Unexpected isomerization of a cis- into a trans-Dihydride Complex. A neutral late transition metal complex as a hydride donor

Article abstract of DOI:10.1021/om970104r

Reaction of HIr(PPh₃)₃(CO) (1) with 1,3-bis[(diisopropylphosphino)methyl]benzene (2) in THF or benzene at 60 °C affords trans-H₂Ir(CO)L (3; L = C₆H₃(CH₂P(i-Pr₂)₂). The cationic complex [HIr(PPh₃)(CO)L]Br (5) was obtained in the reaction of 1 with 1,3-bis[(diisopropylphosphino)methyl]-2-bromobenzene (4). Reaction of 5 with KO-t-Bu leads to the Ir(I) complex Ir(CO)L (6), which adds methyl iodide to form IIr(CO)(CH₃)L (7). Addition of H₂ to 6 results in formation of cis-(L)Ir(H)₂CO) (8). This reaction is reversible, due to the rigid squareplanar geometry of 6. Under H₂ pressure 8 isomerizes into 3, demonstrating cis- into trans-dihydride isomerization, which is unprecedented for octahedral complexes. The trans-dihydride six-coordinate complex 3 exhibits hydridic reactivity which is unusual for a neutral late transition metal complex and is due to the strong mutual irons influence of the hydride ligands. Various electrophiles ([Ph₃C]BF₄, PhC(O)Cl, CS₂, MeI) directly attack the hydride ligand of 3, forming products of selective hydride transfer. Abstraction of the hydride ligand with the electrophiles affords the iridium complexes [HIr(PPh₃)(CO)L]Br (9), HIr(Cl)(CO)L (10), HIr(CO)(SC(S)H)L (11), and HIr(I)(CO)L (12).

Full text of DOI:10.1021/om970104r

3786
Organometallics 1997, 16, 3786-3793
Un exp ected Isom er iza tion of a cis- in to a
tr a n s-Dih yd r id e Com p lex. A Neu tr a l La te Tr a n sition
Meta l Com p lex a s a Hyd r id e Don or
Boris Rybtchinski, Yehoshoa Ben-David, and David Milstein*
Department of Organic Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel
Received February 11, 1997X
Reaction of HIr(PPh3)3(CO) (1) with 1,3-bis[(diisopropylphosphino)methyl]benzene (2) in
THF or benzene at 60 °C affords trans-H2Ir(CO)L (3; L ) C6H3(CH2P(i-Pr2)2). The cationic
complex [HIr(PPh3)(CO)L]Br (5) was obtained in the reaction of 1 with 1,3-bis[(diisopropyl-
phosphino)methyl]-2-bromobenzene (4). Reaction of 5 with KO-t-Bu leads to the Ir(I) complex
Ir(CO)L (6), which adds methyl iodide to form IIr(CO)(CH3)L (7). Addition of H2 to 6 results
in formation of cis-(L)Ir(H)2(CO) (8). This reaction is reversible, due to the rigid square-
planar geometry of 6. Under H2 pressure 8 isomerizes into 3, demonstrating cis- into trans-
dihydride isomerization, which is unprecedented for octahedral complexes. The trans-
dihydride six-coordinate complex 3 exhibits hydridic reactivity which is unusual for a neutral
late transition metal complex and is due to the strong mutual trans influence of the hydride
ligands. Various electrophiles ([Ph3C]BF4, PhC(O)Cl, CS2, MeI) directly attack the hydride
ligand of 3, forming products of selective hydride transfer. Abstraction of the hydride ligand
with the electrophiles affords the iridium complexes [HIr(PPh3)(CO)L]Br (9), HIr(Cl)(CO)L
(10), HIr(CO)(SC(S)H)L (11), and HIr(I)(CO)L (12).
In tr od u ction
tivity. This is exemplified in intermolecular hydride
transfer reactions with various electrophiles.
The stability and reactivity modes of transition-metal
hydrides, e.g. hydridic vs protonic reactivity, is of great
general interest since a wide range of important cata-
lytic and stoichiometric processes involve such com-
pounds.1 While cis-dihydride complexes are abundant,
few stable trans-dihydride complexes have been re-
ported.2 This is thought to be a result of the large trans
influence of the hydride ligand, rendering the cis-
dihydride configuration more stable unless dominant
steric factors disfavor it.
We report here a surprising isomerization of an
octahedral iridium cis-dihydride complex into the cor-
responding trans complex (which was also synthesized
independently), clearly attesting to the unexpected
higher thermodynamic stability of the latter, although
apparently no significant steric factors are involved.
Also, while hydridic reactivity is known for early transi-
tion metals,3 anionic complexes,4 and some polyhydrides4c
and clusters,5 the iridium trans-dihydride reported here
represents an unusual case of a neutral six-coordinate
late transition metal complex possessing hydridic reac-
Resu lts
Syn t h esis a n d Ch a r a ct er iza t ion of tr a n s-Ir -
(DIP P X)(H)2(CO) (3). Careful choice of the metal
precursors for cyclometalation of PCP ligands was
shown to be critical when the phosphine substituents
were less bulky than t-Bu.6 The iridium hydride
complex HIr(PPh3)3(CO) (1) is known to reversibly
dissociate a phosphine ligand in solution7 to yield the
four-coordinate sterically unsaturated trans-HIr(PPh3)2-
(CO). Facile coordination of the PCP ligands to this
intermediate is expected.
Reaction of equivalent amounts of HIr(PPh3)3(CO) (1)
and the ligand DIPPX (2; DiIsoP ropylP hosphinoXylene
(1,3-bis[(diisopropylphosphino)methyl]benzene)) at 60
°C in THF or C6H6 gives 3 in nearly quantitative yield,
as observed by 31P{1H} NMR (eq 1). A small amount
of Ir(DIPPX)CO (6; 5-7%) was also formed (vide infra).
We were not able to separate complex 3 from triphen-
ylphosphine.8
X Abstract published in Advance ACS Abstracts, J uly 15, 1997.
(1) (a) Pearson, R. G. Chem. Rev. 1985, 85, 41. (b) Simo˜es, J . A. M.;
Beauchamp, J . L. Chem. Rev. 1990, 90, 629. (c) Angelici, R. J . Acc.
Chem. Res. 1995, 28, 51. (d) Wang, D.; Angelici, R. J . J . Am. Chem.
Soc. 1996, 118, 935.
(2) (a) Fryzuk, M. D.; MacNeil, P. Organometallics 1983, 2, 682. (b)
Immirzi, A.; Musco, A.; Carturan, G.; Belluco, U. Inorg. Chim. Acta
1975, 12, L23. (c) Shaw, B. L.; Uttley, M. F. J . Chem. Soc., Chem.
Commun. 1974, 918. (d) Yoshida, T.; Otsuka, S. J . Am. Chem. Soc.
1977, 99, 2134. (e) Paonessa, R. S.; Trogler, W. C. J . Am. Chem. Soc.
1982, 104, 1138.
(3) For example see: (a) Sweet, J . R.; Graham, W. A. G. Organo-
metallics 1982, 1, 982. (b) Sullivan, P. B.; Meyer, T. J . Organometallics
1986, 5, 1500. (c) Martin, B. D.; Warner, K. E.; Norton, J . R. J . Am.
Chem. Soc. 1986, 108, 33.
(4) For a review see: (a) Darensbourg, M. Y.; Ash, C. E. Adv.
Organomet. Chem. 1987, 27, 1. See also: (b) Kinney, R. J .; J ones, W.
D.; Bergman, R. G. J . Am. Chem. Soc. 1978, 100, 7902. (c) Linn, D. E.,
J r.; Halpern, J . J . Am. Chem. Soc. 1987, 109, 2969.
Selected spectral data for complex 3 are given in Table
1. It gives rise to a singlet in 31P{1H} NMR centered
(5) [(Ph3P)CuH]6 reactivity: (a) Mahoney, W. S.; Brestensky, D. M.;
Stryker, J . M. J . Am. Chem. Soc. 1988, 110, 291. (b) Mahoney, W. S.;
Stryker, J . M. J . Am. Chem. Soc. 1989, 111, 8818.
