(1-Phenyl-3-methyl-4-acetylpyrazolon-5-ato)rhodium(I) complexes, synthesis, structural and spectroscopical characterization: Reactivity of diolefin- and dicarbonyl-rhodium complexes toward N-, P- and O-donors

Article abstract of DOI:10.1016/S0022-328X(98)00692-5

Novel complexes of rhodium(I) [Rh(diolefin)(Q″)] (where HQ″=1-phenyl-3-methyl-4-acetylpyrazol-5-one and diolefin=cycloocta-1,5-diene (COD), bicyclo[2.2.1]hepta-2,5-diene (NBD) or 1,5-hexadiene (HEX)) were synthesized and characterized by analytical and spectral data. [Rh(COD)(Q″)] interacts with 4,5-dimethyl-1,10-phenanthroline (Me₂Phen) and 2,2′-bipyridil (Bipy) yielding the cationic derivatives [Rh(COD)(Me₂Phen)](Q″)(H₂O), [Rh(COD)(Bipy)](Q″)(H₂O) upon displacement of the (Q″)^- donor from the coordination sphere of the metal center. Whereas [Rh(COD)(Q″)] interacts with 2-benzoylpyridine (Bzpy) yielding the 1:1 adduct [Rh(COD)(Bzpy)(Q″)] in which Bzpy acts as N-monodentate donor. On the other hand the monodentate P-donors triphenylphosphine, triphenylphosphite, tricyclohexylphosphine and the bidentate bis(diphenylphosphino)ethane (DPPE) displace the COD ligand from [Rh(COD)(Q″)] giving the neutral derivatives [Rh(PR₃)₂(Q″)] (PR₃=PPh₃, or P(OPh)₃) and [Rh(DPPE)(Q″)](H₂O). HQ″ reacts with the dinuclear [Rh(CO)₂Cl]₂. The tetradentate cycloocto-tetraene (COT) reacts with [Rh(CO)₂(Q″)] yielding the derivative [Rh(CO)₂(HQ″)Cl] in which HQ″ acts as neutral monodentate O-donor ligand. Whereas in presence of NEt₃ HQ″ reacts with [Rh(CO)₂Cl]₂ yielding [Rh(CO)₂(Q″)]. In this complex, one molecule of CO can be replaced by one mole of Phen and Bipy or by two moles of PPh₃ and AsPh₃ yielding the derivatives [Rh(CO)(L)_n(Q″)]·x(H₂O) (L=Me₂Phen or Bipy, n=1; L=PPh₃ or AsPh₃, n=2) whereas one mole of DPPE displaces both the molecules of CO, yielding [Rh(DPPE)(Q″)] yielding the derivative [Rh(COT)(Q″)]. The X-ray crystal structure determination of [Rh(COD)(Q″)] establishes that the rhodium atom is in a square planar configuration with two adjacent sites occupied by the (Q″)^- ligand in the O₂-bidentate form (Rh-O distances=2.054(2) and 2.061(2) A). The COD ring has a twisted boat conformation with Rh-C distances in the range 2.101(3)-2.110(3) A. Comparison was made with structural data reported for several related tetracoordinated (COD)Rh(I) adducts.

Full text of DOI:10.1016/S0022-328X(98)00692-5

Journal of Organometallic Chemistry 566 (1998) 187–201
(1-Phenyl-3-methyl-4-acetylpyrazolon-5-ato)rhodium(I) complexes,
synthesis, structural and spectroscopical characterization: Reactivity of
diolefin- and dicarbonyl-rhodium complexes toward N-, P- and
O-donors
C. Pettinari a,*, F. Accorroni a, A. Cingolani a, F. Marchetti a, A. Cassetta b, L. Barba b
a Dipartimento di Scienze Chimiche, Uni6ersita` di Camerino, 6ia S. Agostino 1, I-62032 Camerino, Italy
b Istituto di Strutturistica Chimica ‘‘G. Giacomello’’, Consiglio Nazionale delle Ricerche, Padriciano 99, 30412 Trieste, Italy
Received 2 April 1998
Abstract
Novel complexes of rhodium(I) [Rh(diolefin)(Q¦)] (where HQ¦=1-phenyl-3-methyl-4-acetylpyrazol-5-one and diolefin=cy-
cloocta-1,5-diene (COD), bicyclo[2.2.1]hepta-2,5-diene (NBD) or 1,5-hexadiene (HEX)) were synthesized and characterized by
analytical and spectral data. [Rh(COD)(Q¦)] interacts with 4,5-dimethyl-1,10-phenanthroline (Me2Phen) and 2,2%-bipyridil (Bipy)
yielding the cationic derivatives [Rh(COD)(Me2Phen)](Q¦)(H2O), [Rh(COD)(Bipy)](Q¦)(H2O) upon displacement of the (Q¦)−
donor from the coordination sphere of the metal center. Whereas [Rh(COD)(Q¦)] interacts with 2-benzoylpyridine (Bzpy) yielding
the 1:1 adduct [Rh(COD)(Bzpy)(Q¦)] in which Bzpy acts as N-monodentate donor. On the other hand the monodentate P-donors
triphenylphosphine, triphenylphosphite, tricyclohexylphosphine and the bidentate bis(diphenylphosphino)ethane (DPPE) displace
the COD ligand from [Rh(COD)(Q¦)] giving the neutral derivatives [Rh(PR3)2(Q¦)] (PR3=PPh3, or P(OPh)3) and
[Rh(DPPE)(Q¦)](H2O). HQ¦ reacts with the dinuclear [Rh(CO)2Cl]2. The tetradentate cycloocto-tetraene (COT) reacts with
[Rh(CO)2(Q¦)] yielding the derivative [Rh(CO)2(HQ¦)Cl] in which HQ¦ acts as neutral monodentate O-donor ligand. Whereas in
presence of NEt3 HQ¦ reacts with [Rh(CO)2Cl]2 yielding [Rh(CO)2(Q¦)]. In this complex, one molecule of CO can be replaced by
one mole of Phen and Bipy or by two moles of PPh3 and AsPh3 yielding the derivatives [Rh(CO)(L)n(Q¦)]·x(H2O) (L=Me2Phen
or Bipy, n=1; L=PPh3 or AsPh3, n=2) whereas one mole of DPPE displaces both the molecules of CO, yielding
[Rh(DPPE)(Q¦)] yielding the derivative [Rh(COT)(Q¦)]. The X-ray crystal structure determination of [Rh(COD)(Q¦)] establishes
that the rhodium atom is in a square planar configuration with two adjacent sites occupied by the (Q¦)− ligand in the
˚
O2-bidentate form (Rh–O distances=2.054(2) and 2.061(2) A). The COD ring has a twisted boat conformation with Rh–C
˚
distances in the range 2.101(3)–2.110(3) A. Comparison was made with structural data reported for several related tetracoordi-
nated (COD)Rh(I) adducts. © 1998 Elsevier Science S.A. All rights reserved.
Keywords: Rhodium; Diolefin; Phenanthroline; Bipyridyl
1. Introduction
containing the chelating unit of the enolizable i-dike-
tones in a rigid environment has only recently been
recognized [2]. In particular the interest in metal-i-
diketonato olefin compounds stems largely from at-
tempts to elucidate the nature of the metal–olefin
interaction, their use as model compounds in homoge-
neous catalysis and as catalysts in a variety of olefin
isomerizations and polymerizations. For example sev-
Rhodium(I) chelates of i-diketones were prepared
more than 30 years ago [1]. However, the theoretical
and practical importance of this class of complexes
* Corresponding author. Tel.: +39 737 402217 fax: +39 737
637345; e-mail: pettinar@cam.serv.unicam.it
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00692-5

