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Some reactions of iridium(III) cations with unsaturated ligands: formation of carbene and iminoether complexes
Journal of Organometailic
Cl7
Chemistry, 47 (1973) C17-C20 0 Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands
Preliminary communication Some reactions of iridium(II1) cations with unsaturated ligands: fcrmation of carbene and imino-ether complexes
H.C. CLARK and L-E. MANZER
Department ofChemistry,
University
of Westew
Ontario,
London.
Ontario
(ck~&~)
(Received October 9th, 1972)
SUMMARY
Several reactions of iridium(II1) cations with terminal acetylenes and pentafluorobenzonitrile in methanol have yielded methoxy carbene and imino-ether complexes. It is suggested that n-donation either from the carbene hetero-atoms or from the metal is not an important factor in the stabilization of carbene complexes_ As a result of the many recent studies’ of transition metal organometallic /R complexes containing the “carbene” ligand, =C, , the actual importance of M& + Lp, R’ bonding to stabilize these complexes has been questioned. The fact that several stable carbene complexes of metals in high oxidation states have now been prepared2-7 suggests that such n-bonding is not entirely necessary. In this communication we describe the preparation of several carbene complexes of iridium(II1) and other related compounds. The iodide in I, Q = PMez Ph or PMePh, is labile due to the high fans influence of methyl group’ and may readily be removed by the silver salt of a non-coordinating anioxi in methanol or-acetone to give a stable solvent cation II,
(PF,$ Sol=
MeCMe
a-
MeOH
I
(II
The addition of a molar equivalent of the acetylene I-butyn-4ol rapidly leads to the formation of carbene complex III via an intramolecular rearrangement9 .
PF, PP, Pf:, BPh,
PMePh,
PMe, Ph
PMe, Ph
PMe, Ph
1.96 1.90
NH=C[OMc)C,F, ~-_
2.09 1.97
=C(OMe)Me
---
2.12 2.00
2032
6(P-Me)
0.52 0.53 0.83
7.8 9.3 9.2 8.0 8.2 8.2 -_-
0.67
9.0
-
6(OCM,)3.49
7.1
s(OCH,)4*70t 6(OCCH, 10.96p
a(OCH,)4.85t, sK!-CH,) 6(OCCH,)0.96p
6(OCH,)3.91 6(CH,)1.41
..
Other
1.2
7.5
7.0
J(P-H)
Iridium methyl
S(lr-Me) J(P-H) b ---_______.--_
Phosphirle methyls
=&l,CHJH,d
p=EgqE$
L
1.8%
a Spectra were recorded using C!H,CI, at internal lock and reference signal. Chemical shifts are given in ppm downfield from TMS and coupling constants arc given in hertz. t = triplet, d = doublet, p = pentct. b zJ + 4J(PN) is quoted!see ref. 10).
z-
Q
NMR DATA@ FOR CATIONIC fKfDIUM(IIl) COMPLEXES
TABLE !
cs &l
Cl9
PRELIMINARYCOMMUNICATION
!
