Electrophilic As-functionalisation of σ-arsolido complexes.

The σ-arsolido complex [Mo(AsC 4 Me 4 )(CO) 3 (η 5 -C 5 H 5 )] is alkylated at arsenic by MeOTf to afford the pentamethylarsole complex [Mo(MeAsC 4 Me 4 )(CO) 3 (η 5 -C 5 H 5 )](OTf) while iodomethane affords a mixture of [Me 2 AsC 4 Me 4 ]I, [MoMe(CO) 3 (η 5 -C 5 H 5 )], [MoI(CO) 3 (η 5 -C 5 H 5 )] and the arsole complexes cisoid - and transoid -[MoI(MeAsC 4 Me 4 )(CO) 2 (η 5 -C 5 H 5 )] and transoid -[Mo{C(O)Me}(MeAsC 4 Me 4 )(CO) 2 (η 5 -C 5 H 5 )], The arsole ligand in [Mo(MeAsC 4 Me 4 )(CO) 3 (η 5 -C 5 H 5 )](OTf) is readily liberated by NaI in acetone to afford free MeAsC 4 Me 4 and [MoI(CO) 3 (η 5 -C 5 H 5 )]. In a similar manner, the reaction of [Mo(AsC 4 Ph 4 )(CO) 3 (η 5 -C 5 H 5 )] with MeI affords MeAsC 4 Ph 4 and [MoI(CO) 3 (η 5 -C 5 H 5 )], while [Mo{AsC 4 (SiMe 3 )-2-Me 2 -3,4}(CO) 3 (η 5 -C 5 H 5 )] with MeOTf affords [Mo{MeAsC 4 (SiMe 3 )-2-Me 2 -3,4}(CO) 3 (η 5 -C 5 H 5 )](OTf). The reaction of [Mo(AsC 4 Me 4 )(CO) 3 (η 5 -C 5 H 5 )] with activated alkynes (RCCR: R = CF 3 , CO 2 Me) 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(C 4 Me 4 )CRCRCO}(CO) 2 (η 5 -C 5 H 5 )].