Iridium complexes of orthometalated triaryl phosphites: Synthesis, structure, reactivity, and use as imine hydrogenation catalysts

Article abstract of DOI:10.1021/om960239h

Di-orthometalated iridium complexes of triaryl phosphites have been prepared and characterized. The synthesis of the triphenyl phosphite derivative [IrH(cod){P(OC₆H₄)₂-(OC₆H ₅)}], 3, requires a circuitous route by treatment of [IrCl(cod){P(OPh)₃}] with methyllithium and then methanol. However, with the hindered phosphites P(OAr)₃ (Ar = C₆H₄-2-^tBu or C₆H₃-2,4-^tBu₂) the di-orthometalated species 5a,b are readily obtained by reaction of the phosphite with [{Ir(μ-OMe)(cod)}₂] or [Ir(cod)(py)₂][PF₆]. The mechanisms of these reactions have been investigated and are different. Both 5a and 5b are catalysts for imine hydrogenation. The complexes [IrH₅{P(OAr)₃}₂] have been isolated from hydrogenation reactions and synthesized independently.

Full text of DOI:10.1021/om960239h

3990
Organometallics 1996, 15, 3990-3997
Ir id iu m Com p lexes of Or th om eta la ted Tr ia r yl
P h osp h ites: Syn th esis, Str u ctu r e, Rea ctivity, a n d Use a s
Im in e Hyd r ogen a tion Ca ta lysts
Robin B. Bedford,† Sergio Castillo`n,‡ Penny A. Chaloner,*,† Carmen Claver,*,‡
Elena Fernandez,‡ Peter B. Hitchcock,† and Aurora Ruiz‡
School of Chemistry and Molecular Sciences, University of Sussex, Brighton BN1 9QJ , U.K.,
and Departament de Quimica, Universitat Rovira i Virgili, Pl. Imperial Ta´rraco 1,
43005 Tarragona, Spain
Received March 28, 1996X
Di-orthometalated iridium complexes of triaryl phosphites have been prepared and
characterized. The synthesis of the triphenyl phosphite derivative [IrH(cod){P(OC6H4)2-
(OC6H5)}], 3, requires a circuitous route by treatment of [IrCl(cod){P(OPh)3}] with methyl-
lithium and then methanol. However, with the hindered phosphites P(OAr)3 (Ar ) C6H4-
2-tBu or C6H3-2,4-tBu2) the di-orthometalated species 5a ,b are readily obtained by reaction
of the phosphite with [{Ir(µ-OMe)(cod)}2] or [Ir(cod)(py)2][PF6]. The mechanisms of these
reactions have been investigated and are different. Both 5a and 5b are catalysts for imine
hydrogenation. The complexes [IrH5{P(OAr)3}2] have been isolated from hydrogenation
reactions and synthesized independently.
In tr od u ction
(OC6H5)2}{P(OPh)3}3], or [PdCl{P(OC6H4)(OC6H5)2}-
We have recently been investigating the use of iri-
dium complex catalysts for the homogeneous hydroge-
nation of imines.1,2 We became interested in the
synthesis of iridium complexes with orthometalated
triaryl phosphites, and some of these results have
recently been presented as a communication.3
Group 9 complexes with bulky triaryl phosphite
ligands have proved successful catalysts for reduction
of unsaturated organic compounds. For example, rhod-
ium complexes catalyze the hydroformylation of other-
wise unreactive species such as methylenecyclohexane,
limonene, and cyclohexene4 as well as cyclooctene5 and
various terminal6 and hindered7 alkenes, while selective
catalyst systems have been developed with chiral diphos-
phites for the regio- and stereoselective hydroformyla-
{P(OPh)3}]. Orthometalation in these systems appears
to be essential, as no hydrogenation was obtained with
the non-metalated analogues [RuHCl{P(OPh)3}4], [CoH-
{P(OPh)3}4], or [PdCl2{P(OPh)3}2].
The catalytic hydrogenation of imines has attracted
considerable interest in recent years, especially when
the imines are prochiral.10 Processes have been devel-
oped using titanium,11 rhodium,12 ruthenium,13 and
iridium14 complexes as catalysts.
Here we describe the synthesis of iridium complexes
with the bulky triaryl phosphite ligands tris(2,4-di-tert-
butylphenyl) phosphite, Irgafos-168,15 1, and tris(2-tert-
tion of styrene.8 [RuCl{P(OC6H3-2-Me)(OC6H4-2-Me)2}-
(PPh3)2] has been found to be an active catalyst for
alkene and alkyne hydrogenation,9 with activity
equivalent to [RuHCl(PPh3)3] and higher than that of
[RhCl(PPh3)3]. Activity was also noted using
[RuCl{P(OC6H4)(OC6H5)2}{P(OPh3)}3], [Co{P(OC6H4)-
butylphenyl) phosphite, 2, and contrast these with the
related derivatives of P(OPh)3. The mechanisms of
formation of the complexes will be discussed, as will
their use as catalysts for the hydrogenation of N-
benzylidene aniline.
† University of Sussex. E-mail: Penny.Chaloner@sussex.ac.uk.
‡ Universitat Rovira i Virgili. E-mail: claver@quimica.urv.es.
X Abstract published in Advance ACS Abstracts, August 15, 1996.
(1) Bedford, R. B.; Chaloner, P. A.; Claver, C.; Fernandez, E.;
Hitchcock, P. B.; Ruiz, A. In Catalysis of Organic Reactions (Chemical
Industries Series 62); Scaros, M. G., Prunier, M. L., Eds.; Marcel
Dekker: New York, 1994; pp 181-8.
(2) Bedford, R. B.; Chaloner, P. A.; Dewa, S. Z.; Lo´pez, G.; Hitchcock,
P. B.; Momblona, F.; Serrano, J . L. J . Organomet. Chem., in press.
(3) Bedford, R. B.; Chaloner, P. A.; Hitchcock, P. B. J . Chem. Soc.,
Chem. Commun. 1995, 2049.
(4) van Leeuwen, P. W. N. M.; Roobeek, C. F. J . Organomet. Chem.
1983, 258, 343.
(5) van Rooy, A.; Orij, E. N.; Kamer, P. C. J .; van den Aardweg, F.;
van Leeuwen, P. W. N. M. J . Chem. Soc., Chem. Commun. 1991, 1096.
(6) Cuny, G. D.; Buchwald, S. L. J . Am. Chem. Soc. 1993, 115, 2066.
(7) Polo, A.; Claver, C.; Castillo´n, S.; Ruiz, A.; Bayon, J . C.; Real,
J .; Mealli, C.; Massi, D. Organometallics 1992, 11, 3525.
