Syntheses, structures and redox properties of some complexes containing the Os(dppe)Cp* fragment, including [{Os(dppe)Cp*}2(μ- CCCC)]

Article abstract of DOI:10.1039/b712104k

The sequential conversion of [OsBr(cod)Cp*] (9) to [OsBr(dppe)Cp*] (10), [Os(CCH₂)(dppe)Cp*]PF₆ ([11]PF₆), [Os(CCH)(dppe)Cp*] (12), [{Os(dppe)Cp*} ₂{μ-(CCH-CHC)}][PF₆]₂ ([13](PF ₆)₂) and finally [{Os(dppe)Cp*}₂(μ- CCCC)] (14) has been used to make the third member of the triad [{M(dppe)Cp*}₂(μ-CCCC)] (M = Fe, Ru, Os). The molecular structures of [11]PF₆, 12 and 14, together with those of the related osmium complexes [Os(NCMe)(dppe)Cp*]PF₆ ([15]PF₆) and [Os(CCPh)(dppe)Cp*] (16), have been determined by single-crystal X-ray diffraction studies. Comparison of the redox properties of 14 with those of its iron and ruthenium congeners shows that the first oxidation potential E ¹ varies as: Fe ≈ Os < Ru. Whereas the Fe complex has been shown to undergo three sequential 1-electron oxidation processes within conventional electrochemical solvent windows, the Ru and Os compounds undergo no fewer than four sequential oxidation events giving rise to a five-membered series of redox related complexes [{M(dppe)Cp*}₂(μ-C ₄)]ⁿ⁺ (n = 0, 1, 2, 3 and 4), the osmium derivatives being obtained at considerably lower potentials than the ruthenium analogues. These results are complimented by DFT and DT DFT calculations. The Royal Society of Chemistry.

Full text of DOI:10.1039/b712104k

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Syntheses, structures and redox properties of some complexes containing the
Os(dppe)Cp* fragment, including [{Os(dppe)Cp*}2(l-C≡CC≡C)]†‡
Michael I. Bruce,*a Karine Costuas,b Thomas Davin,b Jean-Franc¸ois Halet,b Kathy A. Kramarczuk,a
Paul J. Low,*c Brian K. Nicholson,d Gary J. Perkins,a Rachel L. Roberts,c Brian W. Skelton,e
Mark E. Smithc and Allan H. Whitee
Received 7th August 2007, Accepted 21st September 2007
First published as an Advance Article on the web 11th October 2007
DOI: 10.1039/b712104k
The sequential conversion of [OsBr(cod)Cp*] (9) to [OsBr(dppe)Cp*] (10),
= =
[Os( C CH2)(dppe)Cp*]PF6 ([11]PF6), [Os(C≡CH)(dppe)Cp*] (12),
= =
= =
[{Os(dppe)Cp*} {l-( C CH–CH C )}][PF6]2 ([13](PF6)2) and finally
[{Os(dppe)Cp*}2(l-C≡CC≡C)] (14) has been used to make the third member of the triad
[{M(dppe)Cp*}22(l-C≡CC≡C)] (M = Fe, Ru, Os). The molecular structures of [11]PF6, 12 and 14,
together with those of the related osmium complexes [Os(NCMe)(dppe)Cp*]PF6 ([15]PF6) and
[Os(C≡CPh)(dppe)Cp*] (16), have been determined by single-crystal X-ray diffraction studies.
Comparison of the redox properties of 14 with those of its iron and ruthenium congeners shows that
the first oxidation potential E1 varies as: Fe ≈ Os < Ru. Whereas the Fe complex has been shown to
undergo three sequential 1-electron oxidation processes within conventional electrochemical solvent
windows, the Ru and Os compounds undergo no fewer than four sequential oxidation events giving rise
to a five-membered series of redox related complexes [{M(dppe)Cp*}2(l-C4)]n+ (n = 0, 1, 2, 3 and 4), the
osmium derivatives being obtained at considerably lower potentials than the ruthenium analogues.
These results are complimented by DFT and DT DFT calculations.
of electrons from orbitals which are delocalised over all atoms
Introduction
of the M–(C≡C)n–M bridge,7,11 or from orbitals localised
predominantly either on the carbon chain itself (as in the Mn
complexes4–6) or at the metal centres (for Fe).9,10
Contemporary interest in molecules containing unsaturated
carbon chains linking transition metal–ligand groups1,2 has
resulted in much work centred on complexes of the type
The magnetic properties of these redox-active complexes are
directly linked to their electronic structures and are of consid-
erable interest. With the exception of the Mn derived series,4
all neutral M–C4–M species described to date are diamagnetic
and best described in terms of a buta-1,3-diyne-1,4-diyl structure
(i.e., the limiting valence structure A, Scheme 1).9 In the case of
the manganese complexes, magnetic susceptibility measurements
suggest a triplet ground state for the neutral complex [{trans-
MnI(dmpe)2}2(l-C≡CC≡C)] (i.e., a neutral diradical with formal
d5–d5 configurations at each Mn centre), although it should be
noted that this 34-electron complex offers two fewer electrons than
the other 36-electron buta-1,3-diynediyl complexes. Sequential
one-electron oxidations of [{trans-MnI(dmpe)2}2(l-C≡CC≡C)]
lead to mono- and di-cations with doublet and singlet electronic
structures, respectively, with the Mn centres capping an increas-
ingly cumulenic carbon fragment.4 Similar observations have been
made on other members of the family of Mn2C4 complexes.6
The product derived from one-electron oxidation of
[{Fe(dppe)Cp*}2(l-C≡CC≡C)] (1; A, Scheme 1) also has a buta-
1,3-diynediyl structure with the radical sites localised on the
metal centres (structures B and C).9 The paramagnetic dication
[1]2+ has a singlet (D)–triplet (E) energy gap sufficiently small
(DGST = −18.2 cm−1) for both states to be populated, even at
liquid nitrogen temperatures. Removal of a third electron from
the Fe–C4–Fe substructure is also possible, the use of the very
electron-donating and bulky dippe ligand allowing isolation of
{LxM}(C≡C)n{MLx} (n
=
1–14), containing end-groups
such as Pt(PR3)2(Ar),3 MnI(dmpe)2,4 Mn(dmpe)(g -C5H4Me),5
Mn(C≡CSiR3)(dmpe)2,6 Re(NO)(PPh3)Cp*,7 Fe(CO)2Cp*,8
Fe(PP)Cp* (PP = dppe, dippe)9,10 and Ru(PP)Cpꢀ [PP =
(PPh3)(PR3), R = Me, Ph; dppm, dppe; Cpꢀ = Cp, Cp*],11
many of which have been demonstrated to undergo several
step-wise one-electron oxidations. Their electronic structures have
attracted attention, with theoretical calculations showing that
the HOMOs of these complexes generally have both metal and
carbon character, the relative amounts of which depend on the
length of the carbon chain and the nature of the end-groups.12–14
Consequently, oxidation of these species can involve removal
5
aSchool of Chemistry and Physics, University of Adelaide, Adelaide, South
Australia, 5005, Australia
bLaboratoire des Sciences Chimiques de Rennes, UMR 6226 CNRS-
Universite´ de Rennes 1, F-35042, Rennes, Cedex, France
cDepartment of Chemistry, University of Durham, South Road, Durham,
UK DH1 3LE. E-mail: p.j.low@durham.ac.uk; Fax: + 44 191 384 4737
dDepartment of Chemistry, University of Waikato, Hamilton, New Zealand
eChemistry M313, SBBCS, University of Western Australia, Crawley,
Western Australia, 6009, Australia
† Dedicated to Professor Ken Wade, on the occasion of his 75th birthday,
and in celebration of his remarkable career.
‡ CCDC reference numbers 617825–617829. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b712104k
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Scheme 2 Oxidation processes of compounds 2 and 3. Similar structures
are appropriate for the oxidation of 4.
Scheme 1 Representations of the oxidation processes and products de-
rived from buta-1,3-diynediyl complexes [{M(dppe)Cp*}2(l-C≡CC≡C)].
