Synthesis and Properties of IrRe2(μ-H)2(CO)9(η5-C 9H7)

Article abstract of DOI:10.1021/ic960990i

The slow addition of Re₂(μ-H)₂(CO)₈ to a solution of Ir(CO)(η²C₉H₇) in hexane at reflux provides IrRe₂(μ-H)₂(CO)₉(μ⁵-C ₉H₇) (1) in 80% yield. The molecular structure of 1 shows an IrRe₂ triangle incorporating one Ir(CO)(η⁵-C₉H₇) and two Re(CO)₄ fragments. The strongly different IT-Re distances suggest that one hydride ligand bridges one IT-Re edge and the other hydride bridges the Re-Re edge. Low-temperature ¹H and ¹³C NMR spectra are consistent with this structure; at higher temperatures a dynamic process involving migration of one hydride ligand between the two Ir-Re edges is observed. Cluster 1 is readily deprotonated with KOH/ EtOH, and the resulting anion has been isolated as the PPN salt, [PPN][μ-H)(CO)₉-C₉H₇)] (2). Both the ¹H and low temperature ¹³C NMR spectra of 2 are consistent with a structure in which the remaining hydride ligand bridges the Re-Re edge. Variable-temperature ¹³C NMR spectra indicate that 2 undergoes CO scrambling localized on the Ir-Re edges. The reaction of 1 with PPh₃ leads to IrRe₂(μ-H)₂(CO)₈(PPh₃)(η ⁵-C₉H₇) (3), which contains the phosphine on a rhenium atom, as well as to cluster fragmentation.

Full text of DOI:10.1021/ic960990i

Inorg. Chem. 1997, 36, 4397-4404
4397
Synthesis and Properties of IrRe2(µ-H)2(CO)9(η5-C9H7)
Matthew C. Comstock, Teresa Prussak-Wieckowska, Scott R. Wilson, and John R. Shapley*
School of Chemical Sciences, University of Illinois, Urbana, Illinois 61801
ReceiVed August 14, 1996X
The slow addition of Re2(µ-H)2(CO)8 to a solution of Ir(CO)(η2-C8H14)(η5-C9H7) in hexane at reflux provides
IrRe2(µ-H)2(CO)9(η5-C9H7) (1) in 80% yield. The molecular structure of 1 shows an IrRe2 triangle incorporating
one Ir(CO)(η5-C9H7) and two Re(CO)4 fragments. The strongly different Ir-Re distances suggest that one hydride
1
ligand bridges one Ir-Re edge and the other hydride bridges the Re-Re edge. Low-temperature H and 13C
NMR spectra are consistent with this structure; at higher temperatures a dynamic process involving migration of
one hydride ligand between the two Ir-Re edges is observed. Cluster 1 is readily deprotonated with KOH/
EtOH, and the resulting anion has been isolated as the PPN salt, [PPN][IrRe2(µ-H)(CO)9(η5-C9H7)] (2). Both the
1H and low temperature 13C NMR spectra of 2 are consistent with a structure in which the remaining hydride
ligand bridges the Re-Re edge. Variable-temperature 13C NMR spectra indicate that 2 undergoes CO scrambling
localized on the Ir-Re edges. The reaction of 1 with PPh3 leads to IrRe2(µ-H)2(CO)8(PPh3)(η5-C9H7) (3), which
contains the phosphine on a rhenium atom, as well as to cluster fragmentation.
8-10
11
Introduction
of PtRe2
as well as IrRe2 mixed-metal clusters. For
example, the reaction of Re2(µ-H)2(CO)8 with Pt(η4-C8H12)2
provided the trinuclear cluster, PtRe2(µ-H)2(CO)8(η4-C8H12).8
Reaction of the latter with 2 equiv of PPh3 provided the
compounds PtRe2(µ-H)2(CO)8(PPh3)2, which had been made
previously from the reaction of Re2(µ-H)2(CO)8 with Pt(η2-
C2H4)(PPh3)2.9 Furthermore, the reaction of Re2(µ-H)2(CO)8
with [Ir(CO)4]- led to several clusters based on a IrRe2
framework, such as [IrRe2H2(CO)11]-, with a terminal hydride,
and a hexanuclear cluster, [{IrRe2(µ-H)(CO)11}2]2-, consisting
of two IrRe2 triangles joined by an Ir-Ir bond.11 We now report
that the reaction of Ir(CO)(η2-C8H14)(η5-C9H7)12 with Re2(µ-
H)2(CO)8 gives the trinuclear cluster IrRe2(µ-H)2(CO)9(η5-C9H7)
(1), as shown in Scheme 1. Furthermore, deprotonation of 1
leads to [PPN][IrRe2(µ-H)(CO)9(η5-C9H7)] (2), and the reaction
The incorporation of indenyl-substituted metal fragments into
metal clusters is a potential way to translate the enhanced
reactivity of the “indenyl ligand effect”1 from mononuclear
compounds to polynuclear compounds. We recently reported
that the reaction of Ir(CO)2(η5-C9H7) with Rh(η2-C2H4)2(η5-
C9H7) led to formation of the trinuclear clusters Ir3-xRhx(µ-
CO)3(η5-C9H7)3 (x ) 0-2) in good yields,2 and the compound
Rh3(µ-CO)3(η5-C9H7)3 had been studied previously.3 These
compounds react readily with carbon monoxide to form mono-
nuclear products, whereas the corresponding cyclopentadienyl
compounds are much less reactive. For example, Ir3(µ-CO)3-
(η5-C9H7)3 affords Ir(CO)2(η5-C9H7) quickly at room temper-
ature, but Ir3(CO)3(η5-C5H5)3 generates Ir(CO)2(η5-C5H5) only
slowly in refluxing xylene (140 °C).4 Thus, indenyl ligand
substitution does appear to enhance the reactivity of these
clusters, but facile metal-metal bond scission precludes further
cluster-based chemistry. We have been investigating routes
toward other clusters containing indenyl ligands, and we now
wish to report our results with the mixed-metal cluster, IrRe2-
(µ-H)2(CO)9(η5-C9H7) (1).
(6) (a) Adams, R. D. In ComprehensiVe Organometallic Chemistry II;
Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: New
York, 1995; Vol. 10, Chapter 1, pp 6, 7. (b) Barnes, C. E. In
ComprehensiVe Organometallic Chemistry II; Abel, E. W., Stone, F.
G. A., Wilkinson, G., Eds.; Pergamon: New York, 1995; Vol. 8,
Chapter 4, pp 429-431, 512. (c) Adams, R. D. In The Chemistry of
Metal Cluster Complexes; Shriver, D. F., Kaesz, H. D., Adams, R.