(8) Buisman, G. J . H.; Kamer, P. C. J .; van Leeuwen, P. W. N. M.
Tetrahedron Asym. 1993, 4, 1625.
(10) Zhou, Z.; J ames, B. R.; Alper, A. Organometallics 1995, 14,
4209.
(11) Willoughby, C. A.; Buchwald, S. L. J . Am. Chem. Soc. 1992,
114, 7562.
(12) Levi, A.; Modena, G.; Scorrano, G. J . Chem. Soc., Chem.
Commun. 1975, 6.
(13) Kraslik, P.; Alper, H. Tetrahedron: Asym. 1992, 3, 1283.
(14) Osborn, J . A.; Chan, Y. N. J . Am. Chem. Soc. 1990, 112, 9400.
Ng, Y.; Chan, C.; Meyer, D.; Osborn, J . A. J . Chem. Soc., Chem.
Commun. 1990, 869. Spindler, J .; Pugi, A.; Blaser, M. Angew. Chem.,
Int. Ed. Engl. 1990, 29, 558.
(15) We thank Dr. Hans Zweifel of Ciba-Geigy for a generous gift
of this material.
(9) Lewis, L. N. J . Am. Chem. Soc. 1986, 108, 743.
S0276-7333(96)00239-7 CCC: $12.00 © 1996 American Chemical Society

Iridium Complexes of Triaryl Phosphites
Organometallics, Vol. 15, No. 19, 1996 3991
Ta ble 1. Selected NMR Sp ectr oscop ic Da ta for
Or th om eta la ted Com p lexes
phosphite with 6 does not produce the comparable di-
orthometalated complex 3 but rather the previously
complex
δ(31P) (ppm)
δ(1H)[hydride] (ppm)
2J PH (Hz)
reported [Ir{P(OC6H4)(OC6H5)2}(cod){P(OPh)3}],17 7.
3
5a
5b
155.7
151.1
150.9
-7.65
-7.18
-7.18
195
190
187
Resu lts a n d Discu ssion
Syn t h esis of Di-or t h om et a la t ed Ir id iu m Tr i-
a r yl P h osp h it e Com p lexes. The synthesis of
[IrH{P(OC6H4)2(OC6H5)}(cod)], 3 (cod ) 1,5-cycloocta-
diene), was effected by reaction of [IrCl(cod){P(OPh)3}]
with methyllithium and then methanol3 (eq 1). A related
It appears, therefore, that the ease of di-orthometa-
lation of 1 and 2 is a consequence of the steric bulk of
the phosphites. This may be due to the fact that
complexes containing two bulky phosphite ligands are
unlikely to be thermodynamically stable, as previously
demonstrated by the reaction of 6 with bulky tri-
arylphosphines.18 Also, di-orthometalation may be fa-
vored over mono-orthometalation as a means of mini-
mizing intramolecular interaction between the tBu
groups in the phosphite ligand. However, the previously
reported formation of 8 from [{Ir(µ-SR)(CO)2}2] (R )
(CH2)3NMe2) and 219 indicates that this is not invariably
the case.
(1)
process was used by Parshall to prepare [Rh{(OC6H4)-
(OPh)2}{P(OPh)3}2] from [RhCl{P(OPh)3}3] and Ph-
MgCl.16 The preparation of analogous di-orthometalat-
ed complexes of 1 or 2 is considerably easier. Reaction
of [{Ir(µ-OMe)(cod)}2], 4, with 1 in methanol leads to
the formation of [IrH{P(OC6H2-2,4-tBu2)2(OC6H3-2,4-
tBu2)}(cod)], 5a , in 56% yield (eq 2). This formulation is
The similarity of the NMR spectroscopic data obtained
for 5a ,b with those of the triphenyl phosphite analogue
[IrH{P(OC6H4)2(OC6H5)}(cod)], 3, and the similarity of
the 31P{1H} NMR shifts of the free phosphites20 indicate
that the substitution of the aromatic ring has little effect
on the electronic properties of the phosphorus atom and
that the chemical shift is determined by complex
geometry rather than electronic factors.
(2)
Str u ctu r es of 5a ,b. The single-crystal X-ray struc-
tures of 5a ,b have been determined. Figure 1 shows
the ORTEP drawing of 5a , while Figure 2 shows an
alternative view and Figure 3 shows the structure of
5b. Selected bond lengths and angles for 5a ,b are given
in Tables 2 and 3, respectively. The structures are in
agreement with the spectroscopic data; in particular it
is clear that in both cases the phosphite ligand has been
doubly orthometalated, with the two metal bound rings
occupying cis coordination sites. While the hydride was
not located in either example, the gross structures are
similar to that of 3,3 in which the hydride was located
trans to the phosphorus. A comparison of certain
structural data for 5a ,b with those of 3 is given in Table
supported by the spectroscopic data, in particular the
1H NMR spectrum which shows a high-field doublet at
δ -7.18 ppm with a coupling of 190 Hz to the trans
phosphorus, assigned to the metal hydride. It also
indicates the presence of only one ortho ring proton,
implying orthometalation of the other two rings. The
31P{1H} NMR spectrum shows a singlet at δ 151.1 ppm.
Similarly, the reaction of 4 with 2 in methanol yields
[IrH{P(OC6H3-2-tBu)2(OC6H4-2-tBu)}(cod)], 5b, in 92%
yield, the spectroscopic properties of which are almost
identical with those of 5a (Table 1).
5a can also be produced from 1 and [Ir(cod)(py)2][PF6],
6 (py ) pyridine), in 87% yield. 5b was similarly
prepared in 55% yield. However, 1 did not react with
the analogous [Rh(cod)(py)2][PF6]. Reaction of triphenyl
(17) Haines, L. M.; Singleton, E. J . Organomet. Chem. 1970, 25, C83.
(18) Abbassioun, M. S.; Chaloner, P. A.; Hitchcock, P. B. Acta
Crystallogr., Sect. C 1989, C45, 331. Abbassioun, M. S.; Chaloner, P.
A.; Hitchcock, P. B. Acta Crystallogr., Sect. C 1990, C46, 902. Bedford,
R. B.; Chaloner, P. A.; Hitchcock, P. B. Acta Crystallogr., Sect. C 1993,
C49, 1461. Bedford, R. B.; Chaloner, P. A.; Hitchcock, P. B. Acta
Crystallogr., Sect. C 1994, C50, 356.
(19) Ferna´ndez, E.; Ruiz, A.; Castillo´n, S.; Claver, C.; Piniella, J .
