Aiding factors in the formation of azaplatinacyclobutane rings - X-ray and crystal structure of [Pt{CH(Ph)CH2NEt2-KC,κN}(N,N, N′,N′-tetramethylethylenediamine)]+ and of its open-chain precursor

Article abstract of DOI:10.1002/ejic.200601219

The addition products 2 of a secondary amine to a coordinated olefin, in the cationic complexes [PtCl(η²-CH₂=CHR)-(tmeda)] ⁺ (tmeda = N,N,N′,N′-tetramethylethylenediamine; R = Me, 1a; Ph, 1b, H, 1c), undergo in basic medium an intramolecular nucleophilic substitution with elimination of the chlorido ligand and formation of an azaplatinacyclobutane ring 3. The ring-closing process occurs notwithstanding the absence of a labilizing ligand trans to the leaving chlorido ligand and of bulky substituents on the amino-ethanide chain. If the addition product 2 is a mixture of Markovnikov and anti-Markovnikov isomers, the ring-closing reaction is faster for the anti-Markovnikov form, and this leads to an increase of the relative amount of the anti-Markovnikov isomer in the cyclized species 3. The difference in the rate of formation of the azaplatinacyclobutane ring between the two isomers has been interpreted on the basis of a more favorable stereochemistry in the case of the anti-Markovnikov form. The X-ray crystal structures of [Pt{CH(Ph)CH₂NEt₂-κC,κN}(tmeda)] ⁺ (3bn) and of its open-chain precursor, [PtCl{CH(Ph)CH ₂NHEt₂](tmeda)]⁺ (2bn) fully support this hypothesis. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejic.200601219

FULL PAPER
DOI: 10.1002/ejic.200601219
Aiding Factors in the Formation of Azaplatinacyclobutane Rings – X-ray and
Crystal Structure of [Pt{CH(Ph)CH2NEt2-κC,κN}(N,N,NЈ,NЈ-
tetramethylethylenediamine)]+ and of Its Open-Chain Precursor
Giuseppe Lorusso,[a] Carmen R. Barone,[a] Nicola G. Di Masi,[a] Concetta Pacifico,[a]
Luciana Maresca,*[a] and Giovanni Natile[a]
Keywords: Chelates / Metallacycles / N ligands / Nucleophilic addition / Platinum
The addition products 2 of a secondary amine to a coordi- increase of the relative amount of the anti-Markovnikov iso-
nated olefin, in the cationic complexes [PtCl(η2-CH2=CHR)-
(tmeda)]+ (tmeda = N,N,NЈ,NЈ-tetramethylethylenediamine;
R = Me, 1a; Ph, 1b, H, 1c), undergo in basic medium an intra-
molecular nucleophilic substitution with elimination of the
chlorido ligand and formation of an azaplatinacyclobutane
ring 3. The ring-closing process occurs notwithstanding the
absence of a labilizing ligand trans to the leaving chlorido
ligand and of bulky substituents on the amino–ethanide
chain. If the addition product 2 is a mixture of Markovnikov
and anti-Markovnikov isomers, the ring-closing reaction is
faster for the anti-Markovnikov form, and this leads to an
mer in the cyclized species 3. The difference in the rate of
formation of the azaplatinacyclobutane ring between the two
isomers has been interpreted on the basis of a more favorable
stereochemistry in the case of the anti-Markovnikov form.
The X-ray crystal structures of [Pt{CH(Ph)CH2NEt2-
κC,κN}(tmeda)]+ (3bn) and of its open-chain precursor,
[PtCl{CH(Ph)CH2NHEt2}(tmeda)]+ (2bn) fully support this
hypothesis.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
amido group with the α-carbon atom of the allenyl ligand
and the coordination of the amine to the tungsten metal
center.[2]
Introduction
A number of azametallacyclobutanes have been reported
in the literature; in some cases they have been isolated and
fully characterized, while in other cases they have only been
detected in solution, or proposed as key intermediates in
catalytic processes concerned with the hydroamination of
olefins and allenes.[1–8]
The reaction sequence leading to their formation is very
much dependent upon the nature of the metal involved. In
the case of early transition metals, the azametallacyclo-
butanes are generated by [2+2] cycloaddition of an olefin
to a metalla-imido moiety (M=NR).[1] The reaction
is generally reversible, and in the specific case of
[Cp2(THF)Zr(=N-tBu)] reacting with norbornene, the
formed azazirconacyclobutane was also structurally charac-
terized.[1b]
A different and more complex reaction pathway was pro-
posed for the formation of an azatungstacyclobutane. The
allenyl precursor, Cp(CO)3W–CH=C=CH2, underwent me-
thylamine addition both at a carbonyl ligand (which was
transformed into a carbamoyl group) and at the β-carbon
atom of the allenyl ligand (across the terminal double
bond), accompanied by a regiospecific coupling of the
Also in the case of late transition metals, several pro-
cedures have been reported to lead to the formation of aza-
metallacyclobutanes. For instance, in the iridium-catalyzed
hydroamination of norbornene, reported by Calabrese et
al., a very reactive 14-electron iridium complex first un-
dergoes oxidative addition with aniline followed by [2+2]
cycloaddition of the formed metalla-amido moiety to nor-
bornene to form an azairidacyclobutane complex.[3] An
azairidacyclobutane is also formed by a ring-closing reac-
