Rhodium and iridium complexes with 2-(diphenylphosphanyl)anilido ligands: Reactions with phenylacetylene and dimethyl acetylenedicarboxylate

Article abstract of DOI:10.1039/a906430c

Treatment of[Ir(CO)(PPh₃)('PNMe')] ('PNMe' = 2-Ph₂PC₆H₄NMe^-) with phenylacetylene resulted in oxidative addition and opening of the chelate ring to afford mono- and bis-(alkynyl) derivatives, [IrH(C=CPh)(CO)(PPh₃)-('PNMe')] 1 and [IrH(C=CPh)₂(CO)(PPh₃)(η¹-'PN(Me)H')] 2, respectively. Complex 2 exists as two isomers with trans-located phosphane ligands and cis- or trans-coordinated alkynyl groups. The minimum values of the spinlattice relaxation times, T₁^(min), observed for the hydride ligands of the two isomers ruled out the possibility of short IrH ... HN contacts in 2. Combination of [Ir(CO)(PPh₃)('PNMe')] with dimethyl acetylenedicarboxylate (dmad) gave the irida(III)cyclopropene-like complex [Ir{C₂(CO₂Me)₂}(CO)('PPH₃)('PNMe')] 3 as the expected 1:1 adduct. In contrast [Rh(CO)(PPh₃)('PNMe')] and dmad interacted by insertion of the activated alkyne into the Rh-N bond, forming the seven-membered metallaheterocycle [Rh{C(CO₂Me)=C(CO₂Me)N(Me)C₆H ₄PPh₂-2}(CO)(PPh₃)] 4. [Ir(CO)(PPh₃)('PNH')] ('PNH' = 2-Ph₂PC₆H₄NH^-) and dmad reacted to initially produce a mixture of metallacyclic [Ir{C₂(CO₂Me)₂}(CO)(PPh₃)('PNH')] 5 and unchanged starting materials. Subsequent treatment with methanol resulted in the formation of the iridium(III) complex [Ir{C(O)OMe}{C(CO₂Me)=CH[C(O)OMe]}(PPh₃)('PNH')] 6, which X-ray crystallography showed to contain a chelating vinyl ligand featuring substantial carbenoid character. The Royal Society of Chemistry 1999.

Full text of DOI:10.1039/a906430c

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Rhodium and iridium complexes with 2-(diphenylphosphanyl)anilido
ligands: reactions with phenylacetylene and dimethyl acetylene-
dicarboxylate†
Lutz Dahlenburg* and Konrad Herbst
Institut für Anorganische Chemie der Friedrich-Alexander-Universität Erlangen-Nürnberg,
Egerlandstrasse 1, D-91058 Erlangen, Germany. E-mail: dahlenburg@chemie.uni-erlangen.de
Received 9th August 1999, Accepted 1st October 1999
Treatment of [Ir(CO)(PPh3)(‘PNMe’)] (‘PNMe’ = 2-Ph2PC6H4NMeϪ) with phenylacetylene resulted in oxidative
᎐
addition and opening of the chelate ring to afford mono- and bis-(alkynyl) derivatives, [IrH(C᎐CPh)(CO)(PPh )-
᎐
3
1
᎐
(‘PNMe’)] 1 and [IrH(C᎐CPh) (CO)(PPh )(η -‘PN(Me)H’)] 2, respectively. Complex 2 exists as two isomers with
᎐
2
3
trans-located phosphane ligands and cis- or trans-coordinated alkynyl groups. The minimum values of the spin–
lattice relaxation times, T1(min), observed for the hydride ligands of the two isomers ruled out the possibility of short
IrH ؒ ؒ ؒ HN contacts in 2. Combination of [Ir(CO)(PPh3)(‘PNMe’)] with dimethyl acetylenedicarboxylate (dmad)
gave the irida()cyclopropene-like complex [Ir{C2(CO2Me)2}(CO)(PPh3)(‘PNMe’)] 3 as the expected 1:1 adduct. In
contrast, [Rh(CO)(PPh3)(‘PNMe’)] and dmad interacted by insertion of the activated alkyne into the Rh–N bond,
forming the seven-membered metallaheterocycle [Rh{C(CO Me)᎐C(CO Me)N(Me)C H PPh -2}(CO)(PPh )] 4.
᎐
2
2
6
4
2
3
[Ir(CO)(PPh3)(‘PNH’)] (‘PNH’ = 2-Ph2PC6H4NHϪ) and dmad reacted to initially produce a mixture of metallacyclic
[Ir{C2(CO2Me)2}(CO)(PPh3)(‘PNH’)] 5 and unchanged starting materials. Subsequent treatment with methanol
resulted in the formation of the iridium() complex [Ir{C(O)OMe}{C(CO Me)᎐CH[C(O)OMe]}(PPh )(‘PNH’)] 6,
᎐
2
3
which X-ray crystallography showed to contain a chelating vinyl ligand featuring substantial carbenoid character.
