Synthesis and characterization of a novel hydrido-alkyl complex of rhodium(III) formed by intramolecular activation of a benzylic C-H bond: Trans-bis[N-methyl-N-propionyl-2-(diphenylphosphino)benzylamine] hydridorhodium(III) hexafluorophosphate

Article abstract of DOI:10.1021/om970801j

The phosphine N-methyl-N-propionyl-2-(diphenylphosphino)benzylamine (1), reacting with the precursor complex [Rh(NBD)L][PF₆] (L = 1, NBD = 2,5-norbornadiene) and molecular hydrogen under ambient conditions, undergoes chelate-assisted C-H bond activation at the benzylic position, quantitatively yielding the five-membered chelate complex trans-[RhH(P(C₆H₄-o-(CH₂N(CH ₃)COCH₂CH₃))(C₆H₅) ₂)(P(C₆H₄-o-(CHN(CH₃)COCH ₂CH₃))(C₆H₅)₂)]-[PF ₆] (4). Extensive spectroscopic studies demonstrate that the rhodium is located in the center of a square bipyramid with an apical hydrogen.

Full text of DOI:10.1021/om970801j

Organometallics 1998, 17, 579-583
579
Syn th esis a n d Ch a r a cter iza tion of a Novel
Hyd r id o-Alk yl Com p lex of Rh od iu m (III) F or m ed by
In tr a m olecu la r Activa tion of a Ben zylic C-H Bon d :
tr a n s-Bis[N-m eth yl-N-p r op ion yl-2-(d ip h en ylp h osp h in o)ben zyl-
a m in e]h yd r id or h od iu m (III) Hexa flu or op h osp h a te
Sven Sjo¨vall, Lars Kloo, Antonios Nikitidis, and Carlaxel Andersson*
Inorganic Chemistry 1, Centre for Chemistry and Chemical Engineering, Lund University,
P.O. Box 124, S-221 00 Lund, Sweden
Received September 11, 1997
The phosphine N-methyl-N-propionyl-2-(diphenylphosphino)benzylamine (1), reacting with
the precursor complex [Rh(NBD)L][PF6] (L ) 1, NBD ) 2,5-norbornadiene) and molecular
hydrogen under ambient conditions, undergoes chelate-assisted C-H bond activation at the
benzylic position, quantitatively yielding the five-membered chelate complex trans-
[RhH(P(C6H4-o-(CH2N(CH3)COCH2CH3))(C6H5)2)(P(C6H4-o-(CHN(CH3)COCH2CH3))(C6H5)2)]-
[PF6] (4). Extensive spectroscopic studies demonstrate that the rhodium is located in the
center of a square bipyramid with an apical hydrogen.
In tr od u ction
and therefore the substituent pattern of the reacting
ligand is of importance; ligands with the ability to form
five- or six-membered cyclometalated products are the
ones prone to undergo the insertion reaction. Most
examples reported concern phosphine ligands carrying
a polar functional group (amide, ether) in proximity to
the reacting C-H bond, but insertion of Rh(III) into the
C-H bond of the methyl group in tri-o-tolylphosphine
has also been observed.7 Part of the current interest
in cyclometalated complexes stems from a recent dis-
covery; palladium insertion into the methyl C-H bond
of tri-o-tolylphosphine gives thermally stable pallada-
cycles, which are highly active as catalysts in C-C bond-
forming reactions.8,9 An ongoing project in our group
is to synthesize new metallacyclic complexes by in-
tramolecular C-H activation of suitable phosphine
ligands, using late transition metals and different bulky
phenyl phosphines. The aim is partly to find general
information about how the reactivity and selectivity
leading to C-H activation depend on the nature of the
side chains in phenylphosphines and partly to deter-
mine whether metallacycle formation enhances catalytic
activity or causes catalyst deactivation.9 As an immedi-
ate consequence of this we now report a new rhodium-
containing complex (4) formed by transition-metal
insertion into a benzylic C-H bond.
