Studies of ligand additions to coordinatively unsaturated dirhenium complexes containing the bulky PBu3t ligand

Article abstract of DOI:10.1021/om700790c

Five new complexes were obtained from the reaction of Re ₃(CO)₁₂(μ-H)₃ with PBu₃ ^t. These are Re₂(CO)₈(μ-PBu₂ ^t)(μ-H), 1, Re₂(CO)₇(μ-PBu ₂^t)(PBu₂^tH)(μ-H), 2, HRe(CO) ₄(PBu₃^t), 3, Re₂(CO) ₆(PBu₃^t)(μ-PBu₂ ^t)(μ-H), 4, and Re₂(CO)₅(PBu ₃^t)(PBu₂^tH)(μ-PBu ₂^tO)(μ-H), 5. Compounds 4 and 5 are electronically unsaturated by the amount of two electrons; namely, one of the metal atoms has an 18-electron configuration and the other metal atom has a 16-electron configuration. Compound 4 adds CO and the nitriles MeCN and PhCN, reversibly, to form the electronically saturated 1:1 adducts Re₂(CO) ₇(PBu₃^t)(μ-PBu₂ ^t)(μ-H), 6, Re₂(CO)₆(NCMe)(PBu ₃^t)(μ-PBu₂^t)(μ-H), 7, and Re₂(CO)₆(NCPh)(PBu₃^t)(μ-PB ₂^t)(μ-H), 8, respectively. ¹³CO labeling studies have shown that the CO ligand that is added to 4 to form 6 is added at the electronically saturated metal atom and one of the originally coordinated CO ligands is shifted to the unsaturated metal atom. Compound 5 also adds 1 equiv of CO to form the complex Re₂(CO)₆(PBu₃ ^t)(PBu₂^tH)(μ-PBu₂ ^tO)(μ-H), 9.¹³CO labeling studies have shown that the added CO ligand was added to the unsaturated metal atom in this case. All of the new compounds were characterized structurally by single-crystal X-ray diffraction analyses.

Full text of DOI:10.1021/om700790c

6564
Organometallics 2007, 26, 6564–6575
Studies of Ligand Additions to Coordinatively Unsaturated
Dirhenium Complexes Containing the Bulky PBut3 Ligand
Richard D. Adams,* Burjor Captain, and Perry J. Pellechia
Department of Chemistry and Biochemistry, UniVersity of South Carolina, Columbia, South Carolina 29208
ReceiVed August 2, 2007
Five new complexes were obtained from the reaction of Re3(CO)12(µ-H)3 with PBut3. These are
Re2(CO)8(µ-PBut2)(µ-H), 1, Re2(CO)7(µ-PBut2)(PBut2H)(µ-H), 2, HRe(CO)4(PBut3), 3, Re2(CO)6(PBut3)(µ-
PBut2)(µ-H), 4, and Re2(CO)5(PBut3)(PBut2H)(µ-PBut2O)(µ-H), 5. Compounds 4 and 5 are electronically
unsaturated by the amount of two electrons; namely, one of the metal atoms has an 18-electron
configuration and the other metal atom has a 16-electron configuration. Compound 4 adds CO and the
nitriles MeCN and PhCN, reversibly, to form the electronically saturated 1:1 adducts Re2(CO)7(PBut3)(µ-
PBut2)(µ-H), 6, Re2(CO)6(NCMe)(PBut3)(µ-PBut2)(µ-H), 7, and Re2(CO)6(NCPh)(PBut3)(µ-PBut2)(µ-H),
8, respectively. 13CO labeling studies have shown that the CO ligand that is added to 4 to form 6 is
added at the electronically saturated metal atom and one of the originally coordinated CO ligands is
shifted to the unsaturated metal atom. Compound 5 also adds 1 equiv of CO to form the complex
Re2(CO)6(PBut3)(PBut2H)(µ-PBut2O)(µ-H), 9.13CO labeling studies have shown that the added CO ligand
was added to the unsaturated metal atom in this case. All of the new compounds were characterized
structurally by single-crystal X-ray diffraction analyses.
butylphosphine ligands. Surprisingly, for one of the complexes
the ligand additions occur preferentially at the metal atom that
is coordinatively and electronically saturated. A preliminary
report on this work has been published.7
Introduction
Coordination asymmetry in binuclear metal systems is a
feature that can produce unusual properties and reactivity to
the metal atoms.1 Coordination asymmetry is most pronounced
when the metal atoms have different coordination numbers.2
The metal atoms in binuclear mixed-valence complexes often
have significantly different reactivities at the two metal atoms,3
and most reactions occur preferentially at an electronically
unsaturated metal atom, if one is present. For example, Nocera
has shown that hydrogen activation occurs at the unsaturated
metal atom in certain binuclear mixed-valent metal complexes.4
We have recently shown how an unsaturated metal atom can
activate a neighboring metal atom and also facilitate alkyne
additions to it to promote alkyne insertion reactions.5 Coordina-
tion asymmetry also appears to be very important to the
reactivity of metalloenzymes and multimetallic proteins.6
We now wish to report some unusual coordinatively unsatur-
ated dirhenium carbonyl complexes containing bulky tert-
Experimental Section
General Data. Unless indicated otherwise, all reactions were
performed under an atmosphere of nitrogen. Reagent grade solvents
were dried by the standard procedures and were freshly distilled
prior to use. Infrared spectra were recorded on a Thermo Nicolet
Avatar 360 FT-IR spectrophotometer. 1H NMR and 31P{1H} NMR
spectra were recorded on a Varian Mercury 400 spectrometer
operating at 400.1 and 161.9 MHz, respectively. 13C{1H} NMR
spectra were recorded on a Varian Mercury 300 spectrometer
operating at 75.5 MHz. Proton and phosphorus decoupled
13C{1H}{31P} NMR and the variable-temperature 13C{1H} NMR
experiments were recorded on a Varian Innova 500 spectrometer
operating at 125.8 MHz. 31P{1H} NMR spectra were externally
referenced against 85% ortho-H3PO4. Mass spectrometric (MS)
measurements performed by a direct-exposure probe using electron
impact ionization (EI) were made on a VG 70S instrument.
Electrospray mass spectrometric measurements were obtained on
a MicroMass Q-Tof spectrometer. 13CO (99% 13C, <5% 18O) and
benzonitrile, PhCN (99.9%), were purchased from Aldrich and were
used as received. Tri-tert-butyl phosphine, PBut3, was purchased
from Strem and was used without further purification. The tri-tert-
butyl phosphine was handled under nitrogen and stored at -80 °C.
NMR analysis of the PBut3 showed that it was predominantly PBut3,
but GC-mass spectral analysis showed the presence of significant
amounts of the impurites: OdPBut3, OdP(H)But2, and
OdP(OH)But2. Re3(CO)12(µ-H)3 was prepared according to the
published procedure.8 Product separations were performed by thin-
layer chromatography (TLC) in air on Analtech 0.25 and 0.5 mm
silica gel 60 Å F254 glass plates.
* Corresponding author. E-mail: Adams@mail.chem.sc.edu.
(1) (a) Okawa, H.; Furutachi, H.; Fenton, D. E. Coord. Chem. ReV. 1998,
174, 51–75. (b) Satcher, J. H.; Droege, M. W.; Weakle, T. J. R.; Taylor,
R. T. Inorg. Chem. 1995, 34, 3317–3328.
(2) (a) Gavrilova, A. L.; Bosnich, B. Inorg. Chim. Acta 2003, 352, 24–
30. (b) Bosnich, B. Inorg. Chem. 1999, 38, 2554–2562. (c) McCollum,
D. G.; Yap, G. A. P.; Rheingold, A. L.; Bosnich, B. J. Am. Chem. Soc.
1996, 118, 1365–1379.
(3) (a) Lambert, E.; Chabut, B.; Chardon-Noblat, S.; Deronzier, A.;
Chottard, G.; Bousseksou, A.; Tuchagues, J.-P.; Lagier, J.; Bardet, M.;
Latour, J.-M. J. Am. Chem. Soc. 1997, 119, 9424-9437. (b) Herber, U.;
Pechmann, T.; Weberndorfer, B.; Ilg, K.; Werner, H. Chem.-Eur. J. 2002,
8, 309–319.
(4) (a) Gray, T. G.; Veige, A. S.; Nocera, D. G. J. Am. Chem. Soc.
2004, 126, 9760–9768. (b) Veige, A. S.; Gray, T. G.; Nocera, D. G. Inorg.
Chem. 2005, 44, 17–26.
(5) (a) Adams, R. D.; Captain, B.; Trufan, E.; Zhu, L. J. Am. Chem.
Soc. 2007, 129, 7545–7556. (b) Adams, R. D.; Captain, B.; Zhu, L. J. Am.
Chem. Soc. 2006, 128, 13672–13673.
(7) Adams, R. D.; Captain, B. Angew. Chem., Int. Ed. 2007, 46, 5714–
(6) (a) Belle, C.; Pierrey, J. L. Eur. J. Inorg. Chem. 2003, 4137–4146.
(b) Feig, A. L.; Lippard, S. J. Chem. ReV. 41994, 94, 759–805. (c) Stenkamp,
R. E. Chem. ReV. 1994, 94, 715–726.
5716.
(8) Kaesz, H. D.; Knox, S. A. R.; Koepke, J. W. R.; Saillant, B. Chem.
Commun. 1971, 477.
10.1021/om700790c CCC: $37.00
2007 American Chemical Society
Publication on Web 11/21/2007

