Al2O3 interacting with CO, H2 and C3H6

Journal of Molecular Cafalysis, 24 (1984) 165 - 188

VIBRATIONAL INTERACTING

165

SPECTROSCOPY STUDIES WITH CO, Hz AND C,H,

OF CO~(CO)~(PPI&/AI,O~

S. I. WOO and C. G. HILL, JR. Department (U.S.A.)

of Chemical

Engineering,

University

of

Wisconsin, Madison,

WI 53706

(Received June 9, 1983; accepted September 23, 1983)

Summary Five wt.% of bis(triphenylphosphine)dicobalt hexacarbonyl supported on y-alumina (BDSA) was prepared by grinding Co,( CO),& PPh& and y-alumina together in a glove box. Raman and photoacoustic (PAS) bands of BDSA at room temperature in the range of wave numbers between 950 and 1600 cm-’ indicated an interaction of the phenyl groups in Co2(C0)6(PPh3)2 with hydroxyl groups on the surface of y-alumina. A new Raman band appeared at 1797 cm-’ and was assigned to a carbonyl species hydrogen-bonded to ’ hydroxyl groups on the surface of y-alumina. At elevated temperature under vacuum, this hydrogen-bonded species disappeared and the appearance of a partially decarbonylated species was identified by Raman spectroscopy. The BDSA was equilibrated with CO, Hz and C,H6 at room temperature, at 85 “C and at 170 “C. At 170 “C, the Raman and diffuse reflectance spectra of BDSA are both quite different from those of BDSA below 110 “C. Hydroformylation occurred at 170 “C and ambient pressure to produce aldehydes. The cobalt carbonyl species supported on y-alumina at 170 “C was no longer a dicobalt species; it had been converted into a tetrameric cobalt cluster. Similar results were observed under homogeneous reaction conditions.

Introduction Many heterogeneous catalysts are prepared by impregnating inorganic oxides with metal salts and then calcining and reducing these materials to obtain highly dispersed metal crystallites on the surface of inorganic oxides. Several researchers have reported the use of transition metal carbonyls for the preparation of dispersed metallic catalysts [ 1 - 51. Gerritsen et al. [6] have reported the preparation and characterization of a supported liquidphase rhodium catalyst which is active for the gas phase hydroformylation of propylene. Rony and Roth [7] prepared CO~(CO)~(PBU& supported on activated carbon by impregnation with CO~(CO),(PBU,)~ dissolved in chloroform. This supported catalyst is less active for the hydroformylation reaction 0304-5102/84/$3.00

0 Elsevier Sequoia/Printed in The Netherlands

166

than is its homogeneous counterpart dissolved in a liquid phase. Spek and Scholten [8] prepared Rh(a-C,Hs)CO(PPhs), adsorbed on y-alumina and found that it has catalytic activity for the gas-phase hydrogenation and hydroformylation of ethylene and propylene at atmospheric pressure and 60 - 90 “C. The ally1 ligand in Rh(7r-C,H,)CO(PPh3)2 supported on y-alumina is readily split off under process conditions to produce a coordinatively unsaturated compound. The results of Rony and Roth [7] and of Woo’s preliminary studies [9] of the hydroformylation reaction as catalyzed by bis(triphenylphosphine)dicobalt hexacarbonyl supported on y-alumina (BDSA), indicate that the CO ligand in CO~(CO)JPR&~ (R = C,Hs or C,H, would be labile and that it can be easily lost to produce a coordinatively unsaturated species. Previous studies utilizing infrared spectroscopy and temperature-programmed desorption have identified a relatively stable partially decarbonylated species [Mo(CO),(adsorbent)] in the case of molybdenum carbonyls adsorbed on y-alumina [lo, 111. No similar studies of phosphinated carbonyl compounds have been reported. Hence, Raman spectroscopy, diffuse reflectance spectroscopy, and photoacoustic spectroscopy (PAS) were used to study the adsorption of Co,(C0)6(PPhs)2 on yalumina. Interactions of this catalyst with CO, H, and propylene were also investigated.

Materials and methods Materials

A catalyst with 5 wt.% Co2(C0)6(PPh3)2 (Strem Chemicals, Newburyport, MA) on BDH y-alumina (BDH Chemicals Ltd., Poole, England), was prepared by careful grinding of these materials with a mortar and pestle in a glove box under nitrogen. (Impregnation was not successful, because Co2(CO),(PPh& is only sparingly soluble in either polar or nonpolar solvents.) Co,(CO),(PPh,)z is air stable and decomposes at 188 - 189 “C [U], hence, it should be stable during grinding. Prior to grinding, the BDH yalumina (100 m* g-l) was evacuated under 2 X lo-* torr overnight, heated to 278.5 “C for 10 h, and evacuated at room temperature. For the photoacoustic and the diffuse reflectance studies, undehydroxylated BDH y-alumina was used to prepare BDSA. Carbon monoxide (at least 99.99% pure) was obtained from Matheson (Chicago, IL) and purified by passage through a Cu-deoxo unit and a 5A molecular sieve. Hydrogen (99.95% purity) was further purified with a Pddeoxo unit and a 5A molecular sieve column. Propylene (Matheson CP grade) was purified in the same manner as carbon monoxide. Apparatus

The Raman spectrometer was a Spex Ramalog 5 (Model 14018) equipped with a third monochromator and coupled to a PDP 11/03 minicomputer. The excitation source was a Spectra Physics Model 164 argon ion

167

laser powered by a Spectra Physics model 265 exciter. Rated power output of all laser lines was 2 W. The green (514.5 nm) and blue (488.0 nm) lines had outputs of 800 and 700 mW, respectively. A Nicolet 7199 FTIR instrument was used for the PAS and diffuse reflectance studies. The PAS cell was purchased from Nicolet Instrument Company (Madison, WI) [13]. For the diffuse reflectance study, a vacuum chamber (Model KKK, Harrick Scientific Corporation, Ossining, NY) was used with a Model DRA-PMN (Harrick) diffuse reflectance attachment. A conventional vacuum system was used for sample pretreatment and evacuation and for introduction of adsorbates.

