[PtR(η2-olefin)(N-N)]+ complexes containing the olefin and the alkyl ligand in a cis arrangement. Preparation, structural characterization, and olefin stereochemistry

Article abstract of DOI:10.1021/om970428f

Cationic Pt(II) complexes containing an alkyl and an olefin in cis positions are described. The compounds (1) of general formula [PtR(N-N)(olefin)]BF₄ are obtained either through oxidative addition of the trialkyloxonium salt R₃O

Full text of DOI:10.1021/om970428f

Organometallics 1997, 16, 5981-5987
5981
[P tR(η2-olefin )(N-N)]+ Com p lexes Con ta in in g th e Olefin
a n d th e Alk yl Liga n d in a cis Ar r a n gem en t. P r ep a r a tion ,
Str u ctu r a l Ch a r a cter iza tion , a n d Olefin Ster eoch em istr y
Maria Fusto, Federico Giordano, Ida Orabona, and Francesco Ruffo*
Dipartimento di Chimica, Universita` di Napoli “Federico II”, via Mezzocannone 4,
I-80134 Napoli, Italy
Achille Panunzi
Facolta` di Agraria and Dipartimento di Chimica, Universita` di Napoli “Federico II”,
via Mezzocannone 4, I-80134 Napoli, Italy
Received May 27, 1997X
Cationic Pt(II) complexes containing an alkyl and an olefin in cis positions are described.
The compounds (1) of general formula [PtR(N-N)(olefin)]BF4 are obtained either through
oxidative addition of the trialkyloxonium salt R3O+BF4- to the appropriate three-coordinate
precursor [Pt(N-N)(olefin)] or by substitution of an alkene for the chloride in [PtR(Cl)(N-N)]
complexes. The complexes are involved in a dynamic process involving the alkene ligand.
The rate of alkene exchange is strongly influenced by the steric hindrance of the N-N ligand
above and below the coordination plane. This feature also controls the stereochemistry of
alkene coordination. Thus, for type 1 derivatives of R-olefins containing the highly crowded
diacetyl bis(di-isopropylphenylimine), only one enantiomeric couple has been detected in
the temperature range 203-328 K, and its geometry has been tentatively assigned. Finally,
the X-ray crystal structure of a representative complex has been determined.
In tr od u ction
Resu lts a n d Discu ssion
It is generally accepted1 that the attainment of the
cis arrangement of an unsaturated ligand and an alkyl
group in the coordination sphere of a transition-metal
ion preludes the subsequent insertion reaction. The cis
geometry is generally favored by using suitable ancillary
ligands, e.g. bidentate chelates which leave adjacent
positions in the coordination polyhedron available for
the coordination of the carbon ligands. The most recent
findings2 in line with this approach deal with olefin
polymerization promoted by Ni(II) and Pd(II) complexes
in the presence of suitable N-N nitrogen chelates. The
active species are considered to be cationic complexes
of formula [M(N-N)(Me)(olefin)]+, which in the case of
Pd complexes could be detected in solution at 163 K
through NMR spectroscopy.2a
The increasing interest in these reactive systems
prompted us to investigate the chemistry of stable plati-
num(II) species analogous to those mentioned. This aim
was also suggested by the fact that only very few cat-
ionic Pt(II) complexes showing a cis arrangement of the
olefin and of the alkyl group have been described so far,3
despite a fairly extended knowledge of the analogous
trans species.4 Here we report an extension of the
preliminary study.5
Syn th esis of th e Com p lexes. The N-N ligands and
the olefins used in this work are shown in Chart 1. The
choice of N-N chelates has been dictated by the aim of
obtaining a wide range of steric hindrance, while the
most common olefins have been used as unsaturated
ligands. Table 1 lists the complexes.
Two synthetic procedures have been adopted (eqs 1
and 2 in Scheme 1). The first one5 is the oxidative
addition of a trialkyloxonium salt to the three-coordi-
nate platinum(0) precursor [Pt(phen)(dimethyl fuma-
rate)] (2a ). The resulting products [PtR(phen)(dimethyl
fumarate)]BF4 (R ) Me, 1a ; R ) Et, 1b) can be either
isolated in the solid state or reacted in situ with a
suitable alkene. In the latter case, the electron-poor
dimethyl fumarate is readily displaced by the incoming
olefin, which affords the corresponding type 1 product.
Since this route does not produce any precipitate, it is
particularly useful in cases where the reactions are
performed in NMR tubes.
The alternative procedure, described by eq 2, consists
of the addition of AgBF4 to a dichloromethane solution
of the planar species [PtClMe(N-N)] (3) in the presence
of the appropriate olefin. This method has been used
when N-N is a diacetyl bis(diarylimine), since the cor-
responding type 2 precursors are not easily available.
Type 1 products are air stable and can be stored at
277 K without appreciable decomposition for several
months.
X Abstract published in Advance ACS Abstracts, November 15, 1997.
(1) Collmann, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987.
(2) (a) Rix, F. C.; Brookhart, M. J . Am. Chem. Soc. 1995, 117, 1137-
1138. (b) J ohnson, L. K.; Killian, C. M.; Brookhart, M. J . Am. Chem.
