Trans alkenylpyridine and alkenylamine complexes of platinum

Article abstract of DOI:10.1139/v00-060

Addition of cis-cyclooctene (coe) to K₂PtCl₄ gives trans-[PtCl₂(coe)]₂ (1), which reacts with excess coe to give trans-PtCl₂(coe)₂ (2). Compound 2 was characterized by an X-ray diffraction study and crystals were found to be triclinic, a = 5.7838(5), b = 7.4347(6), c = 9.9972(9) A. α = 83.924(1), β = 87.844(2), γ = 73.546(1)°, Z = 1, with space group P1. Addition of 4-vinylpyridine (4vp) to 1 gave trans-PtCl₂(4vp)₂ (5) which was also characterized by an X-ray diffraction study. Crystals of 5 were monoclinic, a = 8.2255(6), b = 12.8254(10), c = 6.9624(5) A, β = 98.8230(10)°, Z - 2, with space group P2₁/c. Although alkenylamines react with 1 to give a mixture of products, addition of one equivalent of apve (H₂NCH₂CH₂CH₂OCH=CH₂) to 1 cleanly afforded the organometallic product trans-PtCl₂(coe)(thmo) (thmo = tetrahydro-2-methyl-1,3-oxazine) arising from a metal-catalyzed intramolecular hydroamination of the starting alkenylamine. Initial investigations into the functionalization of metal complexes containing pendant alkene groups have shown that catecholborane can be added in some cases, using a rhodium catalyst, 10 give the corresponding organoboronate ester platinum compounds.

Full text of DOI:10.1139/v00-060

568
Trans alkenylpyridine and alkenylamine complexes
of platinum
Michael P. Shaver, Christopher M. Vogels, Andrew I. Wallbank, Tracy L. Hennigar,
Kumar Biradha, Michael J. Zaworotko, and Stephen A. Westcott
Abstract: Addition of cis-cyclooctene (coe) to K2PtCl4 gives trans-[PtCl2(coe)]2 (1), which reacts with excess coe to
give trans-PtCl2(coe)2 (2). Compound 2 was characterized by an X-ray diffraction study and crystals were found to be
triclinic, a = 5.7838(5), b = 7.4347(6), c = 9.9972(9) Å, α = 83.924(1), β = 87.844(2), γ = 73.546(1)°, Z = 1, with
space group P1. Addition of 4-vinylpyridine (4vp) to 1 gave trans-PtCl2(4vp)2 (5) which was also characterized by
an X-ray diffraction study. Crystals of 5 were monoclinic, a = 8.2255(6), b = 12.8254(10), c = 6.9624(5) Å,
β = 98.8230(10)°, Z = 2, with space group P21/c. Although alkenylamines react with 1 to give a mixture of products,
addition of one equivalent of apve (H2NCH2CH2CH2OCHϭCH2) to 1 cleanly afforded the organometallic product
trans-PtCl2(coe)(thmo) (thmo = tetrahydro-2-methyl-1,3-oxazine) arising from a metal-catalyzed intramolecular
hydroamination of the starting alkenylamine. Initial investigations into the functionalization of metal complexes
containing pendant alkene groups have shown that catecholborane can be added in some cases, using a rhodium
catalyst, to give the corresponding organoboronate ester platinum compounds.
Key words: alkenylamines, alkenylpyridines, hydroamination, hydroboration, platinum.
Résumé : L’addition du cis-cyclooctène (coe) au K2PtCl4 conduit à la formation de trans-[PtCl2(coe)]2 (1) qui réagit
avec un excès de coe pour fournir le trans-PtCl2(coe)2 (2) que l’on a caractérisé par une étude de diffraction des
rayons X. On a trouvé que les cristaux sont tricliniques, groupes d’espace P1, avec a = 5,7838(5), b = 7,4347(6) et
c = 9,9972(9) Å, α = 83,924(1), β = 87,844(2) et γ = 73,545(1)° et Z = 1. L’addition de 4-vinylpyridine (4vp) au
composé 1 fournit le trans-PtCl2(4vp)2 (5) que l’on a aussi caractérisé par diffraction des rayons X. Les cristaux de 5
sont monocliniques, groupe d’espace P21/c, avec a = 8,2255(6), b = 12,8254(10) et c = 6,9624(5) Å, β = 98,8230(10)°
et Z = 2. Même si les alcénylamines (L) réagissent avec 1 pour fournir un mélange de produits, l’addition d’un
équivalent d’apve (H2NCH2CH2CH2OCHϭCH2) à 1 fournit proprement le produit organométallique trans-
PtCl2(coe)(thmo) (thmo = tétrahydro-2-méthyl-1,3-oxazine) qui provient d’une hydroamination intramoléculaire
catalysée par un métal de l’alcénylamine de départ. Des études initiales sur la fonctionnalisation de complexes
métalliques contenant des groupes alcènes ont montré que sous l’influence d’un catalyseur de rhodium, on peut, dans
certains cas, additionner du catécholborane pour obtenir les esters organoboronates du platine correspondants.
Mots clés : alcénylamines, alcénylpyridines, hydroamination, hydroboration, platine.
[Traduit par la Rédaction] Shaver et al. 576
Introduction
coupled with the low solubility of cisplatin in water, have
resulted in a large influx of research into derivatives of
cisplatin in an attempt to overcome some of these limita-
tions. With this in mind, we have prepared a number of
trans platinum complexes containing alkenylamine and
alkenylpyridine ligands and hypothesize that further
hydroboration of the pendant CϭC moieties in these com-
plexes may prove to be a facile route to making novel plati-
num compounds containing biologically-active boronic acid
groups. Platinum complexes containing alkenylamines and
Cisplatin, cis-PtCl2(NH3)2, is an anti-cancer agent used
extensively for the treatment of testicular and ovarian tu-
mours, and has moderate use in the treatment of neck, blad-
der and lung tumours (1–6). Unfortunately, widespread
application of this compound has been limited by numerous
drawbacks including nausea, myelosuppression of bone mar-
row, renal tubular necrosis leading to kidney failure, loss of
high frequency hearing, and neuropathy. These side effects,
Received December 22, 1999. Published on the NRC Research Press website on May 8, 2000.
