Complexes of mid-transition metals and unsaturated...

Details Complexes of mid-transition metals and unsaturated... Complexes of mid-transition metals and unsaturated...

1999-10-06

2002-03-12

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S134000, C526S161000, C502S155000

Reexamination Certificate

active

06355746

ABSTRACT:

TECHNICAL FIELD
This invention relates generally to the field of catalysis, and more particularly relates to novel complexes of mid-transition metals and unsaturated nitrogenous ligands that are useful, inter alia, as polymerization catalysts. The invention additionally relates to methods for using the novel compounds as catalysts, particularly in the preparation of polymers such as polyolefins.
BACKGROUND
Many processes and catalysts are known for the preparation of homopolymeric or copolymeric olefins and other polymers. Ziegler-Natta catalyst compositions, developed in the 1950s, were found to be particularly useful in the preparation of polyolefins. These catalyst compositions comprise transition metal compounds such as titanium tetrachloride and an alkylaluminum (e.g., triethylaluminum) cocatalyst. The systems were found to be advantageous because of their high activity, and were largely consumed during polymerization.
Subsequent catalyst systems have been designed to provide more control over polymer structure and properties than could be achieved with Ziegler-Natta catalysts. These later catalysts have well-defined active sites and can be rationally designed to produce a specific polymer product, i.e., having predetermined structure and properties. Such catalysts include, for example, metal complexes known as “metallocenes.” The term “metallocene” was initially coined in the early 1950s to refer to dicyclopentadienyliron, or “ferrocene,” a structure in which an iron atom is contained between and associated with two parallel cyclopentadienyl groups. The term is now used to refer generally to organometallic complexes in which a metal atom (not necessarily iron) is coordinated to at least one cyclopentadienyl ring ligand. A. D. Horton, “Metallocene Catalysis: Polymers by Design,”
Trends Polym. Sci.
2(5):158-166 (1994), provides an overview of metallocene catalysts and their advantages, and focuses on now-conventional complexes of Group IV transition metal complexes and cyclopentadienyl ligands (Cp
2
MX
2
, wherein Cp represents a cyclopentadienyl ligand, M is Zr, Hf or Ti, and X is Cl or CH
3
). Unfortunately, however, although metallocenes do provide significant advantages relative to the traditional Ziegler-Natta catalysts, the high cost and difficulties associated with heterogenization of metallocenes, as well as the oxophilic nature of the early transition metals, have limited the applicability of metallocenes as commercial polymerization catalysts.
Because polyolefins such as polyethylene and polypropylene are such important commercial polymers, there is an ongoing need for improved polymerization techniques and polymerization catalysts. Recently, researchers have developed new catalysts suitable for olefin polymerization that are complexes of late transition metals and substituted diimine ligands. Such catalysts are described, for example, in Bres et al., PCT Publication No. WO 98/49208, published Nov. 5, 1998. Other similar catalysts, comprised of diimine ligands and selected metals, are described in Bennett, PCT Publication No. WO 98/27174, published Jun. 25, 1998, and in Brookhart et al., PCT Publication No. WO 98/30612, published Jul. 16, 1998. While these catalysts have some advantages, they are lacking in several significant respects. Perhaps most importantly, the aforementioned catalysts are incapable of producing commodity polymers such as linear low density polyethylene (“LLDPE,” having a density of about 0.918 to 0.935 g/cm
3
) and isotactic polypropylene (“iPP”).
The present invention is thus addressed to the aforementioned need in the art, and provides novel compounds useful as polymerization catalysts, e.g., in the polymerization of olefins. The catalysts provide for numerous advantages relative to the polymerization catalysts of the prior art, in that they:
(1) are simple and cost-effective to synthesize;
(2) allow for exceptional control over the structure and properties of the polymeric product;
(3) are highly active polymerization catalysts;
(4) can be used in stereospecific polymerization to provide stereoregular polymers, including isotactic and syndiotactic polymers;
(5) enable preparation of commodity polymers such as linear low density polyethylene and isotactic polypropylene;
(6) can be used as either supported or homogeneous polymerization catalysts;
(7) are quite versatile and can be used in conjunction with a variety of monomer types; and
(8) can be used to catalyze reactions other than polymerization reactions, e.g., hydrogenation.
The invention thus represents a significant advance in the field of catalysis, as prior to the development of the catalysts disclosed and claimed herein, only a few of the aforementioned advantages could be achieved with a single catalyst system.
SUMMARY OF THE INVENTION
Accordingly, it is a primary object of the invention to provide novel compounds useful as catalysts, particularly as polymerization catalysts.
It is another object of the invention to provide such compounds which are complexes of a mid-transition metal and at least one unsaturated nitrogenous ligand.
It is yet another object of the invention to provide such compounds containing two unsaturated nitrogenous ligands that are asymmetrically substituted, such that the compounds are useful as stereospecific catalysts.
It is still another object of the invention to provide such catalysts which are isospecific, thus enabling preparation of isotactic polymers.
It is another object of the invention to provide such catalysts which are syndiospecific, thus enabling preparation of syndiotactic polymers.
It is a further object of the invention to provide such compounds which are useful for preparing polyolefins or other polymers deriving from the polymerization of addition polymerizable monomers containing one or more degrees of unsaturation.
It is still a further object of the invention to provide catalyst systems containing a compound of the invention, a catalyst activator such as a metal alkyl, hydride, alkylhydride, alkylhalide or the like, and, optionally, additives such as inert diluents (e.g., a volatile hydrocarbon) and polymerization rate accelerators (e.g., Lewis bases, including amines and anilines).
It is yet a further object of the invention to provide a method for using the novel catalysts to prepare polyolefins or other polymers deriving from the polymerization of addition polymerizable monomers containing one or more degrees of unsaturation.
It is an additional object of the invention to provide a method for using the novel catalysts to prepare stereoregular polymers such as isotactic polypropylene.
It is still an additional object of the invention to provide a method for using the novel catalysts to prepare linear low density polyethylene.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention.
In one embodiment, the novel compounds have the structure L
1
[MQ
1
Q
2
]L
2
in which M is a mid-transition metal, Q
1
and Q
2
are each a univalent radical, and L
1
and L
2
are ligands, wherein each of L
1
and L
2
contains a first coordinating atom that is a nitrogen atom contained within a C═N group, and a second coordinating atom that is either a second nitrogen atom, which may or may not be present in a second C═N group, or an oxygen, sulfur or phosphorus atom. Each C═N group may be a true imine functionality contained within an acyclic molecular segment, or may represent a linkage within a heterocycle such as a pyridine or pyrimidine ring. In this embodiment, the mid-transition metal M is selected from the group consisting of Nb, Ta, Mo, W, Mn and Re, and L
1
and L
2
may be covalently linked to each other, but typically represent separate and distinct ligands. Additionally, L
1
and L
2
may be the same or different. When a stereospecific catalyst is desired, L
1
and L
2
are substituted accordingly.

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