Dimethyl and cationic 1,4-diazabutadiene complexes of platinum(II)

Article abstract of DOI:10.1021/om980551m

The reaction of the 1,4-diazabutadiene ligand glyoxal bis(2-(methoxymethyl)-4,6-di-tert-butylphenyl)diimine (L) with the platinum complex Pt₂Me₄(SMe₂)₂ yields two isomers of the complex PtMe₂L (2a,b)

Full text of DOI:10.1021/om980551m

5102
Organometallics 1998, 17, 5102-5113
Dim eth yl a n d Ca tion ic 1,4-Dia za bu ta d ien e Com p lexes of
P la tin u m (II)
Kaiyuan Yang, Rene J . Lachicotte, and Richard Eisenberg*
Department of Chemistry, University of Rochester, Rochester, New York 14627
Received J une 29, 1998
The reaction of the 1,4-diazabutadiene ligand glyoxal bis(2-(methoxymethyl)-4,6-di-tert-
butylphenyl)diimine (L) with the platinum complex Pt2Me4(SMe2)2 yields two isomers of
the complex PtMe2L (2a ,b) that have been isolated and characterized. The isomers exhibit
distorted-square-planar coordination geometries about the central Pt(II) ion and differ only
in the relative orientation of the methoxymethyl and tert-butyl substituents with respect to
the coordination plane of the complex. Isomerization between 2a and 2b is promoted by
heating solutions of either form of the complex in benzene or chloroform. Upon prolonged
refluxing in chloroform, 2a ,b react with chloroform to yield the methyl chloro derivative
PtMeClL, which is also obtained as syn and anti isomers (3a ,b). Cationic solvento complexes
[PtMe(S)L]BF4 (4 and 5, S ) MeCN, pyridine) are generated by halide abstraction from 3
using AgBF4. In the presence of selected olefins such as ethylene and acrylonitrile, halide
abstraction from 3 by AgBF4 or methyl group abstraction from 2a and 2b by the strong
Lewis acid B(C6F5)3 yields the cationic R-olefin complexes [PtMe(CH2CHR)L]+ (R ) H, CN;
6 and 7 for the BF4 salt, 8 and 9 for the MeB(C6F5)3 salt). All new compounds have been
characterized by IR and NMR spectroscopy. Molecular structures of 2a ,b, and 3a were
determined by X-ray single-crystal diffraction.
In tr od u ction
Shilov16,17 and subsequent studies by others of chloro-
aquoplatinum-catalyzed H/D exchange and oxidation
reactions in acidic media.5-9,18 The cationic Pt methyl
complexes used in the recent C-H bond activation
studies were generated from the corresponding neutral
dimethyl complexes by reaction with either the strong
Brønsted acid (HOEt2)[B(3,5-C6H3(CF3)2)4]2,3 or the
strong Lewis acid B(C6F5)3.19,20 For Pt(II) complexes,
the latter was originally applied by Puddephatt to the
demethylation of PtMe2(dbbpy) (dbbpy ) di-tert-butyl-
bipyridine), which in the presence of CO yielded [PtMe-
(CO)(dbbpy)]+.19,20
Interest in electrophilic complexes of Pt(II) has been
stimulated by the activity of such systems in bond
activation reactions and the relevance of these systems
as models for catalytically active Pd analogues in
polymerization and copolymerization reactions.1-15 With
regard to the former, cationic Pt(II) methyl complexes
have recently been shown by Bercaw2,3 and by Goldberg4
to effect intermolecular alkane C-H bond activation.
These observations build on the seminal work of
(1) Periana, R. A.; Taube, D. J .; Gamble, S.; Taube, H.; Satoh, T.;
Fujii, H. Science 1998, 280, 560-564.
(2) Holtcamp, M. W.; Labinger, J . A.; Bercaw, J . E. J . Am. Chem.
Soc. 1997, 119, 848-849.
(3) Holtcamp, M. W.; Neling, L. M.; Day, M. W.; Labinger, J . A.;
Bercaw, J . E. Inorg. Chim. Acta 1998, 270, 467-478.
(4) Wick, D. D.; Goldberg, K. I. J . Am. Chem. Soc. 1997, 119, 10235-
10236.
(5) Luinstra, G. A.; Wang, L.; Stahl, S. S.; Labinger, J . A.; Bercaw,
J . E. Organometallics 1994, 13, 755-756.
The electrophilic Pd complexes that were reported by
Brookhart in 199610-12 to be active catalysts for R-olefin
polymerization are closely related cationic systems of
the general formula [PdMe(L)]+(B(Arf)4), where L is a
diazabutadiene (DAB) ligand having 2,6-disubstituted
aryl groups on the imine N atoms and B(Arf)4 represents
one of several noncoordinating borate anions having
(fluoroalkyl)phenyl or fluoroaryl substituents. Brook-
hart’s reports follow earlier studies on the electrophilic
behavior of cationic Pd(II) systems and their role in
ethylene/CO copolymerization.15 In this catalysis, it is
(6) Labinger, J . A.; Herring, A. M.; Lyon, D. K.; Luinstra, G. A.;
Bercaw, J . E. Organometallics 1993, 12, 895-905.
(7) Luinstra, G. A.; Wang, L.; Stahl, S. S.; Labinger, J . A.; Bercaw,
J . E. J . Organomet. Chem. 1995, 504, 75-91.
(8) Holtcamp, M. W.; Labinger, J . A.; Bercaw, J . E. Inorg. Chim.
Acta 1997, 265, 117-125.
(9) Stahl, S. S.; Labinger, J . A.; Bercaw, J . E. J . Am. Chem. Soc.
1996, 118, 5961-5976.
(10) Rix, F. C.; Brookhart, M.; White, P. S. J . Am. Chem. Soc. 1996,
118, 4746-4764.
(16) Goldshleger, N. F.; Eskova, V. V.; Shilov, A. E.; Shteinmann,
A. A. Zh. Fiz. Khim. 1972, 46, 1353.
(17) Kushch, K. A.; Lavrushko, V. V.; Misharin, Y. S.; Moravsky,
A. P.; Shilov, A. E. New J . Chem. 1983, 7, 729.
(18) Hutson, A. C.; Lin, M.; Basickes, N.; Sen, A. J . Organomet.
Chem. 1995, 504, 69-74.
(19) Hill, G. S.; Manojlovic-Muir, L.; Muir, K. W.; Puddephatt, R.
J . Organometallics 1997, 16, 525-530.
(20) Hill, G. S.; Rendina, L. M.; Puddephatt, R. J . J . Chem. Soc.,
Dalton Trans. 1996, 1809-1813.
(11) Mecking, S.; J ohnson, L. K.; Wang, L.; Brookhart, M. J . Am.
Chem. Soc. 1998, 120, 888-899.
(12) J ohnson, L. K.; Killian, C. M.; Brookhart, M. J . Am. Chem. Soc.
1995, 117, 6414-6415.
(13) Kacker, S.; Sen, A. J . Am. Chem. Soc. 1997, 119, 10028-10033.
(14) Vrieze, K.; Groen, J . H.; Delis, J . G. P.; Elsevier: C. J .; van
Leeuwen, P. W. N. M. New J . Chem. 1997, 21, 807-813.
(15) Drent, E.; Budzelaar, P. H. M. Chem. Rev. 1996, 96, 663-681.
10.1021/om980551m CCC: $15.00 © 1998 American Chemical Society
Publication on Web 10/22/1998