M.P. Shaver, C.M. Vogels, A.I. Wallbank, and S.A. Westcott.1 Department of Chemistry, Mount Allison University, Sackville,
NB E4L 1G8, Canada.
T.L. Hennigar, K. Biradha, and M.J. Zaworotko.2, 3 Department of Chemistry, St. Mary’s University, Halifax, NS B3H 3C3,
Canada.
1Author to whom correspondence may be addressed. Telephone: (506) 364-2351. Fax: (506) 364-2313. e-mail: swestcott@mta.ca
2Current address: Department of Chemistry, University of South Florida, Tampa, FL 33620–5250, U.S.A.
3Author to whom correspondence about crystallography may be addressed.
Can. J. Chem. 78: 568–576 (2000)
© 2000 NRC Canada

Shaver et al.
569
alkenylpyridines are also of interest as these ligands can co-
ordinate to the metal centre via either the nitrogen lone pair
or the alkene moiety.
Preparation of trans-PtCl2(coe)(2vp) (3)
2-Vinylpyridine (14 mg, 0.13 mmol) in 3 mL of CH2Cl2
was added dropwise at 0°C to a solution of trans-
[PtCl2(coe)]2 (50 mg, 0.07 mmol) in 15 mL of CH2Cl2. The
reaction was stirred for 4 h at which point solvent was re-
moved under vacuum to afford a yellow solid which was
washed with ether (2 × 2 mL) and hexane (3 × 5 mL). Yield:
26 mg (40%); mp 187°C (decomposition). Spectroscopic
Experimental
1
NMR data (in CDCl3): H δ: 1.43 (s, 4H), 1.80 (br s, 4H),
Reagents and solvents used were obtained from Aldrich
Chemicals. THF, hexane, and diethyl ether were distilled
from sodium benzophenone ketyl. Methylene chloride and
chloroform were distilled from CaH2. Potassium tetrachloro-
platinate was obtained from Johnson Matthey Ltd. RhCl(PPh3)3
was prepared as described elsewhere (7). NMR spectra were
recorded on a JEOL JNM-GSX270 FT NMR spectrometer.
1H NMR chemical shifts are reported in ppm and referenced
to residual protons in deuterated solvent at 270 MHz.
11B{1H} NMR chemical shifts are referenced to external
F3B OEt2 at 87 MHz. 13C{1H} NMR chemical shifts are ref-
erenced to solvent carbon resonances as internal standards at
68 MHz. Multiplicities are reported as (s) singlet, (d) dou-
blet, (t) triplet, (q) quartet, (quint) quintet, (m) multiplet, (br)
broad, and (ov) overlapping. Infrared spectra were obtained
using a Mattson Polaris FT-IR spectrometer and reported
in cm–1. Melting points were measured uncorrected with a
Mel-Temp apparatus. Microanalyses for C, H, and N were
carried out at Desert Analytics (Tucson, AZ).
2.22–2.49 (ov m, 4H), 5.53 (m, JH-Pt = 70 Hz, 2H), 5.83 (d,
JH-H = 8 Hz, 1H), 6.06 (d, JH-H = 15 Hz, 1H), 7.31 (t, JH-H
=
5 Hz, 1H), 7.72 (m, 2H), 8.12 (d of d, JH-H = 15, 5 Hz, 1H),
8.68 (d, JH-H = 5 Hz, JH-Pt = 35 Hz, 1H); 13C{1H} δ: 26.1,
27.9, 29.0, 94.5 (JC-Pt = 153 Hz), 121.7, 123.2, 124.0, 135.2,
138.7, 150.3, 156.7. IR (nujol): 761, 793, 939, 957, 1108,
1127, 1163, 1229, 1377, 1465, 1562, 1602, 2857, 2897,
2941, 2966. Elemental analysis calcd. for PtCl2C15H21N: C
37.42, H 4.41, N 2.91; found: C 37.68, H 4.50, N 3.01.
Preparation of trans-PtCl2(coe)(4vp) (4)
4-Vinylpyridine (60 mg, 0.56 mmol) in 5 mL of CH2Cl2
was added dropwise to a stirred solution of 1 (200 mg,
0.27 mmol) in 15 mL of CH2Cl2 at 0°C. The solvent was re-
moved under vacuum after 4 h to afford a yellow solid
which was washed with hexane (3 × 5 mL). Spectroscopic
1
NMR data (in CDCl3): H δ: 1.47 (s, 6H), 1.83 (br s, 2H),
2.36 (br s, 2H), 2.54 (br s, 2H), 5.55 (br d, JH-H = 11 Hz,
JH-Pt = 64 Hz, 2H), 5.61 (d, JH-H = 11 Hz, 1H), 6.06 (d, JH-H
19 Hz, 1H), 6.68 (d of d, JH-H = 11, 5 Hz, 1H), 7.40 (d, JH-H
=
=
5 Hz, 2H), 8.78 (d, JH-H = 5 Hz, JH-Pt = 27 Hz, 2H); 13C{1H}
δ: 26.4, 28.3, 29.4, 94.4 (JC-Pt = 158 Hz), 122.3, 122.9,
133.3, 148.3, 151.7. Attempts to isolate 4 for elemental anal-
ysis were complicated by disproportionation in solution to
give 1 and 5.
Preparation of [PtCl2(coe)]2 (1)
[PtCl2(coe)]2 (1) was prepared by modification of a known
procedure (8). Potassium tetrachloroplatinate (300 mg,
0.70 mmol) was dissolved in a water isopropanol mixture
(10 :7 mL). A catalytic amount of tin chloride (3.8 mg,
0.02 mmol) was added to the red solution along with an ex-
cess of cis-cyclooctene (3.0 mL, 23.0 mmol). After 5 days,
the yellow solution was decanted from a small amount of
black precipitate. Compound 1 was extracted from the aque-
ous phase with 15 mL of methylene chloride and filtered to
afford a clear yellow solution. The solvent was removed in
vacuo to give a yellow solid and a small amount of yellow
liquid. The liquid was dissolved in hexane (10 mL) and de-
canted to afford a bright yellow powder. Yield: 158 mg
(58%). A yellow–orange precipitate appeared in the hexane
phase after 3 days. The hexane was decanted and the solid
dried. Yield: 53 mg (79% total); mp 190°C (decomposition).
