Synthesis of the new chiral (R)- and (S)-aminodiphosphine ligands sec-butylbis(2-(diphenylphosphino)ethyl)amine, sec-butylbis(2-(dicyclohexylphosphino)ethyl)amine, and (α-methylbenzyl)bis(2-(dicyclohexylphosphino)ethyl)amine and their organometallic chemistry when combined with iridium

Article abstract of DOI:10.1021/om9704455

The new chiral aminodiphosphine ligands (R)- and (S)-sec-butylbis(2-(diphenylphosphino)ethyl)amine, (R)- and (S)-sec-butylbis(2-(dicyclohexylphosphino)ethyl)amine, and (R)- and (S)-(α-methylbenzyl)bis(2-(dicyclohexylphosphino)ethyl)amine have been synthesized from optically pure (R)-(-)- and (S)-(4-)-sec-butylamine or (R)-(+)- and (S)-(-)-(α-methylbenzyl)amine. The reactions between these PNP* ligands and [Ir(COD)(OMe)]₂ have been investigated in either aprotic or protic solvents (COD = cycloocta-1,5-diene). Depending on the substituents at either the carbon stereocenter or the phosphorus donors, iridium products with different structures and/or stabilities are obtained. Among the new complexes, there are monohydride, dihydride, and trihydride species. It is observed that (i) cyclohexyl substituents on the phosphorus donors favor the formation of complexes where the PNP* ligand adopts a meridional conformation; (ii) phenyl groups attached to the carbon stereocenter lead to the formation of thermodynamically stable ortho-metalated products. Irrespective of the phosphorus substituents, this C-H insertion reaction is reversible at room temperature. Both the new ligands and the iridium complexes have been characterized by various chemico-physical techniques, including multinuclear NMR spectroscopy. The structure of the monohydride complex [IrH(COD)(PNP*-5a)] (PNP*-5a = (R)-(-)-sec-butylbis(2-(diphenylphosphino)ethyl)amine) has been determined by single-crystal X-ray diffraction. The PNP*-5a ligand uses only the two phosphorus atoms for coordination, which is completed by a terminal hydride ligand and by the two olefinic ends of a COD molecule.

Full text of DOI:10.1021/om9704455

Organometallics 1997, 16, 4403-4414
4403
Syn th esis of th e New Ch ir a l (R)- a n d
(S)-Am in od ip h osp h in e Liga n d s
sec-Bu tylbis(2-(d ip h en ylp h osp h in o)eth yl)a m in e,
sec-Bu tylbis(2-(d icycloh exylp h osp h in o)eth yl)a m in e, a n d
(r-Meth ylben zyl)bis(2-(d icycloh exylp h osp h in o)eth yl)a m in e
a n d Th eir Or ga n om eta llic Ch em istr y Wh en Com bin ed
w ith Ir id iu m
Claudio Bianchini,*,1a Lionel Glendenning,1a,b Maurizio Peruzzini,1a
Graham Purches,1a,c Fabrizio Zanobini,1a Erica Farnetti,2 Mauro Graziani,2 and
Giorgio Nardin2
Istituto per lo Studio della Stereochimica ed Energetica dei Composti di Coordinazione del
CNR, Via J . Nardi 39, 50132 Firenze, Italy, and Dipartimento di Scienze Chimiche,
Universita` di Trieste, Via Giorgieri 1, 34127 Trieste, Italy
Received May 30, 1997X
The new chiral aminodiphosphine ligands (R)- and (S)-sec-butylbis(2-(diphenylphosphi-
no)ethyl)amine, (R)- and (S)-sec-butylbis(2-(dicyclohexylphosphino)ethyl)amine, and (R)- and
(S)-(R-methylbenzyl)bis(2-(dicyclohexylphosphino)ethyl)amine have been synthesized from
optically pure (R)-(-)- and (S)-(+)-sec-butylamine or (R)-(+)- and (S)-(-)-(R-methylbenzy-
l)amine. The reactions between these PNP* ligands and [Ir(COD)(OMe)]2 have been
investigated in either aprotic or protic solvents (COD ) cycloocta-1,5-diene). Depending on
the substituents at either the carbon stereocenter or the phosphorus donors, iridium products
with different structures and/or stabilities are obtained. Among the new complexes, there
are monohydride, dihydride, and trihydride species. It is observed that (i) cyclohexyl
substituents on the phosphorus donors favor the formation of complexes where the PNP*
ligand adopts a meridional conformation; (ii) phenyl groups attached to the carbon
stereocenter lead to the formation of thermodynamically stable ortho-metalated products.
Irrespective of the phosphorus substituents, this C-H insertion reaction is reversible at
room temperature. Both the new ligands and the iridium complexes have been characterized
by various chemico-physical techniques, including multinuclear NMR spectroscopy. The
structure of the monohydride complex [IrH(COD)(PNP*-5a )] (PNP*-5a ) (R)-(-)-sec-
butylbis(2-(diphenylphosphino)ethyl)amine) has been determined by single-crystal X-ray
diffraction. The PNP*-5a ligand uses only the two phosphorus atoms for coordination, which
is completed by a terminal hydride ligand and by the two olefinic ends of a COD molecule.
In tr od u ction
(S)-PhC*H(Me)N(CH2CH2PPh2)2 (PNP*-I)3a and the
achiral ligand n-C3H7N(CH2CH2PPh2)3 (PNP-II).3c Both
of these aminodiphosphines have been demonstrated to
be suitable ligands for the preparation of iridium
catalysts exhibiting excellent chemoselectivity for the
reduction of the CdO functional group in benzylidene-
acetone. Using the chiral ligand PNP*-I, asymmetric
induction was achieved with good enatioselectivity.3a
Our continuing efforts to develop a range of asym-
metric iridium catalysts with chiral aminophosphine
ligands for the reduction of prochiral ketones and R,â-
unsaturated ketones3 has lead us to investigate the
chemistry of the ligands (R)- and (S)-R′C*H-
(Me)N(CH2CH2PR2) (R′ ) Et, R ) Ph, PNP*-5a ,b; R′ )
Et, R ) Cy, PNP*-6a ,b; R′ ) Ph, R ) Cy, PNP*-7a ,b)
(Chart 1). The synthesis and characterization of these
new aminodiphosphines are described in this work and
follow our recent studies of the chiral ligands (R)- and
This paper also examines the organometallic chem-
istry, in association with [Ir(COD)(OMe)]2, of these
PNP* ligands bearing phenyl/methyl or ethyl/methyl
(hydrogen and nitrogen) substituents on the chiral
carbon atom and cyclohexyl or phenyl substituents on
the phosphorus donors (COD ) cycloocta-1,5-diene). The
variation in the design of the new ligands in comparison
with the already reported PNP*-I and PNP-II ligands
was expected to change the organometallic chemistry
with the associated metal as well as the mode of action
or association between the catalysts and prochiral
substrates. Indeed, the design of asymmetric catalysts
relies on, as yet not fully understood, the transfer of
X Abstract published in Advance ACS Abstracts, August, 15, 1997.
(1) (a) ISSECC-CNR. (b) Present address: Research School of
Chemistry, Australian National University, Canberra, Australia. (c)
Present address: Chemistry Department, The University of Sydney,
Sydney, Australia.
(2) Universita` di Trieste.
(3) (a) Bianchini, C.; Farnetti, E.; Glendenning, L.; Graziani, M.;
Nardin, G.; Peruzzini, M.; Rocchini, E.; Zanobini, F. Organometallics
1995, 14, 1489. (b) Bianchini, C.; Peruzzini, M.; Farnetti, E.; Kaspar,
J .; Graziani, M. J . Organomet. Chem. 1995, 488, 91. (c) Bianchini, C.;
Farnetti, E.; Graziani, M.; Nardin, G.; Vacca, A.; Zanobini, F. J . Am.
Chem. Soc. 1990, 112, 9190. (d) Farnetti, E.; Kaspar, J .; Spogliarich,
R.; Graziani, M. J . Chem. Soc., Chem. Commun. 1989, 1264.
S0276-7333(97)00445-7 CCC: $14.00 © 1997 American Chemical Society

