The synthesis, molecular and electronic structure of cyanovinylidene complexes

Article abstract of DOI:10.1016/j.ica.2011.10.067

Reaction of the readily available metal acetylide complexes Ru(CCC ₆H₄R-4)(PPh₃)₂Cp (R = OMe, Me, H, CN, CO₂Me), Ru(CCFc)(PPh₃)₂Cp and Fe(CCC ₆H₄R-4)(dppe)C

Full text of DOI:10.1016/j.ica.2011.10.067

Inorganica Chimica Acta 380 (2012) 358–371
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
The synthesis, molecular and electronic structure of cyanovinylidene complexes
⇑
Ella M. Long, Neil J. Brown, Wing Y. Man, Mark A. Fox, Dmitry S. Yufit, Judith A.K. Howard, Paul J. Low
Department of Chemistry, Durham University, South Rd., Durham DH1 3LE, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 4 November 2011
Reaction of the readily available metal acetylide complexes Ru(C„CC6H4R-4)(PPh3)2Cp (R = OMe, Me, H,
CN, CO2Me), Ru(C„CFc)(PPh3)2Cp and Fe(C„CC6H4R-4)(dppe)Cp (R = Me, H) with 1-cyano-4-dimethyl-
aminopyridinium tetrafluoroborate affords cyanovinylidene complexes [Ru{C@C(CN)C6H4R-4}(PPh3)2-
Cp]BF4, [Ru{C@C(CN)Fc}(PPh3)2Cp]BF4 and [Fe{C@C(CN)C6H4R-4}(dppe)Cp]BF4 in an experimentally sim-
ple fashion. These synthetic studies are augmented by refinements to the preparation of the key iron
reagents FeCl(dppe)Cp and Fe(C„CC6H4R-4)(dppe)Cp. Molecular structure determinations, electrochem-
ical measurements, representative IR spectroelectrochemical studies and DFT studies have been used to
provide insight into the electronic structure of the cyanovinylidene ligand, and demonstrate that despite
Young Investigator Award Special Issue
Keywords:
Vinylidene
Ruthenium
Iron
the presence of the cyano-substituted methylidene fragment, reduction takes place on the vinylidene C
carbon.
Spectroelectrochemistry
Molecular structure
a
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
cyanovinylidene ligands in the earliest reports of this class of li-
gand, cyanovinylidene chemistry has remained largely unexplored
[16], likely due to the less than convenient methods of preparation
known to date.
Within the vast array of hydrocarbyl ligands that have been sta-
bilized through coordination to metal centres, vinylidene C@CH2
and other substituted examples of this prototypical unsaturated
carbene occupy an important position, featuring prominantly from
a historical perspective in the development of the discipline of orga-
nometallic chemistry [1–3], to applications as key intermediates in
modern synthetic chemistry [4–6]. The first organometallic vinyli-
dene complex, Fe2(
featured the diphenylvinylidene moiety in a
formed from the photolysis of Fe(CO)5 with diphenylketene [7,8].
The preparation of both cis- and trans-[Fe2{
1-C@C(CN)2}(
CO)(CO)2Cp2], containing the
1-dicyanovinylidene ligand, fol-
The first preparations of dicyanovinylidene ligand complexes
were based on nucleophilic substitution reactions between
Cl2C@C(CN)2 and metal carbonyl anions. In the case of reactions
between [Fe(CO)Cp]– and Cl2C@C(CN)2, the bimetallic complexes
cis- and trans-[Fe2{l2
in low (<3%) yield (Scheme 1) [9,17], the cis isomer later being crys-
-g l-CO)(CO)2Cp2] were isolated
1-C@C(CN)2}(
l
-g
1-C@CPh2)(CO)8, was reported in 1966 and
1- bridging mode
l
-g
tallographically characterised [18]. Reaction of [Fe2(l-CO)(l-
CSMe)(CO)2Cp2]+ with the carbon nucleophile [CH(CN)2]– provides
l
-g
l
-
and alternative, and higher yielding (53%), route to mixtures of cis
l
-g
and trans-[Fe2{l2-g l-CO)(CO)2Cp2] (Scheme 1) [19].
1-C@C(CN)2}(
lowed in 1972 [9] while the first monometallic vinylidene com-
plexes, which also featured dicyanovinylidene ligands, were
reported in that same year [10]. In the decades that have followed,
the chemistry of vinylidene complexes, and other unsaturated carb-
enes such as allenylidene (:C@C@CH2) [2,11] and butatrienylidene
(:C@C@C@CH2) [12,13] was extensively explored. The practical
applications of the metal chemistry of vinylidenes and other unsat-
urated carbenes are well-established, and vividly illustrated by the
use of these species in the development of catalysts for olefin
metathesis and other organic transformations [14,15]. Somewhat
surprisingly, despite this significant interest in the general area of
vinylidene ligand chemistry, the proliferation of complexes featur-
ing different combinations of metal, supporting ligands and substit-
uents on the vinylidene moiety, and the presence of
The Group 6 metal carbonyl anions [M(CO)3Cp]– (M = Mo, W)
reacted smoothly with Cl2C@C(CN)2 to give 1-chloro-2,2-dicyano-
vinyl derivatives [M{C(Cl)@C(CN)2}(CO)3Cp] in moderate yield
[9,17]. Subsequent thermolysis of the vinyl compounds in the
presence of trivalent phosphorus ligands resulted in carbonyl
substitution and chloride migration to give a mixture of the cis-
and trans-dicyanovinylidene complexes MCl{C@C(CN)2}(PR3)2Cp
[20–22]; reactions of Mo{CCl@C(CN)2}(CO)3Cp with ButNC gave
only the carbonyl substitution product Mo{CCl@C(CN)2}(CO)2(CN-
But)Cp, the chlorovinyl ligand remaining unchanged (Scheme 2)
[23].
A series of anionic mono- and di-cyanovinylidene compounds
has also been obtained following chloride displacement from
M(„CCl)(CO)2Tp⁄ [Tp⁄ = hydridotris(3,5-dimethylpyrazol-1-yl)bo-
rate] by Na[CHX2] [X2 = (CN)2 (M = Mo, W); X2 = (CN)(CO2Et)
(M = Mo)] [24]. These anionic compounds can be represented by
two limiting resonance forms, A and B (Scheme 3), the significance
⇑
Corresponding author. Tel.: +44 (0)191 334 2114; fax: +44 (0)191 384 4737.
E-mail address: p.j.low@durham.ac.uk (P.J. Low).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.10.067

E.M. Long et al. / Inorganica Chimica Acta 380 (2012) 358–371
359
NC
Fe
CN
Fe
C
C
Cp
Cp
C
O
SMe
C
OC
CO
Cl
Cl
CN
CN
Na[Fe(CO)2Cp]
Na[CH(CN)2]
Cp
Cp
C
C
+
Fe
Fe
C
O
NC
Fe
CN
Fe
OC
CO
C
C
Cp
CO
Cp
C
O
OC
Scheme 1. The synthesis of cis- and trans-Fe2{l-C@C(CN)2}(l-CO)(CO)2Cp2 [17,19].
CN
CN
M
C C
R3P
Cl
PR3
+
NC
C
C
Cl
CN
CN
Na[M(CO)3Cp]
CN
PR3
C
C
M
Cl
OC
OC
Cl
CO
CN
CN
M
C
C
Cl
R3P
PR3
M = Mo, W
Scheme 2. The preparation of the terminal cyanovinylidene complexes MCl{C@C(CN)2}(PR3)2Cp (M = Mo, W) [9,17,20–22].
of form A being evidenced by the formation of simple adducts at Cb,
whilst protonation or oxidation afford cyclic products.
and several of the cyanovinylidene products, the structures of
two of the acetylide precursors, Ru(C„CC6H4OMe-4)(PPh3)2Cp
(3) and Ru(C„CC6H4CO2Me-4)(PPh3)2Cp (5), were also deter-
mined, and are briefly described here for completeness. DFT
based computational studies on representative cyanovinylidene
complexes have also been carried out, which together with the
structural, electrochemical and spectroscopic data provide insight
into the electronic structure of the cyanovinylidene ligand. Preli-
minary results in this area from our group have been communi-
cated previously [46].
In seeking to develop more expeditious routes to cyanovinylid-
ene complexes, it is worth noting that half-sandwich ruthenium
acetylide complexes such as Ru(C„CPh)(PPh3)2Cp (1) react with
a variety of electrophilic reagents [25,26] including H+ [27], alkyl
halides [28], trialkyloxonium salts [29], diazonium salts and car-
bon-based electrophiles [30], including the masked example
B(C6F5)3 [31] halogens (Cl2, Br2, I2) [32,33], and cyanogen bromide,
which acts as a halogen transfer agent [34], to form air-stable
vinylidene complexes [Ru{=C@C(E)Ph}(PPh3)2Cp]+. Indeed, whilst
many synthetic routes to vinylidene complexes are known, the
re-arrangement of a terminal alkyne or addition of an electrophile
to the Cb carbon of a metal acetylide are perhaps the most general
methods [1]. Nevertheless, recent reports of the rearrangement of
internal alkynes in the presence of group 8 metal centres [35],
2. Experimental
2.1. General conditions
including MCl(dppe)Cp in the presence of NaBArF (M = Fe, Ru;
4
All reactions were carried out in oven dried (110 °C) glassware
and in a dry high-purity nitrogen environment, using standard
Schlenk techniques. Solvents were dried on an Innovative Technol-
ogies SPS-400 system and degassed prior to use. The compounds
HC„CC6H4OMe-4 [47], HC„CC6H4CO2Me-4 [48], RuCl(PPh3)2Cp
[49], [Ru(C„CC6H5)(PPh3)2Cp] [50], [Ru(C„CC6H4Me-4)(PPh3)2Cp]
[40], [Ru(C„CC6H4CN-4)(PPh3)2Cp] [42], and [Ru(C„CFc)-
(PPh3)2Cp] [43], were prepared according the literature methods.
BrCN was freshly sublimed under nitrogen in a water bath at 60 °C
prior to use. All other reagents were used as received. Preparative
TLC was carried out on silica gel, GF254, 20 ꢀ 20 cm plates.
ArF = 3,5-(CF3)2C6H3) highlight the rich chemistry of vinylidene
complexes that still awaits exploration [36–39].
In this contribution we describe the cyanation of a range of
half-sandwich acetylide complexes Ru(C„CC6H4R-4)(PPh3)2Cp
(R = H (1) [29], Me (2) [40,41], OMe (3), CN (4) [42], CO2Me
(5)), Ru(C„CFc)(PPh3)2Cp (6) [Fc = Fe(g-C5H4)(g-C5H5)] [43,44]
and the iron complexes Fe(C„CC6H4R-4)(dppe)Cp (R = H (7)
[41,45], Me (8) [41] by 1-cyano-4-dimethylaminopyridinium tet-
rafluoroborate ([9]BF4) (Scheme 4). These synthetic studies are
augmented by molecular structure determinations, electrochemi-
cal measurements and representative IR spectroelectrochemical
studies. In addition to the structures of the key reagent [9]BF4
NMR spectra were obtained using Varian Mercury-200 (1H,
199.99 MHz; 13C, 49.98 MHz; 19F 188.18 MHz; 31P, 80.96 MHz),
Scheme 3. The formation of mono and dicyanovinylidenes from chloride displacement from M(„CCl)(CO)2Tp⁄ [24].

