Electronic Interactions in the Electroactive Iron σ‐Ethynyl‐2‐Phenyltetramethyldisilanes [Cp*(dppe)Fe–C≡C–{Si(CH₃)₂}₂–1,4‐C₆H₄X](PF₆)_n (n = 0, 1)

Abstract

Treatment of the triflate complex [Cp*(dppe)FeOTf ] {5; Cp* = η 5 -C 5 (CH 3 ) 5 , dppe = 1,2-bis(diphenylphosphanyl)ethane, OTf = CF 3 SO 3 } with an excess of HC≡C-[Si(CH 3 ) 2 ] 2 -1,4-C 6 H 4 X (6a-e) in a mixture of THF and triethylamine (NEt 3 ) provides the new complexes {1a: X = H; 1b: X = CH 3 ; 1c: X = N(CH 3 ) 2 ; 1d: X = CF 3 ; 1e: X = Br}, which were isolated in 64 to 81 % yields as orange powders. The cyclic voltammetry, and multinuclear NMR, IR, and UV/Vis spectroscopic data obtained for 1a-e, as well as the X-ray crystal structures determined for 1a, 1c, and 1e, reveal the importance of the σ-π conjugation (hyperconjugation) between the Si-Si σ-bond and the vicinal C≡C π-orbitals in the description of the electronic structure of [a] 1364 the ground state of these complexes. When compounds 1a-e are reacted with [(C 5 H 5 ) 2 Fe](PF 6 ) (1 equiv.) at 20°C, they provide [1a-e](PF 6 ), which partially decompose in solution during the reaction process. They were isolated as mixtures with the mononuclear [Cp*(dppe)Fe=C=CH 2 ](PF 6 ) (7) and binuclear [Cp*(dppe)Fe=C=CH-CH=C=Fe(dppe)Cp*](PF 6 ) 2 (8) vinylidenes. Reduction of these mixtures with cobaltocene affords the parent neutral compounds 1a-e in analytically pure forms. The iron(III) complexes were characterized by IR and Mössbauer spectroscopy, which clearly showed that the iron(III) nucleus sensed the electronic effect of the X substituents.

Catalyzed M–C coupling reactions in the synthesis of σ-(pyridylethynyl)dicarbonylcyclopentadienyliron complexes

“…Metal s-alkynyl complexes displaying such peculiar characteristics as linear geometry, high stability, and p-unsaturated character have been demonstrated to constitute promising building blocks for the design of materials, which can possess such properties as optical nonlinearity, [1][2][3][4][5] light-emission, [6][7][8][9][10][11][12] and electrical conductivity. [13][14][15][16][17][18] Moreover, they are an important class of coordination compounds because of their relevance in synthetic chemistry [19][20][21][22][23][24] and proton reduction catalysis. [25][26][27] A variety of methods for the synthesis of transition metal acetylides have been developed.…”