Publisher Summary The rapid development of the chemistry of transition-metal complexes containing terminal carbene (A) or carbyne (B) ligands has been followed more recently by much research centered on bridged methylene compounds (C). As often occurs in new and developing areas of chemistry, some confusion about the nomenclature of these complexes has arisen. Protonation or alkylation of several ethynyl–metal derivatives gives the corresponding vinylidene complexes in high yield. Several vinylidene complexes of the group VI metals have been obtained by heating σ–chlorovinyl derivatives with tertiary phosphines, phosphites, arsines, or stibines. Several complexes containing μ -C=CHR ligands have been obtained directly from 1-alkynes and two equivalents (or excess) of an appropriate precurso. A general route to complexes containing propadienylidene ligands is by loss of water or alcohols from suitable carbene or vinylidene precursors, or of oxo or alkoxy functions from ynolate anions. The majority of the chemistry of vinylidene and propadienylidene complexes is concerned with their synthesis and reactions. Vinylidene is one of the best π-acceptors known and is exceeded only by SO 2 and CS. The vinylidene ligand occupies an important place in the sequence of reactions linking a variety of well-known η 1 -carbon-bonded ligands. Metal cluster complexes containing vinylidene ligands have been considered as models of species present when olefins or alkynes are chemisorbed on metal surfaces.

Vinylidene and Propadienylidene (Allenylidene) Metal Complexes

Thermal evolution of acetylene and ethylene on Pd(111)

Publisher Summary Organometallic chemistry encountered rapid expansion experienced by the synthesis, spectroscopy, structural chemistry, theory, and reactivity of compounds characterized by terminal carbene (methylene, A) and carbyne (methylidyne, B) functionalities. The chemistry of μ-methylene complexes did not develop as extensively as that of its mononuclear counterparts, the latter being characterized by terminal carbene ligands. As in the bonding of carbenes with single atoms metal, the methylene group has a filled orbital (a 1 ) that can act as a sigma donor to the system. Symmetrical methylene (alkylidene) bridges represent the predominant geometry. Stability against thermolysis and photolysis is one of the striking properties of dimetallacyclopropanes, especially of those involving carbonyl and cyclopentadienyl ligands on the metals. There is so far not a single exception to the rule that a μ-methylene complex is at least as stable as its μ-carbonyl counterpart. Substitution reactions at the methylene bridge have been observed, albeit the yields were quite low suggesting that major side reactions had occurred. The molecular regimes in discrete di- and polynuclear complexes are mostly coordinatively saturated, whereas metal surfaces, especially if they are relatively flat and close-packed, have no coordinatively saturated surface atoms, even in the presence of chemisorbed species. There is an array of well-established analogues of the μ-methylene complexes in which the heavier congeners of carbon adopt bridging positions.

The Methylene Bridge

Publisher Summary Metal carbonyls, which were among the earliest discovered organometallic compounds, continue to play a central role in organometallic chemistry. Carbonyl basicity is found for C-bridging CO ligands in metal–metal bonded compounds, CO ligands in anionic metal carbonyls, or CO ligands in donor-substituted metal carbonyls. The interaction of protons with mononuclear metal carbonyls readily occurs at the metal center rather than the CO oxygen; no stable or transient MCO–H species appear to have been observed. The chemical and structural characterization of molecular compounds containing π–CO is of great interest, because the π–CO is implicated as a precursor to the cleavage of CO on metal surfaces, such as those employed in Fischer–Tropsch catalysis. In view of these large physical changes, it perhaps is not surprising that C and O bonding also engenders large changes in CO reactivity. Carbon monoxide insertion into a metal–alkyl bond is a fundamental reaction in organometallic chemistry as well as an important step in the commercial production of oxygen-containing organics, such as aldehydes and acetic acid.

