Direct addition of alcohols to organonitriles activated by ligation to a platinum(IV) center

Article abstract of DOI:10.1021/ic011025h

Treatment of trans-[PtCl₄(RCN)₂] (R = Me, Et) with R′OH (R′ = Me, Et, n-Pr, i-Pr, n-Bu) at 45 °C in all cases allowed the isolation of the trans-[PtCl₄{(E)-NH=C(R)OR′}₂] imino ester complexes, while the reaction between cis-[PtCl₄(RCN)₂] and the least sterically hindered alcohols (methanol and ethanol) results in the formation of cis-[PtCl₄{(E)-NH=C(R)OR′}₂] (R/R′ = Me/Me) or trans-[PtCl₄{(E)-NH=C(Et)OR′}₂] (R′ = Me, Et), the latter being formed via thermal isomerization (ROH, reflux, 3 h) of the initially formed corresponding cis isomers. The reaction between alcohols R′OH and cis-[PtCl₄(RCN)₂] (R = Me, R′ = Et, n-Pr, i-Pr, n-Bu; R = Et; R′ = n-Pr, i-Pr, n-Bu), exhibiting greater R/R′ steric congestion, allowed the isolation of cis-[PtCl₄{(E)-NH=C(R)OR′}){(Z)-NH=C(R)OR′}] as the major products. The alcoholysis reactions of poorly soluble [PtCl₄(RCN)₂] (R = CH₂Ph, Ph) performed under heterogeneous conditions, directly in the appropriate alcohol and for a prolonged time and, for R = Ph, with heating led to trans-[PtCl₄{(E)-NH=C(R)OR′}₂] (R = CH₂Ph, R′ = Me, Et, n-Pr, i-Pr; R = Ph, R′ = Me) isolated in moderate yields. In all of the cases, in contrast to platinum(II) systems, addition of R′OH to the organonitrile platinum(IV) complexes occurs under mild conditions and does not require a base as a catalyst. The formed isomerically pure (imino ester)Pt(IV) complexes can be reduced selectively, by Ph₃P=CHCO₂Me, to the corresponding isomers of (imino ester)Pt(II) species, exhibiting antitumor activity, without change in configuration of the imino ester ligands. Furthermore, the imino esters NH=C(R)OR′ can be liberated from both platinum(IV) and platinum(II) complexes [PtCl_n{NH=C(R)OR′}₂] (n = 2, 4) by reaction with 1,2-bis(diphenylphosphino)ethane and pyridine, respectively. All of the prepared compounds were characterized by elemental analyses (C, H, N), FAB mass spectrometry, IR, and ¹H, ¹³C{¹H} and ¹⁹⁵Pt (metal complexes) NMR spectroscopies; the E and Z configurations of the imino ester ligands in solution were determined by observation of the nuclear Overhauser effect. X-ray structure determinations were performed for trans-[PtCl₄{(E)-NH=C(Me)OEt}₂] (2), trans-[PtCl₄{(E)-NH=C(Et)-OEt}₂] (10), trans-[PtCl₄{(E)-NH=C(Et)OPr-i}₂] (11), trans-[PtCl₄{(E)-NH=C(Et)OPr-n}₂] (12), and cis-[PtCl₄{(E)-NH=C(Et)OMe}₂] (14). Ab initio calculations have shown that the EE isomers are the most stable ones for both platinum(Il) and platinum(IV) complexes, whereas the most stable configurations for the ZZ isomers are less stable than the respective EZ isomers, indicating an increase of the stability on moving from the ZZ to the EE configurations which is more pronounced for the Pt(IV) complexes than for the Pt(II) species.

Full text of DOI:10.1021/ic011025h

Inorg. Chem. 2002, 41, 2041−2053
Direct Addition of Alcohols to Organonitriles Activated by Ligation to a
Platinum(IV) Center
,†
Nadezhda A. Bokach,†,‡ Vadim Yu. Kukushkin,* Maxim L. Kuznetsov,‡ Dmitrii A. Garnovskii,‡
Giovanni Natile,§ and Armando J. L. Pombeiro*
,‡
Department of Chemistry, St. Petersburg State UniVersity, 198904 Stary Petergof,
Russian Federation, Centro de Qu´ımica Estrutural, Complexo I, Instituto Superior Te´cnico, AV.
RoVisco Pais, 1049-001 Lisbon, Portugal, and Dipartimento Farmaco-Chimico, UniVersity of Bari,
Via E. Orabona 4, I-70125 Bari, Italy
Received October 2, 2001
Treatment of trans-[PtCl4(RCN)2] (R ) Me, Et) with R′OH (R′ ) Me, Et, n-Pr, i-Pr, n-Bu) at 45 °C in all cases
allowed the isolation of the trans-[PtCl4{(E)-NHdC(R)OR′}2] imino ester complexes, while the reaction between
cis-[PtCl4(RCN)2] and the least sterically hindered alcohols (methanol and ethanol) results in the formation of cis-
[PtCl4{(E)-NHdC(R)OR′}2] (R/R′ ) Me/Me) or trans-[PtCl4{(E)-NHdC(Et)OR′}2] (R′ ) Me, Et), the latter being
formed via thermal isomerization (ROH, reflux, 3 h) of the initially formed corresponding cis isomers. The reaction
between alcohols R′OH and cis-[PtCl4(RCN)2] (R ) Me, R′ ) Et, n-Pr, i-Pr, n-Bu; R ) Et; R′ ) n-Pr, i-Pr, n-Bu),
exhibiting greater R/R′ steric congestion, allowed the isolation of cis-[PtCl4{(E)-NHdC(R)OR′}{(Z)-NHdC(R)-
OR′}] as the major products. The alcoholysis reactions of poorly soluble [PtCl4(RCN)2] (R) CH Ph, Ph) performed
2
under heterogeneous conditions, directly in the appropriate alcohol and for a prolonged time and, for R ) Ph, with
heating led to trans-[PtCl4{(E)-NHdC(R)OR′}2] (R) CH Ph, R′ ) Me, Et, n-Pr, i-Pr; R ) Ph, R′ ) Me) isolated
2
in moderate yields. In all of the cases, in contrast to platinum(II) systems, addition of R′OH to the organonitrile
platinum(IV) complexes occurs under mild conditions and does not require a base as a catalyst. The formed
isomerically pure (imino ester)Pt(IV) complexes can be reduced selectively, by Ph3PdCHCO Me, to the corresponding
2
isomers of (imino ester)Pt(II) species, exhibiting antitumor activity, without change in configuration of the imino
ester ligands. Furthemore, the imino esters NHdC(R)OR′ can be liberated from both platinum(IV) and platinum(II)
complexes [PtCln{NHdC(R)OR′}2] (n ) 2, 4) by reaction with 1,2-bis(diphenylphosphino)ethane and pyridine,
respectively. All of the prepared compounds were characterized by elemental analyses (C, H, N), FAB mass
spectrometry, IR, and 1H, 13C{1H}, and 195Pt (metal complexes) NMR spectroscopies; the E and Z configurations
of the imino ester ligands in solution were determined by observation of the nuclear Overhauser effect. X-ray
structure determinations were performed for trans-[PtCl4{(E)-NHdC(Me)OEt}2] (2), trans-[PtCl4{(E)-NHdC(Et)-
OEt}2] (10), trans-[PtCl4{(E)-NHdC(Et)OPr-i}2] (11), trans-[PtCl4{(E)-NHdC(Et)OPr-n}2] (12), and cis-[PtCl4{(E)-
NHdC(Et)OMe}2] (14). Ab initio calculations have shown that the EE isomers are the most stable ones for both
platinum(II) and platinum(IV) complexes, whereas the most stable configurations for the ZZ isomers are less stable
than the respective EZ isomers, indicating an increase of the stability on moving from the ZZ to the EE configurations
which is more pronounced for the Pt(IV) complexes than for the Pt(II) species.
Introduction
and C-N bonds due to the addition of nucleophiles to the
nitrile carbon, e.g., in the course of the Pinner1,2 and thio-
Pinner3 reactions. Often such processes require actiVation
of RCN toward the addition, either by an electron-acceptor
It is commonly recognized in organic chemistry that
organonitriles are intrinsic synthons for making C-O, C-S,
* Authors to whom correspondence should be addressed. E-mail:
kukushkin@VK2100.spb.edu (V.Yu.K.); pombeiro@ist.utl.pt (A.J.L.P.).
† St. Petersburg State University.
(1) (a) Dunn, P. J. In ComprehensiVe Organic Functional Group
Transformations; Katrizky, A. R., Meth-Cohn, O., Rees, C. W., Eds.;
Elsevier: Oxford, 1995; Vol. 5, p 741. (b) Granik, V. G. Russ. Chem.
ReV. (Engl. Transl.) 1983, 52, 377.
‡ Instituto Superior Te´cnico.
§ University of Bari. E-mail: natile@farmchim.uniba.it.
10.1021/ic011025h CCC: $22.00 © 2002 American Chemical Society
Published on Web 03/28/2002
Inorganic Chemistry, Vol. 41, No. 8, 2002 2041

Bokach et al.
group R or by use of acids, for instance HX (X ) Cl, Br),1
which, by protonating the N atom, increase the electrophi-
licity of the adjacent carbon atom thus facilitating the reaction
with nucleophiles. Instead of H+, metal ions can be used in
the addition reactions to enhance the reactivity of organo-
nitriles, thus accomplishing the dream of organic chemists
for smooth additions of nucleophiles to RCN molecules
(especially those inactiVated by electron-releasing R radicals).
Many of these metal-mediated processes have been sum-
marized in review articles on the subject.4-6
Our own investigation on the reactivity of coordinated
organonitriles toward nucleophiles has so far been focused
on couplings between platinum(IV) complexes of the type
[PtCl4(RCN)2] and oximes (R1R2CdNOH7), Vic-dioximes
[HONd(spacer)dNOH8], or dialkylhydroxylamines (R1R2-
NOH9) which led to the formation of [PtCl4{NHdC(R)ONd
CR1R2}2], [PtCl4{NHdC(R)ONd(spacer)dNOH})2], and
[PtCl4{NHdC(R)ONR1R2}2], respectively. The latter reac-
tions have also been extended to Re(IV)10 and Rh(III)11
organonitrile complexes. We also found that Ag+ or Cu2+
ions catalyze the coupling of dialkylcyanamides with oximes
at a platinum(II) center12 and that nitrones of the type
O-N+(R3)dC(R1)(R2) can give [2 + 3] cycloaddition to the
acetonitrile ligands in the complex [PtCl4(MeCN)2] furnish-
ing ∆4-1,2,4-oxadiazoline complexes of the type [PtCl4-
{NdC(Me)O-N(R3)-C(R1)(R2)}2] from which the hetero-
cycles can be quantitatively liberated.13 Finally, platinum-
mediated coupling of ligated organonitriles and benzophen-
one imine can lead to coordinated 1,3-diaza-1,3-dienes.14
We have now focused our attention on the addition of
alcohols to (organonitrile)Pt(IV) species leading to formation
of imino ester complexes. Our aim was to clarify the effects
of the oxidation state of the platinum center upon the
coupling reaction by comparing our results with those already
reported for appropriate platinum(II) systems.15,16 Interest in
the chemistry of platinum complexes with imino esters stems
also from the discovery, by one of us, that some of these
complexes break the rule of higher antitumor activity
expected for cis than for trans isomers.17 Moreover, we have
recently found an efficient method18 for the reduction of
platinum(IV) complexes to the corresponding platinum(II)
species, in nonaqueous media, and our idea was to extend
the reduction to imino ester complexes and to verify if there
could be any advantage in the preparation of biologically
relevant (imino ester)Pt(II) compounds starting from the
platinum(IV) rather than from the platinum(II) nitrile com-
plexes.
We have found that, in contrast to platinum(II) systems,
addition of R′OH to organonitrile platinum(IV) complexes
occurs under mild conditions and does not require a base as
a catalyst. The formed isomerically pure (imino ester)Pt-
(IV) complexes can be reduced selectively, by Ph3PdCHCO2-
Me, to the corresponding isomers of (imino ester)Pt(II)
species without change in configuration of the imino ester
ligands. Furthemore, the imino esters can be liberated from
both platinum(IV) and platinum(II) complexes. All of these
results, along with theoretical studies on relative stabilities
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2042 Inorganic Chemistry, Vol. 41, No. 8, 2002

