Interaction of rhodium(I) bisphosphine complexes with semicarbazones to give orthometallated rhodium(III) complexes

Article abstract of DOI:10.1023/B:RUCB.0000019890.55972.90

Interaction of the cis-[Rh(PR₃)₂(Solv) ₂]PF₆ complexes (R = Ar or R₃ = Ph ₂Me, Solv - solvent) under Ar with semicarbazones bearing a phenyl group on the imine-C atom gives the rhodium(III)-hydrido-bis(phosphine)- orthometallated semicarbazone species [RhH(PR₃)₂{(o-C ₆H₄(R′)C=N-N(H)CONH₂}]PF₆ (R′ = Me or Et), which are characterized generally by elemental analysis, ³¹P{¹H} and ¹H NMR spectroscopy, and mass-spectrometry. The PPh₃-containing complex with R′ = Me, structurally characterized by X-ray analysis, reveals coordination of the semicarbazone by the ortho-C atom, the imine-N atom, and the amide-carbonyl group. For a semicarbazone containing no Ph group, the rhodium(I) complex [Rh(PR₃)₂(Et(Me)C=N-N(H)CONH₂)]PF₆, containing the η²-semicarbazone bonded via the imine-N and carbonyl, is formed. Attempts to hydrogenate the C=N moiety in the complexes or to catalytically hydrogenate the semicarbazones were unsuccessful.

Full text of DOI:10.1023/B:RUCB.0000019890.55972.90

Russian Chemical Bulletin, International Edition, Vol. 52, No. 12, pp. 2707—2714, December, 2003
2707
Interaction of rhodium(I) bisphosphine complexes with semicarbazones
to give orthometallated rhodium(III) complexes*
M. B. Ezhova,a B. O. Patrick,a B. R. James,aꢀ M. E. Ford,b and F. J. Wallerb
aUniversity of British Columbia, Department of Chemistry,
Vancouver, BC, V6T 1Z1 Canada.
Fax: +1 (604) 822 2847. Eꢀmail: brj@chem.ubc.ca
bAir Products & Chemical Inc., Allentown, PA, 18195ꢀ1501 USA
Interaction of the cisꢀ[Rh(PR3)2(Solv)2]PF6 complexes (R = Ar or R3 = Ph2Me, Solv —
solvent) under Ar with semicarbazones bearing a phenyl group on the imineꢀC atom gives the
rhodium(III)ꢀhydridoꢀbis(phosphine)ꢀorthometallated semicarbazone species [RhH(PR3)2{(oꢀ
C6H4(R´)C=N—N(H)CONH2}]PF6 (R´ = Me or Et), which are characterized generally by
elemental analysis, 31P{1H} and 1H NMR spectroscopy, and massꢀspectrometry. The
PPh3ꢀcontaining complex with R´ = Me, structurally characterized by Xꢀray analysis, reveals
coordination of the semicarbazone by the orthoꢀC atom, the imineꢀN atom, and the amideꢀ
carbonyl group. For a semicarbazone containing no Ph group, the rhodium(I) complex
2
[Rh(PR3)2(Et(Me)C=N—N(H)CONH2)]PF6, containing the η ꢀsemicarbazone bonded via
the imineꢀN and carbonyl, is formed. Attempts to hydrogenate the C=N moiety in the comꢀ
plexes or to catalytically hydrogenate the semicarbazones were unsuccessful.
Key words: rhodium, phosphines, orthometallation, semicarbazones, complexes, C—H
activation, molecular structure, synthesis.
The findings reported in this paper result from
our fundamental interest in the catalytic asymmetric
hydrogenation of imines,1 in particular in the use of
[Rh(cod)(PR3)2]PF6 (cod is cyclooctaꢀ1,5ꢀdiene, R = Ar)
as catalyst precursors as they are known to function
at ambient conditions of temperature and pressure,
where mechanistic investigations are simplified.2,3 These
precursors react with H2 in coordinating solvents to
generate the cis,trans,cisꢀ[Rh(H)2(PR3)2(Solv)2]PF6 comꢀ
plexes (Solv is a solvent molecule), while subsequent
removal of the H2 atmosphere readily gives the
cisꢀ[Rh(PPh3)2(Solv)2]+ species in solution;4,5 removal of
solvent then produces [Rh(PPh3){(µꢀPh)PPh2}]2(PF6)2.5
The standard imine substrates usually tested are typically
of the type Ph(R)C=NCH2Ph, where R = H, Alk, Ar),1
while reports on more substituted imines such as oxime
ethers and hydrazones are relatively rare.6,7
We decided to study the interaction of these substrates,
as well as the semicarbazones R(R´)C=NꢀN(H)CONH2
(R = Me or Et, with R´ = Ph; and R = Me with R´ = Et)
with the cisꢀ[Rh(PR3)2(Solv)2]+ species (R = Ar or
R3 = Ph2Me), with the ultimate aim of catalytically hyꢀ
drogenating the prochiral imine moiety. The semicarbꢀ
R = Ph, R´ = Me (Еꢀacetophenone semicarbazone);
R = Ph, R´ = Et (Еꢀpropiophenone semicarbazone);
R = Et, R´ = Me (Еꢀbutanone semicarbazone)
azone work is described here, in particular synthesis and
characterization of the rhodium(III)ꢀhydridoꢀbis(phosꢀ
phine)ꢀorthometallated semicarbazone complexes.