Soc. 1995, 117, 6414-6415. (c) J ohnson, L. K.; Mecking, S.; Brookhart,
M. J . Am. Chem. Soc. 1996, 118, 267-268.
(3) (a) Clark, H. C.; J ablonsky, C. R.; von Werner, K. J . Organomet.
Chem. 1974, 82, C51-C52. (b) Cucciolito, M. E.; De Felice, V.; Panunzi,
A.; Vitagliano, A. Organometallics 1989, 8, 1180-1187. (c) Hill, G. S.;
Rendina, L. M.; Puddephatt, R. J . J . Chem. Soc., Dalton Trans. 1996,
1809-1813.
Daproph, daethyph, and daph derivatives are soluble
in chlorinated solvents, in which NMR investigations
can be carried out at low temperatures. Slow addi-
(4) Chisholm, M. H.; Clark, H. C. Inorg. Chem. 1973, 12, 991-998.
(5) Orabona, I.; Panunzi, A.; Ruffo, F. J . Organomet. Chem. 1996,
525, 295-298.
S0276-7333(97)00428-7 CCC: $14.00 © 1997 American Chemical Society

5982 Organometallics, Vol. 16, No. 26, 1997
Fusto et al.
all cases, Pt-13CH3 resonances lie in the range -10 to
0 ppm. The olefin carbons resonate in the range typical
for square-planar Pt(II)-olefin complexes; i.e., ∆δ values
between free and coordinated olefins are within 30-55
ppm.10
Ch a r t 1. N-N a n d Olefin Liga n d s Used in Th is
Wor k
B. Olefin Exch a n ge. In the presence of chelates
which do not introduce substantial steric hindrance
below and above the coordination plane (i.e. phen or
daph), the protons of ethylene, styrene, and allyl alcohol
do not couple to 195Pt at room temperature. More
precisely, ethylene appears as a slightly broadened
singlet, as also observed3c for the related complex [PtMe-
(4,4′-t-Bu-2,2′-bipy)(ethylene)]+. Styrene and allyl al-
cohol give rise to the typical R-olefin pattern (e.g. an
AMX multiplet for styrene).
On the other hand, propylene and trans-2-butene
protons do couple to 195Pt at room temperature in the
spectra of the phen or daph derivatives. However, in
the presence of 0.1 equiv of free propylene, the olefin
protons of 1e, 1f, and 1q lose their satellites and give
rise to averaged signals accounting for the free and the
coordinated molecule.
Thanks to the fair solubility of the daph derivatives
1p , 1r in dichloromethane, their spectra could be re-
corded in the range 328-203 K. At the lower temper-
ature, broadening of the ethylene resonance in 1p is
observed. The behavior of 1r is similar but deserves
further comment (see below).
tion of toluene to their solutions in methylene chloride
allows the formation of well-shaped orange-red single
crystals.
Complexes of phen are white microcrystalline solids
poorly soluble in chlorocarbons but fairly soluble in
nitromethane. This has limited the study of their
solution behavior (see below), since the melting point
of deuterionitromethane is ca. 243 K.
The characterization of type 1 complexes has been
carried out through elemental analyses, NMR spectros-
copy, and, in one case, through the determination of the
X-ray crystal structure (1o; see below).
The above NMR findings11 clearly show that type 1
complexes of phen and daph are involved in a fast
dynamic process, most probably exchange between
coordinated and free olefin12 (eq 3).
NMR Sp ectr oscop y a n d Olefin Dyn a m ic Beh a v-
ior .6 A. Gen er a l F ea tu r es. 1H and 13C NMR spectra
(Tables 1 and 2) show the nonequivalence of the halves
of the complexes.7 The differences in J Pt-H or J Pt-C of
corresponding nuclei in the halves of the N-N ligands
are in agreement with the higher trans influence of alkyl
[PtR(N-N)(olefin)] + olefin* )
[PtR(N-N)(olefin*)] + olefin (3)
The observations that excess alkene enhances the rate
of exchange and that the halves of the N-N ligands are
not equivalent suggest that the process may occur via
an associative mechanism involving a five-coordinate
bis(olefin) intermediate (III in Scheme 2). In this case,
by considering that the N atom labeled with a prime is
always trans to Me, it is clear that the overall process
occurs without exchanging the halves of the N-N che-
late.
The hypothesis concerning an associative mechanism
is supported by the results obtained by using N-N
ligands with steric crowding below and above the
coordination plane. These ligands are known2b to
inhibit the associative exchange of a ligand on a four-
coordinate d8 ion, according to the expectation that the
square-pyramidal initial adducts (in our case II and IV)
would suffer severe steric constraints. This approach
was effectively used in the inhibition of associative
processes in polymerizations promoted by Pd(II).2b In
fact, in daproph type 1 derivatives, the protons of
ethylene, styrene, and allyl alcohol of 1k -n couple to
195Pt in the NMR spectra at room temperature. Notice-
ably, even at 328 K and in the presence of an excess
3
groups relative to olefins.8 As an example, the J Pt-H
coupling constant of the phen proton which is close to
the N atom trans to the alkene is ca. 50 Hz. The value
drops to ca. 15 Hz when the corresponding nucleus
opposite to Me or Et is considered.