tion (with elimination of HCl) of an iridium 2-aminoethan-
ide complex obtained by the photolysis of an iridium hy-
dride species in the presence of tert-butylamine.[4]
More recently, Puddephatt has reported a platinum(IV)
complex containing an azaplatinacyclobutane ring obtained
through oxidative addition of a protonated tethered imine
group present on a platinum(II)-coordinated amine (the
azaplatinacyclobutane ring resulting from the coordination
of the imine carbon and the nitrogen atom of a 2-pyridyl
substituent present on the imine carbon atom to the plati-
num atom).[5]
More often, 2-aminoethanide species are formed through
nucleophilic addition of an amine to a coordinated olefin
followed by a ring-closing process.[6–8] By this procedure
stable azaplatinacyclobutane complexes have been prepared
since the early 1980’s. Their isolation was strictly dependent
[a] Dipartimento Farmaco-Chimico, Università di Bari,
Via E. Orabona, 4, 70125 Bari, Italia
Fax: +390805442230
E-mail: maresca@farmchim.uniba.it
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Aiding Factors in the Formation of Azaplatinacyclobutane Rings
FULL PAPER
upon the nature of the ancillary ligands and the presence Scheme 1. The thermodynamically determined isomeric ra-
of substituents on the metal-coordinated olefin and on the tio is largely in favor of the Markovnikov form in the case
attacking amine.[6,7] Starting from a complex such as cis- of 2an and in favor of the anti-Markovnikov isomer in the
[PtCl2(L)(η2-alkene/allene)], the addition to the olefin of a case of 2bm,n.[10]
secondary amine leads to a zwitterionic species (formal
Under basic conditions, the product of amination (2 in
negative charge on the platinum atom and positive charge Scheme 1) undergoes deprotonation followed by displace-
on the nitrogen ammonium group), which can eliminate ment of the cis chlorido ligand by the amine nitrogen atom
HCl and form an azaplatinacyclobutane ring. The reaction and formation of an azaplatinacyclobutane species (3 in
occurs readily when L is a trans-labilizer (phosphorus or Scheme 1). We have found that the M/anti-M ratio de-
sulfur donor ligand).[6,7] When L is a N-donor ligand, the creases on going from the linear addition product to the
ring-closing reaction is observed only in the case of olefins ring-closed species. Therefore, the linear addition product
bearing substituents on the α and/or β carbon atoms.[7] Aza- 2an, containing at equilibrium a M/anti-M ratio of 95:5,
platinacyclobutanes formed in the case of L = tri- yields, upon ring-closing, compound 3an, in which the M/
phenylphosphane have also been characterized by X-ray anti-M ratio decreases to 75:25. Similarly, the linear ad-
crystallography.[6]
dition product 2bm, in which at equilibrium the M/anti-M
We have recently reconsidered the amination reaction of ratio was 30:70, gives, after the ring-closing process, com-
platinum-coordinated olefins in some cationic complexes pound 3bm, in which the anti-Markovnikov isomer is the
and observed a facile ring closing of the 2-ammonium exclusive form. This behavior can be explained with a
ethanide species obtained therefrom, with the ready forma- greater propensity of the linear anti-Markovnikov addition
tion of azaplatinacyclobutane rings. The results, hereafter product to undergo the ring-closing reaction.
described, have allowed us to gain new insights into factors
The cyclization reaction of 2an and 2bm (leading to 3an
governing this reaction (for a preliminary account see and 3bm, respectively), performed in an NMR tube under
ref.[10]).
basic conditions, did show the formation of trace amounts
of byproducts that were probably due to the reaction of
species 1a and 1b, which are intermediates in the Markovni-
kov/anti-Markovnikov isomerization of 2a and 2b, with the
base.[11] However, by operating on millimolar quantities and
Results and Discussion
The cationic complexes [PtCl(η2-olefin)(tmeda)]+ (1)[9] after work-up procedures, the species of type 3 were ob-
(tmeda = N,N,NЈ,NЈ-tetramethylethylenediamine; olefin = tained in almost pure form (Ͼ 95%).
alkyl or aryl-substituted ethene such as propene, 1a, or sty-
The structures of species 3 could be unequivocally deter-
rene, 1b) react quickly and smoothly with secondary amines mined by NMR techniques (1D and 2D H, H/13C, APT).
(such as dimethylamine, m, and diethylamine, n) to give the The Markovnikov and anti-Markovnikov isomers could be
corresponding η1-2-ammonium ethanide species 2 (see easily distinguished through the different patterns of con-
Scheme 1). Species of type 2 exist as equilibrium mixtures nectivities in the metallacyclobutane ring. The separation
of Markovnikov (M) and anti-Markovnikov (anti-M) of the Markovnikov and anti-Markovnikov isomers of 3an
forms; the interconversion process most likely requires the (3bm,n are essentially formed as the anti-M isomer)[13] has
detachment and re-addition of the amine as illustrated in not been attempted at this stage of the work.
1
1
Scheme 1.
