Unsymmetrical 1,4-diazabutadiene complexes of platinum(II)

Article abstract of DOI:10.1021/om970452t

The new unsymmetrical 1,4-diazabutadiene ligand glyoxal bis(2-(methoxymethyl)-4,6-ditert-butylphenyl)diimine (L) and its reduced analog (LH₄) were synthesized. The reactions of both ligands with bis(benzonitrile) complexes of palladium and platinum, MCl₂(PhCN)₂, were investigated. Two isomers of formula MCl₂L were isolated from the reaction of L with MCl₂(PhCN)₂ (1a and 1b for Pd, 2a and 2b for Pt), while only a single product, MCl₂(LH₄), formed in the reaction with LH₄ (3 for M = Pd, 4 for M = Pt). All new compounds were characterized by elemental analyses and IR and NMR spectroscopies. The molecular structures for L, LH₄, 2b, 3, and 4 were determined by single-crystal X-ray diffraction. The metal complexes exhibit distorted square-planar geometry. The aryl groups of the L and LH₄ ligands lie out of the coordination plane in a manner that blocks potential axial ligation sites. Ligand L crystallizes in the triclinic space group P1 with a = 5.760(1) ?, b = 9.383(2) ?, c = 14.954(3) ?, α = 89.38(2)°, β = 79.67(2)°, γ = 88.14(2)°, and Z = 1. The reduced ligand LH₄ crystallizes in the monoclinic space group P2₁ with a = 5.9758(1) ?, b = 17.4272-(2) ?, c = 15.6222(1) ?, β = 99.063(1)°, and Z = 2. Complex 2b crystallizes in the monoclinic space group P2₁/c with a = 16.9599(2) ?, b = 18.4985(2) ?, c = 12.4976(0) ?, β = 100.945-(0)°, and Z = 4. Complex 3 crystallizes in the monoclinic space group C2/c with a = 36.1506-(8) ?, b = 8.0994 (2) ?, c = 15.5671(1) ?, β = 113.988(1)°, and Z = 4. Complex 4 crystallizes in the monoclinic space group C2/c with a = 36.0649(3) ?, b = 8.1787(2) ?, c = 15.7585(3) ?, β = 112.610(1)°, and Z = 4.

Full text of DOI:10.1021/om970452t

5234
Organometallics 1997, 16, 5234-5243
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)
Kaiyuan Yang, Rene J . Lachicotte, and Richard Eisenberg*
Department of Chemistry, University of Rochester, Rochester, New York 14627
Received May 30, 1997X
The new unsymmetrical 1,4-diazabutadiene ligand glyoxal bis(2-(methoxymethyl)-4,6-di-
tert-butylphenyl)diimine (L) and its reduced analog (LH4) were synthesized. The reactions
of both ligands with bis(benzonitrile) complexes of palladium and platinum, MCl2(PhCN)2,
were investigated. Two isomers of formula MCl2L were isolated from the reaction of L with
MCl2(PhCN)2 (1a and 1b for Pd, 2a and 2b for Pt), while only a single product, MCl2(LH4),
formed in the reaction with LH4 (3 for M ) Pd, 4 for M ) Pt). All new compounds were
characterized by elemental analyses and IR and NMR spectroscopies. The molecular
structures for L, LH4, 2b, 3, and 4 were determined by single-crystal X-ray diffraction. The
metal complexes exhibit distorted square-planar geometry. The aryl groups of the L and
LH4 ligands lie out of the coordination plane in a manner that blocks potential axial ligation
sites. Ligand L crystallizes in the triclinic space group P1h with a ) 5.760(1) Å, b ) 9.383(2)
Å, c ) 14.954(3) Å, R ) 89.38(2)°, â ) 79.67(2)°, γ ) 88.14(2)°, and Z ) 1. The reduced
ligand LH4 crystallizes in the monoclinic space group P21 with a ) 5.9758(1) Å, b ) 17.4272-
(2) Å, c ) 15.6222(1) Å, â ) 99.063(1)°, and Z ) 2. Complex 2b crystallizes in the monoclinic
space group P21/c with a ) 16.9599(2) Å, b ) 18.4985(2) Å, c ) 12.4976(0) Å, â ) 100.945-
(0)°, and Z ) 4. Complex 3 crystallizes in the monoclinic space group C2/c with a ) 36.1506-
(8) Å, b ) 8.0994 (2) Å, c ) 15.5671(1) Å, â ) 113.988(1)°, and Z ) 4. Complex 4 crystallizes
in the monoclinic space group C2/c with a ) 36.0649(3) Å, b ) 8.1787(2) Å, c ) 15.7585(3)
Å, â ) 112.610(1)°, and Z ) 4.
In tr od u ction
contexts. First, DAB ligands possess different possible
modes of coordination as 2-, 4-, 6-, and even 8-electron
donors in terminal, chelating, and bridging arrange-
ments.16-20 These different modes of coordination in
turn confer different reactivities on the complexed metal
ions, as detailed in the review by van Koten and
Vrieze.10 Second, as R-diimine ligands, DAB ligands
have electronic structural similarities to the more
extensively studied heteroaromatic chelating agents
2,2′-bipyridine and 1,10-phenanthroline.21,22 In 1973,
for example, Miller and Dance23 showed that square-
planar Ni(II) diimine dithiolate complexes containing
1,10-phenanthroline and the DAB ligand biactetyl bis-
(anil) (R ) Ph; R′ ) Me) were spectroscopically similar
with a common low-energy charge transfer-to-diimine
absorption.
The recent discovery by Brookhart and co-workers of
Ni(II) and Pd(II) R-olefin polymerization catalysts con-
taining bulky diimine ligands1-9 has stimulated re-
newed interest in the chemistry of 1,4-diazabutadiene
(DAB) ligands and their complexes.10-15 Ligands of this
type have been studied extensively in several different
X Abstract published in Advance ACS Abstracts, November 1, 1997.
(1) Brookhart, M.; Lincoln, D. M. J . Am. Chem. Soc. 1988, 110, 8719.
(2) Brookhart, M.; Volpe, A. F.; Lincoln, D. M.; Hovarth, I. T.; Millar,
J . M. J . Am. Chem. Soc. 1990, 112, 5634.
(3) Brookhart, M.; Rix, F. C.; DeSimone, J . M.; Barborak, J . C. J .
Am. Chem. Soc. 1992, 114, 5894-5895.
(4) Brookhart, M.; Hauptman, E. J . Am. Chem. Soc. 1992, 114, 4437.
(5) Brookhart, M.; Rix, F. C.; DeSimone, J . M.; Barborak, J . C. J .
Am. Chem. Soc. 1992, 114, 5894.
In this paper, we report the syntheses of an unsym-
metrical DAB ligand, its saturated analog, and their Pt-
(II) and Pd(II) dichloro complexes. The ligand synthesis
was originally undertaken to generate a tetradentate
chelating agent that would bind to a six-coordinate
(6) Brookhart, M.; Hauptman, E.; Lincoln, D. J . Am. Chem. Soc.
1992, 114, 10394.
(15) Groen, J . H.; Elsevier, C. J .; Vrieze, K.; Smeets, W. J . J .; Spek,
A. L. Organometallics 1996, 15, 3445-3455.
(7) Rix, F. C.; Brookhart, M. J . Am. Chem. Soc. 1995, 117, 1137.
(8) Rix, F. C.; Brookhart, M.; White, P. S. J . Am. Chem. Soc. 1996,
118, 4746-4764.
(16) van der Poel, H.; van Koten, G.; Vrieze, K. Inorg. Chem. 1980,
19, 1145.
(17) Fru¨hauf, H. W.; Landers, R.; Goddard, R.; Kru¨ger, C. Angew.
Chem. 1978, 90, 56.
(18) Staal, L. H.; van Koten, G.; Vrieze, K.; Ploeger, F.; Stam, C. H.
Inorg. Chem. 1982, 20, 1830.
(19) van der Poel, H.; van Koten, G.; Vrieze, K.; Kokkes, M.; Stam,
C. H. J . Organomet. Chem. 1979, 175, C21.
(9) Rix, F. C.; Brookhart, M.; White, P. S. J . Am. Chem. Soc. 1996,
118, 2436-2448.
(10) van Koten, G.; Vrieze, K. Adv. Organomet. Chem. 1982, 21,
151-239.
(11) Klein, R. A.; Hartl, F.; Elsevier, C. J . Organometallics 1997,
16, 1284-1291.
(20) Shi, Q. Z.; Richmond, T. G.; Trogler, W. C.; Basolo, F. Orga-
nometallics 1982, 1, 1033-1037.
(12) van Asselt, R.; Elsevier, C. J .; Amatore, C.; J utand, A. Orga-
nometallics 1997, 16, 317-328.
(21) McWhinnie, W. R.; Miller, J . D. Adv. Inorg. Chem. Radiochem.
1969, 12, 135-215.
(13) van Asselt, R.; Vrieze, K.; Elsevier, C. J . J . Organomet. Chem.
1994, 480, 27-40.
(22) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry, 5th
ed.; J ohn Wiley and Sons, Inc.: New York, 1988; p 1455.
(23) Miller, T. R.; Dance, G. J . Am. Chem. Soc. 1973, 95, 6970.
