Oxidative Addition Reactions of [RhI(Br)(Tpy*)] (Tpy* = 4′-(4-tert-Butylphenyl)-2,2′:6′,2″-terpyridine) with Alkyl Bromides

Article abstract of DOI:10.1021/om0305418

Oxidative addition reactions with the highly nucleophilic complex [Rh ^I(Cl)(4′-(4-tert-butylphenyl)-2,2′:6′, 2″-terpyridine)] (1) and alkyl halides containing chlorine and bromine atoms gave mixtures of uncharacterized products. In contrast to

Full text of DOI:10.1021/om0305418

Organometallics 2004, 23, 269-279
269
Oxid a tive Ad d ition Rea ction s of [Rh I(Br )(Tp y*)] (Tp y* )
4′-(4-ter t-Bu tylp h en yl)-2,2′:6′,2′′-ter p yr id in e) w ith Alk yl
Br om id es
Boke C. de Pater, Eric J . Zijp, Hans-Werner Fru¨hauf,* J an M. Ernsting,
Cornelis J . Elsevier, and Kees Vrieze
Coordination and Organometal Chemistry, Institute of Molecular Chemistry, University of
Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands
Peter H. M. Budzelaar and Anton W. Gal
Department of Inorganic Chemistry, University of Nijmegen, Toernooiveld 1,
6525 ED Nijmegen, The Netherlands
Received J uly 17, 2003
Oxidative addition reactions with the highly nucleophilic complex [RhI(Cl)(4′-(4-tert-
butylphenyl)-2,2′:6′,2′′-terpyridine)] (1) and alkyl halides containing chlorine and bromine
atoms gave mixtures of uncharacterized products. In contrast to this, oxidative addition
reactions with the complex [RhI(Br)(4′-(4-tert-butylphenyl)-2,2′:6′,2′′-terpyridine)] (2) and
various alkyl bromides, containing (mainly terminal) carbon-bromine bonds, gave clean
single products in almost quantitative yield. The corresponding air-stable yellow Rh(III)-
terpyridine complexes are, in contrast to the parent Rh(I)-terpyridine complex, soluble in
various organic solvents. Consequently, these products have been further characterized by
1
means of H, 13C, 15N, 103Rh and 2D NMR techniques. NMR techniques were also used to
determine the geometry of the studied Rh(III)-terpyridine complexes, which were found to
be octahedral with the alkyl moiety axially positioned with respect to the Rh-terpyridine
plane (except for complexes 3 and 4). The oxidative addition reaction of complex 2 with
1-bromodecane in ethanol was monitored by UV/vis spectrometry. The recorded electronic
absorption spectrum of this reaction showed two distinct isosbestic points in the visible region.
It is most likely that first the carbon-bromine bond of 1-bromodecane is activated by the
Rh metal followed by the arrangement of the alkyl moiety in an axial position. Unfortunately,
on the basis of our findings, no single mechanism for this oxidative addition reaction can be
suggested.
In tr od u ction
and rhodium.13-18 In particular, the oxidative addition
reaction of MeI to carbonylrhodium complexes has been
studied in great mechanistic detail, since it is the key
step in the catalyzed carbonylation of methanol on an
industrial scale.19-22 Furthermore, rhodium-alkyl com-
plexes are considered to be key intermediates in major
industrially important catalytic processes such as hy-
drogenation and hydroformylation.23
Oxidative addition reactions are a general synthetic
method for the formation of carbon-metal σ-bonds.1
Most reported syntheses of carbon-metal σ-bonds in-
volve the reaction of alkyl iodides and bromides with
compounds of gold,2 platinum,3-5 palladium,6 iridium,7-12
* To whom correspondence should be addressed. E-mail: hwf@
science.uva.nl. Fax: +31-20-525 6456.
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10.1021/om0305418 CCC: $27.50 © 2004 American Chemical Society
Publication on Web 12/11/2003

270 Organometallics, Vol. 23, No. 2, 2004
de Pater et al.
Oxidative addition reactions of carbon-halogen bonds
to transition-metal complexes are also applied in a
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Oxidative Addition Reactions of [RhI(Br)(Tpy*)]
Organometallics, Vol. 23, No. 2, 2004 271
in a Bruker DRX 300 spectrometer equipped with a 5 mm
triple-resonance inverse probe with z gradient, operating at
30.42 MHz 15N frequency, and a second 300 W X decoupler
giving a 90° 15N pulse of 10 µs. Spectra were recorded without
decoupling 15N in f2. The spectral width in f1 was 500 ppm,
and 32 increments were used. Three values for J {1H,15N} (2.5,
5, 10 Hz) were used to determine the 15N resonance; after the
15N resonance was found, the final experiment was done with
a spectral width in f1 of 50 ppm and between 64 and 128
increments. This resulted, after linear prediction in f1, in a
resolution better than 0.2 ppm for the 15N resonance. Chemical
shifts were referenced to external nitromethane at 0 ppm;
negative chemical shifts are reported for lower frequencies.
Spectra were recorded at 296 K. The 103Rh NMR measure-
ments were performed as part of the characterization of the
Rh(III) terpyridine complexes. 103Rh measurements were car-
ried out on a Bruker DRX 300 spectrometer under temperature
control at 298 K using a 5 mm triple-resonance inverse probe
addition product, facilitating its full characterization.
Finally, crystallographic studies strongly indicated that
the Rh-C σ-bond, formed after the oxidative addition
reaction with CHCl3 or CH2Cl2 and [RhCl(2,6-(C(R1)d
NR2)2C5H3N], has a metal-carbene (RhdC+Cl-) char-
acter.74,76-79
These interesting features displayed by the square-
planar complexes [RhI(Cl)(2,6-(C(R1)dNR2)2C5H3N)] to-
ward oxidative addition reactions with alkyl halides
prompted us to study similar rhodium complexes of
terpyridine ligands. Unlike the work of Haarman et
al.,74 the oxidative addition reactions with [RhI(X)-
(Tpy*)] (X ) Cl, Br for complexes 1 and 2, respectively)
and chlorocarbons gave mixtures of unidentified prod-
ucts. Only oxidative addition reactions with [RhI(Br)-
(Tpy*)] (2) and mainly primary alkyl bromides afforded
the formation of clean single products (4-24). Here we
report the successful oxidative-addition reactions be-
tween complex 2 and numerous reagents containing
primarily terminal C-Br bonds.
1
head (1H, 31P{BB}) with a z gradient coil (90° H, 7.2 ms; 90°
103Rh, 19.5 ms) using the PFG HMQC sequence.84-86,88 The
acquisition time was 30-90 min for the final experiment. The
spectral width was 10 ppm for 1H. In the first measurement,
the spectral width for 103Rh was 9000 ppm, which was covered
by 128 t1 increments; 16 dummy scans were used. To exclude
folding and improve resolution, a second and sometimes third
measurement with modified n0(Rh) values and smaller spectral
widths were carried out; the final experiment was 500 ppm in
f1 and using 256 increments. The digital resolution of δ(103Rh)
was at least 3.7 Hz pt-1. After a linear prediction in the f1
direction, a 512 × 512 matrix was transformed, applying a
sine bell weighing function. The 103Rh spectra are obtained in
Exp er im en ta l Section
Gen er a l Con sid er a t ion s. The 4′-(4-tert-butylphenyl)-
2,2′:6′,2′′-terpyridine (Tpy*) ligand was synthesized according
to literature procedures,80,81 while its purification was executed
differently: i.e., column chromatography with silica gel using
a 6:1:4 eluent mixture of toluene, diethyl ether, and hexane.82
The syntheses of the complexes 1-24 were performed under
an inert atmosphere of purified argon, using standard Schlenk
techniques. If not stated otherwise, for the syntheses of these
complexes, 0.028 g of [RhBr(COD)]2 (0.048 mmol, COD ) 1,5-
cyclooctadiene) and 0.035 g of Tpy* (0.096 mmol) were used.
