Synthesis of a chelating hexadentate ligand with a P 3 N 3 donor set. Crystal and molecular structure of [ OC -6-22]-[Co{( R P *, R P *, R P *)-CH 3 C(CH 2 PPhC 6 H 4 NH 2 - 2) 3 }](PF 6 ) 3

Abstract

The first structurally authenticated example of a hexadentate chelating tertiary phosphine in which all six donors are bound to a single metal centre is described. The multidentate ligand (RP*,RP*, RP*)- and (RP*,RP*,S P*)-CH3C(CH2PPhC6H 4NH2-2)3 has been prepared in 80% yield via the reaction of five equivalents of sodium (2-aminophenyl)phenylphosphide (generated in situ from (2-aminophenyl)phenylphosphine and sodium in thf) with 1,1,1-tri(bromomethyl)ethane in thf. The diastereomeric mixture has been complexed to cobalt(iii) and the resulting pair of complexes, viz. [Co{(R P*,RP*,RP*)-CH 3C(CH2PPhC6H4NH2-2) 3}]Cl3 and [CoCl{(RP*,R P*,SP*)-CH3C(CH 2PPhC6H4NH2-2)3}]Cl 2, separated by ion exchange chromatography. The structure of the former (as the corresponding hexafluorophosphate salt) has been confirmed by X-ray crystallography and clearly shows all six donors of the P 3N3 ligand coordinated to a single cobalt(iii) centre. The related hexadentate ligand with internal N donors and terminal diphenylphosphino groups, viz. CH3C(CH2NHC 6H4PPh2-2)3, has also been synthesised, albeit in low yield, via the reaction of [Li(tmeda)][2-NHC 6H4PPh2] (generated in situ from (2-aminophenyl)diphenylphosphine, n-butyllithium and tmeda in diethyl ether) with 1,1,1-tri(iodomethyl)ethane in thf. No formation of a P3N 3 ligand has been observed when either Na[2-PPhC6H 4NH2] or [Li(tmeda)][2-NHC6H 4PPh2] is reacted with the related tripodal substrate 1,1,1-tris(tolyl-4-sulfonyloxymethyl)ethane in thf. Rather the P-methyloxetane (±)-[3-{(2-aminophenyl)phenylphosphinomethyl}]-3-methyloxetane and the sulfonamide 2-(4-CH3C6H4SO2)NHC 6H4PPh2 and the corresponding N-methyloxetane [3-{(2-diphenylphosphinophenyl)aminomethyl}]-3-methyloxetane have been isolated from the respective reactions. The structure of the sulfonamide has been confirmed by an X-ray analysis of the platinum(ii) complex trans-[PtCl(CH 3){2-PPh2C6H4NH(SO2C 6H4CH3-4)}2].