(6) (a) Gorla, F.; Venanzi, L. M. Organometallics 1994, 13, 43 and
references therein. (b) Gorla, F.; Togni, A.; Venanzi, L. M. Organome-
tallics 1994, 13, 1607.
(7) (a) Harrod, J . F.; Gilson, D. F. R.; Charles, R. Can. J . Chem.
1969, 47, 2205. (b) Yagupsky, G.; Brown, C. K.; Wilkinson, J . J . Chem.
Soc. A 1970, 1392. (c) Harrod, J . F.; Hamer, G.; Yorke, W. J . Am. Chem.
Soc. 1979, 101, 3987. (d) Harrod, J . F.; Yorke, W. Inorg. Chem. 1981,
20, 1156. (e) Malatesta, L.; Caglio, G.; Angoleta, M. J . Chem. Soc. 1965,
6974. (f) Chatt, J .; Coffey, R. S.; Shaw, B. L. J . Chem. Soc. 1965, 7391.
(8) All attempts to separate 3 from PPh3 by crystallization failed.
Chromatography on alumina or silica and using of PdCl2(CH3CN)2 as
a “phosphine sponge” also did not result in separation of 3 from PPh3.
S0276-7333(97)00104-0 CCC: $14.00 © 1997 American Chemical Society

cis- to trans-Dihydride Isomerization
Organometallics, Vol. 16, No. 17, 1997 3787
Ta ble 1. Selected Sp ectr a l Da ta of Ir -P CP Com p lexes
NMR, ppm
IR,a cm-1
νIr-H
1978.0 (s) 1745.6 (s)
compd
31P{1H}
1H, Ir-H
13C{1H}, Ir-CO
νCO
2
2
3b
5c
57.84 (s)
-9.69 (t, J PH ) 15.0 Hz)
33.65 (d, J PP ) 11.9 Hz), -9.46 (app q, J PH ) 14.8 Hz)
178.63 (t, J PC ) 6.8 Hz)
2
2
2
176.57 (app q, J PC ) 6.3 Hz) 2002.0 (s) 2140.9 (bm)
-6.62 (t)
2
6b
7e
8b
66.18 (s)
31.26 (s)
51.67 (s)
196.51 (t, J PC ) 7.7 Hz)
1920.0 (s)
2004.0 (s)
1950(s)
2
178.44 (t, J PC ) 5.8 Hz)
2
2
-10.87 (td, J PH ) 16.9 Hz, J HH ) 3.2 Hz),
2066.3 (bw),
1965 (w)
2
-11.94 (td, J PH ) 11.9 Hz)
2
2
9d
34.9 (d, J PP ) 12.2 Hz), -12.04 (dt, J PH,trans ) 131.1 Hz,
2012.0 (s) 2161.4 (bm)
-20.0 (t)
2J PH,cis ) 13.1 Hz)
2
2
10b
11b
12b
50.79 (s)
46.53 (s)
42.80 (s)
-18.30 (t, J PH ) 11.6 Hz)
179.19 (t, J PC ) 6.8 Hz)
2003.1 (s) 2197.4 (bm)
2009.7 (s) 2120 (bw)
2005.0 (s) 2193.0 (bm)
2
4
2
-14.70 (td, J PH ) 12.0 Hz, J HH ) 3.7 Hz) 179.03 (t, J PC ) 6.6 Hz)
2
-15.48 (t, J PH ) 10.6 Hz)
a
All samples for IR measurements were prepared as neat films, except for the sample of 8 (benzene solution under 1 atm of hydrogen).
In C6D6. c In CD2Cl2. In CDCl3. e In acetone-d6 31P{1H} NMR), toluene-d8 13C{1H} NMR).
( (
b
d
Sch em e 1
at 57.84 ppm, which is split into a triplet (2J PH,cis ) 15.0
Hz) in 31P{1H} hydride-coupled NMR, consistent with
the presence of two equivalent hydride ligands. 1H
NMR and 13C{1H} NMR reveal that there is a symmetry
plane passing through the PCP-Ir chelate core, in
accordance with the trans arrangement of the two
hydrides in 3. The low stretching frequency of Ir-H
(1745.6 cm-1) is very characteristic of a trans H-M-H
moiety and is due to the strong mutual trans influence
of the hydride ligands.2,9
Syn th esis of Ir id iu m Com p lexes u sin g a Br om o
Der iva tive of a P CP Liga n d . Rea ctivity of a n
Ir id iu m (I) Com p lex. Use of bromo derivatives of PCP
ligands (molecules of the type 1,3-(R2PCH2)2-2-Br-C6H4)
can be a useful route for the synthesis of PCP-based
complexes due to facile Ar-Br bond activation.
Stirring a THF solution containing stoichiometric
amounts of HIr(PPh3)3(CO) (1) and the ligand DIPPX-
Br (4; DIPPX-Br, DiIsoP ropylP hosphinoXylene-Br o-
mide (1,3-bis[(diisopropylphosphino)methyl]-2-bromoben-
zene) at ambient temperature for 12 h, and precipitation
of the product with pentane afforded complex 5 in 84%
yield (eq 2). IR and selected NMR data for 5 are given
carried out. When the reaction was carried out in
acetone-d6, formation of a yellow precipitate (TlBr) was
1
observed and no difference in the 31P{1H} and H NMR
spectra before and after addition of TlPF6 was detected
-
(except for the presence of the P F6 septet in 31P{1H}
NMR), indicating that the reaction is a simple ion
exchange.
The iridium(I) complex Ir(DIPPX)(CO) (6) was pre-
pared in 78% yield by deprotonation of complex 5 at
room temperature with KO-t-Bu in THF. Complex 6 is
an orange oil, air-sensitive and soluble in common
organic solvents. 1H NMR and 13C{1H} NMR confirm
the symmetrical geometry of 6. The relatively low
stretching frequency of the CO ligand of 6 (1920 cm-1
)
reflects significant back-bonding from the metal to the
π* orbital of the carbonyl, as expected for terminal
carbonyls in electron-rich Ir(I) complexes.
Reactions of complex 6 are presented in Scheme 1.
It smoothly reacts with MeI, giving Ir(DIPPX)(CO)-
(CH3)I (7) in nearly quantitative yield. Complex 7 is
remarkably stable and does not decompose upon heating
up to 130 °C. The Ir-CH3 appears in the 1H NMR
spectrum as a triplet at 0.55 ppm (3J PH ) 5.0 Hz) and
as a triplet at -27.18 ppm (J PC,cis ) 4.7 Hz) in the 13C-
{1H} NMR spectrum, as expected for methyl-Ir(III)
complexes.10 The cis orientation of the methyl with
regard to the aromatic ring is confirmed by an NOE
experiment, showing interaction between the Ir-CH3
protons and one set of Ar-CH2-P and (CH3)2CH-P
protons.
in Table 1. The 31P{1H} NMR spectrum of 5 indicates
that the two phosphines of the PCP ligand are trans to
1
each other. 13C{1H} NMR and H NMR spectra reveal
that the compound does not have a symmetry plane
passing through the PCP-metal chelate core. The
signal of the ipso carbon in 13C{1H} NMR appears as a
doublet of triplets centered at 133.07 (2J PC,trans ) 45.2
Hz, 2J PC,cis ) 2.3 Hz), confirming the trans Ar-Ir-PPh3
arrangement in 5. In order to verify the ionic constitu-
tion of the compound, reaction of 5 with TlPF6 was
(9) Geoffroy, G. L.; Lehman, J . R. Adv. Inorg. Chem. Radiochem.
1977, 189.
(10) Mann, B. E.; Taylor, B. F. 13C NMR Data for Organometallic
Compounds; Academic Press: New York, 1981.

3788 Organometallics, Vol. 16, No. 17, 1997
Rybtchinski et al.