(14) Groen, J . H.; Delis, J . G. P.; van Leeuwen, W. N. M.; Vrieze, K.
Organometallics 1997, 16, 68-77.
S0276-7333(97)00452-4 CCC: $14.00 © 1997 American Chemical Society

Unsymmetrical 1,4-Diazabutadiene Complexes of Pt(II)
Sch em e 1
Organometallics, Vol. 16, No. 24, 1997 5235
metal ion in the manner shown as A leaving two
cifically, for the ML moiety of C2 symmetry, diastere-
omeric interactions between the catalyst complex and
prochiral substrates would exist. Additionally, the
design of ligand L and related derivatives with other
groups in place of methoxymethyl affords the possibility
of developing catalysts in which secondary interactions
between ligand and substrate help control the stereo-
chemistry and course of the ensuing transformations.
Resu lts a n d Discu ssion
adjacent sites available for substrate binding and
transformation in the manner of the Brookhart polym-
erization catalysts1-9 and related Pd(II) catalysts stud-
ied by Drent for copolymerization of CO and ethylene.24
In the design of the ligand, bulky organic substituents
serve to enforce the desired geometric constraints while
ensuring the solubility of the resultant complexes in
nonpolar solvents. The specific DAB ligand initially
designed in this exercise is shown as L where the two
additional coordination sites are ether oxygens capable
of weak but significant binding to metal ions. Studies
by Dunbar on complexes of the functionalized phosphine
P(2,4,6-C6H2(OMe)3)3 demonstrate the importance and
versatility of coordination by the ortho methoxy ether
substituents in stabilizing octahedral Rh(II) and Pd(II)
ions.25-27
Syn th esis a n d Ch a r a cter iza tion of Liga n d s. The
synthetic procedure for obtaining glyoxal bis(2-(meth-
oxymethyl)-4,6-di-tert-butylphenyl)diimine (L) is out-
lined in Scheme 1, starting from commercially available
3,5-di-tert-butyltoluene. The details of each step leading
to L can be found in the Experimental Section, and
pertinent spectroscopic data for L, LH 4, and all new
complexes are summarized in Table 1.
The condensation reaction between 2-(methoxy-
methyl)-4,6-di-tert-butylaniline and glyoxal was initially
examined under thermal conditions. Refluxing a 2:1
mixture of 2-(methoxymethyl)-4,6-di-tert-butylaniline
and glyoxal in either methanol or ethanol solvents
overnight produced only traces of the desired product
as determined by monitoring the reactions with TLC
analysis and 1H NMR spectroscopy. Therefore, the
thermal condensation route to L was not pursued fur-
ther. Instead, the catalytic procedure used by tom Dieck
and co-workers28 for preparing similar 1,4-diazabuta-
diene ligands was employed. Treatment of a 2:1 mix-
ture of 2-(methoxymethyl)-4,6-di-tert-butylaniline and
glyoxal in minimum ethanol solvent with a catalytic
amount of formic acid at room temperature affords L
as an analytically pure yellow microcrystalline product
in greater than 90% yield.
A second aspect in the design of L is that, for square-
planar complexes similar to Brookhart’s active cata-
lysts,1-9 two possible isomers for the ML moiety would
existsone having C2 symmetry and the other with
mirror symmetryswith possible stereochemical conse-
quences in reactions promoted or catalyzed by it. Spe-
(24) Drent, E.; Budzelaar, P. H. M. Chem. Rev. 1996, 96, 663-681.
(25) Dunbar, K. R.; Sun, J .-S. J . Chem. Soc., Chem. Commun. 1994,
2387-2388.
(26) Dunbar, K. R.; Haefner, S. C.; Pence, L. E. J . Am. Chem. Soc.
1989, 111, 5504-5506.
(27) Dunbar, K. R.; Matonic, J . H.; Saharan, V. P. Inorg. Chem.
1994, 33, 25-31.
(28) tom Dieck, H.; Svoboda, M.; Greiser, T. Z. Naturforsch., B.:
Anorg. Chem., Org. Chem. 1981, 36B, 823.

5236 Organometallics, Vol. 16, No. 24, 1997
Ta ble 1. 1H NMR Sp ectr a l Da ta for L, LH4, a n d All New Com p lexesa
Yang et al.
compd
1H NMR (δ)
L
1.33 (s, 18H, t-Bu), 1.37 (s, 18H, t-Bu), 3.38 (s, 6H, OCH3), 4.14 (s, 4H, CH2),
7.28 (s, 2H, C6H), 7.42 (s, 2H, C6H), 8.19 (s, 2H, NCH)
LH4
1a
1.32 (s, 18H, t-Bu), 1.46 (s, 18H, t-Bu), 3.26 (s, 4H, NCH2), 3.44 (s, 6H, OCH3),
3.77 (s, 2H, NH), 4.57 (s, 4H, CH2), 7.326 (s, 2H, C6H), 7.331 (s, 2H, C6H)
1.32 (s, 18H, t-Bu), 1.59 (s, 18H, t-Bu), 336 (s, 6H, OCH3), 4.29 (d, J HH ) 12 Hz, 2H,
CHaH), 5.29 (d, J HH ) 12 Hz, 2H, CHHb), 7.18 (d, J HH ) 4 Hz, 2H, C6H),
7.51 (d, J HH ) 4 Hz, 2H, C6H, 7.96 (s, 2H, NCH)
1b
2a
2b
3
1.31 (s, 18H, t-Bu), 1.55 (s, 18H, t-Bu), 3.33 (s, 6H, OCH3), 4.33 (d, J HH ) 12 Hz, 2H,
CHaH), 5.13 (d, J HH ) 12 Hz, 2H, CHHb), 7.18 (d, J HH ) 4 Hz, 2H, C6H),
7.47 (d, J HH ) 4 Hz, 2H, C6H, 8.02 (s, 2H, NCH)
1.36 (s, 18H, t-Bu), 1.54 (s, 18H, t-Bu), 3.31 (s, 6H, OCH3), 4.33 (d, J HH ) 12 Hz, 2H,
CHaH), 5.16 (d, J HH ) 12 Hz, 2H, CHHb), 7.57 (d, J HH ) 4 Hz, 2H, C6H),
7.78 (d, J HH ) 4 Hz, 2H, C6H, 8.73 (s, 2H, NCH)
1.35 (s, 18H, t-Bu), 1.53 (s, 18H, t-Bu), 3.31 (s, 6H, OCH3), 4.40 (d, J HH ) 12 Hz, 2H,
CHaH), 5.10 (d, J HH ) 12 Hz, 2H, CHHb), 7.27 (d, J HH ) 4 Hz, 2H, C6H),
7.55 (d, J HH ) 4 Hz, 2H, C6H, 8.74 (s, 2H, NCH)
1.30 (s, 18H, t-Bu), 1.61 (s, 18H, t-Bu), 2.74 (m, 2H, NCHa),
3.66 (s, 6H, OCH3), 3.26 (m, 2H, NCHb), 4.68 (d, J HH ) 12 Hz, 2H, CHaH),
6.09 (s, 2H, NH), 7.29 (s, 2H, C6H), 7.38 (s, 2H, C6H), 7.62 (d, J HH ) 12 Hz, 2H, CHaH)
1.27 (s, 18H, t-Bu), 1.62 (s, 18H, t-Bu), 2.74 (m, 2H, NCHa), 3.61 (s, 6H, OCH3),
3.74 (m, 2H, NCHb), 4.64 (d, J HH ) 12 Hz, 2H, CHaH), 7.28 (d, J HH ) 2 Hz,
2H, NH), 7.39 (d, J HH ) 2 Hz, 2H, C6H), 7.66 (d, J HH ) 12 Hz, 2H, CHHb),
4
a
All 1H NMR spectra were recorded in CDCl3 solutions. Chemical shift values are reported in ppm. Abbreviations: s, singlet; d, doublet;
m, multiplet.
of the crystallographically imposed symmetry, the meth-
oxymethyl substituents are on opposite sides of the
NdC-CdN plane. The bond distances for the CdN
double bond and the central C-C single bond are 1.273-
(3) and 1.470(4) Å, respectively, which are similar to the
bond distances described in other structurally charac-
terized free diimine ligands.10
Glyoxal bis(2-(methoxymethyl)-4,6-di-tert-butylphen-
yl)diimine (L) can be reduced readily using LiAlH4 as a
reducing agent at room temperature. Treatment of a
bright yellow THF solution of L with excess LiAlH4
affords the saturated colorless product LH4 in high yield
(eq 1). LH4 is very soluble in hexane, toluene, THF,
F igu r e 1. ORTEP diagram of L. Thermal ellipsoids are
shown at 50% probability. Hydrogen atoms are omitted for
clarity.
1
The H NMR spectrum (Table 1) of L in CDCl3 shows
a characteristic imine proton resonance at δ 8.19 ppm
as a sharp singlet,10,28 along with singlets for the
benzylic CH2 protons at δ 4.14, the methoxy protons at
δ 3.38, and the tert-butyl protons at δ 1.37 and 1.33 ppm.
