Reactions of aminoboron compounds with palladium and platinum complexes

Article abstract of DOI:10.1139/v99-106

Reactions of 3-NH₂C₆H₄B(OH)₂ (1, APBA) with [MCl₄]^2- (M = Pd, Pt) give the boronic acid-containing complexes, MCl₂(APBA)₂ (M = Pd, 2; M = Pt, 3). Addition of 1 to [PdCl₂(COE)]₂ (COE = η²-C₈H₁₄) ultimately led to PdCl₂(APBA)₂ (2). The pinacol derivative PdCl₂(APBpin)₂ (5, pin = O₂C₂Me₄) was characterized by an X-ray diffraction study. Crystals of 5 were monoclinic, a = 13.836(5), b = 14.937(5), c = 11.287(5) A, β = 99.042(9)°, Z = 2, with space group P2₁/c. Monoalkene complexes PtCl₂(COE)(APBA) (8) and PtCl₂(COE)(APBpin) (9) were generated from the addition of APBA and APBpin, respectively, to [PtCl₂(COE)]₂. Reactions of 2-NMe₂CH₂C₆H₄B(OH)₂ (10) with palladium complex [PdCl₂(COE)]₂ proceed via selective B - C bond cleavage to give the cyclopalladated dimer [PdCl(2-NMe₂CH₂C₆H₄)]₂ as the major amine-containing product. Likewise, reactions with borinic esters H₂NCH₂CH₂OBR₂ (R = Bu, 14; R = Ph, 15) give products derived from cleavage of the B - O bond. The unique palladium complex PdCl₂[S-NC₅H₄B(OH)₂]₂ (19) was prepared by addition of (3-NC₅H₄BEt₂)₄ (18) to [PdCl₂(COE)]₂ in wet methylene chloride, where adventitious water was used to convert the organoborane product into the corresponding boronic acid moiety.

Full text of DOI:10.1139/v99-106

1196
Reactions of aminoboron compounds with
palladium and platinum complexes
Christopher M. Vogels, Heather L. Wellwood, Kumar Biradha,
Michael J. Zaworotko, and Stephen A. Westcott
Abstract: Reactions of 3-NH2C6H4B(OH)2 (1, APBA) with [MCl4]2– (M = Pd, Pt) give the boronic acid-containing
complexes, MCl2(APBA)2 (M = Pd, 2; M = Pt, 3). Addition of 1 to [PdCl2(COE)]2 (COE = η2-C8H14) ultimately led to
PdCl2(APBA)2 (2). The pinacol derivative PdCl2(APBpin)2 (5, pin = O2C2Me4) was characterized by an X-ray
diffraction study. Crystals of 5 were monoclinic, a = 13.836(5), b = 14.937(5), c = 11.287(5) Å, β = 99.042(9)°, Z = 2,
with space group P21/c. Monoalkene complexes PtCl2(COE)(APBA) (8) and PtCl2(COE)(APBpin) (9) were generated
from the addition of APBA and APBpin, respectively, to [PtCl2(COE)]2. Reactions of 2-NMe2CH2C6H4B(OH)2
(10) with palladium complex [PdCl2(COE)]2 proceed via selective B—C bond cleavage to give the cyclopalladated
dimer [PdCl(2-NMe2CH2C6H4)]2 as the major amine-containing product. Likewise, reactions with borinic esters
H2NCH2CH2OBR2 (R = Bu, 14; R = Ph, 15) give products derived from cleavage of the B—O bond. The unique
palladium complex PdCl2[3-NC5H4B(OH)2]2 (19) was prepared by addition of (3-NC5H4BEt2)4 (18) to [PdCl2(COE)]2
in wet methylene chloride, where adventitious water was used to convert the organoborane product into the
corresponding boronic acid moiety.
Key words: aminoboronic acids, platinum, palladium, cyclometallation.
Résumé : Le 3-NH2C6H4B(OH)2 (1, APBA) réagit avec les ions [MCl4]2– (M = Pd, Pt) pour donner des complexes
contenant de l’acide boronique, MCl2(APBA)2 (M = Pd, 2; M = Pt, 3). L’addition de 1 au [PdCl2(COE)]2 (COE =
η2-C8H14) conduit finalement au PdCl2(APBA)2 (2). Le dérivé du pinacol, PdCl2(APBpin)2 (5, pin = O2C2Me4) a été
caractérisé par une étude de diffraction des rayons X. Les cristaux du produit 5 sont monocliniques, groupe d’espace
P21/c, avec a = 13,836(5), b = 14,937(5) et c = 11,287(5) Å, β = 99,042(9)° et Z = 2. On a généré des complexes
monoalcéniques, PtCl2(COE)(APBA) (8) et PtCl2(COE)(APBpin) (9), par addition respectivement de APBA et de
APBpin sur le [PtCl2(COE)]2. Les réactions du 2-NMe2CH2C6H4B(OH)2 (10) avec le complexe de palladium
[PdCl2(COE)]2
se font avec un clivage sélectif de la liaison B—C et la formation du dimère cyclopalladié
[PdCl(2-NMe2CH2C6H4)]2 comme principal produit contenant de l’amine. De la même manière, les réactions avec des
esters de l’acide boronique, H2NCH2CH2OBR2 (R = Bu, 14; R = Ph, 15), conduisent à la formation de produits dérivés
du clivage de la liaison B—O. On a préparé le complexe de palladium unique, PdCl2[3-NC5H4B(OH)2]2 (19) par
addition de (3-NC5H4BEt2)4 (18) sur du [PdCl2(COE)]2 dans du chlorure de méthylène humide dont l’eau accidentelle
est utilisée sert à transformer le produit organoborane en portion acide boronique correspondante.
Mots clés : acides aminoboroniques, platine, palladium, cyclométallation.
[Traduit par la Rédaction] Vogels et al. 1207
Introduction
(6), porphyrins (7), and amino acids (8). Interestingly,
boronic acids have been found to facilitate the transport of
various ribonucleosides in and out of liposomes (9). Recent
interest in compounds containing boronic acid groups arises
from the ability of the boron atom to coordinate (via an
empty p-orbital) with certain atoms, such as nitrogen and
oxygen, of biomolecules. As a result, compounds containing
boronic acids are able to act as selective targets for specific
The bioinorganic chemistry of compounds containing
boronic acid groups, B(OH)2, is an area of growing interest
and has recently expanded to include boron-containing pu-
rine nucleosides (1), psuedocryptands (2) (which mimic the
naturally occurring antibiotics boromycin and aplasmomycin),
steroids (3), calixarenes (4), carbohydrates (5), fatty acids
Received October 28, 1998.
C.M. Vogels, H.L. Wellwood, and S.A. Westcott.1 Department of Chemistry, Mount Allison University, Sackville, NB E4L 1G8,
Canada.
K. Biradha and M.J. Zaworotko.2 Department of Chemistry, St. Mary’s University, Halifax, NS B3H 3C3, Canada.
1Author to whom correspondence may be addressed. Telephone: (506) 364-2372. Fax: (506) 364-2313. e-mail: swestcott@mta.ca
2Current address: Department of Chemistry, University of Winnipeg, Winnipeg, MB R3B 2E9, Canada.
Can. J. Chem. 77: 1196–1207 (1999)
© 1999 NRC Canada

Vogels et al.
1197
binding sites. For example, aromatic boronic acids have
been shown to inhibit the serine proteases chymotrypsin and
subtilisin (10). Serine proteases are a diverse group of
proteolytic enzymes whose physiological functions include
digestion of proteins, blood clotting, and cell lysis in the im-
mune response. The crystal structure of subtilisin complexed
with either phenylboronic acid or phenylethaneboronic acid
(11) shows that the boron moiety exists as a tetrahedral
adduct with the active hydroxyl site of the serine protease.
Work by Matteson et al. (12d) has shown that (R)-
acetamido-2-phenylethaneboronic acid, a boron analogue of
N-acetyl-phenylalanine, also acts as an effective and revers-
ible inhibitor of serine proteases. Indeed, this compound is
several orders of magnitude more effective than the corre-
sponding aromatic boronic acids for the inhibition of
chymotrypsin even in the micromolar concentration range.
Since this discovery, much effort has focused on the synthe-
sis of related boron-containing amino acid and peptide de-
rivatives for possible applications as enzyme inhibitors (12,
13).
The observed biochemical activities and ability of boronic
acids to facilitate the transport of molecules intracellularly
prompted us to investigate the use of aminoboron com-
pounds as ligands for biologically active transition metals.