In phen complexes, as also observed for closely related
methyl/alkyne [PtMe(phen)(alkyne)]+ derivatives,9 1H
NMR peaks pertaining to Pt-Me groups appear at ca.
1 ppm. The olefin protons resonate within 1 ppm
upfield with respect to the free ligand. The correspond-
ing signals in diacetyl bis(diarylimine) derivatives un-
dergo a larger high-field shift, possibly owing to the
shielding due to the aryl groups, which lie almost
perpendicular to the coordination plane and thus face
the olefin protons (see X-ray structure of 1o).
In 13C spectra, no significant difference ensues be-
tween phen and diacetyl bis(diarylimine) complexes. In
(6) Since the olefin dynamic behavior has been investigated through
NMR spectroscopy, henceforth a process which is slow (or fast) on the
NMR time scale will be simply indicated as slow (or fast).
(7) In the NMR spectra of the dimethyl fumarate derivatives 1a ,1b
both phen and the olefin are symmetric.5 A possible explanation of
the high symmetry displayed by the complexes may be given by
admitting that the electronic properties of the electron-poor alkene
allow the occurrence of a fast dissociative/associative equilibrium.
(8) Purcell, K. F.; Kotz, J . C. Inorganic Chemistry; Saunders:
London, 1985; pp 704-705.
(10) Cooper, D. G.; Powell, J . Inorg. Chem. 1976, 15, 1959-1968.
(11) The conclusions which will be henceforth presented are mainly
derived from 1H NMR spectra. 13C NMR spectra are fully consistent
with them.
(12) Traces of free olefin may be generated after dissolution of the
complexes, either by dissociation or by an associative process involving
the solvent.
(9) Cucciolito, M. E.; De Felice, V; Orabona, I.; Ruffo, F. J . Chem.
Soc., Dalton Trans. 1997, 1351-1355.

[PtR(η2-olefin)(N-N)]+ Complexes
Organometallics, Vol. 16, No. 26, 1997 5983
Ta ble 1. Selected 1H NMR Da ta a for Typ e 1 Com p lexes
H(olefin)b
5.33 (br, 2H)
5.00 (br, 2H)
other signalsc
9.47 (d, 2H)
b
compd no.
1a d,e
formula
Pt-CHx
[PtMe(phen)(dimethyl fumarate)]BF4
[PtEt(phen)(dimethyl fumarate)]BF4
1.10 (75, 3H)
1.60 (br, 2H)
1bf
9.40 (d, 1H)
8.69 (d, 1H)
1cd,e
1d d
[PtMe(phen)(ethylene)]BF4
[PtEt(phen)(ethylene)]BF4
[PtMe(phen)(propylene)]BF4
0.93 (71, 3H)
1.35 (74, q, 2H)
0.93 (73, 3H)
4.54 (br, 4H)
4.45 (br, 4H)
9.20 (50, d, 1H)
8.67 (14, d, 1H)
9.20 (50, d, 1H)
1.09 (29, t, 3H)
1ed,e
5.41 (m, 1H)
4.45 (m, 1H)
4.26 (m, 1H)
9.17 (58, d, 1H)
1fd
[PtEt(phen)(propylene)]BF4
[PtMe(phen)(styrene)]BF4
1.45 (73, q, 2H)
0.77 (73, 3H)
5.40 (m, 1H)
4.3 (m, 2H)
9.30 (48, d, 1H)
1.10 (30, t, 3H)
1gd,e
6.62 (dd, 1H)
4.88 (dd, 1H)
4.53 (m, 1H)
9.16 (53, d, 1H)
8.66 (15, d, 1H)
1h d
[PtEt(phen)(styrene)]BF4
1.35 (69, q, 2H)
6.52 (dd, 1H)
4.92 (d, 1H)
4.54 (d, 1H)
0.83 (t, 3H)
1id
1j
[PtMe(phen)(allyl alcohol)]BF4
[PtMe(phen)(trans-2-butene)]BF4
[PtMe(daproph)(ethylene)]BF4
[PtMe(daproph)(propylene)]BF4
0.95 (73, 3H)
1.11 (74, 3H)
0.18 (70, 3H)
0.25 (70, 3H)
5.39 (m, 1H)
4.45 (m, 2H)
9.20 (45, d, 1H)
5.15 (67, br, 2H)
9.25 (48, d, 1H)
1.97 (46, br, 6H)
1k f
1lf
3.72 (68, 4H)
2.51 (3H)
2.28 (3H)
4.30 (80, m, 1H)
3.75 (m, 2H)
2.48 (3H)
2.27 (3H)
1.61 (60, d, 3H)
1m f
[PtMe(daproph)(styrene)]BF4
-0.26 (72, 3H)
5.73 (87, dd, 1H)
4.05 (58, d, 1H)
3.33 (70, d, 1H)
2.49 (3H)
2.33 (3H)
1n f
1of
1p f
1qf
[PtMe(daproph)(allyl alcohol)]BF4
[PtMe(daethyph)(ethylene)]BF4
[PtMe(daph)(ethylene)]BF4
0.27 (71, 3H)
0.13 (70, 3H)
0.20 (70, 3H)
0.25 (71, 3H)
4.36 (73, m, 1H)
3.70 (m, 2H)
2.45 (3H)
2.23 (3H)
3.68 (68, 4H)
2.50 (3H)
2.20 (3H)
3.71 (br, 4H)
2.39 (3H)
2.12 (3H)
[PtMe(daph)(propylene)]BF4
4.57 (77, dd, 1H)
3.80 (72, d, 1H)
3.57 (64, d, 1H)
2.35 (3H)
2.12 (3H)
1r f
1sf
[PtMe(daph)(styrene)]BF4
-0.04 (70, 3H)
5.50 (br, 1H)
4.15 (br, 1H)
3.75 (br, 1H)
2.37 (3H)
2.12 (3H)
[PtMe(daph)(trans-2-butene)]BF4
0.36 (72, 3H)
