Synthesis and Complexation of Ethene Bridged Bis phosphine Ligands

Synthesis and Complexation of Ethene Bridged Bis(phosphine) Ligands 

Ethene bridged bis(phospliine)s are most conveniently prepared by the reaction of l,2-bis(dichlorophosphino)ethane with organometaUic reagents, usually hthiated or Grignard compounds [52]. This method prevents the time consuming and laborious synthesis of secondary phosphines and easily affords the desired bidentate phosphines via a single-pot procedure. Accordingly, the bromobenzene derivatives 

12b-d were treated with an equimolar amount of n-butyllithium at -70 C in dry tetrahydrofuran. Subsequently, l,2-bis(dichlorophosphino)ethane was introduced. After work-up, pure l,2-bis(di(2,4,6-trimethylphenyl)phosphino)ethane (13b), 1,2-bis(di(2-isopropylphenyl)phosphino)ethane (13c) and l,2-bis(di(2,4,6-triisopropyl-phenyl)phosphino)ethane (13 d) were obtained in moderate to high yields after re-crystaUization of the crude product (Fig. 2.16). Yields of more than 90% for 13b compared to 19% obtained using the method of Chatt et al. [53] clearly underline the big advantage of this straightforward procedure. 

The reaction of 13x with bis(benzonitrile)dichloropalladium(II) [Bn2PdCl2[ and monochloro(l,5-cyclooctadiene)monomethylpalladium(ll) [(COD)PdCIMe] yielded the corresponding palladium(II) complexes 14x and 15x (Fig. 2.16). Upon slow evaporation of an acetonitrile solution, 14 c and 14 d gave crystals that were suitable for structure determination via single crystal X-ray diffraction (Fig. 2.17). Compound 14 b was crystallized by slow diffusion of pentane into a solution of 14b in tetrachloroethane. 

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