᎐
᎐
(M = Rh, Ir; R = H, Me) and the MeO CC᎐CCO Me ligand
Introduction
2
2
have attracted our interest because combination of the more
electron-rich amide complexes of the late transition metals with
alkynes bearing electron-withdrawing substituents has proved
to be a suitable method for facile C–N bond making by addition
of the metal–amide function across the –C᎐C– triple bond of
During the last few years we have been investigating some
aspects of the chelation of bidentate 2-(diphenylphosphanyl)-
aniline and -phenol ligands 2-Ph2PC6H4XH (X = NH, NMe,
O), both in their neutral (‘PXH’) and deprotonated (‘PX’)
forms, in particular with respect to the reactivity of their tung-
sten, rhodium, and iridium complexes towards Brønsted acids.1
Following these studies, we have turned our attention to reac-
tions of terminal and internal alkynes, such as phenylacetylene
and dimethyl acetylenedicarboxylate, with Vaska-type rhodium
and iridium complexes containing anionic 2-(diphenylphos-
phanyl)anilido or 2-(diphenylphosphanyl)-N-methylanilido
ligands, 2-Ph2PC6H4NHϪ (‘PNH’) and 2-Ph2PC6H4NMeϪ
(‘PNMe’), respectively.1b
᎐
᎐
the unsaturated molecule.6
Results and discussion
Reactions with phenylacetylene
Both the rhodium complexes [Rh(CO)(PPh3)(‘PNR’)], where
R = H or Me, and the iridium compound [Ir(CO)(PPh3)-
(‘PNH’)] proved to be completely unreactive towards PhC᎐CH,
᎐
᎐
even if treated with the alkyne in high excess at elevated
temperature. In a similar way, the more metal-basic 2-
(diphenylphosphanyl)-N-methylanilidoiridium() derivative [Ir-
(CO)(PPh3)(‘PNMe’)] underwent only sluggish oxidative C–H
Prior to this work, low-valent iridium compounds possessing
non-chelating amido ligands, e.g., [Ir(NHBut)(CO)(PEt3)2],
᎐
have been reported to react with PhC᎐CH by protonation of
᎐
the amide function and oxidative addition of the alkyne to give
hydrido bis(alkynyl)iridium() derivatives.2 With the chelate
complexes [Ir(CO)(PPh3)(‘PNR’)] (R = H, Me) as starting
᎐
addition with formation of [IrH(C᎐CPh)(CO)(PPh )(‘PNMe’)]
᎐
3
1, requiring five or more equivalents of phenylacetylene in
toluene at 70 ЊC. The overall geometry of 1 shown above was
confirmed by spectral data. In particular, the 31P-{1H} NMR
spectrum of 1 consists of two AB doublets at δ Ϫ7.21 and
3.03, each split by 333.2 Hz, and the proton NMR contains
an IrH triplet which shows equal cis coupling (14.8 Hz) to
the two 31P nuclei and has a chemical shift, δ Ϫ8.88, that
appears to be characteristic of the presence of trans-H–Ir–CO
units in carbonyl hydrido complexes of the general type
materials a similar reaction sequence should allow one to find
᎐
access to ring-opened products of the type [IrH(C᎐CH) (CO)-
᎐
2
(PPh3)(‘PN(R)H’)], resembling the previously reported hydrido-
dichloro derivatives [IrHCl2(CO)(PPh3)(η1-PN(Me)H’)]1b and
[IrHCl2(CO)(PPh3)(η1-‘POH’)],1c whose significance arises from
the observation that they exist as Ir–‘PN(Me)H’ and Ir–‘POH’
rotamers stabilized not only by “classical” intramolecular
IrCl ؒ ؒ ؒ HN or IrCl ؒ ؒ ؒ HO hydrogen bonds but also by “non-
classical”3–5 IrHδϪ ؒ ؒ ؒ δϪHO interactions. Reactions occurring
between the chelated anilido complexes [M(CO)(PPh3)(‘PNR’)]
[IrH(X)(Y)(CO)(PR3)2].7–9
Under the conditions chosen for the PhC᎐CH reaction, the
᎐
᎐
formation of 1 was accompanied by the ring-opened hydrido
1
᎐
bis(alkynyl) complex [IrH(C᎐CPh) (CO)(PPh )(η -‘PN(Me)-
᎐
2
3
† Coordination chemistry of functional phosphanes. Part 9.1a Dedi-
cated to Professor Dr W.-P. Fehlhammer on the occasion of his 60th
birthday.
Supplementary data available: rotatable 3-D crystal structure diagram in
CHIME format. See http://www.rsc.org/suppdata/dt/1999/3935/
H’)] 2 as a minor product which we were unable to separate
from 1, even after repeated attempts at purification using frac-
tional crystallization or chromatography; product ratio 1/2 ca.
7:3 (from 31P NMR). It is not clear whether 2 results from 1 by
J. Chem. Soc., Dalton Trans., 1999, 3935–3939
This journal is © The Royal Society of Chemistry 1999
3935

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Fig. 1 Temperature dependence of the spin–lattice relaxation times,
T1, of 1, 2a, and 2b at 400 MHz.
isomers could only arise from the involvement of the dangling
methylamino substituent in hydrogen bonding to the cis-located
Ir–H bond. Such interactions can be probed easily by the use of
1H NMR NOE and variable temperature T1 measurements.10,11
For a nuclear Overhauser effect between any two dipole–dipole-
coupled nuclei to be detectable, the two nuclei need to be <≈3 Å
apart. This appears to be the case for molecules 2a, where
irradiation at the hydride resonance at δ Ϫ9.11 resulted in a 7%
NOE enhancement for the NH peak at δ 5.42, as opposed to 2b,
where no measurable enhancement was observed for the NH
region on selective irradiation of the hydride triplet at δ Ϫ9.48;
yet isomer 2a cannot be assigned a structure that differs from 2b
by tight N(Me)H ؒ ؒ ؒ HIr hydrogen bonding as measurements
of the spin–lattice relaxation times, T1, made at 400 MHz as a
function of temperature (Fig. 1) resulted in minimum T1 values,
T1(min), for the respective hydride ligands of 537 ms at 266 K for
2a and of 513 ms at 277 K for 2b. These are only slightly lower
(min)
than the T1
of 588 ms measured at 255 K for complex 1,
which lacks any acidic EδϪ–Hδϩ bond that could behave as the
proton donor toward Ir–H. Moreover, T1
(min)
values as low as
≈270 ms (at 400 MHz), in addition to NOE enhancements of
more than 10%, have previously been measured for iridium
complexes featuring unequivocal IrH ؒ ؒ ؒ HN bonding,4b,c
which clearly rules out the possibility of short Hδϩ ؒ ؒ ؒ HδϪ con-
tacts in 2a.
