Neutral square-planar olefin/alkyl platinum(ii) complexes containing a N,N′-imino-amide ligand. Experimental and theoretical evidence of relevant π-back-donation in the platinum-olefin bond

Article abstract of DOI:10.1021/om049968k

A new class of platinum(II) compounds of the formula [PtMe(olefin)(N,N'- imino-amide chelate)] is described (olefin = ethylene, propylene, styrene, allyl alcohol, methyl vinyl ketone, methyl acrylate; N,N'-imino-amide chelate = N,N'-(1,2-dimethyl-1,2-ethanediylidene)bis-(2,6-diisopropylaniline)). The neutral complexes exhibit square-planar coordination with a cis arrangement of the olefin and the alkyl group. The compounds have been characterized through one- and two-dimensional NMR spectroscopy, which has disclosed that only one isomer is present in solution. This isomer exhibits the alkene and the N(amido) atom in trans positions, while the alkene substituent is oriented toward the Pt-Me vector. The nature and the arrangement of the ligands seem suitable to favor a π-back-donation contribution to the Pt-olefin bond to an extent unprecedented for square-planar compounds, as discussed on the basis of NMR parameters and theoretical calculations.

Full text of DOI:10.1021/om049968k

Organometallics 2004, 23, 2137-2145
2137
Neu tr a l Squ a r e-P la n a r Olefin /Alk yl P la tin u m (II)
Com p lexes Con ta in in g a N,N′-Im in o-Am id e Liga n d .
Exp er im en ta l a n d Th eor etica l Evid en ce of Releva n t
π-Ba ck -Don a tion in th e P la tin u m -Olefin Bon d
Luigi Cavallo
Dipartimento di Chimica, Universita` di Salerno, via Salvador Allende,
I-84081 Baronissi (SA), Italy
Alceo Macchioni, Cristiano Zuccaccia, and Daniele Zuccaccia
Dipartimento di Chimica, Universita` di Perugia, via Elce di Sotto 8, 06123 Perugia, Italy
Ida Orabona and Francesco Ruffo*
Dipartimento di Chimica, Universita` di Napoli “Federico II”, Complesso Universitario di
Monte S. Angelo, via Cintia, I-80126 Napoli, Italy
Received J anuary 12, 2004
A new class of platinum(II) compounds of the formula [PtMe(olefin)(N,N′-imino-amide
chelate)] is described (olefin ) ethylene, propylene, styrene, allyl alcohol, methyl vinyl ketone,
methyl acrylate; N,N′-imino-amide chelate ) N,N′-(1,2-dimethyl-1,2-ethanediylidene)bis-
(2,6-diisopropylaniline)). The neutral complexes exhibit square-planar coordination with a
cis arrangement of the olefin and the alkyl group. The compounds have been characterized
through one- and two-dimensional NMR spectroscopy, which has disclosed that only one
isomer is present in solution. This isomer exhibits the alkene and the N(amido) atom in
trans positions, while the alkene substituent is oriented toward the Pt-Me vector. The nature
and the arrangement of the ligands seem suitable to favor a π-back-donation contribution
to the Pt-olefin bond to an extent unprecedented for square-planar compounds, as discussed
on the basis of NMR parameters and theoretical calculations.
In tr od u ction
Recently,1 we described a new family of cationic
Pt(II) compounds (1 in Figure 1), showing a cis arrange-
ment of an alkyl group and an olefin.
The compounds are closely related to the catalyst
resting states involved in the palladium- and nickel-
catalyzed polymerization of alkenes.2 In these cases, an
N,N-chelate with hindrance above and below the coor-
dination plane (i.e. N,N′-bis(2,6-diisopropylphenyl)bu-
tane-2,3-diimine) is used to favor chain growth by
simultaneously inhibiting side reactions. The same
steric feature was employed by us to enhance the kinetic
inertness of type 1 compounds, thus allowing coordina-
tion of a wide variety of alkenes (Figure 1).1
F igu r e 1. Structure of complexes of type 1.
Sch em e 1. Syn th esis of Com p lexes of Typ e 2
In this report, we communicate that a new class of
olefin/alkyl complexes can be generated by removing one
proton from the ligand backbone of type 1 compounds
(Scheme 1).
The corresponding neutral species 2 contain the N,N′-
imino-amide ligand N,N′-(1,2-dimethyl-1,2-ethanediyli-
dene)bis(2,6-diisopropylaniline) (depran), of the general
type recently used as an auxiliary in Zr-,3 Ni-,4 and Al-
catalyzed5 alkene polymerization.
As described below, the complexes exhibit high se-
lectivity of coordination. Furthermore, the NMR fea-
tures suggest that an unprecedented degree of π-back-
donation is involved in the platinum-olefin bond.
* To whom correspondence should be addressed. Tel: +39-081-
674460. Fax: +39-081-674090. E-mail: ruffo@unina.it.
(1) (a) Fusto, M.; Giordano, F.; Orabona, I.; Panunzi, A.; Ruffo, F.
Organometallics 1997, 16, 5981-5987. (b) Ganis, P.; Orabona, I.; Ruffo,
F.; Vitagliano, A. Organometallics 1998, 17, 2646-2650.
(2) Ittel, S. D.; J ohnson, L. K.; Brookhart, M. Chem. Rev. 2000, 100,
1169-1204 and references therein.
10.1021/om049968k CCC: $27.50 © 2004 American Chemical Society
Publication on Web 03/27/2004

2138 Organometallics, Vol. 23, No. 9, 2004
Ta ble 1. Selected 1H NMR Da ta a for Typ e 2 Com p lexes
Cavallo et al.
compd
formula
Pt-Meb
H(olefin)b
dCH2
2a
[PtMe(ethylene)(depran)]
-0.26 (77, s, 3H)
2.51 (54, s, 4H)
4.45 (7, s, 1H)
3.88 (s, 1H)
4.43 (9, s, 1H)
3.81 (s,1H)
2b
2c
2d
2e
2f
[PtMe(propylene)(depran)]
-0.19 (78, s, 3H)
-0.71 (79, s, 3H)
-0.18 (77, s, 3H)
-0.28 (78, s, 3H)
-0.17 (78, s, 3H)
2.93 (62, m, 1H)
2.65 (65, d, 1H)
2.63 (43, d, 1H)
4.45 (74, dd, 1H)
3.05 (42, d, 1H)
2.35 (61, d, 1H)
3.09 (58, m, 1H)
2.69 (42, d, 1H)
2.67 (58, d, 1H)
3.81 (68, dd, 1H)
2.92 (40, d, 1H)
2.27 (56, d, 1H)
3.32 (65, dd, 1H)
3.07 (38, d, 1H)
2.48 (59, d, 1H)
[PtMe(styrene)(depran)]
4.48 (s, 1H)
3.89 (s, 1H)
[PtMe(allyl alcohol)(depran)]
[PtMe(methyl vinyl ketone)(depran)]
[PtMe(methyl acrylate)(depran)]
4.51 (9, s, 1H)
3.91 (s, 1H)
4.61 (9, s, 1H)
4.05 (s, 1H)
4.58 (8, s, 1H)
4.02 (s, 1H)
a
At 298 K and 300 MHz, in CDCl3 (CDCl3, δ 7.26, as internal standard). Abbreviations: s, singlet; d, doublet; dd, double doublet; m,
multiplet. 2J (Pt-H) in parentheses (in Hz; when measurable).
