Rhodium(I) and iridium(I) complexes with β-keto phosphine or phosphino enolate ligands. Catalytic transfer dehydrogenation of cyclooctane

Article abstract of DOI:10.1021/om960814h

The synthesis of new metal complexes containing the keto phosphine ligands R¹₂PCH₂C-(O)R² (R¹ = Ph, R² = Ph, Me, t-Bu, p-C₆H₄F; R¹ = i-Pr, R² = Ph) is described. Reaction of 1 equiv of (diphenylphosphino)acetophenone (Ph₂PCH₂C(O)Ph; L) with [Rh(μ-Cl)(C₂H₄)₂]₂ gave the dimeric complex [Rh(μ-Cl)(C₂H₄)(P～O)]₂ (1) (P～O = η¹(P) coordinated). With 2 equiv of L, [RhCl(P^∩O)(P～O)] (2) was obtained (P^∩O = η²(P,O)-chelated ligand). Reaction of 2 with TlPF₆ afforded the cationic compound [Rh(P^∩O)₂][PF₆] (3). The X-ray crystal structure determination of 3·H₂O shows a distorted-square-planar geometry with the two phosphorus atoms (and oxygen atoms) in cis positions. Treatment of [RhCl(CO)(PPh₃)₂] with 1 equiv of L gave [RhCl(CO)(P～O)(PPh₃)] (5). In the presence of TlPF₆ the cationic complex [Rh(CO)(P^∩O)(PPh₃)][PF₆] (6) was obtained. The X-ray crystal structure determination of 6 shows a slightly distorted square planar geometry with the two phosphorus atoms in trans positions. The reaction of 5 or 6 with 1 equiv of NaOMe produced the phosphino enolate complex [Rh{Ph₂PCH-. .C(-. .O)Ph}(CO)(PPh₃)] (7). ³¹P{¹H} NMR shows 7 to dissociate PPh₃ in solution, giving a 14-electron species, which proved to be particularly useful for transfer-dehydrogenation reactions. When [Rh(μ-Cl)(COE)₂]₂ (COE = cyclooctene) was reacted with 4 equiv of L under carbon monoxide, [RhCl(CO)(P～O)₂] (8) was isolated. Reaction of 8 with TlPF₆ gave [Rh(CO)(P^∩O)(P～O)][PF₆] (9), and in the presence of NaOMe the phosphino enolate complex [Rh{Ph₂PCH-. .C(-. .O)Ph}(CO)(P～O)] (10) formed. In an analogous manner, [Rh{Ph₂PCH-. .C(-. .O)Ph}(CO)L¹] (L¹ = P(o-tolyl)₃ (11), PPh₂(p-tolyl) (12), P(p-C₆H₄F)₃ (13)) were also prepared. In a similar way, L and [RhCl(PPh₃)₃] gave [RhCl(PPh₃)₂(P～O)] (14), which was reacted with TlPF₆, affording [Rh(P^∩O)(PPh₃)₂]-[PF₆] (15), analogous to 6. Reacting 14 or 15 with 1 equiv of NaOMe gave the phosphino enolate complex [Rh{Ph₂PCH-. .C(-. .O)Ph}(PPh₃)₂] (16), analogous to 7. It reacts with PhNCO or Ph₂PCl with formation of a C_enolate-C or O_enolate-P bond, respectively. [Rh{Ph₂PCH-. .C(-. .O)Ph}(p-C₆H₄F)}(PPh₃)₂] (17) has also been reported. By reacting PPh₃, L, and TlPF₆ with [Rh(μ-Cl)(NBD)]₂ (NBD = norbornadiene) the pentacoordinated complex [Rh(NBD)(P^∩O)(PPh₃)][PF₆] (20) was obtained. The X-ray crystal structure determination of 20 showed that the coordination geometry around the Rh atom could be described as intermediate between square pyramidal (with the O atom occupying the apical position) and trigonal bipyramidal (with the P atom and the midpoint of one olefinic bond occupying the apical positions). When the diolefin, L, and NaOMe were added in sequence to a suspension of [Rh(μ-Cl)(COE)₂]₂, [Rh{Ph₂PCH-. .C(-. .6)Ph}(NBD)] (21) and [Rh{Ph₂PCH-. .C(-. .O)Ph}(COD)] (22) were obtained. The related iridium complex [Ir{Ph₂PCH-. .C(-. .O)Ph}(COD)] (26) was obtained in a similar way and reacted with H₂ to give [Ir{Ph₂PCH-. .C(-. .O)Ph}H₂(COD)] (27). The cationic complex 20 and the phosphino enolate complexes 4, 7, and 16 catalyze the hydrogenation and the isomerization of 1-hexene. The rhodium phosphino enolate carbonyl complexes 7 and 13 are very active catalysts for transfer dehydrogenation of cyclooctane with norbornene under hydrogen pressure (7 MPa) at 60-90°C. In the presence of 1 equiv of a triarylphosphine, rhodium phosphino enolate complexes not containing carbon monoxide, such as 22, proved to be active catalysts for transfer dehydrogenation at 70°C, under atmospheric pressure of hydrogen, with turnover numbers up to 240 per mol of rhodium/h.

Full text of DOI:10.1021/om960814h

Organometallics 1996, 15, 5551-5567
5551
Rh od iu m (I) a n d Ir id iu m (I) Com p lexes w ith â-Keto
P h osp h in e or P h osp h in o En ola te Liga n d s. Ca ta lytic
Tr a n sfer Deh yd r ogen a tion of Cycloocta n e†
Pierre Braunstein,*,‡ Yves Chauvin,*,§ J ens Na¨hring,‡,§ Andre´ DeCian,|
J ean Fischer,| Antonio Tiripicchio, and Franco Ugozzoli
Laboratoire de Chimie de Coordination, Associe´ au CNRS (URA 416), Universite´ Louis
Pasteur, 4 rue Blaise Pascal, F-67070 Strasbourg Ce´dex, France, Institut Franc¸ais du Pe´trole,
B.P. 311, F-92506 Rueil-Malmaison Ce´dex, France, Laboratoire de Cristallochimie et de
Chimie Structurale, Associe´ au CNRS (URA 424), Universite´ Louis Pasteur, 4 rue Blaise
Pascal, F-67070 Strasbourg Ce´dex, France, and Dipartimento di Chimica Generale ed
Inorganica, Chimica Analitica, Chimica Fisica, Universita` di Parma, Centro di Studio per la
Strutturistica Diffrattometrica del CNR, Viale delle Scienze 78, I-43100 Parma, Italy
Received J une 21, 1996X
The synthesis of new metal complexes containing the keto phosphine ligands R1 PCH2C-
2
(O)R2 (R1 ) Ph, R2 ) Ph, Me, t-Bu, p-C6H4F; R1 ) i-Pr, R2 ) Ph) is described. Reaction of
1 equiv of (diphenylphosphino)acetophenone (Ph2PCH2C(O)Ph; L) with [Rh(µ-Cl)(C2H4)2]2
gave the dimeric complex [Rh(µ-Cl)(C2H4)(P∼O)]2 (1) (P∼O ) η1(P) coordinated). With 2
equiv of L, [RhCl(PkO)(P∼O)] (2) was obtained (PkO = η2(P,O)-chelated ligand). Reaction
of 2 with TlPF6 afforded the cationic compound [Rh(PkO)2][PF6] (3). The X-ray crystal
structure determination of 3‚H2O shows a distorted-square-planar geometry with the two
phosphorus atoms (and oxygen atoms) in cis positions. Treatment of [RhCl(CO)(PPh3)2] with
1 equiv of L gave [RhCl(CO)(P∼O)(PPh3)] (5). In the presence of TlPF6 the cationic complex
[Rh(CO)(PkO)(PPh3)][PF6] (6) was obtained. The X-ray crystal structure determination of
6 shows a slightly distorted square planar geometry with the two phosphorus atoms in trans
positions. The reaction of 5 or 6 with 1 equiv of NaOMe produced the phosphino enolate
complex [Rh{Ph2PCH‚ ‚C(‚ ‚O)Ph}(CO)(PPh3)] (7). 31P{1H} NMR shows 7 to dissociate
PPh3 in solution, giving a 14-electron species, which proved to be particularly useful for
transfer-dehydrogenation reactions. When [Rh(µ-Cl)(COE)2]2 (COE ) cyclooctene) was
reacted with 4 equiv of L under carbon monoxide, [RhCl(CO)(P∼O)2] (8) was isolated.
Reaction of 8 with TlPF6 gave [Rh(CO)(PkO)(P∼O)][PF6] (9), and in the presence of NaOMe
the phosphino enolate complex [Rh{Ph2PCH‚ ‚C(‚ ‚O)Ph}(CO)(P∼O)] (10) formed. In an
analogous manner, [Rh{Ph2PCH‚ ‚C(‚ ‚O)Ph}(CO)L1] (L1 ) P(o-tolyl)3 (11), PPh2(p-tolyl)
(12), P(p-C6H4F)3 (13)) were also prepared. In a similar way, L and [RhCl(PPh3)3] gave
[RhCl(PPh3)2(P∼O)] (14), which was reacted with TlPF6, affording [Rh(PkO)(PPh3)2]-
[PF6] (15), analogous to 6. Reacting 14 or 15 with 1 equiv of NaOMe gave the phos-
phino enolate complex [Rh{Ph2PCH‚ ‚C(‚ ‚O)Ph}(PPh3)2] (16), analogous to 7. It reacts
with PhNCO or Ph2PCl with formation of a Cenolate-C or Oenolate-P bond, respectively.
[Rh{Ph2PCH‚ ‚C(‚ ‚O)Ph}(p-C6H4F)}(PPh3)2] (17) has also been reported. By reacting
PPh3, L, and TlPF6 with [Rh(µ-Cl)(NBD)]2 (NBD ) norbornadiene) the pentacoor-
dinated complex [Rh(NBD)(PkO)(PPh3)][PF6] (20) was obtained. The X-ray crystal struc-
ture determination of 20 showed that the coordination geometry around the Rh atom could
be described as intermediate between square pyramidal (with the O atom occupying
the apical position) and trigonal bipyramidal (with the P atom and the midpoint of one ole-
finic bond occupying the apical positions). When the diolefin, L, and NaOMe were added
in sequence to a suspension of [Rh(µ-Cl)(COE)2]2, [Rh{Ph2PCH‚ ‚C(‚ ‚O)Ph}(NBD)] (21)
and [Rh{Ph2PCH‚ ‚C(‚ ‚O)Ph}(COD)] (22) were obtained. The related iridium complex
[Ir{Ph2PCH‚ ‚C(‚ ‚O)Ph}(COD)] (26) was obtained in a similar way and reacted with H2 to
give [Ir{Ph2PCH‚ ‚C(‚ ‚O)Ph}H2(COD)] (27). The cationic complex 20 and the phosphino
enolate complexes 4, 7, and 16 catalyze the hydrogenation and the isomerization of 1-hexene.
The rhodium phosphino enolate carbonyl complexes 7 and 13 are very active catalysts for
transfer dehydrogenation of cyclooctane with norbornene under hydrogen pressure (7 MPa)
at 60-90 °C. In the presence of 1 equiv of a triarylphosphine, rhodium phosphino enolate
complexes not containing carbon monoxide, such as 22, proved to be active catalysts for
transfer dehydrogenation at 70 °C, under atmospheric pressure of hydrogen, with turnover
numbers up to 240 per mol of rhodium/h.
S0276-7333(96)00814-X CCC: $12.00 © 1996 American Chemical Society

5552 Organometallics, Vol. 15, No. 26, 1996
Braunstein et al.
In tr od u ction
literature.9 The reaction mechanism probably involves
square-planar/octahedral interconversions of the metal
coordination sphere. This led us to investigate the
coordination modes of â-keto phosphines and related
phosphino enolates to rhodium(I) in relation to the
catalytic activity of the corresponding complexes in
hydrogenation of olefins and transfer dehydrogenation
of alkanes.
Homogeneous catalysis by transition-metal complexes
plays an important role in industrial chemistry.2 Neu-
tral and cationic complexes of rhodium(I) are versatile
catalysts for hydrogenation, isomerization, dimerization,
hydroformylation, and carbonylation reactions.3 Most
of these complexes are stabilized by tertiary phosphines.
In the catalytic steps, solvent molecules play a crucial
role and ketones, alcohols, or ethers, weakly bonded to
the coordinatively unsaturated rhodium center, help
stabilize reactive intermediates.4
In complexes containing phosphorus and oxygen (or
nitrogen) heterobidentate ligands, the “hard” donor
moiety can be considered as an intramolecular solvent
molecule, which may dissociate from the metal revers-
ibly. This allows the use of a noncoordinating solvent
in catalytic reactions. The hemilability of ether, ester,
and keto phosphine ligands is well-documented.5
Resu lts a n d Discu ssion
1. P r ep a r a tion of â-Keto P h osp h in es. In order
to prepare â-keto phosphines of the type R1 PCH2C(O)-
2
R2 Lutsenko et al. reacted chlorophosphines with
mercury or stannyl ketones,10 while Shaw et al. reacted
di-tert-butylphosphine with bromomethyl ketones, fol-
lowed by treatment with a base.11 The latter method
fails for R2 ) Me.12 Other methods involve the reduc-
tion of a functional phosphine oxide with a silane under
reflux or the simultaneous reduction and complexation
of a functional phosphine sulfide on nickel(II) followed
by decomplexation.13 Whereas the reaction of chloro-
methyl ketones with sodium diphenylphosphide did not
yield â-keto phosphines,14 and that of lithium diphe-
nylphosphide with (1R)-endo-(+)-3-bromocamphor in
THF at -78 °C led only to tetraphenyldiphosphine,15
we have found that the reaction of LiPPh2 and chloro-
acetone under similar conditions yielded a mixture of
diphenylphosphine (60%) and the â-keto phosphine Ph2-
PCH2C(O)Me (38%); the latter was isolated by distilla-
tion in 25% yield.
It is also known that phosphino enolate ligands of the
type [R1 PCH‚ ‚C(‚ ‚O)R2]- can be readily obtained
2
from the corresponding â-keto phosphines. They behave
as three-electron donors (2(P) + 1(O)) and stabilize the
square-planar structure of several transition-metal
complexes.6
(Diphenylphosphino)acetophenone, Ph2PCH2C(O)Ph
(L), is readily synthesized by the reaction of the lithium
enolate of acetophenone with diphenylchlorophosphine
at -78 °C in THF.6 This method was easily extended
to other chlorophosphines and ketones (see Experimen-
tal Section). Under these reaction conditions, no O-P
coupling occurred, probably because in THF the lithium
cation is closely associated with the oxygen atom of the
enolate, which directs the reactivity of the ambident
anion to the carbon atom.16 Our method has since been
successfully applied to the synthesis of various diphe-
nylphosphino ketones.17
These important features have led to the development
of very active and selective catalysts for various reac-
tions. Thus, a palladium(II) complex containing 2-(diphe-
nylphosphino)pyridine as a hemilabile heterobidentate
ligand catalyzes the carbonylation of propyne to methyl
methacrylate with very high efficiency.7 Three-electron-
donor enolate-type chelates confer to their nickel(II)
complexes unique catalytic properties for the formation
of R-olefins from ethylene.8
(8) (a) Keim, W. Chem.-Ing.-Techn. 1984, 56, 850. (b) Klabunde, U.;
Tulip, T. H.; Roe, D. C.; Ittel, S. D. J . Organomet. Chem. 1987, 334,
141. (c) Keim, W. Angew. Chem., Int. Ed. Engl. 1990, 29, 235. (d)
Mercier, S. Ph.D. Thesis, Universite´ Paris VI, 1993. (d) Keim, W. New
J . Chem. 1994, 18, 93. (e) Braunstein, P.; Chauvin, Y.; Mercier, S.;
Saussine, L.; DeCian, A.; Fischer, J . J . Chem. Soc., Chem. Commun.
1994, 2203.
(9) (a) Maguire, J . A.; Goldman, A. S. J . Am. Chem. Soc. 1991, 113,
6706. (b) Maguire, J . A.; Petrillo, A.; Goldman, A. S. J . Am. Chem.
Soc. 1992, 114, 9492. (c) Shih, K.-C.; Goldman, A. S. Organometallics
1993, 12, 3390. (d) Miller, J . A.; Knox, L. K. J . Chem. Soc., Chem.
Commun. 1994, 1449.
(10) (a) Novikowa, Z. S.; Proskurnina, M. V.; Petrovskaya, L. I.;
Bogdanova, I. V.; Galitskova, N. P.; Lutsenko, I. F. J . Gen. Chem.
USSR (Engl. Transl.) 1967, 37, 1972. (b) Novikowa, Z. S.; Galitskova,
N. P.; Kozlov, V. A.; Lutsenko, I. F. J . Gen. Chem. USSR (Engl. Transl.)
1971, 41, 838.
(11) Moulton, C. J .; Shaw, B. L. J . Chem. Soc., Dalton Trans. 1980,
299.
Recently the catalytic transfer dehydrogenation of
alkanes using rhodium(I) complexes was reported in the
† Dedicated to Professor G.E. Herberich, on the occasion of his 60th
birthday, with our sincere congratulations and best wishes. Part of
the Doctoral Thesis of J .N. Complexes with Functional Phosphines.
For previous parts in this series, see ref 1.
‡ Laboratoire de Chimie de Coordination, Universite´ Louis Pasteur.
§ Institut Franc¸ais du Pe´trole.
| Laboratoire de Cristallochimie et de Chimie Structurale, Universite´
Louis Pasteur.
Universita` di Parma.
X Abstract published in Advance ACS Abstracts, November 1, 1996.
(1) (a) Braunstein, P.; Chauvin, Y.; Na¨hring, J .; DeCian, A.; Fischer,
J . J . Chem. Soc., Dalton Trans. 1995, 863. (b) Braunstein, P.; Chauvin,
Y.; Na¨hring, J .; Dusausoy, Y.; Tiripicchio, A.; Ugozzoli, F. J . Chem.
Soc., Dalton Trans. 1995, 851.
(12) (a) Brunner, H.; Dylla, M. E.; Hecht, G. A. M.; Pieronczyk, W.
Z. Naturforsch. 1982, 37B, 404. (b) Dylla, M. E. Zulassungsarbeit,
Universita¨t Regensburg, 1980.
(2) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis, 2nd ed.;
Wiley: New York, 1992.
(3) Spencer, A. In Comprehensive Coordination Chemistry; Wilkin-
son, G., Gillard, R. D., McCleverty, J ., Eds.; Pergamon Press: Oxford,
England, 1987; Vol. 6, p. 229.
(4) Halpern, J . Inorg. Chim. Acta 1981, 50, 11.
(5) Bader, A.; Lindner, E. Coord. Chem. Rev. 1991, 108, 27.
(6) Bouaoud, S.-E.; Braunstein, P.; Grandjean, D.; Matt, D.; Nobel,
D. Inorg. Chem. 1986, 25, 3765.
(13) Braunstein, P.; Matt, D.; Mathey, F.; Thavard, D. J . Chem. Res.,
Miniprint 1978, 3041; J . Chem. Res., Synop. 1978, 232.
(14) Eibach, F. Diplomarbeit, Universita¨t Marburg, 1976.
(15) Knight, D. A.; Cole-Hamilton, D. J .; Cupertino, D. C. J . Chem.
Soc., Dalton Trans. 1990, 3051.
(16) Streitweiser, A.; Heathcock, C. H. In Einfu¨hrung in die orga-
nische Chemie; Macmillan: New York, 1980; p 483.
(17) Demerseman, B.; Guilbert, B.; Renouard, C.; Gonzalez, M.;
Dixneuf, P. H. Organometallics 1993, 12, 3906.
(7) Drent, E.; Arnoldy, P.; Budzelaar, P. H. M. J . Organomet. Chem.
1993, 455, 247.