Dirhenium Complexes Containing the Bulky PBut3 Ligand
Organometallics, Vol. 26, No. 26, 2007 6565
Reaction of Re3(CO)12(µ-H)3 with PBut3. Re3(CO)12(µ-H)3
(50.3 mg, 0.056 mmol) and PBut3 (50 µL, 0.201 mmol) were
dissolved in 20 mL of octane. The reaction solution was heated to
reflux for 6 h. After cooling, the solvent was then removed in Vacuo,
and the products were separated by TLC by using a 5:1 hexane/
methylene chloride solvent mixture to yield in order of elution 1.1
mg (2% yield) of colorless Re2(CO)8(µ-PBut2)(µ-H), 1, 2.5 mg (5%
yield) of colorless Re2(CO)7(µ-PBut2)(PBut2H)(µ-H), 2, 1.3 mg (4%)
of colorless HRe(CO)4(PBut3), 3, 15.4 mg (31% yield) of orange
Re2(CO)6(PBut3)(µ-PBut2)(µ-H), 4, and 5.3 mg (9% yield) of
yellow Re2(CO)5(PBut3)(PBut2H)(µ-PBut2O)(µ-H), 5. Spectral
data for Re2(CO)8(µ-PBut2)(µ-H), 1: IR νCO (cm-1 in hexane):
2098 (w), 2074 (m), 1997 (vs), 1987 (s), 1969 (s), 1966 (m). 1H
4CO - H), 853 (M+ - 6CO - H). The isotope pattern is consistent
with the presence of two rhenium atoms.
Preparation of Re2(CO)7(PBut3)(µ-PBut2)(µ-H), 6. Carbon
monoxide gas (1 atm) was bubbled through a solution of 4 (15.4
mg, 0.017 mmol) in 20 mL of hexane. Within a few minutes the
orange-colored solution turned to yellow and then almost colorless.
The CO gas was purged through this solution for a total of 10 min,
and an IR spectrum after this time indicated complete conversion
of the starting material 4. The solvent was removed in Vacuo, and
the product was separated by TLC by using a 5:1 hexane/methylene
chloride solvent mixture to yield 15.4 mg (97%) of colorless 6.
Spectral data for 6: IR νCO (cm-1 in hexane): 2079 (m), 2018 (w),
1983 (m), 1974 (vs), 1953 (s), 1914 (m), 1908 (m). 1H NMR (400
MHz, d8-toluene, rt, TMS): δ 1.53 (d, 3J(P,H) ) 14 Hz, 18H; CH3),
3
NMR (400 MHz, d8-toluene, rt, TMS): δ 1.25 (d, J(P,H) ) 14
Hz, 18H; CH3), -15.15 (d,2J(P,H) ) 6 Hz, hydride 1H). 31P{1H}
NMR (162 MHz, d8-toluene, rt, 85% ortho-H3PO4): δ 118 (s, 1P,
3
2
1.38 (d, J(P,H) ) 12 Hz, 27H; CH3), -14.01 (dd, J(P,H) ) 15
Hz, J(P,H) ) 8 Hz, hydride 1H). 31P{1H} NMR (162 MHz, d8-
2
µ-PBut2). EI/MS: m/z 742 (M+), 714 (M+ - CO), 686 (M+
-
toluene, rt, 85% ortho-H3PO4): δ 120.84 (d, 2J(P,P) ) 71 Hz, 1P,
µ-PBut2), 63.05 (d, 2J(P,P) ) 71 Hz, 1P, PBut3). The isotope pattern
is consistent with the presence of two rhenium atoms. The
assignments of the respective 31P resonances were appropriately
made from the selective phosphorus decoupled 1H{31P} NMR
experiments, which showed the doublet at 1.53 ppm collapse into
a singlet when the resonance at 120.84 ppm in the 31P spectrum
was irradiated. Accordingly, the doublet at 1.38 ppm collapsed into
a singlet when the resonance at 63.05 ppm in the 31P spectrum
was irradiated. EI/MS: m/z 916 (M+), 888 (M+ - CO), 860 (M+
- 2CO), 831 (M+ - 3CO - H), 803 (M+ - 4CO - H). The
isotope pattern is consistent with the presence of two rhenium atoms.
Conversion of 6 to 4. Compound 6 (15.0 mg, 0.016 mmol) in
10 mL of heptane was heated to reflux for 1½ h. IR at this time
showed complete conversion of the starting material 6 to 4. The
solvent was removed in Vacuo, and the product was separated by
TLC by using a 5:1 hexane/methylene chloride solvent mixture to
yield 14.0 mg (96%) of orange 4.
2CO). The isotope pattern is consistent with the presence of two
rhenium atoms. Spectral data for Re2(CO)7(µ-PBut2)(PBut2H)(µ-
H), 2: IR ν (cm-1 in hexane): 2081 (m), 2024 (w), 1985 (m), 1975
(vs), 1954 (s), 1924 (m), 1918 (m), 1915 (m). 1H NMR (400 MHz,
d8-toluene, rt, TMS): δ 4.77 (d,1J(P,H) ) 333 Hz, 1H, P-H),1.50
(d, 3J(P,H) ) 14 Hz, 18 H; CH3), 1.24 (d, 3J(P,H) ) 14 Hz, 18H;
CH3), -15.00 (dd, 2J(P,H) ) 10 Hz, 2J(P,H) ) 7 Hz, hydride 1H).
31P{1H} NMR (162 MHz, d8-toluene, rt, 85% ortho-H3PO4): δ 126
2
2
(d, J(P,P) ) 73 Hz, 1P, µ-PtBu2), 33 (d, J(P,P) ) 70 Hz, 1P,
PtBu2H). EI/MS: m/z 860 (M+), 832 (M+ - CO), 804 (M+ - CO),
804 (M+ - 3CO - H). The isotope pattern is consistent with the
presence of two rhenium atoms. Spectral data for HRe(CO)4(PBut3),
3: IR νCO (cm-1 in hexane): 2071 (m), 1979 (m), 1961 (s), 1956
(sh). 1H NMR (400 MHz, d8-toluene, rt, TMS): δ 1.21 (d, 1J(P,H)
2
) 13 Hz, 27H, CH3) -4.92 (d, J(P,H) ) 18 Hz, hydride 1H).
31P{1H} NMR (162 MHz, d8-toluene, rt, 85% ortho-H3PO4): δ 79
(s, 1P). EI/MS: m/z 501 (M+ - H), 473 (M+ - H - CO), 445 (M+
- H - 2CO), 417 (M+ - H - 3CO). The isotope pattern is consistent
with the presence of one rhenium atom. Spectral data for Re2(CO)6
(PBut3)(µ-PBut2)(µ-H), 4: IR νCO (cm-1 in hexane): 2079 (s), 1993
(vs), 1969 (vs), 1954 (vs), 1923 (s), 1850 (s). 1H NMR (400 MHz,
d8-toluene, rt, TMS): δ 1.37 (d, 3J(P,H) ) 14 Hz, 18H; CH3), 1.24
Preparation of 13CO-Enriched Re2(CO)7(PBut3)(µ-PBut2)
(µ-H), 6. A 15.0 mg amount of 4 was dissolved in 25 mL of heptane
in a 100 mL sidearm flask. The flask was evacuated and then filled
with 13CO. This solution was stirred for 30 min at room temper-
ature, during which time the color of the solution turned from orange
to almost colorless, affording 13CO-enriched Re2(CO)7(PBut3)(µ-
PBut2)(µ-H), 6. The 13CO gas was then removed and the heptane
solution heated to reflux for 1½ h under a purge of nitrogen to
afford 13CO-enriched Re2(CO)6(PBut3)(µ-PBut2)(µ-H), 4. The flask
was then cooled to room temperature, evacuated, filled again with
13CO, and stirred for 30 min at room temperature. These series of
steps were repeated three times to increase the enrichment. The
heptane solvent was then removed in Vacuo, and the 13CO-enriched
6 was purified by TLC by using a 5:1 hexane/methylene chloride
solvent mixture.
3
2
(d, J(P,H) ) 12 Hz, 27H; CH3), -4.46 (dd, J(P,H) ) 12 Hz,
2J(P,H) ) 5 Hz, hydride 1H). 31P{1H} NMR (162 MHz, d8-toluene,
rt, 85% ortho-H3PO4): δ 139.68 (d, 2J(P,P) ) 99 Hz, 1P, µ-PtBu2),
84.31 (d, 2J(P,P) ) 99 Hz, 1P, PtBu3). 13C{1H} NMR 125.8 MHz,
2
d8-toluene): at -110 °C, 190.5 ppm (doublet, J(P2,C) ) 26 Hz);
2
2
at -40 °C, δ 204.5 (2C, t, J(P1,C) ) 5 Hz, J(P2,C) ) 5 Hz),
190.5 (1C, d, 2J(P2,C) ) 26 Hz), 188.5 ppm (1C, d, 2J(P2,C) ) 8
Hz), 187.9 (2C, d, 2J(P2,C) ) 5 Hz); at 25 °C, 204.1, 190.2, 187.9;
at 140 °C, 191.2. EI/MS: m/z 888 (M+), 860 (M+ - CO), 831
(M+ - 2CO - H), 803 (M+ - 3CO - H). The isotope pattern is
consistent with the presence of two rhenium atoms. Spectral data
for Re2(CO)5(PBut3)(PBut2H)(µ-PBut2O)(µ-H), 5: IR νCO (cm-1 in
hexane): 2023 (m), 1926 (vs), 1912 (s), 1909 (s), 1834 (s). 1H NMR
(400 MHz, CDCl3, rt, TMS): δ 5.24 (dd, 1J(P,H) ) 339 Hz,
3J(P3,H) ) 2 Hz, 1H, P-H), 1.53 (d, 3J(P,H) ) 12 Hz, 27H; CH3,
PBut3), 1.44 (d, 3J(P,H) ) 14 Hz, 18H; CH3, PBut2H), 1.25 (d,
3J(P,H) ) 13 Hz, 18H; CH3, µ-PBut2O), -10.37 (ddd, 2J(P1,H) )
26 Hz, 2J(P2,H) ) 8 Hz, 2J(P3,H) ) 12 Hz, hydride 1H). 13C{1H}
NMR (125.8 MHz, d8-toluene, rt, TMS): δ 207.2 (s, br, 2C), 198.8
(s, br, 1C), 197.9 (s, br, 2C); at -60 °C, δ 208.4 (d, 2J(P1,C) ) 4
Hz), 207.4 (d, 2J(P1,C) ) 6 Hz), 199.7 (t, 2J(P2,C) ) 8 Hz,
Selective Addition of 13CO to 4. A sample of 4 (15.0 mg, 0.017
mmol) containing CO ligands at the natural abundance level was
dissolved in approximately 0.5 mL of toluene-d8 in a 5 mm NMR
tube and sealed with a rubber septum. The NMR tube was evacuated
and filled with 13CO. The NMR tube was shaken, and within
minutes the orange-colored solution turned almost colorless. The
13C{1H} NMR spectrum at this time showed only one significant
resonance at 187.2 ppm.
Preparation of 13CO-Enriched Re2(CO)6(PBut3)(µ-PBut2)
(µ-H), 4. A sample of 6 enriched with 13CO to approximately 30%,
as described above, was dissolved in 10 mL of heptane and heated
to reflux for 1½ h. The solvent was removed in Vacuo, and the
product was purified by TLC by using a 5:1 hexane/methylene
chloride solvent mixture. A mass spectrum of the product 4 showed
that it was enriched with 13CO in the amount of approximately
30%.
2
2
2J(P3,C) ) 8 Hz), 199.3 (s), 196.5 (t, J(P2,C) ) 8 Hz, J(P3,C)
) 8 Hz). 31P{1H} NMR (162 MHz, CDCl3, rt, 85% ortho-H3PO4):
δ 138.4 (d, 2J(P,P) ) 114 Hz, 1P, µ-PBut2O), 76.5 (s, 1P, PBut3),
34.0 (d, 2J(P,P) ) 114 Hz, 1P, PBut2H). NOTE: The 1H NMR
spectrum in d8-toluene solvent shows that the CH3 resonances of
the µ-PBut2O and PBut2H ligands are overlapping. EI/MS: m/z 1022
(M+), 965 (M+ - 2CO - H), 937 (M+ - 3CO - H), 909 (M+
-

