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

Addition of the pendant amine ligand (PNP)-P-R ((PNP)-P-R = Ph2PCH2NRCH2PPh2; R = Me, Ph, n-Bu) to Mn(CO)(5)Br gives fac-Mn((PNP)-P-R)(CO)(3)Br. Photolysis of fac-Mn((PNP)-P-R)(CO)(3)Br with dppm [dppm = 1,2-bis(diphenylphosphino)methane] provides mixed bis(diphosphine) complexes, trans-Mn((PNP)-P-R)(dppm)(CO)(Br). Reaction of trans-Mn((PNP)-P-R)(dppm)(CO)(Br) with LiAlH4 leads to trans-Mn((PNP)-P-R)(dppm)(CO)(H), which has been characterized by crystallography. Mn((P2N2Bn)-N-Ph)-(dppm)(CO)(H) [(P2N2Bn)-N-Ph = 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 center dot center dot center dot C distance between one N of the (P2N2Bn)-N-Ph ligand and CO is 3.171(4) angstrom, indicating a, weak interaction between the N of the pendant amine and the CO ligand. Reaction of NaBAr4F (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((PNP)-P-Me)(dppm)(CO)][BAr4F] 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 H-2 to form dihydrogen complexes [Mn(H-2)(P-P)(dppm)(CO)](+) (K-eq = 1-90 atm(-1) in fluorobenzene, for a series of different P-P ligands). Similar equilibria with N-2 produce [Mn(N-2)(P-P)(dppm)(CO)](+) (K-eq generally 1-3.5 atm(-1) in fluorobenzene).