[{Fe(dippe)Cp*}2(l-C4)](PF6)3 ([5](PF6)3), which is a three-spin
carrier at 293 K.10
Various spectroscopic, structural and computational studies
show a smooth transition from the buta-1,3-diynediyl structure of
the diruthenium complexes [{Ru(PP)Cpꢀ}2(l-C≡CC≡C)] [Cpꢀ =
Cp, PP = (PPh3)2 2; Cpꢀ = Cp*, PP = dppe 3] (G, Scheme 2)
to the cumulenic structure H in the derived dications and even-
tually to the acetylide-bridged dicarbyne I in the tetracations.11
Similar observations have been made for the rhenium complexes
[{Re(NO)(PPh3)Cp*}2(l-C4)]n+ ([4]n+, n = 0–2), although no
dirhenium system of this type has yet been oxidised beyond
the dication.4 In contrast to the iron species [1]2+, the dicationic
ruthenium and rhenium complexes [2]2+, [3]2+ and [4]2+ have been
reported to be diamagnetic between 80 and 300 K.7,11
The families of complexes derived from 1 and 3 feature the same
ligand environment about metal centres from the same periodic
Group, yet differ in terms of the number of accessible oxidation
states and their electronic and magnetic structures. Given these
structural similarities, the observed differences in magnetic and
electronic behaviour for the iron and ruthenium complexes suggest
that it is the metal termini which play a decisive role in dictating
the nature of the spin-carriers and their interactions, therefore
underpinning the long-range magnetic and electronic interactions
between them.
A
detailed study of the hetero-bimetallic complexes
[{Cp*(dppe)Fe}C≡CC≡C{Ru(dppe)Cp*}] (7) and [{Cp*(dppe)-
Fe}C≡CC≡C{Ru(PPh3)2Cp}] (8), which undergo step-wise ox-
idation with [FeCp2]PF6 to give the mono- and di-cations,
[7](PF6)n and [8](PF6)n (n = 1, 2), has also been reported.15
Computational work indicates these systems possess delocalised
electronic structures, with a significant contribution from the iron
centre to the highest lying orbitals. This description is supported
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by the available X-ray structural data, together with the IR
spectrum of [8](PF6)2, which shows a decrease in the m(CC)
frequency, and which are consistent with the gradual evolution
of the polycarbon moiety from a diynediyl structure to a more
cumulenic system as oxidation proceeds. These data, together
with 57Fe Mo¨ssbauer, ESR, IR, UV-vis and NIR spectra allow an
estimation of the relative contributions of the metal centres and
ancillary ligands to the properties of the [{MLx}(l-C4){MꢀLx}]n+
assemblies and clearly indicate the dominant role of ruthenium
over iron in dictating the underlying electronic structures of C4-
bridged bimetallic complexes.
sterically congested to be capable of isolation. However, with a
smaller, chelating diphosphine, such as dppe, analogous complexes
containing all three elements of Group 8 can be prepared. It is
obviously of interest to examine the osmium complexes related
to those described above to complete the picture of the changes
attendant on descending the group and this paper describes
some osmium complexes with the same ligand environment
[Os(dppe)Cp*] as in the Fe and Ru complexes previously studied.15
Results
To date, there has been no example of a series of buta-1,3-
diynediyl complexes containing the metals of a triad with the
same ligand environments. In many cases, this has resulted from
difficulties in obtaining such a series, the extensive studies of
compounds containing the Re(NO)(PPh3)Cp* end-groups7 not
being replicated for Mn (this ligand environment has not yet
been accessed) or Tc (because of its radioactive character). Even
with the Group 8 elements, where studies of the chemistry of
Ru(PPh3)2Cp complexes are common, some of which have been
duplicated with osmium, the Fe(PPh3)2Cp group is apparently too
Syntheses
The conversion of OsO4 to [OsBr(cod)Cp*] (9) and thence to
[OsBr(dppe)Cp*] (10) was achieved by the sequence of reactions
shown in Scheme 3. Reduction of OsO4 by HBr to give H2OsBr6,16
followed by reaction with Cp*H in ethanol may give any of three
products, as described by Girolami and coworkers.17 It is necessary
to control reaction times carefully and to exclude oxygen to obtain
the complex [{Os(l-Br)BrCp*}2]. Although this complex does
not react with dppe to give [OsBr(dppe)Cp*], the latter could be
Scheme 3 The preparation of the homometallic osmium diynediyl complex 14, associated intermediates and related compounds.
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obtained via the reactive intermediate [OsBr(cod)Cp*], obtained
from [{Os(l-Br)BrCp*}2] and 1,5-cyclooctadiene (cod).17 More
recently, we have developed methods for accessing these precur-
sors from potassium osmate, K2[OsO2(OH)4], which provides a
more convenient and less hazardous entry into organo-osmium
chemistry.18
31P resonance arising from the dppe ligand lies between d 43.3
and 43.7, while in the cations, it is at d 40.8 ([11]PF6) or 39.5
([13](PF6)2). ES mass spectra contain parent ions or cations at the
calculated m/z values.
Treatment of 14 with one equivalent of [FeCp2]PF6 in
dichloromethane caused a rapid colour change from orange to
deep green. The mono-cation [14]PF6 was isolated by precipitation
from the reaction mixture following addition of hexane. Not
surprisingly, on account of the 35-electron configuration of the
Regardless of the method of preparation of 9, substitution of
the labile cod with dppe in refluxing heptane led to the formation
of 10 in high yield (81%). Complexes 9 and 10 were characterised
1
1
by H, 13C and 31P NMR spectroscopy along with ES-MS and
cation, the H NMR spectrum of the product was broad and
1
elemental microanalyses. In the H NMR spectra of 9 and 10,
considerably paramagnetically shifted. Peaks at dH 12.16 (Cp*),
10.68 (CH2) and multiplets at dH 7.36–8.22 (Ph) were assigned
from their relative intensities. However, satisfactory 13C and 31P
NMR spectra were not obtained. The IR spectrum contained
m(CC) at 1860 cm−1 (cf. [3]PF6 m(CC) 1859 cm−1),11b corresponding
to a decrease in the CaCb bond order. The ES mass spectrum
contained M+ at m/z 1496.
singlet resonances at d 1.61 and 1.68, respectively, arise from
C5Me5. Multiplets between d 1.71 and 4.07 are assigned to CH2
and CH protons of the cod ligand in 9, while for 10, multiplets are
found at d 2.09 and 2.62 (CH2) and at d 6.97–7.92 (Ph). The 13C
NMR spectra of 9 and 10 contained resonances for Cp* at d 9.51
and 9.82 (singlets, Me) and d 85.12 and 94.01 [triplets, J(CP) 3 Hz,
ring C], together with two singlets at d 68.1 and 69.3 (cod in 9) or
multiplets centred at d 30.77 (CH2) and between d 127.75–140.86
(Ph) (dppe in 10). The 31P resonance for the dppe ligand in 10 is at
d 43.0. The electrospray (ES) mass spectrum of 10 contained both
the molecular ion at m/z 804, arising from in-source oxidation,
and the Br-loss ion [Os(dppe)Cp*]+ at m/z 725.
A reaction sequence utilising the coupling of metal acetylide
radical cations was used to convert 10 to [{Cp*(dppe)Os}2(l-
C≡CC≡C)] (14).9a There is a significant decrease in reactivity
of 10 compared with the iron or ruthenium chloro analogues, so
that the reaction between 10 and HC≡CSiMe3 in the presence
of [NH4]PF6 required extended heating (72 h). The vinylidene
Oxidation of 14 with two equivalents of [FeCp2]PF6 in
dichloromethane caused a rapid change in colour through the deep
green of the mono-cation to a deep blue solution, from which the
dicationic [14](PF6)2 was isolated by precipitation with hexane as
1
an analytically pure powder. The H NMR spectrum of this 34-
electron complex displayed well-resolved signals at d 2.13 (Cp*),
3.19–3.31 and 3.58–3.69 (CH2) and 6.99–7.80 (Ph), consistent with
a diamagnetic complex. The diamagnetic character of [14](PF6)2
is in agreement with geometry optimizations performed at the
DFT level of theory on model [14-H]2+ (see Computational
details) which reveal that the low spin (LS) state is energetically
favored by 18 kJ mol−1 over the high spin (HS) state. The same
result was obtained for the ruthenium dication analogue, i.e.,
the LS state is preferred over the HS state, but with an energy
difference somewhat smaller (13 kJ mol−1). The 31P NMRspectrum
contained a slightly broadened singlet at d 81.0 (dppe) and a septet
at d −143.0 (PF6). The dramatic shift of over 37 ppm in the dppe
resonance is consistent with removal of electron density from the
osmium centre upon oxidation. The IR spectrum contains m(CC)
at 1781 cm−1, indicative of a further decrease in CC bond order
towards the metallacumulenic structure. In the ES mass spectrum,
the doubly-charged cation M2+ is found at m/z 748.