188
C. Pettinari et al. / Journal of Organometallic Chemistry 566 (1998) 187–201
eral diolefin-i-diketonato rhodium(I) have tempera-
ture-dependent proton nuclear magnetic resonance
spectra, indicating exchange of olefinic protons between
non-equivalent sites [3]. Depending on the choice of the
diolefin and i-diketone, these complexes showed a
variety of intermolecular reactions, not all of which
caused proton site exchange [4,5].
Electrothermal Instrument. The electronic conductance
of the solutions was measured with a Crison CDTM
522 conductimeter at room temperature.
2.1. Synthesis of the complexes
2.1.1. Synthesis of [Rh(COD)(Q¦)] (1)
The fragment [Rh(P-donor)2] also plays an important
role in several catalytic reactions. The phosphorous
donor influences the activity and selectivity of transfor-
mations such as rhodium catalyzed hydrogenation of
CO2 [6–9]. Surprisingly, only a few attempts have been
made so far to elucidate the intrinsic influence of struc-
tural changes in the phosphine and i-diketone ligands
in [RhP2(i-diketone)-type compounds [10].
Therefore, following on our interest in the field of
organometallic derivatives of N-, S- and O-donor hete-
rocyclic ligands, we decided to investigate the reactivity
of different Rh(I) acceptors towards 4-acyl-5-pyra-
zolones (QH), which are a class of potentially bidentate
ligands originally investigated by Jensen as reagents for
radiochemical separations [11]. These molecules are
comparable to i-diketones because in both the classes
keto-enol tautomerism is possible and they are able to
coordinate in the neutral and the anionic form.
Here we report the results obtained with the donor
1-phenyl-3-methyl-4-acetyl-5-pyrazolone (HQ¦). Some
new diolefin-, phosphino- and carbonyl-rhodium(I)
complexes were synthesized, characterized and com-
pared with related derivatives. The reactivity of dio-
lefin- and dicarbonyl-rhodium(I) compounds was also
examined toward other N- and P-donors, mono or
bidentate. The X-ray crystal structure of [(1-phenyl-3-
methyl-4-acetylpyrazolon-5-ato)rhodium(I)(cycloocta-1,
5-diene)], the first rhodium(I)pyrazolonate structurally
characterized, was also determined. Comparison was
made with some related rhodium(I) compounds.
[Rh(COD)Cl2 (493 mg, 1.0 mmol) was added with
stirring to a solution of the ligand HQ¦ (430 mg, 2.0
mmol) and NEt3 (280 ml, 2.0 mmol) in methanol (30
cm3). The precipitate formed was stirred for 2 h and
then filtered off and washed with methanol. Yield 68%.
M.p. 165–170°C. Anal. Calc. for C20H23N2O2Rh: C,
56.3; H, 5.4; N, 6.6%. Found: C, 56.1; H, 5.6; N, 6.3%.
1H-NMR (CDCl3): l(COD), 1.82q, 2.50qr (8 H, CH2),
4.09br, 4.29br (4 H, –CHꢀCH–); l(Q¦), 2.38s, (3 H,
C6–CH3), 2.42s (3 H, C3–CH3), 7.15t, 7.35t, 7.83d (5
1
H, N1–C6H5); H-NMR (toluene-d8): l(COD), 1.60br,
2.30br (8 H, CH2), 4.22br, 4.26br, (4 H, –CHꢀCH–);
l(Q¦), 1.86s, (3 H, C6–CH3), 2.06s (3 H, C3–CH3),
Table 1
Crystal data: data collection and refinement of the structure for
Rh(COD)(Q¦) 1
Formula
RhO2N2C20H23
426.319
Formula weight
Space group
(
P1
˚
a (A)
10.027(2)
10.251(3)
9.627(2)
105.48(2)
96.10(2)
70.73(2)
900.1(4)
2
˚
b (A)
˚
c (A)
h (°)
i (°)
k (°)
3
˚
Vc (A )
Z
Dcalc. (g cm−3
)
1.5731
9.474
436.0
v(Mo–Kh) (cm−1
F(000)
)
˚
Radiation (monochromated)
T of data collection (K)
Scan mode
Mo–Kh (u=0.71069 A)
296
ꢀ/2q
Scan width
0.6° below Kh1, 0.6° above
Kh2
min=1.502, max=14.648
0.5
4.052q555.0
−13/12; −13/12; 0/12
21–1; 11–3; 31–2
2. Experimental section
Scan speed (° min−1
Background/scan ratio
Data collection range (°)
h k l range
Standards (measured every 97
reflections)
Number of unique reflections
measured
)
[Rh(COD)Cl]2,
[Rh(CO)2Cl]2,
[Rh(NBD)Cl]2,
[Rh(HEX)Cl]2 and [Rh(PPh3)3Cl] were purchased from
Alfa (Karlsruhe) and Aldrich (Milwaukee) and used as
received. The donor HQ¦ was prepared according to
literature [12]. The samples for microanalyses were
dried in vacuo to constant weight (20°C, ca. 0.1 torr).
Elemental analyses (C, H, N, S) were carried out with a
Fison Instrument 1108 CHNS-O Elemental Analyzer.
Molecular weight determinations were carried out with
a Knauer membrane osmometer. IR spectra were
recorded from 4000 to 100 cm−1 with a Perkin Elmer
4538
Number of data with ꢀFoꢀ]6|(ꢀFoꢀ)
3492
Refinement
Full matrix least squares
on F
226
3.11
3.93
1.32
Number of parameters refined
Ra
Rwb
Sc (goodness of fit)
System 2000 FT-IR instrument. H, 13C and 31P-NMR
1
spectra were recorded on a VXR-300 Varian Spectrom-
a R=(ꢁꢀꢀFꢀ−kꢀFcꢀꢀ)/ꢁꢀFoꢀ.
1
eter (300 MHz for H, 75 MHz for 13C and 121.5 MHz
b
2 1/2
Rw=(ꢁw(ꢀFoꢀ−kꢀFcꢀ)2/ꢁwꢀFoꢀ ]
.
for 31P). Melting points were taken on an IA 8100
c S= =[ꢁw(ꢀFoꢀ−kꢀFcꢀ)2/(Nobs−Npar)]1/2
.