Sch em e 2
Bubbling of H2 through a benzene solution of 6 at
room temperature resulted in quantitative formation of
the cis-dihydride 8 (Scheme 1). Complex 8 was char-
acterized by 31P{1H} and 1H NMR and IR. 1H NMR
reveals two hydrides oriented cis to each other (see
Table 1), as expected for the kinetic product of dihydro-
gen oxidative addition. When the NMR tube, containing
a benzene solution of 8 under 1 atm of H2, is opened in
a N2 atmosphere, complex 8 loses H2, giving the Ir(I)
complex 6 quantitatively. Thus, significantly, 6 adds
H2 reversibly at ambient temperature, while other
bisphosphine-iridium(I) carbonyl complexes, which do
not bear a rigid tridentate chelating ligand, form stable
(at room temperature) cis-dihydride complexes.11
Th er m al Isom er ization of th e cis-Dih ydr ide Com -
p lex 8 in to th e tr a n s-Dih yd r id e Com p lex 3. Two
hydride ligands oriented trans to each other are ex-
pected to destabilize metal complexes due to their strong
mutual trans influence. As a result, trans-dihydrides
are rare and usually not stable, whereas many stable
cis-dihydride late transition metal complexes are known
for various ligand arrangments. Surprisingly, when it
is heated at 90 °C under 35 psi of H2 (hydrogen is
needed to suppress formation of 6 from 8), complex 8
quantitatvely converts into 3 (eq 3), clearly showing that
exhibits a triplet at -18.30 ppm, typical for a hydride
positioned trans to a chloride9 and cis to two equivalent
phosphines. The lack of a symmetry plane containing
the Ir-PCP chelate core is evident from the inequiva-
lence of the CH2P protons. Quantitative formation of
benzaldehyde and 4-methoxybenzaldehyde, respectively,
was observed in 1H NMR and confirmed by GC-MS.
Complex 10 was also synthesized by keeping a CDCl3
solution of 3 at room temperature for 5 days.
trans-dihydride complex 3 is thermodynamically more
stable than cis-dihydride complex 8. Assuming that 31P-
{1H} NMR signals can be integrated with an experi-
mental error of about 1%, and since no cis-dihydride 8
was observed in 31P{1H} NMR after 18 h of heating at
90 °C, ∆Gtrans-cis(363) e -3.3 kcal/mol. The isomeriza-
tion (eq 3) most probably involves phosphine arm
opening, but an Ar-H reductive-elimination-oxidative-
addition pathway is also possible. The higher thermo-
dynamic stability of the trans-dihydride 3 in comparison
with the cis-dihydride 8 contradicts the well-known
trans-influence trend (H > Ph) and is unprecedented
for hexacoordinated complexes.
Rea ctivity of tr a n s-Ir (DIP P X)(H)2(CO). The reac-
tions of trans-Ir(DIPPX)(H)2(CO) (3) are presented in
Scheme 2. Selected spectral data for complexes 9-12
are given in Table 1.
Protonation of 3 with p-toluenesulfonic acid or hydride
abstraction with [Ph3C]BF4 (trityl cation) at room
temperature results in nearly quantitative formation of
the cationic complex 9. Formation of Ph3CH was
observed in 1H NMR in the latter reaction. The
observed large hydride-phosphorus coupling (see Table
1) in 9 is consistent with a trans H-Ir-PPh3 arrange-
ment.
Complex 3 reacts with CS2.12,13 When a THF solution
of 3 containing a 20-fold excess of CS2 is kept at room
temperature for 3 days, 3 is converted into 11 in 80%
yield (31P{1H} NMR). 1H and 13C{1H} NMR spectra of
11 reveal that there is no symmetry plane containing
the Ir-PCP chelate core. The signal of the thioformyl
proton appears as a doublet of triplets centered at 11.8
4
ppm (4J HH ) 3.7 Hz, J PH ) 1.2 Hz) in 1H NMR, the
chemical shift and splitting pattern being distinctive of
complexes in which a thioformyl group is oriented trans
to a hydride.13a-d The resonance of the thioformyl
carbon appears as a broad singlet at 176.86 ppm in the
13C{1H} NMR spectrum. No reaction was observed with
CO2.
Complex 3 reacts with MeI smoothly at room tem-
perature, giving 12 in 87% yield (31P{1H} NMR).
Discu ssion
cis- to tr a n s-Dih yd r id e Isom er iza tion . In the case
of complexes Pt(PR3)2H2 containing bulky phosphines
(12) For the reviews on carbon disulfide activation see: (a) Butler,
I. S.; Fenster, A. E. J . Organomet. Chem. 1974, 66, 161. (b) Yaneff, P.
V. Coord. Chem. Rev. 1977, 183. (c) Ibers, J . A. Chem. Soc. Rev. 1982,
57.
(13) CS2 activation: (a) Robinson, S. D.; Sahajpal, A. J . Organomet.
Chem. 1975, 99, C65. (b) Roper, W. R.; Town, K. G. J . Chem. Soc.,
Chem. Commun. 1977, 781. (c) Collins, T. J .; Roper, W. R. J .
Organomet. Chem. 1978, 159, 73. (d) Mishra, A.; Agarwala, U. C. Inorg.
Chim. Acta 1988, 145, 191. (e) Klein, D. P.; Kloster, G. M.; Bergman,
R. G. J . Am. Chem. Soc. 1990, 112, 2022. (f) J ones, W. D.; Selmeczy,
A. D. Organometallics 1992, 11, 889.
Reaction of complex 3 with either benzoyl or anisoyl
chloride results in formation of complex 10 and the
1
corresponding aldehydes. The H NMR spectrum of 10
(11) For example see: (a) J ohnson, C. E.; Eisenberg, R. J . Am. Chem.
Soc. 1985, 107, 3148. (b) Deutsch, P. P.; Eisenberg, R. Chem. Rev. 1988,
88, 1147. (c) Eisenberg, R.; Cleary, B. P. J . Am. Chem. Soc. 1995, 117,
3510. (d) Fryzuk, M. D.; MacNeil, P.; Rettig, S. J . Organometallics
1986, 5, 2469.

cis- to trans-Dihydride Isomerization
Organometallics, Vol. 16, No. 17, 1997 3789
(R ) t-Bu, Cy, t-Bu2Ph, i-Pr3),2b-e the hydride ligands
are forced to be trans to each other, while with the less
bulky PMe3 the electronically more favorable cis-Pt-
(PMe3)2H2 is the major isomer in solution.2e Thus, steric
factors play a major role in the stabilization of four-
coordinate platinum trans-dihydrides. It should be
noted that in the isomerization 8 f 3 the phosphines
remain mutually trans oriented and steric factors are
unlikely to be dominant in this case. However, the
geometry of 8 with the carbonyl ligand cis to the aryl
seems sterically less favorable than that of 3 due to
possible steric interaction of the CO ligand with bulky
isopropyl groups.
The higher stability of complex 3 as compared with 8
cannot be attributed to back-bonding interactions in-
volving the carbonyl ligand. On the contrary, compari-
son of the carbonyl stretching frequencies in 3 (1980
cm-1) and 8 (1950 cm-1) indicates that there is stronger
electron donation to the antibonding orbitals of CO in
the case of the cis-dihydride 8, as expected for a carbonyl
ligand oriented trans to a hydride.
In the cis-dihydride complex the chelate structure
may be destabilized by lengthening of the Ir-Ar bond
as a result of the hydride trans effect. It is known that
31P{1H} NMR chemical shifts of chelate complexes are
very sensitive to the chelate ring size, namely to the
C-P-M angle.14 Comparison of 31P{1H} NMR chemical
shifts of 3 and 8 shows that they differ only by 6 ppm.
We would expect a more dramatic effect if the chelate
rings were significantly distorted.
While the reason for unexpected higher stability of
the trans-dihydride 3 needs further clarification, it is
likely to be a combination of steric and electronic factors.
Both the steric bulk of the ligand cis to the aryl and
destabilization of the chelate rings due to the trans effect
probably contribute to the relative stability of complexes
3 and 8.
Since 3 is an 18-electron chelate complex, with ligands
which do not dissociate at ambient temperature (3 is
stable under 30 psi of CO for days at 45-50 °C),16
precoordination of reagents to the metal center is not
possible, unlike in the case of 14. In the reaction of 3
with benzoyl or anisoyl chloride no decarbonylation
products were observed, suggesting that oxidative ad-
dition of the acid chlorides to the metal center most
probably does not take place. Thus, we propose a direct
attack of the electrophiles on the hydride ligand of 3.
