Multicenter transformations of the methyl ligand in CH3Os3Au carbonyl cluster complexes: Synthesis, characterization and DFT analyses

Article abstract of DOI:10.1016/j.jorganchem.2015.07.041

Os₃(CO)₁₁(NCCH₃) and Os₃(CO)₁₀(NCCH₃)₂ react with (CH₃)AuPPh₃ to yield the new Os3Au cluster complexes, Os₃(CO)₁₀(μ-O=CCH₃) (AuPPh₃), 1 and Os₃(CO)₉(μ-η³-CH) (μ-H)₂(μ-AuPPh₃), 2 containing bridging acetyl and bridging methylidyne ligands, respectively, by two competing reaction pathways: 1) a methyl migration/CO insertion pathway that produces a complex with a bridging acetyl ligand. and 2) C-H bond cleavage transformations via a series of decarbonylated intermediates containing an agostically coordinated bridging methyl group, a bridging methylene group, a triply bridging methylidyne ligand and bridging hydride ligands. It has also been found that carbon monoxide can induce shifts of the bridging hydride ligands back to methylidyne ligand in 2 with subsequent cleavage of Os-Au and Os-Os bonds to yield two open cluster complexes (CH₃)Os₃(CO)₁₂AuPPh₃, 4 and (CH₃)Os₂(CO)₈AuPPh₃, 5 having terminally coordinated methyl ligands. The open cluster complex 4 can be converted back to 1 and 2 via decarbonylation process by using either thermal or irradiation treatments. The CO dissociation mechanisms related to the CH bond transformation processes were studied by DFT computational analyses. It has been demonstrated that the Os₃Au(CH₃) cluster provides a robust platform to studying multicenter C-H bond transformations and for C-C bond formation via methyl migration/CO insertion processes.

Full text of DOI:10.1016/j.jorganchem.2015.07.041

Journal of Organometallic Chemistry xxx (2015) 1e13
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Multicenter transformations of the methyl ligand in CH3Os3Au
carbonyl cluster complexes: Synthesis, characterization and DFT
analyses*
Richard D. Adams*, Zhongwen Luo, Mingwei Chen, Vitaly Rassolov**
Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC, 29208, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Os3(CO)11(NCCH3) and Os3(CO)10(NCCH3)2 react with (CH3)AuPPh3 to yield the new Os3Au cluster
complexes, Os3(CO)10(m-O]CCH3) (AuPPh3), 1 and Os3(CO)9(m-h m-H)2(m-AuPPh3), 2 containing
3-CH) (
Received 6 June 2015
Accepted 29 July 2015
Available online xxx
bridging acetyl and bridging methylidyne ligands, respectively, by two competing reaction pathways: 1)
a methyl migration/CO insertion pathway that produces a complex with a bridging acetyl ligand. and 2) C
eH bond cleavage transformations via a series of decarbonylated intermediates containing an agostically
coordinated bridging methyl group, a bridging methylene group, a triply bridging methylidyne ligand
and bridging hydride ligands. It has also been found that carbon monoxide can induce shifts of the
bridging hydride ligands back to methylidyne ligand in 2 with subsequent cleavage of OseAu and OseOs
bonds to yield two open cluster complexes (CH3)Os3(CO)12AuPPh3, 4 and (CH3)Os2(CO)8AuPPh3, 5 having
terminally coordinated methyl ligands. The open cluster complex 4 can be converted back to 1 and 2 via
decarbonylation process by using either thermal or irradiation treatments. The CO dissociation mecha-
nisms related to the CH bond transformation processes were studied by DFT computational analyses. It
has been demonstrated that the Os3Au(CH3) cluster provides a robust platform to studying multicenter C
eH bond transformations and for CeC bond formation via methyl migration/CO insertion processes.
© 2015 Elsevier B.V. All rights reserved.
Keywords:
Osmium
DFT analyses
CH transformations
Crystal structures
Methyl ligand
Methylidyne ligand
1. Introduction
challenge to the chemistry of methane is the activation of the CeH
bonds. The CeH bond strength in methane is the highest of the
With the boom of shale oil and gas in the U. S. [1], there is a
renewed interest in finding direct routes for the transformation of
methane and other low boiling hydrocarbons into higher value
chemicals and fuels.2 Today, the industrial conversion of methane is
performed in two steps: 1) steam reforming of methane to produce
syngas (CO and H2); and 2) catalytic hydrogenation of the CO (e.g.
Fischer-Tropsch Synthesis, FTS) to make higher boiling hydrocar-
bons for fuels or for the synthesis of methanol and other com-
modities [2,3]. Because of the high capital cost and energy
inefficiencies in the FTS, there is considerable interest in developing
new routes for the utilization of methane [2,4,5]. The greatest
saturated hydrocarbons, 434 kJ/mol [6]. Understanding CeH bond
activation and the transformations of the CH3, CH2 and CH frag-
ments on metal surfaces is essential for optimizing methane utili-
zation by heterogeneous catalysts. The relative stability and
reactivity of CH3, CH2, CH and C ligands on a particular transition
metal surface is important to subsequent chain growth, propaga-
tion and termination steps during FTS [7]. The activation and
transformation of methane on metal surfaces has been investigated
by a variety of computational methods [2e,2f,2h,8]. In a recent
study, Campen, et al. reported that absorbed hydrogen atoms on
Ru(0001) inhibit the CH2 / CH þ H transformation at an activation
barrier of 65 kJ/mol [8].
Organometallic clusters having the empirical formula
M3(CO)9{CH4} are of great interest because of their potential to be
obtained from M3(CO)12 compounds via activation of a CeH bond in
methane. A number of years ago, Shapley studied the trans-
formations of CH3, CH2 and CH ligands in Os3(CO)9{CH4} complexes
*
Dedicated to the memory of Professor Jack Lewis, the Lord Lewis of Newnham, a
pioneer in the chemistry of polynuclear metal carbonyl cluster complexes.
* Corresponding author.
** Corresponding author.
E-mail addresses: adamsrd@mailbox.sc.edu (R.D. Adams), RASSOLOV@mailbox.
sc.edu (V. Rassolov).
that he obtained from the reaction of Os3(CO)10
(m
-H)2 with CH2N2
-CH3) ( -H)
[9]. He showed that the methyl complex Os3(CO)10
(m
m
http://dx.doi.org/10.1016/j.jorganchem.2015.07.041
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R.D. Adams et al. / Journal of Organometallic Chemistry xxx (2015) 1e13
was readily isomerized to the methylene complex, Os3(CO)10
CH2) ( -H)2, by a CH bond cleavage and was in turn transformed to
the methylidyne complex, Os3(CO)9(m3-CH) ( -H)3, by elimination
(
m
-
impact ionization (EI) were made on a VG 70S instrument, Positive/
negative ion mass spectra were recorded on a Micromass Q-TOF
instrument by using electrospray (ES) ionization. (CH3)AuPPh3 and
Os3(CO)12 were obtained from STREM and were used without
further purification. Os3(CO)11(NCCH3) and Os3(CO)10(NCCH3)2
were prepared according to the previously reported procedures
[18,19]. Product isolations were performed by TLC in air on Analtech
0.50 mm silica gel 60 Å F254 glass plates and Analtech 0.25 mm
aluminum oxide UV254 glass plates.
m
m
of a CO ligand. The interconversions of the “Os3(CO)10{CH4}” tau-
tomers was studied by 1H NMR spectroscopy. Fehlner and co-
workers studied the chemistry of the hydrocarbyl ligands in
solution for a series of iron complexes having the empirical formula
“Fe3(CO)9{CH4}” [10]. Norton and coworkers studied the chemistry
of Os(CO)4(CH3)2 obtained by reaction of Na2Os(CO)4 with excess
methyl tosylate [11]. Thermolysis of HOs(CO)4(CH3) yielded
HOs2(CO)8(CH3) and methane [12]. Treatment of HOs2(CO)8(CH3)
2.2. Synthesis of Os3(CO)10(m-O]CCH3) (AuPPh3), 1 and
with
HOs(CO)4(CH3)
yielded
the
triosmium
complex
Os3(CO)9(m3-CH) (H)2(AuPPh3), 2
Os3(CO)12(CH3)2 and molecular hydrogen [13]. The formation of the
dinuclear and polynuclear complexes was proposed to occur by
homolysis of metal-carbon bonds and formation of metalemetal
bonds.