Direct Addition of Alcohols to Organonitriles
Scheme 1
Scheme 2
allowed the isolation of cis-[PtCl4{(E)-NHdC(R)OR′}{(Z)-
NHdC(R)OR′}] (Scheme 2) as major products, whereas cis-
[PtCl4{(E)-NHdC(R)OR′}2] and cis-[PtCl4{(Z)-NHdC(R)-
OR′}2] were only detected, by H NMR spectroscopy, as
minor byproducts.
of the E and Z isomers of imino esters in platinum(II) and
platinum(IV) complexes, are reported herein.
1
Results and Discussion
Nitrile-Alcohol Coupling Leading to (Imino ester)Pt-
(IV) Complexes. We choose as starting materials for this
study the nitrile compounds [PtCl4(RCN)2] (R ) Me, Et,
CH2Ph, Ph). The former two complexes were prepared either
by chlorination of a mixture of the cis- and trans-[PtCl2-
(RCN)2] isomers (ca. 5:1 for R ) Me,19 ca. 6:1 for R )
Et20) giving a mixture of cis/trans-[PtCl4(RCN)2] with almost
the same isomeric ratio or by chlorination of the pure trans-
[PtCl2(RCN)2] isomers (R ) Me,19 Et20) to give the isomeri-
cally pure trans-[PtCl4(RCN)2] complexes. The latter two
materials were obtained as the pure trans-[PtCl4(PhCH2CN)2]
isomer and as a mixture of the cis/trans-[PtCl4(PhCN)2]
isomers by chlorination of pure trans-[PtCl2(PhCH2CN)2]21
and of a mixture of cis- and trans-[PtCl2(PhCN)2],22 respec-
tively.
(A) Reaction of R′OH with Pure trans-[PtCl4(RCN)2]
and cis/trans-[PtCl4(RCN)2] (R ) Me, Et). Treatment of
trans-[PtCl4(RCN)2] (R ) Me, Et) with R′OH (R′ ) Me,
Et, n-Pr, i-Pr, n-Bu) at 45 °C in all cases allowed the isolation
of trans-[PtCl4{(E)-NHdC(R)OR′}2] complexes (route a in
Scheme 1) which are stable both in solution (CDCl3, 45 °C,
1 day) and in the solid state at room temperature. The
reaction between cis-[PtCl4(RCN)2] (which contains also
some trans form, see above) and the least sterically hindered
alcohols (methanol and ethanol) results in the formation of
trans-[PtCl4{(E)-NHdC(R)OR′}2] (R/R′ ) Me/Me) (route
b) or trans-[PtCl4{(E)-NHdC(Et)OR′}2] (R′ ) Me, Et) via
thermal isomerization (ROH, reflux, 3 h) of the initially
formed cis-[PtCl4{(E)-NHdC(Et)OR′}2] (routes c-d).
The reaction between alcohols R′OH and cis-[PtCl4-
(RCN)2] [R ) Me, R′ ) Et, n-Pr, i-Pr, n-Bu; R ) Et; R′ )
n-Pr, i-Pr, n-Bu], exhibiting greater R/R′ steric congestion,
The possibility of isomerization of the coordinated imino
ester ligand was demonstrated by warming up of a CDCl3
solution of pure cis-[PtCl4{(E)-NHdC(R)OR′}{(Z)-NHd
C(R)OR′}] at 45 °C for 3-4 h. Formation of the other two
isomers, i.e., cis-[PtCl4{(E)-NHdC(R)OR′}2] (ca. 15-20%)
and cis-[PtCl4{(Z)-NHdC(R)OR′}2] (ca. 5-10%), was de-
tected by NMR. However, on further heating this mixture is
subject to overall degradation giving a large number of
unidentified products.
All of the prepared compounds gave satisfactory elemental
analyses and show good agreement between observed and
calculated FAB mass spectra. Comparison of the IR spectra
of the products with those of the starting materials indicates
the disappearance of the CtN stretching vibrations and the
appearance of strong ν(CdN) vibrations in the range 1650-
1629 cm-1, a new medium-intensity band at ca. 1250 cm-1
[which might be assigned23 to ν(C-O)], and N-H stretching
vibrations which emerge in the range 3250-3360 cm-1. In
the 13C{1H} NMR spectra, the chemical shifts of the imino
NdC carbon exhibit a relatively low variation (175.4-177.3
ppm) due to rather similar environments introduced by the
OR′ substituents. The 195Pt NMR resonances of the trans and
cis isomers differ, by 140 ppm, with the cis isomer being at
lower field. The same trend has been observed in the 195Pt
NMR spectra of the cis and trans isomers of other [PtCl4L2]
complexes.8,24
In trans-[PtCl4{(E)-NHdC(Me)OR′}2], the E configura-
tion of the imino ester ligands in solution was supported by
the observation of the nuclear Overhauser effect (NOE)
between the NH and the OCH2 protons (OCH3 protons for
R′OH ) MeOH). In cis-[PtCl4{(E)-NHdC(Me)OR′}{(Z)-
NHdC(Me)OR′}], the imino ester ligands display two
1
distinct sets of H NMR signals of 1:1 intensity. For one
(19) Fanizzi, F. P.; Intini, F. P.; Maresca, L.; Natile, G. J. Chem. Soc.,
Dalton Trans. 1990, 199.
(20) (a) Svensson, P.; Lo¨vqvist, K.; Kukushkin, V. Yu.; Oskarsson, A° . Acta
Chem. Scand. 1995, 49, 72. (b) Kukushkin, V. Yu.; Oskarsson, A° .;
Elding, L. I. Inorg. Synth. 1997, 31, 279.
ligand a NOE is observed between the protons of the NH
and those of the CH3 groups, while for the second ligand
the NOE was between the NH and the OCH2 protons (Figure
(21) Kukushkin, V. Yu.; Tkachuk, V. M.; Vorobiov-Desiatovsky, N. V.
Inorg. Synth. 1998, 32, 144.
(22) (a) Uchiyama, T.; Nakamura, Y.; Miwa, T.; Kawaguchi, S.; Okeya,
S. Chem. Lett. 1980, 337. (b) Uchiyama, T.; Toshiyasu, Y.; Nakamura,
Y.; Miwa, T.; Kawaguchi, S. Bull. Chem. Soc. Jpn. 1981, 54, 181.
(23) Bellamy, L. J. The Infrared Spectra of Complex Molecules, 2nd ed;
Methuen: London, 1996.
(24) Kukushkin, V. Yu.; Belsky, V. K.; Aleksandrova, E. A.; Konovalov,
V. E.; Kirakosyan, G. A. Inorg. Chem. 1992, 31, 3836.
Inorganic Chemistry, Vol. 41, No. 8, 2002 2043

Bokach et al.
Figure 1. (a) 1H NMR spectrum (in CDCl3) of cis-[PtCl4{(E)-NHdC(Me)OBu-n}{(Z)-NHdC(Me)OBu-n }]; (*) CHCl3. (b) NOE difference spectrum
upon irradiation at the higher frequency NH (Z configuration). (c) NOE difference spectrum upon irradiation at the lower frequency NH (E configuration).
1, for complex with R′ ) n-Bu), thus indicating that the
imino ester ligands have the Z and E configurations,
correspondingly. It is worthwhile to mention that only one
approach providing the distinction between the E and Z
configurations of ligated imino ester ligands in solution was
known to date, i.e., it was reported15 that the NH proton of
the imino group in the E configuration was shifted to a higher
field in comparison with that of the Z configuration. This
estimate requires availability of both conformers, whereas
the NOE experiment allows the determination of the con-
figuration even when only one form is available. It is
important to note that in the case of cis-[PtCl4{(E)-NHd
C(Me)OR′}{(Z)-NHdC(Me)OR′}] both methods led to the
same conclusions, although the difference in chemical shifts
between E and Z configurations is lower for the platinum-
(IV) complexes (0.3-0.4 ppm; 0.1 ppm for R ) Et) than
for the platinum(II) compounds (0.6-0.7 ppm15).
that, in the case of benzyl and phenyl cyanide complexes,
the alcoholysis reaction failed with R′OH higher than
propanol.
All experiments described in A and B along with literature
data on platinum(II) complexes15,16 indicate that the addition
reaction strongly depends upon the oxidation state of the
metal. In the case of higher oxidation state [platinum(IV)
ion], the RCN-R′OH coupling does not require the use of
a base which, instead, is required for the lower oxidation
state [platinum(II) ion]. The alkoxylation of coordinated
nitriles is dramatically affected by the electronic and steric
properties of the alcohol. Indeed, the reaction proceeds
smoothly with sterically unhindered R′OH, e.g., R′ ) Me,
Et, n-Pr, while it is less efficient with more sterically
demanding alcohols, e.g., R′ ) i-Pr or n-Bu, or does not
proceed at all, e.g., t-Bu. Moreover, no RCN-R′OH coupling
was observed with phenol or even phenolate in this study or
in other works.16a Sterical hindrance of the R and R′ groups
as well as the configuration of the starting complex (trans
vs the more sterically encumbered cis form) affects greatly
the stereochemistry of the addition reaction. Indeed, when
steric factors are less important, the general trend is formation
of the trans-EE form.
(B) Reaction of R′OH with trans-[PtCl4(PhCH2CN)2]
and cis/trans-[PtCl4(PhCN)2]. The complexes [PtCl4-
(RCN)2] (R ) CH2Ph, Ph) exhibit poor solubility in the most
common organic solvents. Hence, the alcoholysis reactions
were performed under heterogeneous conditions, directly in
the appropriate alcohol and for a prolonged time and, for R
) Ph, with heating. As a consequence of such harsh
conditions, (i) the imino ester complexes trans-[PtCl4{(E)-
NHdC(R)OR′}2] (R ) CH2Ph, R′ ) Me, Et, n-Pr, i-Pr; R
) Ph, R′ ) Me) were isolated as solids in moderate yields,
while a broad mixture of byproducts derived from uncon-
trolled hydrolysis and overall degradation of the starting
materials and/or final products remains in solution; (ii) only
the trans-EE form was detected. It is worthwhile to mention
X-ray Structure Determinations of the (Imino ester)-
Pt(IV) Complexes. X-ray structure determinations of [PtCl4-
{NHdC(Me)OEt}2] (2), [PtCl4{NHdC(Et)OEt}2] (10), [PtCl4-
{NHdC(Et)OPr-i}2] (11), and [PtCl4{NHdC(Et)OPr-n}2]
(12) disclosed their overall trans configuration, while the
imino ester ligands in [PtCl4{NHdC(Et)OMe}2] (14) are
mutually cis. The coordination polyhedra of the five com-
plexes are slightly distorted octahedra (Figures 2-6).
2044 Inorganic Chemistry, Vol. 41, No. 8, 2002

Direct Addition of Alcohols to Organonitriles
Figure 2. ORTEP drawing of 2 with atomic numbering scheme.
Figure 6. ORTEP drawing of 14 with atomic numbering scheme.
C(Et)OMe}2] (14), the Pt-Cl bonds trans to N atoms [2.299-
(2) and 2.301(2) Å] are shorter than the other two in mutually
trans positions, 2.322(2) and 2.312(2) Å, and this allows the
assumption of a higher ground state trans influence of Cl as
compared to the imine (however, the difference is rather
subtle and more similar structures are needed to support this
assumption); (ii) in trans-[PtCl4{NHdC(Et)OPr-n}2] (12),
the Pt-Cl(2) bond [2.397(15) Å] is longer than the normal
one, while the Pt-Cl(1) [2.228(15) Å] on the same coordi-
nate is shorter than the average value for PtIV-Cl bonds.
The deviation from the normal bond distances is probably
due to an intermolecular hydrogen bond between the Cl(2)
atom and the imine H atom from a neighboring molecule
[N-H 0.88 Å, H‚‚‚Cl(2) 2.86 Å, N‚‚‚Cl(2) 3.732 Å;
N-H‚‚‚Cl(2) angle is 167°]. A similar trend in values of
the Pt-Cl bond lengths, agreeable within 3σ with our results,
was observed for [PtCl2(NH3)4][C4O4], where one chloride
involved in an intermolecular Cl‚‚‚H-N-Pt hydrogen bond
had a longer Pt-Cl bond distance [2.34(1) Å] while the
chloride in the trans position had a rather short Pt-Cl
distance [2.25(1) Å].26
Figure 3. ORTEP drawing of 10 with atomic numbering scheme.
In all complexes, the imino ester ligands are in the E
configuration. The NdC bond lengths all equal within 3σ
and correspond to the mean values of the NdC double bonds
in (imino ester)Pt(II) complexes15,16 and also the NdC bonds
in the previously characterized Pt(IV)-bound iminoacylated
oximes.7,8 All other bond distances and angles are normal
and agree perfectly with the values already reported for imino
ester complexes of platinum(II).15,16
Figure 4. ORTEP drawing of 11 with atomic numbering scheme.
Theoretical Studies. To the best of our knowledge to date
there are two basic but not coherent reports on the stereo-
chemistry of alcohol addition to coordinated nitriles. Thus,
it was reported27 that the methanol or ethanol additions to
coordinated acetonitrile in the iridium(III) cationic complex
[Cp*Ir(η3-CH2CHCHPh)(NCMe)](SO3CF3) (Cp* ) η5-C5-
Figure 5. ORTEP drawing of 12 with atomic numbering scheme.
(25) Ryabov, A. D.; Kazankov, G. M.; Panyashkina, I. M.; Grozovsky, O.
V.; Dyachenko, O. G.; Polyakov, V. A.; Kuzmina, L. G. J. Chem.
Soc., Dalton Trans. 1997, 4385.
(26) Castan, P.; Deguenon, D.; Fabre, P.-L.; Bernardinelli, G. Polyhedron
1992, 11, 901.
(27) Chin, C. S.; Chong, D.; Lee, B.; Jeong, H.; Won, G.; Do, Y.; Park,
Y. J. Organometallics 2000, 19, 638.
In general, the values of the Pt-Cl bond distances (2.31-
2.32 Å) agree well with previously characterized platinum-
(IV) chloride compounds.7,8,25 However, two noticeable
differences should be pointed out: (i) in cis-[PtCl4{NHd
Inorganic Chemistry, Vol. 41, No. 8, 2002 2045