Two further derivatives of the Os(dppe)Cp* moiety were
prepared to provide a larger set of reference compounds for
comparative purposes. Replacement of Br by NCMe was achieved
by heating 10 in acetonitrile in the presence of [NH4]PF6, which
afforded [Os(NCMe)(dppe)Cp*]PF6 ([15]PF6) as an off-white
powder in 74% yield. Characteristic spectral data include IR m(CN)
and m(PF) bands at 2264 and 838 cm−1, the Cp* resonances at dH
1.80 and dC 9.6 and 89.34 [Cp*; the latter a triplet with J(CP)
3 Hz] and 119.62 (CN) and dP 43.3 (dppe) and −143.7 (PF6).
The characteristic dppe resonance in the 31P NMR spectrum is
consistent with the formal 18-electron count at the metal centre.
The molecular cation was at m/z 766 in the ES mass spectrum.
Reaction of 10 with HC≡CPh in ethanol gave an or-
ange solution, which presumably contains the substituted
= =
[Os( C CH2)(dppe)Cp*]PF6 ([11]PF6) was isolated as a pale
yellow powder in 90% yield. Vinylidene 11 was readily de-
protonated with KOBut in thf to give the osmium ethynyl
[Os(C≡CH)(dppe)Cp*] (12) as a yellow solid in 59% yield. The
ethynyl complex 12 is very air-sensitive in solution, the reaction
mixture turning deep green upon exposure to only traces of
oxygen. Oxidative coupling of 12 with [FeCp2]PF6 afforded the
= =
= =
(bis)vinylidene [{Cp*(dppe)Os}2{l-( C CH–CH C )}](PF6)2
([13](PF6)2) as a grey powder (68%), which was then depro-
tonated with KOBut to give the required diynediyl complex,
[{Os(dppe)Cp*}2(l-C≡CC≡C)] (14) as a bright orange powder in
66% yield. In the presence of oxygen, the reaction mixture rapidly
turns dark green, resulting in loss of product.
Complexes [11]PF6, 12, [13](PF6)2 and 14 were characterised
spectroscopically and all gave satisfactory elemental microanaly-
ses. Thus, the IR spectra contained m(CC) bands at 1633 ([11]PF6),
1929 (12), 1611 ([13](PF6)2) and 1965 cm−1 (14), consistent with
the change in CC bond order as indicated in Scheme 3; other
characteristic bands were at 836 ([11]PF6), 841 ([13](PF6)2 [m(PF)]
1
and 3274 cm−1 [12, m(≡CH)]. In the H NMR spectra, the Cp*
groups gave singlets between dH 1.43–1.99 and dC 9.72–10.99
(C5Me5) and d 88.59–92.17 (ring C). For 12, the ring C resonance
showed a triplet coupling to 31P (3 Hz). In vinylidene complexes
[11]PF6 and [13](PF6)2, the characteristic low-field resonances for
Ca were at d 305.27 and 309.69, respectively, with Cb resonating
at d 100.64 and 100.37. Phenyl resonances are found in the usual
regions, between dH 6.74–7.99 and dC 127.0–140.0. In the alkynyl
complex 12, resonances for Ca and Cb are at d 92.91 and 89.88,
respectively, whilst those for the diynediyl complex 14 are observed
at d 71.32 (Ca) and 95.46 (Cb). In the neutral complexes, the
= =
vinylidene [Os( C CHPh)(dppe)Cp*]Br. This solution was
cooled and treated with NaOEt to give the neutral alkynyl
[Os(C≡CPh)(dppe)Cp*] (16) as a lemon-yellow powder in 83%
yield. The IR spectrum of 16 was characterised by m(CC) at
2085 cm−1, whilst characteristic NMR resonances were observed
at dH 1.68 and dC 10.00 and 89.19 for the Cp* ligand, and for
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Ca and Cb at d 105.99 and 97.04, respectively. The characteristic
phosphine resonance at dP 43.7 ppm was also observed.
Molecular structures
The molecular structures of [11]PF6, 12, 14, [15]PF6 and 16
have been determined by single-crystal X-ray crystallography.
Fig. 1–5 contain plots of single molecules or cations, while
Tables 1–3 contain selected bond distances and angles and
crystallographic refinement details. Compared with the exten-
sive studies that are available for ruthenium, there have been
relatively few structures of mononuclear complexes containing
OsL2Cpꢀ (L = tertiary phosphine, Cpꢀ = Cp, Cp*) groups
reported and only those of [OsX(dppe)Cp*] (X = Cl, Br),18
19
=
[Os( CH2)(dppm)Cp*]OTf, [Os{SiR2(X)}(PMe3)2Cp*] (X =
OTf, R = Me,20 Pri;21 X = Cl, R = Pri21), [Os(L)(PMe3)2Cp*]+
(L = SiMe2, SiPri2),21 [{Os(PMe3)2Cp*}2(l-LL)]2+ (LL = N2, S2),21
[Os(OTf)(dppm)Cp*]22 and [Os(OH2)(dmpm)Cp*]+22 contain Cp*
ligands. However, the similarity of the atomic radii of ruthenium
˚
˚
(1.34 A) and osmium (1.35 A) suggests that there should be few
structural differences between analogous complexes containing
these metals.
Fig. 2 A plot of a molecule of [Os(C≡CH)(dppe)Cp*] (12).
Fig. 3 A plot of a molecule of [{Os(dppe)Cp*}2(l-C≡CC≡C)] (14).
+
=
C
=
Fig. 1 A plot of the cation [Os(
the atom labelling scheme.
CH2)(dppe)Cp*] in [11]PF6 showing
atom is shown by the angles subtended by the non-Cp* ligands,
with P–Os–P falling between 81.18 and 83.35(3)◦, and P–Os–X
between 80.3 and 91.43(8)◦.
The complexes described here all have the usual nearly octahe-
dral geometry containing the Os(dppe)Cp* fragment, for which
The Os–C distances reflect the nature of the carbon ligand. For
˚
˚
=
Os–P distances of between 2.2451(8) and 2.2752(9) A are found
vinylidene 11, the Os C bond length is 1.910(3) A, consistent with
for the neutral compounds, lengthening to between 2.2996(5)
and 2.3151(6) A in cations [11] and [15]+ as a consequence of
the decreased Os–P back-bonding interactions. The Os–C(Cp*)
distances are similar in all complexes, ranging between 2.224(3)
the multiple bond character of this interaction; in contrast, the Os–
+
˚
˚
C≡ distances in 12 and 16 lie between 2.012(3) and 2.043(8) A.
=
Within the carbon ligands, the formal C C double bond in 11 is
˚
unusually short at 1.183(6) A, albeit without libration correction,
˚
˚
and 2.328(3) A (mean 2.26 A). The corresponding values for
but on the basis of extensive data measured at ‘low’ temperatures,
˚
analogous ruthenium complexes lie between 2.223 and 2.275(3) A.
The dppe ligands also have similar geometries in each case, with P–
while the C≡C triple bonds in 12 and 16 are 1.16(1) and 1.202,
˚
1.208(5) A, respectively. Angles at C(1) are 175.4(3) (11), 174.4,
˚
C distances between 1.833(3) and 1.872(7) A and C–C separations
177.2(8) (12) and 174.4, 177.9(3)◦ (16), and 174.1, 176.6(3)◦ at
C(2) in 16 (Table 1).
˚
averaging 1.52 A. The pseudo-octahedral geometry about the Os
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◦
˚
Table 1 Selected bond distances (A) and angles ( ) for some OsX(dppe)Cp* complexes
a
c
[11]PF6·MeOH
12 (molecules 1;2) [X =
C≡CH] (molecules 1;2)
14·C5H12 [X =
16·0.25C6H6 [X =
[15]PF6 b [X = NCMe]
2.2999, 2.2996(5)
2.226–2.264(2)
C≡CPh] (molecules 1;2)
=
Complex
Os–P(1,2)
Os–C(cp)
[X = C CH2]
(–C≡C–)2] Os(1;2)
2.3081(8),
2.3151(6)
2.262–2.328(3)
2.265, 2.263(2); 2.262,
2.258(2)
2.245–2.302(8);
2.235–2.274(7)
2.27; 2.26(2)
2.2583(9), 2.2515(9);
2.2451(8), 2.2548(9)
2.226–2.285(3);
2.224–2.279(3)
2.26; 2.26(2)
2.2625(7), 2.2682(8);
2.2721(8), 2.2752(9)
2.236–2.274(3);
2.230–2.291(3)
(av.)