In our recent studies, it has been shown that aryl-Au(PPh3)
compounds can be readily added to reactive polynuclear metal
carbonyl complexes by cleavage of the Au e C bond to yield com-
plexes containing coordinated aryl ligands that can undergo sub-
sequent transformations at multi metal centers, e.g. eq. (1) [14e16].
In this work, we have investigated the reactions of
(a) Reaction
of
Os3(CO)11(NCCH3)
with
(CH3)Au(PPh3):
Os3(CO)11(NCCH3) (19 mg, 0.021 mmol) were added to a
50 mL three neck flask containing a solution of (CH3)
Au(PPh3) (9.7 mg, 0.021 mmol) in 30 mL methylene chloride.
The reaction mixture was allowed to stir for 5 h with inter-
mittent monitoring by IR spectroscopy. The solvent was then
removed in vacuo, and the products were isolated by TLC by
using pure hexane solvent to yield three bands. In order of
elution they gave 7.0 mg of yellow Os3(CO)10(m-O]CCH3) (m-
AuPPh3), 1 (37% yield), 1.9 mg of the known reddish com-
pound Os3(CO)10 -Cl) ( -AuPPh3) [20], (10% yield) and
(CH3)Au(PPh3) with the triosmium carbonyl complexes
Os3(CO)11(NCCH3) and Os3(CO)10(NCCH3)2. Because of the strong
isolobal similarities between ꢀH and ꢀAu(PPh3) [17], we believe that
(CH3)Au(PPh3) will serve as a viable mimic for CH4 for studies of its
(m
m
6.2 mg of colorless Os3(CO)9(m3-CH) (m-H)2(m-AuPPh3), 2 (33%
yield). Spectral data for 1: IR nCO (cmꢁ1 in hexane): 2091(m),
2039(s), 2032(m), 2013(m), 2005(s), 1989(w), 1972(w),
activation and transformations. The new complexes Os3(CO)10
O]CCH3) ( -AuPPh3), 1, Os3(CO)9(m3-CH) ( -H)2( -AuPPh3), 2 and
Os3(CO)9(m3-CH) ( -H) ( -AuPPh3)2, 3 have been obtained. Inter-
(m-
1959(m). 1H NMR (CD2Cl2, 25 ꢂC, TMS, in ppm)
d
¼ 2.19 (s, 3H,
m
m
m
OCCH3); 31P{1H} NMR (CD2Cl2, 25 ꢂC, 85% ortho-H3PO4)
m
m
d
¼ 85.71 (s,1P, PeAu). Mass Spec. Pos. Ion ES/MS m/z 1354.
estingly, it was found that the hydrido ligands in 2 can be shifted
back to methylidyne ligand by reaction with CO to yield two new
complexes: (CH3)Os3(CO)12AuPPh3, 4 and (CH3)Os2(CO)8AuPPh3, 5
containing terminally coordinated methyl groups. Complex 4 loses
CO spontaneously and goes back to 1 and 2 when heated or irra-
diated with visible light. The nature of CO dissociation and the
transformations of the hydrocarbyl ligands in these triosmium
complexes was studied by single-crystal X-ray diffraction analysis,
mass-spec and 1H NMR analyses and by density functional theory
(DFT) molecular orbital calculations. These results are reported
herein.
Spectral data for 2: IR nCO (cmꢁ1 in hexane): 2093 (m),
2063(s), 2048(s), 2007(s), 1996(m), 1972(m), 1964(sh). 1H
NMR (CD2Cl2, 25 ꢂC, TMS, in ppm)
d
¼ 10.59 (dd, 1H, CH,
3JHeH ¼ 1.1 Hz, JPeH ¼ 1.1 Hz), ꢁ21.12 (dd, 2H, Hydride,
4
3JPeH ¼ 1.1 Hz, JHeH ¼ 1.1 Hz). P{1H} NMR (CD2Cl2, 25 ꢂC,
3
31
ref. 85% ortho-H3PO4)
d
¼ 80.57 (s,1P, PeAu). Mass Spec. EIþ/
MS m/z ¼ 1298 (Mþ).
NMR Analysis of the Reaction of Os3(CO)11(NCCH3) with (CH3)
Au(PPh3): 5.0 mg (0.005 mmol) of Os3(CO)11(NCCH3) were dissolved
in an NMR tube in CD2Cl2. 4.0 mg (0.007 mmol) of (CH3)Au(PPh3)
were added. The H NMR spectra were recorded as a function of time
and are shown in a series of overlays in Fig. 1. In the first spectrum
(5 min), two resonances had appeared at 0.86 and 0.95 ppm. This is
2. Experimental section
2.1. General data
attributed to an intermediate formulated as Os3(CO)11(CH3) (m-
AuPPh3), I1 which was formed by the elimination the NCCH3 ligand
of the Os3(CO)11(NCCH3) and the addition of one equivalent of (CH3)
Au(PPh3). The presence of two resonances indicates that I1 exists as
a mixture of two isomers I1-a and I1-b, see below. There was also a
minor, but important, resonance at ꢁ3.62 ppm. This is attributed to
Reagent grade solvents were dried by the standard procedures
and were freshly distilled prior to use. All reactions were performed
under a nitrogen atmosphere. Infrared spectra were recorded on a
Thermo Nicolet Avatar 360 FT-IR spectrophotometer. 1H NMR and
31P NMR spectra were recorded on a Varian Mercury 300 spec-
trometer operating at 300.1 MHz. Mass spectrometric (MS) mea-
surements performed by a direct-exposure probe using electron
an intermediate formulated as Os3(CO)10(m-CH3) (m-AuPPh3), I2
having an agostically coordinated methyl group that was formed by
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R.D. Adams et al. / Journal of Organometallic Chemistry xxx (2015) 1e13
3
Fig. 1. 1H NMR spectra of the reaction of Os3(CO)11(NCCH3) with (CH3)Au(PPh3) at room temperature in CD2Cl2 solvent as a function of time.
the loss of one CO ligand from I1 [9,21]. Finally, I2 converts to
compound 2 via decarbonylation and subsequent CeH bond
cleavage at the methyl group while I1 transforms to compound 1
through methyl migration/CO insertion steps.
