Reactions of the Disilane Me 3 SiSiCl 3 with P ‐Chlorophosphaalkenes: Transient and Persistent Per‐Silylated Phosphaalkenes

Reactions of P ‐chlorophosphaalkenes (RMe 2 Si) 2 C=PCl ( 1a : R = Me; 1b : R = Ph) with the disilane Me 3 SiSiCl 3 ( 5 ) furnish diphosphenes (Cl 3 Si)(RMe 2 Si) 2 C–P=P–C(SiCl 3 )(SiMe 2 R) 2 ( 4a : R = Me; 4b : R = Ph) by Me 3 SiCl elimination. The structure of the new compound 4b was confirmed by X‐ray diffraction; it displays crystallographic inversion symmetry. Monitoring the reactions with 31 P‐ and 29 Si‐NMR spectroscopy detected P ‐(trichlorosilyl)phosphaalkenes (RMe 2 Si) 2 C=PSiCl 3 ( 2a , R = Me; 2b , R = Ph) as the primary intermediates from reductive P ‐silylation of 4a , 4b , and P ‐[(trichlorosilyl)phosphanyl]phosphaalkenes (RMe 2 Si) 2 C=P–P(SiCl 3 )C(SiCl 3 )(SiMe 2 R) 2 ( 3a : R = Me; 3b : R = Ph) as unsymmetric dimerisation products that rearrange to provide 4a , 4b in step III of the reaction sequence. This step (the P→C 1,3‐trichlorosilyl shift reaction) was mimicked by the synthesis of (Me 3 Si) 2 C=P–P(SiCl 3 ) t Bu ( 7 ), which rearranges into an unsymmetric diphosphene t BuP=PC(SiMe 3 ) 2 SiCl 3 ( 8 ). The bulkier P ‐chlorophosphaalkene ( i PrMe 2 Si) 2 C=PCl ( 1c ) reacts with 5 , eliminates Me 3 SiCl and thereby provides the first persistent acyclic per‐silylated phosphaalkene ( i PrMe 2 Si) 2 C=PSiCl 3 ( 2c ) in an incomplete reaction. 2c exhibits an exceptionally large NMR coupling 1 J ( 31 P, 29 Si) = ±249 Hz. Within weeks, the mixtures of 1c and 2c undergo decomposition with loss of the P=C functions.