2.29(3)
2.245(13)
2.26; 2.26(2)
Os–C(1)
C(1)–C(2)
C(2)–C(X)
1.910(3)
1.183(6)
2.017; 2.043(8)
1.16; 1.16(1)
2.010; 2.015(3)
1.220; 1.224(4)
1.380(4) [C(3)]
2.028(2) [N(01)]
2.026; 2.012(3)
1.202; 1.208(5)
1.443; 1.437(4) [C(21)]
1.128(3)b
1.465(4) [C(02)]
P(1)–Os–P(2)
P(1)-Os-X
P(2)–Os–X
Os–C(1)–C(2)
C(1)–C(2)–C(3)
82.42(3)
83.4(1)
91.43(8)
175.4(3)
82.68; 82.88(7)
80.3; 82.4(2)
90.4; 88.2(2)
81.18(3); 82.66(3)
81.79; 83.19(9)
84.72; 81.03(9)
177.4; 177.2(3)
176.2; 177.4(3)
82.41(2)
88.89(4)
84.82(4)
83.35, 83.35(3)
81.17; 81.62(8)
86.30; 87.16(9)
177.9; 174.4(3)
174.4(8); 177.2(7)
a Difference map residues were modelled in terms of a disordered C5H12; the compound is isomorphous with its hexane solvated ruthenium analogue.11b
In the table read C(4, 3) as C(1, 2) for the parameters related to Os(2). b Os–N(01)–C(01) 177.4(2), N(01)–C(01)–C(02) 178.8(2)◦. c C(1)–C(2)–C(21) 174.1,
176.6(3)◦.
Fig. 5 A plot of a molecule of [Os(C≡CPh)(dppe)Cp*] (16).
arrangement about the carbon chain, arising from rotation of
the –CM(dppe)Cp* fragment about the C(2)–C(3) bond. Along
Fig. 4 A plot of the cation [Os(NCMe)(dppe)Cp*]+ in [15]PF6.
the linear four-carbon bridging ligand, the carbon–carbon bond
distances give rise to a short–long–short pattern consistent with
Structural comparisons of {Cp*(dppe)M}2(l-C≡CC≡C) (M =
the diynediyl structure, with the C≡C bonds being comparable for
Fe, Ru, Os)
˚
all three complexes and falling around 1.22 A, whereas the central
˚
The synthesis of 14 completes a triad of complexes for Group
8 metals with identical ligand environments. This provides the
opportunity for a detailed comparison of their properties, al-
though limited in this account to their spectroscopic properties
and structural similarities in the M–C4–M bridge, as other features
are similar to those described above. Selected bond data for
the three complexes are collected in Table 2. The structure
of 14 as the pentane solvate is isomorphous with that of the
corresponding hexane solvated ruthenium complex.11b In all three
complexes, the two metal fragments adopt a non-centrosymmetric
C–C bond is around 1.38 A. These values show that the C–C bonds
are shortened and the C≡C bonds are lengthened to approximately
the same extent in all complexes, with respect to the C–C bond of
23
24
˚
˚
ethane (1.532(2) A) and C≡C bond of ethyne (1.178(2) A), in
turn suggesting a similar degree of electron delocalisation along
the carbon chain is in effect in each case.
The data summarised in Table 2 show that there is slight
departure from linearity in the M–C4–M chains in the case of each
of the three complexes 1, 3 and 14, with the angles at the C(sp)
atoms lying in the range 175–179(1)◦. A similar observation has
5392 | Dalton Trans., 2007, 5387–5399
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been made for a number of other {MLx}(l-Cn){MꢀLx} complexes,
with the extent of “bending” becoming more pronounced in
complexes with longer chains.25 Though the reason for the non-
linearity of the carbon chains in this kind of complex cannot
be precisely determined in any particular example, we can assume
that interactions with solvent molecules (if present), van der Waals,
electrostatic or electronic p-type interactions are probably at work.
Interestingly, DFT calculations performed on the Fe, Ru, and
Os series in vacuum at 0 K show that a slight bending of a few
degrees of the metal–carbon chain slightly stabilises the molecules
(≤2 kJ mol−1) over the linear form. This is due to a combination
of small orbital and electrostatic interactions, which together sum
to an observable effect.
As can be seen from the preceding discussion, the structures of
the diynediyl complexes of Fe, Ru and Os are very similar. The only
difference of note is the length of the M–C(1) bonds, the Fe–C(1)
˚
bond being significantly shorter [1.889(3) A] than both the Ru–
˚
˚
C(1) and Os–C(1) bonds [2.001(3) A and 2.010(3) A, respectively],
arising from the different sizes of the metal centres.26 The DFT
optimized structural arrangements of the corresponding neutral
model compounds show the same trend, i.e., the Fe–C(1) bond
˚
length (1.917 A) is, as expected, shorter than the Ru–C(1) and Os–
˚
˚
C(1) distances, which are nearly equivalent (2.028 A and 2.026 A,
respectively). Upon oxidation, the Os–C(1) bond is slightly more
˚
affected than the Ru–C(1) bond, with a contraction of 0.068 A
˚
and 0.126 A for the one and two-electron oxidation products,
˚
˚
respectively, vs. contractions of 0.055 A and 0.102 A for the Ru
series. The C(1)–C(2) bond lengths are virtually identical in the
Ru and Os complexes, with the value in the dicationic osmium
compound [14-H]2+ only 0.004 A longer than the ruthenium
˚
homologue.
Redox properties
The cyclic voltammogram of 14 was recorded (298 K, scan rate of
0.2 V s−1; CH2Cl2 solution with 0.1 M [NBu4]BF4 as supporting
electrolyte). Scans between −2.0 and +2.0 V contain four one-
electron oxidation waves consistent with stepwise oxidation of the
neutral diynediyl complex to the mono-, di-, tri- and tetra-cations
(Table 4). The first three processes are fully reversible, with the
fourth oxidation being partially chemically reversible. The redox
processes are all well separated, with the differences in formal
potentials, DE◦, lying in the range 440 to 830 mV. The large values
of DE◦ are an indication of the stability of the various redox
products with respect to disproportionation under the conditions
of the experiment.
Table 4 lists the half-wave potentials of 14, along with the cor-
responding values from the analogous ruthenium11b and iron9a,10
complexes under almost identical conditions. The potentials
of 14, whilst significantly lower than those of the ruthenium
complex, are comparable to those of the iron complex, an
interesting observation, since the oxidation potentials of the
complex {Cp*(dppe)Fe}2(l-C≡CC≡C) are among the lowest for
organometallic complexes of this type reported to date,11b with
only the manganese complexes described by Berke being more
readily oxidised.4
The DFT geometry optimisations performed for each oxidation
state allow the calculation of the adiabatic ionisation potentials
(IP) (Table 5). A rather good fit between experimental oxidation
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Table 3 Crystal data and refinement details for complexes [11]PF6, 12, 14, [15]PF6 and 16
Compound
[11]PF6††
12
14‡‡
[15]PF6
16§§
Formula
M
C38H41F6OsP3·CH4O
926.90
Monoclinic
P21/n
11.724(1)
17.360(2)
18.500(2)
C38H40OsP2
748.89
Triclinic
¯
P1
11.1341(5)
16.7364(8)
18.1183(8)
88.689(1)
88.960(1)
70.906(1)
3189
C76H78Os2P4·C5H12
1567.91
Triclinic
¯
P1
10.971(2)
17.958(3)
17.855(3)
88.677(4)
85.690(4)
87.946(4)
3505
C38H42F6NOsP3
909.87
Monoclinic
C44H44OsP2·0.25C6H6
844.51
Triclinic
¯
P1
11.9922(6)
17.8922(8)
19.8242(9)
114.764(1)
90.682(1)
103.145(1)
3733
Crystal system
Space group
P21/c
˚
a/A
11.4255(6)
17.3798(8)
19.1554(9)
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
103.300(2)
104.383(1)
3
˚
V/A
3664
4
1.680
37
3684
4
1.640
37
Z
4
2
4
Dc/g cm−3
1.560
41
1.486
38
1.502
35
l/cm−1
Crystal size/mm
0.35 × 0.20 × 0.13
0.18 × 0.18 × 0.10
0.3 × 0.25 × 0.2
0.17 × 0.10 × 0.06
0.24 × 0.20 × 0.08
‘T’min/max
0.66
0.77
0.71
0.70
0.71
◦
2hmax
/
75
50
76
75
75
Ntot
N (Rint
No
R
Rw(nw)
76389
19252 (0.054)
13371
0.035
0.035(3)
66158
11193 (0.063)
9206
0.042
0.051(5)
72480
36104 (0.041)
23919
0.036
0.038(5)
76147
19329 (0.044)
13760
0.027
0.024(4)
77398
38378 (0.049)
23364
0.038
0.024(0)
)
Table 4 Comparative electrochemical data for [{Cp(dppe)M}2(l-C4)]
(M = Fe, Ru, Os)a
Guided by the electrochemical results, the redox products
derived from 14 were examined using IR and UV-Vis-NIR spec-
troelectrochemical methods as a complement to the data obtained
from samples of [14]n+ salts obtained by chemical oxidation.
