Toward Highly Metallized Polymers: Synthesis and Characterization of Silicon-Bridged [1]Ferrocenophanes with Pendent Cluster Substituents

Spectroscopic and Structural Study of Some Oligosilanylalkyne Complexes of Cobalt, Molybdenum and Nickel

Metal induced stabilization of α-carbocations is well known for cobalt- and molybdenum complexed propargyl cations. The same principle also allows access to reactivity enhancement of metal coordinated halo- and hydrosilylalkynes. In a previous study, we have shown that coordination of oligosilanylalkynes to the dicobalthexacarbonyl fragment induces striking reactivity to the oligosilanyl part. The current paper extends this set of oligosilanylalkyne complexes to a number of new dicobalthexacarbonyl complexes but also to 1,2-bis(cyclopentadienyl)tetracarbonyldimolybdenum and (dippe)Ni complexes. NMR-Spectroscopic and crystallographic analysis of the obtained complexes clearly show that the dimetallic cobalt and molybdenum complexes cause rehybridization of the alkyne carbon atoms to sp³, while in the nickel complexes one π-bond of the alkyne is retained. For the dicobalt and dimolybdenum complexes, strongly deshielded ²⁹Si NMR resonances of the attached silicon atoms indicate enhanced reactivity, whereas the ²⁹Si NMR shifts of the respective nickel complexes are similar to that of respective vinylsilanes.

En route to dinitroacetylene: nitro(trimethylsilyl)acetylene and nitroacetylene harnessed by dicobalt hexacarbonyl

Dinitroacetylene and other nitroacetylenes are attractive stoichiometric precursors to high energy-density materials, but suffer from high reactivity and thermal instability. Herein, we report that nitroacetylenes can be dramatically stabilized in the form of their dicobalt hexacarbonyl complexes. In particular, we describe the syntheses and characterization of the first two transition-metal complexes of nitroalkynes, [μ-1-nitro-2-(trimethylsilyl)ethyne-1,2-diyl]bis(tricarbonylcobalt)(Co-Co) and [μ-1-nitroethyne-1,2-diyl]bis(tricarbonylcobalt)(Co-Co). The chemistry of these compounds reveals their potential as reaction partners in [2+2+2] cyclotrimerizations, furnishing nitroindane, nitrotetralin, and trinitrobenzene products. The X-ray crystal structure of 1,3,5-trinitro-2,4,6-tris(trimethylsilyl)benzene presents a distorted, yet planar, aromatic ring.

Metal-rich organometallics

The scope of organometallics has recently been expanded considerably, when researchers have started to employ these compounds in the context of materials chemistry. Traditionally, organometallic complexes have been and continue to be important tools for many (catalytic) chemical transformations. This perspective highlights how metal-rich organometallics, that is compounds with more than one type of metal, can play an important role in the advancement of new value-added functional materials.

Synthesis and reactivity of functionalized cycloheptatrienyl-cyclopentadienyl sandwich complexes

This feature article provides an overview of the synthesis and reactivity of functionalized cycloheptatrienyl-cyclopentadienyl transition metal sandwich complexes of the type [(eta(7)-C(7)H(7))M(eta(5)-C(5)H(5))] (M = group 4, 5 or 6 metal), which can be used as building blocks for the preparation of metallopolymers and polymetallic complexes. Emphasis is placed on 16-electron group 4 complexes (M = Ti, Zr, Hf) and their reactivity towards sigma-donor/pi-acceptor ligands, which indicates that these complexes bear a close resemblance to Lewis acidic M(+IV) complexes. Based on theoretical calculations, this behavior can be mainly attributed to the strong and appreciably covalent metal-cycloheptatrienyl interaction with the cycloheptatrienyl ring acting more as a -3 ligand than as a +1 ligand in these mixed ring complexes.

