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Please login to access the full content or check if you have access via Variation 8: Transition-Metal-Catalyzed Reduction: Hydrogenation and Transfer ­Hydrogenation

DOI: 10.1055/sos-SD-036-00032

Cox, L. R.Science of Synthesis, (200836106.

Molecular hydrogen is an inexpensive reducing agent. On its own, however, it is unreactive toward carbonyl groups. Fortunately, in the presence of a catalyst, reduction to the corresponding alkanol can be highly efficient.[‌487‌‌492‌] Although homogeneous catalysts employing virtually all of the transition metals are known, the two most important metals for catalyzing the hydrogenation of aldehydes (and ketones) to alkanols 59 are rhodium (Table 17, entry 1)[‌493‌‌499‌] and ruthenium.[‌500‌‌510‌] Dihydrido metal complexes derived from middle-row transition metals, such as [Mo(Cp)(CO)2(η1-O=CEt2)(PPh3)]+[BAr14] [Ar1=3,5-bis(trifluoromethyl)phenyl],[‌511‌] react through a different reaction mechanism and provide another important class of homogeneous catalyst for effecting this type of reduction.[‌512‌‌514‌] Common problems that arise with transition-metal-catalyzed hydrogenations involve competing hydrogenolysis, decarbonylation of the starting aldehyde, and catalyst deactivation. Fortunately, these selectivity issues can usually be minimized through careful choice of catalyst and reaction conditions.

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Meeee 88 Meeeeeeeee-Meeee-Meeeeeeee Meeeeeeee ee Meeeeeeee[‌888‌,‌888‌,‌888‌,‌888‌]

Meeee M8 Meeeeeeeee Meeee (%) Mee
8 Me [Me(eee)(MeMMe)]MMe,e M8 (8888Meee), MeMM, 88°M, 8e eeeee [‌888‌]
8 Me [MeMe8(MMe8)8], Me8M, MMM8M, MMM, ee 88 [‌888‌]
8 (MM8)8Me [MeMe8(MMe8)8], Me8M, MMM8M, MMM, ee 88 [‌888‌]
8 (MM8)8Me [MeMe(eee)]8, eeee, Me8MM8, eMeMM, eeeeeee, 88°M, 88e 88 [‌888‌]
8 Me [MeMe(eee)]8, (8-MeMM8M8M8)8M, Me8MM8, M8M, eMeMM, 88°M, 8e 88 [‌888‌]

e MeMMe=8,8-eee(eeeeeeeeeeeeeeeeeeee)eeeeeeeee.

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Meeee 88 Meeeeeeee ee Meeeeeeee Meeee Meeeeee Meeeeeeeee Meeee Meeeeeeee[‌888‌,‌888‌,‌888‌,‌888‌]

Meeee M8 Meeeeeeeee Meeee (%) Mee
8 Me MMM+[MeM(MM)8] (8.8 eeeee),e MMM (8.8 eeeee), MMM, eeeeee, 88e 88 [‌888‌]
8 Me MMM+[MeM(MM)8] (8.8 eeeee),e MeMM (8.8 eeeee), MMM, 88°M, 8e 88 [‌888‌]
8 (MM8)8Me Me8M+[Me8(μ-M)(MM)88] (8.8 eeeee), MeMM (8.8 eeeee), MMM, eeeeee, 8e eeeeee [‌888‌]
8 (MM8)8Me Me8M+[Me8M(MM)88] (8eee%), M8 (88 eee), MMM, 888°M, 88e eeeee [‌888‌]
8 8-MM8M8 Me8M+[Me8M(MM)88] (8eee%), M8 (88 eee), MMM, 888°M, 88e eeeee [‌888‌]

e MMM+=eee(eeeeeeeeeeeeeeeeee)eeeeeee.

e Me MM.

Meeeeeeeeeee Meeeeeeee

Meeeee Meeeeee (88, M8=Me; Meeee 88, Meeee 8); Meeeeee Meeeeeeee:[‌888‌]

M MeeeeeMeeeee eeeeee eee eeeeeee eeee MeMMM (888 μM, 8.88eeee), [Me(eee)(MeMMe)]MMe (8.8ee, 8.8 × 888 eeee) (ee eeee eeeeeeeee ee eeeeeeeee), eee eeeeeeee MeMM (8eM) eeeee M8. Meeee eeee eeeeeeeeeeM8 eeeeee ee eeeeee eee eee eeee eee M8 eeeee, eee eeeeeee eee eeeeeeeeeee eeee M8 ee 8888 Meee. Meeee 8e, eee eeeeeee eee eeeeeee ee eeeeee ee eeeeeeeeeee eeeee eeeeeee eeeeeeee eee eeee eeeeeeee eeeeeee e eeeeee eee eeee ee eeeeee eee eeeeeeee. Meeeeee ee eee eeeeeeeee eeeeeee eeee eee eeeeeeee eeeee eeeeeee eeeeeeee eeeeeeee eee eeeeeee; eeeee: 888ee (eeeee).

Meeeee Meeeeee (88, M8=Me; Meeee 88, Meeee 8); Meeeeee Meeeeeeee:[‌888‌]

MMM8M (8.88e, 8.888eee) eee eeeee ee e eeee ee Me8M (8.8eM, 8.88eee) ee MMM (88eM). [MeMe8(MMe8)8] (888ee, 8 × 888 eee) eee eeeee eee eee eeeeeee eee eeeeeee ee eeeeee M8. Meeee 8eee, MeMMM (8.88e, 8.88eee) eee eeeee. Meeee 88eee, eee eeeeeee eee eeeeeeeeeee eeee 8M ee MMe eee eee MMM eee eeeeeee eeeee eeeeeee eeeeeeee. Mee eeeeeee eee eeeee ee ee Me8M, eeeee (MeMM8), eee eee eeeeeee eee eeeeeee eeeee eeeeeee eeeeeeee. Meeeeeeeeeee ee eee eeeee eeeeeee eee ee eeeeeeeeeeee; eeeee: 8.88e (88%).