Acetonitrile ligand, deprotonation

The catalyst reported by Grotjahn and Lev (11-13) for alkyne hydration (2) is capable of isomerizing alkenes, but veiy slowly. Because we knew that the rate of alkyne hydration was unchanged in the presence of excess phosphine ligand, we thought that like alkyne hydration, alkene isomerization would require loss of acetonitrile ligand (14) and alkene binding. Subsequent deprotonation at an allylic position would make an q -allyl intermediate which when reprotonated at the other... 

Despite acetonitrile s feeble acidity (pATa ca 29) compared with enolizable aldehydes (67, pA s 16-17), the combination of a simple ruthenium complex, [RuCp(PPli3)2]+, and diazabicycloundecane (DBU) brings about a nitrile-selective deprotonation to give /I-hydroxynitriles (68).274 A mechanism is proposed in which DBU, aldehyde, and acetonitrile can displace triphenylphosphines, with the metal centre activating acetonitrile to convert it to an NC-CFU- ligand (proposed intermediate, 69). A nickel-diarylamidodiphosphine complex (70) also catalyses this transformation in the presence of DBU.275... 

We have thus been able to show that the acetonitrile-pentacarbonyl complexes M(CO)5NCMe (M = Cr, Mo, W) and cycloheptatriene-iron-tricarbonyl C7H3Fe(CO)3 are deprotonated as follows, without attack at the CO ligands (151). 

An extension of the preparative route via thiol deprotonation (Section II.B.l) is the electrochemical synthesis of copper(I) thiolates. In this latter method, acetonitrile solutions of either a thiol or a disulfide (and a coordinating ligand) are electrolyzed using a platinum cathode and a copper anode (Eq. 5) (55-57). This particular route can be easily extended to the synthesis of both silver(I) and gold(I) thiolates (55). 

Asymmetrical tetradentate trianionic SB ligands bearing both amide and imine groups which are capable of stabilizing high oxidation states of metal ions when coordinated to deprotonated nitrogen have been prepared and characterized by IR, 1H NMR and 13C NMR.86 The Mnm complexes were prepared electrochemically by oxidation of a Mn anode in an acetonitrile solution of the ligand.86... 

Protonation of a polyhydride can occur at the metal, increasing the number of hydride ligands or leading to a rj -Uz ligand, which can liberate as H2. In spite of the low kinetic and thermodynamic (pXa = 25.5 in acetonitrile) acidity of [ReH4(PMe2Ph)4] +, deprotonation occurs by abase like potassium phenolate. Replacement of one phosphine by CO enhances the acidity of the complex by at least 7 orders of magnitude (pXg < 18.5). ... 

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