Results and discussion Interactions of Co,(CO),(PPh,), with the surface of y-alumina at room temperature The Raman spectrum of BDSA at room temperature in the range of wavenumbers between 150 and 450 cm-’ is shown in Fig. 1. A cobalt-tocobalt stretching band at 228 cm-’ is clearly evident. This band is 26 cm-l higher than that of unsupported Co2(CO),(PPh,)2. The Raman bands of BDSA in the range of wavenumbers between 950 and 1300 cm-’ (Fig. 2) contain information concerning the interactions of Co2(C0)6(PPh,)2 with hydroxyl groups on the surface of y-alumina and with the surface itself. This interaction was confirmed in the PAS spectrum (Fig. 3). The ring

h

202

d

266

167

214

cc>

266

1158

2$1

@I

(A)

228 h

172

267

rl'b

550

450

RAMAN

350

SHIFT

250

150

NM\ (B)

1250

RAMAN

(cni’)

I

1150

SHIFT

Fig. 1. Raman spectra of (A) BDSA evacuated at 7 5 “C, (C) unsupported Coz( CO)h(PPh&.

at room temperature,

Fig. 2. Raman Coz(Cok(PPh&.

on BDH y-alumina

spectra

II 1026

of (A) Co2(CO)6(PPh3)2

1050

950

(cr-ri’) (B) BDSA evacuated (950 - 1300 cm-‘),

(B)

168

-J 1700

1300

,

900

WAVENUMBER(d Fig. 3. PAS spectra of (A) Co2(C0)6(PPh&

on BDH y-alumina,

(B) Co2(C0)6(PPh&.

band of the phenyl groups in BDSA is shifted from 999 cm-’ for unsupported Co2(C0)6(PPh3)2 to 993 cm-‘, indicating that some of the 7relectrons in the phenyl ring are transferred to the hydroxyl groups of yalumina or to the surface itself. The medium intensity band (b, /3(CH) (al)) for the BDSA species is shifted from 1028.5 cm-’ to 1011.5 cm-‘. TheS notation describing the vibrational modes of motion is explained elsewhe?j? [14]. The strong band of BDSA (q, X-sensitive (al)) is shifted from 1096.5 cm-’ to 1095.5 cm-’ and is not sensitive to the n-electron density of the phenyl ring. The strong carbon-carbon stretching band (n, vcEc (b,)) is shifted from 1434 cm-’ to 1431.5 cm-‘. Another carbon-carbon stretching band (m, vcEc (al)) is shifted from 1482 cm-’ to 1479 cm-‘. The shifts mentioned above are all related to n-electron transfer to the y-alumina. The Raman-active CO stretching bands of BDSA at room temperature are compared with those of unsupported Co,(C0)6(PPh,)2 in Fig. 4. The bands at 2023 and 1922 cm-’ were broadened and not shifted much. However, a broad, strong band appeared at 1797 cm-‘. The pattern of the carbonyl stretching bands of BDSA is similar to that of unsupported Co2(CO),(PPh&, except for the carbonyl stretching band at 1797 cm-‘. Howe [15] has observed an intense carbonyl band at 1780 cm-’ for Mo(CO), adsorbed on a fully hydroxylated alumina support. He assigned this band to a CO ligand bridging two molybdenum centers, since no Lewis acid sites are available in this case. This assignment cannot be appropriate for the BDSA band at 1797 cm-‘, because the cobalt-to-cobalt stretching frequency does not change much and because the alumina surface contains Lewis acid sites. For Mo(CO), supported on y-alumina, Kazusaka and Howe [16 ] assigned the two lowest frequency infrared bands at 1590 and 1680 cm-* to carbonyl ligands interacting with Lewis acid sites. On the basis of these results, the most probable BDSA species at room temperature is a distorted Co2(CO),(PPh&. Some of the carbonyl ligands in Co,(C0)6(PPh3)2 are stretching

169

1

2150

I

1950

RAMAN

I

1750

SHIFT

1550

(cm’)

Fig. 4. Raman spectra of (A) Co2(C0)6(PPh3)z cm-‘), (B) Co2(COk(PPh&.

supported on BDH y-alumina (1550 - 2150

HETEROGENEOUS 17g°C

[

CO

A

1 1+

(COj2 PPh 3 4

C3H 7CHO+Cobalt

Prolonged time at 170°c

[I F

for

crystallite

above

SS°C

CO, Hp.

I

(n = 1,2.3,4)

Fig. 5. Surface species proposed for BDSA after various pretreatments.

hydrogen-bonded; this type of structure gives rise to the CO stretching band at 1797 cm-’ (Fig. 5). The PAS bands of BDSA at 20 “C are presented in Table 1. No strong bands are present near the band at 1797 cm-‘, which is assigned to a CO stretching species hydrogen-bonded to a hydroxyl group on the basis of the Raman spectroscopy data. This fact does not preclude the presence of

170 TABLE 1 CO stretching bands of BDSA under various pretreatment conditions Co2(COMPPh&

Co2(C0)e(PPh3)2 supported on y-alumina (BDSA)

PAS

DRS

PAS at 20 “C

DRS at 20 “C

2064(w, sh) 1972.5(s) 1936(s) 1899(s) 1810.5(m)

2064.5(w, sh) 2022(w, sh) 1938.5(s) 1899(s) 1810.5(m)

1951(s) 1899(w) 1814(w)

2065(w, sh) 1968.5(s, sh) 1956.5(s) 1899(m) 1848(w) 1830(w) 1810.5(w) 1776(m) 1757(w) 1738(w)

evacuated at 75’C (PAS)

evacuated at 140 ‘C (PAS)

evacuated at 200 “C (PAS1

1948(s) 1899(w) 1821(w)

1958(w,

b) nil

1670(w)

1711(w,

b)

PAS = photoacoustic spectroscopy DRS = diffuse reflectance Fourier transform infrared spectroscopy m = medium intensity band w = weak intensity band s = strong intensity band sh = shoulder b = broad band

hydrogen bonding, because different selection rules are applicable to Raman spectroscopy and infrared spectroscopy. The problem of spectral interpretation is further complicated by the fact that the range of wavenumbers for hydrogen-bonded CO stretching bands overlaps the locations of the rotational bands of physisorbed HzO. Interactions of Co2(CO)6(PPh,)2 with the surface of y-alumina evacuated at elevated temperatures BDSA was heated to 75 “C under 5 X low3 torr for 1 h. The CO stretching bands observed in the room temperature Raman spectrum of BDSA at 2023 and 1921 cm-’ decreased significantly in intensity, and a strong broad band appeared at 1898 cm-” with a shoulder at 1874 cm-’ (see Fig. 6). A new CO stretching band of medium intensity also appeared at 1693 cm-‘. In order to identify any changes in metallic bonding (Co-Co), the Raman bands of BDSA at 75 “C and 25 “C, and of supported Co2(C0)6(PPhJ2 were recorded (see Figs. 1 and 6). Unsupported Co,(CO),(PPh& has a v(Co-Co) band at 202 cm-’ and a Y(CO-P) band at 269 cm-‘. The intensity of the v(Co-P) band is slightly higher than that of the v(Co-Co) band. In the spectrum of BDSA at 20 “C, the v(CO-CO) intensity was greatly enhanced and its location was shifted to 228 cm-‘. This enh~cem~nt in intensity is attributed to the resonance Raman effect of metallic bonding caused by the interaction of metallic bonds with the surface of

171

-_

1

2150

1750

RAMAN

1350

SHIFT

950

(cr6’)

Fig. 6. Raman spectra of (A) Co2(C0)6(PPh& 75 “C for 1 h, (B) Co2(C0)6(PPh3)2.