Alkanes are abundant in nature and are relatively
inexpensive, and any chemical synthesis involving
utilization of hydrocarbons would be of commercial and
environmental importance. Therefore, any possibility
to activate unreactive C-H bonds (bond energies in the
range of 90-100 kcal/mol and very low basicity/acidity)
has been of major interest, but a difficult task, to
chemists for the last few decades. Alkanes have long
been known to undergo a number of solution and gas-
phase reactions involving free radicals as intermediates,
such as photochlorination, autoxidation, and combus-
tion. More recently, “super acids” have been developed
that are capable of adding protons to alkanes.1
A general problem is controlling the selectivity in
hydrocarbons possessing different C-H bonds and mak-
ing sure that the C-H bonds in the product are not
more reactive than those in the starting alkane, or low
yields will be inevitable.2 A fruitful way to achieve this
in chemical synthesis is to use the versatile reactivity
of the carbon-metal bond, and this has been done in
homogeneous reactions with transition-metal complexes
treated with reactive substrates.3ab
The so-called “ortho metalation” reaction and chelate-
assisted insertion into C-H bonds are special examples
of C-H bond activation. The latter reaction type, also
possible in insertion into C-C and Si-H bonds, occurs
readily using bifunctional phosphine4a-c or 8-quinoline5ab
ligands in combination with electron-rich late-transi-
tion-metal centers. A favorable change in entropy6
provides the energy for the cyclometalation processes,
(4) For example see: (a) Werner, H.; Schulz, M.; Windu¨ller, B.
Organometallics 1995, 14, 3659. (b) Auburn, M. J .; Holmes-Smith, D.;
Stobart, S. R. J . Am. Chem. Soc. 1984, 106, 1314. (c) Hedden, D.;
Roundill, D. M.; Fultz, W. C.; Rheingold, A. L. J . Am. Chem. Soc. 1984,
106, 5014.
(5) For example see: (a) Suggs, J . W. J . Am. Chem. Soc. 1978, 100,
640. (b) Suggs, J . W.; J un, C.-H. J . Am. Chem. Soc. 1984, 106, 3054.
(6) Shaw, B. L. J . Organmet. Chem. 1980, 200, 307.
(7) Bennett, M. A.; Longstaff, P. A. J . Am. Chem. Soc 1969, 91, 6266.
(8) Hoechst AG (Herrmann, W. A.; Brossmer, C.; Beller, M.; Fischer,
H.). Ger. Offen. DE 4.421.730 and DE 4.421.753, 1994.
(9) Herrmann, W. A.; Brossmer, C.; O¨ fele, K.; Reisinger, C.-P.;
Priermeier, T.; Beller, M.; Fischer, H. Angew. Chem., Int. Ed. Engl.
1995, 34, 1844.
(1) Arndtsen, B. A.; Bergman, R. G.; Mobley, T. A.; Peterson, T. H.
Acc. Chem. Res. 1995, 28, 154.
(2) Luinstra, G. A.; Wang, A.; Stahl, S. S.; Labinger, J . A.; Bercaw,
J . E. J . Organomet. Chem. 1995, 504, 75.
(3) For example see: (a) Dehand, J .; Pfeffer, M. Coord. Chem. Rev.
1976, 18, 327. (b) J anowicz, A. H.; Bergman, R. G. J . Am. Chem. Soc.
1982, 104, 352.
S0276-7333(97)00801-7 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 01/23/1998

580 Organometallics, Vol. 17, No. 4, 1998
Sjo¨vall et al.
Sch em e 1a
(Scheme 1). The FAB mass spectrum, with the molec-
ular ion peak at m/z 825, indicates a monomeric
structure for 4. An independent osmotic molecular
weight determination supports this interpretation. In
addition, an elemental analysis verifies the stoichio-
metric composition of 4.
All attempts to grow single crystals of 4 have so far
failed, and its structural features are therefore based
on spectroscopic evidence. All NMR spectroscopic analy-
ses of complex 4 were performed at -20 °C in order to
slow down the dynamic processes, probably caused by
the weak coordination of the amide oxygens to the
transition-metal center. On the basis of 31P and 1H
spectra alone it is evident that the complex contains two
nonequivalent phosphine ligands and a hydride. The
results obtained by 31P{1H} NMR spectroscopy reveal
an ABX pattern with two doublets of doublets at 55.5
a
Legend: NBD ) 1,5-norbornadiene; R ) Et; L ) DPPBA.
Phenyls on P are omitted for clarity in 4a .
2
(1J RhP(1) ) 119 Hz, J P(1)P(2) ) 401 Hz) and 33.7 ppm
(1J RhP(2) ) 115 Hz, 2J P(2)P(1) ) 401 Hz), respectively. The
various coupling constants were verified by a 31P{1H}
COSY NMR spectrum (Figure 1).