Preparation of trans-PtCl2(4vp)2 (5)
4-Vinylpyridine (25 mg, 0.24 mmol) in 1 mL of CH2Cl2
was added dropwise to a stirred solution of 1 (45 mg,
0.06 mmol) in 7 mL of CH2Cl2. The mixture was cooled to
0°C for 2 days and the resultant off-white precipitate was fil-
tered and dried under vacuum. Yield: 43 mg (75%); mp
264°C (decomposition). Spectroscopic NMR data (in CDCl3):
1H δ: 5.60 (d, JH-H = 11 Hz, 2H), 6.02 (d, JH-H = 19 Hz,
2H), 6.58 (d of d, JH-H = 19, 11 Hz, 2H), 7.18 (d, JH-H
=
8 Hz, 4H), 8.84 (br d, JH-H = 6 Hz, JH-Pt = 30 Hz, 4H);
13C{1H} δ: 121, 122, 133, 147, 155. IR (nujol): 666, 846,
991, 1206, 1417, 1435, 1499, 1546, 1616, 2943. Elemental
analysis calcd. for PtCl2C14H14N2: C 35.29, H 2.97, N 5.88;
found: C 34.72, H 2.99, N 5.69.
1
Spectroscopic NMR data (in CDCl3): H δ:1.35 (br s, 8H),
1.52 (br s, 8H), 2.18 (br d, JH-H = 5 Hz, 8H), 5.78 (br, 4H);
13C{1H} δ: 26.1, 27.4, 28.9, 109.2 (br). IR (nujol): 762, 817,
868, 955, 1031, 1125, 1170, 1230, 1378, 1464, 2859, 2915.
Yellow crystals of 2 could be isolated from solutions of 1
in the presence of excess coe. The mp was found to be
178°C (decomposition). Spectroscopic NMR data (in
Preparation of trans-PtCl2(coe)(4chp) (6)
4-(3-Cyclohexen-1-yl)pyridine (89 mg, 0.56 mmol) in
5 mL of CH2Cl2 was added dropwise to a stirred solution of
1 (200 mg, 0.27 mmol) in 15 mL of CH2Cl2 at 0°C. The re-
action was allowed to proceed for 4 h at which point the sol-
vent was removed under vacuum. The resultant orange oil
was dissolved in 1 mL of CH2Cl2 after which 5 mL of hex-
ane was added and the reaction mixture stored at 0°C for
18 h. The precipitate was collected and determined to be 7
by NMR spectroscopic data. The solvent was removed from
the filtrate to afford a bright yellow solid. Spectroscopic
1
CDCl3): H δ: 1.45 (br s, 8H), 1.62 (br s, 8H), 2.29 (br d,
JH-H = 5 Hz, 8H), 5.94 (br, 4H); 13C{1H} δ: 26.3, 27.6, 29.2,
113.3 (br). IR (nujol): 762, 818, 953, 1125, 1170, 1233,
1317, 1354, 1380, 1427, 1467, 1529, 2845, 2884, 2972. The
formation of this monomer has been reported previously (8).
Interestingly, C and H elemental analyses from this previous
study varied over time, suggesting loss of the second coe
ligand to give 1 is facile even in the solid state.
© 2000 NRC Canada

570
Can. J. Chem. Vol. 78, 2000
NMR data (in CDCl3) for 6: 1H δ: 1.46 (m, 6H), 1.76 (ov m,
4H), 2.15 (s, 2H), 2.32 (m, 4H), 2.53 (m, 2H), 2.89 (s, 1H),
5.66 (d, JH-H = 8 Hz, JH-Pt = 72 Hz, 2H), 5.72 (s, 2H), 7.29
(d, JH-H = 5 Hz, 2H), 8.73 (br d, JH-H = 5 Hz, JH-Pt = 32 Hz,
2H); 13C{1H}δ: 25.0, 26.3, 28.1, 28.5, 29.3, 31.8, 39.5, 94.1
(JC-Pt = 156 Hz), 124.0, 125.4, 127.3, 151.2, 153.2. Attempts
to isolate 6 were complicated by disproportionation in solu-
tion to give 1 and 7.
calcd. for PtCl2C16H29N: C 38.31, H 5.84, N 2.79; found: C
38.72, H 5.92, N 2.86.
Preparation of trans-PtCl2(coe)(thmo) (10)
Tetrahydro-2-methyl-1,3-oxazine (14 mg, 0.14 mmol) in
3 mL of CH2Cl2 was added dropwise to a solution of 1
(50 mg, 0.07 mmol) in 10 mL of CH2Cl2 at 0°C. Solvent
was removed after 4 h to afford a yellow oil which was
triturated with hexane (3 × 5 mL) and dried under vacuum to
afford a yellow solid. Yield: 25 mg (40%); mp 98°C. Spec-
Preparation of trans-PtCl2(4chp)2 (7)
4-(3-Cyclohexen-1-yl)pyridine (45 mg, 0.29 mmol) in
1 mL of CH2Cl2 was added dropwise to a stirred solution of
1 (50 mg, 0.07 mmol) in 15 mL of CH2Cl2. The solvent was
removed under vacuum after the reaction was allowed to
proceed for 5 h. The resultant yellow oil was dissolved in
1 mL of CH2Cl2 after which addition of hexane (3 mL) to
the solution produced an off-white precipitate. Yield: 53 mg
(68%); mp 272°C (decomposition). Spectroscopic NMR data
1
troscopic NMR data (in CDCl3): H δ: 1.37 (br s, 6H), 1.70
(ov m, 6H), 2.13 (br s, 2H), 2.29 (br s, 2H), 3.39 (m, 2H),
3.70 (t, JH-H = 16 Hz, 1H), 3.92 (m, 1H), 4.45 (br s, 1H),
4.60 (m, 2H), 5.27 (m, 2H); 13C{1H} δ: 22.3, 25.6, 25.9,
27.4, 27.6, 28.9, 48.4, 86.5, 92.9 (JC-Pt = 140 Hz). IR
(nujol): 815, 846, 963, 1017, 1059, 1099, 1139, 1230, 1378,
1461, 2889, 3216, 3433. Elemental analysis calcd. for
PtCl2C13H25NO: C 32.71, H 5.28, N 2.93; found: C 33.10, H
5.23, N 2.90.
