Electronic communication between tungsten alkylidyne and metal isocyanide complex fragments across phenyleneethynylene bridges

Article abstract of DOI:10.1016/j.jorganchem.2006.02.029

Heteronuclear metal complexes of the type [X(CO)₂(LL)W{triple bond, long}C(-C₆H₄-C{triple bond, long}C)_p-C₆H₄-N{triple bond, long}C-]_nML_m (X = Cl, Br; LL = tmeda, dppe

Full text of DOI:10.1016/j.jorganchem.2006.02.029

Journal of Organometallic Chemistry 691 (2006) 4514–4531
www.elsevier.com/locate/jorganchem
Electronic communication between tungsten alkylidyne and
metal isocyanide complex fragments across phenyleneethynylene bridges
a
a,
a
b,
*
Marie Pui Yin Yu , Vivian Wing-Wah Yam *, Kung-Kai Cheung , Andreas Mayr
a
Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China
Department of Chemistry, State University of New York at Stony Brook, Stony Brook, NY 11794-3400, USA
b
Received 28 December 2005; received in revised form 17 February 2006; accepted 20 February 2006
Available online 28 February 2006
Abstract
Heteronuclear metal complexes of the type [X(CO)2(LL)W„C(–C6H4–C„C)p–C6H4–N„C–]nMLm (X = Cl, Br; LL = tmeda, dppe;
p = 0–3; n = 1 for Cr(CO)5, n = 2 for ReX(CO)3, PdCl2, PdI2, and PtI2) have been prepared. The molecular structure of one example,
[Cl(CO)2(tmeda)W„C–C6H4–N„C–]2PdI2, was determined by X-ray crystallography. The extent of electronic communication between
the tungsten alkylidyne and the metal isocyanide centers was probed by various spectroscopic techniques. In the parent systems (p = 0),
the electronic changes due to modification of the isocyanide metal complex fragments could be distinguished clearly by the 13C NMR
chemical shift of the alkylidyne carbon atom and the d ! p* and p ! p* electronic transitions of the metal alkylidyne system. However,
only residual effects could be discerned for the longer systems using these spectroscopic probes. Probes based on the emission property of
the tungsten alkylidyne fragment proved to be the most useful in distinguishing long-range effects in those cases where the isocyanide
metal complex fragment is capable of quenching the emission. This is the case for MLm = PdCl2 and PdI2. Partial quenching effects were
still observed at the longest investigated distance between the metal centers of about 3.1 nm. The available evidence suggests that the
quenching mechanism is electron transfer.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Tungsten alkylidyne complex; Metal isocyanide complex; Photoluminescence; Electron transfer
1. Introduction
sites, but the molecular bridge between them also plays a
crucial role, especially in determining the efficiency of com-
munication [3].
Methods to establish electronic communication between
molecular entities across extended distances are of central
importance to the development of molecular devices for
applications such as energy conversion, sensing, or molec-
ular electronics [1]. The mechanism of interaction may be
electron transfer, energy transfer, or the change of some
spectroscopic or structural parameter upon modification
of one of the interacting sites [2]. The particular mechanism
is primarily determined by the nature of the interacting
Transition metal centers are among the most versatile
active components for establishing electronic communica-
tion [4] and unsaturated organic systems have proven to
be among the most useful bridging units [5]. In this study,
we explore the electronic interactions between tungsten
alkylidyne and metal isocyanide complex fragments across
phenyleneethynylene bridges [6]. Metal alkylidynes are
characterized by the presence of strong metal–carbon
triple bonds [7], and several dinuclear complexes with
bridging conjugated bis(alkylidyne) ligands have been
prepared [8]. In addition, alkylidyne metal complexes
possess photophysical properties which may make them
useful as active molecular device components [9]. The
*
Corresponding authors. Tel.: +852 2859 2153; fax: +852 2857 1586
(V.W.-W. Yam); tel.: +1 631 632 7951; fax: +1 631 632 7960 (A. Mayr).
E-mail addresses: wwyam@hku.hk (V.W.-W. Yam), amayr@notes.cc.
sunysb.edu (A. Mayr).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.02.029

M.P.Y. Yu et al. / Journal of Organometallic Chemistry 691 (2006) 4514–4531
4515
metal–isocyanide linkage is also characterized by the pres-
ence of metal–carbon p interactions, albeit much weaker
ones than those in metal alkylidynes [10]. The advantage
of the metal isocyanide system, in the context of this
study, is the possibility to attach metal complex fragments
with a wide range of electronic properties [11,12]. These
two different types of metal complex fragment are con-
nected via phenyleneethynylene units. Oligo(phenylenee-
thynylene)s (OPE) are widely used as bridges, not only
because of their good electronic transmission properties
[13], but also for their strictly linear geometry and ease
of preparation [14]. With the attachment of M„C– and
–N„C–M0 groups to the ends of OPE chains the metal
centers not only terminate, but become integral parts of
extended p systems. In such a,x-dimetalla-p-systems the
exchange of electronic information between the metal cen-
ters may be expected to be particularly efficient. The pres-
ent heteronuclear metal complexes are members of a
growing family of carbon- and hydrocarbon-bridged
metal complexes in which the metal centers are connected
directly, via metal–carbon r/p bonds, to the ends of
extended p systems [15].
tions were 1.344 and 1.333, respectively. The luminescence
quantum yield of the reference was 0.055 with irradiation
at 453 nm [19]. Cyclic voltammetric measurements were
performed by using a CH Instrument Inc., model CHI
620 Electroanalytical Analyzer, interfaced to a personal
computer. The ferrocenium–ferrocene couple was used
as the internal standard in the electrochemical measure-
ments in acetonitrile (0.1 M nBu4NPF6) (0.38 V versus
SCE) [20]. The working electrode was a glassy carbon
(Atomergic Chemetals V25) electrode, Ag/AgNO3
(0.1 M in CH3CN) as the reference electrode and with a
platinum foil acting as the counter electrode. Melting
points were recorded on a Stuart Scientific SMP1 instru-
ment under nitrogen. Elemental analyses were performed
by Butterworth Laboratories Ltd.
2.1. Synthesis of compound 2
Compound 1 (2.04 g, 6.10 mmol) and 2.23 g of 4-
IC6H4CCSiMe3 (2.23 g, 7.43 mmol) were dissolved in
NEt3 (100 mL), and PdCl2(PPh3)2 (40 mg 0.057 mmol)
and CuI (40 mg, 0.21 mmol) were added. The resulting
solution was stirred at 40 ꢁC overnight. The solvent was
then removed and the residue was dissolved in CH2Cl2.
This organic solution was washed with water. The
organic extract was dried, and the solvent was removed
under reduced pressure. The product was purified by col-
umn chromatography on silica gel using hexane as the
eluent. Removal of the solvent yielded a pale yellow crys-
talline solid. Yield: 2.49 g, 80%. The terms minor isomer
and major isomer in the lists of NMR data refer to the
conformational isomers of the formamide group. 1H
NMR (CDCl3): d 8.48 (s, 1H, minor isomer, NHCHO),
8.04 (d, J = 11.8 Hz, 1H, major isomer, NHCHO),
7.53–7.37 (10H, C6H4CC, C6H2i-Pr2), 7.12 (d,
J = 11.8 Hz, 1H, major isomer, NHCHO), 6.79 (s, 1H,
minor isomer, NHCHO), 3.25–3.16 (m, 2H, major iso-
mer, CHCH3), 3.14–3.06 (m, 2H, minor isomer, CHCH3),
1.24 (d, J = 6.8 Hz, 12H, CHCH3), 0.26 (s, 9H, SiCH3).
13C{1H} NMR (CDCl3): d 164.8 (NHCHO, major iso-
mer), 160.4 (NHCHO, minor isomer), 146.9, 146.5,
131.9, 131.6, 131.5, 131.4, 130.2, 129.9, 127.3, 127.1,
123.5, 123.4, 123.2, 123.1, 123.0, 122.8 (C6H4CC,
C6H2i-Pr2), 104.6, 96.5, 91.0, 90.9, 89.4, 89.0 (C„C),
28.8, 28.4 (CHCH3), 23.5 (CHCH3), 0 (SiCH3). IR
(CH2Cl2, cmꢀ1): 2156 (w, mC„CSi). mp 182–185 ꢁC. MS
(EI): 501 (M+).
2. Experimental
Standard inert atmosphere techniques were used
throughout. Diethyl ether, hexane and THF were purified
by reflux over sodium and distillation. Methylene chloride
was heated to reflux over calcium hydride and distilled. 4-
Iodophenyltrimethylsilylacetylene, 2,6-diisopropylpheny-
lisocyanide, and compounds 1, 5, and 7–9 as well as 10
1
and 11 were prepared as previously reported [16,17]. H,
13C{1H} and 31P{1H} NMR spectra were recorded on
270 MHz JEOL JNMGSX270 FT-NMR, 300 MHz BRU-
KER DPX300 FT-NMR and 500 MHz BRUKER
DRX500 FT-NMR spectrometers. 1H and 13C{1H}
NMR chemical shifts are given in ppm (d) relative to
SiMe4. 31P{1H} NMR spectra are referenced to 85%
H3PO4. IR spectra were recorded on a Shimadzu FT-
IR-8201PC spectrometer. UV/Vis absorption spectra were
recorded on a Hewlett–Packard 8452A diode array spec-
trophotometer. Emission spectra were recorded on a Spex
Fluorolog 111 spectrofluorometer. Solutions were
degassed with not less than four freeze–pump–thaw
cycles. Emission lifetime measurements were performed
using a conventional laser system. The excitation source
was the 355-nm output (third harmonic) of a Quanta-
Ray Q-switched GCR-150 pulsed Nd-YAG laser
(10 Hz). Luminescence decay signals were recorded on a
Tektronix model TDS-620A (500 MHz, 2GS/s) digital
oscilloscope, and analyzed using a program for exponen-
tial fits. The relative luminescence quantum yields were
measured at room temperature by the Parker–Rees
method [18]. [Ru(bpy)3]Cl2 in deionized water has been
used as the reference and all samples were irradiated at
453 nm since all complexes absorb strongly in this region.
The refractive index of the sample and the reference solu-
2.2. Synthesis of compound 3
Compound 2 (0.501 g, 1 mmol) was dissolved in
MeOH (100 mL) and KOH (0.5 g) was added. The solu-
tion was stirred at r.t. for 2 h. The solvent was then
removed, and the residue was dissolved in CH2Cl2. The
organic solution was washed with water. The organic
extract was dried, and the solvent was removed to give
a pale yellow crystalline solid. Yield: 0.408 g, 95%. 1H