Hence, the H and 31P NMR spectral data observed for the
1
protonation of the amide function, followed by dissociation
of the Ir–N(Me)H bond and coordination of an additional
alkynyl ligand, or is formed in competition with 1 directly from
the [Ir(CO)(PPh3)(‘PNMe’)] starting complex by protolytic
cleavage of the Ir–N bond, which would produce the
two isomeric forms of 2 (see above) are most easily accom-
modated if the isomers are assigned structures in which the
Ir–H bond is always cis to two near-equivalent trans-located
phosphane ligands but can have either CO or C2Ph as the trans
ligand. The 13C NMR spectra of the product mixtures contain-
ing 1 and 2a/2b at 7:3 molar ratios are consistent with this view
1
᎐
monoalkynyl derivative [Ir(C᎐CPh)(CO)(PPh )(η -‘PN(Me)-
᎐
3
H’)] as an initial intermediate, prone to coordinate a second
α
᎐
β
2
᎐
as the Ir–C ᎐C Ph region exhibits a triplet split by 3.7 Hz at
᎐
equivalent of PhC᎐CH by oxidative addition. Two isomers, 2a
᎐
δ 109.18 (1) together with three weaker singlets at δ 109.55,
110.22, and 110.37, which are attributed to the equivalent or
non-equivalent carbon atoms Cβ of the trans- and cis-(PhC2)2Ir
forms 2a and 2b, respectively. The carbon atom σ-bonded to the
central metal of 1 gives rise to a well resolved triplet at δ 81.13
(cis-2J(PC) = 12.6 Hz); a less intense and less resolved triplet
(cis-2J(PC) ≈ 12 Hz), assignable to the predominant isomer a
of complex 2, is seen at δ 82.0. It is concluded that this reson-
ance arises from the two equivalent carbon atoms Cα of the
molecules with trans-(PhC2)2Ir geometry (2a), while the corre-
sponding signals caused by the two non-equivalent nuclei Cα
of the cis-(Ph2C)2Ir form (2b) remain unobserved due to the
distribution of intensity over two multiplets and the low con-
centration in solution of that geometric isomer.
and 2b, with separate IrH, NCH3, and NH signals are seen for
CDCl3 solutions of 2; 2a: δH Ϫ9.11 [1 H, t, cis-2J(PH) 15.6 Hz,
IrH], 2.55 [3 H, d, 3J(HH) 4.8 Hz, NCH3] and 5.42 [1 H, q (br),
NH]; 2b: δH Ϫ9.48 [1 H, t, cis-2J(PH) 16.8 Hz, IrH], 2.23 [3 H,
d, 3J(HH) 4.9 Hz, NCH3] and 5.09 [1 H, q (br), NH]; isomeric
distribution as estimated by 31P NMR: 2a, ≈80%; 2b, ≈20%. In
contrast to the formally analogous compounds [IrHCl2(CO)-
(PPh3)(η1-‘PN(Me)H’)] and [IrHCl2(CO)(PPh3)(η1-‘POH’)]
which NMR spectroscopy and X-ray crystallography showed to
exist as mixtures of Ir–PPh2C6H4N(Me)H-o and, respectively,
Ir–PPh2C6H4OH-o rotamers, stabilized by intramolecular
N(Me)H ؒ ؒ ؒ ClIr, OH ؒ ؒ ؒ ClIr, or OH ؒ ؒ ؒ H(Cl)Ir inter-
actions,1b,c neither of the two isomeric forms of complex 2
features such intramolecular hydrogen bonding.
Since metal-to-ligand bonds other than Ir–H that could act
as the weak base components toward the N–H bond as the
weak acid components are absent in 2a and 2b, conceivable
contributions to the preference for such sterically locked
Reactions with dimethyl acetylenedicarboxylate (dmad)
Combination of [Ir(CO)(PPh3)(‘PNMe’)] with dmad in toluene
solution at room temperature, followed by triturating the
3936
J. Chem. Soc., Dalton Trans., 1999, 3935–3939

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evaporated mixture with methanol resulted in the isolation of
[Ir{C2(CO2Me)2}(CO)(PPh3)(‘PNMe’)] 3 as the expected12 1:1
adduct, which is assigned an irida() cyclopropene structure
with the ring carbon atoms trans to two mutually cis-
coordinated phosphane ligands on the basis of IR and NMR
(31P, 13C) evidence. The behaviour of the alkyne as an oxid-
atively added “doubly σ-bonded” chelate ligand manifests itself
Ϫ1
᎐
in a lowering of the ν(C᎐C) wavenumber by ≈460 cm from
᎐
2248 cmϪ1 in free dmad to 1784 cmϪ1 in 3. The alkyne 13C nuclei
resonate at δ 93.60 and 96.93 as doublets of doublets with coup-
ling constants 2J(PC) of >60 Hz and <10 Hz, respectively, and
thus clearly identify the coordination of the ring carbon atoms
as trans with respect to two cis-bonded P donors. The small
2
value of 33.3 Hz observed for J(PP) is a further unequivocal
indication of the mutual cis orientation of the PPh3 and
‘PNMe’ ligands.
The analogous reaction between dmad and the rhodium()
complex [Rh(CO)(PPh3)(‘PNMe’)] resulted in insertion of the
acetylene into the Rh–N bond rather than oxidative addition,
forming the seven-membered metallaheterocycle [Rh{C(CO2-
Fig.
