COMMUNICATIONS
Table 1. Competitive reactivity of RhI complexes in oxidative addition
reactions.
aldehyde or MeI. The observed selectivity may be potentially
useful in reactions where substrates containing formyl groups
(and perhaps other groups with reactive nonpolar bonds) and
electrophilic centers in the same system are involved. An
example of high substrate selectivity in such mixtures is
described herein.
Complex Substrates[a]
Products
Molar ratio of
RCHO/MeI adducts[c]
1
2
MeCHO MeI MeCHO adduct 4
100:0
PhCHO MeI PhCHO adduct 12[b] 100:0
MeCHO MeI mixture of 6, 8, 9
PhCHO MeI mixture of 5, 8, 9
MeCHO MeI mixture of 6, 7, 8, 9
PhCHO MeI mixture of 5, 7, 8, 9
MeCHO MeI mainly 10
80:20
65:35
35:65
15:85
0:100
0:100
Received: October 9, 2000 [Z15928]
11
3
[1] a) J. P. Collman, L. S. Hegedus, J. R. Norton, R. G. Finke, Principles
and Applications of Organotransition Metal Chemistry, University
Science Books, Mill Valley, CA, 1987; b) J. P. Collman, L. S. Hegedus,
J. R. Norton, R. G. Finke, Principles and Applications of Organo-
transition Metal Chemistry, University Science Books, Mill Valley, CA,
1987, pp. 768 ± 775.
[2] H. Werner, J. Wolf, A. Höhn, J. Organomet. Chem. 1985, 287, 395.
[3] M. Aizenberg, D. Milstein, Chem. Commun. 1994, 411.
[4] H. Werner, M. Bosch, M. E. Schneider, C. Hahn, F. Kukla, M. Manger,
B. Windmüller, B. Weberndörfer, M. Laubender, J. Chem. Soc. Dalton
Trans. 1998, 3549.
[5] Crystallographic data (excluding structure factors) for the structures
reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication nos.
CCDC-150421 (1) and CCDC-150420 (4). Copies of the data can be
obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB21EZ, UK (fax: (44)1223-336-033; e-mail: deposit@
ccdc.cam.ac.uk).
[6] To the best of our knowledge, besides Rh complexes,[4] only two
complexes with h2-coordinated triflate to a single metal center have
been characterized: a) titanium: J. G. Donkervoort, J. T. B. H. Jastr-
zebski, B. J. Deelman, H. Kooijman, N. Veldman, A. L. Spek, G.
van Koten, Organometallics 1997, 16, 4174; b) silver: D. Gudat, M.
Schrott, V. Bajorat, M. Nieger, S. Kotila, R. Fleischner, D. Stalke,
Chem. Ber. 1996, 129, 337; c) the proposed h2 coordination of triflate
in the manganese complex (L. S. Stuhl, E. L. Muetterties, Inorg.
Chem. 1978, 17, 2148) may be incorrect, see ref. [6d]; d) for a review on
coordinated triflates, see: G. A. Lawrance, Chem. Rev. 1986, 86,
17.
PhCHO MeI mainly 10
[a] Reaction conditions: room temperature, benzene solution, molar ratio
of RCHO/MeI/RhI complex 10:10:1. [b] Complex 12, [(iPr3P)2Rh-
(OTf)(H)(COPh)], was synthesized analogously to 4.[12] [c] The ratio is
based on 31P and 1H NMR data. Compounds 7 and 9 are included in the
total ratio of the addition products of RCHO and MeI, respectively.
It is apparent that the four similar Rh complexes behave
very differently in the oxidative addition of aldehydes and
MeI. [(iPr3P)2RhOTf] (1) reacts selectively with aldehydes,
leaving MeI untouched, but [(Et3P)3RhCl] (3) reacts selec-
tively with MeI, leaving the aldehydes unconverted. Although
the reactions of [(iPr3P)2RhCl]2 (2) and trans-
[(iPr3P)2Rh(N2)Cl] (11) under the same conditions are not
selective, they exhibit opposite relative reactivity towards
aldehydes and MeI.
Further studies are required to determine the reasons for
the differences in reactivity and selectivity of the phosphane-
rhodium(i) complexes; however, a possible explanation is that
the oxidative addition of aldehydes requires a three-coordi-
nate, 14-electron RhI complex, whereas the oxidative addition
of MeI proceeds via the four-coordinate, 16-electron complex.
The oxidative addition of aldehydes to [(Me3P)3RhCl] was
shown to involve the 14-electron complex,[8] as were other
C H oxidative addition reactions to L3RhCl, which proceed
via a three-centered transition state.[21] On the other hand,
MeI reacts with L3RhCl by means of an SN2-type mechanism,
[7] G. M. Intille, Inorg. Chem. 1972, 11, 695.