b
Ta ble 2. Selected 13C NMR Da ta a for Typ e 2 Com p lexes
c
compd
formula
Pt-Meb
CH2(olefin)b [∆δ]d
CH(olefin)b [∆δ]e
dCH2
ethylene
122.8
propylene
styrene
allyl alcohol
methyl vinyl ketone
methyl acrylate
115.9
113.7
114.9
128.7
136.2
136.9
137.5
137.2
128.2
130.4
2a
2b
2c
2d
2e
2f
[PtMe(ethylene)(depran)]
[PtMe(propylene)(depran)]
[PtMe(styrene)(depran)]
[PtMe(allyl alcohol)(depran)]
[PtMe(methyl vinyl ketone)(depran)]
[PtMe(methyl acrylate)(depran)]
-8.0 (736)
-6.4 (780)
-3.1(777)
-8.0 (750)
-3.0 (731)
-4.2 (738)
55.6 (196) [67.2]
56.5 (173) [59.4]
48.6 (200) [65.1]
55.1 (176) [59.8]
48.3 (188) [80.4]
50.1 (189) [80.3]
92.4 (42)
92.1 (45)
92.7 (47)
93.8 (43)
95.5 (49)
95.2(42)
72.6 (206) [63.6]
71.8 (198) [65.1]
75.0 (224) [62.5]
66.3 (192) [70.9]
57.3 (214) [70.9]
a
b
c
At 298 K and 75.45 MHz, in CDCl3 (13CDCl3, δ 77.0, as internal standard). 1J (Pt-C) in parentheses (in Hz). 3J (Pt-C) in parentheses
(in Hz). Difference between δ(CH2) of the free olefin and δ(CH2) of the coordinated olefin. e Difference between δ(CH) of the free olefin
and δ(CH) of the coordinated olefin.
d
Theoretical considerations are also provided, which give
a rationale of this spectral evidence.
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion of Typ e 2 Com -
p ou n d s. An immediate reaction takes place when
compounds of type 1 are treated with KOH (Scheme 1).
The products 2, isolated in high yields, have been
characterized by standard 1D and 2D multinuclear
NMR spectroscopy (Tables 1 and 2).
The key points that differentiate the proton NMR
spectra of type 2 compounds with respect to type 1 are
F igu r e 2. Possible isomers for complexes of type 2 with
(i) the resonances of one iminic CH3 group are missing
and (ii) two doublets are present in the alkene region
that show scalar correlation with the same carbon
resonances (ca. 95 ppm) and long-range correlation with
the two carbon resonances at higher frequencies. These
observations are consistent with the transformation of
the [NdCCH3] moiety into [NCdCH2]- as a consequence
of proton abstraction by OH-. Accordingly, a low value
of proton-proton scalar coupling constant (ca. 1 Hz) is
observed between HA and HB, as expected for a gem-
R-olefins.
type coupling constant in an sp2 carbon.6 In addition,
the low-field doublet (HB) shows the typical satellites,
due to the scalar coupling with 195Pt (4J PtH ) ca. 5-10
Hz), which also ensures that the ligand is still bonded
to platinum.
With ethylene two isomers can form (2I and 2III
;
Figure 2), while with R-olefins up to four species are
possible (2I-2IV, each one as an enantiomeric couple).
In all cases, a unique spectral pattern has been
observed, thus indicating that only one isomer is present
(3) Kim, Y. H.; Kim, T. H.; Kim, N. Y.; Cho, E. S.; Lee, B Y..; Shin,
D. M.; Chung, Y. K. Organometallics 2003, 22, 1503-1511.
(4) Kim, Y. H.; Kim, T. H.; Lee, B. L.; Woodmansee, D.; Bu, X.;
Bazan, G. C. Organometallics 2002, 21, 3082-3084.
(5) Pappalardo, D.; Tedesco, C.; Pellecchia, C. Eur. J . Inorg. Chem.
2002, 621-628.
(6) Gu¨nter, H. NMR Spectroscopy: Basic Principles, Concepts, and
Application in Chemistry, 2nd ed.; Wiley: Chichester, U.K., 1995; pp
108-114.

Pt(II) Complexes with an N,N′-Imino-Amide Ligand
Organometallics, Vol. 23, No. 9, 2004 2139
1
F igu r e 3. Relevant sections of the H-NOESY NMR spectrum of complex 2b.
in solution. Complete NMR characterization, and in
particular NOESY spectroscopy, allows unambiguous
determination of the geometrical structure of this
isomer.7 In fact, as observed in previous studies on type
1 and similar compounds,7 due to the presence of
restricted rotations around single bonds (for example,
the phenyl rotations around the N-Cipso bond) and to
the chirality of the compounds, all the Me resonances
show separate signals that can be assigned. In the
following, the discussion relative to compound 2b is
given as an example (Figure 3). The low-frequency,
easily assignable Pt-Me resonance serves as a starting
point. Only two of the four septets due to the isopropyl
CH groups give NOESY cross-peaks with Pt-Me, and
they are therefore assigned to CH(Mu) and CH(Md)8
(Figure 3a). The observation of selective strong dipolar
(7) (a) Macchioni, A.; Magistrato, A.; Orabona, I.; Ruffo, F.; Roth-
lisberger, U.; Zuccaccia, C. New J . Chem. 2003, 455-458. (b) Zuccaccia,
C.; Macchioni, A.; Orabona, I.; Ruffo, F. Organometallics 1999, 18,
4367-4372.

2140 Organometallics, Vol. 23, No. 9, 2004
Cavallo et al.
correlations between CH(Mu) and CH(Md) and one of
the two amido-olefinic protons identifies HA in Figure
3b. The latter interact in a dipolar fashion with HB,
which shows NOE with a methyl group assigned to the
backbone Me group (Figure 3c). The resonance of the
imino Me group (1.97 ppm) shows strong cross-peaks
with the remaining two septets due to the isopropyl CH
groups, which are assigned to CH(Ou) and CH(Od).
The further observation that CH(Ou) and CH(Od)
interact in a dipolar fashion with the protons of the η2-
coordinated propylene (Figure 3d) finally demonstrates
that the isomer present in solution is the one in which
the imine arm of the dinitrogen ligand lies in a cis
position with respect to the η2-coordinated propylene
(2I). The spatial orientation of the olefinic moiety
deserves additional comment. In particular, as can be
seen from Figure 3d, the CH2dCH(Me) proton selec-
tively interacts with CH(Od), while the CH2(cis)dCH(Me)
proton interacts with CH(Ou), indicating an almost
forbidden rotation of the R-olefin around the Pt-al-
kene bond.9 The additional observation that the
Pt-Me group strongly interacts with CH2(trans)dCH(Me)
and CH2dCH(Me) groups confirms that the η2-coordi-
nated propylene preferentially orients the Me group
toward Pt-Me (isomer 2I).
In all cases the signals of the R-olefin protons show
the typical pattern and are significantly shifted to high
field with respect to those of the free alkenes of ca. 2-3
ppm. The signals are coupled to 195Pt, which indicates1a
slow exchange between bound and free alkene at room
temperature on the NMR time scale. Rotation of R-ole-
fins along the Pt-alkene bond (i.e., the interconversion
2I f 2II) is also inhibited at room temperature, as
demonstrated by the presence of selective NOE contacts
between the olefin protons and the adjacent ligands, as
just mentioned for the propylene compound. Lack of
rotation has been attributed to the severe contacts
between the olefin substituent and an isopropyl group,
which destabilize the 2II isomer.1a
On the other hand, ethylene appears as a singlet at
2.51 ppm coupled to 195Pt. The equivalence of the four
protons suggests that this unhindered alkene freely
rotates at room temperature. At 253 K the singlet is
already resolved into two apparent doublets (2.57 and
2.12 ppm, AA′BB′ multiplet), as a consequence of
inhibited dynamic behavior. A low-temperature 13C
NMR spectrum (233 K in CDCl3) showed substantially
no modification of the carbon olefin resonance with
respect to those recorded at room temperature (∆δ )
δ298 K - δ233 K ) 0.1 ppm).
to the olefin. Several studies have been addressed to
appraise the magnitude of these contributions. Most of
the studies11 have been performed on platinum olefin
compounds, due to their great chemical inertness and
the wide choice of alkenes and coordination environ-
ments, although sometimes controversial results were
found.11h,i
However, it is accepted12 that in square-planar Pt(II)
compounds σ-donation is by far more important than
π-back-donation, as demonstrated by the remarkable
number of known complexes with electron-rich olefins
compared to those containing alkenes with electron-
withdrawing substituents.1b
Herein, we wish to emphasize that the NMR fea-
tures give evidence that the coordination environment
of type 2 compounds favors π-back-donation to an extent
unprecedented for square-planar compounds. The spec-
tral features, which agree with this assertion, are as
follows.
