Polynuclear Rhenium and Manganese Selenido‐Carbonyl Complexes − Reversible Square to Butterfly Conversion of the Re 4 Se 2 Core by CO Loss in [Re 4 ( µ 3 ‐Se) 2 (CO) 16 (PPh 3 ) 2 ], and the Crystal Structure of [Mn 2 (µ 2 ‐Se 2 )(CO) 5 (PPh 3 ) 2 ]

The reaction of Ph 3 PSe with [Mn 2 (CO) 10 ] leads to the formation of [Mn 4 (μ 3 ‐Se) 2 (μ‐CO)(CO) 14 (PPh 3 ) 2 ], which contains a butterfly “Mn 2 Se 2 core”, along with traces of [Mn 2 (μ 2 ‐Se 2 )(CO) 5 (PPh 3 ) 2 ] ( 1 ), which contains a tetrahedral Mn 2 Se 2 core. The reaction of Ph 3 PSe with [Re 2 (CO) 8 (NCMe) 2 ] affords two new complexes, [Re 4 (μ 3 ‐Se) 2 (CO) 16 (PPh 3 ) 2 ] ( 2 ) and [Re 4 (μ 3 ‐Se) 2 (μ‐CO)(CO) 14 (PPh 3 ) 2 ] ( 3 ). Their molecular structures, determined by X‐ray diffraction methods, exhibit a nearly square‐planar Re 2 Se 2 and a butterfly Re 2 Se 2 core, respectively. These air‐stable tetrarhenium selenido‐carbonyl species display a reversible loss/addition of a CO molecule, which is accompanied by the formation/cleavage of a Re−Re bond and the consequent rearrangement of the Re 2 Se 2 core, from square to butterfly and vice versa. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)