360
E.M. Long et al. / Inorganica Chimica Acta 380 (2012) 358–371
Scheme 4. A schematic representation of the synthesis of cyanovinylidene complexes from half-sandwich metal acetylide precursors and 1-cyano-4-dimethylaminopy-
ridinium [9]+.
Bruker and Varian Mercury-400 (1H, 399.97 MHz; 13C, 100.57 MHz;
19F, 376.36 MHz; 31P, 161.10 MHz), Varian Inova-500 (1H,
499.77 MHz, 13C, 125.67 MHz; 19F 470.25 MHz; 31P, 202.31 MHz)
or Varian VNMRS-700 (1H, 699.73 MHz, 13C, 175.95 MHz; 19F
658.41 MHz; 31P, 279.89 MHz) spectrometers in CDCl3, unless
otherwise stated, and referenced against solvent references (1H,
2.2.2. Ru(C„CC6H4CO2Me-4)(PPh3)2Cp 5
Yield 58%. Anal. Calc. C51H42O2P2Ru: C, 72.07; H, 4.98%. Found: C,
72.62; H, 4.95%. IR (CH2Cl2, cmꢁ1):
m
m
(C„C) 2067(s);
m(C@O) 1707(s);
(C–O) 1595(s). 1H NMR: d 3.88 (s, 3H, CH3), 4.34 (s, 5H, Cp), 7.07 (m,
14H, H4/8 and meta-CH of PPh3), 7.18 (m, 6H, para-CH of PPh3), 7.44
3
(m, 12H, ortho-CH of PPh3), 7.80 (d, JHH = 8 Hz, 2H, H5/7). 13C{1H}
7.26 ppm; 13C, 77.0 ppm) or external H3PO4
(
31P) and CFCl3
(
19F).
NMR: d 51.7 (s, CH3), 85.3 (s, Cp), 115.7 (s, C2), 123.8, 129.3, 130.1,
3
Mass spectra were obtained using a Waters Micromass LCT mass
spectrometer. Infrared spectra were recorded in solution cells fitted
with CaF2 windows on a Nicolet Avatar FT-IR spectrometer.
Electrochemical measurements (Autolab PG-STAT 30) were car-
ried out using CH2Cl2 solutions containing 0.1 M NBu4BF4 electro-
lyte in a standard three-electrode cell using Pt electrodes, and
potentials are reported on the SCE scale using an internal ferro-
cene/ferrocenium couple (Fc/Fc+ = 0.45 V) or decamethylferro-
cene/decamethylferrocenium couple (Fc⁄/Fc⁄+ = ꢁ0.07 V) as
reference. Spectroelectrochemical studies were conducted at room
temperature using a gas-tight cell fitted with CaF2 windows, Pt
gauze working electrode, Ag-wire pseudo reference and Pt counter
electrodes [51].
All ab initio computations were carried out with the GAUSSIAN 09
package [52]. The model geometries were optimised using the
B3LYP functional [53,54], with the 3–21G⁄ basis set [55,56]. Fre-
quency calculations were computed on these optimised geome-
tries and shown to have no imaginary frequencies. A scaling
factor of 0.95 was applied to the calculated vibrational frequencies
for comparison with experimental data [57,58]. The MO diagrams
and orbital contributions were generated with the aid of the GAUSS-
VIEW 5.0 [59] and GAUSSSUM [60] packages, respectively.
135.3 (4 ꢀ s, C3–C8), 127.3 (dd, JCP/5JCP = 5 Hz, meta-C of PPh3),
128.2 (s, para-C of pph3), 133.7 (dd, JCP/4JCP = 5 Hz, ortho-C of
2
PPh3), 138.6 (m, ipso-C of PPh3), 167.5 (s, C@O). C1 not observed.
31P{1H} NMR:
[Ru(PPh3)2Cp]+.
d
51.3 (s). ES(+)-MS (m/z): 851 [M+H]+, 691
2.3. General procedure: synthesis of Fe(C„CC6H4-4)(dppe)Cp (R = H,
7; Me, 8)
A solution of FeCl(dppe)Cp (200 mg, 0.36 mmol) in methanol
(15 ml) was treated with the appropriate alkyne HC„CC6H4R-4 (sev-
eral drops, excess) and the dark reaction solution heated at gentle re-
flux for ca. 1 h. During this time the solution colour changed to a deep,
translucent red characteristic of the vinylidene complex
[Fe{C@C(H)C6H4R-4}(dppe)Cp]Cl. The solution was allowed to cool
to room temperature before being treated with several drops of
DBU, causing the solution colour to change to bright orange. Cooling
the solution in an ice/water bath caused the precipitation of
Fe(C„CC6H4R-4)(dppe)Cp as a bright orange precipitate (R = H, 75%;
R = Me, 80%), identified by comparison with the literature data [41].
2.4. Synthesis of 1-cyano-4-dimethylaminopyridinium
tetrafluoroborate, [9]BF4
2.2. General procedure: synthesis of Ru(C„CC6H4R-4)(PPh3)2Cp
(R = OMe, 3; CO2Me, 5)
A Schlenk flask was charged with BrCN (1.09 g, 10.3 mmol) in
NCMe (45 ml) and 4-dimethylaminopyridine (1.00 g, 8.22 mmol)
was then added. The reaction mixture was allowed to stir for
5 min., before the addition of NaBF4 (1.08 g, 9.79 mmol). After stir-
ringfor a further 2.5 hours, the reaction mixture was filteredthrough
aCeliteplugandconcentratedto drynessto givea whitepowder. The
powder was dissolved in NCMe (15 ml), stirred for 3 min. and then
filtered again through a Celite plug. After concentrating to dryness,
the extraction process was repeated for a final time. Concentration
to dryness and recrystallisation from NCMe/EtOAc afforded nee-
dle-like, white crystals (1.23 g, 64%). Single crystals suitable for X-
ray diffraction were obtained by slow diffusion of ethyl acetate into
a concentrated NCMe solution of the salt. Anal. Calc. C8H10N3BF4: C,
40.89; H, 4.29; N, 17.88. Found: C, 40.89; H, 4.26; N, 17.88%. IR (nujol,
A
Schlenk flask was charged with RuCl(PPh3)2Cp (0.20 g,
0.28 mmol), the appropriate alkyne HC„CC6H4R-4 (ca. 0.35 mmol)
and NH4PF6 (0.09 g, 0.5 mmol) in methanol (15 mL) and refluxed
for 1 h (R = CO2Me) to 3 h (R = OMe). The resulting red solution
was cooled, treated with a few drops of DBU, and stirred for
10 min in an ice-water bath. The resulting yellow precipitate was
collected by filtration, washed with methanol (3 ꢀ 5 mL) and dried
in vacuo. Recrystallisation from acetone/hexane affords crystals
suitable for X-ray crystallography.
2.2.1. Ru(C„CC6H4OMe-4)(PPh3)2Cp 3
cmꢁ1): (CC) 1655(s). 1H NMR (CD3CN): d 3.34 (s,
m(C„N) 2264(m); m
Yield 57%. Anal. Calc. C50H42OP2Ru: C, 73.07; H, 5.15%. Found: C,
6H, CH3); 7.02, 8.09 (2 ꢀ d, J = 8 Hz, 2 ꢀ 2H, C5H4N). 13C{1H} NMR
(CD3CN): d 42.3 (s, CH3), 107.7 (s, CN), 108.5, 141.5, 158.1 (3 ꢀ s,
C5H4N). 19F NMR (CD3CN): d ꢁ152.3 (s, BF4–). ES(+)-MS (m/z): 148
[Me2NC5H4NCN]+, 123 [Me2NC5H4NH]+.
73.64; H, 5.27%. IR (CH2Cl2, cmꢁ1): (C„C) 2077(s). 1H NMR: d 3.77
m
(s, 3H, CH3), 4.30 (s, 5H, Cp), 6.70 (d, 3JHH = 8 Hz, 2H, H5/7), 7.07 (m,
14H, H4/8, meta-CH of PPh3), 7.16 (m, 6H, para-CH of PPh3), 7.48
(m, 12H, ortho-CH of PPh3). 13C{1H} NMR: d 55.2 (s, CH3), 85.0 (s,
2
Cp), 111.6 (t, JCP = 25 Hz, C1), 113.2 (s, C2), 113.2, 123.5, 131.5,
3
155.8 (4 ꢀ s, C3–C8), 127.1 (dd, JCP/5JCP = 4 Hz, meta-C of PPh3),
2.5. General procedure: synthesis of cyanovinylidene complexes
2
128.3 (s, para-C of pph3), 133.8 (dd, JCP/4JCP = 5 Hz, ortho-C of
PPh3), 138.9 (m, ipso-C of PPh3), 31P{1H} NMR: d 51.4 (s). ES(+)-
MS (m/z): 823 [M+H]+, 691 [Ru(PPh3)2Cp]+.
A Schlenk flask was charged with the appropriate metal acety-
lide complex (ca. 0.1 mmol) in CH2Cl2 (10 ml). A separate Schlenk