[8] D. Milstein, Acc. Chem. Res. 1984, 17, 221, and references therein.
[9] a) D. Milstein, Organometallics 1982, 1, 1549; b) D. Milstein, J. Chem.
Soc. Chem. Commun. 1982, 1357; c) D. Milstein, J. Am. Chem. Soc.
1986, 108, 1336.
[10] C. Bianchini, A. Meli, M. Peruzzini, F. Vizza, Organometallics 1991,
10, 820, and references therein.
in which the four-coordinate complex is the active species.[17-
f, 17i, 22]
[11] K. Wang, T. J. Embe, A. S. Goldman, Organometallics 1995, 14,
4929.
The lack of reactivity of 3, and the lower reactivity of 11
with aldehydes than of 1 and 2, may be due to the ability of 1
and 2 to easily generate the three-coordinate species in
solution,[23] whereas phosphane dissociation from 3 and 11
may be more difficult.[24, 25] On the other hand, 3 reacts with
MeI even at low temperatures, since the generation of the
three-coordinate species is probably not required. Apparent-
ly, electron density at the metal center plays a key role in the
addition of MeI.[26] Compound 2 is more reactive than 1,
probably due to the chloride ligand being a better donor than
the triflate. Interestingly, the dimer 2 reacts preferentially
with aldehydes, whereas the monomer 11 reacts preferentially
with MeI. This result is in agreement with the greater ease of
formation of a three-coordinate complex with 2.[23a, 27]
This study demonstrates unprecedented ligand-controlled
selectivity of similar rhodium(i) complexes in classical oxida-
tive addition reactions. The reactivity of complexes of the type
[PnRhX] is strongly dependent on the number and nature of
the alkylphosphane (P) and the halide or triflate (X), and can
be selectively directed to the oxidative addition of an
[12] Selected spectroscopic data of compounds 4, 6, 8, 10, and 12. All NMR
spectra were measured on a Bruker DPX250 spectrometer at 258C in
C6D6. Frequencies used: 1H 250 MHz, 31P 100 MHz, 13C 62.5 MHz.
Standards: 1H NMR: C6D5H (d 7.15, internal); 31P NMR: H3PO4
(aq., 85%, d 0, external); 13C: C6D6 (d 128, internal). 4: 31P{1H}
NMR: d 47.2 (d, 1J(Rh,P) 129 Hz, 2P); 1H NMR: d 2.80 (s, 3H;
COCH3), 2.20 (m, 6H; PCH(CH3)2), 1.08 (dvt, J 7.2 Hz, 18H;
PCH(CH3)2), 1.00 (dvt, J 6.9 Hz, 18H; PCH(CH3)2), 19.23 (dt,
2J(Rh,H) 37 Hz, 3J(P,H) 10 Hz, 1H; RhH); IR (film): nÄ
1
1695cm (C O). The structure of 4 was confirmed by X-ray structure
analysis (Figure 2). 6: 31P{1H} NMR: d 48.1 (d, 1J(Rh,P) 127 Hz,
1
2P); H NMR: d 2.99 (s, 3H; COCH3), 2.32 (m, 6H; PCH(CH3)2),
1.18 (overlapped dvt, 36H; PCH(CH3)2), 15.49 (dt, 2J(Rh,H)
27.6 Hz, 3J(P,H) 9.8 Hz, 1H; RhH); IR (film): nÄ 1687cm
1
(C O). 8: 31P{1H} NMR: d 20.8 (d, 1J(Rh,P) 99.3 Hz, 2P);
1H NMR: d 2.95 (m, 6H; PCH(CH3)2), 1.23 (overlapped dvt, 39H;
PCH(CH3)2 and RhCH3); 13C{1H} NMR: d 3.77 (dt, 1J(Rh,C)
2
24.5 Hz, J(P,C) 5.6 Hz; RhCH3). The structure of 8 was confirmed
by X-ray structure analysis. 10: 31P{1H} NMR: d 19.3 (dt, 1J(Rh,P)
133.5 Hz, 2J(P,P) 26.8 Hz, 1P), 1.3 (dd, 1J(Rh,P) 94.7 Hz, 2J(P,P)
26.8 Hz, 2P); 1H NMR: d 2.20 (m, 12H; PRhP(CH2CH3)3), 1.62 (m,
6H; ClRhP(CH2CH3)3), 1.17 (m, 2J(Rh,H) 1.7 Hz, 3H; RhCH3), 1.00
(dt, 3J(P,H) 13.8 Hz, 3J(H,H) 6.8 Hz, 18H; PRhP(CH2CH3)3), 0.75
Angew. Chem. Int. Ed. 2001, 40, No. 6
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