The fact that the diastereotopic benzylic protons show
only a singlet instead of a four-line AB pattern indicates
that free rotation about single bonds of the DAB
backbone must be faster than the NMR time scale,
despite the bulkiness of the ortho aryl substituents.29,30
A single-crystal X-ray diffraction structure confirms the
identity of L and reveals the preferred conformation of
the free ligand. The ORTEP diagram of L is shown in
Figure 1, with details of the structure determination,
including unit-cell data, summarized in Table 2 and
relevant bond distances, bond angles, and torsion angles
listed in Tables 3-5, respectively.
As seen in Figure 1, L adopts a trans orientation at
each imine functionality with an s-trans conformation
about the central C-C bond of the DAB backbone. L
contains a crystallographically imposed inversion cen-
ter, and therefore the NdC-CdN DAB moiety is
necessarily planar. The phenyl rings of the imine
substituents are tilted out of the NdC-CdN plane by
about 55°, as indicated by torsion angles of -128.19-
(0.24) and 57.14(0.31)° for C(17)-N(1)-C(1)-C(6) and
C(17)-N(1)-C(1)-C(2), respectively. As a consequence
and CH2Cl2 and moderately soluble in CH3OH and
DMF. The 1H NMR spectrum of LH4 (Table 1) in CDCl3
shows resonances of secondary amine NH and NCH2-
CH2N backbone protons at δ 3.77 and 3.26, along with
those for the MeO protons at δ 3.44, the benzylic CH2
protons at δ 4.57, and the tert-butyl groups at δ 1.32
and 1.46 ppm. The IR spectrum of LH4 in KBr reveals
the NH stretches at 3422 and 3328 cm-1
.
Single crystals of LH4 were grown by slow evapora-
tion from a methanol and hexane solution. The ORTEP
diagram of LH4 is shown in Figure 2, with details of
the structure determination, including unit-cell data,
summarized in Table 2 and relevant bond distances,
bond angles, and torsion angles listed in Tables 3-5,
respectively.
(29) Wightman, R. H.; Staunton, J .; Battersby, A. R.; Hanson, K.
R. J . Chem. Soc., Perkin Trans. 1 1972, 2355.
(30) J ennings, B. Chem. Rev. 1975, 75, 307.

Unsymmetrical 1,4-Diazabutadiene Complexes of Pt(II)
Organometallics, Vol. 16, No. 24, 1997 5237
Ta ble 2. Su m m a r y of Cr ysta llogr a p h ic Da ta a n d X-r a y Exp er im en ta l Deta ils for L, LH4, 2b, 3, a n d 4
L
LH4
2b‚CH2Cl2
empirical formula
fw
C34H52N2O2
520.67
C34H56N2O2
524.81
C34H54Cl4N2O2Pt
871.69
cryst syst
space group
Z
triclinic
P1h (No. 2)
1
5.760(1)
9.383(2)
14.954(3)
89.38(2)
79.67(2)
monoclinic
P21 (No. 4)
2
5.9758(1)
17.4272(2)
15.6222(1)
monoclinic
P21/c (No. 14)
4
16.9599(2)
18.4985(2)
12.4976(0)
a, Åa
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
99.063(1)
100.945(0)
88.14(2)
794.7(3)
1.088
1606.61(3)
1.085
3849.58(6)
1.504
F
calc, g cm-3
cryst dimens, mm
temp, °C
0.18 × 0.26 × 0.28
0.14 × 0.14 × 0.38
0.08 × 0.08 × 0.08
-80
-100
-90
radiation; λ, Å
2θ range, deg
limiting indices
Mo; 0.710 73
2-45
Mo; 0.710 73
3-45
Mo; 0.710 73
3-45
-7 e h e 6
-12 e h e 11
-20 e l e 12
4552
-7 e h e 7
-23 e h e 11
-20 e l e 20
6506
-22 e h e 17
-24 e h e 24
-11 e l e 16
14 525
no. of total data
no. unique data
1953
2976
4958
no. of obsd data
1559 (I > 2σ(I))
2697 (I > 2σ(I))
4237 (I > 2σ(I))
agreement between equiv data
no. of parameters varied
µ, mm-1
0.0219
0.0385
0.0342
173
0.066
344
0.066
none
389
3.954
abs cor
empirical (SADABS)
0.695-0.928
5.05, 12.27
6.67, 13.36
1.065
empirical (SADABS)
0.795-0.928
3.13, 6.05
4.33, 6.56
1.049
range of transm factors
R1(Fo), wR2(Fo2) (I > 2σ(I)), %b
R1(Fo), wR2(Fo2) (all data), %
goodness of fitc
4.90, 10.35
5.66, 10.86
1.094
3‚2CH2Cl2
4‚2Me2CO
empirical formula
fw
C36H60Cl6N2O2Pd
871.96
C40H68Cl2N2O4Pt
906.95
cryst syst
space group
Z
monoclinic
C2/c (No. 15)
4
36.1506(8)
8.0994(2)
15.5671(1)
monoclinic
C2/c (No. 15)
4
36.0649(3)
8.1787(2)
15.7585(3)
a, Åa
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
113.988(1)
112.6100(1)
4164.3(1)
1.391
4290.9(1)
1.404
F
calc, g cm-3
cryst dimens, mm
temp, °C
0.04 × 0.18 × 0.20
0.30 × 0.32 × 0.34
-90
-80
radiation; λ, Å
2θ range, deg
limiting indices
Mo; 0.710 73
5-46.5
Mo; 0.710 73
5-56.5
-40 e h e 29
-8 e h e 7
-17 e l e 17
7930
-46 e h e 47
-10 e h e 6
-20 e l e 18
12 954
no. of total data
no. unique data
2915
5067
no. of obsd data
2440 (I > 2σ(I))
4868 (I > 2σ(I))
agreement between equiv data
no. of parameters varied
µ, mm-1
0.0485
0.0169
216
0.863
205
3.433
abs cor
empirical (SADABS)
0.766-0.928
5.65, 11.13
7.41, 11.90
1.059
empirical (SADABS)
0.812-0.928
2.28, 5.49
2.44, 5.56
1.058
range of transm factors
R1(Fo), wR2(Fo2) (I > 2σ(I)), %b
R1(Fo), wR2(Fo2) (all data), %
goodness of fitc
a
It has been noted that the integration program SAINT produces cell constant errors that are unreasonably small, since systematic
b
2
error is not included. More reasonable errors might be estimated at 10 times the listed values. R1 ) (∑||Fo| - |Fc||)/∑|Fo|, wR2 ) [∑[w(Fo
- Fc2)2]/∑[w(Fo2)2]]1/2, where w ) 1/[σ2(Fo2) + (aP)2 + bP] and P ) [f(maximum of 0 or Fo2) + 1 - f)Fc2]. c GOF ) S ) [∑[w(Fo - Fc2)2]/(n
2
- p)]1/2
.
It is interesting to compare the structural features of
LH4 and L. The direct consequence of the reduction is
that the central N-C-C-N skeleton in LH4 is no longer
planar, as shown by the torsion angle of 61.0(0.4)° about
the N(1)-C(33)-C(34)-N(2) backbone. The longer
C-N bond distances (1.468(5) Å for N(1)-C(33) and
1.465(5) Å for N(2)-C(34)) and the smaller C-C-N
bond angles (110.5(3)° for N(1)-C(33)-C(34) and 109.6-
(3)° for N(2)-C(34)-C(33)) in LH 4 are consistent with
the change in the C and N hybridization from sp2 in L
to sp3 in LH4 upon reduction. The orientation of the
phenyl rings relative to the N-C-C-N backbone in
LH4 is not as simple to describe as it is for L. Torsion
angles of -101.00(0.40) and 78.38(0.43)° for C(33)-

5238 Organometallics, Vol. 16, No. 24, 1997
Yang et al.
