Selective C‐alkylation Between Alcohols Catalyzed by N‐Heterocyclic Carbene Molybdenum

Abstract

The first implementation of a molybdenum complex with an easily accessible bis‐N‐heterocyclic carbene ligand to catalyze β‐alkylation of secondary alcohols via borrowing‐hydrogen (BH) strategy using alcohols as alkylating agents is reported. Remarkably high activity, excellent selectivity, and broad substrate scope compatibility with advantages of catalyst usage low to 0.5 mol%, a catalytic amount of NaOH as the base, and H2O as the by‐product are demonstrated in this green and step‐economical protocol. Mechanistic studies indicate a plausible outer‐sphere mechanism in which the alcohol dehydrogenation is the rate‐determining step.

Surmounting Alkoxide Trap Strategy: N-Heterocyclic Carbene Chromium(0)-Catalyzed C-Alkylation between Alcohols

“…Tuning the electronic structure and oxidation state of the metal center is extremely important in the rational design and development of nonprecious metal-based catalysts. − However, little attention has been paid to the fundamental d-wall issue in catalyst design for BH/HA reactions. The metal-alkoxide intermediate is crucial in BH/HA transformations when using alcohols as alkylating agents. − For high oxidation state transition metal centers, the d-p π interaction between half-filled or empty d orbitals and the oxygen lone pair stabilizes the metal-alkoxide intermediate in BH/HA transformations, causing an alkoxide trap . In this instance, a thermodynamic sink is dug to arrest the metal-alkoxide intermediate, and thus, the catalytic activity is inhibited (Scheme c).…”

Ru-Catalyzed Asymmetric Addition of Arylboronic Acids to Aliphatic Aldehydes via P-Chiral Monophosphorous Ligands

“…1-(4-bromophenyl)-3-phenylpropan-1-ol (3af) [88] [a] 20 D = +10.0 (c 1.31, CH 2 Cl 2 ). Yield:91% (132.4 mg) as a yellow oil; 1 H NMR (400 MHz, CDCl 3 ) δ 7.44 (d, J = 7.9, 2H), 7.35-7.03 (m, 7H), 4.59 (dd, J = 6.6, 1H), 2.75-2.56 (m, 2H), 2.12 (s, 1H) and 2.08-1.89 (m, 2H).…”

“…Yield:49% (52.7 mg) as a yellow oil; 1 H NMR (400 MHz, CDCl 3 ) δ 7.45 (t, J = 7.6, 1H), 7.39-6.89 (m, 8H), 5.01 (t, J = 6.5, 1H), 2.90-2.58 (m, 2H) and 2.19-1.98 (m, 3H). 13 1-(2-methoxyphenyl)-3-phenylpropan-1-ol (3aj) [89] [a] 1-(3-chlorophenyl)-3-phenylpropan-1-ol (3ak) [88] [a] 20 D = +15.0 (c 0.55, CH 2 Cl 2 ). Yield: 91% (111.7 mg) as a yellow oil; 1 H NMR (400 MHz, CDCl 3 ) δ 7.46-6.98 (m, 9H), 4.59 (dd, J = 7.9, 5.2, 1H), 2.85-2.53 (m, 2H), 2.26 (s, 1H) and 2.10-1.90 (m, 2H).…”

“…3-phenyl-1-(m-tolyl)propan-1-ol (3al) [88] [a] 20 D = +21.0 (c 0.98, CH 2 Cl 2 ). Yield: 87% (98.3 mg) as a yellow oil; 1 H NMR (400 MHz, CDCl 3 ) δ 7.63-6.82 (m, 9H), 4.59 (dd, J = 7.8, 5.5, 1H), 2.84-2.53 (m, 2H), 2.33 (s, 3H) and 2.18-1.91 (m, 3H).…”

Efficient transfer hydrogenation of ketones using molybdenum complexes by comprehensively verifying the auxiliary ligands

“…12 As a result, the low toxic effect of this metal is observed in living organisms, which enhances its applicability 13 in a number of reactions such as olefin metathesis, 14 oxidation of alkenes and sulfides, 15 reduction of dinitrogen, 16 and acceptor-less dehydrogenation coupling. 17 Due to the relatively rich molybdenum resources in China, it is very interesting for chemists to develop molybdenum catalysts targeting industrial applications. To the best of our knowledge, there have only been a few reports using molybdenum catalysts for the hydrogenation of ketones.…”