1,4-Diazabutadiene Complexes of Pt(II)
Organometallics, Vol. 17, No. 23, 1998 5103
postulated that two adjacent coordination positions of
the catalyst are needed to effect the repetitive addition/
insertion sequence of the reaction. Other DAB com-
plexes of Pt and Pd have been reported over the past
decade,21-25 and recently Elsevier has described rigid
derivatives of these ligands having aryl imino groups,
together with their Pd and Pt dimethyl complexes.24
With respect to the latter, studies of RX oxidative
addition to yield the Pt(IV) and Pd(IV) complexes were
conducted with subsequent reductive elimination slowed
or inhibited by the rigidity of the particular diazabuta-
diene employed.
catalysts having C2 symmetry, we have synthesized the
dimethyl complex PtMe2L (2) and studied its structure
and reaction chemistry. The complex and its corre-
sponding chloro methyl analogue serve as convenient
precursors to the formation of cationic methyl deriva-
tives which are stable models of catalytically interesting
Pd DAB systems.
Resu lts a n d Discu ssion
Syn th esis of P tMe2L. The reaction of Pt2Me4-
(SMe2)2 and the diazabutadiene ligand L in a 1:2 ratio
was initially investigated in dichloromethane and ace-
tone solutions at both ambient room temperature and
solvent reflux conditions. Deep green solutions are
obtained in each case, with spectroscopic evidence of two
different products. Spectroscopic characterization, el-
emental analyses, and subsequent single-crystal X-ray
diffraction studies (vide infra) of the products show them
to be isomerically related forms of the dimethyl complex
PtMe2L (2), as shown in eq 1. Examination of the green
Recently, we described the synthesis of the bulky DAB
ligand L, in which there are different substituents in
the 2- and 6-positions of the arylimino groups, and the
dichloro Pt(II) and Pd(II) complexes of L.26 Two isomers
of each complex were observed, and structural studies
showed them to be syn (1a ) and anti (1b) with respect
to the orientation of the aryl substituents relative to the
coordination plane. The isomers thus possess mirror
reaction solutions by 1H NMR spectroscopy showed that
the ratio of the two isomers differs with temperature.
For example, in acetone solution at ambient room
temperature, a 4:1 ratio of the isomers exists, whereas
under refluxing conditions the ratio changes to 3:2. Also
plane and C2 rotational symmetry, respectively. As part
of an effort to examine the electrophilic behavior of Pt-
(II) complexes containing L and to generate selected
1
seen in the H NMR spectra of the reaction solutions
(21) Van Koten, G.; Vrieze, K. Adv. Organomet. Chem. 1982, 21,
151-239.
(22) van der Poel, H.; van Koten, G.; Vrieze, K. Inorg. Chem. 1980,
19, 1145.
were resonances of free ligand L, in part because of
partial decomposition of the starting complex Pt2Me4-
(SMe2)2, as evidenced by precipitate formation and
generation of a black mirror under reflux conditions.
(23) van der Poel, H.; van Koten, G.; Kokkes, M.; Stam, C. H. Inorg.
Chem. 1981, 20, 2941-2956.
(24) van Asselt, R.; Rijnberg, E.; Elsevier, C. J . Organometallics
1994, 13, 706-720.
Separation of the product isomers 2a ,b in these initial
experiments proved difficult by thin-layer chromatog-
raphy (TLC), since both of the isomers and the free
ligand have similar solubility properties and Rf values.
(25) Groen, J . H.; Delis, J . G. P.; van Leeuwen, W. N. M.; Vrieze, K.
Organometallics 1997, 16, 68-77.
(26) Yang, K.; Lachicotte, R. J .; Eisenberg, R. Organometallics 1997,
16, 5234-5243.

5104 Organometallics, Vol. 17, No. 23, 1998
Ta ble 1. Selected 1H NMR Sp ectr a l Da ta for All New Com p lexes
Yang et al.
compd
1H NMR (δ)a
2a
2.27 (s, J Pt-H ) 40.0 Hz, 3H, PtCH3), 3.23 (s, 6H, OCH3), 4.62 (d, J H-H ) 12 Hz, 2H, CHaH),
4.97 (d, J H-H ) 12 Hz, 2H, CHHb), 8.79 (s, 2H, NCH)
2b
3a
2.24 (s, J Pt-H ) 40.0 Hz, 3H, PtCH3), 3.33 (s, 6H, OCH3), 4.70 (d, J H-H ) 12 Hz, 2H, CHaH),
4.92 (d, J H-H ) 12 Hz, 2H, CHHb), 8.73 (s, 2H, NCH)
2.02 (s, J Pt-H ) 41.2 Hz, 3H, PtCH3), 3.20 (s, 3H, OCH3), 3.21 (s, 3H, OCH3), 4.51 (d, J H-H ) 11.6 Hz, 1H, CHaH),
4.55 (d, J H-H ) 11.6 Hz, 1H, CHHb), 4.82 (d, J H-H ) 11.6 Hz, 1H, CHcH), 5.29 (d, J H-H ) 11.6 Hz, 1H, CHHd),
7.91 (s, 1H, NCHa), 8.56 (s, 1H, NCHb)
3b
4
2.00 (s, J Pt-H ) 40.8 Hz, 3H, PtCH3), 3.17 (s, 3H, OCH3), 3.18 (s, 3H, OCH3), 4.56 (d, J H-H ) 11.6 Hz, 1H, CHaH),
4.59 (d, J H-H ) 11.6 Hz, 1H, CHHb), 4.81 (d, J H-H ) 11.6 Hz, 1H, CHcH), 5.20 (d, J H-H ) 11.6 Hz, 1H, CHHd),
7.81 (s, 1H, NCHa), 8.45 (s, 1H, NCHb)
0.79 (s, J PtH ) 38.8 Hz, 3H, PtCH3), 0.80 (s, J PtH ) 36.8 Hz, 3H, PtCH3), 2.03 (s, NCCH3), 2.04 (s, NCCH3),
3.29 (s, 3H, OCH3), 3.34 (s, 3H, OCH3), 3.36 (s, 3H, OCH3), 3.38 (s, 3H, OCH3), 4.29-4.79 (m, 8H, CH2),
9.00 (s, 1H, NCH), 9.01 (s, 1H, NCH), 9.06 (s, 2H, NCH)
5
6
0.90 (s, J Pt-H ) 35.6 Hz, 3H, PtCH3), 0.92 (s, J Pt-H ) 33.2 Hz, 3H, PtCH3), 3.33 (s, 3H, OCH3), 3.37 (s, 3H, OCH3),
3.49 (s, 3H, OCH3), 3.70 (s, 3H, OCH3), 4.44-4.90 (m, 8H, CH2), 9.13 (s, 1H, NCH), 9.14 (s, 1H, NCH), 9.22 (s, 2H, NCH)
0.40 (s, J Pt-H ) 32.8 Hz, 3H, PtCH3), 0.41 (s, J Pt-H ) 34.4 Hz, 3H, PtCH3), 3.31 (s, 3H, OCH3), 3.36 (s, 3H, OCH3),
3.38 (s, 3H, OCH3), 3.42 (s, 3H, OCH3), 3.93-4.74 (m, 12H, ethylene and benzylic), 9.13 (s, J Pt-H ) 32.8 Hz, 2H, NCH),
9.15 (s, J Pt-H ) 32.8 Hz, 2H, NCH)
0.78 (s, J Pt-H ) 46.0 Hz, 3H, PtCH3), 0.80 (s, J Pt-H ) 42.8 Hz, 3H, PtCH3), 3.28 (s, 3H, OCH3), 3.32 (s, 3H, OCH3),
3.34 (s, 3H, OCH3), 3.36 (s, 3H, OCH3), 4.31-4.79 (m, 12H, CH2), 5.66-5.72 (m, 4 H), 6.22 (d, J H-H ) 12 Hz, 1H),
6.23 (d, J H-H ) 12 Hz, 1H), 9.05 (s, 1H, NCH), 9.06 (s, 1H, NCH), 9.22 (s, 2H, NCH)
7
8
9
0.49 (s, J Pt-H ) 30.0 Hz, 3H, PtCH3), 0.52 (s, J Pt-H ) 26.4 Hz, 3H, PtCH3), 3.27 (s, 3H, OCH3), 3.28 (s, 3H, OCH3),
3.29 (s, 3H, OCH3), 3.31 (s, 3H, OCH3), 3.90-4.90 (m, 8H, CH2), 8.76 (b, 3H, NCH), 8.80 (s, 1H, NCH)
0.91 (s, J Pt-H ) 42.0 Hz, 3H, PtCH3), 0.92 (s, J Pt-H ) 38.4 Hz, 3H, PtCH3), 3.28 (s, 3H, OCH3), 3.29 (s, 3H, OCH3),
3.31 (s, 3H, OCH3), 3.32 (s, 3H, OCH3), 4.21-5.10 (m, 8H, CH2), 5.60 (m, 2H), 6.22 (d, J H-H ) 12 Hz, 2H),
6.23 (d, J H-H ) 12 Hz, 2H), 8.80 (s, 2H, NCH), 8.82 (s, 2H, NCH)
a
All 1H NMR were recorded in C6D6 (2 and 3) and CDCl3 solutions (4-9). Chemical shift values are reported in ppm. Abbreviations:
s, singlet; d, doublet; m, multiplet; b, broad.
Ta ble 2. Selected 13C NMR Sp ectr a l Da ta for New Com p lexes 2-7
compd
13C NMR (δ)a
2a
2b
3a
3b
4
-15.4 (Pt-Me, J Pt-C ) 410.0 Hz), 58.0 (OMe), 71.4 (CH2), 164.8 (NCCN)
-15.2 (Pt-Me, J Pt-C ) 403.5 Hz), 58.4 (OMe), 71.7 (CH2), 164.6 (NCCN)
-11.7 (Pt-Me), 57.8 (OMe), 58.3 (OMe), 71.0 (CH2), 71.1 (CH2), 165.7 (NCCN), 166.7 (NCCN)
-11.6 (Pt-Me), 58.2 (OMe), 58.6 (OMe), 72.4 (CH2), 72.6 (CH2), 165.3 (NCCN), 166.5 (NCCN)
-11.9 (Pt-Me, J Pt-C ) 339.1 Hz), 58.0 (MeO), 58.1 (OMe), 58.2 (OMe), 58.4 (OMe), 71.4 (CH2), 71.5 (CH2), 71.5 (CH2),
71.6 (CH2), 119.2 (MeCN), 167.9 (NCCN), 168.0 (NCCN), 175.6 (NCCN), 175.9 (NCCN)
-5.5 (Pt-Me, J Pt-C ) 340.0 Hz), -5.6 (Pt-Me, J Pt-C ) 334.5 Hz), 57.7 (MeO), 57.9 (OMe), 58.3 (OMe), 58.4 (OMe),
71.29 (CH2), 71.32 (CH2), 72.0 (2C, CH2), 170.0 (NCCN), 170.2 (NCCN), 177.3 (NCCN), 177.4 (NCCN)
-11.7 (Pt-Me, J Pt-C ) 339.1 Hz), 57.9 (OMe), 58.1 (OMe), 58.2 (OMe), 58.3 (OMe), 71.0 (CH2), 71.2 (2C, CH2),
71.6 (CH2), 105.2 (2C, CH2CHCN), 117.4 (1C, CH2CHCN), 117.5 (1C, CH2CHCN), 144.2 (2C, CH2CHCN),
168.5 (NCCN), 168.6 (NCCN), 176.2 (NCCN), 176.8 (NCCN)
6
7b
a
All 13C NMR were recorded in CDCl3 solutions. Chemical shift values are reported in ppm. b Assignments for the acrylonitrile resonances
are based on the 1H-coupled 13C spectrum and the attached proton test for free acrylonitrile.
The dimethyl complex 2 was also found to decompose
slowly on the TLC plate, making rapid separation a
necessity. Two adjustments were therefore made in the
experimental procedure to facilitate product isomer
separation. First, the starting ratio of reactants was
changed in order to have no free L in solution at the
time of product isolation and separation. Second, Me2S
generated upon the reaction shown in eq 1 was removed
after 24 h by evacuating all volatiles; subsequent
redissolution of the reaction system allowed it to proceed
more rapidly to completion. The final separation was
performed on a silica gel column using a 9:1 mixture of
CH2Cl2 and hexane to give 2b as the first green band
and 2a as the second green band. As seen for the
analogous dichloro complex isomers 1a ,b, the syn isomer
2a is slightly more polar than anti isomer 2b, leading
to slower elution of the former.
protons for both isomers exhibit AB coupling patterns
that appear as two doublets centered at δ 4.62 and 4.97
for 2a and at δ 4.33 and 5.16 for 2b, with the same
coupling constant J H-H of 12 Hz for each doublet.
Compared to the free ligand L, the diimine proton
resonances for 2a ,b are shifted to lower field by ∼0.5
ppm, which is opposite to the trend observed for the
dichloro derivatives PtCl2L. The isolability of the two
isomers of 2 results from the greatly hindered rotation
about the C(aryl)-N bonds arising from the steric
repulsions between aryl ring ortho substituents and the
metal-diimine chelate.
In Table 2, 13C NMR spectroscopic data for the
complexes are presented. In CDCl3 2a ,b give very
similar spectra with PtMe2 resonances at δ -15.4 and
-15.2, respectively, and J Pt-C coupling constants of
410.0 and 403.5 Hz. The observed chemical shifts for
the Pt-coordinated methyl resonances of 2 are compa-
rable to those in other dimethylplatinum complexes
reported in the literature. In addition to the PtMe2
resonances, the diimine carbon resonances are seen at
δ 164.8 for 2a and δ 164.6 for 2b, which are ca. 1 ppm
to lower field relative to the free ligand L.
The 1H NMR spectra of 2a ,b, as well as those of other
complexes described in the paper, are summarized in
Table 1. In benzene-d6, the 1H NMR spectra of 2a ,b
show only minor differences, with PtMe2 resonances at
2
δ 2.27 and δ 2.24, respectively, and the same J Pt-H
coupling constant of 40.0 Hz. The diasterotopic benzylic

