WO2012004352A2

WO2012004352A2 - Mesoporous diphosphine-transition metal complex catalyst for hydroformylation

Info

Publication number: WO2012004352A2
Application number: PCT/EP2011/061531
Authority: WO
Inventors: Joost Nicolaas Hendrik Reek; Marc-Olivier Coppens
Original assignee: Technische Universiteit Delft; Stichting voor de Technische Wetenschappen STW; Universiteit Van Amsterdam
Current assignee: Technische Universiteit Delft; Stichting voor de Technische Wetenschappen STW; Universiteit Van Amsterdam
Priority date: 2010-07-08
Filing date: 2011-07-07
Publication date: 2012-01-12
Anticipated expiration: 2013-01-08
Also published as: WO2012004352A3

Abstract

The invention pertains to a diphosphine-transition metal complex comprising a diphosphine-transition metal ligand that is covalently bonded to an insoluble mesoporous support having an average pore diameter of from 4.5 nm to 50 nm, characterized in that the ligand as attached to the support has the formula: wherein R is aryl, C₁-C₄ alkyl, aralkyl, alkylaryl; C₁-C₄ alkoxy, aralkoxy, or alkylaryloxy; P is a phosphorous atom; M is a transition metal; X is a bond, CH₂, 0, S or NH₂; Y is C or N; A is a linking moiety which is bonded to the mesoporous support; the ring formed by X, Y and the two aromatic rings is a 5- or 6-membered ring; and wherein the aromatic rings may be unsubstituted or substituted. The invention further relates to the use of the diphosphine- transition metal complex as a catalyst in a reaction selected from hydroformylation, hydrogenation, carbonylation or carbon-carbon coupling.

Description

MESOPOROUS DIPHOSPHINE-TRANSITION METAL COMPLEX CATALYST FOR HYDROFORMYLATION

The invention pertains to mesoporous supported diphosphine-transition metal complexes and to use of the complex as catalyst.

Homogeneous transition metal catalysts generally display high activity and selectivity in contrast to their heterogeneous counterparts in hydroformylation reactions.

Despite this advantage, many industrial catalytic processes use heterogeneous catalysts, because of their ease of

separation from the reaction product. Several strategies for the separation of homogeneous catalysts from the product mixture have been explored. See for instance Catalyst

Separation, Recovery and Recycling: Chemistry and Process Design, D. J. Cole-Hamilton, R. P. Tooze, Eds. Springer, Dordrecht, The Netherlands, 2006. The covalent anchoring of homogeneous transition metal complexes on solid supports is particularly interesting, as after heterogenization, the catalyst can be applied in reactors typically suited for heterogeneous catalysis. In spite of the huge effort

dedicated to immobilization, there is no important industrial application, mainly because of catalyst leaching and a loss of rate and selectivity upon immobilization. This invention relates to a transition metal catalyst for hydroformylation reactions, that upon immobilization to a support does not lose its rate compared to the homogeneous analogue, and even displays higher rates in some experiments.

Previously, the hydroformylation reaction using tethering of diphosphine ligands on commercially available silica gel was studied by A. J. Sandee, L. A. van der Veen, J. N. H. Reek, P. C. J. Kamer, M. Lutz, A. L. Spek, P. W. N. M. van Leeuwen, Angew. Chem. Int. Ed. Engl., 1999, 38, 3231; and A. J. Sandee, J. N. H. Reek, P. C. J. Kamer, P. W. N. M. van Leeuwen, J. Am. Chem. Soc, 2001, 123, 8468), and was

reported to render recoverable and recyclable rhodium-based catalysts for the conversion of alkenes into aldehydes or alcohols. However, as usual, these covalently supported catalytic systems showed lower activity and selectivity than their homogeneous analogues. The present invention has as one of its objectives to obtain covalently supported catalytic systems with improved activity and selectivity resembling or even improving those as obtained in homogenous reaction systems. It has now been found that this objective can be obtained by using a support with a specific pore size range, which is known as a mesoporous support.

In the early 1990' s a new family of porous silica materials was developed, which were obtained by using

micelles as templates during the preparation, leading to periodically ordered channels of the same size in the

mesoporous range (2 to 50 nm diameter) . Their surface

reactivity, both internal and external, is rather close to that of silica gel, so that grafting or tethering organic functionalities onto these silicates can be readily achieved.

