Ring-Opening Reaction of Phosphorus-Bridged [1]Ferrocenophane via Ring Slippage from η⁵- to η-Cp

Abstract

A reaction mechanism was investigated for a ring-opening reaction of RP(E)-bridged [1]ferrocenophane, where RP(E) = PhP(S) (3a), PhP (3b), and MesP (3c) (Mes = 2,4,6-trimethylphenyl). Irradiation of UV-vis light in the presence of an excess amount of P(OMe)(3) transformed 3a to [Fe(PhP(S)(eta(5)-C(5)H(4))(eta(1)-C(5)H(4)))(P(OMe)(3))(2)] (4a), in which one of the two cyclopentadienyl (Cp) rings of 3a changed its coordination mode from eta(5) to eta(1) and vacant coordination sites thus formed on the iron center were occupied by two P(OMe)(3) ligands. The molecular structure of 4a was determined by X-ray analysis, in which eta(1)-Cp adopted a 1-Fe-2-P-1,3-cyclopentadiene structure. Under the same reaction conditions, 3b and 3c also gave similar ring-slipped products 4b and 4c, respectively. Photolysis of 3a using more strongly coordinating PMe(3) in place of P(OMe)(3) led to complete dissociation of a Cp ligand from the iron center to form [Fe(PhP(S)(eta(5)-C(5)H(4))(C(5)H(4)))(PMe(3))(3)] (5). The formation of the ring-slipped and -dissociated products on the photolysis of 3 strongly supports the view that photolytic ring-opening polymerization of 3 proceeds via an unprecedented Fe-Cp bond cleavage mechanism.

Polyferrocenylsilane‐Based Polymer Systems

“…[92] The molecular structure of the product was determined by Xray crystallography and revealed an h 5 !h 1 haptotropic shift.…”

Photocontrolled Living Anionic Polymerization of Phosphorus‐Bridged [1]Ferrocenophanes: A Route to Well‐Defined Polyferrocenylphosphine (PFP) Homopolymers and Block Copolymers

“…Later, the same group reported the photolytic ROP 2 PPh}] when irradiated by UV light in THF at 0 8C, through a M À Cp bond cleavage mechanism affording PFPs with a broad molecular weight distribution (Scheme 1b). [16] In the work described, no externally added initiator was used and the polymerization was non-living with no control of molecular weight.…”

“…Photolytic ROP of phosphorus-bridged [1]ferrocenophanes. [15,16] Scheme 2. Mechanism for the photolytic polymerization of silicon-bridged [1]ferrocenophanes (S = solvent, for example, THF; * = photoexcited monomer).…”

Photoinduced FeCp Bond Cleavage and Insertion Reactions of Strained Silicon‐ and Sulphur‐Bridged [1]Ferrocenophanes in the Presence of Transition‐Metal Carbonyls

“…[12] Miyoshi and co-workers have demonstrated that strained phospha [1]ferrocenophanes (a % 278) undergo unprecedented Fe À Cp bond cleavage upon photoirradiation and, in the presence of donor solvents such as THF, photolytic ROP was detected. [45,46] [47,48] In addition, in the presence of phosphorus-donor ligands sila [1]ferrocenophanes have been shown to undergo reversible haptotropic shifts of the Cp ligand from h 5 to h 1 on phosphine coordination. [49] The subtle dependence of the reactivity of [1]ferrocenophanes on the nature of the bridging atom is demonstrated by the following example: whereas the aforementioned treatment of bora [1]ferrocenophanes 5 with metal carbonyls leads to reactivity at the FeÀCp bond to yield 6 and 7, [12] the analogous reaction using tin-bridged [1]ferrocenophanes yields products arising from the insertion of metal carbonyl fragments into the Sn À Cp bond.…”