NMR Analysis of the Reaction of Os3(CO)10(NCCH3)2 with (CH3)
Au(PPh3): 5.0 mg (0.005 mmol) of Os3(CO)10(NCCH3)2 were dis-
solved in an NMR tube in CD2Cl2. (CH3)Au(PPh3) of 4.0 mg
(0.007 mmol) were added. The spectra were recorded as a function
of time and are shown in a series of overlays in Fig. 2.
b) Reaction of Os3(CO)10(NCCH3)2 with (CH3)Au(PPh3): 77.0 mg
(0.0825 mmol) of Os3(CO)10(NCCH3)2 were added to a 50 mL
three neck flask containing a solution of (CH3)Au(PPh3) 44.3 mg
(0.093 mmol) in 30 mL methylene chloride. The reaction
mixture was to stir for 6 h at 25 ꢂC. The solvent was then
removed in vacuo, and the product was isolated by TLC by using
pure hexane solvent to yield in order of elution: 49 mg of 2 (64%
In the first spectrum (6 min) a major resonance had appeared
at ꢁ3.62 ppm. This is attributed to an intermediate formulated as
Os3(CO)10(m-CH3) (m-AuPPh3), I2 having an agostic coordinated
methyl group that was formed by the elimination the two NCCH3
ligands of the Os3(CO)10(NCCH3)2 and the addition of one equiva-
lent of (CH3)Au(PPh3), see also Fig. 1. This resonance decreases in
intensity with time. Two small resonances at 4.55 ppm (dt,
3
4
yield), 5.0 mg of Os3(CO)10
(
m
-Cl) (
m
-AuPPh3), (6.5% yield) and
2JHeH ¼ 12 Hz, JHeH ¼ 2 Hz, JPeH ¼ 2 Hz) and 5.62 ppm (dd,
3.8 mg of 1 (5% yield).
2JHeH ¼ 12 Hz, 3JHeH ¼ 3 Hz) and a hydride resonance at ꢁ21.19 ppm
Fig. 2. 1H NMR spectra of the reaction of Os3(CO)10(NCCH3)2 with (CH3)Au(PPh3) at room temperature as a function of time.
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R.D. Adams et al. / Journal of Organometallic Chemistry xxx (2015) 1e13
(t, 2JHeH ¼ 3 Hz, 3JPeH ¼ 3 Hz) had also appeared at 6 min and grow
2.5. Conversions of compound 4 to 1 and 2
with time. These are attributed to a second intermediate formu-
lated as Os3(CO)10
(
m
-CH2) (
m
-H) (
m
-AuPPh3), I3. Additional reso-
a) Thermal Treatment: 16.3 mg (0.012 mmol) of (CH3)
Os3(CO)12AuPPh3, 4 was dissolved in 30 mL heptane solvent in a
50 mL three neck flask. The solution was then heated to reflux
(97 ꢂC) for 2.5 h. The solvent was then removed in vacuo and the
products were then isolated by TLC by using a pure hexane
nances appear at 20 min at 4.61 ppm (2JHeH ¼ 8 Hz) and 6.32
(2JHeH ¼ 8 Hz) and grow with time. This compound is formulated as
Os3(CO)10(m-CH2) (m-AuPPh3)2, I4 and it can be isolated by TLC in a
low yield. Additional spectra for I4: IR nCO (cmꢁ1 in hexane):
2077(w), 2032(m), 2016(s), 2004(s), 1996(sh), 1961(m), 1937(w).
solvent to yield: 8.2 mg of yellow Os3(CO)10(m-O]CCH3)
(AuPPh3), 1, (50% yield), 1.6 mg of colorless 2, (10% yield), and
0.34 mg of light yellow Os3(CO)12, (2% yield).
31P{1H} NMR (CD2Cl2, 25 ꢂC, 85% ortho-H3PO4)
d
¼ 82.94 (s,2P,
PeAu); Mass Spec. Pos. Ion ES/MS m/z. 1785(Mþ). I4 is believed to
be formed by a reaction of I3 with an additional quantity of (CH3)
Au(PPh3) that also results in the formation of CH4 which is also
observed in the spectrum at 0.21 ppm at this time. Finally, small
b) Irradiation with Room Light: 5.0 mg of 4 was dissolved in an
NMR tube in CD2Cl2. The sample was exposed to room light for 9
days at room temperature. A control experiment was performed
by dissolving same amount of 4 in an NMR tube in CD2Cl2, but
the tube was fully covered by aluminum foil to prevent exposure
room light. Based on the 1H NMR analyses, the sample exposed
to room light showed over 90% conversion of 4 to compounds 1
and 2 in a 10/1 ratio, respectively, after 9 days. The sample
maintained in the dark showed less than 2% loss of 4 and only
traces of compound 1 were detected after the 9 day period.
resonances are observed to form at
(s, hydride) (not shown in Fig. 2) which are attributed to a final
product formulated as Os3(CO)9(m3-CH) ( -H) (AuPPh3)2, 3. Com-
pound 3 can also be obtained from the thermal transformation of 2
and was fully characterized including single-crystal X-ray
d
¼ 11.94 (s, 1H, CH) and ꢁ22.50
m
a
diffraction analysis, see below. During the entire reaction period,
the resonances of compound 2, 10.59 ppm and ꢁ21.12 ppm, (the
major product, see above) are forming and growing in intensity.
2.5.1. Crystallographic analyses
X-ray intensity data were measured by using a Bruker SMART
2.3. Synthesis of Os3(CO)9(m3-CH) (
m-H) (m-AuPPh3)2, 3 from 2
APEX CCD-based diffractometer by using Mo
Ka radiation
(l
¼ 0.71073 Å). The raw data frames were integrated with the
A solution of 2 was heated to reflux in octane solvent. 22.9 mg of
2 is dissolved in 30 mL hot octane at a 50 mL three neck flask. The
solution was heated to reflux for 4 h (125 ꢂC). The solvent was
removed in vacuo, and the product was then isolated by TLC using a
5:1 hexane/methylene chloride solvent mixture. 9.0 mg of 2 is
recovered after the reaction, while 7.6 mg (55% yield) of
SAINTþ program by using a narrow-frame integration algorithm
[22]. Corrections for Lorentz and polarization effects were also
applied by using SAINTþ. An empirical absorption correction based
on the multiple measurement of equivalent reflections was applied
by using the program SADABS. All structures were solved by a
combination of direct methods and difference Fourier syntheses,
and refined by full-matrix least-squares on F2 by using the SHELXTL
software package [23]. Crystallographic data for compounds 1e6
are listed in Table 1.
Os3(CO)9(m3-CH) (
m
-H) (AuPPh3)2, 3 and 2.4 mg (17% yield) of
Os3(CO)9(m3-CH) (
m
-H)3 were isolated. Spectral data for 3: IR nCO
(cmꢁ1 in hexane): 2070(s), 2045(s), 2031(s), 1987(m), 1965(m),
1922(w). 1H NMR (CD2Cl2, 25 ꢂC, TMS, in ppm)
d
¼ ꢁ22.50 (s, 1H,
hydride),
ortho-H3PO4)
d
¼ 11.94 (s, 1H, CH); 31P{1H} NMR (CD2Cl2, 25 ꢂC, 85%
2.5.2. Computational analyses
All calculations were performed with ADF2014 program by us-
ing the PBEsol functional with scalar relativistic correction and
d
¼ 82.93 (s,2P, PeAu); Mass Spec. EIþ/MS m/z.1756.
