Synthesis and structures of cationic aluminum and galllium amidinate complexes
Aluminum and gallium amidinate complexes, {l{underscore}brace}RC(NR{prime}){sub 2}{r{underscore}brace}MMe{sub 2} (R, R{prime} = alkyl; M - Al, Ga), react with the ``cationic activators'' [Ph{sub 3}C][B(C{sub 6}F{sub 5}){sub 4}] and B(C{sub 6}F{sub 5}){sub 3} to yield cationic Al and Ga alkyl species whose structures are strongly influenced by the steric properties of the amidinate ligand. The reaction of acetamidinate Al complexes {l{underscore}brace}MeC(NR{prime}){sub 2}{r{underscore}brace}AlMe{sub 2}(R{prime} = {sup i}Pr, 1a; R{prime} = Cy, 3a) with 0.5 equiv of [Ph{sub 3}C][B(C{sub 6}F{sub 5}){sub 4}] or B(C{sub 6}F{sub 5}){sub 3} yields {l{underscore}brace}MeC(NR{prime}){sub 2}{r{underscore}brace}{sub 2}Al{sub 2}Me{sub 3}{sup +} (R{prime} - {sup i}Pr, 2a{sup +}; R{prime} = Cy, 4a{sup +}) as the B(C{sub 6}F{sub 5}){sub 4}{sup {minus}} or MeB(C{sub 6}F{sub 5}){sub 3}{sup {minus}} salts. X-ray crystallographic analyses establish that 2a{sup +} and 4a{sup +} are double-amidinate-bridged dinuclear cations, in which the two metal centers are linked by {mu}-{eta}{sup 1},{eta}{sup 1} and {mu}-{eta}{sup 1},{eta}{sup 2} amidinate bridges. NMR studies show that 2a{sup +} undergoes two dynamic processes in solution: (1) a {mu}-{eta}{sup 1},{eta}{sup 1}/{mu}-{eta}{sup 1},{eta}{sup 2} amidinate exchange and (2) Me exchange between the two metal centers. The reaction of {l{underscore}brace}MeC(N{sup i}Pr){sub 2}{r{underscore}brace} (1b) with 0.5 equiv of B(C{sub 6}F{sub 5}){sub 3} yields {l{underscore}brace}MeC(N{sup i}Pr){sub 2}{r{underscore}brace}{sub 2}Ga{sub 2}Me{sub 3}{sup +} (2b{sup +}), whose structure and dynamic properties are similar to those of 2a{sup +}. The reaction of the bulkier {sup t}Bu-substituted amidinate complexes {l{underscore}brace}{sup t}BuC(N{sup i}Pr){sub 2}{r{underscore}brace}MMe{sub 2} (M - Al, 6a; M - Ga, 6b) with 0.5 equiv of [Ph{sub 3}C][B(C{sub 6}F{sub 5}){sub 4}] yields {l{underscore}brace}{sup t}BuC(N{sup i}Pr){sub 2}{r{underscore}brace}MMe{sub 2}{sm{underscore}bullet}{l{underscore}brace}{sup t}BuC(N{sup i}Pr){sub 2}{r{underscore}brace}MMe{sup +} (M - Al, 7a{sup +}; M - Ga, 7b{sup +}) as the B(C{sub 6}F{sub 5}){sub 4}{sup {minus}} salts, the former of which is thermally unstable. An X-ray crystallographic analysis establishes that 7b{sup +} is a single-amidinate-bridged dinuclear cation, in which the two metal centers are linked by a {mu}-{eta}{sup 1},{eta}{sup 2}amidinate bridge. NMR data establish that the structures of 7a{sup +} and 7b{sup +} are similar and both species are rigid in solution. 6a and 6b also react with B(C{sub 6}F{sub 5}){sub 3} to yield [7a][MeB(C{sub 6}F{sub 5}){sub 3}] and [7b][MeB(C{sub 6}F{sub 5}){sub 3}], respectively, which decompose by C{sub 6}F{sub 5}{sup {minus}} transfer to yield {l{underscore}brace}{sup t}BuC(N{sup i}Pr){sub 2}{r{underscore}brace}M(ME)(C{sub 6}F{sub 5}) (M = Al, 9a; M - Ga, 9b) and boron species. The ``super-bulky'' amidinate complexes {l{underscore}brace}{sup t}BuC(N{sup t}Bu){sub 2}{r{underscore}brace}MMe{sub 2} (M - Al, 12a; M - Ga, 12b)react with 1 equiv of [Ph{sub 3}C][B(C{sub 6}F{sub 5}){sub 4}] to yield {l{underscore}brace}{sup t}BuC(N{sup t}Bu){sub 2}{r{underscore}brace}MMe{sup +} (M = Al, 13a{sup +}; M = Ga, 13b{sup +}) as the B(C{sub 6}F{sub 5}){sub 4}{sup {minus}} salts. The salts [13a][B(C{sub 6}F{sub 5}){sub 4}] and [13b][B(C{sub 6}F{sub 5}){sub 4}] are thermally unstable and could not be isolated. However, the NMR data for 13a{sup +} and 13b{sup +} in C{sub 6}D{sub 5}Cl are consistent with base-free, three-coordinate structures or labile, four-coordinate solvated cations. These results provide a starting point for understanding the mechanism and reactivity trends in ethylene polymerization catalyzed by cationic Al amidinate species.
- Research Organization:
- Univ. of Iowa, Iowa City, IA (US)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FG02-88ER13935
- OSTI ID:
- 20017328
- Journal Information:
- Journal of the American Chemical Society, Vol. 122, Issue 2; Other Information: PBD: 19 Jan 2000; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
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