AU8324287A

AU8324287A - Catalytic conversion of alkanes

Info

Publication number: AU8324287A
Application number: AU83242/87A
Authority: AU
Inventors: Leslie David Field
Original assignee: University of Sydney
Current assignee: SYDNEY THE, University of
Priority date: 1986-11-11
Filing date: 1987-11-10
Publication date: 1988-06-01

Description

CATALYTIC CONVERSION OF ALKANES TECHNICAL FIELD The present invention relates to the catalytic conversion of alkanes using a metal hydride complex as the catalyst, and to the novel alkyl metal hydride complexes produced.

BACKGROUND ART To our knowledge, the catalytic conversion of simple alkanes to alkenes has not been previously demonstrated. Such a process has great commercial potential for the production of alkene feed stocks e.g. propylene, butylene etc. required in industry for the production of polymers .

INVENTION It has now been surprisingly discovered that certain metal hydride complexes have the ability to react with alkanes to form an intermediate alkyl metal hydride, which can be decomposed to produce alkenes and/or other alkane derivatives.

In particular, one aspect of the present invention provides a method for the catalytic conversion of alkanes which comprises

(i) reacting an alkane with a metal dihydride or trihydride complex catalyst of the formula

where

M is a metal or metal ion selected from Group VIII of the Periodic Table,

L₁ to L₄ may be the same or different and are selected from ligands of the formula (II), or bridged ligand wherein two of L₁ to L ₄ form a ligand of formula (III), and a bridged ligand. wherein three of L₁ to L₄ form a ligand of formula (IV):

where

R is a lower alkyl group or a halo-substituted alkyl group or an alkoxy group or a halo-substituted alkoxy group and "n" is an integer from 1 to 4,

so as to liberate hydrogen and produce an alkyl metal hydride complex; and

(ii) decomposing the alkyl metal hydride complex to regenerate the metal hydride complex and liberate the alkene or alkane derivative. A second aspect of the invention provides novel alkyl metal hydride complexes where one or more (but not all) H atoms in Formula IA or IB are replaced by R₁ where R₁ is a C₁-C₂₀ straight or branched alkyl or cycloalkyl group. The catalytic cycle can be summarised as follows C

This illustrates the production of alkenes. However, decomposition of the alkyl metal hydride intermediate may be carried out under conditions such as to liberate other alkane-derivatives, such as alcohols, alkyl halides or aldehydes.

The alkane is a C₁-C₂₀ straight or branched alkyl or cycloalkyl group, particularly C₁-C₁₀ alkanes such as methane, ethane, propane, butane, pentane, cyclopentane, hexane and cyclohexane. Generally, the alkane is bonded to the metal via the terminal carbon atom. For the production of alkenes, a hydrogen atom must be present in the position beta to the metal to allow beta-hydride elimination to occur.

The complex is usually a neutral complex, which assists solubility in the alkane, but in other circumstances might be a charged complex.

M is selected from group VIII of the Periodic Table (comprising Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and Pt).

Preferably the metal is Fe, Co, Ru or Rh. For reasons of economy, Fe is preferred.

In the ligands L₁ and L₄, the R group is preferably a lower alkyl group, particularly a C₁-C₄ alkyl. R is preferably methyl, ethyl or propyl. The integer n is preferably 2 or 3. Where the R group is halo-substituted the or each substituent is preferably fluoro.

The reaction of the alkane with the catalyst in step (i) may occur spontaneously, or may be brought about by heating, or by the use of a coupled chemical reaction, or most usually by irradiation with visible or UV light. Decomposition of the alkyl metal hydride complex in step (ii) may be brought about in the same way but generally proceeds spontaneously.

Preferably, the reaction is carried out in solution of the liquid or liquified alkane, if necessary at reduced temperature. Alternatively the catalyst may be supported on a solid support, for example by bonding to a solid polymer, and the alkane in liquid or gaseous form may be passed over the catalyst. Decomposition of the alkyl metal hydride in the presence of OH or halide donor groups has the potential to produce alcohols and alkyl halides. Similarly the alkene produced may be isolated or used directly in subsequent conversions for which they are basic starting materials for example, in the presence of a polymerisation catalyst the alkene may be polymerised in situ to a polyalkane.