Rh(I) and Ir(I) Complexes with Phosphines
Organometallics, Vol. 15, No. 26, 1996 5553
Sch em e 1
F igu r e 1. ORTEP plot of the cationic complex in 3‚H2O,
showing the numbering scheme used. Ellipsoids are scaled
to enclose 50% of the electron density. Hydrogen atoms are
omitted.
2. Rh od iu m (I) Com p lexes w ith P h 2P CH2C(O)-
P h . Rea ction w ith [Rh (µ-Cl)(C2H4)2]2. Addition of
1 equiv of keto phosphine to a suspension of [Rh(µ-Cl)-
(C2H4)2]2 in pentane afforded the dimeric complex [Rh-
(µ-Cl)(C2H4)(P∼O)]2 (1) (Scheme 1). The IR spectrum
shows absorption bands at 272 and 258 cm-1 for the
bridging chlorides and at 1523 cm-1 for ethylene. A
band at 1665 cm-1 is attributed to the uncoordinated
keto function. The 31P{1H} NMR spectrum shows a
precursor,20 although this has recently been achieved
from palladium alkyl complexes.21 When 1 was reacted
with 1 equiv of keto phosphine, ethylene was evolved
and the bridge was split, affording the mononuclear
compound [RhCl(P∩O)(P∼O)] (2) (Scheme 1). It is ther-
mally stable but decomposes in CH2Cl2 over weeks. IR
spectroscopy indicates free and coordinated keto groups,
and 31P{1H} NMR spectroscopy shows two mutually cis
phosphines. Complex 2 is not fluxional at room tem-
perature. Complexes of this type with ether-phosphine
ligands have been recently reported by Lindner et al.
and Werner et al.22 Their reactivity was found to
depend on the substituents at phosphorus: with R )
Ph or Me, they were not fluxional in solution and were
inert to hydrogen, whereas with R ) cyclohexyl, flux-
ional behavior was observed and under a hydrogen
atmosphere the unstable dihydridorhodium(III) complex
[RhCl(H)2{Cy2P(CH2)2OMe}2] was formed.
1
doublet with a J (RhP) value of 189 Hz, in keeping with
a phosphine coordinated to a rhodium(I) center in a
trans position with respect to a bridging chloride. A
1
variable-temperature H NMR study revealed rotation
of ethylene around the bond axis. Even at 180 K
rotation was not completely frozen, and its activation
energy can be roughly estimated from the Eyring
equation as inferior to 55 kJ mol-1 18
This value is in
.
the range found for [Rh(Cp)L2(C2H4)] (L2 ) C2H4, C2F4,
SO2) complexes, with 62.6 ( 0.8, 57 ( 3, and 51 ( 3
kJ mol-1, respectively.19
Reaction of 2 with an excess of TlPF6 afforded air-
stable red crystals of the square-planar cationic complex
cis-[Rh(PkO)2][PF6] (3). The structure of the cation,
determined by X-ray diffraction (Figure 1), is in agree-
ment with the solution structure derived from other
spectroscopic data: the two phosphorus atoms are in
cis positions (for values of the chemical shift and Rh-P
coupling constant, see the Experimental Section). The
thermal stability of this cationic bis(chelate) complex
is in marked contrast to that of the corresponding
Complex 1 is stable toward ethylene elimination or
splitting of the chloride bridges by the oxygen donor
function of the potentially chelating keto phosphine.
This is consistent with a keto oxygen being a weaker
ligand than ethylene or a chloride in neutral rhodium-
(I) complexes, as no complex such as [Rh(µ-Cl)(PkO)]2
or [RhCl(olefin)(PkO)] was formed.
Addition of 1 equiv of PPh3 to a toluene or THF solu-
tion of 1 afforded a mixture of complexes, as shown by
31P{1H} NMR spectroscopy, but all PPh3 was coordi-
nated to rhodium. A strong band at 1670 cm-1 was
characteristic of an uncoordinated keto group. These
observations indicate that olefin substitution and bridge
cleavage by PPh3 in 1 need about the same energy and/
or that the product redistributes its ligands. Addition
of a second equivalent of PPh3 afforded the unstable
[RhCl(PPh3)2(P∼O)] (14) (vide infra). For comparison,
no mixed-phosphine complex of the type [PdCl2(PR3)-
(P∼O)] has been isolated from a dinuclear palladium
ether-phosphine complexes with R2PCH2CHOCH2-
CH2CH2 (R ) Ph, Cy, Cy2PCH2CH2OCH3), which are
unstable above -30 °C even in the solid state.5,23
(20) Braunstein, P.; Matt, D.; Nobel, D.; Balegroune, F.; Bouaoud,
S.-E.; Grandjean, D.; Fischer, J . J . Chem. Soc., Dalton Trans. 1988,
27, 353.
(21) Andrieu, J .; Braunstein, P.; Naud, F. J . Chem. Soc., Dalton
Trans. 1996, 2903.
(22) (a) Lindner, E.; Wang, Q.; Mayer, H. A.; Bader, A.; Ku¨hbauch,
H.; Wegner, P. Organometallics 1993, 12, 3291. (b) Lindner, E.; Wang,
Q.; Mayer, H. A.; Bader, A. J . Organomet. Chem. 1993, 458, 229. (c)
Werner, H.; Hampp, A.; Peters, K.; Peters, E. M.; Walz, L.; von
Schnering, H. G. Z. Naturforsch. 1990, 45B, 1548. (d) Werner, H.;
Hampp, A.; Windmu¨ller, B. J . Organomet. Chem. 1992, 435, 169.
(23) Lindner, E.; Wang, Q.; Mayer, H. A.; Fawzi, R.; Steinmann, M.
Organometallics 1993, 12, 1865.
(18) Gu¨nther,
H NMR Spectroskopie, 3rd ed.; Thieme Verlag:
Stuttgart, Germany, 1992; p 310.
(19) Cramer, R.; Kline, J . B.; Roberts, J . D. J . Am. Chem. Soc. 1969,
2519.

5554 Organometallics, Vol. 15, No. 26, 1996
Braunstein et al.
Recently the stable cis-phosphine-cis-ether complex
[Rh(η4-{(η5-C5H4)OCH2CH2PPh2}2Fe)]BF4 has been re-
ported.24
In CH2Cl2, 3 was slowly oxidized to the rhodium(III)
complex trans,cis,cis-[RhCl2(PkO)2][PF6], which was
1
identified by its H NMR spectrum.1b Under a hydrogen
atmosphere, 3 does not form a hydride complex (1H
NMR). For similar complexes with ether-phosphines,
the reactivity toward hydrogen depends on the basicity
of the phosphorus donor: cyclohexyl or isopropyl sub-
stituents lead to hydride complexes, although unstable,
whereas a phenyl group does not.22b,23,25
Reaction of complex 3 with 1 or 2 equiv of NaOMe in
toluene or an excess of NaH in THF generated the
phosphino enolate ligand, but no pure product could be
isolated. This transformation was evidenced by the
replacement of the IR absorption at 1565 cm-1 of 3 by
a new one around 1520 cm-1
.
F igu r e 2. View of the structure of the cationic complex
[Rh(CO)(PkO)(PPh3)]+ in 6 with the atom-numbering
scheme.
Addition of TlPF6 to a THF solution of 1 resulted in
a slow color change, from red to almost black-red.
Surprisingly, the IR spectrum showed no band in the
usual range for an uncoordinated keto function but a
strong band at 1520 cm-1, which is characteristic for a
phosphino enolate ligand. Accordingly, the 1H NMR
spectrum in C6D6 showed a doublet at δ 5.22 due to
2J (PH) coupling instead of the doublet found at δ 4.04
for 1. This downfield value is characteristic of a
phosphino enolate ligand. The presence of coordinated
THF was inferred from 1H NMR data. The 31P{1H}
NMR spectrum contained a doublet at 47.6 ppm with
J (RhP) ) 184 Hz, consistent with the phosphorus atom
being in a chelate and in a trans position with respect
to an oxygen donor atom. These data are consistent
Sch em e 2
with the solvento complex [Rh{Ph2PCH‚ ‚C(‚ ‚O)-
Ph}(THF)2] (4), although it could only be characterized
spectroscopically in solution owing to its lability. The
formation of an enolate complex without addition of a
strong base is notable and illustrates the stability
provided by the phosphino enolate chelating ligand in
a square-planar geometry. Related deprotonation reac-
phorus atoms are trans to each other (31P{1H} NMR
spectroscopy). The ν(CtO) frequency for 6 was found
at higher wavenumbers (1995 cm-1) than for 5 (1974
cm-1), in keeping with less electron density on rhodium
being available in the former for back-bonding to CtO.
The crystal structure of 6 (Figure 2) is in agreement
with the structure in solution derived from spectroscopic
tions have been observed in the synthesis of [RhCl{Ph2-
PCH‚ ‚C(‚ ‚O)Ph}(PkO)(P∼O)][PF6]1a and on addition
of t-Bu2PCH2C(O)-t-Bu to an ethanolic solution of nickel-
(II) chloride with formation of trans-[Ni{But PCH‚ ‚C-
2
data. The phosphino enolate complex [Rh{Ph2PC-
(‚ ‚O)Bu}].11 The presence in the IR spectrum of the
reaction mixture of a weaker band at 1570 cm-1 is
consistent with the cationic intermediate [Rh(PkO)-
(THF)2][PF6]. Its formation would be related to the
synthesis of [(η3-C3H5)Pd(solvent)2][BF4] by addition of
2 equiv of AgBF4 to MeNO2 or MeCN solutions of [(η3-
C3H5)Pd(µ-Cl)]2.26
Rea ction w ith tr a n s-[Rh Cl(CO)(P P h 3)2]. Treat-
ment of trans-[RhCl(CO)(PPh3)2] with 1 equiv of L in
toluene afforded [RhCl(CO)(P∼O)(PPh3)] (5) (Scheme 2).
When this reaction was performed in CH2Cl2/acetone
in the presence of 1 equiv of TlPF6, the orange cationic
chelate complex [Rh(CO)(PkO)(PPh3)][PF6] (6) was iso-
lated in high yield. In both complexes the two phos-
H‚ ‚C(‚ ‚O)Ph}(CO)(PPh3)] (7), which proved to be es-
pecially useful for alkane activation (see below), was
obtained by reacting a toluene solution of 5 or a toluene
suspension of 6 with 1 equiv of sodium methoxide in
methanol. 7 could also be obtained by displacement of
the acac ligand from [Rh(acac)(PPh3)(CO)] with the keto
phosphine. Analytical and spectroscopic data support
its formulation. The absorption of the CtO stretching
vibration was shifted to 1956 cm-1, owing to the anionic
oxygen donor, which confers more electron density to
the metal. The absorption band at 1513 cm-1 is
characteristic for the enolate ligand. The enolate proton
1
gives in the H NMR spectrum an overlapping doublet
2
of doublets at 5.31 ppm with coupling constants J (PH)
(24) Allgeier, A. M.; Singewald, E. T.; Mirkin, C. A.; Stern, C. L.
Organometallics 1994, 13, 2928.
(25) Lindner, E.; Wang, Q.; Mayer, H. A.; Fawzi, R.; Steinmann, M.
J . Organomet. Chem. 1993, 453, 289.
3
and J (RhH) of 2.2 Hz. The 31P{1H} spectrum at 200
K is typical for an ABX spin system (A ) B ) P, X )
(26) Sen, A.; Lai, T.-W. Organometallics 1983, 2, 1059.
Rh), and the 2J (PP) coupling of 301 Hz for these two

