Rhodium complexes based on phosphorus diamide ligands: catalyst structure versus activity and selectivity in the hydroformylation of alkenes

Article abstract of DOI:10.1021/om9910120

The rhodium-catalyzed hydroformylation reaction of 1-octene with phosphorus diamide ligands has been investigated. Four monodentate phosphorus diamide ligands and six bidentate phosphorus diamide ligands derived from a 1,3,5-trisubstituted biuret structure have been synthesized. These types of ligands combine steric bulk with π-acidity. The rhodium complexes formed under CO/H₂ have been characterized by high-pressure spectroscopic techniques. Spectroscopic experiments revealed that the monodentate ligands form mixtures of HRhL₂(CO)₂ and HRhL(CO)₃. The ratio HRhL₂(CO)₂:HRhL(CO)₃ depends on the ligand concentration and its bulkiness. The bidentate ligands form stable, well-defined catalysts with a specified structure under hydroformylation conditions. Both monodentate and bidentate ligands have been tested in the hydroformylation reaction of 1-octene. The monodentate ligands form very active catalysts, but the linear-to-branched ratio of the product is low. The bidentate ligands show improved selectivity compared to the monodentate ligands and an activity that is only slightly lower.

Full text of DOI:10.1021/om9910120

2504
Organometallics 2000, 19, 2504-2515
Rh od iu m Com p lexes Ba sed on P h osp h or u s Dia m id e
Liga n d s: Ca ta lyst Str u ctu r e ver su s Activity a n d
Selectivity in th e Hyd r ofor m yla tion of Alk en es
Saskia C. van der Slot,† Paul C. J . Kamer,† Piet W. N. M. van Leeuwen,*,†
J an Fraanje,† Kees Goubitz,† Martin Lutz,‡ and Anthony L. Spek‡
Institute of Molecular Chemistry, University of Amsterdam, Nieuwe Achtergracht 166,
1018 WV Amsterdam, The Netherlands, and Department of Crystal and Structural Chemistry,
Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
Received December 20, 1999
The rhodium-catalyzed hydroformylation reaction of 1-octene with phosphorus diamide
ligands has been investigated. Four monodentate phosphorus diamide ligands and six
bidentate phosphorus diamide ligands derived from a 1,3,5-trisubstituted biuret structure
have been synthesized. These types of ligands combine steric bulk with π-acidity. The
rhodium complexes formed under CO/H2 have been characterized by high-pressure spec-
troscopic techniques. Spectroscopic experiments revealed that the monodentate ligands form
mixtures of HRhL2(CO)2 and HRhL(CO)3. The ratio HRhL2(CO)2:HRhL(CO)3 depends on
the ligand concentration and its bulkiness. The bidentate ligands form stable, well-defined
catalysts with the structure HRhL∩L(CO)2 under hydroformylation conditions. Both
monodentate and bidentate ligands have been tested in the hydroformylation reaction of
1-octene. The monodentate ligands form very active catalysts, but the linear-to-branched
ratio of the product is low. The bidentate ligands show improved selectivity compared to
the monodentate ligands and an activity that is only slightly lower.
In tr od u ction
The steric properties of the ligand influence the
catalyst activity and selectivity considerably. The results
of van Leeuwen et al.17,18 have shown that ligands with
large cone angles19 form catalysts having the structure
HRhL(CO)3, which are very active hydroformylation
catalysts. The regioselectivity is low because only one
bulky monodentate ligand coordinates to the rhodium
center. An important steric property for bidentate
ligands is the bite angle. The bite angle determines
whether both phosphorus atoms of the bidentate ligand
coordinate at equatorial positions of the trigonal bipyra-
mid (ee) or at an equatorial and at an apical position
(ea). Casey13,15 studied the effect of the bite angle on
the selectivity of the hydroformylation catalyst and
found a correlation between the regioselectivity and the
coordination mode of the bidentate ligand in the trigo-
nal-bipyramidal structure. The studies of van Leeuwen
et al.,16 however, showed that the coordination mode of
a bidentate ligand per se does not determine the
regioselectivity, as both isomers (ee and ea) may form
the same four-coordinate intermediate in the hydro-
formylation cycle. Furthermore, they found that the
Since the first publications concerning hydroformyl-
ation using rhodium complexes, this reaction has been
subject of numerous mechanistic studies.1-12 An impor-
tant aspect has been the unraveling of the structure of
the resting state of the catalyst in order to understand
the outcome of the overall catalytic reaction. Recently
it has been shown that the geometry of the catalyst and
the properties of the ligands coordinated to the metal
center, especially the electronic and steric properties
and the bite angle of bidentate ligands, have a large
effect on the catalyst activity and selectivity.13-16
* To whom correspondence should be addressed. E-mail: pwnm@
anorg.chem.uva.nl.
† University of Amsterdam.
‡ Utrecht University.
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W. G. J .; Kamer, P. C. J .; van Leeuwen, P. W. N. M.; Vogt, D.
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R.; Malter, B. A.; Powell, D. R. J . Am. Chem. Soc. 1999, 121, 63.
(16) van der Veen, L. A.; Boele, M. D. K.; Bregman, F. R.; Kamer,
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H.; Bo, C. J . Am. Chem. Soc. 1998, 120, 11616.
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Organomet. Chem. 1997, 535, 201.
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Organometallics 1997, 16, 1065.
(12) Feng, J .; Garland, M. Organometallics 1999, 18, 417.
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1983, 258, 343.
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nomet. Chem. 1991, 421, 121.
(19) Tolman, C. A. Chem. Rev. 1977, 77, 313.
10.1021/om9910120 CCC: $19.00 © 2000 American Chemical Society
Publication on Web 05/23/2000

Rh Complexes with Phosphorus Diamide Ligands
Organometallics, Vol. 19, No. 13, 2000 2505
Ch a r t 1. Mon od en ta te Biu r et-Ba sed Liga n d
Str u ctu r es
ligand basicity also contributes to the catalyst perfor-
mance. Previous studies,7,20 though neglecting bite angle
effects, showed that ligands with electron-withdrawing
groups lead to more active and selective catalysts.
In an extrapolation of the results of steric and
electronic ligand effects, it seems attractive to design
strongly π-accepting ligands that create steric hindrance
close to the rhodium center. Here we report on several
monodentate and bidentate phosphorus diamides as
ligands in the rhodium-catalyzed hydroformylation of
linear alkenes. These ligands create more steric bulk
close to the phosphorus atom compared to the electron-
withdrawing phosphites because of the higher degree
of substitution at nitrogen compared to oxygen, while
their ø values21 can be in the same range as those of
phosphites. This combination will result in crowded,
electron-poor rhodium catalysts, which might influence
both activity and regioselectivity of the hydroformyla-
tion reaction in a desired way. Several examples are
known of phosphorus diamide ligands used in the
hydroformylation reaction.22-25 The results obtained
with these ligands show improved activity compared to
phosphine systems and improved selectivity compared
to phosphite systems.
Ch a r t 2. Bid en ta te Biu r et-Ba sed Liga n d
Str u ctu r es
We synthesized a series of four monodentate phos-
phorus diamide ligands in order to investigate the
performance of the corresponding catalyst systems in
the hydroformylation reaction. The ligands are based
on a 1,3,5-trisubstituted biuret structure.26 The electron-
withdrawing acyl substituent on the nitrogen atom
stabilizes the phosphorus-nitrogen bond and increases
the π-acidity of the ligand. The solution structures of
the rhodium complexes formed under hydroformylation
conditions were determined. The influence of the cata-
lyst structure on the activity and selectivity in the
hydroformylation reaction was investigated. As the
selectivities of the systems containing monodentate
ligands remained low, we synthesized a series of biden-
tate phosphorus diamide ligands to form well-defined
catalyst systems, aiming at hydroformylation catalysts
that combine regioselectivity with high activity.
Ta ble 1. Con e An gle θ Deter m in ed by th e Use of
Sp a ce-F illin g Mod els
ligand
cone angle θ (deg)a
1a
1b
1c
1d
189
161
148
143
Resu lts a n d Discu ssion
Syn th esis a n d Deter m in a tion of Ster ic a n d Elec-
tr on ic Liga n d P r op er ties. The monodentate ligands
1a ,c (Chart 1) were prepared in a straightforward way
by reaction of phenylphosphorus dichloride with N,N′,N′′-
trisubstituted biuret in the presence of a base. 1b,d were
synthesized in two steps by the reaction of phosphorus
trichloride with N,N′,N′′-trisubstituted biuret followed
by the reaction with the corresponding alcohol in the
presence of a base. The ligands 1a -d could easily be
purified by column chromatography. The ligands are
remarkably stable toward water and oxygen.
a
See ref 19.
The bidentate ligands 2a -d (Chart 2) were prepared
by similar procedures from the chlorophosphorus dia-
mide and the corresponding alcohol. Ligands 2e,f were
synthesized in a clean reaction from the dilithiated
xanthene backbone and the corresponding chlorophos-
phorus diamide. No decomposition of the phosphorus-
amide bond was observed in this reaction. Ligand 2c
was purified by washing with water. The bidentate
ligands 2a ,b,d -f are not stable under these conditions,
and therefore, they were purified by column chroma-
tography.
The cone angles θ of the monodentate ligands 1a -d
were determined by the use of space filling models as
described by Tolman.19 Ligands 1a -d have cone angles
between 143 and 189° (Table 1). θ1a is larger than 180°.
This indicates that there is space for only one ligand
1a in the equatorial plane of a trigonal-bipyramidal
(20) Moser, W. R.; Papile, C. J .; Brannon, D. A.; Duwell, R. A. J .
Mol. Catal. 1987, 41, 271.
(21) Tolman, C. A. J . Am. Chem. Soc. 1970, 92, 2953.
(22) van Rooy, A.; Burger, D.; Kamer, P. C. J .; van Leeuwen, P. W.
N. M. Recl. Trav. Chim. Pays-Bas 1996, 115, 492.
(23) Trzeciak, A. M.; Glowiak, T.; Grybek, R.; Zio´lkowski, J . J . Chem.
Soc., Dalton Trans. 1997, 1831.
(24) Breit, B. J . Mol. Catal. 1999, 143, 143.
(25) Naili, S.; Mortreux, A.; Agbossou, F. Tetrahedron: Asymmetry
1998, 3421.
(26) Mu¨ller, C.; Meyer, T. G.; Farkens, M.; Sonnenburg, R.; Schmut-
zler, R. Z. Naturforsch. 1992, 47B, 760.

