New Ruthenium Complexes in the Catalytic Hydrogenation of Alkynes. Study of Structure and Mechanism

Abstract

The reaction of [(η5-Ph4C4COHOCC4Ph4-η5)(μ-H)[(CO)4Ru2] (1) with several alkynes was studied. Two new types of Ru complexes, [(η5-Ph4C4CO)(CO)2RuC(Ph)=CPh] (6) and [(η5-Ph4C4COH)(CO)2 RuC(CO2Me)=CHCO2Me] (7), were isolated and structurally characterized by single-crystal X-ray crystallography. These complexes were found to be implicated in the hydrogenation of alkynes with 1 as a catalyst precursor. While complex 7 was found to function as a catalyst in the hydrogenation cycle, complex 6 acts as a catalysis poison by virtue of its stability and irreversible formation. A catalytic cycle has been proposed.

Reactions of Tetracyclone Molybdenum Complexes with Electrophilic Alkynes: Cyclopentadienone–Alkyne Coupling and Alkyne Coordination

“…In the reaction of Shvo's complex with PhC≡CH to give [Ru(CO) 2 (η 5 , σ-C 4 Ph 4 COCPh=CH)] (the analogue of 5), the 1 H NMR signal for the vinylic proton was observed at 5.81 ppm, on which basis the coupling of the cyclopentadienone oxygen was proposed to occur exclusively to the CPh terminus of the alkyne; only one isomer was present. 12 This shift is far removed from those in 9, implying the opposite regiochemistry in our case, a deduction confirmed crystallographically. 25 Given that the linkage with the tetracyclone ligand is likely to be regiospecific, attacking the CH terminus of the alkyne, we attribute the presence of two isomers to the two possible orientations of the unsymmetrical alkyne ligand.…”

“…The bond lengths in the vinylic portion of the ligand are the same, within experimental error, as those in complex 5. 12,14 The second alkyne is bound to the molybdenum as an η 2 -ligand; the compound therefore belongs to the well established CpM(RC≡CR)LX class. 15,16 Both the C≡C bond length of 1.312 (6) • and the MoÐC bond lengths [2.031(4) and 2.059 (4) •] are commensurate with this ligand acting as a 4-electron donor, as required by electron counting considerations.…”

Shvo’s Catalyst in Hydrogen Transfer Reactions

“…However, there are reports on the hydrogenation of alkenes and alkynes using the Shvo catalyst 1 [6,30,31,39]. The reactions were carried out at a hydrogen pressure of 500 psi at 145 C.…”

(Alkenylalkylidene)(indenyl)ruthenium(II) Complexes: Synthesis by Protonation of Alkenyl Derivatives

“…The most remarkable feature of the structure is the (E) configuration of the alkenyl group which exhibits an RuϪC(1) bond length of 2.030 (12) Å that can be compared with the reported values in other alkenylruthenium(II) complexes with the two CO 2 Me groups in a mutually cis configuration, e.g. 2.07(1) Å and 2.096(7) Å in the complexes [Ru{(E)-C(CO 2 Me)ϭ CH(CO 2 Me)}(η 5 -C 5 H 5 )(dppm)] [18] and [Ru{(E)-C(CO 2 Me)ϭCH(CO 2 Me)}(η 5 -Ph 4 C 4 COH)(CO) 2 ], [19] respectively. The C(1)ϪC(2) bond length of 1.373(17) Å (typical of a carbonϪcarbon double bond) and all the remaining values involving the ester functionalities of the alkenyl group are as expected.…”