True hydride-like reactivity is well-known for early
transition metals,3 anionic complexes,4 and some poly-
hydrides4c and clusters.5 Obviously, complex 3 belongs
to none of these categories. The reactions of neutral
transition-metal hydrides with strong acids or trityl
cation are well-documented.17 They result in hydride
abstraction to form metal complexes with weakly coor-
dinated anion ligands. However, the reactions of these
complexes with less strong electrophiles, as in the case
of 3, have not been reported.
Significantly, the monohydrides (9-12), which are
formed in the reactions of 3 with the electrophiles, are
inert towards the excess of the electrophilic reagents,
suggesting that the hydridic reactivity is a unique
property of the trans-dihydride 3. We suggest that the
main reason for the hydridic reactivity of 3 is the strong
mutual trans influence of the hydride ligands. Weaken-
ing of the normally strong Ir-H bond in the trans-
dihydride results in its susceptibility to the electrophilic
reagents. Both two-electron and single-electron (involv-
ing ion radicals) mechanisms can be operative. We are
unaware of octahedral trans-dihydride complexes other
than 3 whose reactivity was reported.
Mech a n ism of F or m a tion of th e tr a n s-Dih yd r id e
Com p lex 3. H2 addition to the Ir(I) complex 6 is
reversible, as indicated by the observation that the cis-
dihydride complex 8 eliminates dihydrogen in the
absence of H2 pressure to give the starting complex 6.
Significantly, when complex 1 is reacted with ligand 2,
the trans-dihydride 3 is formed in nearly quantitative
yield. If the cis-dihydride complex 8 were generated in
the reaction with a rate comparable to that of formation
of 3, we would expect to observe a significant amount
of complex 6, since under the reaction conditions (heat-
ing at 60 °C, no H2 pressure) H2 elimination from 8 to
give complex 6 takes place immediately, whereas isomer-
ization of 8 into 3 is significantly slower (vide supra).
Since only 5-7% of 6 was observed in the reaction, the
formation of 3 is kinetically controlled. Thus, interest-
ingly, the trans-dihydride 3 is both the kinetic and
thermodynamic product. The suggested reaction path-
way explaining selective formation of 3 is presented in
Scheme 3.
Hyd r id ic Rea ctivity of Com p lex 3. To the best of
our knowledge only a few examples of stable late
transition metal trans-dihydrides were reported.2 Com-
plex 13 is an analog of complex 3; the reactivity of 13
toward electrophiles was not reported.2a The 16-
electron platinum complexes of the type 14 (R ) bulky
substituent) have been extensively studied.2b-e trans-
Pt(PCy3)2H2 exhibits reactivity similar to that of 3. It
reacts with CO2 and CS2 in noncoordinating solvents,
affording the products of insertion into the Pt-H bond,
the structurally characterized formate and thioformate
complexes, respectively.15 The mechanism of carbon
disulfide insertion involves the addition of CS2 to trans-
Pt(PCy3)2(H)2 to give a five-coordinate labile intermedi-
ate, which rapidly collapses to the final product.15b
It is likely that in the transition state T the CO ligand
is oriented trans to the aryl in order to diminish steric
clashing with the bulky i-Pr substituents. The sterically
less demanding hydride ligand bends towards the aryl,
resulting in its cis orientation with regard to the aryl
in the final product (see Scheme 3). Specific interaction
of the carbonyl antibonding orbitals may also be re-
sponsible for preferential formation of complex 3. It was
(14) Lindner, E.; Fawzi, R.; Mayer, H. A.; Elchele, K.; Hiller, W.
Organometallics 1992, 11, 1033.
(15) (a) Albinati, A.; Musco, A.; Carturan, G.; Strukul, G. Inorg.
Chim. Acta 1976, 18, 219. (b) Immirzi, A.; Musco, A. Inorg. Chim. Acta
1977, 22, L35.
(16) Carbonyl dissociation from complex 3 seems unlikely, since the
CO ligand in 3 is strongly involved in back-bonding with the metal
center, as indicated by the low CO stretching frequency (1978.0 cm-1).
(17) Beck, W.; Su¨nkel, K. Chem. Rev. 1988, 88, 1405.

3790 Organometallics, Vol. 16, No. 17, 1997
Rybtchinski et al.
over 4 Å molecular sieves. Deuterated solvents were used as
received. Before introduction into the glovebox, all the solvents
were degassed with argon. They were kept in the box over 4
Å molecular sieves. Commercially available reagents were
used as received. The complex HIr(PPh3)3CO (1) was prepared
according to a literature procedure.20
Sch em e 3
1H, 31P, and 13C NMR spectra were recorded at 400, 162,
and 100 MHz respectively, using a Bruker AMX-400 NMR
spectrometer. 1H and 13C NMR chemical shifts are reported
in ppm downfield from tetramethylsilane and referenced to
the residual hydrogen signal and carbon-13 signal, respec-
tively, of the deuterated solvents. 31P NMR chemical shifts
are reported in ppm downfield from H3PO4 and referenced to
an external 85% solution of phosphoric acid in D2O. All the
NMR measurements of new compounds were performed at 23
°C in C6D6, unless otherwise specified. Abbreviations used in
the description of NMR data: app ) apparent, b ) broad, dist
) distorted, s ) singlet, d ) doublet, t ) triplet, quart )
quartet, m ) multiplet, v ) virtual. IR spectra were measured
with a Nicolet-510 FT-IR spectrometer, using NaCl IR cells.
Field desorption (FD) mass spectrometry was performed at the
University of Amsterdam using a J EOL J MS SX/SX 102A four-
sector mass spectrometer, coupled to a J EOL MS-MP7000 data
system; mass spectra are reported for more abundant isotope,
namely 193Ir. Elemental analyses were performed at the
Microanalysis Laboratory of the Hebrew University of J erusa-
lem.
suggested that the steric preferences of oxidative addi-
tion of H2 to complexes of the type (DPPE)Ir(CO)X (X
) halide, H, CN) are regulated by back-donation to
CO.18
Na tu r e of F a cile Dih yd r ogen Elim in a tion fr om
Com p lex 8. The observed facile H2 elimination from
complex 8, which seems unusual for an Ir(III) hydride
complex, can be explained as follows. Theoretical
calculations19 show that during the course of H2 oxida-
tive addition to square-planar d8 complexes a four-
electron repulsive interaction is dominant, while upon
deviation from square-planar geometry, electron density
donation from the metal filled orbital into the empty
H-H antibonding orbital prevails. Thus, oxidative
addition of H2 to the rigid square-planar complex 6 is
disfavored, i.e. H2 reductive elimination from 8 is
favorable, whereas complexes of distorted square-planar
geometry are likely to form stable dihydrides.
Syn th esis of th e DIP P X Liga n d (2). To 7.12 g (296.7
mmol) of Mg turnings in 20 mL of THF was added 0.5 mL of
neat 1,2-dibromoethane at room temperature. This mixture
was gently heated until ethylene evolution was clearly ob-
served; then 80 mL of THF was added, followed by a solution
of 12.82 g (73.30 mmol) of 1,3-bis(chloromethyl)benzene in 910
mL of THF at room temperature. At the end of the addition
the reaction mixture was stirred at room temperature for 12
h, yielding a green yellowish solution. Filteration to remove
excess Mg followed by titration of this solution with n-butanol
using o-phenanthroline as an indicator revealed formation of
the desired 1,3-bis[(chloromagnesio)methyl]benzene product in
96% yield. A THF solution (1000 mL) of the di-Grignard (70.4
mmol) was added at 0 °C to a solution of 24 g (157 mmol) of
ClP-i-Pr2 in 500 mL of THF. At the end of the addition, the
reaction mixture was warmed to room temperature and was
stirred for an additional 20 h. The solvent was removed by
vacuum, and the waxy residue was extracted with 3 × 500
mL of ether. The ether was distilled at atmospheric pressure,
and the residue was fractionated under high vacuum to give
12.23 g (51%) of the pure product. Bp: 105 °C (2 × 10-3
mmHg). 31P{1H} NMR: 10.23 (s). 1H NMR: 7.37 (bs, 1H, Ar ),
7.11 (m, 3H, Ar ), 2.60 (bs, 4H, 2 Ar-CH2-P), 1.6 (m, 4H, 2
Su m m a r y
The trans-dihydride complex 3 is both the kinetic and
thermodynamic product of the reaction of 1 with the
DIPPX ligand 2. trans-Ir(DIPPX)(H)2(CO) (3) exhibits
true hydride-like reactivity (it readily reacts with vari-
ous electrophiles), which is due to the mutual trans
influence of the hydride ligands.