C. Pettinari et al. / Journal of Organometallic Chemistry 566 (1998) 187–201
189
Table 2
Table 3
˚
Interatomic distances (A) with e.s.d.’s in parentheses, for
Bond angles (°) with e.s.d.’s in parentheses, for Rh(COD)(Q¦) 1
Rh(COD)(Q¦) 1
O(14)–Rh(1)–O(15) 90.82(9) C(5)–C(4)–C(3)
103.6(3)
122.2(3)
131.2(3)
106.6(2)
123.5(3)
Rh(1)–O(14)
Rh(1)–O(15)
Rh(1)–C(17)
Rh(1)–C(20)
Rh(1)–C(21)
Rh(1)–C(24)
Rh(1)–X(1)a
Rh(1)–X(2)b
O(15)–C(5)
O(14)–C(13)
N(1)–N(2)
N(1)–C(5)
N(1)–C(6)
N(2)–C(3)
C(3)–C(4)
C(3)–C(12)
C(4)–C(5)
C(4)–C(13)
C(6)–C(7)
C(6)–C(11)
C(7)–C(8)
C(8)–C(9)
C(9)–C(10)
C(10)–C(11)
C(13)–C(16)
C(17)–C(24)
C(17)–C(18)
C(18)–C(19)
C(19)–C(20)
C(20)–C(21)
C(21)–C(22)
C(22)–C(23)
C(23)–C(24)
2.061(2)
2.054(2)
2.103(3)
2.106(3)
2.101(3)
2.110(3)
1.988(3)
1.979(3)
1.274(3)
1.269(4)
1.397(4)
1.366(4)
1.416(4)
1.294(5)
1.446(4)
1.509(5)
1.421(4)
1.402(5)
1.382(5)
1.391(5)
1.391(5)
1.368(7)
1.351(7)
1.392(6)
1.511(4)
1.397(5)
1.503(6)
1.492(7)
1.508(6)
1.397(6)
1.504(6)
1.500(5)
1.507(5)
X(1)a–Rh(1)–X(2)b
O(14)–Rh(1)–X(1)
O(14)–Rh(1)–X(2)
O(15)–Rh(1)–X(1)
O(15)–Rh(1)–X(2)
88.6(1)
O(15)–C(5)–N(1)
179.0(1) O(15)–C(5)–C(4)
90.4(1)
90.2(1)
N(1)–C(5)–C(4)
O(14)–C(13)–C(4)
178.4(1) O(14)–C(13)–C(16) 114.3(3)
O(14)–Rh(1)–C(17) 160.6(1) C(4)–C(13)–C(16)
122.2(3)
119.3(3)
122.0(3)
118.7(3)
119.6(4)
120.7(5)
120.1(4)
120.7(4)
119.7(4)
O(14)–Rh(1)–C(20) 91.5(1)
O(14)–Rh(1)–C(21) 88.9(1)
C(7)–C(6)–C(11)
N(1)–C(6)–C(7)
O(14)–Rh(1)–C(24) 160.6(1) N(1)–C(6)–C(11)
O(15)–Rh(1)–C(17) 88.4(1) C(6)–C(7)–C(8)
O(15)–Rh(1)–C(20) 159.4(1) C(7)–C(8)–C(9)
O(15)–Rh(1)–C(21) 161.8(1) C(8)–C(9)–C(10)
O(15)–Rh(1)–C(24) 91.9(1)
C(9)–C(10)–C(11)
C(6)–C(11)–C(10)
C(17)–Rh(1)–C(20)
C(17)–Rh(1)–C(21)
C(17)–Rh(1)–C(24)
C(20)–Rh(1)–C(21)
C(20)–Rh(1)–C(24)
C(21)–Rh(1)–C(24)
82.7(2)
97.8(1)
38.7(1)
38.8(2)
92.7(1)
82.6(1)
Rh(1)–C(17)–C(18) 111.1(3)
Rh(1)–C(17)–C(24) 70.9(2)
C(18)–C(17)–C(24) 124.9(4)
C(17)–C(18)–C(19) 114.6(4)
C(18)–C(19)–C(20) 114.7(3)
Rh(1)–O(14)–C(13) 127.8(1) Rh(1)–C(20)–C(19) 112.3(3)
Rh(1)–O(15)–C(5)
N(2)–N(1)–C(5)
N(2)–N(1)–C(6)
C(5)–N(1)–C(6)
C(3)–N(2)–N(1)
N(2)–C(3)–C(4)
N(2)–C(3)–C(12)
C(4)–C(3)–C(12)
C(3)–C(4)–C(13)
C(5)–C(4)–C(13)
C(7)–H(7)…Q(15)
C(11)–H(11)…N(2)
120.6(2) Rh(1)–C(20)–C(21) 70.4(2)
111.1(3) C(19)–C(20)–C(21) 124.5(4)
118.9(3) Rh(1)–C(21)–C(20) 70.8(2)
130.1(3) Rh(1)–C(21)–C(22) 110.7(2)
106.4(3) C(20)–C(21)–C(22) 125.1(3)
112.2(3) C(21)–C(22)–C(23) 115.1(3)
118.4(3) C(22)–C(23)–C(24) 113.4(3)
129.3(4) Rh(1)–C(24)–C(17) 70.4(2)
131.6(3) Rh(1)–C(24)–C(23) 113.0(2)
124.7(3) C(17)–C(24)–C(23) 123.7(3)
123.3(4)
100.2(4)
X(1)…X(2)
O(15)…C(7)
O(15)…H(7)
N(2)…C(11)
N(2)…H(11)
2.771(4)
2.855(5)
2.180(5)
2.760(5)
2.401(5)
a
X(1) is the center of the double bond between C(17) and C(24).
b X(2) is the center of the double bond between C(20) and C(21).
3.20d, J(Rh–H)=1.38 Hz, 3.24d, J(Rh–H)=1.28 Hz,
3.30d, J(Rh–H)=1.39 Hz, 3.34d, J(Rh–H)=1.29 Hz,
4.42br, 4.60br (6 H, –CHꢀCH–); l(Q¦), 2.38s, (3 H,
C6–CH3), 2.41s (3 H, C3–CH3), 7.15t, 7.35t, 7.83d (5
H, N1–C6H5). IR (nujol) cm−1: 1591s, w(CꢀO); 507m,
476s, w(Rh–C), 434m, 417s, 406m, 387m w(Rh–O).
a
X(1) is the center of the double bond between C(17) and C(24).
b X(2) is the center of the double bond between C(20) and C(21).
7.00t, 7.22t, 8.24d (5 H, N1–C6H5). 13C-NMR (CDCl3):
l(COD), 30.4, 30.7, 30.9, 31.0 (CH2), 76.9d, J(Rh–C)
=
14.2 Hz, 77.8d, J(Rh–C)=14.4 Hz (–CHꢀCH–); l(Q¦),
27.3, (C6–CH3), 18.0 (C3–CH3), 106.7 (C4), 139.3 (C3),
190.3 (C5), 163.2 (C6), 120.5, 126.8, 129.0, 148.8 (N1–
C6H5). IR (nujol) cm−1; 1592s, w(CꢀO); 508m, 479s,
w(Rh–C), 403m, 391s, w(Rh–O).
2.1.3. Synthesis of [Rh(NBD)(Q¦)] (3)
TlQ¦ (419 mg, 1.0 mmol) was added with stirring to
a solution of [Rh(NBD)Cl]2 (461 mg, 0.5 mmol) in
dichloromethane (25 cm3). The TlCl formed was filtered
off and the complex was precipitated by the addition of
methanol. Yield 39%. M.p. 178°C dec. Anal. Calc. for
C19H19N2O2Rh: C, 55.6; H, 4.7, N, 6.8%. Found: C,
55.8; H, 4.9; N, 6.9%. 1H-NMR (CDCl3): l(NBD),
1.25s (2 H, CH2), 3.85br (2 H, CH), 3.95br (4 H,
–CHꢀCH–); l(Q¦), 2.35s (3 H, C6–CH3), 2.40s (3 H,
C3–CH3), 7.15t, 7.34t, 7.80d (5 H, N1–C6H5); 1H-
NMR (toluene-d8): l(NBD), 0.91pt (2 H, CH2), 3.40m
(2 H, CH), 3.77q (4 H, –CHꢀCH–); l(Q¦), 1.86s
(C6–CH3), 2.06 (C3–CH3), 6.92t, 7.20, 8.14d (N1–
2.1.2. Synthesis of [Rh(HEX)(Q¦)] (2)
[Rh(HEX)Cl]2 (441 mg, 1.0 mmol) was added with
stirring to a solution of the ligand HQ¦ (430 mg, 2.0
mmol) and NEt3 (280 ml, 2.0 mmol) in methanol (30
cm3). The precipitate formed was stirred for 2 h and
then filtered off and washed with methanol. Yield 58%.
M.p. 142–146°C Anal. Calc. for C18H21N2O2Rh: C,
54.0; H, 5.3; N, 7.0%. Found: C, 53.7; H, 5.5; N, 7.0%.
1H-NMR (CDCl3): l(HEX), 2.20–2.50m (4 H, CH2),

190
C. Pettinari et al. / Journal of Organometallic Chemistry 566 (1998) 187–201
Fig. 1. The olefinic protons Ha and Hb in 1.
C6H5). IR (nujol (cm−1: 1592s, w(CꢀO); 510m, 500m,
472vs, w(Rh–C), 420m, 414s, 404m, 380s w(Rh–O).
Fig. 3. Structure proposed for derivative 6.
2.1.4. Synthesis of [Rh(COD)(Me2Phen)](Q¦)(H2O) (4)
To a solution of [Rh(COD)(Q¦)] 1 (213 mg, 0.5
mmol) in diethyl ether (50 cm3) under nitrogen, the
stoichiometric amount of 4,7-dimethyl-1,10-phenan-
throline (104 mg, 0.5 mmol) was added. A red precipi-
tate formed immediately, which was filtered off and
washed with diethyl ether. Yield 30%. M.p. 168–173°C.
Anal. Calc. for C32H38N4O3Rh: C, 62.6; H, 5.7; N,
8.6%. Found: C, 62.5; H, 5.6; N, 8.5%. Lm (CH2Cl2):
21.9 V−1 cm2 mol−1, 0.9·10−3 M. Lm (acetone): 89.6
V−1 cm2 mol−1, 0.6·10−3 M. 1H-NMR (CDCl3):
l(H2O), 1.85br (2 H); l(COD), 2.15qbr, 2.65mbr (8 H,
CH2), 4.64d, J(Rh–H)ꢀ 1.4 Hz (4 H, –CHꢀCH–);
l(Me2Phen), 2.81s, 2.84s (6 H, CH3), 7.46d, 7.66d,
8.01d, 8.05d, 9.05d (6 H); l(Q¦), 2.44s (3 H, C6–CH3),
2.48s (3 H, C3–CH3), 7.40t, 7.55t, 8.00d (5 H, N1–
C6H5). IR (nujol) cm−1: w(H2O), 3200 br, w(CꢀO),
1623s, w(Rh–C), 511s, 483m, w(Rh–N), 296vs, 248m.
C30H35N4O3Rh: C, 59.8; H, 5.9; N, 9.3%. Found: C,
60.2; H, 5.6; N, 9.5%. Lm (CH2Cl2): 3.4 V−1 cm2
mol−1, 0.8·10−3 M. Lm (Acetone): 25.5 V−1 cm2
1
mol−1, 0.9·10−3 M. H-NMR (CDCl3): l(H2O), 1.81d
br (2 H); l(COD), 1.81d br, 2.46mbr (8 H, CH2),
4.18mbr (4 H, –CHꢀCH–); l(Bipy), 7.30br, 7.83s,
8.42d, 8.68d (8 H); l(Q¦), 2.38s (3 H, C6–CH3), 2.41s
(3 H, C3–CH3), 7.15t, 7.30br, 7.85d (5 H, N1–C6H5).
IR (nujol) cm−1: w(H2O), 3430br, w(CꢀO), 1623s,
w(Rh–C), 509s, 481m, w(Rh–N), 298vs, 254m.
2.1.6. Synthesis of [Rh(COD)(Bzpy)(Q¦)] (6)
To a solution of [Rh(COD)(Q¦)] 1 (213 mg, 0.5
mmol) in diethyl ether (50 cm3) under nitrogen, the
stoichiometric amount of 2-benzoylpyridine (92 mg, 0.5
mmol) was added. A reddish-yellow precipitate formed
immediately, which was filtered off and washed with
diethyl ether. Yield 95%. M.p. 90°C dec. Anal. Calc. for
C36H32N3O3Rh: C, 63.1; H, 5.3; N, 6.9%. Found: C,
63.4; H, 5.4; N, 6.9%. 1H-NMR (CDCl3): l(COD),
1.82qbr, 2.50mbr (8 H, CH2), 4.20dbr (4 H, –CHꢀCH–);
l(Bzpy), 7.50–7.66m, 7.90t, 8.05–8.12m, 8.74d (9 H);
l(Q¦), 2.37s (3 H, C6–CH3), 2.41s (3 H, C3–CH3),
2.1.5. Synthesis of [Rh(COD)(Bipy)](Q¦)(H2O) (5)
To a solution of [Rh(COD)(Q¦)] 1 (213 mg, 0.5
mmol) in diethyl ether (50 cm3) under nitrogen, the
stoichiometric amount of 2,2%-bipyridil (78 mg, 0.5
mmol) was added. A red precipitate formed immedi-
ately, which was filtered off and washed with diethyl
ether. Yield 70%. M.p. 155–156°C. Anal. Calc. for
7.14t, 7.35t, 7.82d (5 H, N1–C6H5). IR (nujol) cm−1
:
w(H2O), 3200 br, wBzpy(CꢀO), 1668vs, wQ¦(CꢀO), 1592s,
w(Rh–C), 509m, 478s, w(Rh–O), 400s, 389m, w(Rh–N),
229m.
Fig. 2. Structure proposed for derivative 4.
Fig. 4. Structure proposed for derivative 10.

