Synthesis, characterization, and reactivity toward Mel of carbonyl Rh(I) complexes containing a PNO hydrazonic ligand

Article abstract of DOI:10.1021/om000562r

The reaction of the potentially tridentate hydrazonic ligand 2-(diphenylphosphino)benzaldehyde benzoylhydrazone (HL, 1) with Rh₂(CO)₄Cl₂ in diethyl ether led to the isolation of Rh(HL)(CO)Cl (2), where the neutral ligand was PN bidentate. Addition of Et₃N or NaOMe caused the deprotonation of the ligand, with the consequent formation of the three-coordinated carbonyl Rh(I) complex Rh(L)(CO) (3), which was X-ray characterized. The 2 → 3 conversion was reversible, as it was found that 2 could be regenerated by bubbling a stoichiometric amount of HC1 into an ethereal solution of 3. On treating a solution of 2 with silver triflate, the cationic carbonyl complex [Rh(HL)(CO)](CF₃SO₃) (4) was obtained, where the neutral ligand showed a tridentate PNO behavior. All the complexes were allowed to react with Mel at room temperature. Complex 2 led to two different acetyl stereoisomers Rh(HL)(MeCO)ClI (5), where the neutral ligand coordinated in a PNO fashion. Complex 3 led to different products depending on the reaction solvent; thus the pentacoordinated acetyl complex Rh(L)(MeCO)I (8) and the solvated octahedral acetyl complex [Rh(L)(MeCO)(THF)I](THF) (9) were isolated in CH₂Cl₂ and in THF, respectively; the X-ray structure of 9 is reported. On carrying out the reaction in Et²O, the immediate precipitation of the hexacoordinated methylcarbonyl complex Rh(L)(CO)(Me)I (7) was observed, which rapidly rearranged into 8 after dissolution in CH₂Cl₂ or CHCl₃. Finally, the reaction between 4 and Mel formed the cationic PNO coordinated acetyl complex [Rh(HL)(MeCO)I](CF₃SO₃) (10). All the oxidative addition reactions were monitored by liquid IR spectroscopy.

Full text of DOI:10.1021/om000562r

5440
Organometallics 2000, 19, 5440-5446
Syn th esis, Ch a r a cter iza tion , a n d Rea ctivity tow a r d MeI
of Ca r bon yl Rh (I) Com p lexes Con ta in in g a P NO
Hyd r a zon ic Liga n d
Paolo Pelagatti,*,† Alessia Bacchi,† Carla Bobbio,† Mauro Carcelli,† Mirco Costa,‡
Corrado Pelizzi,† and Cristiano Vivorio‡
Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica,
Universita` degli Sudi di Parma, Parco Area delle Scienze 17/ A 43100-Parma, Italy, and
Dipartimento di Chimica Organica ed Industriale, Universita` degli Studi di Parma,
Parco Area delle Scienze 17/ A 43100-Parma, Italy
Received J une 29, 2000
The reaction of the potentially tridentate hydrazonic ligand 2-(diphenylphosphino)-
benzaldehyde benzoylhydrazone (HL, 1) with Rh2(CO)4Cl2 in diethyl ether led to the isolation
of Rh(HL)(CO)Cl (2), where the neutral ligand was PN bidentate. Addition of Et3N or NaOMe
caused the deprotonation of the ligand, with the consequent formation of the three-
coordinated carbonyl Rh(I) complex Rh(L)(CO) (3), which was X-ray characterized. The 2 f
3 conversion was reversible, as it was found that 2 could be regenerated by bubbling a
stoichiometric amount of HCl into an ethereal solution of 3. On treating a solution of 2 with
silver triflate, the cationic carbonyl complex [Rh(HL)(CO)](CF3SO3) (4) was obtained, where
the neutral ligand showed a tridentate PNO behavior. All the complexes were allowed to
react with MeI at room temperature. Complex 2 led to two different acetyl stereoisomers
Rh(HL)(MeCO)ClI (5), where the neutral ligand coordinated in a PNO fashion. Complex 3
led to different products depending on the reaction solvent; thus the pentacoordinated acetyl
complex Rh(L)(MeCO)I (8) and the solvated octahedral acetyl complex [Rh(L)(MeCO)(THF)I]-
(THF) (9) were isolated in CH2Cl2 and in THF, respectively; the X-ray structure of 9 is
reported. On carrying out the reaction in Et2O, the immediate precipitation of the
hexacoordinated methylcarbonyl complex Rh(L)(CO)(Me)I (7) was observed, which rapidly
rearranged into 8 after dissolution in CH2Cl2 or CHCl3. Finally, the reaction between 4 and
MeI formed the cationic PNO coordinated acetyl complex [Rh(HL)(MeCO)I](CF3SO3) (10).
All the oxidative addition reactions were monitored by liquid IR spectroscopy.
In tr od u ction
PN coordinationswas a fundamental requirement for
the substrate coordination and then for the catalytic
activity.
The potentially tridentate PNO ligand 2-(diphenylphos-
phino)benzaldehyde benzoylhydrazone (HL, 1), along
with other similar acyl hydrazonic ligands, has been
recently employed by us in the synthesis of Pd(II)
complexes. HL always behaved as a tridentate anionic
ligand, leading to complexes of the type Pd(L)X (X )
OAc, Cl, I), where the deprotonated ligand coordinated
the metal by means of the three P, N, and O donor
atoms.1 These complexes were used as catalysts in the
chemoselective homogeneous hydrogenation of terminal
alkynes; the mechanistic study of the reaction supported
the heterolytic cleavage of the molecular hydrogen,
occurring with protonation of the hydrazonic nitrogen
and formation of a Pd(II) hydride.2 In the proposed
catalytic cycle, the hemilability of the ligandsPNO or
In light of the lack of data concerning the use of
tridentate ligands in organometallic chemistry and
catalysis,3 and with the aim of extending the knowledge
on the coordinating capability of HL toward other soft
metal ions, here we report on the synthesis and char-
acterization of some carbonyl Rh(I) complexes contain-
ing HL as ligand. To our best knowledge, the only exam-
ples of rhodium complexes with a tridentate PNO acyl-
hydrazone ligand are those recently reported by Shaw.4
In view of the enormous importance of the oxidative
addition step in many metal-catalyzed reactions,5 the
reactivity of the isolated carbonyl Rh(I) complexes
toward methyl iodide was investigated. Furthermore,
the X-ray crystal structures of a carbonyl Rh(I) complex
and of an acetyl Rh(III) complex are reported.
† Dipartimento di Chimica Generale ed Inorganica, Chimica Anal-
itica, Chimica Fisica.