A surprizing cis- into trans-dihydride isomerization
was observed. This is unprecedented for 18-electron six-
coordinate complexes. Reversible dihydrogen addition
to the Ir(I)-PCP complex Ir(DIPPX)(CO) (6) is in accord
with theory, which predicts that a rigid square-planar
geometry should disfavor oxidative addition and favor
reductive elimination of nonpolar substrates.
3
3
(CH3)2CH-P), 0.99 (dd, J PH ) 0.4 Hz, J HH ) 7.1 Hz, 12H, 2
3
3
(CH3)2CH-P), 0.96 (dd, J PH ) 2.2 Hz, J HH ) 7.1 Hz, 12H, 2
(CH3)2CH-P).
P r ep a r a tion of tr a n s-Ir (DIP P X)(H)2(CO) (3). A solution
of DIPPX (2; 30 mg, 0.089 mmol) in 3 mL of THF was added
to a THF solution (7 mL) of HIr(PPh3)3CO (1; 89 mg, 0.088
mmol). The resulting yellow solution was heated at 60-62
°C in a closed vessel for 2 h with stirring, upon which it turned
light orange. trans-Ir(DIPPX)(H)2(CO) was formed in 93%
yield (31P{1H} NMR). A small amount of Ir(DIPPX)CO (6; 7%)
was also formed. When benzene is used as a solvent instead
of THF, 3 is formed in 95% yield. All attempts to separate 3
from PPh3 by crystallization or chromatography on alumina
or silica and by use of PdCl2(CH3CN)2 as a phosphine sponge
did not result in complete PPh3 removal. The compound is
very soluble in common organic solvents and is air-stable.
Ch a r a cter iza tion of 3. PPh3 signals are excluded from
the NMR data. 31P{1H} NMR: δ 57.84 (s). 31P{1H} hydride-
coupled NMR: δ 57.84 (t, 2J PH,cis ) 15.0 Hz). 1H NMR: δ 6.99
(m, 2H, Hmeta, Ir-Ar ), 6.91 (m, 1H, Hpara, Ir-Ar ), 3.13 (vt,
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All experiments with metal
complexes were carried out under purified nitrogen in a
Vacuum Atmospheres glovebox equipped with an MO 40-2
inert gas purifier. Ligand synthesis was carried out under
argon. Solvent removal was performed with a high vacuum
system, using precision oil vacuum pumps. All solvents were
reagent grade or better. All non-deuterated solvents (except
for acetone) were refluxed over sodium/benzophenone ketyl
and distilled under an argon atmosphere. Acetone was dried
(18) Sargent, A. L.; Hall, M. B.; Guest, M. F. J . Am. Chem. Soc.
1992, 114, 517.
(19) (a) Dedieu, A.; Strich, A. Inorg. Chem. 1979, 18, 2940. (b)
Saillard, J .-Y.; Hoffmann, R. J . Am. Chem. Soc. 1984, 106, 2006.
(20) Wilkinson, G. Inorg. Synth. 1972, 13, 126.

cis- to trans-Dihydride Isomerization
Organometallics, Vol. 16, No. 17, 1997 3791
J PH,virt ) 4.1 Hz, 4H, 2 Ar-CH2-P), 1.72 (m, 4H, 4 (CH3)2CH-
difference in the spectra before and after the addition of TlPF6,
-
P), 1.1 (app quart, J ) 7.4 Hz, 12H, 2 (CH3)2CH-P), 0.93 (app
except for the P F6 septet in 31P{1H} NMR.
2
quart, J ) 7.1 Hz, 12H, 2 (CH3)2CH-P), -9.69 (t, J PH,cis
)
)
P r ep a r a tion of Ir (DIP P X)(CO) (6). A solution of KO-t-
Bu (12 mg, 0.107 mmol) in 3 mL of THF was added to a
solution of [Ir(DIPPX)(H)(PPh3)(CO)]Br (5; 48 mg, 0.053 mmol)
in 3 mL of THF. After 2 h of stirring at room temperature
the reaction mixture turned orange. The solvent was evapo-
rated, and the residue was extracted with pentane. The
orange pentane extract was filtered, and the solvent was
evaporated, resulting in 28 mg of orange oil, which appeared
to be a mixture of 6 and PPh3 (31P{1H} NMR; 6: PPh3 ) 1:1).
The estimated yield of 6 is 78%. The product is very sensitive
to air and is very soluble in common organic solvents. It was
not separated from PPh3.
2
15.0 Hz, 2H, H-Ir-H). 13C{1H} NMR: δ 178.63 (t, J PC,cis
6.8 Hz, Ir-CO), 151.62 (t, J PC ) 3.2 Hz, Ir-Ar ), 147.23 (t, J PC
) 8.8 Hz, Ir-Ar ), 122.94 (bs, Cpara, Ir-Ar ), 120.83 (t, J PC
)
8.3 Hz, Cmeta, Ir-Ar ), 41.23 (vt, J PC,virt ) 17.6 Hz, Ar-CH2-
P), 25.85 (vt, J PC,virt ) 15.9 Hz, (CH3)2CH-P), 19.57 (vt, J PC,virt
) 1.5 Hz, (CH3)2CH-P), 18.14 (s, (CH3)2CH-P). Assignment
of 13C{1H} NMR signals is confirmed by 13C DEPT 135. IR
(film): 1978.0 cm-1 (s), νCO; 1745.6 cm-1 (s), νH-Ir-H
.
IR
(C6D6): 1980.0 cm-1 (s), νCO; 1750 cm-1 (s), νH-Ir-H
m/ z 560, M+.
. FDMS:
Syn th esis of th e DIP P X-Br Liga n d (4). A mixture of
diisopropylphosphine (0.829 g, 7.97 mmol) and 1,3-bis(bro-
momethyl)-2-bromobenzene21 (1.2 g, 3.53 mmol) in degassed
acetone (5 mL) was heated under reflux with stirring for 40
min under an argon atmosphere, and then the solvent was
evaporated. The solid was washed with ether to remove
unreacted starting material. The resulting diphosphonium
salt was dissolved in distilled degassed water (10 mL) and
treated with a solution of sodium acetate (4 g, 48 mmol) in
distilled degassed water (10 mL). The precipitated diphos-
phine was extracted with ether (3 × 50 mL) and dried over
Na2SO4, and the ether solution was filtered via sinter tube
under argon pressure. The solvent was evaporated under
vacuum, giving 0.800 g (65.9%) of the ligand 4 as a white solid.
31P{1H} NMR (C6D6): δ 6.65 (s). 1H NMR (C6D6): δ 7.35 (bd
Ch a r a cter iza tion of 6. PPh3 signals are excluded from
the NMR data. 31P{1H} NMR: δ 66.18 (s). 1H NMR: δ 7.28
(bd (dist), 2J HH ) 7.4 Hz, 2H, Hmeta, Ir-Ar ), 7.17 (bt (dist), 1H,
H
para, Ir-Ar ), 3.20 (vt, J PH,virt ) 4.0 Hz, 4H, 2 Ar-CH2-P),
2.02 (m, 4H, 4 (CH3)2CH-P), 1.20 (app quart, J ) 7.5 Hz, 12H,
2 (CH3)2CH-P), 0.97 (app quart, J ) 7.1 Hz, 12H, 2 (CH3)2-
CH-P). 13C{1H} NMR: δ 196.51 (t, 2J PC,cis ) 7.7 Hz, Ir-CO),
154.34 (t, J PC ) 11.4 Hz, Ir-Ar ), 125.75 (s, Ir-Ar ), 120.64 (t,
J PC ) 8.7 Hz, Ir-Ar ), 38.94 (vt, J PC,virt ) 15.7 Hz, Ar-CH2-
P), 26.81 (vt, J PC,virt ) 14.5 Hz, (CH3)2CH-P), 19.53 (vt, J PC,virt
) 2.2 Hz, (CH3)2CH-P), 18.81 (s, (CH3)2CH-P). Assignment
of 13C{1H} NMR signals is confirmed by 13C DEPT 135. IR
(film): 1920.0 cm-1 (s), νCO
.
