Polymer-bound metallocarborane catalyst product and process

A heterogeneous metallocarborane catalyst bound to a polymeric support by a carbon-boron bond. Chloromethylated polystyrene beads provide the support. The catalytic beads are characterized as PA1 3,3-(Ph P)-3-H-4 polystyrylmethyl - 3,1,2-Rh C.sub.2 B.sub.9 H.sub.10.

BACKGROUND OF THE INVENTION 
The present invention relates to the formulation of catalysts and in 
particular, to the binding of active catalytic molecules to polymeric 
supports. 
The concept of binding active catalytic molecules to polymeric or other 
supports initially was developed by biochemists who used these systems for 
enzymatic purposes and as a method for conveniently separating or 
recovering the catalytic material from the reaction mixture. More 
recently, as will be described, these systems have been the object of a 
number of studies which, in particular, recognize the advantage gained by 
the inherent simplification and ease of the catalyst recovery and 
separation. 
The polymer-bound catalysts of the present invention can be identified as 
heterogeneous systems as contrasted with the more common and increasingly 
important homogeneous catalytic systems. For the most part, however, the 
present systems are based upon the homogeneous systems. The distinction 
between the two lies principally in the fact that, in the homogeneous 
systems, the active catalytic material is only weakly associated with or 
deposited on its support material whereas, in the heterogeneous systems, 
the material is securely anchored by means of a strong chemical bond. 
Also, the homogeneous catalysts usually are soluble in the reaction 
mixture. In some situations, the distinction becomes difficult. However, 
insofar as the present invention is concerned, the term `heterogeneous` is 
applied to polymer-bound systems in which the catalytic material is 
chemically bonded with sufficient strength to permit ready separation of 
the catalyzed product from catalytic material without appreciable catalyst 
loss or degradation of its activity. In the homogeneous systems, the 
dissociation and/or solubility of the catalytic material renders recovery 
of the material difficult and also presents a problem in separating the 
product itself. Consequently, redeposition of the material is required for 
recycling as opposed to the simplified filtering and recycling procedure 
provided by the heterogeneous catalysts. 
Previous work by others has produced some interesting findings. For 
example, in the later 1960's several catalytic systems based upon 
homogeneous systems were described in the literature. One of the first 
extensively studied polymer bound homogeneous systems was that of the 
polystyrene-bound analog of Wilkinson's catalyst described in the 
following reports: 
Grubbs, R. H., and Kroll, L. C., J. Amer. Chem. Soc. 93, 3062 (1971) 
Grubbs, R. H. Kroll, L. C., and Sweet, E. J., J. Macromol - Sci. Chem. 
A7(5): (1973) 
Wilkinson's catalyst was chosen because of a great deal of work that had 
been published on its catalytic reaction mechanisms. It was found that the 
complex appeared to function in the polymer bead as it would in solution 
for the hydrogenation of olefins. However, the activity was decreased by 
the binding with the lowered activity attributed to the slow diffusion of 
the olefin through the polystyrene matrix. This property, however, allowed 
a good deal of selectivity on the part of the catalyst and the catalyst 
was easily separated and recycled. 
Similar studies were conducted with RhH(CO)(PPh.sub.3).sub.3 in 
hydroformylation reactions. This polymer-bound catalyst retained catalytic 
activity through several successive reaction-separation-reaction cycles 
and no loss of rhodium was observed. See: 
Collman, J. P., et al., J. Amer. Chem. Soc., 94, 1789 (1972) 
Pittman, C. U. and Hanes, R. "Frontiers in Organometallic Chemistry" Ann, 
NY Acad. Sci., 239, 76 (1974) 
Evans, D. Osborn, J. A. and Wilkinson, G., and J. Chem. Soc (A), 3133 
(1968) 
A variety of polymer-attached transition metal catalytic systems also have 
been synthesized and reported in the following publications: 
Pittman, C. U., Smith, L. R., and Hanes, R. J. Amer. Chem. Soc. 97, 1742 
(1975) 
Allum, K. G., Hancock, R. D., Howell, I.V. Pitkethly, R. C. and Robinson, 
P. J., J. Organometal Chem., 87 189 (1975) 
Allum, K. G., Hancock, R. D., Howell, I.V., McKenzie, S. Pitkethly, R. C. 
