Mono and dinuclear tungsten alkenyl-carbyne complexes bridged by cyanide and diisocyanide ligands: Synthesis, electrochemical- and 183W-NMR studies

Article abstract of DOI:10.1002/(SICI)1099-0682(200002)2000:2<341::AID-EJIC341>3.0.CO;2-U

Neutral trans-cyanide alkenylcarbyne complexes 2a and 2b have been prepared by reaction of the complex 1a and 1b with NaCN or [Bu₄N]CN. The reaction of complexes 2a and 2b with an equimolar amount of the acetonitrile complexes 1a and 1b in CH₂Cl₂ leads to the cationic cyanide-bridged bis(alkenylcarbyne) di-tungsten complexes 3a-d. Diisocyanide-bridged bis(alkenylcarbyne) di-tungsten complexes 4a and 4b have been synthesized by the reaction of complexes 1a and 1b with 0.5 equivalents of the diisocyanide 1,4-(CN)₂C₆H₄. IR as well as ¹H-, ³¹P{¹H}-, ¹³C{¹H}-, and ¹⁸³W-NMR data are reported. The spectroscopic data show that in the dinuclear complexes 3a-d, the bridging CN group and the alkenylcarbyne units are located in trans positions, while in the dinuclear complexes 4a and b, the isocyanide groups of the bridging ligand 1,4-(CN)₂C₆H₄ and the two alkenylcarbyne moieties are cis. The ¹⁸³W chemical shifts of complexes 2a, 2b, 3a-d, 4a, and 4b were obtained through two-dimensional indirect ³¹P, ¹⁸³W NMR recording techniques. A downfield shifting of ¹⁸³W resonances of the cyanide-bridged dinuclear complexes 3a-d with respect to the mononuclear ones, 2a and 2b, was observed. The δ¹⁸³W of isocyanide bridging dinuclear complexes 4a and 4b appear at higher field than those of the corresponding mononuclear cyanide 2a and 2b in accordance with the higher π-acceptor electron properties of the isocyanide ligand. The electrochemical behaviour of all the complexes has been investigated by cyclic voltammetry and controlled potential electrolysis in aprotic media and at a Pt (or vitreous C) electrode. Complexes 1, 2, or 3 undergo multi-electron irreversible oxidation processes involving anodically induced proton dissociation from the alkenylcarbyne ligands, and irreversible cathodic processes are also observed for all the complexes. The order of the redox potentials reflects that of the net electron π-acceptor/σ-donor character of the ligands and the ligating alkenylcarbynes are shown to behave as remarkably strong π-electron acceptors (even stronger than CO).

Full text of DOI:10.1002/(SICI)1099-0682(200002)2000:2<341::AID-EJIC341>3.0.CO;2-U

FULL PAPER
Mono and Dinuclear Tungsten Alkenyl-Carbyne Complexes Bridged by
Cyanide and Diisocyanide Ligands: Synthesis, Electrochemical- and
183W-NMR Studies
[a]
[a]
[a]
Lei Zhang,[a,b] M. Pilar Gamasa, Jose Gimeno,* Rodrigo J. Carbajo,
´
[a,c]
[b,d]
´
´
Fernando Lopez-Ortiz,
M. Fatima C. Guedes da Silva,
and
Armando J. L. Pombeiro*[b]
Keywords: Alkenylcarbynes / Dinuclear tungsten complexes / Electrochemistry / Tungsten NMR
Neutral trans-cyanide alkenylcarbyne complexes 2a and 2b
cyanide-bridged dinuclear complexes 3a–d with respect to
have been prepared by reaction of the complex 1a and 1b the mononuclear ones, 2a and 2b, was observed. The δ183
W
with NaCN or [Bu4N]CN. The reaction of complexes 2a and
2b with an equimolar amount of the acetonitrile complexes
1a and 1b in CH2Cl2 leads to the cationic cyanide-bridged
bis(alkenylcarbyne) di-tungsten complexes 3a–d. Diiso-
cyanide-bridged bis(alkenylcarbyne) di-tungsten complexes
4a and 4b have been synthesized by the reaction of
complexes 1a and 1b with 0.5 equivalents of the diisocyanide
1,4-(CN)2C6H4. IR as well as 1H-, 31P{1H}-, 13C{1H}-, and
of isocyanide bridging dinuclear complexes 4a and 4b
appear at higher field than those of the corresponding
mononuclear cyanide 2a and 2b in accordance with the
higher π-acceptor electron properties of the isocyanide
ligand. The electrochemical behaviour of all the complexes
has been investigated by cyclic voltammetry and controlled
potential electrolysis in aprotic media and at a Pt (or vitreous
C) electrode. Complexes 1, 2, or 3 undergo multi-electron
183W-NMR data are reported. The spectroscopic data show irreversible oxidation processes involving anodically induced
that in the dinuclear complexes 3a–d, the bridging CN group
and the alkenylcarbyne units are located in trans positions,
proton dissociation from the alkenylcarbyne ligands, and
irreversible cathodic processes are also observed for all the
while in the dinuclear complexes 4a and b, the isocyanide complexes. The order of the redox potentials reflects that of
groups of the bridging ligand 1,4-(CN)2C6H4 and the two
alkenylcarbyne moieties are cis. The 183W chemical shifts of
complexes 2a, 2b, 3a–d, 4a, and 4b were obtained through
the net electron π-acceptor/σ-donor character of the ligands
and the ligating alkenylcarbynes are shown to behave as
remarkably strong π-electron acceptors (even stronger than
two-dimensional indirect 31P, 183W NMR recording CO).
techniques. A downfield shifting of 183W resonances of the
sponding Fischer-type carbene derivatives have proven to
Introduction
be excellent substrates in modern organic synthesis. Even
more rare derivatives are dinuclear complexes containing
unsaturated carbyne groups.[4] Most of them are dimetallic
species bearing a di-carbyne group acting as a bridging li-
gand: [(η5-C5H5)(CO)2CrϵCϪCPhϭCPhϪCϵCr(η5-C5H5)-
(CO)2],[5] {[Br(CO)4MϵCϪ(p-C6H4)ϪCϵM(CO)4Br] (M ϭ
Cr, W)},[6] {[TpЈ(CO)2MϵCϪCRϭCRϪCϵM(CO)2TpЈ]
(M ϭ Mo; R ϭ H. M ϭ W; R ϭ H, Me, CH2Ph)},
Among the extensively studied chemistry of complexes
with multiple metalϪcarbon bonds, that concerned with
Fischer-type carbyne complexes of group 6 metals has re-
mained a topic of interest during the last years.[1][2] How-
ever, it is now apparent that this chemistry is not as well
developed as that of metal carbene derivatives. In particular,
only a few carbyne complexes bearing α,β-unsaturated sub-
stituents have been described to date,[3] although the corre-
{[TpЈ(CO)2MϵCϪCϵCϪCϵM(CO)2TpЈ] (M
ϭ
Mo,
W)}.[3c] Here we report the synthesis of ditungsten bis(alk-
enylcarbyne) complexes A and B along with the mononu-
clear complexes C (Scheme 1). Complexes of type A and B
belong to a new type of α,β-unsaturated carbyne dimetallic
derivatives in which the metal atoms are linked by a cyanide
and diisocyanide bridging group.[7]
[a]
´
´
Instituto Universitario de Quımica Organometalica “Enrique
Moles” (Unidad Asociada al CSIC),
´
´
´
Departamento de Quımica Organica e Inorganica, Facultad de
Quımica, Universidad de Oviedo,
´
E-33071 Oviedo, Spain
Fax: (internat.) ϩ34-98/510-3446
E-mail: jgh@sauron.quimica.uniovi.es
Centro de Quımica Estrutural, Complexo I, Instituto Superior
We have recently described[3b] the utility of the labile
acetonitrile carbyne complexes D as excellent precursor of
alkenylcarbyne and alkenylketenyl derivatives containing
dithio ligands. In this work we report on an extension of
this synthetic methodology which has led to the synthesis
of dinuclear complexes of type A and B, obtained by the
reaction of complexes D with the cyanide derivatives C and
the diisocyanide ligand CϵNϪ(1,4-C6H4)ϪNϵC, respec-
[b]
´
´
Tecnico,
Av. Rovisco Pais, P-1049-001 Lisbon, Portugal
Fax: (internat.) ϩ351-1/8414455
E-mail: pombeiro@alfa.ist.utl.pt
[c]
´
Current address: Facultad de Ciencias Experimentales, Area de
´
´
Quımica Organica,
´
´
Universidad de Almerıa, E-04120 Almerıa, Spain
Universidade Lusofona de Humanidades e Tecnologias,
[d]
´
Av. Campo Grande 376, P-1749-024 Lisbon, Portugal
Eur. J. Inorg. Chem. 2000, 341Ϫ350
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
1434Ϫ1948/00/0202Ϫ341 $ 17.50ϩ.50/0
341

