Low-co-ordination arsenic and antimony compounds: Synthesis and characterisation of 2-arsa- and 2-stiba-1,3-dionatolithium(I) complexes, [Li{OC(R)EC(R)O}L] (E=As or Sb; R=Bu(3)(t), C6H2Pr3i-2,4,6 or C(6)H(2)Bu(3)(t)-2,4,6; L=Et(2)O or MeOCH(2)CH(2)OMe)

Reactions of [Li{E(SiMe(3))(2)}(dme)] (E = As or Sb, dme = MeOCH(2)CH(2)OMe), with a range of acid chlorides, RCOCl, afforded the novel 2-arsa-1,3-dionatolithium(I) complexes [Li{OC(R)AsC(R)O}L](R = Bu(t), L = 1/2 dme or Et(2)O; R = C6H2Pr3i-2,4,6, L = Et(2)O; R = C(6)H(2)Bu(3)(t)-2,4,6, L = dme), and the first example of a 2-stiba-1,3-dionatolithium(I) complex [{[Li{OC(Bu(t))SbC(Bu(t))O}(dme)(0.5)](2)}(infinity)]. X-Ray crystal structural analyses for the complexes with R = Bu(t), L = 1/2 dme or Et(2)O and the antimony compound show them to be dimeric in the solid state with respect to the metal and anionic ligands, the dimeric units being linked in an infinite polymeric chain by bridging dme molecules or solvated with Et(2)O. A dimeric structure can also be inferred when R = C6H2Pr3i-2,4,6, L = Et(2)O; In solution these four compounds display fluxional behaviour. Treatment with HCl of the monomeric compound having R = C(6)H(2)Bu(3)(t)-2,4,6, L = dme yields the known diacylarsane [As{C(C(6)H(2)Bu(3)(t)-2,4,6)O}{C(C6H2But3-2,4,6)OH}] the crystal structure of which reveals the enol form with the alcoholic proton intramolecularly hydrogen bonded to the opposing oxygen centre of the ligand.