(3) (a) Ru¨lke, E. R.; Kaasjager, V. E.; Wehman, P.; Elsevier: C. J .;
van Leeuwen, P. W. N. M.; Vrieze, K.; Fraanje, J .; Goubitz, K.; Spek,
A. L. Organometallics 1996, 15, 3022. (b) Bhattacharyya, P.; Parr, J .;
Slawin, A. M. Z. J . Chem. Soc., Dalton Trans. 1998, 3609, and
references therein.
(4) Ahmad, M.; Perera, S. D.; Shaw, B. L.; Thornton-Pett, M. J .
Chem. Soc., Dalton Trans. 1997, 2607.
‡ Dipartimento di Chimica Organica ed Industriale.
(1) (a) Bacchi, A.; Carcelli, M.; Costa, M.; Pelagatti, P.; Pelizzi, C.;
Pelizzi, G. Gazz. Chim. Ital. 1994, 124, 429. (b) Bacchi, A.; Carcelli,
M.; Costa, M.; Leporati, A.; Leporati, E.; Pelizzi, C.; Pelizzi, G. J .
Organomet. Chem. 1997, 535, 107.
(2) Pelagatti, P.; Bacchi, A.; Carcelli, M.; Costa, M.; Fochi, A.;
Ghidini, P.; Leporati, E.; Masi, M.; Pelizzi, C.; Pelizzi, G. J . Organomet.
Chem. 1999, 583, 94.
(5) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis, 2nd ed.;
Wiley-Interscience: New York, 1992.
10.1021/om000562r CCC: $19.00 © 2000 American Chemical Society
Publication on Web 11/04/2000

Carbonyl Rh(I) Complexes Containing a PNO Ligand
Organometallics, Vol. 19, No. 25, 2000 5441
Sch em e 1
Sch em e 2
nated CtO ligand. In 3 the electronic density on the
metal is higher than in 2, owing to the anionic tridentate
character of the ligand; this causes a higher metal-CO
back-donation and the consequent lowering of the
carbonyl stretching frequency (1982 cm-1 for 3 and 2005
cm-1 for 2). By slow evaporation of a toluene solution
of 3, crystals suitable for X-ray analysis confirmed the
proposed structure of the complex (vide infra). Interest-
ingly, the 2 f 3 conversion is reversible, as we found
out that by bubbling a stoichiometric amount of gaseous
HCl in an ethereal solution of 3, the fast re-formation
of 2 was observed (Scheme 1). The reaction may proceed
either by direct protonation of the hydrazonic nitrogen
of the ligand and attack of the Cl- anion to rhodium
(as already hypothesized by us for the molecular hy-
drogen activation catalyzed by palladium(II) complexes)
or by a two-step path: oxidative addition of HCl on
rhodium followed by hydrogen shift to the ligand.
To force the protonated ligand to coordinate the metal
in a tridentate fashion, a reaction of 2 with silver triflate
was carried out in dichloromethane. Fast formation of
silver chloride was observed, and [Rh(HL)(CO)](CF3SO3)
(4) was isolated (Scheme 2).
Resu lts a n d Discu ssion
Syn th esis of th e Ca r bon yl Rh (I) Com p lexes.
Reaction of 1 mol of Rh2(CO)4Cl2 with 2 mol of HL in
diethyl ether led to the fast precipitation of Rh(HL)-
(CO)Cl (2), in which the neutral ligand coordinates the
metal by means of the phosphorus and the iminic
nitrogen atoms (Scheme 1).
The 31P NMR spectrum showed a doublet centered
at 49.9 ppm with a J Rh-P ) 163 Hz, typical values for a
phosphine coordinated to Rh(I) and cis to a carbonyl
group.6 The square-planar geometry is completed by a
chlorine ligand trans to the phosphorus atom. The
adopted stereochemistry is fully consistent with the
donating properties of the groups around the metal; that
is, the π-accepting ligands (P and CO) are positioned
trans to the mainly σ-donor ones (Cl and N), thus
reaching the most thermodynamically stable arrange-
1
ment. The hydrazonic proton was not visible in the H
NMR spectrum, but its presence was confirmed by a
weak stretching band at 3205 cm-1 in the IR spectrum.
The remarkable high chemical shift observed for the
iminic proton (10.02 ppm) is attributable to the flex-
ibility of the ligand, which may allow the electron-
withdrawing oxygen atom to point to the iminic proton.
Such an interaction, as intramolecular hydrogen bond-
ing, has already been evidenced by us in the crystalline
structures of a methyl and an acetyl Pd(II) complex
containing the ligand 2-pyridylcarboxaldehyde benzoyl-
hydrazone.7 The IR stretching of the CdO bond in 2 was
well visible with a strong band at 1683 cm-1, while an
intense IR band at 2005 cm-1 demonstrated the pres-
ence of a CtO bonded to Rh(I). Deprotonation of the
ligand by a base such as MeONa or Et3N led to the
isolation of Rh(L)(CO) (3), in which the deprotonated
ligand coordinates rhodium in a tridentate PNO fashion
(Scheme 1). Its 31P NMR spectrum showed a doublet
centered at 49.6 ppm with a J Rh-P ) 160 Hz, while its
1H NMR spectrum strongly resembled those of the Pd-
(L)X complexes.1,2 In the IR spectrum neither the ν(NH)
nor the ν(CdO) bands were present, while an intense
signal at 1982 cm-1 indicated the presence of a coordi-
In this complex the phosphorus atom originates a
doublet at 50.8 ppm with a J Rh-P ) 162 Hz, while the
hydrazonic proton gives rise to a singlet at 13.60 ppm
1
in the H NMR spectrum. In the IR spectrum, a weak
band at 3200 cm-1 was attributed to the ν(NH), while
a strong signal split in two bands at 1603-1555 cm-1
was ascribed to the coordinated CdO amide group of
the ligand,8 where the signal at lower frequencies might
contain the contribution of the CdN stretching. The
metal valence is satisfied by an uncoordinated triflate
anion, originating a strong IR band with two maxima
at 1299 and 1241 cm-1, respectively.9
Complexes 2 and 3 are stable in the solid state,
whereas in solution only complex 3 is stable for weeks
under a nitrogen atmosphere. Complex 4 is poorly stable
even in the solid state, and in order to prevent the
formation of metallic rhodium, it must be stored at low
temperature in an inert atmosphere.
(8) (a) Empsall, H. D.; Hyde, E. M.; Pawson, D.; Shaw, B. L. J . Chem.
