Monophosphanes and Diphosphanes with the Hypersilyl Substituent

The synthesis of (SiMe 3 ) 3 SiPH 2 ( 1 ) (further on denoted as hypersilylphosphane, HypPH 2 ) was achieved by two methods: by the reaction of (SiMe 3 ) 3 Si(OSO 2 CF 3 ) with PH 3 , and alternatively, by the reaction of NaPH 2 with (SiMe 3 ) 3 SiCl (hypersilylchloride). The latter reaction also afforded bis(hypersilyl)phosphane Hyp 2 PH ( 2 ). By the reaction of 1 and known hypersilylbis(trimethylsilyl)phosphane ( 3 ) with t BuOK, the novel hypersilylphosphanides HypPHK ( 4 ) and Hyp(SiMe 3 )PK ( 5 ) were prepared. Compound 1 also reacted with n BuLi to form HypPHLi ( 6 ) and HypPLi 2 ( 7 ). Furthermore, 3 reacted with hexachloroethane and 1,2‐dibromotetrachloroethane to give HypPCl(SiMe 3 ) ( 8 ) and HypPBr(SiMe 3 ) ( 9 ) as well as HypPCl 2 ( 10 ) and HypPBr 2 ( 11 ). Compounds 4 and 5 reacted smoothly with 1,2‐dibromoethane to give diphosphane HypHPPHHyp ( 12 ) as a mixture of the meso ‐ and rac ‐ d,l‐ diastereomers and Hyp(SiMe 3 )PP(SiMe 3 )Hyp ( 13 ) as the d,l ‐modification only. By reducing the known compound t BuHypPCl with potassium, the d,l‐ modification of t BuHypPPHyp t Bu ( 14 ) was obtained. All compounds were characterized by 29 Si‐ and 31 P NMR spectroscopy and elemental analyses with the exception of the phosphanides which were characterized spectroscopically only. The crystal structures of 3 and 4 and of diphosphanes 10 , 11 and 13 are reported. From temperature‐dependent 31 P NMR experiments, the coalescence temperature for the meso ↔ d,l interconversion of 12 was determined at 110 °C and gave an inversion barrier of roughly 69.4 kJ mol –1 , which is corroborated by results of ab initio calculations at the B3LYP/6‐31G(d) level. Two diastereomeric inversion transition structures for diphosphanes R–PH–PH–R with either a syn or an anti arrangement of the P–H bond and the phosphorus lone pair of electrons could be located; bulky substituents seem to prefer the anti arrangement.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)