Synthesis, Structures, and Reactions of Manganese Complexes Containing Diphosphine Ligands with Pendant Amines

Addition of the pendant amine ligand PN^RP (PN^RP = Ph₂PCH₂NRCH₂PPh₂; R = Me, Ph, n-Bu) to Mn(CO)₅Br gives fac-Mn(PN^RP)(CO)₃Br. Photolysis of fac-Mn(PN^RP)(CO)₃Br with dppm [dppm = 1,2-bis(diphenylphosphino)methane] provides mixed bis(diphosphine) complexes, trans-Mn(PN^RP)(dppm)(CO)(Br). Reaction of trans-Mn(PN^RP)(dppm)(CO)(Br) with LiAlH₄ leads to trans-Mn(PN^RP)(dppm)(CO)(H), which has been characterized by crystallography. Mn(P₂^PhN₂^Bn)(dppm)(CO)(H) [P₂^PhN₂^Bn = 1,5-diphenyl-3,7-dibenzyl-1,5-diaza-3,7-diphosphacyclooctane] can be prepared in a similar manner; its structure has one chelate ring in a chair conformation and the second in a boat conformation. The boat-conformer ring directs the nitrogen of the ring toward the carbonyl ligand, and the N···C distance between one N of the P₂^PhN₂^Bn ligand and CO is 3.171(4) Å, indicating a weak interaction between the N of the pendant amine and the CO ligand. Reaction of NaBAr^F₄ (Ar^F = 3,5-bis(trifluoromethyl)phenyl) with Mn(P−P)(dppm)(CO)(Br) produces the cations [Mn(P−P)(dppm)(CO)]⁺. The crystal structure of [Mn(PN^MeP)(dppm)(CO)][BAr^F₄] shows two very weak agostic interactions between C−H bonds on the phenyl ring and the Mn. The cationic complexes [Mn(P−P)(dppm)(CO)]⁺ react with H₂ to form dihydrogen complexes [Mn(H₂)(P−P)(dppm)(CO)]⁺ (K_eq = 1−90 atm⁻¹ in fluorobenzene, for a series of different P−P ligands). Similar equilibria with N₂ produce [Mn(N₂)(P−P)(dppm)(CO)]⁺ (K_eq generally 1−3.5 atm⁻¹ in fluorobenzene).