D., Eds.; VCH: New York, 1990; Chapter 3, pp 153-158. (d) Barr,
R. D.; Green, M.; Howard, J. A. K.; Marder, T. B.; Stone, F. G. A. J.
Chem. Soc., Chem. Commun. 1983, 759. (e) Barr, R. D.; Green, M.;
Howard, J. A. K.; Marder, T. B.; Orpen, A. G.; Stone, F. G. A. J.
Chem. Soc., Dalton Trans. 1984, 2757. (f) Barr, R. D.; Green, M.;
Marsden, K.; Stone, F. G. A.;Woodward, P. J. Chem. Soc., Dalton
Trans. 1983, 507. (g) Barnes, C, E; Dial, M. R.; Orvis, J. A.; Staley,
D. L.; Rheingold, A. L. Organometallics 1990, 9, 1021. (h) Barnes,
C, E.; Dial, M. R. Organometallics 1988, 7, 782.
A general conceptual route to trinuclear clusters is the addition
of mononuclear metal fragments to unsaturated MdM species.5
Compounds of the form M2(µ-CO)2(η5-L)2 (M ) Co, Rh, Ir; L
) C5H5, C5Me5) are well-established metal cluster synthons.6
The related unsaturated compound, Re2(µ-H)2(CO)8,7 has also
shown some applications in cluster synthesis, leading to a variety
(7) Bennett, M. J.; Graham, W. A. G.; Hoyano, J. K.; Hutcheon, W. L. J.
Am. Chem. Soc. 1972, 94, 6232.
(8) (a) Ciani, G.; Moret, M.; Sironi, A.; Antognazza, P.; Beringhelli, T.;
D’Alfonso, G.; Della Pergola, R.; Minoja, A. J. Chem. Soc.,Chem.
Commun. 1991, 1255. (b) Antognazza, P.; Beringhelli, T.; D’Alfonso,
G.; Minoja, A.; Ciani, G.; Moret, M.; Sironi, A. Organometallics 1992,
11, 1777.
(9) (a) Beringhelli, T.; Ceriotti, A.; D’Alfonso, G.; Della Pergola, R.; Ciani,
G.; Moret, M. Sironi, A. Organometallics 1990, 9, 1053. (b)
Beringhelli, T.; D’Alfonso, G.; Minoja, A. P. Organometallics 1991,
10, 394.
(10) Xiao, J.; Puddephatt, R. J. Coord. Chem. ReV. 1995, 143, 457.
(11) Beringhelli, T.; Ciani, G.; D’Alfonso, G.; Garlaschelli, L.; Moret, M.;
Sironi, A. J. Chem. Soc., Dalton Trans. 1992, 1865.
X Abstract published in AdVance ACS Abstracts, September 1, 1997.
(1) (a) Ji, L.-N.; Rerek, M. E.; Basolo, F. Organometallics 1984, 3, 740.
(b) Rerek, M. E.; Basolo, F. J. Am. Chem. Soc. 1984, 106, 5908. (c)
Kakkar, A. K.; Taylor, N. J.; Marder, T. B.; Shen, J. K.; Hallinan, N.;
Basolo, F. Inorg. Chim. Acta 1992, 198-200, 219.
(2) Comstock, M. C.; Wilson, S. R.; Shapley, J. R. Organometallics 1994,
13, 3805.
(3) (a) Caddy, P.; Green, M.; O’Brien, E.; Smart, L. E.; Woodward, P.
Angew. Chem., Int. Ed. Engl. 1977, 16, 648; Angew. Chem. 1977, 89,
671. (b) Al-Obaidi, Y. N.; Green, M.; White, N. D.; Taylor, G. E. J.
Chem. Soc., Dalton Trans. 1982, 319.
(4) Shapley, J. R.; Adair, P. C.; Lawson, R. J.; Pierpont, C. G. Inorg.
Chem. 1982, 21, 1701.
(5) (a) Hoffmann, R. Angew. Chem., Int. Ed. Engl. 1982, 21, 711; Angew.
Chem. 1982, 94, 725. (b) Stone, F. G. A. Angew. Chem., Int. Ed. Engl.
1984, 23, 89; Angew. Chem. 1984, 96, 85.
(12) (a) Szajek, L. P.; Lawson, R. J.; Shapley, J. R. Organometallics 1991,
10, 357. (b) Szajek, L. P.; Shapley, J. R. Organometallics 1994, 13,
1395.
S0020-1669(96)00990-1 CCC: $14.00 © 1997 American Chemical Society

4398 Inorganic Chemistry, Vol. 36, No. 20, 1997
Comstock et al.
Scheme 1
2093 m, 2030 s, 2008 s, 1983 m cm-1). The extracts were dried on a
rotary evaporator, and the orange residue was redissolved in CH2Cl2.
A small amount of neutral alumina I (Aldrich) was added, and the
mixture was dried under vacuum, and then placed on a 15 cm × 1 cm
column of neutral alumina I. Elution with Et2O removed a yellow
fraction that contained unreacted Ir(CO)(η2-C8H14)(η5-C9H7), identified
by infrared spectroscopy.12 Elution with CH2Cl2 removed an orange
band that was dried under vacuum to give orange, crystalline 1.
Yield: 86 mg (0.092 mmol, 80% based on Ir). IR (νCO, hexane): 2104
of 1 with PPh3 provides both IrRe2(µ-H)2(CO)8(PPh3)(η5-C9H7)
(3) as well as considerable cluster fragmentation.
Experimental Section
General Procedures. All reactions were conducted under an
atmosphere of nitrogen with use of standard Schlenk techniques. Ir-
(CO)(η2-C8H14)(η5-C9H7) was prepared by the literature method.12 Re2-
(µ-H)2(CO)8 was prepared by a modification of the literature proce-
dure;13 using benzene rather than hexane led to a higher yield (62% vs
35%). Solvents for preparative use were dried by standard methods
and distilled prior to use. Deuterated solvents for NMR studies, (CD3)2-
CO and CD2Cl2 (Cambridge Isotope Laboratories), were used as
received.