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FULL PAPER
Some significant differences can be observed between the angle of –45.9(5)°. The proximity of the amine group to the
NMR parameters of the open-chain species 2 and the ring- chlorido ligand sets the nitrogen in a suitable position to
closed species 3. In particular, Cα is more shielded in 3 than undergo chlorido substitution and ring-closing reaction.
in 2 while Cβ is more shielded in 2 than in 3 [for the pairs
of compounds: M-2an/M-3an, anti-M-2bm/anti-M-3bm,
and anti-M-2bn/anti-M-3bn; ∆δ(Cα) and ∆δ(Cβ) values are
–17.8 and +6.3, –22.7 and +15.6, and –22.1 and +13.7 ppm,
respectively]. Similarly to the carbon atom, the protons on
the β carbon are also considerably less shielded in the cy-
clized species 3 than in the linear addition product 2 (∆δ in
the range 0.6–1.9 ppm). The deshielding of the β protons
was taken by Green et al. as an indicator for the occurrence
of the ring-closing process[7] (although in that work the re-
action stereochemistry and the possible formation of Mar-
kovnikov and anti-Markovnikov isomers were not discussed
in detail). Another highly distinctive NMR feature of spe-
3
cies 3 is the value of JPt,H for the β protons, which can
nearly reach 100 Hz, well above the observed values for the
corresponding coupling in the linear compounds. It is
worth noting that in the anti-M isomer, where there are two
β protons, these protons are diastereotopic with a disper-
sion which can be as large as 1 ppm. Moreover, only for
3
one of these protons (that at lower field), the JPt,H is very
high (78, 99, and 95 Hz for anti-M-3an, anti-M-3bm, and
anti-M-3bn, respectively), while for the other proton (that
3
at higher field) the JPt,H is much smaller and ill-defined.
Finally we have found that, on going form 2 to 3, the reso-
nance of the 195Pt nucleus shifts downfield by more than
300 ppm (∆δ = +354.4 and +415.7 ppm for M-2an/M-3an
and anti-M-2bn/anti-M-3bn, respectively).
Figure 1. (A) ORTEP drawing of the complex cation [PtCl{CH-
(Ph)CH2NHEt2}(tmeda)]+; the ellipsoids enclose 20% probability.
(B) ORTEP drawing of the complex cation [Pt{CH(Ph)CH2NEt2-
κC,κN}(tmeda)]+; the ellipsoids enclose 20% probability.
Crystals suitable for X-ray analysis were obtained for the
anti-M isomers of 2bn and 3bn. The structures of 2bn and
3bn, together with the numbering scheme, are depicted in
Figure 1 (bond lengths and angles are in Table 1). In both
cases, the coordination around the platinum atom is
roughly square planar, considering the four metal-linked
atoms: the tmeda nitrogen atoms, the carbon, and the chlo-
rine (2bn) or the nitrogen atom of the four-membered che-
late (3bn). The maximum deviation from the mean plane
through the four donor atoms applies to N1 in 2bn and to
C8 in 3bn [–0.019(6) and –0.026(4) Å, respectively]; more-
over, the displacement exhibited by the platinum atom is
Table 1. Selected bond lengths [Å] and angles [°] for 2bn and 3bn.
2bn
3bn
Pt–C8
Pt–N1
Pt–N2
Pt–N3
Pt–Cl1
N3–C7
2.062(4)
2.081(6)
2.174(4)
2.053(4)
2.084(3)
2.209(3)
2.085(3)
2.312(2)
1.516(5)
1.522(6)
100.3(2)
70.4(2)
83.3(2)
106.0(2)
103.5(3)
0.0141(2) and –0.0214(1) Å for 2bn and 3bn, respectively. C7–C8
C8–Pt–N1
91.5(2)
85.2(2)
Bond lengths for Pt–C8, Pt–N1, and Pt–N2 fall in the usual
range. A significant difference (0.09 and 0.12 Å, for 2bn and
3bn, respectively) is found between the two Pt–N bonds per-
taining to the tmeda ligand, as a result of the stronger trans
influence of the carbon atom with respect to the chlorine
or nitrogen donor atoms. The penta-atomic ring, resulting
from chelation of the tmeda ligand to the platinum atom,
is puckered with displacements of the C1 and C2 carbon
atoms on opposite sides of the plane defined by Pt, N1,
C8–Pt–N3
N1–Pt–N2
N3–Pt–N2
N3–C7–C8
C8–Pt–Cl1
N2–Pt–Cl1
C7–C8–Pt
93.1(1)
90.1(2)
93.1(2)
In 3bn, the cyclobutane metallacycle is rather strained
and N2 [–0.44(1) and 0.24(1) Å for 2bn and 0.398(6) and and “quasi” planar; as a consequence, the substituents on
–0.310(6) Å for 3bn].[14] In 2bn, the C9–C8–C7–N3 torsion adjacent atoms of the aminoethanide chain are placed in
angle of –172.5(4)° indicates an antiperiplanar disposition eclipsed positions. Notwithstanding the large deviation
of the phenyl and amine substituents on the ethanide chain. from theoretical values of bond angles, bond lengths within
This brings the amine group in a synclinal disposition with the four-member metallacycle are rather normal and in
respect to the platinum atom with a Pt–C8–C7–N3 torsion agreement with values found in the analogous
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Aiding Factors in the Formation of Azaplatinacyclobutane Rings
FULL PAPER
[Pt(CH2CH2NMe2-κC,κN)Cl(PPh3)] complex, in which,
It can also be noted that, in spite of its strained structure,
however, the ethanide chain had no substituents and the compound 3 appears to have considerable stability. To ac-
Pt–N bond was ca. 0.04 Å longer because of the trans influ- count for such stability, the concept of geometrical rigidity
ence of phosphane.[6] The steric interaction between substit- (steric constraints disfavor the reorganization of the metal
uents on cis ligands [particularly C9···C3 = 3.426(8) and orbital, which is necessary for a reaction pattern to take
C6···C15 = 3.548(8) Å] can fully explain the pyramidal dis- place) can be invoked. The same concept has been proposed
tortion of the platinum coordination center. Moreover, it by Zetterberg for justifying the lack of β-hydrogen elimi-
can be noted that, in both compounds (2bn and 3bn), the nation in azapalladacyclobutane species.[8c]
phenyl ring angle centered on the ipso carbon is smaller
than all the others [C10–C9–C14 = 117.3(5)° and 117.3(4)°
Conclusions
for 2bn and 3bn, respectively]. The distortion of benzene
rings has been the object of careful studies by Domenicano
et al., who have rationalized the deviations from a regular
geometry in terms of electronegativity, resonance, and steric
effects of the substituent. An angle that is less than 120° is
indicative of the accumulation of negative charge on the
ipso carbon induced by an electron-donor substituent (elec-
tron-withdrawing substituents produce the opposite ef-
fect).[15] Therefore, the platinum-bonded carbon atom be-
haves like an electron donor towards the ipso carbon atom
of the phenyl ring, and the electronic characteristics of this
carbon atom are rather similar for the two compounds.
