A closed-shell monomeric rhenium(1−) anion provided by m-terphenyl isocyanide ligation

Abstract

Mixed isocyanide/carbonyl complexes with rhenium in the oxidation states “+1”, “0” and “−1” were prepared assisted by a sterically encumbered.

{MI(CO)X(CNArDArF2)4} (DArF = 3,5-(CF3)2C6H3; M = Re and Tc; X = Br and Cl) Complexes: Convenient Platforms for the Synthesis of Low-Valent Rhenium and Technetium Compounds

“…The significant redshift of the isocyano stretch in comparison to that of the noncoordinated isocyanide (ν CN = 2118 cm −1 ) denotes an efficient π-back-donation, which was not observed in rhenium and technetium complexes with the nonfluorinated m-terphenyl isocyanide CNAr Dipp2 or CNAr Mes2 . 5,14,15 Single-crystal X-ray diffraction confirms the equivalence of the four CNAr DArF2 ligands, which are coordinated in one plane (Figure 2). Selected bond lengths and angles as well as an ellipsoid representation of [Re(CO) 2 Br(CNAr DArF2 ) 3 ] and [Re(CO)Br(CNAr DArF2 ) 4 ] are given in the Supporting Information.…”

“…The interesting results of a previous report, which describes the formation of the tris-isocyanide complex [Mn(CO) 2 Br-(CNAr Mes2 ) 3 ] by a facile reaction of [Mn(CO) 5 Br] and 3 equiv of the sterically encumbered isocyanide CNAr Mes2 (Mes = 2,4,6-Me 3 C 6 H 2 , see Chart 1) in THF, 6 encouraged us to undertake similar reactions with suitable tricarbonylrhenium(I) and -technetium(I) complexes. A summary of the reactions between CNAr DArF2 and [Re(CO) 5 Br] and subsequent reactions of the formed products is given in Scheme 1. Scheme 2 shows similar reactions done with technetium compounds.…”

“…Unexpectedly, the reaction of [Re(CO) 5 Br] with 3 equiv of CNAr DArF2 in boiling THF led only to an intractable mixture from which no crystalline compounds could be isolated. Defined products, however, were obtained at higher temperature.…”

“…1−4 Very recently, we described the isolation and structural characterization of the rhenium monoanion [Re(CO) 3 (CNAr Dipp2 ) 2 ] − (Dipp2 = 2,6diisopropylphenyl, see Chart 1), which is an analog of the wellknown [Re(CO) 5 ] − anion, as a contact ion pair with a K + counterion. 5 Moreover, the extensive π-delocalization and the efficient steric protection of the meta-terphenyl groups enabled us to isolate a rare example of a monomeric rhenium(0) complex, [Re(CO) 3 (CNAr Dipp2 ) 2 ], which was characterized through EPR and IR spectroscopy.…”

Oxidorhenium(V) and Rhenium(III) Complexes with m‐Terphenyl Isocyanides

“…[13,15,29] Two illustrative examples for this fact are given with low-valent carbonyl complexes of rhenium and molybdenum: (i) The reaction of [Re(CO) 5 Br] with an excess of CNAr Dipp2 gives under mild conditions cis-[Re(CO) 3 Br(CNAr Dipp2 ) 2 ] with the common facial tricarbonylrhenium(I) core, while from the same reaction after 5 h reflux in toluene the trans-isomer with the less favored meridional arrangement of the carbonyls can be isolated. [30] (ii) Treatment of the molybdenum(0) complex trans-[Mo(CO) 3 (NCCH 3 )(CNAr Dipp2 ) 2 ] with the strong σ-donor pyridine results in a trans/cis rearrangement of the isocyanide ligands and cis-[Mo(CO) 3 (py)(CNAr Dipp2 ) 2 ] can be isolated from such reactions in good yields. [15] Both above mentioned reactions show that a cis arrangement of two of the sterically encumbered CNAr Dipp2 ligands on octa- hedrally coordinated metal ions is possible, but it was not observed with the oxidorhenium(V) complexes of the present study.…”