1-Zirconacyclobuta-2,3-dienes: synthesis of organometallic analogs of elusive 1,2-cyclobutadiene, unprecedented intramolecular C–H activation, and reactivity studies

Abstract

A detailed study of structure, bonding and reactivity of new 1-zirconacyclobuta-2,3-dienes is presented in comparison to a lighter Ti analog. We found a unique C–H activation at the widely used rac-(ebthi) ligand for that only occurs for Zr.

Selective 1,2-insertion of carbodiimides and substrate-divergent silyl group migration at 1-metallacyclobuta-2,3-dienes

“…Whereas the Ti complex 1a showed no conversion at elevated temperatures, the Zr complexes 2a and 2b were transformed into the C–H activation products 3a / 3b that were described before. 21 In contrast, η 5 -indenyl complexes 2c and 2d could be converted within minutes at room temperature, producing a single new metallocene species that, according to its 1 H and 13 C{ 1 H} NMR spectra is not consistent with the four-membered aza-metallacyclobutene structure (Scheme 3). Instead, well-separated 13 C{ 1 H} resonances at 159.6/174.4 ( P 2c-SiMe3 ) and 157.9/176.0 ppm ( P 2d-SiMe3 ) as well as prominent IR bands at 1852 ( P 2c-SiMe3 ) and 1849 cm −1 ( P 2d-SiMe3 ) suggest the presence of an intact allene unit.…”

“…1b). 21 In these complexes, selective C–H activation at the rac -(ebthi) and rac -(sbthi) (sbthi = dimethylsilylene-1,1′-bis(η 5 -tetrahydroindenyl)) ligands, respectively, produced a new type of tucked-in Zr( iv ) complexes that possesses a η 3 -propargyl/allenyl ligand ( 3a / 3b , Fig. 1b).…”

Mono- and dinuclear zirconocene(iv) amide complexes for the catalytic dehydropolymerisation of phenylsilane

“…In consequence the chloride ligand in meso -4 is sterically protected in the meso -(ebthi) pocket which explains the necessity of higher temperatures and larger amounts of LiNMe 2 for formation of complex meso -3. Notably, attempts to prepare a dinuclear zirconocene amide complex from [( meso -(ebthi)ZrCl) 2 (μ-Me 3 SiC 3 SiMe 3 )] 56 also led to formation of the mononuclear complex meso -3 in low yield (Fig. S6 † ).…”

Metallacyclobuta‐(2,3)‐diene: A Bidentate Ligand for Stream‐line Synthesis of First Row Transition Metal Catalysts for Cyclic Polymerization of Phenylacetylene

“…This strategy is advantageous because it allows access to first row transition metal catalysts for which alkylidynes such as A are exceedingly rare [33–34] . Fortunately, recent studies of Reiß and Beweries [48–49] demonstrated how complexes such as D can be accessed in one‐step using the trimethysilyl substituted 1,3‐dilithioallene “[Li 2 (Me 3 SiC 3 SiMe 3 )]” [50–51] reagent and dihalide precursor G . Their work inspired us to investigate how metallacyclobuta‐(2,3)‐dienes engage in the formation of cyclic ‐PPA and how such as scaffold can be a precursor to a rare alkylidene‐alkynyl motif.…”