Bismuth organometallic chemistry
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The stabilization of bismuth's +3 oxidation state due to the inert pair effect yields a plethora of organometallic bismuth-transition metal compounds and clusters with interesting electronics and 3D structures.[1]
Classical σ bonding
As is typical for bismuth compounds, the 6s electron pair is mainly inert. Organometallic Bi(III) compounds are Lewis acids, similar to group 13 element organometallic chemistry.[2]
Also similar to boron compounds, bismuth forms a wide variety of metal clusters.[2] Most synthetic routes use bismuth trichloride as the bismuth metal source.[6]
Below, compounds are sorted roughly by increasing electron delocalization.
In the simplest case, Bi forms a simple σ bond to another metal. For example, cyclopentadienyldicarbonyliron (Fp) is isolobally a pseudohalide:[7][8]
With cobalt tetracarbonyl instead of Fp, there exist similar compounds,[7] which are Lewis acids. The formal adduct with cobaltocenium tetracarbonylcobalt is the tetrahedral, paramagnetic [Cp2Co][Bi{Co(CO)4}4] complex.[3]
An analogous manganese compound forms a delocalized Mn-Bi-Mn bond:[2][6]
Polybismuth ligands
Other clusters contain a formal dibismuthene or dibismithyne unit, coordinated through the Dewar–Chatt–Duncanson interaction.[2] For example, oligo-trimethylsilylbismuth(I) reacts with pentacarbonyltungsten tetrahydrofuran to give a cluster with a Bi-Bi bond length corresponding to a single bond:[9][10]
Another example comes in the form of a zirconocene unit, side-coordinated to a dibismuth mesitylene moiety (pictured below).[11]
In 2009, Pearl et al. described the synthesis and isomerization of heterometallic complexes containing bismuth and rhenium. The precursors used in synthesis were an alkene-coordinated carbonyl rhenium complex and BiPh3.[5] The reaction yields two types of heteronuclear bismuth-rhenium complexes and a homodinuclear rhenium one as a side product. Upon heating, the hexametallic tribismuth-trirhenium heteronuclear complex undergoes isomerization to cis- and trans-clusters containing the bicyclo [3.3.0] core. Under subsequent irradiation both stereoisomers convert to a common spiro [4.3] cluster compound:[5]
Clusters like closo-[Bi3Cr2(CO)6]3- and [Bi3Mo2(CO)6]3- have been reported to stabilize the ozone-like structure of [Bi3]3-.[4] The [Bi3]3- species, isostructural and isoelectronic with ozone, can be analyzed independently as a moiety bound to the metal carbonyl complexes. The reported Bi-Bi distance falls in between the single and double bond region and is elongated compared to Bi=Bi bond in the [Bi4]2- cluster, the later displaying a bond order of 1.25.[4] This experimental observation is being rationalized by some amount of π-donation to the metal carbonyl center and simultaneously π* back-bonding to the bismuth cluster from the metallocene complex.[4]
PSEPT-type clusters
Bismuth atoms may appear at a wide variety of positions in a polyhedral skeleton:[2][12]
Strained cluster complexes with monodentate as well as bridging carbon monoxide units have also been isolated, such as [{Cp(μ2-CO)Fe}3(μ3-Bi)] and [(μ3-Bi)Co3(CO)6(μ-CO)3]:[2][13]
![Synthesis of [{Cp(μ2-CO)Fe}3(μ3-Bi)]](#/media/File:Synthesis_of_Bi-Fe_cluster.png)
Spiro-like clusters such as [{Ru2(CO)8}(μ4-Bi){(μ-H)Ru3(CO)10} and cubane-like ones as [Bi4Co*4] are representatives as well. The former displays a tetracoordinate bismuth metallic center along with a dicoordinated hydride ligand. The structure of the latter is cubic with the edges alternating bismuth and cobalt metallic centers:[2]
Applications
Organobismuth compounds have been proposed as non-toxic nucleophile partners in Suzuki-Miyaura-type coupling reactions. Transmetallation to organopalladium compounds occurs by two different mechanisms:[2]
In cycle A, Pd(0) oxidative addition occurs faster with the nucleophile's C-Bi bond; in cycle B, it occurs faster with the electrophile's C-O one.
