Bio-Organometallic Chemistry, ansa-Metallocenes, and Frustrated Lewis Pairs: Functional Group Chemistry at the Group 4 Bent Metallocenes

Abstract

Functional group chemistry at the group 4 bent metallocenes is still a challenge, due to the special features of these early-metal systems. Nevertheless, an increasing number of reactions and protocols is being developed for attaching organic functional groups at the bent-metallocene frameworks and for carrying out reactions with them. Here some bio-organometallic bent metallocene systems are discussed. Chemical transformations are presented and discussed, including olefin metathesis and even variants of the Mannich reaction. It is shown that intramolecular [2 þ 2] cycloaddition reactions between alkenyl substituents at the Cp or indenyl rings under dynamic topochemical reaction control can lead to ansa-metallocenes. Frustrated Lewis pair chemistry provides tools, for example, for reduction reactions under very mild conditions.

Crystal structures of a series of 6-aryl-1,3-diphenylfulvenes

“…Pentafulvenes have garnered interested because of their unique cross-conjugated electronic system. Fulvenes have been explored for applications as chromophores (Jayamurugan et al, 2013), frustrated Lewis pair scaffolds (Mö mming et al, 2011), and ligands for metal-fulvene complexes (Erker, 2011). To facilitate the inclusion in transition-metal complexes, reduction to a cyclopentadiene ligand (Gó mez-Ruiz et al, 2005) or reductive coupling to ansa bis-cyclopentadiene ligand (Adas & Balaich, 2018) are the most common reactions.…”

meso-Bis{η5-1-[1-(dimethylamino)ethenyl]-3-(trimethylsilyl)cyclopentadienyl}iron(II) and the cobalt(II) analogue

“…Group 4 ansa-metallocenes have played a significant role in organometallic chemistry and homogeneous Ziegler-Natta olefin polymerization catalysis. Over the years, Erker and coworkers have contributed to these and related aspects of metallocene chemistry (Erker, 2011;Knü ppel et al, 2005). The reaction of (enamino-Cp)Li reagents (Cp = cyclopentadienyl) prepared from the deprotonation of various 6-(dialkylamino)fulvenes with the group 4 metal tetrahalides MCl 4 (M = Ti, Zr or Hf) in a 2:1 stoichiometry gave first the nonbridged bis(enamino-Cp)MCl 2 complexes, which then readily underwent an intramolecular Mannich coupling reaction and thus led to the synthesis of the corresponding C 3 -bridged ansametallocenes (Tumay et al, 2009;Venne-Dunker et al, 2003).…”

Heavier Tetrylenes as Single Site Catalysts

“…Many reports and reviews have already been published describing how main group elements have emulated transition metals in terms of reactivity. [24][25][26][27][28][29][30][31] There are plethora of examples on FLPs (frustrated Lewis pairs) [32][33][34][35][36][37] and Nheterocyclic carbenes [38][39][40][41][42][43] being explored as homogeneous catalysts, but no dedicated review is available for the utilization of tetrylenes as catalysts in organic transformations.In this review we will cover the catalytic efficiency of compounds with heavier group 14 elements in + II oxidation state, which includes heavier tetrylenes and cationic species of Si(II), Ge(II), Sn(II). We have also compared the catalytic efficiency of these species (+ II) with the catalysts in + IV oxidation state for the same organic transformation.…”