It is well known from literature on supported catalysts that mass transfer limitations is one of the crucial issues leading to deteriorated catalytic performance. It was now found that the combination of high surface area with accurate control over the mesopore size and pore

connectivity influences enormously the intrinsic material properties and reduces transport limitations in catalysis, resulting in higher activities and better controlled

selectivity. In addition, the controlled structure of

mesoporous materials can lead to isolated metal species on the support surface which do not interact with each other, thus preventing in most cases their deactivation and

enhancing their activity and productivity.

US 6,544,923 discloses a catalytic system comprising catalysts immobilized on a mesoporous support. The system includes mesoporous silicate covalently bound to a ligand that in turn can covalently bind an organometallic fragment. Bonding of phosphine-transition metal ligands to the mesoporous support is not done via an aromatic system. The catalytic reactions include hydrogenation,

hydroformylation, carbonylation and carbon-carbon coupling reactions, such as Heck or Suzuki reactions.

CN 101642719 discloses an anchor ligand modified metal supported catalyst consisting of a mesoporous support, a metal component and an organic ligand, wherein the

mesoporous support is silicon dioxide, MCM-41 or SBA-15; the metal component is transition metal rhodium; and the organic ligand is an organic phosphine ligand containing an alkoxy silane group. In the catalyst, the organic ligand and the metal component are directly fixed onto the support; and simultaneously the coordination function exists between the organic ligand and the metal, and an active species is generated in situ. The catalyst can be used for

hydroformylation of olefins.

FR 2865664 discloses a solid inorganic support, in particular a mesoporous support, modified at its surface by carrying an organic complex chelating a transition metal. The organic complex has a ring structure that is unrelated to the structures as described herein.

It was now found that diphosphine-transition metal complexes comprising an aromatic ligand as described herein provide catalysts that are advantageously used in

hydroformylation reactions.

To this end, the invention pertains to a diphosphine-transition metal complex comprising a

diphosphine-transition metal ligand that is covalently bonded to an insoluble mesoporous support, having an average pore diameter of from 4.5 nm to 50 nm, characterized in that the complex has the formula

wherein

R is independently aryl, C1-C4 alkyl, aralkyl, alkylaryl; Ci- C₄ alkoxy, aralkoxy, or alkylaryloxy;

P is a phosphorous atom;

M is a transition metal;

X is a bond, CH₂, 0, S or NH₂;

Y is C or N;

A is a linking moiety which is bonded to the mesoporous support;

the ring formed by X, Y and the two aromatic rings is a 5- or 6-membered ring; and wherein

the aromatic rings may be unsubstituted or substituted.

In this definition aryl is preferably phenyl, aralkyl is preferably benzyl and alkylaryl is preferably toluyl, and alkyl is preferably methyl, ethyl or tert-butyl. In the ethers (alkoxy, aralkoxy, or alkylaryloxy) the

meanings of the carbyl groups is the same. All aromatic moieties in the above formula can be substituted with the common aromatic substituents such as alkyl, alkoxy, aryl (as pending substituent or annelated ring), halogen (such as fluoro, chloro or bromo) , nitro, OH and the like.

Examples of suitable transition metals include cobalt, ruthenium, rhodium, palladium, osmium and iridium.

Most preferably one or more of the features of the invention are that the transition metal is rhodium, X is 0, Y is N, A is a silylalkyl group when Y is N, most preferably silylpropyl, or a silylalkylidene group when Y is C, the ring formed by X, Y and the two aromatic groups is a 6-membered ring, and the aromatic rings are unsubstituted .

Catalysts comprising such an aromatic diphosphine transition metal ligand covalently bonded to a mesoporous support display a remarkably high activity in

hydroformylation reactions, an activity that is often higher than that of its homogeneous counterpart.

Mesoporous supports wherein the average pore diameter is less than 4.5 nm appear to be unsuitable for stable hydroformylation catalysis, as was observed with the silicate MCM-41. It is preferred to use mesoporous supports wherein the average pore diameter is 4.5 nm to 15 nm.

It was further found that it is important to control the pore size to obtain the best activity and selectivity. Therefore, confinement of the pore size within narrow ranges is of importance. Preferably at least 90% of the mesopores have a diameter of 4.5 nm to 15 nm.

In a preferred embodiment the diphosphine- transition metal complex has V_micro (microporous volume) 0 - 0.2 cm³g^-1 and V_meSo (mesoporous volume) 0.5 - 2.0 cm³g^_1. The values of the specific surface areas S_BET and S_mes0pores are less important for the intrinsic properties of the catalyst, but are suitably high; values can be around 300-1000 m²g^_1 and 200-1000 m²g^~1, respectively. In fact, high specific surface areas (m²g^-1) (such as those of SBA-15) are an advantage, as they allow for very high chemical rates per unit mass of catalyst .