Ta ble 3. Selected Bon d Dista n ces (Å) for L, LH4,
2b, 3, a n d 4
Ta ble 4. Selected Bon d An gles (d eg) for L, LH4, 2b,
3, a n d 4
L
L
O(1)-C(15)
N(1)-C(17)
C(2)-C(15)
1.423(3)
1.273(3)
1.512(3)
O(1)-C(16)
N(1)-C(1)
C(17)-C(17)′
1.424(3)
1.426(3)
1.470(4)
C(15)-O(1)-C(16) 111.1(2)
C(2)-C(1)-C(6) 120.4(2)
O(1)-C(15)-C(2) 108.2(2)
C(17)-N(1)-C(1)
C(6)-C(1)-N(1)
119.3(2)
119.5(2)
N(1)-C(17)-C(17)′ 118.9(3)
LH4
LH4
O(1)-C(7)
O(2)-C(24)
N(1)-C(1)
N(2)-C(17)
C(33)-C(34)
1.382(5)
1.421(5)
1.426(5)
1.434(5)
1.502(6)
O(1)-C(8)
O(2)-C(23)
N(1)-C(33)
N(2)-C(34)
1.423(5)
1.430(5)
1.468(5)
1.465(5)
C(7)-O(1)-C(8)
C(1)-N(1)-C(33) 114.7(3)
122.7(4)
C(22)-C(17)-N(2) 120.0(3)
N(1)-C(33)-C(34) 110.5(3)
112.2(4)
C(24)-O(2)-C(23) 111.9(3)
C(17)-N(2)-C(34) 118.1(3)
C(2)-C(1)-N(1)
C(6)-C(1)-N(1)
118.5(3)
C(18)-C(17)-N(2) 120.3(4)
N(2)-C(34)-C(33) 109.6(3)
2b‚CH2Cl2
2b‚CH2Cl2
79.4(2) N(1)-Pt-Cl(1)
Pt-N(1)
1.990(4)
Pt-N(2)
2.017(4)
2.2835(14)
1.411(6)
1.427(7)
1.455(6)
1.516(7)
N(1)-Pt-N(2)
N(2)-Pt-Cl(1)
N(2)-Pt-Cl(2)
C(8)-O(1)-C(7)
94.08(13)
173.60(13)
90.95(5)
Pt-Cl(1)
2.2795(13)
1.407(6)
1.408(7)
1.288(7)
1.507(7)
1.432(7)
Pt-Cl(2)
172.25(12) N(1)-Pt-Cl(2)
95.83(13) Cl(1)-Pt-Cl(2)
O(1)-C(8)
O(2)-C(24)
N(1)-C(33)
C(6)-C(7)
C(33)-C(34)
O(1)-C(7)
O(2)-C(23)
N(2)-C(17)
C(22)-C(23)
111.2(4)
C(33)-N(1)-C(1) 118.0(5)
C(24)-O(2)-C(23) 112.1(4)
C(33)-N(1)-Pt 114.8(4)
C(1)-N(1)-Pt
C(34)-N(2)-Pt
C(2)-C(1)-N(1)
O(1)-C(7)-C(6)
127.1(3)
113.8(4)
124.2(5)
109.8(4)
C(34)-N(2)-C(17) 117.3(4)
C(17)-N(2)-Pt
C(6)-C(1)-N(1)
C(22)-C(17)-N(2) 114.2(5)
O(2)-C(23)-C(22) 113.4(4)
N(2)-C(34)-C(33) 116.1(5)
127.0(3)
114.2(5)
3‚2CH2Cl2
Pd-N(1)
2.089(4)
2.279(2)
1.417(7)
1.478(6)
1.506(7)
Pd-N(1)′
2.089(4)
2.279(2)
1.435(7)
1.505(7)
1.493(10)
C(18)-C(17)-N(2) 123.3(5)
N(1)-C(33)-C(34) 115.8(5)
Pd-Cl(1)
O(1)-C(7)
N(1)-C(1)
C(6)-C(7)
Pd-Cl(1)′
O(1)-C(8)
N(1)-C(17)
C(17)-C(17)′
3‚2CH2Cl2
83.2(2) N(1)-Pd-Cl(1)
176.60(13) N(1)-Pd-Cl(1)′
93.47(13)) Cl(1)-Pd-Cl(1)′
N(1)-Pd-N(1)′
N(1)′-Pd-Cl(1)
N(1)′-Pd-Cl(1)′
C(7)-O(1)-C(8)
C(1)-N(1)-Pd
C(6)-C(1)-N(1)
O(1)-C(7)-C(6)
93.48(12)
176.60(13)
89.89(9)
112.9(4)
107.3(3)
119.8(5)
4‚2Me2CO
Pt-N(1)
2.093(2)
2.2955(6)
1.422(3)
1.471(3)
1.512(3)
Pt-N(1)′
2.093(2)
2.2955(6)
1.428(3)
1.503(3)
1.515(5)
111.3(5)
122.3(3)
119.0(5)
111.3(4)
C(1)-N(1)-C(17)
C(17)-N(1)-Pd
C(2)-C(1)-N(1)
Pd-Cl(1)
O(1)-C(7)
N(1)-C(1)
C(6)-C(7)
Pt-Cl(1)′
O(1)-C(8)
N(1)-C(17)
C(17)-C(17)′
C(17)′-C(17)-N(1) 107.4(3)
4‚2Me2CO
82.95(11) N(1)′-Pt-Cl(1)′
N(1)′-Pt-N(1)
N(1)-Pt-Cl(1)′
N(1)-Pt-Cl(1)
C(7)-O91)-C(8)
C(1)-N(1)-Pt
C(1)-N(1)-Pt
C(6)-C(1)-N(1)
O(1)-C(7)-C(6)
93.20(6)
175.80(6)
90.70(3)
112.6(2)
112.6(2)
107.94(13)
119.3(2)
N(1)-C(1)-C(2) and C(33)-N(1)-C(1)-C(6) show that
the phenyl rings, as in the structure of L, are largely
rotated out of the average plane of the ethylenediamine
backbone. As with the structure of L, the methoxy-
methyl substituents of the two aryl groups lie on
opposite sides of the N-C-C-N average plane.
175.80(6)
93.20(6)
111.1(2)
122.3(2)
122.3(2)
119.4(2)
110.5(2)
N(1)′-Pt-Cl(1)
Cl(1)′-Pt-Cl(1)
C(1)-N(1)-C(17)
C(17)-N(1)-Pt
C(17)-N(1)-Pt
C(2)-C(1)-N(1)
N(1)-C(17)-C(17)′ 107.3(2)
Syn th esis a n d Ch a r a cter iza tion of P d Cl2L (1a
a n d 1b). The reaction between L and Pd(PhCN)2Cl2
proceeds rapidly in CH2Cl2 at room temperature to
afford a 1:1 mixture of isomers 1a and 1b, as determined
by TLC analysis and 1H NMR spectroscopy. Com-
pounds 1a and 1b are both very soluble in CH2Cl2,
CHCl3, and THF, moderately soluble in toluene, metha-
nol, and ethanol, and insoluble in hydrocarbons. Both
1a and 1b are air stable in the solid state and in solution
with no evidence of decomposition, even after exposure
of the solutions to air for days.
The separation of 1a and 1b by fractional recrystal-
lization proved to be unsuccessful due to similar solu-
bilities of the two isomers in common organic solvents.
However, a slight difference in polarity between 1a and
1b, arising from the trans and cis orientations of the
methoxymethyl substituents, resulted in a small Rf
differential (<0.1) on the TLC plates. This differential
allowed for the successful separation of the isomers by
preparative thin-layer chromatography using a mixture
of CH2Cl2 and diethyl ether as eluant (30:1). The much
lower yields of 1a and 1b after separation by TLC
stemmed from slow decomposition over the long separa-
tion times needed on the thin-layer plates.
for other geometrically rigid benzylic systems.30-32
Irradiation of either set of the two doublets of benzylic
protons results in a sharp singlet for the second set, a
fact that corroborates the diastereotopic nature of the
two protons attached to the benzylic carbon atom.
Compared to those of the free ligand L, the diimine
proton resonances for 1a and 1b are shifted to higher
field by ∼0.2 ppm.
Rotations around the Caryl-N and central C-C bonds
in free ligand L need to be considered in order to explain
the formation of the two isomers. As discussed previ-
ously, both rotations in the free ligand are fast on the
NMR time scale, as indicated by the single benzyl proton
resonance in the 1H NMR spectrum of L. While rotation
of the central C-C bond is responsible for the change
in conformation of the NdC-CdN backbone from
s-trans in L to s-cis in 1a and 1b, rotation about the
Caryl-N bond determines the orientation of the
MeOCH2- substituents relative to the coordination
plane. The successful separation of isomers 1a and 1b
indicates that rotation about the Caryl-N bonds is
effectively hindered upon coordination as a consequence
of steric repulsions between the aryl ring substituents
and the metal-diimine chelate ring.
Compounds 1a and 1b have very similar 1H NMR
spectra in CDCl3. A characteristic feature of the 1H
spectra for 1a and 1b is the diastereotopic nature of the
benzylic protons which appear as two sets of doublets
centered at δ 5.28 and 4.29 for 1a and at δ 5.12 and
4.33 for 1b, with the same J HH coupling constant of 12
Hz for each set. The benzylic protons for both isomers
thus exhibit an AB coupling pattern similar to that seen
Syn th esis a n d Ch a r a cter iza tion of LP tCl2 (2a
a n d 2b). The reaction between L and Pt(PhCN)2Cl2
(31) Atwood, D. A.; J egier, J . A.; Martin, K. J .; Rutherford, D.
Organometallics 1995, 14, 1453-1460.
(32) Atwood, D. A.; Remington, M. P.; Rutherford, D. Organome-
tallics 1996, 15, 4763-4769.