6566 Organometallics, Vol. 26, No. 26, 2007
Adams et al.
Preparation of Re2(CO)6(NCMe)(PBut3)(µ-PBut2)(µ-H), 7.
Compound 4 (9.9 mg, 0.011 mmol) was dissolved in approximately
0.6 mL of acetonitrile (NCMe) in a medium vial (1 dram size, 3.7
mL). The solution was then concentrated to about half the volume
and placed in a freezer at -25 °C for ∼ 2 days to yield 8.5 mg
(82% yield) of light yellow-colorless crystals of 7. Spectral data
for 7: IR νCO (cm-1 in acetonitrile): 2018 (w), 2000 (s), 1909 (vs),
1889 (sh). 1H NMR (400 MHz, CD3CN, rt, TMS): δ 1.60 (d,
3J(P,H) ) 12 Hz, 27H; CH3), 1.50 (t, 3J(P,H) ) 13 Hz, 18H; CH3),
-11.76 (dd, 2J(P,H) ) 16 Hz, 2J(P,H) ) 9 Hz, hydride 1H).
31P{1H} NMR (162 MHz, CD3CN, rt, 85% ortho-H3PO4): δ 114.09
(d, 2J(P,P) ) 67 Hz, 1P, µ-PtBu2), 65.26 (d, 2J(P,P) ) 67 Hz, 1P,
PBut3); 13C NMR (125.8 MHz, d8-toluene, rt, TMS): δ 203.1 (br),
201.9 (br), 200.1 (s), 196.8 (d, 2J(P2,C) ) 39 Hz), 196.2 (s), 193.5
(d, J(P2,C) ) 9 Hz). When the H NMR spectrum was recorded
on a 300 MHz instrument, the triplet at 1.50 ppm (overlapping
doublet of doublets) splits into a doublet of doublets. ES+/MS: m/z
929 (M+), 887 (M+ - NCMe - H). The isotope pattern is
consistent with the presence of two rhenium atoms. NOTE:
Compound 7 was rapidly converted back to 4 when 7 was dissolved
in any solvent other than acetonitrile.
at 8 °C. Yellow single crystals of 9 were grown at -25 °C under
an atmosphere of CO in hexane solvent. Each data crystal was glued
onto the end of a thin glass fiber. X-ray intensity data were measured
by using a Bruker SMART APEX CCD-based diffractometer using
Mo KR radiation (λ ) 0.71073 Å). The raw data frames were
integrated with the SAINT+ program by using a narrow-frame
integration algorithm.9 Corrections for Lorentz and polarization
effects were also applied with SAINT+. An empirical absorption
correction based on the multiple measurement of equivalent
reflections was applied 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.10 All nonhydrogen atoms
were refined with anisotropic displacement parameters. Hydrogen
atoms were placed in geometrically idealized positions and included
as standard riding atoms during the least-squares refinements.
Crystal data, data collection parameters, and results of the analyses
are listed in Tables 1, 2, and 3.
2
1
All compounds except for compounds 2 and 4 crystallized in
the monoclinic crystal system. For compounds 1 and 3 the
systematic absences in the intensity data were consistent with the
unique space group P21/n. The hydrido ligands in both compounds
were located and refined successfully with isotropic thermal
parameters. For compound 5 the systematic absences in the intensity
data were consistent with either of the space groups Cc or C2/c,
the latter of which was confirmed by the successful solution and
refinement of the structure. The hydrido ligand was located and
refined on its positional parameters with a fixed isotropic thermal
parameter. The hydrogen atom on the PBut2H group was located
and refined successfully with isotropic thermal parameters. The
crystal packing of the molecules of 5 contains voids that are filled
with disordered molecules from cocrystallization of solvent. Despite
many attempts, no reasonable disorder model for these solvent
molecules could be obtained. In the final stages of the refinements
the largest peak in the final difference Fourier map was 2.320 e-/
Å3, with satisfactory low R factors, R1 ) 4.58%. For compounds
6, 7, and 9 the systematic absences in the intensity data were
consistent with the unique space group P21/c. The hydrido ligands
in compounds 6 and 7 were located and refined successfully with
isotropic thermal parameters. For compound 9 all the atoms of the
PBut2H group were disordered over two orientations and were
refined in the ratio 50/50. The carbon atoms were refined with
isotropic thermal parameters. The hydrido ligand and the hydrogen
atom on the PBut2H ligand were both located and refined with a
fixed isotropic thermal parameter. For compound 8 the systematic
absences in the intensity data were consistent with either of the
space groups P21/m or P21. The structure could be solved only in
the latter space group. The hydrido ligand was located and refined
on its positional parameters with a fixed isotropic thermal parameter.
Compound 2 crystallized in the triclinic crystal system. The space
Preparation of Re2(CO)6(NCPh)(PBut3)(µ-PBut2)(µ-H), 8.
Compound 4 (10.0 mg, 0.011 mmol) was dissolved in a few drops
of CH2Cl2 in a small vial (¼ dram size, 0.9 mL). A few drops of
benzonitrile was added, and the vial was then shaken. Immediately,
the orange-colored solution turned yellow. The vial was placed in
a refrigerator at 8 °C for ∼5 days to yield 4.9 mg (44% yield) of
light yellow crystals of 8. IR νCO (cm-1 in benzonitrile): 2018 (m),
1
1999 (s), 1908 (vs, br). H NMR (400 MHz, in ca. 0.5 mL of d8-
toluene and 0.1 mL of PhCN, rt, TMS): δ 1.68 (t, br, 18H; CH3),
3
2
1.48 (d, J(P,H) ) 12 Hz, 27H; CH3), –11.60 (dd, J(P,H) ) 16
Hz, J(P,H) ) 9 Hz, hydride 1H). 31P{1H} NMR (162 MHz, in
2
ca. 0.5 mLof d8-toluene and 0.1 mL of PhCN, rt, 85% ortho-H3PO4):
δ 114.4 (d, J(P,P) ) 68 Hz, 1P, µ-PBut2), 65.4 (d, J(P,P) ) 68
Hz, 1P, PBut3). Anal. Calcd: C, 39.95; H, 5.18. Found: C, 39.96;
H 4.97.
2
2
Preparation of Re2(CO)6(PBut3)(PBut2H)(µ-PBut2O)(µ-H),
9. Compound 5 (10.2 mg, 0.010 mmol) was dissolved in ap-
proximately 0.6 mL of hexane in a 10 mL Schlenk tube. CO gas
was passed through the tube for 15 min, and the orange-colored
solution turned yellow. The Schlenk tube was then sealed under
an atmosphere of CO and placed in a freezer (-80 °C) overnight.
A total of 6.0 mg (57% yield) of compound 9 crystallized and was
collected. Spectral data for 9: IR νCO (cm-1 in hexane): 2038 (m),
2019 (w), 1939 (vs), 1917 (s), 1912 (s), 1901 (m), 1885 (m), 1875
(m). 1H NMR (400 MHz, d8-toluene, rt, TMS): δ 4.82 (d, 1J(P,H)
) 331 Hz, 1H, P-H), 1.44 (d, 3J(P,H) ) 12 Hz, 27H; CH3, PBut3),
1.42 (d, 3J(P,H) ) 13 Hz, 18H; CH3, PBut2O), 1.33 (d, 3J(P,H) )
14 Hz, 18H; CH3,µ-PBut2H), -17.95 (ddd, 2J(P1,H) ) 17 Hz,
2
2J(P2,H) ) 8 Hz, J(P3,H) ) 5 Hz, hydride 1H). 31P{1H} NMR
j
group P1 was assumed and confirmed by the successful refinement
2
(162 MHz, CDCl3, rt, 85% ortho-H3PO4): δ 115.9 (d, J(P,P) )
and solution of the structure. The hydrido ligand and the hydrogen
atom on the PBut2H group were located and refined successfully
with isotropic thermal parameters.
110 Hz, 1P, µ-PBut2O), 71.3 (s, 1P, PBut3), 32.9 (d, 2J(P,P) ) 111
Hz, 1P, PBut2H). Anal. Calcd: C, 38.85; H, 6.23. Found: C, 38.63;
H, 5.96. When a solution of 9 was placed under an atmosphere of
13CO at room temperature, all CO ligand sites were rapidly and
equally enriched with 13CO. 13C NMR (125 MHz, d8-toluene, rt,
Compound 4 crystallized in the orthorhombic crystal system. The
systematic absences in the intensity data were consistent with either
of the space groups Pnma or Pna21. The structure could only be
solved in the latter space group. The hydrido ligand was located
and refined successfully with an isotropic thermal parameter.
Molecular Orbital Calculations. A single-point molecular
orbital calculation on 4 was performed on the molecular structure
as derived from the single-crystal X-ray diffraction analysis. PH3
was used in place of PBut3 in these calculations. The P-H distance
that was used was 1.41 Å. The molecular orbital calculations
2
2
TMS): δ 199.0 (t, J(P2,C) ) 8 Hz, J(P3,C) ) 8 Hz), 196.8 (d,
2J(P1,C) ) 6 Hz), 194.8 ppm (s).
Crystallographic Analyses. Colorless single crystals of 1, 2,
and 3, red single crystals of 4, and orange single crystals of 5
suitable for X-ray diffraction analyses were obtained by slow
evaporation of solvent from a hexane/methylene chloride solvent
mixture at -25 °C. Colorless single crystals of 6 were obtained by
slow evaporation of diethyl ether at -25 °C. Colorless single
crystals of 7 were obtained by slow evaporation from a acetonitrile
solution at -25 °C. Colorless single crystals of 8 were obtained
by slow evaporation from a methylene choride/benzonitrile solution
(9) SAINT+; Bruker Analytical X-ray System, Inc.: Madison, WI, 2001.
(10) Sheldrick, G M. SHELXTL Version 6.1; Bruker Analytical X-ray
Systems, Inc.: Madison, WI, 1997.