Proton NMR spectra were recorded on General Electric QE-300 or
GN300NB spectrometers and were referenced to residual solvent
resonances (δ 2.04 for acetone-d5 and δ 5.32 for CHDCl2). Carbon-
13 NMR spectra were recorded on General Electric GN300NB (at 75
MHz), GN500 (at 125 MHz) or Varian U400 (at 100 MHz) spectrom-
eters and were referenced to solvent resonances (δ 29.8 (CD3)2CO or
δ 53.8 for CD2Cl2). Phosphorus-31 spectra were recorded at 121.6
MHz on a General Electric GN-300NB spectrometer and referenced
to external 85% H3PO4. Infrared spectra were recorded on a Perkin-
Elmer 1750 FT spectrophotometer. Mass spectra were recorded on
either a Finnigan-Mat 731 spectrometer (field desorption, FD) or a VG
ZAB-SE spectrometer (fast atom bombardment, FAB) by the staff of
the Mass Spectrometry Laboratory of the School of Chemical Sciences.
Microanalyses were performed by the staff of the School Microana-
lytical Laboratory.
m, 2076 m, 2013 s, 2000 m, 1988 sh, 1982 m, 1969 m, 1945 m cm-1
.
Anal. Calcd for C18H9O9IrRe2: C, 23.15; H, 0.97. Found: C, 23.17;
H, 0.96. FD-MS (100 °C): m/z (193Ir, 187Re) 936, IrRe2H2(CO)9(C9H7)+.
[PPN][IrRe2(µ-H)(CO)9(η5-C9H7)] (2). A yellow solution of 1 (40
mg 0.042 mmol) in ethanol was treated with KOH in ethanol (2.2 mL,
0.021 M, 0.046 mmol). The color changed immediately to deep red.
A solution of [PPN][Cl] (243 mg, 0.424 mmol) in ethanol (5 mL) was
added via cannula, the volume was reduced to ca. 5 mL under vacuum,
and the mixture was held at -20 °C for 12 h. The red needles that
precipitated were washed with ethanol at 0 °C (6 × 5 mL) and Et2O (4
× 5 mL) and dried under vacuum. Yield: 31 mg (0.021 mmol, 50%).
IR (νCO, EtOH): 2065 m, 2033 m, 1970 s, 1946 m, 1906 m cm-1
.
Anal. Calcd for C54H38IrNO9P2Re2: C, 44.08; H, 2.60; N, 0.95.
Found: C, 44.34; H, 2.89; N, 1.12. FAB(-)-MS (25 °C): m/z (193Ir,
187Re) 935, IrRe2H(CO)9(C9H7)-.
Reaction of 1 with PPh3. A hexane solution (15 mL) of 1 (52.9
mg, 0.0566 mmol) and PPh3 (16.3 mg, 0.062 mmol) was stirred and
heated at reflux for 1 h. The infrared spectrum of the resulting solution
showed the presence of remaining 1 as well as peaks for ReH(CO)4-
(PPh3) at 2081, 1993, 1977, and 1964 cm-1 (lit.15 (hexane): 2079, 1992,
1976, 1963 cm-1). The mixture was placed directly on a 15 cm × 1
cm column of neutral alumina. Elution with hexane/dichloromethane
(8:1) removed an orange band containing 1 (18 mg, 0.019 mmol, 34%
recovery). Elution with hexane/dichloromethane (1:1) removed a
second orange band, which was dried under vacuum and further purified
by preparative TLC (silica gel, hexane/Et2O, 9:1) to give 3 (11.3 mg,
0.010 mmol, 17%). Anal. Calcd for C35H24IrO8PRe2: C, 35.99; H,
2.07. Found: C, 36.04; H, 2.03. IR (νCO, hexane): 2079 m, 2044 w,
2022 w, 1994 s, 1974 m, 1967 m, 1934 m cm-1. FD-MS (100 °C):
m/z (193Ir, 187Re) 1170, IrRe2H2(CO)8(PPh3)(C9H7)+; 1142, IrRe2H2-
(CO)7(PPh3)(C9H7)+; 880, IrRe2H2(CO)7(C9H7)+.
The 1H-13C correlation spectrum (HETCOR) of 1 was recorded on
a GN500 spectrometer. A total of 48 transients of 2k data points were
recorded for each of the 128 increments of t1 (spectral width in F2 )
4808 Hz, spectral width in F1 ) 5291 Hz, relaxation delay ) 1 s). The
2
spectrum was optimized for JCH ) 10 Hz.
IrRe2(µ-H)2(CO)9(η5-C9H7) (1). A solution of Ir(CO)(η2-C8H14)-
(η5-C9H7) (51.3 mg, 0.115 mmol) in hexane (5 mL) was stirred and
heated at reflux, and then a benzene solution (20 mL) of Re2(µ-H)2-
(CO)8 (138 mg, 0.231 mmol) was added slowly through an addition
funnel over 90 min. The mixture was heated at reflux for an additional
30 min, resulting in a dark orange solution. The solvent was removed
under vacuum, and the residue was extracted with hexane (6 × 10
mL) through a filter cannula. The tan residue remaining in the reaction
flask was largely Re3(µ-H)3(CO)12, identified by its infrared peaks in
hexane at 2094 m, 2032 s, 2009 s, 1984 m cm-1 (lit.14 (cyclohexane):
X-ray Crystal Structure Study of 1. The orange, tabular crystal
was mounted using oil (Paratone-N, Exxon) to a thin glass fiber. Data
were measured at 198 K on an Enraf-Nonius CAD4 diffractometer.
Crystal and refinement details are given in Table 1. Systematic
conditions suggested the space group P1h; refinement confirmed the
(13) Andrews, M. A.; Kirtley, S. W.; Kaesz, H. D. Inorg. Chem. 1977, 16,
1556.
(14) Huggins, D. K.; Fellman, W.; Smith, J. M.; Kaesz, H. D. J. Am. Chem.
Soc. 1964, 86, 4841.
(15) Flitcroft, N.; Leach, J. M.; Hopton, F. J. J. Inorg. Nucl. Chem. 1970,
32, 137.

IrRe2(µ-H)2(CO)9(η5-C9H7)
Inorganic Chemistry, Vol. 36, No. 20, 1997 4399
Table 1. Crystallographic Data for IrRe2(µ-H)2(CO)9(η5-C9H7)
formula
space group, system
C18H9IrO9Re2
P1h, triclinic
8.618(4) Å
9.430(2) Å
14.729(4) Å
81.52(2)°
74.97(3)°
64.25(3)°
1040.4(6) Å3
2
fw
933.85
198(2) K
temp
λ
Fcalcd
a
b
c
R
â
γ
V
Z
0.710 73 Å (Mo KR)
2.981 g cm-3
Itot (unique, Ri)
µ
max/min transm
goodness of fit (F2)a
R1,b wR2 [I > 2σ(I)]c
R1,b wR2 (all data)c
3120 (2894, 0.0283)
18.032 mm-1
0.368/0.128
1.149
0.0277, 0.0681
0.0388, 0.0812
a GOF ) [∑[w(Fo2 - Fc2)2]/(n - p)]1/2; n ) number of reflections, p ) total number of parameters refined. b R1 ) ∑||Fo| - |Fc||/∑|Fo|. c wR2
2
2
) [∑[w(Fo - Fc2)2]/∑[w(Fo )2]]1/2
.
