Metal-carbon vibrational modes as a probe of the trans influence in vinylidene and carbonyl rhodium(I) complexes

Article abstract of DOI:10.1039/b104179g

FT-Raman spectroscopy and density functional theory (DFT) calculations have been used to study the trans influence of ligands L in complexes of the general composition trans-[RhX(L)(PiPr₃)₂], where X = F, Cl, Br, I, CH₃ and C≡CPh;L = ¹³C=¹³ CH₂,C=CHPh and CO. For the vinylidene compounds 1-10, the sequence of the trans influence C≡CPh > CH₃ > I > Br > Cl > F has been derived from the order of the v(Rh=C) wavenumbers. In the carbonyl halide complexes 11-14, the sequence of the trans influence for the halide ligands is the same as for the related vinylidene halide derivatives. The trans influence of the ligands X is discussed in terms of both the σ-donor capabilities of these ligands and the electronic repulsion between the d electrons of rhodium and the lone pairs of X.

Full text of DOI:10.1039/b104179g

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Metal–carbon vibrational modes as a probe of the trans inÑuence in
vinylidene and carbonyl rhodium(I) complexes
Damien Moigno,a Wolfgang Kiefer,*a Berta Callejas-Gaspar,b Juan Gil-Rubiob and
Helmut Werner*b
a Institut fur Physikalische Chemie, Universitat W urzburg, Am Hubland, D-97074 W urzburg,
Germany. E-mail: wolfgang.kiefer=mail.uni-wuerzburg.de; Fax: ] 49 931 888 6332;
T el: ] 49 931 888 6330
b Institut fur Anorganische Chemie, Universitat W urzburg, Am Hubland, D-97074 W urzburg,
Germany. E-mail: helmut.werner=mail.uni-wuerzburg.de; Fax: ] 49 931 888 4623;
T el: ] 49 931 888 5260
Received (in Strasbourg, France) 11th May 2001, Accepted 7th August 2001
First published as an Advance Article on the web 17th October 2001
FT-Raman spectroscopy and density functional theory (DFT) calculations have been used to study the trans
inÑuence of ligands L in complexes of the general composition trans-[RhX(L)(PiPr ) ], where X \ F, Cl, Br, I, CH
3 2
3
and C3 CPh; L \ 13C213CH , C2CHPh and CO. For the vinylidene compounds 1È10, the sequence of the trans
2
inÑuence C3 CPh [ CH [ I [ Br [ Cl [ F has been derived from the order of the l(Rh2C) wavenumbers. In the
3
carbonyl halide complexes 11È14, the sequence of the trans inÑuence for the halide ligands is the same as for the
related vinylidene halide derivatives. The trans inÑuence of the ligands X is discussed in terms of both the r-donor
capabilities of these ligands and the electronic repulsion between the d electrons of rhodium and the lone pairs of X.
The changes in the wavenumber of the l(CO) vibrational
Results
Vibrational spectroscopy
mode have often been used as an indirect probe to study the
donor capabilities of the ligands coordinated to the metal
center in transition-metal carbonyl complexes.1h6 However, to
the best of our knowledge, no such studies have been carried
out using the l(MÈCO) mode, even though the metalÈcarbon
stretching mode is expected to be sensitive to variations in the
electronic density on the metal. This is true also for transition-
metal carbene and carbyne complexes, for which very few
vibrational studies have been reported.7h16 Moreover, the
assignment of the metalÈcarbon stretching mode in carbene
and carbyne complexes is relevant because it is an easily avail-
able source of information about the bonding in these types of
compounds. Recently, we reported that the bands correspond-
ing to the l(Rh2C) vibrational modes in the Raman and infra-
red spectra of the compounds trans-[RhF(2C2CH )(PiPr ) ]
The low-wavenumber region of the FT-Raman spectra of
complexes 1È4 is outlined in Fig. 1. The l(Rh213C) mode has
been assigned to a band in the range between 559 and 540
cm~1 on the basis of isotopic substitution and DFT calcu-
lations.17 In the infrared spectra, the corresponding bands
were of very low intensity. The wavenumber of the metalÈ
carbon stretching mode decreases in the order
F [ Cl [ Br [ I.
A coupling between the l(Rh2C) and l(RhX) modes was
observed in the computer-animated vibrational simulation for
the model compounds trans-[RhX(2C2CH )(PMe ) ]. This
2
3 2
coupling should increase from X \ I to X \ F because the
l(Rh213C) and l(RhX) bands are closer to each other (Table
1), the maximum coupling being found for the Ñuoro
complex.1 A probe to test the degree of coupling is the change
2
3 2
and trans-[RhF(213C213CH )(PiPr ) ] could be assigned with
2
3 2
the help of isotopic substitution as well as DFT calcu-
lations.17 The availability of a series of vinylidene and carbon-
yl complexes containing di†erent ligands in the trans position
to the isolelectronic vinylidene and CO ligands gave us the
opportunity to study for the Ðrst time the inÑuence of the
trans ligand on the metalÈcarbon bond of vinylidene complex-
es and to compare the results of this study with those derived
from the comparison of the l(CO) modes.
in position of the l(RhF) band in trans-[RhF(2C2CH )-
2
(PiPr ) ] relative to its 13C containing analog 1. A great dif-
3 2
ference would indicate an extensive coupling of the metalÈ
carbon and metalÈÑuorine stretching vibrations. However, the
l(RhF) band is shifted by only 4 cm~1 to lower wavenumbers
in trans-[RhF(213C213CH )(PiPr ) ] (1) compared to trans-
2
3 2
[RhF(2C2CH )(PiPr ) ], whereas the position of the l(Rh2C)
2
3 2
In this work we present a study on the inÑuence of various
ligands X on the rhodiumÈcarbon bond of square-planar
vinylidene and carbonyl rhodium(I) complexes by using the
wavenumber of the metalÈcarbon stretching modes as a probe
for the weakening of the Rh2C bond. The compounds studied
were trans-[RhX(213C213CH )(PiPr ) ] with X \ F (1), Cl (2),
mode is 13 cm~1 lower in 1 compared with the non-labeled
complex.17 Although this shift is larger than the di†erence in
l(Rh213C) between compounds 1 and 2 (*l \ 8 cm~1), the
e†ect of the coupling together with the e†ect of the increasing
mass of the metal fragment [RhX(PiPr ) ] in going from 1 to
3 2
4 provokes some ambiguity in the interpretation of the change
2
3 2
Br (3) and I (4); trans-[RhX(2C2CHPh)(PiPr ) ] with X \ F
in l(Rh213C) along the series. Moreover, the results of the cal-
culations performed (see below) suggest that the order of
l(Rh213C) reÑects the order of the Rh2C bond strengths.
The complexes 1, 2 and 4 display in their IR spectra a band
in the range 1569È1582 cm~1 that was not observed in the
FT-Raman spectra and is assignable to the vinylidenic
3 2
(5), Cl (6), Br (7), I (8), CH (9) and PhC3 C (10); and trans-
3
[RhX(CO)(PiPr ) ] with X \ F (11), Cl (12), Br (13) and I (14).
