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(SiMe3)(2) (R = Me, Bu-n, Bu-t, Ph, Mes) to afford exclusively the phosphacycloalkyldiones (CH2)(n)(C=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(PEt3){P(Ph)(CO)(2)(CH2)(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 sigma-donors with no appreciable pi-acceptor character.