Bokach et al.
order to keep the Cl‚‚‚H distance short. It is worthwhile to
note that the total energy of the system depends on this
dihedral angle rather weakly. For EE-II, both NHdC(C)-
OC fragments are coplanar and their plane bisects the Pt-
Cl bond angles. In the most stable conformations of both
EZ and ZZ structures, the methoxy group(s) in Z position is
(are) turned toward the Pt or Cl atoms; the other conforma-
tions formed by rotation of the OCH3 group(s) around the
C(2)O bond are less stable and are not discussed further.
The Pt-Cl and Pt-N bond lengths of EE-I and EE-II
are overestimated in comparison with the experimental
values, and the difference is more significant for the Pt(II)
complex (Table 7). The calculated N-H distance is, by 0.08
Å, shorter than the experimental value for EE-I and, by 0.27
Å, longer than that for EE-II most likely as a consequence
of the inaccurate localization of hydrogen atoms by X-ray
methods28 particularly in the case of EE-II. All other
calculated bond lengths are in good agreement with the
experimental data, and the maximum deviations do not
exceed 0.04 Å for EE-I and 0.02 Å for EE-II. Bond lengths
and angles within the imino ester are only slightly affected
by change in the oxidation state of the platinum center
(similar values are found for both I and II).
Figure 7. The EE, EZ, and ZZ conformations of the complexes trans-
[PtCl2{NHdC(Me)OMe}2] (I) and trans-[PtCl4{NHdC(Me)OMe}2] (II)
with numbering of selected atoms.
Me5) proceed readily at room temperature to give mixtures
of the E and Z isomers of [Cp*Ir(η3-CH2CHCHPh){NHd
C(Me)OR′}]+ (R′ ) Me, Et). In the presence of the
appropriate R′OH, the complete E-to-Z isomerization occurs
and this direction is opposite to that found15 for the platinum-
(II) complexes. Although in the current study we did not
observe E-Z transformations, the synthetic experiments are
more supportive of the idea that the E configuration in the
platinum(IV) imino ester complexes is more stable than the
Z configuration. In order to get a quantitative estimate of
the relative stabilities of the E and Z isomers in both
platinum(II) and platinum(IV) systems, a theoretical ab initio
study was performed, and the results are described in this
section.
Full geometry optimization of the EE, EZ, and ZZ isomers
for the platinum(II) and platinum(IV) complexes trans-[PtCl2-
{NHdC(Me)OMe}2] (EE-I, EZ-I, and ZZ-I) and trans-
[PtCl4{NHdC(Me)OMe}2] (EE-II, EZ-II, and ZZ-II) (Fig-
ure 7) at the HF level and the single-point calculations on
the basis of the equilibrium Hartree-Fock geometries at the
MP2//HF level of theory have been performed. The experi-
mental X-ray structure was chosen as the starting geometry
for EE-I,15b and the starting geometry for EE-II was selected
on the basis of the X-ray structure of trans-[PtCl4{NHd
C(Me)OEt}2] (this work), whereas the initial geometries for
the EZ and ZZ isomers were obtained by rotation of one or
two {C(Me)OMe} fragments around the NdC bond.
The coordination polyhedra of the Pt atom are either
square-planar or octahedral for I and II, respectively. The
overall conformations of EE-I and EE-II obtained by the
present calculations correspond to those observed in the
X-ray experiments. One major difference between the
calculated and the experimental parameters for EE-I is the
dihedral angle between imino ester ligands which is greater
in the theoretical model (79.2°) than in the X-ray structure
(33.3°), while this angle decreases to 63.2° and 40.7° in the
EZ-I and ZZ-I isomers, correspondingly. The analysis of
the experimental X-ray data for EE-I indicates that the
internuclear distances Cl‚‚‚H-CH2 between the chlorine
atom and one of hydrogens of the methyl group is about 3
Å. For the theoretical equilibrium structure of EE-I, this
distance remains also of ca. 2.96 Å. Thus, taking into account
the overestimate of the Pt-Cl bond lengths at the HF level
in comparison with experimental values, the imino esters are
forced to be more inclined over the coordination plane in
Both the HF and the MP2 calculations have shown that
the EE isomers are the most stable ones for both types of
complexes, i.e., four-coordinate platinum(II) (I) and six-
coordinate platinum(IV) (II). The most stable configurations
for the EZ isomers are less stable than those for the
corresponding EE isomers by 1.58 kcal/mol (HF) and 0.45
kcal/mol (MP2) for I or by 7.37 kcal/mol (HF) and 6.69
kcal/mol (MP2) for II (Table 8). In turn, the most stable
configurations for the ZZ isomers are less stable than the
respective EZ isomers by 2.39 kcal/mol (HF) and 1.31 kcal/
mol (MP2) for I or by 7.04 kcal/mol (HF) and 6.33 kcal/
mol (MP2) for II, therefore indicating (i) the increase of the
stability on moving from the ZZ to the EE configurations
and (ii) the greater difference in energy for the Pt(IV)
complexes than for the Pt(II) species.
Thus, the theoretical study indicates that the E configu-
ration of the imino ester ligand is more stable in comparison
with the Z form, and this agrees well with previous
experimental results on the Z-to-E transformation in imino
ester15 and amidine29 platinum(II) complexes. It is obvious,
however, that the conclusion cannot be extrapolated to other
metals (namely, to the above-mentioned Ir system18) and that
more examples of E/Z addition/transformation at different
metal centers should be investigated before making a general
conclusion.
Reduction of (Imino ester)Pt(IV) Complexes. We re-
cently reported on an efficient method for generation of
(imine)Pt(II) compounds that involves reduction of the
corresponding Pt(IV)-based imines by carbonyl-stabilized
phosphorus ylides, Ph3PdCHCO2R, in nonaqueous media.18
It was also anticipated in a previous section that the facile
(28) Desiraju, G. R. Acc. Chem. Res. 1996, 29, 441.
(29) Bertani, R.; Catanese, D.; Michelin, R. A.; Mozzon, M.; Bandoli, G.;
Dolmella, A. Inorg. Chem. Commun. 2000, 3, 16.
2046 Inorganic Chemistry, Vol. 41, No. 8, 2002

Direct Addition of Alcohols to Organonitriles
Table 1. Crystal Data and Structure Refinement for trans-[PtCl4{NHdC(Me)OEt}2] (2), trans-[PtCl4{NHdC(Et)OEt}2] (10),
trans-[PtCl4{NHdC(Et)OPr-i}2] (11), trans-[PtCl4{NHdC(Et)OPr-n}2] (12), and cis-[PtCl4{NHdC(Et)OMe}2] (14)
2
10
11
12
14
empirical formula
fw
C8H18N2Cl4O2Pt
511.12
C10H22N2Cl4O2Pt
539.18
C12H26N2Cl4O2Pt
567.23
C12H26N2Cl4O2Pt
567.23
C8H18N2Cl4O2Pt
511.12
space group
cryst syst
a, Å
b, Å
c, Å
monoclinic
P21/c (No. 14)
6.5900(10)
13.268(3)
9.562(2)
90
103.72(3)
90
812.2(3)
2
monoclinic
P21/c (No. 14)
8.701(2)
7.739(2)
13.920(3)
90
108.19(3)
90
539.18(4)
2
triclinic
monoclinic
C2 (No. 5)
8.8090(10)
8.950(2)
12.855(3)
90
99.16(2)
90
1000.6(3)
2
orthorhombic
P212121 (No. 19)
8.839(2)
11.655(2)
15.626(3)
90
90
90
1609.8(6)
4
2.109
P1h (No. 2)
6.325(10)
8.1800(10)
10.7290(10)
98.420(10)
104.790(10)
104.130(10)
507.41(12)
1
1.856
274
7.444
49.94
R, deg
â, deg
γ, deg
V, Å3
Z
Dc, Mg/m3
F(000)
2.090
484
9.288
51.94
2.011
516
8.477
51.98
1.883
548
7.550
51.94
968
9.373
49.96
µ(Mo KR), mm-1
2θmax, deg
refinement method
full-matrixa least
squares on F2
0.10 × 0.26 × 0.28
0 < h < 10,
0 < k < 13,
0 < l < 18
1265
cryst size, mm
index ranges
0.22 × 0.26 × 0.44
0 < h < 8,
0 < k < 16,
-11 < l < 11
1215
0.18 × 0.20 × 0.56
0 < h < 10,
0 < k < 9,
-17 < l < 16
1307
0.06 × 0.17 × 0.40
0 < h < 7,
-9 < k < 9,
-12 < l < 12
1886
0.06 × 0.30 × 0.32
0 < h < 10,
0 < k < 10,
-15 < l < 15
1076
collected reflns
unique reflns
[F(hkl) g 4σ(F)]
refinement params
extinction coeff
GOF
1120
1229
1715
1009
1265
116
0.0246(13)
1.036
133
0.0010(4)
1.086
149
97
0.0005(5)
1.086
155
0.00030(14)
1.057
1.095
R
Rw
0.0239
0.0604
0.0198
0.0489
0.0207
0.0504
0.0326
0.0816
0.0184
0.0444
a Anisotropic for all non-H atoms.
Table 2. Bond Lengths (Å) and Angles (deg) for
trans-[PtCl4{NHdC(Me)OEt}2] (2)a
Table 3. Bond Lengths (Å) and Angles (deg) for
trans-[PtCl4{NHdC(Et)OEt}2] (10)a
Pt(1)-Cl(1)
Pt(1)-Cl(2)
Pt(1)-N(1)
O(1)-C(1)
2.3133(16)
2.3121(14)
2.018(5)
O(1)-C(3)
N(1)-C(1)
C(1)-C(2)
C(3)-C(4)
1.459(8)
1.282(8)
1.482(9)
1.489(12)
Pt-Cl(1)
Pt-Cl(2)
Pt-N
2.3144(13)
2.3120(14)
2.021(3)
1.313(5)
1.451(6)
N-C(1)
1.287(6)
C(1)-C(2)
C(2)-C(3)
C(4)-C(5)
1.485(6)
1.515(7)
1.499(9)
1.319(7)
O-C(1)
O-C(4)
Cl(1)-Pt(1)-Cl(2)
Cl(1)-Pt(1)-N(1)
Cl(1)-Pt(1)-Cl(1)# 180.00
90.49(6)
N(1)-Pt(1)-N(1)#
180.00
93.67(14) Cl(1)#-Pt(1)-Cl(2)#
90.49(6)
93.67(14)
95.43(16)
120.1(4)
135.7(4)
123.5(4)
111.4(6)
25.1(6)
Cl(1)-Pt-Cl(2)
Cl(1)-Pt-N
Cl(1)-Pt-Cl(1)#
Cl(1)-Pt-Cl(2)#
Cl(1)-Pt-N#
Cl(2)-Pt-N
Cl(1)#-Pt-Cl(2)
Cl(2)-Pt-Cl(2)#
Cl(2)-Pt-N#
Cl(1)#-Pt-N
Cl(2)#-Pt-N
88.88(5)
94.77(12)
180.00
91.12(5)
85.23(12)
85.99(11)
91.12(5)
180.00
N-Pt-N#
180.00
Cl(1)#-Pt(1)-N(1)#
Cl(2)#-Pt(1)-N(1)#
Cl(1)-Pt-Cl(2)#
Cl(1)#-Pt-N#
Cl(2)#-Pt-N#
C(1)-O-C(4)
Pt-N-C(1)
88.88(5)
94.77(12)
85.99(11)
120.5(4)
135.1(3)
112.1(4)
122.0(4)
125.9(4)
111.5(4)
107.2(5)
Cl(1)-Pt(1)-Cl(2)#
Cl(1)-Pt(1)-N(1)#
Cl(2)-Pt(1)-N(1)
Cl(1)#-Pt(1)-Cl(2)
89.51(6)
86.33(14) C(1)-O(1)-C(3)
95.43(16) Pt(1)-N(1)-C(1)
89.51(6)
O(1)-C(1)-N(1)
O(1)-C(1)-C(2)
Cl(2)-Pt(1)-Cl(2)# 180.00
O-C(1)-C(2)
O-C(1)-N
N-C(1)-C(2)
C(1)-C(2)-C(3)
O-C(4)-C(5)
Cl(2)-Pt(1)-N(1)#
Cl(1)#-Pt(1)-N(1)
Cl(2)#-Pt(1)-N(1)
84.57(16) N(1)-C(1)-C(2)
86.33(14) O(1)-C(3)-C(4)
84.57(16)
106.3(6)
94.01(11)
85.23(12)
94.01(11)
a Symmetry transformations used to generate equivalent atoms: (#) -x
+ 1, -y + 1, -z + 1.
a Symmetry transformations used to generate equivalent atoms: (#) -x
+ 1, -y + 1, -z + 1.
reduction of isomerically pure (imino ester)Pt(IV) compounds
with the ylides could open up an alternative route to
isomerically pure (imino ester)Pt(II) complexes which, in
some instances, exhibit antitumor activity.17 The reduction
was exemplified for trans-[PtCl4{(E)-NHdC(Me)OR′}2] (R′
) Me, Et) and cis-[PtCl4{(E)-NHdC(Me)OEt}{(Z)-NHd
C(Me)OEt}], and, in accord with our expectations, it
proceeds rapidly and under mild conditions with 1 equiv of
the ylide Ph3PdCHCO2Me to form selectiVely the platinum-
(II) products without change in the complex geometry (cis/
trans) and ligand configuration (E/Z) and without further
reduction of the platinum center (Scheme 3). The reaction
products were purified by column chromatography and
obtained in ca. 50% isolated yield.
1
General features of the IR, H NMR, and 13C{1H} NMR
spectra of trans-[PtCl2{(E)-NHdC(Me)OR′}2] (R′ ) Me, Et)
are similar to those observed for the appropriate platinum-
(IV) complexes. The trans configuration of the complexes
was confirmed by measuring their far-IR spectra, which
display only one band of the ν(Pt-Cl) stretching vibration
characteristic for this geometry.30 In the 1H NMR spectra of
the platinum(II) complexes, a NOE was observed between
the NH and OCH3 or OCH2CH3 protons, thus indicating that
the E configuration persists after the reduction. The most
(30) Konovalov, L. V.; Kukushkin, V. Yu.; Belsky, V. K.; Konovalov, V.
E. Zh. Neorg. Khim. 1990, 35, 1523; Russ. J. Inorg. Chem. (Engl.
Transl.) 1990, 35, 863 and references therein.
Inorganic Chemistry, Vol. 41, No. 8, 2002 2047