Resu lts a n d Discu ssion
A dichloromethane solution of the dimeric rhodium-
olefin complex [Rh(NBD)Cl]2 (NBD ) 2,5-norborna-
diene) and 2 equiv of the ligand DPPBA (1; N-methyl-
N-propionyl-2-(diphenylphosphino)benzylamine), stirred
for 1 h at room temperature, yields after workup a
yellow complex with the composition [Rh(NBD)(DPP-
BA)Cl] (2) (Scheme 1).
A 31P{1H} NMR spectroscopic analysis of this complex
exhibits two doublets at 22.7 (1J RhP ) 164 Hz) and 22.1
ppm (1J RhP ) 165 Hz), respectively. The protons of the
N-methyl group, N-CH3, display two singlets in the 1H
NMR spectrum positioned at 3.15 and 3.05 ppm, re-
spectively. The relative intensity of the two 31P peaks,
also seen for the two N-methyl 1H peaks, is 1:0.7, clearly
indicating an equilibrium between two isomers, prob-
ably caused by two different rotational conformations
1
The H NMR spectrum of 4 exhibits a hydride signal,
a doublet of doublets of doublets, at -16.8 ppm with an
intensity equal to one hydrogen.
A
1H{31P} NMR
experiment results in collapse of the hydride signal into
a doublet at -16.8 ppm (1J RhH ) 24.7 Hz). Irradiation
of the phosphorus signal at 55.5 ppm results in collapse
into a doublet of doublets at -16.8 ppm (1J RhH ) 24.7
2
Hz, J P(2)H ) 13.6 Hz). Analogously, irradiation of the
other phosphorus signal at 33.7 ppm also gives a doublet
2
of doublets at -16.8 ppm (1J RhH ) 24.7 Hz, J P(1)H
)
1
8.84 Hz). Furthermore, the H NMR spectrum exhibits
three nontrivial resonances, with intensities equivalent
to one hydrogen each, a doublet of doublets at 6.37 ppm
and a doublet at 4.23 and 3.50 ppm, respectively. The
assignment of these resonances follows from the 1H
COSY pattern, which reveals that the signals at 6.37
and 3.50 ppm are coupled and are interpreted to stem
from the benzylic protons. Hence, the benzylic protons
in one of the ligands are diastereotopic, which is in
accord with different chemical environments above and
below the plane of the aryl ring. On the other hand,
the doublet at 4.23 ppm shows no 1H coupling and this
feature is indicative of rhodium insertion into the
benzylic C-H bond of the second phosphine ligand,
leaving a single proton at the benzylic carbon and
unmasking the other proton as the observed hydride
1
of the amide. The value of J RhP is typical for a
rhodium(I)-complexed monodentate phosphine ligand
trans to an alkene.10 The infrared spectroscopic analy-
sis shows two strong amide carbonyl absorptions at 1655
and 1645 cm-1, which exactly match the frequencies of
the free ligand 1. Collective IR and NMR spectroscopic
data for 2 are thus in agreement with a complex
expected from a bridge cleavage of the precursor, the
ligand 1 coordinating monodentately by its P donor and
cis to the chloride ligand.
Carrying out an anion metathesis with complex 2 and
potassium hexafluorophosphate yields the complex [Rh-
(NBD)(DPPBA)][PF6] (3) (Scheme 1). Its amide carbo-
ligand. Combined with the 1H{31P} spectrum it is
2
possible to determine the coupling constants: J HH
)
nyl group stretching frequencies, at 1577 and 1569 cm-1
,
14.8 and J PH ) 3.90 Hz at 6.37 ppm, 3J PH ) 15.3 Hz at
4.23 ppm, J HH ) 14.8 Hz at 3.50 ppm. The different
4
are shifted to lower wavenumbers relative to the free
ligand, thus indicating coordination of the carbonyl
group to the formally three-coordinate metal center.
P-O chelate coordination implies a fixed conformation
of the phosphine ligand in complex 3, and this is
confirmed by the NMR spectroscopic data with the 31P-
{1H} NMR spectrum at -20 °C exhibiting a doublet at
2
proton-phosphorus couplings observed, the proton reso-
nance at 4.23 ppm being more strongly coupled, provide
further evidence for the formation of a metallacycle by
insertion into the benzylic C-H bond.