More generally, the diverse coordination chemistry of
semicarbazones has been thoroughly studied,** especially
because of the potential beneficial biological properties of
transition metalꢀsemicarbazone and thiosemicarbazone
complexes.8,9 For the main type of semicarbazone used
in our work (A), coordination can occur via the imineꢀN
and carbonylꢀO atoms to give a fiveꢀmembered metalloꢀ
cyclic derivative10a,11. If orthometallation also occurs via
the oꢀC atom of the Ph group, then two fused, fiveꢀmemꢀ
bered metallocycles are formed.9,10a,12 Coordination via
just the imineꢀN and orthoꢀC atom also generates a fiveꢀ
* Materials were presented at the Mark Vol´pin Memorial Inꢀ
ternational Symposium "Modern Trends in Organometallic and
Catalytic Chemistry" dedicated to his 80th anniversary.a
** In the Database of Chem. Abstracts the semicarbazone comꢀ
plexes of ∼40 elements of the Periodic System were found.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2562—2569, December, 2003.
1066ꢀ5285/03/5212ꢀ2707 $25.00 © 2003 Plenum Publishing Corporation

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Russ.Chem.Bull., Int.Ed., Vol. 52, No. 12, December, 2003
Ezhova et al.
membered metallocycle.12 Demonstrated also is coordiꢀ
nation via the enolic form of the semicarbazone, involvꢀ
ing the carbonylꢀO and an imineꢀN, this giving a fourꢀ or
fiveꢀmembered ring species.10 These four modes of coorꢀ
dination have been demonstrated crystallographically. In
addition, monoꢀ, bisꢀ, and trisꢀ(semicarbazone) metal
complexes are known.10—13
Scheme 1
To our knowledge, in structures showing the orthoꢀ
metallation of the semicarbazone,9,10a,12 the "released"
oꢀhydrogen atom has not been found as a metalꢀcoordiꢀ
nated hydride, and indeed this is rare among even the
more standard imines (see above).2 Our work here preꢀ
sents an example of such a hydridoꢀorthometallated comꢀ
plex within the class of two fused, fiveꢀmembered metalloꢀ
cyclic derivatives.
Results and Discussion
2: R = Ph, R´ = Me (a); R3 = Ph2(pꢀMeC6H4), R´ = Me (b);
R = pꢀOMeC6H4, R´ = Me (c); R = pꢀFC6H4, R´ = Me (d);
R = pꢀClC6H4, R´ = Me (e); R3 = Ph2Me, R´ = Me (f)
3: R = Ph, R´ = Et
Precursor cisꢀ[Rh(PPh3)2(Solv)2]+ complexes. The use
of [Rh(cod)(PR3)2]PF6 complexes to generate in situ
cisꢀ[Rh(PR3)2(Solv)2]+ (1) (R = Ar; Solv = Me2CO,
MeOH) is well documented for R = Ph (1a) or pꢀTol (see
above).4,5 We have now extended the use of this proceꢀ
orthometallated semicarbazone complex in which the
coꢀhydride ligand is structurally located, although we
have also discovered several other examples within the
Rh—"standard imine"” systems2,15 and have reported on
analogous Ir systems.2b In examples of the RuII and
PdIIꢀorthometallated semicarbzones systems,10a,12 the
hydride is commonly replaced by halide. This is also true
for the orthometallated RhIII complex derived from a
"standard imine" and RhCl(PPh3)3 where again the exꢀ
pected hydride has been replaced by chloride.16
The distorted octahedral structure of 2a has transꢀPPh3
ligands that are bent toward the hydride as indicated by
the P—Rh—H angles (89 and 81°) and the P—Rh—P
angle (170.30°); there are possibly weak interactions beꢀ
tween the hydride and some protons of the Ph rings as
judged by three RhH...HC distances (2.23—2.36 Å, see
Table 1) that are less than the van der Vaals distance
between two H atoms (2.40 Å).16,17 Similar, but stronger
interactions (H...H = 2.00—2.20 Å) have been suggested
for a related orthometallated RhIII—azobenzene system.16
There is no interaction between the hydride and the
H atom at C(2) of the orthometallated ring (H...H 2.80 Å).
The Eꢀsemicarbazone is chelated via the imineꢀN
and ꢀO atoms, and these are coꢀplanar with the orthoꢀ
metallatedꢀC atom and the hydride; the hydride is trans
to the imineꢀN (angle N—Rh—H is 176.7°), the C is trans
to the O atom (angle C(1)—Rh—O is 153.3°), and the
system thus has two fused, fiveꢀmembered metallocycles.
The N—Rh—C and N—Rh—O angles (79.7 and 73.6°)
are within 4° of those reported for the orthoꢀmetallated
(but nonꢀhydride containing) semicarbazone complexes
of RhIII,9 RuII,10a and PdII.12
dure for the synthesis of the complexes with R3
=
Ph2(pꢀMeC6H4) (1b), R = pꢀOMeC6H4 (1c), pꢀFC6H4
(1d), and pꢀClC6H4 (1e), and R3 = Ph2Me (1f). Preꢀ
liminary treatment of these complexes with H2, followed
by gentle heating of the solution under vacuum, yields a
red residue; for the R = Ph or pꢀTol species, the resiꢀ
dues have been recently characterized as [Rh(PPh3){(µꢀ
Ph)PPh2}]2(PF6)2 and the analogous pꢀTol complex.5 The
residue is then reꢀdissolved in acetone or MeOH to genꢀ
erate complexes 1, species that are readily identified in situ
by their 31P{1H} NMR data: the triarylphosphine derivaꢀ
tives (1a—e) exhibit doublets at δP 51—54, with JRh,P
≈
200 Hz typical of cisꢀphosphine ligands,5 while the more
basic Ph2Me species (1f) shows a more upfield shift
at δP 37.