Bokach et al.
Table 4. Bond Lengths (Å) and Angles (deg) for
trans-[PtCl4{NHdC(Et)OPr-i}2] (11)a
Table 6. Bond Lengths (Å) and Angles (deg) for
cis-[PtCl4{NHdC(Et)OMe}2] (14)
Pt-Cl(1)
Pt-Cl(2)
Pt-N
2.3128(12)
2.3191(12)
2.022(3)
1.321(6)
1.467(6)
N-C(1)
1.272(5)
1.489(7)
1.504(10)
1.503(9)
1.499(10)
Pt-Cl(1)
Pt-Cl(2)
Pt-Cl(3)
Pt-Cl(4)
Pt-N(1)
2.299(2)
2.322(2)
2.312(2)
2.301(2)
2.038(6)
2.039(6)
1.326(10)
1.441(11)
O(2)-C(5)
O(2)-C(8)
N(1)-C(1)
N(2)-C(5)
C(1)-C(2)
C(2)-C(3)
C(5)-C(6)
C(6)-C(7)
1.308(9)
C(1)-C(2)
C(2)-C(3)
C(4)-C(5)
C(4)-C(6)
1.453(11)
1.291(10)
1.286(10)
1.492(12)
1.539(13)
1.486(11)
1.505(14)
O-C(1)
O-C(4)
Pt-N(2)
Cl(1)-Pt-Cl(2)
Cl(1)-Pt-N
Cl(1)-Pt-Cl(1)#
Cl(1)-Pt-Cl(2)#
Cl(1)-Pt-N#
Cl(2)-Pt-N
Cl(1)#-Pt-Cl(2)
Cl(2)-Pt-Cl(2)#
Cl(2)-Pt-N#
Cl(1)#-Pt-N
Cl(2)#-Pt-N
N-Pt-N#
90.98(4)
84.70(10)
180.00
89.02(4)
95.30(10)
86.04(10)
89.02(4)
180.00
93.96(10)
95.30(10)
93.96(10)
180.00
Cl(1)#-Pt-Cl(2)#
Cl(1)-Pt-N#
Cl(2)#-Pt-N#
C(1)-O-C(4)
Pt-N-C(1)
N-C(1)-C(2)
O-C(1)-N
O-C(1)-C(2)
C(1)-C(2)-C(3)
C(5)-C(4)-C(6)
O-C(4)-C(5)
O-C(4)-C(6)
90.98(4)
84.70(10)
86.04(10)
121.6(3)
136.5(3)
125.3(4)
123.0(4)
111.7(4)
112.5(5)
114.4(5)
110.0(5)
105.0(5)
O(1)-C(1)
O(1)-C(4)
Cl(1)-Pt-Cl(2)
Cl(1)-Pt-Cl(3)
Cl(1)-Pt-Cl(4)
Cl(1)-Pt-N(1)
Cl(1)-Pt-N(2)
Cl(2)-Pt-Cl(3)
Cl(2)-Pt-Cl(4)
Cl(2)-Pt-N(1)
Cl(2)-Pt-N(2)
Cl(3)-Pt-Cl(4)
Cl(3)-Pt-N(1)
Cl(3)-Pt-N(2)
Cl(4)-Pt-N(1)
Cl(4)-Pt-N(2)
91.03(9)
90.82(8)
91.35(9)
N(1)-Pt-N(2)
94.1(3)
C(1)-O(1)-C(4)
C(5)-O(2)-C(8)
Pt-N(1)-C(1)
119.8(7)
118.9(6)
134.6(5)
135.4(5)
123.1(7)
111.7(7)
125.1(7)
112.2(7)
111.3(6)
125.5(7)
123.2(7)
112.9(7)
88.7(2)
176.38(19)
177.77(8)
90.39(8)
84.57(18)
86.99(18)
88.31(8)
96.72(18)
91.10(17)
174.97(18)
85.64(18)
Pt-N(2)-C(5)
O(1)-C(1)-N(1)
O(1)-C(1)-C(2)
N(1)-C(1)-C(2)
C(1)-C(2)-C(3)
O(2)-C(5)-C(6)
N(2)-C(5)-C(6)
O(2)-C(5)-N(2)
C(5)-C(6)-C(7)
a Symmetry transformations used to generate equivalent atoms: (#) -x,
-y, -z.
Table 5. Bond Lengths (Å) and Angles (deg) for
trans-[PtCl4{NHdC(Et)OPr-n}2] (12)a
Table 7. Calculated (Selected) Bond Lengths (Å) for the Complexes
trans-[PtCl2{NHdC(Me)OMe}2] (I) and trans-[PtCl4{NHdC(Me)-
OMe}2] (II) and, for Comparison, Experimental Values for Selected
Complexes
Pt-Cl(1)
Pt-Cl(2)
Pt-Cl(3)
Pt-N
O-C(1)
O-C(4)
2.228(15)
2.397(15)
2.300(3)
2.039(9)
1.317(15)
1.42(2)
N-C(1)
1.34(2)
1.503(19)
1.52(2)
1.49(3)
1.46(4)
C(1)-C(2)
C(2)-C(3)
C(4)-C(5)
C(5)-C(6)
EE-I
EE-I
theor
EZ-I
ZZ-I
exptla
Pt-Cl
Pt-N
CdN
C-C
C(2)O
C(4)O
NH
2.387
2.066
1.273
1.488
1.345
1.444
1.000
2.381, 2.391
2.066, 2.070
1.274
1.488, 1.497
1.345, 1.325
1.444, 1.454
1.000, 0.998
2.384
2.071
1.274
1.497
1.326
1.451
0.999
2.299, 2.300
1.989, 2.009
1.295, 1.306
1.503, 1.518
1.306, 1.314
1.412, 1.456
1.080, 1.081
Cl(1)-Pt-Cl(2)
Cl(1)-Pt-Cl(3)
Cl(1)-Pt-N
Cl(1)-Pt-Cl(3)#
Cl(1)-Pt-N#
Cl(2)-Pt-Cl(3)
Cl(2)-Pt-N
Cl(2)-Pt-Cl3#
Cl(2)-Pt-N#
Cl(3)-Pt-N
Cl(3)-Pt-Cl(3)#
Cl(3)-Pt-N#
180(3)
Cl(3)-Pt-N
N-Pt-N#
Cl(3)#-Pt-N#
C(1)-O-C(4)
Pt-N-C(1)
O-C(1)-C(2)
N-C(1)-C(2)
O-C(1)-N
C(1)-C(2)-C(3)
O-C(4)-C(5)
C(4)-C5-C(6)
92.8(3)
172.4(14)
87.6(3)
93.6(4)
86.2(10)
93.6(4)
86.2(10)
86.4(4)
93.8(10)
86.4(4)
93.8(10)
87.6(3)
172.9(6)
92.8(3)
121.9(12)
129.4(17)
111.6(11)
128.9(13)
119.4(14)
111.7(14)
107.5(14)
112.3(18)
EE-II
EZ-II
ZZ-II
[PtCl4{NHdC(Me)OEt}2]b
Pt-Cl 2.360 2.357-2.363 2.360-2.361
Pt-N 2.045 2.043, 2.064 2.059
CdN 1.279 1.279, 1.285 1.285
C-C 1.487 1.487, 1.503 1.503
C(2)O 1.339 1.339, 1.311 1.312
C(4)O 1.449 1.449, 1.463 1.465
2.312-2.313
2.018, 2.019
1.283
1.482
1.319
a Symmetry transformations used to generate equivalent atoms: (#) -x,
y, -z + 1.
1.459
NH
0.999 0.999
0.999
0.730
significant spectroscopic difference between trans-[PtCl2-
{(E)-NHdC(Me)OR′}2] and the appropriate platinum(IV)
complexes is provided by their 195Pt NMR spectra, which
show the disappearance of the Pt(IV) signals at -176 (R′ )
Me) and -158 (R′ ) Et) ppm, while new resonances emerge
at -1914 and -1910 ppm, respectively. We also reduced
cis-[PtCl4{(E)-NHdC(Me)OEt}{(Z)-NHdC(Me)OEt}] (195Pt
NMR, δ: 14) to give the corresponding platinum(II) complex
a Reference 15b. b This work (EE isomer).
Table 8. Total Energies, Etot (Hartree), and Relative Energies, Erel
(kcal/mol), of the Most Stable Conformations of the EE, EZ, and ZZ
Isomers of Complexes I and II
HF//HF
MP2//HF
Etot
Etot
Erel
0.0
+1.58
+3.97
0.0
Erel
0.0
+0.45
+1.76
0.0
EE-I
EZ-I
ZZ-I
EE-II
EZ-II
ZZ-II
-1531.262980
-1531.260466
-1531.256655
-2450.185206
-2450.173464
-2450.162240
-1532.654603
-1532.653886
-1532.651802
-2451.913625
-2451.902968
-2451.892884
(
195Pt NMR, δ: -1953). The platinum(II) complex cis-[PtCl2-
{(E)-NHdC(Me)OEt}{(Z)-NHdC(Me)OEt}] shows two Pt-
Cl stretching bands in the IR spectrum, specific for the cis
arrangement of the Cl ligands about the Pt(II) center.30 The
NOE experiment also proved that the imino ester ligands
have different configurations. Moreower, the NH proton
resonance of the imino group in the E configuration occurs
at a higher field than that of the Z configuration as observed
for the Pt(IV) complexes and in accord with a previous
report.15
+7.37
+14.41
+6.69
+13.02
instances, is higher than that of the corresponding platinum-
(II) species and the addition reactions in the former case
proceed under milder conditions. This implies that the
platinum(IV) center can be employed as a template for metal-
mediated reactions that are not feasible in pure organic
chemistry or with the use of the platinum(II) complexes.
After the platinum(IV)-mediated transformation has taken
place, the newly formed ligands can be liberated to give free
Liberation of the Imino Ester Ligands. Our studies on
platinum-mediated reactions of organonitriles show that the
reactivity of (organonitrile)Pt(IV) complexes, in many
2048 Inorganic Chemistry, Vol. 41, No. 8, 2002