E.M. Long et al. / Inorganica Chimica Acta 380 (2012) 358–371
361
flask was charged with one-equivalent of [9]BF4 in NCMe (5 ml).
The [9]BF4 solution was transferred by syringe to the solution of
the acetylide and the reaction mixture stirred for 2 h. The resulting
cherry red solution was concentrated to dryness, and the residue
purified by preparative TLC (acetone/hexane, 6/4). The major or-
ange/red band was collected and isolated as a red solid by precip-
itation or crystallisation.
2.5.5. [Ru{C@C(CN)C6H4CO2Me-4}(PPh3)2Cp]BF4
[15]BF4 crystallised from acetone/hexane. Yield 45%. Anal. Calc.
C
52H42NO2P2RuBF4: C, 66.67; H, 4.61, N, 1.52. Found: C, 64.00; H,
4.40; N, 1.46%. IR (CH2Cl2, cmꢁ1):
m
(C„N) 2203(m);
m(C@O)
1721;
m
(C@C) 1607(m), 1578(s). 1H NMR: d 3.92 (s, 3H, CH3);
5.49 (s, 5H, Cp); 7.01 (m, 14H, H4/8 and ortho-CH of PPh3), 7.32
(m, 12H, meta-CH of PPh3), 7.45 (m, 6H, para-CH of PPh3), 7.89
3
(d, 2H, JHH ꢂ 8 Hz, H5/7). 13C NMR: d 52.3 (CH3); 96.9 (s, Cp);
109.4, 109.8 (2 ꢀ s, CN, C2); 126.2 129.4, 129.7, 130.3 (4 ꢀ s, C3–
2.5.1. [Ru{C@C(CN)Ph}(PPh3)Cp]BF4
3
5
C8); 128.9 (dd, JCP, JCP ꢂ 5 Hz, meta-C of PPh3); 131.7 (s, para-C
[11]BF4 crystallised from acetone/hexane. Yield 80%. Anal. Calc.
2
4
of PPh3); 132.2 (m, ipso-C of PPh3); 133.6 (dd, JCP, JCP ꢂ 5 Hz,
C
50H40NP2RuBF4: C, 66.38; H, 4.46; N, 1.55. Found: C, 66.48; H,
2
ortho-C of PPh3); 166.2 (s, C@O); 347.9 (t, JCP = 15 Hz, C1).
4.00; N, 1.36%. IR (CH2Cl2, cmꢁ1):
m(C„N) 2202(s); m(C@C)
31P{1H} NMR: d 38.1 (s). ES(+)-MS (m/z): 876 [Ru{C@C(CN)C6H4-
1582(s). 1H NMR: d 5.41 (s, 5H, Cp); 6.95 (d, 2H, JHH ꢂ 8 Hz, H4/
8); 7.01 (m, 12H, ortho-CH of PPh3); 7.22 (pseudo-t, 2H, 3JHH ꢂ 8 Hz,
H5/7); 7.30 (m, 14H, H6, meta-CH of PPh3); 7.43 (m, 6H, para-CH of
PPh3). 13C NMR: d 96.6 (s, Cp); 109.6, 109.7 (2 ꢀ s, CN, C2); 123.6,
3
CO2Me-4}(PPh3)2Cp]+.
2.5.6. [Ru{C@C(CN)Fc}(PPh3)2Cp]BF4
[16]BF4 crystallised from acetone/hexane. Yield 75%. Anal. Calc.
127.4, 128.7, 129.3 (4 ꢀ s, C3–C8); 128.9 (dd, 3JCP, JCP ꢂ 5 Hz, meta-
5
C
54H44NP2RuFeBF4: C, 64.05; H, 4.39, N, 1.38. Found: C, 63.67; H,
C of PPh3); 131.5 (s, para-C of pph3); 132.2 (m, ipso-C of PPh3);
4.38; N, 1.34%. IR (CH2Cl2, cmꢁ1):
m(C„N) 2220, 2205(w), m(C@C)
2
4
2
133.6 (dd, JCP, JCP ꢂ 5 Hz, ortho-C of PPh3); 348.5 (t, JCP = 16 Hz,
1593 (s). 1H NMR: d 3.68, 4.10 (4H, C5H4); 4.15 (s, 5H, CpFe);
4.71 (s, 5H, CpRu); 6.82 (m, 12H, ortho-CH of PPh3); 7.30 (m,
12H, meta-CH of PPh3); 7.41 (m, 6H, para-CH of PPh3). 13C NMR:
d 67.5, 69.3, 72.1 (3 ꢀ s, C5H4); 70.1 (FeCp); 95.9 (RuCp); 106.3,
C1). 31P{1H} NMR: d 38.8 (s). 19F{1H} NMR: d ꢁ153.0 (s, BF4ꢁ).
11B{1H} NMR:
d
ꢁ0.7 (s, BF4ꢁ). ES(+)-MS (m/z): 857,
[Ru{C@C(CN)Ph}(PPh3)2Cp + K]+; 818 [Ru{C@C(CN)Ph}(PPh3)2Cp]+.
3
5
109.5 (2 ꢀ s, CN, C2); 128.7 (dd, JCP, JCP ꢂ 5 Hz, meta-C of PPh3);
131.5 (s, para-C of PPh3); 132.3 (m, ipso-C of PPh3); 133.1 (dd,
2.5.2. [Ru{C@C(CN)C6H4Me-4}(PPh3)2Cp]BF4
[12]BF4 precipitated from CH2Cl2/Et2O as a red powder. Yield
90%. Anal. Calc. C51H42NP2RuBF4: C, 66.67; H, 4.61, N, 1.52. Found:
2JCP, JCP ꢂ 5 Hz, ortho-C of PPh3); 347.1 (t, JCP = 15 Hz, C1).
4
2
31P{1H} NMR (CDCl3):
d
39.8 (s). ES(+)-MS (m/z): 926
C, 67.01; H, 4.89; N, 1.46%. IR (acetone, cmꢁ1):
m
(C„N) 2200(s);
[Ru{C@C(CN)Fc}(PPh3)2Cp]+.
m
(C@C) 1580(s). 1H NMR: d 2.35 (s, 3H, CH3); 5.38 (s, 5H, Cp);
3
6.81, 7.09 (2 ꢀ d, 2 ꢀ 2H, JHH ꢂ 8 Hz, C6H4); 7.02 (m, 12H, ortho-
CH of PPh3); 7.31 (m, 12H, meta-CH of PPh3); 7.44 (m, 6H, para-
CH of PPh3). 13C NMR: d 21.1 (s, CH3); 96.6 (s, Cp), 109.5, 109.8
(2 ꢀ s, CN, C2); 120.1, 127.5, 130.1, 138.9 (4 ꢀ s, C–C8); 128.9
2.5.7. [Fe{C@C(CN)C6H5}(dppe)Cp]BF4
[17]BF4 crystallised from methanol. Yield 60%. Anal. Calc.
C
40H34NP2FeBF4: C, 65.52; H, 4.67; N, 1.91. Found: C, 65.01; H,
4.58; N, 1.89%. IR (CH2Cl2, cmꢁ1):
m(C„N) 2202(s); m (C@C)
3
5
(dd, JCP, JCP ꢂ 5 Hz, meta-C of PPh3); 131.5 (s, para-C of PPh3);
1584(s). 1H NMR ((CD3)2CO) d 3.30 (m, 2H, dppe); 3.43 (m, 2H,
dppe); 5.82 (s, 5H, Cp); 6.76, 7.04, 7.05 (3 ꢀ m, C6H5); 7.34 (m,
8H, dppe), 7.45 (m, 6H, dppe), 7.62 (m, 6H, dppe). 13C NMR
2
4
132.2 (m, ipso-C of PPh3); 133.5 (dd, JCP, JCP ꢂ 5 Hz, ortho-C of
PPh3); 349.3 (t, 2JCP = 16 Hz, C1). 31P{H} (CDCl3): d 38.9 (s). ES(+)MS
(m/z) 833 [Ru{C@C(CN)C6H4Me-4}(PPh3)2Cp]+.
4
((CD3)2CO): d 27.3 (m, CH2); 90.8 (s, Cp); 108.3 (t, JCP = 4 Hz, C2),
5
118.1 (s, CN); 123.5 (t, JCP = 2 Hz, C3); 126.6, 128.0, 128.8 (C4–
3
C8); 128.0, 128.3 (2 ꢀ dd, JCP
,
5JCP ꢂ 5 Hz, meta-C, C0 of dppe);
2.5.3. [Ru{C@C(CN)C6H4OMe-4}(PPh3)2Cp]BF4
2
130.5, 130.6 (2 ꢀ s, para-C, C0 of dppe); 130.6, 131.5 (2 ꢀ dd, JCP,
4JCP ꢂ 5 Hz, ortho-C, C0 of dppe); 132.6, 134.0 (2 ꢀ m, ipso-C, C0 of
dppe), 355.2 (t, JCP = 34 Hz, C1). 31P NMR ((CD3)2CO) d 92.1.
ES(+)-MS (m/z): 646, [Fe{C@C(CN)C6H5}(dppe)Cp]+.
[13]BF4 crystallised from acetone/Et2O. Yield 50%. Anal. Calc.
C
51H42NOP2RuBF4ꢃ(CH3)2CO: C, 65.33; H, 4.87, N, 1.41. Found: C,
64.49; H, 4.41; N, 1.47%. IR (CH2Cl2, cmꢁ1):
(C„N) 2201(m);
(C@C) 1595(m). 1H NMR: d 3.75 (s, 3H, CH3); 5.37 (s, 5H, Cp),
m
m
6.85 (br, 4H, C6H4), 7.00 (m, 12H, ortho-CH of PPh3); 7.30 (m,
12H, meta-CH of PPh3); 7.41 (m, 6H, para-CH of PPh3). 13C NMR:
d 55.5 (CH3); 96.5 (s, Cp); 108.7, 109.7 (2 ꢀ s, CN, C2); 114.2,
2.5.8. [Fe{C@C(CN)C6H4Me-4}(dppe)Cp]BF4
[18]BF4 crystallised from methanol. Yield 40%. Anal. Calc.
C
41H36NP2FeBF4: C, 65.89; H, 4.86; N, 1.87. Found: C, 64.96; H,
3
5
115.0, 129.4, 160.2 (C3 - C8), 128.9 (dd, JCP, JCP ꢂ 5 Hz, meta-C
of PPh3), 131.5 (s, para-C of PPh3), 132.4 (m, ipso-C of PPh3),
4.66; N, 2.10%. IR (CH2Cl2, cmꢁ1):
m(C„N) 2202(s); m(C@C)
1584(s). 1H NMR: d 2.21 (s, 3H, CH3); 3.03 (m, 2H, dppe); 3.10
2
4
2
133.6 (dd, JCP, JCP ꢂ 5 Hz, ortho-C of PPh3), 349.2 (t, JCP = 15 Hz,
3
(m, 2H, dppe); 5.36 (s, 5H, Cp); 6.49, 6.77 (2 ꢀ d, JHH = 8 Hz,
C1). 31P{1H} NMR (CDCl3):
d 39.1 (s). ES(+)-MS (m/z): 848
C6H4); 7.07, 7.20, 7.29, 7.38 (4 ꢀ m, 20H, dppe). 13C NMR: d 21.0
[Ru{C@C(CN)C6H4OMe-4}(PPh3)2Cp]+.
4
(s, CH3); 28.3 (m, CH2); 91.4 (s, Cp); 109.7 (t, JCP = 4 Hz, C2);
5
119.1 (CN); 120.1 (t, JCP = 2 Hz, C3), 125.4, 129.9, 137.9 (C4–C8);
3
2.5.4. [Ru{C@C(CN)C6H4CN-4}(PPh3)2Cp]BF4
129.3, 129.5 (2 ꢀ dd, JCP
,
5JCP ꢂ 5 Hz, meta-C, C0 of dppe), 131.7,
2
[14]BF4 crystallised from acetone/hexane. Yield 67%. Anal. Calc.
131.8 (2 ꢀ s, para-C, C0 of dppe), 131.3, 132.1 (2 ꢀ dd, JCP,
4JCP ꢂ 5 Hz, ortho-C, C0 of dppe), 132.5, 134.1 (2 ꢀ m, ipso-C, C0 of
dppe), 357.5 (t, JCP = 33 Hz, C1). 31P NMR: d 91.0. ES(+)-MS (m/z):
660, [Fe{C@C(CN)C6H4Me-4}(dppe)Cp]+.
C
51H39N2P2RuBF4ꢃ2.5(CH3)2CO: C, 64.47; H, 4.84, N, 2.64. Found: C,
64.94; H, 4.87; N, 2.67%. IR (CH2Cl2, cmꢁ1):
(C„N) 2230(m),
2202(m);
(C@C) 1603(m), 1571(s). 1H NMR: d 5.52 (s, 5H, Cp);
m
m
7.02 (m, 12H, ortho-CH of PPh3); 7.08, 7.50 (2 ꢀ d, 2 ꢀ 2H,
3JHH ꢂ 8 Hz, C6H4); 7.32 (m, 12H, meta-CH of PPh3); 7.46 (m, 6H,
para-CH of PPh3). 13C NMR: d 97.2 (s, Cp); 109.1, 109.5 (2 ꢀ s, CN,
C2); 111.3, 126.7, 129.8, 132.7 (4 ꢀ s, C3–C8); 118.3 (C6H4CN);
2.6. Synthesis of [Ru{C@C(CN)C6H4R-4}(PPh3)2Cp]PF6 (R = H, [11]PF6;
Me, [12]PF6)
3
5
129.0 (dd, JCP, JCP ꢂ 5 Hz, meta-C of PPh3); 131.6 (s, para-C of
To a solution of BrCN (30 mg, 0.31 mmol) in CH2Cl2 (2 ml), was
added 4-dimethylaminopyridine (80 mg, 0.31 mmol) and the solu-
tion was stirred for 5 min to give a solution containing [CAP]Br. To
2
4
pph3); 131.8 (m, ipso-C of PPh3); 133.5 (dd, JCP, JCP ꢂ 5 Hz,
2
ortho-C of PPh3), 346.5 (t, JCP = 14 Hz, C1). 31P{1H} NMR: d 37.7
(s). ES(+)-MS (m/z): 843 [Ru{C@C(CN)C6H4CN-4}(PPh3)2Cp]+.
this, a solution of Ru(C„CC6H4R-4)(PPh3)2Cp (0.12 mmol) in

