR spectrum of 1 con-
sists of single resonance at 4.05 ppm (NH), while P–CH
fragment should give doublet due to splitting on phospho-
rus nucleus.
Hybrid ligands that contain both soft and hard donor
atoms are currently receiving increasing attention due to
their potentials for generating metal complexes with unu-
sual reactivity as well as bimetallic complexes containing
metals of different nature [1]. Diphenylphosphanyl-deriva-
tive of malononitrile, Ph2P–CH(CN)2 (1) [2] shows
dynamic behavior due to increased mobility of aliphatic
hydrogen.
N
N
NH
H
C
C
C
C
Ph2P
1b
Ph2P
1a
Ph2P
C
1c
Pure diphenylphosphanylmalononitrile is relatively sta-
ble compound while its solutions in THF show limited sta-
bility. So, yellow solution of 1 slowly turned deep red for a
period of a day at room temperature to give a mixture of
products, probably oligomers.
N
N
N
*
Corresponding author. Tel.: +7 8312 627795; fax: +7 8312 627497.
E-mail address: akornev@iomc.ras.ru (A.N. Kornev).
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.06.025

4158
Y.A. Min’ko et al. / Journal of Organometallic Chemistry 692 (2007) 4157–4160
Schwartz reagent [Cp2ZrHCl]n is known to react with
Triethylamine hydrochloride was filtered and the prod-
uct (2) was separated from concentrated filtrate in the man-
ner of greenish-violet crystals, extremely air sensitive.
IR spectrum of 2 in nujol displays two strong absorption
bands of CN groups at 2190, 2145 cmꢀ1. These values are
shifted for ꢁ20 cmꢀ1 as compared with the bands of free
ligand 1 (2170, 2122 cmꢀ1). The structure of 2 was con-
firmed by X-ray diffraction study on a suitable crystal
(Fig. 1). Molecule 2 represents centrosymmetric dimer in
crystal. Both titanium(III) atoms adopting tetrahedral con-
figuration are coordinated to two cyclopentadienyl rings
and two nitrogen atoms of two ketimido-forms of diphe-
nylphosphanylmalononitrile, which are bridge ligands.
12-Member metallocycle is nearly planar, with average
diphenylphosphanylmalononitrile leading to the corre-
sponding zirconocene ketimide complexes [2]. In this com-
munication we report another remarkable example of
fixation of ketimido form of 1 by its interaction with
Cp2TiCl.
2. Results and discussion
Starting diphenylphosphanylmalononitrile was pre-
pared by modified method [2]. Addition of a stoichiometric
amount of chlorodiphenylphosphine to NaHC(CN)2 (pre-
pared by the reaction of sodium bis(trimethylsilyl)amide,
(Me3Si)2NNa, with malononitrile) affords the correspond-
ing phosphino-derivative 1 in 90% preparative yield.
Interaction of 1 with g5-dicyclopentadienyltitanium(III)
chloride in THF in the presence of Et3N (molar ratio 1:1:1)
affords binuclear complex 2 in 60% preparative yield:
˚
deviation of 0.04 A from the plane. Crystal data and struc-
ture refinement for 2 are given in Table 1. Selected bond
lengths and angles for 2 are shown in Table 2. Carbon
atoms C(1), C(1A) adopt planar sp2 configuration with
sum of angles 360ꢁ and C(2)–C(1)–C(3) bond angle
116.95(15)ꢁ. The C–N bonds in the molecule {N(1)–C(2)
PPh2
NH
˚
1.159(2) and N(2)–C(3) 1.154(2) A} are nearly equivalent.
C
Cp2TiCl, THF, rt
Et3N
Similar justification of C–N bond distances in the bridge
(M N„C–CR@C@N–M) is observed in the copper(I)
dimer (Ph3P)2Cu[NC–C(CN)–CN]2Cu(Ph3P)2 [4] (C–N
N
N
Ph2P
1/2
Ti
Ti
- Et HCl
3N
N
N
C
C
˚
˚
N
1b
bond lengths are 1.153 A and 1.145 A in the bridge and
2
˚
PPh2
1.131 A in terminal CN group). So the found distances
Fig. 1. Molecular structure of 2, [l2(N,N0)-Ph2PC(CN)2TiCp2]2. Hydrogen atoms omitted for clarity.

Y.A. Min’ko et al. / Journal of Organometallic Chemistry 692 (2007) 4157–4160
4159
nucleus (31P, I = 1/2, 100%): A1 = 24.2 G; A2 = 16.7 G;
A3 = 6.9 G (Aav = 15.9 G). Calculated average g-factor
gav = 1.985 is in a good accordance with experimental
giso = 1.984. Titanium satellites are not observed probably
due to large line width. In general, g-factor values are typ-
ical for Ti3+ species [5]. Apparently, complex 2 dissociates
in solution and we observe its monomeric form. Coordina-
tion mode of ligand 1 in solution cannot be unambiguously
determined by EPR method. It should note however, that
similar phosphorous isotropic hyperfine coupling constant
(10.8 G) was observed in Cp2TiPMe2, containing direct
phosphorus–metal r-bond [6]. High value of hyperfine
coupling constant for 2 may be attributed to the p-conjuga-
tion in this system and electron–acceptor properties of the
ligand.
Table 1
Crystal data and structure refinement for 2
Empirical formula
Formula weight
Temperature (K)
C58H56N4O2P2Ti2
998.81
100(2)
0.71073
Monoclinic
P2(1)/c
13.2597(9)
8.7973(6)
21.3829(15)
91.145(2)
2493.8(3)
1044
˚
k (A)
Crystal system
Space group
˚
a (A)
˚
b (A)
˚
c (A)
b (ꢁ)
3
˚
V (A )
F(000)
Z
2
Dcalc (Mg mꢀ3
)
2493.8(3)
0.432
0.24 · 0.13 · 0.06
1.91–26.51
21211
5139 (0.0648)
5139/5/419
0.0406, 0.0791
0.0724, 0.0890
1.016
l (mmꢀ1
)
Crystal size (mm)
h Range (ꢁ)
Since Ph2P– group of phosphanylmalononitrile ligand
remains free of coordination, molecule 2 may be considered
as a synton or building block for synthesis of bimetallic
complexes and extended structures.
Reflections collected
Reflections unique (Rint
Data/restraint/parameters
R1, wR2 [I > 2r(I)]
R1, wR2 (all data)
Goodness-of-fit
)
3. Experimental
ꢀ3
˚
Largest difference in peak and hole (e A
)
0.406/ꢀ0.240
3.1. General procedures
The Cp2TiCl and (Me3Si)2NNa reagents are purchased
from Aldrich and used as received. All manipulations were
performed with rigorous exclusion of oxygen and moisture,
in vacuum or under an argon atmosphere using standard
Schlenk techniques. Infrared spectra were recorded on a
Perkin–Elmer 577 spectrometer from 4000 to 400 cmꢀ1 in
nujol. EPR spectra were recorded on a Bruker ER 200
D-SRC spectrometer with ER041 MR microwave bridge,
ER 4105 DR double resonator and ER 4111 VT variable
temperature unite.
Table 2
Selected distances (A) and angles (ꢁ) for 2
˚
Ti(1)–N(1)
Ti(1)–N(2)#1
Ti(1)–C(16)
Ti(1)–C(24)
P(1)–C(1)
2.143(2)
2.144(2)
2.347(2)
2.386(2)
1.797(2)
1.831(2)
1.159(2)
1.154(2)
1.392(2)
1.403(2)
N(1)–Ti(1)–N(2)#1
C(1)–P(1)–C(4)
C(1)–P(1)–C(10)
C(4)–P(1)–C(10)
C(2)–N(1)–Ti(1)
C(3)–N(2)–Ti(1)#1
C(2)–C(1)–C(3)
C(2)–C(1)–P(1)
C(3)–C(1)–P(1)
N(1)–C(2)–C(1)
N(2)–C(3)–C(1)
79.56(5)
105.24(8)
103.98(8)
98.97(8)
169.7(1)
170.3(1)
117.0(2)
124.9(1)
117.8(1)
179.6(2)
179.2(2)
P(1)–C(4)
N(1)–C(2)
N(2)–C(3)
C(1)–C(2)
C(1)–C(3)
The data for single crystal X-ray structure determina-
tion of 2 were collected on a SMART APEX diffractometer
(graphite-monochromated, MoKa-radiation, x–h-scan
Symmetry transformations used to generate equivalent atoms: #1:
ꢀx,ꢀy ꢀ 1,ꢀz.
˚
technique, k = 0.71073 A). The structures were solved by
direct methods and were refined on F2 using SHELXTL [7]
package. All non-hydrogen atoms were refined anisotropi-
cally and the hydrogen atoms in 2 were found from fourier
syntheses of electron density and were refined isotropically.
SADABS [8] was used to perform area-detector scaling and
absorption corrections. One solvate THF molecule was
found in asymmetric unit.
are much less than those usually observed for iminato
2
˚
groups C(sp )–C@N– (1.29–1.35 A) [2].
Bond angles N(1)–C(2)–C(1) and N(2)–C(3)–C(1) are
linear {179.6(2) and 179.2(2)ꢁ, respectively}. Carbon–car-
bon bond distances in malononitrile fragment {C(1)–C(2)
˚
1.392(2) and C(1)–C(3) 1.403(2) A} are close to that
observed in aromatic compounds.
3.2. Synthesis
Both diphenylphosphino-groups do not take part in
coordination to metal. Phosphorus–carbon bond distance
P(1)–C(1) 1.797(2) A corresponds to ordinary P–C bond.
3.2.1. NaHC(CN)2
˚
An equivalent of (Me3Si)2NNa (0.66 M solution in
THF, 3.0 mL) was added to the solution of malononitrile
in THF (0.13 g, 2.0 mmol) at ꢀ78 ꢁC. The resulting mix-
ture was stirred and allowed to warm slowly to room tem-
perature. The crystalline precipitate of sodium salt
(NaHC(CN)2) was filtered, washed with cold solvent and
dried in vacuum. Yield 0.16 g (92%). IR (nujol), m (cmꢀ1):
3511 (w), 3303 (w), 3073 (m, CH), 2142 (vs, CN), 1357
EPR spectrum of 2 in CH2Cl2/toluene (2/1) solution at
ambient temperature (290 K) is a single broad line
(ꢁ10 G, giso = 1.984) without hyperfine structure. At the
same time, frozen solution of 2 (200 K) exhibits anisotropic
EPR spectrum with main parameters of g-tensor:
g1 = 2.025; g2 = 1.987; g3 = 1.942 (Fig. 2). Every spectral
component contains splitting on a single phosphorus

4160
Y.A. Min’ko et al. / Journal of Organometallic Chemistry 692 (2007) 4157–4160
Fig. 2. EPR spectrum of 2 [CH2Cl2/PhMe (2:1), 200 K].
(m), 1250 (w), 1138 (s), 1073 (s), 910 (m), 842 (w), 723 (w),
634 (m), 545 (vs), 470 (s).
in vacuum line. Yield 0.27 g (60%). Anal. Calc. for
C54H48P2N4OTi2: C, 69.98; H, 5.22; P, 6.68, Ti, 10.34.
Found: C, 70.12; H, 5.18; P, 6.73; Ti, 10.28%. IR (nujol),
m (cmꢀ1): 2190 (m, CN), 2146 (s, CN), 1253 (m), 1068
(m), 1012 (m, Cp), 913 (m), 803 (s, Cp), 743 (m), 696
(m), 562 (w), 548 (m), 530 (w).
3.2.2. Ph2P–CH(CN)2 (or Ph2P–C(CN)@C@NH) (1)
A solution of Ph2PCl (1.10 g, 5.0 mmol) in THF (8 mL)
was added dropwise to the suspension of NaHC(CN)2
(0.44 g, 5.0 mmol) in the same solvent at ꢀ20 ꢁC. The reac-
tion mixture turned clear, and then precipitate (NaCl) was
formed (ca. 15 min). The mixture was slowly warmed to
room temperature over 0.5 h, filtered, and the solvent
was evaporated. The resulting solid residue was washed
with Et2O and pumped in a vacuum line over 1 h at
20 ꢁC to give 2 as a bright-yellow non-crystalline solid.
Yield: 90% (1.13 g). 31P{1H} NMR (THF): d = ꢀ6.0 ppm.
1H NMR (THF-d8): d = ꢀ7.00 to ꢀ8.00 (m, 10H, Ph) ppm;
4.05 (1H, NH) ppm. 13C NMR (THF-d8): d = 7.0–7.4 (m,
4. Supplementary material
CCDC 644157 contains the supplementary crystallo-
graphic data for 2. The data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-
336-033; or e-mail: deposit@ccdc.cam.ac.uk.
3
P–CH); 126.8 (s, p-Ph); 127.4 (d, JC,P = 6.4 Hz, m-Ph);
2
References
128.0–128.6 (m, CN); 132.1 (d, JC,P = 19.3 Hz, o-Ph),
1
142.1 (d, JC,P = 11.2 Hz, i-Ph) ppm. IR (nujol), m (cmꢀ1):
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1182 (m), 745 (s), 698 (s), 567 (s), 550 (s), 528 (m), 470
(w), 432 (w).
3.2.3. [[l2(N,N0)-Ph2PC(CN)2TiCp2]2 (THF solvate)
(2)
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A freshly prepared solution of 1 (0.25 g, 1.0 mmol) in
THF (10 mL) was added to the mixture of Cp2TiCl
(0.21 g, 1.0 mmol) and excess of Et3N (0.15 g, 1.5 mmol)
in the same solvent (5 mL) at 20 ꢁC. The resulting mixture
was stirred 2 h at room temperature. The crystalline precip-
itate of triethylammonium hydrochloride was filtered; the
solution was concentrated to 5 mL and maintained at
0 ꢁC. Dark green-violet crystals of 2 was filtered and dried
[6] J.G. Kenworthy, J. Myatt, P.F. Todd, J. Chem. Soc., Chem. Comm.
(1969) 263.
[7] G.M. Sheldrick, SHELXTL v. 6.12, Structure Determination Software
Suite, Bruker AXS, Madison, Wisconsin, USA, 2000.
[8] G.M. Sheldrick, SADABS v.2.01, Bruker/Siemens Area Detector
Absorption Correction Program, Bruker AXS, Madison, Wisconsin,
USA, 1998.