Experimental and Theoretical Investigations of Catalytic Alkyne Cross-Metathesis with Imidazolin-2-iminato Tungsten Alkylidyne Complexes

Abstract

The imidazolin-2-iminato tungsten alkylidyne complexes [Me 3 CC≡W(NIm R )(OR′) 2 ] (4a: R ) tBu, R′ ) CMe 3 ; 4b: R ) Dipp, R′ ) CMe 3 ; 5a: R ) tBu, R′ ) CMe(CF 3 ) 2 ; 5b: R ) Dipp, R′ ) CMe(CF 3 ) 2 have been prepared from [Me 3 CC≡W(OCMe 3 ) 3 ] (2) and [Me 3 CC≡W{OCMe(CF 3 ) 2 } 3 (dme)] (3, dme ) 1,2-dimethoxyethane) by reaction with the lithium reagents Li(NIm tBu ) and Li(NIm Dipp ), generated with MeLi from 1,3-di-tert-butylimidazolin-2-imine (Im tBu NH) or 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-imine (Im Dipp NH), respectively. Reaction of 1) produced the dme-free complex [Me 3 CC≡W{OCPh(CF 3 ) 2 } 3 ] (7), which, upon treatment with Li(NIm tBu ), gave the alkylidene complex 8, presumably formed by activation and addition of an ortho-C-H bond across the W≡C bond in the intermediate alkylidyne complex. Treatment of 1 with Li[OC(CF 3 ) 3 ] led to the substitution of only two chloride ligands and formation of cis-[Me 3 CC≡WCl{OC(CF 3 ) 3 } 2 (dme)] ( 9), which exhibits long-range through-space 19 F-19 F coupling between the fluorine atoms of the two OC(CF 3 ) 3 ligands. Reaction of 9 with Li(NIm tBu ) resulted in partial cleavage of the Im tBu N ligand and ligand redistribution to afford the dinuclear tungsten alkylidyne complex 10. The propylidyne complex [EtC≡W(NIm tBu ){OCMe(CF 3 ) 2 } 2 ] (12) was obtained by treatment of 5a with 3-hexyne, which proceeded via the metallacyclobutadiene complex 11. Complex 5a is able to rapidly catalyze alkyne cross-metathesis of 3-heptyne to give a statistical 1:2:1 mixture of 3-hexyne, 3-heptyne and 4-octyne. The catalytic homodimerization of 1-phenylpropyne under vacuum-driven conditions was studied for 5a, 5b and 6 at 30 and 80 °C. The molecular structures of complexes 2, 3, 4a, 4b, 5b, 8, 9, 10 and 12 were determined by single crystal X-ray diffraction. High-level DFT calculations employing the B3LYP functional have been carried out for a series of experimentally studied and other alkylidyne complexes by choosing alkyne metathesis of 2-butyne as the model reaction.

Synthesis, characterization and reactivity of an imidazolin-2-iminato aluminium dihydride

“…However, treating 2 with another two equivalents of this haloborane significantly improved the yield of 6. Alternatively, compound 6 was synthesized by reaction of bis(2,6-diisopropylphenyl)imidazolin-2-imino lithium 34 {LLi} 2 (8) with aluminium trichloride (cf. the ESI for details on our synthesis of 8 and its molecular structure in the solid state, Fig.…”

“…32,33 Contemporary research on transition metal-and rare earth metal complexes of this imino group is mainly carried out by Tamm and coworkers. [28][29][30]34 For example, striking activity as a catalyst for propylene polymerization is ascribed to the titanium complex VIII 30 ( Fig. 2) which is representative for the field.…”

The Pentamethylcyclopentadienylsilicon(II) Cation: Synthesis, Characterization, and Reactivity

“…Reaction of 1 with the lithium reagent LiL {L=bis[2,6‐di(isopropyl)phenyl]imidazolin‐2‐iminate}80 led to the formation of the complex (π‐Me 5 C 5 )Si(L) ( 11 ) as colorless crystals [Eq. (5)].…”

Highly Active Multidentate Ligand‐Based Alkyne Metathesis Catalysts

“…The ligands (X) in the complex play ac rucial role in catalystp erformance. Great efforts in this field have been devoted to the development of effective ligands, which include various monodentate ligands, such as alkoxide, [25] aryloxide, [31][32][33] amido, [34,35] iminato, [36][37][38] or silanolate ligands. [30,[39][40][41] One of the common problemswith alkylidyne Mo VI catalysts bearing monodentate co-ligands is the availability of two open substrate coordinations ites, which would allow the undesired polymerization of small alkynes, particularly 2-butyne byproduct from reactionso fp ropynyl substrates, to occur through the ring expansionm echanism.…”