2
Molecular structure of [Ir{C(O)OMe}{C(CO2Me)᎐CH-
᎐
[C(O)OMe]}(PPh3)(‘PNH’)] 6. Selected bond lengths (Å) and angles (Њ)
with e.s.d.s: Ir–P(1) 2.3223(18), Ir–P(2) 2.3498(17), Ir–O(3) 2.262(4),
Ir–N 2.105(5), Ir–C(1) 1.985(6), Ir–C(5) 2.032(6), C(1)–O(1) 1.210(7),
C(1)–O(2) 1.367(7), C(3)–O(3) 1.253(8), C(3)–O(4) 1.328(8), C(6)–O(5)
1.199(8), C(6)–O(6) 1.314(8), C(3)–C(4) 1.433(9), C(4)–C(5) 1.342(8)
and C(5)–C(6) 1.494(9); P(1)–Ir–P(2) 168.38(6), P(1)–Ir–O(3) 92.7(1),
P(1)–Ir–N 79.4(1), P(1)–Ir–C(1) 91.9(2), P(1)–Ir–C(5) 94.1(2), P(2)–Ir–
O(3) 84.5(1), P(2)–Ir–N 89.6(1), P(2)–Ir–C(1) 92.2(2), P(2)–Ir–C(5)
96.2(2), O(3)–Ir–N 95.2(2), O(3)–Ir–C(1) 172.5(2), O(3)–Ir–C(5)
77.1(2), N–Ir–C(1) 91.6(2), N–Ir–C(5) 169.8(2), C(1)–Ir–C(5) 96.6(3),
Ir–C(1)–O(1) 128.1(5), Ir–C(1)–O(2) 112.2(5), Ir–O(3)–C(3) 108.7(4),
Ir–C(5)–C(4) 116.6(5), Ir–C(5)–C(6) 128.8(5), O(1)–C(1)–O(2)
119.6(6), O(3)–C(3)–O(4) 121.8(7), O(5)–C(6)–O(6) 124.2(7), O(3)–
C(3)–C(4) 122.0(6), O(4)–C(3)–C(4) 116.1(7), O(5)–C(6)–C(5) 124.2(7),
O(6)–C(6)–C(5) 111.7(6), C(3)–C(4)–C(5) 115.6(6) and C(4)–C(5)–C(6)
114.7(6).
Me)᎐C(CO Me)N(Me)C H PPh -2}(CO)(PPh )] 4. The struc-
᎐
2
6
4
2
3
ture assigned to 4 was easily deduced from (a) the 31P-{1H}
spectrum, indicating trans-positioned phosphane ligands
[2J(PP) 304.1 Hz], and (b) the 13C-{1H} NMR data which
revealed one metal-bonded ring carbon atom at δ 183.06 with
strong coupling to 103Rh [1J(RhC) 30.0 Hz] and two non-
equivalent 31P nuclei [cis-2J(PC) 18.9 and 11.7 Hz], accom-
panied by a non-coordinated vinylic carbon atom at δ 156.60
(d, J = 10.7 Hz) and a decoordinated methylamino function at
δ 38.08 (s).
The formation of the insertion product 4, where the central
rhodium atom retains the ϩ oxidation state, as opposed to
the irida()cyclopropene derivative 3, can be looked on as a
further example underscoring the decreased stability of the
higher oxidation states for the 4d than for the 5d metals, so that
in reactions of RhI and IrI complexes which may or may not
result in oxidative addition, the RhIII species are generally less
prone to form than the corresponding IrIII products.
While no reaction whatsoever occurred on combining
[Rh(CO)(PPh3)(‘PNH’)] with dmad in toluene, the homologous
iridium() complex was observed to sluggishly interact with the
alkyne, giving a 1:1 adduct together with quantities of
unchanged starting materials. The adduct was readily identified
as the metallacyclopropene complex [Ir{C2(CO2Me)2}(CO)-
(PPh3)(‘PNH’)] 5 on the basis of its spectral features which were
perfectly in line with those found for complex 3. In particular,
the triple-bond stretching frequencies of both compounds
were observed to be lowered by ≈460 cmϪ1 as compared to
the free alkyne, and the resonances of the ring 13C nuclei in
5 at δ 91.33 and 95.38 showed similar trans- and cis-
coupling [2J(PC) >70 Hz and ≈10 Hz, respectively] to two
non-equivalent cis-bonded phosphanes [2J(PP) ≈ 36 Hz] as
those in 3.
(‘PNH’)] 6, whose central metal bears a chelating vinyl ligand
which is coordinated through its α-carbon and a carbonyl
oxygen atom of an ester substituent, in addition to an anionic
methoxy(carbonyl) group and two unchanged PPh3 and ‘PNH’
ligands (Fig. 2). The bonding within the metallacycle, where
the CO2Me groups adopt a trans configuration with respect to
the C᎐C double bond can be considered to lie between two
canonical structures, A and B, as previously proposed for a
᎐
number of related vinyl metal complexes derived from dialkyl
acetylenedicarboxylates.13–17 For compound 6, both structural
and spectroscopic data indicate a significant contribution to
the electronic description of the molecule by the carbene-like
resonance structure B which tends to make the two carbon–
carbon bond lengths within the ring more similar, to shorten
the Ir–Cα bond, and to shift the resonance of the α-vinylic 13C
nucleus to lower field. Thus, the Ir–C(5) distance, 2.032(6) Å, is
short for an iridium-to-carbon σ single bond, typically ranging
from 2.13 to 2.20 Å in hexa-coordinate iridium() com-
plexes.18,19 The carbon–carbon bond lengths C(3)–C(4),
1.433(9) Å, and C(4)–C(5), 1.342(8) Å, differ by only 0.09 Å
and thus compare favorably to, e.g., the corresponding inter-
atomic distances of 1.44(2) and 1.32(2) Å measured for the
structurally related vinyl tungsten complex [W{C(CO But)᎐
Attempts to separate metallacycle
5 from unreacted
[Ir(CO)(PPh3)(‘PNH’)] and free dmad resulted in an
unexpected transformation as trituration of the crude solid
with methanol [i.e., the procedure that was successfully
employed in the purification of 3 (see above)] furnished a yellow
solid, displaying neither carbonyl nor alkyne stretching bands
in the infrared. Moreover, the proton NMR of this material
revealed the presence of three rather than two inequivalent
methoxy groups, suggesting that the methanol solvent had
reacted with the mixture. Since the exact nature of the product
so generated could not be elucidated in a straightforward
manner by means of vibrational and NMR spectroscopy, an
X-ray diffraction study was undertaken.