For instance, while both cis and trans amine complexes of
platinum display anticancer properties, the overall efficacy
of these chemotherapeutic compounds is limited by their nu-
merous toxicities and poor cellular-uptake rates (arising
from low solubility in water). As a result, a great deal of re-
search has focused on improving aminoplatinum-based
drugs for use in cancer therapy (14). With this in mind, we
have begun to examine the possibility of generating new
complexes of platinum and palladium containing
aminoboron appendages. The results of our initial investiga-
tions are described herein.
to an isopropanol–water suspension (11:16 mL ratio by vol-
ume) of palladium chloride (500 mg, 2.82 mmol). After 1 h
of stirring, cyclooctene (3 mL, 23.03 mmol) and a catalytic
amount of tin(II) chloride (27 mg, 0.14 mmol) were added.
After 20 h, solvent was removed under vacuum to afford a
dark orange solid. [PdCl2(COE)]2 was extracted with methy-
lene chloride, filtered to remove impurities, and collected
following the removal of methylene chloride under vacuum.
Yield: 620 mg (77%) of an orange solid; mp 164°C (decom-
1
position). NMR spectroscopic data (in CDCl3): H δ: 6.20
(m, 4H, ϭCHR), 2.33 (s, 8H), 1.67 (s, 8H), 1.40 (s, 8H);
13C{1H} δ: 109.5 (br, CHR), 29.1, 28.8, 26.3.
PdCl2(APBA)2 (2)
Method A
Sodium chloride (36 mg, 0.62 mmol) was added in small
portions as a solid to a 25 mL methanol suspension of palla-
dium chloride (50 mg, 0.28 mmol) to generate the methanol
soluble species, sodium tetrachloropalladate. After 1 h of
stirring, a 5 mL methanol solution of 3-aminophenylboronic
acid (87 mg, 0.56 mmol) was added dropwise to the clear
amber solution. Within 2 h, an isomeric mixture of cis and
trans 2 precipitated and was collected by filtration and
washed with methanol (3 × 5 mL) and methylene chloride
(3 × 5 mL). Yield: 110 mg (81%) of a yellow solid.
Method B
In another reaction, 3-aminophenylboronic acid (91 mg,
0.58 mmol) was added in small portions as a solid to a
stirred 25 mL methylene chloride solution of [PdCl2(COE)]2
(75 mg, 0.13 mmol). After 20 h, the reaction was filtered
and a yellow solid was collected. The solid was washed
three times with 10 mL portions of hexane and methylene
chloride. Complex 2 was crystallized from a tetra-
hydrofuran–hexane solution. Yield: 50 mg (39%) of a yel-
low solid; mp 276°C (decomposition). IR (nujol): 3233 (m),
3125 (m), 2946 (s), 1582 (m), 1462 (m), 1377 (m). NMR
spectroscopic data (in DMSO-d6): 1H δ: 8.14 (s, 4H,
B(OH)2), 7.63 (s, 2H), 7.33 (ov, 4H), 6.86 (s, 2H), 6.07 (s,
4H, NH2); 11B{1H} δ: 35.1 (br); 13C{1H} δ: 147.6, 135.2 (br,
C-B), 130.6, 125.0, 122.4, 120.4. Anal. calcd. for
PdCl2C12H16N2B2O4: C 31.94, H 3.58, N 6.21; found: C
32.04, H 3.66, N 5.90.
Experimental
General procedures
Reagents and solvents used were obtained from Aldrich
Chemicals. Palladium chloride and potassium tetrachloro-
platinate were obtained from Strem. NMR spectra were re-
1
corded on a JEOL JNM-GSX270 FT NMR spectrometer. H
NMR chemical shifts are reported in ppm and referenced to
residual protons in deuterated solvent at 270.05 MHz.
11B{1H} NMR chemical shifts are referenced to external
F3B·OEt2 at 86.55 MHz. 13C{1H} NMR chemical shifts are
referenced to solvent carbon resonances as internal standards
at 67.80 MHz. Multiplicities are reported as (s) singlet, (d)
doublet, (t) triplet, (q) quartet, (quint) quintet, (m) multiplet,
(br) broad, and (ov) overlapping. Infrared spectra were ob-
tained using a Mattson Polaris FT-IR spectrometer and re-
ported 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, Ariz.).
PtCl2(APBA)2 (3)
A 25 mL aqueous solution of 3-aminophenylboronic acid
(224 mg, 1.45 mmol) was added dropwise to a 25 mL water
solution of potassium tetrachloroplatinate (300 mg,
0.72 mmol). Within 4 h, the solution became yellow, and a
fine brown–yellow precipitate was collected by filtration and
discarded. The clear yellow filtrate was chilled to 0°C, and
after 24 h, 3 precipitated and was collected by filtration.
Yield: 230 mg (55%) of a yellow solid; mp 267°C (decom-
position). IR (nujol): 3266 (w), 3186 (w), 2885 (s), 1582
(m), 1461 (s), 1377 (s). NMR spectroscopic data (in ace-
1
tone-d6): H δ: 7.88 (s, 2H), 7.72 (d, JH–H = 5 Hz, 2H), 7.45
µ-[Dichloro(cis-cyclooctene)palladium(II)]
µ-[Dichloro(cis-cyclooctene)palladium(II)], [PdCl2(COE)]2,
was prepared by modification of a known synthesis (15a).
Sodium chloride (363 mg, 6.21 mmol) was added as a solid
(m, 2H), 7.24 (t, JH–H = 5 Hz, 2H), 6.74 (s, 4H, NH2);
11B{1H} δ: 30.9 (br); 13C{1H} δ: 141.5, 136.3 (br, C-B),
132.6,
129.5,
129.4,
124.0.
Anal.
calcd.
for
© 1999 NRC Canada

1198
Can. J. Chem. Vol. 77, 1999
PtCl2C12H16N2B2O4: C 26.69, H 2.99; found: C 26.34, H
2.92.
Reaction of [PdCl2(COE)]2 and 4
A 20 mL methylene chloride solution of 4 (114 mg,
0.52 mmol) was added dropwise to a stirred 50 mL methy-
lene chloride solution of [PdCl2(COE)]2 (150 mg,
0.26 mmol). After 30 min, the clear orange solution became
clear red, at which point methylene chloride was removed
under vacuum to afford complex 7, which was washed with
hexane (3 × 5 mL). Yield: 120 mg (91%) of a red–orange
solid; mp 138°C (decomposition). IR (nujol): 3194 (m),
3123 (m), 2973 (s), 2885 (s), 2842 (s), 1583 (m), 1461 (s),
1364 (s), 1146 (m), 695 (m). NMR spectroscopic data of 7
APBpin (4)
3-Aminophenylboronic acid (250 mg, 1.61 mmol) and
10 g of activated molecular sieves (BDH 4A) were added to
a 25 mL methylene chloride solution of pinacol (190 mg,
1.61 mmol). After 5 days, the sieves were removed by filtra-
tion, and methylene chloride was removed under vacuum to
give 4. Yield: 350 mg (95%) of a light yellow solid; mp
93°C. IR (nujol): 3465 (w), 3375 (w), 3125 (s), 1628 (m),
1578 (m), 1452 (s), 1376 (s), 1145 (m). NMR spectroscopic
1
(in CDCl3): H δ: 7.65 (s, 2H), 7.56 (s, 1H), 7.29 (s, 1H),
1
6.03 (m, 2H, ϭCHR), 5.24 (s, 2H, NH2), 2.31 (br s, 4H),
1.60 (br s, 4H), 1.45 (br s, 4H), 1.34 (s, 12H, BO2C2Me4);
11B{1H} δ: 32.1 (br); 13C{1H} δ: 139.0, 132.8, 131.0 (br, C-
data (in CDCl3): H δ: 7.20 (m, 2H), 7.14 (s, 1H), 6.80 (m,
1H), 3.63 (s, 2H, NH2), 1.31 (s, 12H, BO2C2Me4); 11B{1H}
δ: 31.8 (br); 13C{1H} δ: 145.9, 129.2 (br, C-B), 128.4, 124.9,
121.2, 118.1, 83.7 (BO2C2Me4), 24.9 (BO2C2Me4). Anal.
calcd. for C12H18NBO2: C 65.78, H 8.30, N 6.39; found: C
65.87, H 8.39, N 6.33.
B), 129.1, 127.7, 125.5, 117.3 (br,
CHR), 84.2
(BO2C2Me4), 29.3, 27.8, 26.3, 25.1 (BO2C2Me4). Reactions
gave minor amounts of the diamine complex, which compli-
cated elemental analyses.