Soc., Dalton Trans. 1977, 1292. (b) Empsall, H. D.; J ohnson, S.; Shaw,
B. L. J . Chem. Soc., Dalton Trans. 1980, 302. (c) Braunstein, P.; Matt,
D.; Dusausoy, Y. Inorg. Chem. 1983, 22, 2043. (d) Groen, J . H.; Delis,
J . G. P.; van Leeuwen, P. W. N. M.; Vrieze, K. Organometallics 1997,
16, 68. (e) Groen, J . H.; de Zwart, A.; Vlaar, M. J . M.; Ernsting, J . M.;
van Leeuwen, P. W. N. M.; Vrieze, K.; Kooijman, H.; Smeets, W. J . J .;
Spek, A. L.; Budzelaar, P. H. M.; Xiang, Q.; Thummel, R. P. Eur. J .
Inorg. Chem. 1998, 1129.
(6) (a) Roundhill, D. M.; Bechtold, R. A.; Roundhill, S. G. N. Inorg.
Chem. 1980, 19, 284. (b) Anderson, M. P.; Casalnuovo, A. L.; J ohnson,
B. J .; Mattson, B. M.; Mueting, A. M.; Pignolet, L. H. Inorg. Chem.
1988, 27, 1649.
(7) Pelagatti, P.; Carcelli, M.; Franchi, F.; Pelizzi, C.; Bacchi, A.;
Fochi, A.; Fru¨hauf, H.-W.; Goubitz, K.; Vrieze, K. Eur. J . Inorg. Chem.
2000, 463.
(9) (a) Lawrence, G. A. Chem. Rev. 1986, 86, 17. (b) Stang, P. J .;
Huang, Y.-H.; Arif, A. M. Organometallics 1992, 11, 231. (c) Burger,
P.; Baumeister, J . M. J . Organomet. Chem. 1999, 575, 214.

5442 Organometallics, Vol. 19, No. 25, 2000
Pelagatti et al.
Sch em e 3
F igu r e 1. View of the structure of the complex Rh(L)(CO)
(3). Thermal ellipsoids are drawn at the 30% probability
level. The toluene solvation molecule is omitted for clarity.
geometry of the five-membered chelation ring formed
by the negatively charged hydrazonic system compares
well with the one observed in µ-N,N′-dibenzoylhydrazi-
dobis(dicarbonylrhodium),10 where the double negative
charge of the ligand is shared by two symmetry equiva-
lent Rh(I) atoms (Rh-N ) 2.07, N-N ) 1.40, N-C )
1.31, C-O ) 1.25, Rh-O ) 2.03 Å, N-Rh-O ) 78°).
The ligand core, defined by atoms C1-C14, O1, N1,
N2, P is planar within 0.4 Å, and the largest deviations
are due to the terminal C9-C14 phenyl, which is
rotated by 18° around the C8-C9 bond with respect to
the average ligand plane.
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p lex 3
Rh-P
2.184(5)
2.05(1)
2.02(1)
1.77(2)
1.23(2)
N1-N2
N1-C7
N2-C8
C27-O2
1.40(2)
1.23(4)
1.32(4)
1.18(2)
Rh-O1
Rh-N1
Rh-C27
O1-C8
P-Rh-O1
173.1(3)
95.7(4)
87.5(7)
77.5(5)
99.3(7)
176.2(9)
Rh-O1-C8
Rh-N1-N2
Rh-N1-C7
N2-N1-C7
N1-N2-C8
Rh-C27-O2
111(1)
114.6(9)
129(2)
116(2)
109(2)
178(2)
P-Rh-N1
P-Rh-C27
O1-Rh-N1
O1-Rh-C27
N1-Rh-C27
The unit cell contains also a toluene molecule disor-
dered around an inversion center.
Oxid a tive Ad d ition Rea ction s w ith MeI. To in-
vestigate the reactivity of the carbonyl Rh(I) complexes
2-4 toward oxidative addition, solutions of 2, 3, and 4
were allowed to react with an excess of MeI at room
temperature.
Complexes 2, 3, and 4 are examples of the high
versatility of HL, which can adopt a tridentate PNO
coordination both in the neutral (4) and in the anionic
(3) form, as well as a bidentate PN coordination when
it is protonated (2).
The reaction involving 2 was carried out in dichlo-
romethane and led to the precipitation of a yellow
powder. The NMR data of the filtered product Rh(HL)-
(MeCO)ClI (5 in Scheme 3), recorded in deuterated
methanol, showed unequivocally the presence of two
different acetyl isomers, as pointed out by two doublets
in the 31P NMR spectrum (58.4 ppm, J Rh-P ) 150 Hz
and 54.0 ppm, J Rh-P ) 152 Hz, respectively) and by two
The crystal structure of compound 3 is shown in
Figure 1, along with the numbering scheme. The Rh(I)
atom is surrounded by the PNO chelating system of L-
and by a CO ligand, in a square-planar fashion.
Table 1 reports the most relevant bonding parameters
for 3.
The bond angles O1-Rh-N1 (77.5(5)°) and P-Rh-
N1 (95.7(4)°) are strained due to the geometric con-
straints imposed by the five-membered O1-C8-N1-
N2-Rh and six-membered N1-C7-C6-C1-P-Rh
chelation rings, respectively. The Rh-C27 bond (1.77-
(2) Å) to the carbonyl ligand shows a remarkable
shortening compared with the average (1.824(2) Å)
observed for the 419 crystal structures containing a
tetracoordinated rhodium bonded to a CO molecule.
Accordingly, the C27-O2 bond (1.18(2) Å) is weaker
than the average (1.141(1) Å) found in the above
collection of 419 compounds present in the Cambridge
Structural Database. This is in agreement with spec-
troscopic data and indicates a high degree of back-
donation exerted by the metal on the CO molecule,
confirming that the deprotonated ligand is able to
transfer electron density on the metal through N1 and
O1. In fact, the Rh-O1 bond (2.05(1) Å) is among the
shortest ever observed for all known 56 square-planar
rhodium complexes containing the trans O-Rh-P
system, where the Rh-O distances range from 2.03 to
2.25 Å and where bonds shorter than 2.05 Å occur only
in the presence of an acetylacetonate ligand. The
1
singlets in the H NMR spectrum (2.87 and 2.62 ppm,
respectively); only an intense band at 1689 cm-1 was
detected in the acetyl stretching region of the IR
spectrum. The sharpness of the NMR lines ruled out
any fluxional behavior. On the basis of the NMR
integrals, a 2:1 ratio was established between the two
isomers, with the more deshielded NMR lines belonging
to the most abundant one; the ratio did not change
maintaining the solution at room temperature for
several hours. No NMR signal for a hydrazonic proton
was found, but its presence was confirmed by a weak
IR band centered at 3132 cm-1. The coordination of the
carbonyl oxygen of the ligand gave rise to an intense
bifurcated band at 1600-1558 cm-1, as previously
observed in 4. The stability in solution of the coordinat-
ing Rh-O bond (supported by the sharpness of the NMR
lines) excludes the possibility of having coordinating
isomers, and then the two different detected species can
be geometrical or rotational isomers; the presence of two
1
acetyl resonances in the H NMR spectrum is in favor
(10) Doedens, R. J . Inorg. Chem. 1978, 17, 1315.