C. Pettinari et al. / Journal of Organometallic Chemistry 566 (1998) 187–201
191
2.1.8. Synthesis of [Rh(P(OPh)3)2(Q¦)] (8)
P(OPh)3 (310 mg, 1.0 mmol) was added to a solution
of [Rh(COD)(Q¦)]
1
(213 mg, 0.5 mmol) in
dichloromethane (30 cm3). The solution was stirred for
2 h. By the addition of hexane, a yellow precipitate was
afforded, which was filtered off and washed with hex-
ane. Yield 77%. M.p. 111–113°C dec. Anal. Calc. for
C48H41N2O8P2Rh: C, 61.2; H, 4.5; N, 2.9%. Found: C,
1
61.4; H, 4.4; N, 3.0%. H-NMR (CDCl3): l(P(OPh)3),
Fig. 5. Structure proposed for derivatives 12–15.
7.08–7.32 mbr (30 H): l(Q¦), 1.99s (3 H, C6–CH3),
2.27s, (3 H, C3–CH3), 7.08–7.32mbr, 7.52t, 7.85d (5 H,
2.1.7. Synthesis of [Rh(PPh3)2(Q¦)] (7)
N1–C6H5). 31P-NMR (CDCl3): −40.9dd, J(Rh–P)
=
PPh3 (261 mg, 1.0 mmol) was added to a solution of
[Rh(COD)(Q¦)] 1 (213 mg, 0.5 mmol) in diethyl ether
(30 cm3). A yellow precipitate was formed slowly,
which was filtered off and washed with diethyl ether.
Yield 94%. M.p. 77°C dec. Anal. Calc. for
C48H41N2O2P2Rh: C, 68.4; H, 4.9; N, 3.3%. Found: C,
68.6; H, 4.9; N, 3.4%. 1H-NMR (CDCl3): l(PPh3),
6.90–7.75mbr (30 H); l(Q¦), 1.86s, 2.00s, 2.08s, 2.12s
(6 H, C6–CH3 and C3–CH3), 6.90–7.75mbr (5 H,
N1–C6H5). 31P-NMR (CDCl3): 34.51dd, J(Rh–P)=131.7
Hz, J(P–P)=28.6 Hz; 33.32dd, J(Rh–P)=121.7 Hz, J(P–
P)=28.6 Hz. IR (nujol) cm−1: w(CꢀO), 1605s, w(PPh3),
541vs, 523vs, 515s, w(Rh–O), 455m, 439s, 433m.
194.2 Hz, J(P–P)=103.8 Hz; 43.4dd, J(Rh–P)=183.4 Hz,
J
w(P(OPh)3), 507vs, 500vs, 492vs, 482vs, w(Rh–O),
454m, 417m.
(P–P)=104.4 Hz. IR (nujol) cm−1: w(CꢀO), 1609s,
2.1.9. Synthesis of [Rh(DPPE)(Q¦)] (H2O) (9)
1,2-Bis(diphenylphosphino)ethane (199 mg, 0.5
mmol) was added to a solution of [Rh(COD)(Q¦)] 1
(213 mg, 0.5 mmol) in dichloromethane (30 cm3). The
solution was stirred for 2 h. By addition of diethyl ether
a yellow precipitate was afforded, which was filtered off
and washed with diethyl ether. Yield 47%. M.p. 178–
183°C. Anal. Calc. for C38H37N2O3P2Rh: C, 62.1; H,
Fig. 6. An ORTEP view of complex [Rh(COD)(Q¦)] (1).

192
C. Pettinari et al. / Journal of Organometallic Chemistry 566 (1998) 187–201
Fig. 7. Plot of ƒ vs „ for (COD)RhO2-like adducts.
5.1; N, 3.8%. Found: C, 62.4; H, 5.2; N, 3.6%. 1H-
NMR (CDCl3): l(DPPE), 2.02–2.22mbr (4 H, P–
CH2CH2–P), 7.10–7.50mbr, 7.62–7.74mbr (20 H,
P–C6H5); l(Q¦), 2.46s, 2.33s (3 H, C6–CH3), 2.52s,
2.30s (3 H, C3–CH3), 7.10–7.50mbr, 7.95dbr (5 H,
methanol and recrystallized from hot light petroleum
(40–60°C). Yield 92 mg (25%). M.p. 148–152°C. Anal.
Calc. for C14H11N2O4Rh: C, 44.9; H, 3.0; N, 7.5%.
1
Found: C, 44.9; H, 3.0; N, 7.3%. H-NMR (CDCl3):
l(Q¦), 2.45s, (3 H, C6–CH3), n.o. (C4), 138.6 (C3),
191.1 (C5), 162.9 (C6), 121.1, 126.3, 129.3, 148.8 (N1–
C6H5). IR (nujol) cm−1: wQ¦(CꢀO), 1623cbr, w(CO),
2101s, 2084sh, 2064s, 2001vs, w(Rh–C), 468vs, w(Rh–
O), 406m, 386m.
N1–C6H5). 31P-NMR (CDCl3, 20°C): 58.0d, J(Rh–P)
=
133.1 Hz. IR (nujol) cm−1: w(CꢀO), 1589s, w(DPPE),
535vs, 507s, 483s, w(Rh–O), 432s, 385m.
2.1.10. Synthesis of [Rh(CO)2(HQ¦)Cl] (10)
The ligand HQ¦ (212 mg, 1.0 mmol) was added to a
solution of [Rh(CO)2Cl]2 (194 mg, 0.5 mmol) in
methanol (30 cm3). The solution was stirred at 80°C for
2 h, then evaporated to dryness in vacuo. Crystalliza-
tion was induced by addition of hexane. Yield 40%.
M.p. 97–100°C. Anal. Calc. for C14H12ClN2O4Rh: C,
40.9; H, 2.9; N, 6.9%. Found: C, 40.6; H, 3.0; N, 6.6%.
1H-NMR (CDCl3): l(HQ¦), 2.82sbr, (3 H, C6–CH3),
2.52sbr (3 H, C3–CH3), 7.52–7.74mbr (5 H, N1–C6H5).
2.1.12. Synthesis of [Rh(CO)(Me2Phen)(Q¦)](H2O)2
(12)
A suspension of [Rh(CO)2(Q¦)] (187 mg, 0.5 mmol)
in diethyl ether was treated with a stoichiometric
amount of 4,7-dimethyl-1,10-phenanthroline (Me2Phen)
(104 mg, 0.5 mmol). After stirring for 24 h, the precip-
itate formed was filtered off and washed with diethyl
ether. Yield 54%. M.p. 250°C dec. Anal. Calc. for
C25H27H4O5Rh: C, 54.4; H, 4.4; N, 9.1%. Found: C,
IR (nujol) cm−1
:
(OH· · ·O) 2700br, wQ¦(CꢀO),
54.0; H, 4.4; N, 9.3%. H-NMR (CDCl3): l(Me2Phen),
1
1643sbr, w(CO), 2076vs, 2025m, 2007s, 1992m, w(Rh–
C), 489vs, 307vs w(Rh–Cl).
2.85–3.18mbr (6 H, CH3), 7.10–7.85mbr, 7.95–
8.62mbr, 8.78dd (6 H); l(Q¦), 2.20–2.65mbr, (6 H,
C6–CH3 and C3–CH3), 7.10–7.85mbr (5 H, N1–C6H5);
l(H2O), 1.90br (4 H). IR (nujol) cm−1: w(H2O),
3250br, wQ¦(CꢀO), 1602sbr, w(CO), 1975sbr, w(Rh–CO),
481m, w(Rh–O), 406m, 390m, w(Rh–N), 293s.
2.1.11. Synthesis of [Rh(CO)2(Q¦)] (11)
(i) A mixture of RhCl3 ·xH2O (209 mg, 1.0 mmol)
and an excess of the ligand HQ¦ (318 mg, 1.5 mmol) in
dimethylformamide (10 cm3) was refluxed for 1 h. The
complex was precipitated by the addition of water and
recrystallized from dichloromethane–hexane.
2.1.13. Synthesis of [Rh(CO)(Bipy)(Q¦)](H2O)2 (13)
A suspension of [Rh(CO)2(Q¦)] (187 mg, 0.5 mmol)
in diethyl ether was treated with a stoichiometric
amount of 2,2%-bipyridil (Bipy) (78 mg, 0.5 mmol).
After stirring for 24 h, the precipitate formed was
filtered off and washed with diethyl ether. Yield 58%.
M.p. 250°C dec. Anal. Calc. for C23H23N4O5Rh: C,
(ii) The ligand HQ¦ (212 mg, 1.0 mmol) was added to
a solution of [Rh(CO)2Cl]2 (194 mg, 0.5 mmol) and
NEt3 (140 ml, 1.0 mmol) in methanol (30 cm3) at 70°C.
A reddish-brown precipitate was formed which was
stirred for 24 h and then filtered off, washed with

