Aqueous tungsten(VI) alkyl chemistry

Abstract

strate, and therefore the organic halide and/or aldehyde can carry functional groups, such as alcohol, that would have to be protected in the presence of the acid chloride. Allyl chlorides are converted to aldehydes without double-bond migration to the a,@-position.In the conversion of 2-iodobenzyl alcohol to the corresponding aldehyde, the acylpalladium complex ( l ) , under the reaction conditions, apparently undergoes a transmetalation reaction and reductive elimination of the acylpalladium hydride much faster than direct reductive elimination to the lactone.' A limiting side 0 1 reaction in the conversion of halides to aldehydes appears to be the direct reduction of the halide without carbon monoxide insertion. This reduction proceeds only very slowly under the standard reaction conditions in the absence of a palladium catalyst. The slow addition of tributyltin hydride to the reaction mixture under carbon monoxide is necessary in order to optimize the ratio of aldehyde to reduced product, and the reduction also can be suppressed somewhat by increasing the carbon monoxide pressure. For example, the conversion of 4-bromoiodobenzene to 4bromobenzaldehyde by the slow addition of 1 equiv of tributyltin hydride gives a 73% yield under 1 atm CO and an 88% yield under 3 atm. The reduction pathway becomes more serious with an aryl halide that is a good electron acceptor (one-electron transfer) and/or carries +a substituents. The yields of 44trobenzaldehyde and nitrobenzene from 4-nitroiodobenzene are 9% and 84%, respectively, under 1 atm of carbon monoxide but 38% and 62% under 3 atm.Typically, reactions were run under a balloon of carbon monoxide or in a pressure bottle (3 atm) with 1-5 mmol of the organic halide in 2-5 mL of T H F or toluene per mmol of halide and 3.5-4 mol % of tetrakis(triphenylphosphine)palladium(O). A 10-mL solution of an equimolar amount of tributyltin hydride (plus a 10% excess) in the appropriate solvent was added via syringe pump over a 2.5-4-h period while maintaining the reaction mixture at 50 OC. After the addition was completed, the tributyltin halide was removed by conversion to the insoluble tributyltin fluoride.6 The aldehydes were purified by radial or flash column chromatography. Acknowledgment.We have recently reported reactions between neopentylidyne complexes and water to give oxo neopentylidene complexes of the type W(O)(CHCMe3)(PR3),C1,.' We became interested in the possibility of analogous reactions in the absence of potentially problematical phosphine ligands and therefore began exploring (1) Rocklage, S. M.: Schmck. R. R.: Churchill. h Organometallics 198the hydrolysis of simple tungsten(V1) neopentylidyne complexes. We report here two examples of hydrolysis to give oxo neopentyl complexes that are stable to -180 OC in air and to further hydrolysis.When a large excess of water is added to a concentrated solution of W(CCMe3)(CH2CMe3)32 in tetrahydrofuran white crystals form in -30 min and can be isolated in -90% yield. Analytical, NMR, and mass spectral data3 suggest that thi...

Olefin Metathesis by Group VI (Mo, W) Metal Compounds

“…The expected W─C silanolysis step does not occur (Figure 24), even after thermal treatment. Such reactivity is reminiscent of tungsten aqueous organometallic chemistry described by Schrock and Lippard [85,86]. Indeed, the coordination environment of 22 More recently, Schrock et al synthesized new oxo tungsten complexes bearing various ligands and studied their grafting on silica dehydroxylated at 700°C.…”

Unusual reaction of a tungsten alkylidyne complex with water. Formation, characterization, and crystal structures of oxo trimers

“…microelectronic industry. Such reactions with water have attracted much attention [4][5][6][7][8][9][10][11][12][13]. Schrock, Lippard and coworkers reported the formation of the dimer W 2…”

“…Such reactions with water have attracted much attention [4][5][6][7][8][9][10][11][12][13]. Schrock, Lippard and coworkers reported the formation of the dimer W 2 O 3 (CH 2 CMe 3 ) 6 and (NEt 4 )[WO 3 (CH 2 CMe 3 )] from the reactions of H 2 O with W(CH 2 CMe 3 ) 3 (CCMe 3 ) and W(CCMe 3 )(OCMe 3 ) 3 , respectively (Scheme 1) [4,5]. In the former reaction, an alkylidene intermediate, (Me 3 CCH 2 ) 3 W(=CDCMe 3 )(OD), was proposed, and the reaction yields W 2 O 2 (-O)(CH 2 -CMe 3 ) 4 (CD 2 CMe 3 ) 2 containing three alkyl ligands per W atom.…”

“…We found that the best yield of the yellow hexagonal crystals of 2 was obtained by using a 1:2 mixture of water and THF. A representation of the molecular structure and selected bond distances and angles of 2 are given in Figure 1 and [4,5].…”

“…After THF-d 8 and unreacted D 2 O were removed, the solid was re-dissolved in benzene-d 6 . 1 H, 2 H (in benzene) and 13 C NMR spectroscopy studies were used to characterize 4-d 4 . The 1 H NMR studies confirmed the formation of -CD 2 SiMe 3 ligands ( Figure S10) [48].…”