Cationic unsymmetrical 1,4-diazabutadiene complexes of platinum(II)

Article abstract of DOI:10.1021/om000052x

The synthesis of the silyl-protected 1,4-diazabutadiene ligands glyoxal-bis((2-α-triisopropylsiloxymethyl)-6-methylphenyl)diimine (TIPS-6-MPD) and glyoxal-bis((2-α-triisopropylsiloxymethyl)-4-methylphenyl)diimine (TIPS-4-MPD) and their subsequent reactions with trans-Pt(SMe₂)₂(Me)Cl to generate the corresponding complexes (TIPS-6-MPD)Pt(Me)Cl (1a) and (TIPS-4-MPD)Pt(Me)Cl (1b) are described. Cationic complexes of the type [(N,N-chelate)-Pt(Me)(L)]BF₄ (where L = solvent/olefin and N,N-chelate = TIPS-6-MPD and TIPS-4-MPD) are generated by the reaction of chloro methyl complexes 1a and 1b with AgBF₄ in the presence of L. Various exchange reactions were examined for [(TIPS-6-MPD)Pt(Me)(NCCH₃)]-BF₄ (2a), in which it was determined that the coordinated solvent reversibly exchanges with acrylonitrile, ethylene, fumaronitrile, cis-pentenenitrile, benzonitrile, dimethyl sulfide, and carbon monoxide to generate the corresponding cationic complexes 3-9, respectively. Kinetics experiments under pseudo-first-order conditions using 10-, 20-, and 30-fold excesses of benzonitrile demonstrate that 2a undergoes ligand exchange via an associative pathway with a bimolecular rate constant k₂ of (3.2 ± 2.0) × 10^-4 M^-1 s^-1. Complex 2a was found to initiate the polymerization of various electron-rich monomers. A detailed analysis of the reaction demonstrates that the initiation is cationic in nature. The molecular structure of TIPS-6-MPD has been determined by a single-crystal X-ray diffraction analysis. The free ligand adopts an s-trans conformation with a planar N=C-C=N backbone.

Full text of DOI:10.1021/om000052x

Organometallics 2000, 19, 3543-3555
3543
Ca tion ic Un sym m etr ica l 1,4-Dia za bu ta d ien e Com p lexes
of P la tin u m (II)
Paul J . Albietz, J r., Kaiyuan Yang, Rene J . Lachicotte, and Richard Eisenberg*
Department of Chemistry, University of Rochester, Rochester, New York 14627
Received J anuary 21, 2000
The synthesis of the silyl-protected 1,4-diazabutadiene ligands glyoxal-bis((2-R-triisopro-
pylsiloxymethyl)-6-methylphenyl)diimine (TIP S-6-MP D) and glyoxal-bis((2-R-triisopropyl-
siloxymethyl)-4-methylphenyl)diimine (TIP S-4-MP D) and their subsequent reactions with
trans-Pt(SMe2)2(Me)Cl to generate the corresponding complexes (TIPS-6-MPD)Pt(Me)Cl (1a )
and (TIPS-4-MPD)Pt(Me)Cl (1b) are described. Cationic complexes of the type [(N,N-chelate)-
Pt(Me)(L)]BF4 (where L ) solvent/olefin and N,N-chelate ) TIP S-6-MP D and TIP S-4-MP D)
are generated by the reaction of chloro methyl complexes 1a and 1b with AgBF4 in the
presence of L. Various exchange reactions were examined for [(TIPS-6-MPD)Pt(Me)(NCCH3)]-
BF4 (2a ), in which it was determined that the coordinated solvent reversibly exchanges with
acrylonitrile, ethylene, fumaronitrile, cis-pentenenitrile, benzonitrile, dimethyl sulfide, and
carbon monoxide to generate the corresponding cationic complexes 3-9, respectively. Kinetics
experiments under pseudo-first-order conditions using 10-, 20-, and 30-fold excesses of
benzonitrile demonstrate that 2a undergoes ligand exchange via an associative pathway
with a bimolecular rate constant k2 of (3.2 ( 2.0) × 10-4 M-1 s-1. Complex 2a was found to
initiate the polymerization of various electron-rich monomers. A detailed analysis of the
reaction demonstrates that the initiation is cationic in nature. The molecular structure of
TIP S-6-MP D has been determined by a single-crystal X-ray diffraction analysis. The free
ligand adopts an s-trans conformation with a planar NdCsCdN backbone.
In tr od u ction
example, Ruffo et al.10-14 have recently reported the
examination of a number of cationic platinum olefin
complexes containing various ortho alkyl-substituted
Ar2DAB ligands. Successful structural characterization
of two of these platinum-olefin complexes has been
achieved, one in which a crystal structure of an η2-bound
ethylene adduct was determined, and the other in which
connectivity of an η2-bound methyl acrylate complex was
established. Research on these Pt model compounds
provides insight as to how olefins bind and interact with
late transition metals, which in turn may then be
applied to the design of future catalysts to increase
their effectiveness and the types of polymers they can
generate.
Over the past decade, a growing interest in the use
of palladium and other late transition metal diaryldi-
azabutadiene (Ar2DAB) complexes has developed due
to their high activities as R-olefin polymerization cata-
lysts. Some of the most noteworthy of the work regard-
ing such systems has been reported by Brookhart1-3 and
describes the employment of well-defined complexes
with activities comparable to those of the more classical
early transition metal polymerization catalysts. Use of
Ar2DAB molecules as ligands for these systems allows
for flexibility regarding the kinds of polymers that can
be generated, since the ortho alkyl groups on the aryl-
imine moiety influence the structure of the resulting
polymer. Furthermore, synthesis of the ligands is based
on relatively cheap and readily available starting ma-
terials that allow for a great deal of synthetic versatility
at low cost.
The use of electrophilic platinum complexes for C-H
bond activation has also grown over the past few years.
(5) van Asselt, R.; Elsevier, C. J .; Smeets, W. J . J .; Spek, A. L. Inorg.
Chem. 1994, 33, 1521-1531.
(6) van Asselt, R.; Elsevier, C. J .; Amatore, C.; J utand, A. Organo-
metallics 1997, 16, 317-328.
Stimulated by the growing interest in palladium
Ar2DAB complexes as polymerization catalysts, the
study of analogous electrophilic platinum complexes has
also increased. Because of their greater stability, these
platinum complexes constitute excellent model com-
pounds for the more reactive Pd congeners.4-14 For
(7) Albietz, P. J ., J r.; Yang, K.; Eisenberg, R. Organometallics 1999,
18, 2747-2749.
(8) Yang, K.; Lachicotte, R. J .; Eisenberg, R. Organometallics 1997,
16, 5234-5243.
(9) Yang, K.; Lachicotte, R. J .; Eisenberg, R. Organometallics 1998,
17, 5102-5113.
(10) Ferrara, M. L.; Orabona, I.; Ruffo, F.; Funicello, M.; Panunzi,
A. Organometallics 1998, 17, 3832-3834.
(1) Killian, C. M.; J ohnson, L. K.; Brookhart, M. Organometallics
1997, 16, 2005-2007.
(11) Ferrara, M. L.; Giordano, F.; Orabona, I.; Panunzi, A.; Ruffo,
F. Eur. J . Inorg. Chem. 1999, 1, 1939-1947.
(12) Fusto, M.; Giordano, F.; Orabona, I.; Ruffo, F. Organometallics
1997, 16, 5981-5987.
(2) Killian, C. M.; Tempel, D. J .; J ohnson, L. K.; Brookhart, M. J .
Am. Chem. Soc. 1996, 118, 11664-11665.
(3) J ohnson, L. K.; Killian, C. M.; Brookhart, M. J . Am. Chem. Soc.
1995, 117, 6414-6415.
(13) Ganis, P.; Orabona, I.; Ruffo, F.; Vitagliano, A. Organometallics
1998, 17, 2646-2650.
(14) Zuccaccia, C.; Macchioni, A.; Orabona, I.; Ruffo, F. Organome-
tallics 1999, 18, 4367-4372.
(4) van Asselt, R.; Rijnberg, E.; Elsevier, C. J . Organometallics 1994,
13, 706-720.
10.1021/om000052x CCC: $19.00 © 2000 American Chemical Society
Publication on Web 08/01/2000