4.52 (66, m, 1H)
4.00 (70, m, 1H)
2.62 (d, 3H)
2.50 (30, d, 3H)
2.37 (3H)
2.10 (3H)
a
b
At 200 or 270 MHz and 298 K. Abbreviations: no attribute, singlet; br, broad; d, doublet; m, multiplet; q, quartet; t, triplet. 2J Pt-H
(Hz) in parentheses. 3J Pt-H (Hz) in parentheses. Data from ref 5. e In CD3NO2 (CHD2NO2 (δ 4.33 ppm) as internal standard). f In
CDCl3 (CHCl3 (δ 7.26 ppm) as internal standard).
c
d
alkene, no exchange is observed for the R-olefin deriva-
tives 1l-n .
On the other hand, in the case where the unsaturated
ligand is the less bulky ethylene (1k ), the olefin reso-
nance is sharp and is coupled up to 328 K, while
broadening of the signal occurs if some ethylene is added
to the solution at 298 K.
C. Olefin Rota tion a n d Coor d in a tion Selectiv-
ity. As for olefin rotation around the Pt-alkene bond,
the spectra provide information only when the olefin
exchange is slow, i.e. coupling to 195Pt is detectable. In
this situation, one may be able to observe more than
one isomer for a given complex, depending on the
symmetry of the alkene.
(flanked by satellites) clearly indicates that at room
temperature ethylene is rotating rapidly. Only below
213 K does broadening of the signals occur in the NMR
spectra recorded in CD2Cl2, which reflects slower rota-
tion on the NMR time scale.
R-Olefins may give rise to two enantiomeric pairs
(respectively, 1′ and 1′′ in Figure 1 in the case of daph
or daproph). They differ in the orientation of the alkene
substituent, which can be oriented toward the Pt-Me
bond or the opposite side. A 180° rotation of the olefin
(Figure 1) converts each isomer of one enantiomeric pair
into an isomer belonging to the other pair.
The spectra of the R olefin complexes of daproph 1l-n
consist of a unique spectral pattern between 203 and
308 K, with no significative variations of the chemical
shifts along the whole range of temperatures (in Figure
Ethylene can afford only one species. In the case of
the complexes 1k ,o the presence of a sharp singlet

5984 Organometallics, Vol. 16, No. 26, 1997
Fusto et al.
a
Sch em e 1
a
Legend: (i) +R3OBF4, -R2O; (ii) +R′CHdCHR′′, -(dimethyl fumarate); (iii) +AgBF4, + R′CHdCHR′′, -AgCl.
Ta ble 2. Selected 13C NMR Da ta a for Typ e 1 Com p lexes
b
compd no.
1cd,e
formula
Pt-CHx
C(olefin)b
71.3 (br, 2C)
71.2 (br, 2C)
other signalsc
[PtMe(phen)(ethylene)]BF4
[PtEt(phen)(ethylene)]BF4
[PtMe(phen)(propylene)]BF4
-6.7 (673, 1C)
11.4 (613, 1C)
-5.2 (702, 1C)
1d d
1ed,e
18.9 (89, 1C)
96.0 (br, 1C)
67.2 (br, 1C)
1fd
1gd,e
1h d
1id
[PtEt(phen)(propylene)]BF4
[PtMe(phen)(styrene)]BF4
[PtEt(phen)(styrene)]BF4
8.5 (681, 1C)
-2.6 (705, 1C)
11.1 (627, 1C)
-5.5 (636, 1C)
-3.8 (739, 1C)
94.5 (br, 1C)
67.5 (br, 1C)
20.7 (1C)
16.1 (39, 1C)
95.8 (br, 1C)
1Cf
95.8 (br, 1C)
65.4 (br, 1C)
15.9 (35, 1C)
[PtMe(phen)(allyl alcohol)]BF4
[PtMe(phen)(trans-2-butene)]BF4
97.0 (br, 1C)
66.1 (br, 1C)
63.5 (1C)
15.9 (35, 1C)
1j
90.5 (180, 1C)
88.1 (217, 1C)
20.0 (2C)
1k g
1lg
[PtMe(daproph)(ethylene)]BF4
[PtMe(daproph)(propylene)]BF4
-4.7 (1C)
73.8 (192, 2C)
-3.0 (706, 1C)
98.0 (185, 1C)
70.5 (171, 1C)
1m g
1n g
[PtMe(daproph)(styrene)]BF4
0.5 (716, 1C)
96.4 (176, 1C)
61.3 (193, 1C)
[PtMe(daproph)(allyl alcohol)]BF4
-4.2 (687, 1C)
97.9 (205, 1C)
68.3 (173, 1C)
62.1 (1C)
20.2 (1C)
1og
1p g
1qg
[PtMe(daethyph)(ethylene)]BF4
[PtMe(daph)(ethylene)]BF4
[PtMe(daph)(propylene)]BF4
-5.1 (660, 1C)
-4.8 (660, 1C)
-3.2 (699, 1C)
74.0 (190, 2C)
72.2 (br, 2C)
96.6 (188, 1C)
68.8 (121, 1C)
1r g
1sg
[PtMe(daph)(styrene)]BF4
-0.2 (1C)
95.9 (br, 1C)
62.6 (br, 1C)
[PtMe(daph)(trans-2-butene)]BF4
-2.6 (714, 1C)
91.0 (171, 1C)
90.4 (189, 1C)
19.7 (1C)
19.1 (1C)
a
b
c
At 50.3 MHz and 298 K. Abbreviations: no attribute, singlet; br, broad. 1J Pt-C (Hz) in parentheses. 2J Pt-C (Hz) in parentheses.