PdCl2(APBpin)2 (5)
Reaction of 7 and PPh3
Complex 7 (44 mg, 0.09 mmol) was dissolved in 10 mL
of methylene chloride, and a 10 mL methylene chloride so-
lution of triphenylphosphine (25 mg, 0.09 mmol) was added
dropwise to the clear red solution. Within 1 h, a yellow pre-
cipitate formed and was collected by filtration. Yield: 25 mg
of a yellow solid. Selected NMR data (in CDCl3): 1H δ: 7.70
(m, Ar, 2H), 7.41 (m, Ar, 3H); PdCl2(PPh3)2.
Method A
Complex 2 (250 mg, 0.51 mmol) was added slowly as a
solid to a tetrahydrofuran solution of pinacol (140 mg,
1.20 mmol) and 10 g of activated molecular sieves (BDH
4A). After 3 days, the sieves and unreacted 2 were removed
by filtration, and the filtrate was collected. Complex 5 was
collected following the removal of tetrahydrofuran under
vacuum. Yield: 50 mg (16%) of an orange solid.
PtCl2(COE)(APBA) (8)
To a stirred 50 mL methylene chloride solution of
[PtCl2(COE)]2 (100 mg, 0.13 mmol), 3-aminophenylboronic
acid (41 mg, 0.26 mmol) was added in small portions as a
solid. The cloudy, yellow mixture was filtered after 2 days,
and the clear yellow filtrate was stored under dinitrogen at
0°C. Within 48 h, 8 precipitated and was collected by filtra-
tion. The yellow solid was washed with ether (3 × 10 mL),
hexane (3 × 10 mL), and cold methylene chloride (1 ×
2 mL). Yield: 80 mg (29%) of a yellow solid; mp 169°C. IR
(nujol): 3186 (w), 3116 (w), 2965 (s), 2890 (s), 1584 (m),
1462 (s), 1377 (s), 723 (m). NMR spectroscopic data (in ac-
Method B
To a 50 mL methylene chloride solution of [PdCl2(COE)]2
(200 mg, 0.35 mmol), a 15 mL methylene chloride solution
of 4 (305 mg, 1.39 mmol) was added dropwise. The reaction
was allowed to proceed for 2 h before the solvent was re-
moved under vacuum. Complex 5 was crystallized from a
tetrahydrofuran–hexane solution. Yield: 300 mg (70%) of an
orange solid; mp 152°C (decomposition). IR (nujol): 3187
(w), 3121 (w), 2968 (s), 2891 (s), 1583 (w), 1461 (s), 1377
(s), 1148 (m), 722 (w). NMR spectroscopic data (in CDCl3):
1H δ: 7.67 (s, 4H), 7.57 (s, 2H), 7.32 (s, 2H), 5.06 (br s, 4H,
NH2), 1.33 (s, 24H, BO2C2Me4); 11B{1H} δ: 31.5 (br);
13C{1H} δ: 139.3, 132.7, 130.8 (br, C-B), 129.0, 127.7,
125.5, 84.2 (BO2C2Me4), 25.1 (BO2C2Me4). Anal. calcd. for
PdCl2C24H36N2B2O4: C 46.82, H 5.91, N 4.55; found: C
46.46, H 5.89, N 4.48.
1
etone-d6): H δ: 7.95 (s, 1H), 7.77 (s, 1H), 7.54 (m, 2H),
5.95 (s, JH–Pt = 27 Hz, 2H, ϭCHR), 2.46 (s, 4H), 2.14 (s,
4H), 1.81 (s, 4H); 11B{1H} δ: 29.6 (br); 13C{1H} δ: 146.9,
136.4 (br, C-B), 133.6, 129.3, 128.9, 126.4, 93.3 (s, JC–Pt
80 Hz, CHR), 28.4, 26.8, 26.1.
=
PtCl2(COE)(APBpin) (9)
PtCl2(APBpin)2 (6)
To a 50 mL methylene chloride solution of [PtCl2(COE)]2
(145 mg, 0.19 mmol), a 10 mL methylene chloride solution
of 4 (89 mg, 0.41 mmol) was added dropwise. After 5 h,
methylene chloride was removed under vacuum to afford a
yellow solid. Complex 9 was crystallized from a methylene
chloride – hexane solution. Yield: 150 mg (66%) of a yellow
powder; mp 236°C (decomposition). IR (nujol): 3116 (w),
2935 (s), 1578 (w), 1461 (s), 1377 (s), 1145 (m), 726 (m).
NMR spectroscopic data (in CDCl3): 1H δ: 7.70 (s, 2H), 7.61
Complex 3 (360 mg, 0.63 mmol) and 10 g of activated
molecular sieves (BDH 4A) were added to a tetrahydrofuran
solution of pinacol (163 mg, 1.34 mmol). The mixture was
allowed to stand for 3 days before the sieves and unreacted
3 were removed by filtration. Complex 6 was isolated fol-
lowing removal of solvent under vacuum. Yield: 40 mg
(9%) of a yellow solid; mp 224°C. IR (nujol): 1591 (m),
1400 (m), 1359 (m), 1332 (w), 1145 (m), 853 (w). NMR
1
spectroscopic data (in DMSO-d6): H δ: 7.63 (s, 2H), 7.49
(m, 4H), 7.30 (m, 4H), 1.36 (s, 24H), 11B{1H} δ: 32.6 (br);
13C{1H} δ: 148.0, 141 (br, C-B), 128.3, 121.8, 120.1, 116.8,
67.0, 21.7. Anal. calcd. for PtCl2C24H36N2B2O4: C 40.93, H
5.16, N 3.98; found: C 40.63, H 5.31, N 4.02.
(s, 1H), 7.36 (s, 1H), 5.91 (br s, 2H, ϭCHR), 5.35 (s, JH–Pt
=
32 Hz, 2H, NH2), 2.36 (br s, 2H), 2.25 (br s, 2H), 1.74 (br s,
2H), 1.41 (br s, 6H), 1.34 (s, 12H, BO2Me4); 11B{1H} δ: 32.2
(br); 13C{1H} δ: 139.4, 131.7, 131.0 (br, C-B), 129.2, 126.7,
© 1999 NRC Canada

Vogels et al.
1199
124.1, 93.1 (JC–Pt = 164 Hz, CHR), 84.3 (BO2C2Me4),
29.3, 28.2, 26.3, 25.1 (BO2C2Me4). Anal. calcd. for
PtCl2C20H32NBO2: C 40.35, H 5.43, N 2.35; found: C 41.08,
H 5.68, N 2.46.
activated molecular sieves (BDH 4A) were added to the
mixture to facilitate the formation of 11. The reaction was
allowed to stand for 5 days at which point the sieves and
unreacted 10 were removed by filtration. Compound 11 was
isolated following removal of methylene chloride under vac-
uum. Yield: 0.52 g (72%) of an off-white solid; mp 75°C. IR
(nujol): 3150 (s), 1476 (w), 1348 (m), 1151 (s), 1107 (s),
2-NMe2CH2C6H4B(OH)2 (10)
Compound 10 was prepared by modification of a known
procedure (16). To a 20 mL ether solution of N,N-
dimethylbenzylamine (10.0 g, 74 mmol), a 10.0 M solution
of n-butyllithium in hexanes (8.2 mL, 82 mmol) was added
dropwise under an atmosphere of dinitrogen. The lithiation
of N,N-dimethylbenzylamine was allowed to proceed at
room temperature for 18 h. Trimethylborate (10.0 mL,
88 mmol) was added at 0 oC, and the reaction mixture was
allowed to warm to room temperature. After 4 h, 10 mL of
water was added and the aqueous phase separated. The addi-
tion of 20 mL of isopropanol and subsequent cooling of the
1
1043 (s), 748 (m). NMR spectroscopic data (in CDCl3): H
δ: 7.55 (d, JH–H = 5 Hz, 1H), 7.19 (app. quint, JH–H = 8 Hz,
2H), 7.01 (d, JH–H = 8 Hz, 1H), 3.86 (s, 2H, Ar-CH2-N),
2.57 (s, 6H, NMe2), 1.31 (s, 12 H, BO2C2Me4); 11B{1H} δ:
15.3 (br); 13C{1H} δ: 143.9 (br, C-B), 139.8, 131.6, 127.6,
127.5, 123.1, 80.5 (BO2C2Me4), 65.6 (Ar-CH2-N), 45.9
(NMe2), 26.8 (BO2C2Me4). Anal. calcd. for C15H24NBO2: C
68.97, H 9.28, N 5.36; found: C 68.80, H 9.60, N 5.38.