3544 Organometallics, Vol. 19, No. 18, 2000
Albietz et al.
Bercaw,15-19 Periana,20 Goldberg,21 and Tilset22 have
recently reported a number of cationic Pt(II) complexes
that undergo the intermolecular C-H bond cleavage of
various substrates. Knowledge gained from these stud-
ies builds upon the seminal work of Shilov23,24 and may
allow for the catalytic activation and subsequent func-
tionalization of one of the most unreactive bonds in
organic molecules. The observation that cationic Pt(II)
complexes can activate these bonds demonstrates that
a rich field of electrophilic chemistry exists for these
complexes.
Sch em e 1
Recently we reported8,9 the synthesis and character-
ization of a series of Pd(II) and Pt(II) complexes coor-
dinated to a new unsymmetrical 1,4-diazabutadiene
ligand, MOM-4,6-DBP D (vide infra). The different
ortho substituents on each aromatic ring result in a
ligand that may potentially impose a C2 symmetric
environment on the coordinated metal ion. Although the
ligand synthesis is both versatile and straightforward,
it does entail a somewhat lengthy five-step procedure.
Additionally, the presence of the bulky ortho substitu-
ents led to formation of two isolable but hard to separate
isomers (syn and anti) upon complexation that differ in
the relative orientation of the ortho tert-butyl and
methoxymethyl (MOM) groups with respect to the
coordination plane. Therefore, other routes to potentially
C2 symmetric Ar2DAB derivatives have been examined.
Resu lts a n d Discu ssion
Syn th esis of th e Silyl-P r otected Diim in e Ligan ds.
Through the use of the commercially available 3- and
5-methyl-2-aminobenzyl alcohols, a two-step synthesis
of potentially C2 symmetric Ar2DAB ligands was devised
as shown in Scheme 1. It was found that silylation of
the alcohol functionality was first necessary in order to
synthesize the desired Ar2DAB ligands and prevent
oxazole formation by cyclization.25 This was accom-
plished in high yields through the use of standard
conditions (Scheme 1). A dichloromethane solution of
the methyl-2-aminobenzyl alcohol, imidazole, and a
catalytic amount of 4-(dimethylamino)pyridine (DMAP)
in dichloromethane was cooled to 0 °C followed by the
addition of triisopropylchlorosilane (TIPSCl) to result
in the formation of the imidazole-hydrochloride salt as
a white solid. After subsequent workup, the silyl-
protected products were obtained in ca. 90% yield as
pale, yellow oils.
As shown in Scheme 1, reaction of the silyl-ether
derivatives of the methyl-2-aminobenzyl alcohols with
0.5 equiv of glyoxal generates the diazabutadiene ligands
TIP S-6-MP D and TIP S-4-MP D as yellow solids with
yields close to 70%. Both of the ligands demonstrate
high solubilities in most organic solvents and can be
recrystallized from CH2Cl2/ethanol (1:5 v/v) at -10 °C.
Herein we report on the two-step synthesis of two
unsymmetrical Ar2DAB ligands that are based on
readily available starting materials and the synthesis,
characterization, and reactivity of the corresponding
cationic Pt(II) diimine complexes. A kinetics analysis
for ligand exchange of one of the complexes has been
conducted to establish the pathway by which displace-
ment occurs. In this study we also describe the extraor-
dinary ability of a cationic acetonitrile complex contain-
ing one of the Ar2DAB ligands to polymerize various
electron-rich olefins by a cationic mechanism. Part of
this work has appeared in preliminary form.7
1
In the H NMR spectrum of TIP S-6-MP D in CDCl3,
the characteristic imine resonance is observed as a
singlet at δ 8.14. Likewise, the benzylic and methyl
resonances are also singlets at δ 4.66 and 2.19, respec-
tively, indicating effective mirror symmetry for the
molecule. Coupling of the terminal methyl groups on
the triisopropylsiloxy group to the proton on the second-
ary carbon results in splitting of the methyl resonance
into a doublet at δ 1.08 (3J HH ) 6.4 Hz) and splitting of
the methine proton into a septet at δ 1.14.
Due to the symmetry of the molecule, the 13C{1H}
NMR spectrum of TIP S-6-MP D is relatively simple. A
(15) Holtcamp, M. W.; Neling, L. M.; Day, M. W.; Labinger, J . A.;
Bercaw, J . E. Inorg. Chim. Acta 1998, 270, 467-478.
(16) Holtcamp, M. W.; Labinger, J . A.; Bercaw, J . E. J . Am. Chem.
Soc. 1997, 119, 848-849.
(17) Holtcamp, M. W.; Labinger, J . A.; Bercaw, J . E. Inorg. Chim.
Acta 1997, 265, 117-125.
(25) The product is a white solid that precipitates out of the reaction
mixture and is soluble in CH2Cl2, CHCl3, acetone, and THF and
insoluble in hexanes. The 1H NMR spectrum and the elemental
analysis of the compound are consistent with the structure drawn
below. 1H NMR (CDCl3): δ 6.99 (2H,), 6.79 (4H), 5.08 (1H), 5.05 (1H),
4.93 (2H), 4.90(1H), 4.78 (1H), 4.21 (2H), 2.17 (3H), 2.16 (3H). Anal.
Calcd for (C18H20N2O2): C, 72.95; H, 6.80; N, 9.45. Found: C, 73.07;
H, 6.83; N, 9.41. Mp: 170 °C dec.
(18) Luinstra, G. A.; Wang, L.; Stahl, S. S.; Labinger, J . A.; Bercaw,
J . E. J . Organomet. Chem. 1995, 504, 75-91.
(19) Stahl, S. S.; Labinger, J . A.; Bercaw, J . E. J . Am. Chem. Soc.
1996, 118, 5961-5976.
(20) Periana, R. A.; Taube, D. J .; Gamble, S.; Taube, H.; Satoh, T.;
Fujii, H. Science 1998, 280, 560-564.
(21) Wick, D. D.; Goldberg, K. I. J . Am. Chem. Soc. 1997, 119,
10235-10236.
(22) J ohansson, L.; Ryan, O. B.; Tilset, M. J . Am. Chem. Soc. 1999,
121, 1974-1975.
(23) Goldshleger, N. F.; Eskova, V. V.; Shilov, A. E.; Shteinmann,
A. A. Zh. Fiz. Khim. 1972, 46, 1353.
(24) Kushch, K. A.; Lavrushko, V. V.; Misharin, Y. S.; Moravsky,
A. P.; Shilov, A. E. New J . Chem. 1983, 7, 729.

1,4-Diazabutadiene Complexes of Pt
Ta ble 1. Selected 1H NMR Sp ectr a l Da ta for Ma jor Isom er s of New Com p ou n d s
1H NMR (δ)a
Organometallics, Vol. 19, No. 18, 2000 3545
compound
3
TIP S-6-MP D
8.14 (s, 1H, NCH), 7.49 (d, 1H, J HH ) 7.1 Hz, C6H), 7.18-7.12 (m, 2H, C6H), 4.66 (s, 2H, CH2),
3
2.19 (s, 3H, C6H3CH3), 1.14 (sep, 1H, Si(CH(CH3)2)3), 1.08 (d, 9 H, J HH ) 6.4 Hz,
Si(CH(CH3)2)3)
TIP S-4-MP D
8.26 (s, 1H, NCH), 7.47 (s, 1H, C6H), 7.07 (d, 1H, J ortho ) 8.0 Hz, C6H), 6.92 (d, 1H, J ortho ) 8.0
Hz, C6H), 4.95 (s, 2H, CH2), 2.38 (s, 3H, C6H3CH3), 1.17 (sep, 1H, Si(CH(CH3)2)3), 1.08 (d, 9 H,
3J HH ) 6.7 Hz, Si(CH(CH3)2)3)
3
3
2
1a
1b
2a
2b
3
9.38 (s, 1H, J Pt-H ) 104 Hz, NCH), 8.81 (s, 1H, J Pt-H ) 32 Hz, NCH), 4.86 (d, 1H, J HH ) 13 Hz,
2 2 2
CHaH), 4.79 (d, 1H, J HH ) 12 Hz, CHbH), 4.74 (d, 1H, J HH ) 12 Hz, CHcH), 4.70 (d, 1H, J HH
)
2
13 Hz, CHdH), 2.36 (s, 3H, C6H3CH3), 2.26 (s, 3H, C6H3CH3), 1.30 (s, 3H, J Pt-H ) 80 Hz, PtCH3)
3
3
2
9.38 (s, 1H, J Pt-H ) 98 Hz, NCH), 8.85 (s, 1H, J Pt-H ) 32 Hz, NCH), 5.02 (d, 1H, J HH ) 12 Hz,
CHaH), 4.62-4.78 (m, 3H, CHb,c,dH), 2.42 (s, 3H, C6H3CH3), 2.38 (s, 3H, C6H3CH3), 1.38 (s, 3H,
2J Pt-H ) 80 Hz, PtCH3)
2
2
9.08 (s, 1H, NCH), 8.98 (s, 1H, NCH), 5.13 (d, 1H, J HH ) 14 Hz, CHaH), 4.84 (d, 1H, J HH ) 14
2
2
Hz, CHbH), 4.79 (d, 1H, J HH ) 14 Hz, CHcH), 4.68 (d, 1H, J HH ) 14 Hz, CHdH), 2.30 (s, 3H,
2
C6H3CH3), 2.25 (s, 3H, C6H3CH3), 2.06 (s, 3H, CH3CN), 0.73 (s, 3H, J Pt-H ) 74 Hz, PtCH3)
2
2
9.08 (s, 1H, NCH), 8.95 (s, 1H, NCH), 5.27 (d, 1H, J HH ) 13 Hz, CHaH), 4.93 (d, 1H, J HH ) 13
2
2
Hz, CHbH), 4.82 (d, 1H, J HH ) 13 Hz, CHcH), 4.73 (d, 1H, J HH ) 13 Hz, CHdH), 2.43 (s, 3H,
2
C6H3CH3), 2.40 (s, 3H, C6H3CH3), 2.21 (s, 3H, CH3CN), 0.82 (s, 3H, J Pt-H ) 74 Hz, PtCH3)
3
3
9.12 (s, 1H, NCH), 9.01 (s, 1H, NCH), 6.27 (d, 1H, J cis ) 12 Hz, CH2CHCN), 5.97 (d, 1H, J trans
3
3
) 18 Hz, CH2CHCN), 5.52 (dd, 1H, J cis ) 12 Hz, J trans ) 18 Hz, CH2CHCN), 2.31 (s, 3H,
2
C6H3CH3), 2.24 (s, 3H, C6H3CH3), 0.74 (s, 3H, J Pt-H ) 76 Hz, PtCH3)
4
5
9.11 (s, 1H, NCH), 9.06 (s, 1H, NCH), 3.97 (m, 4H, J Pt-H ≈ 64 Hz, ethylene), 2.30 (s, 3H,
2
C6H3CH3), 2.22 (s, 3H, C6H3CH3), 0.37 (s, 3H, J Pt-H ) 68 Hz, PtCH3)
3
9.12 (s, 1H, NCH), 8.95 (s, 1H, NCH), 6.20 (d, 1H, J trans ) 16 Hz, CNCHCHCN), 6.07
3
(d, 1H, J trans ) 16 Hz, CNCHCHCN), 2.30 (3H, C6H3CH3), 2.25 (s, 3H, C6H3CH3),
2
0.77 (s, 3H, J Pt-H ) 72 Hz, PtCH3)
3
6
9.09 (s, 1H, NCH), 9.03 (s, 1H, NCH), 6.68 (m, 1H, NCCHCHCH2CH3), 5.25 (d, 1H, J HH
11 Hz, NCCHCHCH2CH3), 2.32 (s, 3H, C6H3CH3), 2.24 (s, 3H, C6H3CH3), 1.90
)
3
(m, 2H, NCCHCHCH2CH3), 0.95 (t, 3H, J HH ) 7.4 Hz, NCCHCHCH2CH3), 0.74
2
(s, 3H, J Pt-H ) 76 Hz, PtCH3)
7
8
9
9.16 (s, 1H, NCH), 9.05 (s, 1H, NCH), 2.34 (s, 3H, C6H3CH3), 2.27 (s, 3H, C6H3CH3),
2
0.81 (s, 3H, J Pt-H ) 70 Hz, PtCH3)
9.14 (s, 1H, NCH), 9.08 (s, 1H, NCH), 2.61 (s, 3H, C6H3CH3), 2.23 (s, 3H, C6H3CH3),
2.06 (s, 6H, J Pt-H ) 56 Hz, S(CH3)2), 0.65 (s, 3H, J Pt-H ) 74 Hz, PtCH3)
9.22 (s, 1H, NCH), 9.09 (s, 1H, NCH), 2.39 (s, 3H, C6H3CH3), 2.26 (s, 3H, C6H3CH3),
3
2
2
0.80 (s, 3H, J Pt-H ) 80 Hz, PtCH3)
a
All 1H NMR spectra were recorded in CDCl3 solutions. Chemical shift values are reported in ppm. Abbreviations: br, broad; s, singlet;
d, doublet; dd, doublet of doublets; m, multiplet; t, triplet; sep, septet.
Ta ble 2. Selected 13C{1H} NMR Sp ectr a l Da ta for Ma jor Isom er s of New Com p ou n d s TIP S-6-MP D,
TIP S-4-MP D, a n d 1-4
compound
13C{1H} NMR (δ)a
TIP S-6-MP D
TIP S-4-MP D
1a
1b
2a
163.6 (NCCN), 61.6 (CH2), 18.8 (C6H3CH3), 18.1 (Si(CH(CH3)2)3), 12.0 (Si(CH(CH3)2)3)
158.9 (NCCN), 61.3 (CH2), 21.4 (C6H3CH3), 18.1 (Si(CH(CH3)2)3), 12.1 (Si(CH(CH3)2)3)
165.2 (NCCN), 164.1 (NCCN), 62.5 (CH2), 61.0 (CH2), -11.1 (PtCH3, J Pt-C ) 684 Hz)
165.2 (NCCN), 162.7 (NCCN), 62.9 (CH2), 61.4 (CH2), -10.2 (PtCH3, J Pt-C ) 706 Hz)
175.4 (NCCN), 166.5 (NCCN), 119.7 (CNCH3), 60.6 (CH2), 2.59 (CNCH3), -11.7 (PtCH3,
J Pt-C ) 664 Hz)
2b
3
173.9 (NCCN), 163.9 (NCCN), 120.0 (CNCH3), 61.3 (CH2), 60.9 (CH2), 3.73 (CNCH3),
-11.2 (PtCH3, J Pt-C ) 670 Hz)
176.0 (NCCN), 167.2 (NCCN), 142.3 (CH2CHCN), 117.9 (CH2CHCN), 104.8 (CH2CHCN),
60.6 (CH2), 60.5 (CH2), -11.4 (PtCH3, J Pt-C ) 644 Hz)
177.4 (NCCN), 169.7 (NCCN), 77.3 (ethylene, J Pt-C ) 182 Hz), 61.6 (CH2), 60.9 (CH2),
-4.5 (PtCH3, J Pt-C ) 644 Hz)
4b
a
All 13C{1H} NMR spectra were recorded in CDCl3 solutions. Chemical shift values are reported in ppm. b 13C{1H} NMR spectrum
was recorded in CD2Cl2.
single resonance for the diimine carbon is observed at
δ 163.6, and the benzylic carbon atom with the silyl-
ether substituent resonates as a singlet at δ 61.6. The
resonance of the methyl group carbon atoms ortho to
the imine on the ring occur at δ 18.8, and two reso-
nances for the TIPS group are seen at δ 18.1 and 12.0.
Since the silyl-protected Ar2DAB ligands and the cor-
responding platinum complexes demonstrate similar
spectroscopic features, a detailed discussion of only one
of the representative compounds in each section is
necessary. Furthermore, complexes 1a , 2a , 3, 4, 5, 6, 7,
8, and 9 exist as two isomers (vide infra) that differ in
orientation of the triisopropylsiloxy groups with respect
to the coordination plane. In those sections, only the
resonances of the major isomer (ca. 80%) are discussed.
1
Tables 1 and 2 summarize the results of H and 13C-
{1H} NMR characterization of all of the compounds
reported in this paper. Tables of the spectral data for
the minor isomers 1a ′, 2a ′, 3′, 4′, 5′, 6′, 7′, 8′, and 9′ are
contained within the Supporting Information.
A single-crystal X-ray diffraction analysis confirmed
the identity of the ligand. Crystals of the ligand were
grown from a concentrated solution of CH2Cl2/ethanol
(1:4 v/v). The ORTEP diagram of TIP S-6-MP D is shown
in Figure 1, with details of the structure determination
shown in Table 3 and relevant bond distances and bond
angles listed in Tables 4 and 5. As expected, TIP S-6-
MP D adopts an s-trans orientation about the central

