Triple-decker Cation Research Articles

Photochemical replacement of benzene in the tetramethylcyclopentadienyl complex of iron, [η-C5Me4H)Fe(η-C6H6)

Irradiation of the cation [η-C5Me4H)Fe(η-C6H6)]++ (1) and ButNC with visible light in acetonitrile results in the displacement of the benzene ligand, giving [(η-C5Me4H)Fe(ButNC)3]+ (2). Reactions of complex 1 with P(OR)3 and dppe in MeCN yield the complexes [(η-C5Me4H)-Fe(MeCN)P(OR)3 2]+ (R = Me (3) and Et (4)) and [(η-C5Me4H)Fe(MeCN)(dppe)]+ (5) containing two Fe—P bonds. The same reactions in CH2Cl2 give the tris(phosphite) complexes [(η-C5Me4H)FeP(OR)3 3]+ (6, 7). A photochemical reaction of complex 1 with pentaphos-phaferrocene Cp*Fe(η-cyclo-P5) yields the triple-decker cation [(η-C5Me4H)Fe(μ-η:η-cyclo-P5)FeCp*]+ (8) with a bridging pentaphospholyl ligand. Structures [2]PF6 and [3]PF6 were identified by X-ray diffraction.

Metallacarboranes and triple-decker complexes with the (C 4Me 4)Pt fragment

Complex Cp∗PtCl 2 (Cp∗ = η-C 4Me 4) reacts with the carborane anions [7,8-C 2B 9H 11] 2− and [9-SMe 2-7,8-C 2B 9H 10] − giving platinacarboranes Cp∗Pt(η-7,8-C 2B 9H 11) ( 1) and [Cp∗Pt(η-9-SMe 2-7,8-C 2B 9H 10)] + ( 2), respectively. Reactions of the [Cp∗Pt] 2+ fragment (as a labile nitromethane solvate) with the sandwich compounds Cp∗Fe(η-C 5H 3Me 2BMe) and Cp∗Rh(η 5-C 4H 4BPh) afford the triple-decker cations [Cp∗Pt(μ-η:η-C 5H 3Me 2BMe)FeCp∗] 2+ ( 3) and [Cp∗Pt(μ-η 5:η 5-C 4H 4BPh)RhCp∗] 2+ ( 4) with bridging boratabenzene and borole ligands. The structures of 1 and 3(CF 3SO 3) 2 were determined by X-ray diffraction.

Photochemical substitution of benzene in the iron cyclohexadienyl complex [(η5-C6H7)Fe(η-C6H6)

The visible light irradiation of the [(η5-C6H7)Fe(η-C6H6)]+ cation (1) in acetonitrile resulted in the substitution of the benzene ligand to form the labile acetonitrile species [(η5-C6H7)Fe(MeCN)3]+ (2). The reaction of 1 with ButNC in MeCN produced the stable isonitrile complex [(η5-C6H7)Fe(ButNC)3]+ (3). The photochemical reaction of cation 1 with pentaphosphaferrocene Cp*Fe(η-cyclo-P5) afforded the triple-decker cation with the bridging pentaphospholyl ligand, [(η5-C6H7)Fe(μ-η:η-cyclo-P5)FeCp*]+ (4). The latter complex was also synthesized by the reaction of cation 2 with Cp*Fe(η-cyclo-P5). The structure of the complex [3]PF6 was established by X-ray diffraction.

Group 14 triple-decker cations

The triple-decker cations trans-[(Cp*Sn)(2)(mu-eta(5):eta(5)-Cp*)](+) and trans-[(Cp*Pb)(2)(mu-eta(5):eta(5)-Cp*)](+) have been prepared and structurally characterized as their [B(C(6)F(5))(4)](-) salts from the reactions of [Cp*M][B(C(6)F(5))(4)](M = Sn, Pb) with the appropriate decamethylmetallocene. Both triple-decker cations adopt a cisoid arrangement of terminal Cp* groups, whereas the two known triple-decker main-group anions possess a transoid arrangement of terminal Cp groups. The reason for this conformational difference has been probed on the basis of DFT calculations.

From group 13–group 13 donor–acceptor bonds to triple-decker cations

Donor-acceptor bonding between group 13 elements seems counter-intuitive because one normally thinks of e.g. boron and aluminium compounds as classical Lewis acids. Indeed, many such compounds have achieved industrial prominence in this regard. Recently, however, it has become possible to stabilize these and other group 13 elements in the +1 oxidation state as opposed to the archetypical +3 oxidation state. Moreover, it turns out that in the +1 oxidation state these species are excellent donors--hence the formation of these unprecedented donor-acceptor bonds. The discovery of such bonds has led, albeit indirectly, to the development of triple-decker main group cations. This aspect is also covered in the review.

Synthesis, X‐ray and Electronic Structure of Trinickel Tetradecker Sandwich Complexes {(η5‐C5H5)Ni[μ,η5‐(CR1)2(BR2)2CR3]}2Ni

AbstractThe reduction of the 18‐VE complexes (η5C5H5)Ni[η5‐(CR1)2(BR2)2CR3] (2a, b) with potassium in THF leads to the paramagnetic anions 2–, which react with NiBr2 · DME to give the triple‐decker complexes (η5‐C5H5)Ni[μ,η5‐(CR1)2(BR2)2CR3]Ni(η5‐C5H5) (3a, b) and the tetradecker {(η5‐C5H5)Ni[μ,η5‐(CR1)2(BR2)2CR3]}2Ni (4b). Surprisingly, 4b is also obtained by heating the double‐decker complex 2b and H2AlOCMe3 in THF. The reaction between 2c and AlH3 in Et2O leads to the substitution of the ethoxy groups at the boron atoms and to the formation of the tetradecker 4d with four B–H groups. Heating of the 1,3‐benzodiborole ligand 1e and [(C5H5)Ni(CO)]2 in toluene yields small amounts of 2e and 3e, and the tetradecker 4e. X‐ray structure analyses were performed for 4d and 4e. Complex 4d is centrosymmetric with relatively short nickel‐to‐bridging ligand distances (1.69, 1.70 Å). In the tetradecker 4e the two bridging ligands adopt a synclinal conformation (rotating about 36° resp. 41° against each other). The Ni–Ni distance (3.42, 3.43) is slightly longer than in 4d (3.39 Å). The electronic structures of the tripledecker cation 3+ (32 VE) and of the tetradecker 4 (46 VE) have been investigated by means of the Fenske‐Hall method. The findings are in agreement with the experimental results that 3+ is a triplet species and 4 possesses a closed‐shell electron configuration.