Azaplatinacyclobutanes, analogous to those here de-
scribed,[6,7] were already reported in the literature; however,
all of them were characterized by the presence of a labiliz-
ing ligand trans to the ligand displaced in the ring-closing
process (usually a chlorido), and/or by having substituents
on the ethanide chain (the Thorpe–Ingold effect of these
substituents promoting the chelate ring formation).[12]
However, the ring-closing reaction readily occurs in our sys-
tems notwithstanding the absence of a labilizing ligand
trans to the leaving chlorido ligand. Moreover, although
compounds 2an and 2bm,n contain a substituent (a methyl
and a phenyl, respectively) on the ethanide chain, we could
prove that compound [PtCl(η1-CH2CH2NHEt2)(tmeda)]-
(ClO4), 2cn, which has no substituents on the ethanide
chain, can also easily undergo a ring-closing process. In
particular, 2cn in chloroform solution, treated with a slight
excess of NHEt2, affords a new complex species that is
characterized, with respect to the NMR parameters of 2cn,
by a considerable downfield shift of the 195Pt resonance (∆δ
= +440 ppm), a shielding of the C and H atoms in the α
position (∆δ = –20 and –0.6 ppm, respectively), and a de-
shielding of the C and H atoms in the β position (∆δ = +10
and +1.3 ppm, respectively). All these features are charac-
teristic of a ring-closed species. Moreover, the ESI mass
spectrum of the reaction solution did show, besides a peak
at 447.9, due to residual 2cn, another intense peak at 411.5
corresponding to the elimination of HCl from 2cn (the ab-
sence of chlorine was also confirmed by the peak isotopic
pattern).
In the systems under consideration, neither the trans-lab-
ilization of the ligand to be displaced by the entering nitro-
gen, nor the presence of substituents on the ethanide chain
(which facilitates cyclization by the Thorpe–Ingold effect)
are necessary for the ring-closing reaction to take place. The
main difference between our substrates and those pre-
viously investigated[6,7] is the absence of a formal negative
charge on the aminoethanide compound undergoing cycli-
zation (deprotonated 2). Therefore, a greater electrophilicity
of the metal center (which is deprived of formal negative
charge) could be the aiding factor promoting the ring-clos-
ing process.
Another outcome of the present investigation is the
greater propensity of the anti-Markovnikov isomer of 2, as
compared with the Markovnikov one, to undergo ring-clos-
ing reaction. The anti-M isomer of 2 differs from the M
isomer in that it has the two substituents (the methyl or
phenyl group and the amine) on different carbon atoms of
the ethanide chain. Steric repulsion between the two sub-
stituents will set them in an antiperiplanar conformation.
As a consequence, the amine group is brought in a synclinal
conformation with respect to the platinum atom and there-
fore in a suitable position to undergo chlorido substitution
and ring-closing. This aiding effect is not present in the
Markovnikov isomer, for which the hydrocarbon and the
amine substituents are on the same carbon atom of the
ethanide chain. The X-ray structure of compound 2bn has
fully confirmed this prevision. The phenyl ring and the
amine substituents on the ethanide chain are in antiper-
iplanar disposition, which brings the amine group in a syn-
clinal position with respect to the platinum atom and close
to the chlorido ligand, which can therefore be easily dis-
placed.
Experimental Section
General Methods: All reagent-grade chemicals were purchased from
Aldrich and used without purification. Elemental analyses were
performed by using an Elemental Analyzer 1106 Carlo Erba instru-
ment. 1H NMR spectra were recorded with a DPX300 Advance
Bruker instrument equipped with a probe for inverse detection and
The cyclized species 3 of this work are closely related
to the metallacycles proposed by Hartwig for the rhodium-
catalyzed anti-M amination of vinylarenes.[16] Our findings
prove that the formation of such intermediates is very likely,
and the greater propensity of the anti-M isomer to undergo
a ring-closing reaction may be the reason for the anti-M
selectivity observed in the Hartwig reaction.
1
with z gradient for gradient-accelerated spectroscopy. H and 13C
spectra were referenced to TMS; the residual proton signal of the
solvent was used as internal standard. For 195Pt spectra K2PtCl4
was used as external standard (–1643.00 ppm). 1H/13C inversely de-
tected gradient-sensitivity-enhanced heterocorrelated 2D NMR
spectra for normal coupling (INVIEAGSSI) were acquired by
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G. Lorusso, C. R. Barone, N. G. Di Masi, C. Pacifico, L. Maresca, G. Natile
FULL PAPER
using standard Bruker automation programs and pulse sequences.
APT spectra were recorded on a 300-MHz Mercury Varian instru-
ment equipped with z gradient. All spectra were acquired in CDCl3
and at 298 K. ESI mass spectra were obtained through a direct
injection (10 µL/min) of micromolar methanol solutions of all the
compounds into an Agilent 1100 Series LC-MSD Trap System VL
instrument.
