The first class of square-planar platinum(II) complexes containing electron-poor alkenes. Rare insertion of an alkene into a Pt-alkyl bond

Article abstract of DOI:10.1021/om9800750

The first class of square-planar Pt(II) complexes bearing electron-poor alkenes, i.e., [PtMe-N,N-chelate)(η²-CH₂=CHCOR)]BF₄ (R = H, NMe₂, Me, OMe), is described. By using N,N ligands with suitable steric properties, it was possible to inhibit olefin dynamic processes in solution, thus allowing a thorough characterization of the complexes. Insertion of methyl acrylate into the Pt-Me bond provides a rare example of migratory insertion of an alkene into a Pt-alkyl bond.

Full text of DOI:10.1021/om9800750

2646
Organometallics 1998, 17, 2646-2650
Th e F ir st Cla ss of Squ a r e-P la n a r P la tin u m (II) Com p lexes
Con ta in in g Electr on -P oor Alk en es. Ra r e In ser tion of a n
Alk en e in to a P t-Alk yl Bon d †
Paolo Ganis, Ida Orabona, Francesco Ruffo,* and Aldo Vitagliano
Dipartimento di Chimica, Universita` di Napoli “Federico II”, via Mezzocannone 4,
80134 Napoli, Italy
Received February 4, 1998
The first class of square-planar Pt(II) complexes bearing electron-poor alkenes, i.e., [PtMe-
(N,N-chelate)(η2-CH2dCHCOR)]BF4 (R ) H, NMe2, Me, OMe), is described. By using N,N
ligands with suitable steric properties, it was possible to inhibit olefin dynamic processes in
solution, thus allowing a thorough characterization of the complexes. Insertion of methyl
acrylate into the Pt-Me bond provides a rare example of migratory insertion of an alkene
into a Pt-alkyl bond.
In tr od u ction
The recent discovery1 that Pd(II) and Ni(II) complexes
are able to catalyze the homogeneous polymerization of
R-olefins is acknowledged as one of the most promising
findings concerning the chemistry of d8 ions. The ability
of the catalysts (1 and 2 in Figure 1) to produce
polymers with high molecular weights mainly ensues
from the choice of N,N-chelating ligands, i.e., diimines
(a and b in Figure 2) which introduce substantial steric
hindrance above and below the square-planar coordina-
tion plane. This feature inhibits associative exchange
processes and, hence, favors the chain growth.1a
F igu r e 1.
The peculiar ability of this class of N,N ligands of
inhibiting olefin displacement reactions has also emerged
from a recent study of similar platinum(II) complexes
of general formula [PtMe(N,N-chelate)(η2-olefin)]BF4
(3).2 It was found that the kinetic stability of type 3
complexes with the hindered ligands a and b is much
larger than that of the corresponding species containing
the poorly hindered ligands c and d . The ability of a
or b in “freezing” olefin coordination to a 16 e- platinum-
(II) center prompted us to use these ligands for inves-
tigating a poorly studied class of platinum(II) complexes,
i.e., square-planar derivatives containing electron-poor
alkenes. In fact, an accurate characterization of the
rare examples of such complexes described so far3 has
been prevented by the occurrence of exchange processes
involving the alkene.3c,d Furthermore, none of them
have been structurally characterized. On these grounds,
we have undertaken the synthesis of type 3 complexes
of electron-poor alkenes by using a and b as chelates,
F igu r e 2.
with the assumption that useful information would
become available if the dynamic processes involving the
alkene were hindered. This approach was successful
and herein we report the results of our research.
Resu lts a n d Discu ssion
The synthetic procedure described by Scheme 1 was
adopted. By adding AgBF4 to a dichloromethane solu-
tion of [PtMe(I)(N,N-chelate)] (N,N-chelate ) diacetyl
bis(di-i-propylphenylimine), 4a ; diacetyl bis(diethylphe-
nylimine), 4b ) in the presence of the appropriate
CH2dCHCOR ligand, quantitative precipitation of AgI
occurred within a few hours. Addition of diethyl ether
to the filtered solution afforded yellow microcrystals of
the wanted type 3 product.4 Type 3 complexes form the
first homogeneus class of square-planar Pt(II) deriva-
† Dedicated to the memory of Stefano Ganis.
