No abstract

A family of bimetallic complexes [Cp(CO)2FeCCArCCFe(CO)2Cp] {Cp= C5H5; 6a-g, Ar= C4H2S (a); 3-(C4H9)-C4HS (b); 3-(C16H33)-C4HS (c); C6H4 (d); 2,5-bis(OC4H9)-C6H2 (e); 2,5-bis(OC8H17)-C6H2 (f); (C6H4)2 (g)} was prepared by the three-step Pd-catalysed Extended-One-Pot (EOP) synthetic protocol from Bu3SnCCH, XArX (X=I,Br) and Cp(CO)2FeI. Complexes 6a,d,g were then exposed to ultraviolet irradiation in presence of an equivalent amount of 1,2-bis(diphenylphosphyne)ethane (dppe) to form the corresponding bimetallic complexes [Cp(dppe)FeCCArCCFe(dppe)Cp] (7a,d,g). Compounds 6a-g and 7a,d,g were characterised by Ciclic Voltammetry (CV). The most significant electrochemical information comes from the oxidation of the dppe derivatives. The E° separations between the subsequent reversible waves suggest that the efficiency of the metal-metal electronic coupling decreases in the order 6a > 6d > 6g. Complexes 7a and 7g were also chemically oxidised with [Fe(Cp*)]2[BF4] {Cp*= C5(CH3)5} and [Fe(Cp)]2[BF4] respectively, and the Near Infrared (NIR) spectra of the mixed valence species 7a+ and 7g+ were recorded. A strong Charge Transfer band (ICT) was observed only for the radical cation 7a+. While this finding confirms the existence of electronic interaction between the two termini when a 2,5-thiophene group is present in the spacer, the NIR spectrum of 7g+ reveals a reduced efficiency in conveying electrons when the C4H2S moiety is replaced by a 4,4'-biphenyl. In order to rationalise and quantify the extent of electronic communication, ruled by geometrical and electronic factors, Density Functional computational results on selected [Cp (PH3)2Fe and [Cp(CO)2Fe binuclear model complexes are reported

No abstract

The oxidative dehydrodimerization of the phenylvinylidene manganese complexes (Z 5 -C 5 R 5 )(CO)(L)Mn=C=CHPh (5: R=Me, L=CO; 6: R=H, L=PPh 3 ) into the corresponding bisvinylidene compounds (Z 5 -C 5 R 5 )(CO)(L)Mn=C=CPhÐCPh=C=Mn(CO)(L)(Z 5 -C 5 R 5 ) (7: R=Me, L=CO; 8: R=H, L=PPh 3 ) was studied by cyclic voltammetry and chemical experiments. It was found that dehydrodimerization of 5 and 6 proceeds via direct C (b) ÐC (b) In this paper we report on the oxidative dehydrodimerization of manganese vinylidene complexes (Z 5 -C 5 R 5 )(CO)(L)Mn=C=CHPh (5: R=Me, L=CO; 6: R=H, L=PPh 3 ). Despite 5 and 6 having a close similarity to 1, their dehydrodimerization proceeds according to a different scheme, as will be shown below. (7) was carried out using a procedure similar to that for 1, 9 i.e. 5 was oxidized by AgBF 4 in dichloromethane at À40°C, the solution was kept at this temperature for 2 h and finally reduced by (Z-C 6 H 6 ) 2 Cr. The target complex 7 was obtained in 40% yield and characterized by 1 H and 13 C NMR spectroscopy as well as by mass spectrometry. We found that the yield of 7 can be increased to 85±90% if either potassium t-butylate or triethylamine is used in the final reaction step. In order to determine the mechanism of the dehydrodimerization process, we studied the electrochemical behavior of complexes 5 and 7 by cyclic voltammetry in CH 2 Cl 2 solution (see Table 1).Complex 7 displays two one-electron reversible oxidation waves at 0.17 V (peak A) and 0.58 V (peak B) (see Fig. 1). Complex 5 oxidizes irreversibly at 0.77 V (see Fig. 2, peak C). The reverse scanning of potentials revealed new cathodic peaks at 0.67 V and 0.27 V (peaks D and E respectively). These peaks do not coincide with the reduction peaks A', B' of 7 .Thus, 7 is not an initial product of transformation of 5 Á ,i.e. dehydrodimerization of 5 proceeds by a different mechanism than that for complex 1 (Scheme 1). We believe Scheme 1.Scheme 2. Figure 1. CV of bis-vinylidene complex 7 at 20°C. ). In order to confirm the validity of the mechanism shown in Scheme 3, we studied the oxidative dehydrodimerization of the triphenylphosphine-substituted phenylvinylidene complex (Z 5 -C 5 H 5 )(CO)(PPh 3 )Mn=C=CHPh (6), since we expected the product of direct C (b) ÐC (b) that the isomers differ in the orientation of the phenyl group relative to the cyclopentadienyl ring. Oxidative dehydrodimerization of 6 was carried out under the same conditions as the analogous processes for 1 and 5. The bis-vinylidene complex 8 proved to be rather unstable, and was obtained in 20% yield. Its structure was confirmed by IR-, NMR 1 H, and 31 P spectroscopy and mass spectroscopy. According to the NMR spectra, complex 8 exists as a mixture of two diastereomers in 3:1 ratio.Electrochemical oxidation of 6 and 8 was studied by cyclic voltammetry (CV) in dichloromethane solution. The cyclic voltammogram of the bis-vinylidene complex 8 showed two reversible one-electron oxidation peaks at 0.19 V and 0.61 V (Fig. 3, peaks F and G respectively). The cyclic voltam...

No abstract