Journal of Molecular Catalysis, 48 (1988)
319 - 324
RHODIUM-CATALYZED HYDROFORMYLATION PHENYLPHOSPHITE LIGANDS ANNA M. TRZECIAK
and JOSEF J. ZI6EKOWSKI
Institute of Chemistry, University of Wrocfaw, 50-383
(Received November 24, 1987; accepted March 15, 1988)
activity of a series of rhodium(I) complexes - Rh(acac)and Rh(acac)(CO)(PPh,) (Hacac = acetylRh(acac)(CO), acetone), modified by phenylphosphites (P) containing CH3, NO2 or Cl substituents in the phenyl ring (P = P(OR)3; R = substituted phenyl ring) was examined in the hex-l-ene hydroformylation reaction (P = 1 atm, T = 40 “C). With Rh(acac)[P(OPh),12 used as the catalyst precursor, the structure of the modifying phosphite (P) has no influence on the reaction course. The activity of the systems based upon Rh(acac)(CO)z and Rh(acac)(CO)(PPh3) differ depending on the spatial structure of the modifying ligand (P). Three new complexes applied as the hydroformylation catalysts: Rh(acac)P, (P = (2-CH3C6H,0)$, (3-CH,C,9,0)sP, [3,5-(CH,),Cd_130]3p) were synthesized. P(Ow3129
Introduction The advantage of the rhodium(I) phosphite complex Rh(acac)[P(OPh),] 2 as hydroformylation catalyst precursor is its activity at 1 atm and 40 “C [ 11, In such conditions, after 4 h in a small excess of free phosphite (P(OPh)3:Rh = 1.3), the aldehydes were obtained from hex-1-ene with 70% yield and n/iso selectivity = 10 [ 11. In this paper we would like to address two problems: first, the influence of the structure of the catalyst precursor, and second, the role of the spatial and electronic structures of the modifying phosphite ligands (P). Rh(acac) [ P( 0Ph)3] 2, Rh( acac)(CO), (where substitution of CO by P(OPh)3 proceeds very rapidly ) and Rh(acac)(CO)(PPh,) were used as catalyst precursors. Seven phosphites (P) (Table 1) were used to study the steric hindrance effect of modifying ligands. Experimental Rhodium(I) complexes, applied as catalyst precursors, were obtained by the earlier described methods: Rh(acac)(CO)z [ 31, Rh(acac)[P(OPh)s] 2  and Rh(acac)(CO)(PPh,) [ 31. 0304-5102/88/$3.50
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R h(acac)N3-CHFdl,O) $12 To Rh(acac)(CO)s (0.04 g) (3-CH&H,O)Q (0.25 g) was added and left for 5 min. Next 1 ml &HsOH was introduced. The yellow precipitate formed was filtered off, washed with &H,OH and dried in’ uacuo. Yield 0.11 g (62%). ‘H NMR (CDCls): 1.46 (6H) acac CH,; 2.15 (18H); 5.05 (1H) acac CH; 6.90 (6H); 7.05 (18H). IR: no v(C0) bands in the range 1600 - 2100 cm-‘. UV-VIS (CHC1,):27800 (1900); 31500 (9600) cm-‘.
R~(~c~c)[(~,~-(CHJ)~C,H,OI~PI~ The same procedure as above was applied; 0.044 g of Rh(acac)(CO), and 0.21 g of [3,5-(CH,),C&I,0]sP were used. Yield: 0.07 g (41%). ‘H NMR (CDCI,): 1.5 (6H) acac CHs; 2.15 (36H); 5.05 (1H) acac CH; 6.65 (6H); 6.9 (12H). IR: no v(C0) bands. UV-VIS (CHCls):27900 (2400); 31600 (8300) cm-i. Rh(acac)[(2-CH,C,H,O),P],: To Rh(acac)(CO), (0.055 g) (2-CH&H40)Q (0.3 g) was added and the mixture was stirred under vacuum for ca. 10 min. The oil formed was washed with 5 ml HzO; next &HsOH (5 ml) was added and the stirring was continued until the precipitate settled (sometimes the oil had to be rewashed with water). The precipitate was filtered off and dried. Yield: 0.075 g (73%). ‘H NMR (CHCls): 1.3 (6H) acac CHs; 1.95 (18H); 5.0 (1H) acac CH; 6.9 (18H); 7.6 (6H). IR: no u(C0) bands. UV-VIS (CHCls): 27700 (2000); 31600 (9300) cm-l. Hydroformylation reactions at 1 atm were carried out in a thermostatted glass reactor; at 10 atm in a steel autoclave. Hydroformylation reaction products were examined by GLC and ‘H NMR. IR spectra were recorded on a Specord 75 IR spectrometer, electronic spectra on a Specord UV-VIS, ‘H NMR spectra on a Tesla BS 567 A 100 MHz spectrometer.
Results and discussion The results obtained for the catalyzed hydroformylation of hex-l-ene in the presence of substituted phosphites (P) are gathered in Table 1. Two trends are easily observed: with Rh(acac)[P(OPh)slZ used as catalyst precursor, the system has an almost constant activity, independently of which phosphite (P) was used in excess as modifying ligand. Two other complexes (Rh(acac)(CO)z a.nd Rh(acac)(CO)(PPhs)) achieved high activity only in the presence of phosphites less spatially expanded, i.e. (3CH&I&O)JP, [3,5(CH,),C,H,O)Q and (2ClC,H,O)Q.