(1) (a) J ohnson, L. K.; Killian, C. M.; Brookhart, M. J . Am. Chem.
Soc. 1995, 117, 6414. (b) J ohnson, L. K.; Mecking, S.; Brookhart, M.
J . Am. Chem. Soc. 1996, 118, 267. (c) Mecking, S.; J ohnson, L. K.;
Wang, L.; Brookhart, M. J . Am. Chem. Soc. 1998, 120, 888.
(2) Fusto, M.; Giordano, F.; Orabona, I.; Panunzi, A.; Ruffo, F.
Organometallics 1997, 16, 5981.
(3) (a) Paiaro, G.; Panunzi, A. J . Am. Chem. Soc. 1966, 88, 4843.
(b) Meester, A. M.; van Dam, H.; Stufkens, D. J .; Oskam, A. Inorg.
Chim. Acta 1976, 20, 155. (c) Scott, J . D.; Puddephatt, R. J . Organo-
metallics 1986, 5, 1253. (d) Orabona, I.; Panunzi, A.; Ruffo, F. J .
Organomet. Chem. 1996, 525, 295-298.
(4) Type 3 complexes are indicated by a letter (a , diacetyl bis(di-i-
propylphenylimine) or b, diacetyl bis(diethylphenylimine)) followed by
the specification of the R group in the CH2dCHCOR ligand.
S0276-7333(98)00075-2 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 05/20/1998

Insertion of an Alkene into a Pt-Alkyl Bond
Organometallics, Vol. 17, No. 12, 1998 2647
Sch em e 1a
a
One R′ group on an aryl ring has been omitted for clarity.
Ta ble 1. Selected 1H NMR Da ta a for Typ e 3 Com p lexes
formula
Pt-Meb
entry
H(olefin)b
3a (OMe)
[PtMe{diacetyl bis(di-i-propylphenylimine)}(η2-CH2dCHCO2Me)]BF4
0.20 (70, 3H)
4.22 (m, 2H)
3.76 (m, 1H)
3a (Me)
[PtMe{diacetyl bis{di-i-propylphenylimine)}(η2-CH2dCHCOMe)]BF4
0.12 (71, 3H)
4.72 (80, dd, 1H)
4.00 (56, d, 1H)
3.37 (65, d, 1H)
4.97 (84, dd, 1H)
4.24 (53, d, 1H)
c
4.42 (61, d, 1H)
4.21 (63, d, 1H)
3.97 (70, m, 1H)
4.28 (59, d, 1H)
3.96 (dd, 1H)
3.55 (71, d, 1H)
3a (NMe2)
3a (H)
[PtMe{diacetyl bis{di-i-propylphenylimine)}(η2-CH2dCHCONMe2)]BF4
[PtMe{diacetyl bis{di-i-propylphenylimine)}(η2-CH2dCHCHO)]BF4
[PtMe{diacetyl bis{diethylphenylimine)}(η2-CH2dCHCO2Me)]BF4
0.18 (71, 3H)
0.45 (69, 3H)
0.15 (70, 3H)
3b(OMe)
a
At 200, 270, 400 MHz and 298 K. In CDCl3 (CHCl3 (δ ) 7.26 ppm) as internal standard). Abbreviations: no attribute, singlet; d,
b 2
doublet; dd, double doublet; m, multiplet.
J
(Hz) in parentheses (when measurable). c Hidden by more intense resonances.