4404 Organometallics, Vol. 16, No. 20, 1997
Bianchini et al.
experiments were conducted on the same instrument in the
phase-sensitive TPPI mode in order to discriminate between
positive and negative cross peaks. The proton NMR spectra
with broad-band phosphorus decoupling were recorded on the
Bruker AC200 instrument equipped with a 5-mm inverse
probe and a BFX-5 amplifier device using the wide-band
phosphorus decoupling sequence GARP.
Ch a r t 1
In the numbering of the complexes, a and b refer to the two
different stereoisomers that were synthesized when using
optically pure ligands; a always assigned to the R isomer and
b to the S isomer. The absence of such an addition indicates
that the complex was synthesized with the racemic ligand. In
the iridium complexes containing hydrides, the index A
denotes the hydride ligand located trans to the nitrogen donor
atom of the aminodiphosphine ligand.
In the 1H NMR data presented for the iridium complexes,
the resonances of the substituents on phosphorus as well as
those of the organic backbone of the ligands have been
generally omitted as they do not contain any important
structural information.
P r ep a r a t ion of (R)-(-)- a n d (S)-(+)-sec-Bu t ylb is-
(2-(d ip h en ylp h osp h in o)eth yl)a m in e (P NP *-5a ; P NP *-5b).
(i) P r ep a r a tion of (R)-(-)- a n d (S)-(+)-sec-Bu tylbis(2-
h yd r oxyeth yl)a m in e (2a ,b). (R)-(-)-sec-Butylamine (1a )
(8.0 g, 109 mmol) was dissolved in an ethanol/water mixture
(1:2 v/v, 80 mL) under nitrogen, and the stirred reaction
mixture was cooled to -10 °C. Ethylene oxide (12.5 g, 284
mmol, 2.6 equiv) was introduced directly into the reaction
mixture (ca. 3.0 h) at such a rate to minimize the loss of
unreacted oxirane. The reaction mixture was warmed to room
temperature and stirred for a further 18 h. Ethanol and water
were removed by distillation, and the crude diol was purified
by fractional distillation under reduced pressure (139-140 °C/
0.5 mmHg) to give (R)-(-)-sec-butylbis(2-hydroxyethyl)amine
(2a ) as a clear oil (14.9 g, 85%).
chiral information via either a through-space effect,
depending on the chiral auxiliary and substrate to be
proximally close in space, or an electronic (through-
bond) effect.4 Knowledge of both the mode and type of
coordination of different PNP* ligands to iridium may
thus be of paramount importance to increasing our
knowledge of the factors that govern the enantioselec-
tive reduction of prochiral and R,â-unsaturated ketones
by PNP*-Ir catalysts.
Exp er im en ta l Section
(S)-(+)-sec-Butylbis(2-hydroxyethyl)amine (2b) was pre-
pared as a crude oil from its corresponding primary amine,
1b, following a similar method to that described above, yield
83%. Anal. Calcd for C8H19NO2: C, 59.63; H, 11.80; N, 8.70.
Found: C, 59.26; H, 11.80; N, 8.46. MS (m/ e): 130 (57), 74
(95), 56 (58), 28 (91), 18 (100). 1H NMR (CDCl3, 20 °C, 200.13
MHz; the numbering scheme of the hydrogen and carbon
resonances for this product as well as all the other intermedi-
ates and ligands is given in Scheme 1 and in ref 6): δ 0.80 (d,
All of the reactions and manipulations were routinely
performed under a nitrogen atmosphere by using standard
Schlenk-tube techniques. Optically pure (R)-(-)- and (S)-(+)-
sec-butylamine (1a or 1b, respectively) were obtained from
Aldrich and used without further purification. Dicyclohexy-
lphosphine was purchased from Strem Chemicals and distilled
prior to use. Diphenylchlorophosphine was purchased from
Fluka AG and distilled prior to use. All other chemicals were
reagent grade and used as received from commercial suppliers.
[Ir(COD)(OMe)]2 was prepared according to a published pro-
cedure (COD ) cycloocta-1,5-diene).5
3
3
3J H1,H2* ) 7.4 Hz, 3H1), 0.86 (dd, J H3R,H4 ) 7.4 Hz, J H3â,H4
)
2
3
7.4 Hz, 3H4), 1.18 (ddq, J H3R,H3â ) 14.5 Hz, J H3R,H2* ) 7.2
3
2
Hz, J H3R,H4 ) 7.4 Hz, H3R), 1.43 (ddq, J H3R,H3â ) 14.5 Hz,
3J H3â,H2* ) 7.7 Hz, J H3â,H4 ) 7.4 Hz, H3â), 2.45 (dt, J H1′R,H1′â
3
2
Infrared spectra were recorded on a Perkin-Elmer spectro-
photometer interfaced to a Perkin-Elmer 3600 data station.
Deuterated solvents for the NMR measurements (Merck and
Aldrich) were dried over molecular sieves (4 Å). 1H, 13C, and
) 13.5 Hz, 3J H1′R,H2′ ) 5.1 Hz, 2H1′R), 2.53 (dt, 2J H1′R,H1′â ) 13.5
3
3
Hz, J H1′â,H2′ ) 5.1 Hz, 2H1′â), 3.47 (dd, J H1′R,H2′ ) 5.1 Hz,
3J H1′â,H2′ ) 5.1 Hz, 4H2′), 2.55 (ddq, 3J H2*,H3R ) 7.0 Hz, 3J H2*,H3â
3
) 7.0 Hz, J H1,H2* ) 7.0 Hz, H2*), 3.79 (br s, OH). 13C{1H}
31P NMR spectra were recorded on
a Bruker AC 200P
NMR (CDCl3, 20 °C, 50.32 MHz): δ 11.6 (s, C4), 14.2 (s, C1),
26.5 (s, C3), 51.5 (s, 2C2′), 57.5 (s, C2*), 60.0 (s, 2C1′).
(ii) P r ep a r a tion of (R)-(-)- a n d (S)-(+)-sec-Bu tylbis(2-
ch lor oeth yl)a m m on iu m Ch lor id e (3a ,b). To a stirred
solution of thionyl chloride (14.1 mL, 23.0 g, 193 mmol) in dry
chloroform (15 mL) under nitrogen was added dropwise a
solution of (R)-(-)-sec-butylbis(2-hydroxyethyl)amine (10.0 g,
62.1 mmol) (2a ) in dry chloroform (15 mL). The reaction
mixture was refluxed for 10 min then stirred at room temper-
spectrometer (operating at 200.13, 50.32, and 81.01 MHz,
respectively); 2H NMR spectra were acquired at 46.08 MHz
on a Varian VXR 300 spectrometer using a broad-band 10-
2
mm NMR probe. 1H, H, and 13C NMR chemical shifts were
reported relative to tetramethylsilane. 31P NMR chemical
shifts were reported relative to external 85% H3PO4, with
downfield values taken as positive. 13C-DEPT NMR experi-
ments were run on a Bruker AC 200P spectrometer. The
1H,1H-2D COSY NMR experiments were routinely conducted
on a Bruker AC 200P instrument in the absolute magnitude
mode using a 45° or 90° pulse after the incremental delay or
were acquired on an AVANCE DRX 500 Bruker spectrometer
using the phase-sensitive TPPI mode with double quantum
(6) Numbering schemes for the hydrogen and carbon atoms on the
nitrogen tails in the ligands 5, 6, and 7.
1
filter and no-spinning samples. The H,1H-2D NOESY NMR
(4) (a) Takaya, H.; Ohta, T.; Noyori, R. In Catalytic Asymmetric
Synthesis; Ojima, I., Ed.; VCH: New York, 1993. (b) Noyori, R.
Asymmetric Catalysis in Organic Synthesis; J ohn Wiley: New York,
1994.
(5) Farnetti, E.; Kaspar, J .; Spogliarich, R.; Graziani, M. J . Chem.
Soc., Dalton Trans. 1988, 947.

Synthesis of New Chiral Aminodiphosphine Ligands
Organometallics, Vol. 16, No. 20, 1997 4405
Sch em e 1
ature for 18 h. The solvent was then removed in vacuo to leave
the crude chloride salt of (R)-(-)-sec-butylbis(2-chloroethy-
l)ammonium (3a ) as a white precipitate. Removal of excess
thionyl chloride was achieved by repeated addition and evacu-
ation of chloroform (3 × 20 mL) and ethanol (2 × 10 mL). The
purified (R)-(-)-sec-butylbis(2-chloroethyl)ammonium chloride
(3a ) was dried to a constant weight with a pump. (R)-(-)-sec-
butylbis(2-chloroethyl)ammonium chloride (3a ) (11.6 g, 80%),
as a white powder, was stored under nitrogen prior to use.
(1.1, M+), 182 (11), 168 (84), 147 (19), 63 (40), 27 (100). 1H
3
NMR (CDCl3, 20 °C, 299.94 MHz): δ 0.99 (dd, J H3R,H4 ) 7.3
3
3
Hz, J H3â,H4 ) 7.3 Hz, 3H4), 1.37 (d, J H1,H2* ) 6.4 Hz, 3H1),
2
3
3
1.56 (ddq, J H3R,H3â ) 13.7 Hz, J H3R,H2* ) 6.9 Hz, J H3R,H4
)
6.9 Hz, H3a), 2.07 (br m, H3â), 3.50 br m, H2*), 3.60 br m,
3
3
4H1′), 4.20 (t, J H1′,H2′ ) 7.0 Hz, J H1′â,H2′ ) 5.1 Hz, 4H2′).
13C{1H} NMR (CDCl3, 20 °C, 50.32 MHz): δ 10.7 (s, C4), 13.1
(s, C1), 23.7 (s, C3), 37.3 (s, 2C2′), 52.0 (s, C2*), 61.6 (s, 2C1′).
(iv) P r ep a r a tion of P NP *-5a a n d P NP *-5b. A solution
of potassium diphenylphosphide in THF (130 mL) under
nitrogen was prepared in situ from diphenylchlorophosphine
(17.8 g, 80.8 mmol) and potassium metal (6.5 g, 165 mmol).
To this stirred solution was added dropwise (R)-(-)-sec-
butylbis(2-chloroethyl)amine (4a ) (8.0 g, 40.4 mmol), and the
temperature was maintained at 50 °C during the addition.
During the course of the addition, the initial red solution
gradually changed to a creamy color. The reaction mixture
was then refluxed for 5 min and cooled to room temperature
and water (100 mL) was added. The two layers were separated
and the aqueous layer was extracted with ether (2 × 100 mL).
Correspondingly, (S)-(+)-sec-butylbis(2-chloroethyl)ammo-
nium chloride (3b) (80%) was obtained as a white powder.
(iii) P r ep a r a tion of (R)-(-)- a n d (S)-(+)-sec-Bu tylbis(2-
ch lor oeth yl)a m in e (4a ,b). To a solution of (R)-(-)-sec-
butylbis(2-chloroethyl)ammonium chloride (3a ) (10.0 g, 42.7
mmol) in water (20 mL) was added an aqueous 7 M solution
of sodium hydroxide (10 mL). The two immiscible layers which
formed were separated, and the organic layer, (R)-(-)-sec-
butylbis(2-chloroethyl)amine (4a ), was dried over sodium
hydroxide pellets. Anal. Calcd for C8H17NCl2: C, 41.03; H, 7.69;
N, 5.98. Found: C, 40.89; H, 7.52; N, 5.67. MS (m/ e): 197