F.; Alvarez-Larena, A.; Germain, G. J . Chem. Soc., Dalton Trans. 1995,
2137.
(16) Barefield, E. K.; Parshall, G. W. Inorg. Chem. 1972, 11, 964.
Coolen, H. K. A. C.; Nolte, R. J . M.; van Leeuwen, P. W. N. M. J .
Organomet. Chem. 1995, 496, 159.
(20) 31P{1H} NMR (CDCl3; δ): 1, 131.4 ppm; 2, 131.0 ppm; P(OPh)3,
127.8 ppm.

3992 Organometallics, Vol. 15, No. 19, 1996
Bedford et al.
F igu r e 1. ORTEP representation of [IrH{P(OC6H2-2,4-
tBu2)2(OC6H3-2,4-tBu2){(cod)], 5a .
F igu r e 3. CAMERON representation of [IrH{P(OC6H3-
2-tBu)2(OC6H4-2-tBu)}(cod)], 5b.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) w ith Estim a ted Sta n d a r d Devia tion s in
P a r en th eses for 5a
Bonds
Ir-M1a
Ir-P
Ir-C30
Ir-C44
Ir-C48
P-O2
2.154(12)
2.258(3)
2.052(9)
2.264(12)
2.250(10)
1.588(6)
1.426(11)
1.418(11)
Ir-M2a
Ir-C2
Ir-C43
Ir-C47
P-O1
2.130(10)
2.089(11)
2.274(10)
2.242(11)
1.587(8)
P-O3
O2-C15
1.596(7)
1.395(12)
O1-C1
O3-C29
Angles
M1-Ir-M2
M1-Ir-C2
M2-Ir-P
85.6(4)
176.4(4)
108.6(3)
172.6(4)
78.0(3)
108.2(3)
107.7(3)
106.0(4)
115.6(7)
114.4(6)
M1-Ir-P
104.4(3)
89.4(4)
93.5(4)
79.2(3)
91.1(4)
134.1(4)
101.7(4)
96.2(3)
128.9(6)
M1-Ir-C30
M2-Ir-C2
P-Ir-C2
M2-Ir-C30
P-Ir-C30
Ir-P-O1
F igu r e 2. Alternative view of [IrH{P(OC6H2-2,4-
tBu2)2(OC6H3-2,4-tBu2){(cod)], 5a .
C2-Ir-C30
Ir-P-O2
O1-P-O2
O2-P-O3
P-O2-C15
Ir-P-O3
4. From these data it can be seen that the orthometa-
lated moieties of all three compounds are essentially the
same, with the only significant difference being between
the three Ir-P-Oâ angles, which open up slightly as
the steric bulk of the aryl rings increases. The mean
M-Ir-C(trans) angles (172.1-176.4°) indicate little
deviation from octahedral with respect to the metalated
aryl or cod ligands. Significant distortion is noted,
however, in the coordination of the phosphorus atoms,
which are tilted toward the orthometalated rings. The
mean P-Ir-C(metalated) angles of these systems are
O1-P-O3
P-O1-C1
P-O3-C29
a
M1 and M2 are the midpoints of the C43-C44 and C47-C48
bonds.
increase distortion, and would therefore be compara-
tively facile providing that the complex is coordinatively
unsaturated and has an appropriate available oxidation
state. The Ir-C bond lengths in 5a (2.089(11) and
2.052(9) Å) and 5b (2.067(8) and 2.064(8) Å) are similar
to those established21 for [IrCl{P(OC6H3-2-Me)2(OC6H4-
2-Me)}(γ-picoline)2] (2.04-2.05 Å). However the Ir-P
bonds in 5a (2.258(3) Å) and 5b (2.257(2) Å) are slightly
longer than that (2.141(1) Å) in the ortho-tolyl derivative
suggesting that this parameter is more sensitive to
steric hindrance.
Mech a n istic Stu d ies on th e F or m a tion of th e
Or th om eta la ted Com p lexes. In an attempt to un-
derstand the mechanism of formation of 5a , 1 was
treated with 6 in CDCl3/MeOH (4:1) on an NMR tube
scale, and the reaction was monitored by 1H and 31P{1H}
similar to that in the previously reported [IrCl{P(OC6H3-
2-Me)2(OC6H4-2-Me)}(γ-picoline)2]21 (79.5°). Interest-
ingly, the P-Ir-C(metalated) angle of the mono-
orthometalated complex, [Ir{P(OC6H3-2-Me)(OC6H4-2-
Me)2}(cod){P(OCH2)3CMe}],22 is 80°, which implies that
orthometalation of a second ring does not greatly
(21) Singleton E.; van der Stok, E. J . Chem. Soc., Dalton Trans.
1978, 926.
(22) Laing, M.; Nolte, M. J .; Singleton, E.; van der Stok, E. J .
Organomet. Chem. 1978, 146, 77.

Iridium Complexes of Triaryl Phosphites
Organometallics, Vol. 15, No. 19, 1996 3993
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) w ith Estim a ted Sta n d a r d Devia tion s in
P a r en th eses for 5b
Sch em e 1. Mech a n ism of Rea ction of Ir ga fos, 1,
w ith [Ir (cod )(p y)2]+
Bonds
Ir-P
2.257(2)
2.293(9)
2.293(9)
2.067(8)
2.171(9)
Ir-C1
Ir-C5
Ir-C14
Ir-M1a
2.245(9)
2.262(9)
2.064(8)
2.165(9)
Ir-C4
Ir-C8
Ir-C34
Ir-M2a
Angles
P-Ir-C14
C14-Ir-C34
Ir-P-O2
O1-P-O2
O2-P-O3
M1-Ir-P
M1-Ir-C34
M2-Ir-C14
75.8(2)
92.4(3)
P-Ir-C34
Ir-P-O1
78.8(2)
108.1(2)
107.2(2)
104.2(3)
83.7(2)
92.7(2)
106.8(2)
90.8(2)
132.3(2)
100.6(3)
101.5(3)
108.2(2)
172.1(2)
174.3(2)
Ir-P-O3
O1-P-O3
M1-Ir-M2
M1-Ir-C14
M2-Ir-P
M2-Ir-C34
a
M1 and M2 are the midpoints of the C1-C8 and C4-C5 bonds.
Ta ble 4. Com p a r ison of Str u ctu r a l Da ta (Bon d
Len gth s in Å, An gles in d eg) for 3, 5a , a n d 5ba
complex
[Ir(C5Me5){P(OC6H4)(OC6H5)2{P(OPh)3}][PF6].23 While
the intermediates 9 and 11 are not formed in high
enough concentration to be directly observed by NMR
spectroscopy, neither is unprecedented.