362
E.M. Long et al. / Inorganica Chimica Acta 380 (2012) 358–371
CH2Cl2 (4 ml) was added via cannula and the solution stirred for
5 min. Then NH4PF6 (300 mg, 1.84 mmol) was added, the solution
was filtered and the solvent was removed in vacuo. Purification
the red residue by preparative TLC (acetone/hexane 6:4) gave a
major red band which was collected and crystallised (R = H, ace-
tone/hexane, 50%; R = Me, acetone/Et2O, 46%). Spectroscopic data
2.8.3. Crystal data for [9]BF4
C8H10N3 ꢀ BF4, M = 235.00, orthorhombic, space group Pbca,
a = 9.0261(4), b = 11.0956(5), c = 20.2847(10) Å, U = 2031.51
(16) Å3, F(000) = 960, Z = 8, Dcalc = 1.537 mgmꢁ3 = 0.146 mmꢁ1
, l .
Reflections (20483) were collected yielding 2218 unique data
(Rmerg = 0.0214). Final wR2(F2) = 0.1597 for all data (185 refined
parameters), conventional R1(F) = 0.0571 for 2002 reflections with
ꢁ
were consistent with those of the BF4 salt.
I P 2r, GOF = 1.096.
2.7. Synthesis of FeCl(dppe)Cp [61]
2.8.4. Crystal data for [11]PF6
A solution of dppe (5.06 g, 12.7 mmol) in CHCl3 (30 ml) was
transferred into a solution of FeCl2ꢃ4H2O (2.51 g, 12.6 mmol) in
acetone (120 ml). The resulting brown solution was heated at re-
flux for ca. 20 h. After this time the white precipitate that had
formed was collected by filtration, washed with three portions of
Et2O and dried to give FeCl2(dppe) (5.43 g, 82%). This paramag-
netic, high-spin tetrahedral complex was identified by atmospheric
solids analysis probe mass spectrometry (ASAP-MS, m/z 524.0,
[M]+) and used directly in the next step. A Schlenk flask was
charged with FeCl2(dppe) (2.78 g, 5.30 mmol), TlCp (1.33 g,
4.95 mmol) (CARE: Thallium salts are highly toxic) and benzene
(50 ml). The resulting suspension was allowed to stir overnight
to give a characteristically deep purple coloured solution, which
was filtered through Celite to remove precipitated TlCl (CARE!)
and unreacted FeCl2(dppe). The solvent was removed and the dark
coloured residue dissolved in the minimum volume of CH2Cl2.
Addition of an equal volume of Et2O resulted in the almost imme-
diate on set of crystallisation of FeCl(dppe)Cp. When crystallisation
was complete (several hours) the resulting crystalline mass was
collected by filtration, washed with Et2O, hexane and finally a sec-
ond portion of Et2O and dried to give the desired product (2.34 g,
85%).
C50H40NP2Ru ꢀ PF6 ꢀ (CH3)2CO, M = 1020.89, orthorhombic,
space group Pbca, a = 18.1453(5), b = 14.1423(4), c = 36.0979(9) Å,
U = 9263.3(4) Å3, F(000) = 4176, Z = 8, Dcalc = 1.464 mgmꢁ3
, l =
0.507 mmꢁ1. Reflections (81086) were collected yielding 12115
unique data (Rmerg = 0.0825). Final wR2(F2) = 0.0947 for all data
(586 refined parameters), conventional R1(F) = 0.0403 for 8359
reflections with I P 2r, GOF = 1.027.
2.8.5. Crystal data for [12]PF6
C51H42NP2Ru ꢀ PF6 ꢀ (CH3)2CO, M = 1034.91, monoclinic, space
group P21/n, a = 10.0492(2), b = 35.6830(7), c = 12.9509(3) Å,
b = 99.04(1)°, U = 4586.3(2) Å3, F(000) = 2120, Z = 4, Dcalc
=
1.499 mgmꢁ3 = 0.513 mmꢁ1. Reflections (65840) were collected
, l
yielding 14617 unique data (Rmerg = 0.0572). Final wR2(F2) = 0.0928
for all data (595 refined parameters), conventional R1(F) = 0.0337
for 11738 reflections with I P 2
r, GOF = 1.068.
2.8.6. Crystal data for [14]BF4
C51H39N2P2Ru ꢀ BF4 ꢀ 2.5(CH3)2CO, M = 1034.91, monoclinic,
space group C2/c, a = 37.8522(8), b = 14.9728(3), c = 36.7338(8) Å,
b = 99.48(1)°, U = 20534.6(7) Å3, F(000) = 8480, Z = 16, Dcalc
=
1.334 mgmꢁ3 = 0.424 mmꢁ1. Reflections (116691) were col-
, l
lected yielding 31305 unique data (Rmerg = 0.0584). Final
2.8. X-ray structure determinations
wR2(F2) = 0.2239 for all data (1035 refined parameters), conven-
tional R1(F) = 0.0666 for 20178 reflections with
GOF = 1.050.
I P 2r,
Single crystal X-ray data were collected at 120 K on the Rigaku
R-Axis Spider IP ([18]BF4), Bruker SMART 1 K ([11]PF6) and Bruker
SMART 6000 (all other reported compounds) diffractometers,
equipped with the Cryostream (Oxford Cryosystems) nitrogen
2.8.7. Crystal data for [18]BF4
C41H36NP2Fe ꢀ BF4, M = 747.31, orthorhombic, space group
cooling devices and using graphite monochromated Mo K
a radia-
Pbca, a = 15.7333(16), b = 16.6689(17), c = 26.302(3) Å, U =
tion (Mo K , k = 0.71073 Å). The structures were solved by direct
a
6897.8(12) Å3, F(000) = 3088, Z = 8, Dcalc = 1.439 mgmꢁ3
, l =
method and refined by full-matrix least squares on F2 for all data
using SHELXTL [62] and OLEX2 [63] software. All non-disordered
non-hydrogen atoms were refined with anisotropic displacement
parameters, H-atoms were placed in the calculated positions and
refined in riding mode in all structures except [9]BF4 and
[18]BF4, where they were refined isotropically.
0.584 mmꢁ1. Reflections (57139) were collected yielding 9160 un-
ique data (Rmerg = 0.0777). Final wR2(F2) = 0.1105 for all data (595
refined parameters), conventional R1(F) = 0.0488 for 7354 reflec-
tions with I P 2r, GOF = 1.090.
3. Results and discussion
2.8.1. Crystal data for 3
ꢀ
C50H42OP2Ru, M = 821.85, triclinic, space group P1,
3.1. Synthesis and structures of half-sandwich acetylide precursors
a = 15.0237(3) Å, b = 17.1759(3) Å, c = 17.2624(3) Å,
b = 96.20(1),
= 98.22(1)° U = 3877.8(1) Å3, F(000) = 1696, Z = 4,
Dcalc = 1.408 mgmꢁ3 = 0.525 mmꢁ1. 47012 reflections were col-
a = 116.31(1),
c
Treatment of RuCl(PPh3)2Cp with the appropriate alkyne
HC„CC6H4R-4 and NH4PF6 in methanol gave the vinylidene com-
plexes [Ru{C@C(H)C6H4R-4}(PPh3)2Cp]PF6 which were deproto-
nated in situ to give the desired acetylide complexes
Ru(C„CC6H4R-4)(PPh3)2Cp (1–5) in the well-established manner
[29]. The ferrocenyl substituted derivative Ru(C„CFc)(PPh3)2Cp
(6) [43,44] and the iron complexes 7 and 8 were prepared similarly
from FeCl(dppe)Cp and the appropriate alkyne, and characterised
by comparison with literature data [41,45]. In the case of the iron
complexes, the Fe-Cl bond was sufficiently ionised in methanol to
promote smooth formation of the intermediate vinylidene without
the need for a supporting salt to act as halide scavenging agent
[64,65] or the use of the acetonitrile complex [Fe(NCMe)(dp-
pe)Cp]PF6 [45]. This simple procedure also avoids the use of ligand
exchange steps either in the preparation of FeI(dppe)Cp as a
,
l
lected yielding 18680 unique data (Rmerg = 0.0397). Final
wR2(F2) = 0.0843 for all data (973 refined parameters), conven-
tional R1(F) = 0.0336 for 14573 reflections with
I P 2r,
GOF = 1.030.
2.8.2. Crystal data for 5
C51H42O2P2Ru, M = 849.86, monoclinic, space group P21,
a = 8.9199(3), b = 14.7736(4), c = 15.1537(4) Å, b = 90.13(1)°, U =
1996.9(1) Å3, F(000) = 876, Z = 2, Dcalc = 1.413 mgmꢁ3
,
l =
0.515 mmꢁ1. Reflections (19700) were collected yielding 9572 un-
ique data (Rmerg = 0.0372). Final wR2(F2) = 0.1103 for all data (505
refined parameters), conventional R1(F) = 0.0451 for 8437 reflec-
tions with I P 2r, GOF = 1.077.