Rh(I) and Ir(I) Complexes with Phosphines
Organometallics, Vol. 15, No. 26, 1996 5555
mol-1 18
.
We have checked that the disappearence of the
1J (RhP) coupling is not due to exchange with an excess
of phosphine ligand by washing a sample of 7 thoroughly
with ether, in which PPh3 is soluble, before recording
the spectrum. PPh3 dissociation occurs in benzene,
toluene/THF, or CH2Cl2 solutions (eq 1).
Rea ction s w ith [Rh (µ-Cl)(COE)2]2 u n d er Ca r bon
Mon oxid e. When [Rh(µ-Cl)(COE)2]2 (COE ) cy-
clooctene) and 4 equiv of keto phosphine were reacted
in toluene under a carbon monoxide atmosphere [RhCl-
(CO)(P∼O)2] (8) was isolated (Scheme 3). Analytical
and spectroscopic data are in agreement with the
structure drawn and the coordination of two monoden-
tate phosphine ligands. The trans position of the
phosphorus atoms in 8 was inferred from the J (RhP)
value of 128 Hz, close to values observed for 5 and 6.
Reaction of this complex with 1 equiv of TlPF6 in CH2-
Cl2 gave the cationic complex [Rh(CO)(PkO)(P∼O)][PF6]
(9), in which one of the keto phosphines is terminal and
the other chelating (IR absorptions at 1678 and 1561
cm-1, respectively). The 31P{1H} NMR spectrum at 295
K consists of a doublet at 32.5 ppm with J (RhP) ) 128
Hz. The 1H NMR spectrum at room temperature
contains a triplet, which broadened on cooling to 180 K
without reaching coalescence. This is indicative of a
dynamic behavior during which the two keto oxygen
donors compete for a common coordination site, cis to
the P atoms (Scheme 3).
Similarly to the formation of the phosphino enolate
complex 7, reaction of a THF solution of 8 with 1 equiv
of sodium methoxide in methanol quantitatively
afforded [Rh{Ph2PCH‚ ‚C(‚ ‚O)Ph}(CO)(P∼O)] (10)
(Scheme 3). The usefulness of complexes similar to 7
in transfer dehydrogenation (see below) led us to develop
a one-pot synthesis starting from [Rh(µ-Cl)(COE)2]2.
Addition of keto phosphine L and phosphine L1 under
a CO atmosphere afforded neutral intermediates similar
to 5, as shown by IR spectroscopy (L1 ) PPh2(p-tolyl),
ν(CtO) 1973 cm-1 and ν(CdO) 1672 cm-1), which on
addition of sodium methoxide yielded the pure phos-
phino enolato complexes 11-13. These reactions are
summarized in Scheme 3.
Interestingly for the phosphino enolato carbonyl
complexes 7 and 10-13 the carbonyl stretching fre-
quency is independent of the nature of the phosphine
ligand L1. This can be ascribed to extensive electron
delocalization within the enolate system, which redis-
tributes the electron density through the whole complex.
Consistently, the enolate absorption band and the
chemical shift value of the enolate proton are also
independent of L1. The value for the carbonyl stretch
between 1956 and 1961 cm-1 indicates a higher electron
density on the rhodium center than that in [RhCl(CO)-
(PPh3)2] (1975 cm-1) but is comparable to that in [RhCl-
(CO)(PMe3)2] (1956 cm-1).
F igu r e 3. 31P{1H} NMR spectra of [Rh(Ph2PCH‚ ‚C-
(‚ ‚O)Ph}(CO)(PPh3)] (7) at 295 (A), 240 (B), 230 (C), 220
(D), and 200 K (E).
chemically different phosphorus atoms indicates that
PPh3 is coordinated trans to the other phosphorus atom
(see Figure 3). The spectrum at 295 K contains a
doublet for the phosphino enolate ligand and a broad
resonance for PPh3 and no coupling between them. The
disappearance of the coupling between rhodium and
PPh3 indicates partial dissociation (Scheme 3) with
formation of a 14-electron species. Heating of the
solution led to further broadening and decomposition.
The coalescence temperature was reached at 230 K; the
activation energy for this dynamic process was esti-
mated from the Eyring equation as 43.4 ( 0.9 kJ
Rea ction s w ith [Rh Cl(P P h 3)3]. The reactivity of
the keto phosphine L toward [RhCl(PPh3)3] and subse-
quent reactions are very similar to those with [RhCl-

5556 Organometallics, Vol. 15, No. 26, 1996
Braunstein et al.
Sch em e 3
Sch em e 4
Sch em e 5
could also be formed by starting from 1 and 2 equiv of
PPh3 (vide supra).
When 1 equiv of TlPF6 was added to 14, formed in
situ in acetone/CH2Cl2, the cationic complex [Rh(PkO)-
(PPh3)2][PF6] (15) was isolated as red crystals. Analyti-
cal and spectroscopic data are in agreement with the
structure proposed.
The phosphino enolate complex [Rh{Ph2PCH‚ ‚C-
(‚ ‚O)Ph}(PPh3)2] (16), which was found useful for
alkane activation (see below), was obtained by react-
ing a toluene solution of 14 or a toluene suspension of
15 with 1 equiv of sodium methoxide in methanol.
Analytical and spectroscopic data are in agreement
with the formulation. In a manner similar to the
synthesis of 16 but using Ph2PCH2C(O)(p-C6H4F),
(CO)(PPh3)2]. Addition of 1 equiv of L to a toluene
solution of [RhCl(PPh3)3] gave the complex [RhCl-
(PPh3)2(P∼O)] (14), analogous to 5 (Scheme 4). The 31P-
{1H} NMR spectrum of the reaction mixture showed the
presence of 1 equiv of free PPh3, a doublet of triplets
for the keto phosphine, and a doublet of doublets for
the two equivalent Rh-bound PPh3 ligands. IR monitor-
ing of a toluene solution of 14 showed the development
within 3 h of a strong band at 1520 cm-1 characteristic
of a phosphino enolate ligand. The 31P{1H} NMR
spectrum of this toluene solution after 4 days showed
we
synthesized
[Rh{Ph2PCH‚ ‚C(‚ ‚O)(p-C6H4F)}-
(PPh3)2] (17) (Scheme 4). The ambident character of the
enolate moiety in 16 was confirmed in reactions with
phenyl isocyanate and chlorodiphenylphosphine. Thus,
16 reacted readily at room temperature with 1 equiv of
Ph2PCl, affording in good yield the complex [RhCl{Ph2-
PCHdC(Ph)OPPh2}(PPh3)] (18), which resulted from
nucleophilic substitution of the P-Cl bond by the
enolate oxygen atom. Reaction of 16 with phenyl
the presence of mer-[RhCl{Ph2PCH‚ ‚C(‚ ‚O)Ph}-
(P∼O)] and [RhCl(PPh3)3]. As the reaction of [RhCl-
(PPh3)3] with 3 equiv of L has been shown to proceed
via [RhCl(P∼O)3] to the rhodium(III) complex mer-
isocyanate afforded cis-[Rh{Ph2{C[C(O)Ph]dC(O)NHPh}-
(PPh3)2] (19) (Scheme 4). As shown by 31P{1H} NMR
spectroscopy, only one isomer was formed. The 1H NMR
spectra revealed the presence of a signal at δ 10.4 ppm
that was assigned to the amide proton after a D2O-
[RhCl{Ph2PCH‚ ‚C(‚ ‚O)Ph}2(P∼O)],1a it is likely that
phosphine exchange in 14 occurs according to Scheme
5. Note that mixed phosphine complexes such as 14

Rh(I) and Ir(I) Complexes with Phosphines
Organometallics, Vol. 15, No. 26, 1996 5557
Sch em e 6
F igu r e 4. View of the structure of the cationic complex
[Rh(NBD)(PkO)(PPh3)]+ in 20 with the atom-numbering
scheme.
NH exchange experiment. This value reflects hydrogen
bonding with the oxygen atom of the neighboring
carbonyl group, thus forming a stable six-membered
ring. In the IR spectrum no ν(N-H) vibration was
detected. Bands appear in the 1550-1625 cm-1 region
due to the conjugated ligand system. Although coordi-
nation by the nitrogen cannot be ruled out with cer-
tainty (with the enolate oxygen atom occupying the
place of the NPh group), the high value of 216 Hz for
J (RhP) is consistent with a phosphorus trans to oxygen,
and comparison with previous data27 are in favor of the
structure shown in Scheme 4. It results formally from
the nucleophilic attack of the carbon atom R to the
phosphorus of the phosphino enolate ligand on the
carbon atom of PhNCO, followed by a 1,3-hydrogen shift.
These reactions are analogous to those previously
reported for phosphino enolate complexes such as cis-
shift of only 35 cm-1 was observed upon complexation
in the trigonal-planar copper complex [Cu(PkO)(P∼O)].30
In a study of cobalt(II) complexes, it has been found that
chelation of the keto phosphine ligand is considerably
less favored in tetrahedral than in octahedral or square-
planar complexes.31 Together with the IR shift of the
carbonyl stretch upon chelation, this illustrates that the
interaction between the carbonyl oxygen of the keto
phosphine and a metal markedly depends on the angle
of chelation required by the metal orbitals. Octahedral
and square-planar geometries are more favorable than
trigonal-bipyramidal (in the equatorial plane), tetrahe-
dral, and trigonal-planar ones. Treatment of 20 in
toluene with sodium hydride or sodium methoxide led
to decomposition. Apparently the pentacoordinated
environment is unfavorable for enolate formation from
the P,O ligand. Under a hydrogen atmosphere 20
decomposed to 15 (identified by 31P{1H} NMR), norbor-
nane (detected by GC), and an uncharacterized black
precipitate.
[M{Ph2PCH‚ ‚C(‚ ‚O)Ph}2] (M ) Ni, Pd, Pt) with chlo-
rophosphines28 and aryl isocyanates.20,29
When L, norbornadiene (NBD), and TlPF6 were added
in sequence to a solution of [RhCl(PPh3)3] in acetone,
orange crystals were isolated in 50% yield. They were
shown to be identical with the product obtained from
the reaction of PPh3, L, and TlPF6 with [Rh(µ-Cl)-
R ea ct ion s w it h [R h (µ-Cl)(COE )2]2, Dien e, a n d
Ba se. Our interest in catalytic studies of rhodium(I)-
enolate complexes led us to use diolefin coligands in
order to permit isolation. Addition in sequence of an
excess of norbornadiene, 1 equiv of L, and a slight excess
of sodium methoxide to dimeric [Rh(µ-Cl)(COE)2]2 in
toluene led to the isolation in high yield of an orange
1
(NBD)]2 (Scheme 6). An unusually high field H NMR
signal for the PCH2 group at 3.03 ppm motivated an
X-ray structure analysis, which established the formu-
lation as [Rh(NBD)(P∩O)(PPh3)][PF6] (20) (Figure 4).
Although pentacoordinated, this complex is not fluxional
in solution in the temperature range 200-330 K. No
complex analogous to 20 was obtained in reactions
involving 1,5-cyclooctadiene (COD) instead of NBD. This
is in agreement with literature data, since no pentaco-
ordinated rhodium complex with COD and monodentate
phosphine appears to be known. Whereas the ν(CdO)
vibration of the coordinated keto group in square-planar
and octahedral complexes is generally observed around
1575-1565 cm-1 (95-105 cm-1 coordination shift), in
the pentacoordinated complex 20 it occurs at 1620 cm-1
(50 cm-1 shift). In the case of the ferrocenyl-substituted
keto phosphine Ph2PCH2C(O)(η5-C5H4)Fe(η5-C5H5) a
crystalline solid which was analyzed as [Rh{Ph2PC-
H‚ ‚C(‚ ‚O)Ph}(NBD)] (21). The typical ν(CdO) ab-
sorption of the keto group in L is replaced in 21 by a
strong absorption in the range 1520-1510 cm-1, typical
for the ν(C‚ ‚O) + ν(C‚ ‚C) vibration of the enolate sys-
tem. In a similar manner we synthesized [Rh{R1 PC-
2
H‚ ‚C(‚ ‚O)R2}(diolefin)] (22-25) employing
L and
COD (22), Ph2PCH2C(O)Me and NBD (23), Ph2PCH2C-
(O)(p-C6H4F) and NBD (24), or i-Pr2PCH2C(O)Ph and
(27) Bouaoud, S.-E.; Braunstein, P.; Grandjean, D.; Matt, D.; Nobel,
D. Inorg. Chem. 1988, 27, 2279.
(28) Balegroune, F.; Braunstein, P.; Grandjean, D.; Matt, D.; Nobel,
D. Inorg. Chem. 1988, 27, 3320.
(30) Balegroune, F.; Braunstein, P.; Gomes Carneiro, T. M.; Grand-
jean, D.; Matt, D. J . Organomet. Chem. 1989, 367, 117.
(31) Braunstein, P.; Kelly, D. G.; Dusausoy, Y.; Tiripicchio, A. Inorg.
Chem. 1993, 32, 4835.
(29) Braunstein, P.; Nobel, D. Chem. Rev. 1989, 89, 1927.

5558 Organometallics, Vol. 15, No. 26, 1996
Braunstein et al.
Sch em e 7
Sch em e 9
Sch em e 8
hydrogenation of the coordinated diene took place and
a black precipitate was formed.32
3. Hyd r ogen a tion of 1-Hexen e Ca ta lyzed by
Ca tion ic Keto P h osp h in e a n d Neu tr a l P h osp h in o
En ola te Com p lexes. We examined the reactivity of
cationic keto phosphine complexes 3, 15, and 20 and
neutral phosphino enolato complexes 4, 7, and 16
toward 1-hexene at atmospheric pressure. These com-
plexes were chosen for the diversity of ligand sets
available (Scheme 9).
Complex 20 in THF hydrogenates and isomerizes
1-hexene catalytically to hexane and only trans-2-
hexene, respectively. Since isomerization generally
involves monohydride complexes, an equilibrium be-
tween a cationic dihydride and a neutral monohydride
complex is likely to occur. A similar equilibrium has
been suggested for cationic rhodium complexes with
monodentate phosphine ligands.33
NBD (25) (Scheme 7). These complexes are analogous
to the complexes [Rh(acac)(diolefin)]. No high-field H
1
NMR resonance was detected for solutions of complexes
21-25 under hydrogen at atmospheric pressure, but at
0.8 MPa the solutions turned progressively black in over
20 min and the olefinic signals disappeared. Thus
hydrogenation of coordinated diene was accompanied by
Under the conditions employed, 3 and 15 were inac-
tive in acetone. Hydrogenation of unsaturated organic
substrates with metal complexes which do not contain
M-H bonds implies as the initial step the reaction with
molecular hydrogen.34 For 3 no hydride was detected
under hydrogen. This would be consistent with the
electron density at the rhodium center, which is com-
plexed by two relatively hard donor keto groups, being
insufficient for oxidative addition of hydrogen to occur.
When 15 was placed under hydrogen, no hydride was
decomposition of the 12 electron fragment [Rh{R1 PC-
2
H‚ ‚C(‚ ‚O)R2}]. The reaction of [Ir(µ-Cl)(COE)2]2 with
COD, L, and sodium methoxide in toluene yielded [Ir-
{Ph2PCH‚ ‚C(‚ ‚O)Ph}(COD)] (26). Its characteristic
spectroscopic data are similar to those for its rhodium
analog 22. When 26 was placed under an atmosphere
1
detected by H NMR and no dissociation of PPh3 was
1
of hydrogen, the H NMR spectrum showed two high-
observed by 31P{1H} NMR.
field doublets at δ -11.03 (J (PH) ) 18.1 Hz) and -18.04
(J (PH) ) 11.9 Hz), in contrast to the case of 22.
Chemical shifts and coupling constants are indicative
of hydrides cis to the phosphorus atom and trans to an
olefinic double bond and the oxygen atom, respectively.
Four signals were found for the chemically inequivalent
1,5-cyclooctadiene vinyl protons due to the lack of
symmetry caused by the hydride ligands. These data
All phosphino enolate complexes tested were active
hydrogenation and isomerization catalysts. The activity
decreased in the order 4 > 16 > 7, which is also the
order of weakly to strongly coordinating ligands (Table
1). Thus, we propose that ligand dissociation leads to
the active catalytic species [Rh{Ph2PCH‚ ‚C(‚ ‚O)-
Ph}L] (L ) 2e-donor ligand) having vacant coordination
sites. The isomerization activity suggests an equilib-
rium between a Rh(III) phosphino enolate dihydride and
a Rh(I) keto phosphine monohydride complex.
4. Tr a n sfer Deh yd r ogen a tion of Cycloocta n e
w ith Nor bor n en e Ca ta lyzed by P h osp h in o En ola te
Com p lexes. The activation of alkanes by soluble
transition-metal species has aroused considerable inter-
suggest that the hydride complex [Ir{Ph2PCH‚ ‚C-
(‚ ‚O)Ph}(H)2(COD)] (27) was formed (Scheme 8). It
was stable for ca. 1 h at room temperature before
hydrogenation of the COD ligand occurred. Recently,
Oro, Werner, et al. have reported the hydrogenation of
alkynes catalyzed by cationic iridium cyclooctadiene
phosphino-ether complexes, which under hydrogen are
in equilibrium with a cationic hydride complex similar
(32) Esteruelas, M. A.; Lo´pez, A. M.; Oro, L. A.; Pe´rez, A.; Schulz,
M.; Werner, H. Organometallics 1993, 12, 1823.
(33) Schrock, R. R.; Osborn, J . A. J . Am. Chem. Soc. 1976, 98, 2134.
(34) J ames, B. R. Homogeneous Hydrogenation; Wiley: New York,
1973.
1
to 27, as judged by their high-field H NMR data. The
latter could be characterized spectroscopically before