Unsymmetrical 1,4-Diazabutadiene Complexes of Pt(II)
Organometallics, Vol. 16, No. 24, 1997 5239
Ta ble 5. Selected Tor sion An gles (d eg) for L, LH4,
2b, 3, a n d 4
L
C(17)-N(1)-C(1)-C(6)
C(17)-N(1)-C(1)-C(2)
N(1)-C(17)-C(17)′-N(1)′
N(1)-C(1)-C(2)-C(15)
N(1)-C(1)-C(2)-C(11)
C(1)-C(2)-C(15)-O(1)
C(1)-N(1)-C(17)-C(17)
-128.19(0.24)
57.14(0.31)
180.00(0)
-3.61(0.34)
1.46(0.32)
-92.44(0.26)
-175.71(.26)
LH4
N(1)-C(33)-C(34)-N(2)
C(1)-N(1)-C(33)-C(34)
C(17)-N(2)-C(34)-C(33)
C(33)-N(1)-C(1)-C(2)
C(33)-N(1)-C(1)-C(6)
C(1)-C(6)-C(7)-O(1)
N(1)-C(1)-C(6)-C(7)
N(1)-C(1)-C(2)-C(9)
N(2)-C(17)-C(18)-C(29)
N(2)-C(17)-C(22)-C(23)
C(17)-C(22)-C(23)-O(2)
60.96(0.42)
-169.46(0.33)
-178.38(0.34)
-101.00(0.42)
78.38(0.43)
173.77(0.39)
7.55(0.56)
-11.54(0.57)
-0.46(0.54)
-2.29(0.55)
-97.28(0.44)
F igu r e 2. ORTEP diagram of LH4. Thermal ellipsoids are
shown at 50% probability. Hydrogen atoms are omitted for
clarity.
refluxing in chloroform or toluene gave the desired
isomeric products 2a and 2b after several hours, as
depicted in eq 2.
2b‚CH2Cl2
N(1)-C(33)-C(34)-N(2)
Pt-N(2)-C(34)-C(33)
Pt-N(1)-C(33)-C(34)
C(1)-N(1)-C(33)-C(34)
C(17)-N(2)-C(34)-C(33)
C(33)-N(1)-C(1)-C(2)
C(33)-N(1)-C(1)-C(6)
C(34)-N(2)-C(17)-C(18)
C(34)-N(2)-C(17)-C(22)
N(2)-C(17)-C(18)-C(29)
N(2)-C(17)-C(22)-C(23)
C(17)-C(22)-C(23)-O(2)
C(1)-C(6)-C(7)-O(1)
Pt-N(1)-C(1)-C(2)
2.72(0.73)
-0.77(0.59)
-3.28(0.61)
172.57(0.44)
-166.19(0.44)
90.64(0.66)
-88.19(0.60)
94.94(0.66)
82.91(0.61)
-5.20(0.93)
3.18(0.76)
-71.43(0.67)
179.23(0.48)
-94.08(0.58)
87.08(0.53)
101.83(0.55)
-80.32(0.58)
2.55(0.42)
Pt-N(1)-C(1)-C(6)
Pt-N(2)-C(17)-C(18)
Pt-N(2)-C(17)-C(22)
Cl(1)-Pt-N(1)-C(1)
Cl(2)-Pt-N(1)-C(1)
144.17(0.97)
177.96(0.37)
-40.43(1.38)
163.02(0.43)
-21.34(0.41)
-34.11(1.14)
174.93(0.35)
Cl(1)-Pt-N(1)-C(33)
Cl(2)-Pt-N(1)-C(33)
Cl(1)-Pt-N(2)-C(17)
Cl(2)-Pt-N(2)-C(17)
Cl(1)-Pt-N(2)-C(34)
Cl(2)-Pt-N(2)-C(34)
3‚2CH2Cl2
N(1)-C(17)-C(17)′-N(1)′
N(1)-C(1)-C(6)-C(7)
C(1)-C(6)-C(7)-O(1)
N(1)-C(1)-C(2)-C(9)
Pd-N(1)-C(17)-C(17)′
C(1)-N(1)-C(17)-C(17)′
Cl(1)′-Pd-N(1)-C(1)
Cl(1)′-Pd-N(1)-C(17)
Cl(1)-Pd-N(1)-C(17)
Cl(1)-Pd-N(1)-C(1)
Pd-N(1)-C(1)-C(2)
Pd-N(1)-C(1)-C(6)
58.14(0.73)
-174.81(0.50)
-90.85(0.64)
-4.70(0.79)
-43.31(0.53)
-179.03(0.46)
157.22(2.18)
24.40(2.65)
The physical properties of isomers 2a and 2b are very
similar to those of 1a and 1b. The separation of 2a and
2b , however, is easier than for 1a and 1b , as the Rf
differential for the former pair is larger than that for
the latter. The lower yields for the formation of 2a and
2b also arise from the slow decomposition of the isomers
during TLC separations.
24.40(2.65)
-31.49(0.39)
121.29(0.46)
-59.66(0.60)
4‚2Me2CO
N(1)-C(17)-C(17)′-N(1)′
N(1)-C(1)-C(6)-C(7)
C(1)-C(6)-C(7)-O(1)
N(1)-C(1)-C(2)-C(9)
Pt-N(1)-C(17)-C(17)′
C(1)-N(1)-C(17)-C(17)′
Cl(1)-Pt-N(1)-C(17)
Cl(1)-Pt-N(1)-C(1)
Pt-N(1)-C(1)-C(6)
57.02(0.34)
5.41(0.37)
Compounds 2a and 2b give very similar 1H NMR
spectra in CDCl3 relative to those of the Pd analogs
1a and 1b . The diastereotopic protons for the ben-
zylic CH2 groups appear as two doublets centered at δ
5.15 and 4.33 for 2a and at δ 5.10 and 4.40 for 2b, with
the same coupling constant of J HH ) 12 Hz. An ob-
servable difference between the NMR spectra for the
Pd and Pt complexes 1 and 2 is observed in the chem-
ical shifts of the imine protons. Compared to those of
the free ligand L, the imine proton resonances for
both 2a and 2b are shifted downfield about 0.5 ppm;
these shifts are opposite to those observed for 1a and
1b. The reason for these differences is not fully
understood.
-91.47(0.27)
-3.72(0.36)
-42.71(0.25)
179.39(0.22)
-163.14(0.14)
-31.49(0.39)
71.25(0.28)
121.09(0.21)
-107.88(0.25)
71.25(0.28)
Pt-N(1)-C(1)-C(2)
C(17)-N(1)-C(1)-C(2)
C(17)-N(1)-C(1)-C(6)
was performed initially in CH2Cl2 at room temperature,
corresponding to conditions used for the preparation of
1a and 1b. However, no reaction was observed after
stirring the reaction mixture overnight. In contrast,

5240 Organometallics, Vol. 16, No. 24, 1997
Yang et al.
X-r a y Str u ctu r e of LP tCl2 (2b). Attempts to obtain
X-ray-quality single crystals of compounds 1a , 1b, and
2a from a variety of solvents under various conditions
were not successful. Conversely, single crystals of 2b
as a methylene chloride solvate were grown from a
mixture of CH2Cl2 and hexane solution at room tem-
perature. The ORTEP diagram of 2b is shown in Figure
3, with details of the structure determination, including
unit-cell data, summarized in Table 2 and relevant bond
distances, bond angles, and torsion angles listed in
Tables 3-5, respectively.
As shown in Figure 3, complex 2b is a distorted
square-planar complex. The bond angles deviate from
the idealized 90° value by virtue of the constraints
imposed by chelation of L. This distortion is illustrated
by the N(1)-Pt-N(2) bond angle of 79.4(2)°. The metal-
chelate ring in 2b is almost flat as indicated by the
torsion angels of 2.72(0.73), -0.77(0.59), and -3.28-
(0.61)° for N(1)-C(33)-C(34)-N(2), Pt-N(2)-C(34)-
C(33), and Pt-N(2)-C(33)-C(34), respectively. The
aryl rings lie nearly perpendicular to the metal-chelate
ring as shown by the torsion angles of 90.64(0.66),
-88.19(0.60), 94.94(0.66), and 82.91(0.61)°, respectively,
for C(33)-N(1)-C(1)-C(2), C(33)-N(1)-C(1)-C(6),
C(34)-N(2)-C(17)-C(18), and C(34)-N(2)-C(17)-
C(22). These torsion angles are greater by nearly 20°
than the corresponding values for the free ligand L and
may be caused by greater steric repulsions in the
chelated complex. The diffraction study also reveals the
relative orientation of the two CH2OMe groups in 2b
as cisoid, that is, on the same side of the coordination
plane. The bond distances and bond angles for 2b are
very similar to those of other reported square-planar
platinum diimine complexes.16,33
F igu r e 3. ORTEP diagrams of LP tCl2 (2b). Thermal
ellipsoids are shown at 50% probability. Hydrogen atoms
are omitted for clarity.
the benzylic CH2 protons are diastereotopic in 3, but
unlike 1 and 2, the relative chemical shifts are quite
different with two doublets at δ 7.62 and 4.62, both
having coupling constants of J HH ) 12 Hz. The meth-
ylene protons of the NCH2CH2N backbone are also
diastereotopic, exhibiting two sets of multiplets at δ 2.70
and 3.74. The assignments of the NMR data were
confirmed by proton homonuclear decoupling experi-
ments. Irradiating each set of doublets at δ 7.62 and
4.62 results in the decoupling of the second set which
coalesces to a sharp singlet. Similar experiments were
performed for the protons of the NCH2CH2N backbone,
irradiating the multiplets at either δ 3.74 or δ 2.70. The
NH protons are seen at δ 6.09 as a broad resonance.
The large observed chemical shift difference for the two
diastereotopic benzyl protons in 3 is unusual and may
be rationalized by the nature of the central NCH2CH2N
backbone associated with 3 and the resulting confor-
mational effects involving the metal-chelate ring (vide
infra). The IR spectrum of 3 reveals NH stretches at
Syn th esis a n d Ch a r a cter iza tion of P d Cl2(LH4)
(3). The saturated ligand LH4 reacts readily with
Pd(PhCN)2Cl2 in CH2Cl2 at room temperature to give
compound 3 in almost quantitative yield (eq 3). The
3363 and 3320 cm-1
.