Pt-H
Ta ble 2. Selected 13C NMR Da ta a for F r ee Olefin s a n d Typ e 3 Com p lexes
entry
formula
Pt-Meb
CHdb
128.2
137.2
127.6
∆δc
CH2db
130.4
128.7
127.1
∆δd
CH2dCHCO2Me
CH2dCHCOMe
CH2dCHCONMe2
CH2dCHCHO
138.1
137.5
3a (OMe)
3a (Me)
[PtMe{diacetyl bis{di-i-propylphenylimine)}-
-0.2
74.9 (189)
53.3
54.2
48.2
55.9
52.3
69.6 (170)
60.8
61.9
58.1
65.9
60.8
(η2-CH2dCHCO2Me)]BF4
[PtMe{diacetyl bis{di-i-propylphenylimine)}-
(η2-CH2dCHCOMe)]BF4
0.5 (658)
-1.4 (666)
-3.7 (644)
-0.5 (645)
83.0 (209)
79.4 (213)
82.2 (202)
75.9 (216)
66.8 (171)
69.0 (172)
71.6 (194)
69.6 (174)
3a (NMe2)
3a (H)
[PtMe{diacetyl bis{di-i-propylphenylimine)}-
(η2-CH2dCHCONMe2)]BF4
[PtMe{diacetyl bis{di-i-propylphenylimine)}-
(η2-CH2dCHCHO)]BF4
3b(OMe)
[PtMe{diacetyl bis{diethylphenylimine)}-
(η2-CH2dCHCO2Me)]BF4
At 50.3 or 62.9 MHz and 298 K. In CDCl3 (13CDCl3 (δ ) 77.0 ppm) as internal standard).
J
(Hz) in parentheses (when measurable).
Pt-C
a
b 1
c Difference between δ(CH) of the free olefin and δ(CH) of the coordinated olefin. Difference between δ(CH2) of the free olefin and δ(CH2)
of the coordinated olefin.
d
tives containing alkenes with electron-withdrawing
functions (i.e., an aldehyde, a ketone, an ester, and an
amide). They have been characterized through elemen-
tal analysis, NMR spectroscopy (Tables 1 and 2), and,
in one case, X-ray crystallography (see below).
According to our expectations, the olefins did not show
fast exchange processes on the NMR time scale, as
F igu r e 3. Type 3′ and 3′′ isomers. One R′ group on an
suggested by the presence of coupling to 195Pt in both
aryl ring has been omitted for clarity.
the carbon and proton spectra. Furthermore, the pres-
ence of a unique spectral pattern suggests selective
of a and b. Indeed, when c was used as the chelate,
the spectrum of the isolated product mainly consisted
formation of only one enantiomeric pair,5 most probably
3′ (Figure 3) according to the previous discussion made
of broad signals, revealing both the presence of more
for similar complexes of propene and styrene.2 It is
than one species and their fast interconversion in
clear that both results stem from the steric properties
solution.
The absence of fast dynamic processes allowed a
thorough characterization of type 3 complexes, and
important parameters such as olefin carbon chemical
shifts and the corresponding couplings to 195Pt could be
(5) Although both isomers have been detected at 200 K for the Pd-
(II) derivative [PdMe{diacetyl bis(di-i-propylphenylimine)}(η2-
CH2dCHCO2Me)]+,1b,c only one pattern of NMR signals was detected
in the range of temperature 203-298 K in the spectrum of the analogue
Pt(II) complex 3a (OMe).

2648 Organometallics, Vol. 17, No. 12, 1998
Ganis et al.
