Phosphacycloalkyldiones: synthesis and coordinative behaviour of 6- and 7-member cyclic diketophosphanyls

Glutaryl and adipoyl chlorides undergo facile condensation with the bis(silyl)phosphanes RP(SiMe 3 ) 2 (R = Me, n Bu, t Bu, Ph, Mes) to afford exclusively the phosphacycloalkyldiones (CH 2 ) n (C&z.dbd;O) 2 PR ( n = 3, 4). Characterised spectroscopically and, for R = Ph, Mes ( n = 3) crystallographically, the macrocycles are conformationally fluxional in solution and appreciably moisture sensitive. Though seemingly resistant to chemical oxidation at phosphorus, coordination is readily achieved, as illustrated by isolation of trans -[Pt(PEt 3 ){P(Ph)(CO) 2 (CH 2 ) 3 }Cl 2 ] and a series of tungsten pentacarbonyl complexes, which are characterised crystallographically and by infrared and NMR spectroscopy. Together, these data suggest the macrocycles to be relatively weak σ-donors with no appreciable π-acceptor character. Condensation of glutaryl and adipoyl chlorides with bis(silyl)phosphanes RP(SiMe 3 ) 2 (R = Me, n Bu, t Bu, Ph, Mes) affords the conformationally fluxional phosphacycloalkyldiones (CH 2 ) n (C&z.dbd;O) 2 PR ( n = 3, 4); their coordination behaviour is explored.