Table 2. Selected Structural Data for IrRe2(µ-H)2(CO)9(η5-C9H7)
Internuclear Distances
Ir-Re1
Ir-Re2
Re1-Re2
Ir1-C1
Ir1-C2
Ir1-C3
Ir1-C4
Ir1-C9
Ir1-C10
3.020(1)
2.866(1)
3.095(2)
2.26(1)
2.23(1)
2.18(1)
2.35(1)
2.39(1)
1.81(1)
Re1-C11
Re1-C12
Re1-C13
Re1-C14
Re2-C21
Re2-C22
Re2-C23
Re2-C24
1.98(1)
1.95(1)
1.94(1)
1.98(1)
2.01(1)
1.88(1)
1.94(1)
1.98(1)
Bond Angles
Ir-Re1-Re2
Ir-Re1-C11
Ir-Re1-C12
Ir-Re1-C13
Ir-Re1-C14
C11-Re1-Re2
C12-Re1-Re2
C13-Re1-Re2
C14-Re1-Re2
Re2-Ir-Re1
Re1-Ir-C10
Re2-Ir-C10
C13-Re1-C12
55.87(3)
90.2(3)
164.0(3)
103.9(3)
87.6(3)
88.0(3)
108.2(3)
159.5(3)
92.0(4)
63.40(3)
95.2(4)
84.9(4)
92.1(4)
C11-Re1-C14
C23-Re2-C22
C21-Re2-C24
Ir-Re2-Re1
177.2(5)
93.1(6)
176.2(5)
60.73(3)
98.6(4)
170.9(4)
92.0(4)
85.1(3)
89.2(4)
114.6(4)
152.2(4)
91.7(3)
Ir-Re2-C21
Ir-Re2-C22
Figure 1. ORTEP diagram of the molecular structure of 1 (35%
probability ellipsoids).
Ir-Re2-C23
Ir-Re2-C24
C21-Re2-Re1
C22-Re2-Re1
C23-Re2-Re1
C24-Re2-Re1
mixture of Re2(µ-H)2(CO)8 and Ir(CO)(η2-C8H14)(η5-C9H7) in
hexane for the same amount of time leads to lower yields of 1,
recovery of significant amounts of Ir(CO)(η2-C8H14)(η5-C9H7),
and the formation of large amounts of Re3(µ-H)3(CO)12. The
difference apparently relates to the effective lifetime of the
reactive dirhenium species, since it has been observed that
heating a solution of Re2(µ-H)2(CO)8 in hexane at reflux
produces Re3(µ-H)3(CO)12.21 The mass spectrum of 1 is
consistent with the proposed formula, and the IR spectrum in
hexane shows several terminal carbonyl stretching bands. The
1H NMR spectrum contains two peaks in the hydride region
and one set of indenyl resonances. Further NMR spectroscopic
studies of 1 are discussed below.
Molecular Structure of 1. The significant structural results
from the X-ray diffraction study of 1 are summarized in Table
2, and a diagram of the molecule is shown in Figure 1. The
cluster consists of an IrRe2 triangle incorporating one Ir(CO)-
(η5-C9H7) and two Re(CO)4 fragments. Within the metal
triangle, Ir-Re1 ) 3.020(1), Ir-Re2 ) 2.866(1), and Re1-
Re2 ) 3.095(2) Å. The hydride ligands were not located
explicitly, but one presumably bridges the long Ir-Re edge and
one occupies the Re-Re edge. A similar explanation was
offered to explain the two different Pt-Re distances in PtRe2-
(µ-H)2(CO)8(η4-C8H12)8 and in PtRe2(µ-H)2(CO)8(PPh3)2.9 In
the former, the two Pt-Re distances are 2.895(1) and 2.741(1)
Å and the Re-Re distance is 3.115(1) Å. In the latter, the two
Pt-Re distances are 2.906(1) and 2.788(1) Å and the Re-Re
distance is 3.203(1) Å.9 Furthermore, in 1 and in these PtRe2
clusters, the Re-Re distances are longer than that in Re2(CO)10
(3.02 Å)22 and are comparable with the Re(µ-H)Re distances
in Re3(µ-H)3(CO)12 (3.241(2) Å)21 and [Re3(µ-H)2(CO)12]-
presence of a symmetry center. Step-scanned intensity data were
reduced by profile analysis16 and corrected for Lorentz-polarization
effects and for absorption.17 Scattering factors and anomalous disper-
sion terms were taken from standard tables.18 The structure of 1 was
solved by direct methods;19 correct positions for the metal atoms were
deduced from an E-map. One cycle of isotropic least-squares refine-
ment followed by an unweighted difference Fourier synthesis revealed
positions for the remaining non-H atoms. Bridging hydrogens never
surfaced in the difference Fourier maps; the remaining hydrogen atoms
were included as fixed idealized contributors. Non-H atoms were
refined with anisotropic thermal coefficients. Successful convergence
of the full-matrix least-squares refinement of F2 was indicated by the
maximum shift/error for the last cycle.20 The highest peaks in the final
difference Fourier map were in the vicinity of the metal atoms; the
final map had no other significant features. Selected structural data
for 1 are given in Table 2.
Results and Discussion
Synthesis and Characterization of 1. The slow addition
of Re2(µ-H)2(CO)8 to Ir(CO)(η2-C8H14)(η5-C9H7) in refluxing
hexane forms the heterometallic cluster IrRe2(µ-H)2(CO)9(η5-
C9H7), 1, in high yield (80% isolated). In contrast, heating a
(16) Coppins, P.; Blessing, R. H.; Becker, P. J. Appl. Crystallogr. 1972,
7, 488.
(17) Sheldrick, G. M. SHELX-76. Program for crystal structure determi-
nation, Univ. of Cambridge, England, 1976.
(18) Wilson, A. J. C., Ed. International Tables for X-ray Crystallography;
Kluwer Academic Publishers: Dordrecht, The Netherlands, 1992; Vol.
C: (a) scattering factors, pp 500-502; (b) anomalous dispersion
corrections, pp 219-222.
(19) Sheldrick, G. M. SHELXS-86. Acta Crystallogr. 1990, A46, 467.