3546 Organometallics, Vol. 19, No. 18, 2000
Albietz et al.
Ta ble 4. Selected Bon d Dista n ces (Å) for
TIP S-6-MP D
Si(1)-O(1)
Si(1)-C(10)
O(1)-C(9)
N(1)-C(1)
N(1)-C(2)
1.656(1)
C(1)-C(1)′
C(3)-C(9)
C(7)-C(8)
C(10)-C(11)
1.463(2)
1.506(2)
1.505(2)
1.524(2)
1.880(11)
1.423(1)
1.256(2)
1.420(2)
Ta ble 5. Selected Bon d An gles (d eg) for
TIP S-6-MP D
O(1)-Si(1)-C(10) 104.99(6) C(3)-C(2)-N(1)
O(1)-Si(1)-C(13) 110.01(5) C(7)-C(2)-N(1)
C(10)-Si(1)-C(16) 111.74(6) C(4)-C(3)-C(9)
123.04(11)
116.16(11)
118.93(11)
120.92(14)
111.17(10)
C(9)-O(1)-Si(1)
C(1)-N(1)-C(2)
N(1)-C(1)-C(1)′
C(3)-C(2)-C(7)
126.49(8) C(2)-C(7)-C(8)
120.82(11) O(1)-C(9)-C(3)
120.49(14) C(11)-C(10)-C(12) 110.10(13)
120.55(12) C(11)-C(10)-Si(1) 113.48(10)
MP D is rigorously planar, with the triisopropylsiloxy-
methyl substituents located on opposite sides of the
Ar2DAB backbone. Due to steric interactions between
the silyl-ether substituents and the imine protons, the
phenyl rings of the imine N atoms are tilted out of the
plane of the NdCsCdN backbone, as indicated by the
torsion angles of 123.55(0.14)° and -62.15(0.18)° for
C(1)-N(1)-C(2)-C(7) and C(1)-N(1)-C(2)-C(3), re-
spectively. The bond distances for the central C-C
single bond in the backbone and the CdN double bond
are 1.463(2) and 1.256(2) Å, respectively. These bond
lengths are consistent with other structurally character-
ized diimines.8,26
F igu r e 1. ORTEP diagram of TIP S-6-MP D shown in an
s-trans orientation. Thermal ellipsoids are drawn at 30%
probability. Hydrogen atoms are omitted for clarity.
Ta ble 3. Su m m a r y of Cr ysta llogr a p h ic Da ta for
TIP S-6-MP D
Crystal Parameters
chemical formula
C36H60N2O2Si2
fw
609.04
triclinic
P1h
1
8.1101(10)
8.7180(2)
13.2157(3)
86.6100(10)
78.6380(10)
87.3270(10)
913.90(3)
1.107
The 3- and 5-methyl-2-aminobenzyl alcohols differ
only in the placement of the methyl substituent on the
aromatic ring, which in turn leads to Ar2DAB ligands
having one or two ring substituents ortho to the imine
N positions. Once the ligands are complexed to the
metal, the presence of the second ortho substituent on
the aryl-imine moiety has consequences regarding the
ease of rotation about the N-C(ipso) bond. Previous work
has demonstrated9 that hindered rotation about this
bond can result in two isolable isomers differing solely
in the relative orientation of the pairs of ortho substit-
uents with respect to the coordination plane. On the
other hand, use of an Ar2DAB ligand with only one ortho
substituent leads to the synthesis of only a single
product complex.
cryst syst
space group (no.)
Z
a, Åa
b, Å
c, Å
R, deg
â, deg
γ, deg
volume, Å3
F
calc, g‚cm-3
cryst dimens, mm-3
temp, °C
0.28 × 0.32 × 0.40
-80(2)
Measurement of Intensity Data and Refinement Parameters
radiation (λ, Å)
2θ range, deg
total data
Mo, KR (0.71073)
3-57
5682
no. of unique data
R
4021
1.18, 2.36
3622
197
0.129
Syn th esis of (N,N-ch ela te)P t(Me)Cl, w h er e N,N-
ch ela te ) TIP S-6-MP D a n d TIP S-4-MP D (1a a n d
1b). The reaction of the Ar2DAB ligand TIP S-6-MP D
or TIP S-4-MP D with trans-Pt(SMe2)2MeCl in refluxing
dichloromethane proceeds smoothly to yield complexes
1a and 1b, respectively (eq 1). The two complexes are
obtained as dark purple solids with isolated yields for
this reaction in the 70-90% range. The complexes may
be further purified by recrystallization from CH2Cl2/
hexanes (1:4 v/v) at -35 °C. Complexes 1a and 1b are
soluble in most organic solvents, especially in CH2Cl2
and CHCl3, but are slightly less soluble in acetone,
acetonitrile, benzene, and toluene. At low temperatures,
the compounds are essentially insoluble in hydrocarbon
solvents. Both of the platinum complexes are stable to
air and moisture in both the solid state and in solution.
Characterization of 1a and 1b was accomplished by
1H and 13C{1H} NMR spectroscopies as well as by
int, Rsigma (%)b
no. of obsd data (I > 2σ(I))
no. of params varied
µ, mm-1
abs corr
empirical (SADABS)c
0.801-0.648
1.066
range of transmn factors
GOFd
R1(Fo), wR2(Fo2) obsd (%)e
R1(Fo), wR2(Fo2) all (%)
3.66, 10.45
4.03, 10.70
a
It has been noted that the integration program SAINT
produces cell constant errors that are unreasonably small, since
systematic error is not included. More reasonable errors might be
b
2
estimated at 10× the listed value. Rint ) ∑|Fo - Fo2(mean)|/
∑[Fo2]; Rsigma ) ∑[σ(Fo2)]/∑[Fo2]. c The SADABS program is based
on the method of Blessing; see Blessing, R. H. Acta Crystallogr.,
Sect A 1995, 51, 33. GOF ) [∑[w(Fo - Fc2)2]/(n - p]1/2, where n
d
2
and p denote the number of data and parameters. e R1 ) (∑||Fo|
- |Fc||)/∑|Fo|; wR2 ) [∑[w(Fo - Fc2)2]/∑[w(Fo2)2]]1/2 where w )
2
1/[σ2(Fo2) + (aP)2 + bP] and P ) [(Max;0,Fo2) + 2Fc2]/3.
C-C bond in the backbone of the molecule. The molecule
possesses a crystallographically imposed inversion cen-
ter, and therefore the NdCsCdN portion of TIP S-6-
(26) Van Koten, G.; Vrieze, K. Adv. Organomet. Chem. 1982, 21,
151-239.