In CH2Cl2 solutions containing 0.1 M [NBu4]BF4 supporting
electrolyte, 14 exhibited a moderately intense m(C≡C) band at
1970 cm−1, with a shoulder on the higher frequency side. Sequential
oxidation of 14 causeda shift inthe m(CC)band to 1870 cm−1 ([14]+)
and 1780 cm−1 ([14]2+) (Fig. 6). The recovery of the spectrum of
14 by stepwise reduction of [14]2+ in the spectro-electrochemical
cell gives confidence in these assignments, as does the excellent
agreement of the data with those obtained from samples prepared
by chemical oxidation reactions (Table 6). Further oxidation of
[14]2+ gave two further stepwise transformations, with the m(CC)
band shifting initially to 1570 cm−1, and finally to 1960, 1920 cm−1.
However, these latter redox products were not chemically robust,
with reduction failing to result in the recovery of lower oxidation
states of [14]n+, and we refrain from definitive assignment of these
m(CC) bands to [14]3+ and [14]4+. The progression of m(C≡C)
bands observed for the series [14]n+ may be compared with similar
progressions associated with [1]n+ and [3]n+ (Table 6).
Fe (1)
Ru (3)
Os (14)
E1
−0.68
+0.05
+0.95
−0.43
+0.22
+1.04
+1.51
9.64 × 1010
11b
−0.62
E2
−0.01
E3
+0.82
E4
+1.26b
Kc (0/+1/+2)
9.95 × 1011
2.07 × 1010
Ref.
9a
This work
a CH2Cl2/0.1 M [NBu4]PF6, Pt dot working electrode, potentials vs. SCE
such that FeCp2/[FeCp2]+ = 0.46 V. b Peak potential of quasi-reversible
wave.
Table 5 Ionisation potentials (IP, eV) calculated for [{Cp(dHpe)M}2(l-
C4)]n+ (n = 0–4) (M = Fe, Ru, Os)
Fe (1-H)
4.789
8.402
11.751
15.438
15
Ru (3-H)
4.965
8.386
11.757
15.190
15
Os (14-H)
4.653
8.035
11.361
14.466
IP1
IP2
IP3
IP4
Ref.
This work
potentials (in solution) and theoretical ionisation potentials
(vacuum at 0 K) is observed for each series of complexes
[{Cp(dHpe)M}2(l-C4)]n+ (M = Fe, Ru, Os) with the linear regres-
sion coefficient being 0.99 in each case. The only deviation which is
noted between experiment and theory concerns the comparison of
the first oxidation of the Fe and Os species. The neutral Fe complex
is more easily oxidized than the neutral Os analogue (see Table 4),
although the reverse is found in the computational work (Table 5).
On the other hand, both experiment and theory indicate that the
osmium compound becomes the easiest species to oxidise after the
second oxidation process, while the iron system is progressively less
easily oxidised.
Fig. 6 The spectro-electrochemically generated IR [m(C≡C)] spectra of
14 (
), [14]+ (---) and [14]2+ ( · · · ).
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Table 6 IR spectroscopic data (m(CC)/cm−1
[{M(dppe)Cp*}2(l-C4)]n+
)
from the complexes
bridge, has been a topic of considerable interest for many years,
with the interpretations usually being derived from the classical
discussions of mixed-valence complexes based on a two-state
model of weakly interacting metal centres.28 However, in systems
where the bridge orbitals are significantly involved in the semi-
occupied molecular orbitals, the two-state model breaks down.29
The frontier orbitals of poly-ynediyl complexes are, in the simplest
terms, derived from linear combinations of the metal d and
Cn p type orbitals.27 In the case of complexes derived from d6
metal fragments the highest lying orbitals have been thoroughly
described, being of p-symmetry, delocalised over the MC4M chain
with nodal planes between M–C and ≡C–C≡ fragments. The
relative contributions from metal and carbon-based orbitals to
the HOMO (and orthogonal HOMO − 1) is determined by
both the nature of the metal and the length of the polycarbon
fragment,2,9,11,12,15 Indeed, the HOMOs are similar in character for
[14-H] and its neutral Ru analogue, with metallic and carbon chain
character percentages of 24/59 and 26/62 for the HOMO, and
22/68 and 21/69 for HOMO − 1, respectively. The HOMOs of the
iron species show a much stronger metallic character percentage:
41 (Fe2)/46 (C4 chain) for the HOMO and 36 (Fe2)/52 (C4 chain)
for the HOMO − 1. Consequently different behaviour can be
found between examples containing, for example, iron on the one
hand9 and ruthenium, osmium, and rhenium on the other.7,11 Ox-
idation results in depopulation of these high-lying orbitals, which
has been confirmed by the available vibrational and structural
data, as well as by computational investigations.15 Consequently
the frontier orbitals in cations such as [{M(L)2Cp}2(l-Cn)]+ are
rather similar to the HOMOs of the analogous compounds
[{M(L)2Cp}2(l-Cn)].
M = Fea
M = Rub
M = Osb
n = 0
n = 1
n = 2
1880, 1955
1880, 1973
1950, 2160
1963, 1977sh
1860
1770
1965, 1975sh
1860
1781
a CH2Cl2 solution. b Nujol mull.
The data in Table 6 clearly demonstrate the remarkable similar-
ity of the ruthenium ([3]n+) and osmium [14]n+ complexes, and the
equally remarkable distinction from the iron analogue [1]n+. The
IR data from [1]n+ have been interpreted in terms of largely metal-
centred frontier orbitals on the basis of corroborative Mo¨ssbauer
spectroscopy and computational analysis. In contrast, the more
diffuse d-orbitals on the ruthenium lead to more extensively
delocalised frontier orbitals with considerable metal and carbon
bridging ligand character. Consequently, oxidation of 3 leads
to a decrease in the C≡C bonding character and a gradual
progression from a buta-1,3-diynediyl structure (Scheme 2, G)
to more cumulated structures (Scheme 2, H) and, ultimately, to an
ethynediyl-bridged dicarbyne (Scheme 2, I) as the formal electron
count is reduced.2,11,27 The virtually identical IR data obtained
from [14]n+ and [3]n+ indicate that the carbon ligands in both series
are comparable in each oxidation state, as found for the optimized
geometries (see above).
The UV-Vis-NIR spectrum of 14 was relatively featureless, with
only the low energy tail of high energy UV bands apparent in the
visible region, and responsible for the colour of this complex. The
monocationic complex [14]+ exhibited more distinct features at
27 800 cm−1 (e 11 500 M−1 cm−1) and a broad series of overlapping
transitions between 19000–8000 cm−1 (Fig. 7). The electronic
spectrum of the dicationic complex [14]2+ was dominated by
intense bands at 34 000 cm−1 (e 24 000 M−1 cm−1), 28 000 cm−1 (e
16 000 M−1 cm−1) and 17 100 cm−1 (e 20 000 M−1 cm−1). A shoulder
at 19 350 cm−1 (e 7100 M−1 cm−1) was also evident, as was a lower
intensity band near 13 400 cm−1 (e 3200 M−1 cm−1). These general
features are very similar to those observed in the ruthenium series
[2]n+ and [3]n+ (n = 0–3).11
Very recently, TD-DFT calculations on MC2M systems have
indicated that the NIR bands in diruthenium ethynediyl systems
[{Ru(dHpe)Cp}2(l-C2)]+ are derived from transitions between
orbitals whichare rather heavilymetal/phosphine/Cp in character
and the semi-occupied (or more precisely, b-LUSO) orbital which
has considerable [M(d)/Cn(p)]* character.14 These bands can
therefore be approximately described as being metal-to-(metal–
ligand) charge transfer in character. The calculated electronic
excitations for [14-H]+ in its most favoured orientation (metallic
fragments in trans position) contain only one strong excitation
in the NIR region at 15 324 cm−1 (oscillator strength = 0.28).