In another preferred embodiment, the ligand- mesoporous support complex has the formula:

wherein n is an integer of 2 to 10 and Ph is phenyl.

The mesoporous support can be any support that can contain mesopores, such as silica, silicate, aluminosilicate , molecular sieves, titanium oxide, phenol/formaldehyde

polymers and certain clays or zeolites. Most preferably the support is mesoporous silica. The term "silica" means SiC>₂, but the mesoporous silica may further contain small amount of other metal oxides or metal inorganic constituents. Metals that can be found in silica are aluminum, titanium, iron, calcium, magnesium, and the like, however the silica

preferably consist of at least 90% S1O₂, most preferably 100% or close to 100% Si0₂. A suitable example of a mesoporous silica is SBA-15 (ex TU Delft, the Netherlands) .

In a particular embodiment, SBA-15, a mesoporous silica with large surface area and narrow pore size

distribution, was explored as support for the covalent anchoring of rhodium-based transition metal catalysts. The rhodium-diphosphine catalytic system, which is known from the above mentioned Sandee, et al. publications was covalently anchored on both silica gel and SBA-15, and the effect of the mesoporous material on the hydroformylation of 1-octene was studied and compared to both supported silica gel catalyst and its homogeneous analogue. SBA-15 with a pore diameter of about 10 nm was prepared according to literature procedures. The synthesis material 2 is given in Scheme 1:

The rhodium-diphospine-SBA-15 material 2 was analyzed after synthesis by means of elemental analysis to determine the ligand content, based on P content, and ICP-OES analysis to determine the Rh amount. The amounts of rhodium and ligand present on the silica mesoporous support were estimated to be around 1.0 χ 10^~5 mole/g and 1.5 χ 10^~4 mole/g SBA-15 respectively (i.e. ligand-to-metal ratio of 15).

To evaluate the effect of the support in catalysis, the catalytic performance of the silica-supported rhodium- diphosphine complex 2 was investigated in the industrially important hydroformylation of 1-octene (Scheme 2) in a batch reactor, using 1 g of silica material (table 1).

After each catalytic cycle the product mixture was separated from the supported catalyst by simple filtration. Generally, supported transition metal catalysts show lower activities and selectivity with respect to their homogeneous analogues. Rhodium complex 2 supported on silica gel (Table 1; entry 24) indeed shows activities (TOF of 8; TOF is average turn over frequency) that are 15 times lower than its homogeneous analogue (TOF of 120, entry 25) . Also the

regioselectivity is slightly lower (1/b of 19; 1/b is the linear/branched ratio) when applied under the same catalytic conditions. The rhodium catalyst supported on mesoporous SBA- 15 showed much better performance in the hydroformylation reaction than the silica gel supported analogue (Table 1; entries 1-17, 24) . At 50 bars of syn-gas pressure and at 80 °C the SBA-15 supported catalyst 2 showed high activities with a TOF up to 195 and a 1/b regioselectivity of around 34 (Table 1; entries 1-17), demonstrating that both activity and selectivity are much higher than those of the catalyst immobilized on amorphous silica support (Table 1; entry 24).

Remarkably, the activity is comparable with, and in some experiments higher than that of the homogeneous catalyst used under the same catalytic conditions (entries 1, 4-6, 8- 10, 15-17 and 25, respectively) . Under these conditions, catalyst 2 supported on SBA-15 showed activities (TOF of 306 to 995) that are 2 to 7 times as high as the homogeneous rhodium complex (entries 8-10 and 26, respectively) , while the regioselectivity is slightly lower (92% of linear product compared to 96% for the homogeneous phase) . In addition, the hydroformylation reaction using the SBA-15 supported catalyst 2 was performed in pure substrate resulting in very high activities and very high TON' s (entries 9-17; TON is Turn

Over Number) . The facile diffusion of the reactants through the porous solid support of the mesoporous SBA-15 silica material is particularly important under these conditions. Moreover, the supported catalyst 2 could be recycled by simple filtration up to 14 times retaining both activity and selectivity, and no significant metal leaching was observed (< 3 ppb according to ICP-OES (inductively coupled plasma optical emission spectrometry) analysis).