Data from ref 5. e In CD3NO2
(δ 77.0 ppm) as internal standard).
(
13CHD2NO2 (δ 62.81 ppm) as internal standard). f Overlapped by the solvent signal. In CDCl3
(
13CDCl3
d
g
2a we report the olefin region in the spectrum of 1l
recorded at 203 K in CD2Cl2). This may reflect either
a fast interconversion 1′ T 1′′ or the presence of only
one enantiomeric pair, “frozen” by a strongly hindered
rotation.
We propose the latter hypothesis is the more reason-
able and further suggest that only type 1′ isomers form.
We note the following. (i) R-Olefins should suffer more
constraints than ethylene when coordinated to the metal
center. Thus, if ethylene rotation slows down at 203 K
in 1k , the same should hold true for substituted alkenes.
(ii) An inspection of molecular models reveals that very
unfavorable contacts would arise between the substitu-
ent of the R-olefin and one o-substituent of one phenyl
ring in type 1′′ isomers. These constraints do not
operate in 1′. (iii) Attempts to obtain the complex
[PtMe(daproph)(trans-2-butene)]+ failed. This, plausi-
bly, is due to the fact that in this case the aforemen-
tioned unfavorable contacts cannot be avoided. (iv)
When the steric hindrance of the ligand is substantially
reduced by using daph, the trans-2-butene complex
[PtMe(daph)(trans-2-butene)]+ (1s) can be isolated in
high yield. (v) The Pt-Me resonance in the styrene
complex 1m is unusually high field (δ -0.26 ppm). This
might be due to the shielding of the aromatic olefin
substituent, which in a type 1′ isomer lies next to Me.

[PtR(η2-olefin)(N-N)]+ Complexes
Organometallics, Vol. 16, No. 26, 1997 5985
F igu r e 1. Type 1′ and 1′′ isomers (for the sake of clarity,
one R substituent on one Ph group has been omitted).
1
F igu r e 2. Olefin region in the 400 MHz H NMR spectra
of (a) 1l at 203 K and of 1q at (b) 203 K and (c) 298 K.
Asterisks indicate the peaks pertaining to the most abun-
dant isomer (1′) of 1q (see text).
Sch em e 2
steric reasons, as already discussed elsewhere for other
square-planar Pt(II) complexes.14 More precisely, NMR
spectra indicate that rotation of trans-2-butene in 1s is
hindered at room temperature, since the olefin protons
are not equivalent and give rise to two multiplets. The
signals slightly broaden at 328 K. The olefin is more
dynamic in the phen derivative 1j, in which spectrum
broadening of the signals is detectable even at room
temperature.
On the other hand, the spectrum of the propylene
derivative of daph species 1q changes with temperature
(Figure 2). At 298 K only one sharp (and coupled)
spectral pattern is present. Below 233 K broadening
of the signals occurs, and at 203 K the two expected
enantiomeric pairs 1′ and 1′′ become clearly detectable
in a 3:1 ratio. These data indicate that at room
temperature a fast interconversion 1′ T 1′′ occurs, which
is inhibited on cooling. Since at 203 K the olefin
chemical shifts of the most abundant pair are very close
to those of the daproph analogue 1l (Figure 2), it could
be assumed that the former one has a type 1′ structure.
Similarly, the styrene daph complex 1r at 203 K exists
as two pairs of enantiomers in the approximate ratio
4:1. Two broad resonances at -0.32 and 0.38 ppm are
attributed respectively to the Pt-Me groups of the type
1′ and the type 1′′ couple, on the grounds of the
argument already presented (point v).
