Reaction of(
5-C
5Me
5)Re(NO)(PPh
3)(C
CH)and Cu(OAc)
2 (1.5 equiv, 80
C, pyridine) gives theorange-brown ReC
4Re complex(
5-C
5Me
5)Re(NO)(PPh
3)(C
CC
C)(Ph
3P)(ON)Re(
5-C
5Me
5)(
2, 88%) as a 50:50diastereomer mixture. Crystallization affords(
SS,
RR)-
2·2CH
2Cl
2and solutions enriched in (
SR,
RS)-
2(
meso). Additionof Ag
+PF
6- (
2 equiv)yields deep blue (
SS,
RR)- and(
SR,
RS)-
22+2PF
6-(86%), which give two geometric isomers(62:38, 89:11; CD
2Cl
2, -93
C) aboutthe
+Re=C=C=C=C=Re
+linkages. Crystal structures of(
SS,
RR)-
2·2CH
2Cl
2 and(
SS,
RR)-
22+2PF
6-show ReC
4Re units with bond angles (169-178˚) andlengths (C
C, 1.202(7); C-C1.398(5); C=C 1.260-1.305(10) Å) near those of butadiyneor cumulenes. Natural bond order analysis andtopologicalelectron density calculations confirm the valence formulations.Reactions of (
SS,
RR)-
2 with(
SS,
RR)-
22+2PF
6-orAg
+PF
6- (1 equiv) give agreen radical cation(
SS,
RR)-
2+PF
6-(
= 1.74
B; Faraday method).
Edata yield a
Kcvalue of 1.1 × 10
9 (CH
2Cl
2,22.5
C) for the comproportionation. ESR spectra show undecetswith
Aiso,Re values(98 G) half those of related monorhenium radical cations, indicatingspin delocalization over two rheniums (
I =5/2). Accordingly, IR spectra give only one
NOband, positioned between those of
2 and
22+2PF
6-(CH
2Cl
2, 1665vs 1623/1719 cm
-1). Near IR spectra showunique solvent-independent bands (883, 1000, 1200 nm;
15000,9400,3200 M
-1 cm
-1).Sodium naphthalenide reduces (
SS,
RR)- or(
SR,
RS)-
2+PF
6-to (
SS,
RR)- or (
SR,
RS)-
2, establishingconfigurational stability. These and related data are analyzed indetail.