3 2
The results are rationalized with the support of DFT calcu-
lations on model compounds in which the bulky PiPr ligands
3
are replaced by PMe .
3
DOI: 10.1039/b104179g
New J. Chem., 2001, 25, 1389È1397
1389
This journal is ( The Royal Society of Chemistry and the Centre National de la Recherche ScientiÐque 2001

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Fig. 1 The low-wavenumber region of the FT-Raman spectra of
trans-[RhX(213C213CH )(PiPr ) ] (X \ F, Cl, Br, I).
Fig. 2 The high-wavenumber region of the FT-IR spectra of trans-
[RhX(213C213CH )(PiPr ) ] (X \ F, Cl, I).
2
3 2
2
3 2
l(13C213C) vibrational mode (Fig. 2). This band is red-shifted
in the order F [ Cl [ I.
(X \ F, Cl, CH ) using the DFT1 and 2 methods (Table 1).
3
In the Raman spectra of the phenyl-substituted vinylidene
complexes 5È10 (Fig. 3), the l(Rh2C) mode was assigned to an
absorption in the range of 567È579 cm~1 by analogy to trans-
[RhF(2C2CH )(PiPr ) ], for which the l(Rh2C) mode was
The order of the l(Rh2C) wavenumbers for the phenyl-
substituted vinylidene complexes 5È8 is F [ Cl [ Br [ I (Fig.
3), which is similar to the order observed for 1È4, although the
di†erences between the wavenumbers are smaller. We attrib-
ute this result regarding the smaller di†erences in the position
of the metalÈcarbon stretching band to a coupling between
the l(Rh2C) mode and an in-plane ring deformation mode,
2
3 2
found at 572 cm~1.17 Additional support for this assignment
arises from DFT calculations of the metalÈcarbon stretches
for the model compounds trans-[RhX(2C2CHPh)(PMe ) ]
3 2
Table 1 Calculated and experimental fundamental vibrational modes (cm~1) in vinylidene rhodium complexes
Compound
Method
l(C2C)
l(Rh2C)
l(RhÈX)
trans-[RhF(2C2CH )(PiPr ) ]a
IR
R
DFT1
DFT2
DFT3
IR
1628s
È
1656
1655
1654
1653m
1653shm
1652
574m
572vs
571
570
571
577m
579s
582
458vs
458m
451
433
456
469s
469shm
456
439
È
281mw
301
282
È
203m
205
È
150m?
138
452wsh
452m
463
2
3 2
trans-[RhF(2C2CH )(PMe ) ]a
2
3 2
trans-[RhF(2C2CHPh)(PiPr ) ] (5)
3 2
R
trans-[RhF(2C2CHPh)(PMe ) ]
DFT1
DFT2
IR
3 2
1649
574
trans-[RhCl(2C2CHPh)(PiPr ) ] (6)
1649s
1640m
1652
576s
574s
570
3 2
R
trans-[RhCl(2C2CHPh)(PMe ) ]
DFT2
DFT1
IR
R
DFT1
IR
R
DFT1
IR
3 2
trans-[RhCl(2C2CH )(PMe ) ]
1659
563
2
3 2
trans-[RhBr(2C2CHPh)(PiPr ) ] (7)
1649s
1648m
1659
1638s
1639m
1658
1603, 1633m
È
1601
575m
573s
558
573s
572s
553
571m
571m
528
3 2
trans-[RhBr(2C2CH )(PMe ) ]
2
3 2
trans-[RhI(2C2CHPh)(PiPr ) ] (8)
3 2
trans-[RhI(2C2CH )(PMe ) ]
2
3 2
trans-[Rh(CH )(2C2CHPh)(PiPr ) ] (9)
3
3 2
R
trans-[Rh(CH )(2C2CH )(PMe ) ]
DFT1
DFT1
IR
3
2
3 2
trans-[Rh(CH )(2C2CHPh)(PMe ) ]
1610
1611, 1635m
1635vw
573
567m
464
È
3
3 2
trans-[Rh(C3 CPh)(2C2CHPh)(PiPr ) ] (10)
3 2
R
DFT1
567s
571
540vs
543
trans-[Rh(C3 CPh)(2C2CHPh)(PMe ) ]b
1642
3 2
a Ref. 17. b l(C3 C) 2072 cm~1; calculated at 2062 cm~1 using DFT1.
1390
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Fig. 3 The low-wavenumber region of the FT-Raman spectra of
trans-[RhX(2C2CHPh)(PiPr ) ] (X \ F, Cl, Br, I).
Fig. 4 The low-wavenumber region of the FT-Raman spectra of
trans-[RhX(2C2CHPh)(PiPr ) ] (X \ CH , C3 CPh).
3 2
3 2
3
which was conÐrmed by computer-animated vibrational simu-
lation for the model compounds.
cm~1).18 In the FT-Raman spectra of the analogous carbonyl
complexes trans-[RhX(CO)(PiPr ) ] (X \ F, Cl, Br, I), a band
In addition to the l(Rh2C) stretching vibration, two further
modes are of great relevance for this study. First, the deforma-
tion mode d(RhCC), which was observed in the FT-Raman
spectra of the phenyl-substituted vinylidene complexes 5È8
(Fig. 3). This mode was predicted by the DFT2 method to be
at 472 cm~1 for the model compound trans-[RhF(2C2CHPh)-
3 2
in the range between 573 and 546 cm~1 was assigned to the
l(Rh2C) mode (Fig. 5) on the basis of DFT calculations for
the corresponding model compounds (Table 2). The position
of this mode is dependent on the halide ligand, as observed for
the rhodiumÈcarbon stretching mode of the vinylidene com-
plexes 1È10. The l(CO) mode was found at 1929È1943 cm~1
(PMe ) ] and has been assigned to the band of medium inten-
3 2
sity at 475 cm~1 in the FT-Raman spectrum of 5. Second, the
CÈC stretching mode for which a high Raman activity is
Ph
characteristic. This mode was assigned on the basis of DFT
calculations to the strong bands at 1230 (X \ F; calc. 1231
cm~1, DFT2), 1225 (X \ Cl; calc. 1226 cm~1, DFT2), 1224
(X \ Br) and 1220 cm~1 (X \ I) in the FT-Raman spectra of
5È8. It is important to note that these modes have also been
shifted to lower wavenumbers in the order F [ Cl [ Br [ I,
which again reÑects the trans inÑuence of the halide ligand in
the rhodium(I) complexes.
The l(C2C) modes were observed in the range between 1653
and 1603 cm~1 for compounds 5È10 and were active both in
the Raman and infrared spectra. The corresponding order of
X illustrating the trans inÑuence is CH [ C3 CPh [ I [ Br,
3
Cl [ F.
The FT-Raman spectra of compounds 9 and 10 are more
complicated in the low-wavenumber region (Fig. 4). Bands at
571 cm~1 for 9 and at 567 cm~1 for 10 were assigned to the
l(Rh2C) modes. This assignment agrees with the data found
for complexes 5È8 and compares well with the calculated
vibrational modes for the model compounds trans-
[Rh(CH )(2C2CH )(PMe ) ],
trans-[Rh(CH )(2C2CHPh)-
3
2
3 2
3
(PMe ) ] and trans-[Rh(C3 CPh)(2C2CHPh)(PMe ) ] (Table
3 2
3 2
1). The positions of the l(RhÈC) bands were temtatively
located at 452 cm~1 for 9 and at 540 cm~1 for 10, in agree-
ment with the calculated values of 463 and 542 cm~1, respec-
tively.
