Toward an Understanding of the Mechanism of Metal Exchange in (Propargyl Alcohol)Co₂(CO)₆ Clusters:  Syntheses and Structures of [η⁵-C₅Ph₂R₂−C⋮C−TMS)(Fe(CO)₂(μ-H)]Co₂(CO)₆, R = Ph or Et

Abstract

The reaction of (5-alkynylcyclopentadienol)Co 2 (CO) 6 clusters with iron pentacarbonyl in acetone does not yield the expected product in which the hydroxyl substituent is lost and a tricarbonylcobalt vertex is replaced by an Fe(CO) 3 group. Instead, the product contains an (η 5 -C 5 Ph 2 R 2 )Fe(CO) 2 H moiety that is bridged to one of the cobalt vertexes of the intact dicobalt-alkyne cluster. The process is rationalized in terms of a decarboxylation rather than a dehydroxylation process, and the relevance to the mechanism of substitution of one metal vertex by another is discussed.

Alkynyl-Dicobalt Hexacarbonyl Complexes of Menthyl Cations: Isolobal Substitution of [Co(CO)3]+by Fe(CO)3as a Structural Model

“…As noted above, the reaction of (propargyl alcohol)Co 2 (CO) 6 clusters with Fe(CO) 5 in refluxing acetone to yield iron−cobalt clusters was originally reported by Aime and Osella in 1983 and was described as a “dehydroxylation process”; since that time, a number of other examples of this metal exchange process have been reported. − However, the reactions of Fe(CO) 5 with (alkynylcyclopentadienol)Co 2 (CO) 6 complexes yielded unexpected products, 18 , in which an (η 5 -cyclopentadienyl)Fe(CO) 2 moiety was linked to a tricarbonylcobalt cluster vertex via a bridging hydride . As depicted in Scheme , it was proposed that initial attack by the hydroxyl oxygen on an iron carbonyl, migration of hydrogen to form a metal hydride, and loss of two iron carbonyls allowed complexation to the cyclopentadiene ring .…”

“…As a corollary, it was proposed that in the absence of a substituent to which the iron carbonyl could bond, one could instead invoke expansion of the alkynyl-dicobalt tetrahedral cluster to a square-based pyramidal structure, 19 , as in Scheme . While the apical and basal plane cobalts in 19 would formally be assigned 19 and 17 electrons, respectively, the overall electron count is appropriate for a nido octahedral cluster, and numerous examples of such cluster expansion or metal vertex replacements are known. − Subsequent loss of HCo(CO) x and CO 2 can yield the observed products.…”

“…[29][30][31][32][33] However, the reactions of Fe(CO) 5 with (alkynylcyclopentadienol)Co 2 -(CO) 6 complexes yielded unexpected products, 18, in which an (η 5 -cyclopentadienyl)Fe(CO) 2 moiety was linked to a tricarbonylcobalt cluster vertex via a bridging hydride. 37 As depicted in Scheme 6, it was proposed that initial attack by the hydroxyl oxygen on an iron carbonyl, migration of hydrogen to form a metal hydride, and loss of two iron carbonyls allowed complexation to the cyclopentadiene ring. 36 Subsequent decarboxylation furnished the observed products, 18.…”

21 Organometallic chemistry of bi- and poly-nuclear complexes

“…The reaction is thought to proceed via an intermediate carboxylate, formed by attack of the hydroxyl group on an iron carbonyl ligand. 141 The structures of the Co ] in the presence of pinacol and a suitable oxidant therefore results in the catalytic conversion of pinacol to acetone. 152 Chiral dirhodium complexes with orthometallated aryl phosphine ligands and acetate co-ligands have been shown to catalyse intramolecular cyclopropanation of styrenes to give separable diastereoisomers with good optical purity.…”

Reactions of linked tetrahedron clusters [Co2(CO)6(μ-HC2CH2O)–]2R with Rh2(CO)4Cl2 to give mixed-metal linked alkyne-bridged butterfly clusters containing C2Co2Rh2 unit

“…The chemistry of transition metal complexes bridged by unsaturated hydrocarbons developed rapidly and extensively in recent years resulting from the relevance to the chemistry of metal-catalyst surfaces [7,8]. It has been shown that an astonishing variety of alkynebridged clusters, including the synthesis and the reactivity of some linked alkyne-bridged clusters containing Co 2 -(CO) 6 C 2 unit have been reported [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Additionally, rhodium is especially active and implicated in a number of catalytic organic reactions [24,25].…”