Acid-base control of a migratory insertion reaction: p-Aminophenyl derivatives of ruthenium(II) and the crystal structure of Ru(η2-C[O]C6H4NH 2-4)Cl(CO)(PPh3)2

Article abstract of DOI:10.1021/om970714r

Addition of CO to Ru(C₆H₄NO₂-4)Cl(CO)(P-Ph₃) ₂ (1) gives Ru(C₆H_4NO2-4)Cl(CO)₂(PPh₃) ₂ (2), which upon reduction with Zn/HCl followed by treatment with base produces the η²-acyl complex Ru(η²-C[O]C₆H₄NH ₂-4)Cl(CO)(PPh₃)₂ (3), the molecular structure of which has been determined. Treatment of 3 with HBF₄ protonates the amino substituent and brings about a reverse migratory insertion reaction with the formation of [Ru-(C₆H₄NH₃-4)Cl(CO)₂(PPh ₃)₂]BF₄ (4). The process is reversible, and treatment of 4 with DBU returns 3.

Full text of DOI:10.1021/om970714r

Organometallics 1997, 16, 5135-5136
5135
Acid -Ba se Con tr ol of a Migr a tor y In ser tion Rea ction :
p-Am in op h en yl Der iva tives of Ru th en iu m (II) a n d th e
Cr ysta l Str u ctu r e of Ru (η2-C[O]C6H4NH2-4)Cl(CO)(P P h 3)2
George R. Clark, Warren R. Roper,* L. J ames Wright,* and V. Patricia D. Yap
Department of Chemistry, The University of Auckland,
Private Bag 92019, Auckland, New Zealand
Received August 12, 1997X
Sch em e 1
Summary: Addition of CO to Ru(C6H4NO2-4)Cl(CO)(P-
Ph3)2 (1) gives Ru(C6H4NO2-4)Cl(CO)2(PPh3)2 (2), which
upon reduction with Zn/ HCl followed by treatment with
base produces the η2-acyl complex Ru(η2-C[O]C6H4NH2-
4)Cl(CO)(PPh3)2 (3), the molecular structure of which
has been determined. Treatment of 3 with HBF4 pro-
tonates the amino substituent and brings about a reverse
migratory insertion reaction with the formation of [Ru-
(C6H4NH3-4)Cl(CO)2(PPh3)2]BF4 (4). The process is
reversible, and treatment of 4 with DBU returns 3.
The migratory insertion reaction involving a metal-
carbon σ-bond and an adjacent carbonyl ligand is a
central concept of organometallic chemistry and has
been extensively studied.1ab Finding simple ways of
controlling this process is an important goal. The
products of these insertion reactions may have the acyl
ligand bound in either an η1 or η2 mode, and the factors
which drive the migration reaction are both steric and
electronic in nature. Bulky substituents on the migrat-
ing σ-bound group, or sterically demanding accompany-
ing ligands, favor the acyl form,2 while substituents
which strengthen the metal-carbon bond (usually elec-
tron-withdrawing) favor the terminal carbonyl-alkyl (or
aryl) form.3ab
The migration reactions undergone by MRCl(CO)2L2
(M ) Fe, Ru, Os; L ) tertiary phosphine ligand) have
been studied extensively by Cardaci, and although direct
comparison with iron is not possible, because of a
different mechanism, the reaction rates follow the order
Fe < Ru >> Os.4 The alkyl (aryl)-acyl interconversion
is clearly facile for ruthenium(II) compounds, and we
have described previously the complexes Ru(p-tolyl)X-
(CO)2(PPh3)2 (X ) Cl, Br, I), which are in equilibrium
in solution with the acyl forms Ru(η2-C[O]p-tolyl)X(CO)-
(PPh3)2. In dichloromethane, X ) Cl favors the terminal
dicarbonyl-p-tolyl form and X ) I favors the acyl form.5
The structure of solid Ru(η2-C[O]p-tolyl)I(CO)(PPh3)2
has been confirmed by crystallography.6 In this com-
munication we now describe a system where this
equilibrium is controlled not by steric influences but
only by the electronic nature of a substituent on the
phenyl group. Replacement of the p-tolyl group by a
p-aminophenyl group in the above compounds produces
a situation where the electron-releasing NH2 group
gives the acyl form, but protonation of this function to
+
give the electron-withdrawing NH3 brings about an
immediate switch to the dicarbonyl-aryl form.