Rh(I) and Ir(I) Complexes with Phosphines
Organometallics, Vol. 15, No. 26, 1996 5559
Ta ble 1. Hyd r ogen a tion a n d Isom er iza tion of
1-Hexen e Ca ta lyzed by Ca tion ic Rh od iu m Keto
P h osp h in e a n d Neu tr a l Rh od iu m P h osp h in o
En ola te Com p lexesa
Ta ble 2. Tr a n sfer Deh yd r ogen a tion of
Cycloocta n e w ith Nor bor n en e Ca ta lyzed by
Rh od iu m Ca r bon yl P h osp h in o En ola te
Com p lexes: Effect of Ar om a tic P h osp h in es
amt of
amt of
2-cis-
turnover freq
L1 trans to
phosphino
enolate
amt of 2-trans-
entry
no.a
mol of COE
mol of NBA
entry
no.
conversion, hexane, hexene, hexene,
(mol of Rh)-1 h-1 (mol of Rh)-1 h-1
K
complex solvent
%
%
%
%
1
2
PPh3
230
180
130
115
2200
2200
860
0.10
0.08
0.15
0.1
1
2
3
4
4
7
16
20
thf
99.2
10
50
44
45
69
22
27
43
17
48
28
12
14
30
PPh2(p-tolyl)
P(p-C5H4F)3
P(p-C5H4F)3
toluene
toluene
thf
3
4b
1250
85
a
a
Reaction conditions: 0.8 mol of 1-hexene; 5 mmol of rhodium
Reaction conditions: 333 K; 20 mL of COA; 1.9 M NBE; 0.4
b
complex; stirred for 1 h at 300 K; p(H2) ) 0.1 MPa.
mM Rh complex; p(H2) ) 7 MPa. Catalyst in entry 3 reused after
elimination of reactants and products; 323 K.
est.35 It emerged that the catalyst has to be resistant
to dimerization or â-elimination of its ligands, which
represent major deactivation pathways.36 [RhCl(CO)-
(PMe3)2] was reported to be the first efficient (>100
turnovers) organometallic alkane functionalization cata-
lyst, effecting photochemical dehydrogenation of alkanes
to yield the corresponding alkenes with turnover rates
as high as 300/h.37 The proposed mechanism for the
catalytic cycle involved photogeneration of the three-
coordinate fragment RhL2Cl (eq 2, L ) PMe3), transfer
of hydrogen from the alkane (eq 3), and displacement
of H2 from H2RhCl(PMe3)2 with CO to regenerate RhCl-
(CO)L2 (eq 4).
Ta ble 3. Tr a n sfer Deh yd r ogen a tion of
Cycloocta n e w ith Nor bor n en e Ca ta lyzed by
Rh od iu m Ca r bon yl En ola te Com p lexes: Effect of
Va r iou s P h osp h in es
turnover freq
L1 trans to
entry phosphino
mol of COE
mol of NBA
no.a
enolate
(mol of Rh)-1 h-1 (mol of Rh)-1 h-1
K
5
6
7
8
PPh3
PMe3
370
10
7
7000
1700
4700
3600
0.054
0.006
0.001
0
b
P∼O
P(o-tolyl)3
0
a
Reaction conditions: 363 K; 20 mL of COA; 3.4 M NBE; 0.4
b
mM Rh complex; p(H2) ) 7 MPa. Preparation of [Rh(Ph2PC-
RhCl(CO)L2
9
hν8 RhClL2 + CO
(2)
(3)
(4)
H‚ ‚C(‚ ‚O)Ph}(CO)(PMe3)]: [AgI(PMe3)]4 (0.04 mmol) was
heated to 200 °C, and the PMe3 thus liberated was condensed into
a frozen yellow solution of 7 (0.098 g, 0.14 mmol) in toluene (10
mL). When it was stirred at room temperature, the solution
rapidly became orange. Concentration, addition of pentane (40
mL), and cooling to -20 °C precipitated a cream-yellow solid,
which was isolated by filtration (0.057 g) but not fully character-
ized (IR showed it to contain no carbonyl ligand). Evaporation of
the yellow filtrate gave orange crystals of the product, which were
filtered and washed with a small amount of pentane (0.046 g, 64%).
RhClL2 + alkane h H2RhClL2 + alkene
H2RhClL2 + CO h RhCl(CO)L2 + H2
More recently it was found that [RhCl(CO)(PMe3)2]
also catalyzes thermal dehydrogenation of alkanes to
the corresponding alkenes, but exclusively under an
atmosphere of dihydrogen. The catalysis is initiated by
the reverse of eq 4, and the catalytic cycle consists of
eq 3 and its microscopic reverse (where the alkene is a
sacrificial hydrogen acceptor). Thermodynamic studies
corroborated these findings.38 Also, Miller and Knox
reported efficient transfer dehydrogenation of alkanes
with [RhCl(AsPh3)2]2 and [RhCl(CO)(AsMe3)2] as cata-
lyst precursors under 3.4 MPa of hydrogen at 60-100
°C with turnover rates reaching 600/h.9d
We anticipated that, owing to the ability of complexes
7 and 16 to catalyze hydrogenation of 1-hexene (the
reverse reaction of eq 3) and to the facile dissociation
of triphenylphosphine from complex 7 in solution (eq
1), phosphino enolate complexes could be good candi-
dates for the catalytic transfer dehydrogenation of
alkanes under conditions similar to those used by
Goldman. The solubility of the complexes used allows
the catalysis to be performed in neat alkane. Two
important parameters are turnover frequencies of cy-
IR (C6D6): 1961 vs ν(CtO), 1516 s ν(C‚ ‚O) + ν(C‚ ‚C) cm-1 1H
.
NMR (C6D6): δ 8.1-7.25 (15H, m, Ph), 5.33 (1H, s, PCH), 1.10
(9H, s, 3 Me).
clooctene (COE) and norbornane (NBA) formation and
the COE/NBA molar ratio (K), whose ideal value is 1.
The results obtained using complexes 7, 12, and 13
are given in Table 2. The K value increases slightly in
the order PPh2(p-tolyl) < PPh3 < P(p-C6H4F)3 (entries
2, 1, and 3), with decreasing phosphine basicity. This
observation cannot be rationalized on the basis of an
oxidative-addition character of the alkane C-H bond
activation, which has been mentioned before (vide
infra).35b,39 This is further supported by the observation
that when the more basic PMe3 was used as the L1
ligand (entry 6, Table 3) only hydrogenation took place.
The potentially chelating keto phosphine Ph2PCH2C-
(O)Ph (entry 7) considerably decreased the dehydroge-
nation reaction. The complete inactivity of the tri-o-
tolylphosphine-based enolate complex (entry 8) could be
ascribed to a cyclometalation side reaction.40 Cyclo-
metalation has been mentioned as limiting catalyst
activity by providing a pathway for catalyst deacti-
vation,9c,41 and alkane activation is especially sensitive
to it.42 Changing the solution volume (20 or 40 mL in
a 100 mL reactor) did not affect K.43
(35) (a) Crabtree, R. H. In The Chemistry of Alkanes and Cycloal-
kanes; Patai, S., Ed.; Wiley: New York, 1992; p 653. (b) Crabtree, R.
H. Chem. Rev. 1985, 85, 245.
(36) Crabtree, R. H.; Mellea, M. F.; Mihelcic, J . M.; Quirk, J . M. J .
Am. Chem. Soc. 1982, 104, 107.
(37) (a) Nomura, K.; Saito, Y. J . Chem. Soc., Chem. Commun. 1988,
161. (b) Sakakura, T.; Sodeyama, T.; Tokunaga, M.; Tanaka, M. Chem.
Lett. 1988, 263. (c) Maguire, J . A.; Boese, W. T.; Goldman, A. S. J .
Am. Chem. Soc. 1989, 111, 7088. (d) Maguire, J . A.; Boese, W. T.;
Goldman, M. E.; Goldman, A. S. Coord. Chem. Rev. 1990, 97, 179.
(38) Wang, K.; Rosini, G. P.; Nolan, S. P.; Goldman, A. S. J . Am.
Chem. Soc. 1995, 117, 5082.
(39) Another possibility would be that dissociation of the tri-
arylphosphine may precede the approach of the alkane.
(40) Chency, A. J .; Shaw, B. L. J . Chem. Soc., Dalton Trans. 1972,
754, 860.
(41) Garrou, P. Chem. Rev. 1985, 85, 171.
(42) Burk, M. J .; Crabtree, R. H. J . Am. Chem. Soc. 1987, 109, 8025.

5560 Organometallics, Vol. 15, No. 26, 1996
Braunstein et al.
Ta ble 4. Tr a n sfer Deh yd r ogen a tion of
Sch em e 10
Cycloocta n e w ith Nor bor n en e Ca ta lyzed by
Com p lex 13: Effect of Ad d ition of Tr im eth yla m in e
Oxid e
turnover freq
mol of COE mol of NBA
entry
no.a
(mol of
(mol of
catalyst precursor
Rh)-1 h-1
Rh)-1 h-1
K
9
10
13
210
880
4500
18500
0.046
0.047
13 + 0.6 equiv
of ONMe3
a
Reaction conditions: 363 K; 20 mL of COA; 3.4 M NBE; 0.4
mM Rh complex; p(H2) ) 7 MPa.
The catalyst could be recycled after removal of
reactants and products by vaporization under vacuum
(Table 2, entries 3 and 4). Accordingly, IR spectra of
reaction solutions of 7 and 13 after catalysis revealed
no decrease of the characteristic carbon monoxide
stretch at 1960 cm-1 and of the enolate stretch at 1515
Ta ble 5. Tr a n sfer Deh yd r ogen a tion of
Cycloocta n e w ith Nor bor n en e Ca ta lyzed by
Com p lex 22: Effect of Ad d ition of
Tr ip h en ylp h osp h in e
turnover freq
entry
no.a
PPh3/Rh
mol of COE
mol of NBA
cm-1
.
The 1H NMR spectrum in CD2Cl2 solution
molar ratio (mol of Rh)-1 h-1 (mol of Rh)-1 h-1
K
showed a peak at 4.75 ppm which was attributed to the
enolate proton. The solution remains homogeneous, and
catalysis is unaffected by the addition of mercury to the
reaction mixture, implying that the active catalytic
species is not colloidal.44 In fact, the reaction is limited
by complete hydrogenation of the hydrogen acceptor, not
by catalyst decomposition. Accordingly, we found no
trace of benzene (GC) which could have resulted from
phosphorus-phenyl bond hydrogenolysis.
To investigate the fate of the catalyst precursor, an
experiment was carried out with complex 13 under
deuterium. 1H NMR analysis of complex 13 after
several hundred turnovers still showed a peak for the
enolate proton, suggesting that the P,O ligand was only
present in the enolate form throughout the catalytic
cycle (absence of deuterated enolate). An equivalent
amount of norbornane-d0 and dehydrogenated cycloal-
kane was found by GC-MS. The presence of norbor-
nane-d2 and the absence of cyclooctane-d2 shows the
selective hydrogenation of norbornene in the presence
of cyclooctene. No monodeuterated alkanes or olefins
were detected, indicating that the transfer of hydrogen
takes place exclusively via dihydride complexes, con-
sistent with the propensity of Rh(I) to form dihydride
complexes.44,45
11
12
13
14
15b
0
0.5
1
1.8
1
10
100
80
7
25
1000
1700
740
260
490
0.01
0.06
0.11
0.03
0.05
a
Reaction conditions: 343 K; 20 mL of COA; 1.9 M NBE; 0.4
b
mM Rh complex; p(H2) ) 0.1 MPa. Complex 23; 298 K.
compounds MXL2, with M being a d8 metal, has indeed
been cited as promising for alkane activation.35
Accordingly, addition of 0.6 equiv of amine oxide
ONMe3 to the enolate complex 13 considerably in-
creased the reaction rates (Table 4, entry 10). This can
be ascribed to the elimination of carbon monoxide from
the complex (eq 5).46 Addition of more than 1 equiv of
amine oxide resulted in a decrease of the reaction rates,
probably due to partial oxidation of rhodium. The K
value was unchanged.
[Rh{Ph2PCH‚ ‚C(‚ ‚O)Ph}L(CO)] + ONMe3 f
[Rh{Ph2PCH‚ ‚C(‚ ‚O)Ph}L] + CO2 + NMe3 (5)
This led us to investigate phosphino enolate com-
plexes containing no carbon monoxide ligand. The
Our results with phosphino enolato carbonyl com-
fragment [Rh{Ph2P{CH‚ ‚C(‚ ‚O)Ph}L1] can be easily
accessed from 22 and L1 under an hydrogen atmosphere,
thus allowing great flexibility in the choice of L1
(Scheme 10). Table 5 gives the results obtained with
22 after addition of various amounts of PPh3. As
observed by Goldman et al. in the case of [RhCl(PMe3)2-
(PR3)] (R ) i-Pr, Cy, Me),9b the absence of carbon
monoxide in the rhodium phosphino enolate complex
allowed work at atmospheric pressure. Under catalytic
conditions the hydrogen consumption started after an
induction period of 13-50 min and was accompanied
by a color change from yellow to dark orange. Without
plexes are consistent with [Rh{Ph2PCH‚ ‚C(‚ ‚O)Ph}-
L1] being a key intermediate in the catalytic cycle (see
Scheme 10). The K values published for [RhCl(CO)-
(PMe3)2] are in the range 0.16-0.29 using cyclooctane
and various olefins as substrates, and [RhCl(PMe3)2]
was identified as the catalytically active fragment.9a
Interestingly, the carbonyl infrared stretching frequen-
cies for 7 (1960 cm-1) and for [RhCl(CO)(PMe3)2] (1956
cm-1) are similar. For the transfer dehydrogenation of
alkanes under hydrogen pressure with [RhCl(AsPh3)2]2
and [RhCl(CO)(AsMe3)2] as catalyst precursors, no K
values were published.9d The common denominator of
the three systems appears to be the involvement of the
d8 three-coordinate fragment [RhXL2]. The class of
(46) This is in contrast to the previously observed catalytic isomer-
ization of hexene with 7 in toluene (see above). The lower polarity of
the cyclooctane/norbornane solvent compared to that of toluene may
suppress the formation of monohydride species.
(43) For [RhCl(CO)(PMe3)2] the rate decreased with an increasing
ratio of solution to gas phase volume.
(44) Anton, D. R.; Crabtree, R. H. Organometallics 1983, 2, 855.
(45) Sheridan, P. S. In Comprehensive Coordination Chemistry;
Wilkinson, G., Gillard, R. D., McCleverty, J . A., Eds.; Pergamon
Press: Oxford, England, 1987; Vol. 4, p 901.
(47) Further comparison of these catalytic systems is fraught with
difficulties due to their different behavior on changing reaction
conditions, as exemplified by the greater sensitivity to the solution
volume of [RhCl(CO)(PMe3)2] compared to 7 or to a change in the olefin
acceptor.
(48) Albers, M. O.; Coville, N. J . Coord. Chem. Rev. 1984, 53, 227.