4516
M.P.Y. Yu et al. / Journal of Organometallic Chemistry 691 (2006) 4514–4531
NMR (CDCl3): d 8.48 (s, 1H, minor isomer, NHCHO),
8.04 (d, J = 11.8 Hz, 1H, major isomer, NHCHO), 7.56–
7.37 (10H, C6H4CC, C6H2i-Pr2), 7.18 (d, J = 11.8 Hz,
1H, major isomer, NHCHO), 6.82 (s, 1H, minor isomer,
NHCHO), 3.25–3.20 (m, 2H, major isomer, CHCH3),
3.19 (s, 1H, C„CH), 3.16–3.06 (m, 2H, minor isomer,
CHCH3), 1.24 (d, J = 6.8 Hz, 12H, CHCH3). 13C{1H}
NMR (CDCl3): d 164.8 (NHCHO, major isomer), 160.4
(NHCHO, minor isomer), 146.9, 146.5, 132.1, 131.6,
131.5, 130.2, 129.9, 127.3, 127.1, 123.5, 123.4, 123.3,
123.1, 127.1, 123.5, 123.4, 123.3, 123.1, 123.0, 122.7,
122.1 (C6H4CC, C6H2i-Pr2), 91.5, 91.0, 90.8, 89.4, 89.0
(C„C), 83.2 (C„CH), 28.8, 28.5 (CHCH3), 23.5
(CHCH3). IR (CH2Cl2, cmꢀ1): 2108 (w, mC„CH). mp
197–200 ꢁC. MS (EI): 429 (M+).
123.2, 123.0, 122.9, 121.3 (PPh2, CC6H4CC, C6H4,
C6H2i-Pr2), 91.3, 91.1, 91.0, 89.5 (C„C), 28.8, 28.5
(CH(CH3)2), 27.6, 27.2, 27.0 (CH2PPh2), 23.5 (CH3).
31P{1H} NMR (CDCl3): d 39.2 (1JWP = 231 Hz). IR
(CH2Cl2, cmꢀ1): 2008 (s, mCO), 1940 (s, mCO), 1697 (m,
m
C@O). UV (CH2Cl2, nm) (e, Mꢀ1 cmꢀ1): 460 (1500, sh),
380 (77000). mp 150–153 ꢁC (dec.).
2.5. Synthesis of compound 12
Compound 6 (0.300 g, 0.252 mmol) was dissolved in
CH2Cl2 (50 mL), and 0.56 mL NEt3 was added. After
cooling to ꢀ78 ꢁC, a solution of triphosgene (50 mg) in
CH2Cl2 (10 mL) was added. The resulting mixture was
allowed to warm to 0 ꢁC and stirred for 30 min. The sol-
vent was then removed in vacuo. The residue was washed
with hexane and redissolved in THF (30 mL). After filtra-
tion, the solvent was removed in vacuo. The residue was
redissolved in CH2Cl2. After filtration, hexane was added
to the solution to afford yellow-orange crystals. Yield:
0.136 g, 46%. 1H NMR (CDCl3): d 7.75–7.65 (8H,
PPh2), 7.56–7.20 (26H, PPh2, C6H4CC, C6H2i-Pr2), 7.10
(d, J = 8.3 Hz, 2H, CC6H4), 6.45 (d, J = 8.3 Hz, 2H,
CC6H4), 3.37 (hept, J = 6.9 Hz, 2H, CHCH3), 3.01–2.84
(m, 2H, CH2PPh2), 2.75–2.56 (m, 2H, CH2PPh2), 1.30
(d, J = 6.9 Hz, 12H, CH3). 13C{1H} NMR (CDCl3): d
2.3. Synthesis of compound 4
Compound 3 (0.429 g, 1.00 mmol) was dissolved in
CH2Cl2 (30 mL), and NEt3 (2 mL) was added. A CH2Cl2
solution of triphosgene (0.15 g, 50% excess) was added at
ꢀ78 ꢁC. The mixture was warmed to r.t. and stirred for
2 h. Water was then added to the solution to destroy the
excess triphosgene. The organic layer was dried, and the
solvent was removed to give a yellow crystalline solid.
Yield: 0.354 g, 86%. 1H NMR (CDCl3): d 7.53 (s, 4H,
C6H4CC), 7.48 (s, 4H, C6H4CC), 3.42–3.33 (m, 2H,
CHCH3), 3.19 (s, 1H, CCH), 1.30 (d, J = 6.9 Hz, 12H,
CH3). 13C{1H} NMR (CDCl3): d 170.1 (N„C), 145.3,
132.1, 131.6, 131.5, 126.7, 124.1, 123.4, 123.2, 122.8,
122.2 (C6H4CC, C6H2i-Pr2), 90.9, 90.8, 90.6 (C„C), 83.2
(CCH), 79.1 (CCH). IR (CH2Cl2, cmꢀ1): 2118 (s, mC„N).
mp 140–143 ꢁC.
cis
trans
1
265.0 (W„C), 212.3 (CO, 1JPC ¼ 7:0 Hz; JPC
¼ 46:0 Hz), 170.4 (N„C), 149.0, 145.3, 135.5, 133.0,
132.9, 132.7, 132.6, 132.5, 132.4, 131.7, 131.6, 131.5,
130.6, 130.3, 130.1, 129.5, 128.6, 128.5, 128.4, 128.3,
126.8, 126.7, 124.2, 123.4, 123.3, 122.9, 121.4 (CC6H4,
C6H4CC, C6H2i-Pr2), 92.0, 91.3, 91.0, 90.8, 90.7 (C„C),
29.9, 27.5, 27.4, 27.3, 27.2 (CH2PPh2), 22.5 (CH3).
31P{1H} NMR (CDCl3): d 39.2 (1JWP = 231 Hz). IR
(CH2Cl2, cmꢀ1): 2116 (m, mCN), 2008 (s, mCO), 1940 (s,
2.4. Synthesis of compound 6
m
CO). mp 165–168 ꢁC (dec.).
Compound 5 (1.78 g, 2.00 mmol) was dissolved in THF
(30 mL), and HNEt2 (4 mL) was added. To this solution,
2.6. Synthesis of compound 13
compound
3
(1.03 g, 1.47 mmol), cis-PdCl2(PPh3)2
(20 mg), and CuI (20 mg) were added to this solution.
The resulting mixture was stirred at r.t. overnight. The
solvent was removed in vacuo. The residue was washed
with hexane, dried, and redissolved in CH2Cl2. After fil-
tration, hexane was added to the solution to afford yel-
A suspension of Cr(CO)6 (0.050 g, 0.227 mmol) in THF
(20 mL) was irradiated by a UV lamp for 2 h and then
transferred to a solution of 7 (0.115 g, 0.227 mmol) in
THF (30 mL) at 0 ꢁC. The resulting mixture was stirred
at 0 ꢁC for 3 h, and the solvent was removed in vacuo.
The residue was washed with hexane, dried, and redis-
solved in CH2Cl2. After filtration, hexane was added to
the solution to afford a light orange precipitate. Yield:
1
low-orange micro-crystals. Yield: 1.56 g, 65%. H NMR
(CDCl3): d 8.47 (s, 1H, NHCHO, minor isomer), 8.04
(d, J = 11.8 Hz, 1H, NHCHO, major isomer), 7.75–7.19
(30H, PPh2, C6H4, C6H2i-Pr2), 7.10 (d, J = 8.3 Hz, 2H,
CC6H4), 6.91 (d, J = 11.8 Hz, 1H, NHCHO, major iso-
mer), 6.74 (s, 1H, NHCHO, minor isomer), 6.45 (d,
J = 8.3 Hz, 2H, CC6H4), 3.25–3.13 (m, 2H, CH(CH3)2),
3.10–2.84 (m, 2H, CH2PPh2), 2.73–2.58 (m, 2H,
CH2PPh2), 1.24 (d, J = 6.8 Hz, 12H, CH3). 13C{1H}
NMR (CDCl3): d 164.7 (NHCHO, major isomer), 160.4
(NHCHO, minor isomer), 146.9, 146.5, 135.9, 135.3,
133.0, 132.8, 132.7, 132.5, 132.1, 131.6, 131.4, 130.6,
130.3, 130.1, 129.4, 128.6, 128.5, 127.3, 127.1, 123.3,
0.05 g, 33%. 1H NMR (CDCl3):
d 7.23–7.21 (4H,
C6H4NC), 3.21 (s, 6H, NCH3), 3.06–2.92 (br, 4H,
NCH2), 2.96 (s, 6H, NCH3). 13C{1H} NMR (CDCl3): d
257.3 (W„C), 220.4 (CO), 216.4, 214.3 (Cr-CO), 149.3,
130.2, 126.2, 125.9 (C6H4NC), 61.1, 58.2, 52.3
(CH2N(CH3)2). IR (CH2Cl2, cmꢀ1): 2137 (m, mCN), 2056
(s, mCr–CO), 1990 (s, mCO), 1956 (vs, mCr–CO), 1902 (s, mCO).
Anal. Calc. for C21H20ClCrN3O7W: C, 36.15; H, 2.89; N,
6.02. Found: C, 36.14; H, 2.92; N, 5.98%. mp 165–170 ꢁC
(dec.).