E.M. Long et al. / Inorganica Chimica Acta 380 (2012) 358–371
363
Scheme 5. The preparation of FeCl(dppe)Cp and related acetylide complexes.
precursor [66–68], or in the preparation of phosphine-ligand acet-
ylide complexes from Fe(C„CR)(CO)2Cp [69–71]. The key precur-
sor FeCl(dppe)Cp is in turn very easily accessed from reaction of
hydrated ferrous chloride with dppe to give FeCl2(dppe), followed
by treatment with TlCp (Scheme 5) [61]. It was most convenient to
carry out the last step with a small excess of FeCl2(dppe), to pre-
vent the formation of ferrocene and liberation of dppe, the latter
proving to be rather difficult to separate from the half-sandwich
product. The excess insoluble FeCl2(dppe) is simply removed from
the reaction mixture by filtration with the precipitated TlCp, and
the crude reaction mixture crystallised from CH2Cl2/Et2O to afford
well-shaped blocks of FeCl(dppe)Cp, thereby avoiding chromato-
graphic purification [61].
3.2. Molecular structures of acetylide complexes
The molecular structures of Ru(C„CC6H4OMe-4)(PPh3)2Cp (3)
(Fig. 1) and Ru(C„CC6H4CO2Me-4)(PPh3)2Cp (5) (Fig. 2) were
determined and offer the same general trends as observed in other
acetylide complexes based on the Ru(PPh3)2Cp moiety (Table 1)
[28,42,72–80], and together permit the limited influence of the
electron donating or withdrawing substitutents on the structure
to be demonstrated. This is of some interest as the structures of
ruthenium acetylide complexes Ru(C„CC6H4R)(L)2Cp0 featuring
electron-donating R groups are surprisingly rare in comparison
with the large number of examples of systems featuring more elec-
tron-withdrawing substituents [81]. In each case (3, 5) the metal
centre is in a pseudo-octahedral geometry, with the P(1)–Ru–P(2)
bond angle ca. 100° and the P(1,2)–Ru–C(1) angles ca. 90°. The
Ru–C(1) „C(2)–C(3) fragments in 3 and 5 are essentially linear,
and the Ru–C(1), C(1)–C(2), C(2)–C(3) bond lengths are indistin-
guishable between the two complexes. The relatively precisely
determined Ru–P(1,2) bond lengths provide the most informative
Fig. 2. Molecular structure of 5 showing the atom labelling scheme.
trends, and whilst they also fall in a small range, the Ru–P bonds
in 3 are at the shorter end of the range spanned by the structures
established to date, reflecting the electron-donating character of
the OMe substituent and the subsequently increased metal-phos-
phine back-bonding contribution (Table 1).
3.3. Selection, synthesis and structure of 1-cyano-4-
dimethylaminopyridinium tetrafluoroborate ([9]BF4)
It has been established earlier that cyanogen bromide, BrCN, is a
useful reagent for the formation of mono and dibromovinylidenes,
but not cyanated products, from metal acetylides [34], and there-
fore attention was turned to alternative cyanating reagents. Tosyl
cyanide (p-tolylsulfonyl cyanide, TsCN) has been used as a cyanat-
ing reagent in reactions with organometallic compounds [82],
including phenylmagnesium bromide [83] and benzylzinc halides
[84], and acts as a heterodienophile in Diels-Alder reactions
[85,86]. However, reactions of 1 with TsCN in the presence of
NaPF6 were largely unsuccessful, with the desired monocyanoviny-
lidene complex [Ru{C@C(Ph)CN}(PPh3)2Cp]PF6 being obtained in
only ca. 3% isolated yield.
Phenyl cyanate (cyanic acid phenyl ether, PhOCN) [87] has been
used as a source of the cyano moiety in the preparation of organic
[88] and organometallic [89–91] cyanoacetylene derivatives from
acetylide anions. The reaction of 1 with PhOCN was explored under
a variety of conditions. Best results were obtained from room tem-
perature reactions of 1 with 2.5 molar equivalents of PhOCN, con-
ducted in CH2Cl2. After anion methathesis, purification of the
reaction mixture by preparative TLC and crystallisation of the ma-
jor band, [Ru{C@C(Ph)CN}(PPh3)2Cp]PF6 was isolated in 23% yield.
By far the most successful, widely applicable, and straightfor-
ward preparation of cyanovinylidenes was found to involve 1-cya-
no-4-dimethylaminopyridinium tetrafluoroborate ([9]BF4) as the
cyanating agent. Salts of [9]+ have been used in many contexts as
cyanating reagents, including in the cyanation of N-substituted
imidazoles [92], and in the cyanation of cysteine residues in
Fig. 1. Molecular structure of 3 showing the atom labelling scheme.