(i) Several reports11a,c,g,i,13 conclude that the high-field
coordination shift of the olefin carbons increase with the
π-back-donation contribution. As far as we know, the
∆δ values found for type 2 compounds are unmatched
in Pt(II) square-planar complexes.14 This is evident by
inspection of Table 3, which reports relevant 13C NMR
data for a number of representative ethylene and
propylene compounds for useful comparison.23
It is also interesting to note (see Table 2) that the
coordination shift is even more pronounced for the
(10) (a) Dewar, M. J . S. Bull. Soc. Chim. Fr. 1951, 18, C71-C79.
(b) Chatt, J .; Duncanson, L. A. J . Chem. Soc. 1953, 2939-2947.
(11) For relevant studies on platinum(II) complexes, see: (a) Hart-
ley, F. R. In Comprehensive Organometallic Chemistry; Pergamon
Press: New York, 1982; Vol. 6, p 471. (b) J esse, A. C.; Stufkens, D. J .;
Vrieze, K. Inorg. Chim. Acta 1979, 32, 87-91. (c) Meester, M. A. M.;
Stufkens, D. J .; Vrieze, K. Inorg. Chim. Acta 1977, 21, 251-258. (d)
Cooper, D. J .; Powell, J . Inorg. Chem. 1976, 15, 1959-1968. (e) Nyburg,
S. C.; Simpson, K.; Wong-Ng, W. J . Chem. Soc., Dalton Trans. 1976,
1865-1870. (f) Meester, M. A. M.; van Dam, H.; Stufkens, D. J .;
Oskam, A. Inorg. Chim. Acta 1976, 20, 155-160. (g) Chisholm, M. H.;
Clark, H. C.; Manzer, L. E.; Stothers, J . B.; Ward, J . E. H. J . Am.
Chem. Soc. 1975, 97, 721-727. (h) Olah, G. A.; Mo, Y. K. J . Am. Chem.
Soc. 1972, 94, 9244-9246. (i) Chisholm, M. H.; Clark, H. C.; Manzer,
L. E.; Stothers, J . B. J . Chem. Soc. 1972, 94, 5087-5089.
(12) (a) Kurosawa, H.; Ikeda, I. J . Organomet. Chem. 1992, 428,
289-301. (b) Kurosawa, H.; Urabe, A.; Emoto, M. J . Chem. Soc., Dalton
Trans. 1986, 891-893.
(13) See also, for example: (a) Foley, S. R.; Stockland, S. A., J r.;
Shen, H.; J ordan, R. F. J . Am. Chem. Soc. 2003, 125, 4350-4361. (b)
Nicolaides, A.; Smith, J . M.; Kumar, A.; Barnhart, D. M.; Thatcher
Borden, W. Organometallics 1995, 14, 3475-3485. (c) Caruso, F.;
Camalli, M.; Pellizer, G.; Asaro, F.; Lenarda, M. Inorg. Chim. Acta
1991, 181, 167-176. (d) Mink, L.; Rettig, M. F.; Wing, R. M. J . Am.
Chem. Soc. 1991, 113, 2065-2071. (e) Al-Najjar, I. M.; Amin, H. B. J .
Chem. Soc., Dalton Trans. 1990, 429-436.
(14) The only exception is given by an elusive hydrido complex (entry
7 of Table 3), characterized at 180 K due to its tendency to undergo
insertion of ethylene into the Pt-H bond.
(15) Hahn, C.; Herdtweck, E.; Morvillo, P.; Vitagliano, A. Organo-
metallics 2002, 21, 1807-1818.
The NMR parameters give useful insight into the
nature of the metal-olefin bond in type 2 complexes. It
is known that the model originally proposed by Chatt,
Dewar, and Duncanson10 invokes σ-donation from the
olefin to the metal and π-back-donation from the metal
(16) Baar, C. R.; J enkins, H. A.; J ennings, M. C.; Yap, G. P. A.;
Puddephatt, R. J . Organometallics 2000, 19, 4870-4877.
(17) Yang, K.; Lachicotte, R. J .; Eisenberg, R. Organometallics 1998,
17, 5102-5113.
(18) Basickes, N.; Hutson, A. C.; Sen, A.; Yap, G. P. A.; Rheingold,
A. L. Organometallics 1996, 15, 4116-4118.
(8) “M” and “O” indicate groups that stay in cis positions with respect
to methyl and olefin groups, respectively. “u” and “d” discriminate the
up and down isopropyl orientations with respect to the olefin R group.
Finally, “b” and “f” stand for backward and forward with respect to
the plane containing the two phenyl groups (assumed to be coplanar).
(9) Depending on the spectral positions and overlaps of the different
resonances, assignment of the “up” and “down” resonances8 on the
ligand arm trans to the olefin was possible by observation of either a
weak NOE between the olefin R group and “Md” resonances or a weak
NOE between CH(Ou) and CH(Mu) or CH(Od) and CH(Md), respec-
tively.
(19) Carr, N.; Mole, L.; Orpen, A. G.; Spencer, J . L. J . Chem. Soc.,
Dalton Trans. 1992, 2653-2662.
(20) Scott, J . D.; Puddephatt, R. J . Organometallics 1986, 5, 1253-
1257.
(21) Green, M.; Sarhan, G. K. K. Inorg. Chim. Acta 1981, 54, L67-
L68.
(22) Shinoda, H.; Yamaguchi, Y.; Saito, Y. Inorg. Chem. 1979, 18,
673-678.
(23) Higher high-field shifts have been recorded only for three-
coordinate Pt(0)24 or five-coordinate Pt(II)25 complexes, where the
importance of the π-back-donation contribution is acknowledged.