The yield of the products 1-23 was practically quantitative,
while the yield of 24 was ca. 70%. Solvents were dried and
purified by standard procedures. The bromine reagents, used
for the synthesis of complexes 3-24, were purchased from
1
f1 and the H spectra in f2. The absolute 103Rh ppm values are
referenced to ¥ ) 3.16 MHz. Signals at higher frequencies are
taken as positive. Fast atom bombardment (FAB+) mass
spectrometry was carried out using a J EOL J MS SX/SX103a
four-sector mass spectrometer, coupled to a J EOL MS-7000
data system. The samples were loaded in a matrix phase
(glycerol) on a stainless steel probe and bombarded with xenon
atoms with an energy of 3 keV. During the high-resolution
FAB-MS measurements a resolving power of 5000 (10% valley
definition) was used. CsI and glycerol were used to calibrate
the mass spectrometer. Elemental analyses were carried out
by H. Kolbe Mikroanalytisches Laboratorium (Mu¨lheim an der
Ruhr, Germany) and Analytische Laboratorien GmbH (Lind-
lar, Germany). For unknown reasons, the Rh(I) complexes with
the Tpy* ligand, i.e., 1 and 2, notoriously gave unsatisfactory
elemental analyses. Perhaps they are much more sensitive to
air and moisture than analogous complexes without the 4′-(4-
tert-butylphenyl) substituents on the terpyridine, a number
of which we have described and characterized, including
elemental analyses and X-ray structures.89
1
Aldrich.83 The H and 13C NMR spectra were recorded at 294
K with Bruker AMX 300, Bruker DRX 300, Varian Mercury
300, and Varian Inova 500 spectrometers. All 1H and 13C NMR
signal assignments of complexes 3a ,b and 4-24 are based on
NMR studies for the signal assignments of complex 10 also
using mathematical simulations and 2D NMR techniques such
as COSY (H,H) and HMQC (H,C) measurements. The 15N
NMR spectra were recorded using the PFG HMQC sequence84-87
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The reactants for the syntheses of the Rh(III)-terpyridine
complexes are shown in Table 1.
Atom numbering of the Rh(III)-terpyridine complexes for
the assignment of NMR signals is done according to Chart
1.Syn th eses. [Rh I(Cl)(Tp y*)] (1). Toluene (40 mL) was added
to 0.030 g of [RhCl(COD)]2 (0.061 mmol) and 0.044 g of Tpy*
(0.12 mmol). This mixture was stirred at room temperature
for about 5 min, after which a dark blue precipitate was
formed. After the supernatant liquid was decanted, the solid
residue was washed with pentane (3 × 10 mL). After the
product was dried by removing the solvent under reduced
pressure, 0.06 g of complex 1 (yield ca. 99%) was collected as
a dark blue powder. FAB+ MS: m/z 503.07 [M+].
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(82) The products to be separated dissolve, but do not elute, very
well in toluene. Diethyl ether elutes all products adequately. Hexane
enhances the separation of each single product. First, a greenish oil
eluted from the column, followed by the Tpy* ligand (main product).
Finally, the diketone intermediate (incomplete formation of the Tpy*
ligand) was collected. The last two products are colorless (i.e. white).
(83) The bromine reagents provided by Aldrich were superior to
those from Acros Chimica. Deliveries from Acros Chimica always gave
mixtures of products, instead of single clean products when reagents
were purchased from Aldrich.
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272 Organometallics, Vol. 23, No. 2, 2004
de Pater et al.
Ta ble 1. Rea cta n ts for Oxid a tive Ad d ition
Rea ction s
was poured into pentane (150 mL). After the supernatant
liquid was decanted, the remaining solid residue was washed
with pentane (3 × 10 mL). After the product was dried by
removing the solvent under reduced pressure, complex 4 (yield
reactant (complex)
saturated
Br2 (5)
bromomethane (6)
1-bromoethane (7)
unsaturated
1
ca. 95%) was collected as a pale yellow powder. H NMR (500
3
(2-bromobenzylidene)isopropylamine (3, 4)
bromoethene (14)
3-bromopropene (15)
MHz, Varian Inova 500, CD3OD, 298 K, δ): 9.11 (d, J (Rh-
N-H) ) 3 Hz, 1H (19)), 9.03 (s, 2H (3′,5′)), 8.78 (d, 8.0 Hz, 2H
(3,3′′)), 8.22 (t, 8.5 Hz, 2H (4,4′′)), 8.20 (d, 6.0 Hz, 2H (6,6′′)),
8.14 (d, 8.0 Hz, 2H (8,8′)), 7.74 (t, 8.5 Hz, 2H (9,9′)), 7.74 (d,
8.0 Hz, 1H (17)), 7.62 (t, 6.5 Hz, 2H (5,5′′)), 7.05 (t, 7.5 Hz, 1H
(16)), 6.90 (t, 7 Hz, 1H (15)), 6.23 (8 Hz, 1H (14)), 5.29 (m, 6.5
Hz, 1H (20)), 1.85 (d, 6.5 Hz, 6H (21)), 1.44 (s, 9H (tert-butyl)).
13C{1H} NMR (125 MHz, Varian Inova 500, CD3OD, 298 K,
δ): 174.23 (C19), 165.94 (d, 1J (Rh,C13) ) 29.5 Hz), 157.24
(C2′,C6′), 154.92 (C2,C2′′), 154.42 (C10), 153.49 (C4′), 152.07
(6,6′′), 145.35 (C18), 140.23 (4,4′′), 133.16 (C7), 131.77 (C15),
130.75 (C17), 130.15 (C14), 128.28 (C5,C5′′), 127.65 (C8,C8′),
126.61 (C9,C9′), 125.45 (C3,C3′′), 125.01 (16), 121.81 (C3′,C5′),
60.00 (C20), 34.70 (C11), 30.41 (C12), 22.78 (C21). 103Rh NMR
1-bromopropane (8) 3-bromo-2-methylpropene (16)
1-bromobutane (9) 4-bromobutene (17)
1-bromopentane (10) 5-bromopentene (18)
1-bromohexane (11) 6-bromohexene (19)
1-bromooctane (12) 8-bromooctene (20)
1-bromodecane (13) 11-bromoundecene (21)
bromobenzene (22)
benzyl bromide (23)
diphenylbromomethane (24)
Ch a r t 1. Nu m ber in g of th e Tp y* Atom s
(3.16 MHz, 300 Bruker DRX, CD3OD, 298 K, δ): 3220.75. 15
N
NMR (30.42 MHz, 300 Bruker DRX, CD3OD, 298 K, δ):
-112.16 (N2), -140.55 (N1′), -151.92 (N1,N1′′). Anal. Calcd
for C35H35N4RhBr2 (772.03): C, 54.28; H, 4.56; N, 7.23; Br,
20.64. Found: C, 54.15; H, 4.48; N, 7.12; Br, 20.59. FAB+ MS:
m/z 693.11 [(M+) - Br].
[Rh III(Br )3(Tp y*)] (5). At room temperature 100 equiv of
Br2 was added to a deep dark blue mixture of 2 (0.079 mmol)
and EtOH (20 mL). Instantaneously, a yellow emulsion was
formed. The product mixture was poured into pentane (150
mL). After the supernatant liquid was decanted, the remaining
solid residue was washed with pentane (3 × 10 mL). After the
product was dried by removing the solvent under reduced
pressure, complex 5 (yield ca. 99%) was collected as a yellow
powder. 1H NMR (300 MHz, 300 Bruker AMX, CD2Cl2, δ): 9.68
(d, 4.5 Hz, 2H (6,6′′)), 8.36 (s, 2H (3′,5′)), 8.28 (d, 8.4 Hz, 2H
(3,3′′)), 8.13 (t, 7.8 Hz, 2H (4,4′′)), 7.79 (d, 8.7 Hz, 2H (8,8′)),
7.72 (t, 8.0 Hz, 2H (5,5′′)), 7.68 (d, 8.7 Hz, 2H (9,9′)), 1.41 (s,
9H (tert-butyl)). 103Rh NMR (3.16 MHz, 300 Bruker DRX, CD2-
Cl2, δ): 4530.13. Anal. Calcd for C25H23N3RhBr3 (704.85): C,
42.41; H, 3.27; N, 5.93; Br, 33.8. Found: C, 42.36; H, 3.22; N,
5.84; Br, 33.78. FAB+ MS: m/z 627.93 [(M+) - Br].
[(R)Rh III(Br )2(Tp y*)] (6-24). At room temperature ca. 100
equiv of Br-R (Table 1) was added to a deep dark blue mixture
of 2 (0.079 mmol) and EtOH (20 mL). After completion of the
reaction a yellow solution (10-13, 16, 18-21, 23, 24) or
emulsion (6-9, 14, 15, 17, 22) was formed. The product
mixture was poured into pentane (150 mL). After the super-
natant liquid was decanted, the remaining solid residue was
washed with pentane (3 × 10 mL). After the precipitate was
dried by removing the solvent under reduced pressure, the
product was collected as a yellow powder (yield ca. 99% for
6-23 and ca. 70% for 24). Reaction times, FAB mass spectral
data, and elemental analyses are given in Table 2, and atom
numbering is given in Table 3.
[Rh I(Br )(Tp y*)] (2). Ethanol (30 mL) was added to 0.023
g of [RhBr(COD)]2 (0.039 mmol) and 0.029 g of Tpy* (0.079
mmol). This mixture was stirred at room temperature, and
after ca. 10 min a dark blue precipitate was formed. After the
supernatant liquid was decanted, the remaining solid residue
was washed with pentane (3 × 10 mL). After the product was
dried by removing the solvent under reduced pressure, 0.043
g of complex 2 (yield ca. 99%) was collected as a dark blue
powder. FAB+ MS: m/z 547.01 [M+].