Ta ble 3. Selected Geom etr ica l P a r a m eter s for
3b(OMe)
Bond Lengths (Å)
Pt-N(1)
Pt-C(5)
2.16(3)
2.04(4)
2.18(4)
1.52(5)
1.50(4)
1.52(4)
1.36(5)
1.15(4)
1.18(4)
Pt-N(2)
1.92(3)
2.10(3)
1.29(4)
1.28(4)
1.40(6)
1.59(4)
1.07(4)
1.19(4)
Pt-C(6)
Pt-C(7)
N(1)-C(1)
N(2)-C(2)
C(1)-C(2)
C(2)-C(3)
B-F(1)
N(1)-C(20)
N(2)-C(10)
C(1)-C(4)
C(6)-C(7)
B-F(2)
B-F(3)
B-F(4)
Bond Angles (deg)
N(2)-Pt-C(5)
N(1)-Pt-N(2)
N(2)-C(2)-C(1)
174(2)
74(1)
117(2)
N(1)-Pt-C(5)
N(1)-C(1)-C(2)
C(6)-C(7)-C(8)
102(1)
113(2)
136(3)
Torsion Angles (deg)
80 N(2)-Pt-C(6)-C(7)
N(2)-Pt-C(7)-C(6)
-107
C(1)-N(1)-C(20)-C(25)
N(1)-C(1)-C(2)-N(2)
93 C(2)-N(2)-C(10)-C(11)
-7 C(6)-C(7)-C(8)-O(2)
-92
179
28
C(12)-C(11)-C(18)-C(19) 10 C(14)-C(15)-C(16)-C(17)
C(22)-C(21)-C(28)-C(29) 26 C(24)-C(25)-C(26)-C(27)
32
F igu r e 4. ORTEP drawing of 3b(OMe). Except for Pt, all
the atoms have been treated with equal isotropic thermal
parameters.
Sch em e 2. NMR Ch em ica l Sh ifts of th e In ser tion
P r od u cts Sta r tin g fr om 3b(OMe)a
measured for electron-poor alkenes in a square-planar
environment. A large coordination shift (∆δ) of the
olefin protons with respect to those of the free ligands
(ca. 2 ppm) was observed. An important contribution
to the shift ensues from the shielding due to the aryl
rings of the chelates, which are orthogonal to the
coordination plane of Pt. The carbon NMR spectra
deserve some comment. Though not clearly established
whether olefin-to-metal π-back-donation is strongly
reflected by 13C trends,6 ∆δ’s values of alkene carbons
have been previously used as a measure of the extent
of π-back-donation in five-coordinate complexes of for-
mula [PtCl(Me)(N,N-chelate)(η2-olefin)].7 ∆δ’s values
for type 3 complexes of electron-poor olefins are smaller
than those measured on the just mentioned five-
coordinate species (ca. 57 vs. ca. 90 ppm8), where a
substantial contribution of π-back-donation is acknowl-
edged. However, on the average they are ca. 7 ppm
larger than that measured on the related ethylene
complex [PtMe{diacetyl bis(di-i-propylphenylimine)}(η2-
ethylene)]BF4.2 Likely, this shift at higher field can be
ascribed to a significant contributtion of π-back-donation
prompted by the electron-withdrawing substituents.
Hoping to gain further information on the nature of
the Pt-olefin bond, the X-ray crystal structure of a
representative complex, i.e., [PtMe{diacetyl bis(dieth-
ylphenylimine)}(η2-CH2dCHCO2Me)]BF4 [3b(OMe)], was
determined (Figure 4). Unfortunately, as found for
similar cationic diacetyl bis(diarylimine) derivatives,2,9
the structure is characterized by a relevant statistical
desorder due to rotations or wide librations of all of the
four ethyl groups and to the usually imprecise localiza-
a
The abbreviations used for describing NMR multiciplities
are: d, doublet; dd, double doublet; m, multiplet; t, triplet.
standard deviations, the overall molecular features are
not invalidated. As expected, the methyl acrylate
substituent is oriented as in 3′. The aromatic rings of
the ligand lie orthogonal to the coordination plane of
Pt, such as to relieve, at best, any interaction with the
methyl acrylate substituent. Furthermore, a relevant
difference of the bond lengths Pt-N(1) (2.16(3) Å) and
Pt-N(2) (1.91(3) Å) confirms the stronger trans influ-
ence of alkyl groups with respect to olefins.2
The solution behavior of some type 3 complexes was
also preliminarly investigated. When a chloroform
solution of 3b(OMe) was heated at 333 K, formation of
the corresponding cyclometalated insertion product
5b(OMe) quantitatively occurred within a few hours
(Scheme 2).10 The complex could be crystallized by slow
addition of pentane to the reaction mixture. Coordina-
tion of the carbonyl group was suggested by the shift of
-
tion of the BF4 ions. Some reliable and significant
geometrical parameters of the complex are reported in
Table 3.
