Reactions of [(dmpe)MnH(CH)]: synthesis and characterization of manganese() borohydride and hydride complexes

• Published in: Dalton transactions : an international journal of inorganic chemistry 2020-08, Vol.49 (29), p.9983-9994
• Main Authors: Price, Jeffrey S, DeJordy, Declan M, Emslie, David J. H, Britten, James F
• Format: Article
• Language: English
• Subjects: Borohydrides; Cartesian coordinates; Crystal structure; Crystallography; Dihydrides; Hydrides; Isomerization; Isomers; Manganese; Mathematical analysis; NMR spectroscopy; Phosphines; Spectrum analysis; Substitution reactions
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/d0dt01726d

Reactions of trans -[(dmpe) 2 MnH(C 2 H 4 )] ( 1 ) with BH 3 (NMe 3 ), 9-BBN, and HBMes 2 yielded the manganese( i ) borohydride complexes [(dmpe) 2 Mn(μ-H) 2 BR 2 ] ( 3 : R = H, 4 : R 2 = C 8 H 14 , 5 : R = Mes). The reaction of 1 with BH 3 (NMe 3 ) proceeds via ethylene substitution. By contrast, a detuerium labelling study indicates that the reaction of 1 with HBMes 2 involves initial isomerization of 1 to an unobserved 5-coordinate ethyl intermediate, [(dmpe) 2 MnEt], which reacts with the hydroborane to afford EtBR 2 and [(dmpe) 2 MnH], followed by reaction with a second equivalent of hydroborane to generate 5 (an analogous pathway is likely followed for other base-free hydroboranes such as 9-BBN). Identification of 3-5 as κ 2 -borohydride complexes, as opposed to boryl dihydride or hydroborane hydride isomers, is supported by 11 B NMR spectroscopy, X-ray diffraction, and Atoms in Molecules calculations. Two byproducts were observed in the syntheses of 3-5 : [{(dmpe) 2 MnH} 2 (μ-dmpe)] ( 6 ) and [(dmpe) 2 MnH(κ 1 -dmpe)] ( 7 ). These complexes were independently prepared by exposure of 1 to free dmpe under an atmosphere of Ar or H 2 , and the generality of this synthetic route was demonstrated by the reaction of 1 with PMe 3 (under H 2 ) to form [(dmpe) 2 MnH(PMe 3 )] ( 8 ). Complexes 6-8 can exist as isomers with either a trans or a cis relationship between the hydride and κ 1 -coordinated phosphine ligands on manganese. trans to cis isomerization of 6-8 is photochemically induced, whereas the reverse reaction occurs under thermal conditions. X-ray crystal structures were obtained for 3-5 , trans , trans -6 , cis , cis -6 , trans -7 , and trans -8 . Reactions of trans -[(dmpe) 2 MnH(C 2 H 4 )] with hydroboranes and phosphines afforded manganese( i ) borohydride and hydride complexes; reaction pathways, structures and bonding are discussed.