Synthesis and structures of two ruthenium dibenzoylmethanetriphenylphosphine mixed ligand complexes Hung Huy Nguyen•Nham Hoang• Ulrich Abram Received: 20 May 2009 / Accepted: 20 October
Trang 1Synthesis and structures of two ruthenium dibenzoylmethane
triphenylphosphine mixed ligand complexes
Hung Huy Nguyen•Nham Hoang•
Ulrich Abram
Received: 20 May 2009 / Accepted: 20 October 2009 / Published online: 12 November 2009
Ó Springer Science+Business Media B.V 2009
Abstract The reaction of dibenzoylmethane (HDBM)
with [RuCl2(PPh3)3] in benzene in the presence of a
sup-porting base (Et3N) under reflux gives two different
com-plexes, the side product as a green-yellow Ru(III) compound
of composition [RuIIICl2(DBM)(PPh3)2] (2) and the main
product as a red Ru(II) complex of composition [RuII(DBM)2
-(PPh3)2] (3) The products were studied by spectroscopic
methods, cyclic voltammetry and X-ray single crystal
dif-fraction The molecular structure of 2 shows a distorted
octahedral environment around the Ru atom with two
phos-phine ligands in trans positions The octahedral complex 3
shows a cis arrangement of two phosphine ligands
Introduction
To date, many ruthenium mixed-ligand complexes of
b-diketones and phosphines have been synthesized and
characterized [1 4] These complexes possess a diversity
of coordination modes including different isomeric types
and oligomeric compounds [5, 6] Some of them reveal
good catalytic effects [7, 8] and remarkable biological
activities [9,10] However, in spite of extensive work, only
a few fully structurally characterized ruthenium
b-diketo-nate complexes containing phosphines have been
pub-lished, so far [11–15]
In this paper, we report the synthesis, spectroscopic properties, electrochemistry and X-ray single crystal struc-tures of two ruthenium b-diketonate triphenylphosphine mixed ligand complexes, [RuIIICl2(DBM)(PPh3)2] (2) and [RuII(DBM)2(PPh3)2] (3) (where DBM-is dibenzoylmeth-anate) The formation of compound 2 has been reported before; however, its molecular structure was only deduced from spectroscopic evidence [16,17] Compound 3 is newly reported
Experimental
All reagents used in this study were reagent grade and used without further purification Solvents were dried and used freshly distilled unless otherwise stated For synthesis of the complexes, solvents were degassed with Ar for 30 min before use [{RuCl2(PPh3)3}2] was synthesized following a standard procedure [18]
Infrared spectra were measured as KBr pellets on a Shi-madzu FTIR-spectrometer between 400 and 4,000 cm-1 FAB?mass spectra were recorded with a TSQ (Finnigan) instrument using a nitrobenzyl alcohol matrix Elemental analysis of carbon and hydrogen were determined using a Heraeus vario EL elemental analyzer NMR spectra were taken with a JEOL 400 MHz multinuclear spectrometer Cyclic voltammetry measurements were performed on a PCI4 (Gamry Instruments) using a conventional three electrode cell with working and counter platinum wire electrodes and an Ag wire pseudo electrode The measure-ments were carried out in CH2Cl2solutions with a scan rate
of 0.1 V/s at T = 293 K with [n-Bu4N][PF6] as the sup-porting electrolyte Potentials are quoted relative to the Fc/Fc?couple used as internal reference (E1/2 = 0.55 V vs SCE)
H H Nguyen (&) N Hoang
Inorganic Chemistry Department, Hanoi University of Science,
Le Thanh Tong 19, Hanoi, Vietnam
e-mail: hunghuy@zedat.fu-berlin.de
U Abram
Institute of Chemistry and Biochemistry, Freie Universita¨t
Berlin, Fabeckstraße 34-36, 14195 Berlin, Germany
e-mail: abram@chemie.fu-berlin.de
DOI 10.1007/s11243-009-9299-4
Trang 2X-ray structure determination
The intensities for the X-ray structure determinations were