364
E.M. Long et al. / Inorganica Chimica Acta 380 (2012) 358–371
Table 1
Selected bond lengths (Å) and angles for complexes 3, 5, [11]PF6, [11]BF4, [12]PF6, [14]BF4, [18]BF4 and related species.
M–P(1)
M–P(2)
M–C(1)
C(1)–C(2)
C(2)–CAr
P(1)–M–P(2) M–C(1)–C(2) C(1)–C(2)– C(1)–C(2)–CN
CAr
Ru(C„CPh)(PPh3)2Cp [28,72]
2.303/
2.229(3)
2.285/
2.228(3)
2.016(3)/
2.017(5)
1.215(4)/
1.214(7)
1.212(3)
1.219(3)
1.199(6)
1.344(3)
1.338(5)
1.456(4)/
1.462(8)
1.442(3)
1.432(3)
1.441(5)
1.495(3)
1.494(5)
1.494(2)
1.487(4)
1.477(16)
178.0(2)/
177.7(4)
176.38(18) 172.3(2)
175.4(2)
175.6(4)
173.1(2)
173.3(3)
174.13(14) 120.65(15) 120.24(15)
175.0(3)
172.8(11)
171.49(11) 122.60(12) 117.06(12)
174.93(15) 174.84(17)
173.76(18) 123.4(2)
174.7(2)
179.1(5)
173.76(18) 123.4(2)
171.9(3)/
170.6(5)
Ru(C„CC6H4OMe)(PPh3)2Cp
2.2922(6) 2.2902(5) 2.019(2)
2.3134(5) 2.3031(5) 2.011(2)
2.3090(10) 2.2842(10) 2.015(4)
2.3797(7) 2.3547(6) 1.812(2)
2.3756(9) 2.3452(9) 1.811(4)
2.3497(4) 2.3756(4) 1.8186(16) 1.341(2)
2.3706(10) 2.3613(10) 1.808(4)
2.341(3) 2.363(3) 1.863(10)
99.18(2)
Ru(C„CC6H4CN)(PPh3)2Cp [42]
Ru(C„CC6H4CO2Me)(PPh3)2Cp
[Ru{C@C(CN)Ph}(PPh3)2Cp]PF6
[Ru{C@C(CN)Ph}(PPh3)2Cp]BF4
[Ru{C@C(CN)C6H4Me}(PPh3)2Cp]PF6
[Ru{C@C(CN)C6H4CN}(PPh3)2Cp]BF4
[Ru{C@C(Me)Ph}(PPh3)2Cp]I [28]
175.1(2)
172.5(5)
119.4(2)
120.0(3)
99.81(3)
101.12(2)
100.55(3)
100.60(2)
102.04(4)
99.6(1)
119.3(2)
119.3(3)
1.341(5)
1.293(15)
119.5(3)
117.0(11)
120.9(3)
125.1(12)a
[Ru{C„C(CN)C6H4Me}(dppe)Cp⁄]BF4 [46] 2.3260(3) 2.3140(3) 1.8134(13) 1.3343(17) 1.4904(18) 81.62(1)
Fe(C„CC6H4Me)(dppe)Cp [41]
2.1687(6) 2.1714(7) 1.9068(17) 1.220(2)
2.2420(6) 2.1991(6) 1.722(2)
1.439(2)
1.491(3)
1.486(5)
1.923(6)c
1.491(3)
85.95(2)
84.70(2)
85.46(3)
84.30(5)
84.70(2)
[Fe{C„C(CN)C6H4Me}(dppe)Cp]BF4
1.347(3)
1.310(5)
1.192(8)
1.347(3)
119.6(2)
118.8(3)b
125.3(5)
119.6(2)
[Fe{C@C(Ph)C6H4OMe}(dppe)Cp]BArF [36] 2.1927(8) 2.2112(9) 1.759(4)
124.4(2)
122.9(5)
4
[Fe(C@CBr2)(dppe)Cp]BF4 [34]
[Fe{C@C(CN)C6H4Me}(dppe)Cp]BF4
2.2229(14) 2.2164(14) 1.823(6)
2.2420(6) 2.1991(6) 1.722(2)
a
b
c
C(1)–C(2)–Me.
C(1)–C(2)–CArOMe
C(2)–Br.
.
proteins to inhibit the activity of cysteine active enzymes [93], and
aid in peptide sequencing [94]. Solutions of the hygroscopic bro-
mide salt [9]Br are readily prepared from 4-dimethylaminopyri-
dine and cyanogen bromide [46], whilst the air-stable, crystalline
-
BF4 salt, which is also available commercially, has been obtained
by anion metathesis of [9]Br with AgBF4 [93]. We found it to be
expeditious to employ a small excess of cyanogen bromide in the
preparation of [9]+ salts to ensure complete reaction of the dimeth-
ylaminopyridine which can be troublesome to remove from the
products by crystallisation. In contrast, the excess volatile cyano-
gen bromide is simply removed during drying of the crude product
in vacuo. As an alternative to anion metathesis with expensive sil-
ver salts, treatment of NCMe solutions of [9]Br obtained from BrCN
and dimethylaminopyridine with NaBF4, followed by filtration (to
remove NaBr), and recrystallisation (NCMe/EtOAc) can also be used
to give crystalline [9]BF4 in good (64%) yield.
3.4. Molecular structure of 1-cyano-4-dimethylaminopyridinium
tetrafluoroborate ([9]BF4)
A plot of the 1-cyano-4-dimethylaminopyridinium cation [9]+ is
shown in Fig. 3. The contraction of the N(1)–C(1) and N(3)–C(4)
bonds and distortions of the pyridinium ring from an idealised aro-
matic towards quinoidal geometry are similar to those found in 4-
dimethylaminopyridine, 10 (Fig. 4) [95] and related pyridinium
salts [96–101], with due allowance for the different temperatures
used in the data collection. The cation adopts a near planar
conformation, with the dimethylamino group lying just out of
the aromatic plane [dihedral angles C(5)–C(4)–N(3)–C(8), 6.5(2)°;
C(3)–C(4)–N(3)–C(7) 6.5(2)°]. The N(1)–C(1), C(1)–N(2), and
N(3)–C(4) distances clearly distinguish the formal single, triple
and single bond character of these bonds, respectively, albeit with
single bonds contracted as a result of conjugation.
Fig. 3. A plot of the ion pair in 1-cyano-4-dimethylaminopyridinium tetrafluoro-
borate ([9]BF4). Selected bond lengths (Å) and angles (⁄): N(1)–C(1) 1.364(3); N(1)–
C(2, 6) 1.377(3), 1.382(3); C(2)–C(3) 1.348(3); C(3)–C(4) 1.439(3); C(4)–C(5)
1.432(3); C(5)–C(6) 1.342(3); C(1)–N(2) 1.142(3); C(4)–N(3) 1.321(3); N(1)–C(1)–
N(2) 177.6(3); C(4)–N(3)–C(7, 8) 121.8(2), 122.4(2); C(7)–N(3)–C(8) 115.1(2).
3.5. Synthesis and structure of cyanovinylidene complexes
Both donor or acceptor substituted aryl acetylide complexes
Ru(C„CC6H4R-4)(dppe)Cp (R = OMe (3), Me (2), H (1), CN (4),
CO2Me (5)) and the heterometallic complex Ru(C„CFc)(PPh3)2Cp
(6, Fc = ferrocenyl) were readily cyanated by [9]BF4 in a mixed
CH2Cl2/NCMe solvent system (Scheme 4), to give cyanovinylidene
complexes [11–16]BF4 in good to excellent yield after purification
Fig. 4. A sketch of 4-dimethylaminopyridine, 10, showing selected, crystallograph-
ically determined bond lengths (Å) [95].
by preparative TLC and crystallisation or precipitation. The closely
related iron complexes [Fe{C@C(CN)C6H4R-4}(dppe)Cp]BF4 (R = H

E.M. Long et al. / Inorganica Chimica Acta 380 (2012) 358–371
365
([17]BF4), Me ([18]BF4) were prepared in an entirely analogous
fashion from Fe(C„CC6H4R-4)(dppe)Cp (7, 8) and [9]BF4, and iso-
lated in ca. 50% yield. For both metal systems, reactions conducted
in CH2Cl2 also yielded the cyanovinylidene products, but in relaꢁ-
tively poor isolated yield (ca. 30%). In some cases where the BF4
analogues proved to be troublesome to crystallise, the use of solu-
tions of [9]Br prepared in situ followed by anion metathesis gave
ꢁ
convenient access to PF6 salts.
Spectroscopic data for the cyanovinylidene complexes were
consistent with the proposed structures. Key features include the
observation of singlet resonances in the 31P NMR spectra near dP
38 (Ru) or 90 (Fe) ppm, the high frequency/deshielded C reso-
a
nances in the 13C NMR spectra near dC 350 ppm characteristic of
vinylidene complexes [1], with coupling to phosphorus in evi-
dence, and the observation of both m(C„N) and m(C@C) bands in
the IR spectra near 2200 and 1580 cmꢁ1, respectively. These spec-
troscopic features were largely insensitive to the nature of the
vinylidene substituent, indicating little electronic interaction be-
tween the substituent and the metal centre.
3.6. Molecular structures of cyanovinylidene complexes
The molecular structures of the ruthenium cyanovinylidene
complexes [Ru{C@C(CN)Ph}(PPh3)2Cp]X ([11]X, X = BF4ꢁ, PF6ꢁ),
[Ru{C@C(CN)C6H4Me-4}(PPh3)2Cp]PF6 ([12]PF6), which was pre-
pared by reaction of 2 with [9]Br and subsequent anion metathesis
Fig. 6. The structure of the cation [Ru{C@C(CN)C6H4Me-4}(PPh3)2Cp]+ [12]+ show-
ing the atom labelling scheme.
ꢁ
with NH4PF6 [46], as the BF4 salt proved resistant to crystallisa-
tion,
[Ru{C@C(CN)C6H4CN-4}(PPh3)2Cp]BF4
([14]BF4),
and
[Fe{C@C(CN)C6H4Me-4}(dppe)Cp]BF4 ([18]BF4) were determined
by single crystal X-ray diffraction. Illustrative plots of selected
cations are shown in Figs. 5–8, and the structures may be conve-
niently compared with those found in [Ru{C@C(Me)Ph}-
(PPh3)2Cp]I ([19]I) [28], the cyanovinylidene [Ru{C@C(CN)C6H4-
Fig. 7. The structure of the cation [Ru{C@C(CN)C6H4CN-4}(PPh3)2Cp]+ [14]+ show-
ing the atom labelling scheme.
Me}(dppe)Cp⁄]BF4
([20]BF4)
[46],
[Fe(C@C(Ph)C6H4OMe-
4}(dppe)Cp][BArF4] ([21]BArF4) [36] and the sterically unencum-
bered example [Fe(C@CBr2)(dppe)Cp]BF4 ([22]BF4) [34] (Table 1).
The metal centres adopt the usual piano-stool geometry with P–
M–P angles in the case of the Ru(PPh3)2Cp based complexes being
near 100° to relieve steric congestion associated with the PPh3 li-
gands, but constrained to less than 90° by the ethylene bridge of
the dppe ligand in the Fe(dppe)Cp and Ru(dppe)Cp⁄ complexes
contained in Table 1. The relatively short M–C(1) and long M–P
Fig. 5. The structure of the cation [Ru{C@C(CN)Ph}(PPh3)2Cp]+ [11]+ showing the
atom labelling scheme.

