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 P 4 butterfly complex [{Cp*Cr(CO) 3 } 2 (μ,η 1:1 -P 4 )] ( 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 (µ 3 ,η 1:1:1:1 -P 4 ){W(CO) 4 }] ( 2 ) in which 1 serves as a chelating P 4 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 (μ 3 ,η 3:1:1 -P 4 ){M(CO) 5 }] ( 3a,b ) and [{Cp*Cr(CO) 2 } 2 -(μ 4 ,η 3:1:1:1 -P 4 ){M(CO) 5 } 2 ] ( 4a,b ) which contain a folded cyclo-P 4 unit. 4a undergoes an unprecedented P 1 /P 3 -fragmentation yielding the cyclo-P 3 complex [Cp*Cr(CO) 2 (η 3 -P 3 )] ( 5 ) and the as yet unknown phosphinidene complex [Cp*Cr(CO) 2 (Cr(CO) 5 ) 2 (µ 3 -P)] ( 6 ). The identity of 6 is confirmed by spectroscopic methods and by the in situ formation of [{Cp*Cr(CO) 2 ( t BuNC)}P{Cr(CO) 5 } 2 ( t BuNC)] ( 7 ). DFT calculations throw light on the bonding situation of the reported products.