collected on a STOE IPDS 2T instrument with Mo Ka
radiation (k = 0.71073 A˚ ) The programs SHELXS97 [19]
and SHELXL97 [19] were used for the solution and
refine-ment of the structures Details concerning crystal data and
refinements are given in Table1 The structures were solved
with direct methods and subsequently completed by
differ-ence Fourier recycling All the non-hydrogen atoms were
refined anisotropically using full-matrix least-squares
tech-niques The hydrogen atoms were calculated for idealized
positions Comparably big voids between the large complex
molecules in the solid state structures are not occupied with
solvent molecules The highest peaks of electron density in
the final Fourier maps are\1 e/A˚3for both structures
Synthesis of the complexes
The reaction was carried out under Ar atmosphere A
solu-tion of [RuCl2(PPh3)3] (192 mg, 0.2 mmol),
dibenzoylme-thane (90 mg, 0.4 mmol) and Et3N (50 mg, 0.5 mmol) in
degassed benzene (20 mL) was refluxed for 5 h The
resulting precipitate was filtered off The volume of clear red
filtrate was reduced under vacuum to 2 mL, and then
n-hexane (20 mL) was added to precipitate a green–yellow
solid of [RuCl2(DBM)(PPh3)2], which was separated by
filtration The final filtrate was then dried under vacuum, and the residue was recrystallized from MeOH/CH2Cl2giving big red crystals of [Ru(DBM)2(PPh3)2]
Data for [RuCl2(DBM)(PPh3)2]
Yield: 5% (9 mg) Elemental Anal Found: C, 66.2; H, 4.1% Calcd for C51H41Cl2O2P2Ru: C, 66.6; H, 4.5% IR (cm-1): 3055 w (mCH), 1540 vs (mC=O), 1519 s (C=C), 1481 s (dCH), 1091 m (mRu–P), 745 s and 694 s (dCHphenyl),516
w (mMO); FAB?MS (m/z): 919 [M]?, 884 [M–Cl]?
Data for [Ru(DBM)2(PPh3)2]
Yield: 61% (131 mg) For analysis, the compound was dried under vacuum for 1 day Elemental Anal Found: C, 73.7 H, 4.8% Calcd for C66H52O4P2Ru: C, 73.9; H, 4.9%
IR (cm-1): 3055 w (mCH), 1542 vs (mC=O), 1516 s (C=C),
1481 s (dCH), 1091 m (mRu–P), 740 s and 694 s (dCH phe-nyl), 520 m (mMO).1H NMR (CDCl3; d, ppm): 6.16 (s, 2H, C–H), 6.8–7.4 (m, 50H, Car-H)31P NMR (CDCl3; d, ppm): 53.17 FAB?MS (m/z): 1072 [M]?
Results and discussion
The reaction of HDBM and a common precursor for the syn-thesis of ruthenium(II) compounds, namely [RuCl2(PPh3)3],
Table 1 Crystal and refinement
data for complexes 2 and 3 [RuCl2(DBM)(PPh3)2] (2) [Ru(DBM)2(PPh3)2] (3)
Formula C51H41Cl2O2P2Ru C66H52O4P2Ru
Temperature/K 200(2) 200(2) Crystal system; Space group Triclinic; P-1 Triclinic; P-1 Unit cell
V/A˚3; Z; Dcalc/g cm-3 2,075(4); 2; 1.472 2,878.6(7); 2; 1.237 Absorption coefficient/mm-1 0.626 0.374
Reflections collected 21,664 29,962 Independent reflections/Rint 11009/0.1814 15247/0.1596 Observed reflections [I [ 2r(I)] 4,600 5,042 Refined parameters 524 659 Goodness-of-fit on F2 0.861 0.856 R1(F)/wR2(F2) [I [ 2r(I)] 0.0790/0.1007 0.0880/0.1639 R1(F)/wR2(F2) (All data) 0.2056/0.1342 0.2297/0.2162 Largest diff peak and hole 0.810, -0.943 e/A˚3 0.950, -0.769 e/A˚3
Trang 3in benzene in the presence of a supporting base (Et3N) gives
two different complexes; a red complex of composition
[RuII(DBM)2(PPh3)2] (3) as the main product and a small
amount (about 5%) of a green-yellow complex of
composi-tion [RuIIICl2(DBM)(PPh3)2] (2) (Scheme 1)
The formation of complex 2 can be rationalized by the
oxidation of the mono DBM Ru(II) intermediate complex 1
by traces of oxygen (Scheme1) The formation of
com-plexes of type 2 was previously reported in the reactions of
[RuCl2(PPh3)3] and two equivalents of b-diketones in
boiling benzene under aerobic conditions [17] The
exchange of the second DBM ligand proceeds more slowly
Theoretically, both cis and trans isomers should be formed
However, due to its greater thermodynamic stability, the