We have previouly reported the synthesis of the five-
coordinate complex Ru(C6H4NO2-4)Cl(CO)(PPh3)2 (1).7
Reaction with carbon monoxide occurs readily, forming
the six-coordinate dicarbonyl complex Ru(C6H4NO2-4)-
Cl(CO)2(PPh3)2 (2) (see Scheme 1). The reaction is
accompanied by a distinct color change; the five-
coordinate complex is bright red, while the six-coordi-
nate complex is a pale yellow-green, a color typical of
coordinatively saturated complexes. The IR spectrum
of 2 shows two bands at 1435 and 1339 cm-1, which are
assigned to the stretching vibrations of the nitro group.8
The bending mode of this group is observed at 850 cm-1
as a weak band. The p-nitrophenyl ligand exerts a
strong trans influence on the trans carbonyl ligand, and
2 readily loses carbon monoxide when it is under
vacuum, when it is heated in air as a solid, or when a
solution in toluene is heated. After 2 is heated in
toluene at reflux for several hours, the formation of 1
is confirmed by IR spectroscopy through the character-
istic ν(CO) band at 1937 cm-1. The electron-withdraw-
ing nature of the p-nitrophenyl ligand results in a strong
metal-carbon bond, and a solution IR spectrum of 2,
in dichloromethane, shows that the compound exists
only in the dicarbonyl form.
X Abstract published in Advance ACS Abstracts, November 1, 1997.
(1) (a) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987; pp 355-375. (b)
Berke, H.; Hoffmann, R. J . Am. Chem. Soc. 1978, 100, 7224-7236.
(2) Cardaci, G.; Bellachioma. G.; Zanazzi, P. Organometallics 1988,
7, 172-180.
(3) (a) Sugita, N.; Minkiewitz, J . V.; Heck, R. F. Inorg. Chem. 1978,
17, 2809-2813. (b) Cross, R. J .; Gemmill, J . J . Chem. Soc., Dalton
Trans. 1981, 2317-2320.
(4) Aubert, M.; Bellachioma, G.; Cardaci, G.; Macchioni, A.; Re-
ichenbach, G.; Burla, M. C. J . Chem. Soc., Dalton Trans. 1997, 1759-
1764.
In a previous report we have described reduction of
the nitro functionality in the complex Ru(C6H4NO2-
4)(η2-S2CNMe2)(CO)(PPh3)2 with zinc and hydrochloric
(5) Roper, W. R.; Wright, L. J . J . Organomet. Chem. 1977, 142, C1-
C6.
(6) Roper, W. R.; Taylor, G. E.; Waters, J . M.; Wright, L. J . J .
Organomet. Chem. 1979, 182, C46-C48.
(7) Clark, G. R.; Rickard, C. E. F.; Roper, W. R.; Wright, L. J .; Yap,
V. P. D. Inorg. Chim. Acta 1996, 251, 65-74.
S0276-7333(97)00714-0 CCC: $14.00 © 1997 American Chemical Society

5136 Organometallics, Vol. 16, No. 24, 1997
Communications
acid to form the corresponding (p-aminophenyl)ruthe-
nium complex.7 Using similar reaction conditions,
excess zinc and hydrochloric acid followed by base,
compound 2 also undergoes reduction to give the η2-acyl
complex Ru(η2-C[O]C6H4NH2-4)Cl(CO)(PPh3)2 (3) (see
Scheme 1). The electron-donating nature of the p-
aminophenyl ligand leads to a weakening of the metal-
carbon bond, and the migratory insertion reaction then
becomes favorable. The solid-state IR spectrum of 3
shows two very weak ν(CO) bands at 2035 and 1955
cm-1 and one strong ν(CO) band at 1910 cm-1
addition, an acyl ν(CO) band of medium intensity is
observed at 1526 cm-1
The solution spectrum, in
. In
.
dichloromethane, suggests that the ratio of the dicar-
bonyl complex to the acyl-monocarbonyl complex is less
1
F igu r e 1. ORTEP diagram of compound 3 (hydrogen
atoms except those on N omitted for clarity). Selected bond
distances (Å) and angles (deg): Ru-C(1), 1.799(3); Ru-
C(2), 1.958(3); Ru-P(2), 2.3691(9); Ru-P(1), 2.3704(9); Ru-
O(2), 2.375(2); Ru-Cl, 2.4786(8); N-C(6), 1.366(5); C(2)-
Ru-O(2), 31.68(9); P(2)-Ru-P(1), 177.21(3).
than 1:15. The amine protons, in the H NMR, appear
as a broad singlet at δ 3.9. This broad signal disappears
upon addition of deuterium oxide. The 13C NMR data
supports a η2-acyl formation. Only two downfield
signals are observed, both as triplets.8 These cor-
respond to the metal-bound carbonyl and acyl carbons,
respectively, which both couple to the phosphorus atoms
of the two mutually trans triphenylphosphine ligands.
