Electronic communication in phosphine substituted bridged dirhenium complexes - clarifying ambiguities raised by the redox non-innocence of the C4H2- and C4-bridges

Yan Li; Olivier Blacque; Thomas Fox; Sandra Luber; Walther Polit; Rainer F. Winter; Koushik Venkatesan; Heinz Berke

doi:10.1039/c5dt04768d

Electronic communication in phosphine substituted bridged dirhenium complexes - clarifying ambiguities raised by the redox non-innocence of the C4H2- and C4-bridges

Yan Li, Olivier Blacque, Thomas Fox, Sandra Luber, Walther Polit, Rainer F. Winter, Koushik Venkatesan, Heinz Berke^*

^*Corresponding author for this work

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Abstract

The mononuclear rhenium carbyne complex trans-[Re(CCSiMe₃)(C-Me)(PMe₃)₄][PF₆] (2) was prepared in 90% yield by heating a mixture of the dinitrogen complex trans-[ReCl(N₂)(PMe₃)₄] (1), TlPF₆, and an excess of HCCSiMe₃. 2 could be deprotonated with KOtBu to the vinylidene complex trans-[Re(CCSiMe₃)(CCH₂)(PMe₃)₄] (3) in 98% yield. Oxidation of 3 with 1.2 equiv. of [Cp₂Fe][PF₆] at -78 °C gave the C_β-C′_β coupled dinuclear rhenium biscarbyne complex trans-[(Me₃SiCC)(PMe₃)₄ReC-CH₂-CH₂-CRe(PMe₃)₄(CCSiMe₃)][PF₆]₂ (5) in 92% yield. Deprotonation of 5 with an excess of KOtBu in THF produced the diamagnetic trans-[(Me₃SiCC)(PMe₃)₄ReCCH-CHCRe(PMe₃)₄(CCSiMe₃)] 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^-1 higher energy. Oxidation of E-6 with 2 equiv. of [Cp₂Fe][PF₆] resulted in the stable diamagnetic dicationic trans-[(Me₃SiCC)(PMe₃)₄ReC-CHCH-CRe(PMe₃)₄(CCSiMe₃)][PF₆]₂ complex (E-6[PF₆]₂) with an ethylenylidene dicarbyne structure of the bridge. The paramagnetic mixed-valence (MV) complex E-6[PF₆] was obtained by comproportionation of E-6(S) and E-6[PF₆]₂ or by oxidation of E-6(S) with 1 equiv. of [Cp₂Fe][PF₆]. The dicationic trans-[(Me₃SiCC)(PMe₃)₄ReC-CC-CRe(PMe₃)₄(CCSiMe₃)][PF₆]₂ (7[PF₆]₂) complex, attributed a butynedi(triyl) bridge structure, was obtained by deprotonation of E-6[PF₆]₂ with KOtBu followed by oxidation with 2 equiv. of [Cp₂Fe][PF₆]. The neutral complex 7 could be accessed best by reduction of 7[PF₆]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 kcal mol^-1 lower in energy than 7(S). There is experimental evidence that 7(S) prevails in solution. 7 could not be isolated in the crystalline state and is unstable transforming mainly by H-abstraction to give E-6(S). UV-Vis-NIR spectroscopy for the dinuclear rhenium complexes E-6(S), E-6[PF₆] and E-6[PF₆]₂, as well as EPR spectroscopic and variable-temperature magnetization measurements for the MV complex E-6[PF₆] were also conducted. Spectro-electrochemical reduction studies on 7[PF₆]₂ allowed the characterization of the mono- and direduced forms of 7⁺ and 7 by means of IR- and UV-Vis-NIR-spectroscopy and revealed the chemical fate of the higher reduced form.

Original language	English
Pages (from-to)	5783-5799
Number of pages	17
Journal	Dalton Transactions
Volume	45
Issue number	13
DOIs	https://doi.org/10.1039/c5dt04768d
Publication status	Published - 7 Apr 2016
Externally published	Yes

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Copyright the Publisher 2016. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