Dirhenium Complexes Containing the Bulky PBut3 Ligand
Organometallics, Vol. 26, No. 26, 2007 6567
Table 1. Crystallographic Data for Compounds 1, 2, and 3
1
2
3
empirical formula
fw
Re2PO8C16H19
742.68
Re2P2O7C23H38
860.87
RePO4C16H28
501.55
cryst syst
lattice params
a (Å)
b (Å)
c (Å)
monoclinic
triclinic
monoclinic
8.9014(2)
16.2671(3)
14.7419(3)
90
94.751(1)
90
2127.29(8)
P21/n (#14)
4
2.319
11.482
294(2)
56.64
9.1219(2)
12.8748(3)
12.9356(3)
91.103(1)
99.360(1)
95.351(1)
1491.52(6)
8.0633(5)
29.2329(17)
8.4785(5)
90
106.308(1)
90
1918.1(2)
P21/n (#14)
4
1.737
6.432
294(2)
56.58
R (deg)
ꢁ (deg)
γ (deg)
V (Å3)
j
space group
Z value
P1 (#2)
2
Fcalc (g/cm3)
µ(Mo KR) (mm-1
temperature (K)
2θmax (deg)
1.917
8.251
294(2)
56.60
6244
327
)
no. obsd (I > 2σ(I))
no. params
4557
254
3776
212
goodness of fit (GOF)
max. shift in cycle
1.034
0.001
1.085
0.001
0.0240; 0.0569
multiscan 1.000/0.511
1.358
1.091
0.001
0.0332;0.0805
multiscan 1.000/0.597
1.127
residuals:a R1; wR2
absor corr, max./min.
largest peak in final diff map (e-/Å3)
0.0208; 0.0484
multi-scan 1.000/0.535
0.780
a R ) ∑hkl(|Fobs| - |Fcalc|)/∑hkl|Fobs|; Rw ) [∑hklw(|Fobs| - |Fcalc|)2/∑hklwFobs
] .
2 1/2, w ) 1/σ2(Fobs); GOF ) [∑hklw(|Fobs| - |Fcalc|)2/(ndata - nvari)]1/2
Table 2. Crystallographic Data for Compounds 4, 5, and 6
4
5
6
empirical formula
fw
Re2P2O6C26H46
888.97
Re2P3O6C33H65
1023.16
Re2P2O7C27H46
916.98
cryst syst
lattice params
a (Å)
b (Å)
c (Å)
orthorhombic
monoclinic
monoclinic
21.1976(10)
17.2257(8)
8.8901(4)
90
3246.2(3)
Pna21(#33)
4
1.819
7.583
294
56.90
51.0915(17)
8.7205(3)
19.8896(7)
97.067(1)
8794.4(5)
C2/c (#15)
8
1.546
5.644
294(2)
56.60
16.4619(4)
11.8441(3)
16.9897(4)
93.057(1)
3307.88(14)
P21/c (#14)
4
1.841
7.441
294
56.62
ꢁ (deg)
V (Å3)
space group
Z value
Fcalc (g/cm3)
µ(Mo KR) (mm-1
temperature (K)
2θmax (deg)
)
no. obsd (I > 2σ(I))
no. params
7338
345
7897
425
7468
362
goodness of fit (GOF)
max. shift in cycle
1.078
0.002
0.0279; 0.0626
multiscan 1.000/0.512
2.390
1.037
0.005
0.0458; 0.1274
multiscan 1.000/0.569
2.320
1.061
0.001
0.0217; 0.0539
multiscan 1.000/0.582
1.588
residuals:a R1; wR2
absorp corr, max./min.
largest peak in final diff map (e-/Å3)
a R ) ∑hkl(|Fobs| - |Fcalc|)/∑hkl|Fobs|; Rw ) [∑hklw(|Fobs| - |Fcalc|)2/∑hklwFobs2 1/2, w ) 1/σ2(Fobs); GOF ) [∑hklw(|Fobs| - |Fcalc|)2/(ndata - nvari)]1/2
] .
reported herein were performed by using the Fenske–Hall method.
Contracted double-ꢀ basis sets were used for the Re 5d, P 3p, and
C and O 2p atomic orbitals. The Fenske–Hall molecular orbital
method is an approximate self-consistent-field (SCF) nonempirical
method that is capable of calculating molecular orbitals for very
large transition metal systems and has built-in fragment analysis
routines that allow one to assemble transition metal cluster structures
from the ligand-containing fragments.
reflux (127 °C) for 6 h. These have been identified as Re2(CO)8(µ-
PBut2)(µ-H), 1, in 2% yield, Re2(CO)7(µ-PBut2)(PBut2H)(µ-H), 2,
in 5% yield, HRe(CO)4(PBut3), 3, in 4% yield, Re2(CO)6(PBut3)(µ-
PBut2)(µ-H), 4, in 31% yield, and Re2(CO)5(PBut3)(PBut2H)(µ-
PBut2O)(µ-H), 5, in 9% yield. All five compounds were charac-
terized by a combination of IR, 1H and 31P{1H} NMR, and single
crystal X-ray diffraction analyses.
An ORTEP showing the molecular structure of compound 1
is shown in Figure 1. This molecule is a dinuclear complex
that contains two rhenium atoms with a PBut2 ligand and a
hydrido ligand that bridge the Re-Re bond on opposite sides.
The molecule is structurally similar to the compound Re2(CO)8(µ-
PPh2)(µ-H), which has a bridging diphenylphosphido ligand
instead of a di-tert-butyl phosphido ligand.12 The Re-Re
distance in 1, Re1-Re2 ) 3.1291(2) Å, is similar in length to
Results and Discussion
Five new complexes were obtained from the reaction of
Re3(CO)12(µ-H)3 with PBut3 in solution in octane solvent at
(11) (a) Hall, M. B.; Fenskey, R. F. Inorg. Chem. 1972, 11, 768–775.
(b) Webster, C. E.; Hall, M. B. In Theory and Applications of Computational
Chemistry: The First Forty Years; Dykstra, C., Ed.; Elsevier: Amsterdam,
2005; Chapter 40, pp 1143–1165. (c) Manson, J.; Webster, C. E.; Perez,
L. M.; Hall, M. B. http://www.chem.tamu.edu/jimp2/index.html.
(12) Florke, U.; Haupt, H.-J. Z. Kristallogr. 1994, 209, 702.