J. Gimeno, A. J. L. Pombeiro et al.
FULL PAPER
Scheme 1. Alkenylcarbyne Fischer-type tungsten complexes
tively. Since the electrochemical investigation of complexes
IR spectra (CH2Cl2) show the typical pattern of cis-dicar-
with multiple metalϪcarbon bonds is still a rather undevel- bonyl complexes, of two ν(CO) absorptions at 1999 and
oped field of research,[8Ϫ17] and has not been previously 1931 (2a), and 1998 and 1930 (2b) cmϪ1. As expected for
reported for alkenylcarbyne compounds, we have also stud- the transformation of cationic to neutral complexes, a low-
ied the electrochemical behaviour of our novel alkenylcar- ering in absorption frequencies (ca. 12 cmϪ1) is observed.
byne complexes. 183W-NMR data of all the complexes are The presence of the terminal linear CN ligand is confirmed
also reported.
by the IR spectra (CH2Cl2 solution or KBr pellet) which
show a very weak ν(CN) absorption at 2112 cmϪ1 [18][19]
.
The phosphorus resonances appear in the 31P-NMR spectra
(Table 1) as singlet signals, indicating the chemical equival-
ence of the phosphorus atoms of dppe, and are therefore in
accordance with the trans carbyne-cyanide arrangement.
The J(W-P) values (ca. 225.5 Hz) are similar to those found
in analogous complexes
Scheme 2. Two terminal unsaturated carbyne tungsten moieties lin-
ked by bridging ligands with π-electronic delocalized systems
Results and Discussion
Mononuclear Cyanide Alkenylcarbyne Complexes 2a
and 2b
(X ϭ Cl, Br, I) which also show a similar trans arrangement
1
of phosphorus nuclei to the carbonyl ligands.[3a] The H-
The addition of NaCN to an orange solution of com- NMR shows a broad signal for the alkenyl proton
plexes1a and 1b in methanol at room temperature led to the (ϵCϪCHϭ) at δ ϭ 4.98 (2a) and 4.66 (2b). The carbyne
substitution of the acetonitrile ligand by the cyanide anion carbon resonances of these complexes appear in the 13C-
to afford the neutral alkenylcarbyne complexes 2a and 2b NMR spectra as triplet signals at δ ϭ 283.4 [2J(P-C) ca.
(90Ϫ95% yield) isolated as air stable orange solids (Equa- 10 Hz] (Table 2). These signals appear at a lower field with
tion 1). Complexes 2a and 2b are also formed by the treat- respect to those shown by the corresponding halide carbyne
2
ment of 1a and 1b with [NBu4]CN in CH2Cl2.
complexes [δ ϭ 266.9Ϫ269.8, J(P-C) ca. 10 Hz][3a] and at
342
Eur. J. Inorg. Chem. 2000, 341Ϫ350

Tungsten Alkenyl-Carbyne Complexes Bridged by Cyanide and Diisocyanide Ligands
FULL PAPER
1
Table 1. Selected IR[a] and 31P{1H}- and H-NMR[b] data for complexes 2a, 2b, and 3aϪd
IR
ν(CO)
31P{1H}[c]
2 P, 2 PЈ
1H
CHβ
ν(CϵN)
CHβЈ
2a
2b
3a
3b
3c
3d
1999 (vs), 1931 (vs)
1998 (vs), 1930 (vs)
2003 (vs), 1937 (vs)
2004 (vs), 1938 (vs)
2004 (vs), 1937 (vs)
2003 (vs), 1937 (vs)
2112 (vw)
39.8 s (225.7)
4.98 s,br
4.66 s,br
4.67 s,br
4.67 s,br
4.31 s,br
4.31 s,br
2112 (vw)
39.7 s (225.4)
2113 (vw), 2099 (vw)
2113 (vw), 2100 (vw)
2112 (vw), 2098 (vw)
2112 (vw), 2098 (vw)
39.5 s (229.0), 41.0 s (232.5)
39.5 s (230.5), 41.0 s (233.0)
39.4 s (228.7), 40.9 s (232.6)
39.4 s (227.8), 41.0 s (234.0)
4.58 s,br
4.24 s,br
4.58 s,br
4.24 s,br
[a]
[b]
Spectra recorded in CH2Cl2, ν(cmϪ1). Abbreviations: s, strong; vs, very strong; vw, very weak. Ϫ Spectra recorded in CDCl3, δ in
ppm, J in Hz. Abbreviations: s, singlet, br, broad. Ϫ [c] J(WϪP).
Table 2. Selected 13C{1H}-NMR data for the complexes 2a, 2b, and 3a؊d[a]
Cα
CαЈ
Cγ
CγЈ
CϵN
2 cis CO, 2 cis COЈ
2a
2b
3a
3b
3c
283.4 t (10.1)
283.4 t (10.2)
286.7 m
166.0 t (3.2)[b]
164.8 s
140.2 t (10.7)
140.3 t (10.7)
161.6 m
212.4 vr. dd (30.8, 7.0)
212.6 vr. dd (31.4, 7.0)
212.5 m
211.4 vr. dd (29.9, 7.1)
211.5 vr. dd (30.0, 7.1) 213.2
vr. dd (37.2, 7.2)
211.6 vr. dd (30.1, 7.0) 213.2
vr. dd (36.5, 7.0)
289.8 m
169.9 s
168.0 s
166.1 s
167.3 s
286.7 t (9.5)
286.7 t (9.4)
289.8 t (9.6)
289.5 t (9.6)
169.7 s
169.7 s
161.9 m
162.0 m
3d
286.8 m
289.7 m
169.2 s
166.3 s
162.1 m
[a]
Spectra recorded in CDCl3, δ in ppm, J in Hz. Abbreviations: s, singlet; d, doublet; t, triplet; dd, doublet of doublet; m, multiplet; vr,
virtual. Within parenthesis J(P-C). Ϫ [b] 4J(P-C).
2
a higher field (ca. 8.5 ppm) than those of the cationic pre-
IR and NMR spectroscopic data show the molecular
cursor complexes 1a and 1b. The resonances of the Cβ atom asymmetry of these dinuclear complexes even for 3a (n ϭ
of the alkenylcarbyne chain are assigned and distinguished nЈ ϭ 1) and 3d (n ϭ nЈ ϭ 4) containing two identical metal
by DEPT from the Cγ and the carbon atom of the cyanide carbyne moieties. Thus, IR spectra (CH2Cl2) show (Table
group. The resonances of the cis-dicarbonyl ligands appear 1) two weak ν(CϵN) absorptions[18][19] at 2112Ϫ2113 and
as doublet signals in the range of δ ϭ 212.4Ϫ212.6 (Table 2098Ϫ2100 cmϪ1 and two very strong ν(CO) absorptions
2) and are in accordance with the reported data for the at 2003Ϫ2004 and 1937Ϫ1938 cmϪ1 which apparently indi-
similar alkenylcarbyne halide complexes.[3a]
cate an overlapping of the absorptions expected for the two
unsymmetrical cis-dicarbonyl pairs of each tungsten moiety.
Since the ν(CϵN) absorptions at higher frequency appear
at a similar energy to those of complexes 2a and b, they
may be assigned to the ν(NϵCϪW) stretching (side A in
Figure 1) while those at lower energy are assigned to the
corresponding ν(WϪNϵC) (side B in Figure 1).
