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

Abstract

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.