Synthesis and Oxidation of Dirhenium C₄, C₆, and C₈Complexes of the Formula (η⁵-C₅Me₅)Re(NO)(PR₃)(C⋮C)_n(R₃P)(ON)Re(η⁵-C₅Me₅) (R = 4-C₆H₄R‘, c-C₆H₁₁):  In Search of Dications and Radical Cations with Enhanced Stabilities

Abstract

The racemic methyl complexes (η 5 -C 5 Me 5 )Re(NO)(PR 3 )(CH 3 ) (R: b, 4-C 6 H 4 CH 3 ; c, 4-C 6 H 4t-C 4 H 9 ; d, 4-C 6 H 4 C 6 H 5 ; e, c-C 6 H 11 ), which feature phosphines that are more electron rich and/or bulkier than P(C 6 H 5 ) 3 , are elaborated by reactions with HBF 4 ‚OEt 2 /chlorobenzene, HCtCH or HCtCCtCSiMe 3 , and t-BuOK to give the alkynyl complexes (η 5 -C 5 Me 5 )Re(NO)-(PR 3 )(CtCH) (3b,c) and (η 5 -C 5 Me 5 )Re(NO)(PR 3 )(CtCCtCSiMe 3 ) (7b-e). The latter are converted (K 2 CO 3 /MeOH or wet n-Bu 4 N + F -) to butadiynyl complexes (8b-e). Homo-or crosscouplings (3b, 8b-e; Cu(OAc) 2 /pyridine) lead to the µ-butadiynediyl complex (η 5 -C 5 Me 5 )Re-(NO)(PR 3 )(CtC) n (R 3 P)(ON)Re(η 5 -C 5 Me 5 ) (4b; n ) 2) and analogous µ-hexatriynediyl (10b; n ) 3) and µ-octatetraynediyl (9b-e; n ) 4) species. Oxidation of 4b by AgSbF 6 (ca. 1:1 or 1:2) gives the radical cation 4b •+ SbF 6or the dication 4b 2+ (SbF 6 -) 2 . These isolable compounds exhibit delocalized mixed-valence and cumulenic electronic ground states, respectively. The cyclic voltammograms of 9b-e and 10b show oxidations to analogous species, with much better chemical reversibilities than for the P(C 6 H 5 ) 3 analogues. However, these longer chain systems decompose rapidly at -78 °C and could not be isolated or spectroscopically characterized.

Electronic Structure and Chain‐Length Effects in Diplatinum Polyynediyl Complexes trans,trans‐[(X)(R3P)2Pt(CC)nPt(PR3)2(X)]: A Computational Investigation

“…First, on the basis of Koopmans theorem, an increase in ionization potential with chain length would be expected. Accordingly, cyclic voltammograms of the diplatinum complexes trans,trans-[(X)(R 3 P) 2 Pt(CC) n Pt(PR 3 ) 2 (X)], [10][11][12] as well as related dirhenium species, [8,9] indicate thermodynamically less favorable oxidations with increasing chain length. [48] Secondly, other combinations of occupied and unoccupied orbitals mirror the decreasing HOMO-LUMO gap, as illustrated for the LUMO+1 and HOMOÀ1 energies in Table 5.…”

Synthesis and cyclic voltammetry of some new metal carbene substituted cyclopentadienyliron half sandwich complexes

“…In many cases, metals of oligonuclear complexes are connected by p ligands such as fulvalenes [7,14,[16][17][18][19], biphenyl [7,[20][21][22][23][24][25], stilbene [26], oligophenylenes [27], etc. Alternatively there are complexes, in which the metals are directly incorporated in the connecting p system, for example in bimetallic cumulenylidene or oligoalkynediyl complexes [28][29][30][31][32][33][34][35].…”

Polyynes

“…Later, Gladysz and coworkers reported the synthesis of an extensive series of wire-like rhenium(i) alkynyl complexes containing two [(h 5 -C 5 Me 5 )-Re(NO)(PPh 3 )] moieties bridged by polyynyl C 4 , C 8 , C 12 and C 20 ligands using homocoupling reactions (Scheme 10.9) [71][72][73][74][75][76][77][78][79]. In particular, the C 4 -bridged dirhenium complex, [(h 5 -C 5 Me 5 )-Re(NO)(PPh 3 )(CcCaCcC)(PPh 3 )(NO)Re(h 5 -C 5 Me 5 )], has been isolated in three oxidation states and the magnetic, optical and electrochemical properties investigated.…”