1,4-Diazabutadiene Complexes of Pt(II)
Organometallics, Vol. 17, No. 23, 1998 5105
F igu r e 1. ORTEP diagram of 2a . Thermal ellipsoids are shown at 50% probability. Hydrogen atoms are omitted for
clarity.
F igu r e 2. ORTEP diagram of 2b. Thermal ellipsoids are shown at 50% probability. Hydrogen atoms are omitted for
clarity.
Str u ctu r es of P tMe2L (2). The structures of both
isomers of 2 were determined by single-crystal X-ray
diffraction. In each case, single crystals were grown by
slow solvent evaporation from saturated hexane solu-
tions at -10 °C. The ORTEP diagrams of 2a and 2b
are shown in Figures 1 and 2, with details of the
structure determination including unit cell data, data
collection parameters, and refinement information sum-
marized in Table 3. Relevant bond distances, bond
angles, and torsion angles for both structures are
presented in Tables 4-6, respectively. Since there are
two independent molecules in the asymmetric unit for
2a and both molecules have almost the same metrical
parameters, the ORTEP diagram in Figure 2 is given
for one molecule only and the metrical data presented
in Tables 4-6 are for the same molecule. Metrical
parameters for the second molecule are provided in the
Supporting Information.
because of the sterically larger methyl groups in 2
relative to the chloride ligands in 1b. The metal chelate
rings in both isomers are essentially planar, as seen
from the torsion angles given in Table 6. As in the
dichloro derivative 1b, the aryl rings are almost per-
pendicular to the chelate rings in 2a and 2b, with
torsion angles about the imine N-C(ipso) bond of near
90° (see Table 6). The diffraction studies reveal that
the relative orientation of the two CH2OMe groups in
2a is syn or cisoid (i.e., both on the same side of the
coordination plane) while in 2b the groups are anti or
transoid (on opposite sides of the coordination plane).
There are no significant differences observed in the
Pt-C and Pt-N bond distances between the two
isomers, with Pt-C bonds of 2.05(2) and 2.06(2) Å for
2a and 2.059(3) and 2.079(3) Å for 2b and Pt-N bonds
of 2.09(2) and 2.08(2) Å for 2a and 2.094(2) and 2.112-
(2) Å for 2b, respectively. The observed Pt-N bond
distances in 2a and 2b are slightly longer than those
in 1b as a result of the stronger trans influence of the
methyl ligands in the former relative to chloride in the
latter.27
Both 2a and 2b possess slightly distorted square-
planar coordination geometries with bond angles devi-
ating from 90° by virtue of the constraints imposed by
chelation of L (N-Pt-N of 76.0(7) and 77.04 (9)° for 2a
and 2b, respectively). The observed N-Pt-N bond
angles in 2 are slightly but significantly smaller than
that of the dichloro derivative 1b (79.4(2)°), possibly
(27) Atwood, J . D. Inorganic and Organometallic Reaction Mecha-
nisms; Brooks/Cole: Monterey, CA, 1985.