6568 Organometallics, Vol. 26, No. 26, 2007
Adams et al.
Table 3. Crystallographic Data for Compounds 7, 8, and 9
7
8
9
empirical formula
fw
Re2P2O6N1C28H49
930.02
Re2P2O6N1C33H51
992.09
Re2P3O7C34H65
1051.17
cryst syst
lattice params
a (Å)
b (Å)
c (Å)
monoclinic
monoclinic
monoclinic
11.0279(4)
29.6026(10)
10.7886(3)
105.577(1)
3392.63(19)
P21/c (#14)
4
1.821
7.261
294
56.60
11.8592(3)
11.2504(3)
14.1065(4)
94.708(1)
1875.75(9)
P21 (#4)
2
1.757
6.573
294(2)
56.56
19.3906(7)
12.4072(5)
17.2721(8)
91.314(1)
4154.3(3)
P21/c (#14)
4
1.681
5.978
294(2)
52.04
ꢁ (deg)
V (Å3)
space group
Z value
Fcalc (g/cm3)
µ(Mo KR) (mm-1
temperature (K)
2θmax (deg)
)
no. obsd (I > 2σ(I))
no. params
7412
356
8830
400
7154
422
goodness of fit (GOF)
max. shift in cycle
1.101
0.002
0.0227; 0.0532
multiscan 1.000/0.832
1.201
1.055
0.002
0.0174; 0.0487
multiscan 1.000/0.631
0.865
1.298
0.001
0.0490; 0.1141
multiscan 1.000/0.433
1.631
residuals:a R1; wR2
absorp corr, max./min.
largest peak in final diff map (e-/Å3)
a R ) ∑hkl(|Fobs| - |Fcalc|)/∑hkl|Fobs|; Rw ) [∑hklw(|Fobs| - |Fcalc|)2/∑hklwFobs2 1/2, w ) 1/σ2(Fobs); GOF ) [∑hklw(|Fobs| - |Fcalc|)2/(ndata - nvari)]1/2
] .
Figure 2. ORTEP showing the molecular structure of 2 at 30%
thermal ellipsoid probability. Selected interatomic bond distances
(Å) and angles (deg) are as follows: Re1-Re2 ) 3.1524(2),
Re1-H1 ) 1.81(6), Re2-H1 ) 1.80(6), Re1-P2 ) 2.4924(10),
Re2-P2 ) 2.4530(10), Re2-P1 ) 2.4492(10), P1-H2 ) 1.50(5),
Re1-P2-Re2 ) 79.20(3).
Figure 1. ORTEP showing the molecular structure of 1 at 30%
thermal ellipsoid probability. Selected interatomic bond distances
(Å) and angles (deg) are as follows: Re1-Re2 ) 3.1291(2),
Re1-H1 ) 1.88(4), Re2-H1 ) 1.84(4), Re1-P1 ) 2.4906(9),
Re2-P1 ) 2.4975(9), Re1-P1-Re2 ) 77.70(2).
which showed a doublet at 4.77 ppm with appropriate one-bond
that found in Re2(CO)8(µ-PPh2)(µ-H), Re-Re ) 3.165 Å. The
hydrido ligand was located and refined structurally, and it
exhibits the usual high-field resonance, δ ) –15.15 ppm, in its
1H NMR spectrum. The complex is electronically saturated, as
both rhenium atoms have an 18-electron configuration. The
bridging di-tert-butyl phosphido ligand was apparently formed
by the cleavage of one tert-butyl group of a molecule of PBut3.
Several of the other products also contain a bridging di-tert-
butyl phosphido ligand; see below.
1
coupling to 31P, J(P,H) ) 333 Hz. This chemical shift and
1
coupling constant are in good agreement with the H NMR
spectrum of the PBut2H ligand found in the compound FeIr(µ-
CO)(CO)4(µ-PBut2)(PBut2H).13 Compound 2 is also saturated,
having a total of 34 valence electrons with a Re-Re single bond
between the two metal atoms. The PBut2H ligand may have
been formed by the elimination of isobutene from PBut3, but
this has not been confirmed. Such a process might have led to
the formation of the bridging PBut2 ligand and a bridging
hydrido ligand in compounds 1 and 2 and in 4 too; see below.
Compound 2 was characterized crystallographically, and an
ORTEP diagram of its molecular structure is shown in Figure
2. Compound 2 is also a dirhenium complex containing a
bridging PBut2 ligand and a bridging hydrido ligand as found
in 1. The hydrido ligand was located and refined crystallo-
An ORTEP diagram showing the molecular structure of
compound 3 is presented in Figure 3. Compound 3 is a six-
coordinate mononuclear rhenium complex having a pseudo-
octahedral arrangement of ligands. The complex has four
terminal carbonyl ligands, one terminal PBut3 ligand, and one
terminal hydrido ligand that is located cis to the PBut3 ligand.
It is structurally similar to the diphenyl(methoxy)phosphine
1
graphically. It exhibits the usual high-field H NMR signal, δ
) -15.00, with coupling to both phosphorus atoms (2J(P,H) )
2
10 Hz, J(P,H) ) 7 Hz, hydride 1H). In addition, there is a
terminal PBut2H ligand on one of the rhenium atoms, Re2, in
place of one of the CO ligands in 1. The presence of a hydrogen
atom on the phosphorus atom of the terminal di-tert-butyl
(13) Böttcher, H.-C.; Graf, M.; Merzweiler, K J. Organomet. Chem.
1996, 525, 191–197.
1
phosphine ligand was confirmed by the H NMR spectrum,

Dirhenium Complexes Containing the Bulky PBut3 Ligand
Organometallics, Vol. 26, No. 26, 2007 6569
Figure 5. Contour diagrams for some selected Fenske–Hall
molecular orbitals for 4. HOMO-7 1a (-12.25 eV), HOMO-3
2a (-9.05 eV), HOMO 3a (-7.42 eV). A line structure showing
the locations of the atoms in the diagrams is shown at the top right.
Figure 3. ORTEP showing the molecular structure of 3 at 30%
thermal ellipsoid probability. Selected interatomic bond distances
(Å) and angles (deg) are as follows: Re1-H1)1.62(4), Re1-P1
) 2.5795(12), P1-Re1-H1 ) 77.4(16), C12-Re1-P1 )
173.82(18).
structure is stabilized by the bulky PBut3 ligand P1. One of the
tert-butyl groups, C31, partially occupies the vacant coordination
site,asevidencedbytheRe1-P1-C31bondangle,C31-P1-Re2
) 103.65(19)°, which is 10° smaller than the C-P-Re angles
to the other tert-butyl groups on P1, C35-P1-Re2 ) 116.0(2)°,
C39-P1-Re2 ) 113.3(2)°. This could be evidence for a very
weak agostic C-H interaction from methyl group C32, which
makes the closest approach to Re2, Re2 · · · C32 ) 3.216 Å,
although the hydrogen atoms on the methyl groups were not
located in the structural analysis. The M-P-C angles involving
M-PBut3 groups with strong agostic interactions to the methyl
groups are more acute, 96–99°, than that found in 4.15
The hydrido ligand in 4 was located and refined crystallo-
graphically. It exhibits the characteristic high-field resonance
in the 1H NMR spectrum, δ ) –4.46, with appropriate couplings
2
2
to the two phosphine ligands, J(P,H) ) 12 Hz, J(P,H) ) 5
Hz, but its shift is much less than those of the bridging hydrido
ligands in 1 and 2. Although there are not many examples, there
is clear evidence that electronic unsaturation can produce
significant deshielding effects on bridging hydrido ligands. For
example, the hydride resonances of the unsaturated complexes
Re4(CO)12(µ3-H)4 and Os3(CO)10(µ-H)2 are much less shielded
than those of related saturated cluster complexes.16 The Re-Re
bond distance in 4, Re1-Re2 ) 3.1083(3) Å, is slightly shorter
than the Re-Re bond distances in 1 and 2. This may be due to
a decrease in steric interactions about Re(2) because there are
fewer ligands attached to it; however the bond is still signifi-
cantly longer than the Re-Re bond in Re2(CO)10, 3.042(1) Å,
which contains no bulky ligands.17
To develop a better understanding of the electronic structure
of 4, Fenske-Hall molecular orbital calculations were performed
on the structure as found in the solid state. To simplify these
calculations, each tert-butyl group was replaced by one hydrogen
atom at the typical P-H bond distance of 1.41 Å. Contour
diagrams of the most important occupied molecular orbitals
found in 4 are shown in Figure 5. The HOMO 3a consists
predominantly of π-bonding between the metal atoms and two
of the CO ligands, but there is also a significant interaction
between the hydrido ligand and one of the Re atoms, Re2. The
Re-Re bond is represented by the HOMO-3 2a, and the
bonding of the bridging hydrido ligand is represented best by
Figure 4. ORTEP showing the molecular structure of 4 at 30%
thermal ellipsoid probability. Selected interatomic bond distances
(Å) and angles (deg) are as follows: Re1-Re2 ) 3.1083(3),
Re1-P2 ) 2.4874(13), Re2-P2 ) 2.4175(13), Re2-P1 )
2.4831(13), Re1-H1 ) 1.76(5), Re2-H1 ) 2.02(5); C31-P1-Re2
) 103.65(19), C35-P1-Re2 ) 116.0(2), C39-P1-Re2 )
113.3(2).
complex HRe(CO)4{PPh2(OMe)}.14 The hydrido ligand in 3 was
located and refined structurally. The Re1-H1 bond distance,
1.62(4) Å, is similar to the Re-H bond distance, 1.60(8) Å,
found in HRe(CO)4{PPh2(OMe)}. The hydrido ligand exhibits
1
the characteristic high-field resonance, δ ) –4.92, in the H
NMR spectrum with appropriate coupling to the phosphine
2
ligand, J(P-H) ) 18 Hz.
An ORTEP drawing of the molecular structure of 4, the major
product of this reaction, is shown in Figure 4. The parent ion
in the mass spectrum, m/z 888, confirms the molecular formula.
This dirhenium complex contains a bridging PBut2 ligand and
a bridging hydrido ligand across a Re-Re bond, but unlike 1
and 2, compound 4 has only seven additional ligands. Atom
Re(1) has four CO ligands and Re(2) has two CO ligands and
one PBut3 ligand. Compound 4 is thus electron deficient by the
amount of two electrons. Atom Re1 has an 18-electron config-
uration, and atom Re2 formally has a 16-electron configuration,
and there is clear evidence for a vacant coordination site trans
to the CO ligand C21-O21 on Re(2). This ligand-deficient
(15) Cooper, A. C.; Streib, W. E.; Eistenstein, O.; Caulton, K. G. J. Am.
Chem. Soc. 1997, 119, 9069–9070.
(16) Humphries, A. P.; Kaesz, H. D. Prog. Inorg. Chem. 1979, 25, 145–
222.
(14) Albertin, G.; Antoniutti, S.; Garcia-Fontán, S.; Carballo, R.; Padoan,
F. J. Chem. Soc., Dalton Trans. 1998, 2071–2081.
(17) Churchill, M. R.; Amoh, K. N.; Wasserman, H. J. Inorg. Chem.
1981, 20, 1609.

