Novel Dimerization of Maleic Anhydride at a Mo₂ Complex: Phase-Driven Keto/Enol Tautomerism in a Phosphinidenium–Ylide Complex

Abstract

A novel dimerization of maleic anhydride involving olefinic to carbonyl C−C coupling and an [1,7]-H shift is promoted by a strongly nucleophilic pyramidal phosphinidene complex. The resulting carbene is stabilized by coordination of the P atom of the phosphinidene ligand and undergoes keto/enol tautomerization when going from solution to the solid state. This is accompanied by a strong pyramidalization of the ylidic carbon atom, facilitated by the presence of π•••π stacking interactions in the crystal lattice.

P–N and N–Mo Bond Formation Processes in the Reactions of a Pyramidal Phosphinidene-Bridged Dimolybdenum Complex with Diazoalkanes and Organic Azides

“… a IR data were recorded in dichloromethane solution, with C–O stretching bands (ν­(CO)) in cm –1 ; NMR data were recorded in CD 2 Cl 2 solution at 121.48 MHz and 293 K, with chemical shifts (δ) in ppm relative to external 85% aqueous H 3 PO 4 and P–P couplings ( J PP ) in hertz. b Data taken from ref ; IR data were recorded in toluene solution and NMR data in C 6 D 6 solution. c Data recorded at 233 K. …”

“…Solvents were purified according to literature procedures, and distilled prior to use. 30 Compound [Mo2Cp(- 1 : 1 , 5 -PC5H4)( 6 -HMes*)(CO)2(PMe3)] ( 1) was prepared in situ as described previously, 11 typically upon addition of stoichiometric amounts of PMe3 on toluene solutions of [Mo2Cp(- 1 : 1 , 5 -PC5H4)( 6 -HMes*)(CO)2], 12 in a Schlenk tube equipped with a Young´s valve. Reagents N2CPh2, 31 Et2O solutions of N2CH2, 32 Na(BAr'4), 33 and [H(OEt2)2](BAr'4), 34 were prepared as described previously The procedure is completely similar to the one described for 2b, except that neat N2CHCO2Et (8 L, 0.076 mmol) was used instead.…”

“…28 Hz with both P atoms of the molecule. 20 The newly formed phosphanyl ligands display resonances in the range 104.6-144.9 ppm, close to the chemical shift of the parent phosphinidene complex (P 122.0 ppm), 11 and their couplings to the PMe3 ligands are large (ca. 30 Hz).…”

“…10 To further explore the complex reactivity of pyramidal phosphinidene complexes towards azides and diazoalkanes, we decided to study the reactivity of the dimolybdenum complex [Mo2Cp(- 1 : 1 , 5 -PC5H4)(CO)2( 6 -HMes*)(PMe3)] (1, Chart 2) towards these unsaturated organic molecules, which is the purpose of the present work. Previous studies have revealed that 1 displays a strong nucleophilicity that enables it to react under mild conditions with different C-based electrophiles such as organic anhydrides, 11 alkyl halides, 12 and S-containing cumulenes, 13 among other electrophiles. Thus, it could be anticipated that 1 might easily react with organic azides and diazoalkanes, although the subsequent evolution of the products following the initial PN bond formation step would be harder to predict, particularly because of the very different electronic environments of the Mo centers bound to the phosphinidene ligand in this molecule.…”

Cycloaddition Reactions of the Phosphinidene-Bridged Complex [Mo2Cp(μ-κ1:κ1,η5-PC5H4)(CO)2(η6-HMes*)] with Diazoalkanes and Other Heterocumulenes

“…Actually, the unique studies in this respect involve reactions of the cyclopentadienylidene-phosphinidene complex [Mo 2 Cp(- 1 : 1 , 5 -PC 5 H 4 )(CO) 2 ( 6 -HMes*)] (1) with alkenes and alkynes, which are much accelerated by the presence of additional ligands such as CO or isocyanides.…”