The X-ray crystal structure determination of 3 confirms
the η2-coordination mode, and the structure is depicted
in Figure 1.9
When compound 3 is treated with excess HBF4, the
amino group is protonated and thereby becomes electron
withdrawing in nature. As a consequence, the aryl
group migrates back to the metal center, forming the
dicarbonyl complex 4. The solution IR spectrum of 4
shows that only the dicarbonyl complex exists in solu-
tion. Intense ν(CO) bands at 2040 and 1972 cm-1 are
observed. The 13C NMR spectrum of 4 shows three
downfield signals, each of which appears as a triplet.
These arise from the the two carbonyl ligands and the
metal-bound aryl carbon.8
Deprotonation of 4 was easily achieved by treatment
with the strong organic base 1,8-diazabicyclo[5.4.0]-
undec-7-ene (DBU), and the acyl monocarbonyl com-
pound 3 was recovered in excellent yield. This migra-
tory insertion reaction, therefore, could be manipulated
by simply adding acid or base (Scheme 1). In this
reversible process the steric effects remain essentially
constant and so it is the electronic nature of the para
substituent which determines the migratory aptitude
of the aryl ligand. Finally, we note that this facile
migratory insertion is not exhibited by the correspond-
ing osmium system, since Os(C6H4NH2-4)Cl(CO)2-
(PPh3)2 exists exclusively in this dicarbonyl form.10 The
synthesis and further reactions of this compound will
be reported subsequently.
(8) Selected spectroscopic data for 2-4 are as follows. 2: IR (KBr)
ν(CO) 2041 (s) and 1971 (s), ν(NO2) 1435 (ms) and 1339 (s), δ(NO2)
850 (w), δ(CH) 840 (w) cm-1 1H NMR (CDCl3, 400.1 MHz) δ 7.41-
;
7.22 (m, PPh3, C6H4NO2); 13C NMR (CDCl3, 100.6 MHz) δ 198.0 (t,
2J (PC) ) 12.1 Hz, CO), 193.7 (t, 2J (PC) ) 9.1 Hz, CO), 174.2 (t, 2J (PC)
) 12.6 Hz, C1), 144.7 (s, C4), 141.8 (s, C2 or C3), 119.6 (s, C2 or C3),
131.3 (t′11 J (PC) ) 46.3 Hz, PPh3 ipso-C), 134.1 (t′, J (PC) ) 10.1 Hz,
PPh3 m-C), 130.3 (s, PPh3 p-C), 127.9 (t′, J (PC) ) 9.1 Hz, PPh3 o-C). 3:
IR (KBr) ν(NH2) 3462 (w, br) and 3347 (wm, br), ν(CO) 2035 (w), 1955
(w), and 1910 (s), acyl ν(CO) 1526 (m), ν(CN) 1302 (wm) and 918 (ms),
δ(CH) 837 cm-1; 1H NMR (CDCl3, 400.1 MHz) δ 7.59-7.54, 7.36-7.23
(m, PPh3), 6.86 (d, 3J (HH) ) 8.6 Hz, 2,6-C6H4NH2), 6.09 (d, 3J (HH) )
8.6 Hz, 3,5-C6H4NH2), 3.9 (s, br, NH2); 13C NMR (CDCl3, 100.6 MHz)
δ 245.8 (t, 2J (PC) ) 8.0 Hz, η2-CO), 211.4 (t, 2J (PC) ) 16.6 Hz, CO),
150.3 (s, C1), 132.8 (s, C2 or C3), 125.5 (s, C4), 112.8 (s, C2 or C3),
131.9 (t′, J (PC) ) 45.3 Hz, PPh3 ipso-C), δ 134.3 (t′, J (PC) ) 11.1 Hz,
PPh3 m-C), 129.9, (s, PPh3 p-C), 128.0 (t′, J (PC) ) 10.1 Hz, PPh3 o-C).