1
(in CDCl3): H δ: 1.60 (m, 4H), 1.93 (m, 4H), 2.25 (m, 4H),
2.87 (br s, 2H), 5.77 (s, 4H), 7.16 (d, JH-H = 5 Hz, 4H), 8.75
(d, JH-H = 5 Hz, JH-Pt = 32 Hz, 4H); 13C{1H} δ: 25.1, 28.6,
32.0, 39.5, 123.9, 125.6, 127.4, 153.1, 159.2. IR (nujol):
719, 829, 1069, 1212, 1244, 1422, 1616, 2936. Elemental
analysis calcd. for PtCl2C22H26N2: C 45.21, H 4.49, N 4.79;
found: C 44.83, H 4.26, N 4.62.
Catalyzed hydroboration of trans-PtCl2(4vp)2 (5) with
catecholborane
Under an atmosphere of dinitrogen, trans-PtCl2(4vp)2
(25 mg, 0.05 mmol) was suspended in 1 mL of CDCl3 with
7 mol% of Wilkinson’s catalyst, RhCl(PPh3)3. Catechol-
borane (14 mg, 0.12 mmol) in 0.5 mL of CDCl3 was added
dropwise to the stirred suspension and the reaction mixture
was allowed to stand for 48 h and then analyzed by NMR
Preparation of trans-PtCl2(aa)2 (8)
Allylamine (18 mg, 0.32 mmol) in 3 mL of CH2Cl2 was
added to a stirred solution of 1 (50 mg, 0.07 mmol) in
10 mL of CH2Cl2 at 0°C. Within 30 min a yellow precipitate
had formed and was collected by suction filtration. Yield:
37 mg (72%); mp 214°C (decomposition). Spectroscopic
NMR data (in CDCl3): 1H δ: 3.49 (d, JH-H = 5 Hz, 4H), 5.37
(d of d, JH-H = 11, 5 Hz, 2H), 5.97 (m, 4H), 8.18 (br s, 4H);
13C{1H} δ: 44.2, 123.7, 131.9. IR (nujol): 722, 1018, 1108,
1566, 1603, 2928. Elemental analysis calcd. for
PtCl2C6H14N2: C 18.95, H 3.72, N 7.37; found: C 18.95, H
3.97, N 7.23. Complex 8 eventually decomposes in solution
to give a number of unidentified products.
1
spectroscopy. Spectroscopic NMR data (in CDCl3): H δ:
1.22 (t, JH-H = 8 Hz), 1.50 (d, JH-H = 8 Hz), 1.64 (t, JH-H
=
8 Hz), 2.12 (s), 2.69 (q, JH-H = 8 Hz), 3.03 (ov), 5.29 (s),
5.38 (s), 5.63 (m), 7.0 (m), 8.74 (d, JH-H = 5 Hz); 11B{1H} δ:
7.0 (s), 7.8 (s), 12.3 (s), 29.0 (s), 23.2 (br), 35.0 (br).
Catalyzed hydroboration of trans-PtCl2(4chp)2 (7) with
catecholborane
Under an atmosphere of dinitrogen, trans-PtCl2(4chp)2
(52 mg, 0.09 mmol) was dissolved in 1 mL of CDCl3 with 7
mol% catalyst. Catecholborane (24 mg, 0.20 mmol) in
0.5 mL of CDCl3 was added dropwise to the stirred solution
and the reaction was allowed to proceed for 48 h and then
analyzed by NMR spectroscopy. Spectroscopic NMR data
Preparation of trans-PtCl2(coe)(chea) (9)
2-(1-Cyclohexenyl)ethylamine (35 mg, 0.28 mmol) in
15 mL of CH2Cl2 was added to a solution of 1 (100 mg,
0.13 mmol) in 10 mL of CH2Cl2 at 0°C. The reaction was
allowed to proceed for 3 h at which point solvent was re-
moved under vacuum to afford an orange oil. The oil was
dissolved in 1 mL of CH2Cl2 after which hexane (10 mL)
was added and the reaction mixture cooled to 0°C. After
18 h, a pale yellow precipitate was collected by suction fil-
tration and found to be a mixture of products by NMR spec-
troscopy. The solvent was allowed to evaporate from the
filtrate over 48 h to afford bright yellow needles which were
collected and dried under vacuum. Yield: 70 mg (52%); mp
1
(in CDCl3): H δ: 1.45–1.59 (ov m), 2.00–2.18 (ov m), 2.66
(m), 6.92–7.39 (ov m), 8.75 (d, JH-H = 5 Hz), 8.88 (d, JH-H
=
5 Hz); 11B{1H} δ: 12.3 (s), 23.0 (s), 36.3 (br); 13C{1H} δ:
21.2 (br, C-B), 21.8 (br, C-B), 27.1, 27.2, 27.7, 33.3, 33.7,
34.1, 43.6, 44.4, 112.6, 112.8, 121.6, 122.9, 124.0, 148.2,
148.3, 153.5, 159.4.
The platinum aminoboronate ester was formed in situ as
described in the previous procedure and removed from the
dinitrogen atmosphere. Addition of 0.5 mL of D2O to this
product resulted in a convincing change in the solution’s ap-
pearance from brown to orange in colour. Spectroscopic
1
122°C. Spectroscopic NMR data (in CDCl3): H δ: 1.43 (m,
6H), 1.59 (ov m, 4H), 1.78 (br s, 2H), 1.92 (br s, 2H), 2.01
1
(br s, 2H), 2.24 (br m, 4H), 2.39 (ov m, 2H), 3.09 (m, JH-H
8 Hz, 2H), 3.72 (br s, JH-Pt = 59 Hz, 2H), 5.30 (d, JH-H
=
=
NMR data (in CDCl3): H δ: 1.48–1.58 (ov m), 1.99 (m),
2.18 (m), 2.65 (m), 6.70 (d, JH-H = 5 Hz), 6.88 (d, JH-H
=
11 Hz, JH-Pt = 81 Hz, 2H), 5.55 (s, 1H); 13C{1H} δ: 22.4,
22.8, 25.5, 26.4, 27.9, 28.1, 29.5 (JC-Pt = 41 Hz), 39.7, 42.7,
93.6 (JC-Pt = 158 Hz), 126.5, 132.8. IR (nujol): 722, 1001,
1231, 1377, 1461, 1579, 2841, 2968. Elemental analysis
5 Hz), 7.09–7.21 (ov m), 7.39 (m), 8.73 (d, JH-H = 5 Hz);
11B{1H} δ: 19.6 (s, B(OH)3), 36.9 (br); 13C{1H} δ: 21.2 (br,
C-B), 22 (br, C-B), 27.1, 27.2, 27.6, 33.0, 33.6, 33.7, 43.6,
44.3, 115.6, 120.9, 124.0, 148.2, 153.2, 159.5.