(20) Sheldrick, G. M. SHELXL-93, University of Go¨ttingen, 1993.
(21) Masciocchi, N.; Sironi, A.; D’Alfonso, G. J. Am. Chem. Soc. 1990,
112, 9395.
(22) Dahl, L. F.; Ishishi, E.; Rundle, R. E. J. Chem. Phys. 1957, 26, 1750.

4400 Inorganic Chemistry, Vol. 36, No. 20, 1997
Comstock et al.
Table 3. Proton and Carbon NMR Data for Compounds 1-3a
1H chem shifts
Re/Ir carbonyl 13C chem shifts
b, b′ c c, c′ c
7.44-7.51 -16.42 -17.56 191.2, 187.1 190.3, 182.9e 185.9, 182.9e 182.5, 179.5
6.94 184.1
-17.75 189.5h 197.3h 196.3h
6.27 6.22, 5.56 7.69-7.27j 7.69-7.27j -15.19k -17.12 (P),l 192.0
b
b
b
cmpd
H2
6.80 6.71, 5.63 7.90, 7.59
5.64g 5.55g
7.38
H1, H3
H4, H7
H5, H6
Ha
Hb
a, a′
d, d′
e
1d
2f
3i
168.4
174.6
193.1,m 191.3 189.2,m 187.1 187.9,m 183.1 168.4
a The labeling scheme shown above was used for assignments of the resonances of 1, 2, and 3. b Specific assignments of related protons, e.g.,
H1, H3, are not determined for 1 and 3. c For both 1 and 2, the assignments of the b and c sets of resonances are interchangeable. d In acetone-d6
at -70 °C. For the chemical shifts for selected nuclei in CD2Cl2 at -80 °C see Figure 4. e This resonance has an intensity corresponding to 2C.f In
g
CD2Cl2; 1H data at 25 °C and 13C data at -60 °C. J12 ) J23 ) 2.6 Hz. h The undecoupled 13C spectrum of 2 at -60 °C showed these three peaks
as doublets with JHC ) 2.7 (b), 3.0 (c), and 4.0 (a) Hz. i In CD2Cl2 at 25 °C. j The resonances for H4-H7 overlap with those for the phenyl protons
k
on PPh3. JPHa ) 16.4 Hz. l Assumed position of the PPh3 ligand; see text and I. m These three peaks appear as doublets with JPC ) 6.6 (b), 7.9 (c),
and 8.2 (d) Hz.
(3.173(7) and 3.181(7) Å).23 The unbridged Re-Re distance
in the latter complex ion is 3.035(7) Å.23
The Ir-Re distance of Ir-Re2 ) 2.866(1) in 1 may be
compared with other examples of unsupported Ir-Re bonds.
The closed Re2Ir cluster Re2(CO)8(µ-PCy2)(µ-Ir(CO)2PPh3)
shows an average distance of Ir-Re ) 2.962(1) Å.24 The
average Ir-Re distances are 2.879 Å in the iridium-capped,
carbido cluster, [Re7C(CO)21Ir(η2-C2H4)(CO)]2- 25
,
and
2.914(1) Å in the linear compound, {Re(CO)5}2IrH(CO)3.26 The
cluster [IrRe3(µ-H)(CO)16]- has an average Ir-Re distance of
2.93 Å within the IrRe2 triangle and a distance of 2.935 Å for
the spike Ir-Re bond.11 The dinuclear compound, IrRe(µ-CO)2-
(CO)2(η5-C5H5)(η5-C5Me5), containing semi-bridging CO ligands,
has an Ir-Re distance of 2.8081(6) Å.27
As pointed out initially in studies by Churchill, e.g. in [Re3-
(µ-H)2(CO)12]- 23 and Os3H(µ-H)(CO)11,28 the arrangement of
the equatorial carbonyl ligands provide further insight into the
location of bridging hydride ligands. In the structure of 1, the
Ir-Re2-C23 angle of 92.1(4)° is small compared to the Ir-
Re1-C13 angle of 103.9(3)°, consistent with the position of a
hydride ligand along the Ir-Re1 edge that forces an expanded
angle. Furthermore, both the C22-Re2-Re1 angle of
114.6(4)° and the C12-Re1-Re2 angle of 108.2(3)° are
relatively large, again consistent with the presence of a bridging
hydride ligand on the Re1-Re2 edge. All of the axial carbonyl
ligands are nearly orthogonal to the IrRe2 plane.
The mean plane of the indenyl ligand five carbon ring makes
an angle of 46.5(2)° with respect to the IrRe2 plane. The
structural details of indenyl ligand bonding in M(η5-C9H7)
compounds can be described by the slip distortion parameter
(∆), the fold angle, and the hinge angle.29 In compound 1, ∆
Figure 2. Proton NMR spectra of 1 in acetone-d6 at temperatures from
20 to -70 °C, showing the indenyl H1-H3 region.
) 0.15 Å, the fold angle ) 6.6(1.3)°, and the hinge angle )
7.5(1.4)°. These values imply a distortion slightly less than that
for C3V-Ir3(µ3-CO)3(η5-C9H7)3,2 which has average values for
the three indenyl ligands of ∆ ) 0.27 Å, fold angle ) 10.1°,
and hinge angle ) 9.5°. However, the corresponding values
in [Ir3{Au(PPh3)}(CO)3(η5-C9H7)3]+ 30 are ∆ ) 0.11 Å, fold
angle ) 9.1°, and hinge angle ) 6.2°, and in the mononuclear
compound Ir(CO)(η2-C2H2(CO2Me)2)(η5-C9H7)31 are ∆ ) 0.17
Å, fold angle ) 6.0°, and hinge angle ) 7.4°. Thus, the indenyl
ligand in 1 shows no unusual structural features.
Solution NMR spectroscopic studies of 1. At low temper-
atures both the 1H and 13C NMR spectra of 1 (see Table 3 and
Figures 2 and 3) are consistent with the solid-state structure of
the molecule. In particular, the H1 and H3 protons of the indenyl
ligand are inequivalent, which indicates that the ligand occupies
an asymmetric site, and two hydride resonances are observed.
The 13C{1H} NMR spectrum in acetone-d6 shows seven singlets
(23) Churchill, M. R.; Bird, P. H.; Kaesz, H. D.; Bau, R.; Fontal, B. J.
Am. Chem. Soc. 1968, 90, 7135.
(24) Haupt, H.-J.; Flo¨rke, U.; Beckers, H.-G. Inorg. Chem. 1994, 33, 3481.
(25) Ma, L; Wilson, S. R.; Shapley, J. R. Inorg. Chem. 1990, 29, 5133.