Cyanide Bridged Bis(alkenylcarbyne) Dinuclear
Complexes 3a؊d
The reaction of complexes 2a and 2b with an equivalent
of 1a and 1b in dichloromethane at room temperature for
NMR data of 3aϪd are in accordance with the linear
1 hour led to the displacement of the acetonitrile ligand to ϪCϵWϪ(µ-NϵC)ϪWϵCϪ arrangement. Thus, the 31P-
give the cationic bis(alkenylcarbyne) di-tungsten complexes NMR spectra (Table 1) show two singlets at δ ϭ 39.4Ϫ39.5
3a؊d (82Ϫ85% yield) in which the metal atoms are bridged [J(W-P) ϭ 227.8Ϫ230.5 Hz] and 40.9Ϫ41.0 [J(W-P) ϭ
by the cyanide group (Equation 2).
232.5Ϫ234.0 Hz], which are expected for each equivalent
Complexes 3a and 3d have been also prepared in similar pair of phosphorus nuclei of dppe trans to carbonyl groups
yields from the treatment of 1a and 1b in methanol with in sides A and B (Figure 1). As discussed before, since the
NaCN in a 2:1 molar ratio. The reaction probably proceeds higher-field signals are at the same chemical shifts as those
through the formation of complexes 2a and b as intermedi- of 2a and 2b (0.3 ppm higher), they are assigned to the two
ates.
equivalent phosphorus atoms at side A, while those at
Eur. J. Inorg. Chem. 2000, 341Ϫ350
343

J. Gimeno, A. J. L. Pombeiro et al.
FULL PAPER
Diisocyanide-Bridged Bis(alkenylcarbyne) Dinuclear
Complexes 4a and 4b
The reaction of 1a and 1b in dichloromethane with 1,4-
CNC6H4NC (1:0.5 molar ratio) at room temperature for 2
hours afforded the diisocyanide bridged di-cationic bis(alk-
enylcarbyne) di-tungsten complexes 4a (n ϭ 1) and 4b (n ϭ
4) (75Ϫ80% yield) (Equation 3).
The reaction for the formation of complex 4a was moni-
tored by 31P-NMR in CH2Cl2 (D2O as external lock refer-
ence). However only the resonances due to the starting
complex, along with those of the final product, are ob-
served. Although the formation of an intermediate monon-
uclear complex is plausible, apparently the subsequent co-
ordination of the uncoordinated isocyanide group is more
favoured than the formation of the intermediate. All at-
1
Figure 1. Selected IR and H-NMR data for complexes 3a and 3d
lower-field are assigned to the phosphorus atoms of side B. tempts to prepare the mononuclear complexes by using a
We were not able to assign the proton and carbon reson- 1:1 molar ratio failed, giving instead mixtures of the di-
ances (Tables 1 and 2) for each moiety A and B using the nuclear complexes 4a and 4b and the mononuclear ones.
conventional methods due to the similar values of chemical even if a large excess of the ligand was used.
shifts. However, the spectroscopic characterisations have
Elemental analyses, conductivity, and spectroscopic data
been performed through 2D 1H,183W- and 31P,183W-HMQC support the dinuclear nature of the complexes and the pro-
experiments, as will be discussed below (183W-NMR stud- posed symmetric structure. The IR spectra of 4a and 4b
ies). The alkenyl proton resonances appear in the 1H-NMR (CH2Cl2) show two very strong and broad ν(CO) absorp-
spectra (Table 1) as two different broad singlets.
tions at 2006Ϫ2008 and 1960Ϫ1961 cmϪ1, typical of a cis
13C-NMR spectra (Table 2) show two carbyne carbon dicarbonyl arrangement for each tungsten centre. The spec-
resonances at δ ϭ 286.7Ϫ289.8 [J(P-C) ϭ 9.4Ϫ9.6 Hz]. For tra also show one ν(CϵN) absorption at 2130 and 2132
complexes 3b and 3c, bearing two different carbyne groups cmϪ1, for 4a and 4b, respectively (Table 3).
at each side of the bridge, the signals appear as two triplets,
The NMR spectra indicate that the two isocyanide
while for 3a and 3d these resonances are not well defined groups occupy the cis positions with respect to the carbyne
and appear as two multiplets. The assignments of these res- ligand of the corresponding metal centre. Thus, 31P-NMR
onances for each moiety have been done through 2D spectra of 4a and 4b display (Table 3) two singlet resonances
1H,13C-HMBC correlation experiments, on the basis of the at δ ϭ 21.6 and 40.0, and δ ϭ 21.9 and 40.1, respectively,
previously known proton assignments. The carbon reson- indicating the chemical unequivalence of the phosphorus
ances of the cyanide group are shifted to lower field (> atoms of dppe. The J(W-P) values allow the assignment of
20 ppm) (Table 2) appearing very close to those of the Cγ the coordination sites. Thus, the lower-field signals with rel-
atom of the alkenylcarbyne chain, indicating that a signifi- atively large values [J(W-P) ϭ 229.6 and 231.6 Hz] are typi-
cant electron donation has occurred in the formation of the cal of a mutually trans PϪCO arrangement, while those of
dinuclear species through the coordination of the [W]ϪCN the higher-field signals [J(W-P) ϭ 83.9Ϫ85.4 Hz] are
moiety of complexes 2a and 2b. 13C-NMR spectra also characteristic of a phosphorus atom trans to carbyne li-
show carbonyl resonances which appear as virtual doublet- gands.[3a] This reflects the high trans-influence of the car-
of-doublet signals at δ ϭ 211.4Ϫ213.2 [2J(P-C) ϭ 7.0Ϫ7.2, byne ligand,[3a,20] and it is also in accord with previous re-
29.9Ϫ37.3 Hz] (Table 2) as expected for each unequivalent ported data for similar derivatives. The carbyne carbon res-
cis-dicarbonyl pair.
onances in the 13C{1H} NMR spectra (Table 4) which ap-
344
Eur. J. Inorg. Chem. 2000, 341Ϫ350

Tungsten Alkenyl-Carbyne Complexes Bridged by Cyanide and Diisocyanide Ligands
FULL PAPER
1
Table 3. Selected IR[a] and 31P{1H}- and H-NMR[b] data for complexes 4a, and 4b
IR
ν(CO)
31P{1H}[c]
2 P trans to carbonyl
1H
CHβ
ν(CϵN)
2 P trans to carbyne
4a
4b
2008 (vs), 1961 (s)
2006 (vs), 1960 (s)
2132 (m)
2130 (m)
21.6 s (85.4)
21.9 s (83.9)
40.0 s (231.6)
40.1 s (229.6)
6.00 s,br
5.92 s,br
[a]
[b]
Spectra recorded in CH2Cl2, ν (cmϪ1). Abbreviations: s, strong; vs, very strong; m, medium. Ϫ
Spectra recorded in CDCl3, δ in
[c]
ppm, J in Hz. Abbreviations: s, singlet, br, broad. Ϫ within parenthesis J(W-P).
pear as a doublet of doublets at ca. δ ϭ 298 [2J(P-C) ca. 183W-NMR Studies
22, 10 Hz] are also consistent with the trans position of the
carbyne groups with respect to one of the phosphorus atom
183W-NMR data of complexes 2a, 2b, 3a؊d, 4a, and 4b
of dppe. The chemical unequivalence of the carbonyl are collected in Table 5. 183W data were acquired by indirect
groups is also shown by the corresponding carbon reson- detection through H and/or 31P, using standard HMQC
1
ances. Thus, those of carbonyl groups trans to the phos- pulse sequence.[21][22] For transition metal nuclei the chemi-
phorus atom of dppe appear as a double doublet signal at cal shift is dominated by the paramagnetic contribution to
δ ϭ 209.3 [2J(P-C) ϭ 7.3Ϫ8.6, 24.0Ϫ24.5 Hz] while those the total shielding, which can be approximated by Equation
of the cis carbonyl ligands appear as an apparent triplet 4, where r represents the distance to the valence d electrons
signal at δ ϭ 207.5Ϫ207.9 [2J(P-C) ϭ 7.4Ϫ7.5 Hz] (Table from the metal nucleus, ∆E is the average electronic exci-
4). Furthermore, 13C{1H}-NMR spectra also show reson- tation energy, and ∆QN is the angular imbalance of charge.
ances of the equivalent isocyanide groups at δ ϭ 161.6 (4a) The angular imbalance of charge can be considered as con-
and 161.9 (4b) as apparent triplets [2J(P-C) ϭ 7.5Ϫ8.4 Hz] stant for complexes having the same d-electron configura-
along with that of the Cγ atom of the alkenylcarbyne chain tion and symmetry. In this way we can rationalise the
observed as a singlet at δ ϭ 175.0 (4a) or 174.5 (4a).
chemical shifts variations of the complexes studied accord-
Table 4. Selected 13C{1H}-NMR data for complexes 4a and 4b[a]
Cα
Cγ
(WϪCN)2
2 CO cis to P
2 CO trans to P
4a
4b
298.4 dd (22.0, 10.0)
298.3 dd (23.2, 9.0)
175.0 s
174.5 s
161.6 vr. t (8.4)
161.9 vr. t (8.4)
207.5 vr. t (7.4)
207.9 vr. t (7.5)
209.3 dd (24.0, 8.6)
209.3 dd (24.5, 7.3)
[a]
Spectra recorded in CDCl3, δ in ppm, J in Hz. Abbreviations: s, singlet; d, doublet; t, triplet; dd, doublet of doublet; m, multiplet; vr,
2
virtual. Within parentheses, J(PϪC).
