Fully Solvated, Monomeric Re(II) Complexes: Insights into the Chemistry of [Re(NCCH3)6]2+

Abstract

<sup>The chemistry of rhenium complexes covers oxidation state +VII to -I. Some oxidation states such as +II are only rarely found in literature. One of the reasons is the lack of a suitable stable precursor for the oxidation state +II. However, we have developed a two step synthesis to the fully solvated Re(+II) complex [Re(NCCH</sup><sub>3</sub><sup>)</sup><sub>6</sub><sup>]</sup>2+<sup> from [ReO</sup><sub>4</sub><sup>]</sup>-<sup> via the rhenium bis-arene complex [Re(C</sup><sub>10</sub><sup>H</sup><sub>8</sub><sup>)</sup><sub>2</sub><sup>]</sup>+<sup>. This fully solvated Re(+II) was fully characterized by various spectroscopic manners, cyclic voltammetry, and X-Ray diffraction analysis. Its potential as a precursor for Re(+II) chemistry was explored with various substitutions reactions with phosphines and halides, and the obtained products were as well fully characterized.<br></sup>

One Electron Changes Everything: Synthesis, Characterization, and Reactivity Studies of [Re(NCCH3)6]3+

“…[3a](BF 4 ) 2 is easier to reduce than its acetonitrile analogue (−0.56 V for [3a](BF 4 ) 2 and −1.00 V for [2a](PF 6 ) 2 ; in CH 3 CN (0.1 M NBu 4 (PF 6 )) vs Fc + /Fc), whereas oxidation becomes more challenging (+0.44 V for [3a](BF 4 ) 2 and +0.25 V for [2a](PF 6 ) 2 , Figure 1). 6 These electrochemical differences align with findings for other CH 3 CN/PhCN complexes. 12,13 As expected, the PhCN ligands make [3a](BF 4 ) 2 much more lipophilic as compared to its acetonitrile analogue [2a] 2+ , increasing the solubility of [3a](BF 4 ) 2 in solvents such as CHCl 3 , CH 2 Cl 2 , or acetone.…”

“…The Re−N bond lengths determined in [3a](BF 4 ) 2 (2.033(2)−2.0509(18) Å) are slightly shorter than those found in [2a](OTf) 2 (2.041(4)−2.056(3) Å). 6 Similar to those in [Ru(NCPh) 6 ]-(BF 4 ) 2 , the phenyl moieties of the PhCN ligands in the trans position with respect to each other are not in the same plane. 14 Oxidation of [2a](BF 4 ) 2 with the thianthrene radical cation tetrafluoroborate (E 1/2 = +0.86 V vs Fc + /Fc in CH 3 CN) 15 in CH 3 CN results in the formation of [Re(NCCH 3 ) 6 ](BF 4 ) 3 ([2b](BF 4 ) 3 ) in 92% yield (Scheme 2).…”

“…By DFT calculations, we have proposed that the actual oxidation step does not take place directly on [Re(η 6 -C 10 H 8 ) 2 ] + but rather on a CH 3 CN adduct, for example, [Re(η 6 -C 10 H 8 )(NCCH 3 ) 3 ] + . 6 By combining these two observations, we have developed a new procedure for [2a] 2+ that circumvents the low-yield synthesis of [Re(η 6 -C 10 H 8 ) 2 ] + . Heating of [1](BF 4 ) at 60 °C for 1 h in CH 3 CN results in the formation of [Re(η 6 -C 6 H 6 )(NCCH 3 ) 3 ] + (identified by ESI-MS).…”

“…4−7 Recently, we have examined the potential of [Re(NCCH 3 ) 6 ] 2+ as a precursor for the rare oxidation state +2, but one of the major drawbacks of substitution reactions with [Re(NCCH 3 ) 6 ] 2+ was its unexpected inertness. 6 Thus, we have wondered if changing the electron configuration (e.g., by oxidation) would have a significant effect on substitution rates as found in, for example, Fe II /Fe III hexa-aquo complexes.…”

“…Here we present the synthesis, characterization, and reactivity of [Re(NCCH 3 ) 6 ] 3+ , synthesized in a two-step procedure from [ReH(η 5 -C 6 H 7 )(η 6 -C 6 H 6 )] + .…”