(26) Breimair, J.; Robl, C.; Beck, W. J. Organomet. Chem. 1991, 411,
395.
(27) Zhuang, J.-M.; Batchelor, R. J.; Einstein, F. W. B; Jones, R. H.; Hader,
R.; Sutton, D. Organometallics 1990, 9, 2723.
(28) Shapley, J. R.; Keister, J. B.; Churchill, M. R.; DeBoer, B. G. J. Am.
Chem. Soc. 1975, 97, 4145.
(29) (a) Faller, J. W.; Crabtree, R. H.; Habib, A. Organometallics 1985, 4,
929. (b) Baker, R. T.; Tulip, T. H. Organometallics 1986, 5, 839. (c)
Donovan, B. T.; Hughes, R. P.; Trujillo, H. A.; Rheingold, A. L.
Organometallics 1992, 11, 64. (d) Kakkar, A. K.; Taylor, N. J.;
Calabrese, J. C.; Nugent, W. A.; Roe, D. C.; Connaway, E. A.; Marder,
T. B. J. Chem. Soc., Chem. Commun. 1989, 990.
(30) Comstock, M. C.; Prussak-Wieckowska, T.; Wilson, S. R.; Shapley,
J. R. Organometallics, in press.
(31) Du, Y.; Wilson, S. R.; Shapley, J. R. Unpublished results.

IrRe2(µ-H)2(CO)9(η5-C9H7)
Inorganic Chemistry, Vol. 36, No. 20, 1997 4401
Figure 3. Carbon-13 NMR spectra (carbonyl region) of 1 in acetone-
d6 at temperatures between 45 and -80 °C.
between 192 and 179 ppm due to the eight carbonyls on the Re
atoms (two resonances are overlapped) and one singlet at δ
168.4 for the CO ligand on the iridium atom (see Figure 3,
bottom spectrum). The latter assignment is based on further
observations discussed below and on comparison with the
resonances for the CO ligands in Ir(CO)(η2-C2H4)(η5-L), which
appear at δ 169.9 and 168.3 for L ) C5H5 and C9H7,
respectively,12 and in the iridium-capped cluster, [Re7C(CO)21-
Ir(η2-C8H14)(CO)]2-, which has a peak at δ 167.1 assigned to
the Ir-CO ligand.25
1
The H-13C HETCOR spectrum of 1 shown in Figure 4
Figure 4. 1H-13C HETCOR spectrum of 1 in CD2Cl2 at -80 °C.
allows assignment of the hydride resonances and provides partial
assignment of the carbonyl ligand signals. Thus, cross peaks
between the hydride peak at δ -17.6 and the unique 13C peak
near δ 167, which is assigned as the CO ligand on the iridium
atom (e), prompts assignment of the former as the resonance
for the hydride bridging the Ir-Re edge (Hb). Then the cross
peaks between the hydride peak at δ -16.5 due to the hydride
ligand bridging the Re-Re edge (Ha) indicate resonances due
to CO ligands on the rhenium atoms. The specific assignments
of the Re-CO resonances rely on the observation that coupling
between a 1H nucleus and 13C or 31P nuclei in a cis relationship
is larger than that for a trans orientation.32 Therefore, the Re-
CO peak labeled d′ is assigned on the basis of the cross peak
with Hb and the lack of a cross peak with Ha; the CO peak d′
is due to a carbonyl in the equatorial plane in a position cis to
Hb and trans to Ha (see diagram with Table 3). Further, the
cross peak between Hb and the set of peaks near 182.5 ppm
suggests the latter contains resonances for CO ligands b′ and
c′, which are also oriented cis to Hb. On this basis a cross peak
between the signals due to Hb and d is not expected (d is trans
to Hb), but overlap of the b′, c′, and d signals obviates any
conclusion. However, as expected, no cross peak is seen
between Ha and its trans oriented carbonyl a′. The 13C peaks
below 185 ppm are all coupled to Ha, suggesting they are
oriented cis to this hydride. The variable-temperature behavior
of the 13C NMR spectra (see below) provides further support
for these assignments.
Dynamic NMR Behavior of 1. As the sample temperature
is raised from -70 °C, the proton signals for H1 and H3 of the
indenyl ligand broaden and coalesce until at 20 °C only one
broad resonance is observed (see Figure 2). In contrast,
however, the two hydride signals in the 1H spectrum (see spectra
in the Supporting Information) are invariant over the temperature
range explored. Similarly, the peaks between 192 and 179 ppm
in the low temperature 13C spectrum of 1 broaden, coalesce,
and form four broad peaks at 25 °C, but the 13C peak at δ 167.5
remains sharp throughout (see Figure 3). The pairs of signals
that coalesce can be determined by comparing the chemical
shifts of the peaks in the spectrum obtained at 45 °C with the
average chemical shift values calculated from the spectrum at
-80 °C. For example, the a and a′ resonances appear at δ
191.17 and 187.08 at -80 °C, leading to an average value of δ
189.13, which compares to δ 188.71 assigned to the rapid
exchange position of these same peaks. The difference in
calculated and observed values is +0.4 ppm, and this same
discrepancy is consistently seen for the other pairs of CO peaks.
The same amount of line broadening evidenced by each of the
1C peaks in going from -80 to -40 °C implies that a single
dynamic process is responsible for the observed signal equili-
bration.
Taken together the NMR data require a dynamic process that
generates an effective mirror plane perpendicular to the IrRe2
triangle, bisecting the indenyl ligand and passing through the
hydride ligand bridging the Re-Re edge. This process causes
equilibration of the H1 and H3 protons (together with H4/H7
and H5/H6) on the indenyl ligand as well as the CO ligands on
the two rhenium centers as described above. The most likely
(32) (a) Beringhelli, T.; Ciani, G.; D’Alfonso, G.; Freni, M. J. Organomet.
Chem. 1986, 311, C51. (b) Beringhelli, T.; D’Alfonso, G.; Freni, M.;
Minoja, A. P. Inorg. Chem. 1996, 35, 2393.

4402 Inorganic Chemistry, Vol. 36, No. 20, 1997
Comstock et al.