[(2-(isop r op ylim in o)p h en yl)Rh III(X)(Tp y*)]+Y- (3a ,b).
Ethanol (40 mL) was added to 0.028 g of [RhCl(COD)]2 (0.057
mmol) and 0.041 g of Tpy* (0.11 mmol). This mixture was
refluxed for 5 min, and 1 precipitated out of the solution. After
the mixture was cooled to ca. 35 °C, >100 equiv of 2-(isopro-
pylimino)bromobenzene was added to this mixture. When the
reaction mixture was stirred for 2-3 min, a yellow suspension
was formed. The product mixture was poured into pentane
(150 mL). After the supernatant liquid was decanted, the
remaining solid residue was washed with pentane (3 × 10 mL).
After the product was dried by removing the solvent under
reduced pressure, 0.078 g of a 30:70 product mixture of 3a
and 3b (yield ca. 90%) was collected as a yellow powder (3a ,
X ) Cl; 3b, X ) Br; Y ) Cl, Br). With an FAB mass
measurement peaks of m/z 649.16 and 693.11 were detected
for 3a (-Br) and 3b (-Cl), respectively. 1H NMR (300 MHz
Complexes 4-24 are air-stable and soluble in various
organic solvents (e.g. MeOH, EtOH, and dichloromethane).
However, for the measurement of their NMR spectra (cf.
Tables 4 and 5), in various cases (5, 7-9, 14, 15, 17, 18, 22) a
few drops of trifluoroethanol (CF3CH2OH) were added to
enhance their solubility in deuterated dichloromethane for
NMR studies.
3
Varian Mercury 300, CD3OD, 298 K, δ): 9.11 (d, J (Rh,H) )
3.0 Hz, 1H (19)), 9.03 (s, 2H (3′,5′)), 8.78 (d, 8.1 Hz, 2H (3,3′′)),
8.22 (2H (4,4′′)), 8.20 (d, 7.5 Hz, 2H (6,6′′)), 8.14 (d, 8.4 Hz, 2H
(8,8′)), 7.75 (d, 8.1 Hz, 2H (9,9′)), 7.74 (1H (17)), 7.62 (t, 6.8
Hz, 2H (5,5′′)), 7.05 (t, 7.2 Hz, 1H (16)), 6.89 (t, 7.1 Hz, 1H
(15)), 6.31 (3a , d, 7.8 Hz, 1H (14)), 6.23 (3b, d, 7.5 Hz, 1H (14)),
5.30 (3b, t, 6.6 Hz, 1H (20)), 5.13 (3a , t, 6.3 Hz, 1H (20)), 1.85
(d, 6.6 Hz, 6H (21)), 1.44 (s, 9H (tert-butyl)). FAB+ MS: m/z
649.16 [(M3a +) - Br], 693.11 [(M3b+) - Cl].
Mon itor in g th e F or m a tion of Com p lex 13 w ith UV/Vis
Sp ectr oscop y. A standard cuvette was filled with 4 mL of
an ethanolic solution of complex 2 (1.23 × 10-4 M) under an
inert nitrogen atmosphere (glovebox). To this solution was
added 5 µL of 1-bromodecane (50 equiv) for the oxidative
addition reaction, which was monitored with an HP8453 diode-
array spectrophotometer at 298 K. In total, 75 electronic
absorption spectra were recorded with a 60 s interval between
each single measurement (4500 s total measuring time). The
[(2-(isop r op ylim in o)p h en yl)Rh III(Br )(Tp y*)]+Br - (4). A
solution of [RhBr(COD)]2 and Tpy* in 20 mL of ethanol was
refluxed for 10 min, giving [RhI(Br)(Tpy*)] (3) as a dark blue
solid. After cooling, to this mixture was added >100 equiv of
2-(isopropylimino)bromobenzene. After several minutes of
stirring a yellow emulsion was formed. The product mixture

Oxidative Addition Reactions of [RhI(Br)(Tpy*)]
Organometallics, Vol. 23, No. 2, 2004 273
Ta ble 2. Rea ction Tim e for Com p lex 2 (0.079
m m ol) a n d Ca . 100 Equ iv of Alk yl Br om id es in
EtOH (20 m L), F AB/Ma ss (m /z) Da ta for Com p lexes
6-23, a n d Elem en ta l An a lyses for 6, 13, a n d 21
Sch em e 1. Syn th esis P r oced u r e for Com p lexes 1
a n d 2
reacn
time
FAB+ MS
compd
([M+] - Br)
elemental anal. (%)
6
insta
562.04
calcd for C26H26N3RhBr2
(640.95): 48.55 (C),
4.07 (H), 6.53 (N), 24.85 (Br)
found: 48.62 (C), 4.15 (H),
6.39 (N), 24.78 (Br)
Sch em e 2. Rea ction P r oced u r e of 1 w ith CHCl3
a n d CH2Cl2
7
8
9
10
11
12
13
5 min
15 min
30 min
1 h
1 h
1 h
576.05
590.07
604.08
618.10
632.12
660.15
688.18
12 h
calcd for C35H44N3RhBr2
(796.52): 54.63 (C),
5.76 (H), 5.46 (N), 20.77 (Br)
found: 54.56 (C), 5.70 (H),
5.49 (N), 20.69 (Br)
Sch em e 3. Rea ction P r oced u r e of 1 w ith
(2-Br om oben zylid en e)isop r op yla m in e
14
15
16
17
18
19
20
21
5 min
5 min
5 min
30 min
1 h
2 h
2 h
12 h
574.04
588.05
602.07
602.07
616.08
630.10
660.15
700.18
calcd for C36H44N3RhBr2
(779.10): 55.33 (C),
5.86 (H), 5.38 (N), 20.45 (Br)
found: 55.24 (C), 5.61 (H),
5.35 (N), 20.56 (Br)
624.05
22
23
24
72 h
inst
inst
624.05
640.07
640.07
a
inst ) instantaneously.
first spectrum was recorded after 2 min reaction time. 1-Bro-
modecane shows no absorption in the relevant visible region.
Mon itor in g th e F or m a tion of Com p lex 13 w ith UV/Vis
Sp ectr oscop y in th e P r esen ce of 2-Meth ylp h en ol. A
standard cuvette was filled with 4 mL of an ethanolic solution
of complex 2 (5.75 × 10-5 M) and 1 g of 2-methylphenol (ca.
40 equiv) under an inert nitrogen atmosphere (glovebox). To
this solution was added 2.4 µL of 1-bromodecane (50 equiv)
for the oxidative addition reaction, which was monitored with
an HP8453 diode-array spectrophotometer at 298 K. In total,
90 electronic absorption spectra were recorded with a 60 s
interval between each single measurement (5400 s total
measuring time). The first spectrum was recorded after 1 min
and 50 s reaction time. 2-Methylphenol shows no absorption
in the relevant visible region.
oxidative addition reactions involving complexes 1 and
2 were performed in situ in EtOH.
Initially, oxidative addition reactions with complex 1
(ca. 0.01 mmol) and 1-1000 equiv of CHCl3 and CH2-
Cl2 (Scheme 2) were studied.
Unfortunately, the oxidative addition reactions in-
volving 1 and chloroform or dichloromethane gave only
mixtures of uncharacterized products. This is also the
case in reactions of 1 with O2, HCl, C2Cl6, benzyl
chloride, (2-chlorobenzylidene)isopropylamine, silicon
chlorides, benzyl bromide, and MeBr. However, in the
oxidative addition reaction of 1 and (2-bromobenzyli-
dene)isopropylamine two isomeric products (Scheme 3)
were formed, which could be identified by means of
NMR techniques and mass spectrometry.
Resu lts
1
The majority of the H signals of the two isomers of 3
Syn th eses of Com p lexes 1-24. For the synthesis
of complex 1 various solvents can be used (e.g. toluene,
benzene, THF, and EtOH), while the synthesis of
complex 2 is found to be the most successful when using
EtOH as the solvent (Scheme 1). Complexes 1 and 2 are
highly air sensitive, like the Rh(I) terpyridine complexes
described in ref 89. They react with oxygen instantly to
form mixtures of uncharacterized red Rh(III) species,
as evidenced by 1H NMR measurements of the products.
The synthesis of 2 in toluene and MeOH gave un-
characterized red products, while in THF uncharacter-
ized pale yellow products were formed. The synthesis
of 2 in benzene resulted in the formation of uncharac-
terized gray species. Hence, since EtOH is a suitable
solvent for the syntheses of both complexes 1 and 2, all
in the NMR spectrum of the product mixture are
overlapping each other. Only two pairs of nonoverlap-
ping signals indicate the presence of two different
species in the measured sample (Figure 1). The presence
of two different compounds in the product mixture is
also confirmed by FAB mass measurement. Masses of
m/z 649.16 and 693.11 are detected, representative for
3a ([M+] - Br) and 3b ([M+] - Cl), respectively. The
composition of the product mixture is 3a :3b ) 30:70
1
according to the H NMR integrals.