Preparation and characterization of the orthometallated
complexes (2a—f, 3). The in situ 1a—f species react over a
day at room temperature with Eꢀacetophenone semiꢀ
carbazone to form the orthometallated complexes 2a—f,
respectively, while 1a forms an analogous complex 3 with
the Eꢀsemicarbazone of propiophenone; the reactions are
summarized in Scheme 1, where the semicarbazone Ph
group has undergone orthometallation.
The process presumably involves initial formation of a
RhI complex containing N,Oꢀchelated semicarbazone
with loss of acetone ligands (see 4 below), followed by the
well recognized oxidative addition of the orthoꢀC—H
moiety at the metal.2,14
The ORTEP for the cation of 2a is shown in Fig. 1,
and selected bond lengths and angles are given in Table 1.
To our knowledge, 2a represents the first example of an

Orthometallated rhodium(III) complexes
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 12, December, 2003 2709
C(20)
C(19)
C(14)
C(21)
C(15)
C(13)
C(18)
C(24)
C(23)
C(17)
C(12)
C(16)
C(10)
C(22)
P(1)
C(25)
C(26)
C(27)
C(4)
C(11)
C(3)
C(2)
C(5)
C(6)
Rh(1)
H(1)
C(1)
C(7)
N(1)
C(8)
C(35)
C(9)
N(2)
H(10)
O(1)
H(9)
C(36)
H(11)
N(3)
C(34)
C(29)
P(2)
C(41)
C(28)
C(30)
C(31)
C(40)
C(45)
C(42)
C(37)
C(38)
C(39)
C(43)
C(33)
C(44)
C(32)
Fig. 1. ORTEP diagram for the cation of [Rh(H)(PPh3)2(C6H4(CH3)C=N—N(H)C(O)NH2]PF6 (2a), with 50% probability ellipsoids.
Table 1. Selected bond length (d) and bond angles (ω) in complex 2a
Bond
d/Å
Angle
ω/deg
Rh—P(1)
Rh—P(2)
Rh—N(1)
Rh—O(1)
Rh—C(1)
Rh—H(1)
N(1)—C(7)
C(6)—C(7)
C(9)—O(1)
C(9)—N(2)
C(9)—N(3)
N(1)—N(2)
RhH(1)—H(32)C(35)
RhH(1)—H(17)C(17)
RhH(1)—H(27)C(29)
2.3162(8)
2.3218(9)
2.065(3)
2.310(2)
2.009(4)
1.52(4)
1.295(4)
1.471(5)
1.254(4)
1.368(4)
1.319(5)
1.364(4)
2.23(4)
P(1)—Rh—P(2)
P(1)—Rh—H(1)
P(2)—Rh—H(1)
C(1)—Rh(1)—H(1)
N(1)—Rh—C(1)
O(1)—Rh—H(1)
N(1)—Rh—O(1)
P(1)—Rh—O(1)
P(2)—Rh—O(1)
170.3(2)
89(1)
81(1)
97(1)
79.7(1)
110(1)
73.6(1)
94.46(6)
90.09(6)
Rh—H(1)—H(32)C(35) 120.3
Rh—H(1)—H(17)C(17) 121.5
Rh—H(1)—H(27)C(29) 107.7
2.27(4)
2.36(4)

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Ezhova et al.
The Rh—H bond length (1.52 Å) is in the expected
range. Of interest, a Cambridge Database search reveals
only two structures of mononuclear RhIII complexes that
contain two fiveꢀmembered metallocycles and a hydride
(with Rh—H equal to 1.361 and 1.464 Å), generated in
both cases by Rh insertion into an sp3ꢀC—H bond,18,19
unlike the sp2ꢀcarbon system of 2a. There is one structure
of a Rh—H complex with one fiveꢀmembered metallocycle
formed via insertion of Rh into an sp2ꢀCH bond; here, in
a RhIII complex with transꢀP(C6H11)3 ligands, the hydride
(Rh—H is 1.65 Å) is trans to an N atom of azobenzene,
while chloride and the orthometallated C atom are the
other two ligands.16
The other bond lengths are unexceptional: the Rh—P
bond distances,15,16,18 and the Rh—O, Rh—N, and Rh—C
bond lengths are in the ranges reported for orthometallated
rhodium—semicarbazone complexes.9,16 The C=O, C=N,
N—N, C(9)—N(2), and C(9)—N(3) bond lengths of the
coordinated acetophenone semicarbazone again agree well
with the corresponding values within other metalꢀsemiꢀ
carbazones complexes.9,10a,12,13
orthoꢀmetallation has again been replaced by the chloro
ligand of the Rh complex.