Pt(II) Complexes with an N,N′-Imino-Amide Ligand
Organometallics, Vol. 23, No. 9, 2004 2141
Ta ble 3. 13C NMR Olefin Da ta a for Rep r esen ta tive Eth ylen e a n d P r op ylen e Com p ou n d s of P la tin u m (II)
entry
formula
[PtMe(ethylene)(depran)] (2a )
CH2(olefin) [∆δ]b
Ethylene Compounds
CH(olefin) [∆δ]c
δ(CH) - δ(CH2) ref
1
2
3
4
55.6 (196) [67.2]
77.9 (116) [44.9]
78.0 (153) [44.8]
73.8 (192) [49.0]
[Pt(ethylene){2,6-bis((diphenylphosphino)methyl)pyridine}]2+
[Pt(ethylene){cis-1-(NdCHC6H4)-2-(NdCHPh)C6H10}]+
[PtMe(ethylene){N,N′-bis(2,6-diisopropylphenyl)-
butane-2,3-diimine}]+ (1a )
15
16
1a
5
[PtMe(ethylene){glyoxal bis(2-(methoxymethyl)-
74.3 (99)d [48.5]
17
4,6-di-tert-butylphenyl)imine}]+
6
7
8
[Pt2(µ-Cl)2Et2(ethylene)]
63 (260) [59.8]
51.0 (160) [71.8]
72.2 (168) [50.6]
18
19
13e
[PtH(ethylene){1,2-bis(di-tert-butylphosphino)ethane}]+
trans-[PtCl2(ethylene){N-methyl-1-(N-methylpyrrol-1-yl)-
ethanimine}]
9
[Pt2(µ-Cl)2Me2(ethylene)2]
trans-[PtCl2(ethylene)(dimethylamine)]
[PtCl(acetylacetonate)(ethylene)]
63.4 (254) [59.4]
74.8 (156) [48]
20
21
10
11
12
13
14
15
67.0 (214) [55.8]
61.1 (215) [61.7]
67.3 (194) [55.5]
75.3 (165) [47.5]
75.1 (164) [47.7]
11b
11c
11c
11c
11d
trans-[PtCl2(ethylene)(4-methyl-pyridine N-oxide)]
[PtCl3(ethylene)]-
trans-[PtCl2(ethylene)(pyridine)]
trans-[PtCl2(ethylene)(4-methylpyridine)]
Propylene Compounds
56.5 (173) [59.4] 72.6 (206) [63.6]
16
17
18
19
[PtMe(propylene)(depran)] (2b)
16.1
[Pt(propylene){2,6-bis((diphenylphosphino)methyl)pyridine}]2+ 74.3 (138) [41.7] 103.5 (108) [31.1]
29.2
33.0
27.5
15
16
1a
[Pt(propylene){cis-1-(NdCHC6H4)-2-(NdCHPh)C6H10}]+
[PtMe(propylene){N,N′-bis(2,6-diisopropylphenyl)-
butane-2,3-diimine}]+ (1b)
70.8 (155) [45.1] 103.8 (150) [32.4]
70.5 (171) [45.4] 98.0 (185) [38.2]
20
trans-[PtCl2(propylene){N-methyl-1-(N-methylpyrrol-1-yl)-
ethanimine}]
69.8 (160) [46.1] 95.5 (156) [40.7]
25.7
13e
21
22
23
24
25
26
27
trans-[PtCl2(propylene)(dimethylamine)]
trans-[PtCl(propylene){N-methyl-(S)-prolinato}]
[PtCl(acetylacetonate)(propylene)]
71.1 (153) [44.8] 98.2 (144) [38.0]
71.3 (165) [44.6] 98.2 (154) [38.0]
64.9 (210) [51.0] 88.8 (200) [47.4]
59.1 (213) [56.8] 83.4 (202) [52.8]
66.4 (190) [47.3] 86.9 (188) [49.3]
71.4 (159) [44.5] 99.5 (152) [36.7]
71.5 (159) [44.4] 99.2 (151) [37.0]
27.1
26.9
23.9
24.3
20.5
28.1
27.7
21
22
11b
11c
11c
11c
11d
trans-[PtCl2(propylene)(4-methylpyridine N-oxide)]
[PtCl3(propylene)]-
trans-[PtCl2(propylene)(pyridine)]
trans-[PtCl2(propylene)(4-methylpyridine)]
a
b
1J (Pt-C) in parentheses (in Hz). Difference between δ(CH2) of the free olefin and δ(CH2) of the coordinated olefin. c Difference
d
between δ(CH) of the free olefin and δ(CH) of the coordinated olefin. Average value between those of two diastereomers.
electron-poor olefins, i.e. methyl acrylate and methyl
vinyl ketone, where the presence of electron-withdraw-
ing groups is expected to reinforce the charge transfer
from the metal.
that part of the shift is due to the shielding of the aryl
rings of depran which face the olefin protons.
(iv) Finally, J Pt-C coupling constants between olefin
1
carbons and 195Pt for type 2 complexes are among the
highest of those reported in Table 3 for other square-
planar Pt(II) complexes. Also, in this case, a correlation
between this spectral evidence and the extent of π-back-
donation seems to be valid.10d,25
(ii) A small value for δ(CH) - δ(CH2) of coordinated
propylene is also considered diagnostic of high π-back-
donation, because “the chemical shifts of saturated sp3
carbon atoms are less sensitive to methyl substitution
of H relative to an olefin sp2 atom.”11d For complex 2b
this difference is only 16.1 ppm, a value which can be
usefully compared with the figures reported in Table 3
for representative propylene compounds. In all cases,
values higher than 20 have been found, even for
[PtCl3(propylene)]-, where the negative charge on the
metal is likely to be released through an effective
π-back-donation.
DF T Ca lcu la tion s. A theoretical investigation was
undertaken, aiming to verify the actual relationship
between the unusual NMR features and the extent of
π-back-donation and to rationalize the relevant bonding
properties in type 2 compounds. The investigated model
systems are reported in Figure 4.
In all of the cases, i.e. with or without a coordinated
ethylene molecule, the calculated structures assume a
square-planar geometry. The overall structures of the
alkene-free species are substantially unmodified by
ethylene coordination, with the exception of the Pt-N
bond trans to the coordinating olefin. In 1QMa and
2IIIQMa the Pt-N(imino) bond trans to the incoming
ethylene molecule is elongated by 0.13 and 0.12 Å
relative to 1QM0 and 2IIIQM0, respectively. A remark-
ably different case is 2IQM0, in which the Pt-N(amido)
bond elongates by only 0.05 Å upon olefin coordination.
The similar elongation exhibited by the Pt-N(imino)
bonds in 1QMa and 2IIIQMa and the remarkably
different elongation of the Pt-N(imino) and Pt-N-
(amido) bonds in 2IIIQMa and 2IQMa clearly indicate
that the different behaviors of the Pt-N(imino) and
Pt-N(amido) bonds upon ethylene coordination are
(iii) Also, the high-field shift of the olefin protons in
1
the H NMR spectra has been used as a probe of the
extent of π-back-donation.26 In this respect, it should
be noted that ∆δ values for type 2 compounds (2.5-3
ppm) are substantially higher than those typical for
Pt(II) square-planar species,25,27 even by considering
(24) See, for example: van Asselt, R.; Elsevier, C. J .; Smeets, W. J .
J .; Spek, A. L. Inorg. Chem. 1994, 33, 1521-1531.
(25) Albano, V. G.; Natile, G.; Panunzi, A. Coord. Chem. Rev. 1994,
133, 67-114.
(26) See, for example: Fanizzi, F. P.; Intini, F. P.; Maresca, L.;
Natile, G.; Lanfranchi, M.; Tiripicchio, A. J . Chem. Soc., Dalton Trans.
1991, 1007-1015.
(27) (a) van der Poel, H.; van Koten, G. Inorg. Chem. 1981, 20, 2941-
2950. (b) van der Poel, H.; van Koten, G. Inorg. Chem. 1981, 20, 2950-
2956.

2142 Organometallics, Vol. 23, No. 9, 2004
Cavallo et al.
F igu r e 4. DFT structures of the alkene-free and ethylene-
coordinated model systems. 1QMa , 2IQMa , and 2IIIQMa
are models for the 1a , 2Ia , and 2IIIa real systems experi-
mentally investigated. 1QM0, 2IQM0, and 2IIIQM0 indi-
cate the three alkene-free species obtained by subtracting
ethylene from 1QMa , 2IQMa , and 2IIIQMa , respectively.
Distances are given in Å.
F igu r e 5. Most of the relevant molecular orbitals of 1QM0
(left) and 2IQM0 (right). The N-Pt-N bonds lie in the xy
plane, and the incoming ethylene molecule approaches the
Pt atom along the x axis. For the sake of simplicity the
MO1 molecular orbitals of 1QM0 and 2IQM0 have been
sketched as isoenergetic.
Ta ble 4. Ca lcu la ted Va lu es for a Ser ies of
Com m on Descr ip tor s (X) Rela tive to th e CdC
Bon d of F r ee a n d Coor d in a ted Eth ylen e a n d to th e
C-C Bon d of Eth a n ea
we estimated the BO of the CdC double bond of the
coordinated ethylene molecule with the formula BO )
1 + (Xethane - Xcomplex)/(Xethane - Xethylene), where X is a
calculated property between the CdC bond length, the
CdC frequency of stretching, and the chemical shift of
the C atoms of the CdC bond.
bond length
(Å)
frequency
(cm-1
13C NMR
system
)
(∆δ)b
ethylene
1QMa
2IQMa
ethane
1.33 (2.00)
1.40 (1.65)
1.42 (1.55)
1.53 (1.00)
1637 (2.00)
1516 (1.82)
1492 (1.78)
974 (1.00)
0 (2.00)
38 (1.68)
66 (1.45)
120 (1.00)
The values in Table 4 indicate that the three esti-
mates of the CdC BO in 2IQMa are always smaller
than the corresponding ones we calculated for 1QMa .