Rea ction of Com p lex 6 w ith MeI. F or m a tion of Ir -
(DIP P X)(CO)(CH3)I (7). To 2 mL of a benzene solution of
Ir(DIPPX)CO (6; 19 mg of a mixture, 6:PPh3 ) 1:1) was added
3 µL of CH3I. After 10 min of stirring at room temperature
the initial orange color of the mixture almost disappeared and
a white precipitate formed (the phosphonium salt [CH3PPh3]I,
2
(dist), J HH ) 7.4 Hz, 2H, Ar ), 7.05 (bt (dist), 1H, Ar ), 3.06 (d,
2J HP ) 1.7 Hz, 4H, 2 Ar-CH2-P), 1.76 (m, 4H, 2 (CH3)2CH-
P), 1.11 (m, 24H, 4 (CH3)2CH-P).
P r ep a r a tion of [Ir (DIP P X)(P P h 3)(H)(CO)]Br (5).
A
solution of DIPPX (2; 62 mg, 0.149 mmol) in 2 mL of THF was
added dropwise to a THF solution (4 mL) of HIr(PPh3)3CO (1;
150 mg, 0.145 mmol). The mixture was stirred for 24 h at
room temperature until its color turned from deep yellow to
greenish. The product was precipitated with 8 mL of cold
pentane. The white precipitate was collected by filtration,
washed with pentane (3 × 2 mL), and dried under vacuum,
yielding 112 mg (84%) of 5. The compound is soluble in polar
organic solvents such as acetone, THF, chloroform, methylene
chloride and insoluble in pentane, benzene, and toluene.
Ch a r a cter iza tion of 5. 31P{1H} NMR (CD2Cl2): δ 33.65
1
identified by 31P{1H} and H NMR). The mixture was filtered
and the solvent was evaporated under vacuum, giving 16 mg
(98.8%) of pure 7 as a white solid. The compound is soluble
in benzene and toluene and in polar organic solvents such as
acetone, THF, chloroform, and methylene chloride and is
moderately soluble in pentane.
Ch a r a cter iza tion of 7. 31P{1H} NMR (acetone-d6): δ 31.26
2
(s). 1H NMR (acetone-d6): δ 7.04 (bd (dist), J HH ) 7.4 Hz,
2H, Hmeta, Ir-Ar ), 6.80 (bt (dist), 1H, Hpara, Ir-Ar ), 3.86 (dvt,
2
the left part of an AB pattern, J HH ) 16.0 Hz, J PH,virt ) 4.4
2
(d, J PP,cis ) 11.9 Hz, 2P, trans P -Ir-P ), -6.62 (t, 1P, Ir-
Hz, 2H, Ar-CH2-P), 3.70 (dvt, the right part of an AB pattern,
J PH,virt ) 4.1 Hz, 2H, Ar-CH2-P), 3.27 (m, 2H, 2 (CH3)2CH-
P), 2.56 (m, 2H, 2 (CH3)2CH-P), 1.34 (m, 24H, 4 (CH3)2CH-
P Ph3). 1H NMR (CD2Cl2): δ 7.70 (m, 6H, Ir-PP h 3), 7.53 (m,
2
9H, Ir-PP h 3), 7.12 (bd (dist), J HH ) 7.4 Hz, 2H, Hmeta, Ir-
Ar ), 7.02 (bt (dist), 1H, Hpara, Ir-Ar ), 3.48 (m, unresolved AB
pattern, 4H, 2 Ar-CH2-P), 1.69 (m, 2H, 2 (CH3)2CH-P), 1.46
(m, 2H, (CH3)2CH-P), 0.88 (app quart, J ) 7.1 Hz, 6H, (CH3)2-
CH-P), 0.77 (m, 18H, 3 (CH3)2CH-P), -9.46 (app quart, 2J PH
) 14.8 Hz, 1H, Ir-H). 13C{1H} NMR (CD2Cl2): δ 176.57 (app
3
P), 0.55 (t, J PH ) 5.0 Hz, 3H, CH3-Ir). 1H NMR (toluene-d8;
selected signals): δ 3.68 (dvt, the left part of an AB pattern,
2H, Ar-CH2-P), 3.30 (dvt, the right part of an AB pattern,
overlapped with the signal at 3.27, Ar-CH2-P), 3.27 (m,
overall integration with the signal at 3.30 4H, (CH3)2CH-P),
2.14 (m, overlapped with the signal of toluene-d8 methyl group,
2
quart, J PC,cis ) 6.3 Hz, Ir-CO), 144.69 (td, J PC ) 4.9 Hz, J PC
2
) 2.3 Hz), 138.91 (d, J PC ) 71.3 Hz, Cipso, Ir-PP h 3), 134.98
3
(CH3)2CH-P), 0.54 (t, J PH ) 5.0 Hz, 3H, CH3-Ir). The
(d, J PC ) 10.7 Hz), 133.07 (dt, 2J PC,trans ) 45.2 Hz, 2J PC,cis ) 2.3
Hz, Cipso, Ar -Ir), 132.32 (d, J PC ) 2.3 Hz), 129.2 (d, J PC ) 9.9
Hz), 126.92 (s), 122.83 (td, J PC ) 7.3 Hz, J PC ) 3.2 Hz), 39.52
1
assignment of 1H NMR signals is confirmed by H{31P} NMR.
2
13C{1H} NMR (toluene-d8): δ 178.44 (t, J PC,cis ) 5.8 Hz, Ir-
CO), 158.08 (bs, Ar -Ir), 147.12 (t, J PC ) 7.8 Hz, Ar -Ir), 125.16
3
(vtd, J PC,virt ) 18.3 Hz, J PC ) 7.2 Hz, Ar-CH2-P), 26.37 (vt,
(s, Ar -Ir), 121.98 (t, J PC ) 7.8 Hz, Ar -Ir), 40.11 (vt, J PC,virt
)
J PC,virt ) 13.7 Hz, (CH3)2CH-P), 25.70 (vt, J PC,virt ) 15.6 Hz,
(CH3)2CH-P), 19.44 (s, (CH3)2CH-P), 19.35 (s, (CH3)2CH-
P), 17.90 (bs, (CH3)2CH-P), 17.46 (vt, J PC,virt ) 1.1 Hz, (CH3)2-
CH-P). Assignment of 13C{1H} NMR signals is confirmed by
13C DEPT 135. IR (film): 2140.9 cm-1 (bm), νIr-H; 2002.0 cm-1
(s), νCO. Anal. Calcd: C, 52.00; H, 5.71. Found: C, 52.30; H,
6.01. FD-MS: m/ z 821, [Ir(DIPPX)(PPh3)(H)(CO)]+.
17.5 Hz, Ar-CH2-P), 28.33 (vt, J PC,virt ) 15.0 Hz, (CH3)2CH-
P), 22.32 (vt, J PC,virt ) 13.1 Hz, (CH3)2CH-P), 20.11 (s, (CH3)2-
CH-P), 19.73 (s, (CH3)2CH-P), 19.68 (bs, (CH3)2CH-P), 19.16
(s, (CH3)2CH-P), -27.18 (t, J PC,cis ) 4.7 Hz, CH3-Ir). IR
(film): 2004.0 cm-1 (s), νCO. Anal. Calcd: C, 37.77; H, 5.47.