Reaction of Na2PdCl4 + 11
o
mixture to 0 C resulted in the precipitation of lithium bo-
A fresh solution of sodium tetrachloropalladate was gen-
erated by the addition of sodium chloride (22 mg,
0.37 mmol) to a stirred 15 mL methanol suspension of palla-
dium chloride (30 mg, 0.17 mmol). After 1 h of stirring, a
10 mL methanol solution of 11 (88 mg, 0.338 mmol) was
added dropwise. After 3 h, a yellow precipitate had formed
and was collected by filtration. Yield: 35 mg (75%) of a yel-
rate, which was removed by filtration. Complex 10 was iso-
lated upon removal of water under vacuum. Yield: 3.25 g
(25%) of an off-white powder. NMR spectroscopic data (in
1
D2O): H δ: 7.41 (m, 1H), 7.20 (m, 2H), 7.08 (m, 1H), 3.81
(s, 2H, Ar-CH2-N), 2.34 (s, 6H, NMe2); 11B{1H} δ: 8.9 (br);
13C{1H} δ: 150 (br, C-B), 145.5, 135.0, 132.9, 132.4, 128.6,
69.6 (Ar-CH2-N), 49.4 (NMe2).
1
low solid. NMR spectroscopic data (in CDCl3): H δ: 7.16
(m, 1H), 6.97 (m, 2H), 6.87 (m, 4H), 3.93 (s, 4H, CH2N(Me)2),
2.86 (s, 12H, CH2N(Me)2); [PdCl(2-NMe2CH2C6H4)]2.
Reaction of Na2PdCl4 + 10
A fresh solution of sodium tetrachloropalladate was pre-
pared by the addition of sodium chloride (36 mg,
0.62 mmol) to a 30 mL methanol suspension of palladium
chloride (50 mg, 0.28 mmol). After 1 h of stirring, a 10 mL
methanol solution of 10 (111 mg, 0.62 mmol) was added
dropwise. The yellow precipitate that formed over 1 h was
collected by filtration and washed with water (3 × 5 mL).
Selected NMR data (in CDCl3): 1H δ: 7.16 (m, 2H), 6.97 (m,
Reaction of [PdCl2(COE)]2 + 11
A 10 mL methylene chloride solution of 11 (182 mg,
0.70 mmol) was added dropwise to a stirred 25 mL methy-
lene chloride solution of [PdCl2(COE)]2 (100 mg,
0.17 mmol). After 6 h, solvent was removed under vacuum
to yield an orange–brown oil. Selected NMR data (in
(m, 4H), 3.93 (s,
2H), 6.87
4H, Ar-CH2-N), 2.86 (s, 12H,
1
CDCl3): H δ: 7.16 (m, 2H), 6.97 (m, 2H), 6.87 (m, 4H),
NMe2); [PdCl(2-NMe2CH2C6H4)]2.
CH2N(Me)2),
(s, 4H,
3.93
2.86 (s, 12H, CH2N(Me)2)
[PdCl(2-NMe2CH2C6H4)]2; 9.19 (br), 8.06 (m), 7.92 (m),
7.60 (m), 7.42 (m), 4.72 (m), 2.98 (s) [2-
HNMe2CH2C6H4Bpin]2[PdCl4]; 1.38 (s) (Bpin)2O. 11B{1H}
δ: 31.9 (br, [2-HNMe2CH2C6H4Bpin]2[PdCl4]), 23.1 (br,
(Bpin)2O).
Reaction of [PtCl2(COE)]2 + 10
To a stirred 35 mL methylene chloride solution of
[PtCl2(COE)]2 (150 mg, 0.20 mmol), compound 10 (75 mg,
0.42 mmol) was added in small portions as a solid. After
20 h, the reaction was filtered and methylene chloride re-
moved under vacuum. Complex 13 was extracted from the
resulting brown–orange solid with hexane (10 × 10 mL). At-
tempts at isolating compound 13 were complicated by the
ubiquitous presence of a minor amount of an unidentified
compound. IR (nujol): 3060 (w), 3001 (w), 2927 (s), 2854
(s), 1586 (w), 1471 (m), 717 (s), 651 (s). Selected NMR
PtCl2(COE)(2-Me2NCH2C6H4Bpin) (12)
The addition of a 0.5 mL deuterated chloroform solution
of 11 (24 mg, 0.09 mmol) to a 0.5 mL deuterated chloroform
solution of [PtCl2(COE)]2 (35 mg, 0.05 mmol) was per-
formed under an atmosphere of dinitrogen. The reaction was
allowed to proceed for 4 h before characterization by NMR
spectroscopy was performed. IR (CHCl3): 2981 (m), 2929
(s), 2854 (m), 1600 (w), 1471 (m), 1346 (s), 1145 (m), 906
(s), 745 (s), 651 (s). NMR spectroscopic data (in CDCl3): 1H
δ: 8.87 (s, 1H), 7.89 (s, 1H), 7.58 (s, 1H), 7.39 (s, 1H), 5.35
(ov m, JH–Pt = 78 Hz, 2H, =CHR), 4.68 (s, 2H, Ar-CH2-N),
2.80 (s, 6H, NMe2), 2.53 (br, 2H), 2.23 (br, 2H), 1.81 (br,
2H), 1.40 (br, 6H), 1.35 (s, 12H, BO2C2Me4); 11B{1H} δ:
35.1 (br); 13C{1H} δ: 139.9, 136.6, 133.0, 131.0, 129.0 (br,
1
data (crude) for 13 (in CDCl3): H δ: 7.03 (m, 3H), 6.57 (s,
JH–Pt = 43 Hz, 1H), 4.84 (s, JH–Pt = 68 Hz, 2H, ϭCHR), 4.05
(s, JH–Pt = 38 Hz, 2H, Ar-CH2-N), 2.99 (s, JH–Pt = 32 Hz,
6H, NMe2), 2.73 (br s, 4H), 2.28 (br s, 4H), 1.81 (br s, 4H);
13C{1H} δ: 147.3, 133.1, 127.4 (JC–Pt = 43 Hz, C-Pt), 126.2,
124.9, 122.1, 87.7 (s, JC–Pt = 191 Hz, CHR), 74.8 (s, JC–Pt
= 44 Hz, Ar-CH2-N), 51.8 (NMe2), 30.0, 28.5, 26.5.
2-NMe2CH2C6H4Bpin (11)
A 10 mL methylene chloride solution of pinacol (330 mg,
2.79 mmol) was added dropwise to a 35 mL methylene chlo-
ride suspension of 10 (600 mg, 3.35 mmol). Ten grams of
C-B), 128.1, 91.4 (s, JC–Pt = 161 Hz,
CHR), 84.1
(BO2C2Me4), 64.8 (Ar-CH2-N), 52.1 (NMe2), 29.2, 28.1,
26.3, 25.1 (BO2C2Me4).
© 1999 NRC Canada

1200
Can. J. Chem. Vol. 77, 1999
1
Selected NMR data (in CDCl3): H δ: 4.12, (s), 3.24 (br),
Reaction of Na2PdCl4 + 14
2.84 (s), 1.31 (s), 0.89 (s); 11B{1H} δ: 60.5 (br). The product
decomposed (1 h) in solution to give palladium metal.
Sodium chloride (18 mg, 0.31 mmol) was added to a
stirred 15 mL methanol suspension of palladium chloride
(25 mg, 0.14 mmol) to produce sodium tetrachloropalladate.
A 5 mL methanol solution of dibutylborinic acid, ethano-
lamine ester (57 mg, 0.31 mmol) was added dropwise to the
solution, and the reaction was allowed to proceed for 45 h.
The product was obtained upon removal of methanol under
Reaction of [PtCl2(COE)]2 + 14
Under an atmosphere of dinitrogen using an MBraun
glovebox, a 0.5 mL deuterated chloroform solution of
dibutylborinic acid, ethanolamine ester (12 mg, 0.07 mmol)
was added dropwise to a 0.5 mL deuterated chloroform solu-
tion of [PtCl2(COE)]2 (25 mg, 0.03 mmol). The reaction was
allowed to proceed for 3 h before the product was character-
ized by IR and NMR spectroscopy. IR (CHCl3): 3319 (w),
2930 (m), 1571 (w), 1468 (w), 1330 (w), 901 (s), 726 (s),
651 (s). Selected NMR data for PtCl2(COE)(NH2CH2CH2OBBu2)
1
vacuum. NMR spectroscopic data (in D2O): H δ: 3.76 (m,
4H),
3.44
(br,
4H,
NH2),
2.68
(m,
4H);
PdCl2(NH2CH2CH2OH)2.
