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. [ABSTRACT FROM AUTHOR]