Q\“ie2
oc4\Q
(PF6)
+
HCEC-
,CH,CI~,-OH
-
(PF6)
SOI
(II)
The 1 H NMR spectra (see Table 1) of the carbene cations support the structure shown. The iridium methyl group appears as a triplet due to couplingwith the two phosphines, the phosphine methyl resonances (where Q = PMe2 Ph) appear as overlapping triplets indicating “virtually”
coupled trans-phosphines”
and the absence of a plane of
symmetry through the P-Ir-P axis. The (Yand y hydrogens of the carbene appear as triplets and the 0 hydrogens appear as a pentet. A similar reaction occurs with II, Q = PMePhz and H-Cx--H the methylmethoxycarbene ‘Me-Ir+-Sol
in methanol
to give
IV. MeOH
H-CEZC-H
+
,% Me-Ir+-C \
KU
0CH3
mc)
The mechanism of this reaction has been extensively
investigated for platinum
complexes* and presumably is also applicable in the present case. Initial coordination of the acetylene to the iridium cation (V), H- migration, with the formation of an ‘*iridium stabilized carbonium ion” (Vl), and nucleophilic c” Me-h-~
Me--Ir--b--04,
-
(SF)
attack by methanol gives the carbene (VII). MeOH
(XI,
,=Hs Me--It-+--C
\
0CH3
czu)
The only other carbene complexes of transition metals in high oxidation states have utilized chelating carbenes’ 74-6 or carbenes with good heteroatom substituents such as amines v6,7 which are capable of donating electron density into the vacant carbene carbon 2p, orbital to enhance their stabilities. For most low-valent methylmethoxycarbene complexes’ the carbene carbon-oxygen stretching frequencies are in range - 1250 cm-’ . If n-bonding was important, an increase in
on oxidation to compensate for the loss of Md, --f C2pz bonding. However, *he observed for the IrIn complexes (12501260 cm-’ ) are typical of other
values of
meeylmethoxycarbenes. carbon C2p, orbital
Hence, these results suggest that n-bonding into the carbene
(whether
from the metal or heteroatom)
is not responsible for the
stability of transition me+-carbene complexes. Perfluoroaryl nitriles react with methyl platinum cations4 Ys**’ in methanol
MO-ether which Ip
the
to give complexes. These reactions also proceed via a n-bonded intermediate” , in CEN group is activated towards nucleopbilic attack. This is a smooth reaction for
to give the imino-ether
complex
IX in good yield.
c20
PRELIMINARY
COMMUNICATION
*,~,a (PF6)
i
oc~li~o SOI
+
C6F5-CSN
CPF6)
i
These reactions emphasize the similarity of the methyliridium(111) and methylplatinum(I1) cations, as well as the generality of the carbonium ion mechanism for carbene formation from terminal acetylenes. It should be noted that the reaction involves initial n-coordination of the acetylene to the cation; provided the relative energy levels of the acetylene and metal are suitable, carbene formation results..However if the energy separation of the metal “spd” hybrid orbit& and acetylene pn orbitals is too great, only weak association takes place and polymerization occurs more rapidly than the rearrangement required for carbene formation, as noted for several PtN cations’. We have attempted several reactions with terminal acetylenes, silver hexafluorophosphate and trans-I~CG)Cl[PMePh?], and have been unable to isolate carbene complexes. Gtber workers’2~‘3 have isolated quite stable cationic acetylenic complexes of Irr for which the low values of V&X) (- 1800 cm-’ ) suggest that there is sufficient Mdn + Ln* bonding to stabilize the n-bonded acetylene, preventing the achievement of carbonium ionreactivity, and hence preventing intramolecular rearrangement and carbene formation. ACKNOWLEDGMENTS
We are grateful for the award of a Scholarship (to L.E.M.) and for financial support of this work from the National Research Council of Canada. REFERENCES 1 For a review of carbine complexes see F-A. Cotton and CM. Lukehart, Prog. Inorganic Chem., (i972) in press. 2 M-H. Chisholm and H.C. Clark, .f. Amer. tiem. Sot., 94 (1972) 1532. 3 M.F. Lappert and A-J. Oliver, C/rem Common., (1972) 274. 4 H-C. Uark and L.E. Manzer, Inorg. Chem. 11 (1972) in press. 5 H-C. Clark and L.E. Manze‘r, Zrrorg. Chem, in press. 6 A.L. Balch, 3. Organometal. Chem, 37 (1972) C19. 7 B. Cetinkaya, M.F. Lappert and K. Turner, Chem. Gommun., (1972) 85 1. 8 T.G. Appleton, H-C. Clark and L.E. Manzer, Coord. Chem. Rev., in press. 9 M.H. Chisholm and H.C. Clark, Inorg. Cfzem., 10 (1971) 1711. I.0 R.K. Harris, Gzn. f. Chem., 42 (1964) 2275. . 11 -H-C!.Clark and L.E. Manzer, Inorg. Chem., 10 (1971) 2699. 12 A.J. Deeming and B-L. Shaw, 3. Chem Sot. A, (1971) 376. 13 M.J. Church, M-J. Mays. R-N-F. Simpson and F.P. Stefani?i, J. Chem. Sot. A, (1970) 2909.