᎐
2
CH(CO2But)}(CO)(NO)(PMe3)], featuring significant carbe-
noid character,14 but are in sharp contrast to [Ru{C(CO2-
Me)᎐CH(CO Me)}(CO) (PMe Ph) ]ϩ, where carbon–carbon
᎐
2
2
2
2
The structure analysis revealed that treating the [Ir(CO)-
(PPh3)(‘PNH’)]/[Ir{C2(CO2Me)2}(CO)(PPh3)(‘PNH’)] mixture
with methanol had resulted in conversion into the iridium()
bond lengths of 1.49(3) and 1.31(2) Å point to the presence
of localized C–C single and double bonds within the five-
membered chelate ring.15 The 13C resonance of the metal-
bonded carbon atom, δ 193.84, is close to the chemical shift
complex [Ir{C(O)OMe}{C(CO Me)᎐CH[C(O)OMe]}(PPh )-
᎐
2
3
J. Chem. Soc., Dalton Trans., 1999, 3935–3939
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of δ 200.1 reported for the CH2 group of [Ir(᎐CH ){N(Si-
[Ir(CO)(PPh3)(‘PNMe’)]1b in 15 mL of toluene was treated with
᎐
2
Me2CH2PPh2)2}]20 and thus supports the formulation of 6 as
a “keto-vinyl↔enolato-carbene” resonance hybride; all the
more as the latter iridium complex has a carbene carbon trans-
bonded to an amido function, which is a structural feature of
6 as well. The Ir–C(O)OMe bond Ir–C(1), 1.985(6) Å, is rather
short by comparison to the related distances of 2.05(2) and
2.073(8) Å found in [IrI2{C(O)OMe}(CO)(bipy)]21 and [IrCl-
{C(O)OMe}(dmpe)2]O3SF22 and presumably reflects the weak
trans influence of the ester oxygen atom trans to C(1).
100 µL (1.05 mmol) of phenylacetylene and subsequently
stirred at 70 ЊC for 3 h. The cooled mixture was carefully
layered with pentane and allowed to stand at 5 ЊC for 3 d, which
caused the precipitation of the products as an inseparable
mixture of beige microcrystals [91 mg; product distribution
(estimated by 31P NMR): 1: 70%; 2a: 24%, 2b: 6%]. νmax/cmϪ1
᎐
᎐
≈1970w (sh), ≈1985m (sh), 2001vs and 2118vs (C᎐O,C᎐C and
᎐
᎐
IrH); δH(CDCl3) Ϫ9.48 [1 H, t, cis-2J(PH) 16.8 Hz, IrH of 2b],
Ϫ9.11 [1 H, t, cis-2J(PH) 15.6 Hz, IrH of 2a], Ϫ8.88 [1 H, t,
3
The formation of 6 can be accounted for by postulating
cis-2J(PH) 14.8 Hz, IrH of 1], 2.23 [3 H, d, J(HH) 4.9 Hz,
a reaction sequence that involves rapid insertion of MeO2C
NCH3 of 2b], 2.26 (3 H, s, NCH3 of 1), 2.55 [3 H, d, 3J(HH) 4.8
Hz, NCH3 of 2a], 5.09 [1 H, q (br), NH of 2b], 5.42 [1 H, q (br),
NH of 2a] and 6.2 to 7.7 (several m, C6H4 and C6H5);
δC(CDCl3) 21.46 (s, NCH3 of 2a), 29.89 (s, NCH3 of 2b), 30.35
᎐
C᎐CCO Me into a preformed Ir–H bond as a key-step. The
᎐
2
ease of alkyne insertion into the metal–hydride function to give
᎐
M–H/–C᎐C– addition products with cis or trans stereo-
᎐
2
᎐
chemistry has been demonstrated in numerous cases and, in
fact, represents a general route to metal–vinyl complexes.14,16,23
Although an iridium hydride could not be detected on combin-
ing [Ir(CO)(PPh3)(‘PNH’)] with methanol,24 we propose that
the iridium() complex and MeOH can react to form such a
species, e.g., [Ir(H)(OMe)(CO)(PPh3)(‘PNH’)], in an equi-
librium that, at room temperature, lies very far to the IrI side.
This view is consistent with the finding that complexes of the
type [Ir(H)(X)(OMe)(CO)(PR3)2] (formed from [Ir(OMe)(CO)-
(PR3)2] by oxidative addition of HX; X = halide) are actually
observable at low temperature but are unstable with respect to
reductive elimination of methanol at 20 ЊC.25 The σ-vinyl
(s, NCH of 1), 81.13 [t, cis- J(PC) 12.6 Hz, IrC᎐CPh of 1], 82.0
᎐
3
2
᎐
[t, cis- J(PC) ≈12 Hz, IrC᎐CPh of 2a], 109.18 [t, J(PC) 3.7 Hz,
IrC᎐CPh of 1], 109.55, 110.22 and 110.37 [all s (br), IrC᎐CPh
᎐
᎐
᎐
᎐
᎐
of 2a and 2b] (C6H4 and C6H5 resonances omitted; IrCO and
᎐
IrC᎐CPh of 2b not assigned; see main text); δ (CDCl ) Ϫ7.21
᎐
P
3
[1 P, AB-d, trans-2J(PP) 333.2 Hz, 1 (assignment to PPh3
or ‘PNMe’ uncertain)], Ϫ6.39 [2 P, apparent A2 singlet, i.e.,
∆ν Ӷ trans-2J(PP), 2b], 2.64 (2 P, apparent A2 singlet, 2a) and
3.03 [1 P, AB-d, PPh3 or ‘PNMe’ of 1].
