Metal-promoted alkyne trimerisation leading to novel metallacycles. The molecular structures of [Mo{η 3 -C(CF 3 )C(CF 3 )C(Me)C(Ph)SPr i }(CF 3 CCCF 3 )(η 5 -C 5 H 5 )], [WSPr i {η 5 -C(CF 3 )C(CF 3 )C(CF 3 )C(CF 3 )C(Me)C(Ph)}(η 5 -C 5 H 5 )], and [W(SC 6 H 4 Me-4){η 4 -C(CF 3 )C(CF 3 )C(CO 2 Me)C(CO 2 Me)C(CF 3 )C(CF 3 )}(η 5 -C 5 H 5 )]