6570 Organometallics, Vol. 26, No. 26, 2007
Adams et al.
Figure 6. Contour diagram of the lowest unoccupied orbital LUMO
4a (-2.95 eV) in 4 is shown on the left. A line structure showing
the orientation of the molecule and the locations of the atoms in
the MO diagram is shown on the right.
the HOMO-7 1a. The most interesting orbital is the lowest
unoccupied molecular orbital LUMO 4a. The major component
of this orbital lies trans to the CO(21) ligand; see Figure 6. It
clearly defines the so-called “vacant” site.
The 13C{1H} NMR spectrum of compound 4 shows only
three broad resonances in the CO region, 204.1, 190.2, and 187.9
ppm at 25 °C. Suspecting dynamical activity, variable-temper-
ature measurements were made and this was confirmed. A series
of spectra of 4 recorded at several different temperatures are
shown in Figure 7. At -40 °C four resonances were observed:
a triplet at 204.5 ppm (2C) with small and equal coupling to
the two phosphorus atoms, 2J(P1,C) ) 5 Hz, 2J(P2,C) ) 5 Hz;
a doublet at 190.5 ppm (1C) with larger coupling to the bridging
phosphido ligand P2, 2J(P2,C) ) 26 Hz; and a doublet at 188.5
ppm (1C) with small coupling to one of the phosphorus atoms,
2
2J(P2,C) ) 8 Hz, and 187.9 ppm (2C), d, J(P2,C) ) 5 Hz.
The small P-C couplings cannot be seen in Figure 7. The
resonance at 204.5 ppm is assigned to the two CO ligands on
Re2, CO(21) and CO(22), which are still dynamically averaged
at this temperature. The resonance at δ 190.5 is assigned to
CO(14) on Re1. The resonance at 188.5 ppm is assigned
to CO(12) on Re1. The resonance at 187.9 ppm is assigned
to CO(11) and CO(13) on Re1. These ligands are still dynami-
cally averaged at this temperature. As the temperature is lowered
still further, the resonances at 204.5 and 187.9 ppm broaden
and collapse into the baseline due to a slowing of the lower
temperature exchange process. At -110 °C, two very broad
resonances are beginning to resolve at 201 and 208 ppm for
(CO)21 and (CO)22 and there is a very broad resonance in the
baseline at 186 ppm for (CO)11 and (CO)13. The exchange
process is very rapid, and one would have to go much lower in
temperature to reach the slow exchange limit. The coalescence
temperature for this process is estimated to be at -100 °C, and
the rate of exchange at the coalescence temperature (kc) was
estimated by using the expression kc ) π∆ν0/(2)1/2, where ∆ν0
is the chemical shift difference between the maxima of the two
broad resonances observed at -110 °C. Substitution of kc in
the Eyring equation provides the free energy of activation for
the process at the coalescence temperature ∆Gq (at 173 K) )
7.3 kcal/mol. As the temperature is raised above -40 °C, all of
the resonances begin to broaden at approximately the same rate.
They have coalesced at about 108 °C. This broad resonance
continues to sharpen up to 140 °C, the highest temperature that
we could record. The changes are reversible. The broadening
and averaging of the resonances in the range -40 to 140 °C is
due to a second dynamical process leading to exchange of the
CO ligands between the two metal atoms and complete
averaging of all of the CO ligands.
Figure 7. Variable-temperature 13C{1H} NMR spectra for com-
pound 4 in d8-toluene solvent. *The spectrum at -110 °C was
recorded in diethyl ether solvent with a drop of CD2Cl2. **The
spectrum at 140 °C was recorded in xylene solvent with a drop of
d8-toluene.
between the two sides of the Re2P plane involving the bridging
phosphido ligand. In this process the CO ligands 21 and 22 on
Re2 exchange sites. As a consequence of this motion, the CO
ligands 11 and 13 on Re1 also exchange their sites. The structure
4 is converted to its mirror image labeled as 4* in Scheme 1.
In the high-temperature CO exchange process, all of the CO
ligands are exchanged. This requires the CO ligands to be
exchanged between the two metal atoms. For this process we
have adopted a 2 by 2 mechanism similar to that which was
established for the bridging and terminal CO ligands in
[CpFe(CO)(µ-CO)]2 many years ago.18 This mechanism B is
also shown in Scheme 1. In this process two CO ligands, 21
and 13, on opposite sides of the Re2P plane shift into bridging
positions to form the unobserved intermediate 4A. These two
CO ligands then shift to terminal positions on the other metal
atoms, i.e., Re1 for 21 and Re2 for 13, to form the mirror image
4* of the starting structure 4. This completes the first iteration
of the metal-metal exchange of the CO ligands. This structure
can be converted to its mirror image 4 via the low-temperature
The dynamical averaging observed in the variable-temperature
13C NMR can be explained by the two mechanisms. The low-
temperature process in the range -110 to -40 °C can be
explained by the exchange mechanism A shown in Scheme 1.
Through this process the vacant site oscillates back and forth
(18) Adams, R. D.; Cotton, F. A. J. Am. Chem. Soc. 1973, 95, 6589.

Dirhenium Complexes Containing the Bulky PBut3 Ligand
Organometallics, Vol. 26, No. 26, 2007 6571
Scheme 1
mechanism A, and then another pair of CO ligands, 22 and 14,
could be exchanged between the metal atoms by the mechanism
B. A similar process, not drawn, will lead to the exchange of
CO 12 between the two metal atoms. Note: there is no
experimental evidence of a distinction between the CO ligands
12 and 14 on Re1; that is, both participate in this process. These
cycles can repeat themselves until all CO ligands are exchanged.
2.457(2) Å. There are no reported structural characterizations
of rhenium complexes containing bridging dialkyl- or dia-
rylphosphidoxo ligands, but there are some polynuclear ruthe-
nium complexes containing related phosphidoxo ligands.19–21
The source of the oxygen atom bonded to the PBut2 group in
the bridging phosphidoxo ligand has not been definitively
established. Mass spectral and 31P NMR analyses of our PBut3
reagent showed that it contained significant amounts of the
phosphine oxide impurities OPBut3 and OP(H)But2.22 It seems
likely that the OdPBut2 ligand in 5 was derived from one of
these impurities. Diphenylphosphidoxo ligands have been
obtained from phosphine oxide precursors previously.19 The
OdPBut2 ligand serves as a three-electron donor. The P-O
distance in 5, P3-O1 ) 1.587(5) Å, is significantly longer than
that found in the free molecule OP(H)But3,22 where P-O )
1.4819(19) Å, but is similar to the P-O distances, 1.50–1.60
Å, observed for bridging phosphidoxo ligands in other ruthenium
complexes.19 The bridging hydrido ligand lies out of the Re1,
Re2, P3 plane by 0.76(7) Å in the direction of CO(21), and
this CO ligand is pushed away from it and from the Re-Re
bond as shown by the large bond angle C21-Re2-Re1 )
111.3(2)°. By contrast CO(23) on the other side of the molecule
moves toward the Re-Re bond, as shown by the acute angle
C23-Re2-Re1 ) 71.7(2)°. Although this angle is unusually
acute, one should not infer that there is any significant bonding
between the atoms C23 and Re1; in fact, the Re1 · · · C23 distance
of 3.198(1) Å is much too long to permit any significant direct
bonding interaction between these two atoms. The resonance
of the hydrido ligand occurs at δ -10.37, and it is coupled to
The final product obtained from the reaction of Re3(CO)12(µ-
H)3 with PBut3 is the new compound Re2(CO)5(PBut3)(PBut2H)(µ-
PBut2O)(µ-H), 5. The molecular weight of 5 was confirmed by
its mass spectrum, m/z ) 1022. Compound 5 was also
characterized by a single-crystal X-ray diffraction analysis, and
an ORTEP diagram of the molecular structure of 5 is shown in
Figure 8. This dirhenium complex contains a bridging di-tert-
butylphosphidoxo ligand, OdPBut2, and a bridging hydrido
ligand across the Re-Re single bond, Re1-Re2 ) 3.2048(4)
Å. The longer length of the Re-Re bond can be explained by
the presence of the less restrictive two-atom P-O bridge of
the di-tert-butylphosphidoxo ligand. The Re-O distance,
Re1-O1, is 2.067(5) Å. The Re-P distance is Re1-P1 )
2
2
all three phosphorus atoms, J(P1,H) ) 26 Hz, J(P2,H) ) 8
2
Hz, J(P3,H) ) 12 Hz.
As with 4, compound 5 contains only seven terminally
coordinated ligands. Atom Re1 has two CO ligands and one
PBut3 ligand, and Re2 has three CO ligands and a PBut2H ligand.
Thus, like compound 4, compound 5 is electron deficient by
the amount of two electrons. This deficiency resides formally
at atom Re1, which has a 16-electron configuration, but unlike
4 there is no well-defined vacant site on Re1. The 13C NMR
spectra of 5 were obtained by using a sample that was partially
Figure 8. ORTEP showing the molecular structure of 5 at 30%
thermal ellipsoid probability. Selected interatomic bond distances
(Å) and angles (deg) are as follows: Re1-Re2 ) 3.2048(4),
Re1-O1 ) 2.067(5), Re1-P1 ) 2.457(2), Re1-H1 ) 1.67(8),
Re2-P3 ) 2.4329(18), Re2-P2 ) 2.4688(18), Re2-H1 ) 1.93(7),
P2-H2 ) 1.39(6), Re1 · · · C23 ) 3.198, Re1 · · · O23 ) 3.745(1);
P3-Re2-P2 ) 165.56(6), O1-P3-Re2 ) 105.19(19), P3-O1-Re1
) 115.4(3).
(19) Fogg, D. E.; Taylor, N. J.; Meyer, A.; Carty, A. J. Organometallics
1987, 6, 2252.
(20) Bruce, M. I.; Humphrey, P. A.; Skelton, B. W.; White, A. H. J.
Organomet. Chem. 1997, 539, 141–146.
(21) Bennett, D. W.; Siddiquee, T. A.; Haworth, D. T.; Kabir, S. E.;
Hyder, M. I.; Ahmed, S. J. J. Chem. Cryst. 2004, 34, 361.
(22) Dornhaus, F.; Lerner, H.-W.; Bolte, M. Acta Crystallogr. 2005,
E61, o657–o658.