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@article{a849ee0519784675aab249318baf5923,

title = "Electronic communication in phosphine substituted bridged dirhenium complexes - clarifying ambiguities raised by the redox non-innocence of the C4H2- and C4-bridges",

abstract = "The mononuclear rhenium carbyne complex trans-[Re(CCSiMe3)(C-Me)(PMe3)4][PF6] (2) was prepared in 90% yield by heating a mixture of the dinitrogen complex trans-[ReCl(N2)(PMe3)4] (1), TlPF6, and an excess of HCCSiMe3. 2 could be deprotonated with KOtBu to the vinylidene complex trans-[Re(CCSiMe3)(CCH2)(PMe3)4] (3) in 98% yield. Oxidation of 3 with 1.2 equiv. of [Cp2Fe][PF6] at -78 °C gave the Cβ-C′β coupled dinuclear rhenium biscarbyne complex trans-[(Me3SiCC)(PMe3)4ReC-CH2-CH2-CRe(PMe3)4(CCSiMe3)][PF6]2 (5) in 92% yield. Deprotonation of 5 with an excess of KOtBu in THF produced the diamagnetic trans-[(Me3SiCC)(PMe3)4ReCCH-CHCRe(PMe3)4(CCSiMe3)] 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-1 higher energy. Oxidation of E-6 with 2 equiv. of [Cp2Fe][PF6] resulted in the stable diamagnetic dicationic trans-[(Me3SiCC)(PMe3)4ReC-CHCH-CRe(PMe3)4(CCSiMe3)][PF6]2 complex (E-6[PF6]2) with an ethylenylidene dicarbyne structure of the bridge. The paramagnetic mixed-valence (MV) complex E-6[PF6] was obtained by comproportionation of E-6(S) and E-6[PF6]2 or by oxidation of E-6(S) with 1 equiv. of [Cp2Fe][PF6]. The dicationic trans-[(Me3SiCC)(PMe3)4ReC-CC-CRe(PMe3)4(CCSiMe3)][PF6]2 (7[PF6]2) complex, attributed a butynedi(triyl) bridge structure, was obtained by deprotonation of E-6[PF6]2 with KOtBu followed by oxidation with 2 equiv. of [Cp2Fe][PF6]. The neutral complex 7 could be accessed best by reduction of 7[PF6]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 kcal mol-1 lower in energy than 7(S). There is experimental evidence that 7(S) prevails in solution. 7 could not be isolated in the crystalline state and is unstable transforming mainly by H-abstraction to give E-6(S). UV-Vis-NIR spectroscopy for the dinuclear rhenium complexes E-6(S), E-6[PF6] and E-6[PF6]2, as well as EPR spectroscopic and variable-temperature magnetization measurements for the MV complex E-6[PF6] were also conducted. Spectro-electrochemical reduction studies on 7[PF6]2 allowed the characterization of the mono- and direduced forms of 7+ and 7 by means of IR- and UV-Vis-NIR-spectroscopy and revealed the chemical fate of the higher reduced form.",

author = "Yan Li and Olivier Blacque and Thomas Fox and Sandra Luber and Walther Polit and Winter, {Rainer F.} and Koushik Venkatesan and Heinz Berke",

note = "Copyright the Publisher 2016. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.",

year = "2016",

month = apr,

day = "7",

doi = "10.1039/c5dt04768d",

language = "English",

volume = "45",

pages = "5783--5799",

journal = "Dalton Transactions",

issn = "1477-9226",

publisher = "Royal Society of Chemistry",

number = "13",

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TY - JOUR

T1 - Electronic communication in phosphine substituted bridged dirhenium complexes - clarifying ambiguities raised by the redox non-innocence of the C4H2- and C4-bridges

AU - Li, Yan

AU - Blacque, Olivier

AU - Fox, Thomas

AU - Luber, Sandra

AU - Polit, Walther

AU - Winter, Rainer F.

AU - Venkatesan, Koushik

AU - Berke, Heinz

N1 - Copyright the Publisher 2016. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