The l(C3 C) mode of compound 10 appeared as a strong
band at 2072 cm~1 in the FT-Raman spectrum and as a
medium band at 2071 cm~1 in the IR spectrum; it is red-
shifted by 39 cm~1 compared with phenylacetylene (2111
Fig. 5 The l(CO) and l(Rh2C) wavenumber region of the FT-
Raman spectra of trans-[RhX(CO)(PiPr ) ] (X \ F, Cl, Br, I).
3 2
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Table 2 Calculated and experimental fundamental vibrational modes (cm~1) in carbonyl rhodium complexes
Compound
Method
l(Rh2C)
l(RhÈX)
l(CO)
trans-[RhF(CO)(PiPr ) ]a (11)
IR
R
DFT1
IR
R
573m
573vs
570
559mw
559vs
550
561
547
542
555w
555s
552
557
542
546w
546s
551
465s
465m
450
È
277w?
303
285
283
287
È
227m
195
205
214
È
137m?
139
147
1934vs
1929s
1843
1938s
1938s
1965
1848
1958
1954
1941s
1940s
1961
1847
1957
1944s
1943s
1847
1957
3 2
trans-[RhF(CO)(PMe ) ]a
3 2
trans-[RhCl(CO)(PiPr ) ] (12)
3 2
trans-[RhCl(CO)(PMe ) ]
Rb
3 2
DFT1
DFT2
DFT3
IR
R
Rb
DFT1
DFT4
IR
R
DFT1
DFT4
trans-[RhBr(CO)(PiPr ) ] (13)
3 2
trans-[RhBr(CO)(PMe ) ]
3 2
trans-[RhI(CO)(PiPr ) ] (14)
3 2
trans-[RhI(CO)(PMe ) ]
3 2
536
a Ref. 17. b Ref. 41.
and its wavenumber decreases in the order I [ Br [ Cl [ F
(Fig. 5).
DFT calculations
DFT calculations have been carried out for the model com-
pounds trans-[RhX(L)(PMe ) ] (L \ C2CH and CO; X \ F,
Cl, Br, I and CH ) and trans-[RhX(2C2CHPh)(PMe ) ]
Since it is well known that d(MCO) modes of metal carbon-
yl complexes give rise to intense bands at higher wavenumbers
than those caused by metalÈcarbon stretching vibrations,19
the strong band at 601 cm~1 in the FT-Raman spectrum of
the Ñuoro complex 11 can probably be assigned to the
d(RhCO) mode. In the spectra of the chloro, bromo and iodo
carbonyl compounds, the corresponding band for the
d(RhCO) mode is shifted to lower wavenumbers and found at
582, 576 and 566 cm~1, respectively (Fig. 6). In the structur-
3 2
2
3
3 2
(X \ F, Cl, CH and C3 CPh). The isopropyl groups of the
3
experimental complexes have been substituted by methyl
groups in order to reduce the computation time. As expected,
the BPW91 DFT method with the Los Alamos pseudo-
potential plus double zeta (LANL2DZ) for rhodium in com-
bination with the Dunning/Huzinaga full double zeta (D95) or
the Pople basis sets in combination with polarization and
di†use functions gave the best results for the series of the
vinylidene halide and the carbonyl halide complexes. The
agreement between the calculated and the experimental bond
distances and bond angles for analogous compounds was
quite good (see Tables 3 and 4).
ally related compounds trans-[RhX(CO)(PPh ) ], the
3 2
d(RhCO) deformation mode has been assigned at 596, 574,
567 and 558 cm~1 for X \ F, Cl, Br and I, respectively,20
which is in good agreement with our results.
The addition of polarization and di†use functions to the
small basis set LANL2DZ provides in general better structur-
al parameters, particularly for the RhÈP bond lengths and
improves signiÐcantly the resulting l(CO) vibrational modes
(Tables 2È4). It should be noted that the good agreement of
the BPW91/LANL2DZ vibrational modes with the experi-
mental data is most likely due to favorable error cancellation.
The calculated structure of trans-[Rh(C3 CPh)(2C2CHPh)-
(PMe ) ] with the small basis LANL2DZ was acceptable but
3 2
for trans-[Rh(CH )(2C2CHR)(PMe ) ] (R \ H or Ph) the cal-
3
3 2
culated CÈRhÈC and RhÈCÈC bond angles were too small
(157.2 and 158.6¡) for the minimum energy structure. The
freezing of both the CÈRhÈC and RhÈCÈC bond angles to
180¡ leads to a linear structural arrangement with one imagin-
ary harmonic wavenumber corresponding to a CÈRhÈCÈC
bending mode indicating a saddle point. The energy di†erence
between the two structures was less than 6 kJ mol~1.
For the calculation of atomic charges, natural bond orbital
(NBO) calculations were performed for the model compounds
trans-[RhX(2C2CH )(PMe ) ] (X \ F, Cl, Br, I and CH ) and
2
3 2
3
trans-[RhX(CO)(PMe ) ] (X \ F, Cl, Br, I). The resulting
3 2
natural population analysis (NPA)21 gave the partial charges
represented in Tables 5 and 6.
The energies of the molecular orbitals for the model com-
pounds trans-[RhX(L)(PMe ) ] (L \ C2CH , X \ F, Cl, Br, I
3 2
2
and CH ; L \ CO, X \ F, Cl, Br, I) were calculated by using
3
DFT1 and DFT4 (see Table 7). The geometries of the LUMO
and HOMO of the vinylidene (X \ F, CH ) and carbonyl
3
compounds (X \ F) are depicted in Fig. 7. The LUMO of the
Fig. 6 The d(RhCO) and l(Rh2C) wavenumber region of the FT-IR
spectrum of trans-[RhX(CO)(PiPr ) ] (X \ F, Cl, Br, I).