Although no particular meaning can be ascribed to
the molecular parameters due to their very large
(6) Cooper, D. G.; Powell, J . Inorg. Chem. 1976, 15, 1959.
(7) Albano, V. G.; Natile, G.; Panunzi, A. Coord. Chem. Rev. 1994,
133, 67.
(8) ∆δ values increase ca. 9 ppm on going from ethylene to methyl
acrylate in trigonal-bipyramidal complexes.7
(9) Giordano, F. Private communication.
(10) The corresponding Pd(II) complex [PdMe{diacetyl bis(di-i-
propylphenylimine)}(η2-CH2dCHCO2Me)]+ displayed
a
similar
behavior.1b,c

Insertion of an Alkene into a Pt-Alkyl Bond
Organometallics, Vol. 17, No. 12, 1998 2649
its band in the IR spectrum from 1720 cm-1 in 3b(OMe)
to ca. 1600 cm-1 in 5b(OMe).11 By monitoring the
reaction through NMR spectroscopy, it was also possible
to detect signals diagnostic of the intermediate σ-alkyl
compounds 6b(OMe) and 7b(OMe). We suggest that in
the case of 6b(OMe) and 7b(OMe), one carbonyl group
also coordinates to Pt, in analogy with the corresponding
Pd complexes.1b,c Similar results were obtained by
starting from 3a (OMe).
Ta ble 4. Su m m a r y of th e Cr ysta l Da ta a n d
In ten sity Collection for 3b(OMe)
formula
C29H41BF4N2O2Pt
mw
731.55
space group
a/Å
P21/c
12.030(2)
b/Å
c/Å
14.755(2)
18.631(2)
R/deg
90
106.1(1)
90
3177.35
â/deg
γ/deg
V/Å3
We underline the importance of the above-reported
results. Actually, insertion of electron-rich monoalkenes
into Pt-alkyl bonds are not known.12,13 Moreover,
theoretical calculations14 do predict a large activation
barrier for this process. As far as we know, the sole
reported insertion of a monoalkene into a Pt(II)-R bond
involves an electron-poor olefin, i.e., the highly activated
tetrafluoroethylene.15 Detailed studies on the properties
and reactivity of type 3 compounds are now in progress.
Z
4
cryst dimens/mm
F(000)
Dc/g cm-1
µ/cm-1
T/K
0.3 × 0.3 × 0.1
1456
1.53
42.74
298
radiation (λ/Å)
graphite-monochromated
Mo KR (λ ) 0.7107)
take-off angle/deg
3
scan speed/deg min-1
2θ range/deg
2.0 in the 2θ mode
3.0 e 2θ e 45
1924
0.104
0.7
no. of unique reflns [Fo g 2σ(Fo)]
R (on Fo)a
Exp er im en ta l Section
highest map residual/e Å-3
a
R ) ∑||Fc| - |Fo||/∑|Fo|.