M.P.Y. Yu et al. / Journal of Organometallic Chemistry 691 (2006) 4514–4531
4517
2.7. Synthesis of compound 14
After filtration, the solvent was removed in vacuo. The res-
idue was washed with hexane, dried, and redissolved in
CH2Cl2. After filtration, hexane was added to the solution
to afford 7 as dull red crystals. Yield: 66%. 1H NMR
(CDCl3): d 7.39 (d, J = 8.6 Hz, 2H, C6H4NC), 7.26 (d,
J = 8.6 Hz, 2H, C6H4NC), 3.21 (s, 6H, NCH3), 3.03–2.86
(br, 4H, NCH2), 2.96 (s, 6H, NCH3). 13C{1H} NMR
(CDCl3): d 256.0 (W„C), 220.2 (CO), 151.3, 130.2,
126.5, 122.9 (C6H4NC), 61.1, 58.3, 52.4 (CH2N(CH3)2).
IR (CH2Cl2, cmꢀ1): 2199 (m, mCN), 1992 (s, mCO), 1906 (s,
A solution of ReCl(CO)5 (50 mg, 0.14 mmol) in THF
(100 mL) was stirred under reflux overnight. Then 7
(0.15 g, 0.30 mmol) was added. The resulting mixture was
stirred at r.t. for 1 h, and the solvent was removed in vacuo.
The residue was washed with hexane, dried, and redis-
solved in CH2Cl2. After filtration, hexane was added to
the solution to afford a light orange precipitate. Yield:
1
0.118 g, 73%. H NMR (CD2Cl2): d 7.36 (d, J = 8.6 Hz,
2H, C6H4NC), 7.27 (d, J = 8.6 Hz, 2H, C6H4NC), 3.18
(s, 6H, NCH3), 2.95–2.88 (br, 4H, NCH2), 2.91 (s, 6H,
NCH3). 13C{1H} NMR (CD2Cl2): d 257.5 (W„C), 221.5
(CO), 187.6, 184.6 (ReCO), 150.8, 130.6, 127.1, 124.5
(C6H4NC), 61.4, 58.5 (CH2N(CH3)2). IR (CH2Cl2, cmꢀ1):
2185 (w, mCN), 2151 (m, mCN), 2039 (s, mRe–CO), 1992 (s,
mCO). Anal. Calc. for C32H40Cl2I2N6O4PdW2: C, 28.02;
H, 2.94; N, 6.13. Found: C, 27.97; H, 2.98; N, 5.95%. mp
163–170 ꢁC (dec.).
2.11. Synthesis of compound 18
m
CO), 1933 (m, mRe–CO), 1904 (s, mCO). Anal. Calc. for
The synthesis follows the procedure described for 17,
whereby PtI2 was used instead of PdI2. The mixture of 7
and PtI2 was stirred at 0 ꢁC overnight. A subsequent
workup procedures similar to that of 17 afforded 18 as
red crystals. Yield: 46%. 1H NMR (CDCl3): d 7.38 (d,
J = 8.5 Hz, 2H, C6H4NC), 7.26 (d, J = 8.5 Hz, 2H,
C6H4NC), 3.21 (s, 6H, NCH3), 3.01–2.88 (m, 4H,
NCH2), 2.96 (s, 6H, NCH3). 13C{1H} NMR (CDCl3): d
256.1 (W„C), 220.2 (CO), 151.2, 130.2, 126.6, 123.1
(C6H4NC), 61.1, 58.3, 52.4 (CH2N(CH3)2). IR (CH2Cl2,
cmꢀ1): 2193 (m, mCN), 1994 (s, mCO), 1904 (s, mCO). Anal.
Calc. for C32H40Cl2I2N6O4PtW2: C, 26.32; H, 2.76; N,
5.76. Found: C, 26.18; H, 2.84; N, 5.69%. mp 170–180 ꢁC
(dec.).
C35H40Cl3N6O7ReW2: C, 31.92; H, 3.06; N, 6.38. Found:
C, 31.88; H, 2.79; N, 6.08%. mp 190–195 ꢁC (dec.).
2.8. Synthesis of compound 15
The synthesis follows the procedure described for 14,
whereby ReBr(CO)5 and 8 were used. Light-orange precip-
itate. Yield: 56%. 1H NMR (CD2Cl2): d 7.37 (d,
J = 8.6 Hz, 2H, C6H4NC), 7.32 (d, J = 8.6 Hz, 2H,
C6H4NC), 3.24 (s, 6H, NCH3), 3.04 (s, 6H, NCH3), 2.95
(m, 4H, CH2N(CH3)2). 13C{1H} NMR (CD2Cl2): d 258.1
(W„C), 221.4 (CO), 187.1, 184.7 (ReCO), 150.7, 131.2,
127.7, 125.3 (C6H4NC), 62.1, 59.2 (CH2N(CH3)2). IR
(CH2Cl2, cmꢀ1): 2181 (w, mCN), 2151 (m, mCN), 2037 (s,
m
Re–CO), 1992 (s, mCO), 1935 (m, mRe–CO), 1904 (s, mCO).
2.12. Synthesis of compound 19
Anal. Calc. for C35H40BrCl2N6O7ReW2 Æ 0.25C6H14: C,
29.44; H, 2.81; N, 5.64. Found: C, 29.43; H, 2.47; N,
5.74%. mp 190–195 ꢁC (dec.).
The synthesis follows the procedure described for 14,
whereby 9 was used. Light-orange precipitate. Yield:
64%. 1H NMR (CDCl3): d 7.74–7.20 (20H, PPh2), 7.01
(d, J = 8.5 Hz, 2H, C6H4NC), 6.41 (d, J = 8.5 Hz, 2H,
C6H4NC), 3.01–2.89 (m, 2H, CH2PPh2), 2.74–2.62 (m,
2.9. Synthesis of compound 16
To a suspension of PdCl2 (25 mg) in THF (30 mL), com-
pound 7 (0.118 g) was added. The mixture was stirred at r.t.
overnight, and the solvent was removed in vacuo. The res-
idue was washed with hexane, dried, and redissolved in
CH2Cl2. After filtration, hexane was added to the solution
2H, CH2PPh2). 13C{1H} NMR (CDCl3):
d
260.6
cis
trans
1
1
(W„C), 211.9 (CO, JPC ¼ 6:0 Hz; JPC ¼ 46:0 Hz),
186.5, 184.0 (ReCO), 150.4, 146.0, 136.0, 135.4, 133.0,
132.9, 132.7, 132.6, 132.5, 132.3, 132.2, 132.0, 131.7,
130.5, 130.3, 130.0, 128.7, 128.6, 128.3, 126.2, 126.1,
123.6 (PPh2, C6H4NC), 27.5, 27.3, 27.1, 26.9 (CH2PPh2).
31P NMR (CDCl3): d 38.0 (1JWP = 232 Hz). IR (CH2Cl2,
cmꢀ1): 2185 (w, mCN), 2149 (m, mCN), 2039 (s, mRe–CO),
2012 (s, mCO), 1994 (s, mRe–CO), 1944 (s, mCO). mp 168–
170 ꢁC (dec.).
1
to afford a yellow-orange crystalline solid. Yield: 32%. H
NMR (CD2Cl2): d 7.42 (d, J = 8.5 Hz, 2H, CC6H4), 7.29
(d, J = 8.5 Hz, 2H, CC6H4), 3.18 (s, 6H, NCH3), 2.91 (s,
6H, NCH3), 3.00–2.86 (br, 4H, NCH2). 13C{1H} NMR
(CD2Cl2): d 256.3 (W„C), 221.4 (CO), 152.1, 130.7,
127.2, 122.9 (CC6H4), 61.5, 58.6 (CH3NCH2). IR (CH2Cl2,
cmꢀ1): 2228 (w, mCN), 2212 (w, mCN), 1994 (s, mCO), 1906 (s,
2.13. Synthesis of compound 20
m
CO). mp 147–150 ꢁC (dec.).
Compound 9 (0.14 g) was added to a suspension of
PdI2(48 mg) in THF (50 mL). The resulting mixture was
stirred at r.t. for 24 h. After filtration, the solvent was
removed in vacuo. The residue was washed with hexane,
dried, and redissolved in CH2Cl2. After filtration, hexane
was added to the solution to afford orange micro-crystals.
2.10. Synthesis of compound 17
A solution of 7 (0.5 mmol) in THF (50 mL) was trans-
ferred to a supsension of PdI2(0.22 mmol, 0.079 g) in
THF (20 mL). The mixture was stirred at 0 ꢁC for 1 h.

4518
M.P.Y. Yu et al. / Journal of Organometallic Chemistry 691 (2006) 4514–4531
1
Yield: 25%. H NMR (CDCl3): d 7.74–7.22 (20H, PPh2),
7.05 (d, J = 8.6 Hz, 2H, C6H4NC), 6.40 (d, J = 8.6 Hz,
2H, C6H4NC), 3.02–2.87 (m, 2H, CH2PPh2), 2.78–2.64
(m, 2H, CH2PPh2). 13C{1H} NMR (CDCl3): d 260.0
2.16. Synthesis of compound 23
The synthesis follows the procedure described for 20,
using 10 and PdI2. Orange-yellow micro-crystals. Yield:
1
cis
trans
1
1
(W„C), 211.8 (CO, JPC ¼ 7:0 Hz; JPC ¼ 46:0 Hz),
151.4, 135.9, 135.6, 133.0, 132.9, 132.8, 132.6, 132.8,
132.4, 132.3, 132.0, 130.5, 130.4, 130.3, 130.2, 128.9,
128.8, 128.7, 128.6, 128.5, 128.4, 128.0, 125.9, 125.7,
122.6 (PPh2, C6H4NC), 27.5, 27.4, 27.2, 27.1 (CH2PPh2).
31P NMR (CDCl3): d 37.8 (1JWP = 232 Hz). IR (CH2Cl2,
cmꢀ1): 2199 (m, mCN), 2014 (s, mCO), 1946 (s, mCO). mp
150–152 ꢁC (dec.).
30%. H NMR (CDCl3): d 7.75–7.61 (8H, PPh2), 7.59 (d,
J = 6.8 Hz, 2H, C6H4NC), 7.52 (d, J = 6.8 Hz, C6H4NC),
7.50–7.20 (12H, PPh2), 7.11 (d, J = 8.3 Hz, 2H,
C6H4CC), 6.46 (d, J = 8.3 Hz, 2H, C6H4CC), 2.97–2.89
(m, 2H, CH2PPh2), 2.72–2.64 (m, 2H, CH2PPh2).
13C{1H} NMR (CDCl3): d 264.5 (W„C), 212.2 (CO,
cis
trans
1
1JPC ¼ 6:0 Hz; JPC ¼ 46:0 Hz), 149.4, 135.9, 135.3,
133.0, 132.9, 132.8, 132.7, 132.6, 132.5, 132.0, 130.8,
130.3, 130.1, 129.5, 128.6, 128.5, 128.3, 126.8, 124.5,
120.3 (PPh2, C6H4CC, C6H4NC), 94.1, 89.5 (C„C), 27.6,
27.4, 27.2, 27.0 (CH2PPh2). 31P NMR (CDCl3): d 38.5
(1JWP = 231 Hz). IR (CH2Cl2, cmꢀ1): 2201 (m, mCN), 2008
(s, mCO), 1940 (s, mCO). Anal. Calc. for C88H64Cl2I2-
N2O4P4PdW2 Æ 0.5CH2Cl2: C, 48.78; H, 3.01; N, 1.29.
Found: C, 48.67; H, 2.73; N, 1.37%. mp 135–139 ꢁC (dec.).
2.14. Synthesis of compound 21
The synthesis follows the procedure described for 20,
whereby PtI2 was used. The mixture of 9 and PtI2 was stir-
red at r.t. for 2 h to afford 21 as orange microcrystals.
1
Yield: 0.13 g, 72%. H NMR (CDCl3): d 7.74–7.21 (20H,
PPh2), 7.04 (d, J = 8.6 Hz, 2H, C6H4NC), 6.40 (d,
J = 8.6 Hz, 2H, C6H4NC), 3.02–2.86 (m, 2H, CH2PPh2),
2.80–2.62 (m, 2H, CH2PPh2). 13C{1H} NMR (CDCl3): d
2.17. Synthesis of compound 24
cis
trans
260.1 (W„C), 211.8 (CO, 1JPC ¼ 7:0 Hz; JPC
¼ 46:0 Hz), 184.3 (N„C), 151.3, 135.9, 135.6, 134.1,
134.0, 133.0, 132.9, 132.8, 132.6, 132.5, 132.4, 132.3,
132.0, 130.5, 130.4, 130.3, 130.2, 128.8, 128.7, 128.6,
128.5, 128.4, 126.0, 125.9, 122.8 (PPh2, C6H4NC), 27.5,
27.4, 27.3, 27.2 (CH2PPh2). 31P NMR (CDCl3): d 37.8
(1JWP = 232 Hz). IR (CH2Cl2, cmꢀ1): 2191 (m, mCN), 2014
(s, mCO), 1946 (s, mCO). mp 170–172 ꢁC (dec.).
The synthesis follows the procedure described for 21,
using 10 and PtI2. Orange-yellow micro-crystals. Yield:
1
1
30%. H NMR (CDCl3): d 7.74–7.65 (8H, PPh2), 7.58 (d,
J = 8.6 Hz, 2H, C6H4NC), 7.51 (d, J = 8.6 Hz, 2H,
C6H4NC), 7.39–7.20 (12H, PPh2), 7.11 (d, J = 8.3 Hz,
2H, C6H4CC), 6.46 (d, J = 8.3 Hz, 2H, C6H4CC), 3.01–
2.86 (m, 2H, CH2PPh2), 2.74–2.64 (m, 2H, CH2PPh2).
13C{1H} NMR (CDCl3): d 264.4 (W„C), 212.3 (CO,
cis
trans
1
1JPC ¼ 7:0 Hz; JPC ¼ 45:0 Hz), 149.4, 135.8, 135.4,
134.0, 132.9, 132.7, 132.6, 132.5, 132.4, 132.2, 132.0,
131.1, 130.8, 130.5, 130.3, 130.2, 129.5, 129.4, 129.2,
128.8, 128.6, 128.5, 128.4, 128.3, 127.8, 126.9, 126.7,
124.8, 120.4 (PPh2, C6H4NC, C6H4CC), 94.1, 89.6
(C„C), 27.4, 27.3, 27.2, 27.1 (CH2PPh2). 31P NMR
(CDCl3): d 38.5 (1JWP = 231 Hz). IR (CH2Cl2, cmꢀ1):
2197 (m, mCN), 2006 (s, mCO), 1942 (s, mCO). Anal. Calc.
for C88H64Cl2I2N2O4P4PtW2 Æ 0.5CH2Cl2: C, 46.88; H,
2.89; N, 1.24. Found: C, 46.77; H, 2.21; N, 1.45%. mp
147–150 ꢁC (dec.).
2.15. Synthesis of compound 22
ReCl(CO)5 (20 mg) was dissolved in THF (30 mL) and
stirred under reflux overnight. Then 0.118 g (20% excess)
of 10 was added. The resulting mixture was stirred at r.t.
for 4 h. The solvent was removed in vacuo. The residue
was washed with hexane, dried, and redissolved in
CH2Cl2. After filtration, hexane was added to the solu-
tion to afford orange micro-crystals. Yield: 50 mg
1
(43%). H NMR (CDCl3): d 7.72–7.59 (8H, PPh2), 7.56
(d, J = 8.7 Hz, 2H, C6H4NC), 7.47 (d, J = 8.7 Hz, 2H,
C6H4NC), 7.44–7.15 (12H, PPh2), 7.10 (d, J = 8.3 Hz,
2H, C6H4CC), 6.46 (d, J = 8.3 Hz, 2H, C6H4CC), 2.95–
2.88 (m, 2H, CH2PPh2), 2.71–2.59 (m, 2H, CH2PPh2).
13C{1H} NMR (CDCl3): d 264.5 (W„C), 211.9 (CO,
1JcPiCs ¼ 8:0 Hz), 186.3, 183.9 (ReCO), 149.3, 146.6,
135.9, 135.3, 134.1, 133.5, 133.0, 132.9, 132.8, 132.7,
132.5, 132.4, 132.3, 132.0, 131.0, 130.8, 130.7, 130.6,
130.5, 130.3, 130.1, 129.5, 129.2, 128.9, 128.8, 128.6,
128.5, 128.4, 128.3, 127.1, 127.0, 125.6, 120.4 (PPh2,
C6H4NC, C6H4CC), 93.6, 89.7 (C„C), 27.6, 27.4, 27.2,
2.18. Synthesis of compound 25
Compound 11 (290 mg) was added to a suspension of
PdI2 (48 mg) in THF (30 mL). The mixture was stirred at
r.t. overnight, followed by filtration. Then the solvent
was removed in vacuo. The residue was washed with hex-
ane, dried, and redissolved in CH2Cl2. After filtration, hex-
ane was added to the solution to afford a yellow-orange
1
crystalline solid. Yield: 32%. H NMR (CDCl3): d 7.73–
7.67 (8H, PPh2), 7.53 (d, J = 8.4 Hz, 2H, C6H4), 7.49 (d,
J = 8.4 Hz, 2H, C6H4), 7.41–7.21 (14H, PPh2, C6H2i-Pr2),
7.10 (d, J = 8.3 Hz, 2H, CC6H4), 6.46 (d, J = 8.3 Hz, 2H,
CC6H4), 3.59–3.53 (m, 2H, CH(CH3)2), 2.98–2.89 (m,
2H, CH2PPh2), 2.70–2.61 (m, 2H, CH2PPh2), 1.36 (d,
J = 6.8 Hz, 12H, CH3). 13C{1H} NMR (CDCl3): d 264.9
27.0 (CH2PPh2). 31P NMR (CDCl3):
d
39.2
(1JWP = 231 Hz). IR (CH2Cl2, cmꢀ1): 2210 (w, mC„C),
2185 (w, mCN), 2151 (m, mCN), 2039 (s, mRe–CO), 2008 (s,
m
CO), 1994 (s, mRe–CO), 1940 (s, mCO). mp 150–153 ꢁC
(dec.).