4406 Organometallics, Vol. 16, No. 20, 1997
Bianchini et al.
The combined organic layers were dried (Na2SO4) and filtered,
and the ether/THF mixture was removed by distillation to
leave a clear/ivory oil. The crude product was purified by
recrystallization from acetone/ethanol (1:1 v/v) to give (R)-(-
)-sec-butylbis(2-(diphenylphosphino)ethyl)amine (PNP*-5a ) as
white crystals (75%).
Following a similar method to that described above, (S)-
(+)-sec-butylbis(2-(diphenylphosphino)ethyl)amine (PNP*-5b)
was obtained as white crystals (78%). Anal. Calcd for
reaction mixture was then refluxed for 5 min and cooled to
room temperature, and the solvent was removed in vacuo. The
resulting residue was washed with ethanol (2 × 50 mL). The
crude product was purified by recrystallization from THF/
ethanol (1:20 v/v) to give the corresponding aminodiphosphine
ligand (R)-(+)- or (S)-(-)-R-methylbenzyl-bis(2-((dicyclohexy-
lphosphino)ethyl)amine (PNP*-7a or PNP*-7b) as a white
crystalline compound in a yield higher than 70%.
Anal. Calcd for C36H61NP2: C, 75.89; H, 10.79; N, 2.46.
Found: C, 75.76; H, 10.61; N, 2.34. 1H NMR (CDCl3, 20 °C,
200.13 MHz): δ 1.00-1.30 (m, 20CH2(cyclohexyl) and 4CH2-
C
32H37NP2: C, 77.26; H, 7.44; N, 2.82. Found: C, 78.84; H,
7.91; N, 2.94. MS (m/ e): 468 (1.5), 312 (49.4), 298 (62.8), 185
(100). 1H NMR (CD2Cl2, 20 °C, 200.13 MHz): δ 0.80 (d, 3J H1,H2*
3
(P-N)), 1.35 (d, J H1,H2* ) 6.6 Hz, 3H1), 1.40-1.57 (m,
3
3
) 6.5 Hz, 3H1), 0.85 (dd, J H3R,H4 ) 7.3 Hz, J H3â,H4 ) 7.3 Hz,
3H4), 1.12 (ddq, 2J H3R,H3â ) 13.4 Hz, 3J H3R,H2* ) 7.0 Hz, 3J H3R,H4
4CH1(cyclohexyl)), 1.57- 1.93 (m, 20CH2(cyclohexyl)), 2.47-
3
2.72 (m, 4CH2(P-N)), 3.91 (q, J H1,H2* ) 6.7 Hz, 1H2*), 7.1-
2
3
7.39 (m, 5Hph). 13C{1H} NMR (CDCl3, 20 °C, 50.32 MHz): δ
) 7.3 Hz, H3a), 1.33 (ddq, J H3R,H3â ) 13.5 Hz, J H3â,H2* ) 6.7
Hz, 3J H3â,H4 ) 7.3 Hz, H3â), 2.11 (dd, 3J H1′R,H2′ ) 8.3 Hz, 3J H1′â,H2′
17.1 (s, C1), 18.0 (d, J P,CH ) 17.3 Hz, 4CH2(cyclohexyl)), 25.3
2
2
3
) 8.2 Hz, 4H2′), 2.44 (dt, J H1′R,H1′â ) 13.1 Hz, J H1′R,H2′ ) 7.0
(s, 4CH2(cyclohexyl)), 25.9 (d, J P,CH ) 14.3 Hz, 4CH2-
2
2
3
Hz, 2H1′R), 2.53 (dt, J H1′R,H1′â ) 13.1 Hz, J H1′â,H2′ ) 7.0 Hz,
(cyclohexyl)), 26.1 (d, J P,CH ) 14.3 Hz, 4CH2(cyclohexyl)), 27.6
2
2H1′â), 2.63 (ddq, 3J H2*,H3R ) 7.0 Hz, 3J H2*,H3â ) 6.7 Hz, 3J H2*,H1
1
(d, J P,C2′ ) 7.5 Hz, 2C2′), 29.1 (d, J P,CH ) 14.7 Hz, 4CH2-
2
) 6.7 Hz, H2*), 7.27-7.45 (m, 20Hph.
13C{1H} NMR (CD2Cl2,
(cyclohexyl)), 31.8 (d, J P,CH ) 11.9 Hz, 4CH(cyclohexyl)), 47.5
2
20 °C, 50.32 MHz): δ 12.9 (s, C4), 14.7 (s, C1), 27.5 (s, C3),
2
(d, J P,C1′ ) 30.4 Hz, 2C1′), 58.5 (s, C2*), 125.5 (s, Cp), 126.3
28.8 (d, 1J P,C2′ ) 12.2 Hz, 2C2′), 46.9 (d, 2J P,C1′ ) 22.9 Hz, 2C1′),
(s, 2Cm), 127.1 (s, 2Co), 144.0 (s, Ci). 31P{1H} NMR (CDCl3, 20
2
57.4 (s, C2*), 129.0 (s, 4Cp), 129.2 (s, 8Cm), 133.3 (d, J P,C
)
)
20
o
°C, 81.01 MHz): δ -9.53 (s, 2P). 7a : [R]D ) +18.4 (c ) 1,
2
1
3.1 Hz, 4Co), 133.7 (d, J P,C ′ ) 3.1 Hz, 4Co′), 139.8 (d, J P,C
20
o
i
CHCl3). 7b: [R]D ) -19.4 (c ) 1, CHCl3).
14.2 Hz, 2Ci), 140.1 (d, J P,C ′ ) 14.2 Hz, 2Ci′). 31P{1H} NMR
1
i
The racemic aminodiphosphine ligands rac-5, 6, and 7 were
also prepared from the corresponding racemic amines following
the same procedure.
20
(CD2Cl2, 20 °C, 81.01 MHz): δ -20.2 (s, 2P). 5a : [R]D
-24.7 (c ) 1, CHCl3). 5b: [R]D ) +23.0 (c ) 1, CHCl3).
)
20
P r ep a r a t ion of (R )-(-)- a n d (S)-(+)-sec-Bu t ylb is-
(2-(d icycloh exylp h osp h in o)eth yl)a m in e (P NP *-6a ,b). A
solution of lithium dicyclohexylphosphide in THF (100 mL)
under nitrogen was prepared in situ from dicyclohexylphos-
phine (10.0 g, 50.4 mmol) and n-butyllithium (1.6 M in
n-hexane solution, 31.3 mL, 50.5 mmol). To this stirred
solution was added dropwise the free chloroamine (4a or 4b)
(6.2 g, 25.2 mmol), and the temperature was maintained at
room temperature during the addition. During the course of
the addition the initial yellow solution gradually became ivory
colored. The reaction mixture was then refluxed for 5 min and
cooled to room temperature, and the solvent was removed in
vacuo. The resulting residue was washed with ethanol (2 ×
50 mL). The crude product was purified by recrystallization
from THF/ethanol (1:20, v/v) to give the corresponding ami-
nodiphosphine ligand (R)-(-)- or (S)-(+)-sec-butylbis(2-((dicy-
clohexylphosphino)ethyl)amine (PNP*-6a or PNP*-6b) as a
white crystalline compound in yield higher than >70%. Anal.
Calcd for C32H61NP2: C, 73.67; H, 11.79; N, 2.68. Found: C,
P r ep a r a tion of Ir id iu m -P NP * Com p lexes. (R)- a n d
(S)-[sec-Bu t ylb is(2-(d ip h en ylp h osp h in o)et h yl)a m in e]-
ir id iu m Hyd r id e Cycloocta -1,5-d ien e, [Ir H(COD)(P NP *-
5a ,b)] (9a ,b). [Ir(COD)(OMe)]2 (663 mg, 1.0 mmol) was
dissolved in dichloromethane (20 mL) under nitrogen. PNP*-
5a ,b, (1.00 g, 2.0 mmol) was added, and the yellow reaction
mixture was stirred at room temperature for 1 h, during which
time it became orange. After evaporation of the solvent to ca.
10 mL and addition of methanol (15 mL), a crystalline solid
separated. This precipitate was filtered under nitrogen and
washed with methanol and n-pentane to give [IrH(COD)-
(PNP*-5a ,b)] (9a ,b) (124 mg, 78%). This was recrystallized
from a dichloromethane/propan-2-ol mixture (2:1 v/v) to give
white-creamy crystals (111 mg, 70%). IR (Nujol mull): ν(Ir-
H) 2111 (s) cm-1. Anal. Calcd for C40H50NIrP2: C, 60.07; H,
6.30; N, 1.75. Found: C, 59.85; H, 6.18; N, 1.49. 1H NMR
(CD2Cl2, 20 °C, 200.13 MHz): δ -13.80 (t, 2J H
) 22.3
,P
3
hydride
3
Hz, Hhydride), 0.48 (d, J H1,H2* ) 6.4 Hz, 3H1), 0.62 (t, J H3,H4
)
6.4 Hz, 3H4), 0.74 (dq, 3J H2,H3 ) 6.4 Hz, 3J H3,H4 ) 6.4 Hz, 2H3),
1.00-1.30, (m, 4H2′), 1.30-1.80 (m, 4H1′), 2.06 (m, 1H2*),
2.20-2.70 (m, 4CH2(COD)), 3.15-3.60 (m, 4CH(COD)), 7.25-
7.70 (m, 20CHph). 13C{1H} NMR (CD2Cl2, 20 °C, 50.32 MHz):
δ 12.3 (s, C4), 13.4 (s, C1), 26.2 (s, C2), 31.3 (dd, J C,P ) 17.3
73.48; H, 11.72; N, 2.52.
3
1H NMR (CDCl3, 20 °C, 200.13 MHz): δ 0.85 (d, J H1,H2*
)
3
3
7.3 Hz, 3H1), 0.95 (dd, J H3R,H4 ) 5.6 Hz, J H3â,H4 ) 5.6 Hz,
3H4), 1.02-1.35 (m, 20CH2(cyclohexyl)), 1.35-1.61 (m, 4CH1-
(cyclohexyl) and 4CH2(P-N)), 1.61-1.93 (m, 20CH2(cyclohexyl)),
2.40-2.83 (m, 4CH2(P-N) and 1H2*). 13C{1H} NMR (CD2Cl2,
3
2
Hz, J C,P ) 5.0 Hz, CH2-P), 35.0 (d, J C,P ) 18.1 Hz, CH2-N),
2
1
35.5 (d, J C,P ) 16.5 Hz, CH2)N), 36.0 (dd, J C,P ) 16.3 Hz,
20 °C, 50.32 MHz): δ 12.4 (s, C4), 14.9 (s, C1), 22.6 (d, J P,C2′
3J C,P ) 3.0 Hz, CH2-P), 46.8 (d, J C,P ) 5.8 Hz, 4CH2(COD)),
47.0 (dd, J C,P ) 24.7 Hz, J C,P ) 7.4 Hz, 2CH1(COD)), 58.3 (s,
C1*), 78.8 (s, 2CH1(COD)), 127.8- to 143.5 (m, 24Cph). 31P{1H}
) 17.1 Hz, 2C2′), 27.4 (s, C3), 27.7 (s, 4CH2(cyclohexyl)), 28.1
(d, J P,CH ) 7.3 Hz, 4CH2(cyclohexyl)), 28.2 (d, J P,CH ) 11.0
2
2
Hz, 4CH2(cyclohexyl)), 29.9 (d, J P,CH ) 7.3 Hz, 4CH2-
2
2
NMR (CD2Cl2, 20 °C, 81.01 MHz): δ 0.61 (d, J P,P ) 22.5 Hz,
(cyclohexyl)), 31.3 (d, J P,CH ) 14.7 Hz, 4CH2(cyclohexyl)), 34.1
2
2
2
P), 2.34 (d, J P,P ) 22.6 Hz, P).
(d, J P,CH ) 11.0 Hz, 4CH2(cyclohexyl)), 49.9 (d, J P,C1′ ) 30.5
2
Hz, 2C1′), 57.6 (s, C2*). 31P{1H} NMR (CDCl3, 20 °C, 81.01
(R)- a n d (S)-[sec-Bu t ylb is(2-(d ip h en ylp h osp h in o)-
et h yl)a m in e]ir id iu m Tr ih yd r id e, [Ir H3(P NP *-5a ,b )]
(10a ,b). (A) Compound 9a ,b (600 mg, 0.75 mmol) was
dissolved in THF (30 mL) under nitrogen. Hydrogen gas was
slowly bubbled through the reaction mixture for 30 min. The
reaction mixture was concentrated to one-half the original
volume, and propan-2-ol (10 mL) was slowly added to induce
precipitation of cream-colored microcrystals. This product was
filtered and washed with propan-2-ol and n-hexane to give the
iridium trihydride [IrH3(PNP*-5a ,b)] (10a ,b). Recrystalliza-
tion of the crude product from THF and propan-2-ol (2:1 v/v)
gave pure 10a ,b (510 mg, 98%) as cream-colored crystals. GC/
MS analysis of the reaction mixture showed the quantitative
formation of cyclooctene (COE).
MHz): δ -7.19 (s, 2P). 6a : [R]D20 ) -23.2 (c ) 1, CHCl3). 6b:
20
[R]D ) +23.7 (c ) 1, CHCl3).
P r ep a r a tion of (R)-(+)- a n d (S)-(-)-(r-Meth ylben zyl)-
bis(2-((dicycloh exylph osph in o)eth yl)am in e (P NP *-7a an d
P NP *-7b). A solution of lithium dicyclohexylphosphide in
THF (100 mL) under nitrogen was prepared in situ from
dicyclohexylphosphine (10.0 g, 50.4 mmol) and n-butyllithium
(1.6 M solution in n-hexane, 31.3 mL, 50.5 mmol). To this
stirred solution was added dropwise either (R)-(+) or (S)-(-)-
(R-methylbenzyl)bis(2-chloroethyl)amine3a (5.0 g, 25.2 mmol),
and the temperature was maintained at room temperature
during the addition. During the course of the addition, the
initial yellow solution gradually became ivory colored. The

