PX3-induced migratory insertion reactions of half-sandwich-type carbenerhodium(I) complexes

Article abstract of DOI:10.1039/b008601k

The carbenerhodium(I) complexes trans-[RhCl(=CPh₂)(L)₂] (L = PPrⁱ₃, 1a; SbPrⁱ₃, 1b) react with PF₃ by cleavage of the rhodium-carbene bond to give the corresponding PF₃

Full text of DOI:10.1039/b008601k

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PX -induced migratory insertion reactions of half-sandwich-type
3
carbenerhodium(I) complexes¤
Ulrich Herber,a Rita Guerrero Sanchez,b Olaf Gevert,a Matthias Laubendera and
Helmut Werner*a
a Institut fur Anorganische Chemie der Universitat W urzburg, Am Hubland, D-97074 W urzburg,
Germany. E-mail: helmut.werner=mail.uni-wuerzburg.de
b Grupo de Qu•mica Organometalica, Departamento de Ch•mica Inorganica, Facultad de Qu•mica,
Universidad de Murcia, E-30071 Murcia, Spain
Received (in Strasbourg, France) 23rd October 2000, Accepted 15th November 2000
First published as an Advance Article on the web 15th February 2001
The carbenerhodium(I) complexes trans-[RhCl(2CPh )(L) ] (L \ PPri , 1a; SbPri , 1b) react with PF by cleavage
2
2
3
3
3
of the rhodiumÈcarbene bond to give the corresponding PF derivatives trans-[RhCl(PF )(L) ] 5a,b, in good yield.
3
3
2
In contrast, treatment of the half-sandwich-type compound [(g5-C H )Rh(2CPh )(PPri )], 2a, with both PF and
5
5
2
3
3
P(OPh) leads to the migratory insertion of the CPh unit into one of the cyclopentadienyl CÈH bonds to form the
3
2
ring-substituted products [Mg5-C H (CHPh )NRh(PX )(PPri )] (X \ F, 6a; OPh, 6b). The molecular structures of
5
4
2
3
3
6a and 6b have been determined by X-ray crystallography. The reaction of the stibine complex [(g5-C H )Rh-
5
5
(2CPh )(SbPri )], 2b, with PF proceeds by ligand displacement to a†ord the new carbenerhodium(I) compound
2
5
3
3
[(g5-C H )Rh(2CPh )(PF )], 7. The mechanism of the migratory insertion reaction is discussed.
5
2
3
Recently, we reported that square-planar as well as half-
sandwich-type diphenylcarbenerhodium(I) complexes, trans-
[RhCl(2CPh )(PPri ) ], 1a, and [(g5-C H )Rh(2CPh )(PPri )],
CÈH bonds to form a ring-substituted product. Some prelimi-
nary observations have already been communicated.4
2
3 2
5
5
2
3
Results and discussion
2a, upon treatment with CO easily undergo CÈC coupling
reactions (Scheme 1).1 Instead of displacing a phosphine
ligand, carbon monoxide induces cleavage of the rhodiumÈ
Treatment of the square-planar bis(phosphine) complex 1a,
which is easily accessible from 1b and PPri by ligand
3
carbene bond and a†ords, besides trans-[RhCl(CO)(PPri ) ],
exchange,1a,b with PF in benzene at room temperature leads
3 2
3
3, and [(g5-C H )Rh(CO)(PPri )], 4, exclusively diphenyl-
to displacement of the carbene by PF . After recrystallization
5
5
3
3
ketene. By taking the related r-donor/p-acceptor capabilities
from acetone, compound 5a is isolated as a yellow solid in
of CO and PF into consideration,2 we became interested to
68% yield. The reaction of the bis(stibine) counterpart 1b with
3
Ðnd out how the same starting materials 1a and 2a would
PF proceeds analogously and gives compound 5b (Scheme 2).
3
behave toward PF . Although a great number of phosphorus
In this case, no free SbPr i can be detected spectroscopically
3
3
ylides R PCR@ with R@ \ aryl are known,3 to the best of our
in the reaction mixture, which means that PF behaves com-
3
2
3
pletely di†erently towards 1b compared with PPri and other
3
knowledge a corresponding triÑuoro derivative F PCR@ has
not been described in the literature as yet.