Rh(I) and Ir(I) Complexes with Phosphines
Organometallics, Vol. 15, No. 26, 1996 5561
Ta ble 6. Tr a n sfer Deh yd r ogen a tion of
Cycloocta n e w ith Nor bor n en e Ca ta lyzed by
Rh od iu m a n d Ir id iu m P h osp h in o En ola te
Com p lexes: Effect of Va r iou s En ola tes a n d Ad d ed
Liga n d s
turnover freq
mol of COE mol of NBA
entry
no.a
(mol of
(mol of
complex L1 added
Rh)-1 h-1
Rh)-1 h-1
K
16
17
18
19
24
25
26
26
PPh3
PPh3
PPh3
P(p-tolyl)3
70
1
0
1170
160
300
260
0.06
0.004
0
1
0.003
a
Reaction conditions: 323 K; 20 mL of COA; 2 M NBE; 1 mM
enolate metal complex; p(H2) ) 0.1 MPa.
any added phosphine, C-H activation was inefficient
(entry 11). Adding 1 equiv of triphenylphosphine
improved both the stability and the selectivity of the
catalyst (entry 13). With less than 1 equiv, the catalyst
was still unstable (entry 12), whereas more than 1 equiv
strongly inhibited the rates of dehydrogenation and
hydrogenation (entry 14). The NBD complex 23 reacted
even after 18 min at 25 °C (entry 15) and showed the
same color changes. This induction period probably
indicates that the phosphino enolate chelate favors a
square-planar geometry over a pentacoordinated geom-
etry (see reactivity of 20). The latter is required in the
transition state for H-H addition. A much faster
hydrogenation of coordinated NBD versus COD has
been observed for cationic Rh(I) phosphine complexes.33
F igu r e 5. Variation of the norbornene (NBE) and cy-
clooctene (COE) concentrations with time during a catalytic
experiment using 23 and 0.5 equiv of PPh3.
Ta ble 7. Tr a n sfer Deh yd r ogen a tion of
Cycloocta n e Ca ta lyzed by Com p lex 22: Effect of
th e Hyd r ogen Accep tor
turnover freq
entry
no.a
hydrogen
acceptor
mol of COE
mol of alkane
(mol of Rh)-1 h-1 (mol of Rh)-1 h-1
K
20
21
22
norbornene
cyclohexene
neohexene
80
100
30
740
1900
330
0.11
0.05
0.09
The results obtained with rhodium complexes 24 and
25 derived from (diphenylphosphino)-p-fluoroacetophe-
none and (diisopropylphosphino)acetophenone (entries
16 and 17) and with iridium complex 26 are presented
in Table 6. Complex 24 (entry 16) was as efficient as
22. With complex 25 no hydrogen transfer occurred
(entry 17), presumably due to a cyclometalation side
reaction of the isopropyl group similar to that observed
by Goldman and Shih in the dehydrogenation of cy-
clooctane with [RhCl(P-i-Pr3)2] in the absence of any
hydrogen acceptor.9c This suspected cyclometalation
reaction could lead to inactive species in catalytic C-H
activation. A lower activity of P-i-Pr3 compared to PPh3
has been reported by Tanaka et al. on dehydrogenation
of cyclooctane with [RhCl(CO)(PR3)2] under irradia-
tion.49 Arylphosphines are suitable ligands because
they cannot decompose by â-elimination.
a
Reaction conditions: 343 K; 20 mL of COA; 1.9 M hydrogen
acceptor; 0.4 mM Rh complex; p(H2) ) 0.1 MPa.
greater stability of the Ir-H bond compared to Rh-H
in these complexes.
Som e Mech a n istic Con sid er a tion s. An intriguing
feature of both Goldman’s and our systems is that an
alkane can coordinate to the rhodium center in the
presence of strongly coordinating norbornene. Accord-
ingly, monitoring hydrogenation/dehydrogenation reac-
tions at various time intervals revealed that, even at
high conversion of norbornene, cyclooctene is still un-
reactive toward hydrogenation (Figure 5).
Under catalytic conditions the rhodium fragment [Rh-
{Ph2PCH‚ ‚C(‚ ‚O)Ph}L1] may react by three different
routes: (1) the dihydride route beginning with addition
of HsH, (2) the unsaturated route starting with coor-
dination of a CdC bond, and (3) the alkane route
starting with addition of a CsH bond. A concerted
mechanism involving simultaneous coordination of al-
kane and olefin can also be envisioned. Thus, cyclo-
hexene was revealed to be a slightly less favorable
hydrogen acceptor than norbornene (Table 7, entry 21),
whereas tert-butylethylene was less reactive, owing to
steric hindrance. However, the K value was not very
different. This could favor a mechanism where alkane
oxidative addition precedes the approach of the olefin,
because CsH bond addition in a concerted mechanism
would be hindered due to the size of the tert-butyleth-
ylene. Complex 22 is also less sensitive to the steric
bulk of the hydrogen acceptor than Goldman’s catalyst
[RhCl(PMe3)2L1]. Catalytic alkane dehydrogenation by
[IrClH2(P(-i-Pr3)2] has recently been discussed in terms
The iridium complex 26, analogous to 22, was quite
unreactive for dehydrogenation (entries 18 and 19). A
striking difference in H-H activation between rho-
dium and iridium has been previously observed for
-
[M(COD)L2]+A- (M ) Rh, Ir; L ) PR3; A- ) BF4-, PF6
,
ClO4-) as hydrogenation catalyst precursor for hindered
olefins in chlorinated solvents. Iridium was found to
be much more active than rhodium.50 However, the
greater stability of iridium hydride diene complexes
allowed the spectroscopic characterization of 27, an
intermediate before entrance into the catalytic cycle.
The shorter induction period together with the slower
hydrogenation rate of iridium as compared to rhodium
is indicative of an easier H2 addition with iridium and
(49) Sakakura, T.; Sodeyama, T.; Tanaka, M. New. J . Chem. 1989,
13, 737.
(50) Crabtree, R. H.; Demou, P. C.; Eden, D.; Mihelcic, J . M.; Parnell,
C. A.; Quirk, J . M.; Morris, G. E. J . Am. Chem. Soc. 1982, 104, 6994.

5562 Organometallics, Vol. 15, No. 26, 1996
Ta ble 8. Cr ysta l Da ta a n d Da ta Collection P a r a m eter sa
Braunstein et al.
3‚H2O
40H36O3F6P3Rh
6
20
formula
fw
C
C39H32F6O2P3Rh
842.50
C45H40F6OP3Rh
874.5
906.63
cryst system
space group
cryst dimens, mm
cryst color and habit
triclinic
P1h
monoclinic
P21/a
tetragonal
I4h
0.24 × 0.24 × 0.06
0.25 × 0.25 × 0.30
0.22 × 0.30 × 0.40
red
yellow
orange
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
10.398(3)
11.159(3)
17.995(5)
107.53(2)
102.86(2)
84.81(2)
1940.4(8)
2
16.238(6)
19.951(8)
11.411(6)
27.453(8)
27.453(8)
12.311(3)
95.15(2)
3694(3)
4
9278(4)
8
F
calcd, g/mL
F(000)
1.497
888
1.515
1704
1.298
3696
diffractometer
linear abs coeff µ, cm-1
2θ range, deg
octants collected
no. of data collected
no. of unique data used, N
R (Rw)
Enraf-Nonius CAD4F
6.177
Philips PW 1100
6.44
6-54
(h,k,l
7792
3097
0.036 (0.037)
1.108
Philips PW 1100
5.16
6-54
h,k,l
8540
4192
0.059 (0.062)
0.972
4-48
(h,(k,+l
6820
4415
0.047 (0.072)
1.476
GOFb
a
Details in common: T ) 295 K; Mo KR graphite-monochromated radiation (λ ) 0.710 73 Å); θ/2θ scan mode; (θ - 0.6) - (θ + 0.6 +
b
0.346 tan θ) scan width; 2.5-12°/min scan speed; for complexes 7 and 22, one standard reflection measured after 75 reflections. GOF
) [∑w(|Fo| - |Fc|)2/(Nobservns - Nparams)]1/2
.
Ta ble 9. Selected Bon d Dista n ces (Å) a n d
of an alkane association mechanism occurring after
olefin insertion into a IrsH bond.51a
An gles (d eg) for 3‚H2O
Rh-P1
P1-C1
C1-C2
C2-O1
Rh-O1
2.182(2)
1.861(7)
1.495(9)
1.248(7)
2.103(4)
Rh-P2
2.182(2)
1.840(7)
1.499(9)
1.236(7)
2.104(4)
The need for hydrogen as a third reagent, in addition
to olefin and alkane, suggests that hydrogen is not
merely generating the active species but is directly
involved in the catalytic cycle. To test this hypothesis,
we generated the active species by hydrogenation. We
observed catalytic cyclooctene formation under a hy-
drogen atmosphere, which stopped under an atmo-
sphere of argon and restarted under hydrogen. As a
hypothesis, it could be suggested that dihydrogen plays
the role of a particular ligand which, unfortunately,
reacts with olefin.
P2-C21
C21-C22
C22-O2
Rh-O2
P1-Rh-O1
Rh-P1-C1
P1-C1-C2
C1-C2-O1
Rh-O1-C2
P1-Rh-P2
83.8(1)
103.1(2)
110.1(5)
121.1(6)
121.9(4)
104.39(7)
P2-Rh-O2
82.8(1)
100.7(2)
109.9(4)
119.1(6)
121.6(4)
Rh-P2-C21
P2-C21-C22
C21-C22-O2
Rh-O2-C22
graphic data are summarized in Table 8. The molecular
structure is shown in Figure 1 together with the atom-
numbering scheme; selected bond distances and angles
are given in Table 9. The crystal structure consists of
discrete [Rh(PkO)2]+ cations, [PF6]- anions, and water
molecules separated by normal van der Waals contacts
(the nearest contact of the water molecule is with
another one at 2.908 Å, through hydrogen bonding). The
Rh center has a square-planar geometry, slightly dis-
torted toward tetrahedral with the phosphorus atoms
P1, P2 (and oxygen atoms O1, O2) in a cis arrangement
and on opposite sides of the mean plane through them
and the Rh center (distances to this plane 0.060,
-0.0588 Å and -0.0767, 0.0788 Å, respectively). The
two chelating keto phosphine ligands have the same
geometry and similar bond lengths and angles. The bite
angles P1-Rh-O1 and P2-Rh-O2 of 83.8(1) and 82.8-
(1)°, respectively, are in the normal range. The Rh-P
distance of 2.182(2) Å compares well with the average
value for Rh-P (2.16 Å) in [Rh(η4-{(η5-C5H4)OCH2CH2-
PPh2}2Fe)]BF4.23 The Rh-O distances of 2.103(4) and
2.104(4) Å are smaller than Rh-O in the above-cited
phosphine-ether complex (average 2.19 Å), indicating
stronger bonding to the metal of the keto function than
of the ether group.
Kinetic experiments show that during a catalytic run
the K value decreases slightly with decreasing concen-
tration of the acceptor olefin.51b It is not yet clear
whether this is due to (i) the hydrogenation “side”
reaction, the rate of which is known to be dependent
on olefin concentration, (ii) a concerted mechanism
involving simultaneous coordination of alkane and
olefin, or (iii) deactivation of the catalyst. However, we
did not detect benzene in the solution after catalysis
which could have resulted from P-C bond hydrogenoly-
sis. Indeed, the rather low temperatures at which the
reactions were performed could prevent this deactiva-
tion reaction from proceeding at a significant rate.
These results support the view that the 14-electron
fragment Rh{Ph2PCH‚ ‚C(‚ ‚O)Ph}L1, (L1
) phos-
phine) could be the active catalyst for hydrogen transfer
from the alkane. Catalytic transfer dehydrogenation of
cyclooctane has now been reported with rhodium com-
plexes bearing three types of ligands: phosphines,
arsines, and phosphino enolates. The activation of an
aliphatic C-H bond by these quite different ligand
systems makes further developments look promising.
5. Discu ssion of th e Cr ysta l Str u ctu r es. [Rh -
(P kO)2][P F 6]‚H 2O (3‚H 2O) (A.D., J .F ). Crystallo-
[Rh (CO)(P kO)(P P h 3)][P F 6] (6) (A.T., F .U). Crys-
tallographic data are summarized in Table 8. A view
of the structure of complex 6 is shown in Figure 2
(51) (a) Belli, J .; J ensen, C. M. Organometallics 1996, 15, 1532. (b)
Braunstein, P.; Chauvin, Y.; Na¨hring, J . Unpublished results.

Rh(I) and Ir(I) Complexes with Phosphines
Organometallics, Vol. 15, No. 26, 1996 5563
Ta ble 10. Selected Bon d Dista n ces (Å) a n d
An gles (d eg) for 6
Ta ble 11. Selected Bon d Dista n ces (Å) a n d
An gles (d eg) for 20a
Rh-P1
P1-C1
C1-C2
O1-C2
Rh-O1
P1-C4
P1-C10
2.281(3)
1.842(6)
1.505(9)
1.252(6)
2.084(4)
1.814(7)
1.823(6)
Rh-P2
Rh-C3
P2-C22
P2-C28
P2-C34
O2-C3
C2-C16
2.343(3)
1.788(7)
1.814(6)
1.812(6)
1.816(6)
1.144(9)
1.451(8)
Rh-P1
2.272(4)
2.402(9)
1.853(12)
1.819(11)
1.223(14)
1.827(12)
1.53(2)
1.38(2)
1.54(2)
1.54(2)
1.53(2)
Rh-P2
2.406(4)
2.127(11)
1.998(11)
1.811(12)
1.836(11)
1.840(11)
1.48(2)
1.37(2)
1.52(2)
1.46(2)
1.55(2)
Rh-O
Rh-M1
Rh-M2
P1-C9
P1-C1
P1-C3
O-C2
P2-C21
P2-C33
C2-C15
C42-C43
C41-C42
C43-C44
C44-C45
P2-C27
C1-C2
C39-C40
C40-C41
C39-C44
C41-C45
P1-Rh-O1
P2-Rh-C3
Rh-P1-C1
P1-C1-C2
O1-C2-C1
Rh-O1-C2
O1-C2-C16
C1-P1-C4
C1-P1-C10
C4-P1-C10
C22-P2-C34
82.1(1)
94.8(3)
P1-Rh-C3
P2-Rh-O1
Rh-P1-C4
Rh-P1-C10
Rh-P2-C22
Rh-P2-C28
Rh-P2-C34
Rh-C3-O2
C1-C2-C16
C22-P2-C28
C28-P2-C34
93.5(2)
89.1(1)
100.3(2)
111.6(4)
118.3(5)
124.7(3)
119.2(5)
106.1(3)
105.9(3)
104.8(3)
102.4(3)
121.6(2)
116.7(2)
112.1(2)
105.3(2)
123.1(2)
176.5(6)
122.5(5)
105.7(3)
106.9(3)
M1-Rh-M2
O-Rh-M1
P2-Rh-M1
P1-Rh-M2
P1-Rh-O
Rh-P1-C9
Rh-P1-C1
C1-P1-C9
68.7(4)
104.1(4)
98.6(3)
97.5(3)
76.9(2)
O-Rh-M2
126.0(4)
146.1(3)
87.1(2)
163.9(3)
97.4(1)
P2-Rh-M2
P2-Rh-O
P1-Rh-M1
P1-Rh-P2
121.9(4)
106.6(4)
105.6(5)
111.1(4)
116.8(4)
102.5(5)
120.6(8)
120.1(10)
120.0(11)
106.0(11)
100.7(10)
106.9(12)
100.4(10)
100.4(9)
Rh-P1-C3
116.1(4)
100.5(5)
104.4(5)
117.9(4)
104.1(5)
102.6(5)
111.8(8)
119.9(10)
105.1(10)
100.0(9)
101.7(9)
105.7(11)
105.1(10)
91.6(10)
C3-P1-C9
C1-P1-C9
together with the atom-numbering scheme; selected
bond distances and angles are given in Table 10. The
Rh atom displays a slightly distorted square planar
coordination involving a phosphorus atom from the PPh3
ligand (Rh-P2 ) 2.343(3) Å), a carbon atom from a
terminal carbonyl group (Rh-C3 ) 1.788(7) Å), and the
phosphorus and the oxygen atoms from the chelating
Ph2PCH2C(O)Ph ligand (Rh-P1 ) 2.281(3) Å and Rh-
O1 ) 2.084(4) Å). The chelating ligand forms a five-
membered ring with the metal in which the P-C-C-O
moiety is roughly planar and the Rh atom deviates
remarkably from the mean plane passing through the
four atoms (0.331(2) Å). The bite angle, 82.1(1)°, is
comparable to those found in octahedral Rh(III), Co(III),
and Ru(II) complexes with the same ligand (in the 82.0-
82.6° range).1,31 The values of the C1-C2 and C1-P1
bond distances in the chelate ring (1.505(9) and 1.842-
(6) Å) are in agreement with single-bond character and
that of the C2-O1 bond (1.252(6) Å) with an appreciable
double-bond character.
[Rh (NBD)(P kO)(P P h 3)][P F 6] (20) (A.T., F .U). A
view of the structure of complex 20 is shown in Figure
4 together with the atom-numbering scheme; selected
bond distances and angles are given in Table 11. The
Rh center can be considered five-coordinate if the M1
and M2 midpoints of the two olefinic bonds of the NBD
ligand are taken as coordination sites (Rh-M1 ) 2.127-
(11) Å and Rh-M2 ) 1.998(11) Å). The coordination
also involves the P atom from the PPh3 ligand (Rh-P2
) 2.406(4) Å) and the phosphorus and the oxygen atoms
from the chelating Ph2PCH2C(O)Ph ligand (Rh-P1 )
2.272(4) Å and Rh-O1 ) 2.402(4) Å). The Rh-O
distance is much longer than those in 3 or 6. The
geometry around the Rh atom can be described as
intermediate between square pyramidal (with the O
atom occupying the apical position) and trigonal pyra-
midal (with P1 and M1 occupying the apical posi-
tions), both severely distorted. The chelating ligand
forms with the metal a five-membered ring in which the
P-C-C-O moiety is roughly planar and the Rh atom
deviates remarkably from the mean plane passing
through the four atoms (0.557(2) Å). The bite angle of
76.9(2)° is narrower than those of 82.0-82.6° found in
square-planar 3 and 6 or octahedral Rh(III) and Ru(II)
complexes. The C1-C2 and C1-P1 bond distances in
the chelating ligand of 1.529(16) and 1.853(12) Å are
practically equal to those found in 6, whereas the C2-O
distance of 1.223(14) Å is significantly shorter.
Rh-P2-C33
Rh-P2-C21
C21-P2-C33
Rh-O-C2
Rh-P2-C27
C27-P2-C33
C21-P2-C27
P1-C1-C2
O-C2-C1
C1-C2-C15
C40-C39-C44
C40-C41-C45
C42-C41-C45
C42-C43-C44
C43-C44-C45
C41-C45-C44
O-C2-C15
C39-C40-C41
C40-C41-C42
C41-C42-C43
C39-C44-C43
C39-C44-C45
a
M1 and M2 are the midpoints of the two olefinic C42-C43
and C39-C40 bonds.
Con clu d in g Rem a r k s
The formation of P-C coupling products is observed
when the lithium enolates derived from acetone and
acetophenone are reacted with Ph2PCl and i-Pr2PCl,
thus extending the previously reported reaction of
enolates acting as C-nucleophiles toward chlorophos-
phines. This provides a general synthesis of â-keto
phosphine ligands. Neutral and cationic rhodium(I)
complexes with two keto phosphines were inactive in
the hydrogenation of hexene. Their deprotonation led
to decomposition. Neutral mixed-ligand complexes with
one keto phosphine provided access to cationic com-
plexes active in catalytic hydrogenation and to enolate
complexes active in the transfer hydrogenation under
a hydrogen atmosphere between an alkane and an
olefin. The observation that strongly electron donating
ligands disfavor alkane activation in this system seems
to indicate that an elementary oxidative-addition
type step is not rate-determining in this process. The
14-electron species Rh{Ph2PCH‚ ‚C(‚ ‚O)Ph}L1 (L1
phosphine) has been proposed as an important inter-
mediate in the catalytic cycle.
)
Exp er im en ta l Section
All operations were performed in Schlenk-type flasks under
high-purity argon (Air Liquide). Solvents (Analytical Grade)
were dried and distilled under argon: toluene, diethyl ether,
and THF from sodium/benzophenone, pentane and heptane
from sodium/potassium alloy, dichloromethane and chloroform
over P2O5, ethanol from Mg(OEt)2, acetone from B2O3,52 and
acetonitrile from CaH2. Nitromethane was only degassed.
Elemental analyses (C, H, Cl, P) were performed by the
Institut Franc¸ais du Pe´trole and Pascher, Regensburg, Ger-
(52) Burfield, D. R.; Smithers, R. H. J . Org. Chem. 1978, 43, 3966.