Cl7
Chemistry, 47 (1973) C17-C20 0 Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands
Preliminary communication Some reactions of iridium(II1) cations with unsaturated ligands: fcrmation of carbene and imino-ether complexes
H.C. CLARK and L-E. MANZER
Department ofChemistry,
University
of Westew
Ontario,
London.
Ontario
(ck~&~)
(Received October 9th, 1972)
SUMMARY
Several reactions of iridium(II1) cations with terminal acetylenes and pentafluorobenzonitrile in methanol have yielded methoxy carbene and imino-ether complexes. It is suggested that n-donation either from the carbene hetero-atoms or from the metal is not an important factor in the stabilization of carbene complexes_ As a result of the many recent studies’ of transition metal organometallic /R complexes containing the “carbene” ligand, =C, , the actual importance of M& + Lp, R’ bonding to stabilize these complexes has been questioned. The fact that several stable carbene complexes of metals in high oxidation states have now been prepared2-7 suggests that such n-bonding is not entirely necessary. In this communication we describe the preparation of several carbene complexes of iridium(II1) and other related compounds. The iodide in I, Q = PMez Ph or PMePh, is labile due to the high fans influence of methyl group’ and may readily be removed by the silver salt of a non-coordinating anioxi in methanol or-acetone to give a stable solvent cation II,
(PF,$ Sol=
MeCMe
a-
MeOH
I
(II
The addition of a molar equivalent of the acetylene I-butyn-4ol rapidly leads to the formation of carbene complex III via an intramolecular rearrangement9 .
PF, PP, Pf:, BPh,
PMePh,
PMe, Ph
PMe, Ph
PMe, Ph
1.96 1.90
NH=C[OMc)C,F, ~-_
2.09 1.97
=C(OMe)Me
---
2.12 2.00
2032
6(P-Me)
0.52 0.53 0.83
7.8 9.3 9.2 8.0 8.2 8.2 -_-
0.67
9.0
-
6(OCM,)3.49
7.1
s(OCH,)4*70t 6(OCCH, 10.96p
a(OCH,)4.85t, sK!-CH,) 6(OCCH,)0.96p
6(OCH,)3.91 6(CH,)1.41
..
Other
1.2
7.5
7.0
J(P-H)
Iridium methyl
S(lr-Me) J(P-H) b ---_______.--_
Phosphirle methyls
=&l,CHJH,d
p=EgqE$
L
1.8%
a Spectra were recorded using C!H,CI, at internal lock and reference signal. Chemical shifts are given in ppm downfield from TMS and coupling constants arc given in hertz. t = triplet, d = doublet, p = pentct. b zJ + 4J(PN) is quoted!see ref. 10).
z-
Q
NMR DATA@ FOR CATIONIC fKfDIUM(IIl) COMPLEXES
TABLE !
cs &l
Cl9
PRELIMINARYCOMMUNICATION
!