3 H), and 2.94 (s, 3 H), CH3N; 2.47 (1 H), 2.62 (1 H), 2.64 (1 H),
and 3.02 (1 H), -CH2N; 2.85 (dd, 1 H), Pt-CH(Ph)CH2NH-
(CH2CH3)2; 2.52 (1 H) and 3.46 (1 H), Pt-CH(Ph)CH2NH-
(CH2CH3)2; 1.36 (3 H) and 1.38 (3 H), Pt-CH(Ph)CH2NH-
(CH2CH3)2; 3.23 (4 H), 3.49 (2 H), and 3.63 (2 H), Pt-CH(Ph)-
CH2NH(CH2CH3)2; 7.13 (1 H, para), 7.21 (2 H, meta), and 7.59
(2 H, ortho), Pt-CH(Ph)CH2NH(CH2CH3)2 ppm. 13C NMR δ =
48.9 and 51.8, CH3N; 59.8 and 66.6, -CH2N; 14.8, Pt-CH(Ph)-
CH2NH(CH2CH3)2; 61.1, Pt-CH(Ph)CH2NH(CH2CH3)2; 7.8 and
9.5, Pt-CH(Ph)CH2NH(CH2CH3)2; 44.2 and 48.3, Pt-CH(Ph)-
CH2NH(CH2CH3)2; 125.9 (para), 128.2 (meta), and 129.0 (ortho),
Pt-CH(Ph)CH2NH(CH2CH3)2 ppm. 195Pt NMR δ = –3294.4 ppm.
M-2bn: 1H NMR δ = 1.69 (dd, 1 H) and 2.25 (dd, 1 H), Pt-
CH2CH(Ph)NH(CH2CH3)2; 4.66 (1 H), Pt-CH2CH(Ph)NH-
(CH2CH3)2 ppm.
Synthesis
Alkene complexes [PtCl(η2-CH2=CHX)(tmeda)](ClO4) (X = CH3,
1a. C6H5, 1b) were prepared by ethene exchange on the cationic
complex [PtCl(η2-C2H4)(tmeda)](ClO4) (1c) by following a re-
ported procedure.[17]
Amine addition compounds 2xy were prepared by reaction of the
alkene complex 1 (0.4 mmol), suspended in dichloromethane
(8 mL), with a slight excess of the amine (NHMe2, m; NHEt2, n;
1.2-fold the stoichiometric amount). After stirring for 3 h at room
temperature, complete dissolution of the solid was observed. The
solution was filtered, the solvent evaporated under reduced pres-
sure, and the oily residue, after trituration with diethyl ether, af-
forded a white solid which was identified as the amine addition
product. The isolated yield, referred to platinum, was ca. 95% for
all the compounds.
Azaplatinacyclobutane complexes 3xy were prepared by treatment
of a dichloromethane solution of the amine addition product 2xy
(0.2 mmol in 0.4 mL solvent) with a water solution of KOH (1.2
times the stoichiometric amount in 0.4 mL solvent). The mixture
was kept under vigorous stirring for 48 h at room temperature. The
organic phase was then removed, washed twice with water (1 mL),
dried with Na2SO4, and submitted to solvent evaporation under
vacuum. The oily residue, triturated with diethyl ether, afforded a
white solid, which was separated by filtration of the solvent and
dried. It was identified as the azaplatinacyclobutane complex. The
isolated yield, referred to platinum, was ca. 90% for all compounds.
2an(ClO4): C13H33Cl2N3O4Pt (561.40): calcd. C 27.81, H 5.92, N
7.48; found C 27.62, H 5.81, N 7.38. NMR (tmeda signals are given
1
first) M-2an: H NMR δ = 2.65 (s, 3 H), 2.67 (s, 3 H), 2.81 (s, 3
H), and 2.87 (s, 3 H), CH3N; 2.56 (1 H) and 2.73 (1 H), 2.82 (1 H)
3an(ClO4): C13H32ClN3O4Pt (524.94): calcd. C 29.74, H 6.14, N
8.00; found C 29.44, H 6.03, N 7.92. NMR (tmeda signals are given
first) M-3an: 1H NMR δ = 2.79 (s, 6 H), 2.80 (s, 6 H), CH3N;