vinylidene complex is a combination of the p (F), d (Rh) and
3 2
z
xz
1392
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Table 3 Selected bond lengths (pm) and angles (¡) calculated for the model compounds trans-[RhX(2C2CHR)(PMe ) ], together with the
3 2
experimental values found in trans-[RhCl(2C2CHMe)(PiPr ) ]
3 2
Compound
RhÈX
Rh2C
C2C
RhÈP
PÈRhÈX
PÈRhÈC
XÈRhÈC
Method
trans-[RhF(2C2CH )(PMe ) ]
205.5
205.2
247.3
242.1
244.2
243.9
261.8
278.5
214.0
214.8
213.6
203.5
236.6(2)
182.0
181.3
182.3
181.4
181.7
181.1
182.6
182.9
187.7
186.7
187.1
186.4
177.5(6)
134.1
135.1
134.0
132.5
132.7
134.1
133.9
133.9
134.9
133.4
136.0
135.0
132.0(1)
238.5
239.0
239.7
232.9
234.9
236.0
240.0
240.6
238.0
232.6
238.6
239.3
234.4(2)
234.2(2)
84.6
84.5
86.9
87.5
87.3
87.6
87.7
88.7
89.3
89.1
89.2
87.3
91.95(7)
91.19(7)
95.4
95.5
93.1
92.5
92.7
92.4
92.3
91.3
90.8
90.9
90.9
92.7
88.2(2)
89.1(2)
179.4
178.8
179.4
179.8
179.9
179.7
180.0
180.0
157.2
155.8
154.8
171.4
175.8(2)
DFT1
DFT1
DFT1
DFT3
DFT4
DFT2
DFT1
DFT1
DFT1
DFT4
DFT1
DFT1
X-Raya
2
3 2
trans-[RhF(2C2CHPh)(PMe ) ]
3 2
trans-[RhCl(2C2CH )(PMe ) ]
2
3 2
trans-[RhCl(2C2CHPh)(PMe ) ]
3 2
trans-[RhBr(2C2CH )(PMe ) ]
2
3 2
trans-[RhI(2C2CH )(PMe ) ]
2
3 2
trans-[Rh(CH )(2C2CH )(PMe ) ]
3 2
3
2
trans-[Rh(CH )(2C2CHPh)(PMe ) ]
3
3 2
trans-[Rh(C3 CPh)(2C2CHPh)(PMe ) ]
3 2
trans-[RhCl(2C2CHMe)(PiPr ) ]
3 2
a Ref. 42.
Table 4 Selected bond lengths (pm) and angles (¡) calculated for the model compounds trans-[RhX(CO)(PMe ) ], together with the experimen-
3 2
tal values found in trans-[RhF(CO)(PPh ) ] and trans-[RhCl(CO)(PMe ) ]
3 2
3 2
Compound
RhÈX
Rh2C
CÈO
RhÈP
PÈRhÈX
PÈRhÈC
XÈRhÈC
Method
trans-[RhF(CO)(PMe ) ]
205.2
204.4
246.5
241.2
260.7
256.0
277.1
274.4
181.7
181.1
182.0
182.0
182.2
182.7
182.6
183.1
179.6(3)
120.9
117.6
120.7
117.3
120.7
117.8
120.6
117.8
115.1(4)
238.5
231.9
239.6
232.6
240.0
235.0
240.6
235.1
233.0(7)
232.4(7)
230.9(1)
230.7(1)
82.7
84.1
85.6
86.4
86.6
87.0
87.7
87.8
86.9(5)
88.1(9)
88.1(0)
89.3(0)
97.3
95.9
94.4
93.6
93.4
93.0
92.3
92.2
91.3(5)
93.7(9)
91.6(1)
91.0(1)
179.8
179.7
180.0
180.0
180.0
180.0
180.0
180.0
DFT1
DFT3
DFT1
DFT3
DFT1
DFT4
DFT1
DFT4
X-Raya
3 2
trans-[RhCl(CO)(PMe ) ]
3 2
trans-[RhBr(CO)(PMe ) ]
3 2
trans-[RhI(CO)(PMe ) ]
3 2
trans-[RhF(CO)(PPh ) ]
204.6(2)
3 2
trans-[RhCl(CO)(PMe ) ]
235.4(1)
177.0(4)
114.6(4)
179.4(1)
X-Rayb
3 2
a Ref. 43. b Ref. 44.
p (C ) orbitals, the contribution of the p (b-C) orbital being
the most important. For the carbonyl complex, the LUMO is
The shapes of the HOMO and LUMO do not change along
the series of compounds involved in the calculations with the
exception of the methyl vinylidene complex (see Fig. 7).
Similar atomic orbital combinations for the LUMO and
HOMO were obtained by Cauletti and coworkers for trans-
[RhCl(2C2CH )(PMe ) ] using DV-Xa calculations.22
However, the calculated MO energies using the DFT1È4
methods (Table 7) are about 1 eV smaller than those using
DV-Xa. The reason for this di†erence could be due to the fact
that the DV-Xa calculations were performed without a corre-
lation functional in contrast to the exchange and gradient-
corrected correlation functional (BPW91) used in this study
(see computational details). The calculated energies with the
DFT1 method were higher than those calculated using the
DFT2È4 methods, which gave very similar results. However,
for the vinylidene complexes the resulting di†erence
z
2
z
a combination of p (CO) and Rh p-orbitals. The HOMO is
z
mainly composed of the d orbital of Rh in both complexes.
z2
Table 5 Partial charges q on selected atoms of the model complexes
trans-[RhX(2C2CH )(PMe ) ] determined by natural population
2
3 2
2
3 2
analysis
X \
F
X
Rh
C
C
Method
a
b
[0.65
[0.71
[0.59
[0.61
[0.57
[0.55
[0.54
[0.49
[1.02a
[1.03a
]0.03
]0.01
[0.07
[0.10
[0.09
[0.15
[0.11
[0.15
[0.06
[0.09
]0.04
]0.11
]0.05
]0.12
]0.05
]0.11
]0.04
]0.11
[0.07
]0.005
[0.68
[0.75
[0.66
[0.74
[0.66
[0.74
[0.66
[0.74
[0.67
[0.75
DFT1
DFT4
DFT1
DFT4
DFT1
DFT4
DFT1
DFT4
DFT1
DFT4
Cl
Br
I
*E
is nearly independent of the method used. For
LUMO~HOMO
CH
the carbonyl compounds, the calculated di†erences between
the LUMO and the HOMO using DFT1 were 0.2È0.3 eV
smaller than those calculated with the DFT2È4 methods. The
calculated orbital energies for the phenyl-substituted vinyl-
3
a Charge on the carbon atom of the methyl group.
idenes trans-[RhX(2C2CHPh)(PMe ) ] were lower than in the
3 2
Table 6 Partial charges q on selected atoms of the model complexes
related complexes containing the C2CH ligand.
2
trans-[RhX(CO)(PMe ) ] determined by natural population analysisa
The calculated di†erence *E
for the model com-
3 2
LUMO~HOMO
pounds trans-[RhX(2C2CH )(PMe ) ] is in fair agreement
3 2
with the energies of the lowest energy absorption E
in the visible region and also decreases in the order
X \
X
Rh
C
O
2
of 1È10
max
F
[0.64
[0.58
[0.56
[0.52
[0.05
[0.19
[0.21
[0.23
]0.42
]0.45
]0.45
]0.44
[0.50
[0.49
[0.48
[0.48
F [ Cl P Br [ I for 1È4, and F [ CH [ Cl B Br [ I [
Cl
Br
I
3
C3 CPh for 5È10 (Table 7). For the methyl complex, the
LANL2DZ method gave a value of *E
in the
LUMO~HOMO
minimum energy structure that also agrees with the spectro-
a BPW91/LANL2DZ was used for all atoms (DFT1).