supported

on BDH y-alumina

evacuated

at

y-alumina. The Raman spectrum of BDSA evacuated for 1 h under vacuum at 75 “C exhibited several new bands which were not observed in the spectrum of BDSA at 20 “C (Fig. 1). The cobalt-to-cobalt stretching band was
11

oL

po

\

z\

L! C

a

This structure suggests that the surface species looks like structure (C) in Fig. 5. Further evidence for the structure of the bridged carbonyl compound is contained in the carbonyl stretching bands observed at 1898, 1874 and 1693 cm-‘. The latter band is believed to be a bridged carbonyl stretching band associated with an A13+ site on the surface of y-alumina. The carbonyl stretching bands in the region between 1550 and 1800 cm-’ are characteristic of carbonyl ligands interacting with Lewis acids such as A1R3 [ 181. The coordination associated with bridging to a Lewis acid site decreases the CO stretching frequencies by 200 - 300 cm-l. This shift is comparable to that observed in the case of the bridged carbonyl frequencies of the Raman spectrum of BDSA at 75 “C where one has an uncoordinated phosphinesubstituted cobalt carbonyl compound. The stretching frequency for a bridging carbonyl ligand coordinated to AlBr, is 1600 cm-’ for Co2(CO)s, 1548 cm-’ for Fes(C0)r2 and 1535 cm-’ for RUDER. The band at 1693 to A1+3 sites cm-’ is believed to be a bridging carbonyl species coordinated

172 on

the surface of y-alumina. The other two bands observed at 1898 and 1874 cm-’ are also in the region of bridging CO carbonyl stretching bands. However, it is not likely that one could generate three different bridged carbonyl bands from highly symmetric precursor compoundsof the cobalt carbonyl type. This leads us to assume that one of these two bands might arise from a carbonyl species coordinated to an A1+3 site on the surface of y-alumina. One method of identification of weakly-coordinated species is to follow the change in the carbonyl stretching bands with varying temperature of pretreatment within a range which does not cause any significant changes in the structure or physicochemical properties of the surface of y-alumina. The effects of pretreatment temperature on carbonyl stretching band frequencies and on those related to the phenyl ring are presented in Table 2. From Fig. 7, it can be seen that the frequencies of the carbonyl stretching bands vary with temperature. Two frequencies are greatly affected by the-change in pretreatment temperature. These two carbonyl ligands are involved in TABLE 2 Effect of temperature on the Raman carbonyl supported on BDH y-alumina WaveRoom numbers temperature

stretching bands of Co2(CO)e(PPh&

75 “C for 1 h

1550

to 1799

for 2 h

for 3 h

not recorded

not recorded

1693(b, m)

110 “C for 5 h

170 “C for 12 h

1615 1624

1627

1646 1673(vb, m)

1813 1821 1923 2025

1835 1861 1979

1844(vb, vs) 1864(vb, vs)

not recorded

not recorded

963(vs, s j 1042(m, m) 1270(vb, m) 1321(sh)

with CO 170 “C c’

1797(b, s) 1800 to 2150

1874(b, s) 1898(b, s) 1921(b, w) 1923(sh) 2023(b, w) 2023(vw)

Other important bands

999(s, 1032(b, 1056(b, 1077(b, 1115(b, 1210(b, 1589(s,

s) s) s) s) w) w) m)

vb = very broad vs = very sharp s, s = sharp, strong b, s = broad, strong

995(s, 103O(s, 1042(s, 1075(m, 1093(m, 1183(m, 1230(m, 1245(m, 1319(m, 1421(m, 1589(s,

1886(b, s) 1843 1864 1923(sh) 1925 2022(vw) 2022

s) 306O(s, s) not m) recorded m) w) m) m) m) m) w) m) s)

173

75

110

TEMPERATURE

170

(“Cl

Fig. 7. Dependence of CO stretching frequencies of BDSA on pretreatment temperature: (I) linear stretching hand for CO coordinated to A13+ sites on the surface of y-alumina, (II) bridged stretching band for CO not coordinated to the surface of y-alumina, (III) bridged carbonyl species coordinated to A13+sites on the surface of y-alumina.

coordination with the Lewis acid Al’+ sites. This type of bonding is depenlent on the lattice vibrations and on the atomic spacing between the arbonyl ligand and the A13+ sites. These factors are significantly affected by Gemperature. The carbonyl stretching frequency of the carbonyl ligand which is not involved in the interaction with the surface of alumina should not vary much with temperature. The bridged carbonyl which does not interact with the surface of alumina exhibits this behavior. Terminal carbonyl stretching bands are usually located in the region of wavenumbers between 1900 and 2100 cm-i. The terminal carbonyl stretching band of species (C) in Fig. 5 would be present above 1900 cm-‘, if it did not coordinate with Lewis acid sites on the alumina surface. Furthermore, the dependence of the carbonyl stretching frequency on temperature indicates that this terminal carbonyl must be involved in coordination with A13+ on the surface of y-alumina. In order to identify any changes in the structure of the triphenylphosphine ligands, the bands relevant to the phosphine group were recorded. BDSA evacuated at 75 “C for 1 h has a strong ring-breathing band at 995 cm-’ which was shifted by 4 cm-’ from the 999 cm-’ location for BDSA evacuated at room temperature. Other relatively weak in-plane and out-ofplane deformation bands were also shifted by a small amount. The Fermi resonance band observed at 1589 cm-’ was not shifted. The BDSA evacuated at 75 “C for 2 h retained an aromatic C-H stretching band at 3060 cm-‘. This indicates that the phosphine group did not change its structure. The spectrum of BDSA evacuated at 110 “C for 5 h contains a high-intensity band at 1587 cm-‘. However, BDSA evacuated at 170 “C for 12 h exhibits a new broad, strong band at 963 cm-‘. This band still exists under 371 torr of

174

1525

1325

1125

,

925

WAVENUMBER(Cm’) Fig. 8. PAS spectra of (A) BDSA evacuated at 75 “C and of (B) Co2(CO),j(PPh&.

CO at 170 “C. The mass spectrum of the surface compound extracted from BDSA after equilibration with CO, H, and C3H6 at 170 “C indicates the presence of phosphine oxide. More convincing evidence is found in the PAS’ spectrum of BDSA evacuated at 75 “C for 24 h (Fig. 8). The pattern of ban4 between 950 and 1600 cm-’ is quite close to that of phosphine oxide excel for the absence of a strong v(P=O) band [ 191. On the basis of these resul, an interaction between a phosphorus atom and lattice oxygen was proposb in Fig. 5 (D). This interaction is not equivalent to the P=O bond in phos; phine oxide, hence a strong P=O stretching band was not observed even.. though perturbations due to lattice oxygen were noted. The presence of a Raman-active CO stretching band at 1979 cm-’ (well above 1900 cm-‘) leads one to propose the uncoordinated terminal CO species shown in Fig. 5 (D). BDSA evacuated under 10F2 torr at 75 “C for 24 h was placed in the PAS cell. Its CO stretching bands are compared with those of Co2(CO),(PPh,), in Table 1. When BDSA was evacuated at 75 “C for 24 h, a new CO stretching band appeared at 1670 cm-‘. Under the same pretreatment conditions, the Raman spectrum of BDSA has a CO stretching band at 1693 cm-’ which has been assigned to a bridged carbonyl species coordinated to a Lewis acid site, A1+3. Hence the surface compound proposed in Fig. 5 (C) is also consistent with the results of the photoacoustic study. Interactions of BDSA with CO, H2 and propylene BDSA evacuated at 170 “C for 12 h was equilibrated with 371 torr of CO at 170 “C for 7 h. The obvious change involves disappearance of the CO stretching band at 1979 cm-’ (Fig. 9). Subsequently, 215 ton of propylene and 279 ton of CO were equilibrated with BDSA at 170 “C for two days. The corresponding Raman spectrum is shown in Fig. 9 (C); band locations are summarized in Table 3. The broad strong band centered at 1844 cm-’ for BDSA at 170 “C under CO