6572 Organometallics, Vol. 26, No. 26, 2007
Adams et al.
Scheme 2
on Re2. As the temperature is raised, the resonances at 208.4
and 207.4 ppm start to broaden and coalesce at 0 °C. Similarly,
the resonances at 199.7 and 196.5 ppm start to broaden and
coalesce at about +10 °C. The broadening of all four resonances
is approximately the same, indicating that the rate of the
exchange for the two averaging pairs of resonances is the same.
The activation energy for the averaging process, ∆Gq (at 273
K) ) 12.8 kcal/mol, was obtained from the coalescence
temperature. As the temperature is raised to 90 °C, the
resonances sharpen. The observation of P-C coupling in the
fast exchange limit at 90 °C confirms that the exchange process
is a nondissociative one. The resonance at 199.3 ppm assigned
to (CO)22 showed no broadening throughout the entire tem-
perature, and there was no evidence of exchange between the
resonances of the CO ligands on Re1 with those on Re2.
The simplest exchange process that would account for the
pairwise exchange of the CO ligands on Re1 and Re2 is shown
in Scheme 2. This involves a shift of the hydrido ligand to the
other side of the Re-Re bond. CO(21) and CO(23) on Re2
will rock back and forth, but no bonds are broken. The first
structure, 5, is converted into its mirror image, 5*. The
environments of ligands CO(11) and CO(12) on Re1 are
exchanged as a consequence of the changes on Re2.
To investigate the properties of the ligand-deficient complex
4, it was first treated with CO. The reaction of 4 with CO gas
at 25 °C/1 atm was complete in a matter of minutes, and the
product 6 was subsequently isolated in 97% yield. Compound
6 was characterized crystallographically, and an ORTEP diagram
of its molecular structure is shown in Figure 10. Compound 6
is a CO adduct of 4. The basic structure is the same as that of
4 except that there is an additional CO ligand on the metal atom
Re2 that contains the PBut3 ligand. Indeed, a terminal CO ligand,
Figure 9. 13C{1H} NMR spectra at 125.8 MHz for compound 5 at
various temperatures in d8-toluene solvent.
enriched (∼30%) with 13CO. The 13C NMR spectrum of 5 at
room temperature exhibits three broad resonances at 207.2 (s,
2C), 198.8 (s, 1C), and 197.9 ppm (s, 2C). The broad resonances
suggested dynamical activity, and so variable-temperature
spectra were recorded. The 13C{1H} NMR spectra of compound
5 at various temperatures in the carbonyl region are shown in
Figure 9. The limiting low-temperature spectrum was obtained
at -60 °C. This spectrum exhibits five well-resolved resonances
at δ ) 208.4, 207.4, 199.7, 199.3, and 196.5, which correspond
to the five CO ligands. The two resonances at 208.4 and 207.4
2
ppm are doublets with J(P1,C) of 4 and 6 Hz, respectively.
These resonances are assigned to the two CO ligands on Re1.
The two resonances at 199.7 and 196.5 ppm are triplets and
are assigned to the two CO ligands CO(21) and CO(23) on Re2.
Both resonances show two-bond coupling to both P2 and P3
Figure 10. ORTEP of the molecular structure of 6 showing 30%
thermal ellipsoid probability. Selected interatomic bond distances
(Å) and angles (deg) are as follows: Re1-Re2 ) 3.17813(18),
Re1-P2 ) 2.4871(9), Re2-P2 ) 2.4461(8), Re2-P1 ) 2.5931(8),
Re1-H1 ) 1.93(4), Re2-H1 ) 1.87(4); C31-P1-Re2 )
113.76(12), C39-P1-Re2 ) 111.62(12), C35-P1-Re2 )
110.16(14).
2
(2J(P2,C) 8 Hz, J(P3,C) 8 Hz). The resonance at 199.3 ppm
does not exhibit any coupling to P2 or P3. Because of its similar
chemical shift to CO(21) an CO(23), it is assigned to CO(22)

Dirhenium Complexes Containing the Bulky PBut3 Ligand
Organometallics, Vol. 26, No. 26, 2007 6573
Figure 12. ORTEP of the molecular structure of 7 showing 30%
thermal ellipsoid probability. Selected interatomic bond distances
(Å) and angles (deg) are as follows: Re1-Re2 ) 3.18077(19),
Re1-N1 ) 2.150(3), Re1-P2 ) 2.5035(9), Re1-H1 ) 1.93(4),
Re2-P2 ) 2.4661(9), Re2-P1 ) 2.5789(8), Re2-H1 ) 1.72(4);
N1-Re1-Re2 ) 86.92(8).
Figure 11. (a) 13C{1H} NMR spectrum of 6 having all CO sites
enriched to ∼30% with 13CO. (b) 13C{1H} NMR spectrum of 6
formed by the addition of 13CO to a sample of 4 containing CO at
the natural abundance level.
phosphorus atoms are assigned to the carbonyls on Re2. The
two equivalent CO ligands CO(21) and CO(23) are assigned to
the resonance at 199.3 ppm because of the relative peak
intensity, and the resonance at 195.7 ppm is assigned to CO(22).
To identify the site of CO addition, 13CO was added to a sample
of 4 having its 13CO level at the natural abundance level. The
resulting spectrum is shown in the bottom spectrum of Figure
11. Only one resonance was observed, and it corresponds to
the sites (CO)11 and (CO)13. This clearly demonstrates that
the added CO ligand was added at the electronically saturated
metal atom Re1 and was not directly added to the vacant site
on Re2. The CO ligand that occupies the vacant site in 6 must
have been one of the originally coordinated CO ligands, and
the increase in the number of CO ligands on the phosphine-
substituted metal atom Re2 must have been the result of a shift
of one of the CO ligands on Re1 to Re2; see Scheme 3.
Scheme 3
CO(23), lies precisely in the position where the vacant site was
located in 4. Compound 6 thus has 34 valence electrons between
the two rhenium atoms, and it is electronically saturated. The
Re1-Re2 bond distance has increased in length by 0.07 Å to
3.17813(18) Å on going from 4 to 6. The tert-butyl group in 4
that made the close approach to the vacant site, C(31), has
backed away in 6, and all C-P-Re angles are now greater than
110°,C31-P1-Re2)113.76(12)°,C39-P1-Re2)111.62(12)°,
C35-P1-Re2 ) 110.16(14)°. The hydrido ligand H1 was
located and refined crystallographically. It has shifted back into
the Re1, Re2, P2 plane, and its 1H NMR resonance has shifted
One can only speculate as to why ligand addition proceeds
at the saturated metal atom Re1 and not directly to the
unsaturated metal atom Re2, but this might be due to the
presence of the bulky PBut3 ligand on Re2. As noted above,
the methyl group C32 on one of the tert-butyl groups does
appear to cover the vacant site and could block the direct
addition of an uncoordinated molecule to this metal atom. Thus,
it might be easier to shift a coordinated CO ligand from the
neighboring metal atom Re1 to Re2 and the CO addition could
then occur at Re1. The CO shift may precede or more likely
accompanies the CO addition to Re1. It is less likely that the
shift comes after the CO addition to Re1. When a solution of 6
in heptane solvent was heated to reflux for 1½ h, it was
converted back into 4 in 96% yield.
To pursue the study of ligand additions to 4 further, reactions
of 4 with MeCN and PhCN were investigated. Both reactions
yielded 1:1 adducts with these compounds. The MeCN complex
7 was isolated in 82% yield. The PhCN complex 8 was isolated
in 44% yield. The structures of both complexes were established
crystallographically, and ORTEP diagrams of the molecular
structures of 7 and 8 are shown in Figures 12 and 13,
respectively. For both complexes it can be seen that the nitrile
was added to the electronically saturated rhenium atom Re1,
and there is a CO ligand in the former vacant site on Re2. Thus,
as in the CO addition to form 6 from 4, the addition of nitriles
2
to a higher field value, δ ) -14.01 (dd, J(P,H) ) 15 Hz,
2J(P,H) ) 8 Hz). The 13C{1H} NMR spectrum of 6 (enriched
with 13CO to 30%) at room temperature is shown as the top
spectrum in Figure 11. There are five resonances. The observed
splittings are due to 31P-C couplings. A selective phosphorus
decoupling 13C{1H}{31P} NMR experiment revealed that the
three resonances at 188.6 ppm (2J(P2,C) 25.9 Hz), 187.2 ppm
(2J(P2,C) 5.9 Hz), and 185.4 ppm (2J(P2,C) 6.8 Hz) are coupled
only to the bridging phosphorus atom P2, while the two
resonances at 199.3 (2J(P1,C) 8.0 Hz, (2J(P2,C) 5.5 Hz) and
195.7 ppm (2J(P1,C) 5.2 Hz, (2J(P2,C) 3.0 Hz) are coupled both
to P1 and to P2. The three resonances coupled only to P2 are
assigned to the carbonyl ligands on Re(1). The resonance at
188.6 ppm is assigned to (CO)14 trans to P2 and therefore
exhibits the largest P-C coupling of all (2J(P2,C) 25.9 Hz).
The resonance at 187.2 ppm (2C) is assigned to the two
equivalent ligands CO(11) and CO(13) on the basis of the larger
peak intensity, and the resonance at 185.4 ppm is assigned to
CO(12). The two resonances that show coupling to both