The corresponding orthometallated acetophenone
semicarbazone complexes containing paraꢀsubstituents at
the Pꢀaryl rings, 2b, 2d, and 2e, were similarly isolated,
while 2c and 2f (see Scheme 1) were made in situ; their
spectroscopic data (especially the highꢀfield, doublet of
triplets signal for the hydride at δH ∼ –10.5) correspond to
those of 2a and their structures are assumed to be the
same. The 31P{1H} doublets for triarylphosphines species
(2b—e) are at δP 37—41, while for the more basic PPh2Me
species (2f) the doublet is more upfield at δP 21.5; the
JRh,P values (112—122 Hz) are again consistent with
transꢀP atoms. Like 2a, the isolated compounds are comꢀ
pletely airꢀstable in the solid state, and in solution unꢀ
der Ar. The propiophenone semicarbazone derivative (3)
was correspondingly isolated and characterized. Of note,
for 3, the isolated 2e, and the in situ species 2c and 2f, the
1
NH proton was detected in the H NMR spectra in the
range δH 6.28—6.60, ∼3 ppm upfield from the resonance
for the respective, free semicarbazones; as for 2a, the δNH
signal for 2b and 2d is likely buried under the aromatic
proton signals. The elemental analysis for 2e is not very
satisfactory but, with the inclusion of one H2O solvate
molecule per mole of complex, the elemental analysis
becomes in excellent agreement with that calculated
(C, 46.03; H, 3.18; N, 3.58 %). Similarly, the elemental
analysis for 3 agrees well after the inclusion of 0.25 CH2Cl2
The solid state IR spectrum shows the ν(Rh—H),
ν(C=O), and ν(C=N) bands in the expected regions, and
the massꢀspectrum gives a signal for the parent molecular
cation.
The room temperature NMR data for complex 2a in
acetoneꢀd6 show that the structure in this solvent is the
same as in the solid state. The 31P{1H} data give the exꢀ
pected doublet, with a JRh,P value consistent with equivaꢀ
1
per mole of complex, and there was qualitative H NMR
1
lent, transꢀphosphines.4,5 The H NMR shows the highꢀ
data for the presence of this solvent.
field doublet of triplets for the hydride, with JP,H values
typical of a hydride cis to trans phosphines;4,5 signals for
the orthometallated Ph ring protons are shifted 0.5 to
1.0 ppm upfield in comparison to those for the Ph protons
of the free semicarbazone, while signals for the Me and
amino protons are also shifted upfield (∼0.7 and 3.6 ppm,
respectively). The NH proton signal, which is seen at
δ 9.45 in the free acetophenone semicarbazone, is not
detected for complex 2a and is likely buried under the
aromatic proton signals (see below).
Complex 2a is stable in acetone, MeOH, and CH2Cl2,
but its corresponding synthesis in the last two solvents
requires a long reaction time (several days vs. 1 day in
acetone). The synthetic orthometallation reaction is not
reversed on treating 2a with 1 atm H2 for 24 h at room
temperature in any of the three solvents.
Formation
of
[Rh(PPh3)2{EtC(Me)=N—
NHC(O)NH2}]PF6 (4). Semicarbazones that do not have
a Ph substituent at the imineꢀC atom cannot form
orthometallated species, and the reaction of 1a with 1 or
2 equiv. of butanone semicarbazone in acetone at room
temperature produces a dark red, 1 : 1 RhI—semicarbazone
chelate complex (4) that was isolated as a bis(acetone)
solvate species (Scheme 2).
Scheme 2
Of particular interest, a recent paper9 reports on a
stoichiometric reaction of benzaldehyde semicarbazone
with triꢀ or dialkylamines that occurs at the Rh of
RhCl(PPh3)3. The amide NH2 is replaced by the new
dialkylamine fragment, and the product is the orthoꢀ
metallated RhIII complex akin to 2a, but with R´ = H and
the new dialkylamine moiety instead of the NH2 (see
Scheme 1); also the "expected" hydride ligand from the

Orthometallated rhodium(III) complexes
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 12, December, 2003 2711
The massꢀspectrum of compound 4 shows the parent
peak for the cation, and the room temperature H NMR
decreased to –60 °C, the doublet first collapses to a broad
signal, which then resolves to the expected eightꢀline ABX
pattern: δ 53.01 (dd, JRh,P = 207 Hz, JP,P = 60 Hz); 47.49
(dd, JRh,P = 178.8 Hz, JP,P = 60 Hz); a comparison with
the literature data20 suggests that the higherꢀfield shift
should be assigned to the P atom trans to the imineꢀN
atom. The room temperature spectrum is attributed to a
labile equilibrium involving competitive coordination of
acetone (Solv) with the carbonyl of the semicarbazone
(see Scheme 2).
1
spectrum in acetone is consistent with this formulation.
The resonances of the CH2 and both Me groups of the
free semicarbazone (although measured in CDCl3, see
Experimental) are shifted upfield by upto 0.3 ppm on
coordination of the semicarbazone, while the NH2 signals
experience an upfield shift of 3 ppm, which is consistent
with η2ꢀN,Oꢀimine coordination (as are the IR data).
The NH signal (δ 8.5 in the free ligand) is again considꢀ
ered to be buried under the peaks for the Ph protons. The
elemental analysis for 4 suggests the presence of two acꢀ
etone solvates per mole of complex, while the solution
1H NMR data show coordination of the amide carbonyl,
and thus the square planar, fourꢀcoordinate geometry is
strongly preferred. The major MS peak at 279 remains
unidentified; the [Rh(PPh)EtC(Me)N – 2 H]+ species
corresponds to such a mass but is considered unlikely;
perhaps a matrix component is involved.