C. Pettinari et al. / Journal of Organometallic Chemistry 566 (1998) 187–201
193
Fig. 8. Plot of ƒ vs „ for (COD)RhL2-like adducts.
51.3; H, 4.3; N, 10.4%. Found: C, 51.0; H, 4.2; N,
10.3%. 1H-NMR (CDCl3): l(Bipy), 7.15–7.82mbr,
7.90–8.70mbr (8 H), l(Q¦), 2.20–2.75mbr, (6 H, C6–
CH3 and C3–CH3), 7.15–7.82mbr (5 H, N1–C6H5);
l(H2O), 1.85br (4 H). IR (nujol) cm−1: w(H2O),
3300br, wQ¦(CꢀO), 1600sbr, w(CO), 1975sbr, w(Rh–CO),
489m, w(Rh–O), 387m, w(Rh–N), 278m, 295m.
7.50mbr, 7.71d (5 H, N1–C6H5), l(H2O), 1.75br (2 H).
IR (nujol) cm−1: w(H2O), 3180br, wQ¦(CꢀO), 1636sbr,
w(AsPh3), 465vs, 332vs, 320s, w(Rh–CO), 484s.
2.1.16. Synthesis of [Rh(COT)(Q¦)] (16)
Cyclooctatetraene (COT) (52 mg, 0.5 mmol) was
added to a solution of [Rh(CO)2(Q¦)] (374 mg, 1.0
mmol) in dichloromethane (30 cm3). Compound 16 was
separated by the addition of hexane. Yield 34%. M.p.
135–138°C. Anal. Calc. for C20H19N2O2Rh: C, 56.9; H,
4.5; N, 6.6%. Found: C, 56.4; H, 4.6; N, 6.6%. 1H-
NMR (CDCl3): l(COT), 4.23d, J(Rh–H)=1.38 Hz,
4.34d, J(Rh–H)=0.82 Hz, 5.89s (8 H, –CHꢀCH–);
l(Q¦), 2.40s, (3 H, C6–CH3), 2.42s (3 H, C3–CH3),
7.16t, 7.35t, 7.83d (5 H, N1–C6H5). 13C-NMR (CDCl3):
2.1.14. Synthesis of [Rh(PPh3)2(CO)(Q¦)](H2O) (14)
PPh3 (262 mg, 1.0 mmol) was added to a solution of
[Rh(CO)2(Q¦)] (187 mg, 0.5 mmol) in dichloromethane
(30 cm3). Complex 14 was separated by addition of
light petroleum. Yield 32%. M.p. 193–197°C. Anal.
Calc. for C49H43N2O4P2Rh: C, 66.2; H, 4.9; N, 3.1%.
1
Found: C, 66.5; H, 4.8; N, 3.2%. H-NMR (CDCl3):
l(COT): 136.6, 136.1, 132.5, 129.1, 85.5d, J(Rh–C)
=
l(PPh3), 7.30–7.48mbr (30 H), l(Q¦), 1.92s (3 H, C6–
CH3), 2.42s (3 H, C3–CH3), 7.0 6t, 7.18t, 7.55d (5 H,
N1–C6H5), l(H2O), 1.82br (2 H). 31P-NMR (CDCl3):
19.5 Hz, 84.8d, J(Rh–C)=20.0 Hz, 83.5d, J(Rh–C)=19.8
Hz, 82.7d, J(Rh–C)=20.0 Hz (–CHꢀCH–); l(Q¦), 27.0
(C6–CH3), 18.0 (C3–CH3), n.o. (C4), 139.0 (C3), 190.2
(C5), 163.4 (C6), 120.9, 125.7, 129.0, 148.9 (N1–C6H5).
IR (nujol) cm−1: w(CꢀO), 1601s; w(Rh–C), 512m, 481s;
w(Rh–O), 407m, 388m.
28.0d, J(Rh–P)=130.6 Hz, T=20°C; 28.3d J(Rh–P)
=
129.9 Hz, T= −55°C. IR (nujol) cm−1: w(H2O),
3240br, wQ¦(CꢀO), 1636sbr, w(PPh3), 527s, 518s, 506s,
w(Rh–CO), 475m, w(Rh–O), 381m.
2.2. Crystallographic study
2.1.15. Synthesis of [Rh(AsPh3)2(CO)(Q¦)](H2O) (15)
AsPh3 (306 mg, 1.0 mmol) was added to a solution of
[Rh(CO)2(Q¦)] (187 mg, 0.5 mmol) in dichloromethane
(30 cm3). Complex 15 was separated by addition of
light petroleum. Yield 25%. M.p. 166–167°C. Anal.
Calc. for C49H43N2O4As2Rh: C, 60.3; H, 4.4; N, 2.9%.
Crystal and experimental data are summarized in
Table 1. Bond distances and angles are listed in Tables
2 and 3, respectively. Yellow crystals of the compound
were obtained by slow evaporation from
a
dichloromethane/diethyl ether solution of 1. A crystal
with approximate dimensions of 0.3×0.4×0.4 mm
was mounted on Syntex P21 four circle diffractometer
and accurate lattice parameters were obtained by least-
1
Found: C, 60.4; H, 4.4; N, 2.8%. H-NMR (CDCl3):
l(AsPh3), 7.20–7.50mbr, 7.55–7.68mbr (30 H), l(Q¦),
1.98s (3 H, C6–CH3), 2.38s, (3 H, C3–CH3), 7.20–

194
C. Pettinari et al. / Journal of Organometallic Chemistry 566 (1998) 187–201
Fig. 9. ŽC(sp2)C(sp3)C(sp3) angle vs ꢀŽ~ꢀ and regression line.
programs PARST [20] and PLATON97 [21] have been
used for some geometrical calculations.
squares refinement of 40 reflections collected in the
range 10°52q525°. A total of 4538 unique reflections
were collected in the range 4°52q555° by a ꢀ/2q
scan data collection, of which 3492, with I greater than
3|(I), have been used in the successive refinement. A
continuous decay (:3.3%) of the standard reflections
intensity was observed and a correction was apported;
the data were also corrected for Lorentz and polariza-
tion effect. The „-scan of two reflections (3 0 0, 4 1 −
1) gave a minimum and a maximum transmission factor
equal to 0.86 and 1.07; the data were then corrected for
the adsorption using a semi-empirical method [13].
The structure was solved finding all the non-hydro-
gen atoms using the Sir92 program [14]. An isotropic
refinement, carried out with the CRYSTALS package
[15], gave an R factor equal to 0.091, and the successive
anisotropic refinement gave an R equal to 0.040.
3. Results and discussion
The proligand 1-phenyl-3-methyl-4-acetylpyrazol-5-
one, HQ¦, reacts with dinuclear [Rh(diolefin)Cl]2 com-
plexes in the presence of triethyl amine, yielding
mononuclear derivatives of formula [Rh(diolefin)(Q¦)]
(diolefin=1,5-cyclooctadiene
(COD),
bicy-
clo[2.2.1]hepta-2,5-diene (NBD) or 1,5-hexadiene
(HEX)) in accordance with Eq. (1):
[Rh(diolefin)Cl]2+2HQ¦
MeOH
+2NEt3 “ 2[Rh(diolefin)(Q¦)]+2Et3NH+Cl−
(1)
1: diolefin=COD
2: diolefin=HEX
3: diolefin=NBD
The hydrogens were imposed by model with d=1.0
A and Uiso fixed as 30% greater than the bonded atoms.
Complex 1 reacts with 1 mol of 4,7-dimethyl-1,10-
phenanthroline or 2,2%-bipyridil yielding the ionic com-
plexes 4 and 5 upon displacement of the donor (Q¦)−
˚
The structure was then anisotropically refined with the
hydrogens refined as riding. A final refinement was
carried out after an optimization of the weighting
scheme [16–18] using an optimized truncated Cheybi-
shev polynomial with coefficients a1=0.54, a2=0.50,
a3=0.30.
The R factor was equal to 0.031 at the end of the last
refinement cycle, with a maximum r.m.s. shift equal to
0.01.
All the refinements were carried out taking into
account the anomalous scattering contributions; the
scattering factors and the anomalous contribution were
taken from the International Tables [19]. All the calcu-
lations were carried out on a personal computer; the
from the coordination sphere of Rh(I) (Eq. (2)).
[Rh(COD)(Q¦)]+LEt O, N
2[Rh(COD)(L)](Q¦)
5: L=Bipy
(2)
2
“
4: L=Me Phen
2
This indicates that the existence of the anionic 4-
acylpyrazolonate is possible even though compounds of
alkali or alkanine earth metals such as Ba(Q¦)2 ·2H2O
or Na(Q¦)·H2O were reported to have negligible electri-
cal conductance value and presumably to be non-ionic
[22].
On the other hand the less basic 2-benzoylpyridine
reacts with 1 in the same conditions yielding a neutral
non-ionic derivative (Eq. (3)):

