σ-Arsolido complexes.

The σ-stannyl complexes [M(SnnBu3)(CO)n(η5-C5H5)] (n = 3, M = Mo, W; n = 2, M = Fe) serve as mild reagents for the installation of σ-arsolyl ligands in transmetallation reactions with As-chloro-arsoles ClAsC4R4 (R = Me, Ph) to afford [M(σ-AsC4R4)(CO)n(η5-C5H5)]. The reaction of [Cr(SnnBu3)(CO)3(η5-C5H5)] with ClAsC4Ph4 most likely proceeds in a similar manner but is immediately followed by rapid formation of (AsC4Ph4)2 and [Cr2(CO)6(η5-C5H5)2]. The reaction of [Mo(SnnBu3)(CO)3(η5-C5H5)] with ClAsC4(SiMe3)-2,5-Me2-3,4 is accompanied by monodesilylation to afford [Mo{σ-AsC4(SiMe3)-2-Me2-3,4}(CO)3(η5-C5H5)]. The slow reaction of [Fe(SnnBu3)(CO)2(η5-C5H5)] with ClAsC4Me4 produced only traces of [Fe(σ-AsC4Me4)(CO)2(η5-C5H5)] due to competition with the Diels-Alder type dimerisation of the haloarsole. Although attempts to decarbonylate the σ-arsolyl complexes were unsuccessful, computational analysis suggests that the trigonal 'XL' arsolenium coordination mode is viable.

Electrophilic As-functionalisation of σ-arsolido complexes.

The σ-arsolido complex [Mo(AsC4Me4)(CO)3(η5-C5H5)] is alkylated at arsenic by MeOTf to afford the pentamethylarsole complex [Mo(MeAsC4Me4)(CO)3(η5-C5H5)](OTf) while iodomethane affords a mixture of [Me2AsC4Me4]I, [MoMe(CO)3(η5-C5H5)], [MoI(CO)3(η5-C5H5)] and the arsole complexes cisoid- and transoid-[MoI(MeAsC4Me4)(CO)2(η5-C5H5)] and transoid-[Mo{C(O)Me}(MeAsC4Me4)(CO)2(η5-C5H5)], The arsole ligand in [Mo(MeAsC4Me4)(CO)3(η5-C5H5)](OTf) is readily liberated by NaI in acetone to afford free MeAsC4Me4 and [MoI(CO)3(η5-C5H5)]. In a similar manner, the reaction of [Mo(AsC4Ph4)(CO)3(η5-C5H5)] with MeI affords MeAsC4Ph4 and [MoI(CO)3(η5-C5H5)], while [Mo{AsC4(SiMe3)-2-Me2-3,4}(CO)3(η5-C5H5)] with MeOTf affords [Mo{MeAsC4(SiMe3)-2-Me2-3,4}(CO)3(η5-C5H5)](OTf). The reaction of [Mo(AsC4Me4)(CO)3(η5-C5H5)] with activated alkynes (RCCR: R = CF3, CO2Me) does not proceed via [4 + 2] cyclo-addition but rather electrophilic attack at arsenic followed by metallacyclisation with incorporation of a carbonyl ligand in the spirocyclic complexes [Mo{As(C4Me4)CRCRCO}(CO)2(η5-C5H5)].

Poly(imidazolyliden-yl)borato Complexes of Tungsten: Mapping Steric vs. Electronic Features of Facially Coordinating Ligands.

A convenient synthesis of [HB(HImMe)3](PF6)2 (ImMe = N-methylimidazolyl) is decribed. This salt serves in situ as a precursor to the tris(imidazolylidenyl)borate Li[HB(ImMe)3] pro-ligand upon deprotonation with nBuLi. Reaction with [W(≡CC6H4Me-4)(CO)2(pic)2(Br)] (pic = 4-picoline) affords the carbyne complex [W(≡CC6H4Me-4)(CO)2{HB(ImMe)3}]. Interrogation of experimental and computational data for this compound allow a ranking of familiar tripodal and facially coordinating ligands according to steric (percentage buried volume) and electronic (νCO) properties. The reaction of [W(≡CC6H4Me-4)(CO)2{HB(ImMe)3}] with [AuCl(SMe2)] affords the heterobimetallic semi-bridging carbyne complex [WAu(µ-CC6H4Me-4)(CO)2(Cl){HB(ImMe)3}].

Free and coordinated biarsolyls.

A trace side product from the reaction of [Mo(AsC4Me4)(CO)3(η-C5H5)] with [Mn(THF)(CO)2(η5-C5H4Me)] was identified as the biarsolyl complex [Mn2{µ-(AsC4Me4)2}(CO)4(C5H4Me)2] on the basis of a strategic synthesis from [Mn(THF)(CO)2(η5-C5H4Me)] and the pre-formed and structurally characterised biarsolyl (AsC4Me4)2. Crystallographic and computational data for this first example of a biarsolyl complex and free biarsolyls are discussed in the context of those for free biarsolyls.

Bridging arsolido complexes.

The σ-arsolyl complex [Mo(AsC4Me4)(CO)3(η-C5H5)] serves as a metallo-ligand for the strategic construction of µ-arsolido bridged heterobimetallic complexes [MoCr(µ-AsC4Me4)(CO)8(η5-C5H5)], [MoMn(µ-AsC4Me4)(CO)5(η5-C5H5)(η5-C5H4Me)], [MoAu(µ-AsC4Me4)(C6F5)(CO)3(η5-C5H5)] and [MoFe(µ-AsC4Me4)(CO)5(η5-C5H5)2]PF6via reactions with [Cr(THF)(CO)5], [Au(C6F5)(THT)], [Mn(THF)(CO)2(η5-C5H4Me)] and [Fe(THF)(CO)2(η5-C5H5)]PF6, respectively. The reaction of [Mo(AsC4Me4)(CO)3(η-C5H5)] with [Co3(µ3-CH)(CO)9] affords the tetrametallic species [MoCo3(AsC4Me4)(µ3-CH)(CO)11(η-C5H5)]. Crystallographic and computational data for all products are discussed.

Arsolyl-supported intermetallic dative bonding.

The first examples of late transition metal η5-arsolyls (L = CO, P(OMe)3; R = Ph, Me, Et, SiMe3; R' = Ph, H, Me, Et, Me) serve as ditopic donors to extraneous metal centres (M = PtII, AuI, HgII) through both conventional As → M and polar-covalent (dative) Co → M interactions.

Heterocyclic arsinocarbynes via tandem transmetallation.

Gold(i)-catalysed tandem transmetallation (Sn→Au→As) of the stannylcarbyne [W(≡CSnnBu3)(CO)2(Tp*)] (Tp* = hydrotris-(dimethylpyrazolyl)borate) with haloarsines gives direct access to a range of novel arsinocarbyne complexes, LnM≡CAsR2, including unusual heterocyclic phenarsazininyl and arsolyl examples.