2.35–3.30 (m, 4 H), -CH2N; 1.04 (d, 3 H), Pt{CH2CH(CH3)-
and 3.02 (1 H), -CH2N; 1.26 (d,
NH(CH2CH3)2; 1.46 (dd, 1 H) and 1.59 (dd, 1 H), Pt-CH2CH-
(CH3)NH(CH2CH3)2; 3.59 (m, H), Pt-CH2CH(CH3)NH-
1 H), Pt-CH2CH(CH3)-
1
(CH2CH3)2; 1.43 (m, 3 H) and 1.49 (m, 3 H), Pt-CH2CH(CH3)NH-
(CH2CH3)2; 2.77 (m, 1 H) and 3.34 (m, 1 H), 3.05 (m, 1 H) and
3.28 (m, 1 H), Pt-CH2CH(CH3)NH(CH2CH3)2 ppm. 13C NMR
δ = 47.4, 49.1, 51.1, and 52.2, CH3N; 59.9 and 66.1, -CH2N; 1.0,
2
N(CH2CH3)2-κC,κN}; 0.71 (dd, JPt,H = 87.8 Hz, 1 H) and 1.23
(dd, 1 H), Pt{CH2CH(CH3)N(CH2CH3)2-κC,κN}; 4.35 (m, 1 H),
Pt{CH2CH(CH3)N(CH2CH3)2-κC,κN}; 1.26 (t, 3 H) and 1.64 (t,
3 H), Pt{CH2CH(CH3)N(CH2CH3)2-κC,κN}; 2.58 (m, 1 H) and
2.79 (m, 1 H), 2.92 (m, 1 H) and 3.08 (m, 1 H), Pt{CH2CH(CH3)-
N(CH2CH3)2-κC,κN} ppm. 13C NMR δ = 50.1 and 52.7, CH3N;
–16.08 (1JPt,c = 583.7 Hz), Pt{CH2CH(CH3)N(CH2CH3)2-κC,κN};
21.8, Pt{CH2CH(CH3)N(CH2CH3)2-κC,κN}; 73.5, Pt{CH2CH-
(CH3)N(CH2CH3)2-κC,κN}; 11.7 and 16.2, Pt{CH2CH(CH3)-
N(CH2CH3)2-κC,κN}; 57.4 and 57.6, Pt{CH2CH(CH3)-
N(CH2CH3)2-κC,κN} ppm. 195Pt NMR δ = –3029.6 ppm. anti-M-
Pt-CH2CH(CH3)NH(CH2CH3)2;
15.5,
Pt-CH2CH(CH3)NH-
(CH2CH3)2; 62.6, Pt-CH2CH(CH3)NH(CH2CH3)2; 10.9 and 10.6,
Pt-CH2CH(CH3)NH(CH2CH3)2; 42.8 and 46.8, Pt-CH2CH(CH3)-
NH(CH2CH3)2 ppm. 195Pt NMR δ = –3384.0 ppm. anti-M-2an: 1H
NMR δ = 0.95 (d, 3 H), Pt-CH(CH3)CH2NH(CH2CH3)2; 1.39 (m,
1 H), Pt-CH(CH3)CH2NH(CH2CH3)2; 2.34 (dd, 1 H) and 3.21 (dd,
1 H), Pt-CH(CH3)CH2NH(CH2CH3)2 ppm.
1
3
3an: H NMR δ = 0.63 (d, JPt,H = 64.4 Hz, 3 H), Pt{CH(CH3)-
CH2N(CH2CH3)2-κC,κN}; 1.39 (m, H), Pt{CH(CH3)-
2bm(ClO4): C16H31Cl2N3O4Pt (595.42): calcd. C 32.27, H 5.25, N
1
7.06; found C 32.03, H 5.11, N 6.98. NMR (tmeda signals are given
3
1
CH2N(CH2CH3)2-κC,κN}; 3.79 (dd, 1 H) and 4.71 (dd, JPt,H
78.0 Hz, 1 H), Pt{CH(CH3)CH2N(CH2CH3)2-κC,κN} ppm.
=
first) anti-M-2bm: H NMR δ = 2.46 (s, 3 H), 2.69 (s, 3 H), 2.85
(s, 3 H), and 2.98 (s, 3 H), CH3N; 2.48 (1 H), 2.68 (2 H), and 2.98
2
(1 H), -CH2N; 2.76 (dd, JPt,H = 76.2, 1 H), Pt-CH(Ph)CH2NH-
3bm(ClO4): C16H30ClN3O4Pt (558.96): calcd. C 34.38, H 5.41, N
(CH3)2; 2.32 (1 H) and 3.79 (1 H), Pt-CH(Ph)CH2NH(CH3)2; 3.02
(3 H) and 3.12 (3 H), Pt-CH(Ph)CH2NH(CH3)2; 7.12 (1 H, para),
7.19 (2 H, meta), and 7.40 (2 H, ortho), Pt-CH(Ph)CH2NH(CH3)2
ppm. 13C NMR δ = 48.9, 49.0, and 52.0, CH3N; 59.8 and 66.8,
-CH2N; 16.5 (1JPt,C = 846 Hz), Pt-CH(Ph)CH2NH(CH3)2; 67.6, Pt-
CH(Ph)CH2NH(CH3)2; 42.7 and 45.2, Pt-CH(Ph)CH2NH(CH3)2;
125.3 (para), 128.4 (meta), and 129.2 (ortho), Pt-CH(Ph)-
CH2NH(CH3)2 ppm. M-2bm: 1H NMR δ = 1.77 (dd, 1 H) and 2.08
(dd, 1 H), Pt-CH2CH(Ph)NH(CH3)2; 4.64 (1 H), Pt-CH2CH(Ph)-
NH(CH3)2; 7.40 (3 H, meta and para) and 7.57 (2 H, ortho), Pt-
CH2CH(Ph)NH(CH3)2 ppm. 13C NMR δ = –0.6, Pt-CH2CH(Ph)-
NH(CH3)2; 74.5, Pt-CH2CH(Ph)NH(CH3)2; 129.0 (meta and para)
and 129.6 (ortho), Pt-CH2CH(Ph)NH(CH3)2 ppm.