3
2
trialkyl- or triarylphosphines. The latter react with 1b by sub-
We report in this paper that, not unexpectedly, a coupling
stitution of the stibine ligands to a†ord trans-
[RhCl(2CPh )(PR ) ]. The 31P NMR spectrum of 5a exhibits
of the diphenylcarbene ligand of either 1a or 2a with PF does
3
2
3 2
not take place. However, the surprising and most noteworthy
two well-separated resonances at d 111.9 and 46.8, which due
to 31PÈ103Rh, 31PÈ31P and 31PÈ19F couplings appear as
doublets of doublets of quartets. In the 31P NMR spectrum of
5b, a doublet of quartets at d 120.2 is observed. With regard to
the rhodium-free by-products, a GC/MS analysis of the solu-
result is that the half-sandwhich-type complex 2a reacts under
mild conditions with both PF and P(OPh) by migratory
3
3
insertion of the CPh unit into one of the cyclopentadienyl
2
tion revealed that the CPh moiety is mainly transformed into
2
tetraphenylethene. Small amounts of substituted arenes can
also be detected. We note that an analog of 5a with two
triphenyl- instead of two triisopropylphosphine ligands is
known; it has been prepared from the dimer [RhCl(PF ) ]
3 2 2
and PPh by cleavage of the chloro bridges.5
3
Scheme 1
¤ Dedicated to Professor E.-G. Jager on the occasion of his 65th
birthday.
Scheme 2
396
New J. Chem., 2001, 25, 396È399
DOI: 10.1039/b008601k
This journal is ( The Royal Society of Chemistry and the Centre National de la Recherche ScientiÐque 2001

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Scheme 3
The cyclopentadienyl complex 2a also reacts with PF at
3
room temperature. Passing a stream of carefully dried phos-
phorus triÑuoride through a solution of 2a in benzene leads to
a smooth change of color from blue to orange and a†ords,
after chromatographic workup and recrystallization from
pentane, compound 6a (being analytically a 1 : 1 adduct of 2a
and PF ) as an orange air- and moisture-sensitive solid in
3
72% yield (Scheme 3). The most typical spectroscopic features
Fig. 1 An ORTEP plot of compound 6a. The ellipsoids are drawn at
the 50% probability level.
of 6a are the signals for the CHPh proton at d 4.79 in the 1H
NMR and the two resonances for the phosphorus nuclei of
2
the PF and PPri ligands at d 119.4 and 79.0 in the 31P
3
3
NMR spectrum. Both 31P NMR signals show a strong 31PÈ
103Rh coupling of, respectively, 446.3 and 221.0 Hz.
rhodium has a somewhat distorted trigonal coordination
sphere if the midpoint of the substituted cyclopentadienyl ring
is taken as one coordination site. The RhÈPF as well as the
The migratory insertion of the CPh unit into one of the
CÈH bonds of the ring can be induced not only by PF but
also by P(OPh) . The phosphite, however, is less reactive than
2
3
RhÈP(OPh) bonds are signiÐcantly shorter than the Rh-
3
3
PPri distance (see Table 1), which conÐrms the distinct di†er-
ence in the p-acceptor strength of PF and P(OPh) on one
side and of PPri on the other. The CHPh moiety in 6a and
6b is pointing away from the bulky triisopropylphosphine
ligand, which probably reduces the steric repulsion between
the two units. The distance between rhodium and the substi-
tuted ring carbon atom C1 is somewhat larger in the tri-
phenylphosphite complex 6b than in 6a, which could also be
due to steric requirements.
3
3
PF and therefore the reaction of 2a with a four-fold excess of
3
3
3
P(OPh) in toluene at room temperature takes several days.
3
3
2
After removal of the solvent and recrystallization of the
residue from etherÈpentane orange crystals of the insertion
product 6b are obtained; they are considerably more ther-
mally stable than the PF analog 6a. In agreement with the
3
proposed structure, the 1H NMR spectrum of 6b displays two
signals for the pairwise equivalent C H protons at d 4.69 and
5
4
4.47 and the 13C NMR spectrum equally shows two reso-
nances at d 86.5 and 84.5 for the respective ring carbon atoms.
The two resonances in the 31P NMR spectrum of 6b at d
132.4 and 75.3 reveal a smaller 31PÈ31P coupling (64.4 Hz)
than those of 6a (77.6 Hz).