Carbonyl Rh(I) Complexes Containing a PNO Ligand
Organometallics, Vol. 19, No. 25, 2000 5443
Sch em e 4
ligand and an iodine atom completed the square plane,
while a THF molecule and an acetyl group occupied the
apical positions.
The reaction between 3 and MeI was repeated in
diethyl ether. When the alkyl halide was added, the
immediate precipitation of Rh(L)(Me)(CO)I (7) was
observed, for which the stereochemistry depicted in
Scheme 4 is assumed. In its IR spectrum the presence
of the CtO ligand was pointed out by an intense band
at 2075 cm-1, while the remaining part of the spectrum
was identical to that of 3. In deuterated chloroform the
methyl group attached to rhodium was visible as a
triplet at 0.90 ppm, with a J Rh-H ) J P-H ) 2.2 Hz; on
standing the solution at room temperature, such a
signal disappeared in favor of a singlet at 2.95 ppm.
Moreover, the 31P NMR spectrum of 7 recorded in CDCl3
at room temperature showed only the doublet already
seen for 8, while at 233 K a doublet centered at 45.9
ppm with a J Rh-P ) 115 Hz was detected, which are
values similar to those found for a strictly related
carbonyliodomethyl Rh(III) complex.4 These data agree
with the role of intermediate species 7 in the formation
of 8 (Scheme 4).
of the former type of isomerism.11 On considering that
the apical disposition of the acetyl ligand seems to be
the most likely for acetyl rhodium(III) complexes,12 we
assume that in the most abundant isomer of 5 this
ligand occupies an apical position. Complex 5 dissolved
in deuterated Me2SO generated only one set of NMR
signals, with the acetyl group giving rise to a singlet at
The addition of an excess of MeI to a dichloromethane
solution of 4 led to the formation of [Rh(HL)(MeCO)I]-
(CF3SO3) (10 in Scheme 2) as a unique acyl species, in
which the neutral ligand coordinates the metal in a
tridentate PNO fashion. The presence of the NH bond
was clear both in the IR spectrum (weak band at 3191
1
2.47 ppm in the H NMR spectrum and the phosphorus
atom originating a doublet at 50.3 ppm (J Rh-P ) 149
Hz) in the 31P NMR spectrum. In the CI-MS spectrum
of the Me2SO solution two peaks corresponding to the
two acetyl complexes Rh(L)(MeCO)I (6a , m/z ) 679,
relative intensity ) 67) and Rh(L)(MeCO)Cl (6b, m/z )
587, relative intensity ) 55) were visible, pointing out
the solvent-induced de-hydrohalogenation of 5, which
is a known effect for complexes containing neutral acyl
hydrazonic ligands.13 Probably a Me2SO molecule com-
pletes the octahedral geometry, as shown in Scheme 3.
No attempts were made to separate 6a and 6b.
1
cm-1) and in the H NMR spectrum (broad singlet at
13.90 ppm). The involvement of the CdO group of the
ligand in the coordination was pointed out by a bifur-
cated IR band at 1604-1557 cm-1, while the singlet at
1
3.03 ppm in the H NMR spectrum was attributed to
the acetyl group bonded to rhodium. The stretching of
the acetyl ligand was found at 1702 cm-1; in the 31P
NMR spectrum there was a doublet centered at 54.5
ppm with a J Rh-P ) 148 Hz.
In the solid state, complexes 5, 7, and 8 are stable
for weeks; complex 9 partially transforms into 8 after
some days at room temperature by losing THF, whereas
complex 10 decomposes after a few days. In solution
complexes 5, 8, and 9 are stable for days under nitrogen,
whereas complex 10 decomposes rapidly. Complex 8
remains stable also in refluxing CH2Cl2 without observ-
ing any decarbonylation process as described for other
pentacoordinated acetyl Rh(III) complexes.14
The reactions between 2, 3, and 4 with MeI at room
temperature were monitored by liquid IR (CH2Cl2), by
using solutions having comparable complex concentra-
tions.
When complex 3 and MeI were allowed to react in
dichloromethane, the coordinatively unsaturated acetyl
complex Rh(L)(MeCO)I (8 in Scheme 4) was isolated.
The MeCO moiety originates a singlet at 2.95 ppm in
1
the H NMR spectrum and a strong IR stretching band
at 1727 cm-1 (both in KBr and in CH2Cl2). In the 31P
NMR spectrum was present a doublet centered at 49.4
ppm with a J Rh-P ) 144 Hz. On carrying out the
reaction in THF, complex [Rh(L)(MeCO)(THF)I](THF)
(9 in Scheme 4) was isolated; its spectroscopic patterns
were similar to those of 8, but the acetyl stretching band
was centered at 1690 cm-1 (1727 cm-1 in CH2Cl2), and,
1
in the H NMR spectrum recorded in CDCl3, were also
In the reaction with complex 2 after 30 min from the
MeI addition, the stretching band of the starting com-
plex was still present (2015 cm-1) together with a band
at 2084 cm-1, and no signal for an acetyl group was vis-
ible. With the progress of the reaction an intense band
at 1727 cm-1 appeared, and in the carbonyl region was
noted the presence of an additional weak band at 2101
cm-1; within 5 h the signals at 2015, 2084, and 2101
cm-1 vanished in favor of the acetyl stretching band.
In the reaction with complex 3 the CtO stretching
of the starting complex (1975 cm-1) disappeared im-
present the two characteristic multiplets of an uncoor-
dinated THF molecule. From a refrigerated THF/hexane
mixture, crystals of 9 suitable for X-ray analysis were
collected (vide infra). The structure showed an octahe-
dral coordination, where the three donors of the anionic
(11) Baird, M. C.; Mague, J . T.; Osborn, J . A.; Wilkinson, G. J . Chem.
Soc. (A) 1967, 1347.
(12) See X-ray structure of 9 in this paper and: (a) Egglestone, D.
L.; Baird, M. C.; Lock, C. J .; Turner, G. J . Chem. Soc., Dalton Trans.
1977, 1576. (b) Pinillos, M. T.; Elduque, A.; Mart`ın, E.; Navarro, N.;
Oro, L. A.; Tiripicchio, A.; Ugozzoli, F. Inorg. Chem. 1995, 11, 3105.