1,4-Diazabutadiene Complexes of Pt
Organometallics, Vol. 19, No. 18, 2000 3547
observed at 198 K due to substantial broadening, while
spectra obtained for complex 1a show sharpening of the
satellites as the temperature is increased from room
temperature to 355 K. Similar effects are observed for
the Pt-CH3 group that resonates at δ 1.30 (2J Pt-H
)
80 Hz) since the half-width ∆ν1/2 for the platinum-
methyl satellites of 1a decreases from 11 Hz at room
temperature to 6 Hz at 355 K.
In addition to the imine protons and the Pt-CH3
group, four doublets in the range δ 4.70-4.86 (2J HH
≈
13 Hz) are observed that correspond to the benzylic
protons bearing the silyl-ether substituents. These
resonances demonstrate the diastereotopic nature of
each pair of benzylic protons and are consistent with
the AB coupling patterns observed for other geometri-
cally rigid benzylic systems.8,9,28-30 All of the platinum
complexes reported in this paper demonstrate similar
sets of diastereotopic resonances.
The 13C{1H} NMR spectrum of 1a shows two reso-
nances for the diimine carbons at δ 165.2 and 164.1
consistent with the lower symmetry of the complex.
Likewise, a set of 12 resonances corresponding to the
phenyl carbons are found in the aromatic region of the
spectrum (ca. δ 125), and two resonances at δ 62.5 and
61.0 are observed for the benzylic carbon atoms bearing
the silyl-ether substituents. The Pt-CH3 resonance is
seen at δ -11.1 with J Pt-C ) 684 Hz.
1
The room-temperature H and 13C{1H} NMR spectra
of 1b show that only one isomer exists in solution. In
contrast, freshly recrystallized samples of 1a contain a
small amount (approximately 4%) of a second species.
Due to the results reported previously for complexes of
the much bulkier ligand system MOM-4,6-DBP D,8,9 the
existence of syn and anti isomers of the MPD complexes
was investigated. Low-temperature 1H NMR spectral
studies of complex 1b proved to be quite informative.
At 248 K, a considerable amount of broadening was
observed in the benzylic region of the spectrum. At 223
K, decoalescence of the benzylic resonances was seen
to occur, while the aromatic and imine resonances began
to broaden. At 198 K, the slow exchange limit was
reached as sharpened resonances for the syn and anti
isomers of 1b were observed. On the basis of the
coalescence temperature (Tc) of the imine resonances,
the ∆Gq value for interconversion between the two iso-
mers of 1b is estimated to be ca. 12 kcal/mol at 223 K.
When a toluene-d8 solution of complex 1a was allowed
to stand at room temperature (296 K) for 3 days in a
resealable NMR tube, the intensities of the resonances
corresponding to the syn isomer of the complex (1a ′)
eventually increased. While less than 4% of the syn
isomer was initially present, an equilibrium was estab-
lished between the two isomers after 1 day. The equi-
librium constant, Keq, corresponding to [syn isomer]/
[anti isomer], was estimated as 0.2, corresponding to
∆G° of ca. 1.0 kcal/mol for the equilibrium. Two conclu-
sions regarding the aforementioned experiments may
be made. For complex 1b, rapid interconversion is
occurring at room temperature since new resonances are
observed to grow in when lower temperatures are
elemental analyses. In the 1H NMR spectrum of complex
1a in CDCl3, two resonances at δ 9.38 and 8.81 are
observed that correspond to the imine protons on the
backbone of the ligand. The resonances are shifted
considerably downfield from those of the free ligand. The
fact that there are two separate resonances provides
evidence of the different ligands trans to the two
coordinated imines of the TIP S-6-MP D ligand and the
consequent asymmetry of 1a . Both of the resonances
show broad platinum satellites with coupling constants
of 104 and 32 Hz, respectively. The smaller coupling
constant for the latter resonance is due to weaker
binding of the corresponding imine to platinum. Since
the methyl group has a stronger trans-effect ligand than
the chloride, this resonance most likely corresponds to
the proton on the imino group trans to the methyl group.
These observations are consistent with other character-
ized unsymmetrical chloro methyl complexes.12 The
breadth of the 195Pt satellites is probably due to a
contribution from chemical shift anisotropy (CSA). Work
by Sadler et al.27 in 1982 demonstrated that CSA
increases the 195Pt relaxation rate and broadens the
satellites by acting as the dominant spin-lattice relax-
ation mechanism. Additionally, it was noted that broad-
ening of the satellites is temperature dependent, with
effects from CSA increasing as the temperature is
lowered. The results from variable-temperature (VT) 1H
NMR experiments conducted on the chloro methyl
complexes 1a and 1b are consistent with this notion.
The satellites for the imine resonances of 1b are not
(28) J ennings, B. Chem. Rev. 1975, 75, 307.
(29) Atwood, D. A.; Remington, M. P.; Rutherford, D. Organome-
tallics 1996, 15, 4763-4769.
(30) Atwood, D. A.; J egier, J . A.; Martin, K. J .; Rutherford, D.
Organometallics 1995, 14, 1453-1460.
(27) Ismail, I. M.; Kerrison, S. J . S.; Sadler, P. J . Polyhedron 1982,
1, 57-59.

3548 Organometallics, Vol. 19, No. 18, 2000
Albietz et al.
accessed. In contrast, it is evident that rapid intercon-
version does not occur for 1a . The second ortho sub-
stituent on each aromatic ring of 1a impedes intercon-
version between the isomers by making rotation about
the N-C(ipso) bond sterically encumbered. The results
also suggest that interconversion does not proceed by
prior dissociation of the imine N.
Gen er a t ion of t h e Ca t ion ic Com p lex [(N,N-
ch ela te)P t(Me)(CH3CN)]BF 4, Wh er e N,N-ch ela te )
TIP S-6-MP D a n d TIP S-4-MP D (2a a n d 2b) via
Ha lid e Abstr a ction . The chloro methyl complexes
serve as convenient precursors for the generation of
cationic platinum complexes. The reaction between 1a
or 1b and 1.06 equiv of AgBF4 in acetonitrile (eq 2) at
room temperature results in orange-colored solutions.
averaging of the two resonances is not observed when
free MeCN is present in solution. An upper limit on the
rate of exchange at the coalescence temperature Tc
(>333 K) in CDCl3 can be estimated to be 71 s-1 based
on the chemical shift difference between the free and
coordinated acetonitrile resonances at the slow exchange
limit. The actual coalescence temperature could not be
determined due to the low boiling point of CDCl3. In an
attempt to verify that exchange of acetonitrile does
occur, albeit slowly, a reaction of 2a with CD3CN was
carried out in an NMR tube (Scheme 2). Complex 2a
was dissolved in CD3CN and allowed to stand at room
temperature for 1 h. After removal of the solvent, the
residue was redissolved in CDCl3 and the 1H NMR
spectrum was obtained. It was observed that the
resonance for coordinated acetonitrile at δ 2.06 had
disappeared, while the rest of the spectrum remained
completely unchanged. In an analogous fashion, the
reaction of 2a -d 3 with CH3CN regenerates 2a .
For complex 2a , two sets of resonances are seen in
1
the H NMR spectrum, indicating that two complexes
are present in solution in an approximate 80:20 ratio.
As was briefly mentioned in the beginning of this report,
all of the TIP S-6-MP D complexes discussed in this
paper exhibit two sets of resonances in roughly the same
ratio. Given the observations of the related chloro
methyl complex 1a , the minor set of resonances is
attributable to the syn isomer that forms through
hindered rotation about the N-C(ipso) bond. In contrast
to 2a , only one set of resonances is observed in the room-
1
Following subsequent workup, the acetonitrile adducts
2a and 2b are isolated as orange solids in ca. 70% yield.
The products are air- and moisture-stable both in the
solid state and in solution and can be purified by
recrystallization from CH2Cl2/hexanes (1:4 v/v) at -35
°C. The solvento complexes are soluble in acetonitrile,
CH2Cl2, CHCl3, THF, and acetone and insoluble in
diethyl ether, benzene, toluene, and hexanes. Complexes
temperature H NMR spectrum of 2b. Absence of the
ortho methyl groups allows free rotation to occur,
resulting in a time-averaged spectrum of the syn and
anti isomers. This is consistent with the variable-
temperature NMR studies of the neutral chloro methyl
complexes discussed in the previous section.
Syn th esis of [(TIP S-6-MP D)P t(Me)(CH2CHCN)]-
BF 4 (3). Complex 3 can be generated by reaction of 1a
with 1.1 equiv of AgBF4 in the presence of excess
acrylonitrile with dichloromethane as solvent (eq 3). 3
1
2a and 2b were characterized by H and 13C{1H} NMR
spectroscopies as well as by elemental analyses. An
X-ray diffraction analysis of 2a , which has been de-
scribed in the preliminary report on this study,7 shows
the complex to have the expected square-planar coor-
dination geometry with an anti conformation for the two
(i-Pr)3SiOCH2 groups and a difference in Pt-N(imine)
distances arising from the different trans ligands.
1
The H NMR spectrum of 2a in CDCl3 revealed two
singlets at δ 9.08 and 8.98 corresponding to the imine
protons on the backbone of the ligand. A sharp singlet
is observed at δ 2.06 for coordinated acetonitrile, even
in the presence of free MeCN, indicating that any
solvent exchange occurs slowly on the NMR time scale
at ambient temperature (vide infra). The other charac-
teristic feature of this complex is the resonance at δ 0.73
(2J Pt-H ) 74 Hz) assigned to the platinum-bound methyl
group.
is isolated as an orange-yellow, air- and moisture-stable
solid in ca. 70% yield and demonstrates solubility
similar to 2a . Lability of coordinated acrylonitrile in
3 was observed since the complex undergoes revers-
ible exchange between acrylonitrile and acetonitrile
(Scheme 2).
A 13C{1H} NMR spectrum was obtained of the aceto-
nitrile adduct 2a . The observed resonances are very
similar to those seen for the neutral chloro methyl
complexes. The coordinated acetonitrile resonances are
seen at δ 119.7 (CH3CN) and 2.59 (CH3CN) and were
found to be consistent with other examples of cationic
platinum acetonitrile complexes.9
1
The H NMR spectrum of complex 3 is comparable to
the acetonitrile analogue (see Table 1), excluding the
peaks associated with acetonitrile and acrylonitrile
ligands. All resonances for coordinated acrylonitrile are
shifted relative to the same resonances of the free
R-olefin. Two doublets corresponding to the methylene
As noted above, exchange between free and coordi-
nated acetonitrile is slow on the NMR time scale since