The high activity observed for the SBA-15 supported catalyst 2 compared to the homogeneous catalyst at 20 bars and with a ligand-to-metal ratio of 15 (entry 8 and 26 respectively, Table 1) is particularly surprising. It is well established that a high concentration of ligand in the reactor mixture promotes the formation of bis-ligated metal species 4 (Scheme 3) known to be inactive in the

hydroformylation reaction.

Scheme 3

More importantly, high catalyst loading and low pressures facilitate the formation of inactive dinuclear complex 5. The low activity of the homogeneous rhodium- diphosphine complex compared to the SBA-15 supported catalyst under these conditions is explained when a solution of the homogeneous catalyst (1 ^χ 1CT⁵ mole of rhodium) at 20 bars and with a ligand-to-metal ratio of 15 at 80 °C is monitored with high pressure IR spectroscopy during the reaction. Four carbonyl bands typical of the 3ee (v = 2034 cm^-1 and 1969 cm^" ¹) and 3ea (v = 1990 cm^-1 and 1942 cm^-1) conformations denote the presence of rhodium species active in the

hydroformylation reaction. The IR spectra also evidenced a broad carbonyl band around 1720 cm^-1, which clearly indicates the presence of dinuclear rhodium complex 5, the formation of which is most probably suppressed by site isolation effect in the supported SBA-15 complex analogue.

The reproducibility of the catalyst immobilization was studied by making a batch of supported ligand using the same batch of silica SBA-15 under identical conditions. The SBA-15 metal complex 2 showed slightly decreased performance when this second batch was applied in the hydroformylation reaction (Table 1; entries 18-23) . While selectivity remains comparable to the previous batch of SBA-15 material (linear over branched ratios around 30 and 40 respectively at 50 and 20 bars of syn-gas pressure) , the activities decreased by almost a factor 2, with TOF' s going down to 100 and 192 for the process at 50 and 20 bars, respectively. The decreased catalytic performance is also observed in terms of stability of the catalytic material. While the first batch of supported metal complex 2 was recycled up to 15 times leading to a cumulative TON of 67716, the second batch of supported

catalyst already showed deterioration of the material after the fourth cycle (cumulative TON of 4083) , leading to

increased 1-octene isomerization and decreased

regioselectivity . Differences in stability and performance in catalysis between the different batches may be due to the supporting immobilization technique used. Formation of

clusters on the silica support has been proven to occur when standard techniques are used to support rhodium complex 2.

This uncontrollable high local density of catalyst species on porous surface can lead to local depletion of substrates, resulting in degraded outcome of the hydroformylation

reaction .

When used in hydroformylation of alkene with carbon monoxide-hydrogen mixtures the covalently mesoporous support anchored complex in the rhodium-catalyzed hydroformylation of 1-octene up to 94% of linear aldehyde can be obtained, which is free of metal complex, by simple filtration procedures. In other hydroformylation reactions also alcohols can be

obtained, for instance by reducing the aldehyde first

obtained. Moreover, activities that exceed those of

homogeneous analogues were obtained in some other experiments. The fact that the catalyst is heterogeneous is important, because the reaction products can be trivially separated from the expensive catalyst, and the catalyst can now be reused many times, as tested in preliminary investigations. Whereas previously catalytic activity upon attaching such a catalyst on a porous support almost always led to decrease in activity and selectivity, an increase was noted when using the

diphosphine-transition metal complex on the structured

mesoporous support of this invention.

Apart from use in hydroformylation, the catalysts as described herein may advantageously be used in catalytic reactions like hydrogenation, carbonylation and carbon-carbon coupling reactions. For instance, the catalysts can be used for hydrogenation of any compound containing an olefin moiety.

The invention is further illustrated by the following non-restricting examples. General Procedure

Unless stated otherwise, reactions were carried out under an atmosphere of argon using standard Schlenk

techniques. Solvents were distilled under an atmosphere of nitrogen, as follows: THF and Et0₂ from sodium benzophenone ketyl, toluene from sodium, and dichloromethane from CaH₂.