2506 Organometallics, Vol. 19, No. 13, 2000
van der Slot et al.
F igu r e 2. Displacement ellipsoid plot, plotted at the 50%
probability level, of trans-RhClCO(1c)2 (3c).
F igu r e 1. Displacement ellipsoid plot, plotted at the 50%
probability level, of ligand 1c.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for 1c
Bond Distances
P-N(1)
1.709(3)
1.720(3)
1.635(2)
1.398(5)
N(1)-C(1)
N(1)-C(11)
N(3)-C(2)
N(3)-C(31)
1.388(4)
1.450(4)
1.386(4)
1.446(4)
P-N(3)
P-O(3)
O(3)-C(41)
Bond Angles
N(1)-P-N(3)
N(1)-P-O(3)
95.7(1)
105.6(1)
O(3)-P-N(3)
104.3(1)
Ta ble 3. Selected IR, NMR, a n d Cr ysta l Str u ctu r e
F igu r e 3. Displacement ellipsoid plot, plotted at the 50%
probability level, of trans-RhClCO(1d )2 (3d ).
Da ta of tr a n s-Rh COClL2 (L ) 1a -d )
νCO
J RhP
(Hz)
dRh-P
(Å)
a
complex
(cm-1
)
ø
Ta ble 4. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for 3c
b
trans-RhClCO(PPh3)2
1978
2004
2010
2013
2016
2021
13 129 2.323(6)
166
trans-RhClCO(1a )2 (3a )
trans-RhClCO(1b)2 (3b)
trans-RhClCO(P(o-t-Bu-Ph)3)2
trans-RhClCO(P(OPh)3)2
trans-RhClCO(1c)2 (3c)
Bond Distances
156
Rh-C(7)
Rh-P(1)
Rh-P(2)
Rh-Cl
P(1)-N(1)
P(1)-N(3)
1.820(5)
2.3052(8)
2.2694(9)
2.3572(9)
1.688(3)
1.689(3)
P(1)-O(3)
P(2)-N(4)
P(2)-N(6)
C(7)-O(9)
P(2)-O(5)
1.596(2)
1.693(3)
1.685(4)
1.136(6)
1.604(3)
c
28 213 2.2856(7)
29 217
b,d
212 2.2694(9) (P(1))
2.3052(8) (P(2))
209 2.279(1)
trans-RhClCO(1d )2 (3d )
2025
a
b
d
Measured in CH2Cl2. See ref 28. c See ref 26. See ref 27.
Bond Angles
P(1)-Rh-Cl
85.49(3)
99.2(1)
169.19(3)
174.4(2)
90.8(1)
175.3(4)
106.6(1)
126.9(3)
115.9(2)
115.9(2)
125.3(3)
115.2(3)
N(1)-P(1)-O(3)
N(1)-P(1)-N(3)
N(3)-P(1)-O(3)
N(4)-P(2)-O(6)
N(4)-P(2)-N(6)
P(2)-N(6)-C(4)
P(2)-N(6)-C(71)
P(2)-N(4)-C(51)
P(2)-N(4)-C(3)
C(1)-N(1)-C(11)
C(2)-N(3)-C(31)
C(4)-N(6)-C(71)
100.2(1)
97.4(2)
100.2(1)
106.4(2)
98.7(1)
129.5(3)
116.1(1)
116.0(2)
128.6(3)
116.7(3)
116.9(3)
114.1(3)
structure. However, it must be taken into account that
the substituents of the ligands can mesh into one
another to achieve higher coordination numbers than
expected. The crystal structure of 1c (Figure 1, Table
2) shows that the higher degree of substitution at
nitrogen compared to oxygen introduces steric hindrance
close to the phosphorus atom.
The complexes trans-RhClCOL2 (3a -d ) were pre-
pared to determine the electron-withdrawing character
of ligands 1a -d . Table 3 shows selected IR, NMR, and
crystallographic data for 3a -d . The crystal structures
of 3c,d are given in Figures 2 and 3, and selected bond
distances and angles are given in Tables 4 and 5.
Complex 3d has a typical square-planar geometry with
cis-L-Rh-L′ angles near 90° summing to 359°. Complex
3c has a distorted-square-planar geometry with a cis-
P(1)-Rh-Cl angle of 85.5(3)° and cis-P(2)-Rh-Cl angle
of 84.8(3)°. The cis-P(1)-Rh-CO angle is 99.2(1)°, and
the cis-P(2)-Rh-CO angle is 90.8(1)°. The angle sum
at phosphorus atom P(1) (297.8°) is much smaller than
the angle sums at P(2) (311.7°) and at the phosphorus
P(1)-Rh-C(7)
P(1)-Rh-P(2)
Cl-Rh-C(7)
P(2)-Rh-C(7)
Rh-C(7)-O(7)
N(6)-P(2)-O(6)
P(1)-N(1)-C(1)
P(1)-N(1)-C(11)
P(1)-N(3)-C(31)
P(1)-N(3)-C(2)
C(3)-N(4)-C(51)
atom in the free ligand (305.6°). In the crystal structure,
the phenoxy substituent has different conformations for
P(1) and P(2), thereby influencing the angle sums at
P(1) and P(2). In solution, free rotation around this bond
will occur, and the resulting interchange between the
two conformers leads to only one (averaged) signal for
the two phosphorus atoms in the phosphorus NMR
spectrum. The Rh-P(1) distance is in the same range
as the Rh-P distances found in 3d and RhClCO(P(o-t-

Rh Complexes with Phosphorus Diamide Ligands
Organometallics, Vol. 19, No. 13, 2000 2507
Ta ble 5. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for 3d
Bond Distances
Rh-C(9)
Rh-P
1.841(6)
2.279(1)
2.338(1)
1.142(7)
P-N(1)
P-N(3)
P-O(3)
1.669(3)
1.680(3)
1.618(3)
Rh-Cl
C(9)-O(9)
Bond Angles
P-Rh-Cl
89.32(3)
90.68(3)
178.65(4)
180.00(0)
127.2(3)
115.0(3)
116.2(3)
N(1)-P-O(3)
N(1)-P-N(3)
N(3)-P-O(3)
Rh-C(9)-O(9)
P-N(3)-C(2)
C(7)-N(3)-C(2)
C(7)-N(3)-P
106.6(2)
98.9(2)
P-Rh-C(9)
P-Rh-P*
105.6(1)
180.00(0)
125.9(3)
116.2(3)
116.3(3)
Cl-Rh-C(9)
P-N(1)-C(1)
C(3)-N(1)-C(1)
C(3)-N(1)-P
Bu-C6H4)3)2.27 The Rh-P(2) distance is longer than the
Rh-P(1) distance. It seems that in the solid state the
energetically most favored situation is to bend all
substituents of P(2) away from the rhodium center. The
phosphorus atom is positioned further away from the
rhodium atom, thereby creating enough space for the
substituents. The J RhP (NMR) coupling constants of 3c,d
are in the same range as those of phosphite ligands,
while the J RhP coupling constants of 3a,b are smaller.27,28
Comparison of the IR frequencies of the carbonyl ligands
of complexes 3a -d and trans-RhClCO(PPh3)2, trans-
RhClCO(P(OPh)3)2, and trans-RhClCO(P(o-t-Bu-C6H4)3)2
gives insight into the π-acidity of the ligands.27,29 The
ligands 1a -d are stronger π-acids than triphenylphos-
phine. The carbonyl frequencies of 3a -d indicate that
1a ,b are more basic than triphenyl phosphite and tris-
(o-tert-butylphenyl) phosphite, whereas 1c and 1d are
better π-acids. Thus, the conclusion seems to be justified
that the phosphorus diamide ligands derived from
biuret are electronically similar to phosphite ligands,
while the biuret group by itself is a better electron
acceptor compared to two phenoxy groups. We expected
the carbonyl frequencies of complexes 3a ,c to be higher
than the carbonyl frequencies of complexes 3b,d , re-
spectively, based on the electron-withdrawing character
of the phenyl substituents on the nitrogen atoms
compared to the ethyl substituents. Probably the distor-
tion in the complex has a larger influence on the
carbonyl frequency of the carbonyl ligand than the
influence of the electron-donating capacity of the sub-
stituents on the nitrogen atoms.
F igu r e 4. Displacement ellipsoid plot, plotted at the 50%
probability level, of ligand 2a .
Ta ble 6. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for 2a
Bond Distances
P(1)-N(1)
P(1)-N(3)
P(1)-O(3)
N(1)-C(11)
N(1)-C(1)
N(3)-C(31)
N(3)-C(2)
O(3)-C(41)
1.710(3)
1.701(3)
1.640(4)
1.453(5)
1.393(6)
1.458(4)
1.400(6)
1.394(5)
P(2)-N(4)
P(2)-N(6)
P(2)-O(6)
N(4)-C(71)
N(4)-C(6)
N(5)-C(61)
N(5)-C(3)
O(6)-C(81)
1.703(4)
1.698(4)
1.647(3)
1.459(6)
1.393(5)
1.446(5)
1.384(7)
1.398(5)
Bond Angles
N(1)-P(1)-O(3)
N(1)-P(1)-N(3)
N(3)-P(1)-O(3)
P(2)-O(6)-C(81)
96.4(2) N(4)-P(2)-O(6)
99.9(2) N(4)-P(2)-N(6)
98.3(2) N(6)-P(2)-O(6)
124.1(2) P(1)-O(3)-C(41)
96.2(2)
96.9(2)
99.6(2)
124.9(3)
C(81)-C(86)-C(46) 121.5(3) C(86)-C(46)-C(45) 121.0(4)
C(85)-C(86)-C(46) 121.6(3) C(41)-C(46)-C(86) 121.1(3)
even lead to monodentate behavior of 2a . Ligands 2c,d
have very flexible backbones. The bidentate coordination
mode creates steric hindrance close to both phosphorus
atoms and the metal center. The electron-withdrawing
character of ligands 2a ,b will be in the same range as
that of ligands 1c,d because of the similarity of the
substituents on the phosphorus atom. Ligands 2a ,b will
be more π-acidic relative to 2c,d because of the more
electron-withdrawing character of the aryl backbone
compared to the alkyl backbone. The electronic charac-
ter of ligands 2e,f will be comparable to that of 1a ,b.
Ca ta lyst Ch a r a cter iza tion Stu d ies. The hydride
formation under hydroformylation conditions was moni-
tored using high-pressure (HP) NMR and HP IR spec-
troscopy in order to investigate the structures of these
complexes. The hydride formation was studied using
Rh(acac)(CO)2 in the presence of various concentrations
of ligand under 20 bar of CO/H2 (1/1). Ligands 1a ,b gave
complete conversion of Rh(acac)(CO)2 to HRhLx(CO)4-x
(x ) 1, 2) within 1 h at T ) 80 °C. The hydride formation
with ligands 1c,d is very fast, as complete conversion
of Rh(acac)(CO)2 to HRhLx(CO)4-x was reached within
1 h at T ) 40 °C.
The bite angle is an important steric property for
bidentate ligands. Previous research30,31 showed that
the backbones chosen for ligands 2a -f seem to induce
optimal bite angles for selective catalysis in the hydro-
formylation reaction. The bidentate ligands (2a -f) are
based on the same phosphorus diamide structures as
the monodentate ligands. The crystal structure of ligand
2a (Figure 4, Table 6) shows that steric hindrance at
the phosphorus atoms increases by the phenyl substit-
uents on the nitrogen atoms. The huge steric bulk might
(27) Ferna´ndez, E.; Ruiz, A.; Claver, C.; Castillon, S. Organometal-
lics 1998, 17, 2857.
(28) Li Wu, M.; Desmond, M. J .; Drago, R. S. Inorg. Chem. 1979,
18, 679.
(29) Haar, C. M.; Huang, J .; Nolan, S. P.; Petersen, J . L. Organo-
metallics 1998, 17, 5018.
(30) van der Veen, L. A.; Kamer, P. C. J .; van Leeuwen, P. W. N.
M. Angew. Chem., Int. Ed. 1999, 38, 336.
The spectroscopic data of the hydride complexes
HRhLx(CO)4-x (x ) 1-3) with ligands 1a -d are pre-
sented in Table 7. In all cases a mixture of HRhL(CO)3
and HRhL2(CO)2 was observed. The ratio between
HRhL2(CO)2 and HRhL(CO)3 is dependent on the ligand
(31) van Rooy, A.; Kamer, P. C. J .; van Leeuwen, P. W. N. M.;
Goubitz, K.; Fraanje, F.; Veldman, N.; Spek, A. L. Organometallics
1996, 15, 835.