Final proof of the formation of a metallacyclic struc-
ture is obtained by further NMR experiments. The 13C-
{1H} NMR spectrum exhibits two different sets of
signals, which is in accord with the two phosphine
ligands being nonequivalent. Interestingly, there is a
sharp doublet at 53.7 ppm and a broad doublet at 61.8
ppm. These stem from the benzylic carbons. In our
interpretation, the splitting of the former is caused by
24.5 ppm (1J RhP ) 167 Hz) and the H NMR spectrum
1
at -20 °C exhibiting a singlet at 2.58 ppm for N-CH3.
Treatment of complex 3 with 1 equiv of ligand 1 under
an atmosphere of hydrogen for 120 min at room tem-
perature yields the complex [RhH(DPPBA)2][PF6] (4)
(10) Naaktgeboren, A. J .; Nolte, R. J . M.; Drenth, W. J . Am. Chem.
Soc. 1980, 102, 3350.
3
a J PC ()5.13 Hz) coupling, and the splitting of the latter

A Novel Hydrido-Alkyl Complex of Rh(III)
Organometallics, Vol. 17, No. 4, 1998 581
F igu r e 1. 31P{1H} COSY NMR spectrum of complex 4.
Ta ble 1. 1H a n d 13C Ch em ica l Sh ifts a n d Cou p lin g
in th e HMQC Sp ectr u m of 4a ,b
The large coupling constant (J PP ) 401 Hz) is a
consequence of the two phosphine ligands being mutu-
ally trans.12 The magnitude of the coupling constant
can also be explained in terms of trans influence, where
both the hydride and the methine group impose greater
trans influence than the phosphorus.13 The signal at
lower field is assigned to the phosphorus in the metal-
lacycle, which falls within the well-known range 20-
50 ppm downfield for a phosphorus involved in a five-
membered chelate relative to its noncoordinated ana-
logue.14ab Furthermore, the J RhP value for the chelating
ligand is larger than the J RhP value for the unmetalated
ligand, which opposes the trend seen in platinum
complexes when the phosphorus atoms are trans.15
By running an HMBC NMR experiment (2D inverse
functional group
13C
1H
CH3-
CH3-
9.80
10.7
0.55
0.75
CH3CH2-
CH3CH2-
N-CH3
N-CH3
-CH2-
dCH-
29.2
30.4
36.1
42.5
53.7
61.8
1.10; 1.48
1.48; 1.72
1.89
3.08
3.50; 6.37
4.23
a
b
In CD2Cl2 at -20 °C. Omitting chemical shifts of phenyls
for clarity.
1
1
is caused by a J RhC ()31.1 Hz) coupling. J RhC coupling
constants in the range of 31-40 ppm have been
reported.11ab In order to verify this interpretation, an
HMQC NMR experiment (2D inverse H,C correlation,
2
3
H,C long-range correlation, where J CH and J CH spin
couplings can be detected) and comparing the results
with 1H and 13C NMR spectroscopic data, it is also
possible to determine the chemical shifts versus the
position of all the atoms in the side chains of the ligands
(Table 2). Once again, the broad peaks in the 2D
1
where J CH spin couplings can be detected) was made
1
(Table 1). The 13C signal at 61.8 ppm couples to the H
signal at 4.23 ppm, and the 13C signal at 53.7 ppm
couples to the 1H signals at 6.37 and 3.50 ppm.
Unfortunately, the broad peaks in the 2D spectrum
2
spectrum hamper the extraction of the individual J CH
1
hamper the extraction of the individual J CH coupling
3
and J CH coupling constants.
constants.
Once the metallacyclic structure is verified, further
(12) Goodfellow, R. G. Chem. Commun. 1968, 3, 114.
(13) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev.
1973, 10, 335.
features in the 31P{1H} spectrum are worth considering.
(11) (a) van der Zeijden, A. A. H.; van Koten, G.; Ernsting, J . M.;
Elsevier, C. J . J . Chem. Soc. Dalton Trans. 1989, 317. (b) Rybtchinski,
B.; Vigalok, A.; Ben-David, Y.; Milstein, D. J . Am. Chem. Soc. 1996,
118, 12406.
(14) (a) Garrou, P. E. Chem. Rev. 1981, 81, 229. (b) Lindner, E.;
Fawzi, R.; Mayer, H. A.; Eichele, K.; Hiller, W. Organometallics 1992,
11, 1033.
(15) Garrou, P. E. Chem. Rev. 1981, 81, 246.