© 2000 NRC Canada

Shaver et al.
571
Table 1. Crystallographic data collection parameters for trans-PtCl2(coe)2 (2) and trans-PtCl2(4vp)2 (5).
Complex
2
5
C16H28Cl2Pt
486.37
Formula
fw
C14H14Cl2N2Pt
476.26
Crystal system
Space group
a (Å)
b (Å)
c (Å)
α (°)
β (°)
γ (°)
V (Å3)
triclinic
P1
monoclinic
P21/c
8.2255 (6)
12.8254 (10)
6.9624 (5)
—
98.8230 (10)
—
725.81 (9)
2
5.7838 (5)
7.4347 (6)
9.9972 (9)
83.924 (1)
87.844 (2)
73.546 (1)
409.95 (6)
1
Z
ρcalcd (g cm–3)
Crystal size (mm)
Temperature (K)
Radiation
µ, (mm–1)
Total reflectionsa
Total unique relections
No. of variables
Largest difference
peak/hole (e Å–3)
Rb
1.970
0.15 × 0.20 × 0.20
183 (2)
MoKα (λ = 0.71073)
8.869
2602
2.179
0.15 × 0.20 × 0.20
193 (2)
MoKα (λ = 0.71073)
10.021
4464
1807
88
1689
88
1.061/–1.889
0.0232
0.624/–1.177
0.0188
Rw
GoFc
0.0606
0.575
0.0480
1.093
aIo > 3σ (Io).
bR = Σ**Fo* – *Fc**/Σ*Fo*; Rw = [Σ(w(*Fo* – *Fc*)2/Σ(w*Fo*)2]1/2
.
c[Σ(w(*Fo* – *Fc*)2/(NO – NV)]1/2
.
number of unsaturated trans amine and pyridine complexes
from the monoalkene dimer trans-[PtCl2(coe)]2 (1) (coe = η2 –
C8H14) (8). The starting organometallic dimer, which is soluble
in common organic solvents, was readily prepared by the addi-
tion of cis-cyclooctene to aqueous solutions of K2PtCl4, and
appears to be indefinitely stable in the solid state. A recent pa-
per examining reaction mechanisms for alkene exchange with
trans-[PtCl2(C2H4)]2 suggests that a two-step process incorpo-
rating trans-PtCl2(C2H4)2 might be occurring in the steady state
(9). Indeed, the analogous disubstituted alkene complex trans-
PtCl2(coe)2 (2) could be crystallized in minor amounts (<10%)
by addition of excess coe to 1 (10).
We have carried out an X-ray diffraction study on 2 which
shows the platinum metal centre in a square plane with the
cyclooctene ligands lying trans to one another. The structure
of 2 is shown in Fig. 1, summary of the crystallographic data
presented in Table 1, pertinent bond distances and angles
given in Table 2, and atomic coordinates provided in Ta-
ble 3. Platinum–carbon bond distances of 2.258(4) and
2.278(4) Å are somewhat longer than analogous Pt(II) com-
plexes where a chloride ligand lies trans to the alkene group.
For instance, average bond lengths of 2.128(19), 2.13(2),
X-ray crystallographic data for 2 and 5
Crystals of 2 and 5 suitable for X-ray diffraction studies were
obtained by crystallization from solutions of methylene chloride
at 5°C. A summary of the crystal data and parameters for data
collection is given in Table 1. Data were collected at 183 K (for
2) and 193 K (for 5) on a Siemens SMART/CCD diffractometer
equipped with an LT-II low temperature device. Diffracted data
were corrected for absorption using the SADABS4 program.
SHELXTL was used for structure solution and refinement was
based on F2.5 All non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were fixed at calculated posi-
tions and refined isotropically on the basis of the corresponding
carbon atoms [U(H) = 1.2Ueq(C)]. Selected bond distances and
angles are given in Tables 2 and 4 and final atomic coordinates
in Tables 3 and 5. Complete tables of bond distances and angles,
final atomic coordinates, and anisotropic displacement parame-
ters have been deposited as supporting material.6
Results and discussion
As part of our ongoing research into making novel amino-
boron platinum complexes, we decided to initially prepare a
4 G.M. Sheldrick. SADABS Univ. Gottingen (1996).
5 G.M. Sheldrick. SHELXTL Release 5.03; Siemens Analytical X-ray Instruments Inc., Madison, Wis. (1994).
6 A complete set of data may be purchased from: The Depository of Unpublished Data, Document Delivery, CISTI, National Research Coun-
cil Canada, Ottawa, Ontario, Canada, K1A 0S2. Tables of coordinates, bond distances and angles, and alternative views of 2 and 5 have also
been deposited with the Cambridge Crystallographic Data Centre, University Chemical Laboratory, 12 Union Road, Cambridge, CB2 1EZ,
U.K.
© 2000 NRC Canada

572
Can. J. Chem. Vol. 78, 2000
Table 2. Selected bond distances (Å) and an-
gles (°) for trans-PtCl2(coe)2 (2).a
Table 3. Atomic coordinates (× 104) and equivalent isotropic dis-
placement coefficients for trans-PtCl2(coe)2 (2). U(eq) is defined
as one third of the trace of the orthogonalized Uij tensor.