NMR spectra were recorded on a 200-MHz (Varian model
Gemini), 250-MHz (Bruker model AC-250), or 400-MHz spec-
trometer (Bruker model DRX-400). The solvent was CDCl3
(CHCl3 (δ ) 7.26 ppm) or CDCl3 (δ ) 77.0) as internal
standards). The following abbreviations were used for describ-
ing NMR multiplicities: no attribute, singlet; dd, double
doublet; m, multiplet. The complexes [PtCl(Me){diacetyl bis-
(di-i-propylphenylimine)}] and [PtCl(Me){diacetyl bis(diethyl-
phenylimine)}] were prepared according to literature methods.2
Dichloromethane was distilled from CaH2 immediately before
use.
propriate olefin (4-6 equiv) under nitrogen. To the resulting
mixture was added a solution of [Pt(I)Me(N,N-chelate)] (1.0
mmol) in 5 mL of dichloromethane. After 5 h of stirring (12 h
in the case of CH2dCHCONMe2), AgI was removed by filtra-
tion on Celite and the volume of the resulting solution was
reduced to 5 mL under vacuum. Yellow crystals of product
were obtained by careful addition of diethyl ether. The crystals
were washed with diethyl ether (2 × 5 mL) and dried under
vacuum. Yield: 70-80%.
Rea ction s of [P tMe(N,N-ch ela te)(η2-CH2dCHCO2Me)]-
BF 4 [3a (OMe), 3b(OMe)]. A solution of the appropriate type
3 complex (0.10 mmol) in 1 mL of chloroform was heated at
333 K for 12 h. n-Pentane was added to the dark solution,
which was stored 24 h at 253 K. Red crystals of the corre-
sponding type 5 product were collected, washed with n-
pentane, and dried under vacuum. Yield: 60-65%. Selected
1H NMR resonances (δ): 5a (OMe) 3.10 (3H, OMe), 2.32 (2H,
dd, Pt-CH2CH2CH2C(O)), 2.19 and 2.11 (6H, NdC(Me)-C′-
(Me)dN), 1.65 (2H, dd, Pt-CH2CH2CH2C(O)), 0.89 (2H, m, Pt-
CH2CH2CH2C(O)); 5b(OMe) 3.12 (3H, OMe), 2.29 (2H, dd, Pt-
CH2CH2CH2C(O)), 2.12 and 1.95 (6H, NdC(Me)-C′(Me)dN),
1.58 (2H, dd, Pt-CH2CH2CH2C(O)), 0.85 (2H, m, Pt-CH2CH2-
CH2C(O)). Selected 13C NMR resonances (δ): 5a (OMe) 55.0
(OMe), 35.6 (3J Pt-C ) 33 Hz, Pt-CH2CH2CH2C(O)), 28.4 and
28.0 (Ar-CHMe2 and Ar-C′HMe2), 24.1, 23.9, 23.5, 23.2 (Ar-
CHMeMe′ and Ar-C′HMeMe′), 21.7 (Pt-CH2CH2CH2C(O)),
21.5 and 19.7 (NdC(Me)-C′(Me)dN), 9.2 (1J Pt-C ) 748 Hz, Pt-
CH2CH2CH2C(O)); 5b(OMe) 55.0 (OMe), 35.5 (3J Pt-C ) 36 Hz,
Pt-CH2CH2CH2C(O)), 24.0 and 23.2 (Ar-CH2Me and Ar-
C′H2Me), 21.5 (2J Pt-C ) 38 Hz, Pt-CH2CH2CH2C(O)), 20.5 and
19.3 (NdC(Me)-C′(Me)dN), 14.2 and 13.0 (Ar-CH2Me and
Ar-CH2Me′), 8.9 (1J Pt-C ) 745 Hz, Pt-CH2CH2CH2C(O)).
Cr ysta l Str u ctu r e Deter m in a tion of 3b(OMe). Crystals
suitable for diffractometric analysis were obtained from a
chloroform/pentane solution. Crystal data, intensity data, and
procession details are presented in Table 4. The data were
obtained with a Philips PW-100 four-circle automated diffrac-
tometer with a graphite monochromator. Intensity data were
collected at 298 K using the θ-2θ scan method. Two reference
reflections, monitored periodically, showed no significant
variation in intensity. Data were corrected for Lorentz and
polarization effects but not for absorption. The position of Pt
was determined from a three-dimensional Patterson function.