Scheme 2
Scheme 3
mechanism involves migration of hydride Hb between the two
Ir-Re edges (see Scheme 2). The free energy of activation,
∆Gq, for the process causing equilibration of H1 and H3 (∆ν )
323 Hz) was calculated from the rate constant at the temperature
of coalescence (-15 °C) by using the equations, kc ) π∆ν(2)-1/2
Ir-CO peak (e) and four Re-CO peaks (a-d). The peaks
labeled a, b, and c appear as doublets in the undecoupled
spectrum, with JHC ) 2.7, 3.0, and 4.0 Hz, respectively. The
similar JHC coupling constants for these peaks suggest they are
q
) (kbTc/h) exp[-∆Gq/RTc], leading to ∆Gc ) 11.7(6) kcal
2
2
all due to JHC(cis) interactions rather than two JHC(cis) and
mol-1. The error in ∆Gcq was propagated from estimated errors
2
one JHC(trans).32 Furthermore, as described below, the peak
q
in ∆ν and Tc. A similar value of ∆Gc can be estimated from
labeled d occupies the equatorial site trans to the Re(µ-H)Re
bond.
the 13C spectra, since the important parameters are nearly the
same (∆ν ca. 300 Hz, Tc ca. 10 °C; see Figure 3).
Dynamic NMR Behavior of 2. As the temperature is raised
above -40 °C, the 13C NMR spectrum of 2 shows that the a, b,
and c Re-CO peaks as well as the Ir-CO peak (e) all broaden,
while the Re-CO peak labeled d remains invariant. These data
imply the operation of a carbonyl scrambling process that is
localized on the Ir-Re edges but does not include carbonyl d,
which occupies a site trans to the Re(µ-H)Re bond. The cyclic
process shown in Scheme 3 meets these requirements.
A similar situation was observed for the related cluster PtRe2-
(µ-H)2(CO)8(η4-C8H12).8 The 1H NMR peaks for the hydrides
bridging the Re-Re and Pt-Re edges were sharp at all
temperatures. However, the 13C NMR signals for the carbonyl
ligands on the Re atoms, which appeared as three sharp signals
in a 2:1:1 ratio at -10 °C were observed to broaden and collapse
near -88 °C. Thus, a dynamic process caused the apparent
C2V symmetry at higher temperatures, and a mechanism involv-
Considering one cycle of exchange, the proposed mechanism
involves the site exchanges of e f c, c f a, a f b, and b f
e, with the last accompanied by a shift of the indenyl ligand to
the other side of the IrRe2 triangle. Furthermore, this migration
of the indenyl ligand causes exchange of the b and c carbonyls
(b f c, c f b) on the second rhenium atom but leaves site a at
this rhenium center unchanged. Therefore, for each cycle two
spins are exchanged out of both the b and c sites, whereas only
one spin is exchanged out of the a and the e sites. However,
since there are 2C for each of the a, b, and c sites but only 1C
for the e site, the net exchange rate constant is k for the b, c,
ing the migration of one hydride ligand between the two Pt-
Re edges provided a satisfactory explanation.
Synthesis and Spectroscopic Characterization of 2. One
of the bridging hydride ligands in 1 is readily removed by
deprotonation. Addition of an ethanolic solution of KOH to a
suspension of yellow 1 in ethanol results in an immediate color
change to deep red and complete dissolution of remaining solid
1. The infrared spectrum of this solution is similar to that for
1 except that all the peaks are shifted to lower energy. Addition
of excess [PPN]Cl and holding the solution at -20 °C results
in the precipitation of red needles of [PPN][IrRe2(µ-H)(CO)9-
(η5-C9H7)] (2). The molecular formula for 2 is supported by
mass spectrometry and microanalysis. The deprotonation of
Re3(µ-H)3(CO)12 under similar conditions provided [Re3(µ-H)2-
(CO)12]-.23
1
and e sites and /2k for the a site. Since line broadening is
proportional to the first-order rate constant for spins leaving a
given site (k ) π(∆ν - ∆νo), resonances for sites b, c, and e
should broaden faster than that for a. Comparison of the
respective line widths among the 2C signals a, b, and c in the
spectrum at 0 °C in Figure 5 clearly shows that the peaks
assigned to b and c are broader than that for a; the situation for
the 1C signal e is less clear. Nevertheless, the selective line
broadening observed for b/c vs a provides strong support for
the proposed mechanism. The line widths of the b and c peaks
are estimated at ca. 20 Hz in the spectrum at 0 °C and are ca.
3 Hz in the limiting spectrum at -60 °C. Therefore, at 273 K,
k ) π(20 - 3) ) 53 s-1, which leads via the Eyring equation
to ∆Gq ) 13.8(5) kcal mol-1, with errors propagated from
estimated errors in k and T.
1
The H NMR spectrum for 2 shows one hydride resonance
at δ -17.78. In the indenyl region only four peaks are observed,
consistent with a structure in which the indenyl ligand resides
in a symmetric site; in particular H1 and H3 are equivalent (see
1
Table 3). No dynamic behavior is observed in the H NMR
spectra for 2 between -80 and 20 °C; both the indenyl and the
hydride resonances remain sharp, and the line widths are
invariant over the same temperature range. These data indicate
that deprotonation removes the hydride bridging the Ir-Re edge
and the remaining hydride is located on the Re-Re edge, which
is bisected by the resulting mirror plane perpendicular to the
IrRe2 triangle.
An analogous cyclic scrambling mechanism has been deduced
for IrOs2(CO)9(η5-C5H5).33 At -48 °C the 13C NMR spectrum
of this cluster shows five sharp carbonyl peaks, consistent with
The 13C{1H} NMR spectrum of 2 at -60 °C is consistent
with the discussion above (see Figure 4 and Table 3), with one

IrRe2(µ-H)2(CO)9(η5-C9H7)
Inorganic Chemistry, Vol. 36, No. 20, 1997 4403
a position cis to the three remaining CO ligands on the
substituted rhenium center.
The NMR data for 3 are consistent with structures I and II,
which have the phosphine ligand on the rhenium atom that is
Figure 5. Carbon-13 NMR spectra (carbonyl region) of 2 in CD2Cl2
at temperatures between 35 and -60 °C.
not bonded to Hb. If the phosphine ligand were bound to the
rhenium atom involved in the Re(µ-Hb)Ir bridge, some coupling
between Hb and the phosphorus nucleus would be expected.
However, a number of studies on phosphine-substituted hydri-
dorhenium carbonyl cluster compounds by Beringhelli, D’Alfonso,
the expected Cs symmetric structure. At 7 °C only four of these
peaks have collapsed, while one sharp singlet remains. Simula-
tion of the spectrum at -10 °C gave k ) 9(1) s-1 and
correspondingly ∆Gq ) 14.2(3) kcal mol-1, which is remarkably
close to the value we determine for 2. Interestingly, the analog
IrOs2(CO)9(η5-C5Me5) appears to undergo the same process with
a much lower activation barrier, ∆Gq ) 7.4(2) kcal mol-1 at
-116 °C, consistent with stabilization of a carbonyl bridged
intermediate configuration by the more basic Cp* ligand. Note
that in neither of these cases nor in the case of 2 does a process
involving rotation of the Ir(CO)(η5-L) vertex relative to the
remaining M2 unit correlate with the spectral changes observed.