5564 Organometallics, Vol. 15, No. 26, 1996
Braunstein et al.
many. IR spectra were recorded in the 4000-200 cm-1 region
on a Perkin-Elmer 883 infrared photospectrometer. Samples
were prepared as Nujol mulls, CsI or KBr pellets, or solutions
using CaF2 cells. 1H NMR spectra were recorded at 200 MHz
on an FT Bruker AC-F 200 instrument and the 31P{1H} NMR
spectra at 81 MHz on an FT Bruker CXP 200 instrument.
Chemical shifts (in ppm) are positive downfield relative to
(polychlorotrifluoroethylene): 3063 w, 1523 w ν(CdC), 1667 s
ν(CdO) cm-1 1H NMR (C7D8, 350 K): δ 8.3-7.0 (15H, m, Ph),
.
4.04 (2H, d, 2J (PH) 10.7 Hz, PCH2), 3.12 (4H, s, C2H4). 1H
NMR (C7D8, 230 K): 3.87 (2H, d, 2J (PH) 9.8, PCH2), 3.30 (2H,
br s, CH2d), 2.43 (2H, br s, CH2d). 31P{1H} NMR (C7H8/
C6D6): δ 47.4 (d, J (RhP) 189.2 Hz).
[Rh Cl{P h 2P CH2C(O)P h }{P h 2P CH2C(O)P h }] (2). Tolu-
ene (5 mL) was added with stirring to a mixture of L (0.30 g,
0.99 mmol) and [Rh(µ-Cl)(C2H4)2]2 (0.096 g, 0.24 mmol). The
solution changed color immediately to yellow, and bubbles
appeared. Upon addition of pentane a yellow solid precipi-
tated, which was collected by filtration, recrystallized from
toluene/CH2Cl2/pentane, and dried in vacuo (0.254 g, 70%).
Anal. Found: C, 64.1; H, 4.5. Calcd for C40H34ClO2P2Rh: C,
1
external SiMe4 for H and to external 85% H3PO4 in water for
31P{1H} NMR spectra.
The complexes [RhCl(PPh3)3],53 [RhCl(CO)(PPh3)2],54 [Rh-
57
(µ-Cl)(NBD)]2,55 [Rh(µ-Cl)(COE)2]2,56 [Rh(µ-Cl)(C2H4)2]2 and
58
[Ir(µ-Cl)(COE)2]2 were prepared according to published pro-
cedures. TlPF6 was prepared under argon by reacting TlOH
(from Tl2SO4 and BaOH) with [NH4]PF6. The phosphines
PMePh2, P-i-Pr2Cl, and PPh2Cl were distilled before use.
Triphenylphosphine was recrystallized from EtOH and stored
under argon. Lithium was obtained from Metallgesellschaft.
Chloroacetone was distilled before use. 1-Hexene (Aldrich)
was freed from peroxides by passage through an alumina
column. Cyclooctane and norbornene (solution in cyclooctane)
were distilled from sodium prior to use. Ph2PCH2C(O)Ph was
prepared by the method previously described and recrystal-
lized from THF-pentane.6
64.3; H, 4.6. IR (CsI): 1674 s ν(CdO)uncoord, 1575 m ν(CdO)coord
,
322 m ν(RhsCl) cm-1
.
1H NMR (CD2Cl2): δ 8.3-7.0 (30H, m,
2
2
Ph), 5.42 (2H, d, J (PH) 5.37 Hz, PCH2), 4.86 (2H, d, J (PH)
12.2 Hz, PCH2). 31P{1H} NMR (CH2Cl2/CD2Cl2): δ 42.4 (1 P,
dd, 1J (RhP) 125 Hz, 2J (PP) 24 Hz, PkO), 35.8 (1 P, dd, 1J (RhP)
2
119.5 Hz, J (PP) 24 Hz, P∼O).
cis-[Rh {P h 2P CH2C(O)P h }2][P F 6] (3). Solid TlPF6 (0.400
g, 1.1 mmol) was added to a stirred solution of 2 (0.33 g, 0.44
mmol) in CH2Cl2 (10 mL). Overnight the color changed from
dark brown to red. The turbid solution was filtered over Celite
and evaporated to ca. 2 mL, and layering with ether yielded
red crystals (0.35 g, 94%). Anal. Found: C, 55.8; H, 4.1.
Calcd for C40H34F6O2P3Rh: C, 56.1; H, 4.0. IR (THF): 1565
P h 2P CH2C(O)Me. Following a method similar to the
synthesis of Ph2PCH2C(O)Ph but starting from acetone (90
mmol), a clear yellow liquid was obtained (bp 140 °C at 0.04
mmHg, yield 8.7 g, 40%). Anal. Found: C, 74.5; H, 6.4. Calcd
for C15H15OP: C, 74.35; H, 6.24. IR (C6H6): 1700 s ν(CdO)
cm-1 1H NMR (CD2Cl2): δ 7.7-7.3 (10H, m, 2 Ph), 3.29 (2H,
.
vs ν(CdO) cm-1 1H NMR (CD2Cl2): δ 8.25-7.18 (30H, m, Ph),
.
s, PCH2), 2.17 (3H, s, CH3); lit.10a in C6H6 3.05 (2H, s, PCH2).
31P{1H} NMR (C7H8/C6D6): δ -20.2.
4.30 (4H, d, 2J (PH) 10.7 Hz, PCH2). 31P{1H} NMR (THF/THF-
d8): δ 57.5 (2P, d, 1J (RhP) 190.8 Hz), -142.3 (1P, sept, 1J (PF)
705 Hz, PF6).
P h 2P CH2C(O)-t-Bu was synthesized in a manner analo-
gous to that for L, starting from methyl tert-butyl ketone (90
mmol): white solid (11.5 g, 45%). Anal. Found: C, 76.1; H,
7.5. Calcd for C18H21OP: C, 76.0; H, 7.4. IR (CH2Cl2): 1696
[Rh {P h 2P CH‚ ‚C(‚ ‚O)P h }(THF )2] (4). Solid TlPF6 (0.15
g, 0.43 mmol) was added to a red solution of 1 (0.16 g, 0.18
mmol) in THF (20 mL). After 15 h the dark red solution was
filtered over Celite and analyzed only by 31P{1H} NMR and
IR spectroscopic methods. Satisfactory analyses could not be
obtained for stability reasons. A sample was evaporated to
dryness and dissolved in C6D6. IR (THF): 1520 s ν(C‚ ‚O) +
s ν(CdO) cm-1
.
1H NMR (CD2Cl2): δ 7.5-7.3 (10H, m, Ph),
3.36 (2H, s, PCH2), 1.10 (9H, s, C(CH3)3). 31P{1H} NMR (C7H8/
C6D6): δ -21.6.
i-P r 2P CH2C(O)P h was synthesized in a manner analogous
to that for L, starting from acetophenone and P-i-Pr2Cl
(89 mmol): yellow liquid (bp 105-120 °C at 0.002-0.005
mmHg), 12.6 g, 60%. Anal. Found: C, 71.2; H, 9.0. Calcd
for C14H21OP: C, 71.2; H, 9.0. IR (CH2Cl2): 1670 s ν(CdO)
ν(C‚ ‚C) cm-1 1H NMR (C6D6): δ 8.4-6.7 (15H, m, Ph), 5.22
.
(1H, d, 2J (PH) 3.9 Hz, PCH), 3.68 (4H, br, THF), 1.81 (4H, br,
1
THF). 31P{1H} NMR (THF/C6D6): δ 47.6 (1P, d, J (RhP) 184
Hz).
cm-1 1H NMR (CD2Cl2): δ 8.05-7.95 (2H, m, meta), 7.6-7.4
.
tr a n s-[Rh Cl{P h 2P CH2C(O)P h }(CO)(P P h 3)] (5). To solid
[RhCl(CO)(PPh3)2] (0.22 g, 0.32 mmol) and L (0.10 g, 0.34
mmol) was added toluene (25 mL) to give a yellow solution.
After it was stirred for 10 min, the solution was filtered and
concentrated and pentane added to precipitate a yellow
powder. It was washed with pentane and recrystallized at -20
°C from toluene/pentane to yield 5 (0.22 g, 95%). Anal.
Found: C, 64.1; H, 4.6; Cl, 4.8. Calcd for C39H32ClO2P2Rh:
C, 63.9; H, 4.4; Cl, 4.8. IR (CsI): 1974 vs ν(CtO), 1672 s ν-
(CdO), 302 m ν(RhsCl). IR (CHCl3): 1977 vs ν(CtO), 1671
(3H, m, ortho and para), 3.12 (2H, d, J (PH) 1.34, PCH2), 1.85
(2H, m, CH(CH3)2), 1.17-1.06 (12H, m, CH(CH3)2). 31P{1H}
NMR (C7H8/C6D6): δ 5.2.
P h 2P CH2C(O)(p-C6H4F ) was synthesized as described in
ref 6 for L, starting from (p-fluorophenyl)acetophenone (103
mmol): white solid; 13.2 g, 45%. Anal. Found: C, 74.1; H,
5.3. Calcd for C20H16FOP: C, 74.5; H, 5.0. IR(CH2Cl2): 1670
s ν(CdO), 1595 s, 1506 ms, 1480 m cm-1 1H NMR (CD2Cl2):
.
δ 7.5-7.3 (14H, m, aromatic), 3.79 (2H, s, PCH2). 31P{1H}
NMR (CD2Cl2): δ -19.2.
s ν(CdO) cm-1
.
1H NMR (CDCl3): δ 7.9-7.2 (30H, m, Ph),
[Rh (µ-Cl){P h 2P CH2C(O)P h }(C2H4)]2 (1). A suspension of
[Rh(µ-Cl)(C2H4)2]2 (1.27 g, 3.27 mmol) and L (1.99 g, 6.54
mmol) in pentane (70 mL) was stirred overnight. The solid
was filtered off and washed with pentane. Recrystallization
from toluene/pentane yielded an orange powder (2.77 g, 90%).
4.49 (2H, s, PCH2). 31P{1H} NMR (CH2Cl2/CD2Cl2): AB part
1
of an ABX pattern (X ) Rh), δ 26.6 (dd, 1 P, J (RhP) 127 Hz,
2
2J (PP) 387 Hz), 21.6 (dd, 1 P, J (RhP) 130 Hz, J (PP) 387 Hz).
[Rh {P h 2P CH2C(O)P h }(CO)(P P h 3)][P F 6] (6). A solution
of L (0.177 g, 0.58 mmol) in CH2Cl2 (10 mL) was added with
stirring to a solution of [RhCl(CO)(PPh3)2] (0.40 g, 0.58 mmol)
in CH2Cl2 (7.5 mL) and acetone (10 mL). After 10 min, TlPF6
(0.203 g, 0.58 mmol) was added and the solution changed color
from yellow to red while a precipitate of TlCl appeared
overnight. Filtration, concentration, and layering with EtOH
(4 mL) and ether (30 mL) yielded orange crystals (0.480 g,
Anal. Found: C, 55.7; H, 4.4; Cl, 7.2; P, 6.7. Calcd for C44H42
-
Cl2O2P2Rh2: C, 56.1; H, 4.5; Cl, 7.5; P, 6.6. IR (CsI): 1665 vs
ν(CdO), 1522 w ν(CdC), 272 m and 258 m ν(RhsCl). IR
(53) Osborn, J . A.; J ardine, F. H.; Young, J . F.; Wilkinson, G. J .
Chem. Soc. A 1966, 1711.
(54) Stephenson, T. A.; Wilkinson, G. J . Inorg. Nucl. Chem. 1966,
28, 945.
98%). Anal. Found: C, 55.6; H, 3.7; P, 10.5. Calcd for C39H32
-
(55) Abel, E. W.; Bennett, M. A.; Wilkinson, G. J . Chem. Soc. 1959,
3178.
F6O2P3Rh: C, 55.6; H, 3.8; P, 11.0. IR (KBr): 1995 vs ν(CtO),
1555 vs ν(CdO), 845 vs ν(PF) cm-1
.
1H NMR (CD2Cl2): δ
(56) Hoffmann, P.; Meier, C.; Englert, U.; Schmidt, M. U. Chem.
Ber. 1992, 125, 353.
(57) Cramer, R. Inorg. Chem. 1962, 1, 722.
(58) van der Ent, A.; Onderdelinden, A. L. Inorg. Synth. 1990, 28,
90.
7.35-7.9 (30H, m, Ph), 4.63 (2H, d, 2J (PH) 10.3 Hz, PCH2).
31P{1H} NMR (CD2Cl2): AB part of an ABX pattern (X ) Rh),
δ 44.7 (1P, dd, 1J (RhP) 120 Hz, 2J (PP) 296 Hz, PkO),