3
5a
5b
Ir-P
2.246(2)
2.07
1.580(5)
1.606
1.409(8)
1.43
108.1
2.258(3)
2.07
1.588(6)
1.59
1.395(12)
1.42
108.0
2.257(2)
2.07
1.590(6)
1.60
1.430(10)
1.42
107.7
mean Ir-Cγ
P-Oâ
mean P-OR
Oâ-Câ
A hydridic species similar to 10 but lacking the
mean OR-CR
mean Ir-P-OR
Ir-P-Oâ
pyridine ligand, [IrH{P(OC6H2-2,4-tBu2)(OC6H3-2,4-
tBu2)2}(cod)]+, 12, is generated by the reaction of H[BF4]-
130.9(2)
113.7
134.1(4)
115.0
132.3(2)
115.3
mean P-OR-CR
P-Oâ-Câ
mean Ir-Cγ-CR
127.1(4)
119.2
128.9(6)
119.7
126.6(5)
121.0
a
Labeling scheme defining terms:
NMR spectroscopy. The 31P{1H} spectra recorded after
either 20 min or 3 h show the presence of only one
intermediate species, which gives rise to a singlet at δ
96.8 ppm. Even after 20 min formation of some 5a was
evident. The 1H NMR spectrum of the intermediate
recorded after 45 min shows a doublet at δ -17.23 ppm
(aq) with 5a . Its composition was tentatively assigned
on the basis of NMR spectroscopic data. In particular
we note the appearance of a new hydride signal at δ
2
-21.7 with J PH ) 13.9 Hz. The low value of the
coupling constant implies that the hydride and phos-
phorus must be cis. The high downfield shift of the
resonances assigned to two of the cod alkene protons (δ
6.07, 5.79 ppm) suggests that one of the double bonds
is trans to an electronegative substituent. Although the
geometry shown approximates to a square-based pyra-
mid, the evidence we have for the exact stereochemistry
of the complex is limited; the geometry is in any event
likely to be quite distorted. Attempts to isolate 12 have
been unsuccessful. Removal of the excess acid by
washing the reaction mixture with aliquots of water led
to the re-formation of 5a .
2
integrating to one proton with J PH ) 10.7 Hz, indicative
of a cis arrangement of phosphite and hydride ligands.
While the aromatic region of the spectrum appeared
complex, it is clear that only 1 equiv of free pyridine
was produced in the formation of the intermediate,
implying that the other remains coordinated. The
observation of signals ascribed to six tert-butyl environ-
ments is consistent with the orthometalation of a single
ring. We therefore tentatively assign the intermediate
as [IrH{P(OC6H2-2,4-tBu2)(OC6H3-2,4-tBu2)2}(cod)(py)]-
[PF6], 10 (Scheme 1). Attempts to isolate this species
in a pure form have failed. The reaction of 1 with 6 in
dry dichloromethane also leads to the formation of some
5a ; indeed the conversion of 10 to 5a appears to be
faster under aprotic conditions.
Overall the reaction involves an oxidative addition
followed by a deprotonation; thus we would expect it to
be retarded by the presence of acidic solvents such as
alcohols, as was found. Loss of H+ from a cationic metal
center on orthometalation of a triaryl phosphite has
been previously observed in the reaction of [Ir(C5Me5)-
(acetone)3][PF6]2 with triphenyl phosphite to give
The mechanism of Scheme 1 explains why 3 cannot
be produced from 6 and triphenyl phosphite, the reac-
tion giving 7 instead. It would be expected that an
intermediate similar to 10 is formed but with triphenyl
phosphite in place of pyridine. In this case the bis-
(phosphite) complex is not sterically destabilized and
deprotonation leads to 7. The reaction was too rapid to
be studied by NMR spectroscopy, but Singleton and his
(23) Thompson, S. J .; White, C.; Maitlis, P. M. J . Organomet. Chem.
1977, 136, 87.

3994 Organometallics, Vol. 15, No. 19, 1996
Bedford et al.
co-workers24 have previously isolated the proposed
Sch em e 2. Mech a n ism of Rea ction of
P (OC6H4-2-tBu )3, 2, w ith [{Ir (µ-OMe)(cod )}2]
intermediate in this reaction, [IrH{P(OC6H3-2-R)(OC6H4-
2-R)2}(cod){P(OC6H5-2-R)3}]+ (R ) H), by the reaction
of 7 with H[PF6] and have also shown that the analo-
gous compound with R ) Me is readily reconverted to
[Ir{P(OC6H3-2-R)(OC6H4-2-R)2}(cod){P(OC6H5-2-R)3}].
The reaction between 1 and 6 in CD3OD led to the
formation of 5a with 95% of the hydride sites deuter-
ated. This is indicated by a triplet in the 31P{1H} NMR
spectrum at δ 152.2 ppm (2J PD ) 28.4 Hz) and a doublet
2
in the H NMR spectrum at δ -6.99 ppm (2J PD ) 29.8
Hz). Integration of the aryl region of the 1H NMR
spectrum shows that most of the ortho positions are also
deuterated, indicating that metalated and non-meta-
lated rings undergo exchange in a similar way to that
reported for [RuCl{P(OC6H4)(OC6H5)2}{P(OPh)3}3].25
This pattern of deuteration is rationalized by the
exchange of the protons liberated in the reversible
interconversion of 10 and 11 with deuterons. De-
orthometalation of deuterated 10 leads to the formation
of 9 with a deuterium atom in one ortho position.
Assuming that the interconversions of 9-11 are rapid
and reversible, this allows the complete deuteration of
the hydride and all the ortho-sites. The second ortho-
metalation, to give 5a , must be comparatively slower.