More generally, there are many examples of
Rh metallocycles formed via the activation of the
sp2ꢀC—H16,21,22 and sp3ꢀC—H 18,23,24 bonds within a
range of ligand systems. In addition to being possible
intermediates in catalytic hydrogenations (our interest),
such complexes may possess physical properties with pracꢀ
tical applications. For example, some RhIII complexes
containing orthometallated imine ligands have useful
photochemical properties,22 while some PdII and NiII
complexes with a fiveꢀ or sixꢀmembered orthometallated
The room temperature 31P{1H} NMR spectrum for 4
in acetone exhibits a broad doublet at δ 49.7 (JRh,P
194 Hz) resembling those of cisꢀ[Rh(PPh3)2(Me2CO)2]+
(1a). However, complex 4 (unlike 1a) has inequivalent
phosphines, and this is demonstrated by the low temperaꢀ
ture 31P{1H} NMR data (Fig. 2). As the temperature is
=
ring possess nonlinear optical properties.25
Experimental
Materials, reagents, and instrumentation. All syntheses were
performed under Ar using standard Schlenk and/or dryꢀbox techꢀ
niques. The solvents (acetone, ether, and hexanes) were dried
using Naꢀbenzophenone ketyl, degassed, and condensed into a
reaction flask under vacuum immediately prior to use; MeOH
was purified by refluxing over Mg chips; CH2Cl2 was dried with
molecular sieves, and deuterated solvents were dried and deꢀ
gassed prior to use.
25 °C
Phosphines were purchased from Strem Chemicals. Hydroꢀ
gen (Praxair, Extra Dry) was purified by passing through the
Englehard Deoxo catalyst. The [Rh(cod)(PR3)2]PF6 complexes
(R = Ph, pꢀOMeC6H4, pꢀFC6H4, pꢀClC6H4; R3 = Ph2Me,
Ph2(pꢀMeC6H4)) were prepared according to a literature
method.4 The [Rh(PR3)2(Solv)2]+ (Solv = MeOH, Me2CO)
species were generated in situ by removing the H2 atmoꢀ
sphere over the solutions containing the corresponding
cis,trans,cisꢀ[Rh(H)2(PR3)2(Solv)2]PF6 species according to the
literature procedure.4,5
0 °C
–20 °C
NMR spectra were recorded on Bruker ACꢀ200 and Bruker
AVꢀ300 spectrometers, with residual protons of deuterated solꢀ
vents (1H, relative to external SiMe4), solvent carbon (13C,
–40 °C
–50 °C
relative to external SiMe4), and external P(OMe)3
141.00 vs. 85% aq. H3PO4) being used as references; data
(
31P{1H},
δ
P
o
were recorded at room temperature (∼20 °C). The C6H4 notaꢀ
tion used represents assignments of the orthometallated ring
protons. IR spectra (in KBr pellets) were recorded on an ATI
Mattson Genesis FTꢀIR spectrometer. Mass spectral data were
measured on a Kratos Concept IIHQ liquid secondaryꢀion inꢀ
strument using thioglycerol or 3ꢀnitrobenzylalcohol matrix.
Microanalyses were performed by P. Borda in the analytical
Laboratory of the Chemistry Department, University of British
Columbia.
–60 °C
56
54
52
50
48
δ
Fig. 2. Variable temperature 31P{1H} NMR spectra of 4 in acꢀ
etoneꢀd6.
Semicarbazones. These were prepared as the Eꢀisomers by
the standard condensation reaction of the appropriate ketone

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Ezhova et al.
with semicarbazide in H2O/EtOH at room temperature.26 The
three semicarbazones have been reported previously, but the
degree of their characterization has been variable;27,28 given beꢀ
low are more complete data. There is good agreement with the
available, more limited literature data.
Acetophenone semicarbazone. Yield was 97 %. M.p.
195.5—197 °C. Found (%): C, 61.09; H, 6.29; N, 23.33.
C9H11N3O. Calculated (%): C, 61.00; H, 6.26; N, 23.71. IR,
ν/cm–1: 1695 (C=O); 1584 (C=N). 1H NMR (DMSOꢀd6), δ:
2.20 (s, 3 H, Me); 6.60 (s, 2 H, NH2); 7.30—7.40 (m, 3 H,
H arom.); 7.80—7.90 (m, 2 H, H arom.); 9.45 (s, 1 H, NH).
13C NMR (DMSOꢀd6), δ: 13.46 (s, 1 C, Me); 128.07, 128.29
(both s, 2 C each, C arom.); 128.55 (s, 1 C, C arom.); 138.38 (s,
1 C, C—Cimine); 144.29 (s, 1 C, C=N); 157.66 (s, 1 C, C=O).
MS, m/z (Irel (%)): 177 [M]+ (42), 133 [M – CO – NH2]+
(100), 119 [M – N – CO – NH2]+ (35), 103 [PhC(Me) – H]+
(25), 77 [Ph+] (60).
Propiophenone semicarbazone. Yield was 98%. M.p.
176.5—178 °C. Found (%): C, 62.93; H, 6.89; N, 21.94.
C10H13N3O. Calculated (%): C, 62.81; H, 6.85, N, 21.97. IR,
ν/cm–1: 1695 (C=O); 1583 (C=N). 1H NMR (DMSOꢀd6), δ:
1.00 (t, 3 H, Me); 2.75 (q, 2 H, CH2); 6.50 (s, 2 H, NH2);
7.30—7.40 (m, 3 H, H arom.); 7.80—7.90 (m, 2 H, H arom.);
9.50 (s, 1 H, NH). 13C NMR (DMSOꢀd6), δ: 10.59 (s, 1 C, Me);
18.95 (s, 1 C, CH2); 126.09 (s, 3 C, С arom.); 128.48 (s, 2 C,
С arom.); 137.18 (s, 1 C, C—C, imine); 148.29 (s, 1 C, C=N);
157.47 (s, 1 C, C=O). MS, m/z (Irel (%)): 191 [M – 2 H]+ (45);
162 [M – Et]+ (15); 147 [M – Et – NH]+ (100); 130 [M – Et –
NH2 – O]+ (35); 119 [M – Et – CO – NH]+ (50); 77 [Ph]+ (55).