valence triple-
z
þpolarization, relativistically optimized TZP basis
sets, with small frozen cores. All computations were done in gas
phase and the triphenylphosphine ligand geometry was con-
strained throughout the calculations. This choice of computational
model was based on prior testing of various functionals and basis
sets [16]. The PBEsol functional, which was originally developed
primarily for solids, was shown to be superior to other functionals
in the PBE family in the structural parameters of large organic
systems [24] and for metal clusters [25]. For the molecular orbitals
and energy calculations of intermediates I1, I2, I3 and I5, geometry
optimizations (GO) were performed with ADF2014 program [26] by
using the PBEsol functional with scalar relativistic correction and
2.4. Synthesis of (CH3)Os3(CO)12(AuPPh3) 4, (CH3)
Os2(CO)8(AuPPh3), 5 and Os(CO)4PPh3, 6
35 mg (0.027 mmol) of 2 was dissolved in warm octane, trans-
ferred to a Parr high pressure reactor and then filled with CO to 600
psi. The reactor was heated in an oil bath to 100 ꢂC for 4 h and then
allowed to cool to room temperature. The solvent was removed in
vacuo, and the product was isolated by TLC by using a hexane/
methylene chloride solvent mixture (6/1, v/v) to yield in order of
elution: 0.7 mg, of Os(CO)4(PPh3), 6, (2% yield); 2.5 mg (CH3)
Os2(CO)8(AuPPh3), 5, (7% yield); 18.4 mg (CH3)Os3(CO)12(AuPPh3), 4
(53% yield); and 1.6 mg compound 1 (5% yield) and Os3(CO)12 (2.5%
yield). Spectral data for 4: IR nCO (cmꢁ1 in hexane): 2115(w),
2071(m), 2045(w), 2023(s), 2004(s), 1990(m), 1983(w), 1973(w),
valence triple-
z
þpolarization, relativistically optimized TZP basis
sets, with small frozen cores. The molecular orbitals for compounds
2 and 4 and their energies were determined by a geometry opti-
mized calculations that were initiated by using the structures as
determined from the crystal structure analyses. The energy profile
was computed by scanning the defined reaction coordinate with
full geometry optimization of the other degrees of freedom. The
transition states are defined as energy maxima along the reaction
coordinate scan. The determination of the energy for the transition
states is somewhat imprecise because analytic Hessians used to
search for transition states in the ADF library failed to calculate the
exact transition states. In the transition state search calculation, the
transition state geometry reverts back to its intermediate by energy
minimization. Our approximate transition state energies, see
1963(w). 1H NMR (CD2Cl2, 25 ꢂC, TMS, in ppm)
31P{1H} NMR (CD2Cl2, 25 ꢂC, 85% ortho-H3PO4)
d
¼ 0.23 (s, 3H, CH3),
d
¼ 55.31 (s,1P,
PeAu); Mass Spec. EIþ/MS m/z. 1382(Mþ), 1354 (MþꢁCO), 1326
(Mþ-2CO), 1298 (Mþꢁ3 CO). Spectral data for 5: IR nCO (cmꢁ1 in
hexane): 2103(w), 2050(s), 2019(s), 2007(w), 2000(m), 1992(w),
1988(w), 1977(m), 1972(sh). 1H NMR (CD2Cl2, 25 ꢂC, TMS, in ppm)
d
¼ 0.26 (s, 3H, CH3), 31P{1H} NMR (CD2Cl2, 25 ꢂC, 85% ortho-H3PO4)
d
¼ 55.04 (s,1P, PeAu); Mass Spec. EIþ/MS m/z. 1080 (Mþ). Spectral
data for 6: IR nCO (cmꢁ1 in hexane): 2062(s), 1983(m), 1945(s), 31P
{1H} NMR (CD2Cl2, 25 ꢂC, 85% ortho-H3PO4)
d
¼ 7.88 (s,1P, PPh3).
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R.D. Adams et al. / Journal of Organometallic Chemistry xxx (2015) 1e13
5
Table 1
Crystallographic data for compounds 1e6.
Compound
1
2
3
Empirical formula
Formula weight
Crystal system
Lattice parameters
a (Å)
Os3AuPO11C30H18
1353.08
Triclinic
Os3AuPO9C28H18
1297.06
Orthorhombic
Os3Au2P2O9C46H32
1755.19
Triclinic
9.3218(7)
13.0462(10)
14.3573(11)
93.720(2)
94.647(1)
104.564(1))
1677.8(2)
P1 (#2)
2
2.25
7.081
294(2)
52.82
17.1603(5)
14.3830(5)
25.7235(8)
90.00
90.00
90.00
6349.0(3)
Pbca (#61)
8
2.772
7.081
12.0351(6)
17.9004(9)
22.0930(11)
89.326(1)
78.026(1)
89.105(1)
4655.3(4)
P1 (#2)
4
2.504
7.081
294(2)
55.94
b (Å)
c (Å)
a
b
g
(deg)
(deg)
(deg)
V (Å3)
Space group
Z value
rcalc (g/cm3)
m
(Mo K
Temperature (K)
Qmax (ꢂ)
No. Obs. (I > 2
No. parameters
a
) (mmꢁ1
)
294(2)
52.48
5249
389
2
s
(I))
5091
416
12496
1123
Goodness of fit (GOF)
Max. shift in cycle
1.054
0.000
0.0535; 0.1430
Multi-scan
1.000/0.141
2.927
1.106
0.003
0.0357; 0.0677
Multi-scan
1.000/0.268
1.618
0.978
0.001
0.0449; 0.0865
Multi-scan
1.000/0.475
1.861
Residualsa: R1; wR2
Absorption correction,
Max/min
Largest peak in final diff. map (eꢁ/Å3)
Compound
4
5
6
Empirical formula
Formula weight
Crystal system
Lattice parameters
a (Å)
Os3AuPO12.5C31H16.5
1387.48
Monoclinic
Os2AuPO8C27H18
1078.82
Monoclinic
Os1PO4C22H15
564.54
Triclinic
9.9834(5)
16.1827(8)
22.3716(11)
90.00
90.374(1)
90.00
3614.2(3)
P2(1)/n (#14)
4
2.550
7.081
294(2)
52.46
12.8857(7)
17.9703(9)
13.8285(7)
90.00
113.0920(10)
90.00
2945.6(3)
P2(1)/n (#14)
4
2.336
7.081
294(2)
54.12
9.9300(9)
10.5341(9)
10.8638(9)
91.132(2)
112.736(2)
93.529(2)
1044.93(16)
P1 (#2)
2
1.794
7.081
294(2)
55.5
b (Å)
c (Å)
a
b
g
(deg)
(deg)
(deg)
V (Å3)
Space group
Z value
rcalc (g/cm3)
m
(Mo K
Temperature (K)
Qmax (ꢂ)
No. Obs. (I > 2
No. parameters
a
) (mmꢁ1
)
2
s
(I))
6246
444
5543
353
4471
313
Goodness of fit (GOF)
Max. shift in cycle
1.063
0.000
0.0551; 0.1513
Multi-scan
1.000/0.322
2.808
1.026
0.019
0.0328; 0.0833
Multi-scan
1.000/0.465
2.041
1.099
0.001
0.0281; 0.0613
Multi-scan
1.000/0.638
1.080
Residualsa: R1; wR2
Absorption correction,
Max/min
Largest peak in final diff. map (eꢁ/Å3)
a
R ¼ Shkl(rrFobsrꢁrFcalcrr)/ShklrFobsr; Rw ¼ [Shklw(rFobsrꢁrFcalcr)2/ShklwF2
]
1/2; w ¼ 1/
s
2(Fobs); GOF ¼ [Shklw(rFobsrꢁrFcalcr)2/(ndata e nvari)]1/2
.
obs
below, can be safely regarded as upper limits for the true ones. For
the first transition state (TS1) scan which lies between intermediate
I2 and intermediate I3, it was performed by using the H(1) e Os(3)
distance as reaction coordinate. The H(1) is from one of methyl CeH
groups that is agostically coordinated to Os(1). For the second
transition state (TS2) step, I3 to I5, the reaction coordinate was
developed by progressive removal of the axial CO ligand from the
third osmium atom Os(3). For the third transition state (TS3) step,
I5 to 2, it was performed by using the H(2) e Os(2) distance in I5 as
reaction coordinate, the H(2) is from one of the methylene CeH
groups that is agostically coordinated to Os(3). The intermediates
are defined as energy minima along the scan coordinate and are
exact within the GO computational model. Electron densities at the
bond critical points were calculated by using the Bader Quantum
Theory of Atoms in Molecules (QTAIM) model [27].