Regarding the mechanism of formation of 6a and 6b, two
routes are conceivable. Since it is known, mainly due to the
The reaction of the triisopropylstibine complex 2b with PF
3
follows a di†erent pathway than that of the PPri counterpart
3
2a. Instead of the carbene, the stibine ligand is displaced and
following chromatographic workup the C H Rh compound 7
5
5
is isolated as a deep red microcrystalline solid in 72% yield
(see Scheme 4). In this case, PF behaves analogously to CO
3
toward 2b as the starting material. In contrast, tri-
phenylphosphite does not react with 2b by ligand substitution.
While no reaction takes place using equimolar amounts of 2b
and P(OPh) (toluene, room temperature, 2 days), with a four-
3
fold excess of the phosphite a mixture of products is formed,
which could not be separated by either fractional crys-
tallization or column chromatography. Since as discussed
below the half-sandwich-type complexes [(g5-C H )M(L) ]
5
5
2
with M \ Co, Rh and Ir prefer to react with Lewis bases by
an associative mechanism, it is conceivable that the low reacti-
vity of P(OPh) toward 2b is due to the larger size of the
3
phosphite compared with PF .
3
The results of the single-crystal X-ray di†raction studies of
6a and 6b are shown in Fig. 1 and 2. In both compounds, the
Fig. 2 An ORTEP plot of compound 6b. The ellipsoids are drawn at
the 50% probability level.
Scheme 4
New J. Chem., 2001, 25, 396È399
397

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Table 1 Selected bond lenghts (A) and angles (¡) for complexes 6a
and 6b
ferently toward CO and PX (X \ F, OPh). While carbon
3
monoxide reacts with 2a to give the substitution product 4
and diphenylketene, treatment of 2a with PX leads to a
6a
6b
3
migratory insertion of the carbene ligand into one of the ring
CÈH bonds to produce 6a,b. This process has, to the best of
our knowledge and apart from our own work,4,7,9 no prece-
dence.10 The closest analogy to the formation of C H CHPh
RhÈP1
RhÈP2
RhÈC1
RhÈC2
RhÈC3
RhÈC4
RhÈC5
C1ÈC2
C2ÈC3
C3ÈC4
C4ÈC5
C5ÈC1
C1ÈC6
2.275(3)
2.082(4)
2.307(5)
2.220(5)
2.294(6)
2.258(3)
2.304(6)
1.434(6)
1.410(6)
1.385(7)
1.438(6)
1.398(5)
1.518(5)
2.263(2)
2.120(2)
2.356(7)
2.206(8)
2.298(8)
2.304(7)
2.330(7)
1.45(1)
1.43(1)
1.41(1)
1.43(1)
1.40(1)
1.51(1)
5
4
2
from C H and CPh that we are aware of goes back to the
5
5
2
work of Guth and Kirmse, which illustrates that arylcarbenes,
generated from the corresponding diazo compounds, undergo
an intramolecular insertion into the ortho CÈH bond of a con-
nected phenyl ring.11
Experimental
All experiments were carried out under an atmosphere of
P1ÈRhÈP2
C2ÈC1ÈC5
C5ÈC1ÈC6
C2ÈC1ÈC6
97.0(1)
98.54(8)
105.3(7)
129.3(7)
125.3(7)
argon by Schlenk techniques. The starting materials 1a,b,1b
106.2(3)
128.6(4)
125.1(3)
2a,b1c and PF 12 were prepared as described in the literature.
3
NMR spectra were recorded at room temperature on Bruker
AC 200 and Bruker AMX 400 instruments. Melting points
were measured by DTA. Abbreviations used: s, singlet; d,
doublet; t, triplet; sept, septet; m, multiplet; vt, virtual triplet;
br, broadened signal; coupling constants N and J in Hz.
