Supported dendrimer catalyst

Details Supported dendrimer catalyst Supported dendrimer catalyst

1999-07-09

2001-09-11

Shaver, Paul F. (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Heavy metal containing

C556S012000, C556S136000, C556S019000, C556S020000, C556S021000, C556S413000, C556S438000, C502S150000, C502S152000, C502S158000, C549S003000, C560S055000, C560S064000, C585S025000

Reexamination Certificate

active

06288253

ABSTRACT:

The invention relates to a novel method of supporting dendrimers on a solid support, and their use as catalysts.
BACKGROUND
Dendrimers, also known as arbolols, cascade molecules, dendritic polymers, or starburst polymers, have been attracting recent attention because of their unique structure and properties. The name comes from the Greek word for tree, in reference to their branch-like structure. They are a type of 3-dimensional, hyperbranched polymer, but differ in their ability to be prepared in a highly controlled, stepwise manner with narrow molecular weight distributions, many with no variation at all in weight. Dendrimers have a central core and an outer “surface” consisting of a high number of terminal groups which can be functionalized to provide the desired properties.
There are two main strategies for synthesizing dendrimers. In the divergent approach, the molecules are built from the central core out to the periphery. The convergent approach builds the molecule from the outer periphery towards the inner core. The divergent approach is outlined below.
The dendrimer starts with a core having at least two functional end groups capable of further reaction. Monomer units, having at least three functional end groups, are added in cycles to the core via one functional end group each, building a dendrimer framework. A monomer having three such end groups is considered to have a branch multiplicity of 2, indicating that two further monomers can be added to the framework on each existing branch. Each successive cycle is called a generation. In each generation a set number of monomer units are added to the functional end groups of the dendrimer framework, leading to a series of layers. This number is an exact multiple of the multiplicity. These cycles continue until the desired number of generations are added.
A pioneer in this type of chemistry is Donald Tomalia, who wrote an early review summarizing the history of area (D. Tomalia, et al, Angew. Chem. Int. Ed. Engl., 29 (1990), 138-75). Recent developments were reviewed in 1997 (F. Zeng and S. Zimmerman, Chem. Rev., 97 (1990), 1681-1712).
Liu, et al (Angew. Chem. Int. Ed. Engl., 36 (1997), 2114-16, and J. Am. Chem. Soc. 119, (1997), 8720-21) describe a dendrimer covalently attached to a solid support. However, the dendrimer is not attached directly to the support but is attached to reactive sites on an intervening randomly dispersed polymer layer.
One of the many potential uses of dendrimers has been in catalysis. Metals can be attached to the surface of the dendrimers by complexation with appropriate functional groups. They combine the advantages of homogenous catalysis with heterogeneous catalysis since they have a specific number of structurally defined, catalytically active metal centers as in traditional homogenous catalysis, as well the ability for easily separation from the reaction mixture and reuse as in heterogeneous catalysis. Miedaner, et al. (Inorg. Chem., 33 (1990), 5482-5490), Knapen, et al. (Nature, 372 (1994), 659-663), and Reetz et al. (Angew. Chem. Int. Ed. Engl., 36 (1997), 1526-1528) all used small dendrimers complexed with Pd and Ni compounds as homogenous catalysts. The dendrimers were separated after reaction by precipitation and filtration. Recycling of the used catalysts was suggested but not demonstrated.
A published abstract (http://www.sfu.ca/csc98/program/00000383.htm) for the 81st Canadian Society for Chemistry Conference and Exhibition stated that a version of Tomalia's dendrimer complexed to [Rh(CO)
2
Cl]
2
was used as a catalyst for hydroformylation. The paper was withdrawn before presentation.
A need exists for a method to prepare true heterogeneous dendrimer catalysts that are efficient and can be easily removed from reaction mixtures without an added precipitation step, but can also be recycled and used multiple times.
SUMMARY OF THE INVENTION
In accordance with the present invention, a supported dendrimer composition has been found comprising a siloxy core and branches emanating from the core, wherein said core is directly and covalently bonded to a solid support. The solid support is selected from the group consisting of SiO
2
, TiO
2
, Al
2
O
3
, ZrO
2
, clays, zeolites, modified carbons, and organic resins. Preferably, the supported dendrimer composition core and branches are of the formula
Si(O)
m
(OH)
3−m
[ZN](AB)
g
(T)
2g
wherein:
Z is selected from the group consisting of optionally substituted C2-C12 straight chain or branched alkyl chain, cycloalkyl group, and aryl;
A is —(CHR
3
)CHR
4
Y—;
Y is selected from the group consisting of —C(O)NH—, —P(O)(OR
5
)NH—, and —C(N)NH—;
B is —R
6
NH—;
T is selected from the group consisting of H, alkyl, —(CR
8
R
9
)
y
N
2
, —(CR
8
R
9
)
y
P(R
10
)
2
, and —(CR
8
R
9
)
y
P(NH)
2
,
R
3
, R
4
, R
5
, R
8
, and R
9
are independently selected from the group consisting of hydrogen, alkyl or aryl;
R
6
is selected from the group consisting of optionally substituted C2-C12 straight chain or branched alkyl chain, cycloalkyl group, and aryl;
R
10
is selected from the group consisting of hydrogen, alkyl, aryl, alkoxy and aryloxy;
m=0-3;
y=2-12; and
g
=
∑
1
G
⁢
 