Eur. J. Inorg. Chem. 2000, 341Ϫ350
345

J. Gimeno, A. J. L. Pombeiro et al.
FULL PAPER
ing to the fluctuations of the r and ∆E terms, showing an π-acceptor ability of diisocyanide ligand 1,4-(CN)2C6H4
upfield shift of the metal nucleus when r or ∆E increase, with respect to the cyanide group. The 183W chemical shift
and consequently a deshielding when one of the terms be- of complex 4b bearing two eight-membered rings is deshi-
comes smaller.
elded by 19 ppm with respect to 4a, as is also shown in the
spectra of complexes 2a, 2b, and 3a؊d (see above).
In addition, the 183W-NMR spectra allow the assignment
1
of the H and 13C resonances in compounds 3a؊d. Thus,
Table 5. 183W-NMR data for complexes2؊4
the assignment of the alkenyl proton resonance in each moi-
ety (Hβ and HβЈ) was done through their correlations with
1
the metal nuclei in the H, 183W HMQC spectra. On the
δ183
W
δ183
W
A
B
basis of these assignments the rest of the 1H and 13C reson-
ances were identified through the conventional 1H,13C-
HMQC and -HMBC experiments.
2a
2b
4a
4b
Ϫ2116
Ϫ2100
Ϫ2127
Ϫ2108
3a
3b
3c
3d
Ϫ2094
Ϫ2096
Ϫ2078
Ϫ2078
Ϫ1819
Ϫ1804
Ϫ1821
Ϫ1805
Electrochemical Studies
The 183W-NMR spectra of 2a and 2b (δ ϭ Ϫ2116,
The electrochemical behaviour of the alkenylcarbyne
complexes has been investigated by cyclic voltammetry
(CV) and controlled potential electrolysis (CPE) in aprotic
medium (see Experimental Section).
Ϫ2100, respectively) show that the substitution of the
acetonitrile ligand of the starting material 1a and 1b (δ ϭ
Ϫ1786, Ϫ1775, respectively)[21] by the cyanide ligand pro-
duces a shielding of the tungsten nuclei by 330Ϫ325 ppm.
This upfield shift effect is in agreement with the higher π-
acceptor ability of CNϪ compared to CH3CN, which im-
plies an increase in the ∆E term of Equation 4. The 16 ppm
deshielding of 2b with respect to 2a is of the same order
of the 183W chemical shift difference between found in the
starting carbyne complexes (1a and 1b). This fact can be,
and is explained, by the electronic and steric effects induced
by the change in of the carbocyclic moiety size.[21]
With the exception of the dicationic complexes 4 (for
which no anodic wave was detected, their oxidation con-
ceivably occurring only at a potential above that of the on-
set of the solvent/electrolyte discharge), all the compounds
exhibit irreversible anodic and cathodic waves by CV (Table
6). The oxidation peak potential of the first (I) anodic wave
(IEpox) for the cyanide complexes 2 (ca. 1.1 V vs. SCE) is
lower than those shown by the other complexes (ca.
1.3Ϫ1.4 V, for 1 and 3) in agreement with the known[24]
stronger net electron σ-donor minus π-acceptor ability of
cyanide compared with a nitrile or an isocyanide ligand.
The assignment of δ183W for each moiety A and B of
dinuclear complexes 3a؊d (Figure 1) is in accordance with
the corresponding chemical shifts of precursor complexes
1a and 1b, and 2a and 2b. Thus, the δ183W signals at higher
field, which can be compared to those of cyanide complexes
2a and 2b, are assigned to the A moiety, while those at lower
field, which resemble appear at analogous chemical shifts
of the acetonitrile complexes 1a and 1b, are assigned to
moiety B. When moving from the mononuclear complexes
2a and 2b to the dinuclear ones 3a؊d, a downfield shift of
20Ϫ22 ppm in the δ183W of the A substructure is observed.
The bidentate coordination of the CNϪ group, acting as a
bridging ligand, produces a reduction in its π-acceptor
ability and consequently a decrease of the ∆E term. As ob-
served before, an increase in the size of the carbocyclic moi-
ety in either the A or B part of complexes 3a؊d leads to a
deshielding of the metal by 15Ϫ18 ppm. It is worth men-
tioning that in complexes 3b and 3c the larger carbocyclic
ring produces the expected deshielding of the tungsten nu-
cleus bonded to the corresponding carbyne, but also a
2 ppm upfield shift to the signal of the other metal. Al-
Table 6. Cyclic voltammetric data for complexes 1Ϫ4[a]
ox
ox
red
red
Compound
IEp
IIEp
IEp
IIEp
1a
1.34
1.28
1.07
1.09
1.30
1.38
1.26
1.28
Ϫ
1.58
1.59
1.34
1.42
1.38
1.50
1.37
1.43
Ϫ
Ϫ1.58
Ϫ1.65
Ϫ1.89
Ϫ1.88
Ϫ1.58
Ϫ1.65
Ϫ1.70
Ϫ1.73
Ϫ1.25
Ϫ1.20
Ϫ
Ϫ
Ϫ
Ϫ
1b
2a
2b
3a
Ϫ1.89
Ϫ1.90
Ϫ1.94
Ϫ1.96
Ϫ1.48
Ϫ1.43
Ϫ
3b[b]
3c[b]
3d[b]
4a
4b[c]
Ϫ
Ϫ
Ϫ
[d]
[W(CO)4(dppe)]
1.02[e]
[a]
Potentials in Volt ± 0.02 vs. SCE measured in 0.2 mol dmϪ3
[NBu4][BF4]/MeCN {CH2Cl2 for compounds 3a, 4a, and
[W(CO)4(dppe)]} at a scan rate of 0.2 V sϪ1 and at a Pt disc (d ϭ
[b]
0.5 mm) electrode, unless stated otherwise. Ϫ In vitreous C; at a
[c]
Pt electrode, only one broad wave is observed at ca. 1.4 V. Ϫ In
[d]
[e]
vitreous C. Ϫ Included for comparative purposes. Ϫ Reversi-
ox
ble wave (∆E1/2 value given).
5
though J(183W-1H)23 are observed within each moiety A
and B, there are no cross peaks between the tungsten atom
Moreover, the values of oxidation potential for all the
of the A moiety with the proton and phosphorus nuclei of complexes are higher than that for [W(CO)4(dppe)]
ox
B (and vice versa). Hereby, this small shift can be assigned (E1/2 ϭ 1.02 V) which was also measured for comparative
to field or solvent effects.
purposes, indicating that the alkenylcarbyne ligands are be-
As expected, the δ183W of complexes 4a and 4b appear having as even stronger net electron π-acceptors than CO,
at higher field than those of the corresponding 2a and 2b thus compensating for the stronger net electron donor
(8 and 11 ppm, respectively) in accordance with the higher ability of the nitrile, isocyanide, or cyanide ligand compared
346
Eur. J. Inorg. Chem. 2000, 341Ϫ350

Tungsten Alkenyl-Carbyne Complexes Bridged by Cyanide and Diisocyanide Ligands
FULL PAPER
with CO, which should result in a lowering of the oxidation 10 V sϪ1, when it corresponds roughly to a single-electron
potential of our complexes relative to that of process, to 50 mV·sϪ1 for complexes 1) and (ii) with ad-
[W(CO)4(dppe)]. This is consistent with the reported[9] be- dition of a base such as pyridine, which enhances the depro-
haviour
of
the
carbyne
ligands
in
trans- tonation step.