Butanone semicarbazone. Yield was 70%. M.p. 148—150 °C.
Found (%): C, 47.05; H, 8.62; N, 32.17. C5H11N3O. Calcuꢀ
lated (%): C, 46.49; H, 8.58; N, 32.53. IR, ν/cm–1: 1645 (C=O);
1584 (C=N). 1H (CDCl3), δ: 1.15 (t, 3 H, CH3CH2); 1.85 (s,
3 H, MeC=); 2.20 (q, 2 H, MeCH2); 5.80 (br.s, 2 H, NH2); 8.50
(s, 1 H, NH). 13C NMR (CDCl3), δ: 10.56 (s, 1 C, CH3CH2);
15.29 (s, 1 C, CH3C=); 31.88 (s, 1 C, CH3CH2); 151.65 (s,
1 C, C=O); 158.48 (s, 1 C, C=N). MS, m/z (Irel (%)): 129 [M]+
Complex 2a. Found (%): C, 57.09; H, 4.46; N, 4.56.
C45H41F6N3OP3Rh. Calculated (%): C, 56.91; H, 4.35; N, 4.43.
IR, ν/cm–1: 2002 m (Rh—H); 1656 s (C=O); 1577 s (C=N).
1H NMR (acetoneꢀd6), δ: –10.65 (dt, 1 H, RhH, JP,H = 10 Hz,
JRh,H = 15 Hz); 1.53 (s, 3 H, Me); 3.00 (br.s, 2 H, NH2); 6.33 (t,
o
o
1 H, C6H4, JH,H = 8 Hz); 6.66 (m, 2 H, C6H4, JH,H = 8 Hz);
6.82 (d, 1 H, oC6H4, JH,H = 8 Hz); 7.50—8.00 (m, ∼30 H,
PPh3). 31P{1H} NMR (acetoneꢀd6), δ: 41.13 (d, JRh,P = 118 Hz);
–143.2 (septet, PF6–, JP,H = 708 Hz). MS, m/z (Irel (%)): 804
[M – PF6]+ (60); 627 [Rh(PPh3)2]+ (95); 542 [M – PPh3
PF6]+ (100); 287 [Rh(PPh2)]+ (68).
–
The preparation of 2a can also be carried out in MeOH or in
CH2Cl2, when the precursors are [Rh(PPh3)2(MeOH)2]+ or
[Rh(PPh3){(µꢀPh)PPh2}]22+, respectively (see above), but the
reactions with the semicarbazone are much slower, taking sevꢀ
eral days for completion.
Other [Rh(PR3)2(Me2CO)2]+ precursor species (1b—f) were
prepared analogously in situ in acetone, and their room temꢀ
perature 31P{1H} NMR data, together with those for 1a, are
summarized in the Results and Discussion section. From these
precursors, four other orthometallated complexes (2b, 2d, 2e,
and 3) were isolated and characterized by procedures identical
to those described above for 2a, and using 0.063 mmole of each
of the respective precursors and semicarbazones, while two others
(2c and 2f ) were just formed in situ, i.e. prior to addition of
ether. The yields and analytical data for 2b—e and 3 are summaꢀ
rized below, NMR data again being recorded in acetoneꢀd6.
(O,N,oꢀCꢀAcetophenonesemicarbazonato)(hydrido)bis[dipheꢀ
nyl(pꢀmethylphenyl)phosphine]rhodium(III) hexafluorophosphate,
[Rh(H){PPh2(pꢀMeC6H4)}2{oꢀC6H4(Me)C=N—NHC(O)NH2}]PF6
(2b). Yield 63%. Found (%): C, 57.55; H, 4.73; N, 4.39.
C
47H45F6N3OP3Rh. Calculated (%): C, 57.74; H, 4.64; N, 4.30.
IR, ν/cm–1: 2009 m (Rh—H); 1638 s (C=O); 1576.3 s (C=N).
1H NMR, δ: –10.70 (dt, 1 H, RhH, JP,H = 10.4 Hz, JRh,H
=
15.3 Hz); 1.50 (s, 3 H, Me); 2.28 (s, 6 H, pꢀMe); 2.88 (br.s, 2 H,
NH2); 6.31 (t, 1 H, oC6H4, JH,H = 7.1 Hz); 6.62 (d, 1 H, oC6H4,
o
JH,H = 8.5 Hz); 6.66 (t, 1 H, C6H4, JH,H = 7.1 Hz); 6.81 (d,
(85); 114 [M
–
Me]+ (15); 100 [M
–
Et]+ (55); 86
1 H, oC6H4, JH,H = 7.6 Hz); 6.90—7.80 (m, 28 H, H arom.).
31P {1H} NMR, δ: 40.7 (d, JRh,P = 116.6 Hz); –143.2 (septet,
PF6–). MS, m/z (Irel (%)): 832 [M – PF6]+ (45); 655
[Rh{PPh2(pꢀMeC6H4)}2]+ (100); 556 [M – PPh2(pꢀMeC6H4)]+
(90); 301 (40), 136 (40).
[Et(Me)C=NNH2]+ (60); 85 [M – C(O)NH2]+ (35); 69
[EtC=NN]+ (40).
