Synthesis, physicochemical analysis of two new hemilabile ether-phosphine ligands and their first stable bis-ether-phosphine/cobalt(II) tetrahedral complexes

Article abstract of DOI:10.1016/j.molstruc.2016.12.023

New tridentate ether-phosphine {P, 2O} and ether-phosphine oxide {OP, 2O} ligands with P and O donor-atoms have been synthesized starting from ClCH₂CH(OCH₃)₂. The oxidation process of Ph₂PCH₂CH(OCH₃)₂ to its oxide derivative Ph₂P([dbnd]O)CH₂CH(OCH₃)₂ was monitored by ³¹P NMR for the first time. The desired ligands and their Co(II) complexes structures were deduced from IR, EA, MS, NMR, UV–Vis., TG/DTG and XRD physical measurements. The tridentate chelating coordination behavior of the ether-phosphine wasn't detected leading only to the mono-dentate coordination mode through the phosphorous atoms to set up a X₂Co[η¹-Ph₂PCH₂CH(OCH₃)₂]₂ as final isomer formula (X?=?Cl or Br). The Cl₂Co[η¹-Ph₂PCH₂CH(OCH₃)₂]₂ isomer belongs to complex 1 was supported by single crystal measurement. Polar/non-polar intermolecular short contacts were detected by XRD and Hirshfeld surface theoretical analysis.

Full text of DOI:10.1016/j.molstruc.2016.12.023

Accepted Manuscript
Synthesis, physicochemical analysis of two new hemilabile ether-phosphine ligands
and their first stable bis-ether-phosphine/Cobalt(II) tetrahedral complexes
Ismail Warad, Assem Barakat
PII:
S0022-2860(16)31313-8
10.1016/j.molstruc.2016.12.023
MOLSTR 23221
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 8 September 2016
Revised Date: 6 December 2016
Accepted Date: 7 December 2016
Please cite this article as: I. Warad, A. Barakat, Synthesis, physicochemical analysis of two new
hemilabile ether-phosphine ligands and their first stable bis-ether-phosphine/Cobalt(II) tetrahedral
complexes, Journal of Molecular Structure (2017), doi: 10.1016/j.molstruc.2016.12.023.
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ACCEPTED MANUSCRIPT
Synthesis, physicochemical analysis of two new hemilabile ether-phosphine
ligands and their first stable bis-ether-phosphine/Cobalt(II) tetrahedral
complexes
Ismail Warad1,* and Assem Barakat2,3
1Department of Chemistry, AN-Najah National University P.O. Box 7, Nablus, Palestine.
2Department of Chemistry, College of Science, King Saud University, P. O. Box 2455,
Riyadh 11451, Saudi Arabia.
3 Department of Chemistry, Faculty of Science, Alexandria University, P.O. Box 426,
Ibrahimia, Alexandria 21321, Egypt.
Abstract
New tridentate ether-phosphine {P, 2O} and ether-phosphine oxide {OP, 2O} ligands
with P and O donor-atoms have been synthesized starting from ClCH2CH(OCH3)2. The
oxidation process of Ph2PCH2CH(OCH3)2 to its oxide derivative Ph2P(=O)CH2CH(OCH3)2
was monitored by 31P-NMR for the first time. The desired ligands and their Co(II) complexes
structures were deduced from IR, EA, MS, NMR, UV-Vis., TG/DTG and XRD physical
measurements. The tridentate chelating coordination behavior of the ether-phosphine wasn’t
detected leading only to the mono-dentate coordination mode through the phosphorous atoms
to set up a X2Co[η1-Ph2PCH2CH(OCH3)2]2 as final isomer formula (X = Cl or Br). The
Cl2Co[η1-Ph2PCH2CH(OCH3)2]2 isomer belongs to complex 1 was supported by single
crystal measurement. Polar/non-polar intermolecular short contacts were detected by XRD
and Hirshfeld surface theoretical analysis.
Keywords: Cobalt(II) complexes; P~O Hemilabile ligands; XRD; Hirshfeld surface analysis.
*
Corresponding author. Tel. +00970923410003. E–mail address: warad@najah.edu