[ReX(ϵCCH2R)(dppe)2][BF4] (X ϭ F or Cl; R ϭ alkyl,
aryl, or ester).
The proton liberation at the anodic process, now reported
for the first time for alkenylcarbyne ligands, indicates a pro-
For the cyanide-bridged dinuclear complexes 3, two close motion of their acidic character as a result of oxidation of
and extensively overlapped anodic waves are observed. the complexes, and parallels the anodically induced depro-
Since these complexes can be viewed as the assembling of tonation observed for the aminocarbyne (CNH2) and isocy-
the tungsten moieties A (attached to a formal isocyanide anide
(CNH)
ligands
in
trans-[ReCl(CNHn)-
ligand) and B (attached to a formal nitrile ligand) (Figure (dppe)2][BF4]nϪ1 (n ϭ 2 or 1)[10] and trans-[FeH(CNH)-
1) it is expected that the tungsten atom of moiety A un- (dppe)2][BF4],[25] as well as for some aminocarbene com-
dergoes an oxidation process at a more anodic potential plexes[11a] of PdII or PtII. However, the behaviour of the
with respect to that of moiety B. Moreover, IEpox values for alkenylcarbyne ligands of this study contrasts with the sta-
these complexes are close to those of the acetonitrile precur- bility, toward anodically-induced deprotonation, of the car-
sors 1. This is in accord with the 183W chemical shifts for byne ligands ϵCCH2R in the complexes trans-
parts A and B of complexes 3 (see above).
[ReX(ϵCCH2R)(dppe)2][BF4],[9] which undergo a revers-
In the cyclic voltammograms of complexes 1, 2, and 3, ible single-electron oxidation by CV. This difference con-
the first anodic wave (I) is followed, at a slightly higher ceivably results from the higher acidity of the alkenyl pro-
potential, by a second one (II), also irreversible and broad, ton (ϵCϪCHϭ) of our complexes compared to the alkyl
that partially overlaps with the former wave. Although this protons (ϵCϪCH2R) in the Re compounds, and/or the oc-
precluded an accurate discrimination of the respective num- currence of anodically induced ortho-deprotonation of the
bers of electrons, the overall involvement, by CPE, of multi- ring. Hence, the anodic conversion of a ligating alkenylcar-
electron anodic processes with electron-induced proton lib- byne into e.g., an allenylidene or a vinylidene ligand is
eration from the alkenylcarbyne ligand is evident.
plausible, but unfortunately we did not succeed in the
In fact, exhaustive anodic CPE of those complexes, usu- identification of the products of the CPE or of the at-
ally in acetonitrile, corresponds to an overall consumption tempted chemical oxidations by oxidising agents such as the
(waves I ϩ II) of ca. 3 (complexes 1 or 2) or ca. 4 (com- triarylaminium (Magic Blue) salt [N(4-BrC6H4)3][SbCl6].
plexes 3) faradays/mol. The evolution of Hϩ is indicated by
The alkenylcarbyne complexes of this study display, by
the detection, by CV (cathodic sweep) of the electrolysed CV, a single-electron irreversible cathodic wave (as shown
solution, at a Pt electrode, of an irreversible and broad ca- by CPE) (Table 6), which for the dinuclear compounds (3
thodic wave at ca. Ϫ0.5 V, assigned to Hϩ reduction. This and 4), is followed by a second one at a lower potential,
wave shifts to a much lower potential upon replacement of which involves a two-electron process for 4 (as measured by
the Pt by a vitreous carbon electrode, in accord with the CPE). The observation of the two distinct cathodic waves
expected large overpotential required for Hϩ reduction at for complexes 4 with two identical metal centres could sug-
the latter electrode. The proton emission was also measured gest an interaction through a delocalized LUMO along the
by acid-base titration of the electrochemically oxidised bridged aromatic diisocyanide, but the complexity of the
complex solutions: ca. 1 Hϩ/molecule for complexes 2, ca. cathodic processes prevents such an interpretation.
3 Hϩ/molecule for complexes 1, or ca. 4 Hϩ/molecule for
complexes 3. The higher numbers of protons for 1 and 3
relative to 2 are in accord with the expected stronger acidity
of the carbyne ligand in the former complexes, as a result
Conclusions
of the charge and the absence of the stabilising strong elec-
In this work, novel types of dinuclear A and B and
tron-donor mono-hapto cyanide ligand. Moreover, the mononuclear C alkenylcarbyne Fischer-type tungsten com-
highest number of protons lost for compounds 3 may also plexes are reported (Scheme 1). Complexes of type A and B
reflect their biscarbyne (dinuclear) character.
belong to a new type of α,β unsaturated carbyne dimetallic
Proton dissociation can also occur during the time scale derivatives, in which the metal atoms are linked by a cyan-
of CV, at a sufficiently low scan rate, since its cathodic wave ide and diisocyanide bridging group. These novel dinuclear
(with the above features) is detected as well upon scan re- complexes display a π-conjugated system consisting of two
versal following the anodic scan of a solution of an alkenyl- terminal unsaturated carbyne tungsten moieties linked by
carbyne complex.
bridging ligands with π-electronic delocalized systems
Consistent with an anodic multi-electron process, at a (Scheme 2). There is currently much research on this type
sufficiently high time scale, involving electron-induced pro- of derivatives because they disclose appropriate molecular
ton loss followed by further oxidation of the product(s), arrangements, with potential utility as precursors of mixed
the following observations by CV are possible: the anodic valence complexes and materials with enhanced electrical
ox
ox
current-functions ip
C
Ϫ1·vϪ1/2 (ip Ϫ anodic peak cur- conductivities and nonlinear optical (NLO) properties.[26]
rent, C Ϫ concentration, v Ϫ scan rate) increase (i) with a Our study also allowed the investigation, for the first time,
decrease of the scan rate (e.g. by a factor of ca. 2 from v ϭ of the electrochemical behaviour of alkenylcarbyne com-
Eur. J. Inorg. Chem. 2000, 341Ϫ350
347

J. Gimeno, A. J. L. Pombeiro et al.
FULL PAPER
31.9 (s, CH2), 36.3 (s, CH2), 128.3Ϫ136.2 (m, 2 PPh2), 135.7 (s,
Cβ). Ϫ MS (FAB, m/z) [Mϩ Ϫ CN] ϭ 773, [Mϩ Ϫ CO] ϭ 771,
[Mϩ Ϫ CN Ϫ CO] ϭ 745, [Mϩ Ϫ 2 CO] ϭ 743. ϪC39H39NO2P2W:
calcd. C 58.6, H 4.9, N 1.8; found: C 58.2, H 4.7, N 1.3.
plexes, revealing that (i) the alkenylcarbyne ligands are acti-
vated, by oxidation of their complexes, towards heterolytic
CϪH bond cleavage (a behaviour which is of potential syn-
thetic interest for the generation of other unsaturated mul-
tiple metal-carbon bonded species) and that (ii) the alkenyl-
carbyne ligands behave as even stronger π-electron ac-
ceptors than CO.
Preparation of Cyanide-Bridged Bis(alkenylcarbyne) Ditungsten
Complexes (3a؊d): General Procedure: A mixture of complexes 2a
(0.2 mmol) and 1a (0.2 mmol) in 20 mL of dichloromethane was
stirred at room temperature for 1 h. The resulting orange-red solu-
tion was evaporated to dryness and the residue was washed with
hexane (3 ϫ 5 mL) to give an orange solid (3a). The complexes
3bϪd were prepared similarly. The complexes 3a and 3d were also
prepared directly from the reaction of 2 equiv. of 1a and 1b with
[Bu4N]CN in dichloromethane, or with NaCN in methanol, in the
similar yields. Yield: 82Ϫ85%. Ϫ Conductivity (acetone, 20°C, ΩϪ1
cm2 molϪ1): 3a, 123; 3b, 120; 3c, 115; 3d, 118.
