Factors Influencing Chelate Ring Formation by Au I

The NMR spectrum of the mixed ligand complex [Au(dppe)(depe)] (Fig. 9) established the existence of a tetrahedral bis(diphosphine) species in solution. The A2B2 multiple pattern was resolved in the spectrum at room temperature. The two bond P(Et2)-Au- P(Ph2) coupling was 52 Hz, showing that any ring opening and closure occurs at a rate 52 s  

The stability of the bis-chelated complexes [Au(R2P(CH2)2PR02] appears to be dependent on the nature of the phosphine-substituents (R and R ). The P NMR titration of ClAu(depe)AuCl with depe (R=R =Et) in CDCI3 is shown in Fig. 8. In contrast to the dppe titration, the bis-chelated complex [Au(depe)2] (15.8 ppm) was not present in solution until the Au depe ratio exceeded 1 1. It was the only species present at a 1 2 

Au depe ratio, and it showed comparable kinetic stability to [Au(dppe)2] , as shown by the appearance of a separate peak for free depe with addition of excess ligand. This difference can be attributed to a higher stability of the complex with a 1 1 Au P-P 

The formation of bis-chelated complexes is most favourable for phenyl-substituted diphosphines which can form either 5- or 6-membered chelate rings. 

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