cis product [RuII(DBM)2(PPh3)2] (3) was exclusively
obtained after extended reflux times Similar
transforma-tion of the trans isomer to the cis isomer was previously
reported for trans [RuII(Acac)2(PPh3)2] where Acac- is
acetylacetonate [5] The purity of two products was
con-firmed by elemental analysis, which gave good fits to the
expected molecular formulas
The infrared spectra of complexes 2 and 3 exhibit strong
bands in the 1540 cm-1 region but no absorptions at
1634 cm-1 where the mC=Ostretch is present in the
spec-trum of free HDBM This corresponds to a bathochromic
shift of about 100 cm-1 and indicates chelate formation
with a large degree of electron delocalization within the
chelate rings [20] FAB?mass spectra of both complexes
show intense peaks of the molecular ions with the expected
isotopic distributions A fragment resulting from the loss of
a chloro ligand appears in the spectrum of 2 The31P NMR
spectrum of 2 does not show any signal in the normal
chemical shift range, as expected for a paramagnetic
Ru(III) compound The 31P NMR spectrum of 3 contains
one singlet at 53.17 ppm, indicating that the two
triphen-ylphosphine ligands are magnetically equivalent The 1H
NMR spectrum of 3 reveals one broad singlet for the
methine proton at 6.16 ppm The aromatic protons appear
in the range between 6.8 ppm and 7.4 ppm
Figure1 is an ORTEP representation of 2 Selected bond lengths and angles are given in Table2 In 2, the Ru atom, which is coordinated by an O,O-bidentate DBM -ligand, two chloro ligands and two triphenylphosphines exhibits a distorted octahedral geometry Two triphenyl-phosphine ligands are in mutually trans positions The Ru atom, two oxygen atoms of the DBM- ligand and two chloro ligands are placed almost in the same plane with a maximal deviation from the mean least-squares plane of 0.029(3) A˚ for O1 The trans angles that are from 175.5 to 176.9° are only a little deviated from those of the ideal octahedral compound All the C–O and C–C distances in the chelate ring are between those expected for C–O, C–C single and double bonds, indicating delocalization of the p electrons Regarding this ligand arrangement, 2 is only
Ru O
Cl PPh3
PPh 3
Ru O O
PPh3 PPh3
Ru O
Cl PPh 3
PPh3
- HCl
0.25 O
2 , HCl
- 0,5 H2 O
- HCl
O O
2
3 1
HDBM
HDBM [RuCl2(PPh3)3]
Scheme 1
Fig 1 ORTEP representation [ 21 ] of [RuCl2(DBM)(PPh3)2] (2) with 40% probability ellipsoids The hydrogen atoms are omitted for clarity
Trang 4precedented by [RuIIICl2(HFA)(PPh3)2] where HFA is
hexafluoroacetylacetone [22] All Ru–O, Ru–Cl and Ru–P
bond distances of 2 are also in the same region as those in
[RuIIICl2(HFA)(PPh3)2]
The compound 3 is stable in the solid state as well as in
solution In the air, at room temperature, no significant
oxidation of 3 can be detected by means of NMR for at
least several days Single crystals of 3 suitable for X-ray
studies were obtained by slow evaporation of a CH2Cl2
-MeOH solution An ORTEP diagram of 3 is illustrated in
Fig.2, and selected bond lengths and angles are presented
in Table3 The structure of 3 shows that the Ru atom is
coordinated by two bidenate O,O-monoanionic DBM
-ligands and two PPh3ligands The arrangement around the
Ru atom is distorted octahedral; the trans angles fall in the
range between 166.4 and 173.2°, and two
triphenyl-phosphine ligands are mutually cis In this arrangement,
the two phosphine ligands are magnetically equivalent,
which results in a singlet in the31P NMR spectrum The
average Ru–O bond distance in 3 is slightly longer than
that in 2, consistent with the respective Ru oxidation states
of ?2 and ?3 Nevertheless, despite its lower oxidation
state, 3 has shorter average Ru–P bond distance than that
in 2 due to the trans effect of triphenylphosphine in the