Robinson, P. J. Organometal, Chem. 87, 203 (1975) 
These systems appear to be analogous in behavior to the homogeneous 
catalysts from which they were derived. 
Besides varying the active complex, the polymeric support also can be 
designed to provide desired properties and a wide range of supports have 
been utilized. The two Organometal Chem. publications cited supra provide 
examples of this work. 
As far as is known, polymer-bound metallocarborane catalyst systems have 
not been synthesized and described in the literature. Some systems have 
combined a polymer and carborane but the chemical attachment was through a 
phosphine-to-metal bond rather than through the direct bonding of the 
metallocarborane to the polymer which characterizes the present invention. 
In the reactions the phosphine-to-metal bond breaks down with the result 
that some metal catalyst is lost in the mixture so that the recovered 
catalyst loses some of its activity.

DETAILED DESCRIPTION OF THE PRESENT INVENTION 
The present invention is predicated upon the discovery and synthesis of the 
first polymer-bound metallocarborane which is characterized as 
3,3-(Ph.sub.3 P).sub.2 -3-H-4 polystyrylmethyl-3,1,2-RhC.sub.2 B.sub.9 
H.sub.10. Subsequent studies have shown that this polymer-bound 
rhodacarborane is an active heterogeneous catalyst for the hydrogenation 
and isomerization of olefins. As will be discussed, these results strongly 
indicate that a wide variety of heterogeneous catalysts conforming to the 
general composition of (polymer + carborane + metal) may be available 
through an extension of the synthetic routes that have been established. 
A model system for the present discovery was provided when a series of 
boron-substituted derivatives of 7,8-C.sub.2 B.sub.9 H.sub.12 - was 
extended to include the benzyl substituent 9 benzyl-7,8-C.sub.2 B.sub.9 
H.sub.11.sup.- (which, for descriptive purposes, will be referred to as 
Compound I. The point of substitution is the 9-boron atom a polyhedral 
vertex adjacent to carbon and on the open face of the anion. Compound I 
reacted cleanly with Rh(Ph.sub.3 P).sub.3 Cl to give the rhodacarborane 
3,3-(ph.sub.3 P).sub.2 -3-H-4 benzyl 3,1,2-Rh C.sub.2 B.sub.9 H.sub.10 
(Compound II) in greater than 90% yield. 
##STR1## 
Subsequent experiments shows that benzene solutions of compound II 
catalyzed the hydrogenation of olefins such as ethyl acrylate and 
3-methyl-3 phenylbutene-1 at a rate comparable to other 
hydridorhodacarboranes discussed in a manuscript prepared by J. J. 
Wilezynski and soon to be published. 
The above results indicated that 7,8-C.sub.2 B.sub.9 H.sub.11.sup. 2- could 
be reacted with chloromethylated polystyrene beads to form the 
polymer-bound anion analogous to compound II. 
##STR2## 
Chloromethylated polystyrene beads known in the art as Merrifield's Peptide 
Resin were reacted with an excess of K.sup.+, Na.sup.+ -7,8-C.sub.2 
B.sub.9 H.sub.11.sup.= in refluxing THF. Dibenzo-18-crown-6 was used as a 
catalyst to aid in the transfer of the dianion into the lipophilic 
polymer. Filtration and washing afforded colorless beads (compound III 
above) which, on the basis of spectral and elemental analysis (coupled 
with the characterization data for Compound I) were formulated as M.sup.+ 
(9-polystyrylmethyl-7,8-C.sub.2 B.sub.9 H.sub.11 -), or Compound III. 