30 20 25 33 33
10.0 5.4 7.4 5.2 5.0
sReactions carried out in toluene (0.65 ml) at 40 ‘C; [hex-1-ene] b[P] :[ Rh] = 1.1. c[P]:[Rh] = 3.1. dMol % with respect to the hex-1-ene used.
70 80 75 66 67
2-CH3CeH4 3CH3W4 3,5-(CH3)2W3 2,4,6-(CH3)3Wz 2,6(CH3)2CdH3
P(OR)a, R =
30 31 -
= 3.2 mmol (0.4 ml); [Rh] = 2.5
24 70 63 -
43 70 70 -
12 30 25 -
catalyst precursor, modified by substit-
Hydroformylation of hex-1-ene with application of Rh(acac)[P(OPh)a]z, uted phosphites at 1 atm*
P = (3~CH3CeH40)3P
*Reaction conditions - see Table 1.
Phosphorus ligand used in excess
n/is0 5 20
P = (2-CH3C&140)sP
Hy’droformylation of hex-l-ene with Rh(acac)Pz catalysts with addition of substituted phosphite P or P(OPh)sa
The more bulky phosphites seem unable to enter the coordination sphere of complexes Rh(acac)(CO), and Rh(acac)(CO)(PPh,) to form catalytically active species. Therefore we have examined the reactions of both rhodium complexes with all phosphites containing the methyl substituents. Thus three new complexes of general formula Rh(acac)P, were obtained, P = (2(3-MY34OM’,
We have failed, however, to isolate the compound containing [2,6(CH,),C&I,O]Q, which most likely, according to IR spectra still involves the CO ligand. Instead, the [2,4,6-(CH3)3C,J-I,0]3P phosphite does not react with Rh(acac)(CO)* even at elevated temperature. The structure of the new complexes with the substituted phosphites seems to be suitable for their performance as active catalysts; they are analogs of Rh(acac)[P(OPh),],. However, the composition of the complex does not warrant its high catalytic activity. The results achieved for hydroformylation of hex-lene complexes containing the substituted phosphites are presented in Table 2. Within that group is the surprisingly low activity of Rh(acac)[(2-CH,C,H40)Q]2 on application with (2-CH3C,H40)sP or with P(OPh), as modifying ligands. This could be easily understood by assuming that the steric hindrance around the rhodium due to the presence of the bulky phosphite prevents the coordination of the next phosphite molecule and formation of the active intermediate forms of a catalyst of the HRhP4 and HRh(CO)P3 type [51. TABLE
Catalyst precursor Rh(acac)[P(OPh)& at 10 atma P(OR)&
with addition of excess substituted phosphites P,
70 53 39 64 48 65 43 53 41 22 43 41 47 69
20 26 25 18 31 15 46 34 43 11 42 18 28 15
[Rhl 2-CH3C&14 3.CHGW4 3,5-(CH3)2C#3 2,4,6-(CH3)3GjH2 ~,~-(CHSZSHJ
5 10 5 10 5 10 5 10 5 10 5 10 5 10
aReactions in toluene (1.5 ml) 2 X low2 mmol. bMol% versus hex-1-ene used.
at 80 “c;
4.7 6.1 5.2 9.6 5.7 7.7 2.0
= 12 mmol
2.0 2.0 8.0 10.0 1.4 1.5 (1.5
Attempts at synthesis of the HRhP&pe rhodium hydride in reaction Rh(acac)P, + P + H2 (P = (2CHsCsH40)sP) failed, although the analogous reaction for P = P(OPh)s proceeds easily . Instead, the reaction Rh(acac)[(2-CH&H40)Q], + P(OPh)s + Hz produced a small amount of hydride, namely HRh[P(OPh)s],; for (3-CHsC,H40)sP and [3,5-(CH,),C&IsO]sP the mixed hydrides were always obtained. High catalytic activity of the system should not be expected when the formation of labile active complexes is limited by steric or other negative effects of the modifying ligands. Comparison of the results obtained in reactions with the substituted phosphites and with P(OPh)s revealed no special advantages of the substituted phosphites, at least in reactions at low pressure. Thus, a series of experiments was performed at elevated pressure (Table 3). Application of the substituted phosphite caused rather a decrease of the aldehyde yield, with no significant increase of the n/iso aldehyde ratio. Compared with P(OPh)s, the bulky phosphites seem to favor the isomerization rather than hydroformylation of olefins. References 1 A. M. Trzeciak and J. J. Ziblkowski, J. Mol. Catal., 34 (1986) 213. 2 R. van Eldik, S. Aygen, H. Keim, A. M. Trzeciak and J. J. Zitikowski, Tmnsition Metal. Chem., 10 (1985) 167. 3 F. Bonati and G. Wilkinson, J. Chem. Sot., (1964) 3156. 4 A. M. Trzeciak and J. J. Ziblkowski, Znorg. Chim. Acta, 64 (1982) L267. 5 A. M. Trzeciak, J. J. ZibIkowski, S. Aygen and R. van Eldik, J. Mol. Catal., 34 (1986) 337. 6 A. M. Trzeciak and J. J. Ziblkowski, Transition Metal. Chem., 12 (1987) 408.