[Ir{C2(CO2Me)2}(CO)(PPh3)(‘PNMe’)] 3. To a solution of
210 mg (0.27 mmol) of [Ir(CO)(PPh3)(‘PNMe’)] in 15 mL of
toluene 50 µL (0.41 mmol) of dmad was added via syringe.
After stirring for 1 h at ambient conditions, solvent was
removed in vacuo to leave the product as a yellow solid which
was purified by washing with 15 mL of methanol (215 mg, 87%)
[Found: C, 57.62; H, 4.19; N, 1.33. Calc. for C44H38IrNO5P2
intermediate [Ir{C(CO Me)᎐CH(CO Me)}(OMe)(CO)(PPh )-
᎐
2
2
3
(‘PNH’)], resulting from dmad insertion into the Ir–H bond
of the postulated hydride species, could undergo further trans-
formation by adding the ketonic oxygen atom of one of its ester
groups to the central metal to form the five-membered metal-
lacyclic ring and induce cleavage of the Ir–OMe bond.26
Subsequent nucleophilic attack by the methoxide ion on the
(914.94): C, 57.76; H, 4.19; N, 1.53%]. νmax/cmϪ1 1694s (C᎐O),
᎐
᎐
᎐
1784s (C᎐C) and 2003vs (C᎐O); δ (C D ) 2.76 (3 H, s, NCH ),
᎐
᎐
H
6
6
3
proposed cationic carbonyl [Ir{C(CO Me)᎐CH(CO Me)}(CO)-
3.09 (3 H, s, OCH3), 3.74 (3 H, s, OCH3), 6.6 (2 H, m), 6.9 (2 H,
m), 7.0 (1 H, m), 7.2 (12 H, m), 7.3 (4 H, m), 7.5 (6 H, m) and
8.3 (2 H, m) (all C6H4 and C6H5); δC(C6D6) 41.01 (1 C, s,
NCH3), 51.43 (1 C, s, OCH3), 52.22 (1 C, s, OCH3), 93.60 [1 C,
dd, trans-2J(PC) 69.1 Hz, cis-2J(PC) 9.0 Hz], 96.93 [1 C, dd,
᎐
2
2
(PPh3)(‘PNH’)]ϩ, which has ample literature precedence,26,27
would then give 6 as the final product. The quantitative con-
version by methanol of both constituents of the [Ir(CO)-
(PPh3)(‘PNH’)]/[Ir{C2(CO2Me)2}(CO)(PPh3)(‘PNH’)] mixture
into 6 is tentatively explained by postulating partial dissociation
of the irida()cyclopropene complex 5 into [Ir(CO)(PPh3)-
(‘PNH’)] and free dmad. Owing to the presence of a coordin-
ated amido function NHϪ in 5 which makes the central metal
less electron-rich than the the N-methyl amido group NMeϪ
in [Ir{C2(CO2Me)2}(CO)(PPh3)(‘PNMe’)] 3, metallacycle 5 is
expected to have a higher propensity for reductive elimination
than its homologue 3, since influences that arise from the
ligands and tend to decrease the electron density at the central
metal make for an increase in reducibility of the molecule.
2
2
᎐
trans- J(PC) 65.0 Hz, cis- J(PC) 6.0 Hz] (both C᎐C), 162.73
᎐
3
[1 C, t, cis-2J(PC) 8.3 Hz, IrCO], 163.80 [1 C, dd, J(PC) 10.1
2
and 7.6 Hz, C᎐O], 168.73 [1 C, d, J(PC) 26.0 Hz, CarylN] and
᎐
171.04 [1 C, dd, 3J(PC) 8.0 and 5.2 Hz, C᎐O] (C H resonances
᎐
6
5
and C6H4 signals other than CarylN omitted; arbitrary assign-
ments of IrCO and C᎐O, respectively); δ (C D ) 9.99 [1 P,
᎐
P
6
6
AB-d, cis-2J(PP) 33.3 Hz, PPh3] and 35.82 (1 P, AB-d, ‘PNMe’).