Synthesis of New Chiral Aminodiphosphine Ligands
Organometallics, Vol. 16, No. 20, 1997 4407
(B) Compound 9a ,b (200 mg, 0.25 mmol) was dissolved in
THF (10 mL) and propan-2-ol (40 mL) under nitrogen. The
reaction mixture was refluxed for 14 h and then cooled to room
temperature. GC/MS analysis of a sample showed the pres-
ence of COE in the reaction mixture. After concentration to
one-half the original volume under vacuum, n-hexane was
added (20 mL). The crude product which separated was
filtered and recrystallized (as described above) to give 10a ,b
(140 mg, 80%). IR (Nujol mull): ν(Ir-H) 2160 (s), 2025 (s),
1993 (s), cm-1. Anal. Calcd for C32H40NIrP2: C, 55.41; H, 5.81;
N, 2.02. Found: C, 55.30; H, 5.71; N, 1.84. 1H NMR (CD2Cl2,
20 °C, 200.13 MHz): δ -23.20 (dddd, 2J H cis ) 11.3 Hz, 2J H
added, and the yellow reaction mixture became orange while
stirring at room temperature for 1 h. The reaction mixture
was concentrated, and n-pentane was added to induce the
precipitation of 14a as a yellow solid in ca. 90% yield. In a
separate experiment, MeOH was used instead of n-pentane.
As a result, a distinct color change from orange to pink
occurred. Evaporation of the solvent under a brisk current of
nitrogen gave off-white crystals. The precipitate was filtered
under nitrogen and washed with methanol and n-hexane to
give the mer-dihydride complex, mer-[IrH2{C6H4C*H-
(CH3)N[CH2CH2P(C6H11)2]2}] (15a ), in almost quantitative
yield (see below).
(R)- a n d (S)-[(r-Meth ylben zyl)bis(2-(d icycloh exylp h os-
p h in o)eth yl)a m in e]ir id iu m Dih yd r id e, [Ir H2{C6H4C*H-
(CH3)N[CH2CH2P (C6H11)2]2}] (15a ,b). [Ir(COD)(OMe)]2 (210
mg, 0.32 mmol) was dissolved in toluene (30 mL) under
nitrogen. The ligand (PNP*-7a ,b) (355 mg, 0.63 mmol) was
added as a solid, and the yellow solution refluxed for 4 h under
nitrogen. The solvent was removed (in vacuo) from the
resultant dark brown solution to leave a creamy-colored
residue. Recrystallization of this crude product from dichloro-
methane and methanol gave pure mer-[IrH2{C6H4C*H-
(CH3)N[CH2CH2P(C6H11)2]2}] (15a ,b) (410 mg, 85%) as cream-
colored crystals. IR (Nujol mull): ν(Ir-H) 2096 (s), 1912.0 (s)
cm-1. Anal. Calcd for C36H60NIrP2: C, 56.76; H, 7.94; N, 1.84.
Found: C, 56.50; H, 7.76; N, 1.75. 1H NMR (CD2Cl2, 20 °C,
,P
,P
cis
A
) 11.3 Hz, 2J H
) 5.7 Hz, 2J H
)A5.7 Hz, 1HA), -9.75
,H
,H
A
B
A
B′
2
2
2
(dddd, J H
) 129.6 Hz, J H
) 20.9 Hz, J H
) 38.9
,P
,P
,H
B
B
cis
B B′
Hz, 2J H
)tr6an.s0 Hz, 2HB). 13C{1H} NMR (CD2Cl2, 20 °C, 50.32
,H
B
A
1
MHz): δ 13.0 (s, C1), 15.9 (s, C4), 29.2 (s, C3), 34.8 (d, J P,C2′
) 25.6 Hz, 1C2′), 35.8 (d, 1J P,C2′ ) 25.6 Hz, C2′), 54.7 (d, 2J P,C1′
2
) 6.9 Hz, C1′), 56.9 (d, J P,C1′ ) 6.9 Hz, C1′), 69.7 (s, C2*),
128.0-142.0, 24Cph). 31P{1H} NMR (CD2Cl2, 20 °C, 81.01
2
2
MHz): δ 24.42 (d, J P,P ) 5.7 Hz, P), 25.70 (d, J P,P ) 5.7 Hz,
P).
In Situ F or m a tion of (R)- a n d (S)-[sec-Bu tylbis(2-
(d icycloh exylp h osp h in o)eth yl)a m in e]ir id iu m Hyd r id e
Cycloocta -1,5-d ien e, [Ir H(COD)(P NP *-6a ,b)] (13a ,b).
A
5-mm NMR tube was charged with [Ir(COD)(OMe)]2 (6.6 mg,
0.01 mmol), PNP*-6a ,b (10.4 mg, 0.02 mmol), and toluene-d8
(0.75 mL) under nitrogen. The tube was flame sealed under
nitrogen and heated to 37 °C for 1 h. 31P{1H} NMR analysis
showed the formation of the five-coordinate monohydride
complex [IrH(COD)(PNP*-6a ,b)] (13a ,b) as the only iridium-
containing product. 1H NMR (toluene-d8, 20 °C, 200.13
200.13 MHz): δ )21.43 (ddd, 2J H
14.6 Hz, 2J H cis 14.6 Hz,
,P
A
,P
2
A
cis
2
2J H
5.4 Hz, HA), -13.79 (ddd, J H
19.2 Hz, J H
,P
B
19.2
,H
2
,P
A
B
B
cis
cis
Hz, J H
4.6 Hz, HB), 6.28 (m, H1), 6.47 (m, 2H2/3), 7.51 (m,
,H
B
A
H4). 13C{1H} NMR (CD2Cl2, 20 °C, 50.32 MHz): δ 11.4 (s, C1),
27.0-32.0 (all singlets, 20CH2(cyclohexyl) and 2C2′), 33.6 (dd,
2
2
1J P,CH ) 22.9 Hz, J P,CH ) 7.6 Hz, CH1(cyclohexyl)), 35.3 (dd,
3
MHz): δ -14.3 (dd, J H
) 23.9 Hz, J H
) 23.9 Hz,
,P
,P
hydride
hydride
hydride). 31P{1H} NMR (CD2Cl2, 20 °C, 81.01 MHz): δ -1.51
1J P,CH ) 21.9 Hz, J P,CH ) 7.6 Hz, CH1(cyclohexyl); 37.2 (dd,
3
H
(2J P,P ) 16.9 Hz, P), 1.52 (2J P,P ) 16.9 Hz, P).
1J P,CH ) 26.7 Hz, J P,CH ) 7.6 Hz, CH1(cyclohexyl)), 40.2 (dd,
3
1J P,CH ) 18.1 Hz, J P,CH ) 8.6 Hz, CH1(cyclohexyl)), 60.9 (dd,
3
Prolonged heating of this sample to a final temperature of
100 °C resulted in the transformation of this monohydride
species into a number of other iridium-aminodiphosphine
complexes which defied first-order analysis. During this
thermal degradation, free COD was liberated into the solution
(GC/MS).
2J P,C1′ ) 4.2 Hz, J P,C1′ ) 4.2 Hz, C1′), 61.3 (m, C1′), 66.9 (s,
4
C2*), 118.9 (s, Cph), 119.9 (s, Cph), 125.5 (s, Cph), 145.3 (s, Cph),
156.4 (s, Ci), 162.3 (dd, 2J P,C ) 8.6 Hz, 2J P,C ) 8.6 Hz, Co,m).
o,m
o,m
31P{1H} NMR (CD2Cl2, 20 °C, 81.01 MHz): AB system; δ 39.36
(2J P,P ) 348.6 Hz, P), 43.42 (2J P,P ) 348.6 Hz, P).
In Situ F or m a tion of (R)- a n d (S)-[(r-Meth ylben zyl)-
b is (2-(d ic y c lo h e x y lp h o s p h in o )e t h y l)a m in e ]ir id iu m
H yd r id e Cyclooct a -1,5-d ien e, [Ir H (COD)(P NP *-7a ,b ]
(14a,b). A 5-mm NMR tube was charged with [Ir(COD)(OMe)]2
(6.6 mg, 0.01 mmol), PNP*-7a ,b (11.2 mg, 0.02 mmol), and
toluene-d8 (0.75 mL) under nitrogen. The tube was flame
sealed under nitrogen and heated to 37 °C for 1 h. 31P{1H}
NMR analysis showed the formation of the five-coordinate
monohydride [IrH(COD)(PNP*-7a ,b)] (14a ,b) as the only
iridium-containing product. 1H NMR (C7D8, 37 °C, 200.13
Deu t er iu m E xch a n ge R ea ct ion of r a c,m er -[Ir H2-
{C6H4C*H(CH3)N[CH2CH2P (C6H11)2]2}] (15) w ith D2O. (A).
In Situ NMR Exp er im en t. In a 5-mm screw-cap NMR tube,
10 mg (0.01 mmol) of rac,mer-[IrH2{C6H4C*H(CH3)N-
[CH2CH2P(C6H11)2]2}] (15) was dissolved in THF-d8 (0.6 mL)
and the 1H NMR spectrum recorded. One drop of D2O was
added through the serum cap to the solution, and the tube
was agitated for 2 min before recording the 1H spectrum again.
The sample was then agitated for a further 10 min at room
temperature and 1H spectrum recorded again. Comparison
of the proton NMR spectra clearly showed the exchange of the
hydride ligands for deuteride ligands and the selective incor-
poration of deuterium into the ortho-position of the cyclom-
etalated phenyl ring.
MHz): δ -15.3 (dd, 2J H
) 25.1 Hz, Hhydride). 31P{1H}
,P
hydride cis
NMR (C7D8, 37 °C, 81.01 MHz): δ -1.00 (2J P,P ) 14.3 Hz, P),
0.75 (2J P,P ) 14.3 Hz, P).
Prolonged heating of this sample at 60 °C resulted in the
selective transformation of the monohydride species to the
dihydride ortho-metalated complex 15a ,b (see below). Fol-
lowing the thermal degradation of 14a ,b, free COD was
detected in the reaction mixture by GC/MS.
P r ep a r a tion of [Ir H(COD)(P NP *-6a )] (13a ). [Ir(COD)-
(OMe)]2 (200 mg, 0.30 mmol) was dissolved in THF (15 mL)
under nitrogen. The ligand PNP*-6a (350 mg, 0.67 mmol) was
added, and the yellow reaction mixture became orange while
stirring at room temperature for 1 h. The reaction mixture
was concentrated, and n-pentane was added until a yellow
solid precipitated. 31P{1H} NMR analysis showed it to contain
13a (80%) together with some unidentified PNP*-6a /Ir prod-
ucts. Using MeOH in the place of n-pentane to induce
precipitation, several unidentified products separated, none
of which was the (hydride)COD complex 13a .
(B)
P r ep a r a t ion
of
r a c,m er -[Ir D2{C6H 3DC*H -
(CH3)N[CH2CH2P (C6H11)2]2}] (15-d 3). 15 (100 mg, 0.1 mmol)
was dissolved in THF (5 mL), and 1 mL of D2O was added.
After vigorous stirring for 1h, the solution was evaporated to
dryness under vacuum. The solid residue was washed with
CH3OD (2 × 2 mL) and recrystallized from CH2Cl2/CH3OD to
give 15-d 3 in ca. 80% yield. IR (Nujol mull): ν(Ir-D) not
observed. 2H NMR (THF, 20 °C, 46.08 MHz): δ -21.40 (m,
DA), -13.80 (m, DB), 6.28 (m, D1).
r a c,m er -[(r-Meth ylben zyl)bis(2-(d icycloh exylp h osp h i-
n o)et h yl)a m in e]ir id iu m Dich lor id e, [Ir Cl2{C6H 4C*H -
(CH3)N[CH2CH2P (C6H11)2]2}] (18). Complex 15 (250 mg,
0.33 mmol) was dissolved in CHCl3 (10 mL) and heated at 65
°C for 2 h. The solvent was removed under nitrogen, and the
residue was recrystallized from dichloromethane (8 mL) and
methanol (5 mL) to give pure rac,mer-[IrCl2{C6H4C*H-
(CH3)N[CH2CH2P(C6H11)2]2}] (18) (196 mg, 72%) as small
brick-like crystals. Anal. Calcd for C36H58NCl2IrP2‚2CH2Cl2:
P r ep a r a tion of [Ir H(COD)(P NP *-7a )] (14a ). [Ir(COD)-
(OMe)]2 (663 mg, 1.0 mmol) was dissolved in THF (15 mL)
under nitrogen. The ligand PNP*-7a (1.12 g, 2.0 mmol) was

