Bedford Catalysts

Palladacyclic catalysts developed by the Bedford group are examples of a select group of catalysts capable of effecting a variety of coupling reactions using difficult-to-activate aryl chlorides at very low catalyst loadings (Figure 1).1 For example, monomeric complex 1, either as an isolated species or from the in situ treatment of 2 with PCy3, exhibits high catalytic activity in the Suzuki coupling reaction of arylboronic acids and aryl chlorides, with turnover numbers (TONs) exceeding 1,000,000.


Figure 1.

As shown in Table 1, both electronically activated and nonactivated aryl chlorides couple with simple boronic acids at catalyst loadings as low as 0.00005%. The optimized protocol calls for two equivalents of phosphine ligand relative to 2 and the use of Cs2CO3 as a base.


Table 1.

Reaction conditions nearly identical to those applied to Suzuki coupling of aryl chlorides can also be applied to Stille coupling of aryl- or vinyltin reagents with aryl chlorides to give functionalized biaryls or styrene derivatives (Scheme 1).2


Scheme 1.

Lastly, the treatment precatalyst 2 with P(t-Bu)3 generates a catalyst system that is highly active in the amination of aryl chlorides with diarylamines, alkylarylamines, and dialkylamines (Scheme 2).3 Yields typically exceed 80%, and as in other coupling reactions, catalyst loadings are low relative to more commonly used amination protocols.


Scheme 2.

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Materials

     

References

  1. (a) Bedford, R. B. et al. Chem. Commun. 2002, 2610. (b) Bedford, R. B. et al. Angew Chem., Int. Ed. 2002, 41, 4120.
  2. Bedford, R. B. et al. Chem. Commun. 2002, 2608.
  3. Bedford, R. B.; Blake, M. E. Adv. Synth. Catal. 2003, 345, 1107.

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