Synthesis of orthometallated complexes. (O,N,orthoꢀCꢀAceꢀ
tophenonesemicarbazonato)(hydrido)bis(triphenylphosꢀ
phine)rhodium(III) hexafluorophosphate, [Rh(H)(PPh3)2{oꢀ
(O,N,oꢀCꢀAcetophenonesemicarbazonato)(hydrido)bis[tri(pꢀ
methoxyphenyl)phosphine]rhodium(III) hexafluorophosphate,
[Rh(H){P(pꢀOMeC6H4)3}2{oꢀC6H4(Me)C=N—NHC(O)NH2}]PF6
C6H4(Me)C=N—N(H)CONH2}]PF6
(2a).
Complex
[Rh(cod)(PPh3)2]PF6 (55.5 mg, 0.063 mmol) in acetone (5 mL)
was reacted with 1 atm H2 at ∼20 °C for 2 h to form an in situ
sample of cis,trans,cisꢀ[Rh(H)2(PPh3)2(Me2CO)2]+. Hydrogen
and the volatile materials (solvent, cyclooctane) were then reꢀ
moved under vacuum at ∼40 °C for 12 h, and the dark red
residue was then redissolved in acetone (∼3 mL) to form
[Rh(PPh3)2(Me2CO)2]+ (1a).5 Acetophenone semicarbazone
(11.2 mg, 0.063 mmol) was then added, and the mixture was
stirred at ∼20 °C for 1 day, when the colour changed to pale
yellow. Addition of Et2O (∼3 mL) precipitated a white solid that
was collected and dried under vacuo for 12 h; yield of 2a was
41 mg (68%). An alternative procedure for isolation of 2a was
removal of solvent from the reaction mixture, dissolution of
the residue in minimal amount of dichloromethane, and preꢀ
cipitation by addition of hexanes. Crystals of 2a were grown
by layering hexanes over a dichloromethane solution of the
complex.
(2c). 1H NMR, δ: –10.84 (dt, 1 H, RhH, JP,H = 11 Hz, JRh,H
=
16.5 Hz); 2.08 (s, 3 H, MeC); 2.88 (br.s, 2 H, NH2); 3.80 (s,
12 H, OMe); 3.83 (s, 6 H, OMe); 6.28 (br.s, 1 H, NH); 6.36 (t,
1 H, oC6H4); 6.64 (d, 1 H, oC6H4); 6.68 (t, 1 H, oC6H4); 6.82 (d,
1 H, oC6H4); 6.90—7.80 (m, 24 H, H arom.). 31P{1H} NMR, δ:
36.7 (d, JRh,P = 121.5 Hz); –143.2 (septet, PF6–).
(O,N,oꢀCꢀAcetophenonesemicarbazonato)(hydrido)bis[tri(pꢀ
fluorophenyl)phosphine]rhodium(III)
hexafluorophosphate,
[Rh(H){P(pꢀFC6H4)3}2{oꢀC6H4(Me)C=N—NHC(O)NH2}]PF6
(2d). Yield 59%. Found (%): C, 51.03; H, 3.42; N, 3.79.
C45H35F12N3OP3Rh. Calculated (%): C, 51.11; H, 3.34; N, 3.97.
1H NMR, δ: –10.77 (dt, 1 H, RhH, JP,H = 10.8 Hz, JRh,H
=
15.0 Hz); 1.67 (s, 3 H, Me); 2.90 (br.s, 2 H, NH2); 6.46 (t, 1 H,
oC6H4, JH,H = 7 Hz); 6.68 (d, 1 H, oC6H4, JH,H = 8 Hz); 6.73 (t,
1 H, oC6H4, JH,H = 7.4 Hz); 6.92 (d, 1 H, oC6H4, JH,H
=
7.7 Hz); 7.12 (t, 2 H, H arom., JH,H = 8.4 Hz); 7.23 (t, 10 H,

Orthometallated rhodium(III) complexes
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 12, December, 2003 2713
m/z (Irel (%)): 756 [M – PF6]+ (3); 627 [Rh(PPh3)2]+ (20);
H arom., JH,H = 8.8 Hz); 7.55 (m, 10 H, H arom.); 7.70
(m, 2 H, H arom.). 31P{1H} NMR, δ: 38.51 (d, JRh,P
118 Hz); –143.2 (septet, PF6–). MS, m/z (Irel (%)): 912
[M – PF6]+ (25); 735 [Rh{P(pꢀFC6H4)3}2]+ (65); 596 [Rh{P(pꢀ
FC6H4)3}{C6H4(Me)C=NNHC(O)NH2}]+ (100); 323 [Rh{P(pꢀ
FC6H4)2} – H]+ (50).
=
279 (?) (100).
Reactivity
of
[Rh(H)(PPh3)2{oꢀC6H4(Me)C=N—
N(H)CONH2}]PF6 (2a) toward H2. Complex 2a (∼10 mg) was
dissolved in acetone, methanol, or CH2Cl2, and the solution
was exposed to H2 (1 atm) at ∼20 °C. No reaction was observed
1
(O,N,oꢀCꢀAcetophenonesemicarbazonato)(hydrido)bis[tri(pꢀ
by H or 31P{1H} NMR spectroscopy. Attempts to hydrogenate
chlorophenyl)phosphine]rhodium(III)
hexafluorophosphate,
acetone semicarbazone using 1a or 2a as a catalyst with 1—40 atm
H2 at ∼20 °C in acetone or methanol were unsuccessful.