5106 Organometallics, Vol. 17, No. 23, 1998
Yang et al.
Ta ble 3. Su m m a r y of Cr ysta llogr a p h ic Da ta for
Com p lexes 2a ,b a n d 3a
Ta ble 4. Selected Bon d Dista n ces (Å) for 2a ,b a n d
3a
2a
2b
3a
Compound 2a
Pt(11)-C(41)
Pt(11)-N(11)
N(11)-C(11)
N(21)-C(21)
O(21)-C(331)
O(11)-C(351)
Pt(12)-C(32)
Pt(12)-N(12)
2.05(2)
2.09(2)
1.31(3)
1.25(2)
1.33(3)
1.39(2)
2.05(2)
2.13(2)
Pt(11)-C(31)
Pt(11)-N(21)
N(11)-C(51)
N(21)-C(111)
O(21)-C(341)
O(11)-C(361)
Pt(12)-C(42)
2.06(2)
2.08(2)
1.46(3)
1.44(3)
1.39(3)
1.44(3)
2.06(2)
Crystal Parameters
C36H58N2O2Pt C36H58N2O2Pt C47H77ClN2O2Pt
chem formula
fw
cryst syst
space group
(No.)
745.93
745.93
932.65
orthorhombic
Pbca (61)
orthorhombic monoclinic
P212121 (19)
P21/c (14)
Z
8
4
8
a, Åa
10.7170(1)
24.3547(1)
28.1395(3)
14.4682(2)
18.6177(2)
14.5675(1)
116.087(0)
3524.22(7)
1.406
22.0854(4)
11.5173(2)
34.7360(7)
b, Å
c, Å
Compound 2b
Pt(1)-C(35)
Pt(1)-N(1)
O(1)-C(15)
O(2)-C(34)
N(1)-C(17)
N(2)-C(18)
C(1)-C(6)
2.059(3)
2.094(2)
1.414(4)
1.421(4)
1.289(3)
1.283(4)
1.398(4)
Pt(1)-C(36)
Pt(1)-N(2)
O(1)-C(16)
O(2)-C(33)
N(1)-C(1)
N(2)-C(19)
2.079(3)
2.112(2)
1.418(4)
1.423(3)
1.438(4)
1.437(4)
â, deg
V, Å3
7344.67(11)
1.348
8832.8(3)
1.403
F
calcd, g cm-3
cryst dimens,
0.01 × 0.03 × 0.04 × 0.18 × 0.12 × 0.12 ×
0.36 0.24 0.18
-80 -90 -80
mm3
temp, °C
Measurement of Intensity Data and Refinement Parameters
radiation (λ, Å) Mo KR (0.710 73)
Compound 3a
2θ range, deg
total no. of data
no. of unique
data
4-40
21 730
6748
3-56.7
21 064
8193
3-45
11 348
30 399
Pt(1)-N(1)
Pt(1)-N(2)
O(1)-C(10)
O(2)-C(27)
N(1)-C(2)
N(2)-C(3)
C(2)-C(3)
1.994(9)
2.122(9)
1.400(13)
1.31(2)
1.268(13)
1.280(14)
1.47(2)
Pt(1)-C(1)
Pt(1)-Cl(1)
O(1)-C(11)
O(2)-C(26)
N(1)-C(4)
N(2)-C(20)
2.053(10)
2.283(3)
1.41(2)
1.395(14)
1.442(13)
1.457(14)
R
int, Rsigma (%)b
10.10, 10.35
5557
2.88, 4.00
6791
6.90, 5.37
4755
no. of obsd data
(I > 2σ(I))
no. of params
varied
340
370
494
µ, mm-1
3.851
4.013
3.271
Ta ble 5. Selected Bon d An gles (d eg) for 2a ,b a n d
3a
abs cor
empirical (SADABS)c
range of trans-
0.928-0.749
0.928-0.720
0.928-0.789
Compound 2a
mission factors
C(41)-Pt(11)-C(31)
88.8(8)
N(11)-Pt(11)-N(21)
C(11)-N(11)-Pt(11)
C(51)-N(11)-Pt(11)
C(21)-N(21)-Pt(11)
76.0(7)
114.5(14)
127(2)
GOFd
1.081
7.50, 14.62
1.028
2.85, 5.58
1.191
8.06, 13.10
C(41)-Pt(11)-N(11) 173.7(8)
2
R1(Fo), wR2(Fo
)
)
C(31)-Pt(11)-N(11)
C(41)-Pt(11)-N(21)
97.4(8)
97.8(7)
obsd (%)e
114(2)
2
R1(Fo), wR2(Fo
all (%)
9.55, 15.51
4.20, 5.96
10.81, 13.92
C(31)-Pt(11)-N(21) 173.4(8)
Compound 2b
86.90(13) N(1)-Pt(1)-N(2)
C(111)-N(21)-Pt(11) 125(2)
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
C(35)-Pt(1)-C(36)
C(35)-Pt(1)-N(1)
C(36)-Pt(1)-N(1)
C(35)-Pt(1)-N(2)
C(36)-Pt(1)-N(2)
77.04(9)
98.18(12) C(17)-N(1)-Pt(1)
173.19(10) C(1)-N(1)-Pt(1)
174.76(11) C(18)-N(2)-Pt(1)
98.05(11) C(19)-N(2)-Pt(1)
114.4(2)
128.3(2)
113.5(2)
129.0(2)
b
2
2
estimated at 10× the listed value. Rint ) ∑|Fo - Fo (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
d
2
Compound 3a
n and p denote the number of data and parameters. e R1 ) (∑||Fo|
N(1)-Pt(1)-C(1)
N(1)-Pt(1)-N(2)
C(1)-Pt(1)-N(2)
N(1)-Pt(1)-Cl(1)
C(1)-Pt(1)-Cl(1)
95.5(4)
78.1(4)
173.4(4)
175.0(3)
89.1(3)
N(2)-Pt(1)-Cl(1)
C(2)-N(1)-Pt(1)
C(4)-N(1)-Pt(1)
C(3)-N(2)-Pt(1)
C(20)-N(2)-Pt(1)
97.3(3)
116.4(8)
127.6(7)
112.5(8)
125.7(7)
- |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.
Isom er iza tion of 2a a n d 2b. Differences in the
ratio 2a :2b at different temperatures during the syn-
thesis of 2 suggested the possibility of an isomerization
process occurring under relatively mild thermal condi-
tions. This was confirmed when pure samples of either
isomer in either CDCl3 or benzene-d6 were heated in
sealed NMR tubes at 349 K, leading to mixtures of both
isomers after several hours (eq 2). Accordingly, the
interconversion of the two isomers was examined at
several different temperatures.27,28 Figure 3a shows the
changes in benzylic 1H resonances for the isomerization
of 2a in benzene-d6 at 349 K. The equilibrium constant
Keq of the isomerization process was determined to be
ca. 0.79 from NMR peak integrations of the diimine
protons, while the approach to equilibrium, given by the
sum of forward and reverse rates k1 + k-1, was
ascertained from a first-order plot of ln[(Ce - Co)/(Ce -
Ct)] vs time (Figure 3b), where Ce is the concentration
of 2a at equilibrium, Ct is the concentration at time t,
and Co is the concentration at time zero. From these
values, the forward and reverse rates were calculated,
along with their respective free energies of activation,
∆Gfq and ∆Gr , of 27.0 ( 1.2 and 26.8 ( 1.2 kcal/mol.
q
Measurements of Keq and the sum k1 + k-1 as a function
of temperature in order to obtain activation parameters
∆Hq and ∆Sq for the isomerization process were not
successful because equilibrium concentrations over a
large enough temperature range were not accessible,
(28) Bradley, D. H.; Khan, M. A.; Nicholas, K. M. Organometallics
1992, 11, 2598-2607.