It is mainly a transition between the b-SOMO − 1 and the
b-LUSO, involving a metal-to-(metal–ligand) charge transfer
process. Several absorption bands are experimentally observed in
this NIR region. They are most probably due to the superposition
of the spectra of the different conformations adopted in solution.
The next electronic excitations with a non-negligible oscillator
strength are calculated at 27 818 and 28 367 cm−1, in agreement
with the experimental measurements (27 800 cm−1). They involve
charge transfer, mainly metal–carbon chain-to-ligand (phosphine
p* orbitals) in character. The most significant feature in the
experimental spectra of [14]2+ is the intense absorption near
17 240 cm−1, which has a rather similar profile to the NIR
band observed in [14]+ and also to the visible absorption bands
observed in [{Ru(dppe)Cp}2(l-C2)]2+, [2]2+ and [3]2+. The visible
band observed in [14]2+ can therefore be attributed to transitions
between occupied metal-centred orbitals and an unoccupied
[M(d)/C4(p)M(d)]* orbital, noting that the semi-occupied orbital
in [14]+ (LUSO) is the LUMO in the (singlet) [14]2+.
Fig.
7
The spectro-electrochemical conversion of [14]+ to [14]2+
(CH2Cl2/0.1 M [NBu4]BF4).
The analysis of NIR bands exhibited by radical cations of
+
general form {[MLx](l-X)[MꢀLx]} , where X is some conjugated
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Infrared spectroelectrochemical experiments were conducted
with a demountable OTTLE cell fitted with CaF2 windows.31 The
solutions were 10−1 M in the supporting electrolyte ([NBu4]BF4)
and 5 × 10−3 M in the analyte. The working electrode potential of
the spectro-electrochemical cell was controlled with a home-built
potentiostat. The IR spectra were recorded with Nicolet Avatar
FT-IR spectrometers (35 scans, 1–2 cm−1 spectral resolution).
UV-Vis-NIR spectro-electrochemical experiments were carried
out in the same cell using solutions in CH2Cl2 containing
10−1 M [NBu4]BF4 as supporting electrolyte on a Varian Cary 5
spectrophotometer. Analyte concentration was 6.7 × 10−4 M. All
solvents were deoxygenated with dry nitrogen prior to use, and the
cell was filled under a nitrogen atmosphere.
Conclusion
The synthesis and characterisation of 14 completes the first
isoleptic series of butadiynediyl complexes derived from members
of the same metal triad. The osmium complex 14 is readily
oxidised at modest potentials to afford a range of mono-, di-,
tri- and tetra-cationic derivatives, the spectroscopic properties of
which are generally similar to those described for the ruthenium
analogues. The lighter first-row transition metal butadiynediyl
complex derived from iron exhibits largely metal-centred redox
events, whilst the heavier second- and third-row systems based
on ruthenium and osmium feature more carbon character in the
redox-active orbitals, as evidenced by the significant shifts in m(CC)
frequencies which accompany oxidation. When these observations
are taken together with the other systematic studies of poly-ynediyl
complexes [{M(L)2Cpꢀ}2(l-Cn)] that have been reported, it can be
concluded that metal contributions to the frontier orbitals are
most pronounced in systems containing the lighter metals and
for shorter length polycarbon chains. Heavier metals and longer
carbon chains promote more carbon-character in the frontier
orbitals of these bimetallic derivatives of carbyne.
Elemental analyses were performed by Chemical and Micro-
Analytical Services (CMAS), Belmont, Victoria.
Reagents
The compounds HCp*,32 Me3SiC≡CH,33 Me3SiC≡CC≡
CSiMe3,34 and [FeCp2]PF6 were prepared by the cited methods.
35
All other reagents were used as received without further
purification.
Experimental
Syntheses
General
PRECAUTIONARY WARNING: OsO4 is extremely toxic. The
yellow solid melts at 31 ◦C and has an appreciable vapour pressure
even at room temperature. The compound is often liberated when
solutions of osmium compounds are treated with oxidising agents.
Ample precautions to protect eyes, nose and mouth are essential.
All reactions were carried out under high purity dry nitrogen or
argon using standard Schlenk techniques, although normally no
special precautions to exclude air were taken during subsequent
work-up. Common solvents were dried, distilled under argon and
degassed before use. Separations were carried out by preparative
thin-layer chromatography on glass plates (20 × 20 cm2) coated
with silica gel (Merck, 0.5 mm thick).
Preparation of [{Os(l-Br)BrCp*}2]. An ampoule of OsO4
(1.0 g, 3.93 mmol) was broken and immediately dropped into a
flask containing 48% HBr (37 mL). The resulting deep red solution
was heated at reflux point for 2 h in air. The solution was decanted
into another flask and the original flask containing the broken
glass was rinsed with an additional 10 mL of HBr. Water and excess
HBr were removed from the combined solutions under vacuum at
50 ◦C, leaving a dark red-brown residue which was dried under
high vacuum for 16 h, to give H2OsBr6 as a red-brown solid (2.64 g,
100%). A suspension of H2OsBr6 (2.62 g, 3.90 mmol) and Cp*H
(796 mg, 5.85 mmol, 1.5 eq.) in ethanol (50 mL) was de-oxygenated
by bubbling nitrogen through the suspension for 15 min. The de-
oxygenated suspension was heated at reflux point for 40 min and
allowed to cool for 5 min. The resultant dark brown solution was
decanted using Schlenk techniques, with strict exclusion of oxygen,
to leave [{Os(l-Br)BrCp*}2] as a black-brown precipitate which
was used immediately in the next step without further purification.
1H NMR (CDCl3): dH 2.40 (s, 15H, Cp*). 13C NMR (CDCl3): dC
108.42 (s, Cp*), 13.65 (s, Cp*).
Instruments
IR spectra were obtained on a Bruker IFS28 FT-IR spectrometer.
Spectra in CH2Cl2 were obtained using a 0.5 mm path-length
solution cell with NaCl windows. Nujol mull spectra were obtained
from samples mounted between NaCl discs. NMR spectra were
recorded using Varian 2000 [199.98 MHz (1H), 50.29 MHz (13C)],
ACP-300 [300.145 MHz (1H), 75.47 MHz (13C), 121.105 MHz
(31P)] or Varian Inova 600 [599.957 MHz (1H), 150.87 MHz (13C),
242.21 MHz (31P)] instruments. Unless otherwise stated, samples
were dissolved in CDCl3 contained in 5 mm sample tubes. Chem-
ical shifts are given in ppm relative to internal tetramethylsilane
1
for H and 13C NMR spectra and external H3PO4 for 31P NMR
spectra. UV-Vis spectra were recorded on a Varian Cary 5 UV-
Vis/NIR spectrometer. Electrospray mass-spectrometry (ES-MS)
was carried out at the University of Waikato, Hamilton, New
Zealand. Spectra were obtained from samples dissolved in MeOH
unless otherwise indicated. Solutions were injected into a Varian
Platform II spectrometer via a 10 ml injection loop. Nitrogen was
used as the drying and nebulising gas. Chemical aids to ionisation
were used.30
Electrochemical samples (10−3 M) were dissolved in CH2Cl2
containing 5 × 10−1 M [NBu4]BF4 as the supporting electrolyte.
Cyclic voltammograms were recorded using a Princeton Applied
Research model 263 apparatus, with a saturated calomel electrode,
with ferrocene as internal calibrant (FeCp2/[FeCp2]+ = 0.46 V).