To avoid the formation of mixtures, (2-bromobenz-
ylidene)isopropylamine was oxidatively added to the
complex [RhI(Br)(Tpy*)] (2). As expected, this reaction
gave only one product, [(2-N-isopropyliminophenyl)-
(Tpy*)RhIIIBr]+Br- (4) (Scheme 4).

274 Organometallics, Vol. 23, No. 2, 2004
Ta ble 3. Atom Nu m ber in g of Com p lexes 6-24
de Pater et al.
Sch em e 4. Rea ction P r oced u r e of 2 w ith
2-(Isop r op ylim in o)br om oben zen e
Sch em e 5. Rea ction P r oced u r e of 2 w ith ca . 100
Equ iv of Alk yl Br om id e Rea cta n ts
means that all nitrogen atoms of 4 are coordinated to
the rhodium metal. In view of this finding and the
elemental composition of complex 4, it is likely that it
is an octahedral ionic Rh(III)-terpyridine complex with
a bromide acting as a counteranion, as indicated in
Scheme 4.
103Rh NMR Sp ectr oscop y of Com p lexes 4-7, 9,
13-17, a n d 22. Transition-metal NMR shifts can
nowadays easily be measured by modern 2D pulse
techniques and serve as a probe into electronic and
steric effects of ligands and substituents in metal
complexes.90 The influence of these effects on δ(103Rh)
for complexes 4-7, 9, 13-17, 22, and [(R3)RhIII(Cl)2(2,6-
This success prompted us to perform oxidative addi-
tion reactions with complex 2 and ca. 100 equiv of
various alkyl bromides (Table 1). As indicated earlier,
all reactions were carried out in situ using EtOH as the
solvent (Scheme 5). The atom numbering of complexes
6-24 is shown in Table 3, while reaction time and mass
and elemental analyses of complexes 6-24 are sum-
marized in Table 2.
15N NMR Sp ectr oscop y of Com p lex 4, Tp y*, a n d
2-(Isop r op ylim in o)br om oben zen e. The δ(15N) signal
of complex 4 has significantly shifted upfield compared
to the δ(15N) signal for the free ligands (Table 6). This
(90) Von Philipsborn, W. Chem. Soc. Rev. 1999, 28, 95-105.

Oxidative Addition Reactions of [RhI(Br)(Tpy*)]
Ta ble 4. 1H NMR Da ta of Com p lexes 6-24a
1H NMR (δ)
Organometallics, Vol. 23, No. 2, 2004 275
compd
6
9.53 (d, 5.4 Hz, 2H (6,6′′)), 8.24 (s, 2H(3′,5′)), 8.21 (d, 8.1 Hz, 2H (3,3′′)), 8.00 (t, 7.8 Hz, 2H (4,4′′)), 7.76 (d, 8.7 Hz,
2
2H (8,8′)), 7.60 (d, 9 Hz, 2H (9,9′)), 7.59 (m, 2H (5,5′′)), 1.41 (s, 9H (t-Bu)), 1.11 (d, J (Rh,H) ) 2.4 Hz, 3H (13))
7
9.53 (d, 5.5 Hz, 2H (6,6′′)), 8.28 (s, 2H (3′,5′)), 8.25 (d, 8.0 Hz, 2H (3,3′′)), 8.02 (t, 7.8 Hz, 2H (4,4′′)), 7.81 (d, 8.5 Hz,
3
2
2H (8,8′)), 7.63 (d, 8.5 Hz, 2H (9,9′)), 7.62 (m, 2H (5,5′′)), 2.22 (dq, J (H,H) ) 7.5 Hz, J (Rh,H) ) 3 Hz, 2H (13)),
1.44 (s, 9H (t-Bu)), 0.22 (t, 7.5 Hz, 3H (14))
8
9.45 (d, 5.5 Hz, 2H (6,6′′)), 8.25 (s, 2H (3′,5′)), 8.22 (d, 7.5 Hz, 2H (3,3′′)), 8.02 (t, 7.8 Hz, 2H (4,4′′)), 7.79 (d,
8.5 Hz, 2H (8,8′)), 7.62 (d, 8.5 Hz, 2H (9,9′)), 7.60 (t, 7.5 Hz, 2H (5,5′′)), 2.17 (dt, J (H,H) ) 8.5 Hz, J (Rh,H) )
2.5 Hz, 2H (13)), 1.43 (s, 9H (t-Bu)), 0.63 (m, 8.5 Hz, 2H (14)), 0.58 (t, 6.8 Hz, 3H (15))
3
2
9
9.47 (d, 5.4 Hz, 2H (6,6′′)), 8.23 (d, 7.6 Hz, 2H (3,3′′)), 8.21 (s, 2H (3′,5′)), 7.90 (t, 7.1 Hz, 2H (4,4′′)), 7.76
3
(d, 8.4 Hz, 2H (8,8′)), 7.53 (t, 6.5 Hz, 2H (5,5′′)), 7.52 (d, 8.7 Hz, 2H (9,9′)), 2.06 (dt, J (H,H) ) 8.6 Hz,
2J (Rh,H) ) 2.7 Hz, 2H (13)), 1.40 (s, 9H (t-Bu)), 0.91 (m, 7.4 Hz, 2H (14)), 0.48 (m, 2 + 3H)
10
11
9.48 (d, 5.4 Hz, 2H (6,6′′)),b 8.24 (d, 6.9 Hz, 2H (3,3′′)),b 8.23 (s, 2H (3′,5′)), 7.93 (t, 7.8 Hz, 2H (4,4′′)),b 7.77
3
(d, 8.7 Hz, 2H (8,8′)),b 7.56 (t, 7.0 Hz, 2H (5,5′′)),b 7.54 (d, 8.7 Hz, 2H (9,9′)),b 2.07 (dt, J (H,H) ) 8.6 Hz,
2J (Rh,H) ) 2.7 Hz, 2H (13)), 1.41 (s, 9H (t-Bu)), 0.90 (m, 2 × 2H), 0.55 (m, 2H + 3H)
9.49 (d, 5.5 Hz, 2H (6,6′′)), 8.28 (d, 8.0 Hz, 2H (3,3′′)), 8.23 (s, 2H (3′,5′)), 7.90 (t, 7.8 Hz, 2H (4,4′′)), 7.79 (d,
3
2
8.0 Hz, 2H (8,8′)), 7.56 (t, 6.0 Hz, 2H (5,5′′)) 7.52 (d, 8.0 Hz, 2H (9,9′)), 2.08 (dt, J (H,H) ) 7.5 Hz, J (Rh,H) )
2.5 Hz, 2H (13)), 1.42 (s, 9H (t-Bu)), 0.95 (m, 7.0 Hz, 2H (14)), 0.88 (m, 2 × 2H), 0.65 (t, 7 Hz, 3H (17)), 0.52
(m, 7.5 Hz, 2H (16))
12
13
9.50 (d, 5.4 Hz, 2H (6,6′′)), 8.25 (d, 7.8 Hz, 2H (3,3′′)), 8.24 (s, 2H (3′,5′)), 7.95 (t, 8.0 Hz, 2H (4,4′′)), 7.79 (d, 8.0
3
2
Hz, 2H (8,8′)), 7.58 (t, 7.4 Hz, 2H (5,5′′)), 7.57 (d, 8.0 Hz, 2H (9,9′)), 2.10 (dt, J (H,H) ) 7.8 Hz, J (Rh,H) )
2.8 Hz, 2H (13)), 1.43 (s, 9H (t-Bu)), 1.12 (m, 2H), 1.03 (m, 2H), 0.91 (m, 3 × 2H), 0.76 (t, 7.0 Hz, 2H (20)), 0.65 (m, 2H)
9.50 (d, 5.7 Hz, 2H (6,6′′)), 8.25 (d, 8.1 Hz, 2H (3,3′′)), 8.24 (s, 2H (3′,5′)), 7.95 (t, 8.1 Hz, 2H (4,4′′)), 7.79 (d,
3
2
8.4 Hz, 2H (8,8′)), 7.57 (t, 7.4 Hz, 2H (5,5′′)), 7.56 (d, 8.4 Hz, 2H (9,9′)), 2.10 (dt, J (H,H) ) 8.6 Hz, J (Rh,H) )
