Method for the synthesis and use of pentafluorophenyl lithium to produce tetrakis pentafluorophenyl borate

Abstract: A pentafluorophenyl compound (1) is reacted with an alkyl lithium compound (6) in a reaction zone (5), preferably temperature controlled, under conditions such that only a small amount of a predetermined quantity of pentafluorophenyl lithium product is present in the reaction zone (5) at any time. The product may be directly discharged from the reaction zone for combination with another reactant (10).

Description: TECHNICAL FIELD This invention relates to methods for the synthesis of pentafluorophenyl lithium and to the production of chemicals derived from pentafluorophenyl lithium. More particularly, the invention relates to methods which reduce the safety hazards which may be associated with the bulk preparation of pentafluorophenyl lithium and its use to synthesize other chemicals. BACKGROUND OF THE INVENTION Tetrakis (pentafluorophenyl) borate derivatives are extensively used as olefin polymerization co-catalysts with cyclopentadienyl transition metal complexes. See, e.g., U.S. Patent 5,470,993, column 17, line 20 to column 18, line 10 (listing certain trisubstituted ammonium salts of tetrakis (pentafluorophenyl) borates useful as activating co-catalysts). Pentafluorophenyl lithium is frequently used as the source of the pentafluorophenyl group. The synthesis of such borate derivatives is constrained by the tendency of pentafluorophenyl lithium to decompose as the temperature increases. Explosive decomposition has been reported. Hence, pentafluorophenyl lithium is usually generated and used at low temperatures such as -78°C. See generally published European patent application 0604961 A2, Col. 1, 11. 23-28. EP-A-0,608,563 provides a production method of tetrakis(pentafluorophenyl)borate derivatives represented by a following general formula [VII] (C 6 F 5 ) 4 BM (wherein M denotes an alkali metal ion), wherein, with 1 equivalent of pentafluorobenzene represented by a following formula [I], C 6 HF 5 0.5 to 1.5 equivalents of organometallic compound represented by a general formula [II] RM (wherein M denotes an alkali metal ion, R denotes a hydrocarbon group with carbon atoms of 1 to 10 and the said hydrocarbon group may contain functional groups having no influence on the reaction), are reacted at a temperature range from -120 to 80°C in an ether type solvent, a hydrocarbon type solvent or a mixed solvent of the ether type solvent with the hydrocarbon type solvent to generate pentafluorophenyl alkali metal salt represented by a following general formula [III] C 6 F 5 M (wherein M denotes an alkali metal ion), and, with 1 equivalent of boron compound represented by a general formula [IV] BX 3 wherein X denotes a halogen atom, substituent represented by a following general formula [V] OR (wherein R denotes a hydrocarbon group with carbon atoms of 1 to 10 and the said hydrocarbon may contain functional groups having no influence on the reaction) or substituent represented by a following general formula [VI] NRR' (wherein R and R' denote identically or differently hydrogen atoms or hydrocarbon groups with carbon atoms of 1 to 20, said hydrocarbon group may contain functional groups having no influence on the reaction and R and R' may link one another to form a ring), and may form 1:1 complex with the ether type solvent, not less than 3.7 equivalents of pentafluorophenyl metal compound represented by the formula [III] are reacted. SUMMARY OF THE INVENTION This invention provides a method for producing a lithium tetrakis (pentafluorophenyl) borate which comprises: (i) preparing a mixture of a pentafluorophenyl compound and a subsequent reactant in solution in a non-interfering solvent and cooling the resulting mixture to between -10°C and -40°C, wherein the subsequent reactant is selected from (C 6 H 5 ) 3 B, (C 6 F 5 ) 3 B, BX 3 or MXn in which X is a halide or an anionic group, and R is a straight or branched chain 1 to 10 carbon atom alkyl or aryl group, and M is a metal, or metalloid, and n indicates the number of X entities required to satisfy the formal valance of M.; (ii) adding a solution of an alkyl lithium in a non-interfering solvent; and (iii) permitting the resultant reaction mixture to warm to room temperature; wherein lithium tetrakis (pentafluorophenyl) borate is produced. DEFINITIONS Pentafluorophenyl compound or reactant - A compound having the formula C 6 F 5 X in which X is hydrogen, chlorine, bromine or iodine. Alkyl Lithium - A compound having the formula RLi in which R is a straight or branched chain saturated or unsaturated alkyl group having 1 to 8 carbon atoms. R is preferably a normal or branched chain 1 to 6 carbon atom alkyl group. Normal and butyl lithium are preferred. Alkyl lithium compounds are preferably utilized in 1 to 10 molar solution in a non-interfering hydrocarbon solvent, preferably a 5 to 10 carbon atom aliphatic hydrocarbon solvent such as hexane. n-butyl lithium is commercially available in solution in hexanes. Non-interfering Solvent - A solvent or mixture of solvents which does not adversely affect the pentafluorophenyl or the alkyl lithium reactants, the pentafluorophenyl lithium synthesis or the reaction of pentafluorophenyl lithium with a subsequent reactant. Subsequent Reactant - A compound which reacts, preferably directly, with pentafluorophenyl lithium as produced according to the invention. Such subsequent reactants may include but are not limited to (C 6 F 5 ) 3 B, (C 6 H 5 ) 3 B, compounds having the formula BX 3 in which X is a halide, e.g. BF 3 or BCl 3 , or X is an anionic group such as OR - or NR 2 - , in which R is a straight or branched chain 1 to 10 carbon atom alkyl or aryl group, or MZn in which M is a metal, or metalloid, preferably nickel, Z is a halide, preferably chlorine or an anionic group such as OR - or NR 2 - , in which R is as defined above, and n indicates the number of Z entities required to satisfy the formal valance of M. Such compounds include NiCl 2 and NiBr 2 . DETAILED DESCRIPTION OF THE INVENTION Pursuant to the invention, as a first step, a mixture of a subsequent reactant, e.g., (C 6 F 5 ) 3 B, and a pentafluorophenyl compound is prepared. The mixture is pre-cooled to a temperature of, for example, -10°C to - 40°C. As a second step, a solution of an alkyl lithium in a non-interfering solvent is added to the mixture, which is allowed to warm to room temperature. In one embodiment of the invention, an ether, e.g., ethyl ether, may be added to the pre-cooled mixture of pentafluorophenyl compound and the subsequent reactant e.g., (C 6 F 5 ) 3 B. This procedure is illustrated by the following Example 1. EXAMPLE 1 Bromopentafluorobenzene (3.90g) was combined with (C 6 F 5 ) 3 B (7.92g in 222g of Isopar). Ether (50 ml) was added and the mixture was cooled to -32°C. nBuLi (9.67mL, 1.6 M ) in hexanes was added and the mixture was allowed to warm to room temperature. Lithium tetrakis (pentafluorophenyl) borate etherate was isolated (10.1g, 74.9% yield) as the product of the reaction. 19 F NMR indicated a purity of 88.3% and 1 H NMR showed no butyl groups contained in the product.