Bond distances
x
y
z
U(eq)
Pt(1)—C(2)#1
Pt(1)—C(2)
Pt(1)—C(1)#1
Pt(1)—C(1)
Pt(1)—Cl(1)
Pt(1)—Cl(1)#1
C(1)—C(2)
C(1)—C(8)
C(2)—C(3)
C(3)—C(4)
C(4)—C(5)
C(5)—C(6)
C(6)—C(7)
C(7)—C(8)
2.258(4)
2.258(4)
2.278(4)
2.278(4)
2.3107(10)
2.3107(10)
1.389(5)
1.499(6)
1.492(6)
1.543(6)
1.532(6)
1.550(6)
1.536(6)
1.547(6)
Pt(1)
Cl(1)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
0
0
0
16(1)
24(1)
19(1)
18(1)
22(1)
26(1)
26(1)
27(1)
26(1)
23(1)
3265(2)
2409(7)
1241(7)
–681(8)
464(9)
2532(9)
2023(9)
3150(9)
1883(8)
–1340(1)
–1393(6)
–2656(5)
–3230(6)
–5041(6)
–4921(6)
–3197(7)
–1635(6)
–391(6)
1394(1)
–1674(4)
–1051(4)
–1703(4)
–2393(5)
–3369(5)
–4444(4)
–4166(4)
–3057(4)
Table 4. Selected bond distances (Å) and
angles (°) for trans-PtCl2(4vp)2 (5).a
Bond angles
Bond distances
C(2)-C(1)-C(8)
C(1)-C(2)-C(3)
C(2)-C(3)-C(4)
C(5)-C(4)-C(3)
C(4)-C(5)-C(6)
C(7)-C(6)-C(5)
C(6)-C(7)-C(8)
C(1)-C(8)-C(7)
Cm-Pt1-Cl(1)b
125.2(4)
123.8(4)
109.5(3)
114.6(3)
116.4(4)
115.2(4)
115.4(4)
112.2(4)
85.7
Pt(1)—N(1)
Pt(1)—N(1)#1
Pt(1)—Cl(1)
Pt(1)—Cl(1)#1
N(1)—C(5)
N(1)—C(1)
C(1)—C(2)
C(2)—C(3)
C(3)—C(4)
C(3)—C(6)
C(4)—C(5)
C(6)—C(7)
2.020(3)
2.020(3)
2.2996(8)
2.2996(8)
1.350(4)
1.352(4)
1.373(5)
1.398(5)
1.403(5)
1.473(5)
1.368(5)
1.330(6)
aSymmetry transformations used to generate
equivalent atoms: #1 –x, –y, –z.
bCm is in the middle of the C(1)—C(2) bond.
Bond Angles
and 2.12(2) Å have been reported for K[PtCl3(C2H4)] (11),
PtCl(C6H2Me3)(η4-C8H12) (12), and [PtCl2(C7H12)]2 (13), re-
spectively. However, the Pt—C bond distance in 2 is similar
to that reported for the double bond trans to the mesityl
group (C6H2Me3) in the previous example (cf. 2.30(2) Å).
The carbon–carbon bond distance of 1.389(5) Å shows the
expected weakening of the double bond due to π-
backbonding from the metal to the empty π* orbital of the
alkene (14).
Addition of neutral ligands (L) to either 1 or 2 will give
complexes of the type trans-PtCl2(coe)L and, upon addition
of a second equivalent of ligand, the disubstituted species
trans-PtCl2L2 (15). Reactions with alkenylpyridine and
alkenylamine ligands are of special interest because coordi-
nation of these ligands to a transition metal can occur via ei-
ther the alkene moiety and (or) the nitrogen lone pair.
N(1)-Pt(1)-N(1)#1
N(1)-Pt(1)-Cl(1)
N(1)#1-Pt(1)-Cl(1)
N(1)-Pt(1)-Cl(1)#1
N(1)#1-Pt(1)-Cl(1)#1
Cl(1)-Pt(1)-Cl(1)#1
C(5)-N(1)-C(1)
C(5)-N(1)-Pt(1)
C(1)-N(1)-Pt(1)
N(1)-C(1)-C(2)
C(1)-C(2)-C(3)
C(2)-C(3)-C(4)
C(2)-C(3)-C(6)
C(4)-C(3)-C(6)
C(5)-C(4)-C(3)
N(1)-C(5)-C(4)
C(7)-C(6)-C(3)
180.0
89.92(8)
90.08(8)
90.08(8)
89.92(8)
180.0
117.9(3)
120.0(2)
122.1(2)
122.2(3)
120.3(3)
116.8(3)
120.4(3)
122.8(3)
119.9(3)
122.8(3)
125.0(4)
aSymmetry transformations used to generate
equivalent atoms: #1 (–x + 1), (–y + 1), –z.
Alkenylpyridines
A number of transition metal complexes (16–23) contain-
ing alkenylpyridine ligands have been reported. For exam-
ple, addition of 2-vinylpyridine (2vp = 2-NC5H4CHϭCH2)
to [Cu(NCCH3)4][ClO4] gave the binuclear complex [Cu2(µ-
2vp)2(2vp)2][ClO4]2 where two of the alkenylpyridine lig-
ands use the nitrogen and the alkene to bond to two respec-
tive metal centres (16). For this study we decided to prepare
trans complexes from three commercially available
alkenylpyridines (Fig. 2).
Previous work has shown that attempts to prepare cis-
PtCl2(2vp)2 (20) from K2PtCl4 resulted in the formation of
several products where both the alkene and nitrogen groups
are involved in bonding to platinum. Likewise, efforts to
generate the trans derivative from trans-PtCl2(NCCH3)2
have also proven unsuccessful (23). Although we were also
unable to generate trans-PtCl2(2vp)2 from addition of 2vp to
© 2000 NRC Canada

Shaver et al.
573
Table 5. Atomic coordinates (× 104) and equivalent isotropic dis-
placement coefficients for trans-PtCl2(4vp)2 (5). U(eq) is defined
as one third of the trace of the orthogonalized Uij tensor.
