σ-Arsolido complexes.

The σ-stannyl complexes [M(Sn n Bu 3 )(CO) n (η 5 -C 5 H 5 )] ( 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 ClAsC 4 R 4 (R = Me, Ph) to afford [M(σ-AsC 4 R 4 )(CO) n (η 5 -C 5 H 5 )]. The reaction of [Cr(Sn n Bu 3 )(CO) 3 (η 5 -C 5 H 5 )] with ClAsC 4 Ph 4 most likely proceeds in a similar manner but is immediately followed by rapid formation of (AsC 4 Ph 4 ) 2 and [Cr 2 (CO) 6 (η 5 -C 5 H 5 ) 2 ]. The reaction of [Mo(Sn n Bu 3 )(CO) 3 (η 5 -C 5 H 5 )] with ClAsC 4 (SiMe 3 )-2,5-Me 2 -3,4 is accompanied by monodesilylation to afford [Mo{σ-AsC 4 (SiMe 3 )-2-Me 2 -3,4}(CO) 3 (η 5 -C 5 H 5 )]. The slow reaction of [Fe(Sn n Bu 3 )(CO) 2 (η 5 -C 5 H 5 )] with ClAsC 4 Me 4 produced only traces of [Fe(σ-AsC 4 Me 4 )(CO) 2 (η 5 -C 5 H 5 )] 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.