1,4-Diazabutadiene Complexes of Pt
Organometallics, Vol. 19, No. 18, 2000 3549
Sch em e 2
group are centered at δ 6.27 (3J HH ) 12 Hz) and 5.97
(3J HH ) 18 Hz). The larger coupling constant for the
latter resonance indicates that it is the proton on the
â-carbon cis to the nitrile group and trans to the third
olefinic proton. The R-proton of acrylonitrile appears as
a doublet of doublets at δ 5.52 (3J HH ) 12 and 18 Hz)
with both cis and trans couplings to the protons of the
methylene group. All of the coupling constants for free
and coordinated acrylonitrile are identical.
Due to the ambidentate nature of acrylonitrile, a
question arises regarding how the olefin is coordinated
to the metal, i.e., through the olefin or through the
nitrile. A comparison of complex 3 with other known
acrylonitrile complexes reported in the literature31 has
led to the conclusion that coordination is occurring
through the nitrile group. The most compelling evidence
for such an assignment is the observation of a substan-
tial higher energy shift of νCN from 2228 to 2305 cm-1
upon coordination.
Exchange between coordinated acetonitrile of complex
2a and excess ethylene is an additional pathway for
generation of 4 (Scheme 2), further demonstrating the
lability of the coordinated donor molecules.
In the 1H NMR spectrum, ethylene adduct 4 is similar
to the other cationic complexes (Table 1). The coordi-
nated ethylene resonance is centered at δ 3.97 (J Pt-H
≈
64 Hz) and shifted 1.4 ppm upfield from the free olefin.
This difference, i.e., ∆δ in Hz, allows the rate of
exchange between coordinated and free ethylene to be
estimated as 1.2 × 103 s-1 at Tc (>363 K). As shown in
Figure 2, the breadth of the coordinated ethylene
resonance of 4 increases as additional ethylene is
introduced into the NMR tube. The observation that the
features of the resonance are dependent upon the
concentration of free ethylene in solution indicates that
exchange is occurring associatively, not dissociatively.
Additional evidence for associative exchange is dis-
cussed below.
Syn th esis of [(TIP S-6-MP D)P t(Me)(eth ylen e)]-
BF 4 (4). The synthesis of complex 4 can be achieved by
reaction of 1a and 1.1 equiv of AgBF4 in an ethylene-
saturated solution of CH2Cl2 (eq 3). Complex 4 is
isolated as a yellow-orange solid in 75% yield and may
subsequently be purified by recrystallization from
CH2Cl2/hexanes (1:5 v/v) at -35 °C. The complex
demonstrates solubility similar to the other cationic
complexes with the exception that it is soluble in
hexanes and toluene. 4 is stable in the solid state, and
in solution it demonstrates slow decomposition after one
A 13C{1H} NMR spectrum was obtained of the ethyl-
ene adduct in CD2Cl2 and demonstrates ligand chemical
shifts similar to the other cationic complexes of Table
2. Coordinated ethylene is observed as a sharp singlet
at δ 77.3 with J Pt-C ) 182 Hz. Observation of only one
carbon resonance for coordinated ethylene is consistent
with rapid rotation of the olefin, which persists down
to 193 K.
Syn th esis of Ca tion ic P la tin u m Com p lexes 5-9
via Liga n d Exch a n ge w ith 2a . Syn th esis of [(TIP S-
6-MP D)P t(Me)(tr a n s-NCCHCHCN)]BF 4 (5). Com-
plex 5 was generated in a resealable NMR tube in CDCl3
via exchange of the coordinated acetonitrile of 2a with
fumaronitrile present in excess (Scheme 2). The reaction
was slow relative to the other exchange reactions
1
month. Characterization was accomplished by H and
13C{1H} NMR spectroscopies and elemental analyses.
(31) Bryan, S. J .; Huggett, P. G.; Wade, K.; Daniels, J . A.; J ennings,
J . R. Coord. Chem. Rev. 1982, 44, 149-189.

3550 Organometallics, Vol. 19, No. 18, 2000
Albietz et al.
terized by 1H NMR and IR spectroscopies. The reso-
nances of the olefinic hydrogens are observed at δ 6.68
3
(â-proton) and 5.25 (R-proton, J cis ) 11 Hz), and the
methylene and terminal methyl protons of the ethyl
substituent are observed at δ 1.90 and 0.95 (3J HH ) 7.4
Hz), respectively. As for acrylonitrile and fumaronitrile,
cis-pentenenitrile is coordinated to Pt(II) through the
nitrile and not via the olefin. Consistent with this
notion, the stretch seen at 2270 cm-1 (νCN) for 6 is
shifted 50 cm-1 to higher energy relative to free cis-
pentenenitrile.
Com p etitive Bin d in g Stu d ies. To further gauge the
electronic effects of the substituents on the olefin,
competitive exchange reactions were conducted between
the three nitriles. An equimolar mixture of acrylonitrile
and fumaronitrile in CDCl3 was added to an NMR
tube containing complex 2a . After 30 min, only reso-
nances corresponding to 3 were observed, indicating
that acrylonitrile coordinates more strongly to platinum
than fumaronitrile, presumably as a result of the latter’s
reduced nitrile basicity.
In a second competitive binding experiment, an equi-
molar solution of acrylonitrile and cis-pentenenitrile in
CDCl3 was used. After 5 min, the acetonitrile complex
had completely converted to 6. This result demonstrates
that, although acrylonitrile is less bulky than cis-pen-
tenenitrile, electronic effects play a substantial role in
the ligands’ abilities to bind. The ethyl group of cis-pen-
tenenitrile increases its ability to stabilize the cationic
metal center relative to acrylonitrile.
Gen er a t ion of [(TIP S-6-MP D)P t (Me)(L)]BF 4,
Wh er e L ) Ben zon itr ile (7), SMe2 (8), a n d CO (9).
Reversible exchange of the acetonitrile ligand of 2a by
the donor ligands benzonitrile, SMe2, and CO was found
to occur when an excess of the corresponding molecule
was present in solution. Each of the complexes was
characterized via 1H NMR analysis, and the chemical
shifts are recorded in Table 1. A kinetic analysis
involving the exchange reaction of acetonitrile by ben-
zonitrile is described below to provide further insight
into the mechanism by which exchange occurs. Confir-
mation of the correct assignment of the coordinated
dimethyl sulfide resonance of 8 was accomplished by
conducting an exchange reaction between 8 and di-
methyl sulfide-d6 in the manner discussed above for the
acetonitrile adduct. Additionally, the νCO stretch for 9
is observed at 2116 cm-1 in the IR spectrum and further
corroborates the generation of this complex.
F igu r e 2. Section of 1H NMR spectrum of 4. Traces
demonstrate the concentration dependence of free ethylene
on the features of the coordinated ethylene resonance: (a)
0 equiv; (b) 1 equiv; (c) 2 equiv; (d) 4 equiv; (e) ethylene
atmosphere. Asterisks pertain to free (5.35 ppm) and
coordinated (3.97 ppm) ethylene resonances.
discussed in this paper and reached an apparent 1:1
equilibrium of 5:2a after 1 day. Attempts at complete
conversion of the acetonitrile adduct to 5 were unsuc-
cessful. The inability of fumaronitrile to completely
displace acetonitrile is possibly a result of the electron-
withdrawing nature of the second nitrile substituent on
the donor ability of the first.
Due to the inability of fumaronitrile to completely
displace acetonitrile, exchange with the more labile
ethylene ligand of complex 4 was conducted in an NMR
tube. Table 1 summarizes the NMR spectral data for 5,
which are quite similar to those of the other cationic
Kin etic Stu d ies of th e Con cen tr a tion Dep en -
d en ce on th e Exch a n ge Rea ction s. For square-
planar complexes, ligand substitution occurs associa-
tively through a five-coordinate intermediate formed by
the entering ligand binding to the metal at one of its
axial sites. Brookhart has proposed that the aryl sub-
stituents hinder or significantly impede the usual sub-
stitution and metal alkyl decomposition paths, the latter
via â-hydride elimination, so that polymer chain growth
becomes the dominant (most rapid) kinetic process. For
the complexes discussed in this report, it was initially
thought that similar observations would be made re-
garding the ability to undergo various ligand substitu-
tion reactions. However, it was unexpectedly observed
that they demonstrate relatively facile ligand exchange
when qualitatively compared to the systems containing
complexes. Resonances for coordinated fumaronitrile are
3
observed as doublets at δ 6.20 and 6.07 with J trans
)
16 Hz compared to a singlet at δ 6.26 for the free
molecule. Due to the excess fumaronitrile present in the
sample, it was not possible to obtain νNC since the nitrile
stretch of the free ligand obscured the coordinated
ligand’s stretching frequencies. On the basis of the
manner of coordination demonstrated by acrylonitrile
in 3, it is believed that 5 corresponds to a single nitrile-
coordinated complex.
Syn t h esis of [(TIP S-6-MP D)P t (Me)(cis-NCCH-
CHEt)]BF 4 (6). Complex 6 was generated in an NMR
tube by the addition of excess cis-pentenenitrile to 2a .
After 10 min, the excess olefin was removed and the
residue redissolved in CDCl3. The complex was charac-