The comparison between the behaviors of the corre-
sponding daph and daproph complexes (e.g. 1l vs 1q)
points out the effectiveness of the steric features of the
latter ligand in promoting the selective coordination of
R-olefins to a square-planar metal center. We remem-
ber that stereoselectivity in olefin coordination can also
be successfully controlled by electronic factors, e.g.
intramolecular attractive interactions.13
X-r a y Cr ysta l Str u ctu r e of [P tMe(d a eth yp h )-
(eth ylen e)]BF 4 (1o). Complex 1o has been chosen for
X-ray studies because it represents a very close model
of the active species in Pd(II)-catalyzed homogeneous
polymerization.2 However, the lack of X-ray investiga-
tions on similar complexes does not allow a thorough
discussion about its structural features (see below).
Indeed, compounds similar to 1o, i.e. [PtMe{o-phen-
3a
ylenebis(dimethylarsine)}(ethylene)]PF6 and [PtMe-
(4,4′-t-Bu-2,2′-bipy)(ethylene)][B(Me)(C6F5)3],3c have only
been investigated spectroscopically, while those char-
acterized through X-ray studies15 do not display suf-
ficient analogies with type 1 species.
A perspective view of the cation is shown in Figure
3, and the most relevant bond distances and angles are
presented in Table 3.
Pt is in a square-planar coordination environment
with the ethylene ligand nearly perpendicular to the
coordination plane defined by Pt, N(1), N(2), and C(3).
In fact, the C(1)-C(2) axis is tilted by 87(1)° on the
coordination plane and its center is displaced 0.07(2) Å
out of it.
(13) (a) Erickson, L. E.; Hayes, P.; Hooper, J . J .; Morris, K. F.;
Newbrough, S. A.; Van Os, M.; Slangan, P. Inorg. Chem. 1997, 36,
284-290 and references therein. (b) Lazzaroni, R.; Uccello-Barretta,
G.; Bertozzi, S.; Salvadori, P. J . Organomet. Chem. 1985, 297, 117-
129 and references therein.
(14) Holloway, C. E.; Hulley, G.; J ohnson, B. F. G.; Lewis, J . J .
Chem. Soc. A 1969, 53-57.
(15) Hartley, F. R. In Comprehensive Coordination Chemistry;
Pergamon Press: New York, 1982; 642-650.
Finally, trans-2-butene can only afford one couple of
enantiomers, obviously not distinguishable through
NMR spectroscopy. For this olefin a comparatively low
rotation rate is observed. This is reasonably due to

5986 Organometallics, Vol. 16, No. 26, 1997
Fusto et al.
C2D2Cl4, CDCl3, CD3NO2, and CD2Cl2 (C2DHCl4 (δ 5.98 ppm),
CHCl3 (δ 7.26 ppm), CD2HNO2 (δ 4.33 ppm), or CDHCl2 (δ
5.32 ppm) as internal standard). Low-temperature spectra of
daph and daproph derivatives were recorded in CD2Cl2.
[PtClMe(SMe2)2],16 [Pt(phen)(dimethylfumarate)],17 1a ,5 1c,5
19
1e,5 1g,5 diacetyl bis(diarylimines)18 and Et3OBF4 were
prepared according to literature methods. Me3OBF4 (Aldrich)
is commercially available and was used without further
purification. Nitromethane was stored over A4 molecular
sieves. Dichloromethane was distilled from CaH2 immediately
before use. Elemental analyses of the products were satisfac-
tory and are reported in the Supporting Information for
representative compounds.
Syn th eses of Typ e 3 Com p lexes [P tCl(Me)(N-N)] (N-N
) d a p h (3a ), d a eth yp h (3b), d a p r op h (3c). To a suspension
of [PtClMe(SMe2)2] (0.37 g, 1.0 mmol) in 10 mL of diethyl ether
is added the appropriate N-N ligand (1.2 mmol). After 48 h
of stirring at room temperature the orange-red precipitate is
collected, washed with diethyl ether (3 × 3 mL), and dried
under vacuum (70-75% yield). 1H NMR Pt-Me resonance
(δ): 3a (in C2D2Cl4) 0.91 (2J Pt-H ) 79 Hz); 3b (in CDCl3) 0.89
(2J Pt-H ) 79 Hz); 3c (in CDCl3) 0.98 (2J Pt-H ) 80 Hz).
Syn th esis of [P tEt(p h en )(d im eth yl fu m a r a te)]BF 4 (1b).
A solution of Et3OBF4 (0.19 g, 1.0 mmol) in 5 mL of dry
dichloromethane is added to [Pt(phen)(dimethyl fumarate)]
(0.52 g, 1.0 mmol). Diethyl ether (4 mL) is added to the
resulting red solution, affording a brown oil, which slowly
transforms into a solid. This is washed with diethyl ether (2
× 4 mL) and dried under vacuum (80% yield).
F igu r e 3. Ortep view of the 1o cation. For the sake of
clarity, only some of the atoms are labeled.