2508 Organometallics, Vol. 19, No. 13, 2000
van der Slot et al.
Ta ble 7. NMR a n d IR Da ta for HRh Lx(CO)4-x (x ) 1-3) Com p lexes (L ) 1a -d )
b
compd
δ(31P) (ppm)a
J RhP (Hz)
δ(1H) (ppm)a
νCO (cm-1
)
HRh1a (CO)3
HRh(1a )2(CO)2
110
114
186
196
-10.6 (d, J PH ) 6 Hz)
-11.4 (t, J PH ) 12 Hz)
2094, 2047, 2017
2079, 2023
HRh(1b)(CO)3
HRh(1b)2(CO)2
HRh(1b)3CO (4)
104
110
117
177
181
169
-10.3 (d, J PH ) 15 Hz)
-10.6 (s, br)
-10.7 (s, br)
2095, 2045, 2008
2070, 2018
2019
HRh(1c)(CO)3
HRh(1c)2(CO)2
not obsd
126
not obsd
-10.6 (s, br)
2096, 2047, 2020
2071, 2003
221
HRh(1d )(CO)3
HRh(1d )2(CO)2
116
118
220
224
not obsd
-10.5 (s, br)
2098, 2043, 2014
2076, 2020
a
b
Measured in toluene-d8. Complexes with L ) 1a ,c measured in 2-methyltetrahydrofuran; complexes with L ) 1b,d measured in
cyclohexane.
concentrations as well as on the steric and electronic
ligand properties. Lowering of the ligand and rhodium
concentrations resulted in a decreasing amount of
HRhL2(CO)2. The amount of HRhL2(CO)2 measured at
the same ligand concentrations decreased in the order
1d > 1c > 1b > 1a . Rhodium complexes of the form
HRhLx(CO)4-x (x ) 1-3) generally have a (distorted)
trigonal-bipyramidal structure. Crystal structure analy-
ses of transition-metal hydrides have shown that the
hydride ligand coordinates at an apical position of the
bipyramid.32 The phosphorus atoms can coordinate
either at the equatorial positions or at the remaining
apical position. For transition-metal hydrides the ab-
solute phosphorus-hydride (NMR) coupling constant is
substantially larger for complexes having an HRhP
angle approaching 180° than for those having angles of
∼90°.33 Small cis J HP values between 1 and 30 Hz are
reported for hydride carbonyl complexes with bis equa-
torially coordinating diphosphine16 and diphosphite
ligands.8 Larger phosphorus-hydride coupling con-
stants in the range of 110-200 Hz are reported for
axially coordinated phosphorus ligands.33,34 HRh(1a )-
(CO)3 and HRh(1b)(CO)3 have phosphorus-hydride
coupling constants of 6 and 15 Hz, respectively. This
indicates that the phosphorus ligands coordinate in the
equatorial plane of a slightly distorted trigonal bipyra-
mid. The (IR) carbonyl frequencies of the complexes
HRhL(CO)3 (L ) 1a -d ) are almost equal to the fre-
quencies found for these types of complexes formed
using bulky phosphites.18
technique.16 In general, the carbonyl bands of the ea
isomer HRhL2(CO)2 are found at lower wavenumbers
than those of the ee isomer. The infrared spectra showed
that the hydride complexes HRhL2(CO)2 (L ) 1a -d ) are
present as only one isomer. The carbonyl frequencies
indicate an ee coordination in a distorted-trigonal-
bipyramidal structure, as confirmed by published car-
bonyl frequencies for bulky bidentate phosphite li-
gands.31,34 HRh(1a )2(CO)2 was observed as the main
complex in the high-pressure NMR experiments ([Rh]
) 13 mM, [1a ] ) 0.13 M). This is very surprising in view
of the large estimated cone angle (θ ) 189°). We therefor
assume that the bulky moieties of the ligands are
meshing or easily bent away.
The stability of the hydride complexes containing L
) 1a ,b under 1 bar of CO/H2 was investigated by NMR
spectroscopy in the presence of an excess of ligand (Rh/L
) 1/10). The pressure was released from the high-
pressure NMR tube after the spectrum was recorded.
The solution was transferred to a 5 mm NMR tube and
measured again. We could see that the stability of the
hydride complexes HRhLx(CO)4-x depends on the ligand
and the number of phosphorus ligands coordinated.
HRhL(CO)3 (L ) 1a ,b) was never observed at atmo-
spheric pressure in the presence of an excess of ligand.
In this case a phosphorus ligand replaces a carbonyl
ligand to form HRhL2(CO)2. HRh(1a )2(CO)2 is not stable
for a longer period of time in the absence of CO/H2
pressure, and the complex was observed in low concen-
trations only. The major part of the rhodium complex
disproportionate, forming rhodium carbonyl clusters.
HRh(1b)2(CO)2 was formed quantitatively from the
mixture of 1b, HRh(1b)2(CO)2, and HRh(1b)(CO)3 when
the same procedure was followed as for ligand 1a . This
complex is relatively stable in the absence of CO/H2
pressure but converts slowly to HRh(1b)3CO (4), which
was analyzed by a crystal structure determination. The
structure of complex 4 (Figure 5, Table 8) reveals a
slightly distorted trigonal bipyramidal geometry, the
three phosphorus ligands occupying equatorial posi-
tions. The structure has a crystallographic 3-fold axis
along the Rh-CO bond. The rhodium atom is located
slightly under the equatorial plane defined by the
phosphorus atoms, displaced toward the carbonyl ligand.
The hydrogen atom could not be located in the crystal
The hydride complexes HRhL2(CO)2 (L ) 1a -d ) have
PH coupling constants of approximately 3-12 Hz, which
J
is relatively large for a pure cis coordination. Two
explanations can be brought forward. An equilibrium
mixture of ee-ea coordination gives averaged signals
in the NMR spectra, provided that there is a fast
exchange of the phosphorus ligands between equatorial
and apical positions.35 Second, coordination of both
phosphorus atoms in the equatorial plane of a slightly
distorted trigonal bipyramid would lead to the same
coupling constant. If an equilibrium between two iso-
mers occurs, two sets of carbonyl frequencies are
observed in the infrared spectra originating from the
two isomers because of the faster time scale of this
(32) Frenz, B. A.; Ibers, J . A. The Hydride Series; Muetterties, E.
L., Ed.; Marcel Dekker: New York, 1971; Vol. I, Chapter III.
(33) Nozaki, K.; Sakai, N.; Nanno, T.; Higashijima, T.; Mano, S.;
Horiuchi, T.; Takaya, H. J . Am. Chem. Soc. 1997, 119, 4413.
(34) Buisman, G. J . H.; Vos, E. J .; Kamer, P. C. J .; van Leeuwen, P.
W. N. M. J . Chem. Soc., Dalton Trans. 1995, 409.
1
structure, but H NMR spectroscopy indicates that the
hydride occupies the apical position of the trigonal
bipyramid.
The hydride complexes HRh(1c)x(CO)4-x and HRh(1d)x-
(CO)4-x (x ) 1, 2) decomposed when the temperature
(35) Brown, J . M.; Kent, A. G. J . Chem. Soc., Perkin Trans. 2 1987,
1597.

Rh Complexes with Phosphorus Diamide Ligands
Organometallics, Vol. 19, No. 13, 2000 2509
F igu r e 6. Proposed decomposition product of HRh(1d )x-
(CO)4-x
.
Ta ble 9. NMR a n d IR Da ta of HRh L(CO)2 (L )
2a -d ,f)
δ(31P)a J RhP J PP
(ppm) (Hz) (Hz)
νCO
b
compd
δ(1H) (ppm)
(cm-1
)
HRh(2a )(CO)2 140c 244 211 -12.0 (t, J RhH ) 12 Hz)c 2085, 2041
143c 251
HRh(2b)(CO)2 141 218
-11.1 (s, br)
2070, 2019
2086, 2031
HRh(2c)(CO)2 145 225 190 -11.7 (s, br)
147 226
HRh(2d )(CO)2 145 221
-10.6 (s, br)
2067, 2017
-10.2 (dt, J PH ) 17 Hz, 2057, 2004
HRh(2f)(CO)2
96 185
J RhH ) 2 Hz)
F igu r e 5. Displacement ellipsoid plot, plotted at the 50%
probability level, of HRh(1b)3CO (4).
a
b
Measured in toluene-d8. Complexes with L ) 2a ,c measured
in 2-methyltetrahydrofuran; complexes with L ) 2b,d ,f measured
in cyclohexane. c Measured in CD2Cl2.
Ta ble 8. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for 4
observed. The structure consistent with all data is
depicted in Figure 6. The formation of phosphido type
complexes is not uncommon in these systems.39 At-
tempts to isolate this complex were not successful.
The hydride formation for the bidentate ligands 2a -f
was studied using Rh(acac)(CO)2 in the presence of 2
equiv (HP NMR) or 5 equiv (HP IR) of ligand under 20
bar of CO/H2 (1/1). Ligands 2a -d ,f gave complete
conversion of Rh(acac)(CO)2 to HRhL∩L(CO)2 within 1
h at 80 °C. In contrast to the complexes of the mono-
dentate ligands, decomposition was observed for neither
the hydride complexes nor the ligands. Ligand 2e did
not coordinate to rhodium at all. [Rh6(CO)16] is formed
when a mixture of Rh(acac)(CO)2 and 2e under CO/H2
is heated for 1 h at 80 °C. Probably, the ligand is too
bulky to coordinate to the rhodium atom and Rh(acac)-
(CO)2 is converted into the rhodium carbonyl cluster.
The spectroscopic data of the hydride complexes
HRhL∩L(CO)2 formed with ligands 2a -d ,f are pre-
sented in Table 9. The bidentate ligands form one single
rhodium hydride complex, independent of the ligand
concentration. The J RhP coupling constants of the com-
plexes HRhL(CO)2 formed with L ) 2a -d are all in the
same ranges as the J RhP coupling constants found for
the monodentate ligands 1c,d , which indicates that the
electronic character of these ligands is indeed compa-
rable. The J RhP coupling constant of HRh(2f)(CO)2 is in
the same range as the J RhP coupling constants found
for the monodentate ligands 1a and 1b. The hydride
signals of the complexes formed with 2b-d are broad
singlets (W1/2 ≈ 10 Hz). This indicates that both J RhH
and J PH coupling constants are small (<3 Hz). The small
J PH coupling constants are indicative of an ee coordina-
tion mode. The hydride signal of HRh(2f)(CO)2 is a
double triplet (J RhH ) 2 Hz, J PH ) 17 Hz). The J PH
coupling constant indicates ee coordination in a dis-
torted trigonal bipyramid.
Bond Distances
Rh-C(15)
C(15)-O(3)
Rh-P(1)
1.907(6)
1.141(9)
2.2872(9)
P(1)-N(1)
P(1)-C(9)
P(1)-N(3)
1.721(3)
1.827(4)
1.718(4)
Bond Angles
P(1)-Rh-P(1)′
C(15)-Rh-H
Rh-P(1)-N(1)
Rh-P(1)-N(3)
Rh-P(1)-C(9)
119.13(10)
180.0
121.90(12)
115.20(12)
120.02(13)
P(1)-Rh-C(15)
N(3)-P(1)-C(9)
N(1)-P(1)-N(3)
C(9)-P(1)-N(1)
95.38(3)
101.06(17)
95.10(15)
98.92(16)
was raised to 80 °C. HRh(1c)x(CO)4-x converts within 1
h completely to [Rh4(CO)12] (νCO 2074 (s), 2068 (s), 2043
(m), 1885 cm-1 (m), with 2-methyltetrahydrofuran as
solvent),36 and this rhodium carbonyl cluster decom-
poses subsequently to form [Rh6(CO)16] at 80 °C (νCO
2074 (s), 1820 (s), with 2-methyltetrahydrofuran as
solvent).36 The hydride complexes of 1d disproportionate
to form a new hydride complex. We studied the decom-
position of HRh(1d )x(CO)4-x using HP NMR and HP IR
spectroscopy. The phosphorus signals in the 31P NMR
spectrum belonging to the hydride complexes HRh(1d )x-
(CO)4-x disappear when the solution is heated to 80 °C,
and a new multiplet appears at δ 262 ppm. Additionally,
1
a double triplet appears in the hydride region of the H
NMR spectrum (δ -10.7 ppm, J PH ) 18 Hz, J RhH ) 14
Hz in toluene-d8). The 1H-31P COSY NMR spectrum
shows only one correlation between this hydride signal
and the phosphorus signal at 262 ppm. The hydride
signal became a triplet when we decoupled the phos-
phorus signal selectively at 262 ppm. This indicates that
we are dealing with a dimeric rhodium complex in
which, surprisingly, one phosphorus atom is coordinated
to two rhodium atoms. The low-field resonance of the
phosphorus signal is strongly indicative of a phosphido
group that bridges a metal-metal bond.37,38
The IR spectrum of the complex shows two carbonyl
bands at 2041 (m) and 2003 cm-1 (m), indicating
terminal positions. No bridging carbonyl bands were
Even though ligand 2a is very bulky, the ligand
coordinates in a bidentate fashion. The two phosphorus
atoms in HRh(2a )(CO)2 are magnetically inequivalent
(36) Cattermole, P. E.; Osborne, A. G. Inorg. Synth. 1977, 17, 115.
(37) Arif, A. M.; J ones, R. A.; Seeberger, M. H.; Whittlesey, B. R.;
Wright, T. C. Inorg. Chem. 1986, 25, 3943.
(39) Sivak, A. J .; Muettterties, E. L. J . Am. Chem. Soc. 1979, 101,
(38) Garrou, P. E. Chem. Rev. 1981, 81, 229.
4878.

