Heterobimetallic [2.2]Paracyclophane Complexes and Their Application in Photoredox Catalysis

Abstract

The most important goal of current chemistry research is to provide green and sustainable routes to compounds of interest. One way of addressing this is the use of abundant and inexpensive sources of energy to drive reactions, with the prime example being visible light in photoredox catalysis. One recent promising approach is the use of heterobimetallic catalysts where two metals work in a cooperative fashion to achieve the desired transformation. However, very little is known about the exact mechanism of cooperativity. This is due to a lack of heterobimetallic compounds that can be fine-tuned to obtain very specific answers regarding for example spatial design of the catalyst in question. In this work, [2.2]paracyclophane (PCP) is presented as a new platform on which to build distance-variable heterobimetallic complexes. PCP has been described as a "super-atom" molecule for its unique ability to hold up to 16 substituents in a precise spatial relationship to each other. By using PCP as a platform, it is shown that a range of defined heterobimetallic complexes can be designed and prepared (Figure 1.1). The methods necessary for the synthetic transformations are developed and investigated for their broader synthetic applicability. 51 (10-65%) Scheme 3.8 Nickel-catalyzed Kumada arylation of PCP bromide 51. Recently, the Kumada cross-coupling was used for the heteroarylation of electron-rich para-methoxy iodo-PCP 52 with 2-pyridyl magnesium bromide (53) to form biaryl 54 (Scheme 3.9) albeit in not satisfying yields. [88] Thus, a better synthetic strategy to access valuable biaryl 54 is necessary.