Direct Addition of Alcohols to Organonitriles
Scheme 3
were determined on a Kofler table. For TLC, Merck UV 254 SiO2
plates were used. Positive-ion FAB mass spectra were obtained on
a Trio 2000 instrument by bombarding 3-nitrobenzyl alcohol (NBA)
matrixes of the samples with 8 keV (ca. 1.28 × 1015 J) Xe atoms.
Mass calibration for data system acquisition was achieved using
CsI. Infrared spectra (4000-400 cm-1) were recorded on a BIO-
1
RAD FTS 3000MX instrument in KBr pellets. H, 13C{1H}, and
195Pt NMR spectra were measured on Varian UNITY 300 and
Bruker AMX 300 spectrometers at ambient temperature. 195Pt
chemical shifts are given relative to Na2[PtCl6] (by using K2[PtCl4],
δ ) -1630 ppm, as a standard), and the half-height line width is
given in parentheses.
organic material. Since imino esters are useful synthons for
many organic transformations1,2 and their formation easily
occurs at the Pt(IV) center, we attempted to find an efficient
route for the release of the NHdC(R)OR′ species from the
coordination sphere. trans-[PtCln{(E)-NHdC(Me)OEt}2] (n
) 2, 4) were taken as reference compounds, and two
pathways for the liberation (Scheme 3) were explored, i.e.,
(i) displacement, by pyridine, of the imino ester in the
platinum(IV) complex, and (ii) substitution with 1,2-bis-
(diphenylphosphino)ethane, dppe, in the platinum(II) com-
pound. In both cases the substitution results in precipitation
of highly insoluble metal complexes which can be removed,
by filtration, from the solution containing the free imino ester
NHdC(Me)OEt.
Final Remarks. Imino esters are useful synthetic inter-
mediates in organic chemistry,1,2 but, in the vast majority of
cases, their utilization involves the free HNdC(R)OR′ rather
than its much more accessible hydrochloride, HNdC(R)-
OR′‚HCl. Careful neutralization of HCl in nonaqueous media
is sometimes difficult especially when the synthesis is
performed on a micro scale. Moreover, some products of
the neutralization reaction, e.g., H2O, can interfere with the
subsequent transformations. Similarly to protonation, coor-
dination to a metal center makes imino esters quite stable,
and they can be stored in this form for a prolonged time.
When required, their liberation can be performed in an easier
way than starting from the hydrochlorides. If the replacement
is carried out in nonaqueous dried solvents and the formed
complex precipitates from solution and is removed by
filtration (as in the present work), the liberated imino esters,
stable under anhydrous conditions retained in the filtrate, can
be used in situ for further transformations.
Synthetic Work and Characterization. Reactions of [PtCl4-
(MeCN)2] with Alcohols. A suspension of trans-[PtCl4(MeCN)2]
(0.08 g, 0.2 mmol) is heated at 45 °C in methanol, ethanol, or
n-PrOH (5 mL) for 36 h (R ) Me) or 3 day (R ) Et, n-Pr),
whereupon the new precipitate formed is filtered off, washed with
three 5-mL portions of diethyl ether, and dried in air at room
temperature. In the case of i-PrOH and n-BuOH the reaction is
performed in a mixture of dichloromethane (5 mL) and the alcohol
(0.10-0.15 mL).
A suspension of cis-[PtCl4(MeCN)2] (0.08 g, 0.2 mmol; the
complex contains ca. 20% of the trans isomer) is heated at 45 °C
in methanol or ethanol (2 mL) for 36 h (R ) Me) or 3 days (R )
Et), whereupon the new precipitate formed is filtered off, washed
with three 5-mL portions of diethyl ether, dried in air at room
temperature, and then recrystallized from CH2Cl2/Et2O at room
temperature. In the case of n-PrOH and n-BuOH, the reaction is
performed in a mixture of dichloromethane (2 mL) and the alcohol
(0.1 mL) for 3 days, whereupon solvents are evaporated under flow
of dinitrogen and the yellow residues are washed with Et2O (three
2-mL portions), dissolved at 20-25 °C in a minimum amount of
CH2Cl2, and then purified on silica gel by column chromatography.
trans-[PtCl4{(E)-NHdC(Me)OMe}2] (1). Yield: 72%. Anal.
Calcd for C6H14N2Cl4O2Pt: C, 14.90; H, 2.89; N, 5.79. Found: C,
14.53; H, 2.65; N, 5.52. FAB+-MS, m/z: 475 [M - Cl]+, 440 [M
- 2Cl]+. TLC, Rf ) 0.68 (eluent CH2Cl2). IR spectrum in KBr,
selected bands, cm-1: 3250 m-w ν(N-H), 1650 s ν(CdN), 1258
1
4
m ν(C-O). H NMR in CDCl3, δ: 2.75 (s + d, JPtH 2.8 Hz, 3H,
dCMeO), 3.99 (s, 3H, OMe), 6.90 (s, br, 1H, NH). 13C{1H} NMR
in CDCl3, δ: 20.1 (dCMeO), 55.0 (OMe), 177.5 (CdNH). 195Pt
NMR in CDCl3, δ: -176 (450 Hz).
trans-[PtCl4{(E)-NHdC(Me)OEt}2] (2). Yield: 65%. Anal.
Calcd for C8H18N2Cl4O2Pt: C, 18.78; H, 3.52; N, 5.47. Found: C,
18.85; H, 3.31; N, 5.31. FAB+-MS, m/z: 482 [M]+, 412 [M -
2Cl]+. TLC, Rf ) 0.64 (eluent CH2Cl2). IR spectrum in KBr,
selected bands, cm-1: 3358 m-w ν(N-H), 1629 s ν(CdN), 1251
m ν(C-O). 1H NMR in CDCl3, δ: 1.49 (t, 7.0 Hz, 3H, CH3 from
Et), 2.73 (s + d, 4JPtH 3.5 Hz, 3H, dCMeO), 4.24 (quart., 7.0 Hz,
2H, CH2 from Et), 6.78 (s, br, 1H, NH). 13C{1H} NMR in CDCl3,
δ: 13.5 (CH3 from Et), 20.3 (dC(Me)O), 64.7 (CH2 from Et), 176.5
(CdNH). 195Pt NMR in CDCl3, δ: -158 (650 Hz).
trans-[PtCl4{(E)-NHdC(Me)OPr-i}2] (3). Yield: 39%. Anal.
Calcd for C10H22N2Cl4O2Pt: C, 22.26; H, 4.08; N, 5.19. Found:
C, 21.93; H, 4.14; N, 5.03. FAB+-MS, m/z: 468 [M - 2Cl]+. TLC,
Rf ) 0.61 (eluent CH2Cl2). IR spectrum in KBr, selected bands,
cm-1: 3370 m-w ν(N-H), 1631 s ν(CdN), 1247 m ν(C-O). 1H
NMR in CDCl3, δ: 1.45 (d, 6.0 Hz, 6H, CH3 from i-Pr), 2.69 (s +
d,4JPtH 3.0 Hz, 3H, dCMeO), 4.77 (sept, 6.1 Hz, 1H, CH from
i-Pr), 6.82 (s, br, 1H, NH). 13C{1H} NMR in CDCl3, δ: 20.5
(dCMeO), 21.6 (CH3 from i-Pr), 73.2 (CH from i-Pr), CdNH were
not detected. 195Pt NMR in CDCl3, δ: -136 (550 Hz).
Imino esters are much better ligands for soft metal centers
than nitriles. Hence, the high stability of the imino ester
complexes of the platinum group metals, which is a useful
property for stoichiometric reactions, prevents, however, their
usage in catalytic processes, and only one catalytic reaction
of this kind has been reported so far.27 We assume that further
progress in the search of catalytic processes for the metal-
mediated conversion of nitriles to imino esters could well
be connected with the application of hard metal centers,
where the stability of the imino ester species formed should
be lower and therefore could lead to catalysis.
Experimental Section
Materials and Instrumentation. Solvents were obtained from
commercial sources and used as received. [PtCl4(RCN)2] (R ) Me,
Et, CH2Ph, Ph) were prepared according to the published method.7
C, H, and N elemental analyses were carried out by the Microana-
lytical Service of the Instituto Superior Te´cnico. Melting points
Inorganic Chemistry, Vol. 41, No. 8, 2002 2049