However, an interesting example of such metal vertex rotation
in a Re3 cluster has been reported recently.34
2
and co-workers9,32 have demonstrated that JPH(cis) is signifi-
2
cantly larger than JPH(trans). On the basis of these observa-
tions, the relatively large value of JPH ) 16.4 Hz observed for
3 is more consistent with structure I, containing an equatorially
bound phosphine ligand in the position trans to the unsupported
Ir-Re bond and cis to the Re(µ-Ha)Re moiety, than with
2
structure II, for which a smaller coupling, JPH(trans), would
be expected.
When the reaction of 1 with PPh3 was repeated with 2 equiv
of the entering ligand, more 1 was consumed, but more ReH-
(CO)4(PPh3) was observed by infrared spectroscopy, and the
yield of 3 was unchanged. Isolation of 3 as the only significant
substitution product from 1 is at first glance not expected. A
product containing the phosphine ligand on the iridium atom
would appear to be more consistent with the high reactivity
observed for mononuclear indenyl compounds in associative
substitution reactions.1,12 However, we have observed that
reactions of the trinuclear indenyl cluster Ir3(µ-CO)3(η5-C9H7)3
Reaction of 1 with PPh3 and Formation of 3. The reaction
of 1 with PPh3 is neither facile nor clean. From the reaction in
hexane at reflux a significant amount of unreacted 1 was
recovered, and a product subsequently characterized as IrRe2-
(µ-H)2(CO)8(PPh3)(η5-C9H7) (3) was isolated in pure form after
careful chromatography. Other, minor products were produced,
as observed by TLC, but they were not isolated in pure form
and were not characterized. Infrared spectra obtained during
the course of the reaction suggested the concurrent formation
of ReH(CO)4(PPh3).15
The 1H NMR spectrum for 3 (see Table 3) shows the indenyl
H1 and H3 protons are inequivalent; thus, the indenyl ligand
resides in an asymmetric site. In the hydride region, a doublet
at δ -15.19 (JPH ) 16.4 Hz) and a singlet at δ -17.12 appear.
No change in line width is observed for either the indenyl or
the hydride resonances in spectra obtained between 25 and -80
°C. The 31P{1H} spectrum contains a single peak at +14.4 ppm.
The 13C{1H} NMR of a 13CO-enriched sample of 3 clearly
indicates that the phosphine ligand is not on the iridium atom
(see Table 3 and the Supporting Information). A singlet is
observed at δ 168.4 for the Ir-CO ligand. In addition three
doublets and four singlets are observed between 193 and 182
ppm for the Re-CO ligands. The coupling constants for the
three doublets are very similar (JPC ) 6.6, 7.9, and 8.2 Hz),
which suggests an equatorial site for the phosphine ligand, i.e.,
35
with CO2 or PPh3 lead immediately at room temperature to
the mononuclear cluster fragmentation products, Ir(CO)(L)(η5-
C9H7) (L ) CO, PPh3). Therefore, associative attack of PPh3
at the iridium center in 1 may lead to displacement of the Re2-
(µ-H)2(CO)8 pseudoolefin fragment rather than CO, with
consequent formation of Ir(CO)(PPh3)(η5-C9H7). The presence
of Ir(CO)(PPh3)(η5-C9H7) was not detected during the reaction;
however, this compound has been found to react with excess
PPh3 at room temperature, leading to other products.35 Sub-
sequent reaction of Re2(µ-H)2(CO)8 with PPh3 would lead to
ReH(CO)4(PPh3), as observed previously.13,36
Summary
The reaction of Re2(µ-H)2(CO)8 with Ir(CO)(η2-C8H14)(η5-
C9H7) provides the trinuclear cluster, IrRe2(µ-H)2(CO)9(η5-
C9H7), 1, in high yield. The X-ray structure and NMR
spectroscopy of 1 at low temperatures are consistent with
structure having one hydride ligand bridging the Re-Re edge
and the second hydride bridging one Ir-Re edge. A dynamic
(33) Riesen, A.; Einstein, F. W. B.; Ma, A. K.; Pomeroy, R. K.; Shipley,
J. A. Organometallics 1991, 10, 3629.
(34) Beringhelli, T.; D’Alfonso, G.; Freni, M.; Panigati, M. Organometallics
1997, 16, 2719.
(35) Comstock, M. C. Ph.D. Thesis, University of Illinois, 1996.
(36) Prest, D. W.; Mays, M. J.; Raithby, P. R. J. Chem. Soc., Dalton Trans.
1982, 2021.

4404 Inorganic Chemistry, Vol. 36, No. 20, 1997
Comstock et al.
process involving the migration of one hydride between the two
Ir-Re edges has been revealed by variable-temperature 1H and
13C NMR spectroscopy. Deprotonation of 1 with KOH/EtOH
and addition of [PPN][Cl] provides [PPN][IrRe2(µ-H)(CO)9(η5-
C9H7)], 2. Proton and carbon NMR spectra for 2 indicate that
the remaining hydride bridges the Re-Re edge, and variable-
temperature 13C NMR experiments are consistent with a cyclic
carbonyl scrambling process localized on the Ir-Re edges. The
reaction of 1 with PPh3 leads to the carbonyl ligand substitution
product, IrRe2(µ-H)2(CO)8(PPh3)(η5-C9H7), 3, as well as to
cluster fragmentation. On the basis of 1H and 13C NMR
spectroscopy, the phosphine ligand in 3 is bound to a rhenium
atom in an equatorial site, trans to the unbridged Ir-Re bond.
thanks the Department of Chemistry for a fellowship funded
by the Lubrizol Corp. We thank Drs. Vera Mainz and Scott T.
Massey for help with the HETCOR experiment for 1 and the
variable-temperature 13C NMR experiments for 2, respectively.
Supporting Information Available: Complete tables of atom
coordinates, distances and angles, and anisotropic displacement pa-
rameters, for 1, as well as 1H NMR spectra of 1 in the hydride region
between 20 and -70 °C, and the 13C NMR spectrum of 3 (6 pages).
Ordering information and instructions for Internet access are given on
any current masthead page.
Acknowledgment. This research was supported by a grant
from the National Science Foundation (CHE94-14217). M.C.C.
IC960990I