1,4-Diazabutadiene Complexes of Pt
Organometallics, Vol. 19, No. 18, 2000 3551
work. Results of an end group analysis indicated that
aldehyde formation was occurring when the reactions
were worked up by doing a methanol quench and an
aqueous washing. Additionally, the tacticity of the
isolated polymer demonstrated a dependence upon the
polarity of the solvent, specifically a decrease in isotac-
ticity as solvent polarity was increased. The solvent
dependence was larger than would be expected if the
polymerization were occurring directly at the platinum
center. If coordination/insertion chemistry were occur-
ring, the quasi C2 symmetry of complex 2a would result
in higher degrees of isotactic polymer than were ob-
served, especially considering that completely atactic
polymer was obtained for reactions conducted in the
most polar solvent of the series, nitromethane. Finally,
the fact that 2a oligomerizes 2,3-dihydrofuran and not
2,5-dihydrofuran indicates that direct stabilization of
the incipient carbocation by oxygen is necessary for
polymerization to occur.
While the results reported in the preliminary work
were consistent with cationic polymerization of the elec-
tron-rich monomers, the role of the platinum complex
in initiating the polymerization was not unambiguously
determined in that study. Complex 2a may directly
initiate polymerization by formation of a nonclassical
sigma complex, Scheme 3a, as proposed by Baird33,34 in
the [CpTiMe2][BMe(C6F5)3] system, or by generation of
an intermediate due to Lewis acid interaction of 2a with
some species present in the reaction mixture.
F igu r e 3. Kinetic analysis of the exchange reaction
between complex 2a and excess benzonitrile monitoring for
disappearance of coordinated acetonitrile in the H NMR
spectrum. The analysis was done under pseudo-first-order
conditions at 278 K.
1
the MOM-4,6-DBP D ligand. Furthermore, the results
of the ethylene exchange studies with complex 4 indi-
cated that is was undergoing exchange associatively.
A kinetics study examining the rate of ligand substi-
tution as a function of incoming ligand concentration
was conducted for acetonitrile complex 2a . For these
experiments, the concentration of 2a in each of three
NMR tubes was held constant at 0.014 M. Benzonitrile
was added to each of the solutions in 10-, 20-, and 30-
fold excesses at 258 K prior to the respective runs. The
ligand exchange reactions were followed spectroscopi-
cally at 278 K by monitoring the appearance of free
acetonitrile and disappearance of coordinated acetoni-
trile.32 As shown in Figure 3, the 10-, 20-, and 30-fold
excesses of benzonitrile yielded first-order rate constants
It has been well documented35 that some Lewis acids
require water as a co-initiator for the polymerization of
vinyl ethers due to in situ generation of acid. Since it
was not possible to completely rule out initiation by acid
based on the above results, additional experiments were
conducted to probe this pathway. Attempts were made
at the generation of a discrete cationic aquo complex
via halide abstraction from the chloro methyl precursor
1a in the presence of water, but these led to extensive
decomposition. Thus, an aquo analogue of 2a , which
could in principle serve as a possible source of H+, was
found not to be stable at room temperature or under
the reaction conditions in which the polymerizations
were conducted. However, the interaction of an indi-
vidual water molecule with the cationic complex 2a
leading to a Bronsted acid, Scheme 3b, could not be
ruled out.
A series of experiments were conducted in the pres-
ence of base to probe whether generation of adventitious
acid is responsible for initiation. The experiments
described below were carried out using both EVE and
NVC as the monomers. In both sets of experiments, the
observations were identical. To minimize coordination
of the base to complex 2a , 2,6-di-tert-butylpyridine was
one of the bases chosen for the experiments. Polymer
formation was observed when either EVE or NVC was
used, although the rate of polymerization was noticeably
slower. Retardation of the rate of propagation has been
reported35 for other cationically initiated systems when
base is present.
of 5.40(4) × 10-5, 1.17(2) × 10-4, and 1.49(4) × 10-4 s-1
,
respectively, which allowed for calculation of the second-
order rate constant k2 as (3.2 ( 2.0) × 10-4 M-1 s-1
.
While the structure of 2a indicates that it is sterically
encumbered in the axial coordination sites, space-filling
models suggest that a structural reorganization can
occur to accommodate the steric interactions between
the TIPS groups and the incoming ligand. For example,
slight rotation of the phenyl rings about the N-C(ipso)
bond situates the silyl-ether groups farther away from
the metal, allowing bonding interactions between orbit-
als of the entering ligand and the metal to occur.
P olym er iza tion of Electr on -Rich Mon om er s. We
previously communicated7 the observation that complex
2a can polymerize the electron-rich olefins ethyl vinyl
ether (EVE) and N-vinylcarbazole (NVC). Specifically,
2a in chloroform was found to promote formation of
poly-EVE with a Mw of ca. 8900 and a polydispersity of
1.7 when done at 303 K. A corresponding reaction of 2a
and N-vinylcarbazole yielded poly-NVC with a Mw of ca.
23 000 and Mw/Mn of 3.1. Numerous experiments were
conducted probing the nature of the polymerization, the
results of which were found to be consistent with
generation of a stabilized carbocation that would un-
dergo subsequent propagation and polymer formation.
The following observations summarize the preliminary
(32) It was determined that both of these methods resulted in
identical values for the observed rate constants.
(33) Wang, Q.; Baird, M. C. Macromolecules 1995, 28, 8021-8027.
(34) Quyoum, R.; Wang, Q.; Tudoret, M.-J .; Baird, M. C.; Gillis, D.
J . J . Am. Chem. Soc. 1994, 116, 6435-6436.
(35) Kennedy, J . P.; Kelen, T.; Guhaniyogi, S. C.; Chou, R. T. J .
Macromol. Sci.-Chem. 1982, A18(1), 129-152.

3552 Organometallics, Vol. 19, No. 18, 2000
Albietz et al.
Sch em e 3
point the rates of propagation for both of the samples
with and without water are the same. These experi-
ments are reproducible and lend further support to the
notion that the platinum complex is acting as the sole
initiator, Scheme 3a.
Other substrates such as styrene, R-methylstyrene,
p-methoxystyrene, isobutylene, and (+)-â-pinene, which
have been known to undergo cationically initiated
polymerizations or rearrangements, were also examined
using the cationic complexes. When the reaction be-
tween complex 2a and p-methoxystyrene was examined,
1
polymer was observed to form in the H NMR spectrum
over the period of several days at room temperature.
The reaction was found to be extremely slow when
compared to poly-EVE formation, even when run at 333
K. (+)-â-Pinene was observed to react slowly with
complex 439 over several days; however, the nature of
the reaction was not discernible due to poor conversion
and the complexity of the resulting spectrum. Attempts
at increasing product formation by heating the reaction
mixture led to decomposition of the platinum species
in solution, as was evidenced by formation of a black
solid on the walls of the NMR tube.
The lack of reactivity of these substrates may be
explained by considering the relative stability of the
incipient carbocation. It is well known that EVE and
NVC are more active toward cationic initiators than
styrene since the donating ability of the heteroatom
offers the carbocation greater stability.40-42 In the case
of R-methylstyrene, steric effects may explain the
observed inactivity since coordination of this molecule
was not observed to occur with either 2a or 4, even at
elevated temperatures.
F igu r e 4. Influence of water on rate of ethyl vinyl ether
consumption vs time. Water concentration is approximately
20% relative to complex 2a .
Since 2,6-di-tert-butylpyridine had been found to
affect carbocation propagation detrimentally via induced
chain termination36 or even coordination to the catalyst/
initiator,37 a second set of experiments employed a base
that can be removed from the reaction mixture prior to
addition of the monomer. Accordingly, a methylene
chloride solution of complex 2a was treated with the
solid supported-base piperidinomethyl polystyrene for
4 h, after which the base was removed by filtration and
monomer was added. Polymer formation was observed
to occur with both EVE and NVC. The aforementioned
experiments demonstrate that protonic impurities are
not serving as the initiators for these systems in the
presence of base and the rigorous absence of water.
The effect of water on the polymerization of EVE is
shown in Figure 4. From the % conversion vs time plot,
it is evident that water does not co-initiate polymeri-
zation of EVE, but rather that its presence inhibits
polymer formation due to its reaction with the propa-
gating carbocation.38 The polymerization process even-
tually recovers ca. 250 min into the reaction, at which
Con clu sion s
The silyl-protected 1,4-diazabutadiene ligands TIP S-
6-MP D and TIP S-4-MP D and their subsequent coor-
(38) Biswas, M.; Kamannarayana, P. J . Polym. Sci.: Polym. Chem.
Ed. 1976, 14, 2071-2077.
(39) Complex 4 was employed for this reaction since the ethylene
ligand is more labile than coordinated acetonitrile. Thus, no reaction
between 2a and (+)-â-pinene was observed.
(36) Guhaniyogi, S. C.; Kennedy, J . P.; Ferry, W. M. J . Macromol.
Sci.-Chem. 1982, A18(1), 25-37.
(37) Bennevault, V.; Peruch, F.; Deffieux, A. Macromol. Chem. Phys.
1996, 197, 2603-2613.
(40) Elnahas, A. M.; Clark, T. J . Org. Chem. 1995, 60, 8023-8027.
(41) Taft, R. W.; Martin, R. H.; Lampe, F. W. J . Am. Chem. Soc.
1965, 87, 2490-2491.
(42) Sawamoto, M. Prog. Polym. Sci. 1991, 16, 111-172.