Found: C, 39.25; H, 5.63.
1H NOE Differ en ce Exp er im en t (tolu en e-d 8). When the
CH3-Ir group protons of 10 were selectively irradiated, selective
enhancement of the methylene proton signal at 3.30 ppm and
the methyne proton signal at 2.14 ppm was observed.
Rea ction of 5 w ith TlP F 6. A solution of TlPF6 (4 mg,
0.0115 mmol) in acetone-d6 (0.5 mL) was added to a solution
of [Ir(DIPPX)(PPh3)(H)(CO)]Br (5; 10 mg, 0.0111 mmol) in 0.5
mL of acetone-d6, resulting in immediate precipitation. The
mixture was filtered; 31P{1H} and 1H NMR revealed no
Rea ction of Com p lex 6 w ith H2. Rever sible F or m a tion
of cis-Ir (DIP P X)(H)2(CO) (8). Complex 8 was formed quan-
titatively within 10 min upon bubbling of hydrogen gas
through 0.6 mL of a C6D6 solution of Ir(DIPPX)CO (6; 10 mg
(21) Liou, S.-Y. Ph.D. Thesis, The Weizmann Institute of Science,
Rehovot, Israel 1996.

3792 Organometallics, Vol. 16, No. 17, 1997
Rybtchinski et al.
of a mixture, 6:PPh3 ) 1:1) in a closed vessel (septum-capped
NMR tube). A color change from orange to light yellow was
observed. 31P{1H} and 1H NMR of the solution indicated
quantitative formation of complex 8. Upon opening of the tube
in a glovebox and standing for 15 min at room temperature
the solution color turned from light yellow to orange. 31P{1H}
and 1H NMR revealed quantitative formation of Ir(DIPPX)-
CO (6).
Ir-CO), 156.66 (t, J PC ) 2.1 Hz, Ar -Ir), 148.54 (t, J PC ) 8.4
Hz, Ar -Ir), 124.95 (s, Ar -Ir), 121.52 (t, J PC ) 8.3 Hz, Ar -
Ir), 40.01 (vt, J PC,virt ) 17.6 Hz, Ar-CH2-P), 25.47 (vt, J PC,virt
) 14.8 Hz, (CH3)2CH-P), 24.39 (vt, J PC,virt ) 15.3 Hz,
(CH3)2CH-P), 20.32 (vt, J PC,virt ) 1.5 Hz, (CH3)2CH-P), 19.63
(bs, (CH3)2CH-P), 18.70 (s, (CH3)2CH-P), 17.56 (bs, (CH3)2-
CH-P). IR (film): 2197.4 cm-1 (bm), νIr-H; 2003.1 cm-1 (s)
ν
CO. FD-MS m/ z 594, M+
Rea ction of 3 w ith Ben zoyl Ch lor id e. F or m a tion of
Com p lex 10 a n d Ben za ld eh yd e. Benzoyl chloride (3 µL,
0.026 mmol, 1.7-fold excess) was added to a benzene-d6 solution
Ch a r a cter iza tion of 8. PPh3 signals are excluded from
the NMR data. 31P{1H} NMR: δ 51.67 (s). 1H NMR: δ 7.12
(m, 3H, Ir-Ar ), 4.46 (s, H2), 3.22 (m, unresolved AB pattern,
4H, Ar-CH2-P), 1.91 (m, 2H, 2 (CH3)2CH-P), 1.60 (m, 2H, 2
(CH3)2CH-P), 1.03 (m, 18H, 3 (CH3)2CH-P), 0.84 (app quart,
of trans-Ir(DIPPX)(H)2(CO) (3; 20 mg of a mixture, 3:PPh3
)
1:3). After the mixture was kept at room temperature for 4
h, quantitative formation of 3 was observed (31P{1H} NMR).
Quantitative formation of benzaldehyde was observed in 1H
NMR (a known quantity of 4-methoxybenzaldehyde was added
to the reaction mixture as an internal standard). Formation
of benzaldehyde was also detected by GC-MS.
2
J ) 7.0 Hz, 6H, (CH3)2CH-P), -10.87 (td, J PH,cis ) 16.9 Hz,
2J HH,cis ) 3.2 Hz, 1H, Ir-H), -11.94 (td, 2J PH,cis ) 11.9 Hz, 1H,
Ir-H). IR (C6H6, 1 atm of H2): 2066.3 cm-1 (bw), νIr-H; 1965.0
cm-1 (w), νIr-H; 1950.0 cm-1 (s), νCO
.
Isom er iza tion of 8 in to 3. Heating of complex 8 at 90 °C
Rea ction of 3 w ith An isoyl Ch lor id e. F or m a tion of
Com p lex 10 a n d 4-Meth oxyben zyla ld eh yd e. Anisoyl chlo-
ride (5 mg, 0.029 mmol, 2-fold excess) was added to a benzene-
d6 solution of trans-Ir(DIPPX)(H)2(CO) (3; 20 mg of a mixture,
3:PPh3 ) 1:3). After the mixture was kept at room tempera-
ture for 4 h, formation of 5 and 4-methoxybenzylaldehyde was
observed in quantitative yield by H NMR (a known quantity
of benzaldehyde was added to the reaction mixture, and the
integration of aldehyde protons was compared).
in a 5 mm high-pressure NMR tube for 18 h under 35 psi of
1
H2 results in quantitatve formation of 3 (31P{1H} and H NMR
followup).
R ea ct ion of 3 w it h P TSA (p -Tolu en esu lfon ic Acid ).
F or m a tion of [Ir (DIP P X)(P P h 3)(H)(CO)]+ (9). A 2 mL
portion of a THF solution of trans-Ir(DIPPX)(H)2(CO) (3; 20
mg of a mixture, 3:PPh3 ) 1:3) was added to 2 mL of a THF
solution of PTSA (7-fold excess), and the mixture was stirred
at room temperature for 2 h. The product was precipitated
with 3 mL of pentane, washed with pentane (3 × 2 mL), and
dried under vacuum, giving 7 mg (53% yield) of the white
product 9. The product is soluble in polar organic solvents
(CHCl3, CH2Cl2, THF) and insoluble in benzene and toluene.
1
Rea ction of Com p lex 3 w ith CS2. F or m a tion of Ir -
(DIP P X)(H)(HC(S)S)CO (11). CS2 (0.1 mL, 79 mg, 1.039
mmol) was added to a THF solution (2 mL) of trans-Ir(DIPPX)-
(H)2(CO) (3; 80 mg of a mixture, 3:PPh3 ) 1:3), resulting in a
yellow solution. After the mixture was kept for 3 days at room
temperature, the solution turned brown. The solvent was
evaporated under vacuum, giving complex 6 as a brown oil in
80% yield (31P{1H} NMR). The product is very soluble in
common organic solvents. It was not separated from PPh3.
Ch a r a cter iza tion of 11. PPh3 signals are excluded from
the NMR data. 31P{1H} NMR: δ 46.53 (s). 1H NMR: δ 11.8
(dt, 4J HH ) 3.7 Hz, 4J PH ) 1.2 Hz, 1H, HC(S)S-Ir), the signals
of the product aromatic protons are overlapped with the signals
Rea ction of 3 w ith Tr ityl Ca tion ([P h 3C]BF 4). F or m a -
tion of Com p lex 9 a n d P h 3CH. A 2 mL portion of a CH2Cl2
solution of trans-Ir(DIPPX)(H)2(CO) (3; 20 mg of a mixture,
3:PPh3 ) 1:3) was added to 2 mL of a CH2Cl2 solution of [Ph3C]-
BF4 (2-fold excess), and the mixture was stirred at room
temperature for 2 h. Then the product was precipitated with
4 mL of pentane, washed with pentane (3 × 2 mL), and dried
under vacuum, giving 8 mg (estimated yield 60%) of the white
product 9. Formation of Ph3CH was observed in 1H NMR.
2
of PPh3, 3.19 (dvt, the left part of an AB pattern, J HH ) 16.6
Ch a r a cter iza tion of 9. 31P{1H} NMR (CDCl3): δ 34.9 (d,
2J PP,cis ) 12.2 Hz, 2P, trans P -Ir-P ), -20.0 (t, 1P, Ir-P Ph3).