latter complex Crystal structures with the same overall
geometry have been previously published for
cis-bis(acetylacetonato) bis(monodentate phosphine)
ruthe-nium(II) complexes that were synthesized from
cis-[Ru(Acac)2(l2-C8H14)2] starting material [5]
The redox behavior of these complexes revealed some
interesting features in their electrochemistry In dry CH2Cl2
under argon, the cyclic voltammograms of the complexes
show no reduction process from -1.2 V to 0.0 V However,
in the range between 0.0 V and 1.2 V, reversible oxidations
at 0.182 V (DEp = 92 mV) for 2 and 0.428 V (DEp =
88 mV) for 3, which are assigned to the oxidation of Ru(II) compounds to their corresponding Ru(III) species, are observed It is necessary to mention that at the same condi-tion, the DEp value of the Fc/Fc?couple is 83 mV The high oxidative potential of 3 is in good agreement with its stability
in air By contrast, the low potential of the reduction process
Table 2 Selected bond lengths (A ˚ ) and angles (°) for [RuCl 2
(DBM)-(PPh3)2] (2)
Bond lengths (A ˚ )
Ru–O(1) 2.003(5) Ru–P(2) 2.408(4)
Ru–O(5) 2.023(5) O(1)–C(2) 1.295(7)
Ru–Cl(1) 2.342(3) C(2)–C(3) 1.362(10)
Ru–Cl(2) 2.347(3) C(3)–C(4) 1.398(9)
Ru–P(1) 2.425(4) C(4)–O(5) 1.285(7)
Angles (°)
O(1)–Ru–O(5) 87.9(2) O(5)–Ru–P(2) 90.1(2)
O(1)–Ru–Cl(1) 176.4(2) Cl(1)–Ru–Cl(2) 95.5(1)
O(1)–Ru–Cl(2) 87.7(2) Cl(1)–Ru–P(1) 89.5(1)
O(1)–Ru–P(1) 92.1(2) Cl(1)–Ru–P(2) 88.6(1)
O(1)–Ru–P(2) 89.7(2) Cl(2)–Ru–P(1) 91.7(1)
O(5)–Ru–Cl(1) 88.9(2) Cl(2)–Ru–P(2) 91.0(1)
O(5)–Ru–Cl(2) 175.5(2) P(1)–Ru–P(2) 176.9(1)
O(5)–Ru–P(1) 87.5(2)
Fig 2 ORTEP representation [ 21 ] of [Ru(DBM)2(PPh3)2] (3) with 30% probability ellipsoids The hydrogen atoms are omitted for clarity
Table 3 Selected bond lengths (A ˚ ) and angles (°) for [Ru(DBM) 2 -(PPh3)2] (3)
Bond lengths (A ˚ ) Ru–O(1) 2.037(5) C(2)–C(3) 1.427(9) Ru–O(11) 2.042(5) C(3)–C(4) 1.369(10) Ru–O(5) 2.087(5) C(4)–O(5) 1.301(8) Ru–O(15) 2.052(5) O(11)–C(12) 1.297(8) Ru–P(1) 2.319(2) C(12)–C(13) 1.376(10) Ru–P(2) 2.307(2) C(13)–C(14) 1.413(10) O(1)–C(2) 1.275(7) C(14)–O(15) 1.282(8) Angles (°)
O(1)–Ru–O(5) 90.8(2) O(5)–Ru–P(2) 171.3(1) O(1)–Ru–O(11) 173.2(2) O(11)–Ru–O(15) 91.0(2) O(1)–Ru–O(15) 82.8(2) O(11)–Ru–P(1) 89.1(1) O(1)–Ru–P(1) 96.4(1) O(11)–Ru–P(2) 96.4(1) O(1)–Ru–P(2) 86.2(1) O(15)–Ru–P(1) 166.4(1) O(5)–Ru–O(11) 85.7(2) O(15)–Ru–P(2) 89.0(1) O(5)–Ru–O(15) 82.5(2) P(1)–Ru–P(2) 104.5(1) O(5)–Ru–P(1) 83.9(1)
Trang 5of 2 can explain the formation of this compound in the
presence of traces of oxygen (Fig.3)
Conclusion
Two air-stable complexes, [RuIIICl2(DBM)(PPh3)2] (2) and
[RuII(DBM)2(PPh3)2] (3) were isolated from the reaction of
HDBM and [RuCl2(PPh3)3] and structurally characterized
In both compounds, DBM-coordinates to the Ru center as
the expected bidentate ligand and forms distorted
octahe-dral complexes In 3, the Ru atom maintains the oxidation
state ?2 with two triphenylphosphines in a cis
arrange-ment, while 2 is a Ru(III) complex with two
triphenyl-phosphine ligands in trans positions
Supporting information
Crystallographic data for 2 and 3 have been deposited with the Cambridge Crystallographic Data Center as supple-mental publication numbers CCDC 732758 and CCDC
732759 Copies of the data can be obtained free of charge via http://www.ccdc.cam.ac.uk
Acknowledgments The authors would like to thank the Ministry of Science and Technology of Vietnam for financial support and Dr Adelheid Hagenbach (FU Berlin) for her kind help in the collection of the X-ray diffraction data.
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Fig 3 Cyclic voltammograms with scan rate 100 mV/s in CH2Cl2
-0.2 M (NBu4)[PF6] a [Ru III Cl2(DBM)(PPh3)2] (2); b [Ru II (DBM)2
-(PPh3)2] (3)