582 Organometallics, Vol. 17, No. 4, 1998
Sjo¨vall et al.
Ta ble 2. 1H a n d 13C Ch em ica l Sh ifts a n d Cou p lin g
in th e HMBC Sp ectr u m of 4a
by an electron-rich metal center more plausible. Fur-
thermore, we believe that the hydride in complex 4
stems from the activated benzylic group, after passing
through an intermediate dihydrido complex.19ab This
is, of course, speculative, and an isotopic labeling
experiment could clarify this.
functional group
13C
1H
-(CdO)-
-(CdO)-b
182
179
6.37; 3.50; 3.08; 1.72; 1.48; 0.75
4.23; 1.89; 1.48; 1.10; 0.55
a
b
In CD2Cl2 at -20 °C. The chelating ligand.
Exp er im en ta l Section
The two amide carbonyl stretching frequencies, at
1595 and 1575 cm-1, are shifted to lower wavenumbers
relative to the free ligand, verifying that the carbonyl
groups in the ligands are nonequivalent and are coor-
dinated to the rhodium atom.
All experiments with metal complexes and the phosphine
ligand were performed under an atmosphere of argon using
standard Schlenk techniques. All non-deuterated solvents,
reagent grade or better, were distilled over sodium/benzophe-
none ketyl under an atmosphere of nitrogen. Deuterated
solvents were used as received. All solvents were thoroughly
deoxygenated with argon prior to use. Commercially available
reagents were used as received. The complex [Rh(NBD)Cl]2
and the phosphine ligand DPPBA were prepared according to
literature procedures.20 21
This leaves us with the task of describing the actual
geometry of the complex. The compound is a six-
coordinate Rh(III) complex, regular or distorted, with
the ligand donor set {P , P , H, -CH-, CdO, CdO}. On
the basis of the large J PP coupling a trans position of
the two P-donors is highly likely, and this reduces the
number of possible combinations. Furthermore, the P
donor of the ligand forming the metallacycle is at the
terminus, thus capping one of the triangular faces of
the octahedron. Face capping is achieved by two five-
membered metallacycles, Rh-P-C and Rh-O-C, which
are interconnected by the methine carbon. This leaves
two possibilities for the hydride ligand; either trans to
the amide oxygen of the face-capping ligand or trans to
the methine carbon atom. The rather low Rh-H
stretching frequency (2070 cm-1) indicates that the
hydride is situated trans to a ligand high in the trans-
influence series,16 i.e. the methine carbon. However,
taking the trans influence of both the hydride and the
methine carbon and the results of a previous publica-
tion17 into account, it is more likely that the hydride is
located trans to the amide oxygen. The weak coordina-
tion of the second amide oxygen, trans to the methine
carbon atom, then completes the octahedral coordina-
tion.
1H and 31P NMR spectra were recorded at 300 and 121 MHz,
respectively, using a Varian Unity 300 MHz spectrometer. 13C,
1H COSY, HMBC, and HMQC NMR spectra were recorded at
125 and 500 MHz, respectively, using a Bruker ARX 500 MHz
spectrometer. Unless otherwise stated, the NMR measure-
ments were performed in CD2Cl2. 1H NMR and 13C{1H} NMR
chemical shifts are reported in parts per million downfield from
tetramethylsilane. 1H and 1H COSY NMR chemical shifts
were referenced to the residual hydrogen signal of the deu-
terated solvents (7.25 ppm, chloroform; 5.31 ppm, dichlo-
romethane; 2.50 ppm, DMSO). In the 13C{1H} NMR measure-
ments the signal of CD2Cl2 (55.8 ppm) was used as reference.
In the HMQC and HMBC experiments the same references
1
were used separately as in the H and 13C{1H} NMR measure-
ments. 31P NMR chemical shifts are reported in parts per
million downfield from an external 85% solution of phosphoric
acid. Abbreviations used in the description of NMR spectro-
scopic data are as follows: s, singlet; d, doublet; m, multiplet;
b, broad; q, quartet; t, triplet. Fast atom bombardment (FAB)
mass spectroscopic data were obtained on a J EOL SX-102
spectrometer using 3-nitrobenzyl alcohol as matrix and CsI
as calibrant. Infrared spectra were recorded on a Bio-Rad FTS
6000 FT-IR spectrometer. Elemental analyses were performed
by AB Mikro Kemi, Uppsala, Sweden.