Rh(I) and Ir(I) Complexes with Phosphines
Organometallics, Vol. 15, No. 26, 1996 5565
1
2
29.9 (1P, dd, J (RhP) 132, J (PP) 296 Hz, PPh3), -144 (sept,
δ 8.1-7.25 (27H, m, aromatic), 5.09 (1H, dd, 2J (PH) ) 3J (RhH)
) 2 Hz, PCH), 2.36 (9H, s, Me). 31P{1H} NMR (CH2Cl2/C6D6):
1
1 P, J (PF) 705 Hz, PF6).
1
AB part of an ABX pattern (X ) Rh), δ 41.1 (1P, dd, J (RhP)
[Rh {P h 2P CH‚ ‚C(‚ ‚O)P h }(CO)(P P h 3)] (7). A solution
of L (0.031 g, 0.10 mmol) in toluene (5 mL) was added to a
suspension of [RhCl(CO)(PPh3)2] (0.069 g, 0.10 mmol) in
toluene (5 mL). After the mixture was stirred for 10 min,
NaOMe/MeOH (1.5 mL, 0.1 mmol) was added; the solution
became turbid due to precipitation of NaCl. After 15 min the
solution was concentrated, NaCl was filtered off (through
Celite), and the product was precipitated and washed with
pentane: yellow powder; 0.055 g, 80%. Anal. Found: C, 67.5;
H, 4.0. Calcd for C39H31O2P2Rh: C, 67.3; H, 4.5. IR (KBr):
1956 vs ν(CtO), 1513 s ν(C‚ ‚O) + ν(C‚ ‚C). IR (C7H8): 1960
2
1
134 Hz, J (PP) 300 Hz, PCH), 23.4 (1P, dd, J (RhP) 131 Hz,
2J (PP) 300 Hz, P(o-tolyl)3)).
[Rh {P h 2P CH‚ ‚C(‚ ‚O)P h }(CO){P (p-tolyl)P h 2}]
(12).
This complex was prepared similarly to 11, starting from [Rh-
(µ-Cl)(COE)2]2 (0.359 g, 0.5 mmol), PPh2(p-tolyl) (0.316 g, 1
mmol), and L (0.304 g, 1 mmol) in toluene (10 mL). IR showed
ν(CtO) at 1973 and ν(CdO) at 1672 cm-1, respectively. Then
NaOMe (2.2 mL of a 0.46 M MeOH solution) was added.
Evaporation, addition of CH2Cl2 and heptane, filtration, and
concentration yielded on standing at -20 °C yellow crystals
(0.625 g, 88%). Anal. Found: C, 67.5; H, 4.6. Calcd for
vs ν(CtO), 1514 s ν(C‚ ‚O) + ν(C‚ ‚C) cm-1
.
1H NMR (C6D6,
295 K): δ 8.1-6.9 (30H, m, Ph), 5.31 (1H, overlaping dd,
2J (PH) ) 3J (RhH) ) 2.2 Hz, PCH). 31P{1H} NMR (THF/C7D8,
200 K): AB part of an ABX pattern (X ) Rh), δ 42.0 (1P, dd,
1J (RhP) 127.7 Hz, 2J (PP) 301 Hz), 26.0 (1P, dd, 1J (RhP) 136.5
C
40H33O2P2Rh: C, 67.6 H, 4.7. IR(CD2Cl2): 1958 vs ν(CtO),
1514 s ν(C‚ ‚O) + ν(C‚ ‚C) cm-1 1H NMR (CD2Cl2): δ 7.84-
.
2
3
7.17 (29H, m, aromatic), 5.19 (1H, dd, J (PH) ) J (RhH) ) 2
Hz, PCH), 2.39 (3H, s, Me). 31P{1H} NMR (CH2Cl2/CD2Cl2):
Hz, PPh3). 31P{1H} NMR (295 K): δ 41.1 (1P, d, J (RhP) 131
AB part of an ABX pattern (X ) Rh), δ 41.9 (1P, dd, J (RhP)
1
1
2
1
Hz, PCH), 26.6 (s br, PPh3).
128 Hz, J (PP) 305 Hz, PCH), 28.2 (1P, dd, J (RhP) 136 Hz,
2J (PP) 305 Hz, PPh2(p-tolyl)).
tr a n s-[Rh Cl{P h 2P CH2C(O)P h }2(CO)] (8). A mixture of
[Rh(µ-Cl)(COE)2]2 (0.180 g, 0.25 mmol) and L (0.304 g, 1 mmol)
was stirred in toluene (25 mL). Under CO the red solution
became green. It was filtered and concentrated, and the
product was precipitated with pentane. Recrystallization from
THF/Et2O yielded yellow-green crystals (0.349 g, 90%). Anal.
Found: C, 63.6; H, 4.6. Calcd for C41H34ClO3P2Rh: C, 63.5;
H, 4.4. IR (CsI): 1980 vs ν(CtO), 1666 s ν(CdO), 300 m ν-
[Rh {P h 2P CH‚ ‚C(‚ ‚O)P h }(CO){P (p-C6H4F )3}]
(13).
This complex was prepared similarly to 11, starting from [Rh-
(µ-Cl)(COE)2]2 (0.359 g, 0.5 mmol), P(p-C6H4F)3 (0.316 g, 1
mmol), and L (0.304 g, 1 mmol) in toluene (10 mL). IR showed
ν(CtO) at 1978 and ν(CdO) at 1678 cm-1, respectively. Then
NaOMe (2.2 mL of a 0.46 M MeOH solution) was added.
Evaporation, washing of the residue with pentane, addition
of CH2Cl2 and heptane, filtration, and slow evaporation under
a stream of argon yielded an oil, which crystallized at -20
°C: yellow crystals; 0.675 g, 90%. Anal. Found: C, 62.1; H,
4.2. Calcd for C39H28F3O2P2Rh: C, 62.4; H, 3.8. IR (CD2Cl2):
(RhsCl). IR (CD2Cl2): 1970 vs ν(CtO), 1670 s ν(CdO) cm-1
.
1H NMR(CD2Cl2): δ 7.95-7.3 (30H, m, Ph), 4.46 (4H, virtual
t, 2+4J (PH) 7.3 Hz, PCH2). 31P{1H} NMR (THF, C6D6): δ 21.1
1
(2P, d, J (RhP) 128 Hz).
1961 vs ν(CtO), 1516 s ν(C‚ ‚O) + ν(C‚ ‚C) cm-1
.
1H NMR
[Rh {P h 2P CH2C(O)P h }{P h 2P CH2C(O)P h }(CO)][P F6] (9).
Solid TlPF6 (0.075 g, 0.21 mmol) was added to a solution of 8
(0.16 g, 0.21 mmol) in CH2Cl2 (20 mL). After being stirred for
15 h, the turbid solution was filtered over Celite, evaporated
to ca. 3 mL, and layered with ether to yield orange crystals
(CD2Cl2): δ 7.84-7.11 (27H, m, aromatic), 5.21 (1H, s, PCH).
31P{1H} NMR (CH2Cl2/CD2Cl2): δ 42.2 (1P, dd, 1J (RhP) 129
Hz, 2J (PP) 307 Hz, PCH), 25.6 (1P, dd, 1J (RhP) 137 Hz, 2J (PP)
307 Hz, P(p-C6H4F)3).
(0.17 g, 90%). Anal. Found: C, 55.6; H, 3.7. Calcd for C41H34
-
tr a n s-[Rh Cl{P h 2P CH2C(O)P h }(P P h 3)2] (14). A solution
of L (0.030 g, 0.10 mmol) in toluene (5 mL) was added to a
suspension of [RhCl(PPh3)3] (0.092 g, 0.1 mmol) in toluene (5
mL). Upon stirring and gentle heating a red solution was
obtained and characterized spectroscopically. Complex 14 is
unstable and could not be isolated pure. IR (CsI): 1672 s ν-
F6O3P3Rh: C, 55.7; H, 3.9. IR (CsI): 1993 vs ν(CtO), 1678 s,
1561 vs ν(CdO), 840 vs ν(PF). IR (CD2Cl2): 2005 vs ν(CtO),
1675 s, 1555 vs ν(CdO) cm-1
.
1H NMR (CD2Cl2, 295 K): δ
2
3
7.9-7.3 (30H, m, Ph), 4.48 (4H, dd, J (PH) ) J (RhH) ) 4.0
Hz, PCH2). 31P{1H} NMR (CD2Cl2, 295 K): δ 32.5 (2P, d,
1J (RhP) 128 Hz), -144 (sept, 1 P, J (PF) 705 Hz, PF6).
(CdO), 320 m ν(RhsCl). IR (C7H8): 1670 s ν(CdO) cm-1. H
1
1
NMR (C6D6): δ 7.9-7.2 (45H, m, Ph), 4.45 (2H, m br, PCH2).
[Rh {P h 2P CH‚ ‚C(‚ ‚O)P h }(CO){P h 2P CH2C(O)P h }] (10).
NaOMe (0.35 mL of a 0.46 M MeOH solution) was added to a
stirred solution of 8 (0.125 g, 0.16 mmol) in THF (10 mL). After
15 min the solution was concentrated, filtered, and layered
with pentane. Yellow crystals grew overnight (0.10 g, 86%).
Anal. Found: C, 66.9; H, 4.5. Calcd for C41H33O3P2Rh: C,
66.7; H, 4.5. IR (CD2Cl2): 1960 vs ν(CtO), 1668 m ν(CdO),
1
31P{1H} NMR (C7H8/C6D6): δ 46.0 (1 P, dt, J (RhP) 189.9 Hz,
1
2
PCH2 trans to Cl), 29.2 (2 P, dd, J (RhP) 144 Hz, J (PP) 37.8
Hz, PPh3).
[Rh {P h 2P CH2C(O)P h }(P P h 3)2][P F 6] (15). To a solution
of [RhCl(PPh3)3] (0.688 g, 0.74 mmol) in acetone (5 mL) was
added a solution of L (0.226 g, 0.74 mmol) in acetone/CH2Cl2
(5:7 mL). After the mixture was stirred for 5 min, TlPF6 (0.260
g, 0.74 mmol) was added and a precipitate of TlCl formed
overnight. The solution was decanted, filtered over Celite, and
evaporated to a small volume. Addition of EtOH and ether
yielded red crystals. These were recrystallized from CH2Cl2/
EtOH/ether: 0.717 g, 90. Anal. Found: C, 62.3; H, 4.2; P,
11.6. Calcd for C56H47F6OP4Rh: C, 62.5; H, 4.4; P, 11.5. IR
(KBr): 1570 s ν(CdO), 850 vs ν(PF). IR (CH2Cl2): 1565 s
1512 s ν(C‚ ‚O) + ν(C‚ ‚C) cm-1
.
1H NMR (CD2Cl2): δ 8.1-
2 3
7.25 (30H, m, Ph), 5.18 (1H, ddd, J (PH) 2.8 Hz, J (RhH) 0.4
Hz, 4J (PH) 1.5 Hz, PCH), 4.44 (ddd, 2H, 2J (PH) 9.0 Hz,
3J (RhH) 0.6 Hz, 4J (PH) 1.9 Hz, PCH2). 31P{1H} NMR
(CH2Cl2/CD2Cl2): AB part of an ABX pattern (X ) Rh), δ 39.4
1
2
(1P, dd, J (RhP) 130 Hz, J (PP) 313 Hz, PCH), 19.5 (1P, dd,
1J (RhP) 140 Hz, J (PP) 313 Hz, PCH2).
2
[Rh {P h 2P CH‚ ‚C(‚ ‚O)P h }(CO){P (o-tolyl)3}] (11).
A
ν(CdO) cm-1
.
1H NMR (CD2Cl2): δ 7.7-6.9 (45H, m, Ph), 4.12
red solution of [Rh(µ-Cl)(COE)2]2 (0.179 g, 0.25 mmol), P(o-
tolyl)3 (0.152 g, 0.5 mmol), and L (0.152 g, 0.5 mmol) in THF
(10 mL) was stirred under CO until it became green. IR
showed ν(CtO) at 1968 and ν(CdO) at 1672 cm-1, respectively.
Then NaOMe (0.34 mL of a 0.46 M MeOH solution) was added.
Evaporation, dissolution in a minimum of toluene, filtration,
evaporation, and addition of CH2Cl2 and heptane yielded, on
evaporation, yellow crystals. These were washed with a small
amount of pentane (0.325 g, 88%). Anal. Found: C, 68.1; H,
5.2. Calcd for C42H37O2P2Rh: C, 68.3 H, 5.0. IR (CDCl3): 1956
(2H, d, 2J (PH) 9.28 Hz, PCH2). 31P{1H} NMR (CH2Cl2/CD2-
1
2
Cl2): δ 51.2 (1P, dt, J (RhP) 188.2 Hz, J (PP) 35.6 Hz, PPh3
cis to PCH2), 47.3 (1P, ddd, 1J (RhP) 147.5 Hz, 2J (PP) 35.6,
300.1 Hz, PCH2), 28.8 (1P, ddd, 1J (RhP) 142.4 Hz, 2J (PP) 35.6,
300.1 Hz, PPh3 trans to PCH2), -144 (1 P, sept, 1J (PF) 705
Hz, PF6).
[Rh {P h 2P CH‚ ‚C(‚ ‚O)P h }(P P h 3)2] (16). A solution of L
(0.226 g, 0.74 mmol) in toluene (5 mL) was added to a solution
of [RhCl(PPh3)3] (0.688 g, 0.74 mmol) in toluene (5 mL). After
10 min of stirring NaOMe/MeOH (1.5 mL, 0.74 mmol) was
vs ν(CtO), 1512 s ν(C‚ ‚O)+ ν(C‚ ‚C) cm-1 1H NMR (CDCl3):
.