The smaller difference between the BO of 2IQMa and
1QMa is calculated for the CdC frequency of stretching,
with the BO of 1QMa being only 0.04 greater than the
BO of 2IQMa , while the greater difference is calculated
for the chemical shift of the C atoms, with the BO of
1QMa , 0.23 being greater than the BO of 2IQMa .
Incidentally, the coordination shifts calculated for 1QMa
and 2IQMa are in excellent agreement with the experi-
mental value (see Table 3). On average, the three
general molecular descriptors we used indicate that the
BO of 2IQMa is 0.13 greater than the BO of 1QMa ,
which supports the previously discussed experimental
evidence for an enhanced back-donation from the Pt
center toward the CdC double bond in 2IQMa . Inci-
dentally, the higher back-donation in 2IQMa is also
supported by the higher coordination energy of ethylene
to 2IQMa , although ethylene coordination occurs trans
to the N(amido) atom: i.e., the N atom with the stronger
trans effect.
a
Calculated BO values are given in parentheses, according to
the formula BO ) 1 + (Xethane - Xcomplex)/(Xethane - Xethylene).
b
Calculated ∆δ values with respect to free ethylene.
related only to the intrinsic chemical properties of the
amido N function. Finally, we unexpectedly calculated
the Pt-N(amido) bond in 2IQM0 to be longer than the
corresponding Pt-N(imino) bond in 2IIIQM0.
Although the CdC ethylene bond length is rather
similar in all the alkene-bound species, it must be
noted that it is slightly longer on going from 1QMa to
2IIIQMa and finally to 2IQMa . Incidentally, the shorter
CdC double bond in 1QMa corresponds to the longest
Pt-C(ethylene) distances. In all the ethylene-coordi-
nated species the olefin is tightly bound to the metal,
as indicated by the very high ethylene coordination
energies we calculated (47.7, 48.1, and 46.5 kcal/mol for
1QMa , 2IQMa , and 2IIIQMa , respectively). With regard
to the different stabilities of the 2IQMa and 2IIIQMa
isomers, we calculated 2IQMa to be 9.4 kcal/mol more
stable than 2IIIQMa . Rather similarly, we calculated the
alkene-free 2IQM0 species to be 7.8 kcal/mol more stable
than 2IIIQM0. The higher stability of the 2IQM0 and
2IQMa isomers, with the Me group trans to the N(imi-
no) atom, is a clear consequence of the strong trans
effect of the anionic N(amido) atom.
To understand the origin of this increased back-
donation in 2IQMa , in Figure 5 we report the most
relevant molecular orbitals of 1QM0 and 2IQM0.
It is clear that changing the nature of one of the
N(imino) atoms of 1QM0 does not change the relative
energies of the molecular orbitals MO1 and MO2, with
To understand the nature of the Pt-ethylene bond,
and its consequences on the ethylene CdC bond, a series
of common molecular descriptors were calculated for the
CdC bond (Table 4). On the assumption that these
descriptors vary linearly with the CdC bond order (BO),
2
a strong contribution from the metal dz and dyz orbitals,
respectively, and with MO1 roughly 0.1 eV above MO2
in both 1QM0 and 2IQM0. Sharply different is the
behavior of MO3, with a strong metal dxz contribution.

Pt(II) Complexes with an N,N′-Imino-Amide Ligand
Organometallics, Vol. 23, No. 9, 2004 2143
Sch em e 2. Rea ction of 2a w ith HCl
Con clu sion
A new class of neutral olefin/alkyl complexes of
platinum(II) of the general formula [PtMe(N,N′-imino-
amido chelate)(olefin)] (2) is described. The compounds
have been obtained by selective removal of one proton
in the presence of a base from the ligand backbone of
parent cationic species (1) containing an N,N′-diimino
ligand. It should be noted that other examples of the
addition of nucleophiles to nickel triad diimine com-
plexes have been reported.28 However, as far as we
know, they promote alternative transformations, e.g.
ligand substitution28a or addition to the imino double
bond.28b
A thorough NMR investigation has disclosed high
selectivity of coordination for type 2 complexes, as only
one isomer has been observed in solution. Its geometry
seems dictated by both electronic and steric factors: i.e.
the stronger donor ligands Me and N(amido) are in cis
positions and the alkene substituent is oriented toward
the Pt-Me vector in order to release unfavorable steric
congestion.
In 1QM0 this molecular orbital corresponds to HOMO-2
and lies 0.8 eV below HOMO MO1, while in 2IQM0
MO3 is the HOMO and lies 0.9 eV above MO1. The
remarkable increase of energy of the molecular orbital
MO3 on going from 1QM0 to 2IQM0 is a consequence
of the interaction between the dxz orbital on the Pt and
the pz orbital on the N(amido) atom. In fact, the pz
orbital on the N(imino) atom in 1QM0 contributes
marginally to MO3, whereas in 2IQM0 there is a strong
antibonding interaction between the pz orbital on the
N(amido) atom and the dxz orbital on the metal. This
antibonding interaction pushes MO3 up in energy and
renders it more prone to back-donate to the π* orbital
of a coordinated alkene. Incidentally, we believe that
this antibonding Pt-N(amido) interaction is at the
origin of the longer Pt-N(amido) bond in 2IQM0 rela-
tive to the Pt-N(imino) bonds in 1QM0 and 2IIIQM0
and that its release after ethylene coordination is at the
origin of the small elongation of the Pt-N(amido) bond
in 2IQMa relative to the Pt-N(imino) bonds in 1QMa
and 2IIIQMa .
The olefin coordination shifts lie outside the range
commonly observed for square-planar Pt(II) compounds.
This unusual evidence has been correlated with a
relevant π-back-donation in the Pt-olefin bond, prompted
by the nature and the relative arrangement of the
ligands. Theoretical calculations strongly support this
hypothesis.
Aiming to compare the calculated bonding properties
of type 2 compounds with their actual values, several
attempts to grow single crystals for an X-ray diffraction
experiment were performed. Unfortunately, in no case
were we able to obtain crystals of suitable size.
Rea ctivity of Typ e 2 Com p ou n d s. Some aspects
of the reactivity of the new complexes have been ex-
plored. The reaction depicted in Scheme 1 can be re-
versed. In fact, treating the type 2 complexes with a pro-
tic acid containing a poorly coordinating anion readily
restores the parent compounds of type 1. Thus, addition
of ethereal HBF4 to a chloroform solution of 2a results
in immediate and quantitative formation of 1a , accord-
ing to the NMR spectrum of the reaction mixture.
Instead, ligand protonation with an acid containing
a coordinating anion, i.e. HCl, is accompanied by
substitution of the alkene for the chloride, according to
Scheme 2.
Exp er im en ta l Section
1H and 13C{1H} NMR spectra were recorded on Varian XL-
200, Varian Gemini-300, and Bruker Avance DRX-400 spec-
1
1
1
trometers. H-COSY, H-NOESY, H,13C-HMQC, and 1H,13C-
HMBC spectra, using a pulsed field gradient for coherence se-
lection, were recorded on a Bruker Avance DRX-400 spectrom-
eter equipped with a QNP 4-nuclei probe or with a triple-reso-
nance BB inverse probe, both with z-gradient coils. CDCl3 was
used as solvent; residual CHCl3 (δ 7.26) and 13CDCl3 (δ 77.0)
were used as internal standards. Complexes of type 11 were
1
obtained according to published methods. H-NOESY NMR
experiments were recorded using a mixing time of 0.8 s.
Syn th esis of Typ e 2 Com p lexes. A solution of KOH (0.028
g, 0.50 mmol) in methanol (3 mL) was added to a magnetically
stirred suspension of the appropriate precursor (0.50 mmol)
in methanol (4 mL) kept in an ice bath. After the mixture was
stirred for 15 min, the precipitate was separated, washed with
cold methanol, and dried in vacuo. Yield: 70-80%.