Reaction of 2 with [{Ir(µ-OCD3)(cod)}2] in CD3OD led
to the formation of 5b with no deuterium incorporation
in either the hydride or the ortho aryl sites. This is
consistent with two possible mechanisms. â-Hydride
transfer from the methoxy group may occur after
coordination of the phosphite to produce a deuterio-
phosphite complex 14 (Scheme 2) which orthometalates
with the loss of HD. Alternatively, orthometalation
occurs to provide a complex with cis hydride and OCD3
groups which then reductively eliminates HOCD3. A
second orthometalation would then produce 5b. As no
cationic hydride complexes are produced in either of
these mechanisms, exchange and reversible de-ortho-
metalation is not possible and so no deuterium is
incorporated. Precipitates formed in the early stages
(<3 h) of the reactions were analyzed by 31P NMR
spectroscopy. This indicated the presence of a species,
16b, analogous to 7. Broad AB doublets were noted at
δ 85 and 126, and these were not further broadened
when the decoupler was switched off, indicating that
they were not hydride coupled. This should be com-
Ta ble 5. Hyd r ogen a tion of N-Ben zylid en ea n ilin e
conversion (%) after
precatal systema
1 h
2 h
3 h
5 h
5a
48
95
99
5b
99.2
99.4
99.6
98
86.5
6 + 2b
5a + 1c
7
20
1.8
71
2.4
5.4
a
Conditions: 30 atm of H2; 40 °C; 50:1 substrate:precatalyst,
methanol. Precatalyst formed in situ. c Ir:P ) 1:2.
b
in Table 5. The rates of hydrogenation with 5a ,b are
both good, with the reactions complete within 3 h. The
better rate for 5b may be attributed to its lower steric
bulk The species formed in situ from 6 and 2, presum-
ably 5b, was also an excellent catalyst. Interestingly,
the rate of reaction catalyzed by 5a is reduced by the
presence of 1 equiv of free phosphite, suggesting that a
monophosphite species may be more reactive than
species containing two bulky ligands.
pared with the 31P NMR spectroscopic data for 7 (δ 83.1,
2
126.2 ppm, J PP
) 77 Hz) and the analogue
During the hydrogenation of the imine in the presence
of 5b a white powder was precipitated which was shown
to be [IrH5{P(OC6H4-2-tBu)3}2], 17b. 17b could also be
[Ir(cod){P(OC6H4-2-Me)2(OC6H3-2-Me)}{P(OC6H4-2-
2
Me)3}] (δ 86.6, 125.2 ppm, J PP ) 79 Hz).21,23 We
postulate that this was formed by reversible coordina-
tion of free phosphite to 15. The signals in the NMR
spectrum are broad, suggesting a dynamic exchange
which is fast on the NMR time scale at room tempera-
ture. Similar results were obtained with 5a .
Ca ta lytic Hyd r ogen a tion a n d Rea ction of Or th -
om eta la ted Com p lexes w ith H2. The use of iridium
triaryl phosphite complexes as precatalysts in the
homogeneous catalytic hydrogenation of N-benzyli-
deneaniline was studied; the results are summarized
obtained by reaction of 5b with hydrogen at 1 atm. The
31P{1H} NMR spectrum consists of a singlet at δ 83.9
ppm. When the 31P NMR spectrum was recorded
without decoupling the spectrum showed splitting of the
(24) Chalmers, A. A.; de Waal, D. J . A.; Oosthuizen, H. E.; Singleton,
E.; van der Stok, E. S. Afr. J . Chem. 1983, 36, 37.
(25) Lewis, L. N. Inorg. Chem. 1985, 24, 4433.
2
phosphite signal into a sextet with J PH ) 16.5 Hz,

Iridium Complexes of Triaryl Phosphites
Organometallics, Vol. 15, No. 19, 1996 3995
indicating that the compound contains five equivalent
5a ,b can be activated by the reductive elimination of
the hydride and an aryl group to give a 16e Ir(I)
complex.
1
hydrides cis to the phosphites. The H NMR spectrum
shows a high-field triplet at δ -9.47 ppm (2J PH ) 16.5
Hz), indicative of cis coupling to two equivalent phos-
phites. No peaks corresponding to the cyclooctadiene
ligand were observed. The analogous phosphine deriva-
Con clu sion s
i
We conclude that the degree and ease of orthometa-
lation of a triaryl phosphite at a 16e cod-Ir(I) center is
a function of the steric profile of the ligand. The
mechanism of formation of the di-orthometalated com-
plexes depends on whether the starting iridium complex
is neutral or cationic, with deprotonation of a cationic
hydride being a fundamental step in the latter process.
De-orthometalation to provide a vacant coordination site
at the metal center appears to be an important factor
in the activation of these species for catalysis. The scope
of this process and its applications to catalysis will be
investigated further.
tives [IrH5(PR3)2] (R ) Ph, cyclohexyl, or Pr) have been
prepared previously.26 A neutron diffraction study of
one of them (R ) iPr)27 showed that the hydrides adopt
five equivalent equatorial sites in a pentagonal bipyra-
mid. 17b is itself a reasonable hydrogenation catalyst
with activity comparable to those formed in situ from 2
and 6 or 4.
A solution of 5a in CDCl3 was treated with hydrogen
in an NMR tube and the reaction followed by NMR
1
spectroscopy. The H NMR spectrum recorded after 70
min showed a second hydridic species giving rise to a
triplet at δ -9.63 ppm (2J PH ) 16.5 Hz). After 20 h this
was the sole hydride-containing species. Phosphorus
decoupling of this triplet led to collapse to a singlet. The
31P{1H} NMR spectrum at this time showed only a
singlet at δ 88.2 ppm. While the signal became more
complex when the 31P NMR spectrum was run without
proton decoupling, the sextet could not be fully resolved
in this case. These data are indicative of the formation
of the analogue of 17b, [IrH5{P(OC6H3-2,6-tBu2)3}2],
17a . Continued hydrogenation of the reaction mixture
for a further 24 h led to a complex mixture of polyhy-
dridic species. We were not able to isolate pure 17a ,
but further evidence for its formation was obtained from
the positive FAB mass spectrum of a sample of 5a which
had been hydrogenated for 22 h in dichloromethane.
This showed four main peaks at m/ z ) 2514, 1670,
1485, and 943. The species with m/ z ) 943 corresponds
to unreacted 5a while that with m/ z ) 1485 was
assigned to a species of approximate formulation [IrHx{1
- Hy}2]. This is in approximate agreement with the
formula of 17a (molecular mass ) 1491); orthometala-
tion would probably occur in the beam, with loss of
hydrogen, which would account for the lower observed
mass. The highest mass peak seems to arise from a
single trimeric species of approximate formula [{IrHx(1
- Hy)}3]. The peak at 1670 corresponds to dimers of
formula [{IrHx(1 - Hy)}2], the iridium isotope pattern
being suggestive of the presence of more than one
species. Whether the dimeric species observed repre-
sent discreet molecules in the reaction mixture or
fragments from the trimer has not been established.