Experimental Section
Synthesis and Characterization of Alkenylcarbyne Complexes: The
reactions were carried out under dry nitrogen using Schlenk tech-
niques. All solvents were dried by standard methods and distilled
under nitrogen before use. The precursor complexes 1a, and b were
prepared by the literature methods.[3a] NaCN, [Bu4N]CN, and 1,4-
(CN)2C6H4 (Aldrich Chemical Co.) were used as received. Ϫ Infra-
red spectra were recorded on a PerkinϪElmer 1720-XFT spec-
trometer. Ϫ Mass spectra (FAB) were recorded using a VG-Autos-
pec spectrometer, operating in the positive mode; 3-nitrobenzyl al-
cohol (NBA) was used as the matrix. Ϫ The conductivities were
measured at room temperature, in ca. 10Ϫ3 mol dmϪ3 acetone solu-
1
Spectral and Analytical Data for 3a: H NMR (δ, CDCl3) 1.40 (m,
8 H, 4 CH2), 1.69 (m, 4 H, 2 CH2), 1.85 (m, 4 H, 2 CH2), 2.3Ϫ3.0
[m, 8 H, 2 P(CH2)2P], 7.18Ϫ7.70 (m, 40 H, 4 PPh2). Ϫ 13C{1H}
NMR (δ, CDCl3) 25.2 (s, CH2), 25.3 (s, CH2), 25.9 (s, 2 CH2), 28.0
[m, 2 P(CH2)2P], 31.4 (s, CH2), 31.7 (s, CH2), 34.4 (s, CH2), 34.9
(s, CH2), 128.2Ϫ136.4 (m, Cβ, CβЈ,
4
PPh2).
Ϫ
tions, with a Jenway PCM3 conductivimeter. Ϫ The C, H, and N C71H66BF4NO4P4W2: calcd. C 54.1, H, 4.2, N 0.9; found: C 53.4,
analyses were carried out with a PerkinϪElmer 240-B microana-
lyzer. Ϫ NMR spectra were run on Bruker AC300 and AMX400
spectrometers. The parameters used for the indirect detection
experiments 1H,183W 2D HMQC and 31P,183W{1H} 2D HMQC
have been previously described.[3a,21] The spectral reference used
for 183W was Na2WO4. Ϫ Selected IR and 1H-, 13C{1H}-, 31P{1H}-,
and 183W-NMR spectroscopic data for the novel carbyne tungsten
complexes are collected in Tables 1Ϫ5.
H 4.4, N 0.7.
Spectral and Analytical Data for 3b: IR [KBr, ν(CN); ν(CO);
˜ ϭ 2110 (vw), 2099 (vw, sh); 1994 (vs, br), 1925 (vs, br);
ν(BF4)]: ν
1
1059 (m, br). Ϫ H NMR (δ, CDCl3) 1.30 (m, 12 H, 6 CH2), 1.41
(m, 6 H, 3 CH2), 1.69 (m, 2 H, CH2), 2.10 (m, 2 H, CH2), 2.3Ϫ2.9
[m, 8 H, 2 P(CH2)2P], 7.18Ϫ7.70 (m, 40 H, 4 PPh2). Ϫ 13C{1H}
NMR (δ, CDCl3) 25.15 (s, CH2), 25.23 (s, CH2), 25.8 (s, CH2),
26.4 (s, CH2), 26.6 (s, CH2), 26.7 (s, CH2), 27.0Ϫ29.0 [m, CH2, 2
P(CH2)2P], 31.4 (s, CH2), 31.7 (s, CH2), 34.8 (s, CH2), 35.5 (s, CH2),
128.3Ϫ136.4 (m, Cβ, CβЈ, 4 PPh2). ϪC74H72BF4NO4P4W2: calcd.
C 54.9, H 4.5, N 0.9; found: C 53.7, H 4.5, N 0.7.
Preparation of Mononuclear Cyanide Alkenylcarbyne Complexes 2a
and 2b. ؊ General Procedure: A small excess of NaCN solid was
added to an orange solution of 1a or 1b (0.2 mmol) in 20 mL of
methanol. The mixture was stirred at room temperature for 2 h.
The resulting solution was filtered off and the filtrate was evapo-
rated to dryness. The residue was extracted with CH2Cl2 and the
filtrate was dried under vacuum to give an orange solid. Yield: 2a,
90%; 2b, 95%.
Spectral and Analytical Data for 3c: IR [KBr, ν(CN); ν(CO);
ν(BF4)]: 2109 (vw, sh), 2098 (vw); 1993 (vs, br), 1924 (vs, br); 1056
1
(s, br). Ϫ H NMR (δ, CDCl3) 1.38 (m, 10 H, 5 CH2), 1.69 (m, 4
H, 2 CH2), 1.82 (m, 4 H, 2 CH2), 2.07 (m, 4 H, 2 CH2), 2.40- 3.0
[m, 8 H, 2 P(CH2)2P], 7.17Ϫ7.87 (m, 40 H, 4 PPh2). Ϫ 13C{1H}
NMR (δ, CDCl3) 25.1 (s, CH2), 25.8 (s, CH2), 26.3 (s, CH2), 26.6
(s, CH2), 26.7 (s, CH2), 26.8 (s, CH2), 27.0 (s, CH2), 28.0 [m, 2
P(CH2)2P], 31.2 (s, CH2), 31.7 (s, CH2), 34.2 (s, CH2), 35.8 (s, CH2),
127.9Ϫ136.6 (m, Cβ, CβЈ, 4 PPh2). ϪC74H72BF4NO4P4W2: calcd.
C 54.9, H 4.5, N 0.9; found: C 54.0, H 4.8, N 0.7.
The complexes 2a and 2b were also prepared following the pro-
cedure below: An orange solution of 1a or 1b (0.2 mmol) and 1
equiv. of [NBu4]CN in 10 mL of CH2Cl2 was stirred at room tem-
perature for 2 h. After evaporation of the solvent to dryness the
residue was extracted with toluene and filtered of on Alox. Re-
moval of the solvent and washing the resulting solid with diethyl
ether (2 ϫ 10 mL) and hexane (2 ϫ 10 mL) and drying in vacuo
gave an orange solid. Yields ca. 70%.
Spectral and Analytical Data for 3d: 1H NMR (δ, CDCl3) 1.39 (m,
16 H, 8 CH2), 1.68 (m, 4 H, 2 CH2), 1.81 (m, 4 H, 2 CH2), 2.09
(m, 4 H, 2 CH2), 2.3Ϫ3.0 [m, 8 H, 2 P(CH2)2P], 7.17Ϫ7.68 (m, 40
H, 4 PPh2). Ϫ 13C{1H} NMR (δ, CDCl3) 25.3 (s, CH2), 25.4 (s,
CH2), 26.6Ϫ27.1 (m, 8 CH2), 28.2 [m, 2 P(CH2)2P], 31.8 (s, CH2),
31.9 (s, CH2), 35.6 (s, CH2), 36.1 (s, CH2), 128.2Ϫ135.6 (m, Cβ,
CβЈ, 4 PPh2). ϪC77H78BF4NO4P4W2: calcd. C 55.7, H 4.7, N 0.8;
found: C 54.3, H 4.9, N 0.8.
Spectral and Analytical Data for 2a: IR [KBr, ν(CN); ν(CO)] ν˜ ϭ
1
2111 (vw); 1987 (vs), 1917 (vs). Ϫ H NMR (δ, CDCl3) 1.48 (m, 4
H, 2 CH2), 1.94 (m, 4 H, 2 CH2), 2.60 [m, 2 H, P(CHaHb)2P], 2.85
[m, 2 H, P(CHaHb)2P], 7.36Ϫ7.75 (m, 20 H, 2 PPh2). Ϫ 13C{1H}
NMR (δ, CDCl3) 25.5 (s, CH2), 26.1 (s, CH2), 28.5 [m, P(CH2)2P],
31.8 (s, CH2), 34.7 (s, CH2), 128.2Ϫ136.3 (m, Cβ, 2 PPh2).
ϪC36H33NO2P2W: calcd C 57.1, H 4.4, N 1.8; found: C 57.5, H
4.2, N 1.9.