The difficulty to localize the atoms of the ethyl and acrylate
groups and those of the BF4- ions was at once apparent, which
Syn th eses of [P tI(Me)(N,N-ch ela te)] P r ecu r sor s, N,N-
Ch ela te ) Dia cetyl Bis(d i-i-p r op ylp h en ylim in e) (4a ) or
Dia cetyl Bis(d ieth ylp h en ylim in e) (4b). To a solution of
the appropriate complex [PtCl(Me)(N,N-chelate)] (1.0 mmol)
in 10 mL of dichloromethane was added under nitrogen AgBF4
(0.20 g, 1.0 mmol) dissolved in 10 mL of acetonitrile. After 24
h of stirring at room temperature, AgCl was removed by
filtration on Celite and the solvents were removed under
vacuum. The residue was dissolved in 10 mL of chloroform,
and the resulting solution was shaken with 10 mL of a KI-
saturated water solution. The organic phase was separated,
and the water phase was extracted with chloroform (3 × 5 mL).
The combined organic phases were dried over sodium sulfate.
After filtration, removal of the solvent under vacuum afforded
the product as a red-purple solid. Yield 90-95%. 1H NMR
Pt-Me resonance (δ): 3a 1.10 (2J Pt-H ) 77 Hz); 3b 0.98 (2J Pt-H
) 76 Hz).
Syn th eses of [P tMe(N,N-ch ela te)(η2-olefin )]BF 4 Com -
p lexes (3). To a suspension of AgBF4 (0.20 g, 1.0 mmol) in
10 mL of dichloromethane was added an excess of the ap-
(11) Coordination of the carbonyl group to Pt generally causes a
lowering of its stretching frequency, see, for example: De Felice, V.;
De Renzi, A.; Ruffo, F.; Tesauro, D. Inorg. Chim. Acta 1994, 219, 169
and references therein. In the case of 5b(OMe), the band was shifted
in the region pertaining to the aromatic C-C stretchings and, hence,
its frequency could not be accurately determined.
(12) Actually, insertion of an electron-rich alkene into a Pt-C bond
has been described for an alkene hanging from a σ-bonded alkyl chain,
see: Flood, T. C.; Bitler, S. P. J . Am. Chem. Soc. 1984, 106, 6076.
(13) On the other hand, insertion of electron-rich olefins into Pt-
aryl bonds is a well-known process, see, for example: De Felice, V.;
De Renzi, A.; Tesauro, D.; Vitagliano, A. Organometallics 1992, 11,
3669.
(14) Stro¨mberg, S.; Svensson, M.; Zetterberg, K. Organometallics
1997, 16, 3165.
(15) Clark, H. C.; Puddephatt, R. J .Inorg. Chem. 1970, 9, 2670.

2650 Organometallics, Vol. 17, No. 12, 1998
Ganis et al.
implied a noticeable degree of structural disorder due to high
libration of these groups. Most of the coordinates of the
corresponding atoms were chosen among the constellation of
maxima around their expected position with the highest
electron density. They have not been refined, and their
isotropic thermal factors were also blocked. The hydrogen
atoms were not included in the calculations. A detailed
description of the involved disorder could not be established
with certainty from structure refinements and difference
Fourier synthesis. These facts explain the relatively high
value of the final R index and the large standard deviations
of the structural parameters. Blocked cascade least-squares
refinements converged to R) 0.105. The final positional
parameters of the non-hydrogen atoms are listed in Table S2.
Ack n ow led gm en t. We thank the Consiglio Nazio-
nale delle Ricerche and the MURST for financial sup-
port and the Centro Interdipartimentale di Metodologie
Chimico-fisiche, Universita` di Napoli “Federico II” for
NMR and X-ray facilities.
Su p p or tin g In for m a tion Ava ila ble: Text giving elemen-
tal analysis and tables of atomic coordinates, anisotropic
thermal parameters, and bond lengths and angles 3b(OMe)
(4 pages). Ordering information is given on any current
masthead page.
OM9800750