366
E.M. Long et al. / Inorganica Chimica Acta 380 (2012) 358–371
substituents [40,81]. However, the different combinations of sol-
vent, supporting electrolyte, temperature and reference electrode
employed in collecting the range of available data can make direct
comparisons of the results collated from many different research
groups difficult, especially in the absence of a reported potential
for an internal reference compound [105]. Table 2 summarises
the redox behaviour of a number of acetylide complexes pertinent
to the present study in CH2Cl2/0.1 M NBu4BF4, reported on the SCE
reference scale through correction against an internal ferrocene or
decamethylferrocene couple (Fc/Fc+ = 0.45 V; Fc⁄/Fc⁄+ = ꢁ0.07 V).
The cyclic voltammogram (m = 100 mV / s) of the parent com-
pound Ru(C„CPh)(PPh3)2Cp (1) exhibits an oxidation wave at
+0.54 V, which is only partially chemically reversible, even at
ꢁ40 °C [40], as a result of the redox non-innocent nature of the
phenylethynyl ligand and rapid dimerisation of the largely ligand-
based radical cation in solution [106]. A completely irreversible
wave is also observed at higher potentials (+1.34 V). On the time-
scale of the CV experiment, the electrochemically generated tolyl
derivative [Ru(C„CC6H4Me-4)(PPh3)2Cp]+ ([2]+) is more stable,
and the first electrochemical oxidation becomes chemically revers-
ible. The electrochemical behaviour of other complexes
[Ru(C„CC6H4R-4)(PPh3)2Cp] is similar, with E1/2 values following
predictable trends so that electron donating groups (R = OMe (3))
result in a cathodic shift in both redox processes, while electron
withdrawing groups (R = CN (4), CO2Me (5)) cause anodic shifts.
In each case, the chemical reversibility improved at lower temper-
atures, although the slower diffusion and increased solution resis-
tance at low temperatures resulted in more sluggish electron
Fig. 8. The structure of the cation [Fe{C@C(CN)C6H4Me-4}(dppe)Cp]+ [18]+ showing
the atom labelling scheme.
and C(1)–C(2) distances in the cyanovinylidene complexes com-
pared with examples of the same M(PP)Cp0 metal fragment featur-
ing acetylide and vinylidene ligands are consistent with the
cumulated nature of the cyanocarbon ligand, and a degree of en-
hanced electron-withdrawing character brought about by the pres-
ence of the cyano moiety.
There is only a very small energetic preference for vinylidene li-
gands coordinated to half-sandwich group 8 metals to adopt a ‘hor-
izontal’ orientation, in which the plane of the vinylidene ligand lies
perpendicular to the plane containing the centroid of the Cp ring
transfer processes, and larger
DEp values. The electrochemical re-
sponse of the ferrocene derivative Ru(C„CFc)(PPh3)2Cp (6) is char-
acterised by a ferrocene based oxidation at +0.12 V, with the
resulting ferrocenium cation cathodically shifting the metal–ethy-
nyl based oxidation to +0.81 V [43]. The iron complexes
Fe(C„CC6H4R-4)(dppe)Cp (R = H (7), Me (8)) exhibit a more chem-
ically reversible one-electron oxidation wave at modest electrode
potentials in the cyclic voltammograms. These oxidation processes
are some 200 mV less thermodynamically favourable than well-
known and extensively investigated Cp⁄ analogues [107]. For both
supporting metal-ligand fragments (Ru(PPh3)2Cp and Fe(dppe)Cp),
the replacement of the arylethynyl (C„CC6H4R-4) ligand by the
cyanoacetylide (C„CC„N) ligand results in fully reversible redox
system [89,91], with the most anodic oxidation potentials in their
respective series. The shift of the cyanoacetylide oxidation to more
positive potentials relative to the aryl ethynyl systems is smaller for
the iron family (Fe(C„CC„N)(dppe)Cp ca. +250 mV relative to
Fe(C„CC6H4Me-4)(dppe)Cp) than ruthenium (Ru(C„CC„N)-
(PPh3)2Cp ca. +530 mV relative to Ru(C„CC6H4Me-4)(PPh3)2Cp),
which reflects the greater metallic character in the redox active
orbital of the iron systems.
The electrochemical responses of the mono- and di-cyanoviny-
lidene complexes [Ru{C@C(CN)C6H4Me-4}(dppe)Cp⁄]BF4 and
[Ru{C@C(CN)2}(dppe)Cp⁄]BF4 are each characterised by an irre-
versible oxidation and a quasi-reversible reduction in CH2Cl2/
0.1 M NBu4BF4 (Table 2) [46]. Each of the ruthenium cyanovinylid-
ene complexes [11]BF4, [12]BF4, [13]BF4, [14]BF4 and [15]BF4 be-
haved similarly, and exhibited an irreversible oxidation, some
1.1–1.3 V more positive than the analogous acetylide and likely
to have more metallic character, and a chemically irreversible
reduction in CH2Cl2/0.1 M NBu4BF4 (Table 2). The reversibility of
the process did not improve at lower temperatures, and the reverse
waves became even less distinct, probably indicating slow back
electron transfer kinetics. The peak potential of the reduction pro-
cess displayed a systematic shift in line with the electronic proper-
ties of the vinylidene substituent, and whilst the oxidation
potentials spanned ca. 140 mV, no systematic trends were
apparent. In the case of the ferrocenyl complex [16]BF4 an
[denoted Cp(0)], the metal centre and the vinylidene C [102],
a
and in solution the barrier to ligand rotation was determined by
NMR methods to be of the order of 9 kcalmolꢁ1 [103,104]. Never-
theless,
crystallographically
determined
structures
of
M(C = CbR2)(PP)Cp0 (M = Fe, Ru, Os) usually exhibit ligand orienta-
a
tions that conform to the general ‘horizontal’ orientation. For
example, the Cp(0)–MꢃꢃꢃCb–R angles in [19]+, [20]+ and [21]+ are
116.6/ꢁ68.2, 105.7/ꢁ63.7 and 70.1/ꢁ103.8°, respectively, whilst
in the least sterically congested example [22]+ the Cp(0)–MꢃꢃꢃCb–
Br angle falls closer the idealised horizontal geometry (93.72°/
ꢁ88.98°). The Cp(0)–MꢃꢃꢃC(2)–CN angles in the cyanovinylidene
complexes are 123.23/125.03 ([11]PF6/[11]BF4), 102.66 ([12]PF6),
110.87 and 120.26 (two independent molecules [14]BF4) and
ꢁ117.96 ([18]BF4). The plane of the vinylidene is tilted from hori-
zontal in such a way that the cyano substituent is situated away
from the Cp ligand and falls into a pocket formed by the phenyl
rings of the phosphine ligand(s), whilst the aromatic substituent
of the vinylidene ligand is oriented in such a way as to reduce
the steric congestion.
3.7. Electrochemistry
The electrochemical response of ruthenium(II) acetylide com-
plexes of general form Ru(C„CAr)(PP)Cp⁄0 (Ar = aromatic substitu-
ent, PP = phosphine donors, Cp0 = Cp, Cp ) is characterised by an
oxidation event that has considerable ethynyl ligand character,
and as such the potentials of these redox processes, and the chem-
ical stability of the resulting radical cations, is sensitive to the nat-
ure of the aromatic group and the electronic properties of

E.M. Long et al. / Inorganica Chimica Acta 380 (2012) 358–371
367
Table 2
The electrochemical response of aryl acetylide, cyanoacetylide and cyanovinylidene complexes.a
d
e
f
g
h
i
Fc/Fc+b
Fc⁄/Fc⁄+c
Eo
ipa:ipc
D
Ep
Er(1/2)
ipc:ipa
D
Erp
(1/2)
[Ru(C„CC6H5)(PPh3)2Cp] (–40 °C) 1 [40]
[Ru(C„CC6H4Me-4)(PPh3)2Cp] 2 [40]
[Ru(C„CC6H4OMe-4)(PPh3)2Cp] 3
[Ru(C„CC6H4OMe-4)(PPh3)2Cp] 3 (–40 °C)
[Ru(C„CC6H4CN-4)(PPh3)2Cp] 4
[Ru(C„CC6H4CN-4)(PPh3)2Cp] 4 (–40 °C)
[Ru(C„CC6H4CO2Me-4)(PPh3)2Cp] 5
[Ru(C„CC6H4CO2Me-4)(PPh3)2Cp] 5 (–40 °C)
[Ru(C„CFc)(PPh3)2Cp] 6 [43]
[Ru(C„CCN)(PPh3)2Cp] [89]
[Fe(C„CC6H5)(dppe)Cp] 7
[Fe(C„CC6H4Me-4)(dppe)Cp] 8
[Fe(C„CCN)(dppe)Cp] [91]
[Ru{C@C(CN)C6H5}(PPh3)2Cp]BF4 [11]BF4
[Ru{C@C(CN)C6H4Me-4}(PPh3)2Cp]BF4 [12]BF4
[Ru{C@C(CN)C6H4OMe-4}(PPh3)2Cp]BF4 [13]BF4
[Ru{C@C(CN)C6H4CN-4}(PPh3)2Cp]BF4 [14]BF4
[Ru{C@C(CN)C6H4CO2Me-4}(PPh3)2Cp]BF4 [15]BF4
[Ru{C@C(CN)Fc}(PPh3)2Cp]BF4 [16]BF4
[Fe{C@C(CN)C6H5}(dppe)Cp]BF4 [17]BF4
[Fe{C@C(CN)C6H4Me-4}(dppe)Cp]BF4 [18]BF4
ꢁ0.07
ꢁ0.07
ꢁ0.07
ꢁ0.07
ꢁ0.07
ꢁ0.07
ꢁ0.07
ꢁ0.07
0.54
0.48
0.38
0.41
0.64
0.64
1.7
1.0
1.3
1.0
2.2
1.0
115
120
100
240
120
153
0.61 (pa,j irrk)
0.57
0.12, 0.81
0.91
0.06
0.04
0.29
1.86 (pa, irr)
1.86 (pa, irr)
1.77 (pa, irr)
1.72 (pa, irr)
1.86 (pa, irr)
0.58
1.0
1.0, 1.0
1.0
1.0
1.0
83
80, 90
0.45
0.45
0.45
0.45
0.45
0.45
0.45
0.45
0.45
0.45
145
115
1.0
ꢁ0.93 (pa, irr)
ꢁ0.93 (pa, irr)
ꢁ1.11 (pa, irr)
ꢁ0.81 (pa, irr)
ꢁ0.86 (pa, irr)
ꢁ1.06 (pa, irr)
ꢁ0.95
ꢁ0.07
1.0
3.5
1.2
90
0.45
0.45
1.76 (pa, irr)
1.0
1.0
105
115
1.56 (qrl)
ꢁ0.95
a
b
c
d
e
f
For general conditions, see the Section 2.1.
Fc/Fc+ = half-wave potential of an internal ferrocene standard (V).
Fc⁄/Fc⁄+ = half-wave potential of an internal decamethylferrocene standard (V).
Eo1=2 = half-wave potential of an oxidation wave (V).
ipa:ipc = ratio of anodic to cathodic peak current for an oxidation.
D
Ep = separation of anodic and cathodic peaks (V).
Erð1=2Þ = half-wave potential of a reduction wave (V).
g
h
i
ipc:ipa = ratio of cathodic to anodic peak current for a reduction.
D
Erp = separation of cathodic and anodic peaks (V).
j
pa = Anodic peak potential.
irr = Irreversible.
qr = Quasi-reversible.
k
l
Table 3
Selected bond lengths (Å), angles (°) and vibrational frequencies (cm–1) from [11]BF4, [18]BF4 and the optimised structures (B3LYP/3-21G⁄) of [110]n+ and [170]n+ (n = 1,0).
[11]BF4
[110]+
[110]
[18]BF4
[170]+
[170]
M–P(1)
M–P(2)
M–C(1)
C(1)–C(2)
2.3756(9)
2.3452(9)
1.811(4)
1.338(5)
1.4944(5)
100.55(3)
173.3(3)
120.0(3)
119.3(3)
125.03
2.399
2.385
1.840
1.330
1.509
102.4
176.4
119.2
119.9
119.9
2194a
1594a
2.336
2.333
1.960
1.352
1.496
102.0
167.3
122.9
119.9
140.5
2158a
1459a
2.2420(6)
2.1991(6)
1.722(2)
1.347(3)
1.491(3)
84.70(2)
173.76(18)
123.4(2)
119.6(2)
ꢁ117.96
2203
2.216
2.210
1.694
1.335
1.497
86.5
170.3
125.2
117.1
ꢁ113.0
2201a
1589a
2.140
2.140
1.820
1.353
1.493
88.0
162.8
123.5
119.7
C(2)–CAr
P(1)–M–P(2)
M–C(1)–C(2)
C(1)–C(2)–CAr
C(1)–C(2)–CN
Cp(0)–MꢃꢃꢃC(2)–CN
ꢁ150.5
2150a
1457a
m(CN)
2202
1582
m(C@C)
1583
a
0.95 Correction factor applied.
electrochemically reversible ferrocene-based oxidation was ob-
served at 0.58 V which likely arise from a combination of the
gem-cyano moiety and the complex charge, with the irreversible
oxidation associated with the ruthenium centre being found at
1.91 V. A second irreversible oxidation was observed in [13]BF4,
and attributed to oxidation of the anisole moiety. The iron com-
plexes [17]BF4 and [18]BF4 gave more chemically reversible elec-
trochemical response, with the reduction process being reversible
even at room temperature, although the oxidation events still
showed signs of chemical complications. Comparing the electro-
chemical response of cyanovinylidenes across the series derived
from Ru(PPh3)2Cp and Fe(dppe)Cp, whilst the metal-based oxida-
tion event in the case of iron complexes was shifted some ꢁ100
to ꢁ300 mV relative to the ruthenium analogue, the potential of
the reduction event was largely insensitive to the nature of the
metal, thereby supporting the chemically intuitive assignment of
the reduction to a ligand centred process.
3.8. Electronic structure calculations and spectroelectrochemistry
To gain further insight into the nature of the electrochemically
generated products a series of DFT calculations and IR spectroelect-
rochemical studies were undertaken. Related results from
[Ru{C@C(CN)C6H4Me-4}(dppe)Cp⁄]BF4 ([20]BF4) have been com-
municated previously [46].
DFT calculations were carried out on both [Ru{C@C(CN)Ph}-
(PPh3)2Cp]+ (denoted [110]+ to distinguish the experimental and
model systems) and [Fe{C@C(CN)Ph}(dppe)Cp]+ ([170]+), using the
crystallographically determined structures of [11]BF4 and [18]BF4
as starting points for further geometry optimisation. As
a