M.P.Y. Yu et al. / Journal of Organometallic Chemistry 691 (2006) 4514–4531
4519
cis
trans
1
1
(W„C), 212.3 (CO, JPC ¼ 6:0 Hz; JPC ¼ 46:0 Hz),
148.9, 147.2, 135.8, 135.2, 132.9, 132.8, 132.7, 132.5,
132.1, 131.7, 131.5, 130.6, 130.3, 130.1, 129.4, 128.8,
128.6, 128.5, 127.0, 126.0, 123.7, 122.9, 122.3, 121.2
(PPh2, CC6H4CC, C6H4, C6H2i-Pr2), 92.1, 91.9, 91.1, 90.5
(C„C), 29.7 (CH(CH3)2), 27.5, 27.4, 27.1, 27.0 (CH2PPh2),
22.9 (CH3). 31P NMR (CDCl3): d 39.2 (1JWP = 231 Hz). IR
(CH2Cl2, cmꢀ1): 2191 (m, mCN), 2008 (s, mCO), 1940 (s, mCO).
mp 165–168 ꢁC (dec.).
C6H4CC, C6H2i-Pr2), 92.0, 91.9, 91.4, 91.3, 91.0, 90.5
(C„C), 29.7 (CHCH3), 27.5, 27.4, 27.3, 27.2 (CH2PPh2),
22.9 (CH3). 31P NMR (CDCl3): d 39.2 (1JWP = 231 Hz).
IR (CH2Cl2, cmꢀ1): 2193 (m, mCN), 2008 (s, mCO), 1940 (s,
m
CO). mp 170–173 ꢁC (dec.).
2.21. Synthesis of compound 28
Compound 12 (290 mg) was added to a suspension of
PtI2 (60 mg) in THF (30 mL). The mixture was stirred at
r.t. overnight, followed by filtration. The solvent was
removed in vacuo. The residue was washed with hexane,
dried, and redissolved in CH2Cl2. After filtration, hexane
was added to the solution to afford a yellow-orange crystal-
2.19. Synthesis of compound 26
Compound 11 (290 mg) was added to a suspension of
PtI2 (60 mg) in THF (30 mL). The mixture was stirred at
r.t. overnight, followed by filtration. Then the solvent
was removed in vacuo. The residue was washed with hex-
ane, dried, and redissolved in CH2Cl2. After filtration, hex-
ane was added to the solution to afford a yellow-orange
1
line solid. Yield: 0.22 g, 64%. H NMR (CDCl3): d 7.75–
7.66 (8H, PPh2), 7.60–7.20 (26H, PPh2, C6H4CC, C6H2i-
Pr2), 7.10 (d, J = 8.3 Hz, 2H, CC6H4), 6.46 (d,
J = 8.3 Hz, 2H, CC6H4), 3.57 (hept, J = 6.8 Hz, 2H,
CHCH3), 3.01–2.84 (m, 2H, CH2PPh2), 2.75–2.58 (m,
2H, CH2PPh2), 1.37 (d, J = 6.8 Hz, 12H, CH3). 13C{1H}
NMR (CDCl3): d (signals for alkylidyne and carbonyl car-
bon atoms not found) 147.2, 135.9, 135.3, 133.0, 132.9,
132.8, 132.7, 132.6, 132.5, 132.1, 131.7, 131.6, 131.5,
130.6, 130.4, 130.3, 130.1, 129.4, 128.6, 128.5, 127.1,
125.9, 123.5, 123.3, 122.8, 122.5, 121.3 (CC6H4, C6H4CC,
C6H2i-Pr2), 91.9, 91.8, 91.4, 91.3, 90.9, 90.6 (C„C), 29.6,
27.6, 27.4 (CH2PPh2), 22.8 (CH3). 31P NMR (CDCl3): d
38.5 (1JWP = 231 Hz). IR (CH2Cl2, cmꢀ1): 2187 (m, mCN),
2008 (s, mCO), 1940 (s, mCO). mp 170–173 ꢁC (dec.).
1
crystalline solid. Yield: 46%. H NMR (CDCl3): d 7.75–
7.66 (8H, PPh2), 7.54 (d, J = 8.6 Hz, 2H, C6H4), 7.50 (d,
J = 8.6 Hz, 2H, C6H4), 7.40–7.20 (14H, PPh2, C6H2i-Pr2),
7.10 (d, J = 8.3 Hz, 2H, CC6H4), 6.46 (d, J = 8.3 Hz, 2H,
CC6H4), 3.61–3.47 (m, 2H, CH(CH3)2), 3.12–2.86 (m,
2H, CH2PPh2), 2.74–2.55 (m, 2H, CH2PPh2), 1.36 (d,
12H, CH3). 13C{1H} NMR (CDCl3): d (signal for alkyli-
dyne
carbon
atom
not
found)
212.3
(CO,
cis
trans
1JPC ¼ 6:0 Hz; JPC ¼ 46:0 Hz), 156.8, 148.9, 147.1,
135.8, 135.2, 133.8, 132.9, 132.8, 132.7, 132.5, 132.3,
132.1, 131.9, 131.7, 131.5, 130.9, 130.7, 130.6, 130.3,
130.1, 129.8, 129.7, 129.6, 129.4, 129.1, 129.0, 128.8,
128.6, 128.5, 128.3, 128.0, 127.3, 127.0, 126.0, 125.9,
123.7, 123.5, 122.8, 122.3, 122.2, 122.1, 121.8, 121.2,
119.7, 115.8, 106.1 (PPh2, CC6H4CC, C6H4, C6H2i-Pr2),
92.1, 91.9, 91.1, 90.5 (C„C), 29.6 (CH(CH3)2), 27.5,
27.4, 27.1, 27.0 (CH2PPh2), 22.8 (CH3). 31P NMR (CDCl3):
d 39.2 (1JWP = 231 Hz). IR (CH2Cl2, cmꢀ1): 2187 (m, mCN),
2008 (s, mCO), 1940 (s, mCO). mp 168–171 ꢁC (dec.).
1
2.22. Synthesis of compound 29
The synthesis follows the procedure described for 13,
whereby 2,6-diisopropylisocyanobenzene was used. White
1
crystals. Yield: 30%. H NMR (CDCl3): d 7.31 (m, 1H,
C6H3NC), 7.18 (d, J = 7.7 Hz, 2H, C6H3NC), 3.26 (hept,
J = 6.9 Hz, 2H, CHMe2), 1.32 (d, J = 6.9 Hz, 12H, CH3).
13C{1H} NMR (CDCl3): d 216.8, 214.5 (CO), 144.9,
129.1, 123.5 (C6H3NC), 30.2 (CHMe2), 22.4 (CH3). IR
(CH2Cl2, cmꢀ1): 2141 (w, mCN), 2058 (m, mCO), 1956 (s, mCO).
2.20. Synthesis of compound 27
Compound 12 (300 mg) was added to a suspension of
PdI2 (48 mg) in THF (30 mL). The mixture was stirred at
r.t. overnight. After filtration, the solvent was removed in
vacuo. The residue was washed with hexane, dried, and
redissolved in CH2Cl2. After filtration, hexane was added
to the solution to afford a yellow-orange crystalline solid.
2.23. Synthesis of compound 30
The synthesis follows the procedure described for 14,
whereby 2,6-diisopropylisocyanobenzene was used. White
1
crystals. Yield: 40%. H NMR (CDCl3): d 7.36 (m, 1H,
1
Yield: 0.157 g, 43%. H NMR (CDCl3): d 7.75–7.66 (8H,
C6H3NC), 7.20 (d, J = 7.8 Hz, 2H, C6H3NC), 3.38 (hept,
J = 6.9 Hz, 2H, CHMe2), 1.30 (d, J = 6.9 Hz, 12H, CH3).
13C{1H} NMR (CDCl3): d 186.9, 184.1 (CO), 145.9,
130.2, 123.6 (C6H3NC), 30.1 (CHMe2), 22.5 (CH3). IR
(CH2Cl2, cmꢀ1): 2185 (w, mCN), 2154 (w, mCN), 2039 (m,
PPh2), 7.58–7.20 (26H, PPh2, C6H4CC, C6H2i-Pr2), 7.10
(d, J = 8.3 Hz, 2H, CC6H4), 6.46 (d, J = 8.3 Hz, 2H,
CC6H4), 3.56 (hept, J = 6.8 Hz, 2H, CHCH3), 3.01–2.58
(m, 2H, CH2PPh2), 1.37 (d, J = 6.8 Hz, 12H, CH3).
13C{1H} NMR (CDCl3): d 265.0 (W„C), 212.3 (CO,
m
CO), 1989 (s, mCO), 1931 (s, mCO).
trans
cis
1
1JPC ¼ 46:0 Hz; JPC ¼ 7:0 Hz), 149.0, 147.3, 135.9,
135.6, 133.0, 132.9, 132.7, 132.6, 132.4, 132.1, 131.8,
131.7, 131.5, 130.9, 130.6, 130.3, 130.1, 129.5, 129.3,
129.1, 128.9, 128.8, 128.6, 128.5, 128.4, 128.3, 127.1,
126.2, 123.6, 123.4, 123.0, 122.9, 122.6, 121.4 (CC6H4,
2.24. Synthesis of compound 31
To a suspension of PdCl2 (0.25 g) in THF (30 mL), 2,6-i-
Pr2C6H3NC (0.82 g) was added. The mixture was stirred at