2510 Organometallics, Vol. 19, No. 13, 2000
van der Slot et al.
Ta ble 10. Hyd r ofor m yla tion Resu lts of 1-Octen e
Ta ble 11. Hyd r ofor m yla tion Resu lts of 1-Octen e
w ith L ) 1a -d a
w ith L ) 2a -d ,f a n d 5a -ca
L
L/Rh conversn (%) l/b TOFb linear (%) isomeriznd (%)
L
L/Rh conversn (%) l/b TOFb linear (%) isomeriznc (%)
1a
1b
1c 100
1d 100
50
50
30
33
34
32
2.6 24500
2.3 10300
2.3 7700c
2.2 4920c
60
61
56
61
17
12
19
11
2a 100
2b 100
26
29
30
32
26
21
27
30
3.9
6.8
3.1 1600
2.2 7950
10.4
1.2
2.2 1550
49 250
431
780
51
83
59
64
86
48
55
94
36
4
22
7
2c
10
10
5
2d
2fd
381
520
5
a
Conditions: T ) 80 °C, pCO ) pH ) 10 bar, [Rh] ) 0.2 mM,
5a e 16
13
20
4
2
b
[1-octene] ) 0.64 M in toluene. In units of (mol of aldehyde) (mol
5be
5cf
2.5
5
of Rh)-1 h-1
.
c Presuming that all rhodium added is active as a
d
hydroformylation catalyst. Formation of 2-octene.
a
Conditions: T ) 80 °C, pCO ) pH ) 10 bar, [Rh] ) 0.2 mM,
2
b
[1-octene] ) 0.64 M in toluene. In units of (mol of aldehyde) (mol
and show a strongly coupled NMR spectrum. The small
J PH (<3 Hz) and the J RhP coupling constant of 12 Hz in
HRh(2a )(CO)2 are in agreement with those of an ee
coordination mode in a slightly distorted trigonal bipy-
ramidal structure. The distortion in the complex is
probably a result of the bulkiness of the ligand. In HRh-
(2c)(CO)2 the phosphorus atoms lose their time-aver-
aged equivalence on cooling from 80 °C to room tem-
perature. At -25 °C the slow exchange region is
reached, resulting in a strongly coupled NMR spectrum.
The J PH and J RhH coupling constants remain small.
In the IR spectra only two carbonyl bands are
observed. The positions of the carbonyl bands of the
complexes containing ligands 2b,d ,f evidence an ee
coordination of the bidentate ligands in a distorted
trigonal bipyramid, in accordance with previous re-
sults.14,16 The carbonyl frequencies of HRh(2a )(CO)2 and
HRh(2c)(CO)2, however, shift to higher wavenumbers
compared to those of hydride complexes containing
2b,d ,f, and the frequencies of the hydride complexes of
the monodentate ligands. The crystal structure of 2a
(Figure 4) shows huge steric hindrance close to the
phosphorus atoms due to the phenyl substituents on the
nitrogen atoms. Coordination of the bidentate ligands
2a ,c to a metal center will increase this steric strain
and distort the geometry of the trigonal bipyramid. This
distortion does not seem to affect the phosphorus-
hydride coupling constant. The distorted geometry may
explain the difference in carbonyl frequencies of the
hydride complexes of 2a ,c and the hydride complexes
containing 2b,d ,f.
Hyd r ofor m yla tion of 1-Octen e. The ligands 1a -d
were used in the rhodium-catalyzed hydroformylation
of 1-octene. The catalysts were prepared in situ from
Rh(acac)(CO)2, the ligand, CO, and H2 at 80 °C. In the
previous section we have shown that two rhodium
hydride complexes are formed, HRhL(CO)3 and HRhL2-
(CO)2, depending on the ligand properties and the ligand
and rhodium concentrations. The ligand and rhodium
concentrations used in catalysis are much lower than
the concentrations used in the spectroscopic experi-
ments. Therefore, the proportion of HRhL(CO)3 in the
reaction mixture used in catalysis is assumed to be
significantly higher than that in the spectroscopic
experiments.
Rh)-1 h-1 c Formation of 2-octene. [Rh] ) 2 mM. e [Rh] ) 0.4
.
d
mM, [1-octene] ) 1 M.30 f [Rh] ) 1 mM, [1-octene] ) 0.64 M.29
with the electron-withdrawing character of the ligand.
In the case of 1a -d , the activity is determined pre-
dominantly by the type of complex rather than the
ligand properties. A quantitative comparison of the
selectivities and activities of the catalysts formed having
the monodentate ligands is difficult because two rhod-
ium complexes (HRhL(CO)3 and HRhL2(CO)2) are present
in each system and the ratio between these two com-
plexes is not equal in the four systems. An effect of the
decreasing bulkiness of the ligands on the selectivity
in the hydroformylation reaction is not observed. A
rhodium complex of composition HRhL2(CO)2 is more
selective than a complex with the structure HRhL(CO)3.
All catalyst mixtures tested show approximately the
same selectivity, because the amount of HRhL2(CO)2
increases with decreasing bulkiness of the ligand.
Ligands 1c,d were tested under the same conditions
as 1a ,b, although we observed decomposition of the
hydride complexes of the former ligands during the
spectroscopic experiments. Variation of the ligand con-
centrations (Rh/P ) 1/50, 1/100, 1/200) showed that the
best results were obtained (activity versus selectivity
and isomerization) for Rh/L ) 1/100. Probably, the lower
rhodium and higher ligand concentrations used in the
catalysis experiments compared to the spectroscopic
experiments decrease the decomposition rate of the
catalyst.
We were aiming at a catalyst system with improved
activity compared to a catalyst system based on mono-
dentate phosphine ligands and improved selectivity
compared to catalyst systems based on monodentate
phosphite ligands. The present monodentate ligands
form a significant amount of HRhL(CO)3, which unfor-
tunately still gives low linear-to-branched ratios, albeit
at high rates. To obtain higher selectivities, we turned
to bidentate ligands.
The bidentate ligands (2a -d ,f) are more electron
withdrawing than phosphines and introduce more steric
hindrance close to the rhodium center than phosphites.
The spectroscopic experiments described in the previous
section showed that these ligands form stable, well-
defined rhodium complexes having the structure
HRhL∩L(CO)2. The results obtained in the hydroformyl-
ation reaction using these bidentate ligands are pre-
sented in Table 11. Ligand 2e was not used in the
hydroformylation reaction, because no hydride complex
is formed under hydroformylation conditions. The sys-
tems are less active than the catalyst systems derived
from the monodentate ligands (1a -d ), because the
rhodium center is more electron rich when two phos-
The results of the hydroformylation reaction of 1-octene
obtained using L ) 1a -d are presented in Table 10.
The very high activity of the catalysts formed is in the
range of the activity of the bulky phosphite ligands
studied by van Leeuwen et al.40 They could show that
the activity of these bulky phosphite systems increases
(40) van Rooy, A.; Orij, E. N.; Kamer, P. C. J .; van Leeuwen, P. W.
N. M. Organometallics 1995, 14, 34.