scopic data, despite the unusual CÈRhÈC bond angle of
New J. Chem., 2001, 25, 1389È1397
1393

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Table 7 Energies of the molecular orbitals, orbital energy di†erences and energies of the lowest energy visible absorption maxima (all in eV) for
vinylidene and carbonyl rhodium complexes
E
max
Compound
Method
E
E
*E
(Compound)a
LUMO
HOMO
LUMO~HOMO
trans-[RhF(2C2CH )(PMe ) ]
DFT1
DFT2
DFT3
DFT4
DFT1
DFT1
[1.99
[2.23
[2.21
[2.25
[2.24
[2.32
[4.15
[4.39
[4.40
[4.41
[4.26
[4.35
2.16
2.16
2.19
2.16
2.02
2.03
2.37
(1)
2
3 2
trans-[RhF(2C2CHPh)(PMe ) ]
3 2
2.25 (5)
2.20 (2)
2.12 (6)
2.16 (3)
2.13 (7)
2.12
2.06 (8)
trans-[RhCl(2C2CH )(PMe ) ]
2
3 2
trans-[RhBr(2C2CH )(PMe ) ]
DFT1
DFT1
[2.41
[2.47
[4.40
[4.41
1.99
1.94
2
3 2
trans-[RhI(2C2CH )(PMe ) ]
(4)
2
3 2
trans-[Rh(CH )(2C2CH )(PMe ) ]
DFT1
DFT1
DFT1
DFT1
DFT1
DFT1
DFT1
[1.62
[1.82
[2.51
[1.24
[1.55
[1.65
[1.73
[3.77
[3.98
[4.29
[4.11
[4.33
[4.38
[4.42
2.15
2.16
1.78
2.87
2.78
2.73
2.69
3
2
3 2
trans-[Rh(CH )(2C2CHPh)(PMe ) ]
2.22 (9)
2.03 (10)
3.53 (11)
3.43 (12)
3.41 (13)
3.35 (14)
3
3 2
trans-[Rh(C3 CPh)(2C2CHPh)(PMe ) ]
3 2
trans-[RhF(CO)(PMe ) ]
3 2
trans-[RhCl(CO)(PMe ) ]
3 2
trans-[RhBr(CO)(PMe ) ]
3 2
trans-[RhI(CO)(PMe ) ]
3 2
a In hexane.
157.2¡. In contrast, the linear structure gives a *E
absorption maxima both follow the same trend as in the vinyl-
idene complexes, although the di†erence between the calcu-
lated and the experimental energies is larger.
Since the HOMO is mainly located on Rh and the LUMO
mainly on the vinylidene or partially on the carbonyl ligand,
the corresponding absorptions could be classiÐed as metal-to-
ligand charge transfer bands. Also, the absorptions in the
visible spectra of the related compounds trans-[RhX(CY)
LUMO~HOMO
of 1.81 eV (DFT1), which di†ers from the observed trend of
the energies of the absorption maxima in the visible region.
For the carbonyl compounds, the calculated energy di†erences
between LUMO and HOMO and the energies of the observed
(PR ) ] (Y \ O,23 Y \ S24) have been attributed to MLCT
3 2
transitions.
Discussion
For a diatomic molecule, the vibrational mode is directly
related to (k/m)1@2, where k is the force constant of the bond
and m is the reduced mass. Since the force constant reÑects the
bond strength, the conclusion is that the stronger the bond,
the higher its wavenumber. In polyatomic molecules, the same
principle has been generally applied to bands that mainly
originate from the stretching of one particular bond.
Recently, we have studied the vibrational spectra of the
square-planar vinylidene complexes trans-[RhF(2C2CH )-
2
(PiPr ) ] and its 13C-containing isotopomer trans-
3 2
[RhF(213C213CH )(PiPr ) ] (1) and found that, by using FT-
2
3 2
Raman spectroscopy, the l(Rh2C) and l(Rh213C) modes can
be unambiguously assigned.17 In the 13C-substituted com-
pounds, the l(Rh213C) mode gives rise to an intense band that
is separated from the others, while in trans-[RhX(2C2CH )-
2
(PiPr ) ] a band of medium-to-weak intensity, originating
3 2
from the phosphines, overlaps with the l(Rh2C) mode. Due to
these observations, the series of 13C-labeled complexes trans-
[RhX(213C213CH )(PiPr ) ] (1È4) is an appropriate system to
2
3 2
study the variation of l(Rh213C) as a probe of the electronic
inÑuence of the ligand X trans-disposed to the Rh2C bond.
This investigation has been extended to the phenyl-substituted
vinylidene complexes 5È10 and to the related carbonyl deriv-
atives 11È14.
From the data of the Raman spectra of the vinylidene com-
pounds 1È10 (Fig. 1 and Table 1), for di†erent ligands X the
following order of the l(Rh213C) and l(Rh2C) wavenumbers
has been obtained: F [ Cl P Br P I [ CH [ C3 CPh. We
3
have already mentioned that the coupling between the
l(Rh2C) and l(RhX) modes as well as the mass e†ect of the
heavier halogens also contribute to this sequence. However,
the fact that the calculated Rh2C distances for the model com-
pounds trans-[RhX(2C2CH )(PMe ) ] increase in the same
Fig. 7 Representation of the calculated LUMOs and HOMOs (0.04
a.u.) of (a) trans-[RhF(2C2CH )(PMe ) ], (b) trans-[RhF(CO)-
2
3 2
(PMe ) ] and (c) trans-[Rh(CH )(2C2CH )(PMe ) ].
3 2 3 2
3
2
2
3 2
1394
New J. Chem., 2001, 25, 1389È1397

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order as the wavenumber of the l(Rh2C) modes decreases sug-
gests that the observed sequence is mainly due to a variation
in the Rh2C bond strengths.
static behavior of rhodium may also play a role in the
observed variation of the l(CO) mode, since it has been shown
that the electrostatic inÑuence of a positively charged atom
bonded to CO initiates a shift of the CO stretching vibration
to lower wavenumbers.29
Since for the series of halide complexes, the order of the
l(Rh2C) stretching mode is the same for 1È4 as for 5È8, we
assume that the bonding properties of the C2CH and
The discussed repulsion between Ðlled orbitals can also be
used to explain the variation of the calculated energies of the
2
C2CHPh ligands are quite similar. A slightly exceptional
observation is that the wavenumber of the l(Rh2C) mode for
compound 5 is 7 cm~1 higher in the Raman spectrum than for
trans-[RhF(2C2CH )(PiPr ) ]. Although this increase might
HOMOs for the model compounds trans-[RhX(2C2CH )-
2
(PMe ) ] where X \ F, Cl, Br and I (Table 7). The energy of
3 2
the HOMO decreases along the sequence F [ Cl [ Br [ I,
2
3 2
indicate that substitution of H by Ph strengthens the Rh2C
bond, it could also originate from the above-mentioned coup-
ling between the l(Rh2C) and an in-plane ring deformation
mode. By taking this into consideration, we conclude that on
the basis of the vibrational spectra the trans inÑuence of the
ligands X in compounds 1È10 decreases along the series
the di†erence between the Ñuoro and the chloro complex
being the highest. This result agrees with the fact that Ñuorine,
as the group 17 element with the smallest radius and the
largest negative charge, creates the strongest destabiliz-
ing repulsion with the electrons of the HOMO, which is
mainly composed of the d orbital of Rh. Regarding the
z2
C3 CPh [CH [ I [ Br [ Cl [ F.
