The Butterfly Complex [{Cp*Cr(CO)3 }2 (μ,η1:1 -P4 )] as a Versatile Ligand and Its Unexpected P1 /P3 Fragmentation.

The versatile coordination behavior of the P4 butterfly complex [{Cp*Cr(CO)3 }2 (μ,η1:1 -P4 )] (1) towards Lewis acidic pentacarbonyl compounds of Cr, Mo and W is reported. The reaction of 1 with [W(CO)4 (nbd)] (nbd=norbornadiene) yields the complex [{Cp*Cr(CO)3 }2 (μ3 ,η1:1:1:1 -P4 ){W(CO)4 }] (2) in which 1 serves as a chelating P4 butterfly ligand. In contrast, reactions of 1 with [M(CO)4 (nbd)] (M=Cr (a), Mo (b)) result in the step-wise formation of [{Cp*Cr(CO)2 }2 (μ3 ,η3:1:1 -P4 ){M(CO)5 }] (3 a,b) and [{Cp*Cr(CO)2 }2 -(μ4 ,η3:1:1:1 -P4 ){M(CO)5 }2 ] (4 a,b) which contain a folded cyclo-P4 unit. Complex 4 a undergoes an unprecedented P1 /P3 -fragmentation yielding the cyclo-P3 complex [Cp*Cr(CO)2 (η3 -P3 )] (5) and the as yet unknown phosphinidene complex [Cp*Cr(CO)2 {Cr(CO)5 }2 (μ3 -P)] (6). The identity of 6 is confirmed by spectroscopic methods and by the in situ formation of [{Cp*Cr(CO)2 (tBuNC)}P{Cr(CO)5 }2 (tBuNC)] (7). DFT calculations throw light on the bonding situation of the reported products.