368
E.M. Long et al. / Inorganica Chimica Acta 380 (2012) 358–371
Fig. 9. The energy and composition (%) of the HOMO–1 to LUMO+1 calculated for (a) [110]+ and (b) [170]+ with contours plotted at 0.04 (e/bohr3)1/2
.
trade-off against the larger ligand sets, the relatively small 3–21G⁄
basis set was employed with the B3LYP functional, although it
should be noted that the 3–21G⁄ basis set has proven to be suffi-
cient to provide good agreement with experimental data in previ-
ous studies of half-sandwich ruthenium complexes [40]. The
results of geometry optimisations are summarised in Table 3, and

E.M. Long et al. / Inorganica Chimica Acta 380 (2012) 358–371
369
The general features of the electronic structures of [110]+ and
[170]+ are similar (Fig. 9), although there is some re-ordering of
the orbitals associated with the vinylidene phenyl substituent with
respect to the occupied orbitals from the metal fragment. As a re-
sult the phenyl group features in the HOMO-3 in [110]+ and the
HOMO-1 in [170]+. In each case, the HOMO is comprised of a
filled-filled interactions between a metal d-orbital and the vinyli-
dene C@C p-system, which is also delocalised further on the phe-
nylene substitutent in the iron derivative. Such extended
delocalisation is not possible in the ruthenium example given the
conformation of the phenylene ring with respect to the plane of
the vinyldene
character, is anti-bonding in character with respect to the metal d-
orbital of appropriate -symmetry, and is approximately orthogo-
nal to the filled orbitals that comprise the HOMO and C@C -bond.
p-system. The LUMO has considerable C(1) p-orbital
p
p
The higher unoccupied orbitals have more metal fragment charac-
ter, and if the local coordinate system is defined with z along the
M@C@C axis and x and y directed along the M–P bonds, the
LUMO+1 can be considered as the dx2ꢁy2 orbital.
Fig. 10. The IR spectra of [18]+ and [18] collected in a spectroelectrochemical cell
(0.1 M NBu4BF4/CH2Cl2).
Given the more chemically reversible electrochemical reduction
of the iron cyanovinylidene complexes at room temperature, com-
plex [18]BF4 was selected as a suitable candidate through which to
investigate the structural effects of the redox processes by IR spec-
troelectrochemical methods. However, oxidation of [18]BF4 proved
to be chemically irreversible on the longer timescale of the spec-
troelectrochemical experiment, and this process was not investi-
gated further. In contrast, despite the sluggish electron transfer
behaviour observed in the voltammetry cell, [18]_ displayed suffi-
cient chemical stability to be generated within the spectroelectro-
chemical cell, and re-oxidised to permit recovery of the closed-
shell cation [18]+ (Fig. 10). The
2203 cmꢁ1, with the vinylidene
to [18]_ is accompanied by a shift in the
m
(CN) band in [18]+ is observed at
m
(C@C) at 1583 cmꢁ1. Reduction
m
(CN) band by ꢁ39 cmꢁ1
with an evident shoulder on the high frequency side, although
the m(C@C) cannot be observed and is likely obscured by residual
bands from the supporting electrolyte. Similar behaviour has been
noted for the ruthenium complexes [20]+ and [20]_ [46]. In both
cases, the limited shift of the m(CN) band argues against reduction
at the methylene carbon (C(2)). Reduction at the vinylidene alpha
carbon C(1), which is consistent with the composition of the
LUMO, is more in keeping with the spectroelectrochemical results.
The computational model species [110] and [170] were con-
structed to support the observations made during the spectroelect-
rochemical work. Comparison of the structures of [110]+ with [110],
and of [170]+ with [170] reveal an elongation of the M–P(1,2) dis-
tances, consistent with an increase in electron density at the metal
centre. The M–C(1) distances in the neutral radicals are some 7%
longer than in the closed-shell cations, with a smaller elongation
(ca. 1%) also evidence in the C(1)@C(2) distance. The M–C(1)–
C(2) angle is also distorted from linearity, and taken together these
metric data are consistent with an evolution from sp towards sp2
hybridisation at C(1), and occupation of an orbital with M–C
Fig. 11. The a-HOSO of (a) [110] (b) [170], plotted with contour at 0.04 (e/bohr3)1/2
.
anti-bonding character. The
a
-HOSOs in [110] and [170] (Fig. 11)
are similar in composition to the LUMOs in [110]+ and [170]+,
respectively (Fig. 9). The reduced systems can therefore be repre-
sented by the simple valence descriptions shown in Fig. 12.
Finally, frequency calculations for each of [110] and [170] predict
Fig. 12. A simple valence bond representation of the reduction of cyanovinylidene
complexes.
important bond lengths and angles are listed together with data
from the most closely related X-ray data. The calculated bond
lengths differ from those determined crystallographically by less
than 0.035 Å, and the optimised geometries also reproduce details
of the molecular structures, such as the Cp(0)–FeꢃꢃꢃC(2)–CAr torsion
angle (56.39° [170]+; 55.24° [18]+). In addition, the calculated fre-
quencies reproduce the experimental results extremely well (Table
3). The good agreement between these data from the experimental
and computational systems gives confidence in the accuracy of the
computational model, and the subsequent conclusions.
a small shift in the m(CN) to lower frequency. Calculations on a
rotational isomer of [110] (Cp(0)–FeꢃꢃꢃC(2)–CAr = 150.78°), which
was also an energy minimum and essentially isoenergetic with
[110] being only 1 kcalmolꢁ1 more stable) , gave a slightly higher
m
(CN) frequency (2161 cmꢁ1). It is therefore likely that the shoul-
der observed in the spectroelectrochemical experiment arises from
a rotational isomer of [110]; the presence of such isomers is also
consistent with the generally sluggish (non-diffusion controlled)
electrochemical response observed in solution.

370
E.M. Long et al. / Inorganica Chimica Acta 380 (2012) 358–371
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1-cyano-4-dimethylaminopyridinium
tetrafluoroborate
([9]BF4). Despite the presence of the cyanomethylidene fragment,
electrochemical reduction takes place at the carbene C carbon. Gi-
a
ven the recent demonstrations of the facile conversion of disubsti-
tuted vinylidenes to alkynes at half-sandwich ruthenium and iron
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ruthenium-catalysed route to cyanoalkynes [108] from [9]BF4
and terminal alkynes and to make these useful reagents readily
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Acknowledgements
We thank the EPSRC and the University of Durham for financial
support. PJL holds an EPSRC Leadership Fellowship.
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Tables of the energy and composition of selected frontier orbi-
tals calculated for [110]+, [110], [170]+ and [170]. CCDC 843000,
843001, 843002, 843003, 8430004, 843005 and 843006 contain
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2011.10.067.
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