LUMOs, their energy also decreases along the sequence
3
It is interesting to compare the variations of the vibrational
F [ Cl [ Br [ I (see Table 7). A possible explanation for this
trend could be that due to the Rh2C antibonding character of
the LUMOs (see Fig. 7) these orbitals will be higher in energy
if the strength of the Rh2C bond increases. With respect to the
analogous model compounds containing CO instead of
data of the vinylidene compounds 1È4 with those of the iso-
electronic carbonyls trans-[RhX(CO)(PiPr ) ], where X \ F
3 2
(11), Cl (12), Br (13) and I (14). In the FT-Raman spectra of
11È14, the l(Rh2C) mode is shifted to lower wavenumbers in
the order F [ Cl [ Br [ I (Fig. 5), which is the same as found
for the analogous vinylidene complexes 1È4 (Fig. 1). However,
while the l(CO) mode of 11È14 is shifted to higher wavenum-
bers along the sequence F \ Cl \ Br \ I (Fig. 6), the
l(13C213C) and l(C2C) modes of 1È4 (Fig. 2) and 5È8 (Table 1)
are shifted to higher wavenumbers in the opposite sequence.
The observed opposite trends of l(CO) and d(RhCO) for
11È14 (Fig. 5 and 6) is the same as that observed for the tri-
C2CH , the HOMOs are strongly localized on the metal and
2
include only some minor contributions from the CO carbon
atom. Although the calculated energies of the HOMOs for the
carbonyl and the vinylidene complexes are quite similar (see
Table 7), the energies of the LUMOs are somewhat higher for
L \ CO than for L \ C2CH . This di†erence causes the
2
observed blue-shift of the absorption maxima in the visible
region.
phenylphosphine complexes trans-[RhX(CO)(PPh ) ] (X \ F,
An interesting situation results for the model compound
trans-[Rh(CH )(2C2CH )(PMe ) ], in which the methyl
3 2
Cl, Br, I),20,25 and has been explained in terms of an increas-
3
2
3 2
ing p-donor capability of X on going up in group 17. The
surprising situation thus arises that the metal center seems to
be more electron-rich if it is bonded to a more electronegative
halogen. This supposition has been used to explain the varia-
tion of the half-wave reduction potentials and the equilibrium
ligand has no nonbonding electrons that could initiate a
repulsion with the d electrons of rhodium. The minimum
energy structure calculated by the BPW91/LANL2DZ
method for trans-[Rh(CH )(2C2CH )(PMe ) ] reveals a sig-
3
2
3 2
niÐcant distortion from the anticipated linear CÈRh2C2C
chain, the calculated CÈRhÈC and RhÈCÈC bond angles being
157.2 and 158.6¡, respectively. However, the energy of the dis-
torted structure for the vinylidene complex is less than 6 kJ
mol~1 smaller than the energy for the linear arrangement. In
this context, it should be noted that in benzene compound
constants for the halide exchange in trans-[RhX(CO)(PPh ) ]
3 2
(X \ F, Cl, Br, I)20,25 as well as in related halide complexes of
Fe,2 Ru,26 Ir3 and Pd.27 With regard to our work, the same
clue about a push-pull p-interaction, X ] Rh ] C, provides an
explanation for why we Ðnd for both the vinylidene and the
carbonyl complexes the highest RhÈC bond strength when
Ñuoride is the trans-disposed ligand.
9
rearranges to the p-allyl complex [Rh(g3-CH CH-
2
CHPh)(PiPr ) ] by migration of the methyl group to the
3 2
Quite remarkably, the calculated atomic charges for the
vinylidene ligand.30 Therefore, a coupling of the two C-
model compounds trans-[RhX(L)(PMe ) ], where L \
bonded ligands is possible, even without the presence of a sup-
porting Lewis base. Although in this case we should be more
cautious regarding the calculated Rh2C bond distance and the
value of the assigned l(Rh2C) mode, the calculation suggests
that the Rh2C bond is weaker. This can be rationalized by
assuming that the electrostatic repulsion, which in the halide
complexes pushes the d orbitals towards the p orbitals of the
3 2
C2CH or CO and X \ F, Cl, Br, I and CH , are not in
2
3
agreement with the assumption that the metal center becomes
more electron-rich along the sequence F [ Cl [ Br [ I [
CH (see Tables 5 and 6). According to the calculations, the
3
positive charge on Rh increases from X \ I to X \ F while
the charge on the vinylidene and CO ligands does not vary
p
p
signiÐcantly. In addition, the calculated population of the p
orbitals of the halogens does not vary signiÐcantly in the
carbon, is not present in the methyl compound. The calcu-
lated charge of the metal in the methyl rhodium complex lies
between that of the Ñuoro and the chloro derivatives.
p
series, suggesting that the shifts of the vibrational modes are
not caused by di†erences in p donation from the halogen to
p
the metal. In the case of the Ñuoro complexes, the consider-
Conclusions
able di†erence in charge between Rh and F (0.68 for L \
C2CH and 0.59 for L \ CO), calculated by the DFT1
The values of the Rh2C stretching mode for the vinylidene
complexes trans-[RhX(2C2CHR)(PiPr ) ], where R \ H or
Ph, suggest that the strength of the Rh2C bond increases
along the sequence X \ C3 CPh \ CH \ I \ Br \ Cl \ F.
The calculated Rh2C bond distances for the model com-
pounds trans-[RhX(2C2CH )(PMe ) ] decrease in the same
sequence. The NPA analysis reveals that the metal becomes
more electron-rich by varying the ligand X along the sequence
2
method, suggests that (i) the RhÈF bond has a strong electro-
3 2
static component and (ii) the small and highly negatively
charged Ñuorine atom will cause severe electrostatic repul-
sions with the electron density at the metal.28 Thus, the coor-
dination of Ñuoride has two e†ects on the RhÈC bond. On the
one hand, the higher positive charge on the metal leads to an
increase in the r-donation from carbon to rhodium, while on
3
2
3 2
the other hand the repulsion between the p electrons of the
F \ CH \ Cl \ Br \ I. These results can be explained by
p
3
Ñuoride and the
retrodonation from the metal to the empty p orbitals of the
d
electrons of rhodium favors
a
p-
taking two e†ects into consideration. First, with the increase
p
of the electronegativity of X the charge of the metal becomes
more positive and the r-donation from carbon to rhodium
p
vinylidene ligand. In addition to these two e†ects, the electro-
New J. Chem., 2001, 25, 1389È1397
1395

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becomes stronger. Second, with the increase of the charge on
X accompanied by a decrease in size the repulsion between the
116.3, J(Rh,C) 60.7, J(P,C) 16.2, Rh2C], 90.0 [ddt, J(C,C) 55.6,
J(Rh,C) 16.2, J(P,C) 6.1, Rh2C2C], 25.0 (vt,
N 10.1,
nonbonding electron pairs of X and the Ðlled d orbitals of Rh
become stronger. The latter e†ect leads to an increase in p-
PCHCH ), 20.3 (s, PCHCH ); d (162.0 MHz) 40.2 [ddd,
p
3
3
P
J(Rh,P) 132.2, 2J(C,P) 15.3, 3J(C,P) 6.8].
backbonding from the metal to the empty p orbital of
p
trans-[RhBr(2C2CHPh)(PiPr ) ], 7. A solution of 6 (175
carbon. For the series of carbonyl compounds trans-
3 2
mg, 0.31 mmol) in acetone (10 cm3) was treated with KBr (500
[RhX(CO)(PiPr ) ], where X \ F, Cl, Br and I, analogous
3 2
mg, 4.2 mmol). The suspension was stirred at room tem-
perature for 40 min and brought to dryness in vacuo. The
residue was extracted twice with 12 cm3 portions of hexane.
