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

• Published in: Organometallics 2010-10, Vol.29 (20), p.4532-4540
• Main Authors: Welch, Kevin D, Dougherty, William G, Kassel, W. Scott, DuBois, Daniel L, Bullock, R. Morris
• Format: Article
• Language: English
• Subjects: AMINES; CARBONYLS; CATIONS; CHELATES; CRYSTAL STRUCTURE; dihydrogen complex; dinitrogen complex; MANGANESE COMPLEXES; MATERIALS SCIENCE; metal hydrides; NITROGEN; PHOTOLYSIS; SYNTHESIS; WEAK INTERACTIONS; X-RAY DIFFRACTION
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om100668e

Addition of the pendant amine ligand PNRP (PNRP = Ph2PCH2NRCH2PPh2; R = Me, Ph, n-Bu) to Mn(CO)5Br gives fac-Mn(PNRP)(CO)3Br. Photolysis of fac-Mn(PNRP)(CO)3Br with dppm [dppm = 1,2-bis(diphenylphosphino)methane] provides mixed bis(diphosphine) complexes, trans-Mn(PNRP)(dppm)(CO)(Br). Reaction of trans-Mn(PNRP)(dppm)(CO)(Br) with LiAlH4 leads to trans-Mn(PNRP)(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 NaBArF 4 (ArF = 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(PNMeP)(dppm)(CO)][BArF 4] 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).