(c) Gonsalvi, L.; Adams, H.; Sunley, G. J .; Ditzel, E.; Haynes, A. J .
Am. Chem. Soc. 1999, 121, 11233.
(13) Bacchi, A.; Carcelli, M.; Costa, M.; Pelagatti, P.; Pelizzi, C.;
Pelizzi, G. J . Chem. Soc., Dalton Trans. 1996, 4239.
(14) Slack, D. A.; Egglestone, D. L.; Baird, M. C. J . Organomet.
Chem. 1978, 146, 71.

5444 Organometallics, Vol. 19, No. 25, 2000
Pelagatti et al.
mediately after the addition of MeI, and simultaneously
a band at 2080 cm-1 appeared, very similar to that
found in the solid IR of 7 (2075 cm-1); this progressively
diminished in favor of the acetyl band at 1727 cm-1
and the reaction was completed within 15 h.
,
In the reaction with complex 4 the band at 2084 cm-1
was never detected, and only a band at 2101 cm-1
appeared within 2 h, together with an acetyl signal at
1738 cm-1; the CtO stretching of the starting complex
(2018 cm-1) vanished within 9 h, while the band at 2101
cm-1 disappeared within 15 h.
The above-reported data are in agreement with the
initial formation of a hexacoordinated methylcarbonyl
Rh(III) intermediate, having a ν(CtO) at 2080 cm-1 for
2, 2084 cm-1 for 3, and 2101 cm-1 for 4, characteristic
values for a Rh(III)-CtO bond.15 The faster oxidative
addition observed for 3 is attributable to the anionic
tridentate character of the ligand, which makes rhodium
more nucleophile.16 The band at 2101 cm-1 was observed
both in 4 and in 2; this suggests that also in the latter
case a cationic methylcarbonyl intermediate might be
involved, but currently it is hard to say if it derives from
a rearrangement of the neutral methylcarbonyl species
initially formed or from a parallel reaction pathway.
The subsequent step is then the migratory insertion
of the methyl into the Rh-CtO bond, with the conse-
quent formation of the acetyl species. It is worth noticing
that for complexes 5 and 9 the ν(MeCO) found in
solution are shifted to higher frequencies as compared
with those found in the solid state, and moreover they
are very similar to the ν(MeCO) found for the pentaco-
ordinated acetyl complex 8; this finding suggests that
in solution coordinatively unsaturated species would
predominate over hexacoordinated ones. If for 9 the
lability of the coordinated THF molecule has already
been evidenced by NMR spectroscopy, for 5 it remains
difficult to visualize a dissociative equilibrium, unless
hypothesizing the breaking of a Rh-halogen bond.
The lower ν(MeCO) frequencies found in the hexaco-
ordinated complexes suggest that in these cases the
carbene structure Rh+ ) C(O-)(Me) may contribute in
a description of the electronic structure of the Rh-acetyl
moiety.17
F igu r e 2. View of the structure of the complex [Rh(L)-
(MeCO)(THF)I](THF) (9). Thermal ellipsoids are drawn at
the 50% probability level. The THF solvation molecule is
omitted for clarity.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p lex 9
Rh-C27
Rh-N1
Rh-O1
Rh-P
Rh-O3
Rh-I
1.986(6)
2.007(4)
2.070(4)
2.236(1)
2.451(4)
2.665(1)
O1-C8
O2-C27
N1-C7
N1-N2
N2-C8
C27-C28
1.296(7)
1.175(7)
1.277(7)
1.393(6)
1.320(7)
1.503(8)
C27-Rh-N1
C27-Rh-O1
N1-Rh-O1
C27-Rh-P
N1-Rh-P
89.4(2)
92.4(2)
78.9(2)
92.5(2)
93.2(1)
170.7(1)
169.9(2)
86.3(2)
78.6(1)
95.7(1)
93.4(2)
171.9(1)
O1-Rh-I
93.3(1)
94.30(4)
91.8(1)
P-Rh-I
O3-Rh-I
C8-O1-Rh
C7-N1-N2
C7-N1-Rh
N2-N1-Rh
C8-N2-N1
O1-C8-N2
O2-C27-C28
O2-C27-Rh
C28-C27-Rh
109.3(3)
114.3(5)
131.2(4)
114.4(3)
111.7(4)
125.2(5)
121.3(5)
123.7(5)
114.8(4)
O1-Rh-P
C27-Rh-O3
N1-Rh-O3
O1-Rh-O3
P-Rh-O3
C27-Rh-I
N1-Rh-I
deviating by 0.5 Å from the average plane defined by
the remaining five atoms. Besides the constraints
imposed by the chelation, the distortion from regular
octahedral geometry derives from the steric hindrance
of the iodine and triphenylphosphine groups, associated
with the relative lability of the coordinated THF mol-
ecule (Rh-O3 ) 2.451(4) Å). The largest deviations from
regularity involve the bending of the apical ligands
toward the L- side (C27-Rh-O3 ) 169.9(2)°) and the
bending of the THF molecule away from P and I (O1-
Rh-O3 ) 78.6(1)°, N1-Rh-O3 ) 84.3(2)°). The ligand
core is planar within 0.3 Å.
The molecular structure of 9 is shown in Figure 2,
along with the atomic numbering.
Table 2 reports the most significant bonding param-
eters.
The coordination geometry of Rh(III) is an irregular
octahedron, consisting of an equatorial plane containing
the tridentate PNO ligand and a iodine atom trans to
the L- N atom. The apical positions are occupied by the
acyl group and by a THF molecule. The coordination
mode of L- is the same as in 3, and the bite angles of
the five-membered and six-membered chelation rings
(80.7(4)° and 94.7(4)°, respectively) are similar to those
previously observed for 3. The six-membered chelation
ring has a certain envelope character, with the P atom
The most relevant difference in L- coordination
between square-planar Rh(I) and octahedral Rh(III) is
found for the Rh-P bond, which is remarkably longer
in 9, in accordance with the trend observed by examin-
ing four- and six-coordinated complexes of rhodium-
(triphenylphosphine) contained in the Cambridge Struc-
tural Database. In both cases, however, the Rh-P bond
with L- is among the shortest observed for the corre-
sponding coordination geometry. The acyl ligand is
oriented in a staggered geometry with respect to the
equatorial coordination bonds, as shown by the torsion
angle N1-Rh-C27-O2 ) 60°. The acyl oxygen points
toward the P atom (O2‚‚‚P ) 3.127 Å), while the meth-
yl makes an intramolecular short contact with O1
(C28‚‚‚O1 ) 2.981(9) Å).