Reaction of K2PtCl4 + 14
Dibutylborinic acid, ethanolamine ester (29 mg,
0.16 mmol) was added as a solid to a stirred 20 mL aqueous
solution of potassium tetrachloroplatinate (30 mg,
0.07 mmol). The reaction was allowed to proceed for 18 h.
A yellow solid was isolated following the removal of water
1
16 (in CDCl3): H δ: 5.61 (br, 2H, CϭCHR), 5.29 (br, JH–Pt
= 68 Hz, 2H, NH2), 4.10, (br), 3.22 (br), 2.38 (br), 2.27 (br)
2.12, (br) 1.78, (br) 1.47 (br), 1.30 (br), 0.87 (br); 11B{1H}
δ: 56.1 (br). The product decomposed (1 h) in solution to
give platinum metal.
1
under vacuum. Selected NMR data (in D2O): H δ: 3.79 (m,
4H),
3.08
(m,
4H),
2.82
(br,
4H,
NH2),
PtCl2(NH2CH2CH2OH)2; 11B{1H} δ: 19.9 (s, B(OH)3).
Reaction of [PtCl2(COE)]2 + 15
Under an atmosphere of dinitrogen using an MBraun
glovebox, a 0.5 mL deuterated chloroform solution of
diphenylborinic acid, ethanolamine ester (15 mg,
0.07 mmol) was added dropwise to a 0.5 mL deuterated
chloroform solution of [PtCl2(COE)]2 (25 mg, 0.03 mmol).
The reaction was allowed to proceed for 3 h before the clear
yellow solution was characterized by NMR and IR spectros-
copy. NMR data for PtCl2(COE)(NH2CH2CH2OBPh2) (17)
Reaction of Na2PdCl4 + 15
Sodium chloride (22 mg, 0.38 mmol) was added as a solid
to a stirred 15 mL methanol suspension of palladium chlo-
ride (30 mg, 0.17 mmol) to produce the methanol soluble
species, sodium tetrachloropalladate. After 1 h of stirring, a
10 mL methanol solution of diphenylborinic acid,
ethanolamine ester (80 mg, 0.36 mmol) was added dropwise,
and the clear amber solution became black immediately.
Methanol was removed under vacuum, and the aqueous and
organic soluble species were characterized by NMR spec-
troscopy. For the water soluble phase, NMR data (in D2O):
1H δ: 3.76 (m, 4H), 3.44 (m, 4H), 2.68 (m, 4H);
PdCl2(NH2CH2CH2OH)2. 11B{1H} δ: 19.9 (s, B(OH)3). For
1
(in CDCl3): H δ: 7.63 (m, 4H), 7.43 (m, 6H), 5.62 (br s,
2H, CϭCHR), 5.30 (br s, JH–Pt = 62 Hz, 2H, NH2), 4.17 (s,
2H), 3.33 (s, 2H), 2.36 (br, 4H), 2.14 (br, 4H), 1.76 (br s,
4H); 11B{1H} δ: 47.8 (br); 13C{1H} δ: 136.6 (br, C-B),
134.4, 131.7, 130.5, 130.1, 127.7, 93.7 (s, JC–Pt = 165 Hz,
C CHR), 63.5, 46.6, 29.4, 28.0, 26.3. IR (CHCl3): 2929
(w), 2853 (w), 1576 (w), 1470 (w), 1438 (w), 1322 (w), 905
(s), 727 (s), 851 (s).
1
the organic soluble phase, NMR data (in CDCl3): H δ: 8.22
(m), 7.57 (m), 7.45 (ov); 11B{1H} δ: 29.6 (br, PhB(OH)2).
Reaction of K2PtCl4 + 15
PdCl2(3-NC5H4B(OH)2)2 (19)
Diphenylborinic acid, ethanolamine ester (29 mg,
0.13 mmol) was added in small portions as a solid to a
stirred 20 mL aqueous solution of potassium tetrachloro-
platinate (25 mg, 0.06 mmol). Water was removed under
vacuum after 10 h, and the aqueous and organic soluble
products were characterized by NMR spectroscopy. NMR
A
10 mL methylene chloride solution of 3-
(diethylboryl)pyridine (102 mg, 0.69 mmol) was added
dropwise to a stirred 30 mL methylene chloride solution of
[PdCl2(COE)]2 (100 mg, 0.17 mmol). After 48 h, an orange
precipitate was collected by filtration and washed with
methylene chloride (3 × 5 mL). Yield: 60 mg (42%) of an
orange solid; mp 234°C. IR (nujol): 3197 (w), 2923 (s),
2856 (s), 1576 (w), 1462 (m), 1377 (m). Selected NMR data
1
data (in D2O): H δ: 3.79 (m, 4H), 3.08 (m, 4H), 2.82 (m,
4H); PtCl2(NH2CH2CH2OH)2. 11B{1H} δ: 19.9 (s, B(OH)3).
1
1
For the organic soluble phase, NMR data (in CDCl3): H δ:
(in acetone-d6): H δ: 9.24 (s, 4H, B(OH)2), 8.94 (m, 2H),
8.22 (m), 7.57 (ov) 7.45 (ov); 11B{1H} δ: 29.6 (br,
8.41 (m, 4H), 7.61 (m, 2H); 11B{1H} δ: 29.2 (br). Solubility
PhB(OH)2).
problems precluded 13C{1H} NMR data collection.
Reaction of [PdCl2(COE)]2 + 14
PdCl2(3-NC5H4Bpin)2 (20)
Under an atmosphere of dinitrogen using an MBraun
glovebox, a 2 mL THF solution of dibutylborinic acid,
ethanolamine ester (39 mg, 0.21 mmol) was added dropwise
to a stirred 5 mL THF solution of [PdCl2(COE)]2 (30 mg,
0.05 mmol). The reaction was allowed to proceed for 1.5 h
before solvent was removed under vacuum. The resulting
yellow solid was washed with hexane (2 × 3 mL) to remove
cyclooctene. The solid was dried under vacuum, and the
product was extracted with 1 mL of deuterated chloroform.
To a 40 mL methylene chloride suspension of 19 (134 mg,
0.32 mmol), pinacol (45 mg, 0.38 mmol) and 10 g of acti-
vated molecular sieves (BDH 4A) were added. The mixture
was allowed to stand for 7 days before the sieves and
unreacted 19 were removed by filtration. The filtrate was
collected, and methylene chloride removed under vacuum to
afford a yellow solid, which was washed with hexane (3 ×
10 mL) to remove excess pinacol. The product was crystal-
lized from a CH2Cl2–hexane solution. Yield: 160 mg (86%)
© 1999 NRC Canada

Vogels et al.
1201
Table 1. Crystallographic data collection parameters for trans-
PdCl2(APBpin)2 (5).
tances and angles, final atomic coordinates, and anisotropic
displacement parameters have been deposited as supporting
material.5
Complex
5
Formula
C24H36B2Cl2N2O4Pd·4C4H8O
fw
903.88
Monoclinic
P21/c
13.836(5)
14.937(5)
11.287(5)
99.042(9)
2304(2)
2
1.303
0.25 × 0.20 × 0.20
203(2)
MoKα (λ = 0.71073)
0.567
25
ω
4023
3893
258
0.464/–0.532
0.0449
0.1161
Results and discussion
Crystal system
Space group
a, Å
b, Å
c, Å
β, deg
V, Å3
1. Reactions with 3-aminophenylboronic acid
The synthesis of amines containing boronic acid groups is
often a complicated procedure requiring several complex or-
ganic transformations (12d). As a result, the range of com-
pounds containing both an amine and a boronic acid
functionality is surprisingly small. Indeed, the use of amino-
boronic acids as ligands for transition metals has not yet
been explored. As part of our initial investigation into this
area, we set out to prepare palladium and platinum com-
plexes containing commercially available 3-aminophenylboronic
acid (3-NH2C6H4B(OH)2, APBA, 1). We have found that ad-
dition of 1 to aqueous solutions of [MCl4]2– (M = Pd, Pt)
gives the corresponding boronic acid-containing complexes
MCl2(APBA)2 (M = Pd, 2; M = Pt, 3). These complexes are
insoluble in most common organic solvents, and attempts to
dissolve them in coordinating solvents such as DMSO led to
decomposition where the solvent was clearly displacing the
weakly bound aminoboron group. Although aniline deriva-
tives are known to coordinate to palladium and platinum
(17), the addition of an electron-withdrawing boronic acid
group to the phenyl moiety, not surprisingly, severely re-
duces the nucleophilicity of the already weak aniline group
(pKa = 4.6 for conjugate acid, anilinium ion). Attempts to
generate diaqua complexes [M(OH2)2(APBA)2](NO3)2 by
addition of AgNO3 to 2 and 3 in water gave rapid degrada-
tion to the corresponding metals along with the formation of
boric acid.