1H NMR (CDCl3): δ 7.69 (m, 3H, Ir-PP h 3), 7.51 (m, 6H, Ir-
Hz, J PH,virt ) 4.2 Hz, 2H, Ar-CH2-P), 2.88 (dvt, the right part
of an AB pattern, J PH,virt ) 4.3 Hz, 2H, Ar-CH2-P), 2.32 (m,
2H, 2 (CH3)2CH-P), 1.60 (m, 2H, 2 (CH3)2CH-P), 1.16 (app
quart, J ) 7.3 Hz, 6H, (CH3)2CH-P), 0.98 (app quart, J ) 6.9
Hz, 6H, (CH3)2CH-P), 0.84 (app quart, J ) 7.1 Hz, 6H, (CH3)2-
CH-P), 0.67 (app quart, J ) 7.0 Hz, 6H, (CH3)2CH-P), -14.70
(td, 2J PH ) 12.0 Hz, 4J HH ) 3.7 Hz, 1H, Ir-H). Assignment of
the signals in 1H NMR is confirmed by 1H{31P} NMR. 13C-
2
PP h 3), 7.37 (m, 6H, Ir-PP h 3), 7.25 (bt (dist), J HH ) 7.4 Hz,
1H, Hpara, Ir-Ar ), 7.18 (bd (dist), 2H, Hmeta, Ir-Ar ), 5.50 (s,
Ph3CH, when [Ph3C]BF4 is used), 3.48 (dvt, the left part of an
2
AB pattern, J HH ) 17.2 Hz, J PH,virt ) 4.8 Hz, 2H, Ar-CH2-
P), 2.57 (m, 2H, 2 (CH3)2CH-P), 2.38 (dvt, the right part of
an AB pattern, J PH,virt ) 4.4 Hz, 2H, Ar-CH2-P), 1.49 (m, 8H,
2 (CH3)2CH-P and (CH3)2CH-P), 1.38 (app quart, J ) 7.4 Hz,
6H, (CH3)2CH-P), 1.17 (app quart, J ) 7.2 Hz, 6H, (CH3)2-
CH-P), 0.90 (app quart, J ) 7.3 Hz, 6H, (CH3)2CH-P), -12.04
2
{1H} NMR: δ 179.03 (t, J PC,cis ) 6.6 Hz, Ir-CO), 176.86 (bs,
HC(S)S-Ir), 149.22 (bs, Ar -Ir), 148.64 (t, J PC ) 8.0 Hz, Ar -
Ir), 124.98 (s, Ar -Ir), 121.67 (t, J PC ) 8.3 Hz, Ar -Ir), 40.52
(vt, J PC,virt ) 17.6 Hz, Ar-CH2-P), 26.77 (vt, J PC,virt ) 14.9
Hz, (CH3)2CH-P), 24.74 (vt, J PC,virt ) 15.9 Hz, (CH3)2CH-P),
20.18 (bs, (CH3)2CH-P), 20.06 (vt, J PC,virt ) 1.5 Hz, (CH3)2-
CH-P), 18.78(s, (CH3)2CH-P), 17.77 (bs, (CH3)2CH-P). As-
signment of 13C{1H} NMR signals is confirmed by 13C DEPT
2
2
(dt, J PH,trans ) 131.1 Hz, J PH,cis ) 13.1 Hz, 1H, trans H-Ir-
PPh3). IR (film): 2161.4 cm-1 (bm) νIr-H; 2012.0 cm-1 (s), νCO
.
Rea ction of 3 w ith CDCl3. F or m a tion of Ir (DIP P X)-
(H)(CO)Cl (10). Keeping a solution of trans-Ir(DIPPX)(H)2-
(CO) (3; 50 mg of a mixture, 3:PPh3 ) 1:3) in 0.6 mL of CDCl3
at room temperature for 5 days resulted in a clean quantitative
conversion of 3 into 10. Complex 10 was precipitated with 3
mL of pentane and washed with pentane (3 × 1 mL), yielding
19 mg (86.1%) of complex 10 as a white precipitate.
135. IR (film): 2120.0 cm-1 (bw), νIr-H, 2009.7 cm-1 (s), νCO
;
1220 cm-1 (bm), 1025 cm-1 (bs). FDMS: m/ z 636, M+.
Rea ction of Com p lex 3 w ith MeI. F or m a tion of Ir -
(DIP P X)(H)(CO)I (12). MeI (10 µL, 0.161 mmol) was added
to a benzene solution of trans-Ir(DIPPX)(H)2(CO) (3; 30 mg of
a mixture, 3:PPh3 ) 1:3), resulting in formation of a white
precipitate (the phosphonium salt [CH3PPh3]I, identified by
31P{1H} and 1H NMR). The solvent was evaporated, and the
residue was extracted with toluene. The extract was filtered,
and the solvents were evaporated under vacuum, yielding a
greenish residue. 31P{1H} NMR of the residue revealed
formation of Ir(DIPPX)(H)(CO)I (12) in 85% yield (contami-
nated with traces of unidentified complexes).
Ch a r a cter iza tion of 10. 31P{1H} NMR: δ 50.79 (s). 1H
NMR: δ 7.05 (m, 3H, Ir-Ar ), 3.42 (dvt, the left part of an AB
2
pattern, J HH ) 16.4 Hz, J PH,virt ) 4.4 Hz, 2H, Ar-CH2-P),
3.01 (dvt, the right part of an AB pattern, J PH,virt ) 4.3 Hz,
2H, Ar-CH2-P), 2.86 (m, 2H, 2 (CH3)2CH-P), 1.67 (m, 2H, 2
(CH3)2CH-P), 1.33 (app quart, J ) 7.4 Hz, 6H, (CH3)2CH-
P), 1.08 (app quart, J ) 7.2 Hz, 6H, (CH3)2CH-P), 0.91 (app
quart, J ) 7.3 Hz, 6H, (CH3)2CH-P), 0.68 (app quart, J ) 7.0
Hz, 6H, (CH3)2CH-P), -18.30 (t, 2J PH,cis ) 11.6 Hz, 1H, trans-
Ch a r a cter iza tion of 12. 31P{1H} NMR: δ 42.80 (s). 1H
NMR: δ 7.31 (bs, 2H, Hmeta, Ir-Ar ), 7.22 (m, 1H, Hpara, Ir-
2
H-Ir-Cl). 13C{1H} NMR: δ 179.19 (t, J PC,cis ) 6.8 Hz,

cis- to trans-Dihydride Isomerization
Organometallics, Vol. 16, No. 17, 1997 3793
2
Ar ), 3.58 (dvt, the left part of an AB pattern, J HH ) 16.5 Hz,
J PH,virt ) 4.7 Hz, 2H, Ar-CH2-P), 3.31 (m, overlapped with
the signal at 3.26, 2H, (CH3)2CH-P), 3.26 (dvt, the right part
of an AB pattern, J PH,virt ) 4.3 Hz, overall integration with
the signal at 3.31 4H, Ar-CH2-P), 1.79 (m, 2H, 2 (CH3)2CH-
P), 1.56 (app quart, J ) 7.4 Hz, 6H, (CH3)2CH-P), 1.05 (m,
12H, 2 (CH3)2CH-P), 0.79 (app quart, J ) 7.2 Hz, 6H, (CH3)2-
Ack n ow led gm en t. We wish to thank Dr. Alexander
Weisman and Mr. Arkadi Vigalok for valuable discus-
sions. This work was supported by the Israel Science
Foundation, J erusalem, Israel, and by the United
States-Israel Binational Science Foundation, J erusalem,
Israel. D.M. is the holder of the Israel Matz professorial
chair of organic chemistry.
2
CH-P), -15.48 (t, J PH,cis ) 10.6 Hz, 1H, trans H-Ir-I). IR
(film): 2193.0 cm-1 (bm), νIr-H; 2005.0 cm-1 (s), νCO. FD-MS:
m/ z 686, M+.
OM970104R