[2+2] Cyclo-addition reactions of bis-pentamethylcyclopentadienyl zirconium metal complexes containing terminal chalcogenide ligands with the phospha-alkyne PCtBu. Syntheses, crystal and molecular structures of the four complexes [Zr(η5-(C5Me5)2(SC(tBu)P

The chalcogenide complexes [Zr(η5-(C5Me5)2(E))] (E=S, Se), (generated in situ from the corresponding pyridine adducts), undergo [2+2] cyclo-addition reactions with the phospha-alkyne tBuCP to afford the structurally characterised complexes [Zr(η5-(C5Me5)2(SC(tBu)P))] and [Zr(η5-(C5Me5)2(SeC(tBu)P))]. The former complex undergoes ring expansion reactions with either selenium to afford [Zr(η5-(C5Me5)2(SC(tBu)PSe))] or with PhCN to give [Zr(η5(C5Me5)2(SC(tBu)PC(Ph)N))] which have also been characterised structurally.