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

Abstract

The photochemical reactions of the moderately strained sila[1]ferrocenophane [Fe(eta-C(5)H(4))(2)SiPh(2)] (1) and the highly strained thia[1]ferrocenophane [Fe(eta-C(5)H(4))(2)S] (8) with transition-metal carbonyls ([Fe(CO)(5)], [Fe(2)(CO)(9)] and [Co(2)(CO)(8)]) have been studied. The use of metal carbonyls has allowed the products of photochemically induced Fe-cyclopentadienyl (Cp) bond cleavage reactions in the [1]ferrocenophanes to be trapped as stable, characterisable products. During the course of these studies the synthesis of 8 from [Fe(eta-C(5)H(4)Li)(2)TMEDA] (TMEDA=N,N,N',N'-tetramethylethylenediamine) and S(SO(2)Ph)(2) has been significantly improved by a change of reaction solvent and temperature. Photochemical reaction of 1 with excess [Fe(CO)(5)] in THF gave the dinuclear complex [Fe(2)(CO)(2)(mu-CO)(2)(eta-C(5)H(4))(2)SiPh(2)] (9). The analogous photolytic reaction of 8 with [Fe(CO)(5)] in THF gave cyclic dimer [Fe(eta-C(5)H(4))(2)S](2) (10) and [Fe(2)(CO)(2)(mu-CO)(2)(eta-C(5)H(4))(2)S] (11), with the former being the major product. Photolysis of 1 with [Co(2)(CO)(8)] afforded the remarkable tetrametallic dimer [(CO)(2)Co(eta-C(5)H(4))SiPh(2)(eta-C(5)H(4))Fe(CO)(2)](2) (13). The corresponding photochemical reaction of 8 with [Co(2)(CO)(8)] gave a trimetallic insertion product in high conversion, [Co(CO)(4)(CO)(2)Fe(eta-C(5)H(4))S(eta-C(5)H(4))Co(CO)(2)] (14). These reactivity studies show that UV light promotes Fe-Cp bond cleavage reactions of both of the [1]ferrocenophanes 1 and 8. We have found that, whereas the less strained sila[1]ferrocenophane 1 requires photoactivation for Fe-Cp bond insertions to occur, the highly strained thia[1]ferrocenophane 8 undergoes both irradiative and non-irradiative insertions, although the latter occur at a slower rate. Our results suggest that such photoinduced bond cleavage reactions may be general and applicable to other related strained organometallic rings with pi-hydrocarbon ligands.

A Flexible Approach to Strained Sandwich Compounds: Chiral [1]Ferrocenophanes with Boron, Gallium, Silicon, and Tin in Bridging Positions

“…Boron‐containing polymers are an emerging field of material,26 however, low solubilities in organic solvents will severely limit their applications. Interestingly, the exothermy of the ROP measured by differential scanning calorimetry (DSC) was −95 kJ mol −1 [(Me 3 Si) 2 NBfc] and significantly lower than that of the similarly tilted sulfur‐bridged [1]FCP ( α =31.05(10)°; Δ H ROP =−130(±20) kJ mol −1 ) 27–29. The lower than expected enthalpy was attributed to the destabilizing effect of the bulky amino group on the formed polymer 25.…”

Photoinduced iron–cyclopentadienyl (Fe–Cp) bond cleavage reactions and photocontrolled polymerizations of strained [1]ferrocenophanes

“…THF) is used. This study also suggests that relief of ring strain by cleavage of Fe-Cp bond can potentially be applied to [1]ferrocenophanes with other bridging elements [35].…”

“…To gain further insight into the effect of ring-strain on the Fe-Cp bond cleavage, comparative studies have been performed on the photolytic reactivity of the highly strained sulphur-bridged [1]ferrocenophane (9) and the moderately strained diphenylsilicon-bridged [1]ferrocenophane (10) 9 ] and [Co 2 (CO) 8 ]) [35].…”

Strained Ferrocenophanes

“…121, 122 Studies on the photoinduced reactivity of boron 5 ] also yielded the associated Fe−Cp insertion products 70 and 71. 123 In the absence of metal carbonyl complexes, irradiation of 69 yielded the first group 16 bridged [1.1]ferrocenophane 72 in addition to small oligomeric species, a pathway not observed during the photolytic reactivity studies of species 68 (Scheme 17). The differences in reactivity of the two species were attributed to the increased ring strain in 69 (α = 31.1°) 101 relative to 68 (α = 19.1°) 124 Interestingly, irradiation of the same two species in the presence of [Co 2 (CO) 8 ] also results in contrasting reactivity (Scheme 18).…”