Claims: A method for producing a lithium tetrakis (pentafluorophenyl) borate which comprises: (i) preparing a mixture of a pentafluorophenyl compound and a subsequent reactant in solution in a non-interfering solvent and cooling the resulting mixture to between -10°C and -40°C, wherein the subsequent reactant is selected from (C 6 H 5 ) 3 B, (C 6 F 5 ) 3 B, BX 3 or MXn in which X is a halide or an anionic group and M is a metal, or metalloid, and n indicates the number of X entities required to satisfy the formal valance of M.; (ii) adding a solution of an alkyl lithium in a non-interfering solvent; and (iii) permitting the resultant reaction mixture to warm to room temperature; wherein lithium tetrakis (pentafluorophenyl) borate is produced. A method according to claim 1 in which an ether is added to said solution produced in step (i). A method according to claim 1 or claim 2 in which the pentafluorophenyl compound is selected from pentafluorophenyl bromide, pentafluorophenyl chloride and pentafluorobenzene. A method according to claim 1 wherein the subsequent reactant is selected from the group consisting of (C 6 H 5 ) 3 B, (C 6 F 5 ) 3 B, BF 3 , BCl 3 , B(OR) 3 , B(NR 2 ) 3 , NiCl 2 and NiBr 2 , in which R is a straight or branched chain 1 to 10 carbon atom alkyl or aryl group.

Inventors: KRAFFT TERRY E, KRAFFT, TERRY E.
Applicants: BOULDER SCIENT CO, BOULDER SCIENTIFIC COMPANY
Application year: 1997
Main classification: C07F5
IPC codes: C07F1, C07F5