(15) (a) Leipoldt, J . G.; Basson, S. S.; Botha, L. J . Inorg. Chim. Acta
1990, 168, 215. (b) Varshavsky, Yu. S.; Cherkasova, T. G.; Buzina, N.
A.; Bresler, L. S. J . Organomet. Chem. 1994, 464, 239.
(16) See for example: Collman, J . P.; Hegedus, L. S.; Norton, J . R.;
Finke, R. G. In Principles and Applications of Organotransition Metal
Chemistry; University Science Books: Mill Valley, CA, 1987.
(17) (a) Aktogu, N.; Felkin, H.; Davies, S. G. J . Chem. Soc., Chem.
Commun. 1982, 1303. (b) Bianchini, C.; Meli, A.; Peruzzini, M.; Vizza,
F.; Bachechi, F. Organometallics 1991, 10, 820.
The crystal packing is completed by a solvation
molecule of THF.

Carbonyl Rh(I) Complexes Containing a PNO Ligand
Organometallics, Vol. 19, No. 25, 2000 5445
was added to the solution, which was stirred at room temper-
ature for 5 h. The yellow solid was filtered, washed with
dichloromethane, and dried in a vacuum. Yield: 47 mg (68%).
Anal. Calcd for C28H24ClIN2O2PRh‚CH2Cl2: C, 43.45; H, 3.27;
N, 3.49. Found: C, 43.50; H, 3.41; N, 3.37. Data for isomer I:
31P NMR (CD3OD): δ 58.4 (d, J Rh-P ) 150 Hz). 1H NMR (CD3-
Exp er im en ta l Section
Gen er a l Com m en ts. All reactions were performed under
an atmosphere of nitrogen employing standard Schlenk tech-
niques. Solvents were dried prior to use and stored under
nitrogen. Elemental analysis (C, H, N, and S) were performed
by using a Carlo Erba Model EA 1108 apparatus. Infrared
spectra were recorded with a Nicolet 5PCFT-IR spectropho-
tometer in the 4000-400 cm-1 range by using KBr disks or a
NaCl cell. 1H NMR spectra were obtained on a Bruker 300
FT spectrometer using SiMe4 as internal standard, while 31P
NMR spectra were recorded on a Bruker CPX 200 FT using
H3PO4 85% as external standard. All spectra were collected
at 298 K, unless otherwise reported. MS spectra (CI, methane)
were recorded on a Finnigan SSQ 710 spectrometer, collecting
negative ions; in brackets are reported the relative intensities.
2-(Diphenylphosphino)benzaldehyde benzoylhydrazone was
synthesized as previously reported.2 Rh2(CO)4Cl2, AgTfO, and
MeI were purchased by Aldrich.
1
OD): δ 8.84 (br, 1H, HCdN), 8.18 (d, 2Ho, Ph(CdO), J ) 6.6
Hz), 7.63-7.14 (m, Ph), 2.87 (s, 3H, MeCO). Data for isomer
1
II: 31P NMR (CD3OD): δ 54.0 (d, J Rh-P ) 152 Hz). H NMR
(CD3OD): δ 8.87 (br, 1H, HCdN), 2.62 (s, 3H, MeCO). The
integration of the aromatic region of the spectrum is incorrect
owing to the presence of both isomers. IR (KBr): ν/cm-1 (NH)
3132w, (MeCO) 1689s (1727s cm-1 in CH2Cl2). CI-MS: m/z 636
{[Rh(L)I]-, 16}, 537 {[Rh(L)(CO)]-, 100}.
Rh (L)(MeCO)X [X ) Cl (6b) or I (6a )]. The characteriza-
tion was done only in solution. On dissolving 5 (10 mg, 0.01
mmol) in 0.5 mL of Me2SO-d6, the following NMR spectrum
were recorded. 31P NMR: δ 50.3 (d, J Rh-P ) 149 Hz). 1H
1
NMR: δ 8.74 (s, 1H, HCdN), 8.14 (d, 2Ho, Ph(CdO), J ) 7.5
1
Rh (HL)(CO)Cl, 2. Rh2(CO)4Cl2 (50 mg, 0.13 mmol) was
dissolved in 15 mL of diethyl ether. When solid HL (105 mg,
0.26 mmol) was added, the solution turned orange and after 1
h of stirring at room temperature the precipitation of an orange
solid was observed. The solid was filtered and washed with
diethyl ether and then dried in a vacuum. Yield: 111 mg (75%).
Anal. Calcd for C27H21ClN2O2PRh: C, 56.42; H, 3.68; N 4.87.
Found: C, 56.34; H, 3.71; N, 4.91. 31P NMR (CDCl3): δ 49.9
(d, J Rh-P ) 163 Hz). 1H NMR (CDCl3): δ 10.02 (s, 1H, HCd
Hz), 8.06 (tbr, 1H, Ph), 7.83 (t, 1H, Ph, J ) 7.4 Hz), 7.67 (t,
1H, Ph, 1J ) 7.5 Hz), 7.54-7.31 (m, 14H, Ph), 2.48 (s, 3H,
MeCO). CI-MS: m/z 679 {[Rh(L)(MeCO)I]-, 67}, 637 {[Rh(L)I]-,
67}, 587 {[Rh(L)(MeCO)Cl]-, 55}, 544 {[Rh(L)Cl]-, 59}, 537
{[Rh(L)(CO)]-, 100}.
Rh (L)(CO)(Me)I, 7. 3 (50 mg, 0.08 mmol) was dissolved in
5 mL of diethyl ether, and MeI (0.20 mL, 3.17 mmol) was
added, obtaining a clear solution, which was stirred at room
temperature for 5 h. The yellow solid was filtered, washed with
diethyl ether, and dried in a vacuum. Yield: 24 mg (45%).
Anal. Calcd for C28H23IN2O2PRh: C, 49.43; H, 3.41; N, 4.12.
Found: C, 49.48; H, 3.38; N, 4.08. 31P NMR (CDCl3, 233 K):
1
N), 8.44 (d, 2Ho, Ph(CdO), J ) 7.4 Hz), 7.84-7.32 (m, 17H,
Ph). IR (KBr): ν/cm-1 (NH) 3205w, (CdO) 1683s, (CtO) 2005vs
(2015s cm-1 in CH2Cl2). CI-MS: m/z 538 {[Rh(L)(CO)]-, 100}.
Rh (L)(CO), 3. Method a: Rh2(CO)4Cl2 (35 mg, 0.09 mmol)
was dissolved in 15 mL of THF, and solid HL (74 mg, 0.18
mmol) was added. The orange solution was stirred for 30 min
at room temperature, and then Et3N (0.04 mL, 0.27 mmol) or
MeONa (15 mg, 0.27 mmol) was added, stirring again for 2 h.
