Protonation, of carbyne complexes

Protonation of carbyne complexes [M(CR)(C0)2Cp] (R p-tol,Me) by HBF4 affords cationic [W2( -H)((i-RCCR)(CO)4Cp2] which can be reversibly... 

The deprotonation of carbyne complexes is the formal reverse of the addition of a proton to the vinylidene (Equation 1.10, Table 1.4) ... 

In fact, the first isolation ofthe vinylidene pentacarbonyltungsten complexes was reported by Mayr et al. in 1984 [6]. The vinylidene complexes 16 were obtained by the alkylation of anionic pentacarbonyltungsten t-butylacetylide complex 15, obtained by the reaction of [Et4N ] [W(CO)5Cl ] with lithium acetylide, with FS03Me or [Et30 ] [Bp4 ]. Further protonation with CF3SO3H in the presence of Me4N P afforded a unique method for the preparation of carbyne complexes 17 (Scheme 5.4). 

A range of vinylidene complexes [ReX(=C=CFlR)(dppe)2] (X = F, Cl) has been prepared by deprotonation of the corresponding carbynes [ReX(=C-CH2R)(dppe)2]+. The mechanism of the protonation of these complexes has shown that, depending on the reaction conditions, protonation occurs either directly at the vinylidene /3-carbon or at the metal, followed by migration to the referred /3-carbon. ... 

Protonation of the nucleophilic fi-C of vinylidenes originated a one-pot synthesis of a range of carbyne complexes raw5-[ReF(dppe)2(=CCH2R)]BF4 upon treating -a/25-[ReCl(dppe)2(N2)j with HCCR, [NH4][BF4], [NH4]T1, and light. NH4+ provides the protons necessary to the protonation of the vinylidene intermediates trans [ReCl(dppe)2(=C=CHR)j, whereas BF4 provides the F ion that replaces Cl . ... 

Electron-rich isocyanide complexes react with acids from which the addition of a proton to the nitrogen atom takes place leading to the formation of carbyne complexes. Additional H + ions may be bound by the metal atom or by the nitrogen atom. 

Vinylidene complexes are also suitable precursors via protonation of carbynes [Os =GGH(R)Ph (77 -G5H4SiPh3)(GePh3)(PPp3)][BF4] (R = H, Me) and the first isolated hydride-carbyne derivative... 

If a given vinylidene complex is not sufficiently electrophilic, protonation at Cp can promote nucleophilic addition at C by intermediate formation of an electrophilic carbyne complex [89] (Figure 2.9, Section 2.1.8). 

Electron-rich carbyne complexes can react at the carbyne carbon atom with electrophiles to yield carbene complexes. Numerous examples of such reactions, mostly protonations, have been reported [519]. Depending on the nucleophilicity of the carbyne complex, such reactions will occur more or less readily. The protonation of weakly nucleophilic carbyne complexes requires the use of strong acids, such as triflic [533], tetrafluoroboric [534] or hydrochloric acid [535,536]. More electron-rich carbyne complexes can, however, even react with phenols [537,538], water [393,539], amines [418,540,541], alkyl halides, or intramolecularly with arenes (cyclometallation, [542]) to yield the corresponding carbene complexes. A selection of illustrative examples is shown in Figure 3.25. 

The reaction is thought to proceed with the dissociation of CT followed by release of the extra charge of the mthenium complex by dissociating a proton from the alkyhdene hgand. Such an exchange in itself does not lead to the decomposition of the alkyhdene complex. Nevertheless, both the formation of the charged species, both the intermediate existence of the carbyne complex (Scheme 9.5) may open new ways to the deterioration of the ROMP catalysts. 

Electrophilic attack on //-vinylidene complexes can occur either on the methylene carbon, or at the metal-metal bond. With the manganese complexes (45, R = H or Me), protonation affords the//-carbyne complexes (46), which in the case of R = Me, exist in the stereoisomeric forms shown (57). Interconversion of the two forms is slow at room temperature ... 

Several groups have completed computational studies on the relative stabilities of osmium carbyne, carbene, and vinylidene species. DFT calculations on the relative thermodynamic stability of the possible products from the reaction of OsH3Cl(PTr3)2 with a vinyl ether CH2=CH(OR) showed that the carbyne was favored. Ab initio calculations indicate that the vinylidene complex [CpOs(=C=CHR)L]+ is more stable than the acetylide, CpOs(-C=CR)L, or acetylene, [CpOs() -HC=CR)L]+, complexes but it doesn t form from these complexes spontaneously. The unsaturated osmium center in [CpOsL]+ oxidatively adds terminal alkynes to give [CpOsH(-C=CR)L]+. Deprotonation of the metal followed by protonation of the acetylide ligand gives the vinylidene product. 

A dithiocarbamate ligand acts as the source of sulfur, and its counterion, [H2NEt2], provides a proton in the reaction of the carbyne complex 270 (R = Me, Ph) with [H2NEt2][S2CNEt2]. The proton in 271 is bonded to the carbon of the former carbyne ligand, which has been converted to a thioformaldehyde ligand (181). 

The carbyne carbon atoms in both [W(CO)2 HB(pz)3)(CSMe)] (449) (266) and [W(CMe)Cp(CO)2] (450) (267) are nucleophilic and react with protons and the methylthio cation, SMe , to form cationic carbene complexes. Whereas the first type of carbene complex is typically electrophilic (257), the latter one, 451, is nucleophilic, and treatment with trifluoroace-tic acid produces a cationic metallathia cyclopropane complex (452) (268). 

The trigonal bipyramidal osmium carbyne complex 115 adds HCl across the metal-carbon triple bond to give the octahedral carbene complex 116 [Eq. (101)] (56). Protonation of 115 with aqueous HCIO4 gives the cationic... 

Reaction of the tungsten complex 167 with diphenylphosphine at elevated temperatures affords complex 168 [Eq. (140)] (76i). The same compound could be obtained by sequential addition of LiPPh2 and NH4Br. Formation of this product is surprising considering the ease with which some phospines induce carbyne-carbonyl coupling in complex 167 (see Section IV,F). The by-product 169 could possibly be derived from an intermediate ketenyl complex. Protonation of complex 168 in acetonitrile occurs at the former carbyne carbon to give the phosphine complex 170. 

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