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 <i>trans</i> hydrogermane hydride complex <i>trans</i>-[(dmpe)₂MnH(HGeHR₂)] (transHGe-2a-b). The minor isomer of 2a-b is tentatively assigned as the <i>cis</i> germyl dihydrogen complex <i>cis</i>-[(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 <i>trans</i>-[(dmpe)₂MnH(HGeHEt₂)] (transHGe-2b) which co-crystallized with 1b. Reactions of 1a-b with D₂ suggest a pathway that proceeds <i>via</i> 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 <i>via</i> reactions of 1a with isonitriles, affording the manganese(I) germyl isonitrile complexes [(dmpe)₂Mn(GeHPh₂)(CNR)] (3a: R = ^<i>t</i>Bu, 3b: R = <i>o</i>-xylyl, and 3c: R = ^<i>n</i>Bu). These complexes formed as a mixture of <i>cis</i> and <i>trans</i> 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 <i>cis</i> isomers, but the <i>trans</i> isomer is the thermodynamic product in each case, and the <i>cis</i> and <i>trans</i> 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 <i>cis</i> and <i>trans</i> isomers of 5a-b. The silyl dinitrogen derivative [(dmpe)₂Mn(SiHPh₂)(N₂)] (6) was also generated as a mixture of the <i>cis</i> and <i>trans</i> isomers, and the <i>trans</i> isomer was structurally characterized. The <i>trans</i> 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.