A 4-acyl-5-pyrazolone ligand (HQ) in N-unidentate coordination mode in a Rh(CO)2Cl(HQ)-type complex

Article abstract of DOI:10.1016/j.inoche.2003.11.009

A new rhodium(I) dicarbonyl compound containing a neutral 4-acylpyrazolone bonded in N-unidentate fashion has been synthesized and structurally characterized.

Full text of DOI:10.1016/j.inoche.2003.11.009

Inorganic Chemistry Communications 7 (2004) 235–237
www.elsevier.com/locate/inoche
A 4-acyl-5-pyrazolone ligand (HQ) in N-unidentate
coordination mode in a Rh(CO)2Cl(HQ)-type complex
a
a
a,
a,
*
Augusto Cingolani , Fabio Marchetti , Claudio Pettinari *, Riccardo Pettinari
,
b
Brian W. Skelton , Allan H. White
b
a
Dipartimento di Scienze Chimiche, Universitꢀa degli Studi di Camerino, via S. Agostino 1, I-62032 Camerino, MC, Italy
Department of Chemistry, The University of Western Australia, Crawley, Western Australia 6009, Australia
b
Received 29 October 2003; accepted 8 November 2003
Published online: 3 December 2003
Abstract
A new rhodium(I) dicarbonyl compound containing a neutral 4-acylpyrazolone bonded in N-unidentate fashion has been
synthesized and structurally characterized.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Rhodium; b-Diketonate; X-ray; Carbonyl complexes; Tautomerism
Rhodium complexes containing P- and N-ligands and
their catalytic properties have been extensively investi-
gated for many years [1]. Complexes containing b-
diketonate or pyrazole ligands have recently attracted
increasing attention because of their catalytic properties
in reactions such as hydroformylation [2] and hydrob-
oration [3], and because, in some cases, they present li-
quid crystal behavior [4]. 4-Acyl-5-pyrazolones are a
family of heterocyclic proligands analogous to b-dike-
tones which also exhibit keto-enol tautomerism. We
have previously investigated their interaction with Rh(I)
and Rh(III) and in all of the species described to date
containing these pyrazole-type ligands, they have always
been coordinated in anionic O2-chelating mode [5,6].
In order to explore the possibility of an alternative
coordination mode for HQ-type ligands, we have now
synthesized both the tautomeric forms of 1-phenyl-3-
methyl-4-(2-furoyl)-pyrazol-5-one) (HQO). The interac-
tion of the ketonic/anionic form of HQO (prepared
according to the literature [5] with [Rh(CO)2Cl]2 in
methanol in the presence of a base such as triethylamine
or sodium methoxide) yields the derivative
[Rh(CO)2(QO)] (1) [7], analogous to other Rh(I)dicar-
bonyl-b-diketonates previously reported [5a,6,8]. How-
ever, the reaction of the enolic form of HQO (obtained
upon recrystallization from CHCl3/Et2O) with
[Rh(CO)2Cl]2 in the same conditions yields the deriva-
tive [Rh(CO)2(Cl)(HQO)] (2) [9]. The yield is improved if
the reaction is carried out in petroleum ether in the
absence of base. We have found that compound 2 can-
not be obtained by using the ketonic form of HQO, and,
similarly, that compound 1 was always afforded when
the ketonic form of HQO was employed. We have also
investigated the reaction of both forms of HQO with
[Rh(III)(Cp*)Cl2]2 (Cp* ¼ pentamethylcyclopentadienyl)
(3) [10]. It is interesting to note that both enolic and ke-
tonic forms of HQO are unreactive towards Rh(III) in the
absence of base, whereas in the presence of base
the complex [Rh(III)(Cp*)Cl(QO)] (3) is afforded [10].
The same compound can be obtained in higher yield
when the sodium salt NaQO reacts with [Rh(III)(Cp*)
Cl2]2 in toluene.
The complexes 1–3, air- and solution-stable, non-
electrolytes in dichloromethane and acetone solution,
have been fully characterized by IR and NMR spec-
troscopy. It is notable that only slight differences have
been detected in the IR spectra of 1–2, both ligand C@O
* Corresponding author. Tel.: +39-0737-402234; fax: +39-0737-
637345.
E-mail addresses: claudio.pettinari@unicam.it (C. Pettinari),
riccardo.pettinari@unicam.it (R. Pettinari).