1,4-Diazabutadiene Complexes of Pt
Organometallics, Vol. 19, No. 18, 2000 3553
Model 410 differential refractometer using chloroform as
eluant at room temperature. Data were analyzed using
polystyrene calibration curves. Tables 1 and 2 contain the H
dination to Pt(II) have been described. Halide abstrac-
tion from the chloro methyl complexes led to the
generation of a series of cationic solvento/olefin adducts
that were characterized by 1H and 13C{1H} NMR
spectroscopies and elemental analyses. Exchange reac-
tions were examined in which the acetonitrile ligand of
complex 2a was displaced reversibly by acrylonitrile,
ethylene, fumaronitrile, cis-pentenenitrile, benzonitrile,
dimethyl sulfide, and carbon monoxide to generate new
cationic platinum complexes 3-9, respectively. It was
determined through a kinetic investigation of benzoni-
trile exchange that these substitution reactions are
occurring in an associative manner. The acetonitrile
complex 2a demonstrates the extraordinary ability to
induce polymer formation of various electron-rich mono-
mers. A mechanistic analysis addressing the manner
of initiation and propagation was conducted to deter-
mine the nature of the polymerization process. These
studies provide evidence for direct cationic initiation by
complex 2a . Since these complexes contain weakly
bound molecules, they may serve as precursors for
catalysts in bond activation and polymerization pro-
cesses.
1
and 13C{1H} NMR data for the ligands and platinum com-
plexes discussed in this paper. IR spectra were recorded on a
6020 Galaxy series FT-IR spectrometer. Elemental analyses
were obtained from Quantitative Technologies, Inc., White-
house, NJ .
Syn th esis of Liga n d s a n d Com p lexes
(2-r-Tr iisop r op ylsiloxym eth yl)-6-m eth yla n ilin e. A 250
mL round-bottom flask was charged with imidazole (5.88 g,
86 mmol), 2-amino-3-methylbenzyl alcohol (4.74 g, 35 mmol),
4-(dimethylamino)pyridine (0.42 g, 3.4 mmol), and 95 mL of
CH2Cl2. The solution was cooled to 0 °C. Triisopropylchlorosi-
lane (10 g, 52 mmol) was added via syringe, resulting in the
immediate formation of a white precipitate. The reaction
mixture was warmed to room temperature and stirred over-
night. It was filtered, washed with three 100 mL of portions
of water and brine, and then dried over anhydrous Na2SO4 to
give 8.9 g (88%) as a clear, pale yellow oil. Purification was
1
not necessary for the next step. H NMR (CDCl3): δ 6.99 (d,
3
3
1H, J HH ) 7.5 Hz, C6H), 6.90 (d, 1H, J HH ) 7.3 Hz, C6H),
3
6.61 (t, 1H, J HH ) 7.6 Hz, C6H), 4.76 (s, 2H, CH2), 4.30 (br s,
2H, NH2), 2.17 (s, 3H, CH3), 1.13 (sep, 3H, Si(CH(CH3)2)3), 1.01
(d, 18H, J HH ) 6.6 Hz, Si(CH(CH3)2)3).
3
Exp er im en ta l Section
(2-r-Tr iisop r op ylsiloxym eth yl)-4-m eth yla n ilin e. The
same procedure was followed as described above for the
synthesis of (2-R-triisopropylsiloxymethyl)-6-methylaniline.
Imidazole (2.86 g, 42 mmol), 2-amino-5-methylbenzyl alcohol
(2.34 g, 17 mmol), 4-(dimethylamino)pyridine (0.21 g, 1.7
mmol), triisopropylchlorosilane (5.5 mL, 26 mmol), and 80 mL
Ma ter ia ls a n d Gen er a l P r oced u r es. 2-Amino-3-methyl-
benzyl alcohol (Aldrich), 2-amino-5-methylbenzyl alcohol (Al-
drich), glyoxal (Aldrich), triisopropylchlorosilane (Aldrich),
AgBF4 (Strem), N-vinylcarbazole (Aldrich), 2,6-di-tert-butylpy-
ridine (Aldrich), and piperidinomethyl polystyrene HL (200-
400 mesh, 3.48 mmol/g, NovaBiochem) were used as received.
Toluene-d8 (Cambridge Isotope), bromobenzene-d5 (Aldrich),
and nitromethane-d3 (Aldrich) were purchased in ampules and
used without further purification. Chloroform-d1 (Cambridge
Isotope) was dried over CaH2, freeze-pump-thawed, vacuum
transferred to an oven-dried storage flask, and stored in the
dark in the glovebox until use. Molecular sieves (4 Å) were
activated under dynamic vacuum (0.1 mm) for 2 days at 473
K. Tetramethylsilane (Aldrich) was dried over 4 Å activated
molecular sieves, freeze-pump-thawed, vacuum transferred
to an oven-dried storage flask, and stored in a glovebox at 233
K. Dichloromethane-d2 (Cambridge Isotope) was dried over 4
Å activated molecular sieves, freeze-pump-thawed, vacuum
transferred to an oven-dried storage flask, and stored in the
dark in the glovebox. Ethyl vinyl ether (Aldrich) was purified
for the studies probing the effects of base and water on the
polymerization. For those experiments, EVE was dried over
KOH, freeze-pump-thawed, vacuum transferred to an oven-
dried storage flask containing piperidinomethyl polystyrene,
and stored in a glovebox at 233 K. Immediately before use,
the olefin was filtered through a frit in the glovebox to remove
the polymer-supported base. trans-Pt(SMe2)2MeCl was syn-
thesized according to a published procedure.43
1
of CH2Cl2 were used. Yield: 4.4 g (88%). H NMR (CDCl3): δ
6.88 (d, 1H, J ortho ) 7.8 Hz, C6H), 6.83 (s, 1H, C6H), 6.57 (d,
1H, J ortho ) 7.9 Hz, C6H), 4.71 (s, 2H, CH2), 4.10 (br s, 2H,
NH2), 2.20 (s, 3H, CH3), 1.10 (sep, 3H, Si(CH(CH3)2)3), 1.04
3
(d, 18H, J HH ) 9.0 Hz, Si(CH(CH3)2)3).
Glyoxa l-Bis((2-r-t r iisop r op ylsiloxym et h yl)-6-m et h -
ylp h en yl)d iim in e (TIP S-6-MP D). A 25 mL round-bottom
flask was charged with (2-R-triisopropylsiloxymethyl)-6-meth-
ylaniline (2.15 g, 7.3 mmol), glyoxal (0.42 mL, 3.6 mmol, 40%
in water), and 9 mL of absolute ethanol. The color of the reac-
tion mixture changed from colorless to yellow almost instan-
taneously, and a yellow precipitate formed after a few hours.
The reaction was stirred for 24 h before isolation of the
product. The flask was cooled to -35 °C, and the yellow solid
was collected and washed with cold methanol. The product
may be purified further by recrystallization from CH2Cl2/
ethanol (1:5 v/v). Yield: 1.53 g (69%). Anal. Calcd for
C
36H60N2O2Si2: C, 70.99; H, 9.93; N, 4.60. Found: C, 70.92;
H, 9.63; N, 4.53.
Glyoxa l-Bis((2-r-t r iisop r op ylsiloxym et h yl)-4-m et h -
ylp h en yl)d iim in e (TIP S-4-MP D). The same procedure was
followed as described above for the synthesis of TIP S-6-MP D.
(2-R-Triisopropylsiloxymethyl)-4-methylaniline (6.96 g, 24
mmol), glyoxal (1.36 mL, 12 mmol, 40% in water), and 20 mL
of absolute ethanol were used. Yield: 4.9 g (68%). Anal. Calcd
for C36H60N2O2Si2‚1/2CH3CH2OH: C, 70.31; H, 10.05; N, 4.43.
Found: C, 70.38; H, 10.06; N, 4.42.
All reactions and manipulations, unless otherwise stated,
were performed in dry glassware under nitrogen atmosphere
using either standard Schlenk techniques or an inert-
atmosphere glovebox. All NMR spectra were recorded on a
1
(TIP S-6-MP D)P t(Me)Cl (1a ). A 100 mL two-necked round-
bottom flask was charged with trans-Pt(SMe2)2MeCl (0.63 g,
1.7 mmol), TIP S-6-MP D (1.14 g, 1.9 mmol), and 60 mL of
CH2Cl2. An immediate color change from yellow to purple re-
sulted. The flask was fitted with a gas inlet and a reflux con-
denser. The reaction mixture was refluxed under a slow N2
flow overnight or until all of the platinum complex was con-
Bruker AMX or a Bruker Avance 400 MHz spectrometer. H
and 13C chemical shifts (δ in ppm) are relative to tetrameth-
ylsilane and referenced using chemical shifts of residual
solvent resonances. Differential scanning calorimetric (DSC)
measurements were recorded using a TA 2920 system. Gel
permeation chromatography (GPC) experiments were done
using a Waters Model 600E liquid chromatograph fitted with
a Waters Model 996 photodiode array detector and a Waters
1
sumed by monitoring with H NMR spectroscopy. The reaction
mixture was allowed to cool to room temperature, filtered, and
concentrated. The oily, purple residue was thoroughly dried
under vacuum. The product was triturated with hexanes and
(43) Scott, J . D.; Puddephatt, R. J . Organometallics 1983, 2, 1643-
1648.