1
[P tMe(eth ylen e)(d ep r a n )] (2a ). H NMR (CDCl3, 400.13
1
MHz, 298 K, J value in Hz): δ 7.27 (m, aromatic protons cis
to olefin), 7.21 (m, aromatic protons cis to Pt-Me), 4.45 (d,
For all complexes, H NMR spectra at 323 K did not
show any appreciable variation with respect to those
recorded at room temperature, suggesting that dynamic
behaviors, concerning olefin exchange or rotation, are
not present. The possibility of observing insertion of the
alkene into the Pt-Me bond has also been considered.
In a previous work,1b we described a very rare example
of insertion of an olefin into a Pt-alkyl bond, obtained
upon heating a chloroform solution of 1f to 343 K
overnight. The same treatment for 2f was unsuccessful,
and the complex was recovered, accompanied by decom-
position products. This result is not unexpected, given
the higher stability of neutral complexes toward inser-
tion reactions with respect to cationic compounds. At
room temperature the decomposition process is obvi-
ously slower, and it irreversibly leads to unidentified
products within some days.
4
2
2J HH ) 0.9, J PtH ) 7, HB), 3.88 (d, J HH ) 0.9, HA), 3.48 (sept,
3
3J HH ) 7.0, CH(M)), 3.10 (sept, J HH ) 7.0, CH(O)), 2.51 (s,
2J PtH ) 54, CH2dCH2), 1.99 (s, Me(O)), 1.41 (d, J HH ) 7.0,
3
3
3
Me(Ob)), 1.25 (d, J HH ) 7.0, Me(Mf)), 1.21 (d, J HH ) 7.0,
3
2
Me(Md)), 1.16 (d, J HH ) 7.0, Me(Of)), -0.26 (s, J PtH ) 76.7,
Pt-Me). 13C NMR (CDCl3, 100.55 MHz, 298 K, J value in
Hz): δ 176.5 (s, CdN), 162.7 (s, NCdC), 145.3 (s, Cipso cis to
Pt-Me), 145.1 (s, quaternary carbons cis to Pt-Me), 139.8 (s,
Cipso cis to olefin), 139.6 (s, quaternary carbons cis to olefin),
126.9 (s, p-C cis to olefin), 124.9 (s, p-C cis to Pt-Me), 123.8
(s, m-C cis to olefin), 123.0 (s, m-C cis to Pt-Me), 92.4 (s,
1
3J PtC ) 42, NCdC), 55.6 (s, J PtC ) 196, CH2CH2), 27.9 (s,
CH(O)), 27.4 (s, CH(M)), 25.2 (s, Me(Mb), 24.6 (s, Me(Of)), 23.9
(28) (a) Crociani, B.; Antonaroli, S.; Di Bianca, F.; Canovese, L.;
Visentin, F.; Uguagliati, P. J . Chem. Soc., Dalton Trans. 1994, 1145-
1151. (b) Korybut-Daskiewicz, B. J . Coord. Chem. 1992, 27, 219-221.

2144 Organometallics, Vol. 23, No. 9, 2004
(s, Me(Mf)), 23.5 (s, Me(Ob)), 19.8 (s, Me(O)), -8.0 (s, J PtC
736.2, Pt-Me). Anal. Calcd for C31H46N2Pt: C, 58.02; H, 7.22;
N, 4.37. Found: C, 58.29; H, 7.35; N, 4.16.
Cavallo et al.
1
3
3
)
Me(Mdb)), 1.20 (d, J HH ) 6.9, Me(Mub)), 1.18 (d, J HH ) 6.9,
3
2
Me(Odb)), 1.13 (d, J HH ) 6.9, Me(Oub)), -0.18 (s, J PtH ) 77,
Pt-Me). 13C NMR (CDCl3, 100.55 MHz, 298 K, J value in
Hz): δ 177.2 (s, CdN), 162.7 (s, NCdC), 145.2 (s, quaternary
carbon cis to Pt-Me(down)), 145.10 (s, quaternary carbon cis
to Pt-Me(up)),144.6 (s, Cipso cis to Pt-Me), 140.1 (s, quaternary
carbon cis to olefin (down)), 139.8 (s, quaternary carbon cis to
olefin (up)), 138.9 (s, Cipso cis to olefin), 127.4 (s, p-C cis to
[P tMe(p r op ylen e)(d ep r a n )] (2b). 1H NMR (CDCl3, 400.13
MHz, 298 K, J value in Hz): δ 7.27 (m, aromatic protons cis
to olefin), 7.20 (m, aromatic protons cis to Pt-Me), 4.43 (d,
2J HH ) 0.9, 4J PtH ) 9.4, HB), 3.81 (d, 2J HH ) 0.9, HA), 3.64 (sept,
3
3J HH ) 6.9, CH(Md)), 3.42 (sept, J HH ) 6.9, CH(Mu)), 3.15
3
3
olefin), 125.3 (p-C cis to Pt-Me), 124.1 (s, m-C(Od)), 124.0 (s,
(sept, J HH ) 6.9, CH(Ou)), 3.11 (sept, J HH ) 6.9, CH(Od)),
2.93 (m, 3J HH ) 12.7, 3J HH ) 8.4, 3J HH ) 6.2, 2J PtH ) 61.5, CH2d
CH(CH3)), 2.65 (d, 3J HH ) 8.4, 2J PtH ) 65.1, CH2(cis)dCH(CH3)),
3
m-C(Ou)), 123.2 (s, m-C(Md) and m-C(Mu)), 93.8 (s, J PtC
)
1
43, NCdC), 75.0 (s, J PtC ) 194, CH2dCHCH2OH), 61.8 (s,
CH2dCHCH2OH), 55.1 (s, 1J PtC ) 175, CH2dCHCH2OH), 28.0
(s, CH(Od) and CH(Ou)), 27.5 (s, CH(Md) and CH(Mu)), 25.9
(s, Me(Mdb)), 25.6 (s, Me(Mub)), 25.2 (s, Me(Odb)), 25.1 (s, Me-
(Oub)), 24.4 (s, Me(Mdf)), 24.2 (s, Me(Muf)), 24.1 (s, Me(Odf)),
3
2
2.63 (d, J HH ) 12.7, J PtH ) 43.0, CH2(trans)dCH(CH3)), 1.96
3
3
(s, Me(O)), 1.41 (d, J HH ) 6.9, Me(Odf)), 1.40 (d, J HH ) 6.9,
3
3
Me(Ouf)), 1.37 (d, J HH ) 6.2, CH2dCH(CH3)), 1.27 (d, J HH
)
)
)
)