Syntheses
work of Basolo and his group,6 that ligand displacement
reactions of cyclopentadienylrhodium(I) complexes [(g5-
C H )Rh(L) ] with Lewis bases L@ follow second-order
trans-[RhCl(PF )(PPri ) ], 5a. A slow stream of PF was
3
3 2
3
5
5
2
passed through a solution of 1a (95 mg, 0.15 mmol) in benzene
(20 cm3) for 20 min at room temperature. A change of color
from green to yellow occurred. After the reaction mixture had
been stirred for 20 min, the solvent was removed in vacuo and
the oily residue was recrystallized from acetone (5 cm3) at
[60 ¡C. A yellow solid was formed, which was separated from
the mother liquor and dried in vacuo: yield 56 mg (68%); mp
112 ¡C (decomp.) Anal. found: C, 39.13; H, 8.21%.
kinetics, we assume that from 2a and PX a labile 1 : 1 adduct
3
A is initially formed (Scheme 5). This 20-electron intermediate
could a†ord, via ring slippage, a second intermediate B (with
an 18-electron conÐguration at the metal) in which the cyclo-
pentadienyl unit would be g3- coordinated. Alternatively, the
carbene ligand of intermediate A could attack the Ðve-
membered ring to give the diene alkyl compound C, which by
subsequent hydrogen transfer to the CPh carbon and break-
2
C
H
ClF P Rh requires: C, 39.54; H, 7.74%. NMR
ing of the RhÈC r-bond a†ords 6a,b. The Ðnal insertion
18 42
3 3
(C D ): d (400 MHz) 2.69 (6 H, m, PCHCH ), 1.25 [36 H,
product could also be generated from B via migration of the
carbene to the uncoordinated CÈC double bond or from B via
C by insertion of the carbene into an g3-allylic RhÈC bond. A
similar rearrangement probably does occur during formation
of the substituted indenylrhodium(I) complexes [Mg5-C H
6
6
H
3
dvt, N 13.9, J(H,H) 6.6, PCHCH ]; d (100.6 MHz) 24.0 (vt, N
3
C
10.5, PCHCH ), 19.0 (s, PCHCH ); d (162.0 MHz) 111.9
3
3
P
[ddq, J(F,P) 1267.9, J(Rh,P) 390.4, J(P,P) 52.2, PF ], 46.8
3
[ddq, J(Rh,P) 111.9, J(P,P) 52.2, J(F,P) 6.4, PPri ].
3
9
6
(CHPh )NRh(CO)(L)] (L \ SbPri , PPri , PPh , PPriPh ,
2
3
3
3
2
trans-[RhCl(PF )(SbPri ) ], 5b. This compound was pre-
PPri Ph), which were prepared from [(g5-C H )Rh(2CPh )
3
3 2
2
9
7
2
pared as described for 5a from 1b (100 mg, 0.12 mmol) and
(L)] and CO.7 It should be mentioned that the starting
material 2a reacts not only with PF and P(OPh) but also
PF in benzene (20 cm3). Yellow solid: yield 59 mg (68%); mp
3
3
3
3
88 ¡C (decomp.) Anal. found: C, 29.53; H, 5.79%.
with various Bronsted acids HX (X \ Cl, Br, I, CF CO ) by
2
C
H
ClF PRhSb requires: C, 29.68; H, 5.81%. NMR
formal oxidative addition to yield the ring-substituted
hydridorhodium(III) complexes
18 42
3
H
2
(C D ):
d
(200 MHz) 2.37 [6 H, sept, J(H,H) 7.3,
[Mg5-C H (CHPh )N-
6
6
5
4
2
SbCHCH ], 1.38 [36 H, d, J(H,H) 7.3, SbCHCH ]; d (81.0
MHz) 120.2 [dq, J(F,P) 1256.5, J(Rh,P) 356.2].
RhHX(PPri )].4,8 In this case, a labelling experiment using
3
3
P
3
[(g5-C D )Rh(2CPh )(PPri )] and HCl as the substrates sug-
5
5
2
3
gests that the migratory insertion of the carbene occurs via a
g4-cyclopentadienerhodium(I) species as an intermediate.
In conclusion, the present investigations have shown that
the half-sandwich-type compound 2a behaves completely dif-
[{g5-C H (CHPh )}Rh(PF )(PPri )], 6a. A slow stream of
5
4
2
3
3
PF was passed through a solution of 2a (100 mg, 0.20 mmol)
3
in benzene (20 cm3) at room temperature for 20 min. A change
of color from blue to red occurred. After the solution was
stirred for 20 min at room temperature, the solvent was
removed and the oily residue was dissolved in pentane (2 cm3).
