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

abstract

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.