Fig. 1. Molecular structure of trans-PtCl2(coe)2 (2).
x
y
z
U(eq)
Pt(1)
Cl(1)
N(1)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
5000
5000
0
20(1)
31(1)
21(1)
24(1)
25(1)
25(1)
25(1)
24(1)
33(1)
44(1)
3695(1)
6632(3)
6151(4)
7255(4)
8945(4)
9427(4)
8261(4)
10133(5)
11757(5)
5692(1)
6188(2)
7197(3)
8005(3)
7804(3)
6754(3)
5985(3)
8671(3)
8568(4)
2403(1)
343(4)
253(5)
531(5)
909(5)
1009(5)
711(5)
1204(6)
1365(6)
Fig. 2. Alkenylpyridines.
trans-[PtCl2(coe)]2 (1), the novel organometallic complex
trans-PtCl2(coe)(2vp) (3), which is soluble in common or-
ganic solvents such as methylene chloride, could be isolated
in moderate yield (40%). Steric congestion around the nitro-
gen atom in 2-vinylpyridine presumably inhibits addition of
a second equivalent of this ligand to the metal centre. The
1H NMR spectrum for 3 shows a shift for the pyridine ring’s
α-carbon proton from 8.54 ppm for free 2vp to 8.68 ppm in
the complex. Coupling (JH-Pt = 35 Hz) to the 195Pt nucleus
(14) is also observed for this resonance. Shifts for the
1
alkenyl peaks are also observed by H NMR spectroscopy
for this complex, suggesting that the alkenyl group may lie
directly above the plane of the platinum atom (15).
creased solubility in common organic solvents as compared
to 5.
The corresponding 4-vinylpyridine (4vp = 4-NC5H4CHϭCH2)
complex, trans-PtCl2(coe)(4vp) (4), was prepared by addi-
tion of 2 equivalents of 4vp to 1, along with minor amounts
of the disubstituted product trans-PtCl2(4vp)2 (5) and unreacted
1. For complex 4, the diagnostic shift from 8.56 ppm for free
4vp to 8.78 ppm is observed in the 1H NMR spectrum, along
with coupling to platinum (JH-Pt = 27 Hz), for the pyridine
ring’s α-carbon protons. Complex 5 could be readily pre-
pared by the addition of excess 4vp to 1. Although NMR
spectroscopic data show similar trends upon complexation to
platinum, unambiguous assignment of 5 is based upon an X-
ray diffraction study. The molecular structure of 5 is shown
in Fig. 3, relevant bond angles and distances in Table 4, and
atomic coordinates in Table 5. The platinum atom lies in a
distorted square plane with two Cl atoms and two 4vp N at-
oms coordinated to the metal centre in a trans geometry. The
Pt—Cl and Pt—N bond distances of 2.2996(8) and 2.020(3)
Å, respectively, are similar to those reported for cis-
PtCl2(4vp)2 (21). Bond lengths of 1.330(6) Å are typical for
uncomplexed C—C double bonds. The alkenylpyridines are
planar with bond distances and angles similar to those ob-
served in other transition metal pyridine derivatives (21).
The organometallic complex trans-PtCl2(coe)(4chp) (6)
(4chp = 4-(3-cyclohexen-1-yl)pyridine) and the disubstituted
compound trans-PtCl2(4chp)2 (7) were readily prepared from
reaction of the cyclooctene dimer 1 with 2 and 4 equivalents
of 4chp, respectively, (24). Complex 6 has the diagnostic
Alkenylamines
The synthesis of platinum complexes containing neutral
and protonated alkenylamines has been reported previously
(25–28). For example, addition of allylamine (aa
=
NH2CH2CHϭCH2) to acidic solutions of [PtCl4]2– are
known to give zwitterionic PtCl3(CH2ϭCHCH2NH3) where
only the CϭC group of the alkenylamine is coordinated to
the platinum centre (14, 25). In the absence of protonation,
or by treatment with NaOH, the above complex can be trans-
formed into a neutral alkenylamine species where the ligand
is capable of coordinating in a chelating bidentate manner
through both the alkene moiety and the nitrogen lone pair
(26). Another allylamine complex has been reported in
which the ligand bridges two metal centres by binding to
one metal via the nitrogen atom and to the other platinum
using the alkene group (29). We have found that addition of
aa to trans-[PtCl2(coe)]2 (1) afforded the novel diamine
complex trans-PtCl2(aa)2 (8) in high yield (72%). Complex
8 is only sparingly soluble in common organic solvents such
as methylene chloride. The amine hydrogens appear as a
1
broad peak in the H NMR spectrum and shift from 1.23 for
free allylamine to 8.18 ppm in 8. Likewise, the broad methy-
lene peak shifts from 3.36 to 3.49 ppm upon complexation.
The vinyl peaks, however, remain relatively unchanged sug-
gesting that coordination of the allylamine ligand occurs
through the nitrogen atom only. IR data supports this hy-
pothesis as the CϭC π stretch found in free allylamine at
1637 cm–1 only shifts to 1603 cm–1 when the ligand coordi-
nates to Pt(II). For metal complexes containing the
1
shift for the α-hydrogens of the pyridine group in the H
NMR spectrum (8.49 ppm for free 4chp to 8.73 ppm for 6)
along with coupling to the 195Pt nucleus (JH-Pt = 72 Hz). The
cyclohexenyl groups in 7 resulted in this complex having in-
© 2000 NRC Canada

574
Can. J. Chem. Vol. 78, 2000
Fig. 3. Molecular structure of trans-PtCl2(4vp)2 (5).
this area will concentrate on examining the hydroamination
of N-substituted apve derivatives, the results of which will
be reported in due course.
Fig. 4. Alkenylamines.
Hydroboration of Metal Complexes
We hypothesize that hydroboration of pendant alkenyl
groups in the above mentioned alkenylamine and alkenyl-
pyridine compounds, followed by aqueous workup, should
give novel platinum complexes containing boronic acids,
-B(OH)2 (32). Compounds containing boronic acids have
extensive biological activity (33) as well as facilitate the
transport of molecules across lipid bilayers (34, 35). As
hydroborations of the starting alkenylamines and alkenyl-
pyridines are known to give a number of unwanted products
(36,7 footnote 7), this present methodology is advantageous
in that coordination of the ligand to the metal centre deacti-
vates the lone pair of nitrogen.
protonated alkenylamine ligands, where the alkene is di-
rectly bound to the metal centre, this band appears near
1500 cm–1 (26). Efforts to prepare the monoamine complex
trans-PtCl2(coe)(aa) have proven unsuccessful.
