Mechanisms of cis/trans Isomerization of (η⁵-C₅H₅)₂Fe₂(CO)₂(μ-SR)₂, Where R = Methyl or tert-Butyl, Under Photochemical and Thermal Conditions

Abstract

Photolysis of cis,syn-(η 5 -C 5 H 5 ) 2 Fe 2 (CO) 2 (µ-SMe) 2 and mixtures enriched in the trans,anti isomer in frozen Nujol matrixes at ca. 90 K has revealed a complex set of wavelengthdependent photoproducts. These photoproducts include three species with bridging carbonyl groups that appear to be a set of conformers differing in the relative orientation of the S-Me groups, a dicarbonyl species that may be a conformer of the trans,anti isomer, and two species that appear to have a single terminal carbonyl group. Evidence is also presented for the formation of an IR-silent intermediate, (η 5 -C 5 H 5 ) 2 Fe 2 (µ-SMe) 2 . Solution studies have demonstrated that the bridging carbonyl species are sufficiently stable to be observed at room temperature. These bridging isomers readily react with CO to mostly form the trans,anti isomer, providing one mechanism for cis to trans interchange. Photolysis of cis,syn-(η 5 -C 5 H 5 ) 2 -Fe 2 (CO) 2 (µ-SMe) 2 in petroleum ether under 13 CO at room temperature results in formation of both labeled and unlabeled trans,anti isomer, suggesting both a CO-loss and an internal non CO-loss pathway for isomer interconversion. Consistent with this, thermal reequilibration of trans,anti-enriched mixtures in petroleum ether under 13 CO results in formation of labeled trans,anti isomer, labeled (η 5 -C 5 H 5 )Fe(CO) 2 (SMe), and mostly unlabeled cis,syn isomer. Photolysis of cis,syn-(η 5 -C 5 H 5 ) 2 Fe 2 (CO) 2 (µ-S-t-Bu) 2 in frozen Nujol yields a bridging carbonyl photoproduct and the trans,anti isomer. Photolysis of the tert-butyl derivative in petroleum ether at 0 °C results in formation of the trans,anti isomer.

Reactions of the Phosphinidene-Bridged Complexes [Fe2(η5-C5H5)2(μ-PR)(μ-CO)(CO)2] (R = Cy, Ph, 2,4,6-C6H2tBu3) with Diazoalkanes. Formation and Rearrangements of Phosphadiazadiene-Bridged Derivatives

“…10:1. This is likely to follow from a photochemically induced and reversible trans / cis isomerization in the final product, comparable to those previously observed in related species such as phosphide- and thiolate-bridged complexes of the type [Fe 2 Cp 2 (μ-H)(μ-PR 2 )(CO) 2 ] ( trans to cis ) , and [Fe 2 Cp 2 (μ-SR) 2 (CO) 2 ] ( cis to trans ) …”

Heterometallic Derivatives of the Unsaturated Methyl-Bridged Complex [Mo2(η5-C5H5)2(μ-CH3)(μ-PCy2)(CO)2]. Photochemical Generation of Methylidyne-Bridged Clusters

“…In both cases the molecule can be viewed as resulting from the addition of a M(CO) 5 fragment (M = Mo, W) to the unsaturated dimetal center of a dehydrogenated molecule of 1 (thus transformed into a methylidyne-bridged substrate) opposite the dicyclohexylphosphide ligand. This is accompanied by a trans to cis rearrangement of the Mo 2 Cp 2 (CO) 2 moiety, not unexpected under photochemical conditions, while the M(CO) 5 fragments display octahedral geometry, with the sixth coordination position roughly pointing to the center of the Mo 2 C(8) triangle. The Mo−Mo separation of ca.…”

Diphenylphosphide-Bridged Diiron Derivatives of [Fe2(η5-C5H5)2(μ-H)(μ-PPh2)(CO)2]

“…Although complexes 3 and 5 are not very stable, it should be noted that no other carbonyl-bridged phosphide complexes of the type [Fe 2 Cp 2 (μ-PX 2 ) 2 (μ-CO)] appear to have been reported in the literature. Interestingly, similar thiolate-bridged complexes [Fe 2 Cp 2 (μ-SR) 2 (μ-CO)] have been recently detected as transient intermediates in the photolytic isomerization cis- to trans -[Fe 2 Cp 2 (μ-SR) 2 (CO) 2 ] 2 …”