4520
M.P.Y. Yu et al. / Journal of Organometallic Chemistry 691 (2006) 4514–4531
Table 1
r.t. overnight, followed by filtration. Then the solvent was
removed in vacuo. The residue was washed with hexane,
dried, and redissolved in CH2Cl2. After filtration, hexane
was added to the solution to afford yellow micro-crystals.
Crystal and data collection parameters for complex 17
Formula
W2I2PdCl2O4N6C32H40
1371.52
Triclinic
Formula weight
Crystal system
Space group
Yield: 50%. 1H NMR (CDCl3):
d 7.61–7.36 (1H,
ꢀ
P1 ðNo: 2Þ
C6H3NC), 7.27–7.21 (2H, C6H3NC), 3.36 (hept,
J = 6.9 Hz, 2H, CHCH3), 13.2 (d, J = 6.9 Hz, 12H,
CH3). 13C{1H} NMR (CDCl3): d 146.7, 146.4, 131.7,
131.4, 124.0, 123.7 (C6H3NC), 29.8 (CHCH3), 22.7
(CH3). IR (CH2Cl2, cmꢀ1): 2224 (s, mCN), 2210 (s, mCN).
˚
a (A)
11.934(3)
26.196(3)
7.452(2)
97.46(2)
105.19(2)
78.40(2)
105.19(2)
2
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
2.25. Synthesis of compound 32
Z
Dcal (g cmꢀ3
)
2.075
72.07
1280
301
l (cmꢀ1
F(000)
T (K)
)
The synthesis follows the procedure described for 17,
whereby 2,6-diisopropylisocyanobenzene was used. Yel-
low-orange cyrstals. Yield: 75%. 1H NMR (CDCl3): d
7.41 (m, 1H, C6H3NC), 7.23 (d, J = 7.8 Hz, 2H,
C6H3NC), 3.56 (hept, J = 6.8 Hz, 2H, CHMe2), 1.34 (d,
J = 6.8 Hz, 12H, CH3). 13C{1H} NMR (CDCl3): d 146.9,
131.1, 123.7 (C6H3NC), 29.6 (CHMe2), 23.0 (CH3). IR
(CH2Cl2, cmꢀ1): 2197 (s, mCN).
Crystal color
Red
Crystal dimensions (mm3)
Total reflections measured
Unique reflections
R
0.20 · 0.15 · 0.30
6053
5721
0.035
0.044
1.74
0.04
1.08
ꢀ0.68
Rw
Goodness-of-fit
Maximum D/r
Maximum peak in final Fourier map (e A
Minimum peak in final Fourier map (e A
ꢀ3
˚
˚
)
2.26. Synthesis of compound 33
ꢀ3
)
The synthesis follows the procedure described for 18,
whereby 2,6-diisopropylisocyanobenzene was used. Dull
yellow cyrstals. Yield: 55%. 1H NMR (CDCl3): d 7.41
(m, 1H, C6H3NC), 7.23 (d, J = 7.8 Hz, 2H, C6H3NC),
3.56 (hept, J = 6.8 Hz, 2H, CHMe2), 1.34 (d, J = 6.8 Hz,
12H, CH3). 13C{1H} NMR (CDCl3): d 146.9, 131.0,
123.7 (C6H3NC), 29.6 (CHMe2), 23.0 (CH3). IR (CH2Cl2,
cmꢀ1): 2193 (s, mCN).
absorption corrections based on the w-scan of four strong
reflections was applied. The centric space group was based
on statistical analysis of intensity distribution and con-
firmed by the successful refinement of the structure solved
by direct methods (SIR-92 [21]) and expanded by Fourier
methods and refined by full-matrix least-squares using
the software package TEXSAN [22]. The least squares refine-
ments were on F using reflections with I > 3r(I). Hydrogen
atoms at calculated positions with thermal parameters
equal to 1.3 times that of the attached C atoms were
included in the calculations, but not refined.
2.27. Synthesis of compound 34
Compound 4 (0.15 g) was added to a suspension of PdI2
(0.10 g) in THF (30 mL). The mixture was stirred at r.t. for
2 h, followed by filtration. Then the solvent was removed in
vacuo. The residue was washed with hexane, dried, and
redissolved in CH2Cl2. After filtration, hexane was added
to the solution to afford an orange crystalline solid. Yield:
3. Results and discussion
3.1. Synthesis of the metal complexes
1
The synthesis of the tungsten complexes 7–11, which
contain unsaturated alkylidyne ligands with free terminal
isocyano groups, has previously been described [17]. Com-
plex 12 was prepared by a similar procedure, as shown in
Schemes 1 and 2. The heteronuclear metal complexes 13–
28 were prepared by reaction of the respective isocyano-ter-
minated alkylidyne tungsten complexes 7–12 with the metal
complex reagents Cr(CO)5(THF) (13), ReCl(CO)3(THF)2
(14, 19, 22), ReBr(CO)3(THF)2 (15), PdCl2 (16), PdI2 (17,
20, 23, 25, 27), and PtI2 (18, 21, 24, 26, 28) in THF or
dichloromethane solution (see Scheme 3). The compounds
were recrystallized from dichloromethane and hexane. The
simple isocyanide metal complexes 29–33 were prepared
from the same metal complex fragments and 2,6-dii-
sopropylphenylisocyanide under similar conditions. The
combination of PdI2 and isocyanide 4 afforded complex 34.
0.1 g, 46%. H NMR (CDCl3): d 7.54 (s, 4H, C6H4CC),
7.49 (s, 4H, C6H4CC), 7.38 (s, 2H, C6H2i-Pr2), 3.56 (m,
2H, CHCH3), 3.19 (s, 1H, CCH), 1.37 (d, J = 6.8 Hz,
12H, CH3). 13C{1H} NMR (CDCl3): d 147.2, 132.1,
131.7, 131.5, 127.1, 126.0, 123.4, 122.9, 122.5, 122.2
(C6H4CC, C6H2i-Pr2), 91.8, 91.1, 90.7, 90.5 (C„C), 83.2
(CCH), 79.1 (CCH). IR (CH2Cl2, cmꢀ1): 2193 (s, mCN).
mp 185–188 ꢁC (dec.).
2.28. X-ray crystal structure analysis of complex 17
The crystal parameters of compound 17 and informa-
tion on data collection and refinement are summarized in
Table 1. The diffraction data were collected on a Rigaku
AFC7R diffractometer with graphite-monochromatized
˚
Mo Ka X-ray radiation (k = 0.71073 A). Empirical

M.P.Y. Yu et al. / Journal of Organometallic Chemistry 691 (2006) 4514–4531
4521
CO
CO
29: MLm = Cr(CO)5; n = 1
30: MLm = fac-ReCl(CO)3; n = 2
31: MLm = cis-PdCl2; n = 2
32: MLm = trans-PdI2; n = 2
33: MLm = trans-PtI2; n = 2
Cl
W
I
+ 3
P
N
C MLm
P
5
PP = dppe
n
THF/HNEt2/PdCl2(PPh3)2/CuI, r.t.
CO
W
CO
Cl
NHCHO
34
H
N
C
trans-PdI2
P
P
6
2
triphosgene/NEt3
CH2Cl2, -78 oC
CO
W
CO
3.2. Crystal structure analysis of complex 17
Cl
N C
P
P
The crystal structure of complex 17 was determined by
X-ray crystallography. The structure contains two indepen-
dent molecules with similar metric parameters. Selected
bond lengths and bond angles for one of the molecules
are listed in Table 2. Fig. 1 shows a drawing of that mole-
cule. The structure confirms the linear geometry of the dii-
odo-bis-(isocyanide)palladium unit. The strict linearity of
the central C(10)–Pd(1)–C(10*) fragment is imposed crys-
tallographically. The Pd(1)–C(10)–N(3) and C(10)–N(3)–
C(7) angles deviate from linearity by only 3ꢁ. The angle
on the alkylidyne carbon atom, W(1)–C(3)–C(4), is 170ꢁ.
This deviation from linearity is not larger than observed
12
Scheme 2.
for several other benzylidyne metal complexes [23]. All
bond lengths are within the expected ranges.
3.3. Bonding in alkylidyne metal complexes
Alkylidyne metal complexes have been the subject of
several theoretical studies [24]. For octahedral systems,
the qualitative bonding description is straightforward
due to the clean separation of the metal–ligand r and p
bonds. As shown in Fig. 2, the alkylidyne ligand forms
two p bonds with the metal center, involving the metal
dxz and dyz orbitals. In metal–benzylidyne systems the
two p bonds are not degenerate. In the free benzylidyne
ligand, the out-of-plane p orbital of the alkylidyne carbon
atom, i.e., the orbital conjugated with the phenyl p sys-
tem, is about 42 kJ/mol lower in energy than the in-plane
p orbital. In the metal–carbon triple bond, this splitting is
diminished in the M–C p orbitals, but enlarged in the M–
C p* orbitals. The equatorial metal dxy orbital is non-
bonding with respect to the metal–carbon triple bond.
This orbital is stabilized by interaction with a suitable
combination of carbonyl p* orbitals. According to the cal-
culations, the energy of the dxy orbital is below the energy
of the halogen p orbitals in the tetracarbonyl complexes
M(CR)X(CO)4 (M = Cr, Mo, W; X = Cl, Br, I). How-
ever, in the dicarbonyl complexes of the type
M(CR)X(CO)2L2 (L = donor ligand), e.g., those studied
here, the dxy orbital is probably the HOMO, at least for
X = Cl and Br. This assessment is supported by the obser-
vation that the nature of the halide ligand exerts only a
minor influence on the absorption as well as emission
properties [9c]. The carbonyl p* orbitals oriented along
the z direction are essentially nonbonding since the M–
C p orbitals are much lower in energy. Thus, we may
use the simplified molecular orbital scheme shown in
Fig. 2 as a basis for our discussion.
OHCHN
H
+
I
SiMe3
1
NEt3/PdCl2(PPh3)2/CuI, 40 oC
OHCHN
SiMe3
2
KOH/MeOH, r.t.
OHCHN
H
3
triphosgene/NEt3
CH2Cl2, -78 oC
C
N
H
4
Scheme 1.