EXAMPLES Embodiments of the invention will now be described by way of example only. Example 1

The complex Fe(DMPE)₂H₂, [DMPE=1,2-bis-(dimethylphosphino)ethane], synthesised by reduction of the corresponding dichloride with lithium aluminium hydride, was irradiated in a solution of pentane at -20°C. Hydrogen gas was evolved (confirmed by its characteristic signal in the ¹HNMR spectrum of the reaction mixture). 1-Pentene was produced in the reaction mixture (confirmed by its characteristic signals in the ¹H NMR spectrum and by trapping it as 1,2-dibromopentane on reaction with bromine). The intermediate cis-n-C₅H₁₁Fe(DMPE)₂H was trapped, isolated and characterised as trans-n-C₅H₁₁Fe(DMPE)₂Br.

Irradiation was carried out as follows. Samples containing 2-4mg FeH₂(DMPE)₂, in 0.4-0.8ml of solvent, were irradiated in pyrex tubes, positioned ca. 10cm from a 125 watt mercury vapour lamp. The tubes were supported within a quartz cylinder, and cooled by a stream of nitrogen gas. Example 2

Irradiation of the complex Fe(DMPE)₂H₂ in cyclopentane solution in the same manner as described in Example 1 produces cyclopentene in solution. Example 3

Irradiation of the complex Fe(DMPE)₂H₂ in hexane solution in the same manner as described in Example 1 produced 1-hexene in solution. Example 4 Irradiation of the complex Fe(DMPE)₂H₂ in pentane at -80°C in a manner as described in Example 1 produced the complex HFe(DMPE)₂(n-pentyl) in 70% yield after 60% conversion. Treatment of the complex with bromine at

-80°C produced 1-bromopentane .

Claims

THE CLAIMS

1. A method for the catalytic conversion of alkanes which comprises (i) reacting a C₁-C₂₀ alkane with a metal dihydride or trihydride complex catalyst of the formula

where

M is a metal or metal ion selected from Group

VIII of the Periodic Table,

L₁ to L₄ may be the same or different and are selected from a ligand of the formula (II), a bridged ligand wherein two of L₁ to L₄ form a ligand of formula (III), and a bridged ligand wherein three of L₁ to L₄ form a ligand of formula (IV):

where

so as to liberate hydrogen and produce an alkyl metal hydride complex; and

(ii) decomposing the alkyl metal hydride complex to regenerate the metal hydride complex and liberate the alkene or alkane derivative.

2. A method according to claim 1 wherein the alkane is a C₁-C₁₀ straight or branched alkyl or cycloalkyl group.

3. A method according to claim 1 wherein M is selected from Fe, Co, Ru and Rh.

4. A method according to claim 3 wherein M is Fe.

5. A method according to claim 1 wherein the ligands L₁ to L₄ are constituted by two bridged ligands of formula (III) where n is 2 or 3 and R is C₁-C₄ alkyl.

6. A method according to claim 5 wherein the C₁-C₄ alkyl groups are substituted by one or more fluoro.

7. A method according to claim 1 conducted in the presence of ultraviolet light.

8. A method according to claim 1 wherein the catalyst is iron 1,2-bis-(dimethylphosphino)ethane dihydride. An alkyl metal hydride complex of formula

where at least one R₁ is a C₁-C₂₀ straight or branched cycloalkyl group and at least one R₁ is hydrogen; ligands L₁ to L₄ may be the same or different and are selected from a ligand of the formula (II), a bridged ligand wherein two of L₁ to L₄ form a ligand of formula (III), and a bridged ligand wherein three of L₁ to L₄ form a ligand of formula (IV):

where

R is a lower alkyl group or a halo-substituted alkyl group or an alkoxy group or a halo-substituted alkoxy group and "n" is an integer from 1 to 4.