7.52; found C 34.13, H 5.49, N 7.44. NMR (tmeda signals are given
first) anti-M-3bm: H NMR δ = 1.90 (s, 3 H), 2.69 (s, 3 H), 2.82
1
(s, 3 H), and 2.84 (s, 3 H), CH3N; 2.43 (1 H), 2.56 (1 H), 2.64 (1
2
H), and 2.80 (1 H), -CH2N; 2.85 (dd, JPt,H = 105.4 Hz, 1 H),
Pt{CH(Ph)CH2N(CH3)2-κC,κN}; 4.24 (1 H) and 5.21 (3JPt,H
=
99.4 Hz, 1 H), Pt{CH(Ph)CH2N(CH3)2-κC,κN}; 2.85 (3 H) and
2.89 (3 H), Pt{CH(Ph)CH2N(CH3)2-κC,κN}; 7.14 (1 H, para), 7.20
(2 H, meta), and 7.44 (2 H, ortho), Pt{CH(Ph)CH2N(CH3)2-
κC,κN} ppm. 13C NMR δ = 49.8, 50.5, 51.1, and 53.2, CH3N; 60.5
and 64.8, -CH2N; –6.2 (1JPt,C = 564.4 Hz), Pt{CH(Ph)CH2-
N(CH3)2-κC,κN}; 83.2 (2JPt,C
= 188.2 Hz), Pt{CH(Ph)CH2-
N(CH3)2-κC,κN}; 53.0 and 52.4, Pt{CH(Ph)CH2N(CH3)2-
κC,κN}; 124.6 (para), 128.4 (meta), and 127.8 (ortho), Pt{CH(Ph)-
CH2N(CH3)2-κC,κN} ppm. M-3bm: (not isolated in the solid state
but detected in solution by performing the ring-closing reaction in
2bn(ClO4): C18H35Cl2N3O4Pt (623.47): calcd. C 34.68, H 5.66, N
6.74; found C 34.39, H 5.56, N 6.84. NMR (tmeda signals are given
1
1
first) anti-M-2bn: H NMR δ = 2.42 (s, 3 H), 2.68 (s, 3 H), 2.78 (s,
an NMR tube) H NMR δ = 1.44 (dd, 1 H) and 1.65 (dd, 1 H),
2148
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 2144–2150

Aiding Factors in the Formation of Azaplatinacyclobutane Rings
Pt{CH2CH(Ph)N(CH3)2-κC, κN}; 5.20 (1 H), Pt{CH2CH(Ph) sponding carbon atoms. The perchlorate counterion is disordered.
FULL PAPER
N(CH3)2-κC,κN} ppm.
The final difference-Fourier map showed electron-density peaks
(up to 1.839 eÅ–3) lying near the Pt atoms.
3bn(ClO4): C18H34ClN3O4Pt (587.01): calcd. C 36.83, H 5.83, N
7.16; found C 36.54, H 5.73, N 7.08. NMR (tmeda signals are given
first) anti-M-3bn: H NMR δ = 1.91 (s, 3 H), 2.68 (s, 3 H), 2.80 (s,
For compound 3bn(ClO4), also crystallized from CHCl3/pentane, a
total of 25934 reflections (Θmax = 41.00°) were collected. The
1
3 H), and 2.83 (s, 3 H), CH3N; 2.48 (1 H), 2.56 (1 H), 2.62 (1 H), number of independent reflections was 12990. The unit-cell dimen-
2
and 2.80 (1 H), -CH2N; 2.57 (dd, JPt,H = 98.0 Hz, 1 H), sions were calculated from all reflections. The structure was solved
Pt{CH(Ph)CH2N(CH2CH3)2-κC,κN}; 4.28 (1 H) and 5.09 (3JPt,H by direct methods in the P21/c space group. The model was refined
= 94.8 Hz, 1 H), Pt{CH(Ph)CH2N(CH2CH3)2-κC,κN}; 1.49 (3 H)
and 1.75 (3 H), Pt{CH(Ph)CH2N(CH2CH3)2-κC,κN}; 2.62 (1 H),
by full-matrix least-squares methods. Anisotropic thermal param-
eters were applied for all non-hydrogen atoms. H atoms were lo-
2.89 (1 H), 2.90 (1 H), and 3.34 (1 H), Pt{CH(Ph)CH2N- cated in difference maps, and the parameters were freely refined.
(CH2CH3)2-κC,κN}; 7.13 (1 H, para), 7.19 (2 H, meta), and 7.42
The final difference-Fourier map showed electron-density peaks
(2 H, ortho), Pt{CH(Ph)CH2N(CH2CH3)2-κC,κN} ppm. 13C NMR (up to 3.432 eÅ–3) lying near the Pt atoms.
δ = 49.9, 50.8, 51.2, and 52.7, CH3N; 60.7 and 65.1, -CH2N; –7.2
The crystallographic data are listed in Table 2. All calculations and
(1JPt,C = 564.4 Hz), Pt{CH(Ph)CH2N(CH2CH3)2-κC,κN}; 74.8
(2JPt,C = 188.2 Hz), Pt{CH(Ph)CH2N(CH2CH3)2-κC,κN}; 11.1
and 13.8, Pt{CH(Ph)CH2N(CH2CH3)2-κC,κN}; 56.4 and 57.7,
Pt{CH(Ph)CH2N(CH2CH3)2-κC,κN}; 124.8 (para), 127.8 (ortho),
and 128.7 (meta), Pt{CH(Ph)CH2N(CH2CH3)2-κC,κN} ppm. 195Pt
NMR δ = –2878.7 ppm.
molecular graphics were carried out by using the SIR2004,[20]
SHELXL97,[21] PARST97,[22] WinGX,[23] or ORTEP-3 for Win-
dows packages.[24] CCDC-624564 (2bn) and CCDC-269917 (3bn)
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic
data_request/cif.
Data
Centre
via
www.ccdc.cam.ac.uk/
In the case of unsubstituted ethene compounds 2cn/3cn, the reac-
tion was only performed in an NMR tube, and the species were
identified and characterized by ESI-MS and NMR spectroscopy.