4522
M.P.Y. Yu et al. / Journal of Organometallic Chemistry 691 (2006) 4514–4531
R
CO
CO
+
X
W
L
N
C
"MLm"
13 - 28
L
p
R
7: X = Cl; LL = TMEDA; R = H; p = 0
8: X = Br; LL = TMEDA; R = H; p = 0
9: X = Cl; LL = dppe; R = H; p = 0
10: X = Cl; LL = dppe; R = H; p = 1
11: X = Cl; LL = dppe; R = isopropyl; p = 2
12: X = Cl; LL = dppe; R = isopropyl; p = 3
13: X = Cl; LL = TMEDA; n = 1; MLm = Cr(CO)5
14: X = Cl; LL = TMEDA; n = 2; MLm = fac-ReCl(CO)3
15: X = Br; LL = TMEDA; n = 2; MLm = fac-ReBr(CO)3
16: X = Cl; LL = TMEDA; n = 2; MLm = cis-PdCl2
17: X = Cl; LL = TMEDA; n = 2; MLm = trans-PdI2
18: X = Cl; LL = TMEDA; n = 2; MLm = trans-PtI2
19: X = Cl; LL = dppe; n = 2; MLm = fac-ReCl(CO)3
20: X = Cl; LL = dppe; n = 2; MLm = trans-PdI2
21: X = Cl; LL = dppe; n = 2; MLm = trans-PtI2
CO
W
CO
X
N
C
MLm
L
L
n
CO
W
CO
22: LL = dppe; MLm = fac-ReCl(CO)3
23: LL = dppe; MLm = trans-PdI2
24: LL = dppe; MLm = trans-PtI2
Cl
N
C
MLm
L
L
2
CO
W
CO
Cl
N
C
MLm
L
L
2
25: LL = dppe; MLm = trans-PdI2
26: LL = dppe; MLm = trans-PtI2
CO
W
CO
Cl
N
C
MLm
L
L
2
27: LL = dppe; MLm = trans-PdI2
28: LL = dppe; MLm = trans-PtI2
Scheme 3.
Table 2
3.4. IR spectroscopic data of the metal complexes
˚
Selected bond lengths (A) and bond angles (ꢁ) for complex 17
˚
Bond lengths (A)
Bond angles (ꢁ)
Relevant IR data are collected in Table 3. In isocya-
nide metal complexes, the C–N stretching frequency is
a sensitive probe for the electron density of the metal
center. In general, the C–N stretch shifts to higher fre-
quencies with increasing electron acceptor ability of the
metal complex fragment [10]. In the series 13–18, the
increase of the C–N stretching frequency from the free
W(1)–C(3)
W(1)–C(1)
W(1)–C(2)
W(1)–N(1)
W(1)–N(2)
W(1)–Cl(1)
C(3)–C(4)
C(7)–N(3)
N(3)–C(10)
C(10)–Pd(1)
Pd(1)–I(1)
1.79(1)
1.96(2)
2.00(1)
2.291(9)
2.296(8)
2.557(3)
1.47(2)
1.42(1)
1.15(1)
1.96(1)
2.582(1)
W(1)–C(3)–C(4)
Cl(1)–W(1)–C(3)
C(1)–W(1)–C(2)
C(1)–W(1)–N(2)
N(1)–W(1)–N(2)
C(2)–W(1)–N(1)
C(7)–N(3)–C(10)
N(3)–C(10)–Pd(1)
Cl(1)–W(1)–C(1)
Cl(1)–W(1)–C(2)
Cl(1)–W(1)–N(1)
Cl(1)–W(1)–N(2)
C(10)–Pd(1)–I(1)
C(10)–Pd(1)–C(10*)
170(1)
169.3(4)
87.9(6)
95.5(5)
78.8(3)
97.3(5)
177(1)
177(1)
87.3(5)
85.9(4)
87.3(3)
88.6(2)
91.6(4)
180
isocyanide
7
(2124 cmꢀ1
)
is 13 wavenumbers for
Cr(CO)5, 43 for ReX(CO)3 (X = Cl, Br), 69 for trans-
PtI2, 75 for trans-PdI2, and 104 for cis-PdCl2. Thus,
the IR data indicate that the palladium metal complex
fragments are the strongest electron acceptors in this
series.

M.P.Y. Yu et al. / Journal of Organometallic Chemistry 691 (2006) 4514–4531
4523
C(14)
C(13)
N(1)
C(16)
N(2)
C(11)
C(5)
C(15)
Cl(1)
C(12)
C(3)
W(1)
C(6)
C(7)
C(4)
I(1*)
C(2)
O(2)
N(3)
C(10)
C(1)
O(1)
C(9)
C(8*)
Pd(1)
O(2*)
C(2*)
C(8)
C(9*)
O(1*)
Cl(1*)
C(10*)
C(7*)
C(4*)
C(1*)
N(3*)
I(1)
C(3*)
W(1*)
C(6*)
C(5*)
C(12*)
C(15*)
N(2*)
N(1*)
C(11*)
C(16*)
C(13*)
C(14*)
Fig. 1. Molecular structure of compound 17. The thermal ellipsoids are shown at the 40% probability level.
x
Table 3
IR and 13C NMR spectroscopic data of selected compounds
∗
Complex
m(CO)
m(CN)
d(W„C–)
(ppm)
d(W–CO)
(ppm)
π
z
(cmꢀ1
)
(cmꢀ1
)
y
7
9
1992, 1902
2010, 1944
2006, 1940
2008, 1940
2008, 1940
1990, 1902
1992, 1904
1994, 1906
1992, 1906
1994, 1904
2012, 1944
2014, 1946
2014, 1946
2008, 1940
2008, 1940
2006, 1942
2008, 1940
2008, 1940
2008, 1940
2008, 1940
2124
2124
2125
2120
2116
2137
2185, 2151
2228, 2212
2199
2193
2185, 2149
2199
2191
2185, 2149
2201
2197
2191
2187
2193
257.5
261.7
264.6
265.0
265.0
257.3
257.5
256.3
256.0
256.1
260.6
260.0
260.1
264.5
264.5
264.4
264.9
–
220.5
212.0
212.3
212.3
212.3
220.4
221.5
221.4
220.2
220.2
211.9
211.8
211.8
211.9
212.2
212.3
212.3
212.3
212.3
–
10
11
12
13
14
16
17
18
19
20
21
22
23
24
25
26
27
28
dxy
d(M)
p(C)
π
Fig. 2. Simplified molecular orbital scheme for a metal benzylidyne
complex.
265.0
–
The carbonyl stretching frequencies of the W(CO)2 frag-
ment are only marginally affected by the nature of the
metal complex fragment coordinated to the isocyanide
group. For example, even though the isocyanide stretching
frequency of 7 increases by 104 cmꢀ1 upon coordination to
PdCl2, the concomitant change of the carbonyl stretching
frequencies for the W(CO)2 fragment is only 4 cmꢀ1. Con-
sidering that the p bond between the carbonyl ligands and
the metal center involves primarily the dxy orbital, which is
2187
orthogonal to the metal–carbon triple bond, this is not an
unexpected observation. In contrast, replacement of the
equatorial tmeda (tetramethylethylenediamine) ligand by
dppe [bis(diphenylphosphino)ethane] causes the carbonyl
stretching frequencies to shift to higher energies by about

4524
M.P.Y. Yu et al. / Journal of Organometallic Chemistry 691 (2006) 4514–4531
20–30 wavenumbers. Evidently, the orthogonality of the
dxy orbital and the metal–carbon p bonds insulates the
towards lower field when the electronic excitation energy
decreases [25].
dxy orbital from modifications of the extended benzylidyne
The 13C and 31P NMR signals of the carbonyl carbon
and dppe phosphorus atoms of the tungsten alkylidyne
fragments are nearly unaffected by the various modifica-
tions of the alkylidyne ligands.
p system. Conversely, the energy of the dxy orbital may be
changed without significantly perturbing the metal–ben-
zylidyne p system.
3.5. NMR spectroscopic data of the metal complexes
3.6. Electronic absorption spectra of the metal complexes
Relevant NMR data are collected in Table 3 and plotted
in Fig. 3. Even though the 13C NMR signals of the alkyli-
dyne carbon atoms of all complexes fall within the narrow
range of d 256–265, the chemical shift parameter is of diag-
nostic value. Replacement of the tmeda ligand by dppe
causes the signal to shift downfield by about 4 ppm, e.g.,
from 257.5 to 261.7 ppm for complexes 7 and 9. Extension
of the benzylidyne ligand by one phenyleneethynylene unit,
on going from 9 to 10, results in a downfield shift of
2.9 ppm. Insertion of a second phenyleneethynylene group,
changing 10 to 11, causes a further downfield shift of
0.4 ppm, while the influence of a third phenyleneethynylene
group, on going from 11 to 12, can barely be discerned.
Within the two series of phenylene-bridged complexes that
are based on the parents 7 and 9 the isocyanide-coordi-
nated metal complex fragments of 13–18 and 19–21 cause
upfield shifts of the alkylidyne carbon signals of up to
1.6 ppm, roughly mirroring the relative electron acceptor
abilities of the metal centers. Insertion of the phenylenee-
thynylene groups greatly diminishes the influence of the
isocyanide-coordinated metal centers on the chemical shift
of the alkylidyne carbon atom.
The results of the photophysical measurements are sum-
marized in Table 4. Fig. 4a shows the absorption and emis-
sion spectra of complex 18 as a representative example. The
electronic absorption and emission energies of selected
complexes are plotted in Fig. 5. The spectra of all com-
pounds feature two low-energy absorptions. A band of
low intensity (e 6 103 Mꢀ1 cmꢀ1) in the 450–500 nm range
is assigned to the d ! p* transition, while a band in the
340–380 nm range (e = 104–105 Mꢀ1 cmꢀ1) is assigned to
the p ! p* transition [9c]. Replacement of the tmeda ligand
in 7 by the less strongly donating (and weakly p backbond-
ing) dppe ligand in 9 lowers the energy of the dxy orbital.
Consequently, the d ! p* transition occurs at higher
energy in 9 than in 7, by 932 cmꢀ1. At the same time the
energy of the p ! p* transition is less affected, with the
p ! p* transition energy of 9 being lower than that of 7
by 499 cmꢀ1. Replacement of the chloro ligand of 7 by bro-
mide to afford 8 does not noticeably influence the energies
of the d ! p* and p ! p* transitions. The lack of influence
of the halide ligands on the electronic spectra of metal alky-
lidynes has been noted earlier [9c]. A decrease in the energy
of the p ! p* transition in the series 9–12 is observed,
probably due to the extension of the benzylidyne ligand
by phenyleneethynylene groups which would cause a nar-
rowing of the p ! p* gap. This effect appears to have lev-
eled off after insertion of two phenyleneethynylene units.
The fact that in the same series the energy of the d ! p*
transition is dropping considerably less than half of the
decrease of the p ! p* transition energy suggests that the
extension of the p system raises the energy of the p orbitals
more than it lowers the energy of the p* orbitals. The
p ! p* absorption of the rhenium complexes 14 and 15 is
split into two peaks, separated by about 1200 cmꢀ1. The
origin of this feature may be vibronic coupling with the
arene ring [9a] that is enhanced by the cis-arrangement of
the areneisocyanide groups on the rhenium center.
The individual factors contributing to these changes in
chemical shift have not been identified. However, the
downfield shift of the resonance of the alkylidyne carbon
atom upon insertion of phenyleneethynylene units may be
correlated with the extension of the p system of the alkyli-
dyne ligands. 13C NMR chemical shifts generally shift
In the phenylene-bridged series 7/13–18 and 9/19–21,
the isocyanide-coordinated metal center exerts a pro-
nounced influence on the electronic absorption energies.
The addition of metal centers to the isocyanide group low-
ers the energy of the p ! p* transition. Two factors appear
to be at play here, the generic extension of the p system by
an additional metal–carbon bond and the specific influence
of the metal complex fragment. The latter factor may
account for the strikingly low p ! p* transition energies
of complexes 13 and 14. The metal centers in the Cr(CO)5
and ReCl(CO)3 fragments have a d6 electron configuration
and are consequently potential p donors. Thus, p donation
Fig. 3. Plot of the 13C NMR chemical shifts of the benzylidyne carbon
atoms of selected compounds.