175

I

I

I

1950

1750

1550

I

2150

RAMAN SHIFT (mi’) “ig. 9. (A) CO stretching bands of Coz(C0)6(PPh& supported on BDH y-alumina after retreatment at 170 “C for 12 h, (B) CO stretching bands of Co2(CO)e(PPhs)s supported c ‘1 BDH y-alumina and equilibrated with 371 torr of CO at 170 “C for 7 h, (C) CO st etching bands of Co2(CO)&PPh& supported on BDH y-alumina and equilibrated with \ torr of CO and 215 torr of propylene 27$!_ at 170 “C for 2 days. TABLE 3 Comparison

of Raman

bands of BDSA under various conditions

279 torr of CO and 215 torr of C3H6 at 170 “C

at 75 “C

at 20 “C

209 torr of CO, 161.3 torr of C3H6 and 372.3 torr of Hz at 20 “C for 5 h

1464(m, 1497(m, 1588(m, 1644(b, 1836(b, 1845(b, 1926(b, 2099(b,

w) w) m) s) s) s) VW) VW)

1437(b, w) 1597(m, s) 1643(b, s) 1845(m, vs) 2049(m, w)

145O(s, m) 1584(s, s) 1665(s, s) 1867(s, vs) 204O(vw)

1448(m, 1484(m, 1597(m, 1659(m, 1863(m,

at 85 “C for 18 h w) w) vs) m) vs)

1463(b, 1498(b, 1598(m, 1637(sh) 1843(b, 1952(b, 2034(b, 2121(b,

at 170 “C! for 18 h w) w) vs) s) w) w) w)

1476(s, 1909(s, 2097(vs, 2104(sh) 2144(b, 2170(b,

w) w) vs) w) w)

changed to a narrower strong band at 1845 cm-‘. There was some indication of carbonyl stretching bands at 2099 and 1926 cm-‘, but the signal-to-noise ratio was such that a definitive identification was impossible. The band at 1845 cm-’ can be attributed to a bridged carbonyl species which does not coordinate with the A13+ site or to a terminal carbonyl species which coordinates to the Al+3 site on the surface of y-alumina. The strong band at 1644 cm-’ is assigned to the bridged carbonyl band which coordinates to A13+ or

176

the C!=C stretching band of physisorbed propylene. However, propylene cannot be physisorbed on the surface of y-alumina at 170 “C. The suggestion that propylene directly interacts with the cobalt carbonyl species is based on the band at 1588 cm- ‘. This band is located in the v(C=C) region for olefin n-complexed to a transition metal [ 201. The low-frequency vibrational bands located between 150 and 250 cm-’ are similar to those of BDSA evacuated at 75 “C for 1 h. These Raman results suggest that after equilibration with 279 torr of CO and 215 torr of C,H, at 170 ‘C, the surface species has the structure of Fig. 5 (E). Subsequent to recording the Raman spectrum of BDSA evacuated at 170 “C, and equilibrated with 279 torr of CO and 215 torr of propylene at 75 “C!, hydrogen was introduced to give a gas mixture whose composition was 209 torr of CO, 372.3 torr of hydrogen, and 161.3 torr of propylene. BDSA was equilibrated for 5 h at 20 “C with this gas mixture, and a Raman spectrum recorded (Fig. lO( A)). The Raman spectra of this system at 85 “C and 170 “C are presented in Fig. 10(B) and (C), respectively. The changes in the spectrum at 170 “C are dramatic. The intermediate surface species associated with cobalt carbonyl covalently anchored to silica gel, {SIL-(CH,),(PPh,)&o,(CO),} at 108 “C under hydroformylation conditions is thought to: be HCo(CO),(SIL-PPhz)y on the basis of the observed carbonyl stretchin bands [21]. The possibility of forming HCo(CO),(PPh,), on the surface o“i alumina in the absence of any anchoring ligands is slim, because the carbony stretching bands recorded for our sample (2097 and 2104 cm-‘) are locat d PIn at frequencies which are too high relative to those of HCo(CO),(PPh&. addition, a cobalt-to-cobalt stretching band was still observed at 202 cm-‘.

1

I

I

2000

1800

1600

1400

RAMAN

SHIFT

~(crri’)

I

2200

Fig. 10. Raman spectra of (A) BDSA equilibrated with 209 torr CsH6 and 372.3 torr of Hz at 20 “C for 5 h, (B) BDSA equilibrated BDSA equilibrated at 170 “C for 18 h.

of CO, 161.3 torr of at 85 “C for 18 h, (C)

177

Moreover, propylene cannot x-complex with cobalt carbonyl species to a significant extent. Formation of the n-complex would cause the carbonyl stretching band to shift to lower wavenumbers, but such a shift was not observed. The carbonyl stretching bands of (n-allyI)--Co(CO), have been reported by Andrews and Davidson [22]. They assigned the infrared bands at 206O(vs), 198O(vs), and 1962 cm-’ as CO stretching bands. The Raman bands at 2062(m, p)*, and 1989(vs, dp)’ cm-’ were assigned as GO stretching bands [22]. If ~-~lylc~bonyl cobalt is substituted with PPh, or O=PPh,, CO stretching bands should be shifted to lower wavenumbers due to the basicities of the phosphine ligands. Hence the presence of 7rcomplexed propylene was not supported by the spectroscopic results. The CO stretching bands above 2100 cm-‘, at 2144(w), 2104(sh) and 2170(w) cm-l, suggest that the cobalt carbonyl compound formed on the surface of y-alumina is not zero-valent. CO stretching bands in Co(I) and Co(I1) compounds were observed near 2100 cm-‘. Carbon monoxide adsorbed on metallic Co(I) supported on inorganic oxides gives rise to a CO stretching band above 2100 cm-l. The latter argument is partially offset by the fact that the surface compound could be extracted by benzene after pretreatment, whereas a metallic cobalt species ought not to be extracted by organic solvents. After extraction, the BDSA still has a pink color; this observation indicates the presence of Co(I1) supported on y-alumina. However, most surface compounds exist as organometallic species which can be dissolved in organic solvents. The formation of Co(I) and Co(I1) complexes is very unlikely because the mixture of CO, hydrogen and propylene at 170 “C is not an oxidizing agent. Another possible inte~re~tion of the surface compound is that it is some form of cobalt cluster compound. The postulated cluster should be an active catalyst for hydroformylation because BDSA equilibrated with CO, Hz and CsH, at 170 “C promoted the hydroformylation reaction. The C4 aldehyde was condensed on the surface of the alumina after the pretreatment. This species was identified by the PAS spectrum of the BDSA/react~t system at 170 “C and by the mass spectrum of the gas mixture equilibrated at 170 “C. The most plausible species on the surface of y-alumina at 170 “C under the hy~oformylation gas mixture has the general structure {Co(CO),P(C,H,)},. This type of cluster compound has been reported by Sacco [ 231, Pregaglia et al. [ 241, Hayter [ 251, Labroue and Poilblanc 1261, and Huq and Poe f 27 ] . Pregaglia et at. prepared a series of green paramagnetic compounds with the formula {CO(CO)~PR~)~. These compounds have catalytic activities for hydrogenation of monoolefins, diolefins, and aldehydes. Catalytic isomerization of olefins over these compounds has also been reported [ 241. These workers did not test whether these trimeric cobalt clusters had catalytic activity for the hy~oformylation of olefins, Recently Huq and Poe [27] have reported detailed infrared bands for *p = polarized. tdp = depolarized,