Rh Complexes with Phosphorus Diamide Ligands
Organometallics, Vol. 19, No. 13, 2000 2511
Ch a r t 3
reaction, although the linear over branched ratio is low.
The bidentate ligands form catalysts with the structure
HRhL∩L(CO)2, which are active and selective hydro-
formylation catalysts. The combination of ideal elements
(backbone (and thus bite angle), steric bulk, and π-acid-
ity) does not lead to a superior catalyst compared to
catalysts containing PAr2 and P(OAr)2 substituents. It
seems that the aryl substituents in PAr2 and P(OAr)2
play a very specific role in determining the shape of a
selective catalytic site.
Exp er im en ta l Section
Gen er a l In for m a tion . All preparations were carried out
under an atmosphere of argon using standard Schlenk tech-
niques. Solvents were distilled from sodium/benzophenone. All
glassware was dried by heating under vacuum. Column
chromatography was performed using silica gel 60 (230-400
mesh) obtained from Merck or activated neutral alumina 50-
200 µm obtained from Acros Organics. The NMR spectra were
recorded on a Bruker AMX-300 spectrometer (1H, 31P, 13C); the
high-pressure NMR spectra were recorded on a Bruker DRX-
300 spectrometer. Chemical shifts are given in ppm referenced
to TMS or H3PO4 (external). IR spectra (high pressure) were
recorded on a Nicolet 510 FT-IR spectrometer.
phorus ligands are attached to it. The selectivity is
improved compared to that of monodentate ligand
systems. The difference in activity and selectivity of the
various bidentate ligands is less straightforward. The
selectivities of the catalysts formed from ligands 2a ,c
are lower than expected, in view of the phenyl substit-
uents at the nitrogen atoms. The ratio of 2-octene is high
compared to other ligands in this work. In the HP NMR
and HP IR experiments we saw that complete conver-
sion to a hydride complex is reached, although the
carbonyl frequencies of the hydride complexes formed
with 2a ,c are found at slightly higher wavenumbers
than the wavenumbers observed for the hydride com-
plexes using 2b ,d ,f. This led us to conclude that the
compounds assume a distorted-trigonal-bipyramidal
structure. We now tentatively propose that coordination
of carbon monoxide after the hydride migration is
relatively slow in the distorted complexes (L∩L is a
bidentate ligand), thus giving a high preference for
â-hydride elimination and thus isomerization.30
When we compare the hydroformylation results ob-
tained using 2b,d ,f with respect to the selectivity for
the linear aldehyde, we see that both the backbone and
the substituents on the phosphorus atoms determine the
selectivity of the reaction. Comparison of the results of
2b,d with those of phosphite ligands derived from the
same backbones (5a ,b; Chart 3)31 shows that the
selectivity for the linear aldehyde is improved by the
introduction of the nitrogen substituents without any
decrease in activity. The backbone used for ligand 2f
has proven to form very selective hydroformylation
catalysts30 for phosphorus substituents of the type PAr2.
Also for these novel phosphorus diamide ligands the
xanthene backbone provided the most selective ligand,
but aryl substituents on the phosphorus atom give far
higher linear over branched ratios (65).
Hydroformylation experiments were performed in a stain-
less steel autoclave (196 mL). The autoclave is mechanically
stirred and equipped with a reservoir, a pressure transducer,
a thermocouple, and a sampling device. In a typical experiment
the autoclave was flushed four times with 4 bar of syngas. Rh-
(acac)(CO)2 and the ligand were dissolved in 15 mL of toluene,
and this solution was brought into the autoclave. After it was
flushed four times with 4 bar of CO/H2 (1/1), the autoclave
was put under a pressure of 15 bar. The autoclave was heated
to 80 °C. After 1 h the substrate solution (2 mL of alkene, 2
mL of toluene, and 1 mL of decane) was charged into the
reservoir and added to the reaction mixture by overpressure.
The initial pressure of the experiment was 20 bar. The alkene
was filtered over neutral alumina to remove peroxides. During
the reaction several samples were taken and immediately
quenched by adding an excess of P(O-n-Bu)3, to form
a
hydroformylation-inactive rhodium species. The samples were
analyzed by GC using decane as internal standard.
High-pressure NMR experiments were performed in a 10
mm o.d. sapphire NMR tube described by Elsevier et al.41 In
a typical experiment 5 mg (0.019 mmol) of Rh(acac)(CO)2 and
1, 2, 5, or 10 equiv of ligand were dissolved in 1.5 mL of
toluene-d8. For ligand 2a CD2Cl2 was used because of the poor
solubility in toluene. The solution was brought into the argon-
flushed tube. After it was closed, the tube was flushed four
times with 4 bar of syngas (CO/H2 ) 1/1) and put under a
pressure of 20 bar. The tube was heated in the NMR machine
to 80 °C.
High-pressure IR experiments were performed in an SS 316
50 mL autoclave equipped with IRTRAN windows (ZnS,
transparent up to 700 cm-1, 10 mm i.d., optical path length
0.4 mm), a mechanical stirrer, a temperature controller, and
a pressure device. In a typical experiment 5 mg of Rh(acac)-
(CO)2 and 5 or 20 equiv of ligand were dissolved in 15 mL of
solvent under argon. The solution was brought into the CO/
H2 (1/1) flushed autoclave and, after flushing, pressurizing,
and heating of the mixture, the autoclave was placed in the
infrared spectrometer. While the samples were stirred, the IR
spectra were recorded. For the ligands 1b,d and 2b,d ,f
cyclohexane was used as solvent during these measurements.
Because of the low solubility of 1a ,c and 2a ,c freshly distilled
methyltetrahydrofuran was used for these ligands.
Con clu sion s
The introduction of nitrogen substituents on the
phosphorus atom leads to very bulky π-acidic ligands,
thereby combining the good properties of phosphine and
phosphite ligands with respect to the hydroformylation
reaction of terminal alkenes. The monodentate ligands
form a significant proportion of HRhL(CO)3. These
complexes are very active in the hydroformylation
(41) Elsevier, C. J . J . Mol. Catal. 1994, 92, 285.

2512 Organometallics, Vol. 19, No. 13, 2000
van der Slot et al.
Triethylbiuret was synthesized by the method describe by
d’Silva et al.42 Because ethyl isocyanate is extremely toxic,
special precautions were taken to prevent inhalation and
contact with the skin. Triphenylbiuret and ligand 1a were
synthesized according to a literature procedure.25 Instead of
1 equiv of triethylamine, an excess of triethylamine was used.
An extra purification step (filtration over silica, eluent CH2-
Cl2) was performed to exclude the presence of traces of
triethylamine hydrochloride salt in the product. All chemicals
were azeotropically dried before using. All trans-RhClCOL2
complexes were synthesized according to a literature proce-
dure.29
salts are filtered off. The THF was removed under vacuum.
The product was filtered over neutral alumina to remove traces
of triethylamine salts (eluent CH2Cl2, Rf ) 1). Yield: 3.15 g
(98%) of a white powder. Mp: 169 °C. 1H NMR (CDCl3): δ
7.6-7.0 ppm (m, o,m,p-Ph). 31P{1H} NMR (CDCl3): δ 86.3 ppm
(s). 13C NMR (CDCl3): δ 120.6 (d, 3J CP ) 6 Hz, o-PhOP), 125.1
(s, p-PhOP), 128.5 (s, o-PhN(CO)2), 128.6 (s, p-PhN(CO)2),
3
2
128.6 (d, J CP ) 7 Hz, p-PhNP), 129.0 (d, J CP ) 11 Hz,
o-PhNP), 129.7 (s, m-PhN(CO)2), 130.5 (s, m-PhOP), 136.5 (s,
2
ipso- PhN(CO)2), 152.0 (d, J CP ) 6 Hz, CO) 152.4 (s, ipso-
PhOP). IR (CH2Cl2): νCO 1717 (vs), 1681 cm-1 (vs). FAB/MS:
m/e 454, Anal. Calcd for C26H20N3O3P: C, 68.87; H, 4.45; N,
9.27. Found: C, 68.71; H, 4.54; N, 9.11.
The complex syntheses under pressure were performed in
a magnetically stirred stainless steel autoclave with a volume
of 6.5 mL, which was heated in an oil bath.
Crystallization of the product from absolute ethanol gave
colorless crystals suitable for crystal structure determination.
1,3,5-Tr ieth ylbiu r et P h en oxyph osph or u s Diam ide (1d).
A solution of 2.3 mL (26.7 mmol) of phosphorus trichloride in
20 mL of toluene was added dropwise to a solution of 5 g (26.7
mmol) of N,N′,N′′-triethylbiuret in 80 mL of toluene and 20
mL of triethylamine (excess) at room temperature. Triethyl-
amine hydrochloride precipitated directly. The reaction mix-
ture was stirred overnight at 80 °C. The mixture was cooled
to room temperature, the precipitate was filtered off, and the
toluene was evaporated under vacuum. The phosphorus
chloride compound was obtained as a yellow oil and used
directly without further purification. The purity of the com-
pound was checked by NMR. A solution of 2.3 g (24 mmol) of
phenol in 10 mL of THF was added dropwise to a solution of
6.2 g (24 mmol) of N,N′,N′′-triethylbiuret phosphorus chloride
in 50 mL of THF and 5 mL of triethylamine (excess). The
reaction mixture was stirred at room temperature for 1 h. The
triethylamine salts were filtered off, and the THF was
evaporated. The product was filtered over alumina to remove
traces of triethylamine salts (eluent CH2Cl2). The product was
obtained as a white powder after crystallization from pentane.
Yield: 5.3 g (65%). Mp: 49 °C. 1H NMR (CDCl3): δ 0.9 (t, 3H,
N,N′,N′′-Tr ieth ylbiu r et. A 20 g (0.17 mol) amount of 1,3-
diethylurea and 100 g (1.41 mol) of ethyl isocyanate were
mixed together under argon. The suspension was heated to
50 °C. During heating the diethylurea dissolved in the ethyl
isocyanate. The reaction mixture was stirred for 2 days at 50
°C. After this period the excess ethyl isocyanate was distilled
off and carefully destroyed with alcoholic base. Traces of ethyl
isocyanate were removed by adding three 100 mL portions of
benzene to the reaction mixture and distilling it off. The
triethylbiuret was purified by column chromatography on silica
gel (eluent 1/1 petroleum ether 40-60 °C (PE 40-60)/ethyl
acetate (Rf ) 0.4)). The product was obtained as a yellow oil:
1
3
yield 23 g (72%), H NMR (CDCl3): δ 1.1 (t, 6H, J HH ) 7 Hz,
CH3CH2NH), 1.2 (t, 3H, 3J HH ) 5 Hz, CH3CH2N(CO)2), 3.3 (dq,
4H, 3J HH ) 5 Hz, 3J HH ) 1 Hz CH3CH2NH), 3.7 (q, 2H, 3J HH
)
7 Hz, CH3CH2N(CO)2). 13C NMR (CDCl3): 14.1 (s, CH3CH2N-
(CO)2), 15.1 (s, CH3CH2NH), 35.6 (s, CH3CH2NH), 38.0 (s,
CH3CH2N(CO)2), 156.2 (s, N(CO)2). IR (CH2Cl2) νCO 1696 (vs),
1644 (vs), νNH 1542 (vs), 1509 cm-1 (vs). FAB/MS: m/e 188.
Anal. Calcd for C8H17N3O2: C, 51.32; H, 9.15. Found: C, 51.33;
H, 9.39.
3
3J HH ) 7 Hz, CH3CH2N(CO)2), 1.3 (t, 6H, J HH ) 7 Hz, CH3-
1,3,5-Tr ieth ylbiu r et P h en ylp h osp h or u s Dia m id e (1b).
A solution of 1.9 g (11 mmol) PPhCl2 in 10 mL of toluene was
added dropwise to a solution of 2.0 g (11 mmol) of N,N′,N′′-
triethylbiuret (1) in 40 mL of toluene and 5 mL of triethyl-
amine (excess) at room temperature. During addition triethyl-
amine hydrochloride precipitated. When the addition was
completed, the mixture was stirred overnight at 80 °C. Another
5 mL of triethylamine was added, and the mixture was stirred
another 4 h at 80 °C to complete the reaction. The mixture
was cooled to room temperature, the salts were filtered off,
and the toluene was evaporated under vacuum. The product
was purified by column chromatography on silica gel (4/1 PE
40-60/ethyl acetate (Rf ) 0.5)). Yield: 1.86 g (58%). Mp: 52
°C. 1H NMR (C6D6): δ 1.0 (t, 3H, 3J HH ) 7 Hz, CH3CH2N(CO)2),
1.2 (t, 6H, 3J HH ) 7 Hz, CH3CH2NP), 3.3 (dq, 2H, 3J HH ) 7 Hz,
CH2NP), 3.6 (m, 4H, CH3CH2NP and CH3CH2N(CO)2), 3.9 (m,
3
2H, CH3CH2NP), 6.8 (d, 2H, J HH ) 8 Hz, o-PhOP), 7.1 (t, 1
3
3
H, J HH ) 7 Hz, p-PhOP), 7.3 (t, 2 H, J HH ) 8 Hz, m-PhOP).
31P{1H} NMR (CDCl3): δ 87.4 (s). 13C NMR (CDCl3): δ 13.3
(s, CH3CH2N(CO)2), 15.3 (s, CH3CH2NP), 38.5 (s, CH3CH2N-
(CO)2), 42.6 (d, 2J CP ) 35 Hz, CH3CH2NP), 121.0 (d, 3J CP ) 35
Hz, o-PhOP), 125.0 (s, p-PhOP), 130.0 (s, m-PhOP), 151.0 (d,
2
2J CP ) 6 Hz, ipso-PhOP), 152.1 (d, J CP ) 9 Hz, CO). IR (CH2-
Cl2): νCO 1699 (vs), 1656 cm-1 (vs). FAB/MS: m/e 310. Anal.
Calcd for C14H20N3O3P: C, 54.37; H, 6.52; N 13.59. Found: C,
54.60; H, 6.61; N, 13.47.
Com p ou n d 2a . A 2.2 g (12 mmol) amount of 2,2′-hydroxy-
1,1′-biphenyl dissolved in 20 mL of toluene was added dropwise
to a solution of 2.4 g (6 mmol) of N,N′,N′′-triphenylbiuret
phosphorus chloride and 7.6 mL (60 mmol) of triethylamine
in 100 mL of toluene at room temperature. When the addition
was completed, the mixture was stirred at 80 °C for 4 h. The
triethylamine salts were filtered, and the solvent was removed
under vacuum. Purification by column chromatography on
silica gel (eluent 7/3 PE (60-80)/EtOAc, Rf ) 0.15) gave a
white solid, Yield: 5.2 g (95%). Mp: 284 °C dec. 1H NMR
(CDCl3): δ 6.9-7.4 (m, o,m,p-Ph). 31P{1H} NMR (CDCl3): δ
91.0 (s). 13C NMR (CDCl3): δ 129.1, 128.7, 127.8 (s, o,m,p-
Ph-N), 129.3 (s, ipso-Ph-O-P), 132.4-118.1 (s, o,m,p-Ph-
O), 136.2 (s, ipso-Ph-N-P), 137.3 (s, ipso-Ph-N-P), 137.5 (s,
3
3
3J PH ) 7 Hz, CH3CH2NP), 3.8 (dq, 2H, J HH ) 7 Hz, J PH ) 7
3
Hz, CH3CH2NP), 4.0 (q, 2H, J HH ) 7 Hz, CH3CH2N(CO)2),
7.3-6.9 (m, 5H, o,m,p-PhP). 31P{1H} NMR (C6D6): δ 63.4 (s).
13C NMR (CDCl3) δ 13.3 (s, CH3CH2N(CO)2), 15.3 (d, J CP ) 5
3
2
Hz, CH3CH2NP), 38.5 (s, CH3CH2N(CO)2), 43.8 (d, J CP ) 33
Hz, CH3CH2NP), 128.9-130.3 (s, o,m,p-PhP), 139.8 (d, 1J CP
)
24 Hz, ipso-Ph), 154.7 ppm, (d, 2J CP ) 7 Hz, CO). IR (CH2Cl2):
ν
CO 1692 (vs), 1658 cm-1 (vs). FD-MS: FD+ ) 293, Anal. Calcd
for C14H20N3O2P: C, 57.33; H, 6.87; N 14.33. Found: C, 57.23;
H, 6.93; N, 14.02.
1,3,5-tTr ip h en ylbiu r et P h en oxyp h osp h or u s Dia m id e
(1c). A solution of 1.03 g (11 mmol) of phenol in 10 mL of THF
was added to a solution of 2.77 g (11 mmol) of N,N′,N′′-
triphenylbiuret phosphorus chloride in 50 mL of THF and 5
mL of triethylamine (excess) at room temperature. Triethyl-
amine hydrochloride precipitated directly. The reaction is
complete after 1 h of stirring at room temperature, and the
2
ipso-Ph-N-P), 149.9 (s, CO), 151.6 (d, J CP ) 4 Hz, CO). IR
(CH2Cl2): νCO 1719 (vs), 1685 (vs). FAB/MS: m/e 905. Anal.
Calcd for C52H38N6O6P2: C, 69.03; H, 4.20; N 9.29. Found: C,
68.84; H, 4.36; N, 9.08.
Crystallization of the product from absolute ethanol gave
colorless crystals suitable for crystal structure determination.
Com p ou n d 2b. A solution of 2.0 mL (23 mmol) of phos-
phorus trichloride in 20 mL of toluene was added dropwise to
a solution of 4.2 g (23 mmol) of N,N′,N′′-triethylbiuret in 80
(42) d’Silva, T. D. J .; Lopes, A.; J ones, R. L.; Singhawangcha, S.;
Chan, J . K. J . Org. Chem. 1986, 51, 3781.

