Homogeneous CO Hydrogenation: Ligand Effects on the Lewis Acid ...

Reaction of 2-M 1 with 2-P 1 (Crossover Experiment).
To a stirring ~0.6 mL C 6D 5Cl solution of 19.3 mg (0.0240 mmol) [1-M 1][OTf] was added 15.6
mg (0.0240 mmol) [HPt] + partwise as a solid. The solution was transferred to a J-Young NMR
tube, and showed ~90% conversion to 2-M 1 by NMR spectroscopy. The side product was the
bridging alkyl as discussed in the synthesis of 2-M 1. Meanwhile, 2-P 1 was prepared by addition
of 15.6 mg (0.0240 mmol) solid [HPt] + to 20.0 mg (0.024 mmol) [1-P 1][OTf] with stirring. After
one minute of stirring, the contents of the tube containing 2-M 1 were poured into the vial
containing 2-P 1, and the reaction mixture was filtered into a J-Young NMR tube. After ~20
minutes, a mixture of both Re-CHO species and a bridging alkyl-metalloester species were
observed. After 3 hours, no Re-CHO species remained, and the major species (~90%) was
identified by 1 H- 31 P gHMBC NMR as 10-M 1P 1, with the minor product being the initially formed
impurity containing only 1C ligands. The 2-D NMR shows correlation of the CH 2 group to the
31 P signal at 0.1, which also correlates to two multiplets in the 1 H NMR at 2.46 and 1.56,
belonging to the P ligand, and confirming that the CH 2 is bound the same metal as the P ligand.
The other 31 P signal of the major species and the impurity overlap at 2.1 (the amount of impurity
stayed roughly the same through the reaction). This resonance correlates to Ph protons and a
doublet at 1.75, consistent with the other Re of both bimetallic species being ligated by M. As
discussed in the text, this assignment allows for the mechanistic pathway of formation of the
bridging alkyl to be identified as nucleophilic attack by oxygen.
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