Strained metallocenophanes and related organometallic rings containing pi-hydrocarbon ligands and transition-metal centers

The structures, bonding, and ring-opening reactions of strained cyclic carbon-based molecules form a key component of standard textbooks. In contrast, the study of strained organometallic molecules containing transition metals is a much more recent development. A wealth of recent research has revealed fascinating nuances in terms of structure, bonding, and reactivity. Building on initial work on strained ferrocenophanes, a broad range of strained organometallic rings composed of a variety of different metals, pi-hydrocarbon ligands, and bridging elements has now been developed. Such strained species can potentially undergo ring-opening reactions to functionalize surfaces and ring-opening polymerization to form easily processed metallopolymers with properties determined by the presence of the metal and spacer. This Review summarizes the current state of knowledge on the preparation, structural characterization, electronic structure, and reactivity of strained organometallic rings with pi-hydrocarbon ligands and d-block metals.

Polyferrocenylsilane-Based Polymer Systems

The study of metallopolymers has blossomed into a mature field over the last few decades. Especially, polyferrocenylsilane (PFS) chemistry has taken a tremendous leap and continues to raise intense interest. Since the discovery of thermal ring-opening polymerization (ROP) of sila[1]ferrocenophanes, PFSs have been also accessed by anionic, cationic, transition-metal-catalyzed, and photolytic anionic ROP methodologies. A plethora of synthetic strategies have been devised, enabling access to a wide variety of copolymers, polyelectrolytes, and nanostructured materials. The distinctive physical properties and functions of many PFS-based polymers have been explored, leading to their apt exploitation in technical applications. Therefore, it is conceivable that PFS-related platforms might be indispensable nano-objects in the near future, as they stand on the verge of a new generation of sophisticated materials.

Metallized hyperbranched polydiyne: a photonic material with a large refractive index tunability and a spin-coatable catalyst for facile fabrication of carbon nanotubes

A cobalt-containing hyperbranched polydiyne shows refractive indexes (n) as high as 1.713-1.813 in the long wavelength region, which can be tuned to a large extent (Deltan up to approximately 0.048) by UV irradiation; the polymer can also function as a spin-coatable catalyst for the growth of carbon nanotubes.

Synthesis ofansa-[n]Silacyclopentadienyl-Cycloheptatrienyl-Chromium Complexes (n = 1, 2): Novel Precursors for Polymers Bearing Chromium in the Backbone

Reaction of [(eta5-C5H4Li)(eta7-C7H6Li)Cr]tmeda with a variety of dialkyl(dichloro)silanes in aliphatic solvents afforded the corresponding [1]silatrochrocenophanes. Structural characterization by X-ray diffraction analysis of the [1]silatrochrocenophanes bearing Me2Si, (iPr)2Si, and silacyclobutane bridges revealed tilt angles alpha of 15.56(12) degrees , 15.8(1) degrees , and 16.33(17) degrees , respectively. Analogously, a [2]silatrochrocenophane (6) was prepared in excellent yield by reaction of [(eta5-C5H4Li)(eta7-C7H6Li)Cr]tmeda with 1,2-dichloro-1,1,2,2-tetramethyldisilane. This complex also was characterized structurally and exhibited a tilt angle alpha of 2.60(15) degrees. The [1]silatrochrocenophane bearing the Me2Si bridge underwent facile and regioselective carbon-silicon bond cleavage with [Pt(PEt3)4] to give a very high yield of an oxidative addition product. The ring-opening polymerization of these novel [1]silatrochrocenophanes afforded ring-opened chromium-based polymers.

Regioselective Si–C bond activation in silicon-bridged ansa-cycloheptatrienyl-cyclopentadienyl complexes

On treatment with [Pt(PEt3)3], silicon-bridged ansa-cycloheptatrienyl-cyclopentadienyl Ti and V complexes, [1]silatroticenophane and [1]silatrovacenophane, undergo oxidative addition and regioselective insertion of a Pt(PEt3)2 moiety into the silicon-carbon bond to the seven-membered ring; the resulting complexes, [2]platinasilatroticenophane and [2]platinasilatrovacenophane, can be partly used as single-source catalysts for the ring-opening polymerization (ROP) of the original highly strained sandwich molecules.