Ruthenium fragmentation catalyst

The olefin binding site is presumed to be cis to the carbene and trans to one of the chlorides. Subsequent dissociation of a phosphine paves the way for the formation of a 14-electron metallacycle G which upon cycloreversion generates a pro ductive intermediate [ 11 ]. The metallacycle formation is the rate determining step. The observed reactivity pattern of the pre-catalyst outlined above and the kinetic data presently available support this mechanistic picture. The fact that the catalytic activity of ruthenium carbene complexes 1 maybe significantly enhanced on addition of CuCl to the reaction mixture is also very well in line with this dissociative mechanism [11] Cu(I) is known to trap phosphines and its presence may therefore lead to a higher concentration of the catalytically active monophosphine metal fragments F and G in solution. 

Figure 24. Synthetic strategy. Two coordinating fragments bearing terminal olefins are gathered and interlaced around two copper(I) centers. RCM with ruthenium catalyst afforded the knot.

In order to parallel solution-phase reactivity and ion-molecule reactions in the gas phase, the reactivity of a typical homogeneous catalyst, described earlier by Grubbs and co-workers [128], was studied by ESMS [129]. Electrospray of the dichloride salt of 15 and increasing the collisional activation potential first yielded predominantly the monocation 16, but with raising the tube lens potential even higher the intensity of 16 decreased due to loss of the second phosphine ligand, loss of trimethylamine, and loss of HCl. The observed fragmentation pattern was consistent with the assumed structure of the ruthenium complex. 

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