Mixed Phosphane η⁵-CpRuCl(PR₃)₂ Complexes as Ambifunctional Catalysts for Anti-Markovnikov Hydration of Terminal Alkynes

Abstract

The catalytic activity of [CpRu(L)(2)(MeCN)]PF(6) (L = 2-diphenylphosphinopyridine with bulky groups at C-6) for anti-Markovnikov hydration of terminal alkynes to aldehydes is retained when one heterocyclic ligand L is replaced by L' = PPh(3). Equal amounts of CpRuCl(PPh(3))(2) (1) and phosphane L in acetone solution equilibrate to a mixture of 1, CpRuCl(L)(PPh(3)) (2), and CpRuCl(L)(2) (3), which acts as highly active in situ catalyst for preparative anti-Markovnikov hydration of alkynes in water-rich media (2 mol % [Ru], 60 °C, 3-18 h in 4:1 (v/v) acetone/water). Reactions were completed in <15 min at 160 °C.

Configurational Assignment of ‘Cryptochiral’ 10‐Hydroxystearic Acid Through an Asymmetric Catalytic Synthesis

“…The catalytic anti‐Markovnikov hydration of undecynoic acid has already been performed with an in situ CpRuCl(PPh 3 ) 2 –ISIPHOS catalyst (2 mol‐%, 3 h, 70 °C, 97% yield). [27f] We now prefer to perform this reaction under conditions of microwave irradiation (160 °C), which shortens the reaction time to 15 min ( Scheme ). The hydration could also be performed with the crude elimination mixture ( 7 + 17 + 18 , cf.…”

Broad‐Spectrum Catalysts for the Ambient Temperature Anti‐Markovnikov Hydration of Alkynes

“…[8] Subsequently, Hintermann and co-workers showed that mixed phosphine catalysts such as 7 also displayed high hydration activity. [9] Breit and Chevallier reported that the catalyst 8, which contains a selfassembled diphosphine ligand, displayed good substrate scope, but elevated temperatures were required to obtain high yields (120 8C). [10] The catalysts 6 and 7 efficiently hydrate unhindered aliphatic alkynes, but arylacetylenes and hindered aliphatic alkynes require extended heating to obtain high conversion.…”

“…In addition, hydrations of propargylic alcohols and conjugated enynes are complicated by competitive rearrangement [11] or elimination, and the elevated reaction temperatures and Lewis acidity of the catalysts promote aldol addition reactions. We recently discovered [12] that a catalyst derived from (h 5 -cyclopentadienyl) tris(acetonitrile)ruthenium hexafluorophosphate (9) or (h 5 -cyclopentadienyl) (h 6 -naphthalene)ruthenium hexafluorophosphate (10) and 2, 2'-bipyridine (bipy, 11 a) mediated the sequential hydration and hydrogenation of aliphatic and aromatic alkynes (reductive hydration), to provide linear alcohols, at 55-80 8C. The discovery that the hydration step could be promoted by this catalyst was surprising in light of the structures of 3-8, which all contain phosphine-based ligands, and Grotjahns comprehensive mechanistic model, which established the multifunctional role of the (2-heteroaryl)phosphine ligands in the most active catalysts 5-7.…”

Discovery and Comparison of Homogeneous Catalysts in a Standardized HOT‐CAT Screen with Microwave‐Heating and qNMR Analysis: Exploring Catalytic Hydration of Alkynes

“…A glimpse of anti‐Markovnikov hydration activity was seen with [RhCl(COD)] 2 (5.8 % A , 1.4 % K ; Table , entry 14), but only in acetone, and at low activity and chemoselectivity. anti‐Markovnikov selectivity was also observed for Cp*RuCl 2 −ISIPHOS in the 1‐heptyne screen (Table S1, entries 68, 69), where the active species may have been related to known catalyst [CpRu(ISIPHOS) 2 ] + . Albeit low, it is the first demonstration of such activity for a Cp*Ru system.…”