1,4-Diazabutadiene Complexes of Pt(II)
Organometallics, Vol. 17, No. 23, 1998 5107
Ta ble 6. Selected Tor sion An gles (d eg) for 2a ,b a n d 3a
Compound 2a
C(31)-Pt(11)-N(11)-C(11)
N(21)-Pt(11)-N(11)-C(11)
C(31)-Pt(11)-N(11)-C(51)
N(21)-Pt(11)-N(11)-C(51)
C(41)-Pt(11)-N(21)-C(21)
N(11)-Pt(11)-N(21)-C(21)
C(41)-Pt(11)-N(21)-C(111)
N(11)-Pt(11)-N(21)-C(111)
C(51)-N(11)-C(11)-C(21)
172.04(1.63)
-7.63(1.51)
10.25(1.79)
-169.42(1.78)
-173.42(1.61)
5.17(1.56)
-0.28(1.75)
178.31(1.77)
172.55(1.83)
Pt(11)-N(11)-C(11)-C(21)
8.83(2.38)
-175.70(2.05)
-2.26(2.65)
-4.50(3.06)
-99.77(2.47)
-88.92(2.26)
78.98(2.38)
C(111)-N(21)-C(21)-C(11)
Pt(11)-N(21)-C(21)-C(11)
N (11)-C(21)-C(21)-N(21)
Pt(11)-N(11)-C(51)-C(61)
Pt(11)-N(21)-C(111)-C(121)
Pt(11)-N(11)-C(51)-C(101)
Pt(11)-N(21)-C(111)-C(161)
94.81(2.37)
Compound 2b
C(35)-Pt(1)-N(1)-C(17)
N(2)-Pt(1)-N(1)-C(17)
C(35)-Pt(1)-N(1)-C(1)
N(2)-Pt(1)-N(1)-C(1)
C(36)-Pt(1)-N(2)- C(18)
N(1)-Pt(1)-N(2)-C(18)
C(36)-Pt(1)-N(2)-C(19)
N(1)-Pt(1)-N(2)-C(19)
179.71(0.22)
1.89(0.20)
4.91(0.26)
-172.92(0.25)
171.44(0.22)
-3.77(0.20)
-1.62(0.24)
-176.82(0.25)
Pt(1)-N(1)-C(1)-C(6)
Pt(1)-N(1)-C(1)-C(2)
Pt(1)-N(1)-C(17)-C(18)
Pt(1)-N(2)-C(18)-C(17)
N(1)-C(17)-C(18)- N(2)
Pt(1)-N(2)-C(19)-C(24)
Pt(1)-N(2)-C(19)-C(20)
-94.67(0.30)
86.10(0.29)
0.08(0.35)
5.08(0.35)
-3.58(0.44)
-101.09(0.30)
80.48(0.30)
Compound 3a
C(1)-Pt(1)-N(1)-C(2)
N(2)-Pt(1)-N(1)-C(2)
C(1)-Pt(1)-N(1)-C(4)
N(2)-Pt(1)-N(1)-C(4)
N(1)-Pt(1)-N(2)-C(3)
C(1)-Pt(1)-N(2)-C(3)
Cl(1)-Pt(1)-N(2)-C(3)
N(1)-Pt(1)-N(2)-C(20)
C(1)-Pt(1)-N(2)-C(20)
174.36(0.84)
-4.27(0.79)
0.31(1.00)
Cl(1)-Pt(1)-N(2)-C(20)
Pt(1)-N(1)-C(2)-C(3)
Pt(1)-N(2)-C(3)-C(2)
N(1)-C(2)-C(3)-N(2)
Pt(1)-N(1)-C(4)-C(5)
Pt(1)-N(1)-C(4)-C(9)
Pt(1)-N(2)-C(20)-C(25)
Pt(1)-N(2)-C(20)-C(21)
-3.06(0.87)
2.18(1.29)
-6.57(1.22)
3.28(1.52)
82.34(1.22)
-94.74(1.22)
96.10(1.20)
-79.90(1.18)
-178.32(1.00)
5.96(0.78)
-6.06(3.78)
-171.93(0.76)
174.83(0.92)
162.81(3.12)
owing to partial decomposition in benzene-d6 and slow
transformation of 2a ,b to the new purple species, 3a ,b
in CDCl3 (vide infra).
There are two logical pathways for the isomerization
of dimethyl complex 2. The first is via direct rotation
about the C(aryl)-N bonds of the coordinated imine
groups, while the second involves dissociation of one end
of the diazabutadiene ligand from the metal center
followed by bond rotation and recoordination. Both
pathways possess potentially high activation energies,
since the former would involve large steric repulsions
between bulky ortho substituents on the aryl rings and
the diimine chelate ring while the latter would neces-
sitate dissociation of a Pt-N bond. It is uncertain which
pathway is operative for the isomerization at this point,
but the information obtained from isomerization of the
chloro methyl derivative 3 discussed below favors the
mechanism involving hindered rotation about the C(ar-
yl)-N bonds.
Th er m olysis of th e Dim eth yl Com p lex 2. During
the course of investigating the isomerization of 2, we
observed upon heating a CDCl3 solution of the complex
for 24 h at 349 K a color change from deep green to
purple and the appearance of two new species. Partial
decomposition was also seen during this thermolysis,
as evidenced by the formation of a black precipitate and
1H NMR resonances of free ligand L in addition to those
of the new species. TLC analysis of the purple solution
showed two spots, and separation of the new products
was achieved by preparative TLC on silica using CHCl3
as eluant. Characterization of the new products was
achieved by 1H NMR spectroscopy and by an X-ray
diffraction study of one of the two products. The
similarity of the properties and NMR resonances for the
new products indicates that, as in the case of the
dimethyl complex 2, these new species are actually two
isomers of a single compound 3 as shown in eq 3.
F igu r e 3. (a) Benzylic proton resonances for the isomer-
ization of 2 at 349 K: (A) t ) 0 min; (B) t ) 50 min; (C) t
) 350 min. (b) First-order plot for the isomerization of 2
at 349 K.

5108 Organometallics, Vol. 17, No. 23, 1998
Yang et al.
and δ 166.5 for 3b. The observed 13C NMR data are
fully consistent with the unsymmetrical nature of 3.
The chloro methyl complex 3 also isomerizes, but at
much lower temperature than the dimethyl complex 2
(eq 4). An NMR tube containing a solution of pure 3a
in benzene-d6 maintained at ambient room temperature
for 24 h leads to a ca. 2:1 mixture of isomers. The
isomerization proceeds faster at elevated temperature.
Heating a sample of 3a in benzene-d6 to 318 K produces
a 1:1 mixture of isomers within 2 h. Following the same
procedure used to determine the free energy of activa-
tion for the isomerization of 2, the equilibrium constant
Keq of the isomerization process of 3 at 318 K was
determined to be ca. 0.98 ( 0.05, while the sum of
forward and reverse rates, k1 + k-1, was determined to
be 4.2 × 10-4 s-1 from a first-order plot of ln [(Ce - Co)/
(Ce - Ct)] vs time. From these values, the free energies
of activation of the forward and reverse rates, ∆Gfq and
The 1H NMR spectra of isomers 3a ,b in C6D6 each
show two characteristic singlets for the diimine (Nd
CHCHdN) protons (δ 7.91, 8.56 for 3a and δ 7.81, 8.45
for 3b), two resonances for the methoxy protons (δ 3.20,
3.21 for 3a and δ 3.17, 3.18 for 3b), four sets of doublets
for the benzylic protons, and four tert-butyl resonances
(δ 1.57, 1.45, 1.31, 1.26 for 3a and δ 1.62, 1.50, 1.31,
1.26 for 3b) consistent with an unsymmetrical structure
for each of the two isomers (see Table 1). In addition
to the diimine, methoxy, and tert-butyl protons, each
isomer was observed to have only a single Pt-coordi-
nated methyl resonance at δ 2.02 for 3a and δ 2.00 for
3b, with J Pt-H coupling constants of 41.2 and 40.8 Hz,
respectively. From the single-crystal structure deter-
mination discussed briefly below, it was established that
3 corresponds to the chloro methyl complex PtCl(Me)L.
Proton decoupling experiments were used to correlate
and assign the different benzylic proton resonances. The
benzylic proton doublets for 3a are centered at δ 5.29,
4.82, 4.55, and 4.51, and for 3b they are at δ 5.20, 4.81,
4.59, and 4.56, with the same J H-H coupling constant
of 11.6 Hz for each set. Irradiation of the doublet in 3a
at δ 5.29 results in a singlet at δ 4.55, while irradiation
of the doublet at δ 4.82 leads to a singlet at δ 4.51, thus
allowing assignment of the protons at δ 5.29 and 4.82
as belonging to one benzylic group and the protons at δ
4.82 and δ 4.51 comprising the other. Similar decou-
pling experiments were performed to assign the reso-
nances of 3b.
q
∆Gr , were calculated to be 24.1 ( 1.2 and 24.0 ( 1.2
kcal/mol, respectively. The ∆Gq values obtained for the
isomerization of PtCl(Me)L are ca. 3 kcal/mol lower than
those for the isomerization of the corresponding di-
methyl analogues 2a ,b. The easier isomerization of 3
relative to 2 favors simple rotation of the C(aryl)-N
bonds as the mechanism of isomerization since chloride
is sterically smaller than methyl, and chloride as a trans
ligand is not expected to facilitate diimine dissociation.27
The formation of 3 from 2 in chloroform provides an
easy entry to chloromethylplatinum(II) derivatives,
which serve as convenient precursors for cationic elec-
trophilic species via halide abstraction with silver salts.
With regard to the mechanism of formation of 3, the
exchange of one of the methyl groups in 2 for a chloride
probably proceeds via a radical pathway. In support of
this notion, it has been reported previously that Pt(II)
dimethyl diimine complexes undergo free radical oxida-
tive addition reactions with alkyl halides under thermal
as well as photochemical conditions.29
Str u ctu r e of P tMeClL (3a ). The structure of 3a
was determined by single-crystal X-ray diffraction.
Single crystals were grown by the slow diffusion of
heptane into a saturated benzene/hexane solution of the
complex at -10 °C. The ORTEP diagram of 3a is shown
in Figure 4, with details of the structure determination,
including unit cell data, summarized in Table 3 and
The 13C NMR spectra of isomers 3a ,b (Table 2) in
CDCl3 show the Pt-Me carbon resonances at δ -11.7
and -11.6, along with those of 4 tert-butyl groups, 2
methoxy groups, 2 benzylic groups, and 12 phenyl
carbons (Table 2). The resonances for the diimine
carbons are seen at δ 165.7 and 166.6 for 3a and δ 166.3
(29) Hill, R. H.; Puddephatt, R. J . J . Am. Chem. Soc. 1985, 107,
1218-1223.