Table 2. Crystal data and structure refinement parameters for
2bn(ClO4) and 3bn(ClO4).
1
NMR (tmeda signals are given first) 2cn: H NMR δ = 2.72 (s, 6
H) and 2.93 (s, 6 H), CH3N; 2.59 (2 H) and 2.84 (2 H), -CH2N;
1.62 (m, JPt,H = 93.6 Hz, 2 H), Pt-CH2CH2NH(CH2CH3)2; 3.13
2bn(ClO4)
3bn(ClO4)
2
Empirical formula
Formula weight
Crystal system
Space group
a [Å]
b [Å]
c [Å]
C18H35Cl2N3O4Pt C18H34ClN3O4Pt
623.48
monoclinic
Cc
13.4927(3)
13.7925(3)
13.1851(3)
97.424(1)
2433.2(1)
4
1.702
6.013
1232
7.11–36.84
33622
(m,
2
H), Pt-CH2CH2NH(CH2CH3)2; 1.32 (t,
6 H), Pt-
587.02
monoclinic
P21/c
10.1870(5)
15.6315(7)
14.1576(7)
95.348(1)
2244.6(2)
4
1.737
6.397
1160
1.95–41.21
25934
CH2CH2NH(CH2CH3)2; 3.18 (q,
4
H), Pt-CH2CH2NH-
(CH2CH3)2 ppm. 13C NMR δ = 48.8 and 52.5, CH3N; 59.9 and
66.1, -CH2N; –9.3 (1JPt,C = 752.5 Hz), Pt-CH2CH2NH(CH2CH3)2;
57.4, Pt-CH2CH2NH(CH2CH3)2; 8.8, Pt-CH2CH2NH(CH2CH3)2;
44.9, Pt-CH2CH2NH(CH2CH3)2 ppm. 195Pt NMR δ = –3336.0
ppm. 3cn: 1H NMR δ = 2.80 (s, 6 H) and 2.81 (s, 6 H), CH3N;
2.68 (2 H) and 2.73 (2 H), -CH2N; 0.98 (m, 2JPt,H = 91.2 Hz, 2 H),
Pt{CH2CH2N(CH2CH3)2-κC,κN}; 4.46 (m, 3JPt,H = 58.4 Hz, 2 H),
Pt{CH2CH2N(CH2CH3)2-κC,κN}; 1.49 (t, 6 H), Pt{CH2CH2N-
β [°]
V [Å3]
Z
ρcalc[gcm–3]
µ[mm–1]
(CH2CH3)2-κC,κN}; 2.60 (m,
2 H) and 2.90 (m, 2 H),
F(000)
θ Range
Reflections collected
Pt{CH2CH2N(CH2CH3)2-κC,κN} ppm. 13C NMR δ = 50.5 and
52.4, CH3N; 61.0 and 64.1, -CH2N; –29.2 (1JPt,C = 517.4 Hz),
Pt{CH2CH2N(CH2CH3)2-κC,κN}; 67.4 (2JPt,C
=
188.1 Hz),
Data/restraints/parameters 11082/2/263
12990/0/380
1.041
0.0471, 0.0914
0.0888, 0.1080
Goodness-of-fit on F2
R1, wR2[F2 Ͼ 2σ(F2)]
R1, wR2 (all data)
1.029
0.0311, 0.0682
0.0452, 0.0732
Pt{CH2CH2N(CH2CH3)2-κC,κN}; 12.5, Pt{CH2CH2N(CH2-
CH3)2-κC,κN}; 56.7, Pt{CH2CH2N(CH2CH3)2-κC,κN} ppm. 195Pt
NMR δ = –2895.3 ppm.
X-ray Crystallography
X-ray data were collected for the crystals 2bn(ClO4) and 3bn(ClO4)
with a Bruker AXS X8 APEX CCD system equipped with a four-
circle Kappa goniometer and a 4-K CCD detector (Mo-Kα radia-
tion). The crystal-to-detector distance was 40 mm. The SAINT-
IRIX package was employed for data reduction and unit-cell re-
finement.[18] All reflections were indexed, integrated, and corrected
for Lorentz, polarization, and absorption effects by using the pro-
gram SADABS.[19]
Acknowledgments
We are grateful to Prof. Emanuela Schingaro and Prof. Ferdinando
Scordari (University of Bari) for data collection; we thank Dr.
Francesco Cannito (Consorzio Interuniversitario di Ricerca in Chi-
mica dei Metalli nei Sistemi Biologici, C.I.R.C.M.S.B.) for assist-
ance in the preparation of the manuscript. The financial support
of the University of Bari (Contribution ex 60%) and of the Italian
For compound 2bn(ClO4), which was crystallized from CHCl3/pen-
tane, a total of 33622 reflections (Θmax = 37.00°) were collected.
The number of independent reflections was 11082. The unit-cell
dimensions were calculated from all reflections. The structure was
solved by direct methods in the Cc space group. The model was
refined by full-matrix least-squares methods. Anisotropic thermal
parameters were applied for all non-hydrogen atoms. H atoms were
located in difference maps, and were included in the full-matrix
least-squares cycles with isotropic thermal parameters (U) fixed at
1.2 and 1.5 (for methyl group) times the values of U of the corre-
Ministero dell’Università
2005032730) is also gratefully acknowledged.
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2149

G. Lorusso, C. R. Barone, N. G. Di Masi, C. Pacifico, L. Maresca, G. Natile
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[13] In the case of 3bm, by performing the ring-closing reaction in
an NMR tube, it was possible to observe a spin system assign-
Published Online: April 4, 2007
2150
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 2144–2150