1387-7003/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2003.11.009

236
A. Cingolani et al. / Inorganic Chemistry Communications 7 (2004) 235–237
The structure of 2 is of interest, being a cis-complex
[Rh(CO)2Cl(QOH)], (Fig. 1(a)). The ligand, with an in-
tramolecular hydrogen bond O(41) ꢁ ꢁ ꢁ HO(5) 1.70(4),
0
ꢁ
2.508(2) A, now no longer functions as an O; O -chelate,
but, rather, a unidentate N-donor. The rhodium envi-
ronment is four-coordinate planar, Rh–Cl,N(2),
ꢁ
C(01,02) 2.3564(6), 2.118(2), 1.853(2), 1.855(2) A, there
being no perceptible difference in the Rh–C(carbonyl)
distances, despite the disparate nature of their trans-at-
oms. The plane of the Rh environment is considerably
twisted about the Rh–N(2) bond relative to the C3N2
ligand plane (interplanar dihedral angle 71.89(6)°), a
perhaps remarkable result (consequent upon intramo-
Fig. 1. (a) A single molecule of 2, projected normal to the C3N2 plane.
(b) Unit cell content of 2, projected down a.
and C@N bands being only slightly shifted with respect
to those of the free enolic HQO. Two very similar strong
CBO absorptions have been found at ca. 2080 and 2010
cmꢀ1 in the IR spectra of 1 and 2. The most obvious
difference is the presence of the Rh–Cl stretching vi-
bration, easily detectable at 309 cmꢀ1 in the spectrum of
2 and absent in that of 1, while the NMR chemical shifts
of the 3-methyl and ortho-phenyl protons of the ligand
appear to distinguish between an N- or O-bonded Q
1
ligand. In the H NMR spectrum of 1 the ortho phenyl
and methyl protons are at 8.30 and 2.31 ppm, respec-
tively, close to those found in similar O2-bonded com-
plexes, whereas a significant downfield shift for the
methyl (2.71 ppm) and a highfield shift for the ortho
phenyl protons (8.0 ppm) have been found. The IR and
NMR spectra of compound 3 indicate O2-chelation by
the anionic ligand, the rhodium(III) center being in a
pseudooctahedral environment. The N-unidentate co-
ordination of HQO in 2 has been confirmed by a single
crystal X-ray study [11].
Fig. 2. (a, b) Unit cell contents of HQO projected down c; a, respec-
tively. (c) Molecule 1 of HQO (molecule 2 is similar).

A. Cingolani et al. / Inorganic Chemistry Communications 7 (2004) 235–237
237
6.85–6.87, 7.06, 7.30–7.33, 8.29–8.33 (m, 5H, N–C6H5 and 2H,
CHFur).13C NMR (C6D6, 293 K): d, 17.73 (s, 3-CH3), 112.70,
118.66, 121.15, 126.23, 129.38, 139.39, 145.70, 148.30, 151.37, (s,
N–C6H5 and CHFur), 163.70 (s, C5), 173.41 (CO).
lecular steric effects?) in the light of the crystal packing
(Fig. 1(b)); the pendant C(1n)6 plane is pitched at
46.9(8)° to the C3N2 plane, the C(4,41,411)O(41) dihe-
dral being 3.43(8)°, the latter plane in turn effectively
coplanar with its C4O pendant (1.77(8)°). Within the
ligand, cf. the deprotonated chelate form, C(5)–O(5) and
C(4)–C(41) are lengthened, with N(1)–C(5) shorter, the
most profound angular changes being about C(4) and
C(5) in response to the change in O(41) ꢁ ꢁ ꢁ O(5) ÔbiteÕ.
The structure of the free ligand is also recorded [12].
Two molecules comprise the asymmetric unit of the
structure, with similar stacking up one of the lattice axes
(Fig. 2). Geometries of free and complexed HQO and the
chelating anion are compared at length in [13].
In conclusion, we have here demonstrated for the first
time the possibility of obtaining metal derivatives con-
taining 4-acylpyrazolone ligands, coordinated by the
pyridinic nitrogen to ÔsoftÕ metals with the ligand in the
neutral enolic form, IR and NMR spectroscopic mea-
surements assisting in assigning O2- or N-coordination.