4408 Organometallics, Vol. 16, No. 20, 1997
Bianchini et al.
Ta ble 1. Cr ysta llogr a p h ic Da ta a n d Deta ils of
Refin em en ts for
(R)-[Ir H(COD){C2H5C*H(CH3)N(CH2CH2P P h 2)2}]
C, 43.62; H, 6.25; N, 1.40. Found: C, 43.17; H, 6.34; N, 1.40.
1H NMR (CD2Cl2, 20 °C, 200.13 MHz): δ 6.51 (m, H1′), 6.83
(m, H2/3), 6.92 (m, H2/3), 7.91 (m, H4). 13C{1H} NMR (CD2Cl2,
20 °C, 50.32 MHz): δ 11.4 (s, C1), 27.0-32.0 (all singlets,
(9a )
1
20CH2(cyclohexyl) and 2C2′), 33.5 (d, J P,CH ) 23.2 Hz,
formula
fw
C40H50IrNP2
799.0
1
CH1(cyclohexyl)), 35.3 (d, J P,CH ) 26.9 Hz, CH1(cyclohexyl)),
1
1
38.0 (d, J P,CH ) 26.9 Hz, CH1(cyclohexyl)), 39.0 (d, J P,CH
)
cryst syst
space group
cryst dimens, mm
a, Å
b, Å
triclinic
P1h (No. 2)
0.35 × 0.35 × 0.15
9.852(2)
12.689(3)
15.776(3)
68.66(2)
75.27(2)
78.95(2)
1765.8(8)
2
24.4 Hz, CH1(cyclohexyl)), 60.9 (m, C1′), 62.2 (m, C1′), 69.5 (s,
C2*), 120.4 (s, Cph), 122.3 (s, Cph), 126.8 (s, Cph), 134.1 (dd,
2
2J P,C ) 7.3 Hz, J P,Co,m ) 7.3 Hz, Co,m), 135.2 (s, Cph), 151.5
o,m
(s, Ci). 31P{1H} NMR (CD2Cl2, 20 °C, 81.01 MHz): AB system;
δ -2.34 (2J P,P ) 393.1 Hz, P), 4.90 (2J P,P ) 393.1 Hz, P).
P r ep a r a tion of r a c,m er -[(r-Meth ylben zyl)bis(2-(d icy-
cloh exylp h osp h in o)eth yl)a m in e]ir id iu m Hyd r id e Ch lo-
r id e, [Ir (H)Cl{C6H4C*H(CH3)N[CH2CH2P (C6H11)2]2}] (17).
A 5-mm NMR tube was charged with [Ir(COD)(OMe)]2 (6.6
mg, 0.01 mmol), PNP*-7 (11.2 mg, 0.02 mmol), and dichlo-
romethane-d2 (0.75 mL) under nitrogen. The tube was flame
sealed under nitrogen and heated to 95 °C for 14 h. 31P{1H}
NMR analysis gave 60% conversion to the monohydride species
rac,mer-[Ir(H)Cl{C6H4C*H(CH3)N[CH2CH2P(C6H11)2]2}] (17).
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
D(calcd), g cm-3
D(obs), g cm-3
µ(Mo KR), cm-1
F(000)
1.50
1.49
38.8
808
θ range, deg
temp for data collect, K
no. of reflns collcd
no. of reflns indep
no. of reflns indep [I > 3σ(I)]
data/restraints/params
final R indices [I > 3σ(I)]
largest diff peak and hole, e Å-3
1.5-28.0
293
1H NMR (CD2Cl2, 20 °C, 200.13 MHz): δ -18.6 (dd, 2J H
,P
8799
8493
6521
hydride cis
2
2
) 13.4 Hz, J H
) 13.4 Hz, Hhydride), 6.60 (d, J H-H ) 7.5
,P
hydride cis
2
2
Hz, 1Hph), 6.94 (t, J H-H ) 7.3 Hz, 1Hph), 7.02 (t, J H-H ) 7.3
Hz, 1Hph), 7.83 (d, J H-H ) 7.4 Hz, 1Hph). 31P{1H} NMR
2
6521/0/397
R1 ) 0.037, wR2 ) 0.041
0.90 and -0.70
(CD2Cl2, 20 °C, 81.01 MHz): AB spin system; δ 28.00 (2J P,P
355.1 Hz, P), 30.13 (2J P,P ) 355.1 Hz, P).
)
On standing at room temperature overnight, white crystals
(D) A solution of 15 (200 mg, 0.26 mmol) in 30 mL of THF
was pressurized with H2 (20 atm) and then heated to 60 °C
for 1 h. The solvent was removed in vacuo at room temper-
ature. 31P and 1H NMR spectroscopy showed there was no
conversion to the trihydride species and that the only phos-
phorus-containing product was the starting dihydride complex.
of the (hydride)chloride 17 (6 mg) separated out of the orange
solution. IR (Nujol mull): ν(Ir-H): 2080 (s) cm-1
. Anal.
Calcd for C36H61NClIrP2: C, 54.22; H, 7.71; N, 1.76. Found:
C, 53.98; H, 7.85; N, 1.85.
r a c,fa c-[(r-Meth ylben zyl)bis(2-(d icycloh exylp h osp h i-
n o)eth yl)a m in e]ir id iu m Tr ih yd r id e, [Ir H3(P NP *-7)] (16).
(A). [Ir(COD)(OMe)]2 (200 mg, 0.30 mmol) was dissolved in
THF (30 mL) under nitrogen. The ligand rac-R-methylbenzyl-
bis(2-((dicyclohexylphosphino)ethyl)amine, PNP*-7 (350 mg,
0.62 mmol), was added. Hydrogen gas was bubbled through
this solution for 1 h, and the solution was heated to 50 °C for
the first 15 min. GC/MS analysis of the reaction mixture
showed the quantitative formation of COE. After complete
evaporation of the solvent in vacuo at room temperature, a
creamy-colored residue was obtained. 31P{1H} NMR analysis
of the crude product showed the formation of 15 together with
a minor amount of the trihydride rac,fac-[IrH3(PNP*-7)] (16)
(10%) as well as several other minor products. Recrystalliza-
tion of this crude product from dichloromethane and methanol
gave pure 15.
Attem p ted P r ep a r a tion of r a c-[sec-Bu tylbis(2-(d icy-
cloh exylp h osp h in o)et h yl)a m in e]ir id iu m
Tr ih yd r id e
[Ir H3(P NP *-6)]. [Ir(COD)(OMe)]2 (200 mg, 0.30 mmol) was
dissolved in THF (30 mL) under nitrogen. The ligand, rac,sec-
bis(2-((dicyclohexylphosphino)ethyl)amine, PNP*-6 (350 mg,
0.67 mmol), was added. Hydrogen gas was bubbled through
this solution for 2 h at room temperature. 31P NMR spectros-
copy indicated that there was no conversion to a trihydride
species (either mer or fac). Heating the NMR sample under a
positive pressure of H2 resulted in the formation of several
products (some hydride bearing) that were not identified.
X-r a y Da ta Collection a n d P r ocessin g. Crystals of 9a
were grown from a dichloromethane/methanol solution (2:1 v/v)
at 25 °C under a nitrogen atmosphere. Intensities of the
crystal were collected on an ENRAF-Nonius CAD4 diffracto-
meter. Lattice parameters were obtained by a least-squares
refinement of 25 accurately centered reflections. Three stan-
dard reflections were measured every 2 h for the orientation
and intensity control. During data collection no decay of the
specimen was observed. Intensity data were corrected for
Lorentz-polarization factors, and the absorption correction
based on a ψ scan was applied. Crystallographic details are
reported in Table 1.
(B) [Ir(COD)(OMe)]2 (200 mg, 0.30 mmol) was dissolved in
THF (30 mL) under nitrogen. The ligand PNP*-7 (350 mg,
0.62 mmol) was added. Hydrogen gas was bubbled through
this solution for 30 min, and the solution was heated to 30 °C.
After complete evaporation of the solvent in vacuo, a yellow-
1
colored residue was obtained. 31P and H NMR spectra of this
residue showed the formation of 15 and 16 in a ratio of
approximately 1:1 (70% based on integration of the 31P
resonances) together with several minor products. NMR data
for 16: 1H NMR (CD2Cl2, 20 °C, 200.13 MHz) δ -25.12 (dddd,
2
2
2
2J H
) 11.6 Hz, J H
) 11.6 Hz, J H
) 6.1 Hz, J H
,P
A
,P
A
,H
A
,H
cis
cis
B
A
B′
The stucture was solved by conventional Patterson and
Fourier methods and refined by full-matrix least-squares
procedures. The coordinated hydride was located from the
difference Fourier map after anisotropic refinement. The
positions of all of the other hydrogen atoms were calculated
and confirmed by a difference Fourier map. Residual peaks
were found only near the heavy atom. All non-hydrogen atoms
were refined with anisotropic displacement coefficients. The
final cycles of refinement converged at R1(Fo) ) 0.037 and
wR2(Fo) ) 0.041 for 6251 observed reflections with I > 3σ(I).
Scattering factors, anomalous dispersion terms, and programs
were taken from the Enraf-Nonius MOLEN library.7a The
program ORTEP7b was also used.
2
2
) 6.1 Hz, HA), -10.96 (dddd, J H
) 128.8 Hz, J H
)
,P
,P
B
B
cis
26.9 Hz, 2J H
) 29.9 Hz, 2J H
tr)ans 6.1 Hz, 2HB. 31P{1H}
,H
,H
B
B′
B
A
2
NMR (CD2Cl2, 20 °C, 81.01 MHz): δ 37.2 (d, J P,P ) 9.8 Hz,
P), 29.7 (d, J P,P ) 9.8 Hz, P).
2
Heating this NMR sample (prepared under nitrogen) con-
verted all species to 15.
(C) The above reaction was also carried out at 0 °C while
hydrogen was bubbled through the THF solution. 31P NMR
showed that there was only ca. 30% conversion to the trihy-
dride 16, ca. 50% conversion to a monohydride species, and a
small amount of the monohydride COD species. Once again,
the NMR sample was heated (under nitrogen) and all species
were converted to the dihydride 15.

