Dearomatization of Benzene, Deamidization of N,N-Dimethylformamide, and a Versatile New Tungsten π Base

Abstract

The first group VI η 2 -coordinated benzene complex, TpW(NO)(PMe 3 )(η 2 -benzene), is reported. The bound arene is activated toward Diels-Alder cycloaddition, and substitution of the arene with DMF yields a rare example of a η 2 -coordinated amide.Over the past decade, we have endeavored to develop π-basic metal fragments with the ability to bind aromatic molecules and activate them toward otherwise inaccessible organic transformations, with the ultimate goal of expanding the array of reactions available for this ubiquitous class of molecules. 1-3 These electronrich transition-metal fragments such as {Os(NH 3 ) 5 } 2+ and {TpRe(CO)(MeIm)} (Tp ) hydridotris(pyrazolyl)-borate, MeIm ) 1-methylimidazole) coordinate aromatic molecules across only two atoms of the aromatic ring and thereby localize the π-bonds of the uncoordinated portion, rendering the molecule highly nucleophilic. 2,4,5 Recently, the first group VI dearomatization fragment, {TpMo(NO)(MeIm)}, was synthesized 6 by using a strategy of matching d 5 /d 6 reduction potentials with previously developed rhenium(I) and osmium(II) systems. Although this complex forms stable η 2 complexes with naphthalene and furan, complexes of benzene or pyrrole could not be isolated. We hypothesized that a heavymetal analogue of the form {TpW 0 (NO)(L)} could more effectively back-bond with aromatic molecules, thereby strengthening the metal-arene bond to the point that a full range of complexes with aromatic molecules could be isolated and characterized.The difference in d 5 /d 6 reduction potentials between TpRe(CO) 3 7 and TpW(NO)(CO) 2 8 suggests that the fragment {TpW(NO)} is approximately 300 mV more reducing than {TpRe(CO)}. 9 This observation, along with a comparison of electrochemical data for the series of complexes {TpRe(CO)(L)} (L ) NH 3 , MeIm, py, PMe 3

Facile Dearomatization of Nitrobenzene Derivatives and Other Nitroarenes with N‐Benzyl Azomethine Ylide

“…[2] However, metal-free benzene rings have long eluded this type of reactivity under practical conditions because of their inherent stability. [3,4] Herein we report that nitrobenzene derivatives undergo a facile dearomatizing [3+2] cycloaddition when reacted with N-benzyl azomethine ylide.…”

Hydroamination of Dihapto‐Coordinated Benzene and Diene Complexes of Tungsten: Fundamental Studies and the Synthesis of γ‐Lycorane

“…The enantiomer ratios of ( R , S )‐ 32 and ( S , R )‐ 32 were determined using chiral HPLC with a Chiralpak IC‐3 column. Compounds 1 , [48] 2 , 3 , [14] 4 , [15] 5 , [16] 10 , [49] 17 , [15] 18 , 19 , [16] 23 , 24 , [15] and 29 [40] were reported previously.…”

Charge donation to and dearomatization of benzene attending complexation: DFT estimates of binding energies of TpMXO(L) with benzene, for Tp = hydridotris(pyrazolyl) borate, MXO = MoNO, ReCO, and WNO, and L = ammonia, N‐methylimidazole, pyridine, phosphine, methyl isocyanide, and carbon monoxide

“…This is comparable with observed values of free energies of activation for ligand exchange, which is considered to be dissociative. 12 One would expect that stronger binding energies would correspond to shorter M-to-C bond distances. The relation is shown in the graph (Fig.…”