[8] F. Huq, A.C. Skapski, J. Cryst. Mol. Struct. 4 (1974) 411;
F. Bonati, G. Wilkinson, J. Chem. Soc. (1964) 3156.
[9] Synthesis of [Rh(CO)2(HQO)Cl] (2). A light petroleum (40–60°C)
solution (30 mL) containing [Rh(CO)2Cl]2 (0.190 g, 0.48 mmol)
and HQO (0.270 g, 0.96 mmol) was stirred 24 h under reflux to give
a yellow precipitate. The residue obtained was recrystallized from
CH2Cl2 and shown to be compound 2 (0.321 g, 0.67 mmol, 71%
yield). M.p. 160–162 °C. Anal. Calc. for C18H11ClN2O5 Rh, 45.64;
H, 2.34; N, 5.91. Found: C, 45.37; H, 2.64; N, 6.03. IR (nujol,
cmꢀ1): 2082, 2013 s t(C ꢁ ꢁ ꢁ O), 1601s, 1583s, 1567s, 1538sbr, 1505w
t(C ꢁ ꢁ ꢁ C, C ꢁ ꢁ ꢁ N), 501m, 390m, 352m, 309m. 1H NMR (C6D6,
293 K): d, 2.83 (s, 3H, 3-CH3), 5.91, 6.78 (m, 2H, CHFur), 7.05–
7.17, 7.4, 7.79 (m, 5H, N–C6H5 and 1H, CHFur).1H NMR
(CH2Cl2, 293 K): d, 2.99 (s, 3H, 3-CH3), 6.81–6.84 (m, 1H,
CHFur), 7.58–8.12 (m, 5H, N–C6H5 and 2H, CHFur).1H NMR
((CH3)2CO), 293 K): d, 2.71 (s, 3H, 3-CH3), 6.94 (m, 1H, CHFur),
7.49–8.19 (m, 5H, N–C6H5 and 2H, CHFur ). 13C NMR (CH2Cl2,
293K): d, 19.38 (s, 3-CH3), 113.71, 121.07, 128.00, 130.07, 131.07,
134.78, 148.07, 151.18, 152.56 (s, N–C6H5 and CHFur), 162.62 (s,
C5), 180.14 (CO).
[10] Synthesis of [RhCp*(QO)Cl] (3). A toluene solution (5 mL)
containing [RhCp*Cl2]2 (0.054 g, 0.087 mmol) and NaQO (0.050
g, 1.74 mmol) was stirred overnight under N2 at room temper-
ature to give a red precipitate, which was filtered off and washed
with 5 mL of toluene. The red–orange residue obtained was
recrystallized from 1:1 CH2Cl2/light petroleum (40–60 °C) and
shown to be compound 1 (0.130 g, 0.24 mmol, 60% yield). M.p.
200–203 °C. Anal. Calc. for C25H26ClN2O3Rh, C, 55.52; H, 4.85;
N, 5.18. Found: C, 54.4; H, 4.5; N, 4.90. IR (nujol, cmꢀ1): 1604s,
1591s, 1579s, 1520m t(C–C, C–N), 514w, 459w, 279m, 267w. 1H
NMR (CDCl3, 293 K): d, 1.67 (s, 15H, CH3Cpꢂ), 2.13 (s, 3H, 3-
CH3), 6.54–6.57m, 7.13–7.57m, 7.96–8.00d (5H, N–C6H5 and 3H,
CHFur). 13C NMR (CDCl3, 293 K): d, 8.90 (s, CH3Cpꢂ), 17.07 (s,
3-CH3), 92.39, 92.58 (d, CCpꢂ, J(103Rh–13C): 9.5 Hz), 97.82,
112.25, 116.56, 116.70, 121.04, 125.08, 128.61, 139.70, 144.42 (s,
N–C6H5 and CHFur), 148.65 (s, C3), 162.60 (s, C5), CO not
observed.
References
[1] (a) P.M. Maitlis, Chem. Soc. Rev. 10 (1981) 1;
(b) L.H. Pignolet, Homogeneous Catalysis with Metal Phosphine
Complexes, Plenum Press, New York, 1983;
ꢂ
(c) P.A. Chaloner, M.A. Esteruelas, F. Joo, L.A. Oro, Homo-
geneous Hydrogenation, Kluwer Academic Publishers,
Dordrecht, The Netherlands, 1994, pp. 1–48 (Chapter 10);
(d) B.A. Arndtsen, R.G. Bergmann, Science 270 (1995) 1970.