Ta ble 3. Selected Bon d Len gth s (Å) a n d Va len ce
An gles (d eg) w ith Th eir Esd ’s in P a r en th eses
Pt-N(1)
Pt-C(1)
2.075(9)
2.11(2)
2.07(1)
1.28(1)
1.46(2)
Pt-N(2)
2.117(9)
2.14(2)
1.27(1)
1.27(3)
Pt-C(2)
Pt-C(3)
N(1)-C(4)
C(1)-C(2)
N(2)-C(5)
C(4)-C(5)
N(1)-Pt-N(2)
N(1)-Pt-C(2)
N(2)-Pt-C(1)
N(2)-Pt-C(3)
C(1)-Pt-C(3)
Pt-N(1)-C(4)
Pt-C(1)-C(2)
N(1)-C(4)-C(5)
76.3(4)
160.3(7)
99.3(7)
173.2(5)
87.0(8)
116.5(8)
74(1)
N(1)-Pt-C(1)
N(1)-Pt-C(3)
N(2)-Pt-C(2)
C(1)-Pt-C(2)
C(2)-Pt-C(3)
Pt-N(2)-C(5)
Pt-C(2)-C(1)
N(2)-C(5)-C(4)
163.7(7)
97.0(5)
97.8(6)
34.8(7)
88.7(7)
114.8(8)
71(1)
Syn th eses of [P tMe(p h en )(olefin )]BF 4 (1i,j). A solution
of Me3OBF4 (0.15 g, 1.0 mmol) in 2 mL of dry nitromethane is
added to [Pt(phen)(dimethyl fumarate)] (0.52 g, 1.0 mmol). To
the resulting solution containing 1a is added an excess of the
appropriate olefin. The product is crystallized by careful
addition of toluene, washed with toluene (1 × 2 mL) and
pentane (2 × 5 mL), and dried under vacuum (65-70% yield).
Syn th esis of [P tEt(p h en )(eth ylen e)]BF 4 (1d ). To a
solution of 1b in dry dichloromethane prepared as described
above with 0.52 g (1.0 mmol) of [Pt(phen)(dimethyl fumarate)]
as starting material is added an excess of ethylene. Crystal-
lization of the product starts at once. After 10 min the complex
is collected, washed with dichloromethane, and dried under
vacuum (80% yield).
Syn th eses of [P tEt(p h en )(olefin )]BF 4 (olefin ) P r op y-
len e (1f), Styr en e (1h ). To a solution of 1b in dry dichlo-
romethane prepared as described above, with 0.52 g (1.0 mmol)
of [Pt(phen)(dimethyl fumarate)] as starting material, is added
an excess of olefin. The product is crystallized by careful
addition of toluene, washed with toluene (1 × 2 mL) and
pentane (2 × 5 mL), and dried under vacuum (65-70% yield).
Syn th eses of [P tMe(N-N)(olefin )]BF 4 (1k -s). To a
suspension of AgBF4 (0.195 g, 1.0 mmol) in 10 mL of dichlo-
romethane is added an excess of the appropriate olefin. To
the resulting mixture is added a solution of [PtClMe(N-N)] (1.0
mmol) in 5 mL of dry dichloromethane at 273 K. After 48 h
of stirring at room temperature AgCl is removed by filtration
on Celite and the volume of the resulting solution is reduced
to 5 mL under vacuum. Toluene (15 mL) is stratified on the
solution and the mixture kept at 277 K for 24 h. The resulting
crystals are washed with toluene (1 × 5 mL) and pentane (2
× 5 mL) and dried under vacuum (80-90% yield). In the case
of the complexes 1m ,1r crystallization is best achieved by
substituting diethyl ether for toluene.
116(1)
116(1)
The length (1.27(1) Å) of the olefinic bond C(1)-C(2)
is surprisingly short and would require confirmation
from an X-ray analysis where the disorder and absorp-
tion effects were absent and minimized, respectively.
Also, the phenyl groups at N(1) and N(2) are perpen-
dicular to the equatorial plane within a few degrees. The
ethyl groups linked to them were found to be disordered,
-
as were the BF4 ions. According to the NMR results,
the length of the Pt-N(2) bond (2.117(9) Å), which is
opposite to the methyl group, is significantly larger than
that of the Pt-N(1) bond (2.075(9) Å), which faces the
ethene group, most probably as a consequence of the
aforementioned higher trans influence of alkyl groups
relative to olefins.
Con clu d in g Rem a r k s
This paper describes two effective methods for the
synthesis of cationic platinum(II) complexes containing
the cis-{PtR(olefin)} moiety. The complexes are stable
to heat and air and do not undergo insertion of the olefin
into the Pt-R bond. They are involved in a dynamic
exchange process involving the alkene ligand, which has
been investigated through NMR spectroscopy. It has
been found that nitrogen chelates which afford crowding
above and below the coordination plane strongly hinders
the exchange. The same steric feature prompts the
selective coordination of R-olefins, leading to the forma-
tion of a single pair of enantiomers.
Cr ysta l Str u ctu r e Deter m in a tion of [P tMe(d a eth yp h )-
(eth ylen e)]BF 4 (1o). The compound was recrystallized from
Studies on the reactivity of type 1 complexes are now
in progress.
(16) Scott, D.; Puddephatt, R. J . Organometallics 1986, 1643-1648.
