Electronic communication in phosphine substituted bridged dirhenium complexes - clarifying ambiguities raised by the redox non-innocence of the C sub(4)H sub(2)- and C sub(4)-bridges

• Published in: Dalton transactions : an international journal of inorganic chemistry 2016-03, Vol.45 (13), p.5783-5799
• Main Authors: Li, Yan, Blacque, Olivier, Fox, Thomas, Luber, Sandra, Polit, Walther, Winter, Rainer F, Venkatesan, Koushik, Berke, Heinz
• Format: Article
• Language: English
• Subjects: Bridges (structures); Diamagnetism; Joining; Mathematical analysis; Oxidation; Reduction; Rhenium; Spectroscopy
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c5dt04768d

The mononuclear rhenium carbyne complex trans-[Re(C&z.tbd; CSiMe sub(3))(&z.tbd; C-Me)(PMe sub(3)) sub(4)][PFd6 (2) was prepared in 90% yield by heating a mixture of the dinitrogen complex trans-[ReCl(N sub(2))(PMe sub(3)) sub(4)] (1), TlPF sub(6), and an excess of HC&z.tbd; CSiMe sub(3). 2 could be deprotonated with KOtBu to the vinylidene complex trans-[Re(C&z.tbd; CSiMe sub(3))(&z.dbd; C&z.dbd; CH sub(2))(PMe sub(3)) sub(4)] (3) in 98% yield. Oxidation of 3 with 1.2 equiv. of [Cp sub(2)Fe][PF sub(6)] at -78 degree C gave the C sub( beta )-C' sub( beta ) coupled dinuclear rhenium biscarbyne complex trans-[(Me sub(3)SiC&z.tbd ; C)(PMe sub(3)) sub(4)Re&z. tbd; C-CH sub(2)-CH sub(2)-C&z.tbd; Re(PMe sub(3)) sub(4)(C&z.tbd; CSiMe sub(3)) ][PF sub(6)] sub(2) (5) in 92% yield. Deprotonation of 5 with an excess of KOtBu in THF produced the diamagnetic trans-[(Me sub(3)SiC&z.tbd ; C)(PMe sub(3)) sub(4)Re&z. dbd; C&z.dbd; CH-CH&z.dbd; C&z.dbd; Re(PMe sub(3)) sub(4)(C&z.tbd; CSiMe sub(3))] complex (E-6(S)) in 87% yield with an E-butadienediylidene bridge. Density functional theory (DFT) calculations of E-6(S) confirmed its singlet ground state. The Z-form of 6 (Z-6(S)) could not be observed, which is in accord with its DFT calculated 17.8 kJ mol super(-1) higher energy. Oxidation of E-6 with 2 equiv. of [Cp sub(2)Fe][PF sub(6)] resulted in the stable diamagnetic dicationic trans-[(Me sub(3)SiC&z.tbd ; C)(PMe sub(3)) sub(4)Re&z. tbd; C-CH&z.dbd; CH-C&z.tbd; Re(PMe sub(3)) sub(4)(C&z.tbd; CSiMe sub(3))][PF sub(6)] sub(2) complex (E-6[PF sub(6)] sub(2 )) with an ethylenylidene dicarbyne structure of the bridge. The paramagnetic mixed-valence (MV) complex E-6[PF sub(6)] was obtained by comproportionation of E-6(S) and E-6[PF sub(6)] sub(2) or by oxidation of E-6(S) with 1 equiv. of [Cp sub(2)Fe][PF sub(6)]. The dicationic trans-[(Me sub(3)SiC&z.tbd ; C)(PMe sub(3)) sub(4)Re&z. tbd; C-C&z.tbd; C-C&z.tbd; Re(PMe sub(3)) sub(4)(C&z.tbd; CSiMe sub(3))][PFd6 sub(2) (7[PF sub(6)] sub(2) ) complex, attributed a butynedi(triyl) bridge structure, was obtained by deprotonation of E-6[PF sub(6)] sub(2) with KOtBu followed by oxidation with 2 equiv. of [Cp sub(2)Fe][PF sub(6)]. The neutral complex 7 could be accessed best by reduction of 7[PF sub(6)] sub(2) with KH in the presence of 18-crown-6. According to DFT calculations 7 possesses two equilibrating electronic states: diamagnetic 7(S) and triplet 7(F) with ferromagnetically coupled spins. The latter is calculated to be 5.2 kc