1,4-Diazabutadiene Complexes of Pt(II)
Organometallics, Vol. 17, No. 23, 1998 5109
F igu r e 4. ORTEP diagram of 3a . Thermal ellipsoids are shown at 50% probability. Hydrogen atoms are omitted for
clarity.
relevant bond distances, bond angles, and torsion angles
listed in Tables 4-6, respectively.
groups (δ 0.79, 0.80). Additionally, the eight CH2
resonances of the methoxymethyl groups are seen but
cannot be resolved because of overlap. In the 13C NMR
spectrum of 4, both isomers give the same chemical shift
at δ 119.2 for the acetonitrile nitrile carbon.
The chloro methyl compound 3a possesses a slightly
distorted square-planar geometry. The bond angle of
78.1(4)° for N(1)-Pt-N(2) results from the constraints
of chelation by L and is intermediate between corre-
sponding values for the dimethyl and dichloro com-
plexes. As a consequence of the larger structural trans
influence of the Me group relative to chloride, the Pt-
N(2) bond is 0.128 Å longer than the Pt-N(1) bond. As
seen in the structures of the dichloro derivatives 1a ,b,
and the dimethyl complexes 2a ,b, the two aryl rings of
L are nearly normal to the coordination plane defined
by the metal chelate ring, as a result of steric interac-
tions between the bulky ortho substituents of the aryl
rings and the diimine chelate protons. The observed
Pt-Cl (2.283(3) Å) and Pt-C (2.053(10) Å) bond dis-
tances are comparable to those seen in other platinum
diimine complexes.30,31
Ha lid e Abstr a ction a n d th e Gen er a tion of Ca t-
ion ic Com p lexes. Syn th esis of [P tMeL(MeCN)]-
[BF 4] (4). The chloro methyl complex 3 (1:1 mixture
of isomers 3a ,b) reacts with 1.05 equiv of silver tet-
rafluoroborate in acetonitrile to give the cationic sol-
vento complex [PtMeL(MeCN)][BF4] (4) in good yield (eq
5). As with 2 and 3, two isomers of 4 are obtained in a
1:1 ratio. Purification of 4 is achieved by initial removal
of the silver chloride precipitate and subsequent recrys-
tallization from hexane/CH2Cl2 (5:1 v/v).
Characterization of 4 by 1H NMR spectroscopy in
CDCl3 reveals two singlets at δ 2.03 and 2.04 for
coordinated acetonitrile (Table 1). The presence of a
separate resonance at δ 2.00 for free acetonitrile indi-
cates that any acetonitrile exchange in chloroform is in
the slow exchange limit (10 s-1). In addition to the
coordinated acetonitrile resonances for the two isomers
of 4, the H NMR spectrum shows resonances for four
methoxy groups (δ 3.29, 3.33, 3.35, 3.37), four diimine
protons (δ 8.99, 9.01, 9.05 (2H)), and two Pt-bound Me
The existence of slow acetonitrile exchange involving
4 was established by dissolving a sample of the complex
in CD3CN for 1 h, isolating it, and then measuring its
1H NMR spectrum in CDCl3. The spectrum of this
sample showed that MeCN had been completely ex-
changed with CD3CN, by the disappearance of reso-
nances at δ 2.03 and 2.04, while other features of the
spectrum remained identical with those described above
for 4. By the same procedure, coordinated CD3CN was
completely exchanged by CH3CN, showing that the
exchange process, while slow, is fully reversible. The
slowness of the acetonitrile exchange in 4 may be
attributed to the steric bulk of the ortho substituents
on the diaryldiazabutadiene ligand L and consequent
1
(30) Wilkinson, G.; Stone, F. G. A.; Abel, E. W. Comprehensive
Organometallic Chemistry: The Synthesis, Reactions and Structures
of Organometallic Compounds; Wilkinson, G., Stone, F. G. A., Abel,
E. W., Eds.; Pergamon Press: Elmsford, NY, 1982; Vol. 6.
(31) De Felice, V.; Ganis, P.; Vigaliano, A.; Valle, G. Inorg. Chim.
Acta 1988, 144, 57-61.

5110 Organometallics, Vol. 17, No. 23, 1998
Yang et al.
inhibition of associative substitution paths that involve
addition from above or below the coordination plane.
Syn th esis of [P tMeL(p yr )][BF 4] (5). The pyridine-
coordinated complex 5 was prepared by dissolving 4 in
neat pyridine and stirring for 1 h. The procedure was
the same as that used to prepare the CD3CN-coordi-
nated complex 4 (vide supra). The key features in the
1H NMR spectrum of 5 are very similar to those of
acetonitrile complex 4 (see Table 1), except for the
coordinated pyridine resonances in the region between
δ 6.8 and 8.2, which are overlapped with those of the
phenyl protons on L.
obtained by recrystallization three times from a solvent
mixture of dichloromethane and hexane (1:3 v/v). Re-
gardless of which isomer of the chloro methyl complex
3 was used for the preparation, olefin complexes 6 and
7 were obtained as 1:1 mixtures of syn and anti isomers.
Both complexes are very soluble in dichloromethane,
chloroform, and toluene, are insoluble in hydrocarbons,
and are air- and moisture stable both in the solid state
and in solution.
The cationic olefin complexes 6 and 7 were character-
ized by both 1H and 13C NMR spectroscopy. In com-
parison with acetonitrile complex 4, complexes 6 and 7
show very similar spectroscopic features except for those
of the coordinated olefins (Tables 1 and 2). While the
1H NMR spectrum of ethylene complex 6 is not very
informative because of overlap of resonances for ethyl-
ene and benzylic protons, the 13C NMR spectrum in
CDCl3 clearly shows the coordinated ethylene at δ 74.29
and 74.32 ppm with the same J Pt-C coupling of 99 Hz
for the two isomers of 6 having syn and anti orientations
of the methoxymethyl and tert-butyl substituents. Com-
plex 7 shows the coordinated acrylonitrile at δ 5.7
(multiplets, 4H), 6.23 (d, J H-H ) 12 Hz, 1H), and 6.22
Ha lid e Abstr a ction in th e P r esen ce of Olefin s.
Syn th eses of [P tMeL(C2H3R)][BF 4] w ith R ) H, CN.
The preparation of R-olefin complexes of the formula
[PtMeL(C2H3R)][BF4] (R ) H, CN) was explored by both
acetonitrile displacement from 4 and halide abstraction
from 3 in the presence of olefins. The former was
carried out in olefin-containing dichloromethane or
1
chloroform solution. Monitoring these reactions by H
NMR spectroscopy revealed that acetonitrile displace-
ment by dissolved olefin is very slow. The reaction
between 4 and excess acrylonitrile in CDCl3 required
48 h to complete, while the reaction with ethylene was
only 5-10% complete after the same amount of time.
The acetonitrile displacement route was therefore not
pursued further in the synthesis of cationic olefin
complexes.
The halide abstraction reaction proved to be much
more effective. Treatment of a dichloromethane solu-
tion of the chloro methyl complex 3 with 1.05 equiv of
AgBF4 salt in the presence of olefins led to the formation
of cationic olefin complexes 6 and 7 for ethylene and
acrylonitrile, respectively, as red solids in good yields
(eq 6). In these reactions, filtration of the reaction
1
(d, J H-H ) 12 Hz, 1H) in its H NMR spectrum. The
1H resonances for the geminal and trans protons of
bound olefin in the two isomers 7a ,b overlap, while the
cis proton resonances are just resolved. In the 13C NMR
spectrum, overlap of bound olefin resonances is also seen
at δ 105.2 and 144.4, with the third acrylonitrile
resonance for 7a ,b just resolved at δ 117.4 and 117.5.
In accord with this view, the resonances at δ 105.2 and
144.4 appear to correspond to two carbons each, on the
basis of a qualitative assessment of resonance intensi-
ties. Assignment of the acrylonitrile 13C resonances was
made (see Table 2) on the basis of a 1H-coupled 13C
spectrum and the attached proton test (the J -modulated
1
spin-echo experiment) for free acrylonitrile. In the H
NMR spectrum, comparison of coordinated and free
acrylonitrile in CDCl3, the latter occurring at δ 6.21
(J H-H ) 16 Hz), δ 6.06 (J H-H ) 12 Hz), and δ 5.64 (dd,
J H-H ) 12 Hz, J H-H ) 16 Hz), reveals that only the
middle of the three protons in acrylonitrile is shifted
significantly upon coordination. The observed chemical
shifts for coordinated olefins here are comparable to
those of other structurally characterized phenathroline-
and diimine-based cationic olefin complexes.32
The observation of two ethylene 13C resonances for 6
and two acrylonitrile resonances for 7 in both 1H and
13C NMR spectra is consistent with the cationic olefin
complexes existing as mixtures of isomers that inter-
convert slowly, if at all. The fact that only a single 13C
resonance is seen for ethylene in each isomer of 6 while
only three 13C resonances occur for acrylonitrile in each
isomer of 7 indicates that the coordinated olefins in 6
and 7 rotate rapidly about the Pt-alkene bond. For 7,
evidence for hindered rotation about the metal-alkene
bond in the guise of different conformers for each isomer
is not observed.
Exchange of olefins occurs slowly from 6 and 7. While
the addition of free ethylene to a solution of 6 or the
addition of acrylonitrile to a solution of 7 has no
observable effect on coordinated olefin resonances, olefin
mixture through Celite, followed by precipitation of the
crude product with hexane, gave olefin complexes as red
solids. Analytically pure samples of 6 and 7 were
(32) Fusto, M.; Giordano, F.; Orabona, I.; Ruffo, F. Organometallics
1997, 16, 5981-5987.