ꢂ
[2] A.M. Trzeciak, J.J. Ziolkowski, Coord. Chem. Rev. 190–192
(1999) 883.
[3] S.A. Westcott, H.P. Blom, T.B. Marder, R.T. Baker, J. Am.
Chem. Soc. 114 (1992) 8863.
ꢂ
ꢂ
[4] J. Barbera, A. Elduque, R. Gimnez, F.J. Lahoz, J.A. Lopez, L.A.
Oro, J.L. Serrano, B. Villacampa, J. Villalba, Inorg. Chem. 38
(1999) 3085.
[11] Crystal data for 1. C17H12ClN2O5Rh, Mr ¼ 462.7. Monoclinic,
ꢁ
P21=n,
a ¼ 6:9150ð6),
b ¼ 15:521ð1Þ,
c ¼ 16:502ð1Þ
A,
b ¼ 98:824ð2Þ°, V ¼ 1767 A . DcðZ ¼ 4Þ ¼ 1:739 g cmꢀ3. 34,655
total (full sphere) CCD diffractometer reflections ð2hmax ¼ 75°Þ
merging to 9216 unique ðRint 0.042; multiscan absorption
correction), 7505 ðF > 4rðF ÞÞ used in the full matrix least
squares refinement, ðx; y; z; UisoÞH refining meaningfully through-
out. Conventional R; Rw (weights: (r2ðF Þ þ 0:0004F 2Þꢀ1) 0.041,
0.049 at convergence. T ca. 153 K. Monochromatic Mo Ka
3
ꢁ
[5] (a) C. Pettinari, F. Marchetti, A. Cingolani, G. Bianchini, A.
Drozdov, V. Vertlib, S. Troyanov, J. Organomet. Chem. 651
(2002) 5;
(b) C. Pettinari, F. Marchetti, A. Drozdov, V. Vertlib, Inorg.
Chem. Commun. 4 (2001) 290.
[6] F. Bonati, L.A. Oro, M.T. Pinillos, Polyhedron 4 (1985) 357.
[7] Synthesis of [Rh(CO)2QO](1).
A toluene solution containing
[Rh(CO)2Cl]2 (0.194 g, 0.5 mmol), HQO (0.268 g, 1.00 mmol)
and NEt3 (1.00 mmol) was stirred for 15 h under a nitrogen
atmosphere. The dark precipitate was separated by filtration, the
filtrate was completely dry and extracted with C6H6 or Et2O to
give a deep yellow solution. The air-sensitive residue obtained was
dried in vacuum and shown to be compound 1 (0.262 g, 0.60
mmol, 60% yield) M.p. 136–138 °C. Anal. Calc. for
ꢁ
radiation, k ¼ 0:71073 A. Figures show 50% probability ampli-
tude displacement ellipsoids for the non-hydrogen atoms, hydro-
ꢁ
gen atoms (where shown) having arbitrary radii of 0.1 A. CCDC
222559.
[12] Crystal data for HQO. C15H12N2O3, Mr ¼ 268:3. Monoclinic,
ꢁ
P21=c,
a ¼ 12:463ð3Þ,
b ¼ 14:918ð3Þ,
c ¼ 14:683ð3Þ
A,
b ¼ 113:585ð5Þ°, V ¼ 2502 A . DcðZ ¼ 8Þ ¼ 1:424 g cmꢀ3. 23,252
(total), 4406 unique (Rint0:041), 3146 ÔobservedÕ reflections, R; Rw
0.040, 0.050, all ðx; y; z; UisoÞH refined. T ca. 153 K. CCDC 222651.
[13] A. Cingolani, F. Marchetti, C. Pettinari, R. Pettinari, B.W.
Skelton, A.H. White, J. Organomet. Chem. (2003), submitted.
3
ꢁ
C
18H11N2O5Rh, C, 49.34; H, 2.53; N, 6.38. Found: C, 49.58; H,
2.64; N, 6.23. IR (nujol, cmꢀ1): 2074, 2008 s t(C ꢁ ꢁ ꢁ O), 1605s,
1584s, 1560s, 1532s t(C ꢁ ꢁ ꢁ C, C ꢁ ꢁ ꢁ N), 481m, 377m. 1H NMR
(C6D6, 293 K): d, 2.31 (s, 3H, 3-CH3), 5.96–5.98 (m, 1H, CHFur),