3
3
6.9, Me(Mfd)), 1.26 (d, J HH ) 6.9, Me(Muf)), 1.21 (d, J HH
1
3
3
23.9 (s, Me(Ouf)), 20.1 (s, Me(O)), -8.0 (s, J PtC ) 750,
6.9, Me(Mub)), 1.20 (d, J HH ) 6.9, Me(Mdb)), 1.18 (d, J HH
6.9, Me(Odb)), 1.13 (d, 3J HH ) 6.9, Me(Oub)), -0.19 (s, 2J PtH
Pt-Me). Anal. Calcd for C32H48N2OPt: C, 57.22; H, 7.20; N,
78.4, Pt-Me). 13C NMR (CDCl3, 100.55 MHz, 298 K, J value
in Hz): δ 176.7 (s, CdN), 162.5 (s, NCdC), 145.6, 145.3, 145.2
(s, quaternary carbons cis to Pt-Me), 140.0, 139.8, 139.6 (s,
quaternary carbons cis to olefin), 127.0 (s, p-C cis to olefin),
4.17. Found: C, 57.01; H, 7.32; N, 4.36.
[P tMe(m eth yl vin yl k eton e)(d ep r a n )] (2e). 1H NMR
(CDCl3, 400.13 MHz, 298 K, J value in Hz): δ 7.30 (m,
aromatic protons cis to olefin), 7.20 (m, aromatic protons cis
2
4
2
124.9 (s, p-C cis to Pt-Me), 123.9 (s, m-C(Ou)), 123.7 (s, m-C-
to Pt-Me), 4.61 (d, J HH ) 0.9, J PtH ) 9.2, HB), 4.05 (d, J HH
3
) 0.9, HA), 3.81 (dd, 3J HH ) 12.0, 3J HH ) 7.9, 2J PtH ) 68.1, CH2d
(Od)), 123.3 (s, m-C(Md)), 122.8 (s, m-C(Ou)), 92.1 (s, J PtC
)
45, NCdC), 72.6 (s, 1J PtC ) 206.0, CH2dCH(CH3)), 56.5 (s, 1J PtC
) 173.0, CH2dCH(CH3)), 27.9 (s, CH(Od)), 27.8 (s, CH(Ou)),
27.4 (s, CH(Md)), 27.3 (s, CH(Mu)), 25.3 (s, Me(Mub) and
Me(Mdb)), 24.8 (s, Me(Oub), 24.5 (s, Me(Odb)), 24.0 (s,
Me(Muf)), 23.6 (s, Me(Ouf)), 23.4 (s, Me(Odf) and Me(Mdf)),
3
3
CHCOMe), 3.50 (sept, J HH ) 7.0, CH(Md)), 3.31 (sept, J HH
3
) 7.0, CH(Mu)), 3.21 (sept, J HH ) 7.0, CH(Od)), 3.07 (sept,
3
2
3J HH ) 7.0, CH(Ou)), 2.92 (d, J HH ) 12.0, J PtH ) 39.6,
CH2(trans)dCHCOMe), 2.27 (d, 3J HH ) 7.9, 2J PtH ) 55.6, CH2(cis)d
3
CHCOMe), 2.26 (s, COMe), 2.07 (s, Me(O)), 1.51 (d, J HH
)
2
7.0, Me(Odf)), 1.41 (d, 3J HH ) 7.0, Me(Ouf)), 1.22 (m, Me(Muf)
20.0 (s, Me(O)), 18.0 (s, J PtC ) 17.6, CH2dCH(CH3)), -6.4 (s,
1J PtC ) 780, Pt-Me). Anal. Calcd for C32H48N2Pt: C, 58.61;
H, 7.38; N, 4.27. Found: C, 58.34; H, 7.20; N, 4.43.
3
3
and Me(Mdf)), 1.21 (d, J HH ) 7.0, Me(Odb)), 1.19 (d, J HH
)
)
3
3
7.0, Me(Mdb)), 1.18 (d, J HH ) 7.0, Me(Mub)), 1.16 (d, J HH
7.0, Me(Oub)), -0.28 (s, J PtH ) 77.5, Pt-Me). 13C NMR
(CDCl3, 100.55 MHz, 298 K, J value in Hz): δ 200.6 (s, COMe),
176.9 (s, CdN), 162.8 (s, NCdC), 144.9 (s, quaternary carbons
cis to Pt-Me), 144.2 (s, Cipso cis to Pt-Me), 139.9 (s, quaternary
carbon cis to olefin (up)), 139.4 (s, quaternary carbon cis to
olefin (down)), 138.6 (s, Cipso cis to olefin), 127.5 (s, p-C cis to
olefin), 125.6 (p-C cis to Pt-Me), 124.4 (s, m-C(Ou)), 123.9 (s,
m-C(Od)), 123.4 (s, m-C(Mu)), 123.2 (s, m-C(Md)), 95.5 (s, 3J PtC
2
[P tMe(styr en e)(d ep r a n )] (2c). 1H NMR (CDCl3, 400.13
MHz, 298 K, J value in Hz): δ 7.30, 7,10 (m, aromatic protons),
4.48 (d, 2J HH ) 0.9, HB), 4.45 (dd, 3J HH ) 13.0, 3J HH ) 8.7, 2J PtH
2
3
) 74.0, CH2dCHPh), 3.89 (d, J HH ) 0.9, HA), 3.60 (sept, J HH
3
) 7.0, CH(Md)), 3.37 (sept, J HH ) 7.0, CH(Od)), 3.35 (sept,
3J HH ) 7.0, CH(Mu)), 3.26 (sept, J HH ) 7.0, CH(Ou)), 3.05 (d,
3
3J HH ) 13.0, J PtH ) 41.8, CH2(trans)dCHPh), 2.35 (d, J HH
)
2
3
8.7, 2J PtH ) 61.0, CH2(cis)dCHPh), 2.05 (s, Me(O)), 1.50 (d, 3J HH
1
3
3
) 49.5, NCdC), 66.3 (s, J PtC ) 191.8, CH2dCHCOMe), 48.3
) 7.0, Me(Odf)), 1.48 (d, J HH ) 7.0, Me(Ouf)), 1.25 (d, J HH
)
)
)
)
(s, 1J PtC ) 187.7, CH2dCHCOMe), 29.4 (s, COMe), 28.1 (s, CH-
(Od)), 27.9 (s, CH(Ou)), 27.5 (s, CH(Md)), 27.4 (s, CH(Mu)),
25.5 (s, Me(Mdb)), 25.0 (s, Me(Mub)), 24.8 (s, Me(Odb), 24.7
(s, Me(Oub)), 23.9 (s, Me(Odf)), 23.8 (s, Me(Muf)), 23.6 (s, Me-
(Mdf)), 23.5 (s, Me(Ouf)), 20.2 (s, Me(O)), -3.0 (s, 1J PtC ) 730.6,
Pt-Me). Anal. Calcd for C33H48N2OPt: C, 57.97; H, 7.08; N,
4.10. Found: C, 57.75; H, 7.00; N, 4.21.
3
3
7.0, Me(Odb)), 1.21 (d, J HH ) 7.0, Me(Muf)), 1.20 (d, J HH
3
3
7.0, Me(Mdb)), 1.19 (d, J HH ) 7.0, Me(Mub)), 1.18 (d, J HH
7.0, Me(Oub)), 1.07 (d, 3J HH ) 7.0, Me(Mdf)), -0.71 (s, 2J PtH
78.6, Pt-Me). 13C NMR (CDCl3, 100.55 MHz, 298 K, J value
in Hz): δ 176.7 (s, CdN), 162.5 (s, NCdC), 145.1, 145.0, 144.8
(s, quaternary carbons cis to Pt-Me), 140.0, 139.9, 139.2 (s,
quaternary carbons cis to olefin), 139.6 (s, Cipso olefin),128.4
(s, o-C olefin), 127.6 (m-C olefin), 127.2 (s, p-C cis to olefin),
126.2 (s, p-C olefin), 124.9 (s, p-C cis to Pt-Me), 124.1 (s, m-C-
(Ou)), 123.8 (s, m-C(Od)), 123.0 (s, m-C(Md)), 122.9 (s, m-C-
(Ou)), 92.7 (s, 3J PtC ) 47, NCdC), 71.8 (s, 1J PtC ) 198.0, CH2d
[P tMe(m eth yl a cr yla te)(d ep r a n )] (2f). 1H NMR (CDCl3,
400.13 MHz, 298 K, J value in Hz): δ 7.28 (m, aromatic
protons cis to olefin), 7.20 (m, aromatic protons cis to Pt-Me),
2
4
2
4.58 (d, J HH ) 1.1, J PtH ) 8.1, HB), 4.02 (d, J HH ) 1.1, HA),
1
3
CHPh), 48.6 (s, J PtC ) 200.0, CH2dCHPh), 28.1 (s, CH(Od)),
3.55 (s, COOMe), 3.46 (sept, J HH ) 6.9, CH(Md)), 3.34 (sept,
3
3
2
3J HH ) 6.9, CH(Mu)), 3.32 (dd, J HH ) 12.1, J HH ) 8.2, J PtH
) 65.0, CH2dCHCOOMe), 3.21 (sept, 3J HH ) 6.9, CH(Od)), 3.07
(d, 3J HH ) 12.1, 2J PtH ) 38.0, CH2(trans)dCHCOOMe), 3.03 (sept,
3J HH ) 6.9, CH(Ou)), 2.48 (d, 3J HH ) 8.2, 2J PtH ) 59.0, CH2(cis)d
CHCOOMe), 2.05 (s, Me(O)), 1.49 (d, 3J HH ) 6.9, Me(Odf)), 1.41
27.9 (s, CH(Ou)), 27.4 (s, CH(Md)), 27.3 (s, CH(Mu)), 25.6 (s,
Me(Mdb)), 25.0 (s, Me(Mub)), 24.9 (s, Me(Odb), 24.7 (s, Me-
(Oub)), 24.1 (s, Me(Odf)), 23.8 (s, Me(Muf)), 23.6 (s, Me(Ouf)),
1
23.5 (s, Me(Mdf)), 20.2 (s, Me(O)), -3.0 (s, J PtC ) 776.7,
Pt-Me). Anal. Calcd for C37H50N2Pt: C, 61.91; H, 7.02; N, 3.90.