C- and O-Bonded Metal Carbonyls: Formation, Structures, and Reactions

https://escholarship.org/content/qt8gd9h9ps/qt8gd9h9ps.pdf?t=p0fv00

Evidence for the formation of stable alkylidyne structures from C3 and C4 unsaturated hydrocarbons adsorbed on the Pt(111) single crystal surface

Acetylene and substituted acetylenes react with [H2Os3(CO)10] without CO loss at room temperature to give vinyl derivatives of type [HOs3(CR1:CHR2)(CO)10](R1= R2= H or Ph; R1= H, R2= Me or Ph), alkenylene complexes [Os3(CR1:CR2)(CO)10](R1= R2= H or Me; R1= H, R2= Me), and the phenylethynyl complex [HOs3(C2Ph)(CO)10], while other derivatives containing coupled alkynes are formed in low yield, if at all, at room temperature. On heating these complexes in hydrocarbon solvents, hydrogen transfer and CO loss occur to give [H2Os3(C2R2)(CO)9](R = H, Me, or Ph), [HOs3(C2R)(CO)9](R = H or Me), and [HOs3(MeC3H2)(CO)9][in two isomeric forms (A) or (B)]. The dihydrido-complexes may also be prepared by hydrogenation of [Os3-(CR1:CR2)(CO)10](R1= H or Me, R2= Me). Structures are proposed on spectroscopic evidence. The significance of these results to the reactivity of olefins with Os3(CO)12 is discussed.

Reactions of acetylene, methyl- and phenyl-substituted acetylenes, and ethylene with 1,1,1,1,2,2,2,3,3,3-decacarbonyl-2,3-di-µ-hydrido-triangulo-triosmium

Ethylene on reaction with Os3(CO)12 heated under reflux in octane undergoes 1,1-elimination of H2 to give the ethan-1-yl-2-ylidyne complex [H2Os3(CH2C)(CO)9], (I), whereas cyclopentene and benzene undergo 1,2-elimination of H2 to give corresponding cyclopenta-1,2-diylidene and cyclohexa-3,5-dien-1,2-diylidene complexes (II) and (III). Kinetic data are given for intramolecular exchange of the –CH2C hydrogen atoms of complex (I) which is faster than hydride exchange, and mechanisms for these processes are discussed. Diphenyl(o-vinyl-phenyl) phosphine (dpvp) reacts with Os3(CO)12 to give the complex [H2Os3(Ph2P·C6H4·C2H)(CO)8], (IV), which is related to the derivatives above.

Reactions of dodecacarbonyl-triangulo-triosmium with alkenes and benzene; fluxional behaviour of µ3-(ethan-1-yl-2-ylidyne)-di-µ-hydrido-triangulo-tris(tricarbonylosmium)(3Os–Os)

The complexes [Os3(CO)11(EMe2Ph)] or [Os3(CO)10(EMe2Ph)2](E = P or As) on heating give C6H4-bridged complexes [HOs3(C6H4)(EMe2)(CO)9], [HOs3(C6H4)(PMe2)(PMe2Ph)(CO)8]. [Os3(C6H4)(Eme2)2(CO)7], and [HOs3(Me2PC6H4C6H3)(PMe2)(CO)8]. When E = As, dimeric complexes containing bridging C6H4 are also obtained. Structures and mechanisms of the fluxional behaviour of these complexes are discussed in the light of n.m.r. spectra.

Some benzyne complexes of osmium derived from dimethylphenylphosphine or dimethylphenylarsine

Preliminary crystallographic data for the complex H2Os3(CCH2)(CO)9 derived from ethylene and Os3(CO)12 are given and the mechanisms of its fluxional behaviour and hydrogenation to give H3Os3(CCH3)(CO)9 are discussed.

Hydrogenation and fluxional behaviour of H2Os3(CCH2)(CO)9, a vinylidene complex derived from ethylene

The preparation and protonation of H2Os3-(CO)9CCH2 and other related complexes are reported.

Mark Underhill

Papers

Reactions of acetylene, methyl- and phenyl-substituted acetylenes, and ethylene with 1,1,1,1,2,2,2,3,3,3-decacarbonyl-2,3-di-µ-hydrido-triangulo-triosmium

Reactions of dodecacarbonyl-triangulo-triosmium with alkenes and benzene; fluxional behaviour of µ3-(ethan-1-yl-2-ylidyne)-di-µ-hydrido-triangulo-tris(tricarbonylosmium)(3Os–Os)

Some benzyne complexes of osmium derived from dimethylphenylphosphine or dimethylphenylarsine

Hydrogenation and fluxional behaviour of H2Os3(CCH2)(CO)9, a vinylidene complex derived from ethylene

Triruthenium and triosmium carbonium derivatives