3. Results and discussion
The reaction of Os3(CO)11(NCCH3) with (CH3)Au(PPh3) in CH2Cl2
yielded two new complexes: Os3(CO)10 -O]CCH3) ( -AuPPh3), 1
in 37% yield and Os3(CO)9(m3-CH)( -H)2( -AuPPh3), 2 33% yield. In
(
m
m
m
m
the reaction of Os3(CO)10(NCCH3)2 with (CH3)Au(PPh3) at room
temperature for 4 h, the yield of compound 2 was increased to 64%
at the expense of 1 (5%) because Os3(CO)10(NCCH3)2 contains two
labile NCCH3 ligands and fewer CO ligands. Compounds 1 and 2
were both characterized crystallographically, and ORTEP diagrams
of their molecular structures are shown in Figs. 3 and 4, respec-
tively. Complex 1 contains a triangular cluster of three osmium
atoms with a bridging acetyl ligand and a bridging Au(PPh3) group
across the Os(1)ꢁOs(2) bond. The non-bridged osmiumeosmium
bond distances, Os(1) e Os(3) ¼ 2.8716(7) Å and Os(2)
e
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6
R.D. Adams et al. / Journal of Organometallic Chemistry xxx (2015) 1e13
Os(3) ¼ 2.8664(8) Å are nearly identical and are similar to the
osmiumeosmium bond distances found in Os3(CO)12 of 2.877(3) Å
[28]. The acetyl-bridged osmiumeosmium bond distance is
significantly longer, Os(1) e Os(2) ¼ 2.9339(7) Å than the other Os
e Os bonds. Longer OseOs bond distances were also found in two
previously reported triosmium cluster complexes containing
bridging acetyl ligands: Os3(CO)9(
m-O]CCH3)(m-H)(C2H4), 2.934(1)
Å [29] and Os3(CO)9( -O]CCH3) (H)[CH3C(OCH3)], 2.909(2) Å [30].
m
The Au(PPh3) group bridges the same Os e Os bond as the acetyl
ligand. Assuming that the Au(PPh3) group is one-electron donor
and acetyl ligand serves as a three-electron donor, then compound
1 contains a total of 48 valance electrons and all metal atoms
formally have 18 electron configurations.
Compound 2 contains a triangle of three osmium atoms with a
triply bridging methylidyne ligand and is structurally similar to the
triosmium cluster complex Os3(CO)9(m3-CH) (
that it has one bridging Au(PPh3) group in the place of one of the
bridging hydrido ligands of Os3(CO)9(m3-CH) ( -H)3. Both of these
m-H)3 [31], except
m
methylidyne complexes contain 48 valence electrons and the Os e
Os and Os e C(1) bond distances in both compounds are very
similar: for 2: Os(1)
e
Os(2)
¼
2.8967(4) Å, Os(1) e
Os(3) ¼ 2.8943(4) Å, Os(2) e Os(3) ¼ 2.8910(5) Å; Os(1) e
C(1) ¼ 2.093(7) Å, Os(2) e C(1) ¼ 2.077(7) Å, Os(3) e C(1) ¼ 2.112(8)
Å, and for Os3(CO)9(m3-CH) (
C(ave) ¼ 2.101(2) Å.
m
-H)3: Os e Os(ave) ¼ 2.893(2) Å; Os e
Fig. 3. ORTEP diagram of the molecular structure of Os3(CO)10(m-O]CCH3) (m-AuPPh3),
It is proposed that compounds 1 and 2 are formed by two
competing processes, see Scheme 1. In both cases the first step
appears to be a displacement of the NCCH3 ligand that is accom-
panied by the oxidative addition of the Au e C bond of the (CH3)
Au(PPh3) to one of the osmium atoms. An initial intermediate
formulated “Ph3PAuOs3(CO)11(CH3)”, I1 is anticipated in the reac-
tion of Os3(CO)11(NCCH3) with (CH3)Au(PPh3). 1H NMR spectra of
the reaction solution showed an initial formation of two reso-
1, showing 30% thermal ellipsoid probability. The hydrogen atoms in phenyl groups are
omitted for clarity. Selected interatomic bond distances (Å) and angles (ꢂ) are as
follow: Os(1)
Os(3) ¼ 2.8664(8), Os(1) e Au(1) ¼ 2.7667(7), Os(2) e Au(1) ¼ 2.7833(7), Os(2) e
O(1) 2.083(11), Os(1) C(1) 2.097(14), C(1) C(2) 1.45(3), C(1)
e
Os(2)
¼
2.9339(7), Os(1)
e
Os(3)
¼
2.8716(7), Os(2) e
¼
e
¼
e
¼
e
O(1) ¼ 1.281(17); C(1) e Os(1) e Os(2) ¼ 66.3(4), O(1) e Os(2) e Os(1) ¼ 67.1(3), Os(1)
e C(1) e O(1) ¼ 113.5(9), C(1) e O(1) e Os(2) ¼ 113.1(9).
nances,
d
¼ 0.95 and 0.86, that could be attributed to complexes
with terminally-coordinated methyl groups, see Scheme 1.
It appears that I1 exists as a mixture of two isomers, I1-a and I1-
b. There are few examples of well characterized triosmium cluster
complexes containing terminally coordinated methyl ligands, but
the compound Os3(CO)9[
good example which showed the resonance of the Os bonded
methyl group at
dergoes methyl migration/insertion of a CO ligand into the OseCH3
bond resulting in the formation of an acetyl ligand that ultimately
becomes the bridging acetyl ligand in 1 as indicated by the for-
m-h m-CH2) (CH3) is one
2-C7H3(2-CH3)NS](
d
¼ 1.03 [32]. Intermediate I1 subsequently un-
mation of its acetyl methyl resonance at
d
¼ 2.19 in the 1H NMR
spectrum. Alternatively, I1 can eliminate CO and proceed to 2 via a
series of CH bond cleavage steps with the loss of an additional CO
ligand as observed by the accompanying appearance of its 1H NMR
resonances at
d
¼ 10.59 (dd), ꢁ21.11 (dd).
Additional details about this transformation were obtained by a
1H NMR study of the reaction of Os3(CO)10(NCCH3)2 with (CH3)
Au(PPh3). The 1H NMR spectra of the reaction of Os3(CO)10(NCCH3)2
with (CH3)Au(PPh3) as a function of time are shown above in Fig. 2.
The spectrum taken at 6 min shows a prominent resonance at
d
¼ ꢁ3.62. This is attributed to an intermediate triosmium species
formulated as Os3(CO)10 -AuPPh3) ( -CH3), I2 containing an
(m
m
agostic-coordinated bridging methyl group, see Scheme 2.