Preparation of Diisocyanide-Bridged Bis(alkenylcarbyne) Ditungsten
Complexes 4a and 4b: General Procedure: A mixture of complex 1a
or 1b (0.2 mmol) and 0.5 equiv. of 1,4-phenylendiisocyanide
Spectral and Analytical Data for 2b: IR [KBr, ν(CN); ν(CO)] ν˜ ϭ
1
2112(vw); 1984 (vs), 1916 (vs). Ϫ H NMR (δ, CDCl3) 1.40 (m, 4 (0.1 mmol) in 20 mL of dichloromethane was stirred at room tem-
H, 2 CH2), 1.44 (m, 2 H, CH2), 1.53 (m, 2 H, CH2), 1.70 (m, 2 H,
perature for 2 h. The resulting orange-red solution was evaporated
CH2), 1.82 (m, 2 H, CH2), 2.31 (m, 2 H, CH2), 2.58 [m, 2 H, to dryness and the residue was washed with diethyl ether
P(CHaHb)2P], 2.88 [m, 2 H, P(CHaHb)2P], 7.36Ϫ7.88 (m, 20 H, 2 (2 ϫ 5 mL) and hexane (3 ϫ 5 mL) to give an orange-red solid 4a
PPh2). Ϫ 13C{1H} NMR (δ, CDCl3) 25.5 (s, CH2), 26.7 (s, CH2), and 4b. Yield: 75Ϫ80%. Conductivity (acetone, 20°C, ΩϪ1 cm2
26.9 (s, CH2), 26.96 (s, CH2), 27.02 (s, CH2), 28.6 [m, P(CH2)2P], molϪ1): 4a, 200; 4b, 195.
348
Eur. J. Inorg. Chem. 2000, 341Ϫ350

Tungsten Alkenyl-Carbyne Complexes Bridged by Cyanide and Diisocyanide Ligands
FULL PAPER
[1]
[1a]
For recent reviews on metal carbyne complexes see:
P. F.
Transition
Spectral and Analytical Data for 4a: IR [KBr, ν(CN); ν(CO);
[1b]
Engel, M. Pfeffer, Chem. Rev. 1995, 95, 2281. Ϫ
ν(BF4)]: ν˜ ϭ 2133 (m); 2000 (vs), 1947 (s); 1061 (s, br). Ϫ 1H NMR
(δ, CDCl3) 1.76 (m, 8 H, 4 CH2), 2.36 (m, 4 H, 2 CH2), 2.56 (m,
4 H, 2 CH2), 2.7Ϫ3.4 [m, 8 H, 2 P(CH2)2P], 6.42Ϫ7.78 [m, 44 H,
(CN)2C6H4, 4 PPh2]. Ϫ 13C{1H} NMR (δ, CDCl3) 25.4 (s, 2 CH2),
Metal Carbyne Complexes; NATO ASI Series, Kluwer Aca-
demic Publishers, Dordrecht, 1993.
For applications of metal carbyne complexes in organic syn-
thesis see: L. McElwee-White, Synlett 1996, 806.
[2]
[3]
[3a]
For recent developments see:
L. Zhang, M. P. Gamasa, J.
25.5 (m,
2 PCaH2CbH2P), 26.0 (s, 2 CH2), 27.3 (m, 2
´
Gimeno, R. J. Carbajo, F. Lopez-Ortiz, M. Lanfranchi, A. Tiri-
PCaH2CbH2P), 33.2 (s, 2 CH2), 35.6 (s, 2 CH2), 125.7Ϫ133.5 [m,
Cβ, CβЈ, (CN)2C6H4, 4 PPh2]. ϪC78H70B2F8N2O4P4W2: calcd. C
53.1, H 4.0, N 1.6; found: C 52.8, H 4.1, N 1.5.
[3b]
picchio, Organometallics 1996, 15, 4274. Ϫ
L. Zhang, M. P.
Gamasa, J. Gimeno, A. Galindo, C. Mealli, M. Lanfranchi, A.
Tiripicchio, Organometallics 1997, 16, 4099 and references ther-
[3c]
ein. Ϫ
B. E. Woodworth, P. S. White, J. L. Templeton, J.
Am. Chem. Soc. 1997, 119, 828 and references therein. Ϫ [3d] D.
E. Main, L. McElwee-White, J. Am. Chem. Soc. 1997, 119,
4551. Ϫ [3e] L. Weber, G. Dembeck, R. Boese, D. Bläser, Chem.
Ber. /Rec 1997, 130, 1305. Ϫ [3f] B. E. Woodworth, D. S. Frohn-
apfel, P. S. White, J. L. Templeton, Organometallics 1998, 17,
1655.
Spectral and Analytical Data for 4b: IR [KBr, ν(CN); ν(CO);
ν(BF4)] ν˜ ϭ 2128 (m); 1997 (vs), 1944 (s); 1055 (s, br). Ϫ 1H NMR
(δ, CDCl3) 1.50 (m, 12 H, 6 CH2), 1.76 (m, 4 H, 2 CH2), 1.82 (m,
4 H, 2 CH2), 2.20 (m, 4 H, 2 CH2), 2.63 (m, 4 H, 2 CH2), 2.8Ϫ3.2
[m, 8 H, 2 P(CH2)2P], 6.36Ϫ7.79 [m, 44 H, (CN)2C6H4, 4 PPh2].
13C{1H} NMR (δ, CDCl3) 25.6 (m, 2 PCaH2CbH2P), 25.5 (s, 2
[4]
Ϫ
A few examples containing saturated di-carbyne bridging units
are also known:[4a] [TpЈ(CO)2MϵCϪCH(R)ϪCH(R)ϪCϵM-
CH2), 26.5 (s, 2 CH2), 26.7 (s, 2 CH2), 27.2 (s, 2 CH2), 27.5 (m, 2
PCaH2CbH2P), 27.8 (s, 2 CH2), 33.0 (s, 2 CH2), 37.1 (s, 2 CH2),
125.7Ϫ133.6 [m, (CN)2C6H2, 4 PPh2], 136.4 [d, 3J(CϪP) ϭ
16.7 Hz, Cβ, CβЈ]. Ϫ MS (FAB, m/z) 0.5 [Mϩ Ϫ 2 ϫ (BF4) Ϫ
(CN)2C6H4] ϭ 773. ϪC84H82B2F8N2O4P4W2: calcd. C 54.6, H 4.5,
N 1.5; found: C 53.8, H 4.3, N 1.8.
(CO)2TpЈ] (M ϭ Mo. R ϭ H; M ϭ W. R ϭ Me, CH2Ph,
[4b]
CHMe2) (ref 3c).
Ϫ
[TpЈ(CO)2MϵCϪCϵW(CO)-
(PhCϵCPh)TpЈ] (M ϭ Mo, W) B. E. Woodworth, P. S. White,
[4c]
J. L. Templeton, J. Am. Chem. Soc. 1998, 120, 9028. Ϫ
-
[Cp{P(OMe)3}2MoϵCϪC(H)tBuϪC(H)tBuϪCϵMo{P-
(OMe)3}2Cp] R. G. Beevor, M. J. Freeman, M. Green, C. E.
Morton, A. G. Orpen, J. Chem. Soc., Chem. Commun. 1985, 68.
[5]
[6]
N. A. Ustynyuk, V. N. Vinogradova, V. G. Andrianov, Y. T.
Struchkov, J. Organomet. Chem. 1984, 268, 73.
Electrochemical Measurements: The electrochemical experiments
were performed on an EG & G PARC 273 potentiostat/galvanostat
connected to a PC computer through a GPIB interface (National
Instruments PC-2A) or on an EG & G PARC 173 potentiostat/
galvanostat and an EG & G PARC 175 Universal programmer.
Cyclic voltammetry was undertaken in a two-compartment three-
electrode cell, at a platinum- or vitreous carbon-disc working elec-
trode (d ϭ 0.5 or 1 mm, respectively), probed by a Luggin capillary
connected to a silver-wire pseudo-reference electrode; a platinum
auxiliary electrode was employed. Controlled potential electrolyses
were carried out in a two-compartment three electrode cell with
platinum gauze working and counter electrodes in compartments
separated by a glass frit; a Luggin capillary, probing the working
electrode, was connected to a silver wire pseudo reference electrode.