178

{Co(CO),(PR,)}, (R = Ph, OCH,) and CO,(CO),~_.L, (n = 0, 1, 2, 3, 4). Unfortunately the Raman-active CO stretching bands recorded under in situ conditions at 170 “C cannot be explained by the pattern of CO stretching bands of Co4(CO)s(PPh,)+ This compound is presumed to have CqV symmetry, where the A1 mode of the CO stretching band is active in both Raman and infrared spectroscopy. Hence Raman-active CO bands should not have any strong bands located much higher than 2010 cm-‘, which is the At CO stretching band location determined via infrared spectroscopy. However, the in situ Raman spectrum at 170 “C includes a strong CO stretching band at 2097 cm-’ with a shoulder at 2104 cm-‘. This feature is more closely related to Co4(CO)12-,,(PPh&., (n = 1, 2, 3). The possibility of forming Co,(CO) 12is slim because of its instability under the pretreatment conditions employed. In heptane CO,(CO),~(PP~,) has infrared-active CO stretching bands at 2090(s), 205O(sh), 2043(vs), 1880(w) and 1835(m) cm-’ [27]. On the basis, of spectroscopic information, it is not unreasonable to conclude that the surface species is a cobalt tetramer substituted with phosphine ligands. The formation of a cobalt tetramer from Co,(C0)6(PPh3)2 has been noted for the homogeneous reaction [23,24,28], Paramagnetic compounds of (Co(CO),PR,), can be obtained during the hydroformylation of linear olefins via the following reaction [ 291: ~COH(CO)~PR~

+ mC,H2,

+ ; mH,--

[CO(CO)~PRJ,

+

The dimer (CO(CO)~PR& is a precursor of a hydridic species. Our inability to prepare the triphenylphosphine.derivatives is due to the complete insolubility of the initial complex in most organic solvents. In order to achieve appreciable reaction rates, it is necessary for the system to be heated to temperatures higher than 110 “C. This fact is in accord with the results of the 85 “C study, in which the in situ Raman spectrum of BDSA contacted with the hydroformylation reactants was not much different from that at 20 “C. Above 110 “C some degree of thermal decomposition into dimer CO~(CO)~(PR~)~ and metallic cobalt took place. However, more reactive olefins, e.g. ethylene and propylene, reduce the reaction time and give higher yields. The formation of a cobalt(O) cluster under hydroformylation conditions has been reported by Pino et al. [30]. Dodecacarbonyl tetracobalt(0) is formed from hydridotetracarbonyl cobalt(I), olefins and hydrogen as follows: ~COH(CO)~ + 4&H,,

+ 2H, -

Co&O)

12+ 4&H,,

+ GHO)

Compounds of the form (CO(CO)~PR&,, were also obtained by direct hydrogenation of 7r-allyl( trisorganophosphine)cobalt dicarbonyl complexes [28] :

179

7

>40

m(HCCHCH2)Co(C0)2PR,

“C

+ 4 mH, -

mR(CH&CHs

+

~CO(C~V’R~~

+

A similar reaction occurred in the absence of any solvents when COAX(PPh& was supported on y-alumina. In the case of equilibration of the BDSA with 279 torr of CO and 215 torr of propylene at 170 “C, the presence of the surface compound in Fig. 5 (E)has been postulated. Hence, the heterogeneous cou.nterpart reaction for the hydrogenation of a fl-allylcobalt species can be written as shown in Fig. 5 (E)and (F). Spectra obtained in diffuse reflectance FTIR studies of the interactions of BDSA with CO, H2 and C3H, are summarized in Table 4 and Fig. 11. After being evacuated at 140 “C for 55 min, BDSA was equilibrated with 215 torr of CO at 20 “C for 1 h. At 20 “C the introduction of CO caused new weak bands to appear at 2040.5, 2017, and 1991 cm-‘. These bands are TABLE 4 CO stretching spectra)

bands

of BDSA under

various pretreatment

conditions

(diffuse

reflectance

BDSAb

BDSAa Evacuated at 20 “C

215 torr of CO at 20 “C

215 torr of CO at 50 “C

215 torr of CO at 75 “C

1737(w)

1738(w)

1777.5(w) 1819.5(w) 1849(w)

1777.5(w) 1819(w) 1834(w) 1849(w)

1899(w)

1898.5(w)

1946.5(s)

1946(s)

1966(sh)

1966.5(sh)

194.5 torr of Hz and CO, and 420 torr of C3H6 at 20 “C

at 110 “C

at 170 “C 1695.5(w)

1738(w) 1757(w) 1776(m) 1810.5(w) 1830(w) 1848(w) 1899(m)

1956.5(s) 1968.5(s,

1898(w) 1918.5(w) 1944.5(s)

sh)1965.5(sh) 1991(w) 2017(w)

1768(w) 1785(w)

1869(w) 1899(m)

1868(w) 1897.5(s)

1868(s) 1885(s) 1921(s)

1951(s) 1958(s) 1966(sh)

1966(sh)

2022(vw)

202O(vw)

2012(m)

2034.5(vw) 2040.5(w) 2065(w,

2039(w)

sh)

“BDSA was evacuated at 140 “C for 55 min and cooled the adsorbates and temperatures noted. bUnpretreated BDSA.

to 20 “C. It was then exposed

to

180

,

2197

A

1997 WAVENUMBER

1797 (cti’)

1597

Fig. 11. Diffuse reflectance spectra of CO stretching bands of BDSA equilibrated with 215 torr of CO at room temperature (A), at 50 “C (B) and at 75 “C (C); with 194.5 torr of Hz and CO, and 420.0 torr of C3H6 at room temperature (D) and at 170 “C (E).