Chemicals were purchased from Sigma-Aldrich and used without further purification. Silica gel (200-400 micrometer; 60 A) was purchased from Screening Devices B.V., and SBA-15 was synthesized at TU Delft as discussed below. Both materials were pretreated under vacuum at 180 °C for 24 hours prior to use. N R spectra (¹H, ³¹P{^XH}, and ¹³C{¹H}) were measured on Varian Mercury 300 MHz, or Varian INOVA 500 MHz spectrometers. GC analyses were performed on a Shimadzu GC Ultra (F.I.D.

detector) with a Chirasil Dex CB column (internal diameter 0.1 mm, 5 m column, film thickness 0.1 mm). Elemental

analyses were performed at the H. Kolbe Mikroanalytisches Laboratorium in Mulheim (Germany) . Rhodium analysis was performed on an ICP-OES, PerkinElmer Optima 3000XL with detection limit of 1.4 g/L (1.4 ppb) and determination limit of 4.2 μg/L (4.2 ppb) . Synthesis of the mesoporous silica SBA-15

The synthesis of the mesoporous silica SBA-15 was carried out following a procedure adapted from D. Zhao, Q. Huo, J. Feng, B. F. Chmelka, G. D. Stucky, J. Am. Chem. Soc, 1998, 120, 6024, and D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka, G. D. Stucky, Science, 1998, 279, 548. Typically, 4 g of block co-polymer Pluronics P123 (BASF), 15 mL of hydrochloric acid (HC1, 35 %), and 85 mL of water were first mixed and homogenized. 8.5 g of TEOS

( tetraethoxysilane, 98%) were slowly added to the solution under continuous stirring. Hydrolyzation was subsequently performed at 40 °C for 4 hours, followed by aging in an autoclave at 110 °C for 48 hours. The wet solid product was dried at 60 °C. Calcination was performed at 550 °C for 6 hours to obtain dry SBA-15.

Synthesis of the supported rhodium-bisphosphine (2)

The synthetic procedure to achieve the silica supported material 2 followed an adaptation of the previously published procedure for supporting the same catalytic system on silica gel. (A. J. Sandee, L. A. van der Veen, J. N. H.

Reek, P. C. J. Kamer, M. Lutz, A. L. Spek, P. W. N. M. van

Leeuwen, Angew. Chem. Int. Ed. Engl., 1999, 38, 3231; A. J.

Sandee, J. N. H. Reek, P. C. J. Kamer, P. W. N. M. van

Leeuwen, J. Am. Chem. Soc, 2001, 123, 8468).

Synthesis of SBA-15 supported material 2

2 g of SBA-15 mesoporous silica were introduced into a flask and evaporated at 180 °C under reduced pressure for 18-24 hours in a rotary evaporator. Then the mesoporous material was suspended in 50 mL of toluene and rotation was continues in the rotary evaporator. A toluene solution of the ligand (250 mg, 0.35 mmole) was then added to the SBA-15 suspension, and the slurry was rotated under reflux

conditions in the rotary evaporator for 18-24 hours. The supported SBA-15 (1) was then filtered and washed with toluene (3 x 20 mL) and then washed with diethylether (20 mL) . The material was dried under reduced pressure and stored under argon atmosphere.

Synthesis of rhodium-diphosphine supported catalyst

Prior to its use in catalysis the rhodium- diphosphine supported catalyst was prepared as follows:

1 g of SBA-15 was suspended in 20 mL of THF and the slurry was rotated at room temperature in a rotary evaporator. A solution of Rh(acac) (CO)₂ (2.58 mg, 1 x 10^~5 mole) was added to the rotating slurry of SBA-15, and the mixture was rotated at room temperature for 24 hours. The resulting catalyst- support system was filtered, washed with THF (3 x 20 mL) and then with diethylether (1 x 20 mL) , and thereafter dried under reduced pressure before being used in catalysis.

Elemental analysis found: % C 9.58, % H 1.78, % N 0.23.

Metal leaching - Rhodium in the product mixture by ICP-OES analysis

The silica gel was dissolved in 48% aqueous HF (1 mL x 50 mg of silica) and heated under vacuum at 80 °C until all the volatiles were evaporated. The residue was dissolved by adding fuming nitric acid (2 mL) and warming up the solution to 90 °C for 1 hour. Hydrogen peroxide (few drops) was added to the warm sample until the solution became colorless. Water was added to bring the total volume up to 10 mL for analysis. Loading: 0.17 mmole/g.

