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On the Influence of the Bite Angle of Bidentate Phosphane Ligands on theRegioselectivity in Allylic Alkylation
Author(s) -
van Haaren Richard J.,
Oevering Henk,
Coussens Betty B.,
van Strijdonck Gino P. F,
Reek Joost N. H.,
Kamer Paul C. J.,
van Leeuwen Piet W. N. M.
Publication year - 1999
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/(sici)1099-0682(199908)1999:8<1237::aid-ejic1237>3.0.co;2-y
Subject(s) - chemistry , bite angle , regioselectivity , alkylation , tsuji–trost reaction , denticity , ligand (biochemistry) , allylic rearrangement , moiety , stereochemistry , catalysis , medicinal chemistry , crystallography , organic chemistry , crystal structure , biochemistry , receptor
The natural bite angle of bidentate phosphane ligands influences the isomer distribution ( syn and anti ) in (1‐methylallyl)(bisphosphane)Pd OTf complexes. It was found ( 31 P‐ and 1 H‐NMR studies) that the syn / anti ratio changes from 12 (dppp) to 1.3 (sixantphos). Molecular orbital calculations [PM3(tm) level] indicate that for ligands inducing a large bite angle, the phenyl rings of the ligand embrace the allyl moiety, thus influencing the syn / anti ratio. This bite‐angle effect on the syn / anti ratio is transferred to the regioselectivity in stoichiometric allylic alkylation. Ligands inducing large bite angles direct the regioselectivity towards the formation of the branched product 2 . Catalytic alkylation of ( E )‐2‐butenyl acetate showed that for ligands with a small bite angle the regioselectivity of the catalytic and stoichiometric alkylation are in good agreement. This correspondence is worse for ligands with a larger bite angle, which is rationalised in terms of the relative rates of syn / anti isomerisation and alkylation. The ligand with the largest bite angle (sixantphos) gives the most active catalytic species.