Small molecule activation of nitriles coordinated to the [Re₆Se₈]²⁺ core: formation of oxazine, oxazoline and carboxamide complexes

Abstract

Novel oxazine, oxazoline and carboxamide cluster complexes were prepared when different nucleophilic oxygen species reacted with nitriles coordinated to the Lewis acidic [Re6Se8]2+ cluster core. Reaction of ICH2CH2O- (generated in situ) with [Re6Se8(PEt3)5(NCR)]A2 (1A2 (R = Me) and 2A2 (R = Ph) where A = BF4-), leads to the formation of [Re6Se8(PEt3)5(2-methyloxazoline)]2+ (32+) and [Re6Se8(PEt3)5(2-phenyloxazoline)]2+ (42+). Similarly, reaction of BrCH2CH2CH2O- with the same nitrile complexes, 1A2 and 2A2 (where A = BF4- or SbF6-) leads to the corresponding oxazine complexes, [Re6Se8(PEt3)5(2-methyloxazine)]2+ (52+) and [Re6Se8(PEt3)5(2-phenyloxazine)]2+ (62+). In addition, reaction of 2(BF4)2 with KOH leads to the formation of the carboxamide complex, [Re6Se8(PEt3)5(phenylcarboxamide)](BF4) (7(BF4)). The neutral oxazine and oxazoline ligands can be removed using either heat or UV irradiation; UV irradiation was found to be more efficient at ligand removal as indicated by the shorter reaction times. The relative coordination strength of the neutral N-donor ligands was determined by these reaction times. X-ray structure determinations of 5(BF4)2 and 7(BF4) are also reported.

Tuning the Ground- and Excited-State Redox Potentials of Octahedral Hexanuclear Rhenium(III) Complexes by the Combination of Terminal Halide and N-Heteroaromatic Ligands

“…Various neutral and anionic ligands have been introduced at the six terminal positions of sulfide-capped octahedral hexanuclear rhenium­(III) complexes by thermal substitution reactions of the terminal halides or hydroxides in [Re 6 (μ 3 -S) 8 X 6 ] 4– (X = Cl, Br, I, OH) in solution or under melt conditions (see refs , , , , , , − , − , − , , , − , , , , , − ). To our knowledge, several reports have been published on photosubstitution reactions of octahedral hexanuclear metal complexes. ,,− Gray et al reported that the emission lifetime (τ em ) and quantum yield (Φ em ) of a hexanuclear rhenium complex with terminal iodides or solvent molecules in dichloromethane increase in the presence of an added iodide ion or neat solvent molecules [i.e., dimethyl sulfoxide (DMSO)], suggesting the labile nature of the terminal halides in the excited state. , Zheng et al reported that UV irradiation of [Re 6 (μ 3 -Se) 8 (PEt 3 ) 5 {HNC­(OCH 3 ) (CH 3 )}] 2+ in acetonitrile produces [Re 6 (μ 3 -Se) 8 (CH 3 CN) (PEt 3 ) 5 ] 2+ and that of a dichloromethane solution of [Re 6 (μ 3 -Se) 8 (CO)­(PEt 3 ) 5 ] 2+ affords a 23e complex, [Re 6 (μ 3 -Se) 8 Cl­(PEt 3 ) 5 ] 2+ , in which the coordinating chloride ion originates from dichloromethane. , Szczepura et al reported oxazoline and oxazine ligand removal reactions on [Re 6 (μ 3 -Se 8 ) (PEt 3 ) 5 (L)] 2+ (L = 2-methyloxazoline, 2-phenyloxazoline, and 2-methyloxazine) by UV irradiation . In the case of [Mo 6 (μ 3 -Cl) 8 Cl 6 ] 2– , spectroscopic and photophysical measurements in acetonitrile revealed that the bond between the chloride atom and the {Mo 6 (μ 3 -Cl) 8 } 4+ core was excited by UV irradiation .…”

[ReH3(PPh3)4] – A Key Compound in the Rhenium Hydride Chemistry

“…The adjacent C1À C2 bond is a 'normal' CÀ C single bond with a length of 1.44(1) Å. Additionally, the ReÀ N1À C1 bond angle is perfectly linear, while the N1À C1À C2 bond angle is clearly bent suggesting double bonds between Re and N1 and N1 and C1. The observed bonding features, particularly the linear ReÀ NÀ C unit, [48][49][50][51][52][53][54][55][56][57][58][59][60] strongly favor the assignment of compound 4 a as an azavinylidene over an interpretation as an amido complex, which would require a bent unit. [61] Recently, we observed the formation of a similar product as result of a nucleophilic attack of a fluorinated aryl lithium reagent, [62] where the obtained azavinylidene complex shows similar geometric features as discussed for 4 a.…”