The reaction of Compound III with an excess of Rh(Ph.sub.3 P).sub.3 Cl in 
refluxing ethanol yielded bright yellow beads (Compound IV above) which 
subsequently were characterized as 3,3-(Ph.sub.3 P).sub.2 
-3-H-4-polystyrylmethyl-3,1,2-RhC.sub.2 B.sub.9 H.sub.10. 
The beads (IV) - an amount equivalent to 10.sup.-4 in catalyst - in benzene 
solution rapidly isomerized 1-octene (0.3M). Within 24 hours at 40 degrees 
the reaction mixture contained 1-octane (14%), trans - 2 octene (65%) and 
cis-2-octene (20%). 
Under a hydrogen atmosphere (latm) IV (10.sup.-4 M) at 40.degree. in 
benzene catalyzed the hydrogenation of 3-methyl-3-phenyl-1-butene 
(10.sup.-1 M) at a rate comparable to 11 and other hydridorhodocarboranes. 
Although the polystyrene bead metallocarborane catalyst represents the 
present stage of development of the catalytic route which has been 
described, it clearly is recognized that a number of extensions of this 
route simply await application of a substantial amount of carborene 
derivative chemistry that is in existence and to some extent discussed in 
the publications that have been cited. For example, it is felt that the 
extension of this route to include other metallocarborane catalysts of the 
C.sub.2 B.sub.9 H.sub.11.sup.2- family, as well as other cage homoloques 
is most promising. Also, the route can be extended to further generalize 
the method of polymer attachment through the carbon-boron bond to include 
other homoloques in this carborane and carborane anion series. 
Another important approach presently being investigated is one of securing 
and utilizing derivatives of the carborane anions which, in themselves, 
can serve as monomers for polymerization. Thus, as has been discussed, the 
present stage of development involves condensation with a preformed 
polymer backbone, i.e., polystyrene beads. 
However, polymerization itself, as contrasted with the use of the preformed 
beads, should have definite advantages some of which would include: (1) 
effective catalyst concentration (on the polymer) could be greatly 
increased and controlled by homopolymerization or copolymerization of 
monomer molecular catalyst precursors; (2) chiral monomers could be 
polymerized to provide macro-molecular catalysts whose catalytic sites are 
optically active and ideally suited for asymmetric reactions; (3) the 
techniques of polymer processing could be applied to yield catalysts whose 
physical characteristics are best suited to their use as heterogeneous 
catalysts. 
The synthesis of one likely candidate for polymerization is the 
9-vinylbenzyl derivatives of C.sub.2 B.sub.9 H.sub.12.sup.-. The following 
illustrates the path that is being pursued: 
##STR3## 
The reaction is strictly analogous to that which has been successfully 
demonstrated for 9-benzyl-7,8-C.sub.2 B.sub.9 H.sub.11.sup.-. It should be 
noted that such a monomer would exist as a set of enantiomers in that the 
9-boron atom represents a point of asymmetric cage substitution. As such, 
optical resolution by fractional crystallization with an optically active 
cation would lead to a chiral and polymerizable carborane monomer. 
Homopolymerization in solution or suspension polymerization with varying 
degrees of cross linking and/or other monomers then could be engineered to 
produce polymeric catalyst precursors with the desired characteristics. 
Conversion to a catalyst then can be achieved in the demonstrated manner. 
This scheme can be applied, as noted, to the optically active monomer to 
give chiral polymeric catalysts suited for asymmetric induction reactions. 
The polymeric catalyst precursor would be ideal for the synthesis of 
multifunctional catalyst systems by stoichiometric control of metal 
reagents. In such a manner a heterogeneous catalysts adaptable to a 
"one-pot" multistep synthesis could be obtained. Proposals such as these, 
as well as other approaches, as likely candidates for the extensions of 
the presently-disclosed field. 
Obviously, many modifications and variations of the present invention are 
possible in the light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims the invention may 
be practiced otherwise than as specifically described.