We have attempted to prepare platinum complexes with
other alkenylamines (Fig. 4) in an effort to confirm the
bonding modes in these unique ligands. Unfortunately, no
reaction was observed between dimer 1 and secondary
amine N-allylaniline (aA = NH(Ph)CH2CHϭCH2). The in-
creased steric bulk of this amine, as compared with
allylamine, presumably precludes coordination to the metal
centre. Conversely, trans-PtCl2(coe)(chea) (9) was prepared
by addition of 2-(1-cyclohexenyl)ethylamine (chea) to dimer
1. As with the other monoamine complexes, the 13C{1H}
NMR spectrum for 9 exhibits a singlet for the sp2 carbons of
the coe ligand at 93.6 ppm with diagnostic 195Pt satellites
(JC-Pt = 158 Hz). Unfortunately, treatment of 1 with four
equivalents of chea led to a complex mixture of products,
even at low temperatures.
Initial work was conducted on the monoalkene complexes
3, 4, 6, and 9. Not surprisingly, however, hydroborations of
these complexes always gave complex product distributions
arising from attack of the borane at the metal centre follow-
ing initial loss of the labile cyclooctene ligand. We therefore
decided to concentrate our efforts on functionalizing the di-
substituted analogues and proceeded by using the fully char-
acterized pyridine complex trans-PtCl2(4vp)2 (5). Reactions
of 5 with catecholborane (HBcat, cat = O2C6H4), using 7
mol% of RhCl(PPh3)3 (37), gave mixtures of anti-Markovnikov
Addition
of
aminopropylvinylether
(apve
=
H2NCH2CH2CH2OCHϭCH2) to trans-[PtCl2(coe)]2 (1) gave
the unexpected product trans-PtCl2(coe)(thmo) (10) (thmo =
tetrahydro-2-methyl-1,3-oxazine) in moderate yields (40%).
The formation of thmo presumably arises from a platinum
mediated intramolecular hydroamination of the starting apve
group (30). A proposed mechanism for this reaction is
shown in Fig. 5 (31). Coordination of the alkene group to
the metal centre activates it towards nucleophilic attack by
the amine group. Selective attack at the carbon α to the ether
oxygen affords an alkylplatinum intermediate. Subsequent
hydrogen abstraction from the ammonium group yields an
alkylmetal hydride intermediate which undergoes reductive
elimination to produce free thmo and the coordinatively
unsaturated metal species ‘PtCl2(coe)’. This complex, or unreacted
1, rapidly traps free thmo to give trans-PtCl2(coe)(thmo).
This reaction is specific for the hydroamination product as
no other apve derivatives were observed. Further work in
1
(45% by H NMR spectroscopy) and Markovnikov (45%)
hydroboration products, products derived from a dehydro-
genative borylation/hydrogenation (5% each) pathway, as
well as some decomposition to platinum metal. Dehydrogenative
borylation is basically a mechanism that replaces one of the
alkene hydrogens with a Bcat group while generating H2;
this latter species accounts for the observation of products
containing hydrogenated 4-ethylpyridine. The complex prod-
uct distributions observed in these reactions is somewhat
surprising in light of the fact that hydroborations of styrene
derivatives (ArCHϭCH2) using HBcat can give exclusive
formation of either the Markovnikov (ArCH(Bcat)CH3) or
anti-Markovnikov (ArCH2CH2Bcat) products depending
upon the choice of catalyst (37, 38).
It is plausible that the numerous products observed in
hydroborations of 5 may be arising from the low solubility
7 C.M. Vogels, P.E. O’Connor, M.P. Shaver, T.E. Phillips, K.J. Watson, and S.A. Westcott. unpublished results.
© 2000 NRC Canada

Shaver et al.
575
Fig. 5. Intramolecular hydroamination of aminopropylvinylether.
Fig. 6. Hydroboration of trans-PtCl2(4chp)2 (7) with catecholborane.
of the starting platinum material in organic solvents. We
therefore decided to investigate the catalyzed hydroboration
of organic soluble trans-PtCl2(4chp)2 (7). Addition of HBcat
to 7 employing 7 mol% RhCl(PPh3)3 as a catalyst gave the
desired hydroborated product (Fig. 6) as ascertained by
multinuclear NMR spectroscopy. The diagnostic peak at
36 ppm in the 11B{1H} NMR spectrum suggests the forma-
tion of an organoboronate ester (38). Further evidence that
the 1,2-disubstituted alkene is being reduced is indicated by
Coordination in all cases appears to proceed through the
nitrogen lone pair and not the alkene moiety. Several
novel organometallic complexes of the type trans-
[PtCl(coe)L] (L = alkenylpyridine or alkenylamine) have
also been prepared and characterized. Initial investigations
into the functionalization of the pendant alkene groups have
shown that catecholborane can be added to these complexes,
using a rhodium catalyst, to give the corresponding organo-
boronate ester platinum compounds.
1
the disappearance of the vinylic peak in the H NMR spec-
trum. Preliminary results attempting to convert the hydro-
borated product to the corresponding boronic acid
compound have also proven successful. However, because
of the disubstituted nature of the alkene, it appears that this
reaction is not selective as regioisomers are present as ob-
Acknowledgements
Thanks are gratefully extended to the Natural Sciences
and Engineering Research Council of Canada, St. Mary’s
University, and Mount Allison University for financial sup-
port and Johnson Matthey Ltd. for the generous supplies of
platinum salts. We also wish to thank Dan Durant, Roger
and Marilyn Smith, and John E. Marcone (DuPont Co.) for
their expert technical assistance, Dr. Hilary Jenkins (SMU)
for help with the X-ray crystallography, and Drs. Terri
Bright, Sabine Weiguny and Giuliano Muccin (BASF) for
the generous gift of aminopropylvinylether. Anonymous re-
viewers are thanked for helpful suggestions.
1
served by H and 13C{1H} NMR spectroscopy. We are cur-
rently examining the full scope of this reaction in an effort
to improve selectivities and will report our results in due
course.
Conclusions
We have prepared a number of trans platinum alkenyl-
pyridine and alkenylamine complexes from the organo-
metallic dimer trans-[PtCl2(coe)]2 (coe = cis-cyclooctene).
© 2000 NRC Canada

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Can. J. Chem. Vol. 78, 2000
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