The extract was Ðltered, concentrated to ca. 3 cm3 and then
stored for 2 days at [65 ¡C. Dark blue crystals precipitated,
which were washed three times with 4 cm3 portions of
pentane ([40 ¡C) and dried in vacuo: yield 110 mg (59%).
results have been obtained and conÐrmed for the model com-
pounds trans-[RhX(CO)(PMe ) ].
3 2
Experimental
All reactions were carried out under an inert atmosphere of
argon by use of Schlenk techniques. Compounds 1,17 5,31 6,32
9,33 10,34 1131 and 1235 were prepared as reported previously.
NMR spectra were recorded at room temperature on Bruker
AC 200 and Bruker AMX 400 instruments [abbreviations
used: s, singlet; d, doublet; t, triplet; m, multiplet; vt, virtual
triplet; br, broadened signal; coupling constants N and J in
Hz]. The FT-Raman spectra were recorded at room tem-
perature using a Bruker IFS 120-HR spectrometer with an
integrated FRA 106 Raman module (resolution \ 3 cm~1).
Radiation of 1064 nm from a Nd-YAG laser was employed for
excitation of crystalline samples contained in NMR tubes
under argon. The infrared spectra were recorded with a
Bruker IFS 25 spectrometer using Nujol suspensions between
KBr plates. UV-visible spectra were recorded using n-hexane
solutions in the range 300È700 nm using a PerkinÈElmer UV/
VIS/NIR Lambda 19 spectrometer with the wavelength of the
lamp at 319.2 and 860.8 nm and Ðlters at 810.4, 690.4, 562.4
and 379.2 nm. The detector used for the UV/VIS region was a
photomultiplier.
Anal. found: C, 51.72; H, 7.98%. C
H
BrP Rh requires: C,
26 48
2
51.58; H, 7.99%. NMR (C D ) d (400 MHz) 7.16 (2 H, m,
6
6
H
ortho-H of C H ), 7.01 (2 H, m, meta-H of C H ), 6.86 (1 H,
6
5
6 5
m, para-H of C H ), 2.80 (6 H, m, PCHCH ), 1.28 [36 H, dvt,
N 13.5, J(H,H) 6.4, PCHCH ], 1.13 [1 H, t, J(P,H) 3.2,
Rh2C2CH]; d (100.6 MHz) 292.0 [dt, J(Rh,C) 59.8, J(P,C)
15.9, Rh2C], 128.6, 125.9, 125.2, 124.7 (all s, C H ), 112.5 [dt,
6
5
3
3
C
6
5
J(Rh,C) 15.3, J(P,C) 6.4, Rh2C2CH], 24.5 (vt,
N 20.4,
PCHCH ), 20.4 (s, PCHCH ); d (81.0 MHz) 41.9 [d, J(Rh,P)
3
3
P
133.4].
trans-[RhI(2C2CHPh)(PiPr ) ], 8. This compound was
3 2
prepared analogously as described for 7, using 6 (257 mg, 0.46
mmol) and NaI (2.0 g, 13.3 mmol) as starting materials. Blue-
green crystals: yield 210 mg (70%). Anal. found: C, 47.95; H,
7.31%. C
H
IP Rh requires: C, 47.87; H, 7.42%. NMR
26 48
2
(C D ) d (400 MHz) 7.14 (2 H, m, ortho-H of C H ), 7.08 (2
6
6
H
6 5
6 5
H, m, meta-H of C H ), 6.85 (1 H, m, para-H of C H ), 2.89 (6
6
5
H, m, PCHCH ), 1.27 [36 H, dvt, N 13.8, J(H,H) 6.7,
3
Syntheses
PCHCH ], 0.75 [1 H, t, J(P,H) 3.4 Hz, Rh2C2CH]; d (100.6
3
C
MHz) 286.9 [dt, J(Rh,C) 63.6, J(P,C) 15.9, Rh2C], 128.6,
126.1, 125.4, 123.6 (all s, C H ), 113.0 [dt, J(Rh,C) 15.3, J(P,C)
trans-[RhCl(213C213CH )(PiPr ) ], 2. A solution of 1 (230
2
3 2
mg, 0.49 mmol) in acetone (10 cm3) was treated with KCl (73
mg, 0.98 mol) at room temperature. The suspension was
stirred for 7 h and brought to dryness in vacuo. The residue
was extracted twice with 10 cm3 portions of pentane. The
extract was Ðltered, concentrated to ca. 2 cm3 and then stored
for 24 h at [78 ¡C. Dark violet crystals precipitated, which
were washed twice with 2 cm3 portions of pentane ([35 ¡C)
and dried in vacuo: yield 146 mg (62%). NMR (C D ) d (200
6
5
6.4, Rh2C2CH], 25.7 (vt,
N
21.6, PCHCH ), 20.6 (s,
3
PCHCH ); d (81.0 MHz) 41.4 [d, J(Rh,P) 132.2].
3
P
trans-[RhBr(CO)(PiPr ) ], 13. A solution of 12 (201 mg,
3 2
0.41 mmol) in acetone (15 cm3) was treated with NaBr (255
mg, 0.17 mol) at room temperature. The suspension was
stirred for 60 h and brought to dryness in vacuo. The residue
was extracted twice with 10 cm3 portions of C H . The
6
6
H
MHz) 2.84 (6 H, m, PCHCH ), 1.30 [36 H, dvt, N 13.4, J(H,H)
6 6
extract was Ðltered and the solvent was evaporated in vacuo.
The residue was dissolved in 3 cm3 of pentane and the solu-
tion stored for 18 h at [78 ¡C. Yellow crystals precipitated,
which were washed twice with 3 cm3 portions of pentane
([30 ¡C) and dried in vacuo: yield 210 mg (96%); mp 154 ¡C
3
7.3, PCHCH ], [0.15 [2 H, ddt, J(P,H) 3.7, 2J(C,H) 7.3, 1J(C,
3
H) 162.2, Rh2C2CH]; d (50.3 MHz) 290.6 [ddt, J(C,C) 113.2,
C
J(Rh,C) 56.6, J(P,C) 15.9, Rh2C], 89.1 [ddt, J(C,C) 56.0, J(Rh,
C) 16.5, J(P,C) 5.5, Rh2C2C], 23.4 (vt, N 9.2, PCHCH ), 20.2
3
(s, PCHCH ); d (81.0 MHz) 42.4 [ddd, J(Rh,P) 134.9, 2J(C,P)
(decomp.). Anal. found: C, 42.96; H, 7.70%. C
H
BrOP Rh
3
P
15.4, 3J(C,P) 5.0].
