Monocationic μ-Diborolyl Triple-Decker Complexes [CpCo(μ-1,3-C3B2Me5)M(ring)]+: Synthesis, Structures, and Electrochemistry

Charge-compensated nido-carborane derivatives in the synthesis of iron(II) bis(dicarbollide) complexes

A series of stable iron(II) bis(dicarbollide) derivatives [8,8'-(RNHC(Et)HN)2-3,3'-Fe(1,2-C2B9H10)2] (R = Pr, R = Ph, (CH2)2OH, (CH2)3OH, (CH2)2NMe2) was prepared starting from FeCl2 or [FeCl2(dppe)] and the corresponding nido-carboranyl amidines [10-RNHC(Et)HN-7,8-C2B9H11]. In a similar way, the reactions of the oxonium derivatives of nido-carborane with FeCl2 in tetrahydrofuran in the presence of t-BuOK lead to the corresponding stable oxonium derivatives iron(II) bis(dicarbollide) [8,8'-(RR'O)2-3,3'-Fe(1,2-C2B9H10)2] (RR' = (CH2)4, (CH2)2O(CH2)2, (CH2)5; R = R' = Et), which can be alternatively prepared by the reaction of the parent iron(II) bis(dicarbollide) with tetrahydrofuran or 1,4-dioxane in the presence of Me2SO4. The cyclic voltammetry studies of the synthesized iron(II) bis(dicarbollide) derivatives revealed that the introduction of amidinium and oxonium substituents leads to a significant increase in the Fe2+/Fe3+ redox potential relative to the parent iron(II) bis(dicarbollide). The redox potentials of the oxonium derivatives are close to the redox potential of ferrocene and somewhat lower than redox potentials of sulfonium and phosphonium derivatives of iron(II) bis(dicarbollide).

Transition Metal Triple-decker Sandwich Complexes Containing Group 13 Elements

Transition metal triple-decker complexes are an interesting class of sandwich complexes that engrossed great attention due to their structures and properties. Over the decades, synthesis of triple-decker complexes featuring homocyclic, heterocyclic or π-conjugated rings as middle decks have been abundantly reported. In this regard, the chemistry of such complexes bearing boron in the middle deck are well explored due to the ability of boron-containing cycles to readily coordinate bifacially with metal atoms thereby forming triple-decker complexes. On the other hand, electron counting rules and theoretical calculations have strengthened our knowledge of the structure and bonding in these complexes. Further, these complexes can be used as synthons to generate organometallic polymers having interesting electronic, optical and magnetic properties that can be appropriately tuned to cater to a wide range of applications. In our quest for novel metallaboranes and metallaheteroboranes, we have been successful in isolating various triple-decker complexes that feature boron in the middle deck. This review explained elaborately the synthesis, structures, and bonding in such complexes reported by us and others.

Triple-Decker Iron and Cobalt Complexes Featuring a Bridging 1,2-Diboratabenzene Ligand

Neutral triple-decker iron and cobalt complexes with a bridging 1,2-diboratabenzene ligand were accessed by reactions of a dilithium 1,2-diboratabenzene reagent with [Cp*FeCl]₂ and [Cp*CoCl]₂, respectively. While 1,2-diboratabenzene metal complexes are known, these represent the first examples of the ligand bridging two metals.

The First Triple-Decker Complex with a Carbenium Center, [CpCo(μ-C3 B2 Me5 )RuC5 Me4 CH2 ]+ : Synthesis, Reactivity, X-Ray Structure, and Bonding

The first derivative of the methylium cation with the triple-decker substituent, [CpCo(C₃ B₂ Me₅ )RuC₅ Me₄ CH₂ ]PF₆ (2PF₆ ), was synthesized from the reaction of the triple-decker complex CpCo(C₃ B₂ Me₅ )RuCp* (1) with the salt of the trityl cation [CPh₃ ]⁺ . The X-ray crystal structure of 2PF₆ reveals that the methylium carbon is bound to the ruthenium with Ru-C bond length of 2.259 Å and corresponds to the description of its structure as η⁶ -fulvene-ruthenium. Reactions of 2PF₆ with nucleophiles OH^- , Ph₃ P, Et₃ N led to the corresponding derivatives of 1 in high yields. Aromatic amines PhNEt₂ and 4-MeC₆ H₄ NH₂ react with 2PF₆ to give the electrophilic aromatic substitution products quantitatively. Chemical reduction of 2PF₆ with Zn powder in tetrahydrofuran leads to the formation of the bis(triple-decker) derivative (CpCo(C₃ B₂ Me₅ )RuC₅ Me₄ CH₂ )₂ (10) with a CH₂ CH₂ -bridge. The structures of complexes 4, 7-10 were determined by X-ray diffraction. Density functional calculations support the crystallographically determined geometry of 2 and allow rationalization of some characteristics of its structure, spectroscopy, and reactivity.