Fig. 4. ORTEP diagram of the molecular structure of Os3(CO)9(m3-CH)
(m-H)2(m-
The assignments of the methyl, methylene, and methylidyne
ligand resonances in this work are firmly established based on the
elegant work by Shapley in his studies of the Os3(CO)9(“CH4”)
family of compounds [9,21]. Agostically, coordinated methyl groups
exhibit resonance shifts upfield from TMS [15]. In the next step, the
agostic CH bond of the methyl group is cleaved and another in-
AuPPh3), 2, showing 25% thermal ellipsoid probability. The hydrogen atoms in phenyls
are omitted for clarity. Selected interatomic bond distances (Å) and angles (ꢂ) are as
follow: Os(1)
e
Os(2)
¼
2.8967(4), Os(1)
e
Os(3)
¼
2.8943(4), Os(2) e
Os(3) ¼ 2.8910(5), Os(2) e Au(1) ¼ 2.7786(4), Os(1) e Au(1) ¼ 2.7468(4), Os(1) e
C(1)
H(2)
¼
¼
2.093(7), Os(2)
1.908(5), Os(3)
e
e
C(1)
H(2)
¼
¼
2.077(7), Os(3)
1.823(5), Os(2)
e
e
C(1)
H(3)
¼
¼
2.112(8), Os(1)
1.630(6), Os(3)
e
e
H(3) ¼ 1.784(5), C(1) e H(1) ¼ 0.911(5); Os(1) e Os(2) e Os(3) ¼ 60.011(11), Os(2) e
termediate formulated as Os3(CO)10
(m-CH2) (m-H) (m-AuPPh3), I3,
Os(1)
e
Os(3)
¼
59.897(12), Os(1)
e
C(1)
e
Os(2)
¼
88.0(3), Os(2) e C(1) e
Os(3) ¼ 87.3(3), Os(1) e C(1) e Os(3) ¼ 87.0(3).
with inequivalent methylene protons is formed showing
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R.D. Adams et al. / Journal of Organometallic Chemistry xxx (2015) 1e13
7
Scheme 1. Os3(CO)11(NCCH3) reaction pathways with (CH3)Au(PPh3) at room temperature.
Scheme 2. Schematic of the reaction of Os3(CO)10(NCCH3)2 with (CH3)Au(PPh3).
2
3
resonances at 4.55 ppm (dt, JHeH ¼ 12 Hz, JHeH ¼ 2 Hz,
low-field resonance in 3 is due to a triply bridging methylidyne
ligand formed by the loss of a CO ligand from I4 and a CH activation
of one of the CH bonds of the bridging methylene ligand, see
Scheme 2. Compound 3 can also be obtained independently in a
good yield (55%) together with the known compound of
4JPeH ¼ 2 Hz) and 5.62 ppm (dd, 2JHeH ¼ 12 Hz, 3JHeH ¼ 3 Hz) and a
hydride resonance at ꢁ20.19 ppm is formed. This step was analyzed
computationally, see below. During this period, the resonances of
compound 2 (the major final product) appear and grow in intensity.
Compound 2 is formed by the loss of a CO ligand from I3 and a CeH
activation of one of the CH bonds of the bridging CH2 ligand. This
transformation was also analyzed computationally, see below.
Additional resonances appear at 20 min into the reaction at
4.61 ppm (2JHeH ¼ 8 Hz) and 6.32 (2JHeH ¼ 8 Hz) ppm. These are
Os3(CO)9(m3-CH) (m
-H)231 (17% yield) by thermal disproportionation
of compound 2 at 125 ꢂC in octane solvent. Compound 3 was
further characterized by single-crystal X-ray diffraction analysis
and an ORTEP diagram of its molecular structure is shown in Fig. 5.
Compound 3 is structurally similar to that of 2 with a triply-
bridging CH (methylidyne) ligand except that it has a second
bridging Au(PPh3) group in place of one of the bridging hydride
ligands in 2. An interesting structural feature is the existence of a
significant Au e Au bonding interaction between the two Au(PPh3)
groups, Au(1) e Au(2) ¼ 3.0559(7) Å. This Au e Au distance is even
shorter than those observed in other structurally similar
attributed to an intermediate formulated as Os3(CO)10(m-CH2)(m-
AuPPh3)2, I4. I4 can be isolated in low yield (approx. 2%) by TLC and
was shown to contain two Au(PPh3) groups on the basis of its mass
spectrum, m/z ¼ 1785. Finally, small resonances appear at
(methylidyne) and ꢁ22.50 (hydride) which are attributed to a final
product formulated as Os3(CO)9(m3-CH) ( -H) ( -AuPPh3)2, 3. The
d
¼ 11.94
m
m
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8
R.D. Adams et al. / Journal of Organometallic Chemistry xxx (2015) 1e13
Fig. 6. ORTEP diagram of the molecular structure of 4 showing 30% thermal ellipsoid
probabilities. The hydrogen atoms in phenyl groups are omitted for clarity. Selected
interatomic bond distances (Å) and angles (ꢂ) are as follows: Os(1) e Os(2) ¼ 2.9326(7),
Os(2) e Os(3) ¼ 2.9058(7), Os(1) e Au(1) ¼ 2.6389(7), Os(3) e C(1) ¼ 2.11(2); Os(1) e
Fig. 5. ORTEP diagram of the molecular structure of Os3(CO)9(m3-CH)
AuPPh3)2, 3, showing 15% thermal ellipsoid probability. The hydrogen atoms on the
phenyl groups are omitted for clarity. Selected interatomic bond distances (Å) are as
(m-H) (m-
Os(2)
e
Os(3)
¼
175.80(3), C(1)
e
Os(3)
e
Os(2)
¼
87.3(5), Au(1) e Os(1) e
follow: Os(1)
e
Os(2)
¼
2.9079(7), Os(1)
e
Os(3)
¼
2.9121(7), Os(2) e
Os(2) ¼ 83.296(19).
Os(3) ¼ 2.9209(7), Os(1) e Au(1) ¼ 2.8055(6), Os(3) e Au(1) ¼ 2.7481(6), Os(2) e
Au(2) ¼ 2.7777(7), Os(3) e Au(2) ¼ 2.7472(7), Au(1) e Au(2) ¼ 3.0559(7), Os(1) e
C(1)
¼
2.103(10), Os(2)
e
C(1)
¼
2.117(11), Os(3)
e
C(1)
¼
2.075(11), Os(1) e
H(3) ¼ 1.78(2), Os(2) e H(3) ¼ 1.80(2), C(1) e H(1) ¼ 0.98(2).
observed products.
When compound 2 was heated under 600 psi CO in a solution of
octane at 100 C, it was carbonylated and transformed into three
new compounds, (CH3)Os3(CO)12AuPPh3 4, in 53% yield, (CH3)
Os2(CO)8AuPPh3, 5, in 7% yield and Os(CO)4(PPh3) [36] 6 in 2% yield.
Two other compounds 1 and Os3(CO)12 were also isolated in low
yields, 6% and 2.5% yield respectively. An ORTEP diagram of the
molecular structure of 4 is shown in Fig. 6.
polynuclear metal carbonyl complexes containing two Au(PPh3)
groups, e. g. Ru3(CO)9(m3-COCH3) -AuPPh3)2, Au
(
m
-H)
(
m
e
Au 3.176(l) [33], and Ir4(CO)11(m-AuPPh3)2, Au
¼
Å
e
Au ¼ 3.2464(13) [34] and Os4(CO)13 -AuPEt3)2, Au e Au ¼ 3.128 (l)
(m
[35]. Overall, the cluster of 3 can be viewed as a distorted square-
pyramidal structure with two osmium and two gold atoms in the
base and one osmium Os(3) at the apex.
