Manganese germylene complexes: reactivity with dihydrogen, isonitriles, and dinitrogen

The manganese germylene-hydride complexes [(dmpe)₂MnH(GeR₂)] (1a: R = Ph, 1b: R = Et) reacted with H₂ (approx. 1.5 atm) to afford the 'germyl dihdyride' species [(dmpe)₂MnH₂(GeHR₂)] (2a: R = Ph, 2b: R = Et) as an equilibrium mixture with the starting material (1a-b). In solution, 2a-b exist as a mixture of isomers where the major isomer (71-84%) is a trans hydrogermane hydride complex trans-[(dmpe)₂MnH(HGeHR₂)] (transHGe-2a-b). The minor isomer of 2a-b is tentatively assigned as the cis germyl dihydrogen complex cis-[(dmpe)₂Mn(GeHR₂)(H₂)] (cis-2a-b), possibly in rapid equilibrium with a small amount of the germanate complex [(dmpe)₂Mn(H₂GeHR₂)] (central-2a-b). DFT calculations were employed to gain insight into the nature of bonding in the isomers of 2a-b, and an X-ray crystal structure was obtained for trans-[(dmpe)₂MnH(HGeHEt₂)] (transHGe-2b) which co-crystallized with 1b. Reactions of 1a-b with D₂ suggest a pathway that proceeds via conversion of 1a-b to a 5-coordinate germyl intermediate [(dmpe)₂Mn(GeHR₂)] (A) prior to reaction with H₂/D₂. Providing support for this pathway, intermediate A (R = Ph) was trapped via reactions of 1a with isonitriles, affording the manganese(I) germyl isonitrile complexes [(dmpe)₂Mn(GeHPh₂)(CNR)] (3a: R = ^tBu, 3b: R = o-xylyl, and 3c: R = ⁿBu). These complexes formed as a mixture of cis and trans isomers, and X-ray quality crystals were obtained for cis-3a, cis-3b and trans-3c. Complexes 1a-b also reacted slowly with dinitrogen at room temperature to afford germyl dinitrogen complexes [(dmpe)₂Mn(GeHR₂)(N₂)] (5a: R = Ph, 5b: R = Et). Compounds 5a-b were initially formed as cis isomers, but the trans isomer is the thermodynamic product in each case, and the cis and trans isomers were crystallographically characterized for both 5a and 5b. X-ray crystallography, IR spectroscopy, and DFT calculations were employed to compare metal-dinitrogen bonding in the cis and trans isomers of 5a-b. The silyl dinitrogen derivative [(dmpe)₂Mn(SiHPh₂)(N₂)] (6) was also generated as a mixture of the cis and trans isomers, and the trans isomer was structurally characterized. The trans isomers of 5b and 6 show ⁵⁵Mn-³¹P coupling in the ³¹P{¹H} and ⁵⁵Mn{¹H} NMR spectra, affording 1 : 1 : 1 : 1 : 1 : 1 sextets and 1 : 4 : 6 : 4 : 1 quintets, respectively.