Rh Complexes with Phosphorus Diamide Ligands
Organometallics, Vol. 19, No. 13, 2000 2513
3
mL of toluene and 20 mL of triethylamine (excess) at room
temperature. Triethylamine hydrochloride precipitated di-
rectly. The reaction mixture was stirred overnight at 80 °C.
The mixture was cooled to room temperature, the precipitate
was filtered off, and the toluene was evaporated under
vacuum. The phosphorus chloride compound was obtained as
a yellow oil and used directly without further purification. The
purity of the compound was checked by NMR. A solution of
2.1 g (11 mmol) of 2,2′-hydroxy-1,1′-biphenyl in 10 mL of THF
was added dropwise to a solution of 5.6 g (22 mmol) of N,N′,N′′-
triethylbiuret phosphorus chloride in 50 mL of THF and 10
mL of triethylamine (excess). The reaction mixture was stirred
at room temperature for 1 h. The triethylamine salts were
filtered off, and the THF was evaporated. The product was
purified by filtration over neutral alumina to remove phosphite
impurities with toluene as eluent. The product is flushed from
the column with 1/1 PE (40-60)/EtOAc. The product was
obtained as a colorless oil that crystallized after 1 week.
Yield: 4.9 g (73%). Mp: 76 °C. 1H NMR (CDCl3): δ 0.9 (t, 6H,
CH3CH2N(CO)2), 1.3 (t, 12H, J HH ) 7 Hz, CH3CH2NP), 3.2
3
(d, 4H, J HP ) 5 Hz, CH2OP), 3.5 (m, 8H, CH3CH2NP), 3.9 (q,
4H, J HH ) 7 Hz, CH3CH2N(CO)2). 31P{1H} NMR (CDCl3): δ
3
85.4 (s). 13C NMR (CDCl3): δ 13.7 (s, CH3CH2N(CO)2), 16.1
2
(s, CH3CH2NP), 21.6 (s, C(CH3)2), 36.2 (d, J CP ) 3 Hz, CH2-
OP), 38.2 (s, CH3CH2N(CO)2), 42.4 (d, J CP ) 35 Hz, CH3CH2-
NP), 68.5 (d, J CP ) 6 Hz, C(CH3)2), 152.7 (d, J CP ) 10 Hz,
CO),. IR (CH2Cl2): νCO 1695 (vs), 1653 cm-1 (vs). FD-MS: FD+
) 534. Anal. Calcd for C21H40N6O6P2: C, 47.19; H, 7.54; N,
15.72. Found: C, 47.07; H, 7.43; N, 15.47.
2
3
2
Com p ou n d 2e. A 3.2 mL (7.3 mmol) amount of n-BuLi (2.5
M in hexane) was added dropwise to a solution of 1.69 g (3.6
mmol) of 4,5-dibromo-2,7-di-tert-butyl-9,9-dimethylxanthene in
70 mL of THF at -60 °C. The suspension was stirred for 1 h
at -60 °C. The reaction mixture was slowly warmed to 0 °C.
A 2.89 g (7.3 mmol) amount of N,N′,N′′-triphenylbiuret phos-
phorus chloride in 10 mL of THF was added dropwise to the
suspension at -60 °C. The reaction mixture was slowly
warmed to room temperature. The solution was filtered over
neutral alumina, and the THF was evaporated. The white solid
was crystallized from acetonitrile/methanol. Yield: 2.8 g (76%).
Mp: 341 °C. 1H NMR (acetone-d6): δ 1.5 (s, 18H, t-Bu), 1.9 (s,
6H, (CH3)2C), 6.8, 7.0, 7.4 (m, 30H, o,m,p-PhN), 7.6 (m, (broad),
3
3J HH ) 7 Hz, CH3CH2N(CO)2), 1.1 (t, 12H, J HH ) 7 Hz, CH3-
CH2NP), 2.9 (m, 4H, CH3CH2N(CO)2), 3.5 (q, 8H, 3J HH ) 7 Hz,
3
CH3CH2NP), 6.9 (d, 2H, J HH ) 8 Hz, o-Ph), 7.2 (m, 6H, m,p-
Ph). 31P{1H} NMR (CDCl3): δ 89.9 (s). 13C NMR (CDCl3): δ
13.4 (s, CH3CH2N(CO)2), 15.1 (s, CH3CH2NP), 39.4 (s, CH3CH2N-
2H, CHCC(CH3)2CCH), 8.0 (d, J PH ) 2 Hz, CHCP). 31P{1H}
3
2
NMR (CDCl3): δ 69.6 (s). 13C NMR (CDCl3): δ 31.8 (s,
(CH3)3C), 33.4 (s, (CH3)2C), 34.9 (s, (CH3)2C), 35.2 (s, (CH3)3C),
124.4-129.2 (aromatic C xanthene backbone and o,m,p-NPh),
130.5 (s, m-PhC(CH3)2), 137.0 (s, m-PhC(CH3)3), 140.1 (t,
o-OPhP), 154.3 (s, CO). IR (CH2Cl2): νCO 1706 (vs), 1675 (vs),
1670 cm-1 (sh). FAB/MS: m/e 1041.3. Anal. Calcd for
C63H58N6O5P2: C, 72.68; H, 5.62; N, 8.07. Found: C, 72.17; H,
5.72; N, 8.03.
(CO)2), 41.9 (d, J CP ) 35 Hz, CH3CH2NP), 120.8-132.5 (m,p-
Ph), 130.5 (s, o-Ph), 149.2 (d,2J CP ) 3 Hz, ipso-Ph), 151.9 (d,
2J CP ) 8 Hz, CO). IR (CH2Cl2): νCO 1702 (vs), 1660 cm-1 (vs).
FAB/MS: m/e 617. Anal. Calcd for C28H38N6O6P2: C, 54.54;
H, 6.21; N, 13.63. Found: C, 54.80; H, 6.23; N, 13.31.
Com p ou n d 2c. A 0.5 g (4.6 mmol) amount of 2,2′-dimethyl-
1,3-propanediol dissolved in 10 mL of THF was added dropwise
to a solution of 3.6 g (9.2 mmol) of N,N′,N′′-triphenylbiuret
phosphorus chloride and 10 mL (excess) of triethylamine in
150 mL of toluene at room temperature. When the addition
was completed, the mixture was stirred for 1 h at room
temperature. The triethylamine salts were filtered, and the
solvent was concentrated to 20 mL. The product was filtered
and washed with 60 mL of diethyl ether. The product was
dissolved in dichloromethane, and this solution was washed
with water. After evaporation of the dichloromethane the white
solid was washed with 20 mL of ether. Yield:1.6 g (43%). Mp:
240-242 °C dec. 1H NMR (CDCl3): δ 1.1 (s, CH3, 6H), 3.9
(d,3J PH ) 5 Hz, CH2, 4H), 7.4-7.2 (m, Ph, 30H). 31P{1H} NMR
(CDCl3): δ 83.1 (s). 13C NMR (CDCl3): δ 21.8 (s, C(CH3)2), 36.5
(s, CH2), 69.6 (s, C(CH3)2), 129.3-128.1 (m, o,m,p-Ph-N), 137.2
(s, ipso-Ph-(N(CO)2), 137.6 (d, 2J PC ) Hz, ipso-Ph-N-P), 152.3
(CO(NPh)2), 152.4 (s, CO-N-P). IR (CH2Cl2): νCO 1714 (vs),
Com p ou n d 2f. A solution of 1.37 g of (10 mmol) of
phosphorus trichloride in 20 mL of toluene was added dropwise
to a solution of 1.9 g (10 mmol) of N,N′,N′′-triethylbiuret in
80 mL of toluene and 10 mL of triethylamine (excess) at room
temperature. Triethylamine hydrochloride precipitated di-
rectly. The reaction mixture was stirred overnight at 80 °C.
The mixture was cooled to room temperature, the precipitate
was filtered off, and the toluene was evaporated under
vacuum. The phosphorus chloride compound was obtained as
a yellow oil and used directly without further purification. The
purity of the compound was checked by NMR. A 3.96 mL (9.9
mmol) amount of n-BuLi (2.5 M in hexane) was added dropwise
to a solution of 2.11 g (4.5 mmol) of 4,5-dibromo-2,7-di-tert-
butyl-9,9-dimethylxanthene in 70 mL of THF at -60 °C. The
suspension was stirred for 1 h at -60 °C. The reaction mixture
was slowly warmed to 0 °C. A 2.27 g (9 mmol) amount of
N,N′,N′′-triethylbiuret phosphorus chloride in 10 mL of THF
was added dropwise to the suspension at -60 °C. The reaction
mixture was slowly warmed to room temperature. The solution
was filtered over neutral alumina, and the THF was evapo-
rated. The white solid was washed with hot methanol. Yield:
3.1 g (92%). Mp: 259 °C. 1H NMR (CDCl3): δ 1.2 (m, 18H,
CH3CH2N), 1.3 (s, 18H, t-Bu), 1.6 (s, 6H, (CH3)2C), 3.8 (m, 12H,
1673 cm-1 (vs). FAB/MS: m/e 823. Anal. Calcd for C45H40
-
N6O6P2: C, 65.69; H, 4.87; N, 10.22. Found: C, 65.17; H, 4.94;
N, 10.16.
Com p ou n d 2d . A solution of 2.3 mL (26 mmol) of phos-
phorus trichloride in 20 mL of toluene was added dropwise to
a solution of 4.9 g (26 mmol) of N,N′,N′′-triethylbiuret in 80
mL of toluene and 20 mL of triethylamine (excess) at room
temperature. Triethylamine hydrochloride precipitated di-
rectly. The reaction mixture was stirred overnight at 80 °C.
The mixture was cooled to room temperature, the precipitate
was filtered off, and the toluene was evaporated under
vacuum. The phosphorus chloride compound was obtained as
a yellow oil and used directly without further purification. The
purity of the compound was checked by NMR. A solution of
1.1 g (10 mmol) of 2,2′-dimethyl-1,3-propanediol in 10 mL of
THF was added dropwise to a solution of 5.13 g (20 mmol) of
N,N′,N′′-triethylbiuret phosphorus chloride in 50 mL of THF
and 10 mL of triethylamine (excess). The reaction mixture was
stirred at room temperature for 1 h. The triethylamine salts
were filtered off, and the THF was evaporated. The product
was purified by column chromatography over neutral alumina
(eluent 4/1 PE (40-60)/EtOAc, Rf ) 0.6). The product was
obtained as a white powder. Yield: 3.2 g (60%). Mp: 56 °C.
3
CH3CH2N), 7.0 (s (broad), 2H, CHCC(CH3)2CCH), 7.4 (d, J PH
) 2 Hz, CHCP). 31P{1H} NMR (CDCl3): δ 57.1 (s). 13C NMR
(CDCl3): δ 13.6 (s, CH3CH2N(CO)), 14.7 (s, CH3CH2NP), 31.1
(s, (CH3)3C), 33.0 (s, (CH3)2C), 34.5 (s, (CH3)2C), 39.2 (s,
2
CH3CH2N(CO)), 43.0 (d, J CP ) 21 Hz, CH3CH2NP), 43.4 (s,
(CH3)3C), 123.9 (d, J CP ) 39 Hz, ipso-PPh), 124.6 (s, p-PhP),
126.5 (s, o-PhP), 129.6 (s, m-PhC(CH3)2), 145.8 (s, m-PhC-
(CH3)3), 150.0 (t, o-OPhP), 154.5 (d, 2J CP ) 4 Hz, CO). IR (CH2-
Cl2): νCO 1688 (vs), 1653 cm-1 (vs). FAB/MS: m/e 754. Anal.
Calcd for C39H58N6O5P2: C, 62.22; H, 7.77; N, 11.16. Found:
C, 62.06; H, 7.75; N, 11.02.
tr a n s-Rh ClCO(1a )2 (3a ). A solution of 176 mg (0.4 mmol)
of 1a in 2 mL of CH2Cl2 was added dropwise to a solution of
39 mg (0.1 mmol) of [Rh(CO)2Cl]2 in 2 mL of CH2Cl2. When
the ligand was added, CO evolved from the solution directly.
The yellow solution was stirred for 1 h at room temperature.
3
1H NMR (CDCl3): δ 0.8 (s, 6H, Me) 1.1 (t, 6H, J HH ) 7 Hz,