Exp er im en ta l Section
Gen er a l P r oced u r es a n d Ma ter ia ls. All manipulations
of air-sensitive materials were performed under an atmosphere
of dry nitrogen or argon. Solvents were distilled prior to use
from the appropriate drying agent, ethers from sodium-
potassium alloy, alcohols from their magnesium alkoxide, and
dichloromethane from calcium hydride. C, H, and N analysis
were performed by Medac Ltd. or on a Carlo-Erba microana-
lyzer. NMR spectra were recorded on the following
spectrometers: a Bruker AC250Y, a Bruker AMX500, or a
Varian Gemina 300 MHz. FAB mass spectra were obtained
using a Kratos 80RF spectrometer coupled to a Kratos DS55M
data system. Gas chromatography was performed on
a
Hewlett-Packard 5890 II chromatograph with an Ultra-3
(diphenylsilicone 5%, dimethylsilicone 95%) 25 m × 0.2 mm
column. The compounds [{IrCl(cod)}2],28 [Ir(cod)(py)2][PF6],29
4
[{Ir(µ-OMe)(cod)}2],30 and P(OC6H4-2-tBu)3 were prepared
according to literature procedures.
Syn th esis of 5a ,b. Meth od a . A suspension of [{Ir(µ-
OMe)(cod)}2] (0.1 g, 0.15 mmol) and 1 (0.2 g, 0.3 mmol) in
methanol (20 mL) was stirred for 15 h. Recrystallization from
dichloromethane/methanol gave 5a (0.159 g, 56%). 5b (57 mg,
92%) was similarly obtained from [{Ir(µ-OMe)(cod)}2] (26.5 mg,
0.04 mmol) and 2 (76.4 mg, 0.16 mmol).
Meth od b. A suspension of [Ir(cod)(py)2][PF6] (259 mg,
0.489 mmol) and 1 (320 mg, 0.495 mmol) in methanol (30 mL)
was allowed to stir overnight at room temperature. The
mixture was concentrated to about half its volume in vacuo
and the supernatant removed from the white precipitate via
cannula. 5a (0.4 g, 87%) was obtained by recrystallization
from dichloromethane/ethanol as colorless rods. An analogous
procedure gave 5b in 55% yield.
We have not been able to establish what other species
are produced in the disproportionation that gives 17. It
seems unlikely that iridium metal is formed, since none
was visible, and when the formation of 17a was moni-
tored by NMR spectroscopy, no significant broadening
of the signals was observed.
Da ta for 5a . Anal. Calcd for C50H74IrO3P: C, 63.5; H, 7.9.
Found: C, 63.4; H, 7.95. 1H NMR (CDCl3, 250 MHz): δ -7.18
2
(d, 1H, IrH, J PH ) 190 Hz), 1.28 (s, 36H, CH3), 1.34 (s, 9H,
CH3), 1.60 (s, 9H, CH3), 2.19 (m, 2H, cod CH2), 2.27 (m, 2H,
cod CH2), 2.51 (m, 2H cod CH2), 2.94 (m, 2H, cod CH2), 3.87
(m, 2H, cod CH), 4.24 (m, 2H, cod CH), 7.15 (d of d, 1H, m′-H
of unmetalated ring, J HH ) 8.6 Hz, J HH ) 2.5 Hz), 7.49 (d of d,
1H, m-H of unmetalated ring, J HH ) 2.4 Hz, J PH ) 1.2 Hz),
7.66 (d of d, 1H, o-H of unmetalated ring, J HH ) 8.6 Hz, J HH
) 1.4 Hz) and 7.72 (d, 2H, m-H of metalated ring, J HH ) 2.2
Hz) ppm. 13C NMR (CDCl3, 125 MHz): δ 29.9 (s, C(CH3)3,
metalated ring), 30.2 (s, C(CH3)3 unmetalated ring), 31.5 (s,
C(CH3)3 unmetalated ring), 31.6 (d, cod CH2, J PC ) 4.0 Hz),
31.9 (s, C(CH3)3, metalated ring), 33.0 (s, cod CH2), 34.2 (s,
Not only does the triphenyl phosphite complex 7
exhibit a low activity in the catalytic hydrogenation of
N-benzylideneaniline, it also shows no reaction with
hydrogen at atmospheric pressure. This is probably due
to the fact that is a coordinatively saturated species
which can only form a catalytically active 16 electron
species if one of the cod double bonds decoordinates.
(26) Grushin, V. V.; Vymenits A. B.; Vol’pin, M. E. J . Organomet.
Chem. 1990, 382, 185.
(27) Garlaschelli, L.; Khan, S. I.; Bau, R.; Longoni, G.; Koetzle, T.
F. J . Am. Chem. Soc. 1985, 107, 7212.
(28) Winkhaus, G.; Singer, H. Chem. Ber. 1966, 99, 3610.
(29) Crabtree, R. H.; Morehouse, S. M. Inorg. Synth. 1986, 24, 173.
(30) Pannetier, G.; Fougeroux, Bonnaire, R.; Platzer, N. J . Less
Common Met. 1971, 24, 83.

3996 Organometallics, Vol. 15, No. 19, 1996
Bedford et al.
Ta ble 6. Cr ysta l Da ta a n d Da ta Collection a n d Refin em en t P a r a m eter s for 5a ,b
5a 5b
formula
fw
C50H74IrO3P
946.3
C38H50O3PIr
778.0
cryst system
space group
a (Å)
b (Å)
c (Å)
triclinic
P1h (No. 2)
11.093(5)
12.712(4)
18.222(4)
77.71(2)
75.13(3)
78.68(3)
2399(1)
2
monoclinic
P21/n (non-standard No 14)
11.446(3)
14.958(7)
20.610(4)
90
91.48(2)
90
R (deg)
â (deg)
γ (deg)
V (Å3)
3527(1)
4
Z
Dcalc
1.31
1.47
F(000)
980
1576
radiation, λ (Å)
µ, abs coeff (cm-1
crystal size (mm)
monochromated Mo KR, 0.710 73
monochromated Mo KR, 0.710 69
)
28.4
38.5
0.15 × 0.1 × 0.05
0.25 × 0.08 × 0.05
data reflcn ranges, θ min and max h, 0 f 15; k, -17 f 17; l, -25 f 25; 2 f 30
tot. reflcns measd
h, 0 f 13; k, 0 f 17; l, -24 f 24; 2 f 25
6762
tot. unique reflcns measd
Rint
13 948
6443
0.045
3759
-2.8
no
significant reflcns, |F2| > 2σ(F2)
max change in std reflcns (%)
decay corr
9057
-6.5
yes
abs corr, Tmax, Tmin
non-H atoms located
refinement by
1.00, 0.80 from ψ scans
1.12, 0.99 DIFABS
heavy atom methods, SHELXS-86
full-matrix least squares,
heavy atom methods, SHELXS-86
full-matrix least squares,
non-H atoms anisotropic,
non-H atoms anisotropic,
Enraf-Nonius MolEN programs
Enraf-Nonius MolEN programs
H atoms
hydride H omitted, the rest fixed at
hydride H omitted, the rest fixed at calcd positions
calcd posns Uiso ) 1.3Ueq for parent atom
0.082
Uiso ) 1.3Ueq for parent atom
0.040
Ra
R′
0.080
0.040
S
1.6
1.10
no. of variables
496
388
(∆/σ)max
0.02
0.04
+0.63, -0.23
(∆F)max,min (e Å-3
)
+4.00, -0.35 near Ir atom
a
σ(F2) ) {σ2(I) + (0.04I)2}1/2/Lp, w ) σ-2(F), ∑w(|Fo| - |Fc|)2 minimized.