Found: C, 62.18; H, 7.19; N, 3.77.
3
3
(d, J HH ) 6.9, Me(Ouf)), 1.24 (d, J HH ) 6.9, Me(Muf)), 1.19
(m, Me(Mub) and Me(Mdf)), 1.18 (d, 3J HH ) 6.9, Me(Mdb)), 1.17
(d, 3J HH ) 6.9, Me(Odb)), 1.15 (d, 3J HH ) 6.9, Me(Oub)), -0.17
[P tMe(a llyl a lcoh ol)(d ep r a n )] (2d ). 1H NMR (CDCl3,
400.13 MHz, 298 K, J value in Hz): δ 7.29 (m, aromatic
protons cis to olefin), 7.22 (m, aromatic protons cis to Pt-Me),
(s, J PtH ) 78, Pt-Me). 13C NMR (CDCl3, 100.55 MHz, 298 K,
2
2
4
2
4.51 (d, J HH ) 1.0, J PtH ) 9.0, HB), 3.91 (d, J HH ) 1.0, HA),
J value in Hz): δ 176.7 (s, CdN), 169.5 (s, COOMe), 162.9 (s,
NCdC), 145.1 (s, quaternary carbon cis to Pt-Me(down)),
145.10 (s, quaternary carbon cis to Pt-Me(up)), 144.5 (s, Cipso
cis to Pt-Me), 140.1 (s, quaternary carbon cis to olefin (down)),
139.7 (s, quaternary carbon cis to olefin (up)), 138.8 (s, Cipso
cis to olefin), 127.4 (s, p-C cis to olefin), 125.4 (p-C cis to
Pt-Me), 124.2 (s, m-C(Od)), 124.1 (s, m-C(Ou)), 123.3 (s, m-C-
3
3.62 (sept, J HH ) 6.9, CH(Md)), 3.43 (m, CH2dCHCH2OH,
spatially close to CH2(trans)dCHCH2OH) 3.38 (sept, 3J HH ) 6.9,
3
CH(Mu)), 3.28 (m, CH2dCHCH2OH), 3.18 (sept, J HH ) 6.9,
2
CH(Ou)), 3.09 (m, J PtH ) 58.0, CH2dCHCH2OH), 3.04 (sept,
3J HH ) 6.9, CH(Od)), 2.69 (d, J HH ) 13.0, J PtH ) 42.0,
3
2
3
2
CH2(trans)dCHCH2OH), 2.67 (d, J HH ) 8.3, J PtH ) 58.0,
3
3
CH2(cis)dCHCH2OH), 2.01 (s, Me(O)), 1.45 (d, J HH ) 6.9, Me-
(Md)), 123.1 (s, m-C(Mu)), 95.2 (s, J PtC ) 42, NCdC), 57.4 (s,
3
3
(Odf)), 1.43 (d, J HH ) 6.9, Me(Ouf)), 1.26 (d, J HH ) 6.9, Me-
1J PtC ) 175, CH2dCHCOOMe), 51.6 (s, CH2dCHCOOMe), 50.1
3
3
1
(Mdf)), 1.25 (d, J HH ) 6.9, Me(Muf)), 1.21 (d, J HH ) 6.9,
(s, J PtC ) 168, CH2dCHCOOMe), 28.2 (s, CH(Od)), 27.9 (s,

Pt(II) Complexes with an N,N′-Imino-Amide Ligand
Organometallics, Vol. 23, No. 9, 2004 2145
CH(Ou)), 27.5 (s, CH(Md)), 27.4 (s, CH(Mu)), 25.3 (s, Me(Odb)),
25.2 (s, Me(Mdf)), 24.9 (s, Me(Mdb)), 24.8 (s, Me(Mub)), 23.9
(s, Me(Muf)), 23.7 (s, Me(Ouf)), 23.5 (s, Me(Oub)), 23.4 (s, Me-
effects were included self-consistently with the ZORA formal-
ism.36,37 The carbon chemical shifts were calculated with the
NMR program distributed with the ADF package31 and
developed by Ziegler and co-workers.38-40
1
(Odf)), 20.2 (s, Me(O)), -3.8 (s, J PtC ) 730, Pt-Me). Anal.
Calcd for C33H48N2O2Pt: C, 56.64; H, 6.91; N, 4.00. Found: C,
56.48; H, 6.77; N, 3.83.
Ack n ow led gm en t. The authors thank the MURST
(Programmi di Ricerca Scientifica di Rilevante Interesse
Nazionale, Cofinanziamento 2002-2003) and the Centro
Interdipartimentale di Metodologie Chimico-Fisiche,
Universita` di Napoli ”Federico II”, for NMR facilities
and technical support. Thanks are also given to Mr.
Paolo Minichini for technical assistance.
Com p u ta tion a l Deta ils. All the structures discussed were
calculated with the Amsterdam Density Functional (ADF)
program.29-31 The electronic configurationa of the molecular
systems were described by a triple-ú STO basis set on Pt for
4f, 5s, 5p, 5d, 6s, and 6p (ADF basis set IV).31 Double-ú STO
basis sets were used for nitrogen and carbon (2s and 2p) and
hydrogen (1s), augmented with
a single 3d, 3d, and 2p
function, respectively (ADF basis set III).31 The inner shells
on platinum (including 4d) and nitrogen and carbon (1s) were
treated within the frozen core approximation. Energies and
geometries were evaluated by using the local exchange-
correlation potential by Vosko et al.,32 augmented in a self-
consistent manner with Becke’s33 exchange gradient correction
and Perdew’s34,35 correlation gradient correction. Relativistic
OM049968K
(32) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J . Phys. 1980, 58, 1200-
1211.
(33) Becke, A. Phys. Rev. A 1988, 38, 3098-3100.
(34) Perdew, J . P. Phys. Rev. B 1986, 33, 8822-8824.
(35) Perdew, J . P. Phys. Rev. B 1986, 34, 7406-7406.
(36) van Lenthe, E.; Baerends, E. J . Snijders, J . G. J . Chem. Phys.
1994, 101, 9783-9792.
(37) van Lenthe, E.; Ehlers, A. E.; Baerends, E. J . J . Chem. Phys.
1999, 110, 8943-8953.
(29) Baerends, E. J .; Ellis, D. E.; Ros, P. Chem. Phys. 1973, 2, 41-
51.
(38) Schreckenbach, G.; Ziegler, T. J . Phys. Chem. 1995, 99, 606-
(30) te Velde, G.; Baerends, E. J . J . Comput. Phys. 1992, 99, 84-
98.
611.
(39) Schreckenbach, G.; Ziegler, T. Int. J . Quantum. Chem. 1997,
61, 899-918.
(40) Wolff, S. K.; Ziegler, T. J . Chem. Phys. 1998, 109, 895-905.
(31) ADF 2002, Users Manual; Vrije Universiteit Amsterdam:
Amsterdam, The Netherlands, 2000.