2514 Organometallics, Vol. 19, No. 13, 2000
van der Slot et al.
After 1 h the solvent was concentrated to 1 mL and 10 mL of
pentane was added. The complex precipitated directly. The
complex was filtered off and washed with hot benzene. This
resulted in a pure yellow powder. Yield: 177 mg (85%). Mp:
239 °C dec. 1H NMR (CDCl3): δ 7.7-7.1 (m, aromatic H). 31P-
m-PhOP). 31P{1H} NMR (CDCl3) δ 101.2 (doublet, 1J RhP ) 209
Hz), 13C NMR (CD2Cl2): δ 15.0 (s, CH3CH2N(CO)2), 16.3 (s,
CH3CH2NP), 40.7 (s, CH3CH2N(CO)2), 47.5 (dd, CH3CH2NP,
J RhC ) 16 Hz, J PC ) 16 Hz), 130.8 (m, o,m,p-PhOP), 139.0 (dt,
ipso-PhOP, J RhC ) 26 Hz, J PC ) 4 Hz), 154 (s, N(CO)2), 185
(dt, RhCO, J RhC ) 72 Hz, J PC ) 18 Hz). IR (CH2Cl2): νCO 1711
(vs), 1671 cm-1 (vs), νRh-CO 2025 cm-1. FAB/MS: m/e [RhClCO-
(1d )2]+ 785, [RhCl(1d )2]+ 756, [RhCO(1d )2]+ 749, [Rh(1d )2]+
721. Anal. Calcd for C29H40N6O7P2ClRh: C, 44.37; H, 5.14; N,
10.71. Found: C, 44.26; H, 4.91; N, 10.73.
1
{1H} NMR (CDCl3): δ 101.2 (doublet, J RhP ) 166 Hz). 13C
NMR (CD2Cl2): δ 130.5-135.3 (o,m,p-Ph), 138.9-139.3 (ipso-
Ph), 154.1 (NCO); the signal of the carbonyl ligand was not
obtained in 13C NMR because of the combination of low
intensity of the signal and low solubility of the compound. IR
(CH2Cl2): νCO 1719 (vs), 1694 (vs), 1676 cm-1, νRh-CO 2004 cm-1
(vs). FAB/MS: m/e [RhClCO(1a )2]+ 1041, [RhCO(1a )2]+ 1005,
[Rh(1a )2]+ 976. Anal. Calcd for C53H40N6O5P2ClRh‚CH2Cl2: C,
60.16; H, 3.93; N, 7.79. Found: C, 60.19; H, 4.02; N, 7.97.
tr a n s-Rh ClCO(1b)2 (3b). A solution of 117 mg (0.4 mmol)
of 1b in 2 mL of CH2Cl2 was added dropwise to a solution of
39 mg (0.1 mmol) of [Rh(CO)2Cl]2 in 2 mL of CH2Cl2. When
the ligand was added, CO evolved from the solution directly.
The yellow solution was stirred for 1 h at room temperature.
After 1 h the solvent was concentrated to 1 mL and 10 mL of
pentane was added. The complex precipitated directly. The
complex was filtered off and washed with 5 mL of pentane.
This resulted in a pure yellow powder. Yield: 119 mg (79%).
Mp: 158 °C dec. 1H NMR (CD2Cl2): δ 0.7 (t, 6 H, 3J HH ) 7 Hz,
Crystallization of a small fraction from benzene resulted in
crystals suitable for crystal structure determination.
HRh (1b)3CO (4). A 50 mg (0.2 mmol) amount of Rh(acac)-
(CO)2 and 285 mg (1.0 mmol) of 1b were dissolved in 20 mL of
toluene. The solution was brought into the autoclave and
pressurized to 20 bar of CO/H2 (1/1). The autoclave was heated
for 1 h at 80 °C and then heated to room temperature. After
depressurization the clear red solution was brought into a
Schlenk apparatus and saturated with argon. Upon standing
for one night under an argon atmosphere, compound 4 was
formed. Evaporation of the toluene and washing with benzene
gave the pure compound 4. Yield: 20 mg (10%). Mp: 106 °C
1
dec. H NMR (CD2Cl2): δ -10.7 (broad, hydride), 0.5 (broad,
9H, CH3CH2N(CO)2), 2.1 (broad, 18H, CH3CH2NP), 3.5 (broad,
3
18H, CH3CH2N), 7.1 and 7.3 (broad, 15H, o,m,p-PhP). 31P{1H}
(CO)2NCH2CH3), 1.3 (t, 12H, J HH ) 7 Hz, PNCH2CH3), 3.6
(q, 4 H, 3J HH ) 7 Hz, (CO)2NCH2CH3), 4.0 (multiplet, PNCH2-
CH3), 7.4 (multiplet, o,m,p-PhP). 31P{1H} NMR (CD6Cl6): δ
1
NMR (CD2Cl2): δ 117.2 (broad doublet, J RhP ) 169 Hz),;
because of fluxional behavior an accurate 13C NMR could not
be obtained). IR (CH2Cl2): νCO 1695 (vs), 1660 cm-1 (vs), νRh-CO
2019 cm-1. FD MS: FD+ 1012. Anal. Calcd for C43H61N9O7P3-
Rh: C, 51.04; H, 6.08; N, 12.46. Found: C, 51.16; H, 5.91; N,
12.62.
1
91.1 (d, J RhP ) 156 Hz). 13C NMR (CDCl3): δ 13.4 (s, CH3-
CH2NCO), 14.6 (s, CH3CH2NP), 39.4 (s, CH3CH2NCO), 44.8
(dd, J CP ) 10 Hz, J CRh ) 10 Hz, CH3CH2NP), 121.7-131.1
(o,m,p-PhP), 150.7 (dd, J CP ) 8 Hz, J CRh ) 8 Hz, NCO), 150.8
(s, ipso-PhP), 183.1 (dt, J CP ) 17 Hz, J CRh ) 72 Hz, RhCO). IR
(CH2Cl2): νCO 1705 (vs), 1670 cm-1 (vs), νRh-CO 2010 cm-1. FAB/
MS: m/e [RhClCO(1b)2]+ 753, [RhCl(1b)2]+ 724, [RhCO(1b)2]+
717. Anal. Calcd for C29H40N6O5P2ClRh: C, 46.26; H, 5.35; N,
11.16. Found: C, 46.24; H, 5.53; N, 11.02.
Crystallization of a small fraction from benzene resulted in
crystals suitable for crystal structure determination.
Cr ysta l Str u ctu r e Deter m in a tion of 1c, 2a , a n d 3c,d .
Detailed crystallographic information on the structures of 1c,
2a , and 3c,d is summarized in Table 12. An Enraf-Nonius
CAD-4 diffractometer with graphite-monochromated Cu KR
radiation and ω-2θ scan was used for data collection. The
intensities of two reflections were measured hourly. Unit-cell
parameters were refined by a least-squares fitting procedure
using 23 reflections with 80 e 2θ e 84° (1c), 80 e 2θ e 82°
(2a , 3c,d ). Absorption correction was performed with the
program PLATON,43 following the method of North et al.44
using ψ-scans of five reflections, with transmissions in the
range of 0.851-0.922 (1c), 0.677-0.913 (2a ), 0.497-0.989 (3c),
and 0.589-0.991 (3d ). The structure was solved by the PATTY
option of the DIRDIF96 program system.45 The hydrogen atom
positions were calculated. After isotropic refinement of the
initial model for 3c, ∆F synthesis revealed three independent
peaks, which formed a six-membered ring that was interpreted
as benzene, one of the solvents used during crystallization.
Full-matrix least-squares refinement on F, anisotropic for the
non-hydrogen atoms and isotropic for the hydrogen atoms, the
latter restrained in such a way that the carrier remained
constant at approximately 1.0 Å, converged to the following:
R ) 0.058, Rw ) 0.058 (∆/σ)max ) 0.05, S ) 0.99 (1c); R ) 0.066,
tr a n s-Rh ClCO(1c)2 (3c). A solution of 181 mg (0.4 mmol)
of 1c in 2 mL of CH2Cl2 was added dropwise to a solution of
39 mg (0.1 mmol) of [Rh(CO)2Cl]2 in 2 mL of CH2Cl2. When
the ligand was added, CO evolved from the solution directly.
The yellow solution was stirred for 1 h at room temperature.
After 1 h the solvent was concentrated to 1 mL and 10 mL of
pentane was added. The complex precipitated directly. The
complex was filtered off and washed with hot benzene. This
resulted in a pure pale yellow powder. Yield: 202 mg (94%).
Mp: 161 °C dec. 1H NMR (CDCl3): 7.55-6.55 (m, o,m,p-PhN,
1
o,m,p-PhOP). 31P{1H} NMR (CDCl3): δ 105 (doublet, J RhP
)
212 Hz). 13C NMR (CD2Cl2): δ 130-129 (m, o,p-PhN(CO)2, o,p-
PhOP), 131.0 (s, m- PhN(CO)2), 131.9 (s, m-PhOP), 135.8 (dd,
ipso-PhOP, J RhC ) 4 Hz, J PC ) 4 Hz), 137.3 (s, ipso-PhN), 151.0
(s, N(CO)2), 181.8 (dt, J RhC ) 73 Hz, J PC ) 20 Hz). IR (CH2-
Cl2): νCO 1725 (vs), 1692 cm-1 (vs), νRh-CO 2021 cm-1 (vs). FAB/
MS: m/e [RhClCO(1c)2]+ 1073, [RhCl(1c)2]+ 1044, [RhCO-
(1c)2]+ 1037, [Rh (1c)2]+ 1008. Anal. Calcd for C53H40
-
N6O7P2ClRh: C, 59.31; H, 3.76; N, 8.07. Found: C, 59.18; H,
3.93; N, 7.74.
Crystallization of a small fraction from CH2Cl2/Et2O resulted
in crystals suitable for crystal structure determination.
tr a n s-Rh ClCO(1d )2 (3d ). A solution of 124 mg (0.4 mmol)
of 1d in 2 mL of CH2Cl2 was added dropwise to a solution of
39 mg (0.1 mmol) of [Rh(CO)2Cl]2 in 2 mL of CH2Cl2 When
the ligand was added, CO evolved from the solution directly.
The yellow solution was stirred for 1 h at room temperature.
After 1 h the solvent was concentrated to 1 mL and 10 mL of
pentane was added. The complex precipitated directly. The
yellow complex was filtered off and washed with 5 mL of
pentane. Yield: 140 mg (89%). Mp: 158 °C dec. 1H NMR (CD2-
Rw ) 0.070 (∆/σ)max ) 0.32, S ) 1.063 (2a ); R ) 0.045, Rw
)
0.043 (∆/σ)max ) 0.66, S ) 1.008 (3c); R ) 0.045, Rw ) 0.049
(∆/σ)max ) 0.08, S ) 1.094 (3d ). A weighting scheme of w )
[1.5 + 0.01(σ(Fo))2 + 0.01/(σ(Fo))]-1 was used for 1c and 2a . A
weighting scheme of w ) [7.5 + 0.01(σ(Fo))2 + 0.01/(σ(Fo))]-1
was used for 3c. A weighting scheme of w ) [2.5 + 0.01(σ-
(Fo))2 + 0.01/(σ(Fo))]-1 was used for 3d . The secondary isotropic
extinction coefficient46,47 was refined to Ext ) 0.059(5) (1c),
(43) Spek, A. L. Acta Crystallogr. 1990, A46, C34.
(44) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr.
1968, A26, 351.
(45) Beurskens, P. T.; Beurskens, G.; Bosman, W. P.; de Gelder, R.;
Garcia-Granda, S.; Gould, R. O.; Israel, R.; Smits, J . M. M. The
DIRDIF-96 Program System; Crystallography Laboratory, University
of Nijmegen, Nijmegen, The Netherlands, 1996.
3
Cl2): δ 0.6 (t, 6 H, J HH ) 7 Hz, (CO)2NCH2CH3), 1.2 (t, 12H,
3
3J HH ) 7 Hz, PNCH2CH3), 3.4 (q, 4 H, J HH ) 7 Hz, (CO)2-
3
NCH2CH3), 4.1 (multiplet, PNCH2CH3), 6.9 (d, 4H, J HH ) 8
Hz, o-PhOP), 7.2 (t, 2H, 3J HH ) 7 Hz, p-PhOP), 7.3 (multiplet,