The solution was filtered in order to remove the salts formed,
and the resulting clear solution was treated with diethyl ether,
causing the immediate precipitation of a yellow solid, which
was filtered, washed with diethyl ether, and dried in a vacuum.
Yield: 68.5 mg (60%). Method b: 2 (30 mg, 0.05 mmol) was
dissolved in 5 mL of dichloromethane, and MeONa (8 mg, 0.16
mmol) was added, stirring at room temperature for 3 h. The
mixture was filtered, and the resulting clear solution was
treated with diethyl ether in order to precipitate the product,
which was collected, washed with diethyl ether, and dried in
a vacuum. Crystals suitable for X-ray analysis were obtained
from a refrigerated toluene solution. Yield: 18 mg (55%) Anal.
Calcd for C27H20N2O2PRh‚C7H8: C, 64.77; H, 4.48; N, 4.44.
Found: C, 64.71; H, 4.45; N, 4.50. 31P NMR (CDCl3): δ 49.6
1
δ 45.9 (d, J Rh-P ) 115 Hz). H NMR (CDCl3): δ 8.65 (br, 1H,
HCdN), 8.17 (d, 2Ho, Ph(CdO), 1J ) 8.0 Hz), 0.90 (t, 3H, Rh-
2
3
Me, J Rh-H ) 2.2 Hz, J P-H ) 2.2 Hz). The signals of the
aromatic region cannot be correctly assigned owing to the rapid
conversion of 7 into 8. IR (KBr): ν/cm-1 (CtO) 2075s (2080s
cm-1 in CH2Cl2). CI-MS: m/z 679 {[Rh(L)(CO)(Me)I - 1]-, 60},
636 {[Rh(L)I - 1]-, 100}.
Rh (L)(MeCO)I, 8. 3 (50 mg, 0.08 mmol) was dissolved in
10 mL of dichloromethane, and MeI (0.20 mL, 3.17 mmol) was
added stirring for 15 h. The final bright yellow solution was
concentrated and treated with 20 mL of n-hexane, causing the
precipitation of a yellow solid, which was filtered, washed with
n-hexane, and dried in a vacuum. Yield: 32.4 mg (60%). Anal.
Calcd for C28H23IN2O2PRh‚1/2CH2Cl2: C, 47.36; H, 3.35; N,
3.88. Found: C, 47.39; H, 3.32; N, 3.91. 31P NMR (CDCl3): δ
49.4 (d, J Rh-P ) 162 Hz). 1H NMR (CDCl3): δ 8.64 (s, 1H, HCd
1
N), 8.33 (d, 2Ho, Ph(CdO), J ) 8.3 Hz), 7.23-7.72 (m, 17H,
Ph), 2.95 (s, 3H, MeCO). IR (KBr): ν/cm-1 (MeCO) 1727s
(equivalent in CH2Cl2). CI-MS: m/z 680 {[Rh(L)(MeCO)I]-, 4},
636 {[Rh(L)I]-, 21}, 537 {[Rh(L)(CO)]-, 100}.
1
(d, J Rh-P ) 160 Hz). H NMR (CDCl3): δ 8.51 (s, 1H, HCdN),
1
8.18 (d, 2Ho, Ph(CdO), J ) 6.6 Hz), 7.63-7.14 (m, 17H, Ph).
[Rh (L)(MeCO)(THF )I]‚(THF ), 9. The procedure is identi-
cal to that reported for 8, but the solvent was THF. A yellow
solid was isolated. Crystals suitable for X-ray analysis were
obtained by crystallization from THF/n-hexane (1:1.5, v/v).
Yield: 41 mg (68%). The partial loss of THF from the product
prevented a correct elemental analysis. The 31P NMR spectrum
recorded in CDCl3 was equivalent to that of 8, as well as the
1H NMR spectrum recorded in the same solvent, except for
the presence, in the latter, of two multiplets belonging to the
protons of an uncoordinated molecule of THF, centered at 3.74
(4H, R-CH2) and 1.84 (4H, â-CH2) ppm, respectively. IR
(KBr): ν/cm-1 (MeCO) 1690s, (1727s in CH2Cl2). CI-MS: The
signals are the same as those observed for 8.
IR (KBr): ν/cm-1 (CtO) 1982vs (1975s cm-1 in CH2Cl2). CI-
MS: m/z 538 {[Rh(L)(CO)]-, 100}.
[Rh (HL)(CO)](CF 3SO3), 4. 2 (50 mg, 0.09 mmol) was
dissolved in 25 mL of dichloromethane, and solid AgCF3SO3
(45 mg, 0.17 mmol) was added, stirring the resulting mixture
for 2.5 h at room temperature. After removal of the inorganic
salts by filtration over a glass filter, the product was precipi-
tated as an orange solid by addition of n-hexane, filtered,
washed with n-hexane, and dried in a vacuum. Yield: 71 mg
(95%). Anal. Calcd for C28H21F3N2O5PSRh‚CH2Cl2: C, 41.98;
H, 2.94; N, 3.26; S, 3.76. Found: C, 42.05; H, 2.85; N, 3.50; S,
3.70. 31P NMR (CDCl3): δ 50.8 (d, J Rh-P ) 162 Hz). H NMR
1
(CDCl3): δ 13.60 (s, 1H, NH), 9.35 (s, 1H, HCdN), 8.22 (d,
2Ho, Ph(CdO), 1J ) 7.5 Hz), 8.11-7.44 (m, 17H, Ph). IR
(KBr): ν/cm-1 (NH) 3200w, (CtO) 2015vs (2018s cm-1 in CH2-
Cl2), (CdO) 1603s, (SO) 1299s-1241s. CI-MS: m/z 538 {[Rh(L)-
(CO)]-, 100}.
[Rh (HL)(MeCO)I](CF 3SO3), 10. 4 (50 mg, 0.07 mmol) was
dissolved in 15 mL of dichloromethane, and MeI (0.18 mL, 2.90
mmol) was added, stirring the resulting solution for 15 h at
room temperature. After concentration of the solution and
addition of n-hexane, an orange solid was filtered, washed with
n-hexane, and dried in a vacuum. Yield: 40 mg (67%). The
instability of the solid product prevented the carrying out of
Rh (HL)(MeCO)ClI, 5. 2 (50 mg, 0.09 mmol) was dissolved
in 10 mL of dichloromethane, and MeI (0.22 mL, 3.48 mmol)

5446 Organometallics, Vol. 19, No. 25, 2000
Pelagatti et al.