The solution was chromatographed on Al O . With pentane,
2
3
an orangeÈred fraction was eluted, which was evaporated to
dryness in vacuo. Recrystallization of the residue from acetone
(1 cm3) at [78 ¡C led to the precipitation of orange crystals,
which were separated from the mother liquor, washed with a
small amount of pentane at [30 ¡C and dried: yield 48 mg
(41%); mp 42 ¡C (decomp.) Anal. found: C, 55.49; H, 6.35%.
C
H
F P Rh requires: C, 55.68; H, 6.23%. NMR (C D ):
27 36 3 2
(200 MHz) 7.26 (4 H, m, ortho-H of C H ), 7.02 (8 H, m,
6
6
d
H
6 5
meta- and para-H of C H ), 5.09 [4 H, m, C H ], 4.79 (1 H,
6
5
5 4
m, CHPh ), 1.20 [3 H, dsept, J(P,H) 13.3, J(H,H) 7.1,
PCHCH ], 0.82 [18 H, dd, J(P,H) 13.7, J(H,H) 7.1,
PCHCH ]; d (81.0 MHz) 119.4 [ddq, J(F,P) 849.3, J(Rh,P)
2
3
3
Scheme 5
P
398
New J. Chem., 2001, 25, 396È399

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446.3, J(P,P) 77.6, PF ], 79.0 [dd, J(Rh,P) 221.0, J(P,P) 77.6,
c \ 17.401(3) A, a \ 85.68(1), b \ 106.85(1), c \ 88.03(2)¡,
3
PPri ].
U \ 1963.5(7) A
Ž
3, d
\ 1.361 g cm~3; max. 2H \ 48¡ [Mo-
3
calcd
Ka, j \ 0.710 73 A, graphite monochromator, u/H scan, Zr
Ðlter with factor 16.4, T \ 173(2) K]; 6553 reÑections
scanned, 6159 unique [R(int) \ 0.0467], 4323 observed
[I [ 2p(I)], Lorentz polarization and empirical absorption
corrections (t scans, min. transmission 64.12%); direct
methods (SHELXS-86),13 469 parameters, reÑect/parameter
ratio 13.13; R \ 0.0730, wR \ 0.1943; residual electron
[{g5-C H (CHPh )}Rh{P(OPh) }(PPri )], 6b. A solution
5
4
2
3
3
of 2a (150 mg, 0.30 mmol) in toluene (10 cm3) was treated with
P(OPh) (316 ll, 1.20 mmol) and stirred for 3 days at room
temperature. A change of color from deep blue to orange
3
occurred. The solvent was removed in vacuo and the oily
residue was washed three times with 5 cm3 portions of
pentane. The remaining solid was recrystallized from etherÈ
pentane (1 : 10, 3 cm3) at 5 ¡C. Orange crystals were formed,
which were separated from the mother liquor and dried; yield
128 mg (53%); mp 89 ¡C (decomp.) Anal. found: C, 67.59; H,
1
2
density 1.074/ [ 1.273 e AŽ ~3.
CCDC reference number 440/244. See http://www.rsc.org/
suppdata/nj/b0/b008601k/ for crystallographic Ðles in .cif
format
6.14%. C
H
O P Rh requires: C, 67.16; H, 6.39%. NMR
45 51 3 2
(C D ): d (400 MHz) 7.46È6.78 (15 H, m, C H and OC H ),
6
6
H
6
5
6 5
4.69, 4.47 (4 H, both s, C H ), 4.24 (1 H, s, CHPh ), 2.10 [3 H,
Acknowledgements
5
4
2
dsept, J(P,H) 14.4, J(H,H) 7.3, PCHCH ], 1.11 [18 H, dd, J(P,
H) 13.4, J(H,H) 7.3, PCHCH ]; d (100.6 MHz) 153.2 [d, J(P,
C) 7.1, ipso-C of OC H ], 145.9 (s, ipso-C of C H ), 129.8,
128.2, 125.8, 124.5, 123.8, 122.3 (all s, OC H and C H ), 86.5,
84.5 (both s, C H ), 49.6 (s, CHPh ), 28.1 [d, J(P,C) 20.3,
3
We gratefully acknowledge Ðnancial support from the Deut-
sche Forschungsgemeinschaft (SFB 347), the Fonds der Che-
mischen Industrie and BASF AG. We also thank Mrs R.