[Rh{C(CO Me)᎐C(CO Me)N(Me)C H PPh -2}(CO)(PPh )]
᎐
2
2
6
4
2
3
4. The preparation was carried out as described for 3 by treating
260 mg (0.38 mmol) of [Rh(CO)(PPh3)(‘PNMe’)]1b with 47 µL
(0.38 mmol) of dmad in 20 mL of toluene at room temperature
for 9 h. Yield: 225 mg (72%) of 4 as yellow microcrystals
[Found: C, 64.01; H, 4.62; N, 1.52. Calc. for C44H38NO5P2Rh
Experimental
General procedures
(825.65): C, 64.01; H, 4.64; N, 1.70%]. νmax/cmϪ1 1698s (C᎐O)
᎐
All manipulations were performed under nitrogen using
standard Schlenk techniques. Solvents employed were distilled
from the appropriate drying agents prior to use. IR spectra (in
KBr): Mattson Polaris. NMR spectra: Bruker DPX 300 (300.1
MHz for 1H, 75.5 MHz for 13C, 121.5 MHz for 31P) at 20 2 ЊC
with SiMe4 as internal or with H3PO4 as external standard
(downfield positive). Variable temperature T1 measurements
were made at 400.1 MHz (Bruker DRX 400) using the inversion
recovery method. X-Ray structure analysis: Enraf-Nonius
CAD 4 (λ = 0.71073 Å, T = 293 2 K); programs used for
solution and refinement: SIR-97,28 SHELXL-97.29
᎐
and 1974 (C᎐O); δ (C D ) 2.74 (3 H, s, NCH ), 2.92 (3 H, s,
᎐
H
6
6
3
OCH3), 3.29 (3 H, s, OCH3), 6.7 (2 H, m), 7.2 (17 H, m) and 7.9
(10 H, m) (all C6H4 and C6H5); δC(C6D6) 38.08 (1 C, s, NCH3),
50.07 (1 C, s, OCH3), 50.64 (1 C, s, OCH3), 156.60 (1 C, d, J 10.7
Hz, RhC᎐CN), 162.69 (1 C, d, J 1.9 Hz, C᎐O), 170.77 [1 C, dd,
᎐
᎐
3
2J(PC) 30.6 Hz, J(RhC) 2.7 Hz, CarylN], 172.10 (1 C, d, J 2.6
Hz, C᎐O), 183.06 [1 C, ddd, 1J(RhC) 30.0, cis-2J(PC) 18.9 and
᎐
1
11.7 Hz, RhC᎐CN] and 195.41 [1 C, ddd, J(RhC) 60.1, cis-
᎐
2J(PC) 15.4 and 12.3 Hz, RhCO] (C6H5 resonances and C6H4
signals other than CarylN omitted); δP(C6D6) 34.04 [1 P, dd,
1J(RhP) 145.4 Hz, trans-2J(PP) 304.1 Hz, PPh3] and 47.37 [1 P,
dd, 1J(RhP) 141.1 Hz, ‘PNMe’).
Preparations
᎐
᎐
᎐
[IrH(C᎐CPh)(CO)(PPh )(‘PNMe’)] 1 and [IrH(C᎐CPh) -
[Ir{C(O)OMe}{C(CO Me)᎐CH[C(O)OMe]}(PPh )(‘PNH’)]
᎐
2 3
᎐
3
2
(CO)(PPh3)(ꢀ1-‘PN(Me)H’)] 2 (as trans- and cis-(PhC2)2Ir
isomers 2a and 2b). A solution of 150 mg (0.19 mmol) of
6. The mixture of 200 mg (0.26 mmol) of [Ir(CO)(PPh3)-
(‘PNH’)]1b and 33 µL (0.26 mmol) of dmad in 15 mL of toluene
3938
J. Chem. Soc., Dalton Trans., 1999, 3935–3939

View Article Online
4 (a) S. H. Park, R. Ramachandran, A. J. Lough and R. H. Morris,
J. Chem. Soc., Chem. Commun., 1994, 2201; (b) A. J. Lough, S. H.
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Chem., 1996, 35, 3001.
5 (a) J. C. Lee, Jr., A. L. Rheingold, B. Muller, P. S. Pregosin and R. H.
Crabtree, J. Chem. Soc., Chem. Commun., 1994, 1021; (b) J. C. Lee,
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3285.
6 L. A. Villanueva, K. A. Abboud and J. A. Boncella, Organomet-
allics, 1992, 11, 2963, and refs. cited therein.
7 A. J. Deeming and B. L. Shaw, J. Chem. Soc. A, 1969, 1128.
8 B. L. Shaw and R. E. Stainbank, J. Chem. Soc., Dalton Trans., 1972,
223.
9 J. A. van Doorn, C. Masters and C. van der Woude, J. Chem. Soc.,
Dalton Trans., 1978, 1213.
10 (a) D. G. Hamilton and R. H. Crabtree, J. Am. Chem. Soc., 1988,
110, 4126; (b) R. H. Crabtree, Acc. Chem. Res., 1990, 23, 95.
11 M. T. Bautista, K. A. Earl, P. A. Maltby, R. H. Morris, C. T.
Schweitzer and A. Sella, J. Am. Chem. Soc., 1988, 110, 7031.
12 J. P. Collman and J. W. Kang, J. Am. Chem. Soc., 1967, 89, 844.
13 H. Werner, R. Weinand and H. Otto, J. Organomet. Chem., 1986,
307, 49.
14 A. A. H. van der Zeijden, H. W. Bosch and H. Berke,
Organometallics, 1992, 11, 563 and refs. therein.
15 J. R. Crook, B. Chamberlain, R. J. Mawby, F. C. F. Körber,
A. J. Reid and C. D. Reynolds, J. Chem. Soc., Dalton Trans., 1992,
843.
16 G. Hogarth and M. H. Lavender, J. Chem. Soc., Dalton Trans., 1994,
3389 and refs. therein.
17 K. A. Johnson, M. D. Vashon, B. Moasser, B. K. Warmka and W. L.
Gladfelter, Organometallics, 1995, 14, 461.
18 M. R. Churchill, J. C. Fettinger, W. M. Rees and J. D. Atwood,
J. Organomet. Chem., 1986, 304, 227 and refs. therein.
19 E. G. Lundquist, K. Folting, J. C. Huffman and K. G. Caulton,
Polyhedron, 1988, 21, 2171.