Xꢀray diffraction study. Xꢀray diffraction data on a clear,
platelet crystal of 2a (0.50×0.25×0.08 mm3) were collected at
173 K on a Rigaku/ADSC CCD area detector instrument with
graphite monochromated MoꢀKα radiation (0.71069 Å). Crysꢀ
[Rh(H){P(pꢀClC6H4)3}2{oꢀC6H4(Me)C=N—NHC(O)NH2}]PF6
(2e). Yield 51%. Found (%): C, 46.11; H, 3.29; N, 3.31.
C45H35Cl6F6N3OP3Rh. Calculated (%): C, 46.74; H, 3.05;
N, 3.63. 1H NMR, δ: –10.74 (dt, 1 H, RhH, JP,H = 10.3 Hz,
JRh,H = 14.6 Hz); 1.60 (s, 3 H, Me); 3.25 (br.s, 2 H, NH2); 6.47
(t, 1 H, oC6H4, JH,H = 7 Hz); 6.53 (br.s, 1 H, NH); 6.68 (d, 1 H,
tals of 2a, C45H41N3OF6P3Rh•2 CH2Cl2 (M = 1119.52), are
–
o
oC6H4, JH,H = 8 Hz); 6.75 (t, 1 H, C6H4, JH,H = 7.5 Hz); 6.92
triclinic, space group P1(No. 2), a = 12.786(1), b = 14.096(2),
(d, 1 H, oC6H4, JH,H = 7.7 Hz); 7.45—7.75 (m, 24 H, H arom.).
31P{1H} NMR, δ: 40.41 (d, JRh,P = 118 Hz); –143.2 (septet,
PF6–). MS, m/z (Irel (%)): 1010 [M – H – PF6]+ (10);
c = 14.7520(9) Å, α = 96.764(4)°, β = 101.491(5)°,
γ = 105.089(4)°, V = 2474.9(4) Å3, dcalc = 1.502 g cm–3, Z = 2.
Of the 21,307 reflections collected, 9536 were unique
(Rint = 0.049). Data were collected and processed using the
d*TREK 29 program and corrected for Lorentz and polarization
effects. The structure was solved by direct methods30 and exꢀ
panded using Fourier techniques.31 The nonꢀhydrogen atoms
were refined anisotropically; the coordinated H atom was reꢀ
fined isotropically, and the rest were included in fixed positions.
Two CH2Cl2 molecules were found in the asymmetric unit. The
final cycle of fullꢀmatrix leastꢀsquares refinement was based on
9531 reflections and 620 variable parameters. All calculations
were performed using the teXsan crystallographic software.32
The final reliability factors were R1 = 0.042 (based on reflections
with I > 3σ(I )) and wR2 = 0.119 (on F 2, all data). The complete
tables of bond lengths, bond angles, atomic coordinates, and
thermal parameters were deposited with the Cambridge Crystalꢀ
lographic Data Centre (CCDCꢀ228477).
833 [Rh{P(pꢀClC6H4)3}2
–
H]+ (21); 644 [Rh{P(pꢀ
ClC6H4)3}{C6H4—(Me)C=NNHC(O)NH2} – H]+ (100).
(O,N,oꢀCꢀAcetophenonesemicarbazonato)(hydrido)bis[(meꢀ
thyldiphenyl)phosphine]rhodium(III)
[Rh(H)(PPh2Me)2{oꢀC6H4(Me)C=N—NHC(O)NH2}]PF6 (2f).
1H NMR, δ: –11.58 (m, 1 H, RhH, JP,H = 14.7 Hz, JRh,H
hexafluorophosphate,
=
17.9 Hz); 1.18 (s, 6 H, pꢀMe); 2.15 (s, 3 H, MeC); 2.83 (br.s,
2 H, NH2); 6.48 (br.s, 1 H, NH); 6.84—7.65 (m, 24 H,
o
20 H arom. and 4 C6H4). 31P{1H} NMR, δ: 21.52 (d, JRh,P
=
112.3 Hz); –143.2 (septet, PF6–).
(O,N,oꢀCꢀPropiophenonesemicarbazonato)(hydrido)bis(triꢀ
phenylphosphine)rhodium(III) hexafluorophosphate,
[Rh(H)(PPh3)2{oꢀC6H4(Et)C=N—NHC(O)NH2}]PF6 (3).
Yield 65.8%. Found (%): C, 56.34; H, 4.56; N, 4.32.
C46H43F6N3OP3Rh •0.25 CH2Cl2. Calculated (%): C, 56.40;
H, 4.46; N, 4.27. IR: ν/cm–1: 2045 br m (Rh—H); 1670 s (C=O);
1513 s (C=N). 1H NMR, δ: –10.85 (dt, 1 H, RhH, JP,H
=
This work was financially supported by Natural Sciꢀ
ences and Engineering Research Council of Canada
(NSERC), and the Environmental Science and Technolꢀ
ogy Alliance Canada program (ESTAC).
11 Hz, JRh,H = 15 Hz); 0.52 (t, 3 H, Me); 1.88 (q, 2 H, CH2);
o
2.80 (br.s, 2 H, NH2); 6.30 (t, 1 H, C6H4, JH,H = 8 Hz); 6.42
(d, 1 H, oC6H4, JH,H = 8 Hz); 6.60 (br.s, 1 H, NH); 6.73 (t, 1 H,
oC6H4, JH,H = 10 Hz); 6.92 (d, 1 H, oC6H4, JH,H = 8 Hz);
7.10—8.10 (m, 30 H, PPh3). 31P{1H} NMR, δ: 41.58 (d, JRh,P
=
117 Hz); –143.2 (septet, PF6–). MS, m/z (Irel (%)): 818
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Received August 11, 2003