M.P.Y. Yu et al. / Journal of Organometallic Chemistry 691 (2006) 4514–4531
4525
Table 4
Electronic absorption and emission data of the metal alkylidyne complexes in CH2Cl2 (k/nm, e/Mꢀ1cmꢀ1
)
Complex
p ! p*/nm (e/Mꢀ1 cmꢀ1
)
d ! p*/nm (e/Mꢀ1 cmꢀ1
)
Emission/nm
Emission lifetime
Quantum yield Uem · 104
Radiative decay
rate constant/sꢀ1, Uem/s
7
8
344 (19000)
476 (560)
656, 700 (sh)a
s = 0.45 ls
16.0
11.1a
2.5 · 103a
344 (18900)
476 (600)
350 (20700)
360 (sh)
374 (37600)
388 (sh)
382 (69400)
398 (sh)
346 (sh)
9
456 (590)
462 (950)
460 (1650)
462 (1690)
664, 698 (sh)a
s = 0.15 ls
667, 700 (sh)
s = 0.69 ls
670
10
11
12
7.2
3.0
3.4
1.0 · 103
3.5 · 102
3.9 · 102
s = 0.86 ls
670
380 (84700)
404 (sh)
368 (sh)
s = 0.87 ls
13
14
480 (940)
662a
382 (20000)
374 (63800), 358 (65100)
s = 0.47 ls
665, 690 (sh)a
s = 0.32 ls
490 (1640)
19.1
13.6a
4.3 · 103a
6.7 · 103
15
16
17
18
376 (66900), 358 (69200)
358 (54600)
362 (71900)
488 (2050)
500 (1640)
494 (1900)
500 (1760)
ND
ND
NE
NE
14.7
372 (68900)
670, 700 (sh)
s = 0.22 ls
662, 693 (sh)
s = 0.14 ls
ND
19
20
21
22
23
24
25
364 (52500)
382 (52000)
366 (61900)
378 (sh)
474 (1240)
484 (1490)
480 (1650)
464 (2980)
470 (3050)
470 (3130)
464 (3400, sh)
380 (59000)
671, 700 (sh)
s = 0.10 ls
668, 703 (sh)
s = 0.64 ls
670, 704 (sh)
s = 0.12 lsb
670, 704 (sh)
s = 0.63 ls
670
380 (109900)
400 (sh)
380 (106600)
400 (sh)
384 (109000)
404 (sh)
340 (sh)
384 (152700)
404 (sh)
384 (161800)
404 (sh)
6.5
0.6
6.4
1.7
2.0 · 103
0.4 · 103
1.0 · 103
3.5 · 102
s = 0.50 ls
26
27
462 (3420, sh)
466 (3240, sh)
670
s = 0.92 ls
670
3.4
3.3
3.7 · 102
4.2 · 102
340 (sh)
380 (187300)
406 (sh)
360 (sh)
s = 0.80 ls
28
466 (3590, sh)
670
3.5
4.1 · 102
382 (23200)
406 (sh)
s = 0.87 ls
sh = shoulder. NE = non-emissive. ND = not detected.
a
Measured in acetonitrile solution.
Emission intensity is too weak to give reliable s.
b
of electron density from these metal centers may decrease
the gap between the p and p* orbitals by raising the energy
of the p orbitals. The d ! p* transition is also affected by
the addition of the isocyanide metal centers, but less so
than the p ! p* transition. The d ! p* transition moves
to lower energy as the electron-acceptor ability of the metal
center increases. The change appears to be correlated
directly with the electron acceptor ability of the isocyanide
metal complex fragment, reflecting the trend indicated by
the CN-stretching frequencies. The influence of the isocya-
nide-coordinated metal centers on the d ! p* and p ! p*
transitions is still clearly discernible in the series 10/22–
24, but barely so in the more extended series 11/25, 26
and 12/27, 28.
The 2,6-diisopropylphenylisocyanide complexes 29–33
serve as models for the local isocyanide metal complex
fragments of the respective compounds 13–28. The absorp-
tion spectra of compounds 31, 32, and 33 are shown
in Fig. 4b. Relevant spectroscopic data are collected in
Table 5. Complexes 29–33 exhibit only weak absorptions
in the 325–400 nm range and, with the exception of 32,
no absorptions with wavelengths longer than 400 nm.

4526
M.P.Y. Yu et al. / Journal of Organometallic Chemistry 691 (2006) 4514–4531
the unsaturated alkylidyne ligand exert a significant influ-
ence on the emission energy. These observations suggest
that the original excited state relaxes into a long-lived trip-
let excited state which is very similar for all compounds,
and that the excited electron is not extensively delocalized
over the extended p system. The large Stoke’s shift of the
emission, about 6300 cmꢀ1, may imply a significant change
of the molecular geometry in the triplet excited state. One
of the possibilities is bending of the alkylidyne ligand,
e.g., as in A. In that case, the excited electron could remain
localized on the alkylidyne carbon atom in an orbital of the
bent metal alkylidyne unit. Experimental support for this
kind of excited-state structure comes from the observation
of facile protonation of alkylidyne ligands under irradia-
tion [9b]. Other experiments suggest that in carbonylmetal
alkylidyne systems the initial excited state rearranges into a
metal ketenyl species B by forming a bond between the
alkylidyne ligand and a carbonyl ligand. Supporting evi-
dence for structure B derives from the observation that
the excited states of alkylidyne carbonyltungsten complexes
can be trapped as ketenyl derivatives by nucleophiles [26]
or as oxyacetylene species by electrophiles [27]. In B the
excited electron would most likely be associated with the
newly formed carbon–carbon linkage. However, the Stoke’s
shift may also be explained by a bond length change of
the metal–carbon triple bond [9a] or simply the electronic
difference between the initial singlet excited state and the
triplet character of the emissive state [9f].
O
C
O
C
O
O
Fig. 4. (a) Electronic absorption and emission (inset) spectra of com-
pound 18 in CH2Cl2 solution. (b) Electronic absorption spectra of
compounds 31 (ꢁ ꢁ ꢁ ꢁ ꢁ ꢁ), 32 (——), and 33 (------) in CH2Cl2 solution. The
absorption tail of 32 is enlarged.
C
C
Cl
W
L
Cl
W
L
L
L
R
R
Complex 32 features a long absorption tail of low intensity
in the region of 400–600 nm. Consequently, the higher-
energy features of all complexes 13–28 are dominated by
the p ! p* transitions of the extended alkylidyne frag-
ments, and the d ! p* transitions of the complexes contain-
ing Cr(CO)5–, ReX(CO)3–, PdCl2–, and PtI2–isocyanide
metal complex fragments originate exclusively from the
alkylidyne tungsten fragments. Only in the PdI2-containing
complexes 17, 20, 23, 25, and 27, there is a small contri-
bution from the palladium isocyanide fragment to the
low-energy absorption.
A
B
In contrast to the emission energies, the excited state
lifetimes show a distinct dependence on the various molec-
ular components (Table 4 and Fig. 5b). Replacement of
tmeda in 7 by dppe to afford 9 shortens the lifetime by a
small amount. There also appears to be a trend towards
shorter lifetimes as electron-withdrawing metal centers
are attached to the isocyanide group. The value of the
emission lifetime of the platinum complex 26 is an excep-
tion to this trend. Considering the internal consistency of
all other data, it is likely that the slight elevation of this
value is due to some unknown experimental error. Most
interestingly, the PdCl2- and PdI2-containing complexes
16, 17 and 20 do not emit at all, and the emission of the
extended analogues 23, 25, and 27 is partially quenched.
The nature of the quenching mechanism in these complexes
is discussed further below. Insertion of the first phenylenee-
thynylene unit leads to a marked increase of the excited
state lifetime, from 150 ns for 9 to 690 ns for 10. Insertion
of the second and third phenyleneethynylene groups in 11
3.7. Emission properties of the metal complexes
The emission data of the metal complexes are summa-
rized in Table 4. The emission energies and emission life-
times are plotted in Fig. 5b. All complexes except 16, 17,
and 20 are emissive in fluid solution at room temperature.
The maxima of the emission bands occur in the narrow
range between 656 and 671 nm. So neither the substitution
of tmeda by dppe on tungsten, nor the attachment of a
metal center to the isocyanide group, nor the extension of

