Synthesis and coordination chemistry of a diphospha-tetrathia macrocycle, 1,10-diphenyl-1,10-diphospha-4,7,13,16-tetrathiacyclooctadecane

Reaction of 1,2-dichloroethane with PhP(CH2CH2SH)2 and caesium carbonate affords 1,10-diphenyl-1,10-diphospha-4,7,13,16-tetrathiacyclooctadecane (18P2S4) in high yield (ca. 90%). 18P2S4 slowly decomposes in solution to afford insoluble PhP(S)(CH2CH2SCH2CH2SCH2CH2)2P(S)Ph which was characterised by single crystal X-ray diffraction. Reaction of 18P2S4 with [Ni(H2O)6](BF4)2 or Fe(BF4)2 affords [M(18P2S4)](BF4)2 (M = Ni or Fe). The structure of [Ni(18P2S4)]2+ is a tetragonally distorted octahedron in which there are two short Ni–S bonds [2.2152(6) Å] and two long Ni–S bonds [2.9268(6) Å]. For comparison the structure of [Ni(9PS2)2]2+ was determined and found to a have a similar, but less marked distortion, in which the difference between the long and short bonds is ca. 0.5 Å. In contrast the structure of [Fe(18P2S4)]2+ is octahedral with approximately equal Fe–S bonds. The electrospray mass spectra of the cations [M(9PS2)2]2+ and [M(18P2S4)]2+ (M = Ni or Fe) all display ethene loss from the ligands as has been previously observed with trithiacyclononane complexes. The results of P–C and C–S bond rupture were also observed in the reaction of ruthenium(III) triflate with 9PS2 which unexpectedly afforded crystals containing [Ru2(S)2(18P2S4)2], in which the two ruthenium centres are bridged by two sulfides and the two 18P2S4 ligands coordinated only through the phosphine centres. Also present in the crystals was one equivalent of tetrathiacycloundecane (12S4).