attributed to CO adsorbed on cobalt crystallites originating from decarbonylated Co,(C0)6(PPh3),. The location of the strong band at 1944.5 cm-’ differed by 12 cm -’ from that of BDSA at room temperature. A weak band at 1898 cm-’ was also noted. This band grew in intensity after equilibration at 50 “C for 11 h (Fig. 11 (B)). Most of the features in the CO stretching bands of BDSA equilibrated with 215 torr of CO at room temperature were retained at 50 “C and at 75 “C (Fig. 11). Unpretreated BDSA was placed in the vacuum chamber and equilibrated with 194.5 ton: of HZ, 194.5 torr of CO and 420.0 torr of C3Hb at room temperature. Most of the features of the CO stretching bands are similar to those of BDSA at 20 “C in the absence of any adsorbable gases (Fig. 11 (D)) except for the increase in intensity of the band at 1899 cm-’ and the broadening of the band near 1950 cm- ‘. While it is difficult to imagine formation of appreciable amounts of surface intermediates at room temperature or 110 “C in the presence of hydroformylation gases, spectral changes attributed to a new surface species were observed at 170 “C (Fig. 11 (E)). The temperature dependence of the formation of surface species agrees with both the Raman results and kinetic studies of hydroformylation in the vapor phase as catalyzed by BDSA. Below 110 OC, the catalytic activity of BDSA was almost nil; above 140 ‘C, an appreciable rate was observed. The diffuse reflectance spectrum of BDSA equilibrated with 194.5 torr each of CO and H1, and 420.0 torr of C,H, at 170 “C has a new band at 2012 cm-‘. Three broad, strong bands at 1921, 1885, and 1868 cm-l overlap one another but are clearly evident. Careful comparison of the bands ascribed to propylene and y-aIumina with those of BDSA led to the conclusion that three weak bands at 1784.8, 1768.0, and 1695.5 cm-’ can be identified as CO stretching bands. Spectral features of model compounds used to identify possible candidates for the surface species formed by exposure of BDSA to hydroformylation reactants at 170 “C are presented in Table 5. Candidate species

181 TABLE 5 Infrared bands of candidate cobalt carbonyl compounds for the surface species formed by exposure of BDSA to hydroformylation reactant gases at 170 “C Complex

Matrix

Co,(CO)s (bridged)

heptane

2112(vw), 2071(s), 2059(vw), 2044/ 42(vs), 2031(vw), 1866(w), 1856(m)

31

Coz(CO)s (unbridged)

heptane

2107(sh), 2069(s), 2044/42(vs), 2031(vw), 2023(s), 1991(w)

31

HCo(CO)‘,

heptane

2118(w),

2055(s), 2032(s), 1955(w)

32

Co(CO)s(PPh3)2+Co(C0)4-

CHC13

2013(m),

2005(m),

1890(s)

33

2002(s), 1927(s), 1882(vs)

33

.Ref.

v(CC) (cm-‘)

Co(C0)s(PPhs)2+Co(CO)4-

KBr

2072(w),

Co(CO)s(PPh&+Co(CO)4-

acetone

2072(vw),

Coz(CC&(PPh&

KBr

203O(vw), 1960(sh), 1902(vw)

195O(ss),

33

Coz(CC)6(PPh&

neat (PAS)

2064(sh), 1972.5(s), 1899(s), 1810.5(m)

1936(s),

this work

Coz(CC)e(PPhs)z

neat (DRS)

2064.5(sh), 2022(sh), 1899(s), 1810.5(m)

Coz(CC)tj(PPh&

KBr

2032(w), 1811(w)

nujoi mull

1985(m), 1951(vs), 1835(vw), 1797(s), 1788(s)

24

toluene

2000(m), 1967(vs), 196O(vs), 18OO(vs), 1795(sh)

24

nujoi mull

2000(ms), 1979(ms), 1951(vs), 1836(w), 1800(s), 1790(s)

24

co4(coh2

heptane

2113(vw), 206O(vs), 205O(vs), 2045(sh), 2035(m), 1896(vw), 1864(s), 183O(vw)

27

co4(coh2

DCE

211O(vw), 206O(vs), 205O(vs), 2045(sh), 2030(sh), 1896(w), 1860(m)

27

c”4(coh2

hexadecane

2105(vw), 2063(vs), 2054(vs), 2047(sh), 2036(w), 2027(w), 1298(w), 1864(w)

26

heptane

2090(s), 205O(s (sh)), 2043(vs), 2035(s), 1880(w), 1853(m), 1835(m)

27

DCE

2085(s), 205O(s (sh)), 2042(vs), 2030(m (sh)), 1980(m), 1890(m), 1830(m)

27

heptane

2084(s), 2045(s), 2039(vs), 2030(s), 1855(m), 1838(m)

34

2008(s), 1887(vs)

33

this work

1938.5(s),

1959(s), 1943(s), 1898(m),

this work

(continued)

182 TABLE 5 (continued) Complex

Matrix

v(CC) (cm-‘)

Ref.

Co4(CO)ldPPh3)

CHC13

2090,2058,2023,1846,1823

35

Co4(CC)s(PPh&

nujol

2005(s), 1972(w), 1882(s), 1810(w)

1946(vs), 1912(w),

27

Cd4(CC)a(PPhs)4

n-heptane

2005(m), 1965(w), 1945(vs), 1910(w), 1885(s), 1810(m), 1765(w)

27

Co4(CC)a(PPh&

DCE

2010(s), 197O(vw), 1950(s), 1890(s), 1820(w), 1765(w)

27

PAS = photoacoustic spectrum. DRS = diffuse reflectance spectrum. DCE = 1,2-dichloroethane.

were selected on the basis of whether or not they had been identified in previous studies of homogeneous reactions of Co,(C0)6(PPh3)2 with CO, Hz and CsH,. The presence of CO stretching bands below 1800 cm-’ in the spectrum of BDSA ruled out the possibility that the surface compound is a mono- or di-nuclear cobalt species. Trimeric or tetrameric cobalt clusters substituted with phosphine ligands have CO stretching bands below 1800 cm-‘. The pattern of CO stretching bands for BDSA does not match exactly with that of either a trimeric or tetrameric cobalt cluster. However, the surface species is believed to be a tetrameric cobalt cluster since a trimeric cobalt cluster has strong bands below 1800 cm-‘, whereas BDSA has weak bands below 1800 cm-‘. Moreover, a trimeric cobalt cluster substituted with phosphine does not have CO stretching bands above 2000 cm-‘, while tetrameric cobalt clusters do. As shown in Fig. 5 and as discussed above, Co2(CO),(PPh& can react with H, and olefins to produce cobalt clusters and aldehyde via a hydroformylation reaction. At equilibrium an excess of butyraldehyde will suppress the formation of trimeric or tetrameric clusters. In order to observe this equilibrium behavior, an excess of butyraldehyde was put in the sample cell with BDSA at room temperature and 280 torr each of CO and Hz and 150 torr of propylene added. The DRS infrared spectrum of this system is compared with that of BDSA in Fig. 12 (A) and (B). A CO stretching band of medium intensity appeared at 2004 cm-‘. This band was not present in the spectrum of BDSA equilibrated with 45 torr of butyraldehyde at 25 “C for 14 h. This new band arises from coordination of the aldehyde to the cobalt carbonyl compound or from a surface species formed via interaction of the BDSA with CO, Hz and propylene at 25 “C. The latter possibility is slim because of the low temperature at which the experiment was carried out. In the corresponding homogeneous reaction chemistry, transition metal carbony1 compounds coordinated with aldehydes do not often exist as isolated species.

