Syntheses, crystal and solution structures, ligand exchange, and ligand coupling reactions of mixed pentaarylantimony compounds

Schröder Günter

Okinaka Takaaki

Mimura Yasuyuki

Watanabe Mitsuko

Matsuzaki Takayuki

Hasuoka Atsushi

Yamamoto Yohsuke

Matsukawa Shiro

Akiba Kin-ya

Chemistry - A European Journal

All the possible combinations of mixed pentaarylantimony compounds bearing p-methylphenyl and p-trifluoromethylphenyl groups were synthesized, i.e., ArnTol5-nSb (n = 0-5: Ar = p-CF3C6H4, Tol = p-CH3C6H4): Tol5Sb (1), ArTol4Sb (2), Ar2Tol3Sb (3), Ar3Tol2Sb (4), Ar4TolSb (5), and Ar5Sb (6). Compounds 2-5 are the first well-characterized examples of mixed acyclic pentaarylantimony species. The structures of 2-6 were determined by X-ray crystallography to bear trigonal bipyramidal (TBP) geometry with the more electronegative p-trifluoromethylphenyl substituents selectively occupying the apical positions. Considerations based upon the chemical shifts of the ipso carbons of the aryl and the tolyl groups suggested that the solution structures of 1-6 were also TBP although pseudorotation of them could not be frozen even at –80 °C. Ligand exchange reactions (LERs) were found to take place between 1 and 6 at ca. 60 °C in [D6]benzene and all the six species 1-6 were found in the equilibrium mixture. The relative stabilities of 1-6 were determined quantitatively by comparison of the observed molar ratios of 1-6 in equilibrium with calculated statistical molar ratios, and Ar2Tol3Sb (3) was found to be the most stable. The ligand coupling reactions (LCRs) from 2-5 in solution were found to be greatly accelerated by adding Cu(acac)2 or Li+TFPB– [TFPB: B(3,5-(CF3)2C6H3)4], with the rate becoming comparable with the LER. The use of flash vacuum thermolysis (FVT) allowed the LCR to occur with very little ligand exchange except in the case of ArTol4Sb where it was very fast. The selectivities of LCRs determined by the yield of the formed biaryls by FVT were highly consistent with those in the catalyzed reactions in solution, where bitolyl was not obtained at all. The experimental results suggested that the LCR of pentaarylantimony compounds proceeds in the manner of apical-apical coupling.

antimony

hypervalent compounds

ligand effects

ligand-coupling

structure elucidation

Chemistry [ 430 ]

eng

Wiley-VCH Verlag GmbH

Copyright (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

[ISSN] 0947-6539

[DOI] 10.1002/chem.200601439

[NCID] AA11076269

[DOI] http://dx.doi.org/10.1002/chem.200601439