The electrochemical experiments were performed in an inert atmos-
phere (N2) at room temperature. The potentials were measured in
0.2 mol dmϪ3 [NBu4][BF4]/MeCN or CH2Cl2, and are quoted rela-
tive to the saturated calomel electrode (SCE) by using as internal
[6a] E. O. Fischer, W. Röll, N. H. T. Huy, K. Ackermann, Chem.
[6b]
Ber. 1982, 115, 2951. Ϫ
N. O. Dao, H. Fevrier, M. Jouan,
E. O. Fischer, W. Röll, J. Organomet. Chem. 1984, 275, 191.
[7]
To the best of our knowledge only the following analogous
complexes of this type are known: [7a] [W2(µ-Cl)2(µϪPh2AsCH2-
AsPh2)(ϵCPh)2]: E. O. Fischer, A. Ruhs, Chem. Ber. 1978, 111,
[7b]
2774. Ϫ
[M(ϵCϪNEt2)(CO)3(µ-L)]2 (M ϭ Mo, W. L ϭ Br,
I, SPh, NCO, etc.): E. O. Fischer, D. Wittmann, D. Himmelre-
ich, R. Cai, K. Ackermann, D. Neugebauer, Chem. Ber. 1982,
115, 3152.
[8]
A. J. L. Pombeiro, J. A. McCleverty, Molecular Electrochemistry
of Inorganic, Bioinorganic, and Organometallic Compounds,
NATO ASI Series; Kluwer Academic Publishers, Dordrecht,
The Netherlands, 1993.
S. S. P. R. Almeida, A. J. L. Pombeiro, Organometallics, 1997,
16, 4469.
[9]
[10]
M. A. N. D. A. Lemos, M. F. C. Guedes da Silva, A. J. L.
Pombeiro, Inorg. Chim. Acta, 1994, 226, 9.
[11] [11a]
R. Bertani, M. Mozzon, R. A. Michelin, F. Benetollo, G.
Bombieri, T. J. Castilho, A. J. L. Pombeiro, Inorg. Chim. Acta,
1991, 189, 175. Ϫ [11b] G. Facchin, M. Mozzon, R. A. Michelin,
M. T. A. Ribeiro, A. J. L. Pombeiro, J. Chem. Soc., Dalton
Trans., 1992, 2827. Ϫ [11c] R. Bertani, M. Mozzon, R. A. Mich-
elin, T. J. Castilho, A. J. L. Pombeiro, J. Organomet. Chem.,
1992, 431, 117. Ϫ [11d] Y. Wang, A. J. L. Pombeiro, R. A. Mich-
elin, M. Mozzon, R. Bertani, Bull. Pol. Acad. Sci., 1994, 42,
307. Ϫ [11e] U. Belluco, R. Bertani, R. A. Michelin, M. Mozzon,
ox
reference the [Fe(η5-C5H5)2]0/ϩ couple (EϪ ϭ 0.45 or 0.53 V vs.
SCE).
The acid-base potentiometric titrations of the electrochemically
oxidised solutions were carried out by using a solution of NaOH
in MeOH that was standardised by titration against benzoic acid in
MeCN or CH2Cl2. The results have been corrected for background
effects by also performing, in each case, the titration of a blank
electrolyte solution which has been electrolysed under identical
conditions to those used for the corresponding complex solution.
´
M. F. C. Guedes da Silva, J. J. R. Frausto da Silva, A. J. L.
Pombeiro, Y. Wang, Inorg. Chim. Acta, 1995, 235, 397.
[12]
[13]
N. G. Connelly, in: Molecular Electrochemistry of Inorganic, Bi-
oinorganic and Organometallic Compounds (Eds.: A. J. L. Pom-
beiro, J. A. McCleverty), NATO ASI Series; Kluwer Academic
Publishers, Dordrecht, The Netherlands, 1993.
M. K. Lloyd, J. A. McCleverty, J. A. Connor, M. B. Hall, I. H.
Hillier, E. M. Jones, G. K. McEwen, J. Chem. Soc., Dalton.
Trans., 1973, 1743.
Acknowledgments
[14] [14a]
E. O. Fischer, M. Schluge, J. O. Besenhard, Angew. Chem.
Int. Ed. Engl., 1976, 15, 683. Ϫ [14b] E. O. Fischer, F. J. Gammel,
´
This work was supported by the Direccion General de Investiga-
J. O. Besenhard, A. Frank, D. Neugebauer, J. Organomet.
´
´
´
cion Cientıfica y Tecnica (Project PB96-0558) and the EU (Human
Capital Mobility Programme, Project ERBCHRXCT 940501).
L. Z. is grateful to the Spanish Ministerio de Asuntos Exteriores
[14c]
Chem., 1980, 191, 261. Ϫ
E. O. Fischer, D. Wittmann, D.
Himmerlreich, D. Neugebauer, Angew. Chem. Int. Ed. Engl.,
1982, 21, 444.
[15] [15a] I. Kovacik, O. Gevert, H. Werner, M. Schimittel, R. Sollner,
´
(Agencia Espan˜ola de Cooperacion Internacional) for a doctoral
[15b]
Inorg. Chim. Acta, 1998, 275Ϫ276, 435. Ϫ
Kojima, K. Ofele, Angew Chem., Int. Ed. Engl., 1980, 19, 538.
P. J. Krusic, U. Klabunde, C. P. Casey, T. F. Block, J. Am.
Chem. Soc., 1976, 98, 2015. Ϫ [16b] C. P. Casey, L. D. Albin, M.
C. Seaman, D. H. Evans, Organomet. Chem., 1978, 155, C37.
R. D. Rieke, H.
grant and the Fundac¸ao para a Ciencia e a Tecnologia, PRAXIS
XXI Programme (Portugal) for a post-doctoral grant (for doing
the detailed electrochemical studies). R. J. C. thanks the Spanish
[16] [16a]
´
Ministerio de Educacion y Cultura for a predoctoral fellowship.
Eur. J. Inorg. Chem. 2000, 341Ϫ350
349

J. Gimeno, A. J. L. Pombeiro et al.
FULL PAPER
[17] [17a]
[23] 7J(183W-1H) have been described in the literature: A. Mac-
chioni, P. S. Pregosin, P. F. Engel, S. Mecking, M. Pfeffer, J.-C.
Daran, J. Vaissermann, Organometallics 1995, 14, 1637.
´
J. ϪP. Battioni, D. Lexa, D. Mansuy, J.-M. Saveant, J. Am.
Chem. Soc., 1983, 105, 207. Ϫ [17b] M. Lange, D. Mansuy, Tetra-
hedron Lett., 1981, 22, 2561.
[18]
[24]
K. Nakamoto, Infrared and Raman Spectra of Inorganic and
Coordination Compounds, 4th ed., Wiley-Interscience Publi-
cation: New York, 1986, p.283.
J. Chatt, C. T. Kan, G. J. Leigh, C. J. Pickett, D. R. Stanley, J.
Chem. Soc., Dalton Trans., 1980, 2032.
[25]
´
S. S. P. R. Almeida, M. F. C. Guedes da Silva, J. J. R. Frausto
[19]
[20]
[21]
[22]
D. F. Shriver, S. A. Shriver, S. E. Anderson, Inorg. Chem. 1965,
4, 725.
da Silva, A. J. L. Pombeiro, J. Chem. Soc., Dalton Trans.,
1999, 467.
[26] [26a]
E. M. Shustorovich, M. A. Poraikoshits, Yu. A. Buslaev, Coord.
Chem. Rev. 1975, 17, 1.
D. W. Bruce, D. OЈHare Inorganic Materials, Wiley, New
[26b]
York, 1992. Ϫ
Engl. 1991, 30, 673.
M. H. Chisholm, Angew. Chem. Int. Ed.
´
R. J. Carbajo, L. Zhang, F. Lopez-Ortiz, Magn. Reson. Chem.
1998, 36, 807.
Received July 7, 1999
[I99251]
´
F. Lopez-Ortiz, R. J. Carbajo, Current Org. Chem. 1998, 2, 97.
350
Eur. J. Inorg. Chem. 2000, 341Ϫ350