2.6 Hz, 2H (13)), 1.43 (s, 9H (t-Bu)), 1.21 (m, 7.05 Hz, 2H (14)), 1.09 (m, 4 × 2H), 0.90 (m, 2 × 2H), 0.81 (t, 6.8 Hz,
3H (22)), 0.55 (m, 2H)
14
15
16
17
18
19
9.52 (d, 5.4 Hz, 2H (6,6′′)), 8.25 (s, 2H (3′,5′)), 8.23 (d, 6.6 Hz, 2H (3,3′′)), 8.00 (t, 7.8 Hz, 2H (4,4′′)), 7.76 (d, 8.4 Hz,
3
3
2H (8,8′)), 7.60 (t, 6.7 Hz, 2H (5,5′′)), 7.59 (d, 8.7 Hz, 2H (9,9′)), 7.22 (ddd, J (H,H(trans) ) 15.9 Hz, J (H,H(cis) )
2
7.8 Hz, J (Rh,H) ) 3.6 Hz, 1H (13)), 4.55 (d, 6.6 Hz, 1H (14-cis)), 3.72 (d, 16.8 Hz, 1H (14-trans)), 1.41 (s, 9H (t-Bu))
9.45 (d, 5.5 Hz, 2H (6,6′′)), 8.24 (s, 2H (3′,5′)), 8.21 (d, 7.5 Hz, 2H (3,3′′)), 8.00 (t, 7.8 Hz, 2H (4,4′′)), 7.78 (d, 8.5 Hz,
2H (8,8′)), 7.61 (d, 9.0 Hz, 2H (9,9′)), 7.60 (t, 8.0 Hz, 2H (5,5′′)), 5.28 (m, 1H (14)), 4.32 (d, 10.0 Hz, 1H (15-cis)),
3
2
4.20 (d, 17.5 Hz, 1H (15-trans)), 2.97 (dd, J (H,H) ) 8.5 Hz, J (Rh,H) ) 3.0 Hz, 2H (13)), 1.43 (s, 9H (t-Bu))
9.54 (d, 5.5 Hz, 2H (6,6′′)), 8.25 (s, 2H (3′,5′)), 8.24 (d, 8.5 Hz, 2H (3,3′′)), 7.97 (t, 7.5 Hz, 2H (4,4′′)), 7.80 (d, 8.5
Hz, 2H (8,8′)), 7.61 (d, 8.5 Hz, 2H (9,9′)), 7.58 (t, 6.8 Hz, 2H (5,5′′)), 4.15 (s, 1H (15-cis)), 3.63 (s, 1H (15-trans)),
2
3.02 (d, J (Rh,H) ) 3.0 Hz, 2H (13)), 1.45 (s, 9H (t-Bu)), 1.15 (s, 3H (16))
9.47 (d, 5.0 Hz, 2H (6,6′′)), 8.24 (d, 7.0 Hz, 2H (3,3′′)), 8.23 (s, 2H (3′,5′)), 7.97 (t, 7.8 Hz, 2H (4,4′′)), 7.77 (d, 8.5
Hz, 2H (8,8′)), 7.58 (t, 6.8 Hz, 2H (5,5′′)), 7.57 (d, 8.5 Hz, 2H (9,9′)), 5.43 (m, 1H (15)), 4.55 (m, 2H (16)),
3
2
2.10 (dt, J (H,H) ) 8.5 Hz, J (Rh,H) ) 3.0 Hz, 2H (13)), 1.43 (s, 9H (t-Bu)), 1.41 (m, 2H (14))
9.46 (d, 5.5 Hz, 2H (6,6′′)), 8.22 (d, 8.5 Hz, 2H (3,3′′)), 8.23 (s, 2H (3′,5′)), 7.93 (t, 7.8 Hz, 2H (4,4′′)), 7.78 (d, 8.5
Hz, 2H (8,8′)), 7.56 (t, 7.0 Hz, 2H (5,5′′)), 7.55 (d, 8.0 Hz, 2H (9,9′)), 5.43 (m, 1H (16)), 4.63 (m, 2H (17)),
3
2
2.10 (dt, J (H,H) ) 8.8 Hz, J (Rh,H) ) 2.5 Hz, 2H (13)), 1.69 (psq, 7.0 Hz, 2H (15)), 1.43 (s, 9H (t-Bu)), 0.68 (m, 2H (14))
9.50 (d, 5.5 Hz, 2H (6,6′′)), 8.25 (s, 2H (3′,5′)), 8.24 (d, 8.0 Hz, 2H (3,3′′)), 7.98 (t, 8.0 Hz, 2H (4,4′′)), 7.79 (d,
8.5 Hz, 2H (8,8′)), 7.60 (t, 7.0 Hz, 2H (5,5′′)), 7.58 (d, 8.0 Hz, 2H (9,9′), 5.48 (m, 1H (17)), 4.66 (m, 2H (18)),
3
2
2.10 (dt, J (H,H) ) 8.5 Hz, J (Rh,H) ) 3.0 Hz, 2H (13)), 1.69 (psq, 7.2 Hz, 2H (16)), 1.43 (s, 9H (t-Bu)),
1.03 (m, 2H (15)), 0.56 (m, 2H (14))
20
21
9.50 (d, 5.1 Hz, 2H (6,6′′)), 8.24 (s, 2H (3′,5′)), 8.24 (d, 7.2 Hz, 2H (3,3′′)), 7.96 (t, 7.8 Hz, 2H (4,4′′)), 7.79 (d, 8.4 Hz,
2H (8,8′)), 7.59 (t, 7.0 Hz, 2H (5,5′′)), 7.57 (d, 8.1 Hz, 2H (9,9′)), 5.64 (m, 1H (19)), 4.82 (m, 2H (20)), 2.09 (dt,
2
3J (H,H) ) 8.7 Hz, J (Rh,H) ) 2.7 Hz, 2H (13)), 1.81 (psq, 7.0 Hz, 2H (18)), 1.42 (s, 9H (t-Bu)), 1.00 (m, 3 × 2H),
0.58 (m, 2H)
9.48 (d, 5.5 Hz, 2H (6,6′′)), 8.29 (d, 7.5 Hz, 2H (3,3′′)), 8.23 (s, 2H (3′,5′)), 7.87 (t, 8.0 Hz, 2H (4,4′′)), 7.78 (d, 8.0 Hz,
2H (8,8′)), 7.53 (t, 6.5 Hz, 2H (5,5′′)), 7.49 (d, 8.5 Hz, 2H (9,9′)), 5.74 (m, 1H (22)), 4.88 (m, 2H (23)), 2.07 (dt,
2
3J (H,H) ) 8.8 Hz, J (Rh,H) ) 3.0 Hz, 2H (13)), 1.92 (psq, 2H (21)), 1.42 (s, 9H (t-Bu)), 1.22 (m, 2H), 1.09 (m, 2H),
1.02 (m, 2H), 0.90 (m, 3 × 2H), 0.51 (m, 2H)
22
23
24
9.53 (d, 5.5 Hz, 2H (6,6′′)), 8.28 (s, 2H (3′,5′)), 8.23 (d, 8.0 Hz, 2H (3,3′′)), 8.12 (t, 7.8 Hz, 2H (4,4′′)), 7.76 (d, 7.5 Hz,
2H (8,8′)), 7.68 (t, 6.3 Hz, 2H (5,5′′)), 7.65 (d, 8.5 Hz, 2H (9,9′)), 6.73 (m, 2 + 1H (15,16)), 6.65 (d, 7.5 Hz, 2H (14)),
1.41 (s, 9H (t-Bu)); NOESY interaction was found between H(14) and H(6,6′′)
9.42 (d, 6.0 Hz, 2H (6,6′′)), 8.63 (s, 2H (3′,5′)), 8.58 (d, 7.5 Hz, 2H (3,3′′)), 8.27 (t, 7.4 Hz, 2H (4,4′′)), 7.96 (d, 8.7 Hz,
2H (8,8′)), 7.78 (t, 6.6 Hz, 2H (5,5′′)), 7.70 (d, 9.0 Hz, 2H (9,9′)), 6.83 (t, 7.4 Hz, 1H (17)), 6.58 (t, 8.1 Hz, 2H (16)),
2
6.32 (d, 7.5 Hz, 2H (15)), 3.79 (d, J (Rh,H) ) 2.7 Hz, 2H (13)), 1.43 (s, 9H (t-Bu))
9.06 (5.4 Hz, 2H (6,6′′)), 8.09 (s, 2H (3′,5′)), 7.87 (d, 7.8 Hz, 2H (3,3′′)), 7.78 (m, 2 + 2H), 7.62 (d, 8.4 Hz, 2H (9,9′)),
2
7.28 (t, 6.6 Hz, 2H (16)), 6.82 (m, 2 + 2H (15)), 6.65 (t, 7.7 Hz, 2 + 2H (14)), 5.94 (d, J (Rh,H) ) 3.6 Hz, 1H (13)),
1.42 (s, 9H (t-Bu))
a
For atom numbering cf. Table 2. All 1H NMR spectra were measured in CD2Cl2 (except for 23, in CD3OD). Complex 6 was measured
with a Bruker AMX 300 spectrometer and complex 9 with a Bruker DRX 300 spectrometer; complexes 10, 13, 14, 20, 23, and 24 were
measured with a Varian Mercury 300 spectrometer and complexes 7, 8, 11, 12, 15-19, 21, and 22 with a Varian Inova 500 spectrometer.
b
The assignment is based on 2D COSY measurements (Varian Inova 500), performed at room temperature.