C(CH3)3 metalated ring), 34.6 (s, C(CH3)3 free ring), 34.9 (s,
C(CH3)3 metalated ring), 35.3 (s, C(CH3)3 free ring), 75.2 (s,
cod CH), 85.2 (s, cod CH), 119-153 (aryl) ppm. 31P{1H} NMR
(CDCl3, 100 MHz): δ 152.26 ppm. MS (FAB): m/ z 943 (100%)
[M - 3H]+.
diethyl ether (10 mL) was cooled to -78 °C and a 1.6 M
solution of methyllithium in diethyl ether (0.2 mL, 0.32 mmol)
added. The color of the solution changed immediately from
orange to red. The solution was allowed to warm to room
temperature and the reaction then quenched with a few drops
of methanol. The mixture was stirred for 1 h, after which time
the color had changed to yellow-orange. The solution was
filtered, and then the solvent was removed in vacuo from the
filtrate to yield a pale yellow solid. Recrystallization from
Da ta for 5b. Anal. Calcd for C38H50IrO3P: C, 58.7; H, 6.4.
Found: C, 58.6; H, 6.4. 1H NMR (CDCl3, 300 MHz): δ -7.18
2
(1H, d, J PH ) 187 Hz, IrH), 1.24 (s, 9H, C(CH3)3 of unmeta-
lated ring), 1.60 (s, 18H, C(CH3)3 of metalated rings), 2.21 (m,
2H, cod CH2), 2.44 (m, 2H, cod CH2), 2.92 (m, 4H, cod CH2),
3.91 (m, 2H, cod CH), 4.22 (m, 2H, cod CH), 6.5-7.7 (m, 10H,
aryl CH) ppm. 13C{1H} NMR (CDCl3, 75.46 MHz): δ 32.4,
31.9, 29.9, 29.7 (cod CH2, C(CH3)3, CH3), 75.6 (cod CH), 85.9
(cod CH), 119-144 (aryl) ppm. 31P{1H} NMR (CDCl3, 121.47
MHz): δ 150.9 ppm. MS (FAB): m/ z 773 (24%, M - 5H).
P r ep a r a tion of [Ir Cl(cod ){P (OP h )3}]. Triphenyl phos-
phite (0.16 mL, 0.61 mmol) was added to a solution of [{IrCl-
(cod)}2] (0.205 g, 0.305 mmol) in light petroleum (bp 30-40
°C, 5 mL) and dichloromethane (15 mL) and the resultant
mixture allowed to stand overnight at room temperature. The
solution was concentrated in vacuo and the supernatant
removed from the resultant orange precipitate via cannula.
The product was used without further purification (0.30 g,
dichloromethane/methanol gave [IrH{P(OC6H4)2(OC6H5)}(cod)]
as colorless rods (0.06 g, 52%). Anal. Calcd for C26H26IrO3P:
C, 51.2; H, 4.3. Found: C, 51.0; H, 4.4. 1H NMR (CDCl3, 250
2
MHz): δ -7.65 (d, 1H, IrH, J PH ) 194.5 Hz), 2.27 (m, 2H,
cod CH2), 2.49 (m, 4H, cod CH2), 2.89 (m, 2H, cod CH2), 3.80
(m, cod CH), 4.19 (m, 2H, cod CH), 6.62 (m, 2H, aryl), 6.81
(m, 2H, aryl), 6.89 (m, 3H, aryl), 7.54 (m, 4H, aryl), 7.77 (m,
2H, aryl) ppm. 13C NMR (CDCl3, 125 MHz): δ 31.2 (cod CH2),
32.7 (cod CH2), 75.8 (cod CH), 83.7 (cod CH), 111-158 (aryl)
ppm. 31P{1H} NMR (CDCl3, 100 MHz): δ 155.7 ppm.
P r epar ation of [Ir {P (OC6H4)(OC6H5)2}(cod){P (OC6H5)3}],
7. Triphenyl phosphite (0.5 mL, 1.9 mmol) was added to a
stirred solution of [Ir(cod)(py)2][PF6] (0.401 g, 0.660 mmol) in
methanol (25 mL). The mixture was stirred for 30 min and
the supernatant removed from the resulting white precipitate
with a syringe. The residue was washed with methanol (2 ×
20 mL) and recrystallized from dichloromethane/diethyl ether
yielding 7 as colorless blocks (0.14 g, 23%). 1H NMR (CDCl3,
250 MHz): δ 1.7-2.1 (m, br, 7H, cod CH2), 2.4 (m, 2H, 1 cod
CH and 1 cod CH2), 3.01 (s, br, 1H, cod CH), 4.49 (s, br, 1H,
cod CH); 4.71 (s, br, 1H, cod CH) and 6.7-7.4 (m, 29H, aryl).
31P{1H} NMR (CDCl3, 100 MHz): δ 126.2 (d, J PP ) 77.4 Hz)
and 83.1 (d, J PP ) 77.4 Hz) ppm. MS FAB: m/ z 921 (100%,
76%). Anal. Calcd for
C
26H27ClIrO3P: C, 48.3; H, 4.2.
Found: C, 48.9; H, 4.2. 1H NMR (CDCl3, 250 MHz): δ 1.7-
2.0 (m, 8H, cod CH2), 3.26 (m, 2H, cod CH), 5.38 (m, 2H, cod
CH), 7.0-7.4 (m, 15H, aryl) ppm. 13C{1H} NMR (CDCl3, 125
MHz): δ 28.7 (d, cod CH2, J PC ) 3.0 Hz), 33.3 (d, cod CH2, J PC
) 3.6 Hz), 54.5 (d, cod CH, J PC ) 1.9 Hz), 106.0 (d, cod CH,
J PC ) 19.4 Hz), 152 -121 (aryl) ppm. 31P{1H} NMR (CDCl3,
100 MHz): δ 87.8 ppm.
P r ep a r a tion of [Ir H{P (OC6H4)2(OC6H5)}(cod )], 3.