This complex shows remarkable stability under an
atmosphere of air, as a solid for years and in a
homogeneous solution for several weeks, which is an
unusual feature for oxidative-addition products from the
second row of the transition metals.18
Rea ction of [Rh (NBD)Cl]2 w ith Liga n d 1. F or m a tion
of [Rh (NBD)(DP P BA)Cl] (2). To a dichloromethane solution
(5 mL) of [Rh(NBD)Cl]2 (235 mg, 0.501 mmol) was added a
dichloromethane solution (10 mL) of DPPBA (1). After it was
stirred for 1 h, the solution was reduced to 5 mL and n-hexane
(40 mL) was added. The solution was reduced to 10 mL,
yielding a yellow precipitate, which was filtered, washed with
n-hexane (20 mL), and dried under vacuum. Yield: 490 mg
(79%). 31P{1H} NMR in CDCl3: 22.7 (d, 1J RhP ) 164 Hz), 22.1
(d, 1J RhP ) 165 Hz) (relative intensity of the doublets is 1:0.7).
1H NMR in CDCl3: 5.85 (bs, 1H, NBD), 5.50 (bs, 1H, NBD),
5.35 (bs, 2H, NBD), 3.80 (bs, 2H, Ar-CH 2-), 3.40 (bs, 2H,
Con clu sion
The complex [RhH(DPPBA)2][PF6] (4) is rapidly formed
by insertion into a benzylic C-H bond of one of the
ligands. The major driving force for the C-H activation
is the formation of a chelate, but steric and electronic
factors are also of importance. Hydrogenation of the
π-accepting norbornadiene ligand in the precursor 3 and
simultaneous coordination of an additional σ-donating
phosphine increase the steric crowding as well as the
electron density at the Rh center. We believe that the
steric bulk of the phosphine ligand, which brings the
alkane bonds into the vicinity of the rhodium atom,
plays a minor role compared to the electronic factor. In
addition, the capability to form resonance structures in
the side chains of the ligands enhances the acidity of
the benzylic protons, thereby making oxidative addition
3
NBD), 3.15 (s, N-CH3), 3.05 (s, N-CH3), 2.55 (q, J HH ) 7.50
3
Hz, -CH2-), 2.31 (q, J HH ) 7.50 Hz, -CH2-), 1.47 (bd, 2H,
NBD), 1.27 (t, 3J HH ) 7.50 Hz, -CH3), 1.14 (t, 3J HH ) 7.50 Hz,
-CH3) (relative intensity of the alkane signals is 1:0.7). IR
(CsI): 1655 and 1645 cm-1 (s, CdO). Anal. Calcd: C, 60.9;
H, 5.5; P, 5.2. Found: C, 61.2; H, 5.9; P, 4.8.
Rea ction of [Rh (NBD)(DP P BA)Cl] (2) w ith KP F6. F or -
m a tion of [Rh (NBD)(DP P BA)][P F 6] (3). To a dichlo-
romethane solution (15 mL) of [Rh(NBD)(DPPBA)Cl] (2; 260
(19) (a) Brown, J . M.; Chaloner, P. A.; Kent, A. G.; Murrer, B. A.;
Nicholson, P. N.; Sidebottom, P. J . J . Organomet. Chem. 1981, 216,
263. (b) Schrock, R. R.; Osborn, J . A. J . Am. Chem. Soc. 1976, 98, 2134.
(20) Abel, E. W.; Bennet, M. A.; Wilkinson, G. J . Chem. Soc. 1957,
3178.
(21) Nikitidis, A.; Andersson, C. Phosphorus, Sulfur Silicon Relat.
Elem. 1993, 78, 141.
(16) J esson, J . P. Transition Metal Hydrides; Muetterties, E. L., Ed.;
Dekker: New York, 1971; Chapter 4.
(17) Nemeh, S.; J ensen, C.; Binamira-Soriaga, E.; Kaska, W. C.
Organometallics 1983, 2, 1442.
(18) J ones, W. D.; Feher, F. J . Organometallics 1983, 2, 562.

A Novel Hydrido-Alkyl Complex of Rh(III)
Organometallics, Vol. 17, No. 4, 1998 583
2
mg, 0.439 mmol) was added an aqueous solution (7 mL) of
potassium phosphate (298 mg, 1.62 mmol). After 1.5 h the
organic layer was removed, washed with water (4 × 10 mL),
and reduced to ca. 3 mL under vacuum. A 15 mL portion of
diethyl ether was added slowly to complete the precipitation.