Ack n ow led gm en t. We thank The University of
Auckland for the award of a Doctoral Scholarship and
The New Zealand Vice-Chancellors Committee for the
award of a William Georgetti Scholarship to V.P.D.Y.
The University of Auckland Research Committee pro-
vided grants-in-aid toward this work.
+
4: IR (KBr) ν(NH3+) 3133 (w, br), NH3 overtone 2590 (w, br), ν(CO)
-
2040 (s) and 1972 (s), δ(NH3+) 1623 (w), BF4 1091 (s, br), δ(CH) 803
cm-1; 1H NMR (CD3COCD3, 400.1 MHz) δ 13.13 (s, br NH3+), δ 7.56-
+
7.34 (mult, PPh3, 2,6-C6H4NH3 or 3,5-C6H4NH3+), 6.73 (d, 3J (HH) )
7.5 Hz, 2,6-C6H4NH3+ or 3,5-C6H4NH3+); 13C NMR (CD3COCD3, 100.6
MHz) δ 199.0 (t, 2J (PC) ) 12.6 Hz, CO), 195.1 (t, 2J (PC) ) 9.1 Hz,
CO), 163.8 (t, 2J (PC) ) 12.6 Hz, C1), 143.4 (s, C2 or C3), δ 131.8 (s,
C4), 121.97 (s, C2 or C3), 132.8 (t′, J (PC) ) 46.3 Hz, PPh3 ipso-C),
135.1, (t′, J (PC) ) 10.1 Hz, PPh3 m-C), 131.6 (s, PPh3 p-C), 128.8 (t′,
J (PC) ) 9.1 Hz, PPh3 o-C).
Su p p or tin g In for m a tion Ava ila ble: A fully labeled
diagram and tables of crystallographic data, data collection,
and solution and refinement details, positional and thermal
parameters, and bond distances and angles for 3 (10 pages).
Ordering information is given on any current masthead page.
(9) Crystals were obtained from CH2Cl2/EtOH by the isopiestic
method. Crystal data for 3 (from 25 reflections, 11.5° < θ < 12.7°):
triclinic, space group P1h, a ) 12.104(1) Å, b ) 13.565(2) Å, c ) 13.700-
(6) Å, R ) 66.17(2)°, â ) 78.85(2)°, γ ) 68.450(10)°, V ) 1911.2(9) Å3;
Z ) 2, Dcalcd ) 1.406 g cm-3, (µ(Mo KR) ) 0.602 mm-1); crystal size
0.29 × 0.19 × 0.14 mm; Enraf-Nonius CAD4 diffractometer, Mo KR
radiation (0.710 69 Å), graphite monochromator, T ) 295(2) K, ω/2θ
scans, maximum 2θ 54°, 8690 reflections measured, 8333 independent
with R(int) ) 0.0369, intensity data corrected for Lorentz and polariza-
tion effects. An empirical absorption correction (ψ scans, transmission
range 0.952-0.998) was applied.12 The structure was solved by direct
methods (SHELXS-86);13 atomic coordinates and anisotropic thermal
parameters were refined by full-matrix least squares on Fo2 (SHELXL-
96).14 Positions of all hydrogen atoms were located crystallographically
and refined with isotropic thermal parameters. R ) 0.0358 for I > 2σ-
(I), wR2 ) 0.0902. R indices (all data): R ) 0.0619, wR2 ) 0.1008;
reflections/restraints/parameters ratio 8333/0/604; residual electron
OM970714R
(10) Roper, W. R.; Wright, L. J .; Yap, V. P. D. To be submitted for
publication.
(11) Maddock, S. M.; Rickard, C. E. F.; Roper, W. R.; Wright, L. J .
Organometallics 1996, 15, 1793.
(12) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr.
1968, A24, 351.
(13) Sheldrick, G. M. SHELXS-86. Crystallographic Computing 3;
Sheldrick, G. M., Ed.; Oxford University Press: Oxford, U.K., 1995; p
175.
density +0.848/-0.687 e Å-3. wR2 ) [Σw(Fo - Fc2)2/Σw(Fo2)2]1/2; w-1
(14) Sheldrick, G. M. SHELXL-96; University of Go¨ttingen, Go¨ttin-
gen, Germany, 1996.
2
2
) σ2(Fo2) + (0.0602P)2 + 0.5257P, where P ) (Fo + 2Fc2)/3.