Bokach et al.
trans-[PtCl4{(E)-NHdC(Me)OPr-n}2] (4). Yield: 55%. Com-
plex was recrystallized from CHCl3. Anal. Calcd for C10H22N2-
Cl4O2Pt‚0.5CHCl3: C, 21.51; H, 3.90; N, 4.87. Found: C, 21.50;
H, 3.69; N, 5.03. FAB+-MS, m/z 561 [M + Na]+, 505 [M - Cl]+,
491 [M - 2Cl + Na]+, 468 [M - 2Cl]+, 431 [M - 3Cl - 2H]+,
396 [M - 4Cl - H]+. TLC, Rf ) 0.58 (eluent CH2Cl2). IR spectrum
in KBr, selected bands, cm-1: 3356 m-w ν(N-H), 2972 w and
C, 25.00; H, 4.54; N, 4.76. Found: C, 24.89; H, 4.38; N, 4.99. IR
spectrum in KBr, selected bands, cm-1: 3296 m-w ν(N-H), 2960
m, 2932 m-w and 2872 m-w ν(C-H), 1637 s ν(CdN), 1243 m
ν(C-O). FAB+-MS, m/z: 496 [M - 2Cl]+, 422 [M - 4Cl - 2H]+.
TLC, Rf ) 0.44 (eluent Me2CO:CHCl3 ) 3:10). 1H NMR in CDCl3,
δ: two sets of signals in ca. 1:1 ratio, 0.91 (t, 7.4 Hz, 3H, CH3
from Bu-n, E), 0.94 (t, 7.4 Hz, 3H, CH3 from Bu-n, Z), 1.42 (m,
4H, γ-CH2 from Bu-n), 1.69 (m, 4H, â-CH2 from Bu-n), 2.59 (s,
1
2930 w ν(C-H), 1633 s ν(CdN), 1246 m ν(C-O). H NMR in
3
CDCl3, δ: 1.00 (t, 7.3 Hz, 3H, CH3 from Pr-n), 1.82 (m, 2H, â-CH2
from Pr-n), 2.68 (s, 3H, dCMeO), 4.06 (t, 6.3 Hz, 2H, R-CH2 from
OPr-n), 6.82 (s, br, 1H, NH). 13C{1H} NMR in CDCl3, δ: 10.2
(CH3 from Pr-n), 20.21 (dCMe), 21.4 (CH2 from Pr-n), 70.2 (OCH2
of OPr-n), 176.6 (CdNH). 195Pt NMR in CDCl3, δ: -153.1 (655
Hz).
trans-[PtCl4{(E)-NHdC(Me)OBu-n}2] (5). Yield: 50%. Anal.
Calcd for C12H26N2Cl4O2Pt‚0.1C4H9OH: C, 25.91; H, 4.73; N, 4.87.
Found: C, 26.00; H, 5.05; N, 4.75. FAB+-MS, m/z 614 [M - 2H
+ 2Na]+, 576 [M - 2H - Cl + 2Na]+, 540 [M - 2H - 2Cl +
2Na]+, 496 [M - 2H - 2Cl]+, 424 [M - 4Cl]+. TLC, Rf ) 0.68
(eluent CH2Cl2). IR spectrum in KBr, selected bands, cm-1 : 3360
m-w ν(N-H), 2937 m-w ν(C-H), 1637 s ν(CdN), 1247 m ν-
(C-O). 1H NMR in CDCl3, δ: 0.95 (t, 7.3 Hz, 3H, CH3 from Bu-
n), 1.43 (m, 2H, γ-CH2 from OBu-n), 1.77 (m, 2H, â-CH2 from
Pr-n), 2.68 (s, 3H, dCMeO), 4.10 (t, 6.3 Hz, 2H, R-CH2 from OBu-
n), 6.82 (s, br, 1H, NH). 13C{1H} NMR in CDCl3, δ: 13.6 (CH3
from Bu-n), 18.9 (CH2 from Bu-n), 20.2 (dCMe), 29.9 (CH2 from
Bu-n), 70.2 (OCH2 from OBu-n), 176.5 (CdNH). 195Pt NMR in
CDCl3, δ: -155.4 (630 Hz).
3H, dCMeO, E), 2.66 (s, JPtH 13.7 Hz, 3H, dCMeO, Z), 4.12 (t,
6.0 Hz, 2H, R-CH2 from OBu-n, E), 4.28 (t, 6.3 Hz, 2H, R-CH2
from OBu-n, Z), 7.25 (s, br, 3JPtH 31.5 Hz, 1H, NH, E), 7.64 (s, br,
4JPtH 21.9 Hz, 1H, NH, Z). 13C{1H} NMR in CDCl3, δ: 13.6 (two
signals, CH3 from OBu-n), 18.7 (γ-CH2 from OBu-n, E), 19.0 (γ-
CH2 of OBu-n, Z), 19.9 (3JPtC 8.8 Hz, dCMeO, E), 22.6 (JPtC 26.1
Hz, dCMeO, Z), 30.0 (â-CH2 from OBu-n, E), 30.8 (â-CH2 from
OBu-n, Z), 69.4 (JPtC 93.4 Hz, R-CH2 from OBu-n, E), 72.6 (R-
CH2 from OBu-n, Z), 176.2 (CdNH, E), 177.6 (JPtC 75.5 Hz,
CdNH, Z). 195Pt NMR in CDCl3, δ: 4 (375 Hz). A suitable ratio
1
of signals from the E and Z forms in the H NMR spectrum, one
signal in the 195Pt NMR spectrum, and one spot on TLC allow one
to assume that a pure single compound was obtained. Attribution
of the signals due to the E and Z isomers was performed using
NOE, COSY, and HETCOR.
Reactions of [PtCl4(EtCN)2] with Alcohols. The reactions with
either trans- or cis-[PtCl4(EtCN)2] (20 mg, 0.05 mmol) are
performed in suspension of the appropriate alcohol (0.1-0.2 mL)
at 45 °C for 1 day. In the case of trans-[PtCl4(EtCN)2], the
crystalline trans-[PtCl4{(E)-NHdC(Et)OR′}2] formed is filtered off
and washed with one 0.5-mL portion of the alcohol and two 0.5-
mL portions of diethyl ether. Yields are 70-90%. In the case of
cis-[PtCl4(EtCN)2], products and yields are given below for each
particular case. Insofar as cis-[PtCl4(EtCN)2] contains admixtures
of trans-[PtCl4(EtCN)2], NMR parameters of cis addition products
were obtained by subtraction of signals due to trans-E isomers from
the NMR spectra.
cis-[PtCl4{(E)-NHdC(Me)OEt}{(Z)-NHdC(Me)OEt}] (6).
Yield: 60%. Anal. Calcd for C8H18N2Cl4O2Pt: C, 18.78; H, 3.52;
N, 5.47. Found: C, 18.83; H, 3.52; N, 5.46. FAB+-MS, m/z: 533
[M - H + Na], 511 [M], 440 [M - 2Cl]+. TLC, Rf ) 0.30 (eluent
acetone:CHCl3 ) 1:2). IR spectrum in KBr, selected bands, cm-1
:
3313 m-w ν(N-H), 2982 w and 2924 w ν(C-H), 1633 s ν(CdN),
1250 m ν(C-O). 1H NMR in CDCl3, δ: two sets of signals in ca.
1:1 ratio, 1.42 (t, 7.0 Hz, 3H, CH2CH3, E), 1.44 (t, 7.0 Hz, 3H,
CH2CH3, Z), 2.60 (s, 3H, dCMeO, E), 2.61 (s, 3H, dCMeO, Z),
4.35 (quart., 7.0 Hz, 2H, CH2CH3, E), 4.37 (quart., 7.0 Hz, 2H,
CH2CH3, Z), 7.36 (s, br, 1H, NH, E), 7.64 (s, br, 1H, NH, Z). 13C-
{1H} NMR in CDCl3, δ: 13.6 and 14.2 (CH3 from Et), 19.6
(dCMeO), 64.6 and 67.4 (CH2 from Et), 175.4 and 176.4 (CdNH).
195Pt NMR in CDCl3, δ: 14 (860 Hz).
trans-[PtCl4{(E)-NHdC(Et)OMe}2] (9). Anal. Calcd for C8H18N2-
Cl4O2Pt: C, 18.87; H, 3.55; N, 5.48. Found: C, 18.94; H, 3.55; N,
5.36. FAB+-MS, m/z: 440 [M - 2Cl], 367 [M - 4Cl - 2H]. TLC,
Rf ) 0.41 (eluent CH2Cl2). IR spectrum in KBr, selected bands,
cm-1: 3334 m ν(N-H), 2981 and 2941 m-w ν(C-H), 1628 s
ν(CdN), 1229 m ν(C-O). 1H NMR in CDCl3, δ: 1.23 (t, 7.5 Hz,
3H, CH3 from Et), 3.13 (quart., 7.5 Hz, 2H, CH2 from Et), 3.96 (s,
3H, OMe), 6.86 (s, br, 1H, NH). 13C{1H} NMR in CDCl3, δ: 10.6
cis-[PtCl4{(E)-NHdC(Me)OPr-n}{(Z)-NHdC(Me)OPr-n}] (7).
Yield: 40%. Anal. Calcd for C10H22N2Cl4O2Pt: C, 22.27; H, 3.50;
N, 5.20. Found: C, 22.27; H, 3.84; N, 5.13. FAB+-MS, m/z: 468
[M - 2Cl]+, 431 [M - 3Cl - 2H]+, 396 [M - 4Cl - H]+. TLC,
Rf ) 0.55 (eluent Me2CO: CH2Cl2 ) 3:10). IR spectrum in KBr,
selected bands, cm-1: 3300 m-w ν(N-H), 2963 m-w and 2929
3
(CH3) and 26.8 (CH2, JPtC 8.3 Hz)(Et), 54.6 (CH3, OMe), 179.9
(CdNH). 195Pt NMR in CDCl3, δ: -160 (680 Hz).
trans-[PtCl4{(E)-NHdC(Et)OEt}2] (10). Anal. Calcd for
C10H22N2Cl4O2Pt: C, 22.28; H, 4.11; N, 5.2. Found: C, 22.20; H,
4.08; N, 5.05. FAB+-MS, m/z: 468 [M - 2Cl]+, 431 [M - 3Cl -
2H], 396 [M - 4Cl - 2H]. TLC, Rf ) 0.56 (eluent CHCl3). IR
spectrum in KBr, selected bands, cm-1: 3346 m ν(N-H), 2988 m
and 2943 m-w ν(C-H), 1619 s ν(CdN), 1225 m-s ν(C-O). 1H
NMR in CDCl3, δ: 1.22 (t, 7.5 Hz, 3H, CH3 from Et), 1.44 (t, 6.9
Hz, 3H, CH3 from OEt), 3.09 (quart., 7.3 Hz, 2H, CH2 from Et),
4.19 (quart., 7.1 Hz, 2H, CH2 from OEt), 6.80 (s + d, 2JPtH 30 Hz,
NH). 13C{1H} NMR in CDCl3, δ: 10.8 (CH3 from Et), 13.4 (CH3
from OEt), 26.8 (CH2, 3JPtC 8.5 Hz, CH2 from Et), 64.2 (CH2 from
OEt), 179.7 (2JPtC 33 Hz, CdNH). 195Pt NMR in CDCl3, δ: -144
(420 Hz).
1
m-w ν(C-H), 1635 s ν(CdN), 1247 m ν(C-O). H NMR in
CDCl3, δ: two sets of signals in ca. 1:1 ratio, 1.00 (t, 6.9 Hz, 3H,
CH3 from Pr-n, E), 1.02 (t, 6.9 Hz, 3H, CH3 from Pr-n, Z), 1.73
(m, 2H, â-CH2 from Pr-n, Z), (m, 4H, â-CH2 from Pr-n, E), 2.61
(s, 3H, dCMeO, E), 2.65 (s, 3H, dCMeO, Z), 4.12 (t, 6.3 Hz, 2H,
R-CH2 of OPr-n, E), 4.24 (t, 6.3 Hz, 2H, R-CH2 of OPr-n, Z), 7.28
3
3
(s, br, JPtH 31.5 Hz, 1H, NH, E), 7.67 (s, br, JPtH 21.5 Hz, 1H,
NH, Z). 13C{1H} NMR in CDCl3, δ: 10.2 (CH3 from Pr-n, E and
Z), 19.8 (dCMeO, E), 21.6 (â-CH2 from OPr-n, E), 22.3 (â-CH2
from OPr-n, Z), 22.4 (dCMeO, Z), 70.8 (R-CH2 from OPr-n, E),
74.3 (R-CH2 from OPr-n, Z), 176.3 and 177.5 (CdNH). 195Pt NMR
in CDCl3, δ: -11.5 (400 Hz). Attribution of the signals due to the
E and Z isomers was performed using NOE, COSY and HETCOR.
cis-[PtCl4{(E)-NHdC(Me)OBu-n}{(Z)-NHdC(Me)OBu-n}]
(8). Yield: 56%. Anal. Calcd for C12H26N2Cl4O2Pt‚0.25CH2Cl2:
trans-[PtCl4{(E)-NHdC(Et)OPr-i}2] (11). Anal. Calcd for
C12H26N2Cl4O2Pt: C, 25.41; H, 4.62; N, 4.94. Found: C, 25.78;
H, 4.63; N, 4.77. FAB+-MS, m/z: 532 [M - Cl]+, 496 [M - 2Cl]+,
459 [M - 3Cl - 2H], 424 [M - 4Cl - 2H]. TLC, Rf ) 0.73
(eluent CHCl3). IR spectrum in KBr, selected bands, cm-1: 3359
2050 Inorganic Chemistry, Vol. 41, No. 8, 2002

