Strained Metallocenophanes with Late Transition Metals in the Bridge: Syntheses and Structures of Nickel‐ and Platinum‐Bridged [1]Ferrocenophanes

Abstract

Until recently, few classes of strained rings containing transition elements had been explored, but these interesting species are now attracting substantial attention.[1] In particular, strained metallocenophanes (1) and related species containing p-hydrocarbon ligands (e.g. 2-5) [2] have been the focus of recent investigations due to the fascinating questions that surround their electronic structures, bonding, and reactivity. Furthermore, the ability of these compounds to yield functional metallopolymers by ring-opening polymerisation (ROP) has provided an extra impetus to the field. [3] The nature of the transannular bridge, ER x , in such species is of pivotal importance as the size and geometric preferences of the bridging element directly influence the strain present. Moreover, in the ring-opened polymers 6 the metal-metal interactions are modulated by the spacer unit.[4] To date, most work in the area of strained metallorings has involved [1]ferrocenophanes (e.g. 1, M = Fe) containing bridging nonmetallic main group elements E such as Si, P, and more recently S and B.[2a] The incorporation of main group metals (Sn, [5] Al, [2c, 6] and Ga [2c, 7] ) and early d-block metals (Ti, Zr, and Hf) [8] has also been successful. However, to date no transition metals other than the aforementioned Group 4 d 0 tetrahedral centers have been successfully introduced into the bridge. Herein, we report examples of [1]ferrocenophanes with the Group 10 metals Ni and Pt in the bridge, which leads to strained, unexpectedly electron-rich species containing square-planar d 8 centers. The scarcity of metal-bridged [1]ferrocenophanes is at first sight somewhat surprising, given that the main synthetic route to these molecules would appear applicable to any element for which a dichloride is available.[2a] We have found, however, that reaction of many transition-metal dihalides with dilithioferrocene-tmeda complex (tmeda = N,N,N',N'-tetramethylethylenediamine) results in reduction of the metal center. For instance, treatment of Li 2 [Fe(h 5 -C 5 H 4 ) 2 ]·tmeda (7) [9] with trans-[NiCl 2 (PMe 3 ) 2 ], [10] in hexane at À20 8C, only leads to the precipitation of metallic nickel. In striking contrast, the analogous reaction of 7 with trans-[NiCl 2 -(PnBu 3 ) 2 ] (8, Scheme 1) [11] resulted in a cloudy, dark red solution with a single new product detected by 31 P{ 1 H} NMR spectroscopy (d = 13.5 ppm, ca. 20 % conversion). Work-up afforded a dark red crystalline solid in modest yield (11 %) that was subsequently characterized as the first nickel-bridged [1]ferrocenophane [{Fe(h 5 -C 5 H 4 ) 2 }Ni(PnBu 3 ) 2 ] (9). [12] It is of interest that the Ni II component readily undergoes a trans-tocis isomerisation during the reaction and that no product containing the original trans configuration was observed.Compound 9 was fully characterized by 1 H, 13 C{ 1 H}, and 31 P{ 1 H} NMR spectroscopy. It is noteworthy that all three spectra displayed resonances at predictable chemical shifts and as such were consistent with the incorporation of a diam...

Metal‐Containing Polymers: Building Blocks for Functional (Nano)Materials

“…The incorporation of other metals into polymer chains instead of iron has been realized in recent reports using the same ring opening mechanism. [122][123][124] It is especially noteworthy that research into metallocenophanes [125] has also led to the development of the new polymerization technique of light induced living anionic polymerization. [3,4] As with many other metal coordination units, the interactions between metal and cyclopentadiene in metallocenophanes are labile under certain conditions, especially when the coordination bonds are disturbed by a strained ring.…”

Synthesis and Reactivity of Boron‐, Silicon‐, and Tin‐Bridged ansa‐Cyclopentadienyl–Cycloheptatrienyl Titanium Complexes (Troticenophanes)

“…[8] In contrast to ferrocene, the related chemistry of non-iron metallocenes such as ruthenocene, [9] cobaltocene, [10] and nickelocene, [11] Abstract: A novel one-pot method was developed for the preparation of [Ti-A C H T U N G T R E N N U N G (h (h has not been extensively developed, [10] and the situation is even worse for homoleptic non-metallocene systems, such as bisA C H T U N G T R E N N U N G (benzene)vanadium, [12,13] bisA C H T U N G T R E N N U N G (benzene)chromium, [12f, 13, 14] and bisA C H T U N G T R E N N U N G (benzene)molybdenum, [15] even though these sandwich complexes have been known for decades. Recently, the preparation of strained organometallic complexes has been extended to a new class of sandwich compounds of the formula [MA C H T U N G T R E N N U N G (h …”

“…CCDC-778694 (3), 778695 (4), 778696 (5), 778697 (6), 778698 (8), 778699 (9), 778700 (10), and 778701 (11) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.…”

Recent developments with strained metallocenophanes

“…An increase in ring-tilt in this type of transition metal bridged ansa complex was later reported for [1]ferrocenophanes 1 and 3 (Scheme 1), bridged with group 10 metals and prepared utilising salt metathesis reactions of dilithioferrocene$tmeda with Cl 2 M(PnBu 3 ) 2 (M ¼ Ni, Pt) [10]. Interestingly, isolation of these compounds was only achieved employing tri-n-butylphosphine as the ligands on the bridging group 10 metal centre.…”