Ta ble 3. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
prisms) and 9 (yellow prisms). Diffraction data for both
compounds were measured at room temperature on a Siemens
AED diffractometer using Mo KR (λ ) 0.71073 Å) radiation,
graphite monochromator, θ/2θ scan. In both cases the intensity
of one standard reflection was monitored every 100 measure-
ments: only for 9 was a significant decay observed, and data
were rescaled accordingly. The intensity data were processed
with a peak-profile procedure and corrected for Lorentz and
polarization effects. Table 3 reports a summary of relevant
parameters concerning data collection and structure refine-
ment for both compounds. In both cases the phase problem
was solved by direct methods, using SIR97,18 which allowed
the retrieval of all non-hydrogen atoms. Neutral atomic
scattering factors were employed, those for non-hydrogen
atoms being corrected for anomalous dispersion. Structures
were successively refined by full-matrix least-squares on F2
with SHELXL97.19 For 9 data were corrected for absorption
effects,20 resulting in a significant improvement in the isotropic
R-factor and in the quality of the difference Fourier map. In
the last stages of refinement anisotropic displacement param-
eters were used for all non-hydrogen atoms. Phenyl groups in
3 were treated as rigid bodies. Hydrogen atoms were partly
located on the Fourier difference map and refined with
isotropic displacement parameters and partly introduced at
calculated positions, riding on their carrier atoms. The final
geometry was analyzed by the program PARST97,21 and the
drawings were made with ZORTEP.22 All calculations were
performed on a Digital Alpha 255 computer at the Centro di
Studio per la Strutturistica Diffrattometrica del C.N.R. in
Parma. Besides referring to original literature, data for
comparison with other compounds were retrieved and analyzed
by the software packages of the Cambridge Structural Data-
base.23 The full list of final atomic fractional coordinates,
atomic displacement parameters, and bond distances and
angles have been deposited as Supporting Information.
3
9
empirical formula
fw
C
30.5H23.5N2O2PRh
C36H39IN2O4PRh
824.54
583.95
temperature
wavelength
cryst syst
space group
unit cell dimens
293(2) K
0.71069 Å
triclinic
293(2) K
0.71069 Å
monoclinic
P21/c
a ) 9.746(4) Å
b ) 9.576(4) Å
c ) 37.366(9) Å
P1h
a ) 14.051(5) Å
b ) 10.477(4) Å
c ) 9.667(4) Å
R ) 106.75°
â ) 98.44°
γ ) 102.95°
1294(1) Å3
2
â ) 92.98(2)°
volume
Z
calcd density
abs coeff
F(000)
3483(2) Å3
4
1.518 Mg/m3
0.754 mm-1
602
1.435 Mg/m3
1.453 mm-1
1496
cryst size
θ range
no. of reflns
collected/unique
refinement method
0.6 × 0.4 × 0.3 mm 0.5 × 0.5 × 0.3 mm
3.05 to 22.05°
3158/3158
3.05 to 30.07°
10 314/10 182
full-matrix
least-squares
on F2
full-matrix
least-squares
on F2
no. of data/
3158/208/268
10 182/0/463
restraints/params
goodness-of-fit on F2 0.927
0.896
final R indices
[I>2σ(I)]
R1a ) 0.0798,
R1a ) 0.0491,
wR2b ) 0.1523
R1a ) 0.1147,
wR2b ) 0.1893
wR2b ) 0.2283
R1a ) 0.1615,
wR2b ) 0.2648
R indices (all data)
R ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]}1/2
.
a
the elemental analysis. 31P NMR (CDCl3): δ 54.5 (d, J Rh-P
)
148 Hz). 1H NMR (CDCl3): δ 13.9 (br, 1H, NH), 9.5 (s, 1H,
HCdN), 8.36 (d, 2Ho, Ph(CdO), 1J ) 7.3 Hz), 8.23-7.43 (m,
17H, Ph), 3.03 (s, 3H, MeCO). IR (KBr): ν/cm-1 (NH) 3191w,
(MeCO) 1702s (1739s in CH2Cl2), (SO) 1285s-1241s. CI-MS:
m/z 637 {[Rh(L)I]-, 6}, 538 {[Rh(L)(CO)]-, 100}.
Ack n ow led gm en t. The Consiglio Nazionale delle
Ricerche (C.N.R., Rome) is gratefully acknowledged for
financial support. The C.I.M. (Centro Interfacolta` di
Misure “Giuseppe Casnati”) of the University of Parma
is thanked for the technical support. A particular thanks
is due to Dr. C. Vignali for the 31P NMR recordings.
Con ver sion of 3 in to 2. A 14 mg sample of KCl (0.19
mmol) was placed in a three-neck round-bottom flask equipped
with a dropping funnel containing 5 mL of concentrated
H2SO4 (96%). The flask was connected to the nitrogen line and
to an additional flask, wherein 40 mg (0.06 mmol) of 3 had
been dissolved in 20 mL of iced Et2O. H2SO4 was slowly
dropped onto the solid KCl, and the evolved HCl was carried
by nitrogen flux through a trap of H2SO4 (96%) and then
bubbled into the solution containing the metal complex. The
reported Rh/KCl molar ratio was chosen in order to have a
Rh/HCl molar ratio close to 1:1, because a preliminary titration
of an aqueous solution of HCl obtained with the aforemen-
tioned method (NaOH 0.1 M, methyl orange) demonstrated
that only one-third of the HCl thus formed reached the
reactant solution. KCl was completely converted within 2 h,
during which time the solution initially changed color from
light red to orange, and then it released the final product;
filtering, washing with diethyl ether, and drying in a vacuum
yielded 31 mg of 2 as orange solid (85% yield).
Su p p or tin g In for m a tion Ava ila ble: Tables of X-ray data
for complexes 3 and 9. 1H NMR and MS-CI spectra of complex
6. This material is available free of charge via the Internet at
http://pubs.acs.org.
OM000562R
(18) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.;
Burla, M. C.; Polidori, G.; Cavalli, M. J . Appl. Crystallogr. 1994 27,
435.
(19) Sheldrick, G. SHELXL97, Program for structure refinement;
University of Goettingen: Germany, 1993.
(20) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 158.
(21) Nardelli, M. J . Appl. Crystallogr. 1995, 28, 659.
(22) Zsolnai, L.; Pritzkow, H. ZORTEP, ORTEP original program
modified for PC; University of Heidelberg: Germany, 1994.
(23) Allen, F. H.; Kennard O. Chem. Des. Autom. News 1993, 8, 1
and 31-37.
Str u ctu r e Deter m in a tion s. Single crystals suitable for
X-ray diffractometric analysis were obtained for 3 (dark red