C. Pettinari et al. / Journal of Organometallic Chemistry 566 (1998) 187–201
195
Fig. 10. ~ Histogram.
[Rh(COD)(Q¦)]+BzpyEt O, N
2[Rh(COD)(Bzpy)](Q¦)
Instead the addition of HQ¦ to the solution obtained
by refluxing RhCl3 ·xH2O in dimethylformamide results
in the formation of [Rh(CO)2(Q¦)] (Eq. (7)). The latter
complex can also be obtained by the reaction of HQ¦
with [Rh(CO)2Cl]2 in presence of triethylamine (Eq.
(8)).
2
“
6
(3)
As with the corresponding i-diketonates [1,2,10,23],
triphenylphosphine (PPh3), triphenylphosphite
(P(OPh)3) and 1,2-bis(diphenylphosphino)ethane
(DPPE) react with complex 1 in diethyl ether with
displacement of the cycloocta-1,5-diene ligand and for-
mation of [Rh(PPh3)2(Q¦)] (7), [Rh(P(OPh)3)2(Q¦)] (8)
and [Rh(DPPE)(Q¦)]·H2O (9), respectively (Eqs. (4)
and (5)).
RhCl3.xH2O+3HQ¦HCONMe
“
2[Rh(CO)2(Q¦)]
(7)
11
MeOH
[Rh(CO)2Cl]2+2HQ¦+2NEt3 “ 2[Rh(CO)2(Q¦)]
11
+2Et3NH+Cl−
(8)
CH Cl
2
[Rh(COD)(Q¦)]+PR3 “ 2[Rh(PR3)2(Q¦)]+COD
Complex 11 interacts with one mole of Me2Phen or
Bipy with displacement of only one CO ligand and
formation of [Rh(CO)(Me2Phen)(Q¦)](H2O)2 (12) and
[Rh(CO)(Bipy)(Q¦)](H2O)2 (13), respectively (Eq. (9)).
7: R=Ph
8: R=OPh
(4)
[Rh(COD)(Q¦)]
[Rh(CO)2(Q¦)]+N2−donorEt O, H O
“
2
2
+DPPECH Cl /H O
“
[Rh(DPPE)(Q¦)]·H2O+COD
9
(5)
2
2
2
[Rh(CO)(N2−donor)(Q¦)](H2O)2+CO
13: N −donor=Bipy
(9)
As can be seen from the reactions carried out with
[Rh(COD)(Q¦)] y-acceptor ligands displace y-coordi-
nate olefins while mainly |-donor ligands displace i-
diketonate: the entering ligand is able to displace only a
chelate of the same nature. The explanation may be
that an entering y-acceptor group weakens the metal–
olefin bond; on the other hand, mainly |-donor lig-
ands, by increasing the charge density on the rhodium
atom, strengthen the y-olefinic and weaken the metal–
oxygen bond, favoring the displacement of i-
diketonate.
12: N −donor=Me Phen
2
2
2
Triphenylphosphine and triphenylarsine are also
able to displace one CO group from the coordination
sphere of rhodium, giving the complexes [Rh-
(PPh3)2(CO)(Q¦)](H2O)
(14)
and
[Rh(AsPh3)2(CO)(Q¦)](H2O) (15), respectively (Eq.
(10)).
CH Cl H O
2
2%
2
[Rh(CO)2(Q¦)]+EPh3
“
[Rh(EPh3)2CO(Q¦)](H2O)+CO
15: E=As
(10)
14: E=P
The addition of HQ¦ to light petroleum (40–60°)
solution of the dinuclear [Rh(CO)2Cl]2 produces the
derivative [Rh(CO)2(HQ¦)Cl] (10) (Eq. (6)).
This behavior is different from that described in litera-
ture. In fact, it is well known [1,23] that the carbonyl
groups in complexes of the type [Rh(CO)2(i-diketo-
[Rh(CO)2Cl]2+2HQ¦M“eOH2[Rh(CO)2(HQ¦)Cl]
(6)
10

196
C. Pettinari et al. / Journal of Organometallic Chemistry 566 (1998) 187–201
Fig. 11. ŽdRh–X vs ŽdCꢀC.
nate)] can be only partly replaced by ligands such as
triphenylphosphine or triphenylarsine, which, however,
coordinate rhodium in 1:1 ligand to metal ratio, ac-
cording to reaction 11:
ion-pairing effects, all the remaining 4-acetylpyra-
zolonato complexes 1–3 and 6–16 are non-electrolytes
in acetone and dichloromethane. The vaporimetric
molecular weight measurements carried out in chloro-
form only for sufficiently soluble derivatives indicate
that complexes 1–3 and 10–16 are mononuclear in
solution.
[Rh(CO)2(i−diketonate)]+EPh3
“[Rh(EPh3)(CO)(i−diketonate)]+CO
(11)
Selected relevant IR and NMR data are reported for
all the complexes 1–16 in Section 2.
Also in the case of the analogous ligand Q% (HQ%=1-
phenyl-3-methyl-4-benzoylpyrazol-5-one) [24] only one
EPh3 group (E=As or P) coordinates the rhodi-
um(I)carbonyl acceptor, yielding complexes of formula
[Rh(EPh3)(CO)(Q%)]. In our case, an increase of electron
density on rhodium resulting from the coordination of
1-phenyl-3-methyl-4-acetyl-pyrazol-5-onate ligand (Q¦)
which is more basic than (Q%) is likely responsible for
the coordination of two y-acceptor EPh3 groups.
The potentially tetradentate cyclooctatetraene (COT)
displaces all the CO ligands from [Rh(CO)2(Q¦)] yield-
ing the derivative [Rh(COT)(Q¦)] (16) (Eq. (12)).
In the far-IR spectrum of compounds 1–3 it is
possible to assign several medium absorptions at ca.
440 cm−1 to w(Rh–O) stretching vibrations, and also a
doublet in the 520–490 cm−1 region to w(Rh–C)
stretching vibrations [25]. This multiplicity is likely due
to asymmetry of the acylpyrazolonato donor and is in
accordance with a square pyramidal slightly distorted
structure such as found for 1 in the solid state.
According to the bond model of Dewar, Chatt and
Duncanson [26,27], the double bond character of the
olefin decreases upon coordination. In fact in the IR
spectra of 1–3, we observed a lowering in frequency of
w(CꢀC) (1460–1480 cm−1) which is coupled to the
mode l(CH2)scis and/or l(CH2)bend depending on the
olefin [28].
[Rh(CO)2(Q¦)]+COTEt O, H O
“
[Rh(COT)(Q¦)]+2CO
2
2
16
(12)
This is a difference with respect to the behavior
shown by other i-diketonates [2,24], which always gave
dinuclear derivatives of the formula [Rh2(COT)(i-dike-
tonate)2] when a similar reaction was carried out in
excess of [Rh(CO)2(i-diketonate)].
All the complexes 1–16 were identified by elemental
analyses, IR spectroscopy, 1H-NMR and, in some
cases, by 13C and 31P{1H}-NMR spectroscopy. They
are soluble in most common organic solvents. With the
exception of compounds 4 and 5, which show conduc-
tance values in acetone and dichloromethane typical of
partly ionized complexes likely due to the possibility of
1
In the H-NMR of the cycloocta-1,5-diene- (1) and
1,5-hexadiene-(pyrazolonato)rhodium (2) complexes the
feature of interest is the non-equivalence of the Ha and
Hb protons (Fig. 1) due to different CO donor groups
of the i-diketonate. On the other hand in the 1H-NMR
spectrum (CDCl3 or toluene-d8) of bicyclo[2.2.1]hepta-
2,5-diene derivative 3 the Ha and Hb became equivalent
due to a fluxional behavior analogous to that shown by
most of the bicyclo[2.2.1]hepta-2,5-diene rhodium(I)
derivatives synthesized to date [2,29].