(C(R1)dNR2)2C5H3N]74 has been studied with PFG
Mon itor in g th e F or m a tion of Com p lex 13 w ith
UV/Vis Sp ectr oscop y. Besides the electronic absorp-
tion spectra of isolated 2 and 13 (Figure 2), also the
formation of complex 13 was monitored by means of UV/
vis spectrometry (Figure 3). From the monitoring, two
distinct isosbestic points can be observed in the absorp-
1
HMQC H and 103Rh NMR techniques.
The δ(103Rh) values for complexes 4-7, 9, 13-17, and
22 (Table 7) are comparable with the δ(103Rh) values
for the similar complexes [(R3)RhIII(Cl)2(2,6-(C(R1)d
NR2)2C5H3N] for which 103Rh NMR data are avail-
able74,91 (Table 8).
(91) Haarman, H. F. Unpublished results.

276 Organometallics, Vol. 23, No. 2, 2004
Ta ble 5. 13C NMR Da ta of Com p lexes 6-22a
13C NMR (δ)
de Pater et al.
compd
6
157.08 (C2′, C6′), 155.34 (C2, C2′′), 155.00 (C10), 154.94 (C6, C6′′), 150.00 (C4′), 138.36 (C4, C4′′), 132.72 (C7), 127.96
(C5, C5′′), 127.67 (C8, C8′), 126.89 (C9, C9′), 124.09 (C3, C3′′), 120.33 (C3′, C5′), 35.29 (C11), 31.39 (C12, C12′, C12′′),
1
8.39 (d, J (Rh,C13) ) 21.14 Hz)
7
157.15 (C2′, C6′), 155.68 (C2, C2′′), 155.24 (C6, C6′′), 155.19 (C10), 150.75 (C4′), 138.74 (C4, C4′′), 133.44 (C7), 128.39
(C5, C5′′), 127.78 (C8, C8′), 126.19 (C9, C9′), 123.97 (C3, C3′′), 120.79 (C3′, C5′), 35.48 (C11), 31.53 (C12, C12′, C12′′),
1
24.38 (d, J (Rh,C13) ) 21.25 Hz), 17.09 (C14)
8
157.21 (C2′, C6′), 155.72 (C2, C2′′), 155.26 (C6, C6′′), 155.20 (C10), 150.84 (C4′), 138.76 (C4, C4′′), 133.50 (C7), 128.40
1
(C5, C5′′), 127.78 (C8, C8′), 126.18 (C9, C9′), 123.96 (C3, C3′′), 120.80 (C3′, C5′), 35.48 (C11), 33.12 (d, J (Rh,C13) )
21.75 Hz), 31.52 (C12, C12′, C12′′), 25.57, 15.29
9
156.81 (C2′, C6′), 155.27 (C2, C2′′), 154.80 (C6, C6′′), 154.80 (C10), 149.71 (C4′), 138.20 (C4, C4′′), 132.58 (C7), 127.83
(C5, C5′′), 127.46 (C8, C8′), 126.69 (C9, C9′), 123.73 (C3, C3′′), 120.13 (C3′, C5′), 35.10 (C11), 34.10, 31.16 (C12, C12′,
1
C12′′), 30.07 (d, J (Rh,C13) ) 21.25 Hz), 23.96, 13.48
10
11
12
13
14
15
16
17
18
19
20
21
22
156.85 (C2′, C6′),c 155.24 (C2, C2′′),c 154.79 (C6, C6′′),b 154.73 (C10),c 149.30 (C4′),c 138.02 (C4, C4′′),b 132.41 (C7),c
127.72 (C5, C5′′),b 127.54 (C8, C8′),b 126.61 (C9, C9′),b 123.82 (C3, C3′′),b 120.02 (C3′, C5′),b 35.11 (C11),c 33.20, 31.37,
1
31.21 (C12, C12′, C12′′),c 30.19 (d, J (Rh,C13) ) 21.25 Hz), 22.26, 13.75
157.16 (C2′, C6′), 155.57 (C2, C2′′), 155.13 (C6, C6′′), 155.05 (C10), 149.68 (C4′), 138.37 (C4, C4′′), 132.82 (C7), 128.09
(C5, C5′′), 127.87 (C8, C8′), 126.97 (C9, C9′), 124.13 (C3, C3′′), 120.39 (C3′, C5′), 35.46 (C11), 32.09, 31.85, 31.55 (C12,
1
C12′, C12′′), 31,11, 30.76 (d, J (Rh,C13) ) 21.30 Hz), 22.99, 14.21
156.85 (C2′, C6′), 155.24 (C2, C2′′), 154.87 (C6, C6′′), 154.73 (C10), 149.32 (C4′), 138.01 (C4, C4′′), 132.44 (C7), 127.72
(C5, C5′′), 127.53 (C8, C8′), 126.62 (C9, C9′), 123.80 (C3, C3′′), 120.01 (C3′, C5′), 35.11 (C11), 31.83, 31.75, 31.21 (C12,
1
C12′, C12′′), 31.05, 30.26 (d, J (Rh,C13) ) 20.63 Hz), 29.22, 29.19, 22.68, 13.92
156.82 (C2′, C6′), 155.23 (C2, C2′′), 154.82 (C6, C6′′), 154.69 (C10), 149.43 (C4′), 137.98 (C4, C4′′), 132.59 (C7), 127.73
(C5, C5′′), 127.47 (C8, C8′), 126.64 (C9, C9′), 123.68 (C3, C3′′), 120.05 (C3′, C5′), 35.08 (C11), 31.96, 31.73, 31.18 (C12,
1
C12′, C12′′), 31.05, 30.22 (d, J (Rh,C13) ) 21.25 Hz), 29.57, 29.36, 29.23, 29.19, 22.76, 13.98
1
156.79 (C2′, C6′), 155.04 (C2, C2′′), 155.01 (C10), 154.83 (C6, C6′′), 151.28 (C4′), 147.86 (d, J (Rh,C13) ) 26.88 Hz),
138.80 (C4, C4′′), 132.95 (C7), 128.12 (C5, C5′′), 127.45 (C8, C8′), 126.89 (C9, C9′), 123.97 (C3, C3′′), 120.63 (C3′, C5′),
116.45 (C14), 35.12 (C11), 31.13 (C12, C12′, C12′′)
157.21 (C2′, C6′), 155.67 (C2, C2′′), 155.29 (C10), 155.21 (C6, C6′′), 150.83 (C4′), 143.85 (C15), 138.81 (C4, C4′′), 133.34
(C7), 128.38 (C5, C5′′), 127.78 (C8, C8′), 126.20 (C9, C9′), 124.25 (C3, C3′′), 120.82 (C3′, C5′), 111.05 (C14), 35.49 (C11),
1
31.52 (C12, C12′, C12′′), 29.74 (d, J (Rh,C13) ) 19.50 Hz)
157.10 (C2′, C6′), 155.43 (C2, C2′′), 154.98 (C6, C6′′), 154.71 (C10), 151.41 (C4′), 149.90 (C15), 138.08 (C4, C4′′), 133.06
(C7), 127.51 (C5, C5′′), 127.42 (C8, C8′), 126.77 (C9, C9′), 123.85 (C3, C3′′), 120.19 (C3′, C5′), 108.00 (C14), 35.11 (C11),
1
34.06 (d, J (Rh,C13) ) 20.00 Hz), 31.19 (C12, C12′, C12′′), 23.25 (C16)
157.24 (C2′, C6′), 155.69 (C2, C2′′), 155.24 (C10), 155.24 (C6, C6′′), 150.53 (C4′), 139.32 (C16), 138.75 (C4, C4′′), 133.12
(C7), 128.37 (C5, C5′′), 127.83 (C8, C8′), 126.21 (C9, C9′), 124.10 (C3, C3′′), 120.68 (C3′, C5′), 113.37 (C15), 36.28 (C14),
1
35.49 (C11), 31.54 (C12, C12′, C12′′), 28.22 (d, J (Rh,C13) ) 23.00 Hz)
157.19 (C2′, C6′), 155.63 (C2, C2′′), 155.23 (C10), 155.19 (C6, C6′′), 150.14 (C4′), 139.03 (C17), 138.65 (C4, C4′′), 132.89
(C7), 128.26 (C5, C5′′), 127.87 (C8, C8′), 126.22 (C9, C9′), 124.20 (C3, C3′′), 120.55 (C3′, C5′), 114.05 (C16), 35.49 (C11),
1
35.33, 31.55 (C12, C12′, C12′′), 29.84 (d, J (Rh,C13) ) 21.25 Hz), 29.84
157.15 (C2′, C6′), 155.59 (C2, C2′′), 155.26 (C6, C6′′), 155.02 (C10), 150.19 (C4′), 139.46 (C18), 138.41 (C4, C4′′), 133.36
(C7), 128.20 (C5, C5′′), 127.79 (C8, C8′), 127.10 (C9, C9′), 123.90 (C3, C3′′), 120.58 (C3′, C5′), 114.14 (C17), 35.45 (C11),
1
33.72, 31.53 (C12, C12′, C12′′), 31.48, 30.35, 29.87 (d, J (Rh,C13) ) 21.25 Hz)
156.85 (C2′, C6′), 155.23 (C2, C2′′), 154.76 (C6, C6′′), 154.76 (C10), 149.22 (C4′), 139.35 (C20), 138.03 (C4, C4′′), 132.29
(C7), 127.41 (C5, C5′′), 127.56 (C8, C8′), 126.56 (C9, C9′), 123.88 (C3, C3′′), 119.99 (C3′, C5′), 113.83 (C19), 35.11 (C11),
1
33.69, 31.65, 31.22 (C12, C12′, C12′′), 30.86, 30.14 (d, J (Rh,C13) ) 21.13 Hz), 28.89, 28.71
156.86 (C2′, C6′), 155.23 (C2, C2′′), 154.76 (C6, C6′′), 154.76 (C10), 149.18 (C4′), 139.47 (C23), 138.02 (C4, C4′′),
132.26 (C7), 127.70 (C5, C5′′), 127.56 (C8, C8′), 126.59 (C9, C9′), 123.89 (C3, C3′′), 119.96 (C3′,C5′), 113.92 (C22), 35.11
1
(C11), 33.88, 31.72, 31.22 (C12, C12′, C12′′), 31.02, 30.26 (d, J (Rh,C13) ) 20.63 Hz), 29.49, 29.17, 29.21, 29.17, 29.02
156.86 (C2′, C6′), 155.23 (C2, C2′′), 154.76 (C6, C6′′), 154.76 (C10), 149.18 (C4′), 139.47 (C23), 138.02 (C4, C4′′),
132.26 (C7), 127.70 (C5, C5′′), 127.56 (C8, C8′), 126.59 (C9, C9′), 123.89 (C3, C3′′), 119.96 (C3′, C5′), 113.92 (C22), 35.11
1
(C11), 33.88, 31.72, 31.22 (C12, C12′, C12′′), 31.02, 30.26 (d, J (Rh,C13) ) 20.63 Hz), 29.49, 29.17, 29.21, 29.17, 29.02
a
For atom numbering, cf. Table 2. All 13C NMR spectra were measured in CD2Cl2 and recorded at 125 MHz with a Varian Inova 500
b
spectrometer. These NMR assignments are based on 2D HETCOR measurements (Varian Inova 500), performed at room temperature.