M.P.Y. Yu et al. / Journal of Organometallic Chemistry 691 (2006) 4514–4531
4527
Fig. 5. (a) Plot of the absorption and emission energies (in wavenumbers) of selected compounds. (b) Plot of the emission lifetimes (in nanoseconds) of
selected compounds.
acter of the extended p-conjugated linkage in the excited
Table 5
state. Within the PdI2-complex series 20, 23, 25 and 27,
there is a special increment to the emission lifetime increase
with the extension of the bridge. This may be attributed to
a decrease of the efficiency of quenching by the PdI2(C-
NAr)2 fragment with increasing distance. Nevertheless,
even at a separation of 3.1 nm between the tungsten alkyli-
dyne center and the isocyanide-coordinated palladium and
platinum centers in 27 and 28, respectively, the emission
lifetime is still about 9% shorter for the PdI2-containing
complex than for the PtI2-containing complex. Thus, the
tungsten alkylidyne fragment is capable of discerning the
electronic difference between a palladium and a platinum
metal center from a distance of at least 3.1 nm across an
isocyanide-terminated oligo-phenyleneethynylene chain.
The tmeda-substitued tungsten alkylidyne complexes are
stronger emitters than the dppe-substituted complexes. The
luminescence quantum yields of the complexes 7, 14, and
UV/Vis spectroscopic and electrochemical data of the metal isocyanide
complexes 29–33
Compound
k/nm (e/Mꢀ1cmꢀ1); CH2Cl2
Ered/V vs. SCE; THF
ꢀ1.866
29
30
336 (5000, sh), 296 (10300, sh)
344 (4290, sh), 326 (8410, sh),
310 (10500, sh)
31
32
320 (1350), 284 (6440, sh)
422 (100, sh), 352 (2000),
292 (30600)
ꢀ1.150
ꢀ1.143
33
500 (60, sh), 402 (1390, sh),
354 (10700), 262 (72300)
ꢀ1.503
sh = shoulder.
and 12 still leads to longer lifetimes of 860 and 870 ns,
respectively. The increase in emission lifetime with increas-
ing length of the OPE chain in the series 9–12 is likely the
result of an increasing participation of the intraligand char-

4528
M.P.Y. Yu et al. / Journal of Organometallic Chemistry 691 (2006) 4514–4531
18 range from 1.4% to 1.9%, while those of 10, 22, and 24
are approximately 0.7%. Naturally, the luminescence quan-
tum yield for the palladium complex 23 is with 0.06% much
smaller than that of complex 10, for example, which is
0.72%. The relative decrease of the luminescence quantum
yield between complexes 10 and 23 is approximately the
same as the relative decrease of the excited state lifetimes
for the same pair of complexes.
tungsten alkylidyne fragment, E(W+/W*), may be
approximated as E(W+/W0) ꢀ DE0ꢀ0. With oxidation
potentials E(W+/W0) of about +1 V versus SCE for the
tungsten benzylidyne model complexes and estimated 0–0
excitation energies near 18200 cmꢀ1 (550 nm, 2.26 eV),
E(W+/W*) may be estimated to be about ꢀ1.26 V versus
SCE. Thus, E(Ox/Oxꢀ) ꢀ E(W+/W*) = DE > 0 for the pal-
ladium complexes, but DE < 0 for the rhenium and plati-
num complexes [30]. Consequently, electron transfer is
thermodynamically favorable in the palladium complexes,
but not in the rhenium and platinum systems. Thus, the
electrochemical data confirm the conclusion that electron
transfer is the most likely mechanism of quenching in 16.
In addition, these data show that electron transfer is also
a feasible quenching mechanism in the palladium diiodide
complexes 17, 20, 23, 25, and 27. Given the fact that the
reduction potentials of the palladium complexes 31 and
32 are very similar, it appears likely that electron transfer
is also the active quenching mechanism in the palladium
diiodide complexes. Preference of electron transfer over
energy transfer in systems where both are in principle pos-
sible has been observed in other cases [31].
The rate constants of the observed emissions are the
inverse of the emission lifetimes (Eq. (1)). It seems reason-
able to assume that the excited state decay processes in the
palladium complexes 23, 25, and 27 and in the correspond-
ing parent complexes 10–12 are the same except for the
additional independent quenching mechanism in the palla-
dium complexes. This assumption is supported by the
observation that the diiodoplatinum unit in complexes
21, 24, 26, and 28, which is not capable of quenching the
emission but otherwise has electronic properties that are
very similar to those of the diiodopalladium unit, does
not significantly affect the emission properties of the
respective parent systems 9–12. Thus, the rate constants
of the quenching processes are the differences between the
emission rate constants of the palladium complexes and
those of the corresponding parent complexes (Eq. 2).
3.8. Mechanism of the excited-state quenching by the
PdCl2(CNArene)2 and PdI2(CNArene)2 fragments
As stated above, the palladium complexes 16, 17, and 20
are non-emissive and the extended analogues 23, 25, and 27
have reduced emission intensities relative to the parent
complexes 10–12 as well as the platinum complexes 24,
26, and 28. Evidently, the PdCl2(CNAr)2 and PdI2(CNAr)2
units are unique among the tested metal complex fragments
in their ability to quench the excited state of the tungsten
benzylidyne moiety. As mentioned above, the trans-
PdI2(CNAr)2 complex 32 features an absorption tail of
very low intensity that extends towards 600 nm. This
region overlaps slightly with the emission band of the tung-
sten benzylidyne complexes. Thus, there exists the possibil-
ity of the presence of a low-lying ligand-field triplet state in
the palladium moiety of 17 and 20 which deactivates the
excited state of the tungsten benzylidyne fragments via
energy transfer [28]. However, the cis-PdCl2(CNAr)2 com-
plex 31 does not absorb at wavelengths longer than
450 nm. Consequently, energy transfer is not a viable
mechanism of quenching in complex 16. For 16, the likely
quenching mechanism is therefore electron transfer.
In order to provide supporting evidence for the possible
presence of an electron transfer quenching mechanism, the
electrochemical properties of the isocyanide metal com-
plexes 29–33 were investigated. The results are summarized
in Table 5. These compounds exhibit irreversible one-elec-
tron reduction waves. In particular, the data show that the
palladium bis-isocyanide fragments are significantly more
readily reduced, i.e., stronger oxidizing agents, than the
rhenium and platinum bis-isocyanide fragments. It is inter-
esting to note that the IR stretching frequencies of the iso-
cyanide groups, which reflect the electron acceptor abilities
of the metal centers as Lewis acids, also indicate that the
palladium metal centers are the strongest electron accep-
tors. For the tungsten benzylidyne complexes W(CC6H4I-
4)Cl(CO)2(tmeda) and W(CC6H4I-4)Cl(CO)2(dppe), which
may serve as models for the tungsten alkylidyne fragments
in the heteronuclear complexes, irreversible one-electron
oxidation waves were observed at +0.91 and +1.01 V ver-
sus SCE, respectively. In a larger series of tungsten alkyli-
dyne complexes, the potential of this oxidation was found
to be moderately affected by the nature of the donor
ligands on tungsten, but only slightly by an extension of
the benzylidyne ligand [29]. Consequently, the oxidation
waves are assigned to one-electron oxidations of the tung-
sten centers. The oxidation potential of the excited
kem ¼ 1=s;
ð1Þ
ð2Þ
ð3Þ
ð4Þ
k ¼ kemðPdÞ ꢀ kemðParentÞ;
k0 ¼ kemðParentÞ ꢂ ½/ðParentÞ ꢀ /ðPdÞꢃ=½/ðPdÞꢃ;
kðdÞ ¼ k0 eꢀbd
:
In an alternative procedure the relative loss of quantum
yield of emission in the palladium and the corresponding
parent compounds is used to estimate the rate constants
of the quenching process (Eq. (3)) [32]. The calculated
quenching rate constants based on Eqs. (2) and (3) for
Table 6
Calculated rate constants k and k0 for the quenching processes using Eqs.
(2) and (3), respectively
Compound
k (· 105 sꢀ1
)
k0 (· 105 sꢀ1
)
23
25
27
69
8.4
1.0
160
8.9
0.35

M.P.Y. Yu et al. / Journal of Organometallic Chemistry 691 (2006) 4514–4531
4529
readily discerned at a distance of more than 3 nm between
the tungsten and palladium metal centers.
The influence of the isocyanide-coordinated metal cen-
ters on the alkylidyne d ! p* and p ! p* transitions dimin-
ishes rapidly with increasing separation. By means of these
spectroscopic parameters a clear distinction between differ-
ent isocyanide-coordinated metal centers is still possible
after insertion of the first ethynylphenylene spacer, at
metal–metal distances of about 1.6 nm. However, residual
effects are still discernible at the largest investigated dis-
tances of about 3.1 nm. Using the 13C NMR chemical shift
of the alkylidyne carbon atom as a reporter, the ability to
distinguish between different isocyanide-coordinated metal
centers has nearly vanished after insertion of the first phen-
yleneethynylene group, although the extension of the p sys-
tem by a second phenyleneethynylene group does induce a
characteristic downfield increment.
Fig. 6. Plot of ln[k/sꢀ1] vs. the W–Pd distance for 23, 25, and 27. Full
circles: data obtained via Eq. (2). Open circles: data obtained via Eq. (3).
Those spectroscopic parameters of the tungsten alkyli-
dyne fragment that are not directly associated with the
metal–alkylidyne p system, such as the IR stretches of
the carbonyl ligands or the 31P NMR chemical shifts of the
dppe ligand, are quite insensitive to modifications of the
isocyanide-coordinated metal centers, even in the parent
isocyanobenzylidyne systems.
complexes 23, 25, and 27 are listed in Table 6. The linear
plots of the respective ln[k/sꢀ1] values versus the W–Pd dis-
tances d (Fig. 6) show that the distance dependences of the
quenching rate constants may be described by Eq. (4). With
˚
a W–Pd distance of 10.5 A in complex 17 and an increment
˚
of 6.8 A for each phenyleneethynylene unit, the W–Pd dis-
tances in 23, 25, and 27 are estimated to be 17.3, 24.1, and
Acknowledgements
˚
30.9 A, respectively. The resulting attenuation faꢀct1ors b
0
˚
and b of the distance dependences are 0.31 A
and
Support for this work by the Committee on Conference
and Research Grants of The University of Hong Kong and
by the Hong Kong Research Grants Council is gratefully
acknowledged.
0.45 Aꢀ1, respectively. Considering that the intrinsic exper-
imental errors of the luminescence intensity measurements
are about 10% and even larger when the intensity is low,
such as in compound 23, these two values are in reasonable
agreement. These values also fall into the range of ꢄ0.2–
˚
Appendix A. Supplementary data
ꢀ1
˚
0.6 A of previously reported experimental and theoreti-
cal b values for electron transfer processes across OPE
bridges [33]. Thus, an electron transfer mechanism for the
quenching process is consistent with the results.
Crystallographic data for the structural analysis of com-
pound 17 have been deposited with the Cambridge Crystal-
lographic Data Centre, CCDC No. 293397. Supplementary
data associated with this article can be found, in the online
version, at doi:10.1016/j.jorganchem.2006.02.029.
4. Conclusions
The electronic communication between the metal centers
in complexes of the general type LnWBC–C6H4
ð–CBC–C6H4Þp–NBC–M0Lm0 has been explored. The influ-
ence of the isocyanide metal complex fragment on the tung-
sten alkylidyne complex fragment has been tested by a
variety of spectroscopic methods and the dependence of
spectroscopic parameters on the number of inserted ethyn-
ylenephenylene units has been evaluated.
For probing the long-range electronic communication
between the metal centers, the emission property of the
tungsten alkylidyne fragment provides the most sensitive
parameters, provided the isocyanide metal complex frag-
ment is capable of quenching the emission of the tungsten
alkylidyne fragment. This is the case with the palladium(II)
fragments PdCl2(CNAr)2 and PdI2(CNAr)2. In the com-
plexes containing these fragments, electron transfer is the
most likely quenching mechanism. Partial quenching is still
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