Syn t h esis a n d Ch a r a ct er iza t ion of P t Cl2(LH 4)
(4). The reaction between the saturated ligand LH4 and
Pt(PhCN)2Cl2, in either refluxing dichloromethane or
chloroform, affords compound 4 in >60% yield (eq 3).
Purification was achieved by recrystallization of the
crude material from a mixture of acetone and hexane
(1:3) to give 4 as large yellow plates. Attempted
separation of 4 by column chromatography was not
successful because of decomposition.
Compound 4 shows properties very similar to those
of 3. The 1H NMR spectrum of 4 in CDCl3 reveals a
spectrum almost identical to that of 3 with proton
resonances of the tert-butyl groups at δ 1.34 and 1.65
and the methoxy protons at δ 3.64, all as single sharp
singlets. The diastereotopic benzyl protons are observed
as two doublets centered at δ 4.66 and 7.68 with J HH of
12 Hz. The methylene protons of the NHCH2CH2NH
backbone appear as two sets of multiplets centered at
δ 2.80 and 3.89, while the NH protons are seen at δ 5.68
as a broad resonance. As with 3, the assignment of the
NMR data for 4 was confirmed by proton homonuclear
1H NMR spectrum of 3 in CDCl3 shows resonances of
the tert-butyl groups at δ 1.30 and 1.61 and the methoxy
protons at δ 3.36 as sharp singlets. As seen in 1 and 2,
(33) van der Poel, H.; van Koten, G.; Kokkes, M.; Stam, C. H. Inorg.
Chem. 1981, 20, 2941-2956.

Unsymmetrical 1,4-Diazabutadiene Complexes of Pt(II)
Organometallics, Vol. 16, No. 24, 1997 5241
between the backbone and the aryl ring substituents.
As seen in the structure of 2b , the aryl rings in 3
and 4 are rotated out of the coordination plane of the
square-planar M(II) ions. Compared to the case of the
free ligand LH4, the coordination of LH4 to the MCl2
fragments in 3 and 4 also results in longer bond
distances for the C(17)-N(1) (1.507(7) Å for 3, 1.503(3)
Å for 4) and the C(17)-C(17)′ (1.496(1) Å for 3, 1.515-
(5) Å for 4) bonds.
Con clu sion s
The synthesis and characterization of a new DAB
ligand, glyoxal bis(2-(methoxymethyl)-4,6-(di-tert-butyl)-
phenyl)diimine (L), and its reduced analog (LH4) have
been demonstrated. The synthetic procedure for pre-
paring L, as shown in Scheme 1, offers great versatility
for the generation of other potentially tetradentate
ligands as well as novel bidentate ligands for complexes
of possible catalytic interest. With regard to the former,
replacement of the MeO groups in L by other functional
moieties such as R2N, R2P, and SR can in principle be
accomplished easily, thereby generating a variety of N4,
N2P2, and N2S2 ligands with different binding prop-
erties.34-36 The facile reduction of L to LH4 provides a
direct comparison of unsaturated and saturated ligands
for their coordinating abilities to metal ions. Further-
more, the unsaturated LH4 may be easily deproto-
nated to afford diamides LH22- that are also capable of
forming metal complexes by nitrogen coordination to
higher valent metal ions.
F igu r e 4. ORTEP diagrams of P d Cl2(LH4) (3). Thermal
ellipsoids are shown at 50% probability. Hydrogen atoms
are omitted for clarity.
The bidentate complexation of L and LH4 through the
N donors for Pt(II) and Pd(II) has been investigated.
The metal centers in compounds 1a , 1b, 2a , 2b, 3, and
4 possess square-planar coordination geometries with
the aryl groups of the L and LH4 ligands oriented out
of the coordination plane in a manner that inhibits
access to possible axial ligation sites. The formation of
two isomers with cis and trans MeOCH2- groups
indicates hindered rotation about the aryl C-N bond
resulting from the steric bulkiness of the methoxym-
ethyl and tert-butyl groups. The diastereotopic nature
of the benzylic protons, especially for 3 and 4, is
consistent with this view and resultant conformational
effects for the diimine (NdCHCHdN) and diamine
(NHCH2CH2NH) metal-chelate rings.
Efforts to generate alkyl derivatives MR2L, MR2LH4,
and related cationic complexes from 1a , 1b, 2a , 2b, 3,
and 4 and study their potential catalytic activity with
various substrates are in progress. Investigation of the
possible interactions of methoxy groups of L and LH4
with d6 metal centers in cationic complexes is also being
pursued and will be reported in due course.
F igu r e 5. ORTEP diagrams of P tCl2(LH4) (4). Thermal
ellipsoids are shown at 50% probability. Hydrogen atoms
are omitted for clarity.
decoupling experiments. The IR spectrum shows the
NH stretches for 4 at 3353 and 3317 cm-1
.
X-r a y Str u ctu r es of P d Cl2(LH4) (3) a n d P tCl2-
(LH4) (4). Structures of 3 and 4 were determined by
single-crystal X-ray diffraction. Crystals of 3 were
grown from a saturated CH2Cl2/hexane solution, while
crystals of 4 were obtained from a saturated acetone/
hexane solution. The Pd complex 3 crystallizes as a
methylene chloride solvate, while the isostructural Pt
analog 4 forms as an acetone solvate. Figures 4 and 5
show ORTEP diagrams of 3 and 4, and details of the
structure determinations are summarized in Table 2.
Relevant bond distances, bond angles, and torsion
angles for the two structures are listed in Tables 3-5,
respectively.
Exp er im en ta l Section
P r oced u r es a n d Ma ter ia ls. Glyoxal (40% in water), 3,5-
di-tert-butyltoluene, hydrazine hydrate (NH2NH2‚H2O, 98%),
Pd-C (10% Pd), LiAlH4, trifluoroacetic anhydride (TFAA), 1,1′-
azobis(cyclohexanecarbonitrile), NaOMe (powder, 95%), and
N-bromosuccinimide (NBS) were purchased from Aldrich
Chemical Co. The complexes PdCl2(PhCN)2 and PtCl2(PhCN)2
The structural features of 3 and 4 are strikingly
similar. In contrast with that of 2, the metal-chelate
rings of 3 and 4 are distinctly nonplanar with N(1)-
C(17)-C(17)′-N(1)′ torsion angles of 58.1(0.7) and 57.0-
(0.3)°, respectively. The conformation of the metal-che-
late ring also causes the two protons on each methylene
of the ethylenediamine backbone to be inequivalent,
occupying pseudoaxial and pseudoequatorial positions
with respect to the chelate ring. The NMR data indicate
that these protons do not interconvert on the NMR time
scale owing to the large steric interactions that exist
(34) Anderson, D. J .; Eisenberg, R. Organometallics 1996, 15, 1697-
1706.
(35) Mak, S.-T.; Yam, V. W.-W.; Che, C.-M.; Mak, T. C. W. J . Chem.
Soc., Dalton Trans. 1990, 2555-2564.
(36) Zheng, Y. Y.; Saluja, S.; Yap, G. P. A.; Blumenstein, M.;
Rheingold, A. L.; Francesconi, L. C. Inorg. Chem. 1996, 35, 6656-6666.

5242 Organometallics, Vol. 16, No. 24, 1997
Yang et al.
were synthesized according to published procedures.37,38 CH2-
Cl2 and CCl4 were distilled from CaH2 while THF and toluene
were distilled from sodium/benzophenone ketyl radical freshly
before use. All deuterated solvents were dried with appropri-
ate drying agents, vacuum-transferred into Schlenk storage
vessels, and stored under nitrogen.
Unless otherwise noted, all reactions and manipulations
were performed 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 experiments were performed using the pulse
program HOMODEC. IR spectra were recorded on a 6020
Galaxy series FT-IR spectrometer. Elemental analyses were
obtained from Desert Analytics, Tucson, AZ.
CH2Cl2 and hexanes (1:1) as eluant. Yield: 3.5 g. 1H NMR
(CDCl3): δ 1.32 (s, 9H, t-Bu), 1.37 (s, 9H, t-Bu), 3.36 (s, 3H,
OCH3), 4.33 (s, 2H, CH), 7.26 (d, 1H, J HH ) 4 Hz, C6H2), 7.35
(d, 1H, J HH ) 4 Hz, C6H2).
2-(Meth oxym eth yl)-4,6-d i-ter t-bu tyla n ilin e. A 250 mL
Schlenk flask containing 150 mL of degassed ethanol was
charged with 1.5 g (5.4 mmol) of 2-nitro-3,5-di-tert-butyl-R-
methoxytoluene, 0.4 g of Pd-C catalyst (10% Pd), and 5.0 mL
of NH2NH2‚H2O. The above mixture was heated to reflux, and
reaction was monitored by TLC analysis until no 2-nitro-3,5-
di-tert-butyl-R-methoxytoluene was seen (12 h). After the
reaction mixture was cooled to room temperature, the Pd-C
catalyst was removed by filtration and the product was
separated by column chromatography on silica gel. A trace of
the starting material was eluted first with 1:1 mixture of
CH2Cl2 and hexanes, and the product was eluted with pure
CH2Cl2. Yield: 1.26 g (95%). 1H NMR (CDCl3): δ 1.29 (s, 9H,
t-Bu), 1.44 (s, 9H, t-Bu), 3.37 (s, 3H, OCH3), 4.32 (s, 2H, NH2),
4.48 (s, 2H, CH2), 6.98 (d, 1H, J HH ) 2.4 Hz, C6H), 7.24 (d,
1H, J HH ) 2.4 Hz, C6H).