C. Pettinari et al. / Journal of Organometallic Chemistry 566 (1998) 187–201
197
Fig. 12. dX…X vs ŽdRh–X with exponential curve fitting.
addition, in 4 and 5 the w(CꢀO) of (Q¦) falls at ca.
1615–1630 cm−1; this absorption is analogous to that
reported for ionic 1-phenyl-3-methyl-4-acylpyrazolon-5-
ato complexes [24].
Our hypothesis is also supported by the fact that in
the spectra of 4 and 5 the signals due to Ha and Hb
protons of the diolefin are equivalent. According to the
structure hypothesized, the four CH and CH2 groups
experience the same metal orbital shielding.
Derivative 6 is likely covalent both in the solid and
solution state, where it shows a completely non-elec-
trolyte behavior. The 2-benzoylpyridine ligand acts in
the N-monodentate form; in fact, the w(CꢀO) is un-
changed upon complexation. It has been previously
described that (Q)− ligands can act both in the O-
monodentate and O2-bidentate form, so that at least
two different structures (with a four- or a five-coordi-
nate rhodium) are possible; however, in compound 6
the w(CꢀO) due to 4-acetylpyrazolonato donor is
shifted to lower frequencies in accordance with an
involvement of both oxygens of (Q¦)− in the bonding
(Fig. 3). The w(Rh–C) and w(Rh–O) seem almost un-
changed with respect to the spectrum of the starting
derivative 1.
The temperature dependence of the NMR spectra of
complexes 1 and 2 was studied to detect any thermally
induced exchange processes. Their solution were heated
to 100°C and showed no broadening of the Ha and Hb
resonances.
1
In the H and 13C-NMR spectra all the olefin reso-
nances are shifted upfield upon coordination. The
1
2J(103Rh–1H) (1–2 Hz) and the J(103Rh–13C) (14–15
Hz) coupling constants are of the same order of magni-
tude as those reported for other i-diketonato rhodium
complexes [1,2,24,29].
The similarity between the 2J(103Rh–1Ha) and
2J(103Rh–1Hb) and between 1J(103Rh–13Ca) and
1J(103Rh–13Cb) indicates a very similar trans influence
of each oxygen donor of (Q¦).
The shift of the protons and carbons of the pyra-
zolonate ligand does not show appreciable variation on
changing the diolefin. The proton signals are generally
shifted downfield upon coordination: the trend and the
D (D is difference in chemical shift between the free
donor and the corresponding complex) are analogous
to those found in Cu{bis(triorganophosphine)}-
(pyrazolonato) [30] and diorganotin(IV)bis(pirazolo-
nato) derivatives [31].
In the case of derivatives 4 and 5, we hypothesize an
ionic structure with the 4-acylpyrazolonate donor out
of the coordination sphere of rhodium (Fig. 2). In fact,
the w(Rh–O) stretching vibrations are absent whereas
w(Rh–C) and w(Rh–N) are clear distinguishable.
Analogous complexes have been previously obtained
with 2,4-pentanedionato and 1-phenyl-3-methyl-4-ben-
zolypyrazolon-5-ato) ligand [10,24]: the 1H-NMR of
these species show the same multiplicity of signals and
the same chemical shift found in derivatives 4 and 5. In
In addition, in the 1H-NMR spectrum of 6 the
multiplicity of signals and the pattern of chemical shifts
due to olefin and the pyrazolonate moiety are
analogous to that found in the spectrum of compound
1.
Derivatives 7, 8, and 9 likely possess a square planar
structure in the solid state. In fact, the IR spectra of
these compounds are similar to those reported for
analogous derivatives, containing acetylacetonate and
triorganophosphine donors, for which an almost regu-

198
C. Pettinari et al. / Journal of Organometallic Chemistry 566 (1998) 187–201
Fig. 13. dX…X vs ꢀŽ~ꢀ.
lar square planar environment has been found [2,10]. In
the 600–200 cm−1 region it has been possible to assign
with certainty the medium absorption at ca. 400 cm−1
to w(Rh–O) stretching vibrations, whereas a strong
broad triplet near 500 cm−1 and a group of medium or
weak intensity at 270–250 cm−1 are likely due to
Whiffen’s y- and u,x-vibrations, respectively [32].
Compounds 7 and 8 show a very peculiar behavior in
there are four bands due to w(CO) stretching vibrations
typical of a cis-bonded Rh(CO)2 moiety [39] and a
strong w(Rh–Cl) at 307 cm−1 [40]. All these data
concur to indicate the arrangement in Fig. 4.
1
In the H-NMR spectrum of 10, the most interesting
feature is the strong deshielding of the methyl reso-
nances. Analogous downfield shift was observed in the
proton spectra of tin(IV) derivatives containing the
donor in the same neutral keto-enol form [41].
1
solution: in fact, as expected, the H-NMR spectra of
both complexes exhibit only one set of resonances for
each methyl group of Q¦. On the other hand, in both
31P-NMR spectra we found two very near double dou-
blets due to very similar phosphorous environments.
An analogous pattern has been previously observed in
other bis(triorganophosphino)rhodium(I) compounds
containing i-diketonates with two different donor arms
[2]. The values of the 1J(103Rh–31P) and 2J(31P–31P)
coupling constants are of the same order of magnitude
as those found in square-planar P2–Rh type derivatives
[33,34]. According to literature, the signals are shifted
downfield upon coordination; the difference in the
31P(l) between the complex and the corresponding free
donor [35–37] is larger in the complex 8 which contains
the triphenylphosphite ligand, a weaker |-electron
donor and a better y-electron acceptor than PPh3.
The 31P-NMR spectrum of compound 9 is also typi-
cal of a tetracoordinate rhodium(I) derivative: the 31P l
is shifted ca. 70 ppm downfield upon coordination,
while the value of the Rh–P coupling constant is very
close to that of derivative 7 and also to those reported
in literature for similar complexes [10,35–38].
The IR spectrum of derivative 11 exhibits four ab-
sorptions due to w(CO) likely attributable to different
Rh–OC moieties: in 11 the Q¦ ligand is less strongly
bonded to rhodium than in 1–3 or in 7–9: in fact, the
w(CꢀO) due to acylpyrazolonato falls at 1623 cm−1
,
indicating a lower donation due to trans effect of both
the CO groups. In the far-IR region, we observed some
absorptions at ca. 510 and 470 cm−1 assignable to
w(Rh–C) and others to w(Rh–O) at ca. 407 and 386
cm−1
, similar to those found in the analogous
Rh(CO)2(acac) [39].
In the 13C-NMR spectrum of 11, broad resonances
due to coordinate CO groups are found at 182.2 and
184.3 ppm, in accordance with the non-equivalence of
the two carbonyls found in the IR spectrum.
Derivatives 12–15 are hydrated and likely possess a
square-pyramidal geometry with the i-diketonato act-
ing in the bidentate fashion (Fig. 5): the CO stretching
vibrations were found at very low frequencies (ca. 1975
cm−1) typical of pentacoordinate rhodium derivatives
containing a CO donor in the apical position [42–45].
In the 1H-NMR spectra of 12 and 13 the methyl
resonances due to pyrazolonate show the same chemi-
cal shift (ca. 2.40 and 1.90 ppm) of parent compounds
7 and 8 containing two triorganophosphino groups.
The 31P-NMR spectrum of 12 is typical of both penta-
Derivative 10 shows an IR spectrum typical of a
neutral HQ¦ in the keto-enol form. We found a very
broad band centered at ca. 2700 cm−1 due to the
intramolecular H-bond absorption of Q¦. Moreover,