was stirred for 2 h at room temperature. Evaporation of all
volatile material left an oily residue consisting of unreacted
starting materials, together with the metallacyclopropene com-
plex [Ir{C2(CO2Me)2}(CO)(PPh3)(‘PNH’)] 5: νmax/cmϪ1 1697s
᎐
᎐
(C᎐O), 1788s (C᎐C) and 2002vs (C᎐O); δ (C D ) 51.40 (1 C, s,
᎐
᎐
᎐
C
6
6
OCH3), 51.72 (1 C, s, OCH3), 91.33 [1 C, dd, trans-2J(PC) 74.5
Hz, cis-2J(PC) 11.9 Hz], 95.38 [1 C, dd, trans-2J(PC) 92.7 Hz,
2
2
᎐
cis- J(PC) 8.9 Hz] (both C᎐C), 162.42 [1 C, t, cis- J(PC) 11.0
᎐
Hz, IrCO], 163.67 (1 C, virtual t, |3J(PC) ϩ 3J(PЈC)| 22.1 Hz,
C᎐O) and 171.91 (1 C, virtual. t, |3J(PC) ϩ 3J(PЈC)| 16.1 Hz,
᎐
C᎐O) (C H and C H signals not assigned; arbitrary assign-
᎐
6
5
6
4
ments of IrCO and C᎐O, respectively); δ (C D ) 10.83 [1 P, AB-
᎐
P
6
6
d, cis-2J(PP) 35.8 Hz, PPh3] and 39.02 (1 P, AB-d, ‘PNH’). The
mixture was then dissolved in 20 mL of methanol. Partial evap-
oration of solvent caused complex 6 to separate from solution
as orange crystals which were recystallized from toluene/
pentane (195 mg, 80%) [Found: C, 56.45; H, 4.31; N, 1.31. Calc.
for C44H40IrNO6P2 (932.91): C, 56.65; H, 4.32; N, 1.50%]. νmax
/
cmϪ1 1582vs, 1642vs, 1709vs (all C᎐O) and 3227w (NH);
᎐
δH(C6D6) 2.93 (3 H, s), 3.27 (3 H, s), 3.52 (3 H, s) (all OCH3),
4.73 [1 H, s (br), NH], 6.56 (1 H, dt, J 7.2 and 1.6 Hz, C6H4),
6.85 [1 H, s (br), ᎐CH (?)], 6.9 (1 H, m), 7.1 (3 H, m), 7.3 (13 H,
᎐
m), 7.40 [1 H, s (br)], 8.0 (8 H, m) and 8.4 (2 H, m) (all C6H4 and
C6H5); δC(C6D6) 50.43 (1 C, s), 50.95 (1 C, s), 52.22 (1 C, s) (all
OCH ), 122.78 (1 C, s, IrC᎐CH), 146.20 [1 C, t, cis-2J(PC) 7.6
᎐
3
Hz, IrCO2Me], 170.71 [1 C, dd, J(PC) 23.3 and 5.7 Hz, CarylN],
178.32 (1 C, s), 182.94 (1 C, s) (both CCO2Me) and 193.84 [1 C,
t, cis-2J(PC) 6.6 Hz, IrC᎐CH] (C H resonances and C H sig-
᎐
6
5
6
4
nals other than CarylN omitted); δP(C6D6) 24.16 [1 P, AB-d,
trans-2J(PP) 332.7 Hz, PPh3] and 38.62 (1 P, AB-d, ‘PNH’).
Crystal and refinement data for complex 6
C44H40IrNO6P2, M = 932.91, monoclinic, space group P21/n,
a = 13.320(1), b = 18.325(9), c = 16.197(1) Å, β = 98.093(7)Њ,
U = 3914(2) Å3, Z = 4, Dc = 1.583 Mg mϪ3, µ(Mo-Kα) = 3.543
mmϪ1; 8169 reflections collected, 6873 reflections unique
(Rint = 0.0378) which were used in all calculations; Rw = 0.0734
for all data, 490 parameters, and 0 restraints, R = 0.0422 for
4605 data with I > 2σ(I).
20 M. D. Fryzuk, P. A. MacNeil and S. J. Rettig, J. Am. Chem. Soc.,
1985, 107, 6708.
21 V. G. Albano, P. L. Bellon and M. Sansoni, Inorg. Chem., 1969, 8,
298.
22 R. L. Harlow, J. B. Kinney and T. Herskovitz, J. Chem. Soc., Chem.
Commun., 1980, 813.
23 J. M. Bray and R. J. Mawby, J. Chem. Soc., Dalton Trans., 1989, 589
and refs. therein.
2
24 The addition of methanol to solutions containing the 16e complexes
[M(CO)(PPh3)(‘PNR’)] (M = Rh, Ir; R = H, Me) actually results in
slow crystallization of the four compounds as analytically pure
samples.1b
CCDC reference number 186/1677.
See http://www.rsc.org/suppdata/dt/1999/3935/ for crystallo-
graphic files in .cif format.
25 J. S. Thompson, K. A. Bernard, B. J. Rappoli and J. D. Atwood,
Organometallics, 1990, 9, 2727.
Acknowledgements
26 (a) W. M. Rees and J. D. Atwood, Organometallics, 1985, 4, 402; (b)
W. M. Rees, M. R. Churchill, J. C. Fettinger and J. D. Atwood,
Organometallics, 1985, 4, 2179 and refs. therein. These contributions
demonstrate that the carbonylation of alkoxyiridium complexes to
give alkoxy(carbonyl) products occurs by displacement of alkoxide
from the coordination sphere, followed by nucleophilic attack of the
alkoxide on the cationic carbonyl.
Support of this work by the Fonds der Chemischen Industrie
(Frankfurt/Main) and by Degussa AG (Hanau) is gratefully
acknowledged. We are also indebted to Dr A. Zahl for measur-
ing the spin–lattice relaxation times, T1, of compounds 1 and 2
as a function of temperature.
27 A. Del Zotto, A. Mezzetti, G. Dolcetti, P. Rigo and N. Bresciani
Pahor, J. Chem. Soc., Dalton Trans., 1989, 607 and refs. therein.
28 A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, A. G. G.
Moliterni, M. C. Burla, G. Polidori, M. Camalli and R. Spagna,
SIR-97—A Package for Crystal Structure Solution by Direct
Methods and Refinement, Bari, Perugia and Rome, Italy, 1997.
29 G. M. Sheldrick, SHELXL-97—Program for Crystal Structure
Refinement (release 97-2), University of Göttingen, Germany, 1997.
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Paper 9/06430C
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