c These NMR assignments are based on mathematical simulations.
tion spectra of the oxidative addition reaction (Figure
3). Monitoring the formation of complex 13 in the
presence of 2-methylphenol (o-cresol) rendered absorp-
tion spectra similar to those observed without 2-meth-
ylphenol.
ment [Rh(Cl)(Tpy*)] could be detected with some cer-
tainty), it is impossible to characterize the different
products. It is likely that one side product is a Rh(III)
trichloride species. It is known that oxidative addition
reactions between Rh(I) chlorides and alkyl chlorides,
in particular CH2Cl2 and CHCl3, in EtOH can also give
Rh(III) trichloride species as decomposition products
together with diethoxyalkyl compounds.69
Discu ssion
Syn th eses of Com p lexes 1-24. Like the syntheses
of the complexes [RhI(X)(2,2′:6′,2′′-terpyridine)] (X ) Cl,
Br), as described in ref 89, the syntheses of complexes
1 and 2 (blue) were rather simple once the right reaction
conditions were found. Complexes 1 and 2 are air
sensitive and form red Rh(III) species in air.
Furthermore, the oxidative addition reactions with 1
and carbon-bromide bonds also gave mixtures of un-
characterized products, except when 2-(isopropylimino)-
bromobenzene was used as reactant, forming a mixture
of complexes 3a and 3b. The reaction between complex
2 and 2-(isopropylimino)bromobenzene gave the single
Various oxidative addition reactions with 1 and
carbon-chloride bonds gave mixtures of uncharacter-
1
product complex 4. The H chemical shifts of complexes
1
3b and 4 are identical.
ized products. On the basis of H NMR studies (only
broad signals) and mass measurements (only the frag-
Similar to the synthesis of complex 4, oxidative

Oxidative Addition Reactions of [RhI(Br)(Tpy*)]
Organometallics, Vol. 23, No. 2, 2004 277
F igu r e 1. 1H NMR spectrum at 300 MHz of the isolated mixture 3a + 3b.
Ta ble 6. 15N Ch em ica l Sh ifts of Com p lex 4, Tp y*,
a n d (2-Br om oben zylid en e)isop r op yla m in e
Ta ble 8. 103Rh Ch em ica l Sh ifts in CD2Cl2,
Mea su r ed a t Room Tem p er a tu r ea
15N chem shifta
(2-bromobenzylidene)-
4 (in CD3OD)
Tpy* (in CD2Cl2)
isopropylamine
-151.92 (N1, N1′′) -85.39 (N1′)
-34.27 (in CD3OD)
-23.54 (in CD2Cl2)
-140.44 (N1′)
-112.16 (N2)
-71.35 (N1, N1′′)
compd74
R1
R2
R3
δ (ppm)91
a
In ppm, measured at room temperature.
A
B
C
D
E
F
H
H
H
H
CH3
H
H
i-Pr
Cy
CH2Cl
CH2Cl
CH2Cl
CH2Cl
CH2Cl
CH2Ph
Cl
3570
3569
4121
3654
3561
3649
4923
Ta ble 7. 103Rh Ch em ica l Sh ifts in CD2Cl2,
Mea su r ed a t Room Tem p er a tu r ea
t-Bu
p-A
p-A
i-Pr
i-Pr
G
a
Abbreviations: i-Pr ) ipropyl; Cy ) cyclohexyl; t-Bu ) tert-
butyl; p-A ) p-anisyl.
bond of bromobenzene, as indicated by their reaction
time (Table 3). Furthermore, generally, smaller satu-
rated and terminal unsaturated alkyl bromides reacted
more quickly than the larger ones (Table 3). Under the
applied reaction conditions (see the Experimental Sec-
tion), only bromomethane, benzyl bromide, and diphen-
ylbromomethane reacted instantaneously with complex
2.
complex (R)
δ (ppm)
complex (R)
14 (ethenyl)
15 (2-propenyl)
16 (2-methyl-2-propenyl)
17 (3-butenyl)
22 (Ph)
δ (ppm)
4a
3221
4540
3366
3365
3380
3375
3415
3533
3545
3396
3548
5 (Br)
6 (Me)
7 (Et)
9 (Bu)
13 (decyl)
Complexes 5-24 dissolved sufficiently to excellently
in (deuterated) dichloromethane and rather poorly in
(deuterated) methanol. In contrast, complexes 3a ,b and
4 dissolved very well in (deuterated) methanol and not
at all in (deuterated) dichloromethane. Their charged
character could be the reason for the high solubility of
the last three complexes in methanol.
a
Measured in CD3OD at room temperature.
addition reactions in EtOH with complex 2 and various
bromohydrocarbons gave clean products (complexes
5-24) in almost quantitative yields. In contrast to the
dark blue complexes 1 and 2, all synthesized Rh(III)
terpyridine species are air stable and yellow. Primary
sp3 and vinylic sp2 carbon-bromide bonds reacted more
quickly with complex 2 than the sp2 carbon-bromide
Geom etr y of Com p lexes 3-24. Since attempts to
grow crystals of complexes 3-24 failed, the determina-

278 Organometallics, Vol. 23, No. 2, 2004
de Pater et al.
aromatic region; i.e., the differences in charge of 4 and
22 and the deuterated solvents used (CD3OD and CD2-
Cl2 for 4 and 22, respectively) have little influence on
the chemical shifts of e.g. the tert-butyl protons (H12)
and most of the Tpy* aromatic protons (3,3′′; 4,4′′; 5,5′′;
9,9′; 14) of 4 and 22. However, the signals belonging to
H6/H6′′ of 4 and 22 are shifted significantly from each
other. The 1H(6/6′′) NMR signal of 4 is shifted much
more (>1 ppm) upfield compared with the 1H(6/6′′) NMR
signal of 22. A plausible explanation for this would be
that the phenyl ring of complex 4 is in an equatorial
1
position. Hence, due to the anisotropy effect, the H(6/
6′′) NMR signal of 4 is shifted upfield. For complex 22
no anisotropy effect is observed, while NOE interactions
between H(6/6′′) and H(14) is observed. This means that
the benzene ring of complex 22 is in an axial position.
