Silyl manganese pentacarbonyls (CO)₅MnSiR₃ [SiR₃＝SiMe₂Ph (3b), SiMePh₂ (3c), SiPh₃ (3d), SiHPh₂ (3e), SiEt₃ (3f), and SiMe₂Et (3h)] were photolyzed with different hydrosilanes R ₃SiH at 5 ℃ for 1 h, and the equilibrium of the silyl exchange between the two species was established. Moderate free energy gap between the products and reactants makes these reactions essentially reversible. The photocatalysis was preceded via an unsaturated species (CO)₄MnSiR₃ (1), and a transitional intermediate (CO)₄MnH(SiR₃)- (SiR ₃) (4). Feasibility of species 3 as a precatalyst activated via photolysis was confirmed. Due to both electronic and steric factors, the silyls bearing bulkier and more electrons repelling groups (like ethyl) were more readily to be replaced by that bearing smaller and electron accommodating groups (like hydride) from silyl manganese pentacarbonyls.

Key words: photochemistry, silyl manganese pentacarbonyls, silyl exchange