Synthesis of New Chiral Aminodiphosphine Ligands
Organometallics, Vol. 16, No. 20, 1997 4409
Sch em e 2
Resu lts a n d Discu ssion
Syn th esis of Ch ir a l Am in od ip h osp h in e Liga n d s.
Analogous to our methods previously employed to
prepare the chiral (R)-(+)- and (S)-(-)-(R-methylben-
zyl)bis(2-((diphenylphosphino)ethyl)amine ligands PNP*-
I,3a,c the related ligands PNP*-5a ,b, PNP*-6a ,b, and
PNP*-7a ,b bearing different combinations of substitu-
ents on the phosphorus ends (phenyl for 5 and cyclo-
C6H11 for 6 and 7) and/or on the stereoactive nitrogen-
tail (sec-butyl for 5 and 6; R-methylbenzyl for 7) were
prepared according to the general method shown in
Scheme 1.
Descriptively, nucleophilic attack with the chiral
primary amines 1a or 1b on 2.0 equiv of ethylene oxide
(and consequent ring opening) in ethanol/water at 0 °C
gives the corresponding chiral diols 2a or 2b as clear
viscous oils in excellent yields (83 to 85%). Subsequent
transformation of these diols into their dichloro-am-
monium salts 3a or 3b is achieved using thionyl chloride
in dry chloroform. Addition of concentrated sodium
hydroxide to these ammonium salts 3a or 3b gives the
corresponding dichlorides 4a or 4b. These dichloro
tertiary amines are added immediately to stirred solu-
tions of either potassium diphenylphosphide or lithium
dicyclohexylphosphide in THF maintaining a temper-
ature of 50 or 20 °C, respectively, during the addition.
During the course of the reaction, the initial red solution
gradually changes to a creamy color. After work-up, the
crude PNP* ligands can be purified by recrystallization
from acetone/ethanol to give off-white microcrystals
(yields 70 to 78%).
Syn th esis a n d Ch a r a cter iza tion of (R)- a n d (S)-
[Ir H (COD)(P NP *-5a ,b )] (9a ,b ). (R)- and (S)-[IrH-
(COD)(PNP*-5a ,b)] (9a ,b) were routinely synthesized
from the iridium dimer [Ir(COD)(OMe)]2 and 2 equiv of
the corresponding ligand PNP*-5a ,b in good yields
(Scheme 2). Compound 9a is thermally stable in
refluxing THF or toluene. Crystals suitable for X-ray
analysis were obtained by recrystallization from dichlo-
romethane/methanol under nitrogen.
F igu r e 1. ORTEP drawing (thermal ellipsoid; 30% prob-
ability) and labeling scheme for (R)-[IrH(COD){C2H5C*H-
(CH3)NCH2CH2PPh2)2}] (9a ).
coordinated with the COD and the PNP* ligand, via the
two phosphorus atoms only. The hydride ligand is cis
to the two phosphorus atoms and to one of the olefin
bonds of the COD. The other unsaturated bond of the
COD ligand is diagonally opposed to this hydride ligand.
Descriptively, one may envisage dative bonding between
the iridium metal and the center of the two unsaturated
bonds of the COD ligand and thus describe the resulting
structure as a distorted trigonal bipyramid. The iri-
dium, two phosphorus atoms, two ethylene bridges, and
nitrogen atom make up an eight-membered “pseudo-
chair” ring system, with the stereocenter being pushed
diagonally away from the COD ligand. The nitrogen
atom is too far away from the hydride ligand to stabilize
the complex via hydrogen bonding. The exclusive use
of the phosphorus donors for coordination, with a free
amine group, is not common for PNP ligands.3c,8 Indeed,
besides 9a , the only X-ray authenticated metal complex
containing an η2-P,P-PNP ligand is [TcNCl2(PNP-II)].9
In contrast, five-coordinate iridium complexes with η4
COD ligands are much more numerous, with either
The structure of 9a was solved, and an ORTEP
diagram of the molecule is shown in Figure 1. The
structure of 9a consists of the central iridium atom
(7) (a) MOLEN, An Interactive Intelligent System for Crystal Struc-
ture Analysis; Enraf-Nonius: Delft, The Netherlands, 1990. (b) Johnson,
C. K. ORTEP. Report ORNL-5138; Oak Ridge National Laboratory:
Oak Ridge, TN, 1976.

4410 Organometallics, Vol. 16, No. 20, 1997
Bianchini et al.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for
(R)-[Ir H(COD){C2H5C*H(CH3)N(CH2CH2P P H2}] (9a )
to a final temperature of -83 °C, the following changes
in the 31P{1H} NMR spectra occur. The initial AM spin
system is seen to slowly decrease in resolution such that
at -33 °C two broad (w1/2 ≈ 80 Hz) peaks result.
Further lowering the temperature of the sample results
in coalescence of the two resonances at -53 °C. Below
this temperature several peaks emerge from the base
line, and at the final temperature of -83 °C, the
spectrum shows two major peaks (13.00 and -10.00
ppm) and some minor peaks (between 0 and -16.00
ppm). The spectrum displayed at -83 °C compliments
our recent observation and documentation of a similar
series of events in the variable-temperature 31P NMR
spectra of the related (R)- and (S)-[IrH(COD)(PNP*-I)]
complexes.3a As previously proposed for the latter
complexes, the rapid equilibration of the eight-mem-
bered heterocycle at room temperature may be frozen
out in one of a number of possible chair, boat, quasi-
chair, or quasi-boat conformations on lowering the
temperature of the sample of 9a ,b to -83 °C.3a
Bond Lengths
Ir-P1
2.315(1)
2.286(1)
2.240(8)
2.243(7)
Ir-C29
Ir-C30
Ir-H
2.150(6)
2.148(6)
1.81(9)
Ir-P2
Ir-C25
Ir-C26
Bond Angles
P1-Ir-P2
P1-Ir-C25
P1-Ir-C26
P1-Ir-C29
P1-Ir-C30
P1-Ir-H
102.48(5)
120.5(1)
92.5(2)
105.9(2)
143.7(2)
73(2)
P2-Ir-C29
P2-Ir-C30
P2-Ir-H
C25-Ir-H
C26-Ir-H
C29-Ir-H
C30-Ir-H
148.5(2)
110.2(2)
77(2)
160(2)
164(2)
98(2)
P2-Ir-C25
P2-Ir-C26
85.3(2)
114.2(2)
99(2)
square-pyramidal or trigonal-bipyramidal coordination
geometries.10 In the case at hand, the bond distances
and angles point to a distorted trigonal bipyramid.
Selected bond distances and angles are listed in Table
2. The bond lengths and angles involving iridium,
carbon, and phosphorus are in their usual range.11 As
expected from the different π-back-bonding contribu-
tion,12 the Ir-C and C-C distances pertaining to the
equatorial C-C double bond (C29-C30) are shorter and
longer, respectively, than those pertaining to the axial
C-C double bond (C25-C26). The hydride ligand has
been located in the Fourier difference map and refined.
The Ir-H distance, 1.81(9) Å, is somewhat long11a but
comparable to that found in the Ir(III) octahedral
complex fac,exo-(R)-[IrH2{C6H4C*H(CH3)N(CH2CH2-
PPh2)] (Ir-H, 1.64(9) Å, Ir-H1 1.8(2) Å) in which the
hydride ligands are trans to nitrogen and phosphorus3a
or in [1,1,1,1-(CO)H(PPh3)2-arachno-1-IrB3H7] (Ir-H
1.81(8) Å) in which the hydride is trans to CO.11b
Complex 9a maintains the same structure in both the
solid state and solution. The IR spectra (Nujol mulls
or CH2Cl2 solution) contain the characteristic ν(Ir-H)
Like the PNP*-I derivative3a and in contrast to the
achiral PNP-II complex [IrH(COD)(PNP-II)] (vide
infra),3b,c one can exclude that in the temperature range
investigated the terminal hydride ligand in 9a ,b may
migrate to one of the two double bonds of the coordi-
nated COD to give a cyclooctenyl ligand as in [Ir(σ,η2-
C8H13)(PNP-II)] (see Scheme 6).3c
Syn th esis a n d Ch a r a cter iza tion of (R)- a n d (S)-
[Ir H3(P NP *-5a ,b)] (10a ,b). (R)- and (S)-[IrH3(PNP*-
5a ,b)] (10a ,b) were synthesized by either dissolving the
corresponding (COD)hydride precursor 9a ,b in THF and
bubbling hydrogen gas through the solution for 30 min
or dissolving the monohydride 9a ,b in a mixture of THF/
propan-2-ol (1:4) and refluxing for 14 h (Scheme 2).
Reduction of COD to COE was obtained by both
procedures and gave good yields (80 to 98%), with the
crude products recrystallized to purity from THF/
propan-2-ol. Characterization of the trihydride 10a
shows three strong absorptions in the IR spectrum at
1993, 2025, and 2160 cm-1. Further diagnostic evidence
for the formation of a trihydride complex is found in the
1H NMR spectrum with the hydride trans to nitrogen
(HA) at -23.20 ppm and the two hydrides cis to nitrogen
(HB/B′) at -9.75 ppm. Hydride A gives rise to a seven-
line multiplet that is interpreted as an overlapping
doublet of doublets of doublets of doublets, with all the
couplings constants consistent with cis configurations
of both the phosphorus atoms and the two other hydride
ligands. Hydrides B and B′ give rise to a doublet of
doublets of doublets of doublets; one of the couplings is
on the order of 130 Hz, consistent with a trans phos-
phorus-hydride coupling constant in iridium(III) com-
plexes, with the other three coupling constants repre-
senting the cis couplings.13 The 31P{1H} NMR spectrum
shows an AM spin system with doublets of 5.7 Hz at
24.42 and 25.70 ppm, indicative of a facial orientation
of the aminodiphosphine ligand.8a,c
1
band at 2110 cm-1, while the H NMR spectrum shows
an upfield triplet corresponding to cis coupling between
the hydride and the two phosphorus atoms (-13.80
2
ppm, J H
) 22.3 Hz). Evidence for the presence
hydride,P
of a η4-coordinated COD ligand is found in the 13C NMR
spectrum with diagnostic peaks at 46.8 ppm, corre-
sponding to 4CH2, 47.0 ppm, corresponding to 2CH1, and
78.8 ppm, corresponding to 2CH1.10 The AM spin
system in the 31P{1H} NMR, acquired in CD2Cl2 at 25
°C (J P,P ) 22.3 Hz), maintains its symmetry at higher
temperatures (60 °C, THF-d8, J P,P ) 23.0 Hz). On
lowering the temperature of a sample of 9a ,b in CD2Cl2
(8) (a) Bianchini, C.; Casares, J . A.; Peruzzini, M.; Romerosa, A.;
Zanobini, F. J . Am. Chem. Soc. 1996, 118, 4585. (b) Bianchini, C.; Masi,
D.; Peruzzini, M.; Romerosa, A.; Zanobini, F. Acta Crystallogr. 1996,
C52, 1973. (c) Bianchini, C.; Innocenti, P.; Peruzzini, M.; Romerosa,
A.; Zanobini, F. Organometallics 1996, 15, 272. (d) Bianchini, C.; Masi,
D.; Peruzzini, M.; Romerosa, A.; Zanobini, F. Acta Crystallogr. 1995,
C51, 2514. (e) Bianchini, C.; Innocenti, P.; Masi, D.; Peruzzini, M.;
Zanobini, F. Gazz. Chim. Ital. 1992, 122, 461.
(9) Marchi, A.; Marvelli, L.; Rossi, R.; Magon, L.; Uccelli, L.;
Bertolasi, V.; Ferretti, V.; Zanobini, F. J . Chem. Soc., Dalton Trans.
1993, 1281.
(10) (a) Gull, A. M.; Fanwick, P. E.; Kubiak, C. P. Organometallics
1993, 12, 2121. (b) Wehman-Ooyevaar, I. C. M.; Kapteijn, G. C.; Grove,
D. M.; Smeets, W. J . J .; Spek, A. L.; van Koten, G. J . Chem. Soc., Dalton
Trans. 1994, 703.
The trihydride 10a ,b is thermally stable in refluxing
THF or toluene. The low propensity to reductively
eliminate H2 as a thermal step is a typical characteristic
of Ir(III) trihydrides with fac polydentate ligands, see
(11) (a) Orpen G. A.; Brammer, L.; Allen, F. F.; Kennard, O.; Watson,
D. G.; Taylor, R. J . Chem. Soc., Dalton Trans. 1989, S1. (b) Bould, J .;
Greenwood, N. N.; Kennedy, J . D.; McDonald, W. S. J . Chem. Soc.,
Dalton Trans. 1985, 1843.
(13) (a) Pregosin, P. S.; Kunz, R. W. In 31P and 13C NMR of
Transition Metal Phosphine Complexes; Diehl, P., Fluck, E., Kosfeld,
R., Eds.; Springer-Verlag: New York, 1979. (b) Garrou, P. E. Chem.
Rev. 1981, 81, 229.
(12) Rossi, A. R.; Hoffmann, R. Inorg. Chem. 1975, 14, 365.

