Marilin Vivanco

A Fischer Carbene within an Arduengo Carbene

The chemistry of N-heterocyclic carbenes (NHCs) has been an intense area of research in the last several years. The pioneering work by Arduengo et al. and Herrmann on free ligand isolation and catalytic applications of NHC metal complexes, respectively, has significantly contributed to the development of this field. There is currently a widespread interest in developing new strategies for NHC ligand design involving the replacement of the carbon atom backbone with heteroatoms. Apart from the well-known triazol-2-ylidenes, NHCs containing boron and phosphorus as heteroatoms in the N-heterocyclic skeleton have been described. However, NHCs featuring a metal atom within the heterocyclic framework, derived from the standard imidazole cycle, are still unknown. Replacement of the carbon atom at C4 of an Arduengo carbene (Scheme 1, A)

Diphosphanylketenimines: New Reagents for the Synthesis of Unique Phosphorus Heterocycles

Two consecutive [3+2] cycloaddition reactions of the diphosphanylketenimine (PPh(2))(2)C[double bond]C[double bond]NPh (3), involving the phosphanyl groups, with two equivalents of the electron-poor alkynes dimethyl acetylenedicarboxylate or methyl acetylenecarboxylate give rise to the formation of the bicyclic 1 lambda(5),3 lambda(5)-diphospholes 5 a,b, which contain a phosphorane unit with five carbon substituents attached to the phosphorus center. Compound 3 undergoes cyclodimerization by crystallization, affording the unsymmetrical dimer 6, which is converted back to 3 by heating in toluene. Compound 6 can be oxidized stepwise on the three trivalent phosphorus atoms by treatment with H(2)O(2) affording 7, 9, and the transient species 10, which are transformed into their corresponding ketenimine monomers either spontaneously (10) or by heating in toluene (7, 9). In this way, the compound (O[double bond]PPh(2))(PPh(2))C[double bond]C[double bond]NPh (8) is quantitatively obtained. Compound 8 readily reacts with the alkynes MeO(2)CC[triple bond]CCO(2)Me and MeO(2)CC[triple bond]CH, and with phenyl isocyanate and ethyl isothiocyanate through regiospecific [3+2] cycloaddition processes furnishing several lambda(5)-phosphole and lambda(5)-azaphosphole derivatives. Finally, the reaction of 8 with N-methylpropargylamine yields the new 2,3-dihydro-1,4-lambda(5)-azaphosphinine 15 through a cycloaddition process involving two functional groups from each molecule.

Generating and Trapping Metalla‐N‐Heterocyclic Carbenes

By means of a combined experimental and theoretical approach, the electronic features and chemical behavior of metalla-N-heterocyclic carbenes (MNHCs, N-heterocyclic carbenes containing a metal atom within the heterocyclic skeleton) have been established and compared with those of classical NHCs. MNHCs are strongly basic (proton affinity and pK(a) values around 290 kcal mol(-1) and 36, respectively) with a narrow singlet-triplet gap (around 23 kcal mol(-1)). MNHCs can be generated from the corresponding metalla-imidazolium salts and trapped by addition of transition-metal complexes affording the corresponding heterodimetallic dicarbene derivatives, which can serve as carbene transfer agents.

New approach to the chemistry of polysulfides using diphosphanylmethanide complexes of manganese(I).

The study of the nucleophilic degradation of S8 by the methanide complex [Mn(CO)4[(PPh2)2CH]] (2) has led to the preparation of a unique class of polysulfide derivatives of formula [(CO)4Mn[(PPh2)2C-Sn-C(PPh2)2]-Mn(CO)4]. The structures of 3 (n = 6), 4 (n = 2), and 7 (n = 1) have been determined by X-ray crystallography, whereas those polysulfides with the sulfur chains S7, S5, S4, and S3 have been detected by spectroscopic methods. The polysulfides with n > 2 lose sulfur spontaneously, a process that can be accelerated by treatment with PPh3 or Na/Hg. Complexes 3, 4, and 7 were protonated at the two methanide carbon atoms to give the cationic dinuclear derivatives [(CO)4Mn[(PPh2)2C(H)-Sn-C(H)-(PPh2)2]Mn(CO)4]2+ (8, n=6; 9, n=2; 10, n = 1). The 1H NMR spectrum of 9 suggests the existence of intramolecular C-H...S interactions, in agreement with the X-ray structural determination of this complex. By treatment of 4 and 7 with one equivalent of HBF4 it is possible to selectively protonate just one methanide carbon atom, which allows the isolation of the mixed cationic derivatives R(CO)4Mn[(PPh2)2C(H)-Sn-C(PPh2)2]Mn(CO)4]+ (11, n = 2; 6, n = 1). Additionally, heterometallic complexes containing a bridging disulfide unit, of general formula [(CO)4Mn[(PPh2)2C(AuPPh3)S-SC-(AuPPh3)(PPh2)2]Mn(CO)4]2+ (12) and [(CO)4Mn[(PPh2)2C(H)S-SC(AuPPh3)-(PPh2)2]Mn(CO)4]+ (13), were prepared by reaction of 4 and 11, respectively, with [AuCl(PPh3)] in the presence of TlPF6.