Part of the shift difference of H(6/6”) in 4 and 22 may
be attributed to a downfield contribution in 22 by the
adjacent equatorial bromide ligand. Such a downfield
shift of the H(6) proton resonance of a coordinated
pyridyl ligand adjacent to an equatorial halide has been
reported for Pd(II) complexes.92-94 On the basis of the
F igu r e 2. Electronic absorption spectra of complexes 2 and
13 in ethanol.
1
very similar H and 13C chemical shifts of 6-24, it can
be suggested that their Rh-carbon bond is in an axial
position.
103Rh NMR Sp ectr oscop y. Transition-metal nuclei
generally offer very large changes in their chemical shift
(several 100 or 1000 ppm) depending on molecular
structure and, hence, good sensitivity to subtle struc-
tural perturbations, due to a large sensitivity to small
changes in the ligand field.90 In general, transition-
metal complexes containing metal-bonded groups with
more electron withdrawing and/or bulky substituents
show lower shielding of the metal nuclei.90,95-99 The
deshielding effect correlates with the difference in ligand
field energy: i.e., a lower electron density on the metal
correlates with a smaller ligand field splitting and,
hence, a more positive chemical shift of the metal nuclei.
The steric deshielding effect correlates among other
things with the metal-carbon bond length, and thus
also the weakening of this bond, and hence also a more
positive chemical shift of the metal nuclei with increas-
ing M-C bond length.90 However, it must be noted that
the individual influences of the electronic and steric
effects are difficult to separate.90 Furthermore, for the
transition-metal chemical shift, the ligand field (elec-
tronic and stereochemical environment) of transition-
metal-containing complexes is a more dominant factor
than the actual charge of the transition metal.100-104
F igu r e 3. UV-vis reaction spectrum of the oxidative
addition reaction of complex 2 with 1-bromodecane in
EtOH.
1
tion of their geometry is based on their H and 13C NMR
spectra, the 15N NMR experiments of complex 4, and
NOE 2D (1H) NMR experiments of complex 22.
The δ(15N) signals for complex 4 (-112.16, -140.55,
and -151.92 ppm) is not too different from the δ(15N)
signals for the complexes [Pd(N-N)2(CH3)][X] (N-N )
1,10-phenanthroline (phen), 3,4,7,8-tetramethyl-1,10-
-
phenanthroline (tm-phen); X ) OTf (triflate), PF6
;
δ(15N) -123.6 and -130.8 ppm for phen and tm-phen
derivatives, respectively) described by Milani et al.87 The
coordination shifts, i.e. the differences in δ(15N) between
the free ligands and the relevant complexes 4 and [Pd-
(N-N)2(CH3)][X],87 are also similar: i.e., ca. -70 ppm.
It can be concluded that all the nitrogen atoms in
complex 4 are coordinated to the rhodium metal center.
1H/13C/15N NMR spectra, absolute mass measurements,
and elemental analyses (C, H, N, Br) indicate that
complex 4 should be an octahedral ionic Rh(III)-
terpyridine complex with four nitrogen atoms coordi-
nated and one phenyl ring and one bromine atom
σ-bonded to the rhodium center and one bromine atom
serving as counteranion. However, there are two options
for the binding positions of the phenyl group and the
isopropylimino nitrogen atom of complex 4. If the
isopropylimino nitrogen atom is coordinated at the axial
position, than the phenyl group will be in an equatorial
position, and vice versa. Despite the differences between
complex 4 and 22, the coordination spheres around the
rhodium metals are similar. Both contain bromides,
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1
nitrogens, and a σ-bonded aryl group. Therefore, the H
(100) Ramsey, N. F. Phys. Rev. 1950, 77, 567.
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NMR spectra of 4 and 22 should show similar signals
and patterns in the Tpy* aromatic region. Indeed, the
1H NMR spectra of 4 and 22 are very similar in the Tpy*
(104) Griffith, J . S.; Orgel, L. E. Trans. Faraday Soc. 1957, 53, 601.

Oxidative Addition Reactions of [RhI(Br)(Tpy*)]
Organometallics, Vol. 23, No. 2, 2004 279
This is clearly evidenced for complex 4. Although
complex 4 contains a cationic Rh(III) metal, suggesting
an electron-poor metal center, complex 4 has the lowest
δ(103Rh) value of the Rh(III)-terpyridine complexes
studied. This can be explained by the fact that complex
4 contains an additional N atom instead of a bromide,
which accounts for the somewhat lower δ(103Rh) value
compared to e.g. 6 or 14.
The Rh metal nucleus has a great sensitivity to
(small) changes in its coordination environment. This
has been amply demonstrated in previous studies,105-108
which is also observed by comparing the δ(103Rh) values
for the octahedral Rh(III) complexes 4-7, 9, 13-17, 22,
and [(R3)RhIII(Cl)2(2,6-(C(R1)dNR2)2C5H3N].74 The
δ(103Rh) signal for [(R3)RhIII(Cl)2(2,6-(C(R1)dNR2)2C5H3N]
is generally more positive than for complexes 4-7, 9,
13-17, and 22. This is most probably due to the fact
that chloride is lower in the spectrochemical series
compared to bromide (R3, Table 8). Furthermore, the
imine nitrogens in [(R3)RhIII(Cl)2(2,6-(C(R1)dNR2)2C5H3N]
must be regarded as higher in the spectrochemical
series as compared with the pyridine nitrogens in
Rh(III)-terpyridine complexes, since the former are
better π-acceptors.
Apart from relatively small mutual differences, com-
plexes 4-7, 9, 13-17, 22, and [(R3)RhIII(Cl)2(2,6-(C(R1)d
NR2)2C5H3N] show similar trends in chemical shifts
within their respective series in relation to deshielding
of the nuclei. As has been shown before and was
discussed above, the nuclear deshielding correlates
qualitatively at least with the relative ligand field
energy: i.e., a lower electron density on the metal
correlates with a smaller ligand field splitting and,
hence, a more positive chemical shift of the metal nuclei.
For compounds A-G (Table 8), the following qualita-
tive assessment can be made. Compound G contains a
halide directly coordinated to Rh and, hence, a much
higher chemical shift compared to the strong-field CH2X
moiety of the other compounds in this subseries. The
shift of C relative to A and B is explained by the fact
that the coordination angles within the complexes are
far from optimum especially in C;74 hence, the ligand
field splitting is less for this complex, resulting in a
higher chemical shift. Other differences are rather small
and cannot be explained even qualitatively.
The complexes [(R3)RhIII(Cl)2(2,6-(C(R1)dNR2)2C5H3N]
and 4-7, 9, 13-17, and 22 show similar trends. This
is best evidenced by comparing the δ(103Rh) value of
complex 5 and those of complexes 6, 7, 9, 13-17, and
22. Like complex G, complex 5 contains three Rh-X
σ-bonds (X ) Br) and has by far the most positive δ-
(
103Rh) within the subseries, since 4, 6, 7, 9, 13-17, and
22 contain only two Rh-Br σ-bonds. Furthermore,
complexes 14-16 and 22 have more positive δ(103Rh)
values than complexes 6, 7, 9, and 13. Apparently, vinyl,
allyl, and phenyl groups induce a lower ligand field than
alkyl groups.
Mon itor in g th e F or m a tion of Com p lex 13 w ith
UV/Vis Sp ectr om etr y: Mech a n istic Asp ects. When
the formation of complex 13 from complex 2 and
1-bromodecane is monitored, in absence of o-cresol,
isosbestic points in the electronic absorption spectra are
clearly observable (Figure 3). However, the involvement
of possible formed intermediates, during the synthesis
of complex 13, cannot be excluded. Radicals as inter-
mediates can be excluded, since monitoring the oxida-
tive addition reaction in the presence of o-cresol gave
electronic absorption spectra similar to those without
o-cresol.
TD-DFT calculations89 have shown that the HOMO
2
of complex 2 is entirely located on the dz orbital of the
2
Rh metal. This doubly occupied dz HOMO then nucleo-
philically attacks the bromine-bearing carbon bond and
forms the new Rh-carbon bond concurrently with the
breaking of the carbon-bromine bond: i.e., for com-
plexes 6-24 the new Rh-carbon bond is in an axial
position with respect to the equatorial Rh-Tpy* plane.
Only, as evidenced by NMR, in complexes 3 and 4 is
the Rh-carbon bond in an equatorial position.
However, on the basis of the results, it is not possible
to unequivocally propose a mechanism of the overall
oxidative addition of the carbon-halogen bonds to
Rh(I)-terpyridine complexes.
(105) Mann, B. E. Transition Metal Nuclear Magnetic Resonance;
Elsevier: Amsterdam, 1991.
(106) Bonnaire, R.; Davoust, D.; Platzer, N. Org. Magn. Reson. 1984,
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(107) Ernsting, J . M.; Elsevier, C. J .; De Lange, W. G. J . Chem.
Commun. 1989, 585.
(108) Elsevier, C. J .; Kowall, B.; Kragten, H. Inorg. Chem. 1995,
34, 4836-4839.
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