3554 Organometallics, Vol. 19, No. 18, 2000
Albietz et al.
cooled to -35 °C, and the purple solid was collected and
washed with cold hexanes. The product may be purified by
recrystallization from CH2Cl2/hexanes (1:4 v/v). Yield: 1.33
(91%). Anal. Calcd for C37H63ClN2O2PtSi2: C, 52.00; H, 7.43;
N, 3.28. Found: C, 51.99; H, 7.33; N, 3.17.
(TIP S-4-MP D)P t(Me)Cl (1b). The same procedure was
followed as described above for the synthesis of 1a . trans-Pt-
(SMe2)2MeCl (0.79 g, 2.14 mmol), TIP S-4-MP D (1.45 g, 2.37
mmol), and 70 mL of CH2Cl2 were used. Yield: 1.19 g (65%).
Anal. Calcd for C37H63ClN2O2PtSi2‚1/4CH2Cl2: C, 51.10; H,
7.31; N, 3.20. Found: C, 51.40; H, 7.36; N, 3.18.
[(TIP S-6-MP D)P t(Me)(CH3CN)]BF4 (2a). A 50 mL Schlenk
flask was charged with 1a (0.39 g, 0.46 mmol) and 30 mL of
degassed acetonitrile. AgBF4 (0.095 g, 0.49 mmol) was added
as a solid under a nitrogen flow. The reaction mixture was
stirred in the dark for 24 h followed by removal of the solvent
in vacuo. The orange residue was redissolved in dichlo-
romethane, and the silver salt was filtered by passing the
orange solution through a frit packed with glass wool. The
filtrate was then concentrated, yielding an oily, orange residue.
The residue was triturated with hexanes until a fine orange-
yellow solid was present and cooled to -35 °C, and the product
was collected and washed with cold hexanes. Complex 2a may
be recrystallized from CH2Cl2/hexanes (1:4 v/v). Yield: 0.31 g
(72%). Anal. Calcd for C39H66N3O2PtSi2BF4: C, 49.46; H, 7.02;
N, 4.44. Found: C, 49.50; H, 7.06; N, 4.38.
[(TIP S-4-MP D)P t(Me)(CH3CN)]BF 4 (2b). The same pro-
cedure was followed as described above for the synthesis of
2a . 1b (0.43 g, 0.50 mmol), AgBF4 (0.10 g, 0.51 mmol), and 30
mL of CH3CN were used. Yield: 0.40 g (85%). Anal. Calcd for
C39H66N3O2PtSi2BF4: C, 49.46; H, 7.02; N, 4.44. Found: C,
49.29; H, 7.09; N, 4.53.
Syn th esis of [(TIP S-6-MP D)P t(Me)(C2H3CN)]BF 4 (3). A
50 mL Schlenk flask was charged with 1a (0.093 g, 0.11 mmol),
acrylonitrile (20 µL, 0.30 mmol), and 15 mL of degassed
CH2Cl2. AgBF4 (0.023 g, 0.12 mmol) was then added as a solid
under a nitrogen flow. The reaction mixture was stirred in the
dark for 24 h. The silver salt was filtered by passing the orange
solution through Celite. The filtrate was then concentrated,
yielding an oily, orange residue. The residue was triturated
with hexanes until a fine orange-yellow solid was present and
cooled to -35 °C, and the product was collected and washed
with cold hexanes. Yield: 0.075 g (72%). IR (CH2Cl2, cm-1):
2305 (CN), 1000-1100 (BF4). Anal. Calcd for C40H67N3O2PtSi2-
BF4‚1/3CH2Cl2: C, 49.02; H, 6.80; N, 4.19. Found: C, 49.12;
H, 6.62; N, 4.14.
Syn th esis of [(TIP S-6-MP D)P t(Me)(eth ylen e)]BF 4 (4).
A 100 mL Schlenk flask was charged with 1a (0.307 g, 0.36
mmol) and 30 mL of CH2Cl2 (ethylene saturated). AgBF4 (0.077
g, 0.39 mmol) was then added as a solid under an ethylene
flow. The reaction mixture was stirred in the dark for 24 h.
The silver salt was filtered by passing the orange solution
through a frit that was packed with glass wool. The filtrate
was then concentrated, yielding an orange solid. Yield: 0.25
g (75%). Anal. Calcd for C39H67N2O2PtSi2BF4: C, 50.15; H, 7.23;
N, 3.00. Found: C, 49.98; H, 7.19; N, 2.89.
CDCl3 via syringe. After 2 h, a 1H NMR spectrum was
obtained. Complete replacement of CH3CN was evident from
the H NMR spectrum. Due to the presence of excess ethylene
1
(δ 5.35, br), the resonance for coordinated ethylene of 4 was
not visible. (Removal of the volatiles in vacuo followed by
redissolution of the residue in CDCl3 allowed for observation
of the coordinated ethylene resonance at δ 3.97.) IR (CH2Cl2,
cm-1) for 9: 2116 (CO), 1000-1100 (BF4).
Effect of F r ee Eth ylen e on th e Coor d in a ted Eth ylen e
Reson a n ce of 4. A resealable NMR tube was charged with 4
(2 mg, 2.1 µmol) and 0.5 mL of CDCl3 and plugged with a
rubber septum in the glovebox. The NMR tube was removed
from the glovebox, and a 1H NMR spectrum was obtained.
Using a microliter syringe, 1 equiv of ethylene (ca. 52 µL based
on V ) nRT/P) was added to the NMR tube, and it was then
quickly shaken. A 1H NMR spectrum was obtained. The
syringe additions were then subsequently repeated for 2 equiv
and then 4 equiv of ethylene.
Gen er a tion of [(TIP S-6-MP D)P t(Me)(fu m a r on itr ile)]-
BF 4 (5). P r oced u r e A. Complex 5 was generated in an NMR
tube and characterized by 1H NMR spectroscopy. An NMR
tube was charged with 2a (3.5 mg, 3.70 µmol), fumaronitrile
(1.5 mg, 19.2 µmol), and 0.5 mL of CDCl3. The reaction was
monitored by 1H NMR spectroscopy over the period of
about one week. It was determined that the reaction reached
an apparent equilibrium after 24 h. Attempts at complete
conversion to 5 from 2a were unsuccessful. P r oced u r e B. An
NMR tube was charged with 4 (3 mg, 3.21 µmol), fumaroni-
trile (1.3 mg, 16.7 µmol), and CDCl3. The reaction was
monitored by 1H NMR spectroscopy over the period of one
week. Since only 61% conversion to 5 had occurred after 2 days,
the solvent was removed in vacuo and the residue was
redissolved in CDCl3. After an additional day, complete
conversion to 5 had occurred. Due to excess fumaronitrile, the
stretching νCN frequencies could not be determined. Attempts
at converting 4 to 5 with 1 equiv of fumaronitrile were not
successful.
Gen er a l P r oced u r e for Exch a n ge of CH3CN by Ben -
zon itr ile (7), SMe2 (8), a n d SMe2-d 6 (8-d 6). To an NMR tube
containing complex 2a (ca. 4 µmol) in CDCl3 was added the
corresponding reagent (ca. 40 µmol). The reaction mixture was
1
monitored via H NMR analysis until complete conversion was
evident. Generation of 8 and 8-d 6 was observed after 0.5 h.
Displacement of CH3CN by benzonitrile required a longer time
period.
Kin etics of Liga n d Su bstitu tion Rea ction . For the
kinetics experiments, 1,2-dimethoxyethane (DME) was used
as an internal standard in 2 times excess of 2a and was found
to not react with 2a during course of the reaction. Two stock
solutions were made for the kinetics studies. Stock solution A
(0.025 M 2a ): A 1 mL volumetric flask was charged with 2a
(24.1 mg, 0.025 mmol) and 1,2-dimethoxyethane (5 µL, 0.050
mmol), diluted to the mark with CDCl3, and plugged with a
rubber septum. Stock solution B (1.9 M benzonitrile): A 5 mL
volumetric flask was charged with benzonitrile (970 µL, 9.5
mmol), diluted to the mark with CDCl3, and plugged with a
rubber septum.
10-fold Excess. A resealable, oven-dried NMR tube was
charge with 250 µL of stock solution A and 167 µL of CDCl3
in a glovebox. The NMR tube was plugged with a rubber
septum, removed from the glovebox, and cooled to 258 K in
an ice/NaCl bath. A 33 µL sample from stock solution B was
then added via syringe so that it slowly dripped down the wall
of the NMR tube. The tube was shaken and inserted into the
NMR spectrometer with the probe precooled to 278 K. Spectra
were then recorded every 10 min for the duration of the
experiment.
Exch a n ge Rea ction s a n d Kin etics
Mea su r em en ts
Gen er a l P r oced u r e for Exch a n ge of CH3CN by CD3CN
(2a -d 3), Acr ylon itr ile (3), a n d cis-P en ten en itr ile (6). An
NMR tube was charged with 2a (ca. 4 µmol) and an excess
(0.5 mL) of the corresponding nitrile. After 1 h, the volatiles
were removed in vacuo, the residue was redissolved in CDCl3,
and a 1H NMR spectrum was obtained, indicating complete
replacement of CH3CN. IR (CH2Cl2, cm-1) for 6: 2270 (CN),
1000-1100 (BF4).
20-fold Excess. The same procedure was followed as
outlined above adding 250 µL of stock solution A, 134 µL of
CDCl3, and 66 µL of stock solution B. Spectra were recorded
every 5 min for the duration of the experiment.
Gen er a l P r oced u r e for Exch a n ge of CH 3CN by Eth -
ylen e (4) a n d CO (9). To an NMR tube containing 2a (ca. 4
µmol) was added 0.5 mL of either ethylene or CO-saturated

1,4-Diazabutadiene Complexes of Pt
Organometallics, Vol. 19, No. 18, 2000 3555
30-fold Excess. The same procedure was followed as
outlined above adding 250 µL of stock solution A, 101 µL of
CDCl3, and 99 µL of stock solution B. Spectra were recorded
every 5 min for the duration of the experiment.
the NMR spectrometer with the probe preheated to 302
K. Spectra were then recorded every 40 min for the
duration of the experiment. To the second NMR tube
was added water (0.02 µL, 1.1 µmol). (J udging by
integration, the initial spectrum contained 20% water
relative to 2a .) The same procedure was then followed
as described above for the addition of EVE and for
monitoring the reaction in the spectrometer.
X-r a y Cr ysta llogr a p h y. Crystals of TIP S-6-MP D
were grown from a solution of absolute ethanol and
CH2Cl2 (4:1). A pale yellow fragment was cut from a
cluster of crystals, mounted under Paratone-8277 on a
glass fiber, and immediately placed in a cold stream at
-80 °C on the X-ray diffractometer. The X-ray intensity
data were collected on a standard Siemens SMART CCD
area detector system equipped with a Mo-target X-ray
tube operated at 2.0 kW (50 kV, 40 mA). A total of 1321
frames of data (1.3 hemispheres) were collected using
a narrow frame method with scan widths of 0.3° in ω
and exposure times of 30 s/frame using a detector-to-
crystal distance of 5.09 cm. The total data collection time
was approximately 12 h. Frames were integrated with
the Siemens SAINT program to yield a total of 5682
P olym er iza tion Stu d ies
Effect of Ba se on th e P olym er iza tion of EVE a n d
NVC. Control experiments were set up in the absence
of 2a and demonstrated no polymer formation.
Complex 2a (25.5 mg, 27 µmol) was added to a 5 mL
volumetric flask in the glovebox and filled to the mark
with CD2Cl2. A 0.8 mL sample was withdrawn from the
stock solution and added to each of two resealable NMR
tubes (Set 1). 2,6-Di-tert-butylpyridine (5 µL, 21 µmol)
was then added to both of the NMR tubes, and they
were allowed to stand for 4 h at room temperature.
Piperidinomethyl polystyrene (60 mg, 209 µmol) was
then added to the volumetric flask that contained the
remainder of the stock solution (ca. 3.4 mL). The flask
was sealed and allowed to stand with occasional agita-
tion for 4 h at room temperature. The solution was then
filtered through a medium-porosity frit into an Erlen-
meyer flask to remove the solid-supported base. A 0.8
mL sample of this pretreated solution was then with-
drawn and added to each of two resealable NMR tubes
(Set 2). NVC (20 mg, 103 µmol) was then added to an
NMR tube from each of the two sets. The NMR tubes
were removed from the glovebox, and the initial spectra
were obtained. EVE (11 µL, 115 µmol) was then added
to the other two NMR tubes from the two sets, and the
initial spectra were obtained. All of the NMR tubes were
then submerged in an oil bath set to 302 K, kept in the
dark, and periodically analyzed over a period of 3 days.
Effect of Wa ter on th e Ra te of EVE Con su m p -
tion . Experiments were conducted in resealable NMR
tubes in which the consumption of EVE vs time was
monitored at regularly timed intervals. Tetramethylsi-
lane was used as an internal reference in 2.5 times
excess of 2a .
reflections, of which 4021 were independent (Rint
)
1.18%, Rsig ) 2.36%) and 3622 were above 2σ(I). Laue
symmetry revealed a triclinic crystal system, and the
final unit cell parameters (at -80 °C) were determined
from the least-squares refinement of three-dimensional
centroids of 4986 reflections. Data were corrected for
absorption with the SADABS program. The structure
was solved in space group P1h using direct methods and
was refined employing full-matrix least-squares on F2
(Siemens, SHELXTL, version 5.04). For a Z ) 1, half of
the molecule is in the asymmetric unit. All of the atoms
were refined anisotropically, and hydrogen atoms were
included in idealized positions, giving a data-to-param-
eter ratio of approximately 20:1. The structure refined
to a goodness of fit (GOF) of 1.066 and final residuals
of R1 ) 3.66% (I > 2σ(I)), wR2 ) 10.45% (I > 2σ(I)).
Complex 2a (8 mg, 8.4 µmol) was added to a 1 mL
volumetric flask in a glovebox. The flask was then filled
to the mark with dry CD2Cl2. Tetramethylsilane (3 µL,
22 µmol) was then added. A 0.5 mL sample of the stock
solution was withdrawn and added to each of two
resealable NMR tubes. One NMR tube was stored at
233 K until use. To the other NMR tube was added EVE
(10 µL, 105 µmol). It was quickly removed from the
glovebox and cooled in a dewar containing liquid nitro-
gen. The tube was thawed, shaken, and inserted into
Ack n ow led gm en t. We thank the National Science
Foundation (Grant CHE 97-29311) for support of this
work.
Su p p or tin g In for m a tion Ava ila ble: Tables of all the
pertinent crystallographic information and of the spectral data
for the minor isomers 1a ′, 2a ′, 3′, 4′, 5′, 6′, 7′, 8′, and 9′. This
material is available free of charge via the Internet at
http//pubs.acs.org.
OM000052X