Template Synthesis, Metalation, and Self-Assembly of Protic Gold(I)/(NHC)2 Tectons Driven by Metallophilic Interactions.

A new protocol for the synthesis of protic bis(N-heterocyclic carbene) complexes of Au(I) by a stepwise metal-controlled coupling of isocyanide and propargylamine is described. They are used as tectons for the construction of supramolecular architectures through metalation and self-assembly. Notably a unique polymeric chain of Cu(I) with alternate Au(I) /bis(imidazolate) bridging scaffolds and strong unsupported Cu(I) -Cu(I) interactions has been generated, as well as a 28-metal-atoms cluster containing a nanopiece of Cu2 O trapped by peripheral Au(I) /bis(imidazolate) moieties.

An exception to the general mechanism of CO insertion into the alkyl-manganese bond

Two-electron donor ligands L enter trans(and not cis as in other manganese examples) to the acyl group in the reaction of fac-[Mn(CO)3(bipy)(Me)]1 with L to give cis,trans-[Mn(CO)2(L)(bipy)(COMe)]2; the reaction of 1 with *CO (CO 99% enriched in 13C) gives cis,trans-[Mn(CO)2(*CO)(bipy)(COMe)]4, ruling out the formation of the possible intermediate cis,cis-[Mn(CO)2(L)(bipy)(COMe)]3.

Dihydrogen reducing [V{η2-C(Mes)NBut}3] and making a diamagnetic divanadium(IV) complex containing a vanadium-vanadium single bond

The vanadium complex [V{η2-C(Mes)NBut}3]1 reacts at –30 °C with dihydrogen to form [{η2-C(Mes)NBut}V(MesCH2NBut)2]2, thermally rearranging to a divanadium (IV) complex containing a vanadium-vanadium single bond (Mes = 2,4,6-Me3C6H2).

Carbene complexes from coordinated bis(diphenylphosphino)methane. Synthesis and X-ray structure determination of the remarkable heterotrimetallic derivative [{Fe(CNPh)4((PPh2)2C)}2Hg]I2

The bis(diphenylphosphino)methanide complexes fac-[Mn(CNBut)(CO)3{(PPh2)2CH}]1a and [Fe(CNPh)4{(PPh2)2CH}]ClO41b react with HgI2 and KOH to give the heterotrimetallic bis(carbene)derivatives fac-[{Mn(CNBut)(CO}3((PPh2)2C)}2 Hg]4a and [{Fe(CNPh)4[(PPh2)2C]}2 Hg]I24b, respectively; the structure of 4b has been determined by X-ray analysis.

New approach to sulfonated diphosphine complexes: synthesis and amphoteric behaviour of zwitterionic [Mn+(CO4{(PPh2)2C(H)SO3−}]

Oxidation of the thioketone residue in the complex [Mn(CO)4{(PPh2)2C=S}]+ (2) with hydrogen peroxide affords the sulfonate derivative [Mn(CO)4{(PPh2)2C(H)SO3}] (3), which shows amphoteric behaviour in reversible acid-base processes, and is easily chlorinated to give [Mn(CO)4{(PPh2)2C(Cl)SO3}] (8).

Thiocyanogen Insertion into P−C Bonds of Diphosphinomethanide Complexes, Leading to Rare Functionalized Diphosphine and Tetraphosphine Ligands

The complex fac-[Mn(CNtBu)(CO)3{(PPh2)2C−SCN}] (2) reacts with thiocyanogen, affording the unstable derivative fac-[Mn(CNtBu)(CO)3{(PPh2)C(SCN)C(SSCN)N(PPh2)}] (3), as a result of the insertion of the pseudohalogen molecule into one of the P−C bonds of the diphosphinomethanide ligand. This complex undergoes intermolecular sulfur−sulfur coupling processes, with elimination of the pseudohalogen molecules (SCN)2, S(CN)2, and (CN)2, to yield a mixture of the dinuclear complexes fac-[{Mn(CNtBu)(CO)3(PPh2)C(SCN)C(NPPh2)}2−Sn] (4−6) linked through polysulfide chains of different lengths. Treatment of these dinuclear disulfide and trisulfide derivatives with 1 or 2 equiv of HBF4 resulted in the sequential protonation of the nitrogen atoms of the ligand, yielding cationic and dicationic complexes, respectively. In the case of monoprotonated disulfide derivatives 31P NMR experiments reveal the existence of an intramolecular proton-transfer process between the endocyclic nitrogen atoms of both metallic fragments. Si...