Rh Complexes with Phosphorus Diamide Ligands
Organometallics, Vol. 19, No. 13, 2000 2515
Ta ble 12. Cr ysta l Da ta a n d Deta ils of th e Str u ctu r e Deter m in a tion of 1d , 3c,d , a n d 2a
1d
2a
3c
3d
empirical formula
fw
temp, K
C
453.4
room temp
26H20N3O3P
C52H38N6O6P2
904.8
room temp
C29H40N6O7P2ClRh‚C6H6
785.0
253 K
C53H40N6O7P2ClRh
1073.2
233
wavelength (λ, Å)
abs coeff, µ, cm-1
cryst syst
space group
unit cell dimens
a, Å
Cu KR (1.5418)
13.2
monoclinic
P21/n
13.5
triclinic
P1h
51.3
44.6
triclinic
P1h
monoclinic
C2/c
12.4340(10)
13.9618(9)
13.5501(7)
90
100.467(5)
90
2313.2(3)
4
1.302
10.2617(7)
14.1002(9)
17.043(2)
92.463(5)
99.118(6)
100.740(5)
2263.9(4)
2
18.800(4)
14.402(1)
15.312(3)
90
98.45(1)
90
4100.8(12)
2
1.398
10.4140(9)
11.0175(5)
23.401(2)
83.941(7)
79.183(14)
67.480(4)
2434.4(3)
4
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
density, g cm-3
F(000)
1.327
940
1.464
1096
944
1784
cryst size, mm
range of data collecn, deg
index range
0.25 × 0.25 × 0.55
4.4 e θ e 74.8
0 e h e 15
0 e k e 17
-16 e l e 16
4755
0.25 × 0.50 × 0.50
2.6 e θ e 74.8
-12 e h e 12
-17 e k e 17
0 e l e 21
9294
0.30 × 0.40 × 0.65
3.9 e θ e 74.7
-23 e h e 0
0 e k e 17
-18 e l e 19
4205
0.30 × 0.50 × 0.60
3.8 e θ e 74.8
-13 e h e 0
-13 e k e 12
-29 e l e 28
10 043
no. of rflns collcd
final R
0.058 (for 3799
obsd rflns)
0.066 (for 7167
obsd rflns)
0.045 (for 3874
obsd rflns)
0.045 (for 9660
obsd rflns)
0.207(8) (2a ), 0.116(4) (3c), 0.291(7) (3d ). A final difference
Fourier map revealed a residual electron density between
-0.38 and 0.67 e Å-3 (1c), -0.45 and 0.42 e Å-3 (2a ), -0.9
and 1.19 e Å-3 (3c), and -2.0 and 1.44 e Å-3 (3d ) in vicinity of
the heavy atoms. Scattering factors were taken from refs 48
and 49. The anomalous scattering of Rh, Cl, and P was taken
from ref 48. All calculations were performed with XTAL,50
unless stated otherwise.
(SIR-97)52 and refined with the program SHELXL-9753 as an
inversion twin against F2 of all reflections up to a resolution
of ((sin θ)/λ)max ) 0.65 Å-1. The Flack x parameter was
determined as 0.54(4). Non-hydrogen atoms were refined freely
with anisotropic displacement parameters. The hydride hy-
drogen atom was fixed in a calculated position; the other
hydrogen atoms were refined as rigid groups. The drawings,
calculations, and checking for higher symmetry were per-
formed with the PLATON package.51 R(I > 2σ(I)): R1 )
0.0452, wR2 ) 0.1016. R(all data): R1 ) 0.0591, wR2 ) 0.1078.
S ) 1.046.
Cr ysta l Str u ctu r e Deter m in a tion of 4. Crystal data:
C
43H61N9O7P3‚3C6H6, fw ) 1246.15, yellow block, 0.55 × 0.30
× 0.10 mm3, trigonal, R3c (No. 161), a ) b ) 23.2546(17) Å, c
) 19.624(2) Å, γ ) 120°, V ) 9190.4(13) Å3, Z ) 6, F ) 1.351
g cm-3. Intensities were measured on an Enraf-Nonius CAD4T
diffractometer with a rotating anode (Mo KR, λ ) 0.710 73 Å)
at a temperature of 150 K. Absorption correction was based
on ψ-scans (PLATON,51 µ ) 0.416 mm-1, 0.86-0.97 transmis-
sion): 18 616 measured reflections, 4700 unique reflections
(Rint ) 0.0773). The structures were solved with direct methods
Ack n ow led gm en t. The crystal structure determi-
nation of complex 4 was in part supported (M.L., A.L.S.)
by the Council for Chemical Sciences of The Netherlands
Organization for Scientific Research (CW-NWO).
Su p p or tin g In for m a tion Ava ila ble: Listings of crystal
data and collection parameters, atomic coordinates, bond
lengths, bond angles, and thermal displacement parameters
for compounds 1c, 2a , 3c,d , and 4. This material is available
free of charge via the Internet at http://pubs.acs.org.
(46) Zachariasen, W. H. Acta Crystallogr. 1967, A23, 558.
(47) Larson, A. C. Crystallogr. Comput. 1969, 291.
(48) Cromer, D. T.; Mann, J . B. Acta Crystallogr. 1968, A24, 321.
(49) International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, U.K., 1974; Vol. IV, p 55.
OM9910120
(50) Hall, S. R., King, G. S. D., Stewart, J . M., Eds. XTAL3.4 User’s
Manual; University of Western Australia, Lamb, Perth, Australia,
1995.
(51) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool;
Utrecht University, Utrecht, The Netherlands, 1999.
(52) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J . Appl. Crystallogr. 1999, 32, 115.
(53) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure
Refinement; University of Go¨ttingen, Germany, 1997.