183

22bo

2040

l&O 1720 1560 WRVENUMBER (cm-‘)

1rbo

Fig. 12. Diffuse reflectance spectra of (A) BDSA evacuated at 20 %; (B) BDSA equilibrated with 280 torr of CO, 280 torr of Hz, and 150 torr of C3H6 in presence of CaH$HO at 25 “C, (C)at 140 “C, and (D) at 175 “C.

Subsequently the equilibrium temperature was raised to 140 “C. At this temperature the band arising from the aldehyde-coordinated species disappeared. The pattern of CO stretching bands (at 1970(sh), 1941(s), and 1814(w) cm-‘) at 140 “C is not similar to that of HCo(C0)3(PPh3) or of HCo(C0)2(PPh3)z (see Fig. 12 (C)). The DRS infrared spectrum of BDSA equilibrated at 140 “C with CO, Hz and propylene in the presence of butyraldehyde is similar to that of BDSA evacuated at 20 “C (see Fig. 12 (C) and (A)), indicating that BDSA does not react with CO, H, and propylene at 140 “C in the presence of an excess of butyraldehyde. The equilibrium temperature was then raised to 175 ‘C. The CO stretching band at 1941 cm-’ present in the spectrum of BDSA equilibrated at 140 “C decreased significantly in intensity (Fig. 12 (D)). However, the pattern of CO stretching bands of BDSA equilibrated with CO, Hz, &I-I, and an excess of butyraldehyde at 175 “C is similar to that of BDSA evacuated at 20 “C except for the fact that the band intensities are much lower (compare Fig. 12 (A) and (D)). This suggests that Co2(C0)6(PPh3)2 has started to decompose at 175 “C in the presence of CO, Hz propylene and butyraldehyde. It is clearly evident that the pattern of CO stretching bands of BDSA equilibrated at 175 “C with CO, Hz and propylene in the presence of butyraldehyde is totally different from that of BDSA equilibrated with CO,

WAVENUMBER

(cm-I )

Fig. 13. Diffuse reflectance spectra of BDSA equilibrated with (A) 194.5 torr of CO, 194.5 torr of Hz, and 420 torr of C3Hs at 170 ‘C, (B) 235.0 torr of CO, 235 torr of Hz, and 45 torr of C3H&HO at 175 C, (C) 280 torr of CO, 280 torr of Hz, and 150 torr of CsHs in the presence of CJH&HO at 175 “C!.

Hz and propylene 13 (A) and (C)). cobalt clusters in tion gas mixture butyraldehyde.

in the absence of butyraldehyde at 1’70 “C (compare Fig. Hence, it can be concluded that formation of tetrameric the reaction between Co,(CO),(PPh,), and a hydroformylaat elevated temperature is suppressed by the presence of

Comparative study of the interactions of BDSA with gaseous CO, Hz and propylene and the interactions of Coz(CO),(PPh3), with CO, H2 and propylene in the liquid phase The interactions of CO, Hz and propylene with Co2(C0)6(PPhs)2 supported on r-alumina are summarized in Fig. 5. Information relative to the analogous homogeneous reactions is summarized in Fig. 14. The organometallic compounds are dissolved in solvents in which the compounds are molecularly dispersed or solvated. Mid-range interactions such as dipoledipole interactions or specific short range interactions such as hydrogen bonding may occur. These interactions lead to shifts in the locations of some vibrational bands of the compound. If the solvent is reactive enough to displace ligands, chemical reactions might occur. For example, a tricarbonylbenzyl-chromium complex is formed in the reaction of benzene with Cr(CO),. When Co2(CO),(PPh& is supported on the surface of y-alumina at the level of a monolayer or less, the compound is molecularly dispersed in two dimensions, as opposed to being present in 3dimensional solvated cages as in the liquid-phase reaction. Several interactions of Co2(C0)6(PPh3)2 with the surface of r-alumina were noted. These include hydrogen bonding

185 HOMOGENEOUS 0 P-do

\I -co

I\

17tPc

-P

for

)

6

-decomposes

- ‘&y 1 lc/ \

1C(

1Zhrs

Q

Alar3

Al&3 * Sobated co* (co)S

wh3)2

e

Co2 (co),

PPh3

9

Toluene

co_ c-

CqCCO),

-

1oooc

Reflux Hg

I

Na+

If'Ph3

Na Co (CO)4 % H5Gr _

Co4 (CO),2

Co,(CO), , PPh3 Co4 (CO),o (PPh3) 2

TT-C3 HS Co (CO)3 ,

CO~(CO)~(PP~~)~

PPh3

Co2 (CO)S (PPh3 ) 2

-co WC3 H5 CO (CO )2 PPh

3

3H 2

2 >4ooc

( dH 30

Fig. 14. Interactions

of CO, H2 and C3H6 with Co2(C0)&PPh&

in the liquid phase.

between hydroxyl groups and carbonyl ligands and Lewis acid-base adducts between A13+ and the oxygen atoms of the carbonyl ligands. Similar behavior was also found for the homogeneous reactions as illustrated in Fig. 14. Even the chemical reactions of the functionalized support (e.g. phosphinated silica) with organometallic compounds occur in a fashion similar to the reactions of the homogeneous counterparts. An important observation is that in the absence of any solvent the supported organometallic compound can react with simple molecules such as Hz, CO and lower olefins. This observation parallels the chemisorption of simple gases on metal crystallites supported on inorganic oxides. The prerequisite for reaction of supported or covalently anchored organometallic compounds with simple molecules is stability under reaction conditions in the absence of solvent. When studying the immobilization of homogeneous catalysts, one must consider the effects of the immobilization process on the elementary reactions involved in catalytic cycles. Due to steric hindrance, it is sometimes difficult to postulate a 2O-electron intermediate compound (usually postulated in the associative mechanism). It is nearly impossible to have an oxidative addition reaction as an elementary step in the catalytic cycle.

186

Moreover, one must be aware of the possibility of coordinative unsaturation as a consequence of the immobilization process. If a homogeneous reaction is occuring in a solvent, the following equilibria are frequently involved in elementary steps: ML, + Solvent e

ML, _ i(Solvent)

+ L*

where M = metal, L = Ligand, and L* = solvated ligand

and ML, _ ,(Solvent)

+ L’ +

where L’ = simple molecule

ML, _ iL’ + Solvent (CO, olefins etc.)