Q\“ie2
oc4\Q
(PF6)
+
HCEC-
,CH,CI~,-OH
-
(PF6)
SOI
(II)
The 1 H NMR spectra (see Table 1) of the carbene cations support the structure shown. The iridium methyl group appears as a triplet due to couplingwith the two phosphines, the phosphine methyl resonances (where Q = PMe2 Ph) appear as overlapping triplets indicating “virtually”
coupled trans-phosphines”
and the absence of a plane of
symmetry through the P-Ir-P axis. The (Yand y hydrogens of the carbene appear as triplets and the 0 hydrogens appear as a pentet. A similar reaction occurs with II, Q = PMePhz and H-Cx--H the methylmethoxycarbene ‘Me-Ir+-Sol
in methanol
to give
IV. MeOH
H-CEZC-H
+
,% Me-Ir+-C \
KU
0CH3
mc)
The mechanism of this reaction has been extensively
investigated for platinum
complexes* and presumably is also applicable in the present case. Initial coordination of the acetylene to the iridium cation (V), H- migration, with the formation of an ‘*iridium stabilized carbonium ion” (Vl), and nucleophilic c” Me-h-~
Me--Ir--b--04,
-
(SF)
attack by methanol gives the carbene (VII). MeOH
(XI,
,=Hs Me--It-+--C
\
0CH3
czu)
The only other carbene complexes of transition metals in high oxidation states have utilized chelating carbenes’ 74-6 or carbenes with good heteroatom substituents such as amines v6,7 which are capable of donating electron density into the vacant carbene carbon 2p, orbital to enhance their stabilities. For most low-valent methylmethoxycarbene complexes’ the carbene carbon-oxygen stretching frequencies are in range - 1250 cm-’ . If n-bonding was important, an increase in
on oxidation to compensate for the loss of Md, --f C2pz bonding. However, *he observed for the IrIn complexes (12501260 cm-’ ) are typical of other
values of
meeylmethoxycarbenes. carbon C2p, orbital
Hence, these results suggest that n-bonding into the carbene
(whether
from the metal or heteroatom)
is not responsible for the
stability of transition me+-carbene complexes. Perfluoroaryl nitriles react with methyl platinum cations4 Ys**’ in methanol
MO-ether which Ip
the
to give complexes. These reactions also proceed via a n-bonded intermediate” , in CEN group is activated towards nucleopbilic attack. This is a smooth reaction for
to give the imino-ether
complex
IX in good yield.
c20
PRELIMINARY
COMMUNICATION
*,~,a (PF6)
i
oc~li~o SOI
+
C6F5-CSN
CPF6)
i
These reactions emphasize the similarity of the methyliridium(111) and methylplatinum(I1) cations, as well as the generality of the carbonium ion mechanism for carbene formation from terminal acetylenes. It should be noted that the reaction involves initial n-coordination of the acetylene to the cation; provided the relative energy levels of the acetylene and metal are suitable, carbene formation results..However if the energy separation of the metal “spd” hybrid orbit& and acetylene pn orbitals is too great, only weak association takes place and polymerization occurs more rapidly than the rearrangement required for carbene formation, as noted for several PtN cations’. We have attempted several reactions with terminal acetylenes, silver hexafluorophosphate and trans-I~CG)Cl[PMePh?], and have been unable to isolate carbene complexes. Gtber workers’2~‘3 have isolated quite stable cationic acetylenic complexes of Irr for which the low values of V&X) (- 1800 cm-’ ) suggest that there is sufficient Mdn + Ln* bonding to stabilize the n-bonded acetylene, preventing the achievement of carbonium ionreactivity, and hence preventing intramolecular rearrangement and carbene formation. ACKNOWLEDGMENTS
We are grateful for the award of a Scholarship (to L.E.M.) and for financial support of this work from the National Research Council of Canada. REFERENCES 1 For a review of carbine complexes see F-A. Cotton and CM. Lukehart, Prog. Inorganic Chem., (i972) in press. 2 M-H. Chisholm and H.C. Clark, .f. Amer. tiem. Sot., 94 (1972) 1532. 3 M.F. Lappert and A-J. Oliver, C/rem Common., (1972) 274. 4 H-C. Uark and L.E. Manzer, Inorg. Chem. 11 (1972) in press. 5 H-C. Clark and L.E. Manze‘r, Zrrorg. Chem, in press. 6 A.L. Balch, 3. Organometal. Chem, 37 (1972) C19. 7 B. Cetinkaya, M.F. Lappert and K. Turner, Chem. Gommun., (1972) 85 1. 8 T.G. Appleton, H-C. Clark and L.E. Manzer, Coord. Chem. Rev., in press. 9 M.H. Chisholm and H.C. Clark, Inorg. Cfzem., 10 (1971) 1711. I.0 R.K. Harris, Gzn. f. Chem., 42 (1964) 2275. . 11 -H-C!.Clark and L.E. Manzer, Inorg. Chem., 10 (1971) 2699. 12 A.J. Deeming and B-L. Shaw, 3. Chem Sot. A, (1971) 376. 13 M.J. Church, M-J. Mays. R-N-F. Simpson and F.P. Stefani?i, J. Chem. Sot. A, (1970) 2909.