Syn th esis of th e Glyoxa l Bis(2-(m eth oxym eth yl)-4,6-
d i-ter t-bu tylp h en yl)im in e (L). The synthetic procedure
leading to L, starting from 3,5-di-tert-butyltoluene, is outlined
in Scheme 1 with the experimental details for each step
documented below.
2-Nitr o-3,5-d i-ter t-bu tyltolu en e.39 A 50 mL round-bottom
flask was charged with 4.0 g (19.6 mmol) of 3,5-di-tert-
butyltoluene, 1.6 g (20 mmol) of ammonium nitrate, and 15
mL of trifluoroacetic anhydride (TFAA). The reaction mixture
was stirred at room temperature for 3 h, during which
ammonium nitrate gradually dissolved and the color of the
mixture changed from colorless to yellow brown. The reaction
mixture was slowly poured into 150 mL of distilled water, and
the resultant cream-colored solid mass was collected by
filtration. The solid was thoroughly washed with water and
then air-dried. Recrystallization of the crude material from
hot methanol afforded nearly colorless crystals. Yield: 4.7 g
(95%). 1H NMR (CDCl3): δ 1.29 (s, 9H, t-Bu), 1.36 (s, 9H,
t-Bu), 2.21 (s, 3H, CH3), 7.11 (s, 1H, C6H), 7.35 (s, 1H, C6H).
2-Nitr o-3,5-d i-ter t-bu tyl-r-br om otolu en e. To a 250 mL
Schlenk flask were added 4.0 g (16 mmol) of 2-nitro-3,5-di-
tert-butyltoluene, 3.2 g (18 mmol) of N-bromosuccinimide
(NBS), 0.50 g of 1,1′-azobis(cyclohexanecarbonitrile), and 150
mL of carbon tetrachloride. This mixture was heated to reflux
for 10 h and then cooled to room temperature (the reaction
mixture at this point showed about 60-70% of the bromination
product along with unreacted starting material; however,
increasing the amount of NBS to 1.5 equiv and extending the
reaction time led to no improvement in the extent of reaction).
The white precipitate (succinamide) was removed by filtration,
and the filtrate was rotaevaporated to dryness. The filtrate
residue was then passed through a short silica gel column
using a mixture of CH2Cl2 and hexanes (1:1) to remove any
remaining succinamide and decomposed material. The mix-
ture of 2-nitro-3,5-di-tert-butyltoluene and 2-nitro-3,5-di-tert-
butyl-R-bromotoluene was treated with excess NaOMe in
refluxing methanol to convert the bromide to methoxide (vide
infra). The bromination product was characterized by 1H NMR
spectroscopy. 1H NMR (CDCl3): δ 1.29 (s, 9H, t-Bu), 1.36 (s,
9H, t-Bu), 4.40 (s, 2H, CH2), 7.40 (s, 1H, C6H), 7.60 (s, 1H,
C6H).
Glyoxa l Bis(2-(m eth oxym eth yl)-4,6-d i-ter t-bu tylp h en -
yl)im in e (L). A 25 mL round-bottom flask containing 5 mL
of absolute ethanol was charged with 0.80 g (3.2 mmol) of 2-(R-
methoxymethyl)-4,6-di-tert-butylaniline, 0.18 mL of glyoxal
(1.6 mmol, 40% in water), and a few drops of formic acid as
catalyst. The color of the mixture turned from colorless to
yellow immediately, and a yellow precipitate appeared after
5 min. The reaction mixture was stirred for an additional day,
and the yellow solid was collected by filtration and washed
with cold methanol to afford the analytically pure ligand.
Additional crops of product may be obtained by drying the
filtrate and chromatographing the residue on silica gel using
CH2Cl2 as the solvent. Yield: 0.75 g (90%). 1H NMR
(CDCl3): δ 1.33 (s, 18H, t-Bu), 1.37 (s, 18H, t-Bu), 3.38 (s, 6H,
OCH3), 4.14 (s, 4H, CH2), 7.28 (s, 2H, C6H), 7.42 (s, 2H, C6H),
8.19 (s, 2H, NCH). Anal. Calcd for C34H52O2N2: C, 78.41; H,
10.06; N, 5.38. Found: C, 78.58; H, 10.29; N, 5.35.
LH4. A 50 mL Schlenk flask containing 20 mL of THF was
charged with 0.6 g (1.15 mmol) of glyoxal bis(2-(methoxy-
methyl)-4,6-di-tert-butylphenyl)imine (L), to which 6.0 mL of
1 M LiAlH4 solution in THF was added dropwise by syringe.
The yellow color of the solution diminished quickly upon
addition of the LiAlH4, and the reaction mixture was stirred
for an additional 1 h. With caution, 5 mL of methanol was
added slowly by syringe to destroy the excess LiAlH4, and the
resultant mixture was dried using the rotary evaporator. The
purification of LH4 was achieved by passing the crude product
through a short silica gel or alumina column using a mixture
of CH2Cl2 and ethanol (9:1). Alternatively, the product may
be extracted with hexane from the crude material and then
recrystallized from hot methanol. Yield: 0.57 g (90%). 1H
NMR (CDCl3): δ 1.32 (s, 18H, t-Bu), 1.46 (s, 18H, t-Bu), 3.26
(s, 4H, NCH2), 3.44 (s, 6H, OCH3), 3.77 (s, 2H, NH), 4.57 (s,
4H, CH2), 7.326 (s, 2H, C6H), 7.331 (s, 2H, C6H). IR (KBr):
3422 (w), 3328 (w) cm-1
. Anal. Calcd for C34H56O2N2: C,
77.81; H, 10.76; N, 5.34. Found: C, 77.79; H, 10.97; N, 5.30.
2-Nitr o-3,5-d i-ter t-bu tyl-r-m eth oxytolu en e. To a 250
mL Schlenk flask containing 150 mL of degassed methanol
was added 6.0 g of the mixture of 2-nitro-3,5-di-tert-butyltolu-
ene and 2-nitro-3,5-di-tert-butyl-R-bromotoluene (4:6) and 2.5
g of NaOMe (excess). This mixture was heated to reflux, and
the reaction was monitored by TLC analysis until no 2-nitro-
3,5-di-tert-butyl-R-bromotoluene remained present in the reac-
tion solution (3-6 h). After the solution was cooled to room
temperature, the solvent was removed using a rotary evapora-
tor. The residue was dissolved in hexanes and purified by
column chromatography on silica gel using a mixture of
Syn th esis of LP d Cl2 (1a a n d 1b). To a 50 mL Schlenk
flask containing 10 mL of CH2Cl2 were added with 0.05 g
(0.096 mmol) of glyoxal bis(2-(methoxymethyl)-4,6-di-tert-
butylphenyl)imine (L) and 0.037 g (0.096 mmol) of PdCl2-
(PhCN)2, after which the reaction solution was stirred for 2 h.
TLC analysis showed the disappearance of the starting
materials and the presence of two new compounds, 1a and 1b,
in an approximate 1:1 ratio. The solvent was next removed
by vacuum, and purification was achieved by preparative TLC
using a solvent mixture of CH2Cl2 and diethyl ether (30:1).
Analytical samples of both new compounds were obtained by
recrystallization from a 3:1 mixture of CH2Cl2 and hexane.
Yields: 1a , 0.017 g (25%); 1b, 0.020 g (30%). The lowered
yields are caused by partial decomposition of the products on
the TLC plates. 1H NMR (CDCl3): for 1a : δ 1.32 (s, 18H,
(37) Uchiyama, T.; Toshiyasu, Y.; Nakamura, Y.; Miwa, T.; Kawagu-
chi, S. Bull. Chem. Soc. J pn. 1981, 54, 181-185.
(38) Doyle, J . R.; Slade, P. E.; J onassen, H. B. Inorg. Synth. 1960,
6, 218.
(39) Myhre, P. C.; Beug, M.; J ames, L. L. J . Am. Chem. Soc. 1968,
90, 2105-2115.
t-Bu), 1.59 (s, 18H, t-Bu), 3.36 (s, 6H, OCH3), 4.29 (d, J HH
)
12 Hz, 2H, CHaH), 5.29 (d, J HH ) 12 Hz, 2H, CHHb), 7.18 (d,

Unsymmetrical 1,4-Diazabutadiene Complexes of Pt(II)
Organometallics, Vol. 16, No. 24, 1997 5243
J HH ) 4 Hz, 2H, C6H), 7.51 (d, J HH ) 4 Hz, 2H, C6H), 7.96 (s,
2H, NCH). 1H NMR (CDCl3): for 1b: δ 1.31 (s, 18H, t-Bu),
1.55 (s, 18H, t-Bu), 3.33 (s, 6H, OCH3), 4.33 (d, J HH ) 12 Hz,
2H, CHaH), 5.13 (d, J HH ) 12 Hz, 2H, CHHb), 7.18 (d, J HH
) 4 Hz, 2H, C6H), 7.47 (d, J HH ) 4 Hz, 2H, C6H), 8.02 (s, 2H,
NCH). Anal. Calcd for 1a (C34H52O2N2PdCl2): C, 58.57; H,
7.52; N, 4.02. Found: C, 58.68; H, 7.58; N, 3.94. Calcd for
1b (C34H52O2N2PdCl2): C, 58.57; H, 7.52; N, 4.02. Found: C,
58.85; H, 7.59; N, 3.95.
