Rhenium formyl complexes

In contrast, spectroscopic and crystal structure analysis indicates that nucleophilic attack of hydride on 72 occurs on the face of the ligand which is coordinated to the metal (Scheme 17). No intermediate species could be detected for this latter reaction. Monitoring of the reduction of the rhenium analog 74 with sodium borohydride indicated the intermediacy of a rhenium formyl complex 75, presumably formed by attack on a coordinated carbon monoxide. Signals for 75 eventually disappear and are replaced by those of the (diene)rhenium product 76 (Scheme 18)95. 

The rhenium formyl complex was independently synthesized by reaction of K HB(0-/-Pr)3" with Re2(CO)io in THF at 0°C, followed by aqueous basic workup and cation exchange with Et4N" Br". It was recrystallized from THF-hexane, and isolated in 32% yield as a yellow, air-stable solid. 

Other than (CO)4Fe(CHO) and derivatives thereof (22-25), only a few of the formyl complexes in Table I show significant stability at room temperature. Of these, the binuclear rhenium formyl cis-(CO)5ReRe(CO)4(CHO) [19, Eq. (5)] has received the greatest attention (37. 38. 42. 47). The manganese and mixed manganese/rhenium homologs (12, 18) can be similarly prepared, but are less stable (35. 38, 47). 

Formylation, via bismuth(III) compounds, 9, 440 Formyl complexes with rhenium, G-H BDEs, 1, 300 with tantalum, 5, 162... 

Zubieta and coworkers have recently taken advantage of the fluorescent and luminescent properties of organometallic complexes of rhenium (and technetium) comprising certain aromatic ligand systems (Fig. 2.2.6). The nonradioactive Re(CO)3 bioconjugates with a formyl peptide receptor-targeting peptide (flVlLF), enabeled visualization... 

Fig. 2.2.6. Formyl peptide receptor-targeting peptide (fMLF)[(SAACQ-M(C0)3) ] conjugate useful for in vitro fluorescent microscopy (where M = Re) and in vivo single-photon emission computer tomography (SPECT) (where M = Tc) with isostructural technetium and rhenium complexes...

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