[OsBr(cod)Cp*] (9). 1,5-Cyclooctadiene (2.52 mL, 20.6 mmol)
and ethanol (40 mL) were added to a Schlenk flask containing
[{Os(l-Br)BrCp*}2] (prepared as above) and the suspension was
de-oxygenated (as above). The suspension was heated at reflux
point for 90 min during which time the orange colour of the
solution darkened. Solvent was removed under vacuum and the
dark brown residue was extracted with boiling diethyl ether (4 ×
30 mL). The combined orange extracts were filtered and solvent
was removed under vacuum to give [OsBr(cod)Cp*] (9) as a dark
1
orange solid (1.07 g, 54%). H NMR (CDCl3): d 1.68 (s, 15H,
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Cp*), 1.71 (m, 2H, CH2), 1.95 (m, 2H, CH2), 2.19 (m, 2H, CH2),
2.62 (m, 2H, CH2), 3.62 (m, 1H, CH), 4.07 (m, 1H, CH). 13C NMR
(CDCl3): d 94.01 (s, Cp*), 69.3 (s, CH), 68.1 (s, CH), 33.2 (s, CH2),
9.82 (s, Cp*).
61%). Anal. calcd (C38H40P2Os): C, 60.95; H, 5.38; M, 750. Found:
C, 60.81; H, 5.39%. IR (Nujol): m(≡CH) 3274, m(C≡C) 1929 cm−1.
1H NMR (C6D6): d 1.73 (s, 15H, Cp*), 2.10 (s, 1H, C≡CH), 2.03,
2.69 (2 × m, 2 × 2H, PCH2), 7.03–7.95 (m, 20H, Ph). 13C NMR
(C6D6): d 10.04 (s, Cp*), 31.16 (m, PCH2), 88.79 [t, J (CP) 2.7 Hz,
Cp*], 89.88 (s, Cb), 92.91 [t, J(CP) 17 Hz, Ca], 127.02–139.37 (m,
Ph). 31P NMR (C6D6): d 43.6 (s). ES-MS (positive ion mode, m/z):
751, [M + H]+.
[OsBr(dppe)Cp*] (10).
A suspension of [OsBr(cod)Cp*]
(930 mg, 1.81 mmol) and dppe (722 mg, 1.81 mmol) in heptane
(40 mL) was heated at reflux point under nitrogen for 16 h. After
cooling, the resulting precipitate was collected by vacuum filtration
and washed with heptane (3 × 10 ml) to give [OsBr(dppe)Cp*] (10)
as a pale orange powder (1.18 g, 81%). Anal. calcd (C36H39P2OsBr):
C, 53.80; H, 4.89; M, 803. Found: C, 53.51; H, 4.94%. IR (Nujol):
1092 s, 1023 m, 786 m, 741 s, 700 vs, 665 s cm−1. 1H NMR (C6D6):
d 1.61 (s, 15H, Cp*), 2.09, 2.62 (2 × m, 2 × H, PCH2), 6.97–7.92
(m, 20H, Ph). 13C NMR (C6D6): d 9.51 (s, Cp*), 30.77 (m, PCH2),
85.12 [t, J(CP) = 3 Hz, Cp*], 127.75–140.86 (m, Ph). 31P NMR
(C6D6): d 43.0 (s). ES-MS (positive ion mode, m/z): 804, M+; 725,
[Os(dppe)Cp*]+.
= =
= =
[{Os(dppe)Cp*}2{l-( C CH–CH C )}](PF6)2 ([13](PF6)2).
Thoroughly de-oxygenated CH2Cl2 (20 mL) was cooled to −78 ◦C
◦
and transferred via cannula to a Schlenk flask cooled to −78 C
and containing [Os(C≡CH)(dppe)Cp*] 12 (150 mg, 0.20 mmol)
and [FeCp2]PF6 (63 mg, 0.19 mmol, 0.95 eq.) under argon. The
solution was stirred for 3 h at −78 ◦C and then allowed to warm
to r.t. over 12 h. The solution was then filtered into rapidly
stirred hexane to give a gray solid which was collected by vacuum
filtration, washed with hexane (2 × 5 mL) and dried under high
= =
= =
vacuum to give [{Os(dppe)Cp*}2{l-( C CHCH C )}](PF6)2
= =
[Os( C CH2)(dppe)Cp*]PF6 ([11]PF6). HC≡CSiMe3 (55 mg,
=
([13](PF6)2) as a pale gray solid (126 mg, 74%). IR (Nujol): m(C C)
0.558 mmol, 5 mol eq.) was added to a suspension of
[OsBr(dppe)Cp*] (100 mg, 0.112 mmol) and [NH4]PF6 (36.3 mg,
0.223 mmol, 2 mol eq.) in CH2Cl2 (15 mL), and the mixture
was stirred at 45 ◦C for 72 h in a sealed Schlenk flask. The
resulting suspension was filtered to remove precipitated NH4Br
and added dropwise to rapidly stirred diethyl ether to give
−1
1
=
1611, m(PF) 841 cm . H NMR (CDCl3): d 1.00 (s, 2H, CH), 1.73
(s, 30H, Cp*), 2.60–2.72 (m, 8H, PCH2), 7.00–7.56 (m, 40H, Ph).
13C NMR (CDCl3): d 9.46 (s, Cp*), 30.21–31.87 (m, PCH2), 88.21
(s, Cp*), 100.37 (s, Cb), 128.62–134.32 (m, Ph), 309.69 (s, Ca). 31
P
NMR (CDCl3): d 39.5 (s, PPh3), −143.7 [septet, J(PF) = 711 Hz,
PF6]. ES-MS (positive ion mode, m/z): 749, M2+ (calcd M2+, 749).
= =
[Os( C CH2)(dppe)Cp*]PF6 ([11]PF6) (89 mg, 90%) as a pale
[{Os(dppe)Cp*}2(l-C≡CC≡C)]
(14). Thoroughly
oxygenated THF (20 mL) was transferred via cannula to a Schlenk
de-
yellow powder that was collected by vacuum filtration and dried
under high vacuum. An analytical sample was obtained from
methanol and obtained as the methanol solvate. Anal. calcd
(C38H41F6P3Os·MeOH): C, 50.54; H, 4.89; M (cation), 751. Found:
= =
= =
flask containing [{Os(dppe)Cp*}2{l-( C CHCH C )}](PF6)2
(13) (125 mg, 0.07 mmol) and KOBut (15.5 mg, 0.139 mmol,
2 eq.) under argon, and the solution was stirred at r.t. for 30 min.
Solvent was removed under vacuum and the crude solid was
extracted with hexane (3 × 5 mL) to give a bright orange solution
which was filtered to remove residual KPF6. Solvent was removed
to give [{Os(dppe)Cp*}2(l-C≡CC≡C)] (14) as a bright orange
powder (65 mg, 66%). Anal. calcd (C76H78P4Os2): C, 61.03; H,
5.26; M, 1497. Found: C, 61.15; H, 5.34%. IR (Nujol): m(C≡C)
1965 s cm−1. 1H NMR (C6D6): d 1.75 (s, 30H, Cp*), 2.03, 2.64 (2 ×
m, 2 × 4H, PCH2), 7.06–7.99 (m, 40H, Ph). 13C NMR (C6D6): d
10.08 (s, Cp*), 31.39 (m, PCH2), 71.32 [t, J(CP) 19 Hz, Ca], 88.68
(s, Cp*), 95.46 (s, Cb), 127.16–139.99 (m, Ph). 13P NMR (C6D6): d
43.6 (s). ES-MS (positive ion mode, m/z): 1496, M+.
−1
1
=
C, 50.31; H, 4.79%. IR (Nujol): m(C C) 1633, m(PF) 836 cm . H
=
NMR (CDCl3): d 0.66 (s, 2H, CH2), 1.73 [t, J(HP) 1 Hz, 15H,
Cp*], 2.70–2.94 (m, 4H, PCH2), 7.15–7.65 (m, 20H, Ph). 13C NMR
(CDCl3): d 9.72 (s, Cp*), 30.58–31.23 (m, PCH2), 92.17 (s, Cp*),
100.64 (m, Cb), 128.86–133.91 (m, Ph), 305.27 [t, J(CP) 10 Hz,
Ca]. 31P NMR (CDCl3): d 40.8 (s, PPh), −143.7 [septet, J(PF) =
711 Hz, PF6]. ES-MS (positive ion mode, m/z): 751, [M − PF6]+.
[Os(C≡CH)(dppe)Cp*] (12).