Direct Addition of Alcohols to Organonitriles
m ν(N-H), 2979 and 2932 m ν(C-H), 1628 s ν(CdN), 1228 m
ν(C-O). H NMR in CDCl3, δ: 1.21 (t, 7.5 Hz, 3H, CH3 from
Et), 3.04 (quart., 7.5 Hz, 2H, CH2 from Et), 1.43 (d, 6.0 Hz, 6H,
cis-[PtCl4{(E)-NHdC(Et)OPr-i}{(Z)-NHdC(Et)OPr-i}] (16).
The complex was purified by TLC chromatography and isolated
as an oily residue. Despite our inability to obtain satisfactory C,
H, N analyses, all other data agree well with the proposed
composition and structure. FAB+-MS, m/z: 532 [M - Cl] +, 496
[M - 2Cl]+. TLC: Rf ) 0.30 (eluent CH2Cl2:Et2O ) 20:1). IR
spectrum in KBr, selected bands, cm-1: 3258 w ν(N-H), 2976
m-w and 2936 w ν(C-H), 1630 s ν(CdN), 1224 m ν(C-O). 1H
NMR in CDCl3, δ: 1.21 and 1.30 (two t, 7.4 Hz, CH3 from Et),
1.39 and 1.41 (two d, CH3 from OPr-i), 2.76 and 2.82 (q, 7.4 Hz,
CH2 from Et), 4.71 and 4.85 (t, 5.9 and 6.1 Hz, 2H, R-CH2 of
OPr-i), 7.09 and 7.30 (s, br, NH). 195Pt NMR in CDCl3, δ: -63
(530 Hz).
1
CH3 from OPr-i), 4.73 (sept, 6.0 Hz, 1H, CH from OPr-i), 6.74 (s
2
+ d, JPtH 40 Hz, NH). 13C{1H} NMR in CDCl3, δ: 10.8 (CH3
3
from Et), 21.4 (CH3 from OPr-i), 27.0 (CH2, JPtC 8.0 Hz, CH2
from Et), 72.4 (CH from OPr-i), 178.0 (CdNH). 195Pt NMR in
CDCl3, δ: -125 (450 Hz).
trans-[PtCl4{(E)-NHdC(Et)OPr-n}2] (12). Anal. Calcd for
C12H26N2Cl4O2Pt: C, 25.41; H, 4.62; N, 4.94. Found: C, 25.35;
H, 4.57; N, 4.89. FAB+-MS, m/z: 496 [M - 2Cl]+, 459 [M - 3Cl
- 2H], 424 [M - 4Cl - 2H]. TLC, Rf ) 0.64 (eluent CHCl3). IR
spectrum in KBr, selected bands, cm-1: 3302 m ν(N-H), 2972,
1
2934 and 2880 m ν(C-H), 1626 s ν(CdN), 1228 m ν(C-O). H
NMR in CDCl3, δ: 1.02 (t, 7.3 Hz, 3H, CH3 from OPr-n), 1.23 (t,
7.5 Hz, 3H, CH3 from Et), 1.85 (sext, 6.7 Hz, 2H, â-CH2 from
OPr-n), 3.12 (quart., 7.5 Hz, 2H, CH2 from Et), 4.07 (t, 6.3 Hz,
cis-[PtCl4{(E)-NHdC(Et)OPr-n}{(Z)-NHdC(Et)OPr-n}] (17).
The complex was purified by TLC chromatography and isolated
as an oily residue. Despite our inability to obtain satisfactory C,
H, N analyses, all other data agree well with the proposed
composition and structure. FAB+-MS, m/z: 496 [M - 2Cl]+. TLC,
Rf ) 0.42 (eluent CH2Cl2:Et2O ) 5:1). IR spectrum in KBr, selected
bands, cm-1: 3313 w ν(N-H), 2963 w ν(C-H), 1624 s ν(CdN),
1225 m ν(C-O). 1H NMR in CDCl3, δ: two sets of signals in ca.
1:1 ratio, 1.02 (t, 7.4 Hz, 6H, CH3 from OPr-n, E and Z), 1.21 (t,
7.5 Hz, CH3 from Et, 3H, E), 1.34 (t, 7.4 Hz, CH3 from Et, 3H, Z),
1.75 (m, 2H, â-CH2 from OPr-n, Z), 1.84 (m, 2H, â-CH2 from
OPr-n, E), 2.81 (q, 7.4 Hz, 2H, CH2 from Et, Z), 2.95 (q, 7.5 Hz,
2H, CH2 from Et, E), 4.03 (t, 6.3 Hz, 2H, R-CH2 of OPr-n, E),
4.24 (t, 6.8 Hz, 2H, R-CH2 of OPr-n, Z), 7.20 (s, br, 1H, NH, E),
7.29 (s, br, 1H, NH, Z). 13C{1H} NMR in CDCl3, δ: 9.8 (CH3
from Et; Z) 10.2 (CH3 from OPr-n; E and Z), 10.6 (CH3 from Et;
E), 21.4 (â-CH2 of OPr-n, E), 22.4 (â-CH2 of OPr-n, Z), 26.7 (CH2
from Et, E), 27.2 (CH2 from Et, Z), 69.6 (R-CH2 from OPr-n, E),
73.3 (R-CH2 from OPr-n, Z), 178.8 and 181.0 (CdNH). 195Pt NMR
in CDCl3, δ: -29.2 (650 Hz). Attribution of the signals due to the
E and Z isomers was performed using NOE, COSY, and HETCOR.
2
2H, R-CH2 from OPr-n), 6.79 (s + d, JPtH 37 Hz, NH). 13C{1H}
NMR in CDCl3, δ: 10.2 (CH3 from OPr-n), 10.7 (CH3 from Et),
3
21.3 (â-CH2 from OPr-n), 26.9 (CH2, JPtC 8.8 Hz, CH2 from Et),
69.5 (R-CH2 from OPr-n), 179.4 (CdNH). 195Pt NMR in CDCl3,
δ: -147 (500 Hz).
trans-[PtCl4{(E)-NHdC(Et)OBu-n}2] (13). Anal. Calcd for
C14H30N2Cl4O2Pt: C, 28.25; H, 5.08; N, 4.71. Found: C, 28.52;
H, 5.02; N, 4.62. FAB+-MS, m/z: 524 [M - 2Cl]+, 487 [M - 3Cl
- 2H], 452 [M - 4Cl - H]. TLC, Rf ) 0.70 (eluent CHCl3). IR
spectrum in KBr, selected bands, cm-1: 3356 m ν(N-H), 2942
and 2873 m ν(C-H), 1629 s ν(CdN), 1231 m ν(C-O). 1H NMR
in CDCl3, δ: 0.96 (t, 7.2 Hz, 3H, CH3 from OBu-n), 1.23 (t, 7.5
Hz, 3H, CH3 from Et), 1.44 (sext, 7.5 Hz, 2H, γ-CH2 from OBu-
n), 1.80 (quint, 6.6 Hz, 2H, â-CH2 from OBu-n), 3.11 (quart., 7.4
Hz, 2H, CH2 from Et), 4.10 (t, 6.3 Hz, 2H, R-CH2 from OBu-n),
2
6.79 (s + d, JPtH 38 Hz, NH). 13C{1H} NMR in CDCl3, δ: 10.7
3
(CH3 from Et) and 26.9 (CH2, JPtC 8.7 Hz, CH2 from Et), 13.6
(CH3 from OBu-n), 18.9 (γ-CH2 from OBu-n), 29.7 (â-CH2 from
OBu-n), 68.0 (R-CH2 from OBu-n), 179.4 (CdNH). 195Pt NMR in
CDCl3, δ: -147 (410 Hz).
cis-[PtCl4{(E)-NHdC(Et)OBu-n}{(Z)-NHdC(Et)OBu-n}] (18).
The complex was purified by TLC chromatography and isolated
as an oily residue. Despite our inability to obtain satisfactory C,
H, N analyses, all other data agree well with the proposed
composition and structure. FAB+-MS, m/z: 559 [M - Cl]+. TLC,
Rf ) 0.35 (eluent CH2Cl2:Et2O ) 20:1). IR spectrum in KBr,
selected bands, cm-1: 3291 w ν(N-H), 2960 m-w and 2935 w
ν(C-H), 1629 s ν(CdN), 1224 m ν(C-O). 1H NMR in CDCl3, δ:
two sets of signals in ca. 1:1 ratio, 0.92 (t, 7.4 Hz, 3H, CH3 from
OBu-n, Z), 0.96 (t, 7.4 Hz, 3H, CH3 from OBu-n, E), 1.20 (t, 7.4
Hz, CH3 from Et, 3H, E), 1.34 (t, 7.3 Hz, CH3 from Et, 3H, Z),
1.43 (m, 2H, γ-CH2 from OPr-n, Z), 1.45 (m, 2H, γ-CH2 from
OPr-n, Z), 1.68 (m, 2H, â-CH2 from OPr-n, Z), 1.79 (m, 2H, â-CH2
from OPr-n, E), 2.81 (q, 7.3 Hz, 2H, CH2 from Et, Z), 2.95 (q, 7.4
Hz, JPtH 2.9 Hz, 2H, CH2 from Et, E), 4.06 (t, 6.4 Hz, 2H, R-CH2
of OPr-n, E), 4.28 (t, 6.7 Hz, 2H, R-CH2 of OPr-n, Z), 7.19 (s, br,
1H, NH, E), 7.30 (s, br, 1H, NH, Z). 13C{1H} NMR in CDCl3, δ:
9.8 (CH3 from Et; Z), 10.7 (CH3 from Et; E) 13.6 (CH3 from OBu-
n; E and Z), 18.7 (γ-CH2 from OBu-n; Z), 19.0 (γ-CH2 from OBu-
n; E), 26.8 (JPtC 9.0 Hz, CH2 from Et, E), 27.2 (CH2 from Et, Z),
29.9 (â-CH2 of OPr-n, E), 31.0 (â-CH2 of OPr-n, Z), 68.2 (R-CH2
from OPr-n, E), 71.6 (R-CH2 from OPr-n, Z), 178.8 and 181.1
(CdNH). 195Pt NMR in CDCl3, δ: -42.2 (470 Hz). Attribution of
the signals due to the E and Z isomers was performed using NOE,
COSY, and HETCOR.
cis-[PtCl4{(E)-NHdC(Et)OMe}2] (14). Anal. Calcd for C8H18N2-
Cl4O2Pt: C, 18.87; H, 3.55; N, 5.48. Found: C, 18.87; H, 3.54; N,
5.44. FAB+-MS, m/z: 440 [M - 2Cl]+, 403 [M - 2Cl - HCl]+,
367 [M - 2Cl - 2HCl]+. mp ) 115 °C. TLC, Rf ) 0.66 (eluent
acetone:CHCl3 ) 1:2). IR spectrum in KBr, selected bands, cm-1
:
3284 m ν(N-H), 2980 and 2941 m ν(C-H), 1620 s ν(CdN), 1231
m ν(C-O). 1H NMR in CDCl3, δ: 1.23 (t, 7.5 Hz, 3H), 2.94 (quart.,
7.8 Hz, 2H)(Et), 3.99 (s, 3H, OMe), 6.89 (s + d, 2JPtH 30 Hz, NH).
3
13C{1H} NMR in CDCl3, δ: 10.6 (CH3) and 26.7 (CH2, JPtC 8.4
Hz)(Et), 55.6 (CH3, OMe), 180.4 (2JPtC 34 Hz, CdNH). 195Pt NMR
in CDCl3, δ: -53 (390 Hz). Refluxing of a suspension of cis-[PtCl4-
{(E)-NHdC(Et)OMe}2] in MeOH for 8 h leads to pure trans-[PtCl4-
{(E)-NHdC(Et)OMe}2].
cis-[PtCl4{(E)-NHdC(Et)OEt}2] (15). Anal. Calcd for C10H22N2-
Cl4O2Pt: C, 22.28; H, 4.11; N, 5.2. Found: C, 22.20; H, 4.08; N,
5.05. FAB+-MS, m/z: 468 [M - 2Cl]+, 431 [M - 3Cl - 2H],
396 [M - 4Cl - 2H]. TLC, Rf ) 0.64 (eluent acetone:CHCl3 )
1:3). IR spectrum in KBr, selected bands, cm-1: 3297 m ν(N-H),
1
2987 and 2939 m ν(C-H), 1619 s ν(CdN), 1228 m ν(C-O). H
NMR in CDCl3, δ: 1.22 (t, 7.5 Hz, 3H, CH3 from Et), 1.46 (t, 6.9
Hz, 3H, CH3 from OEt), 2.91 (quart., 7.5 Hz, 2H, CH2 from Et),
4.22 (quart., 6.9 Hz, 2H, CH2 from OEt), 6.80 (s + d, 2JPtH 30 Hz,
NH,1H). 13C{1H} NMR in CDCl3, δ: 10.7 (CH3 from Et), 13.5
(CH3 from OEt), 26.7 (3JPtC 8.5 Hz, CH2 from Et), 65.1 (CH2 from
OEt), 179.7 (2JPtC 33 Hz, CdNH). 195Pt NMR in CDCl3, δ: -33
(390 Hz).
Inorganic Chemistry, Vol. 41, No. 8, 2002 2051