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Introduction
The hemilability concept in chelate ligands possessing hard and soft donor atoms
combination, P-and O or N donor atoms composed a very famous families of such ligands [1-
6]. Particularly, ether-phosphine hemilabile as hybrid ligand (P-O) can stabilize varieties of
metal ions complexes, including the geometries and their oxidation states through bidentate or
multidentate coordination modes [3-8]. Indeed, the phosphorus donor π-acceptor stabilizes
metal ions center in a low oxidation state, while the oxygen σ-donor atom makes the center
more susceptible to higher oxidation state reactions. Such features played a critical role in
controlling geometries and oxidation state of metal ions center [4-7]. Due to the hemilabile of
P~O(N) ligands, the O or N σ-donor is generated like a unique intramolecular solvent
behavior preventing degeneration of the desired complexes through vacant coordination sites
preservation [5-12]. Furthermore, the steric and electronic variety of such hemilabile ligands
allow to possess potentially multi-dentate mode of coordination. Mononuclear or homo-/
hetero-, bi- or polymetallic complexes were also isolated [4-11].
As a part of our outstanding studies on preparation of ether-phosphine ligands and
their ruthenium(II) complexes for carbonyl compounds hydrogenation process [9-12], we here
like to presence the synthesis, spectral characterization, thermal and solid state analysis of the
(2,2-dimethoxyethyl)diphenylphosphine, (2,2-dimethoxyethyl)diphenylphosphine oxide and
their tetrahedral X2Co[η1-Ph2PCH2CH(OCH3)2]2 complexes structures.
Experimental
Materials, instrumentations and procedure
The reactions were performed in Argon inert-atmosphere by using Schlenk-line
system. Cobalt(II) salts, ClCH
2
CH(OCH3)
2
and Ph PK available from Sigma–Aldrich,
2

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beforehand, hexane, CH2Cl2, and diethyl ether were distilled over calcium hydride, lithium
aluminum hydride and from sodium / benzophenone, respectively.
1
“31P{1H}, 13C{1H}, and H NMR spectra were recorded on a Bruker DRX250
1
spectrometer at RT. Frequencies: H NMR 250.12 MHz, 13C{1H} NMR 62.9 MHz, and
1
31P{1H} NMR 101.25 MHz. Chemical shifts in the 13C{1H} and H NMR spectra were
measured relative to TMS using CDCl3 as deuterated solvent. p were measured relative to
85% H3PO4 (δ = 0). IR data was recorded on a Bruker IFS 48 FT-IR spectrometer. Mass
spectra: EI-MS; Finnigan TSQ70.” Elemental analyses were carried out on an Elementar
Varrio EL analyzer. FAB-MS; Finnigan 711A (8 kV), modified by AMD and reported as
mass/charge (m/z). The Hirshfeld surface theoretical calculation of complex 1 was performed
using CRYSTAL EXPLORER 3.1 program [13].
Procedure to synthesis of the (2,2-dimethoxyethyl)diphenylphosphine and (2,2-
dimethoxyethyl)diphenylphosphine oxide and their cobalt(II) complexes
(2,2-Dimethoxyethyl)diphenylphosphine
30.0 mmol of ClCH
2
CH(OCH3)
2
in (15 mL) dry THF was drop-wise added (within 60
PK solution
min.) to 30.0 mmol of Ph PK in 50 ml of dry THF until all the red color of Ph
2
2
was totally vanished, during addition the temperature of reaction was kept constant to 0 °C.
Subsequently, at room temperature, the mixture was stirred for 3h to ensure the reaction
completeness. Degassed saturated with NH
reaction mixture, using separatory funnel. The organic layer that contains the ligand was
separated then dried over MgSO drying agent. After evaporation the solvent under vacuum,
4
Cl aqueous solution ~80 mL was placed to the
4
the viscous colorless oily air-sensitive pure ligand product was isolated in a good yield.
Yield: 84%. MS: m/z = 274.22 (M+). FT-IR (KBr, cm−1): 3160 (vPhH) and 2950 (vCH). 1530
(vC=C). UV-visible absorption: λmax = 245 nm. Using CDCl3 solvent, 31P{1H} NMR: δp