Compounds containing boronic acids are extremely diffi-
cult to characterize in terms of elemental composition, ow-
ing to the ease with which they partially dehydrate to the
corresponding trimeric or oligomeric anhydrides (12a). To
alleviate this complication, as well as to increase solubilities
in organic solvents, we replaced the hydroxyl groups on 1
with the more electron donating pinacol-derived group (pin
= O2C2Me4) (18) to give 3-NH2C6H4Bpin (4, APBpin). Un-
fortunately, substitution reactions in water involving 4 and
the tetrachloro salts suffered from competing cleavage of the
pinacol groups to give complicated mixtures of products.
However, transesterification of the boronic acid derivatives
2 and 3 with pinacol ultimately generated the corresponding
complexes MCl2(APBpin)2 (M = Pd, 5; M = Pt, 6) in low
yields (9–16%).
Z
ρcalcd, g cm–3
Crystal size, mm
Temperature, K
Radiation
µ, mm–1
Max 2θ, deg
Data collection method
Total unique reflections
Total observed reflectionsa
No. of variables
Max. res. density/hole, e Å–3
Rb
Rw
GoFc
aIo > 3σ(Io).
1.071
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
.
.
of a yellow solid, mp 276°C. IR (nujol): 2949 (s), 2859 (s),
1603 (w), 1461 (m), 1376 (m). NMR spectroscopic data (in
CDCl3): H δ: 9.13 (s, 2H), 8.85 (d, JH–H = 5 Hz, 2H), 8.12
(d, JH–H = 8 Hz, 2H), 7.33 (t, JH–H = 8 Hz, 2H), 1.35 (s,
24H, BO2Me4); 11B{1H} δ: 31.0 (br); 13C{1H} δ: 158.7,
154.7, 144.5, 126.5 (br, C-B), 124.5, 84.9 (BO2C2Me4), 24.9
(BO2C2Me4). Anal. calcd. for PdCl2C22H32N2B2O4·H2O: C
43.63, H 5.65, N 4.62; found: C 43.61, H 5.39, N 4.89.
1
X-ray crystallographic data for 5
Crystals of 5 suitable for X-ray diffraction studies were
obtained by recrystallization from a THF–hexane mixture at
5°C. A summary of the crystal data and parameters for data
collection is given in Table 1. Data were collected at 203 K
on a Siemens SMART/CCD diffractometer equipped with an
LT-II low-temperature device. Diffracted data were corrected
for absorption using the SADABS3 program. SHELXTL was
used for structure solution, and refinement was based on F2.4
All non-hydrogen atoms were refined anisotropically. Hy-
drogen atoms were fixed at calculated positions. Selected
bond distances and angles are given in Table 2 and final
atomic coordinates in Table 3. Complete tables of bond dis-
The molecular structure of diamine complex 5, which
crystallizes with four molecules of tetrahydrofuran per com-
plex, is shown in Fig. 1, and selected bond distances and an-
gles provided in Table 2. The aminoboron ligands lie in a
trans configuration with Pd—N bond distances of
2.047(3) Å being similar to that observed for the analogous
3 G.M. Sheldrick. SADABS Univ. Gottingen. 1996.
4 G.M. Sheldrick. SHELXTL Release 5.03. Siemens Analytical X-ray Instruments Inc., Madison, Wis. 1994.
5 A complete set of data may be purchased from: The Depository of Unpublished Data, Document Delivery, CISTI, National Research Coun-
cil Canada, Ottawa, Canada, K1A 0S2. Tables of coordinates, bond distances and angles, and alternative views of 5 have also been depos-
ited with the Cambridge Crystallographic Data Centre and can be obtained on request from: The Director, Cambridge Crystallographic Data
Centre, University Chemical Laboratory, 12 Union Road, Cambridge, CB2 1EZ, U.K.
© 1999 NRC Canada

1202
Can. J. Chem. Vol. 77, 1999
Table 2. Selected bond distances (Å) and angles (deg) for trans-
PdCl2(3-NH2C6H4Bpin)2 (5).
Table 2 (concluded).
C(12)-C(7)-C(8)
O(2)-C(8)-C(10)
O(2)-C(8)-C(9)
C(10)-C(8)-C(9)
O(2)-C(8)-C(7)
C(10)-C(8)-C(7)
C(9)-C(8)-C(7)
C(1A)-O(1A)-C(4A)
O(1A)-C(1A)-C(2A)
C(1A)-C(2A)-C(3A)
C(2A)-C(3A)-C(4A)
O(1A)-C(4A)-C(3A)
C(4B)-O(1B)-C(1B)
C(2B)-C(1B)-O(1B)
C(1B)-C(2B)-C(3B)
C(4B)-C(3B)-C(2B)
O(1B)-C(4B)-C(3B)
114.2(3)
108.8(3)
107.0(3)
109.8(3)
102.5(3)
115.1(3)
113.0(3)
105.6(3)
108.4(5)
105.5(5)
103.9(4)
105.4(4)
108.4(4)
106.6(4)
105.7(5)
105.7(5)
107.2(4)
Pd(1)—N(1)
2.047(3)
2.047(3)
2.3028(11)
2.3028(11)
1.354(5)
1.481(4)
1.372(5)
1.464(4)
1.438(4)
1.555(5)
1.382(5)
1.394(4)
1.402(5)
1.390(5)
1.390(5)
1.380(5)
1.512(5)
1.514(5)
1.559(5)
1.518(5)
1.527(6)
1.361(6)
1.424(5)
1.453(7)
1.470(7)
1.493(6)
1.409(5)
1.427(5)
1.417(7)
1.458(7)
1.453(7)
180.0
Pd(1)—N(1)#1
Pd(1)—Cl(1)#1
Pd(1)—Cl(1)
O(1)—B(1)
O(1)—C(7)
O(2)—B(1)
O(2)—C(8)
N(1)—C(1)
B(1)—C(3)
C(1)—C(6)
C(1)—C(2)
C(2)—C(3)
C(3)—C(4)
C(4)—C(5)
C(5)—C(6)
C(7)—C(11)
C(7)—C(12)
bonds in trans-PdCl2(NH2CH2Ph)2 (19). The boronate ester
functionality (BO2R2) lies in the plane of the arene ring and
has two short B—O bonds (1.354(5) and 1.372(5) Å). These
results indicate that “dative” bonding is significant for both
the aromatic ring π-electrons and oxygen atoms with boron.
The slight difference in the two B—O bond lengths has been
observed previously in chelate complexes of phenylboronic
acid (20). To the best of our knowledge, this is the first
structurally characterized example of an aminoboronate–
metal complex.