⁢
2
G
 where G=number of generations in the dendrimer.
More preferably, the solid support is SiO
2
, Z is —(CH
2
)
3
—, A is —(CH
2
)
2
C(O)NH—, B is —(CH
2
)
2
N—, and T is —(CH
2
)
2
NH
2
. The supported dendrimer composition can optionally be complexed at T with a transition metal, preferably Rh.
The invention also provides a process for the preparation of a dendrimer composition supported on a solid support comprising the steps of:
a. directly attaching a siloxy core group to the solid support by covalent bonding between at least one oxygen on the siloxy group and the surface of the solid support;
b. directly attaching a linker group to the core group, wherein the linker molecule contains at least two reactive functional groups; and
c. constructing the arms of the dendrimer utilizing the core group as the starting point of the dendrimer.
Preferably, the supported dendrimer prepared in the above process is composed of core and branches of the formula
Si(O)
m
(OH)
3−m
[ZN](AB)
g
(T)
2g
wherein:
Z is selected from the group consisting of optionally substituted C2-C12 straight chain or branched alkyl chain, cycloalkyl group, and aryl;
A is —(CHR
3
)CHR
4
Y—;
Y is selected from the group consisting of —C(O)NH—, —P(O)(OR
5
)NH—, and —C(N)NH—;
B is —R
6
NH—;
T is selected from the group consisting of H, alkyl, —(CR
8
R
9
)
y
NH
2
, —(CR
8
R
9
)
y
P(R
10
)
2
, and —(CR
8
R
9
)
y
P(NH)
2
,
R
3
, R
4
, R
5
, R
8
, and R
9
are independently selected from the group consisting of hydrogen, alkyl or aryl;
R
6
is selected from the group consisting of optionally substituted C2-C12 straight chain or branched alkyl chain, cycloalkyl group, and aryl;
R
10
is selected from the group consisting of hydrogen, alkyl, aryl, alkoxy and aryloxy;
m=0-3;
y=2-12; and
g
=
∑
1
G
⁢
 
⁢
2
G
 where G=number of generations in the dendrimer.
More preferably, the solid support is SiO
2
, Z is —(CH
2
)
3
—, A is —(CH
2
)
2
C(O)NH—, B is —(CH
2
)
2
N—, and T is —(CH
2
)
2
NH
2
. The supported dendrimer composition can optionally be complexed at T with a transition metal, preferably Rh.
The supported dendrimer composition may be used for a hydroformylation process comprising reacting an ethylenically unsaturated compound with a source of CO and H
2
in the presence of a supported catalyst. Preferably, the supported dendrimer used in the hydroformylation process is composed of core and branches of the formula
Si(O)
m
(OH)
3−m
[ZN](AB)
g
(T)
2g
wherein:
Z is selected from the group consisting of optionally substituted C2-C12 straight chain or branched alkyl chain, cycloalkyl group, and aryl;
A is —(CHR
3
)CHR
4
Y—;
Y is selected from the group consisting of —C(O)NH—, —P(O)(OR
5
)NH—, and —CN)NH—;
B is —R
6
NH—;
T is selected from the group consisting of H, alkyl, —(CR
8
R
9
)
y
NH
2

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