Synthesis of New Chiral Aminodiphosphine Ligands
Organometallics, Vol. 16, No. 20, 1997 4411
Sch em e 3
Sch em e 4
for example the chemistry of [(triphos)IrH3] (triphos )
MeC(CH2PPh2)3).14
hydride resonances appear as an overlapping doublet
of doublets of doublets; a doublet due to the coupling to
the other hydride and a doublet of doublets due to the
coupling to the two different phosphorus atoms. A 2D-
1H-1H phase-sensitive NOESY spectrum showed a clear
cross-peak between the hydride resonance at -21.43
ppm (HA) and the hydride at -13.79 ppm (HB) as well
as the aromatic proton at 7.51 ppm. The latter interac-
tion confirms that the most downfield of the aromatic-
hydrogen resonances is in fact proton H4 (for the
labeling scheme adopted, see Scheme 4). The 2D-1H-
1H COSY NMR spectra showed all of the expected
couplings between the aromatic protons. A very similar
proton spectrum is observed for the dichloride derivative
18 (vide infra), and the o-metalation in this complex has
been confirmed by a single-crystal X-ray diffraction
analysis,15 thus further supporting the determined
structure for the dihydride complex 15a ,b. The 13C{1H}
NMR spectrum also supports the structure determined
as in the low-field region it contains an overlapping
doublet of doublets attributable to the carbon atom of
Syn th esis a n d Ch a cter iza tion of m er (R)- a n d
(S )-[Ir H 2{C6H 4C*H (CH 3)N[CH 2CH 2P (C6H 11)2]2}]
(15a ,b). Synthesis of the dihydride complexes (R)- and
(S)-[R-methylbenzyl-bis(2-(dicyclohexylphosphino)ethy-
l)amine]iridium
dihydride, [IrH2{C6H4C*H(CH3)-
N[CH2CH2P(C6H11)2]2}] (15a,b) (Scheme 3), was achieved
by refluxing a 2:1 mixture of the corresponding ligand
(either PNP*-7a or PNP*-7b) with the iridium dimer,
[Ir(COD)(OMe)]2, in toluene for 4 h. Removal of the
solvent in vacuo gives 15a ,b which can be recrystallized
from dichloromethane and methanol (yield 85%). The
dihydride ortho-metalated complex has been character-
ized by NMR and IR spectroscopies. The 31P{1H} NMR
spectrum consists of an AB spin system centered at
2
about 42 ppm with J P,P ) 348.6 Hz, indicating that the
two phosphorus atoms of the PNP* ligand are in a trans
disposition.3a,13 Important features of the 1H NMR
spectrum show that there are two hydride resonances
at high field, -21.43 ppm (HA, the hydride trans to
nitrogen of the PNP ligand) and -13.79 ppm (HB, the
hydride trans to the cyclometalated ring), as well as only
four aromatic protons appearing as two doublets and
two triplets, the aromatic protons pattern being consis-
tent with an ortho-metalated phenyl ring.3a Both of the
2
an ortho-metalated phenyl group (δ 162.3 (dd, J P,C
o,m
2
) 8.6 Hz, J P,C ) 8.6 Hz).
o,m
On the basis of this spectroscopic evidence, it can thus
be concluded that the PNP*-7 ligand in 15a ,b is oriented
(15) Bianchini, C. et al. X-ray crystal structure of rac-[IrCl2-
{C6H4C*H(CH3)N[CH2CH2P(C6H11)2]2}], manuscript in preparation.
Crystal data: space group Pnma (No. 62); a ) 17.887(9) Å, b )
24.305(3) Å, c ) 9.806(1) Å, R ) 90.00(2)°, â ) 90.00(1)°, γ ) 90.00(2)°;
V ) 4263.05(3) Å3; dcalcd ) 1.428 g cm-3; Z ) 4; R [I > 2σ(I)] ) 0.094,
R (all data) ) 0.143.
(14) (a) Bianchini, C.; Farnetti, E.; Graziani, M.; Kaspar, J .; Vizza,
F. J . Am. Chem. Soc. 1993, 115, 1753. (b) Bianchini, C.; J ime´nez, M.
V.; Meli, A.; Moneti, S.; Vizza, F.; Herrera, V.; Sa´nchez-Delgado, R. A.
Organometallics 1995, 14, 2342.

4412 Organometallics, Vol. 16, No. 20, 1997
Bianchini et al.
in a meridional fashion, with two hydride ligands cis-
coordinated to iridium and the sixth coordination site
occupied by the carbon atom of the ortho-metalated
phenyl substituent attached to the chiral center. No
mer to fac isomerization of the polydentate ligand in the
ortho-metalated complex was observed in toluene-d8 to
the final temperature of 110 °C.
Deu ter iu m Exch a n ge Rea ction . Rea ction of th e
Dih yd r id e 15 w ith D2O. When a THF-d8 solution of
the rac-dihydride 15 is shaken with a drop of D2O and
the 1H NMR followed, it is observed that the resonances
arising from the two hydride ligands disappear along
with the aromatic resonance at 6.28 ppm assigned to
proton H1 (the assignment follows from analysis of both
the NOESY and COSY spectra). Removal of the solvent
from a THF solution of 15 previously treated with D2O
affords [IrD2{C6H3DC*H(CH3)N[CH2CH2P(C6H11)2]2}]
F igu r e 2. ORTEP drawing (thermal ellipsoid; 30% prob-
ability) for [IrCl2{C6H4C*H(CH3)N[CH2CH2P(C6H11)2]2}]
(18).
2
Sch em e 5
(15-d 3). A H NMR spectrum recorded in THF on this
sample, confirmed that the loss of the proton resonances
were in fact matched with corresponding resonances in
2
the H NMR spectrum. This indeed shows deuterium
incorporation exclusively for the two hydrides and
proton H1 (Scheme 4). The selective incorporation of
deuterium in the ortho position of the metalated phenyl
ring suggests that the dihydride is in rapid equilibrium
with a de-ortho-metalated species, most presumably a
four-coordinate species similar to that previously pro-
posed for the intermediate square-planar complex [IrH(P-
NP*-I)].3a This species was observed by 31P and 1H
NMR before o-metalation occurred to give the corre-
sponding dihydride complex. During the conversion of
the COD-hydride complex 14 to the dihydride 15,
which involves the decoordination of COD, no interme-
diate was observed by 31P NMR spectroscopy, however.
A similar case of reversible ortho-metalation occurring
at room temperature has recently been reported by
Caulton et al. for the Ir(III)-hydride complex [IrH(η2-
C6H4PtBu2)(C2Ph)(PtBu2Ph)].16
the nitrogen and the other is trans to the ortho-
metalated phenyl ring. A molecular sketch of the
complex cation is reported in Figure 2.
Id en tifica tion of r a c-[(r-Meth ylben zyl)bis(2-(d i-
cycloh exylph osph in o)eth yl)am in e]ir idiu m Hydr ide
Ch lor id e,
[Ir (H )Cl{C6H 4C*H (CH 3)N[CH 2CH 2P -
(C6H11)2]2}] (17). In the conversion of dihydride 15 to
dichloride 18, an intermediate species was detected, and
this was determined to be the (hydride)chloride complex
rac-[Ir(H)Cl{C6H4C*H(CH3)N[CH2CH2P(C6H11)2]2}] (17)
(Scheme 5). Although this complex was only isolated
in a very small amount (precipitated within an NMR
tube), it was unambiguosly characterized by 1H and
31P{1H} NMR spectroscopies as well as elemental
analysis. As expected, the hydride/chloride exchange
in dichloromethane occurs to a lesser extent than that
in chloroform. Indeed, warming dihydride 15 in dichlo-
romethane causes only a partial exchange of the hydride
ligand trans to the carbon atom of the cyclometalated
ring. The 31P{1H} NMR spectrum shows an AB system
at slightly higher field then the corresponding dihydride,
indicating that the PNP* ligand remains in a meridional
orientation. The 1H NMR spectrum features the dis-
appearence of the hydride resonances of 15 and the
appearance of a new hydride resonance at -18.6 ppm,
appearing as an overlapping doublet of doublets (coupled
to the two different phosphorus atoms). A 2D-1H-1H
NOESY NMR experiment showed that the hydride has
a NOE effect to proton H4 of the ortho-metalated phenyl
ring, indicating that it is the hydride cis to nitrogen to
be exchanged in the process affording 17. The selectiv-
ity of H substitution agrees with the greater trans effect
of the metalated carbon atom as compared to nitrogen.17
In Situ Va r ia ble-Tem p er a t u r e NMR St u d y for
th e F or m a tion of th e Or th o-Meta la ted Dih yd r id e
Syn th esis a n d Ch a cter iza tion of m er ,r a c-[(r-
Me t h y lb e n zy l)b is (2-(d ic y c lo h e x y lp h o s p h in o )-
eth yl)a m in e]ir id iu m Dich lor id e, [Ir Cl2{C6H4C*H-
(CH3)N[CH2CH2P (C6H11)2]2}] (18). The dichloride
complex [IrCl2{C6H4C*H(CH3)N[CH2CH2P(C6H11)2]2}]
(18) was synthesized by dissolving the ortho-metalated
dihydride complex 15 in CHCl3 and heating at 65 °C
for 2 h. After removal of the solvent, recrystallization
from dichloromethane and methanol gave 18 as brick-
like crystals. The 31P and 1H NMR spectra of this
complex are very similar to those acquired for the
dihydride complex (see above), with the obvious excep-
tion that there are no hydride resonances at high field
1
in the H NMR spectra. The 13C NMR spectrum also
supports the ortho-metalated structure as it shows in
the low-field region an overlapping doublet of doublets
attributable to the carbon atom of an ortho-metalated
2
2
phenyl group (δ 134.1 (dd, J P,C ) 7.3 Hz, J P,C
)
o,m
o,m
7.3 Hz)).
A crystal structure was determined for this complex15
and showed that the PNP ligand is in a meridional
orientation about an octahedral iridium center and that
the phenyl ring is indeed metalated through one of the
ortho carbons. The two chloride ligands are found to
be in a cis disposition to one another: one is trans to
1
15. Variable-temperature H and 31P NMR measure-
ments were carried out on a solution prepared by
(17) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Book: Mill Valley, CA, 1987.
(16) Cooper, A. C.; Huffman, J . C.; Caulton, K. G. Organometallics
1997, 16, 1974.