The yellow precipitate was filtered, washed with diethyl ether
(3 × 10 mL), and air-dried. Yield: 290 mg (94%). 31P{1H}
NMR in DMSO: 24.5 (d, 1J RhP ) 167 Hz). 1H NMR in DMSO:
7.80-6.90 (m, 14H, aromatic), 5.68 (bd, 2H, Ar-CH2-), 4.31
(bs, 4H, NBD), 3.80 (bs, 2H, NBD), 2.58 (s, 3H, N-CH3), 1.61
401 Hz). 1H NMR: 7.65-7.15 (m, 28H, Ar), 6.37 (dd, J HH
)
4
3
14.8 Hz, J PH ) 3.90 Hz, 1H, Ar-CH2-), 4.23 (d, J PH ) 15.3
Hz, 1H, Ar-C(R)H-Rh), 3.50 (d, J HH ) 14.8 Hz, 1H, Ar-
CH2-), 3.08 (s, 3H, N-CH3), 1.89 (s, 3H, N-CH3), 1.72 (m,
1H, -CH2-), 1.48 (dm, 2H, -CH2-), 1.10 (m, 1H, -CH2-),
0.75 (t, J HH ) 7.34 Hz, 3H, -CH3), 0.55 (t, J HH ) 7.34 Hz,
2
3
3
1
2
3H, -CH3), -16.8 (ddd, J RhH ) 24.7 Hz, J P(2)H ) 13.6 Hz,
2J P(1)H ) 8.84 Hz) (assignment of 1H NMR signals was
confirmed by H{31P} and H COSY NMR experiments). 13C-
1
1
{1H} NMR: 182 (s, -C(dO)-), 179 (s, -C(dO)-), 144-128
3
(q, J HH ) 7.36 Hz, 2H, -CH2-), 1.22 (bs, 2H, NBD), 0.57 (t,
1
(md, Ar ), 61.8 (bd, J RhC ) 31.1 Hz, Ar-C(R)H-Rh), 53.7 (d,
3J HH ) 7.36 Hz, 3H, -CH3). IR (CsI): 1577 and 1569 cm-1 (s,
CdO). Anal. Calcd: C, 51.7; H, 4.6; N, 2.0; P, 8.8. Found:
C, 51.6; H, 4.8; N, 2.0; P, 8.8.
3J PC ) 5.13 Hz, Ar-CH2-), 42.5 (s, N-CH3), 36.1 (s, N-CH3),
30.4 (s, -CH2-), 29.2 (s, -CH2-), 10.7 (s, -CH3), 9.80 (s,
-CH3) (assignment of 13C{1H} NMR signals was confirmed by
HMQC and HMBC NMR experiments). IR (Nujol): 2070 cm-1
(m, Rh-H), 1595 and 1575 cm-1 (s, CdO). FAB/MS: m/ z 825,
M+. Anal. Calcd: C, 56.8; H, 5.1; N, 2.9; P, 9.6. Found: C,
56.4; H, 4.9; N, 2.8; P, 9.3.
Rea ction of [Rh (NBD)(DP P BA)][P F 6] (3) w ith Liga n d
1. F or m a tion of [Rh (DP P BA)2H][P F 6] (4). A dichlo-
romethane solution (5 mL) of DPPBA (1; 52.9 mg, 0.15 mmol)
and [Rh(NBD)(DPPBA)][PF6] (3; 102 mg, 0.15 mmol) was
cooled to -10 °C. The argon atmosphere was replaced by
molecular hydrogen, and the solution was warmed to room
temperature at ambient pressure. After 2 h the reaction was
terminated by adding 20 mL of diethyl ether, yielding a white
precipitate. The cold suspension (-30 °C) was filtered, and
the precipitate was washed with diethyl ether (2 × 10 mL).
Ack n ow led gm en t. Financial support by the TFR
(The Swedish Research Council for Technological Sci-
ences) and the NFR (The Swedish Natural Science
Research Council) is gratefully acknowledged.
1
Yield: 108 mg (74%). 31P{1H} NMR: 55.5 (dd, J RhP(1) ) 119
2
1
2
Hz, J P(1)P(2) ) 401 Hz), 33.7 (dd, J RhP(2) ) 115 Hz, J P(2)P(1)
)
OM970801J