Bokach et al.
1
Reactions of [PtCl4(RCN)2] (R ) CH2Ph, Ph) with Alcohols.
The appropriate alcohol (0.7 mL, 5-7 mmol) is added to the solid
[PtCl4(RCN)2] (0.12 g, 0.21 mmol). The reaction mixture is left to
stand at room temperature (heated at ca. 50 °C for R ) Ph) for 2
days, and the completeness of reaction is controlled by TLC. The
released new precipitate is filtered off, washed with two 1-mL
portions of ROH, and dried in air at room temperature.
3242 w ν(N-H), 2934 w ν(C-H), 1612 s ν(CdN). H NMR in
CDCl3, δ: 4.05 (s, 3H, OMe), 7.65 (m, 6H, Ph and NH). 13C{1H}
NMR in CDCl3, δ: 61.5 (OMe), 128.3 (CH), 129.0 (Cipso), 129.7
(CH) and 133.6 (CH) (Ph), 179.5 (CdNH). 195Pt NMR in CDCl3,
δ: -154 (580 Hz).
Reduction of (Imine)Pt(IV) Complexes with the Ylide
Ph3PdCHCO2Me. The ylide (7 mg, 0.02 mmol) is added to a
solution of trans-[PtCl4((E)-NHdC(Me)OR)2] (R ) Me, Et) or cis-
[PtCl4((E)-NHdC(Me)OEt)((Z)-NHdC(Me)OEt)] (0.02 mmol) in
cold (0-5 °C) dichloromethane (2 mL). The reaction is complete
after 4 h, whereupon the solvent is evaporated and the yellow
residue formed is washed with two 2-mL portions of Et2O, dissolved
in a minimum amount of CH2Cl2 at room temperature and purified
on silica gel (70-230 mesh; 60 Å, Aldrich) column. Eluation with
CH2Cl2/Et2O gives an individual complex from the first fraction.
trans-[PtCl2{(E)-NHdC(Me)OMe}2] (24). Yield: 50%. Anal.
Calcd for C6H14N2Cl2O2Pt‚0.1Et2O: C, 18.32; H, 3.51; N, 6.68.
Found: C, 18.0; H, 3.27; N, 6.30. FAB+-MS, m/z: 412 [M]+, 375
[M - HCl]+, 339 [M - 2HCl]. TLC, Rf ) 0.34 (eluent CHCl3:
Et2O ) 10:1). IR spectrum in KBr, selected bands, cm-1: 3254 m
ν(N-H), 2983 w and 2852 w ν(C-H), 1632 s ν(CdN), 1231 m
trans-[PtCl4{(E)-NHdC(CH2Ph)OMe}2] (19). Yield: 30%.
Complex was recrystallized from CHCl3. Anal. Calcd for C18H22N2-
Cl4O2Pt‚0.5CHCl3: C, 31.97; H, 3.26; N, 4.03. Found: C, 31.77;
H, 3.17; N, 4.38. FAB+-MS, m/z: 587 [M - 2Cl + Na]+, 564 [M
- 2Cl]+. TLC, Rf ) 0.47 (eluent CHCl3). IR spectrum in KBr,
selected bands, cm-1: 3339 s ν(N-H), 2922 m ν(C-H), 1628 s
1
ν(CdN), 1256 m ν(C-O). H NMR in CDCl3, δ: 3.96 (s, 3H,
OMe), 4.57 (s, 2H, dC{CH2Ph}O), 7.12 (s, br, 1H, NH), 7.36 (m,
5H, CH2Ph). 13C{1H} NMR in CDCl3, δ: 39.2 (dC{CH2Ph}O),
55.2 (OMe), 127.5 (CH), 128.6 (CH), 130.0 (CH) and 133.0 (Cipso)-
(CH2Ph), 177.2 (CdN). 195Pt NMR in CDCl3, δ: -184 (450 Hz).
trans-[PtCl4{(E)-NHdC(CH2Ph)OEt}2] (20). Yield: 28%.
Anal. Calcd for C20H26N2Cl4O2Pt: C, 36.21; H, 3.95; N, 4.22.
Found: C, 35.87; H, 3.80; N, 4.30. FAB+-MS, m/z: 592 [M -
2Cl]+. TLC, Rf ) 0.68 (eluent CHCl3). IR spectrum in KBr, selected
bands, cm-1: 3289 m ν(N-H), 2982 m ν(C-H), 1624 s ν(CdN),
1254 m ν(C-O). 1H NMR in CDCl3, δ: 1.38 (t, 7.0 Hz, 3H, Me),
4.23 (quart., 7.0 Hz, 2H, CH2CH3), 4.53 (s, 2H, CH2Ph), 7.07 (s +
1
ν(C-O), 349 w ν(Pt-Cl). H NMR in CDCl3, δ: 2.64 (s, 3H,
dCMeO), 3.76 (s, 3H, OMe), 7.72 (s, br, 1H, NH) [lit.15b 1H NMR
in CDCl3, δ: 2.64 (dCMeO), 3.76 (OMe), 7.72 (NH)]. 13C{1H}
NMR in CDCl3, δ: 21.41 (dCMeO), 55.0 (OMe), 171.2 (CdNH).
195Pt NMR in CDCl3, δ: -1914 (870 Hz).
2
d, JPtH 40 Hz, 1H, NH), 7.34 (m, 3H) and 7.41 (m, 2H)(CH2Ph).
13C{1H} NMR in CDCl3, δ: 13.2 (CH3 from Et), 39.2 (CH2, 3JPtC
8.2 Hz, CH2Ph), 64.8 (CH2 from Et), 127.3 (CH), 128.5 (CH), 130.0
(CH) and 133.3 (Cipso)(CH2Ph), 176.4 (2JPtC 35 Hz, CdNH). 195Pt
NMR in CDCl3, δ: -165 (600 Hz).
trans-[PtCl2{(E)-NHdC(Me)OEt}2] (25). Yield: 40%. Anal.
Calcd for C8H18N2Cl2O2Pt: C, 21.83; H, 4.12; N, 6.36. Found: C,
21.77; H, 4.13; N, 6.31. FAB+-MS, m/z: 368 [M - 2Cl - H]+.
TLC, Rf ) 0.56 (eluent CHCl3:Et2O ) 10:1). IR spectrum in KBr,
selected bands, cm-1: 3253 m ν(N-H), 2983 w ν(C-H), 1648 s
trans-[PtCl4{(E)-NHdC(CH2Ph)OPr-i}2] (21). Yield: 11%.
Anal. Calcd for C22H30N2Cl4O2Pt: C, 38.22; H, 4.37; N, 4.05.
Found: C, 38.17; H, 4.31; N, 3.94. FAB+-MS, m/z: 620 [M -
2Cl]+, 583 [M - 3Cl - 2H], 548 [M - 4Cl - 2H]. TLC, Rf )
1
ν(CdN), 1226 m ν(C-O), 350 m ν(Pt-Cl). H NMR in CDCl3,
δ: 1.28 (t, 6.9 Hz, 3H, OCH2CH3), 2.63 (s, 3H, dCMeO), 4.03
(quart., 6.9 Hz, 3H, OCH2CH3), 7.58 (s, br, 1H, NH). 13C{1H} NMR
in CDCl3, δ: 13.7 (OCH2CH3), 21.7 (dCMeO), 63.9 (OCH2CH3),
170.6 (CdNH). 195Pt NMR in CDCl3, δ: -1910 (900 Hz).
cis-[PtCl2{(E)-NHdC(Me)OEt}{(Z)-NHdC(Me)OEt}] (26).
Yield: 55%. Anal. Calcd for C8H18N2Cl2O2Pt: C, 21.83; H, 4.12;
N, 6.36. Found: C, 22.08; H, 6.25; N, 4.19. FAB+-MS, m/z: 463
[M + Na]+, 440 [M]+, 367 [M - 2HCl]+. TLC, Rf ) 0.32 (eluent
0.67 (eluent CHCl3). IR spectrum in KBr, selected bands, cm-1
:
3356 m ν(N-H), 2975 and 2928 m ν(C-H), 1623 s ν(CdN), 1242
m ν(C-O). 1H NMR in CDCl3, δ: 1.35 (d, 6.3 Hz, 6H, CH3 from
Pr-i), 4.48 (s, 2H, CH2Ph), 4.78 (sept, 6.0 Hz, 1H, CH from Pr-i),
7.03 (s + d, 2JPtH 44 Hz, 1H, NH), 7.29 (m, 3H) and 7.37 (m, 2H)
(CH2Ph). 13C{1H} NMR in CDCl3, δ: 21.2 (CH3 from Pr-i), 39.4
(CH2, CH2Ph), 73.2 (CH from OPr-i), 127.2 (CH), 128.4 (CH),
129.8 (CH) and 133.6 (Cipso) (CH2Ph), 175.3 (CdNH). 195Pt NMR
in CDCl3, δ: -147 (550 Hz).
CHCl3:Et2O ) 3:1). IR spectrum in KBr, selected bands, cm-1
:
3236 m ν(N-H), 2990 w and 2824 w ν(C-H), 1646 s ν(CdN),
1231 m ν(C-O), 340 m and 321 w ν(Pt-Cl). 1H NMR in CDCl3,
δ: 1.25 (t, 6.9 Hz, 3H, OCH2CH3, E), 1.42 (t, 6.9 Hz, 3H,
OCH2CH3, Z), 2.25 (s, 3H, dCMeO, Z), 2.65 (s, 3H, dCMeO, E),
4.81 (quart., 6.9 Hz, 2H, OCH2CH3, Z), 4.07 (quart., 2H, 6.9 Hz,
OCH2CH3, E), 7.70 (s, br, 1H, NH, E), 8.85 (s, br, 1H, NH, Z).
13C{1H} NMR in CDCl3, δ: 15.1 and 13.7 (OCH2CH3), 21.7 and
22.3 (dCMeO), 66.3 and 64.9 (OCH2CH3), 171.4 and 173.4
(CdNH). 195Pt NMR in CDCl3, δ: -1953 (850 Hz).
Liberation of the Ligand from trans-[PtCl4{(E)-NHdC(Me)-
OEt}2]. Pyridine (0.03 mL, 0.4 mmol) is added to a solution of
trans-[PtCl4{(E)-NHdC(Me)OEt}2] (20 mg, 0.04 mmol) in CDCl3
(0.5 mL) in an NMR tube, and the mixture is left to stand at 40 °C
for 2 days, whereupon the liberated ligand, i.e., NHdC(Me)OEt,
is identified by NMR methods (1H NMR in CDCl3, δ: 1.99 (s,
3H, Me), 4.07 (quart., 7.0 Hz, 2H, OCH2CH3), 1.26 (t, 7.0 Hz,
OCH2CH3). 13C{1H} NMR in CDCl3, δ: 61.2 (OCH2CH3), 23.8
(Me), 14.1 (OCH2CH3), 155.7 (CdN). Addition of water (0.03 mL)
to the reaction mixture allowed the quantitative formation of ethyl
acetate, which is derived from hydrolysis of NHdC(Me)OEt. Before
the deliberate addition of water, ethyl acetate was detected in ca.
35% yield [with 65% yield of NHdC(Me)OEt], being derived from
trans-[PtCl4{(E)-NHdC(CH2Ph)OPr-n}2] (22). Yield: 22%.
Anal. Calcd for C22H30N2Cl4O2Pt: C, 38.22; H, 4.37; N, 4.05.
Found: C, 37.93; H, 4.03; N, 4.38. FAB+-MS, m/z: 620 [M -
2Cl]+, 583 [M - 3Cl - 2H], 548 [M - 4Cl - H]. TLC, Rf ) 0.70
(eluent CHCl3). IR spectrum in KBr, selected bands, cm-1: 3326
m ν(N-H), 2971 m-w and 2928 m-w ν(C-H), 1624 vs ν(CdN),
1251 m ν(C-O). 1H NMR in CDCl3, δ: 0.83 (t, 7.5 Hz, 3H, CH3),
1.73 (sext, 7.5 Hz, 2H, â-CH2 from Pr-n), 4.08 (t, 6.3 Hz, 2H,
2
R-CH2 from Pr-n), 4.54 (s, 2H, CH2Ph), 7.02 (s + d, JPtH 44 Hz,
1H, NH), 7.31 (m, 3H) and 7.40 (m, 2H) (CH2Ph). 13C{1H} NMR
in CDCl3, δ: 9.90 (CH3 from Pr-n), 21.10 (â-CH2 from Pr-n), 39.2
(CH2, 3JPtC 9.2 Hz, CH2Ph), 70.0 (R-CH2 from Pr-n), 127.3 (CH),
128.4 (CH), 130.0 (CH) and 133.2 (Cipso) (CH2Ph), 176.6 (2JPtC 40
Hz, CdNH). 195Pt NMR in CDCl3, δ: -164 (700 Hz).
trans-[PtCl4{(E)-NHdC(Ph)OMe}2] (23). The complex can be
purified by washing with warm (35-40 °C) acetone (2 mL) for
10-15 min. Yield: 50%. Anal. Calcd for C16H18N2Cl4O2Pt: C,
31.65; H, 2.99; N, 4.61. Found: C, 31.47; H, 3.05; N, 4.32. FAB+-
MS, m/z: 629 [M + Na]+. TLC, Rf ) 0.48 (eluent acetone:
chloroform ) 1:40). IR spectrum in KBr, selected bands, cm-1
:
2052 Inorganic Chemistry, Vol. 41, No. 8, 2002

Direct Addition of Alcohols to Organonitriles
the hydrolysis of NHdC(Me)OEt by the moisture contained in the
NMR solvent.
Computational Details. The full geometry optimization of the
EE, EZ, and ZZ isomers of the complexes trans-[PtCl2{NHdC(Me)-
OMe}2] and trans-[PtCl4{NHdC(Me)OMe}2] has been carried out
in Cartesian coordinates using the quasi-Newton-Raphson gradient
method and the restricted Hartree-Fock approximation with help
of the GAMESS program package.36 The single-point calculations
on the basis of the equilibrium Hartree-Fock geometries at the
MP2//HF level of theory have been applied. Symmetry operations
were not applied. For the platinum atom, the Stuttgart quasi-
relativistic pseudopotential for 60 core electrons and the appropriate
contracted basis set for the platinum atom37 have been used. The
standard basis set of Gauss functions 6-31G38,39 was selected for
all other atoms, and d-type polarization functions with exponent
0.7539,40 were added for the Cl atoms.
Liberation of the Ligand from trans-[PtCl2{(E)-NHdC(Me)-
OEt}2]. Dppe (32 mg, 0.08 mmol) is added to a solution of trans-
[PtCl4{(E)-NHdC(Me)OEt}2] (20 mg, 0.04 mmol) in CDCl3 (0.5
mL), and the mixture is left to stand for 10 min until a colorless
precipitate of [Pt(dppe)2]Cl2 is released. The complex is filtered
off, and NHdC(Me)OEt, liberated quantitatively, is identified in
1
the filtrate by H and 13C{1H} NMR methods (for spectral data
see above).
X-ray Structure Determinations. Crystals suitable for X-ray
diffraction analysis were obtained directly from the reaction
mixtures. Diffraction data were collected on an Enraf-Nonius
CAD-4 diffractometer. Cell parameters were obtained from 24
centered reflections with Θ between 11° and 13° (2), 12.8° and
13.9° (10), 11.6° and 12.5° (11), 11.7° and 12.5° (12), and 11.7°
and 12.4° (14). Range of hkl: h ) 0 to 8, k ) 0 to 16, l ) -11 to
11 for 2; h ) 0 to 10, k ) 0 to 9, l ) -17 to 16 for 10; h ) 0 to
7, k ) -9 to 9, l ) -12 to 12 for 11; h ) 0 to 10, k ) 0 to 10,
l ) -15 to 15 for 12; and h ) 0 to 10, k ) 0 to 13, l ) 0 to 18
for 14. Standard reflections were measured every 60 min and
showed practically no change with time ((1%). Diffractometer data
were processed by the program PROFIT31 with profile analysis of
reflections. The structures were solved by means of Fourier
synthesis based upon the Pt atom coordinates obtained from the
Patterson synthesis using the SHELXTL package.32 After that, all
reflections with I < 2σ(I) were excluded from calculations.
Refinement was done by full-matrix least squares based on F2 using
the SHELX-97 package.33 All non-H atoms were treated anisotro-
pically. H atoms were located in a difference Fourier map and
refined isotropically. An extinction correction has been applied for
2, 10, 12, and 14. Lorentz, polarization, and absorption corrections
were made.34 Scattering factors were obtained from International
Tables for X-ray Crystallography.35 Crystal data are given in Table
1 and bond distances and angles in Tables 2-6.
Acknowledgment. N.A.B. express gratitude to the In-
ternational Science Foundation (Soros Foundation) and also
to Centro de Qu´ımica Estrutural, Complexo I, Instituto
Superior Te´cnico, Portugal, for the fellowships. D.A.G.,
M.L.K. and V.Yu.K. thank the PRAXIS XXI program
(Portugal) for Grants BPD16368/98, BPD16369/98 and
BCC16428/98, correspondingly. V.Yu.K. is very much
indebted to the International Science Foundation for a Soros
Professorship. A.J.L.P. thanks the FCT (Foundation for
Science and Technology) and the PRAXIS XXI program for
financial support. We also thank Mr. I. Marques (Centro de
Qu´ımica Estrutural) for the FAB-MS measurements, Dr. G.
Wagner for measuring some preliminary NMR spectra, and
Prof. V. K. Belsky (L. Ya. Karpov Physicochemical Institute,
Moscow) for the X-ray diffraction analysis.
Supporting Information Available: X-ray crystallographic files
in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
IC011025H
(31) Strel’tsov, V. A.; Zavodnik, V. E. Kristallografia 1989, 34, 1369.
(32) Sheldrick, G. M. SHELXTL-93, Programs for Structure Refinement;
University of Go¨ttingen: Go¨ttingen, Germany, 1993.
(33) Sheldrick, G. M. SHELXL-97; University of Go¨ttingen: Go¨ttingen,
Germany, 1997.
(34) Axelrud, L. G.; Grin, Yu. N.; Zavalii, P. Yu.; Pecharsky, V. K.;
Fundamensky, V. S. CSD-universal program package for single-crystal
and/or powder structure data treatment. Collected Abstracts, XII-th
European Crystallographic Meeting, Moscow, August 1989; USSR
Academy of Sciences: Moscow, 1989; p 155.
(35) International Tables for X-ray Crystallography; Kynoch Press: Bir-
mingham, U.K., 1974; Vol. IV.
(36) Schmidt, M. W.; Baldridge, K. K.; Boatz, J. A.; Elbert, S. T.; Gordon,
M. S.; Jensen, J. H.; Koseki, S.; Matsunaga, N.; Nguyen, K. A.; Su,
S. J.; Windus, T. L.; Dupuis, M.; Montgomery, J. A. J. Comput. Chem.
1993, 14, 1347.
(37) Andrae, D.; Haeussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor.
Chim. Acta 1990, 77, 123.
(38) (a) Ditchfield, R.; Hehre, W. J.; Pople, J. A. J. Chem. Phys. 1971, 54,
724. (b) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972,
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(39) Francl, M. M.; Pietro, W. J.; Hehre, W. J.; Binkley, J. S.; Gordon, M.
S.; DeFrees, D. J.; Pople, J. A. J. Chem. Phys. 1982, 77, 3654.
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