PY - 2016/4/7

Y1 - 2016/4/7

N2 - The mononuclear rhenium carbyne complex trans-[Re(CCSiMe3)(C-Me)(PMe3)4][PF6] (2) was prepared in 90% yield by heating a mixture of the dinitrogen complex trans-[ReCl(N2)(PMe3)4] (1), TlPF6, and an excess of HCCSiMe3. 2 could be deprotonated with KOtBu to the vinylidene complex trans-[Re(CCSiMe3)(CCH2)(PMe3)4] (3) in 98% yield. Oxidation of 3 with 1.2 equiv. of [Cp2Fe][PF6] at -78 °C gave the Cβ-C′β coupled dinuclear rhenium biscarbyne complex trans-[(Me3SiCC)(PMe3)4ReC-CH2-CH2-CRe(PMe3)4(CCSiMe3)][PF6]2 (5) in 92% yield. Deprotonation of 5 with an excess of KOtBu in THF produced the diamagnetic trans-[(Me3SiCC)(PMe3)4ReCCH-CHCRe(PMe3)4(CCSiMe3)] 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-1 higher energy. Oxidation of E-6 with 2 equiv. of [Cp2Fe][PF6] resulted in the stable diamagnetic dicationic trans-[(Me3SiCC)(PMe3)4ReC-CHCH-CRe(PMe3)4(CCSiMe3)][PF6]2 complex (E-6[PF6]2) with an ethylenylidene dicarbyne structure of the bridge. The paramagnetic mixed-valence (MV) complex E-6[PF6] was obtained by comproportionation of E-6(S) and E-6[PF6]2 or by oxidation of E-6(S) with 1 equiv. of [Cp2Fe][PF6]. The dicationic trans-[(Me3SiCC)(PMe3)4ReC-CC-CRe(PMe3)4(CCSiMe3)][PF6]2 (7[PF6]2) complex, attributed a butynedi(triyl) bridge structure, was obtained by deprotonation of E-6[PF6]2 with KOtBu followed by oxidation with 2 equiv. of [Cp2Fe][PF6]. The neutral complex 7 could be accessed best by reduction of 7[PF6]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 kcal mol-1 lower in energy than 7(S). There is experimental evidence that 7(S) prevails in solution. 7 could not be isolated in the crystalline state and is unstable transforming mainly by H-abstraction to give E-6(S). UV-Vis-NIR spectroscopy for the dinuclear rhenium complexes E-6(S), E-6[PF6] and E-6[PF6]2, as well as EPR spectroscopic and variable-temperature magnetization measurements for the MV complex E-6[PF6] were also conducted. Spectro-electrochemical reduction studies on 7[PF6]2 allowed the characterization of the mono- and direduced forms of 7+ and 7 by means of IR- and UV-Vis-NIR-spectroscopy and revealed the chemical fate of the higher reduced form.

AB - The mononuclear rhenium carbyne complex trans-[Re(CCSiMe3)(C-Me)(PMe3)4][PF6] (2) was prepared in 90% yield by heating a mixture of the dinitrogen complex trans-[ReCl(N2)(PMe3)4] (1), TlPF6, and an excess of HCCSiMe3. 2 could be deprotonated with KOtBu to the vinylidene complex trans-[Re(CCSiMe3)(CCH2)(PMe3)4] (3) in 98% yield. Oxidation of 3 with 1.2 equiv. of [Cp2Fe][PF6] at -78 °C gave the Cβ-C′β coupled dinuclear rhenium biscarbyne complex trans-[(Me3SiCC)(PMe3)4ReC-CH2-CH2-CRe(PMe3)4(CCSiMe3)][PF6]2 (5) in 92% yield. Deprotonation of 5 with an excess of KOtBu in THF produced the diamagnetic trans-[(Me3SiCC)(PMe3)4ReCCH-CHCRe(PMe3)4(CCSiMe3)] 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-1 higher energy. Oxidation of E-6 with 2 equiv. of [Cp2Fe][PF6] resulted in the stable diamagnetic dicationic trans-[(Me3SiCC)(PMe3)4ReC-CHCH-CRe(PMe3)4(CCSiMe3)][PF6]2 complex (E-6[PF6]2) with an ethylenylidene dicarbyne structure of the bridge. The paramagnetic mixed-valence (MV) complex E-6[PF6] was obtained by comproportionation of E-6(S) and E-6[PF6]2 or by oxidation of E-6(S) with 1 equiv. of [Cp2Fe][PF6]. The dicationic trans-[(Me3SiCC)(PMe3)4ReC-CC-CRe(PMe3)4(CCSiMe3)][PF6]2 (7[PF6]2) complex, attributed a butynedi(triyl) bridge structure, was obtained by deprotonation of E-6[PF6]2 with KOtBu followed by oxidation with 2 equiv. of [Cp2Fe][PF6]. The neutral complex 7 could be accessed best by reduction of 7[PF6]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 kcal mol-1 lower in energy than 7(S). There is experimental evidence that 7(S) prevails in solution. 7 could not be isolated in the crystalline state and is unstable transforming mainly by H-abstraction to give E-6(S). UV-Vis-NIR spectroscopy for the dinuclear rhenium complexes E-6(S), E-6[PF6] and E-6[PF6]2, as well as EPR spectroscopic and variable-temperature magnetization measurements for the MV complex E-6[PF6] were also conducted. Spectro-electrochemical reduction studies on 7[PF6]2 allowed the characterization of the mono- and direduced forms of 7+ and 7 by means of IR- and UV-Vis-NIR-spectroscopy and revealed the chemical fate of the higher reduced form.

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U2 - 10.1039/c5dt04768d

DO - 10.1039/c5dt04768d

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VL - 45

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EP - 5799

JO - Dalton Transactions

JF - Dalton Transactions

IS - 13

ER -

Electronic communication in phosphine substituted bridged dirhenium complexes - clarifying ambiguities raised by the redox non-innocence of the C4H2- and C4-bridges

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