Manganese Carbonyl Compounds Reveal Ultrafast Metal–Solvent Interactions

Abstract

Herein, we exemplify that time-resolved multipleprobe spectroscopy (TR M PS) with infrared detection can be used to observe and quantify the dynamic processes occurring during the solvation of a catalytically competent manganese(I) carbonyl compound. TR M PS has been used to demonstrate that a manganese(I) 2-phenylpyridyl (ppy) complex, [Mn(ppy)-(CO) 4 ], undergoes photochemically induced loss of a carbonyl ligand on a sub-picosecond time scale to give solvent (S) complexes of the type, fac-[Mn(ppy and DMSO). An excited state, assigned as 3 [Mn(ppy)(CO) 4 ], with a lifetime, τ, of ca. 5 ps is also formed as a minor photoproduct. The vibrational modes of the carbonyl ligands in fac-[Mn(ppy)-(S)(CO) 3 ] are diagnostic of the nature of the coordinated solvent and allow for the dynamics of solvation within the coordination of the metal to be observed. For example, in the case of THF, initial interactions with the metal occur through a C−H σ-interaction, assigned based on the similarity to the bands observed for the related heptane metal complex. Isomerization to the thermodynamically preferred O-binding mode was observed, τ ca. 18 ps, with similar behavior evident in 1,4-dioxane and n Bu 2 O. The lifetime for the isomerization shows a correlation with the number of C−H bonds in the solvent. In 1,4-dioxane, there is no evidence for the initial formation of an O-bound complex which indicates that the solvent binding is not stochastic in nature and is likely determined by the topology of the first solvation shell of the metal complex. The insight into these ultrafast metal−solvent interactions is enabled by the dominant photoprocess, CO dissociation, being rapid (<1 ps). Which, taken together with prompt vibrational cooling, enables the subtle interplay between metal and solvent during the solvation event to be characterized and quantified.

Light‐ and Manganese‐Initiated Borylation of Aryl Diazonium Salts: Mechanistic Insight on the Ultrafast Time‐Scale Revealed by Time‐Resolved Spectroscopic Analysis

“…However, in recent years we have demonstrated exactly how time-resolvedm ultiple probe spectroscopy (TR M PS) with infrared detection can be used to interrogate reactions teps pertinentt oc atalysis, from the picosecond to microsecond timescale. [43,[63][64][65] Following photochemical activation of the pre-catalyst, the vibrational modes of the Mn-CO moiety provide the perfect spectroscopic handle for monitoring the accumulationofnew species and intermediates as well as their final fate. Thus, in this study we firstly describe the innovation of the Mn-mediated borylation of aryl/heteroaryl diazonium salts into ag eneral synthetic methodology.T he reactionp roved ideal for generating mechanistic detail and extraordinary insighti nto the Mn speciesi nvolved in the photochemical reactionp rocesses, the findings of which are globally important for aplethora of processes employing Mn-containingc arbonyl initiators/catalysts.…”

Direct Measurement of the Visible to UV Photodissociation Processes for the PhotoCORM TryptoCORM

“…23 However, at the lower excitation energies (465 nm, 2.66 eV) that are preferred for medical applications, 32 fewer CO molecules are released (1.4 equivalent). The CH3CN group of TryptoCORM is labile, 33,34 so that the TryptoCORM-CH3CN complex is likely to exist in a dynamic equilibrium with TryptoCORM in solution, leading to questions around the relative photochemical and hence medicinal effectiveness of the two species. In this work, we are able to directly compare the photochemistry of the TrytoCORM and TryptoCORM-CH3CN moieties for the first time since our mass spectrometry based technique allows us to independently isolate both molecular species prior to photoexcitation.…”

“…[24] However, at the lower excitation energies (465 nm, 2.66 eV) that are preferred for medical applications, [32] fewer CO molecules are released (1.4 equivalent). The CH3CN group of TryptoCORM is labile, [33,34] so that the TryptoCORM-CH3CN complex (i.e. the TryptoCORM molecule minus the acetonitrile ligand) is likely to exist in a dynamic equilibrium with TryptoCORM in solution, leading to questions around the relative photochemical and hence medicinal effectiveness of the two species.…”

A “one pot” mass spectrometry technique for characterizing solution- and gas-phase photochemical reactions by electrospray mass spectrometry

“…For example, solvation of photochemically generated singlet 16electron d 6 metal complexes occurs on a sub-ps timescale so that direct observation of the initial photoproducts in the condensed phase is challenging. 15 The rst report of the use of electrospray ionisation mass spectrometry (ESI-MS) to detect intermediates from a photoinitiated reaction in solution was from Arakawa et al 16 The study focused on solvolysis of ruthenium complexes, and was able to demonstrate that photoinitiated solvolysis, triggered in the electrospray plume, proceeds by an addition-elimination reaction. Turner et al and co-workers used a similar approach, involving irradiation at the tip of the spray capillary, to study iron cyclopentadienyl complexes catalysing epoxides.…”