No abstract

The reaction of [PhC[triple bond]MBr(3)(dme)] (dme=1,2-dimethoxyethane) with the hexafluoro-tert-butoxides LiX or KX [X=OC(CF(3))(2)Me] afforded the benzylidyne complexes [PhC[triple bond]MX(3)(dme)] (2a: M=W, 2b: M=Mo), which further reacted with the lithium reagent Li(Im(tBu)N), generated with MeLi from 1,3-di-tert-butylimidazolin-2-imine (Im(tBu)NH), to form the imidazolin-2-iminato complexes [PhC[triple bond]MX(2)(Im(tBu)N)] (3a: M=W, 3b: M=Mo). The propylidyne complex [EtC[triple bond]MoX(2)(NIm(tBu))] (4) was obtained by treatment of 3b with an excess of 3-hexyne. Complexes 3a and 3b are able to efficiently catalyse alkyne cross metathesis of various 3-pentynyl benzyl ethers 5 and benzoic esters 7 at room temperature, to afford 2-butyne and the corresponding diethers 6 and diesters 8. The tungsten complex 3a proved to be a superior catalyst for ring-closing alkyne metathesis, and the [10]cyclophanes 10 and 12 were synthesised in high yield from 1,3-bis(3-pentynyloxymethyl)benzene (9) and bis(3-pentynyl) phthalate (11), respectively. The molecular structures of compounds 2a, 2b, 3a, 3b, 4, and 12 were determined by single-crystal X-ray diffraction. DFT calculations have been carried out for catalyst systems based on the imidazolin-2-iminato tungsten and molybdenum complexes 3a and 3b by choosing the alkyne metathesis of 2-butyne as the model reaction; the studies revealed a lower activation barrier for the tungsten system.

SummaryThe number of well-defined molybdenum and tungsten alkylidyne complexes that are able to catalyze alkyne metathesis reactions efficiently has been significantly expanded in recent years.The latest developments in this field featuring highly active imidazolin-2-iminato- and silanolate–alkylidyne complexes are outlined in this review.

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.

Four gold complexes were tested as a precursor for focused-electron-beam-induced deposition: [ClAu(III)Me2]2, ClAu(I)(SMe2), ClAu(I)(PMe3), and MeAu(I)(PMe3). Complexes [ClAu(III)Me2]2 and MeAu(I)(PMe3) are volatile, have sufficient vapor pressure at room temperature for deposition experiments, and were found to yield deposits that contain gold (29-41 and 19-25 atom %, respectively). Electrons easily remove the Cl ligand from [ClAu(III)Me2]2, and predominantly both methyl ligands are incorporated into the deposit. Electrons remove at least one methyl group from MeAu(I)(PMe3). Complexes ClAu(I)(SMe2) and ClAu(I)(PMe3) are not suitable as a precursor. They dissociate in vacuum, and the only volatile components are Cl, SMe2, and PMe3, respectively.