1,4-Diazabutadiene Complexes of Pt(II)
Organometallics, Vol. 17, No. 23, 1998 5111
exchange can be effected by using neat olefin as solvent.
When ethylene complex 6 is dissolved in neat acryloni-
trile, complete displacement of the olefin is noted with
the formation of 7. For both 6 and 7, displacement of
the olefin is seen when the complex is dissolved in
acetonitrile, leading to the formation of 4.
a sample of 2 and B(C6F5)3 was treated with a CDCl3
solution containing a stoichiometric excess of acryloni-
trile. For both reactions, the green color of the starting
material 2 diminished quickly and the solution acquired
a red-orange color. The 1H NMR spectrum of [cis-
PtMeL(C2H3CN)]+ [MeB(C6F5)3] clearly shows the pro-
ton resonances of coordinated acrylonitrile at δ 6.23 (J HH
) 12 Hz), δ 5.81 (J HH ) 16 Hz), and δ 5.60 (J HH ) 12
Hz). However, the observed resonances of coordinated
acrylonitrile for both isomers are not well-resolved, with
lines somewhat broader than those of free acrylonitrile.
While the coordinated acrylonitrile does not provide
evidence of two different isomers for 9, the resonances
of ligand L clearly do. The differences in the coordi-
nated acrylonitrile resonances between 7 and 9 may be
attributable to the different modes of preparing [Pt(Me)-
(CH2dCHCN)L]+ and the resultant different counter-
ions.
Recently, Ruffo and co-workers have reported similar
cationic methyl olefin complexes of Pt containing diaza-
butadiene ligands.32,33 The DAB ligands are identical
with the ones used by Brookhart in which the aryl
groups have the same substituents in the 2- and
6-positions. In Ruffo’s studies, the cationic methyl olefin
complexes were generated either by alkylation of a Pt-
+
(0) olefin precursor using OR3 or, as in the present
study, by chloride ion abstraction from the correspond-
ing chloro methyl complex with AgBF4 in the presence
of olefin. A crystal structure of the η2-C2H4 complex
with ethyl groups in the 2,6-positions shows that the
olefin is oriented perpendicular to the coordination
plane.32 A connectivity-quality structure of the methyl
acrylate derivative reveals a similar orientation.33 In
accord with our conclusions for 6 and 7, the occurrence
of 195Pt satellites in the 13C resonances of the bound
olefin indicates that intermolecular exchange of olefin
is slow in these systems.
Syn th esis of [P tMeL(C2H3R)][MeB(C6F 5)3] (R )
H (8), CN (9)). Following Puddephatt’s precedent in
Pt chemistry for methyl group abstraction using strong
Lewis acids, we find that the cationic olefin complexes
can also be generated by reacting dimethyl complex 2
with B(C6F5)3 in dichloromethane solutions in the
presence of olefins (eq 7). For ethylene complex 6, a
Con clu sion
New dimethyl, chloro methyl, and cationic platinum
complexes of the bulky diazabutadiene ligand L have
been synthesized and characterized. The 2,6-aryl sub-
stituents of the ligand L effectively block facile rotation
about the imine N-C(ipso) bond, leading to the observed
formation and isolation of two isomers for each complex.
The structures of the complexes have been shown by
X-ray crystallography and NMR spectroscopy to contain
square-planar-coordinated Pt(II) ions with the isomers
differing in the relative orientation of the methoxy-
methyl and tert-butyl substituents of the aryl groups
with respect to the coordination plane. For the dimethyl
complex PtMe2L (2), the two isomers possess Cs and C2
symmetries. Interconversion of the isomers occurs
slowly for PtMe2L and more rapidly for the chloro
methyl system PtClMeL (3), consistent with a simple
hindered rotation process. Cationic monomethyl com-
plexes have been synthesized by chloride ion abstraction
using AgBF4, which in the presence of ethylene or
acrylonitrile leads to the olefin complexes [PtMe-
(C2H4)L]+ and [PtMe(C2H3CN)L]+. These same com-
plexes have also been prepared in situ by methyl group
abstraction from dimethyl complex 2 using the strong
Lewis acid B(C6F5)3 in dichloromethane. The exchange
processes between coordinated MeCN, CD3CN, and
olefins in the cationic monomethyl complexes have also
been demonstrated. The reactivities of the cationic
solvento complexes toward C-H activation reactions is
currently under investigation and the results will be
reported in due course.
Exp er im en ta l Section
P r ocedu r es an d Mater ials. The 1,4-diazabutadiene ligand
glyoxal bis(2-(methoxymethyl)-4,6-di-tert-butylphenyl)diimine
(L) was prepared by following the published procedure.26 The
complex Pt2Me4(SMe2)2 was prepared by a modification of the
procedure by Elsevier.24 The reagents AgBF4 and B(C6F5)3
were purchased from Strem and used as received. Unless
otherwise noted, all reactions and manipulations were per-
formed in dry glassware under a nitrogen atmosphere using
either standard Schlenk techniques or an inert-atmosphere
glovebox. All NMR spectra were recorded on a Bruker AMX
400 MHz spectrometer. Proton homonuclear decoupling ex-
periments were performed using the pulse program HOMO-
sample of 2 and B(C6F5)3 in an NMR tube was placed
under an ethylene atmosphere and then dissolved in
ethylene-degassed CDCl3. For acrylonitrile complex 7,
(33) Ganis, P.; Orabona, I.; Ruffo, F.; Vitagliano, A. Organometallics
1998, 17, 2646-2650.