5566 Organometallics, Vol. 15, No. 26, 1996
Braunstein et al.
added; the solution became turbid due to precipitation of NaCl.
After 15 min the solution was concentrated and NaCl was
filtered off (through Celite). The product was precipitated and
washed with pentane. Recrystallization from CH2Cl2/pentane
yielded orange crystals (0.65 g, 90%). Anal. Found: C, 69.5;
H, 4.9; P, 9.4. Calcd for C56H46OP3Rh‚0.5CH2Cl2: C, 69.7; H,
4.9; P, 9.55. IR (KBr): 1523 s ν(C‚ ‚O) + ν(C‚ ‚C). IR (C7H8):
33 Hz, PCH2), 23.1 (1P, dd, 1J (RhP) 142 Hz, 2J (PP) 33 Hz,
PPh3), -144 (1 P, sept, J (PF) 705 Hz, PF6).
1
[Rh {P h 2P CH‚ ‚C(‚ ‚O)P h }(NBD)] (21). To a stirred sus-
pension of [Rh(µ-Cl)(COE)2]2 (0.232 g, 0.32 mmol) in toluene
(10 mL) was added norbornadiene (0.8 mL) and L (0.197 g,
0.64 mmol). After 10 min, IR spectroscopy showed bands at
1672 s (ν(CdO) of P∼O), 1645 m, and 1545 s cm-1. On addition
of NaOMe/MeOH (1.3 mL of a 0.5 M MeOH solution) the
yellow solution became orange and cloudy due to precipitation
of NaCl. After being stirred for 15 min, the solution was
concentrated, filtered, and taken to dryness. Recrystallization
of the residue from CH2Cl2/heptane yielded 0.214 g (66%) of
air-sensitive orange crystals. Anal. Found: C, 64.8; H, 4.95.
Calcd for C27H24OPRh: C, 65.1; H, 4.85. IR(CH2Cl2): 1510 s
1515 s ν(C‚ ‚O) + ν(C‚ ‚C) cm-1
.
1H NMR (C6D6): δ 7.8-6.7
(45H, m, Ph), 5.20 (1H, d, 2J (PH) 3.2 Hz, PCH). 31P{1H} NMR
(CH2Cl2/C6D6): values from spectral simulation (PANIC Bruk-
er), δ 49.8 (1P, dt, 1J (RhP) 174, 2J (PP) 38 Hz, PPh3 cis to PCH),
1
2
39.2 (1P, ddd, J (RhP) 149 Hz, J (PP) 304, 38 Hz, PCH), 30.3
(1P, ddd, 2J (PP) 304, 38 Hz, 1J (RhP) 147 Hz, PPh3 trans to
PCH).
ν(C‚ ‚O) + ν(C‚ ‚C) cm-1
.
1H NMR (CD2Cl2): δ 7.78-7.28
[Rh {P h 2P CHC(O)(p-C6H4F )}(P P h 3)2] (17). As for 16
starting from Ph2PCH2C(O)(p-C6H4F) (0.13 g, 0.40 mmol),
[RhCl(PPh3)3] (0.37 g, 0.40 mmol), and NaOMe (0.8 mL of a
0.5 M MeOH solution). Recrystallization from CH2Cl2/pentane
yielded orange crystals, wich were washed with a small
amount of cold pentane (0.18 g, 48%). Anal. Found: C, 70.7;
H, 4.9. Calcd for C56H45FOP3Rh: C, 70.9; H, 4.8. IR (CD2-
(15H, m, Ph), 5.45 (2H, br, dCH-, NBD), 4.88 (1H, s, PCH),
3.97 (2H, br, CH, NBD), 3.74 (2H, br, dCH, NBD), 1.51 (2H,
m, CH2, NBD). 31P{1H} NMR (CH2Cl2/CD2Cl2): δ 25.0 (d,
1J (RhP) 178 Hz).
[Rh {P h 2P CH‚ ‚C(‚ ‚O)P h }(COD)] (22). This complex
was prepared similarly to 21 using 0.8 mL of cyclooctadiene.
Recrystallization from CH2Cl2/heptane yielded 0.28 g (85%)
of a slightly air-sensitive orange powder. Anal. Found: C,
65.5; H, 5.4. Calcd for C28H28OPRh: C, 65.4; H, 5.5. IR (CH2-
Cl2): 1525 s ν(C‚ ‚O) + ν(C‚ ‚C) cm-1
.
1H NMR (CD2Cl2): δ
7.8-6.7 (44H, m, Ph), 4.75 (1H, s, PCH). 31P{1H} NMR
1
2
(CH2Cl2/C6D6): δ 50.9 (1P, dt, J (RhP) 174 Hz, J (PP) 37 Hz,
1
2
PPh3 trans to O), 40.3 (1P, ddd, J (RhP) 149 Hz, J (PP) 303,
37 Hz, PCH), 30.8 (1P, ddd, 1J (RhP) 149 Hz, 2J (PP) 303, 37
Hz, PPh3 trans to PCH).
Cl2): 1515 s ν(C‚ ‚O) + ν(C‚ ‚C) cm-1
. δ
1H NMR (C6D6):
8.13-6.9 (15H, m, Ph), 5.62 (br, 2H, COD), 5.0 (s, 1H, PCH),
3.71 (br, 2H, dCH), 2.12 (m, 4H, CH2), 1.76 (m, 4H, CH2).
1
31P{1H} NMR (CH2Cl2/CD2Cl2): δ 24.9 (d, J (RhP) 155 Hz).
[Rh Cl{P h 2P CHdC(P h OP P h 2}(P P h 3)] (18). A solution of
commercial PPh2Cl (25.3 µl, 0.14 mmol) and pyridine (one
drop) in THF (5 mL) was added to a stirred solution of 16
(0.122 g, 0.13 mmol) in THF (10 mL). After 1 h, the solution
was filtered and the solvent removed in vacuo. The yellow
precipitate was washed with pentane and recrystallized from
CH2Cl2/pentane (0.087 g, 75%). Anal. Found: C, 67.8; H, 4.4;
Cl, 4.6. Calcd for C50H41ClOP3Rh: C, 67.5; H, 4.65; Cl, 4.0.
[Rh {P h 2P CH‚ ‚C(‚ ‚O)Me}(NBD)] (23). This complex
was prepared similarly to 21 by starting from [Rh(µ-Cl)-
(COE)2]2 (0.334 g, 0.465 mmol) in toluene (15 mL), norborna-
diene (1.5 mL), Ph2PCH2C(O)Me (0.237 g, 0.97 mmol), and
NaOMe/MeOH (2.0 mL). Slow evaporation of a CH2Cl2/
heptane (5:30 mL) solution yielded an air-sensitive orange
powder (0.32 g, 79%). Anal. Found: C, 60.7; H, 4.9. Calcd
IR (C6D6): 1593 m, 1569 m, 1517 w cm-1
.
1H NMR (C6D6): δ
for
C22H22OPRh: C, 60.6; H, 5.1. IR (CH2Cl2): 1520 s
7.8-6.8 (40H, m, Ph), 5.92 (1H, br, PCH). 31P{1H} NMR
ν(C‚ ‚O) + ν(C‚ ‚C) cm-1
.
1H NMR (CDCl3): δ 7.78-7.28
1
2
(10H, m, Ph), 5.39 (2H, br, dCH-, NBD), 4.16 (1H, dd, 2J (PH)
2 Hz, 3J (RhH) 0.7 Hz, PCH), 3.90 (2H, br, CH, NBD), 3.63
(2H, br, dCH, NBD), 2.01 (3H, s, C(O)Me), 1.44 (2H, m, CH2,
NBD). 31P{1H} NMR (CH2Cl2/C6D6): δ 24.9 (d, 1J (RhP) 177
Hz).
(THF/C6D6): δ 151.0 (1P, ddd, J (RhP) 203 Hz, J (PP) 61, 30
Hz, Ph2PO), 30.0 (1P, ddd, 1J (RhP) 137 Hz, 2J (PP) 341, 30 Hz,
PPh3 trans to PCH), 2.6 (1P, ddd, 1J (RhP) 132 Hz, 2J (PP) 341,
61 Hz, PCH).
[Rh {P h 2P C[C(O)P h ]dC(O)NHP h }(P P h 3)2] (19). Phe-
nylisocyanate (0.44 mL, ca. 4 mmol) was added dropwise to a
stirred solution of 16 (0.186 g, 0.2 mmol) in THF (10 mL). After
3 days, the solution was filtered and concentrated and pentane
was added. The precipitate was washed with pentane and
recrystallized from CH2Cl2/pentane: 0.10 g, 50%. Anal.
Found: C, 71.7; H, 4.9; N, 1.6. Calcd for C63H51NO2P3Rh: C,
72.1; H, 4.9; N, 1.3. IR (KBr): 1620 m, 1585 s, 1560 m, 1485
[Rh {P h 2P CH‚ ‚C(‚ ‚O)(p-C6H4F )}(NBD)] (24).
This
complex was prepared similarly to 21 by starting from [Rh-
(µ-Cl)(COE)2]2 (0.35 g, 0.48 mmol) in norbornadiene (4 mL),
Ph2PCH2C(O)(p-C6H4F) (0.338 g, 0.98 mmol) in toluene (10
mL), and NaOMe/MeOH (2.0 mL, 0.5 M). After total evapora-
tion, a CH2Cl2/heptane solution (10 mL/20 mL) was added in
two portions and the solution was filtered through Celite. On
concentration orange crystals formed, which were filtered off
and washed twice with pentane (3 mL each): yield 0.235 g,
48%. Anal. Found: C, 62.5; H, 4.3. Calcd for C27H23FOPRh:
w cm-1 1H NMR (CH2Cl2): δ 10.37 (br, 1H, NH, exchanges
.
with D2O), 8.0-7.0 (50H, m, Ph). 31P{1H} NMR (THF/C6D6):
δ 51.4 (1 P, ddd, 1J (RhP) 148 Hz, 2J (PP) 296, 36 Hz, PC), 49.9
1
2
C, 62.8; H, 4.5. IR (CH2Cl2): 1520 s ν(C‚ ‚O) + ν(C‚ ‚C) cm-1
.
(1 P, dt, J (RhP) 216 Hz, J (PP) 36 Hz, PPh3 trans to O), 29.7
(ddd, 1 P, 1J (RhP) 141 Hz, 2J (PP) 296, 36 Hz, PPh3 trans to
1H NMR (CD2Cl2): δ 7.8-7.0 (14H, m, Ph), 5.43 (2H, br, dCH,
NBD), 4.84 (1H, s, PCH), 3.97 (2H, br, CH, NBD), 3.73 (2H,
br, dCH, NBD), 1.50 (2H, m, CH2, NBD). 31P{1H} NMR
P).
[Rh {P h 2P CH2C(O)P h }(P P h 3)(NBD)][P F 6] (20). To a
solution of [Rh(µ-Cl)(NBD)]2 (1.08 g, 1.16 mmol) in CH2Cl2
was added PPh3 (0.305 g, 1.16 mmol), L (0.353 g, 1.16 mmol),
and TlPF6 (0.407 g, 1.16 mmol). When the mixture was stirred
overnight, a precipitate of TlCl formed, which was filtered off
(Celite). Evaporation to a small volume and layering with
EtOH and ether yielded orange crystals (0.53 g, 85%). Anal.
Found: C, 59.4; H, 4.5; P, 9.9. Calcd for C45H40F6OP3Rh: C,
59.6; H, 4.4; P, 10.3. IR (KBr): 1670 w, 1620 s ν(CdO), 846
1
(CH2Cl2/C6D6): δ 25.1 (d, J (RhP) 178 Hz).
[Rh {iP r 2P CH‚ ‚C(‚ ‚O)P h }(NBD)] (25). This complex
was prepared similarly to 21 by starting from [Rh(µ-Cl)-
(COE)2]2 (0.734 g, 1.02 mmol) in toluene (20 mL), norborna-
diene (2.4 mL), i-Pr2PCH2C(O)Ph (0.483 g, 2.04 mmol) in
toluene (10 mL), and NaOMe/MeOH (4.0 mL, 0.5 M). After
filtration, CH2Cl2 (5 mL) and heptane (30 mL) were added and
some rhodium metal filtered off. The solution was evaporated
to give a dark red oil, which crystallized at -20 °C. Recrys-
tallization from pentane at -20 °C gave red-orange crystals
(0.60 g, 68%). Anal. Found: C, 58.8; H, 6.7. Calcd for
vs ν(PF) cm-1
.
1H NMR (CD2Cl2): δ 8.0-7.2 (30H, m, Ph),
2
3
4.06 (4H, dd, J (RhH) 4.4 Hz, J (HH) 1.9 Hz, CH), 3.92 (2H,
large d, 3J (HH) 1.9 Hz, CH), 3.03 (2H, d, 2J (PH) 9.8 Hz, PCH2),
1.47 (br s, 2H, CH2). 31P{1H} NMR (CD2Cl2): AB part of an
ABX pattern (X ) Rh), δ 29.0 (1P, dd, 1J (RhP) 150 Hz, 2J (PP)
C
21H28OPRh: C, 58.6; H, 6.6. IR (CHCl3): 1521 s ν(C‚ ‚O) +
ν(C‚ ‚C) cm-1 1H NMR (CDCl3): δ 8.05-7.95 (m, 2H, meta),
.

Rh(I) and Ir(I) Complexes with Phosphines
Organometallics, Vol. 15, No. 26, 1996 5567
7.20-7.35 (3H, m, ortho and para), 5.39 (2H, br, dCH-, NBD),
head. A systematic search in reciprocal space using an Enraf-
Nonius CAD4-F automatic diffractometer showed that crystals
of 3‚H2O belong to the triclinic system. Quantitative data were
obtained at room temperature. The resulting data set was
transfered to a VAX computer, and for all subsequent calcula-
tions the Enraf-Nonius Molen package was used.59 Three
standard reflections measured every 1 h during the entire data
collection period showed no significant trend. The raw data
were converted to intensities and corrected for Lorentz and
polarization factors. Absorption corrections derived from the
Φ scans of four reflections were applied. The structure was
solved using the heavy-atom method. After refinement of the
heavy atoms, a difference-Fourier map revealed maximas of
residual electronic density close to the positions expected for
hydrogen atoms; they were introduced in structure factor
calculations by their computed coordinates (C-H ) 0.95 Å)
and isotropic temperature factors such as B(H) ) 1.3Beqv(C)
Å2 but not refined. Full least-squares refinements were carried
2
3
4.38 (1H, t, J (PH) ≈ J (RhH) ) 1 Hz, PCHCO), 3.96 (2H, br,
dCH-, NBD), 3.87 (2H, br), 1.95 (2H, m, CH2, NBD), 1.5 (2H,
m, P(CHMe2)2), 1.30-1.15 (12H, m, P(CHMe2)2). 31P{1H} NMR
1
(CH2Cl2/C6D6): δ 47.7 (d, J (RhP) 167 Hz).
[Ir {P h 2P CH‚ ‚C(‚ ‚O)P h }(COD)] (26). This complex was
prepared similarly to 21 by starting from [Ir(µ-Cl)(COE)2]2
(0.249 g, 0.28 mmol) in toluene (10 mL), cyclooctadiene (0.8
mL), and L (0.169 g, 0.56 mmol) to give an orange solution.
After 10 min NaOMe/MeOH (1.1 mL) was added and the
solution became red. After 10 min the solvent was evaporated,
CH2Cl2 and heptane were added, and the orange solution was
filtered. Slow evaporation and cooling to -20 °C yielded air-
sensitive orange crystals (0.287 g, 85%). Anal. Found: C,
55.6; H, 4.6. Calcd for C28H28OPIr: C, 55.7; H, 4.7. IR (CH2-
Cl2): 1518 s ν(C‚ ‚O) + ν(C‚ ‚C) cm-1
.
1H NMR (CD2Cl2): δ
7.88-7.3 (15H, m, Ph), 5.10 (1H, d, 2J (PH) 2.9 Hz, PCH), 5.08
(2H, br, CH, COD), 3.39 (2H, br, CH, COD), 2.24 (4H, m, CH2,
COD), 1.88 (4H, m, CH2, COD). 31P{1H} NMR (C7H8/C6D6): δ
20.3 (s).
out: σ2(F2) ) σ2
+ (pI)2. A final difference map revealed
counts
no significant maxima. The scattering factor coefficients and
anomalous dispersion coefficients come from ref 60.
X-r a y Cr ysta llogr a p h ic An a lysis of 6 a n d 20. Details
are given in Table 8. No correction for absorption was applied
for 6 and 20 in view of the low absorption coefficient. Only
the observed reflections were used in the structure solution
and refinement. The structures were solved by Patterson and
Fourier methods. The refinements were carried out by full-
matrix least squares with isotropic and then with anisotropic
thermal parameters in the last cycles for all non-hydrogen
atoms. Hydrogen atoms were placed at their geometrically
calculated positions (C-H ) 0.96 Å) and refined “riding” on
[Ir {P h 2P CH‚ ‚C(‚ ‚O)P h }H2(COD)] (27). An orange so-
lution of 26 in CD2Cl2 became colorless by bubbling hydrogen
through it, but a pure solid could not be isolated. 1H NMR
(CD2Cl2): δ 7.88-7.3 (15H, m, Ph), 5.54 (1H, br, dCH, COD),
5.12 (1H, d, J (PH) 4.3 Hz, PCH), 5.02 (1H, br, dCH, COD),
3.80 (1H, br, dCH, COD), 3.58 (1H, br, COD), 2.68 (2H, m,
CH2), 2.4 (2H, m, CH2), 2.08 (4H, m, CH2), -11.03 (1H, d,
J (PH) 18 Hz, IrH trans to olefinic double bond), -18.04 (1H,
d, J (PH) ) 12 Hz, IrH trans to oxygen). 31P{1H} NMR (C6D6/
C7H8): δ 27.6 (s).
Ca ta lysis. Hyd r ogen a tion Rea ction s. The catalytic
reactions were carried out at atmospheric pressure in a
thermostated double-jacketed glass reactor (50 mL). The
catalyst precursor was weighed in. Two vacuum/hydrogen
cycles were applied, and the solvent and 1-hexene were added
by syringe. The solution was stirred with a magnetic stirring
bar, and the clock was started at the same time. The reaction
could be followed by pressure decrease of the hydrogen
reservoir. Samples were taken by a syringe through a septum
and analyzed by GC on a Sil5 or PONA column.
the corresponding carbon atoms. The weighting scheme used
2
in the final cycles of refinement was w ) [σ2(Fo) + gFo
]
-1; at
convergence the K and g values were 0.743 and 0.0068 for 6
and 0.595 and 0.0097 for 20. The atomic scattering factors,
corrected for the real and imaginary parts of anomalous
dispersion, were taken from ref 60. All calculations were
carried out on the Gould Powernode 6040 of the “Centro di
Studio per la Strutturistica Diffrattometrica” del CNR, Parma,
Italy, using SHELX-76 and SHELXS-86 programs.61
The final atomic coordinates for the non-hydrogen atoms
are given in Tables S-I-S-III, respectively. Additional mate-
rial available from the Cambridge Crystallographic Data
Centre comprises H-atom coordinates, thermal parameters,
and complete listings of bond distances and angles.
Tr a n sfer -Deh yd r ogen a tion Rea ction s. Reactions con-
ducted at atmospheric pressure were similar to hydrogena-
tions, using cyclooctane as solvent and an olefin as hydrogen
acceptor. Reactions performed at 0.6-7 MPa pressure were
run in a thermostated double-jacketed stainless-steel autoclave
(100 mL) containing a magnetic stirring bar. In a typical run,
a given quantity of the catalyst precursor was weighed in a
Schlenk flask. Under argon, cyclooctane and a norbornene/
cyclooctane solution were added by syringe with stirring. After
a few minutes of stirring a yellow homogeneous solution
resulted which was transferred via cannula into the thermo-
stated autoclave. After two hydrogen purges (0.5 MPa) to free
the autoclave from argon, it was pressurized with hydrogen.
Consumption of hydrogen was followed by pressure decrease
of the ballast but was not determined with high precision,
product analysis by GC being much more precise and reliable.
Before complete consumption of the hydrogen acceptor, the
autoclave was cooled with dry ice. A sample of the solution
was analyzed by GC on a Sil5 column. Sometimes the
remaining solution was transferred to a Schlenk flask and
evaporated to dryness, the residue dissolved in CD2Cl2, and
Ack n ow led gm en t. We are grateful to the Centre
National de la Recherche Scientifique (CNRS) and the
Institut Franc¸ais du Pe´trole (IFP) for financial support.
J .N. is grateful to Dr. L. Saussine, Dr. D. Commereuc,
and Dr. G. Serpe (all IFP) for fruitful discussions.
Su p p or tin g In for m a tion Ava ila ble: Positional param-
eters for the non-hydrogen atoms (Tables S-I-S-III), positional
parameters for the hydrogen atoms (Tables S-IV-S-VI), tem-
perature factors for anisotropic atoms (Tables S-VII-S-X), and
all bond distances and angles (Tables S-X-S-XII) for complexes
3‚H2O, 6, and 20, respectively (30 pages). Ordering informa-
tion is given on any current masthead page.
OM960814H
1
this solution analyzed by H NMR and IR spectroscopy.
(59) Molen, An Interactive Structure Determination Procedure;
Enraf-Nonius, Delft, The Netherlands, 1990.
X-r a y Cr ysta llogr a p h ic An a lysis of 3‚H2O. Details are
given in Table 8. Suitable single crystals of 3‚H2O were
obtained by slow diffusion of ether in a CH2Cl2 solution at room
temperature. Adventitious water gave rise to crystallization
of the complex as a solvate. A single crystal was cut out from
a cluster of crystals and mounted on a rotation-free goniometer
(60) Cromer, D. T.; Waber, J . T. International Tables for X-ray
Crystallography; Kynoch Press: Birmingham, England, 1974; Vol. IV.
(61) Sheldrick, G. M. SHELX-76, Program for Crystal Structure
Determination’ University of Cambridge, Cambridge, England, 1976.
SHELX-86, Program for the Solution of Crystal Structures; University
of Go¨ttingen, Go¨ttingen, Germany, 1986.