C(7)—C(8)
C(8)—C(10)
C(8)—C(9)
O(1A)—C(1A)
O(1A)—C(4A)
C(1A)—C(2A)
C(2A)—C(3A)
C(3A)—C(4A)
O(1B)—C(4B)
O(1B)—C(1B)
C(1B)—C(2B)
C(2B)—C(3B)
C(3B)—C(4B)
N(1)-Pd(1)-N(1)#1
N(1)-Pd(1)-Cl(1)#1
N(1)#1-Pd(1)-Cl(1)#1
N(1)-Pd(1)-Cl(1)
N(1)#1-Pd(1)-Cl(1)
Cl(1)#1-Pd(1)-Cl(1)
B(1)-O(1)-C(7)
B(1)-O(2)-C(8)
C(1)-N(1)-Pd(1)
O(1)-B(1)-O(2)
O(1)-B(1)-C(3)
O(2)-B(1)-C(3)
C(6)-C(1)-C(2)
C(6)-C(1)-N(1)
C(2)-C(1)-N(1)
C(1)-C(2)-C(3)
C(4)-C(3)-C(2)
C(4)-C(3)-B(1)
C(2)-C(3)-B(1)
C(3)-C(4)-C(5)
C(6)-C(5)-C(4)
C(5)-C(6)-C(1)
O(1)-C(7)-C(11)
O(1)-C(7)-C(12)
C(11)-C(7)-C(12)
O(1)-C(7)-C(8)
C(11)-C(7)-C(8)
To avoid problems arising from reactions carried out in
aqueous solutions, we decided to examine the reactivities of
both APBA and APBpin with PtCl2(COD) (COD = 1,5-
cyclooctadiene) in organic solvents. Unfortunately, no reac-
tion, or decomposition, was observed when this platinum
complex was treated with either aminoboron species at room
or elevated temperatures. We then decided to prepare the
analogous trans amine complexes from the monoalkene
metal compounds [MCl2(COE)]2 (M = Pd, Pt; COE = η2-
C8H14) (Scheme 1), as both cis and trans platinum amine
complexes are known to be biologically active (14). The
starting organometallic dimers, which are soluble in com-
mon organic solvents, were prepared by the addition of cis-
cyclooctene to aqueous solutions of the corresponding metal
tetrachloride salts (15). Diamine complex PdCl2(APBA)2
(2) was obtained in moderate yields (39%) from reactions of
boronic acid 1 with [PdCl2(COE)]2. Interestingly, dropwise
addition of 1 equiv. of pinacol derivative 4 to the palladium
dimer gave rapid formation of the novel air-stable
organometallic complex PdCl2(COE)(APBpin) (7). Attempts
to generate the corresponding boronic acid derivative via
this route afforded equal amounts of disubstituted amine 2
along with starting alkene complex [PdCl2(COE)]2. The dif-
ficulty in generating the boronic acid analogue of 7 presum-
ably arises from the insoluble nature of the amine starting
material in organic solvents. In an attempt to generate a
mixed phosphine-amine complex, we have found that addi-
tion of 1 equiv. of PPh3 to 7, however, afforded
PdCl2(PPh3)2 where the phosphines have displaced both the
weakly bound cyclooctene and aminoboron ligands. Interest-
ingly, subsequent addition of a second equivalent of
90.14(11)
89.86(11)
89.86(11)
90.14(11)
180.0
107.1(3)
107.0(3)
114.1(2)
113.8(3)
124.1(3)
122.1(4)
120.0(3)
120.0(3)
120.1(3)
121.0(3)
117.9(3)
121.7(3)
120.4(3)
120.8(4)
120.7(4)
119.5(3)
108.5(3)
106.1(3)
110.7(3)
102.0(3)
114.4(3)
© 1999 NRC Canada

Vogels et al.
1203
Table 3. Atomic coordinates (× 104) and equivalent isotropic displacement coefficients for trans-
PdCl2(3-NH2C6H4Bpin)2 (5).
x
y
z
U(eq)
Pd(1)
Cl(1)
O(1)
O(2)
N(1)
B(1)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
O(1A)
C(1A)
C(2A)
C(3A)
C(4A)
O(1B)
C(1B)
C(2B)
C(3B)
C(4B)
5000
3525(1)
724(2)
0
5000
32(1)
47(1)
43(1)
47(1)
38(1)
38(1)
34(1)
35(1)
35(1)
44(1)
54(1)
43(1)
44(1)
44(1)
66(1)
63(1)
63(1)
67(1)
69(1)
113(2)
112(2)
81(2)
73(1)
80(1)
88(2)
136(3)
124(3)
86(2)
79(1)
3735(1)
6450(2)
8228(2)
6120(3)
7397(4)
6951(3)
6762(3)
7572(3)
8540(3)
8715(4)
7929(3)
6730(3)
7693(4)
7148(4)
8673(4)
5588(4)
7197(4)
9912(3)
10 608(7)
11 042(5)
10 246(5)
9352(4)
7460(3)
7730(5)
8994(5)
9387(5)
8444(5)
872(2)
162(2)
910(2)
429(3)
523(2)
617(2)
259(2)
–228(3)
–333(3)
44(2)
1039(3)
308(3)
–581(3)
585(3)
941(3)
1989(3)
2556(2)
1812(4)
1562(5)
2019(4)
2482(3)
2266(2)
2229(4)
2299(6)
2780(5)
2653(4)
663(2)
4503(3)
1228(3)
3934(2)
2919(2)
2351(3)
2827(3)
3838(3)
4392(3)
–271(3)
–359(3)
–749(3)
–934(3)
–998(3)
–266(3)
3468(2)
3648(4)
2751(5)
1960(3)
2475(4)
5777(2)
6819(3)
7062(5)
6252(5)
5419(4)
Fig 1. Molecular structure of PdCl2(APBpin)2 (5, pin = O2C2Me4) with hydrogen atoms and molecules of THF omitted for clarity.
aminoboronic ester to 7 resulted in facile loss of the labile
cyclooctene ligand with concomitant formation of
PdCl2(APBpin)2 (5). Similar studies on the addition of pyri-
dines to palladium monoalkene complexes have been re-
ported previously (21).
Unlike reactions with palladium, only monoalkene com-
plexes PtCl2(COE)(APBA) (8) and PtCl2(COE)(APBpin)
(9) were generated from the addition of the corresponding
aminoboron derivatives to [PtCl2(COE)]2. Attempts to dis-
place the alkene proved unsuccessful, even with addition of
© 1999 NRC Canada

1204
Can. J. Chem. Vol. 77, 1999
Scheme 1.
Cl
M
( O) B
R
2
H
Cl
M
H
APBA
H
H
)
]
OE
2
[
M
Cl (C
2
N
N
N
or APB
in
p
M = Pd
= Pt
H
Cl
H
(
O
R)2
B
Cl
(
B OR)2
M = Pd, R = pin,
= Pt, R = H,
= Pt, R = pin,
7
M = Pd, R = H,
= Pd, R = pin 5
2
8
-
COE=CIS CYCLOOCTENE
9
excess aminoboron ligand at elevated temperatures.6 This
observation is consistent with the known ability of platinum
to form stronger M–alkene bonds than palladium, owing to
an increase in the amount of π-backbonding (22). Spectro-
scopic and X-ray diffraction studies of similar trans-
PtCl2(η2-alkene)(L) (L = nitrogen-containing ligand) com-
plexes have been reported previously (23).
CH2Cl2. This reaction probably proceeds via initial coordi-
nation of the aminoboron ligand followed by loss of
cyclooctene to provide a 14-electron intermediate “PdCl2L”
(where L = aminoboron ligand) (28). Addition of water or
an extra equivalent of amine may coordinate putatively to
the boron atom and facilitate rapid B—C bond cleavage to
fragment,
give the desired cyclopalladated
which will
subsequently dimerize to give [PdCl(2-NMe2CH2C6H4)]2.
No reaction was observed when [PdCl2(COE)]2 was treated
with 10 in dry solvent under an inert atmosphere. Reactions
2. Reactions with N,N-dimethylbenzylamineboronic acid
Boron derivatives of N,N-dimethylbenzylamine, 2-
NMe2CH2C6H4B(OH)2 (10) and 2-NMe2CH2C6H4Bpin (11),
were prepared by established procedures (16). Significant
intramolecular interaction exists between the nitrogen atom
and the boron atom in solution as evidenced by 11B{1H}
NMR spectroscopy (24). Peaks at δ 8.9 and 15.3 ppm ob-
served for 10 and 11, respectively, are shifted considerably
upfield from phenylboronic acid (δ 29.6 ppm), indicating
that the boron atom is four coordinate. Not surprisingly, a
distinct solvent effect is observed on the rates of N—B bond
dissociation in these systems, as shown previously using
NMR spectroscopy (25).
Reactions of 10 or 11 with Na2PdCl4 in water or methanol
gave the known cyclopalladated dimer [PdCl(2-NMe2CH2C6H4)]2
(26) as the major amine-containing product (identified using
1H NMR spectroscopy and mp) along with formation of bo-
ric acid; this latter species presumably arising from the addi-
tion of water to liberated “Cl-B(OH)2”. The cyclopalladated
compound has been prepared previously from the addition
of N,N-dimethylbenzylamine to Na2PdCl4, along with con-
comitant formation of HCl, where the ortho C(sp2)—H bond
of the phenyl group is broken as a new C(sp2)—Pd bond
forms (26). Our observation is intriguing in that it shows a
preference for activation of the C(sp2)—B bond over the
conventional C(sp2)—H bond. This selectivity suggests that
intramolecular coordination of the nitrogen atom to boron
severely weakens the corresponding C—B bond. A strong
base (typically NaOH or TlOH) is usually required to facili-
tate cleavage of the C—B in the Suzuki–Muyari cross-
coupling reactions of organic halides with organoboronic ac-
ids (27). No reaction was observed in analogous reactions
wet
dimer
of [PdCl2(COE)]2 with 2-NMe2CH2C6H4Bpin 11 in
methylene chloride also generated the cyclopalladated
[PdCl(2-NMe2CH2C6H4)]2 along with pinB-O-Bpin and the
ammonium salt [2-HNMe2CH2C6H4Bpin]2[PdCl4], where an
extra equivalent of the aminoboron ligand has been used to
mop up the liberated Cl-Bpin. Addition of Cl-Bpin to
11 would result in initial formation of [2-
pinBNMe2CH2C6H4Bpin]+Cl–, which would rapidly degrade
with addition of adventitious water to the protonated ammo-
nium salt along with “HO-Bpin,” the latter of which will
further degrade to give pinB-O-Bpin (similar nucleophilic
degradation reactions have been reported previously for
catechol derivatives, see ref. 29).