Synthesis of New Chiral Aminodiphosphine Ligands
Organometallics, Vol. 16, No. 20, 1997 4413
dissolving the iridium dimer [Ir(COD)(OMe)]2 in toluene-
d8 with 2 equiv of PNP*-7. At room temperature, the
31P{1H} NMR spectrum showed the presence of the free
aminodiphosphine ligand (singlet at -9.53 ppm) as well
as the presence of another species (singlet at ca. 10
ppm). The corresponding 1H NMR spectrum showed
that there were no hydride ligands present, and thus
the signal is tentatively assigned to the COD-methoxy
species [Ir(COD)(OMe)(PNP*-7)] (12) (Scheme 3). Heat-
ing the sample to 37 °C, the 31P NMR spectrum showed
the presence of an AM spin system at 1.4 ppm and a
decrease in the intensity of the signals at ca. 10 and
-9.53 ppm. Correspondingly, the 1H NMR spectrum
showed hydride resonance growing in at ca. -13.8 ppm,
appearing as an overlapping doublet of doublets. This
is consistent with the methoxy complex 12 â-eliminating
formaldehyde to give the monohydride COD species 14.3
Heating the sample further to a temperature of 78 °C,
the 31P NMR spectrum showed the appearance of the
AB spin system of 15 centered at ca. 42 ppm and the
disappearance of the AM spin system at 1.4 ppm.
tempted, as it was clear that once the dihydride formed
this would not react with hydrogen. This was attempted
at several temperatures, the details of which are
reported in the Experimental Section. The most suc-
cessful attempt did in fact form ca. 30% of trihydride
16 which could be characterized by 31P and 1H NMR
spectroscopies, particularly with the use of 1H{31P} and
selective 1H homonuclear decoupling experiments. A
direct comparison was made with the 31P NMR spectra
as well as the hydride region of the 1H NMR spectra
acquired for the isolated trihydride 10 and were found
to be very similar, thus giving additional supporting
evidence for the fac structural assignment of 16 gener-
ated in situ. However, on warming a sample of 16
generated in situ to only 40 °C, the complex rapidly
eliminates dihydrogen and cyclometalation to give the
stable ortho-metalated complex 15, indicating that the
range for the thermal stability of the trihydride 16 is
extremely narrow.
From the attempted reactions to form trihydride 16
species, it is clear that the most thermodynamically
stable species is 15. Although the deuterium exchange
reaction showed that the latter compound is in rapid
equilibrium with a (proposed) four-coordinate monohy-
dride species (following the selective incorporation of
deuterium at the ortho position), it was not possible to
trap this proposed species with hydrogen, indicating
that the reductive elimination of hydrogen from the
trihydride is a much more facile process than that of
the reductive elimination of the metalated ring, thus
making the dihydride complex 15 the thermodynamic
sink of the reaction of PNP*-7 with [Ir(COD)(OMe)]2 in
either protic or aprotic solvents.
In Situ Va r ia b le-Tem p er a t u r e NMR St u d y for
t h e Ch a r a ct er iza t ion of (R)- a n d (S)-[Ir H (COD)-
(P NP *-6a ,b)] (13a ,b) a n d (R)- a n d (S)-[Ir H(COD)-
(P NP *-7a ,b)] (14a ,b). In situ variable-temperature
NMR experiments allowed for the NMR (1H and 31P)
characterization of the COD-monohydride species 13a,b
and 14a ,b, which can also be isolated in the solid state
in the absence of protic solvents (Scheme 3). In a typical
experiment, 2:1 mixtures of the appropriate PNP*
ligand and the dimer [Ir(COD)(OMe)]2 were mixed in
toluene-d8 at room temperature under a nitrogen at-
mosphere. The 31P{1H} NMR spectra of these solutions
showed the free PNP* ligands at ca. -9 ppm as a sharp
singlet as well as another singlet resonance shifted
about 20 ppm downfield (δ ≈10). The latter resonance
Con clu sion s
From a comparison of the reactions illustrated in
Scheme 6 with those reported in Schemes 2 and 3, one
may draw out a number of interesting conclusions
regarding the influence of the substituents at either the
stereocenter or the phosphorus donors on the coordina-
tion chemistry of these aminodiphosphine ligands
(Scheme 6).
1
had no associated hydride resonances in the H NMR
spectrum, and a likely candidate for this species is
indeed the methoxy-COD complex [Ir(OMe)(COD)(P-
NP*)] (PNP* ) PNP*-6, 11; PNP*-7, 12). Careful
heating of the NMR tube in the probe of the spectrom-
eter allowed the quantitative formation of each of the
monohydrides (13a ,b and 14a ,b) to be observed (1H and
31P NMR) at a stabilized temperature of 37 °C. Further
heating of the solution containing 14a ,b at 60° C in an
external oil bath quantitatively yielded 15a ,b. By
contrast, prolonged heating of the 13a ,b samples re-
sulted in a number of transformations, during the
course of the experiment, giving rise to various products
which defied first-order analysis.
At first glance, it is clearly apparent that irrespective
of the nature of the other coligands the steric bulk
generated at the terminus of the PNP donor system by
the cyclohexyl substituents favors a meridional confor-
mation of the ligands. This thermodynamic control on
the bonding mode of the PNP ligands is so efficient that
the Ir(III) fac trihydride complexes, generally stable
with the phenylated ligands,14 with the cyclohexyl-
substituted ligands either are not formed at all (PNP*-
6) or spontaneoulsy lose H2 at room temperature (PNP*-
7). On the other hand, mer trihydride complexes have
never been seen with this type of PNP ligands, most
likely because they would bear an overload of the trans
influence.17 In a sense, this result was desired prior to
the synthesis of PNP*-6 and PNP*-7. One of the
reasons for the proposed formulation of these ligands
was, in fact, to derive a series of chiral iridium com-
plexes which, due to the steric bulk of the large
cumbersome cyclohexyl groups, would drive the ketone
or any other prochiral substrate into a “molecular
pocket” different from that of the PNP*-I and PNP-II
ligands already investigated.3 Moreover, the most
energetically favored mer conformation of the ligands
Attem p ted F or m a tion of th e Ir id iu m Tr ih yd r id e
Com p lex r a c-[Ir H3(P NP *-6)] (16). The trihydride
[IrH3(PNP*-6)] (16) was formed in situ, but it was never
isolated in the pure form. One method that was used
in an attempt to form 16 was to take a THF solution of
dihydride 15 and put this under 20 atm of hydrogen
with the idea of forcing the oxidative addition of
molecular hydrogen by the spectroscopically undetected
(but inferred, via the deuterium exchange experiment
previously described) four-coordinate monohydride spe-
cies. This, however, failed to give the trihydride, and
only the starting material was recovered. Reacting
PNP*-6 with [Ir(COD)(OMe)]2 under hydrogen in order
to form the trihydride from the COD-hydride species 14
before it could form the dihydride 15 was also at-

4414 Organometallics, Vol. 16, No. 20, 1997
Bianchini et al.
Sch em e 6
bearing cyclohexyl substituents might decrease the risk
of poor enantioface discrimination due to configurational
instability of the catalysts during the reactions.18 Analo-
gously, the facility with which trihydride 16 thermally
loses H2 is expected to increase the activity of metal
catalysts derived from the cyclohexyl-substituted ligands
PNP*-6 and PNP*-7 in homogeneous reduction reac-
tions under a high pressure of H2.
The influence of the substituent(s) at the R′R′′CHN-
(CH2CH2PR2)2 carbon atom on the coordination chem-
istry of the PNP* ligands is even more pronounced than
that exerted by the phosphorus substituents. First of
all, no intramolecular cyclometalation occurs with the
alkyl substituents, a finding that is in line with the
thermodynamics of the insertion of metal centers into
C-H bonds from either sp2- or sp3-hybridized carbon
atoms.19 When the alkyl substituent at this carbon
atom is associated with cyclohexyl substituents at the
phosphorus donors, extremely reactive metal fragments
are formed, which represents an attractive character-
istic of any efficient catalyst precursor. On the other
hand, the phenyl substituent at the stereocenter does
not seem to inhibit the reactivity of the iridium com-
plexes with PNP*-I or PNP*-7, as the C-H insertion is
a reversible process through which the metal is chemi-
cally and stereochemically stabilized.
reaction with [Ir(COD)(OMe)]2. The linear n-propyl
group favors the formation of the hydride-migration
cyclooctenyl product [Ir(PNP-II)(σ,η2-C8H13)], which only
at high temperature produces small equilibrium con-
centrations of the hydride-COD complex (Scheme 6).3c
The branched sec-butyl group in PNP*-5 forms a very
reactive hydride-COD species that, unlike the PNP-II
one, is hydrogenated by propan-2-ol. A clear cut expla-
nation for this contrasting behavior cannot be provided
by us at this stage, although it seems highly probable
that steric effects may play a major role in driving the
two distinct reactivities.
In light of the results presented in this paper, we are,
at present, continuing our investigations of the hydrogen-
transfer reduction of prochiral and R,â-unsaturated
ketones by iridium catalysis. Preliminary results show
that the catalytic activity decreases in the order PNP*-I
> PNP*-7 > PNP*-6 > PNP*-5, while the chemo- and
enatioselectivities greatly depend on the nature of the
alkyl or aryl substituents at either the ketone or the
chiral ligand. Studies also include the synthesis of other
chiral PNP* ligands either bearing different substitu-
ents at the stereogenic carbon atom or containing the
stereocenter incorporated into the P-N arm, i. e., closer
to the site of reduction.
Ack n ow led gm en t. The authors thank Mr. Dante
Masi for technical assistance. L.G. and G.P. thank the
Italian Ministry of Foreign Affairs for financial support.
Finally, it is worth noticing the striking effect played
by the alkyl substituent at the nitrogen atom on the
(18) Uematsu, N.; Fujii, A.; Hashiguchi, S.; Ikariya, T.; Noyori, R.
J . Am. Chem. Soc. 1996, 118, 2521, 4916.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal-
lographic data, positional parameters, bond distances, bond
angles, and anisotropic thermal parameters for (R)-[IrH-
(COD)(C2H5C*H(CH3)N(CH2CH2PPh2)2)] (9a ) (6 pages). Or-
dering information is given on any current masthead page.
(19) (a) Ianowicz, A. H.; Periana, R. A.; Buchanan, J . M.; Kovac, C.
A.; Stryker, J . M.; Wax, M. J .; Bergman, R. G. Pure Appl. Chem. 1984,
56, 13. (b) J ones, W. D.; Feher, F. J . J . Am. Chem. Soc. 1984, 106,
1650. (c) J ones, W. D.; Feher, F. J . Acc. Chem. Res. 1989, 22, 91. (d)
J ones, W. D.; Feher, F. J . J . Am. Chem. Soc. 1985, 107, 620. (e)
Bergman, R. G. Science 1984, 223, 902. (f) Crabtree, R. H. Chem. Rev.
1985, 85, 245.
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