C6H), 7.66 (d, J HH ) 12 Hz, 2H, CHHb). IR (KBr): 3353 (sh),
3317 (m) cm-1. Anal. Calcd for C34H56O2N2PtCl2: C, 51.63;
H, 7.14; N, 3.54. Found: C, 51.67; H, 7.36; N, 3.25.
X-r a y Cr ysta llogr a p h y. Crystals of L, LH4, 2b, 3, and 4
were each mounted under Paratone-8277 on glass fibers 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 10 s/frame
for L and 30 s/frame for LH4, 2b, 3, and 4 using a crystal-to-
detector distance of 5.094 cm (maximum 2θ angle of 56.52°).
The total data collection time was approximately 5 h for L and
12 h for LH4, 2b, 3, and 4. Frames were integrated with the
Siemens SAINT program to yield the following: for L, a total
Syn th esis of LP tCl2 (2a a n d 2b). To a 50 mL Schlenk
flask containing 10 mL of chloroform (or toluene) were added
0.05 g (0.096 mmol) of glyoxal bis(2-(methoxymethyl)-4,6-di-
tert-butylphenyl)imine (L) and 0.046 g (0.096 mmol) of PtCl2-
(PhCN)2, after which the reaction solution was heated to reflux
for 2 h. The color of the reaction mixture changed from yellow
to dark orange after 15 min. TLC analysis showed the
disappearance of the starting materials and the presence of
two major red spots corresponding to 2a and 2b in an
approximate 1:1 ratio. The amount of the reaction solvent was
reduced to by half via vacuum, and the products were
precipitated from solution by the addition of hexane (20 mL).
2a and 2b were further separated by preparative TLC using
CH2Cl2 as eluant. Analytically pure samples of both new
compounds were obtained by recrystallization from a 1:3
mixture of CH2Cl2 and hexane. Yields: 2a , 0.015 g (20%); 2b,
0.017 g (23%). Like 1a and 1b, both 2a and 2b slowly decom-
posed on the TLC plates, which resulted in low yields. 1H
NMR (CDCl3) for 2a : δ 1.36 (s, 18H, t-Bu), 1.54 (s, 18H,
t-Bu), 3.31 (s, 6H, OCH3), 4.33 (d, J HH ) 12 Hz, 2H, CHaH),
5.16 (d, J HH ) 12 Hz, 2H, CHHb), 7.57 (d, J HH ) 4 Hz, 2H,
C6H), 7.78 (d, J HH ) 4 Hz, 2H, C6H), 8.73 (s, 2H, NCH). 1H
NMR (CDCl3) for 2b : δ 1.35 (s, 18H, t-Bu), 1.53 (s, 18H,
t-Bu), 3.31 (s, 6H, OCH3), 4.40 (d, J HH ) 12 Hz, 2H, CHaH),
5.10 (d, J HH ) 12 Hz, 2H, CHHb), 7.27 (d, J HH ) 4 Hz,
2H, C6H), 7.55 (d, J HH ) 4 Hz, 2H, C6H), 8.74 (s, 2H, NCH).
Anal. Calcd for 2a (C34H52O2N2PtCl2‚CH2Cl2): C, 48.23; H,
6.24; N, 3.21. Found: C, 48.72; H, 5.80; N, 3.69. Calcd for
2b (C34H52O2N2PtCl2‚CH2Cl2): C, 48.23; H, 6.24; N, 3.21.
Found: C, 48.42; H, 5.90; N, 3.50.
of 4552 reflections, of which 1953 were independent (Rint
)
2.19%, Rsig ) 4.42%)40 and 1559 were above 2σ(I); for LH4, a
total of 6506 reflections, of which 2976 were independent (Rint
) 3.85%, Rsig ) 4.54%) and 2697 were above 2σ(I); for 2b, a
total of 14525 reflections, of which 4958 were independent (Rint
) 3.42%, Rsig ) 4.26%) and 4237 were above 2σ(I); for 3, a
total of 7930 reflections, of which 2915 were independent (Rint
) 4.85%, Rsig ) 5.98%) and 2440 were above 2σ(I); for 4, a
total of 12954 reflections, of which 5067 were independent (Rint
) 1.69%, Rsig ) 4.42%) and 4868 were above 2σ(I). The unit
cell parameters, provided in Table 2, were based upon the
least-squares refinement of three-dimensional centroids of
>1500 reflections for each crystal. The space group assign-
ments were made on the basis of systematic absences and
intensity statistics41 by using the XPREP program (Siemens,
SHELXTL 5.04). The structures were solved by using direct
methods and refined by full-matrix least-squares procedures
on F2. Although the frames were integrated to a maximum
2θ angle of 56.50° for L, LH4, and 2b, there were no observed
data >45° and therefore these data were omitted from the
refinement. Frames for 3 and 4 were integrated to maximum
2θ angles of 46.50 and 56.50°, respectively, and no data were
omitted from the refinements. All non-hydrogen atoms were
refined anisotropically, except the atoms of the solvent mol-
ecule in 2b and 4, giving data-to-parameter ratios >10:1. The
CH2Cl2 molecule in 2b was disordered over two sites, and
refinement of the SOFs (site occupation factors) revealed the
solvent to be half-occupied. All hydrogens were included in
idealized positions, except the hydrogens of the disordered
CH2Cl2 molecule in 2b, which were not included. Final resid-
uals and refinement parameters are provided in Table 2.
Syn th esis of P d Cl2(LH4) (3). To a colorless solution of
0.05 g (0.095 mmol) of LH4 in 10 mL of CH2Cl2 was added
0.037 g (0.096 mmol) of PdCl2(PhCN)2, after which the reaction
solution was stirred under room temperature for 2 h. TLC
analysis showed the disappearance of the starting materials
and the presence of desired compound 3 in almost quantitative
yield. The solvent was removed by vacuum, and purification
was achieved by passing the crude product through a short
silica gel column using a mixture of CH2Cl2 and acetone (9:1).
Yield: 0.065 g (96%). 1H NMR (CDCl3): δ 1.30 (s, 18H, t-Bu),
1.61 (s, 18H, t-Bu), 2.74 (m, 2H, NCHa), 3.66 (s, 6H, OCH3),
3.26 (m, 2H, NCHb), 4.68 (d, J HH ) 12 Hz, 2H, CHaH), 6.09 (s,
Ack n ow led gm en t. We wish to thank the National
Science Foundation (Grant CHE 94-04991) for support
of this work and Alfa/Aesar J ohnson Matthey Co. Inc.
for a generous loan of platinum and palladium salts.
2H, NH), 7.29 (s, 2H, C6H), 7.38 (s, 2H, C6H), 7.62 (d, J HH
12 Hz, 2H, CHaH). IR (KBr): 3363 (sh), 3320 (m) cm-1. Anal.
Calcd for 34H56O2N2PdCl2: C, 58.24; H, 8.05; N, 3.99.
)
C
Found: C, 58.38; H, 8.15; N, 3.88.
Syn th esis of P tCl2(LH4) (4). To a colorless solution of 0.05
g (0.095 mmol) of LH4 in 10 mL of chloroform was added 0.046
g (0.096 mmol) of PtCl2(PhCN)2, after which the reaction
solution was heated up to reflux for 2 h. Unlike 3, 4 is not
stable on TLC plates, so purification was performed by
recrystallization of the crude material from a mixture of
hexane and acetone (9:1) after removing the solvent by
vacuum. Yield: 0.047 g (61%). 1H NMR (CDCl3): δ 1.27 (s,
18H, t-Bu), 1.62 (s, 18H, t-Bu), 2.74 (m, 2H, NCHa), 3.61 (s,
6H, OCH3), 3.74 (m, 2H, NCHb), 4.64 (d, J HH ) 12 Hz, 2H,
CHaH), 7.28 (d, J HH ) 2 Hz, 2H, NH), 7.39 (d, J HH ) 2 Hz, 2H,
Su p p or tin g In for m a tion Ava ila ble: Tables of data col-
lection and refinement parameters, non-H atomic coordinates,
anisotropic thermal parameters, calculated hydrogen posi-
tional and isotropic thermal parameters, and complete bond
distances and angles for non-hydrogen atoms (32 pages).
Ordering information is given on any current masthead page.
OM970452T
2
(40) Rint ) Σ|Fo - Fo2(mean)|/Σ[Fo2]; Rsigma ) ∑[σFo2]/Σ[Fo2].
(41) Intensity statistics from CCD data sets are often unreliable,
especially for weakly diffracting crystals.