Compound 4 contains an open cluster of three osmium atoms
having only two Os e Os bonds. The Os e Os distances, Os(1) e
Os(2) ¼ 2.9326(7) Å and Os(2) e Os(3) ¼ 2.9058(7) Å, are similar to
The thermal conversion of compound 2 into 3 and Os3(CO)9(m3
-
CH) ( -H)3 is formally a disproportionation reaction. A possible
m
those found in the linear complex IOs3(CO)12I, Os(1)
e
mechanism for this process is shown in Scheme 3. Competing
reductive eliminations of H2 and “HAu(PPh3)”, could generate un-
Os(2) ¼ 2.9157(2) Å [37]. The Os e Os e Os angle is almost linear,
Os(1) e Os(2) e Os(3) ¼ 175.80(3)ꢂ. A methyl group is terminally
coordinated to Os(3), Os(3) e C(1) ¼ 2.11(2) Å and a terminally
coordinated gold(triphenylphosphine) group is bonded to Os(1),
saturated species such as Os3(CO)9(m3-CH)
Os3(CO)9(m3-CH) ( -H), respectively, which could, in turn, oxida-
tively re-add HAu(PPh3) [17b] and H2, respectively, to yield the
(m-AuPPh3) and
m
Os(1)
e
Au(1)
¼
2.6389(7) Å, almost perpendicular to the
̊
Scheme 3. A proposed scheme for the disproportionation of 2.
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R.D. Adams et al. / Journal of Organometallic Chemistry xxx (2015) 1e13
9
Fig. 8. ORTEP diagram of the molecular structure of Os(CO)4(PPh3), 6, showing 25%
Fig. 7. ORTEP diagram of the molecular structure of (CH3)Os2(CO)8(AuPPh3), 5,
showing 30% thermal ellipsoid probability. The hydrogen atoms in phenyls are omitted
for clarity. Selected interatomic bond distances (Å) and angles (ꢂ) are as follows: Os(1)
e Os(2) ¼ 2.9617(4), Os(1) e Au(1) ¼ 2.6508(4), Os(2) e C(1) ¼ 2.196(10); C(1) e Os(2)
e Os(1) ¼ 90.1(3), Au(1) e Os(1) e Os(2) ¼ 86.941(11).
thermal ellipsoid probability. The hydrogen atoms in phenyls are omitted for clarity.
Selected interatomic bond distances (Å) and angles (ꢂ) are as follows: Os(1)
e
P(1)
¼
2.3904(10), Os(1)
e
C(1)
¼
1.914(5), Os(1)
e
C(2)
¼
1.913(5), Os(1)
e
C(3) ¼ 1.915(4), Os(1) e C(4) ¼ 1.940(5). C(1) e Os(1) e P(1) ¼ 87.99(14), C(1) e Os(1)
e C(4) ¼ 91.3(2).
triosmium chain, Au(1) e Os(1) e Os(2) ¼ 83.296(19)ꢂ. The methyl
as found in intermediate I1. The third CO addition leads to cleavage
of OseOs and Os e Au bonds with the Au(PPh3) group shifting to a
terminal position when the Os3 cluster opens to yield 4. Interest-
ingly, it was found that the compounds 5 and 6 were not formed in
the reaction of 4 with CO in the presence of PPh3. It is possible that
they were formed directly from intermediate I1 by routes involving
cleavages of different metal e metal bonds. For example, carbon-
ylation of I1 by cleavage of the Os(2) - Au and Os(1) e Os(2) bonds
would lead to 4 where the CH3 and Au(PPh3) groups are separated
by an Os(CO)4 grouping. On the other hand, cleavage of the Os(1) e
Os(3), Os(2) e Os(3) and Os(2) e Au bonds would lead to 5, where
the CH3 and Au(PPh3) groups lie on adjacent Os(CO)4 groups, and to
6, see Scheme 4.
Compound 4 was thermally converted back to a mixture of 1
(50% yield) and 2 (10% yield) by heating to 97 ꢂC for 2 h in heptane
solvent. Alternatively, compound 4 was converted back to 1 and 2
in a 10/1 ratio in greater than 90% conversion under irradiation with
room light at room temperature over a period of 9 days.
In order to learn more about the mechanisms of the decarbon-
ylation 4 to 2 (and in turn the microreverse of the carbonylation of 2
to 4) in this system, a series of ADF-based DFT computational an-
alyses were performed. The calculations were initiated by obtaining
a geometry-optimized structure of the compound formulated
resonance in 4 appears at
d
¼ 0.23 in the 1H NMR spectrum. The
methyl and gold(triphenylphosphine) groups serve as one electron
donors, and the three osmium atoms contain a total of 50 valence
electrons; thus, with two Os e Os bonds all of the metal atoms are
formally electronically saturated.
An ORTEP diagram of the molecular structure of 5 is shown in
Fig. 7.
Compound 5 contains only two osmium atoms that are joined
by a Os e Os single bond, Os(1) e Os(2) ¼ 2.9617(4) Å. A terminally-
coordinated methyl group and a Au(PPh3) group are coordinated to
the osmium atoms Os(2) and Os(1), respectively, Os(2)
e
C(1) ¼ 2.196(10) Å, Os(1) e Au(1) ¼ 2.6508(4) Å, perpendicular to
the Os e Os vector, C(1) e Os(2) e Os(1) ¼ 90.1(3)ꢂ, Au(1) e Os(1) e
Os(2) ¼ 86.941(11)ꢂ. The methyl resonance in 5 appears at
¼ 0.26
d
in the 1H NMR spectrum. There are eight linear terminal carbonyl
ligands. The CO ligands cis to the metal e metal bond have adopted
a staggered rotational conformation. The total valence electron
count for the metal atoms in 5 is 34, i.e. both metal atoms have 18
electron configurations.
An osmium group was eliminated from 2 in the formation of 5 in
this carbonylation reaction. It observed in the form of the complex
Os(CO)4(PPh3), 6 which contains only one osmium atom that has
also captured a PPh3 ligand that must have been dissociated from
an AuPPh3 group. Compound 6 was characterized crystallographi-
cally and an ORTEP diagram of its molecular structure is shown in
Fig. 8. The metal atom has a trigonal bipyramidal structure, as ex-
pected for a structure with five ligands, and the PPh3 ligand oc-
cupies an axial position, Os(1) e P(1) ¼ 2.3904(10) Å.
above as Os3(CO)11(CH3) (m-AuPPh3), I1 containing a 48 electron
triangular cluster of three osmium atoms that is formed by the loss
of a CO ligand from 4. The DFT refined structure of I1 contains a
terminally coordinated methyl group, a bridging Au(PPh3) group
and two bridging CO ligands, Scheme 5.
The structure I1 lies 17.3 kcal/mol higher in energy than 4, see
Fig. 9 which shows and energy profile of the overall reaction.
Compound I1 loses one CO ligand at the neighboring osmium atom
of the gold-bridged Os e Os bond and is transformed to I2 which
contains an agostically coordinated bridging methyl group across
the gold-bridged Os e Os bond. Intermediate I2 lies 23.1 kcal/mol
The first addition of CO to 2 presumably induces shifts the two
hydrido ligands back to the methylidyne ligand of 2 leading to the
agostic-bridged methyl intermediate I2 (shown) via the methylene/
hydride intermediate I3, not shown, see Scheme 4. The second CO
addition leads to a shift of the methyl group to a terminal position
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10
R.D. Adams et al. / Journal of Organometallic Chemistry xxx (2015) 1e13
Scheme 4. A schematic of the transformations of 2 by the addition of CO.
Scheme 5. A schematic of the transformations of 4 to 2 by the elimination of CO ligands. The Red atoms and bonds show where the ligand eliminations occurred in the
computational analyses.
higher in energy than I1. The OseC and OseH distances to the
agostically coordinated C e H bond are 2.44 Å and 1.96 Å, respec-
tively. The CeH bond distance of the agostically coordinated C e H
bond is 1.16 Å in length. The blue contour of HOMO-21 of I2 shows
the nature of the bonding of the agostically coordinated CeH group
to the osmium atom Os(1), see Fig. 10. The CeH bond forms a three-
center interaction with the osmium atom in the left hand side in
Fig. 10. In order to obtain evidence about the character of the metal
e agostic CH bond interactions, the electron densities in this region
of the molecule were calculated by using the Quantum Theory of
the Atoms in Molecules (QTAIM) model [26].