Consistent with this proposed pathway, the pinacol deriva-
tive 11 reacts initially with [PtCl2(COE)]2 to give an air-
sensitive species, which we have tentatively assigned as the
coordination complex PtCl2(COE)(η1-2-NMe2CH2C6H4Bpin)
(12). The proton NMR spectrum of 12 indicates that one
C(sp2)-H is significantly deshielded (δ 8.87 ppm) with re-
spect to starting aminoboron compound (δ 7.55 ppm), which
we postulate may lie over the metal square plane, as noted
previously for the bisamine adduct PdCl2(1-tetralone oxime)2
(30). Attempts to grow crystals of this coordination complex
suitable for X-ray diffraction studies were unsuccessful, as
compound 12 decomposes to give a number of unidentified
spectroscopy
products (by NMR
) along with the
cyclopla-
tinated monomer PtCl(COE)(2-NMe2CH2C6H4) (13) (Scheme 2).
Initial loss of cyclooctene followed by oxidative addition
of the B—C bond with subsequent reductive elimination of
the Cl-Bpin fragment and recoordination of the alkene moi-
ety would give the cycloplatinated product (28, 31). Forma-
tion of this cycloplatinated species was also observed in
analogous reactions with the boronic acid 10. Interestingly,
no reaction was observed between alkene complex
with the platinum salt, K PtCl , and either 10 or 11
.
2
4
The cyclometallated dimer [PdCl(2-NMe2CH2C6H4)]2 was
also obtained from reactions of alkene complex
[PdCl2(COE)]2 with 10 in reactions carried out in wet
6 A minor amount (<5%) of the diamine complex trans-PtCl2(APBpin)2 was generated upon heating for prolonged periods (days). An X-ray
diffraction study on this compound was carried out, and the platinum analogue proved to be isostructural with complex 5. Complete details
of this study are provided in the supplementary data.
© 1999 NRC Canada

Vogels et al.
1205
Scheme 2.
Cl
Pt
Cl
Cl
Pt
Me
N
Me
N
NMe2
Bpin
Me
Me
[PtCl2(COE)]2
DAYS
+ unidentified products
-'ClBpin'
O
O
B
12
13
Scheme 3.
Cl
Pt
H
H
H2O
[PtCl2(COE)]2
O
N
decomposition
R2B
NH 2
R = n-Bu, Ph
Cl
O
BR2
R = n-Bu, 16
R = Ph, 17
Scheme 4.
(RO)2B
Cl
BEt2
[PdCl2(COE)]2
WET CH2Cl2
Pd
N
N
N
4
Cl
B(OR)2
R = H, 19
R = pin, 20
[PtCl2(COE)]2 and N,N-dimethylbenzylamine even at ele-
vated temperatures.
NMR δ 47.8 ppm), respectively, both of which rapidly
decompose in air to give a number of unidentified ethanol-
amine-derived products (Scheme 3).
3. Reactions with borinic esters
Reactions of dibutylborinic acid, ethanolamine ester,
H2NCH2CH2OBBu2 (14), or diphenylborinic acid,
ethanolamine ester, H2NCH2CH2OBPh2 (15), with the
tetrachloro salts, [MCl4]2–, in aqueous solvents proceed via
cleavage of the B—O bond to give a mixture of metal–
ethanolamine complexes (32). Formation of these degrada-
tion products was confirmed by independently adding com-
mercially available ethanolamine to the corresponding
metal salts. Reactions with 14 gave boric acid, and presum-
ably butane, while phenylboronic acid, PhB(OH)2, was
generated as the major boron-containing product in reac-
tions using 15. Although the boron atom is initially stabi-
lized by intramolecular coordination of the amine nitrogen
atom in the free ligand, nucleophilic degradation of the
borinic group appears to be rapid once the B←N bond is
broken and the amine coordinates to the metal centre.
Cleavage of the B—O bond in these ligands has been ob-
served previously (33). Likewise, similar degradation prod-
ucts were observed with reactions of 14 and 15 with
[PdCl2(COE)]2. Reactions with [PtCl2(COE)]2, however,
4. Reactions with 3-(diethylboryl)pyridine
3-(Diethylboryl)pyridine (18) was originally prepared in
1983 (34) and its use in coupling reactions is well estab-
lished (35). The remarkable stability of this compound under
ambient conditions is due to its cyclic-tetrameric nature in
the solid state and in solution. Four molecules of 18 are
bound together through intermolecular nitrogen–boron
bonds (36). We hypothesized that reactions of 18 with either
[MCl4]2– or [MCl2(COE)]2 (M = Pd, Pt) would result in the
formation of metal–pyridine complexes by breaking the
N→B bonds. Nucleophilic attack by water on the boron
atom should therefore result in breaking the B—CEt bonds
and concomitantly generating the corresponding pyridine –
boronic acid metal complexes. Interestingly, although no
product formation was observed using the metal chloride
salts, reactions with [PdCl2(COE)]2 in wet methylene chlo-
ride gave modest yields (42%) of the desired boronic acid
complex PdCl2[NC5H4B(OH)2]2 (19) (Scheme 4). This re-
sult implies that coupling reactions carried out in an aqueous
or basic environment may initially transform tetrameric 18
to the corresponding boronic acid analogue in the presence
of a palladium catalyst (35). We are presently investigating
coupling reactions using aminoboronic acid derivatives and
gave
PtCl2(COE)(NH2CH2CH2OBBu2) (16) (11B NMR
56.1 ppm) and PtCl2(COE)(NH2CH2CH2OBPh2) (17) (11B
the
corresponding
monoamine
complexes
δ
© 1999 NRC Canada

1206
Can. J. Chem. Vol. 77, 1999
9. (a) P.R. Westmark and B.D. Smith. J. Pharm. Sci. 85, 266
(1996); (b) J. Am. Chem. Soc. 116, 9343 (1994); (c) G.T.
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will report our findings in due course. Complex
PdCl2(NC5H4Bpin)2 (20) was prepared by transesterification
of 19 with pinacol. Not surprisingly, no reaction was ob-
served using the less reactive platinum complex
[PtCl2(COE)]2.
Conclusions
11. D.A. Matthews, R.A. Alden, J.J. Birktoft, S.T. Freer, and J.
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sponding metal derivatives MCl2(APBA)2. Diamine com-
plexes were also generated by addition of APBA and
APBpin (pin = O2C2Me4) to the palladium alkene dimer
[PdCl2(COE)]2. The aminoboron ligands were ineffective in
displacing the coordinated cyclooctene group in analogous
reactions with the platinum dimer. Interestingly, cleavage of
the B—C and B—O bonds dominated reactions involving
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aminoboron
ligands,
2-NMe2CH2C6H4B(OR)2
and
H2NCH2CH2OBR2, respectively. Although 3-(diethyl-
boryl)pyridine is stabilized by intramolecular N→B interac-
tions, the novel boronic acid-containing complex
PdCl2[NC5H4B(OH)2]2 was prepared by addition of this
aminoboron ligand to the palladium alkene dimer. We are
presently investigating the biological activities of several of
these new platinum derivatives, the results of which will be
published in due course.
Acknowledgements
Thanks are gratefully extended to the Natural Sciences
and Engineering Research Council of Canada, Mount
Allison University, St. Mary’s University for financial sup-
port, as well as Johnson Matthey Ltd. for the generous sup-
plies of platinum salts. We also thank Dan Durant, Roger
and Marilyn Smith, and John Marcone (DuPont) for their
expert technical assistance, Dr. H. Jenkins (S.M.U.) for as-
sistance with the X-ray data, and anonymous reviewers for
helpful comments.
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