Transition metal arsine complexes
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Transition metal arsine complexes are coordination complexes containing one or more arsine ligands. Almost always, the arsine is an organoarsenic compound of the type R3As (R = alkyl, aryl).[1]
Comparison of arsine and phosphine ligands
Arsines are L ligands according to the Covalent bond classification method. In the usual electron counting method, they are two-electron ligands. With respect to HSAB theory, the ligand is soft.
An obvious difference between arsine and phosphine ligands is the larger size of arsenic atoms. Consequently, M-As bonds tend to be about 10 picometers longer than M-P bonds.[3] Furthermore, the ligand cone angle is somewhat smaller for arsines vs phosphines: 141° for AsPh3 vs 145° for PPh3.[4]
The inversion barriers for tertiary arsines are estimated to be near 40 kcal/mol. By contrast, the inversion of a tertiary phosphine occurs with barriers near 30 kcal/mol. Thus, chiral arsines are more optically stable than chiral phosphines.[5]
Arsines are more reluctant to oxidize to As(V) derivatives. For this reason, alkylarsines are more air-stable than the corresponding alkylphosphines.