J. Wouters, R. Klein, C. Elsevier
Nov 1, 1994
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0
Influential Citations
29
Citations
Journal
Organometallics
Abstract
The synthesis and characterization of new trans-bis(triphenylphosphine)(o-alleny1)-platinum(I1) and -palladium(II) halides, prepared by the oxidative-addition reaction of allenyl or propargyl halides with M(PPh& (M = Pt, Pd), are described. Their molecular structure has been confirmed by an X-ray crystal structure determination of trans-[PtBr{ CH=C=C-(CH3)2}(PPh3)2]: space group C2/c, a = 11.498(3) A, b = 15.511(3) A, c = 19.570(6) A, /3 = 90.06(3)", V = 3490(2) Hi3, 2 = 4, R = 0.064, R, = 0.123. Furthermore, a highly uncommon trans to cis isomerization was observed for trans-bis(triphenylphosphine)(a-allenyl)palladium bromides which bear alkyl substituents at the y-positions of the allenyl ligand, with formation of cis-(a-alleny1)palladium bromides which exhibit double atropisomerism, i.e. around the allenic axis and around the Pd-C axis. The trans to cis isomerization proceeds diastereo-selectively when the alkyl groups at the y-position exhibit large steric differences; Le., for cis-[PdBr{CH=C=CMe(t-Bu)}(PPh3)~1 only the M,M/PQ diastereoisomer was formed, whereas for cis-[PdBr{ CH=C=CMe(Et)}(PPh3)2] equal amounts of the M,M/PQ and MQI P,M diastereomers were observed.