Schedl and Mr C. P. Kneis (DTA and elemental analyses) and
Mrs M.-L. Schafer and Dr W. Buchner (NMR spectra).
3
C
6
5
6 5
6 5
6
5
5
4
2
PCHCH ], 20.0 (s, PCHCH ); d (162 MHz) 132.4 [dd, J(Rh,
3
3
3
P
P) 388.3, J(P,P) 64.4, P(OPh) ], 75.3 [dd, J(Rh,P) 191.6, J(P,P)
64.4, PPri ].
3
References
[(g5-C H )Rh(2CPh )(PF )], 7. A slow stream of PF was
5
5
2
3
3
1
(a) P. Schwab, N. Mahr, J. Wolf and H. Werner, Angew. Chem.,
1993, 105, 1498; P. Schwab, N. Mahr, J. Wolf and H. Werner,
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Schwab, E. Bleuel, N. Mahr, P. Steinert and J. Wolf, Chem. Eur.
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B. Windmuller and J. Wolf, Chem. Eur. J., 2000, 6, 4461.
(a) T. Kruck, Angew. Chem., 1967, 79, 27; T. Kruck, Angew.
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(a) G. M. Kosolapo† and L. Maier, Organophosphorus Com-
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(a) T. Kruck, N. Derner and W. Lang, Z. Naturforsch., B, 1966,
21, 1020; (b) D. A. Clement, J. F. Nixon and M. D. Sexton, J.
Chem. Soc., Chem. Commun., 1969, 1509; (c) M. A. Bennett and
D. J. Patmore, J. Chem. Soc., Chem. Commun., 1969, 1510.
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passed through a solution of 2b (59 mg, 0.10 mmol) in benzene
(20 cm3) at room temperature for 20 min. A change of color
from blue to red occurred. After the solution was stirred for 20
min at room temperature, it was worked up as described for
6a. Recrystallization from acetone (1 cm3) at [78 ¡C led to
the formation of deep red crystals. Yield 30 mg (72%); mp
46 ¡C (decomp.) Anal. found: C, 51.02; H, 3.64%.
2
3
C
H
F PRh requires: C, 51.21; H, 3.58%. NMR (C D ):
18 15 3
(200 MHz) 7.30 (4 H, m, ortho-H of C H ), 7.02 (6 H, m,
6
6
d
H
6 5
meta- and para-H of C H ), 4.88 [5 H, d, J(Rh,H) 1.8, C H ];
6
5
5 5
d (81.0 MHz) 117.1 [dq, J(F,P) 1334.9, J(Rh,P) 488.2].
P
4
5
X-Ray crystallography
Single crystals of 6a were grown from pentane (8 ¡C); crystal
size 0.55 ] 0.30 ] 0.25 mm; monoclinic, space group C2/c (no.
15); a \ 34.48(9), b \ 8.96(2), c \ 17.67(3) A, b \ 96.85(2)¡,
U \ 5427(3) A
Ž
3, d \ 1.426 g cm~3; max. 2H \ 48¡ [Mo-
6
7
8
9
calc
Ka j \ 0.71073 A, graphite monochromator, u/H scan, Zr
Ðlter with factor 16.4, T \ 293(2) K]; 4548 reÑections
scanned, 4162 unique [R(int) \ 0.0136], 3736 observed
[I [ 2p(I)], Lorentz polarization and empirical absorption
corrections (t scans, min. transmission 80.0%); direct methods
(SHELXS-86),13 408 parameters, reÑect/parameter ratio 10.2;
R \ 0.0364, wR \ 0.0972; residual electron density 1.058/
E. Bleuel, P. Schwab, M. Laubender and H. Werner, J. Chem.
Soc., Dalton T rans., 2001, 266.
E. Bleuel and H. Werner, C. R. Acad. Sci. Ser. IIc: Chim., 1999,
341.
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1
2
[ 0.425 e AŽ ~3. Ref. code PULRIX, Cambridge Structural
Database System, 2000. Single crystals of 6b were grown from
acetone ([20 ¡C); crystal size 0.12 ] 0.10 ] 0.08 mm; triclinic,
space group P1 (no. 2); a \ 10.170(3), b \ 11.177(2),
New J. Chem., 2001, 25, 396È399
399