The coordinatively unsaturated compound is ML, _ ,(Solvent) if the solvent molecule is not strongly bound and if it can be easily displaced by more favorable ligands such as CO or olefins. These kinds of equilibria are not present in the gas-phase reactions catalyzed by immobilized homogeneous catalysts. The spectrum of (SIL-PPh2)2Co,(C0)6 when a small amount of benzene is still present on the surface of silica gel differs from that of (SIL-PPh2)&02(CO), in the absence of benzene [Q]. This observation indicates that the intermediate compounds formed during catalytic cycles are not necessarily the same as those postulated for the homogeneous reaction. The immobilized organometallic complexes may have a different mode by which a coordinatively unsaturated species is produced. The two equilibria mentioned above can be written as follows if species ML, _ i(Support) and L* are stable enough to sustain an equilibrium with ML, : ML, + Support

4

ML, _ i(Support)

+ L*

where L* can be a simple molecule adsorbed on the support or present in the gas phase or a bulky ligand such as PPhs. This intermediate can then undergo ligand exchange reactions. ML, - i(Support)

+ L’ &

ML, _ iL’ + Support

or rearrangement

ML, _ i( Support)

,

\

m(Mi/,L(,-,,/,A

+ Support

The compounds ML,_ i(Solvent), and ML,_,(Support) should be stable enough not to decompose under reaction conditions. These intermediate compounds should be reactive toward such simple molecules as CO, Hz and olefins. This reasoning is the basis for postulating the surface species (C), (D), and (E) noted in Fig. 5. The coordinatively unsaturated compound (C) formed after partial decarbonylation is believed to be stabilized by the ralumina. The electron density around the cobalt atom is too high for it to be stable after decarbonylation. This excess electron density will then be

18’7

transferred to the Lewis acid sites of y-alumina. The formation of Lewis acid-base adducts has previously been observed for a variety of carbonyl compounds. Examples include CoJCO)s-AlBr,, Fe3(C0)i2-AlBr, and Ru,(C0)i2-AlBr, [36].

Conclusion When supported on ~-alumina, Co,(CO),(PPh& directly interacts with hydroxyl groups and Lewis acid sites (Al+“) on the alumina surface. At room temperature, hydrogen bonding occurs between the oxygen atoms of the carbonyl ligands and the hydroxyl groups. At elevated temperatures under vacuum, hydrogen bonding diminishes and partially decarbonylated Co2(CO),(PPh,), is formed. This carbonyl species is coordinated to Lewis acid sites to form a Lewis acid-base adduct, which stabilizes the coordinatively unsaturated carbonyl species. This species can react with simple molecules such as H,, CO and C,H, in the absence of a solvent to yield aldehydes in a hydroformylation reaction under ambient pressure. The spectroscopic results (Raman, photoacoustic, and diffuse reflectance FTIR) suggest that during this reaction, the partially decarbonylated species is converted to a tetrameric cobalt cluster compound. Similar results were obtained under homogeneous reaction conditions. The ML, _ i( Support), which is the coordinatively unsaturated species in the gas-phase reaction, is analogous to ML, _ ,(Solvent) in the liquid-phase reaction.

Acknowledgements The authors gratefully acknowledge the support of the National Science Foundation (Grant ENG-77-00061) for this research. Additional support for S. I. Woo has been provided by Schulte Scholarship Trust and Department of Chemical Engineering funds.

References 1 N. D. Parkyns, in Proc. 3rd Internat. Congr. Catalysis, North-Holland, Amsterdam, 1965, p. 194. 2 J. R. Anderson and D. E. Mainwaring, J. Catal., 35 (1974) 162. 3 Yu. I. Yermakov and B. N. Kuznetsov, J. Mol. Catal., 2 (1980) 13. 4 E. G. Derouane, J. B. Nagy and J. C. Ve’drine, J. Catal., 46 (1977) 434. 5 J. R. Anderson, P. S. Elmes, R. F. Howe and D. E. Mainwaring, J. Catal., 50 (1977) 508. 6 L. A. Gerritsen, A. Van Meerkert, M. H. Vreugdenhil and J. J. F. Scholten, J. Mol. Catal., 9 (1980) 139. 7 P. R. Rony and J. F. Roth, J. Mol. Catal., 1 (1975/76) 13. 8 Th. G. Spek and J. J. F. Scholten, J. Mol. Catal., 3 (1977/78) 81.

188 9 S. I. Woo, Ph. D. Thesis, Chemical Engineering Department, University of Wisconsin, 10

11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

Madison, WI, 1983. A. Kazusaka and R. F. Howe, J. Mol. Catal., 9 (1980) 183. A. Brenner and R. L. Burwell, Jr., J. Carol., 52 (1978) 353. H. G. Heal, J. Znorg. Nucl. Chem., 16 (1961) 209. Photoacoustic Cell, Nicolet Analytical Instruments Manual, May, 1981. D. H. Whiffen, J. Chem. Sot., (1956) 1350. R. F. Howe,Znorg. Chem., 15 (1976) 486. A. Kazusaka and R. F. Howe,J. Mol. Catal., 9 (1980) 183. S. I. Woo, unpublished data, 1980. D. F. Shriver, J. Organometat. Chem., 94 (1975) 259. G. B. Deacon and J. H. S. Green, Spectrochim. Acta, 24A (1968) 845. E. Maslowsky, Jr., Vibrational Spectra of Organometallic Compounds, Wiley, New York, 1976, p. 233. S. I. Woo and C. G. Hill, Jr., J. Mol. Catal., 15 (1982) 309. D. C. Andrews and G. Davidson, J. Chem. Sot., Dalton Trans., (1972) 1381. A. Sacco, Gazz. Chim. Ital., 93 (1963) 542. G. F. Pregaglia, A. Andreeta, G. F. Ferrari and G. Montrasi, J. Organometal. Chem., 33 (1971) 73. R. G. Hayter, J. Am. Chem. Sot., 86 (1964) 823. D. Labroue and R. Poilblanc, Inorg. Chim. Acta, 6 (1972) 387. R. Huq and A. PO&J. Organometal. Chem., 226 (1982) 277. R. Heck and D. Breslow, J. Am. Chem. Sot., 83 (1961) 1097. C. Morterra, A. Zecchina, S. Coluccia and A. Chiorino, J. Chem. Sot., Faraday Trans. I, 73 (1977) 1544. P. Pino, R. Ercoli and F. Calderazzo, Chim. Ind. (Milan), 37 (1955) 782. G. Bor, Spectrochim. Acta, 19 (1963) 2065. L. Marko, G. Bor, G. Almazy and P. Szabo, Brennstoff Chem., 44 (1963) 18. 0. Vohler, Chem. Ber., 91 (1958) 1235. G. Cetini, 0. Gambino, R. Rossetti and P. L. Stanghellini, Inorg. Chem., 7 (1968) 609. K. J. Karel and J. R. Norton, J. Am. Chem. Sot., 96 (1974) 6812. J. S. Kristoff and D. F. Shriver, Inorg. Chem., 13 (1974) 499.