Method (a). Thoroughly de-oxygenated THF (15 mL)
was transferred via cannula to a Schlenk flask containing
t
= =
[Os( C CH2)(dppe)Cp*]PF6 7 (88 mg, 0.098 mmol) and KOBu
(11.4 mg, 0.098 mmol, 1 mol eq.) in an atmosphere of argon,
and the resulting yellow solution was stirred at room temperature
for 30 min. The solvent was removed under vacuum and the
resultant solid was extracted with benzene and filtered to remove
residual KPF6. The solvent was removed under vacuum to give
[Os(C≡CH)(dppe)Cp*] (12) as a yellow solid that was dried under
high vacuum (44 mg, 59%).
[{Os(dppe)Cp*}2(l-C4)]PF6 ([14]PF6). [FeCp2]PF6 (5.4 mg,
0.016 mmol) was added to a solution of [{Os(dppe)Cp*}2(l-
C≡CC≡C)] (26 mg, 0.017 mmol) in CH2Cl2 (10 ml). The colour
changed immediately from orange to green. After stirring for
30 min, the volume was reduced to 2 ml and hexane (25 ml)
was added dropwise to give green [{Os(dppe)Cp*}2(l-C4)]PF6
([14]PF6) (20 mg, 72%). IR (Nujol, cm−1): m(CC) 1860 w, m(PF)
839 s. 1H NMR (d6-acetone): d 7.36–8.22 (br m, 40H, Ph), 10.68
(br, 8H, CH2), 12.16 (br, 30H, Cp*). ES-MS (positive ion, MeOH,
m/z): 1496, M+; 725, [Os(dppe)Cp*]+.
Method (b). A suspension of [OsBr(dppe)Cp*] (200 mg,
0.248 mmol) and HC≡CSiMe3 (245 mg, 2.48 mmol, 10 eq.) in
EtOH (30 mL) was stirred in a sealed Schlenk flask at 45 ◦C for 5
d under nitrogen. The resulting orange solution was cooled in ice
and a freshly prepared NaOEt solution (25 mg Na in EtOH; 5 mL)
was added dropwise with stirring. An immediate colour change
from orange to pale yellow occurred and a pale yellow precipitate
separated. This was collected by vacuum filtration, washed with
ice-cold EtOH (3 × 5 mL) and dried under high vacuum to give
[Os(C≡CH)(dppe)Cp*] (12) as a pale yellow powder (101 mg,
[{Os(dppe)Cp*}2(l-C4)](PF6)2 ([14](PF6)2). A similar reaction
to the above, using [{Os(dppe)Cp*}2(l-C≡CC≡C)] (10 mg,
0.007 mmol) and [FeCp2]PF6 (4.3 mg, 0.013 mmol) in CH2Cl2
(10 ml), resulted in colour changes from orange to green to
deep blue. After stirring for 30 min, reduction in volume to
2 ml and addition of hexane (25 ml) resulted in precipitation of
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Dalton Trans., 2007, 5387–5399 | 5397
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program system.36 Pertinent results are given in the figures
(which show non-hydrogen atoms with 50% probability amplitude
displacement ellipsoids and hydrogen atoms with arbitrary radii
dark blue [{Os(dppe)Cp*}2(l-C4)](PF6)2 ([14](PF6)2) (8 mg, 67%).
Anal. calcd (C76H70F12Os2P6): C, 51.12; H, 4.40; M (cation), 1496.
Found: C, 51.09; H, 4.31%. IR (Nujol, cm−1): m(CC) 1781 w, m(PF)
1
˚
of 0.1 A) and in Tables 1–3.
836 s. H NMR (d6-acetone): d 2.13 (br, 30H, Cp*), 3.19–3.31,
3.58–3.69 (2 × m, 2 × 4H, CH2), 6.99–7.80 (m, 40H, Ph). 31P NMR
(d6-acetone): d 81.0 (dppe), −143.0 (sept, PF6). ES-MS (positive
ion, MeOH, m/z): 748, M2+; 725, [Os(dppe)Cp*]+.
Density functional calculations
DFT calculations were performed with the amsterdam density
functional package (ADF 2005)37 on models [14-H]n+ (phenyl
groups were replaced by hydrogen atoms), n = 0, 1, 2, 3, 4. The sin-
glet and triplet states were considered for [14-H]2+. The geometries
were fully optimized without constraints (C1 symmetry). Electron
correlation was treated within the local density approximation
(LDA) in the Vosko–Wilk–Nusair parametrization.38 The non-
local corrections of Becke and Perdew were added to the exchange
and correlation energies, respectively.39 The analytical gradient
method implemented by Verluis and Ziegler was used.40 The
standard ADF TZP basis set was used, i.e., triple-n STO basis
set for the valence core augmented with a 3d polarisation function
for C, P, and a 6p polarisation function for Os. Orbitals up to
1s, 2p, and 4f were kept frozen for C, P, and Os, respectively.
Relativistic corrections were added using the ZORA (zeroth
order regular approximation) scalar Hamiltonian.41 The excitation
energies and oscillator strengths were calculated following the
procedure described by van Gisbergen and cowokers.42 The
ionisation potentials were computed adiabatically.
[Os(NCMe)(dppe)Cp*]PF6 ([15]PF6).
A
suspension of
OsBr(dppe)Cp* (100 mg, 0.124 mmol) and [NH4]PF6 (20.5 mg,
0.124 mmol) in MeCN (15 mL) was heated at reflux point for 20 h.
After this time the reaction mixture consisted of solid NH4Br
under a pale yellow solution. Filtration and removal of solvent
under vacuum was followed by dissolving the yellow residue
in CH2Cl2 (5 mL) and adding the solution dropwise to rapidly
stirred diethyl ether. The off-white precipitate was collected by
vacuum filtration, washed with diethyl ether (3 × 5 mL) and
dried under high vacuum to give pure [Os(NCMe)(dppe)Cp*]PF6
([15]PF6) (84 mg, 74%). Anal. calcd (C38H42P3F6OsN): C, 50.16;
H, 4.65; M (cation), 766. Found: C, 49.95; H, 4.97%. IR (Nujol):
m(C≡N) 2264, m(PF) 838 cm−1. 1H NMR (CDCl3): d 1.51 (s, 15H,
Cp*), 1.80 (s, 3H, Me), 2.35–2.56 (m, 4H, PCH2), 7.21–7.55 (m,
20H, Ph). 13C NMR (CDCl3): d 3.49 (s, CH3), 9.58 (s, Cp*),
30.68 (m, PCH2), 89.34 [t, J(CP) = 3 Hz, Cp*], 119.62 (s, C≡N),
128.72–135.25 (m, Ph). 31P NMR (CDCl3): d 43.3 (s, PCH2),
−143.7 [septet, 1J(PF) = 711 Hz, PF6]. ES-MS (positive ion
mode, m/z): 766, [M − PF6]+.
Acknowledgements
[Os(C≡CPh)(dppe)Cp*] (16).
A
suspension of [OsBr-
(dppe)Cp*] (100 mg, 0.124 mmol) and HC≡CPh (32.3 mg,
0.335 mmol) in EtOH (10 mL) was heated at reflux point for 17 h.
The resulting orange solution was cooled on ice and a freshly
prepared NaOEt solution (Na, 25 mg, in ethanol, 5 mL) was
added dropwise with stirring. An immediate colour change from
orange to pale yellow was observed and a pale yellow precipitate
separated. This was collected by vacuum filtration, washed with
ice-cold ethanol (3 × 5 mL) and dried under high vacuum to give
[Os(C≡CPh)(dppe)Cp*] (16) as a pale yellow powder (67.2 mg,
63%). Concentration of the filtrate gave a further 21.2 mg of
product (total yield, 83%). Anal. calcd (C44H44P2Os): C, 64.06; H,
5.37. Found: C, 63.94; H, 5.34%. IR (Nujol): m(C≡C) 2085 cm−1.
1H NMR (CDCl3): d 1.68 (s, 15H, Cp*), 2.12, 2.61 (2 × m, 2 ×
H, PCH2), 6.72–8.14 (m, 25H, Ph). 13C NMR (CDCl3): d 10.00 (s,
C5Me5), 31.38 (m, PCH2), 89.19 (s, C5Me5), 97.04 (s, Cb), 105.99
[t, J(CP) 19.6 Hz, Ca], 127.07–139.92 (m, Ph). 31P NMR (CDCl3):
d 43.7 (s).
We thank the ARC for support of this work and Johnson
Matthey plc, Reading, for generous loans of RuCl3·nH2O and
potassium osmate. These studies were facilitated by travel grants
(ARC, Australia; the Royal Society of Chemistry, UK; the CNRS,
France).
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