In situ high-pressure FT-IR experiments

The high-pressure IR spectra were performed in a stainless steel (SS 316) 50 mL autoclave equipped with ZnS windows (700 cm^-1, i.d. 10 mm, optical path length 0.4 mm), a mechanical stirrer, a temperature controller, and a pressure device. In a typical experiment the high pressure IR

autoclave was filled with 15 mL of a solution of ligand

(1.5xl0^-4 mole) and metal precursor (1*10^-5 mole) in

methyltetrahydrofurane . The autoclave was purged three times with 10 bars of CO/H₂ (1/1 by volume), and pressurized to 18 bars. The mixture was stirred and heated up to 80 °C (final pressure of 20 bars) . Catalyst formation was monitored as a function of time by FT-IR for a period of 14 hours. Hydroformylation experiments

In a typical catalysis experiment a stainless steel 50 mL autoclave, equipped with a glass inner beaker,

mechanical stirrer, substrate vessel, temperature controller, and a sample outlet equipped with a filter internal to the autoclave was filled with 1 g of 1.0 x 10^~5 mole of rhodium- catalyst containing silica and 10 mL of toluene as solvent. The suspension was incubated overnight at 80 °C under 16 bars (or 20 bars) of CO/H₂ (1/1) . A mixture of 1 mL of 1-octene and 1 mL of decane in 3 mL of toluene was added, and the CO/H₂ pressure was increased up to 20 bars (or 50 bars) . The mixture was stirred for 23 hours. The autoclave was cooled at 15-20 °C and the pressure reduced to 5 bars. With this overpressure the liquid was slowly removed from the catalyst via the sample outlet. After the catalyst had been washed with 5 mL of toluene, 10 mL of toluene were added and the pressure was brought to 16 bars (or 20 bars) . The mixture was heated up to 80 °C, and, finally, a second cycle was

performed by adding another mixture of 1 mL of 1-octene and 1 mL of decane in 3 mL of toluene, and increasing the CO/H₂ pressure to 20 bars (or 50 bars) . The experiments carried out in neat 1-octene were performed after the incubation

procedure: the catalyst was washed with 5 mL of toluene after the previous cycle, and 15 mL of 1-octene were added. Then, the pressure was increased to 20 bars, the temperature elevated up to 80 °C, and the cycle started. The experiments show that the activity of the catalyst of the invention (with a mesoporous support) is much higher (as expressed by the higher TOF values) than the same catalyst supported on regular silica (entry 24) . The activity is comparable or better in comparison with homogeneous hydroformylation, but then catalytic cycles are not possible and recovery of catalyst is then cumbersome and attended with substantial loss of catalytic material.

The results of rhodium-catalyzed hydroformylation of 1-octene are given in the Table and are published by

Fabrizio Marras, Jia Wang, Marc-Olivier Coppens, and Joost N. H. Reek (Ordered Mesoporous Materials as Solid Supports for rhodium-diphosphine catalysts with remarkable

hydroformylation activity, Chemical Communications, 2010, 46, 6587-6589) .

Claims

1. A diphosphine-transition metal complex

comprising a diphosphine-transition metal ligand that is covalently bonded to an insoluble mesoporous support having an average pore diameter of from 4.5 nm to 50 nm,

characterized in that the complex has the formula:

wherein

R is aryl, C₁-C4 alkyl, aralkyl, alkylaryl; C₁-C4 alkoxy, aralkoxy, or alkylaryloxy;

P is a phosphorous atom;

M is a transition metal;

X is a bond, CH₂, 0, S or NH₂;

Y is C or N;

A is a linking moiety which is bonded to the mesoporous support;

the aromatic rings may be unsubstituted or substituted.

2. The diphosphine-transition metal complex of claim 1 wherein the average pore diameter is 4.5 nm to 15 nm.

3. The diphosphine-transition metal complex of claim 2 wherein at least 90% of the mesopores have a diameter of 4.5 nm to 15 nm.

4. The diphosphine-transition metal complex of any one of claims 1 to 3 wherein:

micro is 0 - 0.2 cm³g^-1

V_meso is 0.5 - 2.0 cm³g^-1.

5. The diphosphine-transition metal complex of any one of claims 1 to 4 wherein the support is a mesoporous silica consisting of at least 90% S1O2.

6. The diphosphine-transition metal complex of any one of claims 1 to 5 wherein the transition metal is rhodium.

7. The diphosphine-transition metal complex of any one of claims 1 to 6 wherein the linking moiety of the ligand is a silylalkyl or silylalkylidene group.

8 The diphosphine-transition metal complex of any one of claims 1 to 7 wherein the ligand-mesoporous support complex has the formula:

wherein n is an integer of 2 to 10 and Ph is phenyl.

9. Use of the diphosphine-transition metal complex of any one of claims 1 to 8 as catalyst in a reaction selected from hydroformylation, hydrogenation, carbonylation or carbon-carbon coupling.

10. A method for hydroformylation of an alkene to an aldehyde or alcohol wherein the alkene is reacted with a mixture of carbon monoxide and hydrogen in the presence of the diphosphine-transition metal complex of any one of claims 1 to 8 as catalyst.