C. Pettinari et al. / Journal of Organometallic Chemistry 566 (1998) 187–201
199
1
and tetracoordinate species: in fact the J(103Rh–31P)
coupling constant is ca. 130 Hz [10,35–38]. We do not
exclude a partial dissociation of the P and/or O-donor
in solution.
This is evident by considering the angle ƒ between
the interacting atom, the Rh and the normal of the
coordination plane, and the angle „ between the inter-
acting atom, the Rh and the centroid of the four C(sp2)
atoms in COD. Fig. 7 shows that for the structures
investigated (34 different Rh· · ·Y interactions) these
angular values are all clustered around well defined
values for both „ and ƒ: 99.5°5„5128.4° and
15.3°5ƒ540.6° (atoms approaching Rh from ‘above’)
or 143.6°5ƒ5162.1° (atoms approaching Rh from
‘below’). We find for (COD)Rh(Q¦) ƒ=18.5° and „=
107.9°. The distribution of „ and ƒ is independent from
the chemical nature of the atoms, and from the inter or
intramolecular nature of the interaction (we considered
only intramolecular interactions due to atoms far at
least four bonds from Rh). As a general trend (as
expected anyway) C(sp3) have the longest non-bonding
distance (the mean difference D with respect to the Van
In the 1H-NMR spectra of 14 and 15, we found
several broad multiplets of signals for each equivalent
proton group, likely due to the existence of different
isomers in solution.
Complex 16 is likely mononuclear with the cyclooc-
tatetraene ligand coordinated to rhodium in the biden-
tate form: two different sets of signals were found for
the carbons linked to rhodium and also for the corre-
sponding protons. The signals are shifted highfield
upon coordination. The not-bonded CH groups exhibit
a singlet in the H and four singlet in the 13C-NMR
spectrum. These signals are shifted slightly upfield with
respect to the same signals in the spectrum of the
non-coordinated olefins [46,47].
1
˚
der Waals radii is 0.08 A for the intermolecular con-
3.1. Description of crystal structure of [Rh(COD)(Q¦)]
(1)
tacts) with respect e.g. C(sp3), which have a D equal to
˚
0.19 A for the same conditions, or alogens (only one
˚
3.1.1. Rhodium coordination sphere
structure reported with D=0.23 A). Intramolecular
The adduct (Fig. 6) presents a slightly distorted
square planar coordination which is best evident from
the rhodium coordination bond angles (see Table 3)
and from the slightly non-planar arrangement of the
Rh, the oxygens atom of Q¦ and the double bond
centroids of 1,5-cyclooctadiene. This distortion with
respect to the ideal geometry seems to be a common
feature of almost all of the (COD)Rh adducts with
1,3-diketo ligands [2,10,48–56]. The mean value of
X–Rh–X (X’s are the centroids of the double bonds in
COD) and O–Rh–O for 15 similar independent frag-
ments are in fact 88.611 and 89.853°, not far from the
values found in our structure. The distances for Rh–C
and Rh–O agree with those reported for similar struc-
tures. A small but significant difference is observed
between the two Rh–O distances, probably due to the
unequal sharing of the negative charge onto the differ-
ent oxygens and possibly related, through a sort of
trans effect, to the small differences observed for the
two Rh–X and four Rh–C distances.
contacts tend to be shorter with respect to the inter-
molecular ones, probably due to the intrinsic geometri-
cal constraints imposed. We are not able, due to the
generality of the phenomena, to give a precise explana-
tion for these interactions.
Most probably the plot of Fig. 7 just maps, in terms
of the chosen angles, which region around the COD–
Rh–O2 presents the less repulsive potential, in agree-
ment with the qualitative observation of the bulkiness
of COD, and maybe defines a preferential way of
approach to Rh itself. This statement is reinforced from
the fact that a more general analysis, irrespective of the
nature of the ligand, gave us the same general trend
(Fig. 8).
A possible path to pentacoordination, as suggested
for different tetracoordinated adducts [69], cannot be
excluded, but we do not observe any correlation be-
tween the out-of-plane shift of the Rh atom and the
non-bonding distances. This is probably due to the
geometrical constraints imposed by the bidentate COD
in this kind of adduct and even due to weakness of the
interaction.
The adduct does not show any Rh· · ·Rh interaction
˚
below 4.0 A, as observed for other similar square
planar adducts [57–59], but it is interesting anyway to
note the presence of a relatively weak intermolecular
3.1.2. COD geometry
˚
˚
contact at 3.665(5) A, 0.3 A less than the sum of the
Van der Waals radii [60] between Rh and C(11).
This Rh–C(sp2) weak interaction seems to be not
exclusive to this structure: a closer inspection of several
other (COD)Rh square planar adducts with O-donor
ligands, indicates the presence of non-bonding contacts.
We found that for 17 different structures [2,49–52,55–
57,59,61–68] a similar kind of interaction was present,
and the spatial distribution of the weakly interacting
atoms led us to define a preferred way of interaction.
As already indicated in several different adducts of
this type, COD ligand shows a twisted boat conforma-
tion in the Rh(COD)(Q¦) adduct structure. The skew-
ness of COD can be assessed considering several
different descriptors: the puckering parameters [70–72],
the C(sp2)C(sp3)C(sp3)C(sp2) torsion angles (~ here-
after), or the ring-crossed C· · · (non-bonding contacts)
[49]. All of these parameters can be used in order to
describe the COD conformation, the puckering parame-
ters giving probably the most complete description, and

200
C. Pettinari et al. / Journal of Organometallic Chemistry 566 (1998) 187–201
the torsion angles giving the most pictorial. An interest-
ing feature emerging from the conformational analysis
of COD, in square planar rhodium complexes, is the
conformational rearrangement which COD undertakes
upon complexation. It is well established that the free
COD, still in a twisted-boat conformation, presents a
greater skewness with respect to the COD as a ligand in
adducts. Hagen et al. [73] reported a value for ~ of
63.8° for the free COD in gas-phase (C2 symmetry), and
two independent crystallographic structures of differ-
ently substituted dibromoCOD [74,75] give the values
of 65 and 63.8°.
The plot of ŽdX–Rh versus ŽdCꢀC shows a not
unexpected trend (see Fig. 11), with X–Rh distance
decreasing as the ŽCꢀC increase (the same trend is
observed, even if less clear, for dX…X vs ŽdCꢀC). This
result is in agreement with the expected effects of the
donation/backdonation interplay between the olefin
and the metal atom, and of the lengthening of the
double bonds for stronger Rh–olefin interactions. The
dX…X distance versus ŽdX–Rh shows a good correlation
(Fig. 12) of these two parameters. The data have been
best fitted by using an exponential function, relating
force of the olefin–Rh interaction, as represented by
The situation is rather different when we consider the
COD as a ligand as showed by a simple statistical
analysis through the Cambridge Crystallographic Data-
base (CSD hereafter, version 5.14, October 1997) [76]
on the (COD)Rh square planar adducts. The analysis
of 134 independent fragments (104 different Ref. codes)
with a reliable geometry, which have R factors less than
10%, no structural disorder of polymeric structures (but
no restraints were imposed on standard deviations),
showed that C(sp2)C(sp3)C(sp3)C(sp2) torsion angles
are distributed between −49 and 60°, with three max-
ima for ~ at ꢀ 928 and ꢀ0°, and most of the data
are in the range −40 to 40° (we found −20.7 and
−17.7° for Rh(COD)(Q¦)). This behavior of the tor-
sion angle distribution is easily interpreted as a result of
the two major forces acting on the COD conforma-
tions: the intramolecular steric repulsion in COD, and
the geometrical requirements for a y-bond between
COD and Rh, according to the Chatt–Dewar–Dun-
canson model [17,18]. The intramolecular steric repul-
sion obviously tends to distort the molecule from the
more symmetric boat conformation, an extreme case in
this sense is that of 1,2,5,6-tetrakis(trimethylsi-
lylethynyl)COD [77] which assumes a twist-chair con-
formation in order to minimize the interatomic
repulsions between the four bulky trimethylsilylethynyl
groups. On the other side, an ideal y-bond would
require the olefinic fragments symmetrically arranged
around the metal atom, due to the symmetry of its
d-orbitals. Such a restraint would impose a more sym-
metrical C2v conformation on COD, which is in prac-
tice seldom observed because of the steric relief of the
structure, mainly on the bond angles (see Fig. 9) and
less on the bond distances. The distribution reported in
Fig. 10 is therefore indicative of the energy balance
between the two opposite forces acting on the COD
conformation: a gain in bonding energy is possible only
with an increase of the strain, and then in energy, in
COD structure. Many of the structures found in the
CSD have ꢀŽ~ꢀ between 20 and 35°, with a maximum
at around 28°, whereas several others have a torsional
angle nearer to 0°, indicating a dominance of the
bonding effects over interatomic repulsion and angle
strains.
the ŽdX–Rh, with the bite angle requirements (dX…X)
for such a kind of adduct.
Finally a check for possible relationship between
Žꢀ~ꢀ and the dX…X distance was done (Fig. 13), but a
clear correlation was not found. The only observation
we can make is the almost random distribution of dX…X
for 0°BꢀŽ~ꢀB20°, and a broad linear correlation for
values of the mean absolute torsion angle greater than
20°. A possible explanation for this behavior relies on
the plot of Fig. 10, which shows that for values of Žꢀ~ꢀ
less than 20° the internal bond angles in COD are
substantially strained. The COD structural rearrange-
ment, when the torsion angle falls below 20° is there-
fore not purely torsional, but even due to a greater
strain of the structure. For torsion angles greater than
20° the COD rearrangement seems to be due mostly to
a torsion around the C(sp3)–C(sp3) bonds, explaining
the broad correlation between ꢀŽ~ꢀ and dX…X observed
for such values of the absolute torsion angles.
Acknowledgements
Financial support by Universita` degli Studi di
Camerino, Consiglio Nazionale delle Ricerche
(C.N.R.), Rome.
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