A
solution of [IrCl(cod){P(OPh)3}] (0.122 g, 0.189 mmol) in

Iridium Complexes of Triaryl Phosphites
Organometallics, Vol. 15, No. 19, 1996 3997
MH+), 807 (45%, M - cod - 5H), 715 (25%, M - cod - 4H -
C6H6), 607 (45%, M - P(OPh)3 - 2H), 501 (40%, M - P(OPh)3
- cod).
operating in the θ-2θ mode. A total of 25 reflections (7 < θ
< 10°) were used in each case to establish the cell parameters.
Crystal data and data collection and refinement parameters
are given in Table 6.
P r ep a r a tion of Deu ter a ted 5a . A mixture of [Ir(cod)(py)2]-
[PF6] (0.061 g, 0.101 mmol) and 1 (0.066 g, 0.102 mmol) in
CD3OD (2.2 mL) and dichloromethane (1 mL) was stirred
overnight and the solution then concentrated in vacuo to about
1 mL yielding a white precipitate. The supernatant liquid was
removed with a cannula and the residue dried in vacuo. The
product mixture was not purified further but was characterized
by NMR spectroscopy. Yield: 0.078 g, 81%. 1H NMR (CDCl3,
250 MHz): δ 6.87 (d of d, 2H, m′-H metalated ring, J HH ) 2.4
Ca ta lytic Hyd r ogen a tion . Medium-pressure hydrogena-
tion experiments (30 atm) were carried out in a Berghof
autoclave, with electric heating and magnetic stirring. In a
standard experiment a solution of N-benzylideneaniline (4
mmol) catalyst (0.08 mmol) in methanol/1,2-dichloroethane (1:
1, 10 mL) was introduced into the evacuated autoclave and
heated with stirring. Once the system had reached thermal
equilibrium, hydrogen was introduced to reach the working
pressure. Samples were taken at intervals for analysis. After
each run the system was allowed to cool and the gas vented.
Hz, J HP ) 1.0 Hz), 7.23 (d, 1H, m′-H unmetalated ring, J HH
)
2.5 Hz), 7.53 (d of d, 1H, m-H unmetalated ring, J HH ) 2.5
1
Hz, J HP ) 1.1 Hz) and 7.72 (d, 2H, m-H metalated ring, J HH
)
The reaction mixture was then analyzed by GC and H NMR
1.8 Hz) ppm. All other peaks the same as those of 5a . 2H
NMR (CDCl3, 38.38 MHz): δ -6.99 (d, IrD, J PD ) 29.8 Hz),
7.36 (s, br, o-CD) ppm. 31P{1H} NMR (CDCl3, 100 MHz): δ
152.0 (s, PIrH), 152.2 (t, PIrD, J PD ) 28.8 Hz) ppm.
spectroscopy.
P r ep a r a tion of [Ir H5{P (OC6H4-2-tBu )3}2], 17b. A solu-
tion of [IrH(cod){P(OC6H3-2-tBu)2(OC6H4-2-tBu)}], 5b (61.9 mg,
0.08 mmol), in dichloromethane (4 mL) was treated with
hydrogen at 1 atm for 3 h. (The reaction was complete in 15
min at 5 bar of hydrogen pressure) The white precipitate
produced was collected by filtration and washed with methanol
to give 17b (0.087 g, 95%). Anal. Calcd for C60H83IrO6P2: C,
62.4; H, 7.1. Found: C, 62.0; H, 7.3. 1H NMR (CDCl3, 300
Rea ction of 5a w ith H[BF 4]. H[BF4](aq) (48 wt %, 2
drops) was added to a solution of 5a (7.0 mg, 7.4 µmol) in
CDCl3 (0.3 mL) in a 5 mm NMR tube which was shaken
regularly and stirred horizontally to ensure maximum mixing
of the two phase system. The reaction was followed by 1H and
31P{1H} NMR spectroscopy. The data obtained after 20 h are
given. On the basis of these data, the product was assigned
2
MHz): δ -9.47 (5H, t, J PH ) 16.5 Hz, Ir-H), 1.37 (54H, s,
C(CH3)3), 6.5-7.7 (24H, m, aryl) ppm. 13C{1H} NMR (CDCl3,
75.46 MHz): δ 30.4 (CH3), 34.6 (C(CH3)3), 121.0, 123.45, 126.5,
127.0 (aryl) ppm. 31P{1H} NMR (CDCl3, 121.47 MHz): δ 83.9
ppm.
as [IrH{P(OC6H2-tBu2-2,4)(OC6H3-tBu2 2,4)2(cod)][BF4], 12. At-
tempts to isolate this product by washing out the excess of
H[BF4] with aliquots of degassed water led to conversion back
to the starting material.
NMR Sp ectr oscop ic Da ta for 12. 1H NMR (CDCl3, 250
MHz): δ -21.7 (1H, d, 2J PH ) 13.9 Hz, Ir-H), 1.25, 1.28, 1.30,
1.31, 1.33, and 1.35, 6× (9H, s, C(CH3)3); 2.3-1.9 (4H, m, br,
cod CH2); 2.84 (4H, m, br, cod CH2); 4.96 (1H, m, br, cod CH);
5.11 (1H, m, br, cod CH); 5.78 (1H, m, br, cod CH); 6.06 (1H,
m, br, cod CH); 7.11 (1H, s, br, aryl); 7.15 (1H, d, J HH ) 2.5
Ack n ow led gm en t. We thank the University of
Sussex (bursary to R.B.B.), Direccion General de Inves-
tigacion Cientifica y Tecnica (Accion Integrada Ref HB-
096), and Ciba-Geigy (Award for collaboration in Eu-
rope) for financial support. We thank Chambers
Hispania S.L. for a gift of iridium chloride and J ohnson
Matthey plc for a loan of iridium chloride.
Hz, aryl); 7.17 (1H, d, J HH ) 2.3 Hz, aryl); 7.20 (1H, d, J HH
)
2.1 Hz, aryl); 7.30 (1H, d, J HH ) 8.7 Hz, aryl); 7.34 (1H, d, J HH
) 9.3 Hz, aryl) and 7.44 (2H, s, br, aryl) ppm. 31P{1H} NMR
(CDCl3, 100 MHz): δ 98.7 ppm.
X-r a y Diffr a ction Stu d ies. Crystals of 5a suitable for
diffraction studies were grown from dichloromethane/ethanol,
and those of 5b, from methanol. Data were collected on an
Enraf-Nonius CAD4 diffractometer at room temperature
Su p p or tin g In for m a tion Ava ila ble: Tables of X-ray
parameters, positional and thermal parameters, and bond
distances and angles and an ORTEP diagram (25 pages).
Ordering information is given on any current masthead page.
OM960239H