(17) De Felice, V.; De Renzi, A.; Ruffo, F.; Tesauro, D. Inorg. Chim.
Acta 1993, 219, 169-178.
Exp er im en ta l Section
(18) tom Dieck, H.; Svoboda, M.; Greiser, T. Z. Naturforsch. 1981,
36B, 823-832.
NMR spectra were recorded on a 200 MHz (Varian Model
Gemini), a 250 MHz (Bruker Model AC-250), or a 400 MHz
spectrometer (Bruker Model DRX-400). The solvents were
(19) Meerwin, H. Organic Syntheses; Wiley: New York, 1973;
Collect. Vol. V, pp 1080-1082.

[PtR(η2-olefin)(N-N)]+ Complexes
Organometallics, Vol. 16, No. 26, 1997 5987
Ta ble 4. Su m m a r y of Cr ysta llogr a p h ic Da ta
methylene chloride/toluene. X-ray data were collected at room
temperature on an Enraf-Nonius CAD4-F automatic diffrac-
tometer using Cu KR graphite-monochromated radiation
operating in the ω/θ scan mode. The unit cell parameters were
obtained by a least-squares fitting of the setting values of 25
strong reflections in the θ range 24 e θ e 27°. Three
monitoring reflections, measured every 500 reflections, showed
insignificant intensity fluctuations. In addition to the usual
corrections for Lorentz and polarization factors, a semiempiri-
cal correction for absorption20 was applied (maximum and
minimum values of the correction factor were 0.78 and 1.00).
cryst size/mm
formula
fw
0.05 × 0.10 × 0.20
PtN2C27H39‚BF4
673.5
cryst syst
space group
a/Å
monoclinic
Cc
35.834(9)
b/Å
9.856(1)
c/Å
18.207(5)
â/deg
116.89(2)
5735(2)
V/Å3
Z
4 (2 mols. in asymm. unit)
The systematic absences of the diffraction pattern and the
value of measured density are consistent with two space
groups: C2/c (No. 15 in International Tables) with one
molecule and Cc (No. 9) with two molecules in the asymmetric
unit, respectively. The structure was solved by the heavy-atom
method by using the space group C2/c. Throughout the
refinement procedure clear evidence of disorder effects affect-
F(000)
2672
1.56
1.56
1.540 56
72
96.1
5640
3609
259
0.929
0.051
0.060
D
D
measd/g cm-3
calcd/g cm-3
λ(Cu KR)/Å
θ
max/deg
µ/cm-1
no. of indep rflns
no. of rflns above 3σ(I)
no. of refined params
goodness of fit
R
-
ing the ethyl groups and the BF4 anion were detected. In
-
particular, for BF4 the difference Fourier map showed,
unexpectedly, not one but two independent volumes of electron
density apt to describe the ion in a disordered arrangement.
Rw
-
With a best fitting of BF4 in these volumes and assigning
calculated positions, were assigned the isotropic equivalent
thermal parameters of the carrier atoms and included in the
final refinement as riding atoms. The H-atoms of ethyl groups
were neglected. The final Fourier difference map showed no
peaks greater than 0.98 e Å-3. The largest shift to esd ratio
in the final cycle was 0.1.
Full lists of bond distances and angles, atom parameters,
and anisotropic thermal parameters of the non-hydrogen
atoms have been deposited as Supporting Information.
occupancy factors equal to 0.5, the structure was refined to
completeness with a final R index of 0.057.
In an attempt to get a better description of the BF4- anion,
the refinement procedure was repeated by using the space
group Cc, which is the less restrained basis for describing the
crystal structure. Although the results were substantially
unchanged for the complex molecules, the use of the Cc space
group was preferred because it allows a better treatment of
the disordered anions. The skeletons of the two cations related
by a pseudo symmetry center at x ) 0, y ) 0, and z ) 0 were
Ack n ow led gm en t. We thank the Consiglio Nazio-
nale delle Ricerche and the Ministero dell’Universita` e
della Ricerca Scientifica e Tecnologica for financial
support and the Centro Interdipartimentale di Metod-
ologie Chimico-Fisiche, Universita` di Napoli “Federico
II”, for NMR, X-ray, and computing facilities.
constrained in the least-squares procedure. The minimized
-1
quantity was ∑w(∆F)2 with w
) σ2(Fo) + (0.02Fo)2 + 1.0,
where σ is derived from counting statistics. Details of the
structure analysis are listed in Table 4.
The non-hydrogen atoms of the cation skeleton were refined
anisotropically and those of the disordered ethyl groups
-
isotropically. A standard BF4 group with isotropic thermal
Su p p or tin g In for m a tion Ava ila ble: Tables giving aniso-
tropic thermal parameters, bond distances and angles, and
atomic coordinates for 1o and a table of elemental analyses
for representative complexes (5 pages). Ordering information
is given on any current masthead page.
parameters equal for all atoms was fitted as well as possible
in the appropriate regions of the electron density map and
included in structure factor calculations. H-atoms, placed in
(20) North, A. C. T.; Phillips, D. C.; Mathewes, F. S. Acta Crystal-
logr., Sect. A 1968, 24, 351.
OM970428F