The electron density at the QTAIM bond critical point (bcp) of
the agostically coordinated CeH bond, C(1)-H(1), was calculated to
be 0.213 eꢁ/Bohr3. This is slightly less than the values for the two
uncoordinated CeH bonds, C(1) e H(2), 0.261 eꢁ/Bohr3 and C(1) e
H(3) bonds, 0.265 eꢁ/Bohr3. There was a bcp between the osmium
atom Os(1) and the agostic hydrogen atom H(1), Os(1) … H(1)
having the electron density 0.063 eꢁ/Bohr3. Clearly, there was sig-
nificant shift of electron density from the agostic CeH bond toward
Fig. 9. An energy level diagram showing the energies of the intermediates and tran-
sition states for the decarbonylation of 4 to 2 along the reaction coordinate.
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R.D. Adams et al. / Journal of Organometallic Chemistry xxx (2015) 1e13
11
Fig. 10. The HOMO-21 of the intermediate I2 with sketch showing QTAIM electron densities (eꢁ/Bohr3) at selected bond critical points on the right.
the associated osmium atom Os(1). There was no bcp calculated
between Os(1) and C(1), but there was one between Os(2) e C(1) at
0.090 eꢁ/Bohr3. These numbers compare favorably with those
calculated for agostic CH bonding situations involving single metal
atoms [38].
shows the nature of a three-center Os e C e Os bonding interaction
between two osmium atoms of the cluster and the carbon atom of
the bridging CH2 group by the red contour, see Fig. 11.
The Os e C distances to the bridging CH2 group are both 2.19 Å
and are similar to those found for the triosmium complexes
Intermediate I2 was smoothly converted to the methylene/hy-
dride containing intermediate I3 via a 20 kcal/mol transition state
TS1 by cleavage of the agostic CH bond of the methyl group. The
hydrido ligand assumed a position bridging on the neighboring Os
e Os bond and the resultant methylene group assumed a bridging
position on the Au(PPh3) bridged Os e Os bond. The HOMO-4 of I3
Os3(CO)10
Os3(CO)9(PPh3)(
(
m
-CH2)(
m
-H)2, 2.151(5)
Å
and 2.150(6)
Å
and
m-CH2)(
m-H)2, 2.140(6) Å and 2.171(6) Å [20]. The
QTAIM electron densities at the OseC bcps to the bridging CH2
group for I3 were 0.101 eꢁ/Bohr3 and 0.100 eꢁ/Bohr3. The trans-
formation of I3 into 2 involves two steps: 1) loss of a CO ligand from
the CO-rich Os(CO)4 group which leads to an intermediate I5
Fig. 11. The HOMO-4 of the intermediate I3 with a sketch showing QTAIM electron densities (eꢁ/Bohr3) at selected bond critical points on the right.
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12
R.D. Adams et al. / Journal of Organometallic Chemistry xxx (2015) 1e13
Fig. 12. The HOMO-33 of the intermediate I5 with sketch showing QTAIM electron densities (eꢁ/Bohr3) at selected bond critical points on the right.
containing an agostically-coordinated triple bridging CH2 ligand;
and 2) the cleavage of the agostic CeH bond of triple bridging CH2
ligand with formation of the triple bridging methylidyne (CH)
ligand and a bridging hydrido ligand on the third Os e Os bond. In
step (1), the transformation was simulated computationally by
progressively removing the axially coordinated CO ligand proxi-
mate to the CH2 ligand from the third osmium atom. As this
removal progressed, the CH2 ligand shifted toward this osmium
atom Os(3). After passing over transition state TS2, the calculation
formed a stable minimum with the geometry-optimized structure
for I5 shown in Fig. 12.
The HOMO-33 of I5 shows the nature of the bonding of the triple
bridging CH2 ligand to the triosmium cluster. One of the CeH
bonds, C(1) e H(2) has formed an agostic interaction to the third
metal atom by using an sp-hydridized carbon orbital that simul-
taneously bonds the CH2 group to the Au(PPh3) bridged Os e Os
bond. The agostic CeH bond distance in I5 is 1.20 Å while the
uncoordinated CeH bond distance is 1.10 Å. The agostic Os … C and
Os … H bond distances are 2.35 Å and 1.91 Å, respectively. The
QTAIM electron density of the agostic CeH bond at its bcp was
calculated to be 0.196 eꢁ/Bohr3. The QTAIM electron density for the
uncoordinated CeH bond, was 0.270 eꢁ/Bohr3. There was an Os …
H bcp of 0.072 eꢁ/Bohr3 between the metal atom Os(3) and the
agostic hydrogen atom which once again shows there is a signifi-
cant transfer of electron density from the agostic CeH bond toward
the metal atom.
In the final step I5 was converted smoothly to 2 via a small
transition state TS3, þ13.3 kcal/mol. Structure 2 lies 4.1 kcal/mol
lower in energy than I5. The HOMO-4 which shows the bonding of
the triply-bridging methylidyne ligand to the cluster together with
a schematic of 2 showing selected QTAIM electron densities is
shown in Fig. 13.
The Os e C bond distances to the triply bridging methylidyne
ligand are 2.14 Å and are very similar to those observed for 2 in the
Fig. 13. The HOMO-4 of the product 2 with sketch showing QTAIM electron densities (eꢁ/Bohr3) at selected bond critical points on the right.
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R.D. Adams et al. / Journal of Organometallic Chemistry xxx (2015) 1e13
(d) H. Schwarz, Angew. Chem. Int. Ed. 50 (2011) 10096e10115;
13
crystal structure analysis, Os(1) e C(1) ¼ 2.103(10), Os(2) e
C(1) ¼ 2.117(11), Os(3) e C(1) ¼ 2.075(11), see above. The QTAIM
electron densities of the Os e C bonds at bcps were calculated to be
0.111, 0.111 and 0.118 eꢁ/Bohr3; the bcp for the remaining CeH bond
is normal at 0.263 eꢁ/Bohr3.
The loss of each CO ligand and the cleavage of each CH bond,
except for the last one, each produces an increase in the total en-
ergy of the system, so overall the conversion of 4 to 2 results in a net
increase of approximately 64 kcal/mol. Due to complexity of the
system and inherent ambiguity in the accuracy of DFT model, this
value is probably only qualitatively correct, see Fig. 9. The
geometrical features of the various species involved are likely to be
considerably more accurate.
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It has been shown that (CH3)Au(PPh3) reacts with
Os3(CO)11(NCCH3) by the loss of the NCCH3 ligand and the
oxidation-addition of the AueC bond to the methyl group to the
osmium atoms. This is followed by methyl migration/CO insertion
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2 was higher in the reaction of
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activations that involve intermediates containing bridged species
having agostic CH interactions with the metal atoms in the cluster.
In addition, when compound 2 was heated to 125 ꢂC in solution, the
digoldtriosmium compound 3 was formed via ligand exchange
between the AuPPh3 and H ligands or more likely by a reversible
elimination and re-addition of H2 and “HAuPPh3” to the appro-
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will serve as a viable mimic for CH4 for studies of its activation and
transformations. It is very likely that the activation/transformation
of methyl groups at triangular trinuclear metal sites in other
polynuclear metal complexes will proceed similarly and these
might serve as reasonable models for similar transformations on
the triangular {111} faces of metal surfaces.
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Appendix A. Supporting information
Supporting information related to this article can be found at
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