5112 Organometallics, Vol. 17, No. 23, 1998
Yang et al.
DEC. Elemental analyses were obtained from Quantitative
Technologies, Inc., Whitehouse, NJ .
Exchange of CD3CN from this sample can be achieved by
dissolution in CH3CN for 1 h.
Syn th esis of [P tMeL(p yr )]BF 4 (5). Complex 5 was
generated in an NMR tube and characterized by 1H NMR
spectroscopy. The complex [PtMeL(MeCN)]BF4 (4) (10 mg)
was dissolved in 0.5 mL of pyridine in an NMR tube and the
solution then maintained at room temperature for 1 h. The
solvent was next removed under vacuum and the residue was
redissolved in 0.8 mL of CDCl3. The spectroscopic data of
complex 5 is presented in Table 1.
Syn th esis of [P tMeL(C2H4)]BF 4 (6). A solution of 0.10 g
(0.13 mmol) of the chloromethyl complex 3 in 20 mL of CH2-
Cl2 was degassed with ethylene for about 5 min and then
treated with 1.05 equiv of AgBF4. The color of the reaction
mixture changed slowly from purple to red-brown. The
reaction mixture was kept under ethylene and stirred over-
night. The product was isolated by filtering the reaction
mixture through a short Celite column and then adding hexane
to effect product precipitation. The sample of 6 was recrystal-
lized from a solvent mixture of CH2Cl2 and hexane (2:8 v/v).
Yield: 0.08 g (74%). Anal. Calcd for 6 (C37H59BF4N2O2Pt):
C, 52.54; H, 7.03; N, 3.31. Found: C, 50.90; H, 6.74; N, 3.17.
Syn th esis of [P tMeL(C2H3CN)]BF 4 (7). A solution was
made of 0.10 g (0.13 mmol) of chloromethyl complex 3 and 0.2
mL of acrylonitrile in 20 mL of CH2Cl2. The mixture was
treated with 1.05 equiv of AgBF4 and was stirred overnight.
Purification was achieved by following the same procedure as
Syn th esis of P tMe2L (2a ,b). To a 50 mL Schlenk flask
containing 20 mL of CH2Cl2 was added 0.10 g (0.19 mmol) of
glyoxal bis(2-(methoxymethyl)-4,6-di-tert-butylphenyl)imine
(L) and 0.10 g (0.18 mmol) of Pt2Me4(SMe2)2, after which the
reaction solution was stirred for 48 h at room temperature.
The color of the reaction solution slowly changed from yellow
to deep green. The solvent was removed by vacuum, and the
residue was separated by column chromatography using a 9:1
mixture of CH2Cl2 and hexane on silica gel. Yield: 2a , 0.01 g
(7.5%); 2b, 0.05 g (38%). The low yields are caused by partial
decomposition of the product during chromatographic separa-
tion, with decomposed material giving a red color on the
column. Anal. Calcd for 2a (C36H58N2O2Pt): C, 57.96; H, 7.84;
N, 3.75. Found: C, 57.91; H, 7.91; N, 3.47. Calcd for 2b
(C36H58N2O2Pt): C, 57.96; H, 7.84; N, 3.75. Found: C, 57.89;
H, 7.92; N, 3.44.
Isom er iza tion of 2a a n d 2b. An NMR tube containing
0.8 mL of a 13.8 mM benzene-d6 solution of either 2a or 2b
was maintained at the desired temperature, and 1H NMR
spectra were taken at specified time intervals. The reaction
profile was determined by plotting the relative integrations
of 2a and 2b versus time. Slight decomposition of both isomers
was noted when the NMR tube was maintained at tempera-
tures above 323 K for longer than 6 h. The equilibrium
constant Keq of the isomerization process was determined to
be ca. 0.79 from NMR peak integrations of the diimine protons,
while the sum of forward and reverse rates, k1 + k-1, was
determined by a first-order plot of ln [(Ce - Co)/(Ce - Ct)] vs
time, where Ce is the concentration of 2a at equilibrium, Ct is
the concentration at time t, and Co is the concentration at time
zero (Figure 3).
Syn th esis of P tMeClL (3a ,b). A 50 mL Schlenk flask was
charged with 0.13 g (0.17 mmol) of 2 and 20 mL of CHCl3,
and the solution was heated to reflux for 24 h. The color of
the reaction solution changed slowly from deep green to purple.
The reaction was monitored by NMR and TLC analysis until
2 was no longer present in the reaction solution. The solvent
was removed by vacuum, and the residue was separated by
preparative TLC using CHCl3 as eluant. Yield: 3a , 0.025 g
(19%); 3b, 0.017 g (13.1%). The low yields are caused by
partial decomposition of the product complex during column
separation. Anal. Calcd for 3a (C35H55O2N2PtCl): C, 54.85;
H, 7.23; N, 3.65. Found: C, 54.79; H, 7.28; N, 3.45 (3a and
3b were analyzed as a mixture since recrystallizations of either
isomer resulted in a mixture of both isomers as confirmed by
1H NMR spectroscopy).
used for 6. Yield: 0.082 g (73%). Anal. Calcd for 7 (C38H58
-
BF4N3O2Pt): C, 52.41; H, 6.71; N, 4.83. Found: C, 52.77; H,
6.75; N, 4.45.
Disp la cem en t of Eth ylen e by Aceton itr ile a n d Acr ylo-
n itr ile fr om [P tMeL(CH2CH2)]BF 4. To an NMR tube
containing 3.5 mg of [PtMeL(CH2CH2)]BF4 (6) was added 0.3
mL of acetonitrile (or acrylonitrile) by syringe. The solution
was maintained at room temperature for 1 h. All volatiles
were next removed by vacuum, and the residue was redis-
1
solved in 0.8 mL of CDCl3 and its H NMR spectrum recorded.
1
The H NMR spectrum revealed that ethylene in 6 had been
completely replaced by acetonitrile (or acrylonitrile), generat-
ing 4 (or 7).
Syn th esis of [P tMeL(C2H4)][MeB(C6F 5)3] (8). Chloro-
form saturated with ethylene (0.7 mL) was added to an NMR
tube containing 2 (10 mg, 0.015 mmol) and B(C6F5)3 (8 mg,
0.016 mmol) under an ethylene atmosphere. The color of the
solution quickly changed from green to red-orange. The
solution was maintained at room temperature for an additional
20 min, and the formation of the cationic ethylene complex as
its MeB(C6F5)3- salt was confirmed by H NMR spectroscopy.
1
Syn th esis of [P tMeL(MeCN)]BF 4 (4a ,b). To a 50 mL
Schlenk flask containing 20 mL of MeCN was added 0.10 g
(0.13 mmol) of chloro complex 3 and 1.05 equiv of AgBF4. The
resulting reaction mixture was monitored by TLC analysis
until the purple color of the chloromethyl complex 3 was no
longer seen (2 h). The solvent was removed by vacuum, and
the solid residue was redissolved into 10 mL of dichlo-
romethane and the solution filtered. Crude product 4 was
precipitated by adding hexane to the above filtrate. An
analytically pure sample was obtained by recrystallizing the
crude product from a solvent mixture of dichloromethane and
hexane (1:5 v/v). 4 was obtained as a mixture of two isomers
(4a ,b), and attempts to isolate both isomers via fractional
recrystallization were unsuccessful. Yield: 0.08 g (72%). Anal.
Calcd for 4 (C37H58BF4N3O2Pt‚CH2Cl2): C, 48.36; H, 6.41; N,
4.45. Found: C, 48.95; H, 6.60; N, 4.52.
Exch a n ge of MeCN w ith CD3CN in [P tMeL(MeCN)]-
BF 4. To an NMR tube containing 3.5 mg of [PtMeL(MeCN)]
BF4 (4) was added 0.3 mL of CD3CN by syringe. The solution
was then maintained at room temperature for 1 h. After
removal of solvent, the residue was redissolved in 0.8 mL of
CDCl3 and its 1H NMR spectrum taken. The spectrum
revealed complete replacement of MeCN in 4 by CD3CN.
Syn th esis of [P tMeL(C2H3CN)][MeB(C6F 5)3] (9). A pro-
cedure analogous to that used for the generation of ethylene
complex 8 was employed to prepare the acrylonitrile complex
9. A stock solution of acrylonitrile in CDCl3 (0.7 mL) was
added to an NMR tube containing 2a (10 mg, 0.015 mmol) and
B(C6F5)3 (8 mg, 0.016 mol). The color of the solution changed
from green to red-orange quickly. The solution was main-
tained at room temperature for an additional 20 min, and the
formation of the acrylonitrile complex was confirmed by 1H
NMR spectroscopy.
X-r a y Cr ysta llogr a p h y. Crystals of 2a ,b and 3a were
each mounted under Paratone-8277 on glass fibers or in a loop
and immediately placed on the X-ray diffractometer in a cold
nitrogen stream supplied by a Siemens LT-2A low-temperature
device. The X-ray intensity data were collected on a standard
Siemens SMART CCD area detector system equipped with a
normal-focus molybdenum-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
for 2a ,b and 3a using a crystal-to-detector distance of 5.094
cm (maximum 2θ angle of 56.52°). The total data collection
time was approximately 12 h for each crystal. Frames for 2a ,b

1,4-Diazabutadiene Complexes of Pt(II)
Organometallics, Vol. 17, No. 23, 1998 5113
and 3a were integrated with the Siemens SAINT program.
The unit cell parameters, provided in Table 3, were based upon
the least-squares refinement of three-dimensional centroids
of >1500 reflections for each crystal. Data were corrected for
absorption using the program SADABS.
anisotropically. All hydrogens were included in idealized
positions. Pertinent crystallographic data and experimental
conditions are summarized in Table 3.
Ack n ow led gm en t. We wish to thank the National
Science Foundation (Grants CHE 94-04991 and 97-
29311) for support of this work and Alfa/Aesar J ohnson
Matthey Co. Inc. for a generous loan of platinum salts.
We also thank Mr. Paul Albietz for help with the paper
and the J -modulated spin-echo spectrum of acryloni-
trile.
The space group assignments were made on the basis of
systematic absences and intensity statistics by using the
XPREP program (Siemens, SHELXTL 5.04).34 The structures
were solved by employing Patterson interpretation and dif-
ference Fourier methods for 2a and by using direct methods
for 2b and 3a , and all structures were refined by full-matrix
least squares on F2. For Z values of 8 for 2a , 4 for 2b, and 8
for 3a , there are two independent molecules for 2a , one
independent molecule for 2b, and one independent molecule
plus one benzene solvate at full occupancy and half of a half-
occupied hexane for 3a in the asymmetric unit. All of the
atoms were refined isotropically for 2a , except for the platinum
atoms, which were refined with anisotropic thermal param-
eters. All non-hydrogen atoms for 2b and 3a were refined
Su p p or tin g In for m a tion Ava ila ble: Tables of data col-
lection and refinement parameters, refined positional param-
eters and equivalent isotropic temperature factors, anisotropic
thermal parameters, calculated hydrogen positional param-
eters, and complete bond distances and angles for non-
hydrogen atoms for compounds 2a ,b and 3a (28 pages).
Ordering information is given on any current masthead page.
(34) Intensity statistics from CCD data sets are often unreliable,
especially for weakly diffracting crystals.
OM980551M