19 42
2
requires: C, 42.95; H, 7.97%. NMR (CD Cl ) d (400 MHz)
2
2
H
2.70 (6 H, m, PCHCH ), 1.30 [36 H, dvt, N 13.8, J(H,H) 6.8,
trans-[RhBr(213C213CH )(PiPr ) ], 3. This compound was
3
2
3 2
PCHCH ]; d (100.6 MHz) 188.5 [dt, J(Rh,C) 75.8, J(P,C)
14.2, CO], 25.3 (vt, N 11.1, PCHCH ), 20.3 (s, PCHCH ); d
prepared analogously as described for 2, using 1 (150 mg, 0.32
mmol) and KBr (55 mg, 0.46 mmol) as starting materials.
Dark violet crystals: yield 126 mg (77%). NMR (C D ) d
3
C
3
3
P
(162.0 MHz) 47.7 [d, J(C,P) 117].
6
6
H
(400 MHz) 2.92 (6 H, m, PCHCH ), 1.29 [36 H, dvt, N 13.8,
trans-[RhI(CO)(PiPr ) ], 14. This compound was prepared
3
J(H,H) 7.1, PCHCH ], [0.44 [2 H, ddt, J(P,H) 3.4, 2J(C,H)
3 2
analogously as described for 13, using 12 (200 mg, 0.41 mmol)
3
6.7, 1J(C,H) 161.7, Rh2C2CH]; d (100.6 MHz) 287.8 [ddt,
and NaI (285 mg, 1.9 mmol) as starting materials. Yellow crys-
tals: yield 220 mg (93%); mp 144 ¡C (decomp.). Anal. found:
C
J(C,C) 115.3, J(Rh,C) 58.6, J(P,C) 16.2, Rh2C], 89.3 [ddt, J(C,
C) 56.6, J(Rh,C) 17.2, J(P,C) 6.1, Rh2C2C], 23.8 (vt, N 10.1,
PCHCH ), 20.2 (s, PCHCH ); d (162.0 MHz) 40.9 [ddd,
C, 39.41; H, 7.32%. C
H
IOP Rh requires: C, 39.46; H,
19 42
2
7.32%. NMR (C D ) d (400 MHz) 2.70 (6 H, m, PCHCH ),
3
3
P
J(Rh,P) 133.9, 2J(C,P) 15.3, 3J(C,P) 5.1].
6
6
H
3
1.20 [36 H, dvt, N 16.0 J(H,H) 8.0, PCHCH ]; d (100.6
3
C
MHz) 187.5 [dt, J(Rh,C) 75.0, J(P,C) 14.0, CO], 26.5 (vt, N
10.0, PCHCH ), 20.4 (s, PCHCH ); d (162.0 MHz) 47.6 [d,
trans-[RhI(213C213CH )(PiPr ) ], 4. This compound was
2
3 2
prepared analogously as described for 2, using 1 (126 mg, 0.27
mmol) and NaI (53 mg, 0.35 mmol) as starting materials. Dark
violet crystals: yield 110 mg (80%). NMR (C D ) d (400
3
3
P
J(C,P) 117].
Computational details
6
6
H
MHz) 3.03 (6 H, m, PCHCH ), 1.29 [36 H, dvt, N 13.3, J(H,H)
3
6.9, PCHCH ], [0.64 [2 H, ddt, J(P,H) 3.4, 2J(C,H) 6.9, 1J(C,
H) 161.9, Rh2C2CH]; d (100.6 MHz) 283.4 [ddt, J(C,C)
The DFT calculations were performed using GAUSSIAN
9836 and BeckeÏs 1988 exchange functional37 in combination
3
C
1396
New J. Chem., 2001, 25, 1389È1397

View Article Online
16 R. M. Sosa, P. Gardiol and G. Beltrame, Int. J. Quantum Chem.,
1998, 69, 371.
with the PerdewÈWang Ï91 gradient-corrected correlation
functional (BPW91).38 The Los Alamos e†ective core poten-
tial plus double zeta (LANL2DZ)39,40 was employed for
rhodium, whereas the Dunning/Huzinaga full double zeta
basis set with or without polarization and di†use function
[D95, D95 ] (d) and D95 ] (3df, 2p) for P, C, H, F, Cl and O
atoms or 6-31&&G(d) for P, C, H, O, 6-311&&G(d) for Br and
3-21G(d) for I] was used. The calculations were performed
without symmetry restrictions. For both C and C sym-
17 D. Moigno, W. Kiefer, J. Gil-Rubio and H. Werner, J.
Organomet. Chem., 2000, 612, 125.
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Equilibrium constants for halide exchange: (b) F. Araghizadeh,
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1
s
metries, very similar energies were obtained Mthe calculated
energies for trans-[RhF(2C2CH )(PMe ) ] using the BPW91/
2
3 2
LANL2DZ method were [593.301 98 and [593.301 01 a.u.,
respectivelyN. When C symmetry was imposed, the rotation-
al conformations of the phosphine groups caused difficulties in
2v
Ðnding an energy minimum.
The following notation has been used for the computational
methods used. DFT1: BPW91/LANL2DZ for all atoms;
DFT2: BPW91/LANL2DZ for Rh and D95 ] (d) for the
other atoms; DFT3: BPW91/LANL2DZ for Rh and
D95 ] (3df,2p) for the other atoms; DFT4: BPW91/
LANL2DZ for Rh, 6-31&&G(d) for H, P, C and 6-311&&G(d)
for F, Cl, Br and 3-21G(d) for I.
26 J. T. Poulton, M. P. Sigalas, K. Folting, W. E. Streib, O. Eisen-
stein and K. G. Caulton, Inorg. Chem., 1994, 33, 1476.
27 J. P. Flemming, M. C. Pilon, O. Y. Borbulevitch, M. Y. Antipin
and V. V. Grushin, Inorg. Chim. Acta, 1998, 280, 87.
28 K. G. Caulton, New J. Chem., 1994, 18, 25.
29 G. Frenking and N. Frohlich, Chem. Rev., 2000, 100, 717.
30 R. Wiedemann, J. Wolf and H. Werner, Angew. Chem., 1995, 107,
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31 J. Gil-Rubio, B. Weberndorfer and H. Werner, J. Chem. Soc.,
Dalton T rans., 1999, 1437.
Acknowledgements
Financial support from the Deutsche Forschungsgemeinschaft
(SFB 347, projects C2 and D1) and the European Commission
(Contract ERBFMBICT960698) as well as from the Fonds der
Chemischen Industrie is gratefully acknowledged. We also
thank Mrs R. Schedl and Mr C. P. Kneis (DTA and elemental
analyses) as well as Degussa AG (gifts of various chemicals).
32 F. J. Garc•a Alonso, A. Hohn, J. Wolf, H. Otto and H. Werner,
Angew. Chem., 1985, 97, 401; F. J. Garc•a Alonso, A. Hohn, J.
Wolf, H. Otto and H. Werner, Angew. Chem., Int. Ed. Engl., 1985,
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1397