6574 Organometallics, Vol. 26, No. 26, 2007
Adams et al.
Figure 13. ORTEP of the molecular structure of 8 at 30% thermal
ellipsoid probability. Selected interatomic bond distances (Å) and
angles (deg) are as follows: Re1-Re2 ) 3.1644(2), Re1-N1 )
2.142(3), Re1-P2 ) 2.4931(11), Re2-P2 ) 2.4596(10), Re2-P1
)2.5772(10),Re1-H1)1.91(5),Re2-H1)1.69(5);N1-Re1-Re2
) 91.31(10).
Figure 16. Two-dimensional EXSY (NOESY) 13C{1H} NMR
spectrum of 9 at 60 °C in d8-toluene solvent in an atmosphere of
13CO. Data were acquired at 125.8 MHz with a 500 ms mixing
time. Signals labeled with “x” are from traces of impurity of 5.
Scheme 4
shift of one of the CO ligands to Re2. The Re-Re bond lengths
in 7 and 8 are similar to that in 6, 3.18077(19) and 3.1644(2)
Å, respectively. The hydrido ligands were located in both
compounds and were found to be bridging ligands across the
Re-Re bond in the plane of the Re1, Re2, P2 triangle. This is
consistent with the highly shielded resonances observed for these
ligands in their 1H NMR spectra: For 7, δ ) –11.76 (dd, 2J(P,H)
Figure 14. ORTEP showing the molecular structure of 9 at 30%
thermal ellipsoid probability. Selected interatomic bond distances
(Å) and angles (deg) are as follows: Re1-Re2 ) 3.3711(5),
Re1-O1 ) 2.185(6), Re1-P1 ) 2.539(2), Re2-P3 ) 2.465(2),
Re2-P2 ) 2.522(6), P3-O1 ) 1.565(6), Re1-H1 ) 2.10(9),
Re2-H1 ) 1.66(9); P3-Re2-P2 ) 172.42(15), P2-Re2-Re1
103.92(15), O1-P3-Re2 ) 108.7(2), P3-O1-Re1 ) 117.1(3).
2
2
) 16 Hz, J(P,H) ) 9 Hz) and for 8, δ ) –11.60 (dd, J(P,H)
) 16 Hz, 2J(P,H) ) 9 Hz). The nitrile ligands lie trans to a CO
ligand on Re1, precisely the same location that the CO ligand
was added to 4 to form 6. When compounds 7 and 8 were
dissolved in any solvent that does not contain the corresponding
nitrile, they were immediately converted back to 4. The 1H NMR
spectrum of 7 in d3-MeCN solvent did not show the resonance
of the MeCN ligand because it was rapidly exchanged with d3-
MeCN from the solvent. The 13C{1H} NMR spectrum of 7 was
obtained by dissolving a sample of 4 in d3-MeCN that was partially
enriched (30%) with 13CO. There are six resonances of equal
intensity for the six inequivalent CO ligands. Just as in the 13C{1H}
NMR spectrum of compound 6, the three higher field resonances
at 193.5, 196.2, and 196.8 ppm are assigned to the CO’s on
2
Re1. Large coupling, J(P2,C) 38.5 Hz, for the resonance at
196.8 is attributed to CO(13), which is trans to the bridging
phosphine atom P2. The lower field resonances at 200.1, 201.9,
and 203.1 ppm are assigned to the CO’s on Re2. The resonances
at 201.9 and 203.1 ppm are assigned to either CO(11) or CO(13).
It is interesting to note that these two CO ligands were equivalent
in compound 6 at 195.7 ppm; however, they are now inequiva-
Figure 15. 13C{1H} NMR spectrum of 9 at room temperature in
d8-toluene solvent.
to 4 also proceeds mechanistically by addition to the electroni-
cally saturated, 18-electron rhenium atom Re1 followed by a

Dirhenium Complexes Containing the Bulky PBut3 Ligand
Organometallics, Vol. 26, No. 26, 2007 6575
Scheme 5
lent due to the lowering of the symmetry produced by the
presence of the NCMe ligand.
of 9 at 60 °C in the presence of free 13CO. This spectrum is
shown in Figure 16. Most interestingly, cross-peaks were
observed between the free CO, observed at 184 ppm, and the
doublet resonance of 9 at 196.8 ppm. If the assignment of this
resonance is correct, then this indicates that the free CO is
exchanging with the CO ligands on Re1 of 9, and accordingly
with Re1 on 5. This is shown schematically in Scheme 4. Thus,
in contrast to the addition of CO to 4, the addition of CO to 5
occurs at the electron-deficient, 16-electron metal atom, Re1.
To investigate the properties of the ligand-deficient complex
5, it was also treated with CO. The reaction of 5 with CO gas
at 25 °C/1 atm appeared to be complete in a matter of minutes,
and the product 9 was obtained in 57% yield by cooling the
reaction solution to -80 °C overnight, under an atmosphere of
CO. Compound 9 is a CO adduct of 5. It was characterized by
a single-crystal X-ray diffraction analysis, and an ORTEP
diagram of the molecular structure of 9 is shown in Figure 14.
Like 5, compound 9 is a dirhenium complex that contains a
bridging OPBut2 ligand and a bridging hydrido ligand across a
Re-Re bond. The Re-Re bond is longest of all the compounds
that we have reported in this study, Re1-Re2 ) 3.3711(5) Å,
but there is still a Re-Re single bond present. The longer length
of the Re-Re bond in this molecule can be attributed to the
presence of two bulky phosphine ligands and one bulky
phosphidoxo ligand. The phosphidoxo ligand is a two-atom
bridge as in 5 with O1 bonded to Re1 and P3 bonded to Re2,
Re1-O1 ) 2.185(6) Å, Re2-P3 ) 2.465(2) Å. The P-O
distance is similar to that in 5, P3-O1 ) 1.565(6) Å. The
hydrido ligand was located but refined with a fixed isotropic
thermal parameter. In this molecule it lies essentially in the Re1,
Re2, P3 plane. Its resonance is very highly shielded, δ ) –17.95
and it is coupled to all three phosphorus atoms, 2J(P1,H) ) 17
Hz, 2J(P2,H) ) 8 Hz, 2J(P3,H) ) 5 Hz. Unlike 5, compound 9
has eight terminally coordinated ligands. Atom Re1 has three
CO ligands and one PBut3 ligand, and Re2 has three CO ligands
and a PBut2H ligand. Thus, compound 9 is electronically
saturated; both metal atoms have 18-electron configurations.
To try to ascertain the site of CO ligand addition to 5 to form
9, a solution of 9 was placed in an NMR tube under an
atmosphere of 13CO at room temperature. The spectrum was
recorded as quickly as possible and showed that all CO ligand
sites were rapidly and equally enriched with 13CO. This 13C
NMR of 9 is shown in Figure 15. It exhibits only three
resonances of equal intensity. The resonance at 199.0 ppm
appears as a triplet, really as a doublet of doublets, 2J(P2,C) )
Summary and Conclusions
A summary of the products that were obtained from the
reaction of Re3(CO)12(µ-H)3 with PBut3 is given in Scheme 5.
Some years ago, Liu reported that the reaction of Re3(CO)12(µ-
H)3 with PPh3 gave the tris-PPh3 product Re3(CO)9(µ-PPh3)3(µ-
H)3.23 We did not obtain any evidence for a tris-PBut3 product
of Re3(CO)12(µ-H)3 in our studies with the bulky PBut3 ligand.
Instead, mono- and dirhenium products were obtained by
reactions resulting from fragmentations of the Re3 cluster of
the parent compound. This may be due to the extreme steric
crowding effects of the PBut3 ligand. Two of the products, 2
and 5, contained PBut2H ligands that were evidently formed by
degradation of the PBut3 ligand itself. Three of the products, 1,
2, and 4, contained a combination of a bridging PBut2 ligand
and a bridging hydrido ligand also formed by a degradation of
the PBut3.
It was found that the steric influences of the PBut3 ligands
also have profound effects on the coordination chemistry of the
dirhenium complexes. In particular, compounds 4 and 5 are both
electronically unsaturated 32-electron complexes. Compound 4
has a well-defined vacant coordination site that is partially
occupied by one of the methyl groups from a neighboring PBut3
ligand. No vacant site is evident in compound 5, but both
compounds readily add and eliminate CO to form the electroni-
cally saturated adducts 6 and 9. While compound 9 adds CO at
the unsaturated metal atom, surprisingly, compound 4 adds CO
and the nitriles MeCN and PhCN by an addition at the
electronically saturated metal atom, which is accompanied by
a shift of one of the CO ligands from the saturated metal atom
to the unsaturated metal atom.
2
8 Hz, J(P3,C) ) 8 Hz), and is assigned to the two equivalent
CO ligands, CO(21) and CO(23), on Re2; see Figure 14 for
labeling. The resonance at 196.8 ppm is a doublet (2J(P1,C) )
6 Hz) and is assigned to the two equivalent CO ligands, CO(11)
and CO(13), on Re1. There is only one remaining resonance, a
singlet at 194.8 ppm. This is assigned to the two CO ligands
CO(12) and CO(22). These ligands are inequivalent, so it must
be that their resonances are simply accidently shift equivalent.
Since there was no observable selectivity in the addition of 13CO
to compound 9, these experiments did not reveal the site of
CO addition to 5. Evidence for the site of CO addition was
revealed, however, by recording a 2D EXSY 13C NMR spectrum
Acknowledgment. This research was supported by the
Office of Basic Energy Sciences of the U.S. Department of
Energy under Grant No. DE-FG02-00ER14980. Dedicated
to the memory of F. Albert Cotton.
Supporting Information Available: CIF files for each of the
structural analyses are available. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM700790C