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1
(ppm) –22.20. H NMR: δ (ppm) 2.45, 2.48 (d, J = 6.1 Hz, 2H, PCH2), 3.29 (s, 3H, CH3O),
13
4.42 (t, J = 5.2 Hz, H, O2CH), 7.00–7.60 (2 m, 15H, Ar-H). C{1H} NMR: δ (ppm) 32.87,
33.03 (d, 1C, PCH2), 52.85 (s, 2C, OCH3), 102.60, 102.70 (d, 1C, O2CH), 128.7–137.9 (4 m,
12C, Ar). Elemental analysis, Calculated for C16H19O2P. C, 70.06 and H, 6.98%. Found: C,
69.73 and H, 6.65%.
(2,2-Dimethoxyethyl)diphenylphosphine oxide
1.0 g of Ph2PCH2CH(OCH3)2 was dissolved in 60 ml of dichloromethane in 200 ml
Erlenmeyer flask in an open atmosphere and at room temperature the solution was stirred for
31
3 h, by time, samples were taken and subjected to P NMR, in order to monitor the reaction
conversions. Finally, the solvent was evaporated under vacuum and air-insensitive colorless
powder was collected.
o
Yield: 92%. MS: m/z = 290.29 [M+]. m.p = 53 C, IR (KBr, cm−1): 3120 (vPhH) and 2920
(vCH). 1125 (vP=O). 1410 (vC=C), UV-visible absorption: λmax = 255 nm. Using CDCl3
solvent, 31P{1H} NMR: δp (ppm) 28.7. 1H NMR: δ (ppm) 2.67 (t, J = 6.2 Hz, 2H, PCH2), 3.20
13
(s, 3H, CH3O), 4.82 (t, J = 5.0 Hz, H, O2CH), 7.20–7.90 (2 m, 15H, Ph-H). C{1H} NMR:
δ (ppm) 34.70, 35.40 (d, 1C, PCH2), 52.85 (s, 2C, OCH3), 100.32, 100.44 (d, 1C, O2CH),
128.7–139.1 (4 m, 12C, Ar). Calculated for C16H19O3P. C, 66.20 and H, 6.60; %. Found: C,
66.05 and H, 6.45%.
Complexes preparation
The desired complexes were prepared by mixing 40 ml ethanolic solutions of CoX2.6H2O
with equivalent amount of (2,2-dimethoxyethyl)diphenylphosphine in inert atmosphere. Orange

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solution is formed after 5 min. The reaction mixture was stirred for 1.0 h at room temperature
and inert atospehere before it concentrated to ~ 3 ml volume under vacuum, adding 40 ml of
hexane to the concentrated mixture cases the desired complexes to precipitate, the precipitate
was filtered (P4), washed (30 ml of diethyl ether) then finally dried under vacuum.
CoCl2.6H2O (1.0 mmol) in 20 ml of EtOH was mixed with (2,2-dimethoxyethyl)-
diphenylphosphine (2.1 mmol) in 20 ml of EtOH to produce complex 1. 88% Yield of light
o
orange powder, m.p 180 C. FAB-MS (m/z) 677.2 [M+] (theoretical 677.8). Calc., for
C32H38Cl2CoO4P2: C, 56.65 and H, 5.60. Found: C, 56.38 and H, 5.47%.
CoBr2.6H2O (1.0 mmol) was treated with (2,2-dimethoxyethyl)diphenylphosphine (2.1 mmol)
to produce complex 2. 80% Yield, light brown powder, m. p. = 160 oC. FAB-MS (m/z) 764.2
(theoretical 764.9) [M+]. Anal. Calc., for C32H38Br2CoO4P2: C, 50.09 and H, 4.99. Found: C,
49.88 and H, 4.87%.
X-ray structural analyses for complex 1
Crystals of complex 1 was grown by slowly diffusion of Et2O solvent into a solution
of complex 1 dissolved in CH2Cl2. The XRD data was collected at 173(2) K on a BRUKER
APPEX-II CCD diffractometer, using graphite mono-chromated Mo-Kα radiation (λ =
0.71073 Å). Details of crystal data is illustrated in Table 1. Direct methods were served to
solve the structure using SHELXS-97 program [14].

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Table 1. Structure refinement and crystal data for complex 1
Results and discussion
Synthesis of the Ph2PCH2CH(OCH3)2 ether–phosphine, ether–phosphine oxide
Ph2P(P=O)CH2CH(OCH3)2 and ( ether–phosphine)2Cobalt(II) complexes
Tridentate ether-phosphine {P, 2O} hybrid ligand was prepared by reacting equivalent
amount of 2-chloro-1,1-dimethoxyethane with Ph2PK in dry THF under inert atmosphere, as
seen in Scheme1. The prepared ligand showed a high sensitivity to atmospheric oxygen, the
ether–phosphine oxide was form directly by subjecting the ether-phosphine to an open

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atmospheric oxygen under stirring conditions. The oxidation reaction of ether-phosphine to
ether-phosphine oxide was monitored by 31P NMR.
When the ether-phosphine ligand was treated with CoX2.6H2O salt (X = Cl or Br) in
EtOH (Scheme 1), the X2Co[η1-Ph2PCH2CH(OCH3)2]2 complexes are formed directly in very
high yields. The complexes showed somewhat air-sensitivity in solution, while in solid state
they are stable for months. The desired complexes found to be soluble in alcohol,
dichloromethane, chloroform and water solvents and insoluble in most of aliphatic
hydrocarbons.
Scheme 1. Synthesis of hemilabile ligands and their complexes.
Mass Spectral Studies
Mass spectra of the Ph2PCH2CH(OCH3)2, Ph2P(=O)CH2CH(OCH3)2 ligands, complex
1 and complex 2 exhibited molecular ion peak [M]+, m/z at 274.22, 290.29, 677.2 and 764.2,
respectively, corresponding to their molecular weights, the full fragments pattern of complex
2 was illustrated in Figure 1.
Figure 1 reported a typical FAB-MS spectrum of complex 2. Good agreement between
+
real structure formula and expected molecular ion [M ] m/z = 764.2 (764.8 theoretical) with a

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58% peak intensity was recorded. Relevant fragments seen in the spectrum (Figure 1)
+
+
reconcile to m/z at 684.2 (20%) [M-Br] and 606.2 (20%) [M-2Br]
Figure 1. FAB-MS of complex 2.
X-Ray structural determination of complex 1
To collect better insight on structural parameters, complex 1 was subjected to X-ray
structural investigation since good crystals were collected. The crystal structure and packing
mode are presented in Figure 2 and 3, respectively.

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Figure 2. ORTEP of complex 1 with labelled atoms. Thermal ellipsoids are drawn at the 50%
probability level.

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Figure 3. A crystal packing of complex 1 viewed along the crystallographic a axis.
The complex crystallizes as Cl2Co[η1-Ph2PCH2CH(OCH3)2]2 isomer with approximate C2v
symmetry. In the complex structure, cobalt exhibited distorted tetrahedral geometrical
coordination, being surrounded by the phosphprous atoms belong to ether-phosphine in
monodetate coordination mode and two chloride ions ligands, relevant angles and bond
distances are collected in Table 2.

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Table 2. Selected bond distances (Å) and, angles (o) of complex 1.
An analysis of the packing showed seveal polar short intermolecular contacts, the molecules being
separated by Co—Cl….Hph and -CH2)2—O…..HCHP as well as normal van-der-Waals
distances. The complex crystallize in the triclinic/P-1 space group with two molecules per
asymmetric unit.
Hirshfeld surface analysis for complex 1
Using the cif file crystal structure information of complex 1 Hirshfeld surface
theoreticalx caclualation was carried out, the sufficient intermolecular forces and atomsinside
/atomoutside fingerprint map interactions were figured out as in Figure 4 and 5 respectively.
Figure 4 showed surfaces mapped over a dnorm, de and di [15-17]. The red dark-spots on the
dnorm surface may reveal the short interatomic contacts, i.e., Co—Cl….HPh with distance =
2.839 Å with four interactions per molecule and -CH2)2—O…..HCHP with distance 2.708 Å
with two interactions per molecule, the other interactions cited as light-spots, i.e., C—
H…..H/C due to several van-der-Waals interactions [17-18].

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Figure 4. dnorm on Hirshfeld surface intermolecular forces of complex 1.
The 2D-fingerprint plots over the Hirshfeld surfaces of complex 1 revealed the most important
differences between the interaction patterns. Total interactions, H…H (64.3 %), H…Cl (5.6 %),
H…C (4.8 %) and H…O (3.5 %) were illustrated in Figure 5. The detailed fingerprints
intermolecular interaction between atoms inside and outside in molecules were presented in
Table 3

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Figure 5. Hirshfeld surface atom per atom fingerprint with their dnorm of complex 1.

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Table 3. Inside/outside intermolecular interaction percentage by atoms.
100% Hinside
Clinside Oinside Cinside Pinside
Coinside
Houtside
64.3
10.4
7.5
17.0
0
10.4
7.5
0.3
0
17.0
0
0
0
0
0
0
0
0
0
0
0
0
0
Cloutside
Ooutside
Coutside
Poutside
Coinside
0
0
0
0
0
0.7
0
0.7
0
0
0
0
0
NMR of the Ph2PCH2CH(OCH3)2 and Ph2P(P=O)CH2CH(OCH3)2 ligands
The 1H NMR spectra belong to the desired ether–phosphine Ph2PCH2CH(OCH3)2 and
ether–phosphine oxide Ph2P(P=O)CH2CH(OCH3)2 ligands characterized several sets of
signals, phenylic and aliphatic protons were recorded. The correlations between O2CH and
CH2P function groups in the desired ligands were established by 2D-H,H-COSY experiments,
chemical shifts and the splitting of the signals together with integrations of the 1H resonances
are in accordance with ligands compositions, as seen in S1, (for ether-phosphine ligand).
The 13C{1H} NMR spectrum collaborated the schemed structures illustrated in Scheme
13
1. C signals belong to aliphatic and aromatic ether-phosphine carbons are recorded, as seen
in S2, (see the experimental part).
The stepwise oxidation of ether-phosphine to ether-phosphine oxide is monitored by
31P{1H} NMR spectroscopy. The signal of ether-phosphine at δ
p
= -22.2 ppm was displanced to
the positive phosphine oxide chemical shift (δ = 28.7 ppm) due to the oxide-phosphine new
p
double bond fomation (see Scheme 1 and S3). Complete oxidation was recorded after 2h from
stirring of 0.1g of ether-phosphine dissolved in 40 ml of chloroform at RT open atomsphere, look
up Figure 8c S3, which reflects the degree of air-sensitivity of such ligand.

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Electronic spectra and solvatochromism of desired complexes
In order to demonstrate the effect of solvent on the coordination structures around
Co(II) species, UV–Vis. spectroscopy was performed for the desired complexes in different
suitable solvents.
The spectra of the desired complexes in chloroform revealed typical tetrahedral
coordination around the Co2+ center, having several maxima from ~550 to 750 nm, due to the
4A2(F)→4T1(P) electron transition, as seen in Figure 6, significantly higher values than the
4T1g(F)→4T1g(P) octahedral electron transition with splitting belongs to either doublet state
transitions effects or spin-orbit coupling [19-23].
Complex 1 in chloroform has absorptions at 580, 645 and 785 nm (sh) see Figure 6a,
while complex 2 shows absorptions at 610 (sh), 650 and 780 nm see Figure 6b.
Figure 6. Vis. spectra of: a) complex 1 and b) complex 2 dissolved in chloroform at RT.

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In ethanol, the tetrahedral structure of complex 1 exhibited four weak maxims with higher
chemical shift, an extra absorptions in the “octahedral region” ~550 nm was recorded, an
additional coordination of ethanol solvent [20-24], leading to octahedral Co(P)2Cl2(EtOH)2
complex formation toghther with the orginal tetrahedral Co(P)2Cl2 complex, see Figure 7b.
Typical pure octahedral [Co(P)2Cl2(H2O)2] coordinated around Co2+ center was recorded
when complex 1 was dissolved in water (strong polar solvent), all the maxims (in chloroform or
EtOH solvents) were replaced by one broad maximum at ~600 nm, see Figure 7c.
Figure 7. Vis. spectra of complex 1: a) in chloroform, b) in EtOH, c) in water at RT.
FT-IR investigation
The FT-IR spectra of the desired ether-phosphine and its complexes were compared
under identical measurement conditions, as seen in S4, three main sets of functional groups
stretching vibrations in the ranges 3600-3300 (special in complexes), 3150-3050 and 2900-

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2700 cm-1, which assigned to H2O, Ph-H, and alkyl-H groups, respectively. Appearance of
two new bands at 440 and 420 cm-1 in the complexes spectra only (not in the free ligand) were
due to ν(Co-P) new bond formation.
Thermogravimetric analysis of complex 1
o
The weigh lost of complex 1 over 0–1000 C temprature range was carried out at 10
oC min-1 heating rate and in an open atomsphere. The TG/DTG spectrum of complex 1
proceed through two steps of Wt. loss mechanism (Figure 8). The first step is the major one,
o
80% of the complex Wt. was lost over 180-250 C temp. range, due to destruction of the two
ether-phosphine ligands from the desired complex structure ended to CoCl2 complex (79%,
theoretical wt. loss). The second step was removing of Cl ions from CoCl2 and reacting with
atomspheric oxygen to preduce cobalt oxide (as final products), occuring at 430-620 oC with a
10.5% Wt. lost (theoretical 10%).
Figure 8. TG-DTG thermal curves of complexes 1.

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Conclusion
Novel tridentate ether-phosphine {P, 2O}, ether-phosphine oxide {OP, 2O} and their
tetrahedral Co(ƞ1ether-phosphine)2X2 complexes (X= Cl or Br) were synthesized and
spectrally characterized. 31P-NMR was investigated to monitor the oxidation process of
Ph2PCH2CH(OCH3)2 to Ph2P(=O)CH2CH(OCH3)2. The tetrahedral Cl2Co[η1-Ph2PCH2CH-
(OCH3)2]2 structure was solved by X-ray single crystal and showed Triclinic unit cells with P-
1 space group. Solvatochromism (solvents effect) on complexes revealed the formation of
pure tetrahedral structure Co(P)2Cl2 in dichloromethane, mixed tetrahedral and octahedral
structure Co(P)2Cl2(EtOH)2 in ethanol, meanwhile in water, a pure octahedral structure
Co(P)2Cl2(H2O)2 was detected. Together XRD and Hirshfeld surface theoretical analysis
confirmed the formation of several polar and non-polar intermolecular short contacts in the
crystal lattice of complex 1. Complex 1 exhibited a good thermal stability with two steps
thermal decomposition mechanism.
Acknowledgements
The authors extend their appreciation to the Deanship of Scientific Research at King Saud
University for funding the work through the research group project Number (RGP- 257 - 1435-
1436). I. W. thanks Prof. Avelino Corma for UPV-CSIC. De los Naranjos, Spain for providing
free X-ray measurement and for his continuous encouragement.
Appendix A. Supplementary materials
“Crystallographic data for the structural analyses have been deposited with the
Cambridge crystallographic data center, CCDC No. 1486394. These data can be obtained free
of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from thee CCDC, 12 union Road,
Cambridge CB2 IEZ, UK; fax: +44-1223-33633; e-mail: deposit@ccdc.ca.ac.uk)”.

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Highlights
•
New tridentate ether-phosphine, ether-phosphine oxide ligands and their Co(II)
complexes were made available
•
•
The NMR